A superfine bamboo fiber powder grinding process

Abstract

The application discloses a superfine bamboo fiber powder grinding process and belongs to the technical field of bamboo-based new material processing. The process comprises four steps of dry rough grinding, microbial fermentation pretreatment, emulsification wet grinding nanocrystallization and drying post-treatment. The lignin is selectively degraded by white rot fungus complex flora, so that the porosity of bamboo powder is increased by more than 50%. In combination with mineral auxiliary emulsification wet multi-stage series grinding and real-time laser particle size feedback control, superfine bamboo fiber powder with D90 less than or equal to 800nm is prepared. The process is green and environmentally friendly, and the cost is reduced by 30%-50% compared with traditional dry grinding.

Description

Technical Field

[0001] This invention belongs to the field of bamboo-based new material processing technology, specifically relating to a milling process for preparing nanoscale ultrafine bamboo fiber powder by combining microbial fermentation pretreatment with emulsified wet multi-stage tandem milling. This process integrates interdisciplinary technologies such as microbiology, powder engineering, and polymer materials science, and is suitable for preparing nanoscale bamboo fiber powder applicable to new material manufacturing, fine granulation, biodegradable film manufacturing, and high-performance bamboo-plastic composite panels. Background Technology

[0002] Bamboo, as a fast-growing and renewable natural polymer composite material, has cell walls mainly composed of cellulose, hemicellulose, and lignin. Bamboo fiber, due to its high specific strength, good biodegradability, and natural antibacterial properties, shows broad application prospects in composite material reinforcement fillers, biodegradable packaging materials, and functional coatings. Processing bamboo into ultrafine powder is a key step in realizing the high-value utilization of bamboo-based materials. The smaller the particle size, the larger its specific surface area, the stronger its interfacial bonding ability with the polymer matrix, and the better the mechanical properties of the prepared composite material.

[0003] Current bamboo powder processing technologies mainly employ dry grinding. Chinese invention patent CN1311955C discloses a bamboo powder processing method involving steaming and soaking followed by dry grinding, resulting in bamboo powder with a particle size of 80-400 mesh. This process suffers from limitations in particle size reduction, failing to achieve nanoscale levels. Chinese invention patent CN112092130B discloses a method for preparing bamboo fiber powder, using a steaming-microwave carbonization-dry grinding technique. While this increases the porosity of the bamboo powder, the semi-carbonization treatment damages the original cellulose structure of the bamboo fiber, limiting the reinforcing effect of the powder in polymers. Chinese invention patent application CN102715470A discloses a method for preparing ultrafine bamboo shoot powder, using airflow ultrafine grinding to reduce the particle size to below 10 μm. However, this method uses bamboo shoots as raw material, resulting in high energy consumption and lacking fiber surface modification treatment.

[0004] The aforementioned existing technologies generally suffer from the following shortcomings. First, dry milling, due to severe heat generation from inter-particle friction, easily leads to thermal degradation of cellulose, and the particle size is difficult to break through the submicron level. Second, there is a lack of pretreatment methods for the biodegradation of the lignin layer in bamboo, and the residual lignin coating in bamboo powder hinders the effective separation and refinement of fiber bundles. Third, the milling process lacks a real-time particle size monitoring and feedback adjustment mechanism, making it difficult to guarantee batch-to-batch consistency. Fourth, the obtained bamboo powder is mostly not surface-modified, resulting in poor interfacial compatibility and severe agglomeration when the powder is compounded with a polymer matrix. Therefore, there is an urgent need to develop an ultrafine bamboo fiber powder milling process that integrates bio-pretreatment, wet nanomilling, and surface modification. In addition, in the existing bamboo fiber powder preparation processes reported in the literature, although the steam explosion method can achieve fiber bundle separation in a short time, the high-pressure steam released instantaneously during the explosion process can cause irreversible damage to the cellulose crystal structure, leading to a decrease in fiber strength. While chemical pretreatment methods such as alkaline boiling and acid hydrolysis are highly efficient at removing lignin, they generate large amounts of alkaline or acidic wastewater, posing significant environmental risks and increasing production costs. Enzymatic hydrolysis, when used alone, results in slow lignin degradation, making it uneconomical for industrial applications. Regarding milling technology, while air jet milling avoids contamination from the milling media, its milling efficiency is far lower than wet ball milling for highly resilient natural polymers like bamboo fiber. Furthermore, the high-speed airflow during air jet milling causes a rapid increase in fiber temperature, triggering thermal oxidative degradation of cellulose. Wet milling technology has mature applications in mineral powders and inorganic materials, but its systematic application in the nano-processing of bamboo fiber is still lacking, particularly in the absence of process schemes that couple microbial fermentation pretreatment with wet milling. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an ultrafine bamboo fiber powder milling process. This process selectively degrades the lignin barrier layer in bamboo powder through microbial fermentation pretreatment, combines mineral-assisted emulsification wet multi-stage series milling to achieve fiber nano-sizing, and is supplemented by real-time laser particle size feedback control and spray surface coating treatment to obtain ultrafine bamboo fiber powder with a particle size D90 less than or equal to 800 nm. The resulting powder has high specific surface area, high dispersibility and excellent polymer interface compatibility.

[0006] To achieve the above objectives, the present invention adopts the following technical solution. A process for grinding ultrafine bamboo fiber powder includes the following steps: Step 1, dry coarse grinding: Bamboo chips with a length of less than 50mm are fed into a dry coarse grinding mill for crushing to obtain bamboo coarse powder with a particle size of less than 1mm. The bamboo coarse powder is heated and soaked, and the yellow water is separated. The wet bamboo powder is then used for pretreatment. Step 2, microbial fermentation pretreatment: A fermentation broth is prepared by combining white-rot fungi, *Procambarus chrysospora*, cellulase, and *Trichoderma* to form a complex microbial community. The pH of the fermentation broth is adjusted to 5.0-6.5, and the fermentation temperature is controlled at 28-32°C. The wet bamboo powder is mixed with the fermentation broth at a mass ratio of 1:3. The aeration rate is controlled at 0.2-0.5 vvm, and the stirring speed is 30 rpm. Dynamic solid-state fermentation is carried out for 7-15 days. Step 3: Emulsification and wet milling for nano-sizing. A high-speed shear emulsifier is used to mix fermented bamboo powder with water, while talc powder with a particle size of 800nm ​​is added for emulsification and stirring. Zirconia beads of 0.3-0.5mm are used as the milling medium, controlling the solid content to 10%-15%. 0.5% sodium polyacrylate dispersant is added. The emulsified slurry is then sequentially milled through a series of coarse mills, fine mills, and ultrafine mills, with the milling speed controlled at 1500-2500rpm. The milling is repeated 10-15 times, and a wet laser particle size analyzer is used for online monitoring and dynamic feedback adjustment of the milling parameters. Step 4: Drying and post-treatment. The milled bamboo fiber slurry is then subjected to gradient temperature increase and evaporation drying at 120-130°C in a sealed environment until the moisture content is reduced to below 5%. The lumpy material is ball-milled into nanoparticles and then spray-coated with 1%-2% carboxymethyl cellulose for surface modification.

[0007] The beneficial effects of this invention are as follows: First, through the selective biodegradation of the white-rot fungal complex, more than 20% of the lignin in bamboo powder is decomposed and removed under mild conditions, exposing the cellulose microfiber structure and increasing the porosity of the bamboo powder by more than 50%, significantly reducing the difficulty and energy consumption of subsequent milling. Second, the mineral-assisted emulsification wet milling process utilizes the grinding-aiding effect of nano-sized talc and the electrostatic stabilizing effect of sodium polyacrylate to effectively prevent the agglomeration of fiber particles during milling. Combined with multi-stage series milling and a real-time particle size monitoring and feedback system, the particle size of bamboo fiber powder is precisely controlled at the nanoscale level with a D50 of 500-800nm. Third, gradient temperature evaporation drying preserves the porous structure of the fibers, and spray coating surface modification treatment gives the powder excellent anti-agglomeration and polymer compatibility. Fourth, the entire process adheres to the concept of green environmental protection, and the production modification cost is reduced by 30%-50% compared with the traditional dry milling process, making mass production feasible. Fifth, the obtained ultrafine bamboo fiber powder can replace traditional inorganic fillers such as calcium carbonate and talc in the field of polymer composite materials, realizing the efficient and high-value utilization of bamboo resources, and has significant economic and environmental benefits. Detailed Implementation

[0008] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The raw materials and reagents used in the following embodiments are all commercially available analytical grade or industrial grade products, and the equipment used is all conventional laboratory or industrial equipment.

[0009] Example 1 This embodiment provides an optimal implementation scheme for the ultrafine bamboo fiber powder grinding process, and the specific steps are as follows.

[0010] Step 1: Dry coarse grinding and pretreatment. Select bamboo with a growth period of over three years as raw material. After removing the outer green and inner yellow layers, cut the bamboo into strips no longer than 50mm. Feed the bamboo strips into a hammer mill for dry coarse grinding. Set the screen aperture of the mill to 1mm and the rotation speed to 3000rpm. After coarse grinding, collect bamboo powder with a particle size within 1mm. Place the bamboo powder into a stainless steel soaking tank, add pure water at a mass ratio of 4:1, heat to 70°C, and maintain soaking for 3 hours to allow the bamboo powder to fully absorb water, swell, and dissolve some water-soluble organic matter. After soaking, separate the yellow leachate through a 200-mesh sieve. The filter cake is the wet bamboo powder, with a moisture content of approximately 55%-65%.

[0011] Step 2, Microbial Fermentation Pretreatment. The preparation of the complex microbial community was carried out as follows: White-rot fungi, *Phanerochaete chrysospora*, cellulase preparation, and *Trichoderma* spore powder were weighed at a mass ratio of 3:2:1:2. These strains were inoculated separately into potato dextrose liquid medium and cultured at 150 rpm for 48 hours in a 28°C constant temperature shaking incubator to obtain activated culture solutions for each strain. The activated culture solutions were mixed evenly at the above mass ratio to obtain the complex microbial community fermentation broth, and the pH of the fermentation broth was adjusted to 5.5. The wet bamboo powder obtained in Step 1 and the complex microbial community fermentation broth were added to a 50L rotary solid-state fermenter at a mass ratio of 1:3. The tank rotation speed was set to 30 rpm to achieve uniform mixing and agitation of the materials. The aeration rate was controlled at 0.3 vvm to maintain an aerobic fermentation environment, and the fermentation temperature was maintained at a constant 30°C. Samples were taken every 24 hours during fermentation, and the change in lignin content was determined using the Van der Waals method. In this embodiment, the lignin degradation rate reached 25.3% after 10 days of fermentation. Scanning electron microscopy revealed that the bamboo powder fiber bundles were significantly loosened. The porosity of the bamboo powder, determined by the Brunel-Emmett-Taylor method, increased from 8.7% before fermentation to 62.1% after fermentation, indicating that microbial fermentation effectively disrupted the lignin's binding of cellulose microfibrils, exposing a large amount of cellulose microfibril structure and internal pores. Dissolved oxygen concentration and carbon dioxide release were monitored simultaneously in the fermenter during the fermentation process. Days 1-3 of fermentation were the microbial adaptation period, with dissolved oxygen concentration maintained at 4.5-5.0 mg / L and low carbon dioxide release. Days 4-7 of fermentation entered the logarithmic growth phase, with dissolved oxygen concentration decreasing to 2.0-3.0 mg / L, indicating vigorous microbial metabolic activity and the fastest lignin degradation rate during this stage. Days 8-10 of fermentation entered the stationary phase, with the rate of lignin degradation slowing down. Infrared spectroscopy analysis revealed a characteristic absorption peak of lignin in the bamboo powder at 1505 cm⁻¹. - ¹ and 1595cm - The intensity at ¹ is significantly reduced, while the characteristic absorption peak of cellulose is at 1030 cm⁻¹. - The increased relative intensity at ¹ confirms the selective degradation of lignin. X-ray diffraction analysis shows that the crystallinity index of type I cellulose crystals in bamboo powder increased slightly from 65.3% to 67.1% before and after fermentation, indicating that the fermentation process mainly degraded the amorphous components in lignin and hemicellulose, while the cellulose crystalline structure remained largely undamaged. This is crucial for maintaining the mechanical strengthening effect of the subsequent ultrafine powder.

[0012] Step 3: Emulsified Wet Milling for Nano-Sizing. After fermentation, the bamboo powder is drained of excess fermentation liquid and fed into the hopper of a high-speed shear emulsifier. Simultaneously, pure water is added to adjust the solid content to 12%, and talc powder with a particle size of 800 nm is added as a milling auxiliary medium. The amount of talc powder added is 10% of the dry weight of the bamboo powder. The high-speed shear emulsifier is started and run at a shear rate of 8000 rpm for 5 minutes to fully disperse the bamboo powder and talc powder in the aqueous phase and form a uniform emulsion slurry. Sodium polyacrylate dispersant (0.5% of the total solid mass) is added to the emulsion slurry, and after thorough mixing, the slurry is pumped into a series milling system. The milling system consists of three horizontal sand mills connected in series: a coarse mill, a fine mill, and an ultrafine mill. All three mills use zirconia beads with a particle size of 0.3 mm as the milling medium, with a bead filling rate of 80%. The coarse grinding mill speed was set to 1500 rpm, the fine grinding mill speed to 2000 rpm, and the ultrafine grinding mill speed to 2500 rpm. The slurry was pumped into the coarse grinding mill inlet, flowed sequentially through the three mills, and exited from the ultrafine grinding mill outlet, completing one grinding cycle. An online wet laser particle size analyzer (Malvin Mastersizer 3000) was installed at the ultrafine grinding mill outlet to automatically measure the particle size distribution in the slurry after each cycle. When the D50 value was detected to be greater than 800 nm, the system automatically circulated the slurry back to the coarse grinding mill inlet for further grinding. When the D50 value fell within the 500-800 nm range in three consecutive measurements, the grinding was deemed satisfactory, and the slurry was transferred to a collection tank. In this embodiment, after 12 grinding cycles, the D50 of the bamboo fiber in the slurry stabilized at 650 nm, and the D90 was 780 nm, meeting the design requirements. The cumulative energy consumption during the grinding process was recorded in real time using a power meter. The total energy consumption for 12 cycles of milling was 38.5 kWh per kilogram of dry bamboo powder, a 67.9% reduction compared to the estimated energy consumption of 120 kWh / kg required for direct dry ball milling to produce the same particle size. This is mainly attributed to the significant reduction in milling resistance of the bamboo powder due to fermentation pretreatment. During milling, the slurry temperature slowly increased from the initial 25°C to 42°C at the end of milling, a much smaller temperature rise than in dry milling, effectively preventing thermal degradation of cellulose. The viscosity of the milled slurry showed a trend of first increasing and then decreasing with the number of cycles, reaching a peak of 1200 mPa·s during the 5th-7th cycles. Subsequently, due to further reduction in particle size and sufficient adsorption of the dispersant, the viscosity gradually decreased to 680 mPa·s at the end, while maintaining good slurry fluidity.

[0013] Step 4: Drying and Post-processing. The milled bamboo fiber slurry is transferred to a 100L closed high-temperature evaporator, with an initial temperature set at 120°C. A gradient heating method is used for evaporation and drying, specifically increasing the temperature by 10°C every 30 minutes, gradually increasing from 120°C to 130°C, for a total drying time of 4 hours. During the drying process, a slight positive pressure is maintained inside the sealed container to prevent the reabsorption of moisture from the outside air. After drying, the material's moisture content drops to 3.8%, exhibiting a blocky, porous structure. The dried blocky material is then fed into a planetary ball mill and milled at 400 rpm for 30 minutes to pulverize the blocky material into free-flowing nanoparticles. The powder is then fed into a fluidized bed spray coating device, using a 5% carboxymethyl cellulose aqueous solution as the coating liquid. The spray volume is controlled so that the coating layer accounts for 1.5% of the total powder mass. After coating, the powder is dried at 80°C for 30 minutes to obtain the final product: ultrafine bamboo fiber powder.

[0014] The properties of the obtained ultrafine bamboo fiber powder were characterized. The particle size distribution was measured using a laser particle size analyzer, with results showing D50 = 640 nm and D90 = 770 nm. The specific surface area was determined to be 18.5 m² using a Brunel-Emmett-Taylor specific surface area analyzer. 2 / g. The moisture content was determined to be 3.6% by constant temperature drying at 105°C. Ultrafine bamboo fiber powder was melt-blended with polylactic acid at a mass fraction of 10%, and extruded and granulated using a twin-screw extruder at 180°C. After injection molding into standard tensile specimens, the tensile strength was tested and found to be 52.3 MPa, an increase of 26.9% compared to the tensile strength of pure polylactic acid (41.2 MPa). Scanning electron microscopy observation of the cross-sectional morphology showed that the bamboo fiber powder was uniformly dispersed in the polylactic acid matrix, with no obvious agglomeration, and the interfacial bonding between the powder and the matrix was tight.

[0015] Example 2 This embodiment provides a variation of the ultrafine bamboo fiber powder grinding process, which differs from Embodiment 1 in that the fermentation conditions and grinding parameters are adjusted.

[0016] Step one is the same as in Example 1. In Step two, the pH of the fermentation broth was adjusted to 5.0, the fermentation temperature was controlled at 28°C, the aeration rate was set to 0.2 vvm, and the fermentation time was extended to 15 days. After fermentation, the lignin degradation rate was measured to be 30.1%, and the porosity of the bamboo powder increased to 68.5%. The longer fermentation time and lower temperature allowed for more complete lignin degradation, but care should be taken to prevent excessive degradation that could damage the cellulose. In Step three, the solid content was adjusted to 10%, the amount of talc added was 5% of the dry weight of the bamboo powder, and the amount of sodium polyacrylate dispersant remained unchanged at 0.5%. The number of milling cycles was increased to 15, and the final D50 was 580 nm, D90 was 720 nm, and the particle size distribution was narrower than in Example 1. In Step four, the surface modifier was changed to silane coupling agent KH-550, with an addition amount of 1.0% of the powder mass, and the coating method was changed to surface grafting by mixing at 2000 rpm for 10 minutes using a dry high-speed mixer.

[0017] The properties of the obtained ultrafine bamboo fiber powder were characterized. D50 = 575 nm, D90 = 715 nm. Specific surface area was 21.2 m². 2 / g. Moisture content 4.1%. The tensile strength of the ultrafine bamboo fiber powder blended with polylactic acid at a mass fraction of 10% was 48.7 MPa, an increase of 18.2% compared to pure polylactic acid. Although the tensile strength was slightly lower than that of Example 1, the use of silane coupling agent significantly improved the water resistance of the powder. The mass increase rate after soaking in water for 24 hours was only 2.1%, while the water absorption rate of the carboxymethyl cellulose-coated sample in Example 1 was 5.8%. In addition, thermogravimetric analysis of the ultrafine bamboo fiber powder of Example 2 showed that its initial decomposition temperature under nitrogen atmosphere was 272°C, which was higher than that of Example 1 (268°C). This may be because the longer fermentation time allowed for more complete degradation and removal of the low thermal stability hemicellulose component. The microstructure of the ultrafine bamboo fiber powder of Example 2 was observed by transmission electron microscopy. The fibers were found to be nanoscale short rods with an aspect ratio of approximately 3-8. The fiber surface was smooth and there was no obvious lignin residue layer. Energy-dispersive X-ray spectroscopy analysis detected silicon signals on the powder surface, confirming that the silane coupling agent had been successfully grafted onto the fiber surface. Contact angle testing results showed that the water contact angle of the powder in Example 2 was 78.5°, higher than the 32.1° in Example 1, indicating that the silane coupling agent imparted a certain degree of hydrophobicity to the powder, which is beneficial for improving its dispersibility in a non-polar polymer matrix.

[0018] Example 3 This embodiment provides a boundary parameter scheme for the ultrafine bamboo fiber powder grinding process to verify the feasibility of the process parameter range.

[0019] In step one, the bamboo strip length was controlled within 30mm, and the coarse grinding screen aperture was set to 0.8mm. Soaking conditions were 60°C for 2 hours, with a water-to-material ratio of 3:1. In step two, the pH of the fermentation broth was adjusted to 6.5, the fermentation temperature was 32°C, the aeration rate was 0.5 vvm, and the fermentation time was 7 days. After fermentation, the lignin degradation rate was 20.8%, and the bamboo powder porosity increased to 55.3%, meeting the basic requirements for subsequent grinding. In step three, the solid content was increased to 15%, the talc powder addition was 15% of the dry weight of the bamboo powder, and 0.5mm zirconia beads were selected for grinding. After 10 grinding cycles, D50 was 790nm and D90 was 950nm. This result was close to the design upper limit; further increasing the number of cycles to 13 reduced D50 to 720nm and D90 to 860nm. In step four, the gradient heating starts at 120°C and ends at 130°C, with a total drying time of 5 hours. Surface modification uses carboxymethyl cellulose, added at 2.0% of the powder mass.

[0020] The properties of the obtained ultrafine bamboo fiber powder were characterized. D50 = 710 nm, D90 = 850 nm, both within the technical specifications but close to the upper limit. The specific surface area was 15.3 m². 2 / g. Moisture content 4.8%. The tensile strength of the ultrafine bamboo fiber powder blended with polylactic acid at a mass fraction of 10% was 45.6 MPa, an increase of 10.7% compared to pure polylactic acid. This example demonstrates that qualified ultrafine bamboo fiber powder products can still be obtained under conditions of shortened fermentation time to 7 days and 13 milling cycles. It is worth noting that the higher solid content (15%) and larger talc addition (15%) in this example significantly affected the rheological properties of the milled slurry. During milling, the apparent viscosity of the slurry reached 1850 mPa·s, higher than the peak viscosity of 1200 mPa·s in Example 1. This increased the pumping resistance of the slurry in the milling system pipeline, but also improved the shear stress transfer efficiency of the milling media to the bamboo fiber particles. Fourier transform infrared spectroscopy analysis confirmed that although the lignin characteristic peaks of the bamboo powder in this example were weakened, they were still identifiable, indicating that the degree of lignin degradation under 7-day fermentation time was at an acceptable level under boundary conditions. Dynamic light scattering test showed that the polydispersity index of the product in this embodiment was 0.45, which was slightly higher than 0.32 in Example 1 and 0.28 in Example 2, indicating that the shorter fermentation time and fewer milling cycles resulted in a decrease in the uniformity of particle size distribution.

[0021] Comparative Example 1 This comparative example employs a direct dry milling process, without microbial fermentation pretreatment or wet milling. Bamboo chips, after coarse grinding, are directly fed into a planetary ball mill for dry ultrafine milling at 500 rpm for 8 hours. The resulting bamboo powder has a D50 of 12.5 μm and a D90 of 28.3 μm, significantly larger than the nanoscale particle sizes of the embodiments of this invention. When this bamboo powder is blended with polylactic acid (PLA) at a mass fraction of 10%, the tensile strength is only 43.1 MPa, an improvement of only 4.6% compared to pure PLA. Scanning electron microscopy reveals irregularly shaped particles with numerous agglomerates, and a clear gap exists at the interface between the powder and the PLA matrix. This comparative example demonstrates that without fermentation pretreatment and wet milling, dry milling alone is insufficient to achieve nanoscale particle sizes, and the polymer reinforcement effect of the powder is significantly lower than that of the embodiments of this invention. Further analysis of temperature changes during the dry milling process revealed that after 8 hours of ball milling, the internal temperature of the mill jar rose to 85°C, far exceeding the glass transition temperature range of cellulose. This caused some cellulose to undergo thermal softening and chain segment rearrangement, reducing the crystallinity of the powder. Thermogravimetric analysis showed that the initial decomposition temperature of bamboo powder in Comparative Example 1 was only 245°C, lower than the original bamboo powder's 252°C, indicating that the sustained high temperature during the dry milling process had damaged the cellulose structure.

[0022] Comparative Example 2 This comparative example uses microbial fermentation pretreatment but only performs dry milling, without wet milling. The fermentation conditions are the same as step two of Example 1. After fermentation, the bamboo powder is dried and directly fed into a planetary ball mill for dry ball milling, with the milling conditions the same as Comparative Example 1. After dry ball milling, the D50 of the bamboo powder is 5.8 μm and the D90 is 15.2 μm. Although this is an improvement over Comparative Example 1, it is still much higher than the nanoscale particle size of the various embodiments of this invention. The tensile strength of the bamboo powder after blending with polylactic acid is 44.5 MPa. This comparative example illustrates that although fermentation pretreatment can partially improve the grindability of bamboo powder, dry milling itself cannot overcome the submicron particle size bottleneck.

[0023] Comparative Example 3 This comparative example involved wet milling without microbial fermentation pretreatment and without the addition of talc as an auxiliary medium. Bamboo coarse powder was soaked and directly fed into the wet milling system. The milling conditions were the same as in step three of Example 1, but without the addition of talc. After 15 cycles of milling, the D50 was 3.2 μm and the D90 was 8.7 μm. Because the lignin coating in the unfermented bamboo powder was intact, the fiber bundles were difficult to separate and refine effectively, and even increasing the number of milling cycles could not reduce the particle size to the nanoscale. Simultaneously, the absence of talc led to severe particle agglomeration during milling, significantly reducing milling efficiency. The tensile strength of this bamboo powder blended with polylactic acid was 44.8 MPa. This comparative example demonstrates that both fermentation pretreatment and talc as an auxiliary medium are indispensable for achieving nanoscale milling. From a milling kinetics perspective, the lignin content in the unfermented bamboo powder remained at 22%-26%, and these lignins formed a continuous rigid adhesive network between the fiber bundles. During wet milling, most of the impact energy of the milling media is absorbed and buffered by the lignin cementation layer rather than effectively transferred to the fiber bundle interface, making it difficult for the fiber bundles to peel and refine in the radial direction. Without the addition of talc, the direct contact friction coefficient between fiber particles increases, and more milling energy is converted into heat energy rather than surface energy, reducing milling efficiency and exacerbating wear on the milling media. Therefore, microbial fermentation pretreatment to eliminate the lignin barrier and talc-assisted media to reduce frictional energy consumption are two synergistic necessary conditions for achieving nano-scale formation in wet milling.

[0024] Comparative Example 4 This comparative example involved fermentation pretreatment and wet milling, but without surface modification post-treatment. Fermentation and milling conditions were the same as in Example 1. The milled slurry was directly subjected to gradient drying and ball milling without carboxymethyl cellulose spray coating. The resulting bamboo powder had a D50 of 660 nm and a D90 of 790 nm, with particle size parameters similar to Example 1. However, the tensile strength of this bamboo powder blended with polylactic acid at a mass fraction of 10% was only 46.2 MPa, lower than the 52.3 MPa of Example 1. Scanning electron microscopy revealed localized agglomeration of the bamboo powder within the polylactic acid matrix. Furthermore, the bamboo powder exhibited significant agglomeration after 30 days of storage, while the product of Example 1 maintained good powder flowability under the same storage conditions. This comparative example demonstrates that surface modification treatment plays a crucial role in improving powder dispersion stability and polymer interfacial compatibility.

[0025] Comparative Example 5 employed microbial fermentation pretreatment and wet milling, but the milling system was not equipped with an online particle size monitoring and feedback device. The basic conditions for fermentation and milling were the same as in Example 1, but real-time particle size monitoring was not performed during milling; instead, the milling cycle was fixed at 12 times before discharge. The D50 values ​​of the three batches of products were 620 nm, 870 nm, and 540 nm, respectively, with a standard deviation of 166 nm between batches. In contrast, under online particle size monitoring conditions, the D50 values ​​of the three batches of products in Example 1 were 640 nm, 655 nm, and 630 nm, respectively, with a standard deviation of only 12.6 nm. This comparison clearly demonstrates that the online particle size monitoring and feedback control system plays a decisive role in ensuring batch consistency of products.

[0026] The key performance data of the above embodiments and comparative examples were summarized and analyzed. In Example 1, the D50 was 640 nm, the D90 was 770 nm, and the specific surface area was 18.5 m². 2 / g, tensile strength is 52.3MPa. Example 2 has a D50 of 575nm, a D90 of 715nm, and a specific surface area of ​​21.2m². 2 / g, tensile strength is 48.7MPa. Example 3 has a D50 of 710nm, a D90 of 850nm, and a specific surface area of ​​15.3m². 2 / g, tensile strength is 45.6MPa. Comparative Example 1 has a D50 of 12500nm, a D90 of 28300nm, and a specific surface area of ​​1.2m². 2 / g, tensile strength is 43.1MPa. Comparative Example 2 has a D50 of 5800nm, a D90 of 15200nm, and a specific surface area of ​​3.5m². 2 / g, tensile strength is 44.5MPa. Comparative Example 3 has a D50 of 3200nm, a D90 of 8700nm, and a specific surface area of ​​5.1m². 2 / g, tensile strength is 44.8 MPa. Comparative Example 4 has a D50 of 660 nm, a D90 of 790 nm, and a specific surface area of ​​17.8 m². 2 / g, with a tensile strength of 46.2MPa.

[0027] The data above clearly show that the particle size of all three embodiments of the present invention reaches the nanometer level, and the specific surface area is all above 15m². 2 The tensile strength of the polymers blended with polylactic acid (PLA) was superior to that of the comparative examples. Example 1 showed the best performance, with a D50 of 640 nm and a tensile strength of 52.3 MPa, representing a 26.9% increase compared to pure PLA. This enhancement is among the leading levels in bamboo fiber-filled polymer systems.

[0028] The test methods for the various performance indicators in the above embodiments and comparative examples are as follows. Particle size distribution was determined using a Malvern Mastersizer 3000 wet laser particle size analyzer. The dispersion medium was deionized water. After ultrasonic dispersion for 3 minutes, the D50 and D90 values ​​were measured and recorded. Specific surface area was determined using a Mack ASAP 2460 physical adsorption analyzer. High-purity nitrogen was used as the adsorbate. The sample was degassed under vacuum at 120°C for 6 hours before testing, and the specific surface area was calculated according to the Brunel-Emmett-Taylor method. Moisture content was determined according to the GB / T 6284 standard method. 2-3g of sample was dried to constant weight in a 105°C electric thermostatic drying oven, and the percentage of weight loss was calculated. Tensile strength was determined according to the GB / T 1040.2 standard method. A universal testing machine was used to test standard dumbbell-shaped specimens at a tensile rate of 5 mm / min. Five specimens were tested in each group, and the average value was taken. Microscopic morphology was observed using a Hitachi SU8010 field emission scanning electron microscope with an accelerating voltage of 5 kV. The samples were observed after gold sputtering treatment. Lignin content was determined using the Van der Waals method (TAPPI T222 om-02). Porosity was determined using mercury intrusion porosimetry. The blending process of bamboo powder and polylactic acid (PLA) was carried out as follows: Ultrafine bamboo fiber powder and PLA particles were dried separately in an 80°C vacuum drying oven for 8 hours to remove moisture. Raw materials were weighed at a ratio of 10% of the total mass of bamboo fiber powder. They were premixed in a high-speed mixer at 1000 rpm for 5 minutes, and then fed into a twin-screw extruder for melt blending. The extruder temperatures were set as follows: Zone 1: 155°C, Zone 2: 170°C, Zone 3: 180°C, Zone 4: 175°C, and the screw speed was 150 rpm. The extruded strips were water-cooled and granulated. The granules were dried at 80°C for 4 hours and then injection molded into standard tensile specimens using an injection molding machine. The injection temperature was 185°C, the injection pressure was 80 MPa, and the mold temperature was 40°C. Thermogravimetric analysis (TGA) was performed using a Mettler TGA / DSC 1 thermogravimetric analyzer. The test atmosphere was nitrogen, the flow rate was 50 mL / min, the heating rate was 10°C / min, and the test range was from room temperature to 800°C. The results showed that the initial decomposition temperature of the ultrafine bamboo fiber powder in Example 1 under a nitrogen atmosphere was 268°C, which was 16°C higher than the initial decomposition temperature of 252°C of the original bamboo powder without fermentation and milling. This is because the fermentation process removed the lignin component with low thermal stability, while the nano-milling made the cellulose chain segments more regularly arranged.

[0029] The technical solution of this invention achieves efficient conversion from conventional bamboo powder to nano-scale ultrafine bamboo fiber powder through the synergistic effect of three core process steps: microbial fermentation pretreatment, mineral-assisted emulsification wet milling, and surface modification post-treatment. In the microbial fermentation pretreatment stage, lignin peroxidase and manganese peroxidase secreted by white-rot fungi and *Proteus xanthosporium* selectively oxidize and degrade lignin macromolecules in bamboo powder, breaking down the lignin cement layer connecting cellulose microfibers into small molecule phenolic compounds which are discharged with the fermentation broth. Cellulase and *Trichoderma* synergistically act on the amorphous regions on the surface of cellulose microfibers, partially breaking the hydrogen bond network between fiber bundles and significantly enhancing fiber dispersion. The combination of four microorganisms produces a significant synergistic effect, with lignin degradation efficiency and fiber dispersion effect superior to any single strain used alone. Fermentation pretreatment increases the porosity of bamboo powder from 8.7% to 55%-68%, providing numerous crack initiation sites and stress concentration points for subsequent wet milling, a prerequisite for achieving nano-scale milling.

[0030] In the wet milling stage, the addition of nano-sized talc plays a triple role. First, talc particles embed themselves in the micropores and cracks on the surface of bamboo fibers, forming a microscopic wedging effect that promotes the axial separation of fibers into finer filaments during milling. Second, talc itself has a low-friction, lamellar structure, which lubricates and reduces friction between the milling media and bamboo fiber particles, thus reducing milling energy consumption. Third, talc carries a negative charge in the aqueous phase, forming a dual-stabilized system of electrostatics and steric hindrance with the similarly negatively charged sodium polyacrylate dispersant, effectively preventing secondary agglomeration of nano-sized bamboo fiber particles during milling. Multi-stage cascade milling combined with real-time laser particle size monitoring forms a complete closed-loop control system, ensuring a high degree of consistency in particle size distribution for each batch of product.

[0031] In the drying and post-treatment stages, gradient heating evaporation drying avoids the collapse of the fiber pore structure caused by rapid heating, maximizing the preservation of the high specific surface area of ​​the nanoparticles. Carboxymethyl cellulose (CMC) spray coating forms a hydrophilic thin film layer on the powder surface. The carboxyl and hydroxyl groups on its molecular chains can form hydrogen bonds with polymer matrices such as polylactic acid (PLA), significantly improving the interfacial bonding strength between the powder and the matrix. These three interconnected process steps constitute a complete technical system from raw material pretreatment to nanoparticle preparation and surface functionalization modification. At the molecular level, the degree of carboxymethyl substitution in the CMC coating layer is typically 0.6-0.8, with each glucose unit containing approximately 0.6-0.8 carboxymethyl side groups. These carboxymethyl side groups exist as carboxylate ions under neutral and alkaline conditions, imparting a negative charge to the powder surface. The Zeta potential of the powder increases from -15.2 mV before coating to -38.6 mV after coating, and the enhanced electrostatic repulsion effectively inhibits powder agglomeration during storage. When ultrafine bamboo fiber powder is melt-blended with polylactic acid (PLA), the carboxymethyl cellulose coating undergoes partial thermal degradation under high-temperature shear, exposing a large number of hydroxyl active sites on the cellulose surface. These hydroxyl groups interact with the ester groups and terminal carboxyl groups on the PLA molecular chain through hydrogen bonds, forming a chemical bridge between the fiber and the matrix. This interfacial reinforcement mechanism makes the reinforcing efficiency of nanoscale bamboo fiber powder in PLA much higher than that of unmodified coarse-grained bamboo powder. In Example 1, a 10% addition amount can increase the tensile strength by 26.9%, while the same amount of coarse bamboo powder in Comparative Example 1 only brings a 4.6% increase in tensile strength.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A grinding process for ultrafine bamboo fiber powder, characterized in that, Includes the following steps: Step 1, Dry coarse grinding: Bamboo strips with a length of less than 50mm are fed into a dry coarse grinding mill for crushing to obtain bamboo coarse powder with a particle size of less than 1mm; the bamboo coarse powder is heated and soaked to separate the yellow water, and the wet bamboo powder is used for later use. Step 2, Microbial fermentation pretreatment: A fermentation broth is prepared by combining white-rot fungi, *Phanerochaete chrysospora*, cellulase, and *Trichoderma* into a complex microbial community. The pH of the fermentation broth is adjusted to 5.0-6.5, and the fermentation temperature is controlled at 28-32°C. The wet bamboo powder is mixed with the fermentation broth at a mass ratio of 1:3, with an aeration rate of 0.2-0.5 vvm and a stirring speed of 30 rpm. Dynamic solid-state fermentation is carried out for 7-15 days, resulting in a lignin decomposition rate of over 20% and an increase in bamboo powder porosity of over 50%. Step 3, Emulsification and Wet Milling for Nano-Sizing: A high-speed shear emulsifier is used to mix fermented bamboo powder with water, while talc powder with a particle size of 800nm ​​is added as a milling auxiliary medium for emulsification and stirring. Zirconia beads with a particle size of 0.3-0.5mm are used as the milling medium, controlling the solid content to 10%-15%, and sodium polyacrylate dispersant at 0.5% of the solid mass is added. The emulsified slurry is then subjected to multi-stage milling using three mills connected in series: a coarse mill, a fine mill, and an ultrafine mill. The milling speed is controlled at 1500-2500rpm, and the milling is repeated 10-15 times. A wet laser particle size analyzer is used to monitor the particle size distribution online, and the milling parameters are dynamically adjusted to ensure that the median particle size D50 of the bamboo fiber in the slurry is controlled within the range of 500-800nm. Step 4, Drying and Post-treatment: The milled bamboo fiber slurry is placed in a closed high-temperature evaporator and evaporated at 120-130°C with a gradual temperature increase of 10°C to 20°C to reduce the moisture content to below 5% to obtain block material; the block material is then fed into a ball mill and milled into nanoparticles, and surface modified by spraying with 1%-2% carboxymethyl cellulose by mass of the powder to obtain ultrafine bamboo fiber powder with D90 less than or equal to 800nm.

2. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step one, the heating and soaking temperature is 60-80°C, the soaking time is 2-4 hours, and the mass ratio of soaking water to bamboo coarse powder is 3:1 to 5:

1.

3. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step two, the mass ratio of white-rot fungi, *Procambarus chrysospora*, cellulase, and *Trichoderma* in the complex microbial community is 3:2:1:

2.

4. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step two, the dynamic solid-state fermentation is carried out in a rotary fermenter. During the fermentation process, samples are taken every 24 hours to detect the lignin degradation rate. Fermentation is terminated when the degradation rate reaches 20%-35%.

5. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step three, the amount of talc added is 5%-15% of the dry weight of bamboo powder.

6. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step three, the grinding speed of the coarse grinding mill is 1500 rpm, the grinding speed of the fine grinding mill is 2000 rpm, and the grinding speed of the ultrafine grinding mill is 2500 rpm.

7. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step three, the wet laser particle size analyzer is an online laser particle size analyzer. The monitoring frequency is once per cycle. When the D50 in three consecutive measurements all fall within the 500-800nm ​​range, the grinding is deemed to have met the standard.

8. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step four, the heating rate of the gradient heating evaporation drying is 10°C every 30 minutes, and the total drying time is 3-5 hours.

9. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, In step four, the surface modification can also use a silane coupling agent instead of carboxymethyl cellulose, and the amount of the silane coupling agent added is 0.5%-1.5% of the powder mass.

10. The ultrafine bamboo fiber powder grinding process according to claim 1, characterized in that, The D90 of the superfine bamboo fiber powder is less than or equal to 800 nm, the specific surface area is greater than or equal to 15 m 2 / g, the moisture content is less than 5%, and the tensile strength of the superfine bamboo fiber powder after being blended with polylactic acid is greater than or equal to 45 MPa.