Rabindra Nath Datta

Cure Modification Effected by Cycloalkylthioamines in the Vulcanization of NR Accelerated by Thiocarbamyl Sulfenamides and Dibenzothiazyl Disulfide

Abstract The role of the thioamines as retardera in the vulcanization of NR accelerated by the binary system comprising thiocarbamyl sulfenamide and MBTS has been investigated. Several thioamines, namely, cyclohexyl thiomorpholine (CM), cyclohexyl thiopiperidine (CP), cyclohexyl thiodibutylamine (CDBA), cyclohexyl thiodiphenylamine (CDPA), cyclohexyl thiodiisopropyl amine (CDIPA), dicyclohexyl dithiopiperazine (DCDPz), cyclohexyl thiodiethylamine (CDEA), and cyclohexyl thiodibenzopyrrole (CDBP) had been selected for the study. It has been observed that these thioamines provide better cure retardation than CTP and almost in all the cases, cure rates and torque values of the resulting vulcanizates are increased. It is further noticed that the vulcanizates obtained from the stocks containing CDEA, CDBP, and CDPA exhibit notably more heat and age resistance than those obtained from CTP. Some hplc studies were made to understand cure activation. MBT and N-oxydiethylenethiocarbamyl benzothiazole disulfide (OTBD...

Effect of Zinc Dithiocarbamates on NR Vulcanization Accelerated by Thiocarbamyl Sulfenamides and Dibenzothiazyl Disulfide

Abstract The hplc studies with all their limitations have been employed to obtain information regarding the vulcanization of rubber accelerated by CTOS and MBTS in the early part of the reaction. It is noticed that even in the initial part of the induction period (the scorch safety, t2, of the recipe is 10.5 min), CTOS and MBTS react so rapidly with each other and also with rubber that at the end of 10 min we could detect only MBT, while the concentration of the other components formed in the reaction—namely, CTOS, OBTS, CPTD, BPTD, PMTU, CPTM, BPTM, etc.—decreased to an extremely low level. We noticed that under the experimental conditions, OBTS and CPTU have the same retention time. This naturally obscures the path for understanding the individual effect of these accelerators. The sharp disappearance of OBTS, associated with the abundant formation of MBT and nonavailability of CPTU (from CPTD, Figure 11b), gives testimony to the fact that the unsymmetrical thiourea (PMTU) rather than the symmetrical one...

Effect of cyclohexyl thiophthalimide on NR vulcanization accelerated by thiocarbamyl sulfenamide-dibenzothiazyl disulfide system

Abstract Investigations have been carried out on the effect of CTP on thiocarbamyl sulfenamides, either alone or in combination with MBTS, in the vulcanization of NR. It has been observed that CM, CP, CPTCD, OTCD, and CDB formed from various thiocarbamyl sulfenamides like OTOS, OTCS, and CTOS in the presence of CTP play a vital role in cure retardation. CM and CDB under the experimental conditions have been found to prolong the onset of cure, while CP, CPTCD, and OTCD reduce scorch time. The presence of a substituent on the carbamate N-atom of thiocarbamyl sulfenamides greatly influences cure retardation. OTOS and CTOS give rise to CM and CP respectively in the presence of CTP. OTCS, however, generates both CM and CP under the identical conditions and thus differs from OTOS and CTOS. CPTCD and OTCD formed from thiuramdisulfides have been shown to be poor and scorchy accelerators, and these, like CM and CP, play a significant role in cure retardation.

Thermal and age-resistance properties of NR gum vulcanizates in EV systems

Abstract A comparative study of the cure behavior of thiocarbamyl sulfenamides both in the presence of MBTS and thiazole sulfenamides has been made at 140 and 170°C. It is observed that most of the NR vulcanizates obtained at 170°C are capable of retaining a considerable portion of torque, modulus, and tensile values obtained at 140°C. This provides information regarding the heat resistance of these vulcanizates. It is observed that ZDCs up to a certain concentration increases the thermal resistance of the NR vulcanizates, the maximum effect being produced by ZBD and ZPD. ZOD and ZPD above a critical concentration, impart a deleterious effect to NR gum vulcanizates where a drop in the R∞ value is observed. The age resistance property of the various combinations of thiocarbamyl sulfenamides plus MBTS and thiazole sulfenamides plus thiocarbamyl sulfenamides has been discussed. It is evident from the study that the former combination generally provides higher physical properties of the vulcanizates and bett...

Studies on Cure Synergism—Part I: Effect of Bis(Diisopropyl) Thiophosphoryl Disulfide and Thiazole-Based Accelerators in the Vulcanization of NR

Abstract The effect of the synergistic combinations containing diisopropyl thiophosphoryl disulfide (DIPDIS) and a thiazole type of accelerator on the vulcanization of NR has been investigated. MBT, N-oxydiethylene-2-benzothiazole sulfenamide (OBTS), and N-oxydiethylene-2-benzothiazole disulfide (OBDS) represent the thiazole-based accelerators. It has been established from the hplc study that diisopropylthiophosphoryl benzothiazole disulfide (DIBDS) is formed in the synergistic systems along with other rubber additives during the early part of cure. In this exploratory study, it has been observed that DIBDS enhances the torque, modulus, crosslink density, and the tensile strength of the vulcanizates. Chemical characterization of the fine network structure of the NR vulcanizates indicates that synergistic combinations produce about 80% of the monosulfidic linkages. The resultant vulcanizates thus become stable to oxidative aging at 100°C for a considerable length of time. The vulcanizates obtained with DIB...

Cure modification effected by 2-iminothiophthalimides in the vulcanization of NR accelerated by thiocarbamyl sulfenamides and dibenzothiazyl disulfide

Abstract Studies have been made on the effect of N-oxydiethylene thiophthalimide (ODTP) and N-cyclopentamethylene thiophthalimide (CPTP) as retarders in the vulcanization of NR. N-oxydiethylenethiocarbmyl-N′-cyclopentamethylene sulfenamide (OTCS) and N-oxydiethylene thiocarbamyl-N′-oxydiethylene sulfenamide (OTOS) have been used separately with MBTS to form the binary systems of accelerators. Retardation exhibited by the combinations OTCS-MBTS-ODTP and OTOS-MBTS-CPTP is noteworthy. In these systems, both CBDS and OBDS are formed. The enhanced activity with regard to torque, scorch, modulus, tensile strength, etc. is believed to be due to the presence of CBDS and OBDS. Probable reactions for the formation of various compounds responsible for acceleration and retardation of vulcanization of NR have been explored. It has been observed that ODTP and CPTP provide better cure-retardation than CTP and in almost all the cases, the cure rate and torque values of the resulting vulcanizates are increased. In the cas...

Studies on Cure Synergism. II, Effect of Diisopropyl Thiophosphoryl-N-Oxydiethylene Sulfenamide and Dibenzothiazyl Disulfide in the Vulcanization of NR

Abstract Thiazole sulfenamides as well as thiocarbamyl sulfenamides in the presence of dibenzothiazyl disulfide (MBTS) form synergistic combinations of rubber accelerators that provide technologically important rubber vulcanizates. The present investigation explores the feasibility of using thiophosphoryl sulfenamide with MBTS as a binary system of mutually activated accelerators in the vulcanization of rubber. The cure characteristics of the NR compound containing various proportions of diisopropyl thiophosphoryl-N-oxydiethylene sulfenamide (DIPTOS) and MBTS have been investigated keeping the total concentrations of the accelerators at 6 mmol per 100 rubber. The results indicated mutual activity of the mixed accelerators and significant enhancement of torque, modulus, and tensile strength of the resulting vulcanizates. The general character of the reaction of thiophosphoryl sulfenamide and MBTS has been established by replacing DIPTOS by diisopropylthiophosphoryl-N-cyclopentamethylene sulfenamide (DIPTCS...

Dual Activity of Some Modified Thiocarbamyl Sulfenamides in the Vulcanization of NR Accelerated by Dibenzothiazyl Disulfide

Abstract The retarding and the accelerating activities of some modified thiocarbamyl sulfenamides—namely, N-cyclopentamethylene thiocarbamyl-N′-(cyclohexyl, thiocyclohexyl) sulfenamide (CPCTS), N-cyclopenta-methylenethiocarbamyl-N′-(cyclohexyl, N-cyclopentamethylene thio) sulfenamide (CPCCS), and N-cyclopentamethylenethiocarbamyl-N′-(cyclohexyl, N-oxydiethylene thio) sulfenamide (CPCOS)—have been studied in dibenzothiazyl disulfide (MBTS)-accelerated vulcanization of natural rubber (NR). It is found that CPCTS, CPCOS, and CPCCS delay the onset of cure and generate active accelerators during vulcanization. In addition to this, the accelerator systems are quite capable of producing age-resistant vulcanizates. The results indicate that thiocarbamyl sulfenamides modified chemically at the >NH functionality retain their accelerating property. Thus CPCTS, CPCOS, and CPCCS play the dual role of an accelerator and a retarder in the vulcanization of NR accelerated by MBTS.