20
INDUSTRIAL AND ENGINEEKlNG CHEMISTRY
appears exceptional, as i t was more difficult to stabilize than the other untreated gasolines studied or than an acid-treated gasoline from the same stock. 5. The critical oxidation potential of an inhibitor is related to its antioxidant power but is not an exact index of its efficacy. 6. I n predicting storage stability, induction period appears the most reliable single test. High copper-dish gum in some cases accompanies instability in storage, while increase in copper-dish gum and in peroxide number during the early part of a storage period denotes approaching deterioration in other respects, particularly formation of air-jet gum.
LITERATURE CITED (1) Aldrioh, E. W., andRobie, N. P., S. A. E. Journal, 30,198 (1932). (2) Am. SOC.Testing Materials, Proceedings, 32, Part I, 407 (1932).
(3) Am. SOC.Testing Materials, Rept. of Committee D2,1934. (4) Dryer, C. G., Lowry, C. D., Jr., Morrell, J. C., and Egloff, G., IND. ENQ.CHEM..26.885 (1934). (5) Egloff, G., Morrell,' J. C., Lowry; C. D., Jr., and Dryer, C. G., Ibid.,24, 1375 (1932).
Vol. 27, No. 1
(6) H u m , E. B., Fisoher, €3.G. M., and Blackmrood, A. J., S. A . E . Journal, 26,31 (1930). (7) Kraemer, A. J., Garton, E. L., and Lane, E. C., Bur. Mines, Rept. Investigations 3152 (1931). (8) Lowry, C. D., Jr., and Dryer, C. G., U.S. Patents 1,889,835and 1,889,836 (Dec. 6, 1932). (9) Lowry, C. D., Jr., Egloff, G., Morrell, J. C., and Dryer, C. G . , IXD. ExQ. CHEM., 25,804 (1933). (10) Mardles, E. W. J., Proc. WorZdPetroZeum Congr., 2, 57 (1933). (11) Marley, J. P., and Gruse, W. A., IXD.ENQ. CHBM.,24, 1298 (1932). (12) Morrell, J. C., Dryer, C. G., Lowry, C. D., Jr., and Egloff, G., Ibid., 26,497, 655 (1934). (13) Ramsey, J. W., Zbid.. 24.539 (1932). (14) Rogers, T. H., Bussies, J. L.', and Ward, P. T., Zbid., 25, 397 (1933). (15) Thomas, R. M., Proc. WorZdPetroleum Congr., 2,122 (1933). (16) Voorhees, V., and Eisinger, J. O., Am. Petroleum Inst. Proc., IO, No. 2, Sect. 11, 169 (1929). (17) Winning, C., and Thomas, R. M., IND.ENQ.CHEM.,25, 511 (1933). (18) Yule, J. A. C., and Wilson, C. P.. Jr., Zbid., 23, 1254 (1931).
RECEIVED August 27, 1934. Preaented before t h e Diviaion of Petroleum Chemistry a t the 88th Meeting of t h e American Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934.
Dyeing Cotton Substantive Dyes and Salt Sensitivity SAMUEL LENHERAND J. EDWARD SMITH Organic Chemicals Department, E. I. du Pont de Nernours & Company, Inc., Wilmington, Del. Substantive dyes in solution at 25' C. vary and his co-workers have estabf r o m the molecular to the highly colloidal state of lished that the maximum conis to Point out some escentration of dye absorbed by sential beaggregation. The addition of sodium chloride viscose sheet depends upon the tween t h e p a r t i c l e size of a number of water-soluble substanin general increases the size Of the dye particles. concentration of electrolyte and tive dyes in solution and the The tendency of dyes to aggregate is associated of the dye in the bath. Yeale with typical groups in the constitution of the dye. and Stringfellow (12)found that mechanism of their absorption by cotton. The dyes studied ~~~i~~ at 250 on does not progress the rate of absorption of dye by v i s c o s e s h e e t is given by a Of represent readily unless the radius of the dye particles is formula derived by A. v. Hill for varying chemical constitution < x lo-' cm* containing dyes Of the diffusion of o x y g e n i n t o and of known markeddifferences the same particle size do not necessarily exhaust muscle tissue. in application characteristics. The d e g r e e of dispersion of Current theories of substanto the same extent. The dyeing process is reversible, and the extent to which it is rerersed &pen& dyes in solution is determined tive dyeing emphasize the COlmost readily by measurement of loidal nature of the substantive on ihe temperature and the inorganic salt concolors in t h e d y e b a t h a s the rate of diffusion of the dye centration Of lhe well as the relationship between The tendency Of dyes lo and calculation of the related t h e p a r t i c l e sizes of the dye f o r m colloidal aggregates in the presence of particle size b y t h e E i n s t e i n sodium chloride (salt sensitivity) is a qualitative equation (3): micelles and their characteristic dyeing p r o p e r t i e s * Schaffer measure of many of the absorption characteristics. (IC), and Schramek and Gotte 1 D = -RT __ (1) (17)have m e a s u r e d t h e parN * 6nrq where r = av. radius of particles, cm. ticle size of a variety of dyes in solution, and Rose (15) has R = gas constant drawn attention to particle size and the dyeing of cellulose. T = abs. temp. Schaffer states that the particle diameter of 4.5 millimicrons D = dlffusion constant, sq. cm./sec. represents the limiting size above which dyeing does not N = Avagadro's number occur on cotton. Schramek and Gotte ( I T ) , and Oatwald 9 = coefficient of viscosity of solvent (IS) have studied the effect of electrolytes on the dispersion of substantive dyes. Weltzien and Schultze (19) have I n the derivation of this equation it is assumed that the parstudied the effect of electrolytes in the dye bath as well as in ticles are large in comparison with the solvent molecules, are the fibers on the dyeing process. Robinson and Mills (14) spherical, and are electrically neutral. Dye particles are have made an intensive study of solutions of benzopurpurine large compared with water molecules. Ultramicroscopic 4B and its isomer prepared from m-tolidine and have shown examination of solutions of the twelve dyes, which is reported that the highly substantive benzopurpurine 4B is more highly in detail below, shows that these dyes give spherical micelles aggregated in solution than its isomer. Keale (6, 7 , 9, 12) in solution. A two-dimensional structural formula does not HE purpose of this paper
c.
January, 1935
I N I)U S T R I A I, I X D E N G I N E E R I N G C H E M I S T R Y
represent the actual appearance in a space of three dimensions of a molecule such as that of a substantive dye, containing a large number of polar groups. The dye micelle is an aggregate of many molecules, and it is logical to assume that in the process of agglomeration the micelle will approximate a sphere, the form possessing the minimum free surface energy. Dye micelles carry electrical charges. This has been the basis of criticism by Hartley and Robinson (10) of the general practice of calculating the particle radius of dyes in solution by the Einstein equation. They showed theoretically that the diffusion constants of electrolyte-free dyes would be of the order of the diffusion constants of inorganic salts and would be no criterion of the micellar radii of these dyes in solution. They believe that a relatively accurate estimate of the particle size is possible when diffusion is carried out in the presence of a concentration of an inorganic salt sufficient to minimize the accelerating effect of the electrostatic charges on the dye micelles. Recent results (11) obtained in this laboratory confirm this idea. Measurements of diffusion constants and the related radii of dye micelles have been to a large degree semi-quantitative. The microdiffusion method of Fiirth (4) makes possible the rapid and accurate determination of diffusion constants in dye solutions.
J~ATERIALS USED The chemical constitutions of the dyes used in this work are as follows: DYB
INORGANIC SALT CONTENT
COXSTITUTION
% 1 2
3 4 5 6
7 8 9 10 11
12
p-Nitro-disulfo-stilbene-azoxy-o-toluene-azo-2-naph38.9 thalene-4,8-disulfonicacid p-Nitro-disulfo-stilbene-azoxy-p-cresol-methyl ether53.7 azo-2-naphthalene-6,S-disulfonicacid Diphenyl-disazo-salicylic acid-l-naohthvlamine-4- 60.0 sulfonic acid Diphenyl-diaazo-aalicylic acid-2-amino-8-naphthol-639.8 sulfonic acid Diphenyl-disazo-l-naphthylarnine-4-6ulfonicacid-2amino-8-naphthol-6-sulfonic acid 51.6 Dimethoxydiphenyl-disazo-bis-I-naphthylamine” 4 33.7 sulfonic acid Benzene-azo-7,7’-disulfo-5,5’-dihydroxynaphthyl-2. 61.1 2’-urea-azo-benzene Benzene-azo-7,7’-disulfo-5,5’-dihydroxnaphthyl-2, 57.3 2’-urea-azo-p-benzene-carboxhc a c d Benzene-a~o-7,7’-disulfo-5,5’-di~ydroxynaphthyl-2, 2‘-urea-azo-p-acetylam1nobenzene 50.8 Benzene-?-azo-6-benzoyl-p-amino - benzoylamino-1naphbhol-3-sulfonicacid-p-azo-sulfopbenyl-methyl59.0 pyrazolone p-Sulfobenzene-azo- benzene-azo-6-benzoylamino- 1na hthol-3-sulfonicacid 40.8 p-SuPfobenzene-azo-benzene-azo-6-benzoyl-p-aminobenzoyl-amino-1-naphthol-3-sulfonicacid 59.5
-
These products represent four distinct types of azo colors with characteristic groupings. Dyes 1 and 2 are of the stilbene type and contain the group:
H-7i-o Dyes 3 to 6 are of the benzidine type and contain the diphenyl grouping:
Dyes 7 and 8 are from J-acid urea and contain the grouping: H
I
o=c/
N
\N
I
H
21
Dyes 10, 11, and 12 contain, in para positions, the groups:
O H -L*I 1 Dye 9 is distinctive in that it contains both the groups: H
H
All of the compounds used were sodium salts and were commercial products containing sodium chloride and sodium sulfate. Electrolyte-free dyes were not used, since the amount of inorganic matter present was small in comparison with the quantities of electrolytes added to a dye bath. ULTRAMICROSCOPIC OBSERVATIONS Solutions of each of the twelve colors similar to those used in the diffusion experiments described below were examined in the ultramicroscope a t 1450 diameters magnification. Xumerous ultramicrons were observed in all solutions. The ultramicrons appeared in the field as spheres. Even in solutions containing additions of electrolytes sufficient to cause flocculation, no tendency to form rod-like or needle-like particles was observed. DESCRIPTION OF DIFFUSIONMETHOD The diffusion constants of the dyes were measured by the method of Furth and Ullmann (5). The method depends on the measurement of the rate of free diffusion of the dye from its solution into water in a microdiffusion cell. The progress of the diffusion was observed with a micrometer comparator calibrated to 0.01 mm. The microdiffusion c e 11 s h o w n i n Figure 1 was constructed after Fiirth (4, 5 ) : The inside dimensions were: length, 20 mm.; width, 8 mm.; depth, 1 mm. The rubber cell walls, W , were fastened t o a microscope slide, 0, with Picein cement. The cell chamber was divided lengthwise in halves by a celluloid strip, P, which was sealed with Canada balsam into a groove in the microscope slide. The top of the cell was a cover glass sealed to strip P with Canada balsam and t o the walls with Picein cement. The right half of the cell was subdivided horizontally by a movable celluloid strip, S. The slide was sealed and lubricated by stopcock grease and was operated manually. The following uniform Drocedure was adopted in preparing the -dye solutions: The dye was dissolved in boiling distilled *IGUAE D1mUS*oN CELL water: the solution was cooled to 2 5 O C.. and any required sodium chloride wai added. The solution was then diluted t o the desired volume and was aged for 24 hours. The measurements were made as follows: Compartment A was filled with the dye solution and strip S, inserted; cornpartment B was then carefully rinsed to remove all color and filled with distilled water. A reference solution of the dye at a known dilution was placed in compartment C. The strength of the reference solution was from one-fourth to one thirty-second that of the solution in A , depending upon whether the rate of diffusion of the dyestuff was rapid or slow. The cell was clamped in a vertical position, and the hair line in the eyepiece of the microcomparator focused on the lower edge of strip S. The sIide was carefully moved to open the right half of the cell t o allow the contents of A free access for diffusion into B. By careful manipulation, an even color boundary was formed and maintained
I N D U S T R I A L A N D E N G I N E E R I N G C H E hl I S T N Y
22
throughout the experiment. A few seconds after diffusion began, a gradation of color ranging from the colorless solvent to the intense color of the concentrated dye solution was established. The rate of diffusion was determined by measuring the progress into the water of the concentration of dye corresponding to that of the reference solution. The diffusion constant was calculated from Equation 2:
D =
X2
[fWl
(2)
Vol. 27, No. 1
present in a dye bath. The average particle radii of the dye micelles were calculated by Equation 1. The data in Table I demonstrate clearly that the dyestuffs studied are present in aqueous solutions as particles of radii varying between (6 to 40) X cm. This size corresponds to (6 to 40) A. or to (0.6 to 4) millimicrons. The apparent molecular weight of the micelles may be calculated by Equation 3:
where D = diffusion constant, sq. cm./sec. X = distance, mm. t = time, sec. f ( v ) = function of ratio of initial dye concn. to that of reference soln.
4
m =-d g N
3
(3)
where g, the specific gravity of the samples tested, is approximately 1.54. The molecular weights calculated for micelles In ap lying the method, about 30 minutes are required to obtain data &r calculation of the diffusion constant. Eight to ten oh- of the dyestuffs are 935 to 200,000. The formula molecular servations are made a t equal time intervals during a run and weights range from 610 to 935. The data show that the dyes vary in solution from the true or molecular to the colloidal averaged to give the dausion constant. state. The aggregates may contain as many as 225 molecules The microdiffusion method has distinct advantages when per micelle. The degree of aggregation for most colors is applied to the study of dye solutions. The short time of ap- between 10 and 100 molecules per micelle. Particle growth plication makes temperature control easy, minimizes the in these dyes is influenced by the amount of electrolyte preseffects frequently rising from convection currents in the course ent in solution, and, in every case where the electrolyte conof lengthy determinations by other methods, and makes neg- centration is equivalent to that in a dye bath, the particle ligible the effect of changes in the properties of the colloid radius is greater than 12.0 X cm. This corresponds due to aging phenomena. The results are reproducible with to a degree of aggregation greater than ten. a n average error of approximately 5 per cent. The differences in salt sensitivity are closely related to the An independent check on the accuracy of the microdiffu- chemical constitution of the dyes. The stilbene colors are sion method was obtained by means of the ultracentrifuge. least affected by additions of electrolytes. The maximum It was found by measurement of the sedimentation equilib- observed particle radius was 14 X cm. Benzidine dyes rium that particles in a solution of dye (I) a t a concentration are moderately affected by electrolyte additions. Solutions of 1.0 gram per liter have a n average radius of 10.0 X of the commercial dyes examined contained micelles of avercm. This result compares favorably with values ranging age radii less than 17 X cm., while solutions with the from (9.1-11.7) X lo-* cm. calculated from data obtained added salt contained particles of radii varying from (16 to by the microdiffusion method. The variation in the results 26) X cm. The dyes containing a urea group are more obtained is caused by a n aging effect which occurs over a pe- sensitive to salt additions than are the benzidine and stilbene riod of several days in solutions of this dye. The lower types. Solutions of the commercial dyes contained particles value given by the microdiffuqion method was obtained after with a n average radius of 16 X cm., and addition of the solution had aged 18 to 24 hours, while the higher value salt produced marked aggregation. Dye 7 was flocculated was obtained after approximately 100 hours. The measure- by the added salt while the radius of dye 8 micelles was inments with the ultracentrifuge were made over a period of creased to 27 X lo-* cm. Dyes containing combinations 48 hours. of -CONHgroups in para positions are highly aggregated in the presence of the small concentrations of electrolytes TABLEI. DIFFUSIONCONSTANTS AND PARTICLE SIZES present in solutions of the commercial dyes. The micelles OF DYESAT 25' C. of dyes 10 and 12 were larger than 24 X cm.; dye 12 D Y I DYE NaCl was relatively unaffected by the addition of salt, but dye 10 No. CONCN.' CONCN. D X IO-' R X Grams/lifer Grama/liter Sq. cm./eec. Cm. was further agglomerated to particles of a radius of 48 X 1 1.2 cm. Dye 9, containing a combination of the urea and 1i: 0 1.2 1.2 2 -CONHgroups, is as salt-sensitive as dye 12. Dye 11, 12:o 1.2 containing only one -CONHgroup, is the least agglom0.8 3 0.8 i:0 erated of all the products in the presence of electrolytes, and 2.0 4 2.0 i:0 the dye alone is approximately in true solution.
1.0 1.0 6:O 1.0 1.0 i:0 2.0 7 2.0 i:0 1.2 8 1.2 6:O 2.0 9 i:0 2.0 2.0 10 2.0 6:O 3.95 6.1 11 1.0 1.0 6:O 2.04 11.9 0.89 27.3 12 2.0 2.0 i:0 0.98 24.8 a The concentrations refer t o the dye samples described in. the section on Material! Used. From 40 to 60 per cent of the earnples ere inorganic salta. Observations to be published show that these salts exert a marked effect on the agglomeration of molecules to micelles, and it is emphasized that the behavior of the products dencribed I n this paper 18 quantitatively different from that which would be observed for chemically pure dyes.
5
6
Measurements of the diffusion constants of the twelve dyestuffs are summarized in Table I. The measurements include determinations on solutions of the produck alone and on solutions containing added sodium chloride equal to that
RELATION OF
PARTICLE SIZE TO
DYEINGCHARACTERISTICS
Dye tests were carried out t o study the bearing of particle size and salt sensitivity on the wash-fastness and exhaust from the dye bath of the twelve colors. Dyeings were made from solutions DYJXNQ EXPIDRIMENTS. prepared and aged in a manner similar to that used in the preparation of solutions for the partirle size measurements. The dyeings were made on pieces of bleached cotton pongee which had been thoroughly processed in alkali t o remove waxes and oils. The ash content was 0.2 per cent. The diffraction pattern obtained by x-ray analysis showed that the cotton had remained unmercerizrd in the processing operations and W L ~ Rstructurally identical with native cotton. Ten grams of the cotton piece goods and 400 cc. of the dve solution were used in each experiment. Dyeings at 25' to 27" C. were made in Pyrex beakers and were carried out for 45 minutes. The cotton pieces were turned frequently with glass rods to obtain level dyeings. Dyeings with six colors were mnde at 100' C., using porcelain pots heated on a glycerol bath. The volume of the bath was maintained by
January, 1935
INDUSTRIAL AXD ENGINEERING CHEMISTRY
additions of water. After dyeing for 30 minutes at the boil, the pots were allowed to cool to 60" C. over a 15-minute interval. This is the standard method of dyeing substantive colors in the Technical Laboratory of the du Pont Company. Tests of the fastness of the dyes to washing were made by agitat,ing the dyed pieces for 30 minutes at 50" C. in a 0.1 per cent tallow soap solution. In these tests, 0.5-gram pieces of the dyed cotton pongee with ten monel metal balls were placed in pint (0.47-liter) mason jars containing 100 cc. of the soap solution. The solutions were kept agitated by rotation of the jars in a launderometer, the standard washing machine (2) of the American Association of Textile Chemist,sand Colorists.' Measurements of the strengths of the dveings after the absorption test,s and after the wash tests were made and the percentage of dye removed was calculated. The data are summarized in Table 11; the dyes are arranged in the order of increasing salt sensitivity.
the reference curve the concentration of dye required to give the reading for -log R of the dyeing of unknown strength. The accuracy of the method is influenced by the strength of the dyeing. For readings of -log R between 0.40 and 1.50,
TABLE11. DYEING EXPERIMENTS AND WASHTESTS DYED D Y EBATH STRENQTH CONDITIONS Dye Dyea absorbed Dye removed Dye DYE NaCl in pe? 10-g. abper 10-R. reNo. concn T bath piece sorbed piece moved G./L 'C, Mg. MQ. MQ. % 96 1 296.0 21.4 0.5 25 7.2 15.5 72.4 94.8 32.0 12.5 25 296.0 67.9 71.6 13.4 2 222.0 9.6 0.6 25 71.6 6.0 85.6 73.5 12.6 25 222.0 38.6 62.9 18.8 12.2 0.4 25 237.0 64.9 7.9 11 34.2 44.0 77.7 18.6 6.4 25 237.0 b 68.0 54.0 3.75 100 79.4 b 24.2 14.6 3 . 7 5 100 60.3 23.6 128.0 4 6 . 8 36.6 50.4 3 0.5 25 80.4 128.0 112.0 71.8 6.5 25 87.5 25.2 0.3 25 265.0 15.7 62.3 9.5 6 62.9 65.5 265.0 96.1 36.2 6.3 25 b 145.8 39.8 27.3 3 . 7 5 100 b 53.4 14.9 3 . 7 5 100 27.9 19.1 5 0.5 25 193.5 9.9 7.5 39.3 20.4 21.5 54.6 193.5 39.4 6.5 25 b 133.0 44.9 33.8 3 . 7 5 100 b 54.2 11.1 20.5 3.75 100 33.5 4 482.0 21.0 62.7 0.8 25 7.0 33.0 19.6 59.4 482.0 6.8 6.8 25 b 74.0 38.0 51.4 3.75 100 b 37.0 14.5 39.2 3 . 7 5 100 19.4 13.6 8 0.7 25 204.5 9.5 70.4 27.2 18.4 37.6 72.3 6.7 25 204.5 15.9 28.4 56.0 1.2 25 9.1 7 311.0 7.2 25 311.0 29.6 9.5 19.5 65.9
.. ..
.. ..
....
.. ..
R X CM.
... .
..
I
DK4
II
DE9
ESTD. FOR
DYE BATH
9.1 14.0 13.2 12.3 6.1 11.9
.. ..
10.4 17.9 16.6 15.6
.. ,.
12.3 21.0 ,.
.. 11.6 26.1
..
.. 16.0 27.6 15.7 Flocculated 27.3 24.8
2.1 324.0 6.7 2.6 38.8 1.2 25 10.1 3.1 6.4 7.2 25 324.0 63.4 b 111.3 7.3 3.75 100 8.1 6 60.7 12.1 19.9 3.75 100 9 1.0 25 393.5 18.5 4.7 11.8 63.8 23.3 8.4 24.8 75.1 29.2 7.0 25 393.5 33.0 b 64.0 8.0 3.75 100 12.5 b 22.0 .. 3.75 100 1.5 6.8 14.5 10 1.2 25 328.0 4.4 6.55 45.2 37.9 7.2 25 12.8 29.4 328.0 41.9 70.2 48.5 6 The weight of dye is given on a n electrolyte-free basis; the concentrations of sodium chloride include t h a t present in the dye sample. b The amount of dye initially present in the bath for the 100' C. dyeingo is not known accurately. 12
23
... .
.. ..
EVALUATION OF DYEISGS. The evaluation of the dyed strength of the cotton fabric was carried out spectrophotometrically. This method was developed from the observation of Appel (1) that the logarithms of the reflections a t a given wave length for dyeings plotted against the logarithms of the concentration of dye in the fiber give a linear relation over a limited concentration range for a number of dyes. Dyeings covering a range of concentrations up to 2 per cent on a n electrolyte-free basis, were prepared for each of the twelve colors. Values of -log R for each dyeing were determined with a Keuffel and Esser Color Analyzer (visual spectrophotometer) at the maximum of the spectral refleztion. These values of -log R were plotted as ordinates with the Concentrations of dye present in the fibers as abscissas to obtain standard reference curves for each color. Two representative curves are shown in Figure 2. The curves approximate straight lines over the range of dyeing strengths ordinarily encountered. The concentration of dye present in dyeings of any color is readily determined by reading from 1 Manufactured by Atlas Electric Devices Company, 360 West Superior St., Chicago, Ill.
M z OD W Ms
a0,
Q!
42
43 a4
0.6 LV M
2.0
CoNccNTmrm OF DrE IN PERCmr FIGURE2. REPRESENTATIVE SPECTRAL REFLECTION-CONCEXTRATION CURVES FOR DYEINGS WITH SUBST.4NTIVE COLORS
the error is 5 to 10 per cent. The validity of this method was checked for the twelve colors by determination of the areas under the absorption curves in the visible region.
ABSORPTIONTESTSWITH REPRESENTATIVE DYES. In addit,ion to the tests summarized in Table IT, more extensive tests on the absorption characteristics of dyes 4, 9, and 11 were made with solutions prepared as in the previous experiments. However, the dyeings at 25" C. were made in 250 cc. of the dye solution in mason jars rotated in the launderometer for 1 hour. In experiments at the boil, the dyeings were made in porcelain pots and the volume was maintained at 250 cc. The weight of the cotton pongee pieces was in all cases 10 grams. The reversibility of the dyeing process was tested at 25" and 100' C. by rinsing 2.5-gram pieces of the dyed piece goods in distilled water and in salt solutions. The tests were carried out in the launderometer in mason jars containing monel metal balls. The dyed cotton was washed 3 hours; t,he wash water was changed each hour. The amounts of dye on the goods after the absorption and wash tests were determined with the spectrophotometer by the method described above. In the event that the amount of dye removed was too small t o be determined by examining the cloth, measurements were made of the amount of dye in the wash solution. The data for the absorption experiments are summarized in Table 111; the data for the wash tests are given in Table IV. TABLE 111. DYE ABSORPTIONEXPERIMENTS
NaCl D~~ I N DYE DYEABSORBED 100' c. CONCN." BATHb ABSORBED DYE ABSORBED 25' c. 'C. G./1. Me. MQ. 70 18.0 148 26.6 25 0.4 11 1 62.2 42.0 6.4 148 1A 25 17.3 11.7 0.65 148 0.4 2 100 35.3 0.84 148 52.3 6.4 2A 100 10.9 301 32.8 25 0.8 4 3 17.0 301 51.3 25 6.8 3A 52.7 17.5 1.61 301 4 100 0.8 39.0 2.29 301 117.3 100 6.8 4A 13.3 5.4 1.0 246 25 9 5 246 34.3 13.9 25 7.0 5A 40.6 7.52 246 100.0 100 1.0 6 170.0 69.1 4.96 7.0 246 6A 100 The concentrations of sodium chloride include the saIt,in the dye sample. b The quantity of dye is given on a n electrolyte-free basis.
DYE 8ERIES NO. NO.
T
DISCUSSION OF RESULTS The data in Table I1 show that an optimum particle size range exists above which absorption of dye b y cotton does not readily occur. At 25' C. this range corresponds to a n average particle radius of (17 to 20) X IO-* cm. Dyeings from solutions containing particles of a radius greater than
24
INDUSTRIAL AND ENGINEERLKG CHEMISTRY
20 x 10-8 cni. are from one-tenth to five-tenths of the strength of those prepared from solutions containing particles em. These values for with radii smaller than 17 X permissible particle size are of the order of the values estimated for the size of the subniicroscopic pores in cotton (8, 18) and are of the same order as those obtained by Schaffer (16) for the substantive dyeing of cotton. The data in Table I1 prove that baths containing dye particles of the same average particle radius do not necessarily exhaust to the same extent. For example, in solutions of dyes 2 and 6 the size of the dye partjicles is scarcely changed by the addition of 6.0 grams per liter of sodium chloride. However, absorption in the presence of the added salt is from four to six times that from solutions of the commercial color. The addition of electrolyte to the dye bath is essential for absorption of the dye. Whenever dyeings of appreciable strength are obtained, those made in the presence of added electrolyte are from 60 to 500 per cent stronger than those made from solutions containing the commercial dye. The data of Tables I1 and 111 show that, when solutions containing particles of average size >20 x 10-8 cm. a t 25" C. are heated to the boil, an enormous increase in the amount of dye absorbed results. This increase in the absorption of dyes 4 and 9 is from two to five times under these conditions. It has been shown that appreciable dyeing a t 25' C. occurs only when the particle radius is below a limiting value. By analogy a limiting particle size obtains also at, or near, the boil. The highly salt-sensitive dyes 4 and 9 are much more strongly absorbed a t the boil than a t 25' C. during a normal dyeing period, while the less salt-sensitive dye 11 is not absorbed as greatly a t the boil as a t room temperature. It is reasonable to conclude that dyeing with salt-sensitive colors, such as dyes 4 and 9, a t the boil is accompanied by a decrease in the particle size of the micelles to such an extent that ready penetration into the pores of the cotton is obtained.
1'01. 27, No. 1
possesses improved fastness, especially if the dyeings are made a t the boil. Dyeings for the group C are of poor fastness when made a t 25" C. but have the best fastness of all when made a t 100". The data in Table IV show that the wash-fastness (or its equivalent, reversibility of dyeing) is directly dependent on salt sensitivity. It is shown that, if the particle size is maintained above that for dyeing, bleeding of the dye from cotton into water is inhibited. Whenever peptization can occur to bring the particles into the dyeing range, bleeding of the dye into water occurs. Substantive dyes are peptized in water a t the boil to such an extent that the dye may be almost completely removed from cotton in a short time. The data show that the reversibility of the dyeing process on cotton varies widely and depends on the temperature and on the concentration of the salt in the wash water. The affinity of substantive dyes for cotton is qualitatively proportional to the tendency to form colloidal aggregates in solution in the presence of sodium chloride. The degree of absorption of dye a t the boil increases, and the ease of reversibility of the dyeing process decreases with increasing salt sensitivity. It is significant that Weltzien and Schultze found that the electrolyte content of cellulose materials has a marked influence on the amount of dye absorbed. It is probable that the same forces which lead to an agglomeration of molecules of substantive dyes into micelles are instrumental in causing absorption of the dye by cellulose. It is evident from the relations found to exist that the correlation of the substantivity of dyes with their chemical structure is closely associated with their salt sensitivity. Chemical groups known to be instrumental in producing substantivity in a molecule also act to increase the salt sensitivity. The data in this paper show that it is more reliable to use the criterion of salt sensitivity of a dyestuff as a measure of substantivity than to depend on the presence in the molecule of so-called substantive groups. This is illustrated by
TABLEIV. WASHTESTSWITH DYEDFABRICS TESTSAT 25' C. --ODIUM WATER
INITIAL
Washed strength STRENQTA per, 10-g. DYB SERIES PER 10-G. piece moved PIBCB No. No. M g. % MQ 4.70 82.1 26.6 11 1 6.93 88.9 62.2 1.4 4.42 74.5 17.3 2 8.90 83.0 52.3 2.4 1 0 . 6 6 7.7 3 2 . 8 4 3 10.55 79.4 51.3 3A 28.5 45.9 62.7 4 56.0 52.3 117.3 4A 7.35 44.7 13.3 9 5 11.45 66.6 34.3 5A 71.0 29.0 100.0 6 128.0 24.7 170.0 6A a Determined from amount of dye in wash liquor.
.
IMQ.
22.5 39.3 16.15 42.0
.. .. ..
..
... . .. ..
-TESTS
WITH: CHLORIDE-
6.0 grams/liter Washed strength Dye per 10-g. repiece moved
%
Mg.
%
15.4 36.8 6.6 19.7 1.25 4.55 1.3" 2.95 3.1a 2.3" 6.6" 3.30
26.6 59.5 17.3 49.5
4:3
The fastness of dyeings to soap solutions is closely related to the particle size of the colors in the dye bath, as well as to the sensitivity of these dyes towards electrolytes. The data in Table I1 show that, in general, dyeings made at 25" C. in the presence of added sodium chloride are less fast than those made from solutions of the commercial dye. The dyes tested may be divided into three groups with regard to their relative fastness properties: (A) dyes whose micelle radii are smaller than 15 X cm. in the presence of 6.0 grams per liter of sodium chloride a t 25" C.; (B) dyes whose micelle radii in solutions of the commercial color are 17 X lo-* cm.; (C) dyes whose micelle radii in solutions of the commercial color are > 20 X 10 8 cm. Class A has very poor fastness t o soap solutions regardless of whether the dyeings are made a t 25" or 100' C. Class B
... ... .. .. I
.
..
AT
100° C.S O D I C M C A L O R. I D E~ _ ~~
25.0 grams/liter Washed strength Dye per, 10-g. repiece moved
5:3
.. ..
.. .. .. .. ..
WATER
strength Washed
Dye
per 10-g. piece
removed
6.0 grsma/liter strength Washed Dye
per 10-g. piece
removed
MQ.
%
MV.
7%
0.2 0.23 0.28 0.39 0.27 0.48 1.02 1.43 0.69 1.27 6.25 6.05
99.2 99.6 98.4 99.3 99.2 99.1 9S.l 98.8 94.8 96.3 93.7 96.4
2.9 4.05 2.35 3.62 12.75 18.5 18.5 29.5 8.05 17.85 61.0 90.0
89.1 93.5 86.4 93.1 61.1 63.9 65.0 74.8 39.5 47.9 39.0 47.0
the case of dye 11 which contains the substantive J-acid and -COKHgroups. This dye is found to be the least sensitive to salt of the dyes studied, and it is also the least substantive towards cotton; i. e., it shows the poorest wash-fastness. The dyeing process is proved t o follow certain general principles. The point of view of the authors is that limiting particle size and salt sensitivity are two important physicochemical characteristics in substantive dyeing. Substances which are readily salted out are not necessarily substantive to cotton. I n a process as complicated as that of substantive dyeing, it is not possible for any one factor to be used as a criterion of substantivity for the whole range of chemical compounds. However, it is apparent that if attention is restricted to known substantive dyes, the degree of salt sensitivity is closely related to the degree of substantivity.
January, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
This study has purposely been confined to commercial dyes and practical dyeing operations. The dyestuffs examined, and all commercial dyestuffs of these types, are chemically impure. The impurities consist of organic compounds resulting from the complexity of the cheniical reactions in the manufacture, and of inorganic salts formed in processing and added for adjustment of strength. It is recognized that the presence of these impurities in dyestuffs interferes with the study of certain properties of dyestuffs, such as electrical conductivity, transport number, and osmotic pressure. An experimental study of four chemically pure dyestuffs (11) has shown that the relat'ions between dyeing characteristics and the particle size and salt sensitivity hold equally well for the impure and for the chemically pure dyestuffs. The dyeing process is one in which only technical products are used; only chemically impure dyestuffs can be produced commercially. It is essential t'hat studies on the theory of dyeing which are developed with pure dyes should be correlated, when possible, with the application of impure dyes. The method of attack outlined in this paper may be used to advantage in solving many problems in the application of dyes. I t s value lies in its use for qualitative interpretation of the results of a dyeing operation in terms of the mechanism of the process. The concept of salt sensitivity-i. e., the tendency of dyes t o agglomerate in the presence of lorn concentrations of neutral salts-is useful as a description of the application properties of dyes. A few measurements of the salt sensitivity will show the probable affinity of the dye for cellulose as well as the probable temperature range required to obtain maximum dyeing strength with level dyeing properties. It' is possible to forecast the ease with which various dyes can be applied in combination. It is possible to predict the extent to n-liich color may be removed in any operations following dyeing and to suggest the conditions required for the prevention of bleeding of dyed fabrics. The method can be used to demonst,rate an outstanding difference between dyes most suitable for viscose and for cotton. It has been observed that dyes of low salt sensitivity produce level dyeings on rayon, while dyes of high salt sensitivity are difficult t o apply. The5e differences are undoubtedly related to differences in the p x e st'ructure of these chemically identical
fibers. These examples give an idea of the scope of the method of attack and its application. It is not suggested that this method will supplant any of the many procedures now employed for testing dyes but rather t h a t a n auxiliary tool has been found for assisting in the solution of the intricate problems of dyestuffs application. ACKXOWLEDGMENT The check measurements on the accuracy of the microdiffusion method, obtained by means of the ultracentrifuge, were made through the courtesy of J. B. Xchols of the du Pont Experimental Station, Wilmington, Del. The diffraction pattern obtained by x-ray analysiq of the cotton material used in the dyeing experiments was obtained through the courtesy of -A. W.Kenney of the same station. LITERATURE CITED Appel, 1%'. D., "Qualitative Relation between Spectral Reflection of Textile Dyeings and Amount of Dye Used," Textile Research Council, Boston, 1929. Appel, TT'. D., Smith, W.C., and Christison, H., Bm. Dyestuf Rmti.. 17. 679 11928). Einstein; .4., Ann. ' Ph&k, 17,549 (1905). Furth, R., Kolioid-Z., 41,300 (1927). Furth, R., and Ullrnann, E., Ibid., 41,304 (1927). Garvie, W. H., GriEths, L. H., and Seale, S. M., Trans. Faraday SOC., 30,271 (1934). Griffiths, L. H., and Xeale, S.M., Ibid., 30,395 (1931). Haller, R., Kolioid-Z., 20, 127 (1917). Hanson, J., and Neale, S. &I., Trans. Faraday Soc., 30, 386 (1934). Hartley, G. S., and Rohinson, C., Proc. Rou. SOC.(London), 134.1,20 (1931). Lenher, S.,and Smith, J. E., manuscripts submitted to J. Am. Chem. SOC. Neale, S. M.,and Stringfellow, W.A , Trans. Faradau Soc.,. 29, . 1167 (1933). Ostwald, IT.,I b i d . , 29,347 (1933). Robinson, C., and Mills, H. -1.T., Proc. Roy. SOC.(London), 131-4,576, 596 (1931). Rose, R. E., Am. D y e s t i b i f R e p t r . , 21,5 1 (1932). Schliffer, A . , Z . angetu. C'hem., 46, 618 (1933). Schramek, W., and GGtte, E., Kolloid-Beihefte, 34,318 (1932). Urquhard, -1.R . , and Williams, X.hl., Shirley Inst. Mem., 3, 197 (1924).
Weltsien, W., and Schultze, K., Kolloid-Z., 62,46 (1933). RECEIVED October 11, 1934
Courtesy, Westinghozkse Electric
MICART.4
JIGGER ROLLSI N
25
THE
TEXTILEINDUSTRY
