Vulcanization. Part II. Fate of Curing System during Sulfur Curing of Nr Accelerated by MBT Derivatives and Activated by Zinc Stearate

Abstract

As discussed in Part I it was generally believed that during the sulfur vulcanization of rubber, important vulcanization intermediates are formed as a result of reactions between components of the various curing systems, e.g., sulfur, accelerator, zinc oxide and elastomer. A variety of reaction products have been postulated, however, actual supporting evidence for most of these postulations is limited. This is not surprising considering that the complexity of the system makes the identification and quantitative determination of these intermediates by conventional analytical techniques difficult. Part I of this paper described some analytical methods and the application of procedures for determining the fate of the curing system throughout the vulcanization of natural rubber in the presence of sulfur and various benzothiazole type accelerators. This study confirmed that important vulcanization intermediates are formed during the vulcanization process and that they play decisive roles in delay action acceleration. However, in most practical cases zinc oxide and stearate are also required to obtain satisfactory vulcanization and curing characteristics. It was therefore desirable to extend the studies to curing systems which include zinc and stearate ion.