THE ISOTHERMAL CRYSTALLIZATION OF ENGINEERING POLYMERS - POM AND PEEK

The isothermal crystallization of two engineering polymers - POM and PEEK - was studied, both theoretically and experimentally. The experiments were performed by means of differential scanning calorimetry (DSC) and polarized light optical microscopy (OM). Building on previously developed theoretical formalisms (Avrami/Evans, Hillier and Tobin), a new procedure is presented, based on Tobin's model coupled with a modification of Hillier's calculation technique, to accurately describe the kinetics and mechanism of the crystallization of polymers from quiescent melts. First, it is shown that Tobin's model alone, without modification, is more accurate than Avrami/Evans model to describe single-mechanism processes, for a wide range of materials and for longer crystallization times, despite having exactly the same nature and number of parameters (the kinetic, nucleation and growth rate-related, parameter K and the dimensionality n). Then, Hillier's formalism is modified and combined with Tobin's model, to accurately predict the kinetics of dual mechanism crystallization processes; a clear contrast is drawn with Hillier's Avrami-based, original procedure which uses the same number and nature of parameters, but cannot adequately predict the experimental behavior. The parameter values predicted by the model(s) and procedure presented in this work are all given, are then physically interpreted and, in the case of POM, related to independent morphological observations by polarized light optical microscopy. They are also consistent with electron microscopy observations made by other authors on the detailed morphology of the spherulitic crystallization of polymers.