US1687059A - Process of esterifying mercerized cellulose with lower fatty acids - Google Patents

Description

Patented Oct. 9, 1928. I

UNITED STATES;

PATENT OFF-ICE.

HANS T. CLARKE AND CARL J'. MALM, OF ROCHESTER, NEW YORK, ASSIGNOBS TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.

PROCESS OF ESTERIFYING MERCEBIZED CEELULOSE WITH LOWER FATTY ACI IDS.

No Drawing.

Tl is invention relates to. processes of esterifying mercerized cellulose with lower fatty acids, preferably those containing more than 1 and less than 8 carbon atoms.

One object of our invention is to provide an inexpensive and simple process of producing cellulose esters of the lower fatty acids without the aid of anhydrids or catalysts. Another object of the invention is to provide a process of making cellulose esters of the lower fatty acids in a plurality of stages, certain of the'acid groups being combined into the ester during the first stage without use of anhydrids'and catalysts, and the remainder of the acid groups being com bined in the ester by the subsequent treatment of the esters formed in the first stage, thus'efiecting an economy in expensive ingredients, such as the anhydrids of the acids. Another object of the invention is to provide a process in which the first-stage esterificatlon is performed in the absence of any material more hydrolytic than the fatty acids themselves, thus leaving the cellulosic material with the minimum molecular degradation and essentially unchanged in its physical appearance by the first stage of the process; Other' objects will hereinafterappear.

In our application, Serial No. 122,028 filed July 12th, 1926 for cellulose esters of fatty acids and processes of making the same we have shown that unmodified or undegraded cellulose can be esterified, under proper conditions, by the lower fatty acids without the use of catalysts or expensive anhydrids'. and the like. In the case of each of the lower fatty acids, approximately one molecular proportion of acid is combined with an amount of cellulose corresponding to 24 carbon atoms. This first-stage ester is then esterified further by the'usual process,

but with notable economies in the use of anhydrids and with mild catalysts to avoid molecular degradation. 7

We have now found that celluloseesters of the lower fatty acids may be prepared in which more than 2 molecular proportions of acid are combined with anamount of cellulose corresponding'to 24.- carbon atoms and without the use of anhydrids or atalysts,-

Application filed April 23, 1927. Serial No. 186,170.

in fact, with the minimum molecular degradation andwithout modifying the physimercerized cellulose with the acids as the sole acylating agents are very stable, as indicated by their resistance to splitting ofl' acetyl groups when tested by prolonged boiling in Water. In general the fibers of the new compounds are. superficially indistinguishable from the mercerized cellulose fibers from which they are prepared.

It is a useful fact that these esters are 'more readily esterified than plain cellulose Moreover, it

or mercerized cellulose fibers. is necessary to add fewer acetyl groups to them, since they already contain useful amounts. The practical effect is that when these esters are further esterified by using anhydrids, or even acyl chlorides, in the ways previously described for the acylation of cellulose itself, savings of from 20 to 40% of the amount of anhydrid or chlorid may be' obtained. A substantial saving is effected so long as our first-stage esters have more. than one acyl group for each 24 carbon atoms in the cellulose.

Our invention is concerned with the esters of the fatty acids having more than 1 and less than 8 carbon atoms, such as acetic, propionic, butyric, valeric, caproic, heptylic, etc. The rate of esterification falls off rapidly with the higher members of this series of acids. Consequently acetic' acid, propionic acid and butyric acid are those which are preferred, because of their relatively greater commercial availability and their greater speed of reaction. Acetic acid is commercially the most important at present, because of its lower cost.

For the raw cellulose to be mercerized we can employ any of the types customarily used in the manufacture of esters such, for instance, as cotton, surgical cotton wool, tissue paper especially prepared from cotton, and even sulfite wood" pulp, (preferably Ila:

bleached); Our process has a notable whitening tendency on the cellulose where the latter is initially colored, but the general appearance of the fibers is not changed. In

other words, they do not swell, gelatinize,

- or go into solution duringthe treatment with the fatty acids in the first stage.

The first-stage esterification may be conducted over a considerable temperature range. In eneral we prefer to operate above 100 of temperatures above 170 (3., because of the danger of molecularly degrading the cellulose and the products produced from it.

- Within this preferred range the tempera- .a superatmospheric pressure, say in an autoclave', provided the corresponding temperav ture does not reach the point where the product is degraded. While we use the acidsas the sole acylating agents'and prefer to employ tl1em.without admixture with other liquids, nevertheless, the esterification can-be efi'ected,'when the acids-are mixed with non-acylating liquids, such as'chloro form, carbon tetrachloride or benzene. But

these produce no marked advantage.

During the first-stage acylation it is desirable to keep the amount of water present very low.- The total water present, including the water in: the original ingredients,

plus the water formed during the esterification, should never be allowed to reach the point where it prevents the introduction of more than 8% of the acyl-group. We aim to maintain the conditions during the reaction such that the water is removed or diminished in quantity. The use of a frac-. tlODfitlIl this res'u t,'the water vapor being allowed to column is one way of obtaining pass outwhile the fatty acids are condensed I and flowb'ack to the bath. This is possible because all of the fatty acids having more than 1 and less than 8 carbon atoms boil considerably above the boiling point of water. 1 ,7

The .mercerization pretreatment of the cellulose is along customary lines. For ex'-.

' ample, the 'me'rcerization may be conducte'd.

' at room temperature,- by simply nnmersin the cellulose; fibers in a dilute solution of a kali, such as sodium hydroxid. The time of mercerization, known as aging will be longer the more dilute thebath. With an 18% aqueous sodiumrhydroxid solution, we

have obtained satisfactory results u on stoppin the mercerization at the end 24 hours, ut no harm results when the merin order toinsure reasonably rapid action and we do not advise the useressure, a considerable excessof ace-noes ceriaation in such a solution has been car.-

ried out for over 72 hours,--48 hours being a goodmedium time. Moreover, a merceri' zation in a 40% aqueous solution of sodium hydroxid for 24 hours is effective and without harm to the molecule. After soaking in the alkaline solution, the latter is drained oil and the mercerized cellulose fibers washed free from alkali with water and dried in the air at to C.

If desired, the water may be removed by washing witha suitable organic liquid miscible with water, such as alcohol or acetone, previous to drying. Acetic acid may be employed, in which case air-drying is rendered unnecessary. The water may also be re moved by distillation with a water-immiscible liquid of suitable boiling temperature, such as benzene or carbon tetrachloride.

In the' first stage of esterification the mercerized cellulose, thus prepared, is heated in the acid until the acetyl group introduced in the ester is at least 8% of the latter. For example, we may boil 1 part by weight 01" the mercerized cellulose in an excess of acetic acid, say 30 to 40 parts by weight, the

operation being carried out'at atmospheric pressure. The acid is initially substantially free from water, say of 99 to 100% strength,

The boiling. point of the reaction bath is thus'kept at about 117 C. or slightly above. Of course, any suitable precautions are taken to prevent the loss of-acid by loss of its vapor-s, the same being condensed and returned to the bath by the use of any of the expedients familiar to chemists.

As the boiling in acetic acid is continued under these conditions the esterification pro-.

'gressively. takes place. Roughly the pro: portion of acetyl can be carried to well over 14% and even above 20% of the weight of the ester. This strong esterification may be obtained after different lengths of time, according to the method b was dried. Some of them reach approximately 14%: after 96 hours of treatment. But a useful much shorter tune. For instance, the percentage of acetyl in the ester reaches 8 before 48 hours in practically every 1nstance and often reaches 11% in that time. This 8+% ester has. the property of being readily esterified further in t e usual baths 'but with very good economy in acetic anwhich the cellulose I product is obtained after a.

acid? the relation being in-the' proportion of the molecular'weight of the acyl g'roup to the molecular weight of the acid. For 1nstance, 8% of the acetyl group means about 11.2% of combined acetic acid. 4 p

" parts by weight of propionic or The following table illustrates the manner in which acetic acid reacts with cotton cellulose which has been mercerized, washed, and freed of water under different conditions:

Times of boiling in acetic acid.

No 0 Percentages of acetyl experi- 24 hrs. 48 hrs. 96 hrs. 200l1rs. 300m. 400hrs. 500l1rs.

1 1.4 as 11.0 11.6 12.9 14.1 2 1.7 9.3 11.9 12.3 14.5 15.9 a 9.3 11.0 13.5 17.5 19.2 20.9 21.6 4 10.2 13.0 14.8 17.0 19.5 22.2 22.0

In experiment No. 1 the mercerization had been done in an 18% N aOH solution for 48 hours at room temperature but it Was dried after Washing and before boiling in acid. In N o. 2 a solution of N aOH was used in mercerizing the fibers being finally dried as in N o. 1. But in Nos. 3 and 4 after mercerizing, in 18% and- 40% -NaOH solutions respectively, for 48 hours at room temperature and washing out the free alkali,-' the water Was removed from the fiber by repeated washing with glacial acetic acid. The mercerized fibers were thenboiled in acidwithout having been dried. Since No. 1 and No. 2 Were exactly parallel with,

No. 3 and N o. 4, except for the drying operation, it will be seen that the dehydration Without drying greatly speeds up the process, even more than the useof a strong mercerizing solution, as in N o. 2 and No. 4. After this first-stage esterification, the excess of acid is removed if the ester is to be further esterified in a bath containing an anhydrid and acatalyst. Part of the acid can, however, be left with tion as a diluent or a solvent during the sec end stage acylation, as is usual in the ordinary acetylation of plain cellulose. If the acetylated fibers, from the first stage, are desired to be used in that condition, they are, of course, thoroughly Washed in water and dried, in which event the looklike the mercerizedfibersfrom which they were derived. Instead of the acetic acid in the above example, we may employ eqglimolecular utyric acid and employ, preferably, a fractionating column through which the water vapors may pass, While retaining the acid vapors. The time of boiling -is conveniently about 200 hours. When 30 parts of heptylic acid are used with 1 part by weight of mercerized cellulose, the temperature should be kept below 165 C. and preferably above 145 C. This is under the'boiling pointrof the acid, but sufficient to obtain a useful esterificatihn without degradation.

When itis desired mospheric pressures,

to work at superat- 1 part of mercerized the ester to funccellulose may be heated, for example, with 30 parts of acetic acid by weight 'of99 to 100% strength at a temperature between 140 and 160 (3., say in a vessel of the autoclave acetic acid-conducted through the tube. This operation may be conducted either at atmospheric pressure or subatmospheric pressure, provided the temperatures do not go above The excess of acid vapor may be repassed or slightly reheating, through the tube. enables a rapid acetylation to take place. The subsequent esteri'fication of the firststage esters can take place in any of the usual esterifying baths, but with the amount of anhydrid diminished by from 20 to 40%. Moreover, the increased susceptibility of our first-stage esters to further esterification enable: us to carry out the latter operation without the use of strong catalysts, thus avoiding the danger of such catalysts as sulfuric acid are employed. \Ve can operate with a milder and safer one, such as zinc chlorid or magnesium perchlorate trihydrate. As such esterification methods have been previously described, it is unnecessary to go over them in detail here.

Having thus described our invention, what We claim as new and desire to secure by Letters Patent is:

1. In the process-of making a cellulose ester of a fatty acid, mercerizing the cellulose and thereafter heating together the mercerized cellulose and a fatty acid having more than 1 and less than 8 carbon atoms without a catalyst at a temperature between 100 and 170 C. inclusive until the acyl group in the ester thus produced reaches at least 8%,

ing a ent.

2. n the process of making cellulose acetate, mercerizing the cellulose, and heating together the mercerized cellulose and substantially anhydrous acetic acid without a catalyst above 100 C. and below 170 C.

recirculated, preferably after" This degradation when said acid being the sole acylatinclusive until the acetyl group in the ester thus produced reaches at least 8%, said acetic acid being the sole acetylating agent.

3. In the process of making a fatty acid cellulose ester, *mercerizing the cellulose, partially esterifying the. mercerized cellulose with a fatty acid'having more than 1 less than 8 carbon atoms, inthe absence of any anhydrid or catalyst, until there is and more than one acyl group in the ester for each. 24 carbon atoms in the cellulose, and

thereafter esterifying it further with the aid of an anhydrid of a fatty acid and a catalyst. v

4;. In the process of making a fatty. acid cellulose ester, mercerizing the cellulose, heating the mercerized cellulose with a fatty acid having more than 1 and less than 8 carbon atoms without. an catalyst until the acyl group inthe ester t us formed reaches at least 8%, said acid being the sole acylat-. ing agent, and thereafter further esterifying it with the aid of an anhydrid of a fatty acid and a catalyst.

5. In the process of making cellulose acetate, mercerizing the cellulose, heatin the cellulose in an excess of acetic acid at a temperature between 100 and 170 C. in the absence ofa catalyst, the acid being the sole acetylating agent, until the acetyl group in the ester reaches at least 8%, and thereafter further acetylating the-ester thus produced in the presence of acetic anhydrid and a milder catalyst than sulfuric. acid.

6. In the process of making a cellulose ester of a fatty acid, Inercerizing the cellulose in an aqueous alkaline solution, washing out the alkaline solution from the cellulose with water, removing the water from the cellulose with a substantially anhydrous organic liquid and heating the cellulose thus prepared with a fatty acid having more than neeagoce l and less than 8 .carbon atoms in the absence of a catalyst at a temperature between 100 and 170 CL inclusive until the acyl group from said acid in the ester thus produced reaches at least 8%.

' 7. In the process of making cellulose'acetate,merceriz1ng the cellulose in an aqueous alkaline solution, washing out said solution with water, washing out the water with glacial acetic acid, boiling the cellulose in:

glacial acetic acid without a. catalyst until the acetyl group in. reaches at least 8%, said acetic acid being the sole acetylating agent.

8. In the, process of making a cellulose ester of a fatty acid, mercerizing the cellulose in an aqueous alkaline solution, dehydrating the cellulose with a substantially anhydrous organic liquid, and heating the cellulose thus prepared with a fatty acid, having more than 1 and less than 8 carbon atoms at a temperature between 100 and 170 C. inclusive in the absence of catalysts or an= hydrids, until more. than one acyl group is esterified with the cellulose for every 24: carbon atoms in the latter. I

4 Signed at Rochester, New York, this 18th day of April, 1927.

. HANS 'r. CLARK. CARL .1. MALM.

the ester thus produced