US2592355A - Process for manufacturing macromolecular cellulose fiber - Google Patents

Description

Patented Apr. 8, 1952 PROCESS FOR MANUFACTURING MACRO- MOLECULAR CELLULOSE FIBER Shozo Tachikawa, Sanjo, Higashiyama-Ku,

Kyoto, Japan No Drawing. Application February 20.1950, Serial No. 145,307. In Japan November 21, 1949 The present invention relates to a process for manufacturing low alkaline viscose of macrocellulose molecules, consisting in obtaining low alkaline macro-molecular cellulose from cellulose material having initially a degree of polymerization (abbreviation-D. P. will be used hereinafter) above 800, by steeping same in a steeping solution, as low in caustic soda as possible, in accordance with the D. P. of said cellulose material, under reduced pressure at the beginning of steeping and suitable higher pressure later, secondly obtaining macro-molecular low alkaline xanthogenate by pressing-down the cellulose thus obtained forcibly and then by subjecting it to xanthation with suitable addition of carbon bisulphide, under suitable pressure regulated according to the D. P. of said material cellulose, and thirdly dissolving xanthogenate thus obtained again in carbon bisulphide and water. The object of the present invention lies in manufacturing a low alkaline viscose consisting of macro-cellulose molecules-on a commercial scale, which is readily spinnable in either an alkaline, neutral or 3% dilute sulphuric acid bath, from macro-molecular ,cellulose, as raw material, possessing D. P. above 800, for the purpose of manufacturing-the macromolecular rayon fiber with D. P. above 500, 'of high dryand wet-strength and of high durability.

It is well known that, in manufacturing viscose-rayon fiber, a. low cellulose, high alkali and low viscosity viscose is prepared from material pulp-of around 700 D. P., by xanthating and dis-'- solving same in the usual way, under abolition of aging, which lowers the D. P. of the alkali cellulose most remarkably, and that the regenerated fiber obtainable from above viscose by spinning in an ordinary way possesses a D. P. below 400 and can display no characteristic peculiar to the macro-molecular structure.

Various processes have already been introduced for obtaining rayon fiber of fairly high D. P. from material of around 700 D. P., for instance. steeping raw material ina solution of ordinary or higher caustic soda concentration, pressingdown the steeped product to obtain alkali cellu- Qlose and xanthating the unaged cellulose with relatively. a large quantity of carbon bisulphide, or as an alternative procedure, xanthating above unaged cellulose under high pressure in an inert gas, or the like processes. I However, those processes are not satisfactory for such high D. P. cellulose material as above 800 D. P. In fact, even in those processes, it is difficult to obtain such high D. P. rayon fiber as above 500 which.

3 Claims. (01. 1s- -54) possesses characteristic properties inherent in the macro-molecular structure. It is an accepted fact that the higher the D. P. of rayon fiber is, the more the properties of the finished product can be improved. However, the regenerated fiber that can be obtained in the usual process, possesses a D. P. below 500, a value far below that of natural cotton fiber, and by no means satisfactory. This unfavorable result calls for a better process to obtain a product of higher D. P. I In the. present invention, raw material composed of cellulose above 800 D. P., for instance, refined cotton linter or any special pulp is used, in preventing the lowering of D. P. as much as possible. Therefore, entirely new processes are adopted in each stage of manufacturing viscose: First, in the steeping with caustic soda, the caustic soda concentration of the steeping solution is varied substantially inversely with the D. P. of cellulose material. The steeping is conducted at first under 'reducedpressure in order to meet'the decrease in combined caustic soda due to the said dilution, thus facilitating the permeation of the steeping solution into the cellulose material quickly and uniformly, and simultaneously excluding oxygen occluded in the steeping solution as well as in the material fiber, so that the lowering of the D. P. of cellulose that might otherwise be caused by the decomposition due to oxidation duringand after formation of falkali'cellulose, canbe suppressed. Q Thereafter, the formation of cellulose I is accelerated by the subsequent steeping under appropriate pressure adjusted according to the concentration of steeping solution, thus enabling the formation of satisfactory alkali cellulose. In this case, an inert gas such as nitrogen without used as compressing medium. Thus, the lowering of D. P. during the course of steeping has .been prevented by the following means: lowering of the caustic soda concentration for the steeping solution; perfect possible suppression of oxygen effect, as well as shortening of steeping time. Then, it is needless to say that strong possible squeezing is necessary for removing free adsorbed alkali. The fundamental principle is to increase the compressionand hence lower the press weight or ratio as th D. P. of alkali cellulose becomes higher, becausefthe rate of decrease of D. P. of said cellulose due to the reaction of caustic soda is higher according as the D. P. becomes higher.

Shredding is conducted at low temperature in a short interval in nitrogen atmosphere in order that low alkaline macro-molecular cellulose may be obtained by checking the fall of D. P. of said alkali cellulose.

In the subsequent xanthation process, a fairly large quantity of carbon bisulphide (over 45% of the cellulose used) is added to unaged alkali cellulose.

The oxygen in the reaction apparatus which will otherwise effect the decrease of D. P. during xanthation, is replaced beforehand with nitrogen while the apparatus is kept vacuum.

As described above, the' lowering of caustic soda concentration of steeping solution is effected in accordance with the D. P. of cellulose material. Therefore, it is inevitable that the xanthation will be the more difficult as the higher the D. P. of material cellulose is. In order to overcome the difficulty, the xanthation is carried out in an inert gas, under the pressure corresponding to D. P. of material cellulose.

By means of this pressure, we can accelerate the xanthation as much as we desire, without increasing the quantity of carbon bisulphide necessary in order to overcome above difliculty in xanthation. So the dissolving procedure can be brought about very easily and favorably and economically.

Needless to say, it is necessary to control the quantity of carbon bisulphide, the reaction temperature and the pressure properly for uniform reaction and for preventing decrease of D. P.

One might consider simply that increase of carbon bisulphide, high reaction temperature as well as longer reaction time would be desirous for getting favorable results when the alkali cellulose of high D. P. containing a small amount of free alkali is to be treated.

But in fact, such measures only cause a remarkable decrease in D. P.

In the present invention, those obstacles were surmounted by quick and uniform reaction effected in a short period of time under compression, thus allowing as little decrease of D. P. as possible and carrying out a satisfactory reaction.

The sodium xanthogenate cellulose obtained by the xanthation is not dissolved in alkaline water as in the usual process, but is dissolved in a mixture of water and carbon bisulphide. or by water and carbon bisulphide alternatively added, so that a viscose suitable to spinning is obtained.

As described above, free alkali being kept minimum and lowering of D. P. being controlled throughout the whole process. the D. P. of cellulose of viscose obtained is extremely high and free alkali content is low. Therefore, the said viscose can be spun either in an alkaline, a neutral or less than 3% sulphuric acid bath, low in sodium sulphate. In consequence, macromolecular rayon fiber can be obtained having the characteristic properties peculiar to the macromolecular structure.

Following is the explanation of the present invention with regard to the practical procedures. classified according to D. P. of cellulose material.

Case 1.Raw material: Refined cotton linter or special pulp of D. P. 800-1000.

First, the cellulose material is steeped in an alkaline solution (16-17 weight per cent caustic soda solution) for 20-30 minutes under less than 60 mm. pressure. Next the reaction is con- 4 tinued for 30-60 minutes under l-3 atmospheric pressure of inert gas, and it is then pressed down to 2.7-2.9 times the weight of cellulose and immediately shredded in nitrogen atmosphere at as low temperatureand for as short a duration as possible. Thus we obtain an alkali cellulose with sodium hydroxide-cellulose ratio equal to 0.40-0.45. Without subjecting to aging, it is xanthated in a xanthating apparatus, and 45-55% carbon bisulphide is added.

In xanthation, the air in the reaction apparatus is previously replaced with nitrogen gas and a desired quantity of carbon bisulphide is added under reduced pressure. After 30-60 minutes of operation when carbon bisulphide is adsorbed and hence the pressure is reduced, the pressure is raised up to 1-3 atmospheric pressure by introducing such inert gas as nitrogen and the reaction is continued for further -120 minutes.

Then at ordinary pressure, 5- of total dissolving water is sprayed into the solution under agitation. After 20 minutes, carbon bisulphide, 5-10% of cellulose, is added, agitation is continued for further 30 minutes and the remaining dissolving water is added to complete dissolution.

The decrease in D. P. of the cellulose of the viscose thus prepared is very slight and the content of free alkali is very little. A viscose of 4-8% cellulose, 1.60-3.60% total alkali and 400-1,000 second viscosity can be obtained.

Case '2.--Raw cellulose material: D. P.:1,000- 1,200.

In case a cellulose of purified cotton linter of fairly higher D. P. is subjected to steeping with 17-18% sodium hydroxide solution, a quick decrease in D. P. will take place in 10-20 minutes, thus resulting in the formation of alkali cellulose of D. P. that is as low as that obtained from raw material of lower D. P. The final product is not a satisfactory one.

When such a material as given for this case is used, it should be steeped in dilute alkali solution whose alkali content ranges from 15 to 16% at the highest. For ensuring a quick and uniform reaction, first, it should be steeped in 10-20 minutes under such a highly reduced pressure as less than 60 mm., and then after steeping in a fairly short duration under a pressure, higher than that used in Case 1namely 4-10 atmospheric pressure, to complete the formation 0 perfect alkali cellulose.

In this case, the ratio of sodium hydroxide to cellulose in alkali cellulose is 0.37-0.40. It is pressed down to as heavy as 2.6-2.8 times the weight of cellulose and transferred to xanthation after shredding similarly as in Case 1.

In xanthation, the air in the reaction apparatus is replaced with nitrogen gas similar as in Case inert gas as nitrogen as in Case 1.

Next, the xanthogenate is dissolved under agitation as in Case 1 or above processes are repeated until all the sodium xanthogenate cellu- "lose. which is diflicult to diffuse, is completely dissolved.

The composition of the viscouse thus obtained is of 3-8% cellulose and 1.10-3.20% total alkali,

with 5.00-1,500 second viscosity. 7

Case 3.Raw cellulose material:

With raw material of high D. P. as in this case, we meet with more difficulty in each process, owing to inequality of minute structure of raw material or ununiformity of distribution of its D. P.

From these reasons, we sometimes have to take the following procedures:

(a) When the process same as Case 1 is adopted, 11-15% sodium hydroxide solution is used. steeping is carried out first for -20 minutes under less than 60 mm. pressure and then under 10-15 atmospheric pressure as in Cases 1 and 2. In this case, pressing down is taken as heavy as 2.5-2.7 times the weight of cellulose.

(b) After steeping for such fairly short duration of time as 10-20 minutes in ordinary concentration sodium hydroxide solution as 18% alkali content, the product is quickly pressed down and again steeped in alkali solution a little more diluted than in Case a, such as of 13-14% alkali concentration. Above manipulation we find makes the subsequent manipulations easier, though the product gives the similar analytical results. I -i The ratio, sodium hydroxide: Cellulose in the alkali cellulose obtained in both (a) and (b) process was found to be 0.34-0.37.

After this product was treated with carbon disulphide in a similar way as in Case 2, it is treated under 6-10 atmospheric pressure, as in Cases 1 and 2 .The composition of the viscose solution obtained in the above way was found to be of 2-6% cellulose, 0.68-2.22% total alkali, with GOO-3,000 second viscosity.

Case 4.Raw material: D. P.=higher than In this case, it is necessary to use Iii-14% alkali solution and 15 atmospheric pressure for our purpose. The conditions otherwise are followed just as in Cases 1, 2 and 3, while the pressing down is taken to be as heavy as 2.4-2.6 times the weight of cellulose. The sodium hydroxide/cellulose of the alkali cellulose was found to be 0.30-0.34.

In this process, 2 stage steeping as in Case 3 (a) was found to be effective as well.

In xanthation carbon disulphide of similar quantity as in the previous case is used and under 12 atmospheric pressure, the whole process being carried out in similar way as in Cases 2 and 3.

The composition of the viscose obtained in the above way is of 1.5-6.0% cellulose and 0.4-2.00%

total alkali with over 800-3,500 second viscosity. Following are the practical examples related in detail.

EXAMPLE I Linter pulp of D. P. of 870 is used as raw material.

After it is steeped in 16.5% sodium hydroxide solution at deg. C., the steeping is continued for minutes under 100 mm. vacuumand then for more than 60 minutes under 2 atmospheric pressure in nitrogen gas. I I .After being pressed down to as heavy as 2.8 timesthe weight of cellulose, it is shredded for 60 minutes at 15 deg. C.

The alkali cellulose thus obtained was found to be 33.5% of cellulose and 14.1% of total alkali. I Next,.without aging, it is directly subjected to xanthation in an xanthation apparatus, where oxygen is expelled previously under vacuum and filled with nitrogen gas, and then carbon bisulphide (48% of cellulose) is added under reduced 75 The regenerated cellulose has D.

pressure. After xanthation for 45 minutes at 25 deg. C. it is continued for further minutes under2 atmospheric pressure in nitrogen gas.

The produced sodium cellulose xanthogenate is dissolved at 15 deg. C. in such way that first /is of the total dissolving water being sprayed, followed by 30 minute agitation, then carbon bisulphide (5% to cellulose) being added, followed by 30 minute agitation, the remaining waterportion being added finally, with agitation kept throughout above manipulation, we obtain a product, viscose.

The composition of the viscose thus obtained is of 4.5% cellulose, 1.9% total alkali, sodium hydroxide ratio to cellulose=0.42, with 540 second viscosity (time of dropping of a steel ball of 3 inch diameter 20cm. in one second) The regenerated cellulose was found to have D. P. of 550.

EXAMPLE 11 As raw material, refined cotton linter of D. P. of 1,120 was used. It was steeped in 15.4% sodium hydroxide solution at 18 deg. C. for 20 minutes under 60 mm. vacuum and then for 60 minutes under 8 atmospheric pressure in nitrogen gas. The product was pressed down as heavy as 2.7 times the weight of cellulose and shredded similarly as in Example 1. The constituents of the alkali cellulose were found to be 36.4% cellulose and 13.5% total alkali.

This product was xanthated in reaction apparatus similar as used in Case 1. First the air in the apparatus was replaced with nitrogen gas and the product was xanthated under reduced pressure. Then carbon bisulphide (46% to cellu-- lose) was added, and after 60 minutes the reaction was continued for further minutes under 5 atmospheric pressure in nitrogen at 23 deg. C. The resolution was carried out as in Case 1.

The obtained viscose was found to be of 3.0% cellulose, 1.1% total alkali, sodium hydroxide: ce1lulose=0.37 and 620 second viscosity.

The regenerated cellulose had D. P. of 720.

EXAMPLE III As raw material, refined cotton linter of D. P. of 1,350 was used. It was steepedin 18% sodium hydroxide solution at 20 deg. C. for 15 minutes. The product was pressed down as heavy as 2.8 times the weight of cellulose and again steeped in 14.2% sodium hydroxide solution for 20 minutes, under 20 mm. vacuum, and then for 60 minutes at 16 deg.-C. under 12 atmosphericpressure. The product was pressed down. as heavy as 2.6 times the weight of cellulose and shredded similarly as in Example 2.

The constituents of the produced. alkali cellulose werefound to be of 37.2% cellulose and 13.0% total alkali. This was xanthated similarly as in the previous example; with carbon bisulphide (50% to cellulose). for 60 minutes at 23 deg. C. under 8 atmospheric pressure, and [is of total dissolving water was added, followed by 30 minute agitation and then carbon bisulphide (5% to cellulose) added, followed by 30 minute agitation. The similar quantity of carbon bisulphide and water respectively were added by turn, the agitation still being continued until all the carbon bisulphide and water were added to make perfect viscose.

The produced viscose was found to be of 4% cellulose, 1.4% total alkali, sodium hydroxide: ce1lulose=0.35, and 950 second viscosity.

P. of 920.

7 EXAMPLE 1v As raw material, refined cotton linter of D. P. of 1,460 was used. It was steeped in 13.2% sodium hydroxide solution for 20 minutes at 15 deg. C. and 10 mm. vacuum and for 60 minutes under atmospheric pressure, and after pressed down as heavy as times the weight of cellulose treated as in the previous example. The produced alkali cellulose has 38.4% cellulose and 12.6% total alkali.

Carbon bisulphide (50% to cellulose) was added to this alkali cellulose and after xanthation and dissolution under 12 atmospheric pressure similar as in Example III, viscose is obtained.

The composition of the produced viscose is of 6.0% cellulose, 1.98% total alkali, sodium hydroxide: cellulose=0.33, with 2,000 second vis cosity.

The regenerated cellulose has D. P. of 1,150.

Thus we have succeeded in producing a regenerated fiber of macro cellulose molecule of high degree of polymerization from such a low alkali viscose of macro cellulose molecules obtained through each process of the present invention, by spinning in a spinning bath, alkaline, neutral, or of dilute less than 3% sulphuric acid and of low salt content, less than 3% sodium sulphate.

It appears from the foregoing examples that in accordance with this process, the alkali concentration and the pressure for steeping solution, the degree of pressing-down for said alkali cellulose and the magnitude of pressure for Xanthation are adjusted in accordance with the degree of polymerization of the raw material used as shown in the following table:

remarkably high D. P. which shows vividly all the special characteristics of macromolecular cellulose.

I claim:

. 1. In the manufacture of macromolecular cellulose fiber with D. P. above 500, the process consisting in steeping cellulose-containing materials having macromolecular cellulose of not less than 300 D. P. in an alkali bath the concentration of which varies inversely as the D. P. of the cellulose within the range of 17% for 800 D. P. to 13% for 1400 D. P., pressing the alkali cellulose thus formed so that the ratio of the press weight of the material to the weight of the original cellulose varies inversely with the D. P. of the cellulose within the ratios of substantially 2.8 times the cellulose weight to 2.4 times the cellulose weight; shredding the unaged alkali cellulose thus obtained in an atmosphere of inert gas, xanthating the unaged shredded alkali cellulose by adding thereto a quantity of carbon bisulphide of not less than of the alkali cellulose in the presence of an inert gas at a pressure varying directly as the D. P. of the cellulose within the range of substantially 2 atmospheres for 800 D. P. to over 12 atmospheres for 1400 D. P., and dissolving the sodium cellulose xanthogenate thus obtained in water.

2. The process as defined in claim 1 in which the first part of the steeping is carried on under reduced pressure and the rest of the steeping is carried on in an atmosphere of inert gas at a pressure which varies directly with the D. P. of the cellulose within a range of substantially 2 atmospheres, for 800 D. P. to 15 atmospheres for 1400 D. P.

3. The process as defined in claim ltogether The relation between'D. P. of the raw cellulose material and that of the regenerated cellulose, the final product, is as follows:

Moreover, the viscose manufactured according to the new methods of the present invention has many excellent qualities: as the D. P. of the product increases, there is an increase of dryand wet-strength, ratio of dryand wet strength, elastic property and durability and capability of manufacturing rayon fiber of macrocellulose molecules with high practical value.

Speaking in brief, the present invention can prepare economically in practice a. cellulose of D. P. oi cellulose material D. P. of product 3004, 000 5004300 1, 000-1, 200 000-800 1, 200-1, 400 800%, 000 Higher than 1,400 Higher than 1, 000

with'the additional step of regenerating the cellulose by spinning the dissolved sodium cellulose xanthogenate in a dilute acid bath having a strength not in excess oi 3 SEIOZO TACHIKAWA.

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

UNITED STATES PATENTS Number Name Date 1,968,463 Schur et al July 31. 1934 2,076,596 Richter Apr. 13. 1937 2,106,111 Bayerl et a l. Jan. 18, 1938 2,117,038 Richter May 10. 1938 2,521,450 Costa Sept. 5, 1950 2,542,285 Mitchell Feb. 20, 1951 FOREIGN PATENTS Number Country Date 167,201 Great Britain Aug. 2, 1921

Claims (2)

1. IN THE MANUFACTURE OF MACROMOLECULAR CELLULOSE FIBER WITH D.P. ABOVE 500, THE PROCESS CONSISTING IN STEEPING CELLULOSE-CONTAINING MATERIALS HAVING MACROMOLECULAR CELLULOSE OF NOT LESS THAN 800 D.P. IN AN ALKALI BATH THE CONCENTRATION OF WHICH VARIES INVERSELY AS THE D.P. OF THE CELLULOSE WITHIN THE RANGE OF 17% FOR 800 D.P. TO 13% FOR 1400 D.P., PRESSING THE ALKALI CELLULOSE THUS FORMED SO THAT THE RATIO OF THE PRESS WEIGHT OF THE MATERIAL TO THE WEIGHT OF THE ORIGINAL CELLULOSE VARIES INVERSELY WITH THE D.P. OF THE CELLULOSE WITHIN THE RATIOS OF SUBSTANTIALLY 2.8 TIMES THE CELLULOSE WEIGHT TO 2.4 TIMES THE CELLULOSE THUS OBSHREDDING THE UNAGED ALKALI CELLULOSE THUS OBTAINED IN AN ATMOSPHERE OF INERT GAS, XANTHATING THE UNAGED SHREDDED ALKALI CELLLOSE IN THE PRESENCE THERETO A QUANTITY OF CARBON BISULPHIDE TO NOT LESS THAN 45% OF THE ALKALI CELLULOSE IN THE PRESENCE OF AN INERT GAS AT A PRESSURE VARYING DIRECTLY AS THE D.P. OF THE CELLULOSE WITHIN THE RANGE OF SUBSTANTIALLY 2 ATMOSPHERES FOR 800 D.P. TO OVER 12 ATMOSPHERES FOR 1400 D.P., AND DISSOLVING THE SODIUM CELLULOSE XANTHOGENATE THUS OBTAINED IN WATER.

3. THE PROCESS AS DEFINED TO CLAIM 1 TOGETHER WITH THE ADDITIONAL STEP OF REGENERATING THE CELLULOSE BY SPINNING THE DISSOLVED SODIUM CELLULOSE XANTHOGENATE IN A DILUTE ACID BATH HAVING A STRENGTH NOT IN EXCESS OF 3%.