Cardanol derived benzoxazine in combination with boron-doped graphene toward simultaneously improved toughening and flame retardant epoxy composites

A bio-based phosphorus-containing benzoxazine monomer (CBz) was successfully synthesized through the reaction between cardanol and DOPO-based diamine. In order to simultaneously improve the toughness and flame retardancy of epoxy resin (EP), various contents of CBz in combination with boron-doped graphene (BG) nanosheets were incorporated into EP to obtain boron-doped graphene/cardanol derived benzoxazine-epoxy composites (EP/CBz/BG). By comparison, cardanol derived benzoxazine-epoxy co-polymers (EP/CBz) were also fabricated. Results show that the addition of the as-prepared CBz into EP not only endowed EP with excellent flame retardancy, but also improved the glass transition temperature and impact strength . Specifically, the peak heat release rate of EP composite with 13 wt% CBz and 2 wt% BG decreased by 48% compared to that of neat EP, accompanying with an increase of impact strength by 22%. These favorable features of EP/CBz/BG composites are attributed to the unique structure of CBz and high resistance to thermal decomposition of BG.