Volatiles from thin film degradation of bio-based, synthetic and mineral basestocks

Purpose - Workmanship concerns lead to more focus on volatile materials, released by industrial lubricants. Typically, flash point test and thermogravimetrical analysis (TGA) are used to investigate basestock volatility, but they do not address long-term decomposition tendencies of lubricants. The extent of volatile losses due to chemical degradation (oxidation, hydrolysis, dissociation, etc.) remains unclear. Design/methodology/approach - Vaporisation tendencies of eight additive-free bio-based, synthetic and mineral basestocks with similar viscosities were compared experimentally in a 30-80 h degradation test. Thin films (30-50 mu m) of oils were placed on the steel surface and heated to 130-140 degrees C with periodic cooling to room temperatures for gravimetric measurement of volatile losses. Findings - Mineral oils lost some fractions initially, but their evaporation subsided afterwards. To the contrary, PAO, polyglycol and polyol ester type oils showed low losses early into the test, but later they started producing high amounts of volatiles. After approx. 10-15 h the evaporation from mineral oils was clearly lower than that from synthetic or bio-based oils with substantially higher flash points. Originality/value - Test results challenge the existing viewpoint that viscous oils with high flash points are non-volatile. It was found that even fully synthetic and bio-based oils lost more than 30 wt.% contents, despite being considered almost non-volatile. Such extensive decomposition of oil films should be taken into account when making the equipment-engineering or workmanship-related decisions in the industry.