Melting point of polyethylene and polypropylene

The plastic masses are now widelyare used in various industries, as well as in everyday life. That is why, in many situations, it is necessary to pre-select the polymer for certain temperature indicators of their operation.

For example, the melting temperature of polyethylene ranges from 105 to 135 degrees, so you can identify in advance those areas of production, where this material will be appropriate for use.

Features of polymers

Each plastic has at least onetemperature, which makes it possible to assess the conditions of its immediate operation. For example, polyolefins, which include plastics and plastics, have low melting points.

The melting point of polyethylene in degrees depends on the density, and the operation of this material is allowed at parameters from -60 to 1000 degrees.

In addition to polyethylene, polyolefins includepolypropylene. The melting point of low-pressure polyethylene makes it possible to use this material at low temperatures, the material becomes brittle only at -140 degrees.

Melting of polypropylene is observed in the temperature range from 164 to 170 degrees. From -8 ° C this polymer becomes brittle.

The plastic on the basis of the temperature is able to withstand the temperature parameters of 180-200 degrees.

The operating temperature of the operation of plastics based on polyethylene and polypropylene ranges from -70 to +70 degrees.

Among plastics that have a high temperaturemelting, we distinguish polyamides and fluoroplastics, and also niplon. For example, softening of caprolon occurs at a temperature of 190-200 degrees, melting of this plastic mass occurs in the range of 215-220 ° C. The low melting temperature of polyethylene and polypropylene makes these materials in demand in chemical production.

Features of polypropylene

This material is a substance obtained as a result of a polymerization reaction of propylene, a thermoplastic polymer. The process is carried out using metal complex catalysts.

Conditions for obtaining this materialsimilar to those in which low-density polyethylene can be produced. Depending on the catalyst selected, it is possible to obtain any type of polymer, as well as a mixture thereof.

One of the most important characteristics of the properties of thismaterial is the temperature at which this polymer begins to melt. Under normal conditions, it is a white powder (or granules), the density of the material is in the range of up to 0.5 g / cm³.

Depending on the molecular structure, it is customary to subdivide polypropylene into several types:

• atactic;
• syndiotactic;
• isotactic.

Stereoisomers have differences inmechanical, physical, chemical properties. For example, atactic polypropylene is characterized by high fluidity, the material is similar to rubber by external parameters.

This material dissolves well in diethyl ether. In isotactic polypropylene there are some differences in properties: density, resistance to chemical reagents.

Physico-chemical parameters

Melting point of polyethylene, polypropylenehas high indicators, therefore these materials are now widely used. Polypropylene is harder, it has higher resistance to abrasion, it can withstand temperature fluctuations perfectly. Its softening begins at 140 degrees, despite the fact that the melting point is 140 ° C.

This polymer is not subjected to stress-corrosion cracking, it is resistant to ultraviolet irradiation and oxygen. When these stabilizers are added to the polymer, these properties are reduced.

At present, in the industrial sectors, a variety of types of polypropylene and polyethylene are used.

Polypropylene has good chemical stability. For example, when placed in organic solvents, only a slight swelling occurs.

If the temperature rises to 100 degrees, the material can dissolve in aromatic hydrocarbons.

The presence of tertiary carbon atoms in the molecule explains the resistance of the polymer to high temperatures and the influence of direct sunlight.

At a mark of 170 degrees, melting takes placematerial, its shape is lost, as well as the main technical characteristics. Modern heating systems are not designed for such temperatures, so it is possible to use polypropylene pipes.

With a short-term change in the temperature levelthe product is able to maintain its characteristics. If the polypropylene product is used for a long time, temperatures exceeding 100 degrees will significantly shorten the period of maximum use.

Experts advise buying reinforcedProducts that are minimally deformed when the temperature rises. Additional insulation and an internal aluminum or fiberglass layer will help protect the product from expansion, increase the period of its operation.

Differences between polyethylene and polypropylene

The melting point of polyethylene is insignificantdiffers from the melting point of polypropylene. Both materials in the case of heating soften, then melt. They are resistant to mechanical deformations, are excellent dielectrics (do not conduct electric current), have a negligible weight, are not able to react with alkalis and solvents. Despite the numerous similarities, there are between these materials and some differences.

Since the melting point of polyethylene is less important, it is less resistant to ultraviolet radiation.

Both plastics are in solid aggregate state, have no smell, taste, color. Polyethylene of low pressure has toxic properties, propylene is absolutely safe for humans.

Melting point of high-density polyethylenepressure is in the range of 103 to 137 degrees. Materials used in the manufacture of cosmetics, household chemicals, decorative flowerpots, dishes.

Differences of polymers

As the main distinguishing characteristicspolyethylene and polypropylene, we distinguish their resistance to contamination, as well as strength. This material has excellent thermal insulation characteristics. Polypropylene is the leader in these indicators, so it is currently used in large volumes than foamed polyethylene, the melting point of which is of less importance.

Crosslinked polyethylene

The melting point of cross-linked polyethyleneis much higher than that of a conventional material. This polymer is a modified structure of bonds between molecules. The basis of the structure is ethylene, polymerized under high pressure.

This material has the highesttechnical characteristics of all polyethylene samples. The polymer is used to create strong parts that can withstand various chemical, mechanical loads.

The high melting temperature of polyethylene in the extruder predetermines the areas of use of this material.

In cross-linked polyethylene, a wide-mesh meshstructure of molecular bonds formed when there appear in the structure of transverse chains consisting of hydrogen atoms, which are combined into a three-dimensional grid.

Technical specifications

In addition to high strength and density, crosslinked polyethylene has original properties:

• melting at 200 degrees, decomposition into carbon dioxide and water;
• Increase of stiffness and strength with decreasing elongation at break;
• resistance to aggressive chemicals, biological destroyers;
• "Memory of form."

Disadvantages of cross-linked polyethylene

This material when exposed to ultravioletirradiation is gradually destroyed. Oxygen, penetrating into its structure, destroys this material. In order to eliminate these shortcomings, the products are covered with special protective shells made of other materials, or a layer of paint is applied on them.

The resulting material has universal properties: resistance to destructors, strength, high melting point. They allow the use of cross-linked polyethylene for the manufacture of pipes of hot or cold water supply, insulation of high voltage cable, the creation of modern building materials.

Finally

At present, polyethylene and polypropyleneare considered one of the most sought-after materials. Depending on the conditions of the process, it is possible to obtain polymers with specified technical characteristics.

For example, by creating a certain pressure, temperature, choosing a catalyst, it is possible to control the process, direct it towards the production of polymer molecules.

The production of plastics, which have certain physical and chemical characteristics, has significantly expanded the scope of their use.

Manufacturers of products from these polymers tryimprove technology, extend the life of products, increase their resistance to temperature changes, direct sunlight.