Thin-film test to investigate liquid oxypolymerization of nonvolatile analytes: Assessment of vegetable oils and biodegradable lubricants

A thin-film oxidation test was developed to investigate liquid oxypolymeriz ation of nonvolatile analytes. Gel permeation chromatography (GPC) showed t hat the test delivered the required degree of oxidation with better than +/ -5% accuracy. The following oils were ranked according to their decreasing resistance to oxypolymer formation at 150 degreesC: 90% oleic sunflower oil , triolein, meadow foam oil, castor oil, canola oil, lesquerella oil, and s oybean oil. Higher degrees of oxidation demonstrated the occurrence of oxid ative gelation. Oxypolymerization tendencies of hydraulic fluids based on c anola and rapeseed oils were comparable to those of canola oil without addi tives. The relative amount of C-C polyunsaturation present in the fatty aci d chain was a major differentiating factor. However, oxidation inhibitors a lso reduced the rates of oxypolymerization, as demonstrated by sunflower oi l-based hydraulic fluid. Canola and rapeseed lubricants needed better oxypo lymerization control.