EP0853146A2 - Method of producing cellulosic fibres and cellulosic fibres - Google Patents

Abstract

A process is claimed for the production of cellulosic fibres (I) from a solution of cellulose in a tert. amine oxide (TAO) and optionally water, in which the spun solution is coagulated in at least two stages and then washed and dried. In the coagulation process, the residence time of the fibres in the first precipitation stage (PS1) is adjusted so as only to prevent surface stickiness, after which the fibres are kept in an unstretched state in further precipitation stages (PS), leaving the last stage in a fully coagulated state. Also claimed are cellulose fibres obtained from a solution of cellulose as above, in which the parameter F, as given by the expression: F = - 0.8754.P - 3.8532.L(004) + 19.2136.L(110) + 0.05395.L(004).P - 1.6483.L(110)<2> + 4.4283.L(004)/L(110), has a value of less than 4, where P = the porosity of the fibres (%), L(110) = crystallite width (nm) and L(004) = crystallite length (nm).

Description

The invention relates to a method for producing cellulosic Fibers from a solution of cellulose in a tertiary Amine oxide and possibly water, being passed through a spinneret solution formed into fibers coagulated in at least two stages and then the fibers are washed and dried; as well as cellulosic fibers.

A process for making cellulosic fibers from a Solution of cellulose in a tertiary amine oxide and water, which also as Lyocell fibers or solvent-spun Fibers are referred to, for example, in US-A-4,246,221 described. In this so-called Lyocell process, cellulose is produced in an organic solvent, for example N-methylmorpholine-N-oxide (NMMO) solved. The solution, too Water and possibly a stabilizer, such as propyl gallic acid can contain, is through a spinneret into an air gap Fibers or filaments extruded and then in one Precipitation bath coagulates. There is an extractor behind the precipitation bath, like a godet over which the fibers are under tension be performed. With the help of further godets, the fibers transported to the next treatment steps. These are usually the fiber washing, the finishing, the Drying and winding up.

Lyocell fibers have a strong tendency to fibrillate on. In WO95 / 30043, WO96 / 0777, WO96 / 0779 and EP-A-0 691 426 Measures are proposed to reduce the tendency to fibrillation of lyocell fibers. These measures include the addition of additives to the coagulant, the use of special gases in the air gap or the aftertreatment of the Fibers with chemicals such as cross-linking agents. However, these methods have the disadvantage that the additional in chemicals introduced into the process with a view to being environmentally friendly Litigation with special methods again must be recovered, making the process more complex and become more expensive.

WO96 / 20301 also discloses a process for the production cellulosic moldings, such as fibers or filaments, from one Solution of cellulose in a tertiary amine oxide. The according This document produced fibers that are also less Should have a tendency to fibrillation, have a core-shell structure. At the core of the fibers is a high super molecular weight Order with small, finely dispersed pores, and there is a slight super-molecular order in the mantle large heterogeneous cavities. The core-shell structure of the fibers is achieved in that the solution formed into fibers is passed successively through at least two precipitation baths, wherein slower coagulation of the cellulose in the first coagulation bath compared to the last precipitation bath. For example the first precipitation bath is an alcoholic bath, such as hexanol or a Mixture of hexanol / isopropanol used. As a second precipitation bath for example, an aqueous NMMO is used, the the first precipitation bath is arranged directly above the second precipitation bath. This process for the production of core-sheath fibers has the disadvantage that additional chemicals in the process be introduced. In those following the precipitation Baths arrive next to the tertiary amine oxide, which is used to prepare the solution is used, these additional substances ins Wash water.

The Lyocell process is known for its special environmental compatibility known because the used for solution preparation tertiary amine oxide almost completely recovered and again the solution preparation can be supplied. The use of others chemical substances make this recovery difficult is therefore disadvantageous for economic litigation.

The invention is therefore based on the object of a method for the production of Lyocell fibers with reduced tendency to Provide fibrillation by adding additional Chemicals is not required. Furthermore it is Object of the invention to provide lyocell fibers which in addition to reduced fibrillation compared to usual Lyocell fibers have higher staining depth.

This task is accomplished using a cellulosic process Fibers from a solution of cellulose in a tertiary Amine oxide and optionally water dissolved, which by a Spinneret fiber-formed solution in at least two stages is coagulated and the fibers are then washed and dried be, and wherein the coagulation in at least two Stages take place such that the residence time of the fibers in the first precipitation level is set so that when leaving the in the first precipitation step, only the stickiness of the surface the solution formed into fibers is prevented and in others Precipitation stages kept the fibers in a tensionless state and when leaving the last precipitation level the Fibers are coagulated.

In contrast to the method of WO96 / 20301, in which at least two coagulation baths are used, the solubility of the cellulose in amine oxide in different ways to The process involves creating a core-shell structure of the fiber the present invention does not work with precipitation media, which reduce the solubility of cellulose differently. In the context of the present invention is in all precipitation stages with the same or comparable coagulant, worked like aqueous NMMO. According to the invention Process fibers thus also have not the pronounced core-shell structure of WO96 / 20301, in this regard, they have a morphology that is more common Corresponds to Lyocell fibers.

The cellulose solution is passed through a heated spinneret, with a Variety of holes shaped into fibers. The molded solution is then cooled in an air gap and at least around a factor of 1, preferably greater than a factor of 4. According to the invention, the first precipitation stage is carried out in such a way that that in the fiber-shaped solution only the Stickiness of the surface is prevented. The fibers can for this purpose by means of a trigger element arranged behind the first precipitation stage, passed through a precipitation bath like a godet will. The required residence time of the fibers in the first Precipitation level can, for example, over the length or depth of a Precipitation bath and the speed at which the fibers passed through the precipitation bath, i.e. the spinning speed, can be set.

With decreasing dwell time of the fiber bundle in the first Precipitation step, there is an increase in bondage of the fibers, after the individual fibers have been brought together to form the yarn lie side by side. Such an adhesion can be determined in which an approximately 10 to 15 cm long section of the yarn is placed in a bowl filled with water. The Fibers swim apart and bonds can easily be identified. This test is done with five thread sections, that should not be in direct succession, repeated. The number of glue points is a measure of the degree of Fiber bonding. For every spinning speed and for everyone The number of fiber bonds depends on the titer the length or height of the first felling step. For the invention The process is carried out for every spinning speed Length or height of the first precipitation level selected so that maximum fiber bonding occurs.

Because the dwell time in the first precipitation stage is as short as possible should be, the optimization is carried out so that if the length or height for a given spinning speed of the precipitation bath was reached, with a maximum of one bond is reached, checked again in a subsequent test will whether there is a further decrease in the precipitation bath height or length leads to an increase in the number of bonds. So it becomes just for a certain spinning speed Dwell time set in the first precipitation stage at which the criterion of at most one fiber bond is met.

The term "dead state" is within the scope of the present Invention to be understood so that the fibers under the tension they create through their own weight.

In an advantageous embodiment of the method, the fibers, in the context of the present invention under fibers Filaments, so-called continuous fibers, which are also in the form of Hollow fibers can be present, and also shorter fibers, which are usually to be referred to as staple fibers are for the further precipitation stages, i.e. after the first Precipitation stage, placed without tension on a sieve belt.

In the context of the present invention, it has proven to be advantageous proven to perform the coagulation in two stages, taking it but it is crucial that in the first stage only the stickiness of the surface of the fibers is prevented and that the actual coagulation of the fiber in the second Level is without voltage.

The coagulation of the fibers in the further precipitation stages, or in the second precipitation stage does not take place in a separate one Bathroom in which another precipitation medium is used, but is carried out, for example, by the fibers the precipitation bath liquid entrained in the first precipitation stage.

The coagulation of the fibers in the de-energized state To make it slow, it is advantageous if the fibers only carry a little precipitation bath liquid from the first precipitation stage. In an advantageous embodiment of the method the fibers in the further precipitation stages, for example to be treated with water on the sieve belt in addition to already Wash off the precipitation bath liquid.

It is also possible to use the fibers after the first precipitation stage over two godets so that the fibers between the Sagging godets freely, and being coagulated in the second precipitation stage by the from the first precipitation stage coagulants carried by the fibers. in the Difference to fibers that have no slack and are therefore under tension the sagging are located over godets Fibers in a tensionless state in the sense of the present Invention. It is beneficial if the sag is roughly is constant. This can be done by simply regulating the speed of the following godets. For example the second godet may have a lower surface speed exhibit than the first godet.

The distance between the two godets should be large, for example in the order of 2 m to the voltage-free Condition of the fibers upright if possible over a longer period to obtain. It also turned out to be cheap if the fibers dry under a tension of less than 1 cN / tex, preferably kept in a de-energized state will.

As already stated above, the fibers should only be in the first precipitation stage for a very short time. In the method according to the invention, the residence time in the first precipitation stage should only last until the fiber dimension is fixed and a skin has formed which prevents the fibers from sticking to one another. The fibers are therefore preferably passed through the first precipitation stage in a period t _{F of} less than 0.02 s, which can be very advantageously in the form of a funnel precipitation bath, since the height of the precipitation medium can be set quite easily in a funnel precipitation bath, which is the case for the above described optimization of the number of fiber bonds is favorable.

Aqueous NMMO with an NMMO concentration is preferred as the precipitation medium used greater than 10%, in particular greater than 15%. The temperature of the precipitation medium in the first precipitation stage is preferably less than 15 ° C, especially less than 8 ° C.

The inventive method is advantageously carried out so that the size K F = t F · C / T , where c is the cellulose concentration of the solution in kg of cellulose per kg of solution (ie kg / kg), T is the individual titer of the fibers in g / m and t _{F is} the residence time in s in the precipitation bath, less than 12 nm / g, preferably less than 10 sm / g. The individual titer of a fiber is usually given in dtex, where 1 dtex is defined as 1 g / (10,000 m). A fiber with a single titer of 2 dtex thus corresponds to 2 g / (10,000 m) thus 2 10 ^-4 g / m.

A is preferred for the production of the cellulose solution Cellulose used, which is a mixture of cellulose which has a different degree of polymerization (DP) exhibit. The cellulose concentration in the solution should be lower than 15% by weight, preferably less than 12% by weight correspondingly less than 0.15 or 0.12 kg of cellulose per kg of solution.

As already explained above, the tension-free state of the fibers should be present for a longer period after the first precipitation stage. The size K R = t R · C / T , where c is the cellulose concentration of the solution in kg / kg, T is the individual titer of the fibers in g / m and t _{R is} the residence time in s of the fibers in the de-energized state, should therefore be greater than 110 nm / g, preferably greater than 190 nm / g.

The object is also achieved by cellulosic fibers, produced from a solution of cellulose in a tertiary amine oxide and possibly water, the fibers having a parameter F, which is defined as: F = -0.8754P - 3.8532L (004) + 19.2136L (110) + 0.05395L (004) P - 1.6483L (110) 2nd + 4.4283L (004) / L (110) and which is less than 4, and where P is the porosity of the fibers in%, L (110) the crystallite width in nm and L (004) the crystallite length in nm.

The parameter F is preferably less than 3.3.

The fibers preferably have an orientation of the amorphous regions f _{a of} less than 0.46, in particular less than 0.39.

The crystallite width L (110) is preferably less than 3.5 nm, in particular less than 3.2 nm, and the crystallite length L (004) is preferably less than 14 nm, in particular less than 13.5 nm.

The birefringence is preferably less than 0.040, in particular less than 0.035, this on a dry fiber with a diameter of less than 15 microns was determined.

As shown in the examples below, the Fibers according to the invention have only a very low tendency to fibrillate on. The initial module of the fibers according to the invention is less than the usual Lyocell fibers, which is the advantage has that fabric made from the fibers of the invention have a soft grip.

To measure the tendency of the fibers to fibrillate, use the in Figure 1 schematically shown wet scrubber. The Wet scrubbing equipment essentially consists of the elements 1 to 6, which are explained below:

50 fibers 2 are fixed in a PVC block 1. The abrasion is produced by the fibers 2 rotating Glass rod 5 with 6 mm diameter is guided on the a ceramic rod 4 with a 2.5 mm diameter is attached. Of the Glass rod 5 and with it the ceramic rod 4 rotate at 25 revolutions per minute. By dropping water 3, the kept wet by a weight 6 of 3 g of taut fibers. The wet scrub test is carried out for two minutes. With the described apparatus produced defined and reproducible Fibrillation was scored on a scale of 1 to 6 by microscopic evaluation of the scrubbed, about 3 mm long fiber areas assessed.

To assess fibrillation caused by chafing it has proven advantageous to use the terms primary and to introduce secondary fibrillation.

Primary fibrillation means that only on the fiber surface Fibrils are observed.

Secondary fibrillation means that the fibrils are also in deeper layers of the fibers can be observed. The stronger the Secondary fibrillation progresses, the longer and thicker become the fibrils.

• Note 1 keinerlei Fibrillen
• Note 2 schwache Primärfibrillierung
• Note 3 starke Primärfibrillierung
• Note 4 schwache Sekundärfibrillierung
• Note 5 starke Sekundärfibrillierung
• Note 6 die Schädigung der gesamten Faseroberfläche durch Primär- und Sekundärfibrillierung, wie sie an üblichen Lyocell-Fasern beobachtet wird, die nicht speziell behandelt wurden.

A grade scale from 1 to 6 was defined using the terms just described. The means

• Grade 1 no fibrils
• Grade 2 weak primary fibrillation
• Grade 3 strong primary fibrillation
• Grade 4 weak secondary fibrillation
• Grade 5 strong secondary fibrillation
• Grade 6 the damage to the entire fiber surface by primary and secondary fibrillation, as is observed on conventional Lyocell fibers that were not specially treated.

The wet abrasion test was carried out for each of the examples below carried out five times each and an average grade calculated.

The structural data, ie the orientation of the amorphous areas f _a , the orientation of the crystalline areas f _c , crystallite length L (110), crystallite width L (004) and the crystalline orientation angle and birefringence, of the fibers was determined using WAXS Wide Angle X-Ray scattering ) X-ray wide-angle scattering measurements. For this purpose, a diffractometer from STOE & CIE GmbH (45 kV, 40 mA, CU Kα) and a position-sensitive detector from the same company were determined. For this purpose, the examined fibers were wound on frames in parallel, and it was measured in transmission.

The porosity of the fibers is calculated from the water retention capacity WRV of the fibers according to the following equation: P = 1 / [1 + (1 / ((WRV + 1) · ρ Cell )) · (Ρ water / (1 - (WRV + 1) -1 ))] where ρ _{Cell is} the density of cellulose (= 1.5 g / ml) and ρ _{water is} the density of water at 20 ° C (= 0.998 g / ml). The water retention capacity was determined according to the DIN 53814 (2/74) standard.

In the examples, the L value is used as a measure of the depth of staining stated in%. The L value is a measurement value for a reflection. The lower the L value, the higher the dye absorption and thus the staining depth. The determination of the L value was done on a knitted tube made with solophenyl blue dye GL was colored. The L value was determined using a CHROMAMETER CR300 from MINOLTA.

In the following examples and comparative examples Lyocell fibers made in which a solution of cellulose, NMMO, water and gallic acid propyl ester as a stabilizer a spinneret with 50 holes and a hole diameter of 130 µm were spun into fibers. The nozzle temperature was 112 ° C, or 109 ° C in Example 4. The fibers were in one Air gap of 130 mm in length, or 135 mm in Example 4, stretched and blown with air across the fiber bundle. As A funnel precipitation bath was used in the precipitation bath.

example 1

The spinning solution consisted of 9% by weight of a pulp with a Degree of polymerization (DP) of about 650.1% by weight of a pulp with a DP of about 6000, corresponding to a cellulose concentration of 0.1 (kg cellulose / kg solution), 77.8% by weight NMMO, 12.1 % By weight of water and 0.1% by weight of propyl gallic acid. After going through the air gap became the fibers in a funnel precipitation bath coagulates. The liquid level in the precipitation bath was 20 mm, and 25% aqueous NMMO with a Temperature of 5 ° C used.

The fibers emerging from the first precipitation stage were included at a speed of 65 m / min with a godet and led to a second godet. The second godet was at a distance of 2 m from the first godet and was operated at the same surface speed. The fibers were initially attached to the godets that they had a clear passage between them. After Leaving the second godet, there was a washing, finishing and drying the fibers.

The properties of the invention produced according to this example Fibers are summarized in the table below with those of other fibers produced according to the invention and fibers produced according to comparative examples.

Example 2

Cellulosic fibers were carried out as in Example 1 produced. The fibers emerging from the precipitation bath were also directly at a speed of 65 m / min deducted from the precipitation bath with a godet and from there, however placed on a slow-running sieve belt without tension. On this was followed by treatment with water after about 2 min wash out the remaining NMMO. Then the fibers finished and dried and removed from the sieve belt and placed on a Coil wound.

Example 3

The fibers were produced as in Example 1. In In this example, however, the fibers were moving at a rate of 250 m / min directly after the precipitation bath with a Subtracted godet and a second godet at a distance of 2 m led. The speed of the second godet was 3% less than that of the first godet, and the fibers were himself in a tension-free state between the two godets.

Example 4

The spinning solution consisted of 10.5% by weight of a pulp with a DP of about 650, 0.9% by weight of a pulp with a DP of about 6000, corresponding to a cellulose content of 0.114 77.5% by weight of NMMO, 11% by weight of water and 0.1% by weight of propyl gallic acid. After passing through the air gap, the fibers were in a funnel coagulating bath. The liquid level in the precipitation bath was 20 mm, and the precipitation bath liquid was 15% aqueous NMMO used with a temperature of 5 ° C.

The fibers emerging from the precipitation bath were treated with a godet withdrawn and opened at a speed of 100 m / min placed on a sieve belt. There the fibers became dead washed, finished and dried. Then they were from Screen belt removed and wound on a spool.

Example 5 (comparative example)

The spinning solution consisted of 9.6% by weight of a pulp with a DP of about 650, 2.4% by weight of a pulp with a DP of about 1700, corresponding to a cellulose concentration of 0.12, 76.9% by weight of NMMO, 11% by weight of water and 0.1% by weight of propyl gallic acid. After passing through the air gap, the fibers became coagulated in a funnel precipitation bath. The liquid level in the precipitation bath was 38 mm, and as the precipitation bath liquid 5% aqueous NMMO with a temperature of 15 ° C was used.

The fibers emerging from the precipitation bath were treated with a godet withdrawn at a speed of 100 m / min and directly via further godets to a continuous washing section guided. In this example the fibers showed between the galettes no sag, but they were tightened Condition, i.e. under tension, carried over this.

After washing, there was also a continuous finish, Drying and winding up.

Example 6 (comparative example)

The spinning solution consisted of 10.5% by weight of a pulp with a DP of about 650, 0.9% by weight of a pulp with a DP of about 6000, corresponding to a cellulose concentration of 0.114, 77% by weight NMMO, 11.5% by weight water and 0.1% by weight propyl gallic acid. After going through the air gap, the Fibers coagulated in a funnel precipitation bath. The liquid level in the precipitation bath was 40 mm, and was used as the precipitation bath liquid demineralized water with a temperature of 13 ° C is used.

The fibers emerging from the precipitation bath were treated with a godet withdrawn at a speed of 100 m / min and how in Example 5 directly via further godets under tension a continuous washing section. After the wash Avivierung, drying was also carried out continuously and winding up.

The properties and data obtained on the fibers produced according to Examples 1 to 6 are summarized in the following table. example 1 2nd 3rd 4th 5 6 c / (kg / kg) 0.10 0.10 0.10 0.114 0.12 0.114 T / dtex 2.2 2.2 2.2 2.2 2.2 1.6 t _F / s 0.0185 0.0185 0.0048 0.012 0.0228 0.024 K _F / (sm / g) 8.4 8.4 2.2 6.2 12.4 17.1 t _R / s 1.8 > 9 0.5 > 6 0 0 K _R / (sm / g) 818 > 4000 227 > 3000 0 0 Elongation at break /% 12.4 17.2 10.3 10.2 7.6 7.2 Strength / (cN / tex) 23.1 20.4 23.0 21.7 38.4 33.0 Module 0.6% / (cN / tex) 1275 826 1127 779 1654 1454 Birefringence 0.0394 0.0333 0.0351 0.0375 0.0438 0.0453 Crystallinity /% 52.0 53.7 54.7 50.9 52.6 53.4 Orientation crystalline areas f _c 0.943 0.873 0.944 0.920 0.961 0.967 Orientation amorphous areas f _a 0.332 0.162 0.121 0.306 0.466 0.506 Orientation angle 29.5 33.7 32.5 30.9 26.3 25.1 Porosity P /% 55.3 59.4 54.1 57.8 47.1 46.2 L (110) / nm 2.9 3.0 3.1 2.9 3.9 4.1 L (004) / nm 13.4 11.5 13.9 13.3 16.0 15.9 Parameter F 2.3 0.3 3.2 1.8 5.8 6.2 L value /% 38.7 22.74 31.17 21.5 43.3 41.8 Fibrillation grade 1.5 1 3rd 1.5 5.5 6

The data in the table show that manufactured according to the invention Fibers (Examples 1 to 4) are characterized by a very low Show tendency to fibrillization. Except for the example 3, where only a fibrillation grade of 3 is achieved, the fibers show no fibrils (example 2), or only a slight tendency to form primary fibrils (Examples 1 and 4). The through the comparative examples (Examples 5 and 6) represented common Lyocell fibers in contrast show a strong formation of secondary fibrils.

The best fibrillation scores are achieved for the fibers which were placed on the sieve belt without tension (Examples 2 and 4), it also being shown that the fibers which were kept in the de-energized state for a longer period of time, ie longer than 9 s in Example 2, corresponding to a K _R greater than 4000, give the best results.

The data also show that those made according to the invention Fibers have a lower L value and thus a higher depth of dyeing have than the fibers of the comparative examples. A has a higher dye depth in the manufacture of textiles Advantage that faster and more intensive staining is possible is, and the possibilities of a common staining with others Materials, e.g. in blended fabrics.

The examples thus demonstrate that with the method according to the invention in an effective manner and with economical process management, i.e. without the use of other chemicals, fibers with extremely low tendency to fibrillation can. The fibers according to the invention are distinguished, like that in the data listed in the table using x-ray wide-angle scattering measurements were determined, prove, by a new one Structure compared to conventional Lyocell fibers. The firmness The fibers of the invention are more common than those Lyocell fibers lower, but this is for the use of the fibers not disadvantageous in the textile area, since none in this high strength are required. Besides the one above mentioned softer handle of fabrics that the fibers according to the invention result from their lower modulus, processing is due to the lower modulus of the fibers in the production of slip and warp beams and their Further processing on looms and knitting machines made easier.

Claims (20)

Process for the production of cellulosic fibers a solution of cellulose in a tertiary amine oxide and optionally water, the fiber being formed by a spinneret Solution is coagulated in at least two stages and the fibers are then washed and dried, characterized in that the coagulation in at least two stages takes place in such a way that the dwell time of the Fibers in the first precipitation stage is set so that when leaving the first precipitation stage only the Tackiness of the surface of the fiber-shaped solution is prevented and the fibers in further precipitation stages to be kept in a tension-free state and at Leaving the last precipitation stage, the fibers are coagulated are. A method according to claim 1, characterized in that the Fibers for the further precipitation stages without tension placed on a sieve belt. A method according to claim 2, characterized in that the Fibers on the belt are treated with water. A method according to claim 1, characterized in that the Fibers after the first precipitation stage using two godets out that the fibers between the godets free sag, and coagulation in the second precipitation stage through that from the first precipitation stage through the fibers carried along coagulants. A method according to claim 4, characterized in that the second godet a lower surface speed than the first godet. Method according to one or more of claims 1 to 5, characterized in that the residence time t _{F of} the fibers in the first precipitation stage is less than 0.02 s. Method according to one or more of claims 1 to 6, characterized in that the size K F = t F · C / T , where c is the cellulose concentration of the solution in kg of cellulose per kg of solution, T is the individual titer of the fibers in g / m and t _{F is} the residence time in s in the first precipitation stage, less than 12 sm / g, preferably less than 10 sm / g is. Method according to one or more of claims 1 to 7, characterized in that the size K R = t R · C / T , where c represents the cellulose concentration of the solution in kg cellulose per kg solution, T the individual titer of the fibers in g / m. and t _{R is} the residence time in s of the fibers in the de-energized state, greater than 110 sm / g, preferably greater than 190 sm / g. Method according to one or more of claims 1 to 8, characterized in that in the first precipitation stage a funnel precipitation bath is used. Method according to one or more of claims 1 to 9, characterized in that in the first precipitation stage a precipitation medium with a temperature lower than 15 ° C. is preferred is used below 8 ° C. Method according to one or more of claims 1 to 10, characterized in that the fibers during drying under a tension of less than 1 cN / tex, preferred in a de-energized state. Method according to one or more of claims 1 to 11, characterized in that the precipitation medium is aqueous N-methylmorpholine-N-oxide (NMMO) with an NMMO concentration greater than 10%, preferably greater than 15%, used becomes. Method according to one or more of claims 1 to 12, characterized in that a mixture as cellulose from pulps is used, which is a different Have degree of polymerization (DP). Method according to one or more of claims 1 to 13, characterized in that the cellulose concentration in of the solution less than 15% by weight, preferably less than 12 % Is. Cellulosic fibers made from a solution of cellulose in a tertiary amine oxide and possibly water, characterized in that they are a parameter F = -0.8754P - 3.8532L (004) + 19.2136L (110) + 0.05395L (004 )P - 1.6483L (110) 2nd + 4.4283L (004) / L (110) have less than 4, where P is the porosity of the fibers in%, L (110) the crystallite width in nm and L (004) the crystallite length in nm. Cellulosic fibers according to claim 15, characterized in that the parameter F is less than 3.3. Cellulosic fibers according to claim 15 or 16, characterized in that the orientation of the amorphous areas f _{a is} less than 0.46, preferably less than 0.39. Cellulosic fibers according to claim 15 or 16, characterized in that that the crystallite width L (110) is smaller than Is 3.5 nm. Cellulosic fibers according to claim 15 or 16, characterized in that that the crystallite length L (004) is less than 14 nm, preferably less than 13.5 nm. Cellulosic fibers according to one or more of the claims 15 to 19, characterized in that the birefringence is less than 0.040, preferably less than 0.035.

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