Location: Bio-oils Research2011 Annual Report
1a. Objectives (from AD-416)
1. Develop and apply modeling and experimental tools for the investigation and prediction of the tribological properties of farm-based raw materials. 2. Apply tribological knowledge to the development and commercialization of biobased lubricants for use in automotive and related applications.
1b. Approach (from AD-416)
(1) Review existing oxidation and cold flow literature as well as existing models for predicting oxidative stability (OS) and cold flow properties (CFP). Predictive models will be developed and used to design chemical structures that could provide improved OS and CFP without sacrificing biodegradability. Model compounds will be synthesized and evaluated using a variety of cold flow and oxidation tests such as: rotary bomb oxidation test (RBOT), pressurized differential scanning calorimetry (PDSC), pour point (PP), cloud point (CP), cryogenic differential scanning calorimetry (DSC). Models will be further modified as needed and applied in development of new bio-based raw materials and promising structures will be synthesized in large quantities for bench- and pilot-scale evaluations. Tribological and tribochemical properties of model bio-based structures will be investigated and used in model development. Structures to be investigated include: polarity, unsaturation, branching, chain length, cyclic rings (mono- and poly-cyclic aromatic and aliphatic structures), and various combinations of structures. Model structures will be evaluated for boundary, hydrodynamic, mixed, elastohydrodynamic, traction, and tribochemical properties. (2) Develop database on lubricating and hydraulic fluids to set-up target specifications and also to develop predictive structure-property relationships. Various grades of lubricating and hydraulic fluids will be developed using variety of in-house tests such as: RBOT, PDSC, PP, CP, EHD film thickness, thin layer chromatography (TLC), foaming, corrosion, volatility, viscosity, viscosity-index, pressure-viscosity coefficient, friction and wear (anti-wear and extreme pressure), biodegradability, etc. Promising formulations will be further developed using appropriate bench tests. Examples of bench tests used in lubricating oil development include: Thin Film Oxygen Uptake Test; Cold Cranking Simulator; Mini-Rotary Viscometer; gas emission tests; Thermo-Oxidation Engine Oil Simulation Test; Corrosion Bench Test; Distillation; Piston cleanliness; etc. Bench tests to be used in biobased hydraulic fluid development include: vane pump; corrosion; foam; oxidation; water separability; thermal stability; hydrolytic stability; and sludge formation. Promising biobased formulations will be further subjected to qualification tests and long-term evaluations for specific applications. Starch modified by steam-jet cooking or chemical modification will be used to develop starch-based metalworking lubricants. The effect of various structural and formulation variables on performance will be investigated, including starch chemical structure; type and degree of chemical modification; oil chemical structure; oil-to-starch ratio; lubricant additives chemistry and concentration. Tests to be used in these evaluations include: friction and wear; product quality; tool life; productivity; lubricant batch life; ease of lubricant handling; compatibility with machine components; etc. The results will be used to select formulations for further development on small- and pilot-scale equipment.
3. Progress Report
Agricultural Research Service (ARS) scientists are using a variety of approaches to develop methods of improving the oxidation stability (OS) and cold flow properties (CFP) of vegetable oils used in biobased lubricant development. These two properties have been identified as major obstacles to large scale commercialization of biobased lubricants from vegetable oils. In FY11, researchers used oleate ester model compounds to investigate chemical modification for improving OS and CFP. The researchers applied photochemical synthetic methods to replace the unsaturations in the model compounds with alkyl phosphonate branches. Such transformation, where the unsaturation is eliminated and branching introduced, is expected to have a positive effect on both OS and CFP properties. In addition, the introduction of the phosphorous group is expected to provide enhanced lubrication properties. ARS scientists also worked at improving the robustness and scope of a previously developed empirical structure-property model used for predicting OS from the structure of the oils. Such models can be used to identify structures with favorable OS properties and allow for rapid biobased lubricant formulation development. The work involved investigating a wider range of model compounds of varying chemical structures as well as OS measurement methods. The new results will be used to improve both the robustness and scope of the existing model. The progress achieved in FY11 has potential scientific impact for researchers focused on improving the lubrication properties of vegetable oils and will facilitate faster development and commercialization of biobased lubricant formulations.
1. Development of quantitative structure-property model for oxidation stability of vegetable oilS. Extremely short service life due to reaction with air (poor oxidation stability or OS) is one of the major hurdles that must be overcome for successful development and commercialization of biobased lubricants from vegetable oils. A variety of methods are being pursued to improve OS of vegetable oils by scientists worldwide. ARS Bio-Oils Research Unit scientists at the National Center for Agricultural Utilization Research (NCAUR), Peoria, IL, developed a quantitative empirical model between OS measured using rotary pressurized vessel oxidation test (RPVOT), and the bond dissociation energy (BDE) of reactive protons in the oils. The model was tested on data from previously published studies, and successfully correlated published RPVOT with the BDE of the investigated oils. The developed empirical model is a useful tool for scientists and engineers engaged in development of farm-based lubricants with improved OS properties. Such progress can lead to increased market share for environmentally friendly biobased lubricants and thereby increase the demand for farm based products used in lubricant formulations.
2. Investigation of effect of chemical structure on elastohydrodynamic (EHD) film thickness. Vegetable oils and their derivatives used in lubrication must exhibit acceptable film-forming characteristics to ensure lubricated components do not come in contact and cause high friction and wear. This is particularly important for applications where the lubrication condition (e.g., load, speed, temperature) constantly changes during use, such as those encountered in automotive engines. ARS Bio-Oils Research Unit scientists at the National Center for Agricultural Utilization Research (NCAUR), Peoria, IL, investigated the film-forming properties of two derivatives of milkweed oils obtained through chemical modification. It was important to understand how the chemical modifications affect film-forming properties and develop correlations between chemical structure and film thickness. The researchers measured the film thickness of the modified oils and compared it against those predicted by models. They found excellent agreement between measured and predicted film thickness for one structure, but negative deviation (thinner measured film than predicted) for the other structure. A potential consequence of negative deviation could be poor lubrication (e.g., during start of automotive engines), which could lead to excessive wear and premature failure. Such research is essential for developing structure-property relations to guide the chemical modification of vegetable oils into biolubricants of acceptable lubrication properties. Successful implementation of such knowledge can lead to increased commercial application of farm-based lubricants and increase the lubricant market share for farm products.
Bantchev, G.B., Biresaw, G., Mohamed, A., Moser, J.K. 2011. Temperature dependence of the oxidative stability of corn oil and polyalphaolefin in the presence of sulfides. Thermochimica Acta. 513(1-2):94-99.
Biresaw, G., Bantchev, G.B. 2010. Elastohydrodynamic (EHD) traction properties of seed oils. Tribology Transactions. 53(4):573-583.
Evans, K.O., Biresaw, G. 2010. Quartz crystal microbalance investigation of the structure of adsorbed soybean oil and methyl oleate onto steel surface. Thin Solid Films. 519:900-905.
Rudnick, L.R., Mohamed, A., Gul, O., Biresaw, G. 2011. Vaporization and carbonization tendency of vegetable oils as a function of chemical composition: morphology of carbon deposits on steel surfaces at elevated temperatures. In: Biresaw, G., Mittal, K.L., editors. Surfactants in Tribology. Vol 2. Boca Raton, FL: Taylor & Francis. p. 409-433.
Biresaw, G., Bantchev, G.B., Cermak, S.C. 2011. Tribological properties of vegetable oils modified by reaction with Butanethiol. Tribology Letters. 43(1):17-32.
Bantchev, G.B., Biresaw, G. 2011. Film-forming properties of castor oil polyol ester blends in elastohydrodynamic conditions. Lubrication Science. 23(5):203-219.