Superstructural hierarchy developed in coupled high shear/high thermal gradient conditions of injection molding in nylon 6 nanocomposites

The spatial variation of the superstructure developed along and across the flow direction of injection-molded nylon 6 and its nanocomposites are presented using transmission polarized optical photomicrographs and micro-small-angle laser light scattering (SALS). At low mold temperature, 50 °C, the structure of unfilled nylon 6 is made up of steep structural gradient containing oriented threads at the surface surrounding undeformed spherulites in the interior. In nanocomposite samples, on the other hand, the development of complete spherulites is interrupted by high nucleation density caused by the presence of nanoparticles and shear amplification that occurs in small spaces between these particles. The latter phenomenon was found to be prevalent even at high mold temperatures where the cooling rates are greatly suppressed. In the structure gradient, polymer/nanocomposite samples show double shear regions near the surface surrounding the core regions that contain sheaves. The origin of complex superimposed SALS patterns is explained in terms of the short and long-range spatial correlations of these preferentially oriented sheaves and their optic axes.