Pulp pretreatment method and application of pulp pretreatment method in preparation of high-intrinsic-viscosity industrial yarn

Abstract

The invention belongs to the field of regenerated cellulose fiber preparation, and particularly relates to a pulp pretreatment method and application in preparation of high-intrinsic-viscosity industrial yarn. Comprising the following steps: dispersing pulp; carrying out mechanical treatment on the cellulose aqueous dispersion; dehydrating the mechanically treated water cellulose; dispersing and defibering water cellulose after mechanical treatment; and carrying out ethanol replacement and drying on the cellulose. According to the method, the high-intrinsic-viscosity and high-concentration pulp is pretreated by adopting wet mechanical pulping and ethanol activation, so that the technical problem that the high-concentration, high-purity and high-intrinsic-viscosity pulp is difficult to dissolve is solved, and the spinning stock solution capable of meeting production requirements is obtained.

Description

Technical Field

[0001] The invention belongs to the field of regenerated cellulose fiber preparation, and particularly relates to a pulp pretreatment method and application in the preparation of high intrinsic viscosity industrial yarn. Background Art

[0002] Cellulose is the world's largest natural polymer produced annually and is widely found in the cell walls of plants. Due to its abundant sources and multifunctional characteristics, cellulose currently has important application value in the fields of papermaking, textile industry, food industry, medicine and cosmetics, biofuels, environmentally friendly materials, construction and composite materials.

[0003] Cellulose industrial yarn is a high-performance filament made of natural cellulose, which has many excellent properties, making it widely used in many industries. Its important properties include: high strength and modulus, biocompatibility and biodegradability, low thermal expansion coefficient, excellent moisture absorption and air permeability. With its unique physical and chemical properties, cellulose industrial yarn has shown important application value in composite materials, tires and hoses, industrial filters, conveyor belts and industrial fabrics, protective clothing and safety equipment, cables and wires, textiles and other industrial fields, providing new possibilities for the development of various high-performance and environmentally friendly materials.

[0004] Since cellulose is difficult to dissolve due to its rich and complex intermolecular and intramolecular hydrogen bond network structure, the pulp used to prepare cellulose industrial filaments is usually limited to pulps with high purity but relatively low intrinsic viscosity / average molecular weight (the dissolution process of high molecular weight pulp will be uneven due to the high viscosity of the solution). The temperature during the dissolution spinning process is relatively high (above 90°C) and the time is relatively long (above 180 minutes). The pulp with a low molecular weight further aggravates its own degradation, which makes the intrinsic viscosity of the final cellulose industrial filaments often <400ml / g (ISO5351:2004); the product strength and modulus are usually <4.0cN / dtex and <150cN / dtex (ASTM D885 / D885M), respectively, which seriously restricts its application in composite materials (such as wood-plastic composites) and the construction industry (geotextiles, etc.).

[0005] Studies have shown that cellulose molecular weight affects the entanglement, orientation and crystallization between cellulose molecular chains, thus having a huge impact on the mechanical properties of cellulose; in addition, cellulose materials prepared from cellulose raw materials with a high molecular weight portion (DP>2000) greater than 20% and a polydispersity greater than 3 have better mechanical properties. Therefore, a simple, efficient and substantially non-degradable activation method is needed to promote the dissolution of high-purity and high-intrinsic-viscosity cellulose to prepare high-strength and high-modulus cellulose industrial yarns.

[0006] At present, in the industrial production of lyocell fibers, there are mainly two ways to pretreat cellulose pulp:

[0007] One is dry pretreatment of cellulose pulp: the main method is to first dry-crush the pulp, then directly pre-mix it with a high-concentration NMMO solution, and finally enter the reactor to dissolve and prepare a spinning solution. Patent CN1312819A discloses a method for preparing a cellulose suspension, and the specific method is to crush the pulp and mix it with NMMO with a certain water content, and then pass through the first shear zone and the second shear zone to obtain a cellulose suspension. Traditional mechanical treatment will not only lead to disordered cutting of fibers, but also different morphologies of pulp fibers, and then bring about problems such as "local cladding" and "uneven dissolution" during the pulp dissolution process. The spinning solution formed has a high content of undissolved pulp components, and the candle-shaped filter is often easily blocked in the end, and the product has serious broken fibers; in addition, the high-speed blade in the traditional dry pulping process will cause a large amount of mechanical and local thermal degradation of cellulose, resulting in a decrease in the characteristic viscosity after pulp treatment, which ultimately negatively affects the strength of the product industrial yarn.

[0008] The other is wet pretreatment of cellulose pulp: the main method is to prepare a certain concentration of acid, alkali or enzyme solution to treat cellulose pulp, and then mix it with NMMO aqueous solution. Patent CN102234849A discloses a method for pretreating bamboo fiber cellulose, which is to stir the pulp and deionized water in a high-pressure container for 4-6 hours, then cook at 120-200°C for 3-6 hours, and finally press the pretreated cellulose. The process takes a long time and requires high temperature and high pressure during the process, and the equipment requirements are high; in addition, the pulp will also degrade under high temperature and high pressure, which will negatively affect the strength of cellulose industrial yarn. Patent CN103556248A, Patent CN101694019A and Patent CN103556235A disclose a method for pretreating cellulose, wherein the cellulose is first crushed, then deionized water is added for swelling, then cellulase is added, and the pH value is adjusted to between 4-6, 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 9.5-11, and the mixture is stirred for 6-15 minutes to inactivate the enzyme, and then the enzyme-activated cellulose pulp is squeezed to make the pulp water content about 45-60wt.%. This method can indeed solve the problem that high intrinsic viscosity pulp is not easy to dissolve, but the activity of the enzyme is difficult to control, and the uneven temperature inside the equipment and the difference in pH value will cause a large change in the intrinsic viscosity of cellulose, which is not conducive to the stability of the product; in addition, enzymatic treatment will also reduce the intrinsic viscosity of cellulose, which will have a negative impact on the strength of cellulose industrial yarn. Cellulase does not only target the primary wall, but acts on all primary and secondary walls of the pulp. The actual enzyme activity often leads to large batch differences and severe degradation after treatment.

[0009] At present, under the premise of ensuring high solubility (≥8wt%), the ability to uniformly dissolve high intrinsic viscosity pulp with high quality has become an important factor restricting the industrialization of high-strength and high-modulus cellulose industrial yarns. In view of this, the present invention proposes a pretreatment method for cellulose industrial yarn pulp, which solves the technical problem of difficulty in dissolving high-concentration (≥8wt.%), high-purity, and high intrinsic viscosity pulp (>500ml / g) while ensuring the intrinsic viscosity of the pulp. 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 application in the preparation of high intrinsic viscosity industrial yarn) to solve the technical problem in the prior art that the intrinsic viscosity is significantly reduced after pulp pretreatment and high-concentration, high-purity and high intrinsic viscosity pulp is difficult to dissolve.

[0011] In order to solve the above technical problems, an object of the present 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 crushed 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 beating is performed. The beating time is 140-240 min, and the beating degree is 10-70° SR. The solution is adjusted to neutral to obtain mechanically treated aqueous cellulose.

[0014] (3) Dehydration of mechanically treated hydrocellulose: Dehydrating the mechanically treated hydrocellulose obtained in step (2) to obtain mechanically treated hydrocellulose having a moisture content of 40-60%;

[0015] (4) Dispersion and decomposition of mechanically treated hydrocellulose: The mechanically treated hydrocellulose with a water content of 40-60% obtained in step (3) is dispersed and decompressed in a 40-60% ethanol solution (referring to ethanol-water solution), and then centrifuged to remove the solution (the filtrate is recovered and subjected to reduced pressure distillation, and the ethanol is collected and reused) to obtain ethanol-activated cellulose with a liquid content of 40-60%;

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

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

[0018] In the prior art, during the preparation of industrial silk, the purpose of adding alcohol is to partially swell the cellulose, and a high concentration alcohol solution is usually used. In the present invention, a relatively low concentration of ethanol aqueous solution is required for dispersion and decomposition. This step is to ensure that the pulp can be evenly dispersed and decomposed under sufficient shear force (because the pulp has completely different decomposition effects in different dispersion systems and different concentrations of alcohol aqueous solutions). The presence of a certain amount of water can ensure sufficient shear force during the decomposition process, and a certain concentration of ethanol can achieve the purpose of decomposition and impurity removal (some organic extracts on the surface of the pulp can be dissolved in ethanol), thereby activating the pulp for subsequent dissolution; dispersion and decomposition refers to: using ethanol to change the polarity of the dispersion liquid, so that the pulp can be better broken up and dispersed.

[0019] Among them, the dispersion effect is relatively better when the ethanol concentration is between 40-60%. Too low ethanol concentration will cause pulp aggregation; too high ethanol concentration will lead to too small shear force and the pulp is difficult to disperse.

[0020] The replacement uses high-concentration ethanol (such as anhydrous ethanol) to replace the water in the cellulose activated by ethanol with a liquid content of 40-60%, so as to avoid the phenomenon that the water leaves the cellulose during the subsequent drying process of the cellulose and causes the irreversible shrinkage and reduction of the pores inside the cellulose. The shrinkage and reduction of the pores inside the cellulose will greatly reduce the dissolution efficiency in the subsequent preparation of industrial fibers.

[0021] The reason for drying the obtained cellulose is to almost completely volatilize and remove the residual ethanol in the cellulose. If ethanol is directly replaced with deionized water, there will be a certain amount of residual ethanol in the system, which will cause side reactions during the dissolution of cellulose in the ionic liquid, thereby causing the degradation of the pulp. A lower drying temperature is used because high drying temperatures are prone to explosions; lower drying temperatures can also achieve complete removal of residual ethanol, and the low-temperature drying process does not cause changes to the microstructure and internal pores of cellulose.

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

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

[0024] In the prior art, the purpose of beating in the pulp and paper industry is to make the surface of pulp fiber "fiber-fiberized" to increase the specific surface area of ​​the fiber, increase the surface hydrogen bonding ability, and finally meet the requirements for high strength of paper. The mechanical treatment performed by the pulp mill cannot achieve the effect of stripping the primary wall. In the present invention, by using specific pH, knife pressure, pulp concentration and treatment time, the primary wall layer of pulp is destroyed while preventing the mechanical degradation of pulp; wherein too high mechanical treatment intensity will lead to mechanical degradation of pulp (decreased average molecular weight), and insufficient mechanical treatment intensity will not play the role of destroying the primary wall layer of pulp. The pulp used in the present invention itself is the pulp that has been beaten by the pulp mill. The purpose is to fully swell the pulp of the pulp mill, and then adjust the knife pressure and other processes to act evenly and comprehensively on all surfaces of the pulp, strip the insoluble primary wall, expose the more soluble secondary wall, and the more soluble secondary wall will not be stripped. Therefore, the present invention is different from the "fiber-fiberized" in the pulping industry in terms of process (after beating) and action principle (alkali adjustment swelling and combined stripping).

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

[0026] Furthermore, in step (4), the mass ratio of the mechanically treated aqueous cellulose with a moisture content of 40-60% to the 40-60% ethanol solution is 1:4-9. Within this mass ratio range, it helps to ensure that the pulp can be evenly dispersed 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 replacement times of high-concentration ethanol are 1-3 times, and the mass ratio of cellulose (cellulose in the first replacement refers to cellulose activated by ethanol with a liquid content of 40-60%, and cellulose in each subsequent replacement refers to wet cellulose obtained by centrifugation in the previous replacement) to high-concentration ethanol is 1:1.5-2.5. This mass ratio basically ensures that the concentration of ethanol in the whole system is above 85% (and the higher the better) during the replacement, so as to more fully replace water and prevent pulp agglomeration.

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

[0029] Wherein, the high intrinsic viscosity industrial yarn is a cellulose industrial yarn 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°C, the pH of the dissolving solution (cellulose dissolved in a solvent, constituting the dissolving 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°C, and the drafting multiple 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 washing temperature is 30-60℃, and the drying temperature is 60-90℃.

[0033] The present invention adopts wet mechanical beating and ethanol activation to pretreat high intrinsic viscosity, high concentration and high purity pulp, solves the technical problem that high concentration and high purity (high purity refers to high content of type A cellulose in pulp) and high intrinsic viscosity pulp is difficult to dissolve, and obtains a spinning solution that can meet production requirements. The following are the beneficial effects achieved by the present invention:

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

[0035] 2. High intrinsic viscosity pulp (>500ml / g) after mechanical treatment and chemical activation can also achieve good dissolution effect at high concentration (≥8wt%);

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

[0037] 4. The present invention does not have high requirements on the moisture content of the pulp board, and the wet pulp from the pulp factory can be directly used for mechanical treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of cellulose cell wall (where P represents primary wall, S1, S2 and S3 represent three-layer secondary wall);

[0039] Figure 2 It is a schematic diagram of a mechanical beating grinding disc;

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

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

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

[0043] Among them, there are 1 flying knife and 2 bottom knives. DETAILED DESCRIPTION

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

[0045] The pulp used in this patent has a cellulose alpha content (which can be determined by FZ / T 50010.4-2011) of more than 97% by weight. The invention can dissolve high-purity, high-concentration, high-intrinsic viscosity pulp because the primary wall is destroyed by mechanical treatment to make the solvent easily diffuse into the fiber interior; the influence of impurities on the solvent is reduced by ethanol activation and ethanol replacement; the pulp is loosened to reduce cellulose agglomeration.

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

[0047] Example 1 Preparation of 6 wt.% spinning solution of pulp (ethanol activation)

[0048] A pulp sheet (dry weight 1 kg) with an intrinsic viscosity of 626 ml / g was taken, added to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet was soaked in deionized water for 45 min), and crushed using a crusher at a speed of 100 r / min for 20-25 min until no pulp sheet was visible to the naked eye to obtain a cellulose aqueous dispersion, which was centrifugally dehydrated to form water cellulose with a moisture content of 50 wt% (mass of about 2 kg); the water cellulose with a moisture content of 50 wt% was then soaked in 9 kg of 50 wt% ethanol solution and stirred for 45 min (stirring Stirring speed: 100r / min), then centrifuge to remove the solution, and obtain ethanol-activated cellulose with a liquid content of 50wt%; then replace it with anhydrous ethanol twice, and each replacement operation is specifically as follows: add anhydrous ethanol to the cellulose and stir for 20min, the mass ratio of cellulose (the first replacement refers to ethanol-activated cellulose with a liquid content of 50wt%; the second replacement refers to the liquid cellulose after the first anhydrous ethanol replacement centrifugation, the same below) and anhydrous ethanol is 1:2, and then centrifuge to remove the liquid (ethanol + water, mostly ethanol): 13000r / min centrifuge for 10min, remove the filtrate. Finally, low-temperature drying (60℃, 12h, during this process, the residual ethanol slowly evaporates, and after 12h, the ethanol can be basically completely removed) can obtain ethanol-activated pulp cellulose.

[0049] 6 g (dry weight) of ethanol-activated pulp cellulose was mixed with 94 g of [Bmim][Cl] (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then it was dissolved for 3 hours after vacuum dehydration at 90°C. After that, the spinning solution was taken out to characterize the dissolution state, degradation and rheological properties.

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

[0051] 1 kg of pulp sheet (dry weight) with a characteristic viscosity of 626 ml / g is taken, added into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet is soaked in deionized water for 45 minutes), and crushed by a pulverizer, the pulverizer speed is 100 r / min, 20-25 minutes, and the pulverization needs to be performed until there is no pulp sheet visible to the naked eye to obtain a cellulose aqueous dispersion; the pH is adjusted to 10, and the mixture is allowed to stand for 45 minutes (to achieve alkali adjustment and swelling), and then mechanically beating is performed: the knife pressure is set to 5 kg, the distance between the knife 1 and the bottom knife 2 is 10 mm, the treatment is performed for 120 minutes, the beating degree is 30°SR, and then the pH is adjusted to neutral, and finally centrifugal dehydration is performed to form a mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0052] The mechanically treated water cellulose with a moisture content of 50wt% was stirred in a 50wt% ethanol solution for 45min (stirring speed 100r / min), and the mass ratio of the mechanically treated water cellulose with a moisture content of 50wt% to the 50% ethanol solution was 1:4.5; then the solution was centrifuged to obtain ethanol-activated cellulose with a liquid content of 50%; then it was replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20min, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged to remove the liquid: centrifuged at 13000r / min for 10min, the filtrate was removed, and ethanol-activated cellulose was obtained; finally, it was replaced with deionized water for 3 times (replacing the residual ethanol in the ethanol-activated cellulose with deionized water) to obtain the treated wet pulp cellulose (MA+ethanol activation).

[0053] 6 g (dry weight) of wet pulp cellulose (MA+ethanol activation) was mixed with 94 g of [Bmim][Cl] (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then it was dissolved for 3 hours after vacuum dehydration at 90°C. After that, the spinning solution was taken out to characterize the dissolution state, degradation and rheological properties.

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

[0055] 1 kg of pulp sheet (dry weight) with a characteristic viscosity of 626 ml / g is taken, added into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 2 wt.% (the pulp sheet is soaked in deionized water for 45 min), and crushed by a pulverizer with a pulverizer speed of 100 r / min for 20-25 min until no pulp sheet is visible to the naked eye to obtain a cellulose aqueous dispersion; the pH is adjusted to 10, allowed to stand for 45 min, and then mechanically beaten: the knife pressure is set to 2.5 kg, the distance between the knife and the bottom knife is 10 mm, the treatment is performed for 140 min, the beating degree is 32°SR, and then the pH is adjusted to neutral, and finally centrifuged to form a mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0056] The mechanically treated hydrocellulose with a moisture content of 50wt% was stirred in a 50wt% ethanol solution for 45min (stirring speed 100r / min), and the mass ratio of the mechanically treated hydrocellulose with a moisture content of 50wt% to the 50% ethanol solution was 1:4.5; then the solution was centrifuged to obtain ethanol-activated cellulose with a liquid content of 50%; then it was replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20min, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged to remove the liquid: centrifuged at 13000r / min for 10min, the filtrate was removed, and ethanol-activated cellulose was obtained; finally, low-temperature drying (60℃, 12h) was performed to obtain the 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 it was dissolved for 3 h after vacuum dehydration at 90°C. After that, the spinning solution was taken out to characterize the dissolution state, degradation and rheological properties.

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

[0059] 1 kg (dry weight) of pulp sheet with a characteristic viscosity of 626 ml / g is taken, added into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet is soaked in deionized water for 45 minutes), and crushed by a pulverizer with a pulverizer speed of 100 r / min for 20-25 minutes until no pulp sheet is visible to the naked eye to obtain a cellulose aqueous dispersion; the pH is adjusted to 10, allowed to stand for 45 minutes, and then mechanically beaten: the knife pressure is set to 5 kg, the distance between the knife and the bottom knife is 10 mm, the treatment is performed for 120 minutes, the beating degree is 30°SR, and then the pH is adjusted to neutral, and finally centrifuged to form a mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0060] The mechanically treated hydrocellulose with a moisture content of 50wt% was stirred in a 50wt% ethanol solution for 45min (stirring speed 100r / min), and the mass ratio of the mechanically treated hydrocellulose with a moisture content of 50wt% to the 50% ethanol solution was 1:9; then the solution was centrifuged to obtain ethanol-activated cellulose with a liquid content of 50%; then it was replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20min, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged to remove the liquid: centrifuged at 13000r / min for 10min, the filtrate was removed, and ethanol-activated cellulose was obtained; finally, low-temperature drying (60℃, 12h) was performed to obtain the pretreated activated pulp cellulose (MA).

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

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

[0063] 1 kg (dry weight) of pulp sheet with a characteristic viscosity of 697 ml / g is taken, added into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet is soaked in deionized water for 45 minutes), and crushed by a pulverizer with a pulverizer speed of 100 r / min for 20-25 minutes until no pulp sheet is visible to the naked eye to obtain a cellulose aqueous dispersion; the pH is adjusted to 10, allowed to stand for 45 minutes, and then mechanically beaten; the knife pressure is set to 5 kg, the distance between the knife and the bottom knife is 10 mm, the treatment is carried out for 150 minutes, the beating degree is 30°SR, and then the pH is adjusted to neutral, and finally centrifugal dehydration is performed to form a mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0064] The mechanically treated hydrocellulose with a moisture content of 50wt% was stirred in a 50wt% ethanol solution for 45min (stirring speed 100r / min), and the mass ratio of the mechanically treated hydrocellulose with a moisture content of 50wt% to the 50% ethanol solution was 1:9; then the solution was centrifuged to obtain ethanol-activated cellulose with a liquid content of 50%; then it was replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20min, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged to remove the liquid: centrifuged at 13000r / min for 10min, the filtrate was removed, and ethanol-activated cellulose was obtained; finally, low-temperature drying (60℃, 12h) was performed to obtain the 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°C and dissolved for 3 hours, followed by spinning (spinning on a spinneret, air cooling, coagulation bath treatment, three-stage water washing, and drying in sequence; the spinning temperature was 100°C, and the drawing was coagulation bath drawing, i.e., nozzle drawing), the spinning speed was 80 m / min, the pressure in front of the spinneret was 9 MPa (referring to the pressure in front of the spinneret), and the air volume was 60 m 3 / min, blowing humidity 40%, coagulation bath concentration 20%, three-stage water washing temperatures of 40°C, 45°C, 50°C, drying temperature of 90°C, spinning temperature of 100°C, drawing multiple of 4.21 times, and finally the 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] Comparative Example 1 Preparation of 6wt.% spinning solution

[0067] Take a pulp sheet with an intrinsic viscosity of 626 ml / g (dry weight 1 kg), add it into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet is soaked in deionized water for 45 minutes), and use a pulverizer to pulverize it. The pulverizer speed is 100 r / min, and the pulverizer is pulverized for 20-25 minutes until there is no pulp sheet visible to the naked eye to obtain a cellulose aqueous dispersion, which is centrifugally dehydrated to form water cellulose with a moisture content of 50 wt% (mass is about 2 kg).

[0068] 6 g (dry weight) of hydrocellulose with a moisture content of 50 wt% was mixed with 94 g of [Bmim][Cl] (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then it was dissolved for 3 h after vacuum dehydration at 90°C. After that, the spinning solution was taken out to characterize the dissolution state, degradation and rheological properties.

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

[0070] 1 kg (dry weight) of a pulp sheet with an intrinsic viscosity of 626 ml / g is taken, added into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 2 wt.% (the pulp sheet is soaked in deionized water for 45 minutes), and crushed by a pulverizer at a speed of 100 r / min for 20-25 minutes until no pulp sheet is visible to the naked eye to obtain a cellulose aqueous dispersion; the pH is adjusted to 10, allowed to stand for 45 minutes, and then mechanically beaten; the roller knife pressure is set to 2.5 kg, the distance between the flying knife and the bottom knife is 10 mm, the treatment is carried out for 140 minutes, the beating degree is 32°SR, and then the pH is adjusted to neutral, and finally centrifugal dehydration is performed to form a mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0071] The mechanically treated water cellulose with a moisture content of 50wt% was stirred in a 50wt% ethanol solution for 45min (stirring speed 100r / min), and the mass ratio of the mechanically treated water cellulose with a moisture content of 50wt% to the 50% ethanol solution was 1:4.5; then the solution was centrifuged to obtain ethanol-activated cellulose with a liquid content of 50%; then it was replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20min, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged to remove the liquid: centrifuged at 13000r / min for 10min, the filtrate was removed, and ethanol-activated cellulose was obtained; finally, it was replaced with deionized water for 3 times to obtain the treated wet pulp cellulose (MB+ethanol activation).

[0072] 6 g (dry weight) of wet pulp cellulose (MB+ethanol activation) was mixed with 94 g of [Bmim][Cl] (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then it was dissolved for 3 hours after vacuum dehydration at 90°C. After that, the spinning solution was taken out to characterize the dissolution state, degradation and rheological properties.

[0073] Comparative Example 3 Preparation of 8% spinning solution of ethanol activated pulp

[0074] A pulp sheet with an intrinsic viscosity of 626 ml / g (dry weight 1 kg) was added to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet was soaked in deionized water for 45 minutes), and then crushed using a crusher at a speed of 100 r / min for 20-25 minutes until no pulp sheet was visible to the naked eye to obtain a cellulose aqueous dispersion, which was centrifugally dehydrated to form water cellulose with a moisture content of 50 wt% (mass of about 2 kg); then the water cellulose with a moisture content of 50 wt% was soaked in 18 kg of 50 wt% ethyl acetate. The cellulose was stirred in an alcohol solution for 45 minutes (stirring speed: 100 r / min), and then centrifuged to remove the solution to obtain ethanol-activated cellulose with a liquid content of 50%; then replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20 minutes, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged: 13000 r / min for 10 minutes, the filtrate was removed, and ethanol-activated cellulose was obtained; finally, low-temperature drying (60°C, 12h) was performed to obtain pretreated pulp cellulose (ethanol activated).

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

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

[0077] A pulp sheet with an intrinsic viscosity of 697 ml / g (dry weight 1 kg) was taken and added to deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet was soaked in deionized water for 45 minutes), and then crushed using a crusher at a speed of 100 r / min for 20-25 minutes until no pulp sheet was visible to the naked eye to obtain a cellulose aqueous dispersion, which was centrifugally dehydrated to form water cellulose with a moisture content of 50 wt% (mass of about 2 kg); then the water cellulose with a moisture content of 50 wt% was soaked in 18 kg of 50 wt% ethyl acetate. The cellulose was stirred in an alcohol solution for 45 minutes (stirring speed: 100 r / min), and then centrifuged to remove the solution to obtain ethanol-activated cellulose with a liquid content of 50%; then replaced with anhydrous ethanol twice, and each replacement operation was specifically as follows: anhydrous ethanol was added to the cellulose and stirred for 20 minutes, the mass ratio of cellulose to anhydrous ethanol was 1:2, and then centrifuged at 13000 r / min for 10 minutes, and the filtrate was removed to obtain ethanol-activated cellulose; finally, low-temperature drying (60°C, 12h) was performed 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°C and dissolved for 3 hours, followed by spinning (spinning from a spinneret, cooling by blowing, treatment in a coagulation bath, three-stage water washing, and drying in sequence; wherein the spinning temperature was 100°C, and the drawing was coagulation bath drawing, i.e., nozzle drawing), the spinning speed was 80 m / min, the pressure before the plate was 9 MPa, the blowing air volume was 60 L / min, the blowing humidity was 40%, the coagulation bath concentration was 20%, the three-stage water washing temperatures were 40°C, 45°C, and 50°C, respectively, the drying temperature was 90°C, the spinning temperature was 100°C, the drawing multiple was 4.21 times, and the cellulose filaments finally obtained 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 8wt.% spinning solution of pulp (MA+ethanol activation) (without anhydrous ethanol replacement step)

[0081] 1 kg (dry weight) of pulp sheet with a characteristic viscosity of 626 ml / g is taken, added into deionized water to prepare an aqueous solution with a pulp (cellulose) concentration of 1% (wt.) (the pulp sheet is soaked in deionized water for 45 minutes), and crushed by a pulverizer with a pulverizer speed of 100 r / min for 20-25 minutes until no pulp sheet is visible to the naked eye to obtain a cellulose aqueous dispersion; the pH is adjusted to 10, allowed to stand for 45 minutes, and then mechanically beaten: the knife pressure is set to 5 kg, the distance between the knife and the bottom knife is 10 mm, the treatment is performed for 120 minutes, the beating degree is 30°SR, and then the pH is adjusted to neutral, and finally centrifuged to form a mechanically treated aqueous cellulose with a moisture content of 50 wt%.

[0082] The mechanically treated hydrocellulose with a moisture content of 50wt% is stirred in a 50wt% ethanol solution for 45min (stirring speed is 100r / min), and the mass ratio of the mechanically treated hydrocellulose with a moisture content of 50wt% to the 50% ethanol solution is 1:9; then the solution is centrifuged to obtain ethanol-activated cellulose with a liquid content of 50%; then low-temperature drying (60°C, 12h) is performed to obtain the pretreated activated pulp cellulose.

[0083] 8 g (dry weight) of activated pulp cellulose was mixed with 92 g of [Bmim][Cl] (pure [Bmim][Cl]), the pH was adjusted to 10.3, and then the mixture was dissolved at 100°C under vacuum dehydration for 3 hours, after which the spinning solution was taken out.

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

[0085] Figure 1 Schematic diagram of the cellulose cell wall structure; Figure 2 It is a schematic diagram of a mechanical beating grinding disc; Figure 3 The figure shows the morphology of pulp before and after mechanical beating, which indicates that the morphology of pulp has changed after mechanical treatment (the primary cell wall that is difficult to dissolve has been destroyed); Figure 4 The dissolution status of pulp treated by different methods was compared, indicating that the pulp treated by mechanical treatment + ethanol activation had the best dissolution performance; Figure 5 The figure is the weighted relaxation time spectrum of the spinning solution prepared from pulp treated in different ways. The horizontal axis is the relaxation time Lambda, and the vertical axis represents the weighted value H*Lambda of relaxation modulus and relaxation time, which indicates that the relaxation of cellulose molecular chains in the spinning solution prepared from cellulose pulp after pretreatment is extensive and uniform: the peak values ​​of Example 2 (relative to Comparative Example 1) and Example 4 (relative to Comparative Example 3) are biased to the upper right because their more complete dissolution brings about the optimization of viscosity and relaxation time.

[0086] In order 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 refers to the mechanical treatment process in Example 2 and Example 3. The cellulose after mechanical treatment in Example 2 (i.e., the water cellulose after mechanical treatment with a moisture content of 50 wt% in Example 2) is as follows: Figure 3 As shown in c and d in , the cellulose after the mechanical treatment in Example 2 or 3 (i.e., the water cellulose after the mechanical treatment with a moisture content of 50 wt% in Examples 2 and 3) is shown in Table 1.

[0087] Table 1 shows the changes in the morphology and intrinsic viscosity of pulp before and after mechanical treatment (test standard GB / T29779-2013, the equipment used is FMA 100 fiber morphology analyzer). After mechanical treatment, the intrinsic viscosity and fiber length of pulp did not change significantly, and the width increased by 1um compared with the original pulp. After MB treatment, the number of fine fibers and microfibers increased more than MA, about 1.5 times the number of original pulp, and the number of dust increased more significantly. After mechanical treatment, the fiber brooming index of pulp increased by about one time, and the fiber kink index was about 1 / 3 of the original pulp. It can be seen that: this mechanical treatment method will not degrade the pulp, but will increase the width of the fiber, increase the number of fine fibers, microfibers and dust, increase the fiber brooming index, and reduce the fiber kink index.

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

[0089]

[0090] Comparative Example 1 and Comparative Example 1 show that after ethanol activation, the pulp dissolution quality is improved to a certain extent.

[0091] Comparison of Example 1 with Examples 2, 3, and 4 shows that the solubility of the pulp after mechanical treatment is significantly improved. The reason is that the mechanical treatment process can destroy the primary cell wall of cellulose in the pulp, making it easier for the solvent to enter the interior of the cellulose, thereby making the pulp dissolve more thoroughly without a significant change in the intrinsic viscosity.

[0092] Comparative Example 3 and Comparative Example 2 show that the degradation of pulp is less when the pulp is directly dried and dissolved after mechanical treatment and ethanol activation than when the pulp is dissolved after ethanol is replaced with deionized water. This is related to the residual amount of ethanol in the system after ethanol is replaced with deionized water. The use of deionized water to replace ethanol makes it difficult to completely remove ethanol, which triggers side reactions (cellulose and ethanol react to form ethyl levulinate) during the dissolution of wet pulp in the ionic liquid, thereby triggering the degradation of pulp. Laboratory data show that when the step of replacing ethanol with deionized water is deleted in Example 2, the degradation amount of cellulose after dissolving in the ionic liquid is 79 ml / g, which can prove that the residual ethanol in the cellulose significantly increases the degradation of pulp during the dissolution process.

[0093] Comparison of Example 2 and Comparative Example 2 shows that the treatment process of MA+ethanol activation is better than that of MB+ethanol activation, which is related to the conditions of mechanical treatment. Therefore, the mechanical treatment conditions can be adjusted according to the characteristics of pulp to achieve the effect of promoting dissolution. Through the comparison of experimental data, it is found that within a certain range, the lower the pulp concentration and the higher the knife pressure, the more obvious the cellulose treatment effect. MA reduces the concentration of pulp cellulose aqueous solution and increases the knife pressure, and its pretreatment effect is better than MB.

[0094] Comparison of Example 4 and Comparative Example 3 shows that the solubility of pulp after being activated and dried by MA+ethanol is significantly improved. Moreover, the rheological properties and solubility state of the 8% spinning solution prepared by the pulp after being activated and dried by MA+ethanol meet the production requirements.

[0095] 10wt.% spinning solution is difficult to directly sample from the dissolving kettle for rheological properties and characteristic viscosity characterization, so the mechanical properties of the product are used to characterize the effect of the pretreatment method of the present invention after spinning. Comparative Example 5 and Comparative Example 4 illustrate that the mechanical properties of the cellulose industrial filaments prepared after pulp is activated and dried by MA+ethanol are better than those of the cellulose industrial filaments prepared after pulp is activated and dried by ethanol only, which is related to the dissolution condition of pulp in the system. Pulp is more easily dissolved after MA+ethanol activation and drying, and cellulose can be better evenly distributed in the system, thereby improving the breaking strength and elastic modulus of the cellulose industrial filaments. In addition, the characteristic viscosity of the cellulose industrial filaments prepared by Example 5 and Comparative Example 4 is basically the same, indicating that the treatment method of the present invention does not cause a large decrease in the characteristic viscosity of the product.

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

[0097]

[0098]

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

[0100] The pulp platinum pretreatment method of the present invention is suitable for the dissolution of high intrinsic viscosity pulp (>500ml / g) at high purity and high concentration (≥8wt%); there is a certain difference in the decrease in intrinsic viscosity between Examples 1-3 and Comparative Examples 1-2 due to the lower concentration and temperature during dissolution; there is a significant difference in the change of IV between Example 4 and Comparative Example 3 after increasing the dissolution concentration and temperature, and the temperature used in industrial production is also relatively high.

[0101] The purpose of the pulp pretreatment of the present invention is mainly to improve the solubility of the pulp without substantially changing the intrinsic viscosity of the pulp. The beneficial effects are, on the one hand, a small change in the intrinsic viscosity and, on the other hand, an improvement in the dissolution quality, which is ultimately reflected in the performance of the cellulose industrial yarn.

[0102] The above experimental results show that the method can improve the solubility of high intrinsic viscosity and high purity pulp while ensuring that the intrinsic viscosity of the pulp does not change significantly. In addition, the method can also adjust the mechanical treatment conditions according to the characteristics of the pulp to achieve the purpose of customized treatment. Therefore, the present invention can be used for the preparation of high intrinsic viscosity industrial filaments.

[0103] The above shows and describes 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 form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A pulp pretreatment method, characterized in that: The following steps are involved: (1) Dispersion of pulp: Pulp with an intrinsic viscosity of 500-780 ml / g is soaked in deionized water and crushed to obtain a cellulose aqueous dispersion with a concentration of 1-5 wt%; (2) Mechanical treatment of cellulose aqueous dispersion: The cellulose aqueous dispersion obtained in step (1) is adjusted to a pH of 10-11, and mechanical beating is performed for a beating time of 140-240 min, and a beating degree of 10-70°SR. The solution is adjusted to neutral to obtain mechanically treated aqueous cellulose; (3) Dehydration of the mechanically treated hydrocellulose: Dehydrating the mechanically treated hydrocellulose obtained in step (2) to obtain mechanically treated hydrocellulose having a moisture content of 40-60%; (4) Dispersing and decomposing the mechanically treated hydrocellulose: dispersing and decomposing the mechanically treated hydrocellulose with a moisture content of 40-60% obtained in step (3) in a 40-60% ethanol solution, and then centrifuging and desolventizing to obtain ethanol-activated cellulose with a liquid content of 40-60%; (5) Ethanol replacement and drying of cellulose: The ethanol-activated cellulose with a liquid content of 40-60% obtained in step (4) is replaced with high-concentration ethanol. After the replacement, the solution is removed by centrifugation, and the obtained cellulose is dried to obtain pretreated cellulose; the high-concentration ethanol is 98% or more ethanol.

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

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

4. A pulp pretreatment method according to claim 1, characterized in that: In step (3), the mechanically treated hydrocellulose obtained in step (2) is subjected to centrifugal dehydration treatment.

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

6. A pulp pretreatment method according to claim 1, characterized in that: 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 number of replacements with high-concentration ethanol is 1-3 times, and the mass ratio of cellulose to high-concentration ethanol in each replacement is 1:1.5-2.

5.

7. Use of the pulp pretreatment method according to any one of claims 1 to 6 in the preparation of industrial yarns with high intrinsic viscosity.

8. Use of the pulp pretreatment method according to claim 7 in preparing high intrinsic viscosity industrial yarn, characterized in that: The high intrinsic viscosity industrial yarn is a cellulose industrial yarn with an intrinsic viscosity of 500-780 ml / g.

9. Use of the pulp pretreatment method according to claim 7 in preparing high intrinsic viscosity industrial yarn, characterized in that: The pretreated cellulose is dissolved and spun, the dissolution temperature is 90-110°C, the pH value of the dissolving 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°C, and the drafting multiple is 1.5-6 times.

10. Use of the pulp pretreatment method according to claim 9 in preparing high intrinsic viscosity industrial yarn, 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. Use of the pulp pretreatment method according to claim 9 in preparing high intrinsic viscosity industrial yarn, 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 washing temperature is 30-60℃, and the drying temperature is 60-90℃.

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