Study on Effect of Accelerator on Vulcanization of Natural Rubber through Rubber-state NMR Spectroscopy

Abstract

Effect of accelerators on the vulcanization of natural rubber was investigated by analyzing structure of the crosslinking junctions through rubber state NMR spectroscopy. The accelerated sulfur vulcanization of natural rubber was carried out with one of the three accelerators, i.e., Zinc diethyldithiocarbamate (ZDEC), Zinc dibutyldithiocarbamate (ZDBC) and Zinc salt of 2-mercaptobenzothiazole (ZMBT), in the presence of sulfur, ZnO and stearic acid. Structure of the crosslinking junctions of the vulcanized natural rubbers was determined through rubber-state NMR spectroscopy with bilevel complete decoupling (BCM), distortionless enhancement by polarization transfer (DEPT) and attached proton test (ATP). The mechanism of the vulcanization of natural rubber was demonstratively analyzed on the basis of the structure of the resulting crosslinking junctions. It was classified into two schemes: that is, radical mechanism and ionic mechanism followed by radical mechanism, depending on the sort of accelerators used in the present study.