Plastics are a wide variety of synthetic polymers that are delivered usually in form of pellets and can be melted in the heat. The viscous melt can then be formed into a multitude of shapes: Extruded into fibers, films, sheets, tubes or complex profiles or molded into almost any shape imaginable. Depending on the chemistry involved, Thermoplastics are available in a wide range of hardness and heat/light/chemical resistance, so it is no surprise that we find them everywhere in products around us. Plastic parts can be recycled by re-melting. Important materials are polyethylene (PE), polypropylene (PP), polyester (e.g. PET) and polyamide (PA66; “Nylon”).
Rubber can be made out of natural polymers, e.g. latex of the hevea-plant, or a variety of synthetic polymers. However, in order to get a product which shows the typical elasticity, i.e. stretching under stress and immediately recovering without it, the polymer has to undergo a thermal treatment known as vulcanization or cross-linking. The cross-linking is usually done by chemical agents, which have to be mixed into the rubber (amongst other ingredients) prior to the shaping and subsequent vulcanization. A wide variety of rubber polymers are available with different characteristics in terms of mechanical/thermal/chemical stability. Rubber can be found in tires, hose and seals. Because cross-linking is almost irreversible, rubber goods are rather difficult to recycle. Thermoplastic Elastomers do not need vulcanization and are as easy as other plastics to be manufactured into parts; they lack, however, the thermal stability and mechanical resistance of cross-linked rubber.