(200o) Preparation of Modified Graphene Oxide-Containing Styrene Masterbatches for Thermosetting Resin Composite

Incorporating graphene-based nanomaterials into thermosetting resin matrices is one of the key challenges in preparing resin nanocomposites for industrial scale applications. Thermosets, unlike thermoplastics, cannot be processed by melt blending or solvent casting, so graphene nanosheets can only be added to a low-viscosity resin prepolymer, which does not provide high shear during mixing to break down graphene aggregates. The physical form of graphene nanomaterials can also significantly affect the dispersion and the final properties of the composites. Drying of graphene materials often results in significant stacking of nanosheets and makes them hard to redisperse. Freeze-drying has been utilized to mitigate sheet stacking during drying of graphene, but the lengthy treatment is not industrially friendly. In this research, a new process of dispersing chemically modified graphene oxide (mGO) was evaluated to address the above-mentioned issues. This process entails the preparation of an mGO/styrene masterbatch by solvent exchange and a simple mechanical mixing step to generate a homogeneous mGO/resin dispersion. For comparison, two other post-synthesis processes, namely oven drying and freeze-drying, were also studied. The dried mGO was blended into resin using the same mechanical mixing conditions. At low mGO loading levels of 0.02–0.08wt.%, the three processing routes produce resin composites that differ slightly in mechanical properties. Composites made with oven-dried mGO show the highest increase in fracture toughness and the most severe decrease in flexural strength, while the composites prepared from the mGO masterbatch exhibit less toughness increase but a better flexural strength retention. Freeze-dried mGO provides a toughening effect and a reduction in flexural strength with a magnitude in between that offered by oven-dried and masterbatch-derived mGO. However, significant differences in dispersion homogeneity can be observed by visible light microscopy (VLM) and scanning electron microscopy (SEM). The masterbatch process offers an economical way of producing high quality mGO dispersions in unsaturated polyester and vinyl ester resins.