Economical and facile synthesis of a highly efficient flame retardant for simultaneous improvement of fire retardancy, smoke suppression and moisture resistance of epoxy resins

An economical flame retardant additive dimelamine pyrophosphate (DMPY) was synthesized from melamine and sodium pyrophosphate and its chemical structure was well characterized and confirmed. It was used to flame retardant epoxy resin (EP) thermosets and the fire retarded performance, mechanical properties, moisture resistance and flame retardant mechanism of EP thermosets were investigated in details. The samples achieved UL-94 V-0 grade during vertical burning tests and the limiting oxygen index value reached 28.7% when 9 wt% DMPY was incorporated. DMPY stimulated the degradation of EP matrix in advance and the formation of intumescent and compact char layer during combustion. Besides, the nonflammable gases generated from the decomposition of DMPY exerted flame retarded effect in gas phase. Thus, the rate and total amount of heat release and smoke production were significantly suppressed. The moisture resistance of EP/DMPY thermosets was improved comparing with that of pure EP. The samples remained superior flame retardant performance and mechanical properties after water resistance tests due to the excellent water resistance of DMPY. In summary, the EP/DMPY thermosets exhibited excellent flame retardancy, moisture resistance, mechanical properties and fire safety performance. The presented investigation provided a broad application prospect in the high-performance field of flame retardant EP thermosets because of the low cost and easy industrialization of DMPY.