Influence of Molecular Structure on the Physicochemical and Tribological Properties of Biolubricants: A Review

Abstract

The increase in the price of crude oil, the environmental impact, or the depletion of fossil resources has increased the need for bio-based alternatives. This has led to the search for renewable, biodegradable, and environmentally friendly raw materials to obtain lubricants that meet these characteristics. This review deals with the state of the art of biolubricants along with their most common raw materials and molecular structures, processes of chemical modification of bio-oils, as well as the relationship between their structural features and physicochemical/tribological properties. This review concludes that the production of fatty acid alkyl esters from vegetable oils is the most promising chemical route to produce a wide range of biolubricants through double transesterification reactions. It also highlights the need to explore this route for the production of microalgae-derived biolubricants due to its environmental benefits during cultivation and production processes.

Cold-Flow Properties of Estolides: The Older (D97 and D2500) versus the Mini-(D5773 and D5949) Methods

“…The development of bio-based lubricants is under active research (Scopus returned >250 articles when searching for ((bio-based or bio-based or soybean or palm or corn or cooking) and lubricant) in 2023 vs. 126 in 2013). We excluded the term "biolubricants", often used with a similar meaning to "bio-based lubricants" [4][5][6][7]. The "biolubricant" term can be confusing, since it is used to describe lubricants in biological systems [8] or environmentally acceptable lubricants (EAL) [9] both of which may be totally petroleumbased.…”

“…Vegetable oils exhibit better lubricity (lower coefficient of friction and lower wear), better biodegradability, and lower carbon dioxide emission profile than mineral oils. On the other hand, they either have high melting points or low oxidative stability [5][6][7]10,11]. As esters, vegetable oils have lower hydrolytic stability than mineral oils [5][6][7]10,11].…”

“…On the other hand, they either have high melting points or low oxidative stability [5][6][7]10,11]. As esters, vegetable oils have lower hydrolytic stability than mineral oils [5][6][7]10,11]. Good biodegradability is a disadvantage for recirculated emulsion-based metalworking fluid applications, where microbial growth is a major issue [12].…”

“…Still, transesterifications have limited effect on the cold-flow properties and oxidative stability of vegetable oil. Due to this, reacting of the double bonds is often included as part of bio-based lubricant synthesis [5][6][7][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The bio-based lubricants and related materials are used to some extent in almost every application [5][6][7]24,35,36].…”