A method for preparing ultra-high aspect ratio cellulose micro-nanofibers based on plant leaf veins

Abstract

The present invention discloses a method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant leaf veins. The method comprises the following steps: extracting the plant leaf vein fiber raw material with hot water, performing solid-liquid separation, drying the plant leaf vein extraction residue, and subjecting the plant leaf vein extraction residue to oxygen-alkali cooking. The product is filtered through a 350-mesh pulp bag, and the filter residue is washed with clean water until neutral. The product is then sieved through a 0.20 mm sieve plate. The material under the sieve is the plant leaf vein fiber. Deionized water is added for stirring and dispersion. The fiber suspension is then subjected to ultrasonic and multi-stage centrifugal treatment. The micro-nano fiber suspension is freeze-dried to obtain ultra-high aspect ratio cellulose micro-nano fibers. The present invention conforms to the concept of "biomass resource utilization" and can convert plant leaf vein waste materials such as tobacco stems into biodegradable micro-nano cellulose fibers with an ultra-high aspect ratio.

Description

Technical Field

[0001] The present invention relates to the environmental and material fields of biomass resource utilization, and in particular to a method for preparing ultra-high aspect ratio micro-nano cellulose fibers by oxygen-base catalyzed plant vein fiber defibrination combined with ultrasonic etching. Background Art

[0002] Due to the decline in forest resources and the increasing consumption of lignocellulosic products, the utilization of non-wood fiber raw materials has received increasing attention. Large amounts of biomass waste, such as plant veins (such as tobacco stems, banana leaves, and pineapple leaves), are discarded, resulting in both resource waste and a range of environmental issues. Therefore, it is imperative to find appropriate resource utilization methods.

[0003] In addition, a higher aspect ratio and network entanglement are beneficial for enhancing the mechanical strength and flexibility of nanocomposites. Based on this, the preparation of high aspect ratio micro-nanofibers through cleaner, more environmentally friendly and low-energy processes will gradually become the focus of attention in this field.

[0004] Depending on the cellulose source (e.g., wheat straw, rice straw, pineapple leaves, banana stems) and the preparation method used (e.g., TEMPO-mediated oxidation, high-pressure homogenization, and acid hydrolysis), microfibers with varying morphologies and properties can be produced. Currently, the main methods for preparing microfibers and nanofibers include chemical oxidation, mechanical treatment, and a combination of pretreatment and mechanical disintegration. However, purely chemical methods are not only inefficient but also involve chemical recovery and washing processes, which are extremely difficult to recover and cause environmental pollution. Mechanical treatment methods such as high-pressure homogenization, ultrafine grinding, and extrusion to separate wood fibers eliminate these steps, but these methods are energy-intensive. Combining mechanical treatment with chemical pretreatment can reduce energy consumption but is more complex. For example, while 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) oxidation conditions are mild, residual NaClO and difficult-to-recover corrosive chemicals in the washing wastewater have significant negative environmental impacts. Therefore, developing a clean, low-energy method capable of producing microfibers with ultrahigh aspect ratios is crucial. Summary of the Invention

[0005] In order to obtain ultra-long micro-nano cellulose fibers in a cleaner and more cost-effective manner, the present invention proposes a method for preparing ultra-high aspect ratio cellulose micro-nano fibers by oxygen-alkali catalyzed fiber defibrination of plant vein fiber tissue assisted by ultrasound. Based on oxygen-alkali cooking technology, the plant vein fiber raw material is first delignified to achieve the effect of preliminary dissociation, and then assisted ultrasonic etching treatment is used to obtain ultra-high aspect ratio micrometer and nanometer-level fibers.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant vein fibers, comprising the following steps:

[0008] (1) extracting the plant vein fiber raw material with hot water, then separating the solid and liquid, and drying the plant vein extraction residue in an oven at 80°C;

[0009] (2) The plant vein extraction residue is subjected to an oxygen-alkali cooking treatment, the product is filtered with a 350-mesh pulp bag, the filter residue is washed with clean water until neutral, and then sieved with a 0.20 mm sieve plate, and the sieve residue is balanced to obtain plant vein fiber;

[0010] (3) taking the plant leaf vein fiber dried in step (2) into a beaker, then adding deionized water, and stirring the mixture in a magnetic stirrer for 12 to 48 hours to keep the cellulose in a water-swollen state;

[0011] (4) placing the cellulose expanded in step (3) in an ultrasonic disperser (SCIENTZ-1500F) equipped with an ultrasonic probe and ultrasonicating for 60 to 120 minutes;

[0012] (5) centrifuging the dispersion containing the micro-nano cellulose fibers after ultrasonication in step (4) to obtain a micro-nano fiber suspension;

[0013] (6) The micro-nano fiber suspension obtained in step (5) is allowed to stand at -18°C for more than 24 hours, and then freeze-dried to obtain ultra-high aspect ratio cellulose micro-nano fibers.

[0014] The plant vein fiber raw materials in step (1) include tobacco stems, banana leaf veins, pineapple leaf veins and the like.

[0015] The hot water extraction temperature in step (1) is 60-90° C., the extraction time is 2-8 hours, and the mass ratio of water to plant vein fiber raw material is 7:1-9:1.

[0016] The method of oxygen-alkali cooking treatment in step (2) is as follows: mixing the plant vein extraction residue, sodium hydroxide and water, and cooking for more than one stage under an oxygen atmosphere, wherein in each cooking process, the amount of sodium hydroxide added is 5-25% of the mass of the initial plant vein extraction residue, and the mass ratio of water to the initial plant vein extraction residue is 5:1-7:1; in each cooking process, the oxygen pressure of the oxygen atmosphere is 0.3-0.6 MPa, and oxygen is added 2-6 times during the cooking process, each time for 2-5 minutes; in each cooking process, the cooking temperature is 100-120°C, and the cooking time is 1-3 hours.

[0017] The mass percentage concentration of cellulose in the mixture of step (3) is 0.05-3.0wt.%.

[0018] Step (4) ultrasonic power 1000-2000W, time 60-120min (ultrasound 2s, pause 2s).

[0019] The specific process of the three-stage centrifugation in step (5) is as follows: the first stage: centrifugation at a speed of 2000-8000 r / min for 5-20 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the second stage: diluting the first gradient substrate with water, centrifuging at a speed of 2000-8000 r / min for 5-20 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the third stage: centrifuging the supernatant obtained after the first two stages of centrifugation at a speed of 2000-8000 r / min for 5-20 minutes, and finally separating to obtain a micro-nano fiber suspension.

[0020] The temperature of the cold trap for freeze drying in step (6) is less than -55°C and the vacuum degree is 1 Pa.

[0021] Compared with the prior art, the present invention has the following advantages and effects:

[0022] The present invention only uses plant leaf vein tissue of biomass waste as raw material for preparing ultra-long micro-nano cellulose fibers. After oxygen-alkali cooking, a 0.20 mm sieve plate is used to sieve out fine fibers (screened material) and incompletely cooked coarse residue (retained material). The fine fibers can be used to prepare ultra-long micro-nano cellulose fibers through auxiliary ultrasonic etching. At the same time, the coarse residue screened out can be used to prepare activated carbon with a high specific surface area, and the lignin extracted from black liquor can be used to prepare high-value functional materials such as phenolic resin.

[0023] The present invention obtains a waste-free biomass refining mode, which improves the feasibility of industrial application of the process of preparing micro-nano cellulose fibers by oxygen-base catalytic fibrillation assisted by ultrasound from tobacco stems or other similar leaf vein tissue biomass.

[0024] The ultra-long micro-nano cellulose fibers prepared by the present invention can be used to prepare film materials. Since the film materials have good mechanical properties, they can be used as reinforcing agents for biomass composite protective materials.

[0025] The present invention provides a new solution for the waste-free biomass refining model of biomass waste such as plant leaf veins, which reflects the new idea of green chemistry and is of great significance to the circular economy.

[0026] The present invention mainly prepares ultra-long micro-nano cellulose fibers by utilizing oxygen-base catalysis to defibrate plant leaf vein raw materials combined with ultrasonic etching, which can realize waste-free biorefining. The process operation is simple, the principle is feasible, the process is green and environmentally friendly, and at the same time, the preparation of ultra-long micro-nano cellulose fibers is realized, which is in line with the concept of "biomass resource utilization". BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The SEM image and diameter distribution diagram of the ultra-high aspect ratio cellulose micro-nanofiber obtained after freeze-drying in Example 1;

[0028] Figure 2 The SEM image and diameter distribution diagram of the ultra-high aspect ratio cellulose micro-nanofiber obtained after freeze-drying in Example 2;

[0029] Figure 3 The SEM image and diameter distribution diagram of the ultra-high aspect ratio cellulose micro-nanofiber obtained after freeze-drying in Example 3;

[0030] Figure 4 The SEM image and diameter distribution diagram of the ultra-high aspect ratio cellulose micro-nanofiber obtained after freeze-drying in Example 4;

[0031] Figure 5 Length characteristics of ultra-high aspect ratio cellulose micro-nanofibers obtained after freeze-drying in the examples ((a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4). DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] Example 1

[0034] A method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant vein fibers, comprising the following steps:

[0035] (1) Tobacco stem raw material pretreatment: Tobacco stems and water were added to a jacketed reactor with a mass ratio of water to tobacco stems of 9:1, the temperature was 60°C, and stirred for 8 h. Then, the solid-liquid separation was performed, and the tobacco stem extraction residue was placed in an oven at 80°C for drying;

[0036] (2) Pretreatment of tobacco stem residue: The tobacco stem extraction residue treated in step (1), sodium hydroxide and water are added to a high-pressure stainless steel cooking pot, wherein the amount of sodium hydroxide added is 25% of the mass of the tobacco stem extraction residue, the mass ratio of water to tobacco stem extraction residue is 6:1, the partial pressure of oxygen introduced is 0.5 MPa, the oxygenation time each time is 2 minutes, and oxygenation is performed 3 times during the entire cooking process. Then, the temperature is raised from room temperature to 120°C and the temperature is kept for 3 hours for cooking. The cooked slurry is filtered with a 350-mesh slurry bag, washed with clean water until neutral, and sieved with a 0.20 mm sieve plate to obtain tobacco stem fibers;

[0037] (3) Cellulose raw material pretreatment: The dried tobacco stem fibers from step (2) were weighed into a beaker, and deionized water was added to make the fiber mass concentration 0.5 wt.%, and the mixture was soaked for 48 h under stirring with a magnetic stirrer to keep the fiber in a water-swollen state;

[0038] (4) Auxiliary ultrasonic treatment of cellulose raw materials: The water-swollen fibers from step (3) were placed in an ultrasonic disperser (SCIENTZ-1500F) equipped with an ultrasonic probe. The ultrasonic conditions were as follows: ultrasonic power 2000 W, ultrasonic working time 60 min (ultrasonication 2 s, pause 2 s);

[0039] (5) The dispersion containing micro-nano cellulose fibers after ultrasonication in step (4) is subjected to three-stage centrifugation operations, specifically, the first stage: centrifugation at a speed of 8000 r / min for 10 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the second stage: diluting the first gradient substrate with water, centrifuging at a speed of 8000 r / min for 10 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the third stage: centrifuging the supernatant obtained after the first two stages of centrifugation at a speed of 8000 r / min for 10 minutes, and finally separating to obtain a micro-nano fiber suspension;

[0040] (6) The micro-nano cellulose fiber suspension obtained in step (5) was poured into a plastic beaker and then placed in a refrigerator at -18°C for 25 hours. The sample was then placed in a freeze dryer for drying, with a cold trap temperature of <-55°C and a vacuum degree of 1 Pa.

[0041] Figure 1 The SEM image and diameter distribution diagram of the micro-nano cellulose fibers obtained after freeze-drying in this example. The yield of the cellulose micro-nano fibers in this example is 56.43%. Figure 5 (a) is the length characteristic of this embodiment. It can be clearly seen from the figure that ultra-high aspect ratio micro-nano cellulose fibers were successfully separated, and most of their sizes have reached below 500 nm.

[0042] Example 2

[0043] A method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant vein fibers, comprising the following steps:

[0044] (1) Tobacco stem raw material pretreatment: Tobacco stems and water were added to a jacketed reactor with a mass ratio of water to tobacco stems of 9:1, the temperature was 60°C, and stirred for 8 h. Then, the solid-liquid separation was performed, and the tobacco stem extraction residue was placed in an oven at 80°C for drying;

[0045] (2) Pretreatment of tobacco stem residue: Tobacco stem extraction residue, sodium hydroxide and water are added to a high-pressure stainless steel cooking pot for the first stage of cooking. The amount of sodium hydroxide added is 10% of the mass of the tobacco stem extraction residue, the mass ratio of water to tobacco stem extraction residue is 7:1, the partial pressure of oxygen introduced is 0.3 MPa, and the oxygenation time is 3 minutes each time. The whole cooking process is oxygenated twice, and then the temperature is raised from room temperature to 120°C, and the heat preservation time is 2 hours for cooking, and the black liquor is squeezed out; then the second stage is carried out. Two-stage cooking, the amount of sodium hydroxide added is 5% of the mass of the plant vein extraction residue, the mass ratio of water to the plant vein extraction residue is 7:1, the partial pressure of oxygen is 0.3 MPa, the oxygenation time is 3 minutes each time, and oxygenation is repeated twice during the entire cooking process. Then, the temperature is raised from room temperature to 120°C and kept at this temperature for 1.5 hours for cooking. The cooked slurry is filtered through a 350-mesh slurry bag, then washed with clean water until neutral, and sieved through a 0.20 mm sieve plate to obtain tobacco stem fibers;

[0046] (3) Cellulose raw material pretreatment: The fiber dried in step (2) was weighed into a beaker, and then deionized water was added to make the fiber mass concentration 2.0 wt.%, and the fiber was soaked for 36 hours under stirring with a magnetic stirrer to keep the fiber in a water-swollen state;

[0047] (4) Auxiliary ultrasonic treatment of cellulose raw materials: The water-swollen fibers of step (3) were placed in an ultrasonic disperser (SCIENTZ-1500F) equipped with an ultrasonic probe. The ultrasonic conditions were as follows: ultrasonic power 1500 W, total ultrasonic working time 90 min (ultrasonication 2 s, pause 2 s);

[0048] (5) The dispersion containing micro-nano cellulose fibers after ultrasonication in step (4) is subjected to three-stage centrifugation operations, specifically, the first stage: centrifugation at a speed of 8000 r / min for 10 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the second stage: diluting the first gradient substrate with water, centrifuging at a speed of 8000 r / min for 10 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the third stage: centrifuging the supernatant obtained after the first two stages of centrifugation at a speed of 8000 r / min for 10 minutes, and finally separating to obtain a micro-nano fiber suspension;

[0049] (6) The micro-nano cellulose fiber suspension obtained in step (5) was poured into a plastic beaker and then placed in a refrigerator at -18°C for 28 hours. The sample was then placed in a freeze dryer for drying, with a cold trap temperature of <-55°C and a vacuum degree of 1 Pa.

[0050] Figure 2 The SEM image and diameter distribution diagram of the micro-nano cellulose fibers obtained after freeze-drying in this example. The yield of the cellulose micro-nano fibers in this example is 62.28%. Figure 5(b) is the length characteristic of this embodiment. It can be clearly seen from the figure that ultra-high aspect ratio micro-nano cellulose fibers were successfully separated, and most of their sizes have reached below 400 nm.

[0051] Example 3

[0052] A method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant vein fibers, comprising the following steps:

[0053] (1) Tobacco stem raw material pretreatment: Tobacco stems and water were added to a jacketed reactor with a mass ratio of water to tobacco stems of 8:1 and a temperature of 75°C. The mixture was stirred for 4 h, followed by solid-liquid separation. The tobacco stem extraction residue was dried in an oven at 80°C.

[0054] (2) Pretreatment of tobacco stem residue: Tobacco stem extraction residue, sodium hydroxide and water are added to a high-pressure stainless steel cooking pot for the first stage of cooking. The amount of sodium hydroxide added is 15% of the mass of the tobacco stem extraction residue, the mass ratio of water to tobacco stem extraction residue is 7:1, the partial pressure of oxygen introduced is 0.3 MPa, and the oxygenation time is 5 minutes each time. The whole cooking process is oxygenated twice, and then the temperature is raised from room temperature to 120°C, and the heat preservation time is 2 hours for cooking, and the black liquor is squeezed out; then the second stage is carried out. Two-stage cooking, the amount of sodium hydroxide added is 7% of the mass of the plant vein extraction residue, the mass ratio of water to the plant vein extraction residue is 7:1, the partial pressure of oxygen is 0.3 MPa, the oxygenation time is 5 minutes each time, and oxygenation is repeated twice during the entire cooking process. Then, the temperature is raised from room temperature to 120°C and kept at this temperature for 1.5 hours for cooking. The cooked slurry is filtered through a 350-mesh slurry bag, then washed with clean water until neutral, and sieved through a 0.20 mm sieve plate to obtain tobacco stem fibers;

[0055] (3) Cellulose raw material pretreatment: The fiber dried in step (2) was weighed into a beaker, and then deionized water was added to make the fiber mass concentration 1.0 wt.%, and the fiber was soaked for 24 h under stirring with a magnetic stirrer to keep the fiber in a water-swollen state;

[0056] (4) Auxiliary ultrasonic treatment of cellulose raw materials: The water-swollen fibers of step (3) were placed in an ultrasonic disperser (SCIENTZ-1500F) equipped with an ultrasonic probe. The ultrasonic conditions were as follows: ultrasonic power 2000 W, total ultrasonic working time 60 min (ultrasonication 2 s, pause 2 s);

[0057] (5) The dispersion containing micro-nano cellulose fibers after ultrasonication in step (4) is subjected to three-stage centrifugation operations, specifically, the first stage: centrifugation at a speed of 5000 r / min for 5 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the second stage: diluting the first gradient substrate with water, centrifuging at a speed of 5000 r / min for 5 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the third stage: centrifuging the supernatant obtained after the first two stages of centrifugation at a speed of 5000 r / min for 5 minutes, and finally separating to obtain a micro-nano fiber suspension;

[0058] (6) The micro-nano cellulose fiber suspension obtained in step (5) was poured into a plastic beaker and then placed in a refrigerator at -18°C for 26 hours. The sample was then placed in a freeze dryer for drying, with a cold trap temperature of <-55°C and a vacuum degree of 1 Pa.

[0059] Figure 3 The SEM image and diameter distribution diagram of the micro-nano cellulose fibers obtained after freeze-drying in this example. The yield of the cellulose micro-nano fibers in this example is 75.07%. Figure 5 (c) is the length characteristic of this embodiment. It can be clearly seen from the figure that ultra-high aspect ratio micro-nano cellulose fibers were successfully separated, and most of their sizes have reached below 250 nm.

[0060] Example 4

[0061] A method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant vein fibers, comprising the following steps:

[0062] (1) Tobacco stem raw material pretreatment: Tobacco stems and water were added to a jacketed reactor with a mass ratio of water to tobacco stems of 7:1 and a temperature of 90°C. The mixture was stirred for 2 h, followed by solid-liquid separation. The tobacco stem extraction residue was dried in an oven at 80°C.

[0063] (2) Pretreatment of tobacco stem residue: Tobacco stem extraction residue, sodium hydroxide and water are added to a high-pressure stainless steel cooking pot for the first stage of cooking. The amount of sodium hydroxide added is 15% of the mass of the tobacco stem extraction residue, the mass ratio of water to tobacco stem extraction residue is 5:1, the partial pressure of oxygen introduced is 0.6 MPa, the oxygenation time is 5 minutes each time, and oxygenation is performed 6 times during the cooking process. Then the temperature is raised from room temperature to 100°C, and the heat preservation time is 2 hours for cooking, and the black liquor is squeezed out; then the second stage of cooking is performed. The amount of sodium hydroxide added is 7% of the mass of the plant vein extraction residue, the mass ratio of water to the plant vein extraction residue is still 5:1, and the partial pressure of oxygen is 0.3 MPa , each oxygenation time is 2 minutes, and the whole cooking process is oxygenated twice, then the temperature is raised from room temperature to 110°C, and the temperature is kept for 1 hour to cook and squeeze out the black liquor; then the third cooking is carried out, the amount of sodium hydroxide added is 3% of the mass of the plant vein extraction residue, the mass ratio of water to the plant vein extraction residue is 5:1, the partial pressure of oxygen is 0.3 MPa, the oxygenation time is 2 minutes each time, and the whole cooking process is oxygenated twice, then the temperature is raised from room temperature to 110°C, and the temperature is kept for 1 hour to cook and squeeze out the black liquor, the cooked slurry is filtered with a 350-mesh pulp bag, and then washed with clean water until neutral, and sieved with a 0.20 mm size sieve plate to obtain tobacco stem fiber;

[0064] (3) Cellulose raw material pretreatment: weigh the fiber dried in step (2) into a beaker, then add deionized water to make the fiber mass concentration 0.05 wt.%, and soak it for 12 hours under stirring with a magnetic stirrer to keep the fiber in a water-swollen state;

[0065] (4) Auxiliary ultrasonic treatment of cellulose raw materials: The water-swollen fibers of step (3) were placed in an ultrasonic disperser (SCIENTZ-1500F) equipped with an ultrasonic probe. The ultrasonic conditions were as follows: ultrasonic power 1000 W, total ultrasonic working time 120 min (ultrasonication 2 s, pause 2 s);

[0066] (5) The dispersion containing micro-nano cellulose fibers after ultrasonication in step (4) is subjected to three-stage centrifugation operations, specifically, the first stage: centrifugation at a speed of 2000 r / min for 20 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the second stage: diluting the first gradient substrate with water, centrifuging at a speed of 2000 r / min for 20 minutes, and taking out the supernatant of the cellulose dispersion after the centrifugation; the third stage: centrifuging the supernatant obtained after the first two stages of centrifugation at a speed of 2000 r / min for 20 minutes, and finally separating to obtain a micro-nano fiber suspension;

[0067] (6) The micro-nano cellulose fiber suspension obtained in step (5) was poured into a plastic beaker and then placed in a refrigerator at -18°C for 24 hours. The sample was then placed in a freeze dryer for drying, with a cold trap temperature of <-55°C and a vacuum degree of 1 Pa.

[0068] Figure 4 The SEM image and diameter distribution diagram of the micro-nano cellulose fibers obtained after freeze-drying in this example. The yield of the cellulose micro-nano fibers in this example is 71.56%. Figure 5 (d) is the length characteristic of this embodiment. It can be clearly seen from the figure that ultra-high aspect ratio micro-nano cellulose fibers were successfully separated, and most of them have reached the nanometer level.

[0069] The ultra-high aspect ratio cellulose micro-nanofibers obtained by freeze-drying in Example 4 were dispersed in deionized water. The suspension was stirred and dispersed for 20 minutes and then filtered through a sand-core glass filter with a nanofiltration membrane under vacuum conditions. The resulting wet film was flattened between two glass plates overnight and air-dried. The mechanical properties of the film prepared from the resulting micro-nanofibers are shown in Table 1:

[0070] Table 1

[0071]

[0072] As can be seen from Table 1, the film material can be used as a reinforcing agent for biomass-based composite materials due to its good mechanical properties.

Claims

1. A method for preparing ultra-high aspect ratio cellulose micro-nanofibers based on plant leaf veins, characterized in that: The following steps are involved: (1) Adding water to the plant leaf veins for hot water extraction, followed by solid-liquid separation, and drying the plant leaf vein extraction residue at 80°C; the plant leaf veins are tobacco stems; (2) The plant vein extraction residue is subjected to oxygen-alkali cooking treatment, the product is filtered with a 350-mesh pulp bag, the filter residue is washed with clean water until neutral, and then sieved with a 0.20 mm sieve plate. The sieve residue is the plant vein fiber; The oxygen-alkali cooking treatment method is as follows: mixing plant vein extraction residue, sodium hydroxide, and water, and cooking in an oxygen atmosphere for more than one stage, wherein in each cooking stage, the amount of sodium hydroxide added is 5-25% of the mass of the plant vein extraction residue, and the mass ratio of water to the plant vein extraction residue is 5:1-7:1; in each cooking stage, the oxygen pressure of the oxygen atmosphere is 0.3-0.6 MPa, and oxygen is added 2-6 times during the cooking process, each time for 2-5 minutes; in each cooking stage, the cooking temperature is 100-120° C., and the cooking time is 1-3 hours; (3) Add deionized water to the plant vein fiber of step (2), soak the mixture with magnetic stirring for 12 to 48 hours, and then ultrasonicate for 60 to 120 minutes; the ultrasonic power is 1000 to 2000 W, the ultrasonic time is 60 to 120 minutes, and the ultrasonication is performed for 2 seconds and paused for 2 seconds; (4) Centrifuging the dispersion after ultrasonication in step (3) in three stages. The specific process is as follows: the first stage: centrifuging at a speed of 2000-8000 r / min for 5-20 min, and taking out the supernatant of the cellulose dispersion after the centrifugation is completed; Stage 2: Dilute the substrate from stage 1 with water and centrifuge at 2000-8000 rpm for 5-20 min. After centrifugation, remove the supernatant of the cellulose dispersion. The third stage: the supernatant obtained after the first two stages of centrifugation is centrifuged at a speed of 2000-8000 r / min for 5-20 min to finally separate and obtain the micro-nanofiber suspension; The micro-nano fiber suspension is obtained, placed at -18°C for more than 24 hours, and then freeze-dried. The cold trap temperature of the freeze-drying is less than -55°C and the vacuum degree is 1 Pa to obtain ultra-high aspect ratio cellulose micro-nano fibers.

2. The method for preparing ultra-high aspect ratio cellulose micro-nanofibers based on plant leaf veins according to claim 1, characterized in that: The hot water extraction temperature in step (1) is 60-90° C., the extraction time is 2-8 h, and the mass ratio of water to plant veins is 7:1-9:

1.

3. The method for preparing ultra-high aspect ratio cellulose micro-nano fibers based on plant leaf veins according to claim 1, characterized in that: The mass percentage concentration of cellulose in the mixture of step (3) is 0.05~3.0%.

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