Mechanisms for regularization of chain folds during annealing of polyhexamethylene adipamide

The regular fold content of polyhexamethylene adipamide depends on the initial crystallization conditions, the degree of orientation, and the annealing time and temperature. At low annealing temperatures, the regular fold content increases linearly with crystallinity and arises from lamellar crystallization of isolated amorphous or interlamellar regions. At intermediate annealing temperatures, the increase in regular fold content greatly exceeds the crystallinity increase. The excessive increase in folds in this temperature range arises from regularization of loose loops and melting and recrystallization from extended to more folded type of crystals. At the higher annealing temperature, the crystallinity shows an increase relative to the fold content, and this implies that the increase in fold period occurs at the expense of folding.