Natural clay nanosheets and nanofibers for flame-retardant polymer composites

Natural clay nanosheets and nanofibers, particularly kaolinite, montmorillonite and sepiolite, have attracted growing interests as environmentally friendly flame-retardant additives for polymer composites. However, their broader applications are limited by unsatisfactory dispersion, weak interfacial compatibility and unideal flame-retardant efficiency when used alone. This paper first outlines the thermal decomposition and combustion behavior of polymers, highlighting gas-phase, condensed-phase and endothermic mechanisms. The influence of clay nanosheets and nanofibers on the combustion of polymer composites is subsequently discussed. It presents recent progress in improving the performance of natural clays in flame-retardant polymer composites through structural modification and multi-component integration. Focus is the strategies mainly including surface modification, intercalation design and combinations with halogen-free flame retardants, e.g. intumescent systems, metal oxides, carbon-based nanofillers and bio-based additives. These approaches have shown notable improvements in fire resistance, smoke suppression, mechanical strength and environmental safety. The review outlines future research directions for the development of sustainable, high-performance flame-retardant polymer nanocomposites based on natural clays.