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) seem to activate cure, especially in the presence of thioamines. Antioxidants like di-β-napthyl-p-phenylenediamine (DNPD) and N-phenyl-N-sopropyl-p-phenylenediamine (PIPPD), when present in the respective stocks, further enhance both heat and age resistance properties of the resulting vulcanizates.