Model of processing-induced microstructure formation in polymeric materials

A general, mechanistic, kinetic model is presented to predict polymer micro structure formation during processing. Applications of the model are presen ted for three specific cases. The model represents polymer molecules as Kra mers chains which may or may not have nucleated. Three forces (hydrodynamic , Brownian, and intermolecular) that act on polymer molecules during proces sing were considered, which resulted in the presentation of the model as a diffusion equation. The input parameters account for the rheological and th ermal history of the polymer melt, the specific type of polymer molecule, a nd the initial morphology. The solution of the diffusion equation yields a probability distribution function from which the transient and equilibrium morphology can be determined. The three specific cases were chosen to illus trate the versatility of the model and include: the extensional flow-induce d growth of extended chain crystals; the orientation of stiff molecules in solution undergoing shear flow well above the crystallization temperature; and the formation of folded chain vs. extended chain crystals in an extensi onal flow. Data are available for the first two cases and agree favorably w ith the model predictions. (C) 1999 John Wiley & Sons, Inc.