Cotton Fibers Constitution, Structure, and Mechanical Properties

COTTON FIBERS Constitution, Structure, and Mechanical Properties R. F. NICKERSOK Mellon Institute, Pittsburgh, Penna.

Data on the constitution of raw cotton are presented and discussed. Various theories of fiber structure are reviewed. A fiber structure in which the component fibrils are formed from many unit crystalline areas linked by primary-valence glucose chains appears to be the most acceptable. The crystalline units probably represent the crystallization of portions of adjacent glucose chains. Such mechanical properties as tensile strength, elasticity, plasticity, swelling and elastic aftereffect are summarized. A structure of the type just mentioned is compatible with the properties (66). One object of the review has been to assemble for ready reference the available data on cotton fiber constituents and properties. These data are presented in their relation to fiber structure wherever it has been possible.

T

HE study by chemical methods of the constitution, derivatives, and properties of cellulose has yielded a voluminous literature and a wealth of useful information. Microscopic and x-ray investigations have produced much new and valuable knowledge of cellulose and its structure. But relatively little attention is given to the mechanical properties of cellulosic fibers, although such properties reflect fiber structure and frequently determine the suitability to specific applications, An exhaustive review of the relevant literature on cotton has not been undertaken in this paper; rather, the object is to summarize the available data on constitution and properties and, wherever possible, to indicate their relations to the most probable fiber structure. I n this way the material as a whole is integrated into a working concept of the cotton fiber. Constitution of Cotton Raw cotton is composed principally of cellulose. It contains a higher proportion of this substance than does any other

TABLEI.

PROXIMATE PERCENTAQE ANALYSES OF AMERICAN RAWCOTTON

Church and MUller (19) 91 .o Cellulose 0.35 Wax 0.12 Aeh Protoplasm, eto. 0 . 5 3

Dabney (40) Cellulose 83.71 Fat 0.61 Ash 1.65 N-free ext. 5.79 Protein 1.50

Water

Water

8.0

common plant product. Cellulose represents about five sixths by weight of air-dry cotton or about nine tenths of the oven-dry weight. Hemicellulose and lignins, which are associated with celluIose in many plant materials, are not found in cotton or, a t most, occur in small quantities and are nonresistant to extraction. For this reason a few standard treatments suffice to remove the noncellulosic constituents with a minimum of degradation of the fiber ( 3 ) . Purified cotton consisting of over 99 per cent of true cellulose is readily obtainable (5). GROSSANALYSIS. Complete, satisfactory analyses of raw cotton for its chemical constituents apparently do not exist. The data in Table I are indicative. The figures in the first column are undoubtedly incorrect. The known total of the noncellulosic constituents of raw cotton. excluding water, exceeds the very low value given (1 per cent) by several times. This analysis has been quoted widely and criticized adversely at least twice (IO,CY), but i t appeared again in a recent book (83). The analysis represented by the second column accords more closely with established facts. It has been confirmed in part (IO) and is cited in the later editions of a n authoritative source book on cotton (84). A systematic revision seems desirable, however, to make the data conform to present knowledge of constituents and to newer analytical methods. Specifically, the nitrogen-free extract group could be broken down considerably. For comparison, the third column of data (3) is quoted to show the lack of uniformity in the classification of constituents. The figure for fat and wax probably includes considerable nonfatty matter. The last column was compiled from various sources. Limits of variation of the constituents are given because the amount of each substance varies with the fineness and variety of the cotton (3, 93, I W ) , as well as with seasonal factors and different producing areas (9 104). The greater part of the noncellulosic matter can be extracted from cotton by treatment for a few hours with hot sodium hydroxide solution under pressure a t about 120’ C. (kier boiling). Subsequent rinses with water and dilute acid remove the excess alkali and lower the mineral content. The analysis of a cotton prepared in this way is given in Table 11, together with data on “standard cotton cellulose”. Calculations based on Tables I and I1 indicate weight losses during the purification treatment of about 8 per cent (dry basis). This figure is considerably higher than determinations reported by early investigators (12%)but is in excellent agreement with more recent values of 7-8 per cent (44, 93). The

6.74

Raw Wannamaker’s Cleveland (3) Cellulose 89.3-90.5 4.0-4.1 Fat and wax Ash 1.0-1.1 Cuticular matter 0.69-0.72 Dry bask

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Selected Estimates from Various Sources Cellulose 80-85 0.4-1.0 7” 102 Wax, fatty acids 0.8-1.8 (10:4;; 1 4 Ash 0.4-1,l (68,99,IS1 Pectate N as protein 1.2-2.5 (104) Pigments, resins, other constituents 3-5 (44, 47, 83) Water 6-8 (3,40)

i%

KOVEMBER, 1940

INDUSTRIAL AND ENGINEERING CHEMISTRY

weight loss must be influenced somewhat by the amount of noncellulosic matter present in the raw fiber. W a x , Fatty Acids. The wax of cotton has been investigated in great detail. The efficacy of various solvents for its removal has been studied (26, 72) with the conclusion that no single organic solvent effects complete extraction. Carbon tetrachloride and benzene remove the wax and fatty acids but leave the resin; hot chloroform appears to bring about the most complete separation (26). The crude wax has been separated into a number of components, principally montanyl and gossypyl alcohols (45). The remaining fraction of the wax consists of other higher alcohols, glycols, glycerides, and fatty acids in small amounts (27, 45).

PERCENTAQE ANALYSIS (DRYBASIS)OF TABLE 11. PROXIMATE COTTON AFTER PURIFICATION

After a Good Kier Boil (19% Cellulose Nitrogen Fat Mineral matter

99.1 -99.5 0.6 0.1 0.01- 0 . 1 5 0.05- 0 . 7 5

-

“Standard Cotton C:ellulose” (31, Wannamaker’s Clevelanda 99.5-99.43 Nil Nil

0.09

a The analysis of this cotton before purification is given in Table I, column 3.

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vents (26,47,72).Four substances characterized by different xray diagrams have been isolated from young cotton fibers (109). Cellulose. I n quantity and utility, true cellulose i s by far the most important constituent of cotton. Cellulose is a condensation product of glucose and, by definition, consists only of this sugar ( 6 ) . By hydrolysis with strong sulfuric acid, glucose yields as high as 95-97 per cent have been obtained from purified cotton cellulose (88). Forty per cent hydrochloric acid serves this purpose also (106). The residual 3-5 per cent has been attributed to pseudo-cellulosic “cementing material” of pectic nature (48), but adequate proof of this idea has not been obtained (63, 93, 150, 191). The weight of evidence indicates, rather, that pure cellulose consists essentially of anhydroglucose units. Of the glucose isomers, P-glucose (b-glucopyranose) (6, 59) occurs in cotton as well as in celluloses of different origin. It has been established that anhydroglucose units are linked together in cellulose to form long, unbranched chains. Much basic information on the pyranose structure of glucose and on the probable nature of the cellobiose linkage has been summarized (6, 69); accepted structural formulas are shown in Figure 1.

Structure of Cotton Cotton fibers are single-celled outgrowths from parent epidermal cells on the seed coat (4, 8, 42). Fiber development can be differentiated into two fairly distinct stages: a period (25-30 days) of rapid elongation during which the hair attains its mature length and a period (25-30 days) of internal thickening during which the major part of the cellulose is laid down. The period of rapid elongation corresponds to the formation of the thin outside cuticle and primary wall of the fiber; thus the fiber attains its mature width or diameter as fast as it is formed. The second period corresponds to the formation of the secondary wall which consists primarily of celli~lose~The original observations of this development were made on Egyptian cotton (8) and have been confirmed for American cotton (4). PRIMARY WALL.The structure of the cuticle and primary wall nf the mature fibcr is not precisely known. The cuticle coiisists of the wax ( 4 , ?9,96), a large part of the pectic material (4, 93), and surne incrusting mineral matter. The rapid accumiilatiori of these waxes and pectates during the period of cell elongation has been demonstrated by experiments (34,36). Thr primary wall of the fiber is an elastic skin (65) which is resistant to acids (42) and which has been called a modified cellulose or “cutin” (42). Evidence of the presence of cellu-

Ash. The ash of raw cotton has been found to contain mainly sodium, potassium, calcium, and magnesium (10, 78). A spectrogram indicated the presence of twelve different metals (92). Some of the alkaline earths are probably combined with the pectates (58) and some with fatty acids (64), but a considerable portion of the mineral matter is water soluble (78, 127). The early work on the ash content of ram cotton has been criticized on the ground that sand and other impurities influenced the resril ts (46). Pectate. The pectic material in raw cotton occurs chiefly as the calcium and magnesium salts of pectic acid (58, I.%)). Pure pectic acid isolated from cotton (58) is very similar in chemical properties to pectic acid from other plant sources (96). It has been suggested that in cotton, as in other plant tissues, the pectates exist largely in the primary wall ( 4 ) . The observation (34) of decreasing calcium pectate niinibcrs in growing fibers and the variation of pectic acid with fiber fineness (93) tend to confirm this view. Prolein. The nitrogen of raw cotton appears to be associated primarily with a protein in the lumen, the hollow axid region of the fiber (42, 84). It has been shown that the nitrogen content of cotton varies with the varirty ant1 falls between the limits 0.2-0.4 per cent (104). 111Table I these limiting values have been converted to protein- with the usual factor. The suggesY OH cn nu tion that 25-35 per cent of the nitrogen is in the form of nitrates and nitrites (67) has not been confirmed (91). Olher Constituents. Raw cotton appears to CHIOH contain about 3 per cent of uncharricterized matter (44). This amount is intlicated I)y p - g ~ u c o - p y r a n o s e(figiucose) Cellobiose the difference of the weight lost during. purification arid the sum of the known cunstituents. Included in this group are yellow-l)rown pigments, resins, oxy- and hydrocclliiloses (47)formed, perhaps, before the cotton is harvested by the action of moisture, mineral matter, and sunlight (39)-any hemicellul(~ses such as pentosans (67) and similar subPortion of a Cellulose C h a i n stances ( 4 7 ) . That a number of constituents arch present i s suggested by the varving quatitiFIGURE1. STRUCTURAL FORMULAS FOR ~ G L U C O S E CELLOBIOSE, , AND ties of extractables removed by different solS H O R T SECTION OF A C E L L U L O S E C H A I N

A

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lose in the primary wall-i. e., in young fibers before secondary wall formation begins-has been obtained (4,14, lor),but the identity of this cellulose with the cellulose of the secondary wall has not been established. The primary-wall cellulose appears to consist of tiny threads, transversely oriented (4). Its abnormal behavior towards the usual solvents for cellulose (57,66) suggests that its structure differs somewhat from that of secondary wall cellulose. This difference may be one of degree, like that observed in the case of flax fibers (84). SECONDARY FIBERWALL. The major part of the cellulose of cotton occurs in the secondary wall as layers or lamellae which have been observed under the microscope in swollen cross sections of the fiber (8,1d, 48,71). These lamellae have been called growth rings associated with diurnal variations in the rate of cellulose deposition (8, 71) but this has been doubted (12); there may be as few as five lamellae in the whole wall (12). If for any reason, such as the death of the cell, the formation of these lamellae is arrested prematurely, thin-walled or dead fibers of low strength ( 1 4 , anomalous dyeing properties (67),and a tendency to produce neps (24) may result. Thin-walled fibers are brightly colored in polarized light. A recent study yielded the generalizations that cotton fibers vary widely in outside diameter, that outside diameter seems to be a function of variety, and that the state Qf maturity determines the amount of internal thickening (101).

Fibrils. The secondary fiber wall consists of many tiny threads, called “fibrils”, laid side by side to form the ringshaped lamellae. The fibrils constituting each lamella do not lie parallel to the central axis of the fiber but follow a helical course, screw fashion, around the lumen. Some lamellae appear to spiral in one direction, others in the reverse direction. Under the microscope, striations arising from this crisscross organization of fibrils have been observed by many investigators (8, 35, 43, &?), particularly when the fiber is swollen. The earlier suggestion (8) that the fibrils of a lamella may abruptly change direction and adopt the reverse spiral path was con6rmed (4). The size of these fibrils has not been established with any certainty. Various estimates of diameter ranging from a probable value of 1p (7,lZ)down to 0 . 2 5 ~have been discussed in some detail (7, l a ) . They are extremely long in comparison with their widths, but experimental difficulties have precluded any precise determinations of fibril length. The structure of fibrils, like that of fibers, probably involves two distinct regions, surface and internal. Since fibrils appear, under the microscope, to be discrete entities, i t seems likely that their surfaces oppose the cohesion which mould result in fusion into an undifferentiated mass. The evidence which indicates surface discontinuities is as follows: (a) Swelling produces a clearer delineation of fibrils and, consequently, must affect the internal and external regions of the fibril differentially (12); (b) fibrils can be caused to separate from young fibers by mechanical treatment, such as by pressing (@, @), and from mature fibers by the action of the papermakers beater (105); ( c ) carefully ashed cellulosic fibers retain a skeletal structure which suggests that the mineral substances are distributed throughout the tissue (84); ( d ) a substance, probably pectate, has been demonstrated on fibril surfaces with ruthenium red stain (34); and ( e ) microscopic measurements indicate a layer about 0.2g thick separating the lamellae (129). The internal structure of fibrils is essentially the structure of native cellulose and, as such, is far from being settled. I n a hypothesis developed largely from microscopic evidence, the fibril is regarded as a chain of visible ellipsoidal “particles” closely appressed, end to end (48, 49). To the particle has been attributed dimensions of 1.5 X 1 . 1 ~(48) and a n apparent density of 1.5 (36). The particle is said to retain its

VOL. 32, NO. 11

identity when cotton is dispersed in cuprammonium hydroxide reagent (48) and to pass intact through the various processes of viscose manufacture (35). This concept has been so severely criticized that it must be regarded as inadequate in its present form (4, 63, 86, 73, 96, 123, 130). Hypotheses of fibril structure which are more compatible with the chemical and physical properties have been suggested. The anhydroglucose units are considered to be linked together through oxygen bridges to form long-chain polymers (6, 65, 59, 113). The most reliable estimates of length for these macromolecules indicate about 3000 glucose units per chain in native cellulose, corresponding to a molecular weight of roughly 500,000 for the polymer (62, 73, 74, 90, 116). Since the chains are probably nonuniform in length (74, 90), such estimates must be regarded as average values for the constituent chains. From this original chain length, fragmentation to shorter chains tends to occur during such processes as kier boiling, bleaching, and acid washing (50, 62, 73, 90). The glucose chains of cotton cellulose appear to be grouped into submicroscopic bundles or crystallites. The term “crystallites” is applied to dense, discontinuous (1I O ) , crystalline areas in the cellulonse. The crystalljne unit has been visualized as a bundle, 600 A. long and 50 A. wide, consisting of sixty closely packed, parallel glucose chains each about 120 units long (61,86). The latter structure was deduced from chemical and x-ray data, but since the chains are probably longer than 100-200 glucose units (80),the latter figures may be taken to represent apparent rather than true chain lengths (53). More recent estimates based on a a e w technique have placed crystallite lengths a t about 1000 A. (76). Since the crystallites or crystalline areas in cellulose are discontinuous, the noncrystalline or amorphous areas must play an important role in fibril and fiber structure. The nature of the amorphous areas has been indicated in the suggestion that the crystallites are composed of many chains, both long and short, with the longer chains shared by adjoining crystallites (6, I S ) . A somewhat similar concept involves fringe glucose chains which interlink the crystallites (70). Finally, it has been proposed that the crystallites are formed by the free rotation of glucose units around their oxygen bridges; crystalline areas result when portions of a group of adjacent chains coalesce in a preferred arrangement. The divergence of chains between such crystalline regions produces amorphous regions; in consequence, cellulose has a network structure and gives a discontinuous crystalline pattern (54,66,75, 76). For the present a plausible assumption seems to be that the anhydroglucose units are held together in chains by primary valence forces (6, 69, 113). The interrelation of these chains in cellulose takes two forms, an associative which results in the formation of crystallites and a nonassociative which corresponds to the intercrystalline regions. If the data for average chain length in cotton cellulose (3000 units) and for average crystallite length (100-250 units) are accepted, it appears that the same chain may participate in several crystallites and thus supply a primary valence chain interlinkage. The forces which act between chains and, in the extreme case, yield the crystallites are of secondary valence nature (13). The scattering of x-ray radiations by cotton has provided a valuable means of studying its structure. Intact fibers d o not give a powder diagram of the type which characterizes fine, nonoriented crystals. The random arrangement of crystal planes in the powdered crystal causes diffraction to occur uniformly in all directions, with the result that circular patterns are generated. I n the case of intact cotton fibers, the diffracted part of the pencil of x-rays falls only on short arcs of each angular dispersion circle (20, 109). This indicates that the crystallites are highly oriented in a direction parallel to the fiber axis (61).

NOVEMBEII, 1940


1457

The angle subtended by these arcs corresponds almost identically t o t h e a n g l e formed a t the internet i o n of a l t e r n a t e l y spiraling fibrils in the fiher (4.9, 108). In other words, the degree of crystallite orientation in the fibril itself is very high. Crystallite orientation estimated from the lengths of arcs on s-ray diagrams is directly related to fiher strength ( I d , I l l ) ; this orientation pattern is enhanced if fihers are w e t t e d , pulled, and dried in a stretched condition (108) or merAfter 2 hours After 3.5 hours cerized with tension COTTON FIBERS IX POLARIZED b G H T ( X 1100) AFTER BEING SWOLLEh. WITH DILUTE CGPRAM(66). Xevertheleas, the MONIGM HYDROXIDE general usefulness of xThe fibril structure is quite nppwent. rays as a means of estimating :fiber strengths is limited. The s-ray pattern is altered by some constituents, appearance of flat ribbons with from 20 to 100 half-convolusuch as was, which do not influence fiher strengths, but i t does tions per em. (1). The convolutions have been explained by not indicate some types of degradation (tendering) which despiral inequalities among the fibrils (43),by the ratio of fiher crease fiber strengths substantially (37). This finding sugwidth to wall thickness (26), and by irregularities in the crysgests the structural importance of the easily altered intertallite structure (121). crystalline areas. BREAKING STRENGTH. The breaking loads for single cotton Evidence from viscosity measurements (117) indicates that fibers are variable and not closely correlated with fiber diamedilute acids which do not cause crystallites to swell are cater or number of convolutions but, within the same variety, pable of producing only a slow hydrolysis when chain lengths are associated with wall thickness (28). The average breakhave been reduced to 15Q-200 glucose units. These results ing load per fiber is about 5.5 grams (16, 22) for a number of appear to support the idea that the intercrystalline glucose varieties even though cross-sectional areas vary from ahout chains hreak down easily and that the crystallites (150-200 120 to 2 7 0 ~ 2(2%). These data eorrespond to tensile strengths units long) are more resistant by virtue of their higher density. of about 60,OOO pounds per square inch for fihers of the finer varieties and of 30,000 pounds for the coarser (2%). The Properties of Single Cotton Fibers modified Chandler method of determining the effective strength of parallel fibers in a closely wrapped bundle (103) Qualitatively, cottons are much alike hut it is generally yields estimates ranging upnrard from 60,000 pounds per recognized that there are wide quantitative variations among square inch for various cottons. fibers of the same and of different types. For example, within Flaws in the fiber probably lower its strength; repeated the same sample fiber lengths are approximately normally d i e breaking of the same fiber shows that the loads required for tributed; among samples of different types of cotton, average the second and third breaks are often double or treble the staplelengthcanvaryfrom0.5inchfor theveryshortvarieties initial ones (16). up to 2.5 inches (9, I S ) for the very long. The proportionately higher breaking strengths of fine cotThe fineness of fihers, aa measured by the hair weight per tons are ascribed to a skin effect which becomes less prounit length, is determined by wall thickness, which generally nounced as wall thickness or harshness increases (%Z, $8). diminishes as staple length increases. Thus, the very long The phenomenon was described as follows (8%): “It is fihers are usually very fine, while cotton linters are relatively generally known that thin filaments are proportionately coarse. Wall thicknesses for different types of cotton range stronger than thick ones, the surface layer than internal from 0.35 to 1 5 . 5 ~(23, 68); fiher diameters vary from 11.9 to layers. . . . The strength of the cotton hair may be regarded 2 0 . 3 ~(17, 97). Cotton distinguishes itself among plant cells in being from 120&4000 timesa,s long as it is thick (4,@). as due to two elements, an outer relatively more elastic and constant with a varying amount of internal thickening of more The most common varieties of raw cotton have a normal imperfect elasticity.” The transversely oriented cellulose cream color which originates in pigments and residual nitrogethreads of the outer or primary cell wall (4)would have such nous substances of the lumen (42, 84). The unswollen, elastic properties. mature fiber is roughly bean-shaped in cross section (102). The time factor in fiber testing was investigated and found The luster of cottons is attributed to the polish on fiber surto be important (82). The breaking load increases with the faces (68) and to the roundness of the fibers (2). Cotton cellurate of loading, reaches a maximum, and then becomes indelose fluoresces in ultraviolet light (39). Optically, cotton is pendent of loading rate. I n other words, the longer the time doubly refracting; its two indices of refraction consist of a fibers are given to yield, the lower is their resistance a t transverse of 1.53 and an axial of 1.58. rupture. Under a low-power microscope single cotton fihers have the

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Fiber strengths increase with rising relative humidity and reach limiting values at about 60 per cent relative humidity (16, 81). It is claimed that a further strength increase of 20 per cent is obtained if the fibers are immersed in water (94). The higher strength of fibers containing moisture is attributed to a more uniform distribution of loads over the cross section (16, 120). The loss of strength of cotton as a result of the action of acids, alkali, salts, microorganisms, or ultraviolet light (tendering) might be explained by the splitting of connective chains between crystallites. Since the x-ray pattern does not change notably in consequence of tendering (S7), i t would a p pear that chains in the loose, permeable intercrystalline or amorphous areas are more vulnerable to attack than the dense, coherent crystallites. The destruction of essential, primary valence bonds between crystallites would account for tendering effects. Strength falls with decreasing chain lengths (118). ELASTICPROPERTIES OF COTTONFIBERS. The elastic properties of matter are most frequently represented in terms of stress, the force per unit area tending to produce a deformation, and of strain, the resulting deformation. Changes of length and of volume and shears or twists produced by applied stresses are all included in the elastic properties. The stressstrain relations for cotton were in part differentiated (82) as follows : 1. “Elastic” strains are pro ortional to the stress which produces them, are independent or time or past history of the material, and disappear with the stress. 2. “E ibolic” strains increase with time at a decreasing rate, attain a inal equilibrium, and eventually disappear or decrease gradually to a small value after the removal of the stress. This type of strain produces the so-called “elastic aftereffect” or manifests itself in the time decrease in the torsional couple of threads under moderate twist. 3. “Ductile” strains are characterized by a semiviscous flow proceeding indefinitely with time, are irreversible, and lead eventually to attenuation and rupture. In a material such as cotton these three types of strain are appreciable, the proportion of each in a given strain depending on the manner in which the strain was produced. ELASTICITY. The extension of single cotton fibers a t rupture is about 8 per cent (11, 16),but their elasticity is imperfect (11, 98); that is, they fail to regain their initial lengths when the stress causing the cxtensiou is removed. This effect was demonstrated clearly (SO) in a study of the relation between time and stress-strain. The rate of extension of single cotton fibers in water gradually slowed down during the first 30-150 minutes, and a pseudo-equilibrium condition was reached. In explanation the suggestion was made that the stress first causes a slow collapse of the fibers, the fibrils become closer packed, and the free space between them disappears. When this occurs, the effective cohesion or friction between fibrils increases rapidly. After attaining the pseudo-equilibrium condition, fibers become more truly elastic but continue to show a slow extension until a true equilibrium condition, corresponding to equality between applied stress and opposing frictional forces, is established 5000 to 10,000 minutes later. Upon the release of the stress, the elastic recovery of fibers is much more uniform than the initial extension. The recoverable part of the elongation probably represents the elastic extension of fibrils; the nonrecoverable or permanent stretch part of the elongation represents the straightening and denser packing of fibrils. Similar results were obtained in a more recent study (120). The example just discussed indicates that determinations of a Young’s modulus (elastic modulus) for cotton fibers have little meaning unless the history of the sample is known exactly. A Young’s modulus is defined as the ratio of stretching

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stress per unit cross-sectional area to the elongation per unit length produced. The stress-strain ratios of fibers a t the break yield Young’s moduli varying from 2 to 8 x 10’0 dynes per sq. cm. (11, 1 6 ) ; during recovery from an impressed stress the Young’s modulus is only about one third of this value as a result of the permanent stretch (11). The stress-strain curve for single fibers is roughly a straight line when the moisture content is low (16, 119). The essentially linear character of this relation was recognized in the statement that Hooke’s law holds for single cotton fibersi. e., that the elongation is directly proportional to the load (66)*

Moisture has a singular effect on the strength and extension of cotton fibers. A careful study of breaking loads and stress-strain phenomena (16) at different relative humidities yielded the following results: Average fiber elongation at the breaking point rises continuously from about 5.3 per cent a t 10 per cent relative humidity to about 9.5 per cent at 100 per cent relative humidity; the breaking load increases as the relative humidity is raised to 60 per cent, a t which it reaches a constant value and becomes independent of humidity. With fiber elongations as ordinates, the load-elongation curves are convex upward; the higher the relative humidity, the greater is the convexity. The steeper initial slopes of these curves are attributed to the straightening of fibrils, the lesser final slopes, to the true stretching (about 3 per cent) of fibrils. Increasing amounts of absorbed moisture progressively reduce the cohesion between fibrils and permit them to straighten more and more. I n dry, highly cohesive fibers this effect is inappreciable; the elongation is largely accounted for by true fibril extension. The increase of fiber strength with relative humidity is explained by the more uniform distribution of stresses; the fibrils are equalized by the straightening and stretching actions. This effect is appreciable only when relative humidity is greater than 50 per cent (120). This concept appears to be in good agreement with the xray evidence of increased orientation resulting from wetting and pulling fibers-i. e., fibril straightening (108); with the work on stress-strain equilibrium (90) discussed above; and with the observation that convolutions, originating in spiral inequalities of the fiber, are pulled out by tensions or removed by prolonged aqueous swelling (25). The elastic properties of cellulose were explained on the assumption of long, primary valence chains (86, 87). RIGIDITY. The modulus of rigidity or the shear modulus of a material is the ratio of the tangential or torsional force per unit area to the angle of shear or twist i t produces. I n the case of a single cotton fiber a torsional force must create a direct tensile pull on the fibrils which spiral in the direction of the force and a compressing or straightening action on the reverse fibrils. It follows that, where the angles of the fibrils to the central fiber axis are large and when the number of fibril lamellae increases, as in short-staple thick-walled fibers, large torsional forces would be required to produce a displacement. I n cotton spinning and twisting operations this rigid behavior is extremely important. The mean rigidities of cottons were found (97) to vary from 0.010 to 0.111 dyne per sq. cm. for a large number of different varieties. Correlations between rigidity and other fiber characteristics indicate that rigidity varies with the shape, conditions of growth, and largely with the wall thickness of fibers. The high rigidity of thick-walled fibers suggests why coarse cottons must be more highly twisted than fine cottons to produce yarns of the same gage. Temperature and humidity have pronounced influences on rigidity (100) or stiffness to bending (9, 21); a t room temperature the rigidity of a cotton fiber is six times as grea in dry air as it is in a water-saturated atmosphere; a t constant moisture regain, rigidity decreases as temperature increases (100).

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The rigidity of cotton, especially its variation with moidure, to the influence of the less rigid, noncrystalline glucose chains which link the crystallites. can be explained in part by the cohesion of fibrils as outlined in the previous section. The origin of rigidity in each separate VOLUME CHANGES.Volume changes or swelling effects are fibril is less well defined. It would appear that the crystalline elastic properties in the sense that swelling is opposed hy a set portion of the fibrils-i. e., the crystallites-would be relatively of forms which tend to return the structure to its initial condinondefonnable in consequence of intercrystalline forces; in tion when the reagent or stress is removed. If a solid material fact, maximum fibril extension probably does not exceed 3 per has an entirely rigid structure such that a change of shape does not involve a corresponding change in volume, the strain cent (16). The spiraling paths of these inextensible elements bring them into direct produced is a pure shear. ounosition to torsional As the material becomes sGsses or twists applied looser in texture or less to the fiber. Thus, mocoherent-for example, lecular forces represented under the inhence of a by primary valence bonds swelling agent-the act against the torque and amount of shear accompanying a deformation detend to return the fiber to its original shape when creases in proportion and the stress is removed. plasticity increases. Such twisting forces are Cotton fiber swelling is of the nature of shears, a volume change of which since they involve changes two types are recognizedin shape without correnamely, inter- and intrasponding changes in micellar swelling. The volume. essential differenceof these PLASTICITY.In contypes from each other was trast to the rigid, the demonstrated nearly two plastic properties measure decades ago in an x-ray the tendency of material.? study (69). The patterns for celliilose and for hyto be deformed permanently by stresses-i. e., drated C e h t o e were idento act like highly viscous tical and indicated that water did not penetrate liquids. Extremely plastic substances are characterthe crystallites and alter ized by randomorientation their planar characterisUNSNOLLENConon FIBERS MOUNTED IN GLYCEROL AND PHOTOGRAPHED EX POLARIZED LIWT ( X 254) of constituent molecules tics. Swellingwith sodium hydroxide did change the or molecular amreeates or The irreeular suiral convolutions are daiinlv shown. of low cohesion between x-ray pattern whicb: howthem; in such cases when ever, reverted to that for the strem is removed the restoring forces are too weak to eellnlose when the alkali was washed out. Sodium hydroxide had caused a swelling of, and probably a change in, the crysreturn the structure to its original condition. In a quaIitative tallites. The latter type of change may be of the nature of sense, rigidity and plasticity are complementary properties. The plasticity of cotton was investigated in freshly twisted compound formation in the case of the quaternary ammonium hydroxides (11t). yarn (99). The untwisting or restoring forces in the yarn If the structure of cellulose is represented correctly by cryswere found to decrease with time according to a logarithmic tallites linked together with primary valenee chains, i t is function. This decay of torsional restoring forces indicated reasonable to suppose that aqueous swelling involves the plastic changes-i. e., the substitution of epibolic or ductile loose, connecting network and only the outside surfaces of the strains for the purely elastic. In other words, the setting of crystallites. This would be an example of limited (119) or yam twist results from a plastic decay of elastic couples generintemieelhw swelling. It would explain the observation (89) ated in the fiber by the twist; most of this change takes place that in electrical conductivity “the conducting water paths in one day. The original restoring forces never vanish com. . consist, in effect, of elementary Baments which have alterpletely but diminish to residual values which vary with the nately expanded and constricted sections along their length”. amount of twist introduced. The decay is most rapid and The constricted sections would then correspond to the cryscomplete in highly twisted yarns; loose or soft yarns retain a higher proportion of elastic couples. A logarithmic extension tallites. There seems to he little reason to doubt that some of the a b function of the type possibly involved in the setting of twist sorbed water is associated with residual valences of the hyhas been observed for single fihers (120). droxyl groups in cellulose. This was demonstrated directly Cotton fihers show a great increase in plasticity under for cotton (I%, 1%) and indirectly hy the fact that substituhumid heat (29, 99). In fact, processes included under the ents such as acetyl groups lower the affinity of cellulose for term “schreinering” are defined (39) as those which depend on water (I%, 199). The remainder of the water, except that the increase in plasticity of cotton fibers as they swell in water ahsorbed on fibril surfaces, may be associated mechanically \rapor at elevated temperatures. with the intercrystalline regions. Cotton acts like an elastic The plasticity of fibers may involve not only the porosity of the fiber structure and the movement or displacement of gel; the removal of water causes the crystallites to shrink together (1%). A two-uhase theory of water absorution was fibrils under the stress, but other factors also. It has been advanced.(98). shown that strains disappear when fihers are soaked in Intramicellar swelling appears to involve both the effects water (%’, 38,128); consequently, much of the plastic decay just discussed and the-int&ial parts of the crystallites also. effect may in reality be only semipermanent. Cotton fibers I n unlimited swelling (fig), the extreme cases of intramicellar have been considered practically nonplastic (66, 119). The swelling, the cellulose structure disintegrates more or less comobserved plastic behavior of cotton may eventually be traced

__

I

.~

I

.


1460

pletely, and the glucose chains become dispersed as separate entities (73, 116, 124). This is the assumption on which methods of estimating chain length or degree of polymerization from viscosity are based (61, 73, 116). The sequence of events in the latter type of swelling seems to be (a) penetration of the crystallites by the swelling agent and, as a result, a lowering of the chain-chain cohesion (go), and (b) dispersion if conditions are suitable. Limited swelling can be effected with intramicellar swelling agents under the proper conditions.

t /SPRING

the fiber contents escape into the solution (4).Except for any influence the pectates might play in this behavior, the effects can be explained in terms of the transversely oriented cellulose threads (4) of the primary wall. If these threads are similar in properties to cellulose of the secondary wall, then they swell only laterally and do not tend to increase the perimeter of the fiber. They limit fiber swelling, therefore, until the internal pressure ruptures them. The true specific volume of intact cotton fibers in water does not vary appreciably from 0.640 over the temperature range 15-80" C. (41). However, the water adsorbed per gram of cotton and, consequently, the swelling vary considerably and exhibit a minimum a t about 50' C. The apparent specific voIume of fibers in water varies from 0.619 at 0" to 0.628 a t 80" C. (41). Below the saturation point cotton holds water with 17 per cent greater force than water holds water (114).

ESCAPE FRICTIONLESS PtSTON

01 L

t

STRESS

DIAGRAM OF A FIGURE 2. SCHEMATIC MECHANICAL MODELFOR CELLULOSIC FIBERS The behavior of such a spring and dashpot system simulates the behavior of cotton and rayon.

Both of these types of swelling increase the plasticity of cotton. With intermicellar swelling, as produced by water, fibrils become less coherent (as discussed above), and the intercrystalline glucose chains become more elastic (126). When the crystallites themselves are swollen with such agents as strong sodium hydroxide, cuprammonium hydroxide, and the quaternary ammonium bases, fragmentation to smaller crystalline units may occur (80) in consequence of the lessened cohesional forces. The latter effects are turned to advantage in mercerization processes. Among the intermicellar swelling agents for cotton, formamide is better than water, but water is more effective than the aliphatic alcohols whose swelling power decreases as chain length increases (77). The intramicellar swelling agents include, in addition to those already mentioned, strong calcium thiocyanate and zinc chloride solutions, and sulfuric, phosphoric, and hydrochloric acids in the proper concentrations (99).

VOL. 32, NO. 11

Swelling in water increases the diameter of cotton fibers about 20 per cent from the bone-dry diameter, while the length changes only 1 to 2 per cent (32, 52). This represents a volume increase of about 40 per cent. The larger apparent increase in length of swelling fibers is accounted for by the loss of convolutions (SS). The fiber diameter increases about 45 per cent under mercerizing conditions (33). The small true increase in fiber length as a result of aqueous swelling suggests that fiber extension is opposed by the primary valence chains during the process; i. e., only lateral swelling can occur. The fiber tends to shorten during the swelling with mercerizing caustic-i. e., an increase of diameter a t the expense of length. The swelling of raw cotton in water and other mild swelling agents is said to be inhibited to a considerable extent by the cuticle of the fiber (18, 95,58,1S2). The fiber apparently cannot swell beyond the maximum diameter i t had as a living, unshrunken cell in the green boll (18). I n the case of strong swelling agents this outer restricting membrane bursts, and

Estimates of apparent density of cotton fibers indicate that the walls are spongy or porous. Exact data are difficult to obtain experimentally (9), but rough values for pore space ranging from 32 to 41 per cent of the fiber volume have been reported (26); fine cottons are somewhat less porous than the thick-walled types, ELASTIC AFTEREFFECTS.The plasticity of cotton fibers is determined by the amount of swelling, the magnitude and duration of the stress, and the temperature. These four independent variables permit the possible deformations to fluctuate between wide limits, from easily produced, highly stable ones down to none a t all. Mercerization with strong sodium hydroxide or with cuprammonium hydroxide is a process in which great swelling and relatively small stress are combined to give permanent plastic deformations. Conversely, cotton fibers a t the minimum condition of swelling-that is, bone-dry-are practically nonplastic with loads up to their breaking stresses (as discussed above). I n bone-dry unswollen fibers the cohesional forces are at a maximum, and the intercrystalline connecting chains are in their most stabile state. The magnitude of the deforming stress must influence the plastic behavior; when fibers are swollen less and less, stresses must be increased to overcome the greater and greater cohesional forces. That the time the deforming stress acts is important also has been shown indirectly in the discussion of (a) the constant stress elongation of fibers, (b) the slow loading and attenuation of fibers, and (c) the plastic decay of elastic couples. I n the latter case the magnitude of the stress played a part also because decay was most rapid and complete in highly twisted yarns. Temperature may have two functions in the plasticity: It may determine the amount of swelling a liquid can produce, and, i t may set the effective lability of the intercrystalline glucose chains and regulate kinetic activity in the system (116). Semipermanent deformations apparently can be induced in fibers by the proper combination of these factors. For example, fibers wetted, stretched, and dried in an elongated state shrink nearly to their initial lengths upon immersion in water without tension (52). Similarly, soaking in water causes the strains in fibers to disappear completely (28). This behavior is analogous to the elastic aftereffect in rubber which, after a deformation, exhibits a slow recovery of a portion of the displacement. I n cotton the recovery is fairly rapid but only when water is present. While the large pore space (25) of fibers may allow a certain amount of permanent deformation, this recovery effect might be traced to an elastic relaxation phenomenon (66). The slow semiplastic changes produced in air-dry fibers under prolonged stresses (setting of yarn twist) and the more rapid change accomplished by wetting, stretching, and drying are opposed by large co-

NOVEMBER, 1940


hesional forces and primary valence bonds. These forces bring about recovery when the fiber is wetted and cohesion is lowered. Mechanical models consisting of springs and dashpots coupled in various ways have been suggested as means for relating stress-strain phenomena and elastic aftereffects to structure (66). The springs are analogous to elastic structural units, the dashpots to viscous substances. The model (Figure 2) used for rayon is a spring and dashpot coupled in parallel (66). Cotton fiber structure might be visualized in terms of a similar model, but the more complex fiber organization would complicate such a representation.

1461

(50) Farrow, F. D., and Neale, S. M., Shirley I n s t . ikfem., 3, 67 (1924). (51) Flory, P . J., and Stickney, P . B., J . Am. Chem. Soc., Nov., 1940. (52) Foster, G. A. R., Shirley I n s t . M e m . , 5, 1 (1926). (53) Freudenberg, K., Ann. Rev. Biochem., 8 , 81 (1939). (54) Freudenberg, K., Papier-Fabr., 35, 49 (1937). (55) Frey-Wyssling, A., “Submikroskopische Morphologie”, Gebriider Borntraeger, Berlin, 1938. (56) Goldthwait, C. F.. U. S. Patent 1,901,095 (March 14, 1933). (57) Haller, R., Chem.-Ztg., 32, 838 (1909). (58) Harris, S. A., and Thompson, H. J., Contrib. Boyce Thompson Inst., 9, 1 (1937). (59) Haworth, W. N.,“Sugars”, New York, Longmans, Green and Co., 1929. (60) Haworth, W. N., and Machemer, I€., J . Chem. SOC.,2270 (1932). (61) Hengstenberg, J., and Mark, H., 2. Krist., 69, 271 (1928). Literature Cited (62) Hess, K., and Neumann, F., Ber., 70, 710, 721, 728 (1937). Adderley, A., Shirley I n s t . iClem., 1, 151 (1922). (63) Heuser, E., Div. Cellulose Chem., Am. Chem. SOC.,Cincinnati, Ibid., 3, 105 (1924). Ohio, April, 1940. Am. Chem. SOC.,Rept. Comm. Div. Cellulose Chem., IND. (64) Higgins, “Bleaching”, 1919; cited by Fargher and Withers (47). ENG.CHEM.,15, 748 (1923). (65) Hock, C., and Harris, M.,J . Research Natl. Bur. Standurds, Anderson, D. B., and Kerr, T., Ibid., 30, 48 (1938). 24. 743 (1940). ~~.~ Armstrong, E. F., and Armstrong, K. F., “The Carbohydrates”, (66) H i u k n k , R., “Elasticity, Plasticity and Structure of Matter”, 5th ed., London, Longmans, Green and Co., 1934. Cambridge, University Press, 1937. Astbury, W. T., Trans. Faraday SOC.,29, 193 (1934). (67) Ivanova, V. T., and Kurennova, A. M.,Trans. Middle Asiatic Bailey, A. J., and Brown, R. M., IXD.EXQ.Ciisnr., 32, 57 Sci. I n s t . Cotton Culture, I n d . Irrigation, 50, 57 (1931). (1940). (68) Karrer, E., and Bailey, T. L. W., Teztile Research, 8, 381 Balls, W. L., “Development and Properties of Raw Cotton”, (1938). London, Black, 1915. (69) Katz, J. R., Physik. Z . , 25, 321 (1924). Balls, W. L., “Studies of Quality in Cotton”, London, Mac(70) Katz, J. R., “Rontgenspektrographie als Untersuchungsmillan Co., 1928. methode”. 1934. Barnes, J. H., J . SOC.Chem. I n d . , 35, 1191 (1916). (71) Kerr, T., Protoplasma, 27, 229 (1937). Barratt, T., J. Textile Inst., 13, T17 (1922). (72) Knecht, E., and Hall, W., J . SOC. Dyers Colourists, 34, 220 Barrows, F. L., Contrib. Boyce Thompson Inst., 11, 161 (1940). (1918). Bayerl, V., and Roos, K., Kunstseide, 12, 424 (1930). EXG.CHEM.,30, 1200 (1938). (73) Kraemer, E. 0.. IND. Berkley, E. E., Textile Research, 9, 355 (1939). (74) Kraemer, E. O., and Lansing, W. D., J . P h y s . Chem., 39, 153 Brown, H. B., “Cotton”, 2nd ed., New York, McGraw-Hill (1935) * Book Co., 1938. (75) Kratky, O., Silk and R a y o n , 13, 480, 571, 634 (1939). Brown, K. C., Mann, J. C., and Peirce, F. T., J . Tertile Inst., (76) Kratky. O., and Mark, H., 2. physik. Chem.. B36, 129 (1937). 21, T186 (1930). (77) Kress, O., and Bialkowsky, H., Paper Trade J . , 93, 35 (1931). Calvert, M., and Harland, S. C., Ibid., 15, T8 (1924). (78) Lester, Teztile Mercury, Dec. 17, 1904, 24; cited by Fargher Calvert, M., and Summers, F., Shirley I n s t . Mem., 4, 49 and Withers ( 4 7 ) . (1925). (79) Levine, B. S., Science, 40, 906 (1914). Church ’and Muller, quoted by Fargher and Withers, J . Tex(80) Lipatov, S. M., and Krotova, N. A., J . Applied Chem. tile Inst., 13, T1 (1922). (U. S . S . R.),4, 1030 (1931). Clark, G. L., IND.ENQ.CHEM.,22, 474 (1930). (81) Mann, J. C., Shirley I n s t . Mern., 6,53 (1927). Clayton, F. H., and Peirce, F. T., J. Teztile Inst., 20, T315 (82) Mann, J. C., and Peirce. F. T., Ibid., 5. 7 (1926). (1929). (83) Marsh, J. T., and Wood, F. C., “Introduction t o Chemistry Clegg, G. G., Shirley I n s t . M e m . , 2, 357 (1923). of Cellulose”, London, Chapman and Hall, 1938. Ibid., 5 , 223 (1926). (84) Matthews, J M., “Textile Fibers”, 4th ed., New York, John Clegg, G. G., and Harland, S. C., Ibid., 2, 97 (1923). Wiley & Sons, 1924. Ibid., 2, 353, 370 (1923). (85) Meyer, K. H., and Lotmar, W., Helv. Chim. Acta, 19, 68 (1936). Clifford, P. H., Higginbotham, L., and Fargher, R. G., Ibid., (86) Meyer. K . H., and Mark, H., Z . physik. Chem., B2, 115 (1928). 3,31 (1924) (87) Meyer, K. H., Susich, G. v., and Valk6, E., Kolloid-Z., 59, Clifford, P. H., and Probert, M. E., Ibid., 3, 169 (1924). 208 (1932). Collins, G. E., Ibid., 1, 133 (1922). (88) Monier-Williams, G. W., J . Chem. SOC.,119, 803 (1921). Ibid., 2, 204 (1923). (89) Murphy, E. J., and Walker, A. C., *J. Phw. Chem., 32, 761 t3Oj Ibid., 3, 271 (1924). (1928). (31) Collins, G. E., J . Teztile Inst., 21, T311 (1930). (90) Neale, S. M., Chemistry & I n d u s t r y , 14, 602 (1936). (32) Ibid., 30, P46 (1939). (91) Nickerson, R . F., unpublished experiments. (33) Collins, G. E.. and Williams, A. M.. Shirleu I n s t . ikfem.. 2, (92) Nickerson, R. F., and Fontaine, T. D., unpublished observa217 (1923). tions. (34) Compton, J., Div. Cellulose Chem., Am. Chem. SOC.,Cincin(93) Nickerson, R. F., and Leape, C. B., IND. ENG.CHEM.,t o be nati, Ohio, April, 1940. published. (35) COmDtOn. J.. I X D . ENQ.CHEM..31. 1250 (1939). (94) Obermiller, J., and Goertz, M., Melliand Tedilber., 7, 163 (36) Compton, J., and Haver, F.’ E.,’ Contr>b. Boyce Thompson (1926). Inst.. 11. 105 (1940). (95) Olsen, A. G., Stuewer, R. F., Fehlberg, E. R., and Beach, (37) Conrad, C. M.,’and’Berkley, E. E., Textile Research, 8, 341 ENG.CHEM.,31, 1015 (1939). N. M., IND. (1938). (96) Osborne, G. G., Teztile Research, 5 , 275, 307 (1935). (38) Coward, H. F., and Spencer, L., J. Teztile Inst., 14, T32 (97) Peirce, F. T., J . Textile Inst., 14, T1 (1923); Shirley I n s t . Mern., (1923). 2, 1 (1923). (39) Cunliffe, P. W., Shirley I n s t . M e m . , 2, 244 (1923). (98) Peirce, F. T., J . Teztile Inst., 20, T133 (1929). (40) Dabney, U. S. Dept Agr., Bull. 33 (1896); quoted by Mat(99) Peirce, F. T., Shirley Inst. &fern., 2, 278 (1923). thews (84) and Fargher and Withers ( 4 7 ) . (100) Ibid., 3, 253 (1924). (41) Davidson, G. F., Shirley Inst. Mem., 6, 41 (1927). (101) Peirce, F. T., and Lord, E., J . Teztile I w t . , 30, T173 (1939). (42) Denham, H. J., Ibid., 1, 87 (1922). (102) Pickard, R. H., “Research in the Cotton Industry”, Man(43) Ibid., 2, 61 (1923). chester, Eng., Brit. Cotton Research Assoc., 1926. (44) Fargher, R. G., and Higginbotham, L., Ibid., 5 , 63 (1926). (103) Richardson, H. B., Bailey, T. L. W., and Conrad, C. M., (45) Fargher, R. G., and Probert, M. E., J. Textile Inst., 14, T49 U. S. Dept. .4gr., Tech. Bull. 545 (Jan., 1937). (1923). (104) Ridge, B. P., Shirley Inst. M e n . , 3, 20 (1924). (46) Ibid., 17, T46 (1926). (105) Ritter, G. J., R a y o n and Melliand Teztile Monthly, 16, 522, (47) Fargher, R. G.. and Withers, J. C., Ibid., 13, T1 (1922). 606 (1935). (48) Farr, W. K., Contrib. Boyce Thompson Inst., 10, 71 (1938). (106) Sherrard, E. C., and Froehlke, A. W., J. Am. Chem. Soc., 45, (49) Farr, W. K., J . P h y s . Chem.. 42, 1113 (1938). 1729 (1923). I

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1462

Sisson, W. A., Contrib. Boyce Thompson Inst., 8, 389 (1937). Ibid., 9, 239 (1938). Ibid., 9, 381 (1938). Sisson, W. A., IND.ENQ.CHEM., 27, 51 (1935). Sisson, W. A., Textile Research, 7 , 425 (1937). Sisson, W. A., and Saner, W. R., J.P h y s . Chem., 43, 687 (1939). Sponsler, 0. L., and Dore, W. H., Colloid Symposdum Monograph, 4 , 174 (1926). (114) Stamm, A. J., and Hansen, L. A . , J. Phys. Chem., 41, 1007

(107) (108) (109) (110) (111) (112) (113)

(1937). (115) (116) (117) (118) (119) (120) (121) (122)

Staudinger, H., Cellulosechem., 15, 53, 65 (1934). Staudinger, H., Naturwissemchafta, 25, 673 (1937). Staudinger, H., and Sorkin, M., Ber., 70, 1565 (1937). Staudinger, H., Sorkin, M., and Frans, E., Melliand Teztilber., 18, 681 (1937). Steinberger, R. L., Textile Research, 4, 207, 271, 331 (1934). Ibid., 6, 325 (1936). Steinbrinck, C., Naturwissenschaften, 15, 978 (1927). Trotman, S. B., and Pentecost, S. J., J . SOC.Chem. Ind., 29, 4 (1910).

VOL. 32, NO. 11

(123) Turner, H. A., Ann. Rept. SOC.Chem. Ind., 22, 196 (1937); 23, 198 (1938). (124) Ulmrtnn, M., “Molekulegr6ssen-Bestimmung hochpolymerer Naturstoffe”, Steinkopff, Dresden, 1936. (125) Urquhart, A. R., J. Teztile Inst., 20, T125 (1929). (126) Walker, A. C., J . Teztile Inst., 24, T145 (1933). (127) Walker, A. C., and Quell, M. H., Ibid., 24, T123 (1933). (128) %‘eltzien, W., and Gotze, K., “Chemische und physikalische Teohnologie der Kunstseiden”, p. 125, Leipzig, Akademische Verlagsgesellsohaft, 1930. (129) Wergin. W., Naturwissenschaften, 26, 613 (1938). (130) Whistler, R. L., Martin, A. R., and Harris, M., A m . Dyestuf Reptr., 29, 244 (1940). (131) Whistler, R . L., Martin, A. R., and Harris, M., J . Research Natl. Bur. Standards, 24, 13 (1940). (132) Willows, R. S., and Alexander, A . C., J . Textile Inst., 13, T237 (1922). ENG.CHEM.,14, 913 (1922). (133) Wilson, R. E., and Fuwa, T., IND. CONTRIBUTION from the Cotton Research Foundation Fellowship at hlellon Institute.

Removal of Chlorides and Sulfates bv Svnthetic Resins J

A resin prepared from rn-phenylenedi-

M. C. SCHWARTZ, W. R. EDWARDS, JR.,

amine, formaldehyde, and hydrochloric acid has been used to treat a variety of aqueous solutions containing either chlorides or sulfates. The influences of a number of variable factors upon the effectiveness of this resin in removing the solutes have been measured. These factors included : effect of drying before and after rinsing, temperature of water sample, reaction time, particle size, initial concentration, and acidity. From the data thus obtained, tentative attempts have been made to determine the nature of the removal process.

AND GRACE BOUDREAUXI Engineering Experiment Station and Department of Chemistry, Louisiana State University, University, La.

T

H E use of siliceous zeolites for removing cations and the regeneration of these substances by sodium chloride has been known for a long time. The use of carbonaceous substances for removing cations, and regeneration in this instance by either sulfuric acid or sodium chloride, is a recent development. However, the use of synthetic organic resins for removing anions as well as cations is a still more recent development and, as far as the authors are aware, has not yet been applied in full-scale commercial practice in the United States although a number of test units are being operated. At present the chief interest in these methods of removing cations and anions from solutions comes from the field of water treatment, particularly from producers of boiler feed water for large, high-pressure, complete make-up steam power stations. The possibilities are such, however, that it is not unreasonable to expect that further applications will be found in the chemical industries. 1

J

Present address, Mississippi State College for Women, Columbus, Miss.

Although our present interest in the synthetic organic resins concerns the removal of entire molecules, it is worth noting that the literature on the preparation and use of resins for cation removal is expanding rapidly. A considerable portion of available literature is confined to patent issues (1, 6, 26-29, 31-36,38, 40, 41, 48). General articles by Akeroyd and Broughton ( B ) , Austerweil (9),Burrell (i9),and Griessbach (W), have appeared, With respect to anion removal by synthetic resins, it is equally true that most of the available literature is confined to patent issues (2, S, 4, 7, 12, IS, 20, 2i, SO, 36, 37, 39, 42, 43, &). The development of this field may be considered as starting with the paper of Adams and Holmes (6),followed by studies of Austerweil and Fiedler (ii), Bird, Kirkpatrick, and Melof ( l 7 ) , Austerweil (io),Bird (i6),Broughton and Bhatnagar, Kapur, and Bhatnagar (14, 16), GriessLee (i8), bach (Z4), Richter (45, 46), and Goudey (22). In the case of the siliceous zeolites the practical application was far ahead of the fundamental studies on the use of these materials. It is to be hoped that the same situation will not be true in the case of these recent L‘carbonaceouszeolites” and synthetic organic resins. The present paper describes the initial steps in an investigation of the effectiveness of a suitable resin on water samples containing a variety of dissolved substances. One object was to measure the effects produced by alterations of a number of variable factors under control of the operator, to determine which of these factors were material and which were negligible. I n the case of those factors which proved to play a material part, a second object was to gain some idea of optimum con-

Cotton Fibers Constitution, Structure, and Mechanical Properties

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