Thermoplastics are plastics that, once molded, are recyclable. They can repeatedly soften when heated and harden when cooled without losing their properties. This is the reason for the huge interest in the recycling of thermoplastic waste - both domestic and industrial.

The composition of municipal solid waste (MSW) in the capital differs markedly from the average for Russia. About 110,000 tons of municipal solid waste are generated annually in Moscow. Of these, polymers make up 8-10%, and in the commercial waste of large enterprises this figure reaches 25%.

Separately, plastic bottles should be singled out in the structure of MSW. About 50,000 tons of them are thrown away every year in Moscow alone. According to the results of the International Scientific and Practical Conference "Packaging and the Environment", 30% of all polymer waste is bottles made of polyethylene and polyvinyl chloride. However, at present, according to the State Unitary Enterprise "Promothody", no more than 9 thousand tons of polymer waste isolated from MSW are processed annually in Moscow and the region. And half of them - in the territory of the Moscow region. What are the reasons for such insignificant recycling of thermoplastic waste?

Organization of the collection

To date, there are several channels for collecting plastic waste.

The first and main one is the collection and disposal of waste from large shopping malls. This raw material is predominantly used packaging and is considered the most "clean" and best suited for further use.

The second way is selective garbage collection. In the south-west of Moscow, the city administration, together with the State Unitary Enterprise Promothody, is conducting such an experiment. Special German eurocontainers have been installed in the yards of several residential buildings. Lids for containers with holes: round - for PET bottles, a large slot - for paper. Containers are locked and constantly monitored. In two years, 12 tons of plastic bottles were collected. Today the project includes only 19 residential buildings. According to experts, when covering a territory with a population of more than 1 million inhabitants, the benefits of such a system become obvious.

The third option is the sorting of solid waste at specialized enterprises (the pilot industrial waste sorting center Kotlyakovo, the private enterprise MSK-1, and other waste sorting complexes). It is still quite difficult to accurately determine the volume of sorted waste, but the share of this source of secondary raw materials is already noticeable. Some commercial organizations, under the control of municipal authorities, organize their own collection points for secondary raw materials (including polymer waste) from the population. Primary sorting and pressing usually take place there. However, there are very few such places in the city.

A significant proportion of recycled materials going for processing is illegally collected at landfills. This is done by private firms, and sometimes by the management of the landfills themselves. The collected and sorted materials are sold to resellers or directly to manufacturers.

When processing thermoplastics, the uniformity of the polymers used, the degree of contamination, color and type (film, bottles, scrap), the form of the supplied waste (compression, packaging, etc.) are very important. Depending on these and a number of other parameters, the suitability of a particular batch for further processing (and, therefore, its market value) can fluctuate markedly. Waste paper costs the most.

Sorting, crushing and pressing can be carried out by numerous intermediaries, waste sorting complexes, processors themselves, structures of the State Unitary Enterprise "Promotkhody".

In most cases, manual sorting is used, since the appropriate equipment is expensive and not always efficient.

Polymer recycling

The collected and sorted waste can be recycled into secondary granulate or immediately go to the production of new products (shopping bags and bags, disposable tableware, video cassette cases, country furniture, polymer pipes, wood-polymer boards, etc.).

The processing of polymer household waste on an industrial scale in Moscow is carried out only by OAO NII PM (production of products for the needs of the municipal economy as part of the program for separate waste collection in the South-Western Autonomous Okrug and by order of the capital's mayor's office). State Unitary Enterprise "Promotkhody" carries out crushing, washing and drying, then the flakes at a price of $ 400 per ton are transported for further processing to the Research Institute of PM.

Other processors of secondary raw materials are either too small (capacity up to 20 tons per month), or under the guise of processing they are engaged in crushing and further resale, at best they add crushed raw materials to their products. Almost no one is engaged in large-scale production of secondary granulate and agglomerate in Moscow.

According to other sources (N.M. Chalaya, NPO Plastic), many small firms are engaged in the processing of polymers contained in Moscow waste, for which this activity is not the main one. They try not to advertise it, since it is generally believed that the use of recycled materials in the production of products worsens its quality.

A typical company for this market is the production cooperative Vtorpolimer, which works directly with the city's landfill. Homeless people living in the landfill collect everything plastic there: bottles, toys, broken buckets, film, etc. For a fee, the “goods” are handed over to intermediaries, and they deliver it to Vtorpolymer. Here, things that have served their time are washed and sent for recycling. They are sorted by color, crushed and added to plastic, which is used to make installation pipes (they are used in the construction of new houses to insulate electrical wiring). The purchase price of dirty plastic scrap is 1 thousand rubles. per ton, pure - 1.5 thousand. Smaller lots are accepted at a price of 1 and 1.5 rubles. per-kg respectively.

Sorting of polymeric waste is carried out manually. The main selection criterion is the appearance of the product or the corresponding labeling. Without marking, packaging made of polystyrene, polyvinyl chloride or polypropylene cannot be visually distinguished. Bottles are most often considered PET, film - polyethylene (the specific type of PE is usually not determined), although it may well be PP or PVC. Linoleum - mainly PVC, expanded polystyrene (polystyrene) is easily identified visually, nylon fibers and technical products (spools, bushings) are usually made of polyamide. The probability of coincidences with this sorting is about 80%.

An analysis of the activities of firms operating in the secondary materials market allows us to draw the following conclusions:

1) the prices of secondary materials on the market are determined by the degree of their preparation for processing. If we take the cost of virgin low-density polyethylene granulate as 100%, then the price of pure shredded polyethylene film prepared for processing is from 8 to 13% of the cost of virgin polymer. The price of polyethylene agglomerate is from 20 to 30% of the cost of the primary polymer;

2) the price of most granular secondary polymers, averaged by composition, ranges from 45 to 70% of the price of primary polymers;

3) the price of secondary polymers strongly depends on their color, that is, on the quality of the preliminary sorting of polymer waste by color. The difference in the price of recycled polymers of pure and mixed colors can reach 10-20%;

4) the prices for products obtained from primary and secondary polymers are, as a rule, almost the same, which makes the use of secondary polymers in production extremely profitable.

On average, the price of polymer waste isolated from MSW, depending on the degree of preparation, batch and type, ranges from 1 to 8 rubles / kg. Purchase prices from processors, depending on the batch and the level of contamination, are shown in table 1.

The price of clean MSW waste is usually equal to the price of industrial and commercial waste.

The market price of the purchase of polymer waste from MSW by the processor consists of the price of purchase by the intermediary from the population (approximately 25% of the cost), the fee for the formation of large-tonnage batches of waste, sorting, pressing and even washing for the most expensive (pure) raw materials.

Prices for products such as agglomerate and granulate average 12-24 rubles/kg (polyamide is more expensive than the others - 35-50 rubles/kg, PET - from 20 rubles/kg). Further processing increases the surplus value depending on the type of product by 30-200 %.

Investment attractiveness

According to most experts, it is profitable to invest in the processing of polymer waste, but only when relying on state support and a legislative framework focused on the interests of processors of secondary raw materials.

Today, the Moscow market consists of 20-30 small companies involved in the processing of polymer waste, mainly of industrial origin. The market as a whole is characterized by informal relations between processors and suppliers, a large share of companies for which this business is a side business, as well as low processing volumes (12-17 thousand tons per year). It can be assumed that if there is a stable demand on the part of processors for such waste, the volume of offers will grow.

It should be noted that the amount of polymer waste that is actually recycled today is a very small part of urban MSW. And this despite the fact that the demand for polymers and products from them is constantly increasing, and the problem of waste disposal is increasingly worrying the city authorities.

The deterrent in the construction of new processing plants is the underdevelopment of the waste collection system and the lack of serious suppliers. The coincidence of interests of private business and the state in this area should inevitably lead to the adoption of laws that meet the interests of recyclers.

Present and future

1. The annual volume of PET processing in the capital is 4-5 thousand tons per year. The plans of the Moscow authorities include the organization by 2003 of a system for the selective collection of PET containers and the creation of two production complexes for its processing with a capacity of 3,000 tons per year. At present, the construction of two private PET processing plants with a total capacity of 6,000 tons annually is being completed.

In the coming months, the Moscow government should adopt regulations regulating the activities of polymer processors (their exact content is not yet known). The existing and under construction facilities are sufficient to meet the needs of the market. The possibility of state support for the projects of the State Unitary Enterprise "Promotkhody" and the company "Inteko" (potential processing capacity - 7-8 thousand tons per year) is being considered.

2. The volume of PP processing in Moscow is 4-5 thousand tons per year, although about 50-60 thousand tons are thrown out annually in the city - mainly film and big bags. After processing, PP in the form of granules is added to primary raw materials or is entirely used for the production of plastic utensils, shopping bags, etc.).

The lack of large-scale recycling projects for this polymer (as is the case with PET) opens up great investment opportunities. The most profitable at this stage is the processing of recyclable materials into granules, since competition is much tougher in the field of consumer goods production.

3. The volume of PE processing is also 4-5 thousand tons per year. The main type of raw material is film, including agricultural film. In total, about 60-70 thousand tons of polyethylene waste are thrown out in the city every year. As a rule, enterprises involved in the processing of PE also deal with PP. One of the large companies through which about 2.5 thousand tons per year passes is Plastpoliten.

PE is highly resistant to pollution. However, the existing ban on the use of recycled polymer raw materials in the manufacture of food packaging limits the possibility of marketing.

Thus, the most rational for today seems to be the construction of an industrial complex for the processing of polyethylene, polypropylene and PET waste into granules.

This production must include:

a) sorting (requires special training of personnel to reduce the proportion of another type of polymer, which is very important for product quality);

b) washing (the largest potential volumes of raw materials are usually not sorted and not washed);

c) drying, crushing, agglomeration.

It is economically most profitable to locate this complex in the near Moscow region, since the prices for electricity, water, rent of land and industrial space are significantly lower there than in the capital (see Table 2).

For the effective operation of such production, state support is necessary. Perhaps it makes sense to partially revise the existing sanitary standards for the processing of solid waste, as well as to oblige manufacturers of polymer products to make deductions for the processing of polymer waste. In addition, comprehensive measures should be taken at the level of the Moscow government and individual housing and communal services aimed at developing a system of selective collection and creating a network of recycling points.

The increased interest of the state in waste disposal is already reflected in the budget: from 2002 to 2010. it is planned to spend 519.2 million rubles for these purposes. from the federal budget. The budgets of the subjects of the federation are expected to allocate until 2010. 11.4 billion rubles for the implementation of the withdrawal program.

In 2001, Moscow spent 3.1 billion rubles on environmental protection. To date, the cost of already implemented projects for the processing of household waste is 115.5 million rubles.

Andrey Goliney,

INTRODUCTION

Based on polyvinyl chloride (PVC), more than 3,000 types of composite materials and products are used in the electrical, light, food, automotive industries, mechanical engineering, shipbuilding, in the production of building materials, medical equipment, etc., due to its unique physical and mechanical, dielectric and other operational properties.

However, at present, the use of PVC is gradually limited, which is primarily due to environmental problems that arise during the operation of products, their disposal and recycling. During the aging of PVC-based polymers, along with the loss of physical and mechanical properties, there is a negative impact on the environment and humans, due to the processes of PVC dehydrochlorination, which increase at a temperature of 50-80 ° C (highly toxic chlorine-containing polyaromatic compounds are formed).

UTILIZATION OF SECONDARY POLYMER RAW MATERIALS

Currently, there are the following ways of beneficial use of recycled polymer raw materials:

Burning for the purpose of obtaining energy;

Thermal decomposition (pyrolysis, destruction, decomposition to initial monomers, etc.);

Reuse;

Recycling.

Waste incineration in incinerators is not a cost-effective disposal method, as it involves pre-sorting the waste. During combustion, there is an irretrievable loss of valuable chemical raw materials and environmental pollution with harmful substances in flue gases.

A significant place in the recycling of secondary polymeric raw materials is given to thermal decomposition as a method of converting EPS into low molecular weight compounds. An important place among them belongs to pyrolysis. Pyrolysis is the thermal decomposition of organic substances in order to obtain useful products. At lower temperatures (up to 600°C), mainly liquid products are formed, and above 600°C, gaseous products, up to carbon black.

Pyrolysis of PVC with the addition of PE, PP and PS waste at T=350°C and pressure up to 30 atm in the presence of a Friedel-Crafts catalyst and when the mixture is treated with hydrogen makes it possible to obtain many valuable chemical products with a yield of up to 45%, such as benzene, toluene , propane, cumene, alpha-methylstyrene, etc., as well as hydrogen chloride, methane, ethane, propane. Despite a number of disadvantages, pyrolysis, unlike HBO combustion processes, makes it possible to obtain industrial products used for further processing.

Another way to transform recycled polymer raw materials is catalytic thermolysis, which involves the use of lower temperatures. In some cases, gentle modes make it possible to obtain monomers, for example, during the thermolysis of PET, PS, etc. The resulting monomers can be used as raw materials in polymerization and polycondensation processes. In the USA, scarce monomers, dimethyl terephthalate and ethylene glycol, are obtained from used PET bottles, which are again used for the synthesis of PET of a given molecular weight and structure required for the production of bottles.

From an economic and environmental point of view, the most preferred ways of recycling polymeric raw materials are reuse and recycling into new types of materials and products.

Reapplication involves the return to the production cycle of the used packaging after its collection and appropriate processing (washing, drying, etc. operations), as well as obtaining permission from the sanitary authorities for its reuse in direct contact with food products. This route is mainly suitable for PET bottles.

Recycling of waste has become widespread in many countries of the world. In this way, mixed waste from polymeric materials can be processed into products for various purposes (building panels, decorative materials, etc.). In the United States, where the use of polyethylene terephthalate containers is especially high, a national program has been adopted and is being implemented, according to which, by the beginning of the 21st century, the level of recycling of PET bottles will be increased to 25-30% (compared to 9-10% in the early nineties) . The program provides for the implementation of four stages: - organizing the collection of used containers from the population; - sorting of the collected raw materials;

Processing (preliminary and final) into products for national economic purposes;

Sales of received products.

The program also provides for the creation of collection points throughout the country with the involvement of up to 50% of the total population, focal points, the establishment of various communications, advertising, the publication of information on waste collection, the creation of a data bank, public education, the creation of "hot" lines (up to 800) for the transfer timely information and other activities. One of the promising directions in this area is the production of granules from sorted raw materials using various additives that improve its quality (stabilizers, dyes, modifiers, etc.), which are processed into products by various processing methods.

The recycling of waste, for example, in Germany is based on the "Dual System", which includes the sorting and processing of certain types of secondary raw materials at enterprises producing materials and packaging from them. To facilitate waste collection and recycling, a system has been put in place to accept used packaging and recycle it with the Green Dot (Der Grune Punkt) environmental label. This mark indicates that this packaging is recyclable or reusable, and is assigned to packages that have passed a special competition, which is the main principle of the "Dual System". Usually, for efficient processing of EPS, it is subjected to modification. There are the following methods of EPS modification: - chemical (crosslinking with peroxides, for example, dicumyl peroxide, maleic anhydride, organosilicon liquids, etc.);

Physico-chemical (introduction of various additives of an organic nature, for example, technical lignins, soot, thermoplastic elastomers, waxes, etc.), creation of composite materials;

Physical (introduction of inorganic fillers: chalk, oxides, graphite, etc.) and technological (variation of processing modes). The introduction of polyorganosiloxanes together with initiating additives and subsequent homogenization of the processed raw materials makes it possible to regenerate heavily worn materials and restore the required level of their technological properties. Depending on the medium used and the processing mode, the formation of graft copolymers or spatially structured systems with the formation of cross-siloxane bonds occurs. Their high strength and low molecular packing density in polysiloxanes ensures the elasticity of the material while improving mechanical properties, thermal stability, weather and chemical resistance.

The mechanical characteristics of secondary PA from worn products can be significantly improved by thermal treatment of raw materials with various heat-transfer media (water, mineral oil, etc.) with simultaneous IR irradiation. Heat treatment in a heat carrier medium is carried out according to the annealing principle and includes the operations of heating, holding and cooling. At the same time, the level of physical and mechanical indicators is determined by the type of heat carrier, heat treatment mode and drying time, which can be from 1.5 to 2.5 hours. Most of the proposed methods are based on the radical chain mechanism of interaction between the active groups of the added additive or filler and the oxidized fragments of the base polymer. Among all available methods, composite materials from recycled polymer raw materials are of the greatest practical interest. One of the functional modifying additives can serve as a natural polymer - lignin, which is a waste of pulp and paper and hydrolysis processing of wood. It is a metabolic product of wood and other plants accumulated during lignification in the median lamina and cell wall, accounting for 30% of its total mass (the remaining 70% are cellulose and hemicellulose).

By its chemical nature, lignin belongs to polyfunctional phenols, the main class of polymer stabilizers, and has a fairly effective light and heat stabilizing effect on oxidized and oxidized polymers. The technology for obtaining a micronized product from it using electromagnetic grinding was developed at MGUPB.

In addition to an effective modifier of secondary polymeric raw materials, hydrolysis lignin after appropriate processing and preparation in the form of hydrolysis flour (microlignin) can be used to obtain such valuable products in plastics processing technology as aromatic stabilizers, antioxidants, structure formers and modifying additives for thermoplastics, fillers - for thermoplastics , sorbents for medical purposes of the "EKOLIS" type for removing toxins, heavy metals and other substances harmful to a living organism from the body, as a drug in the treatment of liver cirrhosis (studyed on rabbits), for the production of vanillin and other purposes. In a number of European countries, the problem of recycling used plastic packaging is inextricably linked with the establishment of a clear service for their collection, sorting and separation of mixed waste, since these operations are the most labor-intensive.

In the EU countries, the issues of packaging waste disposal are resolved within the framework of a single law for these countries, aimed at preventing the increase in the volume of polymer packaging and containers, rational methods of their disposal, mainly by recycling, organizing a rational collection system, etc.

Works in the field of utilization of secondary polymer raw materials were started in Russia in the late 70s - early 80s.

PVC recycling

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. The 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 rejection 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.

Methods for the preparation of PVC waste

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 exceeding -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.

The issue of preserving the environment is acute in many countries of the world, people understand that their environment cannot accept our waste indefinitely. Therefore, it remains for us to carefully approach the solution of this problem, reduce the amount of waste, recycle it to the extent possible and obtain secondary raw materials. If you pay attention to the amount of polymer waste in the modern world, it is huge, so you need to start processing it.

Some entrepreneurs have created a profitable plastic recycling business that has enriched them . The issue of recycling plastic and other polymers today it is in demand in all cities and towns where people live. Let's look at how polymers are processed, or rather, what equipment is needed for this. It is important to understand that modern recycling lines are completely different technologies that were introduced only a couple of decades ago. Many companies offer us a wide range of polymer processing equipment, but an aspiring entrepreneur needs to know what features are most important when buying. With the right processing equipment, you can significantly increase the profits of your business and eliminate competitors.

Polymers are found in large quantities in our daily life, it is a product of large cities. Plastic waste can accumulate in one city in the amount of several tons. Many do not even think where ordinary plastic bottles or some other polymeric products from a landfill go. In theory, this does not bother anyone, although everyone knows that plastic will not dissolve on its own, it will remain for centuries, slowly breaking down and causing significant harm to the environment. Every day the consumption of products, things and solutions that contain plastic is increasing in the world, and it is even difficult to imagine what will happen to the planet in 100-200 years if plastic waste is not recycled.

Unfortunately, in Russia, few people even from the government pay attention to plastic recycling. In other developed countries, everything is different, for example, in America and Europe, every resident understands the rational use of waste, separating them when thrown into a trash can. And special enterprises process tons of secondary raw materials daily, without littering the environment. In addition to maintaining a clean environment in their cities, a number of countries also receive inexpensive recycled materials, saving their money and energy.

Plastic recycling technologies

It seems to aspiring entrepreneurs that plastic recycling is a complicated procedure. In fact, this is not so, because there is a modern production line that does all the work itself. The main thing is to choose the right equipment, set it up and start it up.

The recycling process is divided into three stages:

1. Shredding of plastic waste to small fractions in the form of crumbs. The size of such fractions should not exceed 0.1-0.3 cm in diameter.
2. Now you need wash the polymer fractions and clean them from contaminants. This is a very important stage, the quality of the resulting product will greatly depend on the degree of contamination. After washing, the raw material is dried.
3. At the next stage, there is agglomeration or granulation, depending on the chosen technology. In the first case, the raw material turns into a small crumb, and in the second - in the form of sand, with a uniform quality. Granules are more expensive than agglomerate due to their higher quality, so it is advisable to choose equipment and technologies, relying specifically on granulation when recycling plastic.

Classification of polymers

Before you start working on recycling plastic, you need to know that there are several types of polymers that differ from each other. Therefore, they will have to be processed separately so as not to spoil the quality and properties.

• LDPE or high pressure polyethylene. When processed, it becomes transparent, does not emit any smoke or odor. In appearance, it strongly resembles paraffin, which has already solidified.
• HDPE, the same polyethylene, but low pressure. It is more durable, but fragile, the rest of the processing properties are the same as the previous instance
• PET or polyethylene terephthalate is a very light and hard material that resists high temperatures well, can withstand solutions and acids, but not alkali
• Polystyrene is very soft, it can bend at large angles, however, it bursts. It smells like flowers, emits very strong smoke during processing

At the initial stage of organizing an enterprise, you need to immediately decide what material you are going to work with, because each requires its own production line. In our country, it is most effective to open a PET processing plant, because these are plastic bottles that are found everywhere. It is also effective to use the film, these are HDPE and LDPE in the recycling process.

Introduction

Recycling homogeneous polymers is a relatively simple task if their structure is preserved and there was no significant degradation either during manufacture or during primary use (see, for example, ). Of course, the degradation process, which may result in structural and morphological changes caused by a decrease in molecular weight, the formation of branches, other chemical groups, etc., leads to a significant deterioration in all physical properties. While recycled materials that retain their properties can be used in the same applications as virgin polymers, recycled materials with reduced properties can only be used in specific applications. Therefore, in the mechanical recycling of homogeneous polymers, the challenge is to avoid further degradation during the process, i.e. avoid deterioration of the properties of the final material. This can be achieved by the right choice of processing equipment, processing conditions (see chapters 4 and 8) and the introduction of stabilizers (see chapters 3 and 7).

In this chapter, we will consider the relationship of the properties of homogeneous polymers with their processing conditions (in the order in which the properties of polymers change with an increase in the number of processing steps), as well as with the type of machines used; in addition, we study the dependence of properties on the initial structure.

Recycling of polyolefins and PVC

Introduction

Mechanical recycling of polyolefins is a very important area of ​​the recycling industry. Of course, raw polyolefins account for the bulk of this and, consequently, a huge number of polyolefin products are produced, and their relative ease of collection leads to simple and economical recycling. As with other polymers, the final properties and economic value of polyolefins depend on the degree of degradation during primary use and on the conditions of recycling. In addition, the chemical structure of polyolefins is very important in shaping the properties of the recycled polymer.

Polyethylenes

The different structural types of commercial polyethylenes (PEs) greatly influence the recycling behavior of these materials. Of course, branching (by short or long chains) affects the degradation kinetics, and then the final properties of the recycled material that has undergone several stages of processing. This behavior is of particular importance for those plastics that are subjected not only to thermomechanical degradation during processing, but also to other destructive influences during further use. Photooxidation and other types of degradation cause various structural and morphological changes depending on the PE structure.

PE recycling is discussed in several monographs and in many articles.

The property/processing steps relationship will be discussed both in terms of the different types of commercial PE and the different types of degradation experienced by the material in use.

High density polyethylene

The main source of recycled high-density polyethylene (HDPE) is liquid containers and packaging film; in addition, the volume of recycling containers from automotive fuel is growing. In all cases, the molecular weight of these used HDPE articles remains very high because the degradation experienced by this type of material is very low in short term use. The latter circumstance suggests that the properties of the recycled material are close to those of the original polymer. In table. Table 5.1 compares samples of HDPE made from recycled bottles and virgin polymer. It is clearly seen that most of the properties are very close. As noted above, this is the result of the short-term use of the bottles and the lack of significant degradation, although some structural change may still have taken place during recycling; this is indicated by the expansion of the molecular weight distribution. In addition, the modulus of elasticity and elongation at break differ significantly, and the recycled material has a slightly higher tensile strength.

These differences may be the result of small changes in structure and morphology. In particular, during the processing of the PE melt, both chain breaks (with a decrease in molecular weight) and branching (increase in molecular weight) can occur, against which cross-linking reactions are difficult to determine from molecular weight measurements, and they can change the final properties of the secondary material.

Recycled polymers go through at least two or three recycling cycles, and in each of them, melting causes additional degradation of the material. In addition, the increase in the amount of recycled polymers and the use of mixtures of recycled and virgin materials (see Chapter 6) leads to a significant proportion of recovered plastics being recycled again and again. This means that the properties of such repeatedly processed polymeric materials are constantly changing with an increase in the number of processing cycles in the direction of their deterioration. For example, in table. Figure 5.2 shows the change in some properties of an HDPE sample (fuel canister) after 15 injection molding recycling cycles.

It is clearly seen that the changes in mechanical properties are relatively small, although the melt flow rate decreases significantly. The latter circumstance can be explained by the strong dependence of viscosity on molecular weight and this means that the machinability of the material has changed significantly.

The result clearly shows that the properties of the recovered HDPE depend not only on the properties of the recovered products, but also on the nature and number of recycling cycles. In addition, both the properties of the melts, which determine the processability of the polymer, and the properties of the solid material are affected to some extent by recycling.

Thus, it is necessary to know the relationship between properties and recycling cycles in order to be able to anticipate to some extent the likely characteristics of recycled plastics and therefore to determine the applications available for these materials. Of course, the final properties will depend not only on the number of processing cycles, but also on the properties of the recovered materials, on the nature of the processing and its conditions.

On fig. 5.1 shows the flow curves of an HDPE sample (canister). The data refer to samples that have gone through several processing cycles on a single-screw extruder. Viscosity decreases with an increase in the number of recycling cycles over the entire range of shear rates. This means that during repeated extrusions, thermomechanical stresses acting on the melt cause a certain degradation of the polymer. This is a simple scheme, however, it is in conflict with what was observed for the same sample passing through a twin screw extruder (Fig. 5.2). In this case, the situation is much more complicated, since a small decrease in viscosity occurs only at high shear rates, and at low rates the effect is reversed. Thermomechanical stress causes both chain breaks and molecular growth, mainly due to the formation of long side branches and stitching. The final molecular structure depends on the relative contribution of these two processes. In particular, an increase in temperature and processing time (on a single screw extruder) is favorable for chain breaking, whereby the viscosity of the final melt decreases. In addition, the nature of the competition between the two mechanisms may change with an excess of oxygen during processing or depending on the specific molecular structure of the HDPE sample. For example, it has been shown that high

the content of vinyl groups leads to a significant increase in the viscosity of the melt - a decrease in molecular weight - and long-chain branching. Vlachopoulos et al. found that chain breaks dominate in copolymers (which manifests itself in chain branching), while crosslinking is the main degradation mechanism in homopolymers. The increase in extrusion pressure as the number of processing cycles for the last sample increases, and the drop in the copolymer sample takes place due to the increase and decrease in molecular weight, which confirm these mechanisms. This means that it is very difficult to predict the change in the structure of recovered HDPE and hence its rheological and mechanical properties, since this material is composed of copolymer and homopolymer polymers. In addition, homopolymers may contain varying amounts of vinyl groups. The extrusion quality of the bottle recycling material tested in the same work was indeed independent of the passes through the extruder, indicating that both mechanisms play the same role and that the recovered material is, as already assumed, a mixture copolymer and homopolymer HDPE.

This data shows that the type of recycling machine and the processing conditions significantly, and sometimes decisively, affect the final properties of the recycled material - in this case the HDPE sample. As an example, in fig. Figures 5.3 and 5.4 show modulus and elongation at break as a function of the number of passes through the extruder. The mechanical properties of the two samples changed completely differently.

The elastic modulus curve goes up with the number of processing steps, while the elongation at break behavior shows the opposite trend. Moreover, the modulus curve of a sample processed in a single screw extruder is higher than that of a sample extruded in a twin screw extruder, but its elongation at break values ​​are lower. The unexpected course of the dependence of the modulus on the number of processing cycles was explained by an increase in crystallinity with a decrease in molecular weight. The same reason that causes a decrease in molecular weight causes a drop in elongation at break. A more pronounced increase in the modulus and a decrease in elongation at break of the sample processed on a single screw extruder reflects the fact that the melt is more significantly destroyed in this machine. This is mainly due to the longer processing time.

The effect of structure on the mechanical properties of recycled HDPE becomes clearer when looking at the stress fracture toughness values ​​shown in Table 1. 5.3. The data refer to homopolymer and copolymer samples, as well as a sample from used material after 0 and 4 passes through a single screw extruder.

The two initial samples show deterioration in crack resistance under external stress, but the drop in properties of the copolymer after repeated recycling is catastrophic. The crack resistance value of the recovered material after four passes through the extruder is reduced by

20%, although it consists mainly of a copolymer. A significant change in the value of the crack resistance of the copolymer, apparently, is balanced by an improvement in the behavior of the homopolymer fraction.

The data presented clearly shows the influence of the HDPE structure and the nature of the processing equipment on the final properties of the recycled polymer.

The main applications of recycled HDPE are liquid containers (among which are multi-layer bottles with a recycled HDPE core), drainage pipes, granules and films for bags and garbage bags.

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In Russia, the level of production and consumption of polymeric materials is relatively low when compared with 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.
• Plasticizing.
• 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 disk.
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.