We explain what polyethylene is, its main properties and the different uses of this famous polymer.
What is Polyethylene?
It is known as polyethylene (PE) or polymethylene to the simplest of the polymers from a chemical point of view, composed of a linear and repeating unit of atoms carbon and hydrogen. It is one of the most economical and simple plastic materials to manufacture, which is why approximately 80 million tons are generated annually throughout the world.
The manufacture of polyethylene is carried out through different polymerization processes, either through free radicals, through anionic or cationic processes or by coordination from ions. Depending on the type of reaction chosen, a different form of it will be obtained plastic.
This material was first obtained by the German chemist Hans von Peachmann in 1898, due to an accident during the diazomethane firing. It was not until 1933 that it was intentionally synthesized, and chemists Reginald Gibson and Eric Fawcett did it in England, applying a pressure of 1,400 bar and a temperature 170 ºC in an autoclave (metal container that allows working at high pressures). The material they obtained is known today as low-grade polyethylene. density.
In later years, Karl Ziegler and Giulio Natta achieved a polymerization to pressures smaller (and therefore cheaper) using catalysts during the reaction and obtaining a higher density polyethylene. Such a discovery resulted in the development of the Ziegler-Natta catalysts, which made them winners of the Nobel Prize in Chemistry in 1963.
Polyethylene properties
Polyethylene is chemically inert, that is, it is almost non-reactive, and has a whitish and translucent appearance. Tenacious and flexible at room temperature, it has a soft and scratchable surface.
His melting point It is 110 ºC and if it is reduced below its ambient temperature, it gains in hardness and brittleness. In liquid state polyethylene behaves like a non-Newtonian fluid, that is, its viscosity is not constant but depends on the temperature and on whether a shear stress is applied to it. His viscosity it decreases at higher temperatures and has a density of 0.80 g / cm3 at about 120 ºC.
Polyethylene is not a good conductor of heat nor of electricity and its density (in solid state) varies according to temperature. In general terms, the mechanical properties of the material will depend on the thermal history of its manufacture, that is, on the specific way in which it has cooled and solidified.
Uses of polyethylene
Polyethylene is an extremely versatile plastic with which many items can be made, such as:
- Plastic bags of all kinds.
- Foils for packaging of all kinds of food, drugs and agro-industrial products.
- Hermetic containers for home use.
- Pipes for irrigation.
- Knobs, tubes, coatings.
- Kitchen film (plastic wrap).
- Containers for detergents, shampoo, bleach, etc.
- Mechanical parts, chain guides.
- Baby bottles, toys, disposable diaper base.
- Buckets of water and drums.
- Covering of lagoons, channels, water tanks, etc.
- Manufacture of wood flour compound.
- Raw material for rotational molding.
- Cables, wires, pipes.