| Abstract: | The synergistic activity of bis(diisopropyl) thiophosphoryl disulfide (DIPDIS) in the presence of dithio bis(N-β-OH ethyl piperazine) (DTEP), a safe amine-based accelerator, has been studied both in gum and filled stock vulcanization of NR. This study, concerning the effect of variation of sulfur concentration on the gum vulcanization of NR, reveals that, although modulus values of the vulcanizates increase with the level of sulfur, the tensile strength values attain a maximum at 1.5 phr sulfur for an equimolar (4.5:4.5) concentration of DIPDIS and DTEP. The concentration of accelertors was varied from 6 mmol to 18 mmol phr, keeping the molar ratio at 1:1. It was noticed that, although the torque and modulus values increased, the tensile strength values decreased after attaining a maximum at 12 mmolar concentration of DIPDIS and DTEP accelerators, when the sulfur concentration was fixed at 1.5 phr. The synergistic activity of DIPDIS-DTEP accelerated mixes is considered to arise from the generation of some intermediate accelerators that are governed by the proportion of accelerators, sulfur, filler, etc., present in the mix. Some investigations were also carried out to optimize the amount of carbon black at these fixed levels of accelerators and sulfur. A regarding tensile strength, it increased up to a loading of 50 phr carbon black, but beyond this level a gradual fall in the value was noticed. However, modulus, torque, and hardness increased with the concentration of carbon black. The optimum dispersion of carbon black for this system was obtained following Lee's method. © 1995 John Wiley & Sons, Inc. |
