Formation of supermolecular structures of semicrystalline polymers under molecular orientation

Abstract

The effect of stretching on the process of structure formation in fiber spinning and film extrusion and in isothermal crystallization of crosslinked polyethylene has been investigated. It has been shown that the stretching forces (jet stretching) in these systems cause the formation of spherulites flattened with respect to the stretching direction. As a rule, the spherulite radius decreases while the degree of flattening increases with the jet stretching. Thermodynamic analysis of the kinetics and morphology of the spherulite growth during stretching enabled us to interpret these effects and to establish relationships connecting the degree of flattening of the spherulites with the characteristics of molecular orientation in the melt. Taking into account the changes in the conformational entropy of the deformed macromolecule (or the network) in the course of nucleation and crystal the deformed macromolecule (or the network) in the course of nucleation and crystal growth it is possible to explain not only the effect of the spherulite flattening but also the formation of tilted crystals and other peculiarities of crystallization taking place with the occurrence of molecular orientation. A general picture is given of the effect of a mechanical field on the morphology of the crystallizing polymers at various degrees of stretching.