Exfoliation of montmorillonite and related properties of clay/polymer nanocomposites

Exfoliating montmorillonite (Mt) to nanolayers is a crucial step during producing clay/polymer nanocomposites (CPN). Only well-exfoliated and well-dispersed Mt. nanolayers in the polymer matrix can significantly improve the properties of the nanocomposites. This review examines the latest scientific advances in the exfoliation methods of Mt., the insights into the exfoliation mechanisms, and the peculiar functionalities of the resultant CPN. The direct exfoliation of Mt. dispersed in water or organic solvents is often intensified by ultrasonication. Grinding of Mt. in the form of solid in a high-energy ball mill can directly exfoliate Mt. to some extent. Exfoliating Mt. for producing CPN is mainly achieved through so-called in situ exfoliation, solution exfoliation and melt exfoliation. The Mt./polymer nanocomposites exhibit typically improved barrier properties, mechanical strength, thermal stability, and fire retardancy. The literature survey suggests that future work should place emphases on developing green and effective exfoliation methods, and deepening understanding of exfoliation mechanisms and the interfacial interactions between the inorganic Mt. nanolayers and organic monomers/polymers. Future research is suggested to assembling exfoliated Mt. nanolayers with functional polymeric molecules or other nano-scale building blocks to produce functional hierarchical nanomaterials with practical applications.