Biobased poly-phosphonate additives from methyl linoleates

Authors: Biresaw, Girma; Bantchev, Grigor; Harry O Kuru, Rogers

Submitted to: Tribology Transactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2019
Publication Date: 2/1/2019
Citation: Biresaw, G., Bantchev, G.B., Harry-O'Kuru, R.E. 2019. Biobased poly-phosphonate additives from methyl linoleates. Tribology Transactions. 62(3):428-442. https://doi.org/10.1080/10402004.2019.1571259.
DOI: https://doi.org/10.1080/10402004.2019.1571259

Interpretive Summary: Successful application of farm products in biobased lubricant formulations will provide a number of environmental, health, and economical benefits over petroleum based formulations. Achieving the maximum benefit will require developing fully biobased lubricant formulations, where both the base oil and the additives are biobased. Currently, there are a few commercial biobased base oils that can be used for such purpose. In contrast, there are no commercial biobased additives that can be used to formulate fully biobased lubricant formulations. In the work described here, methyl linoleate, which is obtained from soybean oil and vegetable oils, was chemically modified to produce a series of poly-dialkylphosphonate additives. These new additives were positively identified and characterized using a variety of analytical methods and their additive properties in high oleic sunflower oil (HOSuO) and polyalphaolefin (PAO-6) base oils investigated. The neat poly-dialkylphosphonates displayed higher density, higher kinematic viscosity, higher oxidation stability, and better cold flow properties. As additive (0-10% w/w) in HOSuO, the poly-di-N-butyl phosphonate provided improved oxidation stability and cold flow properties. Poly-di-N-butyl phosphonate blends in HOSuO also showed lower 4-ball anti-wear coefficient of friction (COF) and wear scar diameter (WSD) than corresponding blends with zinc dialkyl dithio phosphate (ZDDP). As an additive (0-10% w/w) in PAO-6 base oil, poly-di-N-butyl phosphonate displayed lower 4-ball anti-wear COF and comparable WSD relative to similar blends of ZDDP in PAO-6. The results indicate that biobased anti-wear additives derived from farm products can provide comparable or better performance than current petroleum based commercial anti-wear additives such as ZDDP. This knowledge is of considerable importance for scientists and engineers engaged in biobased lubricant development.

Technical Abstract: Poly-dialkyl phosphonates were synthesized by reacting methyl linoleate with dimethyl, diethyl, and di-n-butyl phosphites in the presence of free radical initiator and positively identified and characterized using gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR; 1H, 13C, 31P), and Fourier transform infrared (FTIR). Neat poly-dialkyl phosphonates and their blends in high-oleic sunflower oil (HOSuO) and polyalphaolefin (PAO-6) base oils were investigated for their physical, chemical, and tribological properties. At room temperature, the poly-dialkyl phosphonates displayed much better solubility in HOSuO than in PAO-6. Solubility in the base oils increased in the order dimethyl < diethyl < di-n-butyl. Relative to methyl linoleate, the neat poly-dialkyl phosphonates displayed higher density, higher kinematic viscosity, higher oxidation stability, and better cold flow (lower pour point and cloud point) properties. As additive (0-10% w/w) in HOSuO, increasing concentration of poly-di-n-butyl phosphonate resulted in increasing onset and peak oxidation temperatures and decreasing cloud point. Poly-di-n-butyl phosphonate blends in HOSuO also showed lower four-ball anti-wear (AW) coefficient of friction (COF) and wear scar diameter (WSD) than corresponding blends with zinc dialkyl dithiophosphate (ZDDP). As an additive (0-10% w/w) in PAO-6 base oil, poly-di-n-butyl phosphonate displayed lower four-ball anti-wear COF and comparable WSD relative to similar blends of ZDDP in PAO-6. The results indicate that poly-dialkyl phosphonates are promising biobased AW additives with comparable or better performance than current petroleum-based commercial AW additives such as ZDDP.