Model Compound Vulcanization—Part V. The Effect of Chemical Additives and Fillers

Abstract

Abstract The effect of chemical additives and fillers on the yield and distribution of sulfidic products in model compound vulcanization (MCV) reactions was studied. Several controversial issues were resolved, and a better understanding of the effect of chemical additives on the physical properties of natural rubber vulcanizates has resulted. Additives considered as radical scavengers can increase or decrease the yield of products which correspond to crosslinks. The effect of peroxide depends on the type of accelerator; it is significant with thiuram disulfide acceleration, but negligible with sulfenamide acceleration. The product distribution from an organic dialkyl tetra-sulfide as a sulfur donor is shown. An inorganic disulfide, such as molybdenum disulfide, does not take part in the sulfur vulcanization. An analysis of the effect of fillers on the yield and distribution of those sulfidic products which correspond to crosslinks, and on the sulfidic byproducts was carried out. A similar detailed analysis cannot be achieved in vulcanizates. It was shown that the yield and distribution are significantly affected by inorganic and mineral fillers. MCV was applied to the analysis of the effect of silane coupling agents. Their beneficial effect on the yield and distribution of sulfidic products was shown. The yield of sulfidic byproducts is highest with fumed silica. An equivalent state of cure in filler-containing model vulcanizates should be established by accelerator activator and sulfur variations prior to the evaluation of fillers in the vulcanizates. This would enable a more direct evaluation of fillers, since their chemical and physical effects on the vulcanizate properties would be separable.