Reactive graphene by one-pot grafting toward tough and fire-retardant thermoset nanocomposites

Functionalized graphene with reactive moieties is promising to significantly enhance the interfacial strength of graphene materials with thermoset resins and their dispersion in resins. Most of the previous reactive graphene materials were prepared through the covalent modification of oxidation-produced oxygen-containing groups of the graphene oxides, which, however, have intensive defects and weakened mechanical strength, Young's modulus, and thermal stability. Starting from the commercially available graphene, we herewith developed a one-pot direct grafting approach for the fabrication of epoxy-reactive graphene. This grafting is achieved by the diazonium addition reaction of 10-(2′,5′-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) functionalized 4-aminobenzoic acid with the pristine graphene sheets. We further demonstrated this one-pot grafting approach could be controlled well by simply changing the ODOPB functionalized 4-aminobenzoic acid concentration to fine-tune the grafting density. In the graphene reinforced epoxy composite, ODOPB moieties grafted onto graphenes act as anchors, ensuring the improved dispersion of graphene sheets. The ODOPB functionalized graphene composites demonstrated a dramatically enhanced fracture toughness (a critical-stress-intensity factor, KIC value of 2.1) than graphene-epoxy composites (a KIC value of 1.3) and neat epoxy material (a KIC value of 1.8). Furthermore, its flame retardance, as evaluated by limit oxygen index (LOI) tests, improved by 29.5%. This one-pot approach provides an easily up-scalable and efficient approach for enhancing the interfacial strength and the dispersibility of graphene composites and incorporating new functions into polymer nanocomposites by graphene carriers.