December 1953
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
cotton linters treated with 5 to 25% sodium hydroxide solutions a t 0’ to 50’ C. I n all cases water vapor sorptions were determined from the bone-dry state at 95% relative humidity and the sulfuric acid sorptions were obtained from the water-swollen state at the 15-minute point from 0.5% sulfuric acid in acetic acid a t 20’ C. Data from these measurements are shown in Table 11. The striking similarity of these models demonstrates that either sulfuric acid sorption or water vapor sorption is a satisfactory means of comparative measurement of the degree of mercerization attained by such alkali treatment. If water vapor sorption is accepted as a measurement correlating with the increasing accessibility of cellulose as i t undergoes more severe alkali treatment, it follows from these results that there is a parallel relationship when such alkali-treated celluloses are characterized by the sulfuric acid sorbed from acetic acid solution. A close study of the models reveals that the proportionate increase in sorption levels caused by full mercerization is slightly greater for sulfuric acid than for water vapor. This is in accord with the data plotted in Figure 11, where i t was shown that an intercept on the water vapor sorption axis is obtained when sulfuric acid sorption from weak solutions is plotted against the water vapor sorption of linters or sulfite-base celluloses.
2779
ACKNOWLEDGMENT
Credit is due W. E. Wahtera for all vapor sorption measurements quoted and for construction of models in Figure 12. LITERATURE CITED
Clement, L., and RiviBre, C., BdZ.
SOC.
chim. France, 4, 869
(1 937).
Genung, L. B., and Mallatt, R. C.. IND.ENG.CHEM.,AN+L. CHEM.,13, 369 (1941).
Glasstone, S., “Textbook of Physical Chemistry,” pp. 10045. New York. 1946. Ibid., p. 1199.
Hermans, P. H., J.MalcromoZ. Chem., 6, 27 (1951). Malm, C. J., Barkey, K. T., May, D. C., and Lefferts, E. B., I N D . ENG.CHEM.,44, 2904 (1952). Malm, C. J., and Tanghe, L. J., IND.ENG.CHEM.,ANAL.ED.. 14, 940 (1942).
Malm, C. J., Tanghe, L. J., and Laird, B. C., IND.ENG.CHEM., 38, 77 (1946).
Richter, G. A , , Herdle, L. E., and Wahtera, W. E., Ibzd.,
44,
2883 (1952).
Wise, L. E., Murphy, hl.,and D’Addieco, A. A.. Paper Trade J . , 122, No. 2, 35 (1946). RECEIVED for review M a y 9, 1953.
ACCEPTEDAugust 27, 1953.
Comparative Cleaning of Diphase and Emulsion Systems MEASURED BY RADIOACTIVE TRACERS LLOYD OSIPOW, GONZALO SEGURA, JR., CORNELIA T. SNELL, AND FOSTER DEE SNELL Foster D . Snell, Inc., 29 West Fifteenth S t . , New York 11, N . Y .
E”
’ IULSION and diphase cleaners of identical composition
*I
were prepared. They were used to clean steel surfaces having three tagged versions of the same soil. These contained in successive lots tagged barium carbonate, tagged palmitic acid, and carbon-14 carbon black. A fourth soil contained mixed fission products free from alpha emitters. By comparing weight loss and activity loss, it was shown that both cleaners preferentially remove palmitic acid and barium carbonate. I n no case does the emulsion cleaner in 5 minutes remove as much soil as the diphase cleaner in 1 minute. This is attributed to the monomolecular film of surfactant on the emulsion droplets, which must desorb before the emulsified solvent droplets will spread on a nonpolar soil surface. Previous studies of the relative effectiveness of diphase cleaners and emulsion cleaners showed that the nature of the surface plays an important role in preferential wetting and ultimate cleaning (6). Diphase cleaners proved to be more effective than stable emulsions for cleaning metals, not only in their ability to detach soil from the metal surface, but also to suspend that soil and prevent its redeposition ( 7 ) . The results were only roughly quantitative, based on visual examination of the metal panels after cleaning. Radioactive tracers permit taking two further steps. The amount of soil retained is now measurable. The selective removal of individual tagged components of a complex soil mixture is then quantitatively evaluated.
MATERIALS AND METHODS
As the metal base, SAE 1010 steel panels were cut into squares about 20 mm. on each side. After code letters had been stamped in the corner of each piece, they were cleaned with steel wool and trichloroethylene, then rinsed with acetone. After drying, they were weighed and one side of each panel was coated with radioactive soil, using a small brush. The marked corners were not soiled and the panels were handled with tweezers a t these corners. After soiling, the panels Were weighed, and the activity of the soiled panels was determined with a Geiger-Muller counter. The counting device was a Decade Scaler, model RC. The detection device was a Geiger-Muller tube, model No. GMlWAA.4, with a 2.8-cm. diameter end-window composed of 1.8 mg. per sq. cm. of mica. The tube was placed base u p in a model 5-3 shield (13/&1ch lead wall). Each sample panel to be read was placed in a shallow cup of such geometric arrangement as t o orient all panels in exactly the same position laterally with respect to the tube. Approximately 7 mg. of soil were applied to each steel square to give from 3000 to 30,000 counts per minute, depending on the (‘hot” material used in the soil. The soil used was composed of the following in per cent by weight: white petrolatum 35, Kaydol mineral oil 50, palmitic acid (Neo-fat 1-56) 5, barium carbonate 5, and Excelsior carbon black 5. I n order to study the effectiveness of the cleaner in removing individual components of the soil, three of these were
2180
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE
Radioactive Contaminant Fission products Palmitic acid Barium carbonate Carbon-14 Average Standard deviat.ion of the mean Fission products Palmitic acid Barium carbonate Carbon-14 Average Standard deviation of the mean
I. SOIL REMOVAL USING DIPHASE CLEhSER
1-Minute Wash Activity Weight loss of loss of radioactive total Standard contami- Standard soil, 9% deviation nant, % deviation 88.9 89.1 93.5 96.1
2.2 2.2 0.6 1.7
95.0 99.6 96.8 94.9
91.9
...
96.6
..
1.0
..
13.2 19.7
2.2 0.1 0.5 5.4 . I .
0.7
Weight loss of total soil, %
Diphase Cleaner 89.1 1.6 90.6 2.4 94.4 0.5 98.4 1.9
96.6 99.3 97.2 97.5
...
93.1
..
1.2 Emulsion Cleaner 61.7 2.8 52.9 1.9 59,o 6.1 45.7 5,6
15.5 35.8
20.4
4.7 1.2 4.7 6.2
10.3
9.5
2.8 6.0 2.3 3.5
18.1
...
17.8
...
54.8
...
..
1.6
..
3 3
..
1.7
used in radioactive form. Both barium carbonate and fatty acids have been made containing carbon-14 ( 3 ) . In this work various portions of the above soil were prepared: one contained iadioactive palmitic acid, C H ~ ( C H ~ ) I ~ C ~ ~obtained O O H , from the Tracerlab, in place of ordinary palmitic acid; a second contained radioactive barium carbonate, BaC1403, obtained from the Oak Ridge n’ational Laboratory, in place of ordinary barium carbonate; a third contained radioactive carbon black, carbon14, prepared in our own laboratory by a modification of a published method (I), in place of ordinary carbon black; and a fourth contained 3% of a fission-products solution supplied by the Oak Ridge Sational Laboratory. The fission products consisted of a mixture of many unidentified radioactive salts in minute concentrations, but including no alpha emitters. T r o cleaners of identical composition were employed for washing the soiled metal samples. By using different methods of preparation (d), a diphase liquid resulted in one case, a stable emulsion in the other. The concentrated base had the following composition:
EXULSION CLE.4XER
3-Alinute Wash Activity loss of radioactive Standard contami- Standard deviation nant, deviation
19.0
Kerosine Pine oil (Yarmor 302) Oleic acid (Wecoline 00) Triethanolamine Butyl Cellosolve
ASD
Vol. 45, No, 12
Weight loss of total soil, %
1.1 0.0 0.4 0.4
94.9 90.0 98.4 97.7
97.7
...
95.3
..
0.3
..
58.0 71.3 34.3 18.9
5.G 3.0 4.5
46.6 .,
6.0
5-Minute Wash Activity loss of radioactive Standard contami- Standard1 deviation nant, % deviation, 0.4
...
98.4 99.6 96.6 97.5 98.0
1.2
*.
0.3
4.0
84.9 77.9 88.5 51.6
2.1 5.3 3.1 1 6
...
75.7
...
65.5 73.6 85.7 21.4 61.5
4.1
..
1.0 4.1 1.0 0.9
0.1
O C 0.9
._
9,O
12.7 2.0
8,Y I
.
7 4
ployed, that all measurements made i n the cleaning experiments fell on the linear portion of a plot of counts per minute veisus milligrams of soil. I t was furthei established that wiping the unsoiled side of the panel after washing was sufficient to elinrinateanyerror due to the deposition of radioactive material on the unsoiled side of the panel. RESULTS
Experimental results presented in Table I represent the pcu cent of total soil removal determined by weight difference itlid the per cent removal of the individual radioactive m a t e i d s initially present in the soil. Each value is an average of thiee separate tests.
Parts by Keight 67 0 22 5 5 4 3.6
I5
The diphase cleaner consisted of 1.6 nil. of the above added t o 48.4 ml. of deionized water. The emulsion cleaner was prepared by first combining all the above ingredients, except the triethanolamine. The latter was added to 50 parts of deionized water. The two portions were then combined to form an emulsion. The emulsion cleaner consisted of 2.4 ml. of this emulsion dispersed in deionized water to give 50 ml. of emulsion cleaner. The soiled panels were cleaned by placing them in tubes containing 50 ml. of emulsion or diphase cleaner. After stoppering, the tubes were inverted end over end a t the rate of 15 revolutions per minute. Cleaning times were 1 minute, 3 minutes, and 5 minutes. I n a single experiment, the w-ashing time was extended to 11 minutes. -4fter cleaning, the stoppers were removed and the liquid was poured off through plastic screening. The reverse side of each panel was then wiped clean, and the panels were allowed t o dry. They were then weighed and the hot material remaining was determined in a Geiger-Muller counter. The difference in weight and in counts before and after cleaning gave, respectively, a measure of the efficiency of total soil removal and the efficiency of removal of a tagged component. It was established that the thickness of the soil film was below the coincidence level for each of the radioactive materials em-
Rate of Soil Removal Using Diphase and Emulsion Cleaner
Figure P.
- = Diphase cleaner (A) A
= Emulsion cleaner (B) X = Emulsion cleaner, separate run ( C )
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1953
sr
Figure 1 portrays graphically the difference in the rate of soil removal using a diphase cleaner and a n emulsion cleaner. Curves designated diphase cleaner and emulsion cleaner were plotted from the per cent weight-loss averages reported in Table I. Curve z is a separate run in which another batch of the emulsion cleaner was used; three determinations were made for each point shown. Since these systems are not in thermodynamic equilibrium, it is not surprising that different preparations gave different results. Referring to Table I it can be seen that the diphase cleaner removed about 90% of the total soil in 1 minute, while the emulsion cleaner removed only about 20% of the soil. After 5 minutes, about 95% of the soil was removed by the diphase system, while 76% was removed by the emulsion cleaner. By comparing the weight loss of total soil with the activity loss of a particular radioactive contaminant, it is seen that the diphase cleaner selectively removed fission products and palmitic acid. The emulsion cleaner also removed the palmitic acid preferentially. However, both carbon and barium carbonate were preferentialfy retained by the soiled panel when washed with the emulsion cleaner. They were removed without preference by the diphase cleaner.
2781
no longer sufficient to maintain association of the adsorbed soap anions and these proceed to desorb from the surfaces. Thus it can be seen that desorption of soap precedes collision and spreading of an emulsion droplet on a soil surface. The energy of activation required for contact of the two surfaces may be somewhat less than the energy of activation required for desorption of
DISCUSSION
The rate of cleaning is very much greater with a diphase cleaner than with an emulsion cleaner. The free energy changes accompanying soil removal are not very different for the two systems. However, an energy barrier, due to the presence of a “sorbed” layer of soap on the emulsion droplets and the soil, is responsible for the slow cleaning rate with the emulsion system. When a liquid spreads on a surface, the decrease in free energy is equal numerically to the sum of the products of the interfacial tension and the area of the surfaces that disappear on spreading of the droplet, less the sum of the products of surface area and interfacial tension for the new surfaces that form, or -AF
= I: yiA1
- ZrzAz
= surfaces that vanish
= surfaces that form = interfacial tension A = surface area - AF = decrease in free energy
*
With both emulsified and unemulsified solvent droplets on a nonpolar soil surface, no new surface forms, because the solvent and the soil are miscible. The soil-water interface disappears in both cases. Thus, the free energy change per unit area is the same with both systems. The energy barrier associated with the soil-removal process can be indicated by examination of the interplay of forces which occur when an emulsion droplet is brought into contact with a surface. Referring to Figure 2, it is first noted that both the emulsion droplet and the soil are initially covered with a film of soap, orientated with the hydrophilic portion of the soap molecule directed toward the water. For simplicity, only the soap anions and associated gegenions, but not the ionic atmosphere, are shown. The repulsive force opposing collision of the droplet and the soil is proportional to the effective potential on the two surfaces ( 5 ) . As the emulsion droplet and the soil surface are brought closer, the interaction of charges results in the removal of associated gegenions from the region between the surfaces, further increasing the coulombic repulsion between the surfaces. This is an inevitable consequence of the fact that the potential in the immediate neighborhood of the gegenions is of the same sign as that of the gegenions. When the two gegenion regions are brought into contact, attractive forces are not sufficient to keep the gegenions between the surfaces (4). On closer approach of the emulsion droplet to the soil surface, coulombic forces increase so rapidly that van der Waals forces are
Figure 2. Interaction of Emulsion Droplet and Surface soap, partly because the electrostatic forces tend to favor desorption. The effect of London-van der Waals forces of attraction on the desorption process has not been evaluated. With the diphase system, the very large mass of the solvent drop SO overshadows the surface forces that these have virtually no effect in discouragiqg contact between these solvent drops and the soil. Thus, no activation energy is involved in the process of collision and spreading. The diphase cleaner removed fission products and palmitic acid preferentially. The rapid removal of the former material can be ascribed to its water solubility and the prolonged period of contact of the soil with the water phase, due t o the relatively large volume of this water phase. The ready removal of palmitic acid is presumably due t o presence of alkali in the cleaner that reacts with the palmitic acid to form soluble soap. The barium carbonate and carbon are readily wetted by the solvent phase and they tend to sorb a t the solvent-water interface. Hence, their removal is not retarded. The palmitic acid is also preferentially removed by the emulsion cleaner. Here too, alkalinity is presumably the factor favoring removal. Selective retention of carbon in the soil can be ascribed to failure of the emulsified solvent to wet the carbon. Desorption of soap from the emulsified solvent must take place before the carbon is wetted, Again, the potential energy barrier is high, zarium carbonate, unlike carbon, is also wetted by water and can be removed from the soil by the water phase. However, before this can take place, adhering hydrophobic soil must be completely removed from the barium carbonate particles. Consequently, it is to be expected that barium carbonate would be preferentially.retained by the soil but t o a lesser extent than carbon. CONCLUSIONS
Diphase systems clean greasy soil from metal much more rapidly than do emulsion systems. Free surface energy relationships and energies of activation are adequate to explain not only
2782
INDUSTRIAL AND ENGINEERING CHEMISTRY
the difference in the rate of removal of the bulk soil, out also preferential removal of individual components of the soil, where chemical reaction resulting in a water-soluble product is not a factor. ACKNOW LEDGMEh T
The investigation described herein R as supported by Solvent01 Chemical Products Co. of Detroit, Mich.
Vol. 45, No. 12
( 3 ) Hensley, J. W., Skinner, H. -4.,and Sutter, H. R., Am. SOC. Testing Materials, S p e c i d Tech. Pub. N o . 115, 18-32 (1952). (4)Osipow, Lloyd, and Snell, Foster Dee, paper presented at XIIIth International Congress of Pure and Applied Chemistry, Stockholm, Sweden, July 29 to -4ug. 3 , 1953. ( 5 ) Overbeek, J. Th. G., “Colloid Science,” Vol. 1, ed. by H. R.
Kruyt, Amsterdam, The Setherlands, Elsevier Publishing Co.,
LlTERATURE CITED
1952. (6) Reich, Irving, and Snell, Foster Dee, IND. ENG.CHEM.,40, 1233-7 (1948). (7) Zhid., pp. 2333-7.
(1) Campbell, A. M., and Brown, E. ii., J . Am. Chem. Soc., 60, 3055-60 (1938). (2) Campbell, C. A., U. S. Patent 2,399,205 (1940); 2,583,165 (1952).
RECEIVEDfor review May 25, 1953. ACCEPTED August 17, 1933. Presented before t h e Division of Colloid Chemistry a t the 124th Meeting, AMERICAXCHEMICALSOCIETY, Chicago, Ill., 1953.
Sequestration by Sugar Acids C. L. MEHLTRETTER, B. H. ALEXANDER, -4ND C. E. RIST Northern Regional Research Laboratory, Bureau of Agricultural a n d Industrial Chemistry, U . S . D e p a r t m e n t of Agriculture, Peoria, Ill.
T
HE recent interest in organic sequestering agents ( 2 , 13) has stimulated the investigation of many substances for utilization in this rapidly expanding field. Sugar acids are a class of compounds that show promise for this purpose. Included in this category are the fermentation acids, lactic, citric, gluconic, and 2-ketogluconic as well as the aldonic and dibasic acids produced from sugars by chemical oxidation. The ability of sugar acids, in general, to form water-soluble complexes with metal ions stems from the capacity of their carboxyl and hydroxyl groups to bind cations in ring form by means of coordinate and covalent bonds. A knowledge of the specific conditions under which such complexing is most effective should lead to new outlets for these products. I n this investigation data were obtained on the sequestering ability of a number of readily accessible sugar acids toward calcium, ferric, and cupric ions in acid to strongly alkaline solutions. The effect of such variables as“concentration of sequestrant and of alkali on sequestering power also was observed. Methods (4,14, 16) are known for determining the degree of chelation of calcium by organic sequestrants but those for iron and copper have not been made generally available. Procedures, therefore, were devised for evaluating the sequestering action of sugar acids toward the latter metal ions under acid, neutral, and alkaline conditions. METHODS FWR DETERMINING SEQUESTERING CAPACITY O F SUGAR ACIDS
CALCIUM.The sequestering power of the sugar acids toward calcium ions was measured by Zussman’s method (16). Stock solutions containing 2% (2 grams per 100 ml. of solution) of the sodium or potassium-sodium salts of the sugar acids were prepared, For studies on sequestration in acid solution, 10 ml. of the stock solution (0.20 gram of sequestrant) were diluted to 20 ml. with distilled water in a 50-ml. beaker. Two milliliters of 2% sodium oxalate solution were then added, and the acidity was adjusted to pH 4 with acetic acid. The solution was mechanically stirred, and standard 1% calcium acetate solution introduced dropwise from a buret until the first appearance of permanent turbidity. If considerable precipitation occurred on standing for 24 hours, further titrations were made with a lesser amount of standard solution until only a slight precipitate was observed after 24 hours. Although the slight permanent precipitate obtained immediately was used by Zussman for determining the calcium-
sequestering ability of polyamine carboxylic acid salt, he realized that further precipitation on standing introduced an element of uncertwinty in the results. The sequestering values of the sugar acids calculated on the basis of immediate precipitation of calcium oxalate are considerably higher in most cases than those determined from the slight permanent precipitate obtained in 24 hours. The authors considered the latter to be the more reliable values. For similar studies in alkaline solutions, 10 ml. of 2% stock solution of sequestrant were mixed nith 10 ml. of sodium hydroxide solution containing twice the coilcentration of alkali desired before introduction of the sodium oxalate indicator and standard calcium acetate. IRON.The sequestering pon-er of the sugar acids toward ferric ions in acid and neutral solution was carried out as follows: Ten milliliters of 2% stock solution of the sequestrant were added to 180 ml. of distilled water containing 5 ml. of 2% potassiuni ferrocyanide solution. The resulting mixture was adjusted to p H 4 or 7 with dilute hydrochloric acid. A standard solution containing 90.0 grams of ferric sulfate per liter was then introduced dropwise from a buret with continuous stirring of the sequestrant solution until a permanent precipitate due to the formation of insoluble ferric ferrocyanide appeared. Potassium ferrocyanide reagent is sensitive to small amounts of ferric ion over the p H range 4 to 7 . Control experiments carried out without the addition of sequestrant utilized 0.3 ml. of ferric sulfate solution to obtain a permanent precipitate of ferric ferrocyanide. I n alkaline solution, ferric ions precipitated as the more insoluble ferric hydroxide and ferrocyanide reagent was not required. HOT< ever, the mode of addition of ferric sulfate was important for satisfactory evaluation of sequestration. The direct introduction of standard ferric sulfate solution to alkaline solutions of the sequestrants produced an immediate precipitate of ferric hydroxide which was solubilized t o o slowly for test purposes. If, however, the alkali solution was added to a mixture of the sequestrant solution and an amount of ferric sulfate solution below the chelation limit of the sequestrant, which was determined by trial, the ferric hydroxide precipitate initially formed was rapidly solubilized. By successively increasing the amount of ferric sulfate in separate trials, the quantity required to obtain a permanent slight precipitate of ferric hydroxide was determined. Specifically, 10 ml. of 2% potassium sodium saccharate were mixed with 20 ml. of standard ferric sulfate solution. To this solution were
