Natural color chemical pulp based on bamboo reed as well as preparation method and application of natural color chemical pulp

Abstract

The invention belongs to the technical field of papermaking pulping, and particularly discloses natural color chemical pulp based on bamboo reed and a preparation method and application thereof.The preparation method comprises the following steps that bamboo reed raw materials are crushed into bamboo reed pieces, the bamboo reed pieces are screened and then soaked and washed with hot water of 75-100 DEG C, then a surfactant is added into the bamboo reed pieces, spiral extrusion, even mixing and excessive water removal are conducted, and the bamboo reed pieces are obtained; pre-treated bamboo reed materials are obtained; the pretreated bamboo reed material is cooked, during cooking, the use amount of alkali is 20%-26%, the sulfuration degree is 20%-25%, and / or anthraquinone is 0.2%-0.8%, the liquid ratio is 1: 2.5-5.0, and the heat preservation time is 60-120 min; and spraying the pulp obtained by cooking to obtain paper pulp, and washing and screening the paper pulp to obtain the product. The produced paper pulp has the advantages of high tensile strength, high tearability, high water absorption, high ring crush compression resistance and the like, and can be well applied to the scenes of two-side offset paper, food packaging paper, paper bag paper or kitchen and bath paper and the like.

Description

Technical Field

[0001] This invention belongs to the field of papermaking and pulping technology, and specifically discloses a natural chemical pulp based on reed, its preparation method and application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Arundo donax., also known as reed bamboo, is a perennial herbaceous plant belonging to the genus Arundo in the family Poaceae. Its fiber length is second only to wood pulp, making it a high-quality raw material for papermaking.

[0004] However, the outer wall of the stem of Phyllostachys aurea has a waxy layer formed by resin and lipids. During chemical cooking, the waxy layer reacts with alkaline chemicals to undergo saponification, and the products, such as sodium fatty acid salts, dissolve in the black liquor. During the movement of the black liquor, a large amount of foam is generated, which interferes with the delivery and evaporation of the black liquor and the recovery of alkali. Specifically, the foam occupies a large volume, causing air binding in the pump, reducing the effective delivery flow rate and increasing energy consumption. The foam covers the liquid surface of the heating tubes in the evaporator, forming a heat insulation layer with high thermal resistance, which seriously hinders the transfer of heat from the heating wall to the black liquor body. The substances entrained in the foam may form a scale layer on the heating surface, which seriously reduces the evaporation efficiency.

[0005] Due to low evaporation efficiency, the concentration of solids in the black liquor fed into the alkali recovery furnace may not reach the preset value, resulting in low calorific value of the black liquor and unstable furnace temperature. The uneven spraying and large atomized particles caused by foaming result in incomplete combustion in the furnace, which easily produces reducing sulfides and aggravates the corrosion of the furnace wall. Summary of the Invention

[0006] To address the current shortage of papermaking fiber raw materials, this invention provides a natural chemical pulp based on reed (Prunus armeniaca), its preparation method, and its applications, supplementing the existing market's shortage of pulp fiber raw materials and the high cost of packaging paper and offset paper. The produced pulp has advantages such as high tensile strength, high tear strength, high water absorption, and high ring crush strength, making it well-suited for applications in packaging paper surface layers and offset paper.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a natural chemical pulp based on reed, comprising the following steps: The raw material of Reed is crushed into Reed flakes, sieved, soaked and washed in hot water at 75-100℃, then a surfactant is added, and the mixture is screw-pressed, mixed, and excess water is removed to obtain pretreated Reed material. The pretreated Reed material is steamed. During steaming, the amount of alkali is 20-26%, the degree of sulfidation is 20%-24%, and / or anthraquinone is 0.2-0.8%, the liquid ratio is 1:2.5-5, and the holding time is 60-120 min. The pulp obtained from cooking is sprayed out to produce paper pulp, which is then washed and screened to obtain the final product.

[0009] Secondly, the present invention provides a natural chemical pulp based on reed, prepared by the aforementioned preparation method, with a kappa value of 10-20, a water retention value of 150-170, and a mass ratio of short fibers to long fibers of 55-65:45-35.

[0010] The short fibers have a length of 0.01-0.6 mm, and the long fibers have a length of 0.6-3.2 mm.

[0011] Thirdly, the present invention provides the application of the natural chemical pulp based on reed in the preparation of packaging paper surface layer or offset paper.

[0012] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: Reed shoots are washed with hot water at 75-100℃. A surfactant is used to reduce the surface tension of the reed shoots and penetrate and emulsify the surface wax. The reed shoots are then extruded and mixed using an extrusion tearing machine to remove excess water before being transferred to a cooking pot. This process effectively reduces the amount of alkaline chemicals required during cooking, and the removal of the wax layer effectively reduces the amount of foam in the black liquor, facilitating its recycling.

[0013] This invention fully utilizes the advantages of *Arundinaria repens* (reed bamboo) in its salt and alkali resistance and high yield, combining ecological protection with the pulp and paper industry, developing saline-alkali land while supplementing the domestic shortage of plant fiber raw materials. The process for preparing unbleached chemical pulp using *Arundinaria repens* fully leverages its advantages of high fiber content, low silicon content, and low ash content. Based on the characteristics of *Arundinaria repens*, a suitable chemical pulping process has been developed, which can meet the requirements of mainstream black liquor alkali recovery systems, has low raw material costs, and is simple and easy to promote. The prepared unbleached chemical pulp from *Arundinaria repens* exhibits excellent ring crush, air permeability, and tear strength properties, with water filtration capacity comparable to wood pulp, and fiber length second only to coniferous wood, making it an excellent pulp raw material. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 This is a process flow diagram of preparing natural-colored chemical pulp from Reed tsao-ko in Embodiment 1 of the present invention; Figure 2This is a length grading diagram of chemical pulp fibers prepared from reed in Example 1 of the present invention. Detailed Implementation

[0016] It should be noted that the following detailed description is illustrative 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.

[0017] 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.).

[0018] Cooking: A chemical pulping process in which fiber raw materials are treated with chemical solutions under high temperature and pressure to separate the fibers.

[0019] Alkali dosage: refers to the amount of active alkali used during cooking (active alkali in sulfate cooking refers to sodium hydroxide and sodium sulfide, and active alkali in caustic soda cooking refers to sodium hydroxide) as a percentage of the dry raw material mass.

[0020] Sulfidation degree: refers to the percentage of sodium sulfide to active alkali in the cooking liquor.

[0021] 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.

[0022] Multi-stage countercurrent washing: a highly efficient and energy-saving washing process widely used in pulp and paper making, metallurgy, chemical industry and other fields. Its core principle is that the pulp and washing liquid flow in opposite directions, and high extraction rate and low water consumption are achieved through multi-stage series washing.

[0023] Black liquor alkali recovery: a core process in the pulp and paper industry for treating cooking waste liquor (black liquor) to recover chemicals and heat energy. Through processes such as evaporation, combustion, and causticization, the organic sodium salts in black liquor are converted into alkali that can be reused in cooking, thereby achieving resource recycling and pollution reduction.

[0024] 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.

[0025] 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.

[0026] Kapoor value: A core indicator characterizing the degree of delignification in chemical and semi-chemical pulps, determined by the oxidation reaction of potassium permanganate with residual lignin in the pulp. It can indirectly indicate the degree of pulp delignification.

[0027] 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.

[0028] 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.

[0029] 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.

[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] Air permeability: The average airflow rate through a unit area of ​​pulp sample per unit time under a unit pressure difference. This indicator is an important parameter for evaluating pulp structure and properties.

[0033] 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.

[0034] 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.

[0035] Tear index: An important indicator for evaluating the tear resistance of paper and paperboard.

[0036] To address the technical problems mentioned in the background art, the present invention provides a method for preparing natural chemical pulp based on Reed sphagnum moss, comprising the following steps: The raw material of Reed is crushed into Reed flakes, sieved, soaked and washed in hot water at 75-100℃, then a surfactant is added, and the mixture is screw-pressed, mixed, and excess water is removed to obtain pretreated Reed material. The pretreated Reed material is steamed. During steaming, the amount of alkali is 20-26%, the degree of sulfidation is 20%-25%, and / or anthraquinone is 0.2-0.8%, the liquid ratio is 1:2.5-5, and the holding time is 60-120 min. The pulp obtained from cooking is sprayed out to produce paper pulp, which is then washed and screened to obtain the final product.

[0037] To address the technical problem mentioned in the background art that the presence of the waxy layer on the surface of Reed sphaerocephala causes excessive foaming in the black liquor during cooking, affecting black liquor transportation, evaporation concentration, and combustion, the inventors attempted to pre-impregnate the Reed sphaerocephala material with alkali before cooking. This pre-impregnated waxy layer was broken down to dissolve and soften the bamboo strips before the bamboo strips were fed into the cooking or impregnation reaction section. However, the alkali pre-impregnation solution had a high pollution load, and the weakly acidic washing water of the Reed sphaerocephala strips would increase the amount of alkaline chemicals used, resulting in poor economic efficiency. Furthermore, the alkali pre-impregnation method could easily have adverse effects on the relevant properties of the prepared pulp.

[0038] Reed shoots are washed with hot water at 75-100℃. Surfactants are used to reduce the surface tension of the reed shoots and penetrate and emulsify the surface wax. High temperature accelerates the dissolution of lipids. After being squeezed and mixed by an extrusion tearing machine, excess water is removed, and the reed shoots are then transported to a cooking pot. The dissolved lipids are discharged with the washing water, reducing the generation of black liquor foam during subsequent cooking.

[0039] After the wax layer is removed, foaming substances such as sodium fatty acid salts in the black liquor are reduced, which can prevent the formation of heat insulation layer or scale layer on the heating surface of the evaporator, improve the evaporation efficiency of black liquor, and at the same time reduce the gas binding phenomenon of the pump, ensuring the stable operation of the black liquor transportation and alkali recovery system.

[0040] Reed (Phyllostachys aurea) is a type of grass-based raw material, softer than bamboo but slightly firmer than reeds. Reed (Phyllostachys aurea) strips (stems and bark sheaths) soften during hot water treatment, achieving a moderate hardness that protects the fibers during spiral extrusion. The waxy layer on the outer surface (which is also a region rich in silicon) rubs against itself and the rollers under the mechanical extrusion of the spiral, simultaneously coming into full contact with surfactants. This dissolves and emulsifies the lipids, which are then discharged with the washing water, reducing subsequent cooking energy and chemical consumption, and improving the black liquor transportation and evaporation efficiency in the alkali recovery section.

[0041] Anthraquinones, as highly efficient catalysts in the pulping process, can disrupt the structure of lignin in *Arundo donax* raw materials through redox reactions, promoting the dissolution of lignin in alkaline cooking liquor, thus enabling the cooking process to achieve the target delignification level in a shorter time. Anthraquinones can inhibit the excessive degradation of cellulose and hemicellulose during cooking, reducing carbohydrate loss and thereby increasing crude pulp yield. Because anthraquinones accelerate lignin dissolution and protect carbohydrates, the amount of alkali used or the holding time can be reduced while ensuring delignification effect, thereby reducing the consumption of alkaline chemicals and lowering the energy consumption of the cooking process. The addition of anthraquinones can reduce fiber damage, allowing the fiber length and strength of the resulting pulp to be preserved.

[0042] Since the pretreatment has removed the wax layer and reduced black liquor foam by using hot water, surfactants and screw extrusion, there is no need to dilute the foaming material with a high liquid-to-liquid ratio. Therefore, a liquid-to-liquid ratio of 1:2.5-5 is sufficient to meet the requirements, effectively reducing water consumption.

[0043] Reducing the cooking time not only lowers energy consumption but also prevents excessive fiber degradation.

[0044] The lignin content of *Arundo donax* chips is about 20%, lower than that of bamboo chips, but comparable to that of wheat straw and reeds, while its tissue structure is dense. The optimized cooking process is suitable for *Arundo donax* chip raw materials after extrusion and dewaxing pretreatment, with a pulp kappa value of 10-14 and a fiber water retention value of 155-165.

[0045] In some embodiments, the amount of alkali used during cooking is 20-24%, such as 20%, 21%, 22%, 23%, and 24%.

[0046] In some embodiments, the raw material of reed is reed harvested in the same year after growing for 2-3 years, or reed material that has been air-dried for 3-6 months.

[0047] As a perennial herb, Reed sedge matures after two years of growth, with its fiber length and cellulose content reaching their optimal state. Two-year-old Reed sedge has moderately thick cell walls, high cellulose crystallinity, and a lignin content of about 20%. This composition ratio is conducive to the efficient removal of lignin during cooking, while reducing the degradation of cellulose and hemicellulose, thus ensuring the strength properties of the pulp (such as tensile strength and tear resistance).

[0048] If harvested and stored for too long, the hemicellulose in the raw material is prone to hydrolysis, and the lignin structure may become difficult to remove due to oxidation, thus affecting cooking efficiency and pulp yield. Harvesting in the same year can avoid fiber degradation or mold growth caused by long-term storage of reeds.

[0049] If the drying time is insufficient and the moisture content of the raw material is too high, microorganisms will easily grow during storage, leading to fiber mold. If the drying time is too long (e.g., more than 6 months), long-term exposure will cause hemicellulose hydrolysis and lignin oxidation, making it more difficult to remove the lignin structure, thereby reducing cooking efficiency and pulp yield.

[0050] In some embodiments, the length of the reed strip is 3-8cm and the width is 2-4cm.

[0051] In some embodiments, the raw material of reed includes reed stems and bark sheaths.

[0052] All components of *Arundo donax* (reed bamboo) – stems, bark sheaths, and leaves – have high cellulose content. The bark sheath contains 20% cellulose, while the stem contains 36%. The ratio of bark sheath to stem is approximately 1:2 (w / w), and the ash content in the bark sheath is ≤3%. The entire *Arundo donax* plant is crushed into flakes, significantly improving raw material utilization efficiency and reducing costs compared to traditional bamboo processing methods that only use stem flakes.

[0053] In some embodiments, the sieving is performed using a 4-8 mesh sieve.

[0054] In some embodiments, the dryness of the pretreated Reed material is 33-45%.

[0055] In some embodiments, when washing with hot water, the solid-liquid ratio is 1:6-10, and the soaking and washing time is 10-30 minutes.

[0056] In some embodiments, the spiral extrusion is performed using a twin-spiral extrusion ripper.

[0057] Preferably, the screw speed of the spiral extrusion is 200-300 rpm, the compression ratio is 1:2-3, and the overlap coefficient of the spiral is 5%-15%. In this invention, any twin-screw extruder that meets this overlap coefficient range can be used for Reed sedge raw materials.

[0058] The overlap factor of the screws refers to the percentage of the area of ​​the overlapping portion of the screw blades / threads on the axial projection plane of the two parallel screw shafts in a twin screw extruder, relative to the total side projection area of ​​a single screw blade. This factor describes the degree of meshing between the two screws of the screw extruder.

[0059] Two parallel, meshing screws knead the reed strips together, completing material transport, compression, friction, and fibrillation. Reed strips are softer than bamboo strips and denser than reeds; improper extrusion parameters can easily lead to fiber breakage or excessive fibrillation. The double screws have a moderate degree of meshing (overlap coefficient of 5%-15%), achieving initial fibrillation through the kneading of the screw blades while avoiding shear breakage due to excessively tight meshing (overlap coefficient) or ineffective fiber separation due to excessively loose meshing (overlap coefficient). Providing appropriate pressure (compression ratio of 1:2-3) removes excess moisture while preventing cell wall rupture due to excessive pressure (compression ratio) or failure to achieve mechanical separation of fibers due to insufficient pressure (compression ratio). The screw speed is 200-300 rpm, ensuring a reasonable residence time for the material in the extrusion chamber, allowing sufficient contact with the surfactant without excessive fiber degradation due to high-speed friction from excessive speed.

[0060] A 5%-15% overlap coefficient creates staggered shearing forces on the spiral blades of the double helix shaft. Combined with a compression ratio of 1:2-3, the waxy layer structure is physically torn apart by the friction between the epidermis of the reed strips and between the epidermis and the rollers, exposing the internal fibers. At the same time, it promotes the penetration of surfactants into the waxy layer, achieving emulsification and dissolution. A rotation speed of 200-300 rpm ensures that the reed strips are fully mixed with the surfactants during the extrusion process. High-temperature hot water (75-100℃) accelerates the dissolution of lipids. Combined with mechanical extrusion, the dissolved wax is discharged with the washing water, reducing the generation of black liquor foam during subsequent cooking.

[0061] In some embodiments, the surfactant accounts for 0.1-0.5% of the mass of the oven-dried reed chips.

[0062] Preferably, the surfactant is an alkyl glycoside surfactant, a fatty alcohol polyoxyethylene ether surfactant, a betaine surfactant, a sulfobetaine surfactant, or an amino acid-derived surfactant.

[0063] More preferably, the surfactant is a fatty alcohol polyoxyethylene ether, such as AEO-7 and AEO-9. This type of surfactant is stable in a weakly acidic environment, biodegradable, and inexpensive.

[0064] Preferably, after adding the surfactant, the spiral extrusion time is 5-10 min.

[0065] In some embodiments, the cooking temperature is 160-170°C and the cooking pressure is 0.6-0.8 MPa.

[0066] In some embodiments, the screening machine used is a 0.1-0.25 mm slotted screen or a 0.15-0.4 mm perforated screen, with a vibration frequency of 750-1200 Hz.

[0067] In some embodiments, the excess water removed is grass washing water with a pH of 6-7. After adding a demulsifier to the grass washing water, the sludge is removed by pressure filtration. Then, a flocculant is added to the water, and after sedimentation treatment, the water is recycled.

[0068] Preferably, the demulsifier is a cationic demulsifier (quaternary ammonium salts, alkyl ammonium salts, etc.), a polyether, an inorganic salt demulsifier (sodium silicate, calcium chloride, etc.), or a nonionic demulsifier (phenolic amine resin block polyethers, alkylphenolic acid resin polyethers, etc.).

[0069] More preferably, the demulsifier is an inorganic salt demulsifier.

[0070] More preferably, the demulsifier is calcium chloride. Calcium chloride solution has a stable pH range from weakly acidic to neutral, making it more suitable for the environment of reed washing water. AEO forms an emulsified polymer with waxes, pigments, and fine fibers, and carries a negative charge, which can be effectively neutralized and demulsified by calcium chloride.

[0071] Preferably, the flocculant is cationic polyacrylamide (CPAM), polyaluminum chloride (PAC), polyferric sulfate (PFS), or anionic polyacrylamide (APAM).

[0072] More preferably, the flocculant is CPAM or PAC.

[0073] Flocculants can settle solid impurities in grass washing water, allowing the washing water to be reused.

[0074] Secondly, the present invention provides a natural chemical pulp based on reed, prepared by the aforementioned preparation method, with a kappa value of 10-20, a water retention value of 150-170, and a mass ratio of short fibers to long fibers of 55-65:45-35.

[0075] Thirdly, the present invention provides the application of the unbleached chemical pulp based on Reed in the preparation of offset paper, food packaging paper, paper bag paper or kitchen and bathroom paper.

[0076] The following examples further illustrate the present invention, but do not constitute a limitation thereof. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0077] Example 1 like Figure 1 As shown, a method for preparing natural chemical pulp based on reed includes the following steps: (1) Collect Reed bamboo materials that have grown for two years and harvested in the current year and then air-dried for 6 months.

[0078] (2) The reed is crushed into reed pieces with a length of 3~8 cm and a width of 2~4 cm by a crusher. The reed pieces are then screened through an 8-mesh sieve to remove small fragments.

[0079] (3) Reed flakes were washed with 95℃ hot water at a solid-liquid ratio of 1:7 for 20 min. After adding 0.3% AEO-9 by the oven-dry weight of the reed flakes, they were squeezed and mixed by a screw extruder for 7 min. The screw speed of the screw extruder was 230 rpm, the compression ratio was 1:2.5, and the overlap coefficient of the screw was 10%. Then, excess water was removed to make the reed flakes dry to 35%, and the reed flakes were transported to a cooking pot. The resulting washing water had a pH of 6.5. After adding 0.05% calcium chloride, the sludge was treated by a plate and frame filter press, and 0.1% polyaluminum chloride was added for sedimentation before reuse.

[0080] The specific cooking process is as follows: Sulfate cooking is employed, using 20% ​​alkali, 25% sulfidation, a liquor-to-alkali ratio of 1:4, a maximum cooking temperature of 160℃, and a holding time of 90 min. Specifically, for every ton of oven-dry reed chips, 468.8 kg of liquid alkali (32% mass concentration) and 83.3 kg of sodium sulfide (60%, solid) are added to a 4 m³ solution. 3 The cooking liquor prepared in water is heated to 160°C in the cooking reactor, kept at that temperature for 90 minutes, and then the slurry is sprayed out.

[0081] The specific process of the spraying is as follows: the wood chip 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 extraction after cooking is 69%, the outlet temperature is 72℃, and the pulp after cooking is collected.

[0082] The specific washing process is as follows: the pulp after cooking undergoes a five-stage countercurrent washing process, with a pulp dryness of 29% and a washing efficiency of 89.6% (based on solids).

[0083] The specific screening process is as follows: the washed reed pulp is screened through a vibrating pulp screener with a slit width of 0.15 mm to obtain qualified pulp, with a screening residue rate of 0.28%. The pulp obtained from the screening is the finished reed pulp.

[0084] The length grading diagram of the chemical pulp fiber prepared from Reed in Example 1 is shown below. Figure 2 As shown.

[0085] Example 2 A method for preparing unbleached chemical pulp based on Phragmites australis includes the following steps: (1) Collect Reed bamboo materials that have grown for two years and harvested in the current year and then air-dried for 6 months.

[0086] (2) The reed is crushed into reed pieces with a length of 3~8 cm and a width of 2~4 cm by a crusher. The reed pieces are then screened through an 8-mesh sieve to remove small fragments.

[0087] (3) Reed chips were washed with 100℃ hot water at a solid-liquid ratio of 1:10 for 10 min. After adding 0.5% AEO-7 by the dry weight of the reed chips, they were squeezed and mixed by a screw extruder for 10 min. The screw speed of the screw extruder was 280 rpm, the compression ratio was 1:3, and the overlap coefficient of the screw was 15%. Then, excess water was removed to make the dryness of the reed chips 40%, and the reed chips were transported to a cooking pot. The resulting washing water had a pH of 6.5. After adding 0.1% calcium chloride, the sludge was treated by a plate and frame filter press and 0.1% polyaluminum chloride was added for sedimentation before reuse.

[0088] The specific cooking process is as follows: Sulfate cooking is employed, using 24% alkali, 25% sulfide, a liquor ratio of 1:3, a maximum cooking temperature of 175℃, and a holding time of 120 min. Specifically, for every ton of oven-dry reed chips, 562.5 kg of liquid alkali (32% mass concentration) and 100 kg of sodium sulfide (60%, solid) are added to a 3 m³ solution. 3 The cooking liquor prepared in water is heated to 175°C in the cooking reactor, kept at that temperature for 120 minutes, and then the slurry is sprayed out.

[0089] The specific process of the spraying is as follows: the wood chip reaction liquid after cooking is rapidly depressurized for 15 minutes and sprayed out through channels such as the venting valve. After cooking, 72% of the black liquor is extracted, the outlet temperature is 83℃, and the pulp after cooking is collected.

[0090] The specific washing process is as follows: the pulp after cooking undergoes a five-stage countercurrent washing process, with a pulp dryness of 30% and a washing efficiency of 90.1% (based on solids).

[0091] The specific screening process is as follows: the washed reed pulp is screened through a vibrating pulp screener with a slit width of 0.15 mm to obtain qualified pulp, with a screening residue rate of 0.29%. The pulp obtained from the screening is the finished reed pulp.

[0092] Example 3 A method for preparing unbleached chemical pulp based on Phragmites australis includes the following steps: (1) Collect Reed bamboo materials that have grown for two years and harvested in the current year and then air-dried for 4 months.

[0093] (2) The reed is crushed into reed pieces with a length of 3~8 cm and a width of 2~4 cm by a crusher. The reed pieces are then screened through an 8-mesh sieve to remove small fragments.

[0094] (3) Reed chips were washed with 100℃ hot water at a solid-liquid ratio of 1:6 for 30 min. After adding 0.1% AEO-9 by the oven-dry weight of the reed chips, they were squeezed and mixed by an extrusion shredder for 7 min. The screw speed of the screw extruder was 200 rpm, the compression ratio was 1:3, and the overlap coefficient of the screw was 15%. Then, excess water was removed to make the reed chips dry to 35%, and the reed chips were transported to a cooking pot. The resulting washing water had a pH of 6.5. After adding 0.05% calcium chloride, the sludge was treated by a plate and frame filter press and 0.1% polyaluminum chloride was added for sedimentation before reuse.

[0095] The specific cooking process is as follows: Sulfate cooking is employed, using 22% alkali, 22% sulfidation, a liquor-to-alkali ratio of 1:5, a maximum cooking temperature of 165℃, and a holding time of 120 min. Specifically, for every ton of oven-dry reed chips, 536.3 kg of liquid alkali (32% mass concentration) and 80.6 kg of sodium sulfide (60%, solid) are added to a 3 m³ solution. 3 The cooking liquor prepared in water is heated to 165°C in the cooking reactor, kept at that temperature for 120 minutes, and then the slurry is sprayed out.

[0096] The specific process of the spraying is as follows: the wood chip reaction liquid after cooking is rapidly depressurized for 15 minutes and sprayed out through channels such as the venting valve. After cooking, 69% of the black liquor is extracted, the outlet temperature is 72°C, and the cooked pulp is collected.

[0097] The specific washing process is as follows: the pulp after cooking undergoes a five-stage countercurrent washing process, with a pulp dryness of 32.6% and a washing efficiency of 90.0% (based on solids).

[0098] The specific screening process is as follows: the washed reed pulp is screened through a vibrating pulp screen with a slit width of 0.20 mm to obtain qualified pulp. The vibration frequency of the screen is 1100 Hz, and the screening residue rate is 0.27%. The pulp obtained from the screening is the finished reed pulp.

[0099] Example 4 A method for preparing unbleached chemical pulp based on Phragmites australis includes the following steps: (1) Collect Reed bamboo materials that have grown for two years and harvested in the current year and then air-dried for 4 months.

[0100] (2) The reed is crushed into reed pieces with a length of 3~8 cm and a width of 2~4 cm by a crusher. The reed pieces are then screened through an 8-mesh sieve to remove small fragments.

[0101] (3) Reed chips were washed with 100℃ hot water at a solid-liquid ratio of 1:8 for 25 min. After adding 0.4% AEO-9 by the oven-dry weight of the reed chips, they were squeezed and mixed by a screw extruder for 5 min. The screw speed of the screw extruder was 270 rpm, the compression ratio was 1:2, and the overlap coefficient of the screw was 7%. Excess water was removed to achieve a dryness of 30% for the reed chips, which were then transferred to a cooking pot. The resulting washing water had a pH of 7.0. After adding 0.05% calcium chloride, the sludge was treated by a plate and frame filter press and 0.5% polyaluminum chloride was added for sedimentation before reuse.

[0102] The specific cooking process is as follows: The cooking is carried out using the caustic soda-anthraquinone method, with 20% alkali and 0.5% anthraquinone, a liquid-to-liquid ratio of 1:4, a maximum cooking temperature of 170℃, and a holding time of 90 min. Specifically, for every ton of oven-dry weight of reed chips, 625 kg of liquid alkali (32% mass concentration) and 5 kg of sodium sulfide (60%, solid) are added to a 3 m³ solution. 3 The cooking liquor prepared in water is heated to 175°C in the cooking reactor, kept at that temperature for 120 minutes, and then the slurry is sprayed out.

[0103] The specific process of the spraying is as follows: the wood chip reaction liquid after cooking is rapidly depressurized for 15 minutes and sprayed out through channels such as the venting valve. After cooking, 73% of the black liquor is extracted, and the outlet temperature is 75℃. The cooked pulp is then collected.

[0104] The specific washing process is as follows: the pulp after cooking undergoes a single-stage washing process, with a pulp dryness of 30% and a washing efficiency of 90.7% (based on solids).

[0105] The specific screening process is as follows: the washed reed pulp is screened through a vibrating pulp screen with a slit width of 0.20 mm to obtain qualified pulp. The vibration frequency of the screen is 750 Hz, and the slag rate is 0.29%. The pulp obtained from the screening is the finished reed pulp.

[0106] Example 5 The difference from Example 1 is that in step (3), AEO-9 is replaced with alkyl glycoside surfactant APG0810, and everything else is the same as in Example 1.

[0107] Example 6 The difference from Example 1 is that in step (3), AEO-9 is replaced with betaine surfactant LSB (lauramidopropyl betaine), and everything else is the same as in Example 1.

[0108] Example 7 The difference from Example 1 is that in step (3), AEO-9 is replaced with sulfobetaine surfactant SB-12, and everything else is the same as in Example 1.

[0109] Example 8 The difference from Example 1 is that in step (3), AEO-9 is replaced with amino acid-derived surfactant NIKKOL Sarcosinate LN-30, while the rest is the same as in Example 1.

[0110] Comparative Example 1 The raw material used was changed to wheat straw, and all other steps were the same as in Example 1.

[0111] Comparative Example 2 The raw material used was changed to reeds, and all other steps were the same as in Example 1.

[0112] Comparative Example 3 The difference from Example 1 is that the raw material used is reed that has grown for one year, while everything else is the same as in Example 1.

[0113] Comparative Example 4 The difference from Example 1 is that the raw material used is five-year-old Reed, while everything else is the same as in Example 1.

[0114] Comparative Example 5 The difference from Example 1 is that the raw material used is reed that has been harvested for 1.5 years.

[0115] Comparative Example 6 The difference from Example 1 is that in step (3), the temperature of the washing water is 30°C, while the rest is the same as in Example 1.

[0116] Comparative Example 7 The difference from Example 1 is that in step (3), the spiral extrusion is replaced by stirring, while everything else is the same as in Example 1.

[0117] Comparative Example 8 The difference from Example 1 is that in step (3), the overlap coefficient of the spiral is 20%, and everything else is the same as in Example 1.

[0118] Comparative Example 9 The difference from Example 1 is that in step (3), the compression ratio is 1:1.5, and everything else is the same as in Example 1.

[0119] Comparative Example 10 The difference from Example 1 is that in step (3), the compression ratio is 1:3.5, and everything else is the same as in Example 1.

[0120] Comparative Example 11 The difference from Example 1 is that in step (3), the screw speed of the spiral extrusion is 330 rpm, and everything else is the same as in Example 1.

[0121] The specific test results of Examples 1-8 and Comparative Examples 1-11 of the present invention are shown in Table 1: Table 1 Comparison of Physical Properties of Chemical Pulp project Initial beating degree °SR crude pulp yield % Card value Fiber water retention value Weight-average fiber length mm Ring pressure index N·m / g Breathability mL / min Tear Index mN·m² / g Example 1 14 40.6 11.7 157 1.58 9.4 342.8 8.1 Example 2 14 38.2 13.7 156 1.52 10.2 350.3 7.8 Example 3 14 41.3 12.5 157 1.55 10.1 334.2 8.2 Example 4 14 43.2 24.8 165 1.88 12.3 179.4 8.9 Example 5 14 45.5 29.8 151 1.79 14.3 355.1 8.7 Example 6 14 42.7 13.9 156 1.55 11.7 350.6 8.4 Example 7 14 41.6 11.5 157 1.56 9.9 345.2 8.3 Example 8 14 44.8 15.3 156 1.57 10.3 344.3 8.6 Comparative Example 1 23 44.1 13.9 230 1.23 9.7 5.0 4.6 Comparative Example 2 22 53.0 7.7 164 1.00 10.5 324.2 6.1 Comparative Example 3 15 41.3 19.5 163 1.47 8.3 225.6 7.3 Comparative Example 4 17 35.2 12.2 165 1.45 8.9 297.3 7.1 Comparative Example 5 15 39.5 11.8 159 1.53 9.3 339.6 7.9 Comparative Example 6 15 37.2 11.5 156 1.45 8.7 310.0 7.6 Comparative Example 7 15 44.8 17.3 157 1.89 10.1 330.9 8.7 Comparative Example 8 18 37.6 11.6 158 1.51 8.8 370.5 6.9 Comparative Example 9 13 43.3 35.3 164 1.57 13.4 210.4 7.3 Comparative Example 10 17 35.6 12.2 157 1.50 8.9 377.5 7.0 Comparative Example 11 14 42.4 33.5 167 1.52 13.9 222.6 7.5 Note: Ring crush index, air permeability, and tear index are all based on a Schobold beating degree 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.

[0122] It can be seen that the pulping yield of the natural chemical pulp of *Arundinaria lobata* in Examples 1-4 of this invention is close to that of straw-based fiber raw materials. It also possesses the advantages of high yield and abundant sources of straw-based raw materials. Its pulping performance is similar to that of straw-based raw materials, but its water filtration performance is closer to that of hardwood raw materials. *Arundinaria lobata* that has undergone degumming and extrusion pretreatment reduces alkali consumption during cooking and produces excellent fiber quality during pulping.

[0123] In Example 5, the alkyl glycoside surfactant system was strongly alkaline. This system reacted with numerous silicon impurities on the surface of the reed to form a viscous, gel-like sodium silicate, creating a lubricating layer that reduced the friction effect of the reed sheets during kneading. Furthermore, when using APG0810, excessive foaming occurred during extrusion. The surfactants used in Examples 6-8 were all expensive.

[0124] Comparative data on the pulp performance of Comparative Example 1 and Example 1 show that *Arundinaria lobata*, as a non-wood fiber raw material, has longer fiber length and better water filtration performance, solving the problems of poor water filtration and low strength of wheat straw pulp, making it suitable for producing high-strength packaging paper, offset paper, etc. Pretreatment of *Arundinaria lobata* can effectively remove wax and reduce black liquor foam, while the high silica content of wheat straw easily leads to equipment scaling, increasing the difficulty of alkali recovery. The ecological advantages of *Arundinaria lobata* in saline-alkali land, combined with its pulping performance, can serve as a high-quality substitute for traditional herbal raw materials such as wheat straw, alleviating the shortage of papermaking fiber raw materials.

[0125] Comparative data on the pulp performance of Comparative Example 2 and Example 1 show that Reed sedge has longer fiber length, resulting in superior tear strength and water filtration performance. It is suitable for producing packaging paper surface layers and offset paper with high requirements for tear resistance and air permeability. Furthermore, pretreatment can solve the problem of black liquor foaming caused by wax. Although Reed has high yield and high delignification efficiency, its short fibers result in low tear strength, and the raw material characteristics (such as silicon content) may increase the difficulty of alkali recovery. Therefore, its overall performance is inferior to that of Reed sedge.

[0126] The performance comparison data of the pulp in Comparative Example 3 and Example 1 show that the fiber wall thickness of the raw material of Reed sphagnum moss with insufficient service life is insufficient, which affects the strength index.

[0127] The performance comparison data of the pulp in Comparative Example 4 and Example 1 show that the fiber strength of Reed vines that have been stored for too long will decrease due to decay, affecting the yield and strength.

[0128] The performance comparison data of the pulps from Comparative Example 6 and Example 1 show that high temperature is the key condition for dissolving the wax on the surface of Reed tsao-ko. Combined with surfactants, efficient dewaxing can be achieved, reducing black liquor foam and protecting the fibers. High-temperature washing can improve yield, fiber length, and strength, ensuring that the pulp meets the high-strength application requirements of packaging paper, offset paper, and other similar products. Low-temperature washing leads to wax residue, fiber damage, and decreased water filtration performance, increasing subsequent cooking energy consumption.

[0129] Comparative data on the pulp performance of Comparative Example 7 and Example 1 show that the kappa value of Example 1 is 11.7, significantly lower than that of Comparative Example 8 (17.3). A lower kappa value indicates more complete delignification, suggesting that screw extrusion mechanically tears the waxy layer on the surface of Reed, promoting the penetration of cooking liquor and improving lignin dissolution efficiency. In contrast, stirring cannot effectively destroy the waxy layer, resulting in poor delignification. The air permeability of Example 1 (342.8 mL / min) is higher than that of Comparative Example 8 (330.9 mL / min), indicating that after screw extrusion removes the wax, the pulp structure is more porous and has better water filtration capacity. The residual wax from stirring may clog the fiber gaps and reduce air permeability.

[0130] The equipment with a high spiral overlap coefficient (comparative example 8) is difficult to adapt to Reed spp. raw materials, resulting in high energy consumption and easy equipment blockage. Excessive extrusion of Reed spp. raw materials will produce more fiber fragments, leading to a decrease in yield. Uneven raw material size makes it difficult to stabilize the cooking process.

[0131] The comparative example 9 uses a twin-screw extruder with a low compression ratio, which cannot provide sufficient pressure to the reed slices, making it easier to discharge the material. This results in less friction on the reed slices and low efficiency in removing the wax layer from the surface of the reed slices.

[0132] The comparative example 10 shows that the twin-screw extruder has a high compression ratio setting, making it difficult to feed reed strips, causing the equipment to easily clog and jam, resulting in high energy consumption, uneven extrusion of reed strips, and in severe cases, easy grinding into a paste.

[0133] In Comparative Example 11, increasing the speed of the twin-screw extruder did not increase the yield of reed pulp, which would lead to a shorter residence time of the reed flakes in the equipment, making it impossible to effectively remove the wax.

[0134] 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 natural chemical pulp based on Phragmites australis, characterized in that: Includes the following steps: The raw material of Reed is crushed into Reed flakes, sieved, soaked and washed in hot water at 75-100℃, then a surfactant is added, and the mixture is screw-pressed, mixed, and excess water is removed to obtain pretreated Reed material. The pretreated Reed material is steamed. During steaming, the amount of alkali is 20-26%, the degree of sulfidation is 20%-25%, and / or anthraquinone is 0.2-0.8%, the liquid ratio is 1:2.5-5.0, and the holding time is 60-120 min. The pulp obtained from cooking is sprayed out to produce paper pulp, which is then washed and screened to obtain the final product.

2. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The amount of alkali used during steaming or boiling is 20-24%; Preferably, the raw material of Reed is Reed that has grown for 2-3 years and is harvested in the current year and then air-dried for 3-6 months; Preferably, the length of the reed strip is 3-8cm and the width is 2-4cm; Preferably, the raw material of Reed includes Reed stems and bark sheaths; Preferably, the sieving is performed using a 4-8 mesh sieve.

3. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The dryness of the pretreated Reed material is 33-45%; Preferably, when washing with hot water, the solid-liquid ratio is 1:6-10, and the washing time is 10-30 minutes. Preferably, the spiral extrusion is performed using a twin-spiral extrusion tearing machine; Preferably, the screw speed of the spiral extrusion is 200-300 rpm, the compression ratio is 1:2-3, and the overlap coefficient of the spiral is 5%-15%.

4. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The surfactant constitutes 0.1-0.5% of the mass of the oven-dried reed chips; Preferably, the surfactant is an alkyl glycoside surfactant, a fatty alcohol polyoxyethylene ether surfactant, a betaine surfactant, a sulfobetaine surfactant, or an amino acid-derived surfactant. Preferably, the surfactant is a fatty alcohol polyoxyethylene ether; Preferably, after adding the surfactant, the spiral extrusion time is 5-10 minutes.

5. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The cooking temperature is 160-170℃, and the cooking pressure is 0.6-0.8MPa.

6. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The screening process uses a sieving machine with a 0.1-0.25 mm slotted screen or a 0.15-0.4 mm perforated screen, with a vibration frequency of 750-1200 Hz.

7. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The excess water removed is called grass washing water with a pH of 6-7. After adding a demulsifier to the grass washing water, the sludge is removed by pressure filtration. Then, a flocculant is added to the water, and after sedimentation treatment, the water is recycled. Preferably, the demulsifier is a cationic demulsifier, a polyether, an inorganic salt demulsifier, or a nonionic demulsifier; Preferably, the demulsifier is an inorganic salt demulsifier; Preferably, the demulsifier is calcium chloride.

8. The method for preparing natural chemical pulp based on reed as described in claim 1, characterized in that: The flocculant is cationic polyacrylamide (CPAM), polyaluminum chloride (PAC), polyferric sulfate (PFS), or anionic polyacrylamide (APAM). Preferably, the flocculant is CPAM or PAC.

9. A natural chemical pulp based on reed, characterized in that: Prepared by any one of the preparation methods described in claims 1-8, with a kappa value of 10-20, a water retention value of 150-170, and a mass ratio of short fibers to long fibers of 55-65:45-35.

10. The application of the unbleached chemical pulp based on Reed Root as described in claim 9 in the preparation of offset paper, food packaging paper, paper bag paper or kitchen and bathroom paper.

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