High density polyethylene is a thermoplastic polymer of the olefinic polymer family and it is called HDPE (High Density Polyethylene). This material is used in disposable packaging and also has industrial applications.
HDPE is obtained by addition, i.e. by adding different units or layers of ethylene. To obtain them, the polymerisation process called Ziegler-Natta is used, which is a catalytic polymerisation process. Three types are carried out: in solution, in the gas phase and in suspension. Its molecules have hardly any branching, which gives it a considerable molecular density. It is best known for its strength to density ratio (between 930 and 970 kg/m3).
Properties of HDPE plastic
- It has very good stiffness and resistance to both chemical and thermal stress.
- It is a solid, colourless and almost opaque plastic. In fact, being a paintable and glueable material, it is easy to customise.
- It is easy to produce, low cost and easy to process by injection and extrusion.
- It is highly resistant to temperature (high and low), impact and tensile strength. In fact, its greatest advantage is its stiffness and strength.
Applications and uses
This type of plastic is used in the manufacture of everyday objects, such as bottles, containers, toys, helmets, cosmetic and food containers and all kinds of household objects. In fact, it is the synthetic polymer with the highest production volume worldwide.
Recycling of high density polyethylene
There are different types of plastic and their recycling is different. HDPE is easy to recycle and generally, thermal or mechanical recycling is used to give it a second life. The first step for the recycling of this material would be the separation by type of resin, because if this is not done it would be very difficult or impossible to recycle it.
- Mechanical recycling: once the material is stored and identified, it is crushed into pellets that can be reused in production. Before this, the material should be washed to remove any impurities that may damage the properties of the recycled material. However, this type of recycling is recommended when the material is only slightly contaminated.
- Thermal recycling: this involves burning the plastic, transforming its waste into ash, slag and gases for energy. It is a destructive method and a study is necessary to determine if this process can be used.
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