Multifunctional wet strength agent with flame retardant effect and preparation method thereof

Abstract

The application discloses a preparation method of a multifunctional wet strength agent with a flame-retardant effect. Firstly, nano titanium dioxide particles modified by silane coupling agent KH-560 are prepared; then a methanol solution containing polyethylene imine and benzaldehyde is heated to reflux for a period of time, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is added to continue the reaction, the nano titanium dioxide particles modified by silane coupling agent KH-560 are added, and a light yellow suspension is obtained after complete reaction. The suspension is vacuum dried to obtain a light yellow solid. The solid is cleaned with a hot ethanol solution, then filtered, the filter cake is dried and ground into powder. The wet strength agent with the functions of flame retardation, antibiosis, ultraviolet protection and wet strength is obtained. The product is simple in synthesis and high in yield, and solves the technical problems of poor retention performance, poor wet strength effect of paper, incapability of combining wet strength and flame retardation and single function of traditional wet strength agents.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a papermaking additive. More specifically, this invention relates to a multifunctional wet strength agent with flame retardant effect and its preparation method, which can be used in the production of archival paper, wallpaper, board paper, wettable paper, etc. Background Technology

[0002] In recent years, my country's economy has developed rapidly, and people's living standards have gradually improved. Paper materials are increasingly being used in construction, decoration, and packaging. Currently, most paper is made from natural fibers such as lignin or cellulose, and its flammability poses a significant threat to people's lives and property. Especially with decorative items like wallpaper, flames can easily spread along the wallpaper, expanding the fire area and hindering escape while also greatly complicating firefighting efforts. Therefore, imparting flame-retardant properties to paper is essential. Normally, untreated paper loses most of its strength when soaked in water. Adding wet strength agents can restore the paper's mechanical strength to meet usage requirements even after wetting. Wet strength agents are mainly used in the papermaking industry, with varying dosages depending on the type of paper (e.g., toilet paper, fruit bag paper, cardboard, water-resistant paper). Currently, the wet strength agents used in the papermaking industry are mainly polyamide polyamine epichlorohydrin (PAE) resin, melamine-formaldehyde (MF) resin, urea-formaldehyde (UF) resin, and other types of wet strength agents. Both MF and UF resins can only be used under acidic conditions, limiting their application range. Furthermore, they contain formaldehyde, which is harmful to human health and cannot be used in large quantities. PAE resin is a water-soluble, cationic, thermosetting resin. While it has advantages such as being formaldehyde-free, producing less yellowing paper, being non-toxic, easy to use, and facilitating paper recycling, its low solids content, high organic chlorine content, poor wet strength, and low paper strength after use also limit its widespread application. Therefore, developing an environmentally friendly, high-retention, and significantly effective wet strength agent with flame-retardant properties that can be widely used in the papermaking industry is of great significance.

[0003] CN115125762A discloses a low-chlorine, environmentally friendly papermaking wet strength agent and its production process. This invention modifies polyethyleneimine using a silane coupling agent, causing the epoxy groups in the silane coupling agent to chemically cross-link with polyethyleneimine, thereby improving the wet strength of polyethyleneimine. Under certain conditions, the siloxane groups in the silane coupling agent can hydrolyze to form highly active silanol groups, which then undergo a dehydration reaction with the hydroxyl groups of paper fibers to form strong ether bonds. This results in a three-dimensional network structure with double cross-linking between the polymer and paper fibers, increasing the paper's strength. However, this environmentally friendly papermaking wet strength agent has a single function; besides improving the wet strength of paper to a certain extent, it has no other functions. Although it contains the halogen element chlorine, its content is low and cannot impart a flame-retardant effect to the paper. Furthermore, the wet strength agent has a low retention rate and high usage costs. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of traditional wet strength agents, such as limited functionality, poor wet strength effect, and low paper strength after use. This invention provides a multifunctional wet strength agent with flame retardant properties and its preparation method. The product is simple to synthesize, has a high yield, and the resulting wet strength agent exhibits excellent wet strength, resulting in high paper strength after use, while also possessing good flame retardant properties. During the paper forming process, the application method is simple, significantly enhancing the paper's wet strength and other mechanical properties, and also imparting advantages such as flame retardancy, antibacterial properties, and aging resistance. This invention solves the common technical problems in the industry, such as poor retention, poor wet strength effect, inability to simultaneously achieve wet strength and flame retardancy, and limited functionality, when traditional wet strength agents are used alone. Using the wet strength agent prepared according to this invention during the papermaking process can significantly improve the paper's wet strength, tear resistance, and flame retardancy.

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

[0006] A method for preparing a multifunctional wet-strength agent with flame-retardant effect includes the following steps:

[0007] a. Silane coupling agent modified nanoparticles:

[0008] Weigh a certain amount of nanoparticles into a beaker. Measure an appropriate amount of anhydrous ethanol solution and pour the ethanol into the beaker containing the nanoparticles. Sonicate the mixture for 10–30 minutes to ensure the nanoparticles are fully dispersed in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 90–120°C, and maintain the temperature under reflux. Dissolve a certain amount of silane coupling agent in anhydrous ethanol and add it dropwise into the flask. Continue the reaction for 8–16 hours under constant temperature conditions. Filter the product and wash the filter cake with anhydrous ethanol. Dry the product in an oven at 60–100°C to obtain nanoparticles modified with silane coupling agent of different mass percentages.

[0009] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0010] After the cationic water-soluble polymer is completely dissolved in an organic solvent, a certain amount of aromatic aldehyde is added, the mixture is mixed evenly, and then added to a reaction vessel. The mixture is stirred, heated, and kept warm under reflux for a certain period of time.

[0011] 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in methanol and added dropwise to the reaction system over 0.5–2 hours using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux for a period of time while maintaining a constant temperature. Once the reaction was complete, cationic polymers modified with flame-retardant intermediates of different grafting degrees were obtained.

[0012] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0013] A certain amount of nanoparticles modified with silane coupling agent were added to the reaction system, and the reaction was continued at 75-95℃ for 6-10 hours to obtain a suspension of multifunctional wet strength agent with flame retardant effect in different mass proportions of nanoparticles.

[0014] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0015] The suspension was dried in a vacuum drying oven, the dried product was washed with hot ethanol solution, then filtered, the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV protection, and wet strength properties.

[0016] In this invention, the silane coupling agent mentioned in step a is 3-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560).

[0017] In this invention: the nanoparticles mentioned in step a are nano-titanium dioxide (TiO2).

[0018] In the present invention: the nanoparticles modified with different mass percentages of silane coupling agent mentioned in step a refer to any one of the following: the mass percentage of silane coupling agent is 3% to 80%.

[0019] In this invention: the cationic water-soluble polymer mentioned in step b is any one of polyethyleneimine with an average molecular weight of 500 to 100,000.

[0020] In this invention, the organic solvent mentioned in step b is either methanol or ethanol.

[0021] In this invention, the aromatic aldehyde mentioned in step b is either benzaldehyde or phenylacetaldehyde.

[0022] In this invention, step b, which involves stirring, heating, and refluxing at a temperature of 70–100°C for 5–8 hours, refers to this process.

[0023] In this invention, step b, which involves maintaining a constant temperature and continuing to heat and reflux for a period of time, refers to heating and reacting at a temperature of 70–100°C for 8–14 hours.

[0024] In this invention, grafting degree refers to the mass ratio of the flame-retardant intermediate DOPO to the amino group of polyethyleneimine. The grafting degree of the cationic polymer modified by the flame-retardant intermediates described in step b is any one of 5% to 40%.

[0025] In the present invention: the different mass percentages of nanoparticles mentioned in step c refer to any one of 2% to 60% of the total mass of the wet strength agent.

[0026] In the present invention, step d, which involves drying the suspension in a vacuum drying oven, means drying it in a vacuum drying oven at 70-110°C for 5-8 hours.

[0027] A multifunctional wet strength agent with flame retardant effect is prepared by the above preparation method.

[0028] Compared with the prior art, the present invention has the following features and beneficial effects:

[0029] (1) A method for preparing a multifunctional wet-strength agent with flame retardant effect according to the present invention involves first reacting aromatic aldehydes, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxides with a cationic water-soluble polymer (polyethyleneimine is used in this invention) to graft flame retardant intermediates onto the polyethyleneimine molecular chain. Then, it is further reacted with nano-titanium dioxide particles modified with silane coupling agent KH-560 to graft nanoparticles onto the polyethyleneimine molecular chain, ultimately obtaining a highly branched wet-strength agent that integrates flame retardant, antibacterial, and photo-aging resistant properties. This product modifies typical water-soluble cationic polymers during synthesis, grafting flame-retardant intermediates, photo-aging resistant and antibacterial nanoparticles onto highly branched polymers. This achieves a unified combination of flame retardancy, photo-aging resistant, antibacterial and strengthening properties, solving common industry technical problems such as poor retention, poor paper wet strength effect, and inability to achieve both wet strength and flame retardancy when used alone as a traditional wet strength agent. When used to increase the wet strength of paper, it can significantly improve the paper's wet strength, tear resistance and folding endurance.

[0030] (2) Compared with the prior art, the preparation process of the present invention is simpler, further shortens the preparation time, and improves the yield while reducing the preparation cost, making it suitable for large-scale industrial production.

[0031] (3) The advantages of this invention are: a) The wet strength agent has a highly branched structure, which makes it easy to be adsorbed onto the fiber surface and improves the retention rate of the product; b) During the paper drying process, the amino groups on the molecular chain of the wet strength agent can act on the paper fibers, so that the product can form a cross-linking network between molecules and within molecules, which improves the adhesion strength between paper fibers and greatly improves the wet strength performance of paper; c) Since a certain amount of flame retardant intermediates are grafted onto the molecular chain of the wet strength agent, the product has good flame retardant performance; d) Since the nano-titanium dioxide particles are connected to the highly branched polyethyleneimine through a silane coupling agent, and the polyethyleneimine has a certain adhesion strength with the fiber, the retention rate of nanoparticles can be significantly improved, thereby further improving the mechanical strength of the paper.

[0032] (4) The wet strength agent prepared by this invention is a light yellow solid powder. It is suitable for various types of paper requiring wet strength properties, such as decorative base paper, photographic base paper, filter paper, tea bags, titanium dioxide paper, wallpaper, map paper, nautical chart, coated paper, corrugated paper, refrigerated packaging paper, and various special papers requiring wet strength. In addition to increasing the wet strength of paper, the wet strength agent of this invention can also increase the dry strength to varying degrees. Its characteristics are that it is easily absorbed by fibers, and its wet strength properties can be developed through heating, drying, and storage of paper during the papermaking process. It has good effects and requires a small amount. This wet strength agent can also improve the dimensional stability, strength, and ink absorption properties of paper to a certain extent.

[0033] (5) The operation of this product is simple during the papermaking process. It only requires preparing a suspension of the wet strength agent with a certain concentration using ethylene glycol solvent and adding it to the pulp. The process is simple and does not require large-scale modification of the existing production process and equipment. Attached Figure Description

[0034] Figure 1 and Figure 2 These are transmission electron microscope (TEM) images at different magnifications of a multifunctional wet-strength agent with flame-retardant effect dispersed in ethylene glycol.

[0035] Figure 3 The infrared absorption spectra (FT-IR) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and benzaldehyde before and after modification of polyethyleneimine.

[0036] Figure 4 The infrared absorption spectrum of polyethyleneimine with flame-retardant intermediates grafted onto the main molecular linker of nano-titanium dioxide modified with silane coupling agent KH-560 is obtained.

[0037] Figure 5The thermogravimetric analysis curves of nano-titanium dioxide particles modified with silane coupling agent KH-560 (KH-560 accounts for 30% of the mass).

[0038] Figure 6 The thermogravimetric-differential scanning calorimetry (TGC-DSC) curves of the prepared wet strength agent (DOPO grafting degree of 20% and nano titanium dioxide particle mass ratio of 6.7%) from room temperature to 800℃ are shown.

[0039] Figure 7 Different amounts (5%, 10%, 15%, and 20%) of wet strength agent (DOPO grafting degree of 20% and nano-titanium dioxide particle mass ratio of 6.7%) were added to softwood pulp, and the yield was 90 g / m³ using a Kaisai automatic sheet forming machine. 2 Changes in wet strength agent retention rate during hand-made sheet production.

[0040] Figure 8 It involves adding different amounts (5%, 10%, 15%, 20%) of wet strength agent (DOPO grafting degree of 20%, nano titanium dioxide particle mass ratio of 6.7%), with a papermaking quantity of 90 g / m³. 2 Changes in whiteness during hand-copying.

[0041] Figure 9 The flame retardant properties of paper with different amounts (5%, 10%, 15%, 20%) of wet strength agent were evaluated using the limiting oxygen index method of GB / T2406.2—2009.

[0042] Figure 10 and Figure 11 The relationship between the tensile strength and tear strength of paper with different amounts of wet strength agent added to the pulp and the amount added.

[0043] Figure 12 The results are from tests conducted using the inhibition zone method to assess the antibacterial performance of paper containing different amounts of wet strength agent against Staphylococcus aureus. Detailed Implementation

[0044] The embodiments given below are intended to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0045] Example 1

[0046] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0047] a. Silane coupling agent modified nanoparticles:

[0048] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 10 min to ensure the nanoparticles are fully dispersed in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 90 °C, and maintain the temperature under reflux. Dissolve 0.310 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 90 °C for 8 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 60 °C to obtain modified nano-titanium dioxide with a 3% (w / w) mass fraction of silane coupling agent KH-560.

[0049] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0050] 10.000g of polyethyleneimine (PEI) with a molecular weight of 500 was completely dissolved in 100ml of methanol, and then 1.234g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 70℃, and kept under reflux for 5h.

[0051] 2.514 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 0.5 h using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 70 °C for 8 h. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 5% was obtained.

[0052] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0053] 0.289 g of modified nano-titanium dioxide (with a mass fraction of 3% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 75 °C for 6 h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 2% nanoparticles by mass.

[0054] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0055] The suspension was dried in a vacuum drying oven to obtain a pale yellow granular solid. The solid was washed with a hot ethanol solution, filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV protection, and wet strength properties.

[0056] Example 2

[0057] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0058] a. Silane coupling agent modified nanoparticles:

[0059] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 0.310 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 3%.

[0060] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0061] 10.000g of polyethyleneimine (PEI) with a molecular weight of 500 was completely dissolved in 100ml of methanol, and then 1.234g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 6.5h.

[0062] 2.514 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 5% was obtained.

[0063] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0064] 0.289 g of modified nano-titanium dioxide (with a mass fraction of 3% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85 °C for 8 h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 2% nanoparticles by mass.

[0065] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0066] The suspension was dried in a vacuum drying oven to obtain a pale yellow granular solid. The solid was washed with a hot ethanol solution, filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV protection, and wet strength properties.

[0067] Example 3

[0068] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0069] a. Silane coupling agent modified nanoparticles:

[0070] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 30 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 120 °C, and maintain the temperature under reflux. Dissolve 0.310 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 120 °C for 16 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 100 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 3%.

[0071] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0072] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of ethanol, and then 1.397g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 100℃, and kept under reflux for 8h.

[0073] 2.514 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of ethanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 2 hours using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 100°C for 14 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 5% was obtained.

[0074] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0075] 0.289 g of modified nano-titanium dioxide (with a mass fraction of 3% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 95 °C for 10 h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 2% nanoparticles by mass.

[0076] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0077] The suspension was dried in a vacuum drying oven to obtain a pale yellow granular solid. The solid was washed with a hot ethanol solution, filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV protection, and wet strength properties.

[0078] Example 4

[0079] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0080] a. Silane coupling agent modified nanoparticles:

[0081] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 6.667 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 40%.

[0082] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0083] 10.000g of polyethyleneimine (PEI) with a molecular weight of 100000 was completely dissolved in 100ml of methanol, and then 4.936g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0084] 10.047 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 20% was obtained.

[0085] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0086] 24.983g of modified nano-titanium dioxide (with a mass fraction of 40% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 30% nanoparticles by mass.

[0087] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0088] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0089] Example 5

[0090] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0091] a. Silane coupling agent modified nanoparticles:

[0092] Weigh 10,000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 40,000 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 80%.

[0093] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0094] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 9.872g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0095] 20.094 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 40% was obtained.

[0096] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0097] 124.983g of modified nano-titanium dioxide (with 80% by mass of silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, in which the nanoparticles accounted for 60% by mass.

[0098] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0099] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0100] Example 6

[0101] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0102] a. Silane coupling agent modified nanoparticles:

[0103] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 0.310 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 3%.

[0104] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0105] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 6.170g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0106] 12.559 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 25% was obtained.

[0107] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0108] 5g of modified nano-titanium dioxide (with a mass fraction of 3% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 14.4% nanoparticles by mass.

[0109] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0110] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0111] Example 7

[0112] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0113] a. Silane coupling agent modified nanoparticles:

[0114] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 0.310 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 3%.

[0115] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0116] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 7.404g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0117] 15.082 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 30% was obtained.

[0118] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0119] 5g of modified nano-titanium dioxide (with a mass fraction of 3% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 12.9% nanoparticles by mass.

[0120] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0121] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0122] Example 8

[0123] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0124] a. Silane coupling agent modified nanoparticles:

[0125] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0126] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0127] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 3.702g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0128] 7.541 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over one hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 15% was obtained.

[0129] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0130] 5.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 13.3% nanoparticles by mass.

[0131] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0132] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0133] Example 9

[0134] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0135] a. Silane coupling agent modified nanoparticles:

[0136] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0137] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0138] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 4.936g of phenylacetaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0139] 10.047 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 20% was obtained.

[0140] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0141] 5.000g of modified nano-titanium dioxide (with a mass fraction of 30% for silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 11.7% nanoparticles by mass.

[0142] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0143] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0144] Example 10

[0145] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0146] a. Silane coupling agent modified nanoparticles:

[0147] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0148] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0149] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 6.170g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0150] 12.559 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 25% was obtained.

[0151] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0152] 5.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 10.4% nanoparticles by mass.

[0153] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0154] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0155] Example 11

[0156] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0157] a. Silane coupling agent modified nanoparticles:

[0158] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0159] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0160] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 7.404g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0161] 15.082 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 30% was obtained.

[0162] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0163] 5.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 9.3% nanoparticles by mass.

[0164] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0165] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0166] Example 12

[0167] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0168] a. Silane coupling agent modified nanoparticles:

[0169] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 15.000 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 60%.

[0170] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0171] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 3.702g of phenylacetaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0172] 7.541 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 15% was obtained.

[0173] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0174] 5.000g of modified nano-titanium dioxide (with a mass fraction of 60% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 7.6% nanoparticles by mass.

[0175] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0176] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0177] Example 13

[0178] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0179] a. Silane coupling agent modified nanoparticles:

[0180] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 15.000 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 60%.

[0181] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0182] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 4.936g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0183] 10.047 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 20% was obtained.

[0184] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0185] 5.000g of modified nano-titanium dioxide (with a mass fraction of 60% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 6.7% nanoparticles by mass.

[0186] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0187] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0188] Example 14

[0189] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0190] a. Silane coupling agent modified nanoparticles:

[0191] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 15.000 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 60%.

[0192] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0193] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 6.170g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0194] 12.559 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 25% was obtained.

[0195] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0196] 5.000g of modified nano-titanium dioxide (with a mass fraction of 60% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 5.9% nanoparticles by mass.

[0197] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0198] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0199] Example 15

[0200] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0201] a. Silane coupling agent modified nanoparticles:

[0202] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 15.000 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 60%.

[0203] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0204] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 7.404g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0205] 15.082 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 30% was obtained.

[0206] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0207] 5.000g of modified nano-titanium dioxide (with a mass fraction of 60% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, with a nanoparticle mass ratio of 5.3%.

[0208] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0209] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0210] Example 16

[0211] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0212] a. Silane coupling agent modified nanoparticles:

[0213] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0214] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0215] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 3.702g of phenylacetaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0216] 7.541 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 15% was obtained.

[0217] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0218] 10.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 22.4% nanoparticles by mass.

[0219] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0220] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0221] Example 17

[0222] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0223] a. Silane coupling agent modified nanoparticles:

[0224] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0225] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0226] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 4.936g of phenylacetaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0227] 10.047 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 20% was obtained.

[0228] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0229] 10.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 20.0% nanoparticles by mass.

[0230] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0231] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0232] Example 18

[0233] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0234] a. Silane coupling agent modified nanoparticles:

[0235] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0236] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0237] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 6.170g of phenylacetaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred and heated to 85℃ and kept under reflux for 8h.

[0238] 12.559 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 25% was obtained.

[0239] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0240] 10.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, in which the mass percentage of nanoparticles was 18.1%.

[0241] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0242] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0243] Example 19

[0244] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0245] a. Silane coupling agent modified nanoparticles:

[0246] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0247] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0248] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of methanol, and then 7.404g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0249] 15.082 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of methanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 30% was obtained.

[0250] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0251] 10.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, with a nanoparticle mass ratio of 16.5%.

[0252] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0253] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0254] Example 20

[0255] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0256] a. Silane coupling agent modified nanoparticles:

[0257] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0258] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0259] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of ethanol, and then 7.404g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 85℃, and kept under reflux for 8h.

[0260] 15.082 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of ethanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 85°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 15% was obtained.

[0261] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0262] 10.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 85℃ for 8h to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 22.4% nanoparticles by mass.

[0263] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0264] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0265] Example 21

[0266] A method for preparing a multifunctional wet-strength agent with flame-retardant effect, comprising the following steps:

[0267] a. Silane coupling agent modified nanoparticles:

[0268] Weigh 10.000 g of nano-titanium dioxide into a beaker. Measure 100 ml of anhydrous ethanol solution using a graduated cylinder, pour the ethanol into the beaker containing the nano-titanium dioxide, and sonicate the mixture for 20 min to ensure thorough dispersion of the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 105 °C, and maintain the temperature under reflux. Dissolve 4.286 g of silane coupling agent KH560 in 50 ml of anhydrous ethanol, and add it dropwise to the flask. Continue the reaction at a constant temperature of 105 °C for 12 h. Filter the product, wash the filter cake with anhydrous ethanol, and dry it in an oven at 80 °C to obtain modified nano-titanium dioxide with a silane coupling agent KH-560 mass fraction of 30%.

[0269] b. Preparation of cationic water-soluble polymers grafted with flame-retardant intermediates:

[0270] 10.000g of polyethyleneimine (PEI) with a molecular weight of 10000 was completely dissolved in 100ml of ethanol, and then 7.404g of benzaldehyde was added. After mixing evenly, the mixture was added to the reaction vessel, stirred, heated to 100℃, and kept under reflux for 8h.

[0271] 15.082 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was dissolved in 50 ml of ethanol. The methanol solution containing DOPO was then added dropwise to the reaction system over 1 hour using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux at 100°C for 12 hours. Upon completion of the reaction, DOPO-grafted modified polyethyleneimine with a grafting degree of 15% was obtained.

[0272] c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect:

[0273] 10.000g of modified nano-titanium dioxide (with a mass fraction of 30% silane coupling agent KH-560) was added to the reaction system and the reaction was continued at 100℃ for 8 hours to obtain a suspension of a multifunctional wet strength agent with flame retardant effect, containing 22.4% nanoparticles by mass.

[0274] d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent:

[0275] The suspension was dried in a vacuum drying oven to obtain a pale yellow solid. The solid was washed with a hot ethanol solution, then filtered, and the filter cake was dried and ground into powder. This yields a wet strength agent powder with flame retardant, antibacterial, UV-protective, and wet strength properties.

[0276] Experiment and test instructions

[0277] Figure 1 and Figure 2 Transmission electron microscopy (TEM) images at different magnifications of a multifunctional wet-strength agent with flame-retardant effect prepared in Example 11, dispersed in ethylene glycol. Figure 2 It is known that the wet strength agent is in the form of long strips of granules with an average particle size of 50 nm. Figure 1 The wet strength agent still exhibits micro-agglomeration, but this does not affect its ability to form a uniform suspension in ethylene glycol. When added to the pulp during papermaking, it can be uniformly dispersed in the wet paper after dehydration.

[0278] Figure 3 Example 12: FT-IR absorption spectra of polyethyleneimine before and after modification with benzaldehyde using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. For the infrared spectrum of DOPO, the wavelength at 3054 cm⁻¹ is... -1 2437cm -1 1597cm -1 1450cm -1 1250cm -1 and 1048cm -1 The absorption peaks produced are C Ar Characteristic vibrational peaks for -H, PH, P-Ph, PC, P=O, and Ph-H. After the reaction, the PH bond reaches a wavenumber of 2437 cm⁻¹. -1 The complete disappearance of the characteristic absorption peak at the pH indicates that all the pH bonds have reacted with the carbon group of benzaldehyde and the amino group of polyethyleneimine.

[0279] Figure 4 The infrared absorption spectrum of polyethyleneimine with a flame-retardant intermediate grafted onto nano-titanium dioxide modified with silane coupling agent KH-560 in Example 14 is shown. For the infrared spectrum of the final product, its wavelength at 1450 cm⁻¹ is [missing value]. -1 1250cm -1 1100cm -1 1049cm -1 The resulting absorption peaks are characteristic vibrational peaks of PC, PO, -Si-O-, and -Si-O-Si-, respectively. After the reaction, the KH-560 epoxy group exhibits a characteristic vibrational peak at a wavenumber of 912 cm⁻¹. -1The complete disappearance of the characteristic absorption peak indicates that the nano-titanium dioxide modified with silane coupling agent KH-560 reacted with the amine groups of polyethyleneimine.

[0280] Figure 5 This is the thermogravimetric analysis curve of nano-titanium dioxide particles modified with silane coupling agent KH-560 in Example 17 (KH-560 accounts for 30% of the mass). The curve shows a significant endothermic peak at 181.9℃, because the silane coupling agent attached to the nano-titanium dioxide particles begins to thermally decompose within this temperature range. As the temperature increases, the organic matter on the sample continuously decomposes, with a final residual mass of 67.77%. The final residue consists of titanium dioxide and elements such as silicon and carbon, almost consistent with the theoretical value, indicating that the nano-titanium dioxide particles were successfully modified with silane coupling agent KH-560.

[0281] Figure 6 The thermogravimetric-differential scanning calorimetry (TGC) curves of the wet-strength agent prepared in Example 13 (DOPO grafting degree of 20%, nano-titanium dioxide particle mass ratio of 6.7%) from room temperature to 800°C are shown. The curve exhibits an endothermic peak between 187.4°C and 231.3°C, which corresponds to the thermal decomposition of the silane coupling agent connecting the polyethyleneimine molecular chain and the nano-titanium dioxide particles. A larger endothermic peak occurs between 381.1°C and 422.2°C, representing the thermal decomposition of the flame-retardant intermediate attached to the polyethyleneimine backbone, at which point the mass change reaches 57.47%, consistent with the theoretical contents of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and benzaldehyde. An exothermic peak occurs between 444.0°C and 503.5°C, due to the thermal decomposition of the polyethyleneimine backbone, resulting in a 19.11% thermogravimetric loss.

[0282] Figure 7 Different amounts (5%, 10%, 15%, and 20%) of wet strength agent (Example 13, DOPO grafting degree of 20%, nano-titanium dioxide particle mass ratio of 6.7%) were added to softwood pulp, and the yield was 90 g / m³ using a Kaisai automatic sheet forming machine. 2 Changes in the retention rate of wet strength agent during hand-coating. As shown in the graph, the retention rate of wet strength agent steadily increases with the increase in the amount of wet strength agent used. Under conditions where no retention aid is added, the retention rate is 67.9% when the wet strength agent content is 20%.

[0283] Figure 8 The papermaking yield was 90 g / m² with the addition of different amounts (5%, 10%, 15%, 20%) of wet strength agent (Example 13, DOPO grafting degree of 20%, nano titanium dioxide particle mass ratio of 6.7%). 2The whiteness of the paper was changed during the hand-making process. Since the wet strength agent is a light yellow powder, its addition to the paper during the papermaking process will reduce the whiteness of the paper. However, compared with the blank control, the whiteness of the paper with 20% wet strength agent added only decreased by 4.9%, which meets the industry standard.

[0284] Figure 9 The flame retardant properties of paper with different amounts (5%, 10%, 15%, and 20%) of wet strength agent were evaluated using the limiting oxygen index method (GB / T2406.2—2009). Compared to the blank paper sample, the limiting oxygen index of the paper increased significantly after adding the wet strength agent. When 20% (for oven-dry pulp) of wet strength agent was added, the limiting oxygen index of the paper increased from 15.5% to 23.0%. This indicates that the flame retardant properties of paper are positively correlated with the amount of wet strength agent used. Increasing the amount of wet strength agent added can make the paper meet the standards for flame retardancy.

[0285] Figure 10 and Figure 11 The relationship between tensile strength, tear strength, and the amount of wet strength agent added to the pulp is shown. Compared to the blank paper sample, the paper with added wet strength agent exhibits significantly improved tensile strength and tear strength. This is because during the paper drying process, the amino groups on the wet strength agent molecular chain can interact with paper fibers, forming a cross-linked network both intermolecularly and intramolecularly, thus increasing the adhesion strength between paper fibers. With increasing wet strength agent content, the number of bonding points between fibers and between fibers and fillers increases, raising the density between plant fibers and strengthening the hydrogen bonding force between fibers, thereby significantly improving the wet strength performance of the paper.

[0286] Figure 12 This study presents the results of Staphylococcus aureus antibacterial performance tests on paper containing different amounts of wet strength agent using the inhibition zone method. Paper without added wet strength agent showed no antibacterial effect, while paper with added wet strength agent exhibited a certain degree of antibacterial effect, with the antibacterial performance gradually increasing with the increase of wet strength agent content. The antibacterial mechanism of this wet strength agent is due to its presence of nano-TiO2 particles. The antibacterial mechanism of TiO2 is photocatalytic antibacterial, meaning that it generates reactive oxygen species through ultraviolet light irradiation to directly attack microbial cells, causing protein mutation and lipid decomposition to kill pathogens.

[0287] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific embodiments of the present invention are limited thereto. Several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications or substitutions should be considered to fall within the patent protection scope defined by the claims submitted herein. The present invention is not limited to the above embodiments, and all aspects described herein can be implemented and achieve the aforementioned beneficial effects.

Claims

1. A method for preparing a multifunctional wet-strength agent with flame-retardant effect, characterized in that, Includes the following steps: a. Silane coupling agent modified nanoparticles: Weigh nanoparticles and anhydrous ethanol solution, pour the ethanol into a beaker containing the nanoparticles, and sonicate the mixture for 10–30 minutes to fully disperse the nanoparticles in the ethanol solution. Pour the mixture into a flask equipped with a stirrer, heat to 90–120°C and reflux. Dissolve the silane coupling agent in anhydrous ethanol and add it dropwise into the flask. Continue the reaction for 8–16 hours under constant temperature conditions. Filter the product and wash the filter cake with anhydrous ethanol. Dry the product in an oven at 60–100°C to obtain silane coupling agent modified nanoparticles. The silane coupling agent is 3-(2,3-epoxypropoxy)propyltrimethoxysilane; the nanoparticles are nano-titanium dioxide. b. Preparation of flame-retardant intermediate graft-modified cationic water-soluble polymers: After the cationic water-soluble polymer is completely dissolved in an organic solvent, aromatic aldehydes are added, the mixture is stirred and heated, and then kept warm under reflux. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was dissolved in methanol and added dropwise to the reaction system over 0.5 to 2 hours using a constant-pressure dropping funnel. After the addition was complete, the mixture was heated under reflux while maintaining a constant temperature. Once the reaction was complete, a cationic polymer modified with a flame-retardant intermediate was obtained. The cationic water-soluble polymer was polyethyleneimine with an average molecular weight of 500 to 100,000. c. Preparation of a suspension of a multifunctional wet-strength agent with flame-retardant effect: Nanoparticles modified with silane coupling agent were added to the reaction system and reacted at 75-95℃ for 6-10 hours to obtain a suspension of a multifunctional wet strength agent with flame retardant effect. d. Preparation of powder with flame-retardant effect and multifunctional wet strength agent: The suspension was dried in a vacuum drying oven, the dried product was washed with hot ethanol solution, then filtered, the filter cake was dried and ground into powder to obtain a wet strength agent powder with flame retardant, antibacterial, UV protection and wet strength functions.

2. The preparation method according to claim 1, characterized in that, In step a, the silane coupling agent in the silane coupling agent modified nanoparticles has a mass ratio of 3% to 80%.

3. The preparation method according to claim 1, characterized in that, In step b, the organic solvent is either methanol or ethanol; the aromatic aldehyde is either benzaldehyde or phenylacetaldehyde.

4. The preparation method according to claim 1, characterized in that, In step b, the stirring, heating, and reflux are carried out at a temperature of 70–100°C for 5–8 hours.

5. The preparation method according to claim 1, characterized in that, In step b, the step of maintaining a constant temperature and continuing to heat and reflux means heating the reaction at a temperature of 70–100°C for 8–14 hours.

6. The preparation method according to claim 1, characterized in that, In step b, the grafting degree of the cationic polymer grafted with the flame-retardant intermediate is 5% to 40%.

7. The preparation method according to claim 1, characterized in that, In step c, the nanoparticles in the suspension account for 2% to 60% of the total mass of the wet strength agent.

8. The preparation method according to claim 1, characterized in that, In step d, the step of drying the suspension in a vacuum drying oven involves placing it in a vacuum drying oven at 70–110°C for 5–8 hours.

9. A multifunctional wet strength agent with flame retardant effect prepared by the preparation method according to any one of claims 1-8.

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