Enhancing β-phase content and tensile properties in poly(vinylidene fluoride) by adding halloysite nanotubes and injecting water during extrusion

Poly(vinylidene fluoride) (PVDF) nanocomposites containing 5, 7 and 10 wt% unmodified halloysite nanotubes (HNTs) are prepared by using extrusion with and without water injection. Scanning electron microscopy micrographs show that a large number of single nanotubes are well dispersed in the PVDF matrix with water injection, which is mainly attributed to formation of hydrogen bonds among the fluorine and/or hydrogen atoms of PVDF molecule, the water molecules and the siloxane groups of HNTs. The crystal structure and crystallization behavior of the PVDF are investigated using wide angle X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. The results show that the addition of the HNTs especially their better dispersion induced by injected water is beneficial to improving the crystallinities and forming substantially higher fractions of β-phase crystal (F(β)s) in the PVDF/HNTs nanocomposites. The F(β) for the nanocomposite with 10 wt% HNTs reaches the maximum of 0.689. Moreover, better HNTs dispersion and higher crystallinities and F(β)s improve the Young's moduli, tensile strengths and elongations at break for the PVDF/HNTs nanocomposites.