Microstructure, mechanical and electrical characterizations of bimodal and nanocellular polypropylene/graphene nanoplatelet composite foams

Abstract

In this work, linear and branched polypropylene (PP)/ graphene nanoplatelet (GnP) composite foams were prepared using supercritical CO2. The morphology of nanocomposite foams was imaged on SEM. Branched PP foams revealed bimodal cellular morphology, while linear PP exposed nanocellular structures. The effect of cell modality and adding GnP on the mechanical and electrical properties of nanocomposite foams were investigated. Addition of GnP to linear PP decreased cell density and made cell distribution uniform due to its functionality of crystal nucleating agent While in branched PP foams, it was seen by the dynamic observation that GnP acted as bubble nucleating agent, resulting in a fine cell size and increasing the foam density. Nanocellular foams exhibited better mechanical properties than bimodal but the limited expansion ratio. However, some bimodal foams presented comparable mechanical properties to non-foamed samples, in spite of high expansion ratio. Addition of graphene nanoplatelet to some extent improved the specific tensile modulus and strength of foams. The electrical conductivity of composites was reduced by foaming. However, this reduction was very significant in the case of bimodal foams.