High thermal conductivity and flame-retardant phosphorus-free bismaleimide resin composites based on 3D porous boron nitride framework

High thermal conductivity and high flame retardancy become necessary properties of thermally resistant thermosetting resins for many cutting-edge fields. However, building a phosphorus-free sustainable strategy is still a challenge; besides, sometimes high thermal conductivity and flame retardancy could not be simultaneously achieved, while sometimes they promote to each other, and no report focuses on explicating their relationship and mechanism. Herein, new resins with high thermal conductivity and greatly improved flame retardancy are developed through building phosphorus-free cross-linked network with three-dimensional porous framework based on boron nitride (BN) skeleton (sBN) and bismaleimide resin (BD). With the same loading of BN, sBN/BD has much higher thermal conductivity than the composite based on BN powders (BN/BD). For composites with 12.53 wt% of fillers (sBN or BN powders), the thermal conductivity of 5sBN/BD reaches 1.53 Wm⁻¹ K⁻¹, about 2.4 and 9.4 times of those of 5BN/BD and BD resin, respectively. The exploring relationship between flame retardancy and thermal conductivity shows that sBN/BD composites are somewhat easier to be ignited, and the flame propagation is faster, but under continuous heating, sBN/BD has much weaker burn strength and fewer smoke releasing compared with BN/BD. 5sBN/BD has about 51.9%, 47.5%, 42.5% and 54.8% lower peak heat release rate, total smoke release, specific extinction area and maximum smoke density than BD resin, respectively. The mechanism behind these interesting results is intensively discussed.