Polyethylene is a thermoplastic polymer of ethylene. This plastic, the most popular in the world, is a white waxy mass, chemically resistant, cold-resistant, with insulating and shock-absorbing properties, that softens when heated (at 80-120°C), solidifies when cooled and has low adhesion. Polyethylene is produced by way of ethylene polymerization. There are high-density, low-density and medium-density polyethylenes, depending on the method of production.
Low-density polyethylene (LDPE) has a specific density of 0.91-0.925 g/cm3. Low-density polyethylene is characterized by high rigidity, crack-resistance, transparency, flexibility and high elongation, plus low shrinkage during molding.
LDPE has a melting point of 105°C. It is water-resistant, not reactive in contact with alkali, salt solutions, organic and inorganic acids. It is insoluble at room temperature and does not swell in any known solvents. Around 80% of LDPE is used for the production of films, mainly packaging films, as well as cable insulation and extrusion when producing cardboard coatings and other materials.
Linear low-density polyethylene (LLDPE) has a melting point of 122°C. Advantages: high softening temperature (which allows to use it for hot products packaging), excellent performance characteristics at low and high temperatures, surface gloss and crack-resistance. It is used for the production of stretch films, shrink films and bags for heavy-weight goods and waste. LLDPE is used for the production of frozen food packaging due to its performance characteristics at low temperatures. The use of this polymer in the production of stretch films is rapidly growing.
Medium-density polyethylene (MDPE) has a specific density of around 940 kg/m3. It is highly shock- and fracture-resistant. Medium-density polyethylene has better scratch- and crack-resistance compared to HDPE (high-density polyethylene). MDPE is used for the production of conventional and shrink films, bags, shopping bags and screw caps.
High-density Polyethylene (HDPE) has a specific density of 0.941-0.959 g/cm3. HDPE is characterized by excellent rigidity, wear-resistance, chemical resistance and surface gloss. Since HDPE is more rigid than other polyethylenes, it is used for blow molding of bottles, barrels and cans and the extrusion of gas and water pipes. When mixed with LDPE, it is well suited for the production of films since LDPE and HDPE are fully compatible. This polyethylene is highly suitable for the production of foam materials for thermal insulation and for protection from mechanical damages (PPE).
In addition to main polyethylene types (LDPE, HDPE), medium-density polyethylene (MDPE), cross-linked polyethylene (PE-X) and ultra-high-molecular-weight polyethylene (UHMWPE) are also used for industrial purposes. Polyethylene is processed using all known plastics processing methods - extrusion, extrusion blowing, injection molding, pneumatic molding and rotational molding.