The Effect of Accelerator/Sulphur Ratio on the Cure Time and Torque Maximum of Epoxidized Natural Rubber

Abstract

The cure time of accelerated sulphur vulcanization of Epoxidized Natural Rubber (ENR 25) was studied while one grade of unmodified natural rubber -Standard Malaysian Rubber Light (SMR L) was used as a control. Five accelerators, viz. 2-mercaptobenzothiazole (MBT), tetramethylthiuram disulphide (TMTD), zinc dirnethyldithiocarbamate (ZDMC), N-tert-butyl-2-benzothiazylsulphenamide (TBBS) and diphenylguanidine (DPG) were used in the study and the vulcanization systems used were conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV). Monsanto Moving-Die Rheometer (MDR 2000) was used to determined the cure time in the temperature range of 100-180°C. The results indicate that cure time decreases exponentially with increasing temperature for the two rubbers studied. At a fixed curing temperature, ENR 25 shows shorter cure time compared to that of SMR L. This has been attributed to the activation of the double bond by the adjacent epoxide group in ENR 25. Studies of the effect of varying amounts of M BT at a fixed sulphur concentration show that cure time decreases as the accelerator concentration increases. ENR 25 shows higher torque maximum than SMR L. This observation can be related to the oxiranegroup which is bulky and thus accounts for increased glass transition temperature with increase in the level of epoxidation. Of the vulcanization systems, CV shows the highest torque maximum followed by semi-EV and than EV. This trend can be attributed to the amount of active sulphurating agent which increases with increasing accelerator concentration. It was also found that the influence of accelerator/sulphur ratio becomes less significant as vulcanization temperature increases.

A Self-Healing System Based on Ester Crosslinks for Carbon Black-Filled Rubber Compounds

“…This is attributed to the additional curing substance in the system derived from the EMZ modifier. In addition, the epoxide groups of ENR, the base rubber for the modifier, can boost a sulfur-vulcanization reaction [35]. The rheometer cure torque differences (see Table 1) are in good agreement with the above elucidation regarding more intermolecular interactions taking place in the compounds.…”

Alleviating Molecular-Scale Damages in Silica-Reinforced Natural Rubber Compounds by a Self-Healing Modifier

“…Additionally, the ENRs contained epoxide groups along their chains that could activate the adjacent double bonds to be more reactive toward creating a radical at an allylic position on the rubber chains. Thus, the epoxide group could also increase the vulcanization rate and reduce the scorch and cure times [ 35 ]. The compounds of Set B possessed a higher quantity of EMZ or ENR compared to their counterparts of Set A.…”