Patent Application
20090053268
Not applicable.
Advances in the development of nanocomposite materials have made a significant impact on a number of important technical fields including sensing, biotechnology, electronics, mechanical and structural additives, catalysis and optics. These advances are largely attributable to ongoing research directed to discovering new synthetic routes for making useful nanocomposite materials and characterizing the structural and functional properties of these materials. Nanocomposite materials exhibit structural and/or compositional inhomogeneities on a submicron scale, and often comprise a dispersed phase comprising nanoparticles provided in a liquid or solid continuous phase. The properties of nanocomposite materials may be dependent on a number of variables including the composition of the nanoparticles and continuous phase, and the morphology, physical dimensions, concentration, and interfacial characteristics of the dispersed nanoparticles. In many of these systems, the presence of dispersed nanoparticles gives rise to complex intermolecular interactions providing a molecular scale arrangement of the nanocomposite material resulting in useful mechanical, optical, electric, magnetic, and/or chemical properties.
The development of nontoxic, biodegradable and environmentally safe materials is a major area of research for which nanocomposite materials have potential to play an important role. With the rising costs of petroleum and concerns about the toxicity of petroleum based products to the environment, substantial interest is growing in developing alternatives to petroleum-base lubricants and waxes. Biodegradable lubricants and waxes based on plant and animal materials, such as canola oil, soy bean oil, corn oil and soy wax, show promise and have been used in the lubricant market, to a small extent, for some time. Many of these biodegradable alternatives, however, are currently more expensive to manufacture than petroleum-based products and also tend to have inferior physical and chemical properties as compared to petroleum based materials. Vegetable oil triglycerides, for example, are an abundant and promising class of materials that have great potential for use in a range of biodegradable products. The use of these materials in lubricating oils, however, is currently limited due to their susceptibility to oxidative degradation and their poor low temperature physical properties, such as their relatively high pour point temperatures as compared to comparable petroleum based materials.
As a result of the well recognized potential benefits provided by natural oil derived biodegradable materials, substantial research is currently directed toward developing cost effective strategies to improve the physical characteristics of these materials for a range of useful applications. Research in the field of biodegradable lubricants and waxes based on plant and animal materials, for example, is motivated, in part, by the need for additives for these materials capable of improving oxidative and thermal stability so as to extend their useful lifetimes and performance capabilities. The development of nanocomposite biodegradable materials via the incorporation of nanomaterial additives to vegetable oil derived materials is one strategy that is currently identified as a potentially cost effective route to the enhancement of physical and chemical properties of these materials.
International Publication No. WO 2006/076728 discloses the use of various nanomaterial additives as a viscosity modifier and thermal conductivity improver for lubricating oil compositions, including petroleum derived oils and vegetable oils. Nanoparticle additives including carbon nanostructures (e.g., nanotubes), metal particles, solid lubricants (e.g., molybdenum disulfide) and abrasive particles (e.g., aluminum oxide, silicon carbide) having physical dimension ranging from 1 to 200 nm are described. Use of nanoparticle additives in gear oils is characterized in this reference as providing a higher viscosity index, higher shear stability and improved thermal conductivity as compared to conventional gear oils without a nanoparticle component. In addition, a reduction in the coefficient of friction is also reported for some of the disclosed nanoparticle containing lubricant materials.
U.S. Pat. No. 6,878,676 discloses lubricant compositions containing molybdenum sulfide nanosized particles and related methods of making molybdenum sulfide nanosized particle-containing lubricants. Lubricant compositions containing dispersed molybdenum nanoparticles having diameters of 1 to 100 nm and weight percents ranging from 0.5-30% are described. In addition, the use of surface modified molybdenum sulfide nanosized particles with specific ligands is reported as useful for preventing nanoparticle coagulation, enhancing stability and increasing solubility.
International Publication No. WO 2005/0124504 discloses lubricant compositions having a nanomaterial additive and a dispersing agent. Nanomaterial additives described include carbon nanomaterials, such as carbon nanotubes, carbon nanofibrils and carbon nanoparticles, having physical dimensions less than 500 nanomaters in diameter. Lubricant additives and dispersing agents are reported to provide an enhancement of long-term stability and a high viscosity index. The reference also discloses control of nanomaterial additive size and dispersing chemistry so as to provide a desired viscosity and thermal conductivity.
U.S. Pat. No. 6,783,746 discloses methods of preparing stable dispersions of carbon nanotubes in various materials, including synthetic oils and vegetable oils, for changing the physical and chemical properties of liquids. The disclosed methods include steps of dissolving an appropriate dispersant in a liquid and adding carbon nanotubes via agitation and/or ultrasonication. Improvements in heat transfer, electrical properties, viscosity and lubricity are reported using the disclosed methods and compositions.
While advances in modulating the properties of lubricants via incorporation of nanomaterials have been reported, significantly less attention has been directed toward developing nanomaterials strategies for enhancing the properties of waxes derived from natural materials. U.S. Patent Publication 2005/0065238 discloses wax-containing compositions and oil containing compositions having encapsulated nanoparticles for uses as textile sizing materials and fiber coating materials. U.S. Patent Publication 2005/0155,515 discloses a water in oil emulsion wax containing aluminum oxide particles having particles sizes of 20 microns or less for use as a polishing agent.
Conventional waxes derived from vegetable oil-based materials, are known to exhibit a number of significant deficiencies, such as cracking and air pocket formation, that make them unsuitable for some applications. Candles made of conventional waxes derived from vegetable oils, for example, are known to exhibit problems relating to wax and wick performance, shortened burning time and limited product shelf life. Further, some conventional waxes derived from vegetable oils also exhibit mechanical properties, such as hardness and storage modulus, that are significantly less than petroleum-based waxes. These deficiencies current limit commercial implementation of waxes derived from natural materials for a range of applications such as manufacturing candles, vehicle and boat wax, pharmaceuticals, cleaning agents and cosmetics.
As will be understood from the foregoing, there currently exists a need in the art for methods and compositions for enhancing the physical and chemical properties of lubricants and waxes derived from natural materials, such as vegetable oils. Vegetable oil-based wax compositions are needed that exhibit enhanced mechanical properties, such as hardness and storage modulus. Vegetable oil-based wax compositions are needed that have physical and chemical properties useful for a variety of product applications. Vegetable oil derived compositions, such as waxes and lubricants, are needed that exhibit physical and chemical properties comparable to, or exceeding, those of petroleum-based materials.
The present invention provides compositions and products, such as waxes and lubricants, comprising a plurality of nanoparticles dispersed in a continuous phase comprising a vegetable oil derived material, such as one or more vegetable oils or a synthetic product derived from one or more vegetable oils. A composition of this aspect of the present invention comprises a vegetable oil or synthetic product derived from a vegetable oil, and a plurality of nanoparticles dispersed in the vegetable oil or synthetic product derived from a vegetable oil, wherein the nanoparticles have an average cross-sectional dimension selected from the range of about 1 nanometer to about 100 nanometers, and wherein the nanoparticles comprise between about 1% and about 50% by mass of the composition. Embodiments of this aspect of the present invention include, but are not limited to, vegetable oil derived waxes and vegetable oil derived lubricants having a dispersed nanoparticle phase.
Incorporation of nanoparticles in the present compositions is beneficial for providing mechanical, thermal, optical and/or chemical properties useful for a selected product or product application. In some compositions of the present invention, for example, incorporation of the nanoparticle component provides compositions derived from one or more vegetable oils exhibiting enhanced mechanical stability, hardness, viscosity, thermal stability and mechanical strength. In some compositions of the present invention, for example, incorporation of the nanoparticle component provides wax compositions having enhanced optical properties relevant to exposure of the wax to light, such as ultraviolet light, relative to conventional waxes. Nanoparticle components of some aspects of the present invention have physical properties (e.g., morphology, physical dimensions, size distribution etc.), chemical properties (e.g. composition) and interfacial characteristics that give rise to intermolecular interactions providing a molecular scale arrangement of the nanocomposite material resulting in useful bulk phase mechanical and/or chemical properties. The invention includes products and articles of manufacture comprising the vegetable oil derived materials having dispersed nanoparticles providing enhanced physical and chemical properties.
The present invention also provides cost effective nanomaterials strategies for controlling the physical and chemical properties of natural oils and materials derived from natural oils. In these methods, nanoparticles are provided to a vegetable oil derived material, such as one or more natural vegetable oils or a synthetic product derived from one or more natural oils, in a manner to selectively adjust (or “tune”) one or more mechanical or thermal properties, such as hardness, durability, mechanical stability, viscosity, thermal stability and mechanical strength. In some embodiments, precise control of one or more selected physical and/or thermal properties is achieved by selection of the composition, physical dimensions, size distribution, concentration (e.g., percentage by mass), shape and/or morphology of the nanoparticle component provided to the vegetable oil derived material. The present invention also includes compositions and methods wherein a plurality of nanoparticle types are provided to a vegetable oil derived material, wherein the different nanoparticle types have different compositions, physical dimensions, shapes and/or morphologies selected to provide useful physical and chemical properties.
In an aspect, the present invention provides a wax containing composition comprising: a synthetic wax derived from one or more vegetable oils; and a plurality of nanoparticles dispersed in the synthetic wax. In an embodiment of this aspect, the dispersed nanoparticles have an average cross-sectional dimension selected from the range of about 1 nanometer to about 100 nanometers and the nanoparticles comprise between about 1% and about 50% by mass of the composition. Optionally, the wax containing composition of this embodiment may further comprise one or more additional additives, including, but not limited to, dispersants and/or stabilizers to enhance overall mechanical stability, thermal stability and/or shelf life. For example, compositions of the present invention may further comprise one or more surfactants for reducing or minimizing nanoparticle coagulation and/or settling. Other additives useful in the present compositions include one or more of suspension agents, a colorant, a fragrance and an emulsifying agent.
Synthetic waxes useful in this aspect of the present invention include, but are not limited to, triglyceride-based waxes derived from natural oils. In an embodiment, for example, a wax of the present invention comprises a triglyceride component that is greater than or equal to 20% by mass of the composition. Preferably for some applications a wax of the present invention comprises a triglyceride component having a concentration selected from the range of 20% to 80% by mass of the composition, and more preferably for some applications a triglyceride component having a concentration selected from the range of 20% to 50% by mass of the composition. Triglyceride-based waxes useful for certain compositions of the present invention comprise one or more hydrogenated or nonhydrogenated vegetable oils or are derived from one or more hydrogenated or nonhydrogenated vegetable oils. Exemplary vegetable oils for wax containing compositions of the present methods and compositions include, but are not limited to, soy bean oil; sunflower oil, corn oil, canola oil, castor oil, cottonseed oil, peanut oil, olive oil, sunflower oil, rapeseed oil, and safflower oil. Compositions and products of the present invention comprising soy bean wax or materials derived from soy bean wax are particularly attractive for some commercial applications given the abundance and low cost of this vegetable oil.
Selection of the compositions, physical dimensions, shapes, morphologies and concentrations (e.g., percentage by mass) of nanoparticles provided in the synthetic wax determines, in part, certain physical and chemical properties of compositions of this aspect of the present invention. In an embodiment providing compositions exhibiting enhanced hardness and storage modulus, the nanoparticles are spherical, have an average diameter selected from the range of about 10 nanometers to about 50 nanometers, and/or comprise between about 5% and about 30% by mass of the composition. In an embodiment of this aspect of the present invention, the nanoparticles have an average diameter of about 10 nanometers and comprise about 10% by mass of the compositions. Use of nanoparticles dispersed substantially uniformly throughout the synthetic wax (e.g., deviations within about 10% of an absolute uniform distribution) is beneficial for providing compositions having substantially uniform physical and/or chemical properties.
A variety of nanoparticles are useful in the present compositions and methods. Exemplary nanoparticles include, but are not limited to, (i) one or more silicon-containing nanoparticles selected from the group consisting of: silica nanoparticles, silicon carbide nanoparticles, and silicon nitride nanoparticles; (ii) one or more metal salt nanoparticles selected from the group consisting of: group 1 alkali metal hydroxide nanoparticles, group 1 alkali metal carbonate nanoparticles, group 1 alkali metal sulfate nanoparticles, group 1 alkali metal phosphate nanoparticles; group 1 alkali metal carboxylate nanoparticles, group 2 alkaline earth metal hydroxide nanoparticles, group 2 alkaline earth metal hydroxide carbonate nanoparticles, group 2 alkaline earth metal hydroxide sulfate nanoparticles, group 2 alkaline earth metal hydroxide phosphate nanoparticles; and group 2 alkaline earth metal hydroxide metal carboxylate nanoparticles; (iii) one or more transition metal-containing nanoparticles selected from the group consisting of transition metal oxide nanoparticles, transition metal carbide nanoparticles and transition metal nitride nanoparticles; (iv) one or more carbon nanoparticles selected from the group consisting of single walled carbon nanotubes, multiwalled carbon nanotubes, carbon nanorods, carbon nanofibers, and graphite particles; and (v) one or more metal nanoparticles. In an embodiment providing wax compositions exhibiting enhanced hardness and storage modulus, the nanoparticles are Mg(OH)2, and/or silica (e.g., SiOx) nanoparticles. In an embodiment, the present invention provides compositions and methods wherein the nanoparticles are not encapsulated nanoparticles. The present invention includes, but is not limited to, compositions and methods wherein the nanoparticles are not encapsulated by one or more layers of polymer material
Compositions of this aspect of the invention provide a number of properties useful for a range of product applications. In an embodiment, for example, a wax containing composition of the present invention has a melting point temperature selected over the range of about 45 degrees Celsius to about 60 degrees Celsius. In an embodiment, for example, a wax containing composition of the present invention has a hardness selected over the range of 1.0 to 2.0 base HB (Brinell Hardness Test) 16/2 at 298K. The mechanical properties G′ and G″ were on both the order of magnitude of 10 to 100 Pa at temperatures above their melting points.
A significant benefit of compositions and methods of the present invention is that use of petroleum-based materials is reduced or entirely avoided. This aspect of the present invention is useful for reducing the toxicity of the present compositions and providing biodegradable compositions that are more environmentally safe than conventional petroleum-based materials. Further, the present compositions provide a renewable source of lubricants and waxes, as their vegetable oil derived components are themselves renewable. In an embodiment, for example, a composition of the present invention has less than about 10% by mass of a petroleum-derived chemical component, and preferably for some applications less than about 1% by mass of a petroleum-derived chemical component.
In another aspect, the present invention provides products and articles of manufacture comprising the compositions of the present invention. In an embodiment, for example, the present invention provides a nanoparticle modified wax, water in oil emulsion wax or spray wax comprising the present nanoparticle-containing compositions. In an embodiment, the present invention provides a candle, a coating wax, a polish for a vehicle, boat wax, a cosmetic wax, a pharmaceutical wax or a sealing wax comprising the present nanoparticle-containing compositions.
In another aspect, the present invention provides a method for enhancing at least one mechanical and/or optical property of a wax composition or a lubricant composition derived from one or more vegetable oils; the method comprising: (i) providing a synthetic wax derived from one or more vegetable oil or a synthetic lubricant derived from one or more vegetable oil; and (ii) dispersing in the synthetic wax or lubricant a plurality of nanoparticles thereby making the wax composition or the lubricant composition; the nanoparticles having an average cross-sectional dimension selected from the range of about 1 nanometers to about 100 nanometers; wherein the nanoparticles comprise between about 1% and about 50% by mass of the wax composition or the lubricant composition. Methods of this aspect of the present invention are useful for increasing the hardness, durability and/or solidity of a wax composition. Methods of this aspect of the present invention are useful for enhancing optical properties of a wax composition such as reflectance or extinction. Methods of this aspect of the present invention are useful for increasing the viscosity, thermal stability and/or shear stability of a lubricant composition. Optionally, in a method of the present invention the step of dispersing nanoparticles in the synthetic wax does not result in a decreasing the melting point of a synthetic wax.
In another aspect, the present invention provides a method for making a wax composition derived from one or more vegetable oils; the method comprising the steps of: (i) providing a synthetic wax derived from one or more vegetable oil; and (ii) dispersing in the synthetic wax a plurality of nanoparticles thereby making the wax composition; the nanoparticles having an average cross-sectional dimension selected from the range of about 1 nanometers to about 100 nanometers; wherein the nanoparticles comprise between about 1% and about 50% by mass of the wax composition, thereby making the wax composition derived from one or more vegetable oils.
In another aspect, the present invention provides a candle comprising: (i) a wax composition comprising synthetic wax derived from one or more vegetable oils; and a plurality of nanoparticles dispersed in the synthetic wax; the nanoparticles having an average cross-sectional dimension selected from the range of about 1 nanometer to about 100 nanometers; wherein the nanoparticles comprise between about 1% and about 50% by mass of the wax composition; and (ii) a wick disposed in the wax composition.
Table 1. Comparison of the viscosity deviation temperature to the pour point temperature of several pure vegetable oil systems.
Table 2. Comparison of the temperature of the G′ and G″ crossover to the pour point temperature of several vegetable oil systems.
Table 3. Comparison of the physical properties of the hydrocarbons added to vegetable oil systems.
Table 4. Comparison of the viscosity deviation temperature to the pour point temperature of soybean oil systems with hydrocarbon additives
Referring to the drawings, like numerals indicate like elements and the same number appearing in more than one drawing refers to the same element. In addition, hereinafter, the following definitions apply:
The expression “vegetable oil derived material” refers to one or more natural vegetable oils or a synthetic product derived from one or more natural vegetable oils.
The term “nanoparticle” refers to particles having an average cross-sectional dimension (e.g., diameter, thickness etc.) generally less than about 1,000 nanometers. In some embodiments, compositions of the present invention comprise nanoparticles having a cross-section dimension selected over the range of about 1 nanometer to about 100 nanometers, and preferably for some applications selected over the range of about 10 nanometer to about 50 nanometers.
The term “average cross-sectional dimension” in the context of the present methods and compositions refers to the average cross sectional dimension of a nanoparticle. For spherical and substantially spherical (deviations from absolutely spherical geometry of less than 10%) nanoparticles, the cross sectional dimension refers to the average diameter of the nanoparticle. For nonspherical nanoparticles, the cross section dimensional refers to the average length of the largest dimension of the particle.
The term “vegetable oil” refers to oils derived from plant materials. Vegetable oils useful in the materials of the present invention may be hydrogenated or nonhydrogenated. Vegetable oils in the present methods and compositions include, but are not limited to, soy bean oil; sunflower oil, corn oil, canola oil, castor oil, cottonseed oil, peanut oil, olive oil, sunflower oil, rapeseed oil, and safflower oil. An example of a vegetable oil useful in the present compositions and methods is soybean oil. Pure soybean oils typically have between 10-35% Oleic fatty acid with about 60-90% of the fatty acids being unsaturated.
The term “wax” refers to material that is typically solid and is firm but not brittle. Waxes are generally malleable. Waxes typically have a melting point above approximately 45° C. Waxes of the present invention may comprise one or more triglyceride components. A wax useful in a specific embodiment of the present invention is a 100% soybean oil in the wax without additives, wherein the wax has a melting point of about 122 F(50 degrees Celsius).
The expression “synthetic wax derived from one or more vegetable oils” refers to waxes that are generated by synthetic pathways involving one or more vegetable oils as starting materials, including hydrogenation. A opposed to “true waxes”, such synthetic waxes are not naturally occurring, but rather are synthesized using natural materials, such as vegetable oils, as starting materials, precursors and/or additives. In some embodiments, the base waxes derived from vegetable oils are formed by the use of hydrogenation.
The expression “triglyceride-based wax” refers to a wax that comprises one or more triacylglycerol compounds. In some embodiments, a triglyceride-based wax of the present invention has a triglyceride component that is at least 20% by mass of the composition. Preferably for some applications the triglyceride components of a wax of the present invention comprises a triglyceride component having a concentration selected over the range of 20% to 80% by mass, and more preferably for some application comprises a triglyceride component having a concentration selected over the range of 20% to 50% by mass.
The terms “triglyceride” and “triacylglycerol” are used synonymously in the present description and refer to glyceride in which the glycerol is esterified with three fatty acids. Triglycerides are a main constituent of vegetable oil and animal fats. Some triglycerides have the formula:
wherein R1, R2, and R3, are each independently substituted or unsubstituted aliphatic hydrocarbyl groups. Aliphatic hydrocarbon groups include alkyl groups and alkenyl groups have one or more double bonds. Substituted aliphatic hydrocarbyl groups include groups having one or more non hydrocarbon substituents, such as one or more hydroxyl groups, carbalkoxy group, alkoxy group, aldehyde group and/or alcohol group.
The term “hardness” refers to is the characteristic of a solid material expressing its resistance to permanent deformation. Hardness can be characterized by using the Brinell Hardness test method. This test can be implemented using a glass indenter of 16 mm diameter with an average 2 kg force applied. Hardness is calculated from the formulas associated with this test measurement and compared on the HB hardness scale.
The expression “mechanical stability” refers to the characteristic of the ability of a mechanical property such as G′ or G″ to remain constant for a given set of conditions over a broad range of temperatures.
The term “surfactant” refers to any chemical compound that reduces surface tension of a liquid when dissolved into it, or reduces interfacial tension between two liquids, or between a liquid and a solid.
As used herein, “nanosized” refers to features having at least one physical dimension (e.g. height, width, length, diameter etc.) ranging from a few nanometers to a micron, including in the range of tens of nanometers to hundreds of nanometers.
The term “viscosity” refers to a measure of a fluid's resistance to flow. It is often expressed in terms of the time required for a standard quantity of the fluid at a certain temperature to flow through an orifice of standard dimensions. The higher the value, the higher the viscosity. Viscosity is a variable which typically varies with temperature.
The present invention relates to the use of nanoparticles as additives to improve the physical characteristics of bio-based lubricants and waxes, such as lubricant and waxes derived from vegetable oils. Lubricants of the present invention comprising nanoparticle containing materials derived from vegetable oils exhibit enhanced lubrication properties at high and low temperatures, such as shear viscosities greater than similar vegetable oil-based materials not having a nanoparticle component. For example, upon incorporation of a nanoparticle phase, the shear viscosity of canola oil was doubled at ambient temperatures and increased an order of magnitude at very low temperatures as compared to pure canola oil. Waxes of the present invention comprising nanoparticle containing materials derived from vegetable oils exhibit enhanced mechanical properties, such as improved the rigidity, hardness and resistance of the wax. For example, the rigidity and resistance of soy wax was increased by an order of magnitude at high temperatures upon incorporation of a nanoparticle phase.
The effects of introducing nanoparticles into vegetable oils to form biodegradable lubricants and waxes is described. We show that the inclusion of nanoparticles in these systems significantly improves the physical properties critical for the desired applications of these materials.
In
The introduction of nanoparticles into vegetable oil based waxes of the present invention enhances the mechanical properties (
The results provided here demonstrate that the introduction of nanoparticles increases the viscosity and mechanical properties of vegetable oil based lubricants and waxes. These results indicate that the physical properties of these vegetable oil based systems can be tailored to the desired specifications by varying the composition and type of added nanoparticles.
Applications of the compositions and methods of the present invention include, but are not limited to, lubricants (engines particularly 2-stroke engines), Transformer oil, Greases (moving parts, bearings, chains, engines, hydraulics), Waxes (coatings, car polish, seals, food preparation, pharmaceuticals, cosmetics, candles) and Cutting fluids.
In an embodiment, a nanoparticle-containing wax of the present invention is made via the following method. Nanoparticles are first thermally processed to remove any volatile materials, including water and hydrocarbons. In an embodiment, for example, the nanoparticles are heated to a temperature of approximately 140 degrees Celsius or greater under vacuum conditions for a period of at least 48 hours. The nanoparticles are subsequently cooled to room temperature by lowering the temperature under vacuum conditions. The wax component (e.g., one or more waxes derived from vegetable oils) is provided and heated to a temperature above its melting point to provide a phase change in the wax component from solid to liquid. In an embodiment, for example, the wax is heated using a liquid temperature bath to a temperature selected over the range of 60 degrees Celsius to 80 degrees Celsius. The nanoparticles are added to the wax component in the liquid phase and mixed so as to distribute the nanoparticles throughout the liquid phase. In some embodiments, for example, mixing of the mixture of nanoparticles and liquefied wax(es) is achieved via stirring for a period greater than or equal to 2 hours at a temperature above the melting point of the wax(es). The temperature is then lowered to cause a phase change in the wax component from liquid to solid, thereby generating the nanoparticle-containing wax of the present invention.
In an embodiment, a nanoparticle-containing lubricant of the present invention is made via the following method. Similar to the description above relating to waxes of the present invention, the nanoparticles are first thermally processed to remove any volatile materials, including water and hydrocarbons. In an embodiment, for example, the nanoparticles are heated to a temperature of approximately 140 degrees Celsius or greater under vacuum conditions for a period of at least 48 hours. The nanoparticles are subsequently cooled to room temperature by lowering the temperature under vacuum conditions. The vegetable oil component (e.g., one or more vegetable oils) is provided in the liquid phase at room temperature. The nanoparticles are added to the vegetable oil component in the liquid phase and mixed so as to distribute the nanoparticles throughout the liquid phase. In some embodiments, for example, mixing is achieved via stirring the mixture of nanoparticles and vegetable oil(s) at room temperature for a period greater than or equal to 24 hours, thereby generating the nanoparticle-containing lubricant of the present invention.
Rheological measurements, including viscosity sweeps and small-amplitude oscillatory shearing, was used to characterize the pour point and low temperature behavior of vegetable oil-based lubricants. The shear viscosity of the oils at temperatures above the pour point followed a modified Andrade equation, however, at temperatures below the pour point the measured viscosity of the oils deviated from the fit. Oscillatory measurements of the storage (G′) and loss (G″) moduli also indicated a transition behavior at the pour point temperature of the oils. Vegetable oils at temperatures above the pour point had G′<G″ indicating that the oil was liquid-like, but at temperatures below the pour point had G′>G″ indicating that the oil was gel- or solid-like in nature. This type of crossover in G′ and G″ is often associated with sol-gel systems undergoing a gelation process. Gelation of the vegetable oil systems was further demonstrated by the frequency independence of the loss angle close to the pour point temperature. In addition, the influence of additives on the low temperature properties of the vegetable oils was characterized using the same rheological methodologies. Both organic straight chain hydrocarbons, ranging from hexane to eicosane, and inorganic silicon oxide nanoparticles were characterized as potential additives to pure vegetable oils. A blend of 1-decene and glycerol additives was found to be the most beneficial in creating a vegetable oil lubricant by depressing the pour point temperature (by ˜6° C.) and raising the oil viscosity (by more than a factor of 2).
Vegetable oils are a biodegradable, naturally occurring, and renewable resource that may in the near future replace petroleum-based products as lubricants for a wide range of applications [1-9]. Current limitations to the widespread use of vegetable oil lubricants primarily arise from their poor low temperature properties. The low temperature property of greatest significance is the pour point which characterizes the temperature at which the lubricant ceases to flow under the influence of gravity. Pour point temperatures are determined for all oils using a standardized ASTM test and equipment [10] that are difficult to replicate and that cannot easily be interpreted in terms of conventional thermophysical properties or measurement techniques.
Pure vegetable oils have pour points that are well above those of optimized petroleum-based products. For example, the vegetable oils of interest to this work, e.g. soybean, canola and corn oils, exhibit pour points in the neighborhood of −18° C. In contrast, pure petroleum-based oils have pour points ranging from 49° C. to −18° C. or lower, but commercial oil products when optimized with specially designed additives exhibit pour point temperatures less than −40° C. [11-12]. The most common pour point depressants in petroleum-based systems include poly(methyl methacrylate), polyacrylamides, Friedel-Crafts condensation products of chlorinated paraffin wax with naphthalene and phenol (often referred to as alkylaromatic polymers), and ethylene propylene olefins [12-13].
Pour point depressants similar to those used in petroleum-based lubricants are also of interest in vegetable oil systems. Due to the proprietary nature of many of these additives, the details and molecular-level understanding of these systems remains limited. Typical additives studied as pour point depressants in biodegradable lubricants include synthetic diesters and polyol esters, poly alpha olefins, polymethacrylate backbone branched polymers, and oleates [14]. Asaduaskas et al. [14] studied a number of pour point reducers and found that the addition of poly alpha olefins, mixtures of dimers and trimers of 1-decene, lead to the greatest reduction in the pour point temperatures of sunflower and soybean oils by 9° C. and 12° C., respectively. This work also noted that the addition of 0.4 wt. % 8000 amu poly(alkyl methacrylate) decreased the pour point temperatures of soybean oil and canola oil by 9° C. and 15° C., respectively [14]. Ming et al. [15] demonstrated that the addition of dihydroxy fatty acids reduced the pour point of palm oil-based systems by 7° C. These prior studies, however, have not characterized the effect of these additives on rheological properties. In crude oil-based systems the addition of pour point additives has been found to decrease the shear viscosity of the oil [16,17]. A comparable lowering of the viscosity of vegetable oil-based systems by the additives could potentially limit the applications for which they could function.
Here we begin by demonstrating that rheological characterization can determine the pour point of vegetable oils and that this temperature is associated with the gel formation of the oil. Next we consider the modification of the thermophysical properties of vegetable oils through the blending of pure oils with additives. We extend our current rheological study of vegetable oils to characterize the influence of various classes of additives, including both small molecule organics and inorganic nanoparticles, on the pour point behavior. Consequently, we have first considered additives that have chemical features similar to the chemical features of triglycerides, the main component of vegetable oils (see
Chemicals. All of the vegetable oils used in the study were obtained from the local market. The hydrocarbon additives used in this study include n-eicosane purchased from Alfa Aesar, 94% pure 1-decene purchased from Aldrich, 99% pure n-hexadecane and 99% pure decane purchased from Acros Chemicals, and 99+% pure n-octane and 98.5% hexane reagents purchased from Sigma. The 99.5% pure glycerol used was purchased from Sigma. All nanoparticles used in this study were purchased from Nanostructured & Amorphous Materials Inc. The 99.5% pure 10 nm silicon oxide (SiOx) had a reported specific surface area of 640 m2/g and the 99% pure 80 nm silicon oxide had a reported specific surface area of 440 m2/g. Both SiOx samples had similar reported bulk densities of 0.063 g/cm3 and true densities of 0.063-0.068 g/cm3.
Sample Preparation The SiOx nanoparticles were placed in a vacuum oven at 140° C. for at least 48 hours in order to remove residual water and then immediately mixed with the vegetable oils. All blended systems were stirred for at least 24 hours prior to characterization.
Rheological Measurements. The rheological characterization was performed on a Bohlin CVO 50 constant stress rheometer (Malvern Instruments Ltd., Worcestershire, UK) equipped in a parallel plate geometry. The temperature was controlled by a thermal bath from 20° C. to below −25° C. at constant cooling rates of 0.5 or 1° C./min. To eliminate the effect of ice formation at low temperatures, the samples were held under a nitrogen purge.
Differential Scanning Calorimetry. The DSC thermograms were obtained using a TA Instruments Q100 DSC (New Castle, Del.). The dehydrated samples were scanned from 60° C. to −60° C. (or the desired lower temperature) at 1, 5, or 10° C./min. Duplicate samples were measured and at least two scans were performed for each sample. All measurements were made using sealed aluminum hermetic pans with at least 8 mg of sample, and an empty pan was used as a reference. Data was analyzed using Universal Analysis.
Pour Point Measurements The pour point temperatures of the vegetable oil systems were measured following the specifications of ASTM D97 [10]. A pour point apparatus was constructed in house based on the requirements of the ASTM test. The samples were heated to 50° C. for half an hour prior to the pour point measurements in order to remove any thermal history of the sample.
Rheological characterization to determine the pour point temperature of vegetable oil-based systems was first demonstrated by measuring the shear viscosity versus temperature during controlled cooling sweeps from temperatures above the pour point to temperatures below the pour point (see
ln η=A+B/T+C/T2
In all of these tests, the shear viscosity of the fluid follows a modified Andrade fitting at temperatures above the pour point indicating that the oil is in a liquid-like state. As the temperature of the oils is decreased to the pour point, however, the viscosity behavior of the oils begins to deviate from this functional form. As can be seen in
Small-amplitude oscillatory shear measurements also have been used to characterize the pour point transitions of vegetable oils. Such measurements using temperature sweeps at a constant cooling rate were performed within the viscoelastic regime at a frequency of ω=1 Hz and a shear stress of 0.1 Pa. For each of the pure soybean, canola, and corn oil samples in
In a manner similar to that discussed previously for the shear viscosity measurements, at slow cooling rates the G′ and G″ crossover point occurs at a slightly lower temperature and leads to slightly higher moduli values. Again this result indicates that the slower cooling rates, and the resultant longer times near and at the pour point, enable a stronger gel to form due to molecular-level aggregation and structural arrangement. Gelation processes such as the pour point are time and temperature dependent, therefore, rheological characterizations should be performed at a rate similar to that defined in ASTM D97 in order to determine transition points that match the conventional pour point temperature. Analogous results have been observed in petroleum-based oils (see Table 2). Veneckatesan et al. [20] and Lopes de Silva et al. [21] have shown that the gelation point can be detected for crude oils using oscillatory measurements and that the determined gelation temperature is higher than the measured pour point temperature. Both of these studies, however, used slow cooling rates of 0.1 and 0.2° C./min [21], whereas Visinitin et al. [22] showed that the gelation temperature was similar to the pour point temperature at a faster cooling rate of 1° C./min and higher than the pour point for a slower cooling rate of 0.05° C./min.
The crossover of the G′ and G″ dynamic moduli is often considered a satisfactory characterization of gel behavior and the gelation temperature. This crossover point, however, is not a universal property of the gel point but has long been seen as an acceptable criterion for the characterization of the sol-gel transition [22, 27]. A more reliable and suitable rheological approach to determining gelation has been proposed by Chambon and Winter [28-31] and involves characterizing the frequency independence of the loss tangent. Under this criterion, the storage and loss moduli of the critical gel exhibit a power law scaling with frequency and at the gel point the loss angle is independent of the frequency such that
tan δ=tan(nπ/2)
where n is the relaxation exponent with 0<n<1. A gel is viscous if n is close to 1 and elastic if n is close to 0. Here we find that the loss angle for the vegetable oil-based systems behaves very similarly to what has been observed in branched polymers by Garcia-Franco et al. [27]. As shown in
Vegetable oil-based lubricants have several physical properties that limit their widespread use, namely poor low temperatures properties as quantified by high pour point temperatures and low viscosity values relative to petroleum-based lubricants. Understanding the rheological impact of adding pour point depressants to the vegetable oil-based systems, as well as the effect of molecular structure and chemical functionality on depressing the pour point temperature, will be very useful for the design of vegetable oil-based lubricants. As previously discussed, many studies that have considered the use of pour point depressants in vegetable oil-based lubricants have used pour point depressants that are effective in petroleum products. The chemical nature of petroleum oils, which are mixtures of hydrocarbons, and vegetable oils are very different. Vegetable oils are essentially mixtures of triglycerides, which can be described as having a glycerol head group to which three aliphatic chains are attached (see
Aliphatic, straight chain hydrocarbons ranging from 6 to 16 carbons in length (see Table 3) have been characterized as additives in vegetable oils due to their chemical similarity to the tails of triglycerides. These hydrocarbons were first considered as additives to soybean oil in concentrations of 5 wt. %.
The effect of hydrocarbon additives on the pour point temperature of oils is further illustrated in the DSC thermographs of
Glycerol, which has a chemical structure identical to the triglyceride headgroup, was added to the soybean oil in order to further understand the role of additives in the vegetable oil systems. The addition of glycerol increased the viscosity of pure soybean oil above the pour point temperature by approximately 30% to 50%, while the viscosity below the pour point temperature was more than twice that of the pure oil. The presence of the glycerol also increased the mechanical properties of the oil below the pour point temperature of the system by roughly doubling the G′ values and increasing the G″ values by an order of magnitude (see
The inclusion of multiple additives in vegetable oils has been considered as a route to imparting the oil with the favorable attributes of the independent additives. As demonstrated in the preceding sections, the addition of 1-decene tended to lower both the pour point temperature and the viscosity of soybean oil, while the addition of glycerol was observed to thicken the oil systems but did not change the pour point temperature. An ideal oil system would have the lower pour point temperature accessible with the 1-decene and the higher viscosity of the glycerol additive. Therefore, the behavior of additive mixtures of 5 wt. % 1-decene and varying concentrations of glycerol were experimentally studied in soybean oil. The viscosity of the system increased as the glycerol concentration was raised from 5 to 20 wt. % as shown in
Nanoparticle additives in vegetable oil systems have been studied as a promising approach for modifying the thermal, rheological, and mechanical behavior of the oil and for creating lubricants with suitable properties for widespread application. In the literature the primary focus on nanoparticle additives in lubricating systems has been as tribo-active additives, containing tribologically active elements (P, S, Cl, Zn, N) used to reduce wear, as well as, anticorrosion additives created from alkaline earth metal hydroxides [18, 32-38]. Nanoparticles have long been used to modify the physical properties of polymeric based systems. For example, small amounts of organically-modified layered silicates, or nanoclays, have been used as rheological modifiers in paints and inks. Such types of nanoparticles have also been added to lubricating oils as thickening agents to create non-melting greases for high temperature applications [18]. Numerous studies have shown that the thermal, e.g. the glass transition temperature, and physical, e.g. mechanical, properties of polymer nanocomposite materials can be controlled by the amount and type of nanoparticle used [39-43].
In this work silicon oxide (SiOx) nanoparticles were added in varying amounts to soybean, canola, and castor oil. The shear viscosity was first characterized as shown in
The addition of nanoparticles to vegetable oil systems also increased the mechanical properties of the oils as shown in
A comparison of the shear viscosity as a function of shear rate has been performed for the pure soybean oil and the soybean oil with 10 wt % 10 nm SiOx particles (see
In this Example we have applied rheological experiments in order to characterize and understand the pour point transition. By examining the change in the shear viscosity as a function of temperature while cooling from high temperatures to temperatures below the pour point, we have found that the viscosity behavior of the vegetable oil systems deviates at the pour point temperature. It was found for several different vegetable oils that a crossover of G′ and G″ occurred at the pour point temperature suggesting this transition is in fact a gel transition. Further investigation has shown the phase angle is frequency independent near the pour point temperature, thereby providing additional evidence that the pour point arises due to gelation of the triglyceride molecules. The addition of hydrocarbons can greatly influence the pour point by either increasing or decreasing the transition temperature depending on the melting temperature and molecular size of the additive. The experimental methods presented here can be used to characterize not only the pour point temperature of oil systems, but can simultaneously provide information about the critical physical properties of the lubricant including viscosity.
U.S. Pat. Nos. 6,797,020, issued Sep. 28, 2004, and 5,976,560, issued Nov. 2, 1999, relate to waxes derived from vegetable oils are hereby incorporated by reference in their entireties to the extent not inconsistent with the present description.
All references throughout this application, for example patent documents including issued or granted patents or equivalents; patent application publications; and non-patent literature documents or other source material; are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference, to the extent each reference is at least partially not inconsistent with the disclosure in this application (for example, a reference that is partially inconsistent is incorporated by reference except for the partially inconsistent portion of the reference).
The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.
When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, including any isomers, enantiomers, and diastereomers of the group members, are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. When a compound is described herein such that a particular isomer, enantiomer or diastereomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomers and enantiomer of the compound described individual or in any combination. Additionally, unless otherwise specified, all isotopic variants of compounds disclosed herein are intended to be encompassed by the disclosure. For example, it will be understood that any one or more hydrogens in a molecule disclosed can be replaced with deuterium or tritium. Isotopic variants of a molecule are generally useful as standards in assays for the molecule and in chemical and biological research related to the molecule or its use. Methods for making such isotopic variants are known in the art. Specific names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently.
Many of the molecules disclosed herein contain one or more ionizable groups [groups from which a proton can be removed (e.g., —COOH) or added (e.g., amines) or which can be quaternized (e.g., amines)]. All possible ionic forms of such molecules and salts thereof are intended to be included individually in the disclosure herein. With regard to salts of the compounds herein, one of ordinary skill in the art can select from among a wide variety of available counterions those that are appropriate for preparation of salts of this invention for a given application. In specific applications, the selection of a given anion or cation for preparation of a salt may result in increased or decreased solubility of that salt.
Every formulation or combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated.
Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.
All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art. For example, when composition of matter are claimed, it should be understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosure is provided in the references cited herein, are not intended to be included in the composition of matter claims herein.
As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms “comprising”, “consisting essentially of” and “consisting of” may be replaced with either of the other two terms. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.
One of ordinary skill in the art will appreciate that starting materials, biological materials, reagents, synthetic methods, purification methods, analytical methods, assay methods, and biological methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.
In the following description use of the term “about” when modifying a number or numerical range indicates a value that may vary by a small amount, for example, by 1 percent, 2 percent, 3 percent or 5 percent. Whenever a numerical range is specific with a lower limit (RL) and an upper limit (Ru), any value falling within the range is specifically disclosed, such as values as defined by the expression R=(RL)+k*(Ru−RL), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment (i.e., k=1%, 2%, 3% . . . 50%, 51% . . . 99% or 100%).
This invention was made with government support awarded by the following agencies: Department of Energy DE-FG02-97ER25308. The United States government has certain rights in the invention.
