Structural interpretations on tensile fracture mechanism and elongational rheology of poly(vinylidene fluoride)/halloysite nanotubes nanocomposites

Abstract

Halloysite nanotubes (HNTs)‐filled poly(vinylidene fluoride) (PVDF) nanocomposites were fabricated using continuous mixing extrusion with and without water injection. The HNTs dispersion state was qualitatively and quantitatively analyzed by using transmission electron microscopy and the Halpin‐Tsai equation, suggesting better HNTs dispersion in the nanocomposites fabricated with water injection. To grasp the relationship between the structure and properties, the effect of the HNTs dispersion on the tensile fracture mechanism and melt elongational rheology of the nanocomposites was investigated. It was deduced from morphological observations on the fractured surfaces that for the nanocomposites fabricated without and with water injection, cracks initially formed at the vicinity of HNTs aggregates and the thinner brittle fracture edge region, respectively. This was attributed to the important roles of the PVDF crystallization behavior and HNTs dispersion on the formation of the voids, wedges and ridges, which are the origins for forming cracks and easily formed at region with more HNTs aggregates or lower crystallinity. The nanocomposites fabricated with water injection exhibited lower elongational viscosities and 17–60% increments for the draw ratios at break than those fabricated without water injection, due to better HNTs dispersion induced by injected water. POLYM. ENG. SCI., 59:773–780, 2019. © 2018 Society of Plastics Engineers