INDUSTRIAL AND ENGINEERING CHEMISTRY
474
Vol. 22, No. 5
Cellulose as It Is Completely Revealed b y X-Rays’ Special Application to the Growth and Classification of Cotton, the Structure of Wood, and the Manufacture of Rayon George L. Clark DEPARTMENT OF CHEMISTRY,
U K I V E R S I T Y OF ILLINOIS, U R B A N A ,
A concise account is given of the fundamental structure of cellulose as it has been worked out in detail from x-ray diffraction studies. The data include the size of the unit crystal cell, the presence of long primary valence chains in bundles, the size of the colloidal micelles, and their orientation with respect to the fiber axis. Utilizing this definite structure, rational explanation is given for many of the physical and chemical properties of cellulose fibers. Great improvements in x-ray technic as used in the study of cellulose are outlined. Predictions concerning the manufacture of rayon based upon the fundamental structure of cellulose are presented, and these are compared with actual experimental results primarily for regenerated cellulose of the viscose type. The control of properties of rayon and the details of
ILL.
manufacture in terms of ultimate structure are related to the x-ray patterns. Remarkable new results upon the growth of cotton fibers from the root hairs to the mature fiber are presented to show the various stages in the botanical process. X-ray patterns are also utilized as a possible method of classification of grades of cotton. Diffraction patterns are used to obtain information upon seven classes of facts as regards wood-including comparison of wood structure; comparison of tangential, radial, and cross section; wood swelling, t h e variation in structure upon the leaning side of trunks and the under side of boughs; extension to studies of wood pulp, and fundamental measurements on specimens representing various grades of disintegration down to the “fusiform bodies” discovered by Ritter. ....
FUNDAMENTAL STRUCTURE OF CRYSTALLINE PART OF CELLULOSE
OR all materials which have been subjected to x-ray diffraction analysis there is now probably as complete
F
information on the structure of the crystalline part of cellulose fibers as has been derived for any substance. It is only within the past few months that essential agreement has been reached by x-ray experimenters over the world, following improved experimental technic and the rigorous interpretation of diffraction patterns, particularly by Mark and his associates in the x-ray research laboratory of the I. G. Farbenindustrie A.-G. It is the purpose of the first part of this paper to summarize these results on the fundamental structure of cellulose and to show how the architectural plan accounts for the actual physical and chemical properties of natural and regenerated fibers employed as textiles. For experiments on determination of ultimate structure there have been employed almost universally as nearly ideal specimens as are found in nature-namely, ramie fibers. The experimental technic consists in adjusting a parallel bundle of fibers so that an x-ray beam defined by pinholes passes through the specimen a t right angles to the fiber axis. (Figure 1) The K a radiation from a copper-target x-ray tube with an effective wave length of 1.54 A. is employed. The diffraction pattern is registered on a flat photographic film usually 5 em. behind the specimen. Several hours’ exposure are usually required, but for the patterns made in this laboratory, some of which are reproduced in this paper, a maximum of 15 minutes only was necessary. The metal Hadding-Siegbahn gas-type tube was operated a t 40 kilovolts and 10 milliamperes. Careful regulation of the air pressure, exact adjustment from preliminary experiments of the distance b e b e e n target and cathode for maximum intensity, and a redesigned pinhole system in which the small beryllium foil windows of the tube very close to the target served effectively as the inner defining pinhole permitted a Presented before the Division of Industrial 1 Received April 2 , 1930. and Engineering Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930.
much more intense beam than was deemed possible. With this equipment it is now possible to observe Laue patterns for single crystals of organic compounds on a fluorescent screen. The rapidity gained with this equipment thus compares favorably with the results obtained by Mark and von Susich (IO) with one of the new Ott-Selmayr tubes developed a t the University of Munich and operated a t 40 kilovolts and 30 milliamperes. While in the above technic the x-ray beam is somewhat more divergent than that defined by a long pinhole with strictly parallel base, the diffraction patterns have lost little, if any, definition. As indicated below, these rapid exposures permit certain tests of chemical changes of celIulose with time which are invaluable. The facts which may be deduced from a single x-ray diffraction pattern for a given specimen are (1) crystallinity; (2) crystallographic system and space group; (3) dimensions of the unit crystal cell; (4) number of C6H1005 groups per unit cell; (5) location and binding of groups in cell; (6) size of crystallite or colloidal micelle; (7) lengths of polynierized molecules; (8) type and degree of orientation of micelles with respect to fiber axis; (9) evidences of chemical and physical change; (10) structure and deformation of nonfibrous cellulose. Crystallinity of Cellulose All natural cellulose fibers, such as ramie, hemp, sisal, jute, flax, cotton, wood, etc., and regenerated cellulose or rayon produce diffraction patterns characteristic of crystal fibers. A typical pattern for ramie fibers is shown in Figure 2. A fiber is not a single crystal grain, since a typical Laue pattern would be found if this were true; nor is it an aggregate of small grains in random orientation, since this would produce a pattern of continuous uniform rings. The fiber is constituted of many crystal grains (or crystallites or colloidal micelles) which are oriented so that a common crystallographic direction in all tends t o lie parallel to the direction of the fiber axis. A fiber diffraction pattern which characterizes asbestos, drawn or rolled metals, stretched rubber,
INDUSTRIAL AND ENGINEERING CHEMISTRY
4T6 NO.
ATOMCOORDINATES ( 1 , 9 ) Y Z 0.88 0 0 0.28 0.16 0.08 0.28 0.34 0.92 0.86 0.19 0.02 0.54 0.33 0.00 0.00 0.50 0.12 0.72 0.66 0.92 0.72 0.84 0.08 0.14 0.69 0.98 0.46 0.83 0.00
OXYGEN
x
(3) (6) (7) (8) (9) (10) (11) (12)
C A R B O N ATOX CO6RDINATBS
x 0 0.17 0.17 0
:::; 0 0.83 0.83 0 0.13 0.31
Y
o,ll 0.17 0.33 0.39
::::
o 0 o
0.61 0.67 0.83 0.89
0 0 0
0.80
0 0
Vol. 22, No. 5
protoplasm is involved besides a cellulose surface and the presence of glucose molecules, since the latter may exist in the cell without growth and the cell may grow on one side and not on the other. However, the facts derived from x-ray data go a long way toward explanation of growth. “Grain” or Micelle of Cellulose
0
X-ray data judiciously interpreted have now led us from the dehydrated glucose residue composed of carbon, oxygen, and 10 oxygen atoms a t z 0.5; y + 0.73; z 0.5, and 12 and hydrogen atoms to a pair, bound as a cellobiose residue, by 1-4 oxygen bridge and to a particular grouping in a small carbon atoms a t z 0.5; y 0.73; z 0.5. Such a model of long spiral primary valence chains in bun- unit crystalline cell. An extension to a rational model dedles, in which diffraction periodicities are turns in a screw axis, picts long spiral primary valence chains along the fiber axis is not peculiar to cellulose alone. It may be employed to with cross sections determined by the number of chains in a depict the general method by which Nature constructs such bundle. The question naturally arises as to how long the different complex materials as rubber (stretched) with CsHs chains are, since it is hardly likely that they are as long as the entire fiber itself, and how many are grouped in a bundle. , I n other words, is there a spacial unit of structure larger than the ultimate cell, whose existence and dimensions might be determined from a diffraction pattern? The measurement of particle size, particularly in the range to cm., is now a well-established application of diffraction information. I n the colloidal range the smaller the particle and the fewer the diffracting parallel planes, the less perfect is the sharply unidirectional interference of secondary waves, and the broader will be the diffraction maxima which characterize a given crystalline structure. Hence a measurement of the breadths of diffraction lines or spots a t points of half-maximum intensity leads to an evaluation of grain size in an aggregate. Experiments through the years too numerous to mention have demonstrated the colloidal nature of cellulose, and the ide Views of Model for C&oOs Group Figure 4-Fron x-ray patterns prove that cellulose Serving a s Unit in Cellulose is an aggregate of grains, or crys(Naegeli’s notachains; chitin with acetylglucosamine chains; silk fibroin, tallit’esOr gelatin, collagen, muscular tissue, etc., with polypeptides; tion). Hence measurement Of diffraction breadths for cellulose and even certain silicates with chains of SiOz. . should lead to a t least the correct order of magnitude of the particle Mechanism of Cell-Wall Formation size in cellulose fibers. Herzog (,5) first made such a Upon the concept of long primary valence chains of dehy- calculation with the equation of drated glucose residues backed by further chemical, physical, Scherrer and botanical facts, Sponsler ( I S ) has described in interesting fashion how a cell wall increases in thickness. The ultimate B =2 D COS e/2 layers indicated by x-ray data are only one glucose residue in thickness. KO experimental evidence is available to show where B is the breadth of a diffracthat anhydrous glucose units of the cell wall which constitute tion interference at points of half cellulose are derived directly f r o v glucose molecules which maximum intensity, is the wave originate from photosynthesis. length, D is the edge length of a Assuming that a direct transformation takes place and crystal considered as a cube, e is that deposition occurs at the interface between cytoplasm the angle of diffraction, and b is and cell V‘all, the formation of long chains parallel to the the natural minimum breadth of b i , ” , ’ , g u ~ s : , ; ; ~ o ~ fiber axis becomes a consequence of orderly spacing of the diffraction maximum depend- L I by 0iygen ~ Bridgezof ~ ~ cules due to force fields simihr to deposition On any Crystal ing on apparatus and specimen, T W O Dehydrated G l u c o s e Residues face. If, then, two glucose molecules are thus held in ad- Obviously t h e c u b i c crystal jacent positions of minimum potential energy a t the lattice limitation in this equation is alone sufficient to invalidate it points, they are in most favorable position for condensation as applied t o cellulose. I n 1926 von Laue ( 7 ) deduced from reactions, since hydroxyl groups on each are brought into vector analysis a new equation tvhich in its most general form close proximity so that a water molecule is split out and the is free from the limitations of the cubic system, and permits two residues are bound by an oxygen bridge. Thus the con- size evaluation in different directions and thus the shape of ditions are favorable for such a reaction to take Place in the particle. the simplest rigorous form this equation is only one direction to an indefinite length, since the distance from center to center of the residues is too great laterally for condensation to occur between adjacent units of two chains. B = Sponsler points out that, in spite of this straightforward cos* ?)-l mechanism, a third factor of some kind involving living
+
+
+
+
0.86
+
’
41 +
(5
~~~~ ~
I S D CSTRIAL A N D ENGIA-EERI-Y'G CHE,VISTR Y
May, 1930
Direct Measurement of Large-Spaced Periodicities from Diffraction Interferences
1
where w = - = 0.55
1.8
r = radius of cylindrical preparation, R = radius of camera, and 0 = reflection angle. A simplified expression used with singular success by Hengstenberg and Mark (/i) in determining the shape and size of the colloidal micelles of rubber and cellulose is Rq = 0.088 [ ( b COS
@/?
- (l/b) 7~'r' cos3 0 / ' 2 ) ]
where Rq and e have the same significance; b = BR is the actually measured breadth of interferences, and 7 = X/4irma,, where wzu, is the extension of the crystal particle in the direction a,, or the magnitude which is to be calculated. The micsllar length ( b direction) for mature ramie fiber is about 500A. as calculated from the improved equations. Thus this is also the length of the primary valence chains. The writer has observed lengths of natural fibers ranging from 150 to 500 A. The cross section of the micelles ( a and c directions) is about 50 A., and is determined by the number of chains in a bundle. Generally speaking, therefore, the "grain" or micelle of mature cellulose is an elongated particle with dimensions in the ratios roughly 10 : 1 : 1. The fiber is built from these particles just as a solid column from bricks. Figure 8 shows a plan of the arrangement. Primary valence forces are involved along each chain iri a micelle; secondary valence forces of the van der JJ7aals type hold the chains alongside each other in a micelle; and tertiary forces
Figure 6-Model of U n i t Crystal Cell (Monoclinic) f o r Cellulose S h o w i n g Positions of Long Primar'y Valence Chains of Glucose Residues
Glucose residue Cellobiose residue Unit cell Micelle 1 grain
WEIGHT
-
VOLUME
cc.
...
162
324 6448 100 108
6 . 8 . X 10-22
-
1-2 X 10-18 -0.6
, . .
UNIT GLVCOSRS CGLLOBIOSES UNIT CELLS Glucose residue 1 ... Cellobiose residue 2 1 ... Unit cell 4 2 1 Micelle 6000-12,000 3000-6000 1500-3000 1 grain 3.7 X 1011 1.85 X 102' -9 X 1020
...
In connection with the evaluation of micellar size, a point of great interest is whether there can be any direct evidence of these large periodicities from actual diffraction interferences. In accordance with the Bragg law 9 A = 2d
sin e
it is obvious that such interferences would appear only a t very small angles. On the ordinary pinhole diffraction patterns, therefore, these would be entirely submerged in the trace of the central undiffracted beam onthe film. There are two methods of investigab ing diffraction from these large-spaced periodicities: (1) use of long wave lengths, and (2) use of an ionization spectrometer with extremely narrow slits, or photographic patterns with extremely small pinholes (which is eliminated largely on account of the long times required for exposure). In the x-ray laboratory a t the University of Illinois special researches are in progress with the object of ascertaining the presence of large periodicities on a scale between the unit crystal cell and microscopic sizes. A c o m b i n a t i o n gas-type magnesium-target tube, similar to a Shearer-Hilger tube, and camera has been constructed so that the x-ray beam passes unobstructed through a pinhole to the specimen and film. The entire apparatus is evacuated to the point required for proper operation of the tube. The characterisJic Kcr wave length for magnesium is 9.867 A. After overcoming numerous difficulties, an interference has been observed for cellulose a t a diffraction angle of 11 degrees 20 minutes. This gives a spacing of about 50 A., an identity period which has Figure 7-Side of Model of also been observed by Mark and associates View Part of C h a i n and by Herzog. Using copper radiation S h o w i n g Spiral (1.54 A.) and extremely narrow slits on a F o r m Soci6tB Genevoise ionization spectrometer, a maximum is observed a t about 1 degree 40 minutes, which corresponds also to the same spacing. It is evident, therefore, that the micellar sizes are themselves periodicities which may be observed directly from x-ray diffraction interferences, and that a powerful method is thus available for the direct study of the ranges between microscopic and the ordinary x-ray unit-cell dimensions such as are involved in polymerization and colloid formation. Orientation of Micelles in a Fiber
are involved between the micelles. A further extension might even be made to quaternary forces holding whole fibers in position as in wood, but inert cementing material is more likely. A general summary of the numerical magnitudes involved in cellulose structure is as follows: UNIT
477
SURFACE Sq.
cm.
...
...
S--12'X 10-12 1--3 x 107 MICELLES
...
...
...
1 3.7 X 10'3
Another important fact concerning a cellulose fiber may be deduced from the same diffraction pattern from which has been determined everything from the coordinates of carbon and oxygen atoms in the monoclinic unit cell to the size and shape of the micelle containing a s many as 12,000 C6HI0O5groups. This is the orientation of the micelles, both as to type and degree of perfection. Thus the positions of the intensity maxima on the fiber pattern determine, for example, whether the micelles are oriented with their long dimension parallel to the fiber axis, as in ramie, or in spiral fashion as in cotton (6). Then how nearly the orientation approaches the ideal is readily ascertained from the sharpness of localized maxima. On the one limit, as represented in Figure 9a, the diffraction maxima will be sharp spots lying on circular loci but with little or no trace
INDUSTRIAL AND ENGINEERIlYG C H E - I S T R Y
478
Vol. 2 2 , s o . 5
valence bonds. Each chain has a cross section of about 25 Az., so that in a cross section of 1sq. mm. there will be 4 X lo1* chains parallel to each other. Now the work required to break the C-C, C-H, C-0, etc., bonds in organic compounds is known to be 70 to 90 calories per mol. Hence for a single chain the work of breaking is 6 X ergs, or taking into consideration force times distance of separation necessary for attraction, 2 x kg. per chain. Multiplied by 4 x lo’* chains per 1 sq. mm., the tensile strength comes out 800 kg. per sq. mm., which is much too high as compared with actual values. However, it has been shown that the chains are not endlessly long, but contain 100 glucose residues. Consequently a break may occur, not by rupture of primary valence chains, but by slipping of the chains and of the micelles which are held by much weaker forces of molecular cohesion. The secondary valence forces due to hydroxyl or aldehyde (oxygen bridge) groups are fairly accurately known in organic compounds and a tensile strength of about 200 kg. per sq. mm. Figure 8-Complete Model of Cellulose Structure as Deduced f r o m X-Ray Data S h o w i n g a N u m b e r of Cellulose Micelles the may be calculated for cellulose fibers. Interior O n e of W l h c h Is i n Part Exposed a n d Enlarged to Sho& the A further test of tensile strength may be made by using Chains of Glucose Residue U n i t s the known value for the breaking strength of a sugar crystal. a = primary valence forces; b = secondary association forces; c = tertrary micellar forces (diagram by Seifriz) Here the forces involved are those between molecules in layers due to the secondary valence forces of hydroxy and this characteristic is of great importance, since a difference aldehyde oxygen atoms, exactly as in cellulose. The value only in orientation accompanies wide difference in behavior. 30 kg. per sq. mm. is obviously too low. However, when a This applies with particular emphasis to the regeneration of cellulose fiber 1 sq. mm. in cross section is broken, the new cellulose in rayon fibers as discussed below. surfaces are not plane as in the sugar crystals, but distinctly It is not surprising, in view of the remarkable scope of jagged as in Figure 10. This increases the cross-section information concerning cellulose structure from x-ray dif- surface dimensions sixfold on the average so that the actual fraction patterns, that rational explanations and predictions tensile strength is 6 X 30 = concerning the behavior of textile and wood fibers can be 180 kg. per sq. mm., which A made upon the basis of a model which depicts a complex sub- is more nearly the value obmicroscopic building plan so adequately. served for flax. However, this still reprePROPERTIES OF NATIVE CELLULOSE I N LIGHT OF sents the ideal case in which STRUCTURAL MODEL BASED ON X - R A Y DATA the colloidal micelles are in parallel orientation throughCoefficient of Expansion o u t a l l t h e f i b e r s . This c o n d i t i o n is nerer actually . Hengstenberg, in experiments designed t o test the appearance of reflections, made diffraction patterns a t the realized in natural fibers. temperature of liquid air. A measurement of the pattern Local i m p e r f e c t i o n s a n d led to the calculation of the coefficient of expansion of cellu- weakening of molecular colose micelles parallel and perpendicular to the fiber axis. In hesive forces by a d s o r b e d a b Figure 9-Extremes in Orithe a and c directions the value was about 1.0 X and water, etc., lower the strength. e n t a t i o n of Micelles w i t h ReThis A random o r i e n t a t i o n of s p e c t to a C o m m o n Direction in the b direction along the fiber axis, 0.1 X illustrates again the much stronger forces along the axis or micelles with respect to the a = parallel orientation as in fibers of native ramie; b = ranfiber axis reduces the strength dom chains than perpendicular thereto. or brush-heap arrangement theoretically to one-third the as in Cellophane Tensile Strength of Cellulose Fibers value for the oriented fiber, which is within the range of most cellulose fibers. These Upon the basis of the cellulose model it is interesting to phenomena may be subjected to actual experimental test in consider what is meant by the tensile strength of a fiber. the regenerated celluloses in rayon, as will be demonstrated Mark (8) has made some calculations of great ingenuity. in a later section of this paper. The general conclusion is He lists the following tensile strengths of common materials: that the tensile strength values for cellulose fibers are adequately explained by the model proposed. of the circle. At the other extreme are the preparations in which the micelles are in random “brush-heap” orientation (Figure 9b) and the diffraction patterns concentric, uniform, continuous Debye-Scherrer rings. Between these lie every possible gradation, with long, more intense arcs appearing with improving orientation which shorten to the sharp spots. From the standpoint of physical and chemical properties
Kg.Per
K g . per K E .per mm. sq. mm. sq. mm. 20 Silk 35 Acetate rayon, 170 Cotton 28 ordinary 18-20 40 Flax Over 100 Acetate rayon, 10 Viscose, well oriented 60 3 ordinary 25 Rubber, ordinary 15-20 Viscose, well Rubber, well ori5-16 oriented 80 ented 60
sq.
Cast iron Best steel Copper wire Aluminum Lead Wood in fiber directions
Thus, cellulose in the form of flax, which displays an excellent orientation of micelles parallel to the fiber axis, has a strength comparable to the best steel. The calculation is first made upon the assumption that the fiber is made up of endlessly long chains and that the tensile strength represents the work required to sever the primary
Extensibility of Cellulose Fibers
Metals may be diawn into wires or rolled into sheets by virtue of slipping on crystallographic glide planes and a rotation into positions which mill present maximum resistance to further deformation. Gold, for example, is ductile because after one set of octahedral planes, for example, has turned parallel to the direction of drawing, another set of the octahedral planes is in favorable position for further slipping and extension. Cellulose represents another condition, however. If the micelles are all oriented parallel t o the fiber axis and the direction of stretching, then the only thing which can
Crystalline Cellulose Nitrate and Acetate Fibers
seems to occur in colloidal gels in a coiitinouos series of steps. The structure filially obtained with tension is pseudo-crystalNitrated and acetylated cellulose fibers produce clra,racter- line, in which the molecules occupy essentially the same posiistic fiber patterns which are as clearly marked as those for tions as in the crystal fiber but are not perfectly aligned. the native fiber urhich hus been treated. Naray-Smbo and The presence of a residual amorphous phase serves t o oppose Susiclr (12) have obtained excellent results in their crystal the perfect orientation required hy crystals. This clear interanalyses, which are yet not so complete as t,he iniormat.ion pretation of a difficult problem is obviously entirely in accord oil native arid mercerized eelhilose. 4 . pri:pnrat,ion with with the concept of very long chain molecules and with the a nitrogen content corresponding to the t,ririitratc gave the preferred theories of colloidal gel theory. It explains the clearest patterns iw$h an ident,it,y period along the fiber Ihysiral properties of such films, siicli as great tensile strength axis of 26.6 -i- 0.5 A. For specimens with smaller nitrogen perpendiciilar to the chains and tlie weak Ftreugth and ease content even correspoiiding to a mono- and ilinitrate, the of splitting or tearing parallel to the direction of the long patterns were itlwags those of the triiiit,rati: and tmclianged molecules. Tire variiriis propertics of adsorption, chemical iiperposed. The existence of these siibstances as action, etc., as functions of orientation also follow exactly well-defined stoichionietric compounds is, therefore, very those deduced for the i:ryatalliiie fibers. unlikely. Similarly, only the triaeet.at,e gives a cliarnctcrPositive Identification Test for Cellulose istic pattern iv-ith a film a$ periodicity of 10.3 0.3 il., Frarii the precediiig sections it is clear that cellulose i s tlie same value as in cellu- something more than (CdT,,Os),. It has this empirical comlose. This is but another evi- position it is true, hut the term must also imply structural dence of the existence and factors, such as long primary valence-chains, inicelles of cerpersistence of the long hexose tain size and form, a latt,ice type with definite atomic colirchains, and of entrance of re- dinates, etc. Chemical methods might easily fail, therefore, a c t i n g g r o u p s on the hy- in determining surely whether an unknown preparation were droxyl groups between chain€ true cellulose or not. There is oiie method of identification in a micelle. which is positive atid it involves the folli,r\;ing steps: EsStructure of Films of Cellu- terify (acetate or nitrate) and dissolve in acetone or acetonealcohol; spin the solution into a fiber under tension or, as just lose, Cellulose Nitrate, and Acetate indicated, stretch a film; sapoliify or regenerate the cellulose; teRt the product by an x-ray diffraction pattern. If the It bas been shown tirat original material were cellulose, the final fiber pattern will he swelling of fibers during reac- one which is immistakably characteristic or any native or merFiwre 1Z-Pattern for Cellobane Showing Absence of tion may take place to such cerized eellulow. Celloliiosr, glumse, and all (!hemi(!all?: keferked Orlenfstlon an extent that the chains bo-
similar substances give no such puttem; iiuineruus materials which are not well oriented and which give doubtful original diffraction patterns have been proved to be true cellulose, including tunicin or animal cellulose from the mantle of Phaluaia numillala (If). I n the light of the foregoiiig somewhat extensive account of tlie fundamental structure of cellulose, there are presented in succeeding sections of this paper brief preliminary accounts of individual and coliperative x-ray researches now in progress
nterl an iiiferiur variety. l r l all tliret: cases the diffraction rings liave exactly the same ineasuretneiits currespmding to t.rue cellulose. The differences lie in the degree of preferred orientation and in the sharpness of the ANALYSIS OF GROWTH AND CLASSIFICATION OF COTTON interference maxima. There is a marked difference in tlie FIBERS degree of fibering, which is niaxirnum in the case of the first (Il'ilh Waaun K.Fan*, Division of Cotton Marketing, Buresu of Agrisarnple and minimum in the tliird. For example, the cords riiliiiial I?conomici, U. S. Depnitioent 01 Agriculture, and LVCYW. PICEof the arcs on the diffraction rings produced hy fibering have RTT, Department of Chcmisliy, University of Illinois) the following lcngt,hs: first, 2.8 ctn.; second, 3.25 cm.; Although it has l ~ e nknunn for some time that cobton tliird, 3.8 cm. This gradatioii is exactly the same as tfiat fibers yield a typical cellulose x-ray diffraction pattern, displayed by tin qualitative differentiatiair. Furthermore cmiiaratively little work has been done with this ms,t,erial. an exarninatioii of tlir sharpness of ititerfemices indirates The explanation of this lies in the fact that i i i ramie fibers, tliat the chain lengths in the colloidal micelles are greatest for example, there is a rnuch inore perfect orientation of the i n t,lie first sample nnd least in the third. Therefore, satiscolluidal micelles parallel to the fiber axis than is true in failctory plrgsioal properties are unquestionably connected cotton, which appears to have a spiral arrangement. (0). wit11 colloidal size greater than a critical value and in the best A series of develi~pnentalstages of the fibers of Gwsfypiim possible arran@nicnt of these rnioelles with respect to the fiber hirs?ilum represent.ing growth intervals from 14 to 50 days asis it,sclf. has heen studied thus far, by rneaiis of the diffraction method While these saiiiples represent perllaps extreme conditions, ut,ilizing the copper lia radiation, the pinholo method, and it W no iioolit be nossible to classify cotton within much a liitmlle of parallel films as the spocinicn. The samples from 14 t.o 30 days represent the period of elongation in fiber growth. The 35-day sample, for exainple, rcpresents tho early stages aringthe photographs for a whole-rvmd samnle and the fibers chemicallv dissected by the Rjtter methoh. This material is still Frystalline, though the fibering observed in the original wood is absent as is to be expected, and the diffraction circles are much broader, as is to be expected from the decreasing size. The fusiform sample is particularly remarkable for the appearance of 5 very strong and definite inner ring corresponding to a long spacing. This would indicate that linear orientation is much more perfect than cross-section orientation or that an entirely new diffraction pcriodicity comes into play. The sample is different in tiiis respect from any ever observed.
Comparison of Different Woods
Tangential, Radial, a n d Cros's-Section Structures
Under the first topic we have a comparison of the yellow poplar high-density, redwood sapwood, white ash, and southern yellow pine. All the patterns are typical of cellulose with, . however, a considerable variation in the degree of preferred orientation. The most perfect parallel arrangement of the fibers is shown by yellow poplar, high-density. (Rgnre 14a) This is judged by tho sharpness of the localized diffraction maxima. These spots lying on the equator and also on the principal ring R ~ O T . Oand ixdoiv the equator for yellow pophr are very sharp The ineasiiremcrit gives R pcrfect cellnluae result. 'IVit,li this is to he coinparod roilwood sapwood, sout.herLi yellow pilie smnrner, and white ash dry suinmw w-ood. This can he &me by nxmwiiig Lho lciigtli of tlic intensity rnaxima i n s . Text to puplar, thc liest filiering is shown by ycllo\r pine, arid whit,? ash is ncxrly the same. [,ant ill this respect is ttia redwood. The rod wool^ pattcrll is further distingnished by the presciice of coiisidera.lily more mner darkening due to the jircsericn OS uthcr inaterids, eit.licr m much larger quantities or in the more nearly Ilinr conditioii than is Souird in the other woods. Another imporbant obscrvat.imr can IJO made iii harms of l l i c size of colloidal particles measured honi the Imadili of tlie diffraction spots. In this respect tEie southcrn yellow pine seems to be Iroader than the others, iiidicatiiig a smaller micellar size which wonld mean shorter cellulose primary valence chains and fewer cliaiirs in a bundle. The eonclusio~i is that t,he patterns for the different kinds of wood are all sufficienblpdifferent as to characterize each particular variety.
These three patterns are distinctly different. The tangential pattern is typical of the usual cellulose pattern in which the beam of x-rays passes perpendicular to the fiber axisthat is, tho principal vertical fibers in a tree. I n the cross section the heam passes parallel to these principal fibers, and, as is always observed in fiber strnctures, the pattern indicates a random orientation in this direction. I n other words, the diffraction circles are uniformly intense and continuous. There is no niarked iudicat.iou of the fibers which are radial (medullary cays) in a wood structure, which means either that these are too few or that the orientation in them is far less perfect bhan in the vert.ica1fibers. In the sample cut from a radial section the l m m passes perpendicular t.o both verrical and horizontal fibers. We observe, however, in this pattern a double fihering in the sense that tlie equatorial diffraction rnaxima in the usual ease n o ~ vlie 011two lincs crossing caclr otlier. This type of pattern is obtained when tlir beam impinges at an angle different from 90 degrees upon tile rlircction of the fiber axis, or indeed upon any crystallograpliir axis in a single crystal. This would mein, therefore, tu tlirow considerable light upon the direction of fibers with respect to the bordered pits. Although the specimen is correctly orionfad as regards the axis of the tree, there is a different angular relationship,. The actual angle of inclination can be easily calculated as one-fourth the angle nieasured between the two diameter loci observed in this pattern. The notable differenceobserved in structure when the x-ray beam passes perpendicular to the tangential face and to the
(1)
(8
bodies.
Comparison of different woods. Steps in the process of disintegration down to fusiform
(3) Tangential, radial, and cross-section structures. (4) Comparison of Cross and Bevan and alpha-cellulose. (5)
Differentiation of spring and summer wmd.
(6) Effectof Faking dry wood in water. (7) Compression structures for wood on the leaning side of
radial face of the s:inie bundle of fibers is shown in Yigiims I5iz aid b. The specirncns involved were prepared Irp dcligiiifyiiig spnicc :tiid tlieii arranging the films parallel with tI1c faces iii one direcbion. This clearly indicatw tliat orieiitation xil,li rcslicet to the t\\w directions a t right aiiglcs to tlie Ion. :lais iliifcrs greatly; lor all iitlier crlliili tlIliS ctl I I O rli.&inetiriii
