Stepped processing method and system of plant fiber superfine powder, product and application

Abstract

The invention relates to the technical field of plant fiber processing, and discloses a step processing method and system of plant fiber superfine powder, a product and application, the superfine powder is composed of 85.2%-91.2% of cellulose, 1.2%-2.9% of ash and the balance of lignin and hemicellulose; the particle surface has a microporous structure formed by steam explosion, and the average length-diameter ratio is 21-32; the processing method comprises the following steps: carrying out steam explosion on a pretreated raw material to dissociate a physical structure; purifying cellulose through alkali treatment and removing impurities; supersonic airflow crushing and turbine grading are carried out in a controlled low-temperature and inert gas environment; the superfine powder is applied to a polylactic acid-based composite material, a physical anchoring site is formed by utilizing surface micropores and a matrix, and a stress transfer network is constructed in the matrix by virtue of a length-diameter ratio structure, so that the interface bonding strength, the mechanical property and the thermal stability of the composite material are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of plant fiber processing technology, specifically to a step-by-step processing method, system, product, and application of plant fiber ultrafine powder. Background Technology

[0002] Plant fibers, as an abundant natural biomass raw material, are widely used in reinforcing bio-based resins due to their high specific strength, low density, and biodegradability. In existing plant fiber powder processing, traditional mechanical crushing or ball milling processes are typically used to refine the raw materials. This high-intensity mechanical shearing easily damages the intrinsic structure of the fibers, leading to severe breakage of cellulose molecular chains. This results in a significant reduction in the average aspect ratio of the powder, making it difficult to form an effective reinforcing skeleton in the composite matrix. Simultaneously, the localized high temperatures generated during mechanical processing can trigger thermal degradation and oxidative discoloration of cellulose, affecting the brightness of the product and its processing performance in downstream products.

[0003] Furthermore, natural plant fibers contain a high proportion of hemicellulose and lignin. Without effective component separation, these components are prone to decomposition during the high-temperature melting and processing of composite materials, generating volatile substances and forming defects within the material, thereby reducing the mechanical strength and thermal stability of the product. Regarding interfacial bonding, plant fiber particles obtained through conventional processes lack microstructural features, resulting in insufficient interfacial compatibility with resin matrices such as polylactic acid (PLA), and low stress transfer efficiency at the interface. Therefore, how to achieve fiber miniaturization while maintaining its high aspect ratio and component purity, and improve its surface micromorphology to enhance interfacial bonding, are urgent technical problems to be solved in the current resource utilization of plant fibers. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a step-by-step processing method, system, product, and application of plant fiber ultrafine powder. It solves the problems of mechanical damage, component impurity, and weak interfacial bonding in existing plant fiber processing, which limit its use as a reinforcing filler in improving the mechanical properties and thermal stability of bio-based composite materials.

[0005] To achieve the above objectives, the present invention provides the following technical solution: Firstly, the present invention provides a step-by-step processing method for ultrafine plant fiber powder, employing the following technical solution: A step-by-step processing method for ultrafine plant fiber powder includes the following steps: The pretreated plant fiber raw material is placed in a pressure vessel, saturated steam is introduced and the pressure is increased. The pressure is maintained at the increased pressure, and then the pressure relief valve is opened to release the pressure in the pressure vessel to atmospheric pressure within a preset time, and the explosive material is collected. The explosive product was added to an alkaline aqueous solution and stirred under heating conditions. After the reaction was completed, solid-liquid separation was performed, and the resulting filter cake was washed with hot washing liquid until neutral. Then it was dried to obtain cellulose intermediate. An inert gas is introduced into the supersonic airflow pulverizing system for displacement. Under controlled low temperature conditions, the cellulose intermediate is driven to undergo collision and refinement by high-pressure inert airflow, and then the plant fiber ultrafine powder is obtained by turbine classification.

[0006] By employing the above technical solution, this invention utilizes a tiered processing flow of physical structure pre-dissociation, chemical component purification, and low-temperature mechanical refinement to reduce the structural strength of plant fibers and improve the chemical accessibility of each component. Under saturated steam conditions, moisture enters the fiber tracheids and intercellular layers. The pressure gradient and volume expansion force generated during the instantaneous depressurization cause the fiber bundles to peel longitudinally along the intercellular layers, forming a uniformly distributed microporous structure on the particle surface. This process weakens the hydrogen bonding forces between cellulose, hemicellulose, and lignin, increasing the effective contact area for subsequent chemical reactions.

[0007] In the alkali treatment stage, sodium hydroxide neutralizes and hydrolyzes residual lignin and hemicellulose, producing sodium lignin salts and oligosaccharides that dissolve in the alkaline aqueous solution and are removed during solid-liquid separation. This process improves cellulose purity and removes low-molecular-weight impurities that affect the interfacial properties of the composite material. In the final ultrafine refining stage, a high-pressure inert gas flow drives the fiber particles to collide at supersonic speeds within the crushing chamber, utilizing kinetic energy conversion to achieve pulverization. The low-temperature environment inhibits heat accumulation during the pulverization process, preventing oxidative degradation of cellulose, molecular chain breakage, and particle agglomeration caused by thermal softening, ensuring that the powder has a stable degree of polymerization.

[0008] Preferably, the pretreated plant fiber raw material is prepared by washing the plant fiber raw material with deionized water and drying it at 70℃-80℃ until the moisture content is 8.0%-9.5%; in the step of increasing the pressure with saturated steam and maintaining the pressure, the pressure is 1.5-3.0MPa, the pressure maintenance time is 60-180s, and the pressure release time in the pressure vessel is less than or equal to 0.1s.

[0009] By adopting the above technical solutions, setting the moisture content of the raw materials can ensure sufficient kinetic energy for the flash evaporation of moisture during the steam explosion process; by adjusting the pressure and depressurization rate, the degree of dissociation and pore size distribution of the exploded material can be controlled, avoiding incomplete dissociation due to insufficient energy.

[0010] Preferably, the alkaline aqueous solution is a sodium hydroxide aqueous solution with a mass percentage concentration of 3%-10%, and the solid-liquid mass ratio of the explosive to the alkaline aqueous solution is 1:(8-15); the stirring reaction temperature is 70℃-95℃, and the time is 1-4 hours; the hot washing solution is deionized water at a temperature of 80℃-90℃, and the washing is carried out until the pH value of the resulting washing solution is 6.5-7.5.

[0011] By adopting the above technical solution and controlling the concentration of alkali solution and the reaction temperature, the corrosive and erosive effects on cellulose molecular chains can be slowed down while effectively removing impurities, thus maintaining a high average degree of polymerization.

[0012] Preferably, the drying temperature is 105℃-110℃, and the moisture content of the cellulose intermediate is controlled at 1.2%-1.8%; the inert gas is selected from nitrogen or argon, and the oxygen volume concentration in the supersonic airflow pulverization system is controlled to be less than 2.0%; the low temperature environment is -10℃ to 25℃; and the turbine classification speed is set to 1000-3000 r / min.

[0013] By adopting the above technical solution, the lower feed moisture content improves the collision efficiency of airflow milling. Milling under low oxygen concentration and controlled low temperature conditions blocks the chain oxidation reaction initiated by free radicals during fiber micronization, ensuring the chemical stability and whiteness of the product.

[0014] Secondly, the present invention provides a system for implementing the above-described processing method, which adopts the following technical solution: A system for implementing the above processing method includes: The steam explosion subsystem includes a high-pressure steam generator, an explosion tank equipped with a fast discharge valve, and a cyclone separator collector; The chemical purification subsystem includes an alkali treatment reactor with mechanical stirring and temperature control jacket, a centrifugal filter, and a vacuum constant temperature oven. The ultrafine refining subsystem includes an inert gas source, an auxiliary cooling unit, a supersonic air jet mill, and a turbine classifier equipped with a classifying wheel; the auxiliary cooling unit is connected to the milling chamber of the supersonic air jet mill and is used to maintain the circulating gas in the milling chamber at -10°C to 25°C.

[0015] By adopting the above technical solutions, this system achieves continuous processing from macroscopic plant fibers to ultra-microscale powders through the cooperation of its various subsystems. The steam explosion subsystem completes the physical loosening of the fiber structure; the chemical purification subsystem achieves component optimization through controlled thermochemical reactions; and the ultrafine refining subsystem, through the integration of a cooling unit and an inert gas source, constructs a pulverizing environment that combines low temperature and oxygen isolation characteristics.

[0016] Thirdly, the present invention provides a plant fiber ultrafine powder obtained by the above processing method, which is composed of the following components by weight percentage: Cellulose 85.2%-91.2%, ash 1.2%-2.9%, balance lignin and hemicellulose; The surface of the plant fiber ultrafine powder particles has a microporous structure formed by steam explosion, and the average aspect ratio is 21-32. The plant fiber ultrafine powder is configured to form physical anchoring sites in the matrix resin, and the average aspect ratio is used to construct a force transmission network within the matrix resin.

[0017] By employing the above technical solution, the powder obtained by this invention has a high cellulose content, reducing the risk of thermal decomposition during subsequent processing. The microporous structure on the particle surface can serve as a permeation channel for the matrix resin. Under pressure, the resin fills into the micropores and solidifies, forming a physically interlocked structure, thereby improving the interfacial shear strength. The average aspect ratio of 21-32 endows the powder with the ability to cross crack tips and transfer stress when the resin is under stress.

[0018] Preferably, the median particle size D of the plant fiber ultrafine powder 50 The particle size distribution ranges from 5.8 to 28.5 μm, with a particle size distribution span of (D). 90 -D 10 ) / D 50 Its value is 1.55-1.95, and its specific surface area is 10.5-18.5 m². 2 / g.

[0019] By limiting the range of physical parameters, the narrow particle size distribution reduces the probability of powder agglomeration in the resin, and the higher specific surface area increases the number of effective binding sites between the powder and the resin.

[0020] Preferably, the average degree of polymerization of cellulose in the component is 784-845, and the CIEL of the plant fiber ultrafine powder is [missing information]. ∗ The brightness value is 82.35-87.56.

[0021] This invention maintains the long molecular chain structure of cellulose through a step-by-step, gentle processing technique, thus ensuring the intrinsic mechanical strength of the powder.

[0022] Fourthly, the present invention provides an application of the plant fiber ultrafine powder as described in any one of claims 6-9 in the preparation of polylactic acid-based composite materials to improve interfacial bonding strength, enhance mechanical properties, or improve thermal stability.

[0023] By adopting the above technical solution, plant fiber ultrafine powder utilizes the micro-interlocking effect on the surface and the geometric constraint effect generated by the aspect ratio to optimize the stress distribution state inside the polylactic acid matrix and improve the mechanical stability of bio-based composite materials.

[0024] This invention provides a step-by-step processing method, system, product, and application of plant fiber ultrafine powder. It has the following beneficial effects: 1. This invention constructs a microporous structure on the surface of plant fiber particles through a steam explosion process. During the preparation of bio-based composite materials, the matrix resin can penetrate and fill the interior of the micropores, forming stable physical anchoring sites. This microstructural feature enhances the interfacial bonding force between plant fibers and the resin matrix, enabling the composite material to effectively suppress interfacial delamination when under stress.

[0025] 2. The present invention combines supersonic airflow pulverization with low-temperature environmental control, which enables the product to maintain a high average degree of polymerization of cellulose and an aspect ratio of 21-32. The ultrafine powder with this aspect ratio can build a stress transmission network inside the matrix resin, and play a role in strengthening and toughening by crossing cracks and distributing stress. At the same time, the controlled low-temperature pulverization process avoids thermal oxidation degradation of cellulose, ensuring the intrinsic mechanical strength of the reinforcing filler.

[0026] 3. This invention adopts a step-by-step processing method that combines physical pretreatment and chemical purification, which achieves efficient enrichment of cellulose components and deep removal of impurities; the cellulose content of up to 85.2% in the product reduces the risk of material decomposition during thermal processing; this component optimization improves the compatibility of powder with matrix resins such as polylactic acid, ensuring the thermal stability and mechanical properties of the composite material in practical applications. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of fiber component analysis according to the present invention; Figure 2 This is a schematic diagram illustrating the particle size distribution evaluation of the present invention; Figure 3 This is a schematic diagram of the BET specific surface area test of the present invention; Figure 4 This is a schematic diagram illustrating the comparative analysis of tensile strength in this invention; Figure 5 This is a schematic diagram illustrating the bending strength and modulus analysis of the present invention; Figure 6 This is a schematic diagram comparing the notch impact strength of the cantilever beam according to the present invention; Figure 7 This is a schematic diagram comparing the degree of polymerization of cellulose in this invention; Figure 8 This is a schematic diagram illustrating the energy consumption per ton of product during the processing of this invention; Figure 9 This is a schematic diagram illustrating the correlation between thermal stability and brightness value in this invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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 are within the scope of protection of the present invention.

[0029] Examples 1-3: Example 1: This embodiment provides a step-by-step processing method, system, product, and application of plant fiber ultrafine powder, including the following steps: Raw material pretreatment and first stage: steam explosion macroscopic dissociation Dried rice husks were selected as raw material, washed with deionized water, and then dried at 80℃ until the moisture content was 9.5%.

[0030] The pretreated rice husks were loaded into a steam explosion reactor. Saturated steam was introduced, and the pressure was increased to 1.5 MPa, which was maintained for 60 seconds.

[0031] Open the pressure relief valve to reduce the pressure in the reaction vessel to atmospheric pressure within 0.1 seconds. The rice husks undergo instantaneous flash evaporation under the pressure gradient, and the resulting explosive material is collected.

[0032] Second stage: Alkali treatment and chemical purification Prepare a 3% (w / w) aqueous solution of sodium hydroxide (NaOH) as a chemical purification reagent.

[0033] The explosive material is added to an alkaline solution, and the solid-liquid mass ratio is controlled at 1:8.

[0034] Start mechanical stirring (150 r / min), heat to 70℃ and maintain the temperature for 1 hour. Use alkaline solution to perform preliminary degradation of the lignin exposed after the explosion.

[0035] After the reaction was completed, solid-liquid separation was performed, and the filter cake was washed with 80℃ hot water until the pH value was 7.0±0.5.

[0036] The product was dried at 105°C to constant weight to obtain a high-purity cellulose intermediate (moisture content of approximately 1.8%).

[0037] Third stage: Inert protective airflow ultrafine pulverization and classification The system is purged with high-purity nitrogen (99.9% purity) to replace oxygen and keep the oxygen volume concentration in the system below 2%.

[0038] The system's circulating gas temperature is maintained at 25°C by a chiller unit.

[0039] The intermediate is fed into the grinding chamber, where high-pressure nitrogen gas drives the materials to collide with each other, achieving physical refinement.

[0040] Adjust the turbine classifier speed to 1000 r / min.

[0041] The finished product was collected and tested. The powder D... 50 =28.5μm, particle size distribution span (D 90 -D 10 ) / D 50 =1.95, cellulose purity is 85.2%, ash content is 2.9%, and BET specific surface area is 10.5m². 2 / g, with an aspect ratio of 21.

[0042] Example 2: This embodiment provides a step-by-step processing method, system, product, and application of plant fiber ultrafine powder, including the following steps: Raw material pretreatment and first stage: steam explosion macroscopic dissociation Select bamboo fragments (5-8mm in size), wash them, and dry them at 70℃ until the moisture content is 8.0%.

[0043] The vessel is placed in a steam explosion reactor and saturated steam is introduced. The pressure is increased to 2.2 MPa and maintained at this pressure for 120 seconds.

[0044] The pressure is released by instantaneously opening the discharge valve. The resulting blasted bamboo material exhibits a highly fluffy, fibrous structure with a significantly increased specific surface area compared to the original material.

[0045] Second stage: Alkali treatment and chemical purification Prepare a 6.5% (w / w) aqueous solution of sodium hydroxide (NaOH).

[0046] The blasted bamboo material is added to the alkaline solution, and the solid-liquid mass ratio is set to 1:12.

[0047] Start stirring (220 rpm), heat to 85°C, and continue the reaction for 2.5 hours. The alkali solution penetrates efficiently through the physical channels created by the explosion, breaking the chemical bonds in the LCC complex and allowing lignin and hemicellulose to dissolve fully.

[0048] After centrifugation and filtration, rinse repeatedly with 85℃ hot water until neutral.

[0049] The high-purity cellulose intermediate was obtained by drying at 105℃ to a moisture content of <1.5%.

[0050] Third stage: Inert protective airflow ultrafine pulverization and classification The system continuously injects high-purity nitrogen to ensure that the oxygen volume concentration remains stable below 1.5%.

[0051] Liquid nitrogen-assisted cooling is activated to maintain the system operating temperature at 5°C to prevent the heat from pulverizing the cellulose from causing discoloration or degradation.

[0052] The material undergoes physical stripping and refinement under the action of supersonic nitrogen gas flow.

[0053] Adjust the turbine stager speed to 2000 r / min.

[0054] The finished product was collected and tested; the powder D... 50 =15.2μm, particle size distribution span of 1.62, cellulose purity of 88.5%, ash content of 1.8%, and BET specific surface area of ​​16.8m². 2 / g, with an aspect ratio of 26.

[0055] Example 3: Synergistic cascade processing of plant fiber ultrafine powder under high-strength parameter combinations This embodiment provides a step-by-step processing method, system, product, and application of plant fiber ultrafine powder, including the following steps: Raw material pretreatment and first stage: steam explosion macroscopic dissociation Select short industrial hemp fibers (3-6 mm) and dry them at 80°C until the moisture content is 9.0%.

[0056] The vessel is placed in a high-pressure steam explosion reactor and high-pressure saturated steam is introduced. The pressure is increased to 3.0 MPa and maintained at this pressure for 180 seconds.

[0057] The rapid pressure relief device is triggered, and the material is ejected within <0.1 seconds. The intense physical expansion causes complete macroscopic disintegration of the tightly packed hemp fiber bundles.

[0058] Second stage: Alkali treatment and chemical purification Prepare a 10% (w / w) sodium hydroxide (NaOH) aqueous solution.

[0059] The blasted hemp material is added to the alkaline solution, and the solid-liquid mass ratio is set to 1:15.

[0060] Start forced stirring (300 rpm), adjust the temperature to 95℃, and allow the reaction to proceed for 4 hours. The combination of high-concentration alkali solution and high temperature achieves deep removal of stubborn lignin and gums from hemp fibers.

[0061] After centrifugation, the sample is washed with hot deionized water at a temperature above 90°C until the pH value reaches 7.0.

[0062] The product was dried at 110°C to a moisture content of 1.2% to obtain a pure white, high-purity cellulose intermediate.

[0063] Third stage: Inert protective airflow ultrafine pulverization and classification The system is filled with high-purity argon (Ar) gas to keep the oxygen volume concentration in the system below 1.0%.

[0064] The temperature of the pulverizing chamber and the grading zone is strictly controlled at -10℃ using a liquid nitrogen cryogenic system.

[0065] Materials undergo supersonic collisions driven by high-pressure argon gas, achieving a leap to the micro- and nano-scale.

[0066] Adjust the turbine classifier speed to the upper limit of 3000 r / min.

[0067] Collect the finished product. Testing revealed that the powder D... 50 =5.8μm, particle size distribution span 1.55, cellulose purity 91.2%, ash content 1.2%, BET specific surface area 18.5m². 2 / g, with the aspect ratio maintained at 32.

[0068] Comparative Examples 1-5: Comparative Example 1: Compared with Example 2, the difference is that the first-stage steam explosion treatment is omitted. The pretreated bamboo chips are directly put into the second-stage alkali treatment unit. In order to ensure the reaction proceeds as much as possible, the alkali treatment stirring time is extended from 2.5 hours to 5 hours. The remaining process parameters and steps are the same as in Example 2.

[0069] Comparative Example 2: Compared to Example 2, the difference lies in that the second-stage alkali treatment chemical purification step is omitted. The bamboo material after the first-stage blasting is directly dried and then enters the third-stage airflow pulverizing system. The remaining process parameters and steps are the same as in Example 2.

[0070] Comparative Example 3: Compared to Example 2, the difference lies in the reversed order of the first and second stages. The bamboo fragments are first purified by alkali treatment, then washed and dried before being subjected to steam explosion treatment, and finally airflow pulverization. All other process parameters are the same as in Example 2.

[0071] Comparative Example 4: Compared with Example 2, the difference is that the first and second stages are omitted. The pretreated bamboo scraps are directly fed into a ball mill for long-term (12 hours) pre-crushing, and then enter the air jet milling system. The remaining process parameters are the same as in Example 2.

[0072] Comparative Example 5: Compared with Example 2, the difference is that in the third-stage pulverization process, room temperature air is used as the pulverizing medium instead of high-purity nitrogen, and the cooling system is turned off, allowing the temperature of the pulverizing chamber to rise naturally (measured at about 55-65℃). The other parameters are the same as in Example 2.

[0073] Test Example 1-3: Test Example 1: Physicochemical Indicators and Component Analysis of Plant Fiber Ultrafine Powder Experimental instructions and procedures: Sample preparation and pretreatment: The plant fiber ultrafine powder samples prepared in Examples 1, 2, and 3 were placed in a vacuum drying oven and dried at 60°C for 12 hours to remove the physical moisture adsorbed on the surface of the material. The dried samples were immediately placed in a desiccator containing color-changing silica gel to cool to room temperature for subsequent determination of various physicochemical properties.

[0074] Quantitative analysis of plant components: Van Sossel's method for analyzing detergent fibers was used. 1.00 g of dried powder sample was accurately weighed. First, it was extracted by reflux with neutral detergent solution (NDS) for 1 hour, followed by filtration and washing to obtain neutral detergent fiber (NDF). Then, acid detergent solution (ADS) was added and refluxed for 1 hour to obtain acid detergent fiber (ADF). Finally, it was treated with 72% sulfuric acid solution at 20°C for 3 hours. The mass percentages of cellulose, lignin, and hemicellulose in the sample were calculated by stepwise filtration, drying, and weighing.

[0075] Particle size distribution characteristics determination: A laser particle size analyzer was used for detection. The powder to be tested was dispersed in anhydrous ethanol medium, the circulation pump was turned on, the speed was set to 2000 r / min, and ultrasonic dispersion was performed for 3 minutes. Measurement was taken after the light-blocking degree reached the test range of 10%-15%. The instrument automatically recorded and output D... 10 D 50 and D 90 Indicators, and based on the formula Span = (D 90 -D 10 ) / D 50 The particle size distribution span is calculated to evaluate the homogeneity of powder particles.

[0076] Specific surface area determination: The BET nitrogen adsorption method was used. Approximately 0.5 g of sample was placed in a special sample tube and subjected to vacuum degassing at 100 °C for 6 hours to clean the surface micropores. Using high-purity nitrogen as the adsorbate in a liquid nitrogen environment at 77 K, the adsorption amount of the sample was measured at different relative pressures. The isothermal adsorption curve was linearly fitted using the multi-point BET equation to finally obtain the specific surface area value of the sample.

[0077] Ash and moisture content analysis: Ash content was determined according to GB / T742 standard. Approximately 2g of sample was placed in a crucible of known constant weight and ignited in a muffle furnace at 575±25℃ until the residue reached constant weight. The ash content was calculated by the mass difference. Moisture content was determined according to GB / T2677.2 standard. The sample was dried in an electrically heated forced-air drying oven at 105℃ until constant weight. The moisture content was calculated based on the mass loss.

[0078] Experimental data: Table 1: Comparison of Physicochemical Indicators and Components of Plant Fiber Ultrafine Powder from Different Examples

[0079] Test conclusion: Based on the experimental measurement data in Table 1, combined with the attached... Figures 1 to 3 Visual analysis reveals that the plant fiber ultrafine powder tiered processing scheme described in this invention has clear technical feasibility in achieving precise purification of components and control of physical specifications.

[0080] Regarding changes in chemical composition, such as Figure 1 As shown, a comparison of dark, medium, and light-colored bars clearly demonstrates that with the gradual increase in processing intensity, the cellulose purity in the product significantly increases from 85.23% in Example 1 to 91.18% in Example 3. This trend proves the highly efficient dismantling effect of the first-stage steam explosion on the plant biomass resistance barrier of this invention. Under saturated steam pressures of 1.5 MPa to 3.0 MPa, the instantaneous flash evaporation effect during pressure relief creates a large number of micro-nano pores within rice husks, bamboo, and hemp fibers, enabling the second-stage alkali solution to overcome the physical shielding of the naturally dense structure. Figure 1 The significant shortening of the medium-colored column bars confirms the lignin removal effect. The lignin content in Example 3 was as low as 2.06%, indicating that the ester and ether bonds between lignin functional groups underwent deep dissociation under the thermochemical synergistic effect of blasting pore formation and high-concentration alkaline solution.

[0081] Regarding the physical properties of powder, Figure 2 The curve depicting the variation of characteristic particle size is shown. As can be seen from the figure, the solid line represents D... 50 With the dashed line representing D 90 As the parameters of the examples were optimized, the particle size distribution decreased synchronously, and the longitudinal distance between the two curves gradually narrowed. This not only reflects the transition of powder fineness from the micrometer to the submicrometer level, but also demonstrates the improvement in particle size distribution uniformity through the narrowing difference. Example 3 achieved D at a classification speed of 3000 r / min. 50The particles have an extremely fine size of 5.83 μm and a span value of only 1.55. This extremely narrow distribution is attributed to the protective mechanism of the low-temperature inert gas in the third stage, which effectively suppresses the surface softening and electrostatic agglomeration of cellulose hydroxyl groups caused by frictional heat generation during high-speed collisions, ensuring that the powder particles can be precisely cut according to the hydrodynamic diameter in the classifying wheel.

[0082] also, Figure 3 The BET specific surface area test results show that the specific values ​​above each column increase significantly with the increase of ultra-miniaturization, reaching a maximum of 18.52 m. 2 / g. This data variation pattern profoundly reveals the effect of physical exfoliation mechanism on the exposure of active sites on the fiber surface. As the particle size decreases stepwise, a large amount of the internal surface area originally enclosed within the fiber bundle is released. This well-developed surface structure provides excellent physical anchoring space and chemical bonding sites for subsequent application of powder as a reinforcing filler in composite matrix.

[0083] In summary, the data results of Test Example 1 fully support the synergistic mechanism of physical pre-dissociation, chemical deep purification, and low-temperature physical exfoliation in this invention. This solution not only successfully solves the common problem of inefficient separation of plant fiber components, but also prepares standardized ultrafine powder products with high purity, narrow distribution, and high activity without damaging the integrity of the fiber molecular chains, fully meeting the technical requirements of high-performance industrial fillers.

[0084] Test Example 2: Comparative Test of Mechanical Properties of Bio-based Composite Materials Experimental instructions and procedures: Raw material pretreatment and drying: The plant fiber ultrafine powders prepared in Examples 1-3 and Comparative Examples 1-5, as well as polylactic acid (PLA) particles, were placed in a vacuum drying oven. They were dried continuously at 80°C for 8 hours to ensure that the moisture content of the materials was reduced to below 0.1% by mass, thus avoiding the risk of polyester hydrolysis and degradation during melt extrusion.

[0085] Physical premixing process: Weigh out 15% of the ultrafine powder product by mass, with the remainder being the PLA matrix. Put both into a high-speed mixer, set the speed to 500 r / min, and mix for 5 minutes at room temperature to ensure that the fiber powder is uniformly coated on the surface of the resin particles, reducing feeding fluctuations during subsequent extrusion.

[0086] Melt extrusion granulation: The mixture is melt-sheared using a co-rotating twin-screw extruder. The extruder temperature zones are set as follows: Zone 1 160℃, Zone 2 175℃, Zone 3 185℃, Zone 4 190℃, and die head 185℃. The screw speed is maintained at 200 r / min. The melt is extruded through a die, water-cooled, and then cut into standard particles of 2-3 mm by a pelletizer.

[0087] Standard specimen molding: After secondary drying, the composite particles are molded into standard mechanical specimens using an injection molding machine. The injection pressure is set to 85 MPa, the barrel temperature to 195℃, the mold temperature to 30℃, and the holding time to 15 s. Type I tensile specimens, rectangular bending specimens, and notched impact specimens that meet the standard requirements are prepared.

[0088] Environmental conditioning and equilibration: The molded sample was placed in a constant temperature and humidity chamber (temperature 23±2℃, relative humidity 50±5%) for 48 hours to eliminate internal stress and allow the material to reach the performance test equilibrium point.

[0089] Mechanical property determination: Tests were performed using a computer-controlled universal testing machine. Tensile properties were tested according to GB / T1040.2 at a speed of 5 mm / min; bending properties were tested according to GB / T9341 at a span of 64 mm and a speed of 2 mm / min; notched impact strength of cantilever beams was tested according to GB / T1843. Five valid splines were collected for each data set, and the arithmetic mean of the results was taken.

[0090] Experimental data: Table 2: Summary of Mechanical Property Tests of Modified PLA Composites in Examples and Comparative Examples

[0091] Test conclusion: Based on the experimental data provided in Table 2, and combined with... Figures 4 to 6 The performance characterization results confirm that the step-by-step processing technology described in this invention has significant advantages in improving the mechanical properties of bio-based composite materials.

[0092] According to the data recorded in Table 2, the tensile strength of pure PLA is only 62.43 MPa, while the strength of the composite material after adding the product of Example 3 increases to 79.12 MPa. Figure 4 As shown in the tensile strength comparison chart of the composite materials, the reinforcing effect of Examples 1-3 exhibits a clear gradient upward trend, and all are superior to all comparative examples. This strength improvement directly reflects the improvement effect of this scheme on the matrix properties. By comparing Comparative Example 1 (lacking steam explosion) and Comparative Example 4 (conventional dry pulverization), it can be observed that the fiber lacking the first-stage explosion pore-forming effect has a weak mechanical bonding force with the resin matrix due to its smooth surface; the tensile strength of Comparative Example 4 even drops to 58.23 MPa. This further confirms the scientific validity of the present invention in establishing a strong interfacial bond through steam flash evaporation technology.

[0093] Regarding the evaluation of material rigidity, the flexural strength and flexural modulus of Example 3 reached 114.63 MPa and 6.45 GPa, respectively. Figure 5Bending performance analysis shows that the synchronous upward trend of the curve confirms that the high-purity, narrow-distribution ultrafine powder achieves good physical dispersion in the matrix. In stark contrast, Comparative Example 3 (a reverse process of chemical followed by physical) suffers from severely limited modulus improvement because its fiber aspect ratio is already disrupted by deep chemical degradation before the pulverization stage. This result demonstrates that the present invention follows the ordered logic of physical pre-dissociation, chemical purification, and low-temperature physical exfoliation, which can completely preserve the rigid framework of the fibers, allowing the product to withstand greater effective loads when bent.

[0094] Regarding toughening effect, Figure 6 The notched impact strength test results of the cantilever beam most powerfully highlight the advantages of this invention. The pure PLA matrix exhibits 2.85 kJ / m². 2 The brittle fracture characteristics of Example 3 were observed, while the impact strength of Example 3 increased to 6.82 kJ / m. 2 The increase exceeded 130%. Figure 6 The height of the dark-colored columns in the intermediate example group was significantly higher than that in the comparative example. This was mainly due to the physical refining process under the third-stage low-temperature protection, which maintained the surface activity of the fibers while achieving ultra-micronization. Comparative example 5 used conventional pulverization, and the frictional heat caused oxidative degradation of the fiber surface, resulting in a decrease in interfacial bonding force and making its impact performance improvement effect far less than that of the intermediate example group.

[0095] In summary, the test data and the accompanying figures are completely consistent. This invention achieves synergistic purification of fiber components and preservation of physical morphology through the orderly intervention of physical and chemical energy. This not only improves the tensile and flexural stiffness of the composite material, but also significantly toughens it by utilizing the excellent interfacial bonding force and the bridging effect formed by the aspect ratio, overcoming the common drawback of high brittleness in natural fiber-reinforced materials.

[0096] Test Example 3: Comprehensive Evaluation of Process Energy Efficiency and Product Thermal Stability Experimental instructions and procedures: Determination of average degree of polymerization (DP) of cellulose: Quantitative analysis was performed using the copper ethylenediamine (CED) solution viscosity method according to GB / T1548 standard. 0.5 g of dried plant fiber ultrafine powder was accurately weighed and placed in 50 mL of a 0.5 mol / L copper ethylenediamine solution. The solution was continuously stirred in a constant temperature circulating water bath at 25 ± 0.1 °C until the powder was completely dissolved to form a homogeneous solution. The outflow time of the solution and the pure solvent was measured using a calibrated Ubbelohde viscometer, and the intrinsic viscosity [η] was calculated. This η was then substituted into the empirical formula DP. 0.905 =0.75[η] calculates the average degree of polymerization of cellulose molecules.

[0097] Powder color value (CIE L) ∗ a ∗ b ∗Test: Optical characterization of the sample was performed using a high-precision fully automatic colorimeter. The ultrafine powder to be tested was uniformly packed into a standard powder test dish, and a certain pressure was applied to flatten the surface. The L of the sample was measured under a D65 standard light source and a 10° observation angle. ∗ (Brightness), a ∗ (Red-Green Axis) and b ∗ (Yellow / Blue Axis) Values. Through L ∗ The magnitude and fluctuation of the values ​​are used to assess the degree of degradation of cellulose and lignin color development caused by localized mechanical heat generation or oxidation reactions during processing.

[0098] Unit product energy consumption statistics: Power monitoring instruments were installed on the main power input circuits of the steam explosion system, alkali treatment reaction unit, and low-temperature airflow pulverization module on the pilot production line. The total power consumption (kWh) from raw material pretreatment to finished product output was recorded throughout the entire process, and the total mass of the corresponding qualified product was weighed. Fluctuations during equipment no-load and unstable operation phases were deducted from the statistics, and the specific energy consumption per ton of product (kWh / t) was calculated to evaluate the energy conversion efficiency of each process scheme.

[0099] Thermal stability characterization (TGA): The thermogravimetric behavior of the product was determined using a simultaneous thermogravimetric analyzer under an inert atmosphere. 8-10 mg of sample was weighed and placed in an alumina crucible, and high-purity nitrogen gas was introduced at a flow rate of 50 mL / min. The heating rate was set to 10 °C / min, and the temperature range was 30-600 °C. The initial decomposition temperature Td (defined as the temperature corresponding to a 5% sample mass loss) was extracted from the recorded thermogravimetric curves and used to analyze the thermal stability of the product during subsequent composite material melting and processing.

[0100] Experimental data: Table 3: Summary of Energy Efficiency, Molecular Weight, and Optical and Thermal Stability Data of Plant Fiber Processing under Different Processes

[0101] Test conclusion: Based on the experimental data in Table 3, and in conjunction with the appendix... Figures 7 to 9 The characterization results can verify the technical rationality of the step-by-step process described in this invention in maintaining fiber structure integrity and reducing energy consumption.

[0102] According to the energy consumption statistics in Table 3, the total energy consumption per ton of product in Examples 1-3 showed a steady downward trend with the refinement of process parameters, with the energy consumption of Example 3 decreasing to 486.5 kWh / t. In contrast, Comparative Example 1, which did not employ steam explosion pretreatment, had a total processing power consumption as high as 785.2 kWh / t. Figure 8The energy consumption analysis of ton-of-product processing shows that the energy consumption of the example group with steam explosion stage pretreatment is significantly lower than that of the traditional process group. This data difference reveals the physical mechanism of the first stage process: during the steam explosion process, the mechanical work generated by the instantaneous depressurization of high-temperature and high-pressure steam causes multi-scale peeling inside the fiber cell wall, destroying the natural chemical and physical cross-linking between cellulose, lignin, and hemicellulose, and reducing the overall mechanical resistance of the fiber. This pre-manufactured physical defect significantly improves the mechanical energy utilization rate during the third stage of ultrafine grinding. Comparative Example 4, relying solely on conventional mechanical grinding, has a specific energy consumption (924.6 kWh / t) that is approximately 1.9 times that of Example 3, demonstrating the energy-saving advantage of pre-forming pores and reducing mechanical resistance in the mechanism.

[0103] Regarding molecular chain protection and product color characteristics Figure 7 The comparison of the degree of polymerization of cellulose molecular chains clearly demonstrates the ability of different processes to maintain the cellulose backbone. In the figure, dark gray bars represent the examples, all with a degree of polymerization above 780 (Example 3 reaching 845), while the light gray bars, representing the comparative examples, generally have lower degrees of polymerization, especially Comparative Example 4, which is only 412. This difference in degree of polymerization directly affects the reinforcing potential of the material. Figure 9 Brightness value L in the evaluation of product thermal stability and optical properties ∗ As can be seen from the curve trend, L in Example 3 ∗ The efficiency reached 87.56. Comparing this to Comparative Example 5 (room temperature air pulverization), it can be seen that the lack of low-temperature nitrogen protection leads to the accumulation of frictional heat within the pulverization chamber, triggering the thermal oxidative degradation of cellulose hydroxyl groups. This invention utilizes a third-stage low-temperature inert protective environment to effectively block the oxidative degradation pathway, maintaining the long-chain structure of the original molecules while achieving fiber refinement.

[0104] The change in the initial decomposition temperature Td further confirms the improvement in thermal stability. Figure 9 The solid square representing Td and the square representing luminance L are in the middle. ∗ The dashed dots show a synchronous growth trend, indicating that this process, while improving fiber whiteness, enhances the processing thermal stability of the product through efficient removal of hemicellulose with low thermal stability and component purification. The Td of Example 3 increased to 312.8℃, approximately 58℃ higher than Comparative Example 4. Data from Comparative Example 3 (process sequence reversed) shows its Td is only 268.2℃, indicating that an incorrect processing sequence can cause irreversible damage to the structure of the cellulose crystal regions by chemical reagents.

[0105] In summary, the test data and the accompanying drawings are highly consistent, confirming the advanced nature of the physical pre-dissociation chemical deep purification low-temperature physical exfoliation step-by-step logic of this invention. Through the orderly distribution of physical and chemical energy, this invention not only achieves energy saving and consumption reduction, but also effectively inhibits the thermal degradation and oxidation of fibers during processing, ensuring that the product possesses high polymerization degree, high whiteness, and excellent thermal processing stability, laying the foundation for its application in the field of high-performance bio-based composite materials.

Claims

1. A step-by-step processing method for ultrafine plant fiber powder, characterized in that, Includes the following steps: The pretreated plant fiber raw material is placed in a pressure vessel, saturated steam is introduced and the pressure is increased. The pressure is maintained at the increased pressure, and then the pressure relief valve is opened to release the pressure in the pressure vessel to atmospheric pressure within a preset time, and the explosive material is collected. The explosive product was placed in an alkaline aqueous solution and stirred under heating conditions. After the reaction was completed, solid-liquid separation was performed, and the resulting filter cake was washed with hot washing liquid until neutral. Then, it was dried to obtain a cellulose intermediate. An inert gas is introduced into the supersonic airflow pulverizing system for displacement. Under controlled low-temperature conditions, the cellulose intermediate is driven by high-pressure inert airflow to undergo collisional refinement, and then subjected to turbine classification to obtain plant fiber ultrafine powder.

2. The step-by-step processing method for ultrafine plant fiber powder according to claim 1, characterized in that, The preparation method of the pretreated plant fiber raw material is as follows: The plant fiber raw materials are washed with deionized water and then dried at 70℃-80℃ until the moisture content is 8.0%-9.5%. In the steps of increasing the pressure of the saturated steam and maintaining the pressure, the pressure is 1.5-3.0 MPa, the pressure maintenance time is 60s-180s, and the pressure release time inside the pressure vessel is less than or equal to 0.1s.

3. The step-by-step processing method for plant fiber ultrafine powder according to claim 1, characterized in that, The alkaline aqueous solution is a sodium hydroxide aqueous solution with a mass percentage concentration of 3%-10%, and the solid-liquid mass ratio of the explosive to the alkaline aqueous solution is 1:(8-15). The stirring reaction is carried out at a temperature of 70℃-95℃ for 1-4 hours. The hot washing solution is deionized water at a temperature of 80℃-90℃, and the washing is performed until the pH value of the resulting washing solution is 6.5-7.

5.

4. The step-by-step processing method for plant fiber ultrafine powder according to claim 1, characterized in that, The drying process is carried out at a temperature of 105℃-110℃, and the moisture content of the cellulose intermediate is controlled at 1.2%-1.8%. The inert gas is selected from nitrogen or argon, and the oxygen volume concentration in the supersonic airflow pulverization system is controlled to be less than 2.0%. The temperature of the low-temperature environment is -10℃ to 25℃; The speed of the turbine staged process is set to 1000-3000 r / min.

5. A system for a stepwise processing method of plant fiber ultrafine powder, used to implement the stepwise processing method of plant fiber ultrafine powder according to any one of claims 1-4, characterized in that, include: The steam explosion subsystem includes a high-pressure steam generator, an explosion tank equipped with a fast discharge valve, and a cyclone separator collector; The chemical purification subsystem includes an alkali treatment reactor with mechanical stirring and temperature control jacket, a centrifugal filter, and a vacuum constant temperature oven. The ultra-fine refining subsystem includes an inert gas source, an auxiliary cooling unit, a supersonic airflow pulverizer, and a turbine classifier equipped with a classifying wheel; The auxiliary cooling unit is connected to the pulverizing chamber of the supersonic airflow pulverizer and is used to maintain the circulating gas in the pulverizing chamber at a temperature of -10°C to 25°C.

6. A plant fiber ultrafine powder, characterized in that, Prepared by the processing method according to any one of claims 1-4, and made from components comprising the following weight percentages: Cellulose 85.2%-91.2%, ash 1.2%-2.9%, balance lignin and hemicellulose; The surface of the plant fiber ultrafine powder particles has a microporous structure formed by steam explosion, and the average aspect ratio is 21-32.

7. The plant fiber ultrafine powder according to claim 6, characterized in that, The physical properties of the plant fiber ultrafine powder are as follows: Median particle size D 50 The particle size distribution ranges from 5.8 to 28.5 μm, with a particle size distribution span of (D). 90 -D 10 ) / D 50 Its value is 1.55-1.95, and its specific surface area is 10.5-18.5 m². 2 / g.

8. The plant fiber ultrafine powder according to claim 6, characterized in that, The average degree of polymerization of cellulose in the component is 784-845, and the CIE L of the plant fiber ultrafine powder is... ∗ The brightness value is 82.35-87.

56.

9. The plant fiber ultrafine powder according to claim 6, characterized in that, The raw materials for the plant fiber ultrafine powder are selected from one or more of rice husks, bamboo chips, industrial hemp fiber, crop straw, and wood chips.

10. The application of the plant fiber ultrafine powder as described in any one of claims 6-9 in the preparation of polylactic acid-based composite materials to improve interfacial bonding strength, enhance mechanical properties, or improve thermal stability.

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