Oxidative Stability of Vegetal Oil-Based Lubricants

Abstract

Lipids are widely distributed in nature and are one of the most important components of natural foods, synthetic compounds, and emulsions. To date, there is a strong social demand in the industrial sector for the use of sustainable products with a minimal environmental impact. Depending on their origin and composition, lipids can be employed as a plausible alternative as biodegradable lubricants in order to reduce the use of conventional mineral oil lubricants and mitigate their environmental impact. This perspective provides an overview of the advantages and constrains of vegetal oils under different lubrication regimes and the tribochemical reactions that can take place. Also, the different factors and pathways that influence their oxidation, the key role of moisture, and the changes of physical properties under pressure and temperature are reviewed. Special emphasis is devoted to the oxidation instability of fatty acids and vegetal oils and the physical and chemical approaches to improve oxidative and thermal stability are described in detail.

Lignin-Based Additives for Improved Thermo-Oxidative Stability of Biolubricants

“…1 About 90−95% of lubricants are petroleum-based products. 2 Approximately half of these products end up in the environment, due to total-loss applications, spillage, evaporation, and mishandling, polluting soil, water, and air as a result of their toxicity and lack of biodegradability.…”

“…1,3 Next to their biodegradability, renewable, and nontoxic character, vegetable oils possess advantageous performance features: excellent lubricity, low volatility, high flash point, and viscosity. 2,4 Nonetheless, their biggest drawback is limited thermo-oxidative and hydrolytic stability, which can be overcome by the use of additives or chemical modification of the oil by transesterification, epoxidation, estolide formation, or hydrogenation. 1,2,4 In our view, the focus should be pointed toward biolubricants originating from nonedible vegetable oils, to avoid competition with feed and food resources.…”

“…2,4 Nonetheless, their biggest drawback is limited thermo-oxidative and hydrolytic stability, which can be overcome by the use of additives or chemical modification of the oil by transesterification, epoxidation, estolide formation, or hydrogenation. 1,2,4 In our view, the focus should be pointed toward biolubricants originating from nonedible vegetable oils, to avoid competition with feed and food resources. Castor oil is a good example of such an oil.…”

“…There is a constant growth in the use of lubricants, which are primarily used by the automotive industry, and the estimated global market size is 30–40 million tons annually . About 90–95% of lubricants are petroleum-based products . Approximately half of these products end up in the environment, due to total-loss applications, spillage, evaporation, and mishandling, polluting soil, water, and air as a result of their toxicity and lack of biodegradability.…”

“…An environment-friendly alternative to synthetic petroleum-based lubricants are biolubricants such as vegetable oils. Promising oils for this application include sunflower, rapeseed, soybean, castor, jatropha, and neem oils among others. , Next to their biodegradability, renewable, and nontoxic character, vegetable oils possess advantageous performance features: excellent lubricity, low volatility, high flash point, and viscosity. , Nonetheless, their biggest drawback is limited thermo-oxidative and hydrolytic stability, which can be overcome by the use of additives or chemical modification of the oil by transesterification, epoxidation, estolide formation, or hydrogenation. ,, …”