Morphological investigations on the nanostructured poly(vinylidene fluoride)/polyamide 11 blends by high-shear processing

Nanostructured poly(vinylidene fluoride) (PVDF)/polyamide 11 (PA 11) blends of various compositions were prepared using a high-shear extruder. The lamellar morphology of the nanoblends consisting of two crystalline constituents was investigated by transmission electron microscopy (TEM) and temperature-variable small-angle X-ray scattering (SAXS). The average lamellar long period and the thickness of the amorphous part for the high-shear-processed blends were larger than those for the low-shear-processed sample, indicating the molecular incorporations between PVDF and PA 11 upon high-shear processing. A novel scattering peak, corresponding to the long period of 25.2 nm, is observed when the SAXS measurements were carried out at a temperature between the melting points of PVDF and PA 11. The structural change with time at high temperature was investigated in situ by SAXS. It was found that the intensity of the new peak increased with time at high temperature and the peak position slowly shifted in the low-angle direction, indicating a gradual increase of the long period for PA 11 crystals upon annealing. The novel scattering peak originates from the enlarged PA 11 lamellar long period in the nanodomain because the peak cannot be observed for the same blends prepared by low-shear-processing. It is considered that the melt PVDF chains are gradually diffused into the galleries of PA 11 lamellae in the PA11 nanodomain, which enlarged the long period of PA 11 because of the more favorable interaction at high temperature. The chain diffusion can only occur from the interface between the PVDF and PA 11 phases, and therefore, almost no change was observed for the long period of bulk PA 11 crystals in the nanoblend.