Controlling thermal conductivity of high density polyethylene filled with modified hexagonal boron nitride (hBN)

Abstract

This study is focused on finding a versatile approach for obtaining low cost, lightweight composites with high thermal conductivity and good mechanical properties at the same time. The most promising application for such material is to replace fabric reinforced laminates in circuit board production. We used high density polyethylene (HDPE) as a polymer matrix and two types of hexagonal boron nitride (hBN) powders with average particle size 2–5 μm and 120–140 nm as a functional filler. To improve both filler-matrix adhesion and mechanical properties of the composites we used one of two techniques: treating the filler with silane coupling agent before composite processing or using titanate coupling agent in the process of roller-mixing. The study showed, that while the best thermal conductivity of 2 W/m K was achieved on the sample prepared without any coupling agent the sample was too brittle for further processing. On the other hand the sample with KR TTS additive and HDPE to hBN ratio 1:1 showed quite high ultimate strength of 24.8 MPa coupled with high Young's modulus, good elongation at break and thermal conductivity of 0.9 W/m K. Usage of hBN nanopowder as a filler resulted in good mechanical properties and high elongation at break values with thermal conductivity values significantly lower than for micro-sized fillers (0.43 W/m K).