Bleached bamboo pulp, method for preparing bleached bamboo pulp and technical application of bleached bamboo pulp in water-absorbing kraft base paper

Abstract

The application provides a bleached bamboo pulp, a preparation method of the bleached bamboo pulp and a technical application of the bleached bamboo pulp in water-absorbing base paper, and improves the water absorption performance of bamboo pulp fibers through innovation of a pulping process. Mainly, the bamboo blocks after hot water washing are stored in a bin at 30-55 DEG C, the bamboo blocks are further swelled, the stored bamboo blocks are subjected to extrusion treatment, the specific surface area of the bamboo blocks is increased by 50%-200% compared to that of the stored bamboo blocks, then a fiber grading screening process is added before oxygen delignification of the pulp, the long fiber and short fiber quantity ratio in the screened pulp is 40-62:60-38, and the long fiber and short fiber mass ratio is 45-75:55-25. The three innovative processes and the synergistic effect thereof improve the water absorption capacity of the bamboo pulp fibers, and auxiliary reagents are added in bleaching and pulping, so that the water-absorbing base paper produced by the bleached bamboo pulp is more fluffy and has better water absorption.

Description

Technical Field

[0001] This application relates to the field of pulp and paper making, and more specifically, to a bamboo fiber bleached pulp, a method for preparing the same, and the application of the bamboo fiber bleached pulp in the papermaking field. Background Technology

[0002] Absorbent paperboard can be used in hygiene, medical, and food fields. However, currently, only a portion of absorbent paperboard products on the market are food-grade, and most are made from imported wood pulp, with a small portion made from bagasse or recycled fibers. This technology presents two problems: First, the use of imported wood pulp means that the international market and global situation significantly impact raw material supply, leading to high production costs and hindering market development and promotion. Second, while bagasse pulp or recycled pulp primarily from wood pulp products are used as raw materials, absorbent paperboard has high requirements for physical and hygiene indicators. This method results in a high pollution load per unit product, leading to significant energy and water consumption and wastewater discharge, thus compromising product quality.

[0003] Bamboo is not only abundant, low-cost, and highly renewable, but also has low impurity cell content, high cellulose content, and natural hydrophilicity, making it an effective substitute for wood in the production of absorbent paperboard while ensuring product quality. However, during research on the preparation of bleached bamboo pulp for absorbent paperboard and its production process, the applicant discovered that absorbent paperboard made from bleached bamboo pulp prepared using traditional pulping processes fails to meet required absorbency standards. The main factor affecting the absorbency of absorbent paperboard is the insufficient absorbency of the bamboo pulp fibers used in its preparation. Therefore, improving the absorbency of bamboo pulp fibers has become an urgent technical problem to be solved. Currently, researchers have conducted considerable research on improving the absorbency of bamboo pulp fibers.

[0004] For example, Chinese patent CN112359635B discloses a method for treating bamboo fiber pulp, a method for preparing fluff pulp, and fluff pulp itself, relating to the field of bamboo fiber treatment technology. By catalytically oxidizing bamboo fibers in bamboo fiber pulp under alkaline conditions using a TEMPO / NaBr / NaClO system, hemicellulose, short-chain cellulose, and other organic impurities in the cell walls are oxidized and degraded. This process degrades hydrophobic components on the bamboo fiber surface, increases its hydrophilic groups, purifies the fiber, and reduces the binding force between fibers. This combined effect effectively improves the water absorption and liquid absorption rate of bamboo pulp fibers. While this invention improves the water absorption of bamboo pulp fibers through chemical oxidation degradation, it also increases the consumption of chemical reagents.

[0005] For example, Chinese patent CN106758488A discloses a method for preparing high-strength absorbent bamboo pulp paper. The method involves pulping bamboo fiber pulp at 40-50°C, removing coarse fibers using a delamination machine to obtain fiber bundles with a particle size ≤1mm, adjusting the pH to 7.0-7.5 with alkali, adding an absorbent agent, mixing and beating to obtain a uniform pulp, and then subjecting the pulp to washing, papermaking, pressing, drying, calendering, winding, slitting, and packaging to obtain the desired high-strength absorbent bamboo pulp paper. The bamboo pulp paper prepared by this invention incorporates an absorbent agent prepared from modified starch, which has good compatibility with bamboo pulp, high uniformity, high water absorption rate, and fast water absorption speed, while also improving the strength of the bamboo pulp paper.

[0006] For example, Chinese patent CN108677582A discloses a method for improving the water absorption of bamboo pulp tissue paper base paper. This method uses NFC (nanocellulose) added to the pulp to enhance the water absorption of the bamboo pulp tissue paper base paper. Because of NFC's large specific surface area and high aspect ratio, it easily forms a three-dimensional network structure in the bamboo pulp fiber paper base. This structure creates numerous microcapillary structures in the paper base material, generating a large specific surface area effect, which improves the water absorption of the paper base material through capillary and swelling effects. Furthermore, NFC contains a large number of hydrophilic hydroxyl groups, which are highly polar and easily combine with water, which has a high dielectric constant, thereby improving the water absorption of the finished paper. This invention is simple, feasible, and environmentally friendly, and is of great significance for the production of safe and environmentally friendly kitchen paper.

[0007] For example, Chinese patent CN102040709A discloses a method for preparing a bleached bamboo pulp cellulose-based absorbent material. Its characteristics include the following preparation steps: bleached bamboo pulp is boiled using a sulfate process, followed by a four-stage bleaching process involving oxygen delignification, chlorine dioxide, hydrogen peroxide, and chlorine dioxide to obtain bleached bamboo pulp fibers; then, the bleached pulp fibers are pretreated using a PFI refiner, and graft copolymerized using an aqueous solution polymerization method; subsequently, the copolymer is subjected to precipitation and washing, freeze-drying, grinding, further freeze-drying, and sealing to obtain the finished product. The absorbent material prepared by this invention has high water absorption efficiency and can effectively utilize bleached bamboo pulp cellulose, but the process is relatively complex.

[0008] In summary, methods to improve the water absorption of bamboo pulp fiber include oxidative degradation of hydrophobic substances in the bamboo pulp, or the addition of auxiliary substances that enhance water absorption, such as water-absorbing agents. These methods rely on additional reagents, increasing the consumption of chemical reagents. Clearly, existing technologies do not fully utilize the unique properties of the raw material to improve the water absorption of bamboo pulp fiber, resulting in complex processes, large amounts of additives, and difficulty in controlling their usage. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bleached bamboo pulp that fully utilizes the unique properties of raw materials to improve the water absorption performance of bamboo pulp fibers. This bleached bamboo pulp can be used in the preparation of absorbent cardboard. At the same time, a method for preparing this bleached bamboo pulp is also provided.

[0010] The bleached bamboo pulp provided by this invention has a long-to-short fiber ratio of 40–62:60–38 and a long-to-short fiber mass ratio of 45–75:55–25. This bleached bamboo pulp has a whiteness of 80–88% ISO, a tensile index of 45–65 N·m / g, and a tear index of 10–18 mN·m. 2 / g, with a bulk thickness of 1.6–2.2cm. 3 / g, with a bursting index of 2.8–3.6 kPa·m. 2 / g, pentosan content is 5%–10%, holocellulose content is 80%–90%, fiber crimp is 10%–16%, primary fiber content is 95.5%–97.5%, and secondary fiber content is 2.5%–4.5%. The pentosan content and holocellulose content are percentages of the total weight of bleached bamboo pulp, and the primary fiber content and secondary fiber content are percentages of the total weight of holocellulose.

[0011] Holocellulose contains type I fibers, type II fibers, and other non-fiber compounds. Type I fibers are divided into long fibers (the portion larger than 1.4 mm) and short fibers (the portion between 0.5 and 1.4 mm), while type II fibers are fibers smaller than 0.5 mm and fibrous miscellaneous cells.

[0012] In addition, the bleached bamboo pulp also includes additives, which include 0.02-0.06% of dispersant, 0.01-0.03% of finely ground mineral talc, 0.01-0.03% of fixative, 0.002-0.006% of ternary microparticle glue and 0.02-0.06% of edible corn starch, accounting for 0.02-0.06% of the total weight of the bleached bamboo pulp.

[0013] The combination of dispersant, fixative, and finely ground mineral talc enhances the absorbency of the product by maintaining a certain gap between the fibers. The mechanism involves the fixative adsorbing finely ground mineral talc at one end and the other end onto the fiber surface. Microscopically, the material distribution between the two fibers is roughly divided into two forms: fiber-fixative-finely ground talc-fixative-fiber, or fiber-fixative-finely ground talc-finely ground talc-fixative-fiber. This distribution maintains a certain gap between the fibers, while the added dispersant reduces the binding force between the fibers. Thus, during papermaking, the binding force between fibers is reduced, resulting in more fluffy absorbent paper with better absorbency, while maintaining a certain thickness and bulk. Simultaneously, the finely ground mineral talc undergoes micro-expansion during water absorption, further enhancing the water absorption capacity of the paper fibers. In addition, by adding food-grade ternary microparticle adhesive and corn starch reagent, the uniform bonding between paper webs can be enhanced during the three-layer paper web lamination process, solving the problem of uneven surface of absorbent paperboard caused by the lamination of absorbent paperboard.

[0014] The method for preparing this bleached bamboo pulp includes the following steps: cutting raw materials into bamboo blocks, biological fermentation of bamboo blocks, hot water washing, storage in a silo, making coarse pulp, oxygen deligninization, and bleaching. The silo storage step involves storing the washed bamboo blocks in a silo at 30–55°C to maintain the temperature of the bamboo blocks within this range, resulting in the first bamboo block. After the silo storage step and before the coarse pulp making step, the first bamboo block is extruded to obtain a second bamboo block with a specific surface area 50%–200% larger than the first bamboo block. After the coarse pulp making step and before the oxygen deligninization step, the coarse pulp undergoes fiber grading and screening. The ratio of long to short fibers in the screened pulp is 40–62:60–38, and the mass ratio of long to short fibers is 45–75:55–25.

[0015] The bamboo blocks, after being washed with hot water, are stored in a silo at 30–55°C for 4–8 hours to maintain their temperature. This process fully utilizes the residual heat left in the bamboo blocks after washing with hot water at 35–55°C, allowing the bamboo blocks to swell further during storage. This process helps to redissolve soluble substances in the bamboo fibers, reducing the consumption of chemicals in the subsequent pulping process, and also creates favorable conditions for the subsequent extrusion process.

[0016] The aforementioned process of adding a compression treatment to the first bamboo block after heat preservation and before making coarse pulp involves designing a suitable tooth spacing of the extruder to cause longitudinal / transverse displacement between bamboo fibers. This increases the specific surface area of ​​the bamboo block after heat preservation, which is beneficial for the penetration of chemical reagents, accelerates the processing speed of the cooking stage, and improves the efficiency of delignin removal.

[0017] The aforementioned process of adding a pulp screening treatment after coarse pulp preparation and before oxygen delignination aims to separate the long and short fibers in bamboo pulp. Along with the short fibers, a large number of fine components are also separated, such as bamboo pulp impurities, vessel fragments, and bamboo joint particles.

[0018] Short fibers and fine fractions have a significant impact on the water absorption of bamboo pulp fibers and the physical properties of absorbent paperboard: Firstly, fiber water absorption is mainly due to capillary forces, and the cell lumen diameter of long fibers is larger than that of short fibers. Therefore, the capillary effect of short fibers is weaker than that of long fibers, resulting in lower water absorption. Separating short fibers is beneficial to improving the water absorption of bamboo pulp fibers. Secondly, bamboo pulp impurities in the fine fractions easily absorb water but are difficult to dehydrate. The presence of these impurities slows down the dehydration rate of absorbent paperboard during papermaking, requiring increased vacuum adsorption and mechanical pressing on the paper machine. This leads to a reduction in the thickness of the produced absorbent paperboard, and the bulk of the product does not meet requirements. Thirdly, vessel fragments in the fine fractions are formed from bamboo fibers during the bamboo pulp production process. The surface-peeled material has properties similar to fibers, but poor water absorption. During the papermaking process, it fills the gaps between fibers. Once filled, the gaps between fibers lose their original water absorption capacity. Since the gaps between fibers also generate capillary forces, which are beneficial for paper water absorption, and the hydroxyl groups on the surface of the vessel fragments combine with the hydroxyl groups on the surface of the fibers, the resulting bonding force microscopically shortens the distance between the fibers. Thus, the vessel fragments not only hinder fiber water absorption but also reduce the thickness of the absorbent paper. Fourth, the bamboo-like particles in the fine components will be further reduced in size after mechanical processing during the papermaking process, filling the gaps between fibers. A small number of extremely fine particles may adhere to the fiber ends, blocking the fiber cell cavities and hindering fiber water absorption.

[0019] Furthermore, the inventors discovered that the water absorption of bamboo pulp fiber is not only determined by the specific surface area of ​​the bamboo block, but also by the ratio of long to short fibers. Therefore, there is a certain quantitative relationship between the two process steps of extrusion treatment and fiber grading and screening, and this quantitative relationship determines the water absorption of bamboo pulp fiber. The first quantitative relationship is as follows: the specific surface area of ​​the second bamboo block increases by 140%–180% compared to the first bamboo block, and the ratio of long to short fibers in the pulp after fiber grading and screening is 40–45:60–55, and the mass ratio of long to short fibers is 45–50:55–50. The second quantitative relationship is as follows: the specific surface area of ​​the second bamboo block increases by 100%–130% compared to the first bamboo block, and the ratio of long to short fibers in the pulp after fiber grading and screening is 47–54:53–46, and the mass ratio of long to short fibers is 52–58:48–42. Bamboo pulp fiber prepared under these conditions... The water absorption of the bamboo pulp fiber prepared under the first quantitative relationship condition is better than that of the bamboo pulp fiber prepared under the second quantitative relationship condition. The third quantitative relationship condition is as follows: the specific surface area of ​​the second bamboo block is increased by 60% to 90% compared with that of the first bamboo block, the ratio of long to short fibers in the pulp after fiber grading and screening is 62 to 56: 38 to 44, and the mass ratio of long to short fibers is 75 to 65: 25 to 35. The water absorption of the bamboo pulp fiber prepared under this condition is better than that of the bamboo pulp fiber prepared under the second quantitative relationship condition. That is, the water absorption of the bamboo pulp fiber prepared under the third quantitative relationship condition is the best.

[0020] Because bamboo blocks, after being insulated and swollen, undergo extrusion processing, which "loosens" the bamboo blocks into a fluffy state, the degree of fluffiness varies, resulting in different increases in specific surface area. By adjusting and selecting different extrusion process parameters, bamboo blocks with different increases in specific surface area can be obtained. The greater the degree of processing, the greater the increase in specific surface area of ​​the bamboo blocks. However, during the mechanical processing of bamboo fibers, some long fibers are cut by mechanical force, that is, the fiber length becomes shorter. Therefore, the greater the increase in specific surface area of ​​the bamboo blocks after processing, the smaller the proportion of long fibers after fiber grading and screening. Since long fibers have better water absorption than short fibers, the second bamboo block, with a specific surface area 60% to 90% greater than the first bamboo block, has an increased fiber surface area after extrusion processing, which improves water absorption performance while minimizing damage to long fibers.

[0021] Correspondingly, the extrusion process aims to increase the specific surface area of ​​the fibers, making them fluffier and more absorbent. Therefore, to maximize the proportion of long fibers in the pulp and achieve optimal water absorption in the resulting paper, excess short fibers need to be separated, allowing long fibers to occupy a more favorable position in the pulp. The second bamboo block, with a specific surface area 60%–90% larger than the first bamboo block, experiences the least damage to long fibers during the extrusion process. Furthermore, it produces the highest proportion of both long and short fibers in the pulp after fiber grading and screening, resulting in paper with the best water absorption.

[0022] Absorbent cardboard is prepared from the bleached bamboo pulp described above using the following method: the concentration of bleached bamboo pulp is diluted to 0.5% to 1.2%; the bleached bamboo pulp is composite-formed using a three-layer wire mesh to obtain a wet paper web with a moisture content of 75% to 85%; the paper web is then subjected to vacuum mechanical dehydration, surface smoothing, high-temperature steam heat treatment, and soft calendering to obtain the base paper for absorbent cardboard.

[0023] In summary, this invention, through the combination and synergistic effect of the above-mentioned technical innovations, improves the water absorption of bleached bamboo pulp fibers and the overall performance of absorbent cardboard made using this bleached bamboo pulp, especially its water absorption performance. Detailed Implementation

[0024] The embodiments of this application will now be described in more detail. This application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0025] The term "comprising" and its variations as used in this application are open-ended, meaning "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment". Definitions of other terms will be given in the description below.

[0026] The specific steps for preparing bleached bamboo pulp and producing absorbent cardboard base paper provided by this invention are as follows: (1) Preparation of bamboo pulp fiber raw materials (raw materials are cut into bamboo blocks, and bamboo blocks undergo biological fermentation): One or more bamboo species, including *Phyllostachys edulis*, *Phyllostachys pubescens*, *Phyllostachys nigra*, *Phyllostachys pubescens*, *Phyllostachys nigra*, *Phyllostachys pubescens*, *Phyllostachys nigra*, *Phyllostachys pubescens*, *Phyllostachys nigra*, and *Phyllostachys nigra*, are used as raw materials for bamboo pulping. Bamboo cylinders with a moisture content of 45%–65% are cut into bamboo blocks with a length of 40–100 mm, a width of 20–60 mm, and a thickness of 5–25 mm using a rotary drum chipper. The bamboo blocks are then piled up under natural environmental conditions for biological fermentation. The pile height is 8–15 meters, and the biological fermentation cycle is 25–65 days, yielding bamboo blocks with a cold water extract content of 0.5%–4.5%, ash content of 1.0%–2.5%, moisture content of 10%–20%, and cellulose content of 40%–50%. (2) Pretreatment of bamboo pulp fiber raw materials (hot water washing, silo storage, extrusion treatment): The bamboo blocks after biological fermentation are sent into a hot water pool by a belt conveyor and washed in two countercurrent stages with hot water at 35-55℃, so that the moisture content of the bamboo blocks reaches 40%-55% after absorbing water. After washing, the bamboo blocks are stored in a silo at 30-55℃ by a belt conveyor for 4-8 hours to obtain the first bamboo block. After the heat preservation is completed, the bamboo block is fed into the YDH125 alligator tooth spiral extrusion and kneading machine by a belt conveyor. The tooth pitch is 2-10mm, the pressure is 500-2000N, and the processing time is 5-20 seconds. After processing, the second bamboo block with a specific surface area increased by 50%-200% compared with the first bamboo block is obtained. (3) Preparation of bamboo pulp fiber slurry (preparation of coarse pulp, fiber grading and screening, oxygen deligninization): The loose bamboo block is transferred into a pressure vessel and a pulping solution with a concentration of 6%-10% based on Na2O is added. The material-liquid ratio is 1: (4-6). The coarse pulp is obtained by heating in two stages at 120-140℃ and 145-155℃, with a maximum pressure of 0.50-0.60Mpa. After reacting for 2.0-3.5 hours, coarse pulp is obtained. The coarse pulp is pumped to the pressure screen. The coarse pulp is screened in two stages and the pulping solution is recovered by filtration. Diluting water is added to dilute the pulp concentration by 1%-4%. The diluted pulp is pumped into the fiber grading and screening device. The pulp flow rate entering the fiber grading and screening device is controlled at 600-1800 L / min, and the pressure difference is maintained at 5-20 kPa. The ratio of long to short fibers in the pulp after fiber grading and screening is 40-62:60-38, and the mass ratio of long to short fibers is 45-75:55-25. The screened long fibers enter the pulp production process for absorbent cardboard. The pulp is pumped into the reaction tower, where a reaction solution with a concentration of 0.0025%-0.0045% is added. Industrial oxygen is introduced, the pressure is 0.20-0.40 MPa, the temperature is 55-90℃, and the reaction is carried out for 60-240 min. After that, it is pumped into the ECF bleaching process. (4) ECF bleaching process: In the D0 stage, the dosage of oxidant (chlorine compound) is 1.0-2.5%, the temperature is 55-65℃, and the time is 45-90 min; in the EOP stage, the dosage of pH adjuster (sodium-containing alkaline compound) is 1.5-2.5%, the oxygen pressure is 0.20-0.35 MPa, the dosage of hydrogen oxychloride compound is 0.25-0.50%, the temperature is 60-90℃, and the time is 90-150 min; in the D1 stage, the dosage of oxidant (chlorine compound) is 1.0-1.5%, the temperature is 60-75℃, and the time is 100-180 min; all the listed proportions are the mass ratio of chemical reagents to bamboo fiber. Pulp specifications: Brightness 80–88% ISO, tensile index 45–65 N·m / g, tear index 10–18 mN·m 2 / g, with a bulk thickness of 1.6–2.2cm. 3 / g, with a bursting index of 2.8–3.6 kPa·m.2 / g, pentosan content is 5%–10%, holocellulose content is 80%–90%, fiber crimp is 10%–16%, type I fiber content is 95.5%–97.5%, type II fiber content is 2.5%–4.5%, and the pentosan content and holocellulose content are percentages of the total weight of bleached bamboo pulp, while type I fiber content and type II fiber content are percentages of the total weight of holocellulose; (5) Papermaking of absorbent cardboard: The pulp is transferred to the pulp preparation tank in the papermaking workshop through the flow system, and then pumped to the inlet of the medium consistency refiner. The pulp concentration is 5.0-5.5%, the inlet pressure is 450-520 kPa, the outlet pressure is 90-130 kPa, and the power is 610-750 kW. After two stages of processing, a pulp with a freeness of 285-325 CSF is obtained. Preparation and addition of auxiliary materials for papermaking: Pump the slurry to the mixing tank, and add the following auxiliary reagents through the DCS control system: 0.02-0.06% of dispersant, 0.01-0.03% of finely ground mineral talc, 0.01-0.03% of fixative, 0.002-0.006% of ternary microparticle glue and 0.02-0.06% of edible corn starch, accounting for 0.02-0.06% of the total weight of bleached bamboo pulp; Finally, the slurry with prepared auxiliary reagents is diluted to a concentration of 0.5-1.2%, and then formed and laminated in a three-layer wire to obtain a wet paper web with a moisture content of 75-85%. The paper web is then subjected to vacuum mechanical dewatering, surface smoothing, high-temperature steam heat treatment, and soft calendering to obtain absorbent cardboard base paper.

[0027] The following embodiments are all implemented using the specific steps described above, and the specific different parameters and water absorption values ​​of each embodiment are shown in Table 1: Table 1: Comparison of specific parameters and water absorption values ​​of different embodiments Example 9 did not undergo extrusion treatment, but it was stored in a silo at 35-55°C and the fibers were graded and screened. Example 10 was stored in a silo at 35-55°C and extrusion treatment, but the fibers were not graded and screened. Example 11 was stored in a silo at 35-55°C, but the extrusion treatment and fiber grading and screening were not performed. Example 14 was not stored in a silo at 35-55°C, extrusion treatment, or fiber grading and screening. In addition, Example 12 had a lower degree of delignin removal during pulping because the increase in specific surface area was outside the range. Since lignin is hydrophobic, although the ratio of long and short fibers was high, the water absorption was poor.

[0028] As can be seen from the examples in Table 1, the second bamboo block, with a specific surface area 60% larger than the first bamboo block, produced the best absorbent cardboard from bleached bamboo pulp with a long-to-short fiber ratio of 62:38 and a long-to-short fiber mass ratio of 75:25 after fiber grading and screening. The absorbent value was 1102 g / m³. 2 The absorbency of absorbent cardboard made from bleached bamboo pulp that has not undergone extrusion processing and fiber grading has a value of 938 g / m³. 2 The absorbency of absorbent cardboard made from bleached bamboo pulp that has undergone extrusion processing but not fiber grading and screening is 961 g / m³. 2 Absorbent cardboard made from bleached bamboo pulp that has not undergone extrusion processing but has been graded and screened for fiber absorption has an absorbency value of 957 g / m³. 2 This indicates that extrusion processing and fiber grading and screening have a significant impact on improving the water absorption of bamboo pulp fibers, and that a better effect can only be achieved through the synergistic effect of extrusion processing and fiber grading and screening processes.

[0029] Furthermore, absorbent cardboard made from bleached bamboo pulp with a specific surface area increased by 30% and 220% compared to the first bamboo block both exhibited poor absorbency, with absorbency values ​​of 969 g / m³. 2 and 933g / m 2 Because a small increase in specific surface area leads to a higher content of hydrophobic lignin in the bamboo pulp, resulting in poor water absorption, while an excessive increase in specific surface area can cause damage to long fibers and an increase in short fiber content during mechanical processing, also resulting in poor water absorption. Furthermore, the absorbency of the absorbent cardboard made from the bleached bamboo pulp prepared in Example 14 without storage at 35–55°C is significantly lower than that of the absorbent cardboard made from the bleached bamboo pulp prepared in Example 11 with storage at 35–55°C. Therefore, storage at 35–55°C is also essential for improving the water absorption of bamboo pulp fibers.

[0030] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A method for preparing bleached bamboo pulp, comprising the steps of cutting raw materials into bamboo blocks, biological fermentation of bamboo blocks, hot water washing, storage in a silo, preparing coarse pulp, oxygen deligninization, and bleaching, characterized in that: The aforementioned storage step involves storing the bamboo blocks washed with hot water in a silo at 30-55°C for 4-8 hours to maintain the temperature of the bamboo blocks at 30-55°C, thereby obtaining the first bamboo block. After the material storage step is completed and before the coarse pulp preparation step begins, the first bamboo block is extruded to obtain a second bamboo block with a specific surface area that is 50% to 200% larger than that of the first bamboo block. After the coarse pulping step and before the oxygen delignination step, the coarse pulp is subjected to fiber grading and screening. The ratio of long to short fibers in the screened pulp is 40~62:60~38, and the ratio of long to short fiber mass is 45~75:55~25. Among them, long fibers are fibers with a length greater than 1.4 mm, and short fibers are fibers with a length of 0.5~1.4 mm.

2. The method for preparing bleached bamboo pulp according to claim 1, characterized in that, The first bamboo block is extruded to obtain a second bamboo block with a specific surface area that is 140% to 180% larger than that of the first bamboo block. After the coarse pulping step and before the oxygen delignination step, the coarse pulp is subjected to fiber grading and screening. The ratio of long to short fibers in the screened pulp is 40 to 45: 60 to 55, and the mass ratio of long to short fibers is 45 to 50: 55 to 50.

3. The method for preparing bleached bamboo pulp according to claim 1, characterized in that, The first bamboo block is extruded to obtain a second bamboo block with a specific surface area that is 100% to 130% larger than that of the first bamboo block. After the coarse pulping step and before the oxygen delignination step, the coarse pulp is subjected to fiber grading and screening. The ratio of long to short fibers in the screened pulp is 47 to 54: 53 to 46, and the ratio of long to short fiber mass is 52 to 58: 48 to 42.

4. The method for preparing bleached bamboo pulp according to claim 1, characterized in that, The first bamboo block is extruded to obtain a second bamboo block with a specific surface area that is 60% to 90% larger than that of the first bamboo block. After the coarse pulping step and before the oxygen delignination step, the coarse pulp is subjected to fiber grading and screening. The ratio of long to short fibers in the screened pulp is 62 to 56: 38 to 44, and the ratio of long to short fiber mass is 75 to 65: 25 to 35.

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