Thermal Properties of Thin-Film Polymers by Transient Heating

Abstract

The high‐temperature thermal properties of building material in thick slab form can be measured by a transient method reported earlier by Harmathy. The results here show the technique suitable for thin‐film polymers. Recently available ultrathin (0.00025 cm) constantan foil is shown capable of providing constant thermal flux. This foil reduces the original measurement time by two orders of magnitude, from 400 to 4 sec. Sample volume can be reduced at least 90%. Thermal diffusivity,thermal conductivity, and specific heat are measured on an absolute basis, with errors of 2%, 2.5%, and 3%, respectively. Results are given for polyethylene terephthalate, low‐density polyethylene, and cork composition, all in the range −50° to 30°C. These results support the accuracy and validity of the technique. The experimental sample can be built up from polymer films as thin as 0.0025 cm. Previously the sample consisted of slabs of approximate thicknesses 1 and 3 cm.