Enhancing thermal conductivity of wood-plastic composite

Abstract

Recently new kind of material has entered the market – thermally conductive plastics. These are mostly used in heat management of electronics as heat sinks and covers. They are a more economic and simpler alternative to traditionally used copper and aluminium. At the same time market for wood-plastic composites starts to saturate, prompting search for new applications beyond traditional uses as car interior panels and alternative to pressure-treated wood in outdoor applications. In this thesis, literature about thermally conductive filler - polymer composites were reviewed in detail. The review includes effects of filler material, size, shape and distribution on thermal conductivity, as well as basic physical review about the matter. The effect of wood flour on polypropylene filled with thermally conductive fillers was investi-gated. Tested fillers were irregular copper particles, boron nitride flakes, and a mixture of boron nitride flakes and zinc oxide particles. These fillers were tested with and without wood flour added to the compound. The aim of research was to broaden applications of wood-plastics. Thermal conductivity, mechanical properties, differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and visual light microscopy and scanning electron microscopy were used to study samples manufactured by injection moulding. From tested thermally conductive fillers, boron nitride – zinc oxide system was most effective at increasing thermal conductivity with all volume loadings. This can be attributed to high aspect ratio, larger size of filler and large size difference between components. Addition of wood flour increased thermal conductivity of most filled compounds significantly, in both through- and in-plane directions. Part of improvement is due to wood flour replacing polypropylene, but wood flour also improved mixing and alignment of fillers.