A process for the production of lyocell fibres using low degree of polymerisation pulp and fibres

Abstract

The application discloses a method for preparing Lyocell fiber by using low polymerization degree pulp and the fiber, and comprises the following steps: (1) preparing low polymerization degree pulp with an average polymerization degree of 200-450 by carrying out depolymerization treatment on pulp with high polymerization degree; (2) mixing the low polymerization degree pulp with NMMO aqueous solution, and controlling high solid-liquid ratio, low temperature and low vacuum pressure to carry out dissolution, so as to prepare high-fiber-concentration spinning dope; (3) carrying out defoaming and filtering on the high-fiber-concentration spinning dope, and carrying out spinning by means of dry-jet wet process at high spinning speed, so as to prepare Lyocell fiber; the cellulose concentration of the high-fiber-concentration spinning dope is 13%-20%. By lowering the polymerization degree of the pulp, the application increases the dissolution activity of the cellulose, so that the cellulose concentration and the spinning speed are improved to improve the production efficiency, and the production cost of the Lyocell fiber is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of cellulose fiber preparation, specifically, it relates to a method and fiber for preparing Lyocell fiber using low-polymerization degree pulp. Background Technology

[0002] Lyocell fiber is a novel regenerated cellulose fiber with excellent properties, prepared by dry-spraying wet processing after dissolving cellulose pulp in N-methylmorpholine-N-oxide (NMMO) solvent. Its waste is biodegradable, the production process involves no chemical reactions, and there are no waste liquids or exhaust gases emitted. The solvent has extremely low toxicity and a recovery rate as high as 99.8%.

[0003] Cellulose pulp is derived from natural cellulose, is widely available, renewable, and biodegradable. Lyocell fiber pulp typically has a degree of polymerization of around 400–700, and the cellulose concentration in the spinning solution is usually below 13%. Pulp within this range exhibits uniform swelling and is easily soluble, resulting in good spinnability of the dope solution. Short fiber spinning speeds are generally below 42 m / min, and the resulting fiber strength is typically around 3.2–4.2 cN / dtex, superior to regenerated cellulose fibers prepared using viscose, cuprammonium, and ionic liquid / alkali urea systems. For example:

[0004] Chinese patent application CN1432087A discloses an alkaline pulp with a low average degree of polymerization and its preparation method. The provided pulp can be used to prepare Lyocell fibers. The pulp has a high hemicellulose content, a low copper value, and includes cellulose with a low average degree of polymerization and a narrow molecular weight distribution. The average degree of polymerization of the cellulose is 200-1100, preferably 300-1100, and most preferably 400-700.

[0005] Chinese patent application CN105525376A discloses a method for preparing regenerated cellulose fibers, comprising the following steps: first, dissolving corn cob fiber pulp and a chelating agent in an NMMO solution to obtain a spinning solution; then, using the spinning solution obtained in the above steps to prepare regenerated cellulose fibers. The corn cob cellulose pulp used has short fiber lengths (between 0 and 0.3 mm) and uniform polymerization (between 500 and 600), allowing for rapid and uniform dispersion in the solvent system. Furthermore, the pulp surface has numerous pores, exhibiting strong capillary action, enabling rapid solvent absorption and allowing both the surface and interior of the pulp to participate in the reaction, thus reducing reaction time and improving reaction uniformity.

[0006] However, in existing technologies, such as the patented technology mentioned above, the cellulose concentration is low and the spinning speed is also low, which limits the fiber production efficiency. How to provide a method that can both guarantee the quality of fiber products and improve the spinnability of the spinning solution, thereby increasing fiber production efficiency and reducing production costs, will have significant economic and social value.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] The technical problem this invention aims to solve is to overcome at least one of the shortcomings of existing technologies and provide a method for preparing Lyocell fibers using low-polymerization-degree pulp. This invention depolymerizes high-polymer pulp to obtain low-polymerization-degree pulp, increasing the solubility of cellulose. This allows the high-cellulose-concentration low-polymer pulp to be uniformly mixed and swollen in an NMMO solution. Simultaneously, by using low dissolution temperature and pressure, a high-fiber-concentration spinning solution is obtained. Combined with high spinning speed, this significantly improves production efficiency, reduces the production cost of Lyocell fibers, and ensures that the mechanical properties of the resulting fibers are not reduced, and may even be improved.

[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0010] In a first aspect, the present invention provides a method for preparing Lyocell fibers using low-polymerization degree pulp, comprising the following steps:

[0011] (1) The pulp with high degree of polymerization is depolymerized to prepare pulp with an average degree of polymerization of 200 to 450.

[0012] (2) Mix low-polymerization pulp with NMMO aqueous solution, and dissolve it by controlling high solid-liquid ratio, low dissolution temperature and low vacuum pressure to prepare high fiber concentration spinning solution;

[0013] (3) The high fiber concentration spinning solution is defoamed and filtered, and then spun at a high spinning speed using a dry-spray wet method to prepare Lyocell fiber.

[0014] In the method of this invention, the degree of polymerization of cellulose pulp is first reduced, which can significantly increase the cellulose concentration in the dosing. Combined with a high spinning rate, this improves the yield. Furthermore, the dissolution temperature can be appropriately lowered, mitigating the degradation of NMMO and cellulose during the dissolution process to some extent. In addition, while using low-polymerization-degree cellulose pulp as raw material to produce regenerated fibers can increase the cellulose concentration in the spinning dosing, a lower degree of polymerization in the fiber raw material is not always better. Excessively low cellulose polymerization can severely impact the quality of the dosing, cellulose regeneration, and the quality of the finished fiber. Therefore, the production process requires reasonable control of the pulp polymerization degree and adjustment of the dosing cellulose concentration to effectively improve fiber production efficiency, reduce production costs, and ensure fiber product quality.

[0015] In a further embodiment, in step (1), the average degree of polymerization of the low-polymerization pulp is 300 to 400.

[0016] In a further embodiment, in step (1), the average degree of polymerization of the high-polymerization pulp is 400 to 2000;

[0017] Preferably, the highly polymerized pulp is in the form of rolls, plates, blocks, flocs, or powder.

[0018] Preferably, the raw material for the high-polymerization pulp comes from coniferous trees, broad-leaved trees, or bamboo.

[0019] Preferably, the high-polymerization pulp is one or a mixture of pre-hydrolyzed sulfate pulp, sulfite pulp, or papermaking pulp modified dissolving pulp from softwood, broadwood, or bamboo.

[0020] In a further embodiment, in step (1), the method of depolymerization treatment is selected from one or a combination of several of the following: acid hydrolysis, enzymatic hydrolysis, oxidative degradation, thermal degradation, grinding, microwave, ultrasound or irradiation.

[0021] The depolymerization treatment in this invention can be performed using any feasible method available in the prior art. There are various methods for preparing low-polymerization pulp. The most direct method is to reduce the degree of polymerization of the pulp through cooking and bleaching processes during pulping. However, this method is often not used in actual production to ensure pulp yield. Single or combined treatments such as acid hydrolysis, enzymatic hydrolysis, oxidative degradation, thermal degradation, grinding, microwave, ultrasonic, and electron irradiation can all break the intermolecular glycosidic bonds of cellulose glucose molecules, reducing the degree of polymerization of cellulose to varying degrees. Simultaneously, this reduces the average length and width of the fibers, dramatically increases the reactivity of cellulose, and significantly improves the solubility of the pulp.

[0022] In a further embodiment, the acid hydrolysis includes, but is not limited to, hydrolysis with sulfuric acid, hydrochloric acid, phosphoric acid, or formic acid; the enzymatic hydrolysis is mainly cellulase hydrolysis; and the oxidative degradation includes, but is not limited to, treatment with hydrogen peroxide or sodium hypochlorite. The oligomer pulp prepared by the aforementioned three depolymerization methods needs to be washed with water until the pulp pH is not lower than 6 to adapt to the NMMO dissolution system and avoid affecting the quality of the spinning solution.

[0023] In a further embodiment, in step (1), the low-polymerization pulp is one or more of the following: oligomeric broadleaf pulp, oligomeric softwood pulp, or oligomeric bamboo pulp.

[0024] In a further embodiment, in step (2), the concentration of cellulose in the prepared spinning solution is 13% to 20%.

[0025] Preferably, the concentration of cellulose in the prepared spinning solution is 14% to 17%.

[0026] In a further embodiment, in step (2), the high solid-liquid ratio is the mass ratio of low-polymerization degree pulp to NMMO aqueous solution of 1:4 to 1:8.

[0027] Preferably, the concentration of the NMMO aqueous solution is 70% to 83%.

[0028] In this invention, by controlling the mass ratio of low-polymerization pulp to NMMO aqueous solution to be 1:4 to 1:8, a spinning solution with a cellulose concentration of 13% to 20% can be prepared. This control results in a high concentration of spinning solution with good spinnability, which is beneficial for ensuring the mechanical properties of the fiber and the quality of the product.

[0029] In a further embodiment, in step (2), the temperature for mixing the low-polymerization degree pulp with the NMMO aqueous solution is 80-90°C, and the mixing time is not less than 10 min, preferably 15-30 min.

[0030] In this invention, due to the high cellulose concentration and the presence of mixed pulp, it is necessary to extend the mixing time to ensure that the pulp and solvent are mixed evenly and fully swollen, which is beneficial for further dissolution and preparation of a spinning solution with uniform properties.

[0031] In a further step, in step (2), the dissolution temperature is controlled at 90–130°C and the pressure at 2–11 kPa;

[0032] Preferably, the dissolution temperature is controlled at 90–110°C and the pressure at 6–8 kPa.

[0033] In a further embodiment, in step (3), the high spinning speed is not less than 50 m / min.

[0034] In a further step, in step (3), the temperature of the spinning box is controlled to be no less than 90°C, preferably 95-105°C, based on the viscosity of the spinning solution; the spinneret aperture is selected to be 0.05-0.1mm, preferably 0.07-0.09mm; the air gap cooling height is 10-100mm, preferably 20-50mm; the blowing speed is 1-40m / min, the blowing temperature is 8-28°C, and the blowing humidity is 20-80%; the spinning speed is no less than 50m / min, and Lyocell fibers are continuously prepared.

[0035] In a further step, in step (3), the spun Lyocell fibers are cut, washed, oiled, dried and packaged to obtain Lyocell short fibers.

[0036] In a further embodiment, the fiber production efficiency of the method of the present invention is increased by 19% to 90% within the same time period;

[0037] Secondly, the present invention provides a Lyocell fiber prepared by the method described above;

[0038] Preferably, the dry breaking strength of the prepared Lyocell fiber is 3.2 to 4.2 cN / dtex.

[0039] Generally, Lyocell fibers produced from low-polymerization-degree cellulose pulp tend to have lower strength and are more prone to fibrillation. This is advantageous for the production of filter materials, nonwovens, and paper products containing Lyocell fibers. The fibrillation problem can be addressed through post-treatment methods such as cross-linking. However, in this invention, by employing a suitable lower degree of polymerization, a suitable higher concentration of spinning solution, and adjusting the process to achieve a high solid-liquid ratio of pulp to solvent, a low dissolution temperature, a low vacuum pressure, and an increased spinning speed, production efficiency is improved while maintaining the strength of the resulting fibers.

[0040] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0041] (1) The method for preparing Lyocell fiber using oligomer pulp provided by the present invention uses oligomer pulp as raw material to prepare spinning solution with high cellulose concentration, which has better spinnability and produces Lyocell fiber at high spinning speed. It does not require modification of existing fiber production equipment, which can effectively improve fiber production efficiency, reduce production costs, and ensure fiber product quality.

[0042] (2) The method for preparing Lyocell fiber using oligomeric pulp provided by the present invention can be prepared in a variety of ways, and the preparation process can be flexibly adjusted according to the needs to obtain pulp of different types and different degrees of polymerization.

[0043] (3) In this invention, the lower degree of polymerization is controlled within a suitable range, and the higher concentration of spinning solution is also within a suitable range. At the same time, the process is adjusted to make the solid-liquid ratio of pulp to solvent higher, the dissolution temperature lower, the vacuum pressure lower, and the spinning speed higher. In this way, while improving production efficiency, the spinnability of spinning solution is also guaranteed, and the mechanical properties of the resulting fiber are not reduced or even improved. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0045] The following are some performance indicators for cotton-type lyocell staple fiber:

[0046] Table 1. Performance Items and Index Values ​​of Cotton-Type Lyocell Staple Fiber (FZ / T 52019-2018)

[0047]

[0048] Detection or calculation method:

[0049] (1) Average degree of polymerization: GB / T 1548-2016 "Determination of intrinsic viscosity of copper ethylenediamine (CED) solution in pulp"

[0050] (2) Production efficiency: Based on the comparative ratio, the production efficiency improvement rate is equal to the spinning speed improvement rate.

[0051] Example 1

[0052] A method for efficiently preparing Lyocell fibers using low-polymerization degree pulp includes the following steps:

[0053] Step (1): Preparation of oligomer pulp: A broadleaf acidic sulfite dissolution pulp with a degree of polymerization of 1080 was used. After decomposition, pressing and concentration, dispersion and moisture balancing, it was set aside for later use. A certain amount of the above pulp was weighed and placed in a reaction vessel. 1 wt% dilute sulfuric acid was added and reacted at 140℃ for 60 min for depolymerization treatment. The pulp after washing treatment was adjusted to pH>6. The pulp was then pressed, concentrated, dispersed and air-dried for later use. The washing liquid could be recycled after concentration. The average degree of polymerization of the oligomer pulp was determined to be 298.

[0054] Step (2): Preparation of spinning solution: Take a certain amount of oligomer pulp prepared in step (1) and a certain amount of 72% NMMO solvent and place them in a mixing vessel at a temperature of 90°C. The mass ratio of pulp to solvent is 1:5.7. Stir to fully disperse the oligomer pulp and mix it evenly with the solvent. Then, transport the mixed pulp to a dissolving device at a temperature of 105°C and a vacuum pressure of 6.0 kPa to prepare a spinning solution with a cellulose concentration of 17.5% and a viscosity of 1708 Pa·s.

[0055] Step (3): Spinning: The high-concentration spinning solution was defoamed and filtered, and then spun using a dry-jet wet spinning method. The spinning speed was 66 m / min, the spinning temperature was 95℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 12.2℃, and the blowing humidity was 61.5%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0056] Example 2

[0057] A method for efficiently preparing Lyocell fibers using low-polymerization degree pulp includes the following steps:

[0058] Step (1): Preparation of oligomer pulp: The pre-hydrolyzed sulfate dissolution pulp of needle-leaf with a degree of polymerization of 793 was used. After loosening, pressing and concentrating, dispersing and balancing the moisture content, it was set aside for later use. A certain amount of the above pulp was weighed and placed in a reaction vessel. The system was adjusted to be weakly alkaline. 30wt% hydrogen peroxide was added and reacted at 60℃ for 80min for depolymerization treatment. The pulp after washing was neutral. It was pressed, concentrated, dispersed and air-dried for later use as oligomer pulp. The degree of polymerization of the oligomer pulp was determined to be 446.

[0059] Step (2): Preparation of spinning solution: Take a certain amount of oligomer pulp prepared in step (1) and a certain amount of 76% NMMO solvent and place them in a mixing vessel at a temperature of 90℃. The mass ratio of pulp to solvent is 1:7.6. Stir to fully disperse the oligomer pulp and mix it evenly with the solvent. Then, transport the mixed pulp to a dissolving device at a temperature of 102℃ and a vacuum pressure of 6.2kPa to prepare a spinning solution with a cellulose concentration of 14.0% and a viscosity of 2161Pa·s.

[0060] Step (3): Spinning: The high-concentration spinning solution was deaerated and filtered, and then spun using a dry-spinning wet method. The spinning speed was 50 m / min, the spinning temperature was 105℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 12.6℃, and the blowing humidity was 74.9%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0061] Example 3

[0062] A method for efficiently preparing Lyocell fibers using low-polymerization degree pulp includes the following steps:

[0063] Step (1): Preparation of oligomer pulp: Bamboo pre-hydrolyzed sulfate dissolution pulp with a degree of polymerization of 665 was used. After decomposition, pressing and concentration, dispersion and moisture balancing, it was set aside for later use. The pulp was first ground by disc milling. Then, a certain amount of the above pulp was weighed and placed in a reaction vessel. The pH of the system was adjusted to 5.5. 0.5u / g of cellulase rich in endoglucanase was added, and the reaction was carried out at 55℃ for 120min for depolymerization treatment. The treated pulp was washed and the enzyme was inactivated by hot water. The oligomer pulp was pressed, concentrated, dispersed and air-dried for later use. The degree of polymerization of the oligomer pulp was determined to be 402.

[0064] Step (2): Preparation of spinning solution: Take a certain amount of oligomer pulp prepared in step (1) and a certain amount of 73% NMMO solvent and place them in a mixing vessel at a temperature of 90°C. The mass ratio of pulp to solvent is 1:6.6. Stir to fully disperse the oligomer pulp and mix it evenly with the solvent. Then, transport the mixed pulp to a dissolving device at a temperature of 108°C and a vacuum pressure of 7.7 kPa to prepare a spinning solution with a cellulose concentration of 15.3% and a viscosity of 2802 Pa·s.

[0065] Step (3): Spinning: The high-concentration spinning solution was defoamed and filtered, and then spun using a dry-jet wet spinning method. The spinning speed was 70 m / min, the spinning temperature was 100℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 13.1℃, and the blowing humidity was 71.4%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0066] Example 4

[0067] A method for efficiently preparing Lyocell fibers using low-polymerization degree pulp includes the following steps:

[0068] Step (1): Preparation of oligomer pulp: The alkali-modified pulp of needle-leaf variety with a degree of polymerization of 825 was prepared for use after decomposition, pressing, concentration, dispersion, and moisture balancing; a certain amount of the above pulp was weighed and placed in a microwave reactor, the system was adjusted to be weakly alkaline, 1% hydrochloric acid was added, and the reaction was carried out at 90℃ for 30 min for depolymerization treatment; the pulp after washing was neutral, and the oligomer pulp was prepared by pressing, concentration, dispersion, and air drying; the degree of polymerization of the oligomer pulp was determined to be 215.

[0069] Step (2): Preparation of spinning solution: Take a certain amount of oligomer pulp prepared in step (1) and a certain amount of 70% NMMO solvent and place them in a mixing vessel at a temperature of 90℃. The mass ratio of pulp to solvent is 1:5.0. Stir to fully disperse the oligomer pulp and mix it evenly with the solvent. Then, transport the mixed pulp to a dissolving device at a temperature of 95℃ and a vacuum pressure of 6.6kPa to prepare a spinning solution with a cellulose concentration of 20.0% and a viscosity of 1555Pa·s.

[0070] Step (3): Spinning: The high-concentration spinning solution was defoamed and filtered, and then spun using a dry-spinning wet method. The spinning speed was 80 m / min, the spinning temperature was 100℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 12.5℃, and the blowing humidity was 67.3%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0071] Example 5

[0072] A method for efficiently preparing Lyocell fibers using low-polymerization degree pulp includes the following steps:

[0073] Step (1): Preparation of oligomer pulp: The bamboo alkali modified pulp with a degree of polymerization of 1230 was placed in an electron accelerator for irradiation treatment. The irradiation dose was 35kGy and the belt conveyor speed was 100mm / s. After the treatment, the pulp was left to stand for 10 days and the degree of polymerization of the oligomer pulp was measured to be 356.

[0074] Step (2): Preparation of spinning solution: Take a certain amount of oligomer pulp prepared in step (1) and a certain amount of 74% NMMO solvent and place them in a mixing vessel at a temperature of 90°C. The mass ratio of pulp to solvent is 1:5.8. Stir to fully disperse the oligomer pulp and mix it evenly with the solvent. Then, transport the mixed pulp to a dissolving device at a temperature of 105°C and a vacuum pressure of 7.0 kPa to prepare a spinning solution with a cellulose concentration of 16.8% and a viscosity of 2475 Pa·s.

[0075] Step (3): Spinning: The high-concentration spinning solution was defoamed and filtered, and then spun using a dry-spinning wet method. The spinning speed was 56 m / min, the spinning temperature was 105℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 15.3℃, and the blowing humidity was 65.9%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0076] Example 6

[0077] A method for efficiently preparing Lyocell fibers using low-polymerization degree pulp includes the following steps:

[0078] Step (1): Preparation of oligomer pulp: Acid-processed softwood dissolving pulp with a degree of polymerization of 706 was used. After dehydration, pressing, concentration, dispersion, and moisture balancing, it was set aside for later use. A certain amount of the above pulp was weighed and added to an ultrasonic reactor with a power of 3.0kW and a frequency of 30kHz. 5.5% formic acid was added, and the pulp was ultrasonically treated for 100 minutes to reduce polymerization. The pulp after washing was neutral. After pressing, concentration, dispersion, and air drying, the oligomer pulp was set aside for later use. The degree of polymerization of the pulp was measured to be 277.

[0079] Step (2): Preparation of spinning solution: Take a certain amount of oligomer pulp prepared in step (1) and a certain amount of 75% NMMO solvent and place them in a mixing vessel at a temperature of 90℃. The mass ratio of pulp to solvent is 1:5.6. Stir to fully disperse the oligomer pulp and mix it evenly with the solvent. Then, transport the mixed pulp to a dissolving device at a temperature of 100℃ and a vacuum pressure of 6.1kPa to prepare a spinning solution with a cellulose concentration of 18.0% and a viscosity of 2000Pa·s.

[0080] Step (3): Spinning: The high-concentration spinning solution was defoamed and filtered, and then spun using a dry-spinning wet method. The spinning speed was 63 m / min, the spinning temperature was 103℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 14.8℃, and the blowing humidity was 67.2%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0081] Comparative Example

[0082] Using acid-processed hardwood pulp, commonly used in Lyocell fiber production, as raw material, the pulp had a degree of polymerization of 560. The pulp was placed in a mixing vessel at 90°C with a certain amount of 74% NMMO solvent, with a pulp-to-solvent mass ratio of 1:8.6. The pulp was thoroughly dispersed and mixed evenly with the solvent by stirring. The mixed pulp was then transferred to a dissolving device at 105°C and a vacuum pressure of 4.3 kPa to prepare a spinning solution with a cellulose concentration of 12.0% and a viscosity of 2079 Pa·s.

[0083] Step (3): Spinning: The high-concentration spinning solution was defoamed and filtered, and then spun using a dry-jet wet spinning method. The spinning speed was 42 m / min, the spinning temperature was 100℃, the spinneret orifice diameter was 0.085 mm, the air gap cooling height was 20 mm, the blowing speed was 1-40 m / min, the blowing temperature was 11.1℃, and the blowing humidity was 46.7%, thus producing Lyocell short fibers. The fiber preparation process, fiber properties, and production efficiency are shown in Table 2.

[0084] Table 2 Fiber preparation process, fiber properties and production efficiency

[0085]

[0086] Results analysis:

[0087] Compared with the comparative example which used a spinning solution with a higher degree of polymerization and a lower cellulose concentration, Examples 1-6 of this invention all used oligomeric pulp as raw material to prepare spinning solutions with a high cellulose concentration. The results show that the fiber production efficiency was significantly improved.

[0088] In Example 2, the degree of polymerization of the pulp was 446, and the cellulose concentration of the spinning solution was 14%. Compared with the comparative example, the increase in the concentration of the spinning solution was limited, which also resulted in a limited increase in fiber production efficiency.

[0089] In Example 4, the degree of polymerization of the pulp was 215 and the cellulose concentration of the spinning solution was 20%, which greatly improved the fiber production efficiency, but the dry breaking strength of the fiber was lower than that of the comparative example.

[0090] In Examples 1, 3, 5 and 6, the degree of polymerization of the pulp was between 277 and 402, the cellulose concentration of the spinning solution was in the range of 15-18%, the dry breaking strength of the fibers was comparable to that of the comparative examples, and in some cases even improved, and the fiber production efficiency was also significantly improved.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing Lyocell fibers using low-polymerization degree pulp, characterized in that, Includes the following steps: (1) The pulp with high degree of polymerization is depolymerized to prepare pulp with an average degree of polymerization of 200 to 450. (2) Mix low-polymerization pulp with NMMO aqueous solution, and dissolve it by controlling high solid-liquid ratio, low dissolution temperature and low vacuum pressure to prepare high fiber concentration spinning solution; (3) The high fiber concentration spinning solution is defoamed and filtered, and then spun at a high spinning speed using a dry-spray wet method to prepare Lyocell fiber.

2. The method for preparing Lyocell fibers using low-polymerization degree pulp according to claim 1, characterized in that, In step (1), the average degree of polymerization of the low-polymerization pulp is 300 to 400.

3. The method for preparing Lyocell fibers from low-polymerization degree pulp according to claim 1, characterized in that, In step (1), the average degree of polymerization of the high-polymerization pulp is 400 to 2000; Preferably, the high degree of polymerization pulp is in the form of rolls, plates, blocks, flocs, or powder; Preferably, the raw material for the high-polymerization pulp comes from coniferous trees, broad-leaved trees, or bamboo. Preferably, the high-polymerization pulp is one or a mixture of pre-hydrolyzed sulfate pulp, sulfite pulp, or papermaking pulp modified dissolving pulp from softwood, broadwood, or bamboo.

4. The method for preparing Lyocell fibers from low-polymerization degree pulp according to claim 1, characterized in that, In step (1), the method of depolymerization treatment is selected from one or a combination of several of the following: acid hydrolysis, enzymatic hydrolysis, oxidative degradation, thermal degradation, grinding, microwave, ultrasound or irradiation.

5. The method for preparing Lyocell fibers from low-polymerization degree pulp according to any one of claims 1-4, characterized in that, In step (2), the concentration of cellulose in the prepared spinning solution is 13% to 20%; Preferably, the concentration of cellulose in the prepared spinning solution is 14% to 17%.

6. The method for preparing Lyocell fibers from low-polymerization degree pulp according to any one of claims 1-4, characterized in that, In step (2), the high solid-liquid ratio refers to the mass ratio of low-polymerization degree pulp to NMMO aqueous solution being 1:4 to 1:

8. Preferably, the concentration of the NMMO aqueous solution is 70% to 83%.

7. The method for preparing Lyocell fibers from low-polymerization degree pulp according to any one of claims 1-4, characterized in that, In step (2), the temperature for mixing the low degree of polymerization pulp with the NMMO aqueous solution is 80-90°C, and the mixing time is not less than 10 min, preferably 15-30 min.

8. The method for preparing Lyocell fibers from low-polymerization degree pulp according to any one of claims 1-4, characterized in that, In step (2), the dissolution temperature is controlled at 90–130°C and the vacuum pressure is controlled at 2–11 kPa; Preferably, the melting temperature is controlled at 90–110°C and the vacuum pressure is controlled at 6–8 kPa.

9. The method for preparing Lyocell fibers from low-polymerization degree pulp according to any one of claims 1-4, characterized in that, In step (3), the high spinning speed is not less than 50 m / min.

10. A Lyocell fiber prepared by the method according to any one of claims 1-9; Preferably, the dry breaking strength of the prepared Lyocell fiber is 3.2 to 4.2 cN / dtex.

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