Construction of porous g-C₃N₄@PPZ tubes for high performance BMI resin with enhanced fire safety and toughness

It's acknowledged that the inferior toughness of bismaleimide resin (BMI) is the crucial problem hindering its development and application especially in aerospace, mechanical and electronic fields. While the poor fire safety of toughened BMI is another problem urgently needed to be resolved. Therefore a novel g-C₃N₄@PPZ hierarchical architecture constituted of porous g-C₃N₄ tubes modified by polyphosphazene was designed and fabricated to improve the fire safety and mechanical properties of BMI in this work. Especially compared to pure BMI, the peak heat release rate (PHRR) and peak smoke production rate (PSPR) of BMI with an incorporation of 2 wt% g-C₃N₄@PPZ (BMI/g-C₃N₄@PPZ2.0) are at 246.3 kW/m² and 0.12 m²/s accompanying with 52.1% and 53.8% reduction respectively. The total heat release (THR) and total smoke production (TSP) of BMI/g-C₃N₄@PPZ2.0 are endowed with reductions of 29.4% and 42.9% as well, which demonstrates that the fire safety including heat and smoke hazards of BMI/g-C₃N₄@PPZ2.0 is significantly improved. With regard to the mechanical performance of BMI composites, the impact strength of BMI/g-C₃N₄@PPZ1.5 is 18.89 kJ/m² which increases by 184.0% in comparison with that of pure BMI resin (6.65 kJ/m²). And it's found that the impact strength of BMI/g-C₃N₄@PPZ are still higher than pure BMI in hot-humid environment, which signifies that the BMI/g-C₃N₄@PPZ would be preferred in the industrial applications. Meantime the possible flame retardant and toughening mechanism of g-C₃N₄@PPZ in BMI is detailed investigated and proposed as well.