An introduction to polyethylene - PE
In general, PE is: strong, safe and versatile
PE is used for more than an third of the world's total consumption of plastic materials. PE can be used for a large variety of applications from manufacturing ultra-thin film to robust barrels or bottles. What's more, PE is resistant to aggressive substances. It can withstand extreme climatic changes and does not contaminate ground water, this means when burnt, it releases CO2 and water vapour, both of which exist in vast amounts in nature.
By producing higher or lower density polyethylene, the right material for every application can be created. 90% of applications use the following polyethylene types: LDPE, HDPE and LLDPE.
Polyethylene
LDPE low density polyethylene
Produced under high pressure from 1000 to 3000 bar, and at temperatures of 150 to 300°C. This process creates molecular chains with a relatively high number of long branches.
LDPE
HDPE high density polyethylene
Produced under low pressure from 1 to 50 bar, and at temperatures of 20 to max. 150°C. This process creates long molecular chains with few lateral branches which are also very short. The result of which is densely packed molecular chains and therefore a high density of material can be achieved.
HDPE
LLDPE low density polyethylene
Produced under slightly increased pressure (50 - 100 bar) and a change of catalyst, resulting in molecules similar to HDPE, however, lateral chains are longer. The resulting material is LLDPE.
Particularly useful granulates can be mixed to blend various materials for special applications, e.g. LD / LLDPE.
LLDPE
Which PE for what application? - Characteristics of types of polyethylene
LDPE is a standard material. It is relatively soft and easy to work. LDPE is often mixed with LLDPE as this results in improved welded seam strength and, to a certain extent, improved puncture resistance. However, the welding temperature must be increased, as LL has a higher melting point than LD.
Due to the densely packed molecular chains in PE-HD, significantly thinner films can be produced with this material than with other types, yet preserve a similar resistance to perforation. Due to the short and relatively few side branches, however, the films are susceptible to tearing. If the application is accurately anticipated, PE-HD can offer an inexpensive alternative.
MDPE stands for medium density polyethylene. This is a material which is very similar to a HDPE but with reduced density. It feels softer to touch than HDPE. However it is nearly as tough as HDPE.
PREMIUM recycled material: recycled material which is used for PREMIUM quality products comes from waste arising from production processes. The mechanical characteristics of the material are not as good as with new material, as the molecular chains are destroyed by re-melting and are shorter as a result. The characteristics are, however, definable and can be used in production to achieve excellent high quality products.
Standard recycled material: recycled standard material is made from products which have already been deployed for some other use, e.g. packaging films etc. As the quality of this material cannot be clearly defined, it is harder to assess its characteristics for welding, folding when extruded, etc. The quality of the material is sufficient for many applications but does not by far reach the level of PREMIUM recycled material.
Along with the use of recycled material, so-called NT (non-type) material is also used to produce plastic products. These materials do not meet the required specifications of top quality material and therefore command lower market prices. The problem here is, however, that these materials are not always available or available in sufficient quantities from spot markets.