The thermal diffusivity of polymer melts

Abstract

Abstract A study of the thermal diffusivity of polymer melts as a function of temperature over the range 25–325°C. is described. Measurements were carried out with an apparatus especially designed and constructed for this purpose; this apparatus and the theoretical treatment of data obtained with it are treated in detail. The polymers examined include polystyrene, poly(methyl methacrylate), some of their copolymers, poly(vinyl chloride), linear polyethylene, polyacetal, polycarbonate, cellulose–acetate–butyrate, some “highimpact” polymer blends and terpolymers, and some higher methacrylates. The thermal diffusivities of the melts vary from about 11 × 10 −4 cm. 2 /sec. (for linear polyethylene) to about 5 × 10 −4 cm. 2 /sec. (for poly( sec ‐butyl methacrylate)). In general the thermal conductivity of an amorphous polymer decreases as it passes from the glassy state to a melt, but remains quite constant over a wide temperature range in the melt state. On the basis of a limited amount of data one might tentatively conclude that the thermal diffusivities of the melts of vinyl polymers become lower as larger as longer groups are added to the carbon‐carbon backbone. As regards molecular weights equal to those common for molding powders, molecular weight seems to have no effect on the thermal diffusivity.