Tribological Properties of Biobased Ester Phosphonates

Abstract

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.

Tribological Properties of Limonene Bisphosphonates

“…The AW and EP results of the neat oil investigations are summarized in Table 6, where the data for the bisphosphonates are compared to each other and to the base oils (PAO6 and HOSuO). Examination of the neat oil EP results in Table 6 shows that bisphosphonates provide weld points of about double (*200 kgf) the reported values [60,61] for the neat base oils. Among the bisphosphonates, the methyl product gave a higher (260 kgf) weld point than the n-butyl or ethyl products.…”

“…The specification and detailed description of the instrument hardware and software have been given before [61].…”

“…Among the bisphosphonates, the methyl product gave a higher (260 kgf) weld point than the n-butyl or ethyl products. The EP result suggests that neat bisphosphonates provide improved EP properties over the neat base oils, but the improvements were rather small since commercial EP additives provide much higher weld points ([800 kgf) at much lower concentrations (\20 %) [61]. Thus, more work is needed to develop a commercially viable EP additive based on limonene.…”

Radical‐Initiated Reaction of Methyl Linoleate with Dialkyl Phosphites

“…Organic compounds containing phosphorus have applications in many areas, including lubricants, lubricant additives, flame retardants, antimicrobial agents, herbicides, and plasticizers. Bio-based phosphorus-containing materials were synthesized in the past and were reported as having desirable qualities as lubricant additives [1,2], plasticizers [3], and antimicrobial agents [4].…”

Synthesis and Characterization of Phosphonates from Methyl Linoleate and Vegetable Oils

“…In our previous work, we synthesized phosphonate derivatives of methyl oleate and limonene using radical dialkyl phosphite (H-phosphonate)-ene reactions [9,10]. The products showed promising antiwear and extreme-pressure properties and had good pour and cloud points [10,11]. Taking into account the possible applications of biobased phosphonates, we are extending our work to increase the number of the biobased phosphonates.…”