Characterization and Application of Graphene Nanoplatelets in Elastomers

The physical performance of elastomer composites based on graphene nanoplatelets (GNPs) was investigated regarding the mechanical and fracture mechanical properties, viscoelastic and dielectric responses, and friction, wear and gas permeation properties. Static gas-adsorption measurements at very low pressures demonstrated that pronounced differences in the surface activity and specific surface area can be observed for different GNPs. The surface activity was shown to be large for GNPs that indicate strong polymer–filler couplings for these systems. This is closely related to the energetic heterogeneity (i.e., the number of highly energetic sites) at the filler surface, which determines the polymer–filler interaction strength and is the main factor determining the reinforcing potential. Based on this information, the stress–strain responses of several GNP types and fine graphite were analyzed in styrene butadiene rubber (SBR) and nitrile butadiene rubber (NBR) with and without softener in relation to standard carbon black. Results demonstrated qualitatively different mechanical behaviors. It was revealed that the mechanical response of the composites under quasistatic cyclic loading can be well understood on the basis of quantitative analysis using a micromechanical model. Gas permeation is strongly reduced by GNPs and further reduced in anisotropic samples with orientation of GNPs perpendicular to the gas flow direction. In comparison with carbon black, dynamic crack growth under pulsed excitation remains almost unaltered for all GNP types, although the wear behavior under sharp abrading conditions is worse. The dry and wet friction properties of SBR composites are well described by hysteresis and adhesion friction theory for GNPs and for carbon black. The dry friction coefficient on rough granite and especially on smooth glass decreases significantly when GNPs are used instead of carbon black. However, the wet friction coefficient on rough granite increases slightly at small sliding velocities, which correlates with the higher hysteresis of GNP composites in the rubbery plateau region.