Morphology of cold-crystallized polyamide 6

The structure of cold-crystallized polyamide 6 (PA 6) has been analyzed by wide-angle X-ray scattering, atomic force microscopy, and polarizing optical microscopy. It has been found that ordering of initially fully amorphous and glassy PA 6 on slow heating to temperatures higher than the glass transition temperature results in formation of spatially non-organized short lamellae/nodules with a size depending on the maximum annealing temperature. In contrast, melt crystallization at low supercooling is connected with formation of spherulites and laterally extended lamellae. The observed experimental results demonstrate that crystals of qualitatively different morphology and higher-order organization can be generated by variation of the pathway of crystallization. It is assumed that the different structures obtained in melt- and cold-crystallized samples are related to heterogeneous and homogeneous nucleation, respectively.