American agriculture produces over 16 billion pounds of vegetable oils each year. These domestic oils are extracted from the seeds of soybean, corn, cotton, sunflower, flax, and rapeseed plants.
Although more than 12 billion pounds of these oils are used for food products such as shortenings, salad and cooking oils, and margarines, large quantities serve feed and industrial needs. The latter applications include chemicals such as plasticizers, which add pliability to plastics and other substances; stabilizers, which help other substances resist chemical change; emulsifiers, which enable the mixing of normally unmixable liquids; surfactants, which reduce the surface tension of liquids and are commonly used in detergents; and esters, nylons, and resins, which are basic ingredients in many industrial products. Besides detergents and plastics, products that contain chemicals derived from vegetable oils include lubricants, coatings, corrosion inhibitors, adhesives, cleaners, cosmetics, water repellants, and fuels.
The three domestic oils most widely used industrially are soybean, linseed from flax, and rapeseed. The relatively low cost of soybean oil and its dependable supply make it one of the more important oils; it provides nearly 80 percent of the seed oil produced annually in the United States. Other vegetable oils widely used industrially include palm, palm kernel, coconut, castor, and tung, but these are not of domestic origin.
Nonfood uses of vegetable oils have grown little during the past 30 years. Although some markets have expanded and new ones have been added, other markets have been lost to competitive petroleum products. Public and private researchers are seeking to develop new industrial products or commercial processes. Through these efforts, vegetable oils should maintain—or even add to—their market share while petroleum, which is nonrenewable, becomes more expensive.
Research and development approaches frequently take advantage of the natural physical or chemical properties of the oils or their major constituents—fatty acids and glycerol—but it is often advantageous to modify these properties for specific applications.
Vegetable oils are too viscous and too reactive with atmospheric oxygen to establish significant markets for use in cosmetics, lubricants, and certain chemical additives. Fortunately, properties such as viscosity, pour point, freezing point, and reactivity can be decreased by chemically introducing branching groups or side chains on the straight-chained fatty acids. For example, derivatives of isostearic acid, a byproduct of commercial dimer acid manufacture, can be used in many products—textile lubricants, softeners, and antistatic agents; coupling agents; emulsifiers; greases; and synthetic lubricants—for which the unmodified oil would be too reactive.
Conversely, to make certain products, vegetable oils must be made more reactive. By changing a domestic oil’s physical properties, it can be made to resemble—and replace—imported tung oil in coatings, resins, ink vehicles, and plastics.
Markets for these highly reactive oils are expected to grow with the increasing sophistication of consumers worldwide and with changing and more stringent product performance requirements.
Scientists at USDA’s Agricultural Research Service (ARS) pioneered much of the research that established industrial markets for vegetable oils. Most ARS research on industrial uses for fats and oils takes place at the National Center for Agricultural Utilization Research (NCAUR), Peoria, IL; the Eastern Regional Research Center (ERRC), Philadelphia, PA; and the Southern Regional Research Center (SRRC), New Orleans, LA.
Epoxidized Oils and Films
During World War II, ERRC scientists developed methods for converting vegetable oils to epoxidized oils, for use as plasticizers and stabilizers. Epoxidized oils are highly compatible with commercial resins, and they are nonvolatile. They are also effective stabilizers, thus eliminating the undesirable toxic stabilizers that were previously necessary. Out of the 300 million pounds of soybean oil used annually for industrial products, nearly 122 million pounds are converted to epoxidized oil. Other oils, mainly linseed, produce an additional 15 million pounds.
Linseed oil, containing about 60 percent linolenic acid, reacts rapidly with oxygen in air to form insoluble, flexible, adherent films which are used in paints and coatings. Although its use in paints has plateaued as a result of competition from other technologies, many paint formulations still contain linseed oil because of its superior adhesion characteristics. Also, NCAUR technology has demonstrated that formulations of linseed oil may be used to cure and protect concrete.
Rapeseed oil is principally useful as a source of erucic acid, a long-chain fatty acid consisting of 22 carbon atoms. Derivatives of erucic acid are used in the plastics industry as antiblocking or antistatic agents to make plastics less sticky and self-adhering and therefore easier to work with.
Research and development begun by NCAUR in the early 1940’s led to the commercial production and use of polyamide resins. Polyamides are prepared from dimer acids that have been derived from soybean and other vegetable oils and are used as hot-melt adhesives for shoe soles, book bindings, can-seam solders, and packaging. Production of dimer acids in the United States is about 40 million pounds per year; perhaps more than half of this is used for polyamides. Because polyamides have flexibility, adhesion, and resistance to chemicals and moisture, they are used in flexigraphic inks and moisture-proof coatings. Polyamides are also used to make drip- and sag-resistant paints that do not need stirring and that will not be absorbed into porous surfaces such as open-grained wood and cinderblocks. Two-part adhesives (epoxy resins and polyamide curing agents) are widely used today and are made from the polyamides developed from this ARS research.
Nylon 9, a product of NCAUR research, is a plastic made from oleic acid, a fatty acid found in most vegetable oils, including soybean, cottonseed, and sunflower. Because nylon 9 has a low moisture absorption rate, it does not warp and it is a better electrical insulator than nylon 6, a commonly used, and otherwise comparable, plastic derived from petroleum. Nylon 9 is slightly stronger than nylon 11 and nylon 12, two plastics which have properties similar to nylon 9. Because nylon 9 can withstand high temperatures, it has potential as an excellent material for making molded objects that will be subjected to large variations in air temperature, for example grills on automobiles. Its low rate of moisture absorption makes it ideal for products that require electrical and water resistance, for example insulators and water pumps.
Soybean Oil Inks
Soy inks, alternatives to conventional petrochemical-based inks, were developed by the American Newspaper Publishers Association (ANPA) and were first used in 1987 by the Cedar Rapids Gazette (IA). The ink from soybeans consists of about 50-60 percent degummed soybean oil, 20-25 percent petroleum resin, and 15-25 percent pigments. This ink has gained rapid acceptance by the newspaper industry. The colored inks are especially popular. Because the black inks formulated by the ANPA were not cost-competitive with typical offset news inks they are not widely used.
The technology for making soy inks consists of a direct substitution of soybean oil for the mineral oil portion of the vehicle (the entraining and dispersing agent for the pigments and other solid substances). Therefore, other oils that have a fatty acid composition similar to that of soybean oil should be directly interchangeable. In fact, some formulators have prepared inks from mixtures of soybean and corn oils. Economic considerations and marketing strategies govern the selection of the oils used in the formulation.
At the request of ANPA and the American Soybean Association, NCAUR recently developed a technology in which the vehicle is totally derived from vegetable oils. Although soybean oil was emphasized because of its dependable supply and low cost, this new technology was demonstrated with several commodity oils. Besides replacing petroleum, this technology permits formulation of inks over a broader range of viscosity as well as inks that are more cost-competitive with conventional offset news inks. Further, inks formulated with this technology have rub-off characteristics equal to those formulated and marketed as low rub-off inks.
Although petroleum products have been used in the past as dust suppressants, environmental considerations have virtually eliminated such practices. In the 1980’s, soybean oil was evaluated by ARS researchers and others for dust control in swine confinement operations and in grain elevators. Because vegetable oils are readily biodegradable and edible, they are ideally suited for this purpose.
Vegetable oils have potential as reliable and renewable sources of fuel for compression ignition engines (diesel)—a concept as old as the diesel engine itself. In fact, early engines were demonstrated running on peanut oil. Once cheap petroleum became readily available, the modern engine was designed to use petroleum fuel. Periodically, the alternative vegetable fuel concept has been reestablished, usually during petroleum shortages—and as petroleum shortages and prices eased, interest in alternatives again waned. Consequently, scientists do not yet understand how best to change the chemical and physical properties of vegetable oils to allow their trouble-free use as a fuel source. To fill this knowledge gap, NCAUR scientists are currently focusing on problems of high viscosity, low volatility, and incomplete combustion.
While evaluating vegtable oil fuels, NCAUR researchers have observed several characteristics that can restrict their use as motor fuels. These were grouped in two general categories, operation and durability. The former included ignition quality characteristics such as poor cold-engine startup, misfire, and ignition delay, and the latter included characteristics of incomplete combustion such as carbon buildup in the combustion cylinder and on the injectors, ring sticking, and lube oil dilution and degradation. In addition, the high viscosity of vegetable oil (more than 10 times that of number 2 diesel fuel) causes poor fuel atomization and inefficient mixing with air, further contributing to incomplete combustion. Because of their unsaturation, vegetable oils are more reactive than diesel fuel and are therefore much more susceptible to oxidative and thermal polymerization reactions that can interfere with combustion.
NCAUR researchers have been more successful in reducing viscosity than they have been in increasing volatility. Four approaches have been tried with varying degrees of success: (1) transesterification (reaction of vegetable oil to alcohols to give smaller molecules consisting of methyl, ethyl, or butyl esters), (2) dilution of vegetable oils with petroleum distillates, including diesel fuel, (3) pyrolysis (using heat to break chemical bonds and form new compounds of greater volatility), and (4) micro-emulsification (making heterogeneous mixtures like oil and water become a stable, homogeneous solution).
Fuels produced by each technique have been tested in engines. However, those prepared by approaches (1), (2), and (4) have received the most attention and the more rigorous engine tests. All of the techniques have provided encouraging results, and the transesterification and dilution technologies have achieved some commercial success. In Brazil, fuels developed by dilution may be used under some very specific conditions without loss of engine warranty. Warranties on some vehicles operated on esters are also honored in South Africa and parts of Europe. The oils used are those most readily available in the individual areas—soybean oil in Brazil, sunflower oil in South Africa, and rapeseed oil in Europe. NCAUR efforts are continuing to further develop the technologies and improve the combustion, cold-temperature tolerance, and cost-effectiveness of vegetable oils.
ARS continues in its commitment to identify and develop new nonfood uses of agricultural materials, including new uses for vegetable oils. This commitment was first made in 1938, when Congress established the four Regional Research Centers. Since then, an abundant supply of seeds from oil crops has been the driving force in encouraging research on new uses and technologies for vegetable oils and their derivatives. A major objective of such research is to expand the markets for domestic vegetable oils by producing products that use them instead of imported oils.
Discovery of economically competitive processes for converting oils to shorter chained fatty acids or more highly unsaturated or hydroxy fatty acids would markedly broaden the spectrum of specialty chemicals that can be made from U.S. agricultural surpluses. The possibilities for developing new technologies and products for plant oils are diverse and awaiting discovery.