A preparation method of a lyocell fiber spinning dope

Abstract

The present invention discloses a preparation method of a lyocell fiber spinning dope, belonging to the technical field of cellulose fiber production. The steps include: wet pulverization of pulp raw materials, press pulverization of pulp raw materials, gradient swelling of pulp raw materials, press pulverization of the pulp raw materials after gradient swelling, and direct dissolution of pulp raw materials, etc. The present invention solves the problems of high consumption and high equipment cost caused by evaporation and dehydration during the preparation of the spinning dope in the existing lyocell production process. The present invention can effectively prevent the formation of an incompletely dissolved "white core" due to primary dissolution during the dissolution process, thereby ensuring the quality of the spinning dope.

Description

Technical Field

[0001] The present invention relates to the technical field of cellulose fiber production, and in particular to a method for preparing a lyocell fiber spinning dope. Background Art

[0002] Lyocell fiber is a new type of green cellulose fiber. Using NMMO as a solvent, it realizes dissolution and regeneration through physical dissolution means. The whole production process is green and environmentally friendly, and the fiber has advantages such as high strength and good dyeing performance. Therefore, in recent years, the global market demand for lyocell fiber has been continuously increasing.

[0003] Currently, in the production of lyocell fiber, the preparation of the spinning dope generally follows two process routes: wet process and dry process.

[0004] Among them, in the wet process, the pulp raw material is first mixed with water to a certain concentration, then after wet pulping, it is pressed and crushed to obtain a material with a certain dryness. Then, an NMMO solution with a concentration of 80 - 84% is added for premixing, and finally, it enters the reaction kettle for evaporation and dehydration to prepare the spinning dope. The dry process is to first dry-crush the pulp, then directly add an NMMO solution with a concentration of 75 - 80% for premixing, and finally enter the reaction kettle for dissolution to prepare the spinning dope. However, whether it is the dry process or the wet process, it is necessary to carry out vacuum evaporation and dehydration in a specific reaction kettle to increase the concentration of the NMMO solution to the required concentration for dissolution. This process will result in a large amount of consumption, and the equipment price cost is also very high. In addition, for the dry process, the pulp is directly mixed with a high-concentration NMMO solution for swelling (swelling refers to a physical phenomenon in which a polymer swells in volume after absorbing a liquid. In the field of lyocell production, it usually refers to the state where the NMMO solution penetrates between or inside the pulp fibrils). Since the temperature is relatively high during mixing, it is very easy to cause initial dissolution. The initial dissolution phenomenon will cause the pulp raw material to be insufficiently swollen during swelling, and there will be an "un-dissolved core" that cannot be completely dissolved during dissolution, thus seriously affecting the quality of the sizing solution. Although the swelling effect with the high-concentration NMMO solution can be improved to a certain extent by pulverizing the pulp raw material, during the pulverization process of the pulp, it will increase safety hazards such as dust pollution and explosion.

[0005] In addition to the dry process and the wet process, the lyocell spinning dope can also be prepared by a direct dissolution method. The direct dissolution method is to directly mix a high-concentration NMMO solution with dissolution ability with the treated pulp for direct dissolution. This method does not need to remove water in the reaction kettle during the dissolution process, so it can greatly simplify the process and save production costs. However, this method is more likely to cause initial dissolution than the dry process, resulting in uneven dissolution due to the formation of an "un-dissolved core" because the concentration of the NMMO solution used for mixing with the pulp is higher.

[0006] To solve the above problems, Chinese Patent Application for Invention CN114016141A, a method for preparing a fiber spinning dope by a direct dissolution method, discloses that: first, pulp is mixed and swollen with an NMMO solution having a mass concentration of 72% to 76%, then pressed and crushed, and then mixed with an NMMO solution having a mass concentration of 81% to 85% for dissolution. When the patent method performs the pre-mixing treatment with the NMMO solution for the first time, due to the still relatively high concentration of the NMMO solution, the viscosity of the solution will be relatively high. When contacting the pulp, it is not conducive to penetration, which will affect the swelling effect and is not conducive to subsequent dissolution.

[0007] Chinese Patent Application for Invention CN105037753A, a preparation process and equipment for a cellulose solution, discloses that: first, cellulose pulp is uniformly mixed with an NMMO aqueous solution at 70 - 100 °C (the mass concentration of NMMO is 28% - 60%) to obtain a pre-mixed solution, then the pre-mixed solution is evaporated and dehydrated to obtain a pre-swollen solution (the mass concentration of NMMO is 72% - 84%), then the pre-swollen solution is placed in a swelling kettle for heat preservation and fully swollen to obtain a swollen solution, and finally the swollen solution is dissolved by vacuum evaporation and dehydration to obtain a cellulose solution. After obtaining the pre-mixed solution, the patent method needs to evaporate and dehydrate to concentrate the solution and then perform swelling. During subsequent dissolution, it is still necessary to evaporate and dehydrate again for dissolution. The entire dissolution process requires two evaporation and dehydration processes, which will consume a large amount of steam, electric energy, etc., resulting in an increase in production costs. Summary of the Invention

[0008] The object of the present invention is to provide a method for preparing a Lyocell fiber spinning dope to solve the above problems.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a Lyocell fiber spinning dope, comprising the following steps:

[0010] (1) Wet pulverization of pulp raw materials:

[0011] Put the cellulose pulp raw materials into a pulping device equipped with pre-prepared dissolving water for pulping treatment to obtain pulp porridge;

[0012] (2) Pressing and pulverizing of pulp raw materials:

[0013] Press and pulverize the pulp porridge obtained in step (1) to obtain pulp raw materials containing 50 - 60 wt% of water;

[0014] (3) Gradient swelling of pulp raw materials:

[0015] Mix the pulp raw materials obtained in step (2) with an NMMO solution having a concentration of 50 - 60 wt% for the first swelling at a temperature of 30 - 50 °C;

[0016] The pulp after the first swelling is pressed and crushed to obtain raw material a with a water content of 55-65 wt%, and the pressing temperature is 40-50 °C;

[0017] The pressed and crushed pulp raw material a is mixed with an NMMO solution with a concentration of 60-70 wt% for a second swelling at a temperature of 50-60 °C;

[0018] The pulp after the second swelling is pressed and crushed to obtain raw material b with a water content of 55-65 wt%, and the pressing temperature is 50-70 °C;

[0019] The pressed and crushed pulp raw material b is mixed with an NMMO solution with a concentration of 70-80 wt% for a third swelling at a temperature of 70-80 °C;

[0020] (4) Pressing and crushing of the pulp raw material after gradient swelling:

[0021] The pulp after gradient swelling is pressed and crushed to obtain raw material c with a water content of 55-65 wt%, and the pressing temperature is 60-70 °C;

[0022] (5) Direct dissolution of the pulp raw material: The pressed and crushed pulp raw material c is mixed with an NMMO solution with a concentration of 81-85 wt% for dissolution at a dissolution temperature of 90-100 °C,

[0023] Finally, a Lyocell fiber spinning dope is obtained.

[0024] In the present invention, the pulp raw material and the NMMO solution are mixed and swollen in a gradient manner (the concentration of the NMMO solution increases from low to high), which can fully swell the pulp raw material and effectively prevent the formation of an incompletely dissolved "white core" during the dissolution process. Because at low concentrations, NMMO has little effect on breaking the hydrogen bonds of cellulose, and after the NMMO solvent molecules enter the pulp fibrils, they will not break the hydrogen bonds in the crystalline and amorphous regions of cellulose, thus achieving a good swelling effect and avoiding the possibility of white core appearance. In addition, through repeated pressing, the NMMO solution can penetrate more deeply into the pulp fibrils under the action of external force, maintaining a continuous swelling effect, filling the pulp cellulose with the NMMO solution, and then being directly and fully dissolved in a high-concentration NMMO solution;

[0025] In addition, based on gradient swelling and multiple pressing, the present invention can directly dissolve and prepare Lyocell spinning dope by using a twin-screw extruder, eliminating the need for evaporation and dehydration. This solves the problems of high consumption and high equipment costs (requiring expensive thin-film evaporators and supporting equipment) caused by evaporation and dehydration in the existing Lyocell production process during the preparation of spinning dope. Since gradient mixing swelling is adopted during the swelling process, the NMMO solution can more fully infiltrate the pulp raw material, achieving uniform and stable swelling and a better swelling effect, thus enabling direct dissolution.

[0026] As a preferred technical solution:

[0027] In step (1), the dissolving water is deionized water with a water temperature of 50 - 60°C.

[0028] As a preferred technical solution:

[0029] In step (1), the concentration of cellulose in the pulp porridge is 4 - 5 wt%.

[0030] As a preferred technical solution:

[0031] In step (1), the pulping equipment is a hydraulic pulper commonly used in the paper industry.

[0032] As a preferred technical solution:

[0033] In steps (2), (3) and (4), the pressing equipment and crushing equipment used for pressing and crushing are the corresponding equipment used in the traditional viscose fiber industry.

[0034] As a preferred technical solution:

[0035] In step (3), the swelling time for each time is 20 - 30 min.

[0036] As a preferred technical solution:

[0037] In step (3), a pulp porridge storage tank with stirring is used during swelling, and the stirring speed is 60 - 80 rpm.

[0038] As a preferred technical solution:

[0039] In step (5), the concentration of cellulose in the obtained Lyocell fiber spinning dope is 11 - 12 wt%.

[0040] As a preferred technical solution:

[0041] In step (5), the dissolving device is a twin-screw extruder, the temperature of the extruder is 90 - 100°C, the stirring speed is 60 - 90 rpm, and the dissolving time is 20 - 30 min.

[0042] The present invention can be implemented by only using the equipment commonly used in the paper-making industry and the traditional viscose industry, without the need to additionally increase the special equipment for Lyocell production, such as film evaporators, etc. The equipment investment is greatly reduced, and the production cost is significantly reduced.

[0043] Compared with the prior art, the advantages of the present invention are as follows:

[0044] (1) The present invention performs gradient mixing and swelling of pulp raw materials and NMMO solution (the concentration of NMMO solution increases from low to high), which can fully swell the pulp raw materials. At the same time, through repeated pressing, the NMMO solution can penetrate deeper into the pulp fibrils under the action of external force, and the continuous swelling effect can be maintained, making the pulp cellulose filled with NMMO solution; it can not only effectively prevent the formation of "white cores" that are not completely dissolved during the dissolution process, but also directly dissolve the swollen pulp raw materials in a high-concentration NMMO solution;

[0045] (2) The present invention uses a twin-screw extruder to directly dissolve and prepare Lyocell spinning dope, eliminating the need for evaporation and dehydration, and solving the problems of high consumption and high equipment cost caused by evaporation and dehydration during the preparation of spinning dope in the existing Lyocell production process. Since the swelling process uses gradient mixing and swelling, the NMMO solution can infiltrate the pulp raw materials more fully, achieving uniform and stable swelling and a better swelling effect, so direct dissolution can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a microscope image of the cellulose spinning dope obtained in Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0047] The present invention will be further described below in conjunction with examples.

[0048] Example 1:

[0049] A method for preparing Lyocell fiber spinning dope, comprising the following steps:

[0050] (1) Wet pulverization of pulp raw materials: Put the cellulose pulp raw materials into a pulper equipped with prepared dissolving water for pulping treatment to obtain a pulp porridge with a cellulose concentration of 4.5 wt%.

[0051] The dissolving water in the stirring tank is deionized water with a water temperature of 55°C;

[0052] The pulper is a hydraulic pulper commonly used in the paper-making industry;

[0053] (2) Pressing and pulverizing of pulp raw materials: Press and pulverize the wet pulverized pulp porridge to obtain pulp raw materials with a water content of 57 wt%.

[0054] The pressing equipment and the pulverizing equipment are the same as those used in the viscose fiber industry;

[0055] (3) Gradient mixing and swelling of pulp raw materials: Mix the pulverized pulp raw materials with an NMMO solution having a concentration of 56 wt% for the first swelling at a temperature of 40°C and a stirring time of 20 min; press and pulverize the pulp porridge after the first swelling to obtain raw material a with a water content of 60 wt%, and the pressing temperature is 40°C; then mix the pulverized pulp raw material a with an NMMO solution having a concentration of 67 wt% for the second swelling at a temperature of 50°C and a stirring time of 20 min; press and pulverize the pulp porridge after the second swelling to obtain raw material b with a water content of 60 wt%, and the pressing temperature is 50°C; mix the pulverized pulp raw material b with an NMMO solution having a concentration of 78 wt% for the third swelling at a temperature of 70°C and a stirring time of 20 min;

[0056] The mixing device is a pulp porridge storage tank with stirring, and the rotation speed is 60 rpm;

[0057] The pressing equipment and the pulverizing equipment are the same as those used in the viscose fiber industry;

[0058] (4) Pressing and pulverizing of the pulp raw materials after gradient swelling: Press and pulverize the pulp porridge after gradient swelling to obtain raw material c with a water content of 60 wt%, and the pressing temperature is 70°C;

[0059] The pressing equipment and the pulverizing equipment are the same as those used in the viscose fiber industry;

[0060] (5) Direct dissolution of pulp raw materials: Mix the pulverized pulp raw material c with an NMMO solution having a concentration of 83 wt% for dissolution at a dissolution temperature of 100°C;

[0061] The dissolution device is a twin-screw extruder, the temperature of the extruder is 100°C, the stirring rotation speed is 60 rpm, and the dissolution time is 30 min;

[0062] The cellulose concentration in the spinning dope obtained in this example is 11.7 wt%.

[0063] Example 2

[0064] Based on Example 1, the difference between this example and Example 1 lies in that the experimental conditions for the gradient mixing and swelling of the raw materials are different. The specific operation steps are as follows: Mix the pulverized pulp raw materials with an NMMO solution with a concentration of 60% for the first swelling at a temperature of 50°C and a stirring time of 20 min; press and pulverize the pulp porridge after the first swelling to obtain raw material a with a water content of 60 wt% at a pressing temperature of 50°C; then mix the pulverized pulp raw material a with an NMMO solution with a concentration of 70% for the second swelling at a temperature of 60°C and a stirring time of 20 min; press and pulverize the pulp porridge after the second swelling to obtain raw material b with a water content of 60 wt% at a pressing temperature of 60°C; mix the pulverized pulp raw material b with an NMMO solution with a concentration of 80% for the third swelling at a temperature of 80°C and a stirring time of 20 min. Other process conditions and equipment used are the same as those in Example 1 and will not be elaborated here.

[0065] Example 3

[0066] Based on Example 1, the difference between this example and Example 1 lies in that the stirring time for the three times during the gradient mixing and swelling of the raw materials is 30 min each. Other process conditions and equipment used are the same as those in Example 1 and will not be elaborated here.

[0067] Comparative Example 1

[0068] Based on Example 1, the difference between this comparative example and Example 1 lies in that the pulp raw materials are not subjected to gradient mixing and swelling, but instead, the pulp raw materials are directly mixed and swollen with NMMO with a concentration of 78% at a temperature of 70°C and a stirring time of 20 min. Other process conditions and equipment used are the same as those in Example 1 and will not be elaborated here.

[0069] Comparative Example 2

[0070] Based on Example 1, the difference between this comparative example and Example 1 lies in that the pulp raw materials are only subjected to two times of gradient mixing and swelling. The specific operation steps are as follows: Mix the pulverized pulp raw materials with an NMMO solution with a concentration of 56% for the first swelling at a temperature of 40°C and a stirring time of 20 min; press and pulverize the pulp porridge after the first swelling to obtain raw material a with a water content of 60 wt% at a pressing temperature of 40°C; then mix the pulverized pulp raw material a with an NMMO solution with a concentration of 78% for the second swelling at a temperature of 70°C and a stirring time of 20 min; press and pulverize the pulp porridge after the second swelling to obtain raw material b with a water content of 60 wt% at a pressing temperature of 70°C. Other process conditions and equipment used are the same as those in Example 1 and will not be elaborated here.

[0071] The homogeneity of the spinning dope prepared in the above embodiments and comparative examples of the present invention can be characterized by a polarized light microscope and a laser particle size analyzer. The polarized light microscope can observe the dissolution of cellulose in the solution. If the cellulose is not fully dissolved, undissolved fibers can be observed under the microscope. The laser particle size analyzer can measure the particle size and distribution of gel particles in the solution. The smaller the particle size of the gel particles in the solution and the narrower the distribution, the more fully the cellulose is dissolved, and the better the homogeneity of the solution.

[0072] The Lyocell spinning dope prepared by different methods above was observed and tested. The specific comparison results are as Figure 1 shown in Table 1.

[0073] Table 1 Comparative observation and test results of the cellulose spinning dope in Examples 1-3 and Comparative Examples 1-2

[0074]

[0075] From the results in Table 1 and Figure 1 the following conclusions can be drawn:

[0076] (1) By comparing Example 1 with Comparative Example 1, it can be seen that compared with single mixing and swelling, the gradient mixing and swelling in the present invention can make cellulose fully swell in the NMMO solution, thereby effectively improving the dissolution effect of cellulose in the NMMO solution. No obvious undissolved fibers and cellulose crystals were observed in the solution.

[0077] (2) By comparing Example 1 with Comparative Example 2, it can be seen that the more times of gradient mixing and swelling, the more fully cellulose swells in the NMMO solution, and the better the dissolution effect.

[0078] (3) By comparing Example 1 and Example 2, it can be seen that increasing the temperature during the gradient mixing and swelling process helps cellulose to swell in the NMMO solution and can improve the dissolution effect.

[0079] (4) By comparing Example 1 and Example 3, it can be seen that increasing the stirring time during the gradient mixing and swelling process helps cellulose to swell in the NMMO solution and can improve the dissolution effect.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a lyocell fiber spinning dope, characterized in that, It includes the following steps: (1) Wet pulverization of pulp raw material: Put the cellulose pulp raw material into the pulping equipment filled with the prepared dissolving water for pulping treatment to obtain pulp porridge; (2) Pressurized pulverization of pulp raw material: Perform pressurized pulverization on the pulp porridge obtained in step (1) to obtain a pulp raw material with a water content of 50 - 60 wt%; (3) Gradient swelling of pulp raw material: Mix the pulp raw material obtained in step (2) with an NMMO solution with a concentration of 50 - 60 wt% for the first swelling at a temperature of 30 - 50 °C; Perform pressurized pulverization on the pulp porridge after the first swelling to obtain raw material a with a water content of 55 - 65 wt%, and the pressing temperature is 40 - 50 °C; Mix the pressurized and pulverized pulp raw material a with an NMMO solution with a concentration of 60 - 70 wt% for the second swelling at a temperature of 50 - 60 °C; Perform pressurized pulverization on the pulp porridge after the second swelling to obtain raw material b with a water content of 55 - 65 wt%, and the pressing temperature is 50 - 70 °C; Mix the pressurized and pulverized pulp raw material b with an NMMO solution with a concentration of 70 - 80 wt% for the third swelling at a temperature of 70 - 80 °C; (4) Pressurized pulverization of the pulp raw material after gradient swelling: Perform pressurized pulverization on the pulp porridge after gradient swelling to obtain raw material c with a water content of 55 - 65 wt%, and the pressing temperature is 60 - 70 °C; (5) Direct dissolution of pulp raw material: Mix the pressurized and pulverized pulp raw material c with an NMMO solution with a concentration of 81 - 85 wt% for dissolution at a dissolution temperature of 90 - 100 °C, Finally, obtain the Lyocell fiber spinning dope.

2. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In step (1), the dissolving water is deionized water with a water temperature of 50 - 60 °C.

3. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In step (1), the concentration of cellulose in the pulp porridge is 4 - 5 wt%.

4. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In step (1), the pulping equipment is a hydraulic pulper commonly used in the paper industry.

5. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In steps (2), (3) and (4), the pressing equipment and pulverizing equipment used for the pressurized pulverization are the corresponding equipment used in the traditional viscose fiber industry.

6. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In step (3), the swelling time for each time is 20 - 30 min.

7. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In step (3), a pulp porridge storage tank with stirring is used during swelling, and the stirring speed is 60 - 80 rpm.

8. The method for preparing the Lyocell fiber spinning dope according to claim 1, wherein: In step (5), the cellulose concentration in the obtained Lyocell fiber spinning dope is 11 - 12 wt%.

9. The preparation method of the lyocell fiber spinning dope according to claim 1, wherein: In step (5), the dissolving device is a twin-screw extruder, the temperature of the extruder is 90-100 °C, the stirring speed is 60-90 rpm, and the dissolving time is 20-30 min.

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