Some applications of ultraviolet spectrophotometry in drying oil research

Abstract

ConclusionsAn alkaline‐solution technique has been developed permitting the study of the drying and aging process of an oil film using the ultraviolet spectrophotometer. This technique has been found to be a valuable tool for investigating some of the chemical changes which occur as a vegetable oil film dries and ages.The drying or autoxidation of an oil film has been shown to proceed along the general lines of a three‐stage reaction with the short initial stage being characterized by an accumulation of conjugated diene and triene structures which reaches a maximum at the time the film has set up or becomes continuous. The second or curing stage was characterized by a slow decrease in the measurable conjugated diene and triene structures. The third or deterioration stage was not investigated; however, this method should be readily adaptable to studies involving film breakdown as represented by phenomena such as after‐yellowing since the development of absorption peaks characteristic of linolenic ketones, for example, would permit an early prediction of yellowing long before the concentration of the chromophore groups became great enough for visual observation.During the initial stage of drying there was also evidence for an increase in the alpha‐keto structures capable of enolizing in alkali to give absorption maxima characteristic of triene and tetraene conjugated systems. These enolizable structures also decreased in amount during the film curing period and are not characterizable on the basis of observed absorption maxima and published information.The method of obtaining a spectral solution of a dry, infusible oil film through the medium of alcoholic KOH was applied to investigations on the relationship existing between the light absorption of the film solution and the durability or weather resistance of the straight oil film. The results obtained verified the principle previously reported that the quantity of light absorbed by an oil film in the region of 320–400 mμ was indicative of the durability of the film upon exposure to accelerated weathering conditions.