Preparation method of regenerated cellulose fiber with nanofiber structure

Abstract

The invention discloses a preparation method of regenerated cellulose fiber with a nanofiber structure. The preparation method comprises the following steps: mixing wood pulp cellulose with imidazole ionic liquid to obtain a cellulose spinning solution; taking effective components of imidazolium ionic liquid, diluting the effective components to obtain an ionic liquid aqueous solution, and using the ionic liquid aqueous solution as a coagulating bath; adding the cellulose spinning solution into a material tank of spinning equipment, applying pressure to a spinning needle head, enabling extruded spinning to enter a coagulating bath, washing with water, and drying, so as to obtain the regenerated cellulose fiber with the nanofiber structure. The cellulose dissolving solution used in the method is low in toxicity and harmless, has good cellulose solubility, and is beneficial to improving the concentration of cellulose in the spinning solution, so that the physical and mechanical properties of regenerated fibers are enhanced. The low-concentration ionic liquid aqueous solution is adopted as a coagulating bath, the diffusion rate is reduced, the cellulose regeneration process is slowed down, formation of a nanofiber structure is induced, and the regenerated fiber with a closely-stacked and highly-directionally-arranged nanometer fibril structure is prepared.

Description

Technical Field

[0001] The invention relates to a method for preparing high-strength and high-tenacity regenerated cellulose fibers with a nanofiber structure, belonging to the technical field of regenerated cellulose fibers. Background Art

[0002] Regenerated cellulose fiber made from natural cellulose is a pure natural material that is naturally biodegradable, free of additives, heavy metals, and harmful chemicals. It is skin-friendly and non-irritating, and is an environmentally friendly fiber with excellent performance. It retains the excellent qualities of natural cellulose such as biocompatibility and degradability, and can also make up for the shortcomings of natural fibers themselves, occupying an increasingly higher share in the market.

[0003] During the spinning process, when the cellulose concentration in the spinning solution is high, due to the unique semi-rigid straight-chain structure of cellulose, its molecular chains tend to be arranged in parallel. Using imidazole ionic liquids with strong cellulose dissolving power as dissolving solvents, high-concentration cellulose spinning solutions are obtained. However, high-concentration cellulose spinning solutions are prone to internal stress during the molding process, resulting in poor toughness and low elongation of the prepared regenerated fibers. Through precise control of the cellulose regeneration process, regenerated cellulose fibers with nanofiber structure and directional arrangement can be obtained, effectively solving the contradiction between the strength and toughness of existing regenerated cellulose fibers. Generally, too fast cellulose regeneration speed will cause inherent defects in the regenerated fibers and reduce mechanical properties, while slow and controlled coagulation is conducive to making the regenerated cellulose structure dense, reducing internal stress and improving strength. Selecting a low-concentration ionic liquid aqueous solution as a coagulation bath reduces the diffusion coefficient, slows down the cellulose regeneration process, induces the formation of nanofiber structure, and prepares regenerated fibers with tightly stacked, highly directional nanofibril structure, and exhibits excellent mechanical properties. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing high-strength and high-tenacity regenerated cellulose fibers with a nanofiber structure, so as to solve the problem that the strength and tenacity of existing regenerated cellulose fibers cannot be improved simultaneously.

[0005] In order to solve the above problems, the present invention provides a method for preparing regenerated cellulose fibers with a nanofiber structure, comprising the following steps:

[0006] Step 1): mixing wood pulp cellulose with imidazole ionic liquid, heating and stirring until completely dissolved, and performing ultrasonic heating and defoaming treatment to obtain cellulose spinning solution;

[0007] Step 2): Take another effective component of the imidazole ionic liquid used in step 1), dilute it in deionized water, stir evenly, and the obtained ionic liquid aqueous solution is used as a coagulation bath;

[0008] Step 3): Add the cellulose spinning solution into the material tank of the spinning equipment, apply pressure to the spinneret, and the extruded spinning enters the coagulation bath, is washed with water, and dried to obtain regenerated cellulose fibers with a nanofiber structure.

[0009] Preferably, in step 1), the cellulose is wood pulp cellulose, the mass content of the cellulose is not less than 90%, and the degree of polymerization is 100-1000; and the mass concentration of the cellulose spinning solution is 10-15%.

[0010] Preferably, in step 1), the imidazolium ionic liquid is any one of 1-allyl-3-methylimidazolium chloride (AMIMCl), 1-butyl-3-methylimidazolium chloride (BMIMCl) or 1-butyl-3-methylimidazolium acetate (BMIMAc).

[0011] Preferably, in step 1), the heating and stirring temperature is 80-90° C., and the time is 6-10 h; the stirring method is mechanical stirring, and the speed is 50-100 rpm.

[0012] Preferably, in step 1), the ultrasonic power of the ultrasonic heating defoaming treatment is 15-200 W, the heating temperature is 60-70° C., and the treatment time is 60-120 min.

[0013] Preferably, in step 2), the stirring temperature is room temperature, the stirring speed is 200-400 rpm, and the stirring time is 20-30 min; and the mass concentration of the ionic liquid aqueous solution is 1-3%.

[0014] Preferably, in the step 3), the heating temperature of the material tank is 75-85° C., the spinneret needle is 22G, and the pressure of the air pump is 70-90 PSI.

[0015] Preferably, in step 3), the temperature of the coagulation bath is 5-25°C, and the temperature of the water washing is 20-25°C.

[0016] Preferably, in step 3), the drying temperature is 20-25° C. and the drying time is 15-24 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The cellulose solvent provided by the present invention is an imidazole ionic liquid, which is soluble in water, has low toxicity and is harmless, has a recovery rate of ≥99%, is green and environmentally friendly, and has the potential for industrial production.

[0019] 2. The present invention prepares a high-concentration cellulose spinning solution based on the good solubility of imidazole ionic liquids for cellulose, thereby promoting the pre-oriented arrangement of cellulose molecular chains.

[0020] 3. The present invention adopts low-concentration ionic liquid instead of the original aqueous solution as the coagulation bath, which reduces the diffusion rate of the solvent and the coagulation bath during the spinning process, slows down the cellulose regeneration process, promotes the orderly arrangement of the fibers, induces the formation of nanofiber structure, reduces inherent defects, and prepares regenerated fibers with a tightly stacked and highly oriented nanofibril structure, which greatly improves the mechanical properties of the regenerated fibers.

[0021] 4. The regenerated cellulose fiber with nanofiber structure prepared by the present invention induces the orderly arrangement of cellulose macromolecules through coagulation bath induction, and the subsequent micro-stretching in the air gap section and coagulation molding section further promotes the directional arrangement of cellulose molecular chains, eliminates the internal stress of the fiber, and improves crystallization, so that the mechanical strength and modulus of the fiber are further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the preparation method provided by the present invention;

[0023] Figure 2 is a scanning electron microscope image of the regenerated cellulose fiber obtained in Example 1;

[0024] Figure 3 is a scanning electron microscope image of the regenerated cellulose fiber obtained in Example 2;

[0025] Figure 4 This is a scanning electron microscope image of the regenerated cellulose fiber prepared in Example 3. DETAILED DESCRIPTION

[0026] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0027] Example 1

[0028] A method for preparing regenerated cellulose fibers with a nanofiber structure comprises the following steps:

[0029] (1) The dried wood pulp cellulose is crushed and sieved to control the particle size to 100-140 mesh.

[0030] (2) 5 g of crushed cellulose solid was immersed in 33.5 g of 1-allyl-3-methylimidazolium chloride ionic liquid, swollen and soaked at room temperature for 2 h, and heated in an oil bath at 85° C. for 6 h to obtain a 13 wt % cellulose solution.

[0031] (3) 10 g, 20.2 g and 30.6 g of 1-allyl-3-methylimidazolium chloride were mixed with 990 g of deionized water in a beaker and mechanically stirred for 20 min at room temperature until transparent and clear 1 wt %, 2 wt % and 3 wt % 1-allyl-3-methylimidazolium chloride aqueous solutions were obtained for use as coagulation baths.

[0032] (4) The prepared spinning solution is added into the material tank of the spinning equipment and maintained at 80° C. Under the external force of air pressure, the spinning solution is extruded from the spinneret hole and enters the coagulation bath through a 3 mm air gap section.

[0033] (5) The coagulation bath is a low-concentration 1-allyl-3-methylimidazolium chloride aqueous solution, and the initial coagulation-formed regenerated fiber is immersed in the coagulation bath for ≥5 min. It is then washed three times, dried, and finally wound and collected. The regenerated cellulose fiber with nanofiber structure obtained is measured ( Figure 2 )’s physical and mechanical properties, specific indicators are shown in Table 1.

[0034] Table 1 Performance indexes of regenerated cellulose fibers in Example 1

[0035]

[0036] Example 2

[0037] A method for preparing regenerated cellulose fibers with a nanofiber structure comprises the following steps:

[0038] (1) The dried cotton pulp cellulose is crushed and sieved to control the particle size to 80-100 mesh.

[0039] (2) 5 g of cellulose powder was immersed in 33.5 g of 1-butyl-3-methylimidazolium chloride ionic liquid, swollen and soaked at room temperature for 2 h, and heated in an oil bath at 85° C. for 8 h to obtain a spinning solution with a cellulose concentration of 13 wt %.

[0040] (3) 10 g of 1-butyl-3-methylimidazolium chloride and 990 g of deionized water were mixed in a beaker and mechanically stirred for 20 min at room temperature until a transparent and clear 1 wt % 1-butyl-3-methylimidazolium chloride aqueous solution was obtained.

[0041] (4) The prepared spinning solution is added into the material tank of the spinning equipment and maintained at 85°C. Under the external force of air pressure, the spinning solution is extruded from the spinneret hole and enters the coagulation bath through a 2 mm air gap section.

[0042] (5) The coagulation bath is a 1 wt % aqueous solution of 1-butyl-3-methylimidazolium chloride. The initial coagulation-formed regenerated fiber is immersed in the coagulation bath for ≥ 5 min. It is then washed three times, dried, and finally wound and collected. The regenerated cellulose fiber with nanofiber structure obtained is measured ( Figure 3 )’s physical and mechanical properties, and the specific indicators are shown in Table 2.

[0043] Table 2 Performance indexes of regenerated cellulose fibers in Example 2

[0044]

[0045] Example 3

[0046] A method for preparing regenerated cellulose fibers with a nanofiber structure comprises the following steps:

[0047] (1) The dried wood pulp cellulose is crushed and sieved to control the particle size to 100-140 mesh.

[0048] (2) 5 g of crushed cellulose solid was immersed in 33.5 g of 1-butyl-3-methylimidazolium acetate ionic liquid, swollen and soaked at room temperature for 2 h, and heated in an oil bath at 85° C. for 6 h to obtain a 13 wt % cellulose solution.

[0049] (3) 10 g of 1-butyl-3-methylimidazole acetate and 990 g of deionized water were mixed in a beaker and mechanically stirred for 20 min at room temperature until a transparent and clear 1 wt % 1-butyl-3-methylimidazole acetate aqueous solution was obtained.

[0050] (4) The prepared spinning solution is added into the material tank of the spinning equipment and maintained at 80° C. Under the external force of air pressure, the spinning solution is extruded from the spinneret hole and enters the coagulation bath through a 3 mm air gap section.

[0051] (5) The coagulation bath is a 1 wt% aqueous solution of 1-butyl-3-methylimidazolium acetate. The initial coagulation-formed regenerated fiber is immersed in the coagulation bath for ≥ 5 min. It is then washed three times, dried, and finally wound and collected. The regenerated cellulose fiber with nanofiber structure obtained is measured ( Figure 4 )’s physical and mechanical properties, and the specific indicators are shown in Table 3.

[0052] Table 3 Performance indexes of regenerated cellulose fibers in Example 3

[0053]

Claims

1. A method for preparing regenerated cellulose fibers having a nanofiber structure, characterized in that: The following steps are involved: Step 1): mixing wood pulp cellulose with imidazole ionic liquid, heating and stirring until completely dissolved, and performing ultrasonic heating and defoaming treatment to obtain cellulose spinning solution; Step 2): Take another effective component of the imidazole ionic liquid used in step 1), dilute it in deionized water, stir evenly, and the obtained ionic liquid aqueous solution is used as a coagulation bath; Step 3): Add the cellulose spinning solution into the material tank of the spinning equipment, apply pressure to the spinneret, and the extruded spinning enters the coagulation bath, is washed with water, and dried to obtain regenerated cellulose fibers with a nanofiber structure.

2. The preparation method according to claim 1, characterized in that In the step 1), the cellulose is wood pulp cellulose, the mass content of the cellulose is not less than 90%, and the degree of polymerization is 100-1000; the mass concentration of the cellulose spinning solution is 10-15%.

3. The preparation method according to claim 1, characterized in that: In the step 1), the imidazole ionic liquid is any one of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium acetate.

4. The preparation method according to claim 1, characterized in that: In the step 1), the heating and stirring temperature is 80-90° C., and the time is 6-10 hours; the stirring method is mechanical stirring, and the speed is 50-100 rpm.

5. The preparation method according to claim 1, characterized in that: In the step 1), the ultrasonic power of the ultrasonic heating defoaming treatment is 15-200W, the heating temperature is 60-70°C, and the treatment time is 60-120min.

6. The preparation method according to claim 1, characterized in that: In the step 2), the stirring temperature is room temperature, the stirring speed is 200-400 rpm, and the stirring time is 20-30 min; the mass concentration of the ionic liquid aqueous solution is 1-3%.

7. The preparation method according to claim 1, characterized in that: In the step 3), the heating temperature of the material tank is 75-85° C., the spinneret needle is 22G, and the pressure of the air pump is 70-90 PSI.

8. The preparation method according to claim 1, characterized in that: In the step 3), the temperature of the coagulation bath is 5-25°C, and the temperature of the water washing is 20-25°C.

9. The preparation method according to claim 1, characterized in that: In the step 3), the drying temperature is 20 to 25° C. and the drying time is 15 to 24 hours.

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