WO2025087981A1 - Profiled cellulose fibre having improved tensile strength and method for producing same - Google Patents

Abstract

The present invention relates to profiled cellulose fibres having an aspect ratio of the largest to smallest cross-sectional thickness of the cellulose fibre of at least 1.25, a fineness of at most 50 dtex and a maximum tensile strength of at least 22 cN/tex. Such fibres can be used advantageously for applications requiring high mechanical strength and a high water retention capacity. The present invention further relates to methods for producing such profiled cellulose fibres, to devices which are suitable for producing such cellulose fibres and to uses of the cellulose fibres according to the invention for producing yarns, woven fabrics or non-woven fabrics or as reinforcing material in building materials.

Description

Profiled cellulose fiber with improved tensile strength and process for its production

Description

The present invention relates to profiled cellulose fibers having an aspect ratio of the largest to the smallest cross-sectional thickness of the cellulose fiber of at least 1.25, a fineness of at most 50 dtex, and a maximum tensile strength of at least 22 cN/tex. The present invention further relates to processes for producing such profiled cellulose fibers, devices adapted for producing such cellulose fibers, and uses of the cellulose fibers according to the invention for producing yarns, woven fabrics, or nonwovens, or as reinforcing material in building materials.

State of the art

Compared to conventional viscose filaments with a circular cross-section, multi-link viscose filaments have a larger volume because the circumferential area of the multi-link filaments or fibers is larger than their actual cross-sectional area. Such viscose fibers are therefore preferred in textile applications where bulkiness is desired, such as pile fabrics. A filament yarn consisting of X- or Y-shaped continuous viscose filaments is described, for example, in Japanese patent application JPS-61-113812.

Another advantage of profiled viscose filaments is their increased absorbency compared to filaments with a round cross-section. Profiled filaments processed as staple fibers can therefore be used to produce absorbent products such as tampons, wipes, and swabs. UK Patent 1 333 047, for example, describes an absorbent viscose fiber in which the filaments have a collapsed hollow structure and a multi-segmented cross-section. Although these filaments have a relatively high absorbency compared to conventional viscose filaments, they have the disadvantage of being complicated are difficult to produce, as the filaments must be formed with an inflated, hollow structure and then collapsed. The process specified in UK-1 333 047 also has the disadvantage that fiber collapse is difficult to control to achieve a uniform filament cross-section, so that the resulting filaments usually have irregular, multi-segmented cross-sectional shapes.

US 5,458,835 describes a process for producing viscose filaments in staple fiber form, which have a fineness of at least 5.0 dtex and a multi-segment cross-section, for example, with a Y, X, H, or T-shaped configuration. According to the process in US 5,458,835, viscose is extruded to produce the fibers and introduced into a bath of aqueous sulfuric acid, zinc sulfate, and sodium sulfate. The fibers are then drawn at a ratio of 50%, made into a staple fiber yarn, and washed and dried. The fibers thus produced have a filament tenacity of approximately 15 to 19 cN/tex.

The viscose filaments described in US Pat. No. 5,458,835 exhibit sufficient strength for applications where the absorbency of the fibers is the primary consideration. However, this strength is insufficient for more demanding applications where the fibers are subjected to higher tensile forces (e.g., applications where the fibers are used for reinforcement purposes). Therefore, there is a need for profiled cellulose fibers with improved mechanical properties and, in particular, improved resistance to tensile stress.

Profiled cellulose fibers with a multi-limbed cross-section are described in EP 2732980 B1, which are intended to provide an increased linear density and improved absorbency compared to the prior art. However, mechanical properties such as the maximum tensile strength of the produced cellulose fibers are not specified in this document.

Flat cellulose fibers with a width/thickness ratio of 10:1 or more and a content of at least 98% cellulose, which are intended to be transparent, are described in EP 2785899 B1. In EP 2785899 B1, such fibers are produced by spinning a viscose dope with a coagulation retarder in a spinning bath with a sulfuric acid content of 100 to 140 g/l is produced, whereby the spinning threads are drawn off with a jet draft of 2.0 to 3.0 and drawn at a ratio of 20%-35%.

Another problem with profiled cellulose fibers proposed in the prior art is the process used for their production, in which the material is introduced into a relatively highly concentrated acid bath after extrusion. This bath also contains a relatively high proportion of pure salt (in the form of sodium and zinc sulfate), which results in a high salt load in the precipitation solution and results in high disposal costs for the reaction mixture, especially since the sulfuric acid used must also be neutralized for disposal. This results in relatively high costs for the production of such fibers.

Against this background, there is also a need for profiled cellulose fibers that can be produced in a more cost-effective and economical and environmentally friendly manner.

The present invention addresses this need.

Description of the invention

In the investigations underlying this invention, it was surprisingly found that a profile of cellulose fibers is retained even when the fibers are stretched at a significantly higher ratio compared to the prior art. Normally, one would expect that at higher stretching, a profile would be largely leveled out, especially since the material is still relatively flexible during stretching. However, this leveling can be suppressed by adjusting the processing viscosity of the spinning solution to such an extent that the profile generated by a profile nozzle is retained to a desirable extent. The higher stretching subsequently achieves a higher linear alignment of the cellulose chains, which results in improved tensile properties.

It was further surprisingly found that such profiled cellulose fibers can be produced by a process in which the Cellulose is dissolved in an ionic liquid (as a direct solvent) for spinning, and the strands generated by extrusion are precipitated into cellulose filaments in an aqueous coagulation medium. During this treatment, the profile structure initially created by the extrusion dies undergoes some changes due to the intense stretching, but remains intact to such an extent that a desired profile structure can be specifically realized by adjusting the die geometry.

According to a first aspect, the present invention accordingly relates to a profiled cellulose fiber having an aspect ratio of the largest to the smallest cross-sectional thickness of the cellulose fiber of at least 1.25, a fineness of at most 50 dtex and a maximum tensile strength (dry) of at least 22 cN/tex.

In the context of the invention described here, the aspect ratio is determined as the average of the aspect ratio from the cross-section of 10 randomly selected fibers.

The specified aspect ratio is a measure of the deviation of the profile shape of the specified cellulose fibers from a round profile shape, for which the aspect ratio is "1.0". The larger the aspect ratio, the greater the deviation of the profile shape from a round profile shape. For the aspect ratio, an aspect ratio that deviates more from a round profile shape is preferred, whereby it has proven advantageous if the cellulose fiber has an aspect ratio in the range of 1.3 to 5, in particular in the range of 1.5 to 4.0, and more preferably in the range of 1.7 to 4.0.

The term "regenerated cellulose fiber" refers to a cellulose fiber that is not of natural origin and that can have a thickness and length not achieved in natural fibers. In the context of the invention described here, the terms "cellulose fiber" and "regenerated cellulose fiber" have a synonymous meaning when they refer to products and fibers to be produced according to the invention, since the profiled cellulose fibers according to the invention are regenerated cellulose fibers.

The fineness is a measure of the thickness of the fibers and is limited to a maximum of 50 dtex. The ranges that can be conveniently achieved and adjusted for the maximum tensile strength (dry) are from 25 to 50 cN/tex, in particular in the range from 25 to 32 cN/tex, and more preferably in the range from 25 to 30 cN/tex. Furthermore, it is advantageous if the cellulose fibers according to the invention have a maximum tensile strength (wet) in the range of 10-30 cN/tex and in particular 15-25 cN/tex. "Dry" here refers to the fact that the maximum tensile strength is determined for dry fibers (with respect to water). "Wet," on the other hand, means that the fibers were wet during the determination, in the sense of water present on the fiber surface. Such tensile properties ensure sufficient load-bearing capacity, which is important for the use of the fibers for reinforcement purposes.

Furthermore, it is advantageous if the elongation of the cellulose fibers according to the invention is in the range of 3 to 18%, preferably 5 to 10%, more preferably 5 to 8%. The elongation and maximum tensile force are determined in the context of the invention described here using DIN EN ISO 5079: 2020.

Yet another property that can be adjusted for cellulose fibers according to the invention is the modulus, which for an elongation in the range of 0.2 to 0.4% is preferably in the range of 500 to 2500 cN/tex, in particular 800 to 2000 cN/tex, and more preferably 600 to 1600 cN/tex. In the context of the invention described here, the modulus is measured according to BISFA at 5% elongation.

With regard to their dimensions, the cellulose fibers according to the invention are not subject to any relevant restrictions, provided that they do not exceed the stated fineness of 50 dtex. For most applications of the cellulose fibers, it is expedient if they have a fineness in the range from 2 to 20 dtex, and in particular in the range from 3 to 9 dtex. The fiber diameter has a certain correlation with the fineness of the cellulose fibers, although the profile shape of the cross section results in deviations from round fibers. For this reason, the "largest fiber diameter" is also specified for the cellulose fibers according to the invention. This diameter is obtained by placing a circle that completely encloses the fiber cross-section around it and determining its diameter. For this largest fiber diameter, it is preferred if the cellulose fibers according to the invention is set in a range from 11 to 150 pm, and in particular 12 to 70 pm.

The cellulose fibers according to the invention are characterized in that they can be produced in virtually unlimited lengths (i.e., as continuous fibers or "filaments"). Accordingly, in a preferred embodiment, the cellulose fibers according to the invention are formed as continuous fibers. In a preferred embodiment, the filament is wound up, e.g., on a spool. The fibers can, on the other hand, be cut to any desired length or be formed as staple fibers. For such staple fibers, it is particularly preferred if they have a length of 3 to 150 mm, in particular of 15 to 120 mm, and even more preferably 30 to 80 mm.

The specified profiled cellulose fibers are distinguished from cellulose fibers with a round cross-section (with the same dtex fineness) by their favorable water retention capacity, determined according to DIN 53184. For this purpose, it is particularly preferred if it is in the range of 45 to 120% and preferably 60 to 90%. The significance of this advantageous water retention capacity lies in its close relationship with the amorphous components and the void system between the crystalline regions. This pore system has a decisive influence on the sorption properties of the fibers and plays an important role, for example, in dyeing processes.

With regard to the shape of the profile with which the cellulose fiber according to the invention is formed, this is also not subject to any relevant restrictions, provided that the profile ensures an aspect ratio of at least 1.25. For example, the cellulose fiber according to the invention can be ribbon-shaped, wherein "arms" of the profile extending from the center of the cross-section can be arranged in a plane or at an angle to one another, preferably in the range of 90° to 170°. The cellulose fiber can also be C-shaped. Alternatively, the cellulose fiber can be formed with a trilobal structure, wherein the angles between the "arms" of the profile extending from the center of the cross-section can be the same or different, resulting, for example, in a Y-shape. Furthermore, the cellulose fiber can be formed with a tetralobal structure (i.e., with four "arms" of the profile extending from the center of the cross-section). The angles between the arms of the profile can be the same (as a "+" shape) or different (e.g. as an X-shape). Furthermore, even more global profile shapes are possible.

It is also possible for the profile shape to be H-shaped or H-like, with "arms" of the profile extending from a linear part of the profile and extending from the linear profile part at an angle of preferably in the range of 50° to 140°. Furthermore, the cellulose fibers may have profile shapes as described in EP 2732080 B1 (insofar as these are not already covered by the shapes specified above).

In a second aspect, the present invention relates to a process for producing profiled cellulose fibers as specified above. This process comprises at least the following steps: (i) preparing a dope of cellulose and an ionic liquid; (ii) spinning the dope through a profiled die at a temperature at which the crossover is in a range of 5 to 55 rad/s; (iii) introducing extruded fibers into a coagulation bath; and (iv) drawing the produced fibers to a maximum draw of at least 100%.

In the context of the process described here, maximum stretch refers to the percentage by which a given section is longer after stretching than before. A stretch of at least 100% means that the fiber has been stretched to twice its original length (by 100%).

The "crossover" refers to the point at which the elastic modulus is equal to the viscous modulus during a frequency sweep. The crossover of the spinning solution is specified here as the angular frequency with the unit rad/s and is determined using a rotational rheometer. The crossover is temperature-dependent; the person skilled in the art can determine the temperature at which the crossover of the spinning solution lies in the range of 5 to 55 rad/s by a series of measurements in which the temperature is systematically varied. The temperature in step (ii) is preferably adjusted so that the crossover lies in the range of 8 to 50 rad/s, in particular in the range of 10 to 40 rad/s, and more preferably 13 to 35 rad/s. In a certain correlation to the crossover, there is the zero shear viscosity of the spinning solution, which can be conveniently adjusted to a range of 1500 to 9000 Pa.s and preferably in the range of 2000 to 8000 Pa.s.

For the process according to the invention, it has been shown that setting the temperature in the range where the crossover is in the range of 5 to 55 rad/s enables the fibers produced by extrusion to be very effectively concealed without completely losing the profile structure of the fibers. This makes it possible to stretch the fibers by a percentage significantly greater than 100%. Since improved mechanical properties can be achieved through greater stretching, it is preferred within the scope of the process according to the invention if the maximum stretch is higher than 100%, such as 110% or more, and in particular in the range of 100% to 1600%, and more preferably 300% to 1000%.

The above information indicates that suitable spinning temperatures for most spinning solutions are above 25°C. Particularly favorable spinning temperatures are, for example, in the range of 50 to 85°C and, in particular, 55 to 75°C.

For spinning, it is preferable if the spinning dope, after passing through the profiled nozzle, is passed through an air gap into a coagulation bath. By altering diffusion through the special osmotic conditions, phase inversion can be significantly delayed and homogeneous regeneration of the cellulose can be achieved. Furthermore, these conditions prevent the formation of a fibrillar fiber structure and thus reduce the tendency of fibers spun with an air gap to fibrillate.

The length of the air gap is preferably adjusted to ensure that the extruded fibers are in contact with air for an optimal period of time before being introduced into the coagulation bath. An air gap length in step (ii) in the range of 5 to 25 mm, and in particular 8 to 15 mm, has proven particularly favorable.

When selecting the respective starting cellulose which is included in the process according to the invention and from which the specified cellulose fibres The present invention is not subject to any significant limitations. It is preferably present as fibrous cellulose, in particular wood pulp, linters, paper, and/or in the form of other natural cellulose fibers. Among the natural cellulose fibers, hemp, flax, coconut, jute, bamboo, and/or sisal fibers can be cited as advantageous. In individual cases, it may be advantageous if the cellulose is partially derivatized, with esters or ethers being preferred derivatives. The following considerations, which essentially refer to "cellulose," also apply to derivatized cellulose, unless otherwise understood. The esters can be, for example, phosphoric acid and/or nitrogen-containing esters, such as cellulose carbamate or allophonate, cellulose carboxylates, such as cellulose acetate, cellulose propionate, and cellulose butyrate, and the ethers can be carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, or, for example, cellulose 2,5-acetate. Accordingly, cellulose derivatives are also suitable according to the invention.

When "cellulose" is mentioned below or above, this term should be understood generally and also include cellulose derivatives. Cellulose derivatives are therefore also suitable for the purposes envisaged by the invention.

Of particular value for processing cellulose using the method according to the invention is a molecular weight Mw of 100,000 to 500,000 g/mol, and preferably 200,000 to 400,000 g/mol, determined in each case by GPC (gel permeation chromatography) using suitable standards. By processing higher molecular weight cellulose (Mw > 130,000), improved advantageous product properties, such as strength, elastic modulus, and stiffness, are achieved. Such a molecular weight can be adjusted, for example, by irradiating cellulose with electron beams.

For the successful implementation of the present invention, it is not necessary for further components besides cellulose and the ionic liquid to be included in the spinning mass or the cellulose fibers produced therefrom. However, additional additives can be used at various points in the process according to the invention. For example, they can The additives can be added to the coagulation medium, the spinning solution containing the cellulose, and/or in a subsequent step, for example, in a modification medium. These additives can be, for example, microcapsules, pore formers, plasticizers, matting agents, marking agents, flame retardants, bactericides, crosslinking agents, hydrophobic agents, antistatic agents, and/or colorants.

vorliegen kann. In diesen Verbindungen bezeichnen die Reste R¹, R², R³, R⁴ bzw. die Reste R¹ bis R⁸ in den Formeln (I) bis (VI), unabhängig voneinander, lineare, cyclische, verzweigte, gesättigte oder ungesättigte Alkylreste, mono- oder polycyclische, aromatische oder heteroaromatische Reste oder mit weiteren funktionellen Gruppen substituierte Derivate dieser Reste sind, wobei R¹, R², R³ und R⁴ untereinander verbunden sein können. Das Anion [Z]ⁿ“ liegt vorzugsweise in Form eines Carboxylats, Halogenids, Pseudohalogenids, Amids, in Form von Phosphorbindungen oder Nitroverbindungen vor. The ionic liquid, which is one of the essential components in the process according to the invention as a direct solvent, is not subject to any significant restrictions, provided that in combination with the cellulose, a homogeneous solution with suitable processing properties can be formed. It is particularly advantageous if the ionic liquid is a compound that can be characterized by the general formula [Q ⁺ ] _n [Z] ⁿ ", where [Q ⁺ ] denotes the cation of the ionic liquid, and as a quaternized ammonium [R ¹ R ² R ³ R ⁴ N ⁺ ], phosphonium [R ¹ R ² R ³ R ⁴ P+] or sulfonium [R ¹ R ² R ³ S ⁺ ] cation or an analogous quaternized nitrogen, phosphorus or sulfur heteroaromatic of the following formulas (I), (II), (III), (IV), (V) and (VI)

In these compounds, the radicals R ¹ , R ² , R ³ , R ⁴ and the radicals R ¹ to R ⁸ in the formulas (I) to (VI), independently of one another, denote linear, cyclic, branched, saturated or unsaturated alkyl radicals, mono- or polycyclic, aromatic or heteroaromatic radicals or derivatives of these radicals substituted with further functional groups, where R ¹ , R ² , R ³ and R ⁴ may be bonded to one another. The anion [Z] ⁿ " is preferably in the form of a carboxylate, halide, pseudohalide, amide, in the form of phosphorus bonds or nitro compounds.

A preferred development of these ionic liquids is one in which the carboxylates are represented by the formula R^Oz ", the halides or pseudohalides by the formula F", Cl", Br", I", BF ₄ ", PF ₆ ", AICI ₄ ", AI2CI7", AI3CI10", AIBr ₄ ", FeCI ₄ ", BCI ₄ ", SbF ₆ ", AsF ₆ ", ZnCI ₃ ", SnCI ₃ ", CuCI ₂ ", CF ₃ SO ₃ ", (CN) ₂ N', (CF ₃ SO ₃ ) ₂ N", CF ₃ CO ₂ ", CCI ₃ CO ₂ ", CN", SCN", OCN", the phosphorus compounds as phosphates by the formula PO ₄ ³ ", HPO ₄ ² ", H ₂ PO ₄ ", R ¹ PO ₄ ² ", HR^C ", R ¹ R ² PO ₄ ", phosphonates and phosphinates by the formula R^PO , R ¹ R ² PO ₂ ", R ¹ R ² PO ₃ ", phosphites by the formula PO ₃ ³ ", HPO ₃ ² ", H ₂ PO ₃ ", R^Ch ² ", R^PO , R ¹ R ² PO ₃ " and phosphonites and phosphinites by the formula R ¹ R ² PO ₂ ", R ^X HPO ₂ ", R ¹ R ² PO", R ^X HPO", where R ¹ and R ² have the meaning shown above.

It is furthermore advantageous if the above-described alkyl radical is in the form of a C 1 -C 18 alkyl radical, in particular an alkyl radical having 1 to 4 carbon atoms, preferably a methyl, ethyl, 1-propyl, 2-propyl, 1-butyl or 2-butyl radical, the cyclic alkyl radical is in the form of a C ₃ -C ₁₀ cycloalkyl radical, in particular in the form of a cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl radical, the unsaturated alkyl radical is in the form of a vinyl, 2-propenyl, 3-butenyl, cis-2-butenyl, trans-2-butenyl radical, the aromatic radical is in the form of a phenyl or naphthyl radical which is substituted with 1 to 3 halogen atoms, alkyl radicals having 1 to 4 carbon atoms or phenyl radicals may be substituted, and the heteroaromatic radical is in the form of an O-, S- or N-containing heterocyclic radical having 2 to 5 carbon atoms.

The following ionic liquids can be stated as being particularly suitable for the process according to the invention: imidazolium carboxylates in the form of [EMIM] [acetate], [EMIM] [propionate], [EMIM] [butyrate], [EMIM] [pentanoate], [EMIM] [hexanoate], [EMIM] [heptanoate], [EMIM] [octanoate], [EMIM] [nonanoate], [EMIM] [decanate] and/or imidazolium phosphates [MMIM] [DMP], [MMIM] [DEP], [EMIM] [DEP]. EMIM denotes 1-ethyl-3-methylimidazolium, [MMIM] 1,3-dimethylimidazolium, [DEP] diethyl phosphate, and [DMP] dimethyl phosphate. "EMIM" denotes 1-ethyl-3-methylimidazolium, "MMIM" 1,3-dimethylimidazolium, "DMP" dimethyl phosphate, and "DEP" diethyl phosphate. A particularly preferred ionic liquid in the context of the present invention is [EMIM] [octanoate].

The concentration of cellulose in the ionic liquid is within the usual range for the production of spinning solutions from ionic liquids and cellulose, i.e. in the molecular weight range of the cellulose-based polymers specified above, cellulose solutions can be processed in the concentration range between about 4 and 16, in particular between about 6 and 14 wt.% cellulose in the direct solvent, in particular in the ionic liquids.

Within the scope of the process according to the invention, it was observed that the profile structure is partially impaired by the high degree of stretching, i.e., the profile structure is less pronounced after stretching than when the spinning dope exits the nozzle. This requires that the aspect ratio of the nozzle be greater than the aspect ratio desired in the cellulose fibers produced by the process. Accordingly, it is preferred if the spinning in step (ii) takes place through a nozzle with an aspect ratio of at least 1.5, in particular in the range from 2 to 13, more preferably in the range from 2 to 8, and even more preferably 2 to 5.

To produce a desired fiber profile, spinning in step (ii) preferably takes place through a die with a slot-shaped, trilobal, tetralobal, or especially cross-shaped outlet opening. The "die" refers to the component of the extruder through which the spinning mass leaves the extruder, while "outlet opening" refers to the opening itself. Preferably, the die in the process according to the invention has a plurality of outlet openings, for example 50 or more, preferably 100 or more, and even more preferably 150 to 500 outlet openings. After emerging from the spinneret, the spinning dope is introduced into a coagulation medium, where the ionic liquid can pass into the liquid phase of the coagulation medium; this coagulates the cellulose into filaments and fibers. The coagulation medium is generally not subject to any particular restrictions, although for cost reasons it is preferred to use at least a portion of water as the coagulation medium; water acts as a non-solvent for the cellulose fibers produced. In addition to water, a quantity of another solvent can be present in the coagulation medium to optimize the coagulation rate.

For coagulation, the temperature can be adjusted for an optimal processing result, which can be determined by a professional depending on the substances contained in the coagulation medium. Generally, it is preferred that the coagulation medium be formed from a protic solvent or a mixture of protic solvents, such as, in particular, water and/or alcohols. Among the alcohols, methanol, ethanol, and/or isopropanol are particularly preferred. Furthermore, it is possible for the coagulation medium to further contain one or more carbohydrates; for details on a favorable process procedure for this purpose, reference can be made to DE 10 2013 002 833 B4, and for carbohydrates to be used appropriately, reference can be made to [0028] of this patent.

The spinning solution is discharged from the extruder and transferred into the coagulation medium at a speed that ensures a good compromise between processing speed and contact time of the spinning solution with the air in the air gap. Within the scope of the invention, this speed is preferably set to a range of 2 to 3 m/min, and in particular 2.2 to 2.5 m/min.

For drawing, it is advantageous if it takes place at a time when the filaments are still in a swollen or unwashed state.

The stretching is not restricted to a relevant extent in that it can be carried out directly in the coagulation medium by making the filaments drawn off than introduced. The temperature in the coagulation medium for optimum drawing depends on various conditions which can be determined by a professional depending on the composition of the coagulation medium. In one embodiment, the drawing takes place in a bath containing a coagulation medium which is arranged downstream of a first bath containing a coagulation medium, so that the drawing only takes place at a stage at which part of the ionic liquid has already been dissolved out of the spun mixture. The drawing itself can be achieved, for example, by introducing the fiber into a drawing area at a slower speed, e.g. via the roller, and drawing it out of this area more quickly.

Following the drawing process, the resulting fibers can be washed and dried. This allows cost-relevant solvents, especially ionic liquids, as well as any carbohydrates used, such as sugar, to be recovered.

In a further aspect, the present invention relates to cellulose fibers that were produced or can be produced by the process described above. Such cellulose fibers, or cellulose fibers as specified above, can be used for a variety of purposes, for example in textile materials such as threads, yarns, twisted yarns, and the like, as well as textile fabrics, in particular wovens, knitted fabrics, scrims, nonwovens, and batting. These textiles, and in particular the fibers or yarns, can be advantageously used as reinforcing materials in fiber-based composites.

A further aspect of the present invention relates to a device for producing profiled cellulose fibers, in particular profiled cellulose fibers as specified above, wherein the device comprises a device part for passing a spinning solution through a heatable nozzle head with at least one profiled outlet opening, a coagulation bath arranged downstream of this device part, an air gap arranged between the coagulation bath and the outlet opening and a conveyor device for drawing the cellulose fibers generated via the profiled outlet opening, wherein the profiled outlet opening Aspect ratio of the largest to the smallest cross-sectional thickness of the exit opening in the range of 1.5 to 15.

Yet another aspect of the present invention relates to the use of cellulose fibers as specified above for producing a yarn, woven fabric, or nonwoven fabric, wherein a woven fabric is produced by knitting, weaving, warp knitting, embroidery, or braiding, and the nonwoven fabric is preferably formed as a carded nonwoven fabric, in particular as a needle-punched or spunlaced nonwoven, a thermobonded nonwoven, or as a nonwoven stitchbonded fabric. Alternatively, the cellulose fibers can be processed using a paper, wetlaid, or airlaid process, or by combined processes such as combined carded-wetlaid or carded-airlaid technologies.

Yet another aspect of the present invention relates to the use of cellulose fibers as specified above for producing a compound in which the cellulose fibers are incorporated into a matrix of thermoplastic or curable polymers. Suitable thermoplastic polymers for this purpose may include, in particular, saturated polyester-based resins such as polylactic acid resins; olefin resins such as polyethylene-based resins and polypropylene-based resins; cellulose-based resins such as triacetylated cellulose and diacetylated cellulose; nylon resins, vinyl chloride resins, styrene resins, (meth)acrylic resins, vinyl ether resins, polyvinyl alcohol resins, polyamide-based resins, polycarbonate-based resins, polysulfonate-based resins, and the like. These thermoplastic resins may be used alone or may be used as mixed resins of two or more types. Curable polymers that can be used include photocurable resins or thermosetting resins, such as epoxy resins, phenolic resins, urea resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins, polyurethane resins, silicon-containing resins, polyimide resins, elastomeric resins, and the like. Thermosetting resins can also be used as a single resin or as a combination of two or more types of the aforementioned resins.

Yet another aspect of the present invention relates to the use of cellulose fibers as described above as reinforcing material in building materials. The following examples serve to further explain the invention:

Pulp with a weight-average molecular weight of approximately 600,000 g/mol was irradiated with electron beams at a radiation dose of 80 kGy to obtain cellulose with a weight-average molecular weight of approximately 300,000 g/mol. The Mw/Mn ratio of the resulting cellulose was 8.8.

From this cellulose, a spinning solution or mass with a cellulose concentration of 12 wt.% was prepared by mixing it with l-ethyl-2-methyl-imidazolium octanoate using a thin-film evaporator from VTA at 110°C.

Frequency sweep measurements were first performed on this spinning dope at different temperatures using a plate-on-plate rheometer (Anton Paar MCR 301 Rheometer) to determine the optimal spinning temperature. The frequency range was from 100 to 1 rads at a constant strain of 3%; the temperature was varied in 10°C increments from 110°C to 20°C. The 10 measurements obtained were mathematically combined into a master curve. For each temperature, the zero-shear viscosity and crossover were determined using the Carreau-Yasuda model (see Table 1).

The values determined are shown in the table. A crossover in the range of 10–50 rad s represents ideal spinning conditions for the production of profiled cellulose fibers. The corresponding zero-shear viscosities were between 1000 and 5000 Pa-s.

Table 1: Zero shear viscosities and crossover at different temperatures of the spinning mass

Cellulose Temperature Zero shear viscosity r) _o ^a Cross over co _s

[°C] [Pa ’s] [rad/s]

110 161 366

100 244 225

90 390 135

80 662 76.2 70 1186 40.7

60 2272 20.2

50 4727 9.2

40 10747 3.8

The resulting spinning solutions were processed in an extruder through various cross-profile nozzles. These nozzles had different leg lengths and widths (see Table 2 below). The air gap to the coagulation medium was set at 10 mm. The resulting fibers were then drawn at 65°C. The various processing parameters are shown in Table 2 below:

Table 2: Comparison of stretchability depending on the cross profile

Leg width Leg length Capillary max. stretch @ 65°C; Vout = 2.4 [pm] [pm] [pm] m/min [%]

Nozzle 1 70 100 400 990

Nozzle 2 70 250 400 700

Nozzle 3 90 130 508 850

The maximum drawability could be influenced by varying the spinning temperature. By modulating the spinning temperature of fibers produced using nozzle 2, maximum draws in the range of 350% (at 55°C), 700% (at 65°C), and 1250% (at 70°C) could be achieved.

When comparing the textile mechanical properties of fiber materials produced under identical conditions with the different nozzles, almost identical maximum tensile forces were observed (see Figure 1). However, significant differences were observed for the modules (0.2-0.4%), with fibers produced with nozzle 2 (70 pm, long legs) showing a higher

module (0.2-0.4%) (see Figure 2).

The textile mechanical properties (with standard deviation) determined for the different fibers produced are given in the following Tables 3 to 5: Table 3: Textile mechanical properties drawing row at nozzle 1 (70pm, short legs).

Designation Fiber 1 Fiber 2 Fiber 3 Fiber 4

1 1 1 1nozzle [n]

1 1 1 1

Temp. [°C] 65 65 65 65

Stretching [%] 600 750 890 990

Elongation [%] 4.9±0.6 4.2±0.7 4.3±0.5 3.8±0.4

Hz. Force [cN/tex] 27.3±1.6 27.0±2.3 28.8±1.4 29.5±1.7

Fineness [dtex] 6.90±0.57 6.030.43 5.15±0.42 4.67±0.3

Mod. (0.2-0, 4%) [cN/tex] 1749±95 1652±76 1750±69 1768±89 Table 4: Textile mechanical properties of the drawing row at nozzle 2.

Designation Fiber 5 Fiber 6 Fiber 7 Fiber 8 Fiber 9

Nozzle [n] 2 2 2 2 2

Temp. [°C] 65 65 75 75 75

Stretching [%] 300 600 600 930 1200

Elongation [%] 6.8±l.0 4.0±0.7 5.8±0.8 4.l±0.3 3.8±0.4

Hz. Force [cN/tex] 28.l±2.0 29.0±3.4 24.9±2.3 26.9±1.5 29.5±1.7

Fineness [dtex] 24.49± 12.74± 13.88± 10.23± 7.71±

1.00 1.53 1.10 0.73 0.63

Mod. (0.2- [cN/tex] 1992± 2120± 1567± 1777± 1846±

0.4%) 87 208 126 84 62 Table 5: Textile mechanical properties, drawing row at nozzle 3.

Designation Fiber 10 Fiber 11

Nozzle [n] 3 3

Temp. [°C] 65 65

Stretching [%] 600 750

Elongation [%] 5.5±0.5 4.3±0.6

Hz. Force [cN/tex] 26.8±1.1 26.5±1.2

Fineness [dtex] 10.84±0.47 9.23±0.54

Mod. (0.2-0, 4%) [cN/tex] 1747±50 1813±96

The cross-shaped fibers were clearly visible in all cellulose fibers produced. However, this was less pronounced in the fibers produced with nozzle 1 or nozzle 3 than in the longer-armed fibers produced with nozzle 2. It was observed that the shape of the arms appears to be greater at higher draw rates. However, with increasing spinning temperature, the shape of the arms decreases under otherwise identical spinning conditions. The profile shape for fibers spun with nozzle 2 at 65°C and drawn to 600% is shown in Figure 3.

The water retention capacity of each of the fibers produced was determined according to DIN 53814. The results of these determinations are shown in Table 6 below.

Table 6: Overview of water retention capacity

Test Nozzle Temperature Stretching Fineness WRV

[°C] [%] [dtex] [%]

Fiber 1 1 65 600 6.9 58

Fiber 2 1 65 750 6 64

Fiber 3 1 65 890 5.2 52

Fiber 4 1 65 990 4.7 61

Fiber 5 2 65 300 24.5 60

Fiber 6 2 65 600 12.7 60

Fiber 7 2 75 600 13.9 68

Fiber 8 2 75 930 10.2 60

Fiber 9 2 75 1200 7.7 55

Fiber 10 3 65 600 10.8 52

Fiber 11 3 65 750 9.2 56

Table 6 shows that the water retention capacity of all manufactured fibers is within a comparable range, regardless of fiber cross-section, fiber surface area, or fiber diameter. In comparison, the water retention capacity of lyocell fibers is approximately 60-70%, and that of hydrophilic cotton fibers is approximately 40-60%. The overview in Table 6 thus shows that, depending on the drawing and nozzle geometry, a water retention capacity comparable to that of such fibers can be achieved. However, the elastic modulus of commercial lyocell fibers is only approximately 700 cN/tex; through special spinning, elastic moduli of up to 1800 cN/tex can be achieved. Cotton fibers have an elastic modulus in the range of 300-600 cN/tex.

Claims

Claims 1. Profiled cellulose fibre with an aspect ratio of the largest to the smallest cross-sectional thickness of the cellulose fibre of at least 1.25, a fineness of at most 50 dtex and a maximum tensile strength (dry) of at least 22 cN/tex. 2. Profiled cellulose fiber according to claim 1, characterized in that the cellulose fiber has one or more of the following properties: - a maximum tensile strength (dry) in the range of 25 to 50 cN/tex, preferably 25 to 35 cN/tex, 25 to 30 cN/tex; - a maximum tensile strength (wet) in the range of 10 to 30 cN/tex, preferably 15 to 25 cN/tex, and more preferably 10 to 22 cN/tex; - an elongation of 3% to 18%, preferably 5% to 10% and even more preferably 5% to 8%; - a modulus for elongation in the range of 0.2 to 0.4% in the range of 500 to 2500 cN/tex, preferably 800 to 2000 cN/tex and more preferably 800 to 1600 cN/tex. 3. Profiled cellulose fiber according to claim 1 or 2, characterized in that the cellulose fiber has an aspect ratio in the range of 1.3 to 5 and preferably 1.5 to 4.0. 4. Profiled cellulose fiber according to at least one of claims 1 to 3, characterized in that the cellulose fiber has a fineness in the range of 2 to 20 dtex, and preferably 3 to 9 dtex and/or a largest fiber diameter in the range of 11 to 150 pm, and preferably 12 to 70 pm. 5. Profiled cellulose fiber according to at least one of claims 1 to 3, characterized in that the fiber is designed as a continuous fiber (filament) and is preferably wound up or in the form of stacks, preferably with a length of 3 to 150 mm, more preferably 15 to 120 mm and even more preferably 30 to 80 mm. 6. Profiled cellulose fiber according to at least one of the preceding claims, characterized in that the cellulose fiber has a water retention capacity according to DIN 53814: 1974 in the range of 45 to 120% and preferably 60 to 90%. 7. Profiled cellulose fiber according to at least one of the preceding claims, characterized in that the cellulose fiber has a ribbon-shaped, trilobal, tetralobal, or higher lobal profile. 8. A process for producing a profiled cellulose fiber, preferably a cellulose fiber according to at least one of claims 1 to 6, wherein the process comprises the steps of (i) producing a spinning dope from cellulose and an ionic liquid; (ii) spinning the spinning dope through a profiled nozzle, preferably via an air gap, at a temperature at which the crossover is in a range of 5 to 55 rad/s; (iii) introducing extruded fibers into a coagulation bath; and (iv) drawing the fibers produced with a maximum draw of at least 100%. 9. The method according to claim 8, characterized in that the temperature in step (ii) is adjusted so that the crossover is in the range of 8 to 50 rad/s, preferably 10 to 40 rad/s, and more preferably 13 to 35 rad/s. 10. The process according to claim 8 or 9, characterized in that the maximum stretching in step (iv) is set in the range from 100 to 1600% and preferably from 300 to 1000%. 11. The method according to at least one of claims 8 to 10, characterized in that the temperature in step (ii) is set in the range from 50 to 85°C, preferably 55 to 75°C and/or the air gap in step (ii) has a length in the range from 5 to 25 mm and preferably 8 to 15 mm. 12. The process according to at least one of claims 8 to 11, characterized in that the cellulose included in the process has a molecular weight Mw of 100,000 to 500,000 g/mol and preferably 200,000 to 400,000 g/mol, determined in each case by means of GPC (gel permeation chromatography) using appropriate standards. 13. The process according to at least one of claims 8 to 12, characterized in that the spinning in step (ii) is carried out via a nozzle with an aspect ratio of at least 1.5, preferably in the range from 2 to 13 and more preferably in the range from 2 to 8. 14. The method according to at least one of claims 8 to 13, characterized in that the spinning in step (ii) is carried out via a nozzle with a slot-shaped, trilobal, tetralobal, in particular cross-shaped outlet opening, or several corresponding outlet openings. 15. Cellulose fiber produced or producible by a process according to at least one of claims 8 to 14. 16. Apparatus for producing profiled cellulose fibers with a device part for passing a spinning solution through a heatable nozzle head with at least one profiled outlet opening, a coagulation bath downstream of this device part, an air gap arranged between the coagulation bath and the outlet opening and a conveyor device for drawing the cellulose fibers generated via the profiled outlet opening, wherein the profiled outlet opening has an aspect ratio of the largest to the smallest cross-sectional thickness of the outlet opening in the range from 1.5 to 15. 17. Use of cellulose fibers according to at least one of claims 1 to 7 for producing a yarn, woven fabric or nonwoven fabric, wherein a woven fabric is produced by knitting, weaving, warp knitting, embroidery, braiding, and the nonwoven fabric is preferably designed as a carded nonwoven fabric, in particular as a needle-punched nonwoven or spunlaced nonwoven, thermobonded nonwoven or as a nonwoven stitch-bonded fabric. 18. Use of cellulose fibers according to at least one of claims 1 to 7 as reinforcing material in building materials or for producing a compound in which the cellulose fibers are incorporated into a matrix of thermoplastic or thermosetting polymers.