Process for producing polymer fibers from polymers dissolved in ionic liquids by an air-gap spinning process

Description

[0001] The invention relates to a process for producing polymer fibers from polymers dissolved in ionic liquids by an air gap spinning process, which is characterized in that a) a spinning solution containing an ionic liquid and a dissolved polymer is prepared, the spinning solution being obtained by a1) preparing a heterogeneous mixture of polymer, a non-solvent which does not dissolve the polymer or only partially dissolves it, and an ionic liquid and a2) distilling off the non-solvent, b) this spinning solution is passed through an extruder before being divided into fibers via a nozzle, and c) the fibers obtained are passed through an air gap through a coagulation bath, wherein the fibers are stretched in the air gap and wherein the polymer fibers are cellulose fibers.

[0002] Various spinning processes have been described for the production of polymer fibers. The most important ones are the wet spinning process and the dry spinning process.

[0003] In the wet spinning process, the spinning solution containing the dissolved polymer is fed directly into a coagulation bath. The polymer coagulates in the coagulation bath, and the resulting fibers are spun directly from the coagulation bath.

[0004] In the dry spinning process, the spinning solution is forced through a spinneret and then passed through a temperature-controlled air gap. In the air gap, the emerging jets of spinning solution solidify into fibers. A special form of the dry spinning process is the dry-wet spinning process. In a dry-wet spinning process, the resulting fibers, after passing through the air gap, are fed into a coagulation bath containing a precipitant for the polymer. In this coagulation bath, the fibers further solidify.

[0005] Such a dry-wet spinning process is described for the production of cellulose fibers. DE-A 4444140 and US Pat. No. 4246221 disclose the production of cellulose fibers from spinning solutions containing cellulose and N-methylmorpholine-N-oxide (NMMO) as a solvent (Lyocell® process).

[0006] Such processes are also known for spinning solutions containing cellulose and ionic liquids as solvents, see WO 2006 / 000197, WO 2007 / 076979 and WO 2009 / 118262.

[0007] Cellulose fibers are predominantly produced using the viscose process. The resulting fibers are called viscose fibers. In the viscose process, cellulose, obtained from wood using the kraft process, for example, is dissolved in solution through a chemical reaction. With the help of alkali and carbon disulfide, cellulose xanthate is obtained. This dissolves upon addition of acid, releasing carbon disulfide.

[0008] The processes described above are alternatives to the viscose process. They have the fundamental advantage of eliminating the need for carbon disulfide and reactions involving carbon disulfide.

[0009] The desired performance properties of the cellulose fibers produced using alternative processes are equal to or even better than those of viscose fibers. These properties include, in particular, the fiber's strength, elasticity, and modulus of elasticity. In particular, the resulting fibers should be as uniform and homogeneous as possible, meaning that all fibers should have the same properties.

[0010] The object of the present invention was therefore to provide a process for producing polymer fibers that yields polymer fibers with the best possible performance properties. The process is suitable for the production of cellulose fibers; the resulting cellulose fibers should at least match, and if possible, exceed, the performance properties of viscose fibers. About the polymer fibers

[0011] The polymer fibers produced using the above process are preferably polymer fibers made from renewable raw materials. These are cellulose fibers. About the ionic liquid

[0012] The ionic liquid is preferably a salt that has a melting point below 100°C at atmospheric pressure (1 bar). Particularly preferred are salts that are liquid at 21°C, 1 bar. The term "ionic liquid" also includes mixtures of different salts.

[0013] The ionic liquid is preferably a salt consisting of an organic cation and an anion.

[0014] Suitable organic cations are in particular organic cations with heteroatoms, such as nitrogen, sulfur, oxygen or phosphorus.

[0015] In particular, the organic cations are compounds with an ammonium group (ammonium cations), an oxonium group (oxonium cations), a sulfonium group (sulfonium cations) or a phosphonium group (phosphonium cations).

[0016] It is preferably an organic cation with at least one nitrogen atom.

[0017] In a particular embodiment, the organic cations are ammonium cations, which include non-cyclic cations with tetravalent nitrogen and localized positive charge on the nitrogen atom (quaternary ammonium compounds) or heterocyclic cations with at least one, preferably one to three nitrogen atoms in the ring system.

[0018] Quaternary ammonium cations include, in particular, those with three or four aliphatic substituents on the nitrogen atom. Such aliphatic substituents are, in particular, C1 to C12 alkyl groups or C1 to C12 hydroxyalkyl groups.

[0019] Preferred organic cations with at least one nitrogen are organic, heterocyclic cations with one to three, in particular one or two nitrogen atoms as part of the heterocyclic ring system.

[0020] Monocyclic, bicyclic, aromatic or non-aromatic ring systems are considered.

[0021] Examples include bicyclic systems such as those described in WO 2008 / 043837. The bicyclic systems of WO 2008 / 043837 are diazabicyclo derivatives, preferably consisting of a 7- and a 6-membered ring, which contain an amidinium group; in particular, the 1,8-diazabicyclo(5.4.0)undec-7-enium cation is mentioned.

[0022] Particularly suitable are monocyclic cations, such as pyridinium cations, pyridazinium cations, pyrimidinium cations, pyrazinium cations, imidazolium cations, pyrazolium cations, pyrazolinium cations, imidazolinium cations, thiazolium cations, triazolium cations, pyrrolidinium cations, and imidazolidinium cations. These cations are listed, for example, in WO 2005 / 113702. Where necessary for a positive charge on the nitrogen atom or in the aromatic ring system, the nitrogen atoms are each substituted by a hydrogen atom or an organic group having generally no more than 20 carbon atoms, preferably a hydrocarbon group, in particular a C1 to C16 alkyl group, in particular a C1 to C10, particularly preferably a C1 to C4 alkyl group.

[0023] The carbon atoms of the ring system can also be substituted by organic groups having generally not more than 20 C atoms, preferably a hydrocarbon group, in particular a C1 to C16 alkyl group, in particular a C1 to C10, particularly preferably a C1 to C4 alkyl group.

[0024] Particularly preferred cations are imidazolium cations, pyrimidinium cations and pyrazolium cations.

[0025] Particularly preferred cations are imidazolium cations of the following formula I wherein R1 represents an organic radical having 1 to 20 C atoms and R2, R3, R4 and R5 represent an H atom or an organic radical having 1 to 20 C atoms.

[0026] In formula I, R1 and R3 preferably independently represent an organic radical having 1 to 10 carbon atoms. In particular, R1 and R3 represent an aliphatic radical, especially an aliphatic radical without further heteroatoms, e.g., an alkyl group. Particularly preferably, R1 and R3 independently represent a C1 to C10 or a C1 to C4 alkyl group, respectively; very particularly preferably, R1 and R3 independently represent a methyl group or an ethyl group.

[0027] In formula I, R2, R4, and R5 preferably independently represent a hydrogen atom or an organic radical having 1 to 10 carbon atoms; in particular, R2, R4, and R5 represent a hydrogen atom or an aliphatic radical. Particularly preferably, R2, R4, and R5 independently represent a hydrogen atom or an alkyl group, in particular, R2, R4, and R5 independently represent a hydrogen atom or a C1 to C4 alkyl group. Most preferably, R2, R4, and R5 each represent a hydrogen atom.

[0028] The anion belonging to the organic cation can be any anion.

[0029] In particular, the usual anions of ionic liquids come into consideration, for example Cl-, Br-, BF4-, H3C-COO-, HCOO-, H3C-O-SO3-, H3C-SO3-, F3C-O-SO3-, PF6-, CH3-CH2-COO-SCN-, SO32-, NO3-, ClO4-.

[0030] The anions of the ionic liquids are preferably organic anions with at least one carboxylate group, referred to as carboxylates for short. Preferably, the carboxylates contain only one carboxylate group.

[0031] Such carboxylates include, in particular, organic anions with 1 to 20 C atoms and a carboxylate group.

[0032] In a preferred embodiment, the carboxylates contain no other heteroatoms apart from the oxygen atoms of the carboxylate group. Examples of such anions include the anions of alkanecarboxylic acids, alkenecarboxylic acids, alkynecarboxylic acids, alkadienecarboxylic acids, alkatrienecarboxylic acids, benzoic acid, or phenylacetic acid. Suitable carboxylates of alkanecarboxylic acids, alkenecarboxylic acids, and alkadienecarboxylic acids are also known as fatty acid carboxylates.

[0033] Particularly preferred carboxylates are C1 to C20 alkanoates (carboxylates of alkanecarboxylic acids), especially C1 to C16 alkanoates. These include, in particular, the carboxylates of formic acid (C1 carboxylic acid), acetic acid (C2 carboxylic acid), propionic acid (C3 carboxylic acid), n-butyric acid (C4 carboxylic acid), n-valeric acid (C5 carboxylic acid), n-caproic acid (C6 carboxylic acid), n-caprylic acid (C8 carboxylic acid, octanoic acid), n-capric acid (C10 carboxylic acid, decanoic acid), lauric acid (C12 carboxylic acid, dodecanoic acid), palmitic acid (C16 carboxylic acid, hexadecanoic acid), or stearic acid (C18 carboxylic acid).

[0034] In a particular embodiment, the anions of the salts are carboxylates of C6 to C12 alkanecarboxylic acids (ie C6 to C12 alkanoates), very particularly preferably carboxylates of C8 alkanecarboxylic acids, in particular n-octanoate.

[0035] Ionic liquids are therefore particularly preferably salts whose cation is an organic, heterocyclic cation with one to three nitrogen atoms as part of the heterocyclic ring system and whose anion is a carboxylate.

[0036] Such ionic liquids are preferably: 1-Ethyl-3-methyl-imidazolium acetate, 1-Methyl-3-methyl-imidazolium acetate, 1-Ethyl-3-ethyl-imidazolium acetate, 1-Ethyl-3-methyl-imidazolium octanoate, 1-Methyl-3-methyl-imidazolium octanoate, 1-Ethyl-3-ethyl-imidazolium octanoate, For process step a)

[0037] In process step a), a spinning solution is prepared which contains an ionic liquid and a dissolved polymer.

[0038] The polymer is preferably cellulose, see above comments on polymer fibers.

[0039] Cellulose is mainly obtained from wood or other plant materials, including woods such as beech, spruce, eucalyptus or pine, or other plant materials such as bamboo, straw and grasses.

[0040] Cellulose is separated from wood and other plant materials, for example, by the kraft process and is produced as so-called pulp, which generally consists of more than 90% by weight, in particular more than 92% by weight, and most preferably more than 96% cellulose.

[0041] The average degree of polymerization (DP) of cellulose in pulp can range from 200 to 2000. The DP value indicates the average number of glucose units per cellulose chain.

[0042] The average degree of polymerization of cellulose can be reduced by breaking the polymer chains. To achieve this, dissolved cellulose can be exposed to elevated temperatures and / or brought into contact with acids or bases.

[0043] It is an advantage of the process according to the invention that cellulose with a high DP can also be used and pretreatment of the cellulose or posttreatment of the cellulose dissolved in the spinning solution to reduce the DP is not necessary.

[0044] The spinning solution produced and used in the further process therefore preferably contains a dissolved cellulose with a DP 200 of from 300 to 2000, particularly preferably from 300 to 1000 and most particularly preferably from 400 to 800.

[0045] The spinning solution contains the above ionic liquid as solvent. In addition to the ionic liquid, the spinning solution may contain other solvents. These other solvents should preferably be miscible with the ionic liquid and should only be used in amounts that do not impair the solubility of the polymers or cellulose in the solution. Particularly suitable are polar, protic solvents such as methanol, ethanol, or water in amounts of less than 10 parts by weight, in particular less than 3 parts by weight, per 100 parts by weight of ionic liquid. In a particularly preferred embodiment, the content of other solvents in the spinning solution is less than 1 part by weight and in particular less than 0.1 part by weight per 100 parts by weight of ionic liquid.

[0046] The content of cellulose in the spinning solution is preferably 6 to 20 parts by weight, particularly preferably 10 to 14 parts by weight per 100 parts by weight of ionic liquid.

[0047] The spinning solution may contain additional components. Examples include water to adjust the flow properties and / or flame retardant additives and / or pigments, particularly for coloring the fiber.

[0048] A preferred water content is, for example, 0.1–5 wt.%, based on the total spinning solution. The content of pigments or active ingredients such as stabilizers, e.g., antioxidants, antibacterial agents, UV inhibitors, etc., can be, for example, 0.1–2 wt.%, based on the total spinning solution.

[0049] The spinning solution can be prepared using conventional methods. For example, cellulose can be mixed with the ionic liquid and dissolved at elevated temperature. The polymer or cellulose can be mechanically ground beforehand, e.g., by a grinding process, to simplify the dissolution process. For mechanical grinding, it can be helpful to use swollen polymer or cellulose. The non-solvent described below is particularly suitable as a swelling agent.

[0050] The dissolution process is generally supported by mechanical means such as stirring. In particular, the dissolution process can also be improved or accelerated by ultrasound. If the spinning solution is to contain additional components, these can be added, for example, together with the cellulose or subsequently.

[0051] In a preferred embodiment, the polymer or cellulose is dissolved in the ionic liquid using an auxiliary liquid that does not dissolve or only partially dissolves the polymer or cellulose (hereinafter also referred to as the non-solvent). The non-solvent is largely or completely removed during the dissolution process, preferably by distillation, and is then present in the spinning solution only in the amounts of the other solvents specified above. The non-solvent is preferably miscible with the ionic liquid.

[0052] The spinning solution in process step a) is therefore preferably obtained by a1) Preparation of a heterogeneous mixture of polymer, a non-solvent and optionally ionic liquid and a2) distillation of the non-solvent.

[0053] Suitable non-solvents for cellulose are in particular water and alkanols, preferably water and methanol, particularly preferably water.

[0054] The amount of non-solvent is preferably at least 30 parts by weight, more preferably at least 50, most preferably at least 80 parts by weight of non-solvent, based on 100 parts by weight of polymer or cellulose. The non-solvent can be used in large excess. However, since it is removed again, it is preferable to use no more than 200 parts by weight, in particular no more than 150 parts by weight of non-solvent per 100 parts by weight of polymer.

[0055] Preferably, ionic liquid is used in a1) and a heterogeneous mixture is obtained which contains the cellulose, the non-solvent and the ionic liquid.

[0056] In a particularly preferred embodiment, the total amount of the ionic liquid is used in a1). According to the invention, a heterogeneous mixture is obtained which contains the cellulose, the non-solvent and the ionic liquid in the amounts stated above.

[0057] If only a portion of the ionic liquid is used, the remainder can be added, for example, during the removal of the non-solvent by distillation or subsequently added to the spinning solution.

[0058] The formation of the cellulose solution occurs during the distillation of the non-solvent in a2).

[0059] The non-solvent is preferably distilled off at a temperature of 50 to 150°C, particularly preferably at a temperature of 80 to 130°C.

[0060] In a preferred embodiment, distillation takes place at reduced pressure, i.e., at a pressure of less than 1 bar, in particular at a pressure of not more than 500 millibars, particularly preferably at a pressure of not more than 100 millibars, and most preferably at a pressure of not more than 40 millibars. The pressure can be, for example, 5 to 500 millibars, particularly 20 to 100 millibars.

[0061] In a particularly preferred embodiment, a thin-film evaporator is used to distill off the non-solvent. This can be, for example, a falling-film evaporator or a rotor evaporator.

[0062] Preferably, it is a rotor evaporator. This generally consists of a cylinder containing a rotor. The wall distance between the cylinder and the rotor is preferably a maximum of 10 millimeters, particularly preferably a maximum of 1 millimeter. The cylinder is heated. Mixing elements attached to the rotor, such as wiper blades, ensure thorough mixing of the heterogeneous mixture during distillation.

[0063] The heterogeneous mixture obtained in a1) is preferably introduced at the upper end of the heated cylinder. The heterogeneous mixture spreads over the inner wall of the cylinder. The non-solvent, preferably water, evaporates, and the cellulose dissolves. The resulting spinning solution can be removed at the lower end of the cylinder. The spinning solution can be discharged using conventional pumps, e.g., a gear pump.

[0064] With the help of the thin-film evaporator, the solution can be produced continuously, and the spinning solution at the outlet can be continuously fed into the further spinning process. With the help of the thin-film evaporator, a spinning solution is obtained that is free of gas bubbles and has a very high degree of homogeneity.

[0065] The thin-film evaporator can be operated, for example, at a pressure of 40-80 millibar, a temperature of 80-130°C, and a throughput of 0.5-2 kg / h of heterogeneous mixture. Larger thin-film evaporators, of course, allow for higher throughput. For process step b)

[0066] In process step b, the spinning solution obtained in a) is passed through an extruder.

[0067] In a preferred embodiment, the spinning solution obtained in a) is first filtered before being fed to the extruder. The filtration is intended to separate undissolved components.

[0068] Preferably, the filtration is carried out under pressure; a pressure filter vessel is particularly suitable for carrying out the filtration. Filtration is preferably carried out at a pressure of at least 1.2, in particular at least 1.5 bar. More than 3 bar is generally not necessary.

[0069] In a preferred embodiment, the spinning solution passes directly into the extruder after process step a) and a preferably subsequent filtration.

[0070] The extruder preferably consists essentially of an outer shell, generally in the form of a cylinder, and at least one conveyor screw incorporated therein.

[0071] Preferably, this is an extruder with one or two screws, in particular it is an extruder with one screw.

[0072] The flight depth can remain the same or change over the entire length of the screws.

[0073] In a preferred embodiment, the screws are core-progressive, meaning that the flight depth at the inlet is greater than the flight depth at the outlet of the extruder. In particular, the ratio of the flight depth at the inlet to the outlet is 1.2:1 to 3:1, particularly preferably 1.5:1 to 2:1.

[0074] Conventional screws with a screw diameter D of, for example, 5 to 500 millimeters can be used. In the process according to the invention, screw diameters D of 5 to 250 millimeters are preferred; particularly preferred are 5 to 50 millimeters, and in particular a screw diameter D of 10 to 50 millimeters.

[0075] The length of the screws is usually specified as a multiple of D. Preferred screw lengths are 10 to 50 D, especially 15 to 30 D.

[0076] The speed of the screws is preferably 10 to 300, particularly preferably 25-100 revolutions per minute.

[0077] The temperature of the spinning solution in the extruder is preferably 20 to 150°C, in particular 40 to 120°C, most preferably 40-90°C.

[0078] The pressure with which the spinning solution is conveyed through the extruder can be, for example, 10 to 200 bar, in particular 15 to 150 bar, most preferably 20 to 120 bar.

[0079] After passing through the extruder, the spinning solution is pumped to the spinning head by a pump, e.g., a gear pump. The spinning head generally contains a final filtration device and a distribution block to distribute the spinning solution as evenly as possible across all holes in the die and the die. Upon passing through the die, the spinning solution is divided into polymer fibers.

[0080] For example, nozzles with a hole diameter D of 90 - 60 µm can be considered.

[0081] The ratio of hole length L (also called capillary length) to hole diameter, in short L / D ratio, can be e.g. 2 / 1 to 8 / 1.

[0082] The throughput of the spinning solution through the extruder depends on the number of holes in the nozzle and the pressure. For example, at pressures of 15 to 150 bar and a hole count of 168, the throughput can be 3 to 20 cm³ / min; for a nozzle with a hole count of 1000, the throughput can be 17 to 119 cm³ / min.

[0083] Insofar as connecting elements are present between the devices, these are in the simplest case and therefore preferably connecting lines, in particular pipelines.

[0084] Process steps b) to c) are preferably carried out continuously; particularly preferably, all process steps a) to c) are carried out continuously. Therefore, all elements and devices that contain or convey the spinning solution produced in a), including any connecting lines between the devices, are heated or—in the case of short lines—preferably sufficiently insulated so that the temperature of the spinning solution remains as constant as possible, thus ensuring good flow behavior throughout all process steps up to the exit from the nozzle. For process step c)

[0085] The spinning solution is divided into fibers through the nozzle. Initially, the fibers still consist of the spinning solution. The exit speed of the spinning solution or the forming fibers from the nozzle is, for example, 2.5 to 40 m / min, preferably 4 to 30 m / min, particularly preferably 5.5 to 20 m / min.

[0086] The fibers obtained when passing through the nozzle are passed through an air gap through a coagulation bath.

[0087] The width of the air gap can be, for example, 5 millimeters (mm) to 50 mm. The preferred width is 8 to 20 mm.

[0088] In the air gap, the fibers are preferentially drawn. Drawing lengthens the fibers and simultaneously orients the polymer in the tensile direction.

[0089] After exiting the nozzle, the fiber is transported via so-called godet rolls, as is common in spinning processes. Godet rolls are two rotating rollers arranged one above the other. They serve as drives for advancing the fiber. Both rollers rotate at the same speed in the same direction and have the same diameter. Furthermore, they are generally not completely parallel to each other, but rather at a slight angle. This creates a gap between the wraps when the fiber wraps around both rollers several times. This prevents the fibers from touching and causing mechanical damage.

[0090] Drawing can therefore be achieved simply by increasing the transport speed of the godet pairs. If this speed is higher than the fiber exit speed from the nozzle, the fiber is drawn accordingly immediately after exiting the nozzle.

[0091] The degree of stretching is determined by the ratio of the transport speed of the godet pairs to the exit speed of the fiber from the nozzle. Without stretching, i.e., at the same speeds, the degree of stretching is 1. Preferably, the degree of stretching is between 1.5 and 3.5, particularly preferably between 1.8 and 3.5.

[0092] The transport speed of the godet pairs can be, for example, 1 to 200 meters (m) per minute (min). Preferably, it is 15 to 40 m / min.

[0093] After the air gap, the fibers enter the coagulation bath. The coagulation bath contains a non-solvent for the polymer or cellulose. Non-solvents are described above. The preferred non-solvent is water. In addition to the non-solvent, the coagulation bath can also contain solvents that dissolve the polymer, e.g. ionic liquid. When immersed in the coagulation bath, the fiber generally still contains ionic liquid from the spinning solution and releases this into the coagulation bath. In this way, ionic liquid accumulates in the coagulation bath over time. The content of ionic liquid or other solvents that dissolve the polymer or cellulose should preferably be kept low enough that the coagulation of the polymer is not significantly impaired. The coagulation bath should particularly preferably contain a maximum of 30 wt.%, most preferably a maximum of 10 wt.% of such solvents.The percentages are based on the total weight of the coagulation bath.

[0094] The temperature of the coagulation bath is generally not elevated; it can, for example, be between 10 and 30°C.

[0095] The contact time of the fiber in the coagulation bath can be, for example, 1 second to 60 seconds, preferably 5 to 20 seconds.

[0096] After passing through the coagulation bath, the fibers are essentially solidified in their structure and their mechanical properties are hardly changed by the subsequent process steps, such as washing, finishing with additives, drying and winding.

[0097] Generally, the fiber passes through several washing baths, such as water baths, to ensure that the ionic liquid is removed from the fiber as completely as possible. These baths may be followed by fiber finishing baths. These baths contain common additives, such as phosphorus compounds for fire protection or surface treatment additives. The latter prevent the fiber from sticking together later on. Drying can be achieved using heated godet rollers and / or the supply of hot air in a heating channel. Finally, the fiber is wound onto a spool.

[0098] The fibers ultimately produced in process step c), also known as filaments, are so-called continuous fibers or continuous filaments. Unlike so-called staple fibers, these are not deliberately cut but are obtained as a coiled fiber at the end of the production process.

[0099] The process according to the invention makes it possible to obtain cellulose fibres with very good application properties.

[0100] In particular, the process can be used to obtain cellulose fibers with a defibrillation rating of 1 to 2.5.

[0101] The term defibrillation refers to the formation or presence of fibrils, i.e. fine hairs that protrude from the fiber; these fibrils are generally undesirable for textile applications because they make the fiber rough.

[0102] Defibrillation is assessed visually using a defibrillation grade. The fibers are placed in water and shaken. The presence of protruding fibrils is then examined under a microscope. Grades from 1 to 6 are assigned. A grade of 1 indicates no protruding fibrils (no defibrillation), and a grade of 6 indicates the fiber is fully fibrillated.

[0103] The thickness of the cellulose fibers obtained is preferably 2-20µm,

[0104] The fineness of the fiber, ie weight relative to fiber length, is preferably 1-4 dtex.

[0105] The unit tex stands for grams per 1000 meters of fiber; 1 dtex corresponds to 0.1 tex or grams per 10,000 meters of fiber.

[0106] The maximum tensile strength of the fiber is in particular 10 to 100 cN / tex, particularly preferably 20 to 60 cN / tex.

[0107] The elongation at break of the fiber is in particular 1 to 30%, particularly preferably 10 to 30%, e.g. 12 to 20%. Examples

[0108] Compounds and raw materials used in the examples: EMIM Octanoate: 1-Ethyl-, 3-methyl-imidazolium octanoate (R1 in formula I is ethyl and R3 in formula I is methyl), EMIM Octanoate is an ionic liquid, hereinafter also referred to as IL for ionic liquid) Cellulose: Eucalyptus sulfide pulp (Examples 1 to 5) and cotton linters in Examples 6 to 11. Examples 1 to 5

[0109] In these examples, cellulose fibers were prepared according to the following description: Preparation of the spinning solution

[0110] First, a heterogeneous mixture of the following components was prepared. 11% by weight cellulose, eucalyptus pulp 8.1% by weight water and 80.9% by weight octanoate

[0111] For this purpose, EMIM octanoate was mixed with ice, as the addition of water causes it to warm up. The cellulose was then added. The mixture was mixed for approximately 45 minutes in an AMK kneader at 40 rpm and room temperature.

[0112] The water was then distilled off in a thin-film evaporator (type: VD 83-6-RRS-11 from VTA): Rotation speed: 400 rpm Jacket temperature 120 °C Discharge pump temperature: 110 °C Vacuum: 60 mbar

[0113] After distillation, a spinning solution containing 12 wt.% dissolved cellulose was obtained. Characterization of the spinning solution:

[0114] The spinning solution is characterized using a rheometer. Rheological tests primarily serve to test the spinnability of a spinning dope. Important parameters here are zero-shear viscosity, i.e., the theoretical viscosity at no load, and crossover, i.e., the point at which loss and storage modulus are equal. Frequency sweep tests are conducted to obtain these parameters. Furthermore, the spinning solution should exhibit pseudoplastic behavior and not be a gel. Since spinning takes place through an air gap, the solution must exhibit sufficiently high elastic behavior to form stable filaments, but these filaments must also be stretched. Therefore, sufficient viscous behavior is also required.

[0115] In this case, the spinning solution exhibited a zero shear viscosity of 1000 Pas at 110°C and 20,000 Pas at 50°C, depending on the temperature, as well as a crossover of approximately 16 rad / s at 110°C and approximately 0.8 rad / s at 50°C. It also exhibited pseudoplastic behavior up to 50°C. These values were determined using a Rheometrics SR 500 Dynamic Stress Rheometer. A 25 mm diameter plate served as the measuring head. A force-controlled frequency sweep was measured. The frequency range was from 100 rad / s to 0.1 rad / s at a force of 100 Pas. This measurement was performed from 110°C to 40°C, decreasing in 10 K increments. The measuring gap was 1 mm. Processing of the spinning solution

[0116] The spinning solution was transferred to a "10-liter pressure filtration vessel" designed by Karl Kurt Juchheim. The filter used was a metal mesh made of austenitic stainless steel (material number 1.4401) with a mesh size of 0.043 mm and a wire thickness of 0.035 mm.

[0117] The filtration unit was positioned on a frame above the extruder. The pressure filter vessel was connected to the extruder inlet via a heatable transfer line.

[0118] The extruder was a Haake Polylab Rheocord. The extruder's screw was progressive core with a flight depth ratio of 2:1, meaning the flight depth at the inlet is twice as large as at the outlet. The screw diameter was 19 mm, and its length was 25 times its diameter, or 475 mm.

[0119] The spinning mass was fed through the filter into the extruder at 2 bar pressure. From there, it was conveyed by a screw to the spinning pump. The spinning pump used was a precision gear pump with a flow rate of 0.6 cm³ / rev.

[0120] The spinning solution was passed through the spinning head, where it was evenly distributed to the nozzle via another filter and a distribution block. The nozzle used here has a hole diameter of 60 µm with an L / D ratio of 2 / 1, has 168 holes, and is from Enka Technika. This entire setup, from pressure filtration to the nozzle, was heated to the spinning temperature.

[0121] The filaments emerging from the nozzle were guided through a 10 mm air gap into a coagulation bath. The coagulant contained water as a non-solvent. The temperature of the coagulation bath was 21°C.

[0122] After an immersion depth of 300 mm, the fiber was deflected and drawn from the coagulation bath via a godet duo at a defined speed and transported further. Depending on the desired drawing and exit speed, the draw-off speed varied according to Table

[0123] A wet spinning system from Fourne was used. This comprises a total of nine godet pairs.

[0124] Between the first five of these godet pairs were three wash baths, each 1200 mm long. These contained water at a temperature of 88°C. This washing section concluded with a wash godet pair. Here, the fiber was continuously rinsed with water at room temperature for the final time. The washing process took place directly on the godet.

[0125] After the washing godet pair, two more godet pairs were used for preparation. Between these two drives was an aqueous dip bath through which the fiber was passed. The preparation, i.e., the additives in the dip bath, rendered the fiber non-stick in the usual way, preventing the individual filaments from sticking together during drying.

[0126] The drying step was carried out on a heatable godet duo at 80°C.

[0127] The fiber was then passed through a hot air duct at (1200mm; 120°C) and wound up after the last godet duo using a tension-controlled Oeriklon Barmag winder type WUFF 6E.

[0128] The above-described production of cellulose fibers was repeated under different conditions. The table provides the necessary information on the production and properties of the resulting cellulose fibers.

[0129] The textile mechanical properties were measured using a "Favimat" from Textechno. The mean values of 20 individual fiber measurements were determined. Table with information on production and fiber properties Example 1 Example 2 Example 3 Example 4 Example 5 Solution concentration [%] 12 12 12 12 12 Spinning temperature [°C] 54 60 60 90 90 Exit velocity [m / min] 5,9 5,9 12,8 12,8 27,8 Trigger speed [m / min] 10,7 10,7 22,5 15 39,0 Stretching [%] 80 80 90 120 40 Drives 1-9 [m / min] 10,7 10,7 22,5 28 39 Textile mechanical properties Elongation at break [%] 6 9 6 6 6 Maximum tensile force [cN / tex] 37 34 41 51 31 Single fiber fineness [dtex] 1,8 2,0 1,8 1,7 2,4 Young's modulus [cN / tex] 1900 1600 1900 1900 1600 Example 6-8:

[0130] Execution as in examples 1-5. Cotton linters were used as pulp. The alpha cellulose content leads to significantly improved fiber properties. Example 6 Example 7 Example 8 Solution concentration [%] 12 12 12 Spinning temperature [°C] 54 60 60 Exit velocity [m / min] 5,9 5,9 12,8 Trigger speed [m / min] 13.6 14,1 22,5 Stretching [%] 130 140 90 Drives 1-9 [m / min] 13,6 14,1 22,5 Textile mechanical properties Elongation at break [%] 5 6 6 Maximum tensile force [cN / tex] 56 57 46 Single fiber fineness [dtex] 1,2 1,3 1,8 Young's modulus [cN / tex] 2400 2300 2200 Examples 9-11 (comparison examples)

[0131] The design was as in Example 6-8, but without a screw extruder: The desired stretching could no longer be achieved. A summary of the fiber properties at maximum stretching compared to Example 6-8 is shown in the following table: Example 9 Example 10 Example 11 Solution concentration [%] 12 12 12 Spinning temperature [°C] 54 60 60 Exit velocity [m / min] 5,9 5,9 12,8 Trigger speed [m / min] 8,5 10,2 17,9 Stretching [%] 45 70 40 Drives 1-9 [m / min] 8.5 10,2 17,9 Textile mechanical properties Elongation at break [%] 14 16 15 Maximum tensile force [cN / tex] 23 29 21 Single fiber fineness [dtex] 2,6 2,5 3,2 Young's modulus [cN / tex] 800 900 600

Claims

1. A process for producing polymer fibers from polymers dissolved in ionic liquids by an air gap spinning process, characterized in that a) a spinning solution containing an ionic liquid and a dissolved polymer is prepared, wherein the spinning solution is obtained by a1) preparing a heterogeneous mixture of a polymer, a non-solvent, which does not or only partially dissolve the polymer, and an ionic liquid, and a2) distilling off the non-solvent, b) said spinning solution is passed through an extruder before being divided into fibers via a die, and c) the fibers obtained are passed via an air gap through a coagulation bath, wherein the fibers are drawn in the air gap, and wherein the polymer fibers are cellulose fibers.

2. The process according to claim 1, characterized in that the polymer fibers are fibers from renewable raw materials.

3. The process according to claim 1 or 2, characterized in that the extruder in b) is a core-progressive screw extruder.

4. The process according to any one of claims 1 to 3, characterized in that - the cation of the ionic liquid is an organic, heterocyclic cation having one to three nitrogen atoms as a component of the heterocyclic ring system, and - the anion of the ionic liquid is a compound with a carboxylate moiety.

5. The process according to any one of claims 1 to 4, characterized in that the cation of the ionic liquid is an imidazolium cation of the following formula I wherein R1 represents an organic radical with 1 to 20 C atoms, and R2, R3, R4 and R5 represent an H atom or an organic radical with 1 to 20 C atoms.

6. The process according to any one of claims 1 to 5, characterized in that the polymers in the spinning solution are cellulose with an average degree of polymerization DP of 200 to 2000.

7. The process according to any one of claims 1 to 6, characterized in that the non-solvent is water.

8. The process according to any one of claims 1 to 7, characterized in that the distilling off of the solvent is carried out at a temperature of 50 to 150°C and a pressure of less than 1 bar.

9. The process according to any one of claims 1 to 8, characterized in that in process step b), the temperature of the spinning solution in the extruder is 40 to 120°C.

10. The process according to any one of claims 1 to 9, characterized in that the fibers are drawn after passing through the die with a degree of drawing of 1.5 to 3.5.

11. The process according to any one of claims 1 to 10, characterized in that the contact time in the coagulation bath is 1 second to 60 seconds.

12. The process according to any one of claims 1 to 11, characterized in that process steps a) to c) are carried out continuously.