An unsteady state method for the measurement of polymer thermal diffusivity: I. Development of a cell

In this work the development of a cell able to determine the thermal diffusivity of polymers in their fused or solid state, using an unsteady state technique, is presented. In this case a step down perturbation method was used because of its easy experimental setup. For each experimental run a temperature step down perturbation of 10 °C was applied, and the temperature evolution with time and position were registered and saved. Thermal diffusivities were then determined by regression using those data and a simple analytical model. The polymers used to test the cell were high density polyethylene and polypropylene (PP). For the first polymer, the thermal diffusivity was found to be 2.05×10−7 m2/s, which compare satisfactorily with a value of 1.97×10−7 m2/s calculated from reported values of density, heat capacity and heat conductivity. For the PP the value was found to be 7.08×10−7 m2/s with a positive deviation of 5.05% when compared with a computed value of 6.74×10−7 m2/s. Taking into account experimental errors, and the natural variations between different stocks of materials, the observed differences are acceptable.