Linear low-density polyethylene is now widespread due to the presence of qualities such as strength, ductility and flexibility. The use of such material is in demand due to the fact that it is possible to achieve high results at low cost.
Polymer Properties
The properties of linear material allow its use not only in industry, but also in everyday life. Among the main qualities are the following:
- Properties such as vapor barrier and waterproofing are well suited for long-term storage of products without loss of moisture during this period.
- The material perfectly tolerates the effects of almost all organic solvents. The impact of some compounds is possible only if certain conditions are met, for example, at a temperature of 60 degrees Celsius and above.
- Due to the high elasticity of linear polyethylene, it is possible to produce thin and even ultra-thin films from it.
- It resists ultraviolet rays.
- High resistance to shock type loads .
- Despite its high performance, it has a rather low cost.
Another kind of substance
There is another type of linear polyethylene - high pressure. The characteristics of these two types of one material are quite similar, but the second has a higher strength. In addition, it also better resists mechanical loads, as well as the effects of organic liquids and high temperatures. However, at the same time, it also has a drawback, which lies in less plasticity of polyethylene. Another feature of linear high-pressure polyethylene is that it is multilayer, and this greatly increases the strength of the finished product. For this reason, it can also be operated in high pressure environments.
There is a small drawback that applies to both types of products - this is almost complete absence of decomposition. Because of this, you have to dispose of the used materials on your own.
General characteristics
The main characteristic of linear polyethylene is density. It is this characteristic that affects the structure of matter, and therefore the scope of its application. If the density of the material is different , then its structure is very different. A polymer with a higher density will have a denser lattice structure. An increase in the density of the lattice will lead to an increase in the strength of the product, but also to a decrease in the characteristics of the optical type. The density of linear polyethylene can be not only low, but also high.
Material production
As for the use of linear polyethylene, it is very often used in industry, since its chemical resistance is very high. Most often, different containers are made from this material. To date, three types of LDL production are used.
- The first method is called suspension polymerization. In this case, the manufacturing process takes place in a certain kind of suspension, to which the catalysts are added. In this case, it is necessary to constantly stir the composition. In this case, you can get a composition that will have a completely homogeneous structure, but at the same time it will contain the remains of the stabilizer.
- The second type is solution type polymerization. A feature of this method is that linear polyethylene is made while maintaining a certain temperature, from 60 to 130 degrees Celsius. As a result, it is possible to obtain a material that will perfectly resist abrasion and have high ductility. However, there is a problem associated with the choice of catalyst, since at elevated temperatures, many substances begin to enter into chemical reactions.
- The third type is the oldest production method called gas phase diffusion polymerization. Using this method, it is possible to obtain a material that will be distinguished by its purity, but it will not have uniformity of composition, which will cause different reactions in different areas, to the same composition.
It is worth noting that when using any method, LDL is obtained in granules. To give it the final shape, heat treatment of the material is used.
High Density Polyethylene
High density polyethylene is produced using a different technology. A process for the polymerization of a substance such as ethylene in an autoclave or in a reactor is used. In order to carry out this process, it is necessary to heat ethylene to a temperature of 700 degrees Celsius, after which it must be fed to the first part of the reactor under a pressure of 25 MPa. In this case, there must be oxygen and an initializer. In the first part of the reactor, the substance heats up even more, up to 1800 degrees Celsius.
After reaching this temperature, the material enters the second part of the reactor, where the temperature drops to 190-300 degrees, and the pressure rises to 130-250 MPa. It is here under these conditions that polymerization occurs. It is important to add that a small percentage of initializer will be present in the final product.
Types of LDL
Today, low density polyethylene is used quite widely and most often for the manufacture of various films. Several types of material are known.
- Injection polyethylene. It is mainly used for packing hot food. This is facilitated by high ductility, high resistance to moisture and temperature.
- Film polyethylene. Different bags are usually made from this variety, which are characterized by high elasticity.
- Rotational polyethylene. Used for the manufacture of tanks characterized by chemical neutrality.
LLDPE Linear Polyethylene
This type of substance is low density, which is characterized by the fact that its structure consists of a large number of short branches. The main source of this substance is the copolymerization of ethylene and olefin.
The main scope of this type of polyethylene is films with a small and medium margin of safety. A distinctive feature is that such a material is specifically designed for operation in high temperature environments with high performance. The temperature regime that a product made of such a film can withstand is from -20 to +60 degrees Celsius. It also has high frost resistance and can be used for the production of food packaging.
Linear expansion
Among the diverse characteristics of polyethylene, linear expansion also plays a very important role. For example, if we compare these coefficients for metal and polyethylene, then for the second it will be 14 times higher. If you cover the surface of a convex type with a film of polyethylene, then due to the difference in this coefficient, the adhesion will change significantly, it will increase.
To summarize all of the above, it becomes obvious that polyethylene has recently become increasingly popular. This is facilitated by the fact that less money is spent on its production, due to which its cost is much lower than that of metal, for example, but at the same time its operational characteristics are quite high. In addition, it is also possible to make various containers from it, which can be used both in industry and in the food industry.