The influence of stabilizers on mechanochemical processes in SBR rubbers

Mechanochemical processes in commercial and model SBR rubbers containing di fferent stabilizers were investigated. The influence of chemical structure and concentration of stabilizers in the temperature range from 20-170 degre es C and in the presence of air, i.e., under conditions similar to that in industrial processes, were studied. Stabilizers used were diaryl-p-phenylen e-diamine, alkyl-aryl-p-phenylene diamine, polynuclear phenol, aryl-alkyl p henol, and alkyl-alkyl phenol. It was found that mechanochemical processes in SBR rubbers are less developed in the temperature region from 70-130 deg rees C, so the influence of stabilizer is less expressive. During increasin g temperature (130-170 degrees C) structure and concentration of stabilizer s both show a strong influence on type and intensity of mechanochemical pro cesses in SBR rubbers: p-phenylene-diamines favor processes of linear degra dation, while phenol stabilizers direct them toward branching and crosslink ing, which is more expressed in the presence of aryl-substituted phenols th an alkyl-substituted phenols. This fact is based on the differences in stab ility of free stable radicals of p-phenylene-diamines, alkyl-substituted ph enols and aryl-substituted phenols. The fact that phenol stabilizers are in volved in chain degradation as well as in branching and crosslinking proces ses during rubber processing, can be of high practical importance; (C) 1999 John Wiley & Sons, Inc.