Mechanism of Synergetic Growth of Flexibility and Strength of Biomimetic Nanocomposite Fibre

Nanocomposites with carbon nanotubes (CNTs) can combine the stiffness and multi-functionality of carbon nanotubes with the advantages of high toughness and processability of polymers giving rise to properties different from that of general composites. However, when the content of CNTs increases gradually, the flexibility of the composite fibre can reduce. In this paper, we propose a simple method of softening the composite fibre via dimensional helical deformation of fibre inner macromolecule bundles to avoid the deterioration of fibre flexibility. The theoretical simulations were conducted to predict proper helical deformations of the single fibre to increase fibre softness, followed by practical softening of the polyvinylidene difluoride (PVDF)/CNTs composite by tensional twisting of the single fibres. The fibres with and without tensional twisting were tested by Fourier-transformed infrared spectroscopy, scanning electron microscopy, X-ray diffraction and mechanical drawing. Results showed the reinforcement of the PVDF/multi-walled CNTs composite fibres (tensile strength enhanced from 4.71 to 5.19 cN/dtex) with an evident softness reduction (initial modulus increased from 16.8 to 20.52 cN/dtex) as the CNTs content increased from 0 to 1.5 wt%. After the tensional twisting, the initial modulus of the composite fibre was reduced by 62.5% while the fibre strength remained reinforced because biomimetic helix formation improved the internal structure deformation ability of the fibre.