Establishment of highly effective flame-retardant unsaturated polyester resin system based on multiple strategies

Considered that unsaturated polyester resin (UPR) as one of the most commonly used thermoset materials often exhibit severe fire hazards, graphene can be used to act as barriers to enhance the flame retardancy of UPR. However, graphene easily shows irreversible aggregation when being introduced into polymer matrix, which limits its further application in industry. In this work, we synthesized a novel organophosphorus oligomer (DHP), which contained double bond and multivalent phosphorus (-1 and +5) with highly effective flame retardancy, onto graphene oxide via in situ atom-transfer radical polymerization (ATRP). Then, the obtained graphene-DHP was incorporated into UPR matrix by curing. The homogeneous dispersion of graphene-DHP in UPR matrix was confirmed by transmission electron microscopy (TEM). The addition of 2.0 wt% graphene-DHP significantly improved the flame retardancy of UPR/graphene-DHP nanocomposites, which was demonstrated by the peak of heat release rate (PHRR) decreased by 41.79%. Moreover, it is found that graphene-DHP in nanocomposites cannot only act as barriers, but also catalyze the char formation in condensed phase as well as capture free radicals in gaseous phase. This work provides a feasible approach to combine graphene and phosphorus-containing flame retardant and would also trigger more scientific interest in exploiting new type nanocomposites for flame retardants.