(18) O D ~ NS., , AND WERNER, D . : Arkiv Kemi, Mineral. Geol. 9,No. 32 (1926). (19) STRANSKI, I. N . : Physik. Z. 38,393 (1935). (20)STRANSKI, I. N . : In Jellinek’s Lehrbuch, Vol. V, p. 870. Stuttgart (1937). P . A.: In Eucken-Jakob’s Der Chernie-Ingenieur, Vol. I, Part 3, (21) THIESSEN, p. 170. Leipzig (1933). (22) TEIIESSEN, P. A., AND TRIEBEL, E.: Z. anorg. Chem. 179,267(1929). (23) VANHOOK,A.: J. Phys. Chem. 42, 1191 (1938). (24)VANHOOK,A,: J . Phys. Chem. 42, 1201 (1938). (25) VANHOOK,A,: Northwest Sei. 13, 45 (1939). (26) VOLMER, M.:Z.physik. Chem. 119, 277 (1926);126, 151,236 (1927);Kinetik der PhasenbiEdung, T . Steinkopff, Dresden (1939). (27) VON WEIMARN, P. P . : Chem. Rev. 2, 217 (1925).
INTERMICELLAR HOLE AND TUBE SYSTEM I N FIBER STRUCTURE’ H. MARK Canadian International Paper Company, Hawkesbury, Ontario, Canada Received June 9, lg99 I. INTRODUCTION
Combined chemical and physical investigations of various high-polymeric substances have led to the conviction that they are built up of very long chain-like molecules (3,14, 27, 48, 68, 98, 100, 101). All kinds of information could be obtained regarding the average length of these chains, its distribution over the individual molecules, and its change by different chemical or physical treatment. In connection with these results the question was put forward (36,37,43,50, 51,63,65) as to how the mechanical and optical properties of fibers and films consisting of high-molecular substances may be explained by the molecular picture of their fine structure. The first attempts to tackle this problem led to two divergent suggestions, which we can regard as extreme opposing points of view from which we may visualize our problem. One can start with the idea that the crystallized regions which have been found by x-ray analysis,-the so-called micellae,-have the form of longish rod-like crystals with more or less regular surfaces and are arranged in the fibers or films similarly to the bricks in a wall. Figure la explains schematically this conception, which we might call the extreme micellar structure. I t involves a very distinct difference between the space inside the crystal lattice (a, b) and outside of it (c, d ) ; intramolecular and intermolecular
* Presented at the ninety-seventh meeting of the American Chemical Society, held in Baltimore, Maryland, April, 1939.
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volumes are to be clearly distinguished. Intramolecular swelling would mean that the penetrating molecules enter the crystalline ranges and are divided homogeneously over the whole material. Intermolecular swelling means that only the spaces ( c , d) between the small crystals are accessible to the swelling agent, the inner structure (a, b) of the micelle itself remaining unchanged (45). The other extreme possibility with regard to the structure of a highmolecular material is to assume that there is no formation of defined
I +~,-O' OA:.
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50mp=5xW =L -
I ~ I G . 1. Representation of the possible structures of high-molecular substances
micellae a t all, the long main-valence chains forming a more or less compact mass in which it is impossible to point out certain regions of higher orientation. Figure l b gives a sketch of this other extreme point of view, which might be called an extreme chain structure. This conception was brought forward by Astbury (3) and Staudingr.' (101). In recent years new experimental evidence necessitated the abandonment of these two preliminary pictures and the working out of more detailed idem as to the fine structure of high-polymeric substances in the solid stage.
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In the following a short report of some experiments carried out since 1932 a t the First Chemical Institute of the University of Vienna will be given; the aim was to learn something about the intermicellar spaces in natural and synthetic fibers. Figure IC shows schematically the result, which may be regarded as lying between the two extreme conceptions represented in figures l a and lb. The method used for this purpose was x-ray analysis, which has already given much valuable information about the crystallized portion of cellulosic samples. It may be justifiable to regard the study of this crystallized portion aa more or less completed, and a recent very careful investigation by S. T. Gross and G. L. Clark (29) seems to have settled the last doubtful questions in this field. As a result of a long series of scientific work started in 1918 (1, 3, 10, 29, 39, 40, 42, 46, 62, 76, 77, 81, 83, 84, 85, 89, 93, 94, 100) we can put forward certain lattices for the micellae of the native and mercerized cellulose which imply definite coordinates for all atoms in the elementary cell and describe the relative positions of the glucose residues and the main-valence chains in a more or less quantitative manner. But this picture excludes entirely the non-crystallized portion of the samples, and another series of publications has pointed out with increasing emphasis that this part which has escaped to date the direct attack of the x-ray method may also be of considerable interest, especially for the technical properties of the fibers (2, 8, 11, 15, 21, 28, 32, 36, 37, 38, 43, 51, 53, 54, 55, 60, 62, 66, 69, 70, 81, 97). Therefore the question was acute as to whether it would not be possible to get experimental evidence regarding the amorphous portion by making suitable x-ray investigations. Two possibilities seem to offer themselves for tackling this problem : namely, ( A ) the direct x-ray analysis of the amorphous material in the fibers, and ( B ) the introduction of minute crystals in the intermicellar holes and their observation with x-rays. Let us consider these two ways and refer briefly to the results. 11. THE NON-CRYSTALLIZED PORTION OF CELLULOSE
A . X - r a y study of the non-crystallized portion of cellulose Although the x-ray method refers mainly to crystallized or semi-crystallized materials, its applicability has been lately extended to the study of the structure of liquids and’amorphous solids. Following the ideas of Prim and Debye (16, 17, 49, 64, 90) a number of investigators have satisfactorily cleared up the structure of the liquid state by measuring t)he scattered x-ray radiation under different deviation angles (47, 49, 56, 64, 78, 87, 88, 91, 99, 102, 103, 104, 106, 108). While crystals give the well-known sharp spot- or ring-diagrams, which
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indicate a high-molecular order in the samples investigated, liquids give diffused rings which show roughly that there is a certain order inside the investigated material but that it is distinctly inferior to the degree of orientation in crystals. But it turned out that the angular distribution of the scattered intensity furnished enough information to paint a picturc of the molecular arrangement of liquids. From the point of view of experimental method, it was necessary to follow the whole intensity curve point by point and not to confine the measurements to the deviation angle of the intensive peaks. Hence the study of the liquids means to measure and discuss carefully and quantitatively the intensity of the diffused scattered radiation and not merely the deviation angles of the interference spots (16, 17, 90, 91). If one attempts to apply this method to the diagrams of cellulose fibers, the first question will be whether enough diffused radiation can be observed to indicate that amorphous portions of considerable percentage are present. A first and rough orientation about the problem in question showed that, in fact, practically all x-ray diagrams of natural and synthetic fibers show considerable blackening of the background even when one works with carefully filtered radiation and excludes altogether the scattering from other solid or gaseous material. This fact encouraged us to follow the way just briefly outlined here and to put forward for the investigation the following questions: ( 1 ) How large is the amorphous amount in different fibers? ( 2 ) Can its percentage be changed by mechanical or chemical treatment? ( 3 ) What do the diagrams show about the structure of the amorphous portions? We shall consider these three questions separately : (1) Figure 2 shows the diagrams of three cellulosic samples,-hcmp, ramie, and a highly stretched viscose rayon yarn. In all three cases the same amount of matter (in grams) has been irradiated with filtered radiation. In fact, it can be seen quite clearly that the intensity of the interference spots is practically identical. Yet the amount of diffuse scatterrd radiation is entirely different. A similar effect is given in figure 3. Figure 3a shows a fiber spun from a viscose solution under certain stretching devices. One sees a clear fiber diagram but obwves at the same time an appreciable amount of diffuse scattered radiation. If the fiber is swollen and extended about 60 per cent, it gives the diagram shown in figure 3b. One observes that the orientation of crystallized portions of the filament has slightly improved and a t the same time the general background of the picture has decreased. If one stretches again t o about 120 per cent elongation one gets the diagram in figure 3c, n hich shows another increasr of the intensity of the interference spots and a dccrrasr of thc general blackcning of the picture. Another set of diagrams is shown in figure 4. A thread of rellulosc hydrate was photographrd (a), then cxtcndcd in thr suollcn state and
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wain phot,ographed, after drying (h). One observes that the stretching increwx slightly the orientation of the micellae and at t,hc same time decreases very distinctly the general background of the diagram. The two other diagrams (e and d) show the same effect for et~hyleellulose. This behavior reminds one very much of the well-known phenomenon
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at least, badly oriented, material. T o estimate this amount careful intensity measurements must be carried out. It tias alnady been mentioned t,hat we have a ratlrcr complete knowledge of t.he cellulose lattice, owing to the rfccrit work of G. I,. Clark and his collaborators (29, 93, 100). This cn:~blcsus to construct an ideal diagram of a fiber which consists of up t o
FIG.4. X-ray diagrams oi (a) a thread of cellulose hydrate, (h) the same nftcr .welling and dryins, (c) R thread of ethylcellolose before st,retehing, and (d) n thread of et.l~ylcelluloseafter strctching.
100 per cent of crystallized cellulose. For this purpose we have to combine thc different factors which togcther build up the intensity of a n x-ray
diagram. Figuro 7 shows how this tias to be done in the case of cellulose. Figure 7n kives tlw intemsiiica of tlie different reflections listed in t3rhlc 1. Tlie deviation angles are taken from the cellulose model wliich waa recently and finally proved by G. I,. Clark, and all intensity factors-namely,
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the Lorentz, Dehye, polarization, and frequency factors. Figure 7h shows the atomic form factor, which for the present case was taken &? an average between the values of thiq factor for oxygen and for carbon. The superposition of tlie t,wo parts of figurc 7 gives what wc could ettll the “theowtical diagram of ideal cryst,allized cellulose.” It, is shown in figurc 8b, wtiilc figurc 8a gives the intcnsit,y distribution which one gets txperimentally. The diffemnct: hctaeen thc two can he seen v t ~ yclrarly.
Fro. 5. Monoehrumatic n-ins dingiimfi of (a) unstret,clicd rublxr, (b) a partidly stretclicd rubher, a n d ( e ) a hip-hly stretched robber.
Them is much more diffuse scattered radiat,ion in t,he actual samplc than in the ideal diagram. The same effect is shown in figure 9, where one sees the original photoregistration curve of a native ecllulose fiber. One observes distinct.ly the high amount#of diffuse scattered radiation in the immrdiatc neighborhood of the direct x-ray beam. The evaluation of these diagrams leads to t.he conclusion l.hat in all nahral and artificial cellulosc filaments an apprcciahlc amount of the total matter is present not in crystallized hut in a more or less amorphous form.
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(e) During tliest: studies it turned out that in a normally sett,led viscose filament only about 40 per cent of the fiber is crystallized and 60 pcr cent amorphoiis, while a t tlie end of tire stretching about 70 per cent is crystallized and the rest amorphous. This show~sus that even in the cme of apparently good x-ray diagrams a large amount of [,he material which forms a samplc is not in its crystallized state.
F I ~6.. X-ray d i i w x m s of (Ptj liqiiid wnt,er, ( b j n highly swoI1cn r:ellulose fil:imeet, ;md (
