604
I S D USTRIAL AND ENGINEERI-VG CHEMISTRY
until placed in the refrigerator. The last set showed rust when examined after 5 days. It probably rusted the first night, when the temperature fell below the dew point. The second set did not show rust for some time because the tests were conducted during the summer months and therefore the dew point was not reached until the latter part of the summer. The traces of rust as found under the microscope were identified by placing a small drop of a solution of am-
Vol. 22, s o . 6
monium sulfocyanate in a 10 per cent solution of hydrochloric acid, on the supposed rust. A red color in the solution proved the presence of rust. From the results as shown in the accompanying table it seems that high humidity does not necessarily mean corrosion. Unless the moisture is precipitated on the metal, there will be no corrosion. Therefore, it is a matter of dew point and not humidity.
Use of Ethylene Dichloride in Lacquer Formulation' R. B. Frazier and E. W. Reid MELLOXINSTITUTE OF
INDUSTRIAL
RESEARCH, CNIVERSITY OF PITTSBCRGH, PITTSBURGH, PA.
velopment of a number of new solvents that adequately meet the requirements of the lacquer industry. On the other hand, the lacquer diluents have been limited to the aromatic and petroleum hydrocarbons, which have certain disadvantages but because of their low cost and availability have found universal use. Recently the attention of the industry has been directed to ethylene dichloride as a combined diluent and solvent. This product is a colorless liquid of characteristic odor, boiling a t 83.5' C. It is a n excellent solvent for resins and oils and in combination with alcohol becomes a solvent for nitrocellulose and cellulose acetate. It is available a t a low price and permits the use of minimum amounts of the more expensive lacquer solvents. There is a very definite prejudice against the use of a chlorinated compound by the lacquer industry. This i\ probably due to the tendency of the solvents. heretofore available to hydrolyze in the presence of moisture with the accompanying corrosion of the containers and discoloration of the lacquer. Ethylene dichloride, on the other hand, may he safely handled in the presence of water a t boiling temperature, in iron or other metal vessels without danger of corrosion. Sitrocellulose and cellulose acetate lacquers containing large quantities of ethylene dichloride have been prepared and stored in metal containers for two years with no indication of corrosion of the metal or diwoloration of the lacquer. Under identical conditions the more commonly known chlorinated solvents hydrolyzed readily, corroded the metal cans, and discolored the lacquer within a few days. The Iom flammability of ethylene dichloride is a distinct advantage. This compound is on the border line between the fire-extinguishing hydrocarbons and the combustible d v e n t s . Under the normal conditions of use this compound may be ignited by a flame, but when this flame is removed the draft from the combustion will extinguish the solvent flame. Being heavier than water, its flame is easily extinguished by water in contradistinction to the usual solvents and diluents, which will float and burn on the surface of the water and can be extinguished only by chemical means. Inhalation of the vapor of ethylene dichloride is not dangerous, although, as in the case of any organic solvent, it is to Presented before the Division of Paint 1 Received April 15, 1930. and Varnish Chemistry a t t h e 79th Meeting of the Amerlcan Chemical Society, Atlanta, Ga , April 7 t o 11. 1930
line (1). Solvent Action
Among the most important considerations in the use of ethylene dichloride as a diluent is its solvent action on the non-volatile constituents of the lacquer in the presence of and in conjunction with the usual lacquer solvents and diluents. The solubility of nitrocellulose and cellulose acetate was determined in several three-component solvent mixtures. These data are graphically expressed by means of triangular coordinate charts and indicate the percentage volume composition of solvent mixtures that would dissolve 8 per cent by weight of the cellulose ester. With 1/2-second R. S. nitrocellulose these data show: that the active solvents tolerate a larger amount of an ethylene dichloride-alcohol mixture than of either component alone; that the optimuni ethylene dichloride-alcohol mixture, indicated by the maximum tolerance, consists of from 60 to 80 per cent ethylene dichloride to 40 to 20 per cent alcohol; that the optimum mixture of ethylene dichloride and denatured ethyl alcohol requires but 1 per cent of an active solvent to give a complete sol ut io 11. T a b l e I-Solubility of Some G u m s a n d Resins 807, ETHYLEHE 80% ETHYLENE DICHLORIDE DICHLORIDE 20% DE2 0 7 ~DE-
ETHYLENEN A T U R E D
SCBST.ANCE DICHLORIDE .ILCOHOL Bodied linseed S oil S S Blown castor oil S S S Amberol S S Albertol S S Bakelite S S Cumar S S Camphor PS S Dammar S ss Elemi S S Ester gum Guaiac
ss
ETHYLENE NATCRED
SUBST.ANCE DICHLORIDE .%LCOHOI, Kauri I S Manila S Manila ester ss Mastic S Rosin S Glyptal I Sarpee Sandarac SS SS Shellac X'inylite A S l-inylite 80 S
S
Gliionite S s S = soluble 5 S = slightly soluble soluble
PS = partly soluble
I = Ln
This indicates that a mixture of 80 per cent ethylene dichloride and 20 per cent ethyl or methyl alcohol is practically a solvent for nitrocellulose, requiring only the addition of a very small amount of an active solvent to effect solution. Attempts to determine the dilution ratio of the 80-20 per cent mixture by the usual means were not successful, a- no precipitation of the nitrocotton occurred.
I S D C S T R I d L -4.\TD ESGISEERISG CHEXISTRY
C h a r t 1-Solubility of l/z-Second R.S. Nitrocellulose i n Mixtures of Methyl Cellosolve, Denatured Alcohol, a n d Ethylene Dichloride
GO5
C h a r t 3-Solubility of ’/r-Second R.S. Nitrocellulose in Mixtures of Cellosolve, Den a t u r e d Alcohol, a n d Ethylene Dichloride
CELLDMLYF
MZElnlLrNE WTYi ALCWOL
C h a r t 4-Solubility of I/r-Second R.S. Nitrocellul-se i n Mixtures of Cellosolve, Butyl Alcohol, a n d Ethylene Dichloride
DiCHLDRlOE
L O L D ~ N ~ U R C kD c o m
ETHILCHE OICHLORIDL
C h a r t 5-Solubility of ‘/%-Second R.S. Nitrocellulose i n Mixtures of Cellosolve Acet a t e , Toluene, a n d 88 Per Cent Ethylene Dichloride-20 Per Cent Denatured Alcohol
’..----
ETHYLENE DICHLORIDE
C h a r t 7-Solubility of ]/,-Second R.S. Nitrocellulose i n Mixtures of Cellosolve Acetate, Butyl Alcohol, a n d Ethylene Dichloride
C h a r t 6-Solubility of l/?-Second R.S. Nitrocellulose i n Mixtures of Cellosolve Acetate Denatured Alcohol, a n d Ethylene Dichlorid:
DENATURED hLC-
C h a r t 8-Solubility of ’/%-SecondR.S. Nitrocellulose i n Mixtures of Butyl Cellosolve, Toluene a n d 80 Per Cent Ethylene Dichloride-20 Per Cent Denatured Alcohol
The wlubility relation$ of a cellulose acetate, having an acetyl content of 41.3 per cent and a viscosity of 22.7 poises in a 10 per cent solution with 1,4-dioxan as solvent, indicate that ethylene dichloride has a higher tolerance for the uwal cellulose acetate solvents than any other diluent. A combination of ethyl or methyl alcohol and ethylene dichloride iq a solvent for the lacquer grade of cellulose acetate. The mixture of 70 to 80 per cent ethylene dichloride and 30 to 20 per cent alcohol has the highest solvent polTer and is recommended for general use. Ethylene dichloride and the solvent mixture of 80 per cent ethylene dichloride and 20 per cent ethyl or methyl alcohol are good Folvents for the usual type5 of gums and repins. Table I indicates that the 80-20 per cent mixture is the more
E ~ L V ( L mc*Lmm
C h a r t 9-Solubility of l/r-Second R.S. Nitrocellulose i n Mixtures of Butyl Cellosolve, Denatured Alcohol, a n d Ethylene Dichloride
universal solvent, the alcohol-soluble resins being only partially or slightly soluble in the ethylene dichloride. Use as a Base-Lacquer Solvent
The general properties of ethylene dichloride indicate its value in lacquer formulation. Its fairly rapid rate of evaporation necessitates the use of a small amount of a higher boiling solvent, as a “le\~eler,”in the base-lacquer solvent mixture. This will produce a film of higher gloss and a t the same time Fill meet the requirements of rapid drying. It can be readily recognized that the use of ethylene dichloride in the base-lacquer solvent mixture and the thinner will permit the formulation of fast-drying industrial lacquers of low cost. The fact that a mixture of ethylene dichloride and
606
INDUSTRIAL A N D ENGINEERING CHEMISTRY
TOLUENE
C h a r t 10-Solubility of '/r-Second R.S. Nitrocellulose i n Mixtures of Ethyl Acetate, Toluene, a n d Ethylene Dichloride
C h a r t 11-Solubility of I / ~ S e c o n d R.S. Nitrocellulose in Mixtures of Ethyl Acetate Denatured Alcohol, a n d Ethylene Dichloridi
Vol. 22, No. 6
BPXETnTLElL DIM!DRIOL LO%C€*l.inmu, h u m
C h a r t 12-Solubilitv of l/l-Recnnd R.S. Nitrocellulose in Mixtbres of B u t y l Acetate, Toluene, a n d 80 Per Cent Ethylene Dichloride-20 Per Cent Denatured Alcohol
BUTYL ACEThTE
A
dCi;L%Sk.-
C h a r t 13-Solubility of 1/r-Second R.S. Nitrocellulose i n MIxtures of Butyl Acetate, Toluene, a n d Ethylene Dichloride
C h a r t r14-Solubility of l/r-Second R.S. Nitocellulose i n Mixtures of Butyl Acetate Butyl Alcohol a n d 80 Per C e n t Ethylene Di: chloride-20 Pdr Cent Denatured Alcohol
ElmLLWL DICHLEmDC
C h a r t 15-Solubility of l/r-Second R.S. Nitrocellulose i n Mixtures of Butyl Acetate, Butyl Alcohol, a n d Ethylene Dichloride
RNTWETATE
E ~ Y E P I EDI~UXIIDE
C h a r t 16-Solubility of l/Z-Second R.S. Nitrocellulose i n Mixtures of Pentacetate, Toluene, a n d Ethylene Dichloride
C h a r t 17-Solubility of '/%-Second R.S. Nitrocellulose i n Mixtures of P e n t a c e t a t e Toluene, a n d 80 Per Cent Ethylene Dichlo: ride-20 Per Cent Denatured Alcohol
ethyl or methyl alcohol has an almost infinite dilution ratio requires particular attention in the choice of the highboiling solvent. This solvent should have high solvent power for both the nitrocotton and resin and good resistance to humidity. As a general rule Cellosolve acetate, butyl Cellosolve, and pentacetate are the most satisfactory solvents, although in some formulas butyl acetate and Cellosolve may be used. Some formulators believe that a lacquer solvent should exhibit a straight-line or constant rate of evaporation. The observation of a large number of lacquers in industrial applications has not upheld this idea, but indicates the necessity of maintaining the proper solvent balance in the last solvents to evaporate from the film. A solvent mixture that gives a rapid initial set and a slow final set
C h a r t 18-Solubility of l/z-Second R.S. Nitrocellulose in Mixtures of Pentacetate, Pentasol, a n d Ethylene Dichloride
tends to produce a film of increased toughness and gloss. The modern factory production schedule demands a fastdrying lacquer, giving the minimum time between successive applications. The proper use of ethylene dichloride with particular attention to the Pigh-boiling solvents permits the formulation of a lacquer that meets the most rigid production schedule. I n the formulation of lacquer or thinner mixtures the use of the solubility charts is valuable in determining the most economical formula of the proper solvent power. Several characteristic base-solvent formulas which have been tested and found to be satisfactory are given in Table 11. These formulas are indicated as examples and should be changed to meet the demands and requirements of a specific lacquer.
INDUSTRIAL A N D ENGINEERISG CHEMISTR 2’
June, 1930
i;dit;r” *.
~. ....,
BOZCTHYLLNEDiCnLDiilDE
I
ETMLENE DICHLDRIIX:
ZObDLNhTURED hLCOWL
TOWLNL
C h a r t 20-Solubility of Low-Viscosity Cellulose Acetate in Mixtures of Methyl Cellosolve Toluene a n d 80 Per C e n t Ethyle n e Dichlhride-20 i e r C e n t Denatured Alcohol
C h a r t 19-Solubility of Low-Viscosity Cellulose Acetate in Mixtures of Methyl Cellosolve, Dioxan, a n d Ethylene Dichloride
607
C h a r t 21-Solubility of Low-Viscosity Cellulose Acetate in Mixtures of Methyl Cellosolve Cellosolve Acetate a n d 80 Per C e n t Eth$lene Dichloride-20 Per C e n t Den a t u r e d Alcohol
PIFTHIL CELLOEWE
j..-j_”.n
EniYLENC DlCHLDRiDE
5CLYhTDK
Table 11-Base-Lacquer FORMCLA Ethylene dichloride ToI uene Denatured alcohol Butyl alcohol Ethyl acetate Butyl acetate Cellosolve Pentacetate Cellosolve acetate Butyl Cellosolve
1 40 30 10
10 5
2 50 20 10
3 75
10 5
10
Solvents 4 30 30
5 30 30
6 70
15 10
10 10 13
10
15
10
7 35 30 10 5 15
-
10
0
8 25 40 5
Ethylene dichloride
T o1uen e
Xylene Denatured alcohol Butyl alcohol Ethyl acetate Cellosolve Cellosolve acetate Butyl acetate Pentacetate Butyl Cellosolre
1 72 2.5
2 67
25
a
5
3 45 30
4 40 30
5 40 35
6
7
35
40 30
10
10
13
30 15
15
1,o
3 8
7
!
of the triangular coordinate charts and subsequently tested in actual use, are shown in Table 111. The solvent powers of these thinners are quite high and considerably above the usual demands.
15
Table 111-Thinners
FORMULA
C h a r t 24-Solubility of Low-Viscosity Cellulose Acetate in Mixtures of Dioxan Toluene a n d 80 Per C e n t Ethylene Di: chlorideL20 Per Cent Denatured Alcohol
Dilution Ratios
10
10
~
5
5
CTHXENE DIC’~WIIDL
T~UENC
C h a r t 23-Solubility of Low-Viscosity Cellulose Acetate i n Mixtures of Dioxan, Toluene, a n d Ethylene Dichloride
C h a r t 22-Solubility of Low-Viscosity Cellulose Acetate in Mixtures of Methyl Cellosolve, Solvatone, a n d Ethylene Dichloride
10 in
5 5
5
Use as a Thinner
The dilution ratio of a solvent is a measure of its solvent power and is important in the appraisement of a solvent. It is usually obtained by dividing the volume of the diluent that must be added to produce incipient precipitation of the nitrocellulose by the volume of the solvent in which the cellulose ester is dissolved. The final concentration of the cellulose ester should be approximately 8 per cent. The comparative dilution ratios of a number of the more commonly used solvents with three diluents are given in Table IV. The dilution ratio of 80 per cent ethylene dichloride and 20 per cent alcohol with these solvents approaches infinity and cannot’ be determined by the method used. Table IV-Dilution
The usual type of base lacquer requires a thinner that is a solvent for nitrocellulose and in some cases for the resin. It must cut the base lacquer readily with little stirring and ill work properly in the produce a mixed lacquer that w spray gun. While the thinner components should be chosen with the same care exercised in the formulation of a base lacquer, it is not essential or desirable to maintain as high a solvent power. The graphical solubility data are of special value in the formulation of thinners of low cost. Several thinner type formulas, which were formulated by the use
Ratios
ETHYLENE
V. M. & P. DICHLORIDETOLUENE NAPHTHA 8.6 4.6 0.73 6.8 4.0 0.68 5.4 3.5 1.20 4.3 3.1 1 25 9.2 4.3 0 35 3.7 2.5 1 35 7.6 4.7 0.95 2.7 1.5 1.20 4.2 2.5 0.80 3,s 1.9 1.27 4.3 3.0 1.85 a Solvatone is a mixture consisting of approximately 80 per cent acetone, 10 per cent isopropyl alcohol, and 10 per cent toluene. SOLVENT Acetone Solvatonea Ethyl acetate Isopropyl acetate Methyl Cellosolve Butyl acetate Cellosolve Butyl propionate Cellosolve acetate Pentacetate Butyl Cellosolve
INDUSTRIAL A S D ENGINEERING CHEMISTRY
608
The high dilution ratio of ethylene dichloride indicates the economy of this product in lacquers and thinners. Use in Cellulose Acetate Lacquers
The solvent mixture required in cellulose acetate lacquer depends largely upon the type of acetate used. Completely acetylated cellulose (44.8 per cent acetyl) is relatively insoluble in all ordinary solvents and is therefore unsuited for use in lacquers. The solubility increases rapidly with a decrease in acetyl content, and a cellulose acetate containing 35.5 per cent acetyl is generally considered to be too soluble for ordinary lacquer work as it is completely dissolved by a mixture of water and acetone. Cellulose acetates containing from 38 to 42 per cent acetyl are generally used in lacquers and may be obtained in a wide range of viscosities. The type that has practically the same viscosity as ordinary ‘/*-second nitrocellulose may be used in formulating a lacquer with a high percentage of solids. The solubility data of this type of cellulose acetate in various solvent mixtures are used as an example of solubility in general and to ,-hom the possibilities of solvent formulation. With the exception that solvent mixtures for cellulose acetate lacquers must contain a higher percentage of active solvents than a mixture for a nitrocellulose lacquer to obtain a Satisfactory film, the same methods are followed in their formulation. The choice of solvents naturally depends upon the drying time desired and the demand nil1 undoubtedly be, as it has been in the case of nitrocellulose lacquers, for a rapid drying lacquer that will be applicable in industrial finishing. One of the simplest cellulose acetate solvents of the rapiddrying type is a mixture containing 70 per cent ethylene dichloride and 30 per cent denatured alcohol by volume. This
-
Vol. 22, Xo. 6
mixture has a dilution ratio of 0.4 with toluene, which may be considered a practical margin of safety. By using this mixture as the basic solvent, the drying time may be retarded by the addition of a medium-boiling solvent and a medium-boiling diluent to produce better flow out of the lacquer. Solvents such as 1,4-dioxan and methyl Cellosolve may be used in considerable quantity without materially increasing the drying time, while the high-boiling solvents, such as diacetone alcohol, Cellosolve acetate, and butyl Cellosolve, when used in smaller amounts, have their greatest use in raising the blush resistance of the lacquer. Several type formulas that have been used in cellulose acetate lacquers are shown in Table T’. Table V-Cellulose Formulas 1 2 3 Ethylene dichloride 70 70 70 Toluene Denatured alcohol PO 20 20 Ethyl acetate Solvatone Methyl Cellosolve 10 1,4-Dioxan Diacetone alcohol Cellosolve acetate Ethyl lactate 10 Butyl Cellosolre 10
Acetate Lacquers 4 5 6 7 60 50 50 70 10 15 IO
10
30
8 70
13
PO 13
15 15
9 40 20 10
10 60
30
10
20
15
10
10
5
The solubility data of cellulose nitrate and cellulose acetate tvith the more common solvents and diluents with ethylene dichloride are shown on the triangular coordinate charts. These data indicate the value and economy of this product in the formulation of lacquers. Literature Cited (1) G. S. Pub. Health Service, Pub. Health Rept. 46, N o . 5 (January 31, 1930).
Use of Azeotropic Data for Calculating General Properties of Binary Systems’ Clyve Allen CHEMIC.4L
LABORATORY, UNIVERSITY O F CALIFORNIA, BERKELEY, CALIF.
H E rapidly growing lists of binary constant-boiling mixtures now available, in addition to furnishing the data for which they were primarily intended, may readily be made in many cases to yield much more information; partial pressures and related properties may be estimated for the entire range of composition. Through the relations indicated in this paper a practical method is offered for gaining information concerning the many systems which deviate considerably from Raoult’s law a t finite concentrations, yet not sufficiently to form two liquid phases. For this purpose the equations ( 2 , 3, 4 )
T
RT In ( a l / N I ) = bNZ2 RT In (a,/NJ = ( b
+ cNz3 + d N Z 44- . . . .
(1)
+ 3 / 2 c + 2 d ) N 1 * - ( c + 8/d).N.I.3.+ dN14+ (2)
are eminently suitable. I n these equations the a’s are the activities and the N’s the mol fractions of the components, R is the gas constant, T the absolute temperature, and b, c, d, etc., are empirically determined quantities constant a t a given temperature and pressure with respect to composition. 1
Received March 21, 1930.
These equations are valid for solutions which obey Raoult’s law in very dilute solution-i. e., Limit (al/N,) = 1 NI +1
Limit ( a z / N z )= 1 Ni +1
(3)
Equation 2 follows from Equation 1 by Duhem’s relation. The thermodynamic significance of these equations and methods for estimating and for calculating the quantities b, c, etc., have been set forth by Hildebrand (2, 3, 4 ) . I n applying Equations 1 and 2 to solutions composed of two volatile components, we may without appreciable error replace each of the activities by the equivalent p / p o , where p is the partial pressure of a component and p o its vapor pressure when pure. A number of investigators have shown that the isothermal behavior of a great many systems can be represented quite closely without necessitating powers of N1 and N z higher than the third ( 7 , 8, iO)-i. e., d , etc., may be assumed negligibly small. Moreover, Hildebrand (3) has found that for many systems b, c, etc., vary but little with temperature. Hence, whenever we have the values of the partial pressures a t a given composition and temperature and know the vapor pressures of the pure components a t that temperature, Equations 1 and 2 then enable us to
