Preparation method of degradable napkin based on natural plant fiber

Abstract

The application discloses a kind of based on natural plant fiber's degradable paper napkin preparation method, it is related to the field of sanitary products;The preparation method of a kind of based on natural plant fiber's degradable paper napkin, by using sisal waste slag and banana stem and other natural cellulose raw materials, widely available, low cost.Raw materials are washed, crushed, degummed into coarse fiber bundle, then converted into soft microfibrillated cellulose colloid by enzyme treatment.Partial colloid is defibrated into long fiber base pulp, another part is made into short fiber reinforced pulp by high pressure homogenization, and the two are mixed to obtain reinforced pulp, which is then made into base paper by papermaking, drying and polishing.The process improves the softness and hand feeling of the paper significantly while maintaining its toughness by softening the fibers, making it suitable for paper napkin production.The entire process uses green biotechnology, has low pollution load, and the chemicals are biodegradable, meeting both low cost and environmental protection needs.

Description

Technical Field

[0001] This invention relates to hygiene product technology, specifically to a method for preparing biodegradable napkins based on natural plant fibers. Background Technology

[0002] Paper napkins are a common household paper product, mainly used for wiping lips and fingers or cleaning tables during meals. Made from virgin wood pulp, bamboo pulp, and other fiber raw materials, paper napkins are produced using modern papermaking processes, emphasizing softness, absorbency, and durability. Due to increased global public health awareness and the expansion of the food service industry, the consumption of paper napkins has increased significantly, leading to a growing pressure on solid waste disposal. Traditional paper napkins are difficult to degrade, and long-term accumulation can cause soil pollution, water damage, and ecological burden. This has spurred the research and application of biodegradable paper napkins based on environmentally friendly materials and green design concepts. These products can decompose rapidly under natural or composting conditions, ultimately achieving the goals of waste management that reduce volume, recover resources, and render waste harmless.

[0003] Chinese invention patent CN106835815A discloses a napkin made from the following raw materials by weight: 270-300 parts pulp, 12-15 parts cetyl alcohol, 4-7 parts coconut oil derivative, 3-6 parts olive oil, 5-8 parts sodium lauryl ether sulfate, 3-5 parts α-sulfonyl monocarboxylic acid ester, 2-3 parts nano zinc oxide, 2-3 parts graphene oxide, 0.2-0.5 parts soapberry peel extract, and 10-15 parts plant extract. The napkin made by this invention does not contain fragrances or fluorescent agents, has a natural aroma, and has disinfection, antibacterial, and anti-allergic effects. The bleaching agents used are non-toxic and can be rapidly degraded without causing garbage pollution. The pulp mixture results in exceptionally high fiber quality, with a delicate, dense, tough, and skin-friendly texture. It is also wrinkle-free, water-resistant, and tear-resistant.

[0004] While existing napkins achieve a degree of biodegradability during manufacturing, their production involves complex raw materials, including pulp and various synthetic materials. The pulp used is primarily virgin pulp made from extracted fibers from common wood chips. Although the pulp is based on natural sources, wood chip pulp is expensive, and the use of numerous additives further compresses profit margins during large-scale production. Additionally, the coarse fibers in this virgin pulp result in a rough surface on the final napkins, negatively impacting the user experience. Therefore, napkins manufactured using this method are not only expensive but also of low quality, exhibiting significant technological flaws. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing biodegradable napkins based on natural plant fibers, in order to solve the problems that napkins manufactured by existing technologies are not only expensive, but also of low quality and have significant process defects.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing biodegradable napkin paper based on natural plant fibers, comprising the following steps:

[0007] Sisal processing waste and banana stem waste were selected, washed with clean water and crushed to obtain sisal residue segments and banana stem segments. A mixed degumming solution was prepared, and the sisal residue segments and banana stem segments were mixed at a mass ratio of 6:4 and put into the mixed degumming solution for degumming reaction. After washing, pure mixed coarse fiber bundles were obtained.

[0008] After the mixed coarse fiber bundles are configured into a fiber suspension, they are finely ground to form a microfibrillated cellulose colloid with a three-dimensional network structure. The concentration of the microfibrillated cellulose colloid is diluted and cellulase is added to treat it to obtain a compliant microfibrillated cellulose colloid.

[0009] A portion of the softened microfibrillated cellulose colloid was decomposed to prepare long fiber slurry as the matrix slurry. The remaining portion of the softened microfibrillated cellulose colloid was homogenized under high pressure to prepare nanofiber slurry as the reinforcing slurry. The reinforcing slurry was slowly added to the matrix slurry, and additives were added and mixed evenly to obtain a reinforced mixed fiber slurry.

[0010] After diluting the reinforced mixed fiber pulp, it is formed by using an inclined wire machine to form a uniform wet paper sheet. The wet paper sheet is then pressed through a two-roll press to obtain a wet paper sheet with improved dryness.

[0011] After the cross-linking catalyst is evenly sprayed onto the surface of the wet paper with improved dryness, it is dried to obtain the dried and formed base paper, which is then calendered.

[0012] After the raw paper is cut, folded, packaged and sterilized, biodegradable napkins are obtained.

[0013] Preferably, the mixed degumming solution preparation step involves preparing a mixed aqueous solution of sodium hydroxide with a concentration of 1.5 wt% and sodium silicate with a concentration of 0.5 wt%, heating it to 60°C as the base solution, and then adding 50 mg of a compound biological enzyme to each liter of base solution to obtain the mixed degumming solution. The compound biological enzyme is a mixture of pectinase and xylanase in a mass ratio of 3:1.

[0014] Preferably, the degumming solution is used in a material-to-liquid ratio of 1:10. The reaction is carried out in a constant temperature water bath at 60°C with uniform stirring at 120 rpm for 4 hours. After the reaction is completed, the solution is neutralized with dilute acetic acid to pH=7, and then washed with deionized water. The washing is repeated until the water is clear.

[0015] Preferably, the concentration of the fiber suspension is 2 wt%, the fine grinding gap is adjusted to 50 μm, the cyclic grinding is performed 10 times, and the concentration of the microfibrillated cellulose colloid is diluted to 1 wt%.

[0016] Preferably, the cellulase is added at 1% of the dry fiber mass, and the mixture is gently treated at 50°C for 30 minutes. Immediately after treatment, the temperature is raised to 85°C and held for 10 minutes to inactivate the enzyme, resulting in a compliant microfibrillated cellulose colloid.

[0017] Preferably, when preparing the long fiber slurry, the slurry is prepared at 3000 rpm for 5 minutes to fully disperse the softened microfibrillated cellulose colloid and obtain the long fiber slurry as the matrix slurry. When preparing the nanofiber slurry, the softened microfibrillated cellulose colloid is homogenized five times under 50 MPa pressure using a high-pressure homogenizer to obtain the nanofiber slurry as the reinforcing slurry. The mixing ratio of the reinforcing slurry to the matrix slurry is 3:7.

[0018] Preferably, the additive is chitosan comprising 2% of the total dry weight of the fiber and 1.5% of natural plant gum.

[0019] Preferably, the concentration of the reinforced mixed fiber pulp produced by the inclined wire machine is 0.1 wt%, the wire speed of the inclined wire machine is adjusted to 5 m / min, the vacuum dewatering pressure is -0.05 MPa, the working pressure of the double roll press is 0.5 MPa, and the wet paper sheet dryness is 35%.

[0020] Preferably, the drying process is divided into two stages: the first stage uses infrared preheating at 80°C for 60 seconds to activate the hydroxyl groups on the fiber surface; the second stage uses hot air drying at 105°C for 5 minutes.

[0021] Compared with existing technologies, this invention provides a method for preparing biodegradable napkins based on natural plant fibers. By selecting materials with high natural cellulose content, wide availability, and low cost, such as sisal waste residue and banana waste stems, production costs can be reduced. After washing, crushing, and degumming the raw materials, mixed coarse fiber bundles are obtained. Enzymes are used to treat the mixed coarse fiber bundles into softened microfibrillated cellulose colloids. A portion of the softened microfibrillated cellulose colloids is then decomposed to form long fiber pulp as the matrix pulp. Finally, the remaining softened microfibrillated cellulose colloids are subjected to high pressure. After homogenization, short fiber pulp is made as reinforcing pulp. The matrix pulp and reinforcing pulp are mixed to obtain reinforced mixed fiber pulp. After papermaking, drying and calendering, the reinforced mixed fiber pulp can be formed into large sheets of base paper. The raw materials for base paper preparation are inexpensive, which can meet the low-cost requirements of large-scale manufacturing. Moreover, the preparation process incorporates softening treatment of raw fiber, which can reduce fiber rigidity while maintaining the flexibility and strength of napkin paper. It can also significantly improve the softness and feel of napkin paper. The whole process adopts green chemical and biological technologies, with low wastewater pollution load and biodegradable chemicals. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0023] Figure 1 This is a flowchart of the preparation method provided in an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] As attached Figure 1 As shown:

[0026] Example:

[0027] This invention provides a method for preparing biodegradable napkin paper based on natural plant fibers, the steps of which include raw material processing and fiber separation, modification and softening treatment, gradient pulping and reinforcing agent addition, papermaking and forming, catalytic drying and surface treatment, slitting and packaging.

[0028] Raw material processing and fiber separation: Select mold-free sisal processing waste and harvested banana stems, wash them separately with clean water to remove mud, impurities, and soluble substances, obtaining clean sisal residue and clean banana stems. Feed the clean sisal residue and banana stems separately into a cutting machine to cut them into 2-3 cm long segments, obtaining sisal residue segments and banana stem segments to improve crushing efficiency and effect. Prepare a mixed aqueous solution of 1.5 wt% sodium hydroxide and 0.5 wt% sodium silicate, heat it to 60℃ as the base solution, and then add 50 mg of compound biological enzyme per liter of base solution to prepare a mixed degumming solution. The compound bio-enzyme is a mixture of pectinase and xylanase at a mass ratio of 3:1. Sisal residue and banana stem segments are mixed at a mass ratio of 6:4 and added to a mixed degumming solution with a material-to-liquid ratio of 1:10. The mixture is stirred at 120 rpm for 4 hours in a constant temperature water bath at 60℃. After the reaction, the solution is neutralized to pH=7 with dilute acetic acid and then repeatedly washed with deionized water until the water is clear. This process effectively removes impurities such as pectin, lignin, and hemicellulose between fibers, resulting in a pure mixed coarse fiber bundle. Compared with traditional strong alkali high-temperature cooking, this method is milder, consumes less energy, causes less damage to the fibers, and preserves the natural strength of the fibers to obtain a pure mixed coarse fiber bundle.

[0029] In selecting fiber raw materials, in addition to sisal residue and banana stalks, other natural plant fiber materials with low lignin content and high cellulose content can be used, such as wheat straw, rice straw, and bamboo fiber, to enhance the diversity and adaptability of the raw material system. The selected raw materials should prioritize batches that are freshly harvested in the current season and free from significant pest and disease effects to ensure the stability of the initial fiber quality and the final product performance. For example, high-quality wheat straw should have a golden sheen, strong stalks, and no signs of mold or decay. During the pretreatment stage, the washed raw materials can be soaked in clean water for 2–4 hours to complete the hydration pretreatment. This process helps the fiber fully absorb water and swell, softening non-cellulose components and creating more favorable conditions for subsequent processes such as crushing and degumming, thereby improving fiber extraction efficiency and overall process economy.

[0030] Modification and softening treatment: The mixed coarse fiber bundles were prepared into a 2wt% fiber suspension and fed into a disc mill for fine grinding. The grinding gap was adjusted to 50μm, and the milling was repeated 10 times. This process caused the fiber cell walls to peel off, exposing a large number of microfibrils and forming a microfibrillated cellulose colloid with a three-dimensional network structure. The introduction of the microfibrillated cellulose colloid greatly increased the hydrogen bonding points between fibers, which is the key to significantly improving the strength of the final product. The microfibrillated cellulose colloid was diluted to a concentration of 1wt%, and 1% of its dry fiber weight of cellulase was added. The mixture was gently treated at 50°C for 30 minutes. The cellulase acted on the cellulose in the fiber, causing partial hydrolysis and partial destruction of the fiber structure, increasing the specific surface area and porosity of the fiber. Immediately after treatment, the temperature was raised to 85°C and held for 10 minutes to inactivate the enzyme activity, and then rapidly cooled to obtain the softened microfibrillated cellulose colloid. This step reduced the rigidity of the fiber by slightly etching the fiber surface with enzymes, significantly improving the softness and feel of the final product.

[0031] Gradient pulp preparation and reinforcing agent addition: A portion of the softened microfibrillated cellulose colloid is fed into a high-speed de-fibrillator and de-fibrillated at 3000 rpm for 5 minutes to fully disperse it, obtaining a long-fiber pulp as the matrix pulp. The remaining softened microfibrillated cellulose colloid is homogenized five times under 50 MPa pressure using a high-pressure homogenizer to obtain a nanofiber pulp with more uniform particle size and a denser network as the reinforcing pulp. The mixing ratio of the reinforcing pulp to the matrix pulp is 3:7. The reinforcing pulp is slowly added to the matrix pulp, and after uniform stirring and mixing, 2% of the total dry fiber mass of chitosan (dissolved in 1% acetic acid solution) and 1.5% of natural plant gum (xanthan gum) are added. Stirring is continued for 30 minutes to ensure uniform mixing, resulting in a reinforced mixed fiber pulp. Chitosan and xanthan gum are both natural biodegradable polymers. They form a strong physical cross-linking and hydrogen bond network with cellulose molecules, further enhancing the dry and wet strength of the paper and giving the product natural antibacterial properties.

[0032] During the preparation of the matrix pulp, a series of functional additives can be scientifically added according to the performance requirements of the final product. It is recommended to add a softener, such as fatty acid polyethylene glycol ester compounds, at a ratio of 0.2% to 0.5% of the total dry fiber mass. These substances can effectively reduce the coefficient of friction between fibers, significantly improve the feel of the paper, and enhance its softness and skin-friendly comfort. Simultaneously, a retention aid, such as cationic polyacrylamide, at a ratio of 0.05% to 0.1% of the total dry fiber mass can be added. Through charge neutralization and bridging, it significantly improves the retention rate of fillers and fine fibers, reduces material loss, and not only improves paper uniformity but also enhances overall physical strength.

[0033] In addition, mineral fillers, such as calcium carbonate or talc, accounting for 10% to 20% of the total dry fiber mass, can be introduced. The addition of fillers effectively improves the optical properties of paper, including opacity and whiteness, while optimizing surface smoothness and printability, providing a good foundation for subsequent processing. This composite addition strategy enhances product quality while also considering process feasibility and cost-effectiveness.

[0034] Papermaking and forming: The reinforced mixed fiber pulp is diluted to a concentration of 0.1 wt% and papermaking is carried out using an inclined wire machine. The wire speed is adjusted to 5 m / min, and the vacuum dewatering pressure is -0.05 MPa. During this process, the fibers gradually interweave and form a shape under the action of gravity and vacuum suction. Long fibers form a skeleton, and nanofibers fill the gaps to form a uniform wet paper sheet. The basis weight of the wet paper sheet is controlled at 30-50 g / m². The stability and uniformity of the basis weight of the wet paper sheet are ensured by adjusting parameters such as pulp concentration, flow rate, and forming wire speed. The formed wet paper sheet has a certain shape and a preliminary fiber interweaving structure. It has a high water content and needs further dewatering. The wet paper sheet is pressed through a two-roll press under a linear pressure of 0.5 MPa to further remove water, so that the dryness of the wet paper sheet reaches 35%. This also makes the fibers inside the wet paper sheet more tightly bonded, resulting in a wet paper sheet with improved dryness.

[0035] Catalytic Drying and Surface Treatment: A 5% citric acid solution was prepared as a cross-linking catalyst. Using a spray method, 5g of the citric acid solution was evenly sprayed onto the surface of the wet paper sheet, which had already been moistened. The paper sheet was then placed in an infrared-hot air combined drying oven for drying. During the drying process, it was crucial to control the temperature and time to avoid over-drying, which could lead to embrittlement and affect the paper's quality. The dried paper exhibited good strength and flexibility, meeting the basic requirements for napkins. Therefore, the drying process could be divided into two stages: the first stage involved preheating at 80℃ for 60 seconds to activate the hydroxyl groups on the fiber surface; the second stage involved drying with hot air at 105℃ for 5 minutes. Under the catalysis of citric acid, esterification and cross-linking reactions occur between fibers, forming strong chemical bonds to obtain dried and formed base paper. This low-temperature catalytic cross-linking technology avoids the damage to fibers caused by high temperatures, is environmentally friendly and non-toxic, and greatly improves the physical strength of the paper, especially its wet strength. The dried and formed base paper is then calendered in a soft calender at a temperature of 60℃ and a linear pressure of 50kN / m, with a calendering speed of 100-150 m / min. Calendering makes the paper surface smoother and more even, improving its gloss and printability, resulting in a smooth surface and a soft feel, thus obtaining the final napkin base paper.

[0036] Slitting and Packaging: In the slitting and packaging section, the dried and calendered raw paper rolls are placed on a fully automatic high-speed slitting machine and cut into paper widths of predetermined widths using precision circular cutters according to product specifications. Subsequently, a folding device precisely folds and counts the paper widths according to specific stack numbers (e.g., two or three layers) and folding methods (e.g., Z-fold or roll). The folded tissues are then fed into pre-sterilized packaging materials via an automatic packaging machine, typically using biodegradable polyethylene (PE) film or all-plant-based polylactic acid (PLA) composite materials for sealing, ensuring hygiene and extending shelf life. Finally, the packaged product undergoes thorough sterilization using low-temperature ethylene oxide gas or ultraviolet irradiation to kill any potential microorganisms, resulting in a safe, hygienic, and compliant biodegradable napkin. This section achieves the transformation from semi-finished product to a high-quality final product ready for direct market sale, emphasizing efficiency, hygiene, and packaging sustainability throughout the process.

[0037] This invention provides a method for preparing biodegradable napkins based on natural plant fibers, which has significant advantages in raw material selection. The method uses agricultural byproducts such as sisal waste and banana stalks as the main raw materials. These natural cellulose raw materials are widely available, inexpensive, and represent waste resource utilization, effectively reducing production costs and aligning with the concepts of circular economy and sustainable development. In the pretreatment stage, through systematic cleaning, crushing, and bio-chemical synergistic degumming of the raw materials, impurities are efficiently removed while preserving the fiber structure, ultimately yielding pure mixed coarse fiber bundles, laying the foundation for subsequent fiber refinement.

[0038] In the fiber modification stage, enzyme treatment technology was used to biologically soften and microfibrilize the mixed coarse fiber bundles, successfully preparing a softened microfibrilated cellulose colloid. This process is mild, causes minimal fiber damage, and significantly improves fiber softness and paper feel. Further, through a grading strategy, a portion of the colloid was decomposed to form a long-fiber matrix pulp, imparting a skeletal structure to the paper; the remaining portion was used to prepare a short nanofiber reinforcing pulp using high-pressure homogenization technology, enhancing inter-fiber bonding and overall strength. The resulting reinforced mixed fiber pulp combines excellent mechanical properties with softness.

[0039] After papermaking, catalytic drying, and soft calendering, the pulp can be formed into large-format base paper with excellent physical properties. The entire process route is rationally designed, with high raw material utilization, fully meeting the cost control requirements of large-scale production. Most importantly, by integrating bio-softening treatment into the process, fiber rigidity is effectively reduced, allowing the final product to maintain good flexibility and strength while significantly improving user comfort and softness.

[0040] Furthermore, the entire process adheres to the concept of green manufacturing, mainly using bio-enzyme treatment and biodegradable natural additives. The wastewater pollution load is low, the chemicals are environmentally friendly, and the overall process is clean and efficient, possessing good potential for industrial application and environmental benefits.

[0041] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing biodegradable napkins based on natural plant fibers, characterized in that the steps include... include: Sisal processing waste and banana stem waste were selected, rinsed with water, and crushed to obtain sisal residue segments and banana stem segments. A mixed degumming solution was prepared, and the sisal residue segments and banana stem segments were mixed at a mass ratio of 6:4 and put into the mixed degumming solution for degumming reaction. After washing, pure mixed coarse fiber bundles were obtained. The mixed degumming solution was prepared by preparing a mixed aqueous solution of 1.5wt% sodium hydroxide and 0.5wt% sodium silicate, heating it to 60°C as the treatment base solution, and then adding 50mg of compound biological enzyme per liter of base solution to prepare the mixed degumming solution. The compound biological enzyme is a mixture of pectinase and xylanase at a mass ratio of 3:

1. After the mixed coarse fiber bundles are configured into a fiber suspension, they are finely ground to form a microfibrillated cellulose colloid with a three-dimensional network structure. The concentration of the microfibrillated cellulose colloid is diluted and cellulase is added to treat it to obtain a compliant microfibrillated cellulose colloid. A portion of the softened microfibrillated cellulose colloid was decomposed to prepare long fiber slurry as the matrix slurry. The remaining portion of the softened microfibrillated cellulose colloid was homogenized under high pressure to prepare nanofiber slurry as the reinforcing slurry. The reinforcing slurry was slowly added to the matrix slurry, and additives were added and mixed evenly to obtain a reinforced mixed fiber slurry. After diluting the reinforced mixed fiber pulp, it is formed by using an inclined wire machine to form a uniform wet paper sheet. The wet paper sheet is then pressed through a two-roll press to obtain a wet paper sheet with improved dryness. After the cross-linking catalyst is evenly sprayed onto the surface of the wet paper with improved dryness, it is dried to obtain the dried and shaped base paper, which is then calendered. The drying process is divided into two stages: the first stage uses infrared preheating at 80℃ for 60 seconds to activate the hydroxyl groups on the fiber surface; the second stage uses hot air drying at 105℃ for 5 minutes. After the raw paper is cut, folded, packaged and sterilized, biodegradable napkins are obtained.

2. The method for preparing biodegradable napkins based on natural plant fibers according to claim 1, characterized in that, The degumming solution is used in a material-to-liquid ratio of 1:

10. The reaction is carried out in a constant temperature water bath at 60℃ with uniform stirring at 120 rpm for 4 hours. After the reaction is completed, it is neutralized with dilute acetic acid to pH=7, and then washed with deionized water. The washing is repeated until the water is clear.

3. The method for preparing biodegradable napkins based on natural plant fibers according to claim 1, characterized in that, The concentration of the fiber suspension is 2 wt%, the fine grinding gap is adjusted to 50 μm, and the cyclic grinding is performed 10 times to dilute the concentration of the microfibrillated cellulose colloid to 1 wt%.

4. The method for preparing biodegradable napkins based on natural plant fibers according to claim 1, characterized in that, Cellulase was added at a ratio of 1% of the dry fiber mass, and the mixture was gently treated at 50°C for 30 minutes. Immediately after treatment, the temperature was raised to 85°C and maintained for 10 minutes to inactivate the enzyme, resulting in a compliant microfibrillated cellulose colloid.

5. The method for preparing biodegradable napkins based on natural plant fibers according to claim 1, characterized in that, When preparing the long fiber slurry, the slurry is prepared at 3000 rpm for 5 minutes to fully disperse the softened microfibrillated cellulose colloid and obtain the long fiber slurry as the matrix slurry. When preparing the nanofiber slurry, the softened microfibrillated cellulose colloid is homogenized five times under 50 MPa pressure using a high-pressure homogenizer to obtain the nanofiber slurry as the reinforcing slurry. The mixing ratio of the reinforcing slurry to the matrix slurry is 3:

7.

6. The method for preparing biodegradable napkins based on natural plant fibers according to claim 1, characterized in that, The additives consist of chitosan comprising 2% of the total dry fiber mass and 1.5% of natural plant gum.

7. The method for preparing biodegradable napkins based on natural plant fibers according to claim 1, characterized in that, The concentration of the reinforced mixed fiber pulp produced by the inclined wire machine is 0.1wt%. The wire speed of the inclined wire machine is adjusted to 5m / min, the vacuum dewatering pressure is -0.05MPa, the working pressure of the double roll press is 0.5MPa, and the wet sheet dryness is 35%.

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