The two types of polymers commonly used in the plastics industry are thermoplastics and thermosets.
(i) Thermoplastics
Thermoplastics are the most widely used type of polymer. Thermoplastics polymers are comprised of many long polymeric chains. The entanglement of these polymeric chains is what gives thermoplastics polymers much of their strength.
Thermoplastics are typically melt processed. Melt processing thermoplastics involves heating the polymer until the polymer chains become untangled. Melt processing only changes the physical structure of the material.
After the polymer has been melted, the polymer is forced into a mould or die. This is where the shape of the final product is determined. The melted polymer is cooled and the polymeric chains are re-entangled, giving the rigidity to the once fluid plastics material.
Thermoplastics parts can be ground up and re-processed. Therefore, most thermoplastics parts are recyclable.
(ii) Thermosets
Thermosets, such as phenolics, are not as commonly used as thermoplastics materials. Thermosets are polymers comprised of one large polymer matrix. The interconnection of the polymer matrix gives the thermoset polymer it’s strength.
Thermosets are typically poured or injected into a heated mould or die. The heat from the mould or form causes the thermoset to cure and crosslink.
When thermosets cure and crosslink, both the chemical and physical structure of the polymer has changed. Thermosets cannot be melted and reprocessed, and therefore are not recyclable. However, some scrap may be ground up and used as filler for other polymers.
