Abstract:
The role of the rubber particle in the ultimate failure of High Impact Polystyrene
and Acrylonitrile Butadiene Styrene was investigated by modifying the rubber
content and the shear modulus of the rubber phase in the materials. The rubber
content in a commercial grade HIPS and a commercial grade ABS, both with 8
wt. % rubber, was varied by blending with general purpose polystyrene and
general purpose poly(styrene-aciylonitrile) respectively. The shear modulus of
the rubber phase was varied through blending the materials with sulfur or
irradiating the materials with gamma irradiation. Dynamical mechanical thermal
analysis confirmed that the Tg of the rubber phase increased with increasing
sulfur content. It was found that with decreasing rubber content or increasing
rubber shear modulus, the yield, flow and breaking stresses and the elastic
modulus of the composite increased, while the failure strain decreased.
In a similar experiment to Sjoerdsma and Boyens (1994), the statistics of
failure of the materials were investigated with respect to rubber content and
rubber shear modulus. Batches of specimens numbering not less than 20 were
extended under a constant applied stress until failure occurred. A custom
designed creep rig was built to carry out several long term creep tests
simultaneously. From these tests it was concluded that the probability of failure
increased as the stress on the rubber increased and underpinning this, is a novel
discussion of the high strain deformation and the mechanism controlling failure
in HIPS and ABS. This conclusion was discussed in terms of rubber content and
rubber shear modulus and a model was developed which describes the
maximum failure strain in terms of these variables. The level of applied stress
was also found to have an effect on the probability of failure.
It was found that the success achieved by Sjoerdsma and Boyens (1994),
in correlating failure strain data for a single grade of HIPS, could not be
repeated when their model was applied to another grade of HIPS. The tw oparameter Weibull equation gave an improved correlation between the failure of
HIPS and the strain on the material. Analysis of the relationship between the
experimental failure strain distribution and the Weibull distribution revealed that
the mean stress on the rubber phase at failure may be a better basis for achieving
a Weibull distribution.
