Paper pulp papermaking reinforcing agent and preparation method thereof

Abstract

The invention relates to the technical field of papermaking, and particularly discloses a paper pulp papermaking reinforcing agent and a preparation method thereof.The paper pulp papermaking reinforcing agent is prepared from, by weight, 10-20 parts of polyamide epichlorohydrin resin, 1-2 parts of silicon dioxide, 1-5 parts of polyvinyl alcohol, 0.1-1 part of cross-linking agent, 120-150 parts of deionized water and 0.5-2 parts of modifier; the molecular structure of the modifier contains a fluorine element, a silicon element and an organic amine group, the dry tensile property, the wet tensile property, the folding resistance, the flame retardant property and the wet / dry tensile index ratio of the paper pulp reinforcing agent are jointly improved, and the prepared paper pulp papermaking reinforcing agent can be widely applied to paper reinforcing and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a pulp and papermaking enhancer and a preparation method thereof. Background Art

[0002] The main function of pulp and paper strengthening agents is to improve the physical properties of paper, including tensile strength, tear strength, burst resistance and folding resistance, etc. The improvement of these properties makes the paper stronger and more durable when subjected to external forces, and is not easy to be damaged, which is especially important for the production of high-quality paper, such as high-grade printing paper, packaging paper, specialty paper, etc.

[0003] Papermaking enhancers are a type of chemical additives used in the papermaking process. Their main function is to enhance the various physical properties of paper, including improving the tensile strength, pulling force, abrasion resistance and tear resistance of paper. Polyamide epichlorohydrin resin is a type of papermaking enhancer. It has a significant enhancement effect on the physical properties of paper, especially the improvement of the wet strength property of paper, and has been widely used in the papermaking industry.

[0004] The Chinese patent with publication number CN115012248A discloses a novel papermaking reinforcing agent, its preparation method and its application, comprising the following components: polyamide polyamine epichlorohydrin resin, hydroxyl compound, mixed monomer (composed of lignin sulfonate, sodium chloride, Tween). Compared with polyacrylamide (PAM) reinforcing agent, the invention improves the paper tensile index, folding times, interlaminar strength and bursting index by 14.2%, 15.4%, 1.5% and 7.9% respectively, and when added to cultural paper (wood pulp), the paper tensile index, folding times, interlaminar strength and bursting index are increased by 13.9%, 85.7%, 31.0% and 17.8% respectively. However, the high organic chlorine content of the polyamide polyamine epichlorohydrin resin in the novel papermaking reinforcing agent disclosed in the invention will cause the papermaking reinforcing agent to undergo chemical reactions during storage, such as hydrolysis and oxidation, thereby reducing its storage stability and further affecting the performance of the papermaking reinforcing agent. The Chinese patent with publication number CN111234209A discloses a high-solid content polyamide epichlorohydrin resin paper wet strength agent. Compared with the traditional low-solid content 12.5% ​​polyamide epichlorohydrin resin wet strength agent, the new polyamide epichlorohydrin resin wet strength agent manufactured by the invention has a solid content of up to 25%. The wet strength agent prepared by the invention has good fluidity and excellent storage stability, and has excellent wet strengthening effect on paper. The invention breaks through a series of technical difficulties such as gel production in the process of preparing high-solid content polyamide epichlorohydrin resin paper wet strength agent, high viscosity, poor fluidity, and short storage time of the final product, and successfully develops a new polyamide epichlorohydrin resin paper wet strength agent, which reduces transportation costs. However, the polyamide epichlorohydrin resin paper wet strength agent prepared by the invention has limited functions and cannot make paper suitable for a variety of complex environments. For example, paper has a potential risk of causing fire in a high-temperature environment. Summary of the invention

[0005] The purpose of the present invention is to provide a pulp and papermaking strengthening agent and a preparation method thereof in view of the deficiencies in the prior art. The pulp and papermaking strengthening agent provided by the present invention can not only improve the wet tensile strength, dry tensile strength and other properties of paper, but also effectively resist high temperature environment and greatly reduce the burning loss of paper.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

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

[0008] Step S1, adding KH-550 and epifluoropropane to N,N-dimethylformamide at 70-80° C. with stirring, reacting for 2-4 hours, cooling to room temperature, and purifying to obtain an intermediate;

[0009] Step S2, uniformly mixing the intermediate, 6-aminocaproic acid and concentrated sulfuric acid, reacting at 90-100° C. with stirring for 6-8 hours, cooling to room temperature, and purifying to obtain a modifier;

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

[0011]

[0012] Furthermore, 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] Furthermore, 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 cross-linking agent is one or more of glutaraldehyde, glyoxal, N,N-methylenebisacrylamide and borax.

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

[0016] (1) adding polyamide epichlorohydrin resin, silicon dioxide and a modifier to deionized water at 60-70° C. with stirring, reacting for 1-3 hours, and cooling to room temperature to obtain a modified polyamide epichlorohydrin resin solution;

[0017] (2) adding polyvinyl alcohol to deionized water at 95-110° C., stirring for 1-1.5 hours, and cooling to room temperature to obtain a polyvinyl alcohol solution;

[0018] (3) adding the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2) and the remaining raw materials to the remaining deionized water at 60-70° C., stirring for 0.5-1.5 h, and cooling to room temperature to obtain the product.

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

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

[0021] The present invention selects polyamide epichlorohydrin resin as the main raw material of the pulp and papermaking reinforcing agent. Polyamide epichlorohydrin resin is a water-soluble, cationic, thermosetting resin with good moistening and strengthening effect, no formaldehyde, small amount, less yellowing of finished paper, non-toxic, convenient to use, easy to recycle damaged paper, particularly suitable for medium-alkaline papermaking, and has the advantages of retention and filtration. When polyamide epichlorohydrin resin is used to improve the performance of paper, there are two action mechanisms, one is the homo-crosslinking mechanism: that is, after adding polyamide epichlorohydrin resin, polyamide epichlorohydrin resin is partially deposited between fibers or adsorbed on the surface of fibers, and crosslinking occurs between polyamide epichlorohydrin resin molecules. When the paper sheet is dried, these resins are crosslinked to form a network structure; the other is the co-crosslinking mechanism: polyamide epichlorohydrin resin is a low relative molecular weight, water-soluble resin. After adding it to the pulp, it will penetrate into the surface and interior of the fiber and effectively crosslink with the fiber. However, organic chlorides are used in the preparation process of polyamide epichlorohydrin resin. These chlorides may be released into the environment during the preparation and use process, causing organic chlorine pollution. In addition, the presence of chlorine may affect the bonding effect between polyamide epichlorohydrin resin and paper fibers, thereby affecting the overall properties of paper, such as tensile strength and folding endurance. Therefore, reducing the fluorine content in polyamide epichlorohydrin resin is crucial to improving paper performance.

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

[0023] The present invention adopts a chemical modification method to prepare a modifier, modifies a polyamide epichlorohydrin resin, and then compounds it with other raw materials to obtain a pulp and papermaking reinforcing agent with excellent performance. The synthesis of the modifier firstly obtains an intermediate containing a hydroxyl group by a ring-opening reaction between an amino group of a silane coupling agent KH-550 and an epoxy group of epichlorohydrin, and then obtains the modifier by an esterification reaction between the hydroxyl group of the intermediate and the carboxyl group of 6-aminocaproic acid. The modifier structure contains an organic amine group, a fluorine element, and a silicon element. The organic amine groups in the modifier have strong chelating and adsorption capabilities. They can form stable compounds with the chlorine element in the polyamide epichlorohydrin resin or adsorb on the resin surface, thereby reducing the dissolution of chlorine, helping to reduce the chlorine content in the polyamide epichlorohydrin resin, and thus improving the overall performance of the paper; in addition, the organic amine groups in the modifier also have ion exchange capacity, which can interact with the negative charges on the surface of paper fibers to form chemical bonds. This ion exchange effect not only enhances the binding force between the pulp fibers and the modified substances, but also improves the hydrophilicity of the pulp fibers, making them more hygroscopic, thereby enhancing the wet strength of the paper. The fluorine element in the modifier can react with the fibers in the pulp to form chemical bonds, thereby improving the strength of the paper. This chemical bonding can enhance the bonding force between pulp fibers, improve the tensile strength and folding resistance of the paper, improve the overall performance of the paper, and make the paper tougher and more durable. At the same time, due to the large electronegativity of fluorine atoms, the covalent bonds between fluorine and carbon atoms are more stable and less likely to be interrupted, which can prevent the paper from undergoing violent chemical reactions with oxygen during the combustion process, thereby slowing down the combustion rate. Fluorine-containing compounds can form a protective film on the surface of the paper, isolating oxygen and heat, making it difficult for the paper to maintain the conditions required for combustion during the combustion process, thereby playing a flame retardant role. The silicon element in the modifier can react chemically with the hydroxyl groups on the surface of paper fibers to form a silicate film, thereby closing the pores of paper fibers and enhancing the bonding force between fibers. This chemical bonding can significantly improve key properties of paper such as tensile strength and burst resistance. At the same time, this silicate film can act as a protective layer on the surface or inside of 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, the silicon element can release some flame-retardant gases, such as silicon dioxide, which can dilute combustible gases and reduce flame temperatures.

[0024] The present invention first reacts a modifier with a polyamide epichlorohydrin resin to obtain a modified polyamide epichlorohydrin resin solution, and then compounding the modified polyamide epichlorohydrin resin solution with other raw materials such as silicon dioxide, polyvinyl alcohol, and a crosslinking agent to obtain a pulp and papermaking enhancer, wherein the modified polyamide epichlorohydrin resin can improve the compatibility of silicon dioxide with organic matter in the pulp, and after silicon dioxide is added to the pulp, it can form a chemical bond with the hydroxyl group on the surface of the pulp fiber to enhance the bonding force between the fibers, thereby improving the strength and toughness of the paper, which makes the paper less likely to break when subjected to external forces, thereby improving its durability, and silicon dioxide can strengthen the mutual bonding between the fibers during the papermaking process, making the paper more compact and tough, and this enhancement can improve the overall performance of the paper and extend the service life of the paper. The pulp and papermaking enhancer prepared by the present invention has excellent dry tensile properties, wet tensile properties, folding times and flame retardant properties and a high wet / dry tensile index ratio, and these characteristics make the enhancer have a wide range of application prospects in the papermaking industry. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

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

[0027] Example 1

[0028] A pulp and papermaking reinforcing agent, comprising the following raw materials in parts by weight: 10 parts of polyamide epichlorohydrin resin, 1 part of silicon dioxide, 5 parts of polyvinyl alcohol, 0.1 parts of a crosslinking agent, 120 parts of deionized water, and 0.5 parts of a modifier;

[0029] The cross-linking agent is glutaraldehyde;

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

[0031] Step S1, adding 1 g KH-550 and 0.3 g epifluoropropane to 11.11 mL N,N-dimethylformamide at 70° C. with stirring, reacting for 4 h, cooling to room temperature, and then removing N,N-dimethylformamide from the filtrate by rotary evaporation at 80° C., a rotation rate of 120 rpm, and a vacuum degree of 25-50 mbar to obtain an intermediate;

[0032] Step S2, 1 g of the intermediate, 0.4 g of 6-aminocaproic acid and 0.08 g of concentrated sulfuric acid were mixed evenly, reacted at 90° C. with stirring for 8 h, cooled to room temperature, and then extracted with 20 mL of ethyl acetate, and the organic phase was distilled under reduced pressure to obtain a modifier.

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

[0034]

[0035]

[0036] The NMR results of the modifier are: 1 H 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 papermaking strengthening agent comprises the following steps:

[0038] (1) adding polyamide epichlorohydrin resin, silica and a modifier to deionized water at 60° C. with stirring, reacting for 3 hours, and cooling to room temperature to obtain a modified polyamide epichlorohydrin resin solution, wherein the mass ratio of polyamide epichlorohydrin resin to deionized water is 1:4;

[0039] (2) adding polyvinyl alcohol to deionized water at 95° C., stirring for 1.5 h, and cooling to room temperature to obtain a polyvinyl alcohol solution having 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 hours, and cooled to room temperature to obtain the product.

[0041] Example 2

[0042] A pulp and papermaking strengthening agent, comprising the following raw materials in parts by weight: 20 parts of polyamide epichlorohydrin resin, 2 parts of silicon dioxide, 1 part of polyvinyl alcohol, 1 part of cross-linking agent, 150 parts of deionized water, and 2 parts of modifier;

[0043] The cross-linking agent is borax;

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

[0045] Step S1, adding 1 g KH-550 and 0.4 g epifluoropropane to 9.09 mL N,N-dimethylformamide at 80° C. with stirring, reacting for 2 h, cooling to room temperature, and then removing N,N-dimethylformamide by rotary evaporation of the filtrate at 80° C., a rotation rate of 120 rpm, and a vacuum degree of 25-50 mbar to obtain an intermediate;

[0046] Step S2, 1 g of the intermediate, 0.5 g of 6-aminocaproic acid and 0.12 g of concentrated sulfuric acid were mixed evenly, reacted at 100° C. with stirring for 6 h, cooled to room temperature, and then extracted with 20 mL of ethyl acetate, and the organic phase was distilled under reduced pressure to obtain a modifier.

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

[0048] (1) adding polyamide epichlorohydrin resin, silica and a modifier to deionized water at 70° C. with stirring, reacting for 1 hour, and cooling to room temperature to obtain a modified polyamide epichlorohydrin resin solution, wherein the mass ratio of polyamide epichlorohydrin resin to deionized water is 1:3;

[0049] (2) adding polyvinyl alcohol to deionized water at 110° C., stirring for 1 h, and cooling to room temperature to obtain a polyvinyl alcohol solution having 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 product.

[0051] Example 3

[0052] A pulp and papermaking reinforcing agent, comprising the following raw materials in parts by weight: 15 parts of polyamide epichlorohydrin resin, 1.5 parts of silicon dioxide, 3 parts of polyvinyl alcohol, 0.5 parts of a crosslinking agent, 140 parts of deionized water, and 1 part of a modifier;

[0053] The cross-linking agent is glyoxal;

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

[0055] Step S1, adding 1 g KH-550 and 0.35 g epifluoropropane to 10 mL N,N-dimethylformamide at 75° C. with stirring, reacting for 3 h, cooling to room temperature, and then rotary evaporating the filtrate at 80° C., a rotation rate of 120 rpm, and a vacuum degree of 25-50 mbar to remove N,N-dimethylformamide to obtain an intermediate;

[0056] Step S2, 1 g of the intermediate, 0.45 g of 6-aminocaproic acid and 0.1 g of concentrated sulfuric acid were mixed evenly, reacted at 95° C. with stirring for 7 h, cooled to room temperature, and then extracted with 20 mL of ethyl acetate, and the organic phase was distilled under reduced pressure to obtain a modifier.

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

[0058] (1) adding polyamide epichlorohydrin resin, silica and a modifier to deionized water at 65° C. with stirring, reacting for 2 hours, and cooling to room temperature to obtain a modified polyamide epichlorohydrin resin solution, wherein the mass ratio of polyamide epichlorohydrin resin to deionized water is 1:3.5;

[0059] (2) adding polyvinyl alcohol to deionized water at 100° C., stirring for 1.2 h, and cooling to room temperature to obtain a polyvinyl alcohol solution having a mass fraction of 7.5%;

[0060] (3) Add the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2) and the remaining raw materials to the remaining deionized water at 65° C., stir for 1 hour, and cool to room temperature to obtain the product.

[0061] Comparative Example 1

[0062] A pulp and papermaking reinforcing agent, comprising the following raw materials in parts by weight: 10 parts of polyamide epichlorohydrin resin, 0.1 parts of silicon dioxide, 0.5 parts of polyvinyl alcohol, 0.1 parts of a crosslinking agent, 140 parts of deionized water, and 1 part of a modifier;

[0063] The cross-linking agent is glyoxal;

[0064] The preparation method of the modifier is as follows: 1 g KH-550 and 0.35 g epifluoropropane are added to 10 mL N,N-dimethylformamide at 75° C. with stirring, reacted for 3 hours, cooled to room temperature, and then the filtrate is rotary evaporated to remove N,N-dimethylformamide at a temperature of 80° C., a rotation rate of 120 rpm, and a vacuum degree of 25-50 mbar to obtain the modifier;

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

[0066] Comparative Example 2

[0067] A pulp and papermaking strengthening agent comprises the following raw materials in parts by weight: 15 parts of polyamide epichlorohydrin resin, 3 parts of silicon dioxide, 0.5 parts of polyvinyl alcohol, 0.5 parts of a crosslinking agent, 140 parts of deionized water, and 0.5 parts of KH-550;

[0068] The cross-linking agent is glyoxal;

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

[0070] (1) adding polyvinyl alcohol to deionized water at 100° C., stirring for 1.2 h, and cooling to room temperature to obtain a polyvinyl alcohol solution having a mass fraction of 7.5%;

[0071] (2) Add the polyvinyl alcohol solution obtained in step (1) and the remaining raw materials to the remaining deionized water at 65° C., stir for 1 hour, and cool to room temperature to obtain the product.

[0072] Comparative Example 3

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

[0074] The cross-linking agent is glyoxal;

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

[0076] The properties of the pulp and papermaking strengthening agents prepared in Examples 1-3 and Comparative Examples 1-3 were tested. The testing method is as follows. The test results are shown in Table 1 below.

[0077] Before the test, paper was prepared first. The paper pulp used in the present invention was hardwood pulp and coniferous wood pulp, the mass percentage of which was 85:15, and the mixed pulp was beaten to a beating degree of 37°SR. The filler addition amount was 10%, and the pulp concentration was diluted to 1.0% (mass percentage) with tap water. The papermaking enhancer addition amount was 3‰ (absolute dry weight of papermaking enhancer / absolute dry weight percentage of pulp). The papermaking enhancers prepared in the above embodiments and comparative examples were added and stirred for 1 minute. According to the national standard method for papermaking, 0.03m 2 Round paper sheet, paper weight is 80g / m 2Then, according to GB / T12914-2018 "Determination of tensile strength of paper and paperboard - Constant rate tensile method (20mm / 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 (that is, the ratio of the wet tensile index to the dry tensile index) was calculated, and the number of folding times 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 of plastics by oxygen index method - Part 2: Room temperature test".

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

[0079]

[0080] It can be seen from Table 1 that the performance of the pulp and paper strengthening agent prepared in Examples 1-3 is more excellent. As shown in Table 1, the paper prepared by the pulp and paper strengthening agent of Examples 1-3 has excellent dry tensile properties, wet tensile properties and a higher wet / dry tensile index ratio. The higher dry tensile index means that the paper has better strength and stability when subjected to tension and is not easy to break, while the excellent wet tensile properties and the higher wet / dry tensile index ratio indicate that the paper can still maintain good tensile properties in a humid environment, is not easy to deform or break, and can ensure the use effect of the paper in a specific environment. The paper prepared by the pulp and paper strengthening agent of Examples 1-3 performed well in the folding endurance test, indicating that the paper has good flexibility and durability; the paper prepared by the pulp and paper strengthening agent of Examples 1-3 has a higher oxygen index value, and the paper is not easy to burn, which can reduce the risk of fire.

[0081] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

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

Claims

1. A pulp and papermaking strengthening agent, characterized in that: The invention comprises the following raw materials in parts by weight: 10-20 parts of polyamide epichlorohydrin resin, 1-2 parts of silicon dioxide, 1-5 parts of polyvinyl alcohol, 0.1-1 parts of crosslinking agent, 120-150 parts of deionized water, and 0.5-2 parts of modifier. The preparation method of the modifier is as follows: Step S1, adding KH-550 and epifluoropropane to N,N-dimethylformamide at 70-80° C. with stirring, reacting for 2-4 hours, cooling to room temperature, and purifying to obtain an intermediate, the structural formula of the intermediate is: Step S2, the intermediate, 6-aminocaproic acid and concentrated sulfuric acid are uniformly mixed, reacted at 90-100° C. with stirring for 6-8 hours, cooled to room temperature, purified, and a modifier is obtained. The structural formula of the modifier is:

2. The pulp and papermaking strengthening agent according to claim 1, characterized in that: The mass ratio of KH-550 to epifluoropropane in step S1 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 papermaking 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 papermaking strengthening agent according to claim 1, characterized in that: The cross-linking agent is one or more of glutaraldehyde, glyoxal, N,N-methylenebisacrylamide and borax.

5. The method for preparing the pulp and papermaking strengthening agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) adding polyamide epichlorohydrin resin, silicon dioxide and a modifier to a portion of deionized water at 60-70° C. with stirring, reacting for 1-3 hours, and cooling to room temperature to obtain a modified polyamide epichlorohydrin resin solution; (2) adding polyvinyl alcohol to a portion of deionized water at 95-110° C., stirring for 1-1.5 hours, and cooling to room temperature to obtain a polyvinyl alcohol solution; (3) adding the modified polyamide epichlorohydrin resin solution obtained in step (1), the polyvinyl alcohol solution obtained in step (2) and the remaining raw materials to the remaining deionized water at 60-70° C., stirring for 0.5-1.5 h, and cooling to room temperature to obtain the product.

6. The method for preparing a pulp and papermaking 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 a pulp and papermaking 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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