Method for forming a filament containing cross-linked fibers and filament

Abstract

A method for forming a filament containing crosslinked fibers, comprising: providing an aqueous suspension containing at least natural unmodified microfibrillated cellulose (MFC) fibers and a dichlorotriazine-based crosslinking agent as a crosslinking agent; and drying the aqueous suspension to form at least one filament, wherein the filament contains at least 50% by weight, preferably at least 70% by weight, of MFC.

Description

Technical Field

[0001] The present invention generally relates to fiber suspensions and filaments. More specifically, the present invention relates to methods and filaments for forming filaments comprising crosslinked fibers.

Background Art

[0002] In processes related to the manufacture of filaments, such as those used in the production of woven fabrics, where filaments can be made from fiber suspensions, the properties of the formed filaments are important to ensure that the final product has the desired properties and / or that the processing of the filaments is manageable or in accordance with appropriate specifications.

[0003] It is particularly advantageous to obtain filaments having high strength (wet and / or dry) and / or high elongation. These are properties that can provide strength to the filaments, make their processing easier, and / or result in final products such as fabrics that are tough against wear and tear.

[0004] Alkali resistance is another quality that is preferably improved because the chemicals used in cleaning products are usually alkaline.

[0005] Prior art exists for the production of fiber suspensions and filaments from such fiber suspensions, using crosslinking chemicals to improve some properties of the suspension or formed filaments. In these methods, fibers in a cellulose suspension are crosslinked with each other. Crosslinked cellulose fibers are typically produced by reacting cellulose with a polyfunctional agent that can react with the hydroxyl groups of the anhydroglucose repeat units of cellulose, either simultaneously within the same chain or in adjacent chains. Formaldehyde and urea-formaldehyde products were among the first agents used to crosslink cellulose fibers. However, formaldehyde has many adverse health effects and is a known human carcinogen.

[0006] Monomers with polyfunctional groups, such as carboxylic acid groups and aldehyde groups, are also used as crosslinking agents for cellulose fibers. For example, alkane polycarboxylic acids can crosslink cellulose fibers by forming ester bonds with the hydroxyl groups of the fibers. One problem associated with the use of alkane polycarboxylic acids is that the cellulose fibers crosslinked by them tend to lose their crosslinks during storage and revert to uncrosslinked fibers.

[0007] Several methods are also known in which fiber crosslinking is carried out not in a fiber suspension, but as a post-treatment or finishing step on the formed filaments. These methods may particularly relate to filament properties that affect the appearance of the fabric, such as pilling reduction, by applying chemicals to the formed filaments to reduce pilling or to help impart a cleaner surface appearance by removing split fibrils, for example, via enzymatic treatment.

[0008] It would be advantageous to discover a crosslinking agent for use in a fiber suspension, which may provide selected features to the formed filament, and which may advantageously provide several different desired features. Preferably, it is desirable to use a crosslinking agent that is not harmful to the environment or humans, while also enabling a method for forming the filament that is easy, effective, and may be carried out in an environmentally friendly manner. [Overview of the Initiative]

[0009] An object of the present invention is to alleviate at least some of the problems in the prior art. According to one aspect of the present invention, a method for forming a filament containing crosslinked fibers, - To provide an aqueous suspension containing at least natural unmodified microfibrillated cellulose (MFC) fibers and a dichlorotriazine-based crosslinking agent, A method is provided comprising drying an aqueous suspension to form at least one filament, wherein the filament contains at least 50% by weight, preferably at least 70% by weight of MFC.

[0010] Through embodiments of the present invention, fibers may be crosslinked to form filaments that provide one or more selected qualities. The selected qualities may be, for example, with respect to wet and / or dry strength and / or elongation (or a combination of properties such as processability, which will be further considered below), alkali resistance, and / or dye affinity.

[0011] Through the present invention, the filament may have a higher wet strength compared to the prior art filament, while simultaneously maintaining a dry strength similar to, or at least exceeding a threshold amount and not differing from, the dry strength of the prior art. Many crosslinking agents that increase the wet strength of a filament are known to simultaneously decrease the dry strength, which can be undesirable.

[0012] Alkali resistance may be improved, which is beneficial because the filaments may be exposed to NaOH or alkaline conditions during the weaving process. In this invention, the formed filaments may not dissolve under alkaline conditions, or may dissolve at least less than prior art filaments.

[0013] Due to the favorable wet strength properties and / or less shrinkage of the formed filaments, high dimensional stability of fabrics knitted using filaments that may be formed through the present invention may also be provided.

[0014] In one embodiment, the crosslinking agent may be 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine.

[0015] The crosslinking agent 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine is known to be used in lyocell filaments in a finishing step to reduce fibrillation. Since the crosslinking agent is present only on the surface of the filament and is supplied to the formed filament, other filament qualities, such as strength and / or elongation, may not be improved as desired.

[0016] In this invention, a crosslinking agent may be supplied to an aqueous suspension, resulting in an aqueous fiber suspension in which the crosslinking agent is not applied in a post-processing step after the filament is formed from the suspension. This eliminates one step compared to prior art methods in which the crosslinking agent is supplied in a finishing step. Eliminating a process step can lead to a reduction in manufacturing equipment and a reduction in generated waste such as wastewater.

[0017] The crosslinking agent may penetrate the amorphous regions of the cellulose material. Crosslinking may occur between different regions of separate cellulose fibrils, and / or between different separate fibrils of a suspension or filament. This type of crosslinking behavior may provide many of the benefits related to the present invention. Crosslinking is beneficially carried out in the present invention by providing the crosslinking agent before filament formation when preparing an aqueous suspension.

[0018] Furthermore, because the crosslinking agent is already provided to the suspension before filament formation, improved or selected characteristics, such as improved or selected strength and / or elongation, were observed in the formation of filaments. In addition, fibrillation may be prevented or reduced. Reduced fibrillation may be observed in the filaments and the fabric produced from the filaments. The produced fabric may be wrinkle-free or exhibit fewer wrinkles than other fabrics or than in the absence of the crosslinking agent.

[0019] In embodiments of the present invention, the crosslinking agent may reduce the swelling of the fibers or filaments, thereby reducing the degradation of fibrils within the filaments. The reduction in swelling characteristics may also reduce wrinkles in the manufactured fabric.

[0020] Crosslinked fabrics made from the filaments according to the present invention may also exhibit higher abrasion resistance. While fabrics made from filaments without crosslinked fibers have an abrasion resistance of approximately 3000 labs, fabrics made from the filaments according to the present invention have an abrasion resistance of approximately 4000 to 5000 labs and exhibit less weight change.

[0021] In conventional lyocell crosslinking processes, the pulp must be dissolved as a raw material for lyocell, and then further dissolved in an NMMO solution for extrusion under high pressure and high temperature; therefore, the crosslinking agent cannot be added in the suspension phase. Conversely, the present invention is based on filaments made from nano / microfibrillated cellulose that does not require chemical treatment, i.e., the cellulose is type I cellulose and not regenerated.

[0022] The present invention may provide process control in terms of the reproducibility and distribution of the crosslinking agent, which may contribute to providing desired wetting characteristics of the formed filament.

[0023] The present invention has revealed that the dye affinity of the filament may also be improved. Dye penetration and retention may be improved compared to filaments without a crosslinking agent. When the crosslinking agent is provided to the suspension as in the present invention, the crosslinking agent may penetrate the entire formed filament. Therefore, the improved dye affinity is present not only on the surface of the filament but throughout the entire filament. The color of the dyed filament or fabric may be more uniform and / or deeper compared to those of the prior art. Dyeability may be increased, which may result in the need for less dye.

[0024] In addition to providing a less expensive method for crosslinking fibers, the crosslinking agents used may also allow for the avoidance of the use of other potentially harmful chemicals, such as formaldehyde.

[0025] The amount of crosslinking agent may be 0.1 to 10% by weight of the dry filament, for example, 0.5 to 7% by weight, 3 to 4% by weight, or 3 to 5% by weight. Therefore, the amount of crosslinking agent required may be small, and the amount of chemicals required in the process can be kept low.

[0026] The "dry" filament may refer to a filament having a dry material content of at least 70% by weight. The dry material content may be from 70% to 100% by weight.

[0027] The amount of crosslinking agent used may be selected based on the MFC type used in the aqueous fiber suspension. More specifically, the amount of crosslinking agent may be selected based on the hemicellulose content of the MFC.

[0028] For example, in some embodiments, when the hemicellulose content of the MFC is less than 5% by weight of the dry weight of the MFC, the amount of crosslinking agent may be 2 - 8% by weight of the dry filament, such as 3 - 5% by weight. When the hemicellulose content of the MFC is more than 5% by weight of the dry weight of the MFC, such as more than 10% by weight, the amount of crosslinking agent may be less than 2% by weight of the dry filament, such as about 1% by weight.

[0029] In one embodiment of the present invention, the method may include adjusting the initial pH of the suspension containing MFC before adding the crosslinking agent. A base may be added to the suspension until the pH of the suspension reaches 7 - 12, such as 8 - 11. At least after the final preparation, that is, after all components have been added to the suspension, the pH of the suspension is most preferably 8 - 9 or 8.5 - 9. The adjusted pH may result in a preferred strength and / or elongation of the filament. If the pH is too high, the strength and / or elongation may decrease beyond a preferred amount.

[0030] The method may include providing the selected components to the aqueous suspension in a selected order of addition.

[0031] The selected components in the aqueous suspension may include at least an MFC, at least one base such as NaOH, at least one triazine crosslinking agent, at least one strength resin, optionally polyamidoamine-epichlorohydrin (PAE), anionic polyacrylamide (APAM), and / or glyoxalized polyacrylamide (GPAM), optionally at least one hydrophobic adhesive such as an alkylketene dimer (AKD), and optionally at least one dispersant such as carboxymethylcellulose (CMC).

[0032] A synergistic effect may be provided by at least some of the selected components. For example, at least one wet-strength resin, such as PAE, may enhance some of the effects provided through the use of a crosslinking agent. PAE may be advantageous in use because it may be less harmful than other possible wet-strength resins.

[0033] The order in which the selected components are added may affect the properties of the final product, such as a suspension, filament, and / or fabric. Specifically, the selected addition order may result in selected properties of the filament, such as selected or preferred elongation and / or strength.

[0034] In one embodiment, the selected order of addition may be MFC, at least one base, at least one crosslinking agent, at least one wet strength resin, optionally a hydrophobic adhesive, optionally a dispersant, and optionally a further wet strength resin. However, other orders of addition are also possible.

[0035] The selected components and their order of addition may, in one embodiment, include MFC, NaOH, at least one triazine crosslinking agent, PAE, CMC, and APAM. Further components may be provided, and their order of addition is not specified.

[0036] Filaments are formed by extruding an aqueous suspension through a nozzle to form filaments containing cross-linked fibers. Such processes for forming filaments will be known to those skilled in the art. Specifically, the aqueous suspension may be extruded through at least one nozzle onto a dry surface, on which the extruded aqueous suspension dries to form a dry filament.

[0037] In some embodiments, the method for forming the filament may additionally include a curing step in which the filament is subjected to a selected temperature over a selected period of time in order to heat the filament. The curing step may occur after the filament has dried.

[0038] The selected temperature for the curing step may be 70-200°C, preferably 80-150°C.

[0039] The selected period for the curing step may be 1 to 60 minutes, preferably 5 to 30 minutes.

[0040] A method for forming a filament may further include a humidification step in which the extruded suspension containing the crosslinking agent is subjected to a selected relative humidity for a selected period of time. The humidification step may occur after the filament has dried.

[0041] The selected relative humidity for the humidification step may be 10–80%, preferably 50–70%, more preferably 60–65%. If the humidity is too high, the hydrogen bonds in the filament may break down, reducing the wet strength / strength of the filament, and / or the crosslinking reaction may be hindered. The filament may exhibit improved quality when a curing step is performed in addition to the humidification step. If only the humidification step is performed, the filament may be of less desirable quality.

[0042] The selected period for the humidification step may be at least 10 days, for example, at least 1 to 15 days, or at least 3 to 6 days, for example, at least 4 to 5 days. The duration of the humidification step may depend on the temperature and / or relative humidity used in the humidification step. For example, if the temperature is below approximately 23°C and the relative humidity is approximately 65%, the duration may be at least approximately 10 days.

[0043] In embodiments of the present invention in which the curing step and the humidifying step are performed separately, the curing step preferably occurs before the humidifying step.

[0044] One embodiment of the present invention may include a combined humidification and curing step in which a suspension containing the crosslinking agent is subjected to a selected temperature and selected relative humidity for a selected period of time. The combined humidification and curing step may include subjecting the suspension containing the crosslinking agent to vapor, and includes a temperature of 80 to 150°C, preferably 100 to 120°C, a relative humidity of 50 to 70%, preferably 60 to 65%, and a period of 5 minutes to 6 days, preferably 4 to 5 days.

[0045] In embodiments of the present invention in which curing and humidification steps are provided, the properties of the filament may be adjusted or optimized to exhibit, for example, selected or desired strength, elongation, and / or alkali resistance.

[0046] In another aspect of the present invention, a filament according to independent claim 18 is provided.

[0047] The formed filament may exhibit a structure in which the crosslinking agent permeates the entire filament (as opposed to the method in which the crosslinking agent is applied as a finishing step). Thus, the fiber may be crosslinked not only on the surface but throughout the entire filament.

[0048] Next, the present invention will be described in more detail with reference to exemplary embodiments shown in the accompanying drawings. [Brief explanation of the drawing]

[0049] [Figure 1] The structure of possible crosslinking agents is shown. [Figure 2] An example of a crosslinking reaction is shown. [Modes for carrying out the invention]

[0050] Percentage values ​​presented herein refer to weight percentages (W%) of dry filament unless otherwise indicated. The term “comprising” may be used openly, but also includes the closed term “consisting of.”

[0051] In this document, the term “filament” refers to cellulose fibrils that are linked together after the extrusion process. The formed filament may be a monofilament, and as herein, the term “monofilament” refers to an extruded filament, where the filament is a continuous length of individual fibrils that are grouped and extend substantially along the longitudinal dimension of the cellulose monofilament.

[0052] In this disclosure, the terms “unregenerated cellulose” or “natural cellulose” refer to cellulose or cellulose fibrils or fibers whose macromolecular structure has not undergone chemical or physical modification. The unregenerated MFCs considered herein are substantially unregenerated and consist primarily of the crystalline structure of cellulose I. Cellulose I may have structures Iα and Iβ. For example, artificial cellulose fibers commonly used in the pulp and paper industries are regenerated, and their crystalline structure is primarily other than cellulose I. The conversion from cellulose I to cellulose II (or other forms such as cellulose III or cellulose IV) is irreversible. Therefore, these forms are stable and cannot be converted back to cellulose I.

[0053] Cellulose material (pulp) is constructed from a cellulose fiber matrix. The fibers forming such a matrix are fibril bundles, which are composed of microfibrils. Through the fibrillation process, cellulose fibers are separated into a three-dimensional network of microfibrils with a large surface area. These entangled fibrils are called microfibrillated cellulose (MFC). The width of the entangled fibrils in the MFC may be 50 nm to 2 μm, and the length or longitudinal dimension may be 100 nanometers to 500 micrometers, for example, 100 nanometers to 200 micrometers. The MFC used in connection with the present invention may be non-regenerated MFC.

[0054] The method for producing MFCs is not limited. MFCs may be isolated from cellulose fibers using methods known in the art, for example, via high-pressure, high-temperature, and high-speed impact homogenization. The homogenization process is used to exfoliate or break down the cell walls of the fibers, releasing their underlying fibrils and microfibrils. Enzymatic and / or mechanical pretreatment of woody fibers may also be used.

[0055] The cellulose used in this invention may be derived from any plant-based material. The plant-based raw material may be woody or non-woody material. Woody materials may be based on coniferous trees such as spruce, pine, fir, larch, Douglas fir or hemlock, or on hardwoods such as birch, aspen, poplar, alder, eucalyptus or acacia, or any mixture thereof. Non-woody materials may be cotton, hemp, flax, sisal, jute, kenaf, bamboo, peat or coconut. Non-woody natural cellulose fibers may be derived from agricultural residues, grasses, or other plant materials such as straw, leaves, bark, seeds, shells, flowers, vegetables or fruits. Woody plants have good availability, low environmental impact, and good fiber quality. The above applies to both unregenerated cellulose and cellulose in regenerated and processed forms.

[0056] The present invention provides a method for providing a filament containing a crosslinked fiber, wherein an aqueous suspension is provided comprising at least natural, unmodified microfibrillated cellulose (MFC) fiber and at least one crosslinking agent, and the suspension is dried to form at least one filament containing 50% by weight, preferably at least 70% by weight, of MFC. The composition of the aqueous suspension may be selected according to the desired properties of the suspension and / or the manufactured fiber or filament.

[0057] In one embodiment, the aqueous suspension comprises water, cellulose fibers (MFCs), a crosslinking agent, and at least one dispersant, typically a cellulose derivative.

[0058] During filament production, the aqueous suspension may be guided through a small nozzle that ensures good alignment (orientation) of the fibers with the flow. The nozzle may also supply the aqueous suspension to the surface, after which the filament is dried to obtain a fibrous monofilament. The fibrous monofilament may be produced via a single-step process. Thus, the produced fibrous monofilament is continuous but may be post-processed to shorter lengths. The thickness of the fibrous monofilament may be influenced, at least partially, by adapting the production rate, aqueous suspension concentration, and nozzle shape.

[0059] During the drying process, the moisture content of the filament is essentially removed or at least significantly reduced.

[0060] Of the dry weight of the formed filament, 80–98% by weight may be MFC, and 2–20% by weight may be crosslinking agents and other additives, such as one or more dispersants, strength additives, hydrophobic adhesives, pigments, and / or other modifiers. Additives can be used to fine-tune the properties of the manufactured filament or fabric, as will be understood by those skilled in the art.

[0061] The dispersant may be cellulose derivatives such as carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), ethylhydroxyethylcellulose (EHEC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), hydroxyethylmethylcellulose (HEMC), methylethylhydroxyethylcellulose (MEHEC), hydroxypropylcellulose (HPC), ethylcellulose (EC), and starch, or any mixture thereof. In one embodiment, the dispersant is carboxymethylcellulose (CMC), optionally accompanied by an additional dispersant.

[0062] The dispersant has an effect on the shear strength of the fibrous monofilament. The dispersant may be used in an amount of 0.5 to 20% by weight of the total weight of the dry fibrous monofilament. In one embodiment, CMC is used in an amount of 5 to 20% by weight, or 2 to 16% by weight, or about 10% by weight of the total weight of the material fibrous monofilament.

[0063] For example, CMC may be used in an amount of 0.5 to 20% by weight of the total weight of the dry fibrous monofilament. In one embodiment, CMC is used in an amount of 5 to 20% by weight or about 10% by weight of the total weight of the material fibrous monofilament. In one embodiment, CMC is used in an amount of 4 to 5% by weight of the total weight of the material fibrous monofilament. In one embodiment, CMC is used in an amount of 14 to 16% by weight of the total weight of the material fibrous monofilament.

[0064] Strengthening additives(s) or agents(s) may include polyacrylamide resins (amphoteric / anionic / cationic), starch, plant gum, carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), and latex, or wetting strengthening agents such as cationic glyoxylated resins, polyamidoamine-epichlorohydrin resins (PAE), polyamine-epichlorohydrin resins, urea formaldehyde (UFH), epoxide resins, amphoteric polyacrylamide (APAM), glyoxalized polyacrylamide (G-PAM), or polyethylene oxide (PEO).

[0065] The strengthening agent may be G-Pam. The amount of G-Pam may be 0.5 to 3% by weight of the total weight of the material fibrous monofilament, for example, 2% by weight of the total weight of the dry fibrous monofilament. The use of G-Pam makes it possible to modify the wet strength level from temporary to permanent.

[0066] The strengthening agent may be APAM. The amount of APAM may be 0.5 to 5% by weight of the total weight of the dry fibrous monofilament, for example, 2 to 4% by weight of the dry weight of the fibrous monofilament. The more APAM there is, the better the elasticity of the nonwoven fabric. APAM is a supercoagulant that can also be used as an additional dispersant. It improves the alignment of fibers in the suspension while being extruded onto a solid surface through a small nozzle.

[0067] The strengthening agent may be 0.5 to 5% by weight of the total weight of the dry fibrous monofilament, for example, 1 to 3% by weight of the fibrous monofilament in the form of PEO. The PEO increases the elasticity of the monofilament and fabric described herein.

[0068] The hydrophobic adhesive may be an alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, natural wax, or modified sunflower-based adhesive (MSOHO), or any mixture thereof.

[0069] The hydrophobic adhesive may be AKD. The amount may be 0.5 to 10% by weight of the total weight of the dry fibrous monofilament, for example, 2 to 5% by weight of the total weight of the dry fibrous monofilament. As a hydrophobic adhesive, AKD may reduce the absorption properties of the monofilament or the fabric produced. AKD may also increase the strength of the monofilament or the fabric.

[0070] In one embodiment, the aqueous suspension may comprise at least an MFC, at least one base such as NaOH, at least one crosslinking agent, at least one strength resin, optionally polyamidoamine-epichlorohydrin (PAE), anionic polyacrylamide (APAM), and / or glyoxalized polyacrylamide (GPAM), optionally at least one hydrophobic adhesive such as an alkylketene dimer (AKD), and optionally at least one dispersant such as carboxymethylcellulose (CMC).

[0071] Figure 1 shows exemplary structures of molecules that may be used as crosslinking agents. Figure 1A shows the general structure of a dichlorotriazine-based crosslinking agent that may be used as a crosslinking agent in the present invention. X may be OR, NHR, or SR, where R is a hydrogen atom, a sodium or alkyl chain, or a chromophore group.

[0072] Figure 1B shows the structure of 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine, which is used as a crosslinking agent in exemplary test cases further provided below.

[0073] Figure 1C shows a typical exemplary structure of another group of a dichlorotriazine crosslinking agent where R is an alkyl group, and Figure 1D shows another typical exemplary structure of yet another group of a dichlorotriazine crosslinking agent where D is a chromophore. The example in Figure 1D relates to a group of a molecule known as a reactive dye.

[0074] Figure 2 shows examples of crosslinking reactions that may occur in several embodiments of the method for providing crosslinked filaments according to the present invention. In this figure, the crosslinking agent is 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine. The reaction is a two-step reaction, and the first step (1) may occur at a lower temperature than the second step (2). The first step of the reaction may occur when temperature conditions of at least 5°C to 25°C are provided, and therefore may be carried out at room temperature. This step of the reaction may be started immediately after the aqueous suspension is prepared. The first step relates to the crosslinking agent molecule linking to the cellulose molecule by a cellulose molecule that substitutes one of the Cl atoms of the crosslinking agent.

[0075] The second step of the reaction may be carried out at a temperature higher than room temperature, for example, above 80°C or above 100°C. In this step of the reaction, the crosslinking agent that has gone through the first step of the reaction, so that one of its Cl atoms has been replaced with a cellulose molecule, has the other remaining Cl atom replaced with further cellulose molecules. Thus, after the second step of the crosslinking reaction, the two cellulose molecules are crosslinked together. The second step of the reaction may be made possible by carrying out a curing step as part of a method for providing a filament, which will be discussed further below, or it may be strengthened.

[0076] The alkali resistance of filaments containing a crosslinking agent produced by the present invention (also referred to herein as crosslinked filaments) was tested by preparing such filaments and comparing them with a reference filament. The aqueous solution used to prepare the crosslinked filament and the reference filament, which is otherwise identical to the crosslinked filament except that it contains a crosslinking agent (3% by weight) and NaOH.

[0077] Both 5 grams of reference filament and the filament according to the present invention were subjected to a 0.5 mol NaOH solution for 10 minutes. After immersing the filaments in the NaOH solution for 10 minutes and then drying them at room temperature for 24 hours, the filaments were weighed. It was observed that the crosslinked filament retained a weight of 5 g, while the reference filament had lost 0.07 g, i.e., its weight after NaOH treatment was 14% less (0.43 g). Therefore, it can be concluded that the crosslinked filament does not dissolve under alkaline conditions, thereby providing alkali resistance compared to the reference filament.

[0078] Table 1 shows the effect of the amount of crosslinking agent used on the properties of the formed filaments prepared from aqueous suspensions with two different types of MFCs. Processability refers to the properties of the formed filament, and processability (cN / tex%) = elongation × strength × 10. Strength is a conventional measure of the strength of a fiber or yarn. It is usually defined as the ultimate (breaking) force (grams-force units) of the fiber divided by the linear density. Strength is primarily expressed in cN / tex.

[0079] In the examples, the crosslinking agent used was 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine. Percentages of components refer to weight % of the dry filament. The aqueous suspensions were similar in terms of other components and their amounts, except for the type of MFC used and the amount of crosslinking agent. Tests 1-6 contained MFCs with a hemicellulose content of less than 5%, while tests 7-11 contained hemicellulose content of more than 5%. Other components of the aqueous suspensions were NaOH, PAE, AKD, CMC, and A-PAM. [Table 1]

[0080] Table 1 shows that when the hemicellulose content of the MFC is less than 5%, the wet processability increases as the amount of crosslinking agent increases from 0% to 4%, but when the percentage of crosslinking agent is 8% and 10%, the wet processability decreases slightly compared to that shown with 4% crosslinking agent.

[0081] When the hemicellulose content of MFC exceeds 5%, the wet processability increases as the amount of crosslinking agent increases from 0% to 3%, but when the percentage of crosslinking agent is 5% and 10%, the wet processability decreases from that seen with 3% crosslinking agent.

[0082] Therefore, the optimal amount of crosslinking agent may depend on the type of MFC used in the aqueous solution. The preferred amount of crosslinking agent may depend on the hemicellulose content of the MFC.

[0083] Table 2 shows the effect of the order of addition of selected components to the aqueous suspension. In all test cases, the components of the suspension were identical except for the amount of the crosslinking agent, which was 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine. The other components were NaOH, CMC, A-PAM, AKD, PAE, and MFC (the remainder), and the percentages are the weight percentages of the filament after drying. The processability under drying conditions is given, which is determined after drying the filament but before curing and humidifying. Initial wet-cured processability refers to the wet processability after the drying and curing steps. Wet processability is also given after the humidification step that occurred after the determination of the initial wet-cured processability. During the humidification step, the filament was stored under atmospheric conditions, 23°C, and RH 65% for 10 days. The curing and humidification process steps are discussed further in relation to Table 4. [Table 2]

[0084] Table 2 shows that the best wettability (both initial curing and curing / humidification) is achieved by test number 3 for an aqueous suspension, with the addition order being MFC, NaOH, crosslinking agent, PAE, AKD, CMC, and A-PAM. The amount of crosslinking agent is 5% by weight (2-sodium hydroxy-4,6-dichloro-1,3,5-triazine).

[0085] Table 2 also shows that the wettability (both in the initial curing stage and during curing and humidification) with 3% crosslinking agent is improved compared to the reference case without crosslinking agent, while 5% crosslinking agent provides even higher wettability.

[0086] In the reference example, a decrease in wet workability is observed when comparing the curing and humidification values ​​with the initial curing value. However, in the presence of a crosslinking agent, wet workability increases even further after humidification, providing considerably higher workability than in the reference example.

[0087] In the case of 3% crosslinking agent, the wet-processability after humidification compared to the initial state before humidification increased by 53% and 46% in the tests conducted. In the case of 5% crosslinking agent, an even greater improvement in wet-processability was observed after 10 days compared to the initial state, with increases of 119% and 95%.

[0088] It can be further observed that the dry processability in cases using crosslinking agents is equivalent to, or at least not dramatically reduced to, the reference case. Dry processability decreases by a maximum of approximately 10% compared to the reference case, and the reduction in all cases is approximately 5% to 10%. It should also be noted that the wet processability provided in cases using crosslinking agents (especially in cases where both curing and humidification are performed) may be at a similar level to that of dry processability. The wet processability under curing and humidification conditions in cases using crosslinking agents is only about 3% to 23% lower than that of dry processability. In test number 3, where the amount of crosslinking agent is 5% by weight and the addition order is MFC, NaOH, crosslinking agent, PAE, AKD, CMC, and A-PAM, the difference is only about 3%.

[0089] Furthermore, based on tests 4-5, it can be seen that, with the addition order of MFC, NaOH, PAE, AKD, CMC, crosslinking agent, and A-PAM, a 5% by weight amount of crosslinking agent yields higher (better) processability (initial and curing) than a 3% by weight amount of crosslinking agent.

[0090] Therefore, in a preferred embodiment, the selected components and order of addition may be MFC, NaOH, a crosslinking agent, PAE, AKD, CMC, and A-PAM. Needless to say, other orders of addition are also possible. Furthermore, the selected components may also include other components. The selected components may include further components, and / or some components, such as AKD, may be omitted. AKD may be used, for example, to improve the flexibility of the filament, but its use is optional. The selected order of addition may be MFC, at least one base, a crosslinking agent (in exemplary cases, 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine was used), and at least one wet strength resin. NaOH may be substituted with another base, PAE and / or A-PAM may be substituted with other wet strength resins, and / or CMC may be substituted with another dispersant.

[0091] Table 3 shows the effect of pH (final pH after adding all components) of the aqueous suspension on the filament properties. In Test Examples 2 and 3, the amount of NaOH varies, but 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine is used again as the crosslinking agent. For the row of the Test Example where the amount of crosslinking agent is 0%, the components of the suspension are the same except for the amount of NaOH. These components are MFC, CMC, A-PAM, and PAE. In addition, Test Example 2 shows the row for the amount of 1g of NaOH that imparts 0.5M NaOH. [Table 3]

[0092] Therefore, Table 3 shows that processability is higher when the suspension pH is approximately 8.5 compared to when the suspension pH is at the 12–14 level. In addition, without the use of NaOH, the wet processability exhibits a higher decline over time (from wet, harden, initial to wet, harden, humidification) than the corresponding decline in the case where 1 g of NaOH was used to obtain a pH of 8.5. It may be concluded that a pH of approximately 8–9 or 8.5–9 (after final preparation of the suspension) may be favorable.

[0093] Modification of the suspension pH was carried out using a base in the above examples. Additionally, several other forms of catalysts may be used to facilitate the crosslinking reaction.

[0094] Furthermore, one or more dyes, such as direct dyes and / or reactive dyes, may be provided in the aqueous suspension. For example, in a test comparing a fabric made from filaments formed by the method according to the present invention, in which dye is provided in an aqueous suspension, with a fabric made from filaments containing dye, where the aqueous suspension does not contain the crosslinking agent of the present invention, it may be observed during visual inspection that the color of the fabric made from filaments formed by the method according to the present invention is deeper than the color of the reference fabric.

[0095] In a method for forming a filament, the method may include a curing step and a humidifying step, or a combination of curing and humidifying steps. The filament may be subjected to a selected temperature for a selected period of time and a selected relative humidity for a selected period of time. Here, a suspension containing a crosslinking agent may be extruded through a nozzle and the filament may be formed, preferably already dry. In other words, curing and humidifying are performed on the formed filament. Curing preferably occurs before humidifying (or they occur simultaneously).

[0096] The relative humidity and temperature used affect the duration of the curing and / or humidification step, or a combination of curing and humidification.

[0097] Examples that yield favorable results in terms of wet strength and elongation may include a humidification step of 60-65% relative humidity for at least 4-5 days and a curing step of 100-120 degrees Celsius for 10-20 minutes. The conditions for the curing and / or humidification steps may depend, for example, on the scale or quantity of filaments being processed.

[0098] It is worth noting that curing and humidification may facilitate the penetration of the crosslinking agent into the amorphous regions of the fibril, potentially strengthening the crosslinking and improving the filament properties.

[0099] Table 4 shows the effects of curing and humidification on the properties of filaments containing cross-linked fibers. Storage procedures refer to the storage time while the filaments are stored at room temperature and under RH30 conditions. Determining the filament properties after storage can provide an indicator of how the properties will develop. As Table 4 demonstrates, for example, the properties of a formed filament determined immediately after humidification may differ from those observed after storage. [Table 4]

[0100] Table 4 shows that the strength, determined after a curing step at 120°C for 20 minutes and a humidification step at 23°C, RH60 for 24 hours, followed by storage at room temperature, RH30 for 64 hours, may decrease from a value of 0.99 determined immediately after the first humidification step to a value of 0.63. This may indicate that 24 hours of humidification is not long enough to ensure that the filament properties are preserved.

[0101] Next, the same sample was subjected to curing and humidification steps under curing conditions of 120°C for 20 minutes and humidification conditions of 23°C, RH60, for 48 hours. After this, the sample was subjected to a further humidification step under conditions of 23°C, RH60, for 48 hours. After doing this and storing at room temperature and RH30 for 48 hours, it was observed that the filament properties (particularly strength) did not decrease after storage. Therefore, it may be determined that after a longer humidification period (i.e., humidification is not completed after only 24 hours), the crosslinking properties are maximized and the filament properties no longer show a harmful decrease in value after storage.

[0102] The present invention has been described above with reference to the embodiments described above, and several advantages of the present invention have been demonstrated. It is clear that the present invention is not limited to these embodiments, but includes all possible embodiments within the spirit and scope of the views of the present invention and the following claims.

[0103] The features described in the dependent claims can be freely combined with each other unless otherwise specified.

Claims

1. A method for forming a filament containing cross-linked fibers, - To provide an aqueous suspension containing at least natural, unmodified microfibrillated cellulose (MFC) fibers and a dichlorotriazine-based crosslinking agent, - The aqueous suspension is dried to form at least one filament, wherein the filament contains at least 50% by weight, preferably at least 70% by weight, of MFCs. method.

2. The initial pH of the suspension containing the MFC is adjusted using a base until the pH of the suspension is 7 to 12, for example, 8 to 11, before the crosslinking agent is added. The method according to claim 1.

3. The amount of the crosslinking agent is 0.1 to 10% by weight of the dry filament, for example, 0.5 to 7% by weight, or 3 to 5% by weight. The method according to claim 1 or 2.

4. The amount of the crosslinking agent is selected based on the MFC type and associated hemicellulose content of the MFC, such that the amount of the crosslinking agent decreases as the hemicellulose content increases. The method according to claim 3.

5. If the hemicellulose content of the MFC is less than 5% by weight of the dry weight of the MFC, the amount of the crosslinking agent is 2 to 8% by weight of the dry filament, for example, 3 to 5% by weight; if the hemicellulose content of the MFC is greater than 5% by weight of the dry weight of the MFC, for example, greater than 10% by weight, the amount of the crosslinking agent is less than 2% by weight of the suspension, for example, about 1% by weight. The method according to claim 4.

6. The method includes providing the aqueous suspension with the selected components in a selected order of addition. The method according to any one of claims 1 to 5.

7. The selected components include at least MFC, at least one base such as NaOH, at least one crosslinking agent, at least one strength resin, optionally polyamidoamine-epichlorohydrin (PAE), anionic polyacrylamide (APAM), and / or glyoxalized polyacrylamide (GPAM), optionally at least one hydrophobic adhesive such as alkylketene dimer (AKD), and optionally at least one dispersant such as carboxymethylcellulose (CMC). The method according to claim 6.

8. The selected addition sequence is MFC, the at least one base, the at least one crosslinking agent, the at least one wet strength resin, optionally a hydrophobic adhesive, optionally a dispersant, and optionally a further wet strength resin. The method according to claim 7.

9. The selected components and their order of addition include MFC, NaOH, crosslinking agent, PAE, CMC, and APAM. The method according to claim 7 or 8.

10. The crosslinking agent is 2-sodium hydroxy-4,6-dichloro-1,3,5-triazine. The method according to any one of claims 1 to 9.

11. The aqueous suspension is extruded through a nozzle to form a filament containing cross-linked fibers, thereby forming the filament. The method according to any one of claims 1 to 10.

12. To heat the filament after drying, the process further includes a curing step in which the filament is subjected to a selected temperature over a selected period of time. The method according to any one of claims 1 to 11.

13. The selected temperature is 70 to 200°C, preferably 80 to 150°C. The method according to claim 12.

14. The selected period is 1 to 60 minutes, preferably 5 to 30 minutes. The method according to claim 12 or 13.

15. The additional step includes subjecting the filament, after drying, to a selected relative humidity for a selected period of time. The method according to any one of claims 1 to 14.

16. The selected relative humidity is 10 to 80%, preferably 50 to 70%, and more preferably 60 to 65%. The method according to claim 15.

17. The selected period is at least 10 days, for example, at least 1 to 15 days, or at least 3 to 6 days, preferably at least 4 to 5 days. The method according to claim 15 or 16.

18. A combined humidification and curing step comprising the filament being subjected to a selected temperature and selected relative humidity over a selected period of time, and optionally further comprising the combined humidification and curing step comprising the filament being subjected to steam, the combined humidification and curing step comprising a temperature of 80 to 150°C, preferably 100 to 120°C, a relative humidity of 50 to 70%, preferably 60 to 65%, and a period of 5 minutes to 6 days, preferably 4 to 5 days. The method according to any one of claims 1 to 11.

19. A filament manufactured by the method described in any one of claims 1 to 18.

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