ABSTRACT
Although almost all rubber compounds have activators, retarders are used sparingly. Activators have been described as substances that increase the effects of accelerators. Retarders are ingredients added to a stock to prevent its premature vulcanization under processing conditions. By far the most popular activator system is zinc oxide and stearic acid. The mechanism by which this pair speeds up the cure has not been exhaustively studied, and results to date indicate its complexity. Cure retardation by retarders is easily determined using such rheometers, and the cure index of the stock with and without retarders can be found, as well. A common feature of activators is that they are alkaline and besides zinc oxide include litharge, magnesia, and arnines. The choice of a retarder is determined by considering the rubber used, the accelerator system, the processing temperatures, and the amount of processing involved.
