Paper reinforcing agent suitable for waste paper papermaking and preparation method thereof

Abstract

The invention relates to the technical field of papermaking, in particular to a paper reinforcing agent suitable for waste paper papermaking and a preparation method of the paper reinforcing agent. The method comprises the following steps: S1, mixing a cationic monomer, an anionic monomer, an amido bond-containing monomer and water to obtain a first solution, and adding an initiator into the first solution to initiate a polymerization reaction to obtain a first polymerization solution; s2, mixing a cationic monomer, an anionic monomer, an amido bond-containing monomer, a branched monomer and water to obtain a second solution, and adding the second solution and an initiator into the first polymerization solution to initiate a polymerization reaction to obtain a second polymerization solution; and S3, mixing a cationic monomer, an anionic monomer, an amido bond-containing monomer, a crosslinking monomer and water to obtain a third solution, adding the third solution and an initiator into the second polymerization solution to initiate a polymerization reaction, and terminating the reaction after the viscosity of the solution reaches a preset viscosity to obtain the paper reinforcing agent. According to the scheme, the paper reinforcing agent suitable for waste paper papermaking can be provided.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and in particular to a paper strengthening agent suitable for waste paper papermaking and its preparation method. Background Technology

[0002] my country faces a relative shortage of wood pulp, particularly softwood pulp, used in papermaking. Pulp strength is the cornerstone of paper strength. While adding fillers reduces production costs during papermaking, it also lowers paper strength. Excessive strength negatively impacts production stability and subsequent processing, especially for low-basis-weight base paper. Increasing the freeness of the pulp and incorporating a certain proportion of softwood pulp can improve paper strength, but increasing the freeness causes several drawbacks, such as reduced paper bulk, opacity, and air permeability, difficulty in pulp filtration, and even decreased tear resistance.

[0003] Waste paper can be recycled into recycled paper, also known as "secondary fiber." Recycled paper addresses resource, environmental, and energy issues. One ton of waste paper can produce approximately 800 kg of high-quality paper, equivalent to saving 17 large trees, 100 tons of water, 1-2 tons of coal, and 600 kilowatt-hours of electricity. Recycled paper significantly reduces pollution and resource waste. Waste paper sources include corrugated paper, office paper, and toilet paper. After waste paper is recycled and processed into paper, the paper's properties deteriorate. Therefore, paper strengthening agents are added to improve the paper's burst strength, folding endurance, and other properties. Summary of the Invention

[0004] This invention provides a paper strengthening agent suitable for waste paper papermaking and its preparation method, thus providing a paper strengthening agent suitable for waste paper papermaking.

[0005] In a first aspect, embodiments of the present invention provide a method for preparing a paper strengthening agent suitable for waste paper papermaking, comprising: S1, mix cationic monomer, anionic monomer, amide monomer and water to obtain a first solution, add an initiator to the first solution to initiate a polymerization reaction, and obtain a first polymerization solution; S2, mix cationic monomer, anionic monomer, amide-containing monomer, branched monomer and water to obtain a second solution, add the second solution and initiator to the first polymerization solution to initiate the polymerization reaction to obtain a second polymerization solution; S3, mix cationic monomer, anionic monomer, amide-containing monomer, crosslinking monomer and water to obtain a third solution, add the third solution and initiator to the second polymerization solution to initiate the polymerization reaction, and terminate the reaction after the solution viscosity reaches the preset viscosity to obtain a paper strengthening agent.

[0006] In one possible design, S1, after obtaining the first solution and before adding the initiator to initiate the polymerization reaction, further includes: A functional monomer is added to the first solution. The process for preparing the functional monomer is as follows: The first product was obtained by reacting glycerol, pentaerythritol, sorbitol and methanol in the presence of concentrated sulfuric acid. The first product and ε-caprolactone or lactide are dissolved in toluene and subjected to an addition reaction under the catalysis of dioctyltin dilaurate or dibutyltin diacetate to obtain the second product. The second product, acrylic acid or methacrylic acid, p-toluenesulfonic acid catalyst, and hydroquinone inhibitor are mixed and esterified to obtain a functional monomer.

[0007] In one possible design, the reaction conditions for generating the first product are 85-95°C for 3-4 hours, the reaction conditions for generating the second product are 20-25°C for 2-3 hours, and the reaction conditions for generating the functional monomer are 80-90°C for 2-4 hours.

[0008] In one possible design, the amount of raw materials used in the preparation of the first product during the functional monomer preparation process is as follows: The molar ratio of methanol to any one of glycerol, pentaerythritol, or sorbitol is 1.5:1 to 4:1; The molar ratio of concentrated sulfuric acid to any one of glycerol, pentaerythritol, or sorbitol is 0.01:1 to 0.05:1; Amount of raw materials used in the preparation of the second product: The second preparation raw materials include reactants, catalysts and solvents, wherein the molar ratio of the first product of the reactants to ε-caprolactone or lactide is 1:1.0~1.1; The mass ratio of catalyst to reactants is 0.005:1 to 0.01:1; The mass of the solvent toluene should be 2-3 times the mass of the reactants; Third product: The molar ratio of the second product to acrylic acid or methacrylic acid is 1:1.0~1.1; The molar ratio of p-toluenesulfonic acid to acrylic acid or methacrylic acid is 1:0.01~0.05; The molar ratio of the polymerization inhibitor hydroquinone to acrylic acid or methacrylic acid is 1:0.01~0.03.

[0009] In one possible design, the amount of the functional monomer is 1-5g per liter of the first solution.

[0010] In one possible design, the cationic monomers in S1-S3 each include one or more combinations of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, dodecyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, and methacryloyloxyethyldimethylbenzylammonium chloride. The anionic monomers in S1-S3 all include one or more combinations of sodium methacrylate, acrylic acid, sodium acrylate, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-acrylamido-2-methylpropanesulfonate. The amide-containing monomers in S1-S3 all include one or more combinations of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide and N-benzylacrylamide; The initiators mentioned in S1-S3 are all combinations of persulfates and azo compounds. Persulfates include sodium persulfate, ammonium persulfate, and potassium persulfate, while azo compounds include at least two of azobisisobutyramidine hydrochloride, azobisisobutyramidine imidazoline hydrochloride, and azobisisobutyramidine cyanoformamide. The branched monomers include one or a combination of two or three of pentaerythritol, tetraacrylate or tetraallylpropoxyethane, and triethylenetetramine. The crosslinking monomers include one or more combinations of 1,4-pentadiene, 1,3-butadiene, diethylene glycol diacrylate, hexamethylenebisacrylamide, and diethylenetriamine.

[0011] In one possible design, the reaction temperature in S1 is 40~50℃, the reaction time is 1~5h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6; the reaction temperature in S2 is 70~75℃, the reaction time is 0.5~2h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6; and the reaction temperature in S3 is 90~92℃, the reaction time is 0.5~2h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6.

[0012] In one possible design, in S1, the cationic monomer comprises 2-5 parts by mass, the anionic monomer comprises 1.5-6 parts by mass, the amide-containing monomer comprises 100-150 parts by mass, water comprises 80-150 parts by mass, and the initiator comprises 0.02-0.08 parts by mass. In S2, the mass fraction of cationic monomers is 2.5–4 parts, the mass fraction of anionic monomers is 0.8–3 parts, the mass fraction of monomers containing amide bonds is 60–80 parts, the mass fraction of branched monomers is 2–6 parts, the mass fraction of water is 400–480 parts, and the mass fraction of initiator is 0.02–0.04 parts. In S3, the mass fraction of cationic monomer is 0.5 to 1 part, the mass fraction of anionic monomer is 0.6 to 2.5 parts, the mass fraction of monomer containing amide bond is 13 to 16 parts, the mass fraction of crosslinking monomer is 0.001 to 0.003 parts, the mass fraction of water is 280 to 340 parts, the mass fraction of initiator is 0.01 to 0.05 parts, and the mass fraction of terminator used to terminate the reaction is 0.03 to 0.07 parts.

[0013] In one possible design, in S3, the preset viscosity is 3000~30000cp, and the terminating agent used to terminate the reaction is any one or a combination of several of hydroquinone, p-tert-butylcatechol, and sodium dimethyl dithiocarbamate.

[0014] Secondly, embodiments of the present invention also provide a paper strengthening agent suitable for waste paper papermaking, prepared according to any of the above preparation methods.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: In this embodiment, polymerization reaction S1 yields the main chain structure, polymerization reaction S2 grows side chains on the main chain, and polymerization reaction S3 combines multiple main chains, including side chains, to form a network structure. This gradient structure design of "main chain-side chain-network" provides multi-point anchoring to enhance fiber bonding. The linear framework provided by the main chain penetrates the fiber network, while the numerous side chains derived from the branched structure act like "molecular tentacles," forming multi-point bonds with the hydroxyl groups of cellulose molecules through hydrogen bonds, ester bonds, or urethane bonds. This synergistic effect of "main chain penetration + side chain anchoring" increases the bonding efficiency between the product and fibers by more than 30%, significantly reduces inter-fiber slippage, and fundamentally improves the tensile strength and bursting strength of the paper.

[0016] The cross-linking agent introduced in S3 enables the molecular chains to form a three-dimensional network structure. This structure interweaves with the fibers during the paper drying process to form a "molecular-level support framework." When the paper is subjected to stress, the stress can be quickly dispersed to the entire fiber network through the network structure, avoiding breakage caused by local stress concentration. This is especially suitable for applications requiring high toughness, such as packaging paper.

[0017] The branched structure reduces molecular chain entanglement through steric hindrance, making the product easier to disperse in pulp and increasing the contact area with fibers. At the same time, the active groups at the ends of the branches can enhance the electrostatic adsorption with fibers, improve the retention rate of dry strength agents on the fiber surface, reduce the loss of additives, and lower production costs. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of a method for preparing a paper strengthening agent suitable for waste paper papermaking, provided by an embodiment of the present invention. Detailed Implementation

[0020] 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 with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a paper strengthening agent suitable for waste paper papermaking, comprising: S1, mix cationic monomer, anionic monomer, amide-containing monomer and water to obtain a first solution, add an initiator to the first solution to initiate the polymerization reaction and obtain a first polymerization solution; S2, mix cationic monomer, anionic monomer, amide-containing monomer, branched monomer and water to obtain a second solution, add the second solution and initiator to the first polymerization solution to initiate the polymerization reaction to obtain the second polymerization solution; S3: Cationic monomer, anionic monomer, amide-containing monomer, crosslinking monomer and water are mixed to obtain a third solution. The third solution and initiator are added to the second polymerization solution to initiate the polymerization reaction. The reaction is terminated when the solution viscosity reaches the preset viscosity to obtain a paper strengthening agent.

[0022] In this embodiment, polymerization reaction S1 yields the main chain structure, polymerization reaction S2 grows side chains on the main chain, and polymerization reaction S3 combines multiple main chains, including side chains, to form a network structure. This gradient structure design of "main chain-side chain-network" provides multi-point anchoring to enhance fiber bonding. The linear framework provided by the main chain penetrates the fiber network, while the numerous side chains derived from the branched structure act like "molecular tentacles," forming multi-point bonds with the hydroxyl groups of cellulose molecules through hydrogen bonds, ester bonds, or urethane bonds. This synergistic effect of "main chain penetration + side chain anchoring" increases the bonding efficiency between the product and fibers by more than 30%, significantly reduces inter-fiber slippage, and fundamentally improves the tensile strength and bursting strength of the paper.

[0023] The cross-linking agent introduced in S3 enables the molecular chains to form a three-dimensional network structure. This structure interweaves with the fibers during the paper drying process to form a "molecular-level support framework." When the paper is subjected to stress, the stress can be quickly dispersed to the entire fiber network through the network structure, avoiding breakage caused by local stress concentration. This is especially suitable for applications requiring high toughness, such as packaging paper.

[0024] The branched structure reduces molecular chain entanglement through steric hindrance, making the product easier to disperse in pulp and increasing the contact area with fibers. At the same time, the active groups at the ends of the branches can enhance the electrostatic adsorption with fibers, improve the retention rate of dry strength agents on the fiber surface, reduce the loss of additives, and lower production costs.

[0025] In some embodiments of the present invention, in step S1, after obtaining the first solution and before adding the initiator to initiate the polymerization reaction, the following steps are also included: The functional monomer is added to the first solution. The preparation process of the functional monomer is as follows: The first product was obtained by reacting glycerol, pentaerythritol, sorbitol and methanol in the presence of concentrated sulfuric acid. The first product and ε-caprolactone or lactide are dissolved in toluene and subjected to an addition reaction under the catalysis of dioctyltin dilaurate or dibutyltin diacetate to give the second product. The second product, acrylic acid or methacrylic acid, the catalyst p-toluenesulfonic acid, and the polymerization inhibitor hydroquinone are mixed and subjected to an esterification reaction to obtain the functional monomer.

[0026] In this embodiment, the functional monomer contains double bonds, urethane bonds, and ether bonds simultaneously. The addition of the monomer transforms the originally loose bond that relied on hydrogen bonds into a stronger chemical bond, significantly improving the tensile strength and bursting strength of the paper. The polymer chain containing ester bonds has both rigidity and flexibility, which can fill the gaps between fibers and evenly distribute stress, reducing the risk of local breakage when the paper is under stress. The bond energy of urethane bonds is much higher than that of hydrogen bonds and ordinary ester bonds. The three-dimensional cross-linked network can effectively resist tearing by external forces, making it less likely for the paper to separate between fibers when subjected to tension or impact. It can penetrate deep into the cellulose molecular chains, not only connecting the fibers but also reinforcing the crystalline structure of the fibers themselves, improving the breakage resistance of individual fibers.

[0027] In some embodiments of the present invention, the reaction conditions for generating the first product are 85-95°C for 3-4 hours, the reaction conditions for generating the second product are 20-25°C for 2-3 hours, and the reaction conditions for generating the functional monomer are 80-90°C for 2-4 hours.

[0028] In some embodiments of the present invention, the amounts of each raw material used in the preparation process of the functional monomer include: Amount of raw materials used in the preparation of the first product: The molar ratio of methanol to any one of glycerol, pentaerythritol, or sorbitol is 1.5:1 to 4:1; The molar ratio of concentrated sulfuric acid to any one of glycerol, pentaerythritol, or sorbitol is 0.01:1 to 0.05:1; Amount of raw materials used in the preparation of the second product: The second preparation raw materials include reactants, catalysts and solvents, wherein the molar ratio of the first product of the reactants to ε-caprolactone or lactide is 1:1.0~1.1; The mass ratio of catalyst to reactants is 0.005:1 to 0.01:1; The mass of the solvent toluene should be 2-3 times the mass of the reactants; Third product: The molar ratio of the second product to acrylic acid or methacrylic acid is 1:1.0~1.1; The molar ratio of p-toluenesulfonic acid to acrylic acid or methacrylic acid is 1:0.01~0.05; The molar ratio of the polymerization inhibitor hydroquinone to acrylic acid or methacrylic acid is 1:0.01~0.03.

[0029] In some embodiments of the present invention, the amount of functional monomer used is 1-5g of functional monomer per liter of the first solution.

[0030] In some embodiments of the present invention, the cationic monomers in S1-S3 each include one or more combinations of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, dodecyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, and methacryloyloxyethyldimethylbenzylammonium chloride. The anionic monomers in S1-S3 all include one or more combinations of sodium methacrylate, acrylic acid, sodium acrylate, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-acrylamido-2-methylpropanesulfonate. The amide-containing monomers in S1-S3 all include one or more combinations of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, and N-benzylacrylamide; The initiators in S1-S3 are all combinations of persulfates and azo compounds. Persulfates include sodium persulfate, ammonium persulfate, and potassium persulfate, while azo compounds include at least two of azobisisobutyramidine hydrochloride, azobisisobutyramimidoxoline hydrochloride, and azobisisobutyramisocyanoformamide. Branching monomers include one or a combination of two or three of pentaerythritol, tetraacrylate or tetraallylpropoxyethane, and triethylenetetramine. The crosslinking monomers include one or more combinations of 1,4-pentadiene, 1,3-butadiene, diethylene glycol diacrylate, hexamethylenebisacrylamide, and diethylenetriamine.

[0031] In some embodiments of the present invention, the reaction temperature in S1 is 40~50℃, the reaction time is 1~5h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6; the reaction temperature in S2 is 70~75℃, the reaction time is 0.5~2h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6; and the reaction temperature in S3 is 90~92℃, the reaction time is 0.5~2h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6.

[0032] In some embodiments of the present invention, in S1, the cationic monomer is 2-5 parts by mass, the anionic monomer is 1.5-6 parts by mass, the amide-containing monomer is 100-150 parts by mass, the water is 80-150 parts by mass, and the initiator is 0.02-0.08 parts by mass. In S2, the mass fraction of cationic monomers is 2.5–4 parts, the mass fraction of anionic monomers is 0.8–3 parts, the mass fraction of monomers containing amide bonds is 60–80 parts, the mass fraction of branched monomers is 2–6 parts, the mass fraction of water is 400–480 parts, and the mass fraction of initiator is 0.02–0.04 parts. In S3, the mass fraction of cationic monomer is 0.5 to 1 part, the mass fraction of anionic monomer is 0.6 to 2.5 parts, the mass fraction of monomer containing amide bond is 13 to 16 parts, the mass fraction of crosslinking monomer is 0.001 to 0.003 parts, the mass fraction of water is 280 to 340 parts, the mass fraction of initiator is 0.01 to 0.05 parts, and the mass fraction of terminator used to terminate the reaction is 0.03 to 0.07 parts.

[0033] In some embodiments of the present invention, in S3, the preset viscosity is 3000~30000cp, and the terminating agent used to terminate the reaction is any one or a combination of several of hydroquinone, p-tert-butylcatechol, and sodium dimethyl dithiocarbamate.

[0034] This invention also provides a paper strengthening agent suitable for waste paper papermaking, prepared according to any of the above preparation methods.

[0035] To more clearly illustrate the technical solution and advantages of the present invention, several embodiments are described in detail below.

[0036] Example 1 Raw material preparation: Five parts by weight of cationic monomer (including two parts by weight of methacryloyloxyethyltrimethylammonium chloride, two parts by weight of acryloyloxyethyltrimethylammonium chloride, and one part by weight of acryloyloxyethyldimethylbenzylammonium chloride). In S1, there are 1 part by weight of methacryloyloxyethyltrimethylammonium chloride and 1 part by weight of acryloyloxyethyltrimethylammonium chloride; In S2, there are 1 part by weight of methacryloyloxyethyltrimethylammonium chloride, 1 part by weight of acryloyloxyethyltrimethylammonium chloride, and 0.5 parts by weight of acryloyloxyethyldimethylbenzylammonium chloride; In S3, there are 0.5 parts by weight of acryloyloxyethyl dimethyl benzyl ammonium chloride; 3 parts by weight of anionic monomer (1 part by weight of sodium methacrylate sulfonate, 2 parts by weight of acrylic acid) In S1, sodium methacrylate sulfonate is 0.5 parts by weight and acrylic acid is 1 part by weight; In S2, sodium methacrylate sulfonate is 0.4 parts by weight and acrylic acid is 0.5 parts by weight; In S3, sodium methacrylate sulfonate is 0.1 parts by weight and acrylic acid is 0.5 parts by weight; 192 parts by weight of monomers containing amide bonds (180 parts by weight of acrylamide and 12 parts by weight of methacrylamide). In S1, there are 100 parts by weight of acrylamide and 8 parts by weight of methacrylamide; S2 contains 60 parts by weight of acrylamide and 2 parts by weight of methacrylamide; S3 contains 12 parts by weight of acrylamide and 2 parts by weight of methacrylamide; In S2, branched monomer: 2 parts by mass (pentaerythritol). In S3, there are 0.001 parts by mass of cross-linked monomer (1,4-pentadiene). In deionized water, S1 contains 88.5 parts by mass, S2 contains 434.6 parts by mass, and S3 contains 284.9 parts by mass. 0.05 parts by weight of initiator, 0.02 parts by weight in S1, 0.02 parts by weight in S2, and 0.01 parts by weight in S3; Terminator: 0.03 parts by weight of hydroquinone.

[0037] The preparation steps are as follows: S1, add cationic monomer, anionic monomer, and amide-containing monomer to the polymerization tank, add water and mix well to obtain the first solution, adjust the pH of the system to 3, remove oxygen by purging with nitrogen, raise the temperature to 40°C, add initiator to initiate polymerization, wait for the temperature to rise naturally to the maximum temperature, keep it at the temperature for 3 hours to obtain the first polymerization solution; S2, add cationic monomer, anionic monomer, amide-containing monomer and branched monomer to mixing tank 1, add water and mix evenly, then adjust the pH value to 3, and slowly add it to the first polymerization solution. The dropping time is determined according to the system temperature, and the dropping temperature is controlled at 73℃. After the dropping is completed, add initiator and keep warm for 0.5 hours to obtain the second polymerization solution. S3. Add cationic monomer, anionic monomer, amide-containing monomer, and crosslinking monomer to mixing tank 2. Add water and mix evenly. Adjust the pH value to 3 and slowly add it to the second polymerization solution. The dropping time depends on the system temperature. The dropping temperature is controlled at 91℃. After the dropping is completed, keep it at the temperature for 0.5 hours. Test the viscosity to 6000cp. Add a terminator to terminate the reaction. After filtration, the paper strengthening agent is obtained.

[0038] Example 2 Example 2 is basically the same as Example 1, except that: In Example 2, 10 parts by weight of cationic monomer (including 4 parts by weight of methacryloyloxyethyltrimethylammonium chloride, 4 parts by weight of acryloyloxyethyltrimethylammonium chloride, and 2 parts by weight of acryloyloxyethyldimethylbenzylammonium chloride). In S1, there are 3 parts by weight of methacryloyloxyethyltrimethylammonium chloride and 2 parts by weight of acryloyloxyethyltrimethylammonium chloride; S2 contains 1 part by weight of methacryloyloxyethyltrimethylammonium chloride, 2 parts by weight of acryloyloxyethyltrimethylammonium chloride, and 1 part by weight of acryloyloxyethyldimethylbenzylammonium chloride; S3 contains 1 part by weight of acryloyloxyethyl dimethyl benzyl ammonium chloride; Deionized water, 85.5 parts by mass in S1, 433.1 parts by mass in S2, and 284.5 parts by mass in S3; The remaining parts are basically the same as in Example 1.

[0039] The resulting product is a paper strengthening agent with a viscosity of 6500.

[0040] Example 3 Example 3 is basically the same as Example 1, except that: In Example 3, 10 parts by weight of anionic monomer (2 parts by weight of sodium methacrylate sulfonate and 8 parts by weight of acrylic acid). In S1, sodium methacrylate sulfonate is 1.5 parts by weight and acrylic acid is 4 parts by weight; In S2, sodium methacrylate sulfonate is 0.4 parts by weight and acrylic acid is 2 parts by weight; In S3, sodium methacrylate sulfonate is 0.1 parts by weight and acrylic acid is 2 parts by weight; In deionized water, S1 contains 84.5 parts by mass, S2 contains 433.1 parts by mass, and S3 contains 283.4 parts by mass. The reaction steps and process are the same as in Example 1, and the paper strengthening agent with a viscosity of 6500 is obtained after the reaction.

[0041] Example 4 It is basically the same as Example 1, except that methacryloyloxyethyltrimethylammonium chloride is replaced with dodecyltrimethylammonium chloride; The reaction steps and process are the same as in Example 1, and the paper strengthening agent with a viscosity of 8000 is obtained after the reaction.

[0042] Example 5 This is basically the same as Example 1, except that acrylic acid is replaced with itaconic acid and the branched monomer pentaerythritol is replaced with tetraallylpropoxyethane. The reaction steps and process are the same as in Example 1, and the paper strengthening agent with a viscosity of 9000 is obtained after the reaction.

[0043] Example 6 Example 6 is basically the same as Example 1, except that in S1, 3.g of functional monomer is added per liter of the first solution. The preparation method of the functional monomer is as follows: Step 1: Synthesize intermediates containing ether bonds and free hydroxyl groups (introducing ether bonds) Glycerol, pentaerythritol, and sorbitol were mixed in concentrated sulfuric acid (catalyst) and methanol and reacted at 90°C for 4 hours. The mixture was then purified by distillation to obtain a colorless and transparent liquid first product. The molar ratio of methanol, glycerol, pentaerythritol, sorbitol, and concentrated sulfuric acid was 2:1:1:1:0.03. Step 2: The first product from Step 1 and ε-caprolactone are dissolved in toluene and reacted at 25°C for 2.5 hours with dioctyltin dilaurate as a catalyst to undergo an addition reaction. The second product is then obtained by vacuum distillation. The molar ratio of the first product to ε-caprolactone is 1:1, the mass ratio of the catalyst and reactant (first product to ε-caprolactone) is 0.008:1, and the mass ratio of toluene and reactant (first product to ε-caprolactone) is 2:1. Step 3: Introduce double bonds (by connecting unsaturated groups through esterification). The second product, acrylic acid, p-toluenesulfonic acid (catalyst), and hydroquinone (polymerization inhibitor) were mixed and heated to 85°C to induce esterification of the hydroxyl groups with the carboxyl groups of acrylic acid. After alkali washing, separation, and distillation purification, the functional monomer was obtained. The molar ratio of the second product, acrylic acid, p-toluenesulfonic acid, and hydroquinone was 1:1:0.02:0.01.

[0044] Comparative Example 1 Comparative Example 1 is basically the same as Example 2, except that it does not contain anionic monomers; Comparative Example 2 Comparative Example 1 is basically the same as Example 2, except that it does not contain the branched monomer pentaerythritol. Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that the total amount of cationic monomers is 70 parts by weight (of which 20 parts by weight of methacryloyloxyethyltrimethylammonium chloride, 30 parts by weight of acryloyloxyethyltrimethylammonium chloride, and 20 parts by weight of acryloyloxyethyldimethylbenzylammonium chloride).

[0045] Evaluation method: 1. The retention rate of the paper filler was determined by measuring the absorbance of the first white water during the papermaking process using a spectrophotometer. 2. The paper bursting strength tester (model YT-NPY1600) was used for testing, and the standards ISO2758 "Determination of bursting strength of paper" and GB / T454 "Determination of bursting strength of paper" were followed. 3. The tensile strength of paper was tested according to GB / T 12914-2018 Determination of tensile strength of paper and paperboard - rapid tensile test method; 4. The product's water filtration performance was tested using a dynamic water filtration instrument;

[0046] Tests show that the addition of branched paper retention aids can achieve a retention rate of over 98.5% for the first batch of paper stock, demonstrating a significant retention effect. The resulting paper has a tensile index of 60 N·m / g and a bursting index of over 1.78 Kpam² / g, exhibiting excellent water filtration performance and good overall performance.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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 method for preparing a paper strengthening agent suitable for waste paper papermaking, characterized in that, include: S1, mix cationic monomer, anionic monomer, amide-containing monomer and water to obtain a first solution, add an initiator to the first solution to initiate a polymerization reaction to obtain a first polymerization solution; S2, mix cationic monomer, anionic monomer, amide-containing monomer, branched monomer and water to obtain a second solution, add the second solution and initiator to the first polymerization solution to initiate the polymerization reaction to obtain a second polymerization solution; S3, mix cationic monomer, anionic monomer, amide-containing monomer, crosslinking monomer and water to obtain a third solution, add the third solution and initiator to the second polymerization solution to initiate the polymerization reaction, and terminate the reaction after the solution viscosity reaches the preset viscosity to obtain a paper strengthening agent.

2. The preparation method according to claim 1, characterized in that, In S1, after obtaining the first solution and before adding the initiator to initiate the polymerization reaction, the following steps are also included: A functional monomer is added to the first solution. The process for preparing the functional monomer is as follows: The first product was obtained by reacting glycerol, pentaerythritol, sorbitol and methanol in the presence of concentrated sulfuric acid. The first product and ε-caprolactone or lactide are dissolved in toluene and subjected to an addition reaction under the catalysis of dioctyltin dilaurate or dibutyltin diacetate to obtain the second product. The second product, acrylic acid or methacrylic acid, p-toluenesulfonic acid catalyst, and hydroquinone inhibitor are mixed and esterified to obtain a functional monomer.

3. The preparation method according to claim 2, characterized in that, The reaction conditions for generating the first product are 85-95°C for 3-4 hours, the reaction conditions for generating the second product are 20-25°C for 2-3 hours, and the reaction conditions for generating the functional monomer are 80-90°C for 2-4 hours.

4. The preparation method according to claim 2, characterized in that, The amount of raw materials used in the preparation of the first product during the preparation of functional monomers: The molar ratio of methanol to any one of glycerol, pentaerythritol, or sorbitol is 1.5:1 to 4:1; The molar ratio of concentrated sulfuric acid to any one of glycerol, pentaerythritol, or sorbitol is 0.01:1 to 0.05:1; Amount of raw materials used in the preparation of the second product: The second preparation raw materials include reactants, catalysts and solvents, wherein the molar ratio of the first product of the reactants to ε-caprolactone or lactide is 1:1.0~1.1; The mass ratio of catalyst to reactants is 0.005:1 to 0.01:1; The mass of the solvent toluene should be 2-3 times the mass of the reactants; Third product: The molar ratio of the second product to acrylic acid or methacrylic acid is 1:1.0~1.1; The molar ratio of p-toluenesulfonic acid to acrylic acid or methacrylic acid is 1:0.01~0.05; The molar ratio of the polymerization inhibitor hydroquinone to acrylic acid or methacrylic acid is 1:0.01~0.

03.

5. The preparation method according to claim 2, characterized in that, The amount of the functional monomer used is 1-5g per liter of the first solution.

6. The preparation method according to claim 1, characterized in that, The cationic monomers in S1-S3 all include one or more combinations of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, dodecyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, and methacryloyloxyethyldimethylbenzylammonium chloride. The anionic monomers in S1-S3 all include one or more combinations of sodium methacrylate, acrylic acid, sodium acrylate, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-acrylamido-2-methylpropanesulfonate. The amide-containing monomers in S1-S3 all include one or more combinations of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide and N-benzylacrylamide; The initiators mentioned in S1-S3 are all combinations of persulfates and azo compounds. Persulfates include sodium persulfate, ammonium persulfate, and potassium persulfate, while azo compounds include at least two of azobisisobutyramidine hydrochloride, azobisisobutyramidine imidazoline hydrochloride, and azobisisobutyramidine cyanoformamide. The branched monomers include one or a combination of two or three of pentaerythritol, tetraacrylate or tetraallylpropoxyethane, and triethylenetetramine. The crosslinking monomers include one or more combinations of 1,4-pentadiene, 1,3-butadiene, diethylene glycol diacrylate, hexamethylenebisacrylamide, and diethylenetriamine.

7. The preparation method according to claim 1, characterized in that, The reaction temperature in S1 is 40~50℃, the reaction time is 1~5h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6. The reaction temperature in S2 is 70~75℃, the reaction time is 0.5~2h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6. The reaction temperature in S3 is 90~92℃, the reaction time is 0.5~2h, and the reaction environment is an acidic anaerobic environment with a pH range of 2~6.

8. The preparation method according to claim 1, characterized in that, In S1, the cationic monomer comprises 2-5 parts by mass, the anionic monomer comprises 1.5-6 parts by mass, the monomer containing the amide bond comprises 100-150 parts by mass, water comprises 80-150 parts by mass, and the initiator comprises 0.02-0.08 parts by mass. In S2, the mass fraction of cationic monomers is 2.5–4 parts, the mass fraction of anionic monomers is 0.8–3 parts, the mass fraction of monomers containing amide bonds is 60–80 parts, the mass fraction of branched monomers is 2–6 parts, the mass fraction of water is 400–480 parts, and the mass fraction of initiator is 0.02–0.04 parts. In S3, the mass fraction of cationic monomer is 0.5 to 1 part, the mass fraction of anionic monomer is 0.6 to 2.5 parts, the mass fraction of monomer containing amide bond is 13 to 16 parts, the mass fraction of crosslinking monomer is 0.001 to 0.003 parts, the mass fraction of water is 280 to 340 parts, the mass fraction of initiator is 0.01 to 0.05 parts, and the mass fraction of terminator used to terminate the reaction is 0.03 to 0.07 parts.

9. The preparation method according to claim 1, characterized in that, In S3, the preset viscosity is 3000~30000cp, and the terminating agent used to terminate the reaction is any one or a combination of several of hydroquinone, p-tert-butylcatechol, and sodium dimethyl dithiocarbamate.

10. A paper strengthening agent suitable for waste paper papermaking, characterized in that, Prepared according to any one of the preparation methods in claims 1-9.

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