Tetramethylthiuram Disulfide Vulcanization of Extracted Rubber. V. Low Molecular Products and the Mechanism of Zinc Oxide Activation

Abstract

Abstract The essential features of TMTD vulcanization, as revealed by compounding tudies, were discussed in Part I of this series. Thus, TMTM, a product of TMTD vulcanization, and an active accelerator of sulfur vulcanization, was found to be an inhibitor, and ZnDMDC, a main product of TMTD vulcanization, in the presence of ZnO was found to be devoid of activating properties. As a replacement of ZnO, which is a potent activator, ZnDMDC displayed only mild activating effects. Zinc palmitate was even more potent than ZnO. Zinc sulfide was somewhat less active than ZnO. Palmitic acid and DMADC had little or no effect on the cure. The second paper reported that TMTD could be prepared in good yield by the reaction of TMTM with sulfur and also, as a result of radiosulfur techniques, that the four sulfur atoms in the TMTD molecule are chemically identical. Part II also reported that ZnO reacted with TMTD to form sulfur and ZnDMDC in good yield. Other reactions of TMTD were discussed. Part III, in presenting a short-path distillation technique for studying vulcanizates, reported that the nearly complete removal of zinc from the TMTD vulcanizate is not accompanied by devulcanization. Part IV reported on the behavior of rubber as an acid. This behavior results in the liberation of palmitic acid from zinc palmitate. From the comparison of the reaction of TMTD with acids and the reaction of rubber with TMTD, it was inferred that rubber is an OH-containing acid. Acids in the work reported were found to react rather slowly with TMTD to form dimethylamides and sulfur in good yield. The acidic nature of rubber did not seem to be great enough to contribute in any fundamental way to the vulcanization process. The present paper describes further studies of the TMTD vulcanization problem.