Tensile deformation behavior of carbon nanotube reinforced electrospun fibers

In this study, we use electrospinning to obtain carbon nanotube (CNT) filled electrospun fibers and aim to elucidate the mechanisms of nanoreinforcemenet of CNTs in the fiber matrix. The effects of CNT inclusion on tensile strength and modulus of two types of electrospun fibers, polyamide 6,6 (PA6,6) and polyvinylidene fluoride (PVDF) fibers, were studied. For this purpose, PA6,6 and PVDF solutions were blended with 0, 1, 2 and 3 wt% CNTs before electrospinning. Aided by the high elongational flow of the polymer jet and the high shear forces due to the high electrostatic voltage (~18 kV), the CNTs were embedded within the electrospun fibers and aligned along the fiber axis. The deformation mechanics of the composite fibers as a function of CNT weight fraction were characterized by using tensile tests. Tensile modulus and strength of the fibers were found to improve significantly with CNT content. Hence, for CNT/PA6,6 fibers, addition of 3 wt% CNTs increased the modulus and strength of neat fibers by ~62% and 53%, respectively. The thermal behavior of the fibers indicated that the glass transition of PA6,6 fibers was increased by CNTs. The harder CNT phase served as nucleating agents within the fibers and restricted the segmental motion of neighbouring polymer chains, which strenghtened and stiffened PA6,6 fibers. For CNT/PVDF fibers, addition of 3 wt% CNTs increased the modulus and strength of PVDF fibers by 32% and 28%, respectively. Here, the presence of CNTs induced conformal changes within the PVDF fiber matrix. This resulted in the formation of extended polymer chains which stiffened and strengthened the fibers by providing resistence to the applied axial tensile stress. Therefore, the presence of CNTs in the neat polymer fibers leads to superior stiffening and strengthening in the nanostructured composites.