Polyethylene and polypropylene: similarities and differences

Polypropylene and polyethylene are among the most common types of polymeric materials. They are successfully used in industry, everyday life, agriculture. Due to the unique composition, they have practically no analogues. Consider more important similarities and differences in polypropylene and polyethylene, as well as the scope of materials.

Compound

Like most similar scientific terms, the names of the materials were borrowed from Greek. Present in both words prefix poly- translates from Greek as “a lot”. Polyethylene is a lot of ethylene, and polypropylene – a lot of propylene. That is, in original condition, materials are ordinary combustible gases having formulas:

  • C2H4 – polyethylene;

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

  • C3H6 – polypropylene.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

Both of these gaseous substances relate to special compounds, so-called alkenes, or acyclic unsaturated hydrocarbons.To give them a solid structure, polymerization is carried out – the creation of high molecular weight matter, which is formed using the compound of individual molecules of low molecular weight substances with active centers of growing polymer molecules.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

As a result, a solid polymer is formed, the chemical basis of which only carbon and hydrogen are served. Separate characteristics of materials are formed and rises by adding special additives and stabilizers to their composition.

In the form of primary raw materials, polypropylene and polyethylene do practically do not matter – mostly they are produced in the form of small balls or plates, which, besides the composition, may differ only in size. Already then, by melting or pressing, various products produce various products: water pipes, containers and packaging, boat housings and much more.

Polyethylene and polypropylene: similarities and differences

Properties

According to the world generally accepted in the world, the German standard DIN4102, both material refer to the class B: difficult to be marked (B1) and normally marked (B2). But, despite interchangeability in some areas of activity, polymers have a number of differences in its properties.

Polyethylene

After the polymerization process, polyethylene is a solid material with an unusual surface to the touch, as if covered with a small wax layer. Due to the low density indicators, it is lighter than water and has high characteristics:

  • viscosity;
  • flexibility;
  • Elasticity.

Polyethylene is an excellent dielectric, resistant to radioactive radiation. This indicator has the highest among all such polymers. Physiologically material is absolutely harmless, so widely used in the production of various products for storing or packaging food. Without loss of quality, it is capable of withstanding a fairly wide range of temperatures: from -250 to + 90 °, depending on its brand and manufacturer. The temperature of self-ignition is + 350 °.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

Polyethylene has high resistant to a number of organic and inorganic acids, alkalis, salt solutions, mineral oils, as well as to different substances with alcohol content. But at the same time, like polypropylene, it is afraid of contact with powerful inorganic oxidizers of type HNO3 and H2SO4, as well as with some halogens. Even the insignificant effect of these substances leads to its cracking.

Polypropylene

Polypropylene has high performance of shock viscosity and wear-resistant, waterproof, repeated bends and festers with the loss of quality. Material is harmless physiologically, therefore it is suitable for storing food and drinking water. It does not have a smell, not sinking in water, during fire does not highlight smoke, but melting drops.

Due to the non-polar structure, contact with many organic and inorganic acids, alkalis, salts, oils and alcohol components. It does not respond to the influence of hydrocarbons, but with long-term exposure to their vapors, especially at temperatures above 30 °, material deformation occurs: bloating and swelling.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

Negatively affect the integrity of polypropylene halogen products, various oxidizing gas formations and high concentration oxidizers, such as HNO3 and H2SO4. Self-proposal at + 350 °. In general, the chemical resistance of polypropylene at the same temperature mode is almost no different from polyethylene resistance indicators.

Features of production

Polyethylene is manufactured by polymerizing the ethylene gaseous substance at high or low pressure. The material produced at high pressure is called low density polyethylene (LDPE), it is polymerized in a tubular reactor or a special autoclave. Low pressure and high density polyethylene (HDPE) are obtained using a gas phase or complex organometallic catalysts.

The initial raw material for the production of polypropylene (gas propylene) is mined by refining petroleum products. The fraction selected by this method containing approximately 80% of the required gas, passes additional cleaning from extra moisture, oxygen, carbon and other impurities. The result is a high concentration propylene gas: 99-100%. Then, using special catalysts, the gaseous substance is polymerized at an average pressure in the medium of a special liquid monomer. The copolymer is often used in ethylene gas.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

Scope of application

Polypropylene, as well as chlorinated PVC (polyvinyl chloride), is actively used in the production of water pipes, as well as insulation for electrical cables and wires.Due to the resistance to ionizing radiations, the polypropylene products are widely used in medicine, the nuclear industry. Polyethylene, especially high pressure, has less durability. Therefore, it is often used in the production of various containers (PET), tarpaulin, packaging materials, thermal insulation fibers.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

What to choose?

The choice of material will depend on the type of concrete product and its purpose. Polypropylene has less weight, products from it looks more presentable, it is not so susceptible to pollution and easier to caring compared to polyethylene. But due to the high cost of raw materials, the cost of production of polypropylene products is much higher. For example, With the same performance, polyethylene packaging is almost half cheaper.

Polypropylene is not crushed, retains its appearance when loading-unloading, but it turns worse cold – becomes fragile. Polyethylene can easily withstand strong frosts.

Polyethylene and polypropylene: similarities and differences

Polyethylene and polypropylene: similarities and differences

Rate article
( No ratings yet )
Share to friends
Rebuildhom.info - construction and repair, dacha plot, apartment and country house, useful tips and photos
Add a comment