A Versatile Nomograph for Chemical Engineering Calculations E. L. McMILLEN Iowa State College, Ames, Iowa
A nomographic chart is described which makes possible direct multiplication and division by numbers raised to any power. With this chart it is possible to solve directly a large variety of equations involving fractional exponents, which are encountered in chemical engineering calculations, thus saving considerable time as contrasted to slide rule or logarithmic computations. Accuracy of computation with this chart has been found comparable to that obtained with the slide rule. A combination of slide rule with nomographic chart embodying the same principle is described.
rithm tables, logarithmic graph paper, the ordinary slide rule, or the log-log slide rule, However, none of these methods furnish a direct means for arriving a t a solution of the equations listed, since the terms raised to the fractional exponents must be combined with the other terms by the ordinary processes of multiplication and division. I n the case of the slide rules this usually means transferring a figure from one scale to another before being able to proceed farther. Stated in another way, the slide rule is not capable of solving these equations in the straightforward or direct manner with which it performs simple multiplication and division. If a large number of such computations are to be made, the work involved even on the slide rule becomes tedious. In such a case it is feasible to construct a nomograph for the particular equation involved. The procedure of devising a new nomograph for each new equation involves considerable effort and necessitates keeping a large number of charts on hand. Realizing the advantages of a flexible or universal nomograph that would be capable of performing the operations indicated in the equations listed and many others of a similar nature, Figure 3 was constructed. One well-known form of logarithmic alignment chart (Figure 1) will perform the operation of multiplying two terms, A and B , the second of which is raised to some exponent, E , yielding the result on a logarithmic scale between the first two scales. When the two original scales, A and B , are constructed with the same moduli, the result, X , will be found upon a line located 1/(1 E ) fraction of the distance from the B scale to the A scale, and the modulus of the scale upon this line will be 1/(1 E ) as large as the modulus used for the A and B scales (i. e., the modulus of X is to the modulus of A as the distance from B t o X is to the distance from B to A ) . Since the modulus of the X scale is directly proportional t o its distance from the B scale, it is unnecessary to scale off line X . The result may be read by laying a straight edge from unity
I T H I N recent years a great variety of equations, mostly of an empirical nature, have become available for the calculation of certain variables or coefficients in the unit operations of chemical engineering. These equations are valuable in the design of equipment, particularly in the field of heat transfer and fluid flow. Typical of these equations are the following examples: The Dittus-Boelter equation (1) for film coefficient of heat transfer to a liquid flowing within a pipe: h = 0.0225 - ($P)~.~(C+J)~.' __
The Nusselt equation (3) for heat transfer coefficient of a condensing vapor film outside of a horizontal pipe: h
=
0.725
4'%G
The heat transfer coefficient for an air film when air flows at right angles past staggered vertical pipes ( 5 ): G0.69
h = a -DO.31
(3)
The pressure drop through a gas absorption tower packed with dry Raschig rings ( 2 ) : hul.86 0 8 3
A P = 0.0846
The pressure drop in gases passing through tempering coils (4):
+
+
The power consumption of a paddle agitator ( 6 ):
H. p. =
0.000~2QL2.75~0.14N2.86p0.86D1.1W0.~H0.6
(6)
Most of these equations contain fractional e.xponents. A number can be raised to any power through the use of loga71
VOL. 30. NO. 1
IKDUSTRIAL AND ENGINEERING CHEMISTRY
72
on the B scale through the point upon the X scale and noting the result upon the A scale. This procedure of reflecting the answer to the A scale eliminates the necessity for scaling the central line and also places the result upon the A scale so that further multiplication by another exponential term may be accomplished. In Figure 1 exponent E is 2, and the case illustrated is 10 multiplied by lo2; the result as reflected onto the A scale is 1000.
€ 'ON \
\
\ \ \
\
i:
100
' 0 ° 7
i
0.I-J
A
shown. The original chart, 30 X 20 inches in size, has 4-inch logarithmic cycles upon the A and B scales covering the range 0.001 to 10,000. For greater accuracy when dealing with figures of smaller size, the C and D scales were constructed upon a 12-inch logarithmic cycle. Thus it is intended that the A and B scales should be used together, likewise the C and D. However, by using the A and D scales together,3it is possible to extend the range of exponents from 0.15 to GO.(i. e., exponents three times as large as those shown on scale E ) . The operation of the chart may be accomplished with either one or two straight edges. When using a single straight edge, it is necessary to make light pencil marks upon the chart. Since the result of either a multiplication or division by an exponential term is always read upon the -4(or C) scale, it is obvious that any number of subsequent similar operations may be performed and that the final numerical result is the only one that need be read from the chart. The decimal point is definitely located, thus eliminating uncertainty regarding its position in the final result. Since fewer operations are involved than when using the slide rule, results may be obtained much more quickly and, on the original large chart, with accuracy comparable to the slide rule.
IbO1.
FIGURE1. BASICPRINCIPLE OF MULTIPLICATION SEVERALEXPONENTIAL TERMS
BY
z = AB2
\ \ I
The combination of multiplication and division by exponential terms is illustrated in Figure 2, utilizing typical numerical values secured in laboratory experiments in Equation 3:
--DO. ai
\
(0L27)0.68 h = aGO.69 = 11.5 .--
i
(1.315)0.a'
a = 11.5 (constant obtained from Chemical Engineers' Handhnnk)
G = 0.27 lb./(sq. ft.)(sec.) D = 1.315 in.
T o multiply 11.5 by (0.27)0.69, connect by means of a straight edge 11.5 on the A scale with 0.27 upon the B scale, locate the point where this straight edge crosses the vertical line where E equals 0.69, then through this point and the unity of the B scale place another straight edge, which will indicate the result of this multiplication upon the A scale. Keep the second straight edge in place and proceed with the division by (1.315)0.31, which is done in the reverse fashion. Locate the point where the second straight edge crosses the vertical line for E equals 0.31; by laying the first straight edge through this point and the value of D (1.315) upon the B scale, the value of h wiIl be found upon the A scale. The final chart (Figure 3) is comprised of a number of these simpler charts superimposed upon one another for the range of exponents as shown on the E scale from 0.05 to 20. Actually all exDonents from zero to infinity are within the range of the chart; but accuracy diminishe; rapidly beyond the range
Ad 0.I
FIGVRE2. METHODFOR COMBINING MULTIPLICATION AND DIVISION BY EXPONENTIAL TERMS 11.5(0.27)0.~9 (1.315)0.31
Plans have been drawn for various mechanical or electrical calculating devices based upon the same principle which will simplify the use of the straight edges. One of the simplest of these (Figure 4) is a combination nomograph and slide rule, capable of performing all the operations possible upon the chart of Figure 3 without the multiplicity of unscaled lines corresponding to the various exponents. Any number upon the B scale may be raised to any exponent E by laying a straight edge from the number through the exponent to the AI scale upon which the result will be found. To multiply this result by another number, set the second number on the
JANUARY, i938
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J
A
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e
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E Froum 8. UX~VUWAL NOYOGRAPH
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 30, NO. 1
scale opposite the index of tlie AI male and tlie result will be found upon the A scale opposito tlte value of the exponential tcrm upon the AZ scltle. It is evident that ~ccumulationof results of BUCCCISsive multiplications or divisiono by exponential terms will take place upon the A scale, Rime this device has several logarithmic cycles, it would need to be large for reasonable accuracy. It is not necessary that the exponent scale E be at right angles to the parallel AI and Bscales; any other angle except zero would theoretically be possible. When dealing with numbers always larger than unity, a 2 form of chart may be more useful.
Literature Cited (1) Dittus and Boeltcr, Unio. Cdij. Pub. Eng., 2, 443 (1asa; (2) Mach, Forsch. Gebiete Ingmtieurw., 6, Forschungsheft,
.
16’ AI
375 (1935). (3) Nusselt, 2. Ver. deut. Ing., 60,541, 569 (1916). lid (4) Perry, Chemical Engineers’ Handbook, p. 742, Xew York, McGraw-Hill Book Co.,1934. (5) Ibid.. p. 859. FIGURE 4. COMRlNATION NOMOGRAPH AND SLIDE RULE (0) white, Brenncr, Phillips, nnd Morrison, Trans. Am. Inst. Chmnl. Enpa., 30, 570 (1933). A Opposite the first and read the On RECEIVED July 1, 1937. presented before the Division of IndWtrial I
l
Opposite the index Of the AI To divide a number by :m exponential term, place the number on the A
the A
l
I
Ill
Chemistry at the 14th Mideest Regional Mwting of the American Chemical Society, Omaha, Nebr.. April 29 to Mas I , 1937.
Evaluation of Ethylcellulose Solvents
T
HE solubility of ethylcellulose has been the subject of
numerous publications (6, 24), and an increasing body of information is available on the effect of sclvents upon the viscosity of ethylcellulose solutions (1,8, 11, 14, 17,23}, but comparatively little is known ahout the effect of solvents on the properties of the deposited films. A knowledge of these effects is necessary for efficient formulation of lacquers or any other composition from which a filmor coating of ethylcellulose is deposited by the evaporation of a volatile solvent. A study of the more common solvents and their mixtures has been made with the purpose of establishing a few fundamental rules for formulating ethylcellulose solvents. The present paper describes the results obtained with hydrocarbon and alcohol solvents and their mixtures. Data on the solvent power of various solvents for nitrocellulose and for cellulose acetate indicate that there are two principal methods for evaluating solvents (10). The “dilution ratio method” (6,10,18,82) has been widely used in nitroce!klose lacquer technology, mainly because the high cost of nitrocellulose solvents made advisable the use of large amounts of inert low-cost diluents. In considering ethylcellulose solvents from this point of view, however, the dilution ratio assumes little importance since the best solvents for ethylcellulose are relatively inexpensive. The dilution ratio method does not appear to be applicable to ethylcelldose solvents for other reasons. It is well known that nitrocellulose solvents tolerate a greater dilution with toluene than with petroleum naphtha. In the csse of ethyl-
TOW0 A. KAWPI AND SHAILER L. BASS “he Dow Chemical Company, Midland, Mich.
cellulose, toluene cannot be considered a diluent in any sense, since it forms clear, gel-free solutions of ethylcellulose, and even petroleum naphtha seems to have some “latent” solvent power, as will be shown later. The only true inactive diluent among the common liquids is water, and it is obv;ous that dilution ratios determined with water would have little theoretical or practical value. The “viscosity method” has been used as a measure of solvent power for cellulose esters (3,16,1ti, go), and low solution viscosity has ilsually been found to accompany clarity of solution and high dilution ratio. Studies of the effeLt of various solvents on the viscosity of ethylcellulose have been made, but low solution viscosity should not be considered the sole criterion of solvent utility. Solvent Requisites The ability to disolve a cellulose derivative is only one requirement of 3 solvent or solvent mixture. The evaporation rate of the solvent is of great importance and must be suited, of cowse, to the method of application of the coating and to the drying characteristics required, The solvent should not be toxia and in many applications should not have a disagreeable odor. The solvent should be stable, and should form clear and stable solutions which will not show haBiness or a precipitate on long standing. The solutions
75
formal sboiilcl hnva ns low n viscosity ns posnibla, NO tlirtt n liigli fiolirlsconhiit mny be obtdnctl in nrolntivoly low-viscosity solution, Finnlly, tlic solvcnt must bc cnpnble of dopositing s~noothclear filins of tlia collitlose clcrivntive, and thcsc films dioikl Iinvc good mccliniiicn: propcrtirs, In baginning n n invcstigntion of tlic suitnbility of twlvcnts for et~hylcellulasc,tho mcrst important factors to bo tlolcrinincd seeinccl to Lo clnrity of soistion, viscosity of soluthn, and tho proacrtics or tlic films cnwl from tlio solvatits,
~lcofrohiH eliowii in l?igr-c 1. 'j'lir? ~oliiticmt itirmwity is extreincly high in inixtuiw rich in hlucnc, rspirlly d w w w with Hind1 incrcnscs in alcohol contciit, nnd rertohcs n miniiniiin nt 30 per ccnt alanhol by volwnc. As tlir?& o h I (!on= tent incrcnscs bcycirid 30 par cant, a ribo in viecnrjity Q C C I I P ~ with dl rilcoliolx cxccltt mcthnnol. The viticonity inwcaeo with nlcoliol contcritn tilnva tho 30 pw ctwt rniiiiinrirn is grcntor, tho Iii~licrtho molccular weight of tho nlcol~ol, Mixturm contniniiig i n o ~ thnn ~ ! 60 to 70 per corit of tho lower nlw-
Method Solutions of etlrylcellulose wcrc niatlc in cnch solvcnt in 5 per ccnt concentration by wciglit. Thc viscosity of tlicsc solutions was dctcrmined in niodificd Ostwnld viscornctcrs at 25' C. Anothcr set of solutions, mndo n t 15 per ccnt conccntrntion in the snmc solvents, wns observed for clnrity of solution and used for casting films OD plnte glnss. The conditions for drying, conditioning, nntl dctcrmiiiing the tcnsilc strength and elongation of the films were the snnic ns those previously described ( 4 ) . The ethylcelliilose used in all the experiments reported was the standard commercial material which has about 2.5 moles of ethyl groups per glucose unit, or RII equivalent ethoxyl content of 48.5 per cent. A mcdiurn high viscosity type was selected, giving a viscosity of 100 centipoises on a 5 per cent solution in 80 :20 tohene :ethnnol. The 100-centipoise ethylcellulose was selected for this work since the solvent effects upon the properties of the deposited films have a direct bearing on the preparation of flexible coatings for cables, paper, and textiles. The effects of solvents on solution viscosity and film flexibility of the 10- and 20centipoise, or lacquer viscosity, types are entirely similar to those observed with the 100-centipoise viscosity type except that the relative differences in solution viscosity are smaller. Single Solvents The properties of ethylcellulose solutions in several common solvents are listed in Table I. Although the aromatic hydrocarbons and chlorinated hydrocarbons are excellent solvents, their solutions have high viscosities and are unsuited to most uses. Solutions in the alcohols exhibit lower viscosities but are unsatisfactory because they deposit films which are brittle. The aliphatic esters and ketones are good solvents, produce solutions of relatively low viscosity, and deposit comparatively strong and flexible films. However, thoso estcrs and kotones with an evaporation rate which protiiices satisfactory flow and leveling in the film are relatively mure expensive to use. It is appdrmt, then, that tho use of singlc solvents for ctliylcollulosc is inipraatical. Solvsnt Mixtures Thc effect of solvent composition upon the viscosity of rthylccllulosc solutions in mixtures of toluene with aliphatic
'O
IO
20
30
40
u1
eo
70
M
PCR CCNT ALCDRDL I V V ( x W
w
1. VISCOSXTY OF ETHYI,CELJ,OT,OSE IN 5 PER C E N T SOLUTION IN MIXTURES OF TOLUENE WITH AwoiioLs
FlGURE
hols tend to produce slightly hazy solutions. The effect of small amounts of water in reducing the viscosity of ethylcellulose solutiuns, previously pointed out by Suida (B), is shown by the fact that lower viscosities were obtained with mixtures containing 95 per cent ethanol than with absolute ethanol. -_TABLE11. ETiiYLCELLULOSE VISCOSITIES IN MIXTUIIESOF AROMATIC H fDROCARBONS Solvent Parla bu uol.
Benzene 70 ethnnol 30 Toluene 70 :ethanol 30 Sylene 70 ' echnr.ol 30
WITH ABSOLUTE ETHANOL Ab.Viscosity o f 5 % S 1 In. C'enlipoisrs
93 94
104
Table I1 sliow.: t!:? minimum viscositics of ethylccllulose in mixtures of nbsolutc ethrinol with t t i w aromatic hydrocnrboiis. Tlic difTcrcnccs in viscosity nrc much smnllcr thnn thosc shown in Figurc 1 a t the viscosity ininima chtninetl by the use of diffcrent homologous alcohols with the s m c hydrocarbon. The datlt from Figure 1 and T d d e I1 show tluit the higher the moleculnr weight of thc hydrocnrbon cir the a l ~ o 1101, the higher will be the viscosity of the ethylccllulose solution. This observntion is in good ngrcement with pitblisiied data on solvents for Lenzylcellulo~e(7).
Effect of Solvertts a n Film Properties A cornparibon of the viscoyities of ethylcellulose solutions Viscosity of
Yolvattt l'olitene
E t l ~ ~ l c ndichlurida e ChlGroform Ucnryl alcohol n.Uutanril Eth m o l Mottianal Butyl acotrta Mstlryl rcetate Methyl ethyl kotuno hcatoria Strndrrd rolvont (80:ZO to1um.: ebh anrrl)
6% Soln. Cslltil~daee
Clarity of 15% t i o h
Pi1m Propertiom Excellent Pnir li'sir Poor Poor Poor Paor
Oood CxOOct
Goad
Oood
Excellent
in inixturcs of toluene itnd absolute etlianol with the properties of films cad, frorn them is shown in Figure 2. The cui~ves how that films of thc greatest toiiPi,lc strengbli and elorigntion tare obtnincd from the solvent misturcs rich in toluene. As the content of e t h n o l in the inixturc incrcaaes beyond 30 per c ~ t tlic , tcnsilc ~trcngtliuiid elongrrtiol~of the films deposited tIecreasc i*apitlly. When the ctliniiol conteiit is greator than about (10 per wilt, tho films are hazy and too brittle to bo tested with nucurai~y. Incrcnsiag the toluenc content from 70 to 100 pcr cent docs not gently affect the properties of the cnst films but results in a gi'eat iticrewe in sottition viscosity.
INDUSTRIAL AND ENGINEERING CHEMISTLIY
VOL. so, NO, I
toluene arid 20 to 30 ?arb of 95 por osnf othfmol, Thh soivont produces Rolutions with somewhat high^ VkcMitiuP than tlmc obtained from bongene-mett,*nol rnixturec, but do08 not, lrliisli even in humkl Biirnmer wcathsr whorl film6 are depoRitci1 by casting, Howcvcr, when films are lppplicd by spraying, t h y ldirsh badly ant1 whnw “orntigo pwl,” becaum of thc high r t i k of evaporation of the mivcnt. A rnixturc of 80 part,s of xylene and 20 parts of n-butsnol lias an evaporntion rnto suitable for Rpray application, but solutions of etliylccllulosc in this mixture havu rolativoly high initial viwosities. In addition, the films cafit from this solvent do not hRvc a8 good propertie8 as those obtained froin hlucne-ethanol, Good films c m be obtained from a solvent con&ting of 90 parts of xylene and 10 parte of nbutanol, but the solution8 have very high initial viecosities, A remedy for this situation is the use of a solvent mixture conhting of ethanol, xylene, and n-butanol in such proportion that thc solvent coRtains 20 to 30 parts of the alcohols, For example, a siiitable composition for many uses is composed of ethanol 15, xylene 75, and n-butanol 10 parts by volume. The ethanol lowers the solution viscosity, and the xylene and n-butanol retard the evaporation rate. During the spraying operation, the more volatile ethanol evaporates to a large extent, so that when the lacquer reaches the object PCR CCM K C D ( o L OV a L N E being sprayed, enough of the solvent has evaporated to in2. EFFECTOF COWPOSITION OF TOLUENE-ETNANOLcrease considerably the concentration and viscosity of the SOLVENT ox ETHYLCELLULOSE PROPERTIES
The optimum inixturo of toluone witli ethanol yielding lowest aolrition visaosities and films of good strength and elongation is thus sceii to conhin froin 20 to 30 per cent ethanol, The properties of ethylcellulons films cclst from mixtiwee in which the evaporation rnte of the alcohol vsried wl’dely with respect to that of the hydrocarbon (9)are dmwn by the ourves of Figure 3. Curvcs I show thRt films of maximum tenPile strength and alongation nro obtnined from a composition richcr in methanol than the mixtiiro found to yicld mini-
FIGURE
mum solution viscosity. This indicates that, when the alcohol evaporates much more rapidly than the hydrocarbon, i t may be used in a higher percentage without reducing the film properties. The case in which the hydrocarbon and alcohol have approximately the same evaporation rate has been discussed above and is included as curves I1 for comparison. Curves JJI show the properties of films cast from mixtures of toluene with n-butanol, a case in which the alcohol has a much lower evaporation rate than the hydrocarbon. The curves show that the tensile strengths are lower than those obtained from the two other mixtures and that the elongations are very low, even for compositions quite rich in toluene. The toluene evidently evaporates first, leaving a large excess of butanol in the residual solvent which produces films of reduced strength and flexibility. The elongations of films deposited from two other solvent mixtures, in which the alcohol evaporates slower than the hydrocarbon, are shown by the curves for benzene-ethanol and xylenm-butanol cornpositions in Figure 4. The curve for toluene-ethanol is included for comparison. Since the tensile strength values follow curves similar to thosc for the elongation values, they have riot been included. In both series of mixtures the best film properties are obtained from compositions slightly richer in hydrocarbon t h m the mixture yielding minimum solution viscosity, These results show that, when film of maximum strength and flexibility are desired, the alcohol should leave the film before all the hydrocwtton has evaporated.
Evaporation Requisites Many of the hydrocarbon-alcoliol mixtures in tlic above experiments satisfy the requirement8 of clarity of eolution, low viscosity, and good film propertiw. The mixture best meeting these requiremonte is compoxed of about 70 parts of benzene and 30 parts of methanoi. Thi8 solvent yields the clearent solutions of ethylcellulose, the lowevt viscosihes, arid very p o d film properties when the film is caet under the proper conditions, However, it evaporates too rapidly, and the c u t film readily blushes uniem the hiiiflidity ia very low, The next beat combination is composed of 70 to a0 parb of
lucquer film. This is R desirable chaructcristic for a spreyiag solvent, since it prevents excessive flow of the film before drying. Thc xylene and n butanol evaporrtte slotvly enough, however, so that sufficient time of flow is allotved to pertnit irreguluritics i n the film to level ortt. To increase the factor of eafety for spraying solvents, ilie ethnnol content may be reduccd to 11s low m 5 per cent of tla? total solvent, but thc initial solution viscositlyis t h m incretlsd slightly.
Toluene with Aliphatic &tars and Katonm
When the viecosity of ethylcellulose is determind in mmples of cthyl acetate or butyl acetate obtained from different sourccq widely divergent valuw are found. For
IIUDUSTRIAL ASD EXGINEERING CHEMISTRY
JAKUARY, 1938
instance, the viscosity of an ethylcellulose in the technical grade of butyl acetate was found to be 260 centipoises, but the viscosity of the same ethylcellulose in the 99 per cent grade of butyl acetate was 350 centipoises. The viscosity of solutions in different ethyl acetates varied even more and was very high in a sample of purified ethyl acetate. It is apparent that the viscosity is reduced greatly by the presence of even a small amount of alcohol.
I-
s
I2
u c
a
4
P. BENZENE-ETHANOL
m. XYLENE - BUTANOL 0
'
P ;PER o CENT ' 3 !ALCOHOL " '
1
'
1
1
77
ethylcellulose. In subsequent discussion, the term "aromatic type naphtha" will be used to designate hydrocarbons of the second group. The solution viscosities of ethylcellulose in mixtures of absolute ethanol n-ith Troluoil, Shell Lacquer Diluent A, Solvesso KO. 1, and Union Aromatic Solvent No. 8, are plotted against solvent composition in Figure 5. These materials were selected as examples of two aliphatic naphthas, a hydrogenated naphtha, and a naphtha from a California asphalt-base crude, respectively. The toluene-ethanol curve v a s included for comparison. With each mixture the solution viscosity reached a minimum a t about 30 per cent ethanol. Clear homogeneous solutions were obtained with only 5 to 10 per cent ethanol in the mixtures with aromatic type naphthas. The 90 Troluoil10 ethanol mixture, however, did not completely dissolve the ethylcellulose, and this is believed to be the cause of the very low viscosity observed with this solvent mixture. At about 30 per cent ethanol content the solutions with this naphtha were more homogeneous, though not as clear as those made with the aromatic type naphthas.
BY VOLUME
FIGURE 4. ELONGATION OF ETHYLCELLULOSE FILhls CASTFROM MIXTURES OF HYDROCARBONS WITH ALCOHOLS
The viscosity of solutions of ethylcellulose in mixtures of toluene with commercial samples of ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, and methyl isobutyl ketone was determined. The viscosity values were all found to lie between the viscosity of solutions of ethylcellulose in toluene and in the ester or ketone alone. Compositions showing minimum solution viscosity were not observed with these combinations. The properties of ethylcellulose films cast from toluenebutyl acetate mixtures containing 50 per cent or more of toluene were found to be equal to those obtained from 80:20 to1uene:ethanol solution. Higher contents of butyl acetate have the effect of reducing slightly the tensile strength and elongation of the films. The properties of films cast from mixtures of toluene with ethyl acetat,e, acetone, methyl ethyl ketone, and methyl isobutyl ketone were found to vary with composition in a manner similar to that observed with butyl acetate. The esters and ketones, then, are much less effective than the alcohols in producing low-viscosity solutions of ethylcellulose, but they do produce films of high strength and flexibility even when they are the last solvent to leave the film. Low-viscosity solutions containing esters or ketones and hydrocarbons can be obtained by the addition of 10 to 20 per cent of an alcohol, and the properties of films obtained from such ternary mixtures are very good if the evaporation rates of the constituents are chosen so that the alcohol is not the last solvent to leave the film.
TABLE
The naphthas commercially available for use as nitrocellulose thinners may be divided into two classes on the basis of their behavior with ethylcellulose: (I) Those with purely aliphatic properties, fractions derived from paraffin-base crudes, which require relatively large amounts of an ethylcellulosesolvent to produce clear solutions. (2) Those which possess to a large degree the solvent properties of the aromatic hydrocarbons and behave in general like mixtures of aromatic hydrocarbons n-ith aliphatic hydrocarbons. This class includes fractions from certain asphalt-base crudes and the hydrogenated naphthas. Hydrocarbons of this type require only 5 to 10 per cent of ethanol t o produce clear solutions of
VISCOSITIEs AND DENSITIES O F ETHYLCELLULOSE SOLUTIONS IN VARIOUSSOLVENTS
--Viscosity--5 % soln. by
5 g. ethyl-
cellulose/ 100 cc. Solvent weight solvent Centipoises 96 140 Toluene 70: ethanol 30 Union N o . 8, 70: ethanol 30 88 163 Troluoil 70: ethanol 30 85 199
-Density 5% soh.
by weight
0.8505
0.795 0.757
a t 25' C.5 g. ethylcellulose/ 100 cc. solvent 0.8540 0 8025 0 7635
It is well known in the field of nitrocellulose lacquers that dilution with naphthas produces higher solution viscosities than dilution with aromatic hydrocarbons. At first glance the data of Figure 5 apparently show that ethylcellulose solutions have exactly the opposite behavior, but closer inspection shows that the apparent difference is due to the method of preparation of solutions. Nitrocellulose concentrations are ordinarily stated as pounds of nitrocellulose per gallon of solution, while the solutions of Figure 5 were made up on the basis of weight per cent. 140 IY) 120
g 110
E
100
Y W
z
8i
*O 70
' eo KI
Petroleum Fractions with Aliphatic Alcohols
111.
IO
20
30
40 50 W PER CENT ETHANOL BY VOLUME
70
80
(D
FIGURE 5. VISCOSITYOF ETHYLCELLULOSE IN 5 PER CENT SOLUTION IX MIXTCRES OF H Y D R O C ~ R BWITH O N S ABSOLUTE ETH~NOL
Table I11 shows the densities and viscosities of solutions of an ethylcellulose in mixtures of 30 parts ethanol with 70 parts toluene, Union Aromatic Solvent No. 8, and Troluoil. I n one series the solutions were made on the basis of weight per cent (5 grams of ethylcellulose per 95 grams of solvent) and in the other series on the basis of volume per cent ( 5 grams of ethylcellulose per 100 cc. of solvent). Table 111 shows that, if the solutions are made up by volume per cent, the naphthas pro-
78
INDUSTRIAL AND ENGINEERING CHEMISTRY
duce higher solution viscosities than toluene, just as they do in tlie case of solutions of nitrocellulose. Therefore, in formulating ethylcellulose lacquers containing naphthas as part of the solvent, it should be remembered that naphthas will produce slightly higher solution viscosities than the aromatic hydrocarbons, if the concentration of ethylcellulose in the lacquer is calculated on the basis of pounds per gallon of lacquer.
a P
TRCi.MIL WELL LACWUER OILUENT "&"
I
/
I
l
,
l
I
PFR CENT ALCOHOI. BY VOLUME
ELONGATION OF ETHYLCELLULOSE F I L m CASTFROM MIXTURES OF NAPHTHAS WITH ABSOLUTE ETHANOL
FIGURE6.
The effect of the naphtha-ethanol solvent mixtures on film properties is shown by the curves of Figure 6 . The curves show that mixtures of the aromatic type naphthas with ethanol deposit films whose properties are practically as good as those from toluene-ethanol and substantially better than those from ethanol mixtures with aliphatic naphthas. The curves show that films of the best strength and distensibility were deposited from solvent combinations yielding solutions of about the minimum viscosity. If the relative evaporation rate of either the hydrocarbon or the alcohol is changed, the region in which best film properties are obtained will be displaced in a manner similar to that shown in Figure 3 for combinations of pure aromatic hydrocarbons with alcohols.
Low-Cost Solvents The above data are the basis for the formulation of a very economical solvent for ethylcellulose which produces clear solutions of low viscosity and deposits films of high mechanical strength. Such a solvent is composed of 70 to 80 parts of an aromatic type naphtha and 20 to 30 parts of ethanol by volume. By analogy with the data on the higher aromatic hydrocarbons and alcohols, slower-evaporating solvents can also be formulated. Thus, higher boiling fractions of the aromatic type naphthas, such as Solvesso No. 2 or 3 , or Union Aromatic E o . 10 or 30, may be used in conjunction with butyl or amyl alcohol to secure a desired reduction in the rate of evaporation, and an improvement in flow. It has been found that the higher boiling fractions of these naphthas have greater solvent power for ethylcellulose than the low-boiling fractions, indicating that they are richer in aromatic constituents.
Spraying Solvents
If a solvent is desired for spray application of a lacquer, it should contain enough slow-evaporating constituents to permit the flow necessary for the production of smooth films. The higher boiling aromatic type naphthas can be used with butyl or amyl alcoholfor this purpose. The presence of fastevaporating constituents, such as toluene and ethanol, is necessary to produce low initial solution viscosity, but they should not be present in amounts large enough t o cause
VOL. 30, NO. 1
blushing. For instance, the solvent may consist of 40 parts of toluene, 10 parts of ethanol, 40 parts of Solvesso KO. 2 or Union Aromatic No. 30, and 10 parts of butyl or amyl alcohol. The higher alcohol will remain in the drying film with the slow-evaporating aromatic type naphtha and will serve to keep the viscosity low enough for good leveling of the coating. The use of even slower evaporating fractions of an aromatic type naphtha will produce good results with respect to flow and leveling.
Discussion A review of the data presented shows that no single criterion of solvent power can be found with which to correlate the efficacy of single solvents for ethylcellulose. On the basis of film properties and clarity of solution, toluene is a much better solvent than ethanol; on the basis of solution viscosity and dilution with naphtha, it is 'much poorer than ethanol. However, since a solvent must satisfy a t least three of the above requisites before it can have any general practical value, neither toluene nor ethanol is a good solvent. Mixtures of toluene with ethanol, however, and mixtures of their homologs satisfy all three of the requirements, when the hydrocarbon and alcohol are present in the proper proportions. There are only a few examples in the literature of the effect of solvents on the film properties of cellulose derivatives. Robertson (19) showed that solvents have an effect on the strength and toughness of nitrocellulose films. Jones and Miles (IS) showed that the choice of solvent has a great effect on the properties of nitrocellulose films, and that the relative effects vary with the nitrogen content of the nitrocellulose. Several investigators have studied the effect of solvents and solvent mixtures on the film properties of celluworking lose acetate (2, 15). Danilov and Aleksandrova (8), with ethylcellulose, obtained results with which the data of this paper agree very well. Sakurada and Watanabe (WI), working with cellulose esters, reported that good solvents produce films with high elongation and low tensile strength, while poorer solvents produce films of high tensile strength and low elongation. In the present work on ethylcellulose, high tensile strength was always obtained from films possessing high elongation, and low tensile strength from those films with low elongation. This corroborates the results presented in a previous paper on plasticizers (4) and strengthens the view that tensile strength and elongation are not separate phenomena, but that for any one composition, high tensile strength results from the ability to stretch. The experiments reported in the literature concerning the effect of solvents on the viscosity of ethylcellulose are somewhat a t variance. Suida (25) reported viscosity values for benzene-ethanol solutions of ethylcellulose which agree well with the curves of Figure 1. Danilov and Aleksandrova (8), however, found the minimum viscosity to occur a t a much lower proportion of alcohol (10 to 15 per cent), and explain the discrepancy between their results and those of Suida by differences in the ethylcellulose samples used. This is probably the correct explanation, since differences in ethoxyl content and in manufacturing conditions have a considerable effect on the properties of the derivative (1,24). Danilov and Aleksandrova reported that the higher the concentration of the ethylcellulose in mixtures of hydrocarbons and alcohols, the more alcohol was necessary to produce the minimum viscosity. At low concentration they obtained a viscosity minimum a t 10 per cent alcohol, and a t high concentration the minimum occurred a t 30 per cent alcohol. This has been tested by the authors on toluene-ethanol solutions. A definite minimum was obtained on 2 per cent solutions a t 20 per cent ethanol in the mixture. On 5 per cent
JANUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
solutions the minimum was less pronounced but was observed a t 30 per cent ethanol as shown by curve I11 in Figure 1. With 10 per cent solutions the minimum was even less pronounced but lay between 20 and 40 per cent ethanol. There is, therefore, a slight concentration effect, but perhaps it should be considered as a decrease in the sharpness of the minimum with increased concentration rather than as a displacement of the point of minimum viscosity. The reasons for the sharp reduction of viscosity caused by the addition of alcohols to hydrocarbon solutions of ethylcellulose are rather obscure. The relative amounts of reduction caused by homologous alcohols and by the esters and ketones are in agreement with Highfield’s results on the correlation between solvent power and polarity of the solvent (12). For example, esters and ketones are much less effective than alcohols in producing the viscosity reduction, and a small amount of water reduces the viscosity of a tolueneethanol solution of ethylcellulose. Since a solution of ethylcellulose in toluene differs so markedly in viscosity and appearance from a solution of the same concentration in ethanol, and since the films obtained from these solutions are so widely different in properties, there is evidently a difference in the degree of dispersion caused by the two solvents. The degree of dispersion of ethylcellulose in toluene must be high, since solutions in toluene are clear and since films of high tensile strength and elongation are deposited from them. Conversely, since solutions in ethanol are somewhat cloudy, and the films formed are weak and brittle, the degree of dispersion must be low, so that the films deposited consist of masses of large aggregates rather than of a network of chains or very small aggregates. This is in agreement with the conclusions reached by Jones and Miles (IS)on the tensile strength of nitrocellulose films. The occurrence of a viscosity minimum in mixtures of toluene and ethanol, then, is difficult to explain on the basis of degree of dispersion or particle size, especially since good film properties are obtained from the solution of minimum viscosity. The most plausible explanation is that a solution of ethylcellulose in benzene or its homologs possesses a certain degree of “false viscosity” due t o a gel-like structure in the solution, and that this structure is broken down by the addition of alcohols. This explanation is supported qualitatively by the fact that the viscosity of concentrated ethylcellulose solutions in benzene or toluene can be lowered by agitation to only a fraction of the original value. I n addition, solutions of ethylcellulose in benzene-ethanol mixtures rich in benzene have been shown by Nisizawa (1‘7) and Aleksandrova (1) to possess greater structural viscosity than those in solvents containing less benzene.
Summary 1. Some of the solvents for ethylcellulose have been evaluated on the basis of their solution viscosity and clarity, and the properties of the films deposited from them. 2. Principles of formulating hydrocarbon-alcohol solvent mixtures have been developed, taking account of the relative evaporation rates of,the two types of solvents. 3. Ethylcellulose films of maximum tensile strength and elongation are obtained from alcohol-hydrocarbon solvents formulated in such a way that the last solvent to evaporate from the film consists almost entirely of hydrocarbon. 4. If the evaporation rates of the alcohol and of the hydrocarbon are approximately equal, the solvent mixture producing the lowest viscosity also produces the best films. 5. The hydrocarbons that can be used alone with alcohols are aromatic hydrocarbons, hydrogenated naphthas, or highsolvency naphthas. Kaphthas from paraffin crudes give the best results when used with a small proportion of aromatic hydrocarbon.
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6. T o obtain the flow and leveling characteristics required of spraying lacquers, mixtures of hydrocarbons and alcohols of varying evaporation rates should be used. Since flow is a function of viscosity of the film in the various stages of drying, each hydrocarbon should be matched with the proper amount of alcohol of about the same rate of evaporation. 7 . Solvents consisting of hydrocarbons and aliphatic ketones or esters have higher viscosities than those produced by the use of alcohols, but large amounts of ketones or esters can be used without lowering the film properties. The use of a ternary mixture of a hydrocarbon, an alcohol, and a ketone or ester, produces low viscosity and good film properties. 8. The data show that the value of ethylcellulose solvents cannot be judged by any one criterion. The viscosity and clarity of solution and the properties of the film deposited must all be considered. When these data are used in conjunction with data on rates of evaporation, practical solvents can be formulated and the value of new solvents determined.
Literature Cited Aleksandrova, R. S., Plasticheskie M a s s g , 1937, 31. Atsuki, K., and Shinoda, J., Rept. Aeronaut. Research I n s t . T o k y o I m p . Cniv., 3, 49 (1928). Baker, F.. J . Chem. Soc., 103, 1653-75 (1913). Bass, S. L., and Kauppi. T . A . , IND. ESG. CHEM., 29, 678 (1937). Berl, E., and Schupp, H . , Cellulosechem., 10, 41 (1929): Hagedorn, M., and Moeller, P., Ibid., 12, 29 (1531); Dow Chemical Ann., 455, Co., “Ethocel.” 1937; Hess, K . , and Muller, -4., 205 (1927); Koch, IT.,IXD. ESG. C H E i f . , 29, 687 (1937); Lilienfeld, E. S. Patent 1,188, 376 (1516); Mienes, K., “Celluloseester und Celluloseither,” Berlin-Steglitz Chemischtechnischer Verlag Bodenbender, 1934; AMoll,W. L. H., KolloidZ . , 77, 85 (1936); Ushakov, S.Tu’., and Aleksandrova, R . S., Plastzcheskie M a s s y , 1932, 1; Worden, E. C., “Technology of Cellulose Ethers.” DD. 1770-2061. Vol. IV. 1933. Brown, B. K., andBo&, C., IND.ENG.CHEM.,19, 968 (1927). Clement, L., RiviBre, C., and Honnelaitre, A , , Bull. SOC. chim., [ 5 ] 2, 707 (1935). Danilov, S. N..and Aleksandrova, R . S.,Plasticheskie M a s s u , 1935, 100. Doolittle, A. K . , IND. ESG. CHEM.,27, 1165 (1935) I b i d . , 30, t o be published (1938). Gluckmann, S., Kunststofe, 25, 25 (1935). Highfield, A , , T r a n s . Faraday Soc., 22, 57 (1926). Jones, G. C., and Miles, F. D., J. SOC.Citem. I d . , 52, 258T (1933). Kauppi, T. A , , and Bass, S. L., IND. ESG. CHEU.,29, 800 (1937). Kita, G., and Kanno, G., J . SOC.Chem. I n d . J a p a n , 31, 177B (1928) ., Mardles, E. W. J., J . S O C .Chem. I n d . . 42, 127T, 207T (1923). Xisiaawa, Y . , Kolloid-Z., 56, 59 (1931). Ostwald, TV., and Ortloff, H., Kolloid-Z., 59, 25 (1932). Robertson, R., Ibid., 28, 219 (1921). Sakurada, I., and Shojino, M., Ibid., 68, 300 (1934). Sakurada, I., and Watanabe, I., J. Sac. Chem. Ind. J a p a n , 39, 50 (1936). Sproxton, F., Kolloid-Z., 28, 225 (1921). Suida, H., Cellulosechem., 12, 310 (1931). Traill, D., J . SOC.Chem. I d . , 53, 337T (1934). RECEIVED September 2 3 , 1937. Presented before t h e Division of Paint and Varnish Chemistry a t the 94th Meeting of t h e American Chemical Society, Rochester, N.Y . , September 6 t o 10, 1937.
