Crystallographic factors affecting the structure of polymeric spherulites. I. Morphology of directionally solidified polyamides

Abstract

The morphology of even-even nylons has been reexamined in order to determine whether crystallographic factors can exert a dominant influence on the morphology and growth behavior of polymeric spherulites. Directional solidification of these polyamides produces long oriented spherulites at zone velocities below ∼5 μm/min, while at higher rates unusual patterns are obtained by interaction with small positive spherulites. In most cases, the stable form is that of oriented negative spherulites presenting an extremely fine fibrillar texture. Fluctuations in temperature gradient or in sample motion cause initiation of divergent fronts of spherulitic aggregates, which, however, exhibit interrupted growth patterns and variable growth rates; this exceptional growth behavior is not imposed by the characteristics of zone solidification. In addition, the aggregates appear to posess an unusually coarse texture, whereas that of positive spherulites is intermediate between the textures of the other two spherulitic species. Most aggregates have a totally mixed birefringence; however, the positive birefringence of others is inconsistent with their orientation and polarizabilities.