Flame retardant effect of phosphotungstic acid intercalated ZnAl layered double hydroxides and intumescent flame retardant on epoxy-polyamide resin

The PW₁₂O₄₀-ZnAl layered double hydroxides(LDHs) was prepared by using PW₁₂O₄₀³⁻ ion pillared intercalation NO₃-ZnAl LDHs. The composition and structure were analyzed by XRD, FTIR, inductively coupled plasma(ICP) and SEM. The flame retardant epoxy-polyamide resin(EP-PA) were prepared by NO₃-ZnAl LDHs or PW₁₂O₄₀-ZnAl LDHs compound with intumescent flame retardants(IFRs) containing ammonium polyphosphate, melamine, pentaerythritol. The heat and smoke release rules of different ZnAl LDHs-IFRs flame retardant EP-PA were evaluated by back temperature experiment and cone calorimetry experiment. TGA result shows that the maximum degradation rate of PW₁₂O₄₀-ZnAl-IFRs/(EP-PA) composite is the lowest, and the carbon residue rate is the highest, which indicate that PW₁₂O₄₀-ZnAl LDHs improve the oxidation resistance of PW₁₂O₄₀-ZnAl-IFRs/(EP-PA) composite at high temperature. The back temperature experiment results show that under the same heat radiation intensity, the back temperature of PW₁₂O₄₀-ZnAl-IFRs/(EP-PA) composite reaches to 200℃ and 300℃ with the longest time and the lowest rate of back temperature rise. The results show that PW₁₂O₄₀-ZnAl LDHs can obviously enhance the fire resistance of EP-PA. From cone calorimetry experimental data, it can be seen that PW₁₂O₄₀-ZnAl-IFRs makes PW₁₂O₄₀-ZnAl-IFRs/(EP-PA) composite have the lowest peak of heat release rate(PHRR), mean heat release rate(MHRR), mean effective heat of combustion(MEHC) and total heat release(THR). Its fire growth index (FGI) is only 14.5% of IFRs/(EP-PA) composite, and the total smoke production (TSP) is 27.6% lower than NO₃-ZnAl-IFRs/(EP-PA) composite and 55.3% lower than IFRs/(EP-PA) composite. The results suggest that PW₁₂O₄₀-ZnAl-IFRs is more effective than NO₃-ZnAl-IFRs in reducing the heat release and inhibiting the generation of flue gas.