Investigation of phase change conducting materials prepared from polyethylenes, paraffin waxes and copper

[摘要] English: Phase change materials based on polyethylene (LDPE, LLDPE and HDPE) and copper (micro and nano) blended with soft paraffin wax were studied in this work. The purpose of this study was to form composites that can store energy as well as conduct heat. The influence of wax content, as well as copper content and copper particle size, on the morphology and thermal, mechanical and conductivity properties was investigated. The scanning electron microscopy results show that both the Cu micro-and nano-particles were well dispersed in the matrix. The nano-particles, did, however, also form agglomerates. The results also show that the Cu micro-particles have a greater affinity for the wax than for the polyethylenes, giving rise to preferable crystallization of the wax around the Cu particles. The differential scanning calorimetry results show that the Cu micro- and nano-particles influence the crystallization behaviour of the polyethylenes in different ways. The extent to which the copper particles influence the crystallization behaviour of the polyethylenes also depends on the respective morphologies of the different polyethylenes. All the polyethylene/wax blends are immiscible or only partially miscible at wax contents of 30, 40 and 50%. The presence of wax in the polyethylene/wax blends reduces the melting temperatures of all three polyethylenes, indicating the plasticizing effect of the molten wax in the polyethylene matrix. The thermogravimetric analysis results show observable influence of both the presence of copper and the sizes of the copper particles, as well as the presence and amount of wax, on the thermal stabilities of the blends and composites. The thermal conductivities of the composites show a non-linear increase with an increase in Cu particle content. The presence of wax slightly decreases these values, confirming the preferable crystallization of wax around the Cu particles. The thermal conductivities of the Cu nano-particle containing composites, at the same copper contents, are almost the same as those of the micro-particle containing composites. Young's moduli increased with an increase in copper content in both the polyethylene composites and the polyethylene/wax blend composites, except in the case of HDPE where a decrease was observed. The dynamic mechanical analysis storage moduli determined through dynamic mechanical analysis show the same trends as the Young's moduli. The tensile strengths show variable behaviour, but mostly these values decrease with increasing Cu and wax contents. The energy storage results show that the heat transport is faster in the case of the blend composites compared to the polyethylene/wax blends, and the heat transport in the polyethylene/wax blends is also faster than in the neat polyethylene

[发布机构] University of the Free State