2500
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pression set a t -35" and 194" F. The results of the tests are given in Table IV. The data show that all of the low-styrene copolymers were at least equal to GR-S 10 in tensile properties and a few excelled GR-S 10 in tensile strength. The low-styrene copolymers had about the =me hardness a t 82" F. as GR-S 10, but they were softer a t -35" F. They had lower compression set a t -35" F. than GR-S 10. The 30 to 50% lower cold compdssion sets of these practical stocks, in comparison with the compression sets of the corresponding experimental stocks described earlier in this report, were due to the presence of the ester plasticizer in the practical stocks. I t thus appears that butadiene-styrene copolymers containing less combined styrene than regular GR-S or GR-S 10, and possibly prepared a t a lower polymerization temperature than these rubbers, are a better choice for use in manufacturing gaskets for low temperature service. ACKNOWLEDGMENT
Much of the testing in this investigation was done by John M. Holloway.
Vol. 43, No. 11
LITERATURE CITED
Beu, K. E., Reynolds, W. B., Fryling, C. F., and McMurry, H. L., J. Polymer Sci., 3,465 (1948);Rubber Chem. and Technol., 22,356 (1949). D'Ianni, J. D., Naples, F. J., and Field, J. E., IND.ENG.CHEM., 42,95 (1950).
Gehman, S. D.,Jones, P. J., Wilkinson, C. S., and Woodford, D.E., Ibid., 42,475(1950). Graves, F.L., Rubber WorEd, 113,521 (1946). Johnson, P.H.,and Bebb, R. L., IND.ENQ.CHEM.,41, 1577 (1949).
Juve, R. D., and Marsh, J. W., Ibid.,41,2535 (1949). Lucas. V. E..Johnson. P. H.. Wakefield. L. R.. and Johnson. B. L,, Ibid.', 41,1269 (1949): Meyer, A. W., Zbid., 41, 1570 (1949). Morris, R. E.,Hollister, J. W., and Barrett, A. E., Ibid., 42. 1581 (1950).
Morris, R. E., Hollister, J. W., and Mallard, P. A., Rubber
wmia, 112,455(1945). United Carbon Co., Charleston, W. Va., "Today's Furnace Blacks," 1947. U. S. Military Specification MIL-R-900-4 (March 23, 1950). RECEIVED March 2 , 1951. Presented before the Division of Rubber Chriuistry of the AUERICAN CHEMICAL SOCIETY, Washington, D. C., 1951.
Translucent Films of Acrylic Acid Esters-Acrylonitrile Copolymers J -
FRED LEONARD, IRVING CQRT, AND T. B. BLEVINS A r m y Prosthetics Research Laboratory, A r m y Medical Center, Washington, D . C.
Translucent elastomeric films in pastel shades, low pressure cast from polymeric emulsions, are required for the fabrication of skin-colored cosmetic gloves to be worn by amputees. In order to augment strength properties without unduly affecting translucency, investigationof the reinforcing effect of an isotropic silica was undertaken. Cast films containing the silica showed an enhancement in strength properties over uncompounded films, and films ' containing up to 40 parts of silica per 100 parts of dry COpolymer suffered only slight loss in translucency in the unstrained state. However, as the compounded films were strained they showed a marked increase in whiteness and opacity, as compared to uncompounded films. Possible explanations of this effect are given. Through this study it has been found possible to reinforce latex copolymers in emulsion form with an aqueous dispersed filler, which did not appear to increase the opacity of the cast film.
T
RANSLUCENT elastomeric films in pastel shades, cast a t low pressure from polymeric emulsions, are required for the fabrication of ski-colored cosmetic gloves to be worn by amputees. In the course of a study of the application of emulsion polymerized copolymers and tripolymers of ethyl acrylateacrylonitrile and ethyl acrylate-butyl acrylate-acrylonitrile for this purpose, it became necessary to investigate the possibility of increasing the tensile and tear strength of elastomeric films cast from emulsions of these polymers, through the use of reinforcing fillers that would impart neither color nor inordinately greater visual opacity. A survey of the refractive indexes of white and colorless inorganic compounds indicated that the refractive indexes of the
various silicas were of the same order of magnitude as the determined refractive index of an ethyl acrylate-acrylonitrile copolymer used in the investigation, and it was decided to test silicon dioxide as a reinforcing agent for these copolymers. Other workers have investigated silica of fine particle size as a reinforcingfiller in GR-S (6), natural rubber (I), and vinyl copolymers ( 4 ) . EXPERIMENTAL
MONOMER PURIFICATION. Ethyl acrylate and butyl acrylate (Rohm & Haas) were washed in a separatory funnel with a solution containing sodium hydroxide (5% w./v.) and sodium chlcride (20% w./v.), until the washings were colorlesa, and then with demineralized water, until the washings were neutral to litmus. Acrylonitrile (American Cyanamid) was fractionated through a 16-inch column packed with glass helices a t 10 to 1 reflux ratio (boiling point 77.3" C. a t 760 mm.). The monomers were stored at 0" C. until ready for use. POLYMER RECIPE Monomers Demineralized water Santomerse D Potassium persulfate C.P. Sodium thiosulfate pe'ntahydrate, C.P. Potassium chloride, C.P.
% 55 45
0.010 1.23
]
Based oonoentration on monomer
0.010 0.20-0.25
PREPARATION O F POLYMERS. To a three-necked flask immersed in an ice bath at 0" C. and fitted with a reflux condenser, stirrer, copper-constantan thermocouple in a stainless steel well, and nitrogen inlet tube was added a solution of Santomerse D (Monsanto Chemical Co.) in demineralized water containing the potassium chloride. After 5 minutes of stirring, oxygen-free nitrogen was bubbled through the solution, and continued throughout the course of the reaction. After 0.5 hour the mixed monomers in the desired concentrations were added. TWOhours later, the potaissum persulfate and sodium thiosulfate were introduced. The polymerization started after an induction period of 10 to 30 minutes (as determined by an approximately 0.5" temperature rise recorded on a 4-point Brown recorder). The reaction was allowed to proceed for 24 hours.
November 1951
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
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TABLE I. STRESS-STRAIN PROPERTIES OF SILICA-REINFORCED 90-10 ETHYLACRYLATE-ACRYLONITRILE COPOLYMER Silica Parts per 100 Parts Polymer
0 10 20 30 40
Tensile Strength, Lh./Sq. Inch 710 903 918 1242 la87
Ultimate Elongation,
%
788 710 634 629 594
3007 Tensile S%rase Lb /Sq. inch 71 83 155 272 a63
Tear Resistance, Lb./Inch
..33
68 90 112
To remove excess monomers from the reaction mixture, several drops of an emulsion containing 4 grams of D.C. Antifoam A dissolved in 20 grams of toluene, emulsified with 20 rams of a 2% aqueous solution of Santomerse D, were added to t i e latex, and a vacuum of 10 to 20 mm. was drawn on the flask a t room temperature for 3 houra. The flask was then placed in a water bath a t 65' C., and evacuated a t 30 mm. for 1 hour. After this treatment, the latex was essentially odor-free and had a solids content of 52 to 55%. LATEXCOMPOUNDING. A colloidal dis ersion of silicon dioxide in water, obtained from the Monsanto ehemical Co. under the trade name of Silica Aquasol WX-1, was used in this work. The silica dispersion in the desired amount was added directly to the latex with moderate stirring. The compounded latex appeared to be stable, and there was no evidence of separation of the silica on standing for one month. CASTING FILMS.The films were cast in cylindrical plaster of Paris molds, and dried as described in a previous publication ( I ) . TESTING PROCEDURES. Tensile strength, elongation, and 300% tensile stress were all determined according to ASTM D 4 1 2 4 1 using die C. The testing machine was a Scott L-6 rubber tester, and the jaw separation of 20 inches per minute was used. All samples were conditioned for 7 days a t 50% relative humidity and 75 f 2' F. prior to testing. Tear strength was determined as above using the Graves die. REFRACTIVE INDEX.The refractive index of the 90-10 copolymer of ethyl acrylate and acrylonitrile was determined over a range of temperatures from -40' to 25' C. according to the method of Wiley (7) with slight modifications for temperatures 0 O.,using an Abbe refractometer. below ' The refractive index of the silica in Silica A uasol WX-1 was determined according to the Becke line methoj using a polarizing microscope (3). The sample for this determination was obtamed by evaporating to dryness at 50' c. a 10-m). Portion of the silica dispersion.
t
f
$
"*'
Figure 1. Refractive Index vs. Temperature of Ethyl Acrylate-Acrylonitrile Copolymer
tive index of the polymer a t room temperature-Le., 20' to 25' C.-where the index varied from 1.4735 to 1.4740, The silica used was found to be isotropic, with a refractive index of 1.463 a t spencer 25" c. This was considered t o be Sufficiently close to that of the polymer so that film reinforced with silicon dioxide would not suffer much loss in transparency. Consequently, to a 90-10 ethyl acrylate-acrylonitrile copolymer latex were added varying quantitiw of silica up to 40 parts per 100 parts of dry copolymer. Visual RESULTS AND DISCUSSION observation of the silica-reinforced films showed only a slightly greater opacity than an unloaded copolymer film. The refractive indexes of a 90-10 ethyl acrylate-acrylonitrile copolymer a t varying temperatures are shown in Figure 1. ParThe reinforcing effect of the silica is shown in Table I, in which ticularly pertinent far the purposes of this discussion is the refraccomparisons are made between an unloaded 90-10 ethyl acrylateacrylonitrile copolymer and the same copolymer compounded with varying amounts of silica up to 40 parts per 100 TABLE 11. SILICA-REINFORCED ACRYLIC ACID ESTERS-ACRYLONITRILE TRIPOLYMERS parts of copo]ymer~ ~h~ data indicate Comonomers Silica. Parts Tensile Ultimate 300 0 Tensile Tear that aa the concentration of silica is inEthyl Aqry!oButyl per 100 Parts Strength, Elon ation, &ss Resistance, creased from 0 to 40 parts, the tensile acrylate nitrtle acrylate Polymer Lb./Bq. Inch 6 Lb./Sq. inch Lb./Inch 77.5 12.5 10.0 0 833 725 78 40 strength increases from 710 to 1387 77.5 12.5 10.0 20 1050 600 176 63 pounds per square inch, the tear strength 75.0 12.5 12.5 0 906 684 78 22 75.0 12.5 12.5 20 1012 626 202 48 from 33 t o 112 pounds per square inch, 80.0 12.5 7.5 0 725 725 54 35 and the 300% tensile s t m from 71 to 80.0 12.5 7.5 20 932 642 195 64 70.0 12.5 17.5 0 644 627 98 49 362 pounds per square inch. The ulti70.0 12.5 17.5 20 1207 600 250. 67" 67.5 12.5 20.0 0 573 824 mate elongation decreased from 788 to 67.5 12.5 20.0 20 917 630 177. 58a 594%. 57.5 12.5 30.0 0 355 835 57.5 12.5 30.0 20 703 660 14sa 57.a Table I1 gives further evidence of the 37.5 12.5 50.0 0 398 810 .. 37.5 12.5 50.0 20 823 . 806 640 i45 56 reinforcing and stiffening action of silica 80.0 10.0 10.0 0 643 70 31 on tripolymers of ethyl acrylate-butyl 80.0 10.0 10 0 30 944 696 170 51 85.0 10.0 5.0 0 743 755 80 a8 acrylate-acrylonitrile. In each case the 85.0 10.0 25.0 30 1000 656 172. 62. tensile, tear, and 300% tensile stress 65.0 10.0 25.0 0 427 870 65.0 10.0 25.0 30 849 712 iioD 4Q. increased and the ultimate elongation 60.0 10.0 30.0 0 280 810 60.0 10.0 30.0 30 0 257 696 718 900 liio .. 444 decreased. 50.0 10.0 40.0 50.0 10.0 40.0 30 553 780 70 33 During the determination of the ten75.0 10.0 15.0 0 422 733 74 34 75 0 10.0 15.0 30 1074 654 192 69 sile properties of the films containing 70 0 10.0 20 0 0 708 785 77 33 silica it was observed that as the films 70.0 10.0 20.0 30 932 635 204 60 were elongated, they gradually became Values too low to obtain aocurate results. visually more white and opaque, until
INDUSTRIAL AND ENGINEERING CHEMISTRY
2502
TABLE 111.
WIT11
SAMPLE
Silica-Reinforceda Acrylate Unreinforced Acr late Acrylonitrile Tripolymerb Acrylonitrile Tripogmerb Elongation, % Ed Elongation, % Rd 0 30.8 0 26.2 50 30.5 100 27.4 225 34.4 200 29.4 250 .51.1 250 31.1 450 55.2 350 32.6 550 59.4 300 33.9 600 63.1 650 33 2 625 63.9 ” 57.5 ethyl acrylate. 30% rutyl acrylate. 12.5% acrylonitrile. b 20 parts silica per 100 parts tripolymer.
near the ultimate elongation the samples were very white and opaque. The unloaded film, on the other hand, showed this effect only slightly. Some measure of the increase in whiteness may be observed from Table 111,in which the results of the determination of luminous reflectance, &, measured with a Hunter colorimeter (Gardner Laboratories, Inc., Bethesda, Md.), are listed a t various elongations. A white opaque porcelain tile plate used as a standard has an Rd of 79.5 when measured on this instrument. It may be observed from Table III that with the loaded stock, there is over a twofold increase in luminous reflectance from 0 to 625% elongation, whereas in the case of the unloaded stock the increase is approximately 1.2-fold. It is also significant for the reinforced film that up to22570 elongation the increase in white-
Vol. 43, No, 11
ness is relatively small, but beyond 225% elongation there is a large increase in whitenesR as evidenced by the rise in Rd. Concerning the whitening of strained silica-reinforced films, two possibilities exist. In the first instance, the effect may be due to the stress-induced orientation of the polymer chains contributing to a change in refractive properties of the copolymer films. If such is the case, the refractive indexes of the silica and polymer film, initially equivalent, may be sufficiently different after elongation to permit observation of the silica particles in the film matrix. That the refractive properties of a copolymer film, per se, change as the film is elongated can be substantiated by viewing the unstrained and strained film between crossed polaroids. Unstrained the film is isotropic, whereas the elongated film is anisotropic. The second instance concerns the possibility that when t h e elastomeric copolymer film i s elongated sufficiently, the elastomer may pull away from the particles of silica in the axis of stress, causing separation of the silica from the copolymer film, and whitening (6). LITERATURE CITED (1) Allen, E. M., Gage, F. W., and Wolfe, R. F., Rubber Age, 65, 297 (1949). (2) Blevins, T. B., Wright, W. S., and Leonard, F., Anal. Chem., 22. 1205 (1950). (3) Chamot, E. M., and iMason, C. mi., “Handbook of Chemical Microscopy,” Vol. l, p. 362, New York, John Wiley & Sons, 1944. (4) Moore, R. L., IndiaRubber World, 118,232-4 (1948). (6) Schippel, H. F., IND. ENG.CHEM.,12,33-7 (1920). (6) Schmidt,E., Ibid., 43,679 (1951). (7) Wiley, R. H., J . Polymer Sci., 2, 10 (1947).
RECEIVED M a y 25, 1951.
Digital Computers for Trial and Error Calculations of Distillation Design ARTHUR ROSE, THEODORE J. WILLIAMS, AND HARRY A. KAHN The Pennsylvania State College. State College, Pa. Trial and error calculations are frequently essential in the solution of a variety of engineering and scientific problems, and they often involve extensive computation. This paper describes the use of IBM computers for performing automatically the trial and error calculatione involved in the choice of the proper reflux ratio for a continuous distillation of a binary mixture. The same general method m a y be used for more complex distillation problems and for trial and error calculations of other unit operations.
T
HE advantages of commercially available punched card digital computers for various types of straightforward plateto-plate distillation calculations have been described (5). Methods for the stepwise, plate-to-plate calculation of batch distillation curves with appreciable holdup and for plate-to-plate calculations of steady-state or continuous distillation are applicable to multicomponent as well as binary mixtures, and to cases of variable relative volatility and nonadiabatic operation; plate efficiencies other than 100% can also be taken into account. These procedures offer great savings in time and labor as well as
the elimination of human errors, advantages of major impartance when many plates or many steps are involved in the calculations. The present paper describes the use of the recently developed IBM card-programed electronic calculator for some of the more It ngthy and difficult distillation problems which require a trial and error procedure for successful solution. As an example, there is chosen the problem of estimating the reflux ratio required for separation of a specified binary feed into specified products in a column with a certain definite number of plates. The primary example assumes constant relative volatility, adiabatic column operation, and a 100% plate efficiency. A Recond example, dealing with the corresponding case when relative volatility is not constant, illustrates the approach when one or more of the usual simplifying assumptions are not justified. Simple extension to multicomponent problems of the trial and error type is not possible because the limits of the storage capacity of the machines are reached, and because of the additional degrees of freedom inherent in the general multicomponent problem. The methods illustrated herein are entirely adequatc, however, for many multicomponent problems of practical interest. Thus, Lewis and Matheson-type calculations ( 1 , .$) can be Rolved with ease, as can dny multicomponent problem where all
