Abstract
Toughening of brittle thermoplastics by addition of a separated rubber phase has been an important area of research in industrial material development. Several research groups have focused their efforts to understand the role of the dispersed rubber particles for toughening of plastics. As a result of the research work, the debonding of grafted rubber particles from the surrounding rigid matrix and as well the internal rupture of particles, i.e., cavitations, were considered as a possible dominating contribution of particles to toughening. Recently a method for the detection of rubber cavitation in rubber toughened thermoplastics, based on the observation of the rubber cavitation phenomena occurring during a cooling procedure and detected by means of thermal contraction measurements, has been developed by Dijkstra and co-workers. During such experiments an S-shaped deviation from linear thermal contraction has been observed. This behavior was attributed to the cavitation of rubber particles under thermally induced hydrostatic tensions during cooling. The present paper is aimed at showing that the observed S-shaped deviation from linear thermal contraction during cooling reoccurs during subsequent cooling steps if an appropriate thermal loading of the samples takes place after the first cooling. This result provides an even stronger evidence that the S-shaped deviation from linear thermal contraction during cooling is indeed caused by particle cavitation. It is also shown that the cavitation behavior of rubber particles in toughened thermoplastics depends strongly on thermal history, rubber phase volume of the sample under investigation and experimental conditions as well. Based on these results the method has to be used very carefully for a general quantitative comparison of different rubber modifiers in toughened plastics. However, such contraction tests can be considered as an additional tool to understand basic deformation behavior of rubber modified thermoplastics.
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