The desire to replace petroleum-based lubricants with alternatives that are environmentally friendly and made from sustainable sources has encouraged the development of biolubricants based on vegetable oils. To be good lubricants, the materials should have low melting points, appropriate viscosity and oxidative stability. In this paper, we report the melting point and viscosity of oleate esters of ethylene glycol, 1,2-propanediol, 2,3-butanediol, and pentaerythritol as well as the decanoate esters of 2,3-butanediol and the 12-methyltetradecanoate esters of 1,2-propanediol. Polyol esters that have a free hydroxy group had lower melting points than the completely esterified polyols, but the completely esterified polyol esters exhibited less change in viscosity with temperature than those having a free hydroxy group. 2, 3-Butanediol monooleate, which melted at −48.6°C shows promise as a biolubricant, but its viscosity index was estimated to be 100. Pentaerythritol oleate esters, with melting points below −10°C and viscosity indices in the range of 170–197, may be suitable candidates as biolubricants. The behavior of esters spread as a monomolecular film at air/water interface may provide insight into the way they behave when spread on metal or polar surfaces, so the pressure-area isotherms of 2,3-butanediol monoleate and selected esters are also reported.
Practical applications: The structure and function relationships demonstrated can be used to synthesize biolubricants with desirable physical and performance properties.
This figure shows the melting and viscosity properties of various types of synthesized biolubricants. Abbreviations: BDMO, 2,3-butanediol monooleate; BDM10, 2,3-butanediol monodecanoate; PGMO, 1,2-propanediol monooleate; PET, pentaerythritol; R-Ac, a group of acetylated ricinoleates; BuR, butyl ricinoleate; IsR, isopropyl ricinoleate; BuO, butyl oleate; IsO, isopropyl oleate; MeR-11u, methyl 12-undec-10-enylricinoleate.