Equipment for the secondary processing of polymers. Polymer processing technology. Technological processes of PA waste recycling

INTRODUCTION

Polymer molecules are a broad class of compounds whose main distinguishing characteristics are high molecular weight and high conformational flexibility of the chain. It can be said with confidence that all the characteristic properties of such molecules, as well as the possibilities of their application associated with these properties, are due to the above features.

In our urbanized, rapidly developing world, the demand for polymeric materials has increased dramatically. It is difficult to imagine the full-fledged operation of factories, power plants, boiler houses, educational institutions, electrical household appliances that surround us at home and at work, modern computers, cars and much more without the use of these materials. Whether we want to make a toy or create a spaceship - in both cases, polymers are indispensable. But how can the polymer be given the desired shape and appearance? To answer this question, let us consider another aspect of polymer technology, namely, their processing, which is the subject of this work.

In a broad sense, polymer processing can be viewed as a kind of engineering specialty involved in the transformation of raw polymer materials into the required end products. Most of the methods currently used in polymer processing technology are modified analogs of methods used in the ceramic and metal processing industries. Indeed, we need to understand the ins and outs of polymer processing in order to replace common traditional materials with other materials with improved properties and appearance.

About 50 years ago, there was a very limited number of processes for processing polymers into end products. Currently, there are many processes and methods, the main ones are calendering, casting, direct compression, injection molding, extrusion, blow molding, cold forming, thermoforming, foaming, reinforcement, melt forming, dry and wet forming. The last three methods are used to produce fibers from fiber-forming materials, and the rest are used to process plastic and elastomeric materials into industrial products. In the following sections, I have tried to give a general overview of these important processes. For a more detailed introduction to these and other processes such as dip coating, swirling fluidized bed coating, electronic and thermal sealing, and welding, refer to specific textbooks on polymer processing. Also outside the scope of this abstract are issues related to coatings and adhesives.

Before proceeding directly to the consideration of methods and methods for processing polymers into final products, it is necessary to find out: what are polymers, what are they and where can they be used, i.e. what end products can be obtained from polymers? The role of polymers is very great and we must understand the need for their processing.

1. POLYMERS AND POLYMER MATERIALS

1.1 GENERAL CHARACTERISTICS AND CLASSIFICATION

A polymer is an organic substance, the long molecules of which are built from the same repeatedly repeating units - monomers. By origin, polymers are divided into three groups.

Natural are formed as a result of the vital activity of plants and animals and are found in wood, wool, and leather. These are protein, cellulose, starch, shellac, lignin, latex.

Typically, natural polymers are subjected to isolation, purification, modification, in which the structure of the main chains remains unchanged. The products of this processing are artificial polymers. Examples are natural rubber, made from latex, celluloid, which is nitrocellulose plasticized with camphor to increase elasticity.

Natural and artificial polymers have played a large role in modern technology, and in some areas they remain indispensable to this day, for example, in the pulp and paper industry. However, a sharp increase in the production and consumption of organic materials occurred due to synthetic polymers - materials obtained by synthesis from low molecular weight substances and have no analogues in nature. The development of chemical technology of macromolecular substances is an integral and essential part of modern scientific and technological revolution . Not a single branch of technology, especially new ones, can do without polymers. According to the chemical structure, polymers are divided into linear, branched, network and spatial.

molecules linear polymers are chemically inert with respect to each other and are interconnected only by van der Waals forces. When heated, the viscosity of such polymers decreases and they are able to reversibly transform first into a highly elastic and then into a viscous flow state (Fig. 1).

Fig.1. Schematic diagram of the viscosity of thermoplastic polymers depending on temperature: T 1 - the transition temperature from the glassy to the highly elastic state, T 2 - the transition temperature from the highly elastic to the viscous state.

Since the only effect of heating is a change in plasticity, linear polymers are called thermoplastic. It should not be thought that the term "linear" means straight, on the contrary, they are more characteristic of a serrated or helical configuration, which gives such polymers mechanical strength.

Thermoplastic polymers can not only be melted, but also dissolved, since van der Waals bonds are easily torn under the action of reagents.

branched(grafted) polymers are stronger than linear ones. Controlled chain branching is one of the main industrial methods for modifying the properties of thermoplastic polymers.

mesh structure characterized by the fact that the chains are connected to each other, and this greatly limits the movement and leads to a change in both mechanical and chemical properties. Ordinary rubber is soft, but when vulcanized with sulfur, covalent bonds of the S-0 type are formed, and the strength increases. The polymer can acquire a network structure and spontaneously, for example, under the action of light and oxygen, aging occurs with a loss of elasticity and performance. Finally, if the polymer molecules contain reactive groups, then when heated, they are connected by many strong cross-links, the polymer turns out to be cross-linked, i.e., it acquires spatial structure. Thus, heating causes reactions that dramatically and irreversibly change the properties of the material, which acquires strength and high viscosity, becomes insoluble and infusible. Due to the high reactivity of molecules, which manifests itself with increasing temperature, such polymers are called thermosetting.

Thermoplastic polymers are obtained by the reaction polymerization, flowing according to the scheme pmm p(Fig. 2), where M - monomer molecule, M p- a macromolecule consisting of monomer units, P - degree of polymerization.

In chain polymerization, the molecular weight increases almost instantly, the intermediate products are unstable, the reaction is sensitive to the presence of impurities and, as a rule, requires high pressures. It is not surprising that such a process is impossible under natural conditions, and all natural polymers were formed in a different way. Modern chemistry has created a new tool - the polymerization reaction, and thanks to him a large class of thermoplastic polymers. The polymerization reaction is realized only in complex equipment of specialized industries, and the consumer receives thermoplastic polymers in finished form.

Reactive molecules of thermosetting polymers can be formed in a simpler and more natural way - gradually from monomer to dimer, then to trimer, tetramer, etc. Such a combination of monomers, their "condensation", is called the reaction polycondensation; it does not require high purity or pressures, but is accompanied by a change in the chemical composition, and often by the release of by-products (usually water vapor) (Fig. 2). It is this reaction that occurs in nature; it can be easily carried out with only a little heating in the simplest conditions, even at home. Such high manufacturability of thermosetting polymers provides ample opportunities to manufacture various products at non-chemical enterprises, including radio plants.

Regardless of the type and composition of the starting materials and production methods, materials based on polymers can be classified as follows: plastics, fibre-reinforced plastics, laminates, films, coatings, adhesives. I will not particularly focus on all these products, I will only talk about the most widely used ones. It is necessary to show how great the need for polymeric materials is in our time, and, consequently, the importance of their processing. Otherwise the problem would be simply unfounded.

1.2 PLASTICS

The word "plastic" comes from the Greek language and refers to a material that can be pressed or molded into any shape you choose. According to this etymology, even clay could be called plastic, but in reality only products made from synthetic materials are called plastics. The American Society for Testing and Materials defines what plastic is as follows: "is any member of a wide variety of materials, wholly or partly organic in composition, which can be shaped into desired shape by the application of temperature and/or pressure."

Hundreds of plastics are known. In table. 1 shows their main types and shows individual representatives of each of the species. It should be noted that at present there is no single way to describe the entire variety of plastics due to their large number.

Table 1. Main types of plastics

Type	Typical representatives	Type	Typical representatives
Acrylic plastics Aminoplastics	Polymethylmethacrylate (PMMA) Polyacrylonitrile (PAN) Urea-formaldehyde resin Melamine-formaldehyde resin	Polyesters	Unsaturated polyester resins Polyethyl terephthalate (PET) Polyethyl snadipate
Cellulose	Ethylcellulose Cellulose acetate Cellulose nitrate	Polyolefins Styrene plastics	Polyethylene (PE) Polypropylene (PP) Polystyrene (PS)
Epoxy resins	Epoxy resins	Copolymer of styrene with acrylonitrile
Fluoroplastics	Polytetrafluoroethylene (PTFE) Polyvinylidene fluoride	Copolymer of acrylonitrile with styrene and butadiene (ABS)
Phenoplasts	Phenol-formaldehyde resin Phenol-furfural resin	Vinyl plastics	Polyvinyl chloride (PVC) Polyvinyl butyral
Polyamide plastics (nylons)	Polycaprolactam (PA-6) Polyhexam ethylenadipamide (PA-6,6)	Vinyl chloride-vinyl acetate copolymer

The first thermoplastic that found wide application was celluloid, an artificial polymer obtained by processing natural cellulose. He played a big role in technology, especially in cinema, but due to the exceptional fire hazard (in terms of composition, cellulose is very close to smokeless powder) already in the middle of the 20th century. its production has dropped to almost zero.

The development of electronics, telephone communications, radio urgently required the creation of new electrical insulating materials with good structural and technological properties. This is how artificial polymers appeared, made on the basis of the same cellulose, named after the first letters of the fields of application, etrols. Currently, only 2 ... 3% of the world production of polymers are cellulose plastics, while approximately 75% are synthetic thermoplastics, with 90% of them accounted for by only three: polystyrene, polyethylene, polyvinyl chloride.

Expandable polystyrene, for example, is widely used as a heat and sound insulating building material. In radio electronics, it is used for sealing products when it is necessary to ensure minimal mechanical stress, create temporary insulation from the effects of heat emitted by other elements or low temperatures and eliminate their effect on electrical properties, therefore, in on-board and microwave - equipment.

1.3 ELASTOMERS

Elastomers are commonly referred to as rubbers. Balloons, shoe soles, tires, surgical gloves, garden hoses are typical examples of elastomer products. The classic example of elastomers is natural rubber.

The rubber macromolecule has a helical structure with an identity period of 0.913 nm and contains more than 1000 isoprene residues. The structure of the rubber macromolecule provides its high elasticity - the most important technical property. Rubber has the amazing ability to reversibly stretch to 900% of its original length.

A variety of rubber is less elastic gutta-percha, or balata, the juice of some rubber plants growing in India and the Malay Peninsula. Unlike rubber, the gutta-percha molecule is shorter and has a trans-1,4 structure with an identity period of 0.504 nm.

The outstanding technical significance of natural rubber, its absence in a number of countries, including the Soviet Union, of economically viable sources, the desire to have materials that are superior in a number of properties (oil resistance, frost resistance, abrasion resistance) to natural rubber, stimulated research on the production of synthetic rubber. .

Several synthetic elastomers are currently in use. These include polybutadienes, styrene-butadiene, acrylonitrile-butadiene (nitrile rubber), polyisoprene, polychloroprene (neoprene), ethylene-propylene, isoprene-isobutylene (butyl rubber), polyfluorocarbon, polyurethane, and silicone rubbers. The raw material for producing synthetic rubber according to the Lebedev method is ethyl alcohol. Now, the production of butadiene from butane through the catalytic dehydrogenation of the latter has been developed.

Scientists have been successful and today more than one third of the rubber produced in the world is made from synthetic rubber. Rubber and rubber make a huge contribution to the technological progress of the last century. Let us recall, for example, rubber boots and various insulating materials, and the role of rubber in the most important branches of the economy will become clear to us. More than half of the world's elastomer production is spent on tire production. The manufacture of tires for a small car requires about 20 kg of rubber, of different grades and brands, and for a dump truck almost 1900 kg. A smaller part goes to other types of rubber products. Rubber makes our life more convenient.

1.4 FIBER

We are all familiar with natural fibers such as cotton, wool, linen and silk. We also know synthetic fibers from nylon, polyesters, polypropylene and acrylics. The main distinguishing feature of fibers is that their length is hundreds of times greater than their diameter. If natural fibers (except silk) are staple fibers, then synthetic ones can be obtained both in the form of continuous threads and in the form of staple fibers.

From the consumer's point of view, fibers can be of three types; everyday demand, safe and industrial.

Everyday fibers are called fibers used for the manufacture of underwear and outerwear. This group includes fibers for the manufacture of underwear, socks, shirts, suits, etc. These fibers must have appropriate strength and extensibility, softness, non-flammability, absorb moisture and be well dyed. Typical representatives of this class of fibers are cotton, silk, wool, nylon, polyesters and acrylates.

Safe fibers are fibers used for the production of carpets, curtains, chair covers, draperies, etc. Such fibers must be tough, strong, durable and wear-resistant. From the point of view of safety, the following requirements are imposed on these fibers: they must ignite poorly, do not spread flame, and emit a minimum amount of heat, smoke and toxic gases during combustion. By adding small amounts of substances containing atoms such as B, N, Si, P, C1, Br or Sb to everyday fibers, it is possible to make them fire resistant and thus turn them into safe fibers. The introduction of modifying additives into the fibers reduces their combustibility, reduces the spread of flame, but does not lead to a decrease in the release of toxic gases and smoke during combustion. Studies have shown that aromatic polyamides, polyimides, polybenzimidazoles and polyoxydiazoles can be used as safe fibers. However, during the combustion of these fibers, toxic gases are released, since their molecules contain nitrogen atoms. Aromatic polyesters do not have this drawback.

Industrial fibers are used as reinforcing materials in composites. These fibers are also called structural fibers because they have high modulus, strength, heat resistance, stiffness, durability. Structural fibers are used to strengthen products such as rigid and flexible pipes, tubes and hoses, as well as in composite structures called fiber materials and are used in the construction of ships, cars, aircraft and even buildings. This class of fibers includes uniaxially oriented fibers of aromatic polyamides and polyesters, carbon and silicon fibers.

2. POLYMER RECYCLING

2.1 COMPOUNDING

Polymers in their pure form, obtained from industrial plants after their isolation and purification, are called "primary" polymers or "primary" resins. With the exception of some polymers such as polystyrene, polyethylene, polypropylene, virgin polymers are generally not suitable for direct processing. Virgin PVC, for example, is a horn-like material and cannot be molded without first being softened by the addition of a plasticizer. Likewise, the molding of natural rubber requires the addition of a vulcanizing agent to it. Most polymers are protected from thermal, oxidative, and photodegradation by the addition of suitable stabilizers. The addition of dyes and pigments to the polymer before molding makes it possible to obtain products of a wide variety of colors. To reduce friction and improve polymer flow within processing equipment, lubricants and processing aids are added to most polymers. Fillers are usually added to the polymer to give them special properties and reduce the cost of the final product.

The process involving the incorporation of ingredients such as plasticizers, curing agents, hardeners, stabilizers, fillers, dyes, flame retardants, and lubricants into a primary polymer is referred to as "compounding", and mixtures of polymers with these additives are referred to as "compounds".

Primary plastic polymers such as polystyrene, polyethylene, polymethyl methacrylate and polyvinyl chloride are usually in the form of free-flowing fine powders. The fine powder or liquid ingredients are mixed with the powdered virgin polymer using planetary mixers, V-mixers, ribbon helical mixers, Z-mixers or tipper. The displacement can be carried out either at room temperature or at elevated temperature, which, however, should be well below the softening temperature of the polymer. Liquid prepolymers are mixed using simple high speed agitators.

Primary elastomeric polymers, such as natural rubber, styrene-butadiene rubber or nitrile rubber, are produced in the form of crumbs pressed into thick plates called "bales". They are usually mixed with vulcanizing agents, catalysts, fillers, antioxidants and lubricants. Because elastomers are not free-flowing powders like virgin plastics, they cannot be mixed with the ingredients listed above using methods used for virgin plastics. Mixing of primary plastic polymers with other components of the compound is achieved by mixing, while obtaining a compound of primary elastomers involves rolling crumbs into plastic sheets and then introducing the required ingredients into the polymer. Compounding of elastomers is carried out either in a two-roll rubber mill or in a Banbury mixer with internal mixing. Elastomers in the form of latex or low molecular weight liquid resins can be mixed by simple mixing using high speed agitators. In the case of fiber-forming polymers, compounding is not carried out. Components such as lubricants, stabilizers and fillers are usually directly added to the polymer melt or solution just before the yarn is spun.

2.2 PROCESSING TECHNOLOGY

The fact that polymeric materials are used in a wide variety of forms, such as rods, pipes, sheets, foams, coatings or adhesives, as well as molded articles, implies that there are a variety of ways to process polymer compounds into end products. Most polymer products are obtained either by molding, or processing, or by casting liquid polymers into a mold, followed by curing or crosslinking. The fibers are obtained during the spinning process.

The shaping process can be compared, for example, to sculpting a figure from clay, and the processing process to carving the same figure from a bar of soap. In the molding process, a compound in the form of powder, flakes or granules is placed in a mold and subjected to temperature and pressure, resulting in the formation of the final product. The processing process produces products in simple shapes such as sheets, rods or pipes using stapling, stamping, gluing and welding.

Before moving on to a discussion of various methods for processing polymers, we recall that polymer materials can be thermoplastic or thermoset (thermoset). Once thermoplastic materials have been molded under heat and pressure, they must be cooled below the softening temperature of the polymer before being released from the mold, otherwise they will lose their shape. In the case of thermosetting materials, this is not necessary, since after a single combined exposure to temperature and pressure, the product retains its acquired shape even when it is released from the mold at high temperature.

2.3 CALENDING

The calendering process is commonly used to produce continuous films and sheets. The main part of the apparatus (Fig. 1) for calendering is a set of smoothly polished metal rolls rotating in opposite directions, and a device for fine adjustment of the gap between them. The gap between the rolls determines the thickness of the calendered sheet. The polymer compound is fed onto the hot rolls and the sheet coming from these rolls is cooled as it passes through the cold rolls. At the last stage, the sheets are wound into rolls, as shown in Fig. 1. However, if instead of sheets it is required to obtain thin polymer films, a series of rolls is used with a gradually decreasing gap between them. Typically, polymers such as polyvinyl chloride, polyethylene, rubber, and butadiene-styrene-acrylonitrile are calendered into sheets.

Rice. one. Scheme of the apparatus for calendering

/ - polymer compound; 2 - calender rolls: hot (3) and cold (4); 5 - calendered sheet; b - guide rolls; 7 - winder

When profiled rolls are used in the calendering machine, embossed sheets of various patterns can be obtained. Various decorative effects, such as imitation marbling, can be achieved by introducing a mixture of compounds of different colors into the calender. Marbling technology is commonly used in the production of PVC floor tiles.

2.4 CASTING

MOLD CASTING. This is a relatively inexpensive process that consists of converting a liquid prepolymer into solid products of the desired shape. Sheets, pipes, rods, etc. can be obtained by this method. products of limited length. Schematically, the mold casting process is shown in Fig.2. In this case, the prepolymer, mixed in appropriate proportions with the curing agent and other ingredients, is poured into a petri dish, which serves as a mould. Then the Petri dish is placed for several hours in an oven heated to the required temperature until the curing reaction is completed. After cooling to room temperature, the solid product is removed from the mold. A solid body cast in this way will have the shape of the internal relief of a Petri dish.

Rice. 2. The simplest picture of the mold casting process

b - filling the Petri dish with prepolymer and hardener; b - heating in the furnace; b - extraction from the mold of the cooled product

If, instead of a Petri dish, a cylindrical glass tube closed at one end is used, a product in the form of a cylindrical rod can be obtained. In addition, instead of the prepolymer and hardener, a mixture of monomer, catalyst and other ingredients heated to the polymerization temperature can be poured into the mold. Polymerization in this case will proceed inside the mold until a solid product is formed. Acrylics, epoxies, polyesters, phenols and urethanes are suitable for injection molding.

Casting molds are made of alabaster, lead or glass. During curing, the polymer block shrinks, making it easier to release from the mold.

ROTATIONAL CASTING. Hollow products such as balls and dolls are produced in a process called "rotational casting". The apparatus used in this process is shown in Figure 3.

A compound of thermoplastic material in the form of a fine powder is placed in a hollow mold. The apparatus used has a special device for simultaneous rotation of the mold around the primary and secondary axes. The mold is closed, heated and rotated. This results in a uniform distribution of the molten plastic over the entire inner surface of the hollow mold. The rotating mold is then cooled with cold water. Upon cooling, the molten plastic material, uniformly distributed over the inner surface of the mold, solidifies. Now the mold can be opened and the final product removed.

A liquid mixture of a thermosetting prepolymer with a hardener may also be loaded into the mold. Curing in this case will occur during rotation under the influence of elevated temperature.

Rotational casting produces products from PVC, such as galoshes, hollow balls or heads for dolls. Hardening of PVC is carried out by physical gelation between PVC and liquid plasticizer at temperatures of 150-200°C. Fine PVC particles are uniformly dispersed in the liquid plasticizer along with stabilizers and colorants, thus forming a relatively low viscosity substance. This pasty material, called "plastisol", is loaded into a mold and the air is evacuated from it. The mold is then rotated and heated to the required temperature, which causes the polyvinyl chloride to gel. The wall thickness of the resulting product is determined by the gelation time.

Fig.3. In the rotational casting process, hollow molds filled with polymeric material are simultaneously rotated around the primary and secondary axes.

1 - primary axis; 2 - secondary axis; 3 - detachable form detail; 4 - mold cavities; 5 - gear housing; b-to the motor

After reaching the required wall thickness, the excess plastisol is removed for a second cycle. For the final homogenization of the mixture of PVC particles with a plasticizer, the gel-like product inside the mold is heated. The final product is taken out of the mold after it has been cooled with a jet of water. The rotational casting method using a liquid material is known as the "hollow molding by pouring and rotating a mold" method.

INJECTION MOLDING. The most convenient process for the production of products from thermoplastic polymers is the injection molding process. Despite the fact that the cost of equipment in this process is quite high, its undoubted advantage is high productivity. In this process, a metered amount of molten thermoplastic polymer is injected under pressure into a relatively cold mold, where it solidifies into the final product.

The injection molding apparatus is shown in Fig.6. The process consists of supplying a compounded plastic material in the form of granules, tablets or powder from a hopper at certain intervals into a heated horizontal cylinder, where it softens. A hydraulic piston provides the pressure needed to push the molten material through the cylinder into the mold at the end of the cylinder. When the polymer mass moves along the hot zone of the cylinder, a device called a "torpedo" promotes a uniform distribution of the plastic material over the inner walls of the hot cylinder, thus ensuring uniform heat distribution throughout the volume. The molten plastic material is then injected through the injection hole into the mold cavity.

In its simplest form, the mold is a system of two parts: one of the parts is moving, the other is stationary (see Fig. 6). The stationary part of the mold is fixed at the end of the cylinder, and the movable part is removed and put on it.

With the help of a special mechanical device, the mold is tightly closed, and at this time, the molten plastic material is injected under a pressure of 1500 kg/cm. The closing mechanical device must be designed to withstand high operating pressures. The uniform flow of the molten material in the internal areas of the mold is ensured by preheating it to a certain temperature. Typically, this temperature is somewhat lower than the softening temperature of the molded plastic material. After filling the mold with molten polymer, it is cooled by circulating cold water and then opened to remove the finished product. This entire cycle can be repeated many times both manually and automatically.

CASTING FILMS. The casting method is also used for the production of polymer films. In this case, the polymer solution of the appropriate concentration is gradually poured onto a metal belt moving at a constant speed (Fig. 4), on the surface of which a continuous layer of the polymer solution is formed.

Fig.4. Scheme of the film casting process

/ - polymer solution; 2 - distribution valve; 3 - the polymer solution spreads to form a film; 4 - the solvent evaporates; 5 - endless metal belt; 6 - continuous polymer film; 7 - reel

When the solvent evaporates in a controlled mode, a thin polymer film is formed on the surface of the metal belt. After that, the film is removed by simple peeling. Most industrial cellophane sheets and photographic films are produced in this way.

2.5 DIRECT PRESSING

The direct pressing method is widely used for the production of products from thermosetting materials. Figure 5 shows a typical mold used for direct compression. The form consists of two parts - upper and lower or from a punch (positive form) and a matrix (negative form). There is a notch at the bottom of the mold and a ledge at the top. The gap between the protrusion of the upper part and the recess of the lower part in a closed mold determines the final appearance of the pressed product.

In the direct compression process, the thermosetting material is subjected to a single temperature and pressure application. The use of a hydraulic press with heated plates allows you to get the desired result.

Fig.5. Schematic representation of a mold used in the direct molding process

1 - a mold cavity filled with a thermosetting material; 2 - guide spikes; 3 - burr; 4 - molded product

The temperature and pressure during pressing can reach 200 °C and 70 kg/cm2, respectively. The operating temperature and pressure are determined by the rheological, thermal and other properties of the pressed plastic material. The mold recess is completely filled with polymer compound. When the mold is closed under pressure, the material inside it is compressed and pressed into the desired shape. Excess material is forced out of the mold in the form of a thin film called "burr". Under the influence of temperature, the pressed mass hardens. Cooling is not required to release the final product from the mold.

Fig..6. Schematic representation of the injection molding process

1 - compounded plastic material; 2 - loading funnel; 3 - piston; 4 - electric heating element; 5 - stationary part of the form;

6 - movable part of the form; 7 - main cylinder; 8 - torpedo; 9 - softened plastic material; 10 - mold; 11 - product molded by injection molding

2.6 FORMING

PNEUMOFORMING. A large number of hollow plastic products are produced by blow molding: canisters, soft drink bottles, etc. The following thermoplastic materials can be blow molded: polyethylene, polycarbonate, polyvinyl chloride, polystyrene, nylon, polypropylene, acrylics, acrylonitrile, acrylonitrile butadiene styrene polymer, however In terms of annual consumption, high-density polyethylene occupies the first place.

Blow molding has its origins in the glass industry. The scheme of this process is given in Fig.7.

A hot softened thermoplastic tube, called a "blank", is placed inside a two-part hollow mold. When the form is closed, both halves of it clamp one end of the workpiece and the air supply needle located at the other end of the tube.

Fig.7. Schematic diagram explaining the stages of the blow molding process

a - a workpiece placed in an open mold; b - closed mold;

c - blowing air into the mold; d - opening the mold. 1 - blank;

2 - needle for air supply; 3 - Press form; 4 - air; 5 - air molded product

Under the action of pressure supplied from the compressor through the needle, the hot billet is inflated like a ball until it comes into tight contact with the relatively cold inner surface of the mold. Then the mold is cooled, opened and the finished solid thermoplastic product is removed.

The preform for blow molding can be obtained by injection molding or extrusion, and depending on this, the method is called injection blow molding or extrusion blow molding, respectively.

FORMING SHEET THERMOPLASTICS. The molding of thermoplastic sheets is an extremely important process for the production of three-dimensional plastic products. With this method, even such large products as submarine hulls are obtained from sheets of acrylonitrile butadiene styrene.

The scheme of this Process is as follows. The thermoplastic sheet is heated to its softening temperature. Then the punch presses a hot flexible sheet into a metal mold matrix (Fig. 9), while the sheet takes a certain shape. When cooled, the molded product solidifies and is removed from the mold.

In the modified method, under the action of vacuum, the hot sheet is sucked into the cavity of the die and takes the required shape (Fig. 10). This method is called the vacuum forming method.

2.7 EXTRUSION

Extrusion is one of the cheapest methods for producing widely used plastic products such as films, fibers, pipes, sheets, rods, hoses and belts, the profile of these products being determined by the shape of the extruder head outlet. Molten plastic, under certain conditions, is extruded through the outlet of the extruder head, which gives the desired profile to the extrudate. The diagram of the simplest extrusion machine is shown in Fig. 8.

Fig 8. Schematic representation of the simplest extrusion machine

1 - loading funnel; 2 - auger; 3 - main cylinder; 4 - heating elements; 5 - outlet of the extruder head, a - Loading Zone; b - compression zone; in ~ homogenization zone

In this machine, the powder or granules of the compounded plastic material is loaded from a hopper into an electrically heated cylinder to soften the polymer. A spiral-shaped rotating screw ensures the movement of hot plastic mass along the cylinder. Since friction occurs between the rotating screw and the barrel during the movement of the polymer mass, this leads to the release of heat and, consequently, to an increase in the temperature of the processed polymer. In the process of this movement from the hopper to the outlet of the extruder head, the plastic mass passes through three clearly separated zones: the loading zone (a), the compression zone (b) and the homogenization zone (in)(See Figure 9).

Each of these zones contributes to the extrusion process. The loading zone, for example, takes the polymer mass from the hopper and sends it to the compression zone, this operation takes place without heating.

Rice. nine. Scheme of the molding process of sheet thermoplastics

1 - sheet of thermoplastic material; 2 - clamp; 3 - punch; 4 - heat-softened sheet; 5 - matrix; 6 - product obtained by molding sheet thermoplastics

Fig.10. Diagram of the vacuum forming process for thermoplastics

1 - clamp; 2 - thermoplastic sheet; 3 - Press form; 4 - product obtained by vacuum forming of thermoplastics

In the compression zone, the heating elements ensure the melting of the powdered charge, and the rotating screw compresses it. Then the pasty molten plastic material enters the homogenization zone, where it acquires a constant flow rate due to the screw thread of the screw.

Under the action of the pressure created in this part of the extruder, the polymer melt is fed to the outlet of the extruder head and exits with the desired profile. Due to the high viscosity of some polymers, it is sometimes necessary to have another zone, called a working zone, where the polymer is subjected to high shear loads to improve mixing efficiency. The extruded material of the desired profile leaves the extruder in a very hot state (its temperature is from 125 to 350°C), and rapid cooling is required to maintain its shape. The extrudate enters a conveyor belt passing through a vat of cold water and solidifies. Cold air blowing and cold water spraying are also used to cool the extrudate. The shaped product is further either cut or wound into coils.

The extrusion process is also used to cover wires and cables with polyvinyl chloride or rubber, and rod-like metal rods with suitable thermoplastic materials.

2.8 FOAMING

Foaming is a simple method for obtaining foam and sponge-like materials. The special properties of this class of materials - shock-absorbing ability, light weight, low thermal conductivity - make them very attractive for use in various purposes. Common foaming polymers are polyurethanes, polystyrene, polyethylene, polypropylene, silicones, epoxies, PVC, etc. The foam structure consists of isolated (closed) or interpenetrating (open) voids. In the first case, when the voids are closed, they can contain gases. Both types of structures are shown schematically in Fig. 11.

Fig.11. Schematic representation of open and closed cell structures formed during the foaming process

1- discrete (closed) cells; 2 - interpenetrating (open) cells;

3 - cell walls

There are several methods for producing foamed or cellular plastics. One of them is that air or nitrogen is blown through the molten compound until it is completely foamed. The foaming process is facilitated by the addition of surface active agents. Upon reaching the desired degree of foaming, the matrix is ​​cooled to room temperature. In this case, the thermoplastic material solidifies in a foamed state. Thermoset liquid prepolymers can be cold-foamed and then heated until fully cured. Foaming is usually achieved by adding foam or blowing agents to the polymer mass. Such agents are low molecular weight solvents or certain chemical compounds. The boiling process of solvents such as n-pentane and n-hexane at the temperatures of curing of polymeric materials is accompanied by an intense vaporization process. On the other hand, some chemical compounds at these temperatures can decompose with the release of inert gases. So, azo-bis-isobutyronitrile thermally decomposes, while releasing a large amount of nitrogen released into the polymer matrix as a result of the reaction between isocyanate and water, and is also used to produce foamed materials, such as polyurethane foam:

Since polyurethanes are obtained by the reaction of a polyol with a diisocyanate, additional small amounts of diisocyanate and water must be added to foam the reaction product.

So, a large amount of vapors or gases emitted by foam and gas formers leads to foaming of the polymer matrix. The polymer matrix in the foamed state is cooled to temperatures below the softening temperature of the polymer (in the case of thermoplastic materials) or subjected to a curing or crosslinking reaction (in the case of thermoset materials), as a result, the matrix acquires the rigidity necessary to maintain the foam structure. This process is called the "foam stabilization" process. If the matrix is ​​not cooled below the softening temperature or cross-linked, the gases filling it leave the pore system and the foam collapses.

Foams can be obtained in flexible, rigid and semi-rigid forms. In order to obtain foam products directly, foaming should be carried out directly inside the mold. Styrofoam sheets and rods can also be used to produce various products. Depending on the nature of the polymer and the degree of foaming, the density of the foams can range from 20 to 1000 kg/cm 3 . The use of foams is very diverse. For example, the automotive industry uses large quantities of PVC and polyurethane foams for upholstery. These materials play an important role in the manufacture of furniture. Rigid polystyrene foams are widely used for packaging and thermal insulation of buildings. Foam rubbers and polyurethane foams are used for filling mattresses, etc. Rigid polyurethane foams are also used for thermal insulation of buildings and for the manufacture of prostheses.

2.9 REINFORCEMENT

By reinforcing the plastic matrix with high-strength fiber, systems called "fiber-reinforced plastics" (FRPs) are obtained. WUAs have very valuable properties: they are distinguished by a high strength-to-weight ratio, significant corrosion resistance, and ease of manufacture. The method of fiber reinforcement makes it possible to obtain a wide range of products. For example, when creating artificial satellites in AUAs, designers and creators of spacecraft are primarily attracted by the amazingly high strength-to-weight ratio. Beautiful appearance, light weight and corrosion resistance make it possible to use WUA for ship plating. In addition, WUA is even used as a material for tanks in which acids are stored.

Let us now dwell in more detail on the chemical composition and physical nature of these unusual materials. As noted above, they are a polymeric material, the special properties of which are due to the introduction of reinforcing fibers into it. The main materials from which reinforcing fibers are made (both finely chopped and long) are glass, graphite, aluminum, carbon, boron and beryllium. The most recent developments in this field are the use of fully aromatic polyamide as reinforcing fibers, which provides more than 50% weight reduction compared to traditional fiber reinforced plastics. Natural fibers are also used for reinforcement, such as sisal, asbestos, etc. The choice of reinforcing fiber is primarily determined by the requirements for the final product. However, glass fibers remain widely used to this day and still make the main contribution to the industrial production of WUA. The most attractive properties of glass fibers are low thermal expansion coefficient, high dimensional stability, low production cost, high tensile strength, low dielectric constant, non-flammability and chemical resistance. Other reinforcing fibers are used mainly in cases where some additional properties are required for the operation of ARP in specific conditions, despite their higher cost compared to glass fibers.

HDPE is produced by bonding fibers to a polymer matrix and then curing it under pressure and temperature. Reinforcing additives can be in the form of finely chopped fibers, long threads and fabrics. The main polymer matrices used in ARP are polyesters, epoxides, phenols, silicones, melamine, vinyl derivatives, and polyamides. Most WUAs are produced on the basis of polyester polymers, the main advantage of which is their low cost. Phenolic polymers are used in cases where high temperature resistance is required. Extremely high mechanical properties of AVP are acquired when epoxy resins are used as a polymer matrix. The use of silicone polymers gives WUAs excellent electrical and thermal properties.

Currently, there are several methods of plastic reinforcement. The most commonly used of these are: 1) hand lamination method, 2) fiber winding method, and 3) spray impregnation method.

METHOD OF LAYERING SHEETS MANUALLY. It is likely that this is the simplest method of reinforcing plastics. In this case, the quality of the final product is largely determined by the skill and skill of the operator. The whole process consists of the following steps. First, the mold is covered with a thin layer of adhesive lubricant based on polyvinyl alcohol, silicone oil or paraffin. This is done to prevent the end product from sticking to the mold. Then the form is covered with a layer of polymer, on top of which a fiberglass or mat is placed. This fiberglass is in turn coated with another layer of polymer.

Fig.12. Schematic representation of the manual layering method

1 - alternating layers of polymer and fiberglass; 2 - Press form; 3 - rolling roller

All this is tightly rolled with rollers to uniformly press the fiberglass to the polymer and remove air bubbles. The number of alternating layers of polymer and fiberglass determines the thickness of the sample (Fig. 12).

Then, at room or elevated temperature, the system cures. After curing, the reinforced plastic is removed from the mold and stripped and finished. This method produces sheets, car body parts, ship hulls, pipes and even building fragments.

WINDING METHOD OF FIBER. This method is very widely used for the production of reinforced plastic products such as high-pressure cylinders, chemical storage tanks, and rocket motor casings. It consists in the fact that a continuous monofilament, fiber, fiber bundle or woven tape is passed through a bath of resin and hardener. As the fiber exits the bath, the excess resin is squeezed out. The resin-impregnated fibers or tape are then wound onto a core of the desired shape and cured under the action of temperature.

Fig.13. Schematic representation of the fiber winding method

1- supply coil; 2 - continuous thread; 3 - unit for fiber impregnation and resin pressing; 4 - core; 5 - resin-impregnated fibers wound on a core

The winding machine (Fig. 13) is designed so that the fibers can be wound around the core in a certain way. The tension of the fiber and the method of winding it are very important from the point of view of the final deformation properties of the finished product.

SPRAYING METHOD. In this method, a spray gun with a multi-strand head is used. Jets of resin, hardener and chopped fiber are simultaneously fed from the spray gun to the surface of the mold (Fig. 14), where they form a layer of a certain thickness. Chopped fiber of a certain length is obtained by continuous supply of fibers to the grinding head of the apparatus. After reaching the required thickness, the polymer mass is cured by heating. Spraying is an express method for covering large surfaces. Many modern plastic products, such as cargo platforms, storage tanks, truck bodies and ship hulls, are made using this method.

Fig.14. Schematic representation of the spraying method

1 - form; 2 - sprayed mixture of chopped fiber and resin; 3 - a jet of chopped fiber; 4 - continuous fiber; 5- resin; 6- hardener; 7 - node for cutting fiber and spraying; 8 - resin jet

OTHER METHODS. In addition to the methods described above, others are known in the production of reinforced plastics, each of which has its own specific purpose. Thus, the method of manufacturing continuous laminates is used for the production of continuous sheets of reinforced laminates of various thicknesses. In this process, each individual layer of woven tape coming from rolls is impregnated with resin and hardener and then pressed together through a hot roll system. After curing under the influence of temperature, a laminate I of the required thickness is obtained (Fig. 15). The thickness of the material can be varied by changing the number of layers.

Fig.15. Schematic representation of the production method for continuous laminated materials

1- feed coils; 2 - continuous sheets of fiberglass; 3 - bath for impregnation in a mixture of resin and hardener; 4 - continuous laminate; 5 - laminated plastic, cut into pieces of the required size

Another method, known as the plywood method, makes it possible to manufacture products such as hollow rods or fishing rods from continuous bundles of fibers. This process is relatively simple. A continuous bundle of fibers, previously treated with resin and hardener, is pulled through a die of the corresponding profile (Fig. 16), heated to a certain temperature. At the exit from the die, the profiled product continues to be heated. The cured profile is pulled out of the die by a system of rotating rolls. This process is somewhat similar to extrusion, with the only difference being that in extrusion the polymeric material is pushed through the die from the inside by means of a rotating screw, while in the described method the material is pulled through the die outlet from the outside.

Fig.16. Schematic representation of the method for obtaining pultruded fiber plastic

1 - a continuous bundle of fibers impregnated with resin and hardener; 2 - heating element; 3 - die; 4 - rotating draw rolls; 5 - finished product, cut into pieces; 6 - finished product profile

In addition, the mixture containing cut fibers, resin and hardener may be formed by any other suitable method, such as direct compression. Thermoplastic materials filled with cut fibers can be molded by direct compression, injection molding, or extrusion to produce end products with improved mechanical properties.

2.10 SPINNING FIBERS

Polymer fibers are obtained in a process called spinning. There are three fundamentally different spinning methods: melt spinning, dry spinning and wet spinning. In the melt spinning process, the polymer is in a molten state, and in other cases, in the form of solutions. However, in all these cases, the polymer, in a molten or dissolved state, flows through a multi-channel mouthpiece, which is a plate with very small holes for the exit of fibers.

SPINTING FROM THE MELT. In its simplest form, the spunmelt process can be represented as follows. Initially, the polymer flakes are melted on a heated grid, turning the polymer into a viscous mobile liquid. Sometimes, during the heating process, lumps are formed due to the processes of crosslinking or thermal destruction. These lumps can be easily removed from the hot polymer melt by passing through a block filter system. In addition, to prevent oxidative degradation, the melt should be protected from atmospheric oxygen. This is achieved mainly by creating an inert atmosphere of nitrogen, CO2, and water vapor around the polymer melt. The dosing pump delivers the polymer melt at a constant rate to the multi-channel die. The polymer melt passes through a system of fine holes in the mouthpiece and exits from there in the form of continuous and very thin monofilaments. Upon contact with cold air, the fibers emerging from the spinnerets instantly harden. Cooling and hardening processes can be greatly accelerated by blowing cold air. The solid monofilaments emerging from the spinnerets are wound onto spools.

An important feature to consider in the melt spinning process is that the diameter of the monofilament is highly dependent on the speed at which the molten polymer passes through the spinneret and the rate at which the monofilament is drawn from the spinneret and wound onto spools.

Fig.17. Schematic representation of dry spinning processes (a) and melt spinning (b)

1 - hopper; 2 - polymer flakes; 3 - heated grate; 4 - hot polymer; 5 - dosing pump; b - melt; 7- multi-channel mouthpiece, 8 - freshly spun fiber; 9 - coil; 10 - polymer solution; 11 - filter;

12 - dosing pump; 13 - multichannel mouthpiece; 14 - freshly spun fiber; 15 - on the coil

DRY SPINNING. A large number of traditional polymers such as PVC or polyacrylonitrile are processed into fibers on a large scale in the dry spinning process. The essence of this process is shown in Fig.17. The polymer is dissolved in an appropriate solvent to form a highly concentrated solution. The viscosity of the solution is adjusted by increasing the temperature. The hot, viscous polymer solution is forced through the spinnerets, thus producing thin continuous streams. The fiber from these streams is formed by simple evaporation of the solvent. Evaporation of the solvent can be accelerated by blowing with a counter flow of dry nitrogen. The fibers formed from the polymer solution are finally wound onto spools. The fiber spinning speed can reach 1000m/min. Industrial cellulose acetate fibers obtained from a 35% polymer solution in acetone at 40°C are a typical example of fiber production by dry spinning.

WET SPINNING. In wet spinning, as in dry spinning, highly concentrated polymer solutions are used, the high viscosity of which can be reduced by increasing the spinning temperature. Details of the wet spinning process are shown in Figure 18. In the wet spinning process, a viscous polymer solution is processed into thin strings when passed through spinnerets. Then these polymer jets enter the coagulation bath with a precipitant, where the polymer is precipitated from the solution in the form of thin filaments, which, after washing, drying, etc., are collected on coils. Sometimes, during wet spinning, lumps are formed instead of continuous filaments, which occurs as a result of the breakage of a trickle flowing from a spinneret under the action of surface tension forces.

Fig.18. Schematic representation of the wet spinning process

1 - polymer solution; 2 - filter; 3 - dosing pump; 4 - multichannel mouthpiece; 5 - precipitant; 6 - freshly spun fiber; 7 - bath for coagulation and sedimentation; 8 - washing bath; 9 - drying; 10 - on the coil

This can be avoided by increasing the viscosity of the polymer solution. Coagulation, which is the limiting stage of wet spinning, is a rather slow process, which explains the low solution spinning speed of 50 m/min compared to others. In industry, the wet spinning process is used to produce fibers from polyacrylonitrile, cellulose, viscose fiber, etc.

SINGLE-AXIS ORIENTATION. In the process of spinning fibers from a polymer melt or solution, the macromolecules in the fiber are not oriented and, therefore, their degree of crystallinity is relatively low, which undesirably affects the physical properties of the fiber. To improve the physical properties of the fibers, they are subjected to an operation called uniaxial drawing using some type of stretching apparatus.

The main feature of the device is the presence of a system of two rollers BUT and AT(Fig. 19), rotating at different speeds. Video clip AT rotates 4-5 times faster than the roller BUT. The spun yarn is passed successively through a roller BUT, tensile hairpin 3 and roller AT. Since the roller AT rotates at a speed greater than the roller BUT, the fiber is pulled out under the load given by the pin 3. The fiber is drawn in the zone 2. After going through the roller AT elongated polymer thread is wound on a metal reel. Despite the fact that the diameter of the thread decreases during drawing, its strength properties are significantly improved due to the orientation of macromolecules parallel to the fiber axis.

Fig.19. Schematic representation of the device for uniaxial orientation

1 - unstretched thread; 2 - exhaust zone; 3 - stretching pin; 4- drawn fiber

SUBSEQUENT PROCESSING OF FIBERS. To improve the useful properties of the fibers, they are often subjected to additional special processing: cleaning, lubrication, sizing, dyeing, etc.

Soaps and other synthetic detergents are used for cleaning. Cleaning is nothing more than the removal of dirt and other impurities from the surface of the fiber. Lubrication consists in processing the fibers in order to protect

them from friction with neighboring fibers and rough metal surfaces during processing. Natural oils are mainly used as lubricating agents. Lubrication also reduces the amount of static electricity that builds up on the fibers.

Sizing refers to the process of protective coating of fibers. Polyvinyl alcohol or gelatin are used as sizing materials for most fibers. The sizing keeps the fibers within a compact bundle and thus ensures uniform weaving. Before dyeing the fabric, the gluing should be removed by rinsing in water.

For dyeing, the fibers are placed in a dye solution, the molecules of which usually penetrate only into the amorphous regions of the fiber.

Fibers based on cellulose or proteins quickly adsorb acidic dyes, which easily bind to the amino or hydroxyl groups of the polymers. The dyeing process for synthetic fibers such as polyesters, polyamides or acrylics is much slower. In this case, the dyeing rate can be increased by increasing the temperature. Dyeing of fibers based on polyvinyl chloride, polyethylene, etc. is practically impossible without the introduction of active absorption centers into them during copolymerization and chemical oxidation.

CONCLUSION

As previously noted, polymers include numerous natural compounds: proteins, nucleic acids, cellulose, starch, rubber, and other organic substances. A large number of polymers are obtained synthetically based on the simplest compounds of elements of natural origin through polymerization, polycondensation, and chemical transformations.

In the early 1960s, polymers were considered only cheap substitutes for scarce natural raw materials - cotton, silk, and wool. But soon the understanding came that polymers, fibers and other materials based on them are sometimes better than traditionally used natural materials - they are lighter, stronger, more heat resistant, able to work in aggressive environments. Therefore, chemists and technologists directed all their efforts to the creation of new polymers with high performance characteristics and methods for their processing. And they achieved results in this business, sometimes surpassing the results of similar activities of well-known foreign firms.

Polymers are widely used in many areas of human activity, satisfying the needs of various industries, agriculture, medicine, culture and everyday life. At the same time, it is appropriate to note that in recent years, the function of polymeric materials in any industry and the methods for their production have somewhat changed. More and more responsible tasks began to be trusted to polymers. More and more relatively small, but structurally complex and critical parts of machines and mechanisms began to be made from polymers, and at the same time, polymers began to be used more and more often in the manufacture of large body parts of machines and mechanisms that carry significant loads.

The boundary of the strength properties of polymeric materials was overcome by the transition to composite materials, mainly glass and carbon fiber. So now the expression “plastic is stronger than steel” sounds quite reasonable. At the same time, polymers retained their positions in the mass production of a huge number of those parts that do not require particularly high strength: plugs, fittings, caps, handles, scales and measuring instrument cases. Another area specific to polymers, where their advantages over any other materials are most clearly manifested, is the area of ​​interior and exterior decoration.

By the way, the same advantages stimulate the widespread use of polymeric materials in the aviation industry. For example, replacing an aluminum alloy with graphite plastic in the manufacture of an aircraft wing slat makes it possible to reduce the number of parts from 47 to 14, fasteners from 1464 to 8 bolts, reduce weight by 22%, and cost by 25%. At the same time, the safety margin of the product is 178%. Helicopter blades, jet engine fan blades are recommended to be made from polycondensation resins filled with aluminosilicate fibers, which makes it possible to reduce aircraft weight while maintaining strength and reliability.

All these examples show the huge role of polymers in our life. It is difficult to imagine what materials based on them will still be obtained. But it is safe to say that polymers will take, if not the first, then at least one of the first places in production. It is quite obvious that the quality, characteristics and properties of the final products directly depend on the polymer processing technology. The importance of this aspect forces us to look for more and more new ways of processing to obtain materials with improved performance. In this essay, only the main methods were considered. Their total number is not limited to this.

BIBLIOGRAPHY

1. Pasynkov V.V., Sorokin V.S., Materials of electronic technology, - M .: Higher School, 1986.

2.A. A. Tager, Physicochemistry of polymers, M., chemistry, 1978.

3. Tretyakov Yu.D., Chemistry: Reference materials. – M.: Enlightenment, 1984.

4. Materials Science / Ed. B.N. Arzamasov. - M .: Mashinostroenie, 1986.

5. Dontsov A. A., Dogadkin B. A., Shershnev V. A., Chemistry of elastomers, - M .: Chemistry, 1981.

1. INTRODUCTION

One of the most tangible results of anthropogenic activity is the generation of waste, among which waste plastics occupy a special place due to their unique properties.

Plastics are chemical products made up of high molecular weight, long chain polymers. The production of plastics at the present stage of development is increasing by an average of 5...6% annually and by 2010, according to forecasts, it will reach 250 million tons. Their per capita consumption in industrialized countries has doubled over the past 20 years, reaching 85...90 kg, By the end of the decade, this figure is believed to increase by 45 ... 50%.

THERE ARE ABOUT 150 TYPES OF PLASTICS, 30% OF THEM ARE MIXTURES OF DIFFERENT POLYMERS. TO ACHIEVE CERTAIN PROPERTIES AND BETTER PROCESSING, VARIOUS CHEMICAL ADDITIVES ARE INTRODUCED INTO POLYMERS, WHICH ARE ALREADY MORE THAN 20, AND A SERIES OF THEM ARE RELATED TO TOXIC MATERIALS. THE OUTPUT OF SUPPLEMENTS IS CONTINUOUSLY INCREASING. IF IN 1980 4000 T OF THEM WAS PRODUCED, THEN BY 2000 THE OUTPUT VOLUME ALREADY INCREASED TO 7500 T, AND ALL OF THEM WILL BE INTRODUCED IN PLASTICS. AND OVER TIME, CONSUMED PLASTICS INEVITABLY GO TO WASTE.

ONE OF THE FAST-GROWING DIRECTIONS OF PLASTIC USE IS PACKAGING.

Of all the plastics produced, 41% is used in packaging, of which 47% is spent on food packaging. Convenience and safety, low price and high aesthetics are the defining conditions for the accelerated growth in the use of plastics in the manufacture of packaging.

Such a high popularity of plastics is explained by their lightness, cost-effectiveness and a set of valuable service properties. Plastics are serious competitors to metal, glass, and ceramics. For example, glass bottles require 21% more energy to make than plastic bottles.

But along with this, there is a problem with the disposal of waste, of which there are over 400 different types that appear as a result of the use of polymer industry products.

Today, more than ever before, the people of our planet are thinking about the huge pollution of the Earth by the ever-increasing waste of plastics. In this regard, the textbook replenishes knowledge in the field of recycling and recycling of plastics in order to return them to production and improve the environment in the Russian Federation and in the world.

2 ANALYSIS OF THE STATE OF RECYCLING AND UTILIZATION OF POLYMERIC MATERIALS

2.1 ANALYSIS OF THE STATE OF RECYCLING OF POLYMERIC MATERIALS

Of all the plastics produced, 41% is used in packaging, of which 47% is spent on food packaging. Convenience and safety, low price and high aesthetics are the defining conditions for the accelerated growth in the use of plastics in the manufacture of packaging. Packaging made of synthetic polymers, which makes up 40% of household waste, is practically "eternal" - it does not decompose. Therefore, the use of plastic packaging is associated with the generation of waste in the amount of 40...50 kg/year per person.

In Russia, presumably by 2010, polymer waste will amount to more than one million tons, and the percentage of their use is still small. Taking into account the specific properties of polymeric materials - they do not undergo decay, corrosion, the problem of their disposal is, first of all, of an environmental nature. The total volume of municipal solid waste disposal in Moscow alone is about 4 million tons per year. Of the total level of waste, only 5 ... 7% of their mass is recycled. According to 1998 data, in the average composition of municipal solid waste supplied for disposal, 8% is plastic, which is 320 thousand tons per year.

However, at present, the problem of processing waste polymer materials is becoming relevant not only from the standpoint of environmental protection, but also due to the fact that in the conditions of a shortage of polymer raw materials, plastic waste becomes a powerful raw material and energy resource.

At the same time, the solution of issues related to environmental protection requires significant capital investments. The cost of processing and destroying plastic waste is about 8 times higher than the cost of processing most industrial waste and almost three times the cost of destroying household waste. This is due to the specific features of plastics, which significantly complicate or render unsuitable known methods for the destruction of solid waste.

The use of waste polymers can significantly save primary raw materials (primarily oil) and electricity.

There are many problems associated with the disposal of polymer waste. They have their own specifics, but they cannot be considered unsolvable. However, the solution is impossible without organizing the collection, sorting and primary processing of depreciated materials and products; without developing a system of prices for secondary raw materials, stimulating enterprises to process them; without creating effective methods for processing secondary polymeric raw materials, as well as methods for modifying it in order to improve quality; without creating special equipment for its processing; without developing a range of products manufactured from recycled polymer raw materials.

Waste plastics can be divided into 3 groups:

a) technological production wastes that arise during the synthesis and processing of thermoplastics. They are divided into non-removable and disposable technological waste. Fatal - these are edges, cuts, trimmings, sprues, flash, flash, etc. In industries involved in the production and processing of plastics, such waste is generated from 5 to 35%. Non-removable waste, essentially representing a high-quality raw material, does not differ in properties from the original primary polymer. Its processing into products does not require special equipment and is carried out at the same enterprise. Disposable technological production wastes are formed in case of non-observance of technological regimes in the process of synthesis and processing, i.e. this is a technological marriage that can be minimized or completely eliminated. Technological production wastes are processed into various products, used as an additive to the original raw materials, etc.;

b) industrial consumption waste - accumulated as a result of the failure of products made of polymeric materials used in various sectors of the national economy (damped tires, containers and packaging, machine parts, agricultural film waste, fertilizer bags, etc.). These wastes are the most homogeneous, least polluted, and therefore are of the greatest interest in terms of their recycling;

c) public consumption waste that accumulates at our homes, catering establishments, etc., and then ends up in city dumps; eventually they move into a new category of waste - mixed waste.

The greatest difficulties are associated with the processing and use of mixed waste. The reason for this is the incompatibility of thermoplastics that are part of household waste, which requires their step-by-step isolation. In addition, the collection of worn-out polymer products from the population is an extremely complex event from an organizational point of view and has not yet been established in our country.

The main amount of waste is destroyed - burial in the soil or incineration. However, the destruction of waste is economically unprofitable and technically difficult. In addition, the burial, flooding and burning of polymer waste leads to environmental pollution, to the reduction of land (organization of landfills), etc.

However, both landfill and incineration continue to be fairly common ways of destroying waste plastics. Most often, the heat released during combustion is used to generate steam and electricity. But the calorie content of the combusted raw materials is low, so incinerators are usually economically inefficient. In addition, during combustion, soot is formed from the incomplete combustion of polymer products, toxic gases are released and, consequently, re-pollution of the air and water basins, and rapid wear of furnaces due to severe corrosion.

In the early 1970s of the last century, work began to develop intensively on the creation of bio-, photo-, and water-degradable polymers. Getting degradable polymers caused quite a sensation, and this way of destroying failed plastic products was seen as ideal. However, subsequent work in this direction showed that it is difficult to combine high physical and mechanical characteristics, beautiful appearance, the ability to quickly break down and low cost in products.

In recent years, research into self-degrading polymers has declined significantly, mainly because the production costs of producing such polymers are generally much higher than those of conventional plastics, and this method of destruction is not economically viable.

The main way of using waste plastics is their recycling, i.e. reuse. It is shown that the capital and operating costs for the main methods of waste disposal do not exceed, and in some cases even lower than the costs of their destruction. The positive side of recycling is also the fact that an additional amount of useful products is obtained for various sectors of the national economy and there is no re-pollution of the environment. For these reasons, recycling is not only an economically viable, but also an environmentally preferable solution to the problem of using plastic waste. It is estimated that only a small part (only a few percent) of the annually generated polymer waste in the form of depreciated products is recycled. The reason for this is the difficulties associated with the preliminary preparation (collection, sorting, separation, cleaning, etc.) of waste, the lack of special equipment for processing, etc.

The main ways of recycling waste plastics include:

1. thermal decomposition by pyrolysis;
2. decomposition to obtain initial low molecular weight products (monomers, oligomers);
3. recycling.

Pyrolysis is the thermal decomposition of organic products with or without oxygen. Pyrolysis of polymer wastes makes it possible to obtain high-calorie fuel, raw materials and semi-finished products used in various technological processes, as well as monomers used for polymer synthesis.

The gaseous products of the thermal decomposition of plastics can be used as a fuel to produce working steam. Liquid products are used to obtain heat transfer fluids. The range of application of solid (waxy) products of pyrolysis of waste plastics is quite wide (components of various kinds of protective compounds, lubricants, emulsions, impregnating materials, etc.)

Catalytic hydrocracking processes have also been developed to convert waste polymers into gasoline and fuel oils.

Many polymers, as a result of the reversibility of the reaction of formation, can again decompose to the starting substances. For practical use, the methods of splitting PET, polyamides (PA) and foamed polyurethanes are important. The cleavage products are used again as raw materials for the polycondensation process or as additives to the virgin material. However, the impurities present in these products often do not make it possible to obtain high-quality polymer products, such as fibers, but their purity is sufficient for the manufacture of casting masses, fusible and soluble adhesives.

Hydrolysis is the reverse reaction of polycondensation. With its help, with the directed action of water at the junctions of the components, polycondensates are destroyed to the original compounds. Hydrolysis occurs under extreme temperatures and pressures. The depth of the reaction depends on the pH of the medium and the catalysts used.

This method of using waste is more energetically beneficial than pyrolysis, since high-quality chemical products are returned to circulation.

Compared to hydrolysis, another method, glycolysis, is more economical to break down PET waste. Destruction occurs at high temperatures and pressure in the presence of ethylene glycol and with the participation of catalysts to obtain pure diglycol terephthalate. It is also possible to transesterify carbamate groups in polyurethane according to this principle.

Still, the most common thermal method for processing PET waste is their splitting with methanol - methanolysis. The process proceeds at a temperature above 150°C and a pressure of 1.5 MPa, accelerated by interesterification catalysts. This method is very economical. In practice, a combination of glycolysis and methanolysis methods is also used.

Currently, the most acceptable for Russia is the recycling of waste polymer materials mechanical recycling, since this method of processing does not require expensive special equipment and can be implemented in any place of waste accumulation.

2.2 POLYOLEFIN WASTE DISPOSAL

Polyolefins are the most multi-tonnage type of thermoplastics. They are widely used in various industries, transport and agriculture. Polyolefins include high and low density polyethylene (HDPE and LDPE), PP. The most efficient way to dispose of software waste is to reuse it. Resources of secondary PO are large: in 1995 alone, LDPE consumption waste reached 2 million tons. The use of secondary thermoplastics in general, and PO in particular, allows increasing the degree of satisfaction in them by 15 ... 20%.

Methods for recycling software waste depend on the brand of polymer and their origin. Process waste is most easily recycled, i.e. production waste that has not been subjected to intense light exposure during operation. Do not require complex methods of preparation and consumer waste from HDPE and PP, since, on the one hand, products made from these polymers also do not undergo significant impacts due to their design and purpose (thick-walled parts, containers, accessories, etc.), and on the other hand, virgin polymers are more weather resistant than LDPE. Such waste before reuse needs only grinding and granulation.

2.2.1 Structural and chemical features of recycled polyethylene

The choice of technological parameters for the processing of software waste and the areas of use of the products obtained from them is due to their physicochemical, mechanical and technological properties, which differ to a large extent from the same characteristics of the primary polymer. The main features of recycled LDPE (VLDPE), which determine the specifics of its processing, include: low bulk density; features of the rheological behavior of the melt, due to the high content of gel; increased chemical activity due to structural changes occurring during the processing of the primary polymer and the operation of products obtained from it.

In the process of processing and operation, the material is subjected to mechanochemical influences, thermal, thermal and photo-oxidative degradation, which leads to the appearance of active groups, which, during subsequent processing, are capable of initiating oxidation reactions.

The change in the chemical structure begins already during the primary processing of PO, in particular, during extrusion, when the polymer is subjected to significant thermal-oxidative and mechanochemical effects. The greatest contribution to the changes occurring during operation is made by photochemical processes. These changes are irreversible, while the physical and mechanical properties of, for example, a polyethylene film that has served one or two seasons for sheltering greenhouses are almost completely restored after overpressing and extrusion.

The formation of a significant number of carbonyl groups in the PE film during its operation leads to an increased ability of VLDPE to absorb oxygen, resulting in the formation of vinyl and vinylidene groups in the secondary raw materials, which significantly reduce the thermal-oxidative stability of the polymer during subsequent processing, initiate the process of photoaging of such materials and products from them reduce their service life.

The presence of carbonyl groups does not determine either the mechanical properties (their introduction of up to 9% into the initial macromolecule does not have a significant effect on the mechanical properties of the material), nor the transmission of sunlight by the film (the absorption of light by carbonyl groups lies in the wavelength region of less than 280 nm, and light of such a composition practically absent from the solar spectrum). However, it is the presence of carbonyl groups in PE that determines its very important property - resistance to light.

The initiator of photoaging of PE are hydroperoxides, which are formed during the processing of the primary material in the process of mechanochemical destruction. Their initiating action is especially effective in the early stages of aging, while carbonyl groups have a significant effect in the later stages.

As is known, competing reactions of destruction and structuring occur during aging. The consequence of the first is the formation of low molecular weight products, the second is the formation of an insoluble gel fraction. The rate of formation of low molecular weight products is maximum at the beginning of aging. This period is characterized by a low gel content and a decrease in physical and mechanical properties.

Further, the rate of formation of low molecular weight products decreases, a sharp increase in the content of the gel and a decrease in the relative elongation are observed, which indicates the course of the structuring process. Then (after reaching the maximum), the gel content in the VPE decreases during its photoaging, which coincides with the complete consumption of vinylidene groups in the polymer and the achievement of the maximum allowable values ​​of relative elongation. This effect is explained by the involvement of the resulting spatial structures in the process of destruction, as well as cracking along the border of morphological formations, which leads to a decrease in physical and mechanical characteristics and a deterioration in optical properties.

The rate of change in the physical and mechanical characteristics of WPE is practically independent of the content of the gel fraction in it. However, the gel content must always be taken into account as a structural factor when choosing a recycling method, modification and when determining polymer applications.

In table. 1 shows the characteristics of the properties of LDPE before and after aging for three months and HLDPE obtained by extrusion from aged film.

1 Characteristics of LDPE properties before and after aging

Characteristics		original	After operation	extrusion
Tensile stress, MPa
Elongation at break, %
Crack resistance, h
Light fastness, days

The nature of the change in the physical and mechanical characteristics for LDPE and VLDPE is not the same: the primary polymer exhibits a monotonous decrease in both strength and relative elongation, which are 30 and 70%, respectively, after aging for 5 months. For recycled LDPE, the nature of the change in these indicators is somewhat different: the breaking stress practically does not change, and the relative elongation decreases by 90%. The reason for this may be the presence of a gel fraction in HLDPE, which acts as an active filler in the polymer matrix. The presence of such a "filler" is the cause of the appearance of significant stresses, resulting in an increase in the brittleness of the material, a sharp decrease in relative elongation (up to 10% of the values ​​for primary PE), cracking resistance, tensile strength (10 ... 15 MPa), elasticity, increase in rigidity.

In PE, during aging, not only the accumulation of oxygen-containing groups, including ketone, and low molecular weight products, but also a significant decrease in physical and mechanical characteristics, which are not restored after recycling of the aged polyolefin film, occurs. Structural-chemical transformations in HLDPE occur mainly in the amorphous phase. This leads to a weakening of the interfacial boundary in the polymer, as a result of which the material loses its strength, becomes brittle, brittle, and is subject to further aging both during reprocessing into products and during the operation of such products, which are characterized by low physical and mechanical properties and service life.

To assess the optimal modes of processing of secondary polyethylene raw materials, its rheological characteristics are of great importance. HLDPE is characterized by low fluidity at low shear stresses, which increases with increasing stress, and the increase in fluidity for HPE is greater than for primary. The reason for this is the presence of a gel in the HLDPE, which significantly increases the activation energy of the viscous flow of the polymer. Fluidity can be controlled by also changing the temperature during processing - with an increase in temperature, the fluidity of the melt increases.

So, a material comes for recycling, the background of which has a very significant impact on its physical, mechanical and technological properties. In the process of recycling, the polymer is subjected to additional mechanochemical and thermal-oxidative effects, and the change in its properties depends on the frequency of processing.

When studying the effect of the frequency of processing on the properties of the resulting products, it was shown that 3-5 times processing has an insignificant effect (much less than primary). A noticeable decrease in strength begins at 5 - 10 times processing. In the process of repeated processing of HLDPE, it is recommended to increase the casting temperature by 3...5% or the number of revolutions of the screw during extrusion by 4...6% to destroy the resulting gel. It should be noted that in the process of repeated processing, especially when exposed to atmospheric oxygen, there is a decrease in the molecular weight of polyolefins, which leads to a sharp increase in the fragility of the material. Repeated processing of another polymer from the class of polyolefins - PP usually leads to an increase in the melt flow index (MFR), although the strength characteristics of the material do not undergo significant changes. Therefore, the waste generated during the manufacture of PP parts, as well as the parts themselves at the end of their service life, can be reused in a mixture with the original material to obtain new parts.

From all of the above, it follows that secondary software raw materials should be modified in order to improve the quality and increase the service life of products made from it.

2.2.2 Technology for processing recycled polyolefin raw materials into granules

To convert waste thermoplastics into raw materials suitable for further processing into products, its pre-treatment is necessary. The choice of pre-treatment method depends mainly on the source of waste generation and the degree of contamination. Thus, homogenous wastes from the production and processing of LDPE are usually processed at the place of their generation, which requires little pre-treatment - mainly grinding and granulation.

Waste in the form of obsolete products requires more thorough preparation. Pre-treatment of agricultural PE film waste, fertilizer bags, waste from other compact sources, and mixed waste includes the following steps: sorting (coarse) and identification (for mixed waste), shredding, separation of mixed waste, washing, drying. After that, the material is subjected to granulation.

Pre-sorting provides for a rough separation of waste according to various characteristics: color, dimensions, shape and, if necessary and possible, by types of plastics. Pre-sorting is usually done by hand on tables or conveyor belts; when sorting, various foreign objects and inclusions are simultaneously removed from the waste.

The separation of mixed (domestic) waste thermoplastics by type is carried out by the following main methods: flotation, separation in heavy media, aero separation, electric separation, chemical methods and deep cooling methods. The most widely used method is the flotation method, which allows the separation of mixtures of industrial thermoplastics such as PE, PP, PS and PVC. Separation of plastics is carried out by adding surfactants to water, which selectively change their hydrophilic properties.

In some cases, an effective way to separate polymers may be to dissolve them in a common solvent or in a mixture of solvents. By treating the solution with steam, PVC, PS and a mixture of polyolefins are isolated; purity of products - not less than 96%.

Flotation and separation methods in heavy media are the most efficient and cost-effective of all those listed above.

Waste that has become obsolete and contains no more than 5% of impurities from the raw material warehouse is sent to the waste sorting unit 1 , during which random foreign inclusions are removed from them and heavily contaminated pieces are discarded. Waste that has been sorted is crushed in knife crushers 2 wet or dry grinding to obtain a loose mass with a particle size of 2 ... 9 mm.

The performance of a grinding device is determined not only by its design, the number and length of knives, the rotor speed, but also by the type of waste. Thus, the lowest productivity is in the processing of foam plastic waste, which takes up a very large volume and is difficult to compactly load. Higher productivity is achieved when processing waste films, fibers, blown products.

For all knife crushers, a characteristic feature is increased noise, which is associated with the specifics of the process of grinding secondary polymeric materials. To reduce the noise level, the grinder, together with the engine and fan, is enclosed in a noise-protective casing, which can be detachable and have special windows with shutters for loading the crushed material.

Grinding is a very important stage in the preparation of waste for processing, since the degree of grinding determines the bulk density, flowability and particle size of the resulting product. Controlling the degree of grinding makes it possible to mechanize the processing process, improve the quality of the material by averaging its technological characteristics, reduce the duration of other technological operations, and simplify the design of processing equipment.

A very promising method of grinding is cryogenic, which makes it possible to obtain powders from waste with a degree of dispersion of 0.5 ... 2 mm. The use of powder technology has a number of advantages: reduced mixing time; reduction of energy consumption and the cost of working hours for the current maintenance of mixers; better distribution of components in the mixture; reduction of destruction of macromolecules, etc.

Of the known methods for obtaining powdered polymeric materials used in chemical technology, the most acceptable method for grinding thermoplastic waste is mechanical grinding. Mechanical grinding can be carried out in two ways: cryogenically (grinding in liquid nitrogen or other cold-agents medium and at normal temperatures in the environment of deagglomerating ingredients, which are less energy intensive.

Next, the crushed waste is fed into the washing machine for washing. 3 . Laundering is carried out in several steps with special detergent mixtures. wrung out in a centrifuge 4 a mass with a moisture content of 10 ... 15% is fed to the final dehydration in a drying plant 5 , until the residual moisture content is 0.2%, and then into the granulator 6 (Fig. 1.1).

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Rice. 1.1 Scheme for the recycling of polyolefins into granules:

1 - waste sorting unit; 2 - crusher; 3 - washing machine; 4 - centrifuge; 5 - drying plant; 6 - granulator

Various types of dryers are used for drying waste: shelf, belt, ladle, fluidized bed, vortex, etc.

Plants are produced abroad, in which there are devices for both washing and drying with a capacity of up to 350 ... 500 kg / h. In such an installation, the crushed waste is loaded into a bath, which is filled with a washing solution. The film is mixed with a paddle mixer, while the dirt settles to the bottom, and the washed film floats. Dehydration and drying of the film is carried out on a vibrating screen and in a vortex separator. The residual moisture is less than 0.1%.

Granulation is the final stage in the preparation of secondary raw materials for further processing into products. This stage is especially important for HLDPE due to its low bulk density and the difficulty of transportation. During the granulation process, the material is compacted, its further processing is facilitated, the characteristics of secondary raw materials are averaged, resulting in a material that can be processed on standard equipment.

For plasticization of crushed and cleaned waste products, single-screw extruders with a length of (25 ... 30) are most widely used. D equipped with a continuous filter and having a degassing zone. On such extruders, practically all types of secondary thermoplastics are processed quite effectively with a bulk density of the crushed material in the range of 50 ... 300 kg / m3. However, for the processing of contaminated and mixed waste, worm presses of special designs are required, with short multi-thread worms (length (3.5 ... 5) D) having a cylindrical nozzle in the extrusion zone.

The main unit of this system is an extruder with a drive power of 90 kW, a screw diameter of 253 mm and a ratio L/D= 3.75. At the exit of the extruder, a corrugated nozzle with a diameter of 420 mm was designed. Due to the heat generated by friction and shear effects on the polymer material, it melts in a short period of time, and rapid homogenization is ensured.

melt. By changing the gap between the cone nozzle and the casing, it is possible to adjust the shear force and friction force, while changing the processing mode. Since melting occurs very quickly, thermal degradation of the polymer is not observed. The system is equipped with a degassing unit, which is a prerequisite for the processing of secondary polymer raw materials.

Secondary granular materials are obtained depending on the sequence of cutting and cooling processes in two ways: granulation on the head and underwater granulation. The choice of granulation method depends on the properties of the thermoplastic to be processed, and especially on the viscosity of its melt and adhesion to the metal.

During granulation on the head, the polymer melt is squeezed out through the hole in the form of cylindrical bundles, which are cut off by knives sliding along the spinneret plate. The resulting granules are discarded with a knife from the head and cooled. Cutting and cooling can be carried out in air, in water, or by cutting in air, and cooling in water. For software that have high adhesion to metal and an increased tendency to stick together, water is used as a cooling medium.

When using equipment with a large unit capacity, so-called underwater granulation is used. With this method, the polymer melt is squeezed out in the form of strands through the holes of the spinneret plate on the head immediately into the water and cut into granules by rotating knives. The temperature of the cooling water is maintained within the range of 50...70 °C, which contributes to a more intensive evaporation of moisture residues from the surface of the granules; the amount of water is 20…40 m3 per 1 ton of granulate.

Most often, strands or ribbons are formed in the granulator head, which are granulated after cooling in a water bath. The diameter of the obtained granules is 2…5 mm.

Cooling should be carried out at an optimal rate so that the granules do not deform, do not stick together, and to ensure the removal of residual moisture.

The head temperature has a significant effect on the size distribution of the granules. Grids are placed between the extruder and die outlets to ensure a uniform melt temperature. The number of outlet holes in the head is 20…300.

The performance of the granulation process depends on the type of secondary thermoplastic and its rheological characteristics.

Studies of HPE granulate indicate that its viscous properties practically do not differ from the properties of primary PE, i.e. it can be processed under the same extrusion and injection molding regimes as virgin PE. However, the resulting products are characterized by low quality and durability.

Granules are used to produce packaging for household chemicals, hangers, construction parts, agricultural implements, pallets for transporting goods, exhaust pipes, lining of drainage channels, non-pressure pipes for melioration and other products. These products are obtained from "pure" secondary raw materials. However, more promising is the addition of secondary raw materials to the primary in the amount of 20 ... 30%. The introduction of plasticizers, stabilizers, and fillers into the polymer composition makes it possible to increase this figure to 40–50%. This improves the physical and mechanical characteristics of products, but their durability (when operating in harsh climatic conditions) is only 0.6 ... 0.75 of the durability of products made from virgin polymer. A more efficient way is the modification of secondary polymers, as well as the creation of highly filled secondary polymeric materials.

2.2.3 Methods for modifying recycled polyolefins

The results of the study of the mechanism of processes occurring during the operation and processing of software and their quantitative description allow us to conclude that intermediate products obtained from secondary raw materials should contain no more than 0.1 ... 0.5 mol of oxidized active groups and have optimal molecular weight and MWD , as well as to have reproducible physical, mechanical and technological indicators. Only in this case, the semi-finished product can be used for the production of products with a guaranteed service life to replace the scarce primary raw materials. However, the currently produced granulate does not meet these requirements.

A reliable way to solve the problem of creating high-quality polymeric materials and products from secondary software is the modification of granules, the purpose of which is to shield functional groups and active centers by chemical or physicochemical methods and create a material that is homogeneous in structure with reproducible properties.

Methods for modifying the secondary PO of raw materials can be divided into chemical (crosslinking, the introduction of various additives, mainly of organic origin, processing with organosilicon liquids, etc.) and physical and mechanical (filling with mineral and organic fillers).

For example, the maximum content of the gel fraction (up to 80%) and the highest physical and mechanical properties of cross-linked VLDPE are achieved with the introduction of 2–2.5% dicumyl peroxide on rollers at 130°C for 10 minutes. The relative elongation at break of such material is 210%, the melt flow index is 0.1…0.3 g/10 min. The degree of crosslinking decreases with an increase in temperature and an increase in the duration of rolling as a result of a competing degradation process. This allows you to adjust the degree of crosslinking, physical, mechanical and technological characteristics of the modified material.

A method has been developed for forming products from HLDPE by introducing dicumyl peroxide directly in the process of processing, and prototypes of pipes and molded products containing 70 ... 80% of the gel fraction have been obtained.

The introduction of wax and elastomer (up to 5 mass parts) significantly improves the processability of VPE, increases the physical and mechanical properties (especially elongation at break and crack resistance - by 10% and from 1 to 320 hours, respectively) and reduces their spread, which indicates an increase in the homogeneity of the material.

Modification of HLDPE with maleic anhydride in a disk extruder also leads to an increase in its strength, heat resistance, adhesiveness and resistance to photoaging. In this case, the modifying effect is achieved at a lower concentration of the modifier and a shorter duration of the process than with the introduction of elastomer.

A promising way to improve the quality of polymeric materials from secondary PO is thermomechanical treatment with organosilicon compounds. This method allows to obtain products from recycled materials with increased strength, elasticity and resistance to aging. The modification mechanism consists in the formation of chemical bonds between the siloxane groups of the organosilicon liquid and unsaturated bonds and oxygen-containing groups of secondary POs.

The technological process for obtaining a modified material includes the following stages: sorting, crushing and washing of waste; treatment of waste with organosilicon liquid at 90 ± 10 °С for 4…6 h; drying of modified waste by centrifugation; regranulation of modified waste.

In addition to the solid-phase modification method, a method for modifying VPE in solution is proposed, which makes it possible to obtain an VLDPE powder with a particle size of not more than 20 μm. This powder can be used for processing into products by rotational molding and for coating by electrostatic spraying.

Of great scientific and practical interest is the creation of filled polymeric materials based on recycled polyethylene raw materials. The use of polymeric materials from recycled materials containing up to 30% filler will make it possible to release up to 40% of primary raw materials and send it to the production of products that cannot be obtained from secondary raw materials (pressure pipes, packaging films, transport reusable containers, etc.). This will significantly reduce the shortage of primary polymer raw materials.

To obtain filled polymeric materials from recycled materials, it is possible to use dispersed and reinforcing fillers of mineral and organic origin, as well as fillers that can be obtained from polymer waste (crushed thermoset waste and rubber crumb). Almost all thermoplastic waste can be filled, as well as mixed waste, which for this purpose is also preferable from an economic point of view.

For example, the expediency of using lignin is associated with the presence of phenolic compounds in it, which contribute to the stabilization of VPEN during operation; mica - with the production of products with low creep, increased heat and weather resistance, and also characterized by low wear of processing equipment and low cost. Kaolin, shell rock, shale ash, coal spheres and iron are used as cheap inert fillers.

With the introduction of finely dispersed phosphogypsum granulated in polyethylene wax into WPE, compositions with increased elongation at break were obtained. This effect can be explained by the plasticizing effect of polyethylene wax. Thus, the tensile strength of VPE filled with phosphogypsum is 25% higher than that of VPE, and the tensile modulus is 250% higher.

The reinforcing effect when mica is introduced into the HPE is associated with the features of the crystalline structure of the filler, a high characteristic ratio (the ratio of the flake diameter to the thickness), and the use of crushed, powdery HPE made it possible to preserve the structure of the flakes with minimal destruction.

Compositions containing lignin, shales, kaolin, spheres, sapropel waste have relatively low physical and mechanical properties, but they are the cheapest and can be used in the manufacture of building products.

2.3 RECYCLING OF POLYVINYL CHLORIDE

During processing, polymers are exposed to high temperatures, shear stresses and oxidation, which leads to a change in the structure of the material, its technological and operational properties. The change in the structure of the material is decisively influenced by thermal and thermal-oxidative processes.

PVC is one of the least stable industrial carbon chain polymers. PVC degradation reaction - dehydrochlorination begins already at temperatures above 100 °C, and at 160 °C the reaction proceeds very quickly. As a result of thermal oxidation of PVC, aggregative and disaggregative processes occur - cross-linking and destruction.

The destruction of PVC is accompanied by a change in the initial color of the polymer due to the formation of chromophore groups and a significant deterioration in physical, mechanical, dielectric and other performance characteristics. Crosslinking results in the transformation of linear macromolecules into branched and, ultimately, into crosslinked three-dimensional structures; at the same time, the solubility of the polymer and its ability to be processed are significantly worsened. In the case of plasticized PVC, cross-linking reduces the compatibility of the plasticizer with the polymer, increases the migration of the plasticizer, and irreversibly degrades the performance properties of the materials.

Along with taking into account the influence of operating conditions and the frequency of processing of secondary polymeric materials, it is necessary to evaluate the rational ratio of waste and fresh raw materials in the composition intended for processing.

When extruding products from mixed raw materials, there is a risk of rejects due to different melt viscosities, therefore it is proposed to extrude virgin and recycled PVC on different machines, however, powdered PVC can almost always be mixed with recycled polymer.

An important characteristic that determines the fundamental possibility of recycling PVC waste (allowable processing time, service life of the recycled material or product), as well as the need for additional strengthening of the stabilizing group, is the thermal stability time.

2.3.1 PVC waste treatment methods

Homogeneous industrial waste, as a rule, is recycled, and in cases where only thin layers of material are subjected to deep aging.

In some cases, it is recommended to use an abrasive tool to remove the degraded layer with subsequent processing of the material into products that are not inferior in properties to products obtained from the original materials.

To separate the polymer from the metal (wires, cables), a pneumatic method is used. Typically, isolated plasticized PVC can be used as low voltage wire insulation or injection molded products. To remove metal and mineral inclusions, the experience of the milling industry based on the use of the induction method, the method of separation by magnetic properties can be used. To separate aluminum foil from thermoplastic, heating in water at 95–100 °C is used.

It is proposed to immerse unusable containers with labels in liquid nitrogen or oxygen with a temperature not higher than -50 ° C to make the labels or adhesive brittle, which will then allow them to be easily crushed and separate a homogeneous material, such as paper.

An energy-saving method for the dry preparation of plastic waste using a compactor. The method is recommended for processing artificial leather (IR) waste, PVC linoleums and includes a number of technological operations: grinding, separation of textile fibers, plasticization, homogenization, compaction and granulation; additives may also be added. The lining fibers are separated three times - after the first knife crushing, after compaction and secondary knife crushing. A molding mass is obtained which can be processed by injection molding, which still contains fibrous components which do not interfere with processing, but serve as a filler that reinforces the material.

2.3.2 Methods for recycling PVC plastic waste

Injection molding

The main types of waste based on unfilled PVC are ungelatinized plastisol, technological waste and defective products. At the enterprises of light industry in Russia, the following technology for processing plastisol waste is used by injection molding methods.

It has been established that products from recycled PVC materials of satisfactory quality can be obtained using plastisol technology. The process includes shredding waste films and sheets, preparing PVC paste in a plasticizer, molding a new product by casting.

Ungelatinized plastisol was collected in containers during cleaning of the dispenser, mixer, subjected to gelatinization, then mixed with process waste and defective products on rollers, the resulting sheets were processed on rotary grinders. The plastisol crumb thus obtained was processed by injection molding. Plastisol crumb in the amount of 10 ... 50 wt. h can be used in a composition with rubber to obtain rubber compounds, and this makes it possible to exclude softeners from the formulations.

For waste processing by injection molding, as a rule, intrusion-type machines are used, with a constantly rotating screw, the design of which ensures spontaneous capture and homogenization of waste.

One of the promising methods for using PVC waste is multi-component casting. With this method of processing, the product has outer and inner layers of different materials. The outer layer is, as a rule, high quality commercial plastics, stabilized, dyed, having a good appearance. The inner layer is recycled polyvinyl chloride raw materials. The processing of thermoplastics by this method makes it possible to significantly save scarce primary raw materials, reducing its consumption by more than two times.

Extrusion

At present, one of the most effective methods for processing wastes of PVC-based polymeric materials for the purpose of their disposal is the method of elastic-strain dispersion, based on the phenomenon of multiple destruction under conditions of combined exposure to high pressure and shear deformation at elevated temperature.

Elastic-deformation dispersion of preliminarily coarsely crushed materials with a particle size of 103 μm is carried out in a single-screw rotary disperser. Used waste plasticized duplicated film materials on a different basis (linoleum on a polyester fabric basis, foam on a paper basis, artificial leather on a cotton fabric basis) are processed into a dispersed homogeneous secondary material, which is a mixture of PVC plastics with a crushed base with the most probable particle size 320…615 µm, predominantly asymmetric, with a high specific surface area (2.8…4.1 m2/g). The optimal dispersion conditions under which the most highly dispersed product is formed are the temperature in the dispersant zones 130 ... 150 ... 70 ° C; degree of loading no more than 60%; minimum screw speed 35 rpm. An increase in the processing temperature of PVC materials leads to an undesirable intensification of degradation processes in the polymer, which is expressed in the darkening of the product. Increasing the degree of loading and the speed of rotation of the screw worsens the dispersion of the material.

Recycling of baseless plasticized PVC materials waste (agricultural film, insulating film, PVC hoses) by elastic-deformation dispersion to obtain high-quality highly dispersed secondary material can be carried out without technological difficulties with a wider variation in dispersion modes. A more finely dispersed product is formed with a particle size of 240 ... 335 microns, predominantly spherical in shape.

The elastic-deformation impact during the dispersion of rigid PVC materials (impact-resistant material for bottles for mineral water, sanitary PVC pipes, etc.) must be carried out at higher temperatures (170 ... 180 ... minimum screw speed 35 rpm. When deviating from the specified dispersion modes, technological difficulties and deterioration in the quality of the resulting secondary product in terms of dispersion are observed.

In the process of processing waste PVC materials, simultaneously with dispersion, it is possible to carry out the modification of the polymer material by introducing 1 ... 3 wt. h of metal-containing heat stabilizers and 10 ... 30 wt. h plasticizers. This leads to an increase in the thermal stability margin when using metal stearates by 15...50 min and an improvement in the melt flow rate of the material processed together with ester plasticizers by 20...35%, as well as an improvement in the manufacturability of the dispersion process.

The resulting secondary PVC materials, due to the high dispersion and the developed surface of the particles, have surface activity. This property of the resulting powders predetermined their very good compatibility with other materials, which makes it possible to use them to replace (up to 45 wt %) the initial raw material in the production of the same or new polymeric materials.

Twin screw extruders can also be used to process PVC waste. They achieve excellent homogenization of the mixture, and the plasticization process is carried out under milder conditions. Since twin screw extruders work on the principle of displacement, the residence time of the polymer in them at the plasticizing temperature is clearly defined and its delay in the high temperature zone is excluded. This prevents overheating and thermal degradation of the material. The uniformity of the passage of the polymer through the cylinder provides good conditions for degassing in the low pressure zone, which makes it possible to remove moisture, degradation and oxidation products, and other volatiles, usually contained in waste.

For the processing of polymer composite materials, including IR, cable insulation waste, paper-based thermoplastic coatings, and others, methods based on a combination of extrusion preparation and compression molding can be used. To implement this method, a unit is proposed, consisting of two machines, the injection of each of which is 10 kg. The proportion of non-polymeric materials specially introduced into the waste can be up to 25%, and even the copper content can reach 10%.

The method of co-extrusion of the fresh thermoplastic forming the wall layers and the waste polymer constituting the inner layer is also used, as a result, a three-layer product (for example, a film) can be obtained. Another method - blow molding is proposed in. In the developed design of the blown extrusion plant, a screw-driven extruder with a blown drive is provided as a melt generator. Blow molding of a mixture of virgin and recycled PVC is used to produce bottles, containers and other hollow products.

Calendering

An example of waste recycling by calendering is the so-called Regal process, which consists in calendering the material and obtaining boards and sheets that are used for the production of containers and furniture. The convenience of such a process for processing wastes of various compositions lies in the ease of its adjustment by changing the gap between the calender rolls to achieve a good shear and dispersive effect on the material. Good plasticization and homogenization of the material during processing ensures the production of products with sufficiently high strength characteristics. The method is economically advantageous for thermoplastics plasticized at relatively low temperatures, mainly soft PVC.

For the preparation of IC and lenoleum waste, a unit has been developed, consisting of a knife crusher, a mixing drum and three-roll refining rollers. As a result of high friction, high pressing pressure and mixing between rotating surfaces, the components of the mixture are further crushed, plasticized and homogenized. Already in one pass through the machine, the material acquires a fairly good quality.

Pressing

One of the traditional methods for processing waste polymer materials is pressing, in particular, the Regal-Converter method can be called the most common. Grinding waste of uniform thickness on a conveyor belt is fed into the furnace and melted. The mass plasticized in this way is then pressed. The proposed method processes mixtures of plastics with a content of foreign substances of more than 50%.

There is a continuous way to recycle waste synthetic carpets and IR. Its essence is as follows: the ground waste is fed into the mixer, where 10% of the binder, pigments, fillers (for reinforcement) are added. Plates are pressed from this mixture in a two-belt press. The plates have a thickness of 8…50 mm with a density of about 650 kg/m3. Due to the porosity of the plate, they have heat and sound insulating properties. They are used in mechanical engineering and in the automotive industry as structural elements. With one- or two-sided lamination, these plates can be used in the furniture industry. In the US, the pressing process is used to make heavy plates.

Another technological method is also used, based on foaming in the form. The developed options differ in the methods of introducing blowing agents into secondary raw materials and in the supply of heat. The blowing agents may be introduced in an internal mixer or extruder. However, the method of shaped foaming is more productive, when the pore formation process is carried out in a press.

A significant disadvantage of the method of press sintering of polymer waste is the weak mixing of the mixture components, which leads to a decrease in the mechanical properties of the resulting materials.

The problem of recycling waste PVC plastics is currently being intensively developed, but there are many difficulties associated primarily with the presence of a filler. Some developers have taken the path of isolating the polymer from the composite with its subsequent use. However, these technological options are often uneconomical, time-consuming and suitable for a narrow range of materials.

Known methods of direct thermoforming either require high additional costs (preparatory operations, addition of primary polymer, plasticizers, use of special equipment), or do not allow the processing of highly filled waste, in particular, PVC plastics.

2.4 DISPOSAL OF WASTE POLYSTYRENE PLASTICS

Polystyrene waste is accumulated in the form of obsolete products made of PS and its copolymers (bread boxes, vases, syrniki, various dishes, grills, jars, hangers, facing sheets, parts of commercial and laboratory equipment, etc.), as well as in the form of industrial (technological) waste of general-purpose PS, impact-resistant PS (HIPS) and its copolymers.

Recycling of polystyrene plastics can go in the following ways:

1. disposal of heavily polluted industrial waste;
2. utilization of technological waste of HIPS and ABS plastic by injection molding, extrusion and pressing;
3. disposal of worn out products;
4. recycling of expanded polystyrene (EPS) waste;
5. disposal of mixed waste.

Heavily contaminated industrial waste is generated in the production of PS and polystyrene plastics during the cleaning of reactors, extruders and production lines in the form of pieces of various sizes and shapes. Due to pollution, heterogeneity and low quality, these wastes are mainly destroyed by incineration. It is possible to utilize them by destruction, using the resulting liquid products as fuel.

The possibility of attaching ionogenic groups to the benzene ring of polystyrene makes it possible to obtain ion exchangers on its basis. The solubility of the polymer during processing and operation also does not change. Therefore, to obtain mechanically strong ion exchangers, it is possible to use technological waste and worn-out polystyrene products, the molecular weight of which is adjusted by thermal destruction to the values ​​required by the conditions for the synthesis of ion exchangers (40 ... 50 thousand). Subsequent chloromethylation of the obtained products leads to the formation of compounds soluble in water, which indicates the possibility of using secondary polystyrene raw materials to obtain soluble polyelectrolytes.

Technological waste PS (as well as software) in their physical, mechanical and technological properties do not differ from primary raw materials. These wastes are recyclable and mostly

are used in the enterprises where they are formed. They can be added to the primary PS or used as independent raw materials in the production of various products.

A significant amount of technological waste (up to 50%) is generated during the processing of polystyrene plastics by injection molding, extrusion and vacuum forming, the return of which to the technological processing processes can significantly increase the efficiency of the use of polymeric materials and create waste-free production in the plastics processing industry.

ABS plastics are widely used in the automotive industry for the manufacture of large car parts, in the production of sanitary equipment, pipes, consumer goods, etc.

In connection with the increase in the consumption of styrene plastics, the amount of waste is also growing, the use of which is economically and environmentally feasible, taking into account the increase in the cost of raw materials and the decrease in their resources. In many cases, recycled materials can be used to replace virgin materials.

It has been established that during repeated processing of the ABS polymer, two competing processes occur in it: on the one hand, partial destruction of macromolecules, on the other hand, partial intermolecular crosslinking, which increase with the increase in the number of processing cycles.

When choosing a method for processing extruded ABS, the fundamental possibility of molding products by direct pressing, extrusion, and injection molding was proved.

An effective technological stage of ABS waste processing is polymer drying, which makes it possible to bring the moisture content in it to a level not exceeding 0.1%. In this case, the formation of such defects in the material arising from excess moisture as a scaly surface, silveriness, delamination of products in thickness is eliminated; Pre-drying improves material properties by 20…40%.

However, the direct compression method turns out to be inefficient, and extrusion of the polymer is difficult due to its high viscosity.

Processing of technological wastes of ABS polymer by injection molding seems promising. In this case, to improve the fluidity of the polymer, it is necessary to introduce technological additives. The additive to the polymer facilitates the processing of the ABS polymer, as it leads to an increase in the mobility of macromolecules, the flexibility of the polymer, and a decrease in its viscosity.

The products obtained by this method are not inferior to products from the primary polymer in terms of their performance indicators, and sometimes even surpass them.

Defective and worn products can be disposed of by grinding, followed by the formation of the resulting crumb in a mixture with primary materials or as an independent raw material.

A much more difficult situation is observed in the field of recycling of worn-out PS products, including foamed plastics. Abroad, the main ways of their disposal are pyrolysis, incineration, photo- or biodegradation, and burial. Depreciated products for cultural and community purposes, as well as the industry of polymer, construction, heat-insulating materials and others, can be recycled into products. This mainly concerns products made of impact-resistant PS.

Block PS must be combined with high impact PS (70:30 ratio), modified in other ways or recycled with its copolymer with acrylonitrile, methyl methacrylate (MS) or terpolymers with MS and acrylonitrile (MSN) before reprocessing. MC and MCH copolymers are distinguished by a higher resistance to atmospheric aging (compared to impact-resistant compositions), which is of great importance in subsequent processing. Secondary PS can be added to PE.

To convert waste polystyrene films into secondary polymer raw materials, they are subjected to agglomeration in rotary agglomerators. The low impact strength of PS results in fast grinding (compared to other thermoplastics). However, the high adhesive capacity of PS leads, firstly, to sticking together of material particles and the formation of large aggregates before (80 °C) the material becomes plastic (130 °C), and, secondly, to sticking of the material to the processing equipment. This makes PS much more difficult to agglomerate than PE, PP and PVC.

Waste PPS can be dissolved in styrene and then polymerized in a mixture containing crushed rubber and other additives. The copolymers obtained in this way are characterized by sufficiently high impact strength.

The recycling industry is currently facing the challenge of recycling mixed waste plastics. Mixed waste processing technology includes sorting, grinding, washing, drying and homogenization. Recycled PS obtained from mixed waste has high physical and mechanical properties, it can be added to asphalt and bitumen in the molten state. At the same time, their cost is reduced, and the strength characteristics increase by about 20%.

To improve the quality of recycled polystyrene raw materials, it is modified. For this, it is necessary to study its properties in the process of thermal aging and operation. The aging of PS plastics has its own specifics, which is clearly manifested especially for impact-resistant materials, which, in addition to PS, contain rubbers.

During heat treatment of PS materials (at 100–200 °C), its oxidation proceeds through the formation of hydroperoxide groups, the concentration of which rapidly increases in the initial stage of oxidation, followed by the formation of carbonyl and hydroxyl groups.

Hydroperoxide groups initiate photooxidation processes that occur during the operation of products made of PS under the influence of solar radiation. Photodegradation is also initiated by unsaturated groups contained in rubber. A consequence of the combined effect of hydroperoxide and unsaturated groups at early stages of oxidation and carbonyl groups at later stages is the lower resistance to photooxidative degradation of PS products compared to PO. The presence of unsaturated bonds in the rubber component of HIPS during its heating leads to autoacceleration of the degradation process.

During photoaging of PS modified with rubber, chain breaking prevails over the formation of cross-links, especially at a high content of double bonds, which has a significant effect on the morphology of the polymer, its physical-mechanical and rheological properties.

All these factors must be taken into account when recycling PS and HIPS products.

2.5 RECYCLING OF WASTE POLYAMIDES

A significant place among solid polymeric waste is occupied by polyamide waste generated mainly during the production and processing of fiber products (nylon and anide), as well as obsolete products. The amount of waste in the production and processing of fiber reaches 15% (of which in production - 11 ... 13%). Since PA is an expensive material with a number of valuable chemical and physical-mechanical properties, the rational use of its waste is of particular importance.

The variety of types of secondary PA requires the creation of special processing methods and, at the same time, opens up wide opportunities for their selection.

PA-6.6 wastes have the most stable indicators, which is a prerequisite for the creation of universal methods for their processing. A number of wastes (rubberized cord, trimmings, worn hosiery) contain non-polyamide components and require a special approach for processing. Worn products are contaminated, and the amount and composition of pollution is determined by the conditions of operation of the products, the organization of their collection, storage and transportation.

The main areas of processing and use of PA waste can be called grinding, thermoforming from the melt, depolymerization, reprecipitation from solution, various modification methods and textile processing to obtain materials of a fibrous structure. The possibility, expediency and efficiency of the use of certain wastes are determined, first of all, by their physical and chemical properties.

Of great importance is the molecular weight of the waste, which affects the strength of recycled materials and products, as well as the technological properties of recycled PA. The content of low molecular weight compounds in PA-6 has a significant effect on strength, thermal stability and processing conditions. The most thermally stable under processing conditions is PA-6.6.

To select the methods and modes of processing, as well as directions for the use of waste, it is important to study the thermal behavior of secondary PA. In this case, the structural and chemical features of the material and its prehistory can play a significant role.

2.5.1 PA Waste Treatment Methods

The existing methods of processing PA waste can be classified into two main groups: mechanical, not associated with chemical transformations, and physicochemical. Mechanical methods include grinding and various techniques and methods used in the textile industry to obtain products with a fibrous structure.

Ingots, off-grade tape, cast waste, partially drawn and undrawn fibers can be subjected to mechanical processing.

Grinding is not only an operation that accompanies most technological processes, but also an independent method of waste processing. Grinding allows you to get powdery materials and chips for injection molding from ingots, strips, bristles. Characteristically, during grinding, the physicochemical properties of the feedstock practically do not change. To obtain powdered products, cryogenic grinding processes are used, in particular.

Waste fibers and bristles are used for the production of fishing lines, washcloths, handbags, etc., however, this requires significant manual labor.

Of the mechanical methods of waste processing, the most promising and widely used are the production of non-woven materials, floor coverings and staple fabrics. Of particular value for these purposes are waste polyamide fibers, which are easily processed and dyed.

Physico-chemical methods of processing PA waste can be classified as follows:

1. depolymerization of waste to obtain monomers suitable for the production of fibers and oligomers with their subsequent use in the production of adhesives, varnishes and other products;
2. re-melting of waste to obtain granulate, agglomerate and products by extrusion and injection molding;
3. reprecipitation from solutions to obtain powders for coating;
4. obtaining composite materials;
5. chemical modification for the production of materials with new properties (obtaining varnishes, adhesives, etc.).

Depolymerization is widely used in industry to obtain high quality monomers from uncontaminated process waste.

The depolymerization is carried out in the presence of catalysts, which may be neutral, basic or acidic compounds.

The method of repeated melting of PA wastes, which is carried out mainly in vertical apparatuses for 2–3 hours and in extrusion plants, has become widespread in our country and abroad. With prolonged thermal exposure, the specific viscosity of a PA-6 solution in sulfuric acid decreases by 0.4 ... 0.7%, and the content of low molecular weight compounds increases from 1.5 to 5–6%. Melting in superheated steam, humidification, and melting in vacuum improve the properties of the regenerated polymer, but do not solve the problem of obtaining sufficiently high molecular weight products.

In the process of processing by extrusion, PA is oxidized much less than during prolonged melting, which contributes to the preservation of high physical and mechanical properties of the material. Increasing the moisture content of the feedstock (to reduce the degree of oxidation) leads to some destruction of PA.

Obtaining powders from PA waste by reprecipitation from solutions is a method of purifying polymers, obtaining them in a form convenient for further processing. Powders can be used, for example, for cleaning dishes, as a component of cosmetics, etc.

A widely used method for regulating the mechanical properties of PAs is filling them with fibrous materials (glass fiber, asbestos fiber, etc.).

An example of the highly efficient use of PA waste is the creation of the ATM-2 material based on it, which has high strength, wear resistance, and dimensional stability.

A promising direction for improving the physical, mechanical and operational properties of products from recycled PCA is the physical modification of molded parts by volumetric surface treatment. Volume-surface treatment of samples from recycled PCA filled with kaolin and plasticized with a shale softener in heated glycerin leads to an increase in impact strength by 18%, breaking stress in bending by 42.5%, which can be explained by the formation of a more perfect structure of the material and the removal of residual stresses .

2.5.2 PA waste recycling processes

The main processes used for the recovery of recycled polymer raw materials from PA waste are:

1. regeneration of PA by extrusion of worn-out nylon mesh materials and technological waste to obtain granular products suitable for processing into products by injection molding;
2. regeneration of PA from worn out products and technological waste of nylon containing fibrous impurities (not polyamides) by dissolving, filtering the solution and subsequent precipitation of PA in the form of a powder product.

Technological processes for the processing of worn products differ from the processing of technological waste by the presence of a preliminary preparation stage, including the disassembly of raw materials, their washing, washing, squeezing and drying of secondary raw materials. Pre-prepared worn products and technological waste are sent for grinding, after which they are sent to the extruder for granulation.

Secondary fibrous polyamide raw materials containing non-polyamide materials are treated in a reactor at room temperature with an aqueous solution of hydrochloric acid, filtered to remove non-polyamide inclusions. Powdered polyamide is precipitated with an aqueous solution of methanol. The precipitated product is crushed and the resulting powder is dispersed.

Currently, in our country, technological waste generated in the production of nylon fiber is quite effectively used for the production of non-woven materials, floor coverings and granules for casting and extrusion. The main reason for the insufficient use of failed PA products from compact sources is the lack of highly efficient equipment for their primary processing and processing.

The development and industrial implementation of processes for processing worn-out products from nylon fiber (hosiery, netting materials, etc.) into secondary materials will allow saving a significant amount of raw materials and directing it to the most effective areas of application.

2.6 POLYETHYLENE TEREPHTHALATE WASTE RECYCLING

The recycling of lavsan fibers and worn-out PET products is similar to the recycling of polyamide waste, so in this section we will consider the recycling of PET bottles.

For more than 10 years of mass consumption in Russia of drinks in PET packaging, according to some estimates, more than 2 million tons of used plastic containers, which are valuable chemical raw materials, have accumulated at landfills.

The explosive growth in the production of bottle preforms, the increase in world prices for oil and, accordingly, for primary PET, influenced the active formation in Russia in 2000 of the market for the processing of used PET bottles.

There are several methods for recycling used bottles. One of the interesting methods is the deep chemical processing of recycled PET with the production of dimethyl terephthalate in the process of methanolysis or terephthalic acid and ethylene glycol in a number of hydrolytic processes. However, such processing methods have a significant drawback - the high cost of the depolymerization process. Therefore, at present, rather well-known and widespread mechanochemical processing methods are used more often, during which the final products are formed from a polymer melt. A significant assortment range of products obtained from recycled bottled polyethylene terephthalate has been developed. The main large-scale production is the production of lavsan fibers (mainly staple), the production of synthetic winterizers and non-woven materials. A large segment of the market is occupied by the extrusion of sheets for thermoforming on extruders with sheeting heads, and, finally, the most promising processing method is universally recognized as obtaining granules suitable for food contact, i.e. obtaining material for re-casting preforms.

The bottle intermediate can be used for technical purposes: in the process of processing into products, recycled PET can be added to the virgin material; compounding - recycled PET can be fused with other plastics (eg polycarbonate, WPE) and filled with fibers to produce technical parts; obtaining dyes (superconcentrates) for the production of colored plastic products.

Also purified PET flakes can be directly used for the manufacture of a wide range of products: textile fibers; stuffing and staple fibers - synthetic winterizer (insulation for winter jackets, sleeping bags, etc.); roofing materials; films and sheets (painted, metallized); packaging (boxes for eggs and fruits, packaging for toys, sporting goods, etc.); molded structural products for the automotive industry; parts of lighting and household appliances, etc.

In any case, the feedstock for depolymerization or processing into products is not bottle waste, which could lie for some time in a landfill, and which are shapeless, heavily contaminated objects, but pure PET flakes.

Consider the process of recycling bottles into clean plastic flakes.

If possible, the bottles should already be collected in sorted form, without mixing with other plastics and polluting objects. The optimal object for recycling is a compressed bale of colorless PET bottles (coloured bottles must be sorted and recycled separately). Bottles must be stored in a dry place. Plastic bags with PET bottles in bulk are emptied into the loading hopper. Next, the bottles enter the hopper-feeder. The bale feeder is used both as a storage hopper with a uniform feeding system and as a bale breaker. A conveyor located on the floor of the hopper moves the bale to three rotating augers that break the agglomerates into individual bottles and feed them to the discharge conveyor. Here it is necessary to separate bottles made of colored and uncolored PET, as well as remove foreign objects such as rubber, glass, paper, metal, and other types of plastics.

In a single-rotor crusher equipped with a hydraulic pusher, PET bottles are crushed, forming large fractions up to 40 mm in size.

The crushed material passes through an air vertical classifier. Heavy particles (PET) fall against the airflow onto the vibrating separator screen. Light particles (labels, film, dust, etc.) are blown up by the air stream and collected in a special dust collector under the cyclone. On the vibrating screen of the separator, particles are separated into two fractions: large PET particles "flow" through the screen, and small particles (mainly heavy fractions of contaminants) pass inside the screen and are collected in containers under the separator.

The flotation tank is used to separate materials with different relative densities. The PET particles fall onto the sloping bottom and the auger continuously unloads the PET onto the water separating screen.

The screen serves both to separate the water pumped together with PET from the flotator and to separate the fine fractions of contaminants.

The pre-crushed material is effectively washed in an inclined two-stage rotating drum with perforated walls.

Drying of flakes takes place in a rotating drum made of perforated sheet. The material is turned over in hot air currents. The air is heated by electric heaters.

Next, the flakes enter the second crusher. In this stage, large PET particles are ground into flakes, which are approximately 10 mm in size. It should be noted that the idea of ​​processing is that the material is not crushed into flakes of a marketable product at the first stage of grinding. This process avoids material losses in the system, achieves optimal label separation, improves cleaning performance and reduces knife wear in the second crusher, as glass, sand and other abrasive materials are removed prior to the secondary grinding stage.

The final process is similar to the primary air classification process. Label residues and PET dust are removed with the air flow. The final product - pure PET flakes - is poured into barrels.

Thus, it is possible to solve the serious issue of recycling of recycled plastic containers with the receipt of the product.

A promising way to recycle PET is the production of bottles from bottles.

The main stages of the classical recycling process for the implementation of the "bottle to bottle" scheme are: collection and sorting of secondary raw materials; packaging of secondary raw materials; grinding and washing; separation of crushed stone; extrusion to obtain granules; processing of granules in a screw apparatus in order to increase the viscosity of the product and ensure the sterilization of the product for direct contact with food. But for the implementation of this process, serious capital investments are required, since it is impossible to carry out this process on standard equipment.

2.7 BURNING

It is advisable to burn only certain types of plastics that have lost their properties in order to obtain thermal energy. For example, a thermal power plant in Wolvergemton (Great Britain) for the first time in the world operates not on gas or fuel oil, but on old car tires. The British Office for the Recycling of Non-Fossil Fuels helped to carry out this unique project, which will provide electricity to 25,000 residential buildings.

The combustion of some types of polymers is accompanied by the formation of toxic gases : hydrogen chloride, nitrogen oxides, ammonia, cyanide compounds, etc., which makes it necessary to take measures to protect the atmospheric air. In addition, the economic efficiency of this process is the lowest compared to other plastic waste recycling processes. Nevertheless, the comparative simplicity of the organization of combustion determines its fairly widespread use in practice.

2.8 RTI WASTE RECYCLING

According to the latest statistics in Western Europe, about 2 million tons of used tires are produced annually, in Russia - about 1 million tons of tires and the same amount of old rubber is produced by technical rubber products (RTI). Tire and rubber goods plants generate a lot of waste, a large proportion of which is not reused, such as used butyl diaphragms from tire factories, ethylene propylene waste, etc.

Due to the large amount of old rubber, incineration still occupies a dominant position in recycling, while material recycling still makes up a small share, despite the relevance of this particular recycling for improving the environment and conserving raw materials. Material recycling has not been widely used due to high energy consumption and the high cost of obtaining fine rubber powders and reclaimed materials.

Without economic regulation by the state, tire recycling remains unprofitable. The Russian Federation does not have a system for collecting, depositing and recycling used tires and rubber goods. Methods of legal and economic regulation and stimulation of solving this problem have not been developed. For the most part, worn tires accumulate in car parks or are taken to forests and quarries. Currently, significant amounts of used tires produced annually are a big environmental problem for all regions of the country.

As practice shows, it is very difficult to solve this problem at the regional level. In Russia, a federal program for the disposal of tires and rubber goods should be developed and implemented. The Program should lay down the legal and economic mechanisms that ensure the movement of worn tires according to the proposed scheme.

As an economic mechanism for the operation of the tire recycling system in our country, two fundamental approaches are being discussed:

1. tire recycling is paid directly by their owner – "polluter pays";
2. the manufacturer or importer of the tires pays for the recycling of tires - "the manufacturer pays".

The "polluter pays" principle is partially implemented in such regions as Tatarstan, Moscow, St. Petersburg, etc. Realistically assessing the level of environmental and economic nihilism of our fellow citizens, the successful use of the "polluter pays" principle can be considered unpromising.

The best thing for our country would be to introduce the "producer pays" principle. This principle works successfully in the Scandinavian countries. For example, its use in Finland makes it possible to recycle more than 90% of tires.

2.8.1 Crushing worn tires and tubes

The initial stage of obtaining regenerate by existing industrial methods from worn out rubber products (tires, chambers, etc.) is their grinding.

The grinding of tire rubber is accompanied by some destruction of the rubber vulcanization network, the value of which, estimated from the change in the degree of equilibrium swelling, ceteris paribus, is the greater, the smaller the particle size of the resulting rubber crumb. The chloroform extract of rubber changes very little in this case. At the same time, the destruction of carbon structures also occurs. The crushing of rubbers containing active carbon black is accompanied by some destruction of chain structures along carbon-carbon bonds; in the case of low-activity carbon black (thermal), the number of contacts between carbon particles somewhat increases. In general, changes in the vulcanization network and carbon structures of rubbers during crushing should, as in the case of any mechanochemical process, depend on the type of polymer, the nature and amount of filler contained in the rubber, the nature of cross-links and the density of the vulcanization network, the process temperature, and also the degree of grinding. rubber and the type of equipment used. The particle size of the resulting rubber crumb is determined by the rubber devulcanization method, the type of crushed rubber, and the quality requirements for the final product - the reclaimed product.

The smaller the particle size of the crumb, the more quickly and evenly degraded material, the reduction in the content of insufficiently devulcanized rubber particles (“groats”) in the devulcanizate and, as a result, obtaining a more uniform regenerate in quality, reducing the amount of refining waste and increasing the productivity of refining equipment . However, as the size of crumb rubber particles decreases, the cost of its production increases.

In this regard, with the currently existing methods for producing rubber crumb, the use of tire rubber crumb with a particle size of 0.5 mm or less to obtain reclaimed rubber is, as a rule, not economically feasible. Since worn tires, along with rubber, contain other materials - textiles and metal, when tires are crushed, these materials are simultaneously cleaned from rubber. If the presence of metal in the rubber crumb is unacceptable, then the possible content of textile residues in it depends on the subsequent method of devulcanizing the crumb rubber and the type of textile.

Rollers (in the Russian Federation, Poland, England, USA) and disc mills (in Germany, Hungary, Czech Republic) are most widely used for crushing worn rubber products. They also use impact (hammer) crushers, rotary grinders, for example, Novorotor installations. Rubber is also crushed by the extrusion method, based on the destruction of rubber under conditions of all-round compression and shear.

An apparatus is proposed in which the material to be ground passes between the rotor and the housing wall. The effect of grinding is enhanced by changing the size and shape of the gap between the rotor and the housing wall during the rotation of the rotor. A comparison of a number of existing schemes for crushing worn tires showed that in terms of equipment productivity, energy and labor intensity of the process, the scheme based on the use of rollers has the best indicators than on the use of disk mills or a rotary machine.

The technology of grinding worn-out tires existing at domestic reclaimed plants makes it possible to obtain crumb rubber from tires with a textile cord.

Excerpts from the tutorial

"Utilization and recycling of polymeric materials"

Klinkov A.S., Belyaev P.S., Sokolov M.V.

Recycling of polymers in Russia is becoming more and more promising. The number of projects for separate collection of waste is increasing, and products made using such materials are widely used in various industries. However, the development of the market is still hindered by a number of factors.

On February 16, the Fourth International Conference "Polymer Recycling 2018" was held in Moscow. The partners are Viscotec and KRONES, the general media partner is the Polymer Materials magazine. The event was supported by INTRATOOL, EREMA and PETplanet.

General Director of INVENTRA Rafael Grigoryan, welcoming the participants, noted that in the future regional operators can become the largest players in the segment of polymer recycling. Their main source of income today is the waste management tariff paid by the population, but the volume of incoming funds may not be enough to make a profit. In this regard, regional operators with an extensive resource base are interested in sorting, processing and producing goods from recycled materials in order to extract the maximum benefit.

The discussion of the state of affairs in the segment began with a speech by the Chairman of the Board of Directors of the Clean City Group of Companies, Polina Vergun, who said that the area of ​​waste management in Russia is as follows: 5% is sent for processing, 10% goes to landfills that meet environmental requirements, and 85% end up at facilities that do not provide environmental safety.

Among the main problems of the industry, Ms. Vergun singled out: the placement of waste in unauthorized landfills and the lack of a sufficient number of waste management facilities. And the main difficulties in the recycling segment are the lack of sorting and processing capacities, the fragmentation of the market and the underdevelopment of the separate collection system.

The solution to the above problems, according to the speaker, has already been found: the introduction of the institute of a regional operator in the field of waste management, a ban on the disposal of individual components and an increase in the rates and standards of the environmental fee. The expert also noted that the participation of small businesses in the organization of waste management activities is important.

“Given the ongoing waste management reform, it is important to start building federal ecotechnoparks that process secondary raw materials, which will be taken from the regional technoparks that are currently being commissioned today, because the existing processing capacities will not be enough for the volumes of recyclables in the new system, - continued Ms. Vergun, - within its framework, interaction takes place at the level of regional and federal eco-technoparks, directions for processing secondary raw materials for the purpose of import substitution are determined and joint solutions are developed to improve the regulatory framework , including the rationale for increasing the standards and recycling rates.
In addition, the speaker noted that in the next few years the collection of plastic waste will increase significantly and it is not entirely clear whether there is a sufficient volume of consumption of products made from recycled polymers in Russia today. “We are ready to give certain capacities on our territory for the development of third-party enterprises, if it is expedient and beneficial to both parties,” concluded Ms. Vergun.

The Chairman of the Board of Directors of Ecotechnology, Konstantin Rzayev, spoke about his vision of the situation and recalled that in total Russia consumes 5 million tons of polymer raw materials, an impressive part of which remains in use for decades (window frames, pipes, geomaterials), and in “garbage” first of all, polymer packaging gets into.

According to the speaker, taking into account the expected sharp increase in the collection of plastic waste at sorting by the efforts of regional operators, an additional 100-150 thousand tons of PET and several hundred thousand tons of other polymer packaging can be expected in the next few years.

Mr. Rzayev, continuing the conversation, noted that the previous two or three years had set some trends in the field of plastic waste processing, there were factors that led to the growth of the industry and new opportunities. Among these, the speaker noted the adoption of laws 458 and 503 F3, the introduction of extended producer responsibility, the launch of an increasing number of waste sorting complexes, as well as the implementation of a ban on waste disposal, which includes useful components, which began in 2018. Territorial schemes have been developed in almost all regions, about a third of them have chosen recyclers for the treatment of MSW, more and more organizations are learning about extended producer responsibility and environmental fees.

Of course, environmental friendliness is becoming a trend. But the segment still has problems: the low collection of fractions for processing, the high proportion of players remaining "in the shadows", the unstructured industry - will this change in the coming year? The question remains open.

The expert estimated the consumption of recycled PET (in the form of PET flakes) for 2017 at 151 thousand tons, of which domestic production is 136 thousand tons, about 16 thousand tons were imported, and 877 tons were exported. Almost 100% of imports - PET flakes for the production of polyester fiber. Among the largest supplier countries: Ukraine, Belarus-Kazakhstan-Kyrgyzstan, Lithuania, Azerbaijan and the UK.

The structure of consumption of recycled PET today is as follows: 65.4% falls on polyester fiber, about 18% - preforms, 12.7% - tape, twine, film and sheets - 2.7%, and less than 1% - other segments (resins, etc.). ) The largest processors - manufacturers of polyester fiber (Comitex, RB-Group, Technoplast, Politex, Nomatex, Selena, Vtorkom), Specta (leader in the Russian packaging tape market), as well as the only manufacturer of food-grade PET granulate, the Plarus plant.

The volume of deliveries of recycled polyethylene to Russia, for comparison, in 2014 was 1.9 thousand tons, by 2016 it rose to 3.3 thousand tons, but in 2017 it dropped again and amounted to about 3.1 thousand tons. Among the largest suppliers according to the data over the past year - Poland (2.2 thousand tons) and Bulgaria (777 tons).

In Europe, an average of 492 kg of waste per person per year is produced, of which a smaller part - 42% is recycled, and the remaining 58% is buried or incinerated, Kaspars Fogelmanis, CEO of PET Baltija, said in his report on plastics recycling in Europe.

Today, almost 50% of all plastic collected and recycled in the EU comes from France, Germany and Italy. These countries are joined by Spain and the UK, forming the top five players and collecting about 71% of the total waste in the EU. The European Commission has proposed to increase the percentage of recycling of the entire flow of plastic waste in the EU to 55% by 2025.

PET waste imports to China decreased in the 3rd quarter of 2017 by 177.6 thousand tons, or 26% compared to the figures for 2016, which amounted to 517 thousand tons. By the end of 2017, the Chinese authorities banned the import of 24 types of materials, including paper and plastic. From now on, they will only accept recyclable materials with a pollution level of no more than 0.3%, according to the government of the country.

Clearly, the ban imposed by China has an impact on recycling worldwide: this extends to the EU-27 countries, where 87% of the collected recycled plastic is shipped directly or indirectly via Hong Kong to China. Japan and the US are also taking advantage of China buying up their recycled plastic. Last year, America exported 1.42 million tons of plastic waste, which, according to Mr. Fogelmanis, brought China nearly $500 million.

Lyubov Melanevskaya, executive director of RusPEC, made a report on the mechanisms for implementing extended producer responsibility (which are provided for in two ways: independently or through payment of an environmental fee).

“According to the plan, the state in 2017 was supposed to collect 6.5 billion rubles. as an environmental fee, but in fact collected 1.3 billion rubles. What does it take to make ROP work? Clear rules of the game, equal contribution of business, the state and the population, as well as support for the “first swallows” in the independent implementation of the ROP,” shared Ms. Melanevskaya.

Success in the current situation, according to the speaker, can be achieved through the synchronous adoption of legislative acts, giving the authorities obligations to introduce separate waste collection and responsibility for failure to achieve targets for the RSO, as well as the introduction of infrastructure for the RSO. The North Ossetia Law, adopted at the end of 2017, marked the beginning of changes. Will there be further improvements? Time will tell.

Anna Dautova, head of the TechnoNIKOL project, believes that Russia still lacks a culture and widespread practice of collecting and processing polystyrene waste, but this process can be led by their company, and then an important environmental problem on a national scale will be solved.

Recycling of polystyrene waste requires less than 10% of the total resources spent on the production of virgin polymers. At the same time, for the production of a number of products, secondary ones can be used in large volumes. Speaking about the world experience, the speaker noted that Torox and Ursa are the main players in the European polystyrene recycling market. According to the data provided by the speaker, 50 thousand tons of expanded polystyrene are recycled annually in Europe, and in Japan, with a market capacity of primary foamed polystyrene of 132 thousand tons, 125 thousand tons are collected and reused.

Kaloyan Iliev, General Director of the Yerema subsidiary, presented information on pre-vacuum treatment at elevated temperature before extrusion, due to which, in a stable technological environment, moisture and migratory substances are removed from the material already before extrusion. This processing and the short extrusion screw ensure continuous production of food grade approved PET pellets with high and stable viscosities and good color values.

Global waste collection rates are on the rise, with Asia leading the way. The legislation is getting stricter: recycling of materials is encouraged and at the same time restrictions on waste disposal and energy use are introduced, which, of course, should have a positive impact on the global environment, said Peter Hartel, head of sales at Krones, and spoke about the decisions of the plastics recycling company. Krones modular systems are fully customizable and can be supplied as individual machines or as turnkey plants. MetaPure processing technology produces flakes or granules of various qualities, up to food grade PET in accordance with the FDA and other certification systems.

In conclusion, the conversation turned to PET packaging. According to Starlinger Viscotec representative Gerhard Ossberger, there are three conditions for successful PET packaging: optical appearance (bright color, full transparency and no defects), food safety (100% safe packaging for human health), mechanical characteristics (maximum stackability and warehousing, strength). The deCON dryer and viscoSHEET extrusion line removes dust to reduce visual blemishes, dries raw materials for maximum viscosity yet maximum strength, and cleans incoming recycled materials for 100% food safety. In this way, Viscotec creates high-quality "protection" for the goods.

Products made of polymers are an integral part of our daily lives today, however, along with the growth in the production of such products, it is only natural that the amount of solid waste is also increasing.

Today, polymer waste makes up about twelve percent of all household waste, and their number is constantly growing. And it is natural that the recycling of polymers today is one of the most pressing problems, because without it, humanity can literally drown in mountains of garbage.

The recycling of polymers today is not only a problem, but also a very promising line of business, since it is possible to obtain many useful substances from seemingly waste raw materials - household waste. In addition, this waste recycling technology (MSW) is a much safer method of recycling polymer waste than traditional incineration, which causes significant environmental damage.

Polymer processing technology

So what is polymer recycling?

To convert polymer waste into raw materials suitable for further processing into products, it is necessary to pre-process it. The choice of pre-treatment method primarily depends on the degree of contamination of the waste and the source of their formation. Thus, homogeneous production wastes are usually processed right at the place of their formation, since in this case little pre-treatment is required - just grinding and granulation.

However, waste in the form of obsolete products requires much more thorough preparation. So, the pre-treatment of polymer waste usually includes the following steps:

1. Rough sorting and identification for mixed waste.
2. Waste shredding.
3. Separation of mixed waste.
4. Waste washing.
5. Drying.
6. Granulation.

Pre-sorting provides for a rough separation of polymer waste according to various criteria: type of plastic, color, shape and dimensions. Pre-sorting is usually carried out manually on conveyor belts or tables. Also, the technology of polymer processing implies that various foreign inclusions are removed from the waste during sorting.

Polymeric waste products that have become obsolete and have ended up at the waste processing plant, in which the content of foreign impurities does not exceed 5%, are sent to the sorting unit, where random foreign inclusions are removed from them. Waste that has been sorted is crushed in knife crushers until a loose mass is obtained, the particle size of which is 2 ... 9 mm.

Grinding is one of the most important stages in the preparation of waste for processing, since the degree of grinding determines the flowability, particle size and bulk density of the resulting product. And the regulation of the degree of grinding allows you to improve the quality of the material due to the averaging of its technological characteristics. This also simplifies the processing of polymers.

A very promising method of grinding polymer waste is cryogenic, thanks to which it is possible to obtain powders from polymer waste with a degree of dispersion from 0.5 to 2 mm. The use of this technology has a number of advantages over traditional mechanical grinding, since it allows to achieve a reduction in the mixing time and a better distribution of the components in the mixture.

The separation of mixed plastic waste by type is carried out in the following ways:

1. Flotation.
2. Separation in heavy media.
3. Aeroseparation.
4. Electroseparation.
5. Chemical methods.
6. Deep cooling methods.

The most common of these today is the flotation method, in which the separation of plastics is carried out by adding various surfactants to the water, due to which the hydrophilic properties of the polymers are selectively changed.

In some cases, a fairly effective way to separate polymers is to dissolve them in a common solvent. Processing the resulting solution with steam, PVC, a mixture of polyolefins and PS are isolated, and the purity of the products is not less than 96%.

It is these two methods that are economically more expedient of all those listed above.

Next, the crushed waste polymers are fed into the washing machine for cleaning. Washing is carried out in several steps using special detergent mixtures. The polymer mass squeezed out in a centrifuge with a moisture content of 10 to 15% is fed for final dehydration to a drying plant, where it is dried to a moisture content of 0.2%.

After that, the mass enters the granulator, where the material is compacted, thereby facilitating its further processing and averaging the characteristics of secondary raw materials. The end result of granulation is a material that can be processed by standard polymer processing equipment.

So, it is clear that the processing of polymer waste is quite a difficult task, and requires certain equipment. What kind of polymer recycling equipment is used today?

• Washing lines for polymer waste.
• Crushers of polymers.
• Recycling extruders.
• Belt conveyors.
• Shredders.
• Agglomerators.
• Granulation lines, granulators.
• Sieve substitutes.
• Mixers and dispensers.

If you have all the equipment necessary for processing polymers, then you can get down to business and make sure from your own experience that today waste recycling (MSW) is not only a concern for the planet's ecology, but also an excellent investment, since the profitability of this business is very high.

The penetration of polymer materials into a wide variety of applications, including our daily lives, is now taken for granted around the world. And this despite the fact that their victorious march began relatively late - in the 1950s, when their production volumes were only about 1 million tons per year. However, with the growth in the production and consumption of plastics, the problems of recycling used plastic products have gradually become more acute and have now become extremely relevant. This review discusses the experience of solving these problems in Europe, where Germany is leading in this regard.

Due to their many advantages (in particular, high strength, chemical resistance, the ability to make any shape and any color, low density), they quickly penetrated into all areas of application, including construction, automotive, aerospace, packaging industries, household products, toys , medical and pharmaceutical products.

Already in 1989, polymeric materials overtook such a traditional material as steel in terms of production volumes (meaning volumes, not mass). At that time, their annual output was about 100 million tons. In 2002, the production of polymeric materials overcame the bar of 200 million tons, and now almost 300 million tons of them are produced annually around the world. If we consider the issue in the regional plan, then Over the past decades, there has been a gradual shift in the production of polymeric materials towards the East.

As a result, Asia has now become the most powerful region, where 44% of all world capacities are concentrated. Polyolefins, the most widely used group of plastics, account for 56% of total production; polyvinyl chloride comes in second, followed by other traditional polymers such as polystyrene and polyethylene terephthalate (PET). Only 15% of all produced polymers are expensive technical materials used in special areas. According to the forecasts of the European Association of Polymer Producers PlasticsEurope (Brussels), in the future, the volume of output of polymeric materials per capita will continue to increase at a rate of about 4% per year. Simultaneously with such success in the market, the volumes of used polymeric materials and products also increased. If in the period from the 1960s to the 1980s. The plastics industry may not yet have paid much attention to the appropriate disposal and reuse of used products, but later (especially after the entry into force of the German packaging regulation in 1991) these problems became an important topic. At that time, Germany took on the role of pioneer. It became the first country to develop and implement on the market standards for the disposal and recycling of polymer waste. At present, many other European countries have joined the solution of this problem, having developed very successful concepts for the collection and recycling of polymers.

According to the PlasticsEurope Association, in 2011, about 27 million tons of polymeric materials were used in 27 EU countries, as well as in Switzerland and Norway, of which 40% were for short-term products and 60% for long-term products. In the same year, about 25 million tons of used polymer materials were collected. Of these, 40% were disposed of, and 60% were sent for recycling. More than 60% of plastic waste came from the collection systems for used packaging. In smaller quantities, used polymer products were sourced from the construction, automotive and electronics sectors.

Exemplary waste collection systems exist in nine European countries - Switzerland, Germany, Austria, Belgium, Sweden, Denmark, Norway, Holland and Luxembourg (listed in descending order). The share of collected used polymer products in these countries ranges from 92 to 99%. In addition, six of these nine countries have the highest level of recycling of this waste in Europe: Norway, Sweden, Germany, Holland, Belgium and Austria are far ahead of other countries in this indicator (from 26% to 35% of the volume of waste collected). . The remaining amount of collected waste is subjected to energy utilization.

One cannot but rejoice the fact that over the past five years not only the amount of collected waste has increased significantly, but also the share of waste recycled. As a result, the amount of waste being disposed of has been reduced. Despite this, the polymer recycling sector still has huge potential for further development. To a large extent, this applies to countries with a low level of their utilization.

Critically, experts consider the possibilities of energy recycling of polymeric materials, namely their incineration, which many consider an expedient way to recycle them. In Germany, 95% of all waste incinerators are waste recycling facilities and are thus licensed for energy recycling. Assessing this situation, Michael Scriba, commercial director of mtm plastics, a company specializing in the processing of polymeric materials (Niedergebra), notes that from an environmental point of view, the energy recycling of waste is undoubtedly worse than the material one.

Within the plastics industry, recycling has become an important economic sector in recent years. Another important problem hindering the development of the recycling sector in Europe is the export of polymer waste, mainly to the Far East. For this reason, there remains a relatively small amount of waste that can be reasonably recycled in Europe; this contributes to a significant increase in competition and an increase in costs.

Powerful industry supported by associations and companies

Since the 1990s Several companies and associations have acted as initiators of the intensification of recycling of plastic waste in Germany, which have devoted their activities to these problems and are now actively working on a European scale.

First of all, we are talking about the company Der Gruene Punkt - Duales System Deutschland GmbH (DSD) (Cologne), which was founded in 1990 as the first dual system and today is the leader in offering systems for the return of waste. These include, in addition to household-friendly collection and recycling of commercial packaging, environmentally friendly and cost-effective recycling of plastic elements of electrical and electronic equipment, as well as transport packaging, waste disposal from enterprises and organizations, and cleaning of used containers.

In 1992, RIGK GmbH was founded in Wiesbaden, which, as a certified specialist service provider for brand owners (bottling, distribution, distribution and importers), takes back used and empty packaging from its German partners and sends these packages for recycling.

An important market player is also BKV, which was founded in 1993 with the aim of ensuring guaranteed recycling of plastic packaging collected by dual systems. Currently, BKV serves as a kind of base platform for the recycling of polymeric materials, dealing with the most significant and urgent problems in this area.

Another important association was founded in 1993, the Bundesverband Sekundäerrohstoffe und Entsorgung e. V. (bvse) (Bonn), whose origin is associated with the association of Altpapierverband e. V. In the plastics sector, it provides German companies with professional and locally determined assistance in the collection and recycling of plastic waste. Along with BKV, which is part of the GKV Gesamtverband Kunststoffverarbeitende Industrie e.V. (Bad Homburg), there are other associations and organizations involved in the recycling of polymeric materials. These include, among others, tecpol Technologieentwicklungs GmbH, which specializes in the environmentally efficient recycling of plastic waste, and the compounding and recycling specialist group at TecPart e. V., which is the base association of the GKV association. In 2002, the leading German manufacturers of plastic profiles merged into the initiative group Rewindo Fenster-RecyclingService GmbH (Bonn). The main goal was to increase the share of recycled dismantled plastic windows, doors and roller shutters (see the photo at the title of the article), which would contribute to increased stability and a degree of responsibility in business activities.

It goes without saying that large plastics industry associations with their own working groups for plastics recycling, which have been successful in practice for decades, such as PlasticsEurope and IK Industrieverband Kunststoffverpackungen e, have become involved in solving the problems. V. (Frankfurt).

Successful proven recycling technologies

Accurate information about the recycling of plastics in Germany is provided by the results of the analysis, which is published every two years on the instructions of the companies and associations that are part of the VDMA - BKV, PlasticsEurope Deutschland e. V., bvse, Fachverband Kunststoff und Gummimaschinen, as well as the IK association. According to these data, about 5 million tons of plastic waste was generated in Germany in 2011, the largest part (82%) of which is consumer waste. Of the remaining 18%, which is industrial waste, the share of recyclable materials can reach 90%. As has already been proven in practice, sorted industrial waste can be successfully subjected to in-plant recycling directly at the enterprises where they were generated (photo 1).

In the case of consumer waste, the share of material (that is, without incineration and disposal) reuse is only 30-35%. In this area, there are also already implemented methods for the recycling of sorted waste. Examples include experience with the processing of polyvinyl chloride (PVC) and PET. As a result of its 10 years of activity, Rewindo, using its own technology for the recycling of end-of-life PVC windows and doors, has gained a strong position in the market.

In recent years, the volume of recycled PVC produced from the collected used products by Toensmeier Kunststoffe GmbH & Co. KG (Hechter) and Veka Umwelttechnik GmbH (Herselberg-Heinich) were maintained at about 22 thousand tons with an upward trend.

PET bottles are also collected and recycled after proper sorting. The range of new products made from the resulting recycled materials ranges from fibers and films to new bottles. Various companies such as the Austrian firms Erema GmbH (Ansfelden), Starlinger & Co. GmbH (Vienna) and NGR GmbH (Feldkirchen) have set up special production lines for PET recycling. Recently, the European Food Safety Authority EFSA issued a positive opinion on the recoSTAR PET iV+ technology for the production of recycled PET suitable for food packaging (developed by Starlinger).

The opinion of EFSA serves as the basis for the certification of such technologies by the European Commission and EU member states.

To achieve such a result, the interested company must prove that the technology and equipment developed by it for the processing of polymer waste reduces the degree of pollution of the corresponding PM to a level that is safe for human health.

The standard scenario of the so-called "provocative" tests (challenge-test) for the cleaning efficiency of recycled PET, usually obtained from waste in the form of used bottles, involves the use of five control "polluting" substances - toluene, chloroform, phenylcyclohexane, benzophenone and lindane, which differ in chemical composition , molecular weight and, consequently, migration ability. The tests themselves are carried out in several stages.

First, recycled PET flakes are washed, after which they are “contaminated” with a control substance with a given concentration (3 ppm) and washed again. Then, these rewashed PET flakes are processed according to the tested technology into PET regranulate and the residual concentration of the “polluting” medium is determined, according to which the degree of purification of secondary PET is calculated. In conclusion, both indicators are compared with the maximum permissible values ​​for them and conclusions are drawn about the cleaning efficiency.

In addition to the standard testing, Starlinger independently decided to toughen up their scenario by running them under so-called “worst-case-szenario” conditions, which processed PET flakes that had not been washed after being contaminated with model media. Prior to each type of test, to ensure the purity of the experiment and stable conditions for its implementation, 80–100 kg of transparent primary PET was processed at the recoSTAR PET 165 iV+ plant (photo 2) in order to clean the working parts of the plant from the remnants of the previous batch of material. The tested PET flakes were dyed blue; therefore, the output of only blue PET regranulate from the same plant indicated that it was not mixed with pure PET during the processing and that the FIFO (first-in, first-out) principle was observed. Test results from the standard scenario show that the recoSTAR PET iV process provides such effective purification of recycled PET that its performance is well above the EFSA threshold level (see table). Even in the case of lindane (a non-volatile non-polar substance), the degree of purification was over 99.9%, although the threshold value is 89.67%. Practically the same results were shown by tests conducted according to the "tougher" scenario, with the exception of benzophenone and lindane. But even in these cases, the degree of purification of PET met the requirements of EFSA. The abbreviated name of the company NGR stands for quite ambitiously - as "The Next Generation of Recycling Machines" (Next Generation Recyclingmaschinen). And having become a 100% owner of BRITAS Recycling Anlagen GmbH (Hanau, Germany) in May of this year, NGR has significantly strengthened its position in the European and other regional markets of the world. The fact is that BRITAS is known as a developer and manufacturer of filter systems for melts of highly contaminated polymeric materials, including consumer packaging waste (photo 3).

In turn, NGR develops and manufactures equipment for the recycling of both industrial and consumer polymer waste, having an extensive market for its products.

Both engineering companies are confident in the positive synergy effect from the merger. Gneuss Kunststofftechnik GmbH (Bad Oeynhausen) has achieved great market success with its MRS type extruder (photo 4), which is even approved by the FDA (Food and Drug Administration) of the US Department of Commerce for Food Quality Control, medicines and cosmetics. In addition, machine builders offer various drying systems such as the infrared rotating tube from Kreyenborg Plant Technology GmbH (Senden), as well as special filtration systems for PET processing or crystallization technologies such as the Crystall-Cut process from Automatik Plastics Machinery (g . Grosostheim). Closed cycle systems such as the PETcycle system have been successfully used to make new bottles from used bottles.

Summarizing all of the above, we can state that the PET recycling system with an annual volume of about 1 million tons is successfully implemented in Europe. A similar situation is observed in the field of processing of sorted polyolefin waste, the sorting of which is realized without any special complications using appropriate technologies for their separation. In Germany alone, there are ten large and many small fabricators specializing in the production of injection moldable secondary granulate from municipal and industrial polyolefin waste. This granulate can be further used for the production of pallets, tubs, buckets, pipes and other types of products (photo 5).

Difficulties of recycling

Additional challenges for recycling are plastic products made from several different materials that cannot be reasonably separated from each other, as well as plastic packaging that cannot be completely emptied. Waste in the form of used consumer film is also problematic for recycling due to significant surface contamination, which requires significant processing costs.

According to Scribe, although there are experienced recycling experts in this area, there are no real markets of European importance. Additional complications also arise when handling PET bottles produced in a large variety, not intended for beverages; this significantly limits the volume of their recycling. So far, waste from the automotive and electronics sectors has been difficult to recycle.

In such problematic cases, processors and machine builders require special technical solutions (photo 6). In particular, one such solution regarding the recycling of consumer film waste supplied by DSD was recently provided by Herbold Meckesheim GmbH (Meckesheim) to the waste management company WRZ-Hörger GmbH & Co. KG (Sontheim). The turnkey production plant, consisting of a foreign matter separation system, a wet grinding stage and a compacting device, allows processing 7 thousand tons of waste annually into a free-flowing agglomerate with a high bulk density, suitable for the manufacture of products using injection molding technology (photo 7 ).

In general, Herbold Meckesheim's supply program, which is also known on the Russian market, includes a variety of equipment for processing both highly contaminated and mixed waste, both solid and hard-to-recycle soft plastic waste - washing plants and dryers, shredders, agglomerators, mills for fine grinding.

The main declared priorities in the development of equipment are its compactness, increased performance and energy efficiency. At the K-2013 exhibition, the company will demonstrate a number of new products, including:

New mechanical dryer model HVT with a vertical rotor arrangement, which saves production space, is easy to maintain and consumes significantly less energy when drying PET flakes (photo 8);
shredder model SML SB with forced auger feeding of waste into the cutting unit, which makes it possible to compact the feed material and thereby increase the productivity of processing (Fig. 1);
machine for grinding bulky solid waste in the form of, for example, plates or pipes, which are considered the most difficult object of processing. Especially for the processing of mixed fractions, Erema together with Coperion GmbH & Co. KG (Stuttgart) has developed a combined Corema plant for waste recycling and compounding (photo 9). A characteristic feature of this plant is its suitability for processing a wide range of materials. According to Manfred Hackl, Commercial Director of Erema, Manfred Hackl, this is the optimal solution for the processing of economically produced mixed waste, in particular for the production of a compound containing 20% ​​talc from waste polypropylene nonwovens, or for the processing of waste into in the form of a mixture of PE and PET with additives. Another successful example of several partners joining forces to solve recycling problems is the production line for the recycling of used agricultural films, the recycling of which is difficult and costly due to their thinness, softness and contamination. The problem was solved by combining in one line a specially optimized shredder model Power Universo 2800 (manufacturer - Lindner reSource) and an extrusion plant for the recycling of polymeric materials model 1716 TVEplus (manufacturer - Erema), which made it possible to obtain high-quality regranulate.

Equipment that is universal in terms of the form of waste processed into regranulate (films, fibers, PET bottle flakes, waste of foamed polymeric materials) is offered by the Austrian company ARTEC Machinery. The impetus for further development and expansion of production capabilities was its 100% entry in 2010 into the "family" group GAW Technology, of which ECON is also a member, supplementing the supply program with appropriate extrusion lines for processing shredded waste into regranulate. Due to the design and technological modernization of the manufactured equipment over the years, it was possible to increase its productivity by an average of 25%. The modular principle that ARTEC adheres to when designing its plants allows, as from cubes, to assemble and assemble equipment for a specific application, which is currently produced with a capacity of 150 to 1600 kg per hour (Fig. 2).

A specific extrusion plant with an MRS type extruder (see photo 4), designed for processing shredded waste from polyamide PA11, was also supplied by Gneuss to the British company K2 Polymer.

The feedstock is obtained from the crushing of deep sea oil pipelines, which become redundant once the oil source dries up and must be brought to land.

The MRS extruder (Multi Rotation System) allows, without the use of chemical cleaning, one-stage cleaning and processing of these high-quality, but heavily contaminated polymer wastes during many years of contact with oil. This list could be supplemented with many other examples. In conclusion, it should be noted that the recycling sector has become an important area of ​​economic activity in recent years. Although many technologies have already been successfully tested in practice, there remains great potential for further development in the field of recycling. Solving existing problems should begin with the development and manufacture of polymer products that are as recyclable as possible.

Some room for advancement also remains in the development of optimized technological solutions and the creation of appropriate equipment for the processing of complex waste.

To some extent, progress in this area can also be facilitated by policy measures, which should in each country ensure the wider implementation of optimal concepts for the collection and recycling of waste.

New and proven solutions in the field of polymer recycling will be widely presented from 16 to 23 October 2013 at the K International Fair in Düsseldorf.

Prepared by Ph.D. V. N. Mymrin
using press materials of the exhibition company Messe Duesseldorf
Recycling of Plastics in Europe:
New and Proven Solutions The penetration of plastics in a v ariety of
applications, including our d aily liv es, ar e now seen worldwide as a matter of course. And this
despite the fact that their winning streak started relatively late – 60 years ago, when their output
accounted for only about 1 million tons per year.

However, with the gr owth of production and consumption of plastics gradually sharpened
and has now become a critical problem disposing of used plastic products. Although many
processes hav e alr eaty become established, recycling still has plenty of potential for
improvement. A first step could be the recyclable design of plastics items that should be examined
closely with a view to later recovery. Suitable recycling processes and machine solutions for the
processing of problematical wastes offer a good deal of scope for further dev elopment. This
review discusses the experience of solving these problems in Eur ope, wher e the leading in this
respect is Germany.