Kenaf bark paper, kenaf bark fiber pulp and green pulping method thereof

Abstract

The invention relates to the technical field of pulping and papermaking, in particular to hibiscus cannabinus bark paper, hibiscus cannabinus bark fiber pulp and a green pulping method of the hibiscus cannabinus bark paper. A green pulping method of hibiscus cannabinus bark fiber pulp comprises the following steps: mixing a hibiscus cannabinus bark fiber raw material with a cooking solvent A, and cooking to obtain a solid-liquid mixture; carrying out solid-liquid separation on the obtained solid-liquid mixture, and washing the obtained solid to obtain kenaf peel fiber pulp; the cooking solvent A comprises choline chloride, organic polar small molecules and water; the mass ratio of choline chloride to organic polar small molecules to deionized water in the cooking solvent A is 1: (2-4): (1.97-5.92). The process flow is simple, the reaction conditions are mild, the hibiscus cannabinus pulp can be obtained at the temperature of 80-100 DEG C, and the maximum pulp yield can reach 93.3%. The tensile index of the obtained paper sheet can be up to 49.08 N.m / g, and the tearing index can be up to 12.11 mN.m < 2 > / g.

Description

Technical Field

[0001] This invention relates to the field of pulp and paper technology, and more specifically, to a kenaf paper, kenaf fiber pulp, and a green pulping method thereof. Background Technology

[0002] kenaf is a renewable, high-fiber non-timber biomass resource with significant advantages such as short growth cycle, strong adaptability, and low planting cost. Its bast (kenaf bark) is rich in cellulose fiber, making it an ideal raw material for pulp and paper making, bio-based composite materials, textile raw materials, and other fields. It has important application value in replacing timber resources and alleviating environmental pressure.

[0003] In existing kenaf pulping processes, the alkaline pulping method remains a common route. The alkaline method (caustic soda method, sulfate method) uses strongly alkaline reagents (such as sodium hydroxide and sodium sulfide) under high temperature and pressure (150~180℃, 0.6~1.0MPa) to degrade lignin and hemicellulose in kenaf bark, achieving fiber separation. Although the alkali recovery process is relatively mature and can recover some alkaline reagents, it still faces challenges such as high investment in alkali recovery equipment, high environmental protection costs, and difficulty for small and medium-sized enterprises to adapt.

[0004] Existing kenaf pulping processes have developed various technical routes, including solvent pretreatment, bio-enzyme treatment, and mechanical / physical assistance. Among these, pretreatment methods based on hydrogen-bonded network solvent systems have attracted attention due to their good environmental friendliness and recyclability potential. However, in practical applications of kenaf raw materials and solvent systems during pulping, these methods may encounter issues such as limited mass transfer, affecting the synergistic removal of non-cellulose components and fiber swelling and dissociation, thus increasing energy consumption and post-processing burden.

[0005] CN117166276A discloses a method for preparing biomechanical pulp from kenaf using a ternary eutectic solvent-assisted bio-enzyme treatment. This method requires bio-enzyme assistance, which increases cost and process complexity. The pretreatment involves high temperature (100-150℃) and a high liquid-to-liquid ratio (1:10), and the process includes multi-stage grinding, resulting in high energy consumption and environmental costs.

[0006] CN119507255A discloses a method for preparing kenaf whole-stalk APMP pulp, which requires the use of various chemical reagents such as NaOH, H2O2, DTPA, MgSO4 and ionic liquids, resulting in a high risk of pollution. The method includes multiple steps such as pre-steaming, extrusion and decomposition, pre-impregnation (ultrasonic), first-stage pulping and bleaching, second-stage pulping and bleaching, and multiple centrifugal dewatering, resulting in high energy consumption and equipment investment.

[0007] CN114086414A discloses a lignocellulose pulping method based on an acidic eutectic solvent, using benzyltriethylammonium chloride and formic acid as the solvent. Formic acid is a strong acid, requiring extremely high corrosion resistance from the reaction equipment, necessitating specialized anti-corrosion equipment and significantly increasing equipment purchase and maintenance costs. The cooking temperature is 120-140℃, and the liquor ratio is 1:10~1:20, greatly increasing solvent raw material consumption costs. Furthermore, the load on subsequent solid-liquid separation and solvent recovery doubles, further pushing up operating costs. Therefore, researching a simple, high-yield, low-energy-consumption, mild, and economical pulping technology suitable for kenaf fiber raw materials is essential. How to achieve both high pulping yield and stable improvement in the overall mechanical properties of paper under relatively mild and low-resource-consumption conditions remains a pressing technical problem to be solved. Summary of the Invention

[0008] To overcome the deficiencies of the prior art, the present invention provides a green pulping method for kenaf fiber pulp.

[0009] The present invention also provides a kenaf fiber pulp.

[0010] The present invention also provides a type of red hemp paper.

[0011] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A green pulping method for kenaf fiber pulp includes the following steps: (1) Mix the kenaf fiber raw material with cooking solvent A and cook to obtain a solid-liquid mixture; (2) Separate the solid and liquid mixture obtained from the solid and liquid, and wash the obtained solid to obtain kenaf fiber pulp; The cooking solvent A comprises choline chloride, small organic polar molecules, and water; the molar ratio of choline chloride: small organic polar molecules: deionized water in the cooking solvent A is 1:(2~4):(1.97~5.92). The organic polar small molecules include one of urea, acetic acid, and lactic acid.

[0012] Preferably, the molar ratio of choline chloride: organic polar small molecules: deionized water in the cooking solvent A is 1: (2~4): (1.97~3.94).

[0013] Preferably, the organic polar small molecule includes one of urea and acetic acid.

[0014] Preferably, the mass ratio of the kenaf fiber raw material to the cooking solvent A is 1:(3~5.5).

[0015] Preferably, the mass ratio of the kenaf fiber raw material to the cooking solvent A is 1:(4.8~5.2).

[0016] Preferably, the method for preparing the cooking solvent A includes mixing choline chloride, small organic polar molecules, and deionized water to form a transparent and homogeneous solution, thereby obtaining cooking solvent A.

[0017] Preferably, the length of the kenaf fiber raw material is 3-5 cm.

[0018] Preferably, the cooking temperature is 80~100 ℃.

[0019] Preferably, the cooking process includes heating and holding, with the heating time being 0.8 to 1.2 hours and the holding time being 1 to 2 hours.

[0020] Preferably, the cooking process includes heating and holding the temperature, with the heating temperature reaching 80~100℃ and the holding temperature being 80~100℃.

[0021] Preferably, the cooking process includes heating and holding the temperature, with the heating temperature reaching 80-90°C and the holding temperature remaining at 80-90°C.

[0022] Preferably, the washing in step (2) includes rinsing with deionized water or ethanol, rinsing 3 to 5 times, with each rinse using 8 to 10 times the mass of the solid product, until the pH of the washing solution is 6.8 to 7.2.

[0023] A kenaf fiber pulp is prepared by the preparation method described in this invention.

[0024] A type of sesame bark paper is made by pulping sesame bark fiber pulp and then papermaking.

[0025] Preferably, the pulping includes pulping using a PFI refiner, with a pulping pressure of 3~4 N / mm and a grinding disc rotation speed of 1300~1500 r / min.

[0026] Preferably, the beating degree of the pulp is 29.5°SR~30.5°SR.

[0027] In this invention, a cooking solvent system containing choline chloride, small organic polar molecules, and water is used. This system can form a stable hydrogen bond network, exhibiting a controllable removal effect on lignin and hemicellulose. It has advantages such as simple preparation, recyclability, reusability, and biocompatibility, which meet the characteristics of a green solvent and can reduce the environmental burden caused by the pulping process and waste liquid.

[0028] In this invention, there is no need to pre-treat the sesame bark raw material, the process is simple, the reaction conditions are mild, only low temperature (80~100℃) and short reaction time (heating for 1 hour and holding for 2 hours) are required, which significantly reduces energy consumption and has good industrial adaptability.

[0029] The process of this invention is simple and does not require additional steps such as biological enzyme treatment or ultrasonic / microwave assistance. This method directly involves pulping and grinding, which greatly shortens the process and reduces equipment investment and process complexity.

[0030] In this invention, the kenaf pulp prepared has minimal damage to the kenaf bark fibers, largely preserving the original morphology of the fibers. This fully leverages the raw material advantages of long kenaf bark fibers and contributes to the improvement of the mechanical properties of fiber-based materials.

[0031] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: The process of this invention is simple and the reaction conditions are mild. Red hemp pulp can be obtained by heating at 80~100℃, and the pulp yield can reach up to 93.3%. The cooking solvent used is easy to prepare and has the characteristics of being recyclable and reusable, which helps to reduce solvent consumption and waste liquid treatment burden.

[0032] The technical solution of this invention minimizes damage to kenaf fibers, preserving their original morphology to a greater extent and fully leveraging the advantages of long kenaf fibers, thereby contributing to improved paper mechanical properties. Results show that the resulting paper achieves a tensile index of up to 49.08 N·m / g and a tear index of up to 12.11 mN·m. 2 / g, with a bursting index up to 2.50 kPa·m 2 / g. Attached Figure Description

[0033] Figure 1 The images are scanning electron microscope (SEM) data. (a) is a scanning electron microscope image of the original kenaf bark fiber, and (b) is a scanning electron microscope image of the pulp fiber in Example 1. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0035] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0036] A green pulping method for kenaf fiber pulp includes the following steps: (1) Mix the kenaf fiber raw material with cooking solvent A and cook to obtain a solid-liquid mixture; (2) Separate the solid and liquid mixture obtained from the solid and liquid, and wash the obtained solid to obtain kenaf fiber pulp; The cooking solvent A comprises choline chloride, small organic polar molecules, and water; the molar ratio of choline chloride: small organic polar molecules: deionized water in the cooking solvent A is 1:(2~4):(1.97~5.92). The organic polar small molecules include one of urea, acetic acid, and lactic acid.

[0037] In a preferred embodiment, the molar ratio of choline chloride: small organic polar molecules: deionized water in the cooking solvent A is 1:(2~4):(1.97~3.94).

[0038] In one preferred embodiment, the organic polar small molecule includes one of urea and acetic acid.

[0039] In one preferred embodiment, the mass ratio of the kenaf fiber raw material to the cooking solvent A is 1:(3~5.5).

[0040] In a preferred embodiment, the mass ratio of the kenaf fiber raw material to the cooking solvent A is 1:(4.8~5.2).

[0041] In one preferred embodiment, the method for preparing the cooking solvent A includes mixing choline chloride, small organic polar molecules, and deionized water to form a transparent and homogeneous solution, thereby obtaining cooking solvent A.

[0042] In one preferred embodiment, the length of the kenaf fiber raw material is 3-5 cm.

[0043] In one preferred embodiment, the cooking temperature is 80~100℃.

[0044] In one preferred embodiment, the cooking process includes heating and holding the temperature, with the heating time being 0.8 to 1.2 hours and the holding time being 1 to 2 hours.

[0045] In one preferred embodiment, the cooking process includes heating and holding the temperature, with the heating temperature reaching 80-100°C and the holding temperature being 80-100°C.

[0046] In one preferred embodiment, the cooking process includes heating and holding the temperature, with the heating temperature reaching 80-90°C and the holding temperature remaining at 80-90°C.

[0047] In one preferred embodiment, the ambient temperature is 15℃~40℃.

[0048] In a preferred embodiment, the washing in step (2) includes rinsing with deionized water or ethanol, rinsing 3 to 5 times, with the amount of water used for each rinse being 8 to 10 times the mass of the solid product, until the pH value of the washing solution is 6.8 to 7.2.

[0049] A kenaf fiber pulp is prepared by the preparation method described in this invention.

[0050] A type of sesame bark paper is made by pulping sesame bark fiber pulp and then papermaking.

[0051] In one preferred embodiment, the pulping includes pulping using a PFI refiner, with a pulping pressure of 3~4 N / mm and a grinding disc rotation speed of 1300~1500 r / min.

[0052] In a preferred embodiment, the pulping degree is 29.5°SR~30.5°SR.

[0053] In a preferred embodiment, the main components of the kenaf fiber raw material are: cellulose content of 52%~54% by mass, hemicellulose content of 15%~16% by mass, lignin content of 15%~16% by mass, and benzene alcohol extract content of 7%~8% by mass.

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0055] The kenaf fiber raw material used in the following examples has a sheet length of 3-5 cm (the length of the kenaf fiber raw material is 3-5 cm). The kenaf fiber raw material contains 53.6% cellulose, 15.7% hemicellulose, 15.7% lignin, and 7.49% benzene extract.

[0056] Example 1 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:3:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (42.5 g dry weight).

[0057] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total system weight to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The PFI beating speed is set to 1400r / min, the linear pressure is set to 3.33N / mm, and the initial grinding disc gap is set to 0.35mm, which is gradually reduced to 0.25mm during the beating process. The resulting pulp is used to make paper with a basis weight of 70g / m³. 2 Papermaking was performed using a Kaiser process automated papermaking system (according to ISO 5289 / 2 and DIN 54358 standards). The wet paper sheets were transferred to a drying unit and dried at 90°C and -0.1 MPa for 10 minutes. The dried paper sheets were then calendered at a pressure of 0.6 MPa, six times on each side. The resulting paper sheets had a tensile index of 49.08 N·m / g and a tear index of 12.11 mN·m. 2 / g, with a bursting index of 2.50 kPa·m 2 / g.

[0058] Example 2 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:3:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a clear and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 1 hour to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (45.2 g dry weight).

[0059] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 45.46 N·m / g and a tear index of 8.70 mN·m. 2 / g, with a bursting index of 1.98 kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0060] Example 3 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:3:5.92 and stirred at 500 rpm for 20 minutes at 80°C to form a clear and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (43.2 g dry weight).

[0061] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 44.55 N·m / g and a tear index of 8.92 mN·m. 2 / g, with a bursting index of 2.03 kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0062] Example 4 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:3:3.94 and stirred at 500 rpm for 20 minutes at 80°C to form a clear and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (42.9 g dry weight).

[0063] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 46.38 N·m / g and a tear index of 10.79 mN·m. 2 / g, with a bursting index of 2.37kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0064] Example 5 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:2:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a clear and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (42.8 g dry weight).

[0065] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 48.69 N·m / g and a tear index of 11.85 mN·m. 2 / g, with a bursting index of 2.50 kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0066] Example 6 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:4:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (42.1 g dry weight).

[0067] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 48.89 N·m / g and a tear index of 11.98 mN·m. 2 / g, with a bursting index of 2.47 kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0068] Example 7 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:3:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 80°C in 1 hour, and then maintained at 80°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (46.5 g dry weight).

[0069] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 41.05 N·m / g and a tear index of 9.03 mN·m. 2 / g, with a bursting index of 1.99kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0070] Example 8 A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, urea, and deionized water were mixed in a molar ratio of 1:3:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 100°C in 1 hour, and then maintained at 100°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (36.1 g dry weight).

[0071] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 40.80 N·m / g and a tear index of 8.99 mN·m. 2 / g, with a bursting index of 2.03 kPa·m 2 / g. The pulping conditions and papermaking process in this embodiment are the same as in Example 1.

[0072] Example 9 This embodiment is similar to Embodiment 1, except that lactic acid is used instead of urea in the cooking solvent A.

[0073] A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, lactic acid, and deionized water were mixed in a molar ratio of 1:3:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp.

[0074] The pulping conditions and papermaking process in this embodiment are the same as in Embodiment 1.

[0075] Example 10 This embodiment is similar to Embodiment 1, except that acetic acid is used instead of urea in the cooking solvent A.

[0076] A green pulping method for kenaf fiber pulp includes the following steps: Choline chloride, acetic acid, and deionized water were mixed in a molar ratio of 1:3:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp.

[0077] The pulping conditions and papermaking process in this embodiment are the same as in Embodiment 1.

[0078] Comparative Example 1 This comparative example is similar to Example 1, except that no water is added.

[0079] A method for preparing kenaf fiber pulp includes the following steps: Choline chloride and urea were mixed in a molar ratio of 1:3 and stirred at 500 rpm for 20 minutes at 80°C to form a clear and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8–7.2) to obtain kenaf fiber pulp (43.3 g dry weight).

[0080] Take 30g of oven-dried, fiber-rich kenaf fiber pulp and add deionized water to adjust the total weight of the system to 300g, i.e., adjust the pulp consistency to 10%, and then perform PFI beating to 30°SR. The resulting pulp is used to make paper, and the resulting paper has a tensile index of 39.88 N·m / g and a tear index of 9.23 mN·m. 2 / g, with a bursting index of 1.65kPa·m 2 / g. The pulping conditions and papermaking process for this comparative example are the same as in Example 1.

[0081] Comparative Example 2 Choline chloride and deionized water were mixed at a molar ratio of 1:1.97 and stirred at 500 rpm for 20 minutes at 80°C to form a transparent and homogeneous solution, yielding cooking solvent A. 50.0 g of oven-dried kenaf fiber raw material and 250.0 g of cooking solvent A were weighed and added to a rotary multi-tank digester. The temperature was increased from room temperature (25°C) to 90°C in 1 hour, and then maintained at 90°C for 2 hours to obtain a solid-liquid mixture. After filtration, the solid was thoroughly washed until neutral (pH 6.8~7.2) to obtain kenaf fiber pulp (47.6 g dry weight). The pulp quality was poor, making performance testing impossible. The pulping conditions and papermaking process for this comparative example were the same as in Example 1.

[0082] Comparative Example 3 This comparative example uses the conventional caustic soda method to pulp dried kenaf fiber raw materials (using 12% alkali and 0.1% anthraquinone). The mass ratio of dried kenaf fiber raw materials to cooking reagent is 1:5. The cooking temperature conditions are: heating from room temperature (25℃) to 140℃ for 1 hour, and then holding at 140℃ for 2 hours to obtain alkali-processed kenaf fiber pulp. The pulping yield was only 56.6% when tested.

[0083] Analysis and Testing The determination of pulp freeness refers to GB / T 3332-2004, the tensile strength of paper refers to GB / T 22898-2008, the bursting strength of paper refers to GB / T 454-2020, and the tear strength of paper refers to ISO 1974:2012.

[0084] The test results are shown in Table 1 below: Table 1. Paper data obtained from the examples and comparative examples.

[0085] Table 2. Chemical composition data of raw materials, examples, and comparative slurries

[0086] Results analysis: As can be seen from the results of Examples 1-10, using the technical solution of the present invention, the pulp yield can reach a maximum of 93.3% (Example 10), the tensile index of the resulting paper can reach a maximum of 49.08 N·m / g, and the tear index can reach a maximum of 12.11 mN·m. 2 / g, with a bursting index up to 2.50 kPa·m 2 / g.

[0087] The cooking solvent system of this invention directly uses kenaf bark raw material for one-step pulping to obtain pulp. During the cooking process, it maintains good wetting penetration and mass transfer efficiency, thus alleviating the mass transfer limitation problem that easily occurs in traditional solvent systems. Based on this, this invention achieves controlled (moderate) removal of non-cellulose components from kenaf bark, avoiding both insufficient removal leading to impurity residue affecting fiber bonding and over-treatment causing fiber damage. This allows for a simultaneous balance between pulp yield and the comprehensive mechanical properties of the paper, such as tensile strength, tear strength, and burst strength. Simultaneously, because the effective action of the solvent system can be achieved under relatively mild conditions, this invention further reduces the cooking temperature while ensuring the treatment effect, thereby reducing energy consumption and improving the feasibility and stability of the process.

[0088] Compared to Example 1, Example 2 reduced the heat preservation time by one hour, and the pulp yield increased to 90.4%. However, the tensile index and tear index of the pulp decreased to 45.46 N·m / g and 8.70 mN·m, respectively. 2 / g, the mechanical properties showed a significant decrease. The reason is that when the heat preservation time is insufficient, the cooking solvent does not fully dissolve and remove lignin and hemicellulose from the kenaf bark, and the residual impurities hinder the bonding between fibers, resulting in a decrease in paper strength.

[0089] Compared to Example 1, Examples 3 and 4 increased the water content in cooking solvent A. When the molar ratio of water increased, the yield improved slightly, but the physical properties of the resulting pulp decreased significantly. This indicates that excessive water dilutes the cooking solvent, reduces the targeted removal effect of lignin or hemicellulose, and thus weakens the interfiber bonding force and paper strength.

[0090] Compared to Example 1, Examples 5 and 6 changed the proportion of urea components in the cooking solvent A and adjusted the urea molar ratio. Although the yield and performance remained at a high level, they were slightly lower than those of Example 1. This indicates that a choline chloride:urea ratio of 1:3 is more conducive to balancing the swelling and penetration of the solvent on the fiber with the targeted removal of lignin or hemicellulose. Compared to Example 1, Examples 7 and 8 differed in that the heat preservation temperature was changed. Example 7 achieved a yield of 93.0% and a tensile index of 41.05 N·m / g. However, the low temperature resulted in insufficient solvent activity, low lignin or hemicellulose removal rates, and residual components that affected paper strength. In Example 8, the yield decreased to 72.2%, and the pulp performance declined simultaneously. This was due to the excessively high temperature causing partial cellulose degradation and damage to the fiber structure, leading to a decrease in both yield and performance. The results of Example 1 and Comparative Examples 1 and 3 show that the yield of Comparative Example 1 is 86.6%, while the yield of conventional alkaline pulping is only 56.6%, and the tensile index of the resulting paper is only 39.88 N·m / g, which is much lower than that of Example 1. The addition of deionized water can adjust the solvent viscosity and improve the uniformity of fiber swelling, and is a key component to ensure the performance of the pulp.

[0091] Comparative Example 2 had a yield of 95.2%, but the paper strength was extremely poor, making it impossible to achieve high-quality pulping.

[0092] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A green pulping method for kenaf fiber pulp, characterized in that, Includes the following steps: (1) Mix the kenaf fiber raw material with cooking solvent A and cook to obtain a solid-liquid mixture; (2) Separate the solid and liquid mixture obtained from the solid and liquid, and wash the obtained solid to obtain sesame fiber pulp; The cooking solvent A comprises choline chloride, small organic polar molecules, and water; the molar ratio of choline chloride: small organic polar molecules: deionized water in the cooking solvent A is 1:(2~4):(1.97~5.92). The organic polar small molecules include one of urea, acetic acid, and lactic acid.

2. The green pulping method for kenaf fiber pulp according to claim 1, characterized in that, The molar ratio of choline chloride, organic polar small molecules, and deionized water in the cooking solvent A is 1:(2~4):(1.97~3.94).

3. The green pulping method for kenaf fiber pulp according to claim 1, characterized in that, The organic polar small molecules include one of urea and acetic acid.

4. The green pulping method for kenaf fiber pulp according to claim 1, characterized in that, The mass ratio of the kenaf fiber raw material to the cooking solvent A is 1:(3~5.5).

5. The green pulping method for kenaf fiber pulp according to claim 1, characterized in that, The cooking temperature is 80~100℃.

6. The green pulping method for kenaf fiber pulp according to claim 1, characterized in that, The cooking process includes heating and holding, with the heating time being 0.8 to 1.2 hours and the holding time being 1 to 2 hours.

7. A kenaf fiber pulp, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. A type of red hemp paper, characterized in that, Paper is made from the sesame fiber pulp described in claim 7 after pulping.

9. The red hemp paper according to claim 8, characterized in that, The pulping process includes pulping using a PFI pulper, with a pulping pressure of 3~4 N / mm and a pulping disc rotation speed of 1300~1500 r / min.

10. The red hemp paper according to claim 8, characterized in that, The beating degree of the pulp is 29.5°SR~30.5°SR.

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