Elastic, strength, and viscous properties of polymer (polyethylene and polystyrene) melts

Abstract

AbstractA description is given of a rotational elastoviscometer with a very rigid dynamometer designed for the investigation of the rheological properties of polymer melts and concentrated polymer solutions by the constant deformation rate method. Alkathene‐2 and polystyrene were studied over a wide range of temperatures. The deformation dependences of the shear stress obtained for these polymers became non‐monotonic with rising deformation rates. This was characteristic of the reversible destruction of the polymer structure which increased with growing rates of shear. The maximum on the shear stress vs. deformation curve enabled the ultimate shear strength to be determined as a specific point on this curve. The ultimate shear strengths were reached at a deformations of several hundred per cent, while steady flow conditions were attained at deformations of several thousand per cent. With rising deformation rates, the time for attaining the ultimate strength decreased, as did, to some extent, the time of attainment of steady flow conditions. The deformation corresponding to the ultimate strength increased slightly, and the deformation corresponding to the attainment of steady flow conditions increased greatly with growing deformation rates. The activation energies of steady flow and of the passage through the ultimate strength were close in value. The dependence of the modulus of highly elastic deformation in a polymer of intact structure on the deformation rate is expressed by a function of saturation. The saturation corresponds to the deformation rates at which viscous flow cannot develop without breakdown of the melt structure (without passage through the ultimate strength).