Plastics are now widely 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 point of polyethylene ranges from 105 to 135 degrees, so you can pre-identify those areas of production where this material will be appropriate for use.
Polymer Features
Each plastic has at least one temperature, which makes it possible to evaluate the conditions of its direct 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 with parameters from -60 to 1000 degrees.
In addition to polyethylene, polypropylene refers to polyolefins. 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.
Templin-based plastic can withstand temperature parameters of 180-200 degrees.
The operating temperature for the use of plastics based on polyethylene and polypropylene ranges from -70 to +70 degrees.
Among the plastics having a high melting point, we single out polyamides and fluoroplastics, as well as niplon. For example, the softening of caprolon occurs at a temperature of 190-200 degrees, the melting of this plastic mass occurs in the range of 215-220 ° C. The low melting point of polyethylene and polypropylene makes these materials in demand in the chemical industry.
Features of polypropylene
This material is a substance obtained by the polymerization of propylene, a thermoplastic polymer. The process is carried out using metal complex catalysts.
The conditions for obtaining this material are similar to those under which it is possible to produce low-pressure polyethylene. Depending on the chosen catalyst, any type of polymer, as well as a mixture thereof, can be obtained.
One of the most important characteristics of the properties of this material is the temperature at which this polymer begins to melt. Under ordinary conditions, it is a white powder (or granules), the density of the material is in the range up to 0.5 g / cm³.
Depending on the molecular structure, it is customary to subdivide polypropylene into several types:
- atactic;
- syndiotactic;
- isotactic.
In stereoisomers there are differences in mechanical, physical, chemical properties. For example, atactic polypropylene is characterized by high fluidity, the material is similar to rubber in external parameters.
This material dissolves well in diethyl ether. Isotactic polypropylene has some differences in properties: density, resistance to chemical reagents.
Physicochemical parameters
The melting point of polyethylene, polypropylene is high, so these materials are currently widely used. Polypropylene is harder, it has higher abrasion resistance, it withstands temperature extremes. Its softening starts at 140 degrees, despite the fact that the melting point is 140 ° C.
This polymer is not subjected to corrosion cracking, is resistant to ultraviolet radiation and oxygen. When stabilizers are added to the polymer, such properties are reduced.
Currently, various types of polypropylene and polyethylene are used in industrial sectors.
Polypropylene has good chemical resistance. 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 elevated temperatures and the influence of direct sunlight.
At a mark of 170 degrees, the material melts, its shape is lost, as well as the main technical characteristics. Modern heating systems are not designed for similar temperatures, so it is quite possible to use polypropylene pipes.
With a short-term change in temperature level, the product is able to maintain its characteristics. With prolonged use of a polypropylene product at temperatures above 100 degrees, the period of their maximum operation will be significantly reduced.
Experts advise buying reinforced products that are minimally deformed when the temperature rises. Additional insulation and an internal aluminum or fiberglass layer will help protect the product from expansion and increase its life.
Differences between polyethylene and polypropylene
The melting point of polyethylene is slightly different from the melting point of polypropylene. Both materials soften when heated, then melt. They are resistant to mechanical deformations, are excellent dielectrics (do not conduct electric current), have low weight, are not able to interact with alkalis and solvents. Despite the many similarities, there are some differences between these materials.
Since the melting point of polyethylene is less important, it is less resistant to ultraviolet radiation.
Both plastics are in a solid state of aggregation, have no smell, taste, color. Low-pressure polyethylene has toxic properties, propylene is absolutely safe for humans.
The melting point of high pressure polyethylene is in the range from 103 to 137 degrees. Materials used in the manufacture of cosmetics, household chemicals, decorative flowerpots, dishes.
Polymer differences
As the main distinguishing characteristics of polyethylene and polypropylene, we distinguish their resistance to pollution, as well as strength. This material has excellent thermal insulation characteristics. Polypropylene is the leader in these indicators, so it is currently used in larger volumes than foamed polyethylene, the melting point of which is less important.
Crosslinked Polyethylene
The melting point of cross-linked polyethylene is much higher than that of conventional material. This polymer is a modified structure of bonds between molecules. The basis of the structure is ethylene polymerized under high pressure.
It is this material that has the highest technical characteristics of all polyethylene samples. The polymer is used to create durable parts that can withstand various chemical and mechanical loads.
The high melting point of polyethylene in the extruder determines the use of this material.
In cross-linked polyethylene, a wide-cellular network of molecular bonds is formed when transverse chains consisting of hydrogen atoms appear in the structure and are combined into a three-dimensional network.
Technical specifications
In addition to high strength and density, cross-linked polyethylene has original properties:
- melting at 200 degrees, decomposition into carbon dioxide and water;
- increase in stiffness and strength with a decrease in elongation at break;
- resistance to aggressive chemicals, biological destroyers;
- "Shape memory".
The disadvantages of cross-linked polyethylene
This material is gradually destroyed when exposed to ultraviolet radiation. 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 to them.
The resulting material has universal properties: resistance to destroyers, strength, high melting point. They allow the use of cross-linked polyethylene for the manufacture of pipes for hot or cold water supply, insulation of high voltage cables, the creation of modern building materials.
Finally
Currently, polyethylene and polypropylene are considered one of the most popular 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, you can control the process, direct it towards the production of polymer molecules.
Obtaining plastics, which have certain physical and chemical characteristics, has significantly expanded the scope of their use.
Manufacturers of products from these polymers are trying to improve technology, increase the life of products, increase their resistance to temperature extremes, and direct sunlight.