Institute of Fundamental Technological Research

Flow induced crystallization of polymer systems exhibits strong memory effects. Crystalline structures gradually change when the flow is switched off and the polymer is relaxed prior to crystallization. A simple model based on the multidimensional theory of crystal nucleation[1] is proposed. Steady, potential flow applied to a polymer fluid above melting temperature (Tp > Tm) results in molecular orientation of crystallizing units. The flow controls formation of molecular clusters which convert into athermal nuclei when the system is cooled down to crystallization temperature, Tc < Tm. Orientation effects gradually disappear when the melt is relaxed above Tm in the absence of flow or stress.

Crystallization kinetics of oriented poly(ethylene terephthalate) have been studied in a temperature range close to Tg. It has been shown that orientation of the amorphous phase promotes a substantial increase in crystallization rate. This effect, in turn, depends on the crystallization temperature: the higher the temperature, the stronger is the effect of orientation. From experimental results it was possible to make an estimation of parameters describing quantitatively the crystallization kinetics in the oriented state.