Abstract

In high-speed Banbury mixing, sufficiently high temperatures may be generated at least to partially damage some rubber accelerators and decrease their effective activity. Thus, at a processing temperature of 360° F, the following stability relationships hold. 1. Thiazoles, thiazole derivatives, and activated thiazoles show little loss of activity. 2. Thiurams and dithiocarbamates may be severely affected. 3. Guanidines, as represented by diphenylguanidine, are only moderately affected. 4. Aldehydeamines range in stability from moderate to good. This effect of high temperature on accelerator stability may be considered as constituting a processing hazard. The proper selection of accelerators and the careful consideration of any processing changes which may significantly increase temperature minimize the danger and allow avoidance of harmful results. The fact that some accelerators are relatively unstable at high temperatures does not preclude their use. It is simply necessary to incorporate these materials into the mix at a sufficiently low temperature, such as that at which it is normally considered safe to add sulfur.