Study on the miscibility, crystallization and crystalline morphology of polyamide-6/polyvinylidene fluoride blends

The miscibility, crystalline structure and morphology, as well as, properties of Polyamide 6 (PA6)/poly-vinylidenefluoride (PVDF) blends (with up to 50 wt% of PVDF) were studied. Small Angle X-ray Scattering study above the melting point of PVDF shows that the blends have very limited miscibility with approximately 5 wt% of PVDF inclusion in PA6 amorphous lamellar region. SAXS results also indicate a certain degree of PA6 inclusion into PVDF region though quantitative evaluation is unavailable with the limited blends studied in this work. The fine PVDF dispersion in the PA6 blends with up to 50 wt% of PVDF with an average size about 150 nm is supposed to be the result of the partial miscibility. The partial miscibility has great effects on the morphology and properties of the blends. Crystallization of both components are suppressed in the blends, especially on the PVDF component, which shows a significantly lowered crystallization temperature (up to 30 degrees C) during a cooling and a dramatic drop in crystallinity. Morphological studies together with Small Angle Light Scattering (SALS) show that spherulites, consisting of PA6 skeleton with dispersed PVDF domains (similar to 150 nm) engulfed among PA6 fibrils, are formed in the blends. The PA6 based spherulites become more defective with the increase in PVDF content, resulting in short/broken fibrils and undetectable PA6 spherulites for the blends with 30-50 wt % of PVDF at the temperature over the melting point of PVDF, say 185 degrees C. The blends show a significantly improved toughness compared with neat PA6, due to the partial miscibility which leads to the fine dispersion of PVDF domains in PA6 spherulites. (C) 2017 Elsevier Ltd. All rights reserved.