A method for pretreating pulp and its use in the production of high intrinsic viscosity industrial yarns

Abstract

The present application belongs to the field of regenerated cellulose fiber preparation, and particularly relates to a pulp pretreatment method and application thereof in preparation of high-characteristic-viscosity industrial silk. The method comprises the following steps: pulp dispersion; mechanical treatment of cellulose water dispersion; dehydration of the mechanically treated water cellulose; dispersion and defibration of the mechanically treated water cellulose; ethanol replacement of the cellulose; and drying. The present application adopts wet mechanical beating and ethanol activation to pretreat high-characteristic-viscosity and high-concentration pulp, solves the technical problem that high-concentration, high-purity and high-characteristic-viscosity pulp is difficult to dissolve, and obtains a spinning solution that can meet production requirements.

Description

Technical Field

[0001] This invention belongs to the field of regenerated cellulose fiber preparation, specifically relating to a pulp pretreatment method and its application in the preparation of high intrinsic viscosity industrial yarns. Background Technology

[0002] Cellulose is the world's most produced natural polymer, widely found in plant cell walls. Due to its abundant sources and multifunctional characteristics, cellulose currently has significant applications in the paper, textile, food, pharmaceutical and cosmetic, biofuel, environmental materials, construction, and composite materials industries.

[0003] Cellulose industrial filaments are high-performance filaments made from natural cellulose, possessing a variety of excellent properties that make them widely used in numerous industries. Their key characteristics include: high strength and high modulus, biocompatibility and biodegradability, low coefficient of thermal expansion, and excellent moisture absorption and breathability. Thanks to their unique physical and chemical properties, cellulose industrial filaments have demonstrated significant application value in composite materials, tires and hoses, industrial filters, conveyor belts and industrial fabrics, protective clothing and safety equipment, cables and wires, and textiles, providing new possibilities for the development of various high-performance and environmentally friendly materials.

[0004] Due to the rich and complex intermolecular and intramolecular hydrogen bond network structure of cellulose, it is difficult to dissolve. Therefore, the pulp used to prepare industrial cellulose filaments is usually limited to high-purity pulp with relatively low intrinsic viscosity / average molecular weight (the dissolution process of high molecular weight pulp is uneven due to the high viscosity of the solution). Furthermore, the relatively high temperature (above 90℃) and relatively long time (above 180 min) during the dissolution and spinning process further exacerbate the degradation of the already low molecular weight pulp. This results in the final industrial cellulose filament having an intrinsic viscosity often <400 ml / g (ISO5351:2004); the product strength and modulus are typically <4.0 cN / dtex and <150 cN / dtex (ASTM D885 / D885M), respectively, severely restricting its application in composite materials (such as wood-plastic composites) and the construction industry (geotextiles, etc.).

[0005] Existing research has shown that the molecular weight of cellulose affects the entanglement, orientation, and crystallization of cellulose molecular chains, thus significantly impacting the mechanical properties of cellulose. Furthermore, cellulose materials prepared from cellulose raw materials with a high molecular weight fraction (DP>2000) greater than 20% and a polydispersity greater than 3 exhibit superior mechanical properties. Therefore, a simple, efficient, and essentially non-degradable activation method is needed to promote the dissolution of high-purity and high intrinsic viscosity cellulose to prepare high-strength, high-modulus industrial cellulose fibers.

[0006] Currently, in the industrial production of lyocell fiber, there are two main methods for pretreatment of cellulose pulp:

[0007] One method is dry pretreatment of cellulose pulp: the main method involves first dry-pulverizing the pulp, then pre-mixing it directly with a high-concentration NMMO solution, and finally dissolving it in a reactor to prepare the spinning solution. Patent CN1312819A discloses a method for preparing a cellulose suspension, specifically involving pulverizing the pulp and mixing it with NMMO of a certain water content, passing it through a first shear zone and a second shear zone to obtain a cellulose suspension. Traditional mechanical processing not only leads to disordered fiber cutting and inconsistent pulp fiber morphology, but also causes problems such as "localized coating" and "uneven dissolution" during the pulp dissolution process. The resulting spinning solution has a high content of undissolved pulp components, and the candle filter is often easily clogged, resulting in severe filament breakage in the product. Furthermore, the high-speed blades in the traditional dry pulping process cause significant mechanical and localized thermal degradation of the cellulose, leading to a decrease in the intrinsic viscosity of the pulp after treatment, ultimately negatively impacting the strength of the industrial filaments.

[0008] Another method is wet pretreatment of cellulose pulp: the main approach involves treating the cellulose pulp with a solution of a certain concentration of acid, alkali, or enzyme, and then mixing it with an NMMO aqueous solution. Patent CN102234849A discloses a method for pretreating bamboo fiber cellulose, specifically involving stirring the pulp and deionized water in a high-pressure vessel for 4-6 hours, then cooking it at 120-200℃ for 3-6 hours, and finally pressing it to obtain pretreated cellulose. This process is time-consuming and requires high temperature and pressure, demanding sophisticated equipment. Furthermore, the pulp will degrade under high temperature and pressure, negatively impacting the strength of the cellulose industrial fibers. Patents CN103556248A, CN101694019A, and CN103556235A disclose a method for cellulose pretreatment. First, cellulose is pulverized, then deionized water is added for swelling, followed by the addition of cellulase. The pH is adjusted to between 4 and 6, and the mixture is kept at 40-60°C for 40-100 minutes with continuous stirring. After activation, NaOH is added to adjust the pH to between 9.5 and 11, and the mixture is stirred for 6-15 minutes to inactivate the enzyme. The enzyme-activated cellulose pulp is then pressed to achieve a moisture content of approximately 45-60 wt.%. While this method effectively addresses the problem of high intrinsic viscosity pulp being difficult to dissolve, enzyme activity is difficult to control. Uneven temperature within the equipment and pH differences can cause significant variations in the intrinsic viscosity of cellulose, negatively impacting product stability. Furthermore, enzymatic treatment also reduces the intrinsic viscosity of cellulose, negatively affecting the strength of industrial cellulose fibers. Cellulase does not only target the primary cell wall, but acts on all primary and secondary cell walls of pulp. This often leads to problems such as large batch-to-batch variations and severe degradation due to the actual enzyme activity.

[0009] Currently, the ability to uniformly dissolve high-viscosity pulp with high quality while ensuring high solubility (≥8wt%) has become a significant factor restricting the industrialization of high-strength, high-modulus cellulose industrial fibers. Therefore, this invention proposes a pretreatment method for cellulose industrial fiber pulp that addresses the technical challenge of dissolving high-concentration (≥8wt.%), high-purity, high-viscosity pulp (>500ml / g) while maintaining the pulp's intrinsic viscosity. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a mechanical-chemical cellulose activation and dissolution method (pulp pretreatment method and its application in the preparation of high intrinsic viscosity industrial filaments) to solve the technical problem in the prior art that the intrinsic viscosity of pulp is significantly reduced after pulp pretreatment and that high-concentration, high-purity, and high intrinsic viscosity pulp is difficult to dissolve.

[0011] To address the aforementioned technical problems, one objective of this invention is to provide a pulp pretreatment method, comprising the following steps:

[0012] (1) Dispersion of pulp: Pulp with an intrinsic viscosity of 500-780 ml / g is soaked in deionized water and then pulverized to obtain a cellulose aqueous dispersion with a concentration of 1-5 wt% (preferably 1-3 wt%).

[0013] (2) Mechanical treatment of cellulose aqueous dispersion: The pH of the cellulose aqueous dispersion obtained in step (1) is adjusted to 10-11, and mechanical pulping is performed for 140-240 min with a pulping degree of 10-70°SR. The solution is then adjusted to neutral to obtain mechanically treated aqueous cellulose.

[0014] (3) Dehydration of mechanically treated water cellulose: The mechanically treated water cellulose obtained in step (2) is dehydrated to obtain mechanically treated water cellulose with a water content of 40-60%.

[0015] (4) Dispersion and decomposition of mechanically treated water cellulose: The mechanically treated water cellulose with a water content of 40-60% obtained in step (3) is dispersed and decomposed in a 40-60% ethanol solution (referring to an aqueous ethanol solution), and then centrifuged to remove the solution (the filtrate is recovered and distilled under reduced pressure, and the ethanol is collected for reuse) to obtain ethanol-activated cellulose with a liquid content of 40-60%.

[0016] (5) Ethanol replacement and drying of cellulose: The cellulose activated by ethanol with a liquid content of 40-60% obtained in step (4) is replaced with high-concentration ethanol. After the replacement, the cellulose is centrifuged and dehydrated (the ethanol solution containing a small amount of water is removed, and the removed ethanol is subjected to vacuum distillation to recover and reuse the ethanol). Then the obtained cellulose is dried to obtain the pretreated cellulose. The high-concentration ethanol is ethanol with a purity of 98% or higher, and more preferably anhydrous ethanol.

[0017] If the pulp is dispersed and centrifuged with 40-60% ethanol and then dried directly without high-concentration ethanol replacement, it will clump together. However, in step (5), the pulp is dried after centrifugation with high-concentration ethanol replacement, resulting in a loose pulp. The role of high-concentration ethanol is to replace water and reduce pulp agglomeration.

[0018] In existing technologies, the purpose of adding alcohol in the preparation of industrial filaments is to partially swell the cellulose, typically using a high-concentration alcohol solution. However, in this invention, a relatively low-concentration ethanol-water solution is required for dispersion and loosening. This step ensures that the pulp can be uniformly dispersed and loosened under sufficient shear force (because the loosening effect of pulp varies significantly in different dispersion systems and alcohol-water solutions of different concentrations). The presence of a certain amount of water ensures sufficient shear force during loosening, while a certain concentration of ethanol serves the purpose of removing impurities while loosening (some organic extracts on the pulp surface are soluble in ethanol), thereby activating the pulp and making it more conducive to subsequent dissolution. Dispersion and loosening refers to using ethanol to change the polarity of the dispersion, thereby allowing the pulp to be better broken down and dispersed.

[0019] The dispersion effect is relatively better when the ethanol concentration is between 40-60%. Too low an ethanol concentration will cause the pulp to aggregate; too high an ethanol concentration will result in too little shear force, making it difficult to disperse the pulp.

[0020] The replacement uses high-concentration ethanol (e.g., anhydrous ethanol) to replace the water in ethanol-activated cellulose with a liquid content of 40–60%. This is to prevent water from leaving the cellulose during the subsequent drying process, which would cause irreversible shrinkage and reduction of the pore size inside the cellulose. The shrinkage and reduction of the pore size inside the cellulose would significantly reduce the dissolution efficiency during the subsequent preparation of industrial fibers.

[0021] The reason for drying the obtained cellulose is to almost completely evaporate and remove residual ethanol. If ethanol is directly replaced with deionized water, a certain amount of ethanol will remain in the system, triggering side reactions during the dissolution of cellulose in the ionic liquid and leading to pulp degradation. A lower drying temperature is used because high drying temperatures can easily cause explosions; a lower drying temperature also achieves complete removal of residual ethanol, and the low-temperature drying process does not alter the microstructure or internal pores of the cellulose.

[0022] In a preferred embodiment, in step (1), pulp with an intrinsic viscosity of 500-780 ml / g is soaked in deionized water for 30-90 min.

[0023] Furthermore, in step (2), a mechanical pulping disc is used for pulping. The mechanical pulping disc includes a fly knife and a bottom knife. The distance between the fly knife and the bottom knife is 10-30mm, the fly knife pressure is 1-7kg, and the pulping degree is 28-40°SR.

[0024] In existing pulping and papermaking processes, the purpose of beating is to increase the specific surface area of ​​the pulp fibers by "fibrillating" the surface, thereby increasing the surface hydrogen bonding capacity and ultimately achieving the high strength requirements of the finished paper. However, the mechanical treatment performed by pulp mills cannot effectively remove the primary cell wall. This invention, through specific pH, knives pressure, pulp concentration, and treatment time, destroys the primary cell wall layer of the pulp while preventing mechanical degradation. Excessive mechanical treatment intensity leads to pulp degradation (a decrease in average molecular weight), while insufficient intensity fails to destroy the primary cell wall layer. The pulp used in this invention is pulp that has already undergone beating at the pulp mill. The purpose is to fully swell the pulp and then, through processes such as adjusting the knives pressure, evenly and comprehensively treat all surfaces of the pulp, peeling off the difficult-to-dissolve primary cell wall and exposing the more soluble secondary cell wall, while preventing the more soluble secondary cell wall from being peeled off. Therefore, this invention differs from the "fibrillation" method used in the pulping industry in both its process (after beating) and its working principle (alkaline adjustment for swelling and combined peeling).

[0025] In a preferred embodiment, in step (3), the mechanically treated water cellulose obtained in step (2) is subjected to centrifugal dehydration.

[0026] Furthermore, in step (4), the mass ratio of mechanically treated water cellulose with a moisture content of 40-60% to an ethanol solution of 40-60% is 1:4-9. Within this mass ratio range, it helps to ensure that the pulp can be uniformly dispersed and loosened under sufficient shear force.

[0027] In a preferred embodiment, in step (5), when the ethanol-activated cellulose with a liquid content of 40–60% obtained in step (4) is replaced with high-concentration ethanol, the high-concentration ethanol is replaced 1–3 times. During each replacement, the mass ratio of cellulose (for the first replacement, cellulose refers to ethanol-activated cellulose with a liquid content of 40–60%; for subsequent replacements, cellulose refers to the wet cellulose obtained after the previous replacement and centrifugation) to high-concentration ethanol is 1:1.5–2.5. This mass ratio essentially ensures that the concentration of ethanol in the entire system is above 85% (and the higher the better) during replacement, thereby more fully replacing the water and preventing pulp agglomeration.

[0028] Another object of the present invention is to provide the application of the aforementioned pulp pretreatment method in the preparation of high intrinsic viscosity industrial filaments.

[0029] The high intrinsic viscosity industrial filaments mentioned above are cellulose industrial filaments with an intrinsic viscosity of 500-780 ml / g.

[0030] In a preferred embodiment, the pretreated cellulose is dissolved and spun. The dissolution temperature is 90-110℃, and the pH of the dissolution solution (cellulose dissolved in a solvent to form the dissolution solution) is 9-11. The cellulose concentration of the spinning solution is 6-14%, the spinning speed is 80-200m / min, the spinning temperature is 90-120℃, and the draw ratio is 1.5-6 times.

[0031] Furthermore, the solvent used for dissolution is 1-butyl-3-methylimidazolium chloride [BMIM][Cl], 1-allyl-3-methylimidazolium chloride [AMIM][Cl], 1-ethyl-3-methylimidazolium chloride [EMIM][Cl], 1-ethyl-3-methylimidazolium acetate [EMIM][Ac], or N-methylmorpholine-N-oxide NMMO.

[0032] During spinning, the pressure in front of the plate is 5-12MPa, the air volume is 50-100L / min, the air humidity is 30-50%, the water washing temperature is 30-60℃, and the drying temperature is 60-90℃.

[0033] This invention employs wet mechanical pulping and ethanol activation to pretreat high-viscosity, high-concentration, and high-purity pulp, solving the technical challenge of dissolving high-concentration, high-purity (high purity refers to high cellulose content in the pulp) and high-viscosity pulp. This yields a spinning solution that meets production requirements. The following are the beneficial effects achieved by this invention:

[0034] 1. The intrinsic viscosity of the pulp remains basically unchanged after pretreatment;

[0035] 2. High intrinsic viscosity pulp (>500ml / g) that has undergone mechanical processing and chemical activation can also achieve good dissolution at high concentrations (≥8wt%);

[0036] 3. The cellulose industrial filaments prepared by this invention have the characteristics of high strength and high modulus;

[0037] 4. This invention does not have high requirements for the moisture content of the pulp board, and wet pulp from the pulp mill can be directly used for mechanical processing. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a cellulose cell wall (where P represents the primary cell wall, and S1, S2, and S3 represent the three-layered primary cell wall).

[0039] Figure 2 Schematic diagram of a mechanical pulping grinding disc;

[0040] Figure 3 Comparison of pulp morphology before and after mechanical processing (where a and b are raw pulp, and c and d are pulp after mechanical processing);

[0041] Figure 4 The dissolution of pulp under different pretreatment processes (where a, b, c, and d correspond to Examples 1, 2, 3, and 4, respectively, and e, f, and g correspond to Examples 1, 2, and 3, respectively);

[0042] Figure 5 Comparison of weighted relaxation time spectra of spinning solutions with different pretreatment methods;

[0043] One is a throwing knife, and the other two are bottom knives. Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0045] The pulp used in this patent contains alpha-cellulose (which can be determined using FZ / T 50010.4-2011) with a wt content greater than 97%. The reason this invention can dissolve high-purity, high-concentration, and high-intrinsic-viscosity pulp is that mechanical treatment breaks down the primary cell walls, allowing the solvent to easily diffuse into the fiber interior; ethanol activation and ethanol replacement reduce the influence of impurities on the solvent; and the pulp becomes loose, reducing cellulose agglomeration.

[0046] In all embodiments and comparative examples in this patent, the pure [Bmim][Cl] is prepared to a water content of 20 wt% by adding deionized water before mixing with the ionic liquid, and the pH is adjusted by adding alkali (e.g., sodium hydroxide solution).

[0047] Example 1: Preparation of spinning solution from pulp (activated by ethanol) 6 wt.%

[0048] Take a pulp board with an intrinsic viscosity of 626 ml / g (dry weight 1 kg) and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at 100 r / min for 20-25 min, until no pulp board is visible to the naked eye, obtaining a cellulose aqueous dispersion. Centrifuge and dehydrate to form cellulose water with a moisture content of 50 wt% (approximately 2 kg). Then, soak the cellulose water with a moisture content of 50 wt% in 9 kg of 50 wt% ethanol solution and stir for 45 min (stirring). The mixture was stirred at 100 rpm and then centrifuged to remove the liquid, yielding ethanol-activated cellulose with a liquid content of 50 wt%. This was then replaced twice with anhydrous ethanol. Each replacement involved adding anhydrous ethanol to the cellulose and stirring for 20 minutes. The mass ratio of cellulose (for the first replacement, referring to ethanol-activated cellulose with a liquid content of 50 wt%; for the second replacement, referring to the cellulose containing liquid after the first anhydrous ethanol replacement and centrifugation, the same applies below) to anhydrous ethanol was 1:2. The mixture was then centrifuged (ethanol + water, with ethanol predominant) at 13000 rpm for 10 minutes to remove the filtrate. Finally, it was dried at low temperature (60℃ for 12 hours, during which residual ethanol slowly evaporates, and after 12 hours, the ethanol is essentially completely removed) to obtain ethanol-activated pulp cellulose.

[0049] 6g (dry weight) of ethanol-activated pulp cellulose was mixed with 94g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 90℃ for 3h. The spinning solution was then taken out to characterize the dissolution state, degradation and rheological properties.

[0050] Example 2: Preparation of 6 wt.% spinning solution from wet pulp (MA + ethanol activation)

[0051] Take 1 kg of pulp board (dry weight) with an intrinsic viscosity of 626 ml / g and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye, thus obtaining a cellulose aqueous dispersion. Adjust the pH to 10 and let it stand for 45 min (to achieve alkali adjustment and swelling). Then, mechanically beat the pulp: set the flying knife pressure to 5 kg, the distance between flying knife 1 and bottom knife 2 to 10 mm, and process for 120 min with a beating degree of 30°SR. Then, adjust the pH to neutral and finally centrifuge to dehydrate the pulp to form mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0052] Mechanically treated water cellulose with a moisture content of 50 wt% was stirred in a 50 wt% ethanol solution for 45 min (stirring speed 100 r / min). The mass ratio of mechanically treated water cellulose with a moisture content of 50 wt% to 50% ethanol solution was 1:4.5. Then, centrifugation was performed to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, anhydrous ethanol was used to replace the cellulose twice. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, centrifugation was performed: centrifugation at 13000 r / min for 10 min, and the filtrate was removed to obtain ethanol-activated cellulose. Finally, deionization was performed three times (to replace the residual ethanol in the ethanol-activated cellulose) to obtain the treated wet pulp cellulose (MA + ethanol activation).

[0053] 6g (dry weight) of wet pulp cellulose (MA+ethanol activated) was mixed with 94g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 90℃ for 3h. The spinning solution was then taken out to characterize the dissolution state, degradation and rheological properties.

[0054] Example 3: Preparation of 6 wt.% spinning solution from pulp (MB + ethanol activation)

[0055] Take 1 kg of pulp board (dry weight) with an intrinsic viscosity of 626 ml / g and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 2 wt.% (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye, thus obtaining a cellulose aqueous dispersion. Adjust the pH to 10, let it stand for 45 min, and then mechanically beat it: set the fly knife pressure to 2.5 kg, the distance between the fly knife and the bottom knife to 10 mm, and process for 140 min, with a beating degree of 32°SR. Then adjust the pH to neutral, and finally centrifuge to dehydrate and form mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0056] Mechanically treated water cellulose with a moisture content of 50 wt% was stirred in a 50 wt% ethanol solution for 45 min (stirring speed 100 r / min). The mass ratio of mechanically treated water cellulose with a moisture content of 50 wt% to 50% ethanol solution was 1:4.5. Then, centrifugation was performed to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, anhydrous ethanol was used for replacement twice. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, centrifugation was performed: centrifugation at 13000 r / min for 10 min, and the filtrate was removed to obtain ethanol-activated cellulose. Finally, it was dried at low temperature (60℃, 12 h) to obtain pretreated activated pulp cellulose (MB).

[0057] 6 g (dry weight) of activated pulp cellulose (MB) was mixed with 94 g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 90 °C for 3 h. The spinning solution was then taken out to characterize the dissolution state, degradation and rheological properties.

[0058] Example 4: Preparation of 8 wt.% spinning solution from pulp (MA + ethanol activation)

[0059] Take 1 kg (dry weight) of pulp board with an intrinsic viscosity of 626 ml / g and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye, thus obtaining a cellulose aqueous dispersion. Adjust the pH to 10, let it stand for 45 min, and then mechanically beat it: set the fly knife pressure to 5 kg, the distance between the fly knife and the bottom knife to 10 mm, and process for 120 min with a beating degree of 30°SR. Then adjust the pH to neutral and finally centrifuge to dehydrate the pulp to form mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0060] Mechanically treated water cellulose with a moisture content of 50 wt% was stirred in a 50 wt% ethanol solution for 45 min (stirring speed 100 r / min). The mass ratio of mechanically treated water cellulose with a moisture content of 50 wt% to 50% ethanol solution was 1:9. Then, centrifugation was performed to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, anhydrous ethanol was used to replace the cellulose twice. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, centrifugation was performed: centrifugation at 13000 r / min for 10 min, and the filtrate was removed to obtain ethanol-activated cellulose. Finally, it was dried at low temperature (60℃, 12 h) to obtain pretreated activated pulp cellulose (MA).

[0061] 8g (dry weight) of activated pulp cellulose (MA) was mixed with 92g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 100℃ for 3h. The spinning solution was then taken out to characterize the dissolution state, degradation and rheological properties.

[0062] Example 5: Preparation and spinning evaluation of 10 wt.% spinning solution made from pulp (MA + ethanol activation)

[0063] Take 1 kg (dry weight) of pulp board with an intrinsic viscosity of 697 ml / g and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye, thus obtaining a cellulose aqueous dispersion. Adjust the pH to 10, let it stand for 45 min, and then mechanically beat it. Set the fly knife pressure to 5 kg and the distance between the fly knife and the bottom knife to 10 mm, and process for 150 min with a beating degree of 30°SR. Then adjust the pH to neutral and finally centrifuge to dehydrate the pulp to form mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0064] Mechanically treated water cellulose with a moisture content of 50 wt% was stirred in a 50 wt% ethanol solution for 45 min (stirring speed 100 r / min). The mass ratio of mechanically treated water cellulose with a moisture content of 50 wt% to 50% ethanol solution was 1:9. Then, centrifugation was performed to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, anhydrous ethanol was used to replace the cellulose twice. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, centrifugation was performed: centrifugation at 13000 r / min for 10 min, and the filtrate was removed to obtain ethanol-activated cellulose. Finally, it was dried at low temperature (60℃, 12 h) to obtain pretreated activated pulp cellulose (MA).

[0065] 1 kg (dry weight) of activated pulp cellulose (MA) was mixed with 9 kg (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then vacuum dehydrated at 105℃ for 3 hours. Spinning was then performed (sequentially involving spinneret spinning, air cooling, coagulation bath treatment, three-stage washing, and drying; the spinning temperature was 100℃, and the drafting was coagulation bath drafting, i.e., spinneret drafting), the spinning speed was 80 m / min, the spinneret pressure was 9 MPa, and the air volume was 60 m³ / min. 3The blowing humidity was 40%, the coagulation bath concentration was 20%, the three-stage washing temperatures were 40℃, 45℃, and 50℃, the drying temperature was 90℃, the spinning temperature was 100℃, and the draw ratio was 4.21 times. The final cellulose filaments had a breaking strength of 5.91 cN / dtex, an elastic modulus of 300.97 cN / dtex, and an intrinsic viscosity of 575 ml / g.

[0066] Preparation of 6 wt.% spinning solution (Comparative Example 1)

[0067] Take a pulp board with an intrinsic viscosity of 626 ml / g (dry weight 1 kg) and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize it at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye. A cellulose aqueous dispersion is obtained. Centrifuge and dehydrate to form water cellulose with a water content of 50 wt% (approximately 2 kg).

[0068] Take 6g of water cellulose with a water content of 50wt% (dry weight) and mix it with 94g of [Bmim][Cl] (pure [Bmim][Cl]). Adjust the pH to 10.3, and then dehydrate it under vacuum at 90℃ for 3h. After that, take out the spinning solution to characterize the dissolution state, degradation and rheological properties.

[0069] Comparative Example 2: Preparation of 6 wt.% spinning solution from wet pulp (MB + ethanol activation)

[0070] Take 1 kg (dry weight) of pulp board with an intrinsic viscosity of 626 ml / g and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 2 wt.% (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye, thus obtaining a cellulose aqueous dispersion. Adjust the pH to 10, let it stand for 45 min, and then mechanically beat it. Set the roller pressure to 2.5 kg and the distance between the fly knife and the bottom knife to 10 mm, and process for 140 min to achieve a beating degree of 32°SR. Then adjust the pH to neutral and finally centrifuge to dehydrate the pulp to form mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0071] Mechanically treated water cellulose with a moisture content of 50 wt% was stirred in a 50 wt% ethanol solution for 45 min (stirring speed 100 r / min). The mass ratio of mechanically treated water cellulose with a moisture content of 50 wt% to 50% ethanol solution was 1:4.5. Then, centrifugation was performed to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, anhydrous ethanol was used to replace the cellulose twice. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, centrifugation was performed at 13000 r / min for 10 min to remove the filtrate, resulting in ethanol-activated cellulose. Finally, deionization was performed three times with deionized water to obtain the treated wet pulp cellulose (MB + ethanol activated).

[0072] 6g (dry weight) of wet pulp cellulose (MB+ethanol activated) was mixed with 94g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 90℃ for 3h. After that, the spinning solution was taken out to characterize the dissolution state, degradation and rheological properties.

[0073] Comparative Example 3: Preparation of 8% Ethanol-Activated Pulp Spinning Solution

[0074] Take a pulp board with an intrinsic viscosity of 626 ml / g (dry weight 1 kg) and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at 100 r / min for 20-25 min, until no visible pulp board remains, obtaining a cellulose aqueous dispersion. Centrifuge and dehydrate to form cellulose water with a moisture content of 50 wt% (approximately 2 kg). Then soak the cellulose water with a moisture content of 50 wt% in 18 kg of 50 wt% ethanol. The cellulose was stirred in an alcohol solution for 45 min (stirring speed: 100 r / min), then centrifuged to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, it was replaced twice with anhydrous ethanol. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, it was centrifuged at 13000 r / min for 10 min, and the filtrate was removed to obtain ethanol-activated cellulose. Finally, it was dried at low temperature (60℃, 12 h) to obtain the pretreated pulp cellulose (ethanol activated).

[0075] 8g (dry weight) of pulp cellulose (ethanol activated) was mixed with 92g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 100℃ for 3h. The spinning solution was then taken out to characterize the dissolution state, degradation and rheological properties.

[0076] Comparative Example 4: Preparation and spinning evaluation of 10 wt.% ethanol-activated pulp spinning solution

[0077] Take a pulp board with an intrinsic viscosity of 697 ml / g (dry weight 1 kg) and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at 100 r / min for 20-25 min, until no visible pulp board remains, obtaining a cellulose aqueous dispersion. Centrifuge and dehydrate to form cellulose water with a moisture content of 50 wt% (approximately 2 kg). Then soak the cellulose water with a moisture content of 50 wt% in 18 kg of 50 wt% ethanol. The cellulose was stirred in an alcohol solution for 45 min (stirring speed: 100 r / min), then centrifuged to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Then, it was replaced twice with anhydrous ethanol. The specific replacement operation was as follows: anhydrous ethanol was added to the cellulose and stirred for 20 min. The mass ratio of cellulose to anhydrous ethanol was 1:2. Then, it was centrifuged at 13000 r / min for 10 min, and the filtrate was removed to obtain ethanol-activated cellulose. Finally, it was dried at low temperature (60℃, 12 h) to obtain the treated pulp cellulose (ethanol activated).

[0078] 1 kg (dry weight) of activated pulp cellulose was mixed with 9 kg (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then vacuum dehydrated at 105℃ for 3 h. Spinning was then performed (sequentially involving spinneret spinning, air cooling, coagulation bath treatment, three-stage washing, and drying; the spinning temperature was 100℃, and the drawing was coagulation bath drawing, i.e., spinneret drawing). The spinning speed was 80 m / min, the spinneret pressure was 9 MPa, the air volume was 60 L / min, the air humidity was 40%, the coagulation bath concentration was 20%, the three-stage washing temperatures were 40℃, 45℃, and 50℃, the drying temperature was 90℃, the spinning temperature was 100℃, and the draw ratio was 4.21. The resulting cellulose filaments had a breaking strength of 4.43 cN / dtex, an elastic modulus of 203.7 cN / dtex, and an intrinsic viscosity of 582 ml / g.

[0079] Comparative Example 5

[0080] Preparation of 8 wt.% spinning solution from pulp (MA + ethanol activation) (excluding anhydrous ethanol replacement step)

[0081] Take 1 kg (dry weight) of pulp board with an intrinsic viscosity of 626 ml / g and add it to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp board is soaked in deionized water for 45 min). Use a pulverizer to pulverize the pulp board at a speed of 100 r / min for 20-25 min until no pulp board is visible to the naked eye, thus obtaining a cellulose aqueous dispersion. Adjust the pH to 10, let it stand for 45 min, and then mechanically beat it: set the fly knife pressure to 5 kg, the distance between the fly knife and the bottom knife to 10 mm, and process for 120 min with a beating degree of 30°SR. Then adjust the pH to neutral and finally centrifuge to dehydrate the pulp to form mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0082] Mechanically treated water cellulose with a moisture content of 50 wt% was stirred in a 50 wt% ethanol solution for 45 min (stirring speed 100 r / min). The mass ratio of mechanically treated water cellulose with a moisture content of 50 wt% to 50% ethanol solution was 1:9. Then, centrifugation was performed to remove the solution, resulting in ethanol-activated cellulose with a liquid content of 50%. Finally, it was dried at low temperature (60℃, 12 h) to obtain pretreated activated pulp cellulose.

[0083] 8g (dry weight) of activated pulp cellulose was mixed with 92g (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was vacuum dehydrated at 100℃ for 3h before being taken out as the spinning solution.

[0084] In Comparative Example 5, the pulp agglomerated after drying, resulting in severe visible coating during the subsequent dissolution process. Therefore, the intrinsic viscosity and rheological properties were not characterized.

[0085] Figure 1 This is a schematic diagram of the cellulose cell wall structure. Figure 2 Schematic diagram of a mechanical pulping grinding disc; Figure 3 The comparison of the morphology of pulp before and after mechanical beating shows that the morphology of pulp changed after mechanical treatment (the primary cell walls that are difficult to dissolve were destroyed). Figure 4 The state of pulp after dissolution was compared with that of pulp treated by different methods, and it was found that the pulp treated by mechanical treatment and activated by ethanol had the best dissolution performance. Figure 5 The weighted relaxation time spectrum of spinning solutions prepared from pulp with different treatment methods is shown. The horizontal axis represents relaxation time Lambda, and the vertical axis represents the weighted value H*Lambda of relaxation modulus and relaxation time. This indicates that the relaxation of cellulose molecular chains in the spinning solution prepared from cellulose pulp after pretreatment is extensive and uniform. The peaks of Example 2 (compared to Comparative Example 1) and Example 4 (compared to Comparative Example 3) are biased to the upper right because their viscosity and relaxation time are optimized due to more complete dissolution.

[0086] To confirm the effect of mechanical treatment, this specification compares the morphological changes of pulp before and after mechanical treatment. The specific mechanical treatment process is described in Examples 2 and 3. The cellulose after mechanical treatment in Example 2 (i.e., the water cellulose with a moisture content of 50 wt% after mechanical treatment in Example 2) is as follows: Figure 3 As shown in c and d in the table, the cellulose after mechanical treatment in Example 2 or 3 (i.e., the water cellulose after mechanical treatment with a water content of 50 wt% in Examples 2 and 3) is shown in Table 1.

[0087] Table 1 shows the changes in morphology and intrinsic viscosity of pulp before and after mechanical treatment (test standard GB / T29779-2013, equipment used: FMA 100 fiber morphology analyzer). After mechanical treatment, the intrinsic viscosity and fiber length of the pulp did not change significantly, but the width increased by 1 μm compared to the original pulp. The number of fine and microfibers increased more significantly after MB treatment than after MA treatment, approximately 1.5 times the number in the original pulp, and the increase in dust particles was also more significant. The fibrillation index of the pulp approximately doubled after mechanical treatment, and the fiber kink index was approximately 1 / 3 of that of the original pulp. Therefore, this mechanical treatment method does not degrade the pulp, but it increases fiber width, the number of fine and microfibers and dust particles, increases the fibrillation index, and decreases the kink index.

[0088] Table 1. Comparison of fiber morphology before and after mechanical treatment

[0089]

[0090] Comparative Example 1 and Comparative Example 1 show that the pulp dissolution quality is improved after ethanol activation.

[0091] Comparing Examples 1 and 2, 3, and 4 shows that the solubility of pulp is significantly improved after mechanical treatment. This is because the mechanical treatment process can destroy the primary cell walls of cellulose in the pulp, making it easier for the solvent to enter the cellulose, thus making the pulp dissolve more thoroughly without a significant change in intrinsic viscosity.

[0092] Comparative Example 3 and Comparative Example 2 show that directly drying and dissolving the pulp after mechanical treatment and ethanol activation results in less degradation than dissolving it after replacing the ethanol with deionized water. This is related to the residual ethanol content in the system after replacing the ethanol with deionized water. Replacing ethanol with deionized water makes it difficult to completely remove the ethanol, triggering side reactions (cellulose reacts with ethanol to form ethyl levulinate) during the dissolution of wet pulp in ionic liquids, thus causing pulp degradation. Laboratory data show that when the step of replacing ethanol with deionized water is omitted in Example 2, the degradation of cellulose after dissolving in ionic liquids is 79 ml / g, which corroborates that the residual ethanol in cellulose significantly increases the degradation of pulp during the dissolution process.

[0093] Comparative Example 2 and Comparative Example 2 demonstrate that the MA + ethanol activation process is superior to the MB + ethanol activation process, which is related to the mechanical treatment conditions. Therefore, the mechanical treatment conditions can be adjusted according to the characteristics of the pulp to promote dissolution. Experimental data comparison revealed that within a certain range, lower pulp concentration and higher blade pressure resulted in more significant cellulose treatment effects. MA reduced the concentration of the pulp cellulose aqueous solution and increased the blade pressure, resulting in a better pretreatment effect than MB.

[0094] Comparative Example 4 and Comparative Example 3 show that the solubility of pulp was significantly improved after activation and drying with MA + ethanol. Furthermore, the rheological properties and solubility state of the 8% spinning solution prepared after activation and drying with MA + ethanol meet the requirements for production.

[0095] Since it is difficult to directly sample the spinning solution from the dissolving vessel for rheological properties and intrinsic viscosity characterization, the pretreatment method of the present invention is characterized by the mechanical properties of the product after spinning. Comparative Example 5 and Comparative Example 4 show that the mechanical properties of the cellulose industrial filaments obtained by activating and drying the pulp with MA + ethanol are superior to those obtained by activating and drying the pulp with ethanol only. This is related to the solubility of the pulp in the system; the pulp dissolves more easily after activation and drying with MA + ethanol, allowing for better uniform distribution of cellulose in the system, thereby improving the breaking strength and elastic modulus of the cellulose industrial filaments. Furthermore, the intrinsic viscosity of the cellulose industrial filaments prepared in Example 5 and Comparative Example 4 is basically the same, indicating that the treatment method of the present invention does not significantly reduce the intrinsic viscosity of the product.

[0096] Table 2. Effects of different treatment processes on the rheological properties and intrinsic viscosity of dissolved pulp

[0097]

[0098]

[0099] The intrinsic viscosity test standard is ISO 5351-2010; the rheological test equipment is TA. The fixture is a 40mm thick plate with a plate spacing of 500 micrometers, and the heating plate is Peltier (only the lower plate can be heated).

[0100] The pulp pretreatment method of the present invention is applicable to the dissolution of high intrinsic viscosity pulp (>500 ml / g) at high purity and high concentration (≥8 wt%). The intrinsic viscosity decreases differently in Examples 1-3 and Comparative Examples 1-2 due to the lower concentration and temperature during dissolution. The changes in IV of Examples 4 and Comparative Examples 3 after increasing the dissolution concentration and temperature are significantly different, while the temperature used in industrial production is relatively high.

[0101] The purpose of this invention for pulp pretreatment is to improve the solubility of pulp while keeping its intrinsic viscosity essentially unchanged. Its beneficial effects are, on the one hand, a small change in intrinsic viscosity, and on the other hand, an improvement in solubility, which is ultimately reflected in the performance of cellulose industrial filaments.

[0102] The experimental results above demonstrate that this method can improve the solubility of high intrinsic viscosity and high purity pulp while ensuring that the intrinsic viscosity of the pulp remains largely unchanged. Furthermore, this method allows for the adjustment of mechanical processing conditions according to the characteristics of the pulp, achieving customized processing. Therefore, this invention can be used for the preparation of high intrinsic viscosity industrial filaments.

[0103] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for pretreatment of pulp, characterized in that, Includes the following steps: (1) Dispersion of pulp: Pulp with an intrinsic viscosity of 500-780 ml / g is soaked in deionized water and then pulverized to obtain a cellulose aqueous dispersion with a concentration of 1-5wt%. (2) Mechanical treatment of cellulose aqueous dispersion: The pH of the cellulose aqueous dispersion obtained in step (1) is adjusted to 10-11, and mechanical pulping is performed for 140-240 min with a pulping degree of 10-70°SR. The solution is then adjusted to neutral to obtain mechanically treated water cellulose. (3) Dehydration of mechanically treated water cellulose: The mechanically treated water cellulose obtained in step (2) is dehydrated to obtain mechanically treated water cellulose with a water content of 40-60%. (4) Dispersion and decomposition of mechanically treated water cellulose: The mechanically treated water cellulose with a water content of 40-60% obtained in step (3) is dispersed and decomposed in a 40-60% ethanol solution, and then centrifuged to remove the solution, so as to obtain ethanol-activated cellulose with a liquid content of 40-60%. (5) Ethanol replacement and drying of cellulose: The cellulose activated by ethanol with a liquid content of 40-60% obtained in step (4) is replaced with high-concentration ethanol. After the replacement is completed, the cellulose is centrifuged to remove the solution, and then the obtained cellulose is dried to obtain pretreated cellulose. The high-concentration ethanol is ethanol with a concentration of 98% or higher.

2. The pulp pretreatment method according to claim 1, characterized in that, In step (1), pulp with an intrinsic viscosity of 500-780 ml / g is soaked in deionized water for 30-90 min.

3. The pulp pretreatment method according to claim 1, characterized in that, In step (2), a mechanical pulping disc is used for pulping. The mechanical pulping disc includes a fly cutter and a bottom cutter. The distance between the fly cutter and the bottom cutter is 10-30 mm, and the fly cutter pressure is 1-7 kg.

4. The pulp pretreatment method according to claim 1, characterized in that, In step (3), the mechanically treated water cellulose obtained in step (2) is centrifuged to dehydrate it.

5. The pulp pretreatment method according to claim 1, characterized in that, In step (4), the mass ratio of mechanically treated water cellulose with a water content of 40-60% to ethanol solution with a water content of 40-60% is 1:4-9.

6. The pulp pretreatment method according to claim 1, characterized in that, In step (5), when the cellulose activated by ethanol with a liquid content of 40-60% obtained in step (4) is replaced with high-concentration ethanol, the high-concentration ethanol is replaced 1-3 times, and the mass ratio of cellulose to high-concentration ethanol is 1:1.5-2.5 each time.

7. The application of the pulp pretreatment method according to any one of claims 1-6 in the preparation of high intrinsic viscosity industrial filaments.

8. The application of the pulp pretreatment method according to claim 7 in the preparation of high intrinsic viscosity industrial filaments, characterized in that, The high intrinsic viscosity industrial filaments mentioned above are cellulose industrial filaments with an intrinsic viscosity of 500-780 ml / g.

9. The application of the pulp pretreatment method according to claim 7 in the preparation of high intrinsic viscosity industrial filaments, characterized in that, The pretreated cellulose is dissolved and spun. The dissolution temperature is 90-110℃ and the pH of the dissolution solution is 9-11. The cellulose concentration of the spinning solution is 6-14%, the spinning speed is 80-200 m / min, the spinning temperature is 90-120℃, and the draw ratio is 1.5-6 times.

10. The application of the pulp pretreatment method according to claim 9 in the preparation of high intrinsic viscosity industrial filaments, characterized in that, The solvent for dissolution is 1-butyl-3-methylimidazolium chloride [BMIM][Cl], 1-allyl-3-methylimidazolium chloride [AMIM][Cl], 1-ethyl-3-methylimidazolium chloride [EMIM][Cl], 1-ethyl-3-methylimidazolium acetate [EMIM][Ac], or N-methylmorpholine-N-oxide NMMO.

11. The application of the pulp pretreatment method according to claim 9 in the preparation of high intrinsic viscosity industrial filaments, characterized in that, During spinning, the pressure in front of the plate is 5-12 MPa, the air volume is 50-100 L / min, the air humidity is 30-50%, the water washing temperature is 30-60℃, and the drying temperature is 60-90℃.

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