Page 128 - Engineering Plastics Handbook

102 Engineering Plastics

Acrylonitrile

Chemical resistance
Fatigue resistance
Hardness and rigidity
Melt strength
Butadiene A H 2 C CH
Low-temperature B
ductility C N
Impact resistance
Melt strength
H S Styrene
C R
H C C
2
Heat resistance
Processability
HC CH 2 Coloring
Hardness and rigidity

Figure 6.1 ABS terpolymer and its functionality.

However, in practice, since it is also difficult to prepare ABS resins with
various harmonized properties, many studies have been made during the
past 50 years and more, and currently various studies are underway with
the aim to improve both the properties and the manufacturing processes
in the industrial and academic fields.
The characteristic properties of ABS resins are strongly affected by
molecular characteristics of the styrene/acrylonitrile (SAN) copolymer
forming the elastomeric phase and the matrix.
The methods for preparing grafted ABS are largely classified into three
types, where mass and emulsion polymerization and mass suspension
methods have been widely used.
Among those methods, in general, the emulsion polymerization method
has been mainly used. In the case of the SAN copolymer, it has been pre-
pared by either emulsion polymerization or bulk polymerization.
ABS resins are generally prepared in the compositional ratio of 21 to 27%
acrylonitrile, 12 to 25% butadiene, and 54 to 63% styrene on average,
where styrene gives good processability and stiffness to the final ABS,
butadiene improves the impact strength, and acrylonitrile improves the
chemical resistance.
The increase in the molecular weight of SAN copolymer causes a
decrease in fluidity, an increase in impact strength, and creep inhibition;
it also results in an increase of resistance against surface-active substances
and of tensile strength. The narrow molecular weight distribution (MWD)
causes an increase in tensile strength, shrinkage reduction, improved