Methods for pulping, pulp and paper products

Abstract

This application discloses a method for pulping, pulp, and paper products. The method includes: mixing softened fibers derived from giant reed, water, and a biological enzyme to enzymatically hydrolyze the softened fibers to obtain a bio-enzyme pulp; mixing the bio-enzyme pulp with alkali and cooking it to decompose the fiber bundles in the softened fibers to obtain a cellulose mixed solution, wherein the amount of alkali used is 6%-8% of the dry weight of the softened fibers, and the cooking temperature meets the following requirements: first heating to 130-140℃ and holding for 40-80 minutes, then heating to 150℃-160℃ and holding for 2.6-3.2 hours; the degree of sulfurization during cooking is 10%-15%; and washing and filtering the cellulose mixed solution to obtain pulp. The method of this application can improve pulp yield and pulp quality, meeting the needs of pulping.

Description

Technical Field

[0001] This application belongs to the field of biopulping technology, specifically relating to a method for pulping, pulp, and paper products. Background Technology

[0002] The raw materials for pulp and paper making cannot be separated from plant fibers, which mainly include crop straw such as wheat straw and bamboo.

[0003] On the one hand, with the increase in crop yields, the yield of crop straw also increases, but the burning and discarding of straw is particularly serious. Moreover, the harvest time is seasonal, which makes it a raw material for pulping and papermaking at risk of shortage. On the other hand, forest resources such as bamboo are scarce, resulting in a shortage of pulping raw materials and a high dependence on imported fiber raw materials.

[0004] Therefore, in order to meet the current demand for fiber raw materials, it is necessary to accelerate the adjustment of the papermaking raw material structure, make efficient and rational use of existing plant fiber resources, and improve pulp yield and pulp quality. Summary of the Invention

[0005] In view of this, this application provides a method for pulping, pulp, and paper products, which can improve pulp yield and pulp quality to meet the needs of pulping.

[0006] In a first aspect, embodiments of this application provide a method for pulping, comprising:

[0007] The softening fiber derived from giant reed grass, water, and biological enzymes are mixed to enzymatically hydrolyze the softening fiber, thus producing a biological enzyme syrup.

[0008] The bio-enzyme slurry is mixed with alkali and then cooked to decompose the fiber bundles in the softened fiber, thus obtaining a cellulose mixed solution. The amount of alkali used is 6%-8% of the dry weight of the softened fiber. The cooking temperature meets the following requirements: first heat to 130-140℃ and hold for 40-80 min, then heat to 150℃-160℃ and hold for 2.6-3.2 h; the degree of vulcanization during cooking is 10%-15%.

[0009] The cellulose mixture solution is washed and filtered to obtain pulp.

[0010] According to one embodiment of this application, a method for preparing softening fibers derived from giant reed grass includes:

[0011] Giant Napier grass with a moisture content of 65%-70% is shredded and dried to obtain softened fibers derived from giant Napier grass.

[0012] According to one embodiment of this application, after giant reed grass with a moisture content of 65%-70% is shredded using a shredder, the process includes:

[0013] Remove impurities from the shredded giant reed and / or mix the shredded giant reed with water; the mixing time is 25-40 minutes, and the temperature of the water after mixing is 50-70℃.

[0014] According to one embodiment of this application, the bioenzyme includes one or two of lipase and neutral protease; the amount of lipase added is 0.8%-1.5% of the dry weight of the softened fiber of giant reed; the amount of neutral protease added is 3%-5% of the dry weight of the softened fiber of giant reed.

[0015] According to one embodiment of this application, the mass ratio of neutral protease to lipase is (3-5):1.

[0016] According to one embodiment of this application, the solid-liquid ratio of softening fiber and water is 1:(2-3), optionally 1:2.6.

[0017] According to one embodiment of this application, the pulp is prepared by washing and filtering a cellulose mixture solution, comprising:

[0018] The cellulose mixed solution was countercurrently washed to obtain slurry and washed black liquor, wherein the alkali content in the slurry was 0.25-0.5 g / L;

[0019] The pulp is filtered to remove undissolved fiber bundle components, thus producing paper pulp.

[0020] According to one embodiment of this application, the endpoint of the countercurrent washing is that the Baume degree of the washed black liquor is ≥8.0Be; the content of free alkali in the washed black liquor is ≥5.0g / L; and the fiber content of the washed black liquor is ≤0.01g / L.

[0021] Thirdly, embodiments of this application provide pulp prepared by the method of the first aspect; the moisture content of the pulp is 60%-80%; based on the dry weight of the pulp, the dry matter of the pulp includes ≤2.3% undissociated fiber bundles.

[0022] Fourthly, embodiments of this application provide a paper product prepared by drying pulp obtained by the method of the first aspect or by drying pulp obtained by the second aspect.

[0023] This application has at least the following beneficial effects:

[0024] The method provided in this application, based on the composition and structural characteristics of giant reed grass, uses softened fibers obtained from giant reed grass for biological enzymatic hydrolysis and chemical treatment, which greatly reduces the alkali content used in the chemical treatment in this application, saving alkali content and making it more environmentally friendly; the cooking temperature and time of this application are more suitable for giant reed grass, which is conducive to retaining more α-cellulose, thus greatly improving the yield of the dry matter of the pulp, which is convenient for industrial production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0026] Figure 1 A micrograph of the softened fibers of giant reed after bio-enzyme treatment according to Example 1 of this application is shown.

[0027] Figure 2 A micrograph of the softened fibers of giant reed after bio-enzyme treatment according to Example 2 of this application is shown.

[0028] Figure 3 A micrograph of the softened fibers of giant reed after bio-enzyme treatment according to Example 3 of this application is shown.

[0029] Figure 4 A micrograph of the softened fibers of giant reed after bio-enzyme treatment in Comparative Example 1 of this application is shown.

[0030] Figure 5 The diagram shows the appearance of a paper product obtained according to an embodiment of this application. Detailed Implementation

[0031] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0032] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0033] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0034] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0035] With the growing trend towards environmental protection, the pulp molding industry is developing rapidly. More and more plant fibers are being used in pulp molding, and giant reed grass, which can be supplied year-round and has a large production volume, is a promising plant fiber.

[0036] Giant Napier grass fiber is primarily composed of cellulose, a natural high-molecular-weight polysaccharide with high tensile strength. It is a major component of plant cell walls, giving giant Napier grass fiber its toughness and strength. Cellulose filaments within the cell walls are arranged in a specific pattern, forming the fiber's structural support. Giant Napier grass is rich in α-cellulose, an excellent material for pulping. The cell walls of giant Napier grass typically have a multi-layered structure; these layers overlap to form a robust wall layer, contributing to the fiber's toughness and strength.

[0037] Giant Napier grass cell walls typically have a multi-layered structure, with these layers stacked on top of each other to form a robust wall. These layers include the primary cell wall, meso cell wall, and secondary cell wall. The primary cell wall mainly contains cellulose, hemicellulose, and a small amount of lignin. The meso cell wall is mainly composed of a polysaccharide called pectin, which has a sticky texture. The secondary cell wall is mainly composed of cellulose and a large amount of lignin. Giant Napier grass has a relatively high lignin content, typically between 20% and 30%, but the specific value can vary depending on different growing conditions. Straws such as wheat, barley, and rice usually have a lower lignin content, generally between 15% and 25%. Furthermore, giant Napier grass has a protein content of approximately 5% to 15%, while its fat content is usually below 1%, which is higher than that of straw.

[0038] In related technologies, pulping using purely chemical methods requires the consumption of a large amount of chemical reagents, which causes significant environmental pollution and may also destroy some of the cellulose in giant reed grass, reducing the pulp yield.

[0039] In view of this, this application proposes a method for pulping to improve the above-mentioned problems.

[0040] Methods for pulping

[0041] In a first aspect, embodiments of this application provide a method for pulping, comprising:

[0042] S10. Mix softened fiber derived from giant reed grass, water, and biological enzymes to enzymatically hydrolyze the softened fiber and obtain biological enzyme slurry;

[0043] S20. The bio-enzyme slurry is mixed with alkali and cooked to decompose the fiber bundles in the softened fiber, thereby obtaining a cellulose mixed solution. The amount of alkali used is 6%-8% of the dry weight of the softened fiber. The cooking temperature meets the following requirements: first heat to 130-140℃ and hold for 40-80 min, then heat to 150℃-160℃ and hold for 2.6-3.2 h; the degree of sulfurization during cooking is 10%-15%.

[0044] S30. The cellulose mixture solution is washed and filtered to obtain pulp.

[0045] According to embodiments of this application, softened fibers derived from giant reed grass can be understood as plant fibers obtained by mechanically processing giant reed grass. Generally, these plant fibers are relatively soft and can be processed using a spun yarn machine. The main component of the softened fibers derived from giant reed grass is derived from giant reed grass, and may also contain small amounts of other fibers.

[0046] According to embodiments of this application, cooking is generally carried out using sodium hydroxide and sodium sulfide. In some embodiments, the degree of sulfidation during cooking can be any value or range of 10%, 11%, 12%, 13%, 14%, 15%, or a combination thereof. The degree of sulfidation refers to the percentage of sodium sulfide in the cooking liquor relative to the total amount of sodium hydroxide and sodium sulfide. For example, if 10 parts by mass of sodium sulfide are heated and 90 parts by mass of sodium hydroxide are added, the degree of sulfidation is 10%. Sodium hydroxide and sodium sulfide are commonly used wood cooking agents that facilitate the separation of lignocellulose from wood. Adding sodium sulfide to the cooking liquor can accelerate the delignification reaction and reduce damage to cellulose. At a fixed total alkali content, appropriately increasing the degree of sulfidation can shorten the cooking time, increase the pulp yield, and improve its mechanical strength. However, exceeding a certain limit (approximately 30%–35%) has little effect and may even increase the amount of undigested raw material, reducing the yield of qualified pulp. Adjusting the degree of sulfidation can affect the reaction conditions during the cooking process. In conventional sulfate cooking, the degree of sulfidation can be used to characterize the extent of chemical dissolution during cooking, for example, in the decomposition and removal of lignin.

[0047] In some embodiments, the bio-enzyme slurry is mixed with sodium hydroxide and sodium sulfide and then cooked.

[0048] Based on the composition and structural characteristics of giant reed grass, the softened fiber obtained from giant reed grass is subjected to biological enzymatic hydrolysis and chemical treatment. The amount of alkali used is 6%-8% of the dry weight of the softened fiber, which greatly reduces the alkali content used in the chemical treatment in this application, saving alkali content and making it more environmentally friendly. During cooking, the temperature is first raised to 130-140℃ and held for 40-80 minutes, and then raised to 150℃-160℃ and held for 2.6-3.2 hours. This makes the cooking temperature and time more suitable for giant reed grass, which is conducive to retaining more α-cellulose. As a result, the yield and quality of the dry pulp are greatly improved, which is convenient for industrial production.

[0049] In this embodiment, the dry solids of the pulp refer to the mass of the solid portion after water has been removed from the pulp. This parameter is an important indicator for measuring the solid content in pulp and is commonly used to control and adjust the concentration and mass of the pulp. The mass of the solid portion refers to the mass of the pulp after water removal to constant weight; the mass of the solid portion can be understood as the dry solids when the pulp reaches constant weight after water removal. The sample is dried at a specific temperature (generally around 105 degrees Celsius) until the difference in sample mass between two consecutive weighings does not exceed 0.1% of the sample mass before drying, which is considered to have reached constant weight. The yield of the dry solids is calculated by dividing the mass of the solid portion by the total mass of the pulp.

[0050] Alkali can decompose lignin during pulping, softening and dispersing the fibers. This application does not impose obvious limitations on the type of alkali; any type of alkali that can achieve the purpose of this application may be used. In some optional embodiments, the alkali includes one or more of sodium hydroxide, calcium hydroxide, magnesium hydroxide, ammonia, and sodium carbonate. The amount of alkali used in this application is 6%-8% of the dry weight of the softened fibers; sodium hydroxide may be used.

[0051] In this embodiment, the dry weight of the softened fiber refers to the mass of the solid portion after removing moisture from the softened fiber. Solid mass refers to the mass of the softened fiber after removing moisture, which is considered constant weight. The sample is dried at a specific temperature (generally around 105 degrees Celsius) until the difference in sample mass between two consecutive weighings does not exceed 0.1% of the sample mass before drying, thus reaching constant weight.

[0052] In some alternative embodiments, prior to S10, the method for preparing the softening fibers derived from giant reed grass includes:

[0053] Giant Napier grass with a moisture content of 65%-70% is shredded and dried to obtain softened fibers derived from giant Napier grass.

[0054] According to the embodiments of this application, giant Napier grass with a moisture content of 65%-70% is selected for sizing. The presence of moisture in the giant Napier grass facilitates the sizing process, and the sizing machine helps separate plant fibers from other parts, such as cell walls and intercellular substances. Sizing with a sizing machine helps improve the cellulose extraction rate, reduces the time and cost of subsequent softening fiber processing, helps to evenly disperse and break down the giant Napier grass fibers, which is important for pulp preparation. It can also improve pulp quality and reduce the use of chemicals in the pulping process.

[0055] In some alternative embodiments, after giant reed grass with a moisture content of 65%-70% is shredded using a shredder, the following steps are performed:

[0056] Remove impurities from the shredded giant seaweed.

[0057] According to the embodiments of this application, impurity removal can remove impurities and dust attached to giant reeds.

[0058] In some alternative embodiments, after giant reed grass with a moisture content of 65%-70% is shredded using a shredder, the following steps are performed:

[0059] Mix the shredded giant seaweed with water.

[0060] According to the embodiments of this application, mixing the shredded giant reed with water can further soften the fibers of the giant reed, which facilitates the subsequent processing time and reduces costs of the softened fibers, and helps to disperse the giant reed fibers evenly.

[0061] In some alternative embodiments, after giant reed grass with a moisture content of 65%-70% is shredded using a shredder, the following steps are performed:

[0062] First, remove impurities from the shredded giant seaweed, then mix the shredded giant seaweed with water.

[0063] In some alternative implementations, the mixing time is 25-40 minutes, and the temperature of the water after mixing is 50-70°C.

[0064] According to the embodiments of this application, by controlling the mixing time and temperature of the shredded giant seaweed with water, softened fibers with a certain degree of softening and fiber bundle dispersion can be obtained, which is convenient for subsequent pulping.

[0065] In some alternative embodiments, the length of the softened fibers is 0.5-4 cm. Giant Napier grass with a diameter less than 5 mm is cut into segments 3-4 cm long; those with a diameter greater than 5 mm are cut into segments 0.5-2 cm long.

[0066] In some alternative embodiments, in S10, the biological enzyme includes one or both of lipase and neutral protease. As an example, the neutral protease can be a commercially available product, such as CAS number 9068-59-1. The lipase can be a commercially available product, such as CAS number 9001-62-1.

[0067] In some optional embodiments, the amount of lipase added is 0.8%-1.5% of the dry weight of the softened fibers of giant reed. According to the embodiments of this application, the above-mentioned amount of lipase can effectively decompose the fat in the softened fibers of giant reed, facilitating subsequent pulping and dispersion of cellulose and other components therein.

[0068] In some optional embodiments, the amount of neutral protease added is 3%-5% of the dry weight of the softened fibers of giant reed grass. According to the embodiments of this application, the above-mentioned amount of central protease can effectively break down the fats in the softened fibers of giant reed grass, facilitating subsequent pulping and dispersion of cellulose and other components therein.

[0069] In some optional embodiments, in S10, the mass ratio of neutral protease to lipase is (3-5):1. According to embodiments of this application, controlling the mass ratio of neutral protease to lipase within the above range is beneficial for improving the yield of dry pulp and pulp quality.

[0070] In some optional embodiments, in S10, the solid-liquid ratio of the softening fiber and water is 1:(2-3), optionally 1:2.6.

[0071] According to embodiments of this application, different types of paper and pulp preparation processes may require different solid-liquid ratios. Therefore, in actual production, the solid-liquid ratio needs to be optimized according to specific product specifications and process requirements. An appropriate solid-liquid ratio can improve productivity and also affect the quality characteristics of paper to a certain extent. A higher solid-liquid ratio can usually reduce pulp dilution, accelerate moisture removal, and thus speed up the drying process of the paper.

[0072] In some alternative embodiments, in S30, the cellulose mixture solution is washed and filtered to obtain pulp, comprising:

[0073] The cellulose mixed solution was countercurrently washed to obtain slurry and washed black liquor, wherein the alkali content in the slurry was 0.25-0.5 g / L;

[0074] The pulp is filtered to remove undissolved fiber bundle components, thus producing paper pulp.

[0075] According to embodiments of this application, regulating the alkali content in pulp helps maintain a stable pH value, which in turn helps maintain fiber stability, reduces pulp and paper inhomogeneity, and improves product quality. Furthermore, an appropriate concentration of alkali in the pulp can prevent the growth of microorganisms and fungi, reduce pulp and paper spoilage, and also help control color stability, thus improving paper whiteness and quality.

[0076] In some optional embodiments, the endpoint of the countercurrent washing is that the Baume degree of the washed black liquor is ≥8.0Be; the content of free alkali in the washed black liquor is ≥5.0g / L; and the fiber content of the washed black liquor is ≤0.01g / L.

[0077] According to the embodiments of this application, by controlling the endpoint of countercurrent washing, pulp of better quality can be produced while taking into account production efficiency.

[0078] pulp

[0079] Thirdly, embodiments of this application provide pulp prepared by the method described in the first aspect.

[0080] In some alternative implementations, the pulp moisture content is 60%-80%.

[0081] In some alternative embodiments, the dry matter of the pulp includes ≤2.3% undissociated fiber bundles based on the dry weight of the pulp. Optionally, the dry matter of the pulp includes undissociated fiber bundles at contents of ≤2.0%, 1.5%, 1.0%, etc.

[0082] According to embodiments of this application, undissociated fiber bundles increase the difficulty of stirring and mixing, slowing down pulp preparation. Furthermore, undissociated fiber bundles can lead to the presence of lumpy substances in the pulp, potentially reducing pulp quality and resulting in uneven paper texture and uniformity issues. Controlling the fiber bundle content in the pulp can produce more uniform paper quality and reduce product defects.

[0083] Fourthly, embodiments of this application provide a paper product prepared by drying pulp obtained by the method of the first aspect or by drying pulp obtained by the second aspect.

[0084] According to embodiments of this application, the paper products can be packaging paper, such as cardboard boxes, paper plates, and paper straws. Because these paper products are made from giant reed grass, they possess certain abrasion resistance and tensile strength, resulting in superior product quality.

[0085] Example

[0086] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0087] Examples 1-4

[0088] This application provides a method for pulping, including:

[0089] S10. Mix softened fiber derived from giant reed grass, water, and biological enzymes to enzymatically hydrolyze the softened fiber and obtain biological enzyme slurry;

[0090] S20. The bio-enzyme slurry is mixed with alkali and cooked to decompose the fiber bundles in the softened fiber, thereby obtaining a cellulose mixed solution. The amount of alkali used is 6%-8% of the dry weight of the softened fiber. The cooking temperature meets the following requirements: first heat to 130-140℃ and hold for 40-80 min, then heat to 150℃-160℃ and hold for 2.6-3.2 h; the degree of sulfurization during cooking is 10%-15%.

[0091] S30. The cellulose mixture solution is washed and filtered to obtain pulp.

[0092] This application provides a paper product made by drying pulp obtained by a first aspect method.

[0093] The specific parameters of Examples 1-4 are shown in Table 1.

[0094] Comparative Example 1

[0095] The difference between this comparative example and the embodiment is that no biological enzymes are added. The specific parameters of comparative example 1 are shown in Table 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and the embodiment is that no biological enzymes are added, and the amount of alkali used is 10% of the dry weight of the softened fiber. The specific parameters of comparative example 2 are shown in Table 1.

[0098] Comparative Example 3

[0099] The difference between this comparative example and the embodiment is that the cooking temperature is different. The specific parameters of comparative example 3 are shown in Table 1.

[0100] Comparative Example 4

[0101] The difference between this comparative example and the embodiment is that the cooking temperature is different. The specific parameters of comparative example 4 are shown in Table 1.

[0102] Table 1

[0103]

[0104]

[0105] In this application, the formula for calculating the yield of dry pulp (hereinafter referred to as pulp yield) is: pulp mass (dry weight) divided by the mass (dry weight) of the softened fibers of the initially added giant reed grass.

[0106] Test section

[0107] The softened fibers treated with bio-enzymes in the examples and comparative examples were observed using electron microscopy, and the results were as follows: Figure 1-4 The result. Figures 1 to 4 The images shown are electron microscope images of the softened fibers of Giant Napier Grass from Examples 1-3 and Comparative Example 1, magnified 200x. This demonstrates that the bio-enzymes can effectively dissociate the softened fibers of Giant Napier Grass, facilitating subsequent pulping. Figure 5 Paper products made using the pulp of Example 1.

[0108] As can be seen from the results in Table 1, the pulp prepared by the method of this application in Examples 1-4 has reduced the amount of alkali used and the pulp yield is at a high level.

[0109] Compared with Example 1, Examples 2 and 3 show that Example 1 simultaneously added lipase and protease, which is beneficial to the decomposition of fiber bundles and improves the yield of dry pulp.

[0110] Comparing Comparative Example 1 and Comparative Example 2, it can be seen that without the addition of biological enzymes, the yield of pulp is higher when the amount of alkali added is higher, but slightly lower than that of the Example.

[0111] Compared with Example 1, Comparative Examples 3 and 4 show that if the cooking temperature is too high or too low, it will affect the decomposition of the fiber bundles. If the temperature is too high, it may reduce the pulp yield. If the temperature is too low, some cellulose may not be decomposed and will be filtered out, thus reducing the pulp yield.

[0112] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for pulping, characterized in that, include: Softened fibers derived from giant Napier grass, water, and bio-enzymes are mixed to enzymatically hydrolyze the softened fibers, yielding a bio-enzyme slurry. The bio-enzymes include lipase and neutral protease. The amount of lipase added is 0.8%-1.5% of the dry weight of the softened fibers from giant Napier grass; the amount of neutral protease added is 3%-5% of the dry weight of the softened fibers from giant Napier grass; the mass ratio of the neutral protease to the lipase is (3-5):1; and the solid-liquid ratio of the softened fibers to water is 1:(2-3). The bio-enzyme slurry is mixed with alkali and then cooked to decompose the fiber bundles in the softened fiber, thus obtaining a cellulose mixed solution. The amount of alkali used is 6%-8% of the mass of the bio-enzyme slurry. The cooking temperature meets the following requirements: first, heat to 130-140℃ and hold for 40-80 minutes, then heat to 150℃-160℃ and hold for 2.6-3.2 hours; the degree of sulfurization during cooking is 10%-15%. The cellulose mixture solution is subjected to countercurrent washing to obtain pulp and washed black liquor, wherein the alkali content in the pulp is 0.25~0.5 g / L; the pulp is filtered to remove undissolved fiber bundle components to obtain paper pulp; the endpoint of the countercurrent washing is that the Baume degree of the washed black liquor is ≥8.0 Be; the free alkali content in the washed black liquor is ≥5.0 g / L; and the fiber content in the washed black liquor is ≤0.01 g / L.

2. The method according to claim 1, characterized in that, The method for preparing the softening fiber derived from giant reed includes: Giant Napier grass with a moisture content of 65%-70% is shredded and dried to obtain softened fibers derived from giant Napier grass.

3. The method according to claim 2, characterized in that, After shredding giant reeds with a moisture content of 65%-70%, the following steps are taken: Remove impurities from the shredded giant reed and / or mix the shredded giant reed with water; the mixing time is 25-40 minutes, and the temperature of the water after mixing is 50-70℃.

4. The method according to claim 1, characterized in that, The solid-liquid ratio of the softening fiber to water is 1:2.

6.

5. A type of pulp, characterized in that, The pulp is prepared by the method described in any one of claims 1-4; the moisture content of the pulp is 60%-80%; based on the dry weight of the pulp, the dry matter of the pulp contains ≤2.3% undissociated fiber bundles.

6. A paper product, characterized in that, Pulp is prepared by drying the method described in any one of claims 1-4 or by drying the pulp described in claim 5.

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