Rayon Structure J
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Figure 2.
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Etch Figures of Tire-Cord Rayon
E X P E R I u E N T b L DETAILS.Cellulose or raven samDles of anproximately one gram were digested in 200 ml. of Kickerson's reagent (2.4 N hydrochloric acid-0.6 M ferric chloride) a t 100.0' C., and the loss in weight of sample was determined after various lengths of time in separate experiments. The all-glass apparatus consisted of a 500-ml. round-bottom two-neck flask fitted with a reflux condenser and nitrogen bubbler. T h e flask was deeply immersed in a thermostated oil bath. Rayon samples were cut into conveniently short lengths before use; other cellulose samples were formed into loose mats which readily broke up in the hot acid. All samples were first dried for 36 hours in vacuo over fresh phosphorus pentoxide and weighed, then quickly added to the preheated reagent a t zero time. The reaction was stopped by pouring the hot mixture into 2
liters of cool water, with stirring. I n each case the residue ma8 collerted on a fritted glass filter, washed thoroughly, and neighed aftcr drying in an oven at 105' C. Percentage hydrolysis (weight loss) os. time curves (Figure 1) were constructed and were found to show a n initially rapid rise (for about 2 hours) follorred by a slower, linear rise. Extrapolation of this linear part to percentage hydrolyzed a t zero time (accessibility) was made using 3- and 6-hour values. The slope per hour) was arbitrarily taken a$ of the, Iinvnr part I j~c~centage thc rc:i( tivity oi the, crystalline parts. ACCESSIBILITY RESULTS
Strictly comparable rayons, differing only in degree of stretch during regeneration, were prepared from a single sample of com-
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mercial rayon-grade wood cellulose from southern pine. The viscose (7.5% cellulose, 6.5% caustic) and spin-bath (llyo sulfuric acid, 23% sodium sulfate, 0.85% zinc sulfate, 4y0 glucose a t 50" C.) compositions were representativeof those normally used in the rayon semiForks in this laboratory. An extreme difference in t,he amount of stretching was employed in this series. The most highly stretched rayon was a high tenacity tire-cord type; considerablj. less stretch was given to the normal rayon, and an entirely unstret,ched spinner's fluff was prepared by ejecting the viscose into the spin bath and allowing free shrinkage without tension. The results for these three rayons and the original wood cellulose are shown in the first part of Table I. Stretching under these normal conditions of regeneration produced no significant effect on the crystallinity of the filaments, despite the extreme differences obtained in renacity and elongation. The spinner's fluff, having almost no strength, appeared to be slightly more crystalline than the high strength rayons. Therefore, the increased orientation of cellulose chains which accompanies mechanical stretching of the filaments ( 7 , 15) does not 3eem sufficient to bring additional chain segments into the crystal lattices that are evidently formed by 10 l l i n u t e s 33 Minutes 180 Minutes regeneration alone. Figure 3 . Etch F i g u r e s of Spinner's Fluff from Kegular Bath I t must be emphasized that this lack of effect 'on crystallinity may not always be the case if the conditions during in Tshle I illustrates this kind of divergence between accescoagulation and regenerat,ion are varied so that different sn-ollen sibility and strength; the sample was obtained by coagulating states of the newly formed filaments are obtained. Conrad and and regenerating in two separate steps ( 2 ) , a process t h a t was dcroggie ( 3 ) examined the accessibilities of a number of rayons in supposed to give the least possible orientation in the fdaments, Sickerson reagent and found a range of values from 15 to 31.5%, such as might arise from accidental mechanical stresses. T h e Thusj a large amount of stretch, which appears from the present accessibility of this product was essentially the same as that of results to have no effect on crystallinity under normal conditions, the other unstretched rayon, but the strength was considerably may increase crystallinity if the srTollen state of the filaments is better and the elongation greater. markedly different'when this stretch is being applied. Tire-cord type rayon from cotton linters (Table I) was spun The effect of these changed conditions on yarn strength may under the same conditions as those used for the corresponding be due to a n actual change in orientation or crystallinity, or i t wood cellulose rayon. Although the original linters showed a niay be due to a n improvement in uniformity of structure of the significantly smaller accessibility than the n-ood cellulose, the 6laments in cross section. A second kind of spinner's fluff listed final rayon accessibilities a e i e not very different, and the tcnaci-
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in three dimensions.
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An experimental problem exists, t,berefure,
TABLEI . ACCESSIBILITIESOF CELLITLOSES TO KICKERSOX of rendering visible the obtained planes of weakness; the problem REAGEST consists in making the etched product appear in two dimcmions, Yarn Strength, ~ ~ R ~ ~ ~~Grams/Denier ~ ~i Elongation. Sc Material bility, % tivity" Dry Wet Dry Wet Wood celluloee from So. pine 5 9 1.6 .. Rayon. high stretch 25 5,2 3.4 2.2 10.0 15.7 Rayon, normal 27 4.5 2.1 1.2 23.5 35.2 Spinner's fluff 21 4.3 0.06 0.02 28.7 43.3 &inner's fluff from 2 s t a e e 3.2 1.3 0.6 12 5 63.4 regeneration-' 23 1.2 ... .. Cotton linters 4.5 Rayon, high stretch, from 5.7 3.4 .. I1 8 linters 23 a Arbitrary units, per cent per hour for crystalline portion, ~~
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ties were tlie same. From this result it would again appear that) rayon crystallinity is primarily determined by the process of coagulation and regeneration-at least under normal spinning conditions; thns any effect of original cellulose crystallinity is small. The advantage of the greater reactivity of wood cellulose in viscose processing, which is reflected in accessibility and reactivity figures for vood cellulose compared Kith cotton linters, may, therefore, be utilized without prejudice in this respect to the mpermolecular structure of the final rayon. APPEARANCE OF HYDROLYZED RESIDUES
The total rate of hydrolysis of cellulose by strong acids is the sum of two separate rates as a consequence of the micellar network structure (13). Such rate curves show that after a certain time the initial rapid rate is largely spent, and only a sloa attack on the crystalline micellar region is evident. I n other words, the acid seems to destroy the noncrystalline sections, and leave only the micelles. The interpretation may be made more general by the stateL e n t that the acid first penetrates the more accessible regions of the supermolecular structure and, by hydrolysis, solubilizes t h o v parts of the cellulose chains most open to attack; t h a t is, the acid etches out disordered regions of the netrvork structure. This interpretation, moreover, is supported by the fact (16) that the x-ray diffraction pattern becomes sharper after hydroly913.
If such a mechanism does exist, i t should result in visible etch 6gures t h a t have some relation t o the orientation in cellulose structures. Rayon can be studied by this means more easily than natural fibers because its characteristic netxork structure i s uncomplicated by a superimposed morphological structure The supposition t h a t hot acids must etch out the cellulose structure, in a manner depending on the degree of orientation of tlie structure, leadq t o the conclusion that the etching takes plnw
Tire-Cord Rayon
Normal Rayon
Figure 4.
so that i t may be examined under high magnification with a
microscope. Furthermore, if a two-dimensional view is obtained, two possible planes of t7eakness are revealed: longitudinal (along the filament axis) and transverse (across it,). Hydrolyzed rayon filaments are not changed from their original appearance until they are mechanically treated; that, is, planes of weakness become planes of cleavage, not spontaneously h i t under mechanical stress. This is a well known charactcristic of tendered fabrics in general (4). Such behavior ofEers the possibility of revealing planes of cleavage separately as n-ell :is t ogt,tlier. The technique described below vias designed with all three (actors in mind. K h e n hydrolyzed filaments are allontd l o dry on a glass slide, their shrinkage acts against their atlliesioii l o the glass surface and exerts a force that splits tho filamciits transng versely a t a n y vieakened spots. Application of a c ~ ~ r ~ s h iaction t o the wet filaments forces an increasc in widtli t l i x t split3 any weak planes longitudinally. This is the sour(^ 0 1 so-called fibrillation in regenerated filaments. Finally, by criisliiiig and drying, both planes of cleavage become evident. Tlic :trtual cleavage obtained for a given hydrolyzed samplc is l:~i.gcIy dependent on the mechanical treatmcnt used t o briiig it iiito evidence. However, use of a standardized mec1ianic:i l l reatmerit leads to results for different hydrolytic procesje,~v i l l i tlil'ferent yarns which ara thought to give a good picture of tlic dii'fcwnces in supermolecular structure in the serics.
METHOD. Filaments of rayon m r e added to :in IWCSS 0 1 2.33 N hydrochloric acid a t 100" C. in a large test tube, :riitl left there for various lengths of time. Rcsnction 1 pouring off the acid and adding cold distilled IKI ered filaments, shortened by the action of acid a tvere carefully Tvashed by decantation several tiinvs : i n d kept, under water. The samples R-ere then gently :igit:ilctl with enough water to form a thin suspension; onr drop of t,hc suspension \vas transferred to a microscope slide by means oC :i widemouthed tube serving as a pipet. Two slides were prcpnred from each sample in this manner. One set of slides x a s placed on a moderately warm hot, plate and left to dry. On the slides of the other set, a c o w r pl:iss was placed over each drop of suspension, and the w i t w was drawn a ~ a ywith strips of filter paper held simultaneou. opposite edges of the cover glass. The surface foi liquid caused the cover glass t o he pressed down agairirt the slide with great force. This method of crushing thc fihments could be carried out quickly and easily Ivith a high degree of reproducibility. As each filament was crushed to a width several times its original diameter, i t was presumed that a crushed layer of uniform thickness resulted. The two sets of slides prepared in this way were then photo. third series was obtained by allowing the crushed graphed. % samples to dry in air. Certain samples were also photographed in poluized light (betyeen crossed Kicols) with a first-order red n h t e insrrtcld and with 3.5-mm. Kodachrome film.
Spinner's Fluff, Regular Bath
Cross Sections of Rayons and Spinner's Fluff
Spinner's Fluff, Two-Stage Coagulation-Regeneration
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RES~.I.TS.T h r appearance of hydrolyzed residues of tire-cord rayon, a t diffvrent stages of hyd r o l y s i q , is s h o w n in Figui,c, 2 . A progressive incrraw i I I t r a n s v e r s e s p l i t t i n g (after drying) and i l l longitudinal splitting (alter crushing) is c l e i ~ i , l g e v i d e n t . Unstretcnllcti rayon (spinner’s f l u f f ) .;hon.s t h e s a m e general increase in amount of split tiny, but the appearai1c.c of the cracks (Figurv 3) is markedly differcliit. I n s t , e a d of sharp transverse breaks and II fibrillated appearance longitudinally, the unstrc:t~clrcdrayon shows irregular cracking in every direct ion. The difference is purticxilarly great in the case 0 1 c-rushed and dried samples; the marked regularity of the bricklike elements in hydrolyzed tire-cord rayon contrasts etroiigly rTith the irregul a r i t y of u n s t r e t c h e d rayon. T l l ~unstretched rayon from u. two-stage coagulation-regeneration process, which le:tds to a uniformly r o u n d e d c r o s s section (Figure 4), .shows much less fragmentation (Figure 5) t,Iian the unstretched sample regenerated in the regular bath ; however, the crarlts are characteristically irregular. The. effect of time of hydrolysis on the appearance or these hydrolyzed r e s i d 11t’s suggested that different rayons could be most, clearly differentiated byuseofustandardhydrol10 Minutes 30 Minutes 120 Minute. ysis time of 45 minutes. Figure ci s110u.s the results Figure 5 . Etch Figure of Spinner’? Fluff from Two-Stage Coagulation-Regeneration obt)ained by this method with tliree ravons and a commercial grade of cellophane. For example, normally stretched polarization colora of crushed and dried filanients of hydrolyzed rayon is clearly different from the highly stretched rayon; the tire-cord rayon and spinner’s fluff. In the two positions of transverse splits are more numerous and irregular, the fibrillation maximum brightness, the cellulose crystallites add to, or subis less clearly defined, and the crushed-tliied figures show mort‘ tract from, the birefringence of the first-order red plate; they numerous, smaller, and irregular bricklike elements. appear blue or yellow, depending on the position of the crystalAll t,hese experimental results seem t o be in full agreement lites with respect t o the planes of vibration of the plate (14). with the hypothesis previously discussed, regarding the etching Cniformity of color, therefore, indicates uniformity of crystallite effect) of hot acid in revealing micellar orientation. The regularorientation. I n the case of stretched rayon, the bricklike eleity of the etch figures obtained from the highly stretched rayons ments appeared completely uniform in color in both positions; and their obvious difference from the unstretched rayons may be the spinner’s fluff, on the other hand, was irregularly colored, attributed to struct’ural differences implicit in high micellar orienin agreement with the irregular etch figure. However, if the tat>ion in the one case and lack of it in the other. This view is spinner’s fluff had not possessed a t least molecular orientation in furthrr supported by color photomicrographs’ showing the * I t waa not possible tu reproduce these color photomicrogmphn hem.
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Tire-Cord Rayon from Cotton Linters
Figure 6.
Tire-Cord Rayon
Normal Rayon
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Cellophane
Etch Figures of Various Rayons and Cellophane, Hydrolyzed 45 3Iinutes in 2.33 .VHydrochloric Acid at 100" C.
regions unoriented with respect t o the fiber axis or to one another, no color would have been found. This indicates the presence of a structure of unoriented micelles, as already deduced from accessibility results. Application of the hydrolysis-crushing technique to commercial regenerated cellulose films leads to a similar appearance of splitting that suggests the orientation of cellulose chains in the machine direction. The interpretation of these results indicates that essentially the same thing is shown by the etch figurca and by the technique of swelling and crushing (6, 11) carried out to obtain fibrillation of highly stretched rayon threads. The orientation of crystalline regions is revealed on the one hand by preferential weakening of the amorphous parts by hydrolysis, and on the other hand by
preferential sffelling of the amorphous parts. The hydrolysis method appears to reveal fibrillation in greater detail than does the swelling method, because of the natural limitations inherent in the latter. The swelling method reveals fibrillae in the iwollen state, whereas the hydrolysis method gives etch figures of fibrillae with enhanced sharpness. One result of this work, therefore, is that it makes available a new technique for the study of micellar orientation in rayon yarn; this method offers a greater range of applicability and interpretation than has hitherto been powble. hlost of the early work on orientation in cellulose fiberc and filaments was done with x-ray diffraction methods ( 9 ) . Admittedly ( 1 2 ) , however, those methods are not well suited t o quantitative measurement of the relative amounts of crystalline
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and noncrybtalline components. Chemical methods, such as the one used in this work, permit quantitative estimations t o be made, although it must be kept i n mind that “accessibility” IS determined by the physical and chemical conditions imposed during the test (1). Some support for the present results may be taken from the data of Lauer and co-workers ( I O ) , who found that both isotropic and highly stretched rayons of many different types give essentially the same specific heat of wetting. If heat of wetting is a meawre of the internal accessible hydroxyls, the conclusion must again be drawn that accessibility (or crystallinity) is not affected by stretching, but rather is determined primarily in the procc’.i of coagulation and regeneration. LITERATURE CITED
Haas, R. H.. and Purves, C. B.. J . -4m. C’hcm. Poc.,66, 59-65 (1944). (‘21 Chnrch. W. H., and Underwood, W. F. (to E. I. du Pont de Xeniours & Co.), U. S. Patent 2,249,745 (July 2 2 , 1911) C31 Conrad, C. C., and Scroggie, A. G., IND.ESG. CHEJI.. 37. 111 Assaf, .i. G.,
I
592-8 (1915). Dorte. C., “hIethods of Cellulose Chemistry”, p. 212, New York, D. Vin Sostrand Co., Inc., 1933. ( 5 ) I’rnns, E., Die Chemie, 56, 113-20, 132-6, especially 13-1. Fig. 25 ( 1 913).
817
G r a l h , N., and Samuelson, 0.. Sccnsk P a p p c r s t i d n . , 48; 1-6 (1945). Hermans, P. H., in Rohrs, Staudinger, :and Vieweg’s “Fortschritte der Chemie, Physik, und Technik der makromolekularen Stoffe”, Vol. 11, pp. 17-35, Berlin, J. F. Lehmanns Verlag, 1912. Kratky, O., Angew. Chem., 53, 153-62 (1940). Kratky, O., in Rohrs, Staudinger, and Vien-eg’s “Fortschritte der Chemie, Physik, und Technik der makromolekularen Stoffe”, Vol. I, pp. 172-91, Berlin, J. F. Lehmanns Verlag, 1939. Lauer, K., Doderlein, R.. Jiickel, C. and Wilde, O., .I. m k m mol. Chem., 1, 76-96 (1943). Lauer, K., and Mansch, W.,Z ellzolle 11. Kunstseide, 1, 39-43 (1943). Mark, H., in L. E. Wise’s “Wood Chemistry”, p. 129, New York, Reinhold Pub. Corp., 1914. ESG.CHEX,34, 1180-5 (1012). Nickerson, R. F., IXD. Ritter, G. J., and Mitchell, R. L., Paper ‘7‘mfe J . , 108, No. 8 , 59-63 (1939). Rose, L., J . SOC.Dyers Colourists. 61, 113--18(1945). Sisson, W..1.,in Einil Ott’s “Cellulose and Cellulose Derivatives”, p. 226, Yew York, Interscience Publiehers, Inc.. 1943. Spurlin, H. M.,Ibid., pp. 931-42.
(4)
PRESEVTED a t the Yorthwest Re:ionnl lleeting of the AMERICAN CAEUICAL SOCIETY. Seattle, Wash., October 20, 191.5. Contrihution No. 4 from t h e Central Chemical Laboratory of Rayonier 1 n c o r p o r a . d
The System Acetone-Water1,1,2-Trichloroethane J
TERNARY LIQUID AND BINARY VAPOR EQUILIBRIA Robert E. Treybal, Lawrence D. Weber’, and Joseph F. Daley2 S e w York Cnirersity, S e w Y o r k
T h e solubility, tie lines, density, and refractive index were determined in the ternary system acetone-water1,1,2-trichloroethane at 25’ C. Applications of various tie line correlations are considered, and a convenient method is described for estimating the position of the plait point. Densities, refractive indices, and viscosities at 25’ C. as well as vapor-liquid equilibria at 755 mm. Hg were determined for the binary system acetone-trichloroethane. Vapor pressures of trichloroethane were measured over the range 73.5’ to 113.5” C. The data indicate that 1,1,2-trichloroethane would make an acceptable solvent for extracting acetone from its aqueous solutions.
I
K C O S S E C T I O S n-ith a program for determining the charac-
teristics of liquid-liquid extraction equipment, it was found desirable to have rather complete data on equilibrium and other physical properties for the ternary system acetone-water1,1,2-trichloroethane. These data were accordingly determined, and are reported in this paper. Reagent grade acetone, dried over Drierite, was fractionated in a laboratory column equivalent to approximately 20 theoretical plates, and a central portion of the distillate amounting to about 75% of the still charge was retained for this nork. The fraction had a normal boiling point of 5 6 . 1 ” C. over its entire range, a density d i 5 = 0.7840, and a refractive index n22 = 1.3556; these values agree with the accepted characteristics ( I O ) . I 2
A t present in t h e United Statpa K a r y . I’rwent address, T h e Flintkote Company, E a s t Rutherford, K. .I
53, S. Y .
The 1,1,2-trichloroethane, purchased from the Carbide and Carbon Chemicals Corporation, was distilled by a method similar to that used for acetone, and the central portion of the distillate had a normal boiling point of 113.5’ C. over its entire range. I O ) , with one Published values range from 113.3’to 114’ C!. (6,9, listing of 113.5’ C. (8). The central fraction had a refractive index nzj = 1.4715, whereas previously published values range from 1.4711 (8) to 1.4706 (9), and a density d:’ = 1.4412, which agrees with the published value (9). The third component WBB laboratory-distilled water. TERNARY LIQUID DATA
Determinations were made a t 25” C. of the limiting solubility and the tie lines in the ternary system, according to the CURtomary procedures. Mixtures of acetone and trichloroethane of known concentration were held in a water bath a t 25.0’ * 0.1. C., and nere titrated with water until the appearance of a slight turbidity indicated the limiting solubility concentrations. The refractive index (by -4bbe refractometer) and density (by pycnometer) of the solutions were determined after the turbidity had settled from the solution by standing for a short time in the water bath. Similar measurements n-ere made by titration of acetonewater solutions with trichloroethane. The solubility of trichloroethane in acetone-free water (Table I) is in agreement with the data of van Arkel and Vles (f). Although the solubility of water in trichloroethane has apparently been measured (16), the present determination could not be checked because the published data were unavailable.
