Types of equipment used for the processing of polymeric materials. Recycling of waste polymers: technology, equipment. Characteristics of penp properties before and after aging

Waste classification

Wastes are generated during the processing of polymers and the manufacture of products from them - these are technological wastes, partially returned to the process. What remains after the use of plastic products - various films (greenhouse, construction, etc.), containers, household and large-scale packaging - is household and industrial waste.

Technological waste is subjected to thermal action in the melt, and then, during crushing and agglomeration, also to intense mechanical stress. In the mass of the polymer, the processes of thermal and mechanical destruction proceed intensively with the loss of a number of physical and mechanical properties and, with repeated processing, can adversely affect the properties of the product. So, when returning to the main process, as usual, 10-30 percent of secondary waste, a significant amount of material goes through up to 5 cycles of extrusion and crushing.

Household and industrial waste is not only recycled several times at high temperatures, but also exposed to long-term exposure to direct sunlight, oxygen and moisture in the air. Greenhouse films can also come into contact with pesticides, pesticides, iron ions, which contribute to the degradation of the polymer. As a result, a large amount of active compounds accumulate in the polymer mass, accelerating the breakdown of polymer chains. The approach to recycling of such different wastes should accordingly be different, taking into account the history of the polymer. But first, let's look at ways to reduce the amount of waste generated.

Reducing the amount of process waste

The amount of technological waste, primarily start-up waste, can be reduced by using heat stabilizers before stopping the extruder or injection molding unit, in the form of a so-called stop concentrate, which many people forget or neglect. When the equipment stops for a simple material in the extruder barrel or injection molding machine, it is under the influence of high temperature for quite a long time when cooling and then heating the barrel. During this time, the processes of cross-linking, decomposition and burning of the polymer actively proceed in the cylinder, products accumulate, which after start-up for a long time come out in the form of gels and colored inclusions (burns). Thermal stabilizers prevent these processes, making it easier and faster to clean the equipment after start-up. To do this, before stopping, 1-2 percent of the stop concentrate is introduced into the cylinder of the machine for 15-45 minutes. to a stop at the rate of displacement of 5-7 cylinder volumes.

Processing (extrusion) additives that increase the manufacturability of the process also make it possible to reduce the amount of waste. By their nature, these additives, for example, Dynamar from Dyneon, Viton from DuPont, are derivatives of fluororubbers. They are poorly compatible with basic polymers and, in places of greatest shear forces (dies, sprues, etc.), are precipitated from the melt onto the metal surface, creating a near-wall lubricating layer on it, along which the melt slides during molding. The use of a processing additive in the smallest quantities (400-600 ppm) allows solving numerous technological problems - reducing the torque and pressure on the extruder head, increasing productivity while reducing energy costs, eliminating appearance defects and reducing the extrusion temperature of polymers and compositions sensitive to elevated temperatures, increase product smoothness, produce thinner films. In the manufacture of large-sized or thin-walled molded products of complex shape, the use of an additive can improve spillage, remove surface defects, solder lines and improve the appearance of the product. All this in itself reduces the proportion of marriage, i.e. amount of waste. In addition, the processing additive reduces the sticking of carbon deposits on the die, fouling of sprues, and has a washing effect, i.e. reduces the number of stops to clean equipment, and therefore the amount of start-up waste.

An additional effect is the use of cleaning concentrates. They are used in the cleaning of casting and film equipment for a quick transition from color to color without stopping, most often in a ratio of 1:1-1:3 with polymer. This reduces the amount of waste and time spent on color changes. The composition of cleaning concentrates produced by many domestic (including Klinol, Klinstyr from NPF Bars-2, Lastik from Stalker LLC) and foreign manufacturers (for example, Shulman - Poliklin ”), includes, as a rule, soft mineral fillers and surface-active detergent additives.

Reducing the amount of household and industrial waste.

There are various ways to reduce the amount of waste by increasing the service life of products, primarily films, through the use of thermal and light stabilizing additives. When extending the service life of the greenhouse film from 1 to 3 seasons, the amount of waste to be disposed of decreases accordingly. To do this, it is enough to introduce small amounts of light stabilizers into the film, no more than half a percent. Stabilization costs are low, and the effect of film recycling is significant.

The way back is to accelerate the degradation of polymers by creating photo- and biodegradable materials that quickly degrade after use under the action of sunlight and microorganisms. To obtain photodegradable films, comonomers with functional groups that promote photodegradation (vinyl ketones, carbon monoxide) are introduced into the polymer chain, or photocatalysts are introduced into the polymer as active fillers that promote the breaking of the polymer chain under the action of sunlight. Dithiocarbamates, peroxides or oxides of transition metals (iron, nickel, cobalt, copper) are used as catalysts. The Institute of Water Chemistry of the National Academy of Sciences of Ukraine (V.N. Mishchenko) developed experimental methods for the formation of nanosized cluster structures containing metal and oxide particles on the surface of titanium dioxide particles. The rate of decomposition of films increases 10 times - from 100 to 8-10 hours.

The main directions for obtaining biodegradable polymers:
synthesis of polyesters based on hydroxycarboxylic (lactic, butyric) or dicarboxylic acids, however, so far they are much more expensive than traditional plastics;
plastics based on reproducible natural polymers (starch, cellulose, chitosan, protein), the raw material base of such polymers can be said to be unlimited, but the technology and properties of the resulting polymers do not yet reach the level of the main multi-tonnage polymers;
making industrial polymers (polyolefins in the first place, as well as PET) biodegradable by compounding.

The first two directions require large capital expenditures for the creation of new industries; the processing of such polymers will also require significant changes in technology. The easiest way is compounding. Biodegradable polymers are obtained by introducing biologically active fillers (starch, cellulose, wood flour) into the matrix. So, back in the 80s, V.I. Skripachev and V.I. Kuznetsov from ONPO "Plastpolimer" developed starch-filled films with an accelerated aging period. Unfortunately, the relevance of such material then was purely theoretical, and even now it has not received wide distribution.

Waste recycling

It is possible to give the polymer a second life with the help of special complex concentrates - recyclers. Since the polymer undergoes thermal degradation at each stage of processing, photo-oxidative degradation during the operation of the product, mechanical degradation during grinding and agglomeration of waste, degradation products accumulate in the mass of the material, and a large amount of active radicals, peroxide and carbonyl compounds are contained, which contribute to further decomposition and cross-linking of polymer chains. Therefore, the composition of such concentrates includes primary and secondary antioxidants, thermal and light stabilizers of the phenolic and amine type, as well as phosphites or phosphonites, which neutralize active radicals accumulated in the polymer and decompose peroxide compounds, as well as plasticizing and combining additives that improve physical and mechanical properties. properties of the recycled material and pull them up more or less close to the level of the virgin polymer.

Complex additives of the Siba company. Ciba, Switzerland, offers a family of complex stabilizers for the processing of various polymers - LDPE, HDPE, PP: Recyclostab / Recyclostab and Recyclosorb / Recyclossorb. They are tablet mixtures of various photo- and thermal stabilizers with a wide range of melting temperatures (50-180°C), suitable for input into processing equipment. The nature of the additives in the Recyclostab composition is common for polymer processing - phenolic stabilizers, phosphites and processing stabilizers. The difference lies in the ratio of components and in the selection of the optimal composition in accordance with a specific task. "Recyclossorb" is used when light stabilization plays an important role, i.e. the resulting products are operated outdoors. In this case, the proportion of light stabilizers is increased. Input levels recommended by the firm are 0.2-0.4 percent.

"Recyclostab 421" is specially designed for processing and thermal stabilization of waste LDPE films and mixtures with a high content of it.

"Recyclostab 451" is designed for the processing and thermal stabilization of PP waste and mixtures with a high content of it.

Recyclostab 811 and Recyclossorb 550 are used to extend the life of recycled products used in sunlight, so they contain more light stabilizers.

Stabilizers are used in the production of molded or film products from secondary polymers: boxes, pallets, containers, pipes, non-critical films. They are produced in granulated, non-dusting form, without a polymer base, pressed granules with a melting range of 50-180°C.

Complex concentrates of the Bars-2 company. For the processing of secondary polymers, SPF Bars-2 produces complex polymer-based concentrates containing, in addition to stabilizers, also combining and plasticizing additives. Complex concentrates "Revtol" - for polyolefins or "Revten" - for high-impact polystyrene, are introduced in the amount of 2-3 percent during the processing of secondary plastics and, thanks to a complex of special additives, prevent thermal-oxidative aging of secondary polymers. Concentrates facilitate their processing due to the improvement of the rheological characteristics of the melt (increased MFR), increase the strength characteristics of finished products (their ductility and resistance to cracking) compared to products made without their use, facilitate their processing as a result of an increase in the manufacturability of the material (reduced torque and drive load). When processing a mixture of secondary polymers "Revtol" or "Revten" improve their compatibility, so the physical and mechanical properties of the resulting products also increase. The use of "Revten" allows you to increase the properties of the secondary UPM to the level of 80-90 percent of the properties of the original polystyrene, preventing the appearance of defects.

Now the development of a complex concentrate for the processing of recycled PET is very relevant. The main scourge here is the yellowing of the material, the accumulation of acetaldehyde, and the decrease in the viscosity of the melt. Known additives Western firms - "Siba", "Clarianta", allowing to overcome yellowing and improve the processability of the polymer. However, in the West and we have a different approach to the use of secondary PET. Where 90 percent of it is used to make polyester fibers or technical products, and the additives for this purpose are well developed, our processors are keen to bring recycled PET back into the mainstream - preforms and bottles by injection molding and blowing, or films and sheets by flat slot extrusion. In this case, the target properties of the polymer, which must be affected, are somewhat different - manufacturability, formability, transparency, and the formulation of complex additives must meet the goal.

In the modern world, the problem of recycling polymer waste is considered quite relevant. Every year, millions of tons of this type of product are collected at landfills. And only a small part of polymers is recycled. As a result of its implementation, high-quality raw materials are obtained, suitable for the production of new products.

What is a polymer product?

Every year, the production of polymeric materials increases by approximately 5%. This popularity is due to their many positive properties.

This product is mainly used as packaging. It increases the service life of the products that are inside the package. Also polymers have excellent appearance and long service life.

Modern industry produces the following types of products of this type:

• polyethylene and materials made on its basis - 34%;
• PET - 20%;
• paper with lamination - 17%;
• PVC - 14%;
• polypropylene - 7%;
• polystyrene - 8%.

What products are recyclable?

Not all polymers are recycled.

Thermoplastic synthetic materials, which are able to change their shape when exposed to high temperatures, are most often used for recycling.

Therefore, for this purpose, the following types of waste are collected and prepared in a special way:

• materials that remain in the plastic production process. Most often, these are all kinds of segments. Products of this type are of high quality, since there are no impurities in their composition. They are delivered to processing plants already sorted, which greatly simplifies the preparatory stage of work. Up to 90% of all industrial waste is usually recycled;
• polymers obtained after consumption. They are also called household waste. These are bags, disposable tableware, plastic bottles, window profiles and many other products. A feature of these materials is their contamination. For the processing of polymers of this type, a lot of effort and resources should be expended for sorting and cleaning waste.

What is the main problem of polymer waste recycling?

At the moment, only a small part of all existing waste is recycled. The development of this area is slow, despite its relevance. This is related to the following:

• the state does not provide all the necessary regulatory and technical standards that could ensure the high quality of recyclables. That is why there are no powerful industries that supply the market with recycled waste with optimal characteristics;
• since modern technologies are not used to carry out the processing process, huge financial resources are needed to maintain it;
• due to the lack of government support, the level of waste collection among the population and small businesses is low;
• the received secondary raw materials do not have sufficient competitiveness;
• there is no campaigning among the population that would encourage them to separate waste disposal. Most people do not understand that the use of recyclable materials allows you to limit the consumption of other resources - oil, gas.

How is the collection of recyclable materials for recycling?

Recycling of polymers occurs after all stages of preparation of raw materials have been completed:

1. Special points are being opened that are engaged in the collection and primary sorting of the products received. They cooperate both with the population and with industrial enterprises of various types.
2. Collection of polymers at landfills for household waste. Usually this is done by special companies.
3. Raw materials enter the secondary market after preliminary sorting at special waste processing points.
4. Processing companies purchase recyclable materials from large industrial complexes. Such materials are less polluted and are not subject to such thorough preparation for processing.
5. A small part of recyclables is also collected through a special program that involves separate waste collection.

How are polymers processed?

After collection and primary sorting, the processing of polymer waste occurs in the following way:

1. Grinding of raw materials. It is one of the important stages in the preparation of polymers for further processing. The degree of grinding of materials determines the quality characteristics of products that will be manufactured in the future. To carry out this stage of work, modern plants use a cryogenic method of processing. It allows to obtain a powder with a degree of dispersion from 0.5 to 2 mm from polymer products.
2. Separation of plastics by type. To carry out this operation, the flotation method is most often used. It involves the addition of special surfactants to the water, which are able to act on certain types of polymers and change their hydrophilic properties. The dissolution of raw materials with special substances is also very effective. Subsequently, it is treated with steam, which allows you to select the necessary products. There are other methods for the separation of polymers (aero- and electroseparation, chemical method, deep freezing), but they are less popular.
3. Washing. The resulting raw materials are washed in several stages using special means.
4. Drying. Materials are previously disposed of water in centrifuges. The final drying takes place in special machines. The result is a product with a moisture content of 0.2%.
5. Granulation. The prepared material enters a special installation, where it is compacted as much as possible. The result is a product that is suitable for the production of polymer products of any type.

Recycling plastic bottles

Standard list of equipment for a waste processing plant

Recycling of waste polymers is carried out using the following equipment:

• line for washing, where the purification of raw materials occurs with minimal labor;
• extruder - used to give the plastic mass the desired shape by punching;
• belt conveyors - to move raw materials in the right direction;
• shredders - designed for primary crushing of materials. They are able to work with almost any raw material;
• crushers - are actively used for more thorough grinding of raw materials after using a shredder;
• mixers and dispensers;
• agglomerators - necessary for the processing of thin polymer films;
• granulators - used to compact recycled raw materials;
• dryers;
• refrigerators;
• sinks;
• press and others.

What is the value of waste in the relevant market?

After analyzing prices on the market, it is clear that the cost of waste stored in landfills is 3-6 times lower than the price of recyclable materials (7-10 times relative to primary raw materials). If we analyze pricing using the example of a polyethylene film, we can understand the following:

• the price of polygon material from intermediary companies is 5 rubles per 1 kg;
• after washing and sorting, the cost of the film rises to 12 rubles/kg;
• raw materials in the form of agglomerate or granules have an even greater cost - 25-35 rubles / kg;
• the price of primary polyethylene varies from 37 to 49 rubles/kg.

Such a big difference in prices is not observed for all products. For example, it is almost imperceptible with PVC, polypropylene, polystyrene and ABS plastic. In the case of PET, the cost of landfill raw materials differs from secondary products by only 2-3 times. This is due to the peculiarities of its processing, as a result of which flakes are obtained due to grinding.

Where is the recycled material sold?

Waste recycling companies most often send the resulting product for sale. If such factories have their own equipment, they can be engaged in the production of polymers from the raw materials obtained. But it's not always cost effective.

Manufactured plastic products are most often of the same type, which makes it difficult to sell them in large quantities.

Most often, such companies are engaged in the production of sewer pipes, building materials or some car parts. There is a great demand for this type of product in the market.

Third-party recycling of polymer-type waste is also very popular. This service consists in the fact that the interested company gives its waste to the plant, which, after recycling, returns the finished recyclable material to it. The owner of polymer waste pays about 8-10 rubles/kg for their processing, which is considered a very good deal.

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, efficiency 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 waste plastics 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 destroy, 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 polymeric 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 plastic waste pyrolysis 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 LDPE consumption alone reached 2 million tons. The use of secondary thermoplastics in general, and PO in particular, makes it possible to increase 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, for example, of a polyethylene film that has served for one or two seasons for covering 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 parts from PP, as well as the parts themselves at the end of their service life, can be reused in a mixture with the starting 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 waste from the production and processing of LDPE is 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: die granulation 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 primary 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 polymer 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 PO.

The technological process for obtaining a modified material includes the following stages: sorting, crushing and washing of waste; waste treatment 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 flour 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 retention 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 components of the mixture, which leads to a decrease in the mechanical properties of the resulting materials.

The problem of recycling PVC plastic waste 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, building, 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 wastes is occupied by polyamide wastes, which are formed mainly during the production and processing of fibers (nylon and anid) into products, 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. waste depolymerization in order 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 nylon technological waste 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 used 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.

Provided by INVENTRA, a member of the CREON Group, which organized this event, which brought together leading industry representatives in the Russian capital on February 17th.

Polymer recycling, which is so developed in European countries, is still in its infancy in Russia: separate waste collection has not been established, there is no regulatory framework, there is no infrastructure, and there is no consciousness among the majority of the population. However, market players look to the future with optimism, pinning their hopes on the Year of Ecology, which was announced in the country in 2017 by presidential decree.

Third international conference "Polymer Recycling 2017", organized by INVENTRA, was held in Moscow on February 17. The partners of the event were Polymetrix, Uhde Inventa-Fischer, Starlinger Viscotec, MAAG Automatik, Erema and Moretto; support was provided by Nordson, DAK Americas and PETplanet. The information sponsor of the conference is the Polymer Materials magazine.

“Now the situation is not inspiring, but its improvement is a matter of time,” said the Managing Director of the CREON Group in his welcoming speech. Sergei Stolyarov. – With high prices for primary raw materials, the demand for recycled polymers and products from them will grow. At the same time, the appearance of domestic raw materials will shift the structure of primary consumption towards fibers and films. In this regard, the use of secondary polymers becomes especially promising.”

At the end of 2016, the global collection of PET for recycling amounted to 11.2 million tons, according to PCI consultant Wood Mackenzie Helen McGee. The main share fell on the countries of Asia - 55%, in Western Europe 17% of the world volume was collected, in the USA - 13%. According to the expert's forecast, by 2020 the collection of PET for recycling will exceed 14 million tons, and in percentage terms the collection level will reach 56% (now 53%). The main growth is expected at the expense of Asian countries, in particular, China.

At the moment, the highest level of collection is observed in China, it is 80%, and other Asian countries have reached approximately the same figure.

According to Ms. McGee, out of PET collected in 2016 (and this, we recall, 11.2 million tons), production losses amounted to 2.1 million tons, respectively, 9.1 million tons of flakes were obtained. The main direction of further processing is fibers and threads (66 %).

By 2025, 60% of household waste will be recycled in Europe, in 2030 this figure will grow to 65%. Such amendments are planned in the Waste Framework Directive, said Kaspars Fogelmanis, Chairman of the Board of Directors of Nordic Plast. Now the level of recycling is much lower - in Latvia, for example, it is only 21%, on average in Europe - 44%.

At the same time, the volume of plastic packaging produced in the Baltics is growing every year, the most common recyclable polymers are LDPE film, HDPE and PP.

In Russia, in 2016, the consumption of recycled PET (rePET) amounted to about 177 thousand tons, of which 90% fell to domestic collection. As reported Konstantin Rzaev, Chairman of the Board of Directors of EcoTechnologies Group, almost 100% of imports were PET flakes for the production of polyester fiber. The largest supplier countries are Ukraine (more than 60%), as well as Kazakhstan, Belarus, Azerbaijan, Lithuania and Tajikistan.

Konstantin Rzayev noted that last year the collection rate for the first time exceeded 25%, and this allows us to speak about the emergence in Russia of a full-fledged industry that is already of interest for investment. Today, the main consumer (62% of the total volume) and the price driver is still the recycled PET fiber segment. But changes in legislation and the trend towards the priority use of recycled materials as part of the sustainable development strategies of multinational manufacturing companies (MNCs) provide fertile ground for the development of another key segment of rePET consumption - bottle-to-bottle.

Over the past year, there were no new large-scale productions consuming rePET, but its use in the sheet segment is gradually growing.

However, already in 2017, it is expected to open new recycled PET fiber production facilities and expand existing ones, which, together with the ruble exchange rate, will be the main factor influencing the market balance and prices for rePET.

However, there are many other areas, still undeveloped, but quite promising, where recycled PET is also in demand. As the honorary president of ARPET said Victor Kernitsky, these are threads for furniture fabrics, car upholstery and various types of geosynthetics, foamed materials for heat and sound insulation, sorption materials for wastewater treatment, as well as bitumen reinforcing fibers for road construction.

According to the expert, there are many new processing technologies and applications, and the goal of state policy should not be to limit the use of PET, but to collect and rationally use its waste.

The topic was continued Lyubov Melanevskaya, Executive Director of the RusPEC Association, who spoke about the first results of the introduction of Extended Producer Responsibility (EPR) in Russia. It entered into force in 2016, its goal is to create a constant, solvent and growing demand for the recycling of product and packaging waste. After a year, it is already possible to draw some conclusions, the main of which is that there are a number of problems due to which the mechanism for the implementation of the RPR often simply does not work. As Ms. Melanevskaya said at the conference, there is a need to change and supplement the existing regulation. In particular, when declaring goods, including packaging, manufacturers encountered a discrepancy between the codes for the packaging of goods and the codes specified in the adopted regulatory acts, as a result of which many manufacturers and importers were unable to file declarations, because. did not find themselves in regulation. The solution was the rejection of codes and a proposal to switch to the identification of packaging by materials.

In the future, according to RusPEC, it is necessary to adopt a single end-to-end terminology for all elements of the RPR and determine unambiguous, understandable and transparent conditions for concluding contracts with waste management operators. On the whole, the association supports the law on EPR as necessary and positive for the industry.

When introducing and popularizing PET recycling in the country, the availability of modern technologies (as a rule, they are provided by foreign companies) is of great importance. Thus, Polymetrix offers modern solutions for the recycling of PET, in particular, the SSP technology for recycling into food bottled polyethylene terephthalate. Now there are 21 such lines in the world, said Danil Polyakov, regional sales manager. The technology involves the processing of bottles into pellets for food containers. The first step is washing, when paper fibers and surface contaminants are completely removed, as well as labels and glue. Next, the bottles are crushed into flakes, which are sorted by color. Then comes the removal of impurities (wood, metal, rubber, colored flakes) to a level of less than 20 ppm.

According to Mr. Polyakov, various granules can be obtained in the process of extrusion: cylindrical or spherical, amorphous or crystallized.

Viscotec offers its customers the technology to convert PET bottles into sheets, says company representative Gerhard Osberger. For example, the viscoSTAR and deCON solid phase polycondensation reactors are designed to purify and increase the viscosity of PET pellets and flakes. They are used after the granulator, before the production extrusion equipment or as a stand-alone unit.

The ViscoSHEET line is capable of producing tape made from 100% recycled PET and fully food grade.

Erema representative Christoph Wioss spoke about the in-line production of food plastic bottles from PET flakes. The VACUREMA® inline system allows you to process flakes directly into finished thermoforming sheet, bottle preform, finished packaging tape or monofilament.

Summing up the results of the conference, its participants identified the main factors hindering the development of polymer recycling in Russia. The main one they called the lack of regulatory documents:

“Nevertheless, there is another factor that we cannot ignore, and that is public consciousness,” says the director of the conference. Rafael Grigoryan. “Unfortunately, our mentality today is such that the separate collection of waste is perceived more as pampering than as the norm. And no matter what progress we see in other areas, it is necessary first of all to change the thinking of our fellow citizens. Without this, even the most modern infrastructure will be useless.”

These were the results of the industry conference “Polymer Recycling 2017”. A detailed list can be found in our calendar.

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In Russia, the level of production and consumption of polymeric materials is relatively low compared to other developed countries of the world. Recycling of polymers is carried out only by 30% of the total volume of the material. This is very little, given the total amount of waste of this type.

A little about polymer products

Almost half of all polymers are in packaging. This use of polymeric materials is determined not only by the aesthetic appearance of the product, but also by the safety of the product in the package. Polymer waste is generated in significant quantities - about 3.3 million tons. This number is increasing by about 5% annually.

The main types of polymer waste are represented by the following materials:

• Polyethylene materials - 34%
• PET - 20%
• Laminated paper - 17%
• PVC - 14%. Polystyrene - 8%
• Polypropylene - 7%

Utilization of the main volume of plastic consists in burial in the soil or incineration. However, such methods are unacceptable from an environmental point of view. When materials are buried, soil poisoning occurs due to the presence of harmful substances in the composition. Also, during combustion, toxic substances are released into the atmosphere, which subsequently breathe all living things.

The processing of polymeric materials using new technologies is developing poorly for the following reasons:

1. Absence in the state of the necessary regulatory and technical conditions and production facilities for the creation of high-quality secondary raw materials. For this reason, the secondary polymer raw materials created from waste are characterized by low quality.
2. The resulting products have low competitiveness.
3. The high cost of plastics recycling - the cost estimate for this activity showed that it takes about 8 times more money for processing than for household waste.
4. The low level of collection and processing of such material due to the lack of economic conditions and legislative support.
5. Lack of information base regarding the issue of recycling and separate collection of waste. Few people are aware that polymer recycling is a great alternative to petroleum in manufacturing.

Classification

There are 3 main types of polymer waste:

1. Technological - include two groups: removable and non-removable. The first type is represented by defective products, which are subsequently immediately processed into another product. The second variety is all kinds of waste in the production of polymers, they are also eliminated through processing and manufacturing new products.
2. Public consumption waste is all garbage related to people's daily lives, which is usually thrown away with food waste. The introduction of the habit of collecting garbage in separate bags and also throwing it separately could greatly facilitate the solution of the problem of recycling.
3. Industrial consumption waste - this type contains secondary polymers suitable for processing due to the low level of pollution. These include all packaging products, bags, tires, etc. - all this is written off due to deformation or failure. They are readily accepted by processing enterprises.

Recovery and recycling chain

Extraction and processing of polymer waste is carried out according to the specified technological chain:

1. Organization of points that accept secondary polymer raw materials. In these points, primary sorting is carried out, as well as pressing of raw materials.
2. Collection of material at landfills legally or illegally engaged in the processing of secondary raw materials.
3. The entry of raw materials to the market after preliminary sorting at special waste processing points.
4. Purchase by processing companies of material from large shopping malls. Such recyclables are less polluted and subject to minor sorting.
5. Collection of recyclables through the implementation of the program required to perform separate waste collection. The program is being implemented at a low level due to the lack of activity of citizens. People without a fixed place of residence perform acts of vandalism, which consist in breaking containers intended for separate collection of waste.
6. Preliminary processing of waste polymers.

Processing of polymers begins in the processing industry. It consists of a number of actions:

• Perform coarse sorting for mixed waste.
• Further grinding of recyclables.
• Performing mixed waste separation.
• Washing.
• Drying.
• granulation process.

Not all residents of the Russian Federation are aware of the benefits of recycling. Polymeric materials will not only bring a small income if they are regularly handed over to processing plants, but also save the environment from hazardous substances released during the decomposition of polymeric materials.

Equipment for the processing of polymer waste

The whole complex for processing the necessary raw materials includes:

1. Washing line.
2. extruder.
3. Necessary belt conveyors.
4. Shredders - grind almost all types of polymer products, belong to the first stage.
5. Crusher - they are classified as the second stage of shredders, they are used after using a shredder.
6. Mixers and dispensers.
7. Agglomerators.
8. Sieve substitutes.
9. Granulation lines or granulators.
10. Finished product post-processing machine.
11. Dryer.
12. Dosing device.
13. Refrigerators.
14. Press.
15. Moika.

At present, the production of crushed polymeric materials, the so-called "flaks", is especially important. For their manufacture, a modern installation is used - a crusher for polymers. Most entrepreneurs do not even think about purchasing processing equipment, considering this service to be expensive. However, in reality, it pays off entirely in about 2-3 years of use.

Recycling technology

The most common technology for processing waste polymers is extrusion. This method consists in continuously forcing the molten raw material through a special forming head. With the help of the output channel, the profile of the future product is determined.

Thanks to the implementation of processing in this way, from recycled materials they receive:

• Hoses.
• Pipes.
• Siding.
• Insulation for wires.
• capillaries.
• Multilayer moldings.

Through extrusion, the recycling of polymer raw materials is carried out, as well as granulation. Granulation of polymers allows efficient use of secondary raw materials in various fields of human activity. Waste polymers contribute to the entry into the market of a large number of new products made by recycling. For the implementation of the extrusion process, special equipment is used - a screw extruder.

The technology for processing waste polymers is as follows:

• Melting of the polymer material in the extruder.
• Plasticization.
• Injection into the head.
• Exit through the forming head.

For the processing of plastics in production, different types of extrusion equipment are used:

1. Screwless. The mass is pressed into the head using a specially shaped disc.
2. Disk. They are used when it is necessary to achieve improved mixing of the constituent components of the mixture.
3. Combined extruders. The working device combines the screw and disk parts of the mechanism. It is used when creating products that require high accuracy of geometric dimensions.

The use of waste polymer materials as a secondary raw material helps not only to reduce the amount of waste stored at landfills, but also significantly reduce the amount of electricity consumed and petroleum products used to manufacture polymer products.

To effectively address this issue, the authorities need to inform citizens about the benefits of separate waste collection and processing of all types in order to further produce products necessary for various purposes, including household ones.