Mechanical properties of poly(vinylidene fluoride) nanofiber filaments prepared by electrospinning and twisting

In this study, we propose a novel method for preparing a continuous filament using electrospinning and twisting methods to improve the mechanical properties of nonwoven poly(vinylidene fluoride) (PVDF) nanofibers. The morphologies of the nonwoven nanofiber membranes and the corresponding nanofiber filaments were investigated by scanning electron microscopy. The mechanical properties and crystal structure of both the nanofiber membranes and the nanofiber filaments were investigated by using a universal testing machine and wide-angle X-ray diffraction (WAXD), respectively. We found that the tensile strength and Young's modulus of nanofiber filaments were dramatically improved by increasing either the number of twists of the nanofibers or the width of nanofiber membranes, compared with nonwoven PVDF nanofibers. WAXD analysis indicated that the crystalline transformation from β-phase to α-phase occurred by the shear force driven by repeated twisting. It was concluded that both the crystalline structures of fibers and the fiber morphologies played a crucial role in the mechanical properties of the resultant nanofiber filaments.