Xmultiple Engineering Dept.
butadiene styrene (ABS) (chemical formula (C8H8)x¡P
(C4H6)y¡P(C3H3N)z) is a common thermoplastic. Its melting
point is approximately 105 ¢XC (221 ¢XF).
It is a copolymer 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. For the majority of applications, ABS
can be used between 25 and 60 ¢XC (-13 and 140 ¢XF)
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.
Production of 1 kg of ABS requires the equivalent of
about 2 kg of petroleum for raw materials and energy.
It can also be recycled.
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 ¡X a hydrocarbon obtained in the reaction of
ethylene and benzene.
The advantage of ABS is that this material combines
the strength and rigidity of the acrylonitrile and styrene
polymers with the toughness of the polybutadiene rubber.
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
10 to 80 ¢XC (50 to 176 ¢XF).
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 acceptable operating
range of temperatures.
While the cost of producing ABS is roughly twice the
cost of producing polystyrene, ABS is considered superior
for its hardness, gloss, toughness, and electrical insulation
properties. It is degraded (dissolved) when exposed
to acetone. ABS is flammable when it is exposed to high
temperatures, such as a wood fire. It will melt, boil,
then burst spectacularly into intense, hot flames.
Black ABS plastic pipe (vertical, extreme right in photo)
in use in a wet basement of a paper mill, in Sault Ste.
The list of applications for ABS is long and continuously
growing. Its 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 (recorders and plastic clarinets),
golf club heads (due to its good shock absorbance),
automotive trim components, automotive bumper bars,
enclosures for electrical and electronic assemblies,
protective headgear, whitewater canoes, buffer edging
for furniture and joinery panels, luggage and protective
carrying cases, small kitchen appliances, and toys,
including Lego bricks.