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INDUSTRIAL AND ENGINEERING CHEMISTRY
Table IX. Viscosity, Weight, and Number Average Degrees of Polymerization and Relative Nonuniformity of Nitrated Cotton, Flax, and Ramie Celluloses Material Cotton Flax Ra+
D.P.u 4720 4060 5740
D.P.w 4320 4050 4790
D.P.n 3630 3310 4620
U
0.19
0.23 0.04
Vol. 47, No. 10
(4) Conrad, C. M., IND. ENG.CHEM.,45, 211 (1953). (5) Cragg, L. H., and Hammerschlag, H., Chem. Revs., 39, 79 (1946). (6) Doty, P., and Spurlin, H. M.,in Ott, E., and Spurlin, H. &I.,
“Cellulose and Cellulose Derivatives,” 2nd ed., part 111, X-D, Interscience, New York, 1955. (7) Emery, C., and Cohen, W. E., Australian J. Appl. Sci., 2 , 473 (1951). (8) Golowa, 0. P., and Iwanow, W. J., “Ueber das Molekulargewicht der Cellulose,’’Akademie Verlag, Berlin, 1953. (9) Gralh, N., “Sedimentation and Diffusion Measurements on
Cellulose and Cellulose Derivatives,” dissertation, Uppsala,
crepancy was not entirely unexpected, as different methods were used for determining the intrinsic viscosities of the fractions. CONCLUSIONS
While it is believed that the data presented give a reasonably correct over-all picture of the chain-length distribution of the three celluloses studied, the results should not be looked upon as anything but approximate. Some of the disturbing factors y b a b l y inherent in similar previous studies were minimized. hese factors included the effect of degradation of the nitrates in solution and the great influence exerted on the intrinsic viscosity of the fractions both by the rate of shear existing during the viscosity measurement, and by the degree of substitution. I t Neems evident, however, that a more comprehensive fractionation than that applied here, involving a series of refractionations such as that outlined by Doty and Spurlin (6),would give much more reliable results. A fractionation of this kind wa8 carried out a considerable time ago by Spurlin (29) with a cellulose nitrate of low molecular weight. It seems probable that application of a similar fractionation technique, with due consideration of the difficulties mentioned above, would be able to furnish more detailed information concerning the chain-length distribution of celluloses of very high molecular weight than has so far been forthcoming. ACKNOWLEDGMENT
The author wishes to express his sincere gratitude to C. B. Purves, head of this division, for his kind interest in the present study. LITERATURE CITED
(1) .4lexander, W. A,, and Mitchell, R. L., Anal. Chem., 21, 1497 (1949). (2) Campbell, H., and Johnson, P., J . Polymer Sci., 5 , 443 (1950). (3) Cannon, M. R., and Fenske, 11. P., IND.ENG.CHEM.,ANAL. E D . ,10,297 (1938).
1944. (10) Hermans, P. H., “Physics and Chemistry of Cellulose Fibres,” pp. 117-20, Elsevier, New York, 1949. (11) Herrent, P., and Govaerts, R., J . Polymer Sci., 4, 289 (1949). (12) Heuser, E., and Jorgensen, L., T a p p i , 34, 57 (1951). (13) Huggins, M. L., J . A m . Chem. Sac., 6 4 , 2716 (1942). (14) Jorgensen, L., “Studies on the Partial Hydrolysis of Cellulose,” dissertation, Oslo, 1950. (15) Jullander, I., Arkiv K e m i , Mineral, Geol., 21A, No. 8 (1945). (16) Jurisch, I., Chem.-Ztg., 64, 269 (1940). ENG.CHEM.,30, 1200 (1938). (17) Kraemer, E. O., IND. (18) Lindsley, C. H., and Frank, M.B., Ibid., 45, 2491 (1953). (19) Martin, A. F., Division of Cellulose Chemistry, 103rd Meeting, Memphis, Tenn., 1942; T a p p i , 34,363 (1951). (20) Meyerhoff, G., Naturwissenschaffen, 41, 13 (1954). (21) Mitchell, R. L., IND.ENG.CHEM.,38, 843 (1946). (22) Ibid., 45,2526 (1953). (23) Morey, D. R., and Tamblyn, J. W., J . Phys. Colloid Chem., 51,721 (1947). (24) Newman, S., Loeb, L., and Conrad, C. M., J . Polymer Sei., 10, 463 (1953). (25) Sayre, E. V., Ibid., 10,175 11953). (26) Schulz, G. V., and Marx, M., Makromol. Chem., 14, 52 (1954). (27) Schurz, J., and Immergut, E. H., J. Polymer Sei., 9, 281 (1952). (28) Scott, R. L., IND.ENG.CHEM.,45, 3532 (1953). (29) Spurlin, H. M., Ibid., 30, 538 (1938). (30) Spurlin, H. M., in Ott, E., “Cellulose and Cellulose Derivatives,” pp. 886-90, Interscience, New York, 1943. (31) Staudinger, H., Papier-Fabr., 36, 474 (1938). (32) Staudinger, H., and Feuerstein, K., Ann., 526, 72 (1936). (33) Timell, T. E., Szensk Papperstidn., 57, 777 (1954). (34) Ibid., 5 8 , l (1955). (35) Timell, T. E., unpublished results. (36) Timell, T. E., and Purves, C. B., Srenslc Papperstidn., 54, 303 (1951). (37) Wannow, H. A., and Thormann, F., Rolloid-Z., 112, 94 (1949). RECEIVED for review January 17, 1965. ACCEPTEDApril 1, 1955. Division of Cellulose Chemistry, 127th Meeting ACS, Cincinnati, Ohio, 1955.
Effect of Swelling and Supermolecular Structure on Reaction of Cellulose with Nitrogen Dioxide W. E. ROSEVEARE’ AND D. W. SPAULDING Textile Fibers Department, E. Z. du Pont de Nemours & Co., Znc., Richmond, Vu.
UCH work has been done to show how the-crystalline and amorphous portions of cellulose affect the hydrolytic reactivity of cellulose, but there is little information about how the supermolecular structure affects oxidation. Davidson (1) has shown that as oxidation with chromic acid progresses there is scarcely any effect on the x-ray pattern, but oxidation with periodic acid makes the pattern diffuse. The chromic acid acts very largely on the amorphous regions, while periodic acid acts on the Crystalline regions as well. Completely dry cellulose, the amorphous regions of which are in the glassy state ( 8 ) , is impermeable to small molecules like Preeent address, Research Laboratory, E. I. du Pont de Nemours & Co., Inc., Kinaton, N. C . 1
oxygen and acetic anhydride. I n bhis dry state these materials react initially with only surfaces of the fiber and the reacting layer moves very slowly into the fiber. Swelling or removal of the reacted material even without swelling the unreacted cellulose greatly accelerates the movement of the reacting layer through the fiber. I n contrast t o this topochemical behavior, cellulose in solution reacts homogeneously. In between the dry and solution states the reaction behavior should depend on the degree to which the oxidizing agent can penetrate into the amorphous and crystalline regions. Kenyon and others ( 2 ) showed that high concentrations of nitrogen dioxide with various other liquids dissolved cellulose ; therefore, it appeared probable that the swelling and degree of penetration of nitrogen dioxide into cellulose and the resulting
,
October 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
N e w light on old textiles to help predict oxidation conditions required for production of oxycellulose with particular properties
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2173
ments, as reported by Hermans ( 4 ) . The 57% value obtained with the two lowest concentrations is considerably larger than the amount of crystalline material. This indicates that only pari of the amorphous portion is readily accessible with the 0.5 and 1.5% solutions. It appears that the penetration and swelling of the cellulose increase as the concentration of nitrogen dioxide increases and that there is some particular concentration bel ween 8.3 and 16.6% a t which the nitrogen dioxide can just penetrate the crystalline regions.
reaction behavior could be controlled by varying the concentration of the nitrogen dioxide. The present paper presents data clarifying this effect for reaction of solutions of this oxidizing agent in carbon tetrachloride. The chemistry of' this reaction, as reported by Kenyon and others (6),Head (S), and Sevell(6), is largely an oxidation of the number 6 carbon atom to give a celluronic acid. Relatively small amounts of carbonyl and combined nitrogen are produced by the side reactions. EXPERIMENTAL
The fibers to be oxidized were boiled off in a 0.5yoDuponol WA detergent solution for 30 minutes and washed with water before being dried in an oven a t 110' C. One-gram samples of the dry materials were immersed in 100 grams of a solution of nitrogen dioxide in carbon tetrachloride contained in stoppered flasks. The oxidation was allowed to proceed a t 25" &,0.5. C. with occasional shaking to overcome the effects of slow diffusion. Continuous stirring was used in the case of the more dilute solutions. After oxidation, the yarns were drained, blown free of most of the nitrogen dioxide by a stream of compressed air, and then washed repeatedly with acetone and air-dried overnight. The carboxyl content was determined by dissolving the oxidized yarn in 5 ml. of 0.5N sodium hydroxide, quickly diluting to 25 ml., and titrating with 0.1N hydrochloric acid using bromothymol blue as an indicator. Acidity produced by the action of alkali on oxycellulose (6) was inappreciable during the limited time of this procedure. Moisture regain values were used to correct carboxyl content to dry weight. Hydrolysis of a partially oxidized cellulose was carried out by treating 1.5 grams of the material with 2.5N sulfuric acid a t 96" C. for various lengths of time. After the acid had been neutralized, the residue and solution were transferred to a cellophane dialysis bag of known dry weight and dialyzed overnight in running water. The bag was lifted almost clear of the water and most of the liquid seeped out. The remaining liquid was removed by drying a t 110" C. until the bag gave a constant weight. The dialysis procedure had to be used, because most of the residue was colloidal and would pass through ordinary filters. Ordinary filters were used when unoxidized material was hydrolyzed. OXIDBTION OF RAYON
The oxidation behavior of a tire-cord rayon as a function of time is presented in Figure 1 for various concentrations of nitrogen dioxide. The values of 100 times one minus the degree of substitution on a logarithmic scale are plotted against time, as this will give a straight line if the rate is proportional to the amount of number 6 carbon atom present during the reaction. This appears to be very nearly the case for the 16.6Y0 solution until the reaction is 97y0 complete, as shown by the lower curve in the figure. The constant rate throughout the reaction means that there is no significant difference in rate for the amorphous and the crystalline material. I n contrast t o the above behavior, the more dilute solutions produce a fast initial reaction followed by a relatively slow firstorder reaction. This change in rate suggests that the dilute solutions initially attack the reactive amorphous regions and only after this material is largely used up is there appreciable reaction with the slowly reacting crystalline areas. The extension of the slow-rate portion of these oxidation curves back to zero time indicates t h a t the amount of slowly reacting material is between 40 and 57y0,. The 4Oy0value is approximately the amount of crystalline material present in ordinary rayons from x-ray measure-
5 0
100
200
300
400
5
HOURS OF OXIDATION
Figure 1. Oxidation of tire-cord rayon by solutions of nitrogen dioxide in carbon tetrachloride
OXIDATIO\ O F COTTON
The oxidation of cotton of tire-cord grade by nitrogen dioxide proceeds a t a slower rate than the oxidation of rayon by solutions of the same concentration. Figure 2 shows that in the case of cotton the rate in 16.6% nitrogen dioxide decreases to a relatively low value when about 60% of the number 6 hydroxyls are left. At this concentration nitrogen dioxide oxidizes the disordered regions of cotton with very little effect on the crystalline regions. This solution is apparently unable to penetrate the crystal lattice of native cellulose readily, whereas it can readily enter and react with the less dense regenerated crystal lattice of the rayon to give 97% oxidation in 40 hours. A comparison of the rates of oxidation of cotton and rayon shows that the crystallites of the latter are about 10 times as reactive as the native crystallites in the same concentration of nitrogen dioxide. The intercepts at, zero time of the straight lines exhibiting the slow-reaction behavior give accessible fractions ranging from 23 t o 43%, which is much less than that for the rayons. Further evidence of the effect of concentration on the penetration of the crystalline regions is given in Figure 3. After only a 5-minute treatment of rayon-grade cotton linters with 50% nitrogen dioxide in carbon tetrachloride, followed by washing and drying, the native lattice appears to be completely converted to the regenerated form. This short time is insufficient to produce any appreciable amount of oxidation and, therefore, the
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change in lattice structure must be due to physical swelling and penetration of the crystallites by the 5070 solution. On the other hand, the x-ray pattern of the linters treated for the same length of time in 33.3y0 solution shows little visible alteration, indicating that the crvstallites are not appreciably penetrated by this solution.
Table I.
Vol. 47, No. 10
Hydrolysis of Cotton Linters before and after Largely Oxidizing Amorphous Regions H~~~~of Hydrolysis 1.0 4.0
7.5
% Loss in
W d v h t on Hydrolvsis
Untreated 1.4 3.8
5.3
Oxidized 31.3 31.1 34.2
chains because of the uronic acid units produced in the accessible chains appears unlikely, but some chemical reactivity may be due to side reactions modifying other portions of the anhydroglucose units. The main cause of the hydrolytic sensitivity is probably the inhibition of crystallization of the amorphous material during hydrolysis. Such an explanation has been given for the lowering of the leveling-off degree of polymerization on hydrolysis of cellulose oxidized by dichromate (7).
16.6 Ye NO2
EFFECT OF OXIDATION CONDITIONS ON PROPERTIES OF OXYCELLULOSE
The physical properties of the oxidized cellulose give additional evidence for the selective penetration of the amorphous regions. The variation in stress-strain properties of a rayon produced by oxidation with nitrogen dioxide in carbon tetrachloride for various times and concentrations is given in Figure 4. For the series of samples selected here, the variation in the stress-strain curves is greatest for the least oxidized. This shows that the physical properties depend largely on the concentration of reagent used and very little on the degree of oxidation. The high concentrations which penetrate the crystalline regions t o the greatest extent produce the greatest changes in the stress-strain properties.
I
0
I 100
I
1
1
200
300
400
HOURS
5(
OF OXIDATION
Figure 2. Oxidation of cotton by solutions of nitrogen dioxide in carbon tetrachloride
A sensitive indication of modification of the crystalline regions on mercerization of native cellulose is the change in leveling-off viscmity ( 7 ) . This test finds that only the 50% solution gives the large change produced by mercerization. B 5-minute treatment of the linters with 50y0 nitrogen dioxide drops the levelingoff cupriethylenediamine viscosity from 2.9 to 1.72 cp., a drop oorresponding to complete mercerization, whereas the IeveIingoff viscosity of the linters treated for the same length of time in a 30% solution decreases only to 2.3 cp. HYDROLYSIS OF OXIDIZED COTTON
Increased evidence to support the hypothesis that cotton treated with 8.3% nitrogen dioxide in carbon tetrachloride is oxidized selectively in the less ordered regions was obtained by hydrolyzing this type of oxycellulose by the procedure given above. Table I gives the loss in weight on hydrolysis, based on the original cellulose samples, of untreated cotton linters and a sample oxidizedwith8.3% nitrogen dioxidefor 120 hours st 25" C., a time sufficient to oxidize most of the reactive fraction. The loss in weight on hydrolysis is very much greater for the oxidized samples, as shown by comparing the last two columns of the table. It is apparent from the last column that the hydrolysis of the oxidized material proceeds rapidly during the first hour but very slowly thereafter. It appears that the oxidized accessible cellulose hydrolyzes away quickly and that the remaining cellulose, which is largely crystalline, hydrolyzes very sloudy. It still remains to be explained why the oxidized amorphous material hydrolyzes to a much greater degree than the unoxidized material. High chemical sensitivity of the individual
B
A
C
Figure 3. Change in x-ray patterns of cotton linters produced on swelling with nitrogen dioxide in carbon tetrachloride A . Control Treated with 33.370 nitrogen dioxide C. Treated with 50% nitrogen dioxide
€3.
The changes in moisture regain with degree of oxidation for three concentrations of nitrogen dioxide in carbon tetrachloride are given in Figure 5 . With the low concentrations of 1.5 and 8.3%, the oxidation produces first a decrease in moisture regain and then an increase as the degree of polymerization is increased. The initial effect is probably a filling up of free space in the amorphous regions by the carboxyl groups, so that there is less room for moisture. At the higher degrees of substitution, the crystalline regions will react and swell, permitting moisture to enter. With the 16.6% solution, the regain starts up with the lowest substitution because the crystallites react from the beginning. I n the case of cotton, the 8.39ib solution does not produce any appreciable change in regain until most of the amorphous material has been oxidized. The greater the accessibility, the more homogeneously a given amount of carboxyl groups should be distributed along the chains. I n addition, high accessibility permits the reaction to proceed to a given degree with less t,ime for the side reactions to occur. Since side reactions cause most of the instability of the nitrogen dioxide oxycellulose (5, 8 ) , those made under conditions
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2175
b
0 COTTON
I
3 4
IO
8 1.5
16.6 50.0
30
20 ELONGATION
8.3% NO2
SO 27
1
PERCENTAGE OXIDIZED
4%)
Figure 4. Changes in stress-strain curves of tirecord rayon produced by oxidation under various conditions
Figure 5. Change in moisture regain on oxidation with nitrogen dioxide in carbon tetrachloride LITERATURE CITED
of high accessibility and short times should be chemically most stable and of the highest degree of polymerization after alkaline treatment, Celluloses oxidized in 8.3% nitrogen dioxide in carbon tetrachloride for 100 hours have most of the amorphous material oxidized but are unstable, as the time of reaction is long enough to produce a considerable amount of side reaction. This oxycellulose is soluble in dilute caustic because of degradation of portions of the amorphous segments of the chains, but it precipitates on addition of either acid or large amounts of base. This solution is probably a suspension of crystallites having highly oxidized fringes whose partially ionized carboxyl groups stabilize the suspension.
(1) Davidson, G. F., J . TestiZeInst., 32, T132 (1941). ( 2 ) Fowler, W. F., Unruh, C. C., McGee, P. A., and Kenyon, W. J. Am. Chem. Soc., 69, 1636 (1947). (3) Head, F. S., J . Chem. Soc. (London), 1948, p. 1135.
O.,
(4) Hermans, P. H., “Physics and Chemistry of Cellulose Fibers,’” p. 517, Elsevier, Xew York, 1949. (5) McGee, P. H., Fowler, W. F., Jr., Unruh, C. C . , and Kenyon, W. O . , J.Am. Chem. Soc., 70,2700 (1948). (6) Nevell, T. P., J . TextiZeInst., 42, T91 (1951). (7) Roseveare, W. E., IND. E m . CHEM., 44, 168 (1952). (8) Roseveare, W. E., and Poore, E. L., J . Polymer Sci., 24, 341 (1954). RECEIVEDfor review January 29, 1955. ACCEPTED March 31, 1985. Division of Cellulose Chemistry, Symposium on Degradation of Cellulose and Cellulose Derivatives, 127th NIeeting ACS, Cincinnati, Ohio, 1965.
Effect of icellar Size on Physicochemical Properties of Surfactants A. M. MANKOWICH Paint and Chemical Laboratory, Aberdeen Proving Ground, M d .
N A previous paper (6), it was shown that the micellar molecular weights of commercial, 10070 active surfactants differ greatly and that micellar size is a variable in aqueous surfactant solutions. It is important to know in what way this variable influences physicochemical properties such as micellar solubilization, suspendibility, spreading coefficient, and the boundary tensions. It seems that more fundamental relationships will become apparent if these properties are compared a t fixed micellar sizes. No studies of the subject have been published.
MATERIALS
The sodium dodecyl benzene sulfonate (SDBS) was of the lot previously described ( 6 ) , but a different batch of iso-octyl phenyl nonaethylene glycol ether (IOPNG) was used in this investigation. The difference in micellar size of the two batches of the latter is to be expected in commercial surfactants. The builders were technical grade sodium tripolyphosphate and trisodium phosphate monohydrate and reagent grade sodium sulfate, sodium carbonate, sodium chloride, potassium chloride.
