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Inhibitory effect of phenothiazine on the oxidation of natural rubber in the presence of α,α-diphenyl-β-picrylhydrazyl

J. Hrivíková, A. Hrivík, and V. Kellö

Department of Physical Chemistry, Slovak Technical University, 880 37 Bratislava


Abstract:  The effect of phenothiazine (PT) on the oxidation of natural rubber in the presence of  α,α-diphenyl-ß-picrylhydrazyl (DPPH) was studied. Their inhibitory effect was expressed by means of the length of the induction period of oxidation and the index of the relative inhibitory efficiency Jre . The synergistic effect on the subsequent oxidation of natural rubber thermally treated in an inert medium could be observed only at higher concentrations of phenothiazine and it decreased with increasing total concentration of the antioxidative mixture. Antagonism was observed at high concentrations of DPPH in the presence of PT. At the oxidation of natural rubber without thermal treatment the mixture of DPPH and PT appeared to be synergistic and the synergistic effect increased with the molar fraction of DPPH. The course of the reaction between DPPH and PT, accompanied by the formation of DPPH-H and phenothiazinyl radicals PT ( > N•) , was confirmed and the radicals were detected by the e.p.r. method. Furthermore, basic reactions between DPPH and PT in the presence of a thermally treated and subsequently oxidized rubber as well as the rubber oxidized without a preliminary thermal treatment are described.

Full paper in Portable Document Format: 294a459.pdf


Chemical Papers 29 (4) 459–473 (1975)

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