阅读说明：本技术 一种三元低共熔溶剂预处理制备纳米纤维素微纤丝的方法 (Method for preparing nano-cellulose microfibrils by pretreatment of ternary eutectic solvent ) 是由 周存山 姬青华 余筱洁 张磊 涂姗姗 于 2021-02-03 设计创作，主要内容包括：本发明公开了一种三元低共熔溶剂预处理制备纳米纤维素微纤丝的方法,属于生物质纳米纤维素制备技术领域。本发明首先利用三元低共熔溶剂对木质纤维素生物质进行预处理,分离得到富含纤维素的组分；将富含纤维素的组分配置成1wt％的溶液,通过离心得到纳米纤维素悬浮液,然后通过高强度的超声处理,使纳米纤维原纤化,最后通过冷冻干燥得到纳米纤维素微纤丝。本发明制备的纳米纤维素微纤丝粒径范围在26.84-61.26nm,针对木质素的去除率达到56.28％,效果显著,且操作简单、条件温和、成本低、污染小；同时使用的低共熔溶剂对环境十分友好,符合绿色化学生产的标准,具有较好的实际应用价值。(The invention discloses a method for preparing nano-cellulose microfibrils by pretreating a ternary eutectic solvent, and belongs to the technical field of preparation of biomass nano-cellulose. Firstly, pretreating the lignocellulose biomass by using a ternary eutectic solvent, and separating to obtain a component rich in cellulose; preparing the cellulose-rich component into a 1 wt% solution, centrifuging to obtain a nanocellulose suspension, fibrillating the nanofibers by high intensity ultrasound treatment, and freeze-drying to obtain the nanocellulose microfibrils. The particle size range of the nano-cellulose microfibril prepared by the method is 26.84-61.26nm, the removal rate of lignin reaches 56.28%, the effect is obvious, the operation is simple, the condition is mild, the cost is low, and the pollution is small; meanwhile, the used eutectic solvent is very environment-friendly, meets the standard of green chemical production and has better practical application value.)

1. A method for preparing nano-cellulose microfibrils by pretreatment of a ternary eutectic solvent is characterized by comprising the following specific steps:

(1) choline chloride, lactic acid or oxalic acid and aluminum trichloride are mixed according to a certain molar ratio, and stirred at a certain temperature until uniform and transparent liquid is formed, so that a ternary eutectic solvent is obtained;

(2) weighing a certain mass of bagasse, weighing a certain mass of the ternary eutectic solvent in the step (1), uniformly mixing the bagasse and the ternary eutectic solvent, placing the mixture in a microwave digestion tank, and performing microwave digestion at a certain temperature and for a certain time; after the reaction is finished, immediately placing the mixture into an ice water bath to stop the reaction, carrying out solid-liquid separation after the reaction is stopped, diluting the liquid part with deionized water, and measuring the sugar content in the reaction solution by high performance liquid chromatography; washing the solid part with acetone water solution until the filtrate is colorless, and freeze-drying the solid component to obtain pretreated bagasse;

(3) washing the bagasse pretreated in the step (2) with deionized water for several times, diluting the bagasse with deionized water to a certain concentration, centrifuging to collect supernatant, performing ultrasonic treatment on the collected supernatant by using an ultrasonic generator equipped with a round titanium alloy probe, and finally performing freeze drying on the liquid after ultrasonic treatment to obtain the bagasse nano-cellulose microfibrils.

2. The method for preparing the nano-cellulose microfibrils by the pretreatment of the ternary eutectic solvent according to claim 1, wherein the molar ratio of choline chloride, lactic acid or oxalic acid to aluminum trichloride in the ternary eutectic solvent in the step (1) is 1: 2: 0.2.

3. the method for preparing the nano-cellulose microfibrils by the ternary eutectic solvent pretreatment of claim 1, wherein the certain temperature condition in the step (1) is 70 ℃; the stirring time for forming the uniform and transparent liquid is 4-6 h.

4. The method for preparing the nano-cellulose microfibrils by the ternary eutectic solvent pretreatment of claim 1, wherein the mass of the bagasse and the eutectic solvent in the step (2) is 1: 10.

5. the method for preparing the nano-cellulose microfibrils by the pretreatment of the ternary eutectic solvent according to claim 1, wherein the microwave temperature in the step (2) is 80-120 ℃, the microwave power is 2400W, and the microwave digestion time is 20 min.

6. The method for preparing nano-cellulose microfibrils by ternary eutectic solvent pretreatment according to claim 1, wherein the step (3) comprises diluting the nano-cellulose microfibrils with deionized water to a concentration of 1 wt%.

7. The method for preparing nano-cellulose microfibrils by ternary eutectic solvent pretreatment according to claim 1, wherein the centrifugation conditions in step (3) are as follows: centrifuge at 4000rpm for 5 min.

8. The method for preparing nano-cellulose microfibrils by ternary eutectic solvent pretreatment according to claim 1, wherein the ultrasonic frequency in step (3) is 20kHz, the output power is 650W, the on/off pulse is 2/2s, and the ultrasonic duration is 20 min.

9. The nanofibrillar cellulose microfibrils produced by the process according to any one of claims 1 to 8, wherein the particle size is in the range of 26.84-61.26 nm.

10. Use of the nanofibrils of claim 9 for paper, construction, automotive, food, cosmetics applications.

Technical Field

The invention belongs to the technical field of preparation of biomass nano-cellulose, and particularly relates to a method for preparing nano-cellulose microfibrils by pretreatment of a ternary eutectic solvent.

Background

Energy is the foundation on which human beings rely for survival and is also an important pillar for the development of modern society. At present, the over-development and the over-use of traditional fossil fuels such as coal, petroleum, natural gas and the like cause resource shortage and bring a series of environmental problems. Therefore, sustainable development of new energy has become a central focus of energy work in new times. Cellulose is one of the most widely distributed and abundant renewable resources in nature, and has the advantages of renewability, biocompatibility, degradability, no toxicity and the like required by biomaterials, and also has good mechanical properties. Based on this, cellulose has become an important raw material in conventional industries such as pulp and paper making, textiles, polymer materials, and medicines. Therefore, the efficient development and utilization of renewable resources such as cellulose is of great significance for realizing sustainable development of green economy.

Cellulose nanofibrils are nano-sized cellulose, usually made from natural cellulose by physical, chemical, biological or combined methods. The cellulose nanofibrils have a diameter of 1-100nm and a length of 50-2000nm and are a biomass material. The cellulose nanofibrils have excellent characteristics of biodegradability, high conductivity, high strength, large specific surface area, good reactivity, stability and the like, so the cellulose nanofibrils are widely applied to the fields of food, packaging, printing, buildings, cosmetics, electronic devices and the like.

The cellulose nanofibrils are mainly prepared by mechanical treatment modes such as disc grinding, superfine grinding, high-pressure homogeneous microjet and the like, and the high-speed shearing generally needs a motor which runs at a high speed to provide a power source, so that a large amount of electric energy is consumed in each mechanical treatment. Furthermore, the reagents used to chemically prepare the nanofibrils can have an adverse environmental impact. Therefore, in recent years, many researchers have used a more green solvent system to pretreat lignocellulose to reduce fiber length and weaken the binding force between fibrils in cell walls, and reduce energy consumption of mechanical treatment while ensuring green color of the pretreatment system, in order to solve the problems of high energy consumption and serious environmental pollution in the preparation process of cellulose nanofibrils.

The eutectic solvent is a eutectic mixture consisting of quaternary ammonium salt or metal salt and hydrogen bond donor. The eutectic solvent has the advantages of low vapor pressure, good solubility, low price, easy preparation, no toxicity, biocompatibility and the like, and is widely applied to the fields of organic synthesis, metal electrodeposition, functional material synthesis, separation and the like. The eutectic solvent adopted in the pretreatment of lignocellulose is a binary solvent system consisting of a hydrogen bond acceptor and a hydrogen bond donor, but the effect is poor; at present, the research on pretreatment of lignocellulose biomass and separation and preparation of nano-cellulose by using a multi-eutectic solvent system is reported, so that the research on the three-eutectic solvent has wide application prospects in pretreatment of lignocellulose and preparation of cellulose nano-fiber.

Disclosure of Invention

Aiming at the defects of high energy consumption, high pollution, difficult operation and the like of the traditional pretreatment method, the invention aims to solve one of the problems; the invention aims to provide a method for pretreating lignocellulose biomass and preparing nanocellulose by using a ternary eutectic solvent. The method disclosed by the invention effectively combines the ternary eutectic solvent pretreatment and high-intensity ultrasound to prepare the nano-cellulose, is more environment-friendly and efficient compared with the traditional preparation method, and can effectively improve the preparation technology of the nano-cellulose.

In order to achieve the above purpose, the method comprises the following steps:

(1) synthesis of ternary eutectic solvent: choline chloride, lactic acid or oxalic acid and aluminum trichloride (AlCl)₃·6H₂O) mixing according to a certain molar ratio, and stirring at a certain temperature until uniform and transparent liquid is formed to obtain a ternary eutectic solvent;

(2) pretreatment of lignocellulose: weighing a certain mass of bagasse, weighing a certain mass of the ternary eutectic solvent in the step (1), uniformly mixing the bagasse and the ternary eutectic solvent, placing the mixture in a microwave digestion tank, and performing microwave digestion at a certain temperature and for a certain time; after the reaction is finished, placing the mixture into an ice water bath to stop the reaction, carrying out solid-liquid separation after the reaction is stopped, diluting the liquid part with deionized water, and measuring the sugar content in the reaction solution by High Performance Liquid Chromatography (HPLC); washing the solid part with acetone water solution (50: 50, v/v) until the filtrate is colorless, and freeze drying the solid part to obtain pretreated bagasse;

(3) high-intensity ultrasonic separation of nanocellulose: washing the bagasse pretreated in the step (2) with deionized water for several times, diluting the bagasse with deionized water to a certain concentration, centrifuging to collect supernatant, performing ultrasonic treatment on the collected supernatant by using an ultrasonic generator equipped with a round titanium alloy probe, and finally performing freeze drying on the liquid after ultrasonic treatment to obtain the bagasse nano-cellulose microfibrils.

Preferably, the molar ratio of choline chloride, lactic acid or oxalic acid and aluminum trichloride in the step (1) is 1: 2: 0.2.

preferably, the certain temperature condition in the step (1) is 70 ℃; the stirring time for forming the uniform and transparent liquid is 4-6 h.

Preferably, the mass ratio of the bagasse to the eutectic solvent in the step (2) is 1: 10 (wt/wt).

Preferably, the microwave digestion power in the step (2) is 2400W, the microwave digestion temperature is 80-120 ℃, and the microwave digestion time is 20 min.

Preferably, the step (3) is diluted with deionized water to a certain concentration of 1 wt%.

Preferably, the centrifugation conditions in step (3) are: centrifuging at 3000-4000rpm for 5-10 min.

Preferably, the frequency of the ultrasonic treatment in the step (3) is 20kHz, the output power is 650W, the on/off pulse is 2/2s, and the ultrasonic duration is 20 min.

The invention has the beneficial effects that:

(1) the ternary eutectic solvent pretreatment system used in the invention has simple operation and good pretreatment effect, and can efficiently realize the deconstruction of the lignocellulose biomass; the ternary eutectic solvent is combined with microwave digestion to improve the reaction rate and shorten the reaction time; after microwave digestion is carried out for 20min, the contents of cellulose, hemicellulose and lignin in bagasse are respectively 53.59, 19.03 and 15.98 mol%, and the removal rate of the lignin reaches 56.28%.

(2) The eutectic solvent used in the invention has better chemical stability, is green and environment-friendly, has lower cost, and also has various advantages of the traditional solvent; after being pretreated by the ternary eutectic solvent, the lignin and the hemicellulose in the bagasse can be effectively removed, wherein the contents of glucose, xylose and arabinose in the hydrolysate respectively reach 8.97, 16.25 and 6.82 mol%. Meanwhile, the morphology of the cellulose microfibrils is kept, the cellulose nanofibrils with the particle size range of 26.84-61.26nm are obtained, the crystallinity is 45.64% -58.05%, the obtained nano cellulose microfibrils are smaller in particle size, and the application is more beneficial and better in application effect.

(3) The method for preparing the nano-cellulose has the advantages of mild conditions, simple operation, low cost and little pollution, and the used eutectic solvent can be recovered by methods such as rotary evaporation and the like, so that the method can be recycled, is environment-friendly, accords with the production standard of green chemistry, has good practical application value, and is suitable for industrial production.

Drawings

FIG. 1 is a graph showing the results of the chemical composition of bagasse after pretreatment in examples 1 to 5.

FIG. 2 is a graph showing the results of the content of hydrolyzed sugar in the liquid components after pretreatment in examples 1 to 5.

Fig. 3 is an atomic force microscope image of the nano-cellulose microfibrils prepared in example 2.

Fig. 4 is an atomic force microscope image of the nano-cellulose microfibrils prepared in example 4.

Fig. 5 is an atomic force microscope image of the nano-cellulose microfibrils prepared in example 5.

Wherein DES-LA-80, DES-LA-100 and DES-LA-120 represent bagasse nanocellulose microfibrils prepared with a lactic acid-based eutectic solvent at 80, 100 and 120 ℃ respectively; while DES-OA-80, DES-OA-100, DES-OA-120 represent bagasse nanofibrils prepared with eutectic solvents based on oxalic acid at 80, 100 and 120 ℃ respectively.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

The method for preparing the cellulose nanofibrils through the pretreatment of the ternary eutectic solvent comprises the following steps:

(1) after pretreatment of biomass, the content of cellulose, hemicellulose and lignin in biomass was determined using the National Renewable Energy Laboratory (NREL) method. Calculated by the following formula:

wherein T is the mass of the acid-insoluble residue added to the crucible, A is the mass of the ash added to the crucible, and C_gluAnd C_xylConcentrations of glucose and xylose (mg/mL) measured in the hydrolysate, respectively, 87 are the correction factors for the total volume sample (mL) of 0.90 and 0.88, respectively, for C-5 and C-6 sugars of 500, the mass of the original biomass (mg).

(2) Determining sugar content in hydrolysate by high performance liquid chromatography

Wherein V is the volume after dilution, mL; c means the concentration of the corresponding substance, mg/mL, as measured by HPLC; m refers to the mass of biomass, mg; x is the content of cellulose in the biomass before and after pretreatment,%; x₁Is referred to as pretreatmentContent of hemicellulose in biomass before and after treatment,%.

(3) The surface morphology of the produced nanocellulose microfibrils was observed using an atomic force microscope.

Example 1:

(1) synthesis of ternary eutectic solvent: weighing 28g of choline chloride, 36g of oxalic acid and 9.64g of aluminum trichloride, uniformly mixing the choline chloride, the oxalic acid and the aluminum trichloride, and stirring at 70 ℃ until a uniform and transparent liquid is formed to obtain a ternary eutectic solvent;

(2) pretreatment: adding 0.5g of bagasse into a microwave digestion tank, adding 5g of ternary eutectic solvent, and reacting for 20min at 80 ℃; for the accuracy of experimental data, each group of experiments is performed in three parallels; after the reaction, the reaction solution is immediately put into an ice water bath to stop the reaction, solid-liquid separation is carried out, the liquid part is diluted by 20 times by adding distilled water, standing is carried out, and the content of sugar in the reaction solution is analyzed and determined by HPLC. The solid fraction was washed with aqueous acetone (volume ratio of acetone to water 50: 50, v/v) until the filtrate was colorless, and finally the solid fraction was freeze-dried to obtain pretreated bagasse. The content of cellulose, hemicellulose and lignin in the bagasse after pretreatment was determined using the method of the National Renewable Energy Laboratory (NREL). The results are shown in FIG. 1: the contents of cellulose, hemicellulose and lignin were 53.20, 15.93 and 18.15 mol%, respectively. The liquid components were measured by liquid chromatography and the results are shown in FIG. 2, in which the contents of glucose, xylose and arabinose were 4.46, 9.52 and 4.91 mol%, respectively.

(3) Separating nano cellulose: washing the pretreated bagasse by using deionized water for 3 times, diluting the bagasse to 1 wt%, centrifuging the bagasse for 5min at 4000rpm, and collecting supernatant; and (3) carrying out ultrasonic treatment on the collected supernatant by using an ultrasonic generator provided with a round titanium alloy probe, and finally freeze-drying the liquid after ultrasonic treatment to obtain the bagasse nano-cellulose microfibrils. Ultrasonic treatment the supernatant was subjected to ultrasonic treatment with a JY92-IIN ultrasonic generator equipped with a 25mm cylindrical titanium alloy probe, the ultrasonic treatment frequency was 20kHz, the output power was 650W, the on/off pulse was 2/2s, and the ultrasonic duration was 20 m; and freeze-drying to obtain the bagasse nano-cellulose microfibril with the crystallinity of 45.64 percent and the particle size of 49.73 nm. The morphological structure of bagasse nanocellulose is shown in fig. 3.

Example 2:

(1) synthesis of ternary eutectic solvent: weighing 28g of choline chloride, 36g of lactic acid and 9.64g of aluminum trichloride, uniformly mixing the choline chloride, the lactic acid and the aluminum trichloride, and stirring at 70 ℃ until a uniform and transparent liquid is formed to obtain a ternary eutectic solvent;

(2) pretreatment: adding 0.5g of bagasse into a microwave digestion tank, adding 5g of ternary eutectic solvent, and reacting for 20min at 100 ℃; for the accuracy of experimental data, each group of experiments is performed in three parallels; after the reaction, the reaction solution is immediately put into an ice water bath to stop the reaction, solid-liquid separation is carried out, the liquid part is diluted by 20 times by adding distilled water, standing is carried out, and the content of sugar in the reaction solution is analyzed and determined by HPLC. The solid fraction was washed with aqueous acetone (volume ratio of acetone to water 50: 50, v/v) until the filtrate was colorless, and finally the solid fraction was freeze-dried to obtain pretreated bagasse. The content of cellulose, hemicellulose and lignin in the bagasse after pretreatment was determined using the method of the National Renewable Energy Laboratory (NREL). The results are shown in FIG. 1: the contents of cellulose, hemicellulose and lignin were 37.73, 14.43 and 15.05 mol%, respectively, and the contents of glucose, xylose and arabinose, respectively, of the liquid components were 5.57, 18.60 and 5.11 mol%, respectively, as measured by liquid chromatography, and the results are shown in FIG. 2;

(3) separating nano cellulose: washing the pretreated bagasse by using deionized water for 3 times, diluting the bagasse to 1 wt%, centrifuging the bagasse for 5min at 4000rpm, and collecting supernatant; and (3) carrying out ultrasonic treatment on the collected supernatant by using an ultrasonic generator provided with a round titanium alloy probe, and finally freeze-drying the liquid after ultrasonic treatment to obtain the bagasse nano-cellulose microfibrils. Carrying out ultrasonic treatment on the supernatant by using a JY92-IIN ultrasonic generator equipped with a 25mm cylindrical titanium alloy probe, wherein the ultrasonic treatment frequency is 20kHz, the output power is 650W, the on/off pulse is 2/2s, and the ultrasonic duration is 20 m; and then freeze-drying to obtain the bagasse nano-cellulose microfibril, wherein the crystallinity of the bagasse nano-cellulose microfibril is 49.54 percent, and the particle size of the cellulose microfibril is 61.26 nm.

Example 3:

(1) synthesis of ternary eutectic solvent: weighing 28g of choline chloride, 36g of oxalic acid and 9.64g of aluminum trichloride, uniformly mixing the choline chloride, the oxalic acid and the aluminum trichloride, and stirring at 70 ℃ until a uniform and transparent liquid is formed to obtain a ternary eutectic solvent;

(2) pretreatment: adding 0.5g of bagasse into a microwave digestion tank, adding 5g of ternary eutectic solvent, and reacting for 20min at 120 ℃; for the accuracy of experimental data, each group of experiments is performed in three parallels; after the reaction, the reaction solution is immediately put into an ice water bath to stop the reaction, solid-liquid separation is carried out, the liquid part is diluted by 20 times by adding distilled water, standing is carried out, and the content of sugar in the reaction solution is analyzed and determined by HPLC. The solid fraction was washed with aqueous acetone (volume ratio of acetone to water 50: 50, v/v) until the filtrate was colorless, and finally the solid fraction was freeze-dried to obtain pretreated bagasse. The content of cellulose, hemicellulose and lignin in the bagasse after pretreatment was determined using the method of the National Renewable Energy Laboratory (NREL). The results are shown in FIG. 1: the contents of cellulose, hemicellulose and lignin were 53.59, 19.03 and 15.98 mol%, respectively. The liquid components were measured by liquid chromatography, and the results are shown in FIG. 2, in which the contents of glucose, xylose and arabinose were 8.97, 16.25 and 6.82 mol%, respectively;

(3) separating nano cellulose: washing the pretreated bagasse by using deionized water for 3 times, diluting the bagasse to 1 wt%, centrifuging the bagasse for 5min at 4000rpm, and collecting supernatant; and (3) carrying out ultrasonic treatment on the collected supernatant by using an ultrasonic generator provided with a round titanium alloy probe, and finally freeze-drying the liquid after ultrasonic treatment to obtain the bagasse nano-cellulose microfibrils. Carrying out ultrasonic treatment on the supernatant by using a JY92-IIN ultrasonic generator equipped with a 25mm cylindrical titanium alloy probe, wherein the ultrasonic treatment frequency is 20kHz, the output power is 650W, the on/off pulse is 2/2s, and the ultrasonic duration is 20 m; and then freeze-drying to obtain the bagasse nano-cellulose microfibril, wherein the crystallinity of the bagasse nano-cellulose microfibril is 58.05%, and the particle size of the cellulose microfibril is 26.84 nm.

Example 4:

(1) synthesis of ternary eutectic solvent: weighing 28g of choline chloride, 36g of lactic acid and 9.64g of aluminum trichloride, uniformly mixing the choline chloride, the lactic acid and the aluminum trichloride, and stirring at 70 ℃ until a uniform and transparent liquid is formed to obtain a ternary eutectic solvent;

(2) pretreatment: adding 0.5g of bagasse into a microwave digestion tank, adding 5g of ternary eutectic solvent, and reacting for 20min at 80 ℃; for the accuracy of experimental data, each group of experiments is performed in three parallels; after the reaction, the reaction solution is immediately put into an ice water bath to stop the reaction, solid-liquid separation is carried out, the liquid part is diluted by 20 times by adding distilled water, standing is carried out, and the content of sugar in the reaction solution is analyzed and determined by HPLC. The solid fraction was washed with aqueous acetone (volume ratio of acetone to water 50: 50, v/v) until the filtrate was colorless, and finally the solid fraction was freeze-dried to obtain pretreated bagasse. The content of cellulose, hemicellulose and lignin in the bagasse after pretreatment was determined using the method of the National Renewable Energy Laboratory (NREL). The results are shown in FIG. 1: the contents of cellulose, hemicellulose and lignin were 40.59, 14.86 and 15.25 mol%, respectively. The liquid components were measured by liquid chromatography, and the results are shown in FIG. 2, in which the contents of glucose, xylose and arabinose were 3.96, 8.19 and 3.87 mol%, respectively;

(3) separating nano cellulose: washing the pretreated bagasse by using deionized water for 3 times, diluting the bagasse to 1 wt%, centrifuging the bagasse for 5min at 4000rpm, and collecting supernatant; and (3) carrying out ultrasonic treatment on the collected supernatant by using an ultrasonic generator provided with a round titanium alloy probe, and finally freeze-drying the liquid after ultrasonic treatment to obtain the bagasse nano-cellulose microfibrils. Carrying out ultrasonic treatment on the supernatant by using a JY92-IIN ultrasonic generator equipped with a 25mm cylindrical titanium alloy probe, wherein the ultrasonic treatment frequency is 20kHz, the output power is 650W, the on/off pulse is 2/2s, and the ultrasonic duration is 20 m; and then freeze-drying to obtain the bagasse nano-cellulose microfibril, wherein the crystallinity of the bagasse nano-cellulose microfibril is 48.96%, and the particle size of the cellulose microfibril is 57.42 nm. The morphological structure of bagasse nanocellulose is shown in fig. 4.

Example 5:

(1) synthesis of ternary eutectic solvent: weighing 28g of choline chloride, 36g of oxalic acid and 9.64g of aluminum trichloride, uniformly mixing the choline chloride, the oxalic acid and the aluminum trichloride, and stirring at 70 ℃ until a uniform and transparent liquid is formed to obtain a ternary eutectic solvent;

(2) pretreatment: adding 0.5g of bagasse into a microwave digestion tank, adding 5g of ternary eutectic solvent, and reacting for 20min at 100 ℃; for the accuracy of experimental data, each group of experiments is performed in three parallels; after the reaction, the reaction solution is immediately put into an ice water bath to stop the reaction, solid-liquid separation is carried out, the liquid part is diluted by 20 times by adding distilled water, standing is carried out, and the content of sugar in the reaction solution is analyzed and determined by HPLC. The solid fraction was washed with aqueous acetone (volume ratio of acetone to water 50: 50, v/v) until the filtrate was colorless, and finally the solid fraction was freeze-dried to obtain pretreated bagasse. The content of cellulose, hemicellulose and lignin in the bagasse after pretreatment was determined using the method of the National Renewable Energy Laboratory (NREL). The results are shown in FIG. 1: the contents of cellulose, hemicellulose and lignin were 44.39, 16.80 and 15.60 mol%, respectively. The liquid components were measured by liquid chromatography, and the results are shown in FIG. 2, in which the contents of glucose, xylose and arabinose were 5.83, 21.06 and 7.19 mol%, respectively;

(3) separating nano cellulose: washing the pretreated bagasse by using deionized water for 3 times, diluting the bagasse to 1 wt%, centrifuging the bagasse for 5min at 4000rpm, and collecting supernatant; carrying out ultrasonic treatment on the collected supernatant by using an ultrasonic generator provided with a round titanium alloy probe, and finally freeze-drying the liquid after ultrasonic treatment to obtain bagasse nano-cellulose microfibrils; carrying out ultrasonic treatment on the supernatant by using a JY92-IIN ultrasonic generator equipped with a 25mm cylindrical titanium alloy probe, wherein the ultrasonic treatment frequency is 20kHz, the output power is 650W, the on/off pulse is 2/2s, and the ultrasonic duration is 20 m; and then freeze-drying to obtain the bagasse nano-cellulose microfibril with the crystallinity of 50.68 percent and the particle size of 58.74nm, and the bagasse nano-cellulose morphological structure is shown in figure 5.

Description of the drawings: the above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention; thus, while the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.