Ozonation of Unstretched Natural Rubber: Part I. Effect of Film Thickness

Abstract

Abstract Unstretched films of natural rubber from Hevea brasiliensis were exposed to ozone flow of 5 and 15 mL/min for 4 to 60 min. The effect of reaction time and the film thickness was studied by viscometry and gel permeation chromatography (GPC). For film thicknesses, in the range of 40 to 350 µm, an initial increase in the intrinsic viscosity, [η], was observed within 8 min of reaction, followed by a decrease for longer times. For thin films, only a decrease in the [η] was observed. The viscosity increase, followed by its decrease, suggests the formation of crosslinking and chain cleavage, respectively, both expected by Criegge mechanism. The plot of [η] versus film thickness and the Chromatographic analysis, related either to 8 or to 60 min of reaction, show that the ozone penetration and the ozone reaction progresses into deeper layers than those previously described in the literature (∼0.5 µm), in this case, 170 and 250 µm, respectively. One model was proposed to explain the viscosity, GPC and attenuated total reflection (ATR) results.