The Mechanical Behavior of High Impact Polystyrene under Pressure.
CASE WESTERN RESERVE UNIV CLEVELAND OHIO DEPT OF MACROMOLECULAR SCIENCE
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High-impact polystyrene HIPS, a two-phase polymeric system, has been investigated studying the pressure dependence of stress-elongation behavior in tension over the range from atmospheric pressure to four kilobars at room temperature and constant strain rate. A comparative study of polystyrene PS was also undertaken. HIPS sealed from the environment exhibited ductile behavior at all pressures. Surprizingly, specimens exposed to silicon oil environment exhibited two transitions as the applied hydrostatic pressure was raised a ductile-to-brittle followed by a brittle-to-ductile transition. Stress-whitening was suppressed at relatively low pressures. The dilational requirement for profuse crazing was restrained by the combined effect of fluid under pressure resulting in the suppression of the energy absorption mechanism. Analysis of the stress-elongation curves for sealed specimens indicated that the pressure dependency of craze-initiation stress differs from that of shear band initiation stress. The brittle-to-ductile transition occurred when the initiation stresses of both processes became equal. The principal stress for craze initiation showed almost no pressure dependency.