January, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
An attempt was made to strike a balance of the ethersolubles in the unextracted chips, the I drained alcoholic extract, and the resulting pulp. The total residue recovered from the alcohol extract amounted to 12.8 grams, of which 3.4 grams were soluble in ether. From the data in Table X one can compute the ether-solubles in the original wood to be 11.83 grams and in the resulting pulp from the alcoholextracted chips to be 4.71 grams. Hence, 11.83 (3.4 4.71) = 3.72 grams of the ether-soluble material must have left the system by way of the relief gas from the digester and with the waste liquors from which the pulp was freed. I n other words, of the original ether-soluble material present in the wood, about 29 per cent was removed with the alcohol extract, about 31 per cent was lost in the relief gases and the waste liquor, and about 40 per cent remained with the pulp. On the other hand, the pulp from the unextracted chips contained 9.89 grams of ether-solubles, showing in this case a loss of (11.83 - 9.89) = 1.94 grams, or about 16 per cent of the original, in the relief and in the waste liquors. It is probable that the alcoholic residues which were left in the extracted chips in the parallel cook experiment were largely responsible for the greater eiimination of resins in the waste
-
+
a3.
liquors. It is probable that materially greater percentages of the original ether-soluble matter can be recovered in the alcohol if the chips are smaller and if more favorable conditions of extraction are observed. Other low-cost solvents such as carbon tetrachloride and trichloroethylene should be studied.
Acknowledgment The author wishes to extend full credit to D. H . McMurtrie, M. W. Hayes, C. W. Thing, E. W. Lovering, and others who took active part in the laboratory work.
Literature Cited (1) Assoc. Official Agr. Chem., Methods of Analysis, pp. 96-7 (1920). (2) Hawley and Wise, “Chemistry of Wood”, p. 17B, A. C. S., Monograph, New York, Chemical Catalog Co., 1927; Dore, J. IND. ENG.CHEM.,12, 476, 984 (1920); Ritter and Fleck. I b i d . , 15, 1055 (1923), 18, 608 (1926); Miiller, “Pflanzenfaser”, p. 163 (1876); Konig and Becker, 2. angew. Chem., 32, 155 (1919); Schwalbe and Becker, Ibid., 32, 229 (1919); Barnes, Chem. & M e t . Eng., 28, 504 (1923); Aschan and Rantalainen, BrennstoffChem , 4 , 101 (1923). (3) Hibbert and Phillips, Can. J. Research, 4 , 1-34 (1931). (4) Newlin and Wilson, Dept. Agr., Bull. 556 (1917). ( 5 ) Richter, G. A., IND.ENG.CHEM.,23, 266 (1931).
Distribution of Pectic Acid in Cotton Fibers R. F. NICKERSON AND C. B. LEAPEl, Mellon Institute, Pittsburgh, Penna. The investigation reported in this paper was undertaken as an inquiry into the function of pectic matter in raw cotton. By direct and indirect analyses i t is shown that the pectic material occurs, as does the natural wax, almost exclusively on the outside fiber surfaces where i t can have but little influence on fiber structure and properties.
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presence of pectates in cotton was noted first 1 Schuick (19) wbo isolated a pectic acid from kier liquor. Knecht and Hall (14) affirmed that caustic
soda removed pectic substances from cotton. Clifford and Fargher ( 7 ) detected methanol and acetone in the volatile products of raw cotton and concluded that a pectic material was the precursor. Harris and Thompson (12) made a careful study of the pectic acid from a cotton; they obtained a yield of 0.68 per cent pectic acid which had an equivalent weight of 201 and a n of +225.4 and which released 21.8 per cent of carbon dioxide upon decarboxylation; they concluded that the material occurred in raw fibers as the calcium and magnesium salts of pectic acid. Their figure for the equivalent weight is in good agreement with the corresponding value for fruit pectates (16). Whistler, Martin, and Harris (23) estimated 1.15 per cent of pectic acid in a cotton by converting the differential carbon 1 Present address, Westinghouse Research Laboratories, East Pittsburgh, Penna.
dioxide yield of a raw and a purified sample with a factor of 4.8. The latter value was obtained from isolated cotton pectic acid and corresponds to 20.8 per cent yield of carbon dioxide upon decarboxylation. A conversion factor of 4.5 for carbon dioxide to pectic acid is indicated by the data of Harris and Thompson. Anderson and Kerr (1) reported that the pectic substances of cotton were surface constituents, as a number of earlier investigators (4,9,24) had implied. Several different lines of evidence lead independently to the conclusion that native cellulose contains an amorphous substance or gel in addition to the crystalloid elements (3,I S , 80). Farr (11) made the suggestion that this substance is a pectin or, a t least, a polyuronide which, to a considerable extent is responsible for the high viscosity of cotton dispersed in cuprammonium hydroxide reagent. This hypothesis is objectionable because pectins do not dissolve in cuprammonium hydroxide ( 2 ) ; in fact, the insolubility in this reagent has been used as the basis for the separation of cellulose from pectin preparations (16). While the literature indicates that pectic substances are constituents of raw cotton, it does not show clearly their distribution in the fiber. The present work was undertaken to determine whether or not a polyuronide occurs in appreciable quantities in the internal fiber structure.
Experimental Procedure A fairly good correlation is known to exist between the average fiber length and the fineness of cotton. Fineness,, which depends upon the average thickness of fiber walls and is measured in terms of fiber weight per centimeter, increases with the staple length of the cotton; in general, the longer
a4
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y TABLEI. WAX, PECTIO ACID, AND CARBON DIOXIDE YIELDS FROM MATURE COTTONS, CALCULATED ON BONE-DRYWAX-FREBRAWMATERIAL Av. Wax Content,
Staple Crop Length, Variety of Cotton Season Inches5 % 0.44 1937 Half & Half '/8 1 0.60 1938 Rowden Wilds 0.70 1937 18/81 0.75 1 1938 Acala 0.87 1938 Delfos 11/n Express 11/82 0.90 1938 Sea Island 0.89 1938 1 =/4 a Estimates supplied by Cook & Company, b Wax-free. c Purification oonsisted of kier boiling and
Av. Peotio Acid (Cad),
-%
Cor in 5 Hours-
From
raw cottonb 0.43 0.181 0.58 0.244 0.270 0.60 0.69 0.311 0.71 0.324 0.77 0,325 0.76 0.343 Memphis, Tenn.
70
After oxalate extn. 0.074 0.112 0.127 0.148 0.152 0,142 0.168
washing with dilute acid.
fibers have the thinner walls. For the present investigation, seven varieties of mature cotton, representing a range of staple lengths grown under similar environmental conditions during the 1937 and 1938 crop seasons, were obtained as source material. This series was intended to correspond to a varying fineness or, more specifically, to a varying ratio of fiber volume to surface area. The samples were carded and the clean card sliver used without further preparation. Wax, pectic acid, carbon dioxide evolution after various treatments, and fineness were determined for each sample:
'
WAX. Weighed amounts of the various cottons were extracted in a Soxhlet apparatus for 24 hours with redistilled benzene; the last fraction of solvent was removed from the wax residue over a steam bath with a stream of nitrogen. PECTICACID. For analytical determinations an extraction of pectic acid with potassium carbonate was not satisfactory. A modification of the Carre method (5) gave excellent results. Ten-gram samples on a dry basis of wax-free raw cotton were digested for 24 hours at 85" C. with 200 ml. of 0.5 per cent ammonium oxalate. The hot extracts were liltered OB on a small Buchner funnel and the cottons washed twice. The first wash consisted of 200 ml. of hot water to which 1 ml. of 1.7 per cent ammonium hydroxide was added just prior t o use; the second wash was approximately 150 ml. of hot water. The filtrates for each sample were collected in a 500-ml. volumetrio flask and, after being cooled, were brought to volume with the remains of the liltrate from the last wash. The determinations were made in triplicate. Measured 150ml. portions of extract were concentrated to 25 ml. over burners in a rapid stream of air, cooled to room temperature, and immediately precipitated with 90 ml. of 95 per cent alcohol containing 5 drops of concentrated hydrochloric acid. (Hydrolysis with sodium hydroxide was found to be unnecessary for these cotton extracts.) After several hours the precipitates were washed free of oxalate, taken up in hot water, and reprecipitated with acetic acid and calcium chloride. The calcium pectate was collected in coarse alundum filtering crucibles, washed free of chloride, dried, and weighed. Calcium pectate weights were converted to pectic acid by allowing for 7.5 per cent calcium. CARBONDIOXIDE.1. The total carbon dioxide yield was determined by refluxing 10 grams of wax-free raw cotton with 150 ml. of 12 per cent hydrochloric acid according to the method of Dickson, Otterson, and Link (IO). Each run represented exactly 5 hours of actual boihng. 2. Oxalate-extracted samples of cotton from the pectic acid determinations were thoroughly washed with an additional 500 ml. of hot water, dried, and used for carbon dioxide analyses. 3. Residual carbon dioxide yields from bier-boiled cottons were estimated in the same manner as the total and oxalateextracted values. The kier boiling consisted in placing weighed amounts of the raw cottons in separate containers with ten volumes of 2 per cent sodium hydroxide43 per cent sodium carbonate, and simultaneously boiling a complete set for 5 hours in an autoclave at 250" F. (121' C.) These samples were rinsed several times with boihng water, leached overnight with cold water, washed with dilute acetic acid and finally with water. The dry weights of the purified cottons were then obtained. Since identical purification conditions are represented by the simultaneous kier boiling of the whole series of cottons, the purified samples are held to be strictly comparable. FINENESS. Estimates were obtained by preparing small bundles of parallel fibers, cutting a 1-em. length from the middle of the bundle with carefully spaced razor blades fixed in a metal
After purificationc 0.044 0.046 0.041 0.047
Vol. 33, No. 1
holder and weighing 200 of the 1-em. lengths on a microbalance (at least 80-160 lengths are necessary for reliable determinations, 6.)
Weight Lost during Purification, y0c 7.0 7.1 7.8 8.0 8.6 8.2 8.5
Analytical Data
The analytical data derived from the various determinations are given, in part, in Table I. Each value, except the loss during kier boiling, is an 0.050 0.049 average of two or more analyses. 0.056 It is apparent that the wax contents of the various raw cottons are directly proportional to the corresponding: amounts of extractable pectic acid. Similarly, there is a linear relation between the fiber wax content and the carbon dioxide differential. The latter figure is obtained b y subtraction of the carbon dioxide yield of the oxalate-extracted cotton from the carbon dioxide yield of the wax-free raw cotton; this carbon dioxide differential appears to represent the decarboxylation of in situ pectates. The wax of cotton fibers is probably a surface constituent; this is indicated by microscopical studies with fat stains (1, 9, 17') and by the rapid accumulation of wax during the period of primary fiber wall development (8). The observed linear relations suggest that the pectate is distributed similarly. When cotton samples are refluxed with 12 per cent hydrochloric acid in the determination of carbon dioxide, the fibers disintegrate completely. The main product of this reaction is hydrocellulose which, in turn, slowly breaks down to give glucose or the equivalent. The end products of the hydrolysis have been shown ( W ) to evolve small amounts of carbon dioxide but in reproducible quantities, if time, temperature, and acid concentration are held constant. In the present investigation the samples were weighed as raw cotton and then subjected to the various preparatory treatments. Each carbon dioxide determination represented the same initial weight of pure cellulose; the acid concentration, refluxing time, and oil-bath temperature were uniform throughout the series. Consequently, errors originating in the hydrolytic products should be constant and should vanish when differentials are considered. The order of magnitude of such errors in these experiments is shown by the residual carbon dioxide from kier boiled cottons in Table I. The data indicate that the residual carbon dioxide-i. e., from purified cottons-is practically independent of the amount available from the wax-free raw cottons. This suggests that residual carbon dioxide is not related directly to fiber characteristics but originates in the cellulose. On the other hand, the total carbon dioxide and the carbon dioxide from oxalate-extracted cottons do appear to be related in a
TABLE 11. COMPARISON OF GRAVIMETRIC PECTIC ACIDVALUES AND ESTIMATES DERIVED FROM CARBON DIOXIDE YIELDSFOR VARIOUSCOTTONS --Pectio
COP
Variety
Differentiala
Half & Half Rowden Wilds Acala Delfos Express Sea Island
0.107 0.132 0.143 0.163 0.172 0.183 0.175
Acid-Carre co2 differential (grpvimetX 4.6 3' % nc), 9% 0.48 0.43 0.58 0.59 0.60 0.64 0.69 0.73 0.71 0.77 0.77 0.82 0.76 0.79
Deviation from Gravimetrio +0.05 +0.01
+0.04 +0.04 +0.06 +0.05 f0.03
a Equivalent t o the C o t extraoted by ammonium oxalate and obtained an the differenoe between oolumna 6 a n d 7, Table I.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
January, 1941
way that would signify the presence in varying quantities in the different cottons of carbon-dioxide-yielding substances not extracted by oxalate. The conversion of carbon dioxide differentials to pectic acid was effected with a multiplier of 4.5 (calculated from the data of Harris and Thompson, 18). The pectic acid estimates derived in this way are given in Table 11, together with the deviations from the gravimetric values. The agreement between the results obtained by the two methods is apparent. I.4
I
,
I
,.35
P
W
A-COI
Curve
.PO
a
I E
8
" F I N E N E S S " A S CM. O F F I B E R
P E R MG.
DIOXIDE YIELDS FIQURE 1. WAXAND CARBON IN RELATION TO FIBER FINENESS
The variation of weights and "fineness" of fibers with variety is shown in Table 111. Fineness is given as the length of fiber which would weigh 1 mg. and is the reciprocal of fiber weight per centimeter. The wax and total carbon dioxide are plotted as functions of fineness in Figure 1. There appears to be a similar curvilinear relation between each set of values. A straight line might be expected if all fibers were cylindrical and had the same outside diameters. (The assumption of a cylindrical shape can be justified on the ground that, after being swollen, the fibers are more or less round.) I n such a case fineness would be determined by the amount of internal thickening, and outside surface area would be directly proportional t o length. The nonlinear relation observed indicates that both outside diameter and amount of thickening vary appreciably. This result is in good agreement with the recent finding (18) that outside fiber diameter is determined by the variety and the amount of internal thickening by other factors. TABLE111. FIBERWEIGHTS AND FIN~NESS Variety
Staple Length In.
Half & Half Rowden Wilds A d s Delfoa Express Sea Island
Mean Fiber Wei ht per Cm. ?Obsvd.) NO. 0.00227 0.00217 0.00177 0.00164 0.00121 0.00161 0 * 00118
Av. Length of FibFr We1 h m g 1 Mg. ?Calad.)
Cm. 441 461 566 610 826 621 847
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Discussion of Results The omission of the alkali hydrolysis step in the gravimetric determination of pectic acid may have caused a small error in the final results, but this seems unlikely. Experiments in this laboratory failed to demonstrate the need for hydrolysis. The same conclusion-namely, that the pectic material is
85
present in cotton as pectic acid-has been reached by other investigators (II,22). The estimate of pectic acid in raw cotton made by Whistler and co-workers (23) may be too high, Their figure is derived from the total carbon dioxide, corrected for a residual from the pure cellulose component, and involves the assumption that pectate is the sole carbon-dioxide-yielding substance extracted during alkali purification. As the kier losses indicate, dewaxed raw cotton contains about 5 per cent of nonpectic matter which also may yield carbon dioxide. The present evidence suggests that appreciable quantities of carbon dioxide are evolved by nonpectic substances which remain in the cotton after an oxalate extraction. I n Whistler's method carbon dioxide from such a source would tend to raise the derived estimate of pectic acid. These nonpectic substances are not present after a kier boil. I n Table I the weights lost during a kier boil indicate that the finer cottons have the greater amounts of alkali extractables. In addition to the experiments already described, determinations of pectic acid were undertaken on raw cottons disintegrated with cuprammonium hydroxide. The observed pectic acid yields were identical to those obtained from intact raw fibers. The evidence that the pectates of cotton are largely surface constituents is summarized as follows: (a) Intact fibers yield as much pectic acid as fibers disintegrated with cuprammonium or with hydrochloric acid. (b) The pectate content of fibers is directly proportional to the content of wax-a surface constituent. ( c ) The amount of pectate increases with increasing fiber fineness. ( d ) If pectates were evenly distributed throughout the fiber walls, similar amounts of total carbon dioxide should be obtained from all cottons regardless of fineness, for equal weights of samples would represent the same amount of total fiber wall; actually, the thickest walled fibers (Half & Half, 441 cm. per mg.) yield about half as much total carbon dioxide as is obtained from the disintegration of the thinnest walled variety (Sea Island, 847 cm. per mg.). (e) Since kier boiling appears to remove all the pectates from cotton (2%)and the literature shows only a small loss in fiber strength during this processing (21,82),it is doubtful whether these substances could play a very vital role in the internal structure. It must be pointed out, however, that the present results do not preclude the existence of a nonpectic intercrystalline material. The number of samples employed in this study is insufficient to permit any definite conclusions with respect to fineness. It is suggested, however, that a broader study of wax, total carbon dioxide, and fiber weight per centimeter in conjunction with the necessary microscopic examinations of swollen fibers and fiber cross sections might lead to some simple laboratory methods for assaying dimensional characteristics.
Conclusions 1. Wax and pectate are surface constituents of cotton and vary with the finesss of fibers. Evidence of the presence of nonpectic carbon-dioxide-yielding substances is adduced. 2. The pectic acid content of cotton can be estimated from the difference between the total amount of carbon dioxide evolved by the cotton and the carbon dioxide still available after an oxalate extraction, if constant conditions are maintained. 3. There does not appear to be an appreciable quantity of pectic acid in the internal structure of fibers. 4. A possible method of assaying the dimensional characteristics of cotton fibers is suggested for further investigation. Acknowledgment We are indebted to H. C. McNamara, Delta Experiment Station, Stoneville, Miss., for placing the selected cotton
INDUSTRIAL AND ENGINEERING CHEMISTRY
86
samples at our disposal. The cleaning and carding were done through the courtesy of R. W. Webb and J. ?VI. Cook of the United States Department of Agriculture.
(13) Houwink, R., "Elasticity, Plasticity and Structure of Matter", p. 262 (1937). (14) Knecht, E., and Hall, W., J . SOC.Dyers C o l o u ~ i s t s ,34, 220 (1918). (15) Mangin, L., Compt. rend., 107, 144 (1888); 109, 579 (1889).
Literature Cited (1) Anderson, D. B., and Kerr, T., IND. ENG.CHEM., 30,48 (1938). (2) Baker, G. L., and Goodwin, hI. W., Del. Am. - Exgt. . Sta., Bull. 216 (1939).
Brown, K. C., Mann, J. C., and Peirce, F. T., J . Textile I n s t . , 21, T186 (1930). Calvert, M. A,, and Summers, F., I b i d . , 16, T233 (1925). Car& M. H., et al., Biochem. J . , 1 6 , 6 0 , 7 0 4 (1922) : 19, 257 (1925). Clegg, G. G., and Harland, S. C., J . Textile I n s t . , 14, T489 (1923).
Clifford, P. H., and Fargher, R. G., Ibid., 14,T117 (1923). Compton, J., and Haver, F. E., Contrib. Boyce T h o m p s o n I n s t . , 11; 105 (1940).
Denharn, H . J., J. Teztile Inst., 13, T99 (1922). Diokson, A . D., Otterson, H., and Link, K. P., J . Am. C"hem. S'oc.. 52.775 (1930). Fair, W . K., Contrib.'Boyce T h o m p s o n Inst., 10,71 (1938). Harris, S. A., and Thompson, H. J., I b i d . , 9, 1 (1937).
Vol. 33, No. 1
(16) (17) (18) (19) (20) (21) (22)
Branfoot, Dept. Sei. Ind. Research (Brit.), Food Invest. Special Rept., 33 (1929). Olsen, A. G., Steuwer, R. F., Fehlberg, E. R., and Beach, N. M., I S D . E S G . CHEX.,31, 1015 (1939). Osborne, G. G., Teztile Research, 5, 275, 307 (1935). Peircc, F. T . , and Lord, E., J . Teztile I n s t . , 30,T173 (1939). Schunck, Mem. Manchester Lit.P h i l . Soc., 24, ( 3 ) ,95 (1871). Urquhart, A. R., J . Teztile Inst., 20,T125 (1929). Vincent, P. D., Ibid.,15,T281 (1924). Whistler, Martin, and Harris, M., A m . Dyestuff Reptr., 29,244
(1940). (23) Thistler, Martin, arid Harris, M.,Textile Research, 10, 109 (1940). (24) Willows, R. S., and Alexander, A. C., J . Textile Inst., 13,T237 (1922). P R E S E N T E D before t h e Divisiaii of Cellulose Chemistry a t the 99th Mceting of t h e American Chemical Society, Cincinnati, Ohio. Contribution from the Multiple Fellowship of t h e Cotton Research Foundation a t Mellon Institute.
DRYING OILS AND RESINS Purification of Polymerized Methyl Linoleate by Molecular Distillation THEODORE F. BRADLEY AND WILLIAM B. JOIINSTON American Cyanamid Company, Stamford, Cpnn.
Molecular distillation of polymerized methyl linoleate has been found possible within the range 160-290' C. at 2 microns. The polymerized esters are chieffy the dimer but contain a lesser proportion of trimer. The physical and chemical constants indicate these to be hydroaromatic and their mechanism of formation to be analogous to that already established for buladiene and numerous substituted butadienes (to which latter class 9,ll-linoleic acid belongs). INCE the presentation of the theory that the thermal polymerization of the drying oils involves n primary chemical reaction of the double bonds resulting in the formation of a cyclic dimer, considerable supporting evidence has been published by various workers. Previous cornmunications in this series' have attempted to interpret and expand this evidence, to show that the gelation of the drying oily could be considered the normal reaction of an unsaturated material having the requisite degree of functionality. Polymerization of the drying oils results in three-dimensional polymers which are rigid, insoluble gels ( 2 ) . The difficulty in handling such material-i. e., either to complete the polymerization or to analyze the product-has gradually led
S
1 This paper 18 t h e ninth in t h e series 1939, and in May, June, and July, 1940.
Others appeared in 1937, 1938,
to the study of the methyl or ethyl esters rather than the naturally occurring glycerol esters. Recent investigators (6) made an intensive study of the polymerization of mixed ethyl 9 , l l - and 9,12-Iinoleates which strongly supported previous indications that the end product is essentially a substituted cyclohexene formed by a modified Diels-Alder reaction, and that it involved as an intermediate reaction step the isomerization of nonconjugated to conjugated linoleztes. More recent work of the present authors and their associates (4, 5 ) yielded additional supporting evidence both for the isomerization step and the subsequent loss of the conjugated intermediates by diene polymerization. However, the nonuniformity of the polymeric residues (due apparently both to impurities and to the existence of several classes of polymers), the occurrence of side reactions involving decompositions, and the subsequent reaction of certain of the decomposition products and various other observations which we had made compelled continued investigation of these phenomena. It became imperative to seek some effective means of purifying the polymer residues which had been found nonvolatile up to 300' C. a t 1mm. or, according to others, even in a Hickman high-vacuum still (6). Molecular weight determination. had shown these to be predominantly dimeric and to range between 500 and 600 in molecular weight. It was therefore believed that these polymers should be distillable in high vacuum. Appropriate samples were then subjected to molecular distillation in a cyclic molecular still and analyzed. The methyl esters of the fatty acids of dehydrated castor oil were chosen to initiate the proposed work since they are comprised mainly of the 9,12- and 9,11-octadecadienates (linoleates) and had been indicated to form a monocyclic,
