Fluoride-free waterproof agent as well as preparation method and application thereof

Abstract

The invention provides a fluoride-free waterproof agent, which is prepared from the following components in parts by weight: 5 to 10 parts of modified silicon dioxide, 15 to 25 parts of octadecyl methacrylate, 1 to 3 parts of modified cross-linking agent, 0.5 to 1.5 parts of initiator, 0.3 to 0.8 part of stabilizer and 20 to 30 parts of solvent, the modified silicon dioxide is silane coupling agent modified surface hydroxylated silicon dioxide; the modified cross-linking agent is prepared from chitosan, polyvinyl alcohol, glutaraldehyde and tris (hydroxymethyl) aminomethane; the stabilizer is prepared from butylated hydroxytoluene and potassium sorbate in a mass ratio of 1: (1.5-2.5); the initiator comprises potassium persulfate and hydrogen peroxide in a mass ratio of (2-4): 1. The fluoride-free waterproof agent is prepared from fluoride-free raw materials, the production process is simple, the waterproof layer is stable, and the waterproof performance is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of waterproofing agent preparation, and specifically relates to a fluorine-free waterproofing agent and a preparation method and application thereof. Background Art

[0002] Waterproofing agents are chemicals used to prevent water from penetrating into building materials. They are widely used in the fields of construction, decoration and maintenance to improve the durability and service life of buildings or structures. The main types of waterproofing agents are as follows: Cement-based penetrating crystalline waterproofing materials: This type of waterproofing agent contains active chemicals that can react with free lime in concrete to form water-insoluble crystals, thereby blocking tiny pores and cracks inside the concrete to achieve a waterproofing effect. Polymer-modified cement mortar: By adding polymer emulsion to improve the flexibility and adhesion of ordinary cement mortar, it is suitable for repair and waterproofing. Asphalt-based waterproofing coating: It is made of petroleum asphalt as the base material and various additives. It has good waterproofing properties and a certain degree of elasticity and is suitable for roof waterproofing. Polyurethane waterproofing coating: This waterproofing agent has excellent elasticity and adhesion, can adapt to slight deformation of the base layer, and is widely used in basements, bathrooms and other places where high elasticity waterproofing is required. Acrylic waterproofing coating: Environmentally friendly products, easy to apply, with a variety of colors, can be directly used as a decorative layer, suitable for internal and external wall and roof waterproofing. Silicone sealant: Although it is mainly used for joint sealing, it is also used as a waterproofing agent in certain specific occasions due to its excellent waterproof and weather resistance.

[0003] Fluorinated waterproofing agents usually refer to waterproofing materials containing fluorocarbon compounds. Such products are widely used due to their excellent waterproof, oil-proof and anti-fouling properties. Many traditional waterproofing agents use fluorinated or fluorinated hydrocarbon chemicals, which release harmful substances during use and pollute the environment. In particular, fluorinated compounds have high chemical stability and are difficult to degrade, and their long-term pollution to water sources and soil cannot be ignored. In addition, fluorinated compounds may also have adverse effects on human health, and waterproofing agents using such chemicals face increasingly stringent environmental regulations. For example, some fluorinated compounds are persistent organic pollutants, which are difficult to degrade in the environment and can migrate over long distances, causing long-term effects on the ecosystem; some fluorinated compounds can accumulate in organisms and may be transmitted to humans through the food chain, posing potential risks to human health; some specific types of perfluorinated compounds (such as PFOA and PFOS) may affect the function of the immune system, interfere with the endocrine system, and increase the risk of cancer.

[0004] Although fluoride-based waterproofing agents have good waterproofing effects, the effects of these waterproofing agents may gradually weaken over time, especially when exposed to high humidity, high temperature or chemically corrosive environments for a long time, the waterproofing performance may be affected. In addition, some traditional waterproofing agents may have problems with insufficient adhesion when dealing with specific materials, resulting in an unstable waterproof layer. The synthesis process of traditional waterproofing agents usually involves multiple steps, more chemical additives and complex processes, which makes the production cost high and may generate hazardous waste during the production process. Many existing waterproofing agents can only be used on specific substrates or under specific conditions to maintain good waterproofing performance, and cannot be widely applied to different types of substrates or complex environments.

[0005] Common fluorine-based waterproofing agents include C8 waterproofing agents and C6 waterproofing agents. Although fluorine-based waterproofing agents have excellent waterproofing performance and durable stability, and they combine well with textiles, they will inevitably produce byproducts such as PFOA (perfluorooctanoic acid and salts) and PFOS (perfluorooctane sulfonyl compounds) during production. Since PFOA and PFOS are currently difficult to degrade in the environment, have bioaccumulation and multiple toxicities, and have the common characteristics of persistent organic pollutants, they are considered to be new persistent environmental pollutants that are the focus of research in the 21st century. Therefore, fluorine-free waterproofing agents have gradually become the leading products in the waterproofing agent market and are the development direction of the modern waterproofing industry. Summary of the invention

[0006] The purpose of the present invention is to provide a fluorine-free waterproofing agent and a preparation method thereof. The fluorine-free waterproofing agent is prepared by using raw materials that do not contain fluoride, such as modified silicon dioxide, octadecyl methacrylate, a modified cross-linking agent, an initiator, a stabilizer and a solvent. The production process is simple, the waterproof layer is stable, and the waterproof performance is enhanced.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: A fluorine-free waterproofing agent comprises the following components in parts by weight: 5-10 parts of modified silicon dioxide, 15-25 parts of octadecyl methacrylate, 1-3 parts of modified crosslinking agent, 0.5-1.5 parts of initiator, 0.3-0.8 parts of stabilizer and 20-30 parts of solvent.

[0008] Preferably, the modified silica is silica with a hydroxylated surface modified by a silane coupling agent.

[0009] Preferably, the modified cross-linking agent consists of chitosan, polyvinyl alcohol, glutaraldehyde and tris(hydroxymethyl)aminomethane.

[0010] Preferably, the stabilizer is butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:1.5-2.5.

[0011] Preferably, the initiator is potassium persulfate and hydrogen peroxide in a mass ratio of 2-4:1.

[0012] A fluorine-free waterproofing agent comprises the following steps: S1: Preparation of surface hydroxylated silica and modified silica; S2: preparing a modified cross-linking agent; S3: Compounding to obtain a stabilizer and an initiator; S4: Mix 5-10 parts of modified silica powder, 15-25 parts of octadecyl methacrylate and 1-3 parts of modified crosslinking agent; grind and disperse the mixture in advance before the reaction to ensure a good reaction effect.

[0013] S5: Then add 0.5-1.5 parts of initiator, 20-30 parts of solvent and 0.3-0.8 parts of stabilizer to the mixture and stir the mixture at 60-90°C for 2-4 hours. At this temperature, octadecyl methacrylate and the surface of silica undergo copolymerization. The crosslinking agent makes the reaction more stable to form a crosslinked polymer. After cooling and filtering, the fluorine-free waterproofing agent is obtained. For waterproofing agents that need to be dried, they can be treated by spray drying, vacuum drying and other methods to obtain dry powder waterproofing agents.

[0014] Preferably, the preparation process of surface hydroxylated silica in step S1 is: placing the washed silica in a muffle furnace and calcining it at a temperature of 450-480°C for 35-45min; using a magnesium chloride solution with a mass fraction of 0.025-0.035% as an electrolyte, controlling the voltage per unit length of silica to 1.3-1.5V, and performing an electrically stimulated hydroxylation treatment on the silica for 1-2h to obtain hydroxylated silica.

[0015] Preferably, the preparation process of the modified silica in step S1 is: take 10-20 parts of the hydroxylated silica in step S1, 1-3 parts of coupling agent KH560, 0.5-2 parts of methanol and 10-30 parts of benzene, mix them, and ultrasonically vibrate for 5-10 minutes; react at a temperature of 90-110° C. for 3-5 hours to obtain modified silica.

[0016] Preferably, the preparation process of the modified cross-linking agent in step S2 is: dissolving chitosan in a 5% by mass acetic acid aqueous solution according to a solid-liquid ratio of 1:8-10; heating to 80-90°C, adding cysteine ​​accounting for 0.5% of chitosan, reacting for 3-5 hours, and drying to obtain modified chitosan; mixing 10-20 parts of modified chitosan, 30-40 parts of polyvinyl alcohol, 3-5 parts of glutaraldehyde and 4-7 parts of tris(hydroxymethyl)aminomethane to obtain the modified cross-linking agent.

[0017] Preferably, the preparation process of the stabilizer in step S3 is: butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:1.5-2.5 are stirred and mixed uniformly at room temperature; the preparation process of the initiator is: potassium persulfate and hydrogen peroxide in a mass ratio of 2-4:1 are stirred and mixed uniformly at room temperature.

[0018] The fluorine-free waterproofing agent of the present invention can be applied to different substrates in the following ways: 1. Spraying method: Spray the waterproofing agent evenly on the surface of building exterior walls, textiles, leather and other materials. After spraying, the waterproofing agent reacts chemically with the surface of the substrate to form a waterproof film to ensure the waterproof effect.

[0019] 2. Immersion method: directly immerse the waterproofing agent solution or slurry into the material to be waterproofed, take it out after a certain period of time, and dry it. This method is suitable for some materials with strong water absorption, such as wood, fabric, etc.

[0020] 3. Brushing method: For the treatment of some small areas or irregular surfaces, you can use a brushing method to apply the waterproofing agent on the target surface to ensure uniform coverage.

[0021] Silicon dioxide, also known as silica, is a compound composed of two elements, silicon and oxygen. It is widely found in nature and is the main component of many minerals (such as quartz, chalcedony, etc.). Silicon dioxide has a variety of unique physical and chemical properties. High hardness: The Mohs hardness of silicon dioxide is 7, indicating that it is relatively hard and wear-resistant. High melting point: The melting point of pure silicon dioxide is about 1713℃, and it remains stable at high temperatures. Variable density: Depending on the crystal structure, the density of silicon dioxide can vary from 2.2 to 2.65 g / cm³. Transparent to translucent: Pure silicon dioxide is usually transparent or translucent, which makes it valuable in optical applications. Good thermal stability: In addition to its extremely high melting point, silicon dioxide also exhibits good thermal stability, which allows it to be used in extreme temperature conditions.

[0022] Octadecanyl methacrylate is an ester compound formed by long-chain fatty alcohol and methacrylic acid; it has an 18-carbon alkyl chain. As an acrylate monomer, octadecyl methacrylate can participate in free radical polymerization and can be polymerized alone or copolymerized with other vinyl monomers to prepare various polymer materials. Due to the presence of its long-chain alkyl part, the final polymer is endowed with excellent weather resistance, water resistance and flexibility. It can reduce the glass transition temperature (Tg) of the polymer, thereby improving the low-temperature toughness and processing performance of the material.

[0023] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. The core innovation of the present invention is to use fluoride-free raw materials (such as silicon dioxide and octadecyl methacrylate) to prepare waterproofing agents. Unlike traditional fluorine-containing waterproofing agents, the present invention completely abandons fluoride and its derivatives, has less impact on the environment, does not release persistent organic pollutants (POPs), reduces pollution to soil, water sources and the atmosphere, ensures the safety of the product to the environment and human body during use and treatment, and meets modern environmental protection requirements.

[0024] 2. The present invention modifies the surface of silica and increases the surface hydroxyl active sites by electrically stimulated hydroxylation, thereby greatly increasing the wetting angle of deionized water on the surface of the silica sample, thereby greatly improving the hydrophobicity of the surface of the silica sample; by copolymerizing silica with octadecyl methacrylate, hydrophobic octadecyl methacrylate segments are introduced on the surface of silica, thereby forming a polymer with good waterproof effect; this reaction not only enhances the performance of the waterproof agent, but also improves the adhesion between the waterproof layer and the surface of the substrate.

[0025] 3. The present invention can enhance the stability of the reaction by using cross-linking agents such as glutaraldehyde and tris(hydroxymethyl)aminomethane, so that the waterproofing agent can form a more solid waterproof film after application, which has strong durability. This technical innovation enables the waterproof layer to maintain stability during long-term use and prevents the waterproof effect from fading over time.

[0026] 4. The production process of the present invention is simple, which reduces the dependence on complex chemical reactions and multiple additives and reduces production costs. At the same time, there is less waste in the synthesis process, which meets the standards of green production. The production process of the present invention is simple, improves production efficiency, and has high potential for industrial application.

[0027] 5. The waterproofing agent of the present invention can be widely used in a variety of substrates, such as building materials (exterior walls, roofs, etc.), textiles, leather, etc. Its waterproofing effect remains relatively stable under different materials and environmental conditions, and has strong adhesion and better adaptability. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The raw materials used in the present invention are as follows: Coupling agent KH560 was from Shanghai Yuanye Biotechnology Co., Ltd., product number S15029; chitosan was from Shandong Haiyihua Biotechnology Co., Ltd., product catalog 51; cysteine ​​was from Wuhan Benjamin Pharmaceutical Co., Ltd., product catalog 125; polyvinyl alcohol was from Sichuan Lai Te Ju Xin Pharmaceutical Excipients Co., Ltd., product catalog 40; butylated hydroxytoluene was from Anhui Youtai Bioengineering Co., Ltd., product catalog 750.

[0030] Example 1 This embodiment provides a method for preparing a fluorine-free waterproofing agent, comprising the following steps: S1: The cleaned silicon dioxide is placed in a muffle furnace and calcined at 450°C for 35 minutes; a magnesium chloride solution with a mass fraction of 0.025% is used as an electrolyte, the voltage per unit length of silicon dioxide is controlled to be 1.3V, and the silicon dioxide is subjected to an electric excitation hydroxylation treatment for 1 hour to obtain hydroxylated silicon dioxide; 10 g of the hydroxylated silica described in step S1, 1 g of coupling agent KH560, 0.5 g of methanol and 10 g of benzene were mixed, and ultrasonically vibrated at a power of 300 W for 5 min; the reaction was carried out at a temperature of 90° C. and a speed of 500 r / min for 3 h to obtain modified silica; S2: dissolving chitosan in a 5% by mass acetic acid aqueous solution at a solid-liquid ratio of 1:8; heating to 80°C, adding 0.5% cysteine ​​to chitosan, reacting for 3 hours, and drying at 80°C to obtain modified chitosan; mixing 10g of modified chitosan, 30g of polyvinyl alcohol, 3g of glutaraldehyde and 4g of tris(hydroxymethyl)aminomethane at 60°C for 30 minutes to obtain the modified crosslinking agent; S3: butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:1.5 were stirred and mixed at a rate of 400 r / min at room temperature for 15 min to obtain a stabilizer; potassium persulfate and hydrogen peroxide in a mass ratio of 2:1 were stirred and mixed at a rate of 500 r / min at room temperature for 20 min to obtain an initiator; S4: Mix 5 g of modified silica powder, 15 g of octadecyl methacrylate and 1 g of modified crosslinking agent; S5: Then, 0.5 g of initiator, 20 g of solvent glycerol and 0.3 g of stabilizer were added thereto, and the mixture was stirred at a temperature of 60° C. and a speed of 500 r / min for 2 h. After cooling and filtering, the fluorine-free waterproofing agent was obtained.

[0031] Example 2 This embodiment provides a method for preparing a fluorine-free waterproofing agent, comprising the following steps: S1: The cleaned silicon dioxide is placed in a muffle furnace and calcined at 480°C for 45 minutes; a magnesium chloride solution with a mass fraction of 0.035% is used as an electrolyte, the voltage per unit length of silicon dioxide is controlled to be 1.5V, and the silicon dioxide is subjected to an electric excitation hydroxylation treatment for 2 hours to obtain hydroxylated silicon dioxide; 20 g of the hydroxylated silica described in step S1, 3 g of coupling agent KH560, 2 g of methanol and 30 g of benzene were mixed, and ultrasonically vibrated at a power of 250 W for 10 min; reacted at a temperature of 110° C. for 5 h to obtain modified silica; S2: dissolving chitosan in a 5% by mass acetic acid aqueous solution at a solid-liquid ratio of 1:10; heating to 90°C, adding 0.5% cysteine ​​to the chitosan, reacting for 5 hours, and drying to obtain modified chitosan; mixing 20g of modified chitosan, 40g of polyvinyl alcohol, 5g of glutaraldehyde and 7g of tris(hydroxymethyl)aminomethane to obtain the modified crosslinking agent; S3: butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:2.5 were stirred and mixed at a rate of 500 r / min at room temperature for 20 min to obtain a stabilizer; potassium persulfate and hydrogen peroxide in a mass ratio of 4:1 were stirred and mixed at a rate of 600 r / min at room temperature for 25 min to obtain an initiator; S4: Mix 10 g of modified silica powder, 25 g of octadecyl methacrylate and 3 g of modified crosslinking agent; S5: Then, 1.5 g of initiator, 30 g of solvent and 0.8 g of stabilizer were added thereto, and the mixture was stirred at 90° C. and 500 r / min for 4 h. After cooling and filtering, the fluorine-free waterproofing agent was obtained.

[0032] Example 3 This embodiment provides a method for preparing a fluorine-free waterproofing agent, comprising the following steps: S1: The cleaned silicon dioxide is placed in a muffle furnace and calcined at 460°C for 42 minutes; a magnesium chloride solution with a mass fraction of 0.03% is used as an electrolyte, the voltage per unit length of silicon dioxide is controlled to be 1.4V, and the silicon dioxide is subjected to an electric excitation hydroxylation treatment for 1.5 hours to obtain hydroxylated silicon dioxide; 15 g of the hydroxylated silica described in step S1, 2 g of coupling agent KH560, 1.5 g of methanol and 20 g of benzene were mixed, and ultrasonically vibrated at a power of 200 W for 8 min; reacted at a temperature of 100° C. for 4 h to obtain modified silica; S2: dissolving chitosan in a 5% by mass acetic acid aqueous solution at a solid-liquid ratio of 1:9; heating to 85°C, adding 0.5% cysteine ​​to chitosan, reacting for 4 hours, and drying to obtain modified chitosan; mixing 15g of modified chitosan, 35g of polyvinyl alcohol, 4g of glutaraldehyde and 5g of tris(hydroxymethyl)aminomethane at a rate of 600r / min for 25min to obtain the modified crosslinking agent; S3: butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:2 were stirred and mixed at a rate of 400 r / min at room temperature for 10 min to obtain a stabilizer; potassium persulfate and hydrogen peroxide in a mass ratio of 3.5:1 were stirred and mixed at a rate of 450 r / min at room temperature for 20 min to obtain an initiator; S4: Mix 7 g of modified silica powder, 22 g of octadecyl methacrylate and 2 g of modified crosslinking agent; S5: Then, 1 g of initiator, 25 g of solvent and 0.6 g of stabilizer were added thereto, and the mixture was stirred at 75° C. and 500 r / min for 3.5 h. After cooling and filtering, the fluorine-free waterproofing agent was obtained.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that unhydroxylated silicon dioxide is used in step S1, that is, silicon dioxide is directly used as a raw material for modification, and the other steps are the same.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that the silicon dioxide is not modified in step S1, and the other steps are the same.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that modified chitosan is not used in step S2, and the other steps are the same.

[0036] Comparative Example 4 The difference between this comparative example and Example 1 is that no modified cross-linking agent is used in step S2, and the other steps are the same.

[0037] Performance Test: The same fabric was treated with the waterproofing agent prepared in each embodiment and comparative example, wherein the test fabric was a 55 / 45 polyester-cotton fabric, and the waterproofing treatment steps were: two dips and two rolls (60 g / L, roll residue rate 60%), followed by drying at 80°C for 180s, and then baking at 160°C for 180s to obtain a fabric sample treated with a waterproofing agent.

[0038] Waterproofness test: The water-wetting level was measured according to "GB / T 4745-2012 Testing and Evaluation of Waterproof Performance of Textiles by Water-wetting Method", and the water-wetting level of the fabric samples treated in each embodiment and comparative example was recorded. Washability test: The fabric was drum-washed for 15 minutes with 40°C water, then drum-dried, and then washed repeatedly. After multiple washings, the waterproofness test was performed again according to the waterproofness test. Waterproofing agent emulsion stability test: The waterproofing agent prepared in each embodiment and comparative example was poured into a 10ml centrifuge tube, and centrifuged at 5000r / min using a centrifuge to observe the sedimentation. The results are shown in Table 1 below: Table 1

[0039] From the above performance test results, it can be seen that the fluorine-free waterproofing agent prepared in Examples 1-3 has excellent performance, especially the comprehensive performance of Example 3 is the most outstanding. However, since Comparative Examples 1-4 do not adopt the necessary technical solutions, their corresponding performance tests are significantly worse than those of the Examples. The above experimental results further prove the importance of the technical solutions defined in the present invention for its technical effects.

[0040] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fluorine-free waterproofing agent, characterized in that: The invention comprises the following components in parts by weight: 5-10 parts of modified silicon dioxide, 15-25 parts of octadecyl methacrylate, 1-3 parts of modified crosslinking agent, 0.5-1.5 parts of initiator, 0.3-0.8 parts of stabilizer and 20-30 parts of solvent.

2. A fluorine-free waterproofing agent according to claim 1, characterized in that: The modified silica is silica with a hydroxylated surface modified by a silane coupling agent.

3. A fluorine-free waterproofing agent according to claim 1, characterized in that: The modified cross-linking agent consists of chitosan, polyvinyl alcohol, glutaraldehyde and tris(hydroxymethyl)aminomethane.

4. A fluorine-free waterproofing agent according to claim 1, characterized in that: The stabilizer is butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:1.5-2.

5.

5. A fluorine-free waterproofing agent according to claim 1, characterized in that: The initiator is potassium persulfate and hydrogen peroxide in a mass ratio of 2-4:

1.

6. A fluorine-free waterproofing agent, characterized in that: The steps include: S1: Preparation of surface hydroxylated silica and modified silica; S2: preparing a modified cross-linking agent; S3: Compounding to obtain a stabilizer and an initiator; S4: Mix 5-10 parts of modified silica powder, 15-25 parts of octadecyl methacrylate and 1-3 parts of modified crosslinking agent; S5: Then, 0.5-1.5 parts of initiator, 20-30 parts of solvent and 0.3-0.8 parts of stabilizer are added thereto, and the mixture is stirred and reacted at a temperature of 60-90° C. for 2-4 hours. After cooling and filtering, the fluorine-free waterproofing agent is obtained.

7. A fluorine-free waterproofing agent according to claim 6, characterized in that: The preparation process of surface hydroxylated silica in step S1 is as follows: the cleaned silica is placed in a muffle furnace and calcined at a temperature of 450-480°C for 35-45 minutes; a magnesium chloride solution with a mass fraction of 0.025-0.035% is used as an electrolyte, the voltage per unit length of silica is controlled to be 1.3-1.5V, and the silica is subjected to an electrical excitation hydroxylation treatment for 1-2 hours to obtain hydroxylated silica.

8. A fluorine-free waterproofing agent according to claim 6, characterized in that: The preparation process of the modified silica in step S1 is as follows: 10-20 parts of the hydroxylated silica in step S1, 1-3 parts of coupling agent KH560, 0.5-2 parts of methanol and 10-30 parts of benzene are mixed, ultrasonically shaken for 5-10 minutes; reacted at a temperature of 90-110° C. for 3-5 hours to obtain modified silica.

9. A fluorine-free waterproofing agent according to claim 6, characterized in that: The preparation process of the modified cross-linking agent in step S2 is as follows: dissolving chitosan in a 5% by mass acetic acid aqueous solution according to a solid-liquid ratio of 1:8-10; heating to 80-90°C, adding cysteine ​​accounting for 0.5% of chitosan, reacting for 3-5 hours, and drying to obtain modified chitosan; mixing 10-20 parts of modified chitosan, 30-40 parts of polyvinyl alcohol, 3-5 parts of glutaraldehyde and 4-7 parts of tris(hydroxymethyl)aminomethane to obtain the modified cross-linking agent.

10. A fluorine-free waterproofing agent according to claim 6, characterized in that: The preparation process of the stabilizer in step S3 is: butylated hydroxytoluene and potassium sorbate in a mass ratio of 1:1.5-2.5 are stirred and mixed uniformly at room temperature; the preparation process of the initiator is: potassium persulfate and hydrogen peroxide in a mass ratio of 2-4:1 are stirred and mixed uniformly at room temperature.

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