Thermal analysis of the sulfur vulcanization

It is known that rubber mixes containing vegetable oils and vulcanized vegetable oils give better flow properties, plasticizing action, low temperature flexibility and ozone resistance. Now, in this investigation, the aim was to provide additional information about the effect of two vegetable oils (linseed oil and peanut oil) upon accelerated sulfur vulcanization system using thermal analysis-differential scanning calorimetry (DSC) and thermogravimetry. Several combinations of curatives (ZnO, sulfur and 2-t-butylbenzothiazole sulfenamide or TBBS) with stearic acid or vegetable oils were investigated, and DSC curves showed that vulcanization systems where linseed oil or peanut oil replaced stearic acid as activator proceeded an outline of basic steps similar to conventional mixture. However, the formation of the complex between Zn.sup.2+, sulfur and products of TBBS decomposition, main step in the vulcanization reaction, required much more energy. Exothermic [DELTA]H values of 45.4 and 20.3 J g.sup.-1 were found for ZnO/S/TBBS/linseed oil and ZnO/S/TBBS/peanut oil, respectively, against only 5.8 J g.sup.-1 in the case of ZnO/S/TBBS/stearic acid mixture.