Interfacial charring method to overcome the wicking action in glass fiber-reinforced polypropylene composite

Abstract Glass fiber (GF)-reinforced polypropylene composites show high flammability due to wicking actions, which results in accelerated flow of the polymer melt along the GF surface to the flame zone. The conventional bulk charring mode, in which high loading of flame retardants are evenly distributed in the bulk matrix to catalyze the resin into an integrate char-barrier so that the entire composite surface could be covered, is quite inefficient and uneconomic. In this research, an interfacial charring mode differing from the bulk one has been proposed to solve the challenge. The acid-source flame retardants grafted on the GF surface can rapidly carbonize the interfacial resin to form a char layer, which can locally encapsulate the GF during combustion, thus converting the original smooth and polar GF surface to rough and inert carbonates-covered one and preventing the polymer melts from wetting, spreading and flowing on it. In this manner, it effectively eliminated thermodynamic and dynamic factors that cause wicking actions and remarkably improved flame retardance, even at a much lower flame retardant concentration compared with the bulk mode. In addition, without the stress concentration effect caused by the flame retardant particles directly distributed in the bulk resin, the interfacial flame retardant system also showed much better mechanical properties than the bulk one.