Overview

Polyethylene (PE) can be processed by all known processing operations, including injection moulding, extrusion (fibre and filament), compression moulding, blow moulding, thermoforming, rotational moulding and transfer moulding, casting, sintering and coating, and orientation.

Injection moulding is used for PE with a high melt flow rate (MFR) (low viscosity) and narrow molecular weight distribution (MWD). The viscous resin is squirted by a means of a plunger out of a heated cylinder into a water-chilled mould, where it is cooled before removal. Processing is performed from around 170 to 300 C, depending on the material, but all types begin to decompose above 310 C (and very short processing times are required beyond this temperature). PE does undergo some degree of shrinkage during injection moulding (low-density PE (LDPE) 1.5 3% and high-density PE (HDPE) 2 4%). Injection moulding is used to produce a wide variety of domestic and industrial items, which are too numerous to be listed in full.

Extrusion is the process by which melted PE is extruded at 160 240 C to produce pipes using single-or twin-screw extruders and with mould temperatures of up to 300 C to produce film, sheeting, and monofilaments. Extrusion products are often subdivided into groups that include filaments of circular cross-section, profiles of irregular cross-section, asymmetric tubes and pipes, and flat products such as films and sheets. The extrusion process is also used to cover continuous substrates with a polymeric layer (extrusion covering process) and is a major element of blow moulding and the film blowing...