STRESS WHITENING IN CRYSTALLINE PROPYLENE-ETHYLENE BLOCK COPOLYMERS.

A morphological study of stress whitening in commercially available propyelene(P)-ethylene(E) block copolymers with ethylene contents ranging from 8 to 18 wt-% has been carried out. The morphological features of these block copolymers were established by electron microscopy, x-ray diffraction methods, and differential scanning calorimetry techniques. P-E block copolymers 55 and are composed of two crystalline phases and a noncrystalline EPR phase. Molded sheets of copolymers were stress whitened through drawing and studied mainly by scanning electron microscoy. Globular particles of polyethylene are observed. An initial stage of whitening can be associated with craze-like textures initiated at these globular particle boundaries.