Rapid measurement of the thermal diffusivity of flowing polymer melts

Use of polymer materials for precision parts in advanced technology requires precise control of production processes such as melting, casting, and cooling processes. To achieve this, a reliable knowledge of thermophysical properties is essential. In the present study, submillisecond measurement of the thermal diffusivity of a flowing polymer melt was performed. Laminar flow of polymer melt through a narrow gap between two parallel plates creates a shear stress in the flow layer which then results in molecular orientation of polymer molecules. Once this orientation takes place, anisotropy of the thermal diffusivity is expected to occur. The method used in the present study was that of the so-called forced Rayleigh scattering method, a high-speed optical method. Nagasaka and Nagashima have recently improved the method significantly and applied it to the measurements on various difficult materials including molten salts. Measurement of thermal diffusivity anisotropy of molten polystyrene was successfully performed. Dependence of the thermal diffusivity and its anisotropy on shear force in flowing polymer melt was studied.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.