An Unusual but Consistent View on Flow Induced Crystallization of Polymers

Summary.

There is a considerable difference of more than 40 degrees centigrade between the equilibrium melting point of the α-crystal modification of i-PP and the lower temperature, where the α-spherulites of this polymer melt. The equilibrium melting point represents the temperature, where ideal crystals melt. In these crystals the macromolecules are in a stretched conformation. In contrast, in the spherulites the molecules are contained in lamellae of finite thickness. As a consequence it seems that in the interval between these two characteristic temperatures the nucleation kinetics is very different from the kinetics observed at temperatures below the melting temperature of the spherulites. This observation is of importance because almost all measurements on flow induced crystallization have been carried out below the melting temperature of the spherulites. It can be shown that at these lower temperatures the kinetics of crystallization (including flow induced crystallization) has nothing to do with the classical ideas about sporadic nucleation.