Effect of carboxylic acids on 2-bisbenzothiazole-2,2 '-disulfide- and tetramethylthiuram disulfide-accelerated sulfur vulcanization. III. Reaction between accelerators and zinc salts of the acids

Stearic and benzoic acids were heated with 2-bisbenzothiazole-2,2'-disulfid e (MBTS)/sulfur/ZnO and tetramethylthiuram disulfide (TMTD)/sulfur/ZnO isot hermally at 150 degrees C and in a DSC at 2.5 degrees C/min, in the absence of rubber. The acids readily reacted with ZnO, and at vulcanization temper atures, little or no free acid remains. The zinc salts are less reactive to ward the accelerators and accelerator polysulfides than are the acids, alth ough with benzoic acid/ZnO, MBTS formulations produced small amounts of the accelerator-acid complex 2-benzoylthiobenzothiazole and 2-mercaptobenzothi azole, while with TMTD formulations, limited 2-benzoyldimethyldithiocarbama te formation was detected. These small amounts of the reaction can be attri buted to the incomplete consumption of benzoic acid, zinc benzoate restrict ing the access of benzoic acid to ZnO particles. Although conversion of MBT S and TMTD to accelerator-acid complexes is limited, the zinc salts do prom ote the slow decomposition of MBTS and TMTD above 150 degrees C. It can be concluded that in the presence of ZnO carboxylic acids should not detriment ally effect the vulcanization reaction. (C) 1999 John Wiley & Sons, Inc.