Preparation and Characterization of Graphene Sheet-Polyimide Nanocomposite Films

Graphene oxide (GO) sheets were first synthesized through oxidation of natural graphite by a modified Hummers method, and then their homogeneous and stable dispersion in N, N'-dimethylformamide (DMF) was obtained. Stable and homogeneous solution mixtures of GO and PAA (polyamic acid) in DMF at different mass ratios of GO/PAA were readily prepared. Uniform composite films of GO-FAA were subsequently prepared by solution casting. FAA was turned to polyimides (PT) and GO reduced in situ to grapheme (GS) at the same time by a subsequent thermal imidization of GO-FAA films, leading to composite films of GS-PI. Electrical resistivity, thermal stability and mechanical property of GS-PI films were studied. The results indicate that the surface resistivity of GS-PI films was significantly decreased with the increase in GS content,lowered to about 10(6) Omega, the standard of the anti-static electricity film, in the film prepared with 1.0 wt% of GO in GO-PAA. The tensile strength and the elongation at break of GS-PI composite films were both increased with increase in GS content, reached their maxima in the film prepared with 0.6 wt% of GO in GO-PAA, followed by regular decreases with further increase in GS. Different from the tensile strength and the elongation at break, the tensile modulus of GS-PI was in constant increase with GS content in the film. An increase of 37% was detected in GS-PI film prepared with 3.0 wt% of GO. Moreover, the ductility and the thermal stability of GS-PI were well kept in all the composite films regardless of its GS content.