The Effect of Shear Mixing Speed and Time on the Mechanical Properties of GNP/Epoxy Composites

The aim of this study was to examine the effect of shear mixing speed and time on the mechanical properties of graphene nanoplatelet (GNP) composites. Shear mixing is cited in the literature as one method of making a good dispersion of nanofillers in a polymer that breaks down agglomerates into smaller particles and in the case of GNP can exfoliate layers of graphene. In this paper 0.1 to 5 wt% GNP was mixed with epoxy at different speeds and for different lengths of time. The composites were then cured and the tensile strength and Young’s modulus was measured. Optical microscopy was performed to examine the dispersion of the GNP in the epoxy. The results show that the shear mixing speed and time affect the size of agglomerates, which has an impact on the mechanical properties of the composite. At 3000 rpm and 2 h of mixing the average size of agglomerate was 26.3 μm (30 % reduction compared to that of 1000 rpm and 1 h duration), the tensile strength of epoxy was not affected by the addition of GNP, while a 12 % increase was recorded for the Young’s modulus. It is also found that functionalisation of the surface of the GNP improves the bond formed between the GNP and the resin that enhances its mechanical properties with no effect on the size of the agglomerates. Acetone was used to improve the GNP dispersion and found that shear mixing 5 wt% of GNP with acetone increases the Young’s modulus up to 3.02 from 2.6 GPa for the neat epoxy, an almost 14 % rise.