Superior flame retardancy of glass fiber-reinforced polyamide 6T composites by synergism between DOPO-based derivative and carbon nanotube

How to create high-performance flame-retardant semi-aromatic polyamide with minimum flame retardant loading remain a major challenge. Herein, glass fiber-reinforced polyamide 6T (GFPA6T) composites with superior flame retardancy were obtained by synergism between DOPO-based derivative (PN-DOPO) and carbon nanotube (CNT). The introduction of 9 mass% PN-DOPO and 1 mass% CNT into GFPA6T, which is significantly lower than the loading reported (15 mass%), leads to superior flame retardancy with V-0 rating during UL-94 test and a higher limiting oxygen index (LOI) value of 28.5%. Thermogravimetry, cone calorimeter and char residue analysis suggest that the addition of CNT can enhance the thermal stability and promote the formation of stable char layers, effectively protecting the matrix from fire. By quantitative analysis, the flame retardancy mechanism of the resulting GFPA6T composites includes three aspects: 14.3% flame inhibition, 8.5% charring effect and 34.7% protective-barrier effect. Besides, the introduction of CNTs can compensate the loss of mechanical properties due to the incorporation of flame-retardant PN-DOPO.