Decomposable double-walled hybrid nanorods: formation mechanism and their effect on flame retardancy of epoxy resin composites

Abstract

Double-walled Al–P–Si hybrid decomposable nanorods, which have a silica coated aluminum phosphonate nanostructure, were in situ prepared by thorough but ordered reconstruction of montmorillonite. The reconstruction was facilely performed through hydrothermal reaction of montmorillonite with diphenyl phosphoric acid. The formation process of nanorods involves the decomposition of montmorillonite, the repolymerization to generate aluminum phosphonates, the assembly via π–π stacking interactions to form a 1D nanostructure, and the coating of silica on aluminum phosphonate nanorods. Interestingly, it was found that only layered silicates exhibited such reconstruction into hybrid nanorods. The decomposition of the nano-sized sandwich structure may lead to highly reactive Si–O tetrahedra and a synergistic reaction process. The nanorods showed decomposition around 400 °C, producing nanoparticles mainly composed of aluminum silicates. The fire property test showed that epoxy/Al–Si–P hybrid nanorod nanocomposites exhibited outstanding flame retardant performance. One possible explanation for this is that nano-sized particles resulting from decomposition easily migrated to the surface of epoxy resins, consequently forming protective layers.