Abstract
The work presented and reviewed in this paper leads to the following conclusions: (a) The kinetics of creep in HIPS containing 0.2 µm diameter core-shell rubber particles are similar to those in more conventional HIPS containing larger multiple-inclusion particles. Both deform by multiple crazing. (b) Comparisons of mechanical properties should be made on the basis of equal rubber volume fractions ϕ rather than equal elastomer contents. (c) The kinetics of creep in rubber-toughened PMMA, also containing small core-shell particles, are quite different from those of HIPS. Deformation occurs by shear yielding accompanied by a small volume increase which is probably due to cavitation in the rubber particles. (d) The dependence of deformation rates upon applied stress and temperature is well described by the Eyring model for activated flow. (e) Analysis based on the Eyring slopes can be used to compare stress concentration factors γ in toughened plastics. In polymers that deform by shear yielding, absolute values of γ can be obtained by comparison of data from toughened and untoughened plastics. Difficulties remain in applying a similar approach to polymers that deform by multiple crazing. (f) The rate-determining step occurs in regions of maximum stress concentration in HIPS and appears to be identified with initiation of crazing. (g) The rate-determining step in toughened polymers that deform by shear yield is not associated with regions of maximum stress concentration.