Effect of Metals on Degradation of Vulcanized Natural Rubber

Abstract

The metal-catalyzed thermal-and photo-oxidation of natural rubber (pare crepe RSS No. 1) crosslinked by dicumyl peroxide has been studied by the stress relaxation method.
The metals used were Cu, Cu₂O, CuO, Mn, Fe, Co, Ni, Zn, Pb and Al. The chemical stress relaxation of these samples was mostly measured at 100°CC in air.₂The metals, Cu, Cu₂O, CuO, Mn and Co were effective catalysts for the thermal oxidative degradation of natural rubber. The metals, Fe, Ni, Zn and Pb, showed no effects on the thermal oxidation of rubber. However, the metals, Fe, Zn and Pb were effective catalysts for the photo-oxidative degradation. Aluminum powder retarded the stress relaxation of rubber. Copper among these metals was particularly active as a catalyst for the oxidative degradation of natural rubber. The apparent activation energy (Eα) for the thermal oxidative degradation catalyzed by copper metal was 16.7kcal/mol, while it was 27. 0 kcal/mol for the non-catalyzed one. The copper-catalyzed thermal-and photo-oxidation mechanism of natural rubber has been discussed.