US1953398A - Treatment of cellulose esters - Google Patents

Description

Patented Apr. 3, 193% ITE riser TREATMENT 0F CELLULOSE ESTER$ No Drawing.

Application December 5, 1939,

Serial No. 500,432. Renewed January 23, 1934 8 Claims.

This invention relates to the treatment of cellulose esters, to eifect stabilization, viscosity reduc-- tion; bleaching and clarification thereof. While not restricting the invention thereto, it is, for

definiteness, described with more particular reference to cellulose nitrate, and particularly with reference to cellulose nitrate having a nitrogen content below 12.5% as used in the lacquer and pyroxylin plastic industries.

.In the production of nitrocellulose, an important step is the stabilization of the same, i. e. the treatment of the ester with water at a temperature as closely approaching the boiling point as is practicable in factory operations, in order to hydrolyze such unstable esters, e. g. cellulose sulphate, as may be present in the product. Also, it is frequently desired to reduce the viscosity of nitrocellulose while in its undissolved state, either colloided or uncolloided. By reducing the viscosity the nitrocellulose, I of course mean that the nitrocellulose is so changed that a composition thereof containing a certain amount of nitrocellulose, will have a lower viscosity than a like composition containing an equal amount of the cellulose nitrate untreated to lower its viscosity characteristic. A desirable way of reducing viscosity, is to treat the nitrocellulose in the presence of a direct source of oxygen, such for example as a perioxide, perborate, or the like, having the characteristic that it will give up free oxygen under proper conditions.

I have devised a process whereby the viscosity of a cellulose ester e. g. cellulose nitrate, may be reduced by treatment involving the use of a direct source of oxygen; and furthermore I have devised a process wherein this treatment may be satisfactorily carried on simultaneously with, in practical eifect, as an integral part of the stabilization treatment.

One object of the invention is to provide a pipcess for the reduction of the viscosity of a cellulose ester, by treatment employing the use of a direct source of oxygen. A further object is to provide a combined stabilization and viscosity reduction process, such process preferably further including the feature of bleaching and clariv improve generally on processes of the general character indicated, the invention consists in the various matters hereinafter described and claimed.

In accordance with the invention, as preferably practiced, the stabilization and the viscosity reduction are carried on simultaneously, my discovcries, and the practical application of those discoveries, permitting and providing forthe successful accomplishment of this end. A'desirable way of afiecting this, is to treat cellulose nitrate with hot water containing e. g. hydrogen peroxide as a direct source of oxygen, and an alkali, e. g. sodium hydroxide as an agent for increasing the activity of the peroxide. .An important featureis that although the peroxide can be used in such small amounts that its consumpticn in the process is not a disadvantageous feature, the viscosity reducing action is highly satisfactory. And furthermore, as previously indicated this resuit can he effected at temperature sufficiently high to insure satisfactory stabilization. l 1

By way of illustration merely, and not by way oi limitation, the following will serve as an example of practice in accordance with the invention. Prior to treatment accordance with the example, the nitrocelluloseis nitrated in the usual way to obtain a product. of approximately 11.2% nitrogen content and for reasons of economy a high viscosity, say 2000 cps, and is drowned in the usual manner in a large amount of Water, and the excess acid Water drained offiperoxide, there was added to the bath sufficient dilute sodium hydroxide solution to bring the bath to neutrality. There was then added sufficient sodium hydroxide in water solution to give a concentration of .15% sodium hydroxide. The mixture was then heated at atmospheric pressure to a temperature of 85 to 99 C. After one hour at this temperature the viscosity was reduced to 154 cps. Furthermore the cellulose nitrate was thoroughly bleached and its stability to the methyl violet paper test at 134.5 C. was 40 minutes. Inaddition the solubility and clarity in the oaniphor alcohol mixtures commonly employed with this type nitrocellulose was greatly improved. 1

While, in the above example, a proportion of 1 course, be used various other alkalies. there may be used such other water soluble com pounds as will develop a sufficient alkalinity (i. e.

solution to nitrocellulose of 20 to l is mentioned it will be understood that this liquid-to-solid ratio is not essential to the chemistry of the process, since any convenient ratio may be used, say, from 10 to 1 up to 30 to 1, or higher, governed largely by the type of equipment used in the handling of the mixture, the considerations being that there shall be sufiicient solution to satisfactorily cover and permeate the nitrocellulose, and like operating factors. 20 to 1 is a convenient ratio where the type poacher or boiling tub commonly employed in nitrocellulose purification is used.

Hydrogen peroxide is mentioned because of its leaving no residue. However, other soluble comparable oxidizing agents such as perborates (e. g. sodium perborate) percarbonates (e. g. sodium percarbonate) and so forth, may be used. It will be noted that, in consideration of the other features of the process, the use of oxidizing com-- pounds which are particularly active in alkaline mediums is, generally speaking, to be preferred.

Furthermore, while the use, and addition, of

hydrogen peroxide as such is referred to in the example, it will beplain that if for any reason it be desired, the peroxide can be generated in the solution, as by the use of sodium peroxide and an In place of the particular alkali, sodium hydroxide, mentioned in'the example, there may, of Thus.

a pH greater than 7.0) to produce the desired activity of the peroxide; e. g. sodium carbonate, NHa etc.

Referring to the giving of a definite alkalinity to the solution as mentioned in the example, it will be understood that the alkalinity can be Widely varied from, and greater or less than, that mentioned in the example. A particular consid eration isthat the alkalinity of the solution should be" sufficient to insure that the compound serving as the direct source of oxygen, e. g. hydrogen peroxide, be given an adequate activity. Also, the

concentration of the direct source of oxygen may be considerably varied from the figure given in the example. It is, however, desirable to use a concentration which, in consideration of the particular concentration of alkali that may be used, will bring about the desired reduction in viscosity in, at'most, the time which would be required for adequate stabilization. Furthermore, the concentration of the peroxide and/or alkali may be so far increased that the desired reduction in viscosity can be effected in less than the time required for stabilization merely. The practical effect of this is, that, if desired, the viscosity reduction may occupy but a portion of the stabilizing period. That is, the viscosity reducing items, e. g. sodium hydroxide and hydrogen peroxide, may be added to the water, at the beginning of the stabilizing treatment or later on. Care should be taken of course that, when the introduction of the viscosity reducing items is delayed, the desired reduction shall be efiected by the time stabilization v be completed. This procedure is more particularly applicable to, although not necessarily confined to, the treatment of pyroxylin of approximately 12% nitrogen content.

While it would at first appear to one skilled in the art that the use of the alkali would bring about the permanent discoloration of the cellulose ester under treatment, I have found it to be the fact thatthis is not the case. In fact, the cellulose ester at the completion of the treatment will be found to be of exceptionally good color.

Gf course, after the completion of the stabilizing and viscosity reducing treatment, and after the liquor has been drained off (for reuse if it contains peroxide) such alkali asremains in the ester, should be neutralized, as bythe addition of a small quantity of any suitable acid, or a short acid boil, after which the ester is water-washed free from the treating solution. In certain cases the acid liberated from the nitrocellulose on account of its hydrolysis will be sufficient to neutralize the alkali by the time the normal end of the treatment is reached; and, obviously, in such cases the subsequent acid treatment becomes unnecessary. At the completion of the entire treatment, the fully treated product is thoroughly water washed.

In further illustration of the process the following examples may be cited:

The nitrocellulose, and all the conditions in this example were the same as those in Example I except that at the beginning of the treatment the concentration of hydrogen peroxide was-.40%- and the concentration of sodium hydroxide 30%, and except that treatment was prolonged for six hours.

.4095 and the treatment was prolonged for six hours. At the end of one hours treatment the viscosity had been reduced to 238 cps. and-the peroxide concentration to 03% and after six' hours treatment it was 150 cps. and the peroxide had been entirely consumed.

The nitrocellulose and the conditions in this example were the same as those in Example III except that the addition of the hydrogen peroxide to the bath was postponed until the nitrocellulose had been subjected to treatment for hour at the temperature indicated (85 to 90 C.) with the alkali. The peroxide was then added. After one hours treatment hour with alkali plus hour with peroxide and alkali) the viscosityhad been reduced to 204 cps. and the peroxide concentration had fallen but to 39%. hours total time of treatment the viscosity was 136 cps. and the peroxide had been entirely consumed.

Scrap transparent cellulose nitrate plastic '(i. e

a cellulosic nitrate product of .about, parts'by weight, colloided nitrocellulose (approximately 12% nitrogen) 100, camphor 34, ethyl alcohol 2,) out into small pieces, was: steeped at 85 to 90 C. in a liquor containing 30% sodium hydroxide and 30% hydrogen peroxide. The addition of the hydrogen peroxide was delayed until the caustic steep had been carried out for one hour. After three hours total steep (one hour with caustic plus two hours with caustic plus peroxide) the After treating for one hour the viscosity 7 had been reduced to 81 cps. and after six hours After six lls viscosity of the plastic had been reduced to 476 cps. and after five and one half hours total treatment (one hour with caustic plus four and one half hours with caustic plus peroxide) the viscosity was 354 cps. The viscosity of the plastic before treatment was 1225 cps.

In the above examples, Example II illustrates, in comparison with Example I the eiiect of using one half the amount of peroxide and double the amount of alkali. Example III in comparison with III illustrates the saving of peroxide which may be efiected by delaying the introduction thereof in cases wherein but a short treatment, e. g. one hour, is to beigiven. Example IV illustrates the applicationof the process to the reduction of the viscosity of cellulose nitrate in the colloided state.

In the carrying out of the examples occasional stirring was used in :order to insure uniformity throughout the mass, and, generally speaking, a procedure of this general type is desirable. I have found it particularly satisfactory to provide a circulation of the liquid from top to bottom of the container, by slowly drawing 01? the liquid at the bottom of the container and returning it to the top.

As previously suggested, it is desirable to work at a temperature which will insure the completion of stabilization in a relatively short time. The higher the temperature, the shorter will be the time required for stabilization; but I have found it the better practice to use a temperature somewhat below 100 C. to insure that the activity of the viscosity reducing factors will not become so great as to make accurate control unduly difficult. On the other hand, a temperature not substantially lower than 60 C. is desirable if the treatment is not to require an undue length of time.

I may note that the viscosities of the cellulose nitrate of approximately 11% nitrogen content, used in the examples, were measured as follows: grams of the dry nitrocellulose were dissolved in 313 grams of a solvent consisting of camphor by weight in ethyl alcohol; and the viscosity in centipoises equals 34 times the time in seconds required for a diameter aluminum sphere to fall through 10 inches'of the solution in a 1%" inside diameter tube at 25 C.

While the invention has been discussed with more particular reference to cellulose nitrate, it will be seen that it, in certain aspects, may be applicable to other cellulose esters, e. g. cellulose acetate. Furthermore, while the treatment of cellulose nitrate of a nitrogen content of about 11% has been particularly exemplified, it will be evident that the invention is entirely applicable.

to cellulose nitrate of a higher or a lower nitrogen content. However, when a higher nitrogen content is in question, an increase in the severity of the conditions, such as higher concentration of alkali and peroxide; a longer time of treatment, etc., is recommended.

I claim:

1. The method of treating a cellulose ester which comprises heating the ester in an undissolved state in an aqueous medium having a distinct alkalinity, in the presence of hydrogen peroxide.

2. The process of reducing the viscosity of cellulose nitrate which comprises heating the nitrate in an undissolved state in water contain ing hydrogen peroxide, and sodium hydroxide in quantity sufficient to give the solution a distinct alkalinity.

3. The process of reducing the viscosity of cellulose nitrate which comprises heating the nitrate in an undissolved state to a temperature above C. in water containing hydrogen peroxide, and sodium hydroxide in quantity sufficient to give the solution a distinct alkalinity.

4. The process of reducing the viscosity of cellulose nitrate which comprises heating the nitrate in an undissolved state to a temperature substantially between C. and 95 C. in water containing hydrogen peroxide, and sodium hydroxide in quantity suiiicient to give the solution a distinct alkalinity.

5. The process of treating unstabilized cellulose nitrate to stabilize the same and reduce the viscosity thereof which process comprises immersing unstabilized cellulose nitrate in the undissolved state in water containing hydrogen peroxide and an alkali in suilicient quantity to give the solution a distinct alkalinity, heating at sub stantially 80 C. to 95 C. to effect hydrolysis of unstable esters and viscosity reduction, and removing hydrolyzed esters and residual re-agents.

6. The process of treating unstabilized cellulose nitrate to stabilize the same and reduce the viscosity thereof which process comprises immersing unstabilized cellulose nitrate in the undissolved state in water containing hydrogen peroxdissolved state in water containing hydrogen per- I oxide and an alkali in sufficient quantity to give the solution a distinct alkalinity, heating at substantially 80 C. to 95 C. to effect hydrolysis of unstable esters and viscosity reductions, draining, adding acid to neutralize any retained alkali, and washing.

8. The process of reducing the viscosity of cellulose nitrate which comprises heating the nitrate in an undissolved state in water containing hydrogen peroxide, and an alkali in quantity sufiicient to give the solution a distinct alkalinity.

RODERICK K. ESKEW.