ENERGY EQUATION AND THE CRYSTALLIZATION KINETICS OF SEMICRYSTALLINE POLYMERS - REGIMES OF COUPLING

The processing conditions play an important role in the development of the crystallinity of thermoplastic polymers and the energy equation describing the heat transfer problem can be strongly coupled to the material kinetics. In this paper, the importance and nature of the coupling is evaluated by comparing the temperature and crystallinity distributions obtained from a fully coupled zone model (considered as the most general approach) with two cases: Neumann's solution (sharp interface-moving boundary) and the one-domain diffusion equation with no heat generation (uncoupled solution). Two non-dimensional parameters, Stefan's (St) and Deborah's (De) numbers, that play a key role in determining the extent of the coupling, are isolated. The influence of the coupling and its nature have been demonstrated numerically in selected cases. Results of the parametric studies show that De and St decide the nature of the coupling. The error made by decoupling the problem can be shown graphically and regimes are identified where the coupling is important or negligible. Criteria allowing the identification of the regimes are presented. Finally, an example is presented to demonstrate the importance of the coupling for the cooling of Nylon 6-6 and PET, which exhibit fast and slow crystallization kinetics.