WO1998030740A1

WO1998030740A1 - Process for preparing low-fibrillate cellulose fibres

Info

Publication number: WO1998030740A1
Application number: PCT/EP1997/006972
Authority: WO
Inventors: Sven Jörgen RUSTICUS
Original assignee: Akzo Nobel N.V.
Priority date: 1997-01-09
Filing date: 1997-12-09
Publication date: 1998-07-16
Also published as: NL1004957C2

Abstract

The invention pertains to a process for preparing low-fibrillate cellulose fibres from a solution containing cellulose and/or cellulose derivatives in which the solution is spun using a centrifugal spinning machine and the formed fibres are dried under low tension. The obtained fibres have favourable properties, in particular as regards their use in textiles.

Description

PROCESS FOR PREPARING LOW-FIBRILLATE CELLULOSE FIBRES

The invention pertains to a process for preparing low-fibrillate cellulose fibres from a solution containing cellulose and/or cellulose derivatives.

Such a process is known from various patent publications for making Lyocell fibres, e.g., WO 95/30043, WO 96/0777, WO 96/0779, and EP 691426. In the so-called Lyocell process cellulose is dissolved in an organic solvent (e.g., N-methylmorpholine N-oxide) and then spun in an air gap-wet spinning process and coagulated in a suitable coagulant. Unless additional steps are taken, these fibres exhibit a high degree of fibrillation, particularly when they are subjected to mechanical stress in the wet state. The aforesaid patent publications make mention of a number of steps to counter this fibrillation, such as feeding additives to the coagulant, using specific gases in the air gap, or aftertreating the obtained fibres with certain chemicals, e.g., with a cross-linking agent. The main drawback to such processes is that they require one or more additional steps to be incorporated into the production process as a whole to treat the fibres and/or recover the additionally supplied chemicals, this with a view to conducting the production process in an environmentally safe manner.

Such a process is also known for making cellulose fibres from a solution containing cellulose-derivatives. Accordingly, cellulose fibres prepared via the viscose process exhibit little if any fibrillation when they are subjected to mechanical stress in the wet state. The viscose process includes a number of consecutive steps, e.g., for preparing the spinning solution, and is not particularly environmentally safe without additional measures being taken. WO 95/20629 discloses a process for making cellulose fibres with low fibrillation by spinning a solution of cellulose formate. In this process a number of different chemicals are employed to make the solution and as coagulant, which is disadvantageous in an economic and environmentally safe production process. The fibres are obtained by reducing the extruded solution to a gel phase, followed by coagulation of the extrudates.

The invention relates to a simple process for preparing low-fibrillate cellulose fibres in which there is no need to add or make use of additional chemicals before, during or after the spinning process, by spinning a solution containing cellulose and/or cellulose derivatives using a centrifugal spinning machine, in which process the cellulose fibres formed are dried under low tension.

In this patent application the term "cellulose fibres" refers to continuous filaments as well as short-length fibres (shorter than 100 mm, i.e. staple fibres) and fibres of greater length (> 100 mm). The fibres can be bundled up into yarns, slivers or strands, or be processed to make fabrics or non- wovens.

The term "fibrillation" in this patent application refers to fibrils breaking off, tearing away or tearing loose in the longitudinal direction of the fibre due to mechanical stress. Such fibrillation will give the fibres a hairy or felted appearance.

The term "centrifugal spinning machine" in this application refers to an apparatus which contains a centrifuge encased in a jacket, with one or more spinning orifices distributed more or less evenly over the outer circumference of the centrifuge. Rotation of the centrifuge causes the solution, which is fed to the centrifuge (under pressure) via a feed line, to be extruded through the spinning orifices in the direction of a jacket. Depending on the rotational speed of the centrifuge the solution is drawn after being extruded. On coming into contact with a liquid flowing along the jacket the (drawn) solution coagulates and cellulose fibres are formed. The degree of drawing can be set, int. al., through the diameter of the spinning orifices, the rotational speed of the centrifuge, and the distance between the outer circumference of the centrifuge and the inside of the jacket. In order to obtain proper filament drawing the inner radius of the jacket preferably is at least 10% wider than the radius of the outer circumference of the centrifuge, more particularly, it is at least 25% wider, most particularly, at least 35% wider. The maximum degree of drawing is dependent, int. al., on the cellulose DP and the concentration of cellulose or cellulose derivative in the solution. Exceeding the maximum allowable degree of drawing will lead to filamentation in the space between the centrifuge and the coagulating liquid.

Proper centrifuge action does not require rotation to be restricted to the centrifuge. Alternatively, the jacket along which the coagulating liquid moves may rotate, either in the same direction as the centrifuge or in the one opposite to it.

In a favourable process the axis of rotation of the centrifuge is positioned more or less vertically and the coagulating liquid flows downward along the jacket, in which case the formed fibres/filaments will flow out of the jacket together with the coagulating liquid and can be collected and combined into slivers. The number of fibres and the fibre length play an important part in the formation of such slivers. When the sliver has sufficient cohesion, it can be spun and subjected to further treatment, e.g., neutralising, washing, drying, finishing, cutting and/or crimping in a continuous process. In the process according to the invention preferably use is made of a centrifugal spinning machine such as described in International patent application WO 96/27700.

The diameter of the spinning orifices plays an important part in this centrifugal spinning process according to the invention. As this diameter increases, the risk of clogging as a result of impurities or undissolved particles in the solution will be reduced. Preferably, the spinning orifices used have a diameter of more than 100 μm, more particularly, a diameter in the range of 120 to 500 μm. Employing spinning orifices with a large diameter also has the advantage that the pressure in the spinning machine will not become too high.

A major advantage of centrifugal spinning processes over other known spinning processes, e.g., spinning processes for making staple fibres or continuous filament yarn, is that they make it possible to process a large quantity of spinning solution per unit of time. Furthermore, the extruded spinning solution can be drawn further, without any major deterioration of the final mechanical properties of the obtained fibres, than is possible with the aforesaid known spinning processes.

It was found that if a too high spinning solution viscosity is selected, there may be breakdowns during the spinning process which will give rise to multiple filamentation during drawing and/or coagulation or which may lead to major differences in, say, the formed fibres' cross-sections. Fluctuations may occur in the longitudinal as well as the transverse direction of the fibres. Major differences in the formed fibres' cross-sections are less desirable in view of the fibres' use in textiles. The viscosity of the solution can be affected in ways known to the skilled person, e.g., by altering the cellulose concentration in the solution.

A too low viscosity of the spinning solution likewise is less desirable, since in that case it will be impossible to make cellulose fibres.

In the process according to the invention use is made of solutions which contain cellulose and/or cellulose derivatives. Use may be made of solutions where cellulose is dissolved in an organic solvent, a mixture of organic solvents, an inorganic solvent, a mixture of inorganic solvents, or a mixture of organic and inorganic solvents.

Also, use may be made of solutions of cellulose derivatives where a cellulose derivative or a mixture of cellulose derivatives is dissolved in an organic solvent, a mixture of organic solvents, an inorganic solvent, a mixture of inorganic solvents, or a mixture of organic and inorganic solvents.

It is possible to employ optically isotropic and optically anisotropic solutions in the process according to the invention. If so desired, substances which will facilitate the dissolution of cellulose and/or cellulose derivatives or improve the processability of the solution may be added to the solvent or to the solution, or adjuvants (additives), e.g., to counter the degradation of cellulose and/or cellulose derivatives as much as possible, or dyes and the like.

Examples of suitable solutions are, for instance: • a solution of cellulose in

- a tertiary amine oxide, e.g., a solution of cellulose in N-methyl- morpholine N-oxide, such as described in US 4,246,221 , - a mixture of phosphoric acid and/or its anhydrides and water, such as described in WO 96/06208 (anisotropic solution) or non-prepublished patent application NL 1002236 in the name of Applicant (isotropic solution), - a mixture of phosphoric acid or polyphosphoric acid, sulphuric acid, and water, such as described in Japanese patent application JP 4258648,

- a mixture containing dimethyl acetamide and lithium chloride,

- a mixture containing copper sulphate and ammonium hydroxide, - a mixture containing trifluoroacetic acid and dichloromethane,

- a mixture containing ammonium hydroxide and ammonium thiocyanate,

• a solution of cellulose acetate in - trifluoroacetic acid or a mixture containing trifluoroacetic acid,

- acetone or a mixture containing acetone,

- phosphoric acid or a mixture containing phosphoric acid,

• a solution of cellulose carbamate in caustic soda

• a solution of cellulose formate in

- phosphoric acid or a mixture containing phosphoric acid, e.g., a mixture of phosphoric acid and formic acid,

- dimethyl sulphoxide or a mixture containing dimethyl sulphoxide, e.g., a mixture of dimethyl sulphoxide and water, a mixture of dimethyl sulphoxide and ethylene glycol, or a mixture of dimethyl sulphoxide, ethylene glycol, and water,

- N-methyl-2-pyrrolidone or a mixture containing N-methyl-2- pyrrolidone, e.g., a mixture of N-methyl-2-pyrrolidone and water. However, it is also possible to employ other solutions containing cellulose and/or cellulose derivatives in the process according to the invention.

If use is made of a solution containing cellulose derivatives, the fibres obtained by spinning the solution using a centrifugal spinning machine need to be regenerated in a separate step to obtain low-fibrillate cellulose fibres. Regeneration can take place, e.g., by means of saponification, say with a caustic solution, or by means of a high-temperature steam treatment.

For the coagulation of the spinning solution use may be made of all known coagulants for solutions containing cellulose and/or cellulose derivatives. For instance, it is possible to use an organic solvent (e.g., acetone, methanol or ethanol), a mixture of organic solvents, an inorganic solvent, a mixture of inorganic solvents, a mixture of organic and inorganic solvents, or a mixture of organic and/or inorganic solvents with water as coagulant. It is advantageous to employ water as coagulant, notably when cations have been added to the water, more particularly when monovalent cations, such as Na⁺, K⁺, or NH₄ ⁺, have been added to the water.

It was found that when a solution containing cellulose and/or cellulose derivatives is spun using a centrifugal spinning machine, low-fibrillate cellulose fibres are obtained if the fibres are dried under low tension. By "low tension" is meant in this context, a tension lower than 2 cN/tex (starting from the linear density of the dried fibres). Preferably, the fibres are dried under a tension lower than 1 cN/tex, more particularly under the lowest possible tension. In an especially advantageous process the fibres are dried tension-free. It was found that if the fibres are dried under the lowest possible tension or tension-free, they will shrink 5 - 20% during drying.

Many ways of drying fibres under low tension or tension-free are known. For instance, the fibres can be dried on a porous belt, e.g., with the aid of heated air. Alternatively, the fibres can be dried on a shrink-sleeve.

To obtain low-fibrillate fibres it was also found to be advantageous to subject the fibres in the wet state as little as possible to mechanical stress, more particularly mechanical stress in the longitudinal direction of the fibres, prior to the final drying step in the process.

In the process according to the invention cellulose fibres are obtained which exhibit low fibrillation, in particular when they are subjected to mechanical stress in the wet state. The degree of fibrillation can be measured using the so-called fibrillation test ("Schϋtteltest"), in which high- fibrillate fibres are awarded "6" as an evaluation mark, while the mark given to low- to non-fibrillate fibres is "0" or "1". The evaluation mark of the fibres obtained according to the process of the present invention in the fibrillation test is < 3, more particularly < 2, especially < 1.

Furthermore, it was found that the fibres obtained according to the process of the present invention exhibit a particular combination of properties, which can be characterised as follows: Filament linear density (filament tex) < 10 dtex, Crystalline orientation angle > 20°, and Elongation at break < 30%.

Generally speaking, it appears that in the known spinning processes for manufacturing cellulose fibres a low-molecular orientation (i.e., a high crystalline orientation angle) is achievable only if the fibres are drawn to a low degree. Due to this low degree of drawing, such fibres possess a high filament tex and a high elongation at break.

The low-fibrillate fibres according to the invention preferably have the following combination of properties, rendering them particularly suitable for use in textiles:

- Filament tex: from 0.5 to 5 dtex, preferably 0.5 to 3 dtex,

- Crystalline orientation angle: > 20°, preferably > 30°, more preferably > 40° - Elongation at break: < 30%, preferably in the range of 5 to 20%.

A low filament tex of the fibres is of importance as regards the final properties of the fibres in a fabric, such as gloss and feel. A low molecular orientation (i.e., a high crystalline orientation angle) appears to be of importance as regards the fibrillation properties of the fibres. The elongation at break is of importance as regards the processing of the fibres with a view to their use in textiles.

The thus obtained fibres can be subjected to further treatment with a view to use in textiles, e.g., by cutting the formed sliver up into short-length fibres (staple fibres). Using techniques for textiles known to the skilled person (int. al., carding, annular spinning) these staple fibres can be rendered suitable for use in textiles.

It is because of their low fibrillation among others that these fibres are particularly suited to be used in textiles. Other properties likewise render them highly suitable for such use. For instance, these fibres have better dye uptake than do cotton or cellulose fibres obtained by means of the viscose process. The dye uptake of the fibres can be determined in a standardised dye uptake test using a blue dye (Solophenyl-Bleu). In this test the low-fibrillate fibres according to the present invention display a bath depletion in the range of 70 to 100%. For known cellulose products this test gives a bath depletion of less than 60%.

Fabrics made using these fibres have a particularly fine gloss and a good feel.

Measuring methods

Dye uptake

The dye uptake of the fibres is measured after drying in vacuo at 50°C for 10-16 hours. 1 gram of the fibres is then introduced into 200 ml of water having a temperature of 85°C to which 1 wt.% of Solophenyl Bleu GL 250% and 2 g of Glauber salt (Na₂SO₄»10H₂O) have been added. During measuring (45 minutes) the temperature of the water is kept at 85°C.

Prior to the addition of the fibres and after measuring has finished the absorption of the solution at 490 nm is determined spectrophotometrically.

The bath depletion (in % abs.) is then calculated as the difference in absorption prior to the addition of the fibres and after measuring has finished. A bath depletion of 100% thus means that all dye has been absorbed by the fibres

Mechanical properties

The mechanical properties of the fibres were determined in accordance with ASTM standard D2256-90, using the following settings.

The fibres were clamped with Arnitel^® gripping surfaces of 10x10 mm. The filaments were conditioned for 24 hours at 21 °C and 65% relative humidity.

The length between grips was 20 mm, and the filaments were elongated at a constant elongation of 20 mm/min. The linear density or filament tex, expressed in dtex, was calculated on the basis of the functional resonant frequency (ASTM D 1577-66, Part 25, 1968).

The breaking tenacity and the elongation at break were derived from the load-elongation curve and the measured filament linear density.

Every measured value given was the average of 20 separate measurements.

Orientation angle X-ray diffraction patterns of the cellulose fibres were collected using a (flat plate) Statton camera with monochromated Cu-K radiation. The generator settings were 35 kV and 30 mA. The distance between the sample and the film was 3,34 cm. The camera was evacuated to prevent air scattering. The exposure time was 24 hours. The samples were prepared in a wet state and dried before the measurement.

Azimuthal scans of the 1-1 0 reflections (2Θ = 12,2°, d = 7,48 A) were recorded with a Joyce-Loebl densitometer Mark III. Settings: objective 10x; slitwidth 1 ,8 mm; slitheight 6,2 mm; stepsize; wedge A: 0,024 D/cm; B: 0,55 D/cm; d: 0,09 D/cm; forward speed 8 units; pen damping 10x. The resulting scan was fitted using a split Pearson VII fit. The Full Width Half Maximum of this fit is the orientation angle (OA).

Fibrillation

The fibrillation of the cellulose fibres can be measured with the aid of a so- called "Schϋtteltest." In this test 7 mg of fibrous material is introduced into a 20 ml beaker. 10 ml of water is added to the fibrous material, and the whole is stored in a quiet place for 30 minutes at room temperature. Next, the beaker and its contents are shaken vigorously for 2 hours. After this, the fibrillation is evaluated visually using a microscope, with highly fibrillated fibres being marked 6 and fibres with no or very little fibrillation being marked 0 or 1. Depending on the degree of fibrillation the fibrous material in the test is awarded an evaluation mark from 0 through 6.

Examples

The invention will be elucidated in greater detail with reference to a number of examples. Needless to say, the invention is not restricted to said examples.

Example 1

A slurry containing about 4 wt.% of Cellulose (80 wt.% of Viskokraft ELV, DP=650, and 20 wt.% of Viskokraft VHV, DP=1650) and 96 wt.% of an aqueous N-methylmorpholine N-oxide (NMMO) solution having a water content of about 20 wt.% was fed continuously to a twin-screw extruder equipped with a device for extracting water from the slurry.

In this way, by extracting a portion of the water, a solution was obtained which contained 4 wt.% of cellulose, 16 wt.% of water, and about 80 wt.% of NMMO. The solution further contained < 0.2 wt.% of stabiliser (propyl gallate). This solution was spun using a centrifugal spinning machine such as described in international patent application WO 96/27700 in the name of Applicant, the centrifuge with an outer diameter of 30 cm being provided with 12 spinning orifices each having a diameter of 250 μm. At different temperatures, a mass flow rate of 5.9 kg of solution per hour, and a variable rotational speed of the centrifuge the solution was extruded through the spinning orifices. The formed fibres were coagulated using water of 15°C flowing downward along a jacket. The inner diameter of the jacket was also varied during the experiments. The sliver thus formed was collected, washed under low tension, and after being finished with Leomin was dried tension-free for 10-16 hours at 50°C under vacuum. Table 1 lists some of the properties of the fibres thus obtained.

Table 1

^■"Votor ^jacket ' spin Linear density BT EaB Gfibr

(tpm) (mm) (°C) (dtex) (mN/tex) (%)

1500 500 100 1.8 ± 12% 170 ± 24% 13.1 ± 22% 1

2000 500 100 1.6 ± 8 % 110 ± 26% 10.9 ± 39% 2

3000 500 100 1.0 ± 9 % 200 ± 29% 10.4 ± 22% 1-2

4000 500 100 0.8 ± 19% 140 ± 34% 7.5 ± 25% 2

1500 500 80 1.2 ± 16% 130 ± 29% 7.9 ± 28% 2

1500 500 120 1.2 ± 13% 130 ± 32% 13.4 ± 34% 1-2

1500 600 100 1.6 ± 15% 160 ± 34% 17.6 ± 26% 1-2

2000 600 100 1.1 ± 19% 210 ± 28% 11.4 ± 19% 1-2

3000 600 100 0.8 ± 23% 150 ± 26% 14.3 ± 55% 1

in which R_rot0r ⁼ rotational speed of the centrifuge, D_jacket = inner diameter of the jacket, T_spin = spinning temperature, BT = breaking tenacity, EaB = elongation at break, G_fibr = fibrillation evaluation mark.

The first and the third sample from the above table had an orientation angle of 43° and 36°, respectively.

Example 2

The solution obtained according to the process described in Example 1 was spun using a similar centrifugal spinning machine.

However, the centrifuge with an outer diameter of 30 cm was provided with

12 spinning orifices each having a diameter of 150 μm. At a spinning temperature of 100 °C and a rotational speed of the centrifuge of 2000 rpm several mass quantities of the solution were spun per unit of time. The formed fibres were coagulated with the aid of water of 15°C flowing downward along a jacket (inner diameter 500 mm). The resulting sliver was collected, washed under low tension, and after being finished with Leomin dried tension-free for 10-16 hours at 50°C under vacuum.

Table 2 lists some of the properties of the fibres thus obtained.

Table 2

in which D_S0| = throughput of the spinning solution, BT = breaking tenacity, EaB = elongation at break, G_fibr = fibrillation evaluation mark

Example 3

In the manner described in Example 1 a spinning solution containing 8 wt.% of cellulose was prepared. This solution was spun, in the manner described in Example 1 , using a centrifugal spinning machine, with the temperature of the coagulating liquid being varied.

Table 3 lists some of the properties of the fibres thus obtained.

Table 3

■Votor '-'jacket ' spin ' coag Linear density BT EaB Gf. r

(rpm) (mm) (°C) (°C) (dtex) (mN/tex) (%)

3000 400 100 15 4.1 ± 26% 180 ± 33% 12.4 ± 51%

3000 400 120 15 + + ±

1500 500 120 35 4.1 ± 16 139 + 21 24.2 ± 25 1

1500 500 120 40 3.6 ± 19 147 + 14 9.5 ± 31 2

2000 500 100 15 + + + 3

3000 500 100 15 2.3 ± 14% 280 + 20% 10.7 ± 18% 3

3000 500 120 40 2.0 ± 17 139 + 29 7.6 ± 25 2

4000^* 500 100 15 1.0 ± 28% 270 + 19% 11.7 ± 41 %

2000 600 100 15 ± + +

3000 600 100 15 1.4 ± 18% 290 + 17% 15.7 ± 30% in which R^r¹ rotational speed of the centrifuge, D_jacket= inner diameter of the jacket, T_spin = spinning temperature, τ_coag = temperature of the coagulation liquid, BT = breaking tenacity, EaB = elongation at break, G_fibr = fibrillation evaluation mark ^*): Spinning orifice diameter 150 μm.

The third sample from the above table had an orientation angle of 42°.

Example 4

Various solutions obtained according to the process described in Example 1 were spun using a similar centrifugal spinning machine.

However, the centrifuge having an outer diameter of 30 cm was provided with 12 spinning orifices each having a diameter of 400 μm. At a spinning temperature of 120°C and a rotational speed of the centrifuge of 3000 rpm solutions containing 8, 10, and 12 wt.% of cellulose were spun. The resulting fibres were coagulated with the aid of water of 15°C flowing downward along a jacket (inner diameter 500 mm).

The resulting sliver was collected, washed under low tension, and after being finished with Leomin dried tension-free for 10-16 hours at 50°C under vacuum. Table 4 lists some of the properties of the fibres thus obtained.

Table 4

in which C_ce, = cellulose concentration in the solution, BT = breaking tenacity, EaB = elongation at break, G_fibr = fibrillation evaluation mark

The dye uptake of several samples obtained according to the examples above was measured. Table 5 lists the values measured for the bath depletion of these fibres and compares them with known cellulose fibres for use in textiles.

Table 5

Cellulose concentration in Bath spinning solution depletion (%)

4 84

8 100

10 84

Viscose staple fibre 51

Lyocell staple fibre 55

Cotton 44

Example 5

An anisotropic cellulose solution was prepared by dissolving 2688 g of powdered cellulose (Buckeye V65, DP=700) in a solvent, which solvent was obtained by mixing 19 360 g of H₃PO₄ and 4840 g of PPA. The cellulose and the solvent were kneaded for 65 minutes and mixed at 16°C until a homogeneous anisotropic solution was obtained. During the last 45 minutes the kneader was degassed.

This solution was spun using a centrifugal spinning machine such as described in international patent application WO 96/27700 in the name of Applicant, the centrifuge with an outer diameter of 30 cm being provided with 24 spinning orifices each having a diameter of 250 μm. At a temperature of about 45°C, a mass flow rate of 12 kg of solution per hour, and a rotational speed of the centrifuge of 3500 rpm the solution was extruded through the spinning orifices. The fibres formed were coagulated with the aid of water of 15°C flowing downwards along a jacket. The jacket had an inner diameter of 50 cm.

The resulting sliver was collected and washed with a 2% sodium bicarbonate solution until pH=7 was achieved. Next, after being finished with RT32A, the sliver was dried for 10-16 hours at 25°C at the lowest possible tension.

The fibres in the sliver had an average linear density of 3.3 dtex (± 40%), a breaking tenacity of 77 mN/tex, an elongation at break of 10%, an orientation angle of 51°, and a fibrillation evaluation mark = 1.

Example 6

A solution was prepared by dissolving 2800 g of powdered cellulose (Buckeye V60, DP=820) in a solvent, which solvent was obtained by mixing 19 500 g of H₃PO₄ and 5800 g of formic acid. The cellulose and the solvent were kneaded for 180 minutes and mixed at 20°C until a homogeneous solution was obtained. During the last 120 minutes the kneader was degassed.

This solution was spun using a centrifugal spinning machine such as described in international patent application WO 96/27700 in the name of Applicant, the centrifuge with an outer diameter of 30 cm being provided with 24 spinning orifices each having a diameter of 250 μm. At a temperature of about 60°C, a mass flow rate of 12 kg of solution per hour, and a rotational speed of the centrifuge of 3000 rpm the solution was extruded through the spinning orifices. The fibres formed were coagulated with the aid of water of 15°C flowing downwards along a jacket. The jacket had an inner diameter of 50 cm.

The resulting sliver was collected, washed, regenerated with a 0,5% sodium hydroxide solution, and washed again until pH=7 was achieved. Next, after being finished with RT32A, the sliver was dried for 10-16 hours at 25°C at the lowest possible tension.

The fibres in the sliver had an average linear density of 4 dtex (± 50%), a breaking tenacity of 100 mN/tex, an elongation at break of 8%, and a fibrillation evaluation mark = 2-3.

Comparative example 1

A solution containing 4 wt.% of cellulose obtained according to the process described in Example 1 was spun in a conventional air gap-wet spinning process using a spinneret with capillaries of 250 μm in diameter, drawn in an air gap of 45 mm, and coagulated in water. The filaments in the resulting filament yarn had a linear density of 1.3 dtex (± 19%), a breaking tenacity of 270 mN/tex (± 7%), an elongation at break of 9.5% (± 9%), an initial modulus of 10.6 N/tex (± 4%), and a fibrillation evaluation mark= 5-6.

Comparative example 2

Various solutions obtained according to the process described in Example

1 , having cellulose concentrations of 8 and 10%, were spun using a centrifugal spinning machine in the manner disclosed in Example 1 , with the formed sliver being finished with Leomin, wound onto a tube, and dried on said tube.

The fibrillation evaluation mark for the thus obtained fibres was in the range of 4 to 6.

Claims

1. A process for preparing low-fibrillate cellulose fibres from a solution containing cellulose and/or cellulose derivatives, characterised in that the solution is spun using a centrifugal spinning machine and the formed fibres are dried under low tension.

2. A process according to claim 1 , characterised in that the formed fibres are dried under a tension lower than 1 cN/tex.

3. A process according to claim 2, characterised in that the formed fibres are dried under the lowest possible tension.

4. A process according to claim 3, characterised in that the fibres are dried tension-free.

5. A process according to any one of the preceding claims, characterised in that the solution is optically isotropic.

6. A process according to claim 5, characterised in that the solution contains cellulose and a tertiary amine oxide.

7. A process according to claim 6, characterised in that the solution contains cellulose and N-methylmorpholine N-oxide.

8. A process according to any one of claims 1-4, characterised in that the solution is optically anisotropic.

9. A process according to claim 8, characterised in that the solution contains cellulose and/or a cellulose derivative and phosphoric acid.

10. A process according to claim 9, characterised in that the solution contains cellulose, phosphoric acid and/or its anhydrides and water.

11. A cellulose fibre characterised by the following combination of properties:

- filament tex < 10 dtex, - crystalline orientation angle > 20┬░, and

- elongation at break < 30%.

12. A cellulose fibre according to claim 11 , characterised in that the filament tex of the fibre is 0.5 to 5 dtex, preferably 0.5 to 3 dtex.

13. A cellulose fibre according to claim 11 or 12, characterised in that the fibre has a crystalline orientation angle > 30┬░, preferably > 40┬░.

14. A cellulose fibre according to any one of claims 11 - 13, characterised in that the fibre has an elongation at break in the range of 5 to 20%.