Location: Bio-oils Research2012 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: Rotating Bomb Oxygenation Tester (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 (EHD); traction; and tribochemical properties. (2) Develop a 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 a variety of in-house tests such as: RBOT; PDSC; PP; CP; elastohydrodynamic lubrication (EHL) film thickness; traction coefficient (TC); 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 bio-based hydraulic fluid development include: vane pump; corrosion; foam; oxidation; water separability; thermal stability; hydrolytic stability; and sludge formation. Promising bio-based 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:
Scientists in the Bio-Oils Research Unit at the USDA-ARS National Center for Agricultural Utilization Research (NCAUR), Peoria, IL, in collaboration with colleagues in industry and academia, demonstrated that vegetable oils can enhance the performance of lubricant additives much better (2- to 4-fold time) than petroleum-based oils. Additives, which can comprise 5-30% of formulated lubricants, are the most expensive components of lubricants. The findings indicate that vegetable oil-based lubricants can be formulated with much lower amounts of additives, thereby giving them a big cost advantage over petroleum-based lubricants. However, the mechanism by which vegetable oils provide an extra boost to the performance of additives is not known. Understanding this mechanism will allow lubricant formulators to further extend and take full advantage of this property of vegetable oils. ARS scientists in collaboration with scientists at the University of Illinois Urbana-Champaign (UIUC), Urbana, IL, have began work aimed at shedding light into the mechanism, under friction conditions, of additive interaction and chemical reaction (also called tribochemical reaction) with base oils (vegetable and petroleum) and metallic friction surfaces. In this collaboration, ARS scientists have conducted experiments that produced a metallic specimen under high temperature and high pressure friction experiments. These conditions result in chemical reactions that generate new materials, called tribochemicals, on the friction surfaces. Colleagues at UIUC are in the process of analyzing the friction surfaces using x-ray photoelectron spectroscopy (XPS). This analysis will be used to determine what tribochemicals have been generated from various combinations of additives and base oils. The XPS results will then be used to propose a mechanism for tribochemical reaction and interaction between additives and base oils. The proposed mechanism will be tested and refined with further friction and XPS experiments. This work will allow formulators to take full advantage of the superior properties of vegetable oils in lubricant formulations.
1. Improving properties of vegetable oils through chemical modification. Vegetable oils display poor oxidation stability and cold flow properties. These weaknesses have been linked to their inherent chemical structures; namely, high degrees of unsaturation and lack of branching in their hydrocarbon chains. Scientists in the Bio-Oils Research Unit at the USDA-ARS National Center for Agricultural Utilization Research (NCAUR), Peoria, IL, investigated the tribological friction-reducing properties of soybean, pennycress and milkweed vegetable oils that were chemically modified by converting their unsaturations to formate esters. The chemical modifications removed the unsaturations and also introduced formate branches into the oil structures which will have a positive effect on the oxidation, pour point and cloud point properties of the oils. Evaluation of the new materials showed that they have higher viscosity and superior friction and wear properties. This indicated that chemical modification can improve the properties and also extend the range of applications of vegetable oils in lubrication. The results of this investigation can be used by scientists and engineers working to increase the utilization of surplus vegetable oils in lubricant formulations.
2. Phosphonate-containing value-added structures from bio-based oils. The use of bio-based oils in lubrication requires enhancing their properties by blending them with a variety of additives such as: extreme pressure, antioxidants, pour point depressants, viscosity index improvers, etc. Each additive is used in small quantities (1–20%) but costs much more than the base oil. One way of improving the value of the bio-based oils is to incorporate additive structures chemically or enzymatically. Phosphorous-containing additives are widely used in lubricant formulations to improve their friction and wear properties under extreme lubrication conditions, such as those encountered automotive engines. Scientists in the Bio-Oils Research Unit at the USDA-ARS National Center for Agricultural Utilization Research (NCAUR), Peoria, IL, chemically converted esters of methyl and ethyl oleate and methyl linoleate into the corresponding mono- and di-phosphonates. The tribological properties of the new phosphonate-modified bio-based oils will be characterized and further developed for a variety of lubrication applications. Phosphonate modification will also be extended to other bio-oils including vegetable oils obtained from commodity and new crops. Successful development of phosphonate-containing bio-based oils will increase the value of oil-bearing crops for the United States farmer.
Bantchev, G.B., Biresaw, G., Cermak, S.C. 2012. Elastohydrodynamic study of blends of bio-based esters with polyalphaolefin in the low film thickness regime. Journal of the American Oil Chemists' Society. 89(6):1091-1099.