726
INDUSTRIAL AND ENGINEERING CHEMISTRY
The heats of gelatinization measured in Pacsu’s laboratory (11) are also of interest in connection with the present hypothesis. Since they are negative and of a magnitude consistent with the breaking of one or two hydrogen bridges per glucose residue, these measurements can be considered to agree with the conception that hydration is not the significant process in gelatinization; if it were, heat should be evolved. The problem is, however, not simple, since it is possible that the observed heat of gelatinization is the net effect of endothermic and exothermic processes involving the disruption and reconstitution of more than two hydrogen bridges per residue. Even if as many of these bridges exist after gelatinization as before, there may yet be differences in heat content arising from the nonequivalence of the hydroxyl groups involved.
Literature Cited (1) Alsherg, C. L., Plant Physio’., 13, 295 (1938). (2) Badenhuiaen, N. P., Rec. trav. botan. nEerZancl., 35,559 (1938).
Vol. 35, No. 6
(3) Bear, R. S.,J . Am. Chem. Soc., 64,1388 (1942). (4) Bear, R. S.,and French, D., Ibid., 63, 2298 (1941). (5) Bear, R. S.,and Schmitt, F. O., J . CelZular Comp. Physiol., 9, 289 (1937). (6) Caesar, G. V., and Gushing, M. L., J . Phys. Chem., 45, 776 (1941). (7) Frey-Wyssling, A., Naturwissenschuften, 28, 78 (1940). (8) Furry, M . S.,U. S.Dept. Agr., Tech. Bull. 284 (1932). (9) Kuntael, A., and Prakke, F., Biochem. Z . , 267, 243 (1933). (10) hleyer, K. H., and Bernfeld, P., Helv. Chim. Acta, 23, 890 (1940). (11) Mullen, J. W., and Pacsu, Eugene, IKD,ENG.CHEX., 34, 807 (1942). (12) Samec, M.,“Kolloidchemie der StBrke”, p . 131, Dresden, Theodor Steinkopff, 1927. (13) Schleiden, J. M., “Principles of Scientific Botany”, t r . by Lankester, p. 12, London, Longmans, Green and Co., 1849. (14) Staudinger, H., and Eilers, H., Ber., A69, 819 (1936). (15) Zwikker, J. J. L., Rec. trav. botan. nderland., 18, 1 (1921). JOURNALPaper 5-921, Iowa Agricultural Experiment Station. Project 638. supported in part by a grant from Corn Industries Research Foundation.
Water Adsor tion By
Animal Glue CHARLES ill. MASON1 AND HERBERT E. SILCOX University of New Hampshire, Durham, N. H.
The adsorption of water on thin films of five animal glues and one gelatin have been investigated, the glues covering the range of physical properties commonly employed. Both adsorption and equilibrium moisture content have been studied. The former obeys Freundlich’s law, and the latter is found to be greater than represented by the moisture adsorbed on the surface. It is proposed that water is held by glue in two forms-by true adsorption on the glue surface and by some other mechanism in the voids of the glue itself.
A
S I D E from general interest in the field of colloidal science a knowledge of the water adsorption of animal glue is of great interest to all who use this material in manufacturing processes. Previous publications have been scanty and incomplete. Wilson and Fuwa (11) give some data on glue as part of an extensive study of many materials. Katz (4) and Sheppard, Houck, and Dittmar (7) studied gelatin, a similar material. The present investigation was undertaken to supply data for glues covering as wide a range of physical properties as possible. A t the same time a n investigation has been made of the adsorption of water on glue in relation to Freundlich’s law. 1
Present address, Tennessee Valley Authurity. Wilson Dam, Ala.
ADSORPTIOR OV T H I h FILMS
One bone glue, four hide glues, and a gelatin were chosen which seemed to cover the range of known physical properties of glues. The glues were obtained through the courtesy of a large industrial user who selected those most characteristic of available commercial glues. The gelatin was a sample sold as suitable for bacteriological work and was therefore supposed to be of unusual purity. No attempt was made to purify the samples further because this would have vitiated the results from a practical viewpoint. Table I gives physical characteristics as determined b y the firm which supplied the glues. HTJ?IIDITY CoxDIrIoxs. The basic problem involved in the pxperimental technique is tu obtain reproducible and controllable humidity and temperatures over long periods. Air was passed over saturated salt solutions in saturators of the type designed by Bichowsky and Storch ( 1 ) and then through a chamber containing the glue samples. The whole train was immersed in a water thermostat regulated t o 25 * 0.02’ C. The humidity produced by these salt solutions had previously been determined by extensive calibration at 25” C. The exposure of the glue samples to the humidity conditions was carried out in the form of thin films 0.008 t o 0.01 inch (0.2 to 0.25 mm.) thick. The films were prepared by first mixing equal parts of glue and water and alloving the mixture to stand for 2 hours. Water was then added t o the swollen product and the mixture heated t o 40” C. on the steam bath. When liquefied, the glue was drawn into films by the method of Kallender (S), using moistureproof regenerated cellulose (cellophane) as a supporting medium. The films were then allomed to cool and dry partially in the air. The glue n a s peeled from the support and cut into strips 1 inch vide and 15 or 18 inches long. They were rolled into loose cylinders and placed edgehise in glass weighing bottles, In the case of the glues of lomcr gel strength, which tended to melt down at high humidities, the films w-ere drawn on glass cloth instead of moistureproof regenerated cellulose. This
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
June, 1943
TABLE I. PHYSICAL CHARACTERISTICS Designation
a
Type
pHa
Viscosity, b Millipoises
Bsh,
Gel Strengthc
Determined on 10% solution before film was drawn. 12.5% solution.
b Determined on the c
As measured on t h e Bloom gelometer (6).
MOISTCRE TABLE 11. EFFECTOF TIMEON EQUILIBRIUM CONTENT O F GLUEF I L M S OVER 12-WEEK EXPOSURE PERIOD AT 65 PERCENTRELATIVE HUMIDITY AND 21’ C. Pretreatment of Film before Exposure Dried Not dried
721
water content and approaching the values of the unpredried (25” C.) samples. The whole experiment was repeated over a 12-week period. The results are shown in Table 11. Considering the limit of error involved, i t would appear that predried samples have the same equilibrium moisture content but take much longer t o reach equilibrium. Quick drying in an oven seems to “caseharden” the surface of the film, reduce the diffusion rate, and thus increase the time needed for water to penetrate the film. This experiment also offers considerable evidence to support the contention that the glue undergoes no chemical change when dried a t 110” C. for 16 hours to obtain the anhydrous or bone-dry weight.
% Water Based on Dry Wt. of Glue A B C D E 55 1 51.9 45.2 44 7 43 0 55.2 53.6 44 8 44 5 44 5
was found very satisfactory, and careful testing indicated there
was no difference between moisture adsorbed on glue films and on the glue supported on glass c!oth. The weighing bottles containing the glue samples were placed in the humidified chamber for as long a time as was necessary to reach equilibrium. After each exposure in the humidity chamber, the weighing bottles were stoppered and weighed with contents. When equilibrium had been established, the samples were dried in a desiccator for a week to firm them; otherwise they Rould have melted if placed immediately in a hot oven. They were then dried for 16 hours in an oven at 110’ C. and weighed to obtain the anhydrous weight. Investigation was made of the advisability of using a vacuum oven to obtain a better anhyd’rous weight, but the same value was obtained from the vacuum oven as from the oven at 110’ C. Since vacuum drying was carried out at 60” C., this seemed to confirm the bellef that the glue underwent no chemical changes on air drying at 110’ C. In the beginning some difficulty was encountered with mold formation, but this was overcome by the introduction of mernhenvl acetate in a concentration of 1 t o 5000 which seemed to c--have no effect on the adsorbed water. _I
~
EQUILIBRIUM MOISTURE CONTENT
The results obtained will in some cases be due to desorption of water to a drier atmosphere and in others t o adsorption of water from a more humid atmosphere than that in which the films were prepared. The same final equilibrium should be obtained in either case. The term “equilibrium moisture content” is taken here to signify the number of grams of water adsorbed per gram of anhydrous glue at the final equilibrium. AS will be shown later, it is possible to reach a pseudo equilibrium which obeys Freundlich’s law when the surface of the glue has been casehardened by heat treatment. Sheppard, Houck, and Dittmar (7) observed for gelatin, Houta and McLean (8) for paper, Urquhart and Williams (IO) for cotton, and Speakman and Stott (9) for wool, that the previous thermal history has a pronounced influence on water adsorption. To determine the effect of predrying the glue films before their exposure to a humid atmosphere, the following investigation was carried out: The equilibrium moisture content was determined for a set of duplicate samples which had been split into two parts. One set was heated for 16 hours at 110’ C. and the other was air-dried a t 25’. These glue films were then exposed together to identical conditions (65 per cent relative humidity and 21’ C.) for 6 weeks; they were weighed at the end of each week. After 6 weeks the samples were all dried 16 hours at 110’ C., and the anhydrow weight was obtained. In the early weighings the predried samples seemed to reach a much lower moisture content than the others, but near the end of the &week period it was discovered that the predried samples were rising in
/
.03
8.02.
.o I
/
/
,”
’
J
I
/
Figure 1. Log-Log Plot of Data for
GlueE
.
As a result of this investigation, one may conclude that exposure of previously dried samples results in straight adsorption on the surface whereas a regain technique includes not only adsorbed water but water enclosed in the structure of the glue itself; this may account for the “thermal history effect” mentioned by many authors (9, 7 , 9 , IO). Since it was possible to obtain a preliminary equilibrium due, no doubt, to adsorption on the casehardened surface of the glue, a series of trials were made on predried films which took them only to the first equilibrium point. From these data (Table 111) we should be able to test our adsorption theory by application of Freundlich’s law. TABLE 111. ADSORPTIONOF WATERON GLUEFILMS PREDRIED AT 110” C. BEFORE EXPOSURE Relative Humidity,
% 16.5 28.5 47.0 53.7 62.4 75.3 85.0 99.0
AbsoJu?e Humidity 0.0033 0,0057 0.0094 0.0108 0.0125 0.0151 0.0170
0.0198
Crams Water per B C 0.030 0,037 0.055 0,067 0.096 0.119 0.118 0,142 0.144 0.164 0.219 0,216 0.288 0.271 0.519 0.452
A 0.029 0.043 0.085 0.110 0.141 0.220 0.297 0.551
G r a m D r y Glue D E F 0.038 0.037 0.038 0.068 0.067 0.065 0.127 0.123 0.121 0.151 0.147 0.144 0.174 0.169 0.168 0.219 0.218 0.214 0.273 0.261 0.269 0.447 0.430 ...
From Freundlich’s law, A = K (AH)“ where A = water adsorbed, grams water per gram dry glue (AH) = absolute humidity K,n = constants Rewriting, log A = n log ( A H )
+ log K
INDUSTRIAL AND ENGINEERING CHEMISTRY
728
T ~ B I , IV. E EOUIILBRIUM MOISTERECOUTENT AT 25' C. OF GLUESDRIED4~ COMPLETION OF EXPERIMEXT Relative Humidity, '7,5" 14.5 16.5 28.5 31.0 47.0
Giams Water per A B C 0 . 0 7 7 0.073 0.075 0 , 0 8 0 0,079 0.089 0 , 1 2 4 0,125 0.146 0,127 0 , 1 2 7 0,158 0 , 1 4 3 0.146 0,181 0.153 0.156 0.191 0 . 2 1 1 0 . 2 0 3 0.209 0.306 0 . 2 9 2 0.248 0.378 0.374 0 , 3 2 7 0 , 5 5 2 0,536 0,448
Absolute Humidits 0,0020 0,0033 0,0057 0,0062 0,0094
0,0108 0,0125 0.0151 0,0170 0,0198
53.7 62.4 75.3 85.0 88.0
14 3 16.5 28.5 31.0 47.0 53.7 62 4 75.3 85.0 99.0 64 75 84 95 1on
...
5, however. Sheppard, Houck, and Dittmar ( 7 ) also investigated the effect of film thickness. They report the range between 0.076 and 0.29 mm. RS optimum; the film thickneqses selected here, 0.2 to 0.25 mm., fall within this range. I n the light of these facts, it is reasonable to compare our results for gelatin with those of other authors. Our gelatin was not so pure as the one used by Sheppard, Houck, and Dittmar ( 7 ) , which de-ashed from 2 to 0.02 per cent ash; but the comparison is interesting. The following data for gelatin mere taken for several source' from graphical representations of the various authors.
MOISTURE CONTENT OF GLUES
TABLE V. Relative Humidity, 70
Gram Dry Glue D E F 0.084 0 . 0 8 5 0.082 0 . 0 8 8 0,079 0.089 0.157 0.159 0 . 1 4 9 0.160 0.161 0 , 1 5 4 0,188 0.189 0.175 0.199 0.200 0.186 0.218 0.218 0.217 0 . 2 4 7 0.243 0.289 0.320 0.312 0.380 0.445 0.445
7
A
B
7.2 7.4 11.1 11.3 12.5
13.2 17.4 23 4 27.5 35.6
6.8 7.3 11.1 11.2 12 8 13.5 16.8 22.6 27.2 35.0
11.5 17.5 25.2 34.7 48.0
11.9 17.5 24.2 33.0 47.5
Moisture, yo C D E Temperature 25' C. 7.8 7.8 7.0 7.3 8.2 8.1 13.7 12.7 13.6 13.8 13.7 13.8 15.9 15 3 16.8 16.7 16.0 16.6 17.9 17.3 17.9 19.6 19.9 19.8 24.2 23.8 24.6 30.8 31.0 30.8 Temwerature 35' C. 14.3 13.6 14.2 17.5 17.5 17.3 21.7 20 7 21.8 27.7 26.1 27.8 44.0 41.5 39.4
F 7.6 8.2 12.7 13.3 14 9 15.7 17.4 22.4 27.5
.. ..
..
.. ,
.
..
Vol. 35, NO. .6
Humidity, % 10 20 30 40 60 60 70 80 85 90
Moirture Regain of Dry Gelatin, % Kats (4) Sheppard et al. (7) This papei 9 0 6.0 5 8 12.5 9.0 10 5 16.0 12.0 1.5 0 10.5 14.5 17 5 23.0 17.5 18 0 26.0 20.5 20 3 29.5 24 0 26 0 33 5 30.0 32 9 38.0 38.0 38 n 42 0 46.0 44.0
T h e n we take into account the possible variations which might be expected, the agreement is rather good and well within experimental error in many cases. Our results seem to run a little higher than those of Sheppard, Houck, and Dittmar (7) but are lower than the older values of Katz (4).
Therefore a plot of log A against log (AH) diould be a straight line. Figure 1, typical of all samples except glue A, shows this to be the case u p to about 60 per cent relative humidity. Evidently because of its soft structure, glue A seemed to lack casehardening and hence did not obey Freundlich's law as outlined. The constants for the other glues and gehtin F follow: Glue Sample
n
K
il B C
D
E F
T o obtain the true equilibrium moisture content, it is necessary to approach equilibrium from the unpredried side unless there is time to wait 12 weeks for each point. These points were therefore obtained with samples of glue films which were dried in air before exposure. The films were oren-dried only a t the end of each run to obtain the true anhydrous weight as a basis for calculation. Such a procedure seems to give the correct result within 1 0 . 5 per cent moisture content. The data obtained by this technique are given in Table IV; they are consistently a little higher than corresponding values from Table I11 v-hich represents only water adsorbed on the surface of the film. For comparison, the values are plotted for glues A and E in Figure 2. The data of Wilson and Fuwa (11) are gii-en for comparison. COMPARISON WITH OTHER INVESTIGATIOYS
To compare the results with those of other investigators, we must first take into account the variables affecting the measurements. Sheppard, Houck, and Dittmar (7) showed that pH has a decided effect upon the equilibrium moisture content, arid they report that below p H 5 a wide variation is to be expected. Above p H 5 the effect flattens off and becomes practically constant within the experimental error. The data reported here were obtained a t a p H greater than 5.7 except in one case (gelatin F); the p H of F was still above
3
Figure 2.
%RELATIVE HUMIDITY
Equilibrium Moisture Content of Glue at 25' C.
A, bone glue; E, hide glue; W & F, Wilson and Fuwa (11).
The coniparison of the results for the glue with those of Wilson and Fuwa (11) is not so favorable. These authors obtained much lovc-er results although their curves have the same general form. I n view of the fact, however, that they did not dry their samples at 110' C. and that they used glue in the granulated form, their lon-er results are easily accounted for. GLUE-B 4TER STRUCTURE
The isotherms (Figure 2) resemble, in general, those obtained for silk, wool, ccllulose, a n 3 gelatin. They also are analogous to the data obtained by Rao ( 6 ) in his studies on the adsorption of water on silica gel, titania gel, and ferric oxide gel, shoTving the fundaineiital nature of the phenomena involved. Sheppard, Houck, and Dittmar (7) suggested that the mechanism for gelatin is the same as for cellulose, as suggested by Sheppard and Newoine (8): There are t x o main forces influencing the adiorptiori of \I a h vapor. First, water is initially adsorbed at inner surfaces by the free hydroxyls of thp cellulose material (i. e., those lying exposed, not holding each other in the formation of the crystallized por-
lune, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion), and secondly, further adsorption consists mainly in the condensation of water vapor in the voids of the structure. In the case of gelatin the initial adsorption is probably chiefly due to the amino groups which are freed on the alkaline side of the isoelectric point.
It is then consistent to propose that the behavior of predried glue represents true adsorption on the surface of the structure of the glue. This is substantiated b y two facts. First, the samples obey Freundlich's law in the main. Secondly, the sample which does not is a bone glue so soft in nature that even drying does not join a rigid structure upon which adsorption can take place without penetration of water into the voids of the glue. T o obtain the value represented by the equilibrium moisture content then, a small amount of water must be added representing that which had actually penetrated the voids or interior of the glue molecules. T h a t this value will be reached in 12-week exposure of a casehardened glue is evidence of the fact that the two types of water exist in the glue-water structure. Furthermore, the fact that the soft bone glue A came to a much closer equilibrium in 12 weeks of drying is further confirmation of the whole contention (Table 11). The failure to obey Freundlich's law and to contain moisture in excess of that predicted by the law when the glues are placed in relatively wet atmospheres (above 70 per cent relative humidity) is still further evidence to the point since the higher concentration of water in the gas phase favors penetration of the casehardened film. PRACTICAL APPLICATIONS
Since the foregoing data have been reported on the basis of grams of water per gram of dry glue, it is thought desirable
DESTILLATIO
729
to report the data also in terms of per cent moisture content based on the weight of the glue plus water. This gives directly the percentage water to be expected in a glue at the humidity given and 25" C. For glues in granular form, this value probably represents the maximum which the sample would be expected to reach on long exposure. The data so calculated are given in Table V. Some data were also obtained in this laboratory b y James W. Carroll working under identical conditions but at 35" C. (Table V). Although they are not extensive enough to warrant as full a treatment as those obtained at 25", we have incluqed them here because they are of practical value; under present conditions it will be impossible to extend the data to lower humidities. ACKNOWLEDGMENT
The writers wish to thank William F. Talbot and Charles 'VV. Stillwell for their continued interest and advice. LITERATURE CITED
(1) (2)
Bichowsky and Storch, J . Am. Chem. Soc., 37, 2695-6 (1915). Houtz and McLean, J . Phys. Chem.,43,309-21 (1939); 45,111-
27 (1941). (3) Kallender, IND. ENO.CHEM.,ANAL.ED., 10, 40-1 (193s). (4) Kats, Kolloid-Beihefte,9, 182 (1917). (5) Natl. Assoc. of Glue Mfrs., IND.ENO.CHEM., ANAL. ED., 2, 348-51 (1930). (6) Rao, J. Phys. Chem., 45, 500-39 (1941). (7) Sheppard, Houck, and Dittmar, J . Phys. Chem., 44, 185-207 (1940). (8) Sheppard and Newsome, Ibid.,34, 1158-65 (1930). (9) Speakman and Stott, J . Tertzle Inst., 27, 186-90T (1936). (10) Urquhart and Williams, Ibid., 15, 138-481' f1924). (11) Wilson and Fuwa, IND. ENQ.CHEM.,14, 913-15 (1922).
By Paul Rumler
+We are indeb d to Ernest H. S. va Someren for the use of his photograph of an ornate ceiling panel in the Knights' Hall in the Castle of Fredericksborg, near Copenhagen, Denmark. The panel was painted and the high relief plaster frame was executed between 1615 and 1619 by Paul Rumler, who was appointed Royal Danish Painter in 1610 and again in 1615 and 1623. He died in Copenhagen in January, 1641, having lived there since a t least 1596.
Rumler's original ceiling paintings and decorations were destroyed in 1859 when the castle burned, but were replaced by copies when i t was rebuilt. This is No. 150 in the Berolzheimer series of Alchemical and Historical Reproductions. D. D. BEROLZHEIMER 50 East 41st Street New York, N.Y.
The lists of remoducticns and directions for obtaining copies appearas follows. 1 to 96 January 1939 page 124; 97 to 120, Januar;, 1941,Gag? 114; '121 tb 144, January, 1943,page 106. An additional reproductlon appears each month.
