US2126489A - Process of lowering the viscosity of hydrolyzed cellulose esters - Google Patents

Description

Aug. 9, 1938. Q J MALM 2,126,489

PROCESS OF LOWERING THE VISCOSITY OF HYDROLYZED CELLULOSE ESTERS Filed May 7, 1956 THE EFFECT OF WATER ON THE VISCOJITYOF ACETONf SOLUTIONS OF ORDINARY AND ASH-Hm CflLUlOJE AC1. M7715 SECONDS ACfTO/Vt' macs/"(4:1) r0:

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2 WATER o 2 4 6 a m CONCENTRATION or ACETONE Carl J. Malm ATTORNEYS Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE PROCESS OF LOWERING THE VISCOSITY OF HYDROLYZED CELLULOSE ESTERS Application May 7, 1936, Serial No. 78,448

13 Claims.

The present invention relates to the lowering of the viscosity of hydrolyzed cellulose esters by removing the ash content therefrom. This is accomplished by washing with salt-free water, such as distilled water.

It is commonly accepted in the cellulose acetate art that high viscosity esters, when coated out from their solution in acetone, result in film or sheeting having, as a rule, good flexibility and high tensile strength. The viscosity of the ester is regarded as indicating the complexity of the cellulose micell and, therefore, the high viscosity esters are less degraded than those of low viscosity, hence the high strength of products from high viscosity esters. The high viscosity of esters of undegraded cellulose precludes the use of high concentrations in organic solvents such as acetone and consequently in some instances, such as in lacquers, it is necessary that lower viscosity esters be employed to obtain the desired concen-.

tration even though the cellulose has been broken down to some extent.

One object of the present invention is to lower the viscosity of hydrolyzed cellulose esters without breaking down the cellulose itself, thus making possible high concentrations of esters of undegraded cellulose in organicsolvents. which have not been possible up to the present time. Another object of the invention is not only to reduce the viscosity of the hydrolyzed esters but also to substantially remove the ash content therefrom which has a decided effect on the viscosity and also some effect upon the clarity of the product. depending on the amount and kind of mineral salts present. A still further object of my invention is to provide a cellulose ester having a low viscosity in acetone considering the 'cuprammonium viscosity of the cellulose. A still further object of my invention is to provide a yarn having a great density and hence greater strength for a given denier than that of the yarn ordinarily prepared.

Contrary to the popular conception that the viscosity of a cellulose ester is almost entirely determined by the breakdown of the cellulose micell, I have found that the viscosity of hydrolyzed cellulose esters may be measurably diminished by removing'a substantial proportion of the ash content therefrom, by a thorough washing with salt-free water, preferably while hot. I have found that this reduction in viscosity takes place without any breakdown of the cellulose as evidenced by thezfact that the cuprammonium viscosity of the regenerated cellulose is the same as that of the cellulose regenerated from the ester before the reduction in viscosity occurs. I have found that the resulting product requires only a relatively small amount of solvent to form a flowable solution which may be employed for the manufacture of film and filaments and that in the manufacture of plastics a good flow is obtained with comparatively small amounts of plasticizer. I have found that the tensile strength and flexibility of the film or filaments, prepared from these lowered viscosity esters, are as high as the strength and flexibility of products from high viscosity cellulose esters.

About the only practical way of obtaining saltfree water is by distillation. This distillation may be accomplished naturally, the salt-free water being obtained in the form of rain or snow, or artificially. It is desirable that great care be used that the distilled water or the rain water he collected under conditions which avoid any contact with mineral salts having an alkaline earth metal base.

The viscosity of cellulose acetate or other fatty acid esters of cellulose is lowered in accordance with the present invention by treating the ester with salt-free water, preferably at a high temperature. To be most effective, a series of washings are required to lower the viscosity of the ester. It is desirable, especially when the washlogs are carried out at room temperature to lower the pH of the distilled water. This can for instance be done by bubbling carbon dioxide through the wash water and this carbon dioxide may be introduced into the bath of cellulose ester in distilled water through small Jets located in the washing tank.

This lowering of viscosity can also be accomplished by adding a small, amount of acid such as formic, acetic, oxalic etc. or inorganic acids such as hydrochloric or sulfuric acid to the wash water. It is important to remove the acid by thorough washing with distilled water before the cellulose ester is dried.

The present invention is concerned primarily with the treatment of hydrolyzed cellulose esters, as there is little if any effect upon cellulose esters which are fully esterlfied. It is believed that the hydroxyl groups of the cellulose ester loosely hold the mineral salts and that this loose combination causes the high viscosity of the cellulose ester. Upon washing with hot distilled water, this loose linkage is destroyed and the mineral salts may then be washed out. This, of course, is an explanation based upon the fact that only the hydrolyzed esters are lowered in viscosity by this treatment. It is to be understood, however, that the applicant is not to be limited by his theory as to the lowering of the viscosity by removal of salts in accordance with the present invention.

The amount of reduction in the acetone viscosity of a cellulose ester in accordance with the present invention depends on at least two factors namely:

1. The degree of hydrolysis, and

2 The percentage of alkaline earth metal salts which were removed from the ester.

It may be seen from the second factor that the cellulose esters having a relatively high content of mineral salts are much more susceptible to my viscosity lowering process than those having a lower mineral salt content.

I have found that organic acid esters of cellulose prepared from refined wood pulp as the starting material are particularly susceptible to the lowering of viscosity by my invention. In all of the examples given, esters from refined wood pulp are employed. It may be seen from these examples that the viscosity is reduced considerably, such as more than 50% in most in stances and at least 25% in almost every case.

Under the same conditions, namely a series of at least 4 washes with salt-free water, the acetone viscosity of a hydrolyzed cellulose ester such as cellulose acetate which has been hydrolyzed to acetone solubility, which has been prepared from cotton, is reduced at least 25% ordinarily. 0bviously esters prepared from other types of cellulose material will respond to removal of the ash content with a lowering of the acetone viscosity of the same order. In almost every case a reduction of at least 25% and generally considerably more is accomplished by removal of the mineral salts in accordance with my invention.

That the mineral salts have been removed is very diflicult to determine by analysis due to the very small amount of that material which is present before treatment. That it is the removal of the mineralsalts which causes the reduction in viscosity is concluded from the fact that when the ester whose viscosity has been reduced is treated with a very dilute aqueous solution of a mineral salt having an alkaline earth metal base. the acetone viscosity is increased to its former viscosity or even beyond.

The following examples illustrate the preparation of a lowered viscosity cellulose ester by means of the present invention:

An ordinary commercial grade cellulose acetate, having a viscosity of 40 seconds when dissolved in 4 parts of acetone and an acetyl content of 40.5%, was washed 6 times with boiling distilled water and then dried. The acetyl content of the resulting product was still 40.5%, but the viscosity, when the acetate was dissolved in 4 parts of acetone, was only 10 seconds.

As another example, some of the 40 seconds viscosity acetate was washed using 20 changes of distilled water at room temperature. The acetone viscosity in that case was lowered from 40 to 18 seconds. The 2% cuprammonium visoosity of the cellulose, regenerated from samples before and after the wash treatment, gave in both cases 13 centipoises showing that the Viaeosity of the ester was reduced without in any way affecting the cellulose itself. In two other cases samples of high viscosity cellulose esters were given six washes with hot distilled water. In one case a cellulose acetate, having a viscosity of 1900 seconds, was reduced in viscosity to seconds and with the second ester, a viscosity ofl45wasreducedto40secondsbythistreatment. The degree of drop in viscosity depends upon the amount and nature of the salts present, the number of washes, and the temperature of the distilled water. I have found that the alkaline earth metal salts, such as of calcium, are especially efi'ective in maintaining a high viscosity and where such salts predominate in the ester before the washing with distilled water, a much greater reduction in viscosity is possible. As a general rule, six changes of hot distilled water is sufficient to obtain the minimum viscosity. It is preferred to use water at a high temperature near to the boiling point, although the invention is not restricted to the use of any particular temperature of washing. The boiling of the cellulose ester in distilledwater is unnecessary and may lower the acyl content, however, it may be employed if a slight reduction of the acyl content is not objectionable.

Some further instances of lowering the viscosity of cellulose esters in which the ester was washed in four 4-hour periods with boiling distilled water, being rinsed once with distilled water between each boiling gave the following results:

Viscosity before Viscosity after washing with washing with hot distilled hot distilled water water (in seconds) (in seconds) The viscosity was determined by the falling-ball method in an acetone solution of the ester consisting of 4 parts of acetone to one of ester.

As pointed out above, the present invention is directed to the lowering of the viscosity of hydrolyzed fatty acid esters of cellulose which includes hydrolyzed cellulose acetate but also other hydrolyzed cellulose esters, such as hydrolyzed cellulose acetate propionate or acetate butyrate or other hydrolyzed simple esters such as cellulose propionate or cellulose butyrate. As a matter of fact, I have found that the more free bydroxyl groups which are present in an ester, the more the viscosity of the ester is increased by the presence of mineral salts, or in other words, the more the viscosity may be lowered by removing the ash content therefrom.

The cellulose esters of lowered viscosity of the present invention are also eminently suited for the making of other commercial products. when dissolved in acetone. the solution of one of these esters is much more flowable and consequently more easily handled than a solution of the corresponding concentration of the high viscosity ester. In spite, however, of this lowered viscosity of solution, the sheeting formed therefrom has as good a strength and flexibility as that of the high viscosity ester from which it originated The thoroughly washed cellulose esters of lowered vlscosityof my invention are also adapted to the preparation of yarn. By employing these esters to form synthetic yarn, a product is obtained in which the tensile strength is increased 5-10% without any change in the amount of stretch. Also, the other characteristics of synthetic yarn, such as aflinity for dyes or pigmenting materials are not affected, and the filaments forming the yarn have a more desirable cross section.

The accompanying drawing illustrates the marked advantage of using an ash-free cellulose acetate over using the ordinary commercial product. This drawing shows graphically the relation of the viscosity to the precentage of water in the acetone solution of two acetone-soluble cellulose acetates, the ash-free ester having been prepared from a commercial acetone-soluble cellulose acetate of approximately 40 seconds viscosity upon which the upper curve is based. The upper curve shows that upon the use of a small amount of water in the acetone employed to dissolve the commercial cellulose acetate, the viscosity is much lower than with its solution in acetone alone. With the ash-free cellulose acetate, which was prepared from the ester upon which the upper curve is based, the viscosity in acetone solution is lower than was attained by the addition of water in the previous case as shown by the lower curve of the drawing. It may also be seen that the mixture of water with the acetone employed to dissolve the ash-free cellulose acetate not only does not lower the viscosity, but if more than 2% water is used, the solution is more viscous. v

Because of the low viscosity of the acetone solutions of these ash-free esters, a much greater concentration of the ester in the acetone may be employed without detrimentally ailecting the handling of the material or the spinning of the solution. My process also makes possible the use of esters, the cellulose of which has a higher muprammonium viscosity than that which ispossible to employ at present. Therefore, the yarn of my invention has greater strength than the yarn prepared from cellulose esters, the cellulose of which is more degraded, or in other words. the cellulose of which has a lower cuprammonium viscosity.

The method of making yarn by evaporative spinning is well-known at the present time and reference to the prior art,'such as Stone Patent Nos. 2,000,047 and 2,000,048 and Clarke and Malm Patent No. 1,969,454 may be had to ascertain satisfactory methods of preparing yarn from acetone solutions of cellulose esters.

An example of preparing yarn in accordance with my invention is as follows:

A cellulose acetate prepared from an ordinary commercial grade cellulose acetate, rendered ashfree by washing a number of times with boiling distilled water and drying was employed. The cellulose acetate of 40.5% acetyl content before washing had a viscosity of 40 seconds when dissolved in 4 parts of acetone. After washing. the acetate had the same acetyl content but an ace: tone viscosity of only 10 seconds. Cellulose acetate washed repeatedly with distilled water at room temperature to render it ash-free is also satisfactory. In the latter case the acetone viscosity was lowered from 40 to 18 seconds.

An ash-free cellulose acetate was dissolved in acetone to form a 30% solution of the ester.

This solution was then filtered and passed 7 through a spinneret into an evaporative atmosphere in which warm, dry air circulates. The filaments were then twisted together to form a thread of unusually high strength. The solution was of higher concentration than can be employed ordinarily, the thread was more dense and of greater strength. Although the spinning solution was oi 30% concentration, the solution was easily flowable and the spinning could be performed at the rate ordinarily used with lower concentrations of cellulose esters.

The preferred range of acetyl of cellulose acetate for the preparation of yarn in accordance with my invention is approximately 37-41%. As this invention is primarily directed to making possible the preparation of filaments from esters of less degraded cellulose it is applicable, in general, to processes of making yarn from cellulose esters, although its use in evaporative spinning processes is especially contemplated.

In the preparation of lacquers, it is desirable that the cellulose ester be present in fairly high concentration to contribute to the covering power of the lacquer. Heretofore'the esters, which have been used for this purpose, were the esters of a broken down cellulose in order to give a viscosity sufficiently lowered to make the lacquer flowable and yet assure a considerable concentration of the cellulose ester therein. By my invention a lacquer may be prepared from a cellulose ester in which the viscosity has been lowered by removing the ash content, and, therefore, the ester present in the lacquer will not have the degree of breakdown which, up to the present time, has been thought to be necessary. This results in tougher, stronger and less brittle lacquer coverings.

The lowered viscosity esters of my inventionmay also be employed for various other purposes, such as in the preparation of plastic compositions. Due to the lowered viscosity of these esters, the amount of plasticizer required is less than that ordinarily used, a good flow will be obtained upon the application of heat and in addition a strong durable product will be obtained. These properties are especially desirable in injection moulding. In the laminating field these esters are also useful either for the preparation of sheeting to be laminated with glass, metal or the like, or as a coating solution to be applied to the surfaces of the sheets which are to be laminated. As the esters of my invention have the advantage of the lower viscosity esters in giving a ilowable solution and the advantage of the high viscosity esters in the undegraded condition of the cellulose, they will, of course, suggest themselves for many uses.

I claim:

1. The process of lowering the acetone viscosity of a partially hydrolyzedacetone-soluble organic acid ester of cellulose by thoroughly washing the ester with a series or at least four distilled water washes.

2. The process of lowering the acetone viscosity 5 of a partially hydrolyzed acetone-soluble cellulose acetate by thoroughly washing the ester with a series of at least four distilled water washes.

3. A partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose, the acetone viscosity of which has been lowered at least by a process which comprises thoroughly washing the ester in a series of at least four distilled water baths.

4. A partially hydrolysed acetone-soluble lower fatty acid ester of cellulose prepared from refined wood pulp, the acetone viscosity of which .has been lowered at least 25% by a process which comprises thoroughly washing the ester in a series of at least four distilled water baths.

5. A partially hydrolysed acetone-soluble cellulose acetate prepared from refined wood pulp, the acetone viscosity of which has been lowered at least 25% by a process which comprises thor- 1s series of at least four distilled water washes and drying the cellulose ester.

8. The process of lowering the acetone viscosity, by more than 25%, of a partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose prepared from refined wood pulp which comprises thoroughly washingthe ester with a series 0! at least four distilled water washes and drying the cellulose ester.

9. The process of lowering the acetone viscosity of a partially hydrolyzed acetone-soluble cellulose acetate, by more than 25%, which comprises thoroughly washing the ester with a series of at least four distilled water washes.

10. The process of lowering the acetone viscosity of a partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose by at least 25% which comprises thoroughly washing the ester with a series of at least four distilled water washes, at least one o! the washes being accompanied by the introduction of carbon dioxide into the washing liquid.

11. The process of lowering the acetone viscosity of a partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose by at least 25% which comprises thoroughly washing the ester with a series of at least four distilled water 'washes, the water in the initial wash containing a slight amount of acid.

12. A yarn essentially consisting of a partially hydrolyzed lower fatty acid ester of cellulose, the acetone viscosity of which has been reduced by at least 25% by a process which comprises thoroughly washing the ester in a series of at least four distilled water baths.

13. A yarn essentially consisting of a partially hydrolyzed cellulose acetate, the acetone viscosity of which has been reduced by at least 25% by a process which comprises thoroughly washing the ester in a series of at least four distilled water baths.

CARL J. MALM.

CERTIFICATE OF CORRECTION Patent No. 2,126,h89.

August 9, 1958 CARL J. mm.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 61;, for F2 1/2" read 2 1/2%; and that the said. Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. I

Signed arfi sealed this 13th day of September, A. D. 1958.

(Soul) Henry Van Arsdale Acting Commissioner of Patents.

series of at least four distilled water washes and drying the cellulose ester.

8. The process of lowering the acetone viscosity, by more than 25%, of a partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose prepared from refined wood pulp which comprises thoroughly washingthe ester with a series 0! at least four distilled water washes and drying the cellulose ester.

9. The process of lowering the acetone viscosity of a partially hydrolyzed acetone-soluble cellulose acetate, by more than 25%, which comprises thoroughly washing the ester with a series of at least four distilled water washes.

10. The process of lowering the acetone viscosity of a partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose by at least 25% which comprises thoroughly washing the ester with a series of at least four distilled water washes, at least one o! the washes being accompanied by the introduction of carbon dioxide into the washing liquid.

11. The process of lowering the acetone viscosity of a partially hydrolyzed acetone-soluble lower fatty acid ester of cellulose by at least 25% which comprises thoroughly washing the ester with a series of at least four distilled water 'washes, the water in the initial wash containing a slight amount of acid.

12. A yarn essentially consisting of a partially hydrolyzed lower fatty acid ester of cellulose, the acetone viscosity of which has been reduced by at least 25% by a process which comprises thoroughly washing the ester in a series of at least four distilled water baths.

13. A yarn essentially consisting of a partially hydrolyzed cellulose acetate, the acetone viscosity of which has been reduced by at least 25% by a process which comprises thoroughly washing the ester in a series of at least four distilled water baths.

CARL J. MALM.

CERTIFICATE OF CORRECTION Patent No. 2,126,h89.

August 9, 1958 CARL J. mm.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 61;, for F2 1/2" read 2 1/2%; and that the said. Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. I

Signed arfi sealed this 13th day of September, A. D. 1958.

(Soul) Henry Van Arsdale Acting Commissioner of Patents.

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