(8) Hafford, B. C . , Leonard, F., and Cummins, R. W.,Ind. Eng. Chem., Anal. Ed., 18, 411 (1946). (9) Harris, J. C., ,477~.Dyestuf Reptr., 37, 266 (1945). (10) Harris, J. C., Oil & Soap, 23, 101 (1946). (11) Harris, J. C., and Brown, E. L., Ibid., 22, 3 (1945). (12) Xersberger, A . B.. and Neidig, C. P., Chem. Eng. Xews, 27,
1646 (1949). (13) Nerrill. R. C , and Getty, E., J . Am. Oil Chemists Soc., 26, 5
(1949). (14) Partridge, E. P., Hicks, V., and Smith, G. U7., J . Am. C h n . Soc.. 63, 454 (1941).
(15) (16) (17) (18) (19) (20)
Quimby, 0. T., Chem. Revs., 40, 141 (1947). Raistrick, B., Sci. J . Roy. Coll. Sci.,19, 9 (1949). Reich, I., and Snell, F. D . , IND.ENG.CHCX.,41, 2797 (1949). Robinson, E. A , , Soup Sanit. Chemicals, 28, 34 (1962). Strain, B., U. S.Patent 2,486,922 (Nov. 1. 1949). Stupel, H., Fette 21. Seifen, 56, 209 (1954). (21) Thilo, E., and Seemann, H., 2. anorg. Z L . alZgenz. Chem., 267, 65 (1951). ( 2 2 ) Topley, B., Quart. Revs. (London). 3 , 345 (1949). (23) Katsel, Die Chonie, 55, 356 (1942). RECZIVED for review 3 I a r c h 2 5 , 1954.
J4Y C . HARRIS, 31. R. SULLIVAN,
AVD
ACCEPTEDJuly 13, iQ54.
L. E. WEEKS
Chemical Research D e p a r t m e n t , Monsanto Chemical Co., D a y t o n 7 . Qhio
T h e relationship between whiteness (or reflectance) and retained soil is an important one. Rlost soils for fabrics are comprised of graphite or carbon black, for which no quantitative relationship with reflectance has been established. The present paper reports a n investigation of this relationship, utilizing a quantitative turbidimetric estimation of graphite from which the cellulosic fabric has been removed. This technique is not suggested as a substitute for reflectance wash test measurements but was designed to provide the yuantitative relationship already- mentioned. HE evaluation of surface active agents has been attempted from perhaps as many viewpoints as there are individual properties of the mateiials. Certain chemical, physscochemical, and physical properties are readily measured, but some of the methods have not been universally accepted. One property of the surface active materials that accounts for perhaps the largest usage is cleansing ability, but evaluation of this property remains perhaps less 1% ell standardized than many others. There are many laboratory machines (9)designed for control of soil removal in detergency tests, but the factor of measurement of washed soiled cloths is still under scrutiny. Though reflectance methods for estimation of soil removal are recognized as pobsessing shortcomings, these are perhaps most widely used, probablv because cleaning is recognized as effective nhen an agreeable degiee of TT hiteness has been obtained visually. Removal of soil from a fabric suiface has been nieasuied by Bacon and Smith ( 1 ) as a function of the mechanical work involved. The six general variables listed by them are detel-gent, mechanical force, time, temperature, ease of soil removal, and soil suspension and iedeposition. They applied the Kubellia and AIunk ( 5 ) equation to this problem
where
K = coefficient of reflectivity S = coefficient oi light scattering R = observed reflectivity for monxhrozatic light and calculated the per cent iemoval of black from their soiled fabric through ita use
R I S for soiled fabric K l S for soiled fabric
- K / S for scoured fabric - K / S for unsoiled fabric
loo=
per cent black removed
(2)
Their equation for detergency, which a t that time was still under investigation, was written as
where S K
per cent soil removal a constant ?I = constant slope (' = concentration F = force applied T = time = =
The equation applieh to the linear portions of their logarithmic detergency curves, but these linear portions fall below ordinary use-concentration conditions for most detergents. Since reflectance measurements as a calculation of brightness regained are used rather generally by industry, Reich, Snell, and Osipow (6) investigated the Kubelka-AIunk equation aB applied to soiled fabrics. They concluded that reflectance of soiled cloth can be correlated to the amount of soil present by the equation log
r(l - R)2
i2R
-$"'I
(1 - -___
= n log
G
+ constant
where
I? = reflectance of soiled cloth R' = reflectance of clean cloth G = amount of soil present However, they indicate that n (the slope) during washing is frequently 1 (and the equation becomes the Kubellca-Nunk) but that during artificial soiling (and agglomeration of soil) it has a value between 0.65 to 0.7. Hart and Conipton (4)demonstrated that the Kubelka-Munk equation frequently fails when applied to reflectance systems because of particle distribution, orientation, and specific absorbence. Provided that the specific absorbenee of a pigment, for the fabric system is essentially constant, Equation 2, 13ac0~ and Smiths', can be used, but if the specific absorbence variee, this must be determined. Hart and Cornpton calculate change in specific absorbence
(K/S)T = (K/S)WP f (K/S)RS f ( K / S ) B 1942
(4)
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
(5)
Vol. 46, No. 9
-Synthetic
Detergents-
where
( K / S ) T = total K / S value after washing ( K / S ) W F= K / S value for soiled and washed swatches ( K / S ) R S = K / S value for redeposit swatches ( K / S ) B = K / S value for bath liquor then, Equotlon of the h e -
Loa,, Y.-00345X+19995
in which ( K / S ) s p = K / S valuefor the original soiled swatch. Factors of fabric and yarn structure, nonuniformity of soil distribution and orientation are obviated by using a chopped fabric technique. Utermohlen and Wallace ( 7 ) investigated synthetic soils as applied to fabrics by utilizing a soiling agent capable of being determined chemically. This work indicated that for an iron oxide pigment there was good agreement, a t a medium soiling range, between reflectance and iron analyses. Reich, Snell, and Osipow ( 6 ) , using Utermohlen and Wallace's data showed, however, that the linear relation of K / S against soil content held only for low values of soil content. With higher soil content values, ZC/S becomes less than predicted by linear extrapolation, indicating that reflectance falls off lesp rapidly than calculated. The idea of analytical determination for comparison with reflectance values is an interesting one, and this work is concerned with a comparison of reflectance readinge with analyses of graphite in regularly soiled fabric samples.
\ ~\
\
\
\ \
'
\
\
Graphite In Microprami/milllti(r~
10
EXPERIMENTAL
The idea was conceived that by selection of the proper conditions, the cellulose of the fabric could be dissolved from the graphite deposition on it, and then determine the residual, unchanged graphite by a turbidimetric method. Digestion of Fabric. A 4 X 6 inch piece of soiled fabric was placed in an aluminum weighing dish, oven-dried for 3 hours a t 105" C. in a forced-draft oven, cooled in a desiccator, and weighed to the nearest milligram. -4 blank sample of a 4 X 6 inch piece of white Indian Head fabric was always carried through the analytical process with the soiled samples. The weighed piece of fabric mas then placed in a 100-ml. flat bottomed digestion flask with a 24/40 tapered neck and 50 ml. of concentrated nitric acid, 3 ml. of concentrated sulfuric acid, and several glass beads were added. A water cooled condenser was attached and the contents of the flask allowed to come to a boil on the hot plate. As digestion commenced, the flask was removed from the hot plate until evolution of fumes subsided, then replaced, and allowed to digest a t mild boiling temperature until the blank sample (no graphite present) was clear (18 hours). The flask was then removed from the hot plate and cooled to room temperature. Graphite Standards. A sample of graphite was isolated from Oildag (Acheson Colloids Corp.) by multiple hexane extraction to remove the oil base. This was accomplished by diluting 10 grams of Oildag with 100 ml. of hexane, centrifuging for 30 minutes a t 2000 r.p.m. and decanting the oil solution from the graphite sediment. This procedure was repeated three times; the final mash showed no evidence of further oil removal. The graphite was then oven-dried and stored in a desiccator. A sample of graphite was also obtained by combining a number of digested nitric acid solutions to which Oildag had been added. Separation of the graphite was accomplished by centrifuging, decanting, and washing with distilled water until acid-free. Complete oxidation of the graphite occurred when air-cooled condensers were used and the nitric acid was allowed to concentrate during the digestion by evaporation of water. If watercooled condensers were used, however, the volume remained constant, and no oxidation of graphite occurred. Oxidation of
September 1954
0
4
Figurc 1.
8
12
16
20
24
Standard Curve Data for Graphite us. Transini ttance
the graphite was found to be a function of concentration of acid, not digestion time. Digestion times of 3 to 24 hours at constant volume gave dispersions having the same optical density. It was concluded that no oxidation of the graphite occurred during the digestion as outlined in this report, since various size aliquots from the same Oildag solution, with suitable dilutions after digestion, gave transmittance values that fell in random manner around the average value. Also, the partial oxidation of graphite would probably lead to the formation of graphitic oxide However, the x-ray diffraction pattern of the digested graphite was identical to the pattern of the graphite isolated from Oildag by hexane extraction. Graphite Suspension. A uniform dispersion of the graphite from digestion of the Oildag on soiled fabric was then obtained by ultrasonic irradiation (Brush Development Co., generator model BU-204, transducer model BU-305A-400) of the suspension in the digestion flask. The suspension was subjected to 400 kc. (output voltage, 50 v.) radiation for 15 minutes; 50 ml. of 0.5% aqueous solution of bIethocel 1500 was then added, after Rhich the resulting suspension of graphite was further irradiated for 5 minutes. The suspension (nom stable for 24 hours) was then transferred quantitatively to a 100-ml. volumetric flask and diluted to the mark a t 25.0' C. The digested graphite solutions showed decreasing per cent transmittance as irradiation time increased to about 15 minutes; after this no further decrease in transmittance n-as noted. The minimum per cent transmittance (or maximum dispersion) was not stable, however, and following iiradiation i t increased several per cent after standing 5 to 10 minutes and therefore stabilization of the dispersion with methyl cellulose was necessary. Standard Graphite Curves. The percentage of transmittance a t 525 p wave length, of various dilutions of the standards as prepared, was obtained by use of the Coleman Universal spectrophotometer (Model 14) equipped with 13 X 13 X 100 mm. square cells. The blank solution containing all ingredients except
INDUSTRIAL AND ENGINEERING CHEMISTRY
1943
the graphit,e, and a t the same dilution R S the sample, was used as the 100% t'ransniittance st'andard. The graphite dispersions were diluted so that the transmittance fell within the 80 to 20% working transmittance range of the standard curve.
TABLE 11. STATISTICAL E\-.ii,c.inox
n
1, S o . of samples Indi\ idual values.
pg
/mi
i n . 30
11.70 11.35 10.90 11 90 11.90
-.
K t . ) 111. o n
Origin of Graphite Predigested
Dilution,
Transmittanrc
iL#.
'J.88 I .\IO
5.43 3 95 1.98 31 76 25 41 19.06
Predigested
12.70 8.35 50.74 30.41. 20 30 19.15 3.07 in.2s 8.18 c, 14 -IOD 2.05
Piedigcsted
Hexane washed
Hexane naslied
31.67 25,28 18.94 12.63 6 14
Hexane washed
49.59 29.75 19.84 9.92 4.96
%
41.3 40 , 7 3 . 0 70.6 83.8
8.8 13.7 22.5 36.7 00.4 8: 7 19.z 43
