The decomposition and flame retardant mechanism of a tetrazole based P/N/S multi-element compound for epoxy resin

In this paper, a P/N/S multi-element flame retardant (TATP) was synthesized by 5-amino-1H-tetrazole, 2-thenaldehyde and DOPO. When TATP content reaches 4 wt%, EP/TATP-4 exhibits 38.1 % of LOI value and UL-94 V-0 rating. Compared to the pure EP, the peak of heat release rate, the total heat release and the total smoke production in cone calorimeter test are dropped by 30.8% and 32.4%, and 51.6% respectively. Moreover, the char residue is dramatically increased by 74.0%. Detailed analysis indicates, the tetrazole group decomposes from TATP firstly, which promotes the cleavage of thiophene ring below 380 o C, much lower than experimentally reported degradation temperature of thiophene compounds. Therefore, besides the emission of enough nonflammable gases, the high-energy density characteristics of the tetrazole ring is also benefited to the thermal decomposition of TATP and make the tetrazole, thiophene and DOPO groups play synergistic impacts on fire safety for epoxy resin. Furthermore, the P/N/S elements are found exerting flame retardant effects both in the gas and condensed phases. The obtained EP/TATP-4 maintains the comparable tensile and flexural properties to pure EP. Remarkably, EP/TATP-4 has high transparency and exhibits excellent UV shielding performance for UVA wavelengths, and has an extraordinarily higher Ultraviolet Protection Factor value of 1983.2.