US2478396A - Activation of cellulose for acylation - Google Patents

Description

Patented Aug. 9, 1949 ACTIVATION F CELLULOSE FOR ACYLATION William B; Hincke, Kingsport, Tenn., and Carl J. Malm, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application June 27, 1945, Serial No. 601,918

Claims. (Cl. 260225) This invention relates to the activation of cellulose preparatory to acylation in which the cellulose in the form of a slurry in distilled or demineralized water free of added chemicals is boiled 2-4 hours and the water is removed by means of lower fatty acid.

Cellulose, particularly wood pulp cellulose, as

normally obtained, even that classifiable as re-" fined high a cellulose material, contains a small amount of hornified amorphous material which is particularly resistant to acylation. Even though the cellulose is mechanically disintegrated or opened up to assure contacting of the acylating liquids with all the particles of cellulose it is still difficult to uniformly acylate cellulose containing hornified material with fatty acid anhydride and catalyst. Often a residual haze is found in the reaction mass resulting after acylation which can be removed only with great difficulty.

To facilitate the acylation of cellulose pretreatment with acetic acid has been resorted to. Glacial acetic acid, as normally employed in pretreatment operations, leaves much to be desired as a swelling agent for the horny material found in some cellulose, and the anhydrous fatty acids having more carbon atoms than acetic, such as propionic or butyric, are of much less value than acetic acid for facilitating the acylation reaction with fatty acid anhydride. The use of higher than normal amounts of catalyst, higher temperatures or longer times of reaction in the subsequent esterification step do not compensate for the poor pretreatment and result in more complete acylation of the cellulose but only in more 4 breakdown or acetolysis of the cellulose in the final cellulose ester. Such intensified operations result in a cellulose ester having a viscosity too low for use in preparing commercial products.

One object of our invention is to provide a method of activating cellulose, particularly that having some horny, unreactive particles therein, to render it readily and uniformly reactive with lower fatty acid anhydride in ordinary cellulose acylation processes. Another object of our invention is to provide an effective method of activating cellulose requiring but a short time of treatment. A further object of our invention is to provide a method of activating cellulose, in which water acts as the activating agent yet the pretreated cellulose is obtained in the form of cellulose mixed with only a small proportion of lower fatty acid. Other objects of our invention will appear herein.

by forming the cellulose into a slurry in low mineral content water, without the addition of chemicals thereto, boiling the slurry for 2 to 4 hours and then removing the water from the cellulose with lower fatty acid so that there results an activated cellulose moistened with the lower fatty acid. 1

Our pretreatment method may be applied to any cellulose, suitable for acylation purposes, which can be slurried with water, an advantage being that only a short time of treatment is necessary. Our pretreatment method however is particularly adapted to cellulose which has a nonuniform nature -because of the presence of horny, amorphous particles distributed therethrough. For instance, acetylation grade wood pulp cellulose is supplied ordinarily in the form of rolls of dry sheets'in which hard particles of cellulose are found distributed through the sheet.

The cellulose in accordance with our invention is mixed with or agitated in 15 to 25 parts of distilled or low mineral content water (per part of cellulose) to form a suspension or slurry of the cellulose fibers therein. The water used is one which has a mineral content of less than 20 parts per million. I This may be distilled water or a demineralized water. Obviously the lower the mineral content, the more suitable is the water for use in our activation process. The term .low mineral content water as used herein is to be understood as referring to water having a mineral content of 0-20 parts per million therein. The proportion of water employed is not critical being suificient togive a good slurry and conducive to uniform boiling. At least 15 parts of Water is ordinarily necessary for this. The cellulose after suspending in water is subjected to boilingforfrom z to 4 hours and a highly activated cellulose results.

Before using this cellulose for esterification it is desirable to, remove the water therefrom. It is a feature of our invention that the water is removed from the cellulose in such a manner that the product consists of highly reactive cellulose moistened bylower fatty acid. The water may be directly removed from the cellulose with fatty acid, howevenremoval is best and most economically accomplished by first removin the bulk of the water from the cellulose by mechanical means such as by means of squeeze rolls, screw presses, suction filters, centrifuges or the like. To retain the swollen reactive condition of the cellulose the'remaining 1-2 parts of water present therein is extracted or displaced with a These objects of our invention are accomplished lower fatty acid, either acetic, propionic or butyric tained is suitable for charging directly to the I acylation mixer for direct acylation with fatty acid anhydride and catalyst.

The activated cellulose obtained may be employed for making cellulose acetate or cellulose mixed esters in which acetic anhydride is employed as the esterifying agent or for makin high propionyl or high butyryl cellulose esters. In making the latter at least a large proportion or even the entire anhydride may :be propionic or butyric anhydride as the esterifying agent. As these anhydrides are more sluggish in acylat ing effect than acetic anhydride, it is important that the cellulose employed therein be highly reactive. Although ordinarily acetic acid will be employed to displace the water on the cellulose, in .these cases where little or no acetyl is desired in :the cellulose esterification mixture, butyric .or propionic acid may be employed for this purpose.

tion:

Example I "One part of wood cellulose sulfite pulp, having a high (it-cellulose content was slurried with parts or demineralized water having a mineral content of approximately 10 parts per million and the mass was boiled for 3 hours in a jacketed tank. The slurry was centrifuged to a content of "about 1 part of water per part of cellulose. While still in the rotating centrifuge, the wet cellulose mat was extracted by spraying onto it while the centrifuge was operating successive amounts of acetic acid of'increasing concentration, such as was obtained by saving the effluent from previously dewatered batches. By so doing a counter current system is effected with a minimum use of final glacial dewatering acid. The first obtained, most dilute acid was sent to recovery to oncentrate the same.

The acid wet cellulose was centrifugeddown so as to contain 1 part of acid and 0.01'to 0.03 partof water per part of dry cellulose. This cellulose was then charged directly to an acetyl-a'to'r-containing 3 parts'of acetic anhydride and .05 part of sulfuric acid catalyst and was acety lated therein. The cellulose reacted rapidly-to of unacetylated particles therein. Example II 4 Q The procedure of the preceding example was repeated except that butyric acid was employed to remove the water from the ccllulose'after'the boiling and removal of the bulk of the water by centrifuging. The activated cellulose containing' b'u-tyric acid was charged into an este'rifica tion mixer containing 4 /2 parts of butyric anhydride and .04 part of sulfuric acid catalyst and the cellulose was butyrated, the temperature being controlled so that it did not exceed 90 F. over the entire reaction. The cellulose reacted readily to give amass of high clarity.

Example III :One :part of wood cellulose sulfite pulpuo'f high alpha-0611111086 content was slurried and boiled with parts of demineralized vwater having a mineral :content of approximately'lO :partszcp The following examples illustrate our invenmillion for 3 hours in a jacketed tank. This slurry was then thinned with more water so that the pulp could be formed into a web on a perforated stainless steel belt similar to that used on the wet end of a paper machine. This cellulose web on the perforated belt was then passed over suction boxes to remove the excess water and, following this, over a sequence of suction boxes where it was sprayed with acetic acid of increasing concentration in a counter current manner. From the last spray and suction box the cellulose mat through a picker or hammer mill and charged to an acylation mixer containing 4 parts of butyric anhydride and 0.05 part sulfuric acid catalyst. The cellulose reacted rapidly to a clear dope of cellulose acetate butyrate free from any unreactedcellulose particles.

Example IV The cellulose boiling procedure of Example III was repeated except cotton linters were used. Following this buty'r'icacid was used as the water extractant instead of acetic acid in passing the cellulose web over the counter current spray and suction box dewatering device. The cellulose mat delivered from the last suction box was damp with 2 parts 'butyric acid. This pulp was then charged-without further centrifuging to an acylation mixer containing 4 ,4 parts 'butyric anhydride and'0.05 part sulfuric acid catalyst. The ensuing reaction to a cellulose tributyrate was somewhat slower than to the mixed ester shown in Example III but the reaction was complete to an The same pulping and boiling procedure was used .as .in Example III. However, in order to effect the countercurrent removal of water, an Oliver suction filter was used. This filter was equipped with a number of sprays so that acetic acid :of increasing concentration could be passed through the cellulose mat in a countercurrent manner. After removal from the Oliver filter, the mat was passed through squeeze rolls where the acid was finally removed to 1 remaining part substantially free from water. This acetic acid damp cellulose was then charged to an acylation mixer as in Example III-and a high butyryl mixed ester was prepared b'y rapidly reacting to a dope free from unacylated cellulose particles,

Example VI Que part of high a-lpha sulfite pulp was slurried in 25 parts of :distilled water and the mass was boiled-for- 3.hours; The slurry was centrifuged to removethe' bulk of the water and then dewatered bysprayingaceticacid onto the centrifuging pulpma'ssiun'til acellulose was obtained having .1 :part of acid and substantiall no water (less than 0.02 part) per part of cellulose. The cellulose was picked apart and mixed with butyrlc anhydrideland ;-a little sulfuric acid catalyst in .an acylation mixer cooled so that the temperature :never exceeded F. A cellulose ester of :good rquality was obtained.

When the term fisubstantially free of water is used herein it is to be understood toimean.

less than-0&5 part of Water .and preferably less than 0.03 part is present per part of dry cellulose.

We claim:

1. A method of activating cellulose containing a small amount of hornified amorphous material which is particularly resistant to acylation which consists in boiling a suspension of the cellulose in a large excess of water having a mineral content of less than 20 parts per million for two to four hours, subjecting the cellulose mass to pressure to remove water, at least one part of water remaining per part of cellulose and subsequently displacing the water in the cellulose with a fatty acid of 2-4 carbon atoms so as to give a cellulose containing fatty acid but substantially free of water therein.

2. A method of activating cellulose containing a small amount of hornified amorphous material which is particularly resistant to acylation which consists in boiling a suspension of the cellulose in a large excess of distilled water for two to four hours, subjecting the cellulose mass to pressure to remove Water, at least one part of water remaining per part of cellulose and subsequently displacing the water in the cellulose with a fatty acid of 24 carbon atoms so as to give a cellulose containing fatty acid but substantially free of water therein.

3. A method of activating cellulose containing a small amount of hornified amorphous material which is particularly resistant to acylation which consists in boiling a suspension of the cellulose in a large excess of Water having a mineral content of less than 20 parts per million for two to four hours, subjecting the cellulose mass to pressure to remove water, at least one part of water remaining per part of cellulose and subsequently displacing the water in the cellulose with acetic acid so as to give a cellulose containing acetic acid but substantially free of water.

4. A method of activating cellulose containing a small amount of hornified amorphous material which is particularly resistant to acylaticn which consists in boiling a suspension of the cellulose in a large excess of water having a mineral content of less than 20 parts per million for two to four hours, subjecting the cellulose to pressure to remove water, at least one part of water remaining per part of cellulose and subsequently displacing the water in the cellulose by a concurrent treatement thereof with acetic acid so as to give a cellulose containing acetic acid but substantially free of water therein.

5. A method of preparing cellulose acetate butyrate having a high butyryl content from a cellulose containing a small amount of hornified amorphous material which is resistant to acylation which consists in first boiling the cellulose in suspension in a large excess of low mineral content water, subjectin the cellulose to pressure to remove water, at least one part of water remaining per part of cellulose, displacing the water in the cellulose with acetic acid and then esterifying the cellulose with an esterification mixture comprising butyric anhydride and an acylation catalyst.

WILLIAM B. HINCKE. CARL J. MALM.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,752,596 Hubert et a1 Apr. 1, 1930 2,087,263 Olsen July 20, 1937 2,112,115 Richter Mar. 22, 1938 2,112,116 Richter Mar. 22, 1938 2,152,071 Malm Mar, 28, 1939