The effect of flake diameter on the reinforcement of few-layer graphene–PMMA composites

The effect of the lateral dimensions of the graphene reinforcement on the physical properties of poly(methyl methacrylate) (PMMA) nanocomposites was studied. Electrochemically-exfoliated, few-layer graphene with average diameters of 5 μm (5-FLG) and 20 μm (20-FLG) were incorporated into a PMMA matrix at loadings from 0.5 to 20 wt.% by melt mixing using a twin screw compounder. The smaller graphene flakes were found to have only a slight effect on the rheological properties of the PMMA, whereas the larger flakes significantly increased the viscosity and dynamic moduli of the PMMA melt. Mechanical testing showed that the 5 μm flakes behaved in a similar way to short fibers and reinforced the PMMA matrix poorly compared to the 20 μm flakes, in line with previous predictions on the critical length of graphene. Significantly, these larger flakes gave a linear increase in the modulus with loading even at high loadings, without any of the detrimental aggregation effects seen in most other graphene systems.