Fabrication and properties of PVDF/expanded graphite nanocomposites

Abstract

Poly(vinylidene fluoride) (PVDF) nanocomposites filled with various expanded graphite (EG) contents were prepared via melt-mixing followed by hotpressing. The structure, electrical, and thermal properties of resulting nanocomposites were investigated. X-ray diffraction results indicated that the EG additions do not lead to structural changes of PVDF. Differential thermal calorimetry measurements revealed that EG act as a nucleating agent for PVDF molecular chains. The crystallization temperature shifted to higher temperature with increasing EG content. DMA results showed that the storage modulus and glass transition temperature can be enhanced by adding EG. The nanocomposites were found to exhibit a small percolation threshold of 6.3 vol% due to the large aspect ratio of graphite nano-sheets. A great enhancement of dielectric constant is also found as EG concentration approaches percolation threshold. Both the electrical conductivity and dielectric constant of PVDF/EG nanocomposites can be well described by the percolation theory.