US1919962A - Conditioning of cellulose fiber for nitration - Google Patents

Description

July 25j 1933- M. o. SCHUR `ET AL 1,919,962;A

CONDITIONING OF CELLULOSE FIBER FOR NITRATION Filed Feb`- 20, 1930' and low acid retention.

MILTON o. scnun AND BENJAMNG. Hooson BERL'INNEWHAMPSHIRE, Assrcmon" "TO BROWN COMPANY,IOF"BERLIN, rNEXV HAMPSHIRE, -A CCRPORATION OF "MAINE l connrrfomnc or CELLULOSEFIBER Fon Nr'rnnrron Application ieu February 20,1930; seria11N0.429,92e.-

This invention 'relates 'to the conditioning of cellulose ber for,l conversion into cellulose derivatives. withthe conditioning of cellulose ber of the nature of woodpulp for nitration, with a view toward enhancing` the yqualities, and the yield of nitrocellulose `attainablefrom the `fiber used as rawmaterial; c

In'the cellulose` derivative industry, considerable attention paid to both the chem'- ical and physical characteristics of the cellulose ber to be converted into derivatives. Thisl is particularly true in the eld fof' ni-` tration, where it is essential that the cellulose ber not only answer certain specifications'as'to composition, ybutthat it also be in such physical condition that nitration will proceed with smoothness', uniformity,

' and minimum side reaction and will result in a high yield ofnitrate of good quality In our application VSerial No. 394,370, Patent No. 1,880,052, the discoverywas announced that: when c'ellulosefiberI is 4finely shredded under predetermined conditions of then dried, it takes on ress ofnitration and thefhigh yield of nicovered that :additional striking` advantages may be realized if the beri's inmercerized as well as in moist condition during the shredding operation. These advantages include. astill yhigher yield of nitrated product, a lower acid retention, and atthe same time the opportunity of carrying out the shredding operatio'nwithi `widery limits of moisture in .the ber and with a variety of available shredding machines. zation evidently (so changes the `physical character of thebertha't it is easy to avoid the generation of yfibrous dust while shredding ati'low moisture contents, as, wellv as to while,

do away with hard-packed lumps 'shredding at high moisturecontents. y While some shredding machines lead to-better Aresults than others, with a givenmachine far better results; are obtained in the case of a mercerized ber than in the case of similar It' deals more es eciallyy l various cellulose bers,

,while in the case of rened Wood? puilps ltion mill inbales,

unmercerized ber. Y Forinstance, an impact shreddingmachine, such as a hammer mill, v, whlch leads; to eminently satisfactoryv rei,

lever-,abe `shreddedby the use of other niachines, suchas.` carding machines,.which sometimes lead toeven higher yields` of. nitrate than that'obtained whenusingV a ham- 'mermilL f i Y While the` process of the presentinvention may be practised to ladvantage upon it is especiallyworth wood pulps, such as the content, whichl o r greaterl opportunity for improvement than cotton linters, which has heretofore constituted .practically the only satisfactory source of cellulose for nitration. A major advantageof our process is that the finely shredded, mercerized wood ber may be` handled by the nitration manufacturer, who has been in the custom of usingcotton linters, with no fundamentalchange in the of high alpha cellulose conk process or the-.instrumentalities with which he .is equipped. Thus, shouldthe nitration mill be at a point distant from wheremercerization and I shredding is performed, the

dried shreds maybe shipped tothe nitraas f is cotton linters. Should thev nitration mill be one in which so-called lower nitrocelluloses, e. g., thosegof 11% nitrogen content,:are made, the procedure maybe onewhich is typical in suchy case'. Such aprocedure may besubstantially. as follows; `Care is initially taken' that the shredsl are in dry condition before their addition'k to the nitrating pots.` The Ldry shreds aresteeped ina nitrating acid mixture comprising 18.7% water, 20.5% nitric acid, andy 60.8% sulphuricacid, the ratio of acid to berv being 50 to 1. The

i temperature of the reacting charge is regulated according to the viscosity of the nitrocellulose desired, a typical nitration being carried out at 40 C. for one-half hour. At the end of nitration, the contents of` the nitrating pot are dumped into a centrifuge, wherein the excess acid is whizzed off, and the centrifuged mass. ofv shreds is pitchforked into tanks wherein it is subjected tov high pressure streams of fresh water, which serve to dilute quickly residualacidmassociated with Vthe centrifuged mass. The washed mass isV drained free from excess water, is again washed and drained free,

from excess water, and is then 4boiled in water under atmospheric pressure for from` three to twenty-four hours, with one or more changes of water during the boilingoperav tion. Boiling of the nitratedproduct serves to remove traces of acid and impurities therefrom, and thusto effect its stabilization, The boiled product is vwashed with a large volume of'cold water, and centrifuged to a low water contenti` The water in the centrifuged product is displaced by denatured alcohol, and in this condition the product may be sold or compounded with other materials, such as camphOr, to produce ultimate nitrocellulose products'. f

When subjected to the mercerizingstep ofy our process, the cellulose ber may bev in any one of' a variety of forms, depending upon the conditions at hand. For example, if

mercerization is carried out in a pulp mill Where ber is handled in slush form, the ber is mercerized in such form, but if mercferization is to be effected in a nitration mill operating vdistant from a pulp mill'and to whichv the ber is shipped in the form of 'comparatively thick sheets, such as `used in viscose-rayon manufacture, in the Vform of paper or tissue, or in the form of shreds, the ber may be mercerized in any one of these forms. `The caustic soda solution used for mercerizing the ber may be at room temperature orat much 4lower temperature, de-

pending upon thek mercerizing temperature of the solution employed.` i For instance,

when a caustic-soda solution of 18%` 'strength is used, mercerization may be effected at room temperature, but if the caus-V tic soda solutionV isof lower strength, say

10%, mercerization cannot be effected at above about 0 Cu The -time required for mercerization is eXceedinglyshoru-being as'` vlow as two to three minutes, but, inasmuch as caustic soda solution extracts impurities from cellulose ber, including less-resistant celluloses andligneousand resinous matter, it may be of advantage to maintain the ber in contact with the solution fora substantial period of time, especially when unbleached or relatively impure pulps are used asraw material. If desired, otherpurifying chemicals, such as bleach, which tend to improve and/0r high temperature cooking in dilute ,llquors before or after mercerization. vWhen' the ber' requires mercerization as the only chemical treatment prior to the shredding operation, it is Washed immediately after mercerization and is preferably acidied toward the completion of washing with dilute acid, such as acetic or sulphurous, to ensure complete removal of caustic soda. Itis then necessary tordewater the mercerized ber to the Amoisture con-tent at which `itmay be shredded to the physical condition satisfactory for nitration. To this end, thepulp should be dewatered until it has a yber content of from about 25% to 75%, but optimumk results are obtainable at 'ber contents offrom about 80% to 65%.

When the pulp has been mercerized and washed in the form of comparatively thick sheets, they may be dewa-teredunder action of hydraulic presses to a ber content as high as about 40%. If, however, the pulp is mercerized and washed in the `form of a suspension of individual bers or shreds,

dewateringmay be effected by sheeting on a wet or cylinder machine equipped with .sufficiently heavy couch and pressure rolls to produce sheets of as high as about 25% ber content.y These sheets may then be delwzvltercdunder the action of hydraulic pressesto higher ber content.

r the mercerizcd and Washed j pulp suspension may be dewatered directly to a ber coutent of about 40% by centrifuging. If higher than about 40% ber is desired in the pulp, the partiallydewatered pulp may ,be subjected to a drying operation, in4 W ich case drying should be conducted to. ensure a product throughout which the moisture is uniformly distributed, as; it is necessary that shredding be carried out on a uniformly moist material. Whenrit is desired to carry a comparatively large stock of mercerized ber or when mercerization is carried out at a much higher rate than shredding, andstoring of mercerized berfis necessary, the mercerized berl should be deWa-tered'` to complete dryness inorderto avoid deterioration of the pulp such as takes place when it is stored in moist condition fora long period.V lu such case, however, the` dry, merccrlzcd hber .should beuniformly rewetted to the desired moisture content before shredding.

ensure complete and uniform contact ofthe solution with all the bers. The sheets were thoroughly pulped or suspended inthe solution by agitation, and after aboutthree minutes the ber suspension was thrown on a iilter, the excess liquor drained oil, and' the mercerized ber retained on the lter was thoroughly ,washed 'with'hot water, which tends to enhance the purification of the ber. The ber` was then acidied with a weak solution of'acetic acid and again washed to remove flast traces of chemical. The` washed ber was then centrifuged to a ber content ofabout 30%, was coarsely shredded, and air-driedv to a ber content of about The ber was then passed througha hammer mill, wherein it was nely shredded. The mass of shreds was brought to a bone-dry condition, in which condition it had an appearance closely resembling cotton lin-ters. When nitrated under the conditions hereinbefore described to produce nitrocellulose of 11% nitrogen content, and then centrifuged, the yield of product Was 153.0 and the acid retention 5.3 or 1.7 pounds of spent nitrating acid per pound of nitrocellulose. These results are comparable to those obtained when using high grade cotton linters as a raw material.

The foregoing results are illustrative of those obtained when similar mercerized ber is shredded under other conditions of moisy -ture content and thencompletely dried and and as low as 25%, We obtain good results.

While our discoveries may be applied to advantage in conditioning cellulosebers of various origins for conversion into nitrocelluloses, they have especial signicance when applied to rened woo'd pulp of high alpha cellulose content, say o about 93% alpha cellulose content or higher. Such Wood pulps are highly absorptive as aV result of the removal of non-alpha cellulose impurities therefrom, and when prepared in ued form, as ordinarilyfor nitration, give disappointing results. We believe that secondary reactions are encouraged when such Wood ber is ued, it being our theory that as the mixed nitrating acids react with ber,-

they become weaker in nitric acid and richer in watercontent, tending `to hydrolyze the bers rather than to rnitrate them. Since the bers are in a highly` absorptive condition, nitration of the bers evidently takes place so rapidly Ithat `there is insufficient time for diffusive action to take place to ensure the proper composition of mixed nitrating acids in the bers. The disappointn ing results originally obtained when using rened wood pulps are doubtless traceable to the additive effect of the absorptivity` of, the individual bers,A andI the absorptivity. of the mass. At the early stages of our re.- v

search Work, we were at a loss to account for these results, as `one might expect good re sults because of the desirable chemical composition of the ber. By conditioning such wood ber as hereinbefore described, it is possible to realize the good results to be ex-y pected from'such ber, without incurrin such expense as to nullify the economical a i vantage which such ber now has over cotton.

We claim: s y

1. A process which comprisessuspending preliberated cellulose .ber in a large-excess of caustic soda solution undermercerizing conditions, washing the mercerized ber free from alkaline solution, dewatering the washed ber to a ber content of from about drying the shreds while at such moisture.Y

content from such moist condition, and nitrating the resulting dried shreds.

2.A process Vwhich comprises shredding mercerized wood pulp while associated with water in amount to produce a ber content of from about 25% to 75%, drying the shreds from such moisture content, and nitrating the resulting dried shreds.

3. A process which comprises nely shredding a mass of mercerized cellulose pulp in the'presence of moisture, drying the moist shreds, andnitrating the dried shreds.

4. A process Which'comprises mercerizing woodk pulp, nely shredding the mercerized pulp inthe presence of moisture, drying the

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