A papermaking pulp drainage agent, its preparation method and application

Abstract

The application relates to the technical field of water filtering agents, and provides a papermaking pulp water filtering agent and a preparation method and application thereof, raw materials of the papermaking pulp water filtering agent are prepared in weight parts, and the raw materials include 30-45 parts of acrylamide, 8-14 parts of active hydroxyl crosslinking monomers, 6-10 parts of methacryloyloxyethyl trimethyl ammonium chloride, 4-8 parts of N-vinyl pyrrolidone, 0.2-0.5 parts of ammonium persulfate, 0.1-0.4 parts of sodium bisulfite, 4-6 parts of glyoxal aqueous solution, 0.5-1.5 parts of a buffer stabilizer, 0.5-1.1 parts of sodium hypophosphite, 1.5-4.5 parts of core-shell structure polydopamine coated silica microspheres, 2-5 parts of benzene boronic acid functionalized oxidized glucomannan and 50-70 parts of deionized water. The components in the application have a synergistic effect, so that the prepared papermaking pulp water filtering agent can improve the pulp water filtering efficiency and guarantee the stability of the physical strength of paper.

Description

Technical Field

[0001] This invention relates to the field of filter agent technology, specifically to a paper pulp filter agent, its preparation method, and its application. Background Technology

[0002] In the pulp dewatering section of the paper industry, the performance of the filter agent directly affects production efficiency and the quality of the finished paper. Currently, most mainstream paper pulp filter agents are cationic polyacrylamide polymers and their modified products. These filter agents achieve flocculation of cellulose fibers and fine fillers in the pulp through the electrostatic adsorption of cationic monomers, thereby increasing the floc particle size, reducing water retention space, and improving the filtration rate. To further optimize the filtration effect and retention performance, existing technologies often introduce crosslinking monomers to construct a polymer network structure or compound inorganic powder materials to enhance the support of the floc skeleton, thereby improving the binding ability of the filter agent to the fibers.

[0003] However, existing filter agents still have significant drawbacks in practical applications: On the one hand, although conventional filter agents can improve filtration efficiency, the bonding between polymer chains and fibers and fillers relies mainly on single electrostatic adsorption or hydrogen bonding, resulting in insufficient bonding strength. This makes it easy for flocs to dissociate during subsequent papermaking processes, leading to a decrease in paper uniformity and damage to physical strength. On the other hand, metal ions, which are prevalent in paper pulp systems, are prone to non-specific binding with the active groups of filter agents, damaging the molecular configuration and action sites of the polymer, reducing the stability and long-term effectiveness of the filter agents, and making it difficult to simultaneously meet the dual requirements of improving pulp filtration efficiency and maintaining paper physical strength. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides a paper pulp filtration agent, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention discloses a paper pulp filtration agent, which, by weight, comprises the following raw materials: 30-45 parts acrylamide, 8-14 parts active hydroxyl crosslinking monomer, 6-10 parts methacryloyloxyethyltrimethylammonium chloride, 4-8 parts N-vinylpyrrolidone, 0.2-0.5 parts ammonium persulfate, 0.1-0.4 parts sodium bisulfite, 4-6 parts glyoxal aqueous solution, 0.5-1.5 parts buffer stabilizer, 0.5-1.1 parts sodium hypophosphite, 1.5-4.5 parts core-shell structured polydopamine-coated silica microspheres, 2-5 parts phenylboronic acid-functionalized oxidized glucomannan, and 50-70 parts deionized water.

[0007] Using the above technical solution, acrylamide serves as the core skeleton monomer, providing the basic long-chain polymer structure for the filter agent; the active hydroxyl crosslinking monomer introduces hydroxyl groups into the polymer chain, which can participate in subsequent crosslinking reactions and form hydrogen bonds with fibers; methacryloyloxyethyltrimethylammonium chloride, as a cationic monomer, can be adsorbed onto the surface of negatively charged cellulose fibers and fine materials through electrostatic interactions, improving retention; the carbonyl oxygen atom on the pyrrolidone ring of N-vinylpyrrolidone can undergo coordination reactions with metal ions in the slurry to form stable complexes, preventing metal ions from binding with the polymer's active groups and reducing the interference of metal ions on polymer performance; ammonium persulfate and sodium bisulfite form a redox initiation system, which initiates the process by generating free radicals. Monomers undergo free radical polymerization to form a polymer matrix; glyoxal aqueous solution reacts with hydroxyl groups on the polymer chains under acidic conditions to form an acetal crosslinking reaction, constructing a three-dimensional network structure; buffer stabilizers maintain pH stability in the glyoxal-polymer hydroxyl crosslinking system, ensuring the orderly progress of the crosslinking reaction; sodium hypophosphite, as a molecular weight regulator, can control the polymer molecular weight through chain transfer, preventing polymer gelation; the silica core of core-shell polydopamine-coated silica microspheres provides support in the fiber network, while the polydopamine shell enhances the bonding ability between the microspheres and the fibers and polymers; phenylboronic acid-functionalized oxidized glucomannan forms dynamic bonds with hydroxyl groups on the polymer and fiber surfaces through borate ester bonds. The synergistic effect of these components enables the prepared paper pulp filtration agent to improve pulp filtration efficiency while ensuring stable paper physical strength.

[0008] Preferably, the active hydroxyl crosslinking monomer is one of N-(hydroxymethyl)acrylamide or N-hydroxyethylacrylamide; the mass fraction of the glyoxal aqueous solution is 36%-40%; and the buffer stabilizer is a 0.3-0.5 mol / L sodium bicarbonate solution.

[0009] Using the above technical solution, N-(hydroxymethyl)acrylamide or N-hydroxyethylacrylamide, as active hydroxyl crosslinking monomers, can introduce hydroxyl groups into the polymer chain, providing sites for subsequent crosslinking reactions with glyoxal aqueous solution. Simultaneously, it can form hydrogen bonds with cellulose fibers, improving the bonding effect between the filter agent and the fiber. A 36%-40% glyoxal aqueous solution can undergo an acetal reaction with the aforementioned hydroxyl groups to form a crosslinked structure, enhancing the structural strength of the polymer network. A 0.3-0.5 mol / L sodium bicarbonate solution, acting as a buffer stabilizer, can maintain the pH environment required for the crosslinking reaction, ensuring the orderly reaction between glyoxal and hydroxyl groups, and improving the stability of the filter agent's performance. The combination of these three factors allows the filter agent to better perform its filtering and reinforcing functions in the slurry system.

[0010] Preferably, the raw materials for preparing the core-shell structured polydopamine-coated silica microspheres, by weight, include: 8-12 parts of tetraethyl orthosilicate, 5-8 parts of ammonia water with a mass fraction of 25%-28%, 200-280 parts of anhydrous ethanol, 25-35 parts of deionized water, 0.4-0.6 parts of dopamine hydrochloride, and 20-40 parts of Tris-HCl buffer solution with a concentration of 0.01-0.02 mol / L.

[0011] Using the above technical solution, tetraethyl orthosilicate (TEO) serves as the silicon source, undergoing hydrolysis and condensation in the reaction system to form silica microspheres, providing the core-layer structure for core-shell polydopamine-coated silica microspheres. Ammonia water with a mass fraction of 25%-28% provides an alkaline environment for the hydrolysis and condensation reaction of TEO, promoting the smooth progress of the reaction and the formation of regularly shaped silica microspheres. Anhydrous ethanol, as the reaction medium and diluent, can adjust the polarity and viscosity of the reaction system, facilitating the uniform dispersion and growth of the silica microspheres. Deionized water provides the dissolution and reaction medium for each component, ensuring the orderly conduct of the hydrolysis and condensation and subsequent coating reactions. In a suitable environment provided by Tris-HCl buffer solution with a concentration of 0.01-0.02 mol / L, dopamine hydrochloride undergoes a polymerization reaction and forms a polydopamine shell on the surface of silica microspheres. This gives the core-shell structured polydopamine-coated silica microspheres binding sites with other components of the filtration agent and slurry fibers. The core-shell structure formed by the combination of raw materials can play a synergistic role in skeletal support and interfacial bonding in the slurry system, thereby improving the performance of the filtration agent.

[0012] Preferably, the preparation method of the core-shell structured polydopamine-coated silica microspheres includes the following steps:

[0013] 1) Add 25%-30% of the total mass of anhydrous ethanol, deionized water and ammonia water to the reaction vessel in sequence, and stir at 280-320 r / min for 8-12 min at 25-35℃.

[0014] 2) Weigh out tetraethyl orthosilicate and the remaining anhydrous ethanol according to the proportion, stir at 280-320 r / min for 8-12 min, and then add the resulting mixture dropwise to the system obtained in step 1) over 30-40 min. After the addition is complete, raise the system temperature to 40-50℃ and continue the reaction at a stirring speed of 280-320 r / min for 6-8 h.

[0015] 3) After the reaction is complete, the system obtained in step 2) is centrifuged at 6000-8000 r / min for 15-20 min. The precipitate is washed with anhydrous ethanol 2-4 times and deionized water 2-4 times in sequence. After each washing, it is centrifuged. The obtained solid is dried at 55-65℃ and 10-20 kPa absolute pressure for 8-10 h to obtain silica nanospheres.

[0016] 4) Disperse silica nanospheres in Tris-HCl buffer until the mass fraction of silica nanospheres is 1%-2%, and then use probe-type ultrasonic dispersion for 25-35 min under ultrasonic frequency of 25-35kHz and power of 200-400W.

[0017] 5) Add dopamine hydrochloride to the system obtained in step 4), stir and polymerize at 180-220 r / min at 30-35℃ for 14-18 h, then centrifuge at 6000-8000 r / min for 15-20 min, wash the product with deionized water until clear, and finally vacuum dry at 55-65℃ and 10-20 kPa absolute pressure for 8-10 h to obtain core-shell structured polydopamine-coated silica microspheres.

[0018] By employing the above technical solution, controlling the stepwise addition of anhydrous ethanol and the stirring conditions provides a uniform reaction environment for the hydrolysis and condensation of tetraethyl orthosilicate, which is conducive to the formation of silica nanospheres with regular morphology. Heating and continuous stirring can promote the full reaction and improve the structural integrity of silica nanospheres. Centrifugation and stepwise washing can remove impurities and unreacted raw materials from the reaction system, improving the purity of silica nanospheres. Drying under specific conditions can remove moisture and residual solvent from the solid, ensuring the stability of silica nanospheres. Dispersing silica nanospheres in Tris-HCl buffer followed by ultrasonic treatment can achieve uniform dispersion to facilitate subsequent coating reactions. After adding dopamine hydrochloride, controlling the temperature and stirring speed for polymerization allows polydopamine to uniformly coat the surface of silica nanospheres, forming a core-shell structure. Subsequent centrifugation, washing, and drying further remove impurities, ensuring the purity and structural stability of the core-shell polydopamine-coated silica microspheres.

[0019] Preferably, the raw materials for preparing the phenylboronic acid functionalized oxidized glucomannan, by weight, include: 10-12 parts of konjac glucomannan, 2-3 parts of sodium periodate, 2-3 parts of 3-aminophenylboronic acid, 1.0-1.5 parts of sodium metaborate, 1-2 parts of ethylene glycol, and 300-500 parts of anhydrous ethanol.

[0020] Using the above technical solution, konjac glucomannan serves as the reaction matrix, providing a skeletal structure for subsequent functionalization modifications. Sodium periodate oxidizes specific groups in the konjac glucomannan molecule, introducing aldehyde active sites and laying the foundation for subsequent reactions. 3-Aminophenylboronic acid reacts with the generated aldehyde group, grafting phenylboronic acid functional groups onto the product. Sodium metaborate pre-modifies the hydroxyl groups in the konjac glucomannan molecule, enhancing the formation of the borate ester structure. Ethylene glycol terminates the oxidation reaction of sodium periodate, controlling the reaction process. Anhydrous ethanol acts as a precipitant, allowing the reaction product to precipitate from the system, facilitating subsequent separation and purification. The synergistic effect of each raw material ensures the controllability of the preparation process of phenylboronic acid-functionalized oxidized glucomannan and the integrity of the product structure.

[0021] Preferably, the preparation method of the phenylboronic acid-functionalized oxidized glucomannan includes the following steps:

[0022] (1) Dissolve konjac glucomannan in deionized water to prepare an aqueous solution with a mass fraction of 2%-3%, add sodium periodate under light-protected conditions, and then stir the reaction at 100-150 r / min at 20-25℃ for 4-6 h.

[0023] (2) Add ethylene glycol to the system obtained in step (1), stir at 100-150 r / min for 15-25 min, then add sodium metaborate, adjust the pH to 7.5-8.0 with 0.3-0.5 mol / L sodium bicarbonate solution, stir at 100-150 r / min for 2-4 h at 20-25℃, precipitate the reaction solution with 3-5 times the volume of ethanol / water mixture, centrifuge at 6000-8000 r / min for 15-20 min, collect the precipitate, wash with deionized water 2-3 times to obtain the intermediate;

[0024] (3) Disperse the intermediate in deionized water to prepare an aqueous solution with a mass fraction of 1.8-2.2%, add 3-aminophenylboronic acid, stir at 100-150 r / min for 15-25 min, adjust the pH to 6.0-6.5 with 0.3-0.5 mol / L hydrochloric acid, and react at 100-150 r / min at 25-30℃ for 8-12 h. After the reaction is completed, adjust the pH to 6.5-7.0 with 0.3-0.5 mol / L sodium bicarbonate solution.

[0025] (4) The reaction solution obtained in step (3) is precipitated with 3-5 times the volume of ethanol / water mixture, stirred at 150-200 r / min for 5-10 min, filtered to collect the precipitate, washed with deionized water 2-3 times, and then spray-dried, pulverized and passed through a 150-200 mesh sieve to obtain phenylboronic acid functionalized oxidized glucomannan.

[0026] The spray drying process conditions are as follows: inlet temperature 180-200℃, outlet temperature 80-90℃, and atomizer speed 12000-13000r / min.

[0027] Using the above technical solution, the light-proof and temperature-controlled stirring conditions provide a suitable environment for the oxidation of konjac glucomannan by sodium periodate, promoting the formation of aldehyde active sites. Ethylene glycol can terminate the oxidation reaction, and sodium bicarbonate solution adjusts the pH to create conditions for the reaction between sodium metaborate and hydroxyl groups. Precipitation and centrifugation of the ethanol / water mixture can remove impurities and obtain a high-purity intermediate. 3-Aminophenylboronic acid reacts with the aldehyde group in the intermediate to achieve phenylboronic acid functionalization. pH adjustment can control the reaction process to ensure the functionalization effect. Subsequent precipitation and washing further purify the product. Spray drying with specific parameters can quickly remove moisture while preserving the structural integrity of the product. Pulverization and sieving ensure uniform particle size, meeting the requirements of the filter agent for this component.

[0028] Preferably, in steps (2) and (4), the ethanol / water mixture used is a mixture of anhydrous ethanol and water in a volume ratio of 8:(2-3).

[0029] Using the above technical solution, the volume ratio of ethanol / water mixture can effectively reduce the solubility of the phenylboronic acid-functionalized oxidized glucomannan intermediate and the finished product in the system, promoting their rapid precipitation. The dominant ethanol content ensures precipitation efficiency, while the addition of an appropriate amount of water reduces the co-precipitation of small molecule impurities, improving product purity. Using this mixture consistently in both reaction steps maintains consistent precipitation conditions, ensuring stable separation of the intermediate and finished product, providing high-quality materials for subsequent purification and drying processes, and guaranteeing uniform structure and properties of the final product.

[0030] This invention also discloses a method for preparing a paper pulp filtration agent, comprising the following steps:

[0031] S1. Add 65%-75% of the total mass of deionized water, acrylamide, active hydroxy crosslinking monomer, methacryloyloxyethyltrimethylammonium chloride, N-vinylpyrrolidone and sodium hypophosphite to the reactor. Start stirring and control the speed at 200-350 r / min. Raise the temperature to 40-60℃ and bubble nitrogen gas with a purity ≥99.9% at a rate of 0.4-0.6 L / min to remove oxygen for 20-30 min.

[0032] S2. Prepare aqueous solutions of ammonium persulfate and sodium bisulfite with a mass fraction of 4%-6% respectively. Stir the system obtained in step S1 at 200-250 r / min. Slowly add the aqueous solutions of ammonium persulfate and sodium bisulfite simultaneously over 40-60 min. After the addition is complete, raise the temperature to 70-90℃ and keep the reaction at this temperature for 2.5-4 h until the conversion rate is ≥95% (determined by bromination method) to obtain the hydroxyl-modified prepolymer solution.

[0033] S3. Cool the hydroxyl-modified prepolymer solution obtained in step S2 to 55-65℃, stir at 150-250r / min, adjust the pH to 5.0-5.5 with 0.3-0.5mol / L hydrochloric acid, add glyoxal, and keep the reaction at this temperature for 1-2h.

[0034] S4. Adjust the pH of the system obtained in step S3 to 6.5-7.5 with a buffer stabilizer of 0.3-0.5 mol / L, add core-shell structured polydopamine-coated silica microspheres and phenylboronic acid-functionalized oxidized glucomannan, stir and react at 30-40℃ and 150-200 r / min for 1-2 h, add the remaining deionized water, mix evenly, filter, and obtain paper pulp filter agent.

[0035] Using the above technical solution, nitrogen bubbling provides an inert environment for the polymerization reaction, ensuring sufficient monomer conversion. The bromination method, controlling the conversion rate to ≥95%, ensures the structural regularity and performance stability of the hydroxyl-modified prepolymer. Under specific pH conditions, the addition of glyoxal promotes its acetal reaction with the hydroxyl groups on the prepolymer chain, forming a stable cross-linked structure. A buffer stabilizer adjusts the pH to a suitable range, creating conditions for the bonding of core-shell polydopamine-coated silica microspheres, phenylboronic acid-functionalized oxidized glucomannan, and the prepolymer. Stirring ensures thorough dispersion of the components and their synergistic effect. Residual deionized water adjusts the system concentration, and filtration removes impurities, ultimately yielding a paper pulp filtration agent with uniform performance and synergistic water-filtering and strengthening effects.

[0036] Preferably, in step S4, the filter used for filtration is a 150-200 mesh screen.

[0037] Using the above technical solution, a 150-200 mesh sieve can trap insoluble impurities such as insufficiently dispersed core-shell structured polydopamine-coated silica microspheres and coarse particles of phenylboronic acid-functionalized oxidized glucomannan in the system, preventing large-particle impurities from causing local blockage in the pulp and ensuring the uniform dispersion of the filter agent during application. At the same time, it allows the effective components of the paper pulp filter agent to pass through, ensuring the dispersibility and uniformity of the finished product. It also prevents large-particle impurities from entering subsequent application stages and causing blockage of the pulp filtration channels, maintaining the stability of the filter agent's performance.

[0038] The present invention also discloses the application of a paper pulp filtration agent in papermaking. The filtration agent is added to paper pulp with a chemical mechanical pulp ratio of ≥45% at a dosage of 2-3 kg / t of oven-dry pulp to improve the pulp filtration efficiency and enhance the physical strength of the paper.

[0039] By adopting the above technical solution, the filter agent can play a full role, forming an effective interaction with the pulp fibers and other components, significantly accelerating the pulp filtration rate, and reducing residual moisture and energy consumption during the papermaking process; at the same time, it can strengthen the bonding force between paper fibers, improve the interlayer bonding strength, folding endurance and other physical properties of paper, and meet the requirements of papermaking production for pulp treatment and finished product quality.

[0040] The beneficial effects of this invention are as follows:

[0041] Acrylamide, as the core backbone monomer, provides the basic long-chain polymer structure for the filter agent; active hydroxyl crosslinking monomers introduce hydroxyl groups into the polymer chain, which can participate in subsequent crosslinking reactions and form hydrogen bonds with fibers; methacryloyloxyethyltrimethylammonium chloride, as a cationic monomer, can be adsorbed onto the surface of negatively charged cellulose fibers and fine materials through electrostatic interactions, improving retention; N-vinylpyrrolidone can undergo coordination reactions with metal ions in the slurry to form stable complexes, reducing the interference of metal ions on polymer properties; ammonium persulfate and sodium bisulfite form a redox initiation system, which initiates free radical polymerization of monomers by generating free radicals, forming the polymer matrix. Glyoxal aqueous solution can undergo acetal crosslinking with hydroxyl groups on polymer chains under acidic conditions to construct a three-dimensional network structure. A buffer stabilizer maintains pH stability in the glyoxal-polymer hydroxyl crosslinking system, ensuring the orderly progress of the crosslinking reaction. Sodium hypophosphite, as a molecular weight regulator, can control the polymer molecular weight through chain transfer, preventing polymer gelation. The silica core of the core-shell polydopamine-coated silica microspheres provides support in the fiber network, while the polydopamine shell enhances the binding ability of the microspheres to fibers and polymers. Phenylboronic acid-functionalized oxidized glucomannan can form dynamic bonds with hydroxyl groups on the polymer and fiber surfaces through borate ester bonds. The synergistic effect of these components enables the prepared paper pulp filtration agent to improve pulp filtration efficiency while ensuring stable paper physical strength. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1:

[0044] This embodiment discloses a paper pulp filtration agent, which, by weight, comprises the following raw materials: 30 parts acrylamide, 8 parts active hydroxyl crosslinking monomer, 6 parts methacryloyloxyethyltrimethylammonium chloride, 4 parts N-vinylpyrrolidone, 0.2 parts ammonium persulfate, 0.1 parts sodium bisulfite, 4 parts 36% glyoxal aqueous solution, 0.5 parts buffer stabilizer, 0.5 parts sodium hypophosphite, 1.5 parts core-shell polydopamine-coated silica microspheres, 2 parts phenylboronic acid-functionalized oxidized glucomannan, and 50 parts deionized water. The active hydroxyl crosslinking monomer is N-(hydroxymethyl)acrylamide; the buffer stabilizer is a 0.3 mol / L sodium bicarbonate solution.

[0045] The raw materials for preparing core-shell structured polydopamine-coated silica microspheres, by weight, include: 8 parts of tetraethyl orthosilicate, 5 parts of ammonia water with a mass fraction of 25%, 200 parts of anhydrous ethanol, 25 parts of deionized water, 0.4 parts of dopamine hydrochloride, and 20 parts of Tris-HCl buffer solution with a concentration of 0.01 mol / L.

[0046] The preparation method of core-shell structured polydopamine-coated silica microspheres includes the following steps:

[0047] 1) Add 25% of the total mass of anhydrous ethanol, deionized water and ammonia water to the reaction vessel in sequence, and stir at 280 r / min for 8 min at 25℃.

[0048] 2) Weigh out tetraethyl orthosilicate and the remaining anhydrous ethanol according to the proportion, stir at 280 r / min for 8 min, and then add the resulting mixture dropwise to the system obtained in step 1) within 30 min. After the addition is completed, raise the system temperature to 40℃ and continue the reaction at a stirring speed of 280 r / min for 6 h.

[0049] 3) After the reaction is complete, the system obtained in step 2) is centrifuged at 6000 r / min for 15 min. The precipitate is washed twice with anhydrous ethanol and twice with deionized water. After each washing, it is centrifuged. The obtained solid is dried at 55℃ and 10 kPa absolute pressure for 8 h to obtain silica nanospheres.

[0050] 4) Disperse silica nanospheres in Tris-HCl buffer until the mass fraction of silica nanospheres is 1%, and then use probe-type ultrasonic dispersion for 25 min under ultrasonic frequency of 25 kHz and power of 200 W.

[0051] 5) Add dopamine hydrochloride to the system obtained in step 4), stir and polymerize at 180 r / min at 30°C for 14 h, then centrifuge at 6000 r / min for 15 min, wash the product with deionized water until clear, and finally vacuum dry at 55°C and 10 kPa absolute pressure for 8 h to obtain core-shell structured polydopamine-coated silica microspheres.

[0052] The raw materials for preparing phenylboronic acid-functionalized oxidized glucomannan, by weight, include: 10 parts konjac glucomannan, 2 parts sodium periodate, 2 parts 3-aminophenylboronic acid, 1 part sodium metaborate, 1 part ethylene glycol, and 300 parts anhydrous ethanol.

[0053] The preparation method of phenylboronic acid-functionalized oxidized glucomannan includes the following steps:

[0054] (1) Dissolve konjac glucomannan in deionized water to prepare an aqueous solution with a mass fraction of 2%, add sodium periodate under light-protected conditions, and then stir at 100 r / min at 20℃ for 4 h.

[0055] (2) Add ethylene glycol to the system obtained in step (1), stir at 100 r / min for 15 min, then add sodium metaborate, adjust the pH to 7.5 with 0.3 mol / L sodium bicarbonate solution, stir at 100 r / min for 2 h at 20 °C, precipitate the reaction solution with 3 times the volume of ethanol / water mixture, centrifuge at 6000 r / min for 15 min, collect the precipitate, wash twice with deionized water to obtain the intermediate;

[0056] (3) Disperse the intermediate in deionized water to prepare an aqueous solution with a mass fraction of 1.8%, add 3-aminophenylboronic acid, stir at 100 r / min for 15 min, adjust the pH to 6.0 with 0.3 mol / L hydrochloric acid, stir at 100 r / min for 8 h at 25 °C, and adjust the pH to 6.5 with 0.3 mol / L sodium bicarbonate solution after the reaction is completed;

[0057] (4) The reaction solution obtained in step (3) was precipitated with 3 times the volume of ethanol / water mixture, stirred at 150 r / min for 5 min, filtered and collected, washed twice with deionized water, and then spray-dried, pulverized and passed through a 150 mesh sieve to obtain phenylboronic acid functionalized oxidized glucomannan.

[0058] The spray drying process conditions are: inlet temperature 180℃, outlet temperature 80℃, and atomizer speed 12000r / min. In steps (2) and (4), the ethanol / water mixture used is a mixture of anhydrous ethanol and water at a volume ratio of 8:2.

[0059] This embodiment also discloses a method for preparing a paper pulp filtration agent, comprising the following steps:

[0060] S1. Add 65% of the total mass of deionized water, acrylamide, active hydroxy crosslinking monomer, methacryloyloxyethyltrimethylammonium chloride, N-vinylpyrrolidone and sodium hypophosphite to the reactor, start stirring, control the speed at 200 r / min, raise the temperature to 40℃, and bubble nitrogen gas with a purity ≥99.9% at a rate of 0.4 L / min to remove oxygen for 20 min.

[0061] S2. Prepare aqueous solutions of ammonium persulfate and sodium bisulfite with a mass fraction of 4% respectively. Stir the system obtained in step S1 at 200 r / min. Slowly add the aqueous solutions of ammonium persulfate and sodium bisulfite simultaneously over 40 min. After the addition is complete, raise the temperature to 70℃ and keep the reaction at this temperature for 2.5 h until the conversion rate is ≥95% (determined by bromination method) to obtain the hydroxyl-modified prepolymer solution.

[0062] S3. Cool the hydroxyl-modified prepolymer solution obtained in step S2 to 55°C, stir at 150 r / min, adjust the pH to 5.0 with 0.3 mol / L hydrochloric acid, add glyoxal, and keep the reaction at this temperature for 1 h.

[0063] S4. Adjust the pH of the system obtained in step S3 to 6.5 with 0.3 mol / L buffer stabilizer, add core-shell structured polydopamine-coated silica microspheres and phenylboronic acid-functionalized oxidized glucomannan, stir at 150 r / min for 1 h at 30 °C, add the remaining deionized water, mix evenly, and filter through a 150 mesh sieve to obtain paper pulp filter agent.

[0064] This embodiment also discloses the application of a paper pulp filtration agent in papermaking. The filtration agent is added to paper pulp with a chemical mechanical pulp ratio of ≥45% at a dosage of 2 kg / t of oven-dry pulp to improve the pulp filtration efficiency and enhance the physical strength of the paper.

[0065] Example 2:

[0066] This embodiment discloses a paper pulp filtration agent, which, by weight, comprises the following raw materials: 45 parts acrylamide, 14 parts active hydroxyl crosslinking monomer, 10 parts methacryloyloxyethyltrimethylammonium chloride, 8 parts N-vinylpyrrolidone, 0.5 parts ammonium persulfate, 0.4 parts sodium bisulfite, 6 parts 40% glyoxal aqueous solution, 1.5 parts buffer stabilizer, 1.1 parts sodium hypophosphite, 4.5 parts core-shell polydopamine-coated silica microspheres, 5 parts phenylboronic acid-functionalized oxidized glucomannan, and 70 parts deionized water. The active hydroxyl crosslinking monomer is N-hydroxyethylacrylamide; the buffer stabilizer is a 0.5 mol / L sodium bicarbonate solution.

[0067] The raw materials for preparing core-shell structured polydopamine-coated silica microspheres, by weight, include: 12 parts of tetraethyl orthosilicate, 8 parts of ammonia water with a mass fraction of 28%, 280 parts of anhydrous ethanol, 35 parts of deionized water, 0.6 parts of dopamine hydrochloride, and 40 parts of Tris-HCl buffer solution with a concentration of 0.02 mol / L.

[0068] The preparation method of core-shell structured polydopamine-coated silica microspheres includes the following steps:

[0069] 1) Add 30% of the total mass of anhydrous ethanol, deionized water and ammonia water to the reaction vessel in sequence, and stir at 320 r / min for 12 min at 35℃;

[0070] 2) Weigh out tetraethyl orthosilicate and the remaining anhydrous ethanol according to the proportion, stir at 320 r / min for 12 min, and then add the resulting mixture dropwise to the system obtained in step 1) within 40 min. After the addition is completed, raise the system temperature to 50℃ and continue the reaction at a stirring speed of 320 r / min for 8 h.

[0071] 3) After the reaction is complete, the system obtained in step 2) is centrifuged at 8000 r / min for 20 min. The precipitate is washed 4 times with anhydrous ethanol and 4 times with deionized water. After each washing, it is centrifuged. The obtained solid is dried at 65℃ and 20 kPa absolute pressure for 10 h to obtain silica nanospheres.

[0072] 4) Disperse silica nanospheres in Tris-HCl buffer until the mass fraction of silica nanospheres is 2%, and then use probe-type ultrasonic dispersion for 35 min under ultrasonic frequency of 35 kHz and power of 400 W.

[0073] 5) Add dopamine hydrochloride to the system obtained in step 4), stir and polymerize at 220 r / min at 35°C for 18 h, then centrifuge at 8000 r / min for 20 min, wash the product with deionized water until clear, and finally vacuum dry at 65°C and 20 kPa absolute pressure for 10 h to obtain core-shell structured polydopamine-coated silica microspheres.

[0074] The raw materials for preparing phenylboronic acid-functionalized oxidized glucomannan, by weight, include: 12 parts konjac glucomannan, 3 parts sodium periodate, 3 parts 3-aminophenylboronic acid, 1.5 parts sodium metaborate, 2 parts ethylene glycol, and 500 parts anhydrous ethanol.

[0075] The preparation method of phenylboronic acid-functionalized oxidized glucomannan includes the following steps:

[0076] (1) Dissolve konjac glucomannan in deionized water to prepare a 3% aqueous solution. Add sodium periodate under light-protected conditions and then stir at 150 r / min at 25°C for 6 h.

[0077] (2) Add ethylene glycol to the system obtained in step (1), stir at 150 r / min for 25 min, then add sodium metaborate, adjust the pH to 8.0 with 0.5 mol / L sodium bicarbonate solution, stir at 150 r / min for 4 h at 25 °C, precipitate the reaction solution with 5 times the volume of ethanol / water mixture, centrifuge at 8000 r / min for 20 min, collect the precipitate, wash with deionized water 3 times to obtain the intermediate;

[0078] (3) Disperse the intermediate in deionized water to prepare an aqueous solution with a mass fraction of 2.2%, add 3-aminophenylboronic acid, stir at 150 r / min for 25 min, adjust the pH to 6.5 with 0.5 mol / L hydrochloric acid, stir at 150 r / min at 30℃ for 12 h, and after the reaction is completed, adjust the pH to 7.0 with 0.5 mol / L sodium bicarbonate solution;

[0079] (4) The reaction solution obtained in step (3) was precipitated with 5 times the volume of ethanol / water mixture, stirred at 200 r / min for 10 min, filtered and collected, washed with deionized water 3 times, and then spray dried, pulverized and passed through a 200 mesh sieve in sequence to obtain phenylboronic acid functionalized oxidized glucomannan.

[0080] The spray drying process conditions are: inlet temperature 200℃, outlet temperature 90℃, and atomizer speed 13000r / min. In steps (2) and (4), the ethanol / water mixture used is a mixture of anhydrous ethanol and water at a volume ratio of 8:3.

[0081] This embodiment also discloses a method for preparing a paper pulp filtration agent, comprising the following steps:

[0082] S1. Add 75% of the total mass of deionized water, acrylamide, active hydroxy crosslinking monomer, methacryloyloxyethyltrimethylammonium chloride, N-vinylpyrrolidone and sodium hypophosphite to the reactor, start stirring, control the speed at 350 r / min, heat to 60℃, and bubble oxygen with nitrogen of ≥99.9% purity at a rate of 0.6 L / min for 30 min.

[0083] S2. Prepare aqueous solutions of ammonium persulfate and sodium bisulfite with a mass fraction of 6% respectively. Stir the system obtained in step S1 at 250 r / min. Simultaneously and slowly add the aqueous solutions of ammonium persulfate and sodium bisulfite dropwise over 60 min. After the addition is complete, raise the temperature to 90℃ and keep the reaction at this temperature for 4 h until the conversion rate is ≥95% (determined by bromination method) to obtain the hydroxyl-modified prepolymer solution.

[0084] S3. Cool the hydroxyl-modified prepolymer solution obtained in step S2 to 65°C, stir at 250 r / min, adjust the pH to 5.5 with 0.5 mol / L hydrochloric acid, add glyoxal, and keep the reaction at this temperature for 2 h.

[0085] S4. Adjust the pH of the system obtained in step S3 to 7.5 with 0.5 mol / L buffer stabilizer, add core-shell structured polydopamine-coated silica microspheres and phenylboronic acid-functionalized oxidized glucomannan, stir at 200 r / min for 2 h at 40 °C, add the remaining deionized water, mix evenly, and filter through a 200 mesh sieve to obtain paper pulp filter agent.

[0086] This embodiment also discloses the application of a paper pulp filtration agent in papermaking. The filtration agent is added to paper pulp with a chemical mechanical pulp ratio of ≥45% at a dosage of 3 kg / t of oven-dry pulp to improve the pulp filtration efficiency and enhance the physical strength of the paper.

[0087] Example 3:

[0088] This embodiment discloses a paper pulp filtration agent, which, by weight, comprises the following raw materials: 38 parts acrylamide, 11 parts active hydroxyl crosslinking monomer, 8 parts methacryloyloxyethyltrimethylammonium chloride, 6 parts N-vinylpyrrolidone, 0.35 parts ammonium persulfate, 0.25 parts sodium bisulfite, 5 parts 38% glyoxal aqueous solution, 1 part buffer stabilizer, 0.8 parts sodium hypophosphite, 3 parts core-shell polydopamine-coated silica microspheres, 3.5 parts phenylboronic acid-functionalized oxidized glucomannan, and 60 parts deionized water. The active hydroxyl crosslinking monomer is N-(hydroxymethyl)acrylamide; the buffer stabilizer is a 0.4 mol / L sodium bicarbonate solution.

[0089] The raw materials for preparing core-shell structured polydopamine-coated silica microspheres, by weight, include: 10 parts of tetraethyl orthosilicate, 6.5 parts of ammonia water with a mass fraction of 26.5%, 240 parts of anhydrous ethanol, 30 parts of deionized water, 0.5 parts of dopamine hydrochloride, and 30 parts of Tris-HCl buffer solution with a concentration of 0.015 mol / L.

[0090] The preparation method of core-shell structured polydopamine-coated silica microspheres includes the following steps:

[0091] 1) Add 27.5% of the total mass of anhydrous ethanol, deionized water and ammonia water to the reaction vessel in sequence, and stir at 300 r / min for 10 min at 30℃;

[0092] 2) Weigh out tetraethyl orthosilicate and the remaining anhydrous ethanol according to the proportion, stir at 300 r / min for 10 min, and then add the resulting mixture dropwise to the system obtained in step 1) within 35 min. After the addition is completed, raise the system temperature to 45℃ and continue the reaction at a stirring speed of 300 r / min for 7 h.

[0093] 3) After the reaction is complete, the system obtained in step 2) is centrifuged at 7000 r / min for 18 min. The precipitate is washed three times with anhydrous ethanol and three times with deionized water. After each washing, it is centrifuged. The obtained solid is dried at 60℃ and 15 kPa absolute pressure for 9 h to obtain silica nanospheres.

[0094] 4) Disperse silica nanospheres in Tris-HCl buffer until the mass fraction of silica nanospheres is 1.5%, and then use probe-type ultrasonic dispersion for 30 min under ultrasonic frequency of 30 kHz and power of 300 W.

[0095] 5) Add dopamine hydrochloride to the system obtained in step 4), stir and polymerize at 200 r / min at 32°C for 16 h, then centrifuge at 7000 r / min for 18 min, wash the product with deionized water until clear, and finally vacuum dry at 60°C and 15 kPa absolute pressure for 9 h to obtain core-shell structured polydopamine-coated silica microspheres.

[0096] The raw materials for preparing phenylboronic acid-functionalized oxidized glucomannan, by weight, include: 11 parts konjac glucomannan, 2.5 parts sodium periodate, 2.5 parts 3-aminophenylboronic acid, 1.2 parts sodium metaborate, 1.5 parts ethylene glycol, and 400 parts anhydrous ethanol.

[0097] The preparation method of phenylboronic acid-functionalized oxidized glucomannan includes the following steps:

[0098] (1) Dissolve konjac glucomannan in deionized water to prepare an aqueous solution with a mass fraction of 2.5%. Add sodium periodate under light-protected conditions, and then stir at 125 r / min at 22℃ for 5 h.

[0099] (2) Add ethylene glycol to the system obtained in step (1), stir at 125 r / min for 20 min, then add sodium metaborate, adjust the pH to 7.7 with 0.4 mol / L sodium bicarbonate solution, stir at 125 r / min for 3 h at 22 °C, precipitate the reaction solution with 4 times the volume of ethanol / water mixture, centrifuge at 7000 r / min for 18 min, collect the precipitate, wash with deionized water 3 times to obtain the intermediate;

[0100] (3) Disperse the intermediate in deionized water to prepare an aqueous solution with a mass fraction of 2%, add 3-aminophenylboronic acid, stir at 125 r / min for 20 min, adjust the pH to 6.2 with 0.4 mol / L hydrochloric acid, stir at 125 r / min for 10 h at 28 °C, and adjust the pH to 6.8 with 0.4 mol / L sodium bicarbonate solution after the reaction is completed;

[0101] (4) The reaction solution obtained in step (3) was precipitated with 4 times the volume of ethanol / water mixture, stirred at 175 r / min for 7 min, filtered and collected, washed with deionized water 3 times, and then spray dried, pulverized and passed through 180 mesh sieve in sequence to obtain phenylboronic acid functionalized oxidized glucomannan.

[0102] The spray drying process conditions are as follows: inlet temperature 190℃, outlet temperature 85℃, and atomizer speed 12500r / min. In steps (2) and (4), the ethanol / water mixture used is a mixture of anhydrous ethanol and water at a volume ratio of 8:2.5.

[0103] This embodiment also discloses a method for preparing a paper pulp filtration agent, comprising the following steps:

[0104] S1. Add 70% of the total mass of deionized water, acrylamide, active hydroxy crosslinking monomer, methacryloyloxyethyltrimethylammonium chloride, N-vinylpyrrolidone and sodium hypophosphite to the reactor, start stirring, control the speed at 275 r / min, heat to 50℃, and bubble oxygen with nitrogen of ≥99.9% purity at a rate of 0.5 L / min for 25 min.

[0105] S2. Prepare 5% (w / w) aqueous solutions of ammonium persulfate and sodium bisulfite. Stir the system obtained in step S1 at 225 r / min. Slowly add the aqueous solutions of ammonium persulfate and sodium bisulfite simultaneously over 50 min. After the addition is complete, raise the temperature to 80℃ and keep the reaction at this temperature for 3 h until the conversion rate is ≥95% (determined by bromination method) to obtain the hydroxyl-modified prepolymer solution.

[0106] S3. Cool the hydroxyl-modified prepolymer solution obtained in step S2 to 60°C, stir at 200 r / min, adjust the pH to 5.2 with 0.4 mol / L hydrochloric acid, add glyoxal, and keep the reaction at this temperature for 1.5 h.

[0107] S4. Adjust the pH of the system obtained in step S3 to 7.0 with 0.4 mol / L buffer stabilizer, add core-shell structured polydopamine-coated silica microspheres and phenylboronic acid-functionalized oxidized glucomannan, stir at 175 r / min at 35℃ for 1.5 h, add the remaining deionized water, mix evenly, and filter through an 180 mesh sieve to obtain paper pulp filter agent.

[0108] This embodiment also discloses the application of a paper pulp filtration agent in papermaking. The filtration agent is added to paper pulp with a chemical mechanical pulp ratio of ≥45% at an addition amount of 2.5 kg / t of oven-dry pulp to improve the pulp filtration efficiency and enhance the physical strength of the paper.

[0109] Comparative Example 1:

[0110] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that: core-shell structured polydopamine-coated silica microspheres are not added.

[0111] Comparative Example 2:

[0112] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that: phenylboronic acid-functionalized oxidized glucomannan is not added.

[0113] Comparative Example 3:

[0114] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that N-vinylpyrrolidone is not added.

[0115] Comparative Example 4:

[0116] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that N-(hydroxymethyl)acrylamide is not added.

[0117] Comparative Example 5:

[0118] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that glyoxal is not added.

[0119] Comparative Example 6:

[0120] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that: an equal mass of unmodified glucomannan (98% purity, purchased from Shaanxi Xiazhou Biotechnology Co., Ltd.) is used to replace phenylboronic acid functionalized oxidized glucomannan.

[0121] Comparative Example 7:

[0122] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that: the core-shell structure polydopamine-coated silica microspheres are replaced with silica microspheres of equal mass (99% purity, purchased from Xi'an Qiyue Biotechnology Co., Ltd.).

[0123] Comparative Example 8:

[0124] A paper pulp filtration agent, its preparation method and application, differs from Example 3 only in that: in step S4, the pH is adjusted to 5.0 with 0.4 mol / L hydrochloric acid.

[0125] The water-filtering agents obtained in Examples 1-3 and Comparative Examples 1-8 were tested for water-filtering performance, tensile index, bursting index, folding endurance, amount of chemimechanical pulp that can be replaced, and salt resistance.

[0126] Pulp preparation: Prepare the pulp mixture as follows: Bleached softwood pulp (NBKP): Bleached hardwood pulp (LBKP): Bleached chemimechanical pulp (BCTMP) = 10:45:45 (octane-dry weight ratio), and beat to 45°SR. Add light calcium carbonate filler to bring the ash content of the pulp to 15wt%.

[0127] Application Process: On a standard paper sheet forming machine, add chemicals in the following order and dosage (relative to oven-dry pulp): cationic starch 10 kg / t → stir for 30 s → test filter agent 3 kg / t → stir for 30 s → polyacrylamide dry strength agent 30 kg / t → stir for 30 s → anionic waste trap (polyamine) 150 ppm → stir for 30 s → silica sol 8 kg / t. After addition, the basis weight is 80 g / m³. 2 The paper sheets were equilibrated for 24 hours under standard conditions (23±1℃, 50±2%RH) before testing.

[0128] Testing items and standards:

[0129] 1. Water filtration performance: The test was conducted using a Canadian Standard Freeness (CSF) meter, in accordance with the national standard GB / T 12660-2008 "Determination of Water Filtration Performance of Pulp". A higher freeness value indicates better water filtration performance.

[0130] 2. Interlayer bond strength: The test was conducted in accordance with the national standard GB / T 26203-2023 Determination of interlayer bond strength of paper and paperboard. A Scott interlayer bond strength tester was used, the sample size was 25.4 mm × 25.4 mm, and the pressure was 0.689 MPa.

[0131] 3. Tensile index: The test is conducted in accordance with the national standard GB / T 12914-2018 Determination of tensile strength of paper and paperboard. The formula for calculating the tensile index is: Tensile index = 1000 * tensile strength / basis weight.

[0132] 4. Bursting index: The test is conducted in accordance with the national standard GB / T 454-2020 Determination of bursting strength of paper and paperboard. The formula for calculating the bursting index is: Bursting index = bursting strength / basis weight.

[0133] 5. Folding endurance: Tested in accordance with the national standard GB / T 457-2008 Determination of folding endurance of paper and paperboard (MIT method).

[0134] 6. Evaluation of the amount of chemimechanical pulp that can be substituted: While maintaining the above physical strength of the paper (based on tensile index and bursting index, with fluctuations not exceeding ±3%), gradually increase the proportion of BCTMP, while reducing the proportion of NBKP by the same amount, and test and record the maximum increase in the proportion of chemimechanical pulp.

[0135] 7. Salt resistance test: Add calcium chloride to the slurry corresponding to all groups to adjust the conductivity of the slurry system to 5.0±0.2mS / cm. Perform the papermaking according to the above application process, test the degree of free filtrate, and calculate the relative filtrate retention rate: Relative filtrate retention rate = (high salt system CSF / conventional system CSF) × 100%.

[0136] The results are shown in Tables 1 and 2.

[0137] Table 1. Test results of water filtration performance and the amount of chemical-mechanical pulp that can be substituted.

[0138] Table 2. Test results of paper physical strength and salt resistance

[0139] Using Example 3 as the control group, the performance differences and causes of Comparative Examples 1-8 are analyzed as follows:

[0140] Comparative Example 1 (without core-shell structured polydopamine-coated silica microspheres): filtration performance decreased by 14.6% (from 445 mL to 380 mL), the amount of chemimechanical pulp that could be replaced decreased by 33.3% (from 4.2% to 2.8%), and folding endurance decreased by 30.4% (from 115 folds to 80 folds). The lack of rigid support nodes led to decreased stability of the filtration channels and deterioration of the paper's dynamic strength properties, indicating that core-shell structured polydopamine-coated silica microspheres play an important role in maintaining the stability of the filtration channels and improving paper toughness.

[0141] Comparative Example 2 (without phenylboronic acid-functionalized oxidized glucomannan): interlayer bonding strength decreased by 14.7% (from 190 J / m). 2 Reduced to 162 J / m 2 The substitution of chemimechanical pulp decreased by 28.6% (from 4.2% to 3.0%). The lack of a dual dynamic crosslinking network impaired paper toughness and reduced stress dispersion, indicating that oxidation-boronization modification plays a crucial role in improving interlayer bonding and adapting paper to chemimechanical pulp systems. The mechanism is as follows: sodium periodate oxidation produces active aldehyde groups, sodium metaborate pre-modifies the C6-position hydroxyl group to form a borate ester, and 3-aminophenylboronic acid forms a Schiff base with the aldehyde group, constructing a dynamic BO network through intramolecular / inter-boronate ester exchange. The C=N bond is stable at pH 6.5-7.5, while the BO bond can achieve reversible exchange at pH 6.0-8.0, realizing a graded stress response.

[0142] Comparative Example 3 (without N-vinylpyrrolidone): Relative filtration retention decreased by 13.8% (from 87% to 75%), filtration performance decreased by 15.7% (from 445 mL to 375 mL), and the amount of chemimechanical pulp that could be replaced decreased by 57.1% (from 4.2% to 1.8%). The pyrrolidone ring carbonyl oxygen of N-vinylpyrrolidone forms a coordination bond with metal ions, shielding the polymer's active groups from damage by metal ions and maintaining the stability of the polymer molecular structure. The absence of N-vinylpyrrolidone prevents the complexation of metal ions in the pulp, causing metal ions to bind to the polymer's active groups and disrupt the molecular structure, resulting in a 15.7% decrease in filtration performance in the conventional system; in the high-salt system, the metal ion concentration is even higher, and the relative filtration retention decreases to 75%.

[0143] Comparative Example 4 (without N-(hydroxymethyl)acrylamide): Tensile index decreased by 23.3% (from 73.0 N·m / g to 56.0 N·m / g), and burst index decreased by 28.4% (from 5.10 kPa·m). 2 / g decreased to 3.65 kPa·m 2 / g). Without the addition of active hydroxyl crosslinking monomers, the polymer chain lacks active sites for crosslinking with glyoxal, making it impossible to form a three-dimensional crosslinking network, resulting in a significant decrease in water filtration performance and paper strength.

[0144] Comparative Example 5 (without glyoxal): Filtration performance decreased by 30.3% (from 445 mL to 310 mL), tensile index decreased by 22.1% (from 73.0 N·m / g to 57.5 N·m / g), and the amount of chemimechanical pulp that could be replaced decreased by 61.9% (from 4.2% to 1.6%). Without acetal crosslinking, the polymer had only a linear structure, lacking network support, making the filtration channels prone to collapse. All performance indicators deteriorated across the board, indicating that the post-glyoxal crosslinking process is crucial for improving the polymer's bulk strength and maintaining its overall performance.

[0145] Comparative Example 6 (using an equal mass of unmodified glucomannan to replace phenylboronic acid-functionalized oxidized glucomannan): interlayer bonding strength decreased by 22.1% (from 190 J / m). 2 Reduced to 148 J / m 2 The amount of chemimechanical pulp that can be replaced decreased by 40.5% (from 4.2% to 2.5%). Unmodified glucomannan lacks phenylboronic acid functional groups on its surface, making it unable to form dynamic borate bonds with hydroxyl groups on the polymer and fiber surfaces. This makes it difficult to construct a stress-dispersing network, resulting in a significant decrease in the interlayer bonding strength and the increase in the proportion of chemimechanical pulp.

[0146] Comparative Example 7 (replacing core-shell polydopamine-coated silica microspheres with equal mass of silica microspheres): filtration performance decreased by 22.5% (from 445 mL to 345 mL), and interlayer bonding strength decreased by 23.7% (from 190 J / m). 2 Reduced to 145 J / m 2 The catechol groups in the polydopamine shell are oxidized to quinone structures in a weakly alkaline environment, which can covalently bind with the hydroxyl groups of the fibers and anchor to the polymer matrix through hydrogen bonds. The surface of the unmodified silica microspheres has no active groups and relies solely on physical filling, resulting in poor interfacial compatibility and a significant decrease in water filtration performance and interlayer bonding strength.

[0147] Comparative Example 8 (pH adjusted to 5.0 in step S4): Relative filtration retention decreased by 8.0% (from 87% to 80%), and interlayer bonding strength decreased by 27.4% (from 190 J / m³). 2 Reduced to 138J / m 2 Although the acidic environment of pH 5.0 does not destroy the borate ester bond, it inhibits the covalent bonding between the catechol groups in the polydopamine shell and the cellulose hydroxyl groups, reducing the interfacial compatibility of the core-shell microspheres and resulting in a slight decrease in water filtration performance under high salt conditions.

[0148] In summary, the silica core of the core-shell polydopamine-coated silica microspheres provides support within the fiber network, while the polydopamine shell enhances the bonding between the microspheres and the fibers and polymers. Phenylboronic acid-functionalized oxidized glucomannan can form dynamic bonds with the hydroxyl groups on the polymer and fiber surfaces via borate ester bonds. The synergistic effect of these components enables the prepared paper pulp filtration agent to improve pulp filtration efficiency while ensuring stable paper physical strength.

[0149] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A paper pulp filtration agent, characterized in that, The raw materials for its preparation, by weight, include: 30-45 parts acrylamide, 8-14 parts active hydroxyl crosslinking monomer, 6-10 parts methacryloyloxyethyltrimethylammonium chloride, 4-8 parts N-vinylpyrrolidone, 0.2-0.5 parts ammonium persulfate, 0.1-0.4 parts sodium bisulfite, 4-6 parts glyoxal aqueous solution, 0.5-1.5 parts buffer stabilizer, 0.5-1.1 parts sodium hypophosphite, 1.5-4.5 parts core-shell structured polydopamine-coated silica microspheres, 2-5 parts phenylboronic acid-functionalized oxidized glucomannan, and 50-70 parts deionized water.

2. The paper pulp filtration agent according to claim 1, characterized in that, The active hydroxyl crosslinking monomer is one of N-(hydroxymethyl)acrylamide or N-hydroxyethylacrylamide; the mass fraction of the glyoxal aqueous solution is 36%-40%; and the buffer stabilizer is a 0.3-0.5 mol / L sodium bicarbonate solution.

3. The paper pulp filtration agent according to claim 1, characterized in that, The raw materials for preparing the core-shell structured polydopamine-coated silica microspheres, by weight, include: 8-12 parts of tetraethyl orthosilicate, 5-8 parts of ammonia water with a mass fraction of 25%-28%, 200-280 parts of anhydrous ethanol, 25-35 parts of deionized water, 0.4-0.6 parts of dopamine hydrochloride, and 20-40 parts of Tris-HCl buffer solution with a concentration of 0.01-0.02 mol / L.

4. The paper pulp filtration agent according to claim 3, characterized in that, The preparation method of the core-shell structured polydopamine-coated silica microspheres includes the following steps: 1) Add 25%-30% of the total mass of anhydrous ethanol, deionized water and ammonia water to the reaction vessel in sequence, and stir at 280-320 r / min for 8-12 min at 25-35℃. 2) Weigh out tetraethyl orthosilicate and the remaining anhydrous ethanol according to the proportion, stir at 280-320 r / min for 8-12 min, and then add the resulting mixture dropwise to the system obtained in step 1) over 30-40 min. After the addition is complete, raise the system temperature to 40-50℃ and continue the reaction at a stirring speed of 280-320 r / min for 6-8 h. 3) After the reaction is complete, the system obtained in step 2) is centrifuged at 6000-8000 r / min for 15-20 min. The precipitate is washed with anhydrous ethanol 2-4 times and deionized water 2-4 times in sequence. After each washing, it is centrifuged. The obtained solid is dried at 55-65℃ and 10-20 kPa absolute pressure for 8-10 h to obtain silica nanospheres. 4) Disperse silica nanospheres in Tris-HCl buffer until the mass fraction of silica nanospheres is 1%-2%, and then disperse for 25-35 min under ultrasonic conditions at a frequency of 25-35 kHz and a power of 200-400 W. 5) Add dopamine hydrochloride to the system obtained in step 4), stir and polymerize at 180-220 r / min at 30-35℃ for 14-18 h, then centrifuge at 6000-8000 r / min for 15-20 min, wash the product with deionized water until clear, and finally vacuum dry at 55-65℃ and 10-20 kPa absolute pressure for 8-10 h to obtain core-shell structured polydopamine-coated silica microspheres.

5. The paper pulp filtration agent according to claim 1, characterized in that, The raw materials for preparing the phenylboronic acid-functionalized oxidized glucomannan, by weight, include: 10-12 parts of konjac glucomannan, 2-3 parts of sodium periodate, 2-3 parts of 3-aminophenylboronic acid, 1.0-1.5 parts of sodium metaborate, 1-2 parts of ethylene glycol, and 300-500 parts of anhydrous ethanol.

6. The paper pulp filtration agent according to claim 5, characterized in that, The preparation method of the phenylboronic acid-functionalized oxidized glucomannan includes the following steps: (1) Dissolve konjac glucomannan in deionized water to prepare an aqueous solution with a mass fraction of 2%-3%, add sodium periodate under light-protected conditions, and then stir the reaction at 100-150 r / min at 20-25℃ for 4-6 h. (2) Add ethylene glycol to the system obtained in step (1), stir at 100-150 r / min for 15-25 min, then add sodium metaborate, adjust the pH to 7.5-8.0 with 0.3-0.5 mol / L sodium bicarbonate solution, stir at 100-150 r / min for 2-4 h at 20-25℃, precipitate the reaction solution with 3-5 times the volume of ethanol / water mixture, centrifuge at 6000-8000 r / min for 15-20 min, collect the precipitate, wash with deionized water 2-3 times to obtain the intermediate; (3) Disperse the intermediate in deionized water to prepare an aqueous solution with a mass fraction of 1.8-2.2%, add 3-aminophenylboronic acid, stir at 100-150 r / min for 15-25 min, adjust the pH to 6.0-6.5 with 0.3-0.5 mol / L hydrochloric acid, and react at 100-150 r / min at 25-30℃ for 8-12 h. After the reaction is completed, adjust the pH to 6.5-7.0 with 0.3-0.5 mol / L sodium bicarbonate solution. (4) The reaction solution obtained in step (3) is precipitated with 3-5 times the volume of ethanol / water mixture, stirred at 150-200 r / min for 5-10 min, filtered to collect the precipitate, washed with deionized water 2-3 times, and then spray-dried, pulverized and passed through a 150-200 mesh sieve to obtain phenylboronic acid functionalized oxidized glucomannan. The spray drying process conditions are as follows: inlet temperature 180-200℃, outlet temperature 80-90℃, and atomizer speed 12000-13000r / min.

7. The paper pulp filtration agent according to claim 6, characterized in that, In steps (2) and (4), the ethanol / water mixture used is a mixture of anhydrous ethanol and water in a volume ratio of 8:(2-3).

8. A method for preparing a paper pulp filtration agent as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Add 65%-75% of the total mass of deionized water, acrylamide, active hydroxy crosslinking monomer, methacryloyloxyethyltrimethylammonium chloride, N-vinylpyrrolidone and sodium hypophosphite to the reactor, start stirring, control the speed at 200-350 r / min, raise the temperature to 40-60℃, and bubble nitrogen gas at a rate of 0.4-0.6 L / min to remove oxygen for 20-30 min. S2. Prepare aqueous solutions of ammonium persulfate and sodium bisulfite with a mass fraction of 4%-6% respectively. Stir the system obtained in step S1 at 200-250 r / min. Simultaneously and slowly add the aqueous solutions of ammonium persulfate and sodium bisulfite dropwise over 40-60 min. After the addition is complete, raise the temperature to 70-90℃ and keep the reaction at this temperature for 2.5-4 h to obtain the hydroxyl-modified prepolymer solution. S3. Cool the hydroxyl-modified prepolymer solution obtained in step S2 to 55-65℃, stir at 150-250r / min, adjust the pH to 5.0-5.5 with 0.3-0.5mol / L hydrochloric acid, add glyoxal, and keep the reaction at this temperature for 1-2h. S4. Adjust the pH of the system obtained in step S3 to 6.5-7.5 with a buffer stabilizer of 0.3-0.5 mol / L, add core-shell structured polydopamine-coated silica microspheres and phenylboronic acid-functionalized oxidized glucomannan, stir and react at 30-40℃ and 150-200 r / min for 1-2 h, add the remaining deionized water, mix evenly, filter, and obtain paper pulp filter agent.

9. The method for preparing the paper pulp filtration agent according to claim 8, characterized in that, In step S4, the filter screen used for filtration is a 150-200 mesh sieve.

10. The application of a paper pulp filtration agent as described in any one of claims 1-7 in papermaking, characterized in that, The filter agent is added to paper pulp with a chemimechanical pulp content of ≥45% at a rate of 2-3 kg / t of oven-dry pulp to improve the pulp's filtration efficiency and enhance the physical strength of the paper.

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