In-situ FTIR investigation of isomerisation of cis-butadiene rubber during the vulcanization

The physical properties of cis-butadiene rubber (BR) have been shown to be critically dependent on its stereoregularity. In this work, the evolution process and influencing factors of cis-trans isomerisation of BR based on the conventional formulation system during its vulcanization process are systematically investigated using in-situ Fourier transform infrared spectroscopy (FTIR) technology. The results show that the isomerisation occurs in the BR compound with sulphur vulcanization system in both non-isothermal and isothermal vulcanization processes because of the polysulfide bonds formed by sulphur in the system, and it is more obvious than that with dicumyl peroxide (DCP) vulcanization system. The degree of isomerisation shows a positive correlation with the sulphur dosage and can reach 10% with 3 phr sulphur. Experiments also prove that zinc oxide (ZnO) and antioxidants have a significant inhibitory effect on the isomerisation during the vulcanization. The isomerisation degree of BR/ZnO-4 is reduced by half compared to that of BR/ZnO-0. The effect of antioxidant poly (1,2-dihydro-2,2,4-trimethyl-quinoline) (RD) is greater than that of N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine (6PPD) due to its higher activity. The isomerisation of BR compound in the vulcanization is not affected significantly by the accelerator types. Besides, the isomerisation degree of Nd-BR with higher chain regularity is lower than that of Ni-BR with the same vulcanization system. The investigation above provides new perspectives and inspirations for the optimization of formula and scientific analysis on the structure-property relationship of BR composite.