EFFECT OF FILLERS IN THE BINARY-SYSTEMS CONTAINING TMTD-AMIDINOTHIOUREA AND MBTS-AMIDINOTHIOUREA IN NR VULCANIZATION

In earlier studies,(1,2) we have shown that in MBTS-amidinothiourea an d TMTD-amidinothiourea binary systems of rubber vulcanization, amidino thiourea functions effectively as a secondary accelerator and improves the accelerator activity of these systems. These secondary accelerato rs enhance the physical properties of the vulcanizates and show better cure characteristics of the mixes compared to the reference systems s tudied. In this paper, we present the results of our study on the effe ct of various fillers in the sulfur vulcanization of natural rubber us ing amidinothiourea as the secondary accelerator. We have taken MBTS-a midinothiourea and TMTD-amidinothiourea binary accelerator systems and vulcanizates were prepared with carbon black, precipitated silica, an d china clay as fillers. Different compositions of amidinothiourea wer e used in various mixes using standard recipes. Reference mixes were a lso studied. Curing characteristics of the mixes and various physical properties of the vulcanizates were evaluated. Optimum dosage of amidi nothiourea required has also been derived. Among the different seconda ry accelerators tried including amidinothiourea, it may be stated gene rally that the more nucleophilic the secondary accelerator, the less t he optimum cure times. This fact points to a nucleophilic reaction mec hanism in the systems under review. In the evaluation of tensile and o ther physical properties of the vulcanizates, some of the systems cont aining amidinothiourea show better properties while others give compar able values with the reference mixes. Estimation of crosslink density also supports the above conclusion. (C) 1996 John Wiley & Sons, Inc.