US2979500A - Method of producing viscose - Google Patents

Description

2,979,500 Patented Apr. 11, 1961 Unitedstates Patent 2,979,500 METHOD on PRODUCING vrscosE' Fritz Opderbeck, Okriftel (Main), Bonnemuhle, Germany; and Giinther Trapp and Giinter Wiirner, both of Okriftel (Main), Germany, assignors to Phrix Werke Aktiengesellschaft, Hamburg, Germany No Drawing. Filed May 13, 1958, Ser. No. 734,824

9 Claims. (Cl. 260-217) The present invention relates to an improved method of producing viscose, and more particularly to a method of producing viscose which permits the omission of the ageing step which was always considered essential.

In the known methods of producing viscose wherein the cellulose is steeped in caustic soda solution, pressed and subsequently shredded, the soda cellulose is subjected to an ageing step requiring about one to three days. During this time, in which the soda cellulose is in general subjected to somewhat increased temperature and the action of atmospheric oxygen, a depolymerization of the cellulose occurs which makesit possible to obtain a viscose of desired spinning viscosity after the xanthation, utilizing the usual cellulose content of about 8%. If the ageing step is omitted in the production of viscose, then in the making of solutions of the usual cellulose content the solutions are extraordinarily thickly liquid and highly viscous and by normal means cannot be pumped through the spinning pump, and most important cannot be filtered.

The carrying out of the ageing, which for the reasons given above has always been an essential stage in the production of viscose, required the installation of large storage rooms and apparatus in order to take up the soda cellulose production for the necessary ageing time. This results in a considerable loss in total capital. Attempts to accelerate the ageing by the addition of chemicals to It is another object of the persent invention to provide a method of producing viscose wherein the soda cellulose can be directly, after shredding, subjected to xanthation stage without the need for an intermediate ageing stage, and wherein the subsequent spinning and filtering of the cellulose solution is not interferred with.

Furthermore, in accordance with the object of the present invention the finally produced viscose fibers have the properties which are at least equivalent to the properties of viscose produced in the normal, more expensive manner, in which ageing was utilized.

' It is yet a further object of the present invention to provide a method of producing viscose starting from enzymatically digested cellulose whereby it is possible to completely omit the ageing step in the production of the viscose and whereby the resulting viscose fibers have properties at least equal to the properties of viscose fibers produced in the normal manner.

- Other objects and advantagesof the present invention will be apparent from a further reading of the specification and of the appended claims.

With the above objects in view, the present invention mainly comprises a method of producing viscose in which enzymatically digested cellulose is converted to viscose.

'It has been found that by the action of a cellulosedigesting enzyme on cellulose before the cellulose is subjected to the stages in the production of viscose, it is possible to control with absolute certainty the desired degree of polymerization of the cellulose which goes into the formation of the viscose so that it is possible to completely omit the ageing step in the production of the viscose. By proceeding in this manner, namely subjectingcellulose to enzymatic digestion by means of a cellulose-digesting enzyme, it is possible to maintain a degree of decomposition within the desired ranges. Cellulose treated in this manner can be quickly worked up to solutions of the usual concentration and can be spun in the usual spinning bath into fibers of marked homogeneity. The fibers produced in this manner are in no way inferior to viscose fibers produced according to the classical methods. Although cellulose has been decomposed by enezyme prior to the present invention, the use of such cellulose in the production of viscose was unknown prior to the present invention, and it was completely unexpected that by the use. of such enzymati' cally digested cellulose it would be possible to completely avoid the ageing step in the production of viscose.-

. The digestion of the cellulose by means of the cellulose-digesting enzyme is preferably carried outafter prior milling or other mechanical or chemical pretreatments of the cellulose, wherein for example alkalis or acids maybe utilized. The action of the cellulose advantageously takes place at somewhat increased temperature, for example about 30 C. It is particularly advantageous to utilize for the digestion cellulase-preparations which are obtained from cultures of Aspergillus oryzae or Aspergillus niger. It is most advantageous to carry out this treatment utilizing relatively low pulp consistency, for example in the mill hollander. The pH-value of the solution is preferably maintained in neutral or acid range,

for example at values between 3 and 6. In this manner it is possible within an hour to already lower the Cuoxamviscosity of the cellulose, measured according to standard methods, from 21.6 to 11.1.

It is most advantageous to carry out the digestion of the cellulose by means of the enzyme in order to lower the degree of polymerization of the cellulose in the following manner:

In order to accelerate the action of the enezyme prep,"- aration on the starting material the bio-structure-of the source of cellulose is first structurally changed by mechanically opening the same. This can for example be carried out by milling or other mechanical comminuting devices. It is particularly advantageous to wet mill the substance in a hollander. Since the greater the degree of opening of the starting material the greater the acceleration of the enzymatic digestion, it is advantageous to carry out the milling until a milling degree of about 50 SR (Schopper-Riegler), and most preferably to a still higher milling degree of 70 or SR utilizing a crushing milling. By milling in this manner the degree of polymerization of the starting material is even not at all or only to very slightest degree lowered. Thus, utilizing a starting material having a degree of polymerization of 720, corresponding to a Cuoxam-viscosity of 21.9 cp., and subjecting this starting material to milling up to a millingdegree of 70' SR, the degree of polymerization of the resulting cellulose is 690, corresponding to a viscosity of 20.6 cp. However, the milling in this manner has the efiect of greatly accelerating the subsequent action of the enzyme preparation,

It is possible to carry out the milling and the enzymatic digestion in a single procedure. advantageous since under certain circumstances a local overheating of the reaction solution in the mill might occur which would have a deleterious action on the strength of the enzymatic preparation.

The decomposition by means of the enzyme is preferably carried out in the region of the optimum action of the enzyme. Tests have shown that cellulase-containing enzyme preparations still act rather slowly at C.; the optimum appears to be about C., While further warming of the reaction mixture to about C. results in a slowing of the action of the preparation, and furthermore starts deleterious action on the enzyme preparation.

A great number of organisms are known which have the ability to form cellulase-containing enzyme preparations. In most cases however the isolation of a cellulaserich enzyme preparation from these organisms for technical purposes involve considerable difficulties because of the content of other bacteria in the preparations. For large scale technical purposes for the production of the necessary cellulase-containing preparations, it is suitable to utilize various fungi which, if necessary by repeated breeding in the presence of cellulose are brought to a condition wherein the same form large amounts of cellulase. For large scale carrying out of the process it is possible for example utilizing the principle of surface culturing on wheat bran with the addition of cellulose to utilize cultures originating from Aspergillus oryzae. Milling in the presence of water frees the enzyme and destroys other substances and the cellulase dissolved in water is separated from the nutrient medium by filtration. In similar manner it is possible to produce suitable cellulase-containing enzyme preparations starting from other materials. The culturing can be carried out as surface culturing or submersed culturing. Among the other suitable bacteria that may be used are Myrotheciom veriucaria, Lancites sepiaris, thermal-bacteria and protozoae. In addition use can be made of natural cellulase sources such as vineyard snails.

The concentration of the enzyme in the solution can be maintained within rather wide ranges.

For example, experiments were carried out in such a manner that 100 grams of dry substance of the nutrient were dispersed in 1 liter of tap water and 250 cc. of the filtered extract applied to 10 grams of cellulose. It was found that even by applying an enzyme solution diluted to one half or even to a quarter of the above concentration, the speed of breaking down of the cellulose was not weakened to such an extent that such diluted solutions could not be used successfully for carrying out the present method.

The pI-I-value of enzyme solutions obtained as described is generally about 6.0. It is particularly advantageous to use the solution at a pH of between 4.0 and 6.0 for the splitting of cellulose.

The enzyme solution after being used once can be repeatedly reused after separation of the cellulose which was broken down in the desired manner, without giving rise to any noticeable reduction of the depolymerizing power of the enzymes (except for losses due to adsorption on the cellulose).

This is somewhat less chains, so that a considerable unification (equalization) of the degree of polymerization of the material is achieved. This is of particular advantage for the further treatment of the cellulose, particularly for the forming of cellulose solutions such as viscose, copper oxide ammonia solutions, or for the preparation of cellulose esters and others.

The fact that the longer chains are subjected to the preferred attack by the enzyme, is established by examination of the solubility of the material in sodium hydroxide of varying concentration. The experiment shows that the amount of the cellulose fractions which are soluble in 2% and 6% sodium hydroxide remains substantially unchanged even upon enzyme attack of prolonged duration. However, the amount of cellulose fractions soluble in l0% sodium hydroxide, corresponding to a degree of polymerization of between 400 and 500 rises continuously during the entire course of the enzyme treatment. This means that the short chain cellulose fractions which are soluble in dilute lye are practically not increased by the enzyme attack, while in contrast thereto a continuous increase in the quantity of cellulose fractions which in 10% lye are just still soluble and which correspond to medium chain lengths, occurs under the influence of the enzyme. A polydispersion diagram of fractions of the enzymatic treated cellulose which were separated by their chain lengths and transformed into their nitrates also shows a maximum at a degree of polymerization of be tween 400 and 600.

It is probably of particular importance that the yield of cellulose of reduced degree of polymerization obtained according to the method even upon subjecting the cellulose to the action of the enzyme preparation for many hours, amounts upon optimum conditions to 100%. Thus, the method does not cause any losses of starting material. That in fact the treated cellulose is not damaged by the new method but is only subjected to an evening out of the chain lengths is determined by determination of the copper number of the treated cellulose which represents its reducing ability. The copper number rises only during the first hour of the enzymatic splitting digestion by only a very small amount and remains thereafter, however, within certain margins of errors, constant during the entire length of the treatment. This proves that reducing sugars, particularly glucose are not formed by the method. This at first surprising fact can probably be explained in that by carrying out the new method as described, any cellobiase which may be present in the enzyme preparation and which would cause splitting of the material into simple sugars, can only become active after the starting material has been broken down to dior trisaccharides. However, before this state is reached, any cellobiase which may be present in the enzymatic extract is already weakened to such an extent that it can on longer cause any recognizable effect.

Drying of the treated cellulose under ordinary condi tions results in a strongly horny material, the reactivity of which-due to its compact surface structure, is lower than desired. For this reason, it is recommended to By treating cellulose with the mentioned enzyme preparation, it is possible under the described conditions to achieve within a few hours a breaking down of cellulose to a considerably reduced degree of polymerization. Under favorable conditions, it is possible, for instance, to reduce the viscosity of a cellulose within one hour from 21.6 to 11.1 cp., corresponding to a reduction in degree of polymerization from 720 to 470. Thereby, the breakdown first occurs fast and slows down during the further course of the same.

Surprisingly, the breakdown of the cellulose chains does not occur haphazardly, to the contrary, the enzyme causes the preferred splitting of the longer molecule carry out the drying by replacing the water contained in the final product with organic solvents. For instance, the drying of material obtained in the above way can be carried out in such a manner that the treated cellulose is freed of Water with methanol or ethanol and that the alcohol-containing material is further washed with benzene, pyridine or similar solvents for replacement of the alcohol. In this manner hornification of the material during drying of the same can be excluded to the greatest extent while its reactivity, increased by the inclusion of hydrophobic organic substances, remains intact.

In any event, it is recommended to thoroughly wash cellulose which has been treated as above prior to drying n lq tg f. t m rins due he. messa e of the enzymes further breaking down of the material during storage could occur.

Furthermore, such material when containing remnants of the enzyme solution obviously tends to mold formation; By' short heating or by treating with. a fungicide,

it is possible, however, to stabilize the material in a simple manner.

The following examples which are taken from a large number of experiments will illustrate the method.

Example I 5 Degree of polymerization 690 Cp. 20.6 Copper number 1.59

100 grams drylsubstance of the thus obtained material are now treated with 2.5 liters of an enzymatic extract at a temperature of 30 C. The extract is obtained as follows: v

A strain of Aspergillus oryzae is cultivated on a nutrient consisting of wheat chafl? and cellulose until a dense mass of mold is formed. The entire material is then milled in a hollander for one half hour with times its quantity of tap water (calculated relativeto the dry nutrient) and thereafter filtered through kieselguhr. The thus obtained solution shows slight colloidal turbidity. v

The treatment of the beaten cellulose with this enzyme solution is carried out at 30 C. and at a pH of the solution of 5.2, which pH drops during the treatment to 4.1. A sample of the cellulose taken after 2 hours shows the degree of polymerization of 445 corresponding to a cp. of 9.8. The copper number rises to 2.22. After 5 hours the degree of polymerization drops to 385, corresponding to a cp.-value of 8.2, the copper number still amounts to 2.22.

Example I! The starting material is beaten in the same manner as described in Example I. The treatment, however, is carried out with an enzyme solution diluted to half the strength of the enzyme solution according to Example I. All other conditions are similar to those in Example I. After 5 hours a degree of polymerization of 480 is found corresponding to a cp.-value of 9.9, a repeated dilution of the enzyme solution to half its strength results after 5 hours in a degree of polymerization of 525, corresponding a cp.-value of 12.8.

Example III The depolymerization is carried out as described in Example I, however, the temperature of the solution is kept at 20 C. After 5 hours the degree of polymerization of the thus treated cellulose is 455, corresponding to a cp.-value of 10.0.

Example IV A fir-paper-cellulose which was reduced in a stone hollander to a fineness of 70 SR is used as starting material.

The starting material is evenly distributed in fungus extract so that the concentration of starting material dry substance, amounts. to 2.5 grams per liter of fungus extract. Thereafter, a sheet is formed on the sheet-forming apparatus according to Schopper-Riegler. The still moist fiber felt is couched onto'a carrier cardboard and is stored in moist condition (dry substance 15-20%) for 2, 4, 5 and 8 hours at 20 C.

The fungus extract is formed by grinding 4000 grams fungus culture from Aspergillus oryzae on wheat chaff, in 40 liters water and filtering the aqueous extract through kieselguhr. 1 liter of the thus obtained enzymescontaining solution is used as described above for forming of the sheet.

In these experiments, the concentration of the enzyme in the cellulose pulp is small, since at a dry substance content of the sheet of about 20% the relationship of material to liquid is the same 1:4. 7 After the provided reaction time, the moist sheets are dried at 96 C. for 6 minutes in order to interrupt the depolymerization reactionof the enzyme. The drying is carried out on a Rapid-Kothen sheet drier.

The viscosity of the thus treated cellulose is then determined. The results are tabulated below:

Again it is found, as in the case of beech, that the cellulose structure is first loosened by heating, if at first strongly broken down, and is more slowly further broken down upon prolonged reaction time.

As indicated above, the concentration of the enzyme may be varied within very wide limits, starting with an enzyme'obtained from a fungus such as Aspergillus orzyae on a suitable nutrient medium, for example on wheat bran, which is cultivated until the fungus mycellium is completely developed, the mycellium is dispersed in ten times the amount of water so that 100 g. of said mycellium is dispersed in 1 liter of water. This is used as the standard of measure. This dispersion is filtered and for example 250 cc. of this filtrate may be used on 10 g. of cellulose. As much as 500 cc. of the filtrate may be used on 10 g. of cellulose, and as little as 32.66 cc. of'cellulose may be used in 10 g. of cellulose. Most preferably about -250 cc. of the solution is used on 10 g. of cellulose.

The digestion of the cellulose is carried out in accordance with the present invention until the polymerization degree of the cellulose which is converted to viscose in accordance with the present invention is between 400- 690. The average degree of polymerization at the lower end of the scale will generally be between 400-450 while the average degree of polymerization at the upper end of the scale will generally be between 650 and 690. Most preferably the degree of polymerization of the cellulose which has been digested by enzyme in accordance with the present invention is preferably between 500 and 600.

Cellulose with the above degree of polymerization, such cellulose being obtained by splitting of the longer molecular chains by the cellulose, is particularly suitable for the production of viscose in accordance with the present invention. A peculiarity of the enzymatically digested cellulose is that upon drying it very easily becomes horny. It is therefore advisable to work up the cellulose in wet condition. The cellulose can be converted to dry condition while maintaining its reaction capabilities by displacing the water with suitable organic liquids.

The use of enzymatically digested cellulose in the production of viscose is particularly advantageous when the viscose is produced according to the so-called singlevat process in which thecellulose to be dissolved is converted to the final viscose in a single reaction vessel. The

carrying out of the single-vat process prior to the present invention suffered from the disadvantage that it was not possible to obtain cellulose with certainty within the de sired polymerization degree in the relatively short time needed for technical purposes. The insertion of the normal ageing step for the soda cellulose is not possible in the single-vat method, since it is not advisable to take the reaction vessel out of use for several days in order to obtain the necessary depolymerization of the cellulose. The addition of depolymerization accelerating chemicals, sulfates and the like in order to obtain a more rapid ageing to the desired degree of polymerization, aside from the price of such chemicals, involves great difliculties in trying to use the chemicals in such manner that the quality of the resulting viscose is always maintained at an even level. For this reason, the use of enzymatically partially decomposed cellulose in the production of viscose by the single-vat method is particularly advantageous.

In any event, whether they are carried out in a single reaction vessel, or in several reaction vessels, the production of viscose in accordance with the present invention provides for the highly advantageous elimination of the ageing step for the depolymerization of the cellulose to the desired degree of polymerization, and accordingly represents a considerable saving in time in the production of the viscose starting from the original raw material. The reduction in time is considerable, since in accordance with the present invention the partial decomposition of the cellulose by means of the enzyme requires as little as one hour or less as compared to two to three days of ageing according to the known processes.

Thus, in accordance with the present invention the entire method of producing viscose only involves the following stages:

The starting source of cellulose, for example timber, after removing of the bark, is chipped into small pieces. The chips are mechanically milled, and as desired, subjected to chemical treatment with calcium bisulfite or the like. These chips are then subjected to enzymatic digestion as described above until the degree of polymerization of the cellulose is between 400 and 690, and preferably between about 500 and 600.

The partially decomposed cellulose is then steeped in caustic soda solution of about 17.5% for several hours, e.g. 1 to 4 hours. About 8% of the original pulp dissolves. The cellulose itself is swollen but not dissolved. This results in the formation of soda-cellulose.

The excess alkali is pressed out by a hydraulic ram, the pressing leaving a moist mass of soda cellulose which passes straight into a shredding machine. The shredding machine breaks up the soda cellulose into fine crumbs.

The soda cellulose is then, without intermediate ageing, directly xanthated by treatment with about 10% of their weight of carbon disulfide. The crumbs and disulfide are churned together producing a deep orange, gelatinous mass of sodium cellulose xanthate.

After the churning the sodium cellulose xanthate is passed into mixers wherein the sodium cellulose xanthate is stirred with dilute caustic soda solution for 4 to 5 hours while cooling the vessel. The xanthate dissolves to a clear-brown viscous liquid known as viscose. This contains about 7% alkali and about 8% cellulose. The viscose is transferred to a secondary mixer or blender which generally takes charges from about eight primary mixers. In a secondary mixer or blender the viscose is stirred and pumped round. Since it still contains some undissolved fibers from the original wood pulp, fibers which have resisted all of the chemical treatments, it is filtered. The first filtration is generally carried out through cotton-wool, and the viscose is then twice filtered through cotton filter-cloth.

The viscose solution is then stored for 4 to 5 days generally at a temperature of 10-l8 C. and during storage'it rip-ens. During the ripening the viscosity at first falls, and then rises, so that by the time the solution is ready to spin, the viscosity has risen almost to its original value. The ripening permits the viscose to be spun satisfactorily.

When the viscose solution is ripe, it is forced by compressed air to the spinning frames and there distributed and spun into fibers.

As is clear from the-above description, the omission of the ageing stage of the production of the viscose results in a considerable saving in time, and therefore in considerable saving in money in the overall process of producing viscose.

The following examples are given to further illustrate the present invention. The scope of the invention is not, however, meant to be limited to the specific details of the examples.

400 g. of air-dried beech textile cellulose is milled in a stone hollander at room temperature about 7 /2 hours until the milling degree of the cellulose corresponds to about 67 Schopper-Riegler. The milled substance is mixed in a vat provided with a stirrer with an enzyme solution which is obtained as follows:

A strain of Aspergillus oryzae is cultivated on wheat bran and cellulose nutrient medium until formation of a thick mass of mold-fungus. This culture is then mixed for about one half hour in a suitable mixing apparatus with ten times its volume (measured with respect to the dry nutrient medium) of tap water, intensively worked up, and then by filtration 13 m. of extract are obtained. The biostatic strength of the enzyme solution, which has a direct relation to the cellulose-splitting activity, amounts to 35.2. The consistency of the pulp which is mixed with the fungus extract in the vat amounts to 3% cellulose. The reaction temperature is maintained at 22 C.

After a reaction time of 10 /2 hours the viscosity of the cellulose which was originally 22 cp., was lowered to 13.7 op. The final viscosity of the digested cellulose can be adjusted by variation of the time and strength of the enzyme solution so as to obtain a viscosity of any desired degree.

The cellulose is then filtered through a sieve or a revolving filter to a dry content of about 40% and then subjected to the production of viscose in the usual manner, except for the elimination of the ageing step.

In the following tests the above enzymatically digested cellulose is converted to viscose according to the classical viscose process, and also according to the so-called singlevat process. After the production of the viscose the. same is subsequently spun to fibers.

(a) Single Vat Process.The enzymatically digested cellulose is, while still wet, treated with caustic soda solution of 17.5% strength to produce soda-cellulose. This soda-cellulose is then directly, without ageing, treated for 40 minutes with 38%' carbon disulfide. The Cuoxam-viscosity of the starting cellulose amounted to 6.5 cp. The analysis of the finished viscose (I) showed the following values:

Viscose analysis Viscosity Filtration falling ball Ripeness, value NaOH Cell. S, Permethod SR cent 9 (H) for comparison purposes. The values are indicated in the following tables: g AVERAGE VALUES The data concerning the fibers from the enzymatically digested cellulose after 40 minutes of xanthation compared to that of the normally aged and normal cellulose worked up to viscose in the usual manner, particularly the data concerning the strength surprisingly gives rise to only one conclusion. The viscose produced according to the present invention is at least equivalent to normally produced viscose. This is particularly remarkable since the operation in a single vat in accordance with the present invention omits pressing out of the caustic soda and correspondingly there is no loss of hemi-cellulose.

(b) Usual steeping alkalizing with pressing.The enzymatically digested cellulose is mashed in the usual manner with a corresponding excess of lye and pressed after one hour of immersion. A pressing factor of 3.35 is obtained The xanthation followed without prior ageing of the soda cellulose as described above during 40 minutes with 38% carbon disulfide. The subsequent dissolving of the viscose took place in the same manner in the blender. Again 12 spinning tests were carried out with various times of duration in the bath, various stretching ratios and various speeds of spinning. The values all lay in a limited region. These values are set forth in the following table.

The above table shows that with satisfactory stretching the strength factors are satisfactory as compared to viscose produced from normal air-ripened cellulose. In addition, the relative wet strength is somewhat increased. The filter ability of the viscose produced-in accordance with the present invention is highly satisfactory.

The above tests actually prove that the viscose fibers produced from enzymatically digested cellulose in accordance with the present invention actually have better qualities than fibers produced in the normal manner.

The degree of polymerization of the finished fiber was about 385. The determination of the degree of polymerization by means of the Cuoxam method shows that upon further treatment to produce the viscose fibers no further lowering of the degree of polymerization occurs.

Without further analysis, the foregoing will so fully reveal the gist of thepresent invention that others can by applying current knowledge readily adapt it for various applications without omitting features, that from the standpoint of prior art, fairly constitute essential characteristics of the generic ,or specific aspects of this inven tion and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is: v I

1. In a method of producing viscose, the improvement which comprises converting enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between, about 400 and 690 to viscose. v

2. In a method of producing viscose, the improvement which comprises converting enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between about 500 and 600 to viscose.

3. A method of producing viscose, comprising the steps of converting enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between about 400 and 690 to soda cellulose; xanthating said soda cellulose without intermediate ageing thereof; and converting the thus formed cellulose xanthate to viscose.

4. A method of producing viscose, comprising the steps of treating enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between about 400 and 690 with strong caustic soda solutions to as to convert said enzymatically digested cellulose to soda cellulose; treating said soda cellulose without intermediate ageing thereof with carbon disulfide so as to convert said soda cellulose to sodium cellulose xanthate; and dissolving said sodium cellulose xanthate in an aqueous liquid, thereby converting the same to viscose.

5. A method of producing viscose, comprising the steps of treating enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between about 500 and 600 with strong caustic soda solution so as to convert said enzymatically digested cellulose to soda cellulose; treating said soda cellulose without intermediate ageing thereof with carbon disulfide so as to convert said soda cellulose to sodium cellulose xanthate; and dissolving said sodium cellulose xanthate in an aqueous liquid, thereby converting the same to viscose.

6. A method of producing viscose by a single vat procedure, comprising the steps of treating enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between about 400 and 690 with strong caustic soda solution in a vat so as to convert said enzymatically digested cellulose to soda cellulose; treating said soda cellulose in said vat without pressing and without intermediate ageing thereof with carbon disulfide so as to convert said soda cellulose to sodium cellulose xanthate; and dissolving said sodium cellulose xanthate in an aqueous liquid, thereby converting the same to viscose.

7. A method of producing viscose by a single vat procedure, comprising the steps of treating enzymatically digested cellulose of substantially equimolecular chain length having a degree of polymerization of between about 500 and 600 with strong caustic soda solution in a vat so as to convert said enzymatically digested cellulose to soda cellulose; treating said soda cellulose in said vat without pressing and without intermediate ageing thereof with carbon disulfide so as to convert s-aid soda cellulose to sodium cellulose xanthate; and dissolving said sodium cellulose xanthate in an aqueous liquid, thereby convcrting the same to viscose,

8. A method of producing viscose, comprising the steps of subjecting cellulose to enzymatic digestion until the degree of polymerization of said cellulose is between about 400 and 690, thereby obtaining digested cellulose the molecular size of which is substantially equalized; treating the thus enzymatically digested cellulose of substantially equimolecular chain length with strong caustic soda solution so as to convert said enzymatically digested cellulose to soda cellulose; treating said soda cellulose without intermediate ageing-thereof with carbon disulfide so as to convert said soda cellulose to sodium cellulose Xanthate; and dissolving said sodium cellulose xanthate in an aqueous liquid, thereby converting the same to viscose.

9. A method of producing viscose, comprising the steps of subjecting cellulose to enzymatic digestion until the degree of polymerization of said cellulose is between about 560 and 600, thereby obtaining digested cellulose the molecular size of which is substantially equalized; treating the thus enzymatically digested cellulose of substantially equimolecular chain length with strong caustic soda solution so as to convert said enzymatically digested cellulose to soda cellulose; treating said soda cellulose without intermediate ageing't hereof with carbon disulfide so as to convert said soda cellulose to sodium cellulose xanthate; and dissolving said sodium cellulose xanthate in an aqueous liquid, thereby converting the same to viscose.

References Cited in the file of this patent UNITED STATES PATENTS 2,028,846 Richter Jan. 28, 1936 OTHER REFERENCES Henningsen July 25, 1933

Claims (1)

1. IN A METHOD OF PRODUCING VISCOSE, THE IMPROVEMENT WHICH COMPRISES CONVERTING ENZYMATICALLY DIGESTED CELLULOSE OF SUBSTANTIALLY EQUIMOLECULAR CHAIN LENGTH HAVING A DEGREE OF POLYMERIZATION OF BETWEEN ABOUT 400 AND 690 TO VISCOSE.