Varnishes and Paints From its use no longer depends entirely on fluctuations in the price and supply of linseed oil. Soybeans SOYBEANS GENERALLY contain only about 20 percent of oil ; the linseed oil A, J. Lewis in flax amounts to 38 percent. Almost all the oil is processed by one of three methods—solvent extraction, continuous pressing, or hydraulic press- ing. The first method is preferred be- The use of soybean oil in paints and cause it produces an oil that is lighter varnishes is largely an American de- in color and almost free from foreign velopment and a new one. For more material and a meal that is practically than a century the soybean oil we im- free from oil and well suited, therefore, ported was used for food. Even as late for use in water paints,' plastics, and as 1909, soybean oil was practically un- glues. known as a paint oil. At that time, Soybean oil obtained by any of these how^ever, some chemists advocated the methods is considered as crude oil, development of varieties of soybeans which must subsequently be refined by that would produce superior drying one of three methods. Mechanical re- oils, which, they believed, would sta- fining consists of emulsifying the oil bilize the price of linseed oil. with hot water or steam and then When soybeans started their climb centrifuging out the foreign material. to become the leading oil crop in this Acid refining consists of treating the country, they found favor first as a hay oil with strong sulfuric acid, which crop, then as a source of edible oils, chars the foreign material but not the and finally as a source of drying oils. oil, if handled properly. Alkali refining The climb was swift. The paint and var- consists of emulsifying the oil at room nish industry used 8.5 million pounds temperature with a solution containing of soybean oil in 1933 and 150 million a slight excess of alkali over that re- pounds in 1949. Other drying-oil in- quired for neutralizing the free fatty dustries used another 100 million acids of the oil. pounds to make floor coverings, print- The oil obtained by mechanical or ing inks, and many other items. The acid refining difl'ers from that obtained use of soybean oil as a drying oil has by alkali refining in that the free fatty thus kept pace with the phenomenal acids retained in the oil serve as pig- rise in production of soybeans. ment-whetting agents and make the Even though the 150 million pounds paint easier to grind. The oil obtained of soybean oil used in paints and var- from alkali refining, because of its light nishes represents only 11 percent of the color, is preferred for making oil-modi- total oil produced in 1949, it is 4 per- fied alkyd varnishes, especially those cent more than the amount used in intended for white enamels. However, 1948 and 57 percent more than the the oils obtained from any of the re- total used from 1943 through 1946. fining methods are suitable for pro- The figures indicate that soybean oil tective coatings if they conform to the now has attained a definite place in the requirements of Federal Specification paint and varnish industry, and that JJJ-O-348 for refined soybean oil. 569 570 1950-19 5 1 YEARBOOK OF AGRICULTURE This specification sets standards for been mixed with tung oil in proportions specific gravity, iodine number, saponi- of 70 parts to 30 parts by weight and fication number, loss on heating at heated to 550° F. to make a processed 105° C, unsaponifiable matter per- oil with better drying qualities than centage of foreign material, and acid linseed oil. This processed oil, known number. as a copolymerized oil, can be cooked Besides those requirements, the oil wdth ester gum and other inexpensive must be clear and free from sediment resins to make high-grade varnishes. and suspended matter when examined The polymers of high-viscosity bodied by transmitted light at 65° C. (149° soybean oil are insoluble in acetone and F. ). Its color must not be darker than can be readily separated from the un- that of a solution of 0.38 gram of re- polymerized portion for use in making agent potassium dichromate in 100 good soybean oil-ester gum varnishes. milliliters of sulfuric acid of specific gravity of 1.84, equivalent to the No. SOYBEAN OIL GAINED POPULARITY in 12 tube of the Gardner color scale the varnish industry in the Second (1933). World War when supplies of tung oil were short. Tung oil had been popular A BODIED OIL is one that has been since early in the First World War. Be- heated at high temperatures to "body," fore then, most varnishes w^ere made or thicken, it to a siruplike consistency from linseed oil and natural resins. The by the formation of polymers, which coatings from these varnishes dried too result when molecules combine with slowly to meet the demand for fast pro- one another. The soybean oil used for duction of armaments and w^ar equip- kettle bodying must be free from for- ment. Soon a new type of varnish, Val- eign, or break, material and should spar, appeared. It was made from ester have a high iodine number. The iodine gum (a resin obtained by neutralizing number denotes the amount of iodine rosin acids wdth glycerol), tung oil, that is absorbed by the oil molecules and mineral spirits. It, and others like and is the measure of the degree of un- it, dried rapidly, were waterproof, and saturation, or capacity of the oil to oxi- made excellent grinding materials for dize and to polymerize. Soybean oil paints and hard-drying enamels. that has an iodine number of 130 takes Oil-modified alkyd varnishes, gen- twice as long to body to a certain vis- erally called alkyds, are made commer- cosity as linseed oil with an iodine cially in closed vacuum kettles. The number of 175 when heated at the process usually consists of heating and same temperature. The time required reacting a dibasic acid, such as phthalic for bodying soybean oil can be reduced anhydride, and a polyhydroxy alcohol, by heating the oil to as high a tempera- such as glycerol, with the fatty acids of ture as possible without creating a fire vegetable, animal, or marine oils. The hazard or by using high vacuum. Also, oils serve as plasticizers and are re- a number of chemicals, such as ß- quired because the resin produced by methylanthraquinone, phenanthrene, the reaction of the acid and alcohol is and diphcnylcarboxyanthracene, have too brittle for use in surface coatings been used successfully to accelerate the without modification. A unique char- bodying of oils without injuring their acteristic of alkyds is that the plasticizer quality. becomes a part of the resin by chem- Bodied soybean oils have been used ical combination rather than by phys- to replace all or part of the oil vehicle ical admixture. The first alkyds, known of interior and exterior paints with as glyptals, utilized only the fatty acids some success in drying and in durabil- of hnseed oil, but in the early 1930's ity. Bodied soybean oil that has a vis- small amounts of soybean fatty acids cosity of approximately 5 poises (simi- began to be used in blends with linseed lar to a very heavy lubricating oil) has fatty acids. The production of alkyd VARNISHES AND PAINTS FROM SOYBEANS 571 varnishes increased rapidly because The hardest and most durable var- they could be produced economically nishes have been those made from an and were outstanding for adhesion, oil-reactive, unmodified phenolic resin toughness, durability, flexibility, and and soybean oil. The varnishes were hardness. Also, they could be produced made by heating 20 gallons of refined in large volumes in single closed ket- soybean oil and 100 pounds of phenolic tles, required little supei^dsion, and resin (Bakelite resin No. 254) together utilized the oils then available. in a stainless-steel open kettle at 600° The use of soybean fatty acids has F. until bodied sufficiently to give a 5- been favored for alkyds because of their inch string when a few drops were availability and low linolenic acid con- tested on a cold plate. tent. The low^ acid content enables the The cook was then removed from the manufacturer to produce white and heat, allowed to cool to 200° F., and light-tinted enamel coatings that do thinned wdth 24 gallons of mineral not yellow^ appreciably when applied spirits follow^ed by 5 gallons of toluene. to refrigerators, automobiles, and the Cobalt driers of the naphthenate type like. Although the slow-drying prop- containing 6 percent cobalt metal w^erc erties of soybean acids limited their use added at room temperature and three- in the alkyd field for a long time, im- eighths of a gallon of drier gave satis- proved methods for the forced drying factory drying qualities to the coatings. of coatings by heat ( especially infrared The time of bodying at 600° F. to a lamps) have greatly helped to over- 5-inch string w^as approximately an come this limitation. An increasing hour; the speed of bodying depended number of manufacturers now produce on the use of an oil-reactive resin. alkyds containing 100 percent soybean Phenolic varnishes made by this for- acids. It is likely that half or more of mula and procedure dried rapidly over- the soybean oil used in protective coat- night to hard, glossy coatings, which ings is being used in making alkyd wxTe durable and mar proof when varnishes.