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Tribological Properties of Biobased Ester Phosphonates
Author(s) -
Biresaw Girma,
Bantchev Grigor B.
Publication year - 2013
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-013-2232-1
Subject(s) - phosphonate , degree of unsaturation , alkoxy group , chemistry , alkyl , branching (polymer chemistry) , pour point , organic chemistry , viscosity index , base oil , polymer chemistry , materials science , scanning electron microscope , composite material
Three phosphonate derivatives of methyl oleate (MeO) were chemically synthesized in a radical chain reaction and their physical and tribological properties investigated. The phosphonates differed from each other in the structure of the alkoxy groups attached to the phosphorous, which were as follows: methoxy, ethoxy, and n ‐butoxy. Phosphonylation eliminated the unsaturation in MeO and also introduced branching. The phosphonate oils had higher density and viscosity than MeO, which was attributed to the contribution of the heavier phosphorus atom in their structures, and to their higher molecular weights, respectively. The phosphonates also displayed improved oxidation stability and cold flow properties, which were attributed to the elimination of the double bond and the introduction of branching in their molecular structures, respectively. Tribological investigations were conducted using 4‐Ball anti‐wear (AW) and extreme pressure (EP) methods. Neat phosphonates displayed lower AW coefficients of friction and wear scar diameters than MeO. The improved AW results were attributed to the higher viscosity of the phosphonates, since the AW test is conducted in the mixed film regime. The phosphonates had no effect on EP weld point (WP) as neat oils or as 5 % additives in petroleum‐based oils. In soy base oil, 5 % phosphonate additives displayed smaller improvement in WP than zinc dialkyl dithiophosphate (ZDDP). It is proposed that this lack of EP characteristics could be due to the high dissociation energy of C–P bonds in the phosphonates, compared to, for example, S–P bonds in ZDDP.