The Rheology of Raw Rubber

Abstract

A viscometer of the rotating cylinder type is described which is applicable to rheological measurements of raw rubber. To make the instrument operative with such material the surfaces of the cylinders are fluted, to form rough, gripping surfaces; and pressure devices are added which compress and confine the rubber between the cylinders. At low or moderate stresses the rate of shear in hot, raw rubber follows the equation ${\mathrm{\alpha ̇=A\sigma }}^2$ . At higher stresses the rate of shear increases more rapidly with increasing stress. The elastic recovery of hot, raw rubber requires over 5 hours for completion. During most of this time the recovery angle follows the law α=A+B log t. The modulus of rigidity in small deformations of hot, raw rubber is only slightly less than that of soft, cured rubbers at room temperature. The viscosity of a sample of hot, raw rubber in vibration is many times less than the viscosity of the same sample in continuous shear.