Vulcanization of Guayule Rubber

Abstract

Abstract The vulcanization characteristics of natural guayule rubber (GR) were compared to those of natural hevea rubber (HR). In the case of purified rubbers, vulcanization and tensile properties were shown to be very similar, whereas in the unpurified raw rubbers, HR was faster in vulcanization and attained a higher modulus than GR. These differences between raw rubbers were most pronounced in conventional vulcanization systems using MBT as the sole accelerator. As a result of a variety of different types of measurements on raw and purified rubbers, (relaxed tensile stress [MOD], Monsanto Rheometer curves, degree of crosslinking measurements, and kinetic analysis) it was concluded that the differences between HR and GR were due to the natural occurrence in HR (and absence in GR) of a vulcanization activator of a type similar to a basic secondary accelerator. Finally, in any formulation, the addition of very small quantities of activator or basic secondary accelerator is recommended in GR in order to attain similar properties to those of HR.