Effect of primary particle size and aggregate size of modified graphene oxide on toughening of unsaturated polyester resin

Graphene‐based nanomaterial tougheners can effectively toughen thermosetting resins at an extremely low loading level with minimal change in T_g or modulus. However, previous research has indicated that this toughening effect shows only small responses to changing graphene oxide (GO) surface modifications, resin dispersion processing methods, and GO loading levels. It is hypothesized that the physical dimensions of GO particles affect the toughening behavior of graphene‐based additives. In this study, the sizes of primary and aggregated surface‐modified GO (mGO) particles were measured directly using scanning electron microscopy. The effects of the differences in size on fracture toughness (K_IC), bending modulus, and flexural strength of an unsaturated polyester resin were evaluated. The sizes of primary mGO particles were estimated from the sizes of GO particles prior to their surface modification and the sizes of mGO aggregates after dispersion in the resin. This study shows that as little as 0.005 wt% mGO can increase K_IC by nearly 20%. This toughening effect is independent of primary particle size. Reducing mGO aggregate sizes by chemical modification or sonication shifts the optimal loading level of mGO‐based tougheners to lower concentrations, but the maximal achievable toughness cannot be changed by improving dispersion or particle–matrix interactions. POLYM. COMPOS., 40:3886–3894, 2019. © 2019 Society of Plastics Engineers