Xanthohumol: a plant-based, non-toxic antioxidant for the lubricant industry

Lubricants are essential for industrial and mobility applications; their long-term stability depends on antioxidant additives that are often derived from petrochemistry and are associated with environmental and ecotoxicological concerns. This study investigates xanthohumol (XN), a naturally occurring substance derived from hops and recoverable from brewing industry waste streams, as a sustainable, plant-based antioxidant for lubricant applications. Oxidation stability and tribological performance were evaluated using an ester base oil containing 1 wt% XN and compared to the neat base oil under accelerated oxidative and tribological testing conditions. The addition of XN resulted in a substantial increase in oxidation induction time, reaching approximately 250% relative to the base oil. Oxidative degradation, including oxygen uptake, acid formation, and water accumulation, was effectively suppressed. Following oxidation testing, the base oil exhibited markedly increased friction and wear, whereas the XN-containing formulation remained comparable to fresh oil samples. Beyond its functional performance, XN offers significant sustainability benefits. It is derived from renewable biomass, can be extracted using environmentally benign solvents, and exhibits a favorable toxicological and biodegradability profile compared to conventional phenolic and aminic antioxidants. These characteristics align with circular-economy principles and current sustainability objectives in lubricant formulation, in particular for highly specialized lubricants.