Method for preparing wood fiber pulp from brush wood at low cost

Abstract

The invention provides a low-cost method for preparing wood fiber pulp from brush wood, and belongs to the technical field of papermaking. The preparation method comprises the following steps: S1, activating treatment; s2, primary defibering; s3, primary chemical impregnation; s4, carrying out microfibrillating treatment; s5, secondary chemical dipping; s6, primary grinding; s7, whiteness regulation and pH balance; s8, accurate grinding; and S9, finished product refining and screening. One of poplar, white wax, platanus orientalis, birch and pine and a mixture of the poplar, the white wax, the platanus orientalis, the birch and the pine are used as raw materials, and the performance indexes such as the bulk, the tensile index and the burst index of the prepared paper can be adjusted according to requirements through the process steps of chemical dipping treatment, microfibrillation treatment, accurate grinding and the like. Therefore, the pulp has high adaptability under different production requirements, and has remarkable advantages in the aspects of improving the utilization rate of fiber resources, reducing environmental pollution, reducing the investment cost, improving the quality of the pulp and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of papermaking, in particular to a method for preparing wood fiber pulp at low cost by using branch wood. Background Art

[0002] The level of paper and paperboard consumption is an important indicator of a country's economic and cultural development. In recent years, my country's total pulp consumption and paper and paperboard production have continued to grow rapidly. However, conventional chemical pulping processes present numerous practical challenges. These processes result in low utilization rates of key papermaking raw materials such as cellulose, lignin, and hemicellulose. Furthermore, these processes require high equipment investment, complex production lines, and extensive floor space, increasing initial investment costs. These factors severely restrict the sustainable development of conventional chemical pulping processes.

[0003] While existing high-yield pulps approach traditional chemical pulps in strength and optical properties, they still lack key performance indicators such as bulk and opacity, limiting their application in high-end paper and board production. Therefore, how to efficiently utilize limited fiber resources and improve pulp quality and production efficiency has become a key issue that the pulping industry urgently needs to address. Summary of the Invention

[0004] The purpose of the present invention is to address the above-mentioned problems in the existing technology and to propose a method for preparing wood fiber pulp at low cost using branch wood.

[0005] The object of the present invention can be achieved by the following technical solutions: A method for preparing wood fiber pulp at low cost using branch wood, the method for preparing wood fiber pulp at low cost using branch wood comprises the following steps:

[0006] S1 Activation treatment: After washing and air-drying the wood chips, soak them in hot water, soften them, remove them and drain them to obtain activated wood chips; the wood chips are made from one of the following: poplar, ash, sycamore, birch, poplar + pine, poplar + ash; poplar + sycamore,

[0007] S2 Primary Defibrination: The activated wood chips are initially extruded to obtain coarse wood fibers;

[0008] S3 primary chemical impregnation: impregnating the raw wood wool in an alkaline solution containing EDTA to obtain impregnated raw wood wool;

[0009] S4 microfibrillation treatment: the impregnated coarse wood fibers are subjected to microfibrillation extrusion to obtain fine wood fibers;

[0010] S5 secondary chemical impregnation: chemically impregnating the wood wool in an alkaline solution containing hydrogen peroxide, sodium metasilicate and EDTA to obtain impregnated wood wool;

[0011] S6 initial grinding: the impregnated fine wood fibers are initially ground to obtain an initial slurry;

[0012] S7 Whiteness Control and pH Balance: The initial pulp is bleached and the pH value is adjusted to obtain a bleached pulp. In the bleaching process, an alkaline solution containing hydrogen peroxide, sodium metasilicate, and EDTA is used as the bleaching liquid.

[0013] S8 fine grinding: fine grinding the bleached pulp to obtain finely ground pulp;

[0014] S9 Finished product refining and screening: The refined pulp is subjected to de-latency operations and screening operations to obtain wood fiber pulp.

[0015] The slurry preparation method employed in the previous study utilized a chemical-mechanical process, combining two chemical pre-impregnation stages and two KRK disc refinement stages, leveraging the gentleness of chemical treatment and the efficiency of mechanical treatment. Compared to a single chemical pre-impregnation stage followed by a single KRK disc refinement stage, the two-stage mild chemical pre-impregnation process facilitates fiber separation and softening, while the two-stage KRK disc refinement further refines the fibers and increases their flexibility. This combined process not only enhances fiber bulk and softness, but also preserves fiber strength. For example, during the chemical pre-impregnation process, the sodium hydroxide and hydrogen peroxide gradually dissolve and oxidize lignin, resulting in a purer fiber surface. During the bleaching process, the high temperature and alkaline conditions of hydrogen peroxide more thoroughly oxidize lignin, further improving whiteness. Furthermore, pH adjustment ensures fiber stability in a neutral environment, preventing fiber damage and further enhancing whiteness. After KRK disc refinement, the fibers become more flexible, inter-fiber bonds are weakened, and the fiber fibrillation is enhanced. This allows the fibers to maintain their softness during the subsequent molding process, significantly increasing bulk. During the KRK refining process, bleached fibers are refined to better retain fiber length and reduce fiber cuts, as the lignin on the fiber surface is removed. This not only increases fiber strength but also improves the overall properties of the paper, such as tensile strength, tear strength, and flexibility. Sodium metasilicate is used as a buffer in the chemical treatment of wood. When used with sodium hydroxide, it helps stabilize the alkaline environment and prevent excessive wood damage. It also acts as a protective agent during the reaction, reducing the formation of harmful ions.

[0016] Preferably, in step S1, the wood chip raw materials are from fast-growing forests, landscaping waste, and branches of forest farms. In the wood chip raw materials composed of poplar and pine, the weight ratio of poplar and pine is 99-50:1-50, and the pine is masson pine or radiata pine; in the wood chip raw materials composed of poplar and ash, the weight ratio of poplar and ash is 10-30:70-90; in the wood chip raw materials composed of poplar and sycamore, the weight ratio of poplar and ash is 40-70:30-60. The length of the wood chip raw materials is 20-30 mm; the temperature of the hot water is 60-80 ° C, and the soaking time is 5-20 minutes.

[0017] Wood raw materials come from fast-growing forests, waste branches pruned after gardening and urban greening, and branches in forest farms. Fast-growing forests are characterized by rapid growth, high unit yield, and strong adaptability. Fast-growing wood fibers have the characteristics of short fibers, thin walls, large cavities, and low lignin content. They are suitable for producing high-bulk paper, which helps reduce pulping energy consumption and improve pulping efficiency. Gardening waste and branches are widely available and relatively low in cost. Using them can reduce dependence on virgin wood, reduce pulping costs, and achieve resource recycling. In addition, with the continuous development of urban greening and forestry industries, these wastes and branches will also become one of the rich sources of raw materials for pulping and papermaking. Although branch fibers are relatively short, their wall-to-cavity ratio and cellulose content make them high-quality papermaking raw materials. During the pulping process, the fibers of branch wood are relatively short and fine. Chemical impregnation can effectively remove the lignin on the fiber surface, increase the flexibility and accessibility of the fibers, and thus improve the dispersion and bonding strength of the fibers. Although the fibers of branch wood are relatively short, the fiber surface is roughened through KRK disc grinding treatment, which increases the contact area and bonding strength between the fibers, thereby compensating for the problem of insufficient fiber length.

[0018] As an important raw material, wood fiber pulp is widely used in papermaking, textiles, composite materials, and other fields. Different markets have varying quality requirements for wood fiber pulp, such as whiteness, fineness, and strength. With the diversification of market demand, particularly the varying demands for wood fiber pulp in different regions, the use of a variety of raw materials allows for customized production based on customer needs. The wood raw materials used above are all relatively common and affordable woods, which can effectively control costs and enhance market competitiveness.

[0019] Poplar: It has a light texture, is easy to defibrate, and is widely used in papermaking and wood processing. White wax: It has a high hardness, good compression resistance and corrosion resistance, and is used for materials that require higher strength. Plane: It is relatively soft and easy to defibrate, making it suitable for the production of some paper products. Birch: It has high strength and toughness, and its wood fibers are finer, making it suitable for the manufacture of high-quality paper. Poplar + Pine: The physical properties of paper are significantly improved after combining coniferous wood (Pinus massoniana / Pinus radiata) with poplar during the pulping process. This is because the flexibility and longer fiber length of coniferous wood fibers enable them to form stronger inter-fiber bonding in the paper; while although hardwood fibers are shorter, their higher bulk and stiffness can increase the overall strength of the paper; when mixed, coniferous wood fibers provide the main tensile strength, while hardwood fibers further enhance the overall strength of the paper by increasing the contact area and bonding points between fibers.

[0020] Preferably, in both the initial extrusion operation in step S2 and the microfibrillation extrusion operation in step S4 , a single-screw extruder is used as the extrusion equipment.

[0021] Preferably, a KRK disc mill is used as the grinding equipment in both the primary grinding operation of step S6 and the fine grinding operation of step S8. The reasons are as follows: efficient fiber separation and refinement: shear force control: the disc mill generates controllable shear force through the gap between the rotating grinding discs, which can effectively cut the wood fibers instead of simply crushing them, thereby retaining the natural length and strength of the fibers. This is crucial to the subsequent pulp properties (such as strength and flexibility). Fineness uniformity: compared with equipment such as ball mills, the fiber particle size distribution produced by the disc mill is more concentrated, reducing the proportion of fibers that are too coarse or too fine, and meeting the high requirements of downstream processes such as papermaking and composite materials for pulp homogeneity. Low-temperature grinding and chemical stability: low heat generation: the friction heat generated by the disc mill is less, which avoids the re-crosslinking or degradation of lignin caused by high temperature, especially in pulp containing hydrogen peroxide (bleach), which can prevent the decomposition and failure of chemical substances. Compatible with chemical environment: the KRK disc mill is designed to be corrosion-resistant and is suitable for environments containing alkaline solutions such as EDTA and sodium metasilicate. It is not easily corroded during long-term stable operation, ensuring process continuity. Adapt to multi-stage grinding needs: efficient defibering in primary grinding: in step S6, the disc grinder quickly decomposes the coarse wood fibers into initial pulp, thanks to its large contact area and high shear force, shortening the processing time. Fine control of fine grinding: in step S8, by adjusting the grinding disc spacing and rotation speed, the pulp fineness can be precisely controlled to meet the needs of high-end applications (such as specialty paper and filter materials). Synergistic effect with chemical treatment: pre-softening synergy: the chemical impregnation in steps S3 and S5 has partially softened the wood, and the disc grinder can further utilize the effect of chemical agents to accelerate fiber separation and improve the utilization rate of the impregnating agent. Whiteness maintenance: low-temperature grinding avoids browning of the pulp. When used with bleaching solution (containing hydrogen peroxide), it can maintain a higher whiteness (step S7) to meet high-standard bleaching effects.

[0022] Preferably, in step S3, in the alkaline solution containing EDTA, the concentration of sodium hydroxide is 0.1-3.0%; the concentration of EDTA is 0.001-0.05%; the chemical impregnation operation parameters are as follows: the impregnation temperature is 40-90° C., the impregnation time is 5-25 minutes, and the material concentration is 20-45%.

[0023] Preferably, in step S5, in the alkaline solution containing hydrogen peroxide, sodium metasilicate and EDTA, the concentration of sodium hydroxide is 1.0-4.0%; the concentration of hydrogen peroxide is 1.0-5.0%, the concentration of sodium metasilicate is 0.2-2.0%, and the concentration of EDTA is 0.001-0.02%; the chemical impregnation operation parameters are as follows: the impregnation temperature is 65-95° C., the impregnation time is 20-70 minutes, and the material concentration is 20-45%;

[0024] Preferably, in step S6, the parameters of the initial grinding operation are as follows: the disc grinding concentration is 20-35%, and the gap is 0.1-0.7 mm.

[0025] Preferably, in step S7, in the bleaching solution, the concentration of sodium hydroxide is 1.0-4.0%; the concentration of hydrogen peroxide is 1.0-5.0%, the concentration of sodium metasilicate is 0.2-1.5%, and the concentration of EDTA is 0.001-0.02%; the bleaching operation parameters are as follows: temperature is 75-100° C., bleaching time is 70-110 minutes, and material concentration is 20-40%; and the target pH value of the pH adjustment operation is 6.5-8.0.

[0026] Preferably, in step S8, the fine grinding parameters are as follows: disc grinding concentration of 20-35%, gap of 0.1-0.4 mm. Preferably, in step S9, the latent removal parameters are as follows: latent removal temperature of 70-95°C, latent removal time of 1-10 minutes; in the screening operation, a sieve of 80-120 mesh is used.

[0027] Compared with the existing technology, the method of preparing wood fiber pulp at low cost using branch wood has the following beneficial effects:

[0028] 1. Maximizing resource utilization: By using wood chips from fast-growing forests, landscaping waste, and branches from forest farms as wood chip raw materials, the dependence on virgin wood is reduced, and the cost of raw materials for pulping is lowered. The present invention can effectively convert them into high-quality papermaking raw materials, thus achieving resource recycling. Through the process steps of chemical impregnation, microfibrillation, and fine grinding in the present invention, the lignin on the fiber surface can be effectively removed, the flexibility, accessibility, and dispersibility of the fiber can be increased, and the bonding strength of the fiber can ultimately be improved, thereby improving the quality of the wood fiber pulp. In particular, after being treated with the KRK disc grinding equipment, the fiber surface is roughened, which enhances the contact area and bonding strength between the fibers and compensates for the defect of short fiber length.

[0029] 2. High fiber resource utilization, significantly improving pulp yield: By retaining lignin, this invention significantly improves fiber resource utilization, achieving a pulp yield of 82%-90%, double that of traditional chemical pulping. This efficient resource utilization method can effectively alleviate my country's fiber raw material shortage, especially in the face of a significant gap between wood supply and demand, and provides a more efficient raw material solution for the papermaking industry.

[0030] 3. The use of green chemicals is small, reducing production costs and environmental burdens: The present invention only uses a small amount of green chemicals, which reduces production costs and conforms to the development trend of green chemistry.

[0031] 4. Save water resources: The present invention uses high-concentration pulping and bleaching to complete the process. This water-saving process can effectively alleviate the problem of excessive water consumption in the papermaking industry. After secondary biochemical and deep treatment, it can achieve standard discharge and has little impact on the surrounding water resources environment.

[0032] 5. Low equipment investment and compact and flexible production process: The equipment investment of the present invention is only 1 / 8 of that of traditional chemical pulping. The production line process is compact and flexible, occupies a small area, and is suitable for large-scale production layout.

[0033] 6. Improved Pulp Quality to Meet the Demand for High-End Paper and Board: The high-yield pulp produced by this invention achieves strength and optical properties that approach or match those of traditional chemical pulps, while also exhibiting superior performance in key indicators such as bulk and opacity. This high-quality pulp imparts excellent stiffness, printing properties, and liquid absorption properties to paper and board, making it a viable alternative to traditional chemical pulp in the production of high-end paper and board products such as lightweight coated paper, supercalendered paper, lightweight paper, and liquid packaging board, meeting the growing market demand for high-end paper products.

[0034] In summary, the present invention has significant advantages in improving fiber resource utilization, reducing chemical and water consumption, reducing equipment investment costs, and improving pulp quality, providing the papermaking industry with a new, efficient, environmentally friendly, and economical pulping solution. DETAILED DESCRIPTION

[0035] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0036] Example 1

[0037] A method for preparing chemical mechanical pulp comprises the following steps:

[0038] (1) Select poplar wood chips with a length of 20-30 mm, wash and air-dry;

[0039] (2) soaking the wood chips obtained in step (1) in 70°C hot water for 10 minutes and then removing and draining;

[0040] (3) extruding the wood chips obtained in step (2) into wood fibers in a single screw extruder;

[0041] (4) chemically impregnating the wood wool obtained in step (3) with a NaOH concentration of 0.5%, an EDTA concentration of 0.015%, a reaction temperature of 75° C., a reaction time of 15 minutes, and a material concentration of 40%;

[0042] (5) extruding the wood fibers in step (4) into finer wood fibers in a single screw extruder;

[0043] (6) The fine wood fibers in step (5) are chemically impregnated with NaOH concentration of 3.0%, H2O2 dosage of 4.0%, Na2SiO3 concentration of 0.5%, EDTA concentration of 0.015%, reaction temperature of 85°C, reaction time of 50 minutes, and material concentration of 40%.

[0044] (7) grinding the fine wood fibers in step (6) in a KRK grinding mill with a gap of 0.4 mm and a grinding concentration of 30%;

[0045] (8) The slurry obtained in step (7) was bleached and pH adjusted, with NaOH concentration of 2.5%, H2O2 concentration of 3.5%, Na2SiO3 concentration of 0.5%, EDTA concentration of 0.01%, reaction temperature of 90°C, reaction time of 70 minutes, slurry concentration of 30%, and pH of 7.5.

[0046] (9) grinding the bleached pulp obtained in step (8) in a KRK disc grinder with a gap of 0.2 mm and a grinding concentration of 25%;

[0047] (10) The slurry obtained in step (9) is delatched at 80° C. for 5 minutes and sieved through a 100-mesh sieve to obtain the target chemical mechanical pulp.

[0048] Example 2: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. Select poplar and masson pine wood chips with a length of 20-30 mm (the ratio is 90% poplar and 10% masson pine), wash and air-dry.

[0049] Example 3: The difference from Example 1 is step (1), and the other steps are the same as Example 1. (1) Select poplar and masson pine wood chips with a length of 20-30 mm (the ratio is 85% poplar and 15% masson pine), wash and air-dry.

[0050] Example 4: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select poplar and masson pine wood chips with a length of 20-30 mm (the ratio is 80% poplar and 20% masson pine), wash and air-dry.

[0051] Example 5: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select poplar and radiata pine wood chips with a length of 20-30 mm (the ratio is 90% poplar and 10% radiata pine), wash and air-dry.

[0052] Example 6: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select poplar and radiata pine wood chips with a length of 20-30 mm (the ratio is 85% poplar and 15% masson pine), wash and air-dry.

[0053] Example 7: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select poplar and radiata pine wood chips with a length of 20-30 mm (the ratio is 80% poplar and 20% masson pine), wash and air-dry.

[0054] Example 8: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select ash wood chips with a length of 20-30 mm, wash and air-dry.

[0055] Example 9: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select 20-30 mm long sycamore wood chips, wash them, and air-dry them.

[0056] Example 10: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select birch wood chips with a length of 20-30 mm, wash them, and air-dry them.

[0057] Example 11: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select poplar and ash wood chips (ratio of 20% poplar and 80% ash) with a length of 20-30 mm, wash and air-dry.

[0058] Example 12: The difference from Example 1 is step (1), and the remaining steps are the same as Example 1. (1) Select poplar and tung wood chips (ratio of 60% poplar and 40% tung) with a length of 20-30 mm, wash and air-dry.

[0059] Comparative Example 1: The difference from Example 1 is step (8), and the other steps are the same as Example 1. (8) Only the pH of the slurry is adjusted to 7.5.

[0060] Comparative Example 2: The difference from Example 1 is that step (7) is missing.

[0061] Comparative Example 3: The difference from Example 1 is that the order of steps (8) and (9) is interchanged, that is, the two-stage disc refining is performed first and then the bleaching and pH adjustment are performed.

[0062] Results test: The chemical mechanical pulp prepared in specific examples 1-12 and comparative examples 1-3 was made into paper, and the performance test results were tested. The test results are shown in Table 1.

[0063]

[0064] Table 1

[0065] Data Analysis: 1. Bulk: Bulk reflects the relationship between the density and thickness of paper. Generally, a higher bulk means a looser paper texture, which is suitable for paper that requires a larger volume or softness. From the data in the table, the bulk ranges from 2.55cm 3 / g to 3.04cm 3 / g, which shows that the structure of all paper samples is relatively loose. Especially Example 9 (bulk thickness 3.04cm 3 / g) and Example 4 (bulk 2.90 cm 3 / g) has a relatively high bulk, which can provide good paper volume and softness.

[0066] 2. Tensile Index: The tensile index indicates the strength of paper when subjected to tension. Higher values ​​indicate greater resistance to stretching. Data shows that the tensile index ranges from 15.52 N·m / g (Example 4) to 27.42 N·m / g (Example 8), showing good overall performance. Paper with a higher tensile index (such as Example 8) exhibits greater tensile strength and longevity, making it suitable for applications requiring high strength and durability.

[0067] 3. Burst index: The burst index indicates the paper's resistance to breaking when subjected to external forces. This index reflects the paper's ability to resist damage. The larger the value, the stronger the paper's durability and resistance to breaking. From the data, the burst index ranges from 0.70 kPa·m 2 / g (Example 9) to 1.06 kPa·m 2 / g (Example 8). Higher burst resistance index (such as 1.06kPa·m in Example 8) 2 / g) indicates that the paper is not easy to break during actual use and can withstand greater pressure, which increases its operability and durability.

[0068] 4. Tear index: The tear index reflects the tear resistance of paper when it is torn. The larger the value, the stronger the paper's ability to resist tearing. From the table, the tear index ranges from 2.20m·Nm 2 / g (Example 1) to 8.15m·Nm 2 / g (Example 10). Paper with a higher tear index (such as Example 10) is suitable for use in applications requiring stronger tear resistance, such as packaging materials.

[0069] 5. Whiteness: Whiteness is a measure of paper color; higher values ​​indicate a closer-to-pure white. The values ​​in the table range from 60.38% ISO (Example 10) to 75.05% ISO (Example 1). The overall high whiteness indicates a visually white paper, making it suitable for products requiring a high visual quality, such as printed paper and packaging materials.

[0070] The advantages of the pulp prepared by the present invention are as follows: 1. Advantages of bulk and softness: Samples with relatively high bulk (such as Example 9, with a bulk of 3.04 cm 3 / g) provides good paper thickness and softness. Higher bulk helps improve the tactile feel of the paper, making it more suitable for paper products that require a soft and thick feel.

[0071] 2. High Tensile Strength: Samples with a high tensile index (e.g., Example 8, with a tensile index of 27.42 N·m / g) demonstrate that the pulp produced by this invention can produce paper with high strength, making it suitable for applications requiring strong tensile resistance, such as industrial paper and packaging materials. High tensile strength means that the paper can better withstand external forces during transportation, storage, and use, reducing damage.

[0072] 3. Good Burst and Tear Resistance: Samples with high burst and tear indices (such as Examples 8 and 10) demonstrate that the pulp prepared by the present invention effectively improves the durability and damage resistance of paper. This results in paper with excellent compressive strength and tear resistance, and better performance in high-intensity use environments.

[0073] 4. High Whiteness: The samples exhibited high whiteness overall, particularly Example 1, which achieved a whiteness of 75.05% ISO. This indicates that paper made with this chemimechanical pulp exhibits excellent visual quality and is suitable for applications requiring high visual standards, such as high-quality printing paper. High whiteness also contributes to enhanced gloss and clarity.

[0074] 5. Environmental friendliness and sustainability: This paper utilizes a chemimechanical pulping process to effectively utilize low-cost and waste wood from fast-growing forests, landscaping waste, and branches from forest farms, reducing reliance on traditional wood resources. This approach not only reduces paper production costs but also mitigates overexploitation of wood, contributing to environmental protection and sustainable development.

[0075] 6. Versatile Applicability: By optimizing the pulp formulation, the paper produced by the present invention can adjust performance indicators such as bulk, tensile strength index, and burst resistance index according to demand. This makes the pulp highly adaptable to different production requirements, performing well in everything from high-strength packaging materials to high-whiteness paper. For example, in Example 11, the paper sheet produced by blending high-whiteness poplar and high-strength white wax has both high strength and high whiteness properties. In Example 12, the paper sheet produced by blending high-whiteness poplar and high-bulk sycamore has both high bulk and high whiteness properties.

[0076] 7. Indispensability of process flow: For example, in Comparative Example 1, the bleaching section is missing, and the whiteness of the paper sheet is significantly reduced, accompanied by a decrease in the strength of the paper sheet. This is because the lignin carrying the chromophore group is retained in the paper sheet, and the residual lignin hinders the fiber binding. In Comparative Example 2, a first-stage disc grinding is missing, and the tensile index and tear resistance index of the paper sheet are significantly reduced. This is because the lack of the first-stage disc grinding leads to insufficient fiber fibrillation and brooming, a decrease in specific surface area, reduced hydrogen bonding between fibers, and poor fiber network uniformity. In Comparative Example 3, the order of the bleaching section and the second-stage disc grinding is interchanged, and it can be found that the mechanical strength indicators (tensile strength, tear resistance, and tear resistance) generally decrease, mainly due to premature fiber cutting and chemical damage, resulting in a decrease in fiber length and self-strength; the bulk decreases because the fibers are cut and fibrillated earlier, and the chemical treatment during bleaching further softens the fibers, resulting in tighter fiber binding, a denser paper structure, and a decrease in bulk.

[0077] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the invention.

Claims

1. A method for preparing wood fiber pulp at low cost using branch wood, characterized in that: The method for preparing wood fiber pulp at low cost using branch wood comprises the following steps: S1 Activation treatment: soak the wood chips to obtain activated wood chips; the wood chips are made from one of the following: poplar, ash, sycamore, birch, poplar + pine, poplar + ash; poplar + sycamore, S2 Primary Defibrination: The activated wood chips are initially extruded to obtain coarse wood fibers; S3 primary chemical impregnation: impregnating the coarse wood wool in an alkaline solution containing EDTA to obtain impregnated coarse wood wool; S4 microfibrillation treatment: the impregnated coarse wood fibers are subjected to microfibrillation extrusion to obtain fine wood fibers; S5 secondary chemical impregnation: chemically impregnating the wood wool in an alkaline solution containing hydrogen peroxide, sodium metasilicate and EDTA to obtain impregnated wood wool; S6 initial grinding: the impregnated fine wood fibers are initially ground to obtain an initial slurry; S7 Whiteness Control and pH Balance: The initial pulp is bleached and the pH value is adjusted to obtain a bleached pulp. In the bleaching process, an alkaline solution containing hydrogen peroxide, sodium metasilicate, and EDTA is used as the bleaching liquid. S8 fine grinding: fine grinding the bleached pulp to obtain finely ground pulp; S9 Finished product refining and screening: The refined pulp is subjected to de-latency operations and screening operations to obtain wood fiber pulp.

2. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S1, the wood chip raw materials come from fast-growing forests, greening waste or branches from forest farms. In the wood chip raw materials composed of poplar and pine, the weight ratio of poplar to pine is 99-50:1-50, and the pine is masson pine or radiata pine; in the wood chip raw materials composed of poplar and ash, the weight ratio of poplar to ash is 10-30:70-90; in the wood chip raw materials composed of poplar and sycamore, the weight ratio of poplar to ash is 40-70:30-60.

3. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In both the initial extrusion operation in step S2 and the microfibrillation extrusion operation in step S4 , a single-screw extruder is used as the extrusion equipment.

4. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In both the preliminary grinding operation in step S6 and the fine grinding operation in step S8 , a KRK disc grinder is used as the grinding equipment.

5. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S3, in the alkaline solution containing EDTA, the concentration of sodium hydroxide is 0.1-3.0%; the concentration of EDTA is 0.001-0.05%; the chemical impregnation operation parameters are as follows: the impregnation temperature is 40-90° C., the impregnation time is 5-25 minutes, and the material concentration is 20-45%.

6. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S5, in the alkaline solution containing hydrogen peroxide, sodium metasilicate and EDTA, the concentration of sodium hydroxide is 1.0-4.0%; the concentration of hydrogen peroxide is 1.0-5.0%, the concentration of sodium metasilicate is 0.2-2.0%, and the concentration of EDTA is 0.001-0.02%. The chemical impregnation operation parameters are as follows: the impregnation temperature is 65-95° C., the impregnation time is 20-70 minutes, and the material concentration is 20-45%.

7. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S6, the parameters of the initial grinding operation are as follows: the disc grinding concentration is 20-35%, and the gap is 0.1-0.7 mm.

8. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S7, in the bleaching solution, the concentration of sodium hydroxide is 1.0-4.0%; the concentration of hydrogen peroxide is 1.0-5.0%; the concentration of sodium metasilicate is 0.2-1.5%; and the concentration of EDTA is 0.001-0.02%. The bleaching operation parameters are as follows: temperature is 75-100° C., bleaching time is 70-110 minutes, and material concentration is 20-40%. The target pH value of the pH adjustment operation is 6.5-8.

0.

9. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S8, the fine grinding parameters are as follows: disc grinding concentration is 20-35%, and the gap is 0.1-0.4 mm.

10. The method for preparing wood fiber pulp at low cost using branch wood as claimed in claim 1, characterized in that: In step S9, the parameters for the delatching operation are as follows: the delatching temperature is 70-95° C., and the delatching time is 1-10 minutes; in the screening operation, a sieve with a mesh size of 80-120 is used.

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