Polar crystalline phases of PVDF induced by interaction with functionalized boron nitride nanosheets

Due to their unique structure and excellent physical properties, boron nitride nanosheets (BNNSs) are often used as nano-reinforcing fillers for polymeric composites. In this work, hydroxyl-modified boron nitride nanosheets (OH-BNNSs) and amino-functionalized boron nitride nanosheets (NH2-BNNSs) were blended with poly(vinylidene fluoride) (PVDF) via a solution casting method to form PVDF/OH-BNNS and PVDF/NH2-BNNS nanocomposites. Differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) show that the addition of OH-BNNSs has little influence on the crystal structure of PVDF, and non-polar α-crystals are mainly formed in the PVDF/OH-BNNS nanocomposites, whereas the incorporation of a small amount of NH2-BNNSs can cause exclusive formation of polar β- and γ-phases. X-ray photoelectron spectroscopy (XPS) and FTIR reveal that there exists a stronger interaction between PVDF and NH2-BNNSs than that between PVDF and OH-BNNSs in both solid and melt states, which is responsible for the transformation of the crystalline phase and the accelerated crystallization of PVDF/NH2-BNNS nanocomposites.