Preparation of lyocell pulp by mixing bamboo and wood pulp and directional treatment process

Abstract

The present application relates to the technical field of chemical fibers, and discloses a process for preparing lyocell pulp by mixing bamboo and wood pulp, comprising the following steps: bamboo pretreatment: cutting and shaping the bamboo, and then sequentially performing steam explosion defibration, acid treatment directional silicon removal and biological enzyme assisted delignification; wood pulp pretreatment: sequentially performing airflow sorting impurity removal, low-temperature alkali refining degreasing and biological enzyme deep purification; through the step-by-step directional pretreatment strategy, steam explosion causes microcracks in the cell wall of the short-cut bamboo fibers, and the high selectivity of the oxalic acid-ammonium fluoride composite acid liquid to silicate is used to achieve deep silicon removal of the short-cut bamboo fibers without damaging the cellulose skeleton; at the same time, the biological enzyme system step-by-step dissociates the hemicellulose side chain and the lignin aromatic ring structure, and removes the soluble oligomers, so that the risk of spinning blockage caused by silicon residues is eliminated under the premise of retaining the high polymerization degree cellulose of the bamboo, and the solubility of the pulp in the NMMO solvent is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical fibers, in particular to a process for preparing lyocell pulp by mixing bamboo and wood pulp and directional treatment. BACKGROUND

[0002] Lyocell fiber is made of natural plant fiber and is known as the most valuable product in the history of man-made fiber in the past half century. Lyocell has excellent performance of both natural fiber and synthetic fiber. It is a green fiber, and its raw material is cellulose which is inexhaustible in nature. The production process has no chemical reaction, and the solvent used is non-toxic. Lyocell is made of pulp formed by crushing renewable bamboo and wood. The advanced process improves the solvent recovery rate, which is not only energy-saving and environmentally friendly, but also sustainable development. The clothes made of this fiber not only have natural luster and smooth hand feeling, but also have good moisture permeability and air permeability, and the fabric blended with wool has good effect.

[0003] At present, in the field of lyocell fiber pulp raw material development, due to the regional supply restriction of natural cellulose raw material, the industry generally tries to mix bamboo and wood pulp to expand the source of raw materials. However, in the process of preparing lyocell pulp by mixing bamboo and wood pulp, the compatibility contradiction between high silicon content of bamboo and high lipid content of wood pulp cannot be solved synchronously in the pretreatment process of raw materials.

[0004] Therefore, the present application provides a process for preparing lyocell pulp by mixing bamboo and wood pulp and directional treatment to solve the above problems. SUMMARY

[0005] The main purpose of the present application is to provide a process for preparing lyocell pulp by mixing bamboo and wood pulp and directional treatment to solve the problems raised in the above background.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a process for preparing lyocell pulp by mixing bamboo and wood pulp and directional treatment, comprising the following steps:

[0007] Step 1: bamboo pretreatment: cutting the bamboo into a certain shape and then performing steam explosion defibration, acid treatment directional desiliconization and biological enzyme assisted delignification;

[0008] Step 2: wood pulp pretreatment: the raw wood pulp is subjected to airflow separation and impurity removal, low-temperature alkali refining and degreasing, and biological enzyme deep purification;

[0009] Step 3: mixed treatment: mixing the bamboo pulp obtained in step 1 and the wood pulp obtained in step 2 according to the dry weight ratio, adding a dispersing agent for pulp homogenization, wherein the dry weight ratio is 50-70:30-50;

[0010] Step 4: lyocell pulp forming: washing, dewatering and drying the homogenized pulp to form lyocell pulp;

[0011] wherein the steam explosion pressure is 1.8-2.2 MPa, the pressure maintaining time is 5-8 min, the acid treatment uses a composite acid solution of 1.3-1.8 wt% oxalic acid and 0.08-0.15 wt% ammonium fluoride, the solid-liquid ratio is 1:10-15, and the treatment is carried out in stages, i.e., the first stage is 45-55°C for 25-35 min, and the second stage is 65-75°C for 35-45 min, the biological enzyme-assisted delignification includes the synergistic action of xylanase, laccase and mannanase, the low-temperature alkali refining uses a composite emulsifying system of 0.4-1.0 wt% alkyl polysaccharide APG and 0.2-0.4 wt% EDTA, the treatment temperature is less than 75°C, and the treatment time is less than 70 min, and the dispersing agent includes an anionic polyacrylate and a non-ionic hydroxyalkyl cellulose.

[0012] Preferably, in the steam explosion step:

[0013] The bamboo material is in the form of rectangular bamboo pieces, and the size is 20±2 mm in length, 5±0.5 mm in width and 2±0.2 mm in thickness.

[0014] The water content of the bamboo material is strictly controlled in the range of 40-50%.

[0015] After the explosion, the aspect ratio of the short-cut bamboo fibers is 25-30, and the fiber bundles are dispersed in a flocculent form.

[0016] Preferably, after the acid treatment step, a three-stage countercurrent water washing is included.

[0017] The first stage is deionized water washing until the pH is less than 5.0, so as to remove free silicic acid and residual acid solution.

[0018] The second stage is neutralization treatment in a 0.5 wt% sodium bicarbonate solution for 10 min.

[0019] The third stage is deionized water washing until the pH is greater than 6.0 and the conductivity is less than 50 μS / cm.

[0020] Preferably, the specific conditions of the biological enzyme-assisted delignification treatment are as follows:

[0021] First, xylanase treatment: enzyme activity 18-22 IU / g raw material, pH 4.8-5.2, temperature 48-52°C, time 3.5-4.5 h, and degradation of hemicellulose side chains;

[0022] Then, laccase-ABTS mediator system treatment: laccase activity 9-11 U / g raw material, ABTS concentration 0.1 mM, pH 4.3-4.7, temperature 48-52°C, time 7-9 h, and oxidative degradation of lignin;

[0023] Finally, the hemicellulose main chain is degraded by treating with mannanase: enzyme activity 4-6 IU / g raw material, pH 4.8-5.2, temperature 48-52℃, time 1.5-2.5h.

[0024] Preferably, in the low-temperature alkali refining step:

[0025] The APG concentration is preferably 0.5-0.8wt%, when the APG concentration is less than 0.5wt%, the lipid emulsification rate decreases by 25%, and when the APG concentration is greater than 0.8wt%, the foam volume increases, resulting in a decrease in the utilization rate of active ingredients;

[0026] The EDTA addition amount is 0.28-0.32wt, and chelating calcium ions prevents pectin cross-linking and repolymerization;

[0027] The treatment endpoint is determined by the fiber contact angle being less than 30°, and the lipid residual amount being less than 0.5wt%.

[0028] Preferably, the biological enzyme deep purification includes stepwise enzymatic hydrolysis:

[0029] First step of lipase treatment: using magnetic Fe3O4@SiO2 carrier immobilized lipase, enzyme activity 14-16U / g fiber, pH 7.3-7.7, temperature 43-47℃, time 1.8-2.2h, carrier diameter 100-200nm, enzyme loading greater than 150mg / g carrier;

[0030] Second step of pectinase treatment: enzyme activity 28-32U / g fiber, pH 4.6-5.0, temperature 48-52℃, time 1.8-2.2h.

[0031] Preferably, the wood pulp fiber after the biological enzyme deep purification meets:

[0032] The lipid residual amount is less than 0.2wt%, the pectin removal rate is greater than 98%, and the fiber polymerization degree is greater than 1200.

[0033] Preferably, the dispersant system comprises:

[0034] Sodium polyacrylate: molecular weight 8000-12000, addition amount 0.08-0.12wt%, providing Zeta potential of-35mV or more electrostatic repulsion;

[0035] Hydroxyethyl cellulose: degree of substitution 0.8-1.2, addition amount 0.04-0.06wt%, solution viscosity adjusted to 150-250mPa·s.

[0036] Preferably, in the mixing treatment step:

[0037] The dry weight ratio of bamboo pulp to wood pulp is 58-62:38-42;

[0038] Homogenization conditions: stirring speed 350-450 rpm, time 40-50 min, temperature 45-55℃;

[0039] The Lyocell pulp forming step comprises:

[0040] Washing: using a countercurrent diffusion washing machine, water consumption is less than 20 m³ / ton of pulp;

[0041] Dewatering: double net press machine line pressure 80-100 kN / m, pulp dryness is greater than 35%;

[0042] Drying: flash drying tower inlet air temperature 180-220℃, outlet pulp moisture content less than 10%.

[0043] Preferably, the Lyocell pulp meets:

[0044] The alpha-cellulose content is greater than 93wt%, the ash content is less than 0.25wt%, and the lipid residual amount is less than 0.3wt%.

[0045] The present application has the following beneficial effects:

[0046] 1. In the present application, through the step-by-step directional pretreatment strategy, steam explosion causes microcracks in the cell wall of short-cut bamboo fibers, and the high selectivity of oxalic acid-ammonium fluoride complex acid solution to silicate is used to achieve deep desilication of short-cut bamboo fibers without damaging the cellulose skeleton; at the same time, the biological enzyme system step-by-step dissociates the hemicellulose side chain and the lignin aromatic ring structure, and removes soluble oligomers, so as to eliminate the risk of spinning blockage caused by silicon residues under the premise of retaining high polymerization degree cellulose of bamboo, and ensure the smoothness of pulp in NMMO solvent.

[0047] 2. In the present application, the wood pulp pretreatment stage is purified by two-stage synergy: in the low-temperature alkali refining, alkyl polyglycoside selectively emulsifies lipid molecules, and its hydrophilic end combines with EDTA to chelate calcium ions, and the pectin-metal ion crosslinking network is broken down; in the subsequent biological enzyme deep purification, lipase precisely hydrolyzes the ester bond of triglyceride, and pectinase breaks the alpha-1, 4 glycosidic bond of galacturonic acid at the same time, so that the wax barrier and pectin matrix on the surface of the wood pulp are degraded layer by layer. Thus, a clean microporous channel structure is formed on the surface of the fiber, the lipid-induced solvent decomposition side reaction is eliminated, and the cellulose reaction accessibility is improved.

[0048] 3. In the present application, a bifunctional dispersion system is introduced in the mixing homogenization stage. The polyacrylate inhibits the short-cut bamboo fiber flocculation through electrostatic repulsion, and the hydroxyalkyl cellulose prevents the wood pulp fiber entanglement through steric hindrance. The two work together to form a three-dimensional network of "bamboo short fibers penetrating and anchoring wood pulp long fibers". The problem of suspension stratification caused by fiber morphology difference is solved, and finally a mixed pulp with uniform dispersion and interface combination is obtained, which provides excellent film-forming continuity and mechanical strength basis for lyocell fibers. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0050] Embodiment 1: A lyocell pulp directional processing technology prepared by mixing bamboo and wood pulp, comprising the following steps:

[0051] Step one: bamboo pretreatment: cutting and shaping the bamboo, and then sequentially performing steam explosion defibration, acid treatment directional desiliconization, and biological enzyme assisted delignification;

[0052] Step two: wood pulp pretreatment: sequentially performing airflow sorting impurity removal, low-temperature alkali refining degreasing, and biological enzyme deep purification on the raw wood pulp;

[0053] Step three: mixing treatment: mixing the bamboo pulp obtained in step one and the wood pulp pulp obtained in step two according to the dry weight ratio, and adding a dispersant for pulp homogenization, wherein the dry weight ratio is 50:30;

[0054] Step four: lyocell pulp forming: washing, dewatering, and drying the homogenized pulp to form lyocell pulp;

[0055] The pressure of steam explosion is 1.8 MPa, the pressure maintaining time is 5 min, the acid treatment uses a composite acid solution of 1.3 wt% oxalic acid and 0.08 wt% ammonium fluoride, the solid-liquid ratio is 1:10, the temperature is raised in stages, the first stage is 45℃ for 25 min, and the second stage is 65℃ for 35 min. The biological enzyme assisted delignification includes the synergistic effect of xylanase, laccase and mannanase. The low-temperature alkali refining uses a composite emulsifying system of 0.4 wt% alkyl polysaccharide APG and 0.2 wt% EDTA, the treatment temperature is less than 75℃, and the time is less than 70 min. The dispersant includes anionic polyacrylate and non-ionic hydroxyalkyl cellulose.

[0056] In the steam explosion step:

[0057] The bamboo material is in the form of rectangular bamboo pieces with dimensions of 20±2 mm in length, 5±0.5 mm in width and 2±0.2 mm in thickness;

[0058] The water content of the bamboo material is strictly controlled at 40%;

[0059] The aspect ratio of the short-cut bamboo fibers after the explosion is 25-30, and the fiber bundles are in a flocculent state.

[0060] The acid treatment step includes three-stage countercurrent water washing:

[0061] The first stage is deionized water washing to a pH less than 5.0 to remove free silicic acid and residual acid;

[0062] The second stage is 0.5 wt% sodium bicarbonate solution neutralization treatment for 10 min;

[0063] The third stage is deionized water washing to a pH greater than 6.0 and a conductivity less than 50 μS / cm.

[0064] The specific conditions of the biological enzyme-assisted delignification treatment are as follows:

[0065] First, xylanase treatment: enzyme activity 18 IU / g raw material, pH 4.8, temperature 48°C, time 3.5 h, degradation of hemicellulose side chains;

[0066] Then, laccase-ABTS mediator system treatment: laccase activity 9 U / g raw material, ABTS concentration 0.1 mM, pH 4.3, temperature 48°C, time 7 h, oxidative degradation of lignin;

[0067] Finally, mannanase treatment: enzyme activity 4 IU / g raw material, pH 4.8, temperature 48°C, time 1.5 h, synergistic degradation of hemicellulose main chain.

[0068] In the low-temperature alkali refining step:

[0069] The APG concentration is preferably 0.5 wt%, when the APG concentration is less than 0.5 wt%, the lipid emulsification rate decreases by 25%, and when the APG concentration is greater than 0.8 wt%, the amount of foam increases, resulting in a decrease in the utilization rate of effective components;

[0070] The EDTA addition amount is 0.28 wt, and the chelation of calcium ions prevents the cross-linking and repolymerization of pectin;

[0071] The treatment endpoint is determined by the fiber contact angle being less than 30° and the residual lipid content being less than 0.5 wt%.

[0072] The biological enzyme deep purification includes stepwise enzymolysis:

[0073] First step lipase treatment: magnetic Fe3O4SiO2 carrier immobilized lipase, enzyme activity 14 U / g fiber, pH 7.3, temperature 43℃, time 1.8h, carrier diameter 100nm, enzyme loading greater than 150mg / g carrier;

[0074] Second step pectinase treatment: enzyme activity 28 U / g fiber, pH 4.6, temperature 48℃, time 1.8h.

[0075] The wood pulp fiber after bio-enzyme deep purification meets:

[0076] The lipid residual amount is less than 0.2wt%, the pectin removal rate is greater than 98%, and the fiber polymerization degree is greater than 1200.

[0077] The dispersant system comprises:

[0078] Sodium polyacrylate: molecular weight 8000, addition amount 0.08wt%, providing Zeta potential-35mV or more electrostatic repulsion;

[0079] Hydroxyethyl cellulose: degree of substitution 0.8, addition amount 0.04wt%, solution viscosity adjusted to 150mPa·s.

[0080] In the mixing treatment step:

[0081] The dry weight ratio of bamboo pulp to wood pulp is 58:38;

[0082] Homogenization conditions: stirring speed 350rpm, time 40min, temperature 45℃;

[0083] The lyocell pulp forming step comprises:

[0084] Washing: using a countercurrent diffusion washing machine, water consumption less than 20m³ / ton of pulp;

[0085] Dewatering: double-net press machine line pressure 80kN / m, pulp dryness greater than 35%;

[0086] Drying: flash drying tower inlet air temperature 180℃, outlet pulp moisture less than 10%.

[0087] The lyocell pulp meets:

[0088] The α-cellulose content is greater than 93wt%, the ash content is less than 0.25wt%, and the lipid residual amount is less than 0.3wt%.

[0089] Example 2: Bamboo and wood pulp mixed to prepare lyocell pulp directional treatment process, comprising the following steps:

[0090] Comprising the following steps:

[0091] Step one: Bamboo pretreatment: The cut bamboo was sequentially subjected to steam explosion defibration, acid treatment for directional desilication, and biological enzyme-assisted delignification;

[0092] Step two: Wood pulp pretreatment: The raw wood pulp was sequentially subjected to air flow sorting and impurity removal, low-temperature alkali refining and degreasing, and biological enzyme deep purification;

[0093] Step three: Mixed treatment: The bamboo pulp obtained in step one and the wood pulp obtained in step two were mixed in a dry weight ratio of 60:40, and a dispersing agent was added for pulp homogenization;

[0094] Step four: Lyocell pulp forming: The homogenized pulp was washed, dewatered, and dried to form lyocell pulp;

[0095] The pressure of steam explosion was 2.0 MPa, and the pressure maintaining time was 6 min. The acid treatment used a composite acid solution of 1.5 wt% oxalic acid and 0.10 wt% ammonium fluoride, with a solid-liquid ratio of 1:12, and the temperature was raised in stages: 50°C for 30 min in the first stage and 70°C for 40 min in the second stage. The biological enzyme-assisted delignification included the synergistic effect of xylanase, laccase, and mannanase. The low-temperature alkali refining used a composite emulsifying system of 0.6 wt% alkyl polysaccharide APG and 0.3 wt% EDTA, with a treatment temperature less than 75°C and a time less than 70 min. The dispersing agent included anionic polyacrylate and non-ionic hydroxyalkyl cellulose.

[0096] In the steam explosion step:

[0097] The bamboo material was in the form of rectangular bamboo pieces, with dimensions of 20±2 mm in length, 5±0.5 mm in width, and 2±0.2 mm in thickness;

[0098] The moisture content of the bamboo was strictly controlled within 45%;

[0099] The aspect ratio of the short-cut bamboo fibers after explosion was 28, and the fiber bundles were dispersed in a flocculent state.

[0100] The acid treatment step included three stages of countercurrent water washing:

[0101] First stage: deionized water was used to rinse to a pH less than 5.0 to remove free silicic acid and residual acid solution;

[0102] Second stage: 0.5 wt% sodium bicarbonate solution was used for neutralization treatment for 10 min;

[0103] Third stage: deionized water was used to rinse to a pH greater than 6.0 and an electrical conductivity less than 50 μS / cm.

[0104] The specific conditions for biological enzyme-assisted delignification treatment were:

[0105] Firstly, xylanase treatment: enzyme activity 20 IU / g raw material, pH 5.0, temperature 50℃, time 4.0h, degrading hemicellulose side chain;

[0106] Secondly, laccase-ABTS mediator system treatment: laccase activity 10 U / g raw material, ABTS concentration 0.1 mM, pH 4.5, temperature 50℃, time 8h, oxidizing lignin;

[0107] Finally, mannanase treatment: enzyme activity 5 U / g raw material, pH 5.0, temperature 50℃, time 2.0h, synergistically degrading hemicellulose backbone.

[0108] In the low-temperature alkali refining step:

[0109] The APG concentration is preferably 0.6wt%, when the APG concentration is less than 0.5wt%, the lipid emulsification rate decreases by 25%, and when the APG concentration is greater than 0.8wt%, the foam volume increases, resulting in a decrease in the utilization rate of effective components;

[0110] The EDTA addition amount is 0.30wt, and chelating calcium ions prevents pectin cross-linking polymerization;

[0111] The treatment endpoint is determined by the fiber contact angle being less than 30°, and the lipid residual amount being less than 0.5wt%.

[0112] The biological enzyme deep purification includes stepwise enzymatic hydrolysis:

[0113] First step of lipase treatment: using magnetic Fe3O4SiO2 carrier immobilized lipase, enzyme activity 15 U / g fiber, pH 7.5, temperature 45℃, time 2.0h, carrier diameter 150nm, enzyme loading greater than 150mg / g carrier;

[0114] Second step of pectinase treatment: enzyme activity 30 U / g fiber, pH 4.8, temperature 50℃, time 2.0h.

[0115] The wood wool fiber after biological enzyme deep purification meets:

[0116] The lipid residual amount is less than 0.2wt%, the pectin removal rate is greater than 98%, and the fiber polymerization degree is greater than 1200.

[0117] The dispersant system includes:

[0118] Sodium polyacrylate: molecular weight 10000, addition amount 0.10wt%, providing Zeta potential-35mV or more electrostatic repulsion;

[0119] Hydroxyethyl cellulose: degree of substitution 1.0, addition amount 0.05wt%, solution viscosity adjusted to 200mPa·s.

[0120] In the mixed treatment step:

[0121] The dry weight ratio of bamboo pulp to wood pulp is 60:40;

[0122] Homogenization conditions: stirring speed 400 rpm, time 45 min, temperature 50℃;

[0123] The Lyocell pulp forming step comprises:

[0124] Washing: using a counterflow diffusion washing machine, water consumption is less than 20 m³ / ton of pulp;

[0125] Dewatering: double-net press machine line pressure 90 kN / m, pulp dryness greater than 35%;

[0126] Drying: flash drying tower inlet air temperature 200℃, outlet pulp moisture less than 10%.

[0127] The Lyocell pulp meets:

[0128] The α-cellulose content is greater than 93 wt%, the ash content is less than 0.25 wt%, and the lipid residue content is less than 0.3 wt%.

[0129] Example 3: Bamboo and wood pulp mixed to prepare Lyocell pulp directional processing technology, comprising the following steps:

[0130] Step one: bamboo pretreatment: the cut and shaped bamboo is sequentially subjected to steam explosion defibration, acid treatment directional desiliconization, and biological enzyme assisted delignification;

[0131] Step two: wood pulp pretreatment: the raw wood pulp is sequentially subjected to air flow sorting impurity removal, low temperature alkali refining degreasing, and biological enzyme deep purification;

[0132] Step three: mixed treatment: the bamboo pulp obtained in step one and the wood pulp obtained in step two are mixed according to the dry weight ratio, and a dispersant is added for pulp homogenization, wherein the dry weight ratio is 70:50;

[0133] Step four: Lyocell pulp forming: the homogenized pulp is washed, dewatered, and dried to form Lyocell pulp;

[0134] The pressure of steam explosion is 2.2 MPa, the pressure maintaining time is 8 min, the acid treatment uses a composite acid solution of 1.8 wt% oxalic acid and 0.15 wt% ammonium fluoride, the solid-liquid ratio is 1:15, the temperature is treated in stages, the first stage is 55℃ for 35 min, the second stage is 75℃ for 45 min, the biological enzyme assisted delignification includes the synergistic effect of xylanase, laccase and mannanase, the low temperature alkali refining uses a composite emulsifying system of 1.0 wt% alkyl polysaccharide APG and 0.4 wt% EDTA, the treatment temperature is less than 75℃, the time is less than 70 min, and the dispersant includes anionic polyacrylate and non-ionic hydroxyalkyl cellulose.

[0135] In the steam explosion step:

[0136] The bamboo material is in the form of rectangular bamboo pieces with dimensions of 20±2 mm in length, 5±0.5 mm in width, and 2±0.2 mm in thickness;

[0137] The moisture content of the bamboo material is strictly controlled within 50%;

[0138] The aspect ratio of the short-cut bamboo fibers after explosion is 30, and the fiber bundles are dispersed in a flocculent form.

[0139] The acid treatment step includes three-stage countercurrent water washing:

[0140] First stage: deionized water washing to a pH less than 5.0 to remove free silicic acid and residual acid;

[0141] Second stage: 0.5 wt% sodium bicarbonate solution neutralization treatment for 10 min;

[0142] Third stage: deionized water washing to a pH greater than 6.0 and a conductivity less than 50 μS / cm.

[0143] The specific conditions for the biological enzyme-assisted delignification treatment are as follows:

[0144] First, xylanase treatment: enzyme activity 22 IU / g raw material, pH 5.2, temperature 52°C, time 4.5 h, degradation of hemicellulose side chains;

[0145] Second, laccase-ABTS mediator system treatment: laccase activity 11 U / g raw material, ABTS concentration 0.1 mM, pH 4.7, temperature 52°C, time 9 h, oxidative degradation of lignin;

[0146] Finally, mannanase treatment: enzyme activity 6 U / g raw material, pH 5.2, temperature 52°C, time 2.5 h, synergistic degradation of hemicellulose main chain.

[0147] In the low-temperature alkali refining step:

[0148] The APG concentration is preferably 0.8 wt%, when the APG concentration is less than 0.5 wt%, the lipid emulsification rate decreases by 25%, and when the APG concentration is greater than 0.8 wt%, the amount of foam increases, resulting in a decrease in the utilization rate of effective components;

[0149] The EDTA addition amount is 0.32 wt, and the chelation of calcium ions prevents the cross-linking and repolymerization of pectin;

[0150] The treatment endpoint is determined by a fiber contact angle less than 30°, and the residual amount of lipids is less than 0.5 wt%.

[0151] The biological enzyme deep purification includes stepwise enzymatic hydrolysis:

[0152] First step lipase treatment: magnetic Fe3O4SiO2 carrier immobilized lipase, enzyme activity 14-16 U / g fiber, pH 7.7, temperature 47℃, time 2.2h, carrier diameter 200nm, enzyme loading greater than 150mg / g carrier;

[0153] Second step pectinase treatment: enzyme activity 32 U / g fiber, pH 5.0, temperature 52℃, time 2.2h.

[0154] The wood pulp fiber after biological enzyme deep purification meets:

[0155] The lipid residual amount is less than 0.2wt%, the pectin removal rate is greater than 98%, and the fiber polymerization degree is greater than 1200.

[0156] The dispersant system comprises:

[0157] Sodium polyacrylate: molecular weight 12000, addition amount 0.12wt%, providing Zeta potential-35mV or more electrostatic repulsion;

[0158] Hydroxyethyl cellulose: degree of substitution 1.2, addition amount 0.06wt%, solution viscosity adjusted to 250mPa·s.

[0159] In the mixing treatment step:

[0160] The dry weight ratio of bamboo pulp to wood pulp is 62:42;

[0161] Homogenization conditions: stirring speed 450rpm, time 50min, temperature 55℃;

[0162] The lyocell pulp forming step comprises:

[0163] Washing: using a countercurrent diffusion washing machine, water consumption less than 20m³ / ton of pulp;

[0164] Dewatering: double-net press machine line pressure 100kN / m, pulp dryness greater than 35%;

[0165] Drying: flash drying tower inlet air temperature 220℃, outlet pulp moisture less than 10%.

[0166] The lyocell pulp meets:

[0167] The α-cellulose content is greater than 93wt%, the ash content is less than 0.25wt%, and the lipid residual amount is less than 0.3wt%.

[0168] Comparative Example 1: The difference between this comparative example and Examples 1-3 is that no ammonium fluoride desiliconizing aid is added in the pretreatment of bamboo.

[0169] Comparative Example 2: The difference between this comparative example and Examples 1-3 is that no lipase was used for deep degreasing in the wool pulp pretreatment.

[0170] Comparative Example 3: The difference between this comparative example and Examples 1-3 is that no fiber fractionation homogenization was performed during the mixing process.

[0171] Comparative Example 4: The difference between this comparative example and Examples 1-3 is that no hydroxyalkyl cellulose dispersant was added to the mixed slurry.

[0172] Performance tests were performed on the bamboo and wool mixed lyocell pulp prepared in Examples 1-3 and Comparative Examples 1-4:

[0173] Alpha-cellulose content test: 2.00 g of absolute dry pulp was weighed and treated with 17.5% NaOH solution at 20°C for 30 min, then filtered, washed, and dried to weigh, and the cellulose purity was calculated;

[0174] Gel particle number test: The pulp was prepared into a 12% NMMO solution with 13% water, dissolved at 85°C for 120 min, and the number of insoluble substances greater than 10 μm was detected using a laser particle size instrument;

[0175] Lipid residue test: The Soxhlet extractor was used to extract with ethyl ether as the solvent for 6 h, and the extract was calculated as a percentage of the mass of the absolute dry pulp;

[0176] Polymerization degree DP test: The copper ethylenediamine method was used to determine the intrinsic viscosity of the fiber and calculate the average polymerization degree.

[0177] The test data of the bamboo and wool mixed lyocell pulp prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the following table:

[0178] Group Alpha-cellulose Silicon residue Lipid residue Dispersion index Gel number Filter flux Example 1 93.5 0.08 0.18 0.21 3 215 Example 2 94.1 0.05 0.16 0.18 2 230 Example 3 93.8 0.07 0.17 0.19 4 225 Comparative Example 1 89.2 0.41 0.19 0.23 185 95 Comparative Example 2 90.7 0.06 0.83 0.27 102 110 Comparative Example 3 92.3 0.09 0.21 0.39 67 135 Comparative Example 4 91.6 0.07 0.20 0.26 48 155

[0179] By comparing and analyzing the data in the table, it can be seen that the bamboo and wood pulp mixed lyocell pulp prepared by the processes of Examples 1-3 has better performance than the pulp prepared by the processes of Comparative Examples 1-4. This shows that through the step-by-step directional pretreatment strategy, steam explosion causes microcracks in the cell wall of the short-cut bamboo fiber, and the high selectivity of the oxalic acid-ammonium fluoride complex acid solution to silicates, realizing deep desilication of short-cut bamboo fiber without damaging the cellulose skeleton; At the same time, the biological enzyme system step-by-step dissociates the hemicellulose side chain and the lignin aromatic ring structure, and removes the soluble oligomers, so as to eliminate the risk of spinning blockage caused by silicon residues under the premise of preserving the high polymerization degree of bamboo cellulose, and ensure the smoothness of the pulp in NMMO solvent; In the wood pulp pretreatment stage, two-stage synergistic purification is carried out: in the low-temperature alkali refining, alkyl polyglycoside selectively emulsifies lipid molecules, and its hydrophilic end combines with EDTA to chelate calcium ions, thereby breaking the pectin-metal ion crosslinking network; In the subsequent biological enzyme deep purification, lipase precisely hydrolyzes the ester bond of triglyceride, and pectinase simultaneously breaks the alpha-1, 4 glycosidic bond of galacturonic acid, so that the wax barrier and pectin matrix on the surface of the wood pulp are degraded layer by layer. Thus, a clean microporous channel structure is formed on the surface of the fiber, eliminating the solvent decomposition side reaction induced by lipids and improving the cellulose reaction accessibility; In the mixed homogenization stage, a bifunctional dispersion system is introduced, polyacrylate inhibits short-cut bamboo fiber flocculation through electrostatic repulsion, and hydroxyalkyl cellulose prevents wood pulp fiber entanglement through steric hindrance, and the two synergistically regulate the formation of a three-dimensional network of "short-cut bamboo fiber penetrating and anchoring long wood pulp fiber". The problem of suspension stratification caused by the difference in fiber morphology is solved, and finally a mixed pulp with uniform dispersion and interface combination is obtained, which provides excellent film-forming continuity and mechanical strength basis for lyocell fibers.

[0180] As a green and environmentally friendly fiber in the 21st century, lyocell uses pulp made from renewable plant sources as raw material, and its processing technology is environmentally friendly and waste is biodegradable, so it is considered a sustainable development fiber in the whole life cycle.

[0181] The production process of bamboo lyocell fiber follows the process route of dry crushing, direct dissolution and dry spraying wet spinning. Its production process takes bamboo pulp as the starting raw material, and goes through many links such as bamboo pulp, crushed pulp, solvent, etc., a total of 18-20 rigorous procedures. It is worth mentioning that almost no chemical reaction is involved in the entire production process, mainly physical reaction, thus ensuring the environmental performance of the product. The bamboo pulp used in the production process is a fast-growing plant and a renewable and recyclable material, and the solvent N-methyl morpholine-N-oxide used has the characteristics of non-toxic and non-polluting, and after special process and equipment treatment, 99.7% of the solvent can be recycled and reused. Such a production process truly realizes zero emission, and the product is biodegradable and environmentally friendly.

[0182] Through comparison and analysis of the related data in the table, it can be known that the bamboo and wood flax mixed lyocell pulp prepared by the process has high purity, low impurity residue and excellent solubility, thereby indicating that the bamboo and wood flax mixed lyocell pulp preparation process provided by the application has a wider market prospect and is more suitable for promotion through the triple innovation of raw material hierarchical directional treatment, fiber interface regulation and dissolution structure optimization, and improves resource utilization rate and product added value.

[0183] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of lyocell pulp from bamboo and wood pulp mixture, characterized in that, The method comprises the following steps: Step 1: Bamboo pretreatment: cut and shaped bamboo is subjected to steam explosion defibration, acid treatment and directional silicon removal, and enzyme-assisted delignification in sequence; Step 2: Wood pulp pretreatment: raw wood pulp is subjected to airflow separation and impurity removal, low-temperature alkali refining and degreasing, and enzyme deep purification in sequence; Step 3: Mixed treatment: the bamboo pulp obtained in step 1 and the wood pulp obtained in step 2 are mixed in a dry weight ratio of 50-70:30-50, and a dispersing agent is added for pulp homogenization; Step 4: Lyocell pulp forming: the homogenized pulp is washed, dewatered and dried to form lyocell pulp; wherein the pressure of the steam explosion is 1.8-2.2 MPa, and the pressure maintaining time is 5-8 min; the acid treatment uses a composite acid solution of 1.3-1.8 wt% oxalic acid and 0.08-0.15 wt% ammonium fluoride, the solid-liquid ratio is 1:10-15, and the treatment is carried out in stages, i.e., the first stage is 45-55℃ for 25-35 min, and the second stage is 65-75℃ for 35-45 min; the enzyme-assisted delignification comprises the synergistic effect of xylanase, laccase and mannanase; the low-temperature alkali refining uses a composite emulsifying system of 0.4-1.0 wt% alkyl polysaccharide APG and 0.2-0.4 wt% EDTA, the treatment temperature is less than 75℃, and the treatment time is less than 70 min; and the dispersing agent comprises anionic polyacrylate and non-ionic hydroxyalkyl cellulose.

2. The process for the preparation of Lyocell pulp from bamboo and wood fluff as claimed in claim 1 wherein, In the steam explosion step: the bamboo is in the form of rectangular bamboo pieces, the size of which is 20±2 mm in length, 5±0.5 mm in width and 2±0.2 mm in thickness; the water content of the bamboo is strictly controlled within the range of 40-50%; the length-diameter ratio of the short-cut bamboo fibers after explosion is 25-30, and the fiber bundles are in a flocculent state.

3. The process for the preparation of Lyocell pulp from bamboo and wood wool as claimed in claim 1 wherein, After the acid treatment step, three-stage countercurrent water washing is performed: first stage: deionized water is used for washing until the pH is less than 5.0, so as to remove free silicic acid and residual acid solution; second stage: 0.5 wt% sodium bicarbonate solution is used for neutralization treatment for 10 min; third stage: deionized water is used for washing until the pH is greater than 6.0 and the conductivity is less than 50 μS / cm.

4. The process for the preparation of Lyocell pulp from bamboo and woodflour as claimed in claim 1, wherein the said process is characterized by, The specific conditions of the enzyme-assisted delignification treatment are as follows: firstly, xylanase is used for treatment: enzyme activity is 18-22 IU / g raw material, pH is 4.8-5.2, temperature is 48-52℃, and time is 3.5-4.5 h, so as to degrade the hemicellulose side chain; secondly, laccase-ABTS mediator system is used for treatment: laccase activity is 9-11 U / g raw material, ABTS concentration is 0.1 mM, pH is 4.3-4.7, temperature is 48-52℃, and time is 7-9 h, so as to oxidize and degrade lignin; finally, mannanase is used for treatment: enzyme activity is 4-6 U / g raw material, pH is 4.8-5.2, temperature is 48-52℃, and time is 1.5-2.5 h, so as to synergistically degrade the hemicellulose main chain.

5. The process for the preparation of Lyocell pulp from bamboo and wood fluff as claimed in claim 1 wherein, In the low-temperature alkali refining step: ​ the APG concentration is 0.5-0.8 wt%, when the APG concentration is less than 0.5 wt%, the lipid emulsification rate decreases by 25%, and when the APG concentration is greater than 0.8 wt%, the effective ingredient utilization rate decreases due to the increase of foam amount; EDTA is added in an amount of 0.28-0.32wt%, and chelating calcium ions prevents pectin cross-linking polymerization; The treatment endpoint is determined by the fiber contact angle being less than 30°, and the residual lipid content being less than 0.5wt%.

6. The process for the preparation of Lyocell pulp from bamboo and woodflour as claimed in claim 1 wherein, The biological enzyme deep purification includes stepwise enzymatic hydrolysis: The first step of lipase treatment: the lipase is immobilized on a magnetic Fe3O4SiO2 carrier, the enzyme activity is 14-16U / g fiber, the pH is 7.3-7.7, the temperature is 43-47℃, the time is 1.8-2.2h, the carrier diameter is 100-200nm, and the enzyme loading is greater than 150mg / g carrier; The second step of pectinase treatment: the enzyme activity is 28-32U / g fiber, the pH is 4.6-5.0, the temperature is 48-52℃, and the time is 1.8-2.2h.

7. The process for the preparation of Lyocell pulp from bamboo and wood fluff as claimed in claim 1 wherein, The wood pulp fiber after the biological enzyme deep purification meets: ​ The residual lipid content is less than 0.2wt%, the pectin removal rate is greater than 98%, and the fiber polymerization degree is greater than 1200.

8. The process for the preparation of Lyocell pulp from bamboo and woodflour as claimed in claim 1, wherein the said process is characterized by, The dispersant system comprises: Sodium polyacrylate: molecular weight 8000-12000, added amount 0.08-0.12wt%, providing Zeta potential of-35mV or more electrostatic repulsion; Hydroxyethyl cellulose: degree of substitution 0.8-1.2, added amount 0.04-0.06wt%, solution viscosity adjusted to 150-250mPa·s.

9. The process for the preparation of Lyocell pulp from bamboo and wood wool as claimed in claim 1 wherein, In the mixing treatment step: ​ The dry weight ratio of bamboo pulp to wood pulp is 58-62:38-42; Homogenization conditions: stirring speed 350-450rpm, time 40-50min, temperature 45-55℃; The lyocell pulp forming step comprises: Washing: using a countercurrent diffusion washing machine, water consumption is less than 20m³ / ton of pulp; Dewatering: double-net press machine line pressure 80-100kN / m, pulp dryness is greater than 35%; Drying: flash drying tower inlet air temperature 180-220℃, outlet pulp moisture content less than 10%.

10. A bamboo and wood fluff mixed lyocell pulp prepared by any one of the processes of claims 1 to 9, characterized by, The lyocell pulp meets: The α-cellulose content is greater than 93wt%, the ash content is less than 0.25wt%, and the residual lipid content is less than 0.3wt%. The lyocell pulp meets: