Synthesis of exfoliated graphene–montmorillonite hybrids as the fillers for epoxy composites

Graphene was prepared by microwave reduction of graphite oxide and organic montmorillonite was obtained by the intercalation modification of montmorillonite. The hybrids with various mass ratios of organic montmorillonite/graphene (m_OMMT:m_GNS = 1:1, 5:1, 10:1, 20:1 and 30:1) were primarily prepared, following which the epoxy matrix composites incorporated with organic montmorillonite–graphene hybrids were synthesized. The results indicate that graphene sheets are further exfoliated to fewer-layer structure and organic montmorillonite interlayer has been intercalated by graphene flakes after the combination of graphene and organic montmorillonite, suggesting the synergistic dispersion of these two components. Organic montmorillonite shows completely exfoliated structure at low ratios (1:1 and 5:1) and intercalated structure at high ratios (10:1, 20:1 and 30:1). Among all the hybrids with various organic montmorillonite/graphene ratios, the hybrids at the ratio of 5:1 present better dispersion and are more beneficial to enhancing the mechanical properties of the epoxy matrix composites. Moreover, compared with graphene and organic montmorillonite fillers, the introduction of organic montmorillonite–graphene hybrids into epoxy increases the mechanical strength more efficiently, especially increasing the impact strength of epoxy by 140.8%, indicating the synergistic reinforcement of these two components. The composite filled with organic montmorillonite–graphene hybrids exhibits better thermal stability than pure epoxy, but slightly poorer than the composites incorporated with graphene, which may be attributed to the low volume fraction of the hybrids in epoxy composites.