Linear polyethylene: description, specifications, application

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Linear low-density polyethylene is now widely used due to the presence of such qualities 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.

Properties of polymers

The properties of the linear material allow it to be used 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 food without losing moisture during this period.
• Material perfectly tolerates the effects of almost all organic solvents. The impact of some compounds is possible only under certain conditions, for example, at a temperature of 60 degrees Celsius and above.
• Due to the high elasticity of linear polyethylene, thin and even ultra-thin films can be made from it.
• Good UV resistancerays.
• High impact resistance.
• Despite the high performance, it has a fairly 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 withstands 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 the less plasticity of polyethylene. Another feature of high-density linear polyethylene is that it is produced in multilayer, and this greatly increases the strength of the finished product. For this reason, it can be used in pressurized environments.

There is a small drawback that applies to both types of product - this is the almost complete absence of decomposition. Because of this, you have to dispose of the used materials yourself.

General Features

The main characteristic of linear polyethylene is its density. It is this characteristic that affects the structure of the substance, and hence the scope of its application. If the density of the material is different, then its structure is also very different. A polymer with a higher density will also 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 at the same time to a decrease incharacteristics of the optical type. The density of linear polyethylene can be not only low, but also high.

Material production

With regard to the application of linear polyethylene, it is very often used in industry, as its chemical resistance is very high. Most often, different containers are made from this material. Today, 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 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 stabilizer residues.
• The second type is solution type polymerization. A feature of this method is that linear polyethylene is produced while maintaining a certain temperature, from 60 to 130 degrees Celsius. As a result, you can get a material that will perfectly resist abrasion and have high ductility. However, there is a problem 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 polymerization using diffusion. Using this method, you can get a material that will be distinguished by its purity, but at the same time it will not have uniformity.composition, which will cause different reactions in different areas, to the same composition.

It is worth noting that with any method, LDL is obtained in granules. Heat treatment of the material is used to give it its final shape.

High density polyethylene

High-density polyethylene is produced using a different technology. Here, a method is used to polymerize a substance such as ethylene in an autoclave or in a reactor. In order to carry out this process, it is necessary to heat ethylene to a temperature of 700 degrees Celsius, after which, under a pressure of 25 MPa, it must be fed into the first part of the reactor. 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 such conditions, that polymerization occurs. It is important to add that a small percentage of the 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.

• Moulded polyethylene. It is mainly used for packaging hot food. This is facilitated by high plasticity, highresistance to moisture and temperature.
• Film polyethylene. This variety is usually used to make different bags, which are characterized by high elasticity.
• Rotational polyethylene. Used to make tanks characterized by chemical neutrality.

Linear polyethylene LLDPE

This kind of low density substance, which is characterized by the fact that its structure consists of a large number of short branches. The main source of obtaining this substance is the process of 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 material is specially designed for operation in a high temperature environment 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 various characteristics of polyethylene, linear expansion also plays a very important role. For example, if we compare these coefficients for metal and for polyethylene, then for the second it will be 14 times higher. If the surface of a convex type is covered with a film of polyethylene, then due to the difference in this coefficient, adhesion will greatly change, it will increase.

Summing up all of the above, it becomes obvious that polyethylene inhas become more and more popular lately. This is facilitated by the fact that less money is spent on its production, which is why its cost is much lower than that of metal, for example, but at the same time its performance is quite high. In addition, it can also be used to produce various containers that can be used both in industry and in the food industry.