chemical microscopr~a~jmponium
Chemical Microscopy in Dyeing and Finishing GEORGE L. ROYER Calco Chemical Division, American Cyanamid Company, Bnun,d Brook, N . J .
The microscope has heen of eonsiderahle value i n the textile field. Its earlier use in the identifioation OC textile Bhers has heen expanded through the application of chemical microsoopy, in which analytioal and physicochemical aspects of textile manufacture have heen studied with the aid of the microscope. Its usefulness depends upon the ability of the chemist who is doing the work, and the microscope is no better than the brain that interprets what the eye sees.
amination of the cross sections of textile fibers, threads, and fabrics. Figure 1 shows a view of the Caloo modified Hardy microtome and Figure 2 a diagrammatic sketch of how it is used.
HEMICAL microscopy as described by Chamot and Mason (3) reaches out into many fields, to include "those methods, principles, and phenomena of chemistry which may he studied psrtieulmly advantageously by mean8 of the microscope-not because they exemplify the manifold use of the instrument, but because the technique, theoretical foundation, and interpretation of microscopical studies are all closoly interralated, whatever the materids examined. Chemical mkr0ScOpy claims recognition more because i t yields observations which are direct and vivid, conclusions which are more positive, and results which arc not obtainable by other methods, than because only limited amounts of material are n~cessaryfor study." Dyeing and finishing are arts to which chemical microscopy can be applied in order to obtain a better scientific understanding. Microscopy has been used extensively for the study of the structure of textile fibers and fabrics, and this paper shows haw the microscope can be and has been used as an aid in the solution of L.:-I.:-some of the chemical problems of dyeing
A shows the slot of the instrument with the plunger pulled down and turned out of the way. At this point the microtome slide is out of the base and held or laid on the table tor).
of-the saiie fiber. In this way,"similar samples can be compared more readily because of their proximity on t,he same slide and identical thickness. In C the microtome slide containing the fibers in the slot is placed in the base and a metal plunger holds the fibers tight in the elrn+
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turned to force the plungerhp into tho dot, which thehforces the ends of the fibers out of the top of slot F .
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for special equipment in addition to the microscope, which should be of the petrographic rather than the biological type. He must combine the fields of analytical and physical chemistry and adapt his experiments so that the microscope will be an aid to the solution of the problem. He should have some knowledge of the field of photography, so that he can record his results for examination by his eo-workers who will play an important part in the practical application of his results. Petrographic Microscope. The petrographic or chemical t.ype of microscope is needed because it can be used to obtain m m y more data. than the biological type and be just BS useful for routine examinations. It differsfrom the regular microscope in thht i t is equipped for observations and measurements with polarized light. Thus, it is possible to obtain optical data. on materials being examined which can he studied in comparison with known data for analytical purposes or for information on changes in composition and structure. The binocular type of microseopo is also useful where there is au interest in physical structure that can be rosolved a t relatively low magnification. I t gives a view in three dimensions, which is often of great valuo. Other microscopical apparatus is useful for special problems, provided the microscopist has time to learn the techniques Far it,s use and e m interpret the results. Microtome. The microtome makes possible the examination of very thin sections of materials. Extensive use hes been made of the rotary and sliding microtomes by the histologist in studying biological preparations. These same techniques have been applied in the textile, field. However, a simplified microtome of the Hardy (5) type has been found useful and rapid for the exI
V IV I.I
cotton. and biscosc iayon. cellulaso acetate dissolved in acetone
these solutions, can be embeddea &th etlhylcellulose In water.
ca& the first scetion is too thick and contains xhers of varying
Figure 1.
442
Calco .Modified Hardy Microtome
V O L U M E 21, NO. 4, A P R I L 1 9 4 9
Figure 2
Figure 5
Figure 4
Figure 7
Figure 9
Figure 10
I 4 I
Figure 13
Figure 3
I
Figure 1.1
r Figure 11
Figure 12
Figure 16
I
I
I Figure 17
Figure 18
Figure 21
Figure 22
Figure 19
COLOR PLATE I. MISCELLANEOUS COLOR PHOTOMICROGRAPHS Photomicrographs made in laboratories of Calco Chemical Division, American Cyanamid Company, Bound Brook, N. J.
ANALYTICAL CHEMISTRY
‘444
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cotto
Figure5. Wool
a Figure 3. Same A0at.t. Rwmoved
Figure& Mohair
Figure 4. Human Hair
Figure7. Silk
,
Figure9. Lanital
FLgurelS. Cotton
Figure 17. Acetate Rayon
Figure 21. “Rug” Bemberg
FiyrelO. Aralao
Figure 14. Memuinad Cotton
Figure 18.
Pigmented Aeetata Rayon
Figure 22. Vinyou
Figure 11. S o y h
Figure 15. Vi-
Fi(lpreU. Nylon
Rayon
Figure 19. Bembexg Rayon*
Figure 20. Pigmented Bemberg Rayon*
Figure 23. Fur Felt
Rayon*
COLOR PLATE 11. CROSS SECTIONS OF TEXTILE FIBERS Photomicrographs made in laboratories of Calco Chemical Division, American Cyanamid Company, Bound Brook, N. J.
* “Bembarg,” registered trade mark of Ameriean Bemberg Corporation, for cuprammonium cellulose yarn8 made by that aorporation.
V O L U M E 21, NO. 4, A P R I L 1 9 4 9
445
infrared microscope, but possibly the recent combination of a photoelectric ocular, such as used in the Snooperscope ( I ) , with the regular microscope may open new fields, for now infrared can be changed to A M v i s u a l l i g h t a n d thus be “seen.” Optical Staining. A special microscopical technique known as “optical staining” (11) is illustrated in Color Plate I (Figures 1 to 12). Although these examples are shown on t leather and some pharmaceutical crystals, they are applicable to textiles and textile chemicals for obtaining similar information. The method was originally described by Rheinberg ( 7 ) in 1896 and an instrument made by Zeiss, called J the Mikropolychromar, is versatile for this purpose. It N makes possible the use of various combinations of colored Figure 2. Diagrammatic Sketch Showing Use of Microtome dark- and bright-field illuminations at the same time, lengths, it is discarded. By turning the wheel a given number so that colorless materials will appear colored. of notches, fibers of definite length will be pushed out and sections of the same thickness can be made by repeating the process Color Plate I (Figure 1) is a cross section of leather dyed with as shown in F to J. This may have to be repeated several times Calcomine Red 8BL. This picture was taken a t a magnification before a good section is obtained as observed with a low-power of 15X by the usual bright-field method of microscopical illuminabinocular microscope. tion in which the specimen is shown by transmitted light. Be4 drop of Diaphane (Will Corp., Rochester, N. Y . )or Canada cause of the thickness of the section, it is n o t possible for light t o balsam is placed on a microscope slide as in K and the thin seccome through the dyed portion and show it as the same color as tion in the embedding material is placed on top of the drop of the would be obtained by reflected light. Figure 2 is the same secmounting medium with the film side down. Another drop of tion shown in Figure 1, but photographed by the dark-field mounting solution is placed on top of the section as shown in L method of microscopical illumination. The specimen is shown and a cover slip is placed on top as in M . To set the section so by reflected light using the Mikropolychromar with the direct that it will be flat, it may be put under a small press, N . The beam obstructed and illuminated only by the indirect beam, section is then ready for examination. 1 which in this case was white. light. Figure 3 is again the same section as shown in Figure 1, illuminated by the use of the MikroPhase Microscope. The phase microscope (2) is another tool polychromar, using white indirect illumination and green direct of recent development which offers advantages in the microillumination. The use of the green-colored direct illumination scopical study of special problems where the material being ingives good contrast between the red dyed portion of the leather vestigated yaries only slightly in thickness, optical properties, and the background. Figure 4 is the same cross section shown in Figure 1, illuminated by white indirect light and blue direct and absorption of light. Such material under the phase microlight. Again the blue color gives good color contrast between the scope will exhibit better contrast without staining or modifying red dyed portion of the specimen and the background. Figure the sample. I t cannot be applied to all studies, but there are 5 shows the same cross section as Figure 1, but is illuminated by conditions a here the regular microscope fails and here the phase the Mikropolychromar using white indirect illumination and red direct illumination. This is a very poor choice of color for the contrast microscope may provide the solution. In some cases direct or background illumination in that the color contrast beit may be attached to a regular microscope as an accessorv, but tween the red-dyed leather and the background does not exist. this possibility depends upon the type and manufacturer of both. In all five figures, which are taken a t a magnification of 15X , the Electron Microscope. The electron microscope is finding use indirect illumination used was white light, so that the natural color of the leather and the dyed portion of the section MTould be in the textile field in obtaining a better understanding of the fine shown in their true color and stand out against a colored backstructure of fibers and the dyes, pigments, and finishing agents ground. used on them. Little information has been obtained on the conFigure 6 shows potato starch grains photographed by the dition of dyes within the fibers because of difficulties in obtaining Mikropolychromar method of illumination using blue direct light and red indirect light. The red indirect light shows up a t those Jatisfactory thin sections for examination. Some replica work portions where red light is reflected by the sample; the backon the surface of fibers (4, 6 ) has given information on the imground is the color of the direct illumination. proper application of dyes, so that surface deposition is obtained. Figure 7, a photomicrograph of a single crystal of sulfanilFuture studies with the electron microscope by new techniques amide, was taken with red direct illumination and blue indirect illumination. It shows the crystal edges in blue against a red will give information on how dyes are deposited in fibers. background. Figure 8 is a photomicrograph of a single crystal The fluorescence, ultraviolet, and infrared microscopes are of sulfanilamide taken with the Mikropolychromar, using blue special tools which can be used on problems when applicable. direct illumination and red indirect illumination. It shows the Fluorescence is useful for many analytical identification puredges of the crystal to be red on the blue background. In these crystal pictures, this type of illumination makes the surface eviposes and has been used in dyeing studies for tracing the looation dent. In this way, pits, scratches, and other irregularities on the of small quantities of fluorescent dyes (8). The ultraviolet insurface of the crystals can be clearly seen in one color contrasted strument as such has been difficult to operate and has found little against another colored background. usr in the dyeing and textile field. This has also been true of the Figure 9 is a photomicrogiaph of a number of crystals of sulfa-
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ANALYTICAL CHEMISTRY
diazine photographed by the Xkropolychromar, using blue direct and yellow indirect illumination. Figure 10 shows some of the same crystals as in Figure 9, but using blue direct and red indirect illumination. Figure 11 shows some of the same crystals shown in Figure 9, using red direct and green indirect illumination. Figure 12 also shows some of the same crystals as in Figure 9, using red direct and blue indirect illumination. The crystals shown in Figures 6 to 12 have been magnified 25 X . Striations on the surface and in the internal portions of crystals can be shown readily by optical staining. This may be of interest in connection with the rates of reactivity of certain chemical reactions and may be also related to the physical structure. Similar studies applied to textile fibers give information relative to the deposition of various textile finishes on their surface. Very fine colored particles can be made more distinct because this method of illumination combines both the bright- and darkfield and in addition the possibility of using contrasting colors. Obviously, optical staining cannot replace chemical staining where the differences in structure cause differences in the reaction to the stain. However, optical staining is applicable to show and emphasize physical differences in structure which can be made apparent by optical means and to emphasize previously chemically stained materials. Photography. Photography can be of great aid to the chemical microscopist because it can be used to record his observations. The equipment can be very elaborate or very simple, depending upon the flexibility. The simplest apparatus for photomicrography besides the microscope and a light source is a camera for holding the film. This camera needs no lens because the microscope replaces the lens, but it should have a film holder which can be replaced by a ground glass so that exact focusing can be accomplished. bfanp types of cameras and attachments are available which permit the use of 35-mm. roll film and various sizes of cut film. By a variation in equipment lorn and high magnifications can be used to show the desired view. It is possible to make photomicrographs in color or black and white. Although the black and white photograph is less expensive and more readily reproduced, color makes possible the expression of results that cannot be shown otherxise. The color plates used to illustrate later phases of this article emphasize this. The technique for taking color photomicrographs has been discussed previously (IO). It differs from black and white photography primarily in the type of illumination, and in the greater precision required in determining the exposure. Special equipment can be used to help obtain satisfactory results. APPLICATION TO DYEING STUDIES
Dyeing is an art, the results of which have been determined for years by the esthetic sense through visual observation. The scientist tries to make these results absolute by taking physical measurements which will describe the psychological values. In addition, an attempt is made to discover the factors that cause the results, so that the operation of dyeing can be more reproducible. The microscope, with its ability to see beyond that of the unaided eye, looks within the textile and greatly aids in these scientific interpretations. IDENTIFICATION OF TEXTILE FIBERS
Down through history has come the development of natural fibers for textile purposes. Today cotton and wool are the important natural fibers, but some of the synthetic fibers rival them in many respects. As the textile materials become more complex in regard to the use of blends of fibers, it becomes important to identify the components. Dyes are selective t o certain fibers and, therefore, must be chosen for special jobs. The microscope is a great aid in this fiber identification. The shape, size, fiber length, structure, etc., can be seen readily under the microscope by either longitudinal or cross-sectional examination
Color Plate I1 shows the cross sections of the most common textile fibers. Differences between mohair and woo1 are difficult to discern by microscopical means, but the synthetic protein fibers can be distinguished from each other and from the natural protein fibers. The denier and uniformity of fiber size distribution can readily be determined from cross-sectional examination. Delustered synthetic fibers can be identified by the appearance of the pigment or other delustering agent within the fiber structure. Rlercerized cotton can be recognized readily in cross section, in that the irregular kidney-shaped fibers of regular cotton are swollen and are more nearly round in shape. The degree of mercerization can be estimated by determining the proportion of fibers which have changed and the extent to which swelling has occurred. The composition of fiber blends can be determined by a count, from a cross section, of the number of each type of fiber present and then, if this is corrected by density and diameter, a weight distribution is obtained. It is often possible to make further use of microscopical techniques in a detailed study of minor variations in fiber morphoIogy which often affect the rate of dyeing-for example, the stretch given rayon during manufacture carries through to the finished fiber as greater orientation of the cellulose. The effect of orientation can be determined microscopically by measuring the refractive indexes of the fiber in both directions. The difference between these two values is known as birefringence. Thus, the uniformity along the filament or from filament to filament can be determined and related to the dyeing and physical characteristics. The maturity of cotton depends upon how well the cotton fiber is filled with cellulose. The cotton fiber starts its growth as a tube and the cellulose builds up within this tube as the fiber grows. A fully mature fiber is filled with cellulose, whereas an immature fiber is more or less a collapsed tube. By swelling reactions in alkali it is possible to differentiate between the mature and immature fibers and from a count determine maturity. It is also possible to use polarized light (Figures 17 and 18, Color Plate I) for detection of the extent of maturity because the difference in thickness of the fibers will show up as different colors, and counts of these again can be related to maturity. Often changes in fiber structure due t o mold, bacteria, moths, etc., can be detected by a microscopical examination. PEKETRATIOlV OF DYES
I n dyeing, the dye is removed from the bath and migrates betn-een the fibers, finally diffusing within each fiber to combine in some manner with the material of which the fiber is made. The penetration within the fabric is somewhat controlled by the fabric construction, but can be influenced by the physical or chemical nature of the dye. The latter factors are very important in regard to the diffusion into the fiber itself. The microscope has been of value in studying where the dye goes when certain physical and chemical changes are made in the dyeing process. Cross sections of the finished dyeings and sections of material removed during dyeing make this possible. The distribution of the dye from fiber to fiber, which has been termed fiber levelness, has been related to color value and fastness properties, so that improvements in results and dyeing processes have been possible. Although these studies are usually made with normal visible light, Figures 13 and 14 of Color Plate I show the application of fluorescent microscopy to this field. Figure 13 is a cross section of wool dyed in the cold with Rhodamine B. Dyeing of this coloi in this manner gave very poor fiber levelness and the photomicrograph of this section by fluorescent photomicrographic technique shows very poor distribution of the color and a variation of shade from one fiber to another due to the deposition of different quantities of rhodamine. The magnification of this photomicrograph and of Figure 14 is 70X. Figure 14 is a cross section similar t o that shown in Figure 13, except in this case the rhodamine was applied a t the boil. It shows
V O L U M E 21, NO. 4, A P R I L 1 9 4 9 fairly uniform fiber levelness and indicates that the dye is evenly .distributed from fiber to fiber. An interesting study of ancient fabrics has been made with the aid of cross sections and the microscope. It has been possible t o study the structure of the fabrics and also the penetration and distribution of dyes. Figure 23 of Color Plate I shows a view of an ancient Peruvian fabric and Figure 24 is a cross section of the dark brown wool threads. Although all of the wool is dyed brown, some of the fibers are heavily pigmented. The microscopical examination of the bright red and yelloly yarns from the same fabric showed that the Peruvians had chosen fibers free from pigmentation for the lighter colors, while they found they could use some of the dark pigmented fibers for the darker shades. Such studies of these old fabrics may help us rediscover old arts a n d bring old beauty into the new world. Defects in finished fabrics are a cause for concern and often a microscopical examination will reveal the reaqon and prevent future occurrence. Figure 21, Color Plate I shows a spot on a yellow cotton material a t a low magnification. In Figure 22, fibers were removed -from the spot and after dissection were reduced with dithionite. Because the cotton material was vat dyed, the leuco color of the v a t dye was formed. This figure shows some of the cotton fibers taken from this spot under the microscope after addition of the dithionite. The cotton fibers appear pink, which is the color of the leuco of this vat dye, whereas the material that was causing the spot appears as a blue pigment. Previous examination of this same fiber group before the addition of the dithionite showed this pigment t o be blue. As a result of this and other chemical identification tests, this blue material was shown to be ultramarine blue. The spot appeared green in the original fabric without magnification because the blue pigment and the yellow fiber gave t h e appearance of green. These examinations showed that the green spot was due to the presence of ultramarine probably used for bluing and not due to an impurity in the vat color, or a speck of foreign vat color which had fallen onto the fabric. Many chemicals are used in dyeing and finishing. I t is often necessary to identify products, either because of the loss of labels or to identify chemical constituents sold under a proprietary name. Chemical petrographic methods are reliable and fast a n d require only small quantities of material for identification. T h e latter factor is important if the chemical has been a source of contamination and only a small amount is available Figure 19, Color Plate I, shows crystals of 6-aminoanthraquinone which mere taken a t a magnification of 70X between crossed Nicols i n a polarizing microscope. Polarized light techniques are often useful in detecting and identifying various crystalline materials i n addition to the beautiful color effects which are obtained from normally colorless crystals. Fluorescence is also useful for identification. Figure 15 s h o m crystals of sulfapyradine, photographed by the fluorescence microscope. Many textile and dye intermediate chemicals show fluorescence and so this same technique can be applied.
447 APPLICATION TO FINISHING
Finishing is often only a physical operation, such as shearing or pressing. However, chemicals such as starch and resins are often added to produce special effects. The polarizing microscope can be used in the study of the application of starch. Figure 20, Color Plate I, a photomicrograph of potato starch, was taken a t a magnification of 70 X between crossed Ncols with a polarizing microscope. This technique is useful for the identification of starch in that the small crosses which can be seen in the starch granules appear in what, under the ordinary microscope, are clear, transparent granules. As starch is processed by hydrolysis, the granules swell and change and lose their identity in polarized light. The microscope is, therefore, useful in following these reactions. The application of resins or resin-forming chemicals to textile fibers has been a new field for the use of the microscope both for the identification of the materials and in a study of their function. Identification of the resins themselves is covered in two articles, one on analysis of resins and another on resinography ( 1 2 ) . Some of the microscopical work on textile resins done in this laboratory has been reported (9). I n this study the location of urea and melamine type resins was established by dye-stain tests and this related to their use in wool shrinkage control and creaseproofing of rayons and cottons. The extent of cure and the proper distribution of resin in regard to location and quantity appear to be important and microscopical techniques have been developed to follow these. The microscope has been of value in obtaining a better understanding of these results and future studies should aid in the further development of the processes. LITERATURE CITED
Bailly, R., Science, 108, 143 (1948). Bennett, A. H., Jupnik, H., Osterberg, H., and Richards, 0. W., Trans. Am. hftiroscop. Soc., 65, 99 (1946). Chamot, E. M., and Mason, C. W., “Handbook of Chemical Microscopy,” New York, John Wiley & Sons, 1938. Hamm, F. A., ANAL.CHEM.,20, 861 (1948). Hardy, J. I., U. S. Dept. -4gr., Circ. 378 (1935). Millson, H. E., Watkins, W. H., and Royer, G. L.. Am. Dyestug Reptr., 36, 45 (1947).
Rheinberg, J., J . Roy. Microscop. Soc., 1896, 369, 373-88; 1899, 142-6,243-5.
Royer, G. L., and Maresh, C., J . BioZ. Phot. Assoc., 15, 107 (1947).
Royer, G. L., and Maresh, C., J . SOC.Dyers Colourists, 63, 290 (1947).
Royer, G. L., Maresh, C., and Harding, -4.M., Calco Tech. Bull. 770 (1945). Royer, G. L., Maresh, C., and Harding, A . XI., J . Biol. Phot. Assoc., 13, 123 (1945). Stafford, R. TV., Williams, E. F., Rochow, T. G., and Gilbert, R. L., Chapters on Analysis of Resins and Resinography in “Protertive and Decorative Coatings,” J. J. Mattiello, ed., Kew York, John Wiley & Sons, 1946. RECEIVED February 2, 1949.
