Preparation and characterization of vulcanized natural rubber with high stereoregularity

Abstract

Vulcanized natural rubber with outstanding mechanical properties due to the rapid strain-induced crystallization was prepared by controlling stereoregularity, based on structural analysis of the vulcanized rubbers. The vulcanized rubbers were prepared at 110, 130, 150 and 170 °C for t90 from natural rubber compounded with sulfur, ZnO, stearic acid and N-tert-butyl-2-benzothiazole sulfenamide (TBBS). The vulcanized natural rubbers were characterized by swelling method, rubber-state NMR spectroscopy, tensile test and XRD measurement. Stereoregularity, i.e., contents of cis- and trans-1,4-isoprene units, and strain-induced crystallization depended on vulcanization temperature. The vulcanized natural rubber prepared at 130 °C possessed the highest cis-1,4-isoprene unit content and the lowest trans-1,4-isoprene unit content among the vulcanized rubbers, which resulted in the rapid strain-induced crystallization. The content of carbon linking to sulfur was also low for the vulcanized natural rubber prepared at 130 °C. It was found that the vulcanized natural rubber prepared at 130 °C was superior in tensile properties due to high stereoregularity after vulcanization.