Acrylonitrile butadiene styrene (ABS) (chemical formula (C<sub>8</sub>H<sub>8</sub>)<sub>x</sub>·(C<sub>4</sub>H<sub>6</sub>)<sub>y</sub>·(C<sub>3</sub>H<sub>3</sub>N)<sub>z</sub>) is a thermoplastic polymer, in common use since the 1950s. At room temperature it is an amorphous solid and has no definitive melting point, due to the varying length of monomer chains and various degrees of cross-linking. Its glass transition temperature is approximately .

ABS is a terpolymer 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 crisscrossed 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 acrylonitrile also contributes chemical resistance, fatigue resistance, hardness, and rigidity, while increasing the heat deflection temperature. The styrene gives the plastic a shiny, impervious surface, as well as hardness, rigidity, and improved processing ease. The polybutadiene, a rubbery substance, provides toughness and ductility at low temperatures, at the cost of heat resistance and rigidity. The properties are created by rubber toughening, where fine particles of elastomer are distributed throughout the rigid matrix.

Properties

ABS provides favorable mechanical properties such as impact resistance, toughness, and rigidity when compared with other common polymers. They also offer poor resistance to chlorinated solvents, alcohols and aldehydes.

ABS is flammable when it is exposed to high temperatures, such as those of a wood fire. It will melt and then boil, at which point the vapors burst into intense, hot flames. Since pure ABS contains no halogens, its combustion does not typically produce any persistent organic pollutants, and the most toxic products of its combustion or pyrolysis are carbon monoxide and hydrogen cyanide. ABS is also damaged by sunlight; this caused one of the most widespread and expensive automobile recalls in US history due to the degradation of the seatbelt release buttons.

ABS can be recycled, although it is not accepted by all recycling facilities.

Mechanical properties

ABS is one of many types of thermoplastic with biomedical applications, with injection-molded components being easy to manufacture for single use. It can be sterilized by gamma radiation or ethylene oxide (EtO).

{| class="wikitable"

|+Typical mechanical properties of ABS

Transparent ABS (MABS)

Most ABS is opaque because its components have different refractive indices. Acrylonitrile and styrene make ABS stiff. Butadiene particles are elastic and make ABS impact resistant. Adding methyl methacrylate (MMA) helps to bring the refractive indices closer together, making it transparent, while reducing the product's impact resistance compared to impact grades of ABS. However, the resulting MABS product can still outperform polystyrene, SAN and PMMA (acrylic) for impact resistance.

Production

ABS is derived from acrylonitrile, butadiene, and styrene. 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 ethylbenzene, a hydrocarbon obtained in the reaction of ethylene and benzene.

According to the European plastic trade association PlasticsEurope, industrial production of of ABS resin in Europe uses an average of and is derived from natural gas and petroleum.

Machining

ABS is manufactured in a variety of grades, but for precision machining of ABS structural parts, it is recommended to use Machine Grade ABS. Machine Grade ABS is easily machined via standard techniques, including turning, drilling, milling, and sawing. ABS parts can be welded together by heating the joint surfaces until they begin to melt; reinforcement can be applied to such a joint by melting a thin ABS rod. ABS parts can also be chemically affixed to each other, and to other sufficiently similar plastics, by means of solvents.

Applications

thumb|A "pBone" trombone made from ABS

ABS was patented in 1948 and introduced to commercial markets by the Borg-Warner Corporation in 1954.

ABS's light weight and ability to be injection molded and extruded make it useful in manufacturing products such as drain-waste-vent (DWV) pipe systems. Musical instruments such as plastic recorders, oboes, clarinets, and trombones, and some parts for piano actions, are commonly made out of ABS, as are computer keyboard keycaps.

Other uses include golf club heads (because of its good shock absorbance), automotive trim components, automotive bumper bars, binoculars and monoculars, inhalers, nebulizers, non-absorbable sutures, tendon prostheses, drug-delivery systems tracheal tubes,) and Kre-O bricks, are a common application.

ABS plastic ground down to an average diameter of less than 1&nbsp;micrometer is used as the colorant in some tattoo inks.

3D printing

thumb|upright|An ABS bell manufactured with a [[3D printing|3D printer]]

When extruded into a filament, ABS plastic is a common material used in 3D printers, as it is cheap, strong, has high stability and can be post-processed in various ways (sanding, painting, gluing, filling and chemical smoothing). When being used in a 3D printer, ABS is known to warp due to shrinkage that occurs while cooling during the printing process. The shrinking can be reduced by printing inside an enclosure on a heated print surface, using an adhesive such as a glue stick or hairspray to ensure the first layer of the print is well stuck to the print surface, or printing with a brim/raft at the base of the print to help increase adhesion to the print surface. ABS is only used in FFF/FDM 3D printers, as resin 3D printers cannot melt plastic.

Particular forms of ABS filaments are ABS-ESD (electrostatic discharge) and ABS-FR (fire resistant), which are used in particular for the production of electrostatically sensitive components and refractory prefabricated parts.

Pens

ABS plastic is also used in the manufacture of the Lamy Safari fountain pen due to its hard and relative strength.

Hazard to humans

ABS is stable to decomposition under normal use and polymer processing conditions. Exposure to carcinogens due to normal use and processing is well below workplace exposure limits. However, if the temperature reaches 400&nbsp;°C (750&nbsp;°F), ABS can decompose into its constituents: butadiene, acrylonitrile, and styrene (all of which are carcinogenic to humans). Concerns have been raised regarding airborne UFP concentrations generated while 3D printing with ABS, as UFPs have been linked with adverse health effects, some of which may result from tissue obstruction in the kidneys, lungs, and intestines caused by a buildup of UFPs.

See also

  • Polylactic acid (PLA) – another plastic used for 3D printing
  • Retrobright – a process for reversing the yellowing of white ABS plastic casings

References

  • Comparisons of many physical properties with other plastics
  • Comparison between ABS and PLA for 3D Printing