Mechanism of solvent crazing in unmodified and rubber‐modified polystyrenes

Abstract

AbstractThe dependence of critical strain on time was determined at −20° and 20°C with a Bergen elliptical strain device for unmodified and rubber‐modified polystyrenes immersed in n‐alcohols. Critical strain ϵc decreased with time and attained a lower limiting value ϵcl at long times. The value of ϵcl decreased with increasing chain length of the n‐alcohol and with increasing temperature, while it increased with increasing rubber content. In order to elucidate the mechanism of solvent crazing at longer times, the degree of equilibrium swelling Sveq and the diffusion coefficient D were also determined by sorption experiment. The lower limiting value of critical stress σcl was correlated to the value of Sveq, irrespective of the rubber content. The At, the time necessary to attain ϵcl, was regarded as the time needed for the thin layer of polymer surface to absorb the liquid to equilibrium for craze formation. The thickness of such a layer was estimated to be about 0.1 μm by using the experimental data of At and D. The predominant mechanism of solvent crazing at longer times appears to be a flow process of absorbed polymer at the craze tip.