Method for preparing natural-color semi-chemical pulp from bamboo reed

Abstract

The invention provides a method for preparing natural-color semi-chemical pulp from bamboo reed, and belongs to the field of papermaking. The method makes full use of the advantages of rich fiber content and high yield of the bamboo reed, and fills the vacancy of domestic plant fiber raw materials. The technological method of the bamboo reed natural-color semi-chemical pulp gives full play to the characteristics of high bamboo reed fiber content, low raw material silicon content, low lignin content, easiness in pulping and good water filtration, develops and optimizes cooking, pulping and screening technologies, and is simple in equipment requirement and easy to popularize. The prepared bamboo reed natural-color semi-chemical pulp is excellent in tightness, ring crush resistance and tear strength, and is suitable for oil-proof paper and packaging paper products.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, and in particular relates to a method for preparing unbleached semi-chemical pulp from reed. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Semi-chemical pulp has a high degree of delignification, good stiffness and folding endurance, is easy to beat, and has high transparency, making it a raw material for producing paperboard products such as transparent paper, greaseproof paper, and food packaging paper. However, semi-chemical pulp is currently facing constraints in terms of raw materials. Therefore, making rational use of the high yield of straw and efficiently developing methods for utilizing straw fiber in pulping and papermaking is another urgent problem to be solved by the pulp industry.

[0004] Reed, which grows in the Yellow River Delta, is rich in fiber, with fiber length comparable to that of bamboo. It is low in silicon and is an excellent fiber raw material, second only to wood pulp. It can replace traditional straw-based fiber raw materials such as rice and wheat straw in pulping applications.

[0005] One study provides a mechanical pulping method for Reed Piper longifolia, which involves high-pressure sterilization and extrusion loosening of the raw material. This improves the impregnation effect of Reed Piper longifolia with low alkali dosage (4%-8%), resulting in a high-yield Reed Piper longifolia chemimechanical pulp. This method provides an application method for Reed Piper longifolia and a high-bulk Reed Piper longifolia pulp, but its pulp strength is low due to the mild processing conditions.

[0006] Furthermore, the outer wall of the stem of *Arundinaria lobata* has a waxy layer formed by resin and lipids, which has hydrophobic, isolating, and pest-resistant functions. During pulping and cooking, it reduces alkali penetration, emulsifies with the alkali, increases alkali consumption, and reduces cooking efficiency. In semi-chemical pulping, the cooking intensity should not be too high, and the waxy layer of *Arundinaria lobata* itself is a major obstacle to the development of its semi-chemical pulping process.

[0007] Therefore, there is an urgent need to develop and research a semi-chemical pulping process suitable for Reed spp., and to develop a mechanical pulping method for Reed spp. with higher strength. Summary of the Invention

[0008] In response to the current shortage of semi-chemical pulp raw materials, and in order to effectively develop the semi-chemical pulping potential of Reed spp., this invention provides a preparation process for producing semi-chemical pulp using Reed spp. This invention employs a composite treatment agent composed of a surface penetrant, tetrasodium pyrophosphate, and sodium hydroxide, combined with a hot impregnation process, to remove the waxy layer and soften the Reed spp. This allows for the preparation of Reed spp. semi-chemical pulp at low cooking intensity, significantly improving the physical strength of the pulp while retaining its high yield and high bulk characteristics, thus overcoming the problem of low folding strength in Reed spp. chemimechanical pulp.

[0009] This invention uses a novel type of reed raw material, which undergoes preparation, alkaline hot water soaking, steaming, washing, grinding, desulfurization, and screening to form a pulp (e.g. Figure 1 As shown in the figure, this invention develops a semi-chemical pulping process based on the morphology and chemical composition characteristics of reed fiber. The semi-chemical pulp produced has better bulk and beating adaptability compared to wood raw materials, and the silicon content in the resulting black liquor meets current mainstream alkali recovery requirements.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for preparing natural-colored chemical pulp from reed, comprising: Reed shoots are hot-soaked in a composite treatment agent solution for a predetermined time, and then extruded and dehydrated to obtain pretreated reed shoots; wherein, the composite treatment agent is composed of a surface penetrant, tetrasodium pyrophosphate and sodium hydroxide, and the surface penetrant is selected from at least one of nonionic surfactants and anionic surfactants; The pretreated reed is steamed, sprayed, washed, ground, and screened to obtain a semi-chemical reed pulp.

[0011] In a second aspect, the present invention provides a natural-colored semi-chemical pulp of *Arundo donax* prepared by the above method, wherein the kappa number is 70-100, the water retention value is 160-180, and the mass ratio of short fibers to long fibers is 50-60:50-40.

[0012] A third aspect of the present invention provides the application of the above-mentioned unbleached semi-chemical pulp of Reed hyacinth in the preparation of transparent paper, greaseproof paper or food packaging paper.

[0013] Beneficial effects of the present invention (1) This invention develops Reed Bamboo as a pulp fiber raw material. By utilizing the characteristics of Reed Bamboo such as fast growth rate, high fiber content and large output, it can quickly fill the gap in domestic pulp and paper raw materials.

[0014] (2) In this invention, the low silicon content of the raw material of Reed sphaerocephala makes the pulping black liquor produced during the cooking process able to meet the requirements of mainstream alkali recovery process equipment. The effect is obvious, the process is simple, the cost is low, and it is easy to promote.

[0015] (3) Compared with the existing mechanical pulping method of Reed, the semi-chemical pulp of Reed in this invention retains the high bulk and thickness characteristics of mechanical pulp, increases the breaking length by 2.7 times, increases the tear index by 2 times, and achieves more than 200 folding cycles, significantly improving the strength index of Reed mechanical pulp.

[0016] (4) In the pretreatment degumming stage, the present invention uses a surface penetrant and tetrasodium pyrophosphate to remove the wax layer on the surface of Reed, reducing the emulsification interference of the wax layer on sodium hydroxide, improving the permeability of Reed chips, and enhancing the cooking effect. The surface penetrant and tetrasodium pyrophosphate have a synergistic effect in improving the performance of Reed semi-chemical pulp. The pretreatment product has a high phosphorus content, which is converted into orthophosphate in an alkaline environment and can be used as a raw material for phosphate fertilizer for high-value utilization.

[0017] In summary, this invention develops Reed spp. as a pulping raw material, filling the gap in pulp and paper production that requires fiber raw materials. Reed spp. is suitable for mainstream pulping and papermaking processes and equipment, and the resulting fibers have a wide range of lengths, making them applicable to a variety of products. At the same time, the pulp has advantages such as high tear strength and high ring crush resistance, thus having good practical application value. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 Semi-chemical pulping process flow; Figure 2 Grading of the length of semi-chemical pulp fiber from Phyllostachys edulis. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0022] Terminology Explanation: Non-wood fiber raw materials: refer to plant fiber raw materials other than wood, mainly including grass plants (such as reeds, bamboo, wheat straw, rice straw, bagasse, etc.), bast fibers (such as flax, jute, hemp, mulberry bark, etc.), seed fibers (such as cotton, cotton linters, etc.) and leaf fibers (such as agave, sisal, etc.).

[0023] Material preparation: The process of pre-treating fiber raw materials (wood, grass, waste paper, etc.) to make their shape and size meet the requirements of pulping.

[0024] Cooking: A chemical pulping process in which fiber raw materials are treated with chemical solutions under high temperature and pressure to separate the fibers.

[0025] Spraying: A key step in the pulping and papermaking process, referring to the process of rapidly spraying the pulp into a spray pan or spray bin under high pressure after cooking. This operation, through a sudden pressure drop, fully dissociates the fibers in the pulp and simultaneously achieves the initial separation of black liquor from the pulp.

[0026] Pulping: The core step in pulping and papermaking, referring to the process of separating wood raw materials into pulp fibers using the mechanical action of a wood grinder or refiner, and causing them to undergo varying degrees of fibrillation. This process should minimize damage and cutting to the fibers, ensuring that the fibers have a certain specific surface area and interlacing ability, creating conditions for the formation of hydrogen bonds and other bonds between fibers during the papermaking process.

[0027] Screening: The process of separating impurities or fibers of different sizes from those of impurities and fibers by passing them through a sieve plate with holes or slits.

[0028] Bursting strength: The maximum pressure that paper or paperboard can withstand per unit area, which is perpendicular to the surface of the sample and increases uniformly.

[0029] Initial freeness: The original freeness value of pulp before any beating treatment. This indicator reflects the natural water-filtering properties of the pulp raw material.

[0030] Long fibers: The fiber portion of pulp retained on a 100-mesh sieve or pulp fibers with a length of 0.6 mm or more as determined by a fiber quality analyzer.

[0031] Short fibers: Pulp fibers with a length of less than 0.6 mm as determined by a fiber quality analyzer or by passing through a 100-mesh sieve.

[0032] Pulp yield: an important technical indicator in the pulp and paper industry, referring to the percentage of the weight of oven-dry pulp obtained after cooking to the weight of oven-dry raw materials before cooking. It is a key parameter for evaluating pulping efficiency and raw material utilization.

[0033] Screening residue rate: an important technical indicator for evaluating the performance of screening equipment in the pulp and paper industry, referring to the percentage of pulp residue discharged after screening relative to the amount of pulp fed in.

[0034] Fiber water retention value: A core parameter used in the papermaking industry to characterize the degree of fiber swelling. It quantifies the fiber's water-binding capacity by measuring the water content retained in the pulp using high-speed centrifugation. This indicator directly reflects the degree of fibrillation caused by changes in the spacing between cellulose molecular chains.

[0035] Breaking length: The theoretical length of a paper strip of unit width that breaks due to its own weight when one end is fixed and suspended. It is expressed in kilometers (km).

[0036] Folding endurance: is a mechanical property indicator of the ability of paper and paperboard to resist repeated folding. It refers to the logarithmic number of double folds that a standard width sample can withstand under a specific tension until it breaks.

[0037] Ring crush index: An important indicator for evaluating the compression resistance of paper and paperboard, and a key quality parameter for linerboard and corrugated base paper.

[0038] Tear index: An important indicator for evaluating the tear resistance of paper and paperboard.

[0039] This invention mainly proposes a method for preparing natural-colored chemical pulp from Reed sphagnum moss, comprising: Reed shoots are hot-soaked in a composite treatment agent solution for a predetermined time, and then extruded and dehydrated to obtain pretreated reed shoots; wherein, the composite treatment agent is composed of a surface penetrant, tetrasodium pyrophosphate and sodium hydroxide, and the surface penetrant is selected from at least one of nonionic surfactants and anionic surfactants; The pretreated reed is steamed, sprayed, washed, ground, and screened to obtain a semi-chemical reed pulp.

[0040] Compared to patent CN120401260A, this invention enhances the cooking effect by introducing a composite treatment agent, reduces mechanical processing energy consumption and replaces high-pressure sterilization, retains the mechanical pulp thickness advantage of reed, and significantly improves tensile strength, bursting strength and flexural strength.

[0041] The raw material used is a reed variety that has been growing for more than 2 years in the saline-alkali land of the Yellow River Delta region. The sources of this reed variety include, but are not limited to, large-scale artificial planting, wild growth, and purchase from suppliers.

[0042] The type of surface penetrant affects the effect of hot alkali impregnation and the mechanical properties of Reed pulp. Therefore, this invention studies the types of surface penetrants. Preferably, the surface penetrant is selected from nonionic surfactants (alkyl glycosides, fatty alcohol polyoxyethylene ethers) and anionic surfactants (amino acid derivatives, N-acyl glutamate sodium). More preferably, the surface penetrant is fatty alcohol polyoxyethylene ether or N-lauroyl glutamate sodium. Among them, N-lauroyl glutamate sodium and tetrasodium pyrophosphate have a synergistic effect in improving the folding endurance of Reed pulp.

[0043] This invention does not impose any special limitations on the method of crushing reeds. Preferably, the method used to crush reeds can be a crusher or a combine harvester to improve crushing efficiency.

[0044] The temperature of hot impregnation affects the treatment effect of the waxy layer of Reed sphaerocephala. Therefore, this invention has studied the temperature and time of hot impregnation. Preferably, the hot impregnation temperature is 75~100℃, the time is 20~40 min, and the dryness of Reed sphaerocephala is 33~45% to obtain a better impregnation effect and improve the mechanical properties of Reed sphaerocephala pulp.

[0045] Reed chips are washed with hot water at 75-100℃, then alkaline impregnated to emulsify and disperse the waxy layer on the surface of the reed chips. After being extruded and mixed using an extrusion tearing machine, excess water and dispersed resins, waxes, and other lipid substances are removed. The reed chips are then conveyed to a cooking pot. The dryness of the reed chips is approximately 33-45%, and the alkaline impregnation time is 20-40 minutes. The resulting washing water, called alkaline reed washing water, has a pH of 8-10. After treating the sludge with a plate and frame filter press and adding polyaluminum chloride and lime for sedimentation, it is reused. Preferably, in the composite treatment agent solution, the amount of alkali used is 2-5%, and the total amount of surface penetrant and tetrasodium pyrophosphate is 1-3%, with a surface penetrant to tetrasodium pyrophosphate ratio of 2-3:1. Under this optimized dosage, the surface penetrant can effectively reduce the surface tension of the reed waxy layer and improve the penetration effect of sodium hydroxide and tetrasodium pyrophosphate. Tetrasodium pyrophosphate can efficiently emulsify and disperse the waxy layer, dissolving it in the alkaline water. Surface penetrants and chemicals used include, but are not limited to, sodium hydroxide, caustic soda, and cooking liquor. Within this range of alkali dosage, *Arundo donax* raw materials can be effectively softened and have lignin removed.

[0046] Preferably, alkaline wastewater generated by extrusion tearing and / or plate and frame filter press is treated with polyaluminum chloride sedimentation, and quicklime catalysis is used to promote the hydrolysis and conversion of residual tetrasodium pyrophosphate and complex products into orthophosphate.

[0047] The cooking conditions affect the properties of reed pulp. Therefore, this invention has studied the cooking conditions. Preferably, the specific cooking conditions are: 12-18% alkali, 20-25% sulfidation, and / or 0.2-0.8% anthraquinone; reed slices and medicinal liquid mixed at a ratio of 1:2.5-5.0; cooking temperature of 158-165℃; and holding at this temperature for 30-90 minutes. The chemicals used include, but are not limited to, sodium hydroxide, liquid alkali, cooking liquor, sodium sulfide, and anthraquinone, to obtain better cooking results.

[0048] Preferably, the specific process of the spraying is as follows: the wood chip reaction liquid after cooking is rapidly depressurized and sprayed out through channels such as venting valves, and the cooked pulp is collected. The black liquor extraction rate after cooking is greater than 65%, and the outlet temperature is not less than 60℃. The lignin content dissolved in the black liquor is 100~130 kg / t pulp.

[0049] Preferably, the washing process employs single-stage or multi-stage countercurrent washing; more preferably, the number of multi-stage washing stages is 2 to 5. The pulp dryness at the tail end is 18-22%. In multi-stage countercurrent washing, the washing liquid flows in the opposite direction to the material being washed, forming a concentration gradient, thereby fully utilizing the washing capacity of the washing liquid and improving washing efficiency.

[0050] Compared with single-stage refining, two-stage refining can improve the refining effect. Therefore, the present invention has studied the process of two-stage refining. Preferably, the refining is two-stage refining, with the first stage being low-consistency refining and the second stage being medium-consistency refining, in order to obtain a better refining effect.

[0051] The refining gap and pulp concentration affect pulp quality, energy consumption, and paper performance. Therefore, this invention studies the refining process parameters. Preferably, the first refining gap is 0.4~0.5 mm, and the pulp inlet concentration is controlled at 2~7%; the second refining gap is 0.1~0.15 mm, the pulp inlet concentration is controlled at 14~17%, and the refining temperature is 40~50℃, in order to obtain a better refining effect.

[0052] Screening can remove impurities with low relative density and large volume from pulp, such as pulp clumps, fiber bundles, and straw. Therefore, this invention has studied the screening conditions. Preferably, the screening uses a 0.15~0.30 mm slotted sieve or a 0.25~0.50 mm perforated sieve to obtain better screening results.

[0053] Preferably, the slag ratio is 2-4%. The slag ratio refers to the mass ratio of undisintegrated pulp to raw material.

[0054] More specifically, including: (1) The raw material of Reed is Reed that has grown for two years and is harvested in the same year and then air-dried for 3 to 6 months. The Reed slices are Reed that has been crushed by a crusher into Reed slices with a length of 3 to 8 cm and a width of 2 to 4 cm.

[0055] (2) The reed strips can be screened through an 8-mesh sieve to remove small fragments.

[0056] (3) The specific process for pretreatment and degumming is as follows: Reed chips are washed with hot water at 75-100℃, then alkaline impregnated and the waxy layer on the surface of the reed chips is emulsified and dispersed. The chips are then extruded and mixed using an extrusion tearing machine to remove excess water and dispersed resins, waxes, and other lipids. The reed chips are then transported to a cooking pot. The dryness of the reed chips is approximately 33-45%, and the alkaline impregnation time is 20-40 minutes. The resulting washing water is called alkaline grass washing water, with a pH value of 8-10. After treating the sludge with a plate and frame filter press and adding polyaluminum and lime for sedimentation, it is reused.

[0057] (4) The specific process of steaming is as follows: the reed slices and the medicinal liquid are mixed at a ratio of 1:2.5~5.0 and kept at the highest steaming temperature of 158~165℃ for 30~90 min in the steaming pot.

[0058] (5) The specific process of spraying is as follows: the wood chip reaction liquid after cooking is quickly depressurized and black liquor is sprayed through channels such as the venting valve, and the pulp after cooking is collected.

[0059] (6) The specific washing process is: single-stage or multi-stage countercurrent washing, and the number of multi-stage washing stages can be 2 to 5 stages.

[0060] (7) The specific process of the pulping is: two-stage pulping, the first stage is low-consistency pulping, and the second stage is medium-consistency pulping.

[0061] (8) The specific screening process is as follows: the washed Reed pulp is screened by a pulp screening machine to obtain qualified pulp, and the screened pulp is the finished Reed semi-chemical pulp.

[0062] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0063] In the following examples, the surface penetrant is sodium N-lauroyl glutamate, CAS No.: 29923-31-7, Taian Aidi Biotechnology Co., Ltd.

[0064] Example 1: This embodiment provides a production process for preparing unbleached semi-chemical pulp from Reed Bamboo, including the following steps: (1) Collect raw materials of Reed sphagnum moss that have grown for two years and air-dry them for 6 months.

[0065] (2) The reed is crushed into reed chips with a length of 3-8 cm and a width of 2-4 cm by a crusher. The reed chips are then sieved through an 8-mesh sieve to remove small fragments.

[0066] (3) Reed chips were washed with 60°C warm water and then alkaline-impregnated in a composite treatment agent (2% N-lauroyl glutamate, 1% tetrasodium pyrophosphate, and 4% sodium hydroxide, with the remainder being water). After being squeezed and mixed by an extrusion tearing machine to remove excess water, the reed chips were transported to a cooking pot. The reed chips were transported with a dryness of 35% and the alkaline impregnation time was 30 min. The resulting washing water had a pH of 6.5. After being treated with sludge by a plate and frame filter press and with the addition of polyaluminum sulfate for sedimentation, the water was reused.

[0067] (4) The specific cooking process is as follows: 14% alkali, 25% sulfidation, 1:4 liquor ratio, maximum cooking temperature of 160℃, and holding time of 40 min. The specific formula of the cooking liquor is: 328.1 kg of liquid alkali (32% mass concentration) and 58.3 kg of sodium sulfide (60%, solid) per ton of oven-dried reed slices in a 4 m³ solution. 3 The cooking liquid prepared in water is heated to 160°C in a cooking pot and kept at that temperature for 40 minutes.

[0068] (5) The specific process of the spraying is as follows: the raw material reaction liquid after cooking is rapidly depressurized for 20 minutes and sprayed out through channels such as the venting valve. The pulp after cooking is collected. The black liquor after cooking is extracted at 42%, and the outlet temperature is 70℃. The pulp after cooking is collected. The lignin content in the obtained black liquor is 138 kg / t pulp.

[0069] (6) The specific washing process is as follows: the pulp after cooking is washed in five countercurrent stages, and the pulp dryness is 21%.

[0070] (7) The specific process of the pulping is as follows: pulp temperature 40℃. The first stage of pulping gap is 0.4 mm and pulp consistency is 2%; the second stage of pulping gap is 0.1 mm and pulp consistency is 15%.

[0071] (8) The specific screening process is as follows: the washed Reed pulp is screened by a vibrating pulp screener with a slit width of 0.15 mm to obtain qualified pulp, with a screening residue rate of 2.06%. The pulp obtained from screening is the finished Reed pulp.

[0072] Example 2: This embodiment provides a production process for preparing unbleached semi-chemical pulp from Reed Bamboo, including the following steps: (1) Collect raw materials of Reed sphagnum moss that have grown for two years and air-dry them for 6 months.

[0073] (2) The reed is crushed into reed chips with a length of 3-8 cm and a width of 2-4 cm by a crusher. The reed chips are then sieved through an 8-mesh sieve to remove small fragments.

[0074] (3) Reed chips were washed with 60°C warm water and then alkaline-impregnated in a composite treatment agent (1% N-lauroyl glutamate, 0.5% tetrasodium pyrophosphate, and 4% sodium hydroxide, with the remainder being water). After being squeezed and mixed by an extrusion tearing machine to remove excess water, the reed chips were transported to a cooking pot. The reed chips were transported with a dryness of 40% and the alkaline impregnation time was 40 min. The resulting washing water had a pH of 6.5. After the sludge was treated by a plate and frame filter press and polyaluminum was added for sedimentation, the water was reused.

[0075] (4) The specific cooking process is as follows: 14% alkali, 0.05% anthraquinone, liquid ratio 1:4, maximum cooking temperature 160℃, and holding time 40 min. The specific formula of the cooking liquid is: 437.5 kg of liquid alkali (32% mass concentration) and 0.5 kg of anthraquinone per ton of oven-dried reed slices in a 4 m³ solution. 3 The cooking liquid prepared in water is heated to 160°C in a cooking pot and kept at that temperature for 40 minutes.

[0076] (5) The specific process of the spraying is as follows: the raw material reaction liquid after cooking is rapidly depressurized for 20 minutes and sprayed out through channels such as the venting valve. The pulp after cooking is collected. 53% of the black liquor is extracted after cooking. The outlet temperature is 73℃. The pulp after cooking is collected. The lignin content in the obtained black liquor is 117 kg / t pulp.

[0077] (6) The specific washing process is as follows: the pulp after cooking is washed in five countercurrent stages, and the pulp dryness is 23%.

[0078] (7) The specific process of the pulping is as follows: pulp temperature 40℃. The first stage of pulping gap is 0.5 mm and pulp consistency is 5%; the second stage of pulping gap is 0.1 mm and pulp consistency is 17%.

[0079] (8) The specific screening process is as follows: the washed Reed pulp is screened by a vibrating pulp screener with a slit width of 0.15 mm to obtain qualified pulp, with a screening residue rate of 3.58%. The pulp obtained from screening is the finished Reed pulp.

[0080] Example 3: This embodiment provides a production process for preparing unbleached semi-chemical pulp from Reed Bamboo, including the following steps: (1) Collect raw materials of Reed sphagnum moss that have grown for two years and air-dry them for 6 months.

[0081] (2) The reed is crushed into reed chips with a length of 3-8 cm and a width of 2-4 cm by a crusher. The reed chips are then sieved through an 8-mesh sieve to remove small fragments.

[0082] (3) Reed chips were washed with 60°C warm water and then alkaline-impregnated in a composite treatment agent (2.4% sodium N-lauroyl glutamate, 1% tetrasodium pyrophosphate, and 3% sodium hydroxide, with the remainder being water). After being squeezed and mixed by an extrusion tearing machine to remove excess water, the reed chips were transported to a cooking pot. The dryness of the reed chips was 35%, and the alkaline impregnation time was 30 min. The resulting washing water had a pH of 6.5. After the sludge was treated by a plate and frame filter press and polyaluminum was added for sedimentation, the water was reused.

[0083] (4) The specific cooking process is as follows: 16% alkali, 22% sulfidation, 1:3 liquor ratio, maximum cooking temperature of 160℃, and holding time of 30 min. The specific formula of the cooking liquor is: 390 kg of liquid alkali (32% mass concentration) and 58.6 kg of sodium sulfide (60%, solid) per ton of oven-dried reed slices in a 3 m³ solution. 3 The cooking liquid prepared in water is heated to 160°C in a cooking pot and kept at that temperature for 30 minutes.

[0084] (5) The specific process of the spraying is as follows: the raw material reaction liquid after cooking is rapidly depressurized for 20 minutes and sprayed out through channels such as the venting valve. The pulp after cooking is collected. The black liquor after cooking is extracted at 49%, and the outlet temperature is 67℃. The pulp after cooking is collected. The lignin content in the obtained black liquor is 103 kg / t pulp.

[0085] (6) The specific washing process is as follows: the pulp after cooking is washed in five countercurrent stages, and the pulp dryness is 22%.

[0086] (7) The specific process of the pulping is as follows: pulp temperature 50℃. The first stage of pulping gap is 0.5 mm and pulp consistency is 2%; the second stage of pulping gap is 0.1 mm and pulp consistency is 15%.

[0087] (8) The specific screening process is as follows: the washed Reed pulp is screened by a vibrating pulp screener with a slit width of 0.20 mm to obtain qualified pulp, with a screening residue rate of 3.2%. The pulp obtained by screening is the finished Reed pulp.

[0088] Comparative Example 1: This comparative example uses wheat straw as raw material to prepare unbleached semi-chemical pulp, including the following steps: (1) Collect wheat straw from the current year and air-dry it for 6 months.

[0089] (2) Wheat straw is crushed into straw flakes with a length of 3-5 cm by a crusher, retaining the stems and leaves. The straw flakes are then sieved through a 4-mesh sieve to remove small fragments.

[0090] (3) The wheat straw flakes were washed with 60°C warm water, alkaline impregnation was performed, and then squeezed and mixed by an extrusion tearing machine to remove excess water. The wheat straw flakes were then transported to a cooking pot. The dryness of the wheat straw flakes was 30%, and the alkaline impregnation time was 40 min. The resulting washing water had a pH of 6.5. After the sludge was treated by a plate and frame filter press and polyaluminum was added for sedimentation, the water was reused.

[0091] (4) The specific process of the cooking is as follows: 8% alkali, 25% sulfidation, 1:6 liquid ratio, 140℃ maximum cooking temperature, and 40 min heat preservation time.

[0092] (5) The specific process of the spraying is as follows: the raw material reaction liquid after cooking is rapidly depressurized for 20 minutes and sprayed out through channels such as the venting valve. The pulp after cooking is collected. 42% of the black liquor is extracted after cooking. The outlet temperature is 65℃. The pulp after cooking is collected. The lignin content in the obtained black liquor is 89 kg / t pulp.

[0093] (6) The specific washing process is as follows: the pulp after cooking is washed in five countercurrent stages, and the pulp dryness is 15%.

[0094] (7) The specific process of the pulping is as follows: pulp temperature 50℃. The first stage of pulping gap is 0.3 mm and pulp consistency is 5%; the second stage of pulping gap is 0.1 mm and pulp consistency is 10%.

[0095] (8) The specific screening process is as follows: the washed wheat straw semi-chemical pulp is screened by a vibrating pulp screener with a slit width of 0.20 mm to obtain qualified pulp, with a screening residue rate of 2.05%. The pulp obtained by screening is the finished wheat straw semi-chemical pulp.

[0096] Comparative Example 2: This comparative example uses reeds as raw material to prepare unbleached semi-chemical pulp, including the following steps: (1) Collect the reed stalks of the year and air-dry them for 6 months.

[0097] (2) The reed stalks are crushed into reed pieces with a length of 3-5 cm by a crusher, while retaining the stems and leaves. The reed pieces are then sieved through an 8-mesh sieve to remove small fragments.

[0098] (3) The reed chips were washed with 60℃ warm water, alkaline soaked, squeezed and mixed by an extrusion tearing machine to remove excess water, and then transported to a cooking pot. The dryness of the reed chips was 35%, and the alkaline soaking time was 30 min. The resulting washing water had a pH of 6.5. After the sludge was treated by a plate and frame filter press and polyaluminum was added for sedimentation, the water was reused.

[0099] (4) The specific process of the cooking is as follows: 11% alkali, 25% sulfidation, 1:4 liquid ratio, 160℃ maximum cooking temperature, and 40 min heat preservation time.

[0100] (5) The specific process of the spraying is as follows: the raw material reaction liquid after cooking is rapidly depressurized for 20 minutes and sprayed out through channels such as the venting valve. The pulp after cooking is collected. The black liquor extracted after cooking is 36%, the outlet temperature is 65℃, and the pulp after cooking is collected. The lignin content in the obtained black liquor is 300 kg / t pulp.

[0101] (6) The specific washing process is as follows: the pulp after cooking is washed in five countercurrent stages, and the pulp dryness is 23%.

[0102] (7) The specific process of the pulping is as follows: pulp temperature 50℃. The first stage of pulping gap is 0.3 mm and pulp consistency is 5%; the second stage of pulping gap is 0.1 mm and pulp consistency is 10%.

[0103] (8) The specific screening process is as follows: the washed reed semi-chemical pulp is screened by a vibrating pulp screener with a slit width of 0.20 mm to obtain qualified pulp, with a screening residue rate of 2.49%. The pulp obtained by screening is the finished reed semi-chemical pulp.

[0104] Comparative Example 3 The difference from Example 1 is that only sodium hydroxide is added to the composite treatment agent, that is, 7% sodium hydroxide and the remainder is water.

[0105] Comparative Example 4 The difference from Example 1 is that sodium N-lauroyl glutamate was not added to the composite treatment agent, i.e., 3% tetrasodium pyrophosphate and 4% sodium hydroxide, with the remainder being water.

[0106] Comparative Example 5 The difference from Example 1 is that tetrasodium pyrophosphate was not added to the composite treatment agent, i.e., 3% sodium N-lauroyl glutamate and 4% sodium hydroxide, with the remainder being water.

[0107] Comparative Example 6 The difference from Example 1 is that the raw material is replaced with rice straw, while the rest remains the same.

[0108] Comparative Example 7 The difference from Example 1 is that the raw material is replaced with moso bamboo, while the rest remains the same.

[0109] The specific test results of Examples 1-3 and Comparative Examples 1-7 of the present invention are shown in Table 1. The indicators in Table 1 were measured according to the following standard methods: freeness: GB / T 3332, kappa value: GB / T 1546, fiber water retention value: GB / T 29286, density: GB / T 451.3-2002, folding endurance, ring crush index, breaking length, folding endurance, tear index: GB / T 24323.

[0110] Table 1 Comparison of Physical Properties of Chemical Pulp

[0111] Note: Density, breaking length, flexural endurance, ring crush index, and tear index are all based on a Schobold freeness of 40 and a basis weight of 80 g / m³. 2 The measurements were taken after the sample was equilibrated under constant temperature and humidity (23℃, 50% humidity) conditions for 24 hours.

[0112] It can be seen that the unbleached semi-chemical pulp of *Arundinaria lobata* in Examples 1-3 of this invention, after degumming treatment, has significant advantages in tear and ring crush strength compared to straw and bamboo raw materials, while maintaining excellent water filtration performance, meeting the needs of packaging paper products. The comparative examples show that the water retention value of the semi-chemical pulp of wheat straw (Comparative Example 1) exceeds 230, indicating poor water filtration capacity and severely affecting paper machine speed. Reed (Comparative Example 2) and rice straw (Comparative Example 6) are inferior to *Arundinaria lobata* in terms of folding endurance, tear strength, and other indicators, while moso bamboo (Comparative Example 7) is significantly inferior to *Arundinaria lobata* in folding endurance. The development of unbleached semi-chemical pulp of *Arundinaria lobata* plays an important role in addressing the scarcity of wood raw materials and developing pulping from grass plant fibers.

[0113] As can be seen from the comparison between Example 1 and Comparative Example 3, the addition of surface penetrant and tetrasodium pyrophosphate can significantly improve the folding endurance of natural-colored semi-chemical pulp of Reed sphaerocephala compared with simple hot alkali impregnation.

[0114] As can be seen from the comparison of Example 1 and Comparative Examples 4 and 5, the combination of sodium N-lauroyl glutamate and tetrasodium pyrophosphate has a synergistic effect in improving the folding endurance of natural-colored semi-chemical pulp of Reed sphaerocephala.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing unbleached chemical pulp from Reed spp., characterized in that, include: Reed shoots are hot-soaked in a composite treatment agent solution for a predetermined time, and then extruded and dehydrated to obtain pretreated reed shoots; wherein, the composite treatment agent is composed of a surface penetrant, tetrasodium pyrophosphate and sodium hydroxide, and the surface penetrant is selected from at least one of nonionic surfactants and anionic surfactants; The pretreated reed is steamed, sprayed, washed, ground, and screened to obtain a semi-chemical reed pulp.

2. The method for preparing unbleached chemical pulp from Reed japonica as described in claim 1, characterized in that, The hot impregnation temperature is 75~100℃, the time is 20~40 min, and the dryness of the reed is 33~45%.

3. The method for preparing unbleached chemical pulp from Reed japonica as described in claim 1, characterized in that, In the composite treatment agent solution, the amount of alkali used is 2-5%, the total amount of surface penetrant and tetrasodium pyrophosphate is 1-3%, and the ratio of surface penetrant to tetrasodium pyrophosphate is 2-3:1; Alternatively, the surface penetrant may be fatty alcohol polyoxyethylene ether or sodium N-lauroyl glutamate.

4. The method for preparing unbleached chemical pulp from Reed japonica as described in claim 1, characterized in that, The specific conditions for the cooking process are as follows: 12-18% alkali, 20%-25% sulfidation, and / or 0.2-0.8% anthraquinone; the reed slices and the medicinal liquid are mixed at a ratio of 1:2.5-5.0; the cooking temperature is 158-165℃; and the temperature is maintained for 30-90 minutes.

5. The method for preparing unbleached chemical pulp from Reed japonica as described in claim 1, characterized in that, The washing process employs single-stage or multi-stage counter-current washing. Alternatively, the number of washing segments may be 2 to 5.

6. The method for preparing unbleached chemical pulp from Reed japonica as described in claim 1, characterized in that, The pulp is a two-stage pulp, with the first stage being a low-consistency pulp and the second stage being a medium-consistency pulp.

7. The method for preparing unbleached chemical pulp from Reed japonica as described in claim 6, characterized in that, The first stage grinding gap is 0.4~0.5 mm, and the grinding inlet concentration is controlled at 2~7%; the second stage grinding gap is 0.1~0.15 mm, the grinding inlet concentration is controlled at 14~17%, and the grinding temperature is 40~50℃.

8. The method for preparing unbleached chemical pulp from Reed ferns as described in claim 1, characterized in that, The screening uses a slit sieve with a diameter of 0.15~0.30 mm or a perforated sieve with a diameter of 0.25~0.50 mm. Alternatively, the slag screening rate is 2-4%.

9. The unbleached semi-chemical pulp of *Arundo donax* prepared by the method according to any one of claims 1-8, characterized in that, The natural color semi-chemical pulp of Reed is 70~100 kappa value, 160~180 water retention value, and the mass ratio of short fiber to long fiber is 50~60:50~40.

10. The use of the natural semi-chemical pulp of Reed hyacinth as described in claim 9 in the preparation of transparent paper, greaseproof paper or food packaging paper.

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