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. tested on floors, launches, bow^s and Soybean oil-ester gum varnishes of arrow^s, and such. The coatings were 15- and 20-gallon oil lengths (gallons highly resistant to hot and cold w^ater, of oil to 100 pounds of resin), known acids, alkalies, gasoline, and alcohol. as short-oil varnishes in the trade, have Tested comparatively by outdoor been made by cooking ester gum and w-eathering, they proved to be more refined soybean oil for 3/2 hours at durable than tw^o high-grade com- 600° F. But the coatings from these mercial varnishes that contain tung oil. varnishes soften, or "aftertack," badly Similar varnishes were made with in hot, humid weather. Nevertheless, longer oil lengths, but their coatings the same varnishes, w^hen partly pig- did not dry so hard and w^ere less mented wdth small amounts of calcium resistant than the coatings of the 20- oxide, produce coatings that dry fast, gallon varnish. How^ever, the material hard, and flat, and are durable for costs for varnishes of long oil length interior use. are less, and they are easier to apply by The best soybean oil-ester gum var- brushing. Norelac is another type of nishes have been made from either the varnish that dries by solvent evapo- copolymer of tung and soybean oils, or ration instead of by oxidation and the polymers extracted from bodied polymerization. soybean oils, both of w^hich I have de- scribed. Other soybean oil-ester gum LITTLE SOYBEAN OIL was used in varnish coatings, which have good dry- paints until 1934, when some farmers' ing qualities and resistance to hot and cooperative organizations began to dis- cold water, acids, and alkalies, have tribute exterior paints that contained been made from some of the special small percentages of soybean oil and soybean oils, which are described later. were made by paint manufacturers 1930-1951 YEARBOOK OF AGRICULTURE in accordance with the formulas fur- Similar improvements have been nished by the cooperatives. Many of noted, not only w^hen zinc oxide was the paints were durable in service, but mixed with a single pigment or with a some became discolored because of dirt composite pigment, but also when the collection, a feature that prejudiced paints were made in accordance with many users against soybean-oil paints. either the prewar or the conseivation The excessive dirt collection was paint formulas. found to be caused partly by the slow- ness with which the oil dried and partly A BRIEF EXPLANATION of thosc for- by the pigment formulations used in mulas may be of value. The prewar the paints. Soybean-oil paints, espe- formulas used nearly all raw oil in the cially those containing sobean oil ex- liquid part of paint. The conservation clusively, when formulated with cer- formulas used equal volumes of raw tain pigments, produce coatings that oil, bodied oil, and paint thinner. They remain tacky for a long time after ap- were adopted early in the war to con- plication, a condition known as resid- serve the supply of drying oils. Because ual track. The coatings may tend to the paints made from them have soften and become practically liquid proved generally satisfactory in service, when applied in hot and humid I expect that they will be continued weather. That phenomenon is called with slight modifications. This type of aftcrtack. It is obvious that dirt col- paint presents greater possibilities for lected on a coating that has developed the utilization of soybean oil for several aflertack w^ould become so deeply im- reasons—the fast-drying copolymers of bedded that it could not be washed soybean oil and tung oil require thin- away without injuring the coating, ning before they can be utilized in while the dirt collected on a coating paints, and the slow drying of soybean with residual tack would be removed oil is partly compensated for by the use by the periodic self-cleaning of the of bodied soybean oil because smaller coating as it disintegrated into a pow- percentages of oil arc used in the con- der or chalk, which is usually readily servation of paints. washed off by rain. However, both re- Calcium oxide has improved the sidual and after tack can be eliminated drying quality and other qualities of almost completely from the coatings 100-percent soybean-oil paint coatings of paints that contain even a 100-per- to a greater extent than zinc oxide, ac- cent soybean-oil vehicle by including cording to results obtained when the zinc oxide or calcium oxide in the pig- coatings from outside white paints or ment components. red barn paints were tested compara- Zinc oxide, in amounts of 25 to 30 tively. For example, two comparable percent by w^eight in the pigment por- 100-percent soybean-oil paint coatings tion of 100-percent soybean-oil paints, varying only in their pigmentation— has been found to improve coatings ( 1 ) 75 percent basic carbonate white with respect to residual and after tack, lead and 25 percent zinc oxide; (2) 90 as well as chalking, checking, and percent basic carbonate white lead and cracking failures. Many paints have 10 percent calcium oxide—have dried been similarly formulated from various free from residual tack in 96 and 32 percentages of basic carbonate white days, respectively, as determined by lead ancl zinc oxide and either 100- fine sand falling ofi" completely from percent raw linseed-oil or 100-percent the surface of the coating. The coat- refined soybean-oil vehicles. The coat- ings from paints containing more than ings from these paints have given prac- 10 percent of calcium oxide in their tically equal results when tested com- pigments generally dn^ too hard and paratively by outdoor weathering for brittle for satisfactory service; the op- more than 7 years at Urbana and timum amount of calcium oxide is Peoria. approximately 5 percent. VARNISHES AND PAINTS FROM SOYBEANS 573 Besides residual tack, comparative of the performance of traffic paints outdoor weathering tests of the outside containing principally tung oil, a wa- white and red barn paint coatings terproof oil that dries fast and hard. containing 100-pcrccnt soybean-oil Outside white paint coatings that vehicles have proved that coatings con- contain the drying components of soy- taining 5 to 10 percent of calcium ox- bean oil obtained by the furfural-seg- ide are superior to similar coatings con- regation method have been tested for taining zinc oxide in such respects as durability by outdoor w^eathering in aftertack, color and reflection reten- Florida and Illinois. In comparison tion, and durability. In these tests, cal- with similar coatings which contained cium oxide coatings showed much less raw linseed oil, they were better in dry- dirt retention, yellowing, darkening, ing, equal in resistance to chalking, and cracking, and checking than zinc oxide definitely superior in resistance to dirt coatings. retention, checking, and cracking. The Soybean-oil paints have also been iodine values of the drying components improved in their drying qualities by of soybean oil and of the raw linseed the utilization of special oils that have oil were 170 and 181, respectively. been treated by chemical or physical Water paints that are satisfactory in methods. Besides the copolymers of service tests can be produced from soy- soybean and tung oils previously men- bean oil or from an alkyd varnish tioned, a number of others are obtained modified with soybean oil, by emulsify- by reacting soybean oil with the un- ing either of them in a mixture of soy- saturated organic compounds from the bean protein, water, borax, and w^ater- petroleum industry—styrene, buta- dispersible pigments, through the use diene, cyclopentadiene, terpenes, and of high-speed stirring methods. The vinyls. resin-emulsion paints, among them Another group of special oils is ob- several widely advertised ones, have tained by replacing the glycerol of soy- become popular for interior decorating, bean oil with pentaerythritol, sorbitol, not only because of their excellent hid- mannitol, and others. Excellent drying ing power in one coat, but also because oils are produced when soybean oil is they dry rapidly with a minimum of heated with maleic anhydride in vari- odor, possess good adherence, elastic- ous percentages to viscosities suitable ity, and durability, and have fair for use as either paint or varnish oils. resistance to washing. The large sales These oils are often reacted further volume of this type of paint has resulted with glycerol or pentaerythritol to neu- in the consumption of a large amount tralize the acids present and thus form of soybean oil. a harder drying oil of low acidity. Other methods for improving the SOYBEAN OIL has now won a definite drying qualities of soybean oil are foothold in the paint and varnish based on the separation of the drying industry. components from the nondrying com- The shortages and higher prices of ponents of the oil. Two of the methods the better drying oils have forced the are vacuum distillation and segrega- industry to look with more and more tion by furfural or liquid propane. Al- favor upon soybean oil. The develop- though expensive equipment is re- ment of special or treated oils with quired, good drying oils for paints and better drying properties has enabled also improved nondrying oils for edible paint manufacturers to use more or use are produced. less soybean oil in blends with other oils. Excellent traffic paints, which meet The development of the popular oil- all the specifications of a number of and resin-emulsion water paints has States, have been made from soybean made a market for a good deal of soy- oil treated with maleic anhydride. The bean oil. specifications were set up on the basis The progress now being made by the 574 50-1951 YEARBOOK OF AGRICULTURE paint and varnish industry in the use the drying and other qualities of the of less expensive oils, such as petroleum soybean-oil coatings. and tali, may prove a serious factor of competition to the continued use of A. J. LEWIS has been a research soybean oil and of its improved drying chemist in the Northern Regional Re- treatments must be kept competitive search Laboratory since 1942. He does with the cost of those oils as well as research on the use of soybean oil in wdth that of linseed, tung, dehydrated protective coatings. Previously he was castor, and other faster-drying oils. The a chemist at the National Bureau of use of small amounts of calcium oxide Standards, Franklin Automobile Co., or lime in pigment formulations ap- Norfolk Navy Yard and the United pears to be one method for lowering States Regional Soybean Industrial costs and at the same time improving Products Laboratory.

SYNTHETIC RUBBERS vary widely in their physical and chemical properties— so much so that scientists are constantly searching for new types for special uses. One of the new specialty rubbers is acryhc rubber, a material whose resistance to heat is so superior to that of most other rubbers that its higher cost is out- weighed by its longer life. It also has excellent resistance to lubricating oils. No other rubber has so good a combination of properties. The availability of such a rubber, in itself, stimulates further development. For example, machine de- signers are constantly striving to develop higher-powered and more compact motors, pumps, transmissions, and so on. Such equipment usually operates at higher temperatures, so that the lubrication problem becomes increasingly diffi- cult. Over-all performance may hinge on the heat and oil resistance of such items as the rubber in the oil seals, valve packings, diaphragms, or gaskets used. Lactic acid is one of the potential starting materials for making acrylic rubber. It may be recovered from whey, starch, molasses, and sulfite waste liquors and then converted to one of various acrylates used in making acrylic rubber. De- signers and manufacturers now are giving most attention to ethyl acrylate rubber. Both groups, however, hope to find one with even better properties, particularly improved flexibility at ~50^ F. Two other acrylates, butyl aciylate and octyl acrylate, offer the most promise in the direction of improved resistance to low temperatures. In the development of specialty rubbers, improvement in one property is often at the partial sacrifice of another. Such is the case in butyl aciylate and octyl acrylate rubbers. Improvement in flexibility at low temperatures is accompanied by a tendency to swell and soften in lubricating oils. Scientists of the Department of Agriculture have been investigating acrylic rubber obtained from lactic acid for several years. Recent developments indicate that butyl acrylate rubber oflcrs a suitable compromise between resistance to swelling by oils and flexibility at low^ temperature.—T. J. Dietz, Eastern Regional Research Laboratory,