Novel Rare-Earth Complexes Containing Amino and Sulfhydryl Groups for Natural Rubber Composites with Improved Antioxidative Properties

Abstract Novel rubber antioxidants, cysteine lanthanum and cysteine cerium, were applied in natural rubber composites. The anti-aging behavior of the composites with rare-earth complexes was systematically investigated via mechanical properties retention after aging, Fourier transform infrared spectroscopy-attenuated total reflection, thermo-oxidative stability and thermo-oxidative degradation kinetics. The results showed that rare-earth complexes could improve the mechanical properties of composites, decrease the formation of thermo-oxidative products and increase activation energy of the thermo-oxidative degradation. Compared with commercial antioxidant N -isopropyl- N  '-phenyl- p -phenylenediamine, the vulcanizates with cysteine lanthanum performed better resistance to thermal oxidation aging. The outstanding anti-aging behavior of rare-earth complexes was attributed to not only the anti-oxidative effect between amino and sulfhydryl groups, but the trapping effect of rare-earth ions on free radicals.