Study of crystallization behavior of neat poly(vinylidene fluoride) and transcrystallization in carbon fiber/poly(vinylidene fluoride) composite under a temperature gradient

The crystallization behavior of poly(vinylidene fluoride) (PVDF) and transcrystallization in carbon fiber (CF)/PVDF composite were investigated under a temperature gradient. The crystallization temperature ( T c ) was controlled in the range of 110–180 °C. For neat PVDF, the results showed that exclusive γ phase formed at T c above 164 °C, but coexisted with α phase at T c ranging from 137 to 160 °C. The promotion of γ phase to nucleation of α phase at low T c was observed for the first time. For CF/PVDF composite, a cylindrical transcrystalline (TC) layer formed on the surface of CF when T c was between 137 and 172 °C. The TC layer was exclusively composed of γ phase at T c above 164 °C. The hybrid nucleation was dominated by γ phase though some α phase nuclei emerged on the surface of CF when T c was in the range of 144–160 °C. As T c decreased, competition between the hybrid nucleation of α and γ phase became more intense. The γ phase nuclei was soon circumscribed by the rapidly developed α phase when T c was below 144 °C. Furthermore, some α phase nuclei were induced at the surface of the γ phase TC layer, and developed into α phase TC layer when T c was in the range of 146–156 °C, which resulted in a doubled TC layer of α and γ phase at the interface of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 43605.