Microwave-Exfoliated Graphite Oxide/Polycarbonate Composites

We present the first report of polymer composites using microwave-exfoliated graphite oxide (MEGO) as filler, a high surface area carbon material that resembles graphene on a local scale. MEGO has a wormlike layered structure which can be sheared apart during melt mixing with a polymer host. In this study, we produced MEGO/polycarbonate (PC) composites at various loadings and evaluated their morphology and properties. Transmission electron microscopy and X-ray scattering studies suggested an exfoliated morphology, with wrinkled platelets of approximately 4-5 nm thickness evenly dispersed throughout the PC matrix. Frequency scans of composite melts using shear rheology showed an onset of frequency-independent terminal behavior around 2.1 wt %, suggesting an effective aspect ratio of nearly 50 for the dispersed platelets, in agreement with TEM analysis. The composites showed significant increases in electrical conductivity, with an onset of electrical percolation around 1.3 wt %, but only exhibited modest improvements in thermal conductivity. Long-term thermal annealing was performed to promote disorientation of the dispersed platelets, which further improved the electrical conductivity but had little effect on the thermal conductivity. Dynamic mechanical analysis showed reinforcement by MEGO; however, very little change in the glass transition temperature and in the thermal stability was observed in the composites versus neat PC.