Chemically modified graphene-reinforced polybenzimidazole (PBI) nanocomposites were prepared by liquid-phase exfoliation of graphene oxide (GO) and reduced graphene oxide (rGO) in methanesulphonic acid (CH4O3S), followed by in-situ polymerization using GO–CH4O3S and rGO–CH4O3S suspensions as reaction media. Various reducing agents were used to produce rGOs and their reducing efficiency was examined to attain highly graphitic structure and excellent electrical conductivity of the resulting rGOs. The results of Raman, Fourier transform infrared and X-ray photoelectron spectroscopy indicate higher extent of reduction of GO with hydrazine compared to other reducing agents. The PBI nanocomposite containing 10 wt% rGO derived from hydrazine reduction reaction (rGO–H) exhibits the highest dc conductivity of 2.77 × 10−3 S cm−1 at room temperature, which is 11 orders of magnitude higher than pure PBI. The thermal annealing treatment at 350°C resulted in a substantial increase in dc conductivity of the PBI/GO nanocomposite, whereas the enhancement of conductivity is much less for the PBI/rGO nanocomposites. Compared to pure PBI, both tensile strength and Young’s modulus enhanced by 3.4 times and 6.9 times, respectively, for the PBI nanocomposites with 10 wt% GO content, which is ascribed to strong interfacial interactions and subsequent effective stress transfer between the PBI matrix and GO. The PBI/rGO nanocomposites exhibited relatively lower tensile strength/modulus compared to the GO-reinforced nanocomposite. The thermal stability of PBI was significantly improved upon the incorporation of both GO and rGO nanosheets, whereas higher thermal stability was achieved for rGO-reinforced nanocomposites.
