Simultaneous improvement in thermal conductivity and flame retardancy of epoxy resin via constructing 3D BNNS skeleton with assistance of ammonium polyphosphate

Three-dimensional (3D) boron nitride skeleton has a promising prospect in improving the thermal conductivity and flame retardancy of polymer composites, yet the problems of interface thermal resistance and combustion collapse in the skeleton caused by organic adhesives still need to be solved. In this work, macromolecular flame retardancy, ammonium polyphosphate (APP) with high polymerization degree, was firstly used to modify and assemble boron nitride nanosheets (BNNS) into 3D thermally conductive skeleton, in which APP with rich amino groups can result in the strong grafting modification to reduce the interfacial thermal resistance in BNNS skeleton, meanwhile, the catalytic carbonization of APP can reinforce the 3D skeleton barrier without collapse during combustion. Typically, one-step wet ball-milling with assisted APP was used to exfoliate and modify BNNS, followed by unidirectional freezing to achieve 3D BNNS@APP skeleton with highly oriented structure. As expected, the constructing 3D skeleton with low interfacial thermal resistance can effectively form a heat transfer path in polymer matrix. The obtained epoxy-based composite showed a high thermal conductivity of 3.28 W/mK at 9.28 vol% BNNS@APP. Meanwhile, the producing 3D skeleton barrier during combustion induced the significant improvement in flame retardancy, with heat release rate (HRR) and total heat release (THR) decreasing by 68.3% and 52.7%, respectively. This work provides a new adhesive choice in constructing 3D thermal conductive and flame retardant skeleton, which exhibits high potential in thermal management application.