Preparation method of bamboo fiber ultra-nano micro-powder grading regulation biological fiber material

Abstract

The present application relates to the technical field of biomass material processing, and discloses a preparation method of bamboo fiber ultra-nano micro-powder grading regulation bio-based fiber material, which comprises the following steps: mixing dry bamboo powder, sodium sulfate decahydrate, polyethylene glycol and an interfacial modification dispersant at room temperature to obtain a premix; feeding the premix into a double-screw extruder; using the sodium sulfate decahydrate to release crystal water to penetrate into the fiber under heat, and cooperating with the polyethylene glycol to construct a limited liquid seal environment; triggering in-situ steam micro-explosion under high temperature in the explosion section to preliminarily dissociate the fiber; then using the microcrystals separated out by recrystallization of sodium sulfate in the exhaust section as an embedded abrasive to perform interlayer grinding and peeling; and finally, removing impurities through cleaning and freeze-drying to obtain the product. Through the synergistic effect of thermodynamic phase change and mechanical shearing, the present application realizes efficient nanocrystallization and dissociation of bamboo fiber, and the obtained micro-powder has good dispersibility, and the process is continuous, safe and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of biomass material processing technology, and in particular to a method for preparing bio-based fiber materials by hierarchical regulation of bamboo fiber ultra-nano powder. Background Technology

[0002] Bamboo, as a biomass material with abundant resources and a short growth cycle, possesses fibers with excellent mechanical properties and biodegradability. Processing bamboo to the nanoscale to prepare bamboo fiber ultra-nano powder can significantly improve the specific surface area and aspect ratio of the material, thus showing broad application prospects in fields such as reinforcing composite materials, fluid rheology modification, and functional adsorbent materials. However, bamboo itself has a multi-level cell wall structure, and cellulose is tightly wrapped by lignin and hemicellulose. This dense, anti-dissociation structure presents many challenges to the efficient nano-scale preparation of bamboo fibers.

[0003] Current preparation technologies mainly include mechanical, chemical, and bio-enzymatic methods. Purely mechanical processing methods, such as high-pressure homogenization, microfluidics, or ball milling, typically utilize strong shearing or impact forces to break down the fiber structure. However, due to the high toughness of bamboo fiber, refining it solely through mechanical force requires extremely high energy input. Furthermore, due to the strong hydrogen bonds between fibers, entanglement and equipment blockage easily occur during processing, resulting in a wide particle size distribution and difficulty in obtaining uniform nanoscale powder. While chemical processing methods can effectively remove the matrix and separate microfibers through acid hydrolysis or oxidation, this process often involves the use of strong acids, strong alkalis, or specific oxidants. This not only destroys the natural crystalline structure of cellulose and reduces the thermal stability of the material but also introduces serious wastewater treatment burdens and environmental pollution problems.

[0004] Steam explosion technology, as a physicochemical modification method, has attracted widespread attention due to its excellent dissociation effect. Traditional steam explosion is usually carried out in a closed, high-pressure reactor, requiring a period of high temperature and pressure followed by instantaneous depressurization. This process is intermittent, making continuous manufacturing impossible, and the operation of high-pressure vessels poses safety hazards, making it difficult to meet the needs of large-scale industrial production. Furthermore, existing physical or chemical dissociation methods generally face severe agglomeration problems during the drying process after obtaining wet nanofiber materials. Because the nanofiber surface contains a large number of hydroxyl groups, during water evaporation, capillary tension causes the fibers to approach each other and form irreversible hydrogen bonds, leading to a "keratinization" phenomenon. These hard agglomerates are extremely difficult to redisperse in subsequent applications, severely limiting the practical application performance of bamboo fiber nanopowder. Therefore, developing a continuous, energy-controlled, safe, and environmentally friendly method for preparing bamboo fiber nanoparticles that effectively solves the drying agglomeration problem is a pressing technical challenge in this field. Summary of the Invention

[0005] The technical problem solved by this invention is that the existing mechanical method for preparing bamboo fiber has high energy consumption, uneven fiber particle size distribution, and easy agglomeration, as well as the shortcomings of traditional steam explosion technology which relies on high-pressure containers and is difficult to achieve continuous production.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, comprising the following steps:

[0008] (1) Mixing: The following raw materials in parts by weight are premixed in solid phase at room temperature to obtain a premix: 100 parts of dried bamboo powder; 300-450 parts of sodium sulfate decahydrate; 100-150 parts of polyethylene glycol; 4-6 parts of interface modifier dispersant;

[0009] (2) Extrusion blasting: The premixed material is fed into a twin-screw extruder. During the material conveying process in the barrel, the crystal water released by the heated sodium sulfate decahydrate and polyethylene glycol are used to construct a confined liquid seal environment. The temperature of the blasting section of the extruder is controlled to be higher than the boiling point of water, so that the crystal water in the confined space will vaporize and generate in-situ steam micro-blasting, which will dissociate the bamboo fiber between layers.

[0010] (3) Purification and drying: The extrudate is washed to remove salt and polyethylene glycol, and then dried after solid-liquid separation to obtain bamboo fiber ultra-nano powder.

[0011] By adopting the above technical solution, this invention utilizes thermodynamic phase change control to construct a three-stage linkage micro-processing mechanism of infiltration, bursting, and grinding during continuous extrusion. The specific principle is as follows:

[0012] 1) Phase change water release and osmosis mechanism of sodium sulfate decahydrate

[0013] Sodium sulfate decahydrate, acting as a solid medium carrying moisture, is uniformly dispersed between bamboo powder particles during the mixing stage. When the material enters the heating zone of the extruder, the sodium sulfate decahydrate melts upon heating and releases water of crystallization, forming a high-concentration hot sodium sulfate solution in situ. This salt solution has low water activity and surface tension, allowing it to penetrate deeply into the amorphous regions of the bamboo fibers and the interstitial spaces within the microfiber bundles via capillary action, thus wetting the interior of the fiber bundles.

[0014] 2) In-situ vapor expansion mechanism in a liquid-sealed environment

[0015] Polyethylene glycol forms a high-viscosity liquid medium in the system. When the material, permeated with moisture, enters the high-temperature section, the moisture inside the fiber rapidly vaporizes. The viscous fluid layer formed by polyethylene glycol hinders the rapid escape of water vapor at the microscale, thus creating a confined space within the fiber. The vaporization of the liquid within the confined space generates volume expansion stress. This expansion force from the inside out breaks the hydrogen bonds between the cellulose molecular chains, causing the micron-sized fiber bundles to expand axially and undergo initial dissociation.

[0016] 3) Solute recrystallization-induced shear-grinding mechanism

[0017] As moisture continues to vaporize at high temperatures and is removed in the exhaust section, the sodium sulfate solution in the system reaches a supersaturated state. Sodium sulfate recrystallizes in situ between the fiber layers, which have been stretched open by the expansion force. The precipitated anhydrous sodium sulfate solid particles act as hard abrasives distributed between the fiber layers. Under the shearing action of the twin-screw extruder screws, these solid particles physically grind and delaminate the fibers, thereby further refining the bamboo fibers to the nanoscale.

[0018] Preferably, in the raw materials of step (1): the particle size of the dried bamboo powder is 60-80 mesh and the moisture content is ≤1.0wt%; the average molecular weight of the polyethylene glycol is 600-1000.

[0019] By adopting the above technical solution, the initial particle size and moisture content of bamboo powder are controlled to ensure the uniformity of material mixing; polyethylene glycol with a specific molecular weight is selected to provide a suitable viscosity at high temperature to maintain the liquid seal pressure, while also having good water solubility to facilitate subsequent cleaning and removal.

[0020] Preferably, the interface-modifying dispersant is a compound aqueous solution containing sodium dodecylbenzenesulfonate and sodium lignosulfonate; wherein the mass ratio of sodium dodecylbenzenesulfonate to sodium lignosulfonate is (0.8-1.25):1.

[0021] By employing the above technical solution, sodium dodecylbenzenesulfonate, as an anionic surfactant, reduces the solid-liquid interfacial tension and promotes the penetration of salt solution into the bamboo fiber. Sodium lignin sulfonate, utilizing its structural characteristics similar to bamboo fiber, adheres to the surface of the exfoliated nanofibers through physical adsorption, providing steric hindrance and preventing secondary agglomeration of the fibers during subsequent processing. The combination of these two components enhances the stability of the dispersion system.

[0022] Preferably, the interface-modified dispersant is prepared by the following method: heating deionized water to 60-65°C, adding sodium dodecylbenzenesulfonate and sodium lignosulfonate sequentially, stirring at 400-600 rpm for 30-45 minutes, and then adjusting the pH value to 8.5-9.0 to obtain a dispersant solution with a solid content of 37.5%-47.3%.

[0023] By adopting the above technical solution, heating and stirring conditions promote the full dissolution of components; adjusting the pH to a weakly alkaline environment can improve the ionization degree and dissolution stability of sodium lignosulfonate, ensuring that it maintains its dispersing activity during extrusion.

[0024] Preferably, in step (2), the screw speed of the twin-screw extruder is set to 150-300 rpm.

[0025] By adopting the above technical solution, this rotational speed range provides a suitable mechanical shear rate, which, together with the embedded salt particles, achieves effective frictional peeling, while avoiding thermal degradation of bamboo fibers due to excessive shear heat.

[0026] Preferably, in step (2), the temperature zone control of the extruder is as follows: the temperature of the feeding section in zone 1 is set to 35-50℃; the temperature of the plasticizing section in zone 2 is set to 70-90℃; the temperature of the bursting section in zone 3 is set to 115-130℃; and the temperature of the exhaust section in zone 4 is set to 95-110℃.

[0027] By employing the above technical solution, the process of the physicochemical reaction is controlled through a temperature gradient:

[0028] The low-temperature control in Zone 1 ensures that sodium sulfate decahydrate remains in a solid state, guaranteeing stable transportation.

[0029] The temperature in the second zone is higher than the phase transition point, which induces the release of water of crystallization and the formation of a solution, thus completing the osmosis.

[0030] The high-temperature environment in Zone 3 provides latent heat of vaporization, which triggers in-situ steam micro-explosions under liquid-sealed conditions;

[0031] The cooling process in the four zones, combined with exhaust gas, promotes solvent evaporation and solute supersaturation precipitation, triggering in-situ recrystallization and grinding.

[0032] Preferably, in the fourth exhaust section, as moisture is discharged, dissolved sodium sulfate recrystallizes and precipitates in situ between the loosened bamboo fiber layers. The precipitated anhydrous sodium sulfate microcrystals are used as embedded abrasives to grind and peel the bamboo fibers under the shearing action of the screw.

[0033] By adopting the above technical solution, the solid particles generated by phase change recrystallization directly act on the fiber interlayer, transforming the macroscopic mechanical shear force into the microscopic interlayer peeling force, thereby improving the crushing efficiency.

[0034] Preferably, in step (3), the cleaning specifically involves placing the extrudate in hot water at 75-85°C and stirring to clean it.

[0035] By adopting the above technical solution, high-temperature hot water can accelerate the dissolution rate of sodium sulfate and polyethylene glycol, while the water flow shearing during the cleaning process helps to further loosen the fiber bundles.

[0036] Preferably, in step (3), the drying is carried out by freeze drying.

[0037] By adopting the above technical solution, freeze drying removes moisture using the principle of ice crystal sublimation, avoiding the hard agglomeration of nanofibers caused by liquid phase surface tension contraction during conventional heat drying, and maintaining the high specific surface area of ​​the fibers.

[0038] Preferably, the prepared bamboo fiber ultra-nano powder has a D50 particle size ≤ 0.45 μm and a BET specific surface area ≥ 34 m². 2 / g.

[0039] By adopting the above technical solution, the final product has extremely small particle size and high specific surface area, which verifies the effectiveness of the preparation method in the dissociation and refinement of bamboo fibers.

[0040] In summary, the present invention has at least one of the following beneficial technical effects:

[0041] 1. This invention couples a chemical thermodynamic phase transition mechanism with mechanical shearing action to achieve highly efficient nano-dissociation of bamboo fibers. By utilizing the release of crystal water from heated sodium sulfate decahydrate to penetrate the fiber interior, and combining it with polyethylene glycol to create a liquid-sealed environment, in-situ steam micro-explosions are generated within the extruder, disrupting the hydrogen bonds between cellulose molecules. Subsequently, the microcrystalline particles precipitated from the supersaturated sodium sulfate act as embedded abrasives, performing interlayer delamination of the fibers under screw shearing. This synergistic effect of the inside-out explosive force and the interlayer abrasive force significantly improves the fiber separation efficiency.

[0042] 2. This invention employs a specific interface-modified dispersant system to effectively solve the problem of easy agglomeration of nanofibers. In the system, sodium dodecylbenzenesulfonate reduces the solid-liquid interfacial tension, promoting the wetting and penetration of the salt solution into the dense bamboo fibers; sodium lignin sulfonate, through physical adsorption, coats the surface of the exfoliated nanofibers, providing a steric hindrance effect. The two are compounded in a specific ratio, ensuring both effective dissociation during processing and preventing secondary agglomeration during drying, thereby obtaining well-dispersed and loosely structured ultra-nano powder.

[0043] 3. The process equipment of this invention is highly adaptable and safe, making it suitable for continuous industrial production. Compared to traditional intermittent steam explosion technology, which relies on high-pressure vessels and poses safety hazards, this invention utilizes a twin-screw extruder to achieve localized, confined explosions within an atmospheric pressure device through temperature zone control, ensuring a continuous and controllable process. Furthermore, the sodium sulfate decahydrate and polyethylene glycol used are both water-soluble and environmentally friendly additives that can be completely removed through water washing, leaving no harmful residues and meeting the requirements of green manufacturing. Attached Figure Description

[0044] Figure 1The following are the online rheological parameter monitoring curves for different formulation systems in Test Example 1 during the extrusion process; where (a) is the melt pressure fluctuation monitoring curve; and (b) is the main machine torque fluctuation monitoring curve.

[0045] Figure 2 The TGA-DSC simultaneous thermal analysis curves of each group of samples in Test Example 2 during the simulated extrusion heating process are shown; where (a) is the TG thermogravimetric curve and (b) is the DSC differential scanning calorimetry curve. Detailed Implementation

[0046] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0047] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0048] Bamboo powder is made from moso bamboo as raw material, which is mechanically crushed and sieved. The particle size distribution is 60 to 80 mesh. Before use, it is dried in a 105℃ forced-air drying oven for 24 hours until constant weight. The actual moisture content is ≤1.0wt%.

[0049] Sodium dodecylbenzenesulfonate (SDBS), CAS No. 25155-30-0, is a commercially available chemically pure reagent with a purity ≥90.0%.

[0050] Polyethylene glycol 600 (PEG-600) is a commercially available chemically pure reagent with an average molecular weight of 570–630.

[0051] Polyethylene glycol 1000 (PEG-1000) is a commercially available chemically pure reagent with an average molecular weight of 950–1050.

[0052] Sodium lignosulfonate is a commercially available industrial-grade or analytical-grade reagent with a lignin content ≥50% and a sulfonation degree of 1.5–2.0 mmol / g.

[0053] Preparation Example 1:

[0054] This preparation example provides a method for preparing an interface-modified dispersant, including the following steps:

[0055] Weigh 120 parts by weight of deionized water and add it to a stirred tank with a heating jacket, and heat it to 65°C. Then add 45 parts by weight of sodium dodecylbenzene sulfonate and 45 parts by weight of sodium lignosulfonate in sequence, turn on the mechanical stirrer, set the speed to 500 rpm, and stir at a constant temperature for 40 minutes until a homogeneous dark brown solution is formed. Then slowly add 5% sodium hydroxide aqueous solution to adjust the pH of the system to 8.8, and the interface modified dispersant with a solid content of about 42.8% is obtained.

[0056] Preparation Example 2:

[0057] This preparation example provides a method for preparing an interface-modified dispersant, including the following steps:

[0058] Weigh 150 parts by weight of deionized water and add it to a stirred tank with a heating jacket, and heat it to 60°C. Then add 50 parts by weight of sodium dodecylbenzene sulfonate and 40 parts by weight of sodium lignosulfonate in sequence, turn on the mechanical stirrer, set the speed to 600 rpm, and stir at a constant temperature for 30 minutes until a homogeneous dark brown solution is formed. Then slowly add 5% sodium hydroxide aqueous solution to adjust the pH of the system to 9.0, and the interface modified dispersant with a solid content of about 37.5% is obtained.

[0059] Preparation Example 3:

[0060] This preparation example provides a method for preparing an interface-modified dispersant, including the following steps:

[0061] Weigh 100 parts by weight of deionized water and add it to a stirred tank with a heating jacket, and heat it to 65°C. Then add 40 parts by weight of sodium dodecylbenzene sulfonate and 50 parts by weight of sodium lignosulfonate in sequence, turn on the mechanical stirrer, set the speed to 400 rpm, and stir at a constant temperature for 45 minutes until a homogeneous dark brown solution is formed. Then slowly add 5% sodium hydroxide aqueous solution to adjust the pH of the system to 8.5, and the interface modified dispersant with a solid content of about 47.3% is obtained.

[0062] Example 1:

[0063] This embodiment provides a method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, including the following steps:

[0064] (1) Mixing: Weigh 100 parts by weight of dried bamboo powder, 350 parts by weight of sodium sulfate decahydrate, 120 parts by weight of polyethylene glycol 600 and 5 parts by weight of the interface-modified dispersant obtained in Preparation Example 1, put them into a high-speed mixer, and mix them at 800 rpm for 5 minutes at room temperature to obtain a premixed material with uniform solid-liquid mixing.

[0065] (2) Extrusion blasting: The premixed material is added to the main feed port of the twin-screw extruder and the screw speed is set to 200 rpm. The temperature settings of each temperature zone of the extruder are as follows: Zone 1 (feeding section) 40℃, Zone 2 (plasticizing section) 80℃, Zone 3 (blasting section) 120℃, Zone 4 (venting section) 100℃, Zone 5 (die) 90℃. The material releases crystal water through sodium sulfate decahydrate in the barrel to form a liquid seal environment, and undergoes in-situ steam micro-blasting at high temperature in Zone 3. Then, it is extruded through the die to obtain composite strips.

[0066] (3) Purification and drying: The extruded composite strips were placed in 80°C hot water and stirred and washed three times for 30 minutes each time to remove sodium sulfate and polyethylene glycol carrier. The solid product was collected after centrifugation. The solid product was placed in a freeze dryer and dried for 24 hours to obtain bamboo fiber ultra-nano powder.

[0067] Example 2:

[0068] This embodiment provides a method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, including the following steps:

[0069] (1) Mixing: Weigh 100 parts by weight of dried bamboo powder, 450 parts by weight of sodium sulfate decahydrate, 150 parts by weight of polyethylene glycol 600 and 6 parts by weight of the interface-modified dispersant obtained in Preparation Example 2, put them into a high-speed mixer, and mix them at 1000 rpm for 3 minutes at room temperature to obtain a premix.

[0070] (2) Extrusion explosion: Add the premixed material to the main feed port of the twin-screw extruder and set the screw speed to 250 rpm; the temperature settings of each temperature zone of the extruder are as follows: Zone 1 45℃, Zone 2 90℃, Zone 3 130℃, Zone 4 110℃, Zone 5 95℃; the large amount of crystal water released by the high proportion of salt and the high temperature form a strong steam explosion effect;

[0071] (3) Purification and drying: The extrudate is repeatedly washed in hot water at 85°C until the conductivity of the filtrate is close to that of deionized water. The solid is collected by centrifugation and then freeze-dried to obtain bamboo fiber ultra-nano powder.

[0072] Example 3:

[0073] This embodiment provides a method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, including the following steps:

[0074] (1) Mixing: Weigh 100 parts by weight of dried bamboo powder, 300 parts by weight of sodium sulfate decahydrate, 100 parts by weight of polyethylene glycol 600 and 4 parts by weight of the interface-modified dispersant obtained in Preparation Example 3, put them into a high-speed mixer, and mix them at 600 rpm for 8 minutes at room temperature to obtain a premix.

[0075] (2) Extrusion bursting: Add the premixed material to the main feed port of the twin-screw extruder and set the screw speed to 150 rpm; the temperature settings of each temperature zone of the extruder are as follows: Zone 1 35℃, Zone 2 70℃, Zone 3 115℃, Zone 4 95℃, Zone 5 85℃; use relatively mild temperature and shear force for peeling.

[0076] (3) Purification and drying: The extrudate is washed in hot water at 75°C to remove impurities, and after centrifugation, it is freeze-dried to obtain bamboo fiber ultra-nano powder.

[0077] Example 4:

[0078] This embodiment provides a method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, including the following steps:

[0079] (1) Mixing: Weigh 100 parts by weight of dried bamboo powder, 350 parts by weight of sodium sulfate decahydrate, 120 parts by weight of polyethylene glycol 1000 and 5 parts by weight of the interface-modified dispersant obtained in Preparation Example 1, and put them into a high-speed mixer and mix them evenly at room temperature; Since polyethylene glycol 1000 is solid at room temperature, it is softened by frictional heat during the mixing process and initially coats the material;

[0080] (2) Extrusion burst: Add the premix to the twin-screw extruder and set the screw speed to 200 rpm; set the temperature of each zone of the extruder as follows: Zone 1 50℃, Zone 2 85℃, Zone 3 120℃, Zone 4 100℃, Zone 5 90℃; use the high viscosity liquid seal environment provided by the higher molecular weight PEG to enhance the burst pressure.

[0081] (3) Purification and drying: The subsequent cleaning and drying steps are the same as in Example 1, and bamboo fiber ultra-nano powder is obtained.

[0082] Example 5:

[0083] This embodiment provides a method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, including the following steps:

[0084] (1) Mixing: The formulation components and dosages are exactly the same as in Example 1;

[0085] (2) Extrusion burst: Add the premixed material to the twin-screw extruder and set the screw speed to 300 rpm to enhance the mechanical shearing effect; the temperature settings of each temperature zone of the extruder are as follows: Zone 1 40℃, Zone 2 80℃, Zone 3 120℃, Zone 4 100℃, Zone 5 90℃.

[0086] (3) Purification and drying: The subsequent cleaning and drying steps are the same as in Example 1, and bamboo fiber ultra-nano powder is obtained.

[0087] Comparative Example 1:

[0088] The difference from Example 1 is that 350 parts by weight of sodium sulfate decahydrate were replaced with 154 parts by weight of anhydrous sodium sulfate, while all other aspects remained the same.

[0089] Comparative Example 2:

[0090] Compared with Example 1, the difference is that 350 parts by weight of sodium sulfate decahydrate is replaced with 154 parts by weight of anhydrous sodium sulfate and 196 parts by weight of deionized water, and the rest are the same.

[0091] Comparative Example 3:

[0092] The difference from Example 1 is that polyethylene glycol 600 was not added; otherwise, they are the same.

[0093] Comparative Example 4:

[0094] The difference from Example 1 is that 350 parts by weight of sodium sulfate decahydrate were replaced with an equal part by weight of sodium chloride, while all other aspects remained the same.

[0095] Comparative Example 5:

[0096] The difference from Example 1 is that no interface-modifying dispersant was added; all other aspects are the same.

[0097] Test Example 1:

[0098] The experimental steps are as follows:

[0099] (1) Select a co-rotating twin-screw extruder equipped with a melt pressure sensor and a high-precision torque sensor, clean the barrel and screw to ensure that there is no residual material affecting it; set the temperature of each temperature zone of the extruder to the same process parameters as in Example 1, start the equipment and run it idle for preheating until the temperature of each zone reaches the set value and remains stable for 15 minutes.

[0100] (2) Weigh 5 kg of each of the premixes of the formulations described in Example 1, Comparative Example 2 and Comparative Example 3 respectively; First, add the premix of Example 1 to the main feeder, set the screw speed to 200 rpm, and the feeding speed to 20 kg / h. After the material is continuously and stably extruded from the die head and the fluctuation of the main machine current is less than 5%, mark it as a stable operating state.

[0101] (3) After entering a stable operating state, the head melt pressure (MPa) and main unit torque percentage are continuously recorded for 10 minutes at a sampling interval of 10 seconds using the data acquisition system; during the recording process, observe and mark whether there is obvious steam ejection from the exhaust port.

[0102] (4) After each set of samples is tested, the barrel is cleaned with pure polyethylene material. After it is cleaned, the next set of samples is tested. The test order is Example 1, Comparative Example 2, and Comparative Example 3, keeping all process parameters consistent.

[0103] The test results are shown in Table 1, and the corresponding comparison charts are shown below. Figure 1 As shown.

[0104] Table 1. Recording of pressure and torque monitoring data for different formulation systems in the extrusion stabilization zone:

[0105]

[0106] Analysis of the monitoring data in Table 1 shows that Example 1 established a high and stable melt pressure field (average 7.43 MPa, coefficient of variation only 1.1%) during the extrusion process, while maintaining a high main motor torque (78.4%). This indicates that the water of crystallization released by sodium sulfate decahydrate during the heating process is effectively trapped within the screw channel by the high-viscosity polyethylene glycol 600, constructing a stable liquid-sealed confined space. Under this high-pressure environment, water molecules cannot escape prematurely, thus generating continuous and strong volume expansion stress when instantaneous vaporization occurs in the high-temperature zone. This stress is the key driving force for achieving interlayer dissociation and micro-explosion of bamboo fibers.

[0107] In contrast, although Comparative Example 2 introduced the same amount of water, the average melt pressure was only 3.62 MPa, and the fluctuations were extremely drastic (coefficient of variation as high as 34.8%). The data fluctuation characteristics show that there is severe phase separation between the directly added free water and the hydrophobic bamboo powder and melt. The water undergoes disordered volatilization or passes through in the form of gas pockets in the feeding and plasticizing sections, which prevents the formation of a continuous pressure field in the screw channel and destroys the confined environment required for steam explosion.

[0108] Comparative Example 3 exhibited extremely low melt pressure (average 1.12 MPa) and a significant decrease in torque. This confirms that in the absence of polyethylene glycol as a high-viscosity carrier, even with the release of water of crystallization, the generated water vapor rapidly escapes into the low-pressure zone (feed port or vent port) through the screw gap, failing to accumulate sufficient pressure within the barrel. The lack of a high-pressure environment means that an effective steam explosion effect cannot be generated, and the material is subjected to only limited mechanical shearing, making it difficult to achieve nanoscale fiber peeling.

[0109] In summary, the phase change water release of sodium sulfate decahydrate and the liquid-sealed environment constructed by polyethylene glycol have a synergistic effect, which is a necessary condition for realizing the high-pressure micro-explosion mechanism.

[0110] Test Example 2:

[0111] The experimental steps are as follows:

[0112] (1) Take 10g each of pure sodium sulfate decahydrate crystals, the premix prepared in Example 1 (without extruder) and the premix prepared in Comparative Example 2 (containing anhydrous sodium sulfate and free water); grind each group of samples slightly in an agate mortar to ensure the representativeness of the sampling, but avoid excessive grinding to prevent frictional heat generation and water loss.

[0113] (2) Use a synchronous thermal analyzer and standard indium and zinc for temperature and heat flow calibration; weigh 5-8 mg of the above samples and place them in a 40 μL aluminum crucible. Seal the crucible with a capping machine and punch a 0.1 mm diameter pinhole in the center of the crucible lid to simulate the pressure environment of a semi-confined space and allow the gas to escape in a controlled manner.

[0114] (3) The test atmosphere is high-purity nitrogen, and the flow rate is set to 50 mL / min to prevent the bamboo powder from oxidizing at high temperature and interfering with the heat flow signal; the heating program is set to heat from 25℃ to 200℃, and the heating rate is set to 20℃ / min. This rate is intended to simulate the actual working condition of the material being rapidly heated in the extruder.

[0115] (4) Record the curve of sample mass changing with temperature (TG curve) and the curve of heat flow changing with temperature (DSC curve); perform differential processing on the raw data to obtain the DTG curve, and extract the water loss initiation temperature, the peak temperature of the maximum weight loss rate and the integral area of ​​the endothermic peak.

[0116] The test results are shown in Table 2, and the corresponding comparison chart is shown below. Figure 2 As shown.

[0117] Table 2. Record of thermal analysis characteristic parameters of each group of samples during the simulated extrusion heating process:

[0118]

[0119] According to the thermal analysis data in Table 2, the water release behavior of each group of samples showed significant differences. Pure sodium sulfate decahydrate exhibited standard characteristics of water of crystallization removal, undergoing a melting phase transition at 32.1℃, followed by concentrated water loss near 100℃.

[0120] Comparative Example 2 (physically added free water) showed a dehydration initiation temperature of only 28.7℃, a peak temperature of 92.1℃ for the maximum weight loss rate, and a weight loss rate as high as 31.2% in the 30–100℃ range. This indicates that in the absence of lattice confinement, free water evaporates in large quantities in the low-temperature ranges of Zone 1 (45℃) and Zone 2 (90℃) of the simulated extruder. This premature phase separation results in the material reaching Zone 3 (130℃) with almost all the moisture depleted, making it impossible to form an effective vapor pressure source.

[0121] In Example 1 (sodium sulfate decahydrate + PEG system), the dehydration initiation temperature increased to 45.2℃, and the peak temperature of the maximum weight loss rate shifted significantly to 118.5℃. The main weight loss occurred in the 100–140℃ range (weight loss rate 24.6%), which corresponds to the "three-zone bursting section" (115–130℃) set in the extrusion process. The endothermic peak at 121.2℃ shown in the DSC curve confirms that water in the viscous matrix constructed from PEG is affected by the increased boiling point and diffusion resistance due to colligative properties.

[0122] In summary, Example 1 successfully achieved delayed water release through the lattice confinement of sodium sulfate decahydrate and the coating effect of PEG. This mechanism ensures that the water carrier can be transported to the high-temperature, high-shear region in solid or bound form, and concentratedly released and vaporized within a predetermined temperature window, thereby triggering effective in-situ steam micro-explosions. This verifies the feasibility and controllability of the "sacrificial water carrier" mechanism.

[0123] Test Example 3:

[0124] The experimental steps are as follows:

[0125] (1) The final products of Examples 1-5 and Comparative Examples 1-5 were passed through a 100-mesh standard sieve to remove the insufficiently dispersed agglomerated particles. 10g of each sieved sample was weighed and 50mL of deionized water containing 0.1% sodium hexametaphosphate dispersant was added. The sample was ultrasonically treated for 15 minutes using an ultrasonic cell disruptor at a power of 300W and a working time of 3s / interval of 5s to open the weak agglomerates.

[0126] (2) A laser particle size analyzer was used. Before the test, deionized water was used as the dispersion medium for background correction and instrument calibration. The ultrasonically treated suspension was slowly dripped into the sample cell until the shading reached the optimal test range of 8-12%. The stirring device (2000 rpm) and the ultrasonic-assisted dispersion module (50W) were started. The test was performed 3 times in a row, and the average value was taken as the final result. The D50 and D90 values ​​were recorded.

[0127] (3) Place the remaining powder after laser particle size testing in a vacuum drying oven and dry at 60°C for 24 hours to remove moisture; accurately weigh 0.5-1.0 g of the dried sample, put it into a sample tube, and degas at 200°C for 4 hours, with the degassing vacuum degree controlled at 1×10⁻⁶. -3 Below Pa; using a specific surface area analyzer, employing the nitrogen adsorption method, the test is conducted at 77K temperature, with no fewer than 30 adsorption-desorption curve collection points, and the specific surface area is calculated using the BET multi-point method.

[0128] The test results are shown in Table 3.

[0129] Table 3. Particle size distribution and specific surface area test results for each group of samples:

[0130]

[0131] According to the test data in Table 3, the D50 values ​​of Examples 1 to 5 are all less than 0.5 μm, the D90 values ​​are all less than 2 μm, and the BET specific surface area is all greater than 34 m². 2 / g. This indicates that bamboo fiber achieves significant micronization and interlayer separation through a three-stage linkage mechanism of "penetration-explosion-grinding".

[0132] Example 1 exhibited the best overall performance, with a D50 as low as 0.35 μm and a BET specific surface area as high as 41.3 m². 2 / g. This confirms that at this ratio, the bursting kinetics provided by sodium sulfate decahydrate and the recrystallization grinding density achieve an optimal balance, while the polyethylene glycol coating is sufficient to maintain a stable liquid-sealed environment without causing excessive slippage. In Examples 2-5, the particle size fluctuated slightly (0.38–0.45 μm) with minor adjustments to the formulation ratio, but remained generally at the nano / submicron scale, indicating that the process has a wide operating window and good stability.

[0133] Comparative Example 1 (without explosive) has a D50 as high as 12.6 μm and a specific surface area of ​​only 2.1 m². 2 / g, proving that mechanical shearing alone cannot overcome the natural shear strength of the fiber. Although the D50 of Comparative Examples 2–3 (different moisture addition methods) decreased to 7.2–8.7 μm, it was still in the micrometer range, indicating that simple moisture lubrication or unrestricted vapor expansion cannot achieve effective peeling. The D50 of Comparative Example 4 (sodium chloride substitution) was 5.9 μm, with a specific surface area of ​​6.2 m². 2 / g, with performance far lower than Example 1, confirming the crucial role of the "wedge effect" in the recrystallization process of sodium sulfate in the exfoliation of interlayer fibers. Comparative Example 5 (without dispersant) had a D50 of 0.87 μm, reaching the submicron level, but its specific surface area (18.4 m²) was low. 2 The percentage of the dispersant (g) was only about 45% of that in Example 1, indicating that the lack of dispersant led to secondary agglomeration of nanofibers, limiting further improvement in specific surface area.

[0134] In summary, this invention achieves a leap from micron-scale to nano-scale bamboo fiber by regulating the synergistic effect of "crystallization water permeation-steam explosion-salt crystal grinding", and its refining efficiency is significantly better than traditional mechanical grinding and single physical / chemical treatment methods.

[0135] Test Example 4:

[0136] The experimental steps are as follows:

[0137] (1) Weigh 0.5g of the powder samples prepared in Examples 1-5 and Comparative Examples 1-5 respectively, add 99.5g of deionized water, and prepare an aqueous suspension with a mass fraction of 0.5%; use a magnetic stirrer to stir at 1000rpm for 30 minutes, and then ultrasonically disperse at 200W for 10 minutes to ensure that the initial dispersion state is uniform.

[0138] (2) Immediately transfer the above dispersion into a 100mL stoppered graduated cylinder, seal it, and place it on a vibration-free constant temperature platform (25℃) to stand. After standing for 24 hours and 72 hours respectively, observe and record the volume scale of the supernatant, and calculate the supernatant volume ratio (supernatant volume / total volume × 100%) as the sedimentation stability index.

[0139] (3) Take the freshly prepared 0.5% dispersion and test it using a rotational rheometer equipped with a cone plate rotor (50 mm in diameter and 1° cone angle), set the test gap to 0.105 mm, and control the test temperature at 25°C.

[0140] (4) at 0.1s -1 up to 100s -1 The sample was scanned within a certain shear rate range, and the apparent viscosity change was recorded, with a focus on readings at 0.1 s⁻¹. -1 Zero-shear viscosity at low shear rates.

[0141] (5) The shear rate control mode is adopted, and the program is set as follows: the shear rate in the first stage starts from 0s. -1 linearly increased to 100s -1 (Upward curve), the second stage starts at 100s -1 linearly reduced to 0s -1 (Downward curve) Record the change of shear stress with shear rate, and calculate the area of ​​the hysteresis loop enclosed by the upward and downward curves by integration.

[0142] The test results are shown in Table 4.

[0143] Table 4. Test results of sedimentation stability and rheological parameters of 0.5% aqueous dispersions of each group of samples:

[0144]

[0145] According to the test data in Table 4, the dispersions of Examples 1-5 exhibited excellent suspension stability and typical pseudoplastic fluid characteristics.

[0146] In Example 1, no significant stratification was observed after 24 hours of standing (supernatant ratio 0.0%), and only 0.8% of the supernatant precipitated after 72 hours, indicating the formation of a stable colloidal network. Its low-shear viscosity reached 45.2 Pa·s, and the thixotropic ring area reached 1250.4 Pa / s. This high viscosity and strong thixotropy confirm that the bamboo fibers have been exfoliated to a high aspect ratio nanoscale. In the static state, the nanocellulose forms a three-dimensional network structure through hydrogen bonding and physical entanglement, effectively locking in moisture and resisting gravitational sedimentation; under shear stress, the network structure is disrupted, and the fibers orient along the flow direction, exhibiting significant shear-thinning behavior.

[0147] In contrast, the supernatant proportion of Comparative Example 1 (without explosion) reached as high as 85.4% after 24 hours, with a viscosity close to that of pure water (0.005 Pa·s). Its extremely small thixotropic torus indicates that the coarse micron-sized particles could not form a network structure and settled rapidly under gravity. Comparative Examples 2–4 also showed high settling rates (65.8%–82.4%), with limited viscosity improvement, further confirming their insufficient fiber stripping, low aspect ratio, and inability to form effective steric hindrance.

[0148] Although Comparative Example 5 (without dispersant) showed a smaller particle size (D50 = 0.87 μm) in Test Example 3, its supernatant ratio after 72 hours was as high as 48.7%, and its thixotropic ring area (210.5 Pa / s) was much lower than that of Example 1. This indicates that in the absence of a dispersant, despite the reduction in fiber size, the high surface energy leads to severe secondary aggregation and flocculation of the nanofibers in water, destroying the uniform network structure and resulting in a significant decrease in suspension stability.

[0149] In summary, the high stability and rheological properties of this invention not only verify the achievement of dimensional refinement through the three-stage linkage process, but also demonstrate the necessity of dispersants in maintaining the high aspect ratio and dispersion state of nanofibers.

[0150] Test Example 5:

[0151] The experimental steps are as follows:

[0152] (1) Weigh 0.5g of the dried powder samples prepared in Examples 1-5 and Comparative Examples 1-5 respectively, place them in a 50mL centrifuge tube, add 40mL of deionized water; after sealing, shake vigorously for 1 minute, and then let it stand at room temperature for 24 hours. During this period, shake manually once every 4 hours to ensure that the fiber is fully wetted and reaches the water absorption and swelling balance.

[0153] (2) Transfer the soaked suspension to a special centrifuge tube with a 300-mesh nylon filter at the bottom, place the tube in the centrifuge, set the centrifugal force to 3000×g and the centrifugation time to 15 minutes to remove free water in the fiber gaps; after centrifugation, immediately take it out and weigh the wet sample mass on a balance of 0.01% (recorded as m1).

[0154] (3) Place the wet sample and container in a 105℃ forced-air drying oven to dry to constant weight (approximately 4-6 hours), remove and place in a desiccator to cool to room temperature, then weigh the dry sample (recorded as m2); according to the formula WRV=(m1) The water retention value is calculated as m2) / m2×100%. Each group of samples is tested in parallel 3 times, and the arithmetic mean is taken.

[0155] The test results are shown in Table 5.

[0156] Table 5. Results of centrifugal water retention value (WRV) test for each group of samples:

[0157]

[0158] According to the test data in Table 5, the water retention value (WRV) of Examples 1 to 5 all exceeded 410%, with Example 1 reaching the highest at 485.2%. This value is much higher than the conventional level of ordinary micron-sized plant fibers, indicating that the treated bamboo fiber underwent deep structural dissociation.

[0159] The high WRV value of Example 1 confirms the effectiveness of the "in-situ steam explosion" and "salt crystal wedging" mechanisms. The instantaneous release of high-pressure steam tears apart the fiber cell walls, disrupting the dense encapsulation of lignin and hemicellulose, causing the fiber bundles to split into finer microfibrils. This splitting not only significantly increases the specific surface area, but more importantly, exposes a large number of hydrophilic hydroxyl groups that were originally encapsulated within the fibers. Simultaneously, the resulting loose network structure can still physically retain a large amount of water through capillary action under centrifugal force.

[0160] The WRV of Comparative Example 1 (dry grinding) was only 62.4%, indicating that the mechanical force only cut the fibers into short rods, while the internal structure of the fibers remained dense, making it difficult for water to penetrate into the cell walls. Although water was introduced in Comparative Examples 2 and 3 (WRV 115.8%–134.2%), the lack of explosive expansion force from the phase transition meant that the fiber cell walls were not effectively broken, and water absorption mainly remained at the surface wetting stage. The WRV of Comparative Example 4 (sodium chloride substitution) was 148.6%, significantly lower than that of Example 1. This further confirms that the "wedge effect" generated by the volume expansion of sodium sulfate decahydrate during recrystallization plays an irreplaceable role in opening the interlayer structure of fibers, while sodium chloride, due to its lack of water of crystallization, cannot provide this kind of physical opening force.

[0161] Comparative Example 5 (without dispersant) had a WRV of 290.0%, which, while higher than the other comparative examples, was still significantly lower than the Example Group. This indicates that although the fibers were refined, due to the steric hindrance effect of the lack of a dispersant, irreversible hydrogen bonding (keratinization) occurred in the nanofibers during drying or centrifugation, leading to partial pore closure and reducing the physical water retention capacity. Example 1, through the synergistic effect of PEG and the dispersant, effectively maintained the spatial structure of the fibers after dissociation, thereby achieving optimal water retention performance.

[0162] Test Example 6:

[0163] The experimental steps are as follows:

[0164] (1) Weigh polyvinyl alcohol (PVA-1799, degree of alcoholysis 99%) powder and dissolve it in deionized water. Stir mechanically for 2 hours under 90℃ water bath conditions to prepare PVA aqueous solution with a mass fraction of 8%. Let it stand to remove bubbles and use later.

[0165] (2) Weigh the powder samples prepared in Examples 1-5 and Comparative Examples 1-5 (by dry weight) and add them to the above PVA solution at a mass ratio of 5% relative to the solid content of PVA. Stir the mixture magnetically at 60°C for 1 hour, and then ultrasonically disperse it for 30 minutes (power 200W) to ensure that the filler is evenly dispersed in the polymer matrix. Set up another set of pure PVA solution without filler as a blank control group.

[0166] (3) Pour the uniformly dispersed composite slurry into a clean and dry polytetrafluoroethylene (PTFE) mold, and use a scraper to control the thickness of the wet film to be uniform; place the mold in a 45°C forced-air drying oven to dry for 48 hours to form a film, and then dry it in a vacuum oven at room temperature for 24 hours to remove residual moisture.

[0167] (4) Cut the dried composite film into dumbbell-shaped strips conforming to ASTM D638 (gauge length 25 mm, width 4 mm); place the strips in a constant temperature and humidity environment of 50% relative humidity and 23℃ for 48 hours; use a universal testing machine to perform tensile tests, set the tensile rate to 50 mm / min, test 5 parallel samples for each group of samples, record the maximum tensile strength and elongation at break, and take the average value.

[0168] The test results are shown in Table 6.

[0169] Table 6. Test results of mechanical properties of PVA / bamboo fiber composite film:

[0170]

[0171] According to the test data in Table 6, the micro powders prepared in Examples 1-5 significantly improved the mechanical strength of the PVA matrix as fillers.

[0172] The composite film of Example 1 exhibited a tensile strength of 76.2 MPa, representing a 98.4% increase compared to pure PVA (38.4 MPa), and a 216% increase in elastic modulus. This strengthening effect is attributed to the high aspect ratio nanostructure of the product in this example. The high aspect ratio nanofibers construct a dense percolation network framework within the PVA matrix, effectively bearing and transferring stress. Simultaneously, due to the extensive exposure of hydroxyl groups on the cellulose surface (as shown in Test Example 5), strong hydrogen-bonded interfacial bonds are formed between the nanofibers and the hydrophilic PVA matrix, hindering the slippage of molecular chains.

[0173] In contrast, the tensile strength of the composite film in Comparative Example 1 (dry grinding) was only 34.5 MPa, even lower than that of the pure PVA matrix, and the elongation at break dropped significantly to 62.1%. This is because the product of Comparative Example 1 consists of micron-sized coarse particles with a small specific surface area and weak bonding with the matrix. During the stress process, these coarse particles cannot transmit stress and instead introduce stress concentration points as impurities, inducing premature crack initiation and propagation, leading to brittle fracture of the material.

[0174] The tensile strength of Comparative Example 4 (sodium chloride substitution) was 48.9 MPa, showing some enhancement, but far less than that of Example 1. This indicates that the fiber bundles prepared without the "recrystallization wedging" effect have insufficient dissociation and cannot form an effective nano-reinforcing network. The strength of Comparative Example 5 (without dispersant) was 58.3 MPa, lower than that of the Example group, indicating that the agglomerated nanofibers are difficult to disperse uniformly in the matrix, and the defects existing inside the agglomerates limit the further improvement of the composite material's performance.

[0175] In summary, the excellent reinforcing and toughening effect exhibited by the product of Example 1 in the polymer matrix verifies that the bamboo fiber micropowder prepared by this process has nanoscale size, high dispersibility and good interfacial activity, and has the potential to be used as a reinforcing filler for high-performance composite materials.

[0176] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder, characterized in that, Includes the following steps: (1) Mixing: The raw materials containing the following parts by weight are subjected to solid-phase premixing at room temperature to obtain a premix: 100 parts of dried bamboo powder; 300-450 parts of sodium sulfate decahydrate; 100-150 parts of polyethylene glycol; 4-6 parts of interface-modifying dispersant; the interface-modifying dispersant is a compound aqueous solution containing sodium dodecylbenzene sulfonate and sodium lignosulfonate; wherein the mass ratio of sodium dodecylbenzene sulfonate to sodium lignosulfonate is (0.8-1.25):1; (2) Extrusion blasting: The premixed material is fed into a twin-screw extruder. During the material conveying process in the barrel, the crystal water released by the heated sodium sulfate decahydrate and polyethylene glycol are used to construct a confined liquid seal environment. The temperature zone control of the extruder is as follows: the temperature of the feeding section in zone 1 is set to 35-50℃; the temperature of the plasticizing section in zone 2 is set to 70-90℃; the temperature of the blasting section in zone 3 is set to 115-130℃; and the temperature of the exhaust section in zone 4 is set to 95-110℃. This causes the crystal water in the confined space to vaporize and generate in-situ steam micro-blasting, which dissociates the bamboo fiber between layers. (3) Purification and drying: The extrudate is washed to remove salt and polyethylene glycol, and then dried after solid-liquid separation to obtain bamboo fiber ultra-nano powder.

2. The method for preparing bio-based fiber materials with hierarchical regulation of bamboo fiber ultra-nano powder according to claim 1, characterized in that, In step (1), the raw materials mentioned include: The dried bamboo powder has a particle size of 60-80 mesh and a moisture content of ≤1.0 wt%. The average molecular weight of the polyethylene glycol is 600 to 1000.

3. The method for preparing bio-based fiber materials with hierarchical regulation of bamboo fiber ultra-nano powder according to claim 1, characterized in that, The interface-modified dispersant is prepared by the following method: Deionized water was heated to 60–65°C, and sodium dodecylbenzenesulfonate and sodium lignosulfonate were added sequentially. The mixture was stirred at 400–600 rpm for 30–45 minutes, and then the pH was adjusted to 8.5–9.0 to obtain a dispersant solution with a solid content of 37.5%–47.3%.

4. The method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder according to claim 1, characterized in that, In step (2), the screw speed of the twin-screw extruder is set to 150-300 rpm.

5. The method for preparing bio-based fiber materials with hierarchical regulation of bamboo fiber ultra-nano powder according to claim 1, characterized in that, In the fourth exhaust section, as moisture is discharged, dissolved sodium sulfate recrystallizes and precipitates in situ between the loosened bamboo fiber layers. The precipitated anhydrous sodium sulfate microcrystals are used as embedded abrasives to grind and peel the bamboo fibers under the shearing action of the screw.

6. The method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder according to claim 1, characterized in that, In step (3), the cleaning process specifically involves placing the extrudate in hot water at 75-85°C and stirring to clean it.

7. The method for preparing bio-based fiber materials with hierarchical control of bamboo fiber ultra-nano powder according to claim 1, characterized in that, In step (3), the drying process is freeze drying.

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