METHOD FOR TREATING REGENERATED CELLULOSE FIBER FOR TEXTILES AND NON-WOVEN APPLICATIONS

Abstract

There is provided a method of treating regenerated cellulose fiber for use as a fiber feedstock, the method comprising providing a fiber feedstock comprising regenerated cellulose fiber and treating it in the following steps: (a) contacting the fiber feedstock with a first aqueous solution comprising a reducing agent; (b) contacting the fiber feedstock with a second aqueous solution having a pH of greater than 7 and comprising sodium hypochlorite; wherein step (a) is performed before step (b) or wherein step (b) is performed before step (a).

Description

1 / 19 METHOD FOR TREATING REGENERATED CELLULOSE FIBER FOR TEXTILES AND NON-WOVEN APPLICATIONS TECHNICAL FIELD

[0001] The present invention relates to a method for treating regenerated cellulose fibers, wherein the treated regenerated cellulose fibers are suitable for use as fiber feedstock. In particular, the method comprises contacting the regenerated cellulose fibers with first and second aqueous solutions. The first aqueous solution comprises a reducing agent and the second aqueous solution comprises an oxidizing agent. The present invention relates generally to a final treatment of cellulose fibers produced by a regeneration process (i.e., regenerated cellulose fiber), for example, by rayon processes and non-rayon processes such as the N-methylmorpholine-N-oxide or Lyocell process; phosphoric acid process; carbamate process, etc.The present invention also relates to a treated fiber feedstock comprising treated cellulose fiber and to the use of said treated feedstock for the manufacture of woven textile fabric and / or in nonwoven applications. BACKGROUND

[0002] US document 3318657 refers to the bleaching of cellulose fibers, such as jute, linen, cotton, rayon and wood.

[0003] Document WO 2018 / 073177 refers to a process for recycling cellulose from textiles made of cellulose.

[0004] The WO 2018 / 104330 document refers to a manufactured fiber, for example, using the Lyocell process or viscose process, the latter comprising a mixture of a regenerated cellulose fiber and dissolving pulp.

[0005] Document CN 110644234 refers to the technical field of biomedical materials, in particular to an absorbable oxidized regenerated cellulose material and its method of preparation and application. Petition 870250077700, dated 01 / 09 / 2025, page 12 / 39 2 / 19

[0006] Document DE 1049043 discloses a process for the post-treatment and finishing of artificial silk yarns spun by the viscose process with acid decomposition baths in a continuous operation, characterized by the yarn emerging from the spinning bath and still containing xanthate being, as is known, completely decomposed by treatment with dilute mineral acid at a temperature of at least 80°C and the yarn is then heat-treated with oxidizing chemicals in a neutral or weakly acidic medium and then with organic acids, for example, oxalic acid and / or acetic acid, at a higher temperature, after which the yarn, as usual, is passed through a weakly alkaline bath and finally finished.

[0007] US document 1915952 refers to the finishing of rayon, being more particularly related to the finishing of raw rayon produced by the so-called viscose-rayon process.

[0008] US patent 2016 / 0369456 refers to methods and systems for processing materials containing cellulose, such as textiles, including textile apparel (used and unused) and scraps, biomass, wood pulp, and the like, and for isolating cellulose molecules for use in a variety of downstream applications.

[0009] Viscose (rayon) is a cellulosic fiber whose raw material – cellulose – is of natural origin, as well as from recycled cellulose-based materials, and is manufactured by the so-called viscose process (rayon process). Cellulose originates mainly from trees, which are cut into small wood chips and subjected to a chemical pulping process, with the Kraft process with pre-hydrolysis being the most dominant pulping method, although other chemical pulping methods, such as the sulfite process, are also used.

[0010] The Kraft process, as well as the Kraft process with pre-hydrolysis, are processes that convert lignocellulosic-based materials, such as wood, materials and agricultural waste. Petition 870250077700, dated 01 / 09 / 2025, page 13 / 39 3 / 19 (e.g., plant material and waste which, like wood, consist essentially of cellulose, hemicellulose and lignin) and / or recycled cellulose-based materials in nearly pure useful cellulose fibers. The Kraft process, especially the modified Kraft process, called the Prehydrolyzed Kraft Process (PHK), involves treating wood chips or any non-woody material containing cellulose in a reactor with hot water under pressure, followed by treatment with an aqueous solution of sodium hydroxide (NaOH) and sodium sulfide (Na2S), known as white liquor, which dissolves the lignin and releases the cellulose from the matrix. Document WO 2020 / 013755 A1 discloses a process for separating the cellulosic part of the matrix from the raw material, in particular, a process that is integrated into the alkaline pulping process, such as the Kraft process. Cooking is typically carried out at a temperature > 150°C.The liquor containing dissolved lignin, as well as simple carbohydrates and inorganic materials, known as black liquor, is sent to a recovery area so that the cooking chemicals are regenerated and heat and electricity are also produced.

[0011] Viscose (Rayon) and similar materials (such as Lyocell and others that are well known in the art) are often referred to as regenerated cellulose or, sometimes, artificial fibers. The process of producing regenerated cellulose generally involves dissolving cellulose directly, such as Lyocell, or through many interstage processes, such as rayon, and subsequent coagulation into a stable fibrous material.

[0012] For example, in the viscose process, the cellulosic raw material is first immersed in an aqueous solution of sodium hydroxide (17-18%), which causes the fibers to expand and convert the cellulose into sodium cellulosate, commonly called alkaline cellulose or white granules. After immersion, the swollen mass is pressed to obtain a precise ratio. Petition 870250077700, dated 01 / 09 / 2025, page 14 / 39 4 / 19 of the alkali is used to process cellulose, and then it is ground to provide an adequate surface area for uniform reaction in subsequent process steps. The alkaline cellulose is aged under controlled time and temperature conditions to depolymerize the cellulose by oxidation to the desired degree of polymerization (DP) before reacting with carbon disulfide to form sodium cellulose xanthate. The xanthate, which is a yellow to orange granule, is dissolved in dilute sodium hydroxide to produce a viscous orange solution called viscose. The solution is filtered, deaerated, and matured to the desired coagulation point (called salt index) appropriate for wet spinning. Rayon filaments are formed when the viscose solution is extruded through very small holes of a spinneret into a spinning bath consisting essentially of sulfuric acid, sodium sulfate, zinc sulfate, surfactant, and water.Filament coagulation occurs immediately after the neutralization and acidification of the cellulose xanthate, followed by controlled stretching and simultaneous decomposition of the cellulose xanthate into cellulose. These latter steps are important to obtain the desired tenacity and other properties of the rayon. Finally, the newly formed rayon is washed and chemically treated (desulfurized), either in the form of continuous filament (yarn or sliver) or cut into staple fibers, to remove impurities before the application of a finishing process and packaging.

[0013] In the process known as Lyocell, the cellulosic feedstock is dissolved directly in an N-methylmorpholine-N-oxide (NMMO) solvent, resulting in the preparation of a homogeneous solution (dope) from cellulose in NMMO-water in a reactor, followed by extrusion of the highly viscous spinning mixture at an elevated temperature through an air space into a coagulation bath (wet spinning process with dry jet). The coagulated cellulose is washed, dried, and treated. The NMMO of Petition 870250077700, dated 01 / 09 / 2025, page 15 / 39 5 / 19 coagulation bath is recovered.

[0014] High Wet Modulus (HWM) / Modal / Polynosic Rayon fibers are made using the same chemical process as viscose fibers, but under different process conditions to produce fibers with different mechanical properties and different fiber cross-sectional profiles.

[0015] Other artificial fibers known to those skilled in the art include the phosphoric acid process, cold caustic dissolution, cellulose nitrate, cellulose acetate, carbamate process, cuprammonium process, Ioncell, ionic liquid-based fibers, and deep eutectic solvent-based fibers.

[0016] Regenerated cellulose fibers produced by such methods can then be washed to remove salts and other water-soluble impurities and can be bleached. Conventional treatments, for example, of viscose fibers and other artificial fibers, are based on oxidative treatment. This oxidative treatment can increase the optical properties of the fiber, but reduce the mechanical properties to some extent.

[0017] Sodium hypochlorite is an efficient agent for improving whiteness, but it impacts carbohydrate degradation. Cellulose degradation can be estimated by determining viscosity, copper index, alpha-cellulose content, or fiber tenacity. The total chlorine consumed during treatment is destined for replacement (chlorination) and oxidation, which depends on the reaction conditions and the type of product. Excessive addition of chlorine to the system has little effect on improving whiteness / brightness, while the risk of carbohydrate degradation increases.

[0018] Treatment with hypochlorite has a different mechanism depending on the pH and is usually carried out in excess of hydroxide. The risk of cellulose degradation is lower at higher pH, while at pH below 9.0, degradation will be intense. In addition to the formation of hydrochloric acid from acid Petition 870250077700, dated 01 / 09 / 2025, page 16 / 39 6 / 19 hypochlorous acid, the organic reaction gives rise to carbonic acid and carboxyl groups, which will further reduce the pH when there is no excess hydroxide available. A 25-30% excess of alkali is required to maintain the pH above 8.3 after the reaction. Cellulose subjected to chlorine or hypochlorous acid in neutral or acidic solution contains more carbonyl groups. While the reaction is maintained under alkaline conditions, the oxidized groups are mainly carboxyls, while the carbonyls decrease. HClO ^ ClO3- + 2 Cl- + 3 H+

[0019] Generally, treatment with hypochlorous acid is considered detrimental to the strength of cellulose. In addition, the carbonyl and carboxyl content in cellulose can contribute to color change after some time due to their instability.

[0020] Consequently, there is still a need in the art for suitable methods that provide enhanced mechanical and optical properties to cellulose fibers. Furthermore, there is also a need for such methods to be carried out in a sustainable and environmentally sound manner. The present invention was developed with the aim of at least solving these problems and / or with the aim of at least providing a commercially useful alternative. DESCRIPTION OF THE INVENTION

[0021] In a first aspect of the present invention, a method is provided for treating regenerated cellulose fiber for use as a fiber feedstock, the method comprising providing a fiber feedstock comprising regenerated cellulose fiber and treating it in the following steps: (a) bring the fiber raw material into contact with a first aqueous solution comprising a reducing agent; (b) bringing the fiber raw material into contact with a second aqueous solution with a pH greater than 7 and comprising Petition 870250077700, dated 01 / 09 / 2025, page 17 / 39 7 / 19 sodium hypochlorite; wherein step (a) is performed before step (b) or wherein step (b) is performed before step (a).

[0022] According to a further aspect, a treated fiber feedstock comprising treated cellulose-based fiber obtained by the method described herein is provided. In another aspect, the subsequent use of such treated fiber feedstock in the manufacture of a textile fabric or in nonwoven applications is also provided.

[0023] This disclosure will now be described in more detail. In the following sections, different aspects / implementations of the disclosure are defined in more detail. Each aspect / implementation thus defined may be combined with another aspect / implementation or aspects / implementations, unless clearly indicated otherwise. In particular, any feature indicated as being preferential or advantageous may be combined with another feature indicated as being preferential or advantageous.

[0024] The present invention relates to a method of treating regenerated cellulose fiber for use as a fiber feedstock. That is, the invention relates to a process involving treating cellulose fiber so that the treated cellulose fiber is then suitable for use as a fiber feedstock, for example, for the manufacture of textiles or for nonwoven applications. As described herein, the treatment method can serve as the final steps in a cellulose regeneration process, such as from wood pulp.

[0025] In a first stage, the method uses a regenerated cellulose fiber feedstock. Preferably, the fiber feedstock comprises more than 50% by weight of cellulose fiber relative to the weight of the fiber feedstock, more preferably more than 75% by weight. In some embodiments, the fiber feedstock may be textiles. Petition 870250077700, dated 01 / 09 / 2025, page 18 / 39 Recycled 8 / 19, for example, may contain other non-cellulosic fiber components, although this is not preferable, or may include impurities such as dyes. Generally, it is preferable that the fiber feedstock consists essentially of cellulose fiber. Even more preferably, the fiber feedstock comprises (or consists essentially of) regenerated cellulose fiber, such as viscose and / or Lyocell fiber. The present invention is particularly suitable for treating regenerated cellulose essentially directly after regeneration, i.e., as part of the production process, so that the fiber feedstock consists essentially of regenerated cellulose fiber. Preferably, the method uses a viscose or Lyocell process to produce the fiber feedstock as an input or raw material for the treatment process.In other words, a process for the production or regeneration of cellulose using the viscose or Lyocell process is also described here, including the treatment method described herein performed on the cellulose fiber after regeneration.

[0026] The method comprises a second stage of treatment of the fiber feedstock. The treatment of the fiber feedstock comprises mixing the fiber feedstock with first and second aqueous solutions, as described herein, wherein the first aqueous solution comprises a reducing agent and the second aqueous solution comprises sodium hypochlorite. These treatments may be carried out in any order, so that the fiber feedstock is first mixed with the second aqueous solution and then with the first aqueous solution, or vice versa. Preferably, the fiber feedstock is first mixed with the first aqueous solution comprising a reducing agent and then with the second aqueous solution. After the fiber feedstock has been treated with both aqueous solutions, the feedstock may be referred to as treated fiber feedstock. Petition 870250077700, dated 01 / 09 / 2025, page 19 / 39 9 / 19

[0027] Mixing with a first aqueous solution comprising a reducing agent (i.e., step (a)) can be considered as producing a reduced fiber feedstock (whether carried out before or after treatment with the second aqueous solution). The inventors found that conventional bleaching of cellulose fibers, in particular artificial regenerated cellulose fibers, can reduce the strength of these carbohydrate-based fibers due to cellulose chain degradation. The inventors found that by bringing the cellulose fiber into contact with a reducing agent, the agent converts the terminal groups of the cellulose, such as carbonyl and carboxyl groups, into alcohol groups. This results in more stable mechanical and optical properties of the fiber and ultimately in the reduction of fiber yellowing resulting, among other factors, from the stabilized cellulose chain.

[0028] A reducing agent is a chemical species capable of donating electrons to the cellulose fiber. Preferred reducing agents are selected from the group consisting of: sulfur dioxide, oxalic acid, bis[tetrakis(hydroxymethyl)phosphonium] sulfate, lithium borohydride, sodium borohydride, sodium hydrosulfide, sodium dithionite, sodium dithionate and (optionally) combinations thereof.

[0029] It is particularly preferable that the reducing agent be selected from the group consisting of: lithium borohydride, sodium borohydride, sodium dithionite, sodium dithionate and combinations thereof.

[0030] Generally, the first and second aqueous solutions have a pH greater than 7 (i.e., an alkaline solution). Acidic solutions can be used with acetic acid and / or oxalic acid, but these are less preferred. Thus, it is preferable that the first and / or second aqueous solution have a pH greater than 9 and / or less than 14. More preferably, the pH Petition 870250077700, dated 01 / 09 / 2025, page 20 / 39 10 / 19 of the first and / or aqueous solution is less than 11, such as 9 to 11, even more preferably 9.5 to 10.5. These ranges are especially preferred in combination with the preferred reducing agents above to stabilize the mechanical and optical properties of the treated fiber.

[0031] Similarly, the inventors also determined that it is preferable for the first aqueous solution to contain the reducing agent in an amount of at least 0.1% by weight and / or at most 10% by weight of the fiber raw material, preferably at least 1% by weight, preferably at least 2% by weight and, in some embodiments, preferably at least 3% by weight. Consequently, the preferred ranges include from 0.1% by weight to 10% by weight or from 3% by weight to 10% by weight.

[0032] The method also comprises mixing the fiber feedstock with a second aqueous solution with a pH greater than 7 and comprising sodium hypochlorite (NaOCl). This mixture (i.e., step (b)) can be said to produce an oxidized fiber feedstock.

[0033] Preferably, the second aqueous solution comprises sodium hypochlorite in an amount of at least 0.1 g / L, preferably at least 1 g / L, and / or at most 5 g / L, preferably at most 3 g / L. Consequently, preferred ranges include 0.1 g / L to 5 g / L or 1 g / L to 3 g / L.

[0034] More preferably, the second aqueous solution comprises sodium hypochlorite in an amount of at least 0.5% by weight and / or at most 5% by weight of the fiber raw material.

[0035] Preferably, step (b) further comprises recovering the fiber raw material by filtration to separate the second aqueous solution as a permeate (i.e., filtrate). The fibers retained after filtration may also be washed with water, preferably demineralized, until a permeate with a sufficiently neutral pH is achieved (e.g., pH around 7). Petition 870250077700, dated 01 / 09 / 2025, page 21 / 39 11 / 19

[0036] In a preferred embodiment, the first aqueous solution and / or the second aqueous solution comprise sodium hydroxide and, as such, the pH of these solutions is greater than 7, preferably greater than 9. It is particularly beneficial for both solutions to have an alkaline pH, since this avoids the need to change the pH from acidic to alkaline between steps (a) and (b) of mixing the cellulose fiber with a reducing agent and sodium hypochlorite, respectively.

[0037] The mixing conditions for steps (a) and (b) are not particularly limited. Preferably, the fiber feedstock is mixed with the first aqueous solution and / or the second aqueous solution for at least 1 minute, and optionally up to one hour, for example, from 5 to 30 minutes. Preferably, the fiber feedstock is mixed with the first aqueous solution and / or the second aqueous solution at a temperature of at least 40°C and / or at most 80°C.

[0038] It is generally preferable that step (a) further includes recovering the fiber feedstock by filtration to separate the first aqueous solution as a permeate. The fibers retained after filtration can also be washed with water, preferably demineralized, until a permeate with a sufficiently neutral pH is achieved (e.g., pH around 7). In preferred embodiments, the permeate is recycled in step (a) and mixed with more fiber feedstock to recirculate the first aqueous solution within the process with a plurality of batches of fiber feedstock. The treated fiber feedstock (obtained after treatment in both steps (a) and (b)) is then preferably dried, for example, in an oven up to 100°C, preferably around 50°C.

[0039] It is also preferable that the permeate be recycled as a feedstock in the kraft process. The permeate recycled for use in the Kraft process may be the permeate after the first batch in step (a), or any subsequent batch after the Petition 870250077700, dated 01 / 09 / 2025, page 22 / 39 12 / 19 recirculation. This embodiment is particularly suitable in embodiments where the fiber feedstock comprises regenerated cellulose fiber, such as that manufactured by the viscose or Lyocell process. The cooking feedstock for the Kraft process is typically wood, from which cellulose is extracted from other impurities such as lignin. In this way, recycling the first spent aqueous solution recovered as permeate has been shown to significantly improve the overall operational efficiency of the pulp production process. The permeate can be mixed with the cooking liquor. Preferably, the reducing agent to be used in combination with such recycling is lithium or sodium borohydride, preferably sodium borohydride. The byproduct of cellulose reduction with borohydride is borate (i.e., MBO2, where M is Li or Na).Borate can also have a positive impact on the efficiency of Kraft process recaustification during the recovery process, as it will be transported in the black liquor circulation. Therefore, this use provides a much more sustainable and environmentally friendly pulp production process.

[0040] The treatment process of the present invention is therefore capable of maintaining and even improving the physical-mechanical properties, as well as the optical properties of the cellulose fiber. Thus, the method allows both the tenacity and whiteness of the resulting treated fiber feedstock obtained in steps (a) and (b) to be equal to or greater than those of an equivalent treated fiber feedstock obtained in step (b) only. In another embodiment, the tenacity and whiteness of the fiber feedstock obtained after steps (a) and (b) are equal to or greater than those of the input fiber feedstock supplied before steps (a) and (b). More preferably, the treated cellulose fiber has a tenacity of at least 2.42 cN / dtex and a whiteness of at least 80%. The whiteness and Petition 870250077700, dated 01 / 09 / 2025, page 23 / 39 13 / 19 toughness can be measured by any conventional means in the art, for example, using the Vibrochrom 400 and Vibrodyn 500 instruments, following standard operating procedures in the art.

[0041] The resulting product is a treated fiber feedstock comprising (or consisting of) treated cellulose fiber. The fibers exhibit enhanced optical properties and tenacity and can be used as feedstock in the manufacture of a textile fabric from them or in nonwoven applications.

[0042] Therefore, a particularly preferred embodiment of the present invention is a method for treating regenerated cellulose fiber for use as a fiber feedstock, the method comprising providing a fiber feedstock comprising regenerated cellulose fiber and treating it in the following steps: (a) bringing the fiber raw material into contact with a first aqueous solution comprising a reducing agent at a temperature of at least 40°C, wherein the first aqueous solution comprises the reducing agent in an amount of 0.1% to 10% by weight of the fiber raw material; (b) bringing the fiber raw material into contact with a second aqueous solution with a pH greater than 7 and comprising sodium hypochlorite, wherein the second aqueous solution comprises sodium hypochlorite in an amount of 0.5% to 5% by weight of the fiber raw material; wherein step (a) is performed before step (b) or wherein step (b) is performed before step (a), (preferably where (a) is performed before (b)); and wherein each of the tenacity and whiteness of the fiber feedstock obtained after steps (a) and (b) is equal to or greater than that of a fiber feedstock obtained from step (b) only.

[0043] More preferably, the fiber raw material is Petition 870250077700, dated 01 / 09 / 2025, p. 24 / 39 14 / 19 handled in the following steps: (a) bringing the fiber feedstock into contact with a first aqueous solution comprising a reducing agent at a temperature of at least 40°C and recovering the fiber feedstock by filtration to separate the first aqueous solution as a permeate, wherein the permeate is recycled as a feedstock in the Kraft process, and wherein the reducing agent is lithium or sodium borohydride and the first aqueous solution comprises the reducing agent in an amount of 0.1% by weight to 10% by weight of the fiber feedstock; (b) bringing the fiber raw material into contact with a second aqueous solution with a pH greater than 7 and comprising sodium hypochlorite, wherein the second aqueous solution comprises sodium hypochlorite in an amount of 0.5% to 5% by weight of the fiber raw material; wherein step (a) is performed before step (b) or wherein step (b) is performed before step (a), (preferably where (a) is performed before (b)); and wherein each of the tenacity and whiteness of the fiber feedstock obtained after steps (a) and (b) is equal to or greater than that of a fiber feedstock obtained from step (b) only. FIGURES

[0044] The present invention will now be described in more detail with reference to the following non-limiting Figures, in which: Figures 1A and 1B illustrate embodiments of the process of the present invention.

[0045] Figure 2 is a graph of the tenacity of regenerated cellulose fibers, both raw and after various treatments, including at various concentrations of reducing agent.

[0046] Figure 3 is a whiteness chart for the same regenerated cellulose fibers as in Figure 2. Petition 870250077700, dated 01 / 09 / 2025, page 25 / 39 15 / 19

[0047] Figure 4 is a tenacity graph for regenerated cellulose fibers, both raw and after various treatments, including at various pHs of the first aqueous solution.

[0048] Figure 5 is a whiteness chart for the same regenerated cellulose fibers as in Figure 4.

[0049] Figure 6 is a graph of the tenacity of regenerated cellulose fibers, both raw and after various treatments.

[0050] Figure 7 is a whiteness chart for the same regenerated cellulose fibers as in Figure 6.

[0051] Figure 8 illustrates the recycling process of permeate from the first aqueous solution as a raw material in the Kraft process.

[0052] Figure 1A illustrates a first exemplary embodiment 100 of the process of the present invention and Figure 1B illustrates a second exemplary embodiment 200 of the process of the present invention.

[0053] In the treatment process 100, the first treatment step 105 comprises mixing the raw fiber material with an aqueous solution comprising a reducing agent, for example, for 3 minutes at 60°C. The fiber material is then filtered and washed in a first washing step 110 with demineralized water to obtain a reduced fiber material. This is then mixed in a second treatment step 115 with an aqueous solution of sodium hypochlorite, for example, for 3 minutes at 60°C. The fiber material is then filtered in a second washing step 120 with demineralized water to obtain a treated fiber material, which is finally dried in a drying step 125 in an oven at about 50°C until it is dry.

[0054] In an alternative treatment process 200, treatments equivalent to those of process 100 are used, except for the first treatment step 205 comprising mixing the Petition 870250077700, dated 01 / 09 / 2025, page 26 / 39 16 / 19 raw fiber material with an aqueous solution comprising sodium hypochlorite. The raw fiber material is filtered in a first washing step 210 to obtain an oxidized raw fiber material before being then mixed with the aqueous solution containing a reducing agent in the second treatment step 215. The raw fiber material is then filtered and washed in a second washing step 220 with demineralized water to obtain a treated raw fiber material which is finally dried in a drying step 225 in an oven at about 50°C until it is dry.

[0055] In both processes 100 and 200, the filtrate recovered after treatment with the aqueous solution comprising a reducing agent is preferably recycled for use in the Kraft process 130, so as to preferably produce cellulose pulp for use in a process to produce a crude fiber feedstock comprising cellulose fiber (e.g., the viscose or Lyocell process). More preferably, the reducing agent comprises lithium or sodium borohydride, since the borate byproduct after treatment of the fiber feedstock is able to improve the Kraft cooking yield and therefore the overall efficiency of the entire fiber production process. EXAMPLES

[0056] Unbleached fiber was taken from a viscose production process shortly before the bleaching stage and used as raw material (in 10 g batches). The unbleached fiber was analyzed for moisture content and treatment solutions were prepared to treat 4 to 6% by weight of fiber relative to the treatment solution. Each treatment was carried out for approximately 3 minutes.

[0057] In a first example, the crude fiber is treated with a sodium borohydride solution at a concentration of 0.1% by weight, 0.5% by weight, 1.0% by weight, or 10% by weight. The data shown in Figures 2 and 3 demonstrate that the strength of the regenerated cellulose fiber is preserved even at small concentrations. Petition 870250077700, dated 01 / 09 / 2025, page 27 / 39 17 / 19 concentrations of sodium borohydride. More specifically, a surprising improvement in whitening can be observed at concentrations of 1% by weight and higher.

[0058] In a second example, the raw fiber is treated with a sodium borohydride solution, the pH of which is not adjusted, or is adjusted with sodium hydroxide to a pH of 10 or 11. The data shown in Figures 4 and 5 demonstrate that whiteness is improved with increasing pH of the first aqueous solution comprising sodium borohydride. The tenacity of the treated cellulose fiber is higher at a pH around 10.

[0059] In a third example, the raw fiber is treated with a sodium borohydride solution, optionally followed by treatment with an acetic acid solution or a sodium hypochlorite solution, or the raw fiber is first treated with a sodium hypochlorite solution followed by a sodium borohydride solution. The data shown in Figures 6 and 7 demonstrate that the combination of a first treatment with sodium borohydride followed by a treatment with sodium hypochlorite provides the best combination of tenacity and whiteness for the treated cellulose fiber. The data demonstrate that the tenacity of a fiber treated according to the method of the present invention can maintain and improve the tenacity relative to the input regenerated fiber and exhibit a tenacity greater than 2.42 cN / dtex, while exhibiting a whiteness greater than 80%, which is comparable to the whiteness observed when only sodium hypochlorite is used.Therefore, the data demonstrate that the reducing agent is effective in protecting the strength of the cellulose. Procedure for analyzing whiteness.

[0060] Whiteness measurements are performed using a Vibrochrom 400. Before being placed in the cuvette, the fibers must be homogenized and arranged in the same direction. The measurement is the average of 3 sampling points of 3 grams of fiber. Petition 870250077700, dated 01 / 09 / 2025, pp. 28 / 39 18 / 19 Procedure for analyzing toughness (dry condition)

[0061] Tense measurements comprise denier measurement followed by tenacity for each individual fiber. Denier or count measurement is performed using a Vibroskop 500, which is suitable for counts from 0.5 to 200 dtex, with a minimum length of 24 mm for an individual fiber. The count range used in the study is 1.2 to 1.5 dtex, primarily 1.33 dtex with a maximum deviation of <0.02 dtex. The number of fibers tested for a single measurement is at least 20 individual fibers, generally using a tensile weight of 70 mg, although this value may vary depending on the fiber count range.

[0062] Toughness measurement is performed using a Vibrodyn 500 and the same tensile weight used for count measurement. The fiber that was tested for count is then inserted into the Vibrodyn and the test results (strength and elongation at break) of at least 20 individual fibers are read.

[0063] The denier and tenacity test of each fiber is carried out under conditions of RH: 65% ± 2% and T: 20°C ± 2°C for at least 1 hour, to reach moisture equilibrium.

[0064] As used herein, the singular form of a, an, and the includes plural references unless the context clearly indicates otherwise. The use of the term comprising should be interpreted as including such features, but not excluding other features, and is also intended to include the option of the features necessarily being limited to those described. In other words, the term also includes the limitations of “essentially consisting of” (meaning that other specific components may be present, provided they do not materially affect the essential feature of the element described) and “consisting of” (meaning that no other element may be present). Petition 870250077700, dated 01 / 09 / 2025, pp. 29 / 39 19 / 19 to be included, so that if the components were expressed as percentages according to their proportions, they would add up to 100%, taking into account any unavoidable impurities), unless the context clearly indicates otherwise.

[0065] It is understood that, although the terms first, “second”, etc. may be used here to describe various elements and / or characteristics of the matter in question (such as first and second aqueous solutions), the elements and / or characteristics should not be limited by these terms. These terms are used only to distinguish one element or characteristic from another, or from yet another element or characteristic.

[0066] The foregoing detailed description is provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Various variations of the currently preferred embodiments illustrated herein will be apparent to a person skilled in the art, remaining within the scope of the appended claims and their equivalents. Petition 870250077700, dated 01 / 09 / 2025, pages 30 / 39

Claims

1 / 4 CLAIMS 1. A method for treating regenerated cellulose fiber for use as a fiber feedstock, the method characterized in that it comprises providing a fiber feedstock comprising regenerated cellulose fiber and treating it in the following steps: (a) bringing the fiber feedstock into contact with a first aqueous solution comprising a reducing agent; (b) bringing the fiber feedstock into contact with a second aqueous solution having a pH greater than 7 and comprising sodium hypochlorite; wherein step (a) is carried out before step (b) or wherein step (b) is carried out before step (a).

2. Method according to claim 1, characterized in that step (a) is performed before step (b).

3. Method, according to claim 1 or claim 2, characterized in that the regenerated cellulose fiber comprises viscose, Lyocell, modal, cupra, phosphoric acid cellulose, cellulose nitrates, ethers and esters, cold caustic dissolution, high tenacity rayon, high wet modulus (HWM) rayon, polynosic fiber, carbamate fiber, ionic liquid fiber and deep eutectic solvent (DES) fiber, preferably viscose and / or Lyocell fiber.

4. A method according to any of the preceding claims, characterized in that the reducing agent is selected from the group consisting of: sulfur dioxide, oxalic acid, bis[tetrakis(hydroxymethyl)phosphonium] sulfate, lithium borohydride, sodium borohydride, sodium hydrosulfide, sodium dithionite, sodium dithionate and combinations thereof, preferably selected from the group consisting of: lithium borohydride, sodium borohydride, sodium dithionite, sodium dithionate and combinations thereof.

5. Method, according to any of the preceding claims, characterized in that the first and / or second aqueous solution has a pH greater than 7, preferably greater than 9 and / or less than 14.

6. A method, according to any of the preceding claims, characterized in that the first aqueous solution and / or the second aqueous solution comprises sodium hydroxide.

7. A method, according to any of the preceding claims, characterized in that the fiber feedstock comprises more than 50% by weight of cellulose fiber relative to the weight of the fiber feedstock, preferably more than 75% by weight.

8. A method, according to any of the preceding claims, characterized in that the fiber raw material is mixed with the first aqueous solution and / or the second aqueous solution for at least 1 minute.

9. A method, according to any of the preceding claims, characterized in that the fiber raw material is mixed with the first aqueous solution and / or the second aqueous solution, at a temperature of at least 40°C and / or at most 80°C.

10. A method, according to any of the preceding claims, characterized in that the first aqueous solution comprises the reducing agent in an amount of at least 0.1% by weight and / or at most 10% by weight of the fiber raw material, preferably at least 1% by weight.

11. Method, according to any of the preceding claims, characterized in that step (a) further comprises recovering the fiber feedstock by filtration to separate the first aqueous solution as a permeate.

12. Method according to claim 11, characterized in that the permeate is recycled in step (a) and mixed with fiber feedstock. Petition 870250077700, dated 01 / 09 / 2025, pp. 32 / 39 3 / 4 13. Method, according to claim 11 or claim 12, characterized in that the permeate is recycled as a raw material in the Kraft process, wherein preferably the reducing agent comprises lithium or sodium borohydride.

14. Method, according to any of the preceding claims, characterized in that step (b) further comprises recovering the fiber feedstock by filtration to separate the second aqueous solution as a permeate.

15. A method, according to any of the preceding claims, characterized in that the second aqueous solution comprises sodium hypochlorite in an amount of at least 0.1 g / L, preferably at least 1 g / L, and / or at most 5 g / L, preferably at most 3 g / L.

16. A method, according to any of the preceding claims, characterized in that the second aqueous solution comprises sodium hypochlorite in an amount of at least 0.5% by weight and / or at most 5% by weight of the fiber raw material.

17. Method, according to any of the preceding claims, characterized in that each of the tenacity and whiteness of the fiber feedstock obtained after steps (a) and (b) is equal to or greater than that of a treated fiber feedstock obtained from step (b) only.

18. A method, according to any of the preceding claims, characterized in that the treated cellulose fiber has a tenacity of at least 2.42 cN / dtex and a whiteness of at least 80%.

19. Method, according to any of the preceding claims, characterized in that the method comprises using a viscose or Lyocell process to provide the fiber feedstock comprising cellulose fiber for use in steps (a) and (b). Petition 870250077700, dated 01 / 09 / 2025, pp. 33 / 39 4 / 4 20. Treated fiber raw material characterized in that it comprises treated cellulose fiber obtained by the method as defined in any of the preceding claims.

21. Use of treated fiber raw material, as defined in claim 20, characterized by the fact that it is in the manufacture of a textile fabric and / or for nonwoven applications. Petition 870250077700, dated 01 / 09 / 2025, pp. 34 / 39

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