Green wood fiber dissociation method based on peroxide

Abstract

The invention discloses a wood fiber green dissociation method based on peroxide. The dissociation method comprises the following steps that a peroxide and a wood fiber raw material are stirred in a solvent, a dissociation product is obtained, and the peroxide is selected from sodium percarbonate. According to the method, partial lignin in an intercellular layer in a wood fiber cell wall of sodium percarbonate is used for transverse permeation and depolymerization, mechanical stirring is combined for longitudinal dissociation of the wood fiber cell wall, and a dissociation product with high lignin content and high crystallinity is prepared under the condition of low power consumption.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and specifically to a green dissociation method for wood fibers based on peroxides. Background Technology

[0002] The green and high-value utilization of lignocellulose is a key pathway to achieve efficient and high-quality transformation of low-quality plantation timber resources, playing a vital role in promoting national economic development and improving people's quality of life. The cell wall of lignocellulose is a highly ordered three-dimensional composite structure formed by the cross-linking of cellulose, hemicellulose, and lignin through non-covalent and covalent interactions. Cellulose exists as microfibrils, forming a highly crystalline framework (40%-60% crystallinity) through a hydrogen bond network. Its surface hydroxyl groups are connected to hemicellulose (such as xylan and glucomannan) through hydrogen or ester bonds. Hemicellulose fills the spaces between cellulose microfibrils in an amorphous form, forming a network support structure. Lignin, on the other hand, is covalently cross-linked with hemicellulose through phenolic acid groups (such as ferulic acid and p-coumaric acid) via ester bonds, forming a "hemicellulose-lignin complex" (LCC). This Lignin acts as a filler between the cellulose network structure, ultimately constituting a dense composite of cellulose framework, hemicellulose support, and lignin filling.

[0003] Cellulose accounts for 30-50% of the dry weight of plants and is the skeletal material of cell walls. The supramolecular structure of cellulose can be divided into crystalline and amorphous regions, the ratio of which affects the mechanical properties and chemical reactivity of the material. The crystalline region consists of bundles of 36-120 parallel cellulose chains forming "microfibrils" with a diameter of 3-5 nm, tightly bound together by hydrogen bonds and van der Waals forces. This rigid chain structure makes cellulose difficult to dissolve in water and common organic solvents, dissolving only in highly polar solvents (such as ionic liquids and concentrated sulfuric acid). The amorphous region, with its disordered cellulose chain arrangement and incomplete hydrogen bond network, is easily attacked by hydrolytic enzymes or chemical reagents, and is the main site of biotransformation and utilization.

[0004] Hemicellulose is the second largest component of plant cell walls after cellulose, accounting for 15-35% of plant dry weight. It fills the spaces between cellulose microfibrils, enhancing cell wall toughness and forming the complex network structure of plant cell walls together with cellulose and lignin. The cross-linking of hemicellulose and lignin mainly occurs through the covalent bonding of phenolic acids (such as ferulic acid) to the phenylpropane units of lignin, forming a three-dimensional network structure called the "lignin-carbohydrate complex (LCC)," which enhances the mechanical strength and resistance to degradation of the cell wall. One of the keys to overcoming the degradation barriers of lignin fibers to maximize the resource utilization of its components lies in how to disrupt the LCC structure and reduce hemicellulose loss, thereby minimizing the formation of inhibitors.

[0005] Lignin accounts for 15-30% of the dry weight of plants, primarily providing mechanical support and resistance to microbial degradation. Lignin has a very unique structure, existing as a complex three-dimensional network within plant cell walls. This structure endows lignin with high stability and strength, effectively supporting and protecting plant cells. Simultaneously, lignin's structure also endows it with good biocompatibility and biodegradability, making it a promising candidate for applications in many fields.

[0006] The three components that make up lignocellulose (cellulose, hemicellulose, and lignin) form the polymeric structure of the cell wall through chemical bonds and interactions. This structure not only prevents water, acids, and alkalis from destroying the structure but also inhibits the entry of microorganisms and prevents enzymatic hydrolysis. Therefore, to separate lignin while preserving its original structure, the basic structure of the cell wall needs to be disrupted, followed by solvent dissolution or enzymatic hydrolysis to obtain lignin, which can greatly improve extraction efficiency.

[0007] Over the years, various pretreatment methods have been developed to overcome and reduce the recalcitrant nature of biomass. Currently existing pretreatment methods mainly include physical methods, chemical methods, combined physical and chemical methods, and biological methods, all aimed at disrupting the cell wall structure of lignocellulose and improving its accessibility. Physical methods, such as mechanical ball milling, ultrasonication, microwave treatment, freezing, and pyrolysis, can alter the physical properties of the dissociation products, such as particle size and crystallinity. They do not involve chemical consumption and are simple to operate, but they cannot effectively separate the three main components. Chemical methods, such as acid and alkali solution pretreatment, achieve the separation of the three main components by altering the chemical structure of lignocellulose and can effectively remove lignin. However, the pretreatment wastewater requires neutralization, increasing additional costs. Biological methods involve microorganisms, such as fungi, or their produced enzymes directly acting on the surface of the lignocellulose raw material, causing varying degrees of structural changes. However, these methods are time-consuming and not suitable for large-scale, high-efficiency application.

[0008] In chemical methods, alkali treatment disrupts the cell walls of lignocellulose fibers by dissolving lignin and soluble colloidal substances. Alkali pretreatment induces chemical swelling of lignocellulose, breaking down the cross-links between hemicellulose and other components through saponification, leading to increased porosity in biomass. Sodium hydroxide, calcium hydroxide, and potassium hydroxide are commonly used in alkali treatment, showing significant effects in removing lignin; however, the use of these chemical reagents causes severe environmental pollution and equipment corrosion. CN202410475923.6 discloses a pretreatment method for lignocellulose, in which ethylenediamine and sodium carbonate solution are added to straw, and pretreatment is carried out at 75-85℃ for 2-6 hours, achieving a lignin removal rate of 85.17% and increasing crystallinity from 44.25% (without any treatment) to 49.23%. However, this patent uses organic amine chemicals such as ethylenediamine, which has certain toxicity and corrosiveness, resulting in poor environmental friendliness and safety. Secondly, the patent aims to remove lignin and improve enzymatic hydrolysis efficiency, achieving a lignin removal rate of up to 85.17% (with a retention rate of 14.83%) and increasing the cellulose content to 65.10%. In addition, the patent requires treatment at 75~85℃ for 2~6 hours, resulting in high energy consumption.

[0009] Therefore, it is necessary to obtain the dissociation products with high lignin content, high cellulose content, and high crystallinity without destroying the integrity of the lignocellulose cell wall. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a green dissociation method for wood fibers based on peroxides.

[0011] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0012] The first aspect of this invention protects a green dissociation method for wood fibers based on peroxides, comprising the following steps:

[0013] Peroxide and lignocellulose raw material are stirred in a solvent to obtain dissociation products, wherein the peroxide is selected from sodium percarbonate.

[0014] A second aspect of the present invention protects the dissociation products obtained by the dissociation method described above.

[0015] A third aspect of the present invention protects a product comprising the dissociation products as described above.

[0016] A fourth aspect of the present invention protects the use of sodium percarbonate in the lignin of the middle lamella of the cell wall of lignocellulosic raw materials.

[0017] Compared with the prior art, the green dissociation method for wood fibers based on peroxides of the present invention has the following beneficial effects:

[0018] 1) This invention employs sodium percarbonate to laterally penetrate and depolymerize a portion of the lignin in the middle layer (the outer layer of the cell wall) of lignocellulose raw materials (especially poplar), combined with mechanical stirring to longitudinally dissociate the lignocellulose cell walls. This method produces a dissociation product with high lignin and cellulose content and high crystallinity, while largely retaining the cell wall structure, under low-power conditions. The decomposition products of sodium percarbonate, such as hydroxyl radicals, superoxide ions, and oxygen, can attack phenolic substances present in lignin. Mechanical stirring allows for full interaction between the wood raw material and sodium percarbonate, accelerating fiber separation.

[0019] 2) The dissociation method of the present invention utilizes the non-toxic, odorless, and pollution-free properties of sodium percarbonate. While efficiently dissociating wood fiber raw materials and preserving the structure of most of the wood fiber cell walls, it avoids the problems of high energy consumption and serious pollution in existing wood fiber raw material dissociation methods. Attached Figure Description

[0020] Figure 1A This is a photograph of longitudinally cut wood chips from Embodiment 1 of the present invention.

[0021] Figure 1B This is a photograph of the aqueous dispersion of Example 1 of the present invention.

[0022] Figure 2A The images shown are polarized light microscope images of the dissociation products obtained by treatment with different concentrations of sodium percarbonate in Example 1 of the present invention.

[0023] Figure 2B The images are polarized light microscope images of the dissociation products obtained at different processing times in Example 1 of the present invention.

[0024] Figure 2C The images are polarized light microscope images of the dissociation products obtained at different processing temperatures in Example 1 of the present invention.

[0025] Figure 3 These are microscopic images of longitudinally cut wood chips and dissociation products from Embodiment 1 of the present invention. Wherein, a is a microscopic image of longitudinally cut wood chips; b is a polarized light microscopic image of longitudinally cut wood chips; c is a microscopic image of the dissociation products; and d is a polarized light microscopic image of the dissociation products.

[0026] Figure 4 These are polarized light microscope images of the dissociation products of Example 1 and Comparative Example 1 of the present invention. In the images, a represents products without mechanical stirring; b represents products after mechanical stirring.

[0027] Figure 5 The images shown are scanning electron microscope (SEM) images of the dissociation products of Example 1 of the present invention at different magnifications. A, b, c, and d represent scale bars of 500 μm, 1 mm, 100 μm, and 1 μm, respectively.

[0028] Figure 6 This is a diagram illustrating the dissociation process of the lignocellulose raw material in Example 1 of the present invention. a represents the first stage (before dissociation); b represents the second stage (heating and stirring for 6 hours); c represents the third stage (heating and stirring for 12 hours); and d represents the fourth stage (heating and stirring for 18 hours).

[0029] Figure 7 This is a size distribution diagram of the dissociation products of Example 1 of the present invention.

[0030] Figure 8 The infrared spectra of the wood fiber raw material and dissociation products of Example 1 of the present invention are shown.

[0031] Figure 9A The XRD patterns of the wood fiber raw material and dissociation products of Example 1 of the present invention are shown.

[0032] Figure 9B The content of each component of the wood fiber raw material and dissociation product in Example 1 of the present invention is shown.

[0033] Figure 10 This is the XPS full spectrum of the wood fiber raw material and dissociation product of Example 1 of the present invention.

[0034] Figure 11A This is a C1s peak diagram of the wood fiber raw material of the present invention.

[0035] Figure 11B This is a C1s peak diagram of the dissociation product of the present invention.

[0036] Figure 11C This is the O1s peak diagram of the wood fiber raw material of the present invention.

[0037] Figure 11D This is the O1s peak diagram of the dissociation product of the present invention.

[0038] Figure 12 The image shows the DSC spectrum of the wood fiber raw material and dissociation product of Example 1 of the present invention. Detailed Implementation

[0039] The cell wall of wood fibers is a composite membrane structure composed of cellulose, hemicellulose, and lignin surrounding the wood cells. The cell wall consists of five layers from the outside in: the middle lamella (ML), the primary cell wall (P), and the tertiary cell wall. Lignin accounts for approximately 80% of the distribution in the middle lamella, followed by the secondary cell wall. Traditional alkali treatment (such as NaOH) breaks down the ester and ether bonds between lignin and hemicellulose, causing the lignin to dissolve and be removed, thus exposing cellulose. This process essentially sacrifices lignin (requiring a lignin degradation rate >90%) to obtain a high cellulose content. Furthermore, traditional alkali treatment partially transforms cellulose from its natural crystalline form (cellulose I) to its alkali-treated regenerated form (cellulose II). Cellulose I has a natural parallel-chain structure with high crystallinity and mechanical strength (like plant cell walls), while cellulose II has a regenerated antiparallel-chain structure with reduced crystallinity. The tensile strength and modulus of cellulose II are typically 20%-50% lower than that of cellulose I, limiting its application in high-strength materials (such as composite fibers and bioplastics). Furthermore, XRD and FT-IR evidence show that NaOH treatment causes glucose residues to rotate around glycosidic bonds, resulting in an irreversible change in the crystal structure. In contrast, this application uses sodium percarbonate to degrade lignocellulose raw materials while simultaneously increasing the retention rates of cellulose and lignin; moreover, the crystal morphology remains unchanged; and a greater number of active hydroxyl groups are exposed. A higher number of active hydroxyl groups results in stronger binding forces, better strength, and better hardness, thus facilitating subsequent pressing into fiberboard or filtration into paper.

[0040] The first aspect of this invention protects a green dissociation method for wood fibers based on peroxides, comprising the following steps:

[0041] Peroxide and lignocellulose raw material are stirred in a solvent to obtain dissociation products, wherein the peroxide is selected from sodium percarbonate.

[0042] In some embodiments, the wood fiber raw material is selected from wood chips.

[0043] In some embodiments, the length of the wood chips is 0.3 mm to 1.8 mm, and can also be 0.3 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.6 mm, or 1.8 mm. The length of the wood chips in this invention cannot be too long or too short. If it is too short, it becomes wood flour, and wood flour cannot obtain dissociation products with high lignin and high cellulose content after treatment with sodium percarbonate; if it is too long, sodium percarbonate cannot fully penetrate into the interior of the wood chips, affecting the degradation of lignin and cellulose.

[0044] In some embodiments, the wood chips are derived from one or more of poplar, bamboo, and grass. Preferably, they are made from poplar.

[0045] In some embodiments, the solvent is selected from water.

[0046] In some embodiments, the mass ratio of the lignocellulose raw material to sodium percarbonate is 1:(1.0-7.0), but it can also be 1:(1-1.5), 1:(1.2-2.8), 1:(2.5-3.5), 1:(3-5.0), 1:(6-7.0), 1:1, 1:1.1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, or 1:7. Preferably, it is 1:(2.5-5). In this invention, the mass ratio of lignocellulose raw material to sodium percarbonate cannot be too low or too high. When the mass ratio is less than 1:1, the amount of sodium percarbonate is insufficient, failing to provide enough active oxygen species (such as hydroxyl radicals) to effectively depolymerize the lignin between cellulose microfibrils, resulting in insufficient destruction of the lignin barrier. When the mass ratio is higher than 1:7, the amount of sodium percarbonate is excessive. On the one hand, excessive oxidant will over-attack the cellulose molecular chains, leading to damage to the crystalline structure of cellulose, a decrease in the degree of polymerization, and impaired strength. On the other hand, excessive alkaline environment will exacerbate the alkaline degradation of cellulose (peeling reaction), causing excessive etching of the surface of cellulose microfibrils and reducing the utilization rate of lignocellulose raw material. Excessive reagent dosage will also increase production costs and subsequent washing burden, which is not conducive to the realization of green and environmentally friendly processes. Therefore, controlling the mass ratio within the range of 1: (1.0 to 7.0) can ensure effective depolymerization of lignin while maximizing the preservation of the crystalline structure and mechanical strength of cellulose, achieving the best balance between activation effect and fiber integrity.

[0047] In some embodiments, the processing temperature is 0–100°C, or 0–32°C, or 28–56°C, or 55–81°C, or 78–100°C, or 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C. Preferably, it is not higher than 50°C, such as 5–25°C. The processing temperature in this invention cannot be too long or too short. When the processing time is below 0°C, the fibers are tightly bound but not fully dissociated. When the reaction temperature exceeds 25°C, the excessively high temperature accelerates the attack of sodium percarbonate on the cellulose molecular chains, leading to the destruction of the cellulose crystal structure, a decrease in the degree of polymerization, and damage to the fiber's own strength, thus weakening the effective bonding between fibers. Furthermore, excessively high reaction temperatures also increase energy consumption and production costs.

[0048] In some embodiments, the treatment time is 12–30 h, or 12–15 h, or 12–22 h, or 18–30 h, or 12 h, 13 h, 15 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, or 30 h. Preferably, it is 12–18 h. The treatment time in this invention cannot be too long or too short. When the treatment time is less than 12 h, the reaction time is too short, and the active oxygen generated by the decomposition of sodium percarbonate is insufficient to fully penetrate and depolymerize the lignin in the intercellular layer of the lignocellulose cell wall. This results in the lignin barrier between cellulose microfibrils not being effectively destroyed, and the ideal activation and modification target cannot be achieved. When the treatment time is greater than 30 h, the excessively long reaction time will cause excessive oxidant to continuously attack the cellulose molecular chain, triggering excessive oxidation and degradation of cellulose. This will not only destroy the crystalline structure of cellulose (manifested as a decrease in crystallinity), but may also lead to excessive etching or even pulverization, severely damaging the structure of the lignocellulose itself. Furthermore, excessively long processing times increase energy consumption and production costs, hindering industrial applications. Therefore, controlling the processing time within the range of 12–18 hours ensures effective depolymerization of lignin while preserving most of the cell wall structure, achieving the optimal balance between processing effectiveness and efficiency.

[0049] In some embodiments, the stirring speed is 1000-3000 r / s, or 1000-1800 r / s, or 1500-2400 r / s, or 2200-3000 r / s, or 1000 r / s, 1500 r / s, 2000 r / s, 2200 r / s, 2400 r / s, 2600 r / s, 2800 r / s, or 3000 r / s.

[0050] A second aspect of the present invention protects the dissociation products obtained by the dissociation method described above.

[0051] In some embodiments, the lignin retention rate in the dissociation product is 80-90%, the cellulose retention rate is 85-95%, the length of the dissociation product is 0.6-1.0 mm, and the crystallinity of the dissociation product is 50-70%.

[0052] In one specific embodiment, the lignin retention rate of the dissociation product is 85%, the cellulose retention rate is 95%, the length of the dissociation product is 0.3-1.8 mm, and the crystallinity of the dissociation product is 60%.

[0053] In this invention, the lignin retention rate refers to the mass of lignin in the dissociation product divided by the mass of lignin in the wood fiber raw material; the cellulose retention rate refers to the mass of cellulose in the dissociation product divided by the mass of cellulose in the wood fiber raw material.

[0054] The lignin and cellulose masses were calculated as acid-insoluble lignin and cellulose, respectively, and the determination methods are described in the literature (Sluiter A, Hames B, Ruiz R, et al. Determination of structural carbohydrates and lignin in biomass, Technical Report NREL / TP-510-42618, National Renewable Energy Laboratory, Golden, CO. 2010.).

[0055] A third aspect of the present invention protects a product comprising the post-solution product as described above.

[0056] In some embodiments, the product is selected from one or more of wood fiberboard, paper, and packaging materials.

[0057] A fourth aspect of the present invention protects the use of sodium percarbonate in improving the retention rate of lignin and / or cellulose in the dissociation products of lignocellulose raw materials.

[0058] This study successfully developed a synergistic dissociation technology using sodium percarbonate as a green reagent coupled with mechanical stirring. This technology utilizes the reactive oxygen species generated by the decomposition of sodium percarbonate in water to selectively degrade lignin in the mesocellular layer, achieving highly efficient dissociation of wood fibers under mild conditions (room temperature) while preserving most of the cell wall structure. The technology achieves a lignin retention rate of 80-90%, a cellulose retention rate of over 85-95%, controllable fiber length ranging from 0.3-1.8 mm, and crystallinity maintained at 50-70%. Compared to traditional strong acid / strong alkali methods, the overall energy consumption is significantly reduced.

[0059] This invention uses residual resources such as poplar, bamboo, and grass as the main raw materials, and processes them into fine wood chips using a slicer. The wood chips are added to an aqueous solution of sodium percarbonate, stirred at room temperature, and then washed until neutral to obtain the dissociation product.

[0060] This invention utilizes sodium percarbonate to penetrate laterally into the cell walls of lignocellulose fibers (especially the lignin-rich middle layer) to degrade lignin (breaking the chemical bonds of lignin), combined with mechanical stirring to longitudinally dissociate lignocellulose fibers (separating along the interface of the middle layer or cell wall layer, rather than directly cutting the fibers). The hydroxyl radicals (HO˙) generated by the decomposition of sodium percarbonate selectively attack the aromatic groups of lignin, achieving the mild degradation of lignin in the middle layer. At the same time, mechanical shearing force is used to destroy the physical bonding forces between lignocellulose fibers, avoiding excessive damage to lignin and hemicellulose caused by traditional chemical treatment methods.

[0061] The sodium percarbonate used in this invention has advantages such as being non-toxic, odorless, and pollution-free, while also possessing bleaching, sterilizing, washing, and high water solubility. Sodium percarbonate is biodegradable, with sodium carbonate and water as byproducts, resulting in no toxic organic emissions and significantly reducing harmful waste liquid generation compared to the sodium chlorite method. The dissociation method employed in this invention has lower energy consumption than traditional processes, achieving "low emissions, low energy consumption, and high value" dissociation.

[0062] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0063] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0064] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0065] Example 1

[0066] Dissociation method: Poplar wood blocks were soaked in distilled water, and the soaked poplar wood blocks were cut into wood chips about 0.8 mm long along the longitudinal section using a plant pathology sectioning machine (see...). Figure 1A Weigh 2g of sawdust and add it to 100mL of sodium percarbonate aqueous solutions with concentrations of 1%, 2%, 5%, 10%, and 15%, respectively. Simultaneously, stir the solutions in a magnetically stirred water bath at 25℃ and 2000r / s for 18h to obtain dispersions (e.g., ...). Figure 1BAs shown in the figure, the dispersion was washed and filtered using a Buchner funnel and a circulating water vacuum pump until neutral, and then stored for later use to obtain the dissociated product, which was a liquid. That is, the mass ratio of sawdust to sodium percarbonate was 2:1, 2:2, 2:5, 2:10, and 2:15, respectively.

[0067] The dissociation products after treatment with different concentrations of sodium percarbonate were observed under a polarizing microscope. The results are shown in the figure. Figure 2A .

[0068] from Figure 2A It can be seen that as the sodium percarbonate concentration gradually increases from 1% to 10%, the lignocellulose gradually dissociates. At a concentration of 1%, the lignocellulose remains in a relatively high initial aggregate state, not fully separated, with many fiber bundles. At a concentration of 2%, some lignocellulose begins to dissociate, but the overall structure remains relatively dense. At a concentration of 5%, significant separation begins, but some fiber bundles still remain. At a concentration of 10%, the fiber bundles essentially disappear, and individual fiber filaments exhibit a good dispersion. However, concentrations exceeding 10% not only increase costs but also cause excessive fiber dissociation to some extent, damaging the fiber structure.

[0069] Furthermore, the dissociation products were treated with 10% sodium percarbonate and magnetically stirred at 25℃ and 2000 r / s for 6 h, 12 h, 18 h, 24 h, and 30 h, respectively. The dissociation products at each time point were observed under a polarizing microscope. The results are shown in [Figure number missing]. Figure 2B .

[0070] from Figure 2B It can be seen that as the time gradually increases from 6 hours to 18 hours, the wood fibers gradually dissociate. At 6 hours, most of the wood fibers are clustered together, and the degree of dissociation is relatively low; at 12 hours, some wood fibers begin to dissociate, but there are still many fiber bundles; at 18 hours, they completely dissociate to form single fiber bundles. However, after 18 hours, not only does it increase the cost, but it also causes excessive fiber dissociation to a certain extent, damaging the fiber structure, such as the 30-hour fiber.

[0071] In addition, the mixture was treated with 10% sodium percarbonate and magnetically stirred at 0℃, 25℃, 50℃, 75℃, and 100℃ at 2000 r / s for 18 h. The dissociation products at each time point were observed under a polarizing microscope. The results are shown below. Figure 2C .

[0072] from Figure 2CIt can be observed that within the range of 0–25℃, as the reaction temperature increases, the fiber morphology gradually transforms from a coarse bundle to a dissociated monofilament. At 0℃, the fibers are in a coarse bundle with rich polarized interference colors, indicating that the fiber bonds are tight but not fully dissociated. At 25℃, the fiber bundles have dissociated more fully, and the monofilaments gradually become visible, increasing the specific surface area. At 50℃, some fiber monofilaments begin to curl slightly. At 75℃, the fibers become further refined, mainly in the form of monofilaments. At 100℃, the fiber morphology is similar to that at 75℃. This change indicates that increasing the reaction temperature within the 0–25℃ range helps sodium percarbonate to more fully penetrate and depolymerize lignin in the intercellular layer and cell wall of wood fibers, disrupting the hydrogen bond network between fibers and exposing more active hydroxyl groups, thereby forming a stronger interfiber bond during subsequent hot pressing. When the reaction temperature exceeds 25℃, the excessively high temperature accelerates the attack of sodium percarbonate on the cellulose molecular chains, leading to the destruction of the cellulose crystal structure, a decrease in the degree of polymerization, and damage to the fiber's own strength, which in turn weakens the effective bond between fibers. In addition, excessively high reaction temperatures can lead to increased energy consumption and production costs.

[0073] Microscopic images of longitudinally cut sawdust and dissociation products (dissociation products obtained by stirring with 10% sodium percarbonate for 18 h) are shown below. Figure 3 Wherein, a is a microscopic image of longitudinally cut wood chips; b is a polarized light microscopic image of longitudinally cut wood chips; c is a microscopic image of the dissociation products; and d is a polarized light microscopic image of the dissociation products.

[0074] The dissociation products obtained by treating the product with 10% sodium percarbonate at 25°C and 2000 r / s for 18 h were then used for further experiments.

[0075] Polarized light microscope image of the dissociation products is shown below. Figure 4 b.

[0076] from Figure 4 As can be seen from b, the dissociation products obtained after sodium percarbonate treatment and mechanical magnetic stirring exhibit the phenomenon of fiber separation.

[0077] The dissociation products were uniformly dropped onto a smooth silicon wafer and freeze-dried. The morphology of the dissociation products was observed using a Thermo Fisher Scientific Apreo SHiVac scanning electron microscope (SEM). Low-magnification and high-magnification SEM results are shown below. Figure 5 .

[0078] from Figure 5 As can be seen from AC, the dissociation products are needle-shaped.

[0079] from Figure 5 As can be seen from d, the cell walls of the dissociation products are smooth and the structure can be largely preserved, while a large amount of lignin accumulates on the outer surface of the cell wall (surface protrusions).

[0080] like Figure 6As shown, the dissociation process of wood fiber raw materials exhibits a clear staged evolution.

[0081] Initially, cellulose microfibrils are tightly aggregated, as shown in Figure a. After sodium carbonate infiltration and preliminary reaction, the connections between the cellulose microfibrils begin to loosen, showing a tendency to partially separate, as shown in Figure b (6h). With the continued synergistic effect of chemical treatment and mechanical stirring, the fiber bundles further expand and refine, as shown in Figure c (12h). Finally, complete dissociation is achieved, resulting in morphologically intact and uniformly dispersed individual cellulose microfibrils (Figure d, 18h). This process clearly demonstrates that the dissociation process selectively degrades the lignin in the intercellular layer, thereby effectively weakening the connection between cellulose microfibrils. At the same time, the physical shear force provided by mechanical stirring strengthens the longitudinal separation and dispersion of lignin fibers. The two work synergistically to promote the dissociation process.

[0082] Size distribution of dissociation products

[0083] To verify the effectiveness and reliability of the dissociation method, demonstrate the physical morphological characteristics of the dissociation products, and provide key data support for the practical value of this method, a statistical analysis of the scale distribution of the dissociation products was conducted. The results are shown in [Figure number missing]. Figure 7 .

[0084] from Figure 7 It can be seen that the length range of the dissociation products is mainly concentrated between 0.3 mm and 1.8 mm, among which the fiber with a length distribution between 0.6 mm and 1.0 mm accounts for the highest proportion, showing a typical normal distribution characteristic with 0.8±0.2 mm as the core, which provides an ideal raw material form basis for its subsequent applications in papermaking, composite materials and other fields.

[0085] FT-IR analysis before and after dissociation

[0086] FT-IR analysis: The dried lignocellulose raw material and dissociation products were ground uniformly under an infrared lamp and then compressed into tablets using a tablet press. The compressed samples were then scanned and analyzed using a Thermo Fisher Scientific Nicolet iS20 Fourier transform infrared spectrometer.

[0087] Infrared spectra before and after dissociation are shown below. Figure 8 .

[0088] Both the acetyl group in hemicellulose and the conjugated carbonyl group in the lignin side chain have C=O, and their absorption frequencies are located in the range of 1650–1740 cm⁻¹. -1 between.

[0089] from Figure 8It can be seen that the maximum absorption peak of C=O in the calibrated wood fiber raw material (WF) is located at 1734 cm⁻¹. -1 The maximum absorption peak of C=O in the dissociation product (SPC-WF) is located at 1727 cm⁻¹. -1 The absorption peak of the dissociation product (SPC-WF) not only shifted, but its peak intensity also decreased. The results indicate that the dissociation method caused some hemicellulose and lignin to dissociate, thus reducing the content of hemicellulose and lignin.

[0090] The lignin structure has a unique benzene ring structure, and its carbon skeleton vibration peak is located at 1600 cm⁻¹. -1 .

[0091] from Figure 8 It can be seen that the intensity of the benzene ring carbon skeleton vibration absorption peak in the dissociation product (SPC-WF) increases, indicating that lignin degradation forms small molecules and produces more cyclic structures.

[0092] The CO bending vibration peak in cellulose is located at 1030 cm⁻¹. -1 Place.

[0093] from Figure 8 It can be seen that the CO characteristic peak of cellulose in wood fiber raw material (WF) is located at 1030 cm⁻¹. -1 The CO characteristic peak in the dissociation product (SPC-WF) still exists, only slightly shifted, indicating that the cellulose in the wood fiber raw material does not change its structure after dissociation, but only the cellulose lattice structure and intercellulose hydrogen bonds are destroyed.

[0094] XRD patterns before and after dissociation

[0095] The XRD results were obtained using an X-ray diffractometer from Rigaku SmartLab SE in Japan. Figure 9A .

[0096] from Figure 9A It can be seen that the lignocellulose raw material (WF) and the dissociation product (SPC-WF) exhibit diffraction peaks at 2θ=15.5°, 22.5°, and 34.5°, respectively. The diffraction peak at 2θ=15.5° is the diffraction peak of the mixed crystal plane of cellulose 101 and 101(-); the diffraction peaks at 2θ=22.5° and 34.5° are the diffraction peaks of the (002) crystal plane and the (004) crystal plane of cellulose. This indicates that the crystal form of cellulose was not changed before and after dissociation, and it is still cellulose type I.

[0097] The relative crystallinity is calculated using the Segal method, and the formula is (I 200 -I am ) / I 200 *100% of I 200This refers to the maximum peak intensity of the absorption diffraction peak on the 002 crystal plane, I. am It refers to the minimum peak intensity between the absorption peaks of the diffraction peaks of the 101 crystal plane and the 002 crystal plane.

[0098] from Figure 9A Calculations show that the crystallinity of the dissociation product (SPC-WF) is above 60%.

[0099] The crystallinity of the wood fiber raw material (WF) is 39.1%.

[0100] Content of cellulose and acid-insoluble lignin before and after dissociation

[0101] High performance liquid chromatography (HPLC) was used to quantitatively analyze cellulose and lignin in lignocellulose raw materials and dissociation products.

[0102] The wood fiber raw material and dissociation product were dried, pulverized, and 0.3g of each was taken as test samples.

[0103] 0.3g of the test sample was acid-hydrolyzed at 121℃ for 1h with 3mL of 72wt% sulfuric acid and 84mL of ultrapure water. After cooling, the sample was filtered through a vacuum filtration flask. The lignin on the filter paper was dried and ready for testing. 20mL of the filtrate in the lower flask was collected for testing. This filtrate was glucose produced after the decomposition of cellulose and was used to determine the cellulose content.

[0104] The filtrate, after vacuum filtration, was filtered through a 0.22 μm aqueous filter into a sample vial and then placed into an autosampler for testing. The mobile phase used was a 4 mM sulfuric acid aqueous solution (Wahaha purified water), which was filtered before use to remove impurities and air bubbles. An Aminex HPX-87H organic acid analytical column (300 x 7.8 mm, 5.0 μm) was inserted for testing, using a differential detector. The column temperature was set to 50 °C, and the injection volume was 20 L.

[0105] The component contents of cellulose and acid-insoluble lignin were determined and calculated according to the literature (Sluiter A, Hames B, Ruiz R, et al. Determination of structural carbohydrates and lignin in biomass, Technical Report NREL / TP-510-42618, National Renewable Energy Laboratory, Golden, CO. 2010.). The lignin and cellulose retention rates were calculated as follows:

[0106] Lignin content = Mass of lignin on filter paper / Mass of test sample

[0107] Cellulose content = mass of glucose in filtrate / mass of test sample (mass of glucose is determined by liquid chromatography)

[0108] Cellulose retention % = Mass of cellulose in dissociation products / Mass of cellulose in lignocellulose raw material

[0109] Lignin retention rate % = Mass of lignin in dissociation products / Mass of lignin in wood fiber raw materials

[0110] from Figure 9B The liquid chromatography data showed that the cellulose retention rate in the dissociation products was 97% (degradation rate was 3%) and the lignin retention rate was 85% (degradation rate was 15%). This indicates that under the conditions of sodium percarbonate and stirring treatment, efficient dissociation of lignocellulose and high retention of components (i.e., cellulose and lignin) can be achieved.

[0111] from Figure 9B It can be seen that the cellulose content in the wood fiber raw material (WF) is 51% and the lignin content is 21.54%; while the cellulose content in the dissociation products is 49.47% and the lignin content is 18.31%.

[0112] In the dissociation process of lignocellulose raw materials, the reagent first dissolves the lignin in the secondary wall (because its loose structure makes it easier to react); then it dissociates the lignin in the middle layer (because the lignin in the middle layer has a higher degree of cross-linking; the middle layer is mainly composed of lignin and pectin, unlike the secondary wall which has cellulose as a framework, making it less likely for the reagent to carry it out after the reaction). This invention, through sodium percarbonate and stirring treatment, achieves a lignin degradation rate of 15%. Figure 9B ), while not affecting the cell wall structure ( Figure 5 This demonstrates that the method of the present invention selectively degrades lignin in the intercellular layer.

[0113] Investigation of oxygen-carbon ratio before and after dissociation

[0114] XPS spectra of lignocellulose raw materials and dissociation products were analyzed using a Thermo Scientific ESCALAB Xi+ X-ray photoelectron spectroscopy system (USA). The XPS spectra of the lignocellulose raw materials and dissociation products are shown below. Figure 10 As shown.

[0115] In cellulose dissociation methods, an increased oxygen-to-carbon ratio (O / C) indicates a deeper degree of cellulose dissociation, resulting in a relative increase in cellulose content in the sample, possibly accompanied by a decrease in high-carbon components such as lignin. Cellulose is composed of glucose units linked by β-1,4-glycosidic bonds, with a high proportion of oxygen atoms in the molecule and an oxygen-to-carbon ratio of approximately 0.83; lignin is a complex aromatic polymer with a high carbon content, and an oxygen-to-carbon ratio of approximately 0.33.

[0116] from Figure 10 It can be seen that the relative oxygen content of wood fiber raw material (WF) is 29.36%, the relative carbon content is 70.64%, and the oxygen-carbon ratio (O / C) is 0.42.

[0117] from Figure 10 It can be seen that the relative oxygen content of the dissociation product (SPC-WF) is 34.44%, the relative carbon content is 66.56%, and the oxygen-carbon ratio (O / C) is 0.52.

[0118] The increased oxygen / carbon ratio (O / C) after dissociation treatment indicates that the dissociation products exposed more oxygen-containing groups such as hydroxyl groups (-OH), while selectively degrading lignin to reduce components with high carbon content, demonstrating the success of the dissociation of lignocellulose raw materials.

[0119] XPS fine spectra before and after dissociation

[0120] XPS spectra of wood fibers before and after dissociation were analyzed using a Thermo Scientific ESCALAB Xi+ instrument. Fine XPS spectra of wood fibers before and after dissociation are shown below. Figure 11A-11D As shown.

[0121] from Figure 11A and Figure 11C It can be seen that the area ratio of C1 peak on the surface of wood fiber raw material (WF) is 50.02%, C2 peak area ratio is 33.97%, C3 peak area ratio is 16.01%, O1 peak area ratio is 46.24%, and O2 peak area ratio is 53.76%.

[0122] from Figure 11B and Figure 11D It can be seen that the peak area ratios of C1, C2, C3, O1, and O2 on the surface of the dissociation product (SPC-SF) are 46.24%, 45.95%, 7.81%, 65.75%, and 34.25%, respectively.

[0123] Comparative analysis revealed that the C1 peak area decreased by 3.78%, the C2 peak area increased by 11.98%, the O1 peak area increased by 19.51%, and the O2 peak area decreased by 11.99% on the surface of the dissociation product (SF). From the above process, it can be seen that the dissociation method of this invention can increase the proportion of oxygen atoms with high binding energy (O1, usually belonging to oxygen-containing functional groups such as C=O and OC=O) on the surface of wood fibers. Simultaneously, the significant increase in the area of ​​the C2 peak (CO, representing hydroxyl groups, ether bonds, etc.) directly confirms the increase in the number of surface-active hydroxyl groups. Combined with FT-IR (… Figure 8 The enhancement of the hydroxyl characteristic peak in the qualitative analysis further confirms that the dissociation treatment effectively activates the surface of the dissociation product.

[0124] DSC spectra before and after dissociation

[0125] Lignocellulose is composed of cellulose, hemicellulose, and lignin. Each component contains hydroxyl groups that can react with epichlorohydrin and release heat, resulting in a downward exothermic peak in the DSC curve. Lignocellulose raw materials and dissociation products were blended with epichlorohydrin at a mass ratio of 1:1, and then DSC analysis was performed. A Netzsch DSC 200 F3 differential scanning calorimeter (Germany) was used to analyze the DSC of the lignocellulose raw materials and dissociation products. The DSC spectra of the lignocellulose raw materials and dissociation products are shown below. Figure 12 As shown.

[0126] from Figure 12 It is known that the exothermic peak generated by the reaction of wood fiber raw material (WF) with epichlorohydrin appears at 109℃ and the area of ​​the exothermic peak is very small, indicating that the content of reactive hydroxyl groups in wood fiber raw material (WF) is very low. However, the exothermic peak generated by the reaction of the dissociation product (SPC-WF) with epichlorohydrin appears at 85℃ and the area of ​​the exothermic peak is large, indicating that the dissociation product contains a large number of reactive hydroxyl groups.

[0127] The dissociation products can not only shift the peak value of the exothermic peak towards a lower temperature, but also increase the area of ​​the exothermic peak. This indicates that the dissociation method of the present invention can increase the number of active hydroxyl groups in the dissociation products and introduce more active hydroxyl groups, thereby making it easier for the active hydroxyl groups of the dissociation products to react.

[0128] In summary, the dissociation method of the present invention successfully disrupts the lignin barrier and hydrogen bond network between fibers, releasing a large number of encapsulated active hydroxyl groups, which significantly enhances the surface activity and reactivity of the fibers.

[0129] The chemical activity level of this study verified that the green dissociation method developed can effectively break the dense structure of cellulose microfibrils, providing a key basis for realizing the high-value utilization of fibers.

[0130] Comparative Example 1

[0131] The difference from Example 1 is that no magnetic stirring was performed, but everything else is the same as in Example 1.

[0132] Its polarized microscope image is shown below. Figure 4 a.

[0133] from Figure 4 As can be seen from a, the sawdust that has not undergone mechanical stirring does not exhibit any fiber separation. This fully demonstrates that mechanical stirring plays a crucial role in the fiber dissociation process, playing an indispensable role in promoting the successful dissociation of fibers and providing strong technical support and process assurance for the efficient preparation of wood fibers.

[0134] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications listed herein, as well as variations in the methods and compositions of the invention, will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.

Claims

1. A green dissociation method for wood fibers based on peroxides, characterized in that, Includes the following steps: Peroxide and lignocellulose raw material are stirred in a solvent to obtain dissociation products, wherein the peroxide is selected from sodium percarbonate.

2. The dissociation method as described in claim 1, characterized in that, The wood fiber raw material is selected from wood chips; And / or, the solvent is selected from water.

3. The dissociation method as described in claim 2, characterized in that, The length of the wood chips is 0.3–1.8 mm; And / or, the wood chips are derived from one or more of poplar, bamboo and grass.

4. The dissociation method as described in claim 1, characterized in that, The mass ratio of the lignocellulose raw material to sodium percarbonate is 1:(1.0 to 7.0).

5. The dissociation method as described in claim 1, characterized in that, The processing temperature is 0–100 °C; And / or, the processing time is 6 to 30 hours.

6. The dissociation method as described in claim 1, characterized in that, The stirring speed is 1000-3000 r / s.

7. The dissociation product obtained by the dissociation method according to any one of claims 1-6.

8. The dissociation product as described in claim 7, characterized in that, The lignin retention rate in the dissociation products is 80-90%, and the cellulose retention rate is 85-95%. And / or, the crystallinity of the dissociation product is 50-70%.

9. A product characterized in that, It contains the dissociation products as described in claim 7 or 8.

10. Application of sodium percarbonate in improving the retention rate of lignin and / or cellulose in the dissociation products of lignocellulose raw materials.

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