What is polyethylene made from? Manufacture of polyethylene. Products from polyethylene

In the history of science, some discoveries occurred by chance, and the materials claimed today were often a by-product of some experience. It was quite by chance that aniline dyes for fabrics were discovered, which subsequently gave an economic and technical breakthrough in light industry. A similar story happened with polyethylene.

Opening a material

The first case of polyethylene production occurred in 1898. During the reheating of diamoseotane, a chemist of German origin Hans von Pehman discovered a strange precipitate, not the bottom of the test tube. The material was dense enough to resemble wax, the colleagues of the scientist called it polymethylene. Further randomness of this group of scientists did not work, the result was almost forgotten, no one had any interest. But still the idea hung in the air, demanding a pragmatic approach. So it happened, thirty years later, polyethylene was reopened as a random product of an unsuccessful experiment.

Englishmen pick up and win

A modern polyethylene material was born in the laboratory of the British company Imperial Chemical Industries. E. Fossett and R. Gibson conducted experiments involving high and low pressure gases and noticed that one of the nodes of the technique in which the experiments were performed was covered with an unknown waxy substance. Interested in a side effect, they made several attempts to get the substance, but without success.

The polymer was synthesized by M. Perrin, an employee of the same company, two years later. It was he who created the technology that served as the basis for the industrial production of polyethylene. Later, the properties and qualities of the material were changed only by the use of various catalysts. The mass production of polyethylene began in 1938, and it was patented in 1936.

Raw materials

Polyethylene is a solid polymer of white color. Refers to the class of organic compounds. What is polyethylene made from? The raw material for its production is ethylene gas. The gas is polymerized at high and low pressure, and granules of raw materials are obtained for further use. For some technological processes polyethylene is produced in the form of a powder.

Basic views

To date, the polymer is produced two main brands of LDPE and PPP. The material manufactured at medium pressure relative is a new invention, but in the future the amount of product produced will invariably grow due to improving characteristics and a wide field for application.

For commercial use, the following types of material (classes) are produced:

• Low density or other name - high pressure (LDPE, LDPE).
• High density, or low pressure (LDPE, PNP).
• Linear polyethylene, or medium pressure polyethylene.

There are also other types of polyethylene, each of which has its own properties and scope. In the granular polymer in the manufacturing process, various dyes are added, allowing to obtain black polyethylene, red or any other color.

LDPE

Polyethylene is produced by the chemical industry. Ethylene gas is the main element (of which polyethylene is made), but not the only one required to produce the material.

The production of high-pressure polyethylene takes place in autoclaves, tubular reactors. LDPE marbles made in an autoclave, according to GOST, there are eight. Twenty-one types of high-pressure polyethylene are produced from the tubular reactor.

For the synthesis of PVP, the following conditions must be met:

• The temperature regime is from 200 to 250 ° C.
• The catalyst is pure oxygen, peroxide (organic).
• The pressure is from 150 to 300 MPa.

The poized mass in the first phase has a liquid state, then it moves to the separator, then to the granulator, where the granules of the finished material are formed.

The qualities of LDPE are used for the production of packaging films, thermofilms, multi-layer packaging. Also, high-density polyethylene is used in the automotive, chemical, food industries. It is made of quality high-quality pipes used in the residential sector.

Linear polyethylene

What do medium-density polyethylene or linear polyethylene do?

• The heating temperature is up to 120 ° C.
• Pressure regime up to 4 MPa.
• The process stimulator is a catalyst (Ziegler-Natta, a mixture of titanium chloride with a melalloorganic compound).

The process is accompanied by the loss of polyethylene in the form of flakes, which then go through the process of separation from the solution followed by granulation.

This type of polyethylene is characterized by a higher density, resistance to heat and rupture. The sphere of application is various kinds of packaging films, including for packing hot materials / products. From granular raw materials of this type of polymer, parts for large-sized machines are manufactured by casting, insulating materials, pipes of increased strength, consumer goods ,

Low-pressure polyethylene

The production of PNP has three methods. Most enterprises use the "suspension polymerization" method. The process of obtaining PNP occurs with the participation of a suspension and constant mixing of the feedstock, a catalyst is required to start the process.

The second most common method of production is polymerization in solution under the influence of temperature and catalyst participation. The method is not very effective, since during the polymerization the catalyst reacts and the final polymer loses some of its qualities.

The last of the methods of production of PPP is gas-phase polymerization, it is almost gone, but sometimes it occurs in separate enterprises. The process occurs by mixing the gas phases of the feedstock under the influence of diffusion. The final polymer is obtained with a non-uniform structure and density, which affects the quality of the finished product.

Production of low pressure polyethylene takes place under the following conditions:

• The temperature is maintained at 120 ° C to 150 ° C.
• The pressure should not exceed 2 MPa.
• Catalysts of the polymerization process (Ziegler-Natta, a mixture of titanium chloride with a melaloorganic compound).

The material of this manufacturing method is characterized by rigidity, high density, low elasticity. Therefore, the sphere of its application is industry. Technical polyethylene is used for making large-sized containers with increased strength characteristics. Demanded in the construction industry, chemical industry, for the production of consumer goods it is almost not used.

Properties

Polyethylene is resistant to water, to many types of solvents, acids (organic, inorganic), does not react with salts. When burning, there is a smell of paraffin, there is a glow of a blue hue, fire is weak. Decomposition occurs when exposed to nitric acid, chlorine and fluorine in the gaseous or liquid state. With aging, which occurs in the air, cross-linking between chains of molecules is formed in the material, which makes the material brittle, crumbling.

Consumer qualities

Polyethylene is a unique material, familiar in everyday life and production. It is unlikely that an average consumer will be able to determine with how many items from it he encounters daily. In the world production of polymers, polyethylene occupies the lion's share of the market - 31% of the total gross product.

Depending on what is made of polyethylene and production technology, its quality is determined. This material combines at times the opposite indicators: flexibility and strength, plasticity and hardness, strong tensile and tear resistance, resistance to aggressive media and biological agents. In everyday life we use packages of various densities, disposable dishes, plastic covers, parts of household appliances and much more.

Areas of use

The use of products made of polyethylene is not limited, any industry or human activity is accompanied by this material:

• The most widespread polymer was in the manufacture of packaging materials. This part of the application accounts for about 35% of all produced raw materials. Such use is justified by dirt-repellent properties, lack of environment for the onset of fungal attack and microorganism activity. One of the successful finds is a polyethylene sleeve, which has a wide application. Varying at its own discretion length, the user is limited only by the width of the package.
• Remembering what polyethylene is made of, it becomes clear why it got spread like one of the best insulating materials. One of its demanded qualities in this field was the lack of electrical conductivity. Also its water-repellent properties are irreplaceable, which has found application in the production of waterproofing materials.
• Resistance to the destructive power of water, as a solvent, makes it possible to manufacture polyethylene pipes for domestic and industrial consumers.
• The building industry uses noise-insulating qualities of polyethylene, its low thermal conductivity. These properties were useful in the manufacture of materials based on it for the insulation of residential and industrial facilities. Polyethylene is used for insulation of heat traces, in machine building, etc.
• No less resistant to aggressive media of the chemical industry, polyethylene pipes are used in laboratories and chemical industries.
• In medicine, polyethylene is useful in the form of dressings, prosthetic limbs, use it in dentistry, etc.

Ways of processing

Depending on the manner in which the granulated raw materials were processed, it will depend on which brand of polyethylene will be produced. Common methods:

• Extrusion (extrusion). It is used for the manufacture of pipes, packaging and other types of films, sheet material for construction and finishing, cable manufacturing, a polyethylene sleeve and other products are produced.
• Casting, thermo-vacuum molding. It is mainly used for manufacturing of packing materials, boxes, etc.
• Extruded-blown, rotary. With the help of this method, volumetric containers, large packagings, and vessels are obtained.
• Reinforcement. According to a certain technology, reinforcing elements (metal) are laid in the formed mass of polyethylene, which makes it possible to obtain a building material of increased strength, but with a lower cost.

What is polyethylene made of, besides the main constituents of the substances? Required is a process catalyst and additives that change the properties, qualities of the finished material.

Recycling

Persistence of polyethylene is its plus as a consumer product and its minus, as one of the main polluting factors. To date, recycling is important - recycling. All grades of polyethylene can be recycled and re-converted into granular raw materials, from which you can make a lot of popular consumer goods and industrial consumption.

Polyethylene caps, bags, bottles will decompose in the landfill for hundreds of years, and the accumulated waste will poison natural vital resources. World practice shows an increase in the number of polyethylene processing enterprises. Collecting actually garbage, in such companies spend its sanation, crush. Thus, there is a saving of resources, environmental protection and production of demanded products.