Polyethylene sheets (pe sheet)

Scope of application

The main area of ​​application of LDPE sheets is considered to be waterproofing. LDPE sheets are used in the construction of artificial reservoirs (ponds, canals, dams, dams). With their help, road embankments are strengthened and soils are protected from excessive moisture overflow. The construction of tunnels and various underground structures is also rarely done without this material. It is also widely used in the construction of protective structures for soil in landfills and accumulators at landfills for waste disposal.

Due to the high anti-corrosion properties of LDPE, sheets from it are used to protect against corrosion of various surfaces made of metal, concrete, brick. Low electrical conductivity makes it possible to produce electrolysis baths from such sheets, and to carry out electrical insulation with their help in orthopedics.

Also, LDPE polyethylene sheet is used for thermoforming, fenders and mud flaps for cars, geogrids and geomembranes, floor and roof coverings are made from it.

Basic properties

All polyethylene pipes are created from a thermoplastic polymerization product of a lower hydrocarbon - ethylene, which gives products from it similar characteristics:

• The density of the pipe material is 0.94-0.96 g / cm3,
• The operating temperature ranges from -60 to +90 C, the optimal mode is from 0 to 40 C,
• Permissible operating pressure of the content - up to 16 atm,
• The diameter of polyethylene pipes can be from 20 to 1600 mm,
• The wall thickness is made from 2 to 60 mm.

Advantages

Polyethylene pipes have a very long service life - more than 60 years under standard conditions, which is explained by the following capabilities of this material:

• Elasticity, thanks to which the pipe does not deteriorate even when its contents freeze. In this case, it can only slightly deform - stretch in diameter.
• Resistance to common chemical reagents - various acids, alcohols and alkalis, and for some species even to fats and benzene products. Polyethylene does not withstand contact only with liquid fluorine and chlorine, but these substances in their pure form are extremely rare, so such contact is unlikely.
• Resistance to biodegradation by rot and fungus, as well as destruction by insects and rodents.
• With a natural decomposition period of over 100 years.
• Absolute absence of toxic secretions, which allows them to be used in direct contact with food and lay without additional protection.
• The ability to be an excellent insulator for liquids and gases, which allows you not to let anything unnecessary either inward or outward.
• The smoothness of the inner walls. This factor determines the small percentage of their clogging and the appearance of growths.
• Low weight of products. Polyethylene is even lighter than water, due to which the device of communication systems with the participation of polyethylene pipes does not require strengthening the supports, especially strong fasteners and the use of great physical force.
• Ease of installation work. To connect individual pipe sections, a slight heating or fastening with the help of sockets and couplings is sufficient.

disadvantages

With all the versatility of PE pipes, they have disadvantages associated with the structural features of the material:

1. Products do not withstand high temperatures, they are mainly intended for the transport of cold liquids and gases.
2. Pure polyethylene becomes brittle after prolonged exposure to sunlight. To protect against ultraviolet radiation, the pipes are processed according to one of the following methods:
   • covered with paint (preferably acrylic),
   • obstruct with protective materials,
   • even at the manufacturing stage, special protective substances are added to polyethylene.

Properties of polyethylene

Speaking about the characteristics of PE, you need to understand that the properties of various types of this polymer are very different. Consider, as in the case of synthesis, indicators of the two most common types.

The molecular weight of LDPE ranges from 30,000 to 400,000 atomic units.

MFR, depending on the brand, varies from 0.2 to 20 g / 10 minutes.

The LDPE crystallinity is approximately 60 percent.

The glass transition temperature is minus 4 degrees C.

The melting temperature of grades of material is from 105 to 115 degrees C.

Density is about 930 kg / m3.

Technological shrinkage during processing is from 1.5 to 2 percent.

The main property of the structure of high pressure polyethylene is a branched structure. Hence its low density, due to the loose amorphous-crystalline structure of the material at the molecular level.

The molecular weight of HDPE ranges from 50,000 to 1,000,000 atomic units.

MFR, depending on the brand, varies from 0.1 to 20 g / 10 minutes.

HDPE crystallinity ranges from 70 to 90 percent.

The glass transition temperature is 120 degrees C.

The melting temperature of grades of material is from 130 to 140 degrees C.

Density is about 950 kg / m3.

Technological shrinkage during processing is from 1.5 to 2.0 percent.

Chemical properties. PE has low gas permeability. Its chemical resistance depends on the molecular weight and on the density of the polymer. PE is inert to dilute and concentrated bases, solutions of all salts, some of the strongest acids, organic solvents, oils and greases. Polyethylene is not resistant to 50% nitric acid and halogens such as pure chlorine and bromine. Moreover, bromine and iodine have the property of diffusion through polyethylene.

Physical characteristics. Polyethylene is an elastic rather tough material (LDPE is much softer, HDPE is tougher). Frost resistance of polyethylene products - up to minus 70 degrees C. High impact strength, strength, good dielectric characteristics. The polymer has low water and vapor absorption. From the point of view of physiology and ecology, PE is a neutral inert substance, odorless and tasteless.

Performance properties of polyethylene. The destruction of PE in the atmosphere begins at a temperature of 80 degrees C. Polyethylene without special additives is not resistant to solar radiation and most of all to ultraviolet light, it is easily photodestructed. To reduce this effect, stabilizers are added to the PE composition, for example carbon black for light stabilization. Polyethylene does not emit chemicals harmful to health and nature into the environment, while it decomposes on its own very slowly - the process takes decades. PE is quite fire hazardous and supports combustion, this fact must be taken into account when using it.

Features of LDPE (PNP)

Chemical and physical characteristics

High pressure polyethylene (LDPE) is produced in the form of LDPE granules. It has a density of 900-930 kg / m3, a melting point of 100-115 ° C and a brittleness temperature of up to -120 ° C, as well as low water absorption (about 0.02% per month) and high plasticity. These physicochemical characteristics of LDPE as a substance explain the following properties of objects and materials made from it:

• Softness and flexibility of low density polyethylene products,
• The ability to create especially smooth and shiny surfaces from LDPE granules,
• Resistance of LDPE objects to mechanical damage by rupture and impact, as well as to tensile and compressive deformations,
• High strength of LDPE (LDPE) when exposed to low temperatures,
• Moisture and air tightness of LDPE products,
• Resistance of LDPE to light, in particular to solar radiation.

The difference between LDPE and other polymers

Polyethylenes (LDPE, HDPE, etc.) are materials that are made from one monomer, but can be of different density depending on the manufacturing characteristics. This indicator strongly affects the properties of polyethylene: an increase in density leads to an increase in rigidity, hardness, strength of products and their chemical resistance. But at the same time, other indicators fall: impact resistance, the possibility of stretching at break, permeability to liquids and gases. So, LDPE has significant differences from other similar polymers:

• LDPE and HDPE High pressure polyethylene is also called low density polyethylene (LDPE or LDPE) for a reason. Compared to it, hard polymers such as HDPE (low pressure polyethylene) are more susceptible to rupture under the impact of impact, more likely to break in the cold and crack with increasing load, although they are more resistant to radiation, alkalis and acids. LDPE granules and products made from them tolerate ultraviolet radiation much better, and also have a more beautiful glossy surface.
• LDPE and LDL. Another polymer - LDL (linear polyethylene), like HDPE, has a rigid structure, but its technical characteristics are between LDPE and HDPE. It is more resistant to chemically aggressive environments than LDPE and has better puncture and cracking resistance than HDPE.

What is polyethylene foam, types of material, production technology

All polyethylene foam produced to date is divided into three types:

1. Unstitched (NPE). The cheapest of the line of foamed polyethylene. Europe established its release at the end of the last century. The polymer mass melted in the extruder is saturated with a gas, usually butane. When poured into a mold, polyethylene enters the zone of atmospheric pressure, gas bubbles try to escape to the surface, and, solidifying, form a cellular structure. Uncrosslinked polyethylene foam is a good heat insulator, but due to its low density and loose large-pore structure, products from it are rarely used in construction. Basically, the material is used for the manufacture of packaging.
2. Chemically cross-linked (HPPE). Equipment for the production of expanded polyethylene HPPE is used the same as for non-crosslinked, but at the same time, additional processing with hydrogen peroxide is introduced into the technology. This removes all the disadvantages inherent in uncrosslinked polyethylene - the material becomes denser, the cells are smaller, the polymer can restore its original shape after deformation.
3. Physically or radiation-stitched (PPPE). The most expensive of the foamed polyethylene. The crosslinking of polymer molecules occurs due to the flow of electrons emitted by the emitter. Irradiation forms cross-links that strengthen the molecular network of the polyethylene foam. At the exit, an elastic soft fabric with a smooth surface is obtained, capable of withstanding pressure up to 0.035 MPa. Physically and chemically cross-linked PE have similar characteristics, but FPPE recovers its shape faster after loading and better adheres to the forms being sealed. The underlay for the floor is made of foamed polyethylene, produced by radiation.

Material release stamps

The most common manufacturers of HDPE sheets are polyethylene grades - PE80, PE100, PE300, PE500 and PE1000. They have the following characteristics:

• High thermal stability;
• UV resistance;
• Excellent wear resistance (retain properties for a long time - about 50 years);
• Moderate impact resistance and rigidity;
• Water resistance;
• Good dielectric and electrical insulating qualities;
• Plastic;
• Resistant to fats and oils; Under normal conditions, the material is completely non-toxic and does not have a detrimental effect on the human body.

The main characteristics of the brands:

Production of flat polyethylene sheets

Monolithic flat sheets are produced similarly to plastic wrap by flat-slot extrusion. At the initial stage, the raw materials are dried and mixed with dyes and stabilizers, as well as the necessary additives that improve the properties of the resulting product. With the help of stabilizers and additives, it is possible, for example, to obtain sheets that are resistant to aging and ultraviolet radiation. Before launching the prepared raw materials into production, a trial casting of a small sample is carried out. On the extruder, the polyethylene melt passes through a flat and wide slit. The resulting sheet is calibrated in thickness, then polished and trimmed to the specified parameters. At the final stage of production, the resulting polyethylene sheet is cooled.

The production of pressed polyethylene sheets is carried out after prolonged heating of the feedstock, with its further pressing and cooling. The productivity of this method is rather low, but it allows to obtain sheets of increased strength and increased thickness - from 0.1 to 10 centimeters.

Application

The widespread use of HDPE in industry and in everyday life is explained not only by its high characteristics, but also by the relatively low cost of production. The ease of giving any shape under conditions of heating above the melting temperature makes it possible to manufacture various products from it, therefore, granules of this polyethylene become raw materials for the manufacture of the following necessary materials:

HDPE extrusion method is used to produce:

• films - smooth and bubble,
• film sleeve for making bags,
• communication pipes,
• insulation of electrical cables,
• sheet and mesh materials.

Containers for household chemicals, cans, barrels, etc. are blown out of it.

Cast under pressure:

• household goods (toys, dishes, inventory, products for the kitchen and bathroom, lids for jars, bottle containers, etc.),
• sewing and furniture accessories,
• components for various equipment (cars, household appliances, etc.).

Formed by the rotor method:

• Bucky,
• Road blocks,
• Large-scale structures in the form of playgrounds, wells, overpasses.

In addition, when HDPE is foamed, a qualitatively new product is obtained - polyethylene foam, which is used in heat-insulating construction work.

Production

Foamed polyethylene sheet is made by extrusion or injection molding from a foamed mass obtained from high, low, medium density polyethylene or their mixture (LDPE, HDPE, LPNP, etc.). At the same time, the properties of the final product are influenced not so much by the type of raw material used as by the foaming technology with a subsequent change in the structure - both physical and molecular:

1. With physical foaming, the usual gas supply to the hopper with actively mixed hot polyethylene mass occurs. A sheet of such polyethylene foam has the same molecular structure and practically the same properties as primary polyethylene, as well as a larger cell volume than with other technologies, and less weight.
2. Chemical foaming occurs with the simultaneous "crosslinking" of the molecular structure by chemical or radiation methods. "Crosslinked" sheets are usually much more durable and have a wider operating temperature range (the upper temperature barrier rises to 150 - 200 0C).

The last stage of production is cutting into sheets of the required size for the convenience of subsequent use.

Ecology and recycling of polyethylene

In recent years, polyethylene has come under serious pressure due to its supposedly unfriendliness. In fact, this material is one of the safest. The problem with PE is that it is the main polymer used for the production of films, including thin films, and bags from them. Lacking adequate policies for the separate collection of waste, many underdeveloped countries are dumping huge amounts of PE waste, which leads to the release of polyethylene into the environment and water resources and their pollution.

Fig. 3. Garbage bags - typical applications for recycled PE

At the same time, in the case of proper collection and sorting of waste, polyethylene waste becomes a valuable resource and an excellent secondary raw material. Already a fairly large number of enterprises in the countries of the former USSR purchase polymer waste for recycling, obtaining granules and then using it in their production or selling secondary PE on the market. Thus, the pollution of the planet with polyethylene should soon come to naught.

Applications

Foamed polyethylene can be used in various areas of construction, but most often it is taken to create a reliable layer of sound insulation, as a heater, moisture protection. The material can be attached to floors, ceilings, wall coverings. If you want to enhance the insulating properties of such a base, you can supplement it with thin aluminum foil, which is glued to only one side of the sheet. Such foundations are most often laid on concrete structures - in this case, they act as special heat shields, reflecting infrared radiation into the interior space. In this way, heat will be conserved much more efficiently.

This type of polyethylene in sheets is sometimes used to create packaging. An unstitched variety is better suited for them, while this type is not recommended for installation work. Foamed polyethylene sheets will be the best option for creating an additional sealing layer for doors and glass units. They are also used in cases where it is required to carry out the most accurate transportation of other materials.

Sheets are widely used in mechanical engineering. Most often, such material is used as a reliable insulator for various refrigeration equipment and air conditioning systems. Sometimes such polyethylene is used in the production of double-sided tape, various mounting tapes, individual elements designed to absorb vibrations. In heavy-duty trucks, with the help of such material, insulation is often created in the luggage compartments.

Foamed sheets are also used in the medical field. There they found wide application due to their elasticity and flexibility: products easily regain their shape even after severe deformations. Basics with such characteristics will be an excellent option for the production of various corsets, shoe insoles.

In the next video, you will find a detailed overview of expanded polyethylene sheet.

Scope of expanded polyethylene sheet

Due to its chemical inertness, resistance to aggressive media, low thermal conductivity, good sound-insulating properties, polyethylene foam is widely used for arranging the interior cladding of yachts, boats, cars.

Polyethylene foam is also used in construction. It is a more effective insulation compared to many materials used for this. So, for example, polyethylene sheet 10mm thick can replace 50mm mineral wool. This explains its popularity when insulating walls and floors in rooms.

Most often, metallized polyethylene foam sheet is used, which is also a very light material. It is easy to use, easy to cut, and easily attaches to any surface.However, it should be remembered that the metallized side of the sheet should always face the room. In this case, its reflective properties will be maximized.

Good vapor barrier properties make it possible to use a similar material for arranging ceilings in wooden houses. Due to the softness and elasticity of polyethylene foam, as well as the ability to damp small vibrations, it is used as a substrate when laying laminate, parquet, linoleum or underfloor heating. It is also used in the construction of interior partitions.

The same properties make it possible to produce reliable packaging from such a foam material, which ensures safety and protects fragile or expensive items from damage. At the same time, it can serve as a cushioning material that protects objects from damage if a large number of them are packed in one container.

Foamed polyethylene sheets are widely used in instrumentation, in the manufacture of household appliances and refrigeration units. Due to a number of valuable properties, polyethylene foam sheet has become an irreplaceable material used in many areas of industry, construction and interior decoration.