Mechanical properties of natural rubber reinforced with graphene oxide nanoplatelets

Motivation for the current paper comes from the expected enhancements in mechanical and viscoelastic properties of unvulcanised Natural Rubber (NR) reinforced with nano-dimensioned Graphene Oxide (GO). Due to their large aspect ratio, specific surface area and tensile stiffness these nano-dimensioned particles are expected to provide significant property enhancements compared to conventional fillers (e.g. Carbon Black). The NR-GO nanocomposites are made in concentrations up to 1.00 wt %, prepared by "latexmixing" with aqueous dispersions of GO platelets, a procedure that requires no heat or chemical input and very little processing. Three sets of specimens have been tested from the same master batch. Two sets of specimens have been tested 4 weeks apart in order to look at the effect of crystallisation on the quasi-static properties and give clearer information on the strength of the GO networks. The third set of specimens undergoes stress relaxation tests to better understand the viscous properties. The quasi-static behaviour shows that the Young's Modulus increases, the strength increases and strain to failure decreases as GO concentration increases. The continuous increase in strength as the concentration of GO is increased gives a good indication that the dispersion of filler is homogeneous, with few agglomerations or stress concentrations. The most significant effects of the GO are at low strain levels, causing the well understood phenomenon of 'strain amplification'. This has significant effects upon the materials ability to crystallise under high strain, and by testing specimens to non-destructive stress levels we have shown evidence of the rotation of GO nanoplatelets under high strain. Stress relaxation of the specimens shows that, in addition to an increase in the elastic properties, the viscous properties also increase; caused by the presence of GO nanoplatelets restricting the movement of the elastomer chains.