A low residual single paper reinforcing agent, its preparation method and application

Abstract

The application relates to the field of papermaking chemicals, and particularly discloses a low-residual paper strengthening agent, a preparation method and application thereof, which comprises the following components in parts by weight: 0.5-2 parts of a sodium carboxymethyl cellulose solution, 0.1-0.5 parts of an amphoteric ion polymer solution, 0.5-3 parts of a low-residual cationic high-molecular strengthening agent solution, 94-99 parts of deionized water, and 2-5 parts of ethanolamine, wherein the amphoteric ion polymer is configured as a polysulfobetaine. The low-residual paper strengthening agent has the effect of improving the paper strengthening agent under low residual, and can be applied to the manufacturing of food packaging paper, medical paper, high-grade cultural paper or high-strength packaging paperboard.

Description

Technical Field

[0001] This application relates to the field of papermaking chemicals, and more specifically, to a low residual single-sheet paper strengthening agent, its preparation method, and its application. Background Technology

[0002] Paper strength is one of the core indicators for measuring paper quality. Currently, widely used paper strength enhancers are mainly synthetic polymers such as polyacrylamide (PAM) and natural modified polymers such as starch. However, PAM products carry the risk of residual acrylamide monomer (AM), which is neurotoxic and poses a potential threat to human health, particularly limiting its application in food packaging paper, medical paper, and other fields. Existing technologies have adopted various measures to reduce residual monomers, such as optimizing the polymerization process and adding monomer trapping agents. However, reducing residual monomers often results in poor enhancement. Summary of the Invention

[0003] To address the problems existing in the prior art and to improve the effect of paper strengthening agents under low residual sizing conditions, this application provides a low residual sizing paper strengthening agent comprising the following components in parts by weight: 0.5-2 parts sodium carboxymethyl cellulose solution, 0.1-0.5 parts zwitterionic polymer solution, 0.5-3 parts low residual sizing cationic polymer strengthening agent solution, 2-5 parts ethanolamine, and 94-99 parts deionized water, wherein the zwitterionic polymer is polysulfobetaine.

[0004] By adopting the above technical solution, the low-residue paper reinforcing agent provided in this application achieves a synergistic effect among its components. The sulfobetaine group can bind a large number of water molecules through ionic solvation, forming a dense hydrated layer on its surface. After being added to pulp, the hydration of the sulfobetaine group helps water molecules enter the fiber cell wall more quickly, softening the fiber, increasing the contact area between fibers, and promoting hydrogen bonding. Simultaneously, the hydrated layer acts as a lubricant, helping other components to distribute more evenly on the fiber surface, avoiding local flocculation, and thus more effectively exerting its reinforcing effect. Sodium carboxymethyl cellulose has fiber swelling function; its addition increases fiber flexibility, exposing more hydroxyl binding sites, facilitating the subsequent bonding of the low-residue cationic polymer reinforcing agent with the fiber. The carboxyl groups on the sodium carboxymethyl cellulose molecular chain form ionic bonds with the zwitterionic polymer and the low-residue polymer reinforcing agent, further strengthening the network structure. The low-residue cationic polymer reinforcing agent possesses a long molecular chain structure and functional groups, forming a high-strength bond with pre-swollen fibers. Simultaneously, its groups interact electrostatically with sodium carboxymethyl cellulose and zwitterionic polymers, constructing a stable three-dimensional network structure. The amino groups of ethanolamine possess a certain free radical scavenging ability, selectively binding with free acrylamide free radicals in the system, preventing their polymerization to form ungrafted polyacrylamide homopolymers. This application achieves a synergistic reinforcing effect through the complementary functions of the three components, significantly improving the physical strength of paper while reducing the amount of low-residue cationic polymer reinforcing agent solution used. It also limits the cationic polymer reinforcing agent to low-residue cationic polymer reinforcing agents, reducing residual fibers and ensuring the product's environmental friendliness and safety. This results in a low-residue paper reinforcing agent.

[0005] Preferably, the low-residue monocationic polymer reinforcing agent is an organic polymer reinforcing agent obtained by modifying natural polymers.

[0006] By adopting the above technical solution, using natural polymers as starting materials, the possibility of monomers remaining in the product after synthesis of polymers is reduced, further promoting low monomer residue in paper strengthening agents.

[0007] Preferably, the organic polymer reinforcing agent is a modified cationic starch graft copolymer, wherein the modified cationic starch graft copolymer has a grafting rate of 60%-120%, a cationic substitution degree of 0.02-0.10, and a residual monomer content of less than 50 ppm.

[0008] By adopting the above technical solution, starch, as the main backbone, can effectively reduce the retention of polymer molecules in the final product while ensuring paper strength. However, if the grafting rate of the modified cationic starch graft copolymer is below 60%, the synthetic polymer will have insufficient branching, resulting in insufficient paper reinforcement. If the grafting rate is above 120%, there may be problems with excessively long molecular chains and large molecular weights, leading to poor product solubility and extremely high solution viscosity, affecting the dispersion of the reinforcing agent in the pulp. A grafting rate of 60%-120% ensures the possibility of successful grafting of cationic starch molecules, with a cationic substitution degree of 0.02 to 0.10, providing the product with a suitable cationic charge. The limitations of grafting rate and ionic substitution degree allow the modified cationic starch graft copolymer to combine the affinity of cationic starch with the efficient bridging ability of the synthetic polymer.

[0009] Preferably, the modified cationic starch graft copolymer is a cationic starch-acrylamide graft copolymer.

[0010] By adopting the above technical solution, the cationic starch-acrylamide graft copolymer possesses both cationic charges and amide groups. The cationic charges can be quickly and firmly adsorbed onto the negatively charged fiber surface through electrostatic interactions, improving the product retention rate. The amide groups, through hydrogen bonding, cause the long-chain polyacrylamide branches to entangle and connect to the surrounding fibers, significantly enhancing the bonding force between fibers. Preferably, the organic polymeric reinforcing agent is configured as a chitosan-acrylamide graft copolymer solution.

[0011] By employing the above technical solution, chitosan molecules possess excellent electrostatic adsorption capabilities, enabling them to adsorb onto pulp fibers more quickly and firmly, resulting in a good retention rate. Simultaneously, chitosan exhibits good film-forming properties; when used as a paper reinforcing agent, it can form a dense film on the fiber surface, significantly improving the paper's surface strength, burst strength, and wet and dry strength. The synergistic effect with polyacrylamide branches enhances the paper reinforcing agent's effectiveness, and as a natural substance, it can reduce residual residue in the entire reinforcing agent system.

[0012] Preferably, the polysulfonated betaine is configured as poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate).

[0013] By adopting the above technical solution, poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) exhibits good compatibility with other substances in the system, effectively preventing phase separation or flocculation caused by charge conflict. It enhances the stability of the compound system, as the sulfonate group can bind to the cationic groups in its polymer, while its quaternary ammonium cation can bind to the negatively charged groups of fibers and CMC. This bidirectional binding capability makes it a highly efficient "molecular bridge" connecting components with different charges in the system, weaving together components that might otherwise act independently into a robust and dense overall network, thereby achieving a synergistic reinforcement effect that surpasses the simple superposition of the effects of using reinforcing agents alone.

[0014] On the other hand, this application also provides a method for preparing a low residual paper strengthening agent, comprising the following steps: S1: Modify natural polymers to obtain an organic polymer reinforcing agent solution; S2: Mix the sodium carboxymethyl cellulose solution and the polysulfobetaine solution thoroughly to obtain a premixed solution; S3: Under stirring conditions, ethanolamine and organic polymer reinforcing agent solution are mixed to form a blend, and the blend is added to the premix and mixed thoroughly to obtain reinforcing agent premix; S4: Add deionized water to the reinforcing agent premix, dilute to the required concentration, and mix evenly to obtain a low residual paper reinforcing agent.

[0015] Preferably, S1 further includes the addition of a monomer trapping agent.

[0016] By adopting the above technical solution, it is possible to effectively reduce the monomer substances in the reinforcing agent while mixing and compounding the system, and increase the amount of residual monomers in the final product.

[0017] In another aspect, this application also provides an application of a low residual paper strengthening agent, which is added into the pulp during the paper preparation process, and the amount added is 0.5% - 2.0% of the oven-dry pulp weight.

[0018] By adopting the above technical solutions, it is ensured that the amount of paper used can effectively enhance paper strength while reducing the retention of defective sheets.

[0019] Preferably, the paper is food packaging paper, medical paper, high-grade cultural paper, or high-strength packaging paperboard.

[0020] In summary, this application has at least the following beneficial effects: The sulfobetaine group can bind a large number of water molecules through ionic solvation, forming a dense hydrated layer on its surface. When added to pulp, the hydration of the sulfobetaine group helps water molecules penetrate the fiber cell wall more quickly, softening the fiber, increasing the contact area between fibers, and promoting hydrogen bonding. Simultaneously, the hydrated layer acts as a lubricant, helping other components to distribute more evenly on the fiber surface, avoiding localized flocculation, and thus more effectively exerting its reinforcing effect. 2. Through the complementary functions of the three components, a synergistic strengthening effect is achieved when the components are used in combination. Under the condition of achieving the same strength effect, the use of acrylamide monomer can be reduced. At the same time, in the compounded components, the cationic polymeric reinforcing agent is limited to a low residual monomer cationic polymeric reinforcing agent. The amount of residual monomer in the paper reinforcing agent is controlled by the monomer capturing agent, thereby reducing the retention of residual monomer and ensuring the environmental protection and safety of the product. The compounded components form a low residual monomer paper reinforcing agent. Detailed Implementation

[0021] The present application will be further described in detail below with reference to the embodiments. Unless otherwise specified, the raw materials required for the embodiments and comparative examples in this application are all from conventional commercially available brands or obtained through conventional preparation processes.

[0022] Example 1 S1: Add 100 parts cationic starch and 400 parts deionized water to a reactor, heat to 95℃ and gelatinize for 30 minutes. Cool to 65℃, purge with nitrogen to remove oxygen, add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate and 0.3 parts sodium bisulfite, and react for 4 hours. Cool to 60℃, add 0.1 parts of a self-made sulfite monomer catcher, and react for 1 hour to obtain a cationic starch-acrylamide graft copolymer solution with a solid content of approximately 20%. Testing showed that the residual acrylamide monomer content was 20 ppm, the grafting rate was 85%, and the degree of ionic substitution was 0.02.

[0023] S2: In a stirrer, add 0.5 parts of 1% sodium carboxymethyl cellulose solution and 0.5 parts of 5% poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain a premix.

[0024] S3: Mix 0.5 parts of the cationic starch-acrylamide graft copolymer solution prepared in S1 with 2 parts of ethanolamine to form a blend. Add the blend to the premix and stir at low speed for 15 minutes until the mixture is uniform. Continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0025] S4: Add 94 parts of deionized water to the premixed strengthening agent solution and continue stirring for 30 minutes to obtain a low residual paper strengthening agent.

[0026] Example 2 S1: Add 100 parts cationic starch and 400 parts deionized water to a reactor, heat to 95℃ and gelatinize for 30 minutes. Cool to 65℃, purge with nitrogen to remove oxygen, add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate and 0.3 parts sodium bisulfite, and react for 4 hours. Cool to 60℃, add 0.1 parts of a self-made sulfite monomer catcher, and react for 1 hour to obtain a cationic starch-acrylamide graft copolymer solution with a solid content of approximately 20%. Testing showed that the residual acrylamide monomer content was 40 ppm, the grafting rate was 110%, and the degree of ionic substitution was 0.05.

[0027] S2: In a stirrer, add 2 parts of 1% sodium carboxymethyl cellulose solution and 0.1 parts of 5% poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain a premix.

[0028] S3: Mix 0.5 parts of the cationic starch-acrylamide graft copolymer solution prepared in S1 with 5 parts of ethanolamine to form a blend. Add the blend to the premix and stir at low speed for 15 minutes until the mixture is uniform. Continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0029] S4: Add 99 parts of deionized water to the premixed strengthening agent solution and continue stirring for 30 minutes to obtain a low residual paper strengthening agent.

[0030] Example 3 S1: Add 100 parts cationic starch and 400 parts deionized water to a reactor, heat to 95℃ and gelatinize for 30 minutes. Cool to 65℃, purge with nitrogen to remove oxygen, add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate and 0.3 parts sodium bisulfite, and react for 4 hours. Cool to 60℃, add 0.1 parts of a self-made sulfite monomer catcher, and react for 1 hour to obtain a cationic starch-acrylamide graft copolymer solution with a solid content of approximately 20%. Testing showed that the residual acrylamide monomer content was 45 ppm, the grafting rate was 115%, and the degree of ionic substitution was 0.08.

[0031] S2: In a stirrer, add 2 parts of 1% sodium carboxymethyl cellulose solution and 0.1 parts of 5% poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain a premix.

[0032] S3: Mix 3 parts of the cationic starch-acrylamide graft copolymer solution prepared in S1 with 2 parts of ethanolamine to form a blend. Add the blend to the premix and stir at low speed for 15 minutes until the mixture is uniform. Continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0033] S4: Add 99 parts of deionized water to the premixed strengthening agent solution and continue stirring for 30 minutes to obtain a low residual paper strengthening agent.

[0034] Example 4 S1: Add 10 parts chitosan powder, 5 parts glacial acetic acid, and 385 parts deionized water to a reactor. Start stirring and slowly heat to 60°C, continuing stirring at this temperature for 3 hours until the chitosan is completely dissolved. Cool the chitosan-acetic acid solution to 50°C. Continuously purge the reactor with nitrogen gas for 30 minutes. Add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate, and 0.3 parts sodium bisulfite sequentially. Perform a graft copolymerization reaction at 50°C under nitrogen protection and continuous stirring for 5 hours. After the reaction, cool the system to 45°C, add 0.1 parts of a self-made sulfite monomer catcher, and continue stirring and maintaining the temperature for 1.5 hours to ensure complete removal of unreacted acrylamide monomer. The product was found to have a solid content of approximately 13%, a residual acrylamide monomer content of 40 ppm, and a grafting rate of 105%.

[0035] S2: In a stirrer, add 2 parts of 1% sodium carboxymethyl cellulose solution and 0.1 parts of 5% poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain a premix.

[0036] S3: Mix 3 parts of the chitosan-acrylamide graft copolymer solution obtained in S1 with 2 parts of ethanolamine to form a blend. Add the blend to the premix and stir at low speed for 15 minutes until the mixture is uniform. Continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0037] S4: Add 99 parts of deionized water to the premixed strengthening agent solution and continue stirring for 30 minutes to obtain a low residual paper strengthening agent.

[0038] Example 5 S1: Add 10 parts cationic guar gum and 440 parts deionized water to a reactor, stir at high speed, and dissolve at room temperature for 2 hours. Then heat the reactor to 55°C. Continuously purge the solution with nitrogen for 40 minutes, then add 50 parts acrylamide monomer, 0.6 parts ammonium persulfate, and 0.4 parts sodium bisulfite sequentially. Under nitrogen protection and continuous stirring at 55°C, carry out a graft copolymerization reaction for 4 hours. After the reaction, cool the system to 50°C, add 0.1 parts of a self-made sulfite monomer catcher, and continue stirring and maintaining the temperature for 1 hour to ensure complete removal of unreacted acrylamide monomer. The product was found to have a solid content of approximately 12%, a residual acrylamide monomer content of 41 ppm, and a grafting rate of 95%.

[0039] S2: In a stirrer, add 2 parts of 1% sodium carboxymethyl cellulose solution and 0.1 parts of 5% poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain a premix.

[0040] S3: Mix 3 parts of the guar gum-acrylamide graft copolymer solution prepared in S1 with 2 parts of ethanolamine to form a blend. Add the blend to the premix and stir at low speed for 15 minutes until the mixture is uniform. Continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0041] S4: Add 99 parts of deionized water to the premixed strengthening agent solution and continue stirring for 30 minutes to obtain a low residual paper strengthening agent.

[0042] Comparative Example 1 S1: In a stirrer, add 2 parts of 1% sodium carboxymethyl cellulose solution and 0.1 parts of 5% poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain a premix.

[0043] S3: Mix 3 parts starch solution with 2 parts ethanolamine to form a blend, add the blend to the premix, stir at low speed for 15 minutes until uniformly mixed, and continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0044] S4: Add 99 parts of deionized water to the premixed strengthening agent solution and continue stirring for 30 minutes to obtain the paper strengthening agent.

[0045] Comparative Example 2 S1: Add 100 parts cationic starch and 400 parts deionized water to a reactor, heat to 95℃ and gelatinize for 30 minutes. Cool to 65℃, purge with nitrogen to remove oxygen, add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate and 0.3 parts sodium bisulfite, and react for 4 hours. Cool to 60℃, add 0.1 parts of a self-made amine composite monomer catcher, and react for 1 hour to obtain a cationic starch-acrylamide graft copolymer solution with a solid content of approximately 20%. Testing showed that the residual acrylamide monomer content was 45 ppm, the grafting rate was 115%, and the degree of ionic substitution was 0.08.

[0046] S2: In a stirrer, add 2.1 parts of 1% sodium carboxymethyl cellulose solution and 3 parts of the cationic starch-acrylamide graft copolymer solution prepared in S1 in sequence, stir at low speed for 15 minutes until the mixture is uniform, and continue stirring for 45 minutes to obtain the reinforcing agent premix.

[0047] S3: Add 2 parts of ethanolamine to the premixed strengthening agent solution to form a blend solution. Add the blend solution to the premixed strengthening agent solution, add 99 parts of deionized water, and continue stirring for 30 minutes to obtain the paper strengthening agent.

[0048] Comparative Example 3 S1: Add 100 parts cationic starch and 400 parts deionized water to a reactor, heat to 95℃ and gelatinize for 30 minutes. Cool to 65℃, purge with nitrogen to remove oxygen, add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate and 0.3 parts sodium bisulfite, and react for 4 hours. Cool to 60℃, add 0.1 parts of a self-made amine composite monomer catcher, and react for 1 hour to obtain a cationic starch-acrylamide graft copolymer solution with a solid content of approximately 20%. Testing showed that the residual acrylamide monomer content was 45 ppm, the grafting rate was 115%, and the degree of ionic substitution was 0.08.

[0049] S2: In a stirrer, add 5 parts of the cationic starch-acrylamide graft copolymer solution prepared in S1 and 0.1 parts of a 5% concentration poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution in sequence, and stir at low speed for 15 minutes until the mixture is uniform to obtain the reinforcing agent premix.

[0050] S3: Add 2 parts of ethanolamine to the premixed strengthening agent solution to form a blend solution. Add 99 parts of deionized water to the blend solution and continue stirring for 30 minutes to obtain the paper strengthening agent.

[0051] Comparative Example 4 S1: Add 100 parts cationic starch and 400 parts deionized water to a reactor, heat to 95℃ and gelatinize for 30 minutes. Cool to 65℃, purge with nitrogen to remove oxygen, add 50 parts acrylamide monomer, 0.5 parts ammonium persulfate and 0.3 parts sodium bisulfite, and react for 4 hours. Cool to 60℃, add 0.1 parts of a self-made amine composite monomer catcher, and react for 1 hour to obtain a cationic starch-acrylamide graft copolymer solution with a solid content of approximately 20%. Testing showed that the residual acrylamide monomer content was 45 ppm, the grafting rate was 115%, and the degree of ionic substitution was 0.08.

[0052] S2: Take 5.1 parts of the cationic starch-acrylamide graft copolymer solution prepared in S1 and add 2 parts of ethanolamine to form a blend. Add 99 parts of deionized water to the blend and continue stirring for 30 minutes to obtain a paper strengthening agent.

[0053] Comparative Example 5 A paper strengthening agent was obtained by mixing 5.1 parts of a 1% sodium carboxymethyl cellulose solution with 99 parts of deionized water.

[0054] Comparative Example 6 A paper strengthening agent was obtained by mixing 5.1 parts of a 5% concentration poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate) solution with 99 parts of deionized water.

[0055] Comparative Example 7 Commercially available paper strengthening agents.

[0056] The reinforcing agents of the examples and comparative examples were applied to 80 g / m³, respectively. 2 In the bleached sulfate wood pulp hand-made sheets, each sheet of paper has 100g of oven-dry pulp, and the amount of reinforcing agent added is 1.0% of the oven-dry pulp weight, and the method of addition is to add it into the pulp.

[0057] Test standards: Tensile strength index (ISO 1924-2), bursting strength index (ISO 2758), tear strength index (ISO 1974). Test results are as follows: Example 1 58 4.35 8.98 20ppm Example 2 62 4.39 9.19 40ppm Example 3 66 4.47 9.27 45 ppm Example 4 64 4.41 9.25 40 ppm Example 5 65 4.46 9.21 41ppm Comparative Example 1 37 3.45 7.20 / Comparative Example 2 34 3.43 7.11 45 ppm Comparative Example 3 36 3.24 7.21 45 ppm Comparative Example 4 32 3.12 7.03 45 ppm Comparative Example 5 28 2.81 6.75 / Comparative Example 6 21 2.75 6.80 / Comparative Example 7 23 3.01 6.98 73ppm Comparing Examples 1 to 5 with Comparative Examples 1 to 6, the residual sheet quantity was kept below 50 ppm, significantly lower than the 73 ppm of Comparative Example 7. This shows that by controlling the low residual sheet cationic polymer reinforcing agent solution, the residual sheet quantity of the compound formulation can be controlled. Comparing tensile strength and tear resistance, Examples 1 to 5 are significantly higher than Comparative Examples 1 to 6, and Examples 1 to 5 and Comparative Examples 1 to 6 are better than commercially available solutions. Therefore, the compound formulation of this application can effectively improve paper strength while maintaining low residual sheet quantity.

[0058] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-residue paper strengthening agent, characterized in that, The components include the following parts by weight: 0.5-2 parts of sodium carboxymethyl cellulose solution 0.1-0.5 parts of zwitterionic polymer solution 0.5-3 parts of low-residue monocationic polymer reinforcing agent solution 94-99 parts deionized water 2-5 parts of ethanolamine The zwitterionic polymer is structured as polysulfobetaine; The polysulfonated betaine is configured as poly(3-((2-methacryloyloxyethyl)dimethylamino)propane-1-sulfonate). The low-residue monocationic polymer reinforcing agent is an organic polymer reinforcing agent obtained by modifying natural polymers, and a monomer scavenging agent is added during the process of obtaining the organic polymer reinforcing agent solution from the natural polymer modification. The organic polymer reinforcing agent is a modified cationic starch graft copolymer, wherein the grafting rate of the modified cationic starch graft copolymer is 60%-120%, the degree of cationic substitution of the modified cationic starch graft copolymer is 0.02-0.10, and the residual monomer content of the copolymer is less than 50 ppm.

2. The low residual paper strengthening agent according to claim 1, characterized in that, The modified cationic starch graft copolymer is a cationic starch-acrylamide graft copolymer.

3. The low residual paper strengthening agent according to claim 1, characterized in that, The organic polymer reinforcing agent is a chitosan-acrylamide graft copolymer solution.

4. A method for preparing a low-residue paper strengthening agent as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Modify natural polymers to obtain an organic polymer reinforcing agent solution; S2: Mix the sodium carboxymethyl cellulose solution and the polysulfobetaine solution thoroughly to obtain a premixed solution; S3: Under stirring conditions, ethanolamine and organic polymer reinforcing agent solution are mixed to form a blend, and the blend is added to the premix and mixed thoroughly to obtain reinforcing agent premix; S4: Add deionized water to the reinforcing agent premix, dilute to the required concentration, and mix evenly to obtain a low residual paper reinforcing agent.

5. The application of a low-residue paper strengthening agent as described in any one of claims 1-3, characterized in that, The reinforcing agent is added to the pulp during the papermaking process, and the amount added is 0.5%-2.0% of the oven-dry pulp weight.

6. The application according to claim 5, characterized in that, The paper is food packaging paper, medical paper, high-grade cultural paper, or high-strength packaging paperboard.