2001-11-14
10:15 at ML H43

Development of a flow induced crystallization model for flow induced crystallization

Jan van Meerveld

Institute of Polymers, ETH Zurich

Recently, several models for flow-induced crystallization have been proposed, mostly based on the correlation between rheological parameters and enhancement of the crystallization kinetics instead of non-equilibrium thermodynamic considerations. A continuum non-isothermal two-phase system in conjunction with adapted Schneider equations to describe phase transitions is considered. The melt is described by a reptation model for fast flow, discriminating between the orientation and stretching of the polymer chain and the corresponding relaxation behavior. The characteristics of this model show similarities between experimental observed influence of strain and strain rate on the induction time. The emerging microstructure due to nucleation is modeled using a pom-pom or (thermoreversible) network model depending on the nuclei density and nuclei topology. Firstly classical nucleation theory is used for the transition from inactive to active groups. Secondly the transformation of the latter to nuclei is modeled based on a mean-field multiple junction network theory, coupling nucleation dynamics with changes in microstructure properties without introducing additional phenomenological relationships.