A method for producing fine denier lyocell fibers

Abstract

The application relates to the technical field of fiber manufacturing, and particularly discloses a preparation method of fine denier lyocell fiber, which comprises the following steps: spinning liquid preparation; mixing cellulose pulp and NMMO aqueous solution according to a proportion, adding an additive, and preparing spinning liquid through swelling and vacuum dehydration and dissolution; dry-jet wet spinning; conveying the spinning liquid prepared in the first step to a spinneret through a metering pump, extruding in a high-temperature environment, entering a coagulation bath after passing through an air gap, and forming nascent fiber; drafting and post-treatment; the fine denier lyocell fiber prepared by the method can systematically solve the fine denier problem: through synergistic regulation and control of five aspects of air blowing cooling, low-temperature circulation of the coagulation bath, reduction of a drafting ratio, optimization of the pulp and introduction of the additive, technical problems in the spinning of the fine denier lyocell fiber such as yarn breakage, plate sticking and hole blocking are solved, stable and continuous spinning of fiber with a fineness of less than or equal to 1.2 dtex is realized; the drafting ratio is significantly reduced; the component pressure is controllable; and the fiber performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of fiber manufacturing technology, specifically relating to a method for preparing fine denier lyocell fiber. Background Technology

[0002] Lyocell fiber is a green regenerated cellulose fiber prepared by dry-jet wet spinning process using N-methylmorpholine-N-oxide (NMMO) as solvent. It has environmental advantages such as renewable raw materials, recyclable solvent, and biodegradable products. In recent years, fine denier (fineness ≤1.2dtex) has become an important development direction for lyocell fiber. Fine denier fiber has advantages such as softer hand feel, better drape, and is more suitable for making high-end textiles and non-woven fabrics. However, the stable preparation of fine denier lyocell fibers faces significant technical bottlenecks. Existing dry-jet wet spinning processes can operate stably when spinning fibers with conventional fineness (above 1.33 dtex), but when the target fineness decreases to 1.2 dtex and below, problems such as yarn breakage, sticking to the spinning plate, and clogging commonly occur. Research indicates that this is mainly due to the following contradictions: Excessive draw ratio: The draw ratio required for finer denier yarns is >500% in the current process, which is far greater than the 300% of conventional production lines, resulting in drastic fluctuations in spinning tension. The spinneret is not compatible with the process: the existing spinneret orifice diameter (0.08-0.10mm) is too large, and the extrusion expansion effect is significant when the denier is refined; Unsuitable coagulation conditions: Conventional coagulation bath temperature and blowing conditions cannot meet the requirements for rapid and uniform coagulation of fine denier fibers. Therefore, developing a systematic process for preparing fine denier lyocell fibers to solve the above-mentioned technical challenges has significant industrial value. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing fine denier lyocell fibers to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing fine denier lyocell fiber includes the following steps: Step 1: Preparation of spinning solution; Cellulose pulp and N-methylmorpholine-N-oxide (NMMO) aqueous solution are mixed in a certain proportion, auxiliaries are added, and the mixture is swollen and dissolved under vacuum to obtain the spinning solution; Step 2: Dry-jet wet spinning; The spinning solution obtained in Step 1 is delivered to the spinneret through a metering pump, extruded under high temperature, and enters the coagulation bath after passing through the air gap to form nascent fibers. Step 3: Stretching and post-treatment; The nascent fibers from Step 2 are first stretched in a coagulation bath, followed by a second stretch in hot water. The stretched fibers are then washed, oiled, and dried to obtain the finished fine denier lyocell fiber.

[0005] Preferably, the cellulose pulp in step one is a single or mixed pulp, comprising softwood sulfate pulp and hardwood pulp in a mass ratio of (60-85):(15-40). Preferably, the degree of polymerization of the pulp is 500-700, and the α-cellulose content is ≥92%.

[0006] Preferably, the adjuvants in step one include: propyl gallate (PG), nanocellulose, and rheology modifier; Propyl gallate (PG) is present in amounts of 0.01-0.5 parts by weight; The amount of nanocellulose is 0.1-2.0 parts by weight; The rheology modifier (selected from polyacrylamide or hydroxyethyl cellulose) is 0.05-1.0 parts by weight.

[0007] Preferably, the cellulose mass concentration in the spinning solution of step one is 12%-14% (higher than the conventional 8-12%), the mass concentration of N-methylmorpholine-N-oxide (NMMO) is 72-78%, and the balance is water; The spinning solution is vacuum dehydrated to the above concentration at 90-110℃, and then defoamed and filtered before use.

[0008] Preferably, in step two, the orifice diameter of the spinneret is 0.06-0.75 mm (significantly lower than the conventional 0.08-0.10 mm), and the number of orifices is 36-209.

[0009] Preferably, the high-temperature environment in step two is 105-115℃.

[0010] Preferably, the air gap in step two is equipped with a multi-stage air-blowing cooling system; The initial airflow height is 10-30mm, the airflow temperature is 15-30℃, and a gradient cooling method is used, with the first stage at 20-30℃ and the second stage at 15-20℃. The airflow speed is 0.5-1.5 m / s.

[0011] Preferably, in step two, the coagulation bath is an aqueous solution of N-methylmorpholine-N-oxide (NMMO) with a concentration of 10-25% and a temperature of 15-25°C, and a circulating cooling system is used to maintain a constant temperature.

[0012] Preferably, in step three, the first draw ratio is 1.5-3.0 times, the hot water temperature is 60-90℃, the second draw ratio is 1.2-2.0 times, and the total draw ratio is controlled at 300-400%.

[0013] Preferably, the fineness of the finished fine denier lyocell fiber in step three is 0.9-1.2 dtex.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. Systematically solve the problem of fine denier spinning: Through the synergistic regulation of five aspects, namely air cooling, low temperature circulation in coagulation bath, reduction of draw ratio, pulp optimization and introduction of additives, the technical problems of yarn breakage, sticking to the plate and pore blockage in fine denier lyocell fiber spinning have been solved, and stable continuous spinning of fibers with a fineness ≤1.2dtex has been achieved. 2. Significantly reduced draw ratio: By controlling the total draw ratio at 300-400%, spinning stability is greatly improved; 3. Controllable component pressure: Through multi-parameter collaborative optimization, the component pressure is reduced from >7MPa to 3-5MPa, extending the component's service life; 4. Excellent fiber properties: The fine denier lyocell fiber obtained has a fineness deviation rate of ≤5%, a breaking strength of ≥4.0cN / dtex, and a soft hand feel, making it suitable for producing high-grade textiles and non-woven fabrics. Attached Figure Description

[0015] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: Please see Figure 1 As shown, a method for preparing fine denier lyocell fiber includes the following steps: Take 165g of sulfate softwood pulp and 55g of hardwood pulp (mixing ratio 75:25), add 2800g of 50% N-methylmorpholine-N-oxide (NMMO) aqueous solution, add 0.25g of propyl gallate (PG), 1.0g of nanocellulose and 0.3g of polyacrylamide, swell at 80℃ for 1 hour, and gradually raise the temperature to 90℃, 100℃ and 110℃ for vacuum dehydration to obtain a spinning solution with 13% cellulose concentration and 75% N-methylmorpholine-N-oxide (NMMO) concentration.

[0018] The spinning solution is pumped at 110°C to a spinneret with 108 orifices and a diameter of 0.075 mm. A gradient airflow is set in the air gap: the first airflow temperature is 25°C and the speed is 1.0 m / s, the second airflow temperature is 18°C ​​and the speed is 0.8 m / s, and the initial airflow height is 20 mm. The spinneret enters a 18°C, 15% N-methylmorpholine-N-oxide (NMMO) coagulation bath. The first draw is 2.0 times. Then, the spinneret is drawn 1.7 times in hot water at 75°C. The total draw ratio is 340%. After washing, oiling and drying, fine denier lyocell fiber with a fineness of 1.0 dtex is obtained.

[0019] It should be noted that the adjustment of each parameter in this invention follows the following priority order: Reduce draw ratio (primary): Achieve this by reducing the spinneret orifice diameter and increasing the solid content of the adhesive solution; Stabilize component pressure (minor): Control the component pressure at 3-5 MPa by adjusting the spinning speed (15-35 m / min) and the solid content of the sizing solution; Maintain metering pump speed (basic): Ensure metering pump speed > 5 rpm by adjusting spinning speed, number of holes and cellulose content; When there are contradictions in the direction of parameter adjustment, the above priority order shall be used to determine the appropriate direction.

[0020] Example 2: Take 176g of sulfate softwood pulp and 44g of hardwood pulp (mixing ratio 80:20), add 2600g of 65% N-methylmorpholine-N-oxide (NMMO) aqueous solution, add 0.20g of propyl gallate (PG), 1.5g of nanocellulose and 0.2g of hydroxyethyl cellulose, and after dehydration, a spinning solution with a cellulose concentration of 12.5% ​​and an N-methylmorpholine-N-oxide (NMMO) concentration of 76% is obtained.

[0021] The spinning solution is extruded through a 209-hole spinneret with a diameter of 0.065 mm at 105℃, with the blowing temperature at 28℃ in the first stage and 20℃ in the second stage, the coagulation bath temperature at 15℃ and the concentration at 12%, and the total draw ratio at 320% to produce fine denier lyocell fibers with a fineness of 0.9 dtex.

[0022] Comparative Example 1: Using conventional processes (i.e., spinneret orifice diameter 0.08mm, air blowing temperature 25℃, coagulation bath temperature 25℃, total draw ratio >500%), with other conditions the same as in Example 1, severe filament breakage and pore blockage occurred when spinning fibers with a target fineness of 1.0dtex, making continuous production impossible.

[0023] Conclusion: The above analysis shows that the fine denier lyocell fiber prepared by the method of the present invention can achieve a fineness of 0.9-1.0 dtex, a fineness deviation rate of ≤5%, a breaking strength of ≥4.2 cN / dtex, good spinning stability, and controllable component pressure. It successfully solves the technical problems of fiber breakage and pore blockage in the fine denier process. The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

[0024] In summary, the beneficial effects of the fine denier lyocell fibers prepared by the method of this invention are: 1. Systematically solve the problem of fine denier spinning: Through the synergistic regulation of five aspects, namely air cooling, low temperature circulation in coagulation bath, reduction of draw ratio, pulp optimization and introduction of additives, the technical problems of yarn breakage, sticking to the plate and pore blockage in fine denier lyocell fiber spinning have been solved, and stable continuous spinning of fibers with a fineness ≤1.2dtex has been achieved. 2. Significantly reduced draw ratio: By controlling the total draw ratio at 300-400%, spinning stability is greatly improved; 3. Controllable component pressure: Through multi-parameter collaborative optimization, the component pressure is reduced from >7MPa to 3-5MPa, extending the component's service life; 4. Excellent fiber properties: The fine denier lyocell fiber obtained has a fineness deviation rate of ≤5%, a breaking strength of ≥4.0cN / dtex, and a soft hand feel, making it suitable for producing high-grade textiles and non-woven fabrics.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing fine denier lyocell fiber, characterized in that, Includes the following steps: Step 1: Preparation of spinning solution; Cellulose pulp and N-methylmorpholine-N-oxide aqueous solution are mixed in a certain proportion, auxiliaries are added, and the mixture is swollen and dissolved under vacuum to obtain spinning solution; Step 2: Dry-jet wet spinning; The spinning solution obtained in Step 1 is delivered to the spinneret through a metering pump, extruded under high temperature, and enters the coagulation bath after passing through the air gap to form nascent fibers. Step 3: Stretching and post-treatment; The nascent fibers from Step 2 are first stretched in a coagulation bath, followed by a second stretch in hot water. The stretched fibers are then washed, oiled, and dried to obtain the finished fine denier lyocell fiber.

2. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: In step one, the cellulose pulp is a single or mixed pulp, comprising softwood sulfate pulp and hardwood pulp in a mass ratio of (60-85):(15-40). Preferably, the degree of polymerization of the pulp is 500-700, and the α-cellulose content is ≥92%.

3. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: The additives in step one include: propyl gallate, nanocellulose, and rheology modifiers; Propyl gallate is present in quantities of 0.01-0.5 parts by weight; The amount of nanocellulose is 0.1-2.0 parts by weight; The rheology modifier is 0.05-1.0 parts by weight.

4. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: The cellulose mass concentration in the spinning solution of step one is 12%-14%, the N-methylmorpholine-N-oxide mass concentration is 72-78%, and the balance is water; The spinning solution is vacuum dehydrated to the above concentration at 90-110℃, and then defoamed and filtered before use.

5. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: In step two, the spinneret has an aperture of 0.06-0.75 mm and a number of holes of 36-209.

6. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: The high-temperature environment in step two is 105-115℃.

7. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: In step two, a multi-stage air-blowing cooling system is installed in the air gap; The initial airflow height is 10-30mm, the airflow temperature is 15-30℃, and a gradient cooling method is used, with the first stage at 20-30℃ and the second stage at 15-20℃. The airflow speed is 0.5-1.5 m / s.

8. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: In step two, the coagulation bath is an aqueous solution of N-methylmorpholine-N-oxide with a concentration of 10-25% and a temperature of 15-25°C. A circulating cooling system is used to maintain a constant temperature.

9. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: In step three, the first draw ratio is 1.5-3.0 times, the hot water temperature is 60-90℃, the second draw ratio is 1.2-2.0 times, and the total draw ratio is controlled at 300-400%.

10. The method for preparing fine denier lyocell fiber according to claim 1, characterized in that: The fineness of the finished fine denier lyocell fiber in step three is 0.9-1.2 tex.

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