Experimental study on the synergistic flame retardant effect of bio-based magnesium phytate and rice husk ash on epoxy resins

Bio-based flame retardant magnesium phytate (Mg-Phyt) was synthesized by a facile chelation reaction and characterized. The feasibility of Mg-Phyt as flame retardant for epoxy resins was studied. In order to enhance its flame retardancy, the synergistic flame retardancy between Mg-Phyt and agricultural waste material rice husk ash (RHS) and the synergistic effects of different ratios of these two were investigated. The results show that the addition of 10 mass% Mg-Phyt can reduce the thermal decomposition rate and achieve good flame retardant performance for epoxy resins. Furthermore, the combination of Mg-Phyt with RHS can have a synergistic flame retardant effect. Among them, the synergistic effect of 5 mass% Mg-Phyt and 5 mass% RHS is the best when the two substances are added into epoxy resins. More specifically, compared to pure epoxy resins, the peak heat release rate, total heat release, peak smoke production rate, and total smoke release of epoxy resins with 5 mass% Mg-Phyt and 5 mass% RHS are reduced remarkably by 28.6%, 10.6%, 33.0%, and 7.8%, respectively. The burning rate is also reduced by 42.4%. During the combustion process, this synergistic flame retardant effect is attributed to the formation of a compact silica-rich char layer containing Si-P and P-O-C structures with strong thermal stability to hinder the heat transfer into the epoxy resins substrate and reduce flammable gas emission, so that a better flame retardancy and smoke suppression of epoxy resins can be attained.