MILKWEED SEED OIL Potential Value in Protective Coatings The seeds of the common milkweed are obtained as byproducts in the production of milkweed floss. These seeds contain about 22% oil which can be readily refined to a very pale color. The physical and chemical characteristics of the oil are reported. On the basis of its fatty acid composition, the oil may be classified as semidrying. In the field of protective coatings, the most promising application is in the preparation of oil-modified alkyd resins. Several long-oil and medium-oil length alkyds were prepared from milkweed seed oil,and were compared with the corresponding alkyds made with soybean oil in both pigmented and unpigmented coatings. The milkweed seed oil alkyds possess superior color retention and flexibility, although they are only slightly slower in drying than the corresponding soybean oil alkyds.
T
HE common milkweed plant, Asclepias svriaca, has been
the subject of limited investigation in this country. Rheineck in 1933 (’7) made a phytochemical study of the whole plant; several years previously Gerhardt (8) had briefly considered some of its commercial possibilities. Technologically this plant offers several materials of importance. The rubber and resin component has created considerable interest and recently became the subject of technological study (8). The stem of the plant contains a bast fiber with valuable properties, and i t has been proposed for commercial use. Gerhardt suggested that the floss and oil from the seeds might be of commercial value, but before the war the over-all economic and agricultural picture was not favorable for the establishment of any significant milkweed industry in this country. However, as a result of the stoppage of kapok imports from the East Indies, the seed hairs or milkweed floss has become of great technical importance. The floss, the air-borne carrier of the seed, is used extensively today in life preservers and fliers’ jackets, and recent tests have indicated its superiority over kapok. Although the plant is perennial and grows wild in many sections of the United States and Canada, a large amount is being cultivated t o satisfy the great demand for the floss. The plant is hardy and requires little attention after the first year of cultivation, and its growth is valuable in preventing soil erosion. Collection of the pods is being sponsored in twenty-six states by the Federal Government, and a plant has been built by the Defense Plant Corporation to separate the floss from the seeds. The present yield from cultivated milkweed plant is 300-400 pounds of floss per acre, Recent experiments indicate that the yield can be doubled by proper selection and cross breeding. The 1944 quota calls for 1,500,000 pounds of floss, fifteen times the 1943 production. From this quantity of floss 3,000,000 pounds each of seeds and pod shells will remain in addition to leaves. At present these materials are, in effect, waste products, and the introduction of milkweed cultivation in our permanent agricultural economy depends upon finding uses for them. Accordingly, a program of research was begun during the past year in this laboratory t o study the constituents of the seeds and to indicate their commercial possibilities. This report is concerned only with the oil component and its possible utilization in protective coatings. 1
HERMAN J. LANSONl, .DAVID HABIB, AND P. E. SPOERRI Polytechnic Institute of Brooklyn, N. Y .
The seeds of the milkweed plant are rather flat and circular in shape with a diameter of about ‘/P inch. They were freed from foreign matter and ground t o about 50 mesh in a Quaker mill. The oil was extracted with chloroform i n a large Soxhlet apparatus having a capacity of 1 kg. of ground seeds. The oil was freed of solvent by distillation, the final traces being removed in vacuo while a fine stream of nitrogen gas was passed through the oil. A 221-gram yield of brown colored oil, representing 22.1% of the weight of the seeds, was obtained. The physical and chemical constants of the freshly extracted oil are shown in Table I. The methods of the American Oil Chemists Society (1) were followed in determining the acid, saponification, iodine, ReichertMeissl, and Polenske values. The unsaponifiable matter was determined by the modified Kerr-Sorber method (4) and the acetyl value by a modification of the West, Hoagland, and Curtis method (8). A portion of the oil was saponified, and the unsaponifiable matter removed by repeated extraction of the soap solution with ethyl ether. The fatty acids were recovered in the usual manner by acidification. The iodine value (129.4) and thiocyanogen value (89.8) of the mixed acids were determined by the A.O.C.S. official methods. The following fatty acid composition was calculated by the empirical thiocyanogen values of Kass et al. (6): Linoleic acid Oleic acid Saturated acids
46.8% 60.1 3.3
On standing, mucilaginous matter separated from the oil; rapid heating of a portion of the supernatant oil to 600’ F. gave a separation of “break”. The oil was alkali-refined by the A.O.C.S. method for hydraulic-pressed soybean oil. The rcsulb ing oil, after treatment with fuller’s earth and decolorizing carbon, was limpid and very pale. Several analytical constants u ere determined t o be as follows: Iodine value Saponifioation value Acid value Refractive index, n g
122.3 190.4 0.38 1.4722
Unsaponifiable-free mixed fatty acids from this refined oil were obtained by the following procedure which eliminated the formation of troublesome emulsione usually formed in the conventional extraction of the soap solutions with ether: To 25 grams of the oil in a 2-liter Erlenmeyer flask, 25 ml. of 95% ethyl alcohol were added, The flask was placed in a boiling water bath for several minutes, and 10 cc. of concentrated potassium hydroxide solution (100grams KOH in 100 ml. water) was added dropwise from a pipet. After further heating in the bath for 5 minutes, the flask was removed and 125 ml. of ethyl alcohol were added. Ethyl ether (250 ml.) was added, and the contents of the flask well mixed. The resulting clear solution was transferred to a 2-liter separatory funnel, and 500 ml. of 0.2 N KOH solution added in a. slow steady stream. The funnel was rotated gently and allowed to stand 10 minutes. The soap solution was withdrawn, 100 ml. of 0.2 N KOH solution was added to the ether layer, and the funnel was gently rotated as previously.
Present address, Crown 011Produots Corporation, Long IeIand City,
N.Y . 179
INDUSTRIAL AND ENGINEERING CHEMISTRY
180
TABLEI. PHYSICAL AND CHEMICAL CHARACTERISTICS OF UNREFINED MILKWEED SEEDOIL Density, df! Refractive index, ng Viscosity (25' C.), poise Hedine value Saponification value Acid value
0.9221 1.4730 0.5 122.8 191.9 11.0
Acetyl value Reichert-Meissl value Polenske value Unsa onifiable matter, % Hexagromide value
12.9 0.2 0.0
2.63 0.0
TABLE 11. DATAON 52-R-13 LONGOILALKYDS Acid value Viscosity (70% in mineral spirits) Color (Hellige) Phthalic anhydride, % Dust-free time Tack-free time
Soybean Oil 7.4 Z 3 24.0 80 min. 6 hr.
Milkweed Seed Oil 7.1
52-R-13 Specification 6.7-10
4 24.0 120 min. 73/4 hr.
4 (max.) 2 3 . 0 (rnin.)
