I
INGVAR JULLANDER Research Laboratory, Mo och Domsja AB Ornskoldsvik, Sweden
Wa te r-Soluble Ethy Ihydroxyethylcellulose
Abundance of ethyl alcohol, a by-product from sulfite liquor in paper manufacture, led to development of Modocoll, a water-soluble ethylhydroxyethylcellulose. It dissolves in cold water without lumping, and is finding new uses as a paper-hanging paste, emulsifier in latex paints, and core binder
to those used in industry \viis investiT w o DISTINCT types of ethylgated ( 1 6 ) . hydroxyethylcellulose are no\v available. Etti?-l chloride as the etherifying agc'nt .A product soluble only in organic soland sulfitc p u l p of dissolving grade a i tlic. vents has been marketed recently by cellulose rajv material Ivere used. Dethe Hercules Polvder C o . under the gree of suhsritution \\.as varied b y changname of EHEC ( l j ! 23), and ethers soluing concentration of the steeping s o d i u i i i ble in water and alkali have been proh!.droxidc. Dissolved in tiatcr at 20" duced commercially since 134.7 by hfo (:., thc products gave a dispersion o f och Domsjo .AB Ornskoldsvik, Sveden, s\vollen particles a n d nut proper soluand sold main1)- under the trade iianir tions. .\frrr freczing the solutions. ITof r\fodocoll. TYater-soluble ethylh~dros~~erliylcellii- measuring at the same te~iipcraturc~ lose \vas first desc! ibed bb- Sonncrskog sho\ved considerable inil~rovcnicnr in (,37-33) ; studies of its ~'h)'sicoclie~iiicsl viscosity and clarity. :\ sharp viscosit!masiniuni and turbidity ininimum \vrw Iroperties \ v u e published b y Jullander found a t 1)s 1.2. (76-21) and others (27) ; and a thorough The rdtige of solubility is too sttiall i'or study of its molecular properties has been recently completed by hfanley (26). ethylcellnlose to be useful as i i \va iersoluble derivative. althotigh ii is i i - e l l Ethylcellulose is \vater-solublc \\.ithin sitired as a thickeiiinq agent solublc a small degree of substitution (DS) rangt-, only i n alkali (27). 51eth~~leellulosc.. but inforrnatiori regarding thr, position ho\vt:ver. has a broader rangc eauscd b y of this range is confusing. Rock (i'l Lveakcr Iiydr~opliobic properties of rhc. found that by homogeneous etherificanlcth!~l group. tion in quaternar). amrnonium bases, TVatrr solubility of ethylcellrilose c a n \\.ater solubility \vas obtained at a bc considerably improved b y C'[Jeth(Tidegree of substitution of 0.6 but disfication irirh ethylene oside ; like i i i < ~ r t i > . l appeared again at a point lo\ver than cellulose-, its soliitions sho\v wvcrsiblc 1.2. g e l l i n ~ u ~ m n heating. Hydroxyrh\ lThe only plausible incans of comniercellulose. o n the other hand, is also soluhlia cia1 production is etherification of celluin hot Lvarer. From the rnanufacturiny lose in the fibrous state. Thus, a more point of vie\\.. it is desirable to rrtain non-random distribution of ethoxyl insolubility in hot w'ater becdusc it groups is unavoidable, and the desired greatly facilitates purification of the solubility in water should necessitate a raw product obtained from etherification. higher degree of substitution. .Although Therefore, technical as \vel1 as ecoscattered information about degree of nomic considerations limit the amount ethylation required for such solubility of ethylene oxide that should be coniis obtainable from the literature, values bined with cellulose. vary from a degree of substitution of 0.7 Effect of increasing hydroxyethyl conto 1.5, and little or no information is tent on the thermal gel point is demongiven about raw material? conditions strated in Figure 1. The rakv material for etherification, and measurement of was a sulfite solution of dissolving grade solubility. Therefore, maximum solumade from spruce: having an alpha bility in water when etherification is content of 9O(r;. and \,iscosit)- of 19 cp. accomplished under conditions similar
364
INDUSTRIAL AND ENGINEERING CHEMISTRY
Manufacture Plant manufacture of erh!.lhydroxbethylcellulose starts ivitli tilcxlicd sulfite pulp of dissolving grade. Sheets of' pulp are steeped in sodium hydroside, pressed. shredded. and then placed in autoclaves with ethylenc oside and ethyl chloride, which are miscible. Ethylene oxide is more reactive rhan ethyl chloride. and \vith increasing temperature. hydroxyethylation o f thr cc-llu-
I
!
.
!
20
,
!
LO
,
!
,
60
!
,
!
,
I
Temp.,*C. Figure 1. Transmittance as a function of temperature for ethylcellulose coetherified with different amounts of ethylene oxide Chemical Analysis of Cellulose Ethers
os Cellulose Ether, 0.5% Sol.
1 2
3
Ethylhydroxyethyl
4) 5
6, Ethylhydroxyethyi (Modocoll M) Ethylhydroxyethyl (Modocoll E 100) Methocel 400 Methylhydroxyethyl (Glutolin Kleister)
lose chain will take place before ethylation. The r a y product is washed with hot water, centrifuged, gxound, and dried. The flowsheet in Figure 2 shows how manufacture of ethylhydroxyethylcellulose fits into the production scheme of a sulfite mill which, like most Scandinavian mills, is equipped with a plant for producing ethyl alcohol by fermentation of sulfite waste liquor, and with a plant for sodium chloride electrolysis to produce chlorine and alkali needed for bleaching and refining pulp. The only major raw materials are wood and sodium chloride. Analysis
The formula for ethylhydroxyethylcellulose can be written schematically as
7
/"\ / C
E
-C
?C2"5
\
H
< c
/ \0/
0
CHaOCH&H2OH
Ethyl 1.20 1.28 1.25
1.30 1.33
Hydroxyethyl . a .
0.20
0.44
1.25
0.68 0.87 1.11
1.33
0.51
0.68
0.87
1.970
...
1.37"
0.30
The first analytical problem is to determine the degree of substitution of ethyl and -hydroxyethyl groups. I t is not possible to estimate this from the amounts of ethylene oxide and ethyl chloride consumed because unwanted side reactions always otcur to a considerable extent (29, 37). Therefore, ethyl content was determined by oxidation of ethoxyl groups to acetic acid with chromic acid according to Lemieux and Purves (25) and the total ethyl plus hydroxyethyl content by alkoxyl analysis according to Morgan (28). T h e hydroxyethyl substitution is then found from the difference between the two determinations. When the Lemieux and Purves method is compared with that of Viebock and Schwappach (35) as modified by Samsel and McHard (30), it gives for low substituted ethylcellulose values lower by about 5% ( 2 4 ) . This is just outside the experimental error and no correction was applied. From a series of duplicate measurements, the standard error was found to be 0.4% in ethoxyl and alkoxyl content for both the Purves and Morgan analyses. Little has been done to determine the position of the substituents in ethyl-
hydroxyethylcellulose. One factor contributes to the complexity of this problem -even though the degree of substitution for the hydroxyethyl groups is usually less than 1, it is not unreasonable that diethylene glycol groups might be found to a certain extent. T h e ethyl chloride, reactive after the hydroxyethylation, may react with either the original hydroxyl groups of cellulose molecule or those of the hydroxyethyl groups. Investigations by Weibull and Nycander (36) of the reaction between ethylene oxide and ethyl alcohol indicate that the velocity constant is lower for the first reacting ethylene oxide molecule than for the second and those following. I n fact, chromatographic separations performed on hydroxyethylcellulose by Croon and Lindberg (7) confirm the formation of a considerable number of diethylene glycol groups a t DS 0.6. Hydroxyethylcellulose was prepared from linters through etherification with ethylene oxide mixed with petroleum ether as diluent. A sample was hydrolyzed with sulfuric acid and chromatographically separated on a carbon column. Fifteen different components were obtained through elution. Ten of them have so far been identified with certainty (7). Of the total amount of ethylene oxide fixed to the cellulose, 2$Z0 reacted with a hydroxyethyl group.
Physicochemical Properties
T h e properties of ethylhydroxyethylcellulose are generally similar to those of water-soluble methylcellulose ; consequently, its main uses-as binders, and as thickening, emulsifying, and dispersing agents-are similar. This article, however, deals mainly with properties different from methylcellulose or with information heretofore unpublished. Molecular Properties. Recently, a thorough investigation of the molecular properties of ethylhydroxyethylcellulose was completed by Manley (26) whose starting material had a degree of -substitution of 0.9 and 0.7 for ethyl and hydroxyethyl, respectively. Several methods for fractional precipitation were tried without success, and finally fractional solution from acetone-water was used. A 500-gram sample was fractionated into 12 fractions and considerable time was necessary to establish equilibrium-3 days at the start of the fractionation and 14 days toward the end. Chemical composition of the fractions was constant within reasonable limits, except for the first, which had a low alkoxyl value. T h e result seems to establish the existence of a double peak in the frequency curve. The reason for this is not known. Four fractions were chosen for further study by means of viscosity, osmotic pressure, sedimentation equilibrium, sediVOL. 49, NO. 3
MARCH 1957
365
mentation velocity, diffusion. and lightscattering methods. Viscosity was measured in capillary viscometers of the Ubbelohde type provided with four bulbs. The dependence of the viscosity ratio on the rate of shear is not pronounced even for the highest fraction. The measurements \cere made a t four different temperatures; the significance of temperature dependence for the limiting viscosity number \vas discussed by Flory I O ) . Because of the surface activity of ethylhydroxyethylcellulose, determination of its osmotic pressure in any osmometer provided \vith a capillary manometer is probably impossible. Therefore, the interference osmoiiieter of Claesson and Jacobsson (5) ivas used. The manometer consists of glass tubes having a diameter of 20 mm.. and error from surface tension differences is insignificant. The osmotic pressure \vas measured dynamically ( 2 6 ) . Sedimentation in the oil-turbine ulrracentrifuge shows ivell-defined peaks (26j, Diffusion measurements show only a small skewness. and the concentration dependence is correspondingly small. Quotient D,,'Dd [diffusion constant calculated according tu the nionient (Dm) and area ( D A )methods] is approximately 1.2, indicating heterogeneity of the fractions. Purification necessary for light-scattering measurcmcnts offered many difficulties and ivas finally accomplished by centrifuging in a Spinco centrifuge followed by filtration through membrane filters. Data for molecular Meights and values for the frictional ratio, f fo, were deter-
c
ulfite
mined, Values from sedimentation q u i librium and sedimentation plus diffusion (Akfww) agree well. The lo\ver values of .\I, indicate a considerable heterogeneity of the fractions. hfolecular weights from light scattering are improbably high; the solutions may still contain submicroscopic aggregates insufficient for detection by thr ultracentrifuge but sufficient to increase light scattering considerably. High values for the frictional ratio indicate srilf chains. The Staudinger relation bctlveen viscosity and molecular \\.eight at 25'C. assumes the form. [ a ] = 3.7
x
10-4
x
Alf;:
I n f l u e n c e of Salts. Like nonionic \vatu-soluble cellulose derivatives i n general, eth~-lhydroxyetli~lcellulose cannot form insoluble salts with metal ions. but i t is: honxver, often easily salted out of its solutions. mvesriqation of thr salting-out properties of about -0 different salts !vas made (27). using a r r c h riiq~ie\vhicIi is essentiall\- an adaptation of the routine method for salt point drtermination used in the viscosr industr!for controlling the ripening of viscosr ( O j . Series of salt solutions with increasing concentration \vex prepared in beakrrs and kept at constant temperature of 20' C:. .\ fe\v droljs of 2';'; cellulose e t h r r solution Ivrre added to each beakrr: and the concentration (iloccularion point) \vas observed a t ivhich rhr cellulose e t h r r solution was no longer readi1)dispersed, but remained as a highly s\\-ollen gel similar to a coacervate. From such values for meth~.lcellulosc and ~ r h y l h y d r o s y e t l i y l c c l ~ i ~isl o snoted ~ that
liquor
1 - Sodium hydroxide
1-1
1
1 I IEthylone o x i d o l L Ethyl chloride 1
-
I
I
Ethylene oxide Ethql chloride
1
I
p 7 I akq Cellulose Glue
Cellulose Poste j
.. - -. -. . . I
/ / I
1
Figure 2. cellulose
366
O D
,L .__..-__ J
Row moterial Chemical added Process
Intermediate
Final producl
product
Flowsheet for production of ethylhydroxyethyl-
INDUSTRIAL AND ENGINEERING CHEMISTRY
30
1i 0
5
10
I5
K S C N ,wt.%
Figure 3. Flocculation temperature of 0.5% solutions of ethylhydroxyethylcellulose containing potassium thiocyanate
figure 4.
Viscometer for studying rate of solution for cellulose ethers
Actual salting in has been reported by Heymaqn (72) for potassium thiocyanate a t 40' C., whereas salting out at 20' C. was found in these laboratories (27). Figure 3 shows how in this special case the samesubstance can cause both salting in and salting out, depending on the salt concentration. Ethylhydroxyethylcellulose: represented by curve 3 in Figure 1, was used. A stock solution of the cellulose ether was frozen, thawed, centrifuged, and then diluted with solutions of potassium thiocyanate to a constant cellulose ether concentration of 0.5y0and a salt content from 0 to 20 grams per 100 grams of solution. Turbidity measurements a t increasing temperatures were performed as in Figure 1 and the temperatures giving 50% transmittance were plotted against salt concentration. Solubility in Water-Alcohol Mixtures. Solubility of ethylhydroxyethylcellulose and other cellulose ethers in mixtures of alcohol and water was investigated (77). I n some cases a marked solubility minimum was found, which was studied by transmittance and viscosity measurements. The effect is very sensitive to changes in composition of the ether. Ethylhydroxyethylcellulose with slightly lower ethyl content and higher hydroxyethyl content shows only a small effect. Methylcellulose and
methylhydroxyethylcellulose show no effect at all. An explanation is suggested by the behavior of ethylcellulose and hydroxyethylcellulose. A small addition of propanol markedly decreases solubility of ethylcellulose which increases again above 30% alcohol concentration. Hydroxyethylcellulose can withstand a much higher alcohol concentration before its solubility diminishes. Mixtures of water and alcohol show many anomalies such as contraction and viscosity maxima, explained by the formation of fairly strong aggregates such as CzH60H. 3 HzO. It is believed that these aggregates are an excellent solvent for ethylhydroxyethylcellulosebecause of their simultaneous solvation of the ethyl and hydroxyl groups. Viscosity. Manley (26) showed that influence of the velocity gradient on viscosity is small in dilute solutions of 0.2570 or less. At concentrations usually used in practice, however, this does not apply. Measuring at 2% concentration where typical pseudoplasticity is found is more or less standard for viscosity determinations (20). Thixotropy or yield value has not been observed. Within the interval investigated, experimental points fit a simple power formula. Some practical consequences of this pseudoplasticity can be seen when measurements of apparent viscosity made
with four different instruments are compared (20). Values found on the same solution but with different viscometers could differ by a factor of 2 or even more. The viscometers were all calibrated with Newtonian oils of known viscosity. Cellulose ether solutions used in practice contain gel particles and fiber fragments, unleh special precautions have been taken to eliminate them. This incompletely dissolved material may increase or decrease the viscosity. The relationship between viscosity and concentration has been investigated for solutions with and without gel particles (20) and viscosity was plotted against total concentration of the cellulose ether in the solution. The two curves intersect because at high concentrations the mutual interaction between the gel particles results in viscosity increase. This effect can be more clearly illustrated in another way. For studying rate of dissolution for ethylhydroxyethylcellulose, an apparatus was built which functions simultaneously as a stirrer and viscometer (Figure 4) ; thus, viscosity of the suspension can be observed continuously. The viscometer consists essentially of a cup inserted in a float. The float is held in position by a rod, 1 mm. in diameter, positioned in a slightly larger hole in a metal plate. The cup is filled with a newly mixed suspension of cellulose ether in water and stirred at constant speed. Momentum transferred from the stirrer to the cup and float through the increasingly viscous liquid medium is counteracted via the nylon line by the balance shown to the right in Figure 4. The circumference of the float is divided in 100 parts and its movement is read as a function of time. The apparatus was calibrated with ethylhydroxyethyl solutions of known viscosity as determined by a Brookfield viscometer. Further details concerning this instrument will be published elsewhere. Dissolution experiments were performed on ethylhydroxyethylcellulose
Solrllac tim. min.
Figure 5. Variation of viscosity with solution time at 20" C. for ethylhydroxyethylcellulose in granular form VOL. 49, NO. 3
MARCH 1957
367
of high viscosity (Figure 5). Degree of substitution for ethyl \vas 0.82 and for hydroxyethyl 0.92. Esperirnents showing reproducibilitJ- of dissolution were made u4th granular poivder; these mrasurements arc shoivn in Fiqurr 5 as a broken line. \\+ith coarser granules. shoirn by solid lines: die time oi‘ dissolution naturally increases but a curious effect occurs at sufficiently high concentrations --viscosity passes through 3 iiiasirnum during dissolution at consrant temperacure. The granular matrrial of approximately spherical s!iape had i~ei.11hoiliogWave length. mu, enized betiveen s t a n d a d sio,rs. DIN 12 and 16 [mesh per centinictcr (I/)]. Figure 6. Light absorption curves of This is believed to be c a u s r d bv contacc aqueous solutions betiveen the stronsly sivollen halfx Ethylhydroxyethylcellulose, 0.1 yo dissol-ved granules. 0 Ethylhydroxyethylcellulose, 0.12 and Congo Effect of Substantive Dyes. I t is red, 0.00270 knoism from patent literature thar vis0 Congo red, 0.002% cosit)- of ivater solutions of poIy(vin~~1 alcohol) iiicreascs \\.it11 addition of mine subsrantive dyes. Recently. Ditrrnar and Priest (S) studied this lilienoiiicnon more carefully. In 1940. C:trniola published a short article ( 2 ) aliout this same effect for solutions of iricth!-lci.llulose! ivhich induced tile sliidy of e t l i ~ ~ l h y d r ~ x y eth~~lcellalose i n [his 1-cspect. Rcceiirly: Centola published ;I cuntinuation of ihis ivork (3:-/) a n d i:i til(’ miit: yrar Inokawa (7-1) alqo ~i~iblisliecl data. Rccuirs o n e t l i ~ ~ l h y d r o s y e r l i ~ - l c e land l i ~ l ~i i ~i t ~~ l~i > . l crllulose s w i n 10 agrct’.
Table I. Effect of Congo Red on Viscosity of Ethylhydroxethylcellulose Solutions ( 2 % liigli ~ i i r , l c ~ u l n i . - r ~ - pceIlulo.-c e crlicr di;iolverl iti n’:iter cotitainiiiE (‘(jtigo rcJ) collgo Red.
5 of
Ce1lulo.c Erhcr 0
0.1 0.5
Cll. 2750 2850 3320
2.0
4210 5700
5.0 10.0
29700
1.0
a
17i-c,o-it:. r nroill~field1 ,‘I
16700
d t 203 c.
Table 11. Effect of Salt Addition on Viscosity of Ethy1hydroxyethylcel;ulose Solutions Containing Congo Red (1%
Congo red, based U I I cellt~loaeether, ~ high nioleculnr-type 7 m itddetl) YlS-
cosity (BrookSolute 2% cellulose ether without Congo red With Congo red.
368
Solvent
field), Cp.
Dist. water Dist. water Tap water NaCl, 1% NaCI, 57,
2750 4100 4050 2420 315
Acknowledgment
The author is indebted to 0 . Lagerstroni and his staff for the analytical \vork performed. J. hlanley as ~ v r l las
B. Lindberg and I. Croon kindly placed the result of their investigations at his disposal before publication. literature Cited ( 1 ) Bock, L. H., IND.ENG. CHEDI.29, 985 (1937). ( 2 ) Centola, G., Ricerca sci 11, 905 (1940). [3j Centola; G., Tinctoria 52,’ 341 (1955).
(4) Centola, G., Borruso, D., Prati, G., Gnzz. chin!.ita/. 85, 1468 (1955).
INDUSTRIAL AND ENGINEERING CHEMISTRY
( 5 ) Claesson, S., Jacotisson, (;,,
.kin
Chem. Scand. 8, 1835 (1954). ( 6 ) Cohen, S. G., Haas, €4. C . , larnr,y, la., Valle, C . , Isn. l l s f ; . C:iir..hi. 45, 200 ( 1 953 I. ( 7 ) Croon, I., I . i n d t x ~ y , 13.. . ’ ~ L . P N J / , Poihhrls/id,/. 59. -94 i19.56).
