COTTONWAX.. Properties and. Constituents
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N fibers are coated with a thin layer of waxy organic material which is present to the extent of only a fraction of 1% of the weight of the cotton. This substance, called "cotton wax", has a consistency similar to that of beeswax, has a characteristic bad odor, and is dark greenish-brown in color. Numerous research workers (1, 2, 4-9, 14, 19) have investigated the constituents of the wax and found it to consist mainly of gossypol and montanyl alcohols, small amounts of other alcohols, glycols, glycerol, sitosterol, a- and 8-amyrin, lupeol, hydrocarbons, palmitic, stearic, and carnaubic acids, small amounts' of gossypic, montanic, and oleic acids, and unidentified resinous substances. Palmitic, stearic, oleic, and melissic acids occur as esters only; palmitic, stearic, and oleic acids are also present :s glycerides. Carnaubic and montanic acids, in the light of more recent terminology, are actually mixtures of several acids. Previous investigators were handicapped by the small amount of wax present on the bulky cotton and, consequently, had difficulty in working with large quantities of cotton to obtain workable quantities of cotton wax. Samples of 330 and 750 grams, respectively, have been investigated (6, 9). Because of the nature of the w&x and the difficulties encountered, previous analytical work has included only qualitative reports on the individual constituents present and incomplete data on the characterizing constants. The wax for this investigation was obtained as a by-product of a pilot plant operation in which 100-pound batches of Texas cotton fiber were extracted with hot benzene. The wax is present to the extent of 0.2 to 0.7% of the weight of the fiber, so that approximately 25 pounds of wax were recovered from the 10 bales of cotton extracted in the pilot plant. The benzene solution of the crude wax was filtered through a wire mesh screen t o remove stray fibers, leaf particles, stems, hull fragments, and sand, and was blended with the wax solutions from other extractions. The solvent was then evaporated t o obtain a homogeneous representative sample of wax which was used for all investigations. The wax had a dark greenish-brown color and a characteristic disagreeable odor. To ensure complete removal of the wax from the fiber, the use of numerous solvents was studied, such as diethyl ether, benzene, toluene, xylene, petroleum hydrocarbon solvents (Skelly solvents), chloroform, and carbon tetrachloride. All gave complete r e m o h of the wax from the fiber.
University of Texas, Austin, Texas
The saponification value was found by the standard procedure on 3-gram samples dissolved in 10 ml. of toluene and refluxed for 8 hours with 0.5 N potassium hydroxide. A blank was run, and corrections were made accordingly in calculating the saponification value. If n-propane01 is used as solvent for potassium hydroxide instead of ethanol, the saponification time can be reduced from 8 to 2 hours witK no loss in accuracy. The acid value was determined on triplicate samples of cotton wax, which were dissolved in 50-ml. portions of hot isoamyl alcohol and titrated with 0.5 N alcoholic potassium hydroxide using phenolphthalein as the indicator. A blank was also necessary. The esker value is the numerical difference between the sapomfication and acid values. It indicates the degree to which the fatty acids present are combined as esters. The iodine number is a measure of unsaturation and is expressed in terms of grams of 1; per gram of wax. Huhl's method (17) was followed. The acetyl value is a measure of the alcoholic hydroxylic groupings of one gram of wax. It is expressed as the number of milligrams of potassium hydroxide required to neutralize the acetic acid liberated from the hydrolysis of one gram of acetylated fat or wax. The procedure given Hilditch (12) was followed. The percentage of unsaponifiable matter and mixed fatty acids was determined in the same analysis. Twenty grams of wax were dissolved in 100 ml. of benzene and saponified with 750 ml. of 0.5 N potassium hydroxide. After refluxing 12 hours, 350 ml. of alcoholic calcium chloride (40 grams per 500 ml. .of ethanol) were added, and refluxing was continued for another 2 hours. Completeness of the reaction was checked by adding a drop of sodium oxalate solution to test for excess calcium chloride which should be present. The insoluble soap mixture was then extracted with hot ethanol in a Soxhlet extractor followed by hot acetone and ethyl ether. The solvent extractables were collected, the solvent was evaporated and any alkalinity present was neutralized with sodium bicarbonate, washed thoroughly, dried, and weighed. The washing was accomplished by heating with boiling water; the alcohols, being insoluble, rise to the surface as a separate liquid layer which can be removed as a cake after they have cooled and hardened. Since the alcohols have a strong tendency t o form emulsions, they can be dried by redissolving in benzene, followed by evaporating the solvent. The calcium soaps were refluxed with 20% hydrochloric acid and cooled, and the cake of mixed acids was removed from the surface of the liquid. The acids were washed with boiling water, dried, and weighed. The difference between the weight of original sample and the sum of acids and unsaponifiables was reported as insolubles or inert matter.
PHYSICAL CONSTANTS
The physical constants determined on cotton wax include those customarily reported for waxes and are listed in Table I. The melting point of the wax was determined according t o the following procedure: The lower 12 mm. of a 5-cm. glass tube, 7 mm. in diameter, was filled with molten wax which was then allowed t o cool and solidify. The tube was attached with a rubber band t o a calibrated thermometer and placed in a n agitated water bath so that the lower part of tube extended to a depth of 4 cm. below the surface of the liquid. The water was heated and, after thermometer corrections had been applied, the temperature at which the wax plug moved up in the tube was recorded as the melting point. Specific gravity was determined by the conventional manner of weighing the wax sample in air and in distilled water at 15 O C. 1
W. H. TO", JR.', ANI) E. P. SCHOCH
TABLE I. PROPERTIES OF COTTON WAX Melting point C. Specific gr?vi$y, 15/15' C. Sauonification value. mn. KOH/gram
68-71 0.959 70.6 32.0 38.6 73.1 24.5 25 69
100 0
Present address, Massachusetts Institute of Technology. Cambridge,
Mass.
413
414
INDUSTRIAL AND ENGINEERING CHEMISTRY
The Hehner value was obtained by the commercial method described by Hilditch (11). The Reichert-Meissl value \?-as determined by the usual distillation procedure (16).
Vol. 38, No. 4
TABLE 11. C l o v r o s ~ v ~OFo ~COTTOSWAX Fatty acids Saturated Unsaturated Unssponifiahle matter
:4
Sterols Hydrocarbons Inert matter
The wax was saponified with alcoholic potassium hydroxide The acids were precipitated as calcium salts, extracted, etc., by a method similar to that described for determining fatty acids and unsaponifiables. The diff erence was that 200-gram samples in triplicate were employed, and the amounts of all reagents were increased proportionally. The fatty acids, which n e r e recovered from their calcium salts by treatment with 20Y0 hydrochloric acid, were collected on the surface as a liquid, cooled, removed, washed, dried, and weighed. The cake was black in color and very hard and brittle in texture. The melting point, acid value, saponification value, and mean molecular weight (calculated by dividing 56.1 by the grams of potassium hydroxide required t o neutralize 1 gram of fatty acid mixture) of the fraction were determined to gather some knowledge as to the properties and constitution of the fatty acids and to the completeness of separation. The acids were separated into saturated and unsaturated frartions by taking advantage of the difference in solubility of metalsalts of fatty acids in organic solvents (10). The mixed fatty acids were converted to the lead salts according to the method given by Hilditch (13, 18) and extracted with slightly warm diethyl ether. The ether solution was evaporated, and the acid was recovered by regeneration with 20% hydrochloric acid, dried, and weighed. The insoluble lead salts were treated similarly. The unsaponifiable extract, consisting mainly of alcohols. sterols, and hydrocarbons, was separated into two portions. One contained the hydrocarbons, which were isolated and weighed according to Leys' method (15) employing isoamyl alcohol and fuming hydrochloric acid. The other, the alcohol and sterol portion, was further separated by the method described by Cochenhausen (31to give a quantitative measure of the amounts of sterols and alcohols present. This procedure employs concentrated sulfuric acid and extraction with petroleum ether and absolute ethyl alcohol to separate the sterols and alcohols via alkyl sulfate formation of the alcohol portion. The unaccounted for portion of the wax is recorded as insoluhles or inert matter; it includes any water-soluble glycols and glycerol obtained in the saponification and also the inherent experimc.nta1 errors accompanying an analysis of this type. Table I1 gives the proximate analysis of the m-ax, and Table, I11 shows the properties of the individual components separated.
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DECOLORIZATION
The dark color of cotton wax, which makes it unnuitable for some industrial purposes, can be reduced and in some instances completely removed. The resulting decolorized wax ranged in color from a faint yellow through lemon yellow to a light orange, depending on the method employed. Among the substances xhich removed the objectionable dark color were activated carbon, fuller's earth, and combinations of the two. The wax can be treated either in the molten state a t elevated temperature or in solvent iolution; the latter gives better results. The degree of decolorization JTaq proportional, but not linearly, to the amount of agent used. Several successive small dosage treatments mere much more efficient than a single large dose and gave a final product of better color. The length of contact time for the agent and the wax was not critical. Absorption was almost instantaneous so that the detention period required was only a few minutes. The degree of decolorization finally obtained a t equilibrium conditions increased xith temperature.
2570 ti9
Alcohols
CHEMICAL ANALYSIS
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52 in
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TABLE111. PROPERTIES O F ACIDS,.4LCOHOLS, RYDROCARBOXS IS COTTON \F7ax Melting Point,
c.
Fatty acids
Alcohols Hydrocarbons
Boiling Pomt,
c.
84
..,..
61 68
26413iO
ANI)
1Ig. K O H / G r a m & I Saponifica- \lol. Tlon value Weight
Arid
value
132.0 0 0
132.0 0 0
425
... ...
I n removing the color, activated carbon and fuller's earth removed some of the fatty acids, as shown by lower acid and saponification values for the decolorized wax (14.9 and 40.1 mg. potassium hydroxide per gram of wax, respectively) ; but no change of melting point (70 O C.) occurred. The highest efficiency in color removal obtained in any case was 97.570. Numerous chemicals have been used to bleach waxes; among them are chlorine, hydrogen peroxide, sodium metal, calcium hypochlorite, nitric acid, sodium chromate, potassium permanganate, benzoyl peroxide, sodium peroxide, and magnanese dioxide. All of these were tried in concentrations varying from 1 to 2070, with the wax a t temperatures varying from room to 100" C.; however, only calcium hypochlorite, chlorine, and hydrogen peroxide provided any bleaching action. Basic bleaching agents such as sodium peroxide could not be used because they saponified the \=,-ax. Pon-erful oxidizing agents like potassium dichromate in dilute acid or acidified potassium permangante, when used in concentrations in excess of jm0, carbonized the wax. Combinations of bleaching and treatment with activated carbon also gave decolorization. Xonr of these treatments alter the melting point of the m x . SLM\I4Rl
Cotton xax is medium high melting, compared t o other vegetable w a x r ~ ~It . differs from most commercial waxes in that it is not predominantly an ester, but contains smaller amounts of fatty acids and larger amounts of free alchols as shown by high acetyl value and percentage unsaponifiables. The v a x is not hard and brittle a t room temperature but has a consistency comparable to that of beeswax; its dark color and obnoxious odor can be removed by decolorizing and bleaching agents. The mean molecular weight of the fatty acids portion indicates that the preponderance of acids present may be cerotic and melissic. The wax blends well Tvith other natural waxes and resins and has been formulated into pastes and emulsion polishes, lubricants, leather dressings, waterproof preparations, crayons, paints, paper auxiliaries, adhesivei, etr., individually and as blends with other waxes. IF7heneverrequirements demand a wax of medium-high melting point, qualifications generally filled by a vegetable wax, cotton wax should be satisfartory. LITERATURE CITED
Clifford, P. H., a n d P r o b e r t , M . E., J . Textile I n s t . . 15, T337 (1925) Clifford. P. H., a n d P r o b e r t , M . E.. Shirley I n s t . Ifem..3, 169 (1924). Cochenhausen, E., J . SOC.Chem. Ind., 1 3 9 , 4 4 7 (1897). F a r g h e r , 1%. G., a n d Higgenbotham. L., .I. Teztile Inst., 15, T75-80 [ 1924). Ibid.. 15, T120-37 (1924).
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April, 1946 (6) (7) (8) (9) (10) (11)
INDUSTRIAL AND ENGINEERING CHEMISTRY
Fargher, R. G . , and Probert, M. E., Ibid., 14, T49-65 (1923). Ibid., 14, T53 (1923). Ibid., 15, T337-46 (1924). Ibid., 15, T419-33 (1924). Hilditch, T . P., Fette u . Seijen, 43, 97-100 (1936).
Hilditch, T. P., “Industrial Chemistry of Fats and Waxes”, 2nd ed., p. 55, New York, D. Van Nostrand Co., 1941. (12) Ibid., p. 60. (13) Ibid., p. 87.
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(14) Lane, N. J., J. Am. Chem. SOC.,15, 110 (1893). (15) Leys, A,, J . pharm. chim., 3, 577 (1912). (16) Lewkowitsch, J., “Chemical Technology and Analysis of Oils. Fats, and Waxes”, 6th. ed., Vol. 1, p. 416, London, Macmillan co.,,1921. (17) Ibzd., p. 428. (18) Ibid., pp. 459-63. (19) Matthews, J. M., “Textile Fibers”, 4th ed., pp. 468-75, New York, John Wiley & Sons, 1924.
Solubilitv in Common Solvents J
T
HE solubility of cotton wax was studied by Fargher with reference to complete removal of the wax from the fiber (I), but because of the limited quantities of wax available, no attempt was made to obtain solubility curves. Pickett (2) suggested that solubility-temperature curves be determined by dissolving weighed amounts of wax in 100 grams of solvent, heating to dissolve wax, cooling, and recording the cloud point as the saturation temperature. This method allows the least soluble constituents to dictate the cloud point, and it is impossible to observe accurately the cloud points of dark colored solutions like those of cotto’n wax. A wide range of representative solvents were chosen, including those commonly employed industrially as wax solvents: benzene, toluene, xylene, turpentine, chloroform, carbon tetrachloride, carbon disulfide, Skelly solvent C, methyl, ethyl, n-propyl, nbutyl alcohol, tert-butyl, and isoamyl alcohols, acetone, diethyl ether, ethyl acetate, and glacial acetic acid. All were reagent grade. Cotton wax was placed in 250-ml. flasks with 200 grams of solvent. The flask was put into a thermostatically controllcd water
bath a t the desired temperature, and agitated or shaken until equilibrium was reached between the solvent and the wax (generally 2-4 hours). This time was increased to 8 hours in order to ensure complete penetration of the solvent into the granulated wax. Care was taken that a large excess of wax is present a t all times. Then samples were siphoned off into closed, tared weighing bottles and weighed, the solvent was evaporated a t 105’ C., and the remaining wax was weighed. The temperature range of the bath, which had both heating elements and cooling coils, was controllable from 0 ” to 95” C. However, since most of the boiling points of the solvents were considerably lower than 95 C., the upper limit of the bath was no handicap. No solubility values were determined above 70” C., the melting point of Cotton wax. A minimum of ten temperatures a t which the solubility of the wax was experimentally measured were rhosen for each solvent between 0 ” and 70’ C.; thus, there were always ten points from which to plot the curve. The solubility is expressed as grams of wax per 100 grams of solvent. The solvents can be broken down into two general groups. I n one (Figure 1) the cotton wax was readily soluble (more than
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0 TEMPERATURE -‘C.
10
20
30
‘
40
T E M P E RAT U R E
Figure 1. Curves for Solvents in Which Cotton Wax Is Readily Soluble
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50 C.
I
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