Chemically-reduced graphene reinforced polyetherimide nanocomposites: dielectric behavior, thermal stability and mechanical properties

Recently, the research on improvement of dielectric and mechanical performances of the high-performance polymers like polyether imide (PEI) by reinforcement of modified graphene nanosheets has received enormous attention in both defence and commercial sectors. Reduced graphene oxide (rGO) reinforced PEI nanocomposites were fabricated by dispersion of rGO nanosheets in the polyamic acid (PAA) followed by in situ partial thermal reduction and imidization of the as-prepared PAA/rGO nanocomposites. Chemically synthesized graphene oxide was reduced with hydrazine hydrate. Compared to pure PEI, the dielectric permittivity of the PEI nanocomposite with 5 wt% rGO revealed remarkable increase by about 132 times, which is attributed to the enhanced interfacial polarization (Maxwell-Wagner-Sillars effect) at the rGO-PEI interfaces. The PEI nanocomposite exhibited noticeably low dielectric loss (0.43 at 1 kHz) even at high rGO content (5 wt%) due to the low current leakage. The maximum dielectric performance of the nanocomposites was observed near percolation threshold (approximate to 1.12 vol%). Upon thermal annealing, both AC conductivity and dielectric permittivity (<10 kHz) of the nanocomposites were substantially decreased. With incorporation of rGO nanosheets, the mechanical properties of the nanocomposite films were remarkably increased with maximum tensile strength of 423 MPa and Young's modulus of 2.93 GPa at 5 wt% rGO loading, suggesting excellent stress transfer between PEI-matrix and rGO nanosheets. The PEI/rGO nanocomposites exhibited significant improvement in thermal stability with high char yield (>40%) in N-2 atmosphere compared to pure PEI.