Ozone Deterioration of Elastomeric Materials. Preliminary Results of a Study by Infrared Spectroscopy

Abstract

The work described consists of explorative studies with the ultimate objective of developing an accelerated ozone aging test for elastomers based primarily on compositional changes rather than on the conventional variation in physical characteristics. Infrared spectrographic techniques were found to be admirably suited for the reflection of accumulation or depletion of specific structural linkages in polymer molecules undergoing ozonization. Purified gum specimens of Hevea, GR-S, nitrile rubber, Neoprene, and GR-I were dissolved in chlorinated hydrocarbon solvents such as ethylene dichloride or o-dichlorobenzene, and subjected to a stream of ozonized oxygen containing approximately 50 p.p.m. of ozone. Infrared spectrograms of films cast from the treated solutions show progressive intensification of clearly defined absorption bands at 2.9 and 5.8 mµ, reflecting the functional groups hydroxyl and carbonyl, respectively. Methods for quantitating these changes by calibration against reference compounds are described. A means is available for following ozone degradation of polymers in terms of specific variations in molecular structure. Basic information of this nature is potentially useful in the development of an accelerated ozone aging test correctable with aging under conditions of actual service.