Stress Relaxation in Guayule Rubber

Abstract

The modulus E(t) variations were determined for natural Guayule rubber, natural Hevea rubber, and synthetic polyisoprene. This was done with unvulcanized samples, with and without carbon black; and with vulcanized samples, with and without carbon black. Using the time‐temperature superposition principle, the corresponding master curves were obtained. Using the procedure by Tobolsky and Murakami, a generalized Maxwell model was adjusted to each master curve. Finally, using the approximations due to Ferry and Williams and to Alfrey, the storage and loss modulus were obtained for each sample. It is shown that when unvulcanized Guayule rubber behaves very similar to synthetic polyisoprene; but having lower modulus, lower relaxation time, and lower storage modulus than Hevea. Vulcanized Guayule rubber can behave either very similar to Hevea rubber or present lower modulus, lower relaxation time, lower storage modulus, and higher loss modulus than Hevea; depending on the Guayule rubber vulcanizing system.