On the mechanisms of recrystallization after melting in semicrystalline polymers: The effect of the initial melt state

Abstract

The mechanisms of recrystallization after melting during a heating scan of syndiotactic polypropylene (sPP) and isotactic polystyrene (iPS) were studied. This was done by monitoring the structure evolution during the recrystallization process and its changes during a subsequent heating scan via time- and temperature-dependent SAXS measurements, respectively. The results of this study showed that the sPP samples exhibited a recrystallization mechanism similar to the multistage route found upon initial crystallization of semicrystalline polymers from an entangled melt. Meanwhile, a different recrystallization mechanism was shown by the iPS samples. In this case, the recrystallization process proceeded as a direct growth into the melt in a one-step process. This is the first time we observed such a mechanism that resembles the picture presented by the classical models for crystallization from an entangled polymer melt. The reason for such different mechanisms may be related to the initial melt state prior to crystallization. It seems as though when crystallization sets in in an entangled polymer melt, it follows the multistage route, whereas if the melt is locally disentangled, it proceeds by a direct growth mechanism.