Modified bamboo pulp, preparation method and application thereof in bamboo pulp roll board for pulp molding direct-press process

Abstract

The application provides a modified bamboo pulp, a preparation method and application of the modified bamboo pulp in a bamboo pulp roll for a paper pulp molding direct-press process. The mass ratio of short fibers and long fibers in the bamboo pulp is 45-75:55-25 by utilizing the more compact cross-linking characteristics between the short bamboo fibers, and the bamboo pulp is modified by adding a pulp modifier with a mass fraction of 0.1%-0.5% of the bamboo pulp, wherein the pulp modifier is a mixture of a vinyl alkyl polymer, an imidazoline quaternary ammonium salt, an ester quaternary ammonium salt and sodium hydroxide, so that the tightness of the modified bamboo pulp is 0.65-0.70 g / cm 3 , the stiffness is 25-55 mN.m, the swelling of the fibers in the modified bamboo pulp is uniform, and the binding force is better, and the compactness between the fibers is further improved by the fine components in the bamboo pulp and the addition of auxiliary reagents; the three-dimensional structure of the fibers in the bamboo pulp roll produced by using the modified bamboo pulp is more uniform and the compactness is higher, so that the uniformity of the thickness is ensured, and the dimensional stability and mechanical performance indexes of the bamboo pulp roll for the paper pulp molding direct-press process are met.

Description

Technical Field

[0001] This application relates to the field of bamboo pulp preparation technology, and more specifically, to a method for preparing modified bamboo pulp and its application. Background Technology

[0002] Pulp molding, as an environmentally friendly material, is of great significance to today's society that pursues sustainable development. Compared with traditional plastic packaging materials, pulp molding is made from natural cellulose materials, which does not pollute the environment and can be recycled. Currently, pulp molding products are mainly used for tableware and packaging. Its raw materials include sugarcane fiber, grass fiber, wood fiber, and bamboo fiber. Among them, sugarcane fiber is a medium-length fiber with the advantages of moderate strength and moderate toughness, and is currently the most widely used fiber. Grass fibers include wheat straw fiber and reed fiber. Wheat straw fiber is short and has good stiffness, but the product is brittle and has poor toughness. Reed fiber has more impurities and low whiteness. Wood fiber is divided into softwood fiber and hardwood fiber. Softwood fiber is long and thin, with fewer impurities and good toughness, while hardwood fiber is coarse and short, and contains more impurities, resulting in relatively lower strength of the finished product. Bamboo fiber is a medium-length fiber with properties between softwood fiber and hardwood fiber. Products made from bamboo fiber have strong toughness and a smooth and delicate surface.

[0003] Different fibers possess different properties. In pulp molding product production, one or more fibers are often selected as raw materials to balance the disadvantages of each fiber and control the toughness and strength of the final product. Bamboo fiber, compared to other fibers, is more abundant and, like sugarcane fiber, is a medium-length fiber with a wide range of applications, offering good toughness and strength. Furthermore, in the direct compression molding process of pulp molding, the fiber raw material becomes loose on the forming mesh. Due to differences in the bonding forces between different types of fibers, the resulting fiber network structure is uneven. During subsequent hot pressing, the secondary bonding between fibers is also uneven, resulting in uneven product thickness. Therefore, the dimensional stability and mechanical properties of the product fail to meet requirements. Bamboo fiber, however, can be used alone to produce molding composite materials without adding other types of fibers. The single fiber type results in better bonding forces between fibers, producing products with good uniformity, good formability, high strength, and biodegradability, making it an excellent material for molding composite materials. Currently, there are some reports on using bamboo fiber as a raw material for molding products.

[0004] For example, Chinese patent CN115369679A discloses a refined bamboo pulp, its preparation method, and its application in papermaking. The refined bamboo pulp has a fiber length of 1.2–1.6 mm, a fiber width of 17–20 μm, and a fiber length-to-width ratio of 60–90. The ratio of long fibers to short fibers is 3–4:7–6. The pentosan content is 10–20%, the holocellulose content is 80–90%, the fiber crimp is 11–14%, the content of first-type fibers is 94.5–96.5%, and the content of second-type fibers is 3.5–5.5%. This invention is a general... Improving the quality of bamboo pulp products by controlling the ratio between the length and width of the fiber raw materials and the total fiber content mainly utilizes the interaction between the length and width of short and long fibers to make the paper products have higher bulk. Short fibers have a relatively larger width and a smaller lumen ratio than long fibers, making the fibers stiffer. Controlling the ratio of long and short fibers makes the interweaving and connection between fibers higher. More short fibers make the paper products stiffer, which utilizes the stiffness characteristics of short fibers. However, it does not mention the effect of dense cross-linking between short fibers on the density of bamboo pulp, nor does it modify the bamboo pulp.

[0005] For example, Chinese patent CN115341402A discloses a 100% bamboo pulp molded product and its preparation method, including selecting raw material slices, stacking for biological pretreatment, adding NaOH for reaction, and removing lignin to obtain coarse pulp raw material. The coarse pulp raw material then undergoes washing, oxidative lignin removal, screening for impurities, bleaching, refining, and beating steps to obtain beated and unbeated bamboo pulp. The beated and unbeated bamboo pulp are then mixed in a certain proportion to prepare a mixed bamboo pulp. Finally, the mixture is prepared with 92 parts of mixed bamboo pulp, 6 parts of waterproofing agent, and 2 parts of TG-8811 food-grade oil-resistant agent, and then pressed into shape. This method utilizes the fact that the fibers of beated and unbeated bamboo pulp, with their different properties, are more likely to interweave. It leverages the morphological changes in fibers caused by beating to make the fibers more tightly bonded, thereby effectively enhancing the internal bonding strength of bamboo fibers, improving the printability of molded pulp products, and effectively solving the technical problem of surface fuzzing. However, it does not distinguish between long and short fibers.

[0006] For example, Chinese patent CN111516073A discloses a method for preparing bamboo fiber molding composite material. The method is as follows: bamboo strips are crushed into a loose state, immersed in a nano-calcium carbonate solution, a chelating agent is added, and flash explosion treatment is performed to obtain modified bamboo fiber crude product. The residual solution is filtered to obtain a bamboo basic tissue crude product. The bamboo fiber crude product is immersed in a nano-calcium carbonate solution and ultrasonically treated to obtain modified bamboo fiber. The residual solution is filtered to obtain a bamboo basic tissue crude product. The two bamboo basic tissue crude products are combined, washed with water and dried to obtain bamboo basic tissue. The bamboo basic tissue is soaked in water, a starch-based thickener is added, stirred, and filtered to obtain a modified bamboo basic tissue. The dried modified bamboo fiber and modified bamboo basic tissue are mixed and molded to obtain bamboo fiber molding composite material. In this invention, the basic structure of bamboo is thin-walled cells. The fiber and thin-walled cells are fully separated through separation and modification to improve the purity of bamboo fiber. The two are then mixed after modification to increase the uniformity and strength of the product. However, this requires multiple separation, extraction and modification of bamboo, which may damage the structure of the fiber and thin-walled cells themselves. Furthermore, it does not mention long and short fibers.

[0007] For example, Chinese patent CN111394802A discloses a method for preparing long bamboo fibers for molding composite materials. This method utilizes bio-enzyme extraction of bamboo fibers. Specifically, bamboo strips are crushed and washed to obtain loose bamboo strips. Bamboo tissue and microbial inoculum are added to the extract for fermentation. The resulting bio-enzyme is then separated and purified, and mixed with xylanase, pectinase, and water to obtain an enzyme preparation. The bamboo strips are then treated with the activated enzyme preparation, followed by washing, draining, loosening, and drying to obtain long bamboo fibers for molding composite materials. The long bamboo fibers prepared by this invention have advantages such as long length, fineness, high tensile strength, and high fracture strength.

[0008] In summary, most existing technologies employ the mixing of bamboo fibers in different states or the addition of modifiers such as starch to modify the fibers, thereby enhancing the strength, toughness, and other mechanical properties of molded composite materials and improving their uniformity. They also utilize bio-enzymatic extraction of long bamboo fibers as raw materials for producing molded composite materials, leveraging the inherent characteristics of long bamboo fibers to improve the strength and toughness of molded products. Patent CN114635312A further proposes adding starch additives to improve the bonding force between fibers, thereby increasing the strength and density of paper. However, none of these technologies mention utilizing the inherent cross-linking and dense characteristics of short bamboo fibers and improving the density of bamboo pulp through interface modification, thus enhancing the dimensional stability and mechanical properties of pulp molded products. Summary of the Invention

[0009] This invention provides a modified bamboo pulp, its preparation method, and its application in bamboo pulp rolls for direct pressing pulp molding. The modified bamboo pulp preparation method combines the development of a graded utilization method for bamboo fiber raw materials. By utilizing the more dense cross-linking characteristics between the short bamboo fibers screened out, the resulting bamboo pulp rolls have higher density. Furthermore, the pulp modification further improves the bonding force and uniformity between fibers, thereby solving the problem of insufficient density and uneven structure of pulp rolls prepared from fiber raw materials for pulp molding, which leads to the failure of pulp molding products to meet the requirements of dimensional stability and mechanical properties. This enables bamboo fiber raw materials to meet the requirements of the direct pressing pulp molding production process.

[0010] This invention provides a modified bamboo pulp with a density of 0.65–0.70 g / cm³. 3 The stiffness is 25-55 mN·m.

[0011] The modified bamboo pulp also contains a pulp modifier, which is a mixture of vinyl alkyl polymer, imidazoline quaternary ammonium salt, ester quaternary ammonium salt and sodium hydroxide.

[0012] The mass ratio of vinyl alkyl polymer, imidazoline quaternary ammonium salt, ester quaternary ammonium salt and sodium hydroxide is 2-6:1-4:3-7:2-5.

[0013] The mass ratio of short fibers to long fibers in the modified bamboo pulp is 45–75:55–25.

[0014] The modified bamboo pulp also includes formulation additives, which include the following auxiliary reagents in parts by weight: 0.02 to 0.06 parts of dispersant and 0.005 to 0.012 parts of finely ground mineral talc.

[0015] The dispersant is a fatty amide quaternary ammonium salt.

[0016] This invention also provides a method for preparing modified bamboo pulp, comprising the following steps in sequence: cutting bamboo raw materials into bamboo blocks, biological fermentation of bamboo blocks, hot water washing, storage in a silo at 30-55°C, extrusion treatment, preparation of coarse pulp, fiber grading and screening of coarse pulp, oxygen deligninization, ECF bleaching, preparation of pulp for papermaking, and formulation of auxiliary materials for pulp for papermaking. The method is characterized in that the bamboo pulp is modified after ECF bleaching.

[0017] First, the bleached bamboo pulp is diluted to a mass concentration of 1.5%–4.5%. Then, 0.1%–0.5% of a pulp modifier is added, which consists of vinyl alkyl polymer, imidazoline quaternary ammonium salt, ester quaternary ammonium salt, and sodium hydroxide mixed in a mass ratio of 2–6:1–4:3–7:2–5. The mixture is then pumped into a pulp storage tower and kept at 45℃–60℃ for 60–240 minutes to obtain modified pulp. The modified pulp is then used for papermaking pulp preparation and the addition of auxiliary materials to obtain modified bamboo pulp.

[0018] Furthermore, a modified bamboo pulp of the present invention is also used in bamboo pulp rolls for pulp molding direct pressing (PMP) processes. The basis weight of the bamboo pulp rolls prepared from the modified bamboo pulp for PMP PMP PMP PLC processes is 475–525 g / m³. 2 The thickness is 700–800 μm, and the density is 0.65–0.70 g / cm³. 3 .

[0019] The modified bamboo pulp of this invention involves modifying bamboo pulp with a high content of short fibers after fiber grading and screening. Firstly, it utilizes the denser cross-linking between short fibers compared to long fibers, resulting in higher density bamboo pulp and its rolled sheets. The modified bamboo pulp has a short-to-long fiber mass ratio of 45-75:55-25, with short fibers having a length of 0.5-1.4 mm and long fibers having a length of 1.4 mm or more. Secondly, it uses a pulp modifier to modify the bamboo pulp, appropriately increasing the water resistance and reducing the swelling of fibers that are more easily swollen when exposed to water. This improves the uniformity of swelling between fiber cells of different sizes, achieving uniform swelling between fibers. This results in a more uniform fiber network structure in the bamboo pulp rolled sheets during the loosening process, with evenly distributed bonding forces between fibers during the secondary molding process, leading to uniform thickness and stable structure in the finished product.

[0020] Bamboo pulp fibers have exposed free hydroxyl groups on their surface, exhibiting hydrophilicity. Since water molecules are polar, the hydroxyl groups in the cellulose and hemicellulose of bamboo pulp attract water molecules, causing water to enter the amorphous region of the cellulose, leading to fiber deformation and swelling. The free hydroxyl groups on the fiber surface adsorb a certain thickness of water film around the fiber. In this invention, a pulp modifier is added to react with the phenolic hydroxyl groups of lignin in the bamboo pulp fiber, breaking down the lignin and causing it to flow out of the fiber cell wall. This outflowing lignin, along with the remaining leachate, undergoes a flocculation reaction with sodium hydroxide in the modifier, forming flocculent material around the fiber. This flocculent material blocks the pores of the easily absorbent fiber, reducing the permeability of the aqueous solution and decreasing the swelling of this part of the fiber. This improves the swelling uniformity between fibers with different structures, achieving uniform swelling between fibers, and exposing more hydroxyl groups on the fiber surface in a polar aqueous environment, resulting in a more uniform thickness of the water film layer adsorbed on the fiber surface.

[0021] Meanwhile, during fiber grading and screening, along with most short fibers, a large number of fine components are also separated, such as bamboo fiber miscellaneous cells, fine fiber fragments, vascular fragments, bamboo joint particles, etc. During the bamboo pulp roll making process, these fine components will fill the pores between fibers, and the hydroxyl groups on their surface will combine with the hydroxyl groups on the fiber surface. This binding force will bring the distance between fibers closer on a microscopic level, making the fibers more tightly bonded. In addition, while modifying the fibers, the hydration reactivity of the fine components in the bamboo pulp can also be improved to a certain extent. All these characteristics have a positive effect on improving the density of bamboo pulp rolls.

[0022] The direct pressing process for pulp molding requires that the bamboo pulp rolls used have a certain degree of density. This means that during the papermaking process, the fibers of the bamboo pulp rolls must be tightly bonded, and the porosity between the fibers should be as small as possible. This is conducive to forming a relatively uniform fiber network structure during the subsequent loose molding process of pulp molding. This ensures that the pulp molded product has a uniform thickness and good structural stability after secondary hot pressing, and is not easily deformed during use. Modified bamboo pulp meets this requirement, resulting in bamboo pulp rolls with higher density, which guarantees the improvement of the structural stability and mechanical properties of pulp molded products.

[0023] In addition, during the papermaking process of bamboo pulp rolls, dispersants are added to make the fibers of the bamboo pulp rolls more evenly dispersed during the papermaking process, and finely ground mineral talc is added to fill the gaps between the fibers, making the three-dimensional structure of the produced fiber rolls more uniform, further improving the density of the three-dimensional structure of the roll fibers, increasing the bonding force between the fibers, and helping to improve the physical strength indicators of pulp molded products.

[0024] In this invention, after adding the pulp modifier, the modified bamboo pulp is kept at a temperature of 45℃~60℃ for 60~240 minutes. The treatment at a certain temperature can increase the rate of the modification reaction, and the heat treatment for a certain time can make the modification process more complete.

[0025] The method for preparing bamboo pulp rolls for pulp molding direct pressing process using the modified bamboo pulp of the present invention is as follows: the modified bamboo pulp with prepared auxiliary materials is diluted to a concentration of 0.5-1.2%, and a wet paper web with a moisture content of 75-85% is obtained by three-layer wire forming and compounding. The paper web is then subjected to vacuum mechanical dewatering, surface smoothing, high-temperature steam cylinder heat treatment, and soft calendering surface finishing to obtain bamboo pulp rolls.

[0026] In summary, this invention focuses on the selection of fiber raw materials in bamboo pulp, fully utilizing the dense characteristics of short bamboo fibers and the advantage that fine components can reduce the pore distance between bamboo fibers, thus improving the compactness of the bamboo pulp. Furthermore, fiber modification is achieved through pulp modifiers, adjusting the different swelling patterns caused by differences in bonding forces between fibers in the bamboo fiber raw material, resulting in uniform swelling and a more uniform capillary effect. This leads to a more uniform three-dimensional structure of the fibers in the produced bamboo pulp rolls, further increasing the density of the three-dimensional structure and ensuring uniform thickness within a certain range. Consequently, during the loosening process of preparing bamboo pulp rolls using the pulp molding direct pressing process, the fibers in the bamboo pulp rolls form a relatively uniform three-dimensional network structure. This results in uniform stress and similar compression and tightening between fibers during hot pressing, leading to consistent wall thickness in the resulting bamboo pulp rolls and ensuring high dimensional stability. Detailed Implementation

[0027] 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.

[0028] The embodiments of the present invention are implemented with the following specific technical solutions, including:

[0029] (1) Preparation of bamboo fiber raw materials: bamboo pulp is made by mixing one or more bamboo species such as Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, Phyllostachys edulis, and Phyllostachys edulis. Bamboo cylinders with a moisture content of 45% to 65% are first cut into bamboo blocks with a length of 40 to 100 mm, a width of 20 to 60 mm, and a thickness of 5 to 25 mm by a rotary drum chipper. The bamboo blocks are piled up under natural environmental conditions for biological fermentation. The pile height is 8 to 15 meters and the biological fermentation cycle is 25 to 65 days. The resulting bamboo blocks have a cold water extract content of 0.5% to 4.5%, an ash content of 1.0% to 2.5%, a moisture content of 10% to 20%, and a cellulose content of 40% to 50%.

[0030] (2) Pretreatment of bamboo fiber raw materials: The bamboo blocks after biological fermentation are sent into a hot water tank by a belt conveyor and washed in two countercurrent stages with hot water at 35-65℃, so that the moisture content of the bamboo blocks reaches 40%-55% after water absorption. After washing, the bamboo blocks are sent into an insulated silo by a belt conveyor for storage for 4-8 hours to allow the bamboo blocks to further swell. After the insulation is completed, the bamboo blocks are sent into a YDH125 alligator tooth spiral extrusion and rubbing mill by a belt conveyor for processing. The tooth pitch is 2-10mm, the pressure is 500-2000N, and the processing time is 5-20 seconds. After processing, fluffy bamboo blocks with a specific surface area increased by 50%-200% are obtained.

[0031] (3) Preparation of bamboo fiber pulp: Loose bamboo blocks are transferred into a pressure vessel and a pulping solution with a concentration of 6% to 10% based on Na2O is added. The material-liquid ratio is 1:4 to 6. The mixture is heated in two stages at 120 to 140°C and 145 to 155°C, with a maximum pressure of 0.50 to 0.60 MPa. After reacting for 2.0 to 3.5 hours, coarse pulp is obtained and pumped into a coarse pulp tank. Then, the coarse pulp is pumped to a pressure screen. The coarse pulp is screened in two stages and the pulping solution is recovered by filtration. Diluent water is added to dilute the pulp concentration by 1% to 4%. The diluted pulp is then pumped into a fiber grading screen.

[0032] The flow rate of the pulp entering the fiber grading screen is controlled at 600-1800 L / min, and the pressure difference is maintained at 5-20 kPa. The grading ratio of the fibers is long fiber: short fiber = 45-75: 55-25. The bamboo pulp with a long fiber: short fiber ratio of 55-25: 45-75 is pumped into the reaction tower. The short fibers are bamboo fibers with a length of 0.5-1.4 mm, and the long fibers are bamboo fibers with a length of more than 1.4 mm.

[0033] Subsequently, a reaction solution with a concentration of 0.0025% to 0.0045% was added to the reaction tower, industrial oxygen was introduced, the pressure was 0.20 to 0.40 MPa, the temperature was 55 to 90°C, and the reaction was carried out for 60 to 240 minutes before being pumped into the ECF bleaching process.

[0034] (4) ECF bleaching process: In the D0 stage, the oxidant is a chlorine compound, with a dosage of 1.0-2.5%, a temperature of 55-65℃, and a time of 45-90 min; in the EOP stage, the pH adjuster is a sodium-containing alkaline compound, with a dosage of 1.5-2.5%, an oxygen pressure of 0.20-0.35 MPa, a hydroxyl compound dosage of 0.25-0.50%, a temperature of 60-90℃, and a time of 90-150 min; in the D1 stage, the oxidant is a chlorine compound, with a dosage of 1.0-1.5%, a temperature of 60-75℃, and a time of 100-180 min.

[0035] (5) Modification treatment of bamboo pulp: The bleached bamboo pulp is diluted to a mass concentration of 1.5% to 4.5%, and a pulp modifier with a mass fraction of 0.1% to 0.5% of the bamboo pulp is added. The pulp modifier is a mixture of vinyl alkyl polymer, imidazoline quaternary ammonium salt, ester quaternary ammonium salt and sodium hydroxide in a mass ratio of 2 to 6: 1 to 4: 3 to 7: 2 to 5. The mixture is pumped into a storage tower and kept at a temperature of 45℃ to 60℃ for 60 to 240 minutes. Then it is pumped to the papermaking workshop for bamboo pulp roll papermaking.

[0036] The vinyl alkyl polymer is obtained by copolymerization of vinyl alkyl ether and maleic anhydride in the presence of azobisisobutyronitrile;

[0037] The modified bamboo pulp has a whiteness of 78–86% ISO, a tensile index of 35–50 N·m / g, and a tear index of 8–14 mN·m. 2 / g, density is 0.65~0.70g / cm 3 The stiffness is 25–55 mN·m, and the bursting index is 3.0–3.6 kPa·m. 2 / g, fiber crimp degree is 4% to 12%;

[0038] (6) Fabrication of bamboo pulp rolls:

[0039] Preparation of pulp for bamboo pulp roll making: 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 4-6%, the inlet pressure is 380-550 kPa, the outlet pressure is 90-160 kPa, and the power is 550-800 kW. After two-stage processing, a pulp with a freeness of 215-345 CSF is obtained.

[0040] Preparation and addition of auxiliary materials for papermaking: Pump the slurry to the mixing tank, and add the following auxiliary reagents by weight through the DCS control system: 0.02-0.06 parts of dispersant and 0.005-0.012 parts of finely ground mineral talc; wherein the dispersant is a fatty amide quaternary ammonium salt;

[0041] Bamboo pulp roll sheet making: The pulp 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 cylinder heat treatment, and soft calendering surface finishing to obtain bleached bamboo pulp roll sheet.

[0042] The specific preparation conditions of the embodiments and comparative examples of the present invention are shown in Table 1. Table 2 shows the quality index test results of the modified bamboo pulp and the bamboo pulp rolls prepared by the conditions of the embodiments and comparative examples corresponding to Table 1. Table 3 shows the thickness difference test results of the bamboo pulp rolls of the embodiments and comparative examples corresponding to Table 2.

[0043] Table 1: Specific preparation conditions for the examples and comparative examples.

[0044]

[0045] Table 2: Test results of quality indicators of modified bamboo pulp and bamboo pulp rolled sheets.

[0046]

[0047] Table 3: Detection results of thickness difference of bamboo pulp rolls.

[0048]

[0049] During the papermaking process of bamboo pulp sheets, on the one hand, the modification of bamboo pulp increases the bonding force between fibers, reducing the distance between them. Macroscopically, this results in bamboo pulp sheets made from modified bamboo pulp being thinner than those made from unmodified pulp. On the other hand, the fiber swelling of modified bamboo pulp is uniform, and the surface water film layer is more uniform in thickness. During the bonding process through hydrogen bonds provided by free hydroxyl groups, the distance between fibers is more uniform, resulting in more even stress distribution during the bonding process. Macroscopically, this results in bamboo pulp sheets made from modified bamboo pulp having more uniform thickness at different locations. Therefore, using these bamboo pulp sheets to process pulp molding products using the direct pressing method results in a smaller thickness difference in bamboo pulp sheets compared to those made from unmodified bamboo pulp, due to the high density and uniform thickness of the sheets. Because of the uniform thickness, deformation does not occur during the pressing process, resulting in a smoother product surface after pressing. Furthermore, the produced paper bowls have better compressive strength, and the lunch boxes have a lower deformation rate under load.

[0050] The test results in Tables 2 and 3 also prove the above: the performance of the modified bamboo pulp and its rolled sheets in Examples 1-6 are all within the range of process indicators, and the density of the bamboo pulp and its rolled sheets is 0.65-0.68 g / cm³. 3The thickness of the bamboo pulp rolls was 730–795 μm, with a standard deviation of 1.46–2.72%, while the density of the unmodified bamboo pulp and the bamboo pulp rolls prepared in Comparative Example 3 was 0.63 g / cm³. 3 The thickness of the bamboo pulp roll was 813 μm, with a thickness standard deviation of 6.91%, proving that the modified bamboo pulp had better density. The bamboo pulp roll prepared with it had greater density, less thickness, and more uniform thickness. At the same time, the paper bowls made from the bamboo pulp rolls of Examples 1 to 6 had better compressive strength, ranging from 415 to 480 N, while Comparative Example 3 only had 386 N. The load deformation rate of the lunch boxes was also smaller, ranging from 3.5 to 4.7%, while the comparative example had 5.3%. This further illustrates that the bamboo pulp rolls produced by the modified bamboo pulp had more uniform thickness and better performance.

[0051] Furthermore, the modified bamboo pulp of Example 3 with a short fiber:long fiber mass ratio of 60:40 and the bamboo pulp rolls made from it exhibited the best density, at 0.68 g / cm³. 3 The thickness standard deviation was the smallest at 1.46%, and other properties were also good. In Example 6, the modified bamboo pulp with a short fiber:long fiber mass ratio of 45:55 and the bamboo pulp rolls made from it had the worst density, only 0.65 g / cm³. 3 The thickness standard deviation was relatively large, at 2.47%, and other properties were also relatively poor. In Comparative Example 1, the density of the modified bamboo pulp with a short fiber:long fiber mass ratio of 25:75 and the density of the bamboo pulp rolls made from it were 0.62 g / cm³. 3 The thickness of the modified bamboo pulp (7.78%) did not meet the standard value, and the resulting bamboo pulp rolls had poor performance and failed to meet the standard requirements. In Comparative Example 2, the modified bamboo pulp with a short fiber:long fiber mass ratio of 80:20 and the resulting bamboo pulp rolls had a density of only 0.64 g / cm³. 3 The thickness standard deviation was relatively large at 7.09%, and other properties also failed to meet the standard requirements. The bamboo pulp rolls made from the four bamboo pulps modified with no fiber ratio in the comparative example also failed to meet the standard requirements, and the thickness standard deviation was relatively large at 6.46%. Therefore, in summary, it is necessary not only to modify the bamboo pulp with pulp modifiers, but also to have a suitable ratio of short and long fibers in order to fully meet the overall performance requirements of bamboo pulp rolls, making them denser and more uniform in thickness, thereby improving their compressive strength and deformation resistance.

[0052] 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 modified bamboo pulp, comprising the following steps in sequence: cutting bamboo raw materials into bamboo blocks, biological fermentation of bamboo blocks, hot water washing, storage in a silo at 30-55°C, extrusion treatment, preparation of coarse pulp, fiber grading and screening of coarse pulp, oxygen deligninization, ECF bleaching, preparation of pulp for papermaking, and formulation of auxiliary materials for pulp for papermaking, characterized in that, Bamboo pulp was modified after ECF bleaching: First, the bleached bamboo pulp is diluted to a mass concentration of 1.5%–4.5%. Then, 0.1%–0.5% of a pulp modifier is added, wherein the pulp modifier is a mixture of vinyl alkyl polymer, imidazoline quaternary ammonium salt, ester quaternary ammonium salt, and sodium hydroxide in a mass ratio of 2–6:1–4:3–7:2–5. The mixture is then pumped into a pulp storage tower and kept at 45℃–60℃ for 60–240 minutes to obtain modified pulp. The modified pulp is then used to prepare pulp for papermaking and to mix auxiliary materials for papermaking pulp to obtain modified bamboo pulp. The vinyl alkyl polymer is obtained by copolymerization of vinyl alkyl ether and maleic anhydride in the presence of azobisisobutyronitrile; The process of preparing coarse pulp involves transferring the extruded bamboo blocks into a pressure vessel, adding a pulping solution with a concentration of 6%–10% (based on Na2O), and maintaining a material-to-liquid ratio of 1:4–6. The mixture is heated in two stages at 120–140°C and 145–155°C, with a maximum pressure of 0.50–0.60 MPa. After reacting for 2.0–3.5 hours, coarse pulp is obtained and pumped into a coarse pulp tank. The coarse pulp is then pumped to a pressure screen, where it undergoes two stages of screening and filtration to recover the pulping solution. Diluent water is then added to dilute the pulp concentration to 1%–4%. The coarse pulp fiber grading and screening process involves feeding the coarse pulp into a fiber grading screen. The flow rate of the pulp entering the fiber grading screen is controlled at 600–1800 L / min, and the pressure difference is maintained at 5–20 kPa. The grading ratio of the fibers is long fibers: short fibers = 45–75: 55–25. The bamboo pulp with a long fiber: short fiber ratio of 55–25: 45–75 is then pumped into a reaction tower. The short fibers are bamboo fibers with a length of 0.5–1.4 mm, and the long fibers are bamboo fibers with a length of 1.4 mm or more.

2. The method for preparing modified bamboo pulp according to claim 1, characterized in that, In the step of preparing auxiliary materials for papermaking slurry, the auxiliary materials include the following auxiliary reagents in parts by weight: 0.02 to 0.06 parts of dispersant and 0.005 to 0.012 parts of finely ground mineral talc.

3. The method for preparing modified bamboo pulp according to claim 2, characterized in that, The dispersant is a fatty amide quaternary ammonium salt.

4. A modified bamboo pulp, characterized in that, The modified bamboo pulp is prepared by the method for preparing modified bamboo pulp as described in claim 1.

5. A bamboo pulp roll for pulp molding direct pressing process, characterized in that, The bamboo pulp rolls used in the pulp molding direct pressing process are prepared from a modified bamboo pulp as described in claim 4.

6. The bamboo pulp roll sheet for pulp molding direct pressing process according to claim 5, characterized in that, The basis weight of the bamboo pulp rolls used in the pulp molding direct pressing process is 475-525 g / m2, the thickness is 700-800 μm, the density is 0.65-0.70 g / cm3, and the standard deviation of the thickness is less than 2.8%.

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