Influence of Flow on the Crystallization of Polymer Melt and Solution
Morphology of plastic parts is strongly influenced by the processing conditions. Crystallization in quiescent and flowing polymer melts gives rise to unique and complex microstructures in the final product. Given the influence of microstructure on a range of product properties, there is a need for the development of models which link the processing history of the material to the morphology of the final product. Processing of polymer melts and solutions involves flows in complex-shaped cavities and free surfaces. This research aims at modelling the mechanics and the materials aspects of polymer processing under actual industrial conditions.
To this end, the crystallization of quiescent polymer melts is being studied in simple geometries. This involves coupling of the crystallization kinetics model and the transient heat diffusion equation. The crystallization kinetic model used assumes a hetrogeneous nucleation of the crystallizing polymer melt as observed in industrial applications. The effects of various polymer properties, melt temperature, and undercooling is being studied. Further the influence of flow on the crystallization kinetics is being studied by solving the momentum and energy equations including the crystallization kinetics model. The effect of flow on polymer crystallization is obtained through a source term in the energy equation. Some preliminary results have been obtained for the above cases.
Future research is aimed at a more detailed study of polymer crystallization under quiescent and flow conditions. The crystallization of polymers is to be studied from a more fundamental view point using the general crystallization theory under nonisothermal conditions. This model would take into account the crystal growth including the number of nuclei, the probability of their growth, the growth rate, and the probability of impingement of growing crystallites. The effect of temperature on the growth rates and the nucleation rates of a crystallizing polymer will be considered.
A 3D finite element analysis code will be developed to model the flow and heat transfer under various polymer processing operations where the effect of polymer crystallization is important. This code will be capable of solving for complex geometries, the flow of a non-Newtonian fluid using suitable constitutive models. The kinetics of polymer crystallization will be linked to the above mechanics problem through the development of a constitutive model taking into account the influence of flow and temperature on the nucleation and the anisotropic growth of the crystallizing polymer. The developed model would be very general to account for the various flow and temperature conditions encountered during actual polymer processing.
1. Abstract