Waterproof and mildew-proof gypsum putty powder and preparation method thereof

Abstract

The present invention discloses a waterproof and mildew-proof gypsum putty powder and a preparation method thereof, belonging to the field of building material filling slurry. The raw materials of the putty powder include gypsum-talcum powder complex, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and composite antibacterial agent. The durability of the putty powder waterproof performance of the present invention is relatively excellent. The putty powder is subjected to artificial accelerated aging test in a hot and humid environment. After artificial accelerated aging, the compressive strength is 5.5-5.7MPa, and the flexural strength is 3.3-3.5MPa after artificial accelerated aging.

Description

Technical Field

[0001] The invention relates to waterproof and mildew-proof gypsum putty powder and a preparation method thereof, and belongs to the field of building material filling slurry. Background Art

[0002] Putty powder for building exterior walls is a base material used for leveling walls. Its primary function is to fill wall imperfections and smooth the surface during construction, providing a smooth base for subsequent coating application and ensuring a smooth finish. Gypsum-based putty powder is primarily made from gypsum as the primary inorganic gel material, mixed with heavy calcium carbonate, lime calcium, and other auxiliary materials.

[0003] Flue Gas Desulfurization Gypsum (FGD gypsum) is a byproduct produced during the flue gas desulfurization process in coal-fired power plants. Its main components are the same as natural gypsum. Desulfurization gypsum is superior to natural gypsum in terms of environmental friendliness, purity, and mechanical properties. It is a model for the resource utilization of industrial by-products. Using desulfurization gypsum instead of natural gypsum, its lower impurity content allows for the production of high-grade building materials. Furthermore, under the same process, the compressive and flexural strengths of desulfurization gypsum products are typically 10%-20% higher than those of natural gypsum.

[0004] Since desulfurized gypsum and natural gypsum are inherently water-absorbent, they form calcium sulfate dihydrate crystals after hydration. Their structure contains a large amount of crystalline water, which is easily dissolved or softened when exposed to water. The prepared putty powder has poor waterproof performance and a low softening coefficient. Its strength will drop significantly after being immersed in water. In the later stage, after the gypsum hardens, open pores will be formed, and capillary action will cause water to penetrate rapidly.

[0005] Studies have shown that a silane coupling agent (KH-550) can reduce the water absorption of desulfurized gypsum by over 60%, while siloxane emulsions (such as sodium methyl silicate and potassium methyl silicate) can significantly improve water resistance. Sodium methyl silicate and potassium methyl silicate are relatively low-cost, but while improving water resistance, they can also reduce the interfacial adhesion of putty powder. The silane coupling agent γ-aminopropyltriethoxysilane (KH-550) can simultaneously improve the water resistance and interfacial adhesion of putty powder, providing particularly improved adhesion when used with ceramic tiles and metal surfaces.

[0006] In actual applications, it was found that when putty powder with desulfurization gypsum as the main component was used in combination with KH-550, the waterproofing effect was seriously attenuated. The reason was that the alkalinity of desulfurization gypsum would cause the hydrolysis of KH-550. A large amount of KH-550 was consumed during the water-adding and stirring stage of the putty powder, reducing the effective film-forming amount. The alkalinity of desulfurization gypsum comes from the unreacted lime substances in the desulfurization process. In addition, the process water of the desulfurization system may contain alkaline additives such as NaOH and Na2CO3.

[0007] In summary, desulfurized gypsum can be used in the prior art to improve the compressive strength and flexural strength of putty powder, but the waterproof effect is poor. When the silane coupling agent γ-aminopropyltriethoxysilane is used to improve the waterproof performance and interfacial adhesion of putty powder, the alkalinity of desulfurized gypsum will cause the waterproof effect of putty powder to be seriously attenuated. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the defects of the existing technology. Chitosan is grafted onto the surface of talc powder, and then desulfurized gypsum treated with citric acid, chitosan grafted talc powder, and magnesium stearate are mixed by air flow. During the mixing process, γ-aminopropyltriethoxysilane is slowly sprayed into to prepare a gypsum-talc powder complex, and putty powder is finally prepared by combining with other raw material components. When using the silane coupling agent γ-aminopropyltriethoxysilane to improve the waterproof performance and interfacial adhesion of the putty powder, the alkalinity of the desulfurized gypsum is avoided from affecting the waterproof durability of the putty powder.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] Disclosed is a waterproof and mildew-proof gypsum putty powder. Raw materials of the putty powder include a gypsum-talcum powder complex, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and a composite antibacterial agent, and the mass ratio of the raw materials is 1000-1200:400-500:9-11:75-125:1.8-2.2:25-35:17-23.

[0011] The following are further improvements to the above technical solution:

[0012] The fineness of the heavy calcium powder is 200 mesh;

[0013] The fineness of the bentonite is 100 mesh;

[0014] The latex powder is VAE latex powder;

[0015] The composite antibacterial agent is a mixture of zinc oxide and carbendazim, and the mass ratio of zinc oxide to carbendazim is 9-11:1;

[0016] The preparation method of the gypsum-talc powder composite comprises preparing chitin-grafted talc powder and preparing the gypsum-talc powder composite;

[0017] The method for preparing chitosan grafted talc comprises: mixing talc and deionized water, stirring them uniformly, adding itaconic anhydride thereto, controlling the temperature to 73-77° C., stirring for 100-125 minutes, filtering, washing, and drying to obtain itaconic anhydride-treated talc; mixing talc treated with itaconic anhydride and N,N-dimethylformamide, stirring them uniformly, adding chitosan and p-toluenesulfonic acid thereto, controlling the temperature to 90-97° C., stirring for 140-170 minutes, filtering, washing, and drying to obtain chitosan grafted talc;

[0018] The mass ratio of the talc, deionized water, and itaconic anhydride is 9-11:105-135:14-16;

[0019] The fineness of the talcum powder is 800 mesh;

[0020] The mass ratio of the talc powder treated with conic anhydride, N,N-dimethylformamide, chitin and p-toluenesulfonic acid is 45-55:475-525:18-22:2.5-3.5.

[0021] The method for preparing the gypsum-talc composite comprises: mixing desulfurized gypsum and a citric acid solution, controlling the stirring time to be 25-35 minutes, filtering, washing, and drying after the stirring is completed to obtain citric acid-treated desulfurized gypsum, then feeding the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate into an air flow mixer, and then continuously spraying a γ-aminopropyltriethoxysilane solution into the air flow mixer, controlling the spraying amount per minute to account for 4.5wt%-5.5wt% of the total amount of the γ-aminopropyltriethoxysilane solution, maintaining the air flow velocity of the air flow mixer at 30-40m / s during spraying, and the air flow humidity at 25%-35%, and drying after the spraying is completed to obtain the gypsum-talc composite;

[0022] The mass ratio of the desulfurized gypsum and the citric acid solution is 1:9-11;

[0023] The desulfurization gypsum is first-grade desulfurization gypsum;

[0024] The concentration of the citric acid solution is 0.20wt%-0.30wt%;

[0025] The mass ratio of the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate is 18-22:4.5-5.5:0.9-1.1;

[0026] The amount of the γ-aminopropyltriethoxysilane solution is 18wt%-22wt% of the total amount of desulfurized gypsum, chitin grafted talc, and magnesium stearate;

[0027] The concentration of the γ-aminopropyltriethoxysilane solution is 0.45wt%-0.55wt%;

[0028] The preparation method of the putty powder comprises the following steps: dry-mixing a specified mass of a gypsum-talcum powder composite, heavy calcium powder, and bentonite in the raw materials for 3-8 minutes, then adding cellulose ether and latex powder and continuing to mix for 2-5 minutes, and finally adding sodium citrate and a composite antibacterial agent and continuing to mix for 8-12 minutes to obtain a waterproof and mildew-proof gypsum putty powder.

[0029] Compared with the prior art, the present invention achieves the following beneficial effects:

[0030] In the preparation process of gypsum-talc powder composite, chitosan grafted talc powder is first prepared, and the talc powder is surface treated with itaconic anhydride, which reacts with the hydroxyl groups on the surface of the talc powder to introduce carboxyl groups and carbon-carbon double bonds on the surface of the talc powder. Then, chitosan is dissolved by a solvent, and chitosan is grafted with the talc powder treated with itaconic anhydride under the catalysis of p-toluenesulfonic acid to obtain chitosan grafted talc powder. After grafting, a three-dimensional network structure is formed, which not only forms strong interface adhesion but also improves stress transfer efficiency. In the subsequent step, an air flow mixer is used to mix the desulfurized gypsum treated with citric acid, chitin-grafted talc, and magnesium stearate. At a specific air flow velocity and humidity, a γ-aminopropyltriethoxysilane solution is slowly sprayed into the mixer to ensure that all components are fully and evenly mixed to obtain a gypsum-talc complex. This avoids the effect of the alkalinity of the desulfurized gypsum itself on the γ-aminopropyltriethoxysilane. Experiments have shown that the waterproof performance and durability of the putty powder have been effectively improved.

[0031] The putty powder of the present invention has high strength. According to the method in GB / T28627-2023, the compressive strength and flexural strength of the putty powder are tested. The compressive strength is 6.5-6.7 MPa, and the flexural strength is 4.0-4.2 MPa.

[0032] The putty powder of the present invention has good interfacial bonding performance. According to the method in GB / T23455-2009, the tensile bonding strength between the putty powder and the ceramic tile is tested, including the tensile bonding strength under the standard state, the tensile bonding strength under water treatment, and the tensile bonding strength under freeze-thaw cycle treatment. The tensile bonding strength under the standard state is 0.82-0.85 MPa, the tensile bonding strength under water treatment is 0.63-0.66 MPa, and the tensile bonding strength under freeze-thaw cycle treatment is 0.69-0.71 MPa.

[0033] The putty powder of the present invention has excellent waterproof performance and water resistance. According to the method in ASTM C1305, the water absorption rate and compressive strength retention rate of the putty powder after immersion in water for 7 days were tested. The water absorption rate after immersion in water for 7 days was 2.5%-2.6%, and the compressive strength retention rate after immersion in water for 7 days was 89.5%-90.2%;

[0034] The putty powder of the present invention has excellent durability of waterproof performance. The putty powder is subjected to an artificial accelerated aging test in a hot and humid environment. The test conditions are: placing it at 40°C and 95% relative humidity for 7 days, then drying it for 7 days, a total of 14 days as one cycle, and a total of 3 cycles. After the cycle is completed, the compressive strength and flexural strength of the putty powder are tested according to the method in GB / T28627-2023. After artificial accelerated aging, the compressive strength is 5.5-5.7 MPa, and the flexural strength after artificial accelerated aging is 3.3-3.5 MPa.

[0035] The putty powder of the present invention has excellent crack resistance. According to the method in GB / T23455-2009, the flexibility of the putty powder is tested, including the flexibility under the standard state and the flexibility after 5 hot and cold cycles, and no cracks are found. DETAILED DESCRIPTION Example 1

[0036] A waterproof and mildew-proof gypsum putty powder, whose raw materials include gypsum-talcum powder composite, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and composite antibacterial agent, and the mass ratio of the raw materials is 1100:450:10:100:2:30:20;

[0037] The fineness of the heavy calcium powder is 200 mesh;

[0038] The fineness of the bentonite is 100 mesh;

[0039] The latex powder is VAE latex powder;

[0040] The composite antibacterial agent is a mixture of zinc oxide and carbendazim, and the mass ratio of zinc oxide to carbendazim is 10:1;

[0041] The preparation method of the gypsum-talc powder composite comprises preparing chitin-grafted talc powder and preparing the gypsum-talc powder composite;

[0042] The method for preparing chitosan grafted talc comprises: mixing talc and deionized water, stirring them uniformly, adding itaconic anhydride thereto, controlling the temperature at 75° C., stirring for 120 minutes, filtering, washing, and drying after the stirring is completed to obtain itaconic anhydride-treated talc; mixing talc treated with itaconic anhydride and N,N-dimethylformamide, stirring them uniformly, adding chitosan and p-toluenesulfonic acid thereto, controlling the temperature at 95° C., stirring for 150 minutes, filtering, washing, and drying after the stirring is completed to obtain chitosan grafted talc;

[0043] The mass ratio of the talc, deionized water, and itaconic anhydride is 10:120:15;

[0044] The fineness of the talcum powder is 800 mesh;

[0045] The mass ratio of the talc powder treated with conic anhydride, N,N-dimethylformamide, chitin and p-toluenesulfonic acid is 50:500:20:3.

[0046] The method for preparing the gypsum-talc composite comprises: mixing desulfurized gypsum and a citric acid solution, controlling the stirring time to be 30 minutes, filtering, washing, and drying after the stirring is completed to obtain citric acid-treated desulfurized gypsum, then feeding the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate into an air flow mixer, and then continuously spraying a γ-aminopropyltriethoxysilane solution into the air flow mixer, controlling the spraying amount per minute to account for 5wt% of the total amount of the γ-aminopropyltriethoxysilane solution, maintaining the air flow velocity of the air flow mixer at 35m / s and the air flow humidity at 30% during spraying, and drying after the spraying is completed to obtain the gypsum-talc composite;

[0047] The mass ratio of the desulfurized gypsum to the citric acid solution is 1:10;

[0048] The desulfurization gypsum is first-grade desulfurization gypsum;

[0049] The concentration of the citric acid solution is 0.25wt%;

[0050] The mass ratio of the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate is 20:5:1;

[0051] The amount of the γ-aminopropyltriethoxysilane solution is 20wt% of the total amount of desulfurized gypsum, chitin grafted talc, and magnesium stearate;

[0052] The concentration of the γ-aminopropyltriethoxysilane solution is 0.5wt%;

[0053] The preparation method of the putty powder comprises the following steps: dry-mixing a specified mass of a gypsum-talcum powder composite, heavy calcium powder, and bentonite in the raw materials for 5 minutes, then adding cellulose ether and latex powder and continuing to mix for 3 minutes, and finally adding sodium citrate and a composite antibacterial agent and continuing to mix for 10 minutes to obtain a waterproof and mildew-proof gypsum putty powder. Example 2

[0054] A waterproof and mildew-proof gypsum putty powder, whose raw materials include gypsum-talcum powder composite, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and composite antibacterial agent, and the mass ratio of the raw materials is 1000:400:9:75:1.8:25:17;

[0055] The fineness of the heavy calcium powder is 200 mesh;

[0056] The fineness of the bentonite is 100 mesh;

[0057] The latex powder is VAE latex powder;

[0058] The composite antibacterial agent is a mixture of zinc oxide and carbendazim, and the mass ratio of zinc oxide to carbendazim is 9:1;

[0059] The preparation method of the gypsum-talc powder composite comprises preparing chitin-grafted talc powder and preparing the gypsum-talc powder composite;

[0060] The method for preparing chitosan grafted talc comprises: mixing talc and deionized water, stirring them uniformly, adding itaconic anhydride thereto, controlling the temperature at 73° C., stirring for 125 minutes, filtering, washing, and drying after the stirring is completed to obtain itaconic anhydride-treated talc; mixing talc treated with itaconic anhydride and N,N-dimethylformamide, stirring them uniformly, adding chitosan and p-toluenesulfonic acid thereto, controlling the temperature at 90° C., stirring for 170 minutes, filtering, washing, and drying after the stirring is completed to obtain chitosan grafted talc;

[0061] The mass ratio of the talc, deionized water, and itaconic anhydride is 9:105:14;

[0062] The fineness of the talcum powder is 800 mesh;

[0063] The mass ratio of the talc powder treated with conic anhydride, N,N-dimethylformamide, chitin and p-toluenesulfonic acid is 45:475:18:2.5.

[0064] The method for preparing the gypsum-talc composite comprises: mixing desulfurized gypsum and a citric acid solution, controlling the stirring time to be 25 minutes, filtering, washing, and drying after the stirring is completed to obtain citric acid-treated desulfurized gypsum, then feeding the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate into an air flow mixer, and then continuously spraying a γ-aminopropyltriethoxysilane solution into the air flow mixer, controlling the amount sprayed per minute to account for 4.5wt% of the total amount of the γ-aminopropyltriethoxysilane solution, maintaining the air flow velocity of the air flow mixer at 30m / s and the air flow humidity at 25% during spraying, and drying after the spraying is completed to obtain the gypsum-talc composite;

[0065] The mass ratio of the desulfurized gypsum and the citric acid solution is 1:9;

[0066] The desulfurization gypsum is first-grade desulfurization gypsum;

[0067] The concentration of the citric acid solution is 0.30wt%;

[0068] The mass ratio of the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate is 18:4.5:0.9;

[0069] The amount of the γ-aminopropyltriethoxysilane solution is 18 wt % of the total amount of desulfurized gypsum, chitin grafted talc and magnesium stearate;

[0070] The concentration of the γ-aminopropyltriethoxysilane solution is 0.55wt%;

[0071] The preparation method of the putty powder comprises the following steps: dry-mixing a specified mass of a gypsum-talcum powder composite, heavy calcium powder, and bentonite in the raw materials for 3 minutes, then adding cellulose ether and latex powder and continuing to mix for 5 minutes, and finally adding sodium citrate and a composite antibacterial agent and continuing to mix for 12 minutes to obtain a waterproof and mildew-proof gypsum putty powder. Example 3

[0072] A waterproof and mildew-proof gypsum putty powder, whose raw materials include gypsum-talcum powder composite, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and composite antibacterial agent, and the mass ratio of the raw materials is 1200:500:11:125:2.2:35:23;

[0073] The fineness of the heavy calcium powder is 200 mesh;

[0074] The fineness of the bentonite is 100 mesh;

[0075] The latex powder is VAE latex powder;

[0076] The composite antibacterial agent is a mixture of zinc oxide and carbendazim, and the mass ratio of zinc oxide to carbendazim is 11:1;

[0077] The preparation method of the gypsum-talc powder composite comprises preparing chitin-grafted talc powder and preparing the gypsum-talc powder composite;

[0078] The method for preparing chitosan grafted talc comprises: mixing talc and deionized water, stirring them uniformly, adding itaconic anhydride thereto, controlling the temperature at 77° C., stirring for 100 minutes, filtering, washing, and drying to obtain itaconic anhydride-treated talc; mixing talc treated with itaconic anhydride and N,N-dimethylformamide, stirring them uniformly, adding chitosan and p-toluenesulfonic acid thereto, controlling the temperature at 97° C., stirring for 140 minutes, filtering, washing, and drying to obtain chitosan grafted talc;

[0079] The mass ratio of the talc, deionized water, and itaconic anhydride is 11:135:15;

[0080] The fineness of the talcum powder is 800 mesh;

[0081] The mass ratio of the talc powder treated with conic anhydride, N,N-dimethylformamide, chitin and p-toluenesulfonic acid is 55:525:22:3.5.

[0082] The method for preparing the gypsum-talc composite comprises: mixing desulfurized gypsum and a citric acid solution, controlling the stirring time to be 35 minutes, filtering, washing, and drying after the stirring is completed to obtain citric acid-treated desulfurized gypsum, then feeding the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate into an air flow mixer, and then continuously spraying a γ-aminopropyltriethoxysilane solution into the air flow mixer, controlling the spraying amount per minute to account for 5.5wt% of the total amount of the γ-aminopropyltriethoxysilane solution, maintaining the air flow velocity of the air flow mixer at 40m / s and the air flow humidity at 35% during spraying, and drying after the spraying is completed to obtain the gypsum-talc composite;

[0083] The mass ratio of the desulfurized gypsum and the citric acid solution is 1:11;

[0084] The desulfurization gypsum is first-grade desulfurization gypsum;

[0085] The concentration of the citric acid solution is 0.20wt%;

[0086] The mass ratio of the citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate is 22:5.5:1.1;

[0087] The amount of the γ-aminopropyltriethoxysilane solution is 22 wt % of the total amount of desulfurized gypsum, chitin grafted talc and magnesium stearate;

[0088] The concentration of the γ-aminopropyltriethoxysilane solution is 0.45wt%;

[0089] The preparation method of the putty powder comprises the following steps: dry-mixing a specified mass of a gypsum-talcum powder composite, heavy calcium powder, and bentonite in the raw materials for 8 minutes, then adding cellulose ether and latex powder and continuing to mix for 2 minutes, and finally adding sodium citrate and a composite antibacterial agent and continuing to mix for 8 minutes to obtain a waterproof and mildew-proof gypsum putty powder.

[0090] Comparative Example 1

[0091] Different from Example 1, in the preparation method of the gypsum-talc composite, the step of preparing the chitosan-grafted talc was omitted. While the amount remained unchanged, the untreated talc was directly used to prepare the gypsum-talc composite. The remaining steps were the same to prepare the putty powder.

[0092] The fineness of the untreated talcum powder is 800 mesh.

[0093] Comparative Example 2

[0094] Different from Example 1, in the method for preparing the gypsum-talcum powder composite, the steps for preparing the gypsum-talcum powder composite are changed to the following operations:

[0095] The desulfurized gypsum and chitin-grafted talc are mixed uniformly to obtain a mixed powder, and then the γ-aminopropyltriethoxysilane solution is mixed uniformly with the mixed powder, and then dried to obtain a gypsum-talc composite;

[0096] The mass ratio of the desulfurized gypsum and chitin-grafted talc is 20:5;

[0097] The desulfurization gypsum is first-grade desulfurization gypsum;

[0098] The amount of the γ-aminopropyltriethoxysilane solution is 20% of the total amount of desulfurized gypsum and chitin grafted talc;

[0099] The concentration of the γ-aminopropyltriethoxysilane solution is 0.5%;

[0100] The remaining steps are the same to prepare putty powder.

[0101] Test Example 1 Compression and flexural strength test

[0102] The compressive strength and flexural strength of the putty powders of Examples 1-3 and Comparative Examples 1-2 were tested according to the method in GB / T 28627-2023. The results are shown in Table 1.

[0103] Table 1

[0104] In Example 1-3, chitosan was grafted onto the surface of talc, and then desulfurized gypsum treated with citric acid, chitosan-grafted talc, and magnesium stearate were mixed by airflow. During the mixing process, γ-aminopropyltriethoxysilane was slowly sprayed into the gypsum-talc composite, and the composite was finally prepared by combining with other raw materials. The putty powder had high compressive strength and flexural strength.

[0105] Comparative Example 1: In order to prepare a composite by directly combining talc powder without chitosan grafting with desulfurized gypsum, the lack of chitosan grafting would lead to a more serious decrease in the compressive strength and flexural strength of the putty powder.

[0106] In the step of preparing the gypsum-talc composite in Comparative Example 2, the desulfurized gypsum and the chitin-grafted talc are directly mixed evenly to obtain a mixed powder, and then the γ-aminopropyltriethoxysilane solution is evenly mixed with the mixed powder, and then dried. Although the mixing step is relatively simple and direct, the effect on the compressive strength and flexural strength is limited, and the compressive strength and flexural strength decrease to a small extent.

[0107] Test Example 2 Interface Adhesion Performance Test

[0108] The putty powders of Examples 1-3 and Comparative Examples 1-2 were tested for tensile bonding strength between the putty powders and the ceramic tiles according to the method in GB / T23455-2009, including the tensile bonding strength under standard conditions, the tensile bonding strength under water immersion treatment, and the tensile bonding strength under freeze-thaw cycle treatment. The results are shown in Table 2.

[0109] Table 2

[0110] In Example 1-3, chitosan was grafted onto the surface of talc, and then desulfurized gypsum treated with citric acid, chitosan-grafted talc, and magnesium stearate were mixed by airflow. γ-aminopropyltriethoxysilane was slowly sprayed into the mixture during the mixing process to prepare a gypsum-talc composite. The composite was then combined with other raw materials to prepare a putty powder. The putty powder had good interfacial bonding properties, and the tensile bond strength under water immersion treatment and the tensile bond strength under freeze-thaw cycle treatment were both maintained at a high level.

[0111] Comparative Example 1: A composite was prepared by directly combining talc powder without chitin grafting with desulfurized gypsum. The lack of chitin grafting resulted in a decrease in the interfacial bonding performance of the putty powder. Although the interfacial bonding strength under standard conditions was not high, the decrease in the tensile bonding strength under water immersion treatment and the tensile bonding strength under freeze-thaw cycle treatment was relatively low.

[0112] In the step of preparing the gypsum-talc composite in Comparative Example 2, the desulfurized gypsum and the chitin-grafted talc are directly mixed evenly to obtain a mixed powder, and then the γ-aminopropyltriethoxysilane solution is mixed evenly with the mixed powder, and then dried. Although the relatively simple mixing step has little effect on the interfacial bonding strength under the standard state, with only a slight decrease, it will cause a more serious decrease in the tensile bonding strength of the putty powder under water immersion treatment and the tensile bonding strength under freeze-thaw cycle treatment.

[0113] Test Example 3 Waterproofness and Waterproof Durability Test

[0114] The putty powders of Examples 1-3 and Comparative Examples 1-2 were tested for water absorption and compressive strength retention after immersion in water for 7 days according to the method of ASTM C1305.

[0115] The putty powders of Examples 1-3 and Comparative Examples 1-2 were subjected to an artificial accelerated aging test in a hot and humid environment. The test conditions were 40°C and 95% relative humidity for 7 days, followed by drying for 7 days. A total of 14 days constituted one cycle, and three cycles were performed in total. After the cycle was completed, the compressive strength and flexural strength of the putty powders were tested according to the method in GB / T28627-2023.

[0116] The results are shown in Table 3.

[0117] Table 3

[0118] In Example 1-3, chitosan was grafted onto the surface of talc, and then desulfurized gypsum treated with citric acid, chitosan-grafted talc, and magnesium stearate were mixed by airflow. During the mixing process, γ-aminopropyltriethoxysilane was slowly sprayed into the gypsum-talc composite, and the composite was finally prepared by combining with other raw material components. The putty powder had high water resistance and waterproof durability. After being immersed in water for 7 days, it could maintain a low water absorption rate and a high compressive strength retention rate. In an artificial accelerated aging test, it could maintain high compressive strength and flexural strength.

[0119] Comparative Example 1: The composite was directly prepared by combining talc powder without chitin grafting with desulfurized gypsum. The lack of chitin grafting resulted in a serious decrease in the waterproofness and waterproof durability of the putty powder. After immersion in water for 7 days, the water absorption rate increased significantly, and the compressive strength retention rate also decreased significantly. In addition, in the artificial accelerated aging test, the compressive strength and flexural strength also decreased significantly.

[0120] In the step of preparing the gypsum-talc composite in Comparative Example 2, the desulfurized gypsum and the chitin-grafted talc are directly mixed evenly to obtain a mixed powder, and then the γ-aminopropyltriethoxysilane solution is mixed evenly with the mixed powder, and then dried. The relatively simple mixing step will also affect the waterproofness and waterproof durability. After immersion in water for 7 days, the water absorption rate increases significantly, and the compressive strength retention rate also decreases to a certain extent. In addition, in the artificial accelerated aging test, the compressive strength and flexural strength decrease to a certain extent.

[0121] Test Example 4: Crack resistance test

[0122] The putty powders of Examples 1-3 and Comparative Examples 1-2 were tested for flexibility according to the method in GB / T23455-2009, including flexibility under standard conditions and flexibility after 5 hot and cold cycles. The presence or absence of cracks was used as an evaluation index. The results are shown in Table 4.

[0123] Table 4

[0124] In Example 1-3, chitosan was grafted onto the surface of talc, and then desulfurized gypsum treated with citric acid, chitosan-grafted talc, and magnesium stearate were mixed by airflow. γ-aminopropyltriethoxysilane was slowly sprayed into the mixture during the mixing process to prepare a gypsum-talc composite. The composite was then combined with other raw materials to prepare a putty powder. The putty powder had good flexibility and showed no cracks in the flexibility test under standard conditions and in the flexibility test after five hot and cold cycles.

[0125] Comparative Example 1: A composite was prepared by directly combining talc powder without chitosan grafting with desulfurized gypsum. The lack of chitosan grafting resulted in decreased flexibility of the putty powder. Although no cracks were observed in the flexibility test under standard conditions, fine cracks appeared in the flexibility test after five hot and cold cycles.

[0126] In the step of preparing the gypsum-talc composite in Comparative Example 2, the desulfurized gypsum and the chitin-grafted talc are directly mixed evenly to obtain a mixed powder, and then the γ-aminopropyltriethoxysilane solution is mixed evenly with the mixed powder, and then dried. Although the mixing step is relatively simple and direct, it has no obvious effect on the flexibility. No cracks will appear in the flexibility test under standard conditions and the flexibility test after 5 hot and cold cycles.

Claims

1. A waterproof and mildew-proof gypsum putty powder, characterized in that: The raw materials of the putty powder include gypsum-talcum powder composite, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and composite antibacterial agent; The mass ratio of the gypsum-talcum powder complex, heavy calcium powder, cellulose ether, bentonite, sodium citrate, latex powder, and composite antibacterial agent is 1000-1200:400-500:9-11:75-125:1.8-2.2:25-35:17-23; The preparation method of the gypsum-talc powder composite comprises preparing chitosan-grafted talc powder and preparing the gypsum-talc powder composite; The method for preparing chitosan grafted talc comprises: mixing talc and deionized water, stirring them uniformly, adding itaconic anhydride thereto and stirring, filtering, washing, and drying to obtain itaconic anhydride-treated talc; mixing itaconic anhydride-treated talc and N,N-dimethylformamide, stirring them uniformly, adding chitosan and p-toluenesulfonic acid thereto and stirring, filtering, washing, and drying to obtain chitosan grafted talc; The mass ratio of the talc, deionized water, and itaconic anhydride is 9-11:105-135:14-16; The mass ratio of the itaconic anhydride-treated talc, N,N-dimethylformamide, chitin, and p-toluenesulfonic acid is 45-55:475-525:18-22:2.5-3.5; The method for preparing the gypsum-talc composite comprises mixing desulfurized gypsum and a citric acid solution, and then filtering, washing, and drying to obtain citric acid-treated desulfurized gypsum. The citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate are then fed into an air flow mixer. A γ-aminopropyltriethoxysilane solution is then continuously sprayed into the air flow mixer. After spraying, the mixture is dried to obtain the gypsum-talc composite. The mass ratio of the desulfurized gypsum and the citric acid solution is 1:9-11; The mass ratio of citric acid-treated desulfurized gypsum, chitin-grafted talc, and magnesium stearate is 18-22:4.5-5.5:0.9-1.1; The amount of the γ-aminopropyltriethoxysilane solution used is 18 wt%-22 wt% of the total amount of the desulfurized gypsum, chitin-grafted talc, and magnesium stearate.

2. The waterproof and mildew-proof gypsum putty powder according to claim 1, characterized in that: In the raw materials of the putty powder, the fineness of the heavy calcium powder is 200 mesh; The fineness of the bentonite is 100 mesh; The latex powder is VAE latex powder; The composite antibacterial agent is a mixture of zinc oxide and carbendazim, and the mass ratio of zinc oxide to carbendazim is 9-11:

1.

3. The waterproof and mildew-proof gypsum putty powder according to claim 1, characterized in that: In the method for preparing chitosan-grafted talc, the method for adding itaconic anhydride and stirring is to control the temperature to 73-77° C. and stir for 100-125 minutes; The method of adding chitosan and p-toluenesulfonic acid and stirring is to control the temperature to 90-97° C. and stir for 140-170 minutes.

4. The waterproof and mildew-proof gypsum putty powder according to claim 1, characterized in that: In the method for preparing chitin-grafted talc powder, the fineness of the talc powder is 800 mesh.

5. The waterproof and mildew-proof gypsum putty powder according to claim 1, characterized in that: In the method for preparing the gypsum-talcum powder composite, the desulfurized gypsum and the citric acid solution are mixed and stirred, and the stirring time needs to be controlled to be 25-35 minutes; The γ-aminopropyltriethoxysilane solution is then continuously sprayed into the air flow mixer, and the amount sprayed per minute needs to be controlled to account for 4.5wt%-5.5wt% of the total amount of the γ-aminopropyltriethoxysilane solution. During spraying, the air flow velocity of the air flow mixer needs to be maintained at 30-40m / s and the air flow humidity needs to be maintained at 25%-35%.

6. The waterproof and mildew-proof gypsum putty powder according to claim 1, characterized in that: In the method for preparing the gypsum-talcum powder composite, the desulfurized gypsum is primary desulfurized gypsum; The concentration of the citric acid solution is 0.20wt%-0.30wt%; The concentration of the γ-aminopropyltriethoxysilane solution is 0.45 wt %-0.55 wt %.

7. The method for preparing a waterproof and mildew-proof gypsum putty powder according to claim 1, wherein: The preparation method comprises the following steps: dry-mixing a specified mass of a gypsum-talcum powder composite, heavy calcium powder, and bentonite in the raw materials for 3-8 minutes, then adding cellulose ether and latex powder and continuing to mix for 2-5 minutes, and finally adding sodium citrate and a composite antibacterial agent and continuing to mix for 8-12 minutes to obtain a waterproof and mildew-proof gypsum putty powder.

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