Oxidative decomposition of thin films of oleyl and stearyl alcohols on steel surface

Abstract

Fatty alcohols and their derivatives are popular additives in shampoos, cosmetics, paints, lubricants and other functional fluids, whose films are exposed to the environment. Often these films degrade due to oxidative, thermal, catalytic and other stress factors, producing volatile emissions. Decomposition of fatty materials is rarely viewed as a significant contributor to vapour losses, however, it cannot be assumed that fatty alcohols are completely non-volatile. In this study, oxidative degradation of thin films of oleyl and stearyl alcohols was investigated on the steel surface. Tests at 90 °C showed that within several hours significant portions of these alcohols were lost to volatile emissions. Initially the absolute evaporation rates did not depend on the film thickness and appeared quite similar for both alcohols. In later stages, the evaporation rate of thinner films went down due to the formation of oxidative polymers and functional group oxidation. Acidity of oleyl alcohol increased much more rapidly than that of stearyl. After long-term degradation oleyl alcohol produced gel-like solids, while films of stearyl alcohol began to retain a liquid state at room temperature. Since the volatile emissions amounted to more than 60%, the decomposition products in final applications should be investigated in more detail when stearyl or oleyl alcohols are used as major constituents in commercial liquids.