Effect of char sulfonic acid and ammonium polyphosphate on flame retardancy and thermal properties of epoxy resin and polyamide composites

Char sulfonic acid and ammonium polyphosphate were used to improve the flame retardancy of composites. A synergistic effect between char sulfonic acid and ammonium polyphosphate on the flame retardancy of epoxy resin and polyamide composites was proposed. The results showed that the optimal synergistic effects were achieved when the weight ratio of char sulfonic acid:ammonium polyphosphate was 1:3. Thermogravimetric analysis indicated that the flame retardants improved the amount of residue. The char sulfonic acid and ammonium polyphosphate additives greatly decreased the peak heat release rate and suppressed smoke according to cone calorimetry testing. Scanning electron microscope results showed that a compact and thick char layer was formed, which hindered the transfer of heat flow and combustible gases in the condensed phase. Thus, the combination of char sulfonic acid and ammonium polyphosphate had been proved to be a promising flame retardant system for epoxy resin and polyamide composites.