2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16
Every day, new materials obtained by artificial means are introduced into the sphere of human activity. One of these is high molecular weight polyethylene, which has become a commercial product since the 1950s, but it is only now gaining real popularity.
Description
High molecular weight polyethylene is a type of thermoplastic polymerized ethylene. Its main feature is very long molecular chains. They are better perceived and transmit loads, "compensating" them with intermolecular interactions.
The appearance of the material is no different from other types of plastic. It is odorless, tasteless, non-toxic. It can be given any color by the introduction of colors. At the same time, it has a set of properties that set it apart from other polymers.
High molecular weight polyethylene is a tough material with great impact strength. He is able to withstandsignificant stresses. It does not absorb moisture, which is why it does not interact with human skin and feels slippery. In addition, it has high abrasion resistance (more than steel) and a low coefficient of friction.
Properties of high molecular weight polyethylene
As already noted, the main feature of this high molecular weight polymer are long molecular chains. Moreover, they are oriented in the same direction. They are located almost parallel to each other. This explains the strength of the material.
Despite the fact that high molecular weight polyethylene forms long chains, the bond between individual molecules is weak. This figure is an order of magnitude lower than that of Kevlar, which is no less durable material. This feature makes the polymer not heat resistant - it melts at a temperature of 144 degrees Celsius.
This polyethylene contains no esters, amines or hydroxyl groups that make materials susceptible to reactive and heavy environments. Thanks to this, the substance is not subject to water, moisture, aggressive reagents, microorganisms and UV rays.
Main recycling methods
The requirements according to which high molecular weight polyethylene should be produced, GOST 16338-85 contains. According to them, the synthesis of the material is carried out by the action of metallocene catalysts on the monomer - ethylene. For the production of products directly, the following main types of processing are used:
- Gel spinning. raw materialmixed with solvent. The resulting mass is forced through the holes into the water. The resulting filaments are fired in kilns while drawing them out and removing the solvent.
- Hot pressing and sintering. The powdery mass is compressed with great force, thereby obtaining a homogeneous material. Then it is subjected to heat treatment - sintering at a temperature of 150-200 degrees.
- Plunger extrusion. The raw material is melted to a homogeneous, rubber-like mass, and then squeezed out through special nozzles.
Gel spinning is the most widespread. After all, it is in this way that high-molecular polyethylene fibers with great strength are obtained.
Military use
Fibers, for the production of which a high molecular weight polymer is used, are widely used to create personal protective equipment, in particular bulletproof vests. Due to such properties of the threads as low specific gravity and high yield strength (the ratio of these indicators is 7-8 times higher than that of steel), the armor is light and resistant to bullets, shrapnel and other damaging elements.
Body armor is made from sheets obtained by applying fibers on top of each other at different angles. Thanks to this technology, multiaxial fabrics appear - a special kind of vitreous fabrics that endure stresses in any direction. High molecular weight polyethylene is used to protect the torso, limbs. Propertiesmulti-axial fabrics allow armored vehicles to be protected, as well as the use of fibers to create cut-resistant gloves.
Medical applications
In medicine, high molecular weight polyethylene is used mainly to create implants for the hip joint and spine, knee joints. It was first used for this purpose back in 1962. And since then began to dominate.
Widely used and modified material - mesh or cross-linked polymer. It is obtained by shelling the fibers of high molecular weight polyethylene with gamma quanta or electrons, which sew the threads together. After that, it is exposed to heat, which reduces its redox ability.
Fibers based on this raw material are also used for suturing. The leader in the production of these products is DSM, which supplies the medical market with suture threads called Dyneema Purity.
Industrial use
High-molecular-weight polyethylene sheet, which is supplied to the manufacturing market in flat billets 2 cm thick, has found the greatest application in the industry. Prestige-class plastic windows, PVC panels and PVC profiles of various configurations are made on its basis.
In mechanical engineering for the production of sealing rings, bearings, the creation of parts operating in a hydraulic or oil environment, andalso in pneumatic installations with high operating pressure, high molecular weight polyethylene 1000 is most often used - one of the main types of polymer.
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