With the emerging concerns on the use of nitrosamine evolving accelerators, safer alternatives are desirable for the rubber industry. In the present study, cure characteristics, physicomechanical properties, crosslink density, aging, dynamic mechanical, and thermal properties of vulcanizates prepared with two nitrosamine safe binary accelerator systems containing diisopropyl xanthogen polysulfide (DIXP) and tetrabenzyl thiuram disulfide (TBzTD), and DIXP and dibenzyl dithiocarbamate (ZBeC) were investigated for efficient sulfur vulcanization of natural rubber (NR) compounds. Synergistic effect in both cure and physicomechanical properties was observed for all the combinations of the two accelerator systems. The composition containing DIXP with a lower loading (0.6 phr) of TBzTD, and ZBeC, demonstrated the highest technological performance. Retention of tensile properties on oxidative aging was highest for the vulcanizate prepared with DIXP/TBzTD (1.4/0.6). Dynamic mechanical and thermogravimetric analysis further confirmed the crosslink density and thermal stability of the network structure of the binary systems. In overall, DIXP shows the potential to be used as a safer accelerator in the manufacture of appropriate dry NR-based rubber products.
An outstanding interest on elimination of nitrosamine generation in traditional sulfur vulcanization systems has led to introduce nitrosamine safe accelerator/s to produce safe natural rubber (NR) vulcanizates. It is an effective way to prevent formation of carcinogenic N-nitroso compounds during manufacture of rubber products. In the present study, behavior of nitrosamine safe binary accelerator system consisting of diisopropyl xanthogen polysulfide (DIXP) with commonly used non-regulated accelerator N-tert-butyl-2-benzothiazole sulfenamide (TBBS) was investigated in efficient sulfur vulcanization of NR. Cure characteristics, physico-mechanical properties and crosslink density of vulcanizates prepared with different combinations of the accelerator system were evaluated and compared with those of individual accelerators. The study reveals that moduli and strength properties of the vulcanizate prepared with DIXP accelerator are inferior to those of the vulcanizate prepared with TBBS accelerator. Nevertheless, optimum cure time of the DIXP compounds is lower in comparison to TBBS compounds. Moreover, progressive replacement of DIXP with TBBS in the accelerator system showed a synergistic effect in regard to cure characteristics and physico-mechanical properties.
An attempt was made to replace conventional ZnO with nanoZnO in low ammonia, tetramethylthiuramdisulphide (TMTD)/Zinc oxide (ZnO) natural rubber latex preservative system (LATZ). Different percentages of TMTD and nanoZnO dispersions containing equal portions were prepared and used to preserve the latex. Centrifuged natural rubber latex (CNRL) thus prepared were tested for VFA (volatile fatty acid) number and MST (mechanical stability time) periodically over a period of 75 days. Mechanical properties of vulcanized latex thin films made out of CNRL preserved were measured. Development of VFA number in CNRL samples preserved with nanoZnO was lower than the sample prepared with the conventional ZnO (control). Both the VFA number results and surface plots of the matured CNRL samples showed that preservative action of the modified preservative system was mainly governed by the amount of nanoZnO in the system. MST values of CNRL preserved with nanoZnO substituted systems were significantly high when compared to the control. Tensile and tear properties of the vulcanized films prepared using CNRL preserved with nanoZnO were almost comparable with those of the vulcanized films prepared using control system. The statistical analysis indicated that CNRL preserved with modified preservative system of 10% and 15% of TMTD/nanoZnO could be stored up to 55 and 75 days respectively, without exceeding VFA value above 0.02.
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