Antiplasticization of polyvinyl chloride in relation to crazing and fracture behaviour

Experiments were carried out to study the effects of small amounts (10 p.h.r.) of tricresylphosphate in polyvinylchloride on the crazing behaviour and fracture toughness over a wide range of temperatures. Crazing was induced by water/methanol mixtures and the critical crazing strain was measured as a function of immersion time and methanol concentration. Fracture toughness was measured on single-edge notched specimens in tension over three decades of strain rate in the temperature range −80 to 60°C. The 60 sec isochronous critical crazing strain displayed a minimum at around room temperature in an approximately parabolic fashion; the plasticized polymer exhibiting lower trough values, while the two curves intersected at both low and high temperatures. The fracture toughness curves, on the other hand, exhibited intermediate peaks, associated with β relaxations. The addition of plasticizers to the polymer reduced considerably the heights of the peaks and, once more, the two curves intersected at high temperature and merged at low temperature. From a comparison of the two sets of data, it is suggested that embrittlement due to antiplasticization is associated with a reduction in stability of the crazes as a result of the depression of β relaxations.