Core–shell rubbery fillers for massive electrical conductivity enhancement and toughening of polystyrene–graphene nanoplatelet composites

Graphene nanoplatelets (GNPs) are an attractive additive for polymers to provide electrical conductivity to a composite. If the GNP surface and the polymer are incompatible, the interfaces are weak, resulting in a large drop in the flexural strength and toughness of the composite compared to the native polymer. In the present study, we show that adding core–shell rubbery (CSR) nanoparticles, that have a polyisobutadiene (PIB) core and a thin, polystyrene (PS) compatible shell, to a PS–GNP composite enhances the dispersion of the GNP and suppresses their restacking, increasing the electrical conductivity of the composite by several orders of magnitude. In addition, there is complete recovery of the flexural strength and a large increase in toughness compared to PS samples without fillers. The recovery of the mechanical properties is related to a uniform distribution of the CSR and good binding at the interfaces because of the compatibility of the filler surface with the PS matrix, as well as the rubbery nature of the PIB core. This strategy of using a second filler as both a toughening agent as well as a dispersion aid breaks a commonly encountered tradeoff between electrical and mechanical property enhancement by fillers. It can be deployed for applications where both a high electrical conductivity and excellent mechanical properties of polymer composites are desired.