Where are LDPE granules made from recycled materials used? Waste polymer films

One of the promising directions entrepreneurial activity currently is polyethylene recycling. This type of business is attractive due to the fact that the products of its production are in great demand in many industries, construction, and growing crops. Before investing in a polyethylene processing business, you should carefully familiarize yourself with all the subtleties and nuances of the process, as well as the requirements for the production itself.

Our business assessment:

Starting investment - 1,500,000 rubles.

Market saturation is low.

The difficulty of starting a business is 7/10.

For whom to produce products?

Starting any business, as a rule, is carried out with a preliminary study of demand, and indeed the demand for the final product or service that will be the main activity.

So, polyethylene processing - who will be the main consumer of the product produced by your enterprise? If you are planning to set up the production of polyethylene granules, then the main clients will also be processing plants producing the following products:

and containers for food and household purposes;
as packaging – consumer and for packaging any type of product on an industrial scale;
Decorative elements for equipping the interior and exterior of an apartment and house, garden, vegetable garden, swimming pool;
Insulating materials for construction;
For the production of finishing tiles;
Pipes for organizing irrigation, water supply, heating;
Cleaning drainage systems;
Materials for equipping stormwater systems.

So, as can be seen from this list, having established the production of polyethylene granules (and it is produced in the form of such small units), you will be a desirable supplier of raw materials for many small workshops and large enterprises.

Of course, in this case, you should not forget that important indicators for buyers will be the quality of your products, your ability to deliver in the required volume and within a clearly defined time frame, and also that the cost is at the level of existing competitors, and at first and even lower.

What types of products will leave the workshop?

The technology for processing polyethylene, first of all, involves the use of already used material as a raw material - practically your main focus is the so-called recycling of polyethylene waste. It is more often called waste recycling, as a result of which, through transformation, cleaning and change physical condition, a product comes out that can become the basis for production large quantity useful things.

The technology for processing polyethylene, which will need to be used when opening production, allows us to produce the following types of products:

Features of production technology

Let's consider how the processing process is carried out. First of all, I would like to immediately note that the processing of polyethylene waste into granules produces a product that is identical in properties to those materials produced from chemical components. In addition, when organizing such a business, it is also important that when processing secondary raw materials, you can count on various subsidies from the state, allocation of funds for opening, and also special favorable conditions when paying taxes.

So, polyethylene recycling consists of the following basic operations:

Collection of waste for polyethylene and acceptance of raw materials for production. In the best way in this case, you will independently organize a collection point for polyethylene waste, of course, if you have sufficient funds for this.
Sorting of received raw materials. It is aimed at separating it from debris and impurities, and also dividing it according to the degree of suitability for recycling.

During the sorting process, waste is divided into types according to the following characteristics:

By size. The largest types of raw materials are sent for cutting using circulation saws or special band saws;
By composition - bags, waste plastic film, bottles, trays, etc. are distributed separately;
If possible, carry out recycling - in practice, from 2 to 10% of collected raw materials must be recycled due to the impossibility of using for industrial purposes;
By pollution. Basically, all collected raw materials are pre-washed, but excessively dirty ones undergo this operation twice.

Basically, the process of sorting raw materials is carried out manually - the currently existing equipment for processing polyethylene does not allow completely mechanizing this process. Due to this circumstance, it will be necessary to hire workers to carry out such a process. It is very important to carefully sort raw materials, since they get into total weight other substances can significantly change the original quality of the polyethylene produced by your plant. As a result, when you purchase it and continue the production cycle, the finished product may turn out to be of poor quality and it is unlikely that you will be contacted again.

Grinding to required size particles. The equipment used for this processing is crushers or shredders;
Washing of crushed raw materials using washing machines. With a large volume of finished products, installed washing lines are used, in which loading into the devices, washing itself, partial drying and transportation for the next stage are automatically carried out. Washing of raw materials is also important stage the entire processing process, since remaining impurities can deteriorate the resulting primary polyethylene granules - they will be of low quality, cloudy and foamy.
Processing in a centrifuge. Under the influence of centrifugal force in such equipment, the particles directly for production are separated from the remaining elements of dirt and impurities, as well as excess moisture, which is unnecessary during the following technological processing operations.
Placing washed and dried raw materials into agglomerators for polyethylene processing. In these devices, due to the influence high temperatures the raw material is melted and sintered. The resulting semi-finished product significantly increases the productivity of subsequent machines along the technological chain and facilitates the main operation of raw material granulation. If a polyethylene processing line is installed in your workshop, then the best option will choose one in which a plastic compactor is installed, which performs a similar operation to an agglomerator, but provides higher quality of the processed product.
The granulation process itself. The output from this operation is a secondary polyethylene granule. The process of its formation itself is as follows: the material is transported using a screw to the granulator, where a cycle of heating and cleaning from foreign impurities is carried out mechanically. The resulting mass, which, as a result of exposure to temperatures, heats up to 200 degrees, falls on the molding hole. The hole has thin slits - dies, through which thin streams of hot polymer are formed. At the exit, these streams are quickly cooled, hardened and cut by a mechanical device using sharp knives. Next, cooling occurs with water or a stream of air.
Recycled polyethylene granules are packaged in bags according to a predetermined weight. This process can be carried out manually, but it will be much more productive to purchase special apparatus, which, moreover, ensures the accuracy of measurements and simultaneously carries out the sealing operation.

Special requirements for the premises

Polyethylene recycling plant due to the fact that it is associated with some particularly harmful conditions and increased danger production should be located exclusively in industrial zones. In addition to this requirement, the following requirements apply to the production premises:

Availability of access to the area for unloading raw materials and loading finished products;
Square production premises should start with a size of 100 square meters;
It is necessary to have a sewerage system and a hot and cold water system;
The room must be equipped good system ventilation;
It is desirable that the entire building be divided into the following four main zones: reception and storage of raw materials, primary processing (sorting), main processing - a workshop in which the semi-finished product is exposed to pressure and high temperature, an area for storing raw materials and shipping finished products.

Necessary personnel for organizing production

The main workers you will need to get started full-fledged work workshops and sales of finished products are as follows:

Head of the enterprise;
Accountant. If the production volumes are not too large, then it is possible to combine the functions of an accountant and a manager in one person;
Production Technologist;
Technological line maintenance workers – from 3 people;
Ancillary workers who perform operations such as unloading raw materials, sorting them, storing finished products, and loading them into vehicles for further shipment to suppliers.

Approximate costs and expected profits

How much money will you need to invest in setting up a polyethylene processing plant in order to open a competitive production facility that will provide you with income for a long period of time?

The main costs, in this case, will be the purchase of equipment, which will cost from 800 thousand rubles and the initial supply of raw materials, in an amount not less than 100 thousand rubles. In general, the total amount of funds that will be needed to open will be from 1.2 million rubles.

The profitability level of such enterprises averages 15% and allows the investment to recoup within a period of one to two years. With enough effort and high professionalism employees, you will be able to expand production in the future by organizing a workshop for the production of any type of product from the resulting recycled granulate, thus increasing the amount of potential profit.

The production of granules from polyethylene waste is one of the most profitable business in terms of profitability and ecology. Recycled LDPE or HDPE granules make it possible to reduce the cost of production of new goods without compromising their quality. Many products made from recycled materials are in no way inferior in quality to goods made from primary raw materials.

Secondary PVD granule

What is a recycled polyethylene granule?

PVD granules — This is a fine-grained bulk material consisting of spherical or cylindrical grains with a diameter of 0.2 to 0.5 mm. It is made from polyethylene high pressure(PVD). Polyethylene granules are also available low pressure- HDPE, and some other less commonly used types of this polymer material.

Primary polyethylene is produced from oil, the reserves of which are not endless. Therefore, the production of recycled LDPE and HDPE granules is becoming increasingly economically important every year.

The color of the granules depends on the color of the feedstock. They are mostly whitish-translucent. At the recycling plant, recyclables are sorted by color, so green bottles and bags, for example, are recycled separately from clear ones.

Where does recycled polyethylene come from?

Manufacturers of HDPE and LDPE granules replenish raw material reserves by buying used plastic container- bottles of any color and volume, stretch film, etc. The company sorts raw materials by color.

Recycled low-density polyethylene is obtained primarily through the recycling of plastic bottles. The volumes of their daily dumping in major cities are huge, they amount to tens of tons, despite the lightness of the raw materials. Recycling of plastic boxes, pipes and other similar waste is also used. Waste of non-woven covering material, shrink film, some types of construction waste, etc.

For the “secondary” production of LDPE granules, waste of primary, synthesized high-density polyethylene is also used. In this case, you only need to ensure that you do not allow a third recycling cycle. It is impossible to recycle polymers a third time - the quality of the product deteriorates sharply.

Processing technology

Polyethylene granules are obtained from LDPE agglomerate - polyethylene crumbs. The processing process consists of the following stages:

Sorting. Produced at garbage dump or directly at the processing plant. Raw materials are sorted by type - bottles, bags, wire insulation, etc., by size, by degree of contamination. Raw materials that are too dirty are not used or are thoroughly washed.
Grinding raw materials to such sizes that the enterprise’s machines can process them - on average from 0.5 to 15 mm.
Washing in special washing chambers. Necessary because dirty raw materials will produce cloudy, low-quality granulated polyethylene. The quality of the resulting product directly depends on the quality and purity of the raw materials.
Blowing in centrifuges to remove excess moisture.
Pre-drying.
Agglomeration - partial melting of washed and dried crumbs followed by sintering. Produced under pressure. Preliminary stage before obtaining polyethylene granulate.
Granulation - processing of polyethylene into granules. At modern enterprises it is produced simultaneously with agglomeration in plastic compactor installations. On previous generation equipment it was a separate stage of the process.

The LDPE granulator is a device that heats the polyethylene mass simultaneously with its last, final filtration from possible inclusions of metals and other foreign impurities. After melting (the polyethylene mass is heated to a temperature of 200 degrees Celsius), it is fed under pressure to a die - a fine-mesh frame. Passing through it, the semi-liquid melt takes the form of thin sausages, which are cut with screw knives in a split second. Next, the resulting polyethylene granules are sent for cooling and packaging.

At this stage, the production of polyethylene granules ends.

What is made from recycled pellets?

Recycled polyethylene granules are used in the manufacture of:

packaging (recycled stretch film, technical film, plastic bags);
bottles for non-alcoholic or low-alcohol liquids;
disposable tableware;
decorative items;
materials for hydro- and thermal insulation;
water pipes (used in low pressure systems);
polymer tiles;
plastic garden furniture;
any other products that do not have to withstand significant physical and electrical loads during operation. This means that insulation for electrical cables, for example, is no longer made from pure “recycled” HDPE. But in some cases it is used in the form of additives - up to 50% by weight, in order to reduce the cost of production.

Fittings and pipes, car parts, hoses, non-woven material, cable insulation, roofing felt and polymer tiles, housings for various machines and mechanisms are made from recycled LDPE.

Why recycling of HDPE and LDPE is beneficial

Polyethylene recycling is one of the most profitable types of modern environmental business:

Purchasing HDPE in granules is much more profitable than using virgin polyethylene. Its synthesis requires oil; the synthesis process is technologically complex. Recycled polyethylene is easier to produce, so it costs several times less than primary polyethylene.
Recycled polyethylene in granules, packaged in any container (usually big bags are used), can be stored in a warehouse for several years. He's not afraid of anything high humidity, nor other unfavorable conditions.
Enterprises engaged in processing recycled polyethylene have a high percentage of profitability, since their costs for raw materials are minimal, process it is not complex and does not require expensive equipment, and the demand for the final product is high and constant.
With actively used recycling plastic bottles, packages and others packaging materials it is possible to significantly reduce the area allocated for landfills for used packaging and improve environmental situation in the city, country and world. When decomposing (the decomposition period is about 300 years), polyethylene releases harmful substances into the atmosphere. Given the volume of its production, this could become a serious problem in the future.

Recycling polyethylene is a profitable and environmentally friendly business. It allows you to use available resources for production, which significantly saves mineral reserves on the planet and reduces the cost of the resulting polymer products.

Pollution problem environment waste becomes more and more problematic every year. Polyethylene is used everywhere. It is used for packaging products, producing pipes, machine parts and building materials. The long process of decomposition of the material threatens the harmony on the planet. Therefore, it is so important to understand what technologies exist for recycling polyethylene.

Importance of Elimination

Modern material is not afraid of water, acids of various origins, alkali and solutions chemical salts. For the production of products such resistance to external influences only on the hand, but she may threaten an environmental disaster.

Polyethylene waste is very dangerous. The substance is subject to thermal aging and slow decomposition under the influence of heat, sun and air. During this period, the material begins to release caustic substances that pollute waste water and soil.

The decomposition lasts at least a century. Looking at this, environmentalists are sounding the alarm and trying to prevent a catastrophe.

It is impossible to significantly reduce the production of polyethylene products, but to organize it correctly production process- quite real. To do this, it is necessary to create and improve methods for recycling polyethylene. The modernization process will give waste another life: it can be used as secondary raw materials.

Every year the number of organizations whose activities are related to the processing of hazardous waste is growing. This is due not only to the deterioration of the atmosphere. Recycling of harmful substances is considered a profitable business sector.

From used film and polyethylene you can create raw materials for:

Garbage bins.
Panels.
Household and industrial containers.

Despite the emergence of new recycling technologies, the production of goods from such raw materials has limitations.

The recycling of polyethylene waste itself is not complicated. Materials used in everyday life, remain unchanged, since their use does not last long, and their service life for industrial use is much longer.

Impact on polyethylene in such conditions has a large scale. The sun's rays and constant temperature changes have a strong impact on the material. Dust that appears during operation cannot be removed. Recycled raw materials are not famous high quality, therefore it is not suitable for production in any field.

Subtleties of waste recycling

The types of products that can be made from recycled products have some limitations. The first phase has minimal effects on the important properties of new products, but each new cycle reduces them. Raw materials become suitable only for the manufacture of products mechanical characteristics which are not so important for comfortable use.

Stages classical processing polyethylene waste:

Selection of equipment for the process

Creating raw materials for reuse from polyethylene is impossible without professional equipment. It is similar to plastic recycling machines.

The fully equipped line includes:

Washing machine.
Unit for crushing material.
Centrifuge.
Drying unit.
Extruder.
Agglomerator.
Granulator.

It is also recommended to use a conveyor or pneumatic conveyor. They automate production, simplifying the waste feeding process. The agglomerator is the main device. It is here that the main process of film processing takes place. Under the influence of high temperatures, waste is converted into secondary raw materials called agglomerate. On the machine he becomes finished products. For high productivity recycling it is necessary to use agglomerators with high power. The price of these machines is much higher than regular ones, but the quality is comparatively better.

Polyethylene granulation is the next step after grinding and agglomeration. A pellet making machine is most often included in the production line, but its use is not a requirement.

But it is worth remembering that the sale of polyethylene granules is in demand. Their production can significantly increase profits and expand the customer base.

The technology for processing polyethylene film is improving every year. Cross-linked polyethylene is especially popular. This is a material that has improved properties. It has a wide scope of application. It is used to produce gloves, packaging film for products, heat shrinkable tubes and polymer pipes. The stitched material is very rigid. His operating temperature after processing it can reach up to 120 degrees.

Why is it important to recycle polyethylene and why is polyethylene interesting for a recycling business?

Polyethylene is the most widely used of all types of plastics. It can be harvested in large quantities at relatively low cost and therefore a recycling business can use economies of scale to reduce costs and increase profits.

In what quantities is polyethylene consumed and what products are made from it?

In Russia, the annual consumption of polyethylene is 1.6-1.7 million tons, a significant part of which is spent on products with short term services, feeding the waste stream.

What is polyethylene?

Polyethylene is a polymer, that is, a material consisting of very long molecules in which homogeneous groups of carbon and hydrogen atoms are connected into chains. Polyethylene has the simplest structure of all polymers. In it, in the center of the chain there are carbon atoms, to which hydrogen atoms are attached.
The structure looks like this

In some places, instead of a hydrogen atom, a carbon atom is attached to the side of the chain, which also forms a chain or branch. Molecules can be in varying degrees branched and the properties of the material greatly depend on this.

What raw materials is polyethylene made from?

The very name of polyethylene suggests that it is an ethylene polymer, that is, the polymer chains consist of identical pieces, chemical formula of which C₂H₂ (ethylene). These components are called monomer. In ethylene, each tetravalent carbon atom is connected to two hydrogen atoms and to an adjacent carbon atom, with the latter covalent bond double Therefore, ethylene is also called an unsaturated compound. In chemistry, compounds with a double bond are called olefins, hence the common name for polyethylene and some other polymers - polyolefins.
So, polyethylene is produced by combining ethylene molecules into chains (polymerization).
In this case, ethylene can be from different sources, depending on which raw material is more accessible to petrochemists in each specific region and in each specific case. The main groups of raw materials are naphtha (a derivative from oil refining), ethane, isolated from natural gas or associated gas, and increasingly, ethylene is now being produced from ethyl alcohol, which can be obtained from many types of plant materials, including ethanol from sugar cane that is now used on a commercial scale.

What determine the properties of polyethylene?

The industry produces many brands of polyethylene, but they all differ mainly in only two parameters. This is the size of the molecules and the degree of their branching. These parameters do not depend on the feedstock from which ethylene is obtained, but depend on the conditions of the polymerization process, pressure in the reactor, temperature, presence and type of catalyst.
The industry learned to make the first polyethylene at high pressure, in which polymerization was initiated free radicals. This material is now called LDPE, it is characterized by great branching. That is, on each polymer chain there are many side branches, which in turn also have branches consisting of the same chains.
Later, with the help of catalysts, they learned to produce polyethylene at a lower pressure, it is called HDPE. Its molecules are much less branched.
To understand how the branching of molecules affects the properties of a polymer, imagine two panicles. One of them consists of smooth twigs, without side branches. They are packed tightly and the panicle is so tough and durable. The other consists of twigs with side branches. The density is already much less, and it is more pliable and flexible.
In the same way, HDPE, also called high-density polyethylene, and LDPE, called low-density polyethylene, differ. The first material is tougher and its strength is high. The second is plastic, products made from it bend under lower loads.

Is it possible with secondary LDPE processing convert to HDPE and vice versa?

No, it’s impossible, the structure and size of molecules are set during synthesis, that is, at the plant where the primary polymer was produced; during recycling, it is little subject to change. However, it is possible to add rigidity to a LDPE material by adding a more rigid HDPE or other material, and it is also possible to add plasticity to a LDPE material by adding LDPE accordingly. This is often done in the manufacture of products from secondary polymers. Mix different types.

What determine the rheological properties of polyethylene and the melt yield strength?

On the size of the molecules. The larger and longer the molecules in a polymer, the less fluid it is. The fluidity of the polymer is measured under load and at elevated temperature.

What types of polyethylene raw materials are available for recycling?

Production waste and consumer waste are available.
Industrial waste differs, in most cases, in purity and is homogeneous, however, each source contains relatively small quantity. This is understandable, because production facilities are not designed to produce waste. Often, recycling industrial waste is a relatively simple process, and those who generate it increasingly use it themselves after minimal processing, for example, crushing or granulating on a small, simplified granulator.
Large volume but complex in composition consumer waste, that is, waste of used products or packaging. Recycling such waste is usually difficult; recyclers must have a large number equipment, so economies of scale make their processing enterprises relatively large. They collect waste from a variety of sources (landfill and commercial sources).

What polyethylene consumer waste can be recycled?

The following types of polyethylene waste are available on the existing market for secondary raw materials in Russia:

Waste films made from low-density polyethylene, including stretch films, collected by sorting from commercial sources - stores, are relatively clean; cleaning them from contaminants does not require washing; filtering the melt in an extruder and degassing is sufficient.
Film waste collected from consumer waste requires washing, as it is also contaminated food waste.
Stretch - collected separately, most often it is linear low-density polyethylene with additives.
Blow molded bottles for liquid products and goods - consist of HDPE, require washing and thorough degassing of the melt to remove product residues that are absorbed into the walls of the bottles. Abroad, milk bottles are usually collected separately, but this applies to those countries where a significant percentage of milk is packaged in high-density polyethylene bottles.
Canisters can be of different quality depending on what was poured into them before. As written above, recycling oil cans is difficult due to oil residues.
Multilayer films, most of which are polyethylene - processing of such films presents technological difficulties, the description of which is beyond the scope of this article.
Cable waste - they often use cross-linked polyethylene, that is, one in which bridges between individual molecules have been deliberately created. Its processing is difficult because the material does not flow at melting temperatures, but only softens. The percentage of gel there is very high.
Agricultural film is a film that was used in agriculture. It can usually be significantly damaged by photo-oxidative degradation

Which products are made from which types of recycled materials?

Type of waste for recycling	Density	Melt yield strength	Products
Waste LDPE films collected from commercial sources	0,915 – 0,925	0,8 -4	New film, including for packaging
Waste, films collected from waste sorting stations	0,915-0,945	0,6- 4	Granules for injection molding products
Stretch			Granules for mixing into other types of raw materials as a modifier
Blown bottles for household chemicals and food products	0,945 – 0,955	0,1- 0,8	Unloaded pipes, drainage pipes
Canisters	0,945-0,955	0,1-0,8	Unloaded pipes, drainage pipes, wood-polymer composites, geomembranes, sheets for other purposes.
Multilayer films			Non-responsible products, additives for other granules
Waste cables and wires		0,1	Additive for other granules
Agricultural film	0,915-0,925	0,8-6	Granules for adding to new film and for injection molded products.

What methods of polyethylene processing are used?

There are two main methods of processing: mechanical recycling, when the material is used as a polymer for the manufacture of products or other purposes, as well as thermo-chemical recycling, pyrolysis, which results in liquid and gaseous products of thermal destruction of the polymer. Next we will talk about mechanical recycling.
What processes does polyethylene recycling involve?
The main processes are sorting, grinding, washing, drying and agglomeration or granulation. Depending on the feedstock and productivity, the combination of these processes can be different, for example, grinding can be carried out in one stage or in two stages. Also, if the raw materials are collected from relatively clean sources, the washing and drying stage can sometimes be omitted.

What equipment is used for processing?

Polyethylene waste that has been in contact with products and is contaminated is washed on the washing lines. Typically, a washing line includes the following elements:

- Equipment for grinding and giving regular shape to particles. Shredders or crushers. The former are preferable in most cases, as they are more resistant to solid objects such as stones or metals, but shredders are more expensive than crushers. In crushers, the rotor speed is higher, hitting hard object can immediately damage the crusher; in especially severe cases, all knives will need to be replaced. But crushers are often made with a pre-cleaning function; for this purpose, water is supplied to them. On high-capacity lines, both a shredder and a crusher are used, that is, grinding is organized in two stages, between which equipment for separating heavy particles must be installed in order to protect the crusher.

- Equipment for separating heavy particles such as sand, stones, metals and plastics incompatible with polyethylene, such as polyethylene terephthalate, which sinks in ordinary water.
Two types of equipment are used to separate heavy particles: flotation baths and hydrocyclones. The latter are almost exclusively used in high-capacity lines, for example 2 tons per hour.

- Equipment for intensive cleaning of plastic. For this purpose, friction washers and (or) centifuges are used.

Equipment for extraction is usually centrifuges and screw presses. After mechanical pressing, the moisture content of the films can be from 6 to 12 percent. This may be too much for effective further agglomeration, so mechanical drying is often not limited to.

- Equipment for thermal drying - they, as a rule, organize the movement of plastic particles along with the flow of heated air in labyrinths (long pipes or channels) of different designs. Sometimes final drying is not done in the lines and is left to the agglomeration or granulation stage.

The operation of agglomerators and plastic compactors is based on heating the material mechanically and then clumping and compacting it using various technological methods.

The operation of the granulator is based on heating the material using electric heaters to melting temperatures, mixing the resulting melt and cleaning it by filtering, pumping out the gases formed during heating and then forming granules by squeezing the melt through dies (matrices with holes) and cutting the resulting strands in one way or another way. (water ring and strand granulators). The advantage of granulators over agglomerators and plastic compactors is that they make it possible to obtain a more reliable product, since mechanical impurities that could remain after the washing line are filtered out on the granulators and impurities of fats or other substances that decompose when heated can be removed by degassing the melt.

More details about the equipment with examples of lines on the website http://moykaplastica.ru

What is polymer degradation?

During recycling, polymer molecules are inevitably damaged for three reasons. This is, firstly, a mechanical load, for example, in an extruder, when high blood pressure the material is mixed. Secondly, this is heat, which contributes to more active movement of molecules and the bonds between atoms become not as strong as at ordinary temperatures. Thirdly, this is the action of atmospheric oxygen, which, being an active oxidizing agent, tends to oxidize the elements of the polymer chain, hydrogen and carbon. Thus, during recycling, the polymer molecules change, some of them become shorter, breaking into pieces. Every time a polymer chain breaks for one reason or another, a radical is formed, that is, an atom or group of atoms whose valencies are not closed, there is a vacant place on the outer electron cloud. Such radicals are extremely active; they form compounds with neighboring molecules, and damage to a neighboring molecule forms a new radical, which in turn damages another chain. When molecules are cross-linked by separate adhesions, the resulting structure is called a gel. The content of gels in secondary granules changes mechanical properties, usually not for the best
side.

Why are the properties of recycled polyethylene worse than those of primary polyethylene?

The main culprit for the decrease in properties appears to be oxygen. When destroyed, it not only creates radicals, as described above, but it can also be incorporated into the material, replacing hydrogen and carbon atoms, and oxidize polyethylene. The presence of oxygen atoms in a material changes its properties. Initially, polyethylene is non-polar. This means that it only contains hydrogen and carbon atoms, which have a non-polar bond with each other, because their electronegativity is quite close. That is, they are connected through a common cloud of electrons, which is more or less in the middle ( in simple words, actually more difficult). But as soon as an atom of oxygen, the second most electronegative element after fluorine, appears nearby, oxygen immediately affects all bonds that are nearby. It polarizes them to some extent. Attracts electrons to itself. This reduces their strength under mechanical stress and reduces the resistance of neighboring bonds to other oxygen atoms, which also tend to snatch and oxidize something from the polymer molecule.
Hence, the important practical knowledge is that the more polyethylene is oxidized (destructed), the faster it oxidizes further and its properties drop even faster. This explains more unsuccessful than successful experiments to improve the properties of recycled plastic by adding unspoiled primary plastic. The secondary, if it has already destroyed, then quickly poisons the primary with its influence, and this is precisely because of oxygen and its magnetic activity in relation to electrons in molecules.

For example, according to the link, an article by Swedish researcher Michael Hamskog (with whom I have worked before), the article concluded that mixing primary polyolefin with secondary polyolefin is ineffective and that adding additives is more effective. which will be discussed below.
https://www.sciencedirect.com/scienc...41391005003629

How does the MFI of polyethylene change during recycling?

So the MFR can change both up and down, depending on which process is developing more strongly, shortening or stitching, and this in turn depends on the processing conditions. Most often, shortening of molecules is observed, that is, an increase in fluidity.

How to reduce polymer degradation during recycling?

In order to slow down the destruction, special substances are added to the polymer that can absorb the resulting radicals and do not allow the process to develop according to a chain scenario, when damage to one polymer chain leads to damage to neighboring ones.
Unfortunately, these substances are consumable. That is, over time, their effect weakens and they are already working off. Sometimes, in order to restore the dose of stabilizers, they are added to the polymer during recycling. For example, a composition such as Recyclestab.
In order to minimize destruction, in general it is necessary to minimize the mechanical and thermal loads on the polymer during the recycling process, that is, do not overheat it above the required level, do not use excessive mixing under pressure in the extruder.

How do polymer contaminations affect the properties of the recycled material?

When processing post-consumer waste, contamination is always a major problem. They are acquired from contact with other substances, including the substance that was packaged in polyethylene packaging. Pollution can be superficial or internal.
Thus, oil cans contain some residual amount of these oils in the form of surface contaminants, but some of the oil is dissolved in the walls of the canister and during recycling, even if the material is well washed, an odor may appear, and the properties of the secondary polymer may change due to plasticization of polyethylene with oil (partial dissolving oil in polyethylene).
This is typical not only for such pronounced substances as oil and detergents, but also for ordinary milk. Bottles made from HDPE that previously contained milk, even after washing, contain in their walls a certain amount of lactic acid, which has dissolved in polyethylene. Odor may occur during processing.
Other contaminants such as sand or soil or pieces of paper also reduce the mechanical properties of the polymer and must be removed.
To remove surface contaminants, washers are used in which the material is thoroughly washed with water in combination with some mechanical forces (friction washers), and dry cleaning units can also be used, for example, those produced by MAS, but the latter do not cope well with sticky contaminants even in cases where There are sticky components.

How to recycle cross-linked polyethylene?

Cross-linked polyethylene is one in which ligaments (bridges) are additionally made between individual macromolecules. This is usually done for those products that are used for elevated temperatures eg for electrical insulation. Such polyethylene can withstand a slightly higher melting point than its melting temperature. So, for example, the cable insulation will not drain, but will only soften. In fact, cross-linked polyethylene is no longer a thermoplastic plastic. It does not melt, as it should, but softens, so it is impossible to process it using conventional methods.
There are two possible approaches to processing cross-linked polyethylene. Firstly, it can be processed by thermal methods, such as pyrolysis, to produce liquid and gaseous products.
Secondly. Theoretically, cross-linked polyethylene can be ground to a particle size smaller than 0.5 mm and used as an additive in conventional polyethylene products. The author worked on this idea for a long time and was already planning to test it in practice, but somehow didn’t get around to it. The difficulty is that cross-linked polyethylene grinds very poorly, so it was not possible to obtain powder from it at a very low price. The estimated price was up to 10 rubles per kilogram. Secondly, it is unclear how cross-linked polyethylene will affect the Melt Yield Strength. Apparently it will reduce PTR, but this needs to be checked.

Maybe, great potential processing of cross-linked polyethylene consists in mastering new methods of grinding it. For example, if you use the natural cold in the Siberian part of the country, then you can probably get a more productive grinding process in conventional mills than has been the case until now. At a low enough cost, this material could compete in the filler market because it has the same density as polyethylene, meaning there would be no increase in the density of granules or products and it would likely have less impact on the properties of the polymer than when compared with mineral fillers. If you are interested in equipment for grinding cross-linked polyethylene, please write to the contacts below.

Where to start a polyethylene recycling project?

From establishing contacts. First of all, we need contacts with waste sorting stations and other sources of recycled polyethylene, then contacts with manufacturers of plastic products who are ready to consider proposals for the use of recycled polyethylene.
Once you have an understanding of the available volume of raw materials and possible sales, you can begin to select equipment and, together with suppliers, design a production line for processing.

Information about advanced processing equipment:

For questions regarding the sale of waste polyethylene, film, bags, substandard products, call
+7 916 103 1486
or write mail.ru

Polyethylene collection

Our company does not process all types of plastic bags, but only film, bags, sacks, production defects of stretch film (the so-called shrink film) and LDPE.

LDPE is high-density polyethylene or, as it is also called, low-density polyethylene. LDPE waste can be generated during the direct production of polyethylene film. There is a lot of waste - in stores (packaging bottles, boxes, boxes), at glass factories (from packaging bottles, cans), at distilleries and beer factories (from packaging containers or finished products).

Stretch film is linear high-density polyethylene (LDPE). It can stretch a lot. Due to this property, as well as increased resistance to punctures and tearing, stretch film is used for packaging various goods, in particular on pallets. Stretch film waste is mainly generated and accumulated in warehouses of any size, at customs terminals, logistics centers, etc.

But we do not recycle the popular T-shirt bags made of HDPE (low-density polyethylene) and “biodegradable” bags, which can be found, for example, in ABC of Taste. Polypropylene film, PVC film, bubble film, polyamide film, multilayer PVD+PP, PVD+PA films, as well as double-sided two-color films are also not suitable. Finally, we do not accept film contaminated with oils, grease, food waste or toxic chemicals.

Sorting

We take the collected polyethylene to the warehouse. Up to 100 tons of film waste can be stored here, naturally in pressed form. At the first stage, the raw materials undergo careful sorting. Stretch is separated from LDPE, and types of films that cannot be processed by our facilities are rejected.

Crusher

After sorting, bags of a certain color are put into a crusher. It uses V-shaped knives (in our circles this type is also called “ dovetail") the film is crushed to particles of uniform size. The knives are driven by an electric motor.

Washing

From the crusher, through a pneumatic conveyor, the so-called “crushed material” enters the sink. In it, with the addition of special cleaning solutions, the “crushed” is cleaned of dust and other non-polyethylene inclusions.

Cooking

The next stage of processing is agglomeration. The so-called “cooking” takes place in it. The operator loads clean “crushed material” into the working chamber through the loading window. The raw materials fall along the guides onto the rotating rotor, are crushed by knives and, due to friction against the body and among themselves, are heated to the plasticization temperature. In this case, the entire volume of loaded raw materials becomes like a mushy mass.

When the material becomes homogeneous, “shock” water is added to it, as a result of which the material is sharply cooled and sintered into individual small balls of irregular shape. For some more time, the agglomerate is dried at natural ambient temperature and unloaded into prepared containers to go to the final stage. The cooking process itself lasts from 5 to 10 minutes.

Granulation

The granulation process can be compared to minced meat through a meat grinder. The agglomerate that we obtained at the previous stage is loaded into the extruder hopper. It is called so because the production of granules is based on the extrusion method - forcing the molten mass through a molding hole.

In general, our “minced meat” from boiled bags is melted under the action of heaters and pressure created by a rotating screw. The polymer melt is forced through a filter into the rotating extruder head. Already from it come the so-called threads. To cool, we pass them through a water hose and then into knives, where we cut them into uniform granules.

Storage

The granules are packaged in clean polypropylene bags, approximately 50 kg each. No special storage conditions are required, but it is advisable that it be in a dry room.

Finished raw materials

We sell the resulting granules, depending on the composition and color. Stretch granules of natural color are used for the production of secondary stretch. LDPE granules of natural color are used for the production of secondary shrink or technical film. Colored LDPE granules are mainly used for the production of garbage bags.