Effect of casting conditions on polymorphism of nylon‐12

Abstract

Polymorphism in nylon‐12 film, which appears on casting from a phenol‐ethanol solution, has been investigated by x‐ray diffraction and infrared absorption. The casting temperature was varied from 30 to 130°C and the ambient atmospheric pressure from 50 to 760 Torr. Casting at 30°C gives only the α form, while casting above 90°C yields only the γ form. At intermediate temperatures, both α and γ forms are obtained, with the γ content increasing as the casting temperature and/or the rate of evaporation of solvent are increased. The ethanol component of the casting solvent appears to act only as a melting‐point depressant for phenol. In contrast, nylon‐6 film cast from the same solvent system between 30 and 160°C gives only the α form. It is proposed that the difference in polymorphism of nylons‐12 and ‐6 is caused by differences in molecular flexibility due to the length of the methylene chain.