Cellulose carbamate textile fibre, and use and manufacturing method thereof

Abstract

This invention relates to a method for manufacturing cellulose carbamate fabric fibers, comprising the following steps: dissolving cellulose carbamate in an aqueous alkaline medium to form a zinc-containing cellulose carbamate stock solution; spinning the cellulose carbamate stock solution into an alkaline aqueous spinning bath in a spinning unit to form filaments or tows; and drawing the filaments or tows to obtain cellulose carbamate fibers. In the spinning bath, the sodium hydroxide and sodium carbonate contents are maintained within predetermined ranges by withdrawing and recirculating a portion of the spinning bath.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing cellulose carbamate textile fibers, cellulose carbamate textile fibers that can be obtained by this method, their uses, and articles made using cellulose carbamate textile fibers. [Previous Technology]

[0002] Cellulose is the most abundant renewable organic material on Earth, exhibiting outstanding properties for fiber applications. Despite environmental challenges, the viscose process remains the most widely used technology for manufacturing regenerated cellulose fibers and membranes. Therefore, there is a need to develop sustainable textile fibers that are simpler and have improved properties than traditional manufacturing methods.

[0003] European Patent Application Publication EP 1470162 A1 describes the manufacture of cellulose carbamates from high-quality cellulose solutions. Cellulose carbamates are known as environmentally friendly alternatives for the manufacture of synthetic cellulose fibers. International Patent Application Publication

[0004] EP 1509548 A1 describes the manufacture of fibers, films, and other molded bodies from cellulose carbamates by direct dissolution in a sodium hydroxide solution and spinning the solution in an acidic spin bath. WO 2021 / 038136 A1 provides a method for pretreating cellulose for the formation of cellulose carbamates. Cellulose carbamate obtained by a carbamation process is dissolved to produce cellulose carbamate fibers by a wet spinning process. The wet spinning of the cellulose carbamate dope is carried out using an acidic spin bath optimized for the cellulose carbamate process, containing, for example, sodium sulfate and free sulfuric acid.

[0005] Document GB 2164942 B illustrates a method for dissolving cellulose carbamates and for precipitating cellulose carbamates from an alkaline solution using a precipitant solution containing sodium carbonate. The solution in the spinning and precipitation processes also contains sodium hydroxide. WO 2018 / 169479 illustrates regenerated cellulose fibers spun from an aqueous alkaline spin dope. This method incorporates a nanofiller additive to enhance the strength of the cellulose fibers. WO 2020 / 171767 also describes spinning a cellulose spin dope in an alkaline coagulation bath with a pH greater than 7.0.

[0006] Carbamate hydrolysis stops when coagulation occurs in the acidic spinning bath. When spinning into the alkaline coagulation bath, cellulose regeneration occurs gradually during the coagulation and stretching of the filament bundle. However, although shaped bodies have been successfully formed, alkaline spinning technology has so far been unable to produce fibers with satisfactory strength properties and textile quality.

[0007] Therefore, despite the many recent research and development projects in this field, there is still a need to provide alternative manufacturing methods that can better utilize textile waste materials. [Summary of the Invention]

[0008] One object of the present invention is to overcome at least some problems associated with the prior art and to provide man-made cellulose carbamate fibers with textile quality. Through the implementation of the invention, it was unexpectedly discovered that by modifying the conditions of the spin bath and the fiber stretching, man-made cellulose carbamate fibers with improved properties can be obtained. In particular, this method enables the manufacture of cellulose carbamate fabric fibers from waste material in at least a portion, and also yields fibers strong enough for use in the textile industry.

[0009] This invention is defined by the features of the independent items. Some specific embodiments are defined in the appendices.

[0010] According to one embodiment, the present invention relates to a method for manufacturing cellulose carbamate fabric fibers, comprising the following steps: - dissolving cellulose carbamate having a maximum nitrogen content of 2.5 wt% in an aqueous sodium hydroxide medium to form a cellulose carbamate dope, wherein the dope contains zinc; - spinning the cellulose carbamate dope in an alkaline aqueous spin bath in a spinning unit to form filaments or filament tows, wherein the temperature of the alkaline aqueous spin bath is in the range of 35-60°C; and - stretching the filaments or tows to obtain cellulose carbamate fibers; In this process, a portion of the alkaline spinning bath is withdrawn from the spinning unit for recycling, so that the sodium hydroxide content of the spinning bath is maintained in the range of 1.0-1.99 wt-%, and the sodium carbonate content of the spinning bath is maintained at a maximum of 30 wt-%.

[0011] According to another embodiment, the present invention relates to cellulose carbamate textile fibers obtainable by this method, and the use of cellulose carbamate textile fibers obtainable by this method in yarn, textiles, woven or knitted fabrics, textile garments, or non-woven fabrics. Furthermore, the present invention relates to yarns, textiles, woven or knitted fabrics, textile garments, or non-woven articles comprising cellulose carbamate textile fibers obtainable by this method.

Implementation Method

[0013] Man-made cellulose fiber is a fiber whose structure and properties are modified during the manufacturing process. Man-made fibers differ from natural fibers such as silk, cotton, and wool. Man-made cellulose fibers are made from the same cellulose polymers that constitute the structural fibers of materials such as cotton, hemp, flax, and wood. In the case of man-made cellulose fibers, the cellulose is obtained in a modified state, such as cellulose from wood pulping operations, or it is modified to regenerate usable cellulose-based fibers.

[0014] The cellulose carbamate fabric fibers of this invention refer to fibers in the form of staple fibers, shortcut fibers, flocks, filament yarns, or tows of filaments. The cellulose carbamate fabric fibers of this invention also refer to fibers used in non-woven applications. The term "filament" in this description should be understood to include filament tows.

[0015] Linear density (a measure of the mass of fiber per unit length) is used by fiber manufacturers as a measure of fineness. Linear density, expressed in decitex (dtex), is the weight (in grams) of 10,000 m of fiber. Decitex is an approved SI unit for linear density. Linear density in dtex is measured according to ISO 1973:2021.

[0016] Tenacity is a measure of the strength of a fiber. It is usually defined as the ultimate (breaking) force of the fiber (in grams-force units) divided by the linear density. Tenacity is defined as the ratio between the ultimate (breaking) force of the specimen and the load and the linear density. The toughness of a specimen can be expressed in the following units: cN / dtex, grams / tex, grams / denier, Newton / tex, etc. Fiber toughness (cN / dtex) is measured according to ISO 5079:2020.

[0017] In textiles, the term initial modulus describes the initial resistance of a fabric material to extension, and it is measured using ISO 5079:2020. In other words, it is a measure of the fiber's resistance to small initial extension. When a fiber has high resistance to stretching, it will have a high modulus. The tangent of the angle between the initial curve and the horizontal axis is equal to the ratio of stress to strain. This ratio is called the initial modulus, but in textile science, it is known as the initial Young's modulus. The initial modulus of a textile material depends on the fiber's chemical structure, crystallinity, orientation, etc. The initial modulus is tan α = stress / strain.

[0018] Elongation at break is the elongation of a fiber caused by breaking force. Breaking extension (%) = breaking extension x 100 / original length of the sample. It is measured using ISO 5079:2020.

[0019] The nitrogen content in cellulose carbamate fabric fibers or cellulose carbamate refers to the amount of nitrogen chemically bonded to cellulose as carbamate groups. The nitrogen content (wt% of total weight) is measured according to SFS 5505:1988.

[0020] The average intrinsic viscosity, expressed in ml / g, was determined by ISO 5351:2010 (CED viscosity measurement), and the average value is the arithmetic mean. The content of p-terephthalate and / or p-terephthalic acid and / or unhydrolyzed or partially unhydrolyzed polyester (in wt%) was determined by gas chromatography-mass spectrometry (GC-MS), as explained in more detail in the experimental section (Examples 4 and 6).

[0021] In this description, when weight percentage (wt-%) is used, it means the weight percentage in the relevant material unless otherwise indicated.

[0022] Raw material can be various types of cellulose-rich textile waste, such as post-consumer waste, pre-consumer waste, industrial textile waste, or side stream from textile manufacturing. Textile waste can be collected and sorted. The terms recycled waste material and waste material are also used interchangeably.

[0023] Unless otherwise specified, the term hot bath shall mean a bath containing a liquid in the range of 75 degrees Celsius to 100 degrees Celsius.

[0024] According to the first embodiment, the present invention relates to a method for manufacturing cellulose carbamate fabric fibers, comprising the following steps: - dissolving cellulose carbamate having a maximum nitrogen content of 2.5 wt% in an aqueous sodium hydroxide medium to form a cellulose carbamate dope, wherein the dope contains zinc; - spinning the cellulose carbamate dope in a spinning unit into an alkaline aqueous spin bath to form filaments or filament tows, wherein the temperature of the alkaline aqueous spin bath is in the range of 35-60°C; and - stretching the filaments or filament tows to obtain cellulose carbamate fibers; Specifically, by withdrawing a portion of the alkaline spinning bath from the spinning unit for recycling, the sodium hydroxide content of the spinning bath is maintained in the range of 1.0-1.99 wt-%, and the sodium carbonate content of the spinning bath is maintained at a maximum of 30 wt-%.

[0025] "Spinning cellulose carbamate solution into an alkaline aqueous spinning bath in a spinning unit to form filaments or bundles" means that the cellulose carbamate is coagulated and formed into filaments when extruded through a spinneret.

[0026] This method is based on research on the pre-treatment of cellulose carbamates, their dissolution in NaOH, and wet spinning of fabric fibers using an alkaline spinning bath. It has been observed that the spinning of carbamate fibers can be enhanced by changing the composition of the spinning bath, thereby obtaining cellulose carbamate products with modified properties. If coagulation in an alkaline spinning bath is slow, fibers, filaments, or tows with specific fabric fiber properties cannot be obtained; in other words, a linear density of 0.8-1.8 dtex, a toughness of 2.0-2.9 cN / dtex, and an initial modulus of 50-120 cN / dtex (optionally) cannot be achieved. Therefore, it is important that coagulation occurs at an optimal rate.

[0027] To accelerate fiber cohesion, the amount of sodium hydroxide needs to be at a certain low level. The portion of the alkaline spinning bath drawn from the spinning unit (which has the composition of the spinning bath at that moment and location) contains sodium carbonate and less than 2 wt% sodium hydroxide, preferably 1.5 to 1.99 wt%, particularly 1.6 to 1.9 wt% sodium hydroxide. The sodium carbonate content of the spinning bath is maintained at a maximum of 30 wt%.

[0028] In prior art solutions, such as WO 2020 / 171767, the coagulation bath contains sodium hydroxide, and the provided numerical range is preferably 3-10 wt% sodium hydroxide. Examples of provided sodium hydroxide content are 5.3 and 5.6 wt%, which are significantly higher than those of the present invention. The toughness of the urethane fibers obtained in that document is 16.9 and 18.9 cN / dtex (Table 1), i.e., 1.69 and 1.89 cN / dtex. The toughness values ​​obtained by the method of this invention can yield urethane fibers with a toughness of at least 2.0 cN / dtex, or even at least 2.3 cN / dtex. Toughness is a measure of fiber strength; therefore, this cellulose urethane fiber with high strength can be used with other fibers commonly used in yarn and fabric manufacturing, and at least 2.0 cN / dtex is considered an acceptable strength for fabric fibers. This limitation is not met in the examples of WO 2020 / 171767. Furthermore, WO 2020 / 171767 teaches that zinc typically begins to precipitate (in the form of zinc hydroxide) when the NaOH concentration in the washing liquid reaches approximately 2 wt-%, thus indicating to those skilled in the art that the amount of sodium hydroxide should not be lower than 2 wt-%.

[0029] In the prior art disclosed in WO 2018 / 169479, which generally pertains to regenerated cellulose fiber and not just cellulose carbamates, the preferred spinning bath is diluted sodium hydroxide (the concentration of sodium hydroxide is substantially lower than that in the spinning solution, provided to be 6-9%), and the spinning bath is preferably maintained at a temperature of about 10-40°C. Examples of cellulose used in the document for preparing the spinning solution include natural cellulose, such as pulp, cotton, and cotton linter; and regenerated cellulose obtained from cellulose solutions such as viscose or lyocell. Cellulose can be derivatized, for example, carbamized. The document does not provide any examples or specific values ​​for the sodium hydroxide concentration in the spinning bath. Only wet tensile strength is provided, but no example of how to obtain that equivalent value is provided.

[0030] Document GB 2164942 B mentions a maximum NaOH content of 3 wt-%, and also mentions values ​​as high as 5-6 wt-% in the spinning bath, and the use of 3 wt-% in examples to manufacture urethane fibers with completely satisfactory properties according to the patentee. The properties are not specifically described. Prior art therefore provides a significantly higher amount of sodium hydroxide in the spinning bath.

[0031] Compared to prior art, in the method of this invention, spinning is optimized for cellulose carbamate to obtain optimal fiber properties, most importantly, the maximum strength of the resulting fiber. Therefore, one objective is to allow a portion of the zinc to dissolve in the spinning bath and be recycled, and for a portion of the zinc to be removed from the spinning bath along with the fiber or filament, and subsequently washed out and individually recycled. This minimizes the amount of zinc precipitated in the spinning bath. Furthermore, even with a low sodium hydroxide content in the spinning bath, the temperature of the spinning bath (i.e., 35-60°C) has been optimized to accelerate fiber formation and simultaneously increase zinc solubility. Thus, the selected sodium hydroxide content and temperature in the spinning bath have been observed to result in improved outcomes.

[0032] A preferred (1.5 to 1.99 wt%) or better (1.6 to 1.9 wt%) range of sodium hydroxide also minimizes zinc precipitation in the spinning bath. Another advantage of using a preferred range of sodium hydroxide in the spinning bath is that recycling the spinning bath remains economically viable within this range. If the sodium hydroxide content in the spinning bath is not maintained at a minimum of 1.0 wt%, the volume of the spinning bath requiring recycling (i.e., treatment to reduce the amount of sodium hydroxide) would be too large for commercial use. In fact, the recycling of the spinning bath involves various precipitation and evaporation steps, which not only require initial equipment investment but also increase operating costs and energy demands. Therefore, it is also important to try to avoid zinc remaining in the spinning bath.

[0033] Therefore, a fundamental feature of the present invention is the recycling of the spinning bath, and through this recycling, the sodium hydroxide and sodium carbonate contents of the spinning bath are maintained within the specified range. In practice, the cellulose carbamate stock solution is alkaline, therefore sodium (especially sodium hydroxide) also enters the spinning bath along with the cellulose carbamate stock solution, thereby increasing the sodium hydroxide content of the spinning bath. Therefore, the amount of sodium hydroxide in the recycled spinning bath (i.e., the spinning bath with reduced sodium hydroxide content) needs to be lower than the amount of sodium hydroxide required in the spinning bath. Zinc is also recovered and recycled to the cellulose carbamate stock solution.

[0034] During the use of this method, the amounts of sodium hydroxide and sodium carbonate in the spinning bath vary in different parts of the spinning bath because sodium hydroxide is added to the spinning bath (in the dope). The amounts defined above are the arithmetic average of the amounts in the spinning bath.

[0035] A portion of the spinning bath may be removed from the spinning bath at any suitable location or at several different locations, such as from one or more points at the bottom of the spinning bath or as an overflow of the spinning bath. A portion of the spinning bath may also be removed from the spinning bath (i.e., the container used for spinning) or from the recycling conduit.

[0036] Furthermore, the cellulose carbamate solution preferably possesses certain qualities, such as suitable viscosity. In practice, if the viscosity of the solution exceeds 15 Pas (at 20 degrees Celsius), the handling of the solution (pumping, filtration, air removal, etc.) becomes extremely difficult. The concentration of cellulose carbamate in the spinning solution also needs to be sufficiently high, preferably at least 8.0 wt% for optimal spinning. The viscosity of the cellulose carbamate solution is increased by impurities, unhomogeneous raw material, and the high molecular weight of the cellulose chains. Therefore, according to one embodiment, cellulose carbamate has a polydispersity index value (also known as polydispersity) in the range of 2.0 to 5.0, preferably 2.0-4.0, and more preferably 2.0-3.5, as measured by gel permeation chromatography (GPC) / size exclusion chromatography (SEC), and an average intrinsic viscosity of 147 to 225 ml / g and 161 to 197 ml / g, as measured by CED viscosity measurement according to ISO 5351:2010. These properties are particularly important when using waste materials, as in a preferred embodiment, because tailoring the properties of cellulose carbamate allows for the production of high-quality stock solutions. Therefore, in order to obtain the optimal properties of cellulose carbamate fibers, the viscosity of the spinning solution should be at most 15 Pas (at 20 degrees Celsius). This requires the cellulose carbamate to have the aforementioned polydispersity and intrinsic viscosity, that is, to have a homogeneous and sufficiently narrow molecular weight distribution and a sufficiently small particle size.

[0037] The polydispersity index can be modified, for example, by adjusting the temperature, residence time and acid concentration in the acidic treatment step, by adjusting the pH and ozone charge in the ozone bleaching and / or decolorization steps, by adjusting the hydrogen peroxide charge, pH and residence time in the hydrogen peroxide bleaching step, and / or by adjusting the pH and alkalinity, residence time, urea charge, carbamation temperature and pressure in the carbamation step.

[0038] According to one embodiment, the cellulose carbamate comprises a cellulose carbamate obtained from cellulose-containing waste material, preferably selected from the group consisting of textile waste, paper waste, cardboard waste, agricultural waste, and mixtures thereof, and preferably in an amount of at least 25 wt% and more preferably at least 50 wt% of the cellulose carbamate. Waste material means materials collected for recycling, such as used textiles, paper, or cardboard. Agricultural waste means various plant-based materials that cannot be used as human or animal food, such as crop residue, weeds, leaf litter, sawdust, and forest waste. Additionally, straw can be used as a raw material.

[0039] According to one embodiment, the cellulose carbamate comprises cellulose carbamate obtained from textile waste, in an amount of at least 50 wt% and preferably at least 90 wt% of the cellulose carbamate. According to one embodiment, the raw material for the textile fiber is 100% textile waste, that is, only textile waste is used as the raw material. Therefore, the fiber of the present invention and its manufacturing method can produce textile fibers that contain recycled material and still have properties that make them usable in the textile industry (such as for weaving).

[0040] The cellulose-based material may comprise virgin cellulose and / or may comprise recycled cellulose from sources such as jute, hemp, hemp, kenaf, cotton, bagasse, and such sources. Manmade cellulose carbamate fiber according to the embodiment has good resistance against wear, i.e., good strength properties. The fiber has an initial modulus similar to that of cotton, and the fiber of the embodiment described herein thus provides good strength properties for threads, yarns, and fabrics made by the combination of virgin cellulose (e.g., cotton) and intertwine.

[0041] In one embodiment, the cellulose urethane fabric fiber contains 90 wt% or more, particularly 95 wt% or more, of cellulose on a dry weight basis. Non-cellulose components such as plastics, nylon, polyethylene, polypropylene, elastane, and potentially nitrogenous impurities such as biuret may also be present in small amounts. Furthermore, spinning finishing chemicals are used to improve processability, for example, in carding and / or yarn production. Optionally, additional additives may be incorporated into the cellulose urethane fabric fiber. Optional chemicals may be used to modify processability and / or to modify the physical properties of the final product, such as tensile strength, modulus, or elasticity. Optional chemicals may be used as tracers. Processing aids, surfactants, lubricants, wetting agents, stability, color and brightness modifiers, delustrants (such as titanium dioxide, for example anatase or rutile titanium dioxide), dyes, pigments, flame retardants, fillers, antistatic agents, and auxiliaries used to reduce fiber friction can also be found in cellulose urethane fabric fibers.

[0042] In another embodiment, the cellulose-based material comprising recycled waste material, preferably at least 50 wt-%, preferably at least 75 wt-%, the cellulose of the cellulose-based material is formed from recycled textile waste. Manmade fiber may be combined with virgin cotton fiber and / or mechanically recycled cotton fiber, which can be intertwine to provide thread or yarn with properties of concern. Thus, man-made fibers (e.g., as deemed necessary to be manufactured from chemically recycled cotton) may be used as a substitute for virgin cotton that is at least a portion of threads, yarns and fabrics, and other objects comprising cellulose aminoformate fibers.

[0043] In practice, according to one embodiment, the raw material of at least 50 wt-% of the fabric fiber is a cellulose-containing waste, and at least 50 wt-% of the cellulose-containing waste is a fabric waste. At least 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 wt-% of cellulose-containing waste may also be used as feedstock. Of the waste containing cellulose, at least 50 wt-% is fabric waste, and the fabric waste may be at least 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 wt-% of cellulose-containing waste. As discussed below, cellulose-containing scraps may also include, for example, paper or cardboard scraps, or polycotton blends.

[0044] Cellulose may come from various sources and in various forms of pulp (pulp). In one embodiment, cellulose is selected from the group consisting of chemical pulp, mechanical pulp, thermomechanical pulp, chemical thermomechanical pulp, and mixtures thereof.

[0045] In another embodiment, the chemical pulp is selected from the group consisting of organic solvent pulp, soda pulp, dissolving pulp, kraft pulp, sulfite pulp, hot water extraction pulp, and mixtures thereof. In this embodiment, paper grade pulp is used. In another embodiment, dissolving grade pulp is used. Recycled pulp, such as deinked pulp, may also be used in the embodiments. In one specific embodiment, the cellulose is dried dissolving pulp.

[0046] The source of feedstock may be virgin form of chemical or dissolving pulp or recycled feedstock, such as chemical or dissolving pulp containing recycled paper and / or paperboard.

[0047] Natural plant fibers, such as those in or in the form of chemical pulp or dissolving pulp, can also be used as feedstock. Natural plant fibers can be derived in their virgin form or from fabrics containing natural plant fibers or fabrics containing recycled natural fibers. Natural plant fibers include seed fibers such as cotton and kapok; bast fibers such as hemp, jute, kenaf, ramie, abaca, and flax; leaf fibers such as manila, sisal, pineapple, and banana; and fruit fibers such as coir.

[0048] In one embodiment, the cellulose is obtained from recycled cellulose selected from the group consisting of paper, paperboard, cotton, cotton linter, wheat straw, rice straw, corn stover, hemp, kenaf, bagasse, bamboo, flax, jute, and mixtures thereof. This embodiment of the method is particularly effective for the pre-treatment of demanding pulps with multiple fibril layers, such as cotton, cotton linter, hemp, flax, linen, and other stalk and seed fibers.

[0049] Similarly, the virgin source of cellulose also applies. Therefore, in one embodiment, cellulose is obtained from virgin cotton, virgin cotton linter, virgin wheat straw, virgin rice straw, virgin corn stover, virgin hemp, virgin kenaf, virgin bagasse, virgin bamboo, virgin flax, virgin jute, and mixtures thereof.

[0050] The embodiment relates to the manufacture of cellulose amino ester fabric fibers. In one embodiment, the method includes the following steps: pre-treating a cellulose-based material; performing cellulose carbamation to form cellulose carbamate; providing a cellulose carbamate solution by dissolving the cellulose carbamate in an aqueous alkaline medium to form a dope; spinning the cellulose carbamate solution by feeding the dope into a spinning unit in an exhibiting aqueous spin bath; coagulating the cellulose carbamate from the dope into an aqueous alkaline spin bath to form cellulose carbamate filaments or filament tows; stretching the filaments or tows in one or more stretching units; and, as needed, washing in one or more washing units. The process involves washing and cutting the fibers as needed in a unit to obtain cellulose carbamate fibers. Cellulose carbamate fabric fibers produced by this method can be in the form of filaments or staple fibers.

[0051] Cellulose carbamates can be prepared by pre-treating cellulose-based materials and by cellulose carbamation of the pre-treated cellulose-based materials. In one embodiment, the pre-treating of the cellulose-based fabric material involves mechanically treating it to a predetermined particle size, subjecting the mechanically treated material to acidic and alkaline treatments in a desired order in cooking liquor, and, if necessary, bleaching or other decolorization treatments. In the embodiment, the cellulose pre-treating may include the following steps: providing a mixture comprising cellulose and a liquid, and mechanically working the mixture, for example, by shear mixing in a continuous mechanical mixing device. This pre-treating method is disclosed, for example, in WO 2021 / 181007.

[0052] During the treatment of cellulose, the method includes providing a mixture having a solid content, the mixture comprising cellulose and liquid, the mixture preferably having an initial solid content of at least 50% by weight of the mixture, more preferably 50% by weight or more of the mixture, such as 51% by weight, 52% by weight or, for example, 55% by weight of the mixture, preferably at least 65% by weight of the mixture, particularly up to 75% by weight of the mixture, preferably up to 71% by weight or 72% by weight or 73% by weight or 74% by weight of the mixture. Mechanical working of extra-high consistency pulp (compared to low consistency pulp) provides improved dislocation of lamellae within the fiber cell wall, resulting in improved absorption of chemicals (such as urea) at the molecular level within the mixture or pulp. An initial solids content of at least 50 wt% ensures efficient handling of cellulose, i.e., sufficient shear force acting on the cellulose wall to effectively break down the cell wall and improve the accessibility of solvents and chemicals to the cellulose fibrils. Initial solids contents below 50 wt%, such as less than about 45 wt%, result in less efficient handling of cellulose. Therefore, a solids content of 50-75 wt% is advantageous when adding urea. In the embodiment, the solid content preferably does not exceed 90% by weight of the mixture, and more preferably does not exceed 75% by weight of the mixture. Maintaining a high consistency pulp with a solid content not exceeding 90% by weight of the mixture, and more preferably not exceeding 75% by weight of the mixture, ensures that hornification or recrystallization caused by deactivation due to the loss of free hydroxyl groups does not occur, thus preventing the cell wall structure from closing and thus preventing the absorption of chemicals.

[0053] Within the above limits, the space is sufficient for shear force to act on cellulose without tearing the fibrils from the cellulose surface, thus improving the accessibility of the fibrils on the fiber cell walls to solvents and chemicals, which is optimal. A mixture with the solids content within the above limits is optimal for cotton, for example because the six-layer fibril structure does not become soaked at such a solids content. When cotton is soaked through, the fibril structure is locked and becomes more difficult to break, thereby improving the accessibility of cellulose carbamate fibers.

[0054] Carbamation can be performed, for example, as disclosed in Finnish Patents FI 112869, FI 112795 and Finnish Patent Application FI 20195717.

[0055] The carbamate group is stable under slightly alkaline, neutral, and acidic conditions (e.g., under alkaline spinning and stretching conditions). The carbamate group hydrolyzes under concentrated alkaline conditions (e.g., dissolved cellulose carbamate in an aqueous alkaline solution having, for example, a dope containing at least 6.5% by weight of NaOH). The cellulose carbamate begins to hydrolyze upon dissolution under alkaline conditions used to manufacture the dope, and some carbamate groups hydrolyze during the dissolution and deaeration of the dope. Higher temperatures in the stock solution and longer delays between dissolving and coagulation result in a higher rate of hydrolysis and a lower amount of bound carbamate groups in cellulose (i.e., the nitrogen content bound to cellulose). The hydrolysis rate determines the degree of substitution of the cellulose carbamate. In an embodiment, the nitrogen content of the cellulose carbamate can be adjusted by changing the dissolution conditions, such as time, temperature, and / or sodium hydroxide concentration. The nitrogen content used in the wet spinning of the cellulose carbamate is adjusted to produce textile-quality fiber.

[0056] In some embodiments, the cellulose carbamate has an intrinsic viscosity of 147 to 225 ml / g, preferably 161 to 197 ml / g, based on a CED viscosity measurement according to ISO 5351:2010. These intrinsic viscosities correspond to an average degree of polymerization (DP) of 181 to 290, and 200 to 250, respectively. For a cellulose carbamate suitable for wet spinning of fibers, the degree of polymerization of the cellulose carbamate is preferably reduced from conventional values ​​to the range described herein.

[0057] According to another embodiment, the nitrogen content of the cellulose carbamate, as measured according to SFS 5505:1988, is 0.5-2.0 wt-% of the total weight of the cellulose carbamate, preferably 0.8-1.5 wt-%.

[0058] In one embodiment, the polydispersity (PD) of the cellulose carbamate is adjusted by an acid, such as a mineral acid or an organic acid or a combination of acids. Sulfuric acid can be used as the acid for adjusting the PD. It is advantageous for the feedstock to have an optimal molecular weight distribution by including the PD adjustment via an acidic treatment step in the preparation of the cellulose feedstock, or for the feedstock to be treated with acid before mixing cellulose and urea in carbamate esterification, preferably before alkaline treatment for at least partial hydrolysis of the polyester. Cellulose carbamates with polydispersity indexes ranging from the conventional value (typically 8-11) to values ​​in the range of 2.0 to 5.0, preferably 2.0 to 4.0, and most preferably 2.0 to 3.5 provide fibers with modified tensile strength. Fibers with modified yield tenacity can be obtained by using cellulose carbamate polymers with a narrower molecular weight distribution (lower polydispersity index) than materials containing a wider molecular weight distribution and higher average intrinsic viscosity (i.e., the property disclosed herein). The solubility of cellulose carbamates with optimal average degree of polymerization and optimal polydispersity is improved due to a more uniform cellulose carbamate solution. The nitrogen content of cellulose carbamate can be changed, for example, by adjusting the pH and alkalinity, residence time, urea charge, carbamate temperature and / or carbamate pressure in the carbamate esterification step.

[0059] Following pre-treating and carbamation to provide cellulose carbamate, in one embodiment, the carbamate is dissolved in an alkaline aqueous medium to provide a cellulose carbamate stock solution. In one embodiment, the cellulose carbamate is dissolved in an aqueous alkaline solution prepared from sodium hydroxide and zinc salts (preferably zinc oxide and / or zinc hydroxide). The addition of zinc has been shown to improve the solubility of cellulose carbamate and the stability of the cellulose carbamate solution. The alkaline solution is prepared from sodium hydroxide and zinc oxide and / or zinc hydroxide, thereby forming a zincate. Therefore, in the embodiment, the alkaline solution contains sodium zincate.

[0060] According to one specific embodiment, the cellulose carbamate stock solution comprises 8-11 wt-%, preferably 8.5-10 wt-%, of cellulose carbamate, 5-8 wt-%, of sodium hydroxide, and 0.08-1.6 wt-%, preferably 0.08-1.2 wt-%, of zinc. The stock solution may also contain processing aids and / or other additives. The weight percentage (wt-%) is calculated from the total weight of the cellulose carbamate stock solution. If zinc oxide (ZnO) is used, the amount is 0.1-2 wt-%, preferably 0.1-1.5 wt-%. Other zinc compounds, such as zinc hydroxide or a mixture of zinc oxide and zinc hydroxide, may also be used to prepare sodium zincate. In fact, cellulose carbamate is soluble in an aqueous alkaline solution prepared from sodium hydroxide and zinc oxide.

[0061] According to one embodiment, the solution has a viscosity of 15 Pas (at 20 degrees Celsius) or lower, preferably in the range of 4-15 Pas, and more preferably 4-10 Pas, as measured by ASTM D1343-93:2019. These conditions are considered most suitable for forming strong textile fibers of good quality because (in conjunction with the spinning bath) it ensures the formation of fibers or filaments at an appropriate rate, which in turn ensures that they can be stretched to a sufficient degree. These fibers or filaments can therefore be stretched to a suitable draw ratio. Due to the high dry matter content, which is sufficient to cause rapid coagulation of the fibers, the amount of cellulose carbamate in the solution has indeed been observed to be advantageously in the range of 8-11 wt%.

[0062] According to one embodiment, the sodium hydroxide content of the spinning bath is maintained in the range of 1.0-1.99 wt%, preferably 1.5-1.9 wt%. According to another embodiment, the alkaline spinning bath contains sodium hydroxide and sodium carbonate in a weight ratio of 1:11-1:20. According to yet another embodiment, the sodium carbonate content of the spinning bath is maintained in the range of 22-30 wt%, preferably 23-29 wt%, particularly 24-28 wt%. According to a preferred embodiment, the sodium hydroxide content of the spinning bath is maintained in the range of 1.0-1.99 wt%, and the sodium carbonate content of the spinning bath is maintained in the range of 22-30 wt%. According to another preferred embodiment, the sodium hydroxide content of the spinning bath is maintained in the range of 1.5-1.9 wt%, and the sodium carbonate content of the spinning bath is maintained in the range of 23-29 wt%, or 24-28 wt%. The portion of the alkaline spinning bath extracted from the spinning unit thus contains at least 22 wt%, preferably at least 23 wt%, and particularly at least 24 wt% sodium carbonate. The alkaline spinning bath thus contains sodium carbonate in the range of 22-30 wt%, preferably in the range of 23-29 wt%, and particularly in the range of 24-28 wt%.

[0063] According to another embodiment, the temperature of the alkaline spinning bath is 40-55°C, preferably 45-50°C, to accelerate coagulation. Even with a low sodium hydroxide content in the spinning bath, it has been observed that these preferred temperatures of the spinning bath further accelerate fiber formation while increasing the solubility of zinc.

[0064] Essentially necessary for this method is that the composition of the spinning bath is maintained within given values ​​for sodium hydroxide and sodium carbonate, as well as the temperature. Furthermore, it is preferable to remove any precipitated zinc particles from the spinning bath, for example, by filtering. Similarly, if any sodium carbonate crystallizes, the crystals are removed. In addition, to maintain a consistent composition in the coagulation bath, carbon dioxide can be flushed into the coagulation bath during the process. Carbon dioxide reacts with free sodium hydroxide to form sodium carbonate.

[0065] Recycling to reduce the sodium hydroxide content in the withdrawn portion of the spinning bath may include removing crystals and / or precipitates and / or impurities, or this may be performed as a separate step. The sodium hydroxide content in the withdrawn portion of the spinning bath is reduced by first partially removing water and crystallized sodium carbonate, for example, by vacuum crystallization combined with evaporation and lowering the temperature, and then diluting the concentrated sodium hydroxide (containing zinc) to the desired level for reintroduction into the process.

[0066] Following the recycling treatment, at least a portion of the recycled alkaline spin bath is preferably returned to the spinning unit. The sodium hydroxide content of the returned portion is preferably 0.2-1.9 wt-%, i.e., lower than the maximum content of the spin bath. A lower sodium hydroxide content is preferred because sodium hydroxide preferably enters the spin bath primarily in the (cellulose carbamate) spinning solution. Similarly, the sodium carbonate content of the returned portion is preferably lower than 30 wt-%. The recycled alkali recovered from the spin bath can also be used to form the cellulose carbamate solution, or zinc can be removed separately from the recycled alkaline spin bath.

[0067] A portion of the recovered sodium hydroxide (preferably containing a small amount of zinc still in dissolved form) may also be recycled to cellulose carbamate dissolution. Recycling may therefore also include the separation of sodium carbonate from sodium hydroxide. The different components of the spinning bath can also be completely separated from each other and reused in the dissolution unit or spinning unit.

[0068] According to one embodiment, after coagulation, the nitrogen content of the cellulose carbamate filament is in the range of 0.40-1.0 wt%. The cellulose carbamate is therefore at least partially hydrolyzed before spinning, thus the carbamate content in the fiber or filament is at the correct level and / or the need for reducing the nitrogen content of the fiber or filament as a post-treatment is lower.

[0069] According to one embodiment, spinning has a spinneret draw ratio in the range of 0.75-1.4, preferably 0.8-1.2. Furthermore, the total stretching in the stretching unit after the filament or filament tow has been condensed can be at least 70% of the length, preferably greater than or equal to 90% of the length, particularly greater than or equal to 95% of the length, or 70-120% of the length. The stretching unit is preferably a bath containing a hot liquid or a liquid. An alkaline liquor containing a bath with a pH value greater than 7 in the stretching unit may, for example, contain sodium hydroxide and sodium carbonate in amounts maintained at approximately 2 / 3 the level of the amount in the spinning bath.

[0070] In a spinning bath, cellulose carbamate is aggregated into cellulose carbamate filaments, preferably through one or more spinnerets having multiple pores. These filaments can be recovered from the spinning bath and stretched, optionally cut into fibers, and, if necessary, subjected to washing, bleaching and / or decolorization and / or spin finish after-treatment. The spinnerets may have a hole diameter of 45-60 µm, preferably 50-55 µm. The spinneret draw ratio (Dr) in alkaline cellulose carbamate spinning is adjusted by the dope composition and spinning conditions to ensure sufficiently rapid cellulose regeneration. Spinning is carried out with a nozzle extension ratio in the range of 0.75-1.5, preferably 0.8-1.2.

[0071] Based on the purpose of the implementation, - the draw ratio is a ratio between the take-up roller and the extrusion rate, and - the draw ratio is Dr=v, take-up / v, extrusion; where v is the speed, that is, the speed at which the spindle enters and leaves the nozzle. Where, a = 1.1150(1 + fiber moisture -% / (100 + fiber moisture -%), fiber moisture -% = expected to be 13.0% b = 1.1350(1 + fiber shrinkage -% / 100), fiber shrinkage -% = expected to be 13.5% ρ = density of spinning solution at feeding temperature (kg / m3) α = cellulose carbamate content of spinning solution (wt-%) = spinneret hole diameter (µm) DTEX = linear density of filament (dtex) Ω = total godet stretching (%) measured between the first and last godet rollers.

[0072] The main purpose of filament drawing is to produce filaments with the desired strength by inducing sufficient orientation of polymer molecules along the axial direction. A high degree of orientation of cellulose molecules often increases fiber modulus and tenacity. Therefore, when fibers are spun into an alkaline spinning bath, fiber properties (such as fiber form, molecular orientation, and fiber strength) can be manipulated during coagulation and stretching, depending on the alkalinity, temperature, and residence time at each step. Further post-hydrolyze treatments (such as washing) and further after-treatment regeneration affect the nitrogen content of the finished fiber. Cellulose carbamate filament bundles are stretched in the first spinning bath or immediately after the first spinning bath to improve the final initial modulus and toughness of the fiber. The shape of the fiber can be controlled by adjusting the degree of substitution of the cellulose carbamate entering the spinning process and the stretching conditions. For example, roundish oval, bean, or lobed fibers can be obtained by controlled spinning and stretching of nitrogen-containing cellulose carbamate, resulting in a smooth surface.

[0073] In one embodiment, dissolved cellulose is wet-spun, and the filaments or filament tows are stretched in a stretching unit. In a specific embodiment, the stretching bath is a hot bath with a temperature of 75-100°C, preferably 85-95°C, and more preferably about 90°C. The stretching bath can be the same as the spinning bath, but typically has a lower concentration of sodium hydroxide and sodium carbonate. For example, if the two baths are common, the parts are preferably partially divided and can be operated on a counter-current principle. Thus, both the spinning bath and the stretching bath are vessels, usually open at the top, while the stretching bath is usually covered with a lid, containing a hot liquid at a given temperature (or a narrow temperature range), through which the fibers or filaments are immersed, and usually under stretching.

[0074] The stretching unit may contain one or more stretching baths, which typically contain sodium hydroxide and sodium carbonate in approximately two-thirds the amount found in the spinning bath. Therefore, the amount of sodium hydroxide in the stretching unit is approximately 0.66-1.32 wt%, and the amount of sodium carbonate is less than 20 wt%, such as 14.5-19.9 wt%. An optimal salt concentration is maintained in the stretching bath to enhance filament or filament tow formation under stretching. (Horizontal) The amounts of sodium hydroxide and sodium carbonate vary in the stretching bath. A portion of the more concentrated spinning bath composition drifts into the stretching bath along with the fibers or filaments. Thus, stretching bath balance is maintained by water and / or a circulating salt composition. The amount of sodium hydroxide and sodium carbonate returned to the stretching bath must be lower than the required amount of sodium hydroxide and sodium carbonate in the stretching bath circulation. The above amounts are the arithmetic average of the amounts in the stretching bath.

[0075] In a suitable embodiment, the filament or tow is stretched in a stretching unit by at least 70% of length, preferably greater than or equal to 90% of length, particularly greater than or equal to 95% of length, or typically 70-120% of length, preferably 90-120% of length, particularly in a hot bath. Length stretching refers to total godet stretching caused by adjusting the stretching stress of the filament or tow between rotating rollers with different circumferential speeds. For example, the circumferential speed of the first roller is 25 m / min and the speed of the last roller is 50 m / min, thus resulting in godet stretching of 100% of length. When the temperature of the stretching bath is 75-100°C, such high levels of stretching help to provide products with high initial modulus.

[0076] The carbamate groups are hydrolyzed in an alkaline bath. Thus, since the regeneration of carbamate cellulose occurs during coagulation, stretching, and / or after-treatment, in one embodiment, fiber properties can be manipulated during regeneration, particularly using conditioned stretching and / or conditioned after-treatment. When spinning in an alkaline coagulation bath, cellulose regeneration typically occurs gradually during the coagulation and stretching of the tow, with the aim of ensuring that the cellulose is sufficiently regenerated at the start of spinning to allow for adequate stretching.

[0077] In one embodiment, nitrogen removal can be carried out continuously during the filament formation phase. Spinning parameters and stretching affect fiber orientation, crystallinity, and the final shape of the fabric fibers, thus affecting the mechanical properties of the fibers. In another embodiment, the nitrogen content of the final product can be adjusted during the washing and after-treatment stages, particularly in the alkaline washing step, to remove (hydrolyze) most of the residual carbamate groups. In a preferred embodiment, the nitrogen content of the final product is in the range of 0.10-1.2 wt% based on the dry weight of the fibers, preferably 0.15-1.0 wt%, particularly 0.2-0.9 wt%. This corresponds to a degree of substitution (DS) of 0.012-0.144 for cellulose.

[0078] If improved wet properties such as low wet elongation and high wet tenacity are desired, a low nitrogen content in the final product is beneficial. In one embodiment, the nitrogen content in the final product is in the range of 0.10-0.75 wt% and corresponds to a degree of substitution of cellulose of 0.012-0.09.

[0079] Stretching under controlled process conditions allows for the adjustment of the properties of cellulose carbamate fibers. The cross-sectional shape of the fiber can be altered by stretching under controlled process conditions; for example, roundish / oval, bean-shaped, or lobed cross-sections can be obtained through controlled stretching, resulting in a smooth surface with a cotton-like feel.

[0080] As an example, compared to viscose fibers with an irregularly serrated surface, this fiber has a more homogeneous and smooth surface and internal structure (i.e., cross-section). The rounded structures of elliptical, bean-shaped, or leaf-shaped fibers provide a high initial modulus.

[0081] The relative wet strength (i.e., tenacity at break) of the fibers in this case is improved compared to viscose, which has low wet tenacity at break. In particular, the relative wet elongation of the cellulose carbamate fabric fibers in this case is very good. In one embodiment, the cellulose urethane fabric fiber, in a conditioned state, exhibits a wet elongation at break of 85-110% of the dry elongation at break, preferably less than 100%, such as 85-99.9%, particularly 90-99.9% (wet / dry relative %), a wet strength of at least 0.9 cN / dtex, preferably greater than or equal to 1.0 cN / dtex, and a relative wet strength of 40-80% (wet tenacity / dry tenacity), preferably 45-80%. (Relative means the wet elongation at break / dry elongation at break relative to the typical wet / dry elongation at break of approximately 120% of the viscosity).

[0082] The fibers or filaments may be washed (at least partially) before cutting to reduce the total salt content of the filaments or tows. The washing unit may contain one or more washing baths, which typically contain sodium hydroxide and sodium carbonate in amounts approximately one-third that of the spinning bath and half that of the drawing unit. Therefore, the amount of sodium hydroxide in the washing unit is approximately 0.33-0.66 wt%, and the amount of sodium carbonate is less than 10 wt%, such as 7.3-9.9 wt%.

[0083] Sodium hydroxide and / or sodium carbonate, and zinc are preferably also retrieved from the solutions in the stretching and washing units and recycled back to the process. The process therefore preferably includes tools for monitoring the pH and the amount of components in the various baths, as well as tools for withdrawing and returning the solutions to these units.

[0084] This method may optionally include one or more of the following process steps: a) acidic washing to remove zinc salt precipitate residues, b) water washing, c) post-hydrolysis of the carbamate groups by hot alkaline liquor, d) acidic and / or neutral and / or alkaline bleaching step, and / or e) spin finishing. Steps a) and c) may be in any order, preferably with the water washing step included. The carbamate groups are stable in the acidic system and hydrolyzed in the alkaline bath. One purpose of this optional post-treatment may be to reduce the nitrogen content of the filament to the range of 0.05-0.4 wt%.

[0085] One example of post-hydrolysis is to perform post-hydrolysis on cellulose carbamate fibers with a nitrogen content of 0.8 wt-% that have been coagulated in an alkaline spinning bath and stretched in an alkaline stretching process by treating the fibers at 95°C with a post-hydrolysis liquor containing Na2CO3 and NaOH for 3 min in an after-treatment process. The nitrogen content of the recovered fibers is 0.17 wt-%.

[0086] In one embodiment, washing is performed using water or effluent from previous or subsequent treatment steps in a countercurrent washing manner. In a preferred embodiment, the after-treatment unit operates on a countercurrent principle.

[0087] Zinc and its compounds are transferred from the filament bath to the spinning bath, and further, during post-treatment, they can ultimately be dissolved out of the fibers. Zinc carbonate is slightly soluble in the spinning bath and washing liquid, so it can partially precipitate in the spinning bath, and most of it is transferred with the filament to the stretching bath and washing liquid, where it also partially precipitates. Some zinc may also remain in the filament until subsequent treatment steps as needed. If some zinc remains in the fiber or filament after washing, it can be removed from the stabilized fibers by means of acid washing, for example, by dissolving it in a suitable acidic liquor.

[0088] Finally, the obtained silk or fiber is dried by any known drying method.

[0089] It has also been unexpectedly discovered that the presence of the aforementioned cellulose carbamate fabric can be determined by fluorescence detection. Therefore, the present invention provides a method for determining the presence of cellulose carbamate fibers or articles containing such fibers.

[0090] In one embodiment, the method includes exposing the object to UV light, preferably 365 nm, and detecting fluorescence of the cellulose carbamate fiber in the wavelength range of 400 to 520 nm. In one embodiment, the object is yarn, tow of filament, staple fiber, shortcut fiber, or flock. In another embodiment, the object is a textile garment containing such fibers, such as a bleached and / or dyed garment. As described above, in one embodiment, if cellulose carbamate has been mixed with viscose, lyocell, or modal in fibers, filaments, yarns, or fabrics, the presence of cellulose carbamate in the man-made cellulose carbamate fiber mixture can be detected by fluorescence because the other regenerated fibers are not fluorescent.

[0091] Fluorescence is the light emitted by a substance that has absorbed light or other electromagnetic radiation. A cellulose urethane fabric fiber according to an embodiment exhibits fluorescence. Typically, the light emitted by fluorescent materials has a longer wavelength. The cellulose urethane fabric fiber according to an embodiment emits blue / turquoise light, for example, in the wavelength range of 450-490 nm, which can be visually observed when the fiber is exposed to UV light, particularly UV light with a wavelength of 365 nm. The fluorescence emission wavelength depends on the excitation wavelength. The fiber according to an embodiment exhibits fluorescence in the wavelength range of 420 to 520 nm (blue) when excited by UV light, particularly at 365 nm, and fluorescence in the wavelength range of 600 to 750 nm (red) when excited at 546 nm.

[0092] Further embodiments relate to cellulose carbamate fabric fibers obtainable by the method, the uses of the fibers obtainable by the method, and the uses of the cellulose carbamate fabric fibers. Therefore, one embodiment provides cellulose carbamate fabric fibers obtainable by the method described above herein. In one embodiment, the fiber contains 0.00005-0.5 wt% of phthalate and / or phthalic acid and / or unhydrolyzed or partially unhydrolyzed polyester, particularly polyethylene terephthalate, which is determined by gas chromatography-mass spectrometry as explained in more detail in the examples below. This amount may be, for example, less than 0.2% by weight, preferably less than 0.1% by weight. The presence of phthalates and / or phthalic acid and / or unhydrolyzed or partially unhydrolyzed polyesters indicates that textile waste material has been used as a raw material in the manufacture of cellulose carbamates.

[0093] According to yet another embodiment, the fiber has a linear density of 0.8-1.8 dtex, a tenacity of 2.0-2.9 cN / dtex, and an initial modulus of 50-120 cN / dtex. In a preferred embodiment, the linear density is 1.1-1.5 dtex, the tenacity is 2.1-2.8 cN / dtex, and the initial modulus is 70-120 cN / dtex. The measurement method is as described above. Fibers having a lower end dtex of, for example, 0.8 to 1.3 within this range are suitable for providing lightweight textiles, for example, typically derived from fibers having a titer of about 1.5 or lower. Cotton fibers typically exhibit higher tensile strength at the higher end of this range, while conventional wet-spun man-made cellulose urethane fibers typically exhibit tensile strength at the lower end of this range. The cN / dtex values ​​of man-made cellulose urethane fabric fibers, based on the embodiment, are measured in the dry state, i.e., the conditioned state. Initial modulus values ​​of 50-120 cN / dtex are higher than those of conventional man-made viscose fibers, which typically have a modulus in the range of 20-40 cN / dtex when measured in the dry state.

[0094] In another embodiment, the cellulose amino carbamate fabric fiber of any of the above embodiments is used in yarn, fabric, woven fabric, knitted fabric, woven garment or non-woven article, such as weave tow, fiber scrap, filament yarn or tow of filament.

[0095] Further embodiments relate to articles comprising the cellulose carbamate fabric fibers described above. In one embodiment, the yarn comprises the cellulose carbamate fabric fibers as described above. In another embodiment, the textile garment comprises the cellulose carbamate fabric fibers as described above. In a specific embodiment, the woven or knitted fabric comprises the cellulose carbamate fabric fibers as described above. In a suitable embodiment, the non-woven article comprises the cellulose carbamate fabric fibers as described above. In another embodiment, the cellulose carbamate fibers in the yarn, fabric, or woven fabric are combined with cotton fibers, particularly with virgin cotton fibers. Therefore, by means of these embodiments, synthetic cellulose carbamate fibers can replace at least a portion of the cotton fibers, particularly virgin cotton fibers, thereby reducing, for example, the environmental impact of the textile industry. The synthetic cellulose carbamate fiber of this invention has an initial modulus similar to that of cotton fiber, which allows it to replace cotton. (Detailed description of the drawings)

[0096] Figure 1 schematically illustrates a method according to an embodiment. Cellulose carbamate 1 is fed into a dissolving unit 2. In this embodiment, the amount of cellulose carbamate is 8-11 wt%, sodium hydroxide is 5-7 wt%, and zinc is 0.16-1.2 wt%, with the remainder being water. The dissolved cellulose carbamate, in the form of a cellulose carbamate spinning dope, is extruded from the dissolving unit to a spinning bath 3 via a spinneret. In the spinning bath, the amount of sodium hydroxide is maintained in the range of 1.0-1.99 wt%, and the amount of sodium carbonate (Na2CO3) is maintained in the range of 22-30 wt%. The spun filaments or fibers are then fed to one or more stretching units 4. In the stretching unit, the amounts of sodium hydroxide and sodium carbonate are maintained at approximately two-thirds of those in the spinning bath. The stretching unit may comprise one or more units, which may be completely separate or partially connected to each other in the case of several units.

[0097] After stretching, the fiber or filament system is washed in washing unit 5, wherein the amount of sodium hydroxide and sodium carbonate is maintained at approximately 1 / 3 of the amount in the spinning bath. After washing, the fiber or filament system is cut in cutting unit 6 and post-treated as needed in one or more post-treatment units 7, 8, 9, and 10. The first optional post-treatment unit 7 is an alkaline washing unit, in which nitrogen is hydrolyzed. The second post-treatment unit 8 is a washing unit, in which the cut fiber or filament system is washed with water. The third optional post-treatment unit 9 is an acid washing unit, the purpose of which is to dissolve zinc using sulfuric acid. The alkaline washing unit may contain Na2CO3 and NaOH. The fourth post-treatment unit 10 is an alkaline bleaching step using hydrogen peroxide. The fifth post-treatment unit 11 is a spin finishing unit. Typically, post-treatment units 8 and 11 are always used, while post-treatment units 7, 9, and 10 are more optional and can be determined, for example, by upstream process conditions and / or the intended use of the material. After drying in the drying unit 12, the cellulose carbamate fibers 13 are recovered.

[0098] This diagram further illustrates some of the recycling paths of this process. Indeed, both sodium hydroxide and sodium carbonate (both denoted by element symbol 17) are led from the spinning bath 3 to the separation unit 14 and, if necessary, back to the spinning bath. Similarly, sodium hydroxide and sodium carbonate (both denoted by element symbol 18) are extracted from the stretching unit 4 and led to the separation unit 14. These compounds may also be extracted from other units downstream of the stretching unit if necessary, but it is believed that the need for this is significantly lower.

[0099] The separation unit can also separate zinc 16 from its incoming flow and recycle it back to the dissolution unit 2. Furthermore, sodium hydroxide and / or sodium carbonate can be directed to the pre-treatment unit 15, or, if necessary, to carbamation. Example 1. Chemical pre-treatment and carbamation

[0100] Recycled mixed-color sorted cotton textile waste and polyester-cotton feedstock (CED viscosity 800 ml / g (ISO 5351:2010), containing 4.0 wt% non-fiber (mainly polyester, but also trace amounts of nylon, isoprene-containing material (elastic band), polyethylene / polypropylene)) are mechanically shredded to disintegrate the fabric structure into small pieces of fiber with an average fiber length of 6 nm. The shredded material is chemically pre-treated using a two-stage cooking procedure and bleaching / decolorization: in the first acidic stage, the material is treated with sulfuric acid. In the second alkaline stage, the washed acid-treated material is chemically treated with sodium hydroxide to hydrolyze most of the polyester.

[0101] In the first acid stage, the shredded material was treated with sulfuric acid at 95°C for 60 min. The textile waste consistency was 10 wt% and the initial acid charge was 5.0 g / L. The medium consistency pulp was processed in a continuous plug flow reactor. The pH of the final washing liquid, measured in the wash filtrate, was 3.2, corresponding to 0.6 g of free sulfuric acid per kilogram of dry acid-treated material. The viscosity of the acid-treated material was 294 ml / g (based on CED viscosity measurements according to ISO 5351:2010).

[0102] In the second alkaline stage, the washed, acid-treated material was chemically treated with sodium hydroxide at 110°C for 120 min in a pressure reactor equipped with a medium consistency pump. The textile waste consistency was 8.3 wt-%, and the initial alkali charge was 72 g / L. The pH of the final washing liquid was 10.0. The viscosity of the chemically pre-treated material was 290 ml / g (based on CED viscosity measurements according to ISO 5351:2010). The average yield through the alkaline stage was 92 wt-% solids, based on oven-dried material.

[0103] In the decolourisation stage (which includes both ozone and alkaline hydrogen peroxide treatment stages), the polymerization degree is further adjusted. Ozone treatment in the alkaline range does not significantly reduce the CED viscosity of the material; in particular, the loss of viscosity is less than that obtained under acidic conditions with ozone. Therefore, the narrow polydispersity index obtained in the previous processing stage is maintained in the alkaline decolourisation phase. The material obtained from the decolourisation process is appropriately dehydrated in a press and with an air flow for use in the subsequent carbamation process.

[0104] Ozone decolorization is carried out using a medium consistency loop and pressure reactor. The loop is first filled with warm softened water, and shredded textile (300 kg, bone dry) is emptied into the system. Next, raw material and water slurry are fed into the pressure reactor. 20 kg / BDT (bone dry metric ton of raw material) of NaOH is fed into the reactor to obtain a textile waste consistency of 8.5 wt% at pH 11.8. The pre-treated textile-water slurry is heated to 70°C. The estimated ozone concentration from feed to reaction was 16 wt% and the feeding time was 150 minutes. The total ozone charge was 4.0 kg / BDT. After the ozone stage, the slurry was cooled by adding 4.0 m³ of water. The cooled and diluted slurry was dewatered in a screw press. The pH of the filtrate was 10.0. The viscosity of the ozone-decolorized material was 279 ml / g (ISO 5351:2010).

[0105] Next, a peroxide stage is performed on the ozone-decolorized textile material. The ozone-treated material is pumped into the reactor, and the consistency of the slurry in the pressure reactor is 8.0 wt%. The reaction mixture is heated to a reaction temperature of 80°C, and the pH is adjusted to 11.6 with NaOH. The reaction time in the peroxide stage is 60 minutes, and the hydrogen peroxide charge is 5 kg / BDT. The decolorized material is thoroughly washed with a screw press. The consistency of the screw press feed is 2.2 wt%, and the thickening factor is 21 in the first washing sequence. In the second wash sequence, the thickening factor is 25. The viscosity of the obtained decolorized pulp was 265 ml / g (ISO 5351:2010).

[0106] The carbamation process is performed as described in Finnish Patents FI 112869, FI 112795, and International Patent Application Publication No. WO 2021 / 038136 A. During the carbamation stage, the degree of polymerization of cellulose and the polydispersity of the final product are optimized by chemical treatment, time, grinding, and temperature. After carbamation (as described above) of the decolorized sample, the obtained cellulose carbamate has a viscosity of 210 ml / g (ISO 5351:2010), corresponding to a DP of 268 and a PD of 3.28. Example 2. Wet spinning of cellulose carbamate stock solution in an alkaline spinning bath.

[0107] The cellulose carbamate (samples 1 to 5 and comparative samples 1 and 2) obtained from the carbamate esterification process in Example 1 was further dissolved to manufacture cellulose carbamate fibers by a wet spinning process: ground air-dry cellulose carbamate powder was slurried and dissolved in a solution of 6.5 wt% sodium hydroxide and 1.2 wt% sodium zincate. The target cellulose carbamate content in the stock solution was between 7.3 and 8.5 wt%. Sample 6 was prepared from the obtained cellulose carbamate using a similar manufacturing process. The viscosity of the cellulose carbamate used in Sample 6 was 195 ml / g (ISO 5351:2010), corresponding to a degree of polymerization (DP) of 247 and a polydispersity (PD) of 3.41. The cellulose carbamate stock solution obtained by the dissolving process was then filtered in the second filtration stage using 20 μm filter media through a two-stage backflush filtering process.

[0108] Wet spinning of the filtered and deaerated cellulose carbamate solution is carried out using an alkaline spin bath optimized for the cellulose carbamate process, containing 22.1-27.6 wt% sodium carbonate and 1.2-2.8 wt% sodium hydroxide. The cellulose solution is coagulated in the spin bath (temperature 45°C), and the total godet stretching stress applied in the hot bath (temperature 90°C) is 60-115%. The filament tow obtained from spinning is cut into staple fibers with a cut length of 40 mm. The linear density (dtex), fiber tenacity (cN / dtex), elongation (%), and initial modulus (cN / dtex) of the fiber were measured according to ISO 1973:2021 and ISO 5079:2020. The dried fibers were conditioned at a relative humidity of 65±2% and a temperature of 20±2℃ for at least 24 h. The test speed was 20 mm / min and the gauge length was 20 mm, representing the average of 20 measurements (Favigraph, Textechno). Dope characteristics, spinning conditions, stretching conditions, and the measured stable fiber properties are summarized in Table 1, where NR indicates no results. Example 3. Recirculation of the alkaline spinning bath

[0109] A spinning bath in equilibrium state, containing 1.69 wt% sodium hydroxide, 22.1 wt% sodium carbonate, and 0.13 wt% zinc, is extracted from the spinning unit at a rate of 912 l / h. A spinning solution (40 l / h) containing 8.5 wt% cellulose carbamate, 6.5 wt% sodium hydroxide, and 0.62 wt% zinc is continuously extruded into the spinning bath to form and recover fiber filaments. The majority (762 l / h) of the used spinning bath, containing the aforementioned amounts of sodium hydroxide, sodium carbonate, and zinc, is recycled back to the spinning unit without recovery or manipulation. The remaining solution is extracted from the spinning unit for recycling to reduce the sodium hydroxide content in the spinning bath. The 138 l / h recycled spinning bath was returned to the spinning unit. The returned portion of the recycled alkaline spinning bath contained 0.43 wt% sodium hydroxide and 28.1 wt% sodium carbonate. Most of the recycled sodium hydroxide was recycled together with the recycled soluble zinc compound back to the cellulose carbamate dissolution stage to form the spinning solution. Example 4. Determination of phthalic acid content

[0110] The terephthalic acid content in the cellulose carbamate fiber manufactured as described in Example 1 was measured using a GC / MS (gas chromatography-mass spectrometry) system. The sample was acidified with hydrochloric acid (pH < 3) and dried in an oven overnight. Free terephthalic acid was extracted from the sample using a pyridine / methanol solvent and concentrated to 5 ml. The extracted terephthalic acid was methylated and analyzed by GC / MS. The free terephthalic acid content in the sample was calculated against an external calibration standard. The amount of terephthalic acid was 10 mg / kg (of dry cellulose carbamate fiber). Example 5. Determination of Terephthalic Acid Content

[0111] The content of p-phthalic acid in the cellulose carbamate fibers (cut length 40 mm) manufactured as described in Example 2 was measured by a GC / MS (gas chromatography-mass spectrometry) system. The sample was first refluxed in sodium hydroxide (10 wt%) for 4 hours to hydrolyze the polyethylene terephthalate in the sample. P-phthalic acid was extracted from the sample, dissolved in pyridine / methanol solvent, and concentrated to 5 ml. The extracted p-phthalic acid was methylated and analyzed by GC / MS. The p-phthalic acid content was calculated against an external calibration standard. The amount of p-phthalic acid was 85 mg / kg (of dried cellulose carbamate fibers).

[0112] It is understood that the embodiments of the disclosed invention are not limited to the specific structures, processes or materials disclosed herein, but extend to equivalents that would be recognized by a person of ordinary skill in the art. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0113] Throughout this specification, the term "one embodiment" or "an embodiment" means that at least one embodiment of the invention includes the specific features, structures, or characteristics described in relation to that embodiment. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing in different places throughout this specification do not necessarily refer to the same embodiment. When numerical values ​​are mentioned using terms such as, for example, about, or substantially, the exact numerical value is also disclosed.

[0114] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may exist in a common list. However, such lists should be considered as each member of the list being independently identified as a separate and unique member. Thus, unless otherwise indicated, an individual member of this list should not be considered a de facto equivalent of any other member of the same list simply because it exists in a common group. Furthermore, various embodiments and examples of the invention may be mentioned herein together with alternatives to its various components. It is understood that such embodiments, examples, and alternatives should not be construed as de facto equivalents of each other, but should be considered as separate and autonomous representations of the invention.

[0115] Furthermore, in one or more embodiments, the aforementioned features, structures, or characteristics may be combined in any suitable manner. Numerous specific details, such as, for example, length, width, shape, etc., are provided in the following description to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will recognize that the invention may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring the embodiments of the invention.

[0116] Although the foregoing examples illustrate the principles of the invention in one or more specific applications, it will be clear to those skilled in the art that many modifications in form, use, and implementation details can be made without employing inventive capabilities and without departing from the principles and concepts of the invention. Therefore, the invention is not intended to be limited except as set forth in the claims below.

[0117] The verb "comprise / include" is used in this text as an open limitation, which neither excludes nor requires the existence of features not listed. Unless otherwise expressly stated, the features described in the appendix can be freely combined with each other. Furthermore, it is understood that the use of "a / an" (i.e., the singular form) throughout this text does not exclude plurals. [Simplified Explanation of the Diagram]

[0012] [Figure 1] Schematic illustration of a method according to an implementation mode.

Claims

1. A method for manufacturing cellulose carbamate textile fiber, comprising the following steps: - dissolving cellulose carbamate having a maximum nitrogen content of 2.5 wt% as measured according to SFS 5505:1988 in an aqueous sodium hydroxide medium to form a cellulose carbamate dope, wherein, The stock solution contains zinc; - the cellulose carbamate stock solution is spun in a spinning unit into an alkaline aqueous spinning bath to form filaments or filament tows, wherein the temperature of the alkaline aqueous spinning bath is in the range of 35-60°C; and - the filaments or filament tows are stretched to obtain cellulose carbamate fibers; wherein a portion of the alkaline spinning bath is withdrawn from the spinning unit for recycling, so that the sodium hydroxide content of the spinning bath is maintained in the range of 1.0-1.99 wt-% and the sodium carbonate content of the spinning bath is maintained at a maximum of 30 wt-%.

2. As in request item 1, where, The cellulose carbamate comprises cellulose carbamate obtained from cellulose-containing waste materials.

3. As in request item 2, wherein, The waste material is selected from the group consisting of textile waste, paper waste, cardboard waste, agricultural waste, and mixtures thereof.

4. As in request item 2 or 3, wherein, At least 25 wt% of the cellulose carbamate is obtained from the cellulose-containing waste material.

5. As in request item 4, where, At least 50 wt% of the cellulose carbamate is obtained from the cellulose-containing waste material.

6. As in request item 1 or 2, wherein, The cellulose carbamate comprises cellulose carbamate obtained from textile waste, in an amount of at least 50 wt%.

7. As in request item 6, wherein, The cellulose carbamate comprises cellulose carbamate obtained from textile waste, in an amount of at least 90 wt%.

8. As in request item 1 or 2, wherein, The nitrogen content of this cellulose carbamate is 0.5-2.0 wt%.

9. As in request item 8, wherein, The nitrogen content of this cellulose carbamate is 0.8 to 1.5 wt%.

10. As in request item 1 or 2, wherein, The cellulose carbamate has a polydispersity in the range of 2.0 to 5.0 as measured by gel permeation chromatography / size exclusion chromatography, and an average intrinsic viscosity of 147 to 225 ml / g as measured by CED viscosity measurement according to ISO 5351:2010.

11. As in request item 10, wherein, This cellulose carbamate has a polydispersity in the range of 2.0-4.0 as measured by gel permeation chromatography / size exclusion chromatography, and an average intrinsic viscosity of 161 to 197 ml / g as measured by CED viscosity measurement according to ISO 5351:2010.

12. As in request item 11, wherein, The cellulose carbamate exhibits polydispersity in the range of 2.0–3.5, as measured by gel permeation chromatography / size exclusion chromatography.

13. As in request item 1 or 2, wherein, This cellulose carbamate is prepared by pretreating a cellulose-based material and then performing cellulose carbamation on the pretreated cellulose-based material.

14. As in request item 13, wherein, The pretreatment includes mechanical treatment to obtain the cellulose-based material of a predetermined particle size, followed by acidic treatment and alkaline treatment in cooking liquor.

15. The method of claim 14 further includes bleaching and / or decolorization treatment.

16. As in request item 1 or 2, wherein, The cellulose carbamate stock solution contains 8-11 wt% cellulose carbamate, 5-8 wt% sodium hydroxide, and 0.08-1.2 wt% zinc, and the stock solution has a viscosity of 15 Pa·s or less as measured by ASTM D1343-93:2019 (measured at 20 degrees Celsius).

17. As in request item 16, wherein, The cellulose carbamate stock solution contains 8.5-10 wt% cellulose carbamate and has a viscosity range of 4-15 Pa·s (measured at 20 degrees Celsius) as measured by ASTM D1343-93:2019.

18. As in request item 1 or 2, wherein, The sodium hydroxide content in the spinning bath is maintained in the range of 1.0-1.99 wt%.

19. As in request item 18, wherein, The sodium hydroxide content in the spinning bath is maintained in the range of 1.5-1.9 wt%.

20. As in request item 1 or 2, wherein, The alkaline spinning bath contains sodium hydroxide and sodium carbonate in a weight ratio of 1:11 to 1:

20.

21. As in request item 1 or 2, wherein, The sodium carbonate content of the spinning bath is maintained in the range of 22-30 wt%.

22. As in request item 21, wherein, The sodium carbonate content of the spinning bath is maintained in the range of 23-29 wt%.

23. As in request item 22, wherein, The sodium carbonate content of the spinning bath is maintained in the range of 24-28 wt%.

24. As in request item 1 or 2, wherein, The temperature of this alkaline spinning bath is in the range of 40-55℃.

25. As in request item 24, wherein, The temperature of the alkaline spinning bath is in the range of 45-50℃.

26. As in request item 1 or 2, wherein, The spinneret draw ratio of this spinning process is in the range of 0.75-1.

4.

27. As in request item 26, wherein, The spinneret draw ratio of this spinning process is in the range of 0.8-1.

2.

28. As in request item 1 or 2, wherein, Following the coagulation of the filament or bundle, the total stretching of the stretching unit is at least 70 mm in length.

29. As in request item 28, wherein, After the coagulation of the filament or bundle, the total stretching of the stretching unit is greater than or equal to 90 mm.

30. The method as described in request item 29, wherein, After the coagulation of the filament or bundle, the total stretching of the stretching unit is greater than or equal to 95% of the length.

31. As in request item 28, wherein, Following the coagulation of the filament or bundle, the total stretching of the stretching unit is 70-120 mm in length.

32. As in request item 28, wherein, The stretching unit is placed in a hot bath.

33. The method of claim 1 or 2, further comprising at least one post-treatment step selected from acid treatment for removing zinc oxide residue from the filament and post-hydrolyse treatment for reducing the nitrogen content of the filament to the range of 0.05-0.4 wt% 34. As in request item 1 or 2, wherein, The nitrogen content of cellulose carbamate filaments after coagulation is in the range of 0.40-1.0 wt%.

35. A cellulose amino ester fabric fiber having a linear density of 0.8-1.8 dtex and a tenacity of 2.0-2.9 cN / dtex.

36. The cellulose carbamate fabric fiber of claim 35, having a content of p-terephthalate and / or p-terephthalic acid and / or unhydrolyzed or partially unhydrolyzed polyester of 0.00005-0.5 wt% as determined by gas chromatography-mass spectrometry.

37. Cellulose urethane fabric fibers as claimed in claim 35 or 36, having an initial modulus of 50-120 cN / dtex and a toughness of 2.1-2.8 cN / dtex.

38. The cellulose aminocarbamate fabric fiber of claim 37, having a linear density of 1.1-1.5 dtex.

39. Cellulose urethane fabric fibers as claimed in claim 37, having an initial modulus of 70-120 cN / dtex.

40. The use of a cellulose urethane fabric fiber having a linear density of 0.8-1.8 dtex and a tenacity of 2.0-2.9 cN / dtex for use in yarn, textile, woven or knitted fabric, textile garment or nonwoven fabric.

41. A yarn, fabric, woven or knitted fabric, woven garment or nonwoven article comprising cellulose urethane fabric fibers having a linear density of 0.8-1.8 dtex and a tenacity of 2.0-2.9 cN / dtex.

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