ABSTRACT Polymers are an electrical insulator with low thermal conductivity. In new applications, such as heat sinks in electronic packaging, new composites with higher thermal conductivity are required. By addition of fillers or even metallic powders to polymers, their thermal behaviour can improve. In fact metal filled polymer composites are widely used for electromagnetic interference shielding. They have a lower density than metals as well as the lower cost. One of the most important fillers with higher thermal conductivity is copper powder. The presence of copper powder in polymer matrix composite affects on thermal properties [1-3]. This study evaluated the effect of presence of copper particles on thermal properties of a kind of commodity plastic. Medium density polyethylene (MDPE) was considered as matrix material. It was supplied by Tabriz Petrochemical complex, Iran. A 99.9% pure copper powder was used as filler. The volume percent of copper in MDPE/Cu composites varied between 0 to 3%. Copper powders and MDPE were first mechanically mixed in different volume ratios, to achieve desired composition, shown in Table I. The composite powders were squeezed between two glass plates, and heated at about 100ºC under pressure for 5 minutes, followed by cooling to room temperature. In order to investigate the thermodynamic properties of pure MDPE and MDPE/Cu composites, heat flow differential scanning calorimetery (DSC60) was used. At first, the temperature calibration of DSC was done by measuring the melting temperature of Indium. The samples, weighted between 2-3 milligrams. The material crimped in an aluminium pan using a simple press. For determination of thermal properties, the s​a​m​p​l​

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