Exploring the effects of cardanol-based co-curing agents with different phosphorus structures on the mechanical and flame-retardant properties of bismaleimide resin

Aiming to address the problems of flammability and brittleness of BMI and reduce the use of petroleum-based materials, three kinds of cardanol-based co-curing agents (CDPO, CDPC, CDCP) were synthesized and applied to prepare advanced BMI. Compared to the neat BMI, the modified BMI exhibited better thermal stability with higher decomposition temperatures and char yields. The BMI/CDCP-10 containing 4.5 wt% CDCP possessed the best flame retardancy with 50.4% reduction in PHRR , 27.5% reduction in THR and 21.2% reduction in TSP compared to those of neat BMI. Moreover, with the 4.5 wt% incorporation of CDPO, CDPC and CDCP, the impact strength of BMI was enhanced by 95%, 133.8% and 127.5% respectively, due to the flexible fatty chains and the decreased crosslinking density . The reason for different modification effects among modified BMI systems is studied from the structure of modifiers, finding that the phosphorylated cardanol with higher content of O and higher valence of P can be utilized to improve the mechanical property and fire safety of BMI. This work provides a new way to reduce the dependence on the petroleum-based materials and expand the application areas of BMI. • Three cardanol-based co-curing agents (CDPO, CDPC, CDCP) with different phosphorous structure were synthesized. • The PHRR, THR and TSP of BMI with 4.5 wt% CDCP can be declined by 50.4%, 27.5% and 21.2%, respectively. • The impact strength of BMI was maximally increased by 133.8% with the 4.5 wt% CDPC. • The thermal stability, flame retardancy and mechanical performance of BMI were greatly elevated by the modifiers.