ABS is derived from acrylonitrile, butadiene, and styrene and carbon. Acrylonitrile is a synthetic monomer produced from propylene and ammonia; butadiene is a petroleum hydrocarbon obtained from the C4 fraction of steam cracking; styrene monomer is made by dehydrogenation of ethyl benzene — a hydrocarbon obtained in the reaction of ethylene and benzene.
ABS is a common thermoplastic that has a melting point of approximately 105 °C (221 °F). A thermoplastic is a polymer that softens and turns to liquid when heated and conversely solidifies to a glass-like state when cooled. ABS is a copolymer, actually a terpolymer because of its three monomer constituents, made by
polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30% butadiene and 40 to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups from neighboring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures.
ABS pellets for injection molding. Image source: eBay.
For the majority of applications, ABS can be used between −25 and 60 °C (−13 and 140 °F) as its mechanical properties vary with temperature. The properties are created by rubber toughening, where fine particles of elastomer are distributed throughout the rigid matrix.