SURFACE STUDY OF OZONE ATTACK AND ANTI-OZONANT PROTECTION OF CARBON-BLACK LOADED NATURAL-RUBBER COMPOUNDS

This work reports a direct surface analysis of ozonization of carbon black loaded NR compounds by ATR and SEM. On ozonization of raw NR or NR containing carbon black, a thick layer builds up consisting of ozonides and carbonyl compounds. It is suggested that this layer is composed principally of the reaction products of ozone with unsaturated fatty acids and unsaturated fatty acid esters found in NR. On ozonization of cured and uncured carbon black loaded NR compounds containing curatives, the NR is attacked causing a decrease of rubber on the surface and a corresponding increase in the surface concentration of carbon black. The thick ozonide/carbonyl layer did not form, probably due to the coordination of the fatty acids and esters with ZnO, which was added with the curatives. These results are consistent with a dual scavenger and protective layer mechanism for antiozonant protection.