Processing-property relationships of polycarbonate/graphene composites

Polycarbonate composites reinforced with graphite and functionalized graphene sheets (FGS) were produced using melt compounding. Composite samples with different degrees of graphite orientation were processed via injection, compression molding and long-term annealing. Electron microscopy and Xray scattering revealed that FGS was nearly exfoliated. However, graphite remained multi-layer even after melt processing. Flow induced orientation of graphite was observed from both injection and compression molded samples. Graphite particles in samples after long-term annealing exhibited more random orientation. Composites with the exfoliated FGS required a smaller amount of reinforcement for rigidity and connectivity percolation, as determined by melt rheology and electrical conductivity measurements. FGS also showed better performance in suppressing gas permeability of polycarbonate. However, improvements by FGS dispersion in tensile modulus and dimensional stability were not as significant. This may be due to defects in the sheet structure formed during oxidation and pyrolysis used to exfoliate. (C) 2009 Elsevier Ltd. All rights reserved.