A pulp paper strengthening agent and a method for preparing the same

Abstract

The application relates to the papermaking technical field, and particularly discloses a paper pulp papermaking reinforcing agent and a preparation method thereof, which comprises the following raw materials in parts by weight: polyamide epoxy chloropropane resin 10-20 parts, silicon dioxide 1-2 parts, polyvinyl alcohol 1-5 parts, crosslinking agent 0.1-1 part, deionized water 120-150 parts, modifier 0.5-2 parts, wherein the modifier contains fluorine elements, silicon elements and organic amine groups in a molecular structure, and the dry tensile property, the wet tensile property, the folding resistance, the flame resistance and the wet / dry tensile index ratio of the paper pulp reinforcing agent are improved, and the paper pulp papermaking reinforcing agent prepared by the application can be widely applied to paper strengthening and has a wide application prospect.

Description

Technical Field

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

[0002] The main function of pulp and paper strengthening agents is to improve the physical properties of paper, including tensile strength, tear strength, bursting strength, and folding endurance. These improved properties make the paper more robust and durable under external forces, less prone to breakage, which is especially important for producing high-quality paper, such as high-grade printing paper, packaging paper, and specialty paper.

[0003] Paper strengthening agents are a class of chemical additives used in the papermaking process. Their main function is to enhance various physical properties of paper, including improving tensile strength, tear resistance, and abrasion resistance. Polyamide epichlorohydrin resin is one type of paper strengthening agent, which has a significant enhancing effect on the physical properties of paper, especially its wet strength, and is widely used in the papermaking industry.

[0004] Chinese Patent Publication No. CN115012248A discloses a novel papermaking reinforcing agent, its preparation method, and its application, comprising the following components: polyamide polyamine epichlorohydrin resin, hydroxyl compounds, and mixed monomers (composed of lignin sulfonate, sodium chloride, and Tween). Compared to polyacrylamide (PAM) reinforcing agents, this invention increases the tensile index, folding endurance, interlaminar strength, and burst index of paper by 14.2%, 15.4%, 1.5%, and 7.9%, respectively. When added to cultural paper (wood pulp), the tensile index, folding endurance, interlaminar strength, and burst index increase by 13.9%, 85.7%, 31.0%, and 17.8%, respectively. However, the high organic chlorine content of the polyamide polyamine epichlorohydrin resin in this novel papermaking reinforcing agent can lead to chemical reactions during storage, such as hydrolysis and oxidation, thereby reducing its storage stability and affecting its performance. Chinese patent CN111234209A discloses a high-solids-content polyamide epichlorohydrin resin wet strength agent for paper. Compared with the traditional low-solids-content (12.5%) polyamide epichlorohydrin resin wet strength agent, the novel polyamide epichlorohydrin resin wet strength agent produced by this invention has a solids content as high as 25%. The wet strength agent prepared by this invention has good flowability and excellent storage stability, and provides excellent wet strength for paper. This invention overcomes a series of technical difficulties in the preparation of high-solids-content polyamide epichlorohydrin resin wet strength agents, such as the easy formation of gels, resulting in high viscosity, poor flowability, and short storage time of the final product. It successfully developed a novel polyamide epichlorohydrin resin wet strength agent for paper, reducing transportation costs. However, the polyamide epichlorohydrin resin wet strength agent obtained by this invention has limited functionality and cannot make the paper suitable for various complex environments. For example, the paper poses a potential fire risk in high-temperature environments. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a pulp and paper strengthening agent and its preparation method. The pulp and paper strengthening agent provided by this invention can not only improve the wet tensile strength and dry tensile strength of paper, but also effectively resist high-temperature environments and significantly reduce paper combustion losses.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0007] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 10-20 parts polyamide epichlorohydrin resin, 1-2 parts silica, 1-5 parts polyvinyl alcohol, 0.1-1 part crosslinking agent, 120-150 parts deionized water, and 0.5-2 parts modifier. The preparation method of the modifier is as follows:

[0008] Step S1: KH-550 and fluoropropylene oxide are added to N,N-dimethylformamide at 70-80℃ with stirring. The reaction is carried out for 2-4 hours, cooled to room temperature, and purified to obtain the intermediate.

[0009] Step S2: Mix the intermediate, 6-aminocaproic acid and concentrated sulfuric acid evenly, react at 90-100℃ with stirring for 6-8 hours, cool to room temperature, purify, and obtain the modifier.

[0010] The synthetic route for the modifier is as follows:

[0011]

[0012] Further, in step S1, the mass ratio of KH-550 to epifluoropropane is 1:0.3-0.4, and the amount of KH-550 added to N,N-dimethylformamide is 0.09-0.11 g / mL.

[0013] Further, in step S2, the mass ratio of the intermediate, 6-aminocaproic acid and concentrated sulfuric acid is 1:0.4-0.5:0.08-0.12.

[0014] Furthermore, the crosslinking agent is one or more of glutaraldehyde, glyoxal, N,N-methylenebisacrylamide, and borax.

[0015] This invention also provides a method for preparing a pulp and paper strengthening agent, comprising the following steps:

[0016] (1) Under stirring conditions at 60-70℃, polyamide epichlorohydrin resin, silica and modifier are added to deionized water and reacted for 1-3 hours. The mixture is then cooled to room temperature to obtain a modified polyamide epichlorohydrin resin solution.

[0017] (2) At 95-110℃, polyvinyl alcohol is added to deionized water, stirred for 1-1.5h, and cooled to room temperature to obtain a polyvinyl alcohol solution.

[0018] (3) At 60-70℃, the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2) and the remaining raw materials are added to the remaining deionized water, stirred for 0.5-1.5h, and cooled to room temperature to obtain the final product.

[0019] Further, the mass ratio of the polyamide epichlorohydrin resin to deionized water in step (1) is 1:3-4.

[0020] Furthermore, the mass fraction of the polyvinyl alcohol aqueous solution in step (2) is 7-8%.

[0021] This invention selects polyamide epichlorohydrin resin as the main raw material for pulp and paper strengthening agents. Polyamide epichlorohydrin resin is a water-soluble, cationic, thermosetting resin with good wet strength, no formaldehyde, low dosage, less yellowing of paper, non-toxic, easy to use, and easy to recycle damaged paper. It is particularly suitable for medium-alkaline papermaking and also has the advantages of retention and filtration aids. When polyamide epichlorohydrin resin is used to improve paper performance, there are two mechanisms of action. One is the homo-crosslinking mechanism: after the addition of polyamide epichlorohydrin resin, some of the polyamide epichlorohydrin resin is deposited between fibers or adsorbed on the surface of the fibers, and crosslinking occurs between polyamide epichlorohydrin resin molecules. When the paper is dried, these resins crosslink to form a network structure. The other is the co-crosslinking mechanism: polyamide epichlorohydrin resin is a low relative molecular mass resin that is soluble in water. After it is added to the pulp, it penetrates into the surface and interior of the fibers and effectively crosslinks with the fibers. However, the preparation of polyamide epichlorohydrin resin involves the use of organochlorine compounds, which may be released into the environment during preparation and use, causing organochlorine pollution. Moreover, the presence of chlorine may affect the bonding effect between polyamide epichlorohydrin resin and paper fibers, thereby affecting the overall performance of paper, such as tensile strength and folding endurance. Therefore, reducing the fluorine content in polyamide epichlorohydrin resin is crucial for improving paper performance.

[0022] The present invention has the following beneficial effects:

[0023] This invention employs a chemical modification method to prepare a modifier. The modifier is modified with polyamide epichlorohydrin resin and then compounded with other raw materials to obtain a pulp and paper strengthening agent with excellent properties. The synthesis of the modifier begins with a ring-opening reaction between the amino group of the silane coupling agent KH-550 and the epoxy group of epichlorohydrin to obtain an intermediate containing a hydroxyl group. Then, the modifier is obtained through esterification of the hydroxyl group of the intermediate with the carboxyl group of 6-aminohexanoic acid. The modifier structure contains organic amine groups, fluorine, and silicon. The organic amine groups in the modifier have strong chelating and adsorption capabilities. They can form stable compounds with chlorine in polyamide epichlorohydrin resin or adsorb onto the resin surface, thereby reducing the leaching of chlorine and helping to reduce the chlorine content in polyamide epichlorohydrin resin, thus improving the overall performance of paper. In addition, the organic amine groups in the modifier also have ion exchange capabilities, which can interact with the negative charge on the surface of paper fibers to form chemical bonds. This ion exchange not only enhances the bonding force between pulp fibers and the modified material, but also improves the hydrophilicity of pulp fibers, making them more hygroscopic, thereby enhancing the wet strength of paper. The fluorine element in the modifier can react with the fibers in the pulp to form chemical bonds, thereby increasing the strength of the paper. This chemical bonding enhances the bonding force between pulp fibers, improves the tensile strength and folding endurance of the paper, and improves the overall performance of the paper, making it more durable. At the same time, due to the high electronegativity of fluorine atoms, the covalent bonds between fluorine and carbon atoms are more stable and less likely to be broken. This can prevent the paper from undergoing a violent chemical reaction with oxygen during combustion, thereby slowing down the burning rate. Furthermore, fluorine compounds can form a protective film on the paper surface, isolating oxygen and heat, making it difficult for the paper to maintain the conditions required for combustion during combustion, thus playing a flame-retardant role. The silicon element in the modifier can chemically react with the hydroxyl groups on the surface of paper fibers to form a silicate film, thereby sealing the capillaries of the paper fibers and enhancing the bonding force between fibers. This chemical bonding can significantly improve the key properties of paper, such as tensile strength and bursting strength. At the same time, this silicate film can act as a protective layer on or inside the paper. This protective layer can isolate oxygen and heat, thereby slowing down the burning rate of the paper. In addition, during the combustion process, silicon can release some flame-retardant gases, such as silicon dioxide. These gases can dilute combustible gases and reduce the flame temperature.

[0024] This invention first reacts a modifier with polyamide epichlorohydrin resin to obtain a modified polyamide epichlorohydrin resin solution. Then, the modified polyamide epichlorohydrin resin solution is compounded with silica, polyvinyl alcohol, crosslinking agents, and other raw materials to obtain a pulp and paper strengthening agent. The modified polyamide epichlorohydrin resin improves the compatibility of silica with organic substances in the pulp. After silica is added to the pulp, it can form a chemical bond with the hydroxyl groups on the surface of the pulp fibers, enhancing the bonding force between fibers, thereby improving the strength and toughness of the paper. This makes the paper less prone to breakage under external forces, improving its durability. Furthermore, silica strengthens the inter-fiber adhesion during papermaking, making the paper denser and tougher. This strengthening effect improves the overall performance of the paper and extends its service life. The pulp and paper strengthening agent prepared by this invention has excellent dry tensile properties, wet tensile properties, folding endurance, flame retardant properties, and a high wet / dry tensile index ratio. These characteristics make this strengthening agent promising for broad applications in the papermaking industry. Detailed Implementation

[0025] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] All raw materials used in the following examples are commercially available products. Silica is hydrophilic with a particle size of 20-30 nm; the polyamide epichlorohydrin resin has a viscosity of 25-90 mPa·s, is model FT-DL2, and was purchased from Fengtai Environmental Protection Technology (Shandong) Co., Ltd.; the polyvinyl alcohol is polyvinyl alcohol 2488, purchased from Jinan Guangxun Trading Co., Ltd.

[0027] Example 1

[0028] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 10 parts polyamide epichlorohydrin resin, 1 part silica, 5 parts polyvinyl alcohol, 0.1 parts crosslinking agent, 120 parts deionized water, and 0.5 parts modifier.

[0029] The crosslinking agent is glutaraldehyde;

[0030] The preparation method of the modifier is as follows:

[0031] Step S1: At 70℃ and under stirring, 1g KH-550 and 0.3g epifluoropropane were added to 11.11mL N,N-dimethylformamide and reacted for 4h. After cooling to room temperature, the filtrate was rotary evaporated at 80℃, 120rpm and 25-50mbar to remove N,N-dimethylformamide, and the intermediate was obtained.

[0032] Step S2: Mix 1g of intermediate, 0.4g of 6-aminocaproic acid and 0.08g of concentrated sulfuric acid evenly, react at 90℃ with stirring for 8h, cool to room temperature, and then extract with 20mL of ethyl acetate. Take the organic phase and distill under reduced pressure to obtain the modifier.

[0033] The synthetic route for the modifier is as follows:

[0034]

[0035]

[0036] The NMR results of the modifier are as follows: 1 ¹H NMR (300 MHz, acetone-d6) δ 5.30–5.35 (m, 1H), 4.18–4.43 (m, 2H), 3.81–3.88 (m, 6H), 3.7 (s, 1H), 2.65–2.90 (m, 4H), 2.53 (t, 2H), 2.35 (t, 2H), 1.5–1.58 (m, 6H), 1.33–1.37 (m, 4H), 1.21 (t, 9H), 0.56 (t, 2H).

[0037] A method for preparing a pulp and paper strengthening agent includes the following steps:

[0038] (1) At 60°C and under stirring conditions, polyamide epichlorohydrin resin, silica and modifier were added to deionized water and reacted for 3 hours. The mixture was then cooled to room temperature to obtain a modified polyamide epichlorohydrin resin solution. The mass ratio of polyamide epichlorohydrin resin to deionized water was 1:4.

[0039] (2) At 95°C, polyvinyl alcohol was added to deionized water and stirred for 1.5 h. The mixture was then cooled to room temperature to obtain a polyvinyl alcohol solution with a mass fraction of 7%.

[0040] (3) At 60°C, the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2), and the remaining raw materials are added to the remaining deionized water, stirred for 1.5 h, and cooled to room temperature to obtain the final product.

[0041] Example 2

[0042] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 20 parts polyamide epichlorohydrin resin, 2 parts silica, 1 part polyvinyl alcohol, 1 part crosslinking agent, 150 parts deionized water, and 2 parts modifier.

[0043] The crosslinking agent is borax;

[0044] The preparation method of the modifier is as follows:

[0045] Step S1: At 80℃ and under stirring, 1g KH-550 and 0.4g epifluoropropane were added to 9.09mL N,N-dimethylformamide and reacted for 2h. After cooling to room temperature, the filtrate was rotary evaporated at 80℃, 120rpm and 25-50mbar to remove N,N-dimethylformamide, and the intermediate was obtained.

[0046] Step S2: Mix 1g of intermediate, 0.5g of 6-aminocaproic acid and 0.12g of concentrated sulfuric acid evenly, react at 100℃ with stirring for 6h, cool to room temperature, and then extract with 20mL of ethyl acetate. Take the organic phase and distill under reduced pressure to obtain the modifier.

[0047] A method for preparing a pulp and paper strengthening agent includes the following steps:

[0048] (1) At 70°C and under stirring conditions, polyamide epichlorohydrin resin, silica and modifier were added to deionized water and reacted for 1 hour. The mixture was then cooled to room temperature to obtain a modified polyamide epichlorohydrin resin solution. The mass ratio of polyamide epichlorohydrin resin to deionized water was 1:3.

[0049] (2) At 110℃, polyvinyl alcohol was added to deionized water, stirred for 1 hour, and cooled to room temperature to obtain a polyvinyl alcohol solution with a mass fraction of 8%.

[0050] (3) At 70°C, the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2), and the remaining raw materials are added to the remaining deionized water, stirred for 0.5 h, and cooled to room temperature to obtain the final product.

[0051] Example 3

[0052] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 15 parts polyamide epichlorohydrin resin, 1.5 parts silica, 3 parts polyvinyl alcohol, 0.5 parts crosslinking agent, 140 parts deionized water, and 1 part modifier.

[0053] The crosslinking agent is glyoxal;

[0054] The preparation method of the modifier is as follows:

[0055] Step S1: At 75°C and under stirring, 1g KH-550 and 0.35g epifluoropropane were added to 10mL N,N-dimethylformamide and reacted for 3h. After cooling to room temperature, the filtrate was rotary evaporated at 80°C, a rotation speed of 120rpm, and a vacuum of 25-50mbar to remove N,N-dimethylformamide, thus obtaining the intermediate.

[0056] Step S2: Mix 1g of intermediate, 0.45g of 6-aminocaproic acid and 0.1g of concentrated sulfuric acid evenly, react at 95℃ with stirring for 7h, cool to room temperature, and then extract with 20mL of ethyl acetate. Take the organic phase and distill under reduced pressure to obtain the modifier.

[0057] A method for preparing a pulp and paper strengthening agent includes the following steps:

[0058] (1) At 65°C and under stirring conditions, polyamide epichlorohydrin resin, silica and modifier were added to deionized water and reacted for 2 hours. The mixture was then cooled to room temperature to obtain a modified polyamide epichlorohydrin resin solution. The mass ratio of polyamide epichlorohydrin resin to deionized water was 1:3.5.

[0059] (2) At 100℃, polyvinyl alcohol was added to deionized water and stirred for 1.2 h. The mixture was then cooled to room temperature to obtain a polyvinyl alcohol solution with a mass fraction of 7.5%.

[0060] (3) At 65°C, the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2), and the remaining raw materials are added to the remaining deionized water, stirred for 1 hour, and cooled to room temperature to obtain the final product.

[0061] Comparative Example 1

[0062] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 10 parts polyamide epichlorohydrin resin, 0.1 parts silica, 0.5 parts polyvinyl alcohol, 0.1 parts crosslinking agent, 140 parts deionized water, and 1 part modifier.

[0063] The crosslinking agent is glyoxal;

[0064] The modifier is prepared as follows: 1g KH-550 and 0.35g epifluoropropane are added to 10mL N,N-dimethylformamide at 75℃ and under stirring conditions. The reaction is carried out for 3h, cooled to room temperature, and then the filtrate is rotary evaporated at 80℃, a rotation speed of 120rpm, and a vacuum degree of 25-50mbar to remove N,N-dimethylformamide, thus obtaining the modifier.

[0065] The preparation method of a pulp and paper reinforcing agent is the same as that described in Example 3.

[0066] Comparative Example 2

[0067] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 15 parts polyamide epichlorohydrin resin, 3 parts silica, 0.5 parts polyvinyl alcohol, 0.5 parts crosslinking agent, 140 parts deionized water, and 0.5 parts KH-550.

[0068] The crosslinking agent is glyoxal;

[0069] A method for preparing a pulp and paper strengthening agent includes the following steps:

[0070] (1) At 100℃, polyvinyl alcohol was added to deionized water and stirred for 1.2 h. The mixture was then cooled to room temperature to obtain a polyvinyl alcohol solution with a mass fraction of 7.5%.

[0071] (2) At 65°C, the polyvinyl alcohol solution obtained in step (1) and the remaining raw materials are added to the remaining deionized water, stirred for 1 hour, and cooled to room temperature to obtain the final product.

[0072] Comparative Example 3

[0073] A pulp and paper reinforcing agent comprises the following raw materials in parts by weight: 15 parts polyamide epichlorohydrin resin, 3 parts polyvinyl alcohol, 0.5 parts crosslinking agent, 140 parts deionized water, and 0.5 parts KH-550.

[0074] The crosslinking agent is glyoxal;

[0075] A method for preparing a pulp and paper reinforcing agent is the same as that described in Comparative Example 2.

[0076] The properties of the pulp and paper reinforcing agents prepared in Examples 1-3 and Comparative Examples 1-3 were tested. The test methods are as follows, and the test results are shown in Table 1 below.

[0077] Before testing, paper was first prepared. The paper pulp used in this invention was hardwood pulp and softwood pulp, with a mass ratio of 85:15. The pulp was mixed and beaten to a freeness of 37°SR. 10% filler was added, and the pulp concentration was diluted to 1.0% (mass percentage) with tap water. 3‰ (paper strengthening agent dry weight / pulp dry weight percentage) was added to the pulp and paper strengthening agents prepared in the above embodiments and comparative examples, respectively. After stirring for 1 minute, the pulp was formed into 0.03m sheets according to the national standard method for papermaking. 2 Round sheets of paper with a basis weight of 80g / m³ 2Then, according to GB / T12914-2018 "Determination of Tensile Strength of Paper and Paperboard - Constant Rate Tensile Method (20 mm / min)" and GB / T 465.2-2008 "Determination of Tensile Strength of Paper and Paperboard after Immersion in Water", the dry tensile index and wet tensile index were tested respectively (the wet tensile index was measured after immersion in water for 1 hour), and the wet / dry tensile index ratio (i.e., the ratio of wet tensile index to dry tensile index) was calculated. The number of folds was tested according to GB / T457-2008 "Determination of Folding Endurance of Paper and Paperboard", and the oxygen index value was tested according to GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test".

[0078] Table 1. Tests of dry tensile index, wet tensile index, wet / dry tensile index ratio, folding endurance, and oxygen index of paper.

[0079]

[0080] Table 1 shows that the pulp and paper strengthening agents prepared in Examples 1-3 have superior performance. As shown in Table 1, the paper prepared with the pulp and paper strengthening agents of Examples 1-3 exhibits excellent dry tensile properties, wet tensile properties, and a high wet / dry tensile index ratio. A higher dry tensile index means that the paper has better strength and stability when subjected to tensile force and is less prone to breakage. Excellent wet tensile properties and a high wet / dry tensile index ratio indicate that the paper maintains good tensile properties even in humid environments, is less prone to deformation or damage, and can ensure the paper's performance in specific environments. The paper prepared with the pulp and paper strengthening agents of Examples 1-3 performs excellently in the folding endurance test, indicating that the paper has good flexibility and durability. The paper prepared with the pulp and paper strengthening agents of Examples 1-3 has a high oxygen index value, making it less flammable and reducing the risk of fire.

[0081] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0082] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pulp and paper reinforcing agent, characterized in that, The modified polyamide epichlorohydrin resin solution is prepared by mixing the following raw materials in parts by weight: 10-20 parts polyamide epichlorohydrin resin, 1-2 parts silica, 1-5 parts polyvinyl alcohol, 0.1-1 parts crosslinking agent, 120-150 parts deionized water, and 0.5-2 parts modifier. The polyamide epichlorohydrin resin, silica, and modifier are added to a portion of the deionized water at 60-70°C with stirring, and the reaction is carried out for 1-3 hours. The solution is then cooled to room temperature. The modifier is prepared as follows: Step S1: KH-550 and epifluoropropane were added to N,N-dimethylformamide at 70-80℃ with stirring. The reaction was carried out for 2-4 hours, cooled to room temperature, and purified to obtain an intermediate. The structural formula of the intermediate is as follows: ； Step S2: Mix the intermediate, 6-aminohexanoic acid, and concentrated sulfuric acid evenly, and react at 90-100℃ with stirring for 6-8 hours. Cool to room temperature, purify, and obtain the modifier. The structural formula of the modifier is: 。 2. The pulp and paper strengthening agent according to claim 1, characterized in that, In step S1, the mass ratio of KH-550 to epifluoropropane is 1:0.3-0.4, and the amount of KH-550 added to N,N-dimethylformamide is 0.09-0.11 g / mL.

3. The pulp and paper strengthening agent according to claim 1, characterized in that, The mass ratio of the intermediate, 6-aminocaproic acid and concentrated sulfuric acid in step S2 is 1:0.4-0.5:0.08-0.

12.

4. The pulp and paper strengthening agent according to claim 1, characterized in that, The crosslinking agent is one or more of glutaraldehyde, glyoxal, N,N-methylenebisacrylamide, and borax.

5. The method for preparing the pulp and paper strengthening agent according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Under stirring conditions at 60-70℃, polyamide epichlorohydrin resin, silica and modifier are added to part of deionized water and reacted for 1-3 hours. The mixture is then cooled to room temperature to obtain a modified polyamide epichlorohydrin resin solution. (2) At 95-110℃, polyvinyl alcohol is added to part of deionized water, stirred for 1-1.5h, and cooled to room temperature to obtain a polyvinyl alcohol solution; (3) Under the condition of 60-70℃, the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2) and the remaining raw materials are added to the remaining deionized water, stirred for 0.5-1.5h, and cooled to room temperature to obtain the product.

6. The method for preparing the pulp and paper strengthening agent according to claim 5, characterized in that, The mass ratio of the polyamide epichlorohydrin resin to part of the deionized water in step (1) is 1:3-4.

7. The method for preparing the pulp and paper strengthening agent according to claim 5, characterized in that, The mass fraction of the polyvinyl alcohol aqueous solution in step (2) is 7-8%.

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