SULFUR VULCANIZATION OF NATURAL-RUBBER ACCELERATED WITH 2-MERCAPTOBENZOTHIAZOLE PLUS TETRAMETHYLTHIURAM DISULFIDE

The sulfur vulcanization of NR by a MBT‐TMTD mixed accelerator system both in the presence and absence of ZnO and stearic acid with or without DCP has been studied. The rate of decomposition of DCP in the presence of both MBT and TMTD is quite similar to that in the MBT system alone. The reduction in crosslinking due to DCP is dependent mainly on MBT. The decomposition product of TMTD may contribute to it only at the later stage of vulcanization. Though TMTD has no influence on the decomposition rate, it reacts with MBT at least in the initial stage of vulcanization and suppresses the retardation caused by MBT on DCP vulcanization in accordance with the free sulfur decrease, the nature of crosslinking formation both in the presence and absence of DCP, and the methyl iodide treatment of the vulcanizates. The vulcanization process of the MBT‐TMTD‐S‐NR system has been interpreted in terms of both free radical and polar mechanisms. The domination of either of these depends on the dominant amount of either MBT or TMTD in the acclerator ratio. According to the initial high rate of crosslink formation, free sulfur decrease and also the initial additiveness of crosslinking in stocks containing DCP, the vulcanization process of MBT‐TMTD‐ZnO‐St. acid‐S‐NR system has been explained in terms of an ionic mechanism. The pronounced synergistic nature of such systems has been interpreted by the enhanced activation of MBT‐S‐ZnO‐St. acid complex due to the dithiodicarbamate ion formed in the initial stages of vulcanization, and also by the activation of TMTD accelerated vulcanization due to the mercaptobenzothiazylion. Copyright © 1979 John Wiley & Sons, Inc.