Solidification of poly(ethylene terephthalate) with incomplete crystallization

Cooling is a critical step in any crystalline polymer molding or extrusion process. A simulation is proposed which will predict the transient temperature and crystallinity profiles developed when a finite polymeric slab comes in contact with a cooling fluid. A generalized, phenomenological model of the crystallization kinetics of polymers is incorporated to account for the effect of the latent heat of crystallization on the thermal history as well as on the crystalline structure at any point in the slab. The model assumes heterogeneous nucleation and temperature‐dependent radial growth of spherulites. DSC cooling thermograms for the polymer are used to verify the kinetic model for comparing experimental measurements against simulated results. Observed spherulite sizes should also be matched by the simulation. Kinetic data have been obtained for two grades of poly(ethylene terephthalate) which have the same growth rate expression but different nucleation characteristics. Crystallinity of these two polymers decreases rapidly as either quench temperatures or nucleation densities are decreased independently. Calculations have been carried out for 1/16 in. thick sheets of polymer exposed to a cooling medium with a heat transfer coefficient of 100 Btu/hr/ft 2 /°F. Temperature gradients are also presented. The simulation can be used for optimizing quench conditions in polyester film extrusion.