Acrylonitrile butadiene styrene(ABS) (chemical formula(C8H8)x· (C4H6)y·(C3H3N)z) is a commonthermoplastic. Itsglass transitiontemperature is approximately 105 °C (221 °F).ABS isamorphousand therefore has no true melting point.
ABS is aterpolymermade by polymerizingstyreneandacrylonitrilein the presence ofpolybutadiene. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30%butadieneand 40 to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). Thenitrilegroups from neighboring chains, being polar, attract each other and bind the chains together, making ABS stronger than purepolystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, arubberysubstance, provides resilience even at lowtemperatures. For the majority of applications, ABS can be used between −20 and 80 °C (−4 and 176 °F) as its mechanical properties vary with temperature.The properties are created byrubber toughening, where fine particles of elastomer are distributed throughout the rigid matrix.
ABS is derived from acrylonitrile, butadiene, and styrene. Acrylonitrile is a synthetic monomer produced frompropyleneandammonia; butadiene is a petroleum hydrocarbon obtained from the C4 fraction ofsteam cracking; styrene monomer is made bydehydrogenationofethyl benzene — a hydrocarbon obtained in the reaction ofethyleneandbenzene.
ABS combines the strength and rigidity of acrylonitrile and styrenepolymerswith the toughness of polybutadiene rubber. While the cost of producing ABS is roughly twice the cost of producing polystyrene, it is considered superior for its hardness, gloss, toughness, and electrical insulation properties.
According to the European plastictrade associationPlasticsEurope, industrial production of 1 kg (2.2 lb) of ABS resin in Europe uses an average of 95.34 MJ(26.48 kWh) and is derived fromnatural gasandpetroleum.
The most important mechanical properties of ABS are impact resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. The impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and also acrylonitrile, although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads. Thus, changing the proportions of its components ABS can be prepared in different grades. Two major categories could be ABS for extrusion and ABS for injection moulding, then high and medium impact resistance. Generally ABS would have useful characteristics within a temperature range from −20 to 80 °C (−4 to 176 °F).
The final properties will be influenced to some extent by the conditions under which the material is processed to the final product. For example, molding at a high temperature improves the gloss and heat resistance of the product whereas the highest impact resistance and strength are obtained by molding at low temperature. Fibers (usually glass fibers) and additives can be mixed in the resin pellets to make the final product strong and raise the operating range to as high as 80 °C (176 °F). Pigments can also be added, as the raw material original color is translucent ivory to white. The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. Other factors include exposure to ultraviolet radiation, for which additives are also available to protect against.
ABS polymers are resistant to aqueous acids, alkalis, concentratedhydrochloricandphosphoricacids,alcoholsand animal, vegetable and mineral oils, but they are swollen byglacial acetic acid,carbon tetrachlorideandaromatichydrocarbons and are attacked by concentratedsulfuricandnitricacids. They are soluble inesters,ketones,ethylene dichlorideandacetone.
Even though ABS plastics are used largely for mechanical purposes, they also have electrical properties that are fairly constant over a wide range of frequencies. These properties are little affected by temperature and atmospheric humidity in the acceptableoperating range of temperatures.
ABS is flammable when it is exposed to high temperatures, such as a wood fire. It will melt then boil, at which point the vapors burst into intense, hot flames. Since pure ABS contains nohalogens, its combustion does not typically produce anypersistent organic pollutants, and the most toxic products of its combustion or pyrolysis arecarbon monoxideandhydrogen cyanide.ABS is also damaged by sunlight. This caused one of the most widespread and expensive automobile recalls in US history.
ABS can be recycled, although it is not accepted by all recycling facilities.