Numerical Simulation Study On Influence Of Shear On Polymer Crystallization

Crystallization behavior in polymer molding process has important influence on final capabilities of products. Crystallization in polymer processing completes under flow field associated with rheological process and its behavior is quite different from quiescent condition, which is not only related to thermal history, but also to flow history and rheological response. The study on influence of flow on polymer crystallization is the research hotspot in polymer physics and polymer processing field at present and has certain guiding significance in controlling capabilities of polymer products by molding.The effect of shear flow on polymer crystallization process is studied by numerical simulation in this paper. The main work included:1. Based on Leonov viscoelastic constitutive model, the establishment of material elastic deformation and the first normal stress difference in flow process and relaxation process after flow stopping was simulated. The influence of shear rate and temperature on steady elastic deformation and the first normal stress difference was studied.2. Crystallization in quiescent condition was simulated based on Avrami equation and Lauritzen-Hoffman crystal growth model. The influence of crystallization temperature on number of activated nuclei, crystal growth rate, half crystallization time, induction time and relative crystallinity was researched.3. On the assumption that flow accelerate nucleation rate but not effect crystal growth rate, the number of activated nuclei is the sum of the activated nuclei in quiescent condition and the activated nuclei induced by the flow. On the base, combining Avrami equation with Lauritzen-Hoffman crystal growth model, crystallization process in flow process and after flow stopping was simulated. The effect of temperature, shear rate and shear strain on number of activated nuclei, crystallinity, half crystallization time and induction time was studied. The change of viscosity in crystallization process was researched. The simulation results were qualitative agreement with experimental results.