A process for the production of lyocell fibres from conventional chemical pulp

Abstract

This invention provides a method for preparing Lyocell fibers using ordinary chemical pulp. The method involves first pretreating the ordinary chemical pulp, then purifying the pretreated pulp using two stages of dilute NMMO solutions of different concentrations to remove hemicellulose. The purified pulp is then spun using a dry-jet wet-spinning process to obtain Lyocell fibers. The resulting Lyocell fibers possess the same or some superior properties as Lyocell fibers prepared using dissolving pulp. This invention provides a simple, green, and environmentally friendly preparation method that can be effectively combined with existing Lyocell fiber manufacturing processes, significantly reducing the manufacturing cost of Lyocell fibers.

Description

Technical Field

[0001] This invention belongs to the field of textile fiber preparation, and more specifically, relates to a method for preparing lyocell fibers using ordinary chemical pulp. Background Technology

[0002] Lyocell fiber, also known as Lyocell fiber, is a regenerated cellulose fiber produced by dry-jet wet spinning using N-methylmorpholine-N-oxide (NMMO) as a solvent. The waste is biodegradable, and the NMMO solvent used in the production process can be recovered at a rate of up to 99.5%. It does not pollute the environment and is hailed by the international textile industry as the "green fiber of the 21st century".

[0003] Currently, dissolving pulp is commonly used as a raw material for the preparation of Lyocell fibers, resulting in high costs. With global economic development and increasing environmental protection requirements, the production and supply of dissolving pulp face even greater challenges and pressures. The high cost of dissolving pulp keeps the price of Lyocell fibers high, which to some extent affects their market competitiveness and widespread application. Therefore, how to prepare Lyocell fibers using ordinary chemical pulp has become a current research hotspot. Patent CN115094660A has achieved a purification upgrade of ordinary chemical pulp through methods such as alkali extraction, enzyme treatment, and acid treatment. The main factors affecting the preparation of Lyocell fibers from ordinary chemical pulp are the large amounts of hemicellulose and metal ions it contains. The presence of hemicellulose leads to increased viscosity of the spinning solution, insufficient pulp impregnation, decreased product strength, and high solvent recovery load. Metal ions are effective inducers of the homolytic cracking reaction of NMMO, accelerating its decomposition, leading to decreased viscosity of the spinning solution and poor spinnability. If the metal ion content is too high, the spinning solution will decompose rapidly, releasing a large amount of heat, which could cause an explosion if out of control. Therefore, the removal of hemicellulose and the control of metal ion content are key to the preparation of Lyocell fibers from ordinary chemical pulp.

[0004] To improve the solubility and spinnability of ordinary chemical pulp, reduce costs, and enhance the competitiveness of Lyocell fibers, researchers are working hard to explore more economical preparation methods, and improving production processes has become an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing Lyocell fibers using ordinary chemical pulp. The preparation method provided by the present invention is a green method with recyclable solvents, which can effectively remove hemicellulose and metal ions from ordinary chemical pulp, and prepare Lyocell fibers through dry-jet wet spinning, thus solving the problem of high cost of dissolving pulp for Lyocell fibers.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing lyocell fibers using ordinary chemical pulp, comprising the following steps:

[0008] (1) Acid treatment and chelation treatment are performed on papermaking grade bleached chemical pulp to obtain pretreated pulp with low metal ion content; the pretreated pulp is mechanically refined to obtain refined pulp.

[0009] (2) The obtained pulp is mixed with a low-concentration NMMO dilute solution and an antioxidant, treated at a certain temperature for a period of time, and then pressed in a drum press to obtain cellulose cake.

[0010] (3) The obtained cellulose cake is mixed again with a high concentration of NMMO dilute solution and antioxidant, treated at a certain temperature for a period of time, pressed under a drum press, and then placed in an oven to dry to obtain cellulose solid cake.

[0011] (4) The cellulose solid cake is shredded in a paper shredder, mixed with NMMO solution and antioxidant in a reaction vessel, and subjected to shearing force and vacuum treatment to obtain a cellulose solution; the cellulose solution is used for wet spinning to obtain Lyocell fiber.

[0012] The preferred method for preparing bleached chemical pulp in step (1) includes the following steps: tearing the chemical pulp board into small pieces of 1cm*1cm, soaking them in deionized water, and dispersing them with a dispersing machine until the fibers are evenly dispersed; wringing out the water, tearing them into pieces, and drying them in an oven to obtain the bleached chemical pulp; placing it in a self-sealing bag to balance the moisture content and measuring the moisture content for later use.

[0013] The bleaching chemical pulp used in step (1) preferably includes one or more of wood pulp, bamboo pulp, wheat straw pulp, and hemp pulp.

[0014] The acidic solution in step (1) preferably includes sulfuric acid solution, hydrochloric acid solution or acetic acid solution; the acid treatment time is preferably 10-90 min, more preferably 30-50 min; the acid treatment temperature is preferably 10-50℃, more preferably 10-30℃.

[0015] In step (1), the pH value of the acid treatment is preferably 1 to 5, and more preferably 2 to 4. The present invention does not have special requirements on the concentration and amount of the acidic solution; it is sufficient to adjust the pH value of the acid treatment to 1 to 5.

[0016] In step (1), the mass concentration of the slurry during acid treatment is preferably 1-10%, more preferably 2-7%, and even more preferably 3-5%. This invention achieves a slurry mass concentration of 1-10% by controlling the water content in the acidic solution system.

[0017] In step (1), the chelating agent preferably includes ethylenediaminetetraacetic acid (EDTA), diethyltriaminepentaacetic acid (DTPA), or diethylenetriaminepentamethylenephosphonic acid (DTPMPA). The chelation treatment time is preferably 10–60 min, more preferably 20–40 min; the chelation treatment temperature is preferably 25–50 °C, more preferably 30–45 °C. The amount of chelating agent added is preferably 0.2–0.7% of the oven-dry weight of the acid-treated slurry, more preferably 0.4–0.6%.

[0018] In step (1), the chelation treatment process preferably involves a slurry concentration of 3-10%, more preferably 4-7%. During the chelation treatment, the present invention controls the water content in the acid-treated slurry and / or adds a certain amount of water to maintain a slurry concentration of 3-10%.

[0019] In step (1), the refining speed of the mechanical pulping is preferably 4000-14000 r, and more preferably 8000-10000 r; the beating degree of the pulp after mechanical pulping is preferably 13-81°SR, and more preferably 30-50°SR.

[0020] In step (2), the antioxidant is propyl gallate, which is an essential component in the preparation of cellulose spinning solution. It can prevent NMMO from degrading at high temperatures and other side reactions, and is a stabilizer for NMMO solution. In addition, propyl gallate can also inhibit cellulose degradation.

[0021] In step (2), the preferred mass of the antioxidant is 0.04 to 0.1% of the total mass of the modified pulp, NMMO solution, and antioxidant.

[0022] In step (2), the concentration of the low-concentration NMMO dilute solution is preferably 30-60%, more preferably 40-60%; the treatment time is preferably 20-120 min, more preferably 30-80 min; the treatment temperature is preferably 80-110℃, more preferably 85-100℃; the weight percentage concentration of cellulose in the cellulose cake is preferably 30-65%, more preferably 40-60%; and the pressure of the roller press for the purification treatment is preferably 100-500 bar, more preferably 100-300 bar.

[0023] In step (3), the concentration of the high-concentration NMMO dilute solution is preferably 60-80%, more preferably 60-75%; the treatment time is preferably 20-120 min, more preferably 30-80 min; the treatment temperature is preferably 80-110℃, more preferably 85-100℃; the weight percentage concentration of cellulose in the cellulose cake is preferably 30-65%, more preferably 40-60%; and the pressure of the roller press for the purification treatment is preferably 100-500 bar, more preferably 100-300 bar.

[0024] In step (4), the spinning process is as follows: the spinning solution is metered by a metering pump under a pressure of 0.3 to 0.5 MPa and then extruded through the micro-holes of the spinneret. It enters the coagulation bath through an air section of 10 to 20 mm (between the surface of the spinneret and the surface of the coagulation bath liquid), and solidifies in the coagulation bath at 5 to 30°C. After stretching, washing, and drying, Lyocell fiber is obtained.

[0025] Beneficial effects

[0026] The dilute NMMO solution used in this invention is the same solvent used in the existing Lyocell fiber production process, with a recovery rate of over 99%, and is green, pollution-free, and recyclable.

[0027] This invention employs mechanical pulping to pretreat chemical pulp, thereby controlling the specific surface area and accessibility of the chemical pulp fibers. This promotes the penetration of NMMO solution and effectively enhances the removal efficiency of NMMO solution for hemicellulose. Throughout the process, the molecular structure and crystal form of cellulose remain unchanged, enabling selective and efficient removal of hemicellulose.

[0028] This invention effectively reduces hemicellulose and metal ions in ordinary chemical pulp through purification treatment, allowing the pulp to reach a pre-swelled state, thereby making the pulp dissolve faster and improving the solubility and spinnability of the pulp.

[0029] The preparation method disclosed in this invention is to first purify the ordinary chemical pulp modified pulp in two stages using a dilute NMMO solution, then dissolve the modified pulp in NMMO, and finally spin it using a dry-jet wet spinning method. The Lyocell fiber obtained has the same or some better properties than the Lyocell fiber prepared by dissolving pulp.

[0030] This invention utilizes lower-cost cellulose pulp, such as paper-grade pulp, as raw material, reducing the raw material cost of cellulose pulp and thus lowering the cost of Lyocell fiber products, thereby improving the product's economic efficiency and market competitiveness. Furthermore, the preparation process is simple, and the preparation technology, raw materials, and methods are more environmentally friendly, resulting in significant economic and social benefits. Detailed Implementation

[0031] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following detailed description, in conjunction with preferred embodiments, details the specific implementation, structure, features, and effects of a method for preparing Lyocell fibers using ordinary chemical pulp according to the present invention. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] Example 1

[0033] Ordinary bleached chemical pulp sheets were shredded and loosened using a delamination machine until the fibers were evenly dispersed. The excess water was wrung out, and the shredded pulp was dried in an oven at 60°C for 24 hours. The pulp was then placed in a self-sealing bag to equilibrate and the moisture content was measured for later use. The loosened bleached chemical pulp was mixed with hydrochloric acid solution and acid-treated at 10°C for 60 minutes. The concentration of the hydrochloric acid solution was 6 mol / L, and the dosage was 1.5% relative to the oven-dry pulp mass. The pH value of the acid treatment was 4.6. The resulting pulp concentration was controlled at 3 wt%, yielding acid-treated pulp. The acid-treated pulp was washed until the pH value reached 5–7, while maintaining a pulp concentration of 3%. Then, EDTA, a metal ion chelating agent, was added for chelation treatment at 30°C for 60 minutes. The dosage of the chelating agent was 0.5% relative to the oven-dry pulp mass. The formed metal chelates were removed, and the resulting pulp was washed to neutral and dried to obtain low-metal-content pulp.

[0034] Take 50g of oven-dried pulp and soak it in deionized water for 24 hours. Then add deionized water to loosen it. After loosening, adjust the pulp mass concentration to 10%. Place the pulp evenly in a PFI refiner for refining. Adjust the refining speed to 8000r. Then wash it with deionized water, dry it, and place it in a self-sealing bag to balance the moisture before use.

[0035] The refined pulp was mixed with propyl gallate and a 50% dilute NMMO solution (propyl gallate was 0.1 wt%) to form a pulp / NMMO / H2O blend with a pulp mass fraction of 5 wt%. The blend was treated in a 90°C water bath for 30 min, and then the pulp was pressed using a roller press at 200 bar to obtain a solid cake, which was then dried in a 60°C oven for 24 h. The solid cake was then mixed again in a 70% NMMO solution, and the above operation was repeated to obtain the final dissolving pulp for Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0036] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0037] The spinning solution was metered by a metering pump at a pressure of 0.92 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 3.64 CN / dtex, and the wet tensile strength was 3.12 CN / dtex.

[0038] Example 2

[0039] The preparation steps are the same as in Example 1, except that 60% and 75% NMMO solutions are used for purification. The purification steps are as follows:

[0040] The refined pulp was mixed with propyl gallate and a 60% dilute NMMO solution (propyl gallate was 0.1 wt%) to form a pulp / NMMO / H2O blend with a pulp mass fraction of 5 wt%. The blend was treated in a 90°C water bath for 30 min, and then the pulp was pressed using a roller press at 200 bar to obtain a solid cake, which was then dried in a 60°C oven for 24 h. The solid cake was then mixed again in a 75% NMMO solution, and the above operation was repeated to obtain the final dissolving pulp for Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0041] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0042] The spinning solution was metered by a metering pump at a pressure of 0.93 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 3.46 CN / dtex, and the wet tensile strength was 3.04 CN / dtex.

[0043] Example 3

[0044] The preparation steps are the same as in Example 1, except that the purification time in the water bath is extended to 60 minutes, i.e., the purification steps are as follows:

[0045] The refined pulp was mixed with propyl gallate and a 50% dilute NMMO solution (propyl gallate was 0.1 wt%) to form a pulp / NMMO / H2O blend with a pulp mass fraction of 5 wt%. The blend was treated in a 90°C water bath for 60 min, and then the pulp was pressed using a roller press at 200 bar to obtain a solid cake, which was then dried in a 60°C oven for 24 h. The solid cake was then mixed again in a 70% NMMO solution, and the above operation was repeated to obtain the final dissolving pulp for Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0046] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0047] The spinning solution was metered by a metering pump at a pressure of 0.91 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 3.49 CN / dtex, and the wet tensile strength was 3.03 CN / dtex.

[0048] Example 4

[0049] The preparation steps are the same as in Example 1, except that the purification process is carried out at a temperature of 100°C in a water bath. The purification steps are as follows:

[0050] The refined pulp was mixed with propyl gallate and a 50% dilute NMMO solution (propyl gallate was 0.1 wt%) to form a pulp / NMMO / H2O blend with a pulp mass fraction of 5 wt%. The blend was treated in a 100°C water bath for 30 min, and then the pulp was pressed using a roller press at a pressure of 200 bar to obtain a solid cake, which was then dried in a 60°C oven for 24 h. The solid cake was then mixed again in a 70% NMMO solution, and the above operation was repeated to obtain the final dissolving pulp for Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0051] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0052] The spinning solution was metered by a metering pump at a pressure of 0.91 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 3.51 CN / dtex, and the wet tensile strength was 3.06 CN / dtex.

[0053] Comparative Example 1

[0054] The preparation steps are the same as in Example 1, except that only one purification step is used, i.e., the purification step is as follows:

[0055] The refined pulp was mixed with propyl gallate and a 70% dilute NMMO solution (propyl gallate was 0.1 wt%) to form a pulp / NMMO / H2O blend with a pulp mass fraction of 5 wt%. The blend was treated in a 90°C water bath for 30 min, and then the pulp was pressed using a roller press at 200 bar to obtain a solid cake, which was then dried in a 60°C oven for 24 h to obtain the final dissolving pulp for preparing Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0056] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0057] The spinning solution was metered by a metering pump at a pressure of 0.95 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 3.12 CN / dtex, and the wet tensile strength was 2.74 CN / dtex.

[0058] Comparative Example 2

[0059] The preparation steps are the same as in Example 1, except that a purification step is not used;

[0060] Ordinary bleached chemical pulp sheets were shredded and loosened using a delamination machine until the fibers were evenly dispersed. The excess water was wrung out, and the shredded pulp was dried in an oven at 60°C for 24 hours. The pulp was then placed in a self-sealing bag to equilibrate and the moisture content was measured for later use. The loosened bleached chemical pulp was mixed with hydrochloric acid solution and acid-treated at 10°C for 60 minutes. The concentration of the hydrochloric acid solution was 6 mol / L, and the dosage was 1.5% relative to the oven-dry pulp mass. The pH value of the acid treatment was 4.6. The resulting pulp concentration was controlled at 3 wt%, yielding acid-treated pulp. The acid-treated pulp was washed until the pH value reached 5–7, while maintaining a pulp concentration of 3%. Then, EDTA, a metal ion chelating agent, was added for chelation treatment at 30°C for 60 minutes. The dosage of the chelating agent was 0.5% relative to the oven-dry pulp mass. The formed metal chelates were removed, and the resulting pulp was washed to neutral and dried to obtain low-metal-content pulp.

[0061] Take 50g of oven-dried pulp and soak it in deionized water for 24 hours. Then add deionized water to loosen it. After loosening, adjust the pulp mass concentration to 10%. Place the pulp evenly in a PFI refiner for refining. Adjust the refining speed to 8000r. Then wash it with deionized water, dry it, and place it in a self-sealing bag to balance the moisture before use.

[0062] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0063] The spinning solution was metered by a metering pump at a pressure of 0.95 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 2.91 CN / dtex, and the wet tensile strength was 2.59 CN / dtex.

[0064] Comparative Example 3

[0065] The preparation steps are the same as in Example 1, except that the purification process is carried out at a temperature of 70°C in a water bath. The purification steps are as follows:

[0066] The refined pulp was mixed with propyl gallate and a 50% dilute NMMO solution (propyl gallate was 0.1 wt%) to form a pulp / NMMO / H2O blend with a pulp mass fraction of 5 wt%. The blend was treated in a 70°C water bath for 30 min, and then the pulp was pressed using a roller press at 200 bar to obtain a solid cake, which was then dried in a 60°C oven for 24 h. The solid cake was then mixed again in a 70% NMMO solution, and the above operation was repeated to obtain the final dissolving pulp for Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0067] The obtained pulp was torn into pieces of about 1cm×1cm, and 40g was weighed. Then, 554g of 72wt% NMMO aqueous solution was weighed. The pulp was added to the NMMO solution and 0.5g of 0.1% propyl gallate was added to the reaction vessel. The mixture was stirred and swollen for 0.5h. Then, the mixture was vacuumed at 100℃ for 2h to obtain the spinning solution.

[0068] The spinning solution was metered by a metering pump at a pressure of 0.91 MPa and a temperature of 90°C, and then extruded through a spinneret at a rate of 10 mL / min for spinning. The filter screen had a mesh size of 100 mesh, the spinneret cap had an orifice diameter of 0.12 mm and 30 orifices, and the side-blowing air temperature was room temperature. After passing through an air section of 10-15 mm, the fibers entered a coagulation bath at a temperature of 25°C. After drawing, washing, and drying, Lyocell fibers were obtained. The dry tensile strength of the obtained Lyocell fibers was 3.16 CN / dtex, and the wet tensile strength was 2.66 CN / dtex.

[0069] Although the above embodiments have provided a detailed description of the present invention, the technical scope of the present invention is not limited to the content described above. People can make various modifications and variations to the above embodiments without departing from the technical concept of the present invention, and all such modifications and variations should fall within the protection scope of the present invention.

Claims

1. A method for preparing lyocell fibers from ordinary chemical pulp, characterized in that, Includes the following steps: (1) Acid treatment and chelation treatment are carried out on papermaking grade bleached chemical pulp to obtain pretreated pulp with low metal ion content; The pretreated pulp is mechanically refined to obtain refined pulp. (2) The obtained pulp is mixed with a low concentration of NMMO dilute solution and an antioxidant, purified at a certain temperature for a period of time, and then pressed in a drum press to obtain cellulose cake; (3) The obtained cellulose cake is mixed again with a high concentration of NMMO dilute solution and antioxidant, purified at a certain temperature for a period of time, pressed under a drum press, and then dried in an oven to obtain cellulose solid cake. (4) The cellulose solid cake is shredded in a paper shredder, mixed with NMMO solution and antioxidant in a reaction vessel, and subjected to shearing force and vacuum treatment to obtain a cellulose solution; the cellulose solution is used for wet spinning to obtain Lyocell fiber; In step (2), the antioxidant is propyl gallate, and the mass of the antioxidant is 0.04-0.1% of the total mass of the pulp, NMMO solution, and antioxidant. In step (2), the NMMO concentration during purification is 40-60%; the purification time is 50-80 min; the purification temperature is 85-100 ℃; the weight percentage concentration of cellulose in the cellulose cake is 40-60%; and the pressure of the roller press during purification is 100-300 bar. In step (3), the NMMO concentration during purification is 60-75%; the purification time is 50-80 min; the purification temperature is 85-100 ℃; the cellulose weight percentage concentration in the cellulose cake is 40-60%; and the pressure of the roller press during purification is 100-300 bar.

2. The preparation method according to claim 1, characterized in that, The bleached chemical pulp in step (1) includes one or more of wood pulp, bamboo pulp, wheat straw pulp, and hemp pulp.

3. The preparation method according to claim 1, characterized in that, The acidic solution in step (1) includes sulfuric acid solution and hydrochloric acid solution; the acid treatment time is 30~50 min; the acid treatment temperature is 10~30℃.

4. The preparation method according to claim 1, characterized in that, In step (1), the pH value of the acid treatment is 2-4; the mass concentration of the slurry during the acid treatment process is 3-5%.

5. The preparation method according to claim 1, characterized in that, The chelating agent in step (1) includes ethylenediaminetetraacetic acid (EDTA), diethyltriaminepentaacetic acid (DTPA), or diethylenetriaminepentamethylenephosphonic acid (DTPMPA); the chelation treatment time is 20-40 min; the chelation treatment temperature is 30-45℃; and the mass concentration of the slurry during the chelation treatment is 4-7%.

6. The preparation method according to claim 1, characterized in that, The beating degree of the pulp after mechanical refining is 30~50°SR.

7. The preparation method according to claim 1, characterized in that, In step (4), the spinning process is as follows: the spinning solution is metered by a metering pump under a pressure of 0.3~0.5MPa and then extruded through the micro-holes of the spinneret. It enters the coagulation bath through an air section of 10~20mm and solidifies in the coagulation bath at 5~30℃. After stretching, washing and drying, Lyocell fiber is obtained.