Mildew-proof and antibacterial water-based acrylic resin paint and preparation method thereof

Abstract

The application discloses a mildew-proof and antibacterial type water-based acrylic resin paint and a preparation method thereof, and relates to the technical field of functional paint, and comprises the following steps: step 1, a functional HNTs mildew-proof and antibacterial solution and an oil phase solution are mixed and prepared in a mass ratio of 1:3.5-4.2 to obtain a pre-emulsion, and then the pre-emulsion is subjected to mechanical stirring to obtain a Pickering emulsion; step 2, the Pickering emulsion is heated in a constant-temperature water bath, an initiator is added under the stirring condition of an inert gas atmosphere, and after stirring treatment, a reaction emulsion is obtained; and step 3, a pH regulator is added to the reaction emulsion, and the pH value is adjusted to neutral to obtain an HNTs / acrylic resin composite emulsion. The functional HNTs mildew-proof and antibacterial solution realizes effective mildew-proof and antibacterial performance, and the mold inhibition effect based on bamboo is significantly enhanced, so that the purpose of persistent protection is achieved.

Description

Technical Field

[0001] This application relates to the field of functional coatings technology, and in particular to an anti-mildew and antibacterial waterborne acrylic resin coating and its preparation method. Background Technology

[0003] To address the technical challenge of bamboo's susceptibility to mold growth, surface coating with anti-mold and antibacterial water-based coatings is currently the mainstream and effective protective method that balances environmental friendliness, practicality, and protective efficacy. Among these, water-based acrylic resins, with their advantages of good film-forming properties, strong adhesion, excellent weather resistance, low VOC content, and convenient application, have become the core film-forming matrix for bamboo protective coatings and are widely used in the field of bamboo surface protection. To overcome the deficiency of pure water-based acrylic resins lacking anti-mold and antibacterial properties, the industry commonly employs modification methods by adding anti-mold and antibacterial agents to acrylic emulsions to prepare anti-mold and antibacterial composite coatings. To improve the problems of uneven dispersion and short action period of antibacterial agents, existing technologies are gradually introducing nanomaterial carriers to modify antibacterial agents. Halloysite nanotubes (HNTs), as a natural hollow tubular nanomaterial, possess characteristics such as large specific surface area, excellent water dispersibility, strong loading and adsorption capacity, stable physicochemical properties, and being green and non-toxic. They are ideal antibacterial agent loading carriers suitable for water-based coating systems and can effectively improve the dispersion and release performance of antibacterial agents. Currently, some technologies combine halloysite nanotubes with antibacterial materials to enhance the antibacterial properties of coatings. Chinese patent CN104725956B discloses a modification scheme of chitosan-modified halloysite loaded with silver nanoparticles, which can impart good antibacterial properties to water-based varnishes. Chinese patent CN114085591B discloses a system using halloysite loaded with pentachlorophenol and barium metaborate, achieving excellent antifungal effects.

[0004] However, existing bamboo anti-mildew coatings, due to the direct addition of antibacterial agents for modification, suffer from poor compatibility, uneven dispersion, and uncontrollable release rate between the antibacterial agents and the acrylic emulsion matrix. This easily leads to problems such as short-term failure of the anti-mildew effect, decreased mechanical properties of the coating film, and cracking and peeling of the coating, which need to be improved. Summary of the Invention

[0005] In view of this, the first objective of this application is to provide a method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating, so as to solve the problems of insufficient mildew-resistant and antibacterial properties of waterborne acrylic resin coatings and the resulting mold growth on the coating. The specific solution is as follows: A method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating includes the following steps: Step 1: Mix functionalized HNTs antifungal and antibacterial solution with oil phase solution at a mass ratio of 1:3.5-4.2 to prepare a preemulsion, and then mechanically stir the preemulsion to obtain Pickering emulsion; Step 2: Heat the Pickering emulsion in a constant temperature water bath, add the initiator under stirring in an inert gas atmosphere, and obtain the reaction emulsion after stirring. Step 3: Add a pH adjuster to the reaction emulsion and adjust the pH value to neutral to obtain HNTs / acrylic resin composite emulsion.

[0006] Preferably, in step 1, the functionalized HNTs antifungal and antibacterial solution is obtained by ultrasonic mixing of deionized water and functionalized HNTs antifungal and antibacterial agent, and the concentration is controlled at 1-2 wt%.

[0007] Preferably, the ultrasonic power of the ultrasonic mixing process is 35W, and the ultrasonic time is 10-15min.

[0008] Preferably, the pre-emulsion is obtained by ultrasonic mixing for 2 seconds every 3 seconds for a total of 5 minutes.

[0009] Preferably, the mechanical stirring time is 8-10 minutes and the rotation speed is 1000 rpm.

[0010] Preferably, the preparation method of the functionalized HNTs antifungal and antibacterial agent includes mixing halloysite nanotubes with a 3 mol / L hydrochloric acid solution at a mass ratio of 1:10, heating and stirring at a controlled temperature of 63-67℃ for 9-11 hours to obtain acidified expanded-pore halloysite nanotubes, and then successively centrifuging, washing, drying and grinding to obtain acidified halloysite nanotube powder; mixing the acidified halloysite nanotube powder with a natural antifungal and antibacterial agent, controlling the mass ratio of acidified halloysite nanotube powder to natural antifungal and antibacterial agent to be 1:(8-12), and then performing post-treatment to obtain the finished functionalized HNTs antifungal and antibacterial agent.

[0011] Preferably, the natural antifungal and antibacterial agent is capsaicin, vanillin, or citral; the post-treatment includes vacuum negative pressure, centrifugation, washing, and drying, and the ultrasonic time of the vacuum negative pressure is 20-60 min, the pressure is 0.1 MPa, and the holding time is 30-120 min, and it is repeated 2-4 times.

[0012] Preferably, the washing process uses anhydrous ethanol, and the drying process is controlled at a temperature of 45°C.

[0013] Preferably, the natural antifungal and antibacterial agent is chitosan, tea polyphenols, or thymol; the acidified halloysite nanotube powder is prepared with deionized water to obtain a 0.5-2 wt% nanotube powder dispersion, and the natural antifungal and antibacterial agent is prepared with deionized water to obtain a 0.5-2 wt% antifungal and antibacterial dispersion, and then the nanotube powder dispersion and the antifungal and antibacterial dispersion are mixed and stirred evenly; the post-treatment includes electrostatic adsorption and centrifugation, washing, and drying; the electrostatic adsorption time is 30-120 min.

[0014] Preferably, the oil phase solution comprises methyl methacrylate and butyl acrylate in a mass ratio of (1-4):4, and 0.001-6% acrylic acid is added to the total mass.

[0015] Preferably, in step 2, the initiator is ammonium persulfate, which is added after being prepared by mixing with deionized water to obtain an ammonium persulfate solution with a mass concentration of 1.5-2.5%.

[0016] Preferably, the amount of the initiator is 0.5-2 wt% of the monomer mass. Confirm the ratio of the initiator to any other substance, or its mass percentage relative to any other material.

[0017] Preferably, the ammonium persulfate solution is added by first adding 30-40% ammonium persulfate solution, stirring for at least 0.5 hours, and then continuing to add the ammonium persulfate solution dropwise, controlling the dropping rate to 7-17 seconds per drop.

[0018] Preferably, the inert gas is nitrogen.

[0019] Preferably, in step 3, the pH adjuster is a sodium bicarbonate solution; the HNTs / acrylic resin composite emulsion is heat-treated at 85-90℃ for 1-1.5h.

[0020] Preferably, the concentration of the sodium bicarbonate solution is 0.2 mol / L.

[0021] The second objective of this application is to provide a mildew-resistant and antibacterial waterborne acrylic resin coating, including a mildew-resistant and antibacterial coating prepared by the method described above for use in bamboo furniture and bamboo products.

[0022] As can be seen from the above solutions, this application provides a mildew-resistant and antibacterial waterborne acrylic resin coating and its preparation method. This mildew-resistant and antibacterial waterborne acrylic resin coating and its preparation method have the following beneficial effects: 1. By applying this mildew-proof and antibacterial water-based acrylic resin coating to bamboo furniture and bamboo products, the goal of achieving green safety, environmental friendliness, long-lasting and stable antibacterial effect, and excellent overall coating performance can be achieved. 2. By mixing halloysite nanotubes with natural antifungal and antibacterial agents, functionalized HNTs antifungal and antibacterial agents are obtained, giving them the functions of stabilizers, carriers, and reinforcing fillers. This improves the hardness and adhesion of the paint film formed by its application, while achieving the purpose of long-lasting protection. 3. By employing vacuum negative pressure and electrostatic adsorption, the volatility of natural antifungal and antibacterial agents is reduced and their high-temperature resistance is improved, thereby enhancing the antifungal and antibacterial performance of natural antifungal and antibacterial agents in the application of this antifungal and antibacterial water-based acrylic resin coating. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a SEM image of halloysite nanotubes according to an embodiment of this application; Figure 2 This is a SEM image of the acidified expanded-pore halloysite nanotubes of Embodiment 1 of this application; Figure 3 This is a SEM image of the functionalized HNTs antifungal and antibacterial agent of Embodiment 1 of this application. Detailed Implementation

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

[0026] The following is a detailed description of a mildew-proof and antibacterial waterborne acrylic resin coating and its preparation method.

[0027] A method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating includes the following steps: Step 1: Mix functionalized HNTs antifungal and antibacterial solution with oil phase solution at a mass ratio of 1:3.5-4.2 to prepare a pre-emulsion, and then mechanically stir the pre-emulsion to obtain Pickering emulsion.

[0028] The functionalized HNTs antifungal and antibacterial solution was obtained by ultrasonic mixing of deionized water and functionalized HNTs antifungal and antibacterial agents. The ultrasonic power was 35W, the ultrasonic time was 10-15 min, and the concentration was controlled at 1-2 wt%. The pre-emulsion was obtained by ultrasonic mixing for 2 seconds every 3 seconds for 5 min. The mechanical stirring time was 8-10 min, and the speed was 1000 rpm.

[0029] It should be noted that the preparation method of functionalized HNTs antifungal and antibacterial agent includes mixing halloysite nanotubes with 3 mol / L hydrochloric acid solution at a mass ratio of 1:10, heating and stirring at a controlled temperature of 63-67℃ for 9-11 hours to obtain acidified expanded pore halloysite nanotubes, and then centrifuging, washing, drying and grinding to obtain acidified halloysite nanotube powder; mixing the acidified halloysite nanotube powder with a natural antifungal and antibacterial agent, controlling the mass ratio of acidified halloysite nanotube powder to natural antifungal and antibacterial agent to be 1:(8-12), and then performing post-treatment to obtain the finished functionalized HNTs antifungal and antibacterial agent.

[0030] When the natural antifungal and antibacterial agents used are capsaicin, vanillin, or citral, the post-treatment includes vacuum negative pressure, centrifugation, washing, and drying. The ultrasonic treatment under vacuum negative pressure lasts for 20-60 minutes at a pressure of 0.1 MPa and is maintained for 30-120 minutes, repeated 2-4 times. Washing is performed with anhydrous ethanol, and drying is carried out at a controlled temperature of 45°C.

[0031] When the natural antifungal and antibacterial agent used is chitosan, tea polyphenols, or thymol, acidified halloysite nanotube powder is prepared with deionized water to obtain a 0.5-2 wt% nanotube powder dispersion, and the natural antifungal and antibacterial agent is also prepared with deionized water to obtain a 0.5-2 wt% antifungal and antibacterial dispersion. The nanotube powder dispersion and the antifungal and antibacterial dispersion are then mixed and stirred evenly. Post-treatment includes electrostatic adsorption and centrifugation, washing, and drying. The electrostatic adsorption time is 30-120 min.

[0032] Meanwhile, the oil phase solution includes methyl methacrylate and butyl acrylate in a mass ratio of (1-4):4, and adds 0.001-6% acrylic acid by mass.

[0033] Step 2: Heat the Pickering emulsion in a constant temperature water bath, add the initiator under stirring in an inert gas atmosphere, and obtain the reaction emulsion after stirring.

[0034] The initiator is used at a rate of 0.5-2 wt% of the total monomer mass. The monomers include functionalized HNTs (antifungal and antibacterial agents) and an oil-phase solution. In this embodiment, ammonium persulfate is used as the initiator. The ammonium persulfate is prepared by mixing it with deionized water to obtain a 1.5-2.5% (w / w) ammonium persulfate solution before addition. The ammonium persulfate solution is added by first adding 30-40% of the solution, stirring for at least 0.5 hours, and then continuing to add the solution dropwise at a rate controlled to 7-17 seconds per drop. Nitrogen is used as the inert gas.

[0035] Step 3: Add a pH adjuster to the reaction emulsion and adjust the pH value to neutral to obtain HNTs / acrylic resin composite emulsion.

[0036] The pH adjuster is sodium bicarbonate solution. The HNTs / acrylic resin composite emulsion is treated at 85-90℃ for 1-1.5 hours. Meanwhile, the concentration of the sodium bicarbonate solution is 0.2 mol / L.

[0037] An anti-mildew and antibacterial waterborne acrylic resin coating includes an anti-mildew and antibacterial coating material prepared by the method described above and used in bamboo furniture and bamboo products.

[0038] Example 1 A method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating includes the following steps: Step 1: Mix functionalized HNTs antifungal and antibacterial solution with oil phase solution at a mass ratio of 1:4 to prepare a pre-emulsion, and then mechanically stir the pre-emulsion to obtain Pickering emulsion.

[0039] The functionalized HNTs antifungal and antibacterial solution was obtained by ultrasonic mixing of deionized water and functionalized HNTs antifungal and antibacterial agents. The ultrasonic power was 35W, the ultrasonic time was 12 minutes, and the concentration was controlled at 1.5 wt%. The pre-emulsion was obtained by ultrasonic mixing for 2 seconds every 3 seconds for 5 minutes. The mechanical stirring time was 8 minutes and the speed was 1000 rpm.

[0040] It should be noted that the preparation method of functionalized HNTs antifungal and antibacterial agent includes mixing halloysite nanotubes with a 3 mol / L hydrochloric acid solution at a mass ratio of 1:10, heating and stirring at a controlled temperature of 65℃ for 10 hours to obtain acidified expanded-pore halloysite nanotubes, and then centrifuging, washing, drying and grinding to obtain acidified halloysite nanotube powder; mixing the acidified halloysite nanotube powder with a natural antifungal and antibacterial agent, controlling the mass ratio of acidified halloysite nanotube powder to natural antifungal and antibacterial agent at 1:10, and then performing post-processing to obtain the finished functionalized HNTs antifungal and antibacterial agent.

[0041] In Example 1 of this application, capsaicin is used as the natural antifungal and antibacterial agent. Post-treatment includes vacuum negative pressure, electrostatic adsorption, centrifugation, washing, and drying. The vacuum negative pressure treatment involves ultrasonic treatment for 30 minutes, a pressure of 0.1 MPa, and a holding time of 30 minutes, repeated three times. The electrostatic adsorption time is 30 minutes. Washing is performed using anhydrous ethanol, and drying is carried out at a controlled temperature of 45°C.

[0042] Meanwhile, the oil phase solution includes methyl methacrylate and butyl acrylate in a mass ratio of 1:2, and adds 5% acrylic acid by mass.

[0043] Step 2: Heat the Pickering emulsion in a constant temperature water bath, add the initiator under stirring in an inert gas atmosphere, and obtain the reaction emulsion after stirring.

[0044] The initiator is used at 2 wt% of the total monomer mass. In this embodiment, ammonium persulfate is used as the initiator, and it is prepared by mixing ammonium persulfate with deionized water to obtain a 2% (w / w) ammonium persulfate solution before addition. The ammonium persulfate solution is added by first adding 1 / 3 of the solution, stirring at 300 rpm for 1 hour, and then continuing to add the remaining solution dropwise at a rate controlled at 10 seconds per drop. Nitrogen is used as the inert gas.

[0045] Step 3: Add 0.2 mol / L sodium bicarbonate solution to the reaction emulsion and adjust the pH to neutral. Then, keep the temperature at 90℃ for 1 hour to obtain HNTs / acrylic resin composite emulsion.

[0046] An anti-mildew and antibacterial waterborne acrylic resin coating includes an anti-mildew and antibacterial coating material prepared by the method described above and used in bamboo furniture and bamboo products.

[0047] Example 2 The difference between Example 2 and Example 1 is that the natural antifungal and antibacterial agent in Example 2 is vanillin.

[0048] Example 3 The difference between Example 3 and Example 1 is that the natural antifungal and antibacterial agent in Example 3 is citral.

[0049] Example 4 The difference between Example 4 and Example 1 is that the natural antifungal and antibacterial agent in Example 4 is chitosan. Acidified halloysite nanotube powder was mixed with deionized water to obtain a 1.5 wt% nanotube powder dispersion, and chitosan was mixed with deionized water to obtain a 1.5 wt% antifungal and antibacterial dispersion. The nanotube powder dispersion and the antifungal and antibacterial dispersion were then mixed and stirred evenly. Post-treatment included electrostatic adsorption and centrifugation, washing, and drying. The electrostatic adsorption time was 30 minutes.

[0050] Example 5 The difference between Example 5 and Example 4 is that the natural antifungal and antibacterial agent in Example 5 is tea polyphenols.

[0051] Example 6 The difference between Example 6 and Example 4 is that the natural antifungal and antibacterial agent in Example 6 is thymol.

[0052] Example 7 The difference between Example 7 and Example 1 is that the natural antifungal and antibacterial agents in Example 7 include capsaicin and chitosan. Furthermore, the functionalized HNTs antifungal and antibacterial agent from Example 1 is prepared with deionized water to obtain a 1.5 wt% functionalized nanotube powder dispersion. Chitosan is also prepared with deionized water to obtain a 1.5 wt% antifungal and antibacterial dispersion. The functionalized nanotube powder dispersion and the antifungal and antibacterial dispersion are then mixed and stirred evenly. Post-treatment includes electrostatic adsorption and centrifugation, washing, and drying. The electrostatic adsorption time is 30 minutes.

[0053] Example 8 The difference between Example 8 and Example 2 is that the natural antifungal and antibacterial agents in Example 8 include capsaicin and tea polyphenols. Furthermore, the functionalized HNTs antifungal and antibacterial agent from Example 1 was prepared with deionized water to obtain a 1.5 wt% functionalized nanotube powder dispersion. Chitosan was also prepared with deionized water to obtain a 1.5 wt% antifungal and antibacterial dispersion. The functionalized nanotube powder dispersion and the antifungal and antibacterial dispersion were then mixed and stirred until homogeneous. Post-treatment included electrostatic adsorption and centrifugation, washing, and drying. The electrostatic adsorption time was 30 minutes.

[0054] Example 9 The difference between Example 9 and Example 3 is that the natural antifungal and antibacterial agents in Example 9 include capsaicin and thymol, and the functionalized HNTs antifungal and antibacterial agent from Example 1 is prepared with deionized water to obtain a 1.5 wt% functionalized nanotube powder dispersion. Chitosan is also prepared with deionized water to obtain a 1.5 wt% antifungal and antibacterial dispersion. The functionalized nanotube powder dispersion and the antifungal and antibacterial dispersion are then mixed and stirred evenly. Post-treatment includes electrostatic adsorption and centrifugation, washing, and drying. The electrostatic adsorption time is 30 minutes.

[0055] Performance testing: 1. Use scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe the morphological characteristics of the samples.

[0056] 2. The pore structure and loading of the antifungal and antibacterial agent were investigated by specific surface area analysis.

[0057] 3. Following GB / T 18261-2013 "Experimental Methods for the Control Efficacy of Antifungal Agents against Wood Molds and Discoloration Fungi", *Aspergillus niger*, *Penicillium citrinum*, *Escherichia coli*, and *Staphylococcus aureus* were used as test strains. Uncoated bamboo strips and bamboo strips coated with ordinary water-based acrylic resin paint were used as blank controls. Mold samples were incubated in an incubator at (28±1)℃ and (85±5)% relative humidity for 28 days, while bacterial samples were incubated in an incubator at (37±1)℃ for 24 hours. The infection level of the bamboo surface was observed and recorded regularly.

[0058] 4. Inject the HNTs composite emulsion into a polytetrafluoroethylene mold and dry it in an oven at 60℃ to form a film. Following the dip-coating method of GB / T1727-2021, immerse the sanded and cleaned bamboo strips in the emulsion, remove and cure for 12 hours, then humidify and cure for 24 hours according to the conditions of GB / T 9278-2008 before testing mechanical properties, film hardness, and adhesion.

[0059] 5. Perform mechanical tensile testing on the coating using a universal testing machine.

[0060] 6. Test according to GB / T 6739-2006 "Determination of Hardness of Paint Film by Pencil Method" and GB / T 9286-2021 "Cross-cut Test of Paint Film" standard. Observe the degree of peeling with a magnifying glass and rate it.

[0061] The performance test results are analyzed as follows: like Figure 1 , Figure 2 , Figure 3 As shown, in the functionalized HNTs antifungal and antibacterial solution prepared with capsaicin in Example 1, the carbon mass fraction increased from 11.3% before loading to 14.56%, indicating that capsaicin effectively entered the interior of halloysite nanotubes, rather than just adsorbing onto the outer surface. The tubular morphology of the halloysite nanotubes and the functionalized HNTs antifungal and antibacterial agent did not change significantly, proving that the capsaicin loading process did not damage the structure of the halloysite nanotubes as a carrier, and the dispersion and structural integrity of the acidified and expanded-pore halloysite nanotubes remained good. At the same amount of capsaicin, the capsaicin loading capacity of the acidified and expanded-pore halloysite nanotubes was 9.8% higher than that of the unacidified halloysite nanotubes. This was attributed to the directional etching effect of the acidification treatment on the inner wall of the halloysite nanotubes. Nitrogen adsorption-desorption and pore size distribution data confirmed that after etching, more surface defects and pores formed on the tube wall, increasing the inner diameter and effective volume of the tube, providing more loading sites and storage space for capsaicin molecules.

[0062] When the ratio of capsaicin to acid-treated halloysite nanotubes increased from 1:6 to 1:8, the loading increased from 10.34% to a maximum of 14.68%. Further increasing the ratio to 1:12, the loading stabilized at 13.09% and did not increase further. This phenomenon indicates that at a fixed concentration of 3 mol / L hydrochloric acid, the pore-expanding effect of acid etching is limited, and the effective volume inside the tube cavity is fully utilized, reaching loading saturation. If the hydrochloric acid concentration is further increased, excessive acid etching will destroy the layered crystal structure of the halloysite nanotubes, and may even cause tube wall rupture or cavity collapse, leading to the removal of the loaded capsaicin during the washing process, and the loading will actually decrease. Therefore, acid etching with 3 mol / L hydrochloric acid at a ratio of 1:8 ensures that the natural antifungal and antibacterial agent, acting as a carrier, achieves efficient loading while maintaining structural stability.

[0063] Under constant temperature conditions, the rate of mass loss of free capsaicin gradually increased with prolonged storage time, reaching a retention rate of only 8.6% after 72 hours. This indicates that Brownian motion of small molecules intensifies under high temperature, increasing the kinetic energy gained by capsaicin molecules and causing them to dissipate into the external environment. In contrast, functionalized HNTs (hydroquinone-based antifungal and antimicrobial agents) possess the ability to inhibit capsaicin's natural antifungal and antimicrobial activity. Protected by the physical barrier of the halloysite tube wall and the spatial confinement effect, the volatilization rate is significantly reduced, and the retention rate reaches 92.34% after 72 h, a substantial improvement compared to the free state. This demonstrates that acidified halloysite nanotube powder exhibits excellent sustained-release protective properties for capsaicin, effectively delaying its release rate and significantly improving its insufficient persistence due to its small molecular weight and high volatility. This provides technical support for long-lasting antifungal and antibacterial effects in coating systems.

[0064] It is worth mentioning that functionalized HNTs antifungal and antibacterial agents were incorporated into water-based acrylic resin coatings at addition levels of 0.5%, 1.0%, 1.5%, and 2.0%, respectively, and applied to bamboo surfaces using a dip-coating method. Coating performance tests showed that the functionalized HNTs antifungal and antibacterial agents improved the hardness of the coating film; the nanoparticles, by restricting the freedom of the polymer molecular chains, enabled the coating film to achieve a hardness of 2-3H. However, compared to the composite emulsion of halloysite nanotubes without capsaicin, the HNTs / acrylic resin composite emulsion with added functionalized HNTs antifungal and antibacterial agents exhibited significantly improved stability, as evidenced by an increase in emulsion gelation rate from 14.5% to 18.6%, a solid content of approximately 22%, and an improvement in coating film peeling level from level 2 to level 1, demonstrating a significant improvement in adhesion to bamboo.

[0065] Bamboo strips coated with ordinary water-based acrylic resin were used as a blank control for comparative testing of their anti-mildew and antibacterial properties.

[0066] After four weeks of constant temperature and humidity incubation, the bamboo strips in the blank control group were extensively covered with Aspergillus niger and Penicillium citrinum colonies, with dense mycelial growth and an infection value of 4.0, rendering them completely unusable. In contrast, the bamboo strips treated with the HNTs / acrylic resin composite emulsion from Example 1 showed a significant reduction in the number of colonies and the coverage area, with an infection level significantly lower than that of the control group.

[0067] Among them, the 1.5% addition treatment group showed control efficiencies of 51.33% and 66.57% against Aspergillus niger and Penicillium citrinum, respectively, indicating that the functionalized HNTs antifungal and antibacterial agents in the functionalized HNTs antifungal and antibacterial solution have a definite inhibitory effect on common mold-causing fungi in bamboo. As the addition amount increased from 0.5% to 2%, the infection value of bamboo chips gradually decreased, and the control efficacy increased accordingly, showing a clear dose-dependent effect.

[0068] The functionalized HNTs antifungal and antibacterial agent achieved 100% antibacterial rates against both *Escherichia coli* and *Staphylococcus aureus*, with no significant increase in colonies observed during the 7-day observation period, maintaining a constant antibacterial rate, confirming its universal and long-lasting antibacterial properties. Even at a low addition level of 0.5% (w / v), the antibacterial rate against *Escherichia coli* and *Staphylococcus aureus* remained at 100%, and the antibacterial rate against *Penicillium citrinum* reached 79.2%, indicating that even a low addition level has a strong inhibitory effect on molds and bacteria. The antibacterial mechanism lies in the amphiphilic nature of capsaicin molecules, which allows them to insert into the phospholipid bilayer of microbial cell membranes, disrupting membrane integrity and fluidity. This leads to a decrease in membrane potential and ATP depletion, ultimately causing the cell membrane to lose its barrier function and triggering the leakage of intracellular macromolecules (such as DNA, RNA, and proteins), resulting in microbial death. Furthermore, capsaicin also exerts its antibacterial effect synergistically through pathways such as inhibiting ergosterol synthesis or inducing reactive oxygen species production.

[0069] In summary, this application provides a mildew-resistant and antibacterial waterborne acrylic resin coating and its preparation method. This mildew-resistant and antibacterial waterborne acrylic resin coating can be used in bamboo furniture and bamboo products to achieve the goals of being green and safe, environmentally friendly, providing long-lasting and stable antibacterial effects, and exhibiting excellent overall coating performance. The preparation method of this mildew-resistant and antibacterial waterborne acrylic resin coating involves modifying halloysite nanotubes with natural mildew-resistant and antibacterial agents to obtain functionalized HNTs mildew-resistant and antibacterial agents, giving them the functions of stabilizers, carriers, and reinforcing fillers. This improves the hardness and adhesion of the resulting paint film while achieving long-lasting protection. Simultaneously, by employing vacuum negative pressure and electrostatic adsorption, the volatility of the natural mildew-resistant and antibacterial agents is reduced and their high-temperature resistance is improved, thereby enhancing the mildew-resistant and antibacterial performance of the natural mildew-resistant and antibacterial agents in the application of this mildew-resistant and antibacterial waterborne acrylic resin coating.

[0070] The terms “first,” “second,” “third,” “fourth,” etc., used in this application (if applicable) are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, or apparatus that includes a series of steps or units is not necessarily limited to those explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, or apparatus.

[0071] It should be noted that the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of those features. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0072] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating, characterized in that, Includes the following steps: Step 1: Mix the functionalized HNTs antifungal and antibacterial solution with the oil phase solution at a mass ratio of 1:3.5-4.2 to prepare a pre-emulsion, and then mechanically stir the pre-emulsion to obtain a Pickering emulsion; Step 2: Heat the Pickering emulsion in a constant temperature water bath, add the initiator under stirring in an inert gas atmosphere, and obtain the reaction emulsion after stirring. Step 3: Add a pH adjuster to the reaction emulsion and adjust the pH value to neutral to obtain HNTs / acrylic resin composite emulsion.

2. The method for preparing an anti-mildew and antibacterial waterborne acrylic resin coating according to claim 1, characterized in that: In step 1, the functionalized HNTs antifungal and antibacterial solution is obtained by ultrasonic mixing of deionized water and functionalized HNTs antifungal and antibacterial agent, and the concentration is controlled at 1-2 wt%.

3. The method for preparing an anti-mildew and antibacterial waterborne acrylic resin coating according to claim 2, characterized in that: The preparation method of the functionalized HNTs antifungal and antibacterial agent includes mixing halloysite nanotubes with a 3 mol / L hydrochloric acid solution at a mass ratio of 1:10, heating and stirring at a controlled temperature of 63-67℃ for 9-11 hours to obtain acidified expanded-pore halloysite nanotubes, and then centrifuging, washing, drying and grinding to obtain acidified halloysite nanotube powder; mixing the acidified halloysite nanotube powder with a natural antifungal and antibacterial agent, controlling the mass ratio of acidified halloysite nanotube powder to natural antifungal and antibacterial agent to be 1:(8-12), and then performing post-treatment to obtain the finished functionalized HNTs antifungal and antibacterial agent.

4. The method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating according to claim 4, characterized in that: The natural antifungal and antibacterial agent is capsaicin, vanillin, or citral; the post-treatment includes vacuum negative pressure, centrifugation, washing, and drying, and the ultrasonic time of the vacuum negative pressure is 20-60 min, the pressure is 0.1 MPa, and the holding time is 30-120 min, and it is repeated 2-4 times.

5. The method for preparing an anti-mildew and antibacterial waterborne acrylic resin coating according to claim 3, characterized in that: The natural antifungal and antibacterial agent is chitosan, tea polyphenols, or thymol; the acidified halloysite nanotube powder is prepared with deionized water to obtain a 0.5-2 wt% nanotube powder dispersion, and the natural antifungal and antibacterial agent is prepared with deionized water to obtain a 0.5-2 wt% antifungal and antibacterial dispersion, and then the nanotube powder dispersion and the antifungal and antibacterial dispersion are mixed and stirred evenly; the post-treatment includes electrostatic adsorption and centrifugation, washing, and drying; the electrostatic adsorption time is 30-120 min.

6. The method for preparing an anti-mildew and antibacterial waterborne acrylic resin coating according to claim 1, characterized in that: The oil phase solution comprises methyl methacrylate and butyl acrylate in a mass ratio of (1-4):4, and adds 0.001-6% acrylic acid by mass.

7. The method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating according to claim 6, characterized in that: In step 2, the initiator is ammonium persulfate, which is added after being prepared by mixing with deionized water to obtain an ammonium persulfate solution with a mass concentration of 1.5-2.5%.

8. The method for preparing a mildew-resistant and antibacterial waterborne acrylic resin coating according to claim 7, characterized in that: The ammonium persulfate solution is added by first adding 30-40% ammonium persulfate solution, stirring for at least 0.5 hours, and then continuing to add the ammonium persulfate solution dropwise, controlling the dropping rate to 7-17 seconds per drop.

9. The method for preparing an anti-mildew and antibacterial waterborne acrylic resin coating according to claim 1, characterized in that: In step 3, the pH adjuster is a 0.2 mol / L sodium bicarbonate solution; the HNTs / acrylic resin composite emulsion is treated at 85-90℃ for 1-1.5 h.

10. A mildew-proof and antibacterial water-based acrylic resin coating, characterized in that: This includes anti-mildew and antibacterial coatings prepared using the method described in any one of claims 1-7 for use in bamboo furniture and bamboo products.

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