When producing regenerated cellulose fibers by the viscose method a reduction of chemical substances used in the process, such as carbon disulphide, will probably in a future be determinant necessary for both environmental and economical reasons. In a traditional viscose process the amount of carbon disulphide added in the process is between 30 and 36% by weight of the a-cellulose. To recover the outlet of carbon disulphide into the air or water, is both difficult and costly.

One of the more promising ways to reduce the con- sumption of carbon disulphide in the viscose process and to maintain or improve good economy are to use highly re- active cellulose obtained by irradiation with ionizing particles of high energy. It is wellknown'that the higher the reactivity of the cellulose, the lower amount of car- bon disulphide is required. For example the patent publi- cation DE-A-2 941 624 describes a method of producing vis- cose from the pulp irradiated with electron beams. In the patent it is stated that a viscose solution is produced by using a content of 24-28% by weight of carbon disulphide based on the a-cellulose at the xanthation instead of the conventional 30-36% by weight. The a-cellulose content and the sodium hydroxide content were 8% and 5.8% respectively based on the weight of the viscose solution. The Russian patent 1 669 916 also describes a method of producing vis- cose from irradiated a-cellulose. In the process the xan- thation is performed by using 10-15% by weight of carbon disulphide. The viscose produced contained 8.4% by weight

of a-cellulose and 6.4% by weight of sodium hydroxide.

The properties of the viscose solutions prepared from irradiated a-cellulose with low amounts of carbon di- sulphide differ significantly from the properties of con- ventional viscose solutions. Thus, viscose solution of the Russian patent has - a low degree of etherification (cos2 is from 22 to 25 instead of from 45-50), - a low amount of by-products (1.5-2.5% by weight instead of from 10-14% by weight), - a low maturity index (9-12 ml measured by 1 N NH4Cl instead of 18-21 ml), - a high viscosity (120-135 sec by a falling ball instead of 50-60 sec).

However, regenerated cellulose fibers produced from viscose solutions obtained from irradiated a-cellu- lose exhibit unsatisfactory tensile strength. Thus, the journal "Chemical Fibers International" 1996 reports that it is possible to produce viscose fibers with tensile strength of 190-200 m N/tex and 18-20% elongation from irradiated a-cellulose with low amounts of carbon di- sulphide. Better results are not possible to achieve due to the properties of the viscose solution itself.

The objectives of the present invention are to provide an improved process for the production of viscose solution in relationship to the traditional viscose method from environmental point of view and to produce a viscose solution with suitable properties for the production of regenerated fibers. For example the spinnability of the viscose solution and the strength of the fibers are to be improved.

It has now been found that the above objectives can be achieved by producing a viscose solution by using irradiated a-cellulose and low amounts of carbon disul-

phide combined with the addition of certain surfactants.

In more detail the present invention relates to a method of producing a viscose solution by a) irradiating an a-cellulose with ionizing particles, b) mercerizing the irradiated a-cellulose with alkali, c) xanthating the irradiated mercerized a-cellulose with an amount less than 28% of carbon disulphide based on the weight of a-cellulose, and d) dissolving the xanthated a-cellulose in an aqueous alkali solution, characterized in that a surfactant chosen from the group consisting of a water-soluble nonionic and/or cationic surfactant is added to the process in an amount of 0.02-5% by weight of the amount of a-cellulose. The method results in a viscose solution having improved quality in compari- son with the corresponding viscose solutions produced without the use of the surfactants. The improvments com- prise higher purity, lower viscosity and better filter- ability and thereby better spinnability. Regenerated cellulose fibers produced from the viscose solutions ob- tained by the method according to the invention exhibits essentially higher tensile strength than the prior known viscose solutions obtained when using low amounts of carbon disulphide.

When using non-irradiated cellulose and 30-36% of carbon disulphide based on a-cellulose, surfactants are widely used in order to improve the properties of viscose solution and viscose fibers. It is established that the effect of the surfactants on the fiber quality is exhi- bited at relatively high content of by-products. Usually, in such a viscose solution the amount of by-products is in the range of 10-14% of the amount of a-cellulose.

Surprisingly it has now been found that even in a viscose solution with so low amount of by-products as in the range of from 1.5 to 2.5% by weight of the a-cellulose an essential improvment can be obtained by adding certain surfactants during the process. The surfactants may be added at any stage in the viscose process. An addition fdr example by spraying an aqueous solution of the surfactant on the a-cellulose after the irradiation but before the mercerization is preferred, although it is also possible to add the surfactant during the mercerization step or during the dissolving step or to the cellulose before the irradiation.

The nonionic and cationic surfactants suitable for use in the method normally contain a hydrocarbon group having 6-24, preferably 6-14 carbon atoms. Suitable examples of nonionic surfactants are ethoxylates, derived from alcohols, phenols and diols. Suitably the cationic surfactants are ethoxylated and contains at least one tertiary ammonium group. Examples are ethoxylated mono- or dialiphatic amines as well as ethoxylates of aliphatic polyamines and ethoxylates of acyl-substituted polyamine compounds.

In addition to these surfactants it is also possible to add certain solubilising agents, such as di- ethylene glycol and polyethylene glycols.

The viscose solution of the present invention, when used in the production of generated cellulose fibers, also contribute to a better fiber quality, such as an in- creased tensile strength. A suitable aqueous viscose solu- tion to be used in formation of regenerated fibers con- tains 8-10% by weight of a-cellulose, 5-6% by weight of alkali, 8-28, preferably 10-25% by weight of carbon di- sulphide based on the a-cellulose content and 0.02-5% by weight of a surfactant chosen from the group consisting of

a water-soluble nonionic and/or cationic surfactant based on the weight of a-cellulose and has a filterability above 175 ccm/l0 min, preferably above 200 ccm/10 min defined by the volume of the viscose solution filtered through a metal net filter according to N0071, USSR State Standard 3584-53, with 71 um meshes and a diameter of 38 mm under a pressure of 300 mm of the viscose solution for 10 minutes.

The wire diameter in the net is 0.055 mm, the number of wires is 800 per dm, the number of meshes is 6400 per cm2 and the size of mesh is 0.071 mm.

The invention is further illustrated by the following examples.

Comparison example a-cellulose was irradiated by accelerated elec- trons in a dose of 10 kGrey. The irradiated a-cellulose having a DP of 440 was treated with a 16% by weight aqueous solution of sodium hydroxide at 19"C during 70 minutes. The alkaline a-cellulose obtained was pressed up to 2.85 fold weight and then shredded during 120 minutes at the temperature of 10"C and loaded into the xanthator.

Into the xanthator 15-16% of CS2 based on the a- cellulose weight in the alkaline cellulose were intro- duced. The xanthation took place for 150 minutes at a temperature from 15 to 200C. Thereafter the xanthate was dissolved in a dissolver with propeller-type mixer (350 rpm) for 3 hours at 10°C during the addition of an aqueous alkaline solution.

The viscose solution obtained contained 9.0% by weight a-cellulose and 5.6% by weight of sodium hydroxide and 15% of carbon disulphide based on the weight of a- cellulose and exhibited the following properties.

Viscosity (falling ball, sec) 135 Maturity (1N NH4Cl, ml) 9.1 Undissolved particles (pieces) 1.1 Filterability, cm3 per 10 min. 114 Spinnability 320 The amounts of undissolved particles were defined under a microscope (x 200) at 10 visual fields and an average value was calculated. Particles larger than 15 microns were registered. The filterability was defined by the amounts of cm3 of viscose filtered through a metal filter (a net according to N0071 USSR State Standard 3584- 53, with 71 um meshes and a diameter of 38 mm) for 10 minutes. The viscose column above the filter was maintain- ed 300 mm high. The viscose spinnability was defined by the method of maximal stretching directly after the spinneret.

Example 1 Example 1 was carried out similarly to Comparison example, except that during the mercerizing of the irradi- ated a-cellulose a surfactant in accordance with the table 1 was added in an amount of about 2 kg per tonne of a- cellulose into the mercerizing alkali.

Example 2 Example 2 was carried out similarily to Comparison example except that during dissolving of a xanthate a surfactant in accordance with table 1 was added in an amount of about 2 kg per 1 tonne of a-cellulose to the aqueous alkali solution used for the dissolving.

Examples 3-7 Examples 3-7 were carried out similarily to Com- parison example except that during mercerizing a surfac- tant according to table 1 was added to the mercerizing alkali at an amount of 2 kg per 1 tonne of irradiated cellulose and another 2 kg of the surfactant per tonne

irradiated a-cellulose to the dissolving aqueous alkali solution.

Example 8 Example 8 was carried out similarily to control example except that a surfactant according to table 1 was applied onto the irradiated a-cellulose prior to merceri- zation in an amount of 1 kg per 1 tonne of cellulose by spraying a water solution with a weight ratio between the surfactant and the water of 1 to 10.

Example 9-13 Example 9-13 were carried out similarily to Ex- ample 4 except that a surfactant in accordance with table 1 was applied in an amount of 2 kg per 1 tonne of a-cellu- lose.

Example 14 Example 14 was carried out similarily to Example 4 except that a surfactant according to table 1 was applied in an amount of 4 kg per 1 tonne of a-cellulose.

Example 15 Example 15 was carried out similarily to Example 5 except that a surfactant according to table 1 was applied by spraying a water solution with a weight ratio between the surfactant and the water of 1 to 600.

Surfactants and test results The following surfactants were used in the Examples.

Designation Surfactant A Cocos fatty amine + 11 EO B 90% phenol + 15 EO and 10% polyethylene glycol (2 000) C Ethoxylated condensate of tall fatty acid and polyamine D D C12-14-alkyl ether diol + 20 EO E 90% of A and 10% dioctylamine + 10 EO The viscose solution manufactured in Examples 1-15 were tested with regard to viscosity, maturity, filter- ability, undissolved particles and spinnability in the same manner as in the Comparison example. The following results were obtained.

Table 1 Examples Surfactant Place of Spray fac- Visc. Maturity Filter- Particles Spinn- addition tor, kg (s) (ml) ability (pieces) ability Type kg/ton α- surfactant (ccm/10 (%) cellulose /kg water min) Comparison - - - - 135 9.1 114 1.1 320 1 E 2 Merc. - 101 10.0 190 0.5 385 2 E 2 Diss. - 100 8.7 180 0.6 370 3 A 2 Merc. - 100 8.5 180 0.7 360 2 Diss. 4 B 2 Merc. - 102 9.3 185 0.7 370 2 Diss. 5 C 2 Merc. - 100 9.7 180 0.6 370 2 Diss. 6 D 2 Merc. - 108 9.5 200 0.4 385 2 Diss. 7 E 2 Merc. - 101 10.1 195 0.5 385 2 Diss. 8 E 1 Spray 1:10 101 10.7 205 0.4 390

9 A 2 Spray 1:10 101 9.7 210 0.5 380 10 B 2 Spray 1:10 98 10.3 215 0.4 385 11 C 2 Spray 1:10 100 9.8 200 0.4 380 12 D 2 Spray 1:10 105 10.0 220 0.3 400 13 E 2 Spray 1:10 100 10.9 230 0.2 410 14 E 4 Spray 1:10 95 11.1 235 0.2 410 15 E 2 Spray 1:600 70 13.4 320 0.1 450

From the results it is evident that the addition of a nonionic or cationic surfactant in the manufacturing process improves the quality and spinnability of the viscose solutions.

Example 16 Some of the viscose solutions manufactured in the Examples and the Comparison example were subjected to a spinning process performed at a spinning rate of 70 m/minut. The following results were obtained.

Table 2 Viscose Linear Tensile Elongation solution density strength at break mM/tex % Control 0.17 200 17.5 Example 3 0.17 240 18.0 Example 4 0.17 220 17.9 Example 5 0.17 230 17.8 Example 7 0.17 252 18.1 From the results it is evident that the improved quality of the viscose solution also results in an improv- ment of the regenerated cellulose fiber properties.