Restructuring of confined crystalline morphology in the drawing process of VGCF-iPP nanocomposite filaments

Solid-state drawing to high extension ratios of melt-extruded VGCF-iPP nanocomposite filaments results in remarkable increases in modulus and strength, which mask any contribution of nano-reinforcement or inter-particle confinement observed previously. Based on X-ray diffraction and thermal analyses it is shown that the drawing process involves crumpling of the original 'shish-kebab' structure, accompanied by lateral shrinkage of the 'kebabs', disappearance and reorientation of daughter lamellae and significant increases in the degree of crystallinity by solid-state recrystallization. The effects of the initial diameter of the as-extruded filaments and those of the nanofibers and the 'shish-kebab' structure are dominated by the drawing process, which produces a highly aligned fibrillar structure with superior mechanical properties. A cartoon model of the effect of solid-state drawing of extruded iPP and nanocomposite filaments on the transition from 'shish-kebab' to fibril morphology is presented.