Production of polyethylene granules from recycled materials. Secondary PVD

Polyethylene is the most widely used polymer material in the world with a share of about 39% in the global production of thermoplastics. The closest competitor, polypropylene, occupies only 24%. In this article we will look at the most common methods of processing polyethylene and their technological features.

Recycling of virgin polyethylene

Primary is called polyethylene, synthesized in production by polymerization of ethylene. Most often, this granular raw material is milky-white in color (if the brand has not been dyed). Here are the most common ways to process polyethylene:

• Extrusion. More than 70% of polyethylene in Russia is processed using the extrusion method, as it is very versatile. The essence of the method is to supply the polymer melt to the extruder head under pressure. In this case, the head may have different shape, and, passing through it, the polymer takes on the required shape. First of all, PE of “pipe” and “film” grades is processed in this way for the production of corresponding products. In addition, cable insulation and PE sheets of various thicknesses are produced using the extrusion method.
• Rotational formation. The method is used for the manufacture of various hollow PE containers: from small food containers to large containers with a volume of up to 10 thousand liters. The essence of the method is to load required quantity polyethylene granules of a grade suitable for rotational molding into a special mold, which is simultaneously heated and rotated in several axes. As a result, a melt is formed inside, which evenly covers the walls of the mold and allows you to obtain a product with different wall thicknesses.
• Injection molding. The technology is suitable for the manufacture of products for various purposes, most often from HDPE grades. The essence of the method is to supply melted polyethylene into a mold of the desired geometry under pressure. Injection grades are characterized by increased melt fluidity, which allows the polymer to accurately replicate the shape of the mold and achieve the correct geometry of the finished product.

Recycling of recycled polyethylene

Considering Negative influence PE waste on the environment, the issue of processing waste raw materials and their reuse is very relevant. Almost any PE waste goes through the following algorithm:

• Sorting. The polymer is separated from other waste on semi-automatic lines: part of the work is done by people manually, partly the mechanical mixture of waste is sorted by machines.
• Washing and cleaning. In order for polyethylene to be recycled, it must be as clean as possible from impurities, for which it is washed under streams of water and steam.
• Grinding in crushers and filtration using a centrifuge. The material is finally cleaned of foreign impurities.
• Another wash and dry. After the crushed mixture is dried again, the secondary raw materials can be considered ready for further processing.

For recycled materials, the most commonly used method is extrusion and injection molding. At the same time, not all types of products can be made from recycled PE, since the technological properties of the material after such processing still significantly deteriorate.

Neglect of polyethylene waste is dangerous for ecological situation. Processing polyethylene into granules makes it possible to give it new life, because many useful products can be made from these raw materials.

Limit the production of packaging for polyethylene products in modern world quite difficult, but proper waste management solves the problem. Polyethylene raw materials are perfectly recyclable; modern recycling technology is environmentally friendly and does not require significant expenditure of natural resources.

Why is it important to recycle waste instead of throwing it into landfills?

1. In natural natural environment Polyethylene takes more than 300 years to decompose, releasing toxic substances into the soil and water.
2. Recycling allows you to use raw materials rationally, produce necessary goods from recycled polyethylene cheaper, and save resources.
3. Recycling has virtually no effect on the quality of the material; recycled polyethylene has almost the same properties as primary polyethylene.

Processing stages

1. Collection of raw materials.
2. Sorting, separation from household waste.
3. Cleaning – polyethylene must be washed from contaminants in special washing machines.
4. Grinding – the material is crushed in special crushers.
5. Processing in a centrifuge removes residual impurities and excess moisture from raw materials.
6. Drying – polyethylene undergoes heat treatment in special drying chambers.
7. Agglomeration - on special equipment under temperature and pressure, as well as using catalysts, raw materials are melted and sintered into granules.

Polyethylene granulation

1. The bulk material enters the granulator, several heating cycles clean it of foreign impurities (garbage, metal, water, air inclusions).
2. At a temperature of 200°C, the molten polyethylene mass is passed through forming holes (dies), from where the molten polymer flows out in thin streams.
3. The raw materials are cut with knives and cooled with cold water.
4. Collection of the product into a storage bin and packaging into containers.

Necessary equipment

The line for processing polyethylene waste includes:

• washing machine;
• crusher;
• drying unit;
• centrifuge;
• agglomerator;
• granulator;
• extruder

To automatically supply raw materials to the line, a conveyor or pneumatic conveyor is used. Polyethylene is processed into granules directly in the agglomerator. Finished products are formed using special machines. Granulation equipment is not always included in the production line.

Granulated polyethylene can be of different quality; it is divided into 3 grades:

• Higher - made from unpainted packaging films; according to their characteristics, such granules are universal, suitable for the production of cast products and recycled film;
• 1st – physical characteristics similar to the highest grade, the production of granules is based on light-colored packaging material;
• 2nd - made from sorted raw materials of dark color (black, gray), then construction materials and household goods are produced from processed granules.

Application

From recycled polyethylene you can obtain:

1. New bottles for bottling drinks.
2. Disposable containers.
3. Packaging films and bags.

Recycled polyethylene can become the basis for production building materials:

• finishing and decorative tiles;
• heat and waterproofing;
• sanitary communications (pressure pipes, drainage systems);
• decorative fences and pool accessories.

The use of pellets for the production of useful goods can be much wider. The technology is constantly being improved, experts are looking for new areas of application of recycled polyethylene.

Recycling polyethylene waste into granules is very profitable. Residents big cities, delivering raw materials to special items reception can help improve the environmental situation. As a result, production receives inexpensive raw materials, which makes it possible to produce high-quality goods at a lower price. affordable prices. In the recycling process, the main difficulty is to arrange regular collection and delivery of raw materials to the site. A civilized method of waste disposal helps to relieve public landfills and improve the quality of life of people in megacities.

To reduce costs and reduce costs for the production of polymer products, commodity producers are increasingly using recycled polyethylene high pressure (PVD granules). Recycled polyethylene recyclables produce first-class and very profitable granular material, which in terms of quality characteristics is not inferior to raw materials from virgin polyethylene. Each secondary LDPE granule has a low density and has the same branched molecular structure as before processing.

At the moment, obtaining secondary granules from LDPE waste helps solve a whole complex environmental problems for the recycling of polymers, and also allows you to significantly reduce the costs of producing products from high-pressure polymers.

Technological processing cycles. Equipment used.

LDPE granules are produced by polymerization of ethylene under high pressure (150-300 mPa). Various methods for processing LDPE waste are based on chemical mechanisms of coordination and interaction of recycled polyethylene with added modifying additives. Technologically, the technique consists of the following stages:

• Collection of raw materials and their sorting. Recycled material is distributed by grade and separated from sand, dirt, metal, tape, and other foreign matter and debris.
• Washing and drying waste in washing and drying complexes. When washing the secondary LDPE, the pre-washing unit can be supplemented with: special reagents and chemicals for removing complex contaminants from raw materials (petroleum products, fat, oil). Mini-flotation and metal separation operations can be performed. Before being sent to the drying chamber, the raw material is sent to a centrifuge to separate excess moisture and remaining solid fractions. So that there is no education various kinds defects (swells, cavities, pores) at this stage of processing, the polymer drying process will be carried out at high humidity;
• Grinding and crushing. For plastic materials, cutting and abrasion methods are used; fragile recycled polyethylene is pre-crushed by shearing or impact, and crushed. To carry out these technical processes, knife crushers (dicers), hammer and rotary types of crushers, and jet mills are used;
• Direct processing of prepared LDPE, obtaining agglomerate. In the agglomerator, as a result of thermal action (friction against the body), recycled polyethylene is heated to the plasticization temperature and sintered, after which it is sharply cooled and separated into individual balls (pellets). Agglomerators can perform both individual stages of processing recycled LDPE and a full cycle of polymer regeneration, including all the above-mentioned stages. The resulting agglomerate can be used for the production of finished products;
• Granulation of polymers and composites. At this stage, special granulators are used, in which the molten thermoplastic polymer flows through an extruder. After the resulting material has cooled in water or air, the high-density polyethylene extruded into threads or strands is cut into granules. During the process, the recycled material can be combined with dyes, plasticizers, antioxidants, bactericidal materials, and volatile impurities and water are removed from it. Recycled PVD granules can be produced in colored and unpainted forms.

In the process of producing recycled high-density polyethylene, you should pay attention to the density of the material; the consumer characteristics of the finished products significantly depend on it. An increase in its indicators leads not only to an increase in the hardness and strength of the material, resistance to aggressive environments, but also at the same time makes it less impact-resistant and easily permeable to gases.

Special characteristics of granules and agglomerate

The resulting secondary LDPE is characterized by:

• perfect dielectric abilities;
• lack of absorption of moisture, steam and maintaining a constant mass of granules;
• resistance to a wide variety of chemical substances As a result, the storage and transportation process does not require the creation of special conditions;
• odorless and completely inert. Products made from recycled LDPE granules are distinguished by the almost complete absence of the chemical smell of plastic;
• high bulk density;
• resistance to ultra-low temperatures.

Application of recycled granules

• For casting: thin-walled and large-sized products, fittings, auto parts, bottles, consumer containers for non-food products.
• For the production of: irrigation, drip irrigation, pressure and polyethylene pipes, corrugated hoses, geomembranes, foam products, non-woven materials and threads, cable insulation of low-quality films.
• For the production of: roofing felt, polymer-sand tiles, heat-shrinkable, greenhouse, covering, insulating films, household items, housings and components of electrical appliances and refrigerators, building materials, containers for liquid and bulk chemicals, furniture plastic.

Improving methods for processing LDPE waste leads to the creation of completely new, universal materials. Today, cross-linked polyethylene is in demand and in great demand. It has improved physical properties and a wide range of applications.

Thanks to modern technologies, produced from high-quality polyethylene waste secondary PVD, in its physical and mechanical properties and purity is close to the primary product. It is also important that from the point of view of environmental friendliness and economic feasibility, recycled polyethylene is very beneficial as an inexpensive and accessible material for industrial production.

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We all understand that waste is somehow recycled, but how is this done? Few people know. There are certain differences between the processing of industrial and household plastics, since polymers have different properties.

Similarly, secondary raw materials, that is, polyethylene, have their own properties, which often do not meet the requirements. This is comparable to the fact that polyethylene processing involves materials that differ in molecular structure. In addition, the plasticization process improves the quality of the processed material.

Recycling processes

Ordinary polyethylene, including the material used for packaging, has long term applications. It must be remembered that when using industrial film, it is exposed to atmospheric factors:

• temperature difference
• Sun rays
• the film may become covered with a layer of dust that is difficult to remove when thoroughly cleaning the film

As for the conditions, the processing of polyethylene is, in principle, no different from the processing of primary material. But the processing of polyethylene waste, in some cases, undergoes minor changes, so there are restrictions on the number of polyethylene processing cycles.

Our days

IN modern times The most advanced way to process polyethylene is to use an intermediate material to replace wooden materials. The recycling process itself requires special cleaning of the secondary product (for example, containers for fuels and lubricants).

Most wide application recycled PE has found its way into the production of canisters using blow molding. These canisters are made entirely from waste or with extrusion, primary granulate (in this case, a layer of secondary polymer creates a core between 2 layers of 1 polymer). The resulting products are used by quite a few companies to bottle a variety of detergents.

The second method is considered to be irrigation pipes. The diameter of these pipes reaches up to 630 mm. When performing injection molding, recycled polyethylene has a lower percentage. This technology is used for cladding panels, garbage containers, etc.

As for equipment, polyethylene processing includes different kinds and brands. Many manufacturers produce equipment and successfully enter the Russian market.

Polyethylene recycling various types is important for ecology and industry, but we must not forget that the process of processing household and industrial polyethylene components is largely different (this is due to differences in technical specifications). Sometimes recyclable materials, namely polyethylene, may have some characteristics that do not meet the required parameters. It is also quite significant that plasticization has an extremely positive effect on increasing the quality of the material.

Features of polyethylene recycling

Polyethylene has a wide range of applications, which undoubtedly includes its use as packaging. It is important to take into account that the service life of such packaging is very long, as well as the impact on it of a variety of weather factors:

Action different temperatures, as well as their sudden change;
- exposure to direct sunlight;
- exposed to contamination.

A process such as polyethylene recycling is not much different from obtaining primary materials. But a change in the process still takes place, and therefore the number of processing cycles is also different.

Technologies for processing polyethylene waste

Today, the most advanced method of processing polyethylene is the replacement of wooden materials with intermediate ones. During the process, a special degree of purification of secondary materials is required (as an example, containers for fuel and lubricants can be cited).

At the same time, it is very popular to use recycled materials for the manufacture of various containers. They are either made entirely from recycled materials, or virgin material is added during the manufacturing process. Such containers are very actively used by a variety of companies.

An alternative method for processing polyethylene components, which is based on the use of irrigation pipes, is also very actively used. The diameter of such pipes can exceed 600 mm. Polyethylene can be processed using the application method. An important factor is that the quality of the resulting material becomes lower. But such materials are also in demand; for example, panels for garbage cans are made from them.

Equipment for polyethylene processing

Recyclable materials must be processed into granules; agglomerates are optimally used for this. This is a special one, which consists of several modules. It is worth noting that to work with plastic bottles you can connect the appropriate module, which will wash and crush them.

Polyethylene processing is carried out on equipment that has a number of advantages that simplify the ongoing work process:

Very high productivity and efficiency, very successfully combined with small dimensions;
- the loading hole is located at a fairly low level, which allows you to do without auxiliary devices (ladders, platforms, etc.);
- equipped with an easily removable housing, which increases ease of repair and maintenance;

Aerodynamic swirlers allow even the smallest and thinnest recycled materials to be processed;
- all vital components and mechanisms are perfectly protected from the ingress of working mass, as well as dust and dirt;
- reliable insulation from moisture.

Using recycled polyethylene materials to produce new household and industrial products is more appropriate than using only primary raw materials. Products made from recycled polyethylene products, which are the result of polyethylene recycling, cost significantly less than products made from virgin materials.