Method for preparing lyocell fiber by using common chemical pulp

Abstract

The invention provides a method for preparing a Lyocell fiber by using a common chemical pulp. The preparation method of the Lyocell fiber comprises the following steps: pretreating common chemical pulp, purifying the pretreated pulp through two sections of NMMO dilute solutions with different concentrations so as to remove hemicellulose in the pulp, and preparing the Lyocell fiber from the purified pulp in a dry-jet wet-spinning manner, and the prepared Lyocell fiber has the same or partially better performance as the Lyocell fiber prepared from the dissolving pulp. The preparation method disclosed by the invention is simple, green and environment-friendly, can be effectively combined with an existing Lyocell fiber manufacturing process, and can remarkably reduce the manufacturing cost of the Lyocell fiber.

Description

Technical Field

[0001] The invention belongs to the field of textile fiber preparation, and in particular relates to a method for preparing lyocell fiber by using common chemical pulp. Background Art

[0002] Lyocell fiber, also known as Lyocell fiber in English, is a regenerated cellulose fiber made by dry-jet wet spinning process with N-methylmorpholine-N-oxide (NMMO) as solvent. The waste can be naturally degraded and the recovery rate of the solvent NMMO used in the production process can reach 99.5%. It does not pollute the environment and is hailed as the "green fiber of the 21st century" by the international textile industry.

[0003] At present, dissolving pulp is generally used as raw material for preparing Lyocell fiber, which leads to higher cost. With the development of global economy and the improvement of environmental protection requirements, the production and supply of dissolving pulp are facing more challenges and pressures. The high cost of dissolving pulp makes the price of Lyocell fiber remain high, which affects its market competitiveness and promotion and application to a certain extent. Therefore, how to prepare Lyocell fiber with ordinary chemical pulp has become a hot topic in current research. The patent with publication number CN115094660A completes the purification and upgrading of ordinary chemical pulp through alkali extraction, enzyme treatment and acid treatment. The main factors affecting the preparation of Lyocell fiber from ordinary chemical pulp are that it contains a large amount of hemicellulose and metal ions. The presence of hemicellulose will lead to increased viscosity of spinning solution, insufficient pulp impregnation, decreased product strength performance and large solvent recovery load. Metal ions are effective inducers of NMMO homolysis reaction, which will accelerate the decomposition of NMMO, resulting in decreased viscosity of spinning solution and poor spinnability. If the metal ion content is too high, the spinning solution will accelerate the decomposition and release a large amount of heat, which will cause explosion if out of control. Therefore, the removal of hemicellulose and the control of metal ion content become the key to preparing Lyocell fibers using ordinary chemical pulp.

[0004] In order to improve the solubility and spinnability of ordinary chemical pulp, reduce costs and improve the competitiveness of Lyocell fibers, researchers are working hard to explore more economical preparation methods, and improving the production process has become a pressing issue to be addressed. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing Lyocell fiber using ordinary chemical pulp. The preparation method provided by the present invention is an environmentally friendly method in which the solvent can be recycled and reused, which can effectively remove hemicellulose and metal ions in ordinary chemical pulp, and prepare Lyocell fiber by dry-jet wet spinning, thereby solving the problem of high cost of dissolving pulp for Lyocell fiber.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing lyocell fiber by using common chemical pulp, comprising the following steps:

[0008] (1) subjecting paper-grade bleached chemical pulp to acid treatment and chelation treatment to obtain pretreated pulp with low metal ion content; subjecting the pretreated pulp to mechanical refining treatment to obtain refined pulp;

[0009] (2) mixing the obtained refined pulp with a low-concentration NMMO dilute solution and an antioxidant, treating the mixture at a certain temperature for a period of time and then pressing the mixture under a roller press to obtain a cellulose cake;

[0010] (3) mixing the obtained cellulose cake with a high concentration NMMO dilute solution and an antioxidant again, treating it at a certain temperature for a period of time, pressing it under a roller press, and then drying it in an oven to obtain a cellulose solid cake;

[0011] (4) Chopping the cellulose solid cake in a shredder, mixing it with an NMMO solution and an antioxidant in a reactor, applying shear force and vacuum treatment to obtain a cellulose solution; and wet spinning the cellulose solution to obtain Lyocell fibers.

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

[0013] The bleached chemical pulp 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 time of the acid treatment is preferably 10 to 90 minutes, more preferably 30 to 50 minutes; the temperature of the acid treatment is preferably 10 to 50°C, more preferably 10 to 30°C.

[0015] The pH value of the acid treatment in step (1) is preferably 1 to 5, more preferably 2 to 4. The present invention has no particular requirements on the concentration and amount of the acid solution, and the pH value of the acid treatment can be adjusted to 1 to 5.

[0016] The mass concentration of the slurry during the acid treatment in step (1) is preferably 1-10%, more preferably 2-7%, and more preferably 3-5%. The present invention controls the water content in the acid solution system to make the mass concentration of the slurry between 1 and 10%.

[0017] The chelating agent in step (1) preferably includes ethylenediaminetetraacetic acid (EDTA), diethyltriaminepentaacetic acid (DTPA) or diethylenetriaminepenta(methylenephosphonic acid) (DTPMPA). The time of the chelating treatment is preferably 10 to 60 minutes, more preferably 20 to 40 minutes; the temperature of the chelating treatment is preferably 25 to 50°C, more preferably 30 to 45°C. The amount of the chelating agent added is preferably 0.2 to 0.7% of the absolute dry mass of the acid-treated slurry, more preferably 0.4 to 0.6%.

[0018] The mass concentration of the slurry during the chelation treatment in step (1) is preferably 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 make the slurry mass concentration 3-10%.

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

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

[0021] The mass of the antioxidant in step (2) is preferably 0.04-0.1% of the total mass of the modified pulp, NMMO solution and antioxidant.

[0022] The concentration of the low-concentration NMMO dilute solution in step (2) 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° C., more preferably 85-100° C.; the weight percentage concentration of cellulose in the cellulose cake is preferably 30-65%, more preferably 40-60%; the pressure of the roller press for the purification treatment is preferably 100-500 bar, more preferably 100-300 bar.

[0023] The concentration of the high-concentration NMMO dilute solution in step (3) 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° C., more preferably 85-100° C.; the weight percentage concentration of cellulose in the cellulose cake is preferably 30-65%, more preferably 40-60%; the pressure of the roller press for the purification treatment is preferably 100-500 bar, more preferably 100-300 bar.

[0024] The spinning in step (4) is specifically as follows: the spinning solution is metered by a metering pump at a pressure of 0.3 to 0.5 MPa and then extruded from the micropores of the spinneret, passes through an air section of 10 to 20 mm (between the surface of the spinneret and the surface of the coagulation bath liquid), and coagulates in a coagulation bath at 5 to 30° C., and then is stretched, washed with water, and dried to obtain Lyocell fibers.

[0025] Beneficial Effects

[0026] The NMMO dilute solution used in the present invention is the same as the solvent used in the existing Lyocell fiber production process, and its recovery rate exceeds 99%. It is green and pollution-free and can be repeatedly recycled.

[0027] The present invention adopts mechanical refining to pretreat chemical pulp, regulates the specific surface area and accessibility of chemical pulp fibers, promotes the penetration of NMMO solution, and effectively improves the removal effect of NMMO solution on hemicellulose. During the whole process, the molecular structure and crystal form of cellulose do not change at all, and hemicellulose can be selectively and efficiently removed.

[0028] The invention effectively reduces hemicellulose and metal ions in common chemical pulp through purification treatment, so that the pulp reaches a pre-swelling state, thereby making the pulp dissolve faster and improving the solubility and spinnability of the pulp.

[0029] The preparation method disclosed in the present invention is to first purify the modified pulp of ordinary chemical pulp in two stages using a dilute NMMO solution, then dissolve the modified pulp in NMMO, and then use a dry-jet wet spinning method to spin the Lyocell fiber. The obtained Lyocell fiber has the same or partially better performance than the Lyocell fiber prepared from dissolving pulp.

[0030] The present invention can use low-priced cellulose pulp such as paper-grade pulp as raw material, which reduces the raw material cost of cellulose pulp, thereby reducing the cost of Lyocell fiber products and improving the economic benefits and market competitiveness of products. In addition, the preparation process is simple, and the preparation technology, production raw materials and methods are more environmentally friendly, with good economic and social benefits. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the method for preparing Lyocell fiber using ordinary chemical pulp according to the present invention, its specific implementation, structure, characteristics and effects, in combination with the preferred embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0032] Example 1

[0033] The ordinary bleached chemical pulp board is torn into pieces, and the pulp board is deflaked by a deflaking machine until the fibers are evenly dispersed, the water is wrung out, the pieces are put into an oven at 60°C for 24 hours for drying, and the pieces are put into a ziplock bag for moisture balance, and the moisture content of the pulp is measured for standby use; the deflaked bleached chemical pulp is mixed with a hydrochloric acid solution and acid-treated at a temperature of 10°C for 60 minutes, the concentration of the hydrochloric acid solution is 6 mol / L, the dosage is 1.5% relative to the mass of the absolute dry pulp, and the pH value of the acid treatment is 4.6; at the same time, the mass concentration of the obtained pulp is controlled to be 3wt% to obtain an acid-treated pulp; the obtained acid-treated pulp is washed to a pH value of 5-7, and at the same time, the mass concentration of the pulp is controlled to be 3%, and then a metal ion chelator EDTA is added to perform a chelation treatment at a temperature of 30°C for 60 minutes, and the dosage of the chelator is 0.5% relative to the mass of the absolute dry pulp; the formed metal chelate is removed, and then the obtained pulp is washed to neutrality and dried to obtain a pulp with a low metal content.

[0034] Take 50g of absolutely dry pulp, soak it in deionized water for 24h, then add deionized water to loosen it, adjust the pulp mass concentration to 10% after loosening, place the pulp evenly in a PFI refiner for refining treatment, adjust the refining speed to 8000r, then wash it with deionized water, dry it, put it in a ziplock bag to balance the moisture and set it aside.

[0035] The pulp after refining is mixed with propyl gallate and 50% NMMO dilute solution, the amount of propyl gallate is 0.1wt%, and finally a pulp / NMMO / H2O blend with a pulp mass fraction of 5wt% is formed. The blend is treated in a 90°C water bath for 30min, and then the pulp is squeezed at a pressure of 200bar using a roller press to obtain a solid cake, which is placed in a 60°C oven for drying for 24h. After that, the solid cake is placed in a 70% NMMO solution for secondary mixing, and the above operation is repeated to obtain the final dissolving pulp for preparing Lyocell fiber. The extruded NMMO is recovered during the experiment.

[0036] The obtained pulp was torn into sheets of about 1 cm × 1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (ie 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0037] The spinning solution was measured by a metering pump at a pressure of 0.92MPa and 90°C, and then extruded from a spinneret at a speed of 10mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12mm, the number of holes was 30, and the side blowing temperature was room temperature. After passing through an air section of 10-15mm, it entered a coagulation bath at a temperature of 25°C, and after drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 3.64CN / dtex and a wet breaking strength of 3.12CN / dtex.

[0038] Example 2

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

[0040] The pulp after refining is mixed with propyl gallate and 60% NMMO dilute solution, the amount of propyl gallate is 0.1wt%, and finally a pulp / NMMO / H2O blend with a pulp mass fraction of 5wt% is formed. The blend is treated in a 90°C water bath for 30min, and then the pulp is squeezed at a pressure of 200bar using a roller press to obtain a solid cake, which is placed in a 60°C oven for drying for 24h. After that, the solid cake is placed in a 75% NMMO solution for secondary mixing, and the above operation is repeated to obtain the final dissolving pulp for preparing Lyocell fiber. The extruded NMMO is recovered during the experiment.

[0041] The obtained pulp was torn into sheets of about 1 cm × 1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (ie 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0042] The spinning solution was measured by a metering pump at a pressure of 0.93MPa and 90°C, and then extruded from a spinneret at a speed of 10mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12mm, the number of holes was 30, the side blowing temperature was room temperature, and it entered a coagulation bath at a temperature of 25°C after passing through an air section of 10-15mm. After drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 3.46CN / dtex and a wet breaking strength of 3.04CN / dtex.

[0043] Example 3

[0044] The preparation steps are the same as those in Example 1, except that the treatment time in the water bath is extended to 60 min during purification, that is, the purification steps are:

[0045] The pulp after refining is mixed with propyl gallate and 50% NMMO dilute solution, the amount of propyl gallate is 0.1wt%, and finally a pulp / NMMO / H2O blend with a pulp mass fraction of 5wt% is formed. The blend is treated in a 90°C water bath for 60min, and then the pulp is squeezed at a pressure of 200bar using a roller press to obtain a solid cake, which is placed in a 60°C oven for drying for 24h. After that, the solid cake is placed in a 70% NMMO solution for secondary mixing, and the above operation is repeated to obtain the final dissolving pulp for preparing Lyocell fiber. The extruded NMMO is recovered during the experiment.

[0046] The obtained pulp was torn into sheets of about 1 cm × 1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (ie 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0047] The spinning solution was measured by a metering pump at a pressure of 0.91 MPa and 90°C, and then extruded from a spinneret at a speed of 10 mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12 mm, the number of holes was 30, and the side blowing temperature was room temperature. After passing through an air section of 10-15 mm, it entered a coagulation bath at a temperature of 25°C, and after drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 3.49 CN / dtex and a wet breaking strength of 3.03 CN / dtex.

[0048] Example 4

[0049] The preparation steps are the same as those in Example 1, except that the treatment temperature in the water bath during purification is 100° C., that is, the purification steps are:

[0050] The pulp after refining is mixed with propyl gallate and 50% NMMO dilute solution, the amount of propyl gallate is 0.1wt%, and finally a pulp / NMMO / H2O blend with a pulp mass fraction of 5wt% is formed. The blend is treated in a 100°C water bath for 30min, and then the pulp is squeezed at a pressure of 200bar using a roller press to obtain a solid cake, which is placed in a 60°C oven for drying for 24h. After that, the solid cake is placed in a 70% NMMO solution for secondary mixing, and the above operation is repeated to obtain the final dissolving pulp for preparing Lyocell fiber. The extruded NMMO is recovered during the experiment.

[0051] The obtained pulp was torn into sheets of about 1 cm × 1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (ie 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0052] The spinning solution was measured by a metering pump at a pressure of 0.91 MPa and 90°C, and then extruded from a spinneret at a speed of 10 mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12 mm, the number of holes was 30, and the side blowing temperature was room temperature. After passing through an air section of 10-15 mm, it entered a coagulation bath at a temperature of 25°C, and after drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 3.51 CN / dtex and a wet breaking strength of 3.06 CN / dtex.

[0053] Comparative Example 1

[0054] The preparation steps are the same as those in Example 1, except that only one step of purification is used during purification, that is, the purification steps are:

[0055] The pulp after refining was mixed with propyl gallate and 70% NMMO dilute solution, the amount of propyl gallate was 0.1wt%, and finally a pulp / NMMO / H2O blend with a pulp mass fraction of 5wt% was formed, the blend was treated in a 90°C water bath for 30min, and then the pulp was squeezed by a roller press at a pressure of 200bar to obtain a solid cake which was placed in a 60°C oven and dried for 24h to obtain a dissolving pulp for preparing Lyocell fibers. The extruded NMMO was recovered during the experiment.

[0056] The obtained pulp was torn into sheets of about 1 cm × 1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (ie 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0057] The spinning solution was measured by a metering pump at a pressure of 0.95MPa and 90°C and then extruded from a spinneret at a speed of 10mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12mm, the number of holes was 30, the side blowing temperature was room temperature, and the solution entered a coagulation bath at a temperature of 25°C after passing through an air section of 10-15mm. After drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 3.12CN / dtex and a wet breaking strength of 2.74CN / dtex.

[0058] Comparative Example 2

[0059] The preparation steps are the same as those in Example 1, except that no purification step is used;

[0060] The ordinary bleached chemical pulp board is torn into pieces, and the pulp board is deflaked by a deflaking machine until the fibers are evenly dispersed, the water is wrung out, the pieces are put into an oven at 60°C for 24 hours for drying, and the pieces are put into a ziplock bag for moisture balance, and the moisture content of the pulp is measured for standby use; the deflaked bleached chemical pulp is mixed with a hydrochloric acid solution and acid-treated at a temperature of 10°C for 60 minutes, the concentration of the hydrochloric acid solution is 6 mol / L, the dosage is 1.5% relative to the mass of the absolute dry pulp, and the pH value of the acid treatment is 4.6; at the same time, the mass concentration of the obtained pulp is controlled to be 3wt% to obtain an acid-treated pulp; the obtained acid-treated pulp is washed to a pH value of 5-7, and at the same time, the mass concentration of the pulp is controlled to be 3%, and then a metal ion chelator EDTA is added to perform a chelation treatment at a temperature of 30°C for 60 minutes, and the dosage of the chelator is 0.5% relative to the mass of the absolute dry pulp; the formed metal chelate is removed, and then the obtained pulp is washed to neutrality and dried to obtain a pulp with a low metal content.

[0061] Take 50g of absolutely dry pulp, soak it in deionized water for 24h, then add deionized water to loosen it, adjust the pulp mass concentration to 10% after loosening, place the pulp evenly in a PFI refiner for refining treatment, adjust the refining speed to 8000r, then wash it with deionized water, dry it, put it in a ziplock bag to balance the moisture and set it aside.

[0062] The obtained refined pulp was torn into sheets of about 1 cm×1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (i.e. 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0063] The spinning solution was measured by a metering pump at a pressure of 0.95 MPa and 90°C, and then extruded from a spinneret at a speed of 10 mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12 mm, the number of holes was 30, and the side blowing temperature was room temperature. After passing through an air section of 10-15 mm, it entered a coagulation bath at a temperature of 25°C, and after drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 2.91 CN / dtex and a wet breaking strength of 2.59 CN / dtex.

[0064] Comparative Example 3

[0065] The preparation steps are the same as those in Example 1, except that the treatment temperature in the water bath during purification is 70° C., that is, the purification steps are:

[0066] The pulp after refining is mixed with propyl gallate and 50% NMMO dilute solution, the amount of propyl gallate is 0.1wt%, and finally a pulp / NMMO / H2O blend with a pulp mass fraction of 5wt% is formed. The blend is treated in a 70°C water bath for 30min, and then the pulp is squeezed at a pressure of 200bar using a roller press to obtain a solid cake, which is placed in a 60°C oven for drying for 24h. After that, the solid cake is placed in a 70% NMMO solution for secondary mixing, and the above operation is repeated to obtain the final dissolving pulp for preparing Lyocell fiber. The extruded NMMO is recovered during the experiment.

[0067] The obtained pulp was torn into sheets of about 1 cm × 1 cm, 40 g was weighed, and then 554 g of 72 wt% NMMO aqueous solution was weighed, the pulp was added to the NMMO solution and 0.1% (ie 0.5 g) of propyl gallate was added and placed in a reactor, mixed and stirred for swelling for 0.5 h, and then vacuumed at 100°C for 2 h to obtain a spinning solution.

[0068] The spinning solution was measured by a metering pump at a pressure of 0.91 MPa and 90°C, and then extruded from a spinneret at a speed of 10 mL / min for spinning. The filter mesh was 100 meshes, the spinneret aperture was 0.12 mm, the number of holes was 30, and the side blowing temperature was room temperature. After passing through an air section of 10-15 mm, it entered a coagulation bath at a temperature of 25°C, and after drawing, washing, and drying, Lyocell fibers were obtained. The obtained Lyocell fibers had a dry breaking strength of 3.16 CN / dtex and a wet breaking strength of 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 contents in the above description. People can make various deformations and modifications to the above embodiments without departing from the technical idea of ​​the present invention, and these deformations and modifications should all fall within the protection scope of the present invention.

Claims

1. The present invention provides a method for preparing lyocell fiber from ordinary chemical pulp, characterized in that: The following steps are involved: (1) subjecting paper-grade bleached chemical pulp to acid treatment and chelation treatment to obtain pretreated pulp with low metal ion content; subjecting the pretreated pulp to mechanical refining to obtain refined pulp; (2) mixing the obtained refined pulp with a low-concentration NMMO dilute solution and an antioxidant, treating the mixture at a certain temperature for a period of time and then pressing the mixture under a roller press to obtain a cellulose cake; (3) mixing the obtained cellulose cake with a high concentration NMMO dilute solution and an antioxidant again, treating it at a certain temperature for a period of time, pressing it under a roller press, and then drying it in an oven to obtain a cellulose solid cake; (4) Chopping the cellulose solid cake in a shredder, mixing it with an NMMO solution and an antioxidant in a reactor, applying shear force and vacuum treatment to obtain a cellulose solution; and wet spinning the cellulose solution to obtain Lyocell fibers.

2. The preparation method according to claim 1, characterized in that: The bleached chemical pulp in step (1) preferably 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) preferably includes sulfuric acid solution, hydrochloric acid solution, etc.; the time of the acid treatment is 30 to 50 minutes; and the temperature of the acid treatment is 10 to 30°C.

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

5. The preparation method according to claim 1, characterized in that: The chelating agent in step (1) preferably includes ethylenediaminetetraacetic acid (EDTA), diethyltriaminepentaacetic acid (DTPA) or diethylenetriaminepenta(methylenephosphonic acid) (DTPMPA). The chelating treatment time is 20 to 40 minutes; the chelating treatment temperature is 30 to 45°C. The amount of the chelating agent added is 0.4 to 0.6% of the absolute dry mass of the acid-treated slurry. The mass concentration of the slurry during the chelating treatment is 4 to 7%.

6. The preparation method according to claim 1, characterized in that: The refining speed of the mechanical refining in the step (1) is 8000-10000r; the beating degree of the pulp after the mechanical refining is 30-50°SR.

7. The preparation method according to claim 1, characterized in that: In the step (2), the antioxidant is propyl gallate, and the mass of the antioxidant is 0.04-0.1% of the total mass of the modified pulp, the NMMO solution and the antioxidant.

8. The preparation method according to claim 1, characterized in that: The NMMO concentration in the purification process in step (2) is 40-60%; the purification time is 50-80 minutes; the purification temperature is 85-100°C; the weight percentage concentration of cellulose in the cellulose cake is 40-60%; and the pressure of the roller press in the purification process is 100-300 bar.

9. The preparation method according to claim 1, characterized in that: The NMMO concentration in the purification process in step (3) is 60-75%; the purification time is 50-80 minutes; the purification temperature is 85-100°C; the weight percentage concentration of cellulose in the cellulose cake is 40-60%; and the pressure of the roller press in the purification process is 100-300 bar.

10. The preparation method according to claim 1, characterized in that: The spinning in step (4) is specifically as follows: the spinning solution is metered by a metering pump at a pressure of 0.3 to 0.5 MPa and then extruded from the micropores of the spinneret, passes through an air section of 10 to 20 mm (between the surface of the spinneret and the surface of the coagulation bath liquid), and coagulates in a coagulation bath at 5 to 30° C., and then is stretched, washed with water, and dried to obtain Lyocell fibers.