Accessible Cellulose as Measured by Sorption of Sulfuric Acid G. A. RICHTER, L. E. HERDLE, AND 1. L. GAGE Wood Cellulose Development Division, Eustmun Kodak Co., Rochester 4 , N . Y.
?
T HAS long been known that sulfuric acid is extracted from
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its fatty acid solution by cellulose and t h a t the quantity removed depends in p a r t on the nature of the cellulose used. It is now recognized t h a t the sulfuric acid in such a system exists in at least three states, which can be distinguished by the nature of their association with the cellulose and the ease with which they can be removed. Sulfuric acid which has actually esterified with the cellulose is termed “combined” sulfuric acid (8),t h a t which is associated with the cellulose but is easily removed by washing is termed “sorbed” sulfuric acid (1,6), and t h a t which is in solution in the fatty acid is simply termed “dissolved” or “free” sulfuric acid. The work reported here was prompted by the ques-
$ OO1
MD I
2
AD
LD
3
0 4
5
Time (minutes of opplicotton of H2SQ solution)
Figure 1. Influence of Preswelling A . Acetate grade sulfite wood pulp L. Acetate grade cotton linters M . Fully mercerized cellulose of softwood origin
solution through a sheet of cellulose usually swollen previously by flooding with u,ater and by displacement of the water with acetic acid. This allows an equilibrium sorption level of sulfuric acid t o be established without change in the sulfuric acid concentration of the treating solution. l\7hen long exposures are studied, the sheet is then submerged in the sulfuric acid solution and is subjected a t intervals to contact of fresh liquor drawn through by suction. The sheet is pressed between rollers to remove most of the clinging liquor and is washed by slushing and rinsing in water. The combined water washes are then analyzed. Analysis may be carried out by either of two methods. If the preferred gravimetric procedure is used, the combined washings are titrated with standard alkali t o the phenolphthalein end point to determine the total acid retained by the cellulose and the sulfate is then precipitated with barium, dried, and weighed. B y the volumetric method the combined water washings, or simply the suspension of treated cellulose in water, is titrated to the sulfuric acid end point, using the p H meter and t h e titration is then continued t o the phenolphthalein end point to determine the retained liquor (normally acetic acid). I n t h e first titration pH readings are plotted against the quantity of alkali added and t h e point of maximum slope is the sulfuric acid end point ( 3 ) . These analyses measure the total sulfuric acid and i t is necessary to subtract the dissolved acid present in the retained liquor to obtain the sorbed figures. After separation of the liquor, the washed cellulose is dried at 105’ C. and weighed. All percentages of sorbed and combined sulfuric acid given are based on this weight of oven-dried cellulose. I n experiments where combined as well as sorbed sulfuric acid1 was determined, the washed cellulose was stabilized by an overnight soak in saturated magnesium carbonate solution before drying and combined sulfate content of the dried and weighed
Cellulose containing 2-394 water preswollen by tumbling with 250% acetic acid based on cellulose for 1 hour a t 38’ C. Oven-dried cellulose adjusted to 2.0% water SS. Cellulose preswollen by flooding with water and displacement of t h e water with acetic acid A11 sulfuric acid solutions contained 1.0% HnSOi and 0.2% HzO in AcOH a t 30’ C. H. D.
*
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tion of whether or not differences in sorption levels could be explained on the basis of the accessible cellulose contents as has been done with water vapor sorption and hence whether the sulfuric acid sorption can be considered a function of the accessible or reactive fraction of a cellulose t h a t is intended for paper making or esterification. PROCEDURES
Previously reported analyses of the sulfuric acid removed have been made by determining the concentration in the acetic acid solution before and after the exposure of the cellulose, the loss in sulfuric acid being regarded as sorbed. I n accordance with the definition given above, this calculated value comprises both sorbed and combined sulfuric acid. For short exposure periods the combined sulfuric is very low, in fact negligible, but with longer exposure periods it becomes an important item. The method used here is to draw large volumes of sulfuric acid
2
,
I
4
6
Percent woter in H,SO,
Figure 2.
c.
solution
rade wood pulp treated with 1.0% H z b a~t 30’ Water-swollen acetate grade linters treated with 1.0% H%SO4, a t 30° C. WaFer-swollen acetate grade linters treated with 0.5% HISO, at: 200
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Sulfuric Acid Sorption from Acetic AcidWater Mixtures
a. Water-swollen acetate
b.
I 8
c.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2774 20
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AcOH
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2
3
4
5
1
Time (minutes) Figure 3.
Sorption of Sulfuric Acid from Different Fatty Acids
Water-swollen acetate grade w w d pulp treated with 1.0% HgSO, solutions i n fatty acids containing 0.2% H20 at 30° C.
sample described above was determined by the oxidation method of Malm and Tanghe ( 7 ) . The gravimetric procedure of sulfuric acid determination is preferred because of slightly better precision and is mandatory when the quantity of sulfuric acid to be measured is small. For measurements to within &0.2% based on cellulose the more rapid volumetric procedure is satisfactory. Although the ultimate objective was to use the sulfuric acid sorption as a measure of accessibility in celluloses, much preliminary work was necessary to establish the most suitable conditions of treatment. Factors studied included preswelling of the fibers, influence of u-ater in the sulfuric acid solution, fatty acid composition, temperature and time of application of the solution, and concentration of sulfuric acid.
Vol. 45, No. 12
ized fiber-4.7 us. 3.4% a t the 3-hour point-the reverse is true in the case of the celluloses with no preswelling--0.2% sorbed by mercerized pulp us. 0.7% by unmercerized. The need of water preswelling to reach the increased sorption levels as brought about by mercerization is paralleled in earlier reported data in which it yas demonstrated that with mercerized fiber high percentages of nonaqueous vapor can be sorbed but only after a first exposure over water (9). This is also consistent with acetylation experience, where it is readily shown that mercerization increases the activity of a given fiber if adequate preswelling is provided, whereas such dry mercerized cellulose is less active than the unmercerized when acetylation reagents are applied with no preliminary soaking in water or with limited soaking in acetic acid. The water-swelling step was adopted in the procedure that was used in comparing celluloses with respect to accessibility, for the reasons that highest sulfuric acid sorptions were obtained quickly on the water-swollen celluloses and that such sorption figures would be expected to correlate best with water vapor sorption data, in the measurement of which some similar swelling is produced by the sorbed vapor. EFFECT OF WATER IN THE SYSTEM
Control of water in the sulfuric acid solution is also of prime importance. Thus, as illustrated in Figure 2, under given conditions of temperature and sulfuric acid concentration in the acetic acid the presence of 0.8 to 1.0% of water results in a higher sulfuric acid sorption than is obtained when the preswollen cellulose is treated with liquors of higher or lower water content. Other data not presented here show this influence of water present during such treatments of cellulose to be even more marked when the sulfuric acid is dissolved in the higher fatty acids.
INFLUENCE O F PRESWELLING
The influence of cellulose preswelling is important, as greatest accessibility of a cellulose cannot be realized unless it is swollen before or during the exposure to the sulfuric acid solution. It became evident early in the investigation t h a t a fully watersn-ollen cellulose is best suited to assure maximum sorption in a reasonable time period. Some of the data are plotted in Figure 1. A refined cotton linters, an acetate grade of wood pulp, and a substantially mercerized wood cellulose were used in these experiments, The sorption curves q-ere determined using three states of fiber activation: The water-activated sheet had the water displaced successively with acetic acid and the sulfuric-acetic acid solution; the cellulose containing 4% water was swollen with 250% acetic acid based on cellulose for 1 hour a t 38" C. before displacement with the sulfuric-acetic acid solution; and the dry fiber containing 2 to 3% xater was subjected directly to a sulfuric-acetic acid solution pull-through, removing substantially all of its moisture. In this first series of experiments all sorptions were measured from a 1.0% sulfuric acid solution in 99.8% acetic acid a t 30" C. From Figure 1 it is observed that the xater-swollen cellulose sorbs its maximum sulfuric acid rapidly. The acetic acid-swollen fiber has a slightly lower maximum and requires longer to reach it. The cellulose which has undergone no preliminary sffelling sorbs sulfuric acid very slowly and in the 5-minute exposures plotted the sorption by this unswollen cellulose is nearly zero. In longer exposures to these solutions an interesting reversal of sorptions is obtained with the mercerized and the unmercerized cellulose, depending on whether the fiber has undergone a preswelling in water or the dried cellulose is immersed directly in the sulfuric acid solution. Thus, while water-swollen mercerized cellulose shows substantially higher sorption than the unmercer-
,
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I
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I
2
3
4
5
Time (minutes) Figure 4.
Effect of Temperature on Sulfuric Acid Sorption
Water-swollen acetate grade wood pulp treated with LO70 H ~ S O in I acetic acid containing 0.270 water
This maximum sorption level found a t 0.8 to 1 0 % of water in the acetic acid medium is not paralleled in the study of combined sulfuric acid. Highest combined sulfuric acid contents of cellulose are obtained from anhydrous acetic acid and are lowered progressively as the water content of the acetic acid medium is raised. With oven-dried cellulose that has not been water swollen, high sorptive power can be achieved more readily by the direct addition of limited amounts of water to the cellulose before application of the sulfuric acid solution than by immersing the dry cellulose directly in acetic acid that has been adjusted .Ivith the same percentage of water based on cellulose. The influence oi small amounts of water added to the dry cellulose and of water added directly to the acetic acid is seen in Table I. The data are particularly interesting when viewed from the angle of total water present in the system.
December 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. MOISTURE DISTRIBUTION AND SORPTION BY UNSWOLLEN ACETATEGRADE WOOD PULP
(All exposures to HzSOI soIutions were made by drawing 1.0% HzSO4 in aoetio acid at 30° C. through unswollen sheet pulp continuously for time indicated.) Approximate Adjusted Total HIO Original % HnO % Hz0 in Based on State of Based on HzSOa Cellulose in Sorbed HaSOr Pulp Cellulose Method of Adjustment Solution System 2 min.5 10min.a Oven-dry 0 0 3 120 0.1 0 0 6 Additionb 0.3 125 0.3 0 9 10 Additionb 0 3 130 1.4 2 9 40 Additionb 0.3 160 6 1 6 2
maximum more slowly than at the higher temperatures and reached higher levels. Largely for reasons of convenience and reproducibility, the sorption method finally adopted specifies a choice of either 20" or 30" C.
......
EXTENDED TIME OF EXPOSURE TO SULFURIC ACID SOLUTIONS
A variety of celluloses waa examined using extended exposures to the sulfuric acid solutions to show the course of a b itself uniformly on cellulose. sorption increase and subsequent decrease. The longer time periods also gave opportunity to investigate the slower build-up of combined sulfuric The procedure ultimately adopted for the comparative measureacid as well as its gradual decrease a t longer exposures. ment of accessible cellulose prescribes a sulfuric acid solution in a Except where otherwise noted, the procedure in this supplefatty acid that has been adjusted to 0.2% water; this concenmentary work used water-swollen fibers exposed to 0.5% sultration was chosen because it approximates the percentage mainfuric acid and 0.2% water in acetic acid a t 20' C. tained practically in the acetic acid used in cellulose acetate manufacture. FATTY ACID MEDIUM I , Figure 3 shows the increased sorption resulting from the use of a higher fatty acid than acetic as the medium carrying the sulfuric acid. The time required to approach maximum sorption is greater and the maxima are higher than are obtained in corresponding experiments using acetic acid. These high levels may be due in part to a lesser compatibility of sulfuric acid or its hydrates with these higher fatty acids or t o a greater tendency for association of sulfuric acid or its hydrates. The standard sorption test adopted for comparison of accessibilities in celluloses specifies the use of acetic acid. 5.5 Over HaSOr 0.4 5.5 Over HzSOd 0 6 5.5 Over HzSOc 1.0 Time of exposure to HzSOI solution. After addition of water, time was allowed for water to distribute
Air-dry
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165 245 405
0 5
08
0.7
1 5
0 8
1.7
TEMPERATURE OF SULFURIC ACID SOLUTION
As expected, the temperature maintained during application of the sulfuric acid solution has a major influence both on rate of sorption and on the maximum sorption level. Data appearing in Figure 4 are typical. These measurements were made with a water-swollen acetate grade wood cellulose treated with 1% sulfuric acid solution in acetic acid. Maximum sorptions were reached in all cases in less than 5 minutes. It is observed, however, that a t the lower temperatures sorption approached its
-I
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Time (hours) Figure 5.
Change in Sulfuric Acid Sorption with Time
Water-swollen celluloses treated with 0.5% Has01 i n 99.8% acetic acid at 20' C. A . Acetate grade wood pulp from hemlock L . Acetate grade cotton linters M . Mercerized by treatment with 18% NaOH solution at 20' C. S . Substantiallv mercerized bv treatment with 16%NaOH solution a t 50' C. V . Viscose grade sulfite wood pulp from hemlock
I
01
Figure 6.
10
1
I
10
100
Time (hours) Rate of Formation of Combined Sulfuric Acid
Water-swollen cellulosea treated with 0.5% HiSol in 99.8% acetic acid a t Z O O C. Acetate grade wood pulp from hemlock Acetate grade cotton linters Mercerized by treatment with 18% NaOH solution at 20° C. Substantially mercerized by treatment with 16% NaOH solution at 50' C. V . Viscose grade sulfite wood pulp from hemlock
A. L. M. S.
Figure 5 shows sorption values so obtained with typical unmercerized and alkali-treated celluloses. I n all cases a maximum sorption was reached after a 15-minute exposure and in all cases thereis a progressive falling off in sorption as the time is extended from the 1-hour to the 96-hour point. Maximum combined sulfuric acid is reached much more slowly, requiring about 24 hours, after which it also declines as the exposure to the liquor is extended (see Figure 6). Recognized changes in the cellulose occurring during the long exposure to the sulfuric acid solutions are threefold; a continuing reduction in degree of polymerization, the gradual formation of combined sulfuric acid referred to above, and a slow introduction of small percentages of acetyl groups. It seems reasonable to assume that under the mild conditions of treatment selected as well as because of rapid attainment of maximum sorption these cellulose changes have but little effect on this highest value. The reduction in degree of polymerization, the introduction of acetyl, and to a lesser degree the introduction of combined sulfuric acid cause major changes in the sulfuric acid sorptive properties of the base cellulose. When, for instance, a water-swollen sample of acetylation grade wood pulp with a 15-minute sorption level of 4.7% was exposed to the sulfuric acid solution in acetic acid
INDUSTBIAL AND ENGINEERING CHEMISTRY
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has an original 15-minute equilib~iuni sorption level of 4.7%$, if first acetylated in this manner to contain 2% acetyl, shon. a sulfuric acid sorption of only 3.4%. Figure 7 shows the relationship found experimentally between the sorption levels and the acetyl contents of cellulose treated for periods up to 72 hours mith the sulfuric-acetic acid solution. 113 this plot the acetyl contents are expressed as per cent bawd on cellulose and have been coirected for the combined sulfuric acid The relationship is not linear, supporting the viewpoint pieviously expressed that other facto1 E than the acetyl content are also influential in determining the sorption level after such prolonged exposures. The S-shape of the curves is more pronounced mith the pulp sample than in the samples from the cotton ba$e ,4s sorption of sulfuric acid, the formation of acetyl, the chain breakage responsible for viscosity reduction, and the formatioil of combined sulfuric acid are all expected to occur in the noncrystalline fraction of the cellulose, it is perhaps not surprlqing that the causes of the decrease in sorption mith time are found to be complex.
1
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1 2 3 4 5 %Acetyl based on cellulose
Vol. 45, No. 12
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Figure 7. Relationship of Sulfuric Acid Sorption to Acetyl Content Water-swollen celluloses held in 0.5% HtSO4 in 99.8% AcOH for 1 t o 72 hours a t 20' C. Acetate-grade wood pulp Acetate grade linters .\Z. Mercerized with 18% NaOH solution at 20' C. A. L.
for 24 hours and then was water-washed, dewatered, and again exposed to the sulfuric acid solution, the 15-minute sorptioii level was almost exactly that obtained after the initial 24-hour exposure (2.3%). The acetyl content of this washed sample is about 2.0%. Removal of the acetyl groups from this 24-hour sample by a modified Eberstadt procedure ( 2 ) restored a large portion of the lost capacity for sorption and the new 15-minute sorption was found to be 4.1% based on cellulose. The failure to reach the full 4.7% Fith removal of acetyl is probably largely accounted for by influence of chain breakage. Thus if the original cellulose is depolymerized to the same approximate degree by hydrochloric acid vapor and washed, the resulting water-activated cellulose then shows a sulfuric acid sorption of 4.1 %.
-40%
3
3.0%
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0
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20
30
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50
50
Yo H2S04 Bosed on solution
Figure 9.
t
Sulfuric Acid Sorption Isotherms
Water-swolien celluloses treated with sulfuric acid solutions in acetic acid at 20' or 30' C. A . Acetate grade wood pulp from hemlock L . Acetate grade linters M. Mercerized by treatment w i t h 1870 NaOH solution at 20' C, I
ob Figure 8.
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2 3 Time (minutes)
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Effect of Sulfuric Acid Concentration on Sorption
Water-swollen acetate grade wood pulp treated with H>SOa i n acetic acid at 30' C.
The influence of small percentages of acetyl can be demonstrated in another manner as it is possible by the use of very mild catalysts to introduce small percentages of acetyl into cellulose without greatly changing the degree of polymerization. Standard sulfuric acid sorption measurements on such celluloses always show greatly reduced sorption levels, again indicating the marked influence of the acetyl content on the sorption of sulfuric acid. The acetate grade wood pulp referred to above, which
CONCENTRATIOY OF SULFURIC ACID
The variation in sulfuric acid sorption from acetic acid solutiorir of increasing concentration is shown in Figure 8. It is evident that the effect on the sorption level of a given increment in s o h tion concentration depends on the concentration level being considered, larger effects being produced a t low concentrations. If the sulfuric acid pickup by cellulose from a fatty acid solution is a sorption phenomenon, one would expect the principles of the Langmuir sorption isotherm t o apply. This isotherm can be written in the form ( 4 ) ,
P
C r n
=
i klh.2 +
P
i;,
in which p is the gas pressure, z is the weight of sorbed gas, 1 1 ~:D the weight of adsorbent, and kl and l i ~a r e conatants. Traw-
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1953
20
-
16
-
I2
/'
8-0
4-
4
8
I2
16
20
24
28
H20 Vapor sorption (95%re1 humidity) Figure 11.
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H20 Vapor sorption (95%rel. humid ) Figure 10. Correlation between M Values and Water Vapor Sorption A . Acetate grade wood pulp A R . Acetate grade wood pulp refined with cold alkali B . Birch-base kraft wood pulp L M . Fully mercerized linters L. Acetate grade linters S. Spruce-base unbleached kraft wood pulp
No. 1 2 3 4
6
7 8
s
= ka -I- kdc
in which c is the concentration of sulfuric acid in the fatty acid solutions, s is the sulfuric acid sorbed (normally expressed as per cent based on cellulose), and 11'3and ka are constants. From this equation, it is evident that a straight line should result if the ratio of the concentration of sulfuric acid in solution to the equilibrium sorbed sulfuric acid level is plotted against the solution concentration. Such a plot showing these linear relationships is presented ia Figure 9 using a series of measurements of sulfuric acid sorption from acetic acid solutions containing 0.270 water by acetate grade linters, acetate grade wood pulp, a cord alkalirefined wood pulp of 97% a-cellulose content, and the acetate grade linters mercerized by treatment with 18% sodium hydroxide a t 20" C. Although the points are not shown in Figure 9, the isotherms d o not remain linear when very low sulfuric acid concentrations are used. At solution concentrations below 0.5% it is suspected that a sulfuric acid hydrate is the unit being sorbed and a different equilibrium is set up between sorbed and dissolved acid, resulting in higher relative sorption figures. By extrapolation of such isotherms as those of Figure 9 we mag estimate maximum sorption levels that should be reached from acetic acid. These maximum levels obtained by this extrapolation appear to be inherent characteristics of the celluloses and are referred to in subsequent discussion as " M values." For linters these M values are 9.4 and 9.20/,, obtained by extrapolation of the 20' and 30" C. isotherms, respectively. If, for the moment, we accept the water-accessible cellulose content of cotton linters as 31% (5, 9 ) this would mean a sorption of 48 grams of sulfuric acid per mole of water-accessible cellulose and would empirically indicate that one sulfuric acid molecule can be sorbed from acetic acid for each two water-accessible glucose units. The isotherms for the acetylation grade wood pulp, considered to contain approximately 38% celluloseaccessible to water, when similarly treated show M values of about 11.3% also equivalent to 0.5 mole of sorbed sulfuric acid per water-accessible glucose unit. Since the M value of the fully mercerized linters sample is 16,370,application of the above empirical principle t h a t 0.5 mole of sulfuric acid is sorbed from acetic acid per water-
us.
Water
Water-swollen celluloses treated for 15 minutes with 0.5% HnSO4 solutions in 99.8% AcOH a t 20' C. Equilibrium water sorptions shown from bone-dry state a t 95% relative humidity
5
lated into terms used in these experiments, in which sorption occurs from solution, this becomes
Sulfuric Acid Sorption Vapor Sorption
9
Cellulose Acetate grade linters Washed unbleached linters Acetate grade sulfite base wood pulp of hemlock origin Cold alkali-refined acetate grade wood pulp Viscose grade sulfite pulp from hemlock Unbleached sulfite pulp from hemlock Bleached semirefined hardwood sulfite pulp Bleached hemlock sulfite D - U -~ D(87% or-cellulose) Unbleached hemlock sulfite D U ~ D
Acetate rade sulfite pulp treated with 1 8 8 NaOH at 20' C. 14 Acetate rade linters treated with 18% N a 8 H a t 20° C . 15 Unbleached spruce base kraft pulp with 18% NaOH a t 20' C. 16 Unbleached northern spruce kraft Pulp 17 Bleached kraft pulp from Swedish softwood 18 Cold alkali-refined kraft pulp from spruce 19-22 Laboratory kraft pulp from hemlock 23-27 Laboratory kraft pulp from white birch Miscellany 28 Holooellulose from hemlook, 29 Groundwood of spruce origin 30 HCHO-treated acetate grade wood Pulp 13
Sorbed H&04
Sorbed Hz0
3.9 4.3
14.4 14.4
4.7
16.2
5.7
18.4
4.7
16.4
3.7
15.2
4.7
16.9
5.3
17.9
5.7
18.6
5.1
18.0
7.4
22.6
7 1
23.4
6.9
24.3
7.2
24.7
7.7
24.9
4.8
19.9
4.7
18.8
5.4
18.4
4.3-4.8
17.1-18.3
3.0-3.9
17.4-19.3
7.6 7.3
23.6 24.2
2.2
10.4
accessible glucose unit would indicate a n accessibility in this case of 54%, which is considered a reasonable figure (6, 9). CORRELATION BETWEEN SULFURIC ACID SORPTION AND WATER VAPOR SORPTION
The above is essentially a demonstration that a direct correlation exists between the cellulose fractions accessible to sulfuric acid and to water and that the M value is a measurement of the cellulose accessible to sulfuric acid. Plotting the M values against the water vapor sorption (Figure 10) produces a straight line, again demonstrating the direct relationship between these two measurements. The observation t h a t the extension of the straight line of Figure 10 passes approximately through the origin suggests t h a t all of the cellulose t h a t is accessible to water is also accessible to sulfuric acid under the conditions of the M value determination. At least the two fractions, respectively accessible to sulfuric acid and to water, must be proportional. This is discussed at greater length below. If a proportionate part of the M value is found when a maximum sorption is established using a weak sulfuric acid solution,
INDUSTRIAL AND ENGINEERING CHEMISTRY
277%
Figure 12.
Vol. 45, No. 12
Sorption of Water Vapor a n d Sulfuric Acid by Alkali-treated Linters
it should be permissible also to regard that figure as a relative Grouping of the kraft pulps in Figure 11 reveals that those of hemlock origin come closer to the linear relationship of the measurement of the cellulose accessible to sulfuric acid just as is done when determining water-accessible cellulose by water vapor cottons and sulfite pulps than do the spruce kraft fibers and that the kraft pulps of birch origin are even farther from the sorption a t relative humidities below 100%. Maximum sulfuric line. Whether the alkali-resistant pentosan contents of the acid sorptions by a variety of water-swollen celluloses were kraft pulps from hemlock, spruce, and birch (approximately 5, 8, measured from acetic acid containing 0.2% water and 0.5% sulfuric acid a t 20" C., these conditions being chosen as most desiraand 20%, respectively) are partly responsible for their behavior ble on the basis of the studies discussed previously. Figure 11 is not known. Other possible explanations for the above experimental results are that (1) the molar ratio between the M value shows these sulfuric acid sorption levels plotted against the water and the water-accessible glucose units is lower for the kraft pulps vapor sorptions by these celluloses measured from the bone-dry than for the sulfite and cotton fibers and ( 2 ) the fraction of the 3f state a t 95% relative humidity. For most wood pulps of sulfite value actually sorbed by kraft pulps from such dilute solutions origin and for cotton-base celluloses the correlation between sulmay be less than for sulfites and cottons, indicating a displacefuric acid sorption measured under these conditions and water ment of the sorption equilibrium toward dissolved sulfuric acid vapor sorption is good. with these pulps. This is being studied further, and of these Highest sulfuric acid sorption levels were found using mercerpossibilities the preliminary data seem to point to the last as the ized samples of either cotton or wood origin and withholocellulose most probable. prepared by extraction of wood shavings with chlorous acid solutions (10). Groundwood also shows high sulfuric acid sorption MEASUREMENT OF DEGREE O F MERCERIZATION and, surprisingly, in view of the high lignin content, fits the linear It has many times been demonstrated that the water vapor relationship fairly well. The lowest sulfuric acid sorption level sorption exhibited by mercerized celluloses is higher t h i n t h a t was found using the formaldehyde-treated wood pulp. The low shown by the base cellulose before mercerization. This imsorption of both water vapor and sulfuric acid in this case is plies t h a t the vapor sorption measurement can lie used probably due to the formal linkages which inhibit swelling of the to determine the degree of mercerization in celluloses 01 the same fiber. base, treated with alkali under varying conditions of concentraExtrapolation of the line of Figure 11 to zero sulfuric acid sorption and temperature. Figure 12 shows photographs of threetion shows an intercept suggesting either that some sorption of dimensional models of sulfuric acid sorption and water vapor a a t e r vapor takes place in a cellulose fraction which does not sorption measurements on identical samples of acetylation grade sorb sulfuric acid from the 0.5% sulfuric acid solution or that the equilibrium sulfuric acid sorption level from such a weak solution does not bear the same relation to the 114 value for all TABLE11. DEQREE O F MERCERIZATION -4s MEASURED B Y SORPTION O F SULFURIC celluloses. In either case, in view of the ACID AND WATERVAPOR fact that all mercerized celluloses tested i.4cetate grade linters treated with alkali for 1 hour as indicated were tested for water sorption from show approximately the same sulfuric the oven-dry state at 95% relative humidity and for sorption of HzSO4 from the water-swollen state acid and water vapor sorption, it appears using 0.5% HzSOa in acetic acid at 20' C. Figures are plotted in models shown in Figure 12.) that the water-accessible unmercerized Temperatures of Alkali Treatment, ' C. 0 10 20 30 50 20 30 50 0 10 celluloses sorb less sulfuric acid from the Water Vapor Sorption Sulfuric dcid Sorption 5% S a O H dilute solution than is sorbed by the 15.3 15.0 14.9 14.8 14.9 3.6 3.6 3.6 5 3.9 3.6 water-accessible cellulose that has under14.9 l5,l 14.7 16.7 3.6 14.8 3.6 3.6 7.5 4.1 3.7 22.1 18.9 15.7 15.4 14.9 3.6 10 6.5 5.0 3.9 3.6 gone strong alkali treatment. 22.5 21.6 18.7 15.7 24.0 3.8 12.5 6.7 6.4 5.6 4.9 23.3 22.7 18.4 23.6 22.6 The kraft wood pulps do not fit the 5.1 S5 6.7 6.7 6.6 6.3 23.3 23.1 23.6 22.4 21.4 6.2 6.6 6.6 17.5 6.8 6.7 relationship described above but show 23.4 23.0 22.6 21 9 23 6 6.5 6.8 6.7 6.9 6.8 20 23.7 23.3 21.7 24.3 22.8 6.7 6.9 6.9 25 7.1 7.1 lower sulfuric acid somtion levels for their respective water sorptions.
December 1953
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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. D a t a 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 t h a t 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 t h a t 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 t o 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 t o 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 t o give from 3000 t o 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 t o study the effectiveness of the cleaner in removing individual components of the soil, three of these were
