High Dk and ultra-high thermal conductivity ST/μBN/polyolefin composites for microwave applications

Abstract In this work, we examined the structure, microwave dielectric, thermal and mechanical characteristics of composites containing SrTiO 3 /xμBN/polyolefin (with x at 0, 6, 8, 10 and 12 weight percent). SrTiO 3 (ST) and micro boron nitride (μBN) powders were fabricated with 1,2-PB/EPDM/SBS (1,2-PB, EPDM and SBS are abbreviations of 1,2-polybutadienes, ethylene-propylene-dicyclopentadiene and styrene-butadiene-styrene triblock copolymer, respectively) by hot-press process after modified by Vinyltrimethoxysilane (VTMS) and 3-aminopropyltriethoxysilane (KH550), respectively. The ball mill and surface modification procedure enhanced the dispersion of the boron nitride in the solution and promoted compatibility between ceramic particles and polyolefin matrix. The incorporation of BN created more effective boron transfer pathways with ST particles, significantly improving the thermal conductivity of the composite. However, as μBN content increased, more ceramic agglomerates and pores were introduced, deteriorating dielectric, thermal and mechanical properties of the samples. The particle size test and XPS were conducted to determine the effect of surface modification on the dispersion and surface properties of ceramics. Cross-plane thermal conductivity, TGA and stress-strain curves were used to evaluate the thermal and mechanical properties of the composites. In all, a composite with high-D k and high thermal conductivity was obtained when x = 10 wt.%: D k = 17.4, D f = 0.0071 and λ = 1.784 W/(m*k), which is promising for microwave applications.