[–CH 2 -CH 2 –] n exists in two main modifications, which differ in the structure of polyethylene molecules, and, as a result, in their properties. Both modifications are obtained from ethylene CH 2 = CH 2 . In one form, the monomers are linked in linear chains with a degree of polymerization (DP) typically 5000 or more; in the other, branches of 4-6 carbon atoms are attached to the main chain in a random way. Linear polyethylenes are produced using special catalysts, polymerization proceeds at moderate temperatures (up to 150 0C) and pressures (up to 20 atm).
Basic properties and characteristics of polyethylene
Polyethylene- a thermoplastic polymer which:
- opaque in a thick layer;
- crystallizes in the temperature range from -60 °С to -269 °С;
- not wetted by water;
- at room temperature it does not dissolve in organic solvents;
- at temperatures above 80 °C, it first swells and then dissolves in aromatic hydrocarbons and their halogen derivatives;
- PE resistant to aqueous solutions of salts, acids, alkalis, but at temperatures above 60 ° C, sulfuric and nitric acids quickly destroy it;
- short-term processing PE an oxidizing agent (for example, a chromium mixture) leads to the oxidation of the surface and wetting it with water, polar liquids and adhesives. In this case, PE products can be glued.
Gaseous ethylene can be polymerized in several ways, depending on this, polyethylene is divided into:
- high pressure polyethylene (LDPE) or low density polyethylene (LDPE);
- low pressure polyethylene (HDPE) or high density polyethylene (HDPE);
- and also on linear polyethylene.
LDPE polymerized by a radical method under pressure from 1000 to 3000 atmospheres and at a temperature of 180 degrees. The initiator is oxygen. HDPE it is polymerized at a pressure of at least 5 atmospheres and a temperature of 80 degrees using Ziegler-Natta catalysts and an organic solvent.
Linear polyethylene(there is also the name medium pressure polyethylene) is obtained at 30-40 atmospheres and a temperature of about 150 degrees. Such polyethylene is, as it were, an “intermediate” product between HDPE and LDPE, with regard to properties and qualities. Not so long ago, technology began to be applied, where the so-called metallocene catalysts are used. The meaning of the technology lies in the fact that it is possible to achieve a higher molecular weight of the polymer, which, accordingly, increases the strength of the product.
In their structure and properties (despite the fact that the same monomer is used), LDPE, HDPE, linear polyethylene differ, and, accordingly, are used for various tasks. LDPE is a soft material, HDPE and linear polyethylene have a rigid structure.
Differences also appear in density, melting point, hardness, and strength.
Comparative characteristics of high and low pressure polyethylene (LDPE and HDPE)
The main reason for the differences in the properties of PE, is the branching of the structure of its macromolecules: the more branches in the chain, the higher the elasticity and the lower the crystallinity of the polymer. Branching makes it difficult to pack macromolecules more tightly and prevent the achievement of a degree of crystallinity of 100%; along with the crystalline phase, there is always an amorphous phase containing insufficiently ordered regions of macromolecules. The ratio of these phases depends on the method of obtaining PE and the condition of its crystallization. It also determines the properties of the polymer. Films from LDPE 5-10 times more permeable than HDPE films.
The mechanical properties of PE increase with increasing density (degree of crystallinity) and molecular weight. In the form of thin films, PE (especially a low density polymer) has more flexibility and some transparency, and in the form of sheets it becomes more rigid and opaque.
Impact resistant polyethylene. Among the most important properties of polyethylene, frost resistance can be noted. Products made of polyethylene can be used at temperatures from -70°С to 60°С (LDPE) and up to 100°С (HDPE), some grades retain their valuable properties at temperatures below -120°С.
A significant disadvantage of polyethylene is its rapid aging.. The aging period is increased by special additives - antioxidants (phenols, amines, carbon black).
Electrical properties of polyethylene characteristic of a non-polar polymer, so it belongs to high-quality high-frequency dielectrics. The dielectric permittivity and dielectric loss tangent change little with changes in the frequency of the electric field, temperature in the range from -80 °C to 100 °C, and humidity. However, the catalyst residues in HDPE increase the dielectric loss tangent, especially with temperature changes, which leads to some deterioration in the insulating properties.
Characteristics of low density polyethylene (minimum and maximum values for industrial grades)
| Indicators (at 23°С) | |
| Density | 0.94-0.97 g / cm 3 |
| Vicat heat resistance (in liquid medium, 50°C/h, 50N) | 18-32 MPa |
| 10-19 MPa | |
| 610-1600 MPa | |
| Tensile elongation (50mm/min) | 600-700 % |
| 2-NB kJ/m2 | |
| Ball indentation hardness (358 N, 30 s) | 38-59 MPa |
| 10^14-10^15 ohm | |
| 0,1 % |
High density polyethylene
Polyethylene HDPE (high density) It is used mainly for the production of containers and packaging. Abroad, about a third of the produced polymer is used for the manufacture of containers by blow molding (containers for food products, perfumes and cosmetics, automotive and household chemicals, fuel tanks and barrels). At the same time, it should be noted that, compared with other areas, the use of HDPE for the production of packaging films is growing at a faster pace. HDPE also finds application in the production of pipes and pipeline parts, where such material advantages as durability (service life - 50 years), ease of butt welding, low cost (on average 30% lower compared to metal pipes) are used.
Other designations: PE-LD, PEBD (French and Spanish designation).
Light elastic crystallizing material with heat resistance without load up to 60°C (for some grades up to 90°C). Allows for cooling (various grades ranging from -45 to -120°C).
LDPE properties highly dependent on the density of the material. An increase in density leads to an increase in strength, stiffness, hardness, and chemical resistance. At the same time, with an increase in density, impact resistance at low temperatures, elongation at break, crack resistance, and permeability to gases and vapors decrease. Prone to stress cracking. Not dimensionally stable.
- It has excellent dielectric characteristics.
- It has a very high chemical resistance.
- Not resistant to fats, oils.
- Not resistant to UV radiation.
- Differs in the increased radiation firmness.
- Biologically inert.
- Easily processed.
Characteristics of high density polyethylene (minimum and maximum values for industrial grades)
| Indicators (at 23°С) | Values for unfilled marks |
| Density | 0.91-0.925 g / cm 3 |
| Tensile yield strength (50mm/min) | 8-13 MPa |
| Tensile Modulus (1mm/min) | 118-350 MPa |
| Tensile elongation (50 mm/min) | 100-150 % |
| Charpy impact strength (notched specimen) | NB |
| Specific surface electrical resistance | 1014-1015 Ohm |
| Water absorption (24 hours, humidity 50%) | 0,01 % |
Structure of polyethylene consumption in various sectors of industry, %
Insulation of electrical wires made of polyethylene.
The high dielectric properties of polyethylene and its mixtures with polyisobutylene, low water vapor permeability allow it to be widely used for insulating electrical wires and manufacturing cables used in various means of communication (telephone, telegraph), signaling devices, dispatch telecontrol systems, high-frequency installations, and for winding wires motors operating in water, as well as for the insulation of submarine and coaxial cables.
Polyethylene insulated cable has advantages over rubber insulated cable. It is lighter, more flexible and has greater electrical strength. A wire coated with a thin layer of polyethylene may have a top layer of plasticized polyvinyl chloride, which forms a good mechanical protection against damage.
In the production of cables, LDPE cross-linked with small amounts (1-3%) of organic peroxides or irradiated with fast electrons is used.
Films and sheets made of polyethylene.
Films and sheets can be made from PE of any density. In the production of thin and elastic films, LDPE is more widely used. Sheets of PE film are produced by two methods: extrusion of a molten polymer through an annular slot followed by blowing or extrusion through a flat slot followed by drawing. They are produced with a thickness of 0.03-0.30 mm, a width of up to 1400 mm (in some cases up to 10 m) and a length of up to 300 m.
In addition to thin films, polyethylene is produced in sheets with a thickness of 1-6 mm and a width of up to 1400 mm. They are used as a lining and electrical insulating material and are processed into technical and household products by vacuum forming.
Most of the LDPE products serve as packaging material, competing with other films (cellophane, PVC, PVC, PVC, polyethylene terephthalate, polyvinyl alcohol, etc.), a smaller part is used for the manufacture of various products (bags, sacks, lining for boxes, boxes and other types of containers).
Films are widely used for packing frozen meat and poultry, in the manufacture of balloons and balloons for meteorological and other studies of the upper layers of the atmosphere, for corrosion protection of main oil and gas pipelines. In agriculture, transparent film is used to replace glass in greenhouses and greenhouses. The black film is used to cover the soil in order to retain heat when growing vegetables, fruit and berry and legume crops, as well as to line silo pits, the bottom of reservoirs and canals. More and more plastic film is used as a material for roofs and walls in the construction of crop storage facilities, agricultural machinery and other equipment.
Household items are made from plastic film: raincoats, tablecloths, curtains, napkins, aprons, scarves, etc. The film can be applied on one side to various materials: paper, fabric, cellophane, metal foil.
Reinforced polyethylene film is more durable than ordinary film of the same thickness. The material consists of two films, between which there are reinforcing threads made of synthetic or natural fibers or a rare glass fabric.
Tablecloths are made from very thin reinforced films, as well as films for greenhouses; from thicker films - bags and packaging material. Reinforced film, reinforced with a rare glass fabric, can be used for the manufacture of protective clothing and used as a lining material for various containers.
On the basis of PE films, sticky (adhesive) films or tapes can be made, suitable for repairing cable lines of high-frequency communication and for protecting steel underground pipelines from corrosion. Polyethylene films and tapes with an adhesive layer contain on one side a layer of low molecular weight polyisobutylene, sometimes mixed with butyl rubber. They are produced with a thickness of 65-96 microns, a width of 80-I50 mm.
LDPE and HDPE are also used to protect metal products from corrosion. The protective layer is applied by flame and vortex spraying.
Pipes and pipe products made of polyethylene
Of all types of plastics, PE has found the greatest application for the manufacture of extrusion and centrifugal casting of pipes, characterized by lightness, corrosion resistance, low resistance to fluid movement, ease of installation, flexibility, frost resistance, and ease of welding.
The continuous method produces pipes of any length with an internal diameter of 6-300 mm and a wall thickness of 1.5-10 mm. Polyethylene pipes of small diameter are wound on drums. Injection molding produces fittings for pipes, which include elbow pipes bent at an angle of 45 and 90 degrees; tees, couplings, crosses, branch pipes. Pipes of large diameter (up to 1600 mm) with a wall thickness of up to 25 mm are produced by centrifugal casting.
Polyethylene pipes due to their chemical resistance and elasticity, they are used to transport water, solutions of salts and alkalis, acids, various liquids and gases in the chemical industry, for the construction of internal and external water supply networks, in irrigation systems and sprinkler installations.
LDPE pipes can operate at temperatures up to 60°C, and HDPE pipes up to 100°C. Such pipes do not collapse at low temperatures (up to - 60 ° C) and when water freezes; they are not subject to soil corrosion.
If earlier, when installing a water supply system, sewerage, when conducting gas, only metal or cast-iron pipes were always used. There was simply no alternative. Today, polymer products are increasingly being used, and, in particular, polyethylene pipes. They are increasingly replacing metal counterparts from the market, and all thanks to their low price, ease of handling, and long service life. The ease of installation adds to the polarity of PE pipes - there are fittings that are installed by hand. This is very convenient, for example, when installing a water supply or irrigation system in the country.
Properties, advantages, disadvantages
Polyethylene pipes are used to transport various liquid and gaseous substances. In the literature, you can find an abbreviated designation: in the Russian version it is PE, in the international version it is PE or PE-X for cross-linked polyethylene.
They have excellent properties:
An excellent set of properties has led to the fact that polyethylene pipes are becoming more and more popular. But in order to avoid surprises, it is necessary to know their shortcomings. There are not very many of them, but they are quite serious.
- Polyethylene burns, and when burned, it releases harmful substances.
- Poor UV resistance. Under the influence of the sun, the material becomes brittle and brittle. But pipes made of cross-linked polyethylene are not affected by this disease; they have recently become leaders in sales.
- Large thermal expansion - it is 10 times greater than that of steel. To neutralize this shortcoming, a compensator is installed.
- If the liquid in the pipeline freezes, the polyethylene can break. Therefore, when using polyethylene pipes to organize the water supply of a private house or cottage, it is laid below the freezing depth or insulated from above, additional heating methods are used ().
These are all shortcomings. Now for the varieties. According to the production method, there are three types of polyethylene pipes:
There is a certain paradox in these names. When talking about high or low pressure polyethylene pipes, they mean the way they are produced. But often this is perceived as an area of use. In reality, it's the other way around. Pipes produced at high pressure are less durable. They can only be used for non-pressure systems (no pumps). They are made for pressure water supply systems, but the strength is increased due to the thickness of the walls. With a normal wall thickness, their area of \u200b\u200buse is sewage, drainage systems, stormwater, etc. Here their qualities are optimal.
In pressure pipelines, where there is high pressure, low-pressure polyethylene pipes are used. They are more durable but, at the same time, more fragile, bend much worse. This is also not very good. But they can withstand significant pressure drops without any harm. And I must also say that both of these types of polyethylene pipes are only suitable for cold water - they cannot withstand hot water, they can melt.
But the third type - made of cross-linked polyethylene - is an option with high strength, flexibility. Such products withstand high pressure (up to 20 Atm) and temperatures up to +95 ° C, that is, PE-X pipes can be used for hot water supply, as well as for heating systems. By the way, metal-plastic pipes make them of this type of polymer. However, there is one “but” here - this type of material is not welded. When installing a pipeline made of cross-linked polyethylene, fittings with gaskets are used. The second type of assembly is adhesive, when the joints of the elements to be joined are smeared with glue.
Markings and diameters
Polyethylene pipes are usually black or bright blue, XLPE pipes can be bright red. They are painted this way on purpose - to make it easier to distinguish them from other polymers. Blue stripes can be applied along the wall if it is intended for cold water, yellow if it is used for a gas pipeline. The release form is in coils from 20 to 50 meters long (usually small diameters) and in pieces of 12 meters (or the desired length by agreement).
The diameters of polyethylene pipes vary in a wide range - from 20 mm to 1200 mm. Products of small section (up to 40 mm) are used mainly for water supply and heating systems in private houses and apartments, more serious ones (up to 160 mm) go to the risers of water supply, heating and sewerage systems. Large diameters are already an industrial and manufacturing area. It is practically not used for private buildings and apartments.
Density of polyethylene
For the manufacture of pipes, polyethylene of different densities is used. The density is indicated by the numbers that come after the abbreviation:
What else may be interesting: polyethylene pipes can also be reinforced. In general, they are produced by extrusion - in a softened state, the material is squeezed out through a nozzle, then sent for calibration, where it is given the required section and size. In the production of reinforced polyethylene pipes, nylon, polystyrene or polyvinyl chloride (PVC) fibers are sealed inside the wall. The equipment for this process is much more complex, and therefore the price of reinforced PE pipes is much higher.
The diameter of polyethylene pipes and what is SDR
There is a significant difference in the marking of polymer pipes - the outer diameter is indicated. But the wall thickness varies within wide limits, so that the inner diameter has to be calculated - twice the wall thickness should be subtracted from the outer one. The wall thickness in the marking is prescribed after the indication of the outer diameter (usually they put * or the “x” sign). For example: 160 x 14.6. This means that this pipe has an outer diameter of 160 mm, a wall thickness of 14.6 mm. You can also calculate the inner diameter of a polyethylene pipe: 160 mm - 14.6 mm * 2 = 130.8 mm.
The marking also contains the abbreviation SDR and some numbers. The numbers are the ratio of the outside diameter to the wall thickness. This indicator reflects the strength of the walls and their ability to withstand pressure surges.
The lower the SDR, the stronger (but also heavier) the pipe. True, this is true within products of the same density. For example, PE 80 SDR11 is stronger than PE 80 SDR 17.
| Name of PE pipe | Characteristics | Application area |
|---|---|---|
| PE 63 SDR 11 | Low density, does not tolerate temperature extremes | Internal cold piping |
| HDPE PE-63 SDR 17.6 | GOST 18599-2001(2003), pressure not higher than 10 atm | Low pressure indoor plumbing for cold water supply |
| PE 80 SDR 13.6 | Density is higher, but temperature changes are poorly tolerated | Water pipelines for supplying cold water, irrigation systems |
| PE 80 SDR 17 | Density is higher, but temperature differences | Plumbing both indoors and outdoors, pressure irrigation systems |
| PE 100 SDR 26 | High density, ability to tolerate temperature changes | Any pipelines for transporting liquids (water, milk, juices, etc.) |
| PE 100 SDR 21 | Increased wall thickness | Any pipelines, including gas |
| PE 100 SDR 17 | Increased wall thickness, but also a large mass | Mostly used for industrial purposes |
| PE 100 SDR 11 | Low density polyethylene, high strength, high chemical resistance | Can be used when installing sewer collectors, laid in any type of soil |
Pipe series and pressure rating
The next parameter that may be important when choosing is the series. Denoted by the letter S, followed by numbers. Displays the ability of the walls to resist pressure. This is the ratio of the pressure that it can withstand (determined in the laboratory) to the working one. The larger the number, the stronger the pipe.
Nominal pressure of PE pipes of different density with different SDR
In practice, this indicator is rarely taken into account, since it is more "laboratory" than practical. Much more important may be the nominal pressure for which the walls are designed. These data are shown in the photo above. The pressure is at the intersection of columns and rows, indicated in Atmospheres. For example, for a PE 80 SDR 13.6 pipe, the working pressure is PN10 (10 Atm). This means that when transporting media with a temperature of no more than +20°C and a pressure of no more than 10 atm, the service life of this pipe is 50 years.
Regulations
GOSTs and industry standards were developed to standardize manufactured products. The regulatory framework for this type of materials appeared not so long ago - already in the current millennium - after 2000. The label usually indicates the standard that this type of product meets. The scope of application is determined by the name of the GOST (from the names of the GOSTs), but it is easier for non-professionals to focus on the presence of stripes of the corresponding color (blue for cold water, yellow for gas).
Here are the standards for Russia:
There are standards for Ukraine:
- DSTU B V.2.7-151:2008 "Polyethylene pipes for cold water supply"
- DSTU B V.2.5-322007 "Free-flow pipes made of polypropylene, polyethylene, non-plasticizable polyvinyl chloride and fittings for them for external sewerage networks of houses and structures and cable ducts"
- DSTU B V.2.7-73-98 "Polyethylene pipes for the supply of combustible gases"
You can explore them all if you wish. For the most part, they are tables in which the entire range of products is indicated with an indication of the parameters.
For identification, polyethylene pipes are marked. The inscriptions are applied at every meter or so. The name of the manufacturer is indicated first, the campaign logo may be placed. This sign is optional, but it is a good sign that the company is not afraid for its product.
- pipe material designation, in this case - PE - polyethylene;
- the density of polyethylene is for this example 80;
- then SDR pipes - 11;
- the following is the outer diameter and wall thickness: 160 mm pipe diameter, 14.6 mm - wall thickness;
- the last position indicates GOST or DSTU, which corresponds to this type of pipe.
The pipe shown in the photo - for gas pipelines this is emphasized three times - with yellow stripes, the inscription "gas" in the marking and the name GOST - 50838-2009 - this is the standard by which plastic pipes for gas pipelines are produced.
In the history of science, some discoveries happened by accident, and the materials that are in demand today are often the by-product of some kind of experience. Quite by accident, aniline dyes for fabrics were discovered, which later gave an economic and technical breakthrough in light industry. A similar story happened with polyethylene.
material discovery
The first case of obtaining polyethylene occurred in 1898. During the heating of diamesotane, German-born chemist Hans von Pechmann discovered a strange precipitate at the bottom of the test tube. The material was quite dense and resembled wax; the scientist's colleagues called it polymethyllin. This group of scientists did not go further than chance, the result was almost forgotten, no one had any interest. But still the idea hung in the air, requiring a pragmatic approach. And so it happened, after more than thirty years, polyethylene was rediscovered as an accidental product of an unsuccessful experiment.
The English take over and win
The 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 units of the equipment in which the experiments were carried out was covered with an unknown waxy substance. Interested in the side effect, they made several attempts to obtain the substance, but to no avail.
M. Perrin, an employee of the same company, succeeded in synthesizing the polymer two years later. It was he who created the technology that served as the basis for the industrial production of polyethylene. In the future, the properties and qualities of the material changed only with the help of various catalysts. Mass production of polyethylene began in 1938, and it was patented in 1936.
Raw material
Polyethylene is a white solid polymer. Belongs 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, at the output raw material granules are obtained for further use. For some technological processes, polyethylene is produced in the form of a powder.
Main types
To date, the polymer is produced in two main grades of LDPE and HDPE. Material made at medium pressure is a relatively new invention, but in the future, the number of manufactured products will steadily increase due to improving characteristics and a wide field of application.
For commercial use, the following types of material (classes) are produced:
- 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. During the production process, various dyes are added to the granular polymer, which make it possible to obtain black polyethylene, red or any other color.
LDPE
Polyethylene is produced by the chemical industry. 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.
- The process stimulator is a catalyst (Ziegler-Natta, a mixture of titanium chloride with an organometallic compound).
The process is accompanied by precipitation of polyethylene in the form of flakes, which then undergo a process of separation from the solution followed by granulation.
This type of polyethylene is characterized by a higher density, resistance to heat and tear. The scope of application is various types of packaging films, including those for packaging hot materials/products. From granulated 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 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 production method is solution polymerization under the influence of temperature and the participation of a catalyst. The method is not very effective, because during the polymerization process, the catalyst reacts, and the final polymer loses some of its qualities.
The last of the methods for the production of PNP is gas-phase polymerization, it has almost become a thing of the past, but is sometimes found in individual enterprises. The process occurs by mixing the gas phases of the raw materials under the influence of diffusion. The final polymer is obtained with a heterogeneous structure and density, which affects the quality of the finished product.
Production takes place in the following mode:
- The temperature is maintained at 120°C to 150°C.
- The pressure should not exceed 2 MPa.
- Catalysts for the polymerization process (Ziegler-Natta, a mixture of titanium chloride with an 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. It is in demand in the construction industry, the chemical industry, it is almost never used for the production of consumer goods.
Properties
Polyethylene is resistant to water, many types of solvents, acids does not react with salts. When burning, the smell of paraffin is released, a glow of 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. During 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, familiar in everyday life and production. It is unlikely that an ordinary consumer will be able to determine how many items from it he encounters daily. In the global production of polymers, polyethylene occupies the lion's share of the market - 31% of the total gross product.
Depending on what polyethylene is made of and production technologies, its qualities are determined. This material sometimes combines opposite indicators: flexibility and strength, ductility and hardness, strong stretching and tear resistance, resistance to aggressive media and biological agents. In everyday life, we use bags of various densities, disposable tableware, plastic lids, parts of household appliances and much more.
Areas of use
The use of polyethylene products has no restrictions, any industry or human activity is 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 dirt-repellent properties, the absence of an environment for the occurrence of fungal infection and the vital activity of microorganisms. One of the successful finds is a polyethylene sleeve, which is widely used. By varying the length at its own discretion, the user is limited only by the width of the package.
- Remembering what polyethylene is made of, it becomes clear why it has gained popularity as one of the best insulating materials. One of its sought-after qualities in this area was the lack of electrical conductivity. Its water-repellent properties are also indispensable, which has found application in the production of waterproofing materials.
- Resistance to the destructive power of water as a solvent makes it possible to produce 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 thermal 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 granulated raw materials were processed, it will depend on what brand of polyethylene will be obtained. Common ways:
- Extrusion (extrusion). It is used for packaging and other types of films, sheet material for construction and decoration, the manufacture of cables, polyethylene sleeves and other products are produced.
- Casting, way. Mainly used for packaging materials, boxes, etc.
- Extrusion-blown, rotational. Using this method, volumetric containers, large containers, 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 at a lower cost.
What is polyethylene made of, besides the main constituents? Mandatory is the process catalyst and additives that change the properties and qualities of the finished material.
Recycling
The durability of polyethylene is its plus as a consumer product and its minus as one of the main environmental pollutants. Today, recycling is becoming important. All grades of polyethylene can be recycled and recycled 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 hundreds of years, and the accumulated waste poisons natural vital resources. World practice shows an increase in the number of enterprises processing polyethylene. Collecting actually garbage, in such companies they carry out its sanitation, crush it. Thus, there is a saving of resources, environmental protection and production of demanded products.
In recent years, polyethylene pipes (PE) have been widely used, especially in the construction industry. PE pipes are used in the installation of gas pipelines, water pipelines, swimming pools are equipped with it, irrigation is automated, and are widely used in other industries. Polyethylene itself is a thermoplastic material, obtained by polymerization of a petroleum product. In this article, we will consider the characteristics of various types of products and understand what the marking “PE SDR pipe” means.
The equipment used for the production of such pipes is not cumbersome and particularly complex. and are made of various diameters in accordance with GOST, they are marked accordingly. Depending on the purpose, they differ in characteristics, each type of PE pipe has a corresponding brand.
Polyethylene grades
The brand PE 80, PE 63, PE 100 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, petrocarbons, alkalis, salt, etc.
Polyethylene grades PE 100, PE 80 and PE 63 are widely used at the present time, its main distinguishing feature is density, strength and of course cost.
A 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, resistant 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 drinking water supply, and products with a yellow stripe are used for laying a gas pipeline.
Pipe PE 100
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 wall thickness 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 the supply of food products in liquid form (juices, milk, wine, beer, etc.).
These products are wear-resistant, quite light, 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 multi-apartment residential buildings. In addition, they can be used for small-diameter pressure water supply in a small area.
Products are certified and can be used for their intended purpose.
At the same time, experts do not recommend using them in some cases. Due to the small thickness of the wall, it is not recommended to install a gas pipeline and a main pipeline from such products.
Pipe PE 63
Polyethylene of this brand has in its composition mainly ethylene molecules, it is characterized by short-term strength, at the same time it tends to crack and collapse. Due to these characteristics, it is less often used in civil and industrial construction for the installation of drainage systems for road communications, basements of buildings, foundations and sites.
These pipes are used in the laying of fiber-optic lines, where they are used as a case for utilities. Sometimes these pipes are used in agriculture, with their help, moisture is drained 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 according to the formula:
SDR=D/s, where
- D = external diameter of the PE pipe (mm);
- s = pipe 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 small SDR is able to withstand more pressure than the same product with a higher SDR. Thus, polyethylene pipes whose wall thickness is more able to withstand quite a noticeable pressure.
The ability of polyethylene to be resistant and neutral to gaseous and liquid substances determined the scope of its application. In addition to gas and water mains, PE pipes are used in 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 brand 100:
- The PE 100 SDR 17 pipe is irreplaceable in systems of gas pipelines and pressure water supply, especially in pipelines of big cross section. Its technical characteristics allow the use of such pipes for the installation of a pipeline with a long length. 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.
- The pipe polyethylene SDR 11 is made from the polyethylene received at a low pressure. Moreover, its high density makes it possible to use these products on high-pressure water pipes. In addition, this type can be used for arranging sewer collectors due to its resistance to aggressive environments. Laying can be carried out in almost any soil.
- Products made of polyethylene PE 100, such as the PE SDR 26 pipe, can withstand pressures up to 6.3 atm., It is used mainly in non-critical water supply systems, in gravity sewers and to protect communications.
- Pipe PE SDR 21 brand 100 - its main purpose is to install water pipes, according to experts in this product, the water does not have an extraneous taste and retains its taste qualities well.
- Polyethylene brand 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 the supply of cold water, in addition, if necessary, it can be used for sewerage and gasification.
- Pipe PE 80 SDR 13.6 is used for installation and repair of water pipes and pipes of liquid chemicals, to which polyethylene is neutral.
- PE 80 SDR 17 pipes are the best choice for low-rise construction, as they have sufficient strength for it and at the same time affordable cost.
- The pipe PE 63 SDR 11 is made from various kinds of polymers. It can be used for plumbing in the water supply system, as sewer pipes, as well as a protective case for communication communications and power supply.
Benefits of using PE pipes
The wide range of applications of these products is explained by many advantages over their metal counterparts, such as:
- products made of polyethylene have a warranty period of about 50 years;
- they are not exposed to moisture, aggressive environment, corrosion, stray currents, do not need cathodic protection;
- have a small weight;
- installation is simple, while achieving maximum tightness, 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, deposits do not form on the walls;
- prices for the purchase and installation of pipes are acceptable.
Polyester is the world's leading synthetic fiber. The technology of its production has become one of the great discoveries of the forties of the last century. On an industrial scale, fabric began to be produced since 1947 from acids and alcohol, coal and oil with the addition of water and air.
Polyester fibers are widely used in the production of clothing fabrics: skirts, trousers, dresses, suits, blouses, jackets, outerwear. Its mixtures are very popular: with cotton, wool, they are called classic. The ratio of wool and polyester is assumed in the ratio of 55% to 45%. In 2013, Germany produced 198,000 tons of polyester fibers, and other countries are not far behind, making this type of production leader.
Description
Get polyester by melt. The raw material is heated to obtain a spinning mass, then forced through the finest holes. Already during production, the scope of the fiber is taken into account, it is given a triangular, rounded, oval shape to create various effects: transparency, brilliance, tactile comfort. Fiber with corners forms a tough fabric. Hollow fibers are used to make lightweight, shock-absorbing fabrics with insulating properties. Products can be given any color: a calm neutral or a bright, brilliant shade. The fibers are polished to give shine, textured to acquire waviness.
Properties
The characteristics of the fiber are highly appreciated by manufacturers of various products and consumers. One of its advantages is resistance to weather factors: intense sun, frost, rain. At the same time, it is a thin and light fabric that blends well with natural fibers.
Such products are not demanding to care, have a high resistance to wear. On products made from these fibers, it is easy to form arrows and folds by heat treatment.
The most common are two varieties:
- PET- a very durable type of fabric, fibers are used in combination with other types to give them strength and shape stability; the main raw material for production is ethylene, obtained from oil; yarn is formed from soft fibers;
- PCDT- has elasticity and resilience, the fibers are used for the manufacture of furniture upholstery and curtains; raw material - terephthalic acid condensate, threads are formed from the melt.
The presented fabric, completely made of polyester, is absolutely wrinkle-resistant, even after moistening, it dries very quickly.
After extrusion, the fibers are formed and stretched, after contact with air they solidify. For greater strength, the fibers are woven into threads, which are wound on bobbins and sent to the production of fabrics.
Tulle, voile and organza are examples of 100% polyester sheer fabric. A common application is the manufacture of elastic lace underwear, shirts and blouses. Nets and ropes are made from thick threads.
100% polyester properties:
- smooth surface, a variety of colors;
- a wide variety of textures - thick and thin fabric, with a silky sheen or matte;
- the material is very pleasant to the touch and when dressing things;
- wear resistance without loss of color;
- light weight;
- the fabric is not prone to the appearance of stable creases when crushed;
- easy care - wash in cool water, quick ironing with a slightly heated iron;
- affordable price compared to natural silk.
- it is a suture material suitable for sewing any things.
The disadvantage of 100% polyester is its high density, which makes it impossible to wear products made from it in hot climates.
Combinations with other types of fibers
There are several types of combinations:
- With polyamide. This combination makes it possible to obtain very resilient, elastic, wear-resistant fabrics that do not lose color during operation. Women's underwear is sewn from them, which has the softness and nobility of silk, the elasticity and wear resistance of real synthetics. Diluted with polyamide, polyester loses some of its heat resistance, the fabric is slightly electrified, does not absorb moisture.
- with spandex. Allows you to get a durable and very elastic material for the manufacture of hosiery, durable sportswear, tight-fitting knitwear, gloves. Thanks to spandex threads, the material becomes less dense and more breathable, stretches well. The combination is not as resistant to fading as pure polyester, snow-white fabrics may turn yellow in the sun.
- With cotton. Cotton is a classic example of hygroscopicity, hygiene, naturalness and simplicity. Its combination with polyester in a ratio of 65% and 35%, deprives the fabric of the disadvantages inherent in cotton. Jerseys made of cotton with polyester do not fade, do not stretch, are worn and used longer. Cotton and polyester bed linen has twice the lifespan of pure cotton, does not wrinkle and dries very quickly.
- With viscose. Due to the presence of polyester, viscose acquires stability, hygroscopicity, it does not stretch, does not shed. From it sew clothes for work and leisure. A very popular option is viscose 30 polyester 70. Detailed characteristics of viscose fabric can be found in this article.
- Yarn. Knitting yarn packages can be labeled as "Polyester", "Polyester", "PEF". It has thermal conductivity and wrinkle resistance. Products knitted from this yarn are difficult to distinguish from woolen ones, they are not subject to moth damage, dry quickly, wear-resistant, and do not stretch.
Polyester is a relatively inexpensive fabric, its price is about 300 rubles per meter, depending on the policy of the store.
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