US1716422A - Process of making organic esters of cellulose - Google Patents

Description

Patented June 11, 1929.

UNITED mm. cLAnxE AND CARL .1. mum, on ROCHESTER, NEW roux, AssIGNons T EASTMAN. KODAK COMPANY, or ROCHESTER,-1\TEW YORK, A CORPORATION on NEW YORK.

No Drawing.

This invention relates to processes of making organic esters of cellulose. One Object of our invention is to pronide an inexpensive and simple process in which we can 5 utilize satisfactorily forms of cellulose which have proven difficult to esterify. Another object is to provide a process in which the cellulosic material is brought intosuch a condition that it will rapidly and uniformly esterify in the known reaction mixtures, such asthose cutomarily employed for making cellulose acetate, for example. Still another object is to retreat the cellulosic material before esteri cation in a mercerizing bath and then rovide an auxiliary pretreatment which Wlll conserve the good effects of the mercerization and yet avoid the resistance to esterification, which ordinarily follows the mercerization process. A further object is to provide a process in which the cellulosic material is especially prepared for esterification and may be dried and stored before esterification, without impairing its good qualities. A still further object is to provide a process of making the esters in which neither the pretreating nor the esterification causes any serious molecular degradation, as is evidenced by the qualities of films made therefrom. Other objects will hereinafter appear.

I It has been generally customary to make cellulosic organic esters, especially cellulose acetate for the manufacture of films, from purified cotton of good grade and length. Clearly it is desirable to be able to utilize cheaper sources of' cellulose, such as cotton linters, cotton dust, wood pulp, such as bleached sulfite pulp, soda pulp, etc. F urthermore, when utilizing cotton fibers, of

40' good grade, different batches'often behave differently toward the esterification baths. Some of them require longertimes :for

carrying out the reaction, and others show an. unexpectedtendency to leave incompletely esterified fiber particles in the reac tion mixture. It is, therefore, desirable to find a wayto minimize these peculiarities.

We have found that the less expensive,

' but more resistant, sources of cellulose may 60.119 used, and more uniform results: may be rnocnss or MAKING ORGANIC ESTERS or cnnnunosn Application filed April 23, 1927. Serial No. 186,169.

obtained when employing the high grade celluloses, if the fibers are given a mercerizing pretreatment and dehydrated by means fication bath while still containing some of H the anhydrous liquid.

While we do not wish to be restricted to any particular theory, since the advantages of our process may be obtained irrespective of theoretical considerations, nevertheless we believe that our process owes much of its eflicacy to the condition which it brings about'in the surfaces of the cellulose fibers. When such fibers are mercerized, and the alkali washed out with water, and then the water driven ofi' fromthemby an ordinary slow-drying method in the air, they become undesirably resistant to esterification. We believe that this is due to the formation of a hard, horny surface on the fibers which does not react readily with the esterification agents, the latter bein unable to react with the inner parts of the bers while this tough cuticle remains. our dehydrating of the washed mercerized fibers by means of inert organic anhydrous liquids prevents the formation of this hardened and unreactive outer surface on the fibers. Whether the fibers be then dried by evaporating off the organic liquid, or are We further believe that stirred into the esterification mixture with some of the liquid still clingin to them, their surface remams in a soft an reactive condition which permits the esterification agents to react quickly with the surfaces of the fibers and then quickly with the interior portionsthereof. v We shall now give several examples of our invention, but it will be understood that The cellulosic material, pre erably in the fibrous form, is treated with a mercerizing it is notlimited to the details thus set forth, except, as indicated in the ap ended claims.

bath of the usual type, such as an aqueous solution of sodium hydroxid of 10% to 40% strength. \Vhile raised temperatures may be employed to hasten the mercerization, we find it ordinarily most convenient to work at room temperature. A bath consisting of and 18% solution of caustic soda in water works well. So long as a useful mercerization of the fibers is obtained, and the latter are not-degraded, the time of the mercerizing is relatively unimportant. Using said 18% solution, we have obtained satisfactory results after one days treatment at room temperature, but no harm has appeared after three days treatment in such solution, and the time could obviously be prolonged without ill effect. Two days is a good average period. Caustic potash can be similarly used.

After the mercerization, the cellulosic material is washed with water, preferably at room temperature, or the temperature of the ordinary supply of water, which maybe slightly below room temperature in the winter, or slightly above it in the summer. The fibers are thus rendered free from detectable quantities of alkali. lVarm water can be used but is not necessary.

After this washing step, the excess of water is removed from the cellulosic material by pressure, say in a centrifuge, or better, in a hydraulic press. But care is taken that the fibers arenot allowed to dry while they are still wet withthe wash water.

The fibers are then dehydrated by means of a substantially neutral organic anhydrous liquid. Ethyl alcohol is a useful dehydrating agent, and may be employed to remove the water from the mercerized and washed fibers in practically the same way that it is often used for removing water from nitrocellulose fibers which have been previously washed in water. Methyl, propyl, butyl and amyl alcohols can also be used, but the higher boiling members of this group offer no marked advantages and .are more expensive. Acetone has been found to be excel lent as a dehydrating liquid, and ether, either mixed with ethyl or methyl alcohol, or applied after methyl or ethyl alcohol, has also been very eflective in dehydrating the fibers and leaving them with their surfaces in the best condition for the subsequent esterification.

The lower members of the benzene series of hydrocarbons, such as benzol, toluol and xylol are also effective in this respect, ben- 201 being preferred. When the latter is employed, the mercerized fibers carrying the residue of wash water are immersed in the benzol and kept below the surface of it during the treatment, The bath containing the fibers is then brought to its boiling point, which is less than that of benzol, owing to the formation of an azeotropic mixture of the latter with water. Thus the water is carried away by the distillation and the mercerized cellulose fibers remain wetted only with benzol and substantially free from water.

Of course, the benzol which distills off with the water may be condensed and recovered for further use in the process.

After the cellulosic material is dehydrated, it may be freed from the dehydrating agent by evaporation, the vapors of the dehydrating liquid, such as alcohol, acetone, benzol etc, being condensed and thus recovered for future use. Or the cellulosic material may enter an esterifying bath with the dehydrating agent still in it. As a rule oratb off and recover the dehydrating liquid. Then the mercerized cellulosic material may be stored and kept indefinitely, until it is esterified, the surfaces of the fibers remaining in their reactive condition.

\Vhen the mercerized cellulosic fibers have been dehydrated with benzol, it may be economical to introduce them, while still wet with benzol, into an esterifying bath of the type in which there is present enough benzol, or other non-solvent to produce cellulose esters in the form of fibers. Of course, the benzol could be evaporated off before the films enter the bath, but that is an extra operation.

Our mercerized and dehydrated cellulosic material may be esterified in any of the usual cellulose esterifying baths in which organic acid anhydrids are employed. Since cellulose acetate is at present the most widely used of the organic esters of cellulose, we shall give examples of the many ecetylating baths which can be used, but it will be understoood that the known baths for forming cellulose propionates, butyrates,

stearates and various mixed esters, such as aceto stearates, may be employed with equal facility. Our pretreatment brings the fibers into especially good condition for all of these baths.

In one illustrative embodiment of our invention, long fiber surgical cotton, properly cleaned, is mercerized in an 18% aqueous caustic soda solution at room temperature for one day and then washed with water at room temperature, being finally dehydrated with methyl alcohol, followed by ether. After dehydration the ether is evaporated and 5 parts by weight of the fibers stirred into a bath'comprising 25 parts of acetic acid, 20 parts of acetic anhydrid,'20-parts of chloracetic acid, .1 part of magnesium perchlorate, and. the reaction mixture kept at 60 to C. until it becomes homogeneous and the fibers have all substantially dissolved. This is ordinarily reached in about three and one-half hours.

This is much less than the time required to acetylatc the same long-'fibered surgical it is slightly more convenient to evapcotton after the same mercerizing treatment taln'ng the color much more deeply than:

where no dehydrating step has taken place,

, but the washed mercerized fibers have been heated at 40 C. to drive ofi' the water. Such air-dried mercerized fibers, when immersed in the above acetylating bath, are in such ahighly resistant condition that they are only partially acetylated even aftereight hours, numerous pieces. of fiber being still visible in the reaction mixture. In fact, they require longer for acetylation than do the plain untreated long-fibered cotton. Our treatment brings about the acetylation in the shortest time of all and with a greater smoothness of reaction.

In another example of our invention, 10 parts by weight of mercerized and washed cellulose fibers are soaked in a 10% solution of magnesium perchlorate and pressed until the weight of the residue is 30 parts. This is then dehydrated by immersing in benzol and distilling as hereinabove described. The 10 parts of dehydrated fibers will thus be thoroughly associated with, 2 parts by weight of magnesium perchlorate and the remaining anhydrous benzol, say 15 parts of the latter. This mixture is then added to a bath of drid and 160 parts by weight ofcarbon tetrachlorid. In place. of the latter any suitable diluent maybe suhstitnted,-say 90 90 parts by weight of benzol or toluol. The thoroughly mixed reaction mass thus obtained is kept at 50 to .0. until a sample shows that .acetylation is complete. This may take several days. The= fibers do not disappear during the reaction. They are separated from the other ingredientsof the reaction mass in the usual way. I T

Our mercerized and dehydrated fibers may likewisehe used to advantage in any of the esterification processes disclosed in our copendingapplications, Serial Nos. 179,176

and 179,177, filed 'March 28, 1928, entitled Processes of making organic esters of 'cellulose containing acyl groups having more than two carbon atoms and Process of making cellulose esters of organic. acids.

' They are very satisfactory-in forming the estersof the fatty acids by the steps there disclosed.

In the above examples, in place of the long fiber surgical cotton, we can use less expensive materials, such as cotton linters,

cotton dust, wood pulp, suchfas bleached sulfite pulp, soda pulp, and reverted cellulose, such as rayon fibers from-the viscose or cuprammonium processes, these being'substituted weight for weight in the above ex-fl I I I I which comprises mercerlzmg cellulose, .in a

amples.

It is also noted that when mercerized cellulosic fibers have been dehydrated and dried by our treatment, their surfaces are in an especially susceptible condition toward the ordinary dyesused oncellulose fabrics,

parts by Weight of acetic anhybath, washing out mercerized fibers dried. I I

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

l. The process of making organic esters of cellulose which comprises mercerizing cellulosic material with an aqueous alkaline bath, dehydrating it with a substantially anhydrous. neutral organic liquid, and thereafter subjecting the mercerized and dehydrated cellulosic material to an esterifying agent.

2. The process of making organic esters of cellulose which comprises'mercerizing the V the action of which have been directly" cellulosic material in an aqueous bath having-an alkalinity corresponding to from 10' to 40% ofNaOll-ll, Washing out the alkali with water, roving the water with a. sub

stantially anhydrous and neutral organic liquid which a nonsolvent or the ester; to be produced, and thereafter treating the mercerized and dehydrated oellulosic "material in an esteri 5;: acid anhydrid.

bath containing a fatty .100 f 4. The pro'ce'ssofmaking organicfesters 1 of cellulose which comprises mercerizing the" cellulosic material with an aqueous alkaline l the alkali' fromfthe material with water, removing' the water from 305 I the material with 'a substantially anhydrous neutral I volatileorganic liquid. evaporating I I said organic liquid from said material, and

thereafter treat' drated and dried I organic esterifying, agent.

g said merce'rized dolly-- cellulosic material with an.

The process'of making cellulose acetate which comprises mercerizing'cellulose, inf'a form whichis resistant to esteri'fication by acetic anhydrid, in an aqueous alkaline bath having an alkalinity corresponding to from 10 to 40% ofNaOH,' washing out the ali fromfsaid material withfiwater, removing the water from the material with a: substantiall anhydrous -i1eutral-volatile organic liqui and thereafter acetylating' the mercerized,

washed and dehydrated, cellulose an acetylating bath containing acetic anhydrid.

v 6. The process of mg cellulose acetate an alkalinitycorresponding'to from 10 to:

40% Nafildh at room temperature, washing.

out the a all from the cellulose Wltll water,

removing the water cerized, washed and from said cellulose with dehydrated cellulose in an acetylatlng bath containing acetic an- 5 hydrid.

7. In the process for subsequent treatment the steps of mercerizing with an aqueous alkaline bath, removing of preparing cellulose in chemical baths, the raw (2811111016 the alkali, and dehydrating the me'rcerized 10 cellulose with a substantially anhydrous neutral organic liquid, whereby drying oil water from the mercerized cellulose in air is avoided. v

Signed at Rochester, New York this 18th 5 day of April, 1927.

HANS T. CLARKE. CARL J. MALM.