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Saturday, April 14, 2012

Acrylonitrile butadiene styrene (ABS)

Acrylonitrile butadiene styrene, abbreviated ABS,  has the chemical formula (C8H8)x· (C4H6)y· (C3H3N)z , CAS Registry Number 9003-56-9, and ChemSpider 23143.

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.

acrylonitrile

acrylonitrile

1,3-butadiene 

1,3-butadiene

styrene

styrene

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

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.

Resin code 7

For the purposes of recycling, ABS is in group 7.  For more information about  plastics recycling codes, click here for a pdf published by the American Chemistry Council.


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