Wood fiber microfibril and method for preparing the same

Abstract

The application discloses lignocellulose microfibril and a preparation method thereof, and comprises the following steps: 1) performing enzyme treatment on agricultural straw; 2) performing alkali activation treatment on the agricultural straw treated in the step 1); and 3) performing mechanical grinding on the agricultural straw treated in the step 2) to obtain lignocellulose microfibril. The application directly performs microfibril treatment on the whole component of the agricultural straw lignocellulose by combining the biological treatment, the alkali activation treatment and the mechanical grinding with different gradient concentrations, has high production efficiency, avoids the cost increase and the environmental load caused by the component separation of the agricultural waste in the traditional method, and the prepared lignocellulose microfibril has both the mechanical strength of cellulose and the thermosetting property of lignin, and can be applied in the fields of thermosetting resin, plastic blown film and hot-press forming and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a lignocellulose microfibril and a preparation method thereof, and belongs to the field of materials. BACKGROUND

[0002] Lignocellulose is the most abundant biomass in nature. It usually exists in the form of a complex of cellulose, lignin and hemicellulose through covalent and non-covalent bonds. In the plant cell wall, long cellulose chains are combined in a certain way to form sub-elementary fibrils with a size of 1 nm, which are further aggregated into elementary fibrils, and finally, four 3.5 nm elementary fibrils form a microfibril with a diameter of 25 nm and a length of about 30 nm. Since the microfibril is the most basic structural unit of the cell wall skeleton material, and hemicellulose and lignin are the "filler" and "adhesive" between the microfibrils, the microfibril structure is not stable, and after chemical treatment to dissolve lignin, 12 nm microfibrils can be separated. In the current biomass utilization process, lignin is usually dissolved by chemical agents to obtain cellulose, so as to be used in a specific way. However, this process has problems such as high energy consumption, low yield, and serious pollution.

[0003] Agricultural straw waste has a large output, but the output value is very low. This is because the component content of the straw waste is complex, the chemical cooking efficiency is low, and the recovery cost is high. Therefore, the resource utilization of agricultural straw has become an important economic and social problem. Compared with wood lignocellulose, agricultural straw lignocellulose has a short growth period and weak binding force between each other. This makes it possible to obtain lignin-adhered microfibrils by mechanically and physically treating agricultural straw.

[0004] Such lignin-adhered microfibrils are called lignocellulose microfibrils, which are a kind of nanofiber materials. Since the nanomaterial has both the aromatic ring structure of lignin and the glucose chain structure of cellulose, it not only retains the excellent performance of traditional nanofiber materials, but also has special performance different from them. For example, good thermosetting, amphiphilic and cross-linking flexibility characteristics, which make it expected to be applied in the fields of drug release, intelligent response gel, polymer material enhancer, dialysis filter membrane, etc.

[0005] Therefore, in recent years, domestic and foreign nanofiber material researchers have also carried out certain research work on the preparation and application of the material, but there are still many problems in its industrialization road, which can be summarized as the following three points: 1) The raw materials are mostly concentrated in wood fibers, which are difficult to handle and have high energy consumption; 2) Although the preparation of nanofibers has a history of nearly thirty years, the preparation equipment still relies on a high-pressure homogenizer to act on the fibers, and the original design of the high-pressure homogenizer is not intended to serve the fiber grinding, so the lignin particles with strong adhesion will often block the homogenization hole, which greatly affects the continuous production of wood fiber microfilaments, and the energy consumption of pure mechanical grinding is also huge; 3) The microfibrillation process of wood fiber often needs to be carried out in a water-swollen state, and as the grinding degree deepens, the viscosity of the slurry system increases, and the water content increases, so the maximum solid content of the obtained product is only 1%~4%, which undoubtedly increases the transportation cost or evaporation energy consumption. SUMMARY

[0006] The purpose of the present application is to provide a preparation method for continuously producing stable wood fiber microfilaments with energy saving, using agricultural straw waste as raw material. The method first uses biological enzyme treatment to reduce the size of wood fibers and fully swell them, then uses alkali activation treatment to deprotonate the wood fibers and weaken the hydrogen bond between them, uses a high-concentration mill to reduce the length of the wood fibers, then uses a medium-concentration mill to separate and fibrillate the wood fibers, and then sends the slurry into a colloid mill for high-speed low-concentration fine grinding to obtain uniform wood fiber microfilaments. During mechanical grinding, organic macromolecules or inorganic nanoparticles are added to stabilize the wood fiber microfilament particles, so as to achieve the purposes of energy saving and drying and dispersion. The present application provides a preparation method for agricultural straw wood fiber microfilaments, which has the characteristics of continuous production process, high yield, small environmental load, low cost, various product types and stable quality, and can effectively solve the problems of high-value utilization of agricultural straw waste and production of amphiphilic wood fiber nanomaterials.

[0007] According to one aspect of the present application, a preparation method for agricultural straw microfilament is provided, which has the characteristics of continuous production process, high yield, small environmental load, low cost, various product types and stable quality, and can effectively solve the problems of high-value utilization of agricultural straw waste and production of amphiphilic wood fiber nanomaterials.

[0008] The preparation method for agricultural straw microfilament, comprising the following steps:

[0009] 1) Enzyme treatment of agricultural straw;

[0010] 2) Alkali activation treatment of the agricultural straw treated in step 1);

[0011] 3) mechanically grinding the agricultural straw treated in step 2) to obtain wood fiber filaments.

[0012] Optionally, in step 3), the mechanical grinding is specifically at least one selected from a high consistency refining, a medium consistency refining and a fine refining, wherein the refining consistency of the high consistency refining > the refining consistency of the medium consistency refining > the refining consistency of the fine refining.

[0013] Optionally, the refining consistency of the high consistency refining is 25-35wt%, the refining temperature is 80-140℃, the knife gap is 0.20-0.30mm, the standard rotation speed is 1500rpm, the inlet pressure is 1.5-4.0bar, and the outlet pressure is 3.0-7.0bar.

[0014] Optionally, the refining consistency of the high consistency refining is selected from any value or a range value between two values selected from 25wt%, 27.5wt%, 30wt%, 32.5wt%, 35wt%.

[0015] Optionally, the refining temperature of the high consistency refining is selected from any value or a range value between two values selected from 80℃, 100℃, 120℃, 140℃.

[0016] Optionally, the knife gap of the high consistency refining is selected from any value or a range value between two values selected from 0.20mm, 0.22mm, 0.25mm, 0.27mm, 0.30mm.

[0017] Optionally, the inlet pressure of the high consistency refining is selected from any value or a range value between two values selected from 1.5bar, 2.0bar, 2.5bar, 3.0bar, 4.0bar.

[0018] Optionally, the outlet pressure of the high consistency refining is selected from any value or a range value between two values selected from 3.0bar, 4.0bar, 5.0bar, 6.0bar, 7.0bar.

[0019] Optionally, the high consistency refining is further followed by a latent heat removal treatment.

[0020] Optionally, the refining consistency of the medium consistency refining is 10-25wt%, the refining temperature is 100-140℃, the knife gap is 0.10-0.20mm, the standard rotation speed is 1500rpm, the inlet pressure is 1.5-4.0bar, and the outlet pressure is 5.0-7.0bar.

[0021] Optionally, the refining consistency of the medium consistency refining is selected from any value or a range value between two values selected from 10wt%, 12.5wt%, 15wt%, 20wt%, 25wt%.

[0022] Optionally, the refining temperature of the two-stage high consistency refiner is selected from any value or a range between two values of 100℃, 110℃, 120℃, 130℃, 140℃.

[0023] Optionally, the knife gap of the two-stage high consistency refiner is selected from any value or a range between two values of 0.10mm, 0.12mm, 0.15mm, 0.17mm, 0.20mm.

[0024] Optionally, the inlet pressure of the two-stage high consistency refiner is selected from any value or a range between two values of 1.5bar, 2.0bar, 2.5bar, 3.0bar, 4.0bar.

[0025] Optionally, the outlet pressure of the one-stage high consistency refiner is selected from any value or a range between two values of 5.0bar, 6.0bar, 7.0bar.

[0026] Optionally, the refining consistency of the three-stage refiner is 4-10wt%, the rotational speed is 9000-14000rpm, the inlet pressure is 12-13bar, and the number of circulation refining is 5-10, wherein the number of first-stage circulation refining is 1-5, and the number of second-stage circulation refining is 6-10.

[0027] Optionally, the refining consistency of the three-stage refiner is selected from any value or a range between two values of 4wt%, 6wt%, 8wt%, 10wt%.

[0028] Optionally, the rotational speed of the three-stage refiner is selected from any value or a range between two values of 9000rpm, 11000rpm, 12000rpm, 14000rpm.

[0029] Optionally, the inlet pressure of the three-stage refiner is selected from any value or a range between two values of 12bar, 12.5bar, 13bar.

[0030] Optionally, the number of circulation refining of the three-stage refiner is selected from any value of 5, 6, 7, 8, 9, 10.

[0031] Optionally, organic macromolecules or inorganic nanoparticles are added in the process of the three-stage refiner.

[0032] Optionally, in the first-stage circulation refining, 0.5wt%-1.0wt% of organic macromolecules with a molecular weight of 8000-10000 or 0.5wt%-1.0wt% of inorganic nanoparticles with a particle size of 0.5-45μm are added relative to the mass of the absolute dry material.

[0033] Optionally, during the second stage of cyclic fine grinding, 1.0wt% to 2.0wt% of organic polymers with a molecular weight of 2000 to 4000 or 1.0wt% to 2.0wt% of inorganic nanoparticles with a particle size of 0.5 to 15 μm are added relative to the oven-dry material mass.

[0034] Optionally, during the first stage of cyclic fine grinding, 0.5wt% to 1.0wt% of organic polymers with a molecular weight of 8000 to 10000 or 0.5wt% to 1.0wt% of inorganic nanoparticles with a particle size of 0.5 to 45 μm may be added in any of the third, fourth, or fifth cyclic fine grinding cycles relative to the oven-dry material mass.

[0035] During the second stage of cyclic fine grinding, 1.0wt% to 2.0wt% of organic polymers with a molecular weight of 2000 to 4000 or 1.0wt% to 2.0wt% of inorganic nanoparticles with a particle size of 0.5 to 15μm can be added relative to the dry mass of the material before the sixth cyclic fine grinding.

[0036] Optionally, the organic polymer is polyethylene glycol, and the molecular weight of the polyethylene glycol is 600 to 20,000;

[0037] Optionally, the inorganic nanoparticles are selected from at least one of heavy calcium carbonate and light calcium carbonate.

[0038] Optionally, the inorganic nanoparticles have a particle size of 0.5–45 μm.

[0039] Optionally, the enzyme used for enzyme treatment is selected from at least one of endoglucanase, exoglucanase, and β-glucosidase.

[0040] Optionally, the alkali used for alkali activation treatment is selected from at least one of sodium hydroxide, sodium bicarbonate, and sodium carbonate.

[0041] Optionally, the agricultural straw is selected from at least one of corn straw, rice straw, wheat straw, rice husk, cotton straw, tobacco straw, sugarcane bagasse, and grape pruning.

[0042] Optionally, the process parameters for the enzyme treatment are: reaction pH of 5.6 to 6.6, reaction temperature of 45 to 60°C, reaction time of 10 to 20 h, and relative dry enzyme dosage of 10 U / g to 50 U / g.

[0043] Optionally, the pH of the enzyme treatment reaction is selected from any value of 5.5, 5.8, 6.0, 6.4, 6.6 or a range between two values.

[0044] Optionally, the reaction temperature for the enzyme treatment is selected from any value or a range between two of 45°C, 47°C, 50°C, 55°C, and 60°C.

[0045] Optionally, the reaction time for the enzyme treatment is selected from any value of 10h, 12h, 15h, 17h, 20h or a range between two values.

[0046] Optionally, the relative amount of enzyme used for enzyme treatment is selected from any value of 10 U / g, 30 U / g, 50 U / g, or a range between two values.

[0047] Optionally, the process parameters for the alkali activation treatment are: alkali dosage of 30wt% to 35wt%, reaction temperature of 30 to 36℃, and reaction time of 30 to 60 min.

[0048] Optionally, the amount of alkali used in the alkali activation treatment is selected from any value of 5wt%, 15wt%, 25wt%, 40wt%, 50wt%, or a range between two values.

[0049] Optionally, the reaction temperature for the alkali activation treatment is selected from any value of 30°C, 32°C, 34°C, or 36°C, or a range between two values.

[0050] Optionally, the reaction time for the alkali activation treatment is selected from any value among 30 min, 40 min, 50 min, and 60 min, or a range between two values.

[0051] According to another aspect of this application, a wood fiber microfiber is provided, wherein the width of the wood fiber microfiber is 100-500 nm and the length is 1-10 μm, and the solid dried particles of the wood fiber microfiber have redispersibility.

[0052] Optionally, the solid content of the wood fiber microfibrils is 4 to 100 wt%.

[0053] As one specific implementation method, the specific steps are as follows:

[0054] A method and manufacturing process for preparing lignin-carbohydrate complex microfibrils with a length of 1–100 μm and a width of 100–500 nm: The preparation method includes...

[0055] 1) Raw materials and chemicals required for the preparation of micron-sized wood fiber filaments;

[0056] (ii) The preparation process of micron-sized wood fiber filaments adopts a combination of biological treatment, chemical pretreatment and mechanical high, medium and low concentration grinding.

[0057] (iii) The final micron-sized wood fiber filament product has a solid content of 10% or less in the aqueous phase system and can be dried and redispersed with the help of organic and inorganic additives.

[0058] The specific method and process steps are as follows:

[0059] 1) Raw materials and biological and chemical reagents required for the preparation of micron-sized wood fiber filaments

[0060] 1) Applicable types of agricultural straw waste

[0061] Including: corn stalks, wheat stalks, rice husks, rice straw, cotton stalks, tobacco stalks, sugarcane bagasse, and grape pruning branches.

[0062] 2) Types of biological and chemical products used

[0063] Includes: cellulase (including one or more of endoglucanase, exoglucanase, and β-glucosidase), acetic acid, sodium hydroxide, sodium bicarbonate, sodium carbonate, calcium carbonate, and polyethylene glycol.

[0064] (ii) Preparation of micron-sized wood fiber filament particles

[0065] 1) Material preparation

[0066] From the raw materials described in section 1) that come from farmland and are to be processed by a straw crusher with a length of 1cm, one type is selected as the raw material. The raw material is then ground using a grinding equipment with the following grinding parameters: power: 2.2kw~3kw, hammer blades: 12 blades, rotation speed: 4600r / min, machine weight: 100kg, and overall dimensions: 900mm*700mm*750mm. The ground product particles pass through a 20-100 mesh sieve.

[0067] 2) Bioenzyme treatment

[0068] The milled wood fiber material is transferred to a glass reactor and adjusted to the specified pulp concentration using slightly acidic industrial water. The pulp system is continuously heated and stirred using a stirrer and heating device. After the pulp system stabilizes for 10-30 minutes, a certain amount of cellulase is added to initiate the hydrolysis reaction. During this process, the pH value can be adjusted using acetic acid. After the reaction is complete, the system is separated into solid and liquid phases using a vacuum filtration device. The resulting solid fiber is transferred to the next process, while the filtrate is recycled by mixing it with fresh enzyme solution.

[0069] Enzymatic hydrolysis process parameters:

[0070] Reaction slurry concentration: 1wt%~5wt%

[0071] Stirring speed: Low speed is controlled between 10 r / min and 200 r / min, and high speed is controlled between 200 r / min and 1000 r / min.

[0072] Reaction pH: 5.6–6.6

[0073] Reaction temperature: 45℃~60℃

[0074] Enzyme dosage: 10U / g~50U / g (relative to oven-dry material),

[0075] Reaction time: 10h~20h

[0076] Dehydrated dryness: 30wt%~40wt%

[0077] Total enzyme activity loss rate: 40%–50%;

[0078] Reaction equipment information:

[0079] Reaction vessel: Explosion-proof 100L double-layer glass reactor, model: PRG-100, manufacturer: Nantong Pury Technology Instrument Co., Ltd.;

[0080] Filtration device: Circulating water type multi-purpose vacuum filtration pump, model: SHB-Ⅲ, Zhengzhou Great Wall Science & Industry Co., Ltd.

[0081] 3) Alkali activation treatment

[0082] The enzyme-hydrolyzed wood fiber material with a certain degree of dryness is transferred to a kneader, a certain amount of alkali is sprayed evenly, and kneading and mixing are continued until the reaction is complete. The material is then transferred to the next process.

[0083] Alkalization reaction process parameters:

[0084] Alkali dosage: 5wt%~20wt% (relative to oven-dry material),

[0085] Reaction slurry concentration: 30wt%~36wt% (aqueous phase system)

[0086] Reaction temperature: 30℃~35℃

[0087] Reaction time: 30 min to 60 min;

[0088] Reaction equipment information:

[0089] Vertical kneading machine model: LRN3, production capacity: 4-7 t / h, motor power: 90kw, Luoyang Guoao Heavy Industry Machinery Co., Ltd.

[0090] 4) One-stage pressurized high-concentration mill

[0091] The experimental pulping equipment is a double-disc pulper. The inner disc is a moving disc connected to the rotating shaft, and the outer disc is a fixed disc. The high-concentration pulp after alkalization is axially fed into the center of the grinding zone via a screw conveyor and discharged outward from the disc-grinding gap into the spray line. The pulp is collected and transferred in the spray line.

[0092] In industrial production, a three-disc, double-grinding mill can be selected as the grinding equipment. The middle disc is a moving disc connected to the rotating shaft, and the two sides are fixed discs. The slurry enters the center of the grinding zone axially from the two side inlets, and is discharged outward from the disc grinding gap to the spray pipeline. The slurry is collected in the spray pipeline and transferred to the anti-submersion tank.

[0093] The purpose of this high-consistency pulping process is to generate heat and steam through the friction between fibers and between fibers and the pulping disc, softening the fibers and making them easier to peel and separate. At the same time, it allows the alkali reaction to work synergistically with mechanical shearing.

[0094] High-consistency pulping process parameters:

[0095] Pulp concentration: 25%–35%,

[0096] Pulping temperature: 140℃

[0097] Tool clearance: 0.20~0.30mm,

[0098] Standard speed: 1500 rpm

[0099] Inlet pressure: 1.5~4.0 bar

[0100] Export pressure: Max: 7.0 bar;

[0101] Equipment information parameters:

[0102] Double-disc refiner, model: 2500-Ⅱ, spindle speed: 3000rpm, manufacturer: KRK Corporation, Japan.

[0103] 5) Eliminate potential

[0104] After high-consistency pulping, the pulp exists in a state known as the latent state. This latent state is caused by the bending and twisting of wood fibers during the pulping process due to thermal and mechanical stress. If cooled quickly, the bending and twisting of the fibers will become fixed, resulting in a loss of elasticity and some strength properties, and it will also hinder the subsequent splitting of the wood fiber bundles. Therefore, after high-consistency pulping, latent state must be eliminated to remove this latent state and maintain the proper strength properties of the fibers.

[0105] Process parameters:

[0106] Concentration for stirring: 4%–7%,

[0107] De-flammation temperature: 70℃

[0108] Stirring speed: 500–1000 rpm

[0109] Dissipation time: 30 minutes;

[0110] 6) Slurry washing

[0111] After the slurry has been dewatered, it will be transferred to a plate and frame filter press for washing and dewatering. The resulting washing waste liquid will be recycled and reused, while the cleaned slurry will be transferred to the next process.

[0112] 7) Second-stage medium-thickness pulping

[0113] The slurry transferred from the washing equipment is then fed into a dual-disc mill at a certain concentration for medium-consistency grinding. After grinding, the slurry is collected in a spray line and transferred to the next process.

[0114] Two-stage medium-consistency pulping process parameters:

[0115] Pulp concentration: 10%–25%,

[0116] Pulping temperature: 140℃

[0117] Tool clearance: 0.10~0.20mm,

[0118] Standard speed: 1500 rpm

[0119] Inlet pressure: 1.5~4.0 bar

[0120] Export pressure: Max: 7.0 bar;

[0121] Equipment information parameters:

[0122] Double-disc refiner, model: 2500-Ⅱ, spindle speed: 3000rpm, manufacturer: KRK Corporation, Japan.

[0123] 8) Three-stage low-concentration fine grinding

[0124] The slurry from the second-stage medium-consistency grinding process is sent to a colloid mill for circulating low-consistency grinding. Once the slurry viscosity increases and it becomes gel-like, it is removed from the mill and transferred to a drying device.

[0125] In order to obtain wood fiber filament particles with different activities, and to save energy and prevent particle agglomeration, different proportions of organic or inorganic additives need to be added sequentially during the three-stage low-concentration fine grinding process to stabilize the wood fiber filament particles and prevent flocculation in order to obtain a colloidal product.

[0126] Process parameters:

[0127] Pulp concentration: 4%–10%,

[0128] Speed: 9000~14000rpm

[0129] Inlet pressure: 12-13 bar

[0130] Number of grinding cycles: 5-10 times

[0131] Methods for adding organic polymer additives:

[0132] When the grinding cycle reaches the third stage, add 0.5% to 1.0 wt% of polyethylene glycol with a molecular weight of 8000 to 10000 relative to the oven-dry material.

[0133] After five grinding cycles, add 1.0% to 2.0 wt% of polyethylene glycol with a molecular weight of 2000 to 4000 relative to the oven-dry material.

[0134] Inorganic additives addition method:

[0135] When the grinding cycle reaches the third stage, add 0.5% to 1.0% of heavy calcium carbonate with a particle size of 0.5 to 45 μm relative to the oven-dry material mass.

[0136] After five grinding cycles, add 1.0%–2.0% (by weight of the oven-dry material) of light calcium carbonate with a particle size of 0.5–15 μm.

[0137] Equipment information parameters:

[0138] Inline high-shear colloid mill, model: CM2000 / 4, power 2.2KW, speed 0~14000rpm, linear speed 0~44m / s, voltage 380V, machine output 0~700 liters / hour (water), weight 45KG, dimensions (LWH 450X250X350)mm, manufacturer: Shanghai Yiken Machinery Equipment Co., Ltd.

[0139] (iii) Drying and dehydration of micron-sized wood fiber filaments

[0140] The colloidal agricultural waste wood fiber filaments obtained from three stages of low-concentration fine grinding are transferred to a large-scale freeze-drying equipment to finally obtain redispersible solid micron-sized wood fiber filaments.

[0141] The beneficial effects that this application can produce include:

[0142] 1) The preparation method provided in this application can achieve continuous production and has good prospects for industrialization;

[0143] 2) The preparation method provided in this application directly processes and utilizes all components of agricultural straw waste, thus avoiding the waste of biomass resources;

[0144] 3) The preparation method provided in this application uses a combination of biological treatment, chemical pretreatment and mechanical high, medium and low concentration grinding to directly prepare wood fiber microfibers, which improves the problems of high cost, high energy consumption and large environmental impact caused by the traditional chemical method of separating wood fiber into three components.

[0145] 4) The wood fiber microfibers provided in this application have uniform fiber size distribution, stable quality, and can be dehydrated and redispersed. They are a high value-added product with a wide range of applications. Attached Figure Description

[0146] Figure 1 This is a process flow diagram of the preparation of wood fiber microfibers #1 in Example 1 of this application;

[0147] Figure 2 Flowcharts of the process for preparing granular wood fiber microfibers #2 and #3 in Examples 2 and 3 of this application;

[0148] Figure 3 This is a transmission electron microscope image of the wood fiber microfibrils #1 prepared in Example 1 of this application;

[0149] Figure 4 Figure A shows the aqueous suspension of wood fiber microfibers #1 prepared in Example 1 of this application, and Figure B shows the solid appearance of wood fiber microfibers #2 prepared in Example 2 or 3 of this application.

[0150] Figure 5 This is a particle size distribution diagram of the wood fiber microfibers #1 prepared in Example 1 of this application;

[0151] Figure 6 FTIR test of the wood fiber microfibers #1 prepared in Example 1 of this application. Detailed Implementation

[0152] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0153] Unless otherwise specified, the raw materials, enzymes and alkalis used in the embodiments of this application were all purchased commercially.

[0154] The analysis method in the embodiments of this application is as follows:

[0155] Transmission electron microscopy (TEM) was used to analyze wood fiber microfibrils #1.

[0156] Fourier transform infrared spectroscopy (TENSOR27) was used to test the wood fiber microfibrils #1.

[0157] In this embodiment, the relevant calculation formula is as follows:

[0158] Enzyme activity loss rate (%) = (Enzyme activity before hydrolysis - Enzyme activity after hydrolysis) / Enzyme activity before hydrolysis * 100%;

[0159] Wood fiber microfiber yield (%) = Wood fiber microfiber product (dry weight, g) / Agricultural straw raw material (dry weight, g).

[0160] Implementation Case 1

[0161] A method for preparing microfibers from corn stalks includes: 1) mechanical grinding of the stalks; 2) enzyme treatment; 3) alkali activation; 4) a first-stage high-concentration grinding; 5) a second-stage medium-concentration grinding; 6) desulfurization; 7) slurry washing; 8) a third-stage low-concentration fine grinding; and 9) freeze-drying dehydration. The process flow diagram is shown below. Figure 1 As shown, the specific operation is as follows:

[0162] 1) Mechanical grinding of straw

[0163] 1-1 Raw materials for preparing microfibrillated fibers

[0164] This implementation case uses corn stalk fragments with a length of 1cm, processed by a straw crusher, from Gaizhou, Liaoning Province, as raw material;

[0165] 1-2 Mechanical grinding

[0166] Weigh 20kg of absolutely dry corn stalk fragments and put them into a grinding equipment to grind the stalk fragments. The grinding parameters are as follows: power: 3kw, hammer blades: 12 blades, speed: 4600r / min, machine weight: 100kg, external dimensions: 900mm*700mm*750mm. The slurry after grinding is passed through a 100-mesh sieve.

[0167] 2) Bioenzyme treatment

[0168] 2-1 Enzyme Types

[0169] In this embodiment, commercially available powdered solid cellulase SUKACell PW200, which is composed of a mixture of endoglucanase, exoglucanase and β-glucosidase, was selected. Its enzyme activity is 1303 U / g (for solid cellulase).

[0170] 2-2 Enzyme Treatment

[0171] 15 kg of oven-dried material was transferred to an enzyme-treated glass reactor. The slurry concentration was adjusted to 5 wt% with tap water. The slurry system was continuously stirred and mixed using the reactor, which was equipped with a stirrer and heating device. In this embodiment, the high-speed stirring was controlled at 500 r / min, the reaction temperature at 50℃, and the pH value at 6. After the slurry system was uniformly mixed and stabilized for 5 minutes, cellulase was added to the slurry system. The enzyme dosage in this embodiment was designed to be 39 U / g (for oven-dried material), and the reaction time was designed to be 10 h. After the cellulase-slurry system reaction was completed, the slurry system was transferred to a vacuum filtration device for solid-liquid phase separation. The obtained solid phase was the enzyme-treated lignocellulose, and the liquid phase was the enzyme hydrolysate, whose main components included glucose monosaccharide, cellobiose, fiber fragments, and cellulase complex. The obtained solid phase was transferred to the next process, while the filtrate was remixed with fresh enzyme solution for recycling.

[0172] The following detection methods were used to test the quality of enzyme-treated lignocellulose:

[0173] a. Slurry yield: The yield is 92% after weighing the obtained wet slurry and converting it to the slurry dryness.

[0174] b. Enzyme activity assay: See national standard (GB / T 23881-2009).

[0175] Measurement results:

[0176]

[0177] 3) Alkali activation treatment

[0178] 15 kg of oven-dry enzymatically hydrolyzed lignocellulose was transferred to a kneader and 35 kg of 2 wt% NaOH alkaline solution was sprayed evenly. The mixture was kneaded and mixed evenly at 30°C until the pulp consistency was 30 wt%. After reacting for 30 minutes, the mixture was transferred to the next process.

[0179] 4) One-stage pressurized high-concentration mill

[0180] The high-concentration slurry with a solid content of 30wt% after alkali activation treatment is axially conveyed to the center of the grinding zone via a screw conveyor. The pressure at the inlet is 1.5 bar, the grinding temperature in the grinding zone is 140℃, the disc mill cutter gap is adjusted to 0.20 mm, and the rotation speed is 1500 rpm. After the slurry is discharged from the disc mill gap into the discharge pipeline, the outlet pressure is 3.0 bar. The slurry is diluted with water in the discharge pipeline and then enters the demineralization tank together with the slurry.

[0181] 5) Eliminate potential

[0182] Add water to the slurry from the high-concentration pan to adjust the concentration to 10%, keep the temperature at 70℃, and stir at 1000 rpm for 30 minutes.

[0183] 6) Slurry washing

[0184] The slurry from the dewatering tank is washed and dewatered using a plate and frame filter press until the solid content is 20 wt%.

[0185] 7) Second-stage medium-thickness pulping

[0186] A medium-concentration slurry with a solid content of 20 wt% is axially conveyed to the center of the grinding zone via a screw conveyor. The temperature at the center of the grinding zone is 140℃, the pressure at the inlet is 2.0 bar, the gap between the disc mill cutters is adjusted to 0.10 mm, the rotation speed is 1500 rpm, and the pressure at the outlet is 5.0 bar.

[0187] 8) Three-stage low-concentration fine grinding

[0188] The slurry from the second-stage medium-concentration grinding process is transferred to a colloid mill for circulating low-concentration grinding. The inlet pressure is 13 bar, the slurry concentration is maintained at 10 wt%, and the colloid mill speed is 14000 rpm. After six cycles, the slurry viscosity increases and the product becomes colloidal, which is the corn stalk wood fiber microfibrillated filament gel, labeled as #1 wood fiber microfibrillated filament.

[0189] The prepared lignocellulose microfibrils were labeled as sample #1, with a yield of 70.4%, a cellulose content of 44 wt%, a lignin content of 15.8 wt%, and a hemicellulose content of 17.1 wt%.

[0190] Electron microscopic morphology observation of wood fiber microfibrils #1

[0191] Figure 3 TEM images of the wood fiber microfibrils show that the prepared wood fiber microfibrils have uniform morphology and size, with a length range of about 5 μm, and the outer layer of the cellulose fiber is wrapped with lignin.

[0192] Suspension of wood fiber microfibers #1

[0193] Figure 4 As can be seen from Figure A, the suspension and viscosity of the wood fiber microfiber sample #1 after standing for one day in Example 1 did not change.

[0194] Particle size distribution test of wood fiber microfibers #1

[0195] Figure 5 The particle size distribution data of wood fiber microfibers are given. According to the statistical data, the average particle size distribution range of corn straw wood fiber microfibers in Example 1 is calculated to be 1-100 μm, with an average of 59 μm, and it maintains a normal distribution.

[0196] FTIR testing of wood fiber microfibers #1

[0197] Figure 6 FTIR analysis of corn stalk lignin fiber microfibrils was presented. The infrared spectrum showed characteristic peaks of both lignin aromatic rings and cellulose glucose rings, indicating that the obtained microfibrils are lignin-carbohydrate complexes.

[0198] Implementation Case 2:

[0199] A method for preparing redispersible corn stalk microfibers, the process flow diagram is as follows: Figure 2 As shown, its preparation method and specific operation are the same as in Example 1, except that polyethylene glycol of different molecular weights is added and freeze-drying treatment is added during the three-stage low-concentration fine grinding process. The specific operation is as follows:

[0200] Sections 1), 2), 3), 4), 5), 6), and 7) are the same as in Implementation Case 1.

[0201] 8) Three-stage low-concentration fine grinding

[0202] The slurry from the second-stage medium-consistency grinding process is transferred to a colloid mill for cyclic low-consistency grinding, maintaining a slurry concentration of 10 wt% at a mill speed of 14,000 rpm. On the third grinding cycle, 1.0 wt% of polyethylene glycol with a molecular weight of 8000 relative to the oven-dry weight of the slurry is added. After five grinding cycles, 1.0 wt% of polyethylene glycol with a molecular weight of 4000 relative to the oven-dry weight of the slurry is added. After six cycles, the slurry viscosity increases and it exhibits a colloidal product.

[0203] 9) Freeze-drying treatment

[0204] The colloidal product obtained from the three-stage low-concentration fine grinding was transferred to a large-scale freeze-drying device. After drying for 12 hours, redispersible corn stalk wood fiber microfiber filament solid particles were obtained, labeled as wood fiber filament #2. Figure 4 Figure B shows the dry state of wood fiber microfiber sample #2.

[0205] The prepared lignocellulose microfibrils were labeled as sample #2, with a yield of 65.5%, a cellulose content of 43 wt%, a lignin content of 16 wt%, and a hemicellulose content of 15 wt%.

[0206] Implementation Case 3:

[0207] A method for preparing redispersible corn stalk microfibers, the process flow diagram is as follows: Figure 2 The preparation method and specific operation shown are the same as in Example 1, except that different types of inorganic calcium carbonate are added and freeze-drying treatment is added during the three-stage low-concentration fine grinding process. The specific operation is as follows:

[0208] Sections 1), 2), 3), 4), 5), 6), and 7) are the same as in Implementation Case 1.

[0209] 8) Three-stage low-concentration fine grinding

[0210] The slurry from the second-stage medium-consistency grinding process is transferred to a colloid mill for cyclic low-consistency grinding, maintaining a slurry concentration of 10 wt% at a mill speed of 14,000 rpm. On the third grinding cycle, 1.0% of the relative dry weight of heavy calcium carbonate with a particle size of 0.5–45 μm is added. After five grinding cycles, 1.0% of the relative dry weight of light calcium carbonate with a particle size of 0.5–15 μm is added. After six cycles, the slurry viscosity increases and it exhibits a colloidal product.

[0211] 9) Freeze-drying treatment

[0212] The colloidal product obtained from three stages of low-concentration fine grinding was transferred to a large-scale freeze-drying equipment. After drying for 12 hours, redispersible corn stalk wood fiber microfiber solid particles were obtained, which were labeled as wood fiber microfiber #3.

[0213] The prepared lignocellulose microfibrils were labeled as sample #3, with a yield of 72%, a cellulose content of 44 wt%, a lignin content of 15 wt%, and a hemicellulose content of 17 wt%.

[0214] Implementation Case 4:

[0215] A method for preparing corn stalk microfibers is provided, the preparation method and specific operation of which are the same as in Example 1, except that NaOH is replaced with NaHCO3, thereby reducing the environmental burden in the preparation process.

[0216] The prepared lignocellulose microfibrils were labeled as sample #4, with a yield of 80%, a cellulose content of 44 wt%, a lignin content of 16 wt%, and a hemicellulose content of 15 wt%.

[0217] Implementation Case 5:

[0218] A method for preparing corn stalk microfibers is provided, the preparation method and specific operation of which are the same as in Example 1, except that NaOH is replaced with Na2CO3, thereby reducing the environmental burden in the preparation process.

[0219] The prepared lignocellulose microfibrils were labeled as sample #5, with a yield of 77%, a cellulose content of 40 wt%, a lignin content of 22 wt%, and a hemicellulose content of 18 wt%.

[0220] Implementation Case 6:

[0221] A method for preparing corn stalk microfibers with high particle size distribution is the same as that in Example 1, except that the two-stage medium-consistency grinding is eliminated, and the high-consistency grinding directly enters the low-consistency fine grinding.

[0222] The prepared lignocellulose microfibrils were labeled as sample #6, with a yield of 80%, a cellulose content of 40 wt%, a lignin content of 20 wt%, and a hemicellulose content of 17 wt%.

[0223] Implementation Case 7:

[0224] A method for preparing rice husk powder microfibers is the same as that in Example 1, except that the raw material is changed to rice husk powder.

[0225] The prepared lignocellulose microfibrils were labeled as sample #7, with a yield of 77%, a cellulose content of 28.4 wt%, a lignin content of 23 wt%, and a hemicellulose content of 13 wt%.

[0226] Implementation Case 8:

[0227] A method for preparing wheat straw microfibers is provided, the preparation method and specific operation of which are the same as in Example 1, except that the raw material is changed to wheat straw:

[0228] The prepared lignocellulose microfibrils were labeled as sample #8, with a yield of 80%, a cellulose content of 34.4 wt%, a lignin content of 22 wt%, and a hemicellulose content of 19 wt%.

[0229] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing microfibrils from agricultural straw, characterized in that, Includes the following steps: 1) Enzyme treatment of agricultural straw; 2) The agricultural straw treated in step 1) is subjected to alkali activation treatment; 3) The agricultural straw processed in step 2) is mechanically ground to obtain wood fiber filaments; in step 3), the mechanical grinding specifically includes a high-concentration grinding stage, a medium-concentration grinding stage, and a fine grinding stage, wherein the pulp concentration of the high-concentration grinding stage is greater than that of the medium-concentration grinding stage and the fine grinding stage. The number of cycles for the three-stage fine grinding is 5 to 10. During the three-stage fine grinding process, organic polymers or inorganic nanoparticles are added, and the organic polymer is polyethylene glycol. The process parameters for the enzyme treatment are as follows: reaction pH is 5.6~6.6, reaction temperature is 45~60℃, reaction time is 10~20h, and the relative dry dosage of enzyme is 10 U / g~50 U / g. The alkali used for alkali activation is selected from at least one of sodium hydroxide, sodium bicarbonate and sodium carbonate. The process parameters for the alkali activation treatment are: alkali dosage of 5wt%~20wt%, reaction temperature of 30~36℃, and reaction time of 30~60min.

2. The preparation method according to claim 1, characterized in that, The high-consistency mill has a slurry concentration of 25~35wt%, a slurry temperature of 80~140℃, a tool gap of 0.20~0.30mm, a standard rotation speed of 1500rpm, an inlet pressure of 1.5~4.0bar, and an outlet pressure of 3.0~7.0bar. The high-consistency mill section requires a de-emergence treatment of the grinding pulp after the grinding process. The slurry concentration of the second-stage thick mill is 10~25wt%, the slurry temperature is 100~140℃, the tool gap is 0.10~0.20mm, the standard speed is 1500rpm, the inlet pressure is 1.5~4.0bar, and the outlet pressure is 5.0~7.0bar. The slurry concentration for the three-stage fine grinding is 4~10wt%, the rotation speed is 9000~14000rpm, and the inlet pressure is 12~13bar.

3. The preparation method according to claim 1, characterized in that, The inorganic nanoparticles are selected from at least one of heavy calcium carbonate and light calcium carbonate.

4. The preparation method according to claim 1, characterized in that, The enzyme used in the enzyme treatment is selected from at least one of endoglucanase, exoglucanase, and β-glucosidase.

5. The preparation method according to claim 1, characterized in that, The agricultural straw is selected from at least one of the following: corn straw, rice straw, wheat straw, rice husk, cotton straw, tobacco straw, sugarcane bagasse, and grape pruning.

6. The preparation method according to claim 1, characterized in that, The first stage of cyclic fine grinding consists of 1 to 5 cycles. During the first stage of cyclic fine grinding, 0.5 wt% to 1.0 wt% of organic polymers with a molecular weight of 8,000 to 10,000 or 0.5 wt% to 1.0 wt% of inorganic nanoparticles with a particle size of 0.5 to 45 μm are added relative to the dry material mass.

7. The preparation method according to claim 1, characterized in that, The second stage of cyclic fine grinding is repeated 6 to 10 times. During the second stage of cyclic fine grinding, 1.0wt% to 2.0wt% of organic polymers with a molecular weight of 2000 to 4000 or 1.0wt% to 2.0wt% of inorganic nanoparticles with a particle size of 0.5 to 15μm are added relative to the dry material mass.

8. A type of wood fiber microfiber, characterized in that, It includes cellulose and lignin, wherein the cellulose content is 30-50 wt% and the lignin content is 15-25 wt%. The wood fiber microfibers are prepared by the preparation method according to any one of claims 1 to 7.

9. A wood fiber microfiber according to claim 8, characterized in that, The width of the wood fiber microfibrils is 100~500nm and the length is 1~10μm; The solid content of the wood fiber microfibrils is 4~100wt%.

Images