USRE24116E

USRE24116E - Ethyl oxyethyl cellulose derivative

Info

Publication number: USRE24116E
Authority: US
Publication date: 1956-01-31

Description

United Sta es Pat nt f Re. 24,116 lcg Reiasued Jan- 3 6 24,116 I ETHYL OXYETHYL CELLULO SE DERIVATIVE iND METHOD OF PREPARATION OF THE Matter enclosed in heavy brackets [.1 appears in the original patent but forms no art of reissue specification; matter printed= in ital cs" indicates the additions made by reissue. Y

This invention relates to cellulose-atheisand more particularly to modified cellnlose ietbers of high solubility in organic solvents. I

It is known that ethyl cellulose canv be prepared ina wide range of solubility characteristics and that solu bility in organic solvents including its tolerance for lowpriced aliphatic hydrocarbons in general increases with increase in the degree of substitution (D. S.) of the cellulose but that ethyl cellulose having a high ethoxyl D. S. in the range of about 3 is brittle and has poor filmforming properties. Moreover, the production of ethyl cellulose of sufficiently high degree of substitution to provide high tolerance for aliphatic hydrocarbon solvents heretofore has required repeated alkylation with diminishing conversion per treatment as the degree of. substitution increases. Any commercially suitable process for the production of ethyl cellulose of high solubility in organic solvents must be simple, economical of reagents, and give a controlled degree of degradation of the cellulose molecule. The' present invention is directed toward such 'a process.

In accordance with the present invention, it has been found that ethyl cellulose of high tolerance foraliphatic hydrocarbons and high. degree of substitution is produced in relatively high percentage conversion by first hydroxyethylating cellulose uniformly to a low degree of substi tution within the range of 0.3 to 0.9 and then ethylating' the hydroxyethyl cellulose so produced to the desired ethoxyl content up to the range of optimum solubility.

and other characteristics which correspond to an ethoxyl D. S. within the rangeof; 2.6 to 2.9-. Inaccordance with the present invention,- such. a-modified ethyl cellulose of a high degree of substitution showing good film-forming.

characteristics, excellent solubility in the aromatic hydro carbon solvents, and high tolerance for aliphatic hydrocarbons is obtained by first reacting. alkali cellulose, in a system in which the sodium hydroxidezcellulose ratio (by weight) is within the range of. 0.25:1. to 05:1 and the waterzcellulose ratio (by weight) iswithin the range 0.7:1 to 1.6:1, with ethylene oxide in anrarnount. sufficient to give a D. S. of about 0.3 to about 0.9 mole per mole cellulose (anhydroglucose unit) at. a temperature within the range of about 20"C. to about 80 C and subsequently reacting thepartially hydroxyethylatedprodg uct in a system in which the sodium hydroxide'zhydroxyethyl cellulose ratio is within the range of-about 2:1 to

8:1 and the waterzhydroxyethyl cellulose ratio is within The modified ethyl cellulose obtained s eepwear, this invention has an oxyethyl (.ROCHgCHa R= I-l or.

, 2 and is characterized by having a high degree of uniformity of substitution as indicated by an enhanced solubility in aromatic hydrocarbons and tolerance for aliphatic hydrocarbons over the range of oxyethyl and ethoxyl contents indicated above. In order .to achieve these high solubility characteristics, the alkali cellulose must be uniformly hydroxyethylated until at least a hydroxyethyl D. S. of about 0.3 is reached.

The following examples wherein parts are by Weight exemplify the process by which the ethyl cellulose of this invention is produced.

Example" 1' A slurry of 400 parts chemical cellulose in 11,300 parts diethyl ether was stirred vigorously while 800 parts sodium hydroxide solution was added slowly over hydroxide component amounted to 160' parts, and the water component amounted to 640 parts. This filter cake containing about 2200 parts residual ether was placed in an autoclave from. which air had been displaced by nitrogen, along with about 1400 parts ethyl. ether and 118 parts ethylene oxide. This reaction mixture' was heated to 70 C. over a one-halt. hour, period and then maintained at 70 C. with agitation for 3 hours. At. the end of time the low-boiling components of the mixture were bled oil and a sample of the product was taken for analysis. Analysis showed hydroxyethyla tion efliciency to be 35%. To the remainder of the product in the autoclave was then added. 2620 parts 48.3% sodium hydroxide, 600 parts hydroxide pellets, and 1600 parts ethyl chloride. The autoclave was then heated to 130 C. with stirring and maintained at that. temperature for 5 hours. After this reaction. period, theproduct wasv workedup by neutralizing the alkali with acetic acid, wet milling, and water washing until freed of salts. The resulting ethyl cellulose was'then dried at 70 C- Analysis of this modified ethyl cellulose indicated the presence of 0.39 5- oxyethyl' group per anhydroglu cose unit and 2.48 ethoxyl groups per anhydroglucose unit. The ethoxyl analysis includes the total ethoxyl whether combined as ethoxyethyl groups or as ethoxy;

. groups substituted directly on the cellulose molecule.

hydroxide solution and-alsoshowed 13.5% oxyethyl cal- I culated as hydroxyethyl. The modified ethyl cellulose so produced had excellent solubility characteristics in toluenezalcohol (4:1) and had an aliphatic hydrocarbon tolerance (.as defined in Examples 3-14) of about 40 compared with 10 for ethyl cellulose of 2.5 D. S.

. Example 2 Alkali cellulose prepared by steeping 400 parts chemical cellulose. in an excess .of..20.% sodium hydroxide.

solution. for 1. hour and then pressing out all residual sodium hydroxide to a pressed weight of 1344 parts was C. .to C.. to an ethoxylpD. S.- of.

CaHs-) degree of substitution (115.); range. 7

about 0.3 to 0.9 and a: total ethoxy' content corresponding. l to a degree of substitution within the range of 2.6 to 2.9

masticated in a shredder and was then placed inan auto= ether and 1600 parts ethyl chloride.

ethylation efficiency of about 32%.

' To the remaining hydroxyethyl cellulose in the autoclave were added 2090 parts 49.7% sodium hydroxide, 976 parts sodium hydroxide pellets, and 80 parts ether, and the 1600 parts ethyl chloride which were withdrawn were replaced along with the ether contained dissolved therein. This reaction mixture was then heated in the autoclave with agitation for hours at 130 vC. The modified ethyl cellulose product was worked up in the same manner as the product in Example 1. It was shown by analysis to have a D. S. of 2.64 ethoxyl groups and a D. S. of 0.38 oxyethyl group, the ethoxyl analysis being the total number of ethoxyl groups in the product. The solubility in toluene: alcohol (4:1) was excellent and the aliphatic hydrocarbon tolerance was about 65 compared with about 45 for ethyl cellulose of ethoxyl D. S.=2.64.

Examples 3-14 A series of hydroxyethyl cellulose'samples having a hydroxyethyl D. S. within the range of 0.35 to 0.85 were prepared in the manner described for the first step of the process of Example 2. Each of these samples was then further reacted with ethyl chloride to produce a modified ethyl cellulose in accordance with this invention. In general, the procedure involved placing in an autoclave 30 parts of the hydroxyethyl cellulose containing suifieient added sodium hydroxide to correspond to 234 parts 50% sodium hydroxide in the mixture along with 161 parts sodium hydroxide pellets. The autoclave was cooled and 125 parts ethyl chloride were added so as to displace the air. Ethylation was then carried out by mixing these reagents in the autoclave for 16 hours at 130 C. The degree of ethylation was controlled in the various examples by the length of thetime at which the ethylation was carried out. In the procedure just described, a product of 2.74 ethoxyl D. S. was obtained.

Each of these modified ethyl cellulose products was worked up by distilling off the volatile products from the autoclave, grinding the solids, washing the product with wateruntil free of chlorides and subsequently drying in vacuo at 65 C. Each of the hydroxyethyl cellulose samples was analyzed for oxyethyl D. S. before ethylation by the total ether analysis of Morgan (Ind. Eng. Chem., Anal. Ed. 18, 500-604 (1946)) and the ethylated product was analyzed by total carbon analysis by combustion. The Morgan method of analysis in showing total ether content shows the hydroxyethyl D. S. and this is assumed to carry over as oxyethyl D. S. after ethylation. By using the total carbon analysis it is possible by means of simultaneous equations to estimate the relative composition as to oxyethyl D. S. and ethyl D. S.

Each of these samples was of good solubility in a toluenezalcohol (4:1) solution and was tested for aliphatic tolerance by determining the highest per cent by weight of heptane in a heptane-toluene mixture which will dissolve the cellulose ether to give a good 2% solution. The analytical results for oxyethyl D. S. and ethoxyl D. S. along with the aliphatic tolerances so determined are tabulated in the table below:

Each of these samples within the scope of this invention is seen to have a good aliphatic hydrocarbon tolerance and it is substantially higher than the aliphatic hydrocarbon tolerance of an ethyl cellulose having substantially the same total ethoxyl D. S. Examples 13 and 14 show that the range of substitution is critical.

The modified ethyl cellulose of this invention is insoluble in water and dilute alkali and appears to have oxyethyl groups so uniformly distributed in the molecule along the cellulose chain as to give the enhanced solubility characteristics which the product shows. The allphatic hydrocarbon tolerance of these products falling within the scope of this invention is in every case substantially greater than ethyl cellulose of the same ethoxyl D. S. and no other substituents. By high aliphatic hydrocarbon tolerance as used in this specification and claims is meant substantially higher aliphatic hydrocarbon tolerance than obtains for ethyl cellulose of the same ethoxyl D. S. in which no other substituents are present. Aliphatic hydrocarbon tolerance is defined by the procedure set forth in the examples.

The step of hydroxyethylation tends to improve the reactivity of the cellulose molecule; but the hydroxyethyl groups must be uniformly distributed with respect to the cellulose molecules so as to give the optimum in improved aliphatic hydrocarbon tolerance in the ethylated product. Since the hydroxyethyl groups are probably more reactive toward ethylation than are the hydroxyl groups of the cellulose molecule, it is believed that a high proportion of the oxyethyl groups may be present as' ethoxyethyl groups. The term oxyethy is used herein to cover both hydroxyethyl and ethoxyethyl. The improved solubility characteristics of the product are dependent not onlyupon the uniformity of distribution of the oxyethyl groups among and within the cellulose molecules, but also upon the degree of substitution of these groups.

0.3 to about 0.9. Below about 0.3 the ethylated product shows very little improvement in solubility characteristics and above about 0.9. the softening point drops rapidly with further substitution. The oxyethyl groups within this range of substitution and uniformly distributed not only improve reactivity in the ethylation process but they also improve the solubility and aliphatic hydrocarbon tolerance by the influence of the oxyethyl groups in preventing orientation of the highly ethylated cellulose chains.

Since uniform distribution of the oxyethyl groups is a requisite for the improved solubility characteristics, the hydroxyethylation must be carried out under optimum conditions for promoting uniformity of substitution.

' -Due to the greater reactivity of a partially hydroxyethylated cellulose, itis much easier to obtain uniform distribution of the ethoxy groups subsequently introduced than in the case of the ethylation of cellulose itself with the net result that more complete ethylation under mild conditions takes place with high percentage conversion. Nevertheless, it is still necessary to use more concentrated alkali and higher temperatures for the ethylation step than is satisfactory for the hydroxyethylation step whereby uniform substitution is attained. Attempts to carry out bothhydroxyethylation and ethylationsimultaneously have not led to a product of improved solubility because hydroxyethylation cannot be satisfactorily carried out under the conditions of concentrated alkali and high temperatures required for ethylation and the amount .of oxyethyl D. S. is incontrollable. Hydroxyethylation, for instance, may go almost explosively under the ethylation conditions and some ethylation may under such conditions take place prior to hydroxyethylation. These conditions lead to poor ellieiency, below 20%, in the utilization of the Thus, an extended study has shown that, the oxyethyl D. 8. must be within the range of about ethylene oxide and the product of web ai'proccssalso.

possesses poor solubility.

.The process for produc' g the modified ethyl cellulose of this invention having the improved solubility characteristics is thus carried out by uniformly hydroxyethylating cellulose under the conditions specified which lead to atmiformly substituted active hydroxyethyl cellulose of low degree of substitution and subsequently ethylati'ng the product under such conditions specified above as lead to ethylation of the hydroxyethyl groups and also part of the cellulose hydroxyl groups. The process can be carried out in two separate steps with intermediate purification of the hydroxyethyl cellulose. However, an important advantage of the present invention is that'the two steps of the reaction can be carried out without an intermediate purification step simply by increasing the alkali concentration and increasing the temperature for the secand step. The caustic used for hydroxyethylation then becomes available for et hylation. The ethylene oxide may be added as the sole reagent in. the first step, or part or. all of the ethyl chloride needed for the second step may" be present during the hydroxyethylation. In this latter case the alkali concentration and temperature of reaction are such that the ethylation reaction does not take place. Regardless of whether the ethylene oxide is present alone or along with ethyl chloride in the first step of the reaction, the second step of the reaction is carried out by first increasing the alkali concentration by the addition of aqueous sodium hydroxide of high concentrationor by the addition of aqueous sodium hydroxide of special conditio low concentration along with solid sodium hydroxide in order to produce the desired relationship between the amounts of cellulose, sodium hydroxide, and water r..- quired' for optimum ethylation conditions. Since sodium hydroxide is consumed in the ethylation step, the alkali concentration normally changes during the course of. the In order that. the alkalinity conditions may reaction.

be maintained more constant-during the ethylation, a

preferred embodiment which brings aboutimproved results with respect to efiiciency of reaction comprises adding part of the alkali stepwise or'gradually during the course of the ethylation so as to avoid wide limits of alkalinity during that process. Likewise, theethyl chloridemay be introduced gradually during. the course of the ethylation with advantageous results. By adding both the ethyl chloride and the sodium hydroxide solution gradually during the course of the ethylation, a still greater efficiency of reaction is attained. By predetermination of rate of reaction, it is possible to addthe ethyl chloride at substantially the rate it is consumed. Since no intermediate purification step .is.necessary, t he process of this invention is economical tocarry outand competes with the usual process of ethyl'a'tion for theproduction of certain grades of ethyl cellulose of lower ethox'yl D. S. 3

"Besides hydroxyethylation in the presence of. 'water immiscible organic solvents, the proccss may also be a so-callcd dry process using no organic; solvent. The ratio of water to cellulose as set forth herein is to be maintained regardless of the process'used, and that ratio is based upon the water loosely bound to the cellulose material. In the process 'usingan organicsolvent, thesolvent must, therefore, contain suffifcien't dissolved water to prevent withdrawal of water from thecellul'osic niaterial.

Although ethylene oxide has be'enfindicated as the hydroxyethylating agent, ethylene chlorohydrin may likewise be used provided that the alkalinity during the entire hydroxyethylation step is maintained ,within the same as have been indicated for the casein which ethyleneoxide is used as thereagent. The-alkalinityma'y be maintained within these limits during the hydroxyethylation step by gradually adding alkali during the course of the hydroxyethylation. Moreover, the ethylene chlorohydrin and alkali may both be added gradually during the course of the reaction. When ethylene chlorohydrin tolerance leads Mire" is used at the reagent, it is believed that ethylene oxide is an intermediate and that such a process would, there fore, involve the reaction between cellulose and ethylene oxide as is' preferred in the present process because of the somewhat greater uniformity of: substitution obtained thereby. r

The process of this invention for'production ofa modified ethyl cellulose having high aliphatic hydrocarbon to a product having an ethyl D. SJin the range of about 2.6 to 2.9 which is a higher ethyl D. S. than is readily attainable in an ethyl cellulose produced by any known process for direct ethylationof cellulose. Moreover, the modified ethyl cellulose of. this invention is distinctly superior in aliphatic hydrocarbon tolerance as compared with ethyl cellulose of the same ethyl D. S. The oxycthyl groups introduced intothe celluloseinv the present process thus not only improve thjeeas'e of intro ducing ethyl groups but also contribute to the'improved solubility as measured by aliphatic hydrocarbon tolerance. The improved? product results from the improve-1 ment in the ethylation process not only with respect to the use of hydroxyethyl celluloseofa narrow range of hydroxyethyl D S. but also with respect to the use of the 'hydroxyethylation. processwith the ethylation process provides such a uniformly substituted hydroxyethyl'cellulose in the first step. Although thisembodiment is preferred, it is not critical for the end result, since uniformly hydroxyethylatedcellulose of. hydroxyethyl D'. S. in. the range of about 0.3 to about 0.9, regardless of how produced, may be used in the ethylation step. a

What I claim and desire to protect by Letters Patcntis:

[1. The process for producing a water-insoluble, alkaliinsoluble ethyl oxyethyl cellulose. having. a h ghv aliphatic hydrocarbon tolerance which comprises uniformly hy-, droxyethylating cellulose to a hydroxyethyl D. S. within the range of 0.3 to 0.9 ina system in which the sodium hydroxidezcellulose ratio is within the rangeof: 0.25 :l to 05:1 and the waterzcellulose ratio is within the range of 0.7:1 to 1.6:1 with ethylene oxide at a temperature within the range of 20-80 C. and subsequently ethylating the product with ethyl chloride at a temperature within the range of about 95-l60' C. toan ethoxyl D. S. (total) within the range of 2.6 to 2.9 in a system in which the sodium hy'droxidczcellulose ratio is within the range of 2:1 to 8:1: and. the .waterzcellulose ratio within the range of 1:1 to 8:1.1 2. The process, for producing a water-insoluble, alkaliinsoluble ethyl oxyethylcellulose having a high aliphatic hydrocarbon tolerance which. comprises reacting. an alkalicellulose in an aqueous system in which the ratio of so dium hydroxidemellulose is within the range of 0.25:1 to- 0.'5:1 and in which the watcrzcellulose ratiois within'thc range of 0.7:1 to 1.6:1 with ethylene oxide in anamount within the range of about 0.3 to about 0.9 mole per mole cellulose {anhydroglucose unit) at a temperature .within the range of. about 20 to about C; and .then adding sodiumhydroxide and water in sufiicientamount to bring" the total in the system up to a sodium hydroxidezhydroxyethyl. cellulose ratio within the range. of about'2.0:-1 to 8:1 and waterzhydroxyethyl' cellulose ratio within the range of 1:1 to 8:1 and reacting with ethyl chloride in an amount within the range ofabout 2.6 to about 2.9 moles per mole hydroxyethyl cellulose at a'tern'perature within'the range oia'bout to. C.

[3: Theproce's's for producing a water insolnbl;"alkali insoluble ethyl oxyethyl cellulose having a high aliphatic hydrocarbon tolerance which comprises treating an aqueous alkali cellulose composition, in which the ratio of sodium hydroxidezcellulose is within the range of about 0.7 to 1.6 times'the weight of the cellulose, with ethylene oxide in a molecular amount sufli cientto give a D. S. iu the range of about 0.3 to about 0.9 and ethyl chloride in an amount within the range of about 3 to about based on the cellulose, heating at a temperature within the range of about to C. until the ethylene oxide has reacted substantially completely, adding sutficient aqueous sodium hydroxide to increase the so-- dium hydroxide content to '2 to 8 times the weight of the cellulose and the water content to l to 8 times the weight of the cellulose, and heating at a temperature within the range of about 95 to 160 C. until a modified ethyl cellulose having an ethoxyl corresponding to a D. S. within the range of 2.6 to 2.9 is obtained] [4. The process for producing a water-insoluble, alkaliinsoluble ethyl oxyethyl cellulose having a high aliphatic hydrocarbon tolerance which comprises reacting an alkali cellulose in an aqueous system in which the ratio of sodium hydroxidezcellulose is in the range of 0.25 :1 to 0.5 :1 and the ratio of waterrcellulose is in the range of 0.7:1 to 1.6:1 with ethylene oxide in an amount within the range of about 0.3 .to about 0.9 mole per mole cellulose (anhydroglucose unit) at a temperature within the range of about 20 to about C. and then raising the temperature to a temperature within the range of about to C. and adding aqueous sodium hydroxide to increase the sodium hydroxidezcellulose ratio to the range of 2:1 to 8:1 and the waterzcellulose ratio to the range of 1:1 to 8:1 and subsequently adding ethyl chloride and aqueous sodium hydroxide in substantially equivalent ratio at substantially the rate consumed while maintaining a temperature within the range of about 95 to 160 C. untila modified ethyl cellulose having a total ethoxyl content corresponding to a D. S. of 2.6 to 2.9 is reached] 5. In the process of producing an ethyl oxyethyl cellulose having oxyethyl and ethyl substituents, the improvement, by which a modified ethyl cellulose having a high aliphatic hydrocarbon tolerance is produced, which comprises causing hydroxyethyl cellulose, having a hydroxyethyl D. S. within the range of about 0.3 to about 0.9, in intimate admixture with sodium hydroxide and water in respective amounts within the range of 2m 8 and 1 to 8 times the weight of the hydroxyethyl cellulose, to react with about 2.6 to about 2.9 moles ethyl chloride.

6. As a new composition of matter a modified ethyl oxyethyl cellulose having an oxyethyl degree of substitution within the range of 0.3 to 0.9 and a total ethoxyl content corresponding to a degree of substitution within the range of 2.6 to 2.9 and characterized by solubility in organic solvents and tolerance for aliphatic hydrocarbons substantially greater than ethyl cellulose 'of the same ethoxyl content.

7. As a new composition of matter a modified ethyl ethoxyethyl cellulose having an oxyethyl degree of substitution within the range of 0.35 to 0.45 and a'total ethoxyl content corresponding to a degree of substitution within the range of 2.75 to 2.9 and characterized by solubility in organic solvents and tolerance for aliphatic hydrocarbons substantially greater than ethyl cellulose of the same ethoxyl content.

8. In the process of producing an ethyl oxyethyl cellulose having oxyethyl and ethyl substituents, the improvement, by which a modified ethyl cellulose having a highaliphatic hydrocarbon tolerance is produced, which comprises causing hydroxyethyl cellulose, having a hydroxyethyl D. -S. within the range of about 0.3 to about 0.9, inintimate admixture with sodium hydroxide and water to react with about 2.6 to about 2.9 moles ethyl chloride.

9. The process of producing a modified ethyl cellulose having a high aliphatic hydrocarbon tolerance, which comprisesre acting alkali cellulose with ethylene oxide in 0.25 :1 to 0.5 :1 and in which the water in the system is an amount sufiicient to give a D. S. of about 0.3 to about.

0.9 mole per mole cellulose (anhydroglucose unit) at a temperature within the range of 20 C. to 80 C. and subsequently reacting the partially hydroxyethylated prodact with ethyl chloride at a temperature within the range of 95 C. to 160 C. to an ethoxyl D. S. of 2.6 to 2.9.

10. The process for producing a water-insoluble, alkaliinsoluble ethyl oxyethyl cellulose having a high aliphatic hydrocarbon tolerance which comprises uniformly hydroxyethylating cellulose to a hydroxyethyl D. S. within the range of 0.3 to 0.9 in a system in which the sodium hydroxidexellulose ratio is within the range of 0.25:1 to

0.5:] and the water:cellulose ratio is within the range of.

0.7:1 to 1.6:] with ethylene oxide at a temperature within the range of 2080 C. and subsequently ethylating the product with ethyl chloride at a temperature within the range of about 95-160 C. to an ethoxyl D. S.

(total) within the range of 2.6 to 2.9 in a system in which the sodium hydroxide'hydroxyethyl cellulose ratio is within the range of 2:1 to 8:1 and the water:hydroxyethyl cellulose ratio is within the range of I :1 to 8:1.

11. vThe process for producing a water-insoluble, alkaliinsoluble ethyl oxyethyl cellulose having a high aliphatic hydrocarbon tolerance which comprises treating an aqueous alkali cellulose composition, in which the ratio of sodium hydroxide.'cellulose is within the range of about 0.25:] to 0.5:] and in which the water in the system is 0.7 to 1.6 times theweight of the cellulose, with ethylene oxide in a molecular amount sufiicient to give a D. S. in the range of about 0.3 to about 0.9 and ethyl chloride in an amount suflicient for the ethylation reaction to be described subsequently, heating at a temperature within the range of about 50 to 75 C. until the ethylene oxide has reacted substantially completely, adding suflicient aqueous sodium hydroxide to increase the sodium hydroxide content to 2 to 8 times the weight of the hydroxyethyl cellulose and the water content to I to 8 times the weight of the hydroxyethyl cellulose, and heating at a temperature within the range of about 95 to 160 C.

v until a modified ethyl cellulose having an ethoxyl corree spondin'gto a D. S. within the range of 2.6 to 2.9 is obtained.

12. The process for producing a water-insoluble, alkali-' insoluble ethyl oxyethyl cellulose having a high aliphatic hydrocarbon tolerance which comprises reacting an alkali cellulose in an aqueous system in which the ratio of sodium hydroxidexellulose is in the range of 0.25 :1 to 0.5:] andthe ratioof water:cellulose is in the range of 0.7:1 to 1.6:] with ethylene .oxide in an amount within the range of about 0.3 to about 0.9 mole per mole cellulose (anhy-" droglucose unit) at a temperature within the range of about 20 to about 80 C. and then raising the temperature to a temperature within the range of about 95"- to 160 C. and adding aqueous sodium hydroxide to increase the sodium hydroxiderhydroxyethyl cellulose ratio to the range of 2:1 to 8:1 and the water:hydr0xyethyl cellulose ratio to the range of 1:1 to 8:1 and subsequently adding ethyl chloride and aqueous sodium hydroxide in substantially equivalent ratio at substantially the rate consumed while maintaining a temperature within the range of about 95 to 160 C. until a modified ethyl cellulose having a total ethoxyl content corresponding to a D. S. of 2.6 to 2.9 isreached.

References Cited in the file of this patent or the original patent UNITED STATES PATENTS 1,483,738 Lilienfeld Feb. 12, 1924' 1,877,856 Hagedorn Sept. 10, 1932 2,033,126 Dreyfus Mar. 10, 1936