Interfacial carbonation for efficient flame retardance of glass fiber-reinforced polyamide 6

Wicking action, a typical physicochemical phenomenon, always causes high flammability of glass fiber (GF)-reinforced thermoplastic polymer composites due to the rapid and oriented flow of the polymer melt along the GF surface to the fire zone. This paper introduces an interfacial carbonation mode to solve the global challenge of flame resistance for these composites. Unlike the conventional bulk flame resistance mode, in which a high load of phosphorus flame retardants must be added and evenly distributed in the polymer matrix and the acid sources released by the flame retardants would catalyze the resin into a continuous and compact carbonate layer (the carbonates distributed in the bulk region are uncombined with the GFs), the interfacial mode enriches flame retardants in the GF-resin interfacial regions where wicking actions occur. After the composite burns, the released phosphorus acids can effectively carbonize the interfacial resin and the formed interfacial carbonate layer combining with the GF will convert the original smooth and high-energy GF surface to an inert and rough carbonate surface. The change of interfacial properties makes the adsorption, wetting, spreading and flow of the polymer melt along the GFs much more difficult, thus greatly weakening the wicking effects and improving the flame retardance efficiency of the composites.