Polymers or more popular name Plastics are substances containing a large number of structural units joined by the same type of linkage. Polymers in the natural world have been around since the beginning of time. These substances often form into a chain-like structure. Starch, cellulose, and rubber all possess polymeric properties. Artifical polymers have been studied since 1832. Today, the polymer industry has grown to be larger than the aluminum, copper and steel industries combined. Plastics which are most widely used today are:
High Density Polyethylene (HDPE): a rugged material which is easily moulded, has a high resistance to impact and is not affected by most chemicals. Mainly used in blow and injection moulding it may also be vacuum formed or extruded.
Polyvinyl Chloride (PVC): a very common plastic and one of the earliest types developed. PVC’s often contain chemicals called plasticisers which can leach from the plastic over time. You will find it in roofing gutters, electrical insulation and fittings and waste pipes. For food use a special grade has been developed called uPVC and is “unplasticised”. Be careful in selecting a PVC product for food contact. The qualities of PVC vary and they can be flexible or rigid. It is commonly injection moulded, extruded, blow moulded and vacuum formed. PVC is subject to attack by solvents.
Polypropylene (PP): Although mainly used in injection moulding, it may be blow or rotationally moulded, vacuum formed or extruded. PP is an easy to mould material which has medium impact resistance, high structural strength and is resistant to a wide range of chemicals.
Polyethylene Terephthalate (PET): a form of polyester and its most visible use is in fizzy drink bottles and honey jars. Soft drink bottles can be recycled into clothing fibre. It has very high impact resistance and modest structural strength. It is resistant to many solvents and is particularly suitable for food contact. You can freeze it but not boil or microwave. It is commonly injection and blow moulded.
Polypropylene Co-Polymer (PPCO): Because it is a Polypropylene molecule with about 2% HDPE added it has a mixture of the properties of HDPE and Polypropylene including very high impact resistance and moderate structural strength. Primarily used in injection moulding. It is resistant to a wide range of chemicals.
Low Density Polyethylene (LDPE or LLDPE): It is rotationally, blow and injection moulded though it may be vacuum formed or extruded. LDPE has very high impact resistance, modest structural strength and good resistance to a huge range of chemicals.
Acrylonitrile Butadiene Styrene (ABS): It has a shiny impervious surface, good impact resistance and very good structural strength. It is commonly vacuum formed or extruded.
Styrene Acrylonitrile (SAN): It has medium impact resistance, very good structural strength and has a shiny impervious surface. It is mostly injection moulded however it is not the best at high or low temperatures.
Nylon: It generally has excellent structural and impact strength, great working temperature range and is resistant to petrol, oils and solvents. It comes in many and varied forms. It is commonly injection moulded and extruded. It is subject to attack by acids.
High Impact Polystyrene (HIPS): Medium impact resistance and excellent structural strength. It is commonly injection moulded.
Not very good at high or low temperatures.
Polycarbonate (PC): It has an incredibly high resistance to impact. For this reason it is a major component in bullet-proof “glass” and commonly used for beer jugs and conservatories. Subject to attack from solvents. It is commonly injection moulded, extruded, and blow moulded. It has ability to handle high temperatures for that reason it is used in microwave cookware.
Nitrile Rubber (Nitrile): It is synthetic, as opposed to natural latex. Although it is not considered to be a “plastic” it can be injection moulded. Car tyres are made of Nitrile.
Styrene: a generic name given to a range of polymers. It is an organic compound with the chemical formula C6H5CH=CH2. Excellent stuctural strength and clarity offset poor impact resistance and susceptibility to attack from solvents. It is commonly injection moulded.