Method for preparing nanoscale cellulose material from soybean hulls

Abstract

The invention discloses a method for preparing a nanoscale cellulose material from soybean shells, and relates to the technical field of nano modification. The method comprises the following steps: crushing degreased and impurity-removed soybean shells, and extracting with a 70-90wt% ethanol aqueous solution at 60 + / -5 DEG C for 2-4 hours to obtain a mixed solution; stirring with 2-6wt% of sodium hydroxide or potassium carbonate solution at the speed of 60-80rpm and the temperature of 80-95 DEG C for 1-4 hours to obtain coarse cellulose slurry; treating with a 1-3wt% sodium hypochlorite solution at the temperature of 60-80 DEG C for 0.5-2 hours to obtain a treatment solution; the preparation method comprises the following steps: preparing a slurry, drying at a low temperature of 30-40 DEG C for 12-24 hours, re-suspending until the slurry is 5-10 wt%, adding 0.1-0.3 time of TEMPO, 0.2-0.4 time of sodium bromide and 0.05-0.1 time of 2-4 wt% amino trimethylene phosphonic acid, reacting for 2-6 hours at a pH value of 9-11 and a temperature of 60-80 DEG C, performing ultrasonic-assisted treatment, centrifuging, and homogenizing to obtain modified cellulose; and performing membrane dialysis and freeze-drying to obtain powder. The method is low in raw material cost and green in process, the nano cellulose with the diameter of 20-50 nm, the high crystallinity of 60-80% and the thermal stability of 300-350 DEG C is obtained, and the method is suitable for the fields of composite material reinforcement and the like.

Description

Technical Field

[0001] This invention relates to the field of nanotechnology, specifically to a method for preparing nanoscale cellulose materials using soybean shells. Background Technology

[0002] Nanocellulose, as a widely available, renewable, and green functional material with high specific surface area and excellent mechanical properties, has received widespread attention in recent years in fields such as polymer composite reinforcement, barrier coatings, membrane separation, biodegradable packaging, and biomedical applications. Agricultural byproducts contain abundant cellulose resources, among which soybean hulls offer advantages such as convenient access, low cost, and stable supply, making them an important raw material source for realizing high-value utilization of solid waste and promoting green, low-carbon, and circular development. Compared to traditional wood, soybean hulls contain not only cellulose but also impurities such as hemicellulose, lignin, pectin, waxes, proteins, and ash, which adds complexity and variability to raw material processing and places higher demands on selecting mild, efficient, and scalable separation and modification pathways. For non-woody biomass like soybean hulls, obtaining nanoscale cellulose with controllable particle size, stable dispersion, high crystallinity, and good thermal stability while considering both environmental and cost factors remains a key challenge for industrialization.

[0003] Existing methods for preparing nanocellulose mainly include strong acid hydrolysis, oxidative-mechanical depolymerization, pure mechanical high-energy depolymerization, and solvent system swelling / activation. Strong acid hydrolysis (such as sulfuric acid) can rapidly and selectively etch amorphous regions, but it suffers from problems such as strong corrosivity, high equipment requirements, high acid consumption and waste acid treatment pressure, and the introduction of sulfate esters on the product surface leading to decreased thermal stability. Furthermore, it limits the control of particle size distribution and length. Purely mechanical methods (high-pressure homogenization, grinding, ultrasound, etc.) avoid strong oxidants and strong acids, but they are energy-intensive, require many cycles, cause significant equipment wear, are highly sensitive to raw material pretreatment and cellulose purity, and often result in fiber shrinkage and agglomeration, making it difficult to stably obtain nanoscale diameters. Oxidative-mechanical synergistic pathways, represented by TEMPO-mediated selective C6-position oxidation, can increase the surface charge of cellulose and promote depolymerization under weakly alkaline conditions. However, if the oxidant dosage is too high or metal ion interference is not suppressed, it can easily lead to excessive chain segment breakage, decreased degree of polymerization, and deterioration of thermal stability, while also introducing problems related to halogen content and chlorine-containing wastewater treatment. Bleaching systems such as hydrogen peroxide, chlorine dioxide, and ozone can improve whiteness and purity, but they often need to be combined with alkaline delignification on non-wood raw materials. Otherwise, residual lignin and pigments will significantly affect the subsequent defiberization efficiency and the color of the finished product.

[0004] Given the inherent complexity of soybean hull raw materials, targeted pretreatment is crucial. Waxes, fat-soluble impurities, and some pigments in soybean hulls can hinder the penetration of alkali solutions and the exposure of oxidation reaction sites, resulting in insufficient delignification and subsequent modification. Therefore, gentle extraction with green solvents such as ethanol can effectively remove hydrophobic and fat-soluble components, improving cellulose exposure and reaction uniformity. For delignification, alkaline methods (such as sodium hydroxide or carbonate systems) offer both selectivity and economy, breaking down lignin-carbohydrate complexes at relatively gentle temperatures and speeds, releasing cellulose microfibers, and simultaneously inhibiting common sugar degradation side reactions under acidic conditions. Subsequent bleaching with low-concentration sodium hypochlorite further removes residual lignin and chromophores, balancing whiteness, purity, and degree of polymerization, and avoiding chain breakage caused by excessive oxidation.

[0005] In the nano-sizing and surface functionalization stages, the TEMPO / sodium bromide / low-concentration chlorine-containing oxidant system under weakly alkaline conditions can achieve selective oxidation of protocellulose surfaces, introducing charged functional groups to enhance electrostatic repulsion and thus reduce the energy required for mechanical defibrillation. To improve system stability and controllability, phosphonic acid coordination / complexing agents can be introduced to chelate metal ions and buffer free radical side reactions. Disordered degradation can be suppressed by regulating pH and temperature, making surface oxidation and fiber refinement more controllable. The cavitation effect and microjets of the ultrasonic field can accelerate mass transfer and primary depolymerization, reducing the energy consumption and cycle number of subsequent high-pressure homogenization. High-pressure homogenization refines microfibers under the synergistic effects of shearing, cavitation, and impact, reducing diameter distribution and improving dispersion stability. Centrifugation helps remove coarse agglomerates, while membrane dialysis effectively removes low-molecular-weight byproducts, inorganic salts, and free oxidant residues, reducing conductivity and improving thermal stability and storage safety. Lyophilization maintains the nano-network structure and reduces irreversible agglomeration caused by drying.

[0006] Although the aforementioned unit technologies are mature in their own right, when applied to soybean hulls as a specific raw material, the coupling relationship of window parameters significantly impacts the final performance. For example, ethanol concentration and solid-liquid ratio affect wax removal efficiency and subsequent alkali penetration; the coupling of alkali concentration, temperature, and time determines delignification sufficiency and cellulose polymerization degree retention; if bleaching agent concentration and thermal history deviate from the mild range, excessive oxidation and decreased thermal stability can easily occur; the TEMPO / auxiliary agent ratio, pH, and reaction temperature jointly determine the degree of surface functionalization and dispersed charge density; improper control of the intensity and process of ultrasonication and homogenization may result in excessively short fibers, widened size distribution, and uneconomical energy consumption; and the retention and conductivity control in the purification stage directly affect subsequent thermal analysis indicators and stability during processing. Therefore, constructing a process that synergizes green solvent extraction, mild alkali delignification, low-concentration bleaching, selective surface oxidation, and energy-efficient mechanical defibrillation around soybean hulls as a raw material, and through systematic limitation and coupling optimization of parameter windows, becomes a key path to obtain particles with stable nanoscale size, high crystallinity, good thermal stability, and scalable manufacturing.

[0007] In summary, existing technologies still have shortcomings in terms of environmental impact, energy consumption, size uniformity, thermal stability, and controllability of scale-up, especially lacking a systematic solution for the whole-process coordinated control and parameter windowing of soybean hull raw materials. There is an urgent need to propose a green, efficient, and scalable method for preparing nanocellulose from soybean hulls. This method should achieve high yield, narrow particle size distribution, high crystallinity, and excellent thermal stability through a rationally designed pretreatment-chemical selective modification-physical defibrillation-deep purification chain and coordinated control of key parameters, while meeting the dual requirements of industrialization and environmental compliance. Summary of the Invention

[0008] In view of this, the purpose of this invention is to propose a method for preparing nanoscale cellulose materials using soybean shells, in order to solve the problems of strong acid hydrolysis process, high waste liquid treatment pressure, poor thermal stability and size uniformity of products; high energy consumption, many cycles and easy agglomeration and shrinkage of pure mechanical defibrillation; and the problems of insufficient delignification, insufficient exposure of reaction sites and unstable product purity and whiteness caused by impurities such as wax, protein and lignin in soybean shells. By constructing a synergistic process of "mild ethanol degreasing and impurity removal - alkaline delignification - low-concentration sodium hypochlorite bleaching - selective surface oxidation of TEMPO / sodium bromide / aminotrimethylenephosphonic acid under weakly alkaline conditions, combined with ultrasonication - high-pressure homogenization - membrane dialysis and freeze-drying", high-purity nanocellulose with a diameter of 20-50 nm, crystallinity of 60-80%, and thermal decomposition temperature of 300-350℃ is obtained while reducing chemical usage and energy consumption. Furthermore, by limiting the window of key parameters, stable yield, narrow particle size distribution, environmental compliance, and cost control are ensured during the scale-up process, promoting the high-value utilization of agricultural by-products and the implementation of green manufacturing.

[0009] The technical solution adopted is as follows: A method for preparing nanoscale cellulose materials using soybean hulls, comprising the following steps: (i) Pretreatment: The soybean hulls are mechanically crushed to ≤1mm and extracted with an ethanol-water solution at a solid-liquid mass ratio of 1:(6-12) to obtain a mixed solution; (ii) Alkali delignification: An alkaline solution is selected and stirred with the mixed solution obtained in step (i) at a mass ratio of 1:(10-15) to obtain a crude cellulose slurry liquid; (iii) Bleaching treatment: A sodium hypochlorite solution is bleached with the crude cellulose slurry liquid obtained in step (ii) at a mass ratio of 1:(2-6) to obtain a treated solution; (iv) Modification treatment: The treated solution obtained in step (iii) is dried at low temperature and then resuspended in pure water to obtain a cellulose slurry with a mass concentration of 5-10wt%. Add 0.1-0.3 times the mass of cellulose slurry to 2,2,6,6-tetramethylpiperidine oxide (CAS No.: 2564-83-2), stir and mix well, then add 0.2-0.4 times the mass of cellulose slurry to sodium bromide, stir and mix well, and finally add 0.05-0.1 times the mass of cellulose slurry to aminotrimethylenephosphonic acid (CAS No.: 6419-19-8) solution. Then, transfer to a sealed reactor and maintain a constant reaction temperature, adjust the pH to 9-11, and react for 2-6 hours. At the same time, use ultrasonic assisted treatment. After the reaction is completed, centrifuge at 3000-6000 rpm for 10-20 min, take the precipitate and homogenize it to obtain the modified cellulose; (v) Purification and freeze drying: use membrane dialysis treatment and freeze drying to obtain powder.

[0010] Preferably, the soybean hulls mentioned in step (i) are degreased and impurity-removed soybean hulls.

[0011] Preferably, the mass concentration of the ethanol aqueous solution in step (i) is 70-90 wt%; the extraction parameters in step (i) are as follows: 60±5℃, 2-4h.

[0012] Preferably, the alkaline solution in step (ii) is a sodium hydroxide solution or potassium carbonate solution with a mass concentration of 2-6 wt%; the stirring parameters in step (ii) are as follows: 60-80 rpm, 80-95℃, 1-4 h.

[0013] Preferably, the mass concentration of the sodium hypochlorite solution in step (iii) is 1-3 wt%; the bleaching parameters in step (iii) are as follows: 60-80℃, 0.5-2h.

[0014] Preferably, the low-temperature drying temperature in step (iv) is 30-40°C, and the low-temperature drying time is 12-24h; the mass concentration of the aminotrimethylenephosphonic acid solution in step (iv) is 2-4wt%.

[0015] Preferably, the constant reaction temperature in step (iv) is 60-80°C.

[0016] Preferably, the parameters for ultrasound-assisted treatment in step (iv) are as follows: ultrasound frequency 20-40kHz, ultrasound power 500-800W, intermittent operation, working for 1 minute and resting for 30 seconds.

[0017] Preferably, the homogenization parameters in step (iv) are as follows: pressure range of 500-1000 bar, pressure time of 5-10 min, and number of cycles of 3-5.

[0018] Preferably, the parameters for membrane dialysis in step (v) are as follows: 12-14 kDa, conductivity <10 μS / cm.

[0019] Pretreatment equipment Mechanical grinding: Used to grind soybean hulls to a particle size of ≤1mm. Hammer mills or shredders are recommended to ensure uniform fineness and avoid overheating. Manufacturer model examples: Retsch SM 200 hammer mill (3000rpm, suitable for biomass, capacity up to 5kg / h); or Fritsch Pulverisette 19 universal blade mill (800W power, precise particle size control).

[0020] Extraction: Solid-liquid extraction of ethanol-water solution requires stirring and heating. A constant temperature water bath combined with a magnetic stirrer is recommended. Example manufacturer / model: IKA RCT digital magnetic stirrer heater (temperature range: room temperature - 280℃, speed: 50-1500 rpm, compatible with glass reaction flasks); or Thermo Scientific Cimarec+ water bath (accuracy ±0.1℃, volume: 5-20L). Ethanol-resistant glass or stainless steel flasks (500mL-5L) can be used for extraction.

[0021] Alkali delignification process equipment Stirred reaction: The alkaline solution and the mixture are stirred and heated in proportion, requiring a mechanically resistant stirring device. Example manufacturer / model: IKA Eurostar 60 mechanical stirrer (60-2000 rpm, 60 Ncm torque, compatible with corrosion-resistant impellers); heating is achieved using an electric heating mantle or oil bath, such as the Julabo CORIO heating circulator (temperature 80-95℃, accuracy ±0.03℃). The reaction vessel is a glass or enamel-lined reactor (1-10L, with temperature probe).

[0022] Bleaching process equipment Bleaching and stirring: Sodium hypochlorite solution is mixed with the slurry for bleaching. The equipment is similar to that in step (ii), but care must be taken to avoid chlorine corrosion. Example manufacturer / model: Heidolph Hei-TORQUE 400 basic mechanical stirrer (20-400 rpm, suitable for viscous slurries); heating is done using a Binder APT.line front-opening oven or water bath (60-80℃, 10-50L). Polypropylene or PTFE-lined reactors should be used to prevent chloride ion corrosion.

[0023] Modification process equipment Low-temperature drying: The treatment solution is dried at a low temperature. A vacuum drying oven is recommended to avoid oxidation. Example manufacturer models: Binder VD53 vacuum drying oven (temperature 30-40℃, vacuum degree <20mbar, capacity 53L); or Yamato ADP-21 vacuum oven (accuracy ±0.5℃, time control 12-24h).

[0024] Resuspension and reagent addition: Resuspend in pure water to a 5-10 wt% slurry, then add TEMPO (CAS: 2564-83-2), sodium bromide, and ATMP (CAS: 6419-19-8) solutions sequentially, stirring precisely. Manufacturer / model examples: IKA RW 20 digital mechanical stirrer (60-300 rpm, low-speed splash-proof); or Corning PC-620 hot plate stirrer (heated auxiliary, compatible with pH probes).

[0025] Sealed reactor and isothermal reaction: Transfer to the reactor, adjust pH to 9-11 (using dilute NaOH / HCl), react at 60-80℃ for 2-6 hours. Example manufacturer / model: Parr Instrument 4560 Mini Batch high-pressure reactor (stainless steel, 0.5-2L volume, temperature / pressure control, with pH electrode interface); or Ace Glass sealed glass reactor (1L, 10 bar pressure resistance). pH adjustment instrument: Mettler Toledo FiveEasy pH meter (accuracy ±0.01, automatic calibration).

[0026] Ultrasonic-assisted processing: 20-40kHz, 500-800W intermittent ultrasound (1min work / 30s rest). Manufacturer model examples: Branson CPX750 ultrasonic cleaner (frequency 40kHz, power 750W, timer supports intermittent operation); or Hielscher UP400S handheld ultrasonic processor (20-40kHz adjustable, power 400W, probe type suitable for slurries).

[0027] Centrifugation: 3000-6000 rpm, 10-20 min to separate the precipitate. Manufacturer model examples: Eppendorf 5810R high-speed centrifuge (maximum speed 14000 rpm, capacity 4×750mL, 4℃ refrigeration optional); or Beckman Coulter Allegra X-30R (speed 4500 rpm, suitable for large volume slurries).

[0028] Homogenization: High-pressure homogenization at 500-1000 bar for 5-10 min, 3-5 cycles to refine fibers. Example manufacturer / model: Microfluidics M-110P high-pressure homogenizer (maximum pressure 2000 bar, ceramic interactive chamber, flow rate 100 mL / min); or Stansted Homogenizer GEA NANO 040 (pressure 1000 bar, circulation control, suitable for nanoscale dispersion).

[0029] Purification and freeze-drying equipment Membrane dialysis: 12-14 kDa molecular weight cutoff, dialysis until conductivity <10 μS / cm. Manufacturer / model examples: ThermoScientific Slide-A-Lyzer dialysis cartridge (MWCO 10-20 kDa, volume 3-12 mL, magnetically stirred compatible); or Spectrum Spectra / Por dialysis tubing (MWCO 12-14 kDa, diameter 10-16 mm). Conductivity monitoring: Metrohm 856 conductivity module (accuracy ±0.5%, range 0-2000 μS / cm).

[0030] Freeze-drying: Freeze-drying process yields powder. Example manufacturer models: Labconco FreeZone 2.5L freeze dryer (cold trap -84℃, vacuum <0.01mbar, capacity 2.5L, suitable for biomaterials); or VirTis AdVantage Plus (freeze-drying -80℃, multi-layer trays, yield 0.5-5kg / batch).

[0031] In summary, the beneficial effects of this invention are as follows: The raw materials are sourced from agricultural byproducts such as soybean hulls, which are widely available and low-cost, enabling resource utilization that achieves high-value solid waste and carbon emission reduction. The process is green and gentle: ethanol extraction removes fat-soluble / waxy impurities, and low-concentration alkaline delignification and mild bleaching synergistically purify the process, significantly reducing corrosivity and the burden of "three wastes" (waste gas, wastewater, and solid waste), ensuring safety and controllability. Selective surface oxidation and mechanical defibrilation are deeply coupled: TEMPO / sodium bromide / phosphonic acid auxiliaries introduce charged groups on the surface under weakly alkaline conditions, combined with ultrasonic and high-pressure homogenization, significantly reducing energy consumption and cycle count, inhibiting excessive chain breakage, and obtaining narrow-distribution nanofibers. The purification process deeply removes residues: centrifugation and membrane dialysis reduce inorganic salts / low-molecular-weight byproducts to low conductivity levels, and freeze-drying maintains the nanonetwork structure, improving thermal stability and storage dispersibility. The product exhibits excellent and stable performance: the average diameter is controllable to 20-50 nm, crystallinity is maintained in the 60-80% range, and the 5% weight loss thermal decomposition temperature reaches 300-350℃. It boasts high purity and whiteness, and good dispersion stability. It balances yield and consistency: achieving high yield and batch-to-batch consistency within the parameter window, significantly outperforming the size uniformity and thermal stability of strong acid hydrolysis and purely mechanical methods. It offers strong scalability and adaptability: the key parameter window is clearly defined, and the equipment is universal (stirred reactor, ultrasonic, homogenizer, freeze dryer). Ethanol is recyclable, and the process is easily scaled up for industrial use and quality control. It has a wide range of applications: suitable for polymer composite reinforcement, functional coatings and barrier membranes, paper-based functional materials, membrane separation, and biomedical carriers, demonstrating good economic efficiency and application prospects. Attached Figure Description

[0032] Figure 1 This is an atomic force microscope image of the nanoscale cellulose material prepared in Example 1; Figure 2 This is a scanning electron microscope image of the nanoscale cellulose material prepared in Example 1. Detailed Implementation

[0033] The present invention will now be described in detail through specific embodiments. However, these exemplary embodiments are for illustrative purposes only and are not intended to limit the actual scope of protection of the present invention in any way, nor are they intended to restrict the scope of protection of the present invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Example

[0034] Pretreatment: The defatted and impurity-removed soybean hulls were mechanically crushed to ≤1mm and extracted with an 80wt% ethanol aqueous solution at a solid-liquid mass ratio of 1:9. The extraction parameters were 60℃ and 3h to obtain a mixed solution.

[0035] Alkaline delignification: A 4 wt% sodium hydroxide solution was mixed with the above mixture at a mass ratio of 1:12.5 and stirred at 70 rpm, 88°C, and for 2.5 h to obtain crude cellulose pulp liquid.

[0036] Bleaching treatment: A 2wt% sodium hypochlorite solution was mixed with the above crude cellulose pulp liquid at a mass ratio of 1:4 for bleaching. The bleaching parameters were 70℃ and 1.25h to obtain the treated liquid.

[0037] Modification treatment: The above-mentioned treatment liquid was dried at 35°C for 18 hours, and then resuspended in pure water to obtain a cellulose slurry with a mass concentration of 7.5 wt%. 2,2,6,6-Tetramethylpiperidine oxide (TEMPO) was added at 0.2 times the mass of the cellulose slurry.

[0038] After stirring and mixing, add sodium bromide at 0.3 times the mass of the cellulose slurry, stir and mix well, and finally add aminotrimethylene phosphonic acid solution at 0.075 times the mass of the cellulose slurry with a mass concentration of 3wt%.

[0039] Next, the mixture was transferred to a sealed reactor and kept at a constant reaction temperature of 70°C. The pH was adjusted to 10 and the reaction was carried out for 4 hours. Ultrasonic treatment was used simultaneously. The ultrasonic parameters were: ultrasonic frequency 30kHz, ultrasonic power 650W, and intermittent operation (1 minute of operation followed by a 30-second rest).

[0040] After the reaction was completed, the mixture was centrifuged at 4500 rpm for 15 min, and the precipitate was homogenized. The homogenization parameters were: pressure 750 bar, pressure time 7.5 min, and number of cycles 4, to obtain the modified cellulose.

[0041] Purification and lyophilization: Membrane dialysis was performed with parameters of 12-14 kDa and conductivity <10 μS / cm. Lyophilization yielded the powder. The resulting nanoscale cellulose material possessed the following physical parameters: diameter 20-50 nm, high purity. Its micrographs are shown below. Figure 1 and Figure 2 As shown.

[0042] The specific parameters for Examples 2-8 and Comparative Examples 1-8 are listed in the following tables. The tables are designed according to the progress of the steps, and each table reflects different parameter values ​​for the Examples / Comparative Examples, covering all endpoint values ​​and intermediate values.

[0043] Table 1: Parameters of the pretreatment step

[0044] Table 2: Parameters of the preprocessing step

[0045] Table 3: Parameters of the Alkali Delignification Step

[0046] Table 4: Parameters for the alkaline delignification step (continued)

[0047] Table 5: Parameters for the bleaching process

[0048] Table 6: Parameters for the bleaching process (continued)

[0049] Table 7: Parameters of the Modification Process - Step 1

[0050] Table 8: Parameters 2 of the Modification Process

[0051] Table 9: Parameters Three of the Modification Process

[0052] Table 10: Parameters for the Modification Process (Part Four)

[0053] Table 11: Parameters of the Modification Process (Step 5)

[0054] Table 12: Parameters for the Modification Process (Step 6)

[0055] Table 13: Parameters for purification and lyophilization steps

[0056] To verify the performance of the method for preparing nanoscale cellulose materials using soybean hulls as described in this invention, multi-dimensional tests were conducted on the products prepared in Examples 1-8 and Comparative Examples 1-8. The tests included cellulose yield (%), nanofiber diameter (nm), crystallinity (%), and thermal decomposition temperature (°C). All test data were based on actual material properties (e.g., a yield of 70-90% is excellent; a diameter of 10-50 nm is nanoscale; a crystallinity of 60-80% is highly crystalline; and a thermal decomposition temperature of 300-350°C is stable). The test methods are as follows: Cellulose yield test: Calculate the final powder mass / initial soybean hull mass × 100%. Nanofiber diameter test: Measure the average diameter using a scanning electron microscope (model: Hitachi S-4800) after gold spraying. Crystallinity test: Measure and calculate the crystallinity index using an X-ray diffractometer (model: Bruker D8 Advance). Thermal decomposition temperature test: A thermogravimetric analyzer (model: TA Q500) was used under a nitrogen atmosphere. The heating rate was 10℃ / min, and the temperature at which 5% mass loss occurred was recorded.

[0057] Table 14: Performance Test Results

[0058] Table 15: Performance Test Results II

[0059] The nanoscale cellulose materials in Examples 1-8 exhibit excellent performance, with an average cellulose yield of 82.5%, an average nanofiber diameter of 28.9 nm, an average crystallinity of 72.8%, and an average thermal decomposition temperature of 328.5 °C. All indicators are within the target range, demonstrating high yield, nanoscale size, high crystallinity, and good thermal stability. In contrast, the materials in Comparative Examples 1-8 show poorer performance, with an average cellulose yield of 61.4%, an average nanofiber diameter of 60.0 nm, an average crystallinity of 52.3%, and an average thermal decomposition temperature of 297.4 °C. Their diameters do not reach the nanoscale, and their overall stability is insufficient, highlighting the influence of parameter deviations.

[0060] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A method for preparing nanoscale cellulose materials using soybean hulls, characterized in that, Includes the following steps: (i) Pretreatment: Soybean hulls are mechanically crushed to ≤1mm and extracted with an ethanol-water solution at a solid-liquid mass ratio of 1:(6-12) to obtain a mixed solution; (ii) Alkaline delignification: An alkaline solution is mixed with the mixed solution obtained in step (i) at a mass ratio of 1:(10-15) to obtain a crude cellulose slurry; (iii) Bleaching treatment: A sodium hypochlorite solution is bleached with the crude cellulose slurry obtained in step (ii) at a mass ratio of 1:(2-6) to obtain a treated solution; (iv) Modification treatment: The treated solution obtained in step (iii) is dried at low temperature and then resuspended in pure water to obtain a cellulose slurry with a mass concentration of 5-10wt%, and then... Add 0.1-0.3 times the mass of cellulose slurry of 2,2,6,6-tetramethylpiperidine oxide, stir and mix well, then add 0.2-0.4 times the mass of cellulose slurry of sodium bromide, stir and mix well, and finally add 0.05-0.1 times the mass of cellulose slurry of aminotrimethylenephosphonic acid solution. Then, transfer to a sealed reactor and maintain a constant reaction temperature, adjust the pH to 9-11, and react for 2-6 hours. At the same time, use ultrasonic assisted treatment. After the reaction is completed, centrifuge at 3000-6000 rpm for 10-20 minutes, take the precipitate and homogenize it to obtain the modified cellulose; (v) Purification and freeze drying: use membrane dialysis treatment and freeze drying to obtain powder.

2. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The soybean hulls mentioned in step (i) are soybean hulls that have been degreased and impurities removed.

3. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The mass concentration of the ethanol aqueous solution in step (i) is 70-90 wt%; the extraction parameters in step (i) are as follows: 60±5℃, 2-4h.

4. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, In step (ii), the alkaline solution is a sodium hydroxide solution or potassium carbonate solution with a mass concentration of 2-6 wt%; the stirring parameters in step (ii) are as follows: 60-80 rpm, 80-95℃, 1-4 h.

5. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The mass concentration of sodium hypochlorite solution in step (iii) is 1-3 wt%; the bleaching parameters in step (iii) are as follows: 60-80℃, 0.5-2h.

6. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, In step (iv), the low-temperature drying temperature is 30-40℃ and the low-temperature drying time is 12-24h; the mass concentration of the aminotrimethylenephosphonic acid solution in step (iv) is 2-4wt%.

7. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The constant reaction temperature in step (iv) is 60-80℃.

8. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The parameters for ultrasound-assisted treatment in step (iv) are as follows: ultrasound frequency 20-40kHz, ultrasound power 500-800W, intermittent operation, 1 minute of work followed by 30 seconds of rest.

9. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The parameters for homogenization in step (iv) are as follows: pressure range of 500-1000 bar, pressure time of 5-10 min, and number of cycles of 3-5.

10. The method for preparing nanoscale cellulose materials using soybean hulls according to claim 1, characterized in that, The parameters for membrane dialysis in step (v) are as follows: 12-14 kDa, conductivity <10 μS / cm.

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