Method for improving strength of regenerated cellulose fiber

Abstract

The invention relates to a method for improving the strength of regenerated cellulose fibers, and belongs to the field of regenerated cellulose fiber preparation. According to the method for improving the strength of the regenerated cellulose fiber, the regenerated cellulose fiber is prepared through the processes of cellulose pretreatment, spinning solution preparation, spinning, post-treatment and the like. In the spinning process, in order to avoid the problem that as nascent fibers which are just sprayed out of a spinning nozzle and are in a viscous flow state are broken, only negative stretching, non-stretching or small positive stretching can be adopted, and the fiber strength is not high; effective secondary drafting is carried out on nascent fibers which are not completely regenerated and still in a large plastic state, so that cellulose macromolecules and associates are highly oriented in the stretching direction, and the fiber strength is effectively improved; the first-stage draw ratio is 0.769 to 2.308, and the second-stage draw ratio is 1.0 to 1.4. The strength of the regenerated cellulose fiber is improved by utilizing the interaction response of the first-stage drafting and the second-stage drafting; the breaking strength of the regenerated cellulose fiber is 2.11 cN / dtex, and the breaking work of the regenerated cellulose fiber is 110623.90 cN * mm.

Description

Technical Field

[0001] The invention relates to a method for improving the strength of regenerated cellulose fibers, and belongs to the field of regenerated cellulose fiber preparation. Background Art

[0002] Regenerated cellulose fiber is widely used in many fields such as clothing, construction, high-end packaging, smart wearable devices, etc. due to its unique advantages such as abundant resources, natural environmental protection, good moisture absorption and air permeability, and excellent dyeing and fixing performance. It is gradually becoming an important representative of green and sustainable materials. The preparation methods of regenerated cellulose fiber mainly include traditional viscose method, NMMO (N-methylmorpholine oxide) solvent method and ionic liquid solvent method. Among them, the traditional viscose method is the most widely used process, but it has problems such as complex dissolution process, long time, and serious pollution, which seriously affects production efficiency and environmental friendliness. In contrast, the NMMO solvent method and ionic liquid solvent can effectively dissolve natural cellulose, simplify the production process, reduce environmental pollution, and provide more dissolution options and process optimization space. They have low environmental toxicity and good recyclability, and have received widespread attention in recent years. At the same time, a patent application with publication number CN111394817A points out a new preparation process for regenerated fibers, which greatly improves the dissolution effect of cellulose, improves the dissolution efficiency, improves the stability and spinnability of the cellulose solution by improving the mixing ratio of DMSO and TBAH aqueous solvents, and can effectively reduce the viscosity of the cellulose solution, which is beneficial to the long-distance transportation of the cellulose solution at room temperature. However, the fiber breaking strength produced by this method is not high, with a maximum of only 1.73 cN / dtex, which hinders its practical application. Summary of the invention

[0003] In response to the above-mentioned problem of low fiber breaking strength, the applicant of the present invention has found that in the wet spinning preparation process using the TBAH / DMSO aqueous solvent system, when the spinning solution is ejected from the spinneret, since it is still in a viscous flow state, it is not advisable to apply too high a stretching speed, otherwise it is easy to cause broken or filamentary fibers; in order to avoid the breakage of the nascent fibers in a viscous flow state just ejected from the spinneret, only negative stretching can be used, and no stretching or small positive stretching can be used, which leads to low fiber strength; based on this, the present invention proposes to perform effective secondary stretching on the nascent fibers that have not been fully regenerated and are still in a relatively large plastic state, so that the cellulose macromolecules and aggregates are highly oriented along the stretching direction, thereby effectively improving the fiber strength; that is, the present invention utilizes the interactive response of primary stretching and secondary stretching to improve the strength of the regenerated cellulose fibers; the breaking strength and breaking work of the obtained regenerated cellulose fibers are 2.11 cN / dtex and 110623.90 cN·mm, respectively.

[0004] The technical solution of the present invention:

[0005] The present invention provides a preparation method for improving the strength of regenerated cellulose fiber, the method adopts cellulose pretreatment, preparation of spinning solution, spinning molding and post-treatment processes to prepare regenerated cellulose, wherein a secondary stretching is introduced in the spinning molding process, firstly, a first drafting roller is used to negatively stretch the viscous flow state spinning solution just ejected from the spinneret, and a positive stretching without stretching or with a low stretching speed is performed to avoid the breakage of the primary fiber; then a second drafting roller is used to effectively secondary stretch the newly formed TBAH / DMSO water solvent regenerated cellulose fiber, because the primary fiber just leaving the coagulation bath has been uniformly coagulated, but has not been completely regenerated, and is still in a relatively large plastic state, and the cellulose macromolecular chain still has a large room for movement, and a strong stretching can make the cellulose macromolecules and the association body oriented along the stretching direction; therefore, the cellulose is basically regenerated while stretching, so that the stretching effect is consolidated. The primary drafting ratio is 0.769-2.308, and the secondary drafting ratio is 1.0-1.4.

[0006] Furthermore, the spinning process is as follows: the spinning solution is controlled to enter a coagulation bath through a primary drawing process to form primary fibers, and then enters a drawing bath through a secondary drawing process; and finally the solvent is removed by water washing.

[0007] Furthermore, in the spinning process, the coagulation bath is selected from: deionized water or aqueous sulfuric acid solution; the concentration range of the aqueous sulfuric acid solution can be selected from 5wt% to 45wt%; and the drawing bath is deionized water.

[0008] Furthermore, the mass concentration of cellulose in the spinning solution is 5wt% to 7wt%, which can be made into fibers. The higher the concentration, the higher the fiber breaking strength, but if the concentration is too high, the spinning solution cannot be transported due to the high viscosity of the spinning solution.

[0009] Furthermore, the solvent used in the spinning solution is a TBAH (tetrabutylammonium hydroxide) / H2O / DMSO (dimethyl sulfoxide) solvent system, and the mass ratio thereof is preferably 1:1:8.

[0010] Furthermore, the post-treatment includes washing, oiling, drying and winding processes.

[0011] Furthermore, the cellulose is preferably cotton pulp cellulose.

[0012] Beneficial effects of the present invention:

[0013] The invention discloses a method for improving the strength of regenerated cellulose fiber: based on a DMSO / TBAH aqueous solvent system, a regenerated cellulose spinning solution is firstly prepared, and then the spinning solution extruded through a spinneret is controlled to enter a coagulation bath through a primary drafting to obtain a preliminary shape, and then is controlled to enter a drafting bath through a secondary drafting to further refine and fix the shape, and finally a regenerated cellulose fiber is obtained through water washing, oiling, drying and winding; the obtained regenerated cellulose fiber has a breaking strength and a breaking work of 2.11 cN / dtex and 110623.90 cN·mm respectively, and has important practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 (a) is a finished product diagram of the regenerated cellulose fiber prepared by the present invention, Figure 1 (b) is a scanning electron micrograph of the finished fiber surface.

[0015] Figure 2 This is a stress-strain curve of the regenerated cellulose fiber prepared in the present invention under the optimal stretching ratio (the primary stretching ratio and the secondary stretching ratio are 1.115 and 1.4 respectively). DETAILED DESCRIPTION

[0016] The invention discloses a method for improving the strength of regenerated cellulose fiber: firstly, cotton pulp is crushed, and then soaked with a dimethyl sulfoxide (DMSO) solvent, and after the cellulose is pre-impregnated, a tetrabutylammonium hydroxide (TBAH) aqueous solution is added and stirred to dissolve, and then vacuum degassing and filtering are performed; then, the spinning stock solution extruded through the spinneret is controlled to enter a coagulation bath through a primary drafting to obtain a preliminary shape, and then is controlled to enter a drafting bath through a secondary drafting to further refine and fix the shape, and then washed, oiled, dried, and wound to obtain the final regenerated cellulose fiber.

[0017] The present invention introduces two-stage stretching, in which the first stretching roller performs negative stretching on the viscous flow spinning solution just ejected from the spinneret, and positive stretching without stretching or with a low stretching speed to avoid the breakage of the primary fibers; the second stretching roller performs effective secondary stretching on the newly formed TBAH / DMSO water solvent regenerated cellulose fibers, because the primary fibers just leaving the coagulation bath have been uniformly coagulated but not completely regenerated, and are still in a relatively plastic state, and the cellulose macromolecular chains still have a large room for movement, and strong stretching can orient the cellulose macromolecules and the aggregates along the stretching direction; while stretching, the cellulose is basically regenerated, so that the stretching effect is consolidated; it can be seen that the present invention provides a method for improving the strength of regenerated cellulose fibers, and the breaking strength and breaking work of the obtained regenerated cellulose fibers are 2.11 cN / dtex and 110623.90 cN·mm, respectively.

[0018] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0019] Comparative Example 1 Preparation of regenerated cellulose fiber by primary drawing

[0020] The preparation of regenerated cellulose fiber comprises the following steps:

[0021] S1 Cellulose pretreatment: First, cellulose pulp (purchased from Xinxiang Chemical Fiber Co., Ltd.) was cut into squares of about 50 cm × 50 cm, placed in a grinder and crushed at 30,000 rpm for 2 min, and then the obtained fluffy cellulose was dried at 60°C to constant weight. Finally, 70 g of the dried cellulose was weighed and immersed in 744 g of DMSO at room temperature for 30 min.

[0022] Preparation of S2 spinning solution: 186 g of a solution with a mass ratio of TBAH:H2O=1:1 was added to the pre-impregnated spinning solution, and then a double-helix ribbon stirring paddle was used to stir at a speed of 800 rpm for 1 hour; finally, a spinning solution with a cellulose content of 7% and a solvent ratio of DMSO:TBAH:H2O=8:1:1 was obtained.

[0023] Subsequently, the spinning solution is added to the spinning kettle, and the air inlet is closed, the air outlet is opened and the vacuum pump is connected. The bubbles in the spinning solution are continuously removed for 12 hours at a pressure of -0.1MPa in the spinning kettle until no bubbles are observed in the spinning solution. After the degassing process is completed, the air outlet is finally closed, the air inlet is opened and nitrogen is connected to pressurize the spinning kettle to 0.3MPa, so that the spinning solution passes through the bottom filter plate to remove impurities in the spinning solution (those larger than 25 microns are filtered out).

[0024] S3 spinning: turn on the metering pump under the spinning kettle, and the spinning solution enters the spinneret with a diameter, number of holes and pore size of 16mm, 100 and 0.14mm respectively through the conveying pipe, candle filter and gooseneck tube; the spinning solution is extruded from the spinneret (the extrusion speed of the spinning solution in the spinneret is 6.5m / min), and then enters the 30°C coagulation bath sulfuric acid aqueous solution (concentration range is 25wt%) through a first-level drawing control (the length of the coagulation bath is 1 meter) to form raw fibers; finally, it enters the first-level water washing tank, the second-level water washing tank and the third-level water washing tank with a temperature of 80°C in turn for water washing to remove the residual solvent in the fiber.

[0025] S4 post-treatment: The washed fibers are drawn through rollers and sent into an oiling box for oiling to increase the fiber's cohesion; the oiled fibers are sequentially sent into two groups of heated rollers at a temperature of 90°C, and finally the fibers are wound onto the rollers through the traction of the guide rollers.

[0026] Table 1 shows the mechanical properties of the regenerated cellulose fibers obtained in Comparative Example 1 when the draft ratios (primary drafting speed ratio is V1 / V0) are 0.769 (negative stretching), 1.115, 1.154, 1.923 and 2.308 (when the fiber exceeds this value, it breaks due to excessive drafting); in Table 1, V0 is the extrusion speed of the spinning solution; V1 is the linear speed of the fiber at the first drafting roller; V2 is the linear speed of the fiber at the second drafting roller.

[0027] Table 1

[0028]

[0029] It can be seen from Table 1 that when the regenerated cellulose fiber is not stretched, the breaking strength and breaking work are only 1.3 cN / dtex and 29936.90 cN·mm, respectively; when only subjected to primary stretching, with the increase of the primary stretching ratio, the maximum fiber breaking strength is only 1.60 cN / dtex, which is lower than the qualified grade of viscose fiber (≥1.65 cN / dtex), greatly limiting the widespread application of regenerated cellulose fiber under this solvent system.

[0030] Example 1 Preparation of regenerated cellulose fibers by secondary drawing

[0031] The preparation of regenerated cellulose fiber comprises the following steps:

[0032] S1 Cellulose pretreatment: First, cellulose pulp (purchased from Xinxiang Chemical Fiber Co., Ltd.) was cut into squares of about 50 cm × 50 cm, placed in a grinder and crushed at 30,000 rpm for 2 min, and then the obtained fluffy cellulose was dried at 60°C to constant weight. Finally, 70 g of the dried cellulose was weighed and immersed in 744 g of DMSO at room temperature for 30 min.

[0033] S2 Preparation of spinning solution: 186 g of a solution with a mass ratio of TBAH:H2O=1:1 was further added to the spinning solution after pre-impregnation, and then a double helix ribbon stirring paddle was used to stir at a speed of 800 rpm for 1 hour; finally, a spinning solution with a cellulose content of 7% and a solvent ratio of DMSO:TBAH:H2O=8:1:1 was obtained.

[0034] Subsequently, the spinning solution was added to the spinning kettle, and the air inlet was closed, the air outlet was opened and the vacuum pump was connected. The bubbles in the spinning solution were continuously removed for 12 hours at a pressure of -0.1 MPa in the spinning kettle until no bubbles were observed in the spinning solution. After the degassing process was completed, the air outlet was finally closed, the air inlet was opened and nitrogen was connected to pressurize the spinning kettle to 0.3 MPa, so that the spinning solution passed through the bottom filter plate to remove impurities in the spinning solution.

[0035] S3 spinning: the metering pump under the spinning kettle is turned on, and the spinning solution is metered by the metering pump, and enters the spinneret with a diameter, number of holes and pore size of 16mm, 100 and 0.14mm respectively through the conveying pipe, candle filter and gooseneck tube; the spinning solution is extruded from the spinneret (the extrusion speed of the spinning solution in the spinneret is 6.5m / min), and then through the first-stage drawing (the length of the coagulation bath is 1 meter), it is controlled to enter the 30°C coagulation bath sulfuric acid aqueous solution (concentration range is 25wt%) to form a primary fiber, and then through the second-stage drawing (the length of the drawing bath is 1 meter) It enters the drawing bath deionized water; finally, it enters the second-stage water washing tank and the third-stage water washing tank with a temperature of 80°C for washing to remove the residual solvent in the fiber; during the spinning process, the first-stage drawing ratio is 1.155, and the second-stage drawing ratios (V2 / V1) are 1.0, 1.1, 1.2, 1.3 and 1.4 respectively;

[0036] S4 post-treatment: The washed fibers are drawn through rollers and sent into an oiling box for oiling to increase the fiber's cohesion; the oiled fibers are sequentially sent into two groups of heated rollers at a temperature of 90°C, and finally the fibers are wound onto the rollers through the traction of the guide rollers.

[0037] Table 2 shows the mechanical properties of the regenerated cellulose fibers obtained in Example 1 when the primary drafting ratio is 1.155 and the secondary drafting ratios (V2 / V1) are 1.0, 1.1, 1.2, 1.3 and 1.4, respectively.

[0038] Table 2

[0039]

[0040] It can be seen from Table 2 that when the primary draft ratio remains unchanged, with the increase of the secondary draft ratio, the breaking strength of the regenerated cellulose fiber under this solvent system is 2.11 cN / dtex, which is significantly improved. This value is much higher than the superior grade of viscose fiber (≥1.85 cN / dtex), which greatly increases the actual value of the regenerated cellulose fiber under this solvent system.

[0041] Example 2 Preparation of regenerated cellulose fibers by secondary drawing

[0042] The other preparation methods are the same as those in Example 1, except that the primary drafting ratio and the secondary drafting ratio are different from those in Example 1, as shown in Table 3; the properties of the final fiber are shown in Table 3.

[0043] Table 3

[0044]

[0045] Figure 2The stress-strain curve of the regenerated cellulose fiber prepared in the present invention under the optimal draft ratio (the primary draft ratio and the secondary draft ratio are 1.115 and 1.4 respectively). Figure 2 As can be seen from Tables 1 and 2, when the primary and secondary stretching ratios were 1.115 and 1.4 respectively, the optimal comprehensive mechanical properties of the regenerated cellulose fibers in the TBAH / DMSO aqueous solvent system were obtained, with a breaking strength and breaking work of 2.11 cN / dtex and 110623.90 cN·mm respectively.

[0046] In the present invention, the fibers obtained in each embodiment and comparative example are tested according to GB-T 13758-2008, and the test method is as follows:

[0047] (1) Characterization of fineness

[0048] First, the yarn frame speed and the number of test turns of the yarn length measuring instrument are set to 60r / min and 25 turns respectively, of which the number of pre-deceleration turns is 3 turns. Then the filament tube is placed on the yarn tube and the shaking yarn frame is propped up. A bundle of fibers is taken and passed through the yarn guide frame, tension regulator, tension rod and transverse yarn arrangement device in sequence, and fixed on the yarn frame. Finally, the test is started. After the measurement stops, the fibers are cut at the place where the yarn frame fixes the fibers. The fibers wound on the yarn frame are removed, the grams of the fibers are weighed, and the fiber fineness D is calculated by formula (1) in dtex; the experiment is repeated 5 times, and the average value of the test results is taken.

[0049] D = 400 × g (1)

[0050] (2) Determination of fiber mechanical properties

[0051] According to GB-T 13758-2008 standard, firstly, the electronic single yarn strength tester test gauge and stretching speed are set to 500mm and 250mm / min respectively, then a bundle of fibers is taken out from the filament tube and passed through the guide wheel, the bundle of fibers is guided between the upper and lower clamps, the fibers clamped by the upper clamp are fixed, and the lower part is clamped between the tension wire clamp handle and the lever. At this time, the tension lever should be kept horizontal, and the force value displayed on the display is the pre-tension value. Finally, the test is started. After the stretching is completed, the breaking strength P (cN) and breaking work (cN·mm) of the bundle of fibers can be obtained, and the fiber breaking strength σ is calculated by formula (2) in units of cN / dtex. The experiment is repeated 5 times, and the average value of the test results is taken.

[0052] σ=P / D (2)

[0053] The present invention is not limited to the above-mentioned specific embodiments. Those skilled in the art to which the present invention belongs may make various modifications, supplements or substitute the described specific embodiments in similar ways without departing from the spirit of the present invention or exceeding the scope defined by the attached claims, which are all within the scope of protection required by the present invention.

Claims

1. A method for improving the strength of regenerated cellulose fiber, the method comprising preparing regenerated cellulose by cellulose pretreatment, preparation of spinning solution, spinning molding and post-treatment processes, characterized in that: In the spinning process, a two-stage drafting process is adopted, wherein the first-stage drafting ratio is 0.769-2.308, and the second-stage drafting ratio is 1.0-1.

4.

2. A method for improving the strength of regenerated cellulose fibers according to claim 1, characterized in that: The spinning process is as follows: the spinning solution is controlled to enter a coagulation bath through a primary drawing process to form primary fibers, then enters a drawing bath through a secondary drawing process, and finally the residual solvent is removed by water washing.

3. A method for improving the strength of regenerated cellulose fibers according to claim 2, characterized in that: The coagulation bath is selected from: deionized water or sulfuric acid aqueous solution; the drawing bath is deionized water.

4. A method for improving the strength of regenerated cellulose fibers according to claim 3, characterized in that: The concentration of the aqueous sulfuric acid solution is in the range of 5 wt % to 45 wt %.

5. A method for improving the strength of regenerated cellulose fibers according to claim 1, characterized in that: The mass concentration of cellulose in the spinning solution is 5wt% to 7wt%.

6. A method for improving the strength of regenerated cellulose fibers according to claim 6, characterized in that: The solvent used in the spinning solution is a TBAH / DMSO water solvent system.

7. A method for improving the strength of regenerated cellulose fibers according to claim 1 or 2, characterized in that: The post-treatment process includes washing, oiling, drying and winding procedures.

8. The method for improving the strength of regenerated cellulose fibers according to claim 1, characterized in that: The cellulose is cotton pulp cellulose.

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