What does pe 100 mean. SDR PE pipe - what does the marking mean. Getting low-pressure polyethylene

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

Material opening

The first case of obtaining polyethylene occurred in 1898. While heating the diamezotane, a German-born chemist Hans von Pechmann discovered a strange sediment in the bottom of the test tube. The material was quite dense and resembled wax, the scientist's colleagues called it polymethylline. This group of scientists did not go further than chance, the result was almost forgotten, no one was interested. Still, the idea hung in the air, requiring a pragmatic approach. And so it happened, over thirty years later, polyethylene was rediscovered as an accidental product of a failed experiment.

The British pick up and win

The modern material polyethylene was born in the laboratory of the British company Imperial Chemical Industries. E. Fossett and R. Gibson carried out experiments with the participation of gases of high and low pressure and noticed that one of the nodes of the equipment in which the experiments were carried out was covered with an unknown waxy substance. Curious about the side effect, they made several attempts to obtain the substance, but to no avail.

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. Subsequently, the properties and qualities of the material changed only with the use of various catalysts. The mass production of polyethylene began in 1938, and it was patented in 1936.

Raw materials

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

Main types

Today the polymer is produced in two main grades of LDPE and PNP. The material made at medium pressure is a relatively new invention, but in the future the amount of the produced product will invariably grow due to the improving characteristics and a wide field of application.

The following types of material (classes) are produced for commercial use:

Low density or another 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. Various dyes are added to the granular polymer during the production process, which make it possible to obtain black polyethylene, red or any other color.

LDPE

The chemical industry is engaged in the production of polyethylene. Ethylene gas is the main element (from which polyethylene is made), but not the only one required to obtain the material.

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

The process is accompanied by the precipitation of polyethylene in the form of flakes, which then undergo a separation process from the solution, followed by granulation.

This type of polyethylene is characterized by higher density, heat and tear resistance. The scope of application is various types of packaging films, including for the packaging of hot materials / products. From granular raw materials of this type of polymer, parts for large-sized machines are made by casting, insulating materials, high-strength pipes, consumer goods, etc.

Low-pressure polyethylene

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

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

Gas-phase polymerization is the last of the methods for producing LDPE, it is almost a thing of the past, but sometimes it is found in individual enterprises. The process takes place by mixing the gas phases of the raw material 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 takes place in the following mode:

The temperature is maintained between 120 ° C and 150 ° C.
The pressure should not exceed 2 MPa.
Polymerization process catalysts (Ziegler-Natta, mixture of titanium chloride with organometallic compound).

The material of this manufacturing method is characterized by rigidity, high density, low elasticity. Therefore, the scope of its application is industry. Technical polyethylene is used for the manufacture of large-sized containers with increased strength characteristics. In demand in the construction industry, chemical industry, for the production of consumer goods, it is almost never used.

Properties

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

Consumer qualities

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

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

Areas of use

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

The polymer is most widely used in the manufacture of packaging materials. This part of the application accounts for about 35% of all raw materials produced. Such use is justified by the dirt-repellent properties, the absence of an environment for the occurrence of fungal infections and the vital activity of microorganisms. One of the successful finds is a polyethylene sleeve, which is widely used. By varying the length at his own discretion, the user is limited only by the width of the package.
Keeping in mind what polyethylene is made of, it becomes clear why it has gained popularity as one of the best insulating materials. One of his demanded qualities in this area was the lack of electrical conductivity. Its water-repellent properties are also irreplaceable, which has found application in the production of waterproofing materials.
Resistance to the destructive force of water as a solvent allows the manufacture of polyethylene pipes for domestic and industrial consumers.
The construction industry uses the 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. Technical polyethylene is used for insulation of heating routes, in mechanical engineering, etc.
The material is no less resistant to aggressive environments of the chemical industry; polyethylene pipes are used in laboratories and chemical industries.
In medicine, polyethylene is useful in the form of dressings, limb prostheses, it is used in dentistry, etc.

Processing methods

Depending on how the granular raw materials were processed, what grade of polyethylene will be obtained will depend. Common ways:

Extrusion (extrusion). It is used for packaging and other types of films, sheet material for construction and decoration, cable manufacture, polyethylene sleeves and other products are produced.
Casting, way. Mainly used for making packaging materials, boxes, etc.
Extrusion blow molding, rotary. Using this method, bulk containers, bulky containers, and vessels are obtained.
Reinforcement. According to a certain technology, reinforcing elements (metal) are laid in the formed polyethylene mass, which makes it possible to obtain construction material increased strength, but at a lower cost.

What is polyethylene made of, in addition to the main constituents of substances? A process catalyst and additives that change the properties and quality of the finished material are required.

Recycling

The durability of polyethylene is its plus as a consumer product and its minus as one of the main pollutants. environment factors. Today, waste processing is becoming important - recycling. All grades of polyethylene can be recycled and re-converted into granular raw materials, from which many popular consumer and industrial goods can be made.

Plastic caps, bags, bottles will decompose in a landfill for more than one hundred years, and the accumulated waste will poison natural vital resources. World practice demonstrates an increase in the number of polyethylene processing enterprises. Collecting actually garbage, in such companies they reorganize it, crush it. Thus, resources are saved, the environment is protected and products in demand are produced.

PE pipe marking

The PE pipe marking indicates that the raw material for the production was polyethylene (PE) obtained by the polymerization of ethylene, which has high thermal insulation and dielectric properties.

PE pipes have flexibility, strength, and they are also non-toxic, which allows them to be used for water supply (including drinking).

Advantages of PE pipes:

polyethylene pipes do not react to alkaline drugs, hydrochloric acid, gasoline, alcohol, various oils;

Resistant to shocks, do not crumble at subzero temperatures, the walls of the pipes are vapor-tight;

Easy and simple hot-soldering assembly. NSWith proper operation, it can function for several decades;

smooth inner and outer surface is not subject to corrosion by salts dissolved in water, organic solvents, bacteria and microbes,do not have calcareous build-up;

increased throughput compared to metal products;

The high coefficient of linear expansion of polyethylene allows the pipe walls to stretch if water freezes there in winter;

polyethylene pipes do not require thermal insulation.

SDR marking

SDR (Standart Dimension Ratio) is the ratio of the outer diameter of a polyethylene (or any other) pipe to its wall thickness.

Thus, with an increase in the SDR indicator, the pipe wall becomes thinner, and vice versa, the wall thickness increases with a decrease in the indicator, i.e. the higher the SDR value, the thinner the pipe.

Previously, the indicator of the performance of polyethylene pipes was the MRS (Minimum Required Strength) standard, which shows the minimum load at which the pipes will remain intact and undamaged.

GOST 18599-2001, which has the name "Polyethylene pressure pipes", regulates the quality of pipes and describes their main technical specifications, including the diameters of polyethylene pipes.

PE-80 Pipe Marking

PE-80 pipes are made of medium pressure polyethylene material. They are often used when carrying out a water supply system in residential buildings, but they are not applicable for the main water system, because the thickness of the walls will not be able to withstand the pressure of a large flow of water.

Advantages of PE80 pipe:high wear resistance; light weight; long-term operation;environmental friendliness and safety during operation.

Pipes PE 80 SDR 21

Low pressure pipes used in private housing construction when carrying out a gravity sewage system in a small one-story building, as well as a drinking water supply system. They are not suitable for creating pressurized water systems in high-rise buildings, because thin walls will not withstand such a heavy load. Also, they cannot be buried in the ground, the soil pressure is fraught with an accident.

The SDR 21 marking indicates that under a constant load of 6 atmospheres at a water temperature of 20 ° C, the pipes will serve uninterruptedly for up to 50 years. They begin to deform at water temperatures above + 40 ° C.

Pipes PE 80 SDR 17

Polyethylene pipe SDR 17 is distinguished by the average value of the ratio of the outer diameter of pipes produced today to their wall thickness. Pipes PE 80 SDR 17 are recommended for use in a very wide range.For plumbing systems designed to supply drinking water, for water supply systems for household purposes from the facilities where water treatment is carried out to the consumer,also for the installation of irrigation systems.

The choice of these pipes for the installation of communications in a low-rise building is considered optimal, since during their installation they will ensure high strength, lightness of pipelines, and the cost of purchasing the material will be relatively low.

At a water temperature of 20 ° C, the pipes will withstand a load of 8 atmospheres. They are good in private housing construction, but such pipes are not suitable for high-rise buildings.

Pipes PE 80 SDR 13.6

Pipes PE 80 SDR 13.6 are low pressure pipes and are recommended for use when installing pipelines transporting cold drinking water,for various needs in country houses, as well as pipes allow you to move liquid food products (wine, juice, milk). Compared to cast iron or steel pipes, polyethylene counterparts are much stronger, while they are lightweight and are mounted by hot soldering.

They belong to the category of low-pressure polyethylene products, which makes them the most durable among the PE-80 brand. After all, its working pressure can be considered 10 atmospheres. The pipe walls are capable of withstanding the temperature range from -40 ° C to + 60 ° C, therefore they can be used in northern latitudes.

PE-100 Pipe Marking

Pipes of the PE-100 brand belong to the category of low pressure pipes and have high strength. They are considered more durable than counterparts with marking 80, therefore they are used for gasification and water supply.

Advantages of PE100 pipe:successfully withstand high pressure inside the pipe;incredibly durable, withstand any impact;easy to assemble and transport due to their low weight (there is a possibility of transportation "pipe in pipe" - with a difference in diameters).

PE 100 SDR 26

For the production of such pipes, PE100 polyethylene is used, the distinctive qualities of which are high density, due to which pipes made of this material are superior to products made of PE80. in many respects, including long-term strength and resistance to cracking.

These pipes are used for the transportation of household and drinking water in urban environments and outside the city, also use in sewage systems, when carrying out artesian wells, creating a reclamation system. In factories and factories, they serve to serve milk, juice or wine.

In addition, the quality indicators of the material made it possible to significantly reduce the thickness of the walls of the product, which facilitated its weight, but at the same time their throughput is 10-15% higher. The working pressure can be considered 6.3 atmospheres.

PE 100 SDR 21

Pipes PE 100 SDR 21 are used for the construction of water supply systems. Passing through pipes of this type, the water retains its taste and is characterized by the absence of extraneous odors.They are often used not only in suburban construction, to create amelioration and irrigation systems, when carrying out a suburban water supply system. High-strength polyethylene is able to withstand high pressure, and PE 100 SDR 21 pipes can be used as an element of a cold water supply system in high-rise buildings.

These pipes have excellent strength characteristics and are ideal for plumbing. They are compatible with metal pipes (steel, cast iron) using special adapters.Corrosion processes, other types of destruction and blockages are not terrible for such pipes.At constant water temperature +20 ° From the pipe they will be able to withstand a pressure of 8 atmospheres.

PE 100 SDR 17

Pipes marked PE 100 SDR 17 are new generation pipes. Their feature is uniquely high strength indicators, which has a significant impact on enhancing the performance of polyethylene pipes.They tolerate a constant pressure of 10 atmospheres well.

Pipes of this type are recommended for use in pressure water supply systems and gas pipelines. Moreover, such pipes are considered ideal for the installation of pipelines with a large cross section. In the manufacture of pipes of this type, material savings turn out to be very significant due to the possibility of reducing the wall thickness while maintaining the high strength of the product. Specifications such pipes allow their widespread use in the construction of pipelines, characterized by a large length.

PE 100 SDR 11

The PE100 SDR 11 pipe is made of low pressure polyethylene. At the same time, the high density of the material allows the use of such pipes for high-pressure water supply systems. The material used for the manufacture of pipes ensures high quality and environmental safety of drinking water.

Reliable and sturdy, they can withstand a constant pressure of 16 atmospheres for 50 years. Such reliability and tolerance to aggressive media makes it possible to use these pipes for gasification settlements... They are not afraid of stray currents, they can easily withstand variable ground loads. Pipes of this brand can be laid by pulling in the ground. The density of polyethylene allows them to be used as sewers.

Pipes PE 100 RC

Single and multilayer pipes for water supply systems made of PE 100 RC.The pipes are made of a new material, 4th generation polyethylene grade PE 100 RC (Resistance Crack), with increased resistance to the appearance and propagation of cracks(in terms of resistance to MRI (slow cracking of cracks), polyethylene PE 100RC is several times superior to traditional PE100).

Subject to the rules of installation and operation, the service life of networks made of PE100 RC pipes is 100 years.

Such pipes are designed for laying wastewater systems and water pipelines in difficult geological and climatic conditions. Applicable for:construction of pressure-type water supply and sewerage pipelines;construction of gas pipelines;traditional trenching without sand bed;pipe-in-pipe reconstruction;trenchless installation by various methods, including HDD and "puncture".

Pipes of this type: MULTIPIPE pipes

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Polyethylene is a synthetic thermoplastic non-polar polymer belonging to the class of polyolefins. Ethylene polymerization product. White solid. Produced in the form of low-pressure polyethylene (high-density polyethylene) obtained by slurry polymerization of ethylene at low pressure on complex organometallic catalysts in suspension or by gas-phase polymerization of ethylene in the gas phase on complex organometallic catalysts on a carrier, and high-pressure polyethylene (low-density polyethylene) obtained at high pressure by polymerization of ethylene in tubular reactors or reactors with a stirring device using radical initiators. In addition, there are several subclasses of polyethylene that differ from the traditional in higher performance characteristics. In particular, ultra-high molecular weight polyethylene, linear low density polyethylene, polyethylene obtained on metallocene catalysts, bimodal polyethylene.
As a rule, polyethylene is produced in the form of stabilized granules with a diameter of 2-5 millimeters in a colored and unpainted form. But industrial production of polyethylene in powder form is also possible.

The usual designation for polyethylene in the Russian market is PE, but other designations can also be found: PE (polyethylene), LDPE or LDPE or LDPE or PEBD or PELD (low density polyethylene, high density polyethylene), HDPE or HDPE or HDPE or PEHD (high density polyethylene) low density polyethylene), LDPE or MDPE or PEMD (medium density polyethylene), ULDPE (ultra low density polyethylene), VLDPE (very low density polyethylene), LLDPE or LLDPE or PELLD (linear low density polyethylene), LMDPE (linear low density polyethylene) density), HMWPE or PEHMW or VHMWPE (high molecular weight polyethylene). HMWHDPE (high molecular weight polyethylene), PEUHMW or UHMWPE (ultra high molecular weight polyethylene), UHMWHDPE (ultra high molecular weight polyethylene), PEX or XLPE (cross-linked polyethylene), PEC or CPE (chlorinated polyethylene), polyethylene or EPE (foamed) metallocene linear low density polyethylene).

The conventional designation of the domestic suspension low-pressure polyethylene consists of the name of the material "polyethylene", eight digits characterizing a specific brand, and the designation of the standard in accordance with which the polyethylene is made.
The first number 2 indicates that the ethylene polymerization process takes place on complex organometallic catalysts at low pressure. The next two digits indicate the serial number of the base brand. The fourth digit indicates the degree of homogenization of the polyethylene. Low-pressure polyethylene is subjected to averaging by cold mixing, which is indicated by the number 0. The fifth digit conventionally defines the density group of polyethylene:
6 - 0.931-0.939 g / cm 3;
7 - 0.940-0.947 g / cm 3;
8 - 0.948-0.959 g / cm 3;
9 - 0.960-0.970 g / cm 3.
When determining the density group, the average density of a given brand is taken. The following numbers, separated by a dash, indicate the tenfold average value of the melt flow rate of a given grade.
An example of the designation of the base grade of suspension low-pressure polyethylene with the serial number of grade 10, averaged by cold mixing, with a density of 0.948-0.959 g / cm 3 and an average melt flow rate of 7.5 g / 10 min:
Polyethylene 21008-075 GOST 16338-85.
The designation of a low-pressure polyethylene composition that does not contain a dye additive consists of the name of the material "polyethylene", the first three digits of the base brand designation, the number of the additive formulation, written through a dash, and the designation of the standard according to which the polyethylene is made.
An example of the designation of a composition of suspension low-pressure polyethylene of base grade 21008-075 with additives in accordance with recipe 04:
Polyethylene 210-04 GOST 16338-85.
An example of the designation of a composition of gas-phase low-pressure polyethylene grade 271 with additives in accordance with recipe 70:
Polyethylene 271-70 GOST 16338-85.
The designation of the composition of low-pressure polyethylene with the addition of a dye consists of the name of the material "polyethylene", the first three digits of the base brand, the number of the additive recipe (if any) written through a dash, the name of the color written through a comma, a three-digit number indicating the color recipe, and the designation of the standard , according to which the polyethylene is made.
An example of the designation of the base grade of low-pressure polyethylene 21008-075 and composition 210-04 based on it, colored red according to recipe 101:
Polyethylene 210, red rec. 101 GOST 16338-85,
Polyethylene 210-04, red rec. 101 GOST 16338-85.

Basic grades of suspension low-pressure polyethylene: 20108-001; 20208-002; 20308-005; 20408-007; 20508-007; 20608-012; 20708-016; 20808-024; 20908-040; 21008-075.

Basic grades of gas-phase low-pressure polyethylene: 271-70; 271-82; 271-83; 273-71; 273-73; 273-79; 273-80; 273-81; 276-73; 276-75; 276-83; 276-84; 276-85; 276-95; 277-73; 277-75; 277-83; 277-84; 277-85; 277-95.

The conventional designation of domestic high-pressure polyethylene consists of the name "polyethylene", eight numbers, grade and designation of the standard in accordance with which the polyethylene is made.
The first number - 1 indicates that the ethylene polymerization process takes place at high pressure in tubular reactors or reactors with a stirrer device using radical initiators.
The next two digits indicate the serial number of the base brand. The fourth digit indicates the degree of homogenization of the polyethylene:
0 - without homogenization in the melt;
1 - homogenized in the melt.
The fifth digit conventionally defines the density group of polyethylene, g / cm 3.
1 – 0,900-0,909
2 – 0,910-0,916
3 – 0,917-0,921
4 – 0,922-0,926
5 – 0,927-0,930
6 – 0,931-0,939
When determining the density group, take its nominal value for a given brand.
The following numbers, separated by a dash, indicate ten times the melt flow rate.
An example of the designation of high-pressure polyethylene of the serial number of grade 15, without homogenization in the melt, with a density of 0.917-0.921 g / cm 3 and a nominal value of the melt flow rate of 7 g / 10 min of the 1st grade:
Polyethylene 11503-070, grade 1, GOST 16337-77
The designation of high-pressure polyethylene compositions consists of the name of the material "polyethylene", the first three digits of the base brand designation, the number of the additive recipe, written through a dash, the colors and recipes of dyeing, the grade and designation of the standard in accordance with which the polyethylene is made.
An example of the designation of a composition of high-pressure polyethylene of the base grade 10204-003 with additives in accordance with recipe 03, 1st grade:
Polyethylene 102-03, grade 1, GOST 16337-77
In the case of colored HDPE compositions, a color and a three-digit number indicating the color formulation are added to the designation.
An example of the designation of a composition of high-pressure polyethylene of the base grade 10204-003, painted pink according to recipe 104, 1st grade:
Polyethylene 102, pink 104, grade 1, GOST 16337-77
In the designation of high-pressure polyethylene intended for the manufacture of films for various purposes, products in contact with food, drinking water, cosmetic and drugs, toys, as well as polyethylene subject to long-term storage, additionally indicate the corresponding purpose.

Basic grades of high-pressure polyethylene obtained in reactors with a stirring device: 10204-003; 10604-007; 10703-020; 10803-020; 11304-040; 11503-070; 12003-200; 12103-200.

Basic grades of high-pressure polyethylene obtained in tubular reactors: 15003-002; 15303-003; 15503-004; 16305-005; 17603-006; 17504-006; 16005-008; 17703-010; 16603-011; 17803-015; 15803-020; 16204-020; 16405-020; 18003-030; 18103-035; 16904-040; 18203-055; 16803-070; 18303-120; 17403-200; 18404-200.

In the cable industry, compositions based on high pressure (low density) and low pressure (high density) polyethylene with stabilizers and other additives are used, intended for the application of insulation, sheaths and protective covers of wires and cables by extrusion.
Grades of polyethylene compositions for the cable industry are established on the basis of basic grades of high-pressure polyethylene 10204-003, 15303-003, 10703-020, 18003-030, 17803-015 and additive formulations 01, 02, 04, 09, 10, 93-97, 99, 100, grade 10703-020 and formulations 61 and low-pressure polyethylene (suspension method) 20408-007, 20608-012, 20708-016, 20808-024 and formulations of additives 07, 11, 12, 19, 57 low-pressure polyethylene ( gas-phase method) based on grade 271-powder and formulations of additives 70, 82, 83, grade 273-powder and formulations of additives 71, 81.
The designation of grades of polyethylene compositions for the cable industry consists of the name of the material "polyethylene", the first three digits of the designation of the base grade of polyethylene, the number of the additive formulation, written through a dash, and the letter "K", denoting the use of polyethylene compositions in the cable industry, and the designation of the standard, in according to which polyethylene is made for the cable industry.
Example symbol compositions for the cable industry based on high-pressure polyethylene of base grade 10204-003 with additives in accordance with recipe 09:
Polyethylene 102-09K GOST 16336-77
An example of a conventional designation of a composition for the cable industry based on low-pressure polyethylene of the base grade 20408-007 with additives in accordance with recipe 07:
Polyethylene 204-07K GOST 16336-77

When ordering polyethylene, the grade is indicated after the brand designation. For polyethylene intended for the manufacture of electrical products and products in contact with food, drinking water, cosmetic and medicinal products, toys in contact with and not in contact with the oral cavity, as well as for polyethylene subject to long-term storage, the corresponding purpose is additionally indicated.

But there are other grades of polyethylene on the market, since most manufacturers work in accordance with their own specifications, reflecting the development of the industry. polymer materials, which the standardization system does not always keep up with.

Structure: Polyethylene is a polymerization product of ethylene, the chemical formula of which is C 2 H 4. In the process of polymerization, the double bond of ethylene is broken and a polymer chain is formed, the elementary link of which consists of two carbon atoms and four hydrogen atoms:

N N
- C - C -
H H During polymerization, branching of the polymer chain can occur when a short polymer group is attached laterally to the growing backbone.
The branching of the polymer chain prevents the dense packing of macromolecules and leads to the formation of a loose amorphous-crystalline structure of the material and, as a consequence, to a decrease in the density of the polymer and a decrease in the softening temperature. The different degree of branching of the polymer chain of high and low pressure polyethylenes determines the difference in the properties of these materials.
So, for high-pressure polyethylene, the branching of the chain is 15-25 branches per 1000 carbon atoms of the chain, and for low-pressure polyethylene - 3-6 per 1000 carbon atoms of the chain. Accordingly, the density, melting and softening points, the degree of crystallinity in LDPE, which is also called "branched-chain polyethylene", is lower than that of HDPE, the polymerization method of which causes low branching.

Properties: Polyethylene is a plastic material with good dielectric properties. Shock-resistant, non-breaking, with little absorption. Physiologically neutral, odorless. It has low vapor and gas permeability. Polyethylene does not react with alkalis of any concentration, with solutions of any salts, carboxylic, concentrated hydrochloric and hydrofluoric acids. Resistant to alcohol, gasoline, water, vegetable juices, oil. Destroyed by 50% nitric acid, as well as liquid and gaseous chlorine and fluorine. Insoluble in organic solvents and swells to a limited extent in them. Polyethylene is resistant to heating in vacuum and inert gas atmosphere. But in air it degrades when heated already at 80 ° C. Resistant to low temperatures down to -70 ° С. Under the influence of solar radiation, especially ultraviolet rays, it undergoes photodegradation (soot, benzophenone derivatives are used as light stabilizers). It is practically harmless, substances hazardous to human health are not released from it into the environment.
Polyethylene is easily recyclable by all major plastics processing methods. Easy to modify. Through chlorination, sulfonation, bromination, fluorination, it can be given rubbery properties, improved heat resistance, chemical resistance. By copolymerization with other olefins, polar monomers, to increase resistance to cracking, elasticity, transparency, adhesion characteristics. By mixing with other polymers or copolymers to improve the toughness and other physical properties.
The chemical, physical and operational properties of polyethylene depend on the density and molecular weight of the polymer, and therefore are different for different types polyethylene. For example, LDPE (branched chain polyethylene) is softer than HDPE, therefore HDPE films are stiffer and denser than HDPE films. Their tensile and compressive strength is higher, the tear and impact resistance is lower, and the permeability is 5-6 times lower than that of LDPE films.
Ultra-high molecular weight polyethylene with a molecular weight of more than 1,000,000 has increased strength properties. The temperature range of its operation is from -260 to +120 ° С. It has a low coefficient of friction, high wear resistance, resistance to cracking, chemical resistance in the most aggressive environments.

HDPE properties in accordance with GOST 16338-85.
1. Density - 0.931-0.970 g / cm 3.
2. Melting temperature - 125-132 ° С.
3. Vicat softening temperature in air - 120-125 ° С.
4. The bulk density of the granules is 0.5-0.6 g / cm 3.
5. Bulk density of the powder - 0.20-0.25 g / cm 3.
6. Breaking stress in bending -19.0-35.0 MPa
7. Ultimate shear strength - 19.0-35.0 MPa.
8. Hardness of ball indentation under a given load - 48.0-54.0 MPa.
9. Specific surface electrical resistance - 10 14 ohms.
10. Specific volumetric electrical resistance - 10 16 -10 17 Ohm · cm.
11. Water absorption in 30 days - 0.03-0.04%.
12. The tangent of the angle of dielectric losses at a frequency of 10 10 Hz - 0.0002-0.0005.
13. Dielectric constant at a frequency of 10 10 Hz - 2.32-2.36.
14. Specific heat at 20-25 ° С - 1680-1880 J / kg · ° С.
15. Thermal conductivity - (41.8-44) · 10 -2 V / (m · ° С).
16. Linear coefficient of thermal expansion - (1.7-2.0) · 10 -4 1 / ° С.

LDPE properties in accordance with GOST 16337-77.
1. Density - 0.900-0.939 g / cm 3.
2. Melting temperature - 103-110 ° С.
3. Bulk density - 0.5-0.6 g / cm 3.
4. Hardness of ball indentation under a given load - (1.66-2.25) · 10 5 Pa; 1.7-2.3 kgf / cm 2.
5. Shrinkage during casting - 1.0-3.5%.
6. Water absorption in 30 days - 0.020%.
7. Breaking stress in bending - (117.6-196.07) · 10 5 Pa; 120-200 kgf / cm 2.
8. Tensile strength - (137.2-166.6) · 10 5 Pa; 140-170 kgf / cm 2.
9. Specific volumetric electrical resistance - 10 16 -10 17 Ohm · cm.
10. Specific surface electrical resistance - 10 15 ohms.
11. Brittleness temperature for polyethylene with a melt flow rate in g / 10 min
0.2-0.3 - not higher than minus 120 ° С,
0.6-1.0 - not higher than minus 110 ° С,
1.5-2.2 - not higher than minus 100 ° С,
3.5 - not higher than minus 80 ° С,
5.5 - not higher than minus 70 ° С,
7-8 - not higher than minus 60 ° С,
12 - not higher than minus 55 ° С,
20 - not higher than minus 45 ° С.
12. Modulus of elasticity (secant) for polyethylene with a density in g / cm 2
0.917-0.921 - (882.3-1274.5) · 10 5 Pa; 900-1300 kgf / cm 2,
0.922-0.926 - (1372-1764.7) · 10 5 Pa; 1400-1800 kgf / cm 2,
0.928 - 2107.8 10 5 Pa; 2150 kgf / cm 2.
13. The tangent of the angle of dielectric losses at a frequency of 10 10 0 Hz - 0.0002-0.0005.
14. Dielectric constant at a frequency of 10 10 Hz - 2.25-2.31.

Comparative analysis of the characteristics of HDPE and LDPE shows that HDPE, due to its higher density, has higher strength characteristics: heat resistance, stiffness and hardness, is more resistant to solvents than LDPE, but less frost resistance. The high-frequency electrical characteristics are somewhat worse than that of LDPE (due to catalyst residues), but this does not limit the use of HDPE as an electrical insulating material. In addition, the presence of catalyst residues does not allow the use of HDPE in contact with food (cleaning of catalysts is required). Due to the denser packing of macromolecules, the permeability of HDPE is approximately 5-6 times lower than that of LDPE. In terms of chemical resistance, HDPE also surpasses LDPE (especially in terms of resistance to oils and fats). But LDPE films are more permeable to gases, and therefore unsuitable for packaging products that are sensitive to oxidation.

Receiving: In industry, polyethylene is obtained by polymerizing ethylene at high (LDPE, LDPE) and low pressures (HDPE, HDPE).

High pressure (low density) polyethylene is obtained by polymerizing ethylene at high pressure in tubular reactors or stirred tank reactors using radical initiators.
High-pressure polyethylene is produced without additives - basic grades, or in the form of compositions based on them with stabilizers and others and additives in colored and unpainted form.

Low pressure (high density) polyethylene is obtained by slurry polymerization of ethylene at low pressure on complex organometallic catalysts in suspension or by gas-phase polymerization of ethylene in the gas phase on complex organometallic catalysts on a carrier or by polymerization of ethylene in solution in the presence of a titanium-magnesium catalyst or CrO 3 on silica gel.
Polyethylene obtained by the suspension method (suspension polyethylene) is produced without additives (basic grades) and in the form of compositions based on them with stabilizers, dyes and other additives.
Polyethylene obtained by gas-phase method (gas-phase polyethylene) is produced in the form of compositions with stabilizers.

The polymerization process at high pressure proceeds according to a radical mechanism, the initiators are oxygen, peroxides, for example, lauryl or benzoyl, or mixtures thereof.
In the production of LDPE in a tubular reactor, ethylene mixed with an initiator, compressed by a compressor to 25 MPa and heated to 70 ° C, enters first into the first zone of the reactor, where it is heated to 180 ° C, and then into the second, where it polymerizes at 190-300 ° C and a pressure of 130-250 MPa. The average residence time of ethylene in the reactor is 70-100 s, the degree of conversion is 18-20%, depending on the amount and type of initiator. Unreacted ethylene is removed from the polyethylene, the melt is cooled to 180-190 ° C and granulated. The granules, cooled with water to 60-70 ° C, are dried with warm air and packed in bags.
The schematic diagram of LDPE production in an autoclave with a stirring device differs from production in a tubular reactor in that the initiator in paraffin oil is supplied by a special high-pressure pump directly into the reactor. The process is carried out at 250 ° C and a pressure of 150 MPa. The average residence time of ethylene in the reactor is 30 s. The conversion is about 20%.
Commercial high-pressure polyethylene is produced colored and unpainted, in granules with a diameter of 2-5 mm.

The polymerization process at low pressure proceeds according to the coordination-ionic mechanism.
Obtaining HDPE in suspension includes the following stages: preparation of a catalyst suspension and an activator solution in the form of a combination of triethylaluminum and titanium derivatives; polymerization of ethylene at a temperature of 70-95 ° C and a pressure of 1.5-3.3 MPa; removal of solvent, drying and granulation of polyethylene. The conversion of ethylene is 98%. The concentration of polyethylene in suspension is 45%. The unit capacity of reactors with an improved heat removal system is up to 60-75 thousand tons / year.
The technological scheme for obtaining HDPE in solution is carried out, as a rule, in hexane at 160-250 ° C and a pressure of 3.4-5.3 MPa in the presence of a titanium-magnesium catalyst or CrO 3 on silica gel. The contact time with the catalyst is 10-15 minutes. Polyethylene is isolated from the solution by removing the solvent sequentially in the evaporator, separator and vacuum chamber of the granulator. Polyethylene granules are steamed with water vapor at a temperature exceeding the melting point of polyethylene, so that low molecular weight fractions of polyethylene pass into water and the catalyst residues are neutralized. The advantages of polymerization in solution over polymerization in suspension are that the stages of squeezing and drying of the polymer are excluded, it becomes possible to utilize the heat of polymerization for evaporation of the solvent, and the regulation of the molecular weight of polyethylene is facilitated.
Gas-phase polymerization of ethylene is carried out at 90-100 ° C and a pressure of 2 MPa with chromium-containing compounds on silica gel as a catalyst. In the lower part, the reactor has a perforated grid for uniform distribution of the supplied ethylene in order to create a fluidized bed, in the upper part there is an expanded zone designed to reduce the gas velocity and trap particles of the formed polyethylene.
Commercial low-pressure polyethylene is produced colored and unpainted, usually in granules with a diameter of 2-5 mm, less often in the form of a powder.

The use of various catalysts makes it possible to commission varieties of polyethylene with improved performance.
Thus, polymerization in a solvent in the presence of Co, Mo, V oxides at 130-170 ° C and a pressure of 3.5-4 MPa produces medium-pressure polyethylene (PESD), the chain branching of which is less than 3 branches per 1000 carbon atoms, which increases its strength. quality and heat resistance compared to HDPE.
Metallocene catalysts enable controlled polymerization along the chain length, which makes it possible to obtain polyethylene with desired consumer characteristics.
If the polymerization process takes place at low pressure in the presence of organometallic compounds, then polyethylene with a high molecular weight and a strict linear structure is obtained, which, unlike conventional HDPE, has increased strength characteristics, a low coefficient of friction and high wear resistance, resistance to cracking, chemical resistance in the most aggressive environments.
By chemical modification of LDPE, we obtained linear low-density polyethylene - LLDPE, which is a light elastic crystallizable material with Vicat heat resistance up to 118 ° C. More resistant to cracking, has greater impact strength and heat resistance than LDPE.
By filling the LDPE with starch, a material of interest as a biodegradable material can be obtained.

The main manufacturers of low-density polyethylene for the Russian market:
Stavrolen - in particular, Stavrolen PE4FE69, Stavrolen PE4EC04S, Stavrolen PE3IM61, Stavrolen PE0BM45, Stavrolen PE3OT49, Stavrolen PE4BM42, Stavrolen, PE4BM50V, Stavrolen PE4BM41, Stavrolen REEC05, Stavrolen PE4RP25V;
Kazanorgsintez - in particular, HDPE 277-73, HDPE 276-73, HDPE 293-285D, HDPE 273-83, HDPE PE80B-275, HDPE PE80B-285D, HDPE 273-79;
Shurtan Gas Chemical Complex - in particular, B-Y456, B-Y460, I-0760, I-1561.

The main manufacturers of high density polyethylene for the Russian market:
Kazanorgsintez - in particular, LDPE 15813-020, LDPE 15313-003, LDPE 10803-020;
Tomskneftekhim - in particular, LDPE 15803-020, LDPE 15313-003;
Ufaorgsintez - in particular, LDPE 15803-020.

The main manufacturers of polyethylene of cable grades for the Russian market:
Kazanorgsintez - in particular, LDPE 153-02K, LDPE 153-10K, 271-274K;
Shurtan Gas Chemical Complex - in particular, WC-Y436.

Polyethylene of pipe grades P-Y337 MDPE, P-Y342 HDPE, P-Y456 HDPE is produced by Shurtan Gas Chemical Complex. The same enterprise produces film polyethylene F-Y346, F-0220S, F-0120S, F0120, F0220.

Application: Polyethylene is the most widely used polymer. It is the leader in the world production of polymeric materials - 31.5% of the total volume of produced polymers. Manufacturing technology of polyethylene products is relatively simple. It can be processed by all known methods. It can be welded by all main methods: hot gas, filler rod, friction, resistance welding.
Working with polyethylene does not require the use of highly specialized equipment, such as for PVC processing, and modern industry produces hundreds of brands of additives and dyes to give polyethylene products a wide variety of consumer qualities.
Using injection molding, a wide range of household goods, stationery, and toys is made from polyethylene. When using extrusion, polyethylene pipes are obtained (there are special brands - pipe PE63, PE80, PE100), polyethylene cables (cross-linked polyethylene is very promising), polyethylene sheets for packaging and construction, as well as a wide variety of polyethylene films for the needs of all industries. Extrusion blow molding and rotational molding of polyethylene create all sorts of containers, vessels, containers. Thermal vacuum forming - a variety of packaging materials. Various special types polyethylene, such as cross-linked, foamed, chlorosulfonated, ultra-high molecular weight, are successfully used to create special building materials. Separate segment modern market- recycling of polyethylene. Many companies in Russia and the world specialize in the purchase of polyethylene waste with further processing and sale or use of recycled polyethylene. As a rule, for this, the technology of extrusion of purified waste is used, followed by crushing and obtaining a secondary granular material suitable for the manufacture of products.
The most widely used polyethylene for the production of films for technical and household purposes. The advantages of all types of polyethylene for packaging purposes: low density, good chemical resistance, low water absorption, good transparency, easy processability, good weldability, water vapor impermeability, high viscosity, flexibility, extensibility and elasticity. Plastic films are used for the production of bags for bread, vegetables, meat, poultry, garbage bags, packaging films for securing loads. LDPE is used for the production of combined films by coextrusion with other thermoplastic polymers and for application on paper, cardboard, cellophane, aluminum foil. In all these combined films, the LDPE layer gives the film excellent weldability, and the other layers give strength and odor resistance. To obtain certain properties, the polyethylene is converted with vinyl acetate. These films, with good strength, are more transparent and weld better. Due to this, when heated and adhered to other materials, they also become suitable for application to cardboard and other packaging materials. Domestic copolymer of ethylene with vinyl acetate, obtained by joint polymerization of ethylene and vinyl acetate in bulk under high pressure, is known under the Sevilen trademark, which is widely used in the production of coiled hoses for air suction from various equipment.
Polyethylene is used for the production of:
films: agricultural, packaging, shrink, stretch;
pipes: gas, water supply, pressure, non-pressure;
containers: tanks, cans, bottles;
building materials;
fibers;
household items;
sanitary ware;
parts of cars and other equipment;
insulation of electrical cables;
polyethylene foam;
internal organs prostheses;
And this is far from the limit of the possibilities of using polyethylene. Moreover, new brands of this polymer with new consumer properties are constantly entering the market.
For example, ultra-high molecular weight polyethylene (UHMWPE), used for the manufacture of high-strength technical products that are resistant to impact, cracking and abrasion: gears, bushings, couplings, rollers, rollers, sprockets, as well as insulating parts of equipment operating in the range of high and ultra-high frequencies. In addition, UHMWPE is widely used in the manufacture of porous products: filters, noise mufflers, gaskets, and in endoprosthetics - in the creation of joints, cranial and maxillofacial prostheses.

The main brands of polyethylene produced:
High density polyethylene composition PE2NT26-16
Sevilen's composition 113-27
Sevilen's composition 113-31
Linear low density polyethylene F-0120
Linear low density polyethylene F-0220
Linear low density polyethylene F-Y620
Linear low density polyethylene F-Y720
High-pressure polyethylene (LDPE) 15303-003 GOST 16337-77 premium grade
High pressure polyethylene (LDPE) 15303-003 GOST 16337-77 first grade
High pressure polyethylene (LDPE) 15803-020 GOST 16337-77 premium grade
High pressure polyethylene (LDPE) 15803-020 GOST 16337-77 first grade
High density polyethylene B-Y250
High density polyethylene B-Y456
High density polyethylene B-Y460
High density polyethylene F-Y346
High density polyethylene I-0754
High density polyethylene I-0760
High density polyethylene I-1561
High density polyethylene O-Y446
High density polyethylene O-Y750
High density polyethylene O-Y762
High density polyethylene P-Y342
High density polyethylene P-Y456
High molecular weight polyethylene of low pressure 21606 of the second grade
High-molecular low-pressure polyethylene 21606 of the first grade
Polyethylene for the cable industry 153-01K GOST 16336-77 of the highest grade
Polyethylene for the cable industry 153-01K GOST 16336-77, first grade
Polyethylene for the cable industry 153-02K GOST 16336-77 of the highest grade
Polyethylene for the cable industry 153-02K GOST 16336-77 of the first grade
Polyethylene for the cable industry 153-10K GOST 16336-77 of the highest grade
Polyethylene for the cable industry 153-10K GOST 16336-77, first grade
Polyethylene grade HFP-4612H
Polyethylene grade HMI-6582M
Polyethylene grade HXF 4810H
Polyethylene grade HXF-4607
Polyethylene grade HXF-5115
Polyethylene grade LLI-2420
Polyethylene grade MXP-3920H
Polyethylene brand SHF-2680РН
SHF-3080H polyethylene
Polyethylene grade SMF 2210
Polyethylene grade SMF-1810
Polyethylene brand SMF-1810H
Polyethylene grade НХВ 5115Н
Polyethylene grade НХВ 5210Н
Low pressure polyethylene grade 271-70 K
Low-pressure polyethylene grade 271-81 K
Low pressure polyethylene grade 273-79
Low pressure polyethylene grade 273-83
Low pressure polyethylene grade 276-73
Low pressure polyethylene grade 277-73
Low pressure polyethylene grade F 3802B
Low pressure polyethylene grade PE 3 OT 49
Low pressure polyethylene grade PE 4 BM 41
Low pressure polyethylene grade PE 4 FE 69
Low pressure polyethylene grade PE 4 EC 04S
Low pressure polyethylene grade PE 4 PP 21 V
Low pressure polyethylene grade PE 4 PP 25 V
Low pressure polyethylene grade PE 6 GP 26 B
Low density polyethylene I-0525
Low density polyethylene I-1625
Low density polyethylene WC-Y436
Low density polyethylene WC-Y736
Medium density polyethylene F-Y240
Medium density polyethylene F-Y336
Medium density polyethylene P-Y337
Medium density polyethylene R-0333 U
Medium density polyethylene R-0338 U
Sevilen 11104-030
Sevilen 11205-040
Sevilen 11306-075
Sevilen 11407-027
Sevilen 11507-070
Sevilen 11607-040
Sevilen 11708-210
Sevilen 11808-340
Sevilen 11908-125
Sevilen 12206-007
Sevilen 12306-020
Sevilen 12508-150

In recent years, polyethylene pipes (PE) have been widely used, especially in the construction industry. PE pipes are used in the construction of gas pipelines, water pipelines, swimming pools are equipped with it, irrigation is automated, and are widely used in other industries. By itself, polyethylene is a thermoplastic material; it is obtained by polymerizing a petroleum product. In this article, we will look at the characteristics of various types of products and figure out what the marking "SDR PE pipe" means.

The equipment used for the production of such pipes is not bulky and complex. and are made of various diameters in accordance with GOST, the corresponding marking is applied to them. Depending on the purpose, they differ in characteristics, each type of PE pipe has a corresponding brand.

Polyethylene grades

PE 80, PE 63, PE 100 grade corresponds to the strength index MRS 8; 6,3 and 10, i.e. means the minimum long-term strength of the polyethylene from which these pipes are made. Pipe polyethylene of these grades is obtained from a rigid polymer with a linear structure and a high degree of crystallinity. These products have good resistance to most inorganic and organic acids, petroleum hydrocarbons, alkalis, salt, etc.

Polyethylene grades PE 100, PE 80 and PE 63 have become widespread at the present time, its main distinguishing feature is density, strength and, of course, cost.

The PE 32 SDR pipe is also produced, its quality is regulated, the scope of its use is water supply (at a nominal pressure of 2.5 atm.) And sewerage.

It seems that PE 100 is the most reliable, durable and cheaper grade of polyethylene, in fact, each of these grades has its own individual application.

In addition, such pipes have a visual difference depending on the purpose. For example, pipes with a blue (blue) stripe are used for installing a drinking water supply system, and products with a yellow stripe are used for laying a gas pipeline.

PE 100 pipe

It is characterized by high working pressure, maximum tensile strength and resistance to mechanical stress. For its manufacture, certified raw materials are used. Qualitative characteristics made it possible to reduce the thickness of the walls of these products and reduce their weight. Pipes of this brand are most often used for the following purposes:

water and gas pipelines;
arrangement of pipelines for feeding food products in liquid form (juices, milk, wine, beer, etc.).

These products are wear-resistant, quite lightweight, medium-pressure plastic is used for their manufacture. Pipes of this brand belong to low-pressure pipes, the main purpose of which is to install low-pressure and non-pressure in apartment buildings. In addition, they can be used for the device of pressurized water supply of small diameter in a small area.

The products are certified and can be used for their intended purpose.

At the same time, experts do not recommend using them in a number of cases. Due to the small wall thickness, it is not recommended to install a gas pipeline and a main pipeline from such products.

PE pipe 63

Polyethylene of this brand contains mainly ethylene molecules, it is characterized by short-term strength, at the same time it is prone to cracking and collapsing. Due to these characteristics, it is less often used in civil and industrial construction for the construction of drainage systems for road communications, basements of buildings, foundations and sites.

These pipes find application in laying and fiber-optic lines, where they are used as a case for engineering communications. Sometimes these pipes are used in agriculture, with their help, water drainage is organized from waterlogged areas and swamps.

Polyethylene pipe and its SDR

What is SDR

One of the main indicators characterizing a PE pipe is SDR. It displays the ratio of the outer diameter of a polyethylene pipe and the thickness of its wall, it is calculated according to the table or by the formula:

SDR = D / s, where

D = outer diameter of the PE pipe (mm);
s = tube wall thickness (mm).

This indicator characterizes the strength of the pipe: the higher it is, the weaker the pipe and vice versa.

Accordingly, a product with a low SDR is able to withstand more pressure than a similar product, but with a higher value. Thus, polyethylene pipes whose wall thickness is more capable of withstanding a rather tangible pressure.

The ability of polyethylene to be stable and neutral to gaseous and liquid substances determined the scope of its application. In addition to gas and water mains, PE pipes are used for the transportation of gaseous and liquid materials and for other purposes.

Polyethylene pipes with different SDR

Each type of pipe has its own characteristics, consider them:

Polyethylene grade 100:
- The PE 100 SDR 17 pipe is indispensable in gas pipelines and pressure water supply systems, especially in large pipelines cross section... Its technical characteristics make it possible to use such pipes for the installation of a long-distance pipeline. Such a polyethylene pipe SDR 17 belongs to a new generation of products, which is obtained by using modern technologies used in the manufacture of PE 100. Excellent performance characteristics of pipes made of this material are achieved due to the high strength properties of polyethylene.
- Polyethylene pipe SDR 11 is made from low pressure polyethylene. Moreover, its high density makes it possible to use these products on high pressure water pipelines. In addition, this type can be used for the construction of sewer collectors due to its resistance to aggressive environments. Installation can be carried out in almost any soil.
- Products made of PE 100 polyethylene, such as the SDR 26 PE pipe, can withstand pressures up to 6.3 atm., Are mainly used in non-critical water supply systems, in gravity sewers and to protect communications.
- The SDR 21 grade 100 PE pipe - its main purpose is to install water supply systems, according to experts in this product, the water does not have an off-taste and retains its taste well.

Polyethylene grade 80:
- A product such as a pipe PE 80 SDR 11 belongs to a new generation of products, the characteristics are much higher than those of PE 63. Its main purpose is cold water supply, in addition, if necessary, it can be used for sewerage and gasification.
- The PE 80 SDR 13.6 pipe is used for the installation and repair of water pipelines and pipes for liquid chemicals, to which polyethylene is neutral.
- Pipes PE 80 SDR 17 are the best choice for low-rise construction, as they have sufficient strength for it and at the same time affordable cost.

The PE 63 SDR 11 pipe is made from different kinds of polymers. It can be used for piping in the water supply system, as sewer pipes, and also as a protective case for communications and power supply.

Benefits of using PE pipes

The wide range of applications of these products is explained by many advantages over their counterparts made of metal, such as:

polyethylene products have a warranty period of about 50 years;
they are not susceptible to moisture, aggressive environment, corrosion, stray currents, do not need cathodic protection;
are lightweight;
installation is simple, while maximum tightness is achieved, and there is no need for professional equipment;
pipes are frost-resistant, do not burst even when water freezes in them;
Due to the ideal inner surface of the pipe, no deposits form on the walls;
prices for the purchase and installation of pipes are reasonable.

Polyethylene is a thermoplastic polymer with a relatively low hardness, odorless and tasteless. Various methods studies (microscopic, X-ray and electron diffraction, etc.) show that polyethylene has a crystal structure similar to the structure of normal paraffins (for example, C60H122, etc.). The degree of crystallinity of the polymer obtained by polymerization of ethylene does not reach 100%: along with the crystalline phase, there is always an amorphous one. The ratio of these phases depends on the method of obtaining the polymer and the temperature. Like high melting waxes and paraffins, it ignites slowly and burns with a weak flame without soot. In the absence of oxygen, polyethylene is stable up to 290 ° C. Within the range of 290 - 350 ° C, it decomposes into low molecular weight polymers such as wax, and above 350 ° C, the decomposition products are low molecular weight liquid substances and gaseous compounds - butylene, hydrogen, carbon monoxide, carbon dioxide, ethylene, ethane, etc.

1.1. Molecular structure of polyethylene

A polyethylene molecule is a long chain of methylene groups containing some side groups. The more side groups in the polymer chain and the longer they are (the polymer has a branched structure), the lower the degree of crystallinity. Typically, in low density polyethylene, there is one methyl group per 30 carbon atoms, however, polymers can be obtained containing one methyl group per 10 carbon atoms and 1000 or more carbon atoms. Research shows that methyl groups are most commonly found at the ends of side chains of at least four carbon atoms:

Insufficiently ordered regions of polymer molecules constitute amorphous regions. The fact that the size of the amorphous regions increases in proportion to the degree of branching of the molecule allows us to conclude that parts of the branched molecules enter the amorphous regions.

In the molten state, polyethylene is in an amorphous state. Regardless of the rate of cooling of the melt, polyethylene is not obtained completely in the amorphous state even upon instant cooling of thin films with liquid air. The rapid crystallization of polyethylene can be explained by the short length of the elementary units (2, 53 Å), corresponding to one zigzag of the carbon chain, the high symmetry of the molecules, and their arrangement in the form of a bundle. The bundles are much longer than macromolecules and consist of many rows of chains. Crystallization begins in packs and proceeds sequentially either through the formation of "ribbons", "petals" and regular crystals, or through the appearance of "ribbons", "petals" and spherulite structures. The structure of the polyethylene molecule is shown in Fig. 1.

Fig. 1 Polyethylene molecule structure

The cooling rate of the polyethylene melt determines the size of the crystalline regions and the degree of crystallinity. Rapid cooling (quenching) leads to a decrease in the percentage of the crystalline phase and an increase in the size of the crystalline regions.

A clearly expressed bond is observed between crystallinity and the content of methyl groups.The dependence of the content of the amorphous phase on the concentration of methyl groups in polyethylene is shown below:

Number of CH3 groups per 100 C atoms Amorphous phase content,%

The difference in the degree of crystallinity determines the density of the polymer. So, low density polyethylene contains 55-65% of the crystalline phase, 66-73% in the middle, and 74-95% in the high.

In polyethylene samples with a high degree of branching, the weight fraction of the crystalline phase can reach 40%.

As the temperature rises, the degree of crystallinity of the polymer decreases: the decrease becomes more and more sharp as the softening temperature is approached (Fig. 2).

Fig 2. Change in the proportion of the crystalline phase in polyethylene with increasing temperature

Crystalline regions in polyethylene are up to several hundred angstroms long and correspond not to a whole molecule, but to a small part of it, so that one polymer molecule (its length reaches 1000 Å) can pass through several crystal regions.

The configuration and packing of linear polyethylene molecules in crystallites are the same as those of normal olefin molecules. This is evidenced by the dimensions of a rectangular unit crystal cell: a = 7.40 Å, b =4.93 Å, c = 2.534 Å.

The identity period of 2.534 Å corresponds to the repeating distance of the zigzag carbon chain between the carbon atoms C-C 1.54 Å and the angle between the carbon bonds 109 28 "

Adjacent molecules are at a distance of 4.3 Å from each other; the hydrogen atoms of neighboring molecules are so located in relation to each other that the distance between their centers becomes almost constant at 2.5 Å, i.e., equal to twice the effective van der Waals radius of 1.25 Å. The crystallinity of a polymer at ordinary temperatures affects indirectly many of its properties: density, surface hardness, flexural modulus, ultimate strength and yield strength, solubility and swelling in organic solvents, vapor and gas permeability.

In the presence of Ziegler and Phillips catalysts, ethylene and α-olefins can be copolymerized and thus the number of branches can be controlled. For example, a copolymer of ethylene and propylene (6.25% by weight of propylene) contains 21 methyl groups per 1000 carbon atoms and has a crystallinity of 20% less than that of polyethylene. A copolymer of ethylene and 1-butene (5.6% by weight of 1-butene) in the presence of 14 ethyl branches per 1000 carbon atoms reduces crystallinity by 20%, i.e. 1 ethyl group is equivalent to 1.5 methyl groups in terms of the effect on reducing the degree crystallinity of copolymers.