| Summary: | This dissertation describes preliminary work carried out in a general study of the thermal properties of polymeric material, the measurements described being those of the effect of density on the temperature behaviour of the thermal conductivity of polyethylene. Specimens of different densities have been employed to carry out measurements in the temperature range from 80 K to 370 K using two different methods in order to be able to cover this whole range. Due to particular difficulties in dealing with undesired heat transfer, this range of temperature is a difficult one in which to carry out measurements. As a necessary preliminary, a description of the morphology and properties of polymers and also of the fundamental processes that govern the thermal conductivity of non-metallic materials and polymers is presented. A critical review is made of previous experimental investigations of the variation of thermal conductivity with temperature and specimen density. The review consists of two parts. The first part deals with methods which have been employed to measure the thermal conductivity of polymers, and the second part with results obtained for the thermal conductivity of polyethylene in particular. The agreement between these results is good, in general, being best at the higher temperatures (room temperature to 370 K). The present results for the temperature dependence of thermal conductivity of polyethylene are in general agreement with those of previous workers, a better agreement being obtained with the theoretical results of Eiermann (1961-1965). Furthermore, the present results show clearly the dependence of thermal conductivity on specimen density indicated in previous work. Suggestions for the best means of carrying out further measurements are discussed.
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