The effect of melt history, pressure, and crystallization temperature on spherulite size in bulk isotactic polypropylene

Abstract Melt history, pressure, and crystallization temperature are three variables that may be used to vary spherulite size in polymer systems. In this study, bulk polypropylene samples were given various melt treatments and then isothermally crystallized under constant pressure. Spherulite size was found to increase with increasing severity (i.e., increased temperature or time at temperature) of melt treatment, explained by the thermal deactivation of nucleation sites. Spherulite size also increases with increasing crystallization temperature, owing to a smaller driving force for nucleation and the deactivation of increasing numbers of nuclei at higher crystallization temperatures. An analogous effect of pressure was also found, and a simple model to compare increased pressure and decreased crystallization temperature was derived.