The Proöxygenic Effect and the Resulting Deterioration of Rubber

Abstract

Abstract Three particularly important conclusions can be drawn as a result of the investigation described in the present paper. (1) The proöxygenic effects of the various organic salts of copper, iron, manganese and cobalt which were tested are not confined to the surface alone. All these salts are soluble in organic solvents, and it is to be presumed that they are likewise at least slightly soluble in rubber hydrocarbon. Actually it was observed that immediately after impregnation of rubber with the solution, the proöxygenic substance had penetrated into the interior of the sample, although this penetration was not uniform. This concentration gradient resulted in a preferential attack at the surface by gaseous oxygen. This attack was manifest in the formation of a sticky surface coating which acted, to a certain extent, as an obstacle to further penetration of oxygen into the core of the small pieces of rubber. It was also observed that, after autoöxidation, deterioration of the samples was chiefly on the surface. This deterioration was very pronounced, e.g., even after only 15–30 minutes in the manometer at 80° C ; the pieces of rubber adhered strongly to one another. (2) When present as binary mixtures, salts of manganese, iron and cobalt showed true mutual exaltation effects in their catalytic activities. A mutual inhibitory effect was likewise observed in some cases. (3) In the form of ternary mixtures, and within a limited range of compositions, these same salts induced more rapid autoöxidation than was to be expected of them by application of the law of mixtures. This effect was particularly great with a eucoactive mixture of cobalt, manganese and iron salts in the proportion of 1:1:3 (based on the metals), in which case an exaltation effect 300 per cent of the calculated effect was found.