Preparation And Properties Of Thermally Conductive Boron Nitride/epoxy Composites

Thermally conductive polymeric composites, kind of highly promising functional materials, are progressively utilized in microelectronics, aerospace, electronic information, electric insulation and other fields. Epoxy resin has been widely applied as the preferred matrix material due to its good electrical insulation, thermal stability, superior adhesion, good mechanical properties, ease of processing and low cost, etc. Boron nitride(BN) has many unique advantages such as prominent electrical insulation, excellent thermal conductivity and chemical stability, ultralow dielectric constant and thermal expansion coefficient. These properties make BN a promising candidate for preparing composites with enhanced thermal conductivity. In this study, a series of highly thermally conductive epoxy composites were fabricated from surface functionalized BN particles uniformly embedded in the matrix with an effective BN-epoxy interface interaction. The effects of surface modification and loading level of BN particles on the properties of the composites were investigated.To enhance wettability and improve chemical activity of surface groups, the BN particles were initially oxidized in strong acid solutions to yield the sufficient hydroxyl groups on BN edge, and then hydroxylated BN surface was grafted with 3-aminopropyl triethoxysilane(APTES). The modified BN(APBN) was used to fabricate thermally conductive EP/APBN composites by solution blending and casting method. The APBN particles exhibited desirable homogeneity and dispersion in epoxy matrix with an enhanced interfacial compatibility that evidenced by SEM observation. The thermal conductivity of the composites increased with the addition of filler content, and the growth rate was accelerated. The thermal conductivity was 1.178W/m·K with loading of 30wt% APBN particles, which was 6.14 times higher than that of pure epoxy resin, whereas a lower value of 1.037W/m·K could be obtained by adding the same content of raw BN particles. In addition, the fabricated EP/APBN composites exhibited improved thermal stability, storage modulus, and glass transition temperature with increased APBN content, but the tensile strength showed a decrease trend. The composites also possessed excellent electrical insulation properties. These results revealed that EP/APBN composites are promising as efficient heat-releasing materials for thermal management and microelectronic encapsulation.Based on the template induced self-assembly feature of cyclomatrix polyphosphazene micro/nano materials, novel poly(cyclotriphosphazene-co-bisphenol A)-coated BN(HBBN) were designed and synthesized by in-situ polycondensation on the surface of BN particles with the reaction of hexachlorocyclotriphospazene(HCCP) and bisphenol A(BPA) as co-monomers. It was found that incorporation of HBBN particles in the epoxy matrix significantly enhanced the thermal conductivity of the composites. With 20wt% HBBN loading, the thermal conductivity of the composites was 0.708W/m·K. Meanwhile, the EP/HBBN composites possessed good electrical insulation and thermal stability simultaneously. The fabricated composites also exhibited improved flame retardancy and superior dimensional stablility during combustion.