The effects of melt history,crystallization pressure,and crystallization temperature on the crystallization and resultant structure of bulk isotactic polypropylene

A study of the effects of constant-pressure isothermal crystallization on polymer structure was conducted in bulk isotactic polypropylene. The investigation was designed to determine the influence of pressure, temperature, and melt history variables on the structure of this bulk polymer. Results demonstrate that the effects of pressure and crystallization temperature can be quite adequately combined into one processing parameter, undercooling (defined as the melting temperature minus the crystallization temperature), by use of the Clausius-Clapeyron equation. This parameter is demonstrated to be important in determining the kinetics of crystallization and the resultant structure. The moderate to high undercoolings involved in this study are representative of commercial injection-molding processes, and a number of conclusions regarding commercial processing are made based on these laboratory investigations.