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The tensile strength, |
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Hardness, |
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Heat resistance, |
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Chemical resistance Etc. |
Butadiene improves the impact strength
And Styrene improves the processability
ABS plastics possess an excellent combination of mechanical,
thermal and chemical resistance.
In short ABS plastics are termed as -
Tough - Hard - Rigid materials.
The outstanding attribute of ABS is that by adjusting the composition
of various monomers, it is possible to vary the mechanical properties
considerably in terms of impact strength. But the increase in impact
strength always bring down the tensile and flexural strength.
The impact strength of ABS is in the range of 10 to 60 kg.cm/cm
notch. This value is higher than most of the engineering thermoplastics
like acetal resin, nylons etc. It also exceeds that of metals like
magnessium alloys, tin bronze alloys etc. This impact strength does
not fall drastically with the fall in temperature. At low temperature
also, ABS has good impact strength. The impact strength of ABS is
not highly directional and hence there is a minimum tendency towards
orientation during processing. Furthermore, the effect of section
thickness on impact strength is not so predominant with ABS and
this material is not as notch sensitive as certain types of PVC.
Hence mouldings from ABS exhibit better impact strength in all directions.
The ultimate tensile strength of ABS is generally in the range
of 350 to 550 kg/cm2 at normal temperature. This tensile strength
is retained over a wide range of temperatures. The retention of
a fairly high tensile strength at forming temperature makes ABS
sheet a good vacuum forming material.
The hardness of ABS is rockwell R 80 to R 114. This is a measure
indicative of scratch resistance. The higher the number, the harder
the material.
Thus ABS offers a good balance of impact strength, tensible strength,
flexural modulus, and hardness, while creep at stress level below
150 kg/cm2 is negligible. This characteric imparts high resistance
to dimensional changes under loads and enables different parts of
the assembly to retain tolerances and tight fit.
It is probably the combination of these properties that makes ABS
such a stand out. There are thermoplastics that are stiffer but
their impact strength is lower, while there are other thermoplastics
that have higher impact strength but lower stiffness.
As regards to heat resistance, the Vicat softening point of ABS
plastics ranges from 90� C to 100� C. There are high heat resistance
grades available having heat resistant temperature as high as 115�
C. The coefficient of thermal expansion of ABS is approximately
ten times higher than metal and it is 9 x 10-5 cm/cm�C.
The electrical properties of ABS are unaffected by temperature
and humidity.Its dielectric constant is sufficiently good to allow
ABS to be used in electrical applications like coil formers, connectors
etc.
Some plastic materials absorb certain quantities of moisture and
change their mechanical properties with the quantity of moisture
absorbed. Also the dimensions of such materials change with the
quantity of moisture absorbed. However, in case of ABS, the moisture
absorbed does not affect the properties of the finished item as
well as the dimensional stability. Moisture absorption in case of
ABS plastics is less than one percent.
As regards to flame and fire resistance, ABS plastics are slow
burning and do not drip while burning. The flame retarding grades
of ABS are now developed and available. These flame retarding grades
comply with the international norms required by the electric, electronic
and building industries. The major outlet for the flame retarding
ABS grade is in the manufacture of T.V. housings and back, in electrical,
electronic applications like junction and switch boxes, in housings
for electronic equipments, etc.
ABS Plastics have better chemical resistance. They are resistant
to Aqueous Acids, Alkalies, Salts, Concentrated Hydrochloric and
Phosphoric Acids, Alcohols and Oils. ABS Plastics are swollen by
Glacial Acetic Acid, Carbon Tetrachloride and Aromatic Hydrocarbons
and are attacked by concentrated Sulfuric and Nitric Acids. They
are soluble in Esters, Ketone aned Ethylene Dichloride.
The Introduction of proper ABS formulations has been made possible
by the Electroplating of ABS - a commercial and technological success.
Being an Engineering plastic it replaces many metals and alloys
like Zinc die casting. ABS plastic parts can be injection moulded
at a lower cost and with greater freedom in design as compared to
die-cast parts. They are corrosion resistant and comparatively lower
in weight. The final polishing and buffing process of die-cast metal
parts are eliminated for electroplated ABS plastic parts. The Electroplated
ABS parts show improvement in properties like surface hardness,
tensile and flexural strength, heat resistance, chemical resistance,
weather resistance etc., over non-plated ABS parts. The plated ABS
parts replace die-cast metal parts in industries such as bath-room
fittings and hardwares, radios and television, refrigerators, fans,
measuring tapes, novelty articles, automotive, umbrella etc.
Thus the complete range of mechanical, thermal and electrical
properties have made ABS a versatile engineering plastic.
-BY SURESH JAVERI
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