Change of Volume of Rubber on Stretching: Effects of Time, Elongation, and Temperature

Abstract

Abstract 1. Two dilatometers have been described which are suitable for measuring the change of volume of rubber on stretching. 2. The volume of pure gum rubber remains constant up to a critical elongation, above which it decreases. Coarse fillers and other inhomogeneities tend to increase the volume because of the formation of vacuoles on stretching. Carbon-black compounds, however, decrease in volume above a critical elongation, which is lower than for pure gum. 3. The decrease in volume of rubber on stretching is greater the higher the elongation, the lower the temperature, or the longer the time the rubber is kept stretched. 4. After the first few minutes the volume of stretched rubber decreases at an approximately uniform rate with the logarithm of the time. No final or equilibrium state was attained in periods up to 3 or 4 weeks. 5. Stretched rubber shows a greater coefficient of expansion than unstretched rubber. 6. Poisson's ratio for rubber in the absence of coarse fillers is 0.5 or greater, the numerical value being a function of the composition, the elongation, the temperature, and the time after stretching.