Thermal Conductivity and Thermal Diffusivity of Molten Polymers

In order to determine the thermal conductivity of molten polymers with greater accuracy, we improved the measurement device proposed in our previous paper. The accuracy of measurement of the improved device was within ±2.5∼3%. This improvied device was used to investigate experimentally the effects of molecular structure and polymer temperature dependence on the thermal conductivity of liquid crystalline polymers (LCP), and general-purpose polymers (GPP). The results showed that both of the thermal conductivity of LCP and GPP increased with raising of polymer temperature, while the thermal conductivity of LCP is 1.2∼1.7 times larger than that of GPP. The measured results also showed that thermal conductivity of LCP excepting LCP-XD 138 is influenced by the molecular structure. Namely, the thermal conductivity of III type-LCP which has flexible structure is 40% larger than that of the I type-LCP which has rigid structure. Furthermore, using a relation between the thermal conductivity and the thermal diffusivity a (=v·λ/C_p, where v: specific volume, λ: thermal conductivity, C_p: specific heat), the temperature dependence of the thermal diffusivity of the GPP was examined and the thermal properties which dominate the behavior of those thermal diffusivity were discussed. The thermal diffusivity shows various behavior in accordance with raising of temperature. The temperature dependence of the thermal diffusivity is dominated by that of thermal conductivity in PC, PMMA and PA-6, by that of specific heat in PP, respectively. For all of these GPPs, the density change due to polymer temperature has little effect on the thermal diffusivity.