Reactions between Compounding Ingredients during Vulcanization of Rubber

Abstract

Abstract The calculations indicate that reactions (1), (3), and (5) can take place and proceed to virtual completion, whereas reactions (2) and (4) are not possible. They indicate also that the addition of extra sulfur to mixes containing litharge is necessary, and is in accordance with a custom long established empirically. It is evident that oxygen or nascent oxygen is not formed by any of these reactions; therefore no accelerated aging can take place by reactions between sulfur and litharge or zinc oxide. One peculiarity is that, although sulfur will react with litharge according to reaction (1), it appears that no oxygen is evolved by reaction (2), one possible reason being that the formation of lead sulfate takes place with a large decrease in free energy and is therefore readily formed. A possible explanation of the reaction between litharge and sulfur is that reaction (2), a possible first stage in reaction (1), is made to proceed to the right by the readiness with which lead sulfate can be formed. With respect to the reactions of zinc oxide, the assumption that zinc sulfide is formed by the action of hydrogen sulfide appears to be true.