Abstract

The enhanced crystallizability of guayule rubber (GR) in comparison to Hevea-based natural rubbers (NR) gives rise to better failure properties in unfilled, or “gum,” GR. The origin of this behavior is the ability of the non-polymeric contaminants in GR to nucleate strain crystallization; a similar effect is operative in less pure grades of NR. However, when compounded with carbon black, this superiority of GR over NR is lost. The mechanical hysteresis arising from the carbon black, along with the latter's enhancement of strain crystallization, supercede the contribution from the contaminants. Consequently, in contrast to the behavior of the gum rubbers, the fatigue lifetimes of GR- and NR-based compounds are equivalent.