plastics: Materials that can beshaped by applying heat or pressure.Most plastics are made from polymericsynthetic resins, although afew are based on natural substances(e.g. cellulose derivatives or shellac).They fall into two main classes. Thermoplasticmaterials can be repeatedlysoftened by heating and hardenedagain on cooling. Thermosetting materialsare initially soft, but change irreversiblyto a hard rigid form onheating. Plastics contain the syntheticresin mixed with such additivesas pigments, plasticizers (toimprove flexibility), antioxidants andother stabilizers, and fillers. SeeChronology overleaf.
