W. A . , ANAL. CHEM. 28, 207 (1956). (57) Sue, P., Bull. soc. chim. France 1946, 102. (58) Sue, P., S u t u r e 157, 622 (1946); Bull. soc. chim. France 1947, 405. (59) Theurer, IC., Sweet, T. R., ANAL. CHEM.25, 119 (1953). (60) Trenner, N. R., Walker, R. W.,
Arison, B., Buhs, R. P., Ibid., 21, 285 (1949). (61) Trenner, N. R., Walker, R. W., Arison, B., Trumbauer, C., Ibid., 23, 487 (1951). (62) Udenfriend, S., J . Bzol. Chem. 187,65 ( 1951). (63) U. S. Pharmacopeia XV, First Supplement, p. 21, 1956.
(64) II’agner, C.D., Guinn, V. P., J. S m . Chem. SOC.75, 4861 (1953). (65) Wieland T., Schmeiser, K., Fischer, E., hlaier-Leibnitx, H., Naturwissenschuften 36, 280 (1919). RECEIVED for review July 29, 1957. Accepted September 27, 1957.
Tenth Annual Summer Symposium-Nucleonics and Analytical Chemistry
Tracer Techniques in Fiber Research H O W A R D J. WHITE, Jr, Textile Research Institute, Princeton, N. 1.
b A brief review of the applications of tracers in fiber research is given. Although the emphasis is primarily on applications involving textile fibers, some examples involve fibers in paper and biological systems. Textile processes can b e broken down into mechanical processes and chemical processes. Applications of tracers to studies in each category are outlined. In addition, several studies have been made of the physics and chemistry of the fibers themselves either in bulk form or singly. Particular emphasis has been placed on the thermodynamics and kinetics of absorption processes.
C
fibers suggest textiles and most of the work discussed in this review was done on textile materials. However, paper, leather, skin, muscle, and nerves are composed of fibers and in some respects the fibrous character transcends the end use of the fiber. Thus somewhat related problems in blending and uniformity occur in paper making and yarn making; problems encountered in studying absorption by single fibers are akin whether the ultimate objective is a study of dyeing or of muscle action. The operations involved in the utilization of fibers can be broken down into two main categories, mechanical processing and chemical processing. I n addition to these categories which involve the treatment of fibers in aggregate, a third category, the physical and chemical properties of the individual fibers themselves, must be added in any discussion of research on fibers.
duces a loose web or bat, and the conversion of this web into the yarn by a combination of processes involving drawing, combing, twisting, and often doubling. A typical drawing operation involves the passage of the web through two sets of rollers, the second of which is rotating faster than the first. I n ideal operations this drawing would be completely uniform; in practice periodic nonuniformities known as “drafting waves” occur. To study this drawing process it is useful to be able to follow the passage of individual fibers through the rollers. Taylor (19) has devised an ingenious technique for doing this. His equipment is shown schematically in Figure 1.
ONVESTIOSALLY
A and B represent Geiger counters equipped with collimating slits set perpendicular to the web. Counter A is fixed and counter B can be moved along the web. The distance between the counters is D. A radioactive fiber of length L is introduced into the web and the rollers are set in motion. Because the web is moving with the velocity of the back roller when the fiber is in the field of counter A , the time of discharge for its passage past A L is t g v,. The value of L and the time of passage through the field of B determine its velocity a t B; the interval between the discharge of A and the discharge of B determines the
+
average velocity for traversing the distance D. It is necessary that L be directly measurable, because fibers of different lengths behave differently in the drafting operation. Taylor used wool fibers tagged rvith in his experiphosphorus-32 (H3P3204) ments; and, although the experiment was not quite as simple as this brief discussion suggests, he was able to get much interesting information on the mechanics of drafting from his device. Chaikin, Baird, Stutter, and Curtis (6)used ~voolfibers tagged with phosphorus-32 in the same way for another purpose. Wool fibers used for clothing are crimped rather than straight. This crimp reflects differences in chemical composition and morphological structure throughout the fiber. Hon-ever, because wool is a viscoelastic material, forces introduced in processing can cause changes in the extent and character of the crimp in the fibers. At first thought the crimp might seem to be an extraneous or incidental property; actually it confers desirable processing characteristics and yarn and fabric properties, so much so that the introduction of crimp into synthetic fibers is receiving much attention. Chaikin and coworkers were able to study changes in configuration of wool fibers by making radioautographs of samples containing radioactive fibers taken a t various stages of processing. This
I
EXPERIMENTS INVOLVING MECHANICAL PROCESSING
The production of yarn or thread from a raw stock of staple (short length as opposed to continuous) fibers involves a combing process, which pro1744
ANALYTICAL CHEMISTRY
Figure 1. Schematic diagram of apparatus for studying drafting (19)
method has the advantage of allolying the crimp to be examined with a minimum disturbance of the sample. I n Figure 2 the radioautographs of a loose fiber and a fiber in a yarn are compared; the changes resulting from processing are apparent. The potentialities of tracers in problems involving fiber distribution and blending are obvious. Perhaps the classic experiment of this kind \\as the work of Sanliey, Mason, Allen, and Keating (I?), which is noteworthy because large-scale equipment was used and it clearly demonstrated the sensitivity of the tracer technique. They were interested in the pattern of flow of fibers through a papermaking machine which was fed by six filter units (Bird screens). Fibers were tagged with iodine-131 ( A g F ) and fed into one of the filter units. The distribution of the tagged fibers in the resulting sheet of paper n a s determined. At the end of the experiment 8 X 10-7 gram of iodine-131 was distributed throughout 31/2 tons of paper having an area of 6 x lo5 square feet. The distribution of radioactive fibers in the paper sheet was measured easily with conventional rounting equipment.
Figure 2.
EXPERIMENTS INVOLVING CHEMICAL PROCESSING
One of the operations of common occurrence in chemical processing is padding. A fabric is passed through a trough containing a slurry or solution (usually thickened with a soluble polymer) and then through a set of squeeze rolls n.hich express unwanted liquid. The trough may contain such materials as dye, a dye precursor, a pigment, or a resinous material. Padding is particularly useful when the fabric is being impregnated with a substance which has low solubility in water. As in the case of oiling, the padding operation must be uniform and reproducible. The amount padded on depends on such variables as the concentration, temperature, and viscosity of the liquid in the trough, the time of immersion, and the pressure of the squeeze rollers. Hampson and Jones (4) incorporated phosphorus-32 (KaP320a) into the liquid used in padding on a resist salt (a substance to keep certain portions of a piece of fabric from becoming colored in a subsequent printing operation). Uniformity of padding can be followed continuously and corrections made immediately. The
Radioautographs
(2)
A . Single wool fiber before processing B. Fiber Tithin a yarn
Another type of distribution problem which has been successfully attacked with the use of tracers involves the oiling of yarns. Yarns are given a light oiling to improve their behavior in weaving or knitting. The oil should be distributed uniformly along the yarn and from fiber t o fiber in the minimum amount capable of giving efficiency. The last requirement arises not only for economic reasons but also because usually the oil is removed a t a later stage, Trotman (20) and Robson (14) have studied oiling of yarns. Trotman used an oil containing ethylene dibromide containing bromine-82 on nylon and Robson used sodium oleate containing sodium-24 on rayon. I n both cases radioautographic methods were used to determine the distribution.
method cannot be used with substantive materials; however, appropriate niodifications should be easy, a t least for esperimental purposes. When a fabric is printed in more than one color the colors are applied one a t a time. I n spite of all precautions, color is carried from one box to the next by the fabric and the backing cloth and offcolor shades result. If a box is known to be contaminated, it can be recharged; however, a method of testing for contamination is necessary. Meitner and Ilampson (8) have devised a method whereby phosphorus-32 [(NH&P3204] is put in with the dye in the first box and an appropriate set of counters are attached to the second. The counting circuit can then be adjusted to give a signal when the concentration of the
contaminant dye in the second box becomes excessive. This application is not just experimental, but could be used as a routine control method. However, use of tracers on a continuing basis for control would obviously introduce special problems involving radiative hazards to plant operations personnel and to the public. The potential utility of a control process would involve considerations of the necessary safety precautions as well as of the sensitivity of the process. Khen cloth is to be waterproofed, oils and’ wetting agents must be removed thoroughly from the fabric. The degree of removal could be continuously checked by monitoring the amount remaining if the possible contaminants viere suitably radioactive. A brief reT-iew is given by Pinault (12). Detergent action and washing are ne11 suited for study with tracers because the amount of soil involved is a small fraction of the fabric sample involved. Lambert (6) and Phansalkar and Vold (11)have used tracers in studying detergency. Lambert studied the absorption of calcium-45 from hard water containing various soaps and detergents during several wash cycles. He concluded that the amount of calcium absorbed correlated indirectly with the absorption of the anionic detergents and through this with the detersive effectiveness of the bath. Phansalkar and Vold labeled a dispersion of colloidal carbon with a zirconium-95-niobium-95phosphorus tracer and determined the amount taken up from a detergent solution by a cotton strip. Their results disagreed with the reflectance method of measuring uptake. They concluded that the reflectance method was in error because of changes in carbon particle size in the detergent solution. Millson (9) proved, through the use of cobalt-60, that sequestering agents prevented the deposition on wool of precipitates of dye with tracers of metals such as iron or cobalt. Such precipitates are objectionable because they cause spots and changes of color. EXPERIMENTS INVOLVING PHYSICS AND CHEMISTRY OF FIBERS
Applications involving the physics and chemistry of the fibers can be separated into two groups; those in which some feature of the chemical composition of the fiber is determined, and those in which the tracers are used as a tool in the study of the mechanism of some interaction. Analysis of Fibers. Most of these applications are concerned with the natural fibers. Robson (15) has taken advantage of the fact that copper forms complexes with amino acids a t pH 9 to measure the amount of amino VOL 29,
NO. 12, DECEMBER 1957
0
1745
acid present in fractions resulting from the hydrolysis of wool. By adding copper-64 and precipitating out excess copper, the amount of amino acid present can be determined by counting the resulting filtrate. Ryder (16) injected cystine labeled with sulfur-35 into lambs and subsequently made radioautographs of cross sections of the wool. Wool is radially asymmetrical, consisting of two components, the orthocortex and the paracortex, in roughly equal amounts. 81though there is evidence that the orthocortex and the paracortex differ in cystine content, Ryder found that the radioautograph was of uniform density across the fiber. This apparent discrepancy has not yet been resolred. Richards and Speakman ( I S ) have developed a n iodination process which gives a quantitative measure of the amount of tyrosine in ~ o o l . B y using iodine-131 and making a radioautograph of the treated fiber, variations in tyrosine content along the length of the fiber can be estimated. These variations presumably result from changes in diet and from neathering of the ~vool. The number of carboxylic acid groups present in cellulose has been determined by Valls, Tenet, and Pouradier (25), who used cerium-141. When cellulose is immersed in a solution of a cerium salt, the cerium ion is so strongly absorbed by the carboxylic acid groups that excess salt absorbed on the surface of the fibers can be removed without removing any appreciable amount of bound cation. The bound cation can then be counted. Analysis of Mechanism. These experiments were concerned with the mechanism of the absorption of ions by fibers or with properties of such absorbed ions. I n some cases the tracers were used solely as convenient tools, in others the experiments could not have been made without them. Meader and Fries ( 7 ) and more recently Fava and Eyring (3) have studied the uptake of labeled anionic detergents. The detergents were tagged with carbon-14 or sulfur-35, depending on the structure of the specific detergent. A correction was made for solution held in interstices within the cloth samples that were used. The use of tracers enables the concentration range covered to be extended far beyond that available when the usual technique of determining uptake from the change in concentration of the treating bath was used. I n a similar may Wall and Swoboda (26) have extended the utilizable concentration range for the treating bath in measurements on the amount of sodium absorbed from sodium hydroxide solutions. Sodium-24 was used as the tracer and a correction mas made for adhering liquid. The next example concerns a film
1746
ANALYTICAL CHEMISTRY
rather than a fiber. The substrate that was used, horn keratin, is closely related chemically to wool and hair fibers and the results can be considered qualitatively applicable to keratin fibers. TT'right (28, 29) has measured the selfdiffusion of hydrogen bromide and sodium bromide across a keratin membrane and also the specific conductivity of the membrane. Membrane potentials for small concentration differences in the same range of concentrations were also measured. Sodium-24 and bromine-82 were used. From his results Wright could calculate the ionic mobilities within the film. Results for hydrogen bromide are shown in Figure 3. The ionic mobilities are much smaller than in aqueous solution, showing the restrictive effect of the keratin matrix. The hydrogen ion contributes
little to the conductance until S mmoles per gram are present within the keratin. This value is, to a close approximation, the number of sites which can bind hydrogen ions strongly within the keratin fiber. When sodium bromide is used, the mobilities of sodium ion and bromide ion are similar. Returning now to fibrous samples, occasions may arise Rhen it is inconvenient or too inaccurate to correct for adhering solution. I n such cases the entrained or adhering solution must be separated from the absorbed material. This is a very difficult task when a bulk fiber sample is used unless the absorhate is held firmly by the fiber. When a single fiber sample is used, a satisfactory separation can be made in favorable cases. This fact has opened the way for a series of studies of the interactions of
24
16
Figure 3. ionic mobilities of hydrogen and bromine ions in horn keratin as a function of amount absorbed
(28)
H Nae
s
.020-
r
0 so4
5 o* ,016v)
8 .0122
b g
.008-
s
a
3
.004-
Ob
I
t
I
I
I
2
4
6
8
IO
12
PH
Figure 4. Uptake of Nu2 and SO4 from sodium sulfate solutions by viscose monofil as a function of pH (70)
liuman hair nnd viscose rayon with salt solutions and of the properties of ions absorbed by these fibers. Such measurements are of importance in connection with dyeing and other M et processing operations. The original papers ( 1 , 10, 18. 21, 27) glve details of the experimental methods and results. However, t n o exaniples follon-. Cellulose contains cation exchange sites to a greater or lesser degree depending on its previous history. The uptake of sodium and sulfate ions from solutions containing a constant amount of sodium sulfate by a viscose monofil is shonn in Figure 4 as a function of p H ( I O ) . The tracers used 11-ere sodium-22 and sulfur-35. The dwrease in sodium content with decreaqing p H results from the conipetition of the hydrogen ions for the cation exchange sites. The increare in sulfate uptake results in part from the increasing in sulfate concentration of the solution (sulfuric acid TYBS used to lower the pH) and in part from the fact that the cation exchange sites (niohtly -COO-) become un-ionizcd when hydrogen ions are absorbed. The alisorption also of sodiuni sulfate by human hair has been studied. Perliap5 the nioet interesting results n err obtained from a series of desorption measurements ( 2 2 ) . Hairs, which had been brought to equilibrium n ith solutions Containing tracers, were transferred to nater or to solutions of the same concentration but containing no radioactive material and the rate of loss of radioactivity was followed. The results are shonn in Figure 5 . It is evident that the radioactive exchange processes (1:ibeled inactive) have a different character from the desorption processes. The cation is always the faster moving ion. although it is partially slowed down h j the anion in the desorption into water. The difference between the amount of sodium ion present in the fiber a t any
time in the case of desorption into water and the amount of anion present represents hydrogen ion which has entered the fiber through exchange with the sodium ion. The presence of the hydrogen ion gives an explanation for the unusual shape of the sulfate desorption curve and the slowness of the sulfate desorption. The sulfate desorption curve is a composite curve, the first part of n hich results primarily from the desorption of sodium sulfate and the last part from the desorption of sulfuric acid, a notoriously slow process as far as protein fibers are concerned. LIuscles, nerves, skin, and cellulose material in general are usually in contact with aqueous solutions containing many solute components, some of which are ionic. The functions of these (often predominantly fibrillar) materials are obviously related to the tliermodynamics and kinetics of their interactions with the surrounding solutions and as a result these interactions have been studied extensively. Transport across the membranes a t the surface of cells, for example, is apparently characterized by the fact that different mechanisms may exist for ions than for nonionic organic material (the ions appear to flow through pores) and “active transport” may occur. Active transport has been used to describe the process whereby a demonstrably permeable membrane can maintain unequal concentrations of certain ions on its two sides, a t the same time maintaining a potential difference across itself. Transport resulting only from the existence of a chemical potential gradient across the membrane is termed passive. By using pairs of radioactive isotopes such as chlorine-36 and chlorine-38 or sodium-22 and sodium-21, the flux through a membrane in each direction can be determined. Bjcomparison of these fluxes n-ith theoretical relationships between tlic fluxes
and the chemical potentials it is possible to tell Fhether a transport process can be characterized as active or passive. Many variations on tracer experiments of this type ha\-e been made; an interesting review is given by Cssing (23). Other recent related work has been presented by Keynes ( 6 ) and Ussing and Deyrup (24). LITERATURE CITED
Barnard, IT. S., Palm, d., Stain, P. B., Underwood, D. L., White, H. J.. Jr.. Textire Research J . 24, 863 (1954).
Chaikin, RI., Baird, IC., Stutter, A. G., Curtis, J., “Proceedings of the International Wool Textile Conference, ;lustralia 1955,” Vol. E, Part 1, E 168, Commonrealth Scientific and Industrial Research Organization, Melbourne, 1956. Fava, A , , Eyring, H., J . Phys. Cheni. 60, 890 (1966).
Hampson, H. B., Jones, E. W., J . SOC.Dyers Colozcrists 69, 620 (1953).
Keynes, R. D., Proc. Rou. SOC. ( L o n d o n ) B 142. 359. 383 (1954). Limbert, J. 31 ,‘ Znd. Eng. Chem. 42, 1394 (1950).
Rleader, A. L., Fries, B. A,, Zbzd., 44, 1636 (1952).
RIeitner, IT., Hampson, H. B., J . SOC. Dyers Colourzsts 69, 283 (1953).
RIillson. H. E., -4m.Duestuff ReDtr. 45, P. 66 (1956). Moncrieff-Yeates, AI., A I . , White, H. J., Jr., Zbid., 46, P. 8 i (1957). Vold, R. D., J . Phys. Phansalkar, A , , Vc ”
Y
.
Che 59,885 (1955). Chem.
Pinault, Pinau R. K.,Text& Woild 107, 78 (1957). ( Richa Richards. H. R.. Sneakman. J. B.. J . Soc. Dyers Cdlourists 71, 53f (1955).
Robson, .1.,Atomics and Atomic Technol. 4,320 (1953).
Robson. d..J . SOC.Dziers Colourists 68. 7 i1952).
T 310 (1954). Trotman, E. R., Textzle Recorder 69, 93 (1951).
-I0
Underwood, D. I,., White, H. J., Jr., Discussion Faradau SOC. No. 16, 66 (1954). (22) Underwood, D. L., White, H. J., Jr.,
in preparation.
(23) Ussing, H. H., in “Ion Transport
dcross Membranes,” H. T. Clarke, ed., -4cademic Press, X e r Tori;, 1954.
(24) Ussing, H. H., Delrup, I. J., J . Gen. Physiol. 38, 599 (1955). (25) Valls, P., Tenet, -1.AI , Pouradier, J., Bull. sac. chzm. Fiance 1953, 1ne
(26) KiilYF. T., Swoboda, T. J , J . Phys. Chem. 56,55 (1952). (27) White, H. J., Jr., Proc. Intern. Conf.
Peaceful Uses Atomic Energy, Geneva, 1955, 15, 39 (Pub. 1956). (28) Wrip.ht. M.L.. Trans. Faradau SOC. Figure 5. Rates of desorption or exchange of ions for hair fibers containing sodium sulfate immersed in water or a nonradioactive sodium sulfate solution {inactive) (22)
49; 9b (1953). (29) Ibid., 50, 89 (1954).
RECEIVEDfor review M a y 28, 1957. Accepted August 14, 1957. VOL. 29, NO. 12, DECEMBER 1957
1747
