Effect of annealing on fracture behavior of poly(propylene-block-ethylene) using essential work of fracture analysis

The influence of annealing conditions on the fracture behavior of poly(propylene-block-ethylene) sheets was investigated by means of the essential work of fracture method, and was complemented by the study of the effect of annealing on crystal structure, using differential scanning calorimetry. It was shown that both the crystal perfection degree and crystallinity could be improved substantially as annealing temperature (Ta) increased, while the prolonged annealing time at 80 degrees C mainly resulted in the improvement of crystallinity. The reasons for an increase in the specific essential work of fracture and a decrease in the specific plastic work item as crystal perfection degree and crystallinity grew are discussed. The displacement to failure of double edge notched tension specimens decreased gradually with increasing T,, and the double-plastic zone could be observed in all specimens. hi addition, a novel method to aid the accurate measurement of intense stress-whitening outer plastic zone height by adjustment of illumination conditions is proposed. (c) 2006 Wiley Periodicals, Inc.