INDUSTRIAL AND ENGINEERING CHEMISTRY
1292
OF BORICACIDON SPEEDOF FILM CASTING TABLE 111. EFFECT
Film
Blank Borated Blank Borated Blank Borated Blank Borated Blank Borated
Min. after Casting
Load,
Lb./
Sq. In.
6 6
15 15
9 9
20 20 30 30 30 30 30 30
11
11
15 15 18 18
Elongation, %
Seo. under Load TOO TOQ
10 30
5 60 30
Permanent 60 Permanent
soft Soft Broke 150 Broke 100 Broke 50 200 Nil
For example, 25 parts of a polyvinyl acetal resin (Alvar 15-80) and 5 parts dibutyl phthalate are dissolved in 70 parts ethyl acetate containing 2 per cent water. T o this solution are added 0.5 part boric acid, enough to cause complete insolubility of the evaporated film but not enough to make it brittle. I n this condition it is neither dissolved nor softened by dry ethyl acetate or any other anhydrous nonalcoholic solvent but dissolves at once if small amounts of water or alcohol are added to the latter. The capacity of borated resins to hold plasticizers or solvents dispersed as an internal phase is remarkable, amounting to proportions as high as 1:15 or more. These compounds are nontacky nonsweating gels which can be used in the preparation of hectograph masses, coatings for printing rolls, etc. As an illustration, the above example of an insoluble coating can be modified to a mixture of 20 parts resin and 80 parts dibutyl phthalate, dissolved in 40 parts ethyl acetate containing 2 per cent water and 0.4 part boric acid. When cast, the viscous but entirely fluid solution leaves a firm nontacky gel, which absorbs and retains printing inks, stains, and dyes, and is little affected by tempemture changes. I t is generally insoluble but can be readily dissolved and recast using aqueous solvents. FILM CASTING
An important factor in casting films from solutions by the usual methods is the rate at which the solvent is released in the final stage when the film is supposed to become self-supporting. I n
Vol. 35, No. 12
many cases small amounts of solvent are retained so tenaciously that subsequent operations are seriously delayed; in nearly all cases faster and more economical casting would result if the tensile strength of the "green" film could be improved without resorting to enforced drying methods. This is readily achieved by the phase inversion caused by small amounts of boric acid added to responsive film-forming media, such as all cellulose derivatives and polyvinyl acetal resins. Although the last remnants of solvent are not removed, these films gel upon reaching the stationary retentive condition and assume full physical strength which allows subsequent handling without delay. The data in Table I11 show this effect in films cast from a solution of 100 parts polyvinyl acetal resin (Alvar 15-80) in 250 parts ethyl acetate containing 5 parts water and 2 parts boric acid. The films were cast on a glass plate, lifted after a given number of minutes, and immediately placed under load. Blank tests were carried out without boric acid.
TABLEIV. Boric Acid, yo None 0.2 0.5 1.0 2.0
EFFECT OF BORICACID ON SINTERING TEMPERATURE
% Elongation a t 80 5 min. Infinite 300 25
d;
25 min.
In'iiit e 100 20 4
C. after: 60 min.
..
€%?,%.
.. ..
25 6
135
175
180 195
205
Entirely analogous results were obtained with the same resin plasticized with 15 per cent triethylene glycol hexoate, using the same solvent, and also with a solution of 60 parts cellulose acetate, 40 parts triacetin, and 2 parts boric acid in 400 parts methyl ethyl ketone containing 2 per cent water. I n amounts up to 2 per cent, boric acid remains dissolved or homogeneously dispersed in the films and does not interfere with their transparency. It contributes markedly to their heat resistance as shown in Table IV. Films of the polyvinyl acetal resin referred to in Table I11 (Alvar 15-80) were completely dried at 60' C. and suspended at 80" C. under a load of 50 pounds per square inch. The sintering temperatures were observed by slowly heating without load.
High-Temperature Heat Content of CALCIUM CARBIDE G. E. MOORE Pacific Experiment Station, U. S. Bureau of Mines, Berkeley, Calif.
P
ART of the program of thermodynamic investigation of metallurgically important substances being conducted a t this station involves measurement of heat contents above 25" C. by the so-called drop method; this paper presents some data obtained on a high-grade commercial sample of calcium carbide in the range 200° to 1000° C. This sample was part of that used by Kelley (2) in low-temperature specific-heat measurements, and i t is probably of the highest purity available at present (91 per cent). Although there is considerable uncertainty in correcting for the impurities, i t nevertheless seemed desirable to obtain and report these data on this important substance.
b T H E method and apparatus were described previously (6). The sample was contained in a sealed platinum-rhodium alloy capsule; there was some action of the carbide on the container after the measurements a t 1000" C., but it was insufficient to cause any appreciable error. The error in the measurements is certainly not more than one per cent throughout the entire range studied, and the results are in general reproducible t o a few tenths per cent. Correction was made for the major impurities reported by Kelley (%)-namely, 6.47 per cent CaO, 1.15 per cent SiOn, and 0.77 per cent ALO,-using data from his tables (3). The mate-
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1943
1293
all results are corrected t o this final temperature. Column 3 presents the result of correcting column 2 for the major impurities, and column 4 gives the heat content per gram molecular weight of calcium carbide (64.10 grams, in accordance with the 1941 International Atomic Weights). The latter are shown also in Figure 1. Table I1 summarizes vrtlues read a t even 100' C. intervals from the smooth curve through the data, together with the calculated entropy increments from 298.16' K.t o temperature T.
16000
Q
b T H E only previous measurements in this range are three results reported by Ruff and Josephy (4), which differ from the present values by a n average of about 10 per cent. I n view of the differences in experimental methods and the fact t h a t uncertainties in both methods are greatest near room temperature, the data reported here agree satisfactorily with Kelley's results a t room temperature. 8
Gys
a 700
500
900
Determinations of the heat content, above 25' C., of a sample of calcium carbide of 91.0 per cent purity were made in the range 200° to 1000° C. Correction for the major impurities was applied. Thedata show a transition at 447' 5' C., with a heat effect of 1330 calories per gram molecular
1100
T,*K. Figure 1.
Heat Content .of Calcium Carbide above 298.16" K.
rial was not reanalyzed, but it had been carefully preserved in a sealed glass container during the interim between Kelley's work (S) and the present measurements. The correction for these impurities averages about 2 per cent, and as the assumption of additivity of special heats may be considered only as a n approximation] an over-all accuracy of better than 2 per cent cannot be claimed. The results, expressed in defined calories (1 calorie =I 4.1833 International joules) are assembled in Table I. Column 1 gives the absolute temperature, and column 2 the heat liberated per gram of material in dropping from temperature T to 298.16' K.;
weight. Below the transition temperature the data are represented by the equation: Hp
-
H ~ 0 s . i5 ~
16.402'
+ 1.42 X 10-8 TZ+
2.07 X lo6 - 5710 T
and above the transition by the equation:
HT - H a p 8 . 1 ~
15.40T
+ 1.00 X
T 2- 3156
cw4 The data show a transition at 720" * 5 ' K. (447"C.)with an accompanying heat effect of 1330 calories per gram molecular CARBIDE weight. Bredig ( I ) reported the existence of a transformation in H T - Haae.te, H T Hra.16, H T - Hna 16 this region, t o which he assigned the temperature 450" * 20" C.; T, K. cal./gram cal./gram (cor.) cal./gram moi. A . the work described in the present paper was done before Bredig's 652.3 90.96 92.51 5,930 work was published and constitutes a n independent observation. 653.s 91.26 92.86 5,950 667.2 91.73 93.29 5 980 As the method employed in the present work involvea mild 168.6 172.1 1 1 :030 873.3 873.2 169.0 172.5 11,060 quenching of the sample in each measurement, presumably the 1097.6 230.3 234.0 15,000 final form was the one designated "111" by Bredig, and the trans1096.Q 230.1 234.0 15,000 1271 277.7 281.4 18.040 formation observed here is I11 -+IV (tetragonal + cubic). The 1262 275.5 279.2 17,900 481.a 45.09 45.87 2,940 other forms described by Bredig are not involved in these meas480.8 45.24 46.0a 2,950 urements. Assuming that the entropy obtained by Kelley at 778.6 143.4 147.0 9 420 716.6 113.0 115.0 7:370 298" K. is that of the usual tetragonal form (111) and hence t h a t 741.5 134.5 137.9 8,840 719.g 125.6 128.2 8,220 of the final state of these measurements, the application of these 708.1 108.3 110.0 7,050 data above 450" C. is unambiguous. 749.4 135.3 138.6 8,880 The following equations express the heat content above 298.16' K. and the heat capacity per gram molecular weight for TABLE 11. HIQH-TEMPERATURE HEAT CONTBNT AND ENTROPY each of the two forms as a function of the absolute temperature OF CALCIUM CARBIDE ABOVE 298.16" K. AT 100' INTERVALS within the indicated range. The equations for C, were obtained ST f3ans.i~ ST SlB8.16, by differentiating the heat content equations. H T - H 2 ~ s . w ~oal./gram md. H T - Hms.rs, oal./gram mol. I
TABLE I. HIGH-TEMPERATURE HEATCONTENT OF CALCKM
-
-
-
T,* K.
csl./oram mol. wt.
wt./deg.
400
500 600 700 720" 720b a
b
Low-temperature form. High-temperature form.
4.62 8.32 11.47 14.19 14.70 16.65
T,a K. 800
900 1000 1100 1200 1300
oal./gram mol.wt. 9,790 11,520 13,250 15 020 16:780 18,590
wt./deg.
18.32 20.36 22.19 23.87 25.41 26.86
From 300' to 720° K.:
HT - Hm.la
= 16.40 T
+ 1.42 X
T 2+ 2'07
C, = 16.40
T
lo'
- 5710
+ 2.84 X IO+ T - 2.07 -X IO6 TP
(1)
vor. 35, N ~ 12 .
INDUSTRIAL AND ENGINEERING CHEMISTRY
L294 From 720" to 1275" K.:
H,,,
-H
, ~= ~ 1. 5~. 4~0 ~+ 1.00
x
10-3
~2
- 3156
(3)
+
C, = 15.40 2.00 X T (4) Equation 1 was derived from CP = 14.93 a t 298.16" K.( 2 ) and two heat content values from Table 11; it fits the data to 0.4 per cent. Equation 3 represents the data to about 0.2 per cent. ACKNOWLEDGMENT
The sample of calcium carbide was furnished by the National Carbide Corporation through the courtesy of F. Pruyn, Jr., under
whose direction it had been sclected over a period of time, presumably in the course of ordinary manufacture. The sample w a s kindly analyzed by G. W. Marks, Western Region, U. S. Buream of Mines. LITERATURE CITED
(1) Bredig, M. A., J. Phys. Chem., 46,801 (1942). (2) Kelley, K.K., IND. ENO.CREM.,33, 1314 (1941). (3) Kelley, K. K., U. S. Bur. Mines, Bull. 371 (1934). (4) Ruff, O.,and Josephy, B., 2. anorg. allgem. Chem., 153,17 (1926y. (5) Southard, J. C., J.Am. Chem. soc., 63,3142 (1941). PUBLISHBID by permission of the Director, U. S.Bureau of Mines.
Pectin as an Emulsifying Agent COMPARATIVE EFFICIENCIES OF PECTIN, TRAGACANTH, KARAYA, AND ACACIA HARRY LOTZICAR AND W. DAYTON MACLAY Western Regional ReJearch Laboratory, U. S. Department of Agriculture, Albany, Calif.
Pectin as an emulsifying agent is compared with gums tragacanth, karaya, and acacia in a study of aqueous emulsions of olive, cottonseed, and mineral oils under various conditions of acidity, ratio of oil to water, and concentration of agent by measurement of changes with time in the specific interfacial surface of the dispersed oil, hydrogen-ion concentration, and viscosity.
H E importation of gums tragacanth, karaya, acacia, and carob was approximately 24 million pounds in 1939 (9). Shipping difficulties have curtailed the importation of these gums, and it has therefore become advisable for the pharmaceutical, cosmetic, and food industries t o look for satisfactory domestic substitute materials. Pectin, potentially available from the culls and cannery wastes of apples and citrus fruits in amounts in excess of 50 million pounds per year, has shown promise. Goldner and other investigators (1,7) have declared pectin unsatisfactory as a substitute emulsifying agent for tragacanth and acacia. However, in a subsequent paper Goldner ( 2 ) reversed himself and pronounced pectin satisfactory. So far as can be ascertained, no quantitative study has been made on the relative merits of pectin and these gums as emulsifying agents. King and Mukherjee (3, 4), in defining the stability coefficient of an emulsion as the reciprocal of the rate of change of the interfacial area per unit area of fresh emulsion interface, established a quantitative criterion of emulsion stability. The present study was undertaken to determine quantitatively the stability of emulsions of olive oil, cottonseed oil, and mineral oil with water, stabilized with pectin, tragacanth, karaya, and acacia under diverse conditions of acidity, ratio of oil to water, and concentration of emulsifying agent. Changes in the emulsions were followed by measuring the pH, viscosity, and
' 80
O
O
c
T
I
0
Figure 1.
I
2
I
4
TIME
I
I
-
8
WGEEKS
Emulsion Interfacial Areas
ws.
Storage Time
