*
nee of Molecular Structure on Properties H. MARK Polyteebic Irutituts of Bmoklyn, Brooklyn 2, N. Y.
m
the ultimate consumer. purpose of this T h e following faetorn appear to be of particular dgnifipaper in to viaualiw, in This has the consequence cpnce for the development of good fiber-forming properthe frame of thin symthat the exaggerated appliti- of a polymers Average molecular weight should not be cation of any kind of guidpasium, the synthesis and too h w , b u w tende strength, elongation to break, and devdoDment of a new fiber ing principle will be danmistance against abrasion and fatiguing decraus sharply former- fmm the point of gerous and that conaideras the dof polymerization of the material becomes able tactand restmint muat view of the research chemist too low. Present experience indicntsm that mo low molecbe exerted in using fundawho in aatuslly charged with ulpr weight fiaetions cpuw brittleness, whereas too high mental knowledge in any inthe responsibility for such molecular weight constituents a n be responsible for d i 5 dividual case. work in the laboratory of e d t p-ing in filtration, deaeration, and spinning. his company. In synthesisA tendency to form of crystalline character on Two PRINmLBs W R ing the macromolecules of a stretching, slashing, or drawing is of importance in obBUIWING UPTENSILE new fiber former there are taining a complomise between tensile strength, haneSTRENGTH an overwhelming number of vernal propcnies, and break elongation. Strong and nyIf a Bber that conaista of poasible combinations beIwly distrihutsd intermolecular force centern, stiff SEEmacromolecules going unintween more or lese easily ments in the chains, and mymmettic arrangements of the terruptedly fmm one end to available basic materials. substituents favor the tendency for crystallization. High the other could be conIf it were necessary to exsoftening point, low btittle point, and a bigh resistance structed, ita tensile strength plore every single one of .eninst the attack of chemioale.,oxygen, light. a n d microwould be given by the force them, very expensive and orpnisms are den eswntial. necessary to break one intime-conmlming labmtory dividual single carbon-te work would be nweassry which would he followed carbon. carbon-to-nitmnen, or carbon-te-oxygen bond by more expenaite and . . timen +e @&..of chains more time-conauminn oilot per unit cmss section. Appmximate ~ t i oarried m out ph&o&ations; only way to shorten this tesk, to rule for oellulGe fibers severs! yeara ago (4, ll-f& rasulted in the out a large number of combinations as evidently inferior, and following values for theae two quantities:. to pick fmm .*e beginning 'thme which offer the best ohsnae . . for 8&d development would be to r e l y , q~ certain phnForce to break a single C-C+ '2-0, or &N bond: -2.5 X &plea w ~ d the of a w m l e c u l e ,+i* U)-'.d.ywa ' . , ita abilitq b..@as'a gwd fiber former. ,l%&&pripcipl~~widently.heve,tobe formulatad a renult of Number of cellul& c h e p e r sqoare.am.: -8.0 X 10'' of the ..lstiapB betrsaeh molecular The product of these two quantities' g i v ~for -the tensile propetties of 'dnting h with wellstrength an &timate of 7.2 X l o w d y n e per aquare em., corm For a long *.there were only f aponding to 'about 70 gmnn denier. for such ntu-, +ton, silk, This in much larger than the d mdionly a compsrstitrely narmw basis c&s that on the average during the breaking of a fiber only relasuch principl". Beaently, however, e tiyely few h e chemical bonds are severed. In fact the incandidatea .for bmh fundamental studies greatly di+dual macromoleculeg gre only a few micro- long and c ~ n , tended by synthetic and &ere'-, as a d t , therefore, never go from one end of a mtmlwmpic fiber a rather rapid m u d a t i o n of data whieh other. What is easentiany lnoLepin the tenaile teat of a fi lation ofwoh prjhoipleu. Even so, presest b d , b o n d s between the i n d i v i d d ohsfn ?noleculea whbh tions between molecular stsuchrie and fiber overlap each other and starb slipping d&g each other as Bwn as pmriminsry state; & d m still to work qdbtiie their lateral conneotiow sre w v e~d . In order to proiluoe desmhrhwithq-*tivelah. ~ ~ d ~ tensile strengt6 it in,' h f m , necessary to d n % h , * m e rthat the of a fiber in textile depend on its owtanding perform- , . latersl coheaion. There are two' € u n ~ e n t a l l ydifferent ways not d% to scwmp'inh &in one.singlepmp&y, such as tensile s e n g t h , &odulun of
T
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,
,
~
-
e
tbia:
~
elrtiaity, or recovery power but much ratherah a Well balanoed cornbination of several properties Extreme performance in one ly exhibited tit the expense of .a loss of other WSandiny* from thepoint *vi& of t h tex trialidt and
2110
'
1. -bU& do%the length of the individual chain molecule groups which &bit noticeable intermolecular forcea, such ~ ~ ~ extended attraction betweepl adjscent ahslns w% becomes particularly noticeable if the ohains are paraflelized along the
&..%kef MBE'a8W.Q :'CH E M I STR Y
,:m.a,ne. 9
B
1
Lateral bonds of this ty e lead to the forma. tion of crystallined arrays which repres~?lateral cohesion and produce tensile strength. , . 2. Establish at Certain strictly~'k%limlepo&.stmn cram linka in the form of c h d d honda,.which kmn.bvo ,&want chains irrevemibly tied to each other and, rovide in this manner for the Bxietence of an network opwidely spaoed peuent fix points or cross 1 a. This pMcpidunt is common practice in producing strong snd.reve~niblyexh.sible rubbers. axis of the fiber.
I
.
Strength can, therefore, in principle be b&t h8 fiber either by a dull me trio ally extended n o m of intermolecularattraction which leads to crystalli.atiou or by strong l d i z e d bonds which repreeent cross linking. PUINCIPLE OF CRYSTALLIZATION A N 0 ITS SIGNIUIC*NCE FUIIlmBR.HIRM*TION '.
In view of the importance of the total amount of the laterally ordered phaae. and of the c&acter$,ti~~ of ,ita distribution in the aample the tendency of a given polymer to c r y s ~ l l &b& coqes a matter of important conSideration. Although the &ct fonnulation of this tendency is a complex problem, it aeemn that a few factore arc of preppndemt influence (16): 1. Macromolecules havingrelacivelyrigid and inflexible chains crystallize more easil than thaee with chains of a high, d-e ,of mternal flexibility. h e stiffniss can be c a d by r 'd chain links,,eucb as the glucose rings in cellulose or the p$enylene rings u1 T e r y j F e , P y m n , &pd ance of substlhlents,such aa rn 2. If stmwiy ~ l a r g r o u p s gen b o n d i n g $ p d are.iegul the individu nqaomdecule lose and p o l ~ y l . . ~ orb the l -C&-IiHups in polyarmdes and pel ptitla, there resulta a dktinc$otendency for the formation O&ally ordered domain@. . T h e c l wtbe p u p a and the bettei thtir lateral fit, the more p@n6ynted is their effect on cryatallinity (5,7). . . 3. Bulky, nonpolar and irregularly diat&uted. subatituenta, which space tbe individual chain molecules ap& f&meach other and prevent the eebhishment of hydrogeu b r i w s , noticeablly decrease the tendency for crystallization. The enme effect 18 produced b the exktence of asymmetrically aubatituted carbon atom whicx permit the existence of D- and L-configurations in random aeauencee alone the l e d of the individual macro-
Thia prinoiple ia responsible for the high tensile strength of fibers such 811 h, cotton, nylon, wan, and Dacmn. Fibers of theae materials can be cowidered ne an interconnect& system of latarslly ordered or orystalline domaha embedded in a matrix ofIatgrally disordered or amorphous areas. It..appears that the crystglline domains are mainly responsible for a high resistance of 8"pi.e. teat pieqe agsinet aweliing and softening-for ita rigidity and denaityyhereaa the laterally less oqIered areas contribnte noftnees, k i b i l i t y , and reversible extensibility. 4. The symmetry in the arrangement of the individual substituents along the chain appears LO be of im nance; symrnetriIn thia sense it could be aaid thst it.would be desirable to have a cal aubatitution such as in a a r a n and wl&f&vlene favor crvamaterial of which .the cr~~talline dom& posa+y a high melt@ tallinitv as c o m m d with the less &&et&arranaement"of point while, at the -e time, the amorphov'areaa have a low the suhtituents-in polyvinyl chloride br polypro yleni. woalled s&nd order tramnition temperature. If, in a minple 6. Copqlymerisation, @ general, decreases tge tendency for ervaallnat~onand. d earned out between monomers. which form of such nature, tlie crystalli line" &d "amorphous" regions form t icaliy cr stalliiie polymers: l e d to phenomena similar to interpenetmting t h r ~ s i o bnetworks l the ultimate macm tCeutecticietmvior in metallic a ~ ~ o y s . soopic yielding ofthe materlalwithincreasing~mporaturewill be controlled by the highmelting, laterally ordered domains, whereas There is, in fact, a striking similarity in the phase transitions of its final stiffening and 6nibrittlement at 'low temperatures will bulk polymers and of metallic systems with the reservation that be a matter of aegment'mobility in the disordered are&. One organic polymers consist of macromoldar chainn whereas migbt consider the "cryatale" to act a8 a h i softening reinmetals crystallize in atomic lattices. forcing filler for the *rphoua system, ,which in turn plaaticises If a fiber is spun from a polymer melt or solution, the randomly the crystalline matrix *the dopain of lower tamperatuy;. . In arranged macromoleoules of the initial system aasume a certam order that t h i s beneficial interaction take place, it is, however, degree of longitudinal and l a w order. The &st depende necessary that the ementially on the two di6erent phases degree of polymerizsr be very finely dL tion and the degree tributed and. inti-.' of axial stretch that mately mixed. If,in is applied to the afber, a higbly c r y filament during spintalline skin were. only ning; the second is looeely co&ted contmlled by the inwith an amotphous trinsic tendency of c o r e , t h e specithe material to c r y s men would not show t a k e . The higher b. an advantageous the tendency the c o o p e r a t i o n of. more lateral order its two phaaee; 'it " will develop, and 88 would collapse at the a consequence the softening point of the stronger and more laterally disordered rigid will be the recore and crack on mltingfiber. ItTaI, bending of the rigid however, bemuse of and brittle akin, alita denser packready at relatively ing, also shoa..less high ..temperatures. s d l i n g and leas Whenwera wmbillg oapwity to accept tion of desirable propdy&'s. Them& erties over a wider favorable com~w C. temperature range is wanted. it an-
...-.
-.".-I.
00
w ..
carefully established in each iiidivitlual caw and depends on the chosen polymer and on the contemplated use of the resulting fiber. With a certain degree of oversimplification, it can be said that any good fiber former of the type discussed in this aection should show a distinct tendency to crystallization. The resulting strong lateral cohesion causes, however, in general a high melting point and poor solubility so that it is difficult to prepare and maintain the polymer in its molten or dissolved state,
b.
a.
Figure 2. Schematic: Kepresentations of Crystalline and Amorphous Domains o. b.
Completely lined up aliiug fiber axis Macromolecules extend through amorphous areas in orossmse direction
Thit has led to the dilemma that niany excellent fiber former,. c-annot be put to practical use because of their high melting point and difficult solubility. I t appears, however, that there existi 111 a way to this if linear macrolllolecules can be synthesized that have a tendency to fold back on themselves &nd that can fornl more +,Ilan one stab]e crystal( 3 ) at thr2 line modification. Barnford and his Maidenhead Research Laboratory of Cour taulds, Ltd., h a w tound that the copolymer made in benzene solution from leucine-,~~-carboxyanhydride and phenylalanine-rV-carboxyanhydride represents, on precipitation from solution, a low melting, easily soluble material in vc hich, according to x-ray and infrared investigations, the individual ,,hain molecules are present in a folded configuration. The folding of the chains in this socalled alpha modification is repreqented b j the scheme
R
H
I t contains the chain molecules in their extended zigzag form so t,hat all hydrogen bond capacity can serve to bond adjacent macromolecules strongly together, once they are parallelized by stretching or drawing. Hence the beta form has a very high melting point and is soluble only in strong hydrogen bond opening solvent,ssuch as anhydrous formic acid. Polymers of this type, which can exist in two different crystalline modifications, evidently are very interesting fiber formere because they may be prepared and spun in their easily solubls alpha form and then, after they have been given the form of a fiber, may be drawn into the high melting and difficultly soluble t)et,a form. K i t h some degree of oversimplification, it may be stated that a polymer that crystallizes easily will be a good fiber former, but. a polymer that can exist in two crystalline modificat,ions, such as shown above, will be a, still bett,er fiber former. Another consideration that appears t,o be of importance in combining high tensile strength with good resistance against xhrasion and fatigue concerns the manner in which the amorphous areas connect the crystalline domains in the final fiber. The formation of a fiber from a polymer melt or solution involves essentially the conversion of a mass of initially randomly entangled chains into a system having a properly rontrolled degree of axial and lateral order. This transition can be followed in a convenient way by the x-ray diffraction pattern. Figure l a represents the diagram of molten or dissolved macromolecules in their random state: the presence of diffuse rings - manifests the absence of any kind of order-the chains are randomly entangled. Figure I d , on the other hand, shows the diagram of the final fiber; the rings have narrowed down to short segments indicating axial order or orientation, and the diffuse character of the rings in Figure l a has changed to sharp segments in Figure Id proving the existence of lateral order or crystallinity. In principle the lransition from l a to Id can be effected in two different pays: 1. F'irbt the chains may be oriented by stretching the melt or bolution in a hemisolid state and establishing axial but not lateral order. hi^ leads to an intermediate state p i g u r e I b ) where the appearance of ditfuse segments indicates the existence of orientation without crystallinity. Then lateral order is produced by annealing ox ietting the fiber in the stretched state. Certain spinning techniques follow this pattern, orienting first in the swollen o1 qemipolidifiedstate and then part of the material to obtain the final balance between axial and lateral order. 2. Part of the material can first be crystallized by cooling or coagulating without tension whereby lateral but not axial order is established. This leads to an intermediate state (Figure IC) where the appearance of sharp rings indicates the existence of crystallinity without orientation. Then orientation may be produced by stretching or drawing the fiber in its semicrystalline state. Certain spinning techniques fol13,,,h\'H low this pattern, first crystallizing a fraction C of the material and then orienting the crystals R by drawing.
i
R
R
and involves the existence of seven-membered hydrogen bonded rings. The hydrogen bonding capacity of the peptide groups along the length of any individual chain is here used to stabilize the folding and hence is saturated in an intramolecular manner. AB a consequence there is no hydrogen bond capacity left for intermolecular attraction which makes the material relatively low melting and easily soluble. It Bas then observed that fibers or films of the alpha modification can be converted into another modification by stretching. This so-ralled beta modification iq represented by 0 0 €I R \c/ H N\c/;\x/ \c/ \c/&/ C\ CH / R 11 H R /I H R 0 0
)IH;
2112
Both ways, a-b-d and a-c-d, start with the same system and lead to the same end product, a t least as far as the x-ray diagram is concerned; yet it has been found that procedure a-c-d seems to be more favorable for combining high tensile strength with good resistance against abrasion and fatigue. The reason for this can probably be found in a different character of the amorphous domains mhich does not show up in the x-ray diffraction diagram. If orientation is first established it is probable that in the final fiber the amorphous areas are formed essentially by chains which pass from one crystallite to another situated directly above or below. Hence, a noticeable tendency to form distinct strands or fibrils, which are not interwoven by chain molecules extending in a transversal direction, may be expected. If, on the other hand, crystallization is first established it is possible that in the final fiber the amorphous areas are formed by chains
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol.
44. No. 9
which paas through them in a random manner and establish certain t r a m e d connections between the cryatalline m a p (14). Figure 2a given a echematic picture of this situationFigure 2a corresponding essentially td route a-bd and Figure 2b to alternate r o u t e d .
A
B
--
STRAIN. ?& SMALL CELLS LARQE CELLS
Figure 3. EBeot of Network Density on Initial Modulus a. bnet&
b.
a--k
&s hi& initid mdulua +ea law iaitid mdoluu
It should be pointed out that each actual spinning procedure will never correepond to either of the extreme c m s , W or d, but will always be a certain superposition of both. The art of spinning consists in choosing the beat compromise between W and a-cd in view of the polymer selected for spinning and of the combination of properties which the 6nal fiber is expected to pOW?E5. This brief discussion of the questions connected with the application of the principle of cryatallimtion in fiber formation intends to show bow important this principle hae been in the paet and how many poasible variations and refinements are atill ahead in the future.
sional networks and the idealized stresestrain C U N ~ B appertaining to the two cases. The cells of the network are depicted in this 6gure 88 being empty, but in reality they are 6lled with a maaa of randomly wiled chains of the macromolecules that build up the bulk of the substsnce. The exact shape of the atrssstrsine curve between ita origin and ita end point depends in a very characteristic way on the chemical nature of this filling. If the chains which fill the cells between the c r w links exhibit only weak intermolecular attraction and hence are not capable of forming stahle crystalline domains, there results up to about 50 to 60% extension a linear relation between strain and stress with a low modulus am represented by curve 1 in Figure 4. A randomly entangled maw of such chains opposes to elongation eseentially k u e e of the entropy loss which the ayatem suffers if the segmenta of the individual macromolecules are forced into con6.g~rations of leaaer statistical probability by the orienting influence of the stretching force. This oppoeition, however, is weak and corresponds to a modulus of elasticity between 10. and 10' dynes per square cm. As Boon am the external force in relaxed. the segments rapidly diffuse back into their most probable wuiiguration and the atmswtrain curve is essentially revereed a8 shown by curye 1' in Figure 4. Such behavior is characteristicfor soft elastomers with long range, low modulus, completely reversible extensibility. Materials of this type are satisfactory rubbers but not good fibers; they are too limp and too snappy for a textile material. The strewstrain o w e of a good fiber with a high recovery power should have the shape as indicated by curye 1in Figure 5. Initially. it offers a considerable resistance against extansion, which is a very necessary property for the m o o t b performance of spinning, knitting, and weaving operations and also guarantees to the ultimate fabric a certsin desirable dimensional stability. At
0.6
c
PRINCIPLE OF CROSS LINKING AND ITS SIGNIFICANCEIWR ETBER IWRMATION
1
The principle of o m linking is extensively used in the ehemiatry and technology of elastomers; it consists in the establishment of strictly localized permanent chemical bonds between macromolecules which o t h e h exhibit only weak lateral attraction on eacb other. The chain molecules in rubbery materials are uaually built up from hydrocarbon type units such am in natural rubber, G R 8 , and Butyl rubber, where isoprene, bntadiene, styrene, and iaobutene are the monomeric constituents. However, there are other elastomers, such 88 neoprene, Buna-N, and Vulcollan which contain chloroprene, butadiene. acrylonitrile, and a aeries of polyester-forming acids and glycols. The croaa links in conventional elastomers are SulfuFCarbon, sulfur-sulfur, s n d c a r b o n - c a r b o n b , but anyetrongcbemicalbondsuchaeare present in ethers, esters, amides, or acetates can effectivelx cro88 link a system of linear macromolecules. In order to permit a subatantially reversible extemibility of the msterial, it is nece8sary that the c m links form a random, widely spaced network of 6x pinta. The details of ita structure determine essentially the poeition of the end point of the stree-atrai~~curve. If provision is made for relatively few croaa links at large average distances, the tensile strength will be comparatively small but the elongation to break, large; on the other hand. if a relatively dense wetem of 6x pointa is aet up, the tensile strength will be comparatively high, but the elongation to break will he small. Figure 3 is a schematic picture of this situation for t y d i m e n september 1952
Figure 4.
Strew-Swain and Relaxation Curve of Fiber
P
higher stresses, above tbe inflection point, P, the extensibility increaees; this is necessary to permit adjustment of the aye tem to more or leea permanent deformations 88 they are desirable in presaing and &aping fahrics. In order to produce a high initial r e s i h c e against extension together with a gradual increase in compliance, am represented by curve 1 in Figure 5, it appears advisable to estsblieh a certain degree of hydrogen bonding or polar attractmn between the segments
INDUSTRIAL AND ENGINEERING CHEMISTRY
2113
of the mass which fills the cells of the network. The initial stretching, then, requires the breaking of interinolecular bonds which needs substantially more stress than the disentangling of randomly coiled chains. As more and more of these bonds are severed, the average molar cohesion decreases, the resistance softens, and above point P , the material exhibit’s essentially rubberlike ehsticity. If a t that point the stress is relaxcd, the material
1.5
e
1
l
1
I
I
10
20
30
LO
STRAIN, %
Figure 5 .
Typical Stress-Strain Curie of a Woollike
Fiber Dotted line is characteristic of its reooverv b r l i a ~ i o r
does not return to its original sha,pe along curve 1, but along curve 1’. The reason for this hysteresis is the folloxing: at point R a large number of intermolecular bonds have actually been broken by the stretching force, but the potential for such bonds still exists in the form of polar groups and of groups vith hydrogen bonding capacity. As soon as the stress is relaxed these groups will reform hydrogen bonds in the best, possible manner compatible with their geometrical positions. As a consequence the system cdlapses into a state of h e r potential energy without undergoing any considerable configurational change:: by contraction. This is clearly represented by the steep drop in stress on the relaxation curve 1’ in Figure 5 , wit’hout much reduction in strain. This spontaneous consolidation of the system which fills the network cells leads to increased internal viscosity, so that the final recovery, which occurs at l o ~ stress, r is a slow rediffusion of the individual chain segments into the statistically most probable configuration. Expressing thc sequelice of these phenomena in terms of t’hermodynamics it can be haid that t,he steep parts of curves 1 and 1’ in Figure 5 are ewentially accompanied by changes of internal energy, A H j whereas the gent,le slopes correspond to changes of entropy, A S . Experimental and theoretical studies of the behavior of wool and other protein fibers have shown tha,t this is essentially what happens during extention and contraction of these materials ( I j Z, 8). If similar properties are desirable in a synthetic fiber, the following requirements should be considered: 1. A permanent loose network of strong chemical boiids between linear flexible macromolecules should be produced 2 . These molecules should be endowed with groups having a distinct hydrogen bond capacit’y 3. The molecules should be sufficiently irregular and unsymmetrical, so that crystallization cannot take place
Materials that satisfy these condit’ions should exhibit a stressstrain behavior essentially analogous to that of wool. There exists as yet no real large scale production of a synthetic fiber former of this type, but it seems that filaments of crosslinked polyvinyl alcohol such as the Kuralon fiber of the Kurishiki Co. in Japan and the P-32 fiber of the American Celanese Corp. 2114
are very interest,ingattempts to materialize in practice the building up of woollike properties by t’heprinciples of cross linking. The spinning of dissolved animal or vegetable proteins such as casein, ,,zein, soybean protein, and chicken feather keratin represents +nother interesting attempt to build up a random matrix of flexible chains with hydrogeri bonding capacity but without any tendency for crystallization. After formation of the filament, a system of fix points is esta,bhhed by cross linking with formaldehyde, glyoxal, or another suitable cross-linking agent. Fibers of this type show recovery properties siniilar t,o that of wool but are still not satisfactory from thc. point of vicw of dimensional st’ability and ultimate tensile strength. It seeins that in these cases the presently used cross-linking operation does not produce ti thin homogeneous network with uniformly and widely spaced joints but. rather establishes clusters of cross links in ceytain areas of t’hefiber-for instance in the skin-and leaves other parts insufficiently reinforced. It also appears that the specifics chemical nature of these cross link-namely, acetal or ester type bond8does not make them q u i k resist.ant enough against chemical influences such as produced by frequent laundering or prolongd wear under humid and hot atmospheric conditions. Thew relative shortcomings, hon-ever, do not. disprove the gencral validity of the cross-linking principle in fiber formation; they only show that the systems chosenfor its application are not yet quite suitable to conform satisfactorily wit,h the many demands imposed on the material by its ultimate consumers. It is well known thattheaft,ertreatment of mollen cellulose fiber, such as cotton and viscose rayon, with cross-linking agents or resin formers has been u x i l for a long time to improve dimensional stahilit>-, \$-et strength, and resistance against creasing and wrinkling. The TRL and thc: Heckert processes represent early attempts of this kind whirh were followed b y man)- more recent formulatioiis such as the Sanforizing and the X-2 treatment. I n all these cases, it, appears that the object, is to establish c r o ~ slink6 betnxen the cellulose chains in the amorphous domains or to deposit a very fine crosfilinked resinous network in these areas and on the surface of the individual fibers and fibrils. Aldehydes, dialdehydes, diiiocyanates, silicon esters, and diepoxides have been used for this purpose, and prior modification of the cellulose by the addition of acrylonitrile, allyl chloride, and methylacrylates have been tried. Very interesting and promising results ha.ve been obtained by some of these combinations shoving that the principle of cross linking may not only be a useful guide in producing new synthetic fibers but also in improving exkting and already wellestablished materials. REFERENCES Alfrcy. T., ,Jr., “Mechanical Behavior of High Polymers,” p. 414, S e w York, Interscience Publishers, 1948. Astbury, TT. T., “Fundamentals of Fiher Structure,” London, Oxford Univ. Press, 1933. Barnford, C. H., Hanby, W. E., and Happey, F.,n’ature, 164, 138, 751 (1949); Proc. Rog. Soc. ( L o n d o n ) , 205A, 30 (1951). Boer, .I. I€. de, Trans. P a m d u y Soc., 32, 10 (1936). Edgar, 0. B., and Hill, R., J . Polrlmer Sci., 8, 1 (19.X?). Fuller, (1. S., Baker, W.(I.,and Paper. N. R., J . Am. C i ~ o x . Soc.. 62, 3295. (1940). Fuller, C . S.. Frosch, C . ,J., and Payer. 3’. R . , Ibid., 62, 1905 (1940); 64,154 (1942). Harris, LI., Mizell, I,., R.. and Fourt, L., I m . EXG.C I ~ C M 34, ,, 833 (1942). Hill, It., and Walker. E. E., J . Polvmer Sei., 3, 609 (1948) Mark, H., IND. ENG.CHEX.,34,439, 1343 (1942). Mark, H., “Phy-sik und Chemie der Zellulose,” p. 30, 13erlir1, Julius Springer, 1932. Rleyer, K. H., and Lotniar, W., HeZu. Chin&.Acta, 19, 68 (1936). Ott,, E., “Chemistry of Cellulose,” p . 999, Xew York, Interscience Publishers, 1943. Roseveare, W.E., Dirision of Cellulose Chemistry, Symposium o n Fundamentals of Celluloje Chemistry, 120th Meeting, Science,” Vol. 11, p. 57, New York, Interscience Publishers, 1946. RECEIVED for review April 15, 1952. ACCEPTED July 11, 1932. Lecture given a t t h e Symposium o n Fiher Structure a t t h e Polytechnic Ins t i t u t e of Brooklyn, March 29, 1947.
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
Vol. 44, No. 9
