US 2101263 A
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Patented Dec. 7, 1937 CONTINUOUS PREPARATION or cEnLUwsn nanrva'nvns Robert W. Maxwell, Wilmington, DeL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation oi Delaware No Drawing. Application August 1, 1935,
Serial No. 34,133
This invention relates to the manufacture of cellulose ethers and particularly to a continuous process therefor,
Heretofore the preparation of cellulose ethers has been confined to the action of etherifying agents on alkali cellulose in a loose or shredded state.
lose ethers from alkaltcellulose are slow, expensive and inconvenient.
the cellulose, press, shred, age, and then effect reaction in a shredder, barratte, autoclave, or other apparatus. Each of these are separate .operatlons requiring large pieces ofapparatus and extensive floor space. The mixing in the reaction vessel is generally poor and leads to a nonuniform product especially when low degrees of substitution are sought. While it has been proposed to etherify alkali cellulose in the form of pulp board by the action .of gaseous etherifying 23 agents, this method requires a gas tight reaction vessel and a careful separation of the pulp sheets to permit contact with the gas. Penetration of the gas into the alkali cellulose sheet is neces sarily slow and is attended by poor uniformity.
In addition, non-volatile etherifying agents are obviously not applicable. 3
While U. S. Patent 1,736,714 to Lilienfeld discloses the treatment of spun or woven fabric of cotton with etherifying-agent in the presence of alaklL'this process is contraindicative to the proc- 'ess of the present invention, and it would not be expected from the success of that process that a uniform etheriflcation could be obtained by the present invention, inasmuch as the process of this Lilienfeld patent discloses a method of obtaming a surface'efiect. therefore an essentially non-uniform effect, on a fabric. This invention has as an object the preparation of cellulose ethers from alkali cellulose in a simplified-manner. A further object is a process whereby celluloseethers of greatly improved unilormity are prepared from alkali cellulose. A still further object is a process for the preparation of improved low substituted cellulose ethers. A still further object is a. continuous process of cellulose etherification. Other objects will ap-, pear hereinaften These objects are accomplished by the follow ing invention wherein cellulose pulp in the form of individual sheets or a continuous roll is continuously impregnated with alkali, the excess removed and the alkali cellulose then continuously impregnated with a liquid etherifying composition, the excess removed and the impregnated sheet allowed to react. The impregnation with These customary preparations of cellu- It is necessary to steep This simplest procedure is, however, limited to etherifications with etherifying reagents soluble in and at least moderately stable towards caustic alkali. If the reagent is not stable to caustic alkali it becomes decomposed to an appreciable extent before mixing with the cellulose is accomplished.
In a further, likewise preferred, embodiment of the invention which is particularly desirable when the etherifying agent is rather sensitive to caustic alkali, the alkali cellulose is formed continuously,
by running cellulose pulp in continuous or individual sheet form through aqueous caustic alkali and then through rolls to squeeze out the excess.
The .alkali cellulose sheet or sheets is then impregnated continuously with the etherifying agent.
The impregnation may be effected in several ways. sheet through a bath containing the etherifying reagent and then through squeeze rolls to remove the excess. This procedure works best for those materials such as aqueous solutions which swell the alkali cellulose, thus penetrating rapidly It would be expected that passing alkali cellulose into an aqueous solution would result in the extraction of much of the caustic. Sur- The simplest is to pass the alkali cellulose Q prisingly, however, the loss is very small, usually considerably less than 10%.
A second method of introducing the substituting. reagent is to pass the alkali cellulose sheet through squeeze rolls which are provided with a means of supplying the reagent to the sheet. Theroll may be covered with a felt or spongy material saturated with reagent or the roll may carry suitable engravings adapted to carry considerable liquid or' in some instances a smooth roll itself through the sheet. .The reagent should preferably be applied in as small excess as possible to prevent washing out the caustic when the excess is expressed. However, an excess must be applied to make sure that each fibre of the sheet is flooded with re:
I agent for an instant.
' The pressure applied at the impregnation roll may be controlled by the pressure on the impre'g-.
nation rolls and the concentration of reagent in the impregnating solution. Sincean excess of water is usually undesirable in cellulose reactions, when the reagent is added in aqueous solutions the concentration should be as high as other conditions will permit. The press weight of the sheet after passing the rolls is between 2.5 and 6 times and preferably 34 times that of the original cellulose sheet.
An important feature of the process is the introduction of the reagent into the sheet at the place where it is to react.- Too high mobility, i. e. rapid evaporation or diifusiomof the reactant is undesirable. Accordingly, reagents which are not easily lost by volatilization under the conditions 'of the reaction are preferably used; Also since the alkali cellulose is wet most readily by aqueous solutions and thus aqueous reagents are taken up very uniformly, when convenient those reagents which are water soluble are preferably used. Wetting agents such as salts of acids prepared from primary branch chain alcohols of 68 carbon content prepared by catalytic hydrogenation of carbon oxides atelevated temperatures and pressures are of great assistance both in the impregnation of the cellulose with alkali and in the impregnation of the alkali cellulose with reagents. The large area and uniformtexture of chemical cellulose in pulp form permits impregnationof the alkali cellulose sheet with reagent with a degree of uniformity which cannot be equalled by cellulose in any other form.
The treatment of the impregnated sheets depends upon the nature of the reaction. In some instances it is sufflcient to allow' them to stand at room temperature, 1. e. 20-30 C. in a vessel protected from the air. In other instances, temperatures as high as 150 or as low as 0 may be desirable depending on the nature of the material. Although aging of the'alkali cellulose impregnated sheets takes place more slowly than aging of shredded alkali cellulose, in some instances it is desirable to replace the air about the sheets with nitrogen to preserve viscosity.
The concentration of the steeping caustic varies with the nature of the reaction and the quantity of reagent used; Solutions of from 10 to 70% concentration may be used successfully, but the preferred concentration in the freshly impregnated sheetis 15-25% calculated on the water and caustic present.
The concentration of etherifying agent may vary from as in the case of a liquid reagent added directly, down to a much lower concentration. 'In general, the reagent should be present purified by washing with water.
2,101,263 sure of the rolls forcing the liquid uniformly in the pressed sheet in an amount equal to 0.1 to 2 mols of reagent per glucose unit of the cellulose for the formation of those ethers in the production of which the present invention is so particularly advantageous-namely, the alkali soluble low substituted cellulose eth'ers, i. e. those containing 'up to 1 mol. substituent and preferably up to .mol. substitutent per glucose unit of the cellulose. The process of the present invention is applicable to the preparation of cellulose ethers in general so. that more than 2 mols even up to 5, 10, or more mols of reagent per glucose unit of the cellulose may be introduced into the alkali cellulose sheet, depending on the degree of substitution desired.
The process is also particularlysuited for preparation of cellulose ethers of extremely low degrees of substitution such as the methyl celluloses made from as little as .005 mols. of reagent.
Having outlined the general principles and purposes of the invention, the following exemplifications thereof are added in illustration but not in limitation of the invention.
Example 1Methylcellulose Cellulose in roll or sheet form was run continuously through a bath containing 480 parts of 18% sodium hydroxide and 102 parts of sodium methylsulfate. The steeped material was run through squeeze rolls which reduced the weight to 3.34 times that of the original pulp. The product was aged for 96 hours at 30 andwas then The Inethylcellulose product when dissolved to give 5% methylcellulo-se and' 7% sodium hydroxide at 8 C.
gave a viscous, stable and clear solution. It filtered a great deal better and was much stronger in acid film casting baths than products of the same viscosity and methyl content prepared by the action. of methylating agents on alkali cellulose from the same cellulose in batch processes.
Example 2Methylcellulose The procedure was the same as in Example 1 except that the sodium methylsulfate-alkali cellulose sheets were aged in an atmosphere of nitrogen for ten days. I The product was much more viscous than the product of Example 1 but was of the same degree of solubility.
Example 3C'ellulose glycolic acid Cellulose in sheet or roll form was steeped continuously in a small volume of a solution of sodium chloroacetate in sodium hydroxide. The solution was prepared by mixing together at temperatures below 10, 162 parts of 36% sodium hydroxide solution with a solution of 59 parts of sodium chloroacetate in 162 parts of water. The
freshly mixed causticsodium chloroacetate solution was fed constantly into the steeping tank at the same rate as it was removed by the steeping process. The temperature of steeping the liquor was held below 10 to minimize hydrolysis I on the sodium chloroacetate. The sheets after steeping were passed through squeeze rolls under such pressure that the pressed sheets were 3.36
- times the weight of the original cellulose. This 6% sodium hydroxide to give solutions of high viscosity which contained very little insoluble Iii q Ih) except that a' 15% solution of .sodium chloro-,
fiber and which filtered readily. Solutions of the product contained muchless insoluble fibre and filtered more readily than glycolic acid ethers of cellulose of the same'degree of etherification and viscosity made from alkali cellulose from the same cellulose using batch processes.
Example 4-'Cellul0se glycolic acid Cellulose in roll or sheet form was steeped continuously in 28% sodium hydroxide solution. It
wasthen run through squeeze rolls which reduced the weight of the sheet to three times that of the original cellulose. The alkali cellulose sheet was next run through wringer rolls, the lower member of which was covered. with an alkali resistant felt which dipped in a 30% aqueous sodium chloroacetate solution. The felt was of such a nature thatit carried suflicient of ,the solution that, as the alkali cellulose sheet passed through thesqueeze rolls sodiumchloroacetate solution was forced through the alkali cellulose sheet in such quantity that a very small ripple of the solution was to be seen between the sheets a passing through the rolls and the upper roll. The appearance of the ripple was an indication that thorough impregnation was taking place. The pressure on the rolls was so adjusted that the impregnated sheet weighed four times that of the original cellulose. The sheet was then rolled onto a core or if in the form of separate sheets, these were piled in a closed container and set aside at 25 C. to react. After 48 hours the product was washed caustic free with hot water and was then dissolved to 6% cellulose and 7% sodium hydroxide in water at 7 C. The product was of much better solubility, containing fewer undissolved fibers'and filtering with much greater case than products of the same degree of substitution and viscosity made from the'same alkali cellulose with batch processes. tity of sodium chloroacetate used equalled approximately one-half mol. per glucose unit of cellulose.
Example 5--Cellulose glycolic acid The procedure wasthe same as in Example 4 except that the-pressure on the impregnation rolls was increased so that the impregnated sheet weighed 3.5 times the weight of the original celiulose. The product after purification dissolved in 7% sodium hydroxide at C to give viscous, almost fibre free solutions. This procedure utilized A; mol. of sodium chloroacetate per glucose unit of the cellulose.-
uct of the same viscosity and solubility, it was necessary to use mol. of sodium chloroacetate.
Example 6-Cellulosc glycolic acid The procedure was the same as in Example 4.
acetate was used as the impregnating bath. The
quantity of sodium chloroacetate used equalled mol."per,glucose unit of the cellulose. The
product resembled that of Example 5, except that it was of slightly poorer. solubility andwas of somewhat higher viscosity.
Example 7Cellul0sc iycoztc acid The procedure was the same as in Example '5, except that the impregnating solution contained of sodium chloroacetate. -The product dissolved in 8% sodium hydroxide at -l0-to give almost fibre free, viscous solutions. The quantity of reagent used was mol.,per glucose unit The quan- Using batch processes. with the same alkali cellulose, to obtain a prodof. the cellulose. These solutions differed from those of the higher substituted products in that. they are much more opalescent. However, the material cast to brilliantly clear films with excellent wet strength in .acid baths. tions contained fewer undissolved fibres and filtered better than products of the same viscosity made from the same cellulose with one-fourth mol. of sodium chloroacetate per glucose unit using alkali cellulose and batch processes.
Emmple 8-Cellulose glycolic acid Cellulose in roll or sheet form was steeped continuously in 28% sodium hydroxide solution and was then passed through pressure rolls which reduced the weight of. the sheetto 2.8 times the Example 4 closely.
In this procedure a small quantity of sodium hydroxide is expressed from the alkali cellulose sheet. To counteract its effect in saponiflcation of the sodium chloroacetate, the bath may be replenished constantly with a sodium chloroacetate solution containing enough free chloroacetic acid or other tic present.
Example 9-Cellulose glycolic acid Alkali cellulose in roll or sheet form was passed continuously under av spray of sodium chloroacetate solution. The sheets were then passed through squeeze rolls which reduced the weight of etherifying solution to that of the original cellulose. The product resembled that of Example 4. chloroacetate solution by a spray, it may be fed to the sheets by means of brushes.
Example 10--Methylcellulose One hundred sixty-two parts of wood cellulose were steeped in an aqueous 28% sodium hydroxide solution for one hour and then pressed to 480 parts. The pressed sheets were run rapidly through squeeze rolls which were covered with a spongy material saturated with 2.45% aqueous solution of sodium methylsulfate. The pressure on the rolls and the quantity of sodium methyl- The soluacid to react with the caus- In lieu of supplying the sodium sulfate on the roll were so adjusted that 147 parts of the sodium methvlsulfate solution were taken aside to age for 5 days at"30 C. and then purified and the product-dried. It gave a high viscosity solution in 7% sodium hydroxide when cooled to -10.".
Example 11 Methyleellulose Alkali cellulose was prepared continuously in roll or sheet form by steeping in 18% sodium hydroxide solution and pressing to a weight three times that of the" original cellulose. The sheets were next run through squeeze rolls covered with a spongy material which was saturated with dimethyl sulfate under such pressure that dimethyl sulfate was squeezed through the sheets. The
up by the alkali cellulose. The sheets were set v agent per glucose unit of the cellulose.
siderably less fibrethan solutions of -methylcel--.
lulose of the same methyl content. and viscosity prepared from the same cellulose by the action of dimethyl sulfate-on alkali cellulose in batch op- Example 12Etl zylcellulose The procedure was the same as inExample-ll, except that'the impregnating material was diethyl sulfate. A quantity of diethyl sulfate equivalent to the weight of the original cellulose was introduced. This was one moi. of alkylating The sheets were set aside and allowed to react for 48 hours at 30 C. The product dissolved in 7% caustic at -5 C. to give fibre free solutions which filtered much better than products of the same viscosity and degree of substitution made from the same alkali cellulose using batch processes.
Example 13-Hydro:cyethylcellulose (glycol cellulose) The procedure was the same as in Example 11, except that the impregnating material was ethylene chlorohydrin. The quantity of reagent introduced in the impregnating step equalled'onehalf the weight of the original cellulose. This I wasone mol. of ethylene chlorohydrin per glucose unit of the cellulose. The productafter aging for one day at C. dissolved in 6% sodium hydroxide to give solutions which were practically free from fiber.
Emample 14'- Hydr0ayethylcellulose The procedure was the same as in Example 13, except that the impregnating medium was a 50% solution of ethylene chlorohydrin in benzene.
The quantity of solution introduced was equal to one-half the weight of the cellulose. This gave one-half mol. of etherii'yingereagent per glucose unit of the cellulose. The impregnated sheets were set aside to ,age at for 72 hours.
room temperature to give practically fibre free solutions. r
Example 15Hydro a:ypropylcellulose The procedure was the same as in Example'13.
except that the impregnating medium was a.70% solution oi. propylene oxide in benzene. The weight of the etherii'ying solution introduced equalled the weight of the starting cellulose. The operation was carried out at 10 C! and t he impregnated sheets were stored at 10 for 48 hours after which the temperature was allowed to rise to for 24 hours. completely soluble in water especially below 15 C. and was completely soluble in the presence of a small quantity of sodium hydroxide. After once being dissolved in the presence of caustic the product became completely water soluble. f Example 16Dihydromypropylcellulose (qylcerul cellulose) The procedure was the same as in Example 11.
except that theimpregnating material was glyc- The product dissolved in 7% sodium .hydroxide at a The product was almosteryl monochiorohydrin. YI'he quantity of etherifying agent introduced into the alkali cellulose sheet equalled 70% of the weight of the starting cellulose. This gave one moi. of glyceryl monochlorohydrin per glucose unit of the cellulose. The product after aging for 48 hours at 30 C. dissolved readily in 7% .sodium hydroxide at room temperature to give viscous, fibre free,"solutions.
Example 17-'-Dihydroa:yprom lcellulose A' solution was prepared of 49 parts of'sodium hydroxide, 56 parts of glyceryl monochlorohydrin and 220 parts of water.\ In this was steeped continuously in'roll or sheet form cellulose pulp i which was pressed between rolls to three times the original weight of the,cellu lose. The pressed 1 material was stored in a closed container at 30 C. for 72 hours. They product dissolved in sodium hydroxide 7% at 8 C. to give viscous fibre free solutions. The solutions were of better solubility and filtered more readily than products of the same viscosity and degree of substitution made from the same cellulose by :batch processes.
Example 18Benzylcellulose Cellulose in roll or sheet form was steeped in 18% sodium hydroxide solution and pressed to 2.7 times the original weight oi. the cellulose. The alkali. celluloseshee'ts were then fed through rolls provided with a means described in Example 4 for introducing-benzy chloride into the ssheet. The pressure on the rolls was so adjusted that the weight of benzyl chloride introduced equalled 79% of the weight of the original cellulose. The sheets were stored at 85 C. for 18 hours and were then purified by washing with water in a beater, followed by extraction with chloroacetate, other liquid etherifying agents, i. e.
liquid as such or by solution in water, may thus be employed. The agents are preferably substantially non-volatile under the conditions of the reaction. a The term, improved solubility; as usedin the examples refers to the greater freedom from fibre of 'solutionspf the product. In the preparation of low -substituted derivatives it is necessary-to quantity'of fibrous cellulose. do uniformly and in the processes of the prior art some of thefibres receive more reagent than is necessary to make them soluble and some do not receive enough. Upon dissolving the product therefore some of the fibres dissolve completely .j .while others .remain undissolved. The uniformlty of the product is greatly increased by the process of the present invention and therefore the diserepancy'in solubility between difierent batches of fibres is greatly decreased while the average degree of substitution of the materials might be approximately the same.
In the conventional manufacture of low-substituted cellulose ethers, where solubility is poor, the proportion of insoluble fibre may be reduced by increasing the quantity of etherifying agent, because the larger quantity of reagent may be spread farther than a smaller quantity and thus more of the fibres receive suflicient etherifying agent to make them soluble. The product is, however, still non-uniform inasmuch as much .of the fibre is more highly etherified than the rest.
mix a small quantity of reagent with a large This is diflicult to The process of the present invention which gives a high degree of uniformity renders it possible to achieve the same degree of solubility (proporgether ina shredder 'or other agitator.
tion of soluble fibre) with a smaller quantity of reagent than is necessary with the prior art processes which result in poor uniformity. Thus by impregnating alkali cellulose sheet, according to the process of the present invention, with 0.25 mol. of sodium chloroacetate, a product of the same solubility at 6 .in 6% caustic resulted, as was obtained by'treating alkali cellulose from the same cellulosein a high-speed shredded with 0.5 mol. of sodium chloroacetate. The first product contained 0.15 glycolic acid other groups,
while the second contained 0.25 groups. The solution of the first product when 'cast to films in acid film casting baths gave sheets of improved wet strength both in the casting bath and in the finished state. This distinct advantage is due to the lower number of solubilizing groups in-the precipitated film.
This type of partial solubility above discussed is to be clearly distinguished from that type wherein the whole product is only partially soluble.
cellulose ethers is by mixing the reagents to- The ' present process is an entirely new type of procethe etherifying process the same may be run in-- due involving the impregnation of pulp board without any mixing operation. While it would be'expected that flushing an aqueous solution of etherifying agent through a sheet of alkali cellulose in pulp board form would result in substantial removal of alkali from the sheet, it has been found that, contrary to expectation, but little alkali is removed by the process of thefpresent invention. From the somewhat similar process of Lilienfeld it would be expected that the process of the present invention would result in a mere surface treatment. It has been found, however, contrary to expectation, that a uniform effect throughout the sheet is obtained by following the principles laid down in the present application.
While one of the advantages of the present process is the fact that by a novel alteration in a continuous manner, the process affords a further advantage in the great improvement in the uniformity of the product.
Although the process works best for aqueous solutions of etherifying agents since these seem to give best penetration into the fibre, very good results are obtained with solutions of alkylating agents in organic solvents or mixtures of organic solvents with water, for example, glycerine monochlorohydrin in alcohol or aqueous alcohol, dimethylsulfate in benzene, benzyl chloride in gasoline or propylene oxide in dibutyl ether.- Any solvent which ,will not react with the cellulose or' alkylating agent under the conditions of the reaction, 1. e. an inert solvent, may be used. The boiling point is preferably-sufficiently low to permit easy purification but high enough that the solvent does notescape rapidly.
As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.
1. Process for the preparation of cellulose ethers which comprises continuously impregnat- The .usual process of making low-substituted ing agent is substantially non-volatile at the temperature of reaction.
4. The process of claim 1 wherein the etherifying agent is substantially non-volatile at the tem-' erature of reaction and is water soluble.
5. Process for the preparation of cellulose ethers which comprises continuously impregnating alkali cellulose in sheet form with an aqueous solution of etherifying agent, continuously expressing the excess thereof, allowing the impregnated pulp sheet to react, and then terminating the reaction.
6. Process for the preparation of cellulose ethers which comprises continuously impregnating cellulose in sheet form with a solution of an etheri-,
fying agent in aqueous caustic alkali, continuously expressing the excess thereof, allowing the impregnated sheet to react and thenterminating the reaction.
7. Process for the preparation of low substituted cellulose ethers which comprises continuously impregnating alkali'cellulose in sheet form with an aqueous solution of etherifying agent, continuously expressing the excess thereof, allowing thejmpregnated pulp sheet to react, and then terminating the reaction,
8. Process for the preparation of low substituted lower alkyl celluloses which comprises continuously impregnating alkali cellulose in sheet form with a lower alkyl etherifying agent in liquid form, expressing excess etherifying agent until up to 2 mols per glucose unit remain in the sheet, allowing the thus impregnated sheet to react, and then stopping the etherification.
9. Process for the preparation of low substituted. lower alkyl celluloses which comprises continuously impregnating cellulose in sheet form with a .solution of a lower alkyl etherifying agent in aqueous caustic alkali, expressing excess etherifying agent until up to 2 mols per glucose unit remain in the sheet, allowing the thus impregnated sheet to react and then stopping the reaction.
10. Process for the preparation of low substituted alkyl celluloses which comprises continuously impregnating alkali cellulose in sheet-form with an alkylating agent in iquid form, expressing excess etherifying agent, until up to 2 mols per glucose unit remain in the sheet, allowing the thus impregnated sheet to react, and then stopping the alkylation.
11. Process for the preparation of low substituted alkylcellulose which comprises continuously impregnating a sheet of cellulose pulp with a liquid composition comprising a solution of a lower alkyl etherifying agent in aqueous caustic alkali, continuously expressing excess reagents, allowing the impregnated pulp sheet to age and react, and then terminating the alkylation.
12. Process for the preparation of low substituted methylcellulose which comprises passing cellulose pulp in sheet form through an aqueous steeping bath containing sodium hydroxide and sodium methylsulfate, expressing excess etherification mixture continuously by passing through squeeze rolls to a press product containing up to 2 mols sodium methylsulfate, allowing the impregnated sheet to age andreact, and then stopping the etherlflcation.
13. Process for the preparation of low substituted methylcellulose which comprises passing cellulose pulp in a continuous sheet form through an aqueous'steeping bath containing approximately 15% sodium hydroxide and approximately tinuously impregnating alkali cellulose in' sheet form with an alkali chloroacetate solution, ex-
' pressing excess solution until up to 2 mols per until the impregnated sheet weighs approximately glucose unit remain in the sheet, allowing the thus impregnated sheet to react, and then stopping the etherification.
15. Process for the preparation of low substituted cellulose glycolic acid which comprises continuously impregnating alkali cellulose in sheet form with sodium chloroacetate solution, expressing, excess sodium chloroacetate solution four times the weight of the original cellulose, allowing the thus-impregnated sheet to react, and then stopping the etheriflcation.
16. Process for the preparation oi low substituted cellulose glycolic acid which comprises continuously impregnating alkali cellulose in sheet form with a liquid alkylating mixture comprising an alkali metal chloroacetate, continuously pressing the sheet to a press ratio of approximateto react and ,thenstopping the etherification.
17. Process for the preparation or low substitut- .ed cellulose glycolic acid which comprises continuously impregnating a sheet of alkali cellulose pulp with a liquid composition comprising an alkali metal chioroacetate, continuously expressing excess alkali chloroacetate solution, allowing the impregnated pulp sheet to age and react, and then terminating the reaction.
18. Process for the preparation low substituted hydroxyalkyl cellulose which comprises continuously'impregnating a sheet of alkali cellulose pulp with a liquid composition comprising a hydroxyalkylating agent, continuously expressing excess hydroxyalkylating mixture, allowing the impregnated pulp sheet to age and react} and then terminating the hydroxyalkylation.
19. Process for the preparation of low substituted glyceryl cellulose which comprises continuously impregnating a sheet of alkali cellulose pulp with a liquid glycerylating composition, continuously expressing excess glycerylating mixture, allowing the impregnated pulp sheet to age and react, and then terminating the reaction.
ROBERT w. MAXWELL.