The study of cracking and fracturing of spherulitic isotactic polypropylene

Isotactic polypropylene was melted and crystallized at 125°C. Crystallization was observed dynamically on a microscopic heating stage. Spherulites, when first formed, appear to have a lower order of birefringence than after some growth. Between 4–4.5 min. of crystallization cracking occurs between spherulitic boundaries. In a parallel experiment samples crystallized at 125°C. were quenched after different degrees of spherulization. The effect of degree of spherulization on stress‐strain properties was studied and the necks and fractures of the samples studied. The completely spherulitic samples broke abruptly at spherulitic boundaries without necking. The rate of elongation affected the nature of the fracture of completely spherulitic samples. At low rates of elongation the spherulites have a tendency to “pull out” at the fracture. At high rates of elongation the spherulites break more sharply at their boundaries.