A polylactic acid / polydopamine / mica nanocomposite coating material, a preparation method and application thereof

Abstract

The application relates to the technical field of composite coating, and provides a polylactic acid / polydopamine / mica nano composite coating as well as a preparation method and application thereof. The polylactic acid / polydopamine / mica nano composite coating adopts polydopamine modified mica as a nano filler, can improve the interface compatibility of mica and polylactic acid, realizes stable dispersion of mica in polylactic acid, and has excellent mechanical properties, thermal stability and ultraviolet shielding performance. The polylactic acid / polydopamine / mica nano composite coating is used to prepare a coating on the surface of a substrate, can improve the surface gloss and hardness of the substrate, and has strong interface bonding force between the substrate and the coating.

Description

Technical Field

[0001] This invention relates to the field of composite coating technology, and in particular to a polylactic acid / polydopamine / mica nanocomposite coating, its preparation method, and its application. Background Technology

[0002] Polylactic acid (PLA) is considered a promising material due to its excellent safety, biocompatibility, and biodegradability. However, its widespread use is still limited by its performance limitations (such as low heat resistance and low mechanical strength) or complex and costly manufacturing processes. To further improve PLA's performance, fillers are often added, with inorganic fillers being widely used due to their high aspect ratio and abundant quantity. Compared to graphene oxide, boron nitride, and other artificially synthesized nanoscale fillers, nano-mica sheets exhibit superior mechanical strength, thermal stability, and UV shielding properties, while also offering significant cost advantages.

[0003] The interfacial adhesion between polymers and fillers is one of the most important factors affecting the mechanical and thermal properties of polymer composites. Due to the different hydrophobicities of polylactic acid (PLA) and mica, mica tends to agglomerate when added to PLA. Therefore, it is necessary to employ an effective and robust strategy to improve the polarity, roughness, and surface activity of mica, thereby enhancing the interfacial compatibility between mica and PLA.

[0004] In recent years, biomimetic modified materials inspired by mussels have attracted researchers' attention due to their environmentally friendly properties. Polydopamine (PDA), as a representative of mussel-inspired biomimetic materials, has gradually become a research hotspot due to its superior adhesion to nanomaterials, biocompatibility, and hydrophilicity. However, there are no reports in this field on improving the interfacial compatibility between mica and polylactic acid through PDA modification. Summary of the Invention

[0005] In view of this, the present invention provides a polylactic acid / polydopamine / mica nanocomposite coating, its preparation method, and its application. The present invention utilizes polydopamine to modify mica, which can significantly improve the interfacial compatibility between mica and polylactic acid. The resulting composite coating exhibits uniform dispersion of polydopamine-modified mica, and the films or coatings prepared using this composite coating demonstrate excellent performance.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A polylactic acid / polydopamine / mica nanocomposite coating comprises polylactic acid, polydopamine-modified mica, and an organic solvent; the mass of the polydopamine-modified mica is 0-25% of the mass of the polylactic acid, and is not 0; the polydopamine-modified mica comprises mica and polydopamine loaded on the mica.

[0008] Preferably, the mass of the polydopamine-modified mica is 5-25% of the mass of the polylactic acid.

[0009] This invention also provides a method for preparing the polylactic acid / polydopamine / mica nanocomposite coating described above, comprising the following steps:

[0010] Water, alkaline buffer solution, mica and dopamine were mixed first, and the resulting mixture was centrifuged to obtain polydopamine-modified mica.

[0011] Polylactic acid, organic solvent and the polydopamine-modified mica were mixed to obtain a polylactic acid / polydopamine / mica nanocomposite coating.

[0012] Preferably, the first mixing comprises: adding mica to water and ultrasonically dispersing it to obtain a mica dispersion; adding an alkaline buffer solution to the mica dispersion to adjust the pH of the system to 8-10, and then adding dopamine and stirring; the alkaline buffer solution is a Tris-HCl buffer solution; the ultrasonic dispersion power is 280-320W and the time is 10-20min; the stirring time is 23-25h; and the mass ratio of mica to dopamine is 3:4-3:5.

[0013] Preferably, the mica is pretreated before being added to water; the pretreatment method includes: ultrasonically cleaning the mica in water and then drying it.

[0014] Preferably, the second mixing comprises: mixing polylactic acid and an organic solvent to obtain a polylactic acid solution; adding the polydopamine-modified mica to the polylactic acid solution and then performing homogenization and ultrasonic dispersion in sequence.

[0015] Preferably, the organic solvent is one or both of dichloromethane and trichloromethane; the ratio of polylactic acid to organic solvent is 1-2 g: 20-40 mL; the homogenization speed is 8000-10000 rpm and the time is 10-15 min; the ultrasonic dispersion power is 280-320 W and the time is 15-20 min.

[0016] The present invention also provides a polylactic acid / polydopamine / mica nanocomposite material, comprising polylactic acid and polydopamine-modified mica dispersed in the polylactic acid; the polylactic acid / polydopamine / mica nanocomposite film is obtained by drying the polylactic acid / polydopamine / mica nanocomposite coating prepared by the above-described method or the polylactic acid / polydopamine / mica nanocomposite coating prepared by the above-described method.

[0017] The present invention also provides a coating composite comprising a substrate and a polylactic acid / polydopamine / mica nanocomposite coating disposed on the surface of the substrate; the polylactic acid / polydopamine / mica nanocomposite coating comprising polylactic acid and polydopamine-modified mica dispersed in the polylactic acid; the polylactic acid / polydopamine / mica nanocomposite coating is obtained by coating the substrate surface with the polylactic acid / polydopamine / mica nanocomposite coating described in the above-described scheme or the polylactic acid / polydopamine / mica nanocomposite coating prepared by the preparation method described in the above-described scheme and then drying it.

[0018] Preferably, the substrate is wood.

[0019] This invention provides a polylactic acid / polydopamine / mica nanocomposite coating, comprising polylactic acid, polydopamine-modified mica, and an organic solvent; the mass of the polydopamine-modified mica is 0-25% of the mass of the polylactic acid, and not zero; the polydopamine-modified mica comprises mica and polydopamine loaded on the mica. This invention uses polydopamine-modified mica (PDA@MICA) as an effective nanofiller, which can improve the interfacial compatibility between mica and polylactic acid, and achieve stable dispersion of mica in polylactic acid; the film or coating prepared using the coating of this invention has excellent mechanical properties, thermal stability, and ultraviolet shielding performance.

[0020] Furthermore, PDA is a polymeric macromolecular system formed by the continuous oxidation of dopamine between catechol groups and amino groups under moderate reaction conditions through hydrogen bonding, π-π interactions, hydrophobic interactions, and electrostatic interactions. The rich cross-linking network provided by non-covalent interactions helps improve the mechanical properties of coatings and their adhesion to various substrates. Moreover, the catechol groups, amino groups, and imide groups exposed on the PDA surface can also serve as reaction platforms, enabling it to be coated onto the surfaces of substrates such as wood.

[0021] This invention also provides a method for preparing the polylactic acid / polydopamine / mica nanocomposite coating described above. This invention prepares the polylactic acid / polydopamine / mica nanocomposite coating through solution blending and self-assembly. The process is very simple, highly operable, environmentally friendly, and low in cost, and has broad prospects for practical application.

[0022] This invention also provides a polylactic acid / polydopamine / mica nanocomposite material, obtained by drying the polylactic acid / polydopamine / mica nanocomposite coating described in the above scheme. This invention introduces one of the most effective biomimetic models, the "brick-and-sand structure," to improve the mechanical properties of the composite material. In the composite material provided by this invention, PDA@MICA can be uniformly dispersed in the polylactic acid matrix, and the resulting composite film has a unique interlayer network structure, significantly improving its mechanical strength. Furthermore, PDA@MICA improves the morphology, thermal stability, and ultraviolet absorption properties of polylactic acid. The resulting composite material overcomes the inherent shortcomings of polylactic acid, such as low thermal stability and low mechanical strength, promoting its widespread development in the field of nanocomposite materials industry.

[0023] This invention also provides a coating composite comprising a substrate and a polylactic acid / polydopamine / mica nanocomposite coating disposed on the surface of the substrate. The coating composite prepared on the surface of the substrate using the polylactic acid / polydopamine / mica nanocomposite coating of this invention exhibits high surface gloss, high hardness, and strong interfacial adhesion between the substrate and the coating. Attached Figure Description

[0024] Figure 1 Mechanical curves of PLA / PDA@MICA composite films with different PDA@MICA mass fractions;

[0025] Figure 2 Thermal stability of PLA / PDA@MICA composite films with different PDA@MICA mass fractions;

[0026] Figure 3 The UV shielding performance of PLA / PDA@MICA composite films with different PDA@MICA mass fractions;

[0027] Figure 4 The results show the UV shielding performance of the composite film obtained in Comparative Example 2.

[0028] Figure 5 The results of pencil hardness tests on wood with different surface coatings;

[0029] Figure 6 The results of surface gloss tests on wood with different coatings are shown.

[0030] Figure 7 The results of adhesion tests between different coatings and wood;

[0031] Figure 8 The results show the adhesion strength test results between different coatings and wood. Detailed Implementation

[0032] This invention provides a polylactic acid / polydopamine / mica nanocomposite coating, comprising polylactic acid, polydopamine-modified mica, and an organic solvent; the mass of the polydopamine-modified mica is 0-25% of the mass of the polylactic acid, and is not 0; the polydopamine-modified mica comprises mica and polydopamine loaded on the mica.

[0033] The polylactic acid / polydopamine / mica nanocomposite coating provided by the present invention includes polylactic acid; the present invention does not have special requirements for the polylactic acid, and any polylactic acid well known to those skilled in the art can be used.

[0034] The polylactic acid / polydopamine / mica nanocomposite coating provided by the present invention includes polydopamine-modified mica; in the present invention, the polydopamine-modified mica includes mica and polydopamine loaded on the mica; the mass of the polydopamine-modified mica is preferably 5-25% of the mass of the polylactic acid, more preferably 5-20%.

[0035] In this invention, the organic solvent is preferably one or both of dichloromethane and trichloromethane, more preferably dichloromethane; the mass-to-volume ratio of polylactic acid to organic solvent is preferably 1-2 g: 20-40 mL.

[0036] This invention also provides a method for preparing the polylactic acid / polydopamine / mica nanocomposite coating described above, comprising the following steps:

[0037] Water, alkaline buffer solution, mica and dopamine were mixed first, and the resulting mixture was centrifuged to obtain polydopamine-modified mica.

[0038] Polylactic acid, organic solvent and the polydopamine-modified mica were mixed to obtain a polylactic acid / polydopamine / mica nanocomposite coating.

[0039] This invention involves first mixing water, an alkaline buffer solution, mica, and dopamine, then centrifuging the resulting mixture to obtain polydopamine-modified mica. In this invention, the preferred mass ratio of mica to dopamine is 3:4 to 3:5; the preferred mica is mica nanosheets, and the preferred mesh size of the mica nanosheets is 200 to 400 mesh.

[0040] In this invention, the first mixing preferably includes: adding mica to water and ultrasonically dispersing it to obtain a mica dispersion; adding an alkaline buffer solution to the mica dispersion to adjust the pH of the system to 8-10, preferably 8.5, and then adding dopamine and stirring. The water is preferably deionized water; the volume ratio of the deionized water to the mass of dopamine is preferably 475:1-500:1; this invention utilizes an alkaline buffer solution to adjust the pH of the system, providing weakly alkaline conditions for the self-polymerization of dopamine; the ultrasonic dispersion power is preferably 280-320W, more preferably 300W, and the time is preferably 10-20 min, more preferably 15 min; the stirring and mixing time is preferably 23-25 ​​h, more preferably 24 h; during the stirring and mixing process, dopamine undergoes self-polymerization and adheres to the mica surface. In a specific embodiment of this invention, the color of the solution changes from colorless to dark brown during the stirring and mixing process.

[0041] In this invention, the mica is preferably pretreated before being added to water; the pretreatment method includes: ultrasonically cleaning the mica in water and then drying it; the ultrasonic cleaning power is preferably 280-300W, more preferably 300W, and the ultrasonic cleaning time is preferably 10-20min, more preferably 15min; this invention does not have special requirements for the drying conditions, as long as the water is completely removed; this invention can improve the dispersibility of mica through pretreatment.

[0042] After the first mixing is completed, the present invention centrifuges the resulting mixture to obtain a solid sample; the solid sample is dark brown; after centrifugation, the present invention preferably washes and dries the obtained solid sample to obtain the polydopamine modified mica (PDA@MICA); the detergent for washing is preferably ethanol.

[0043] After obtaining polydopamine-modified mica, the present invention mixes polylactic acid, an organic solvent, and the polydopamine-modified mica to obtain a polylactic acid / polydopamine / mica nanocomposite coating. In this invention, the organic solvent is preferably one or both of dichloromethane and trichloromethane, more preferably dichloromethane; the preferred ratio of polylactic acid to organic solvent is 1–2 g: 20–40 mL; the mass of the polydopamine-modified mica is 0–25% of the mass of the polylactic acid, but not 0, preferably 5–25%, more preferably 5–20%, and even more preferably 10–15%.

[0044] In this invention, the second mixing preferably includes: mixing polylactic acid and an organic solvent to obtain a polylactic acid solution; adding the polydopamine-modified mica to the polylactic acid solution and then performing homogenization and ultrasonic dispersion sequentially; the homogenization speed is preferably 8000-10000 rpm, more preferably 10000 rpm, and the homogenization time is preferably 10-15 min; the ultrasonic dispersion power is preferably 280-320 W, more preferably 300 W, and the time is preferably 15-20 min.

[0045] This invention also provides a polylactic acid / polydopamine / mica nanocomposite material, comprising polylactic acid and polydopamine-modified mica dispersed in the polylactic acid; the polylactic acid / polydopamine / mica nanocomposite material is obtained by drying a polylactic acid / polydopamine / mica nanocomposite coating; the polylactic acid / polydopamine / mica nanocomposite coating is the polylactic acid / polydopamine / mica nanocomposite coating described in the above scheme or the polylactic acid / polydopamine / mica nanocomposite coating prepared by the preparation method described in the above scheme. In this invention, the drying is preferably natural air drying, and the natural air drying temperature is preferably room temperature; in this invention, the polylactic acid / polydopamine / mica nanocomposite material is preferably in the form of a film; in this invention, the polylactic acid / polydopamine / mica nanocomposite coating is preferably poured into a flat mold, air dried, and then demolded to obtain a polylactic acid / polydopamine / mica nanocomposite film; the thickness of the polylactic acid / polydopamine / mica nanocomposite film is preferably 100-120 micrometers, more preferably 100 micrometers; the polylactic acid / polydopamine / mica nanocomposite film can be applied in packaging, industrial production, and other fields.

[0046] This invention also provides a coating composite comprising a substrate and a polylactic acid / polydopamine / mica nanocomposite coating disposed on the surface of the substrate; the polylactic acid / polydopamine / mica nanocomposite coating comprises polylactic acid and polydopamine-modified mica dispersed in the polylactic acid; the polylactic acid / polydopamine / mica nanocomposite coating is obtained by coating the substrate surface with the polylactic acid / polydopamine / mica nanocomposite coating described in the above-described scheme or the polylactic acid / polydopamine / mica nanocomposite coating prepared by the preparation method described in the above-described scheme, followed by drying; this invention does not have special requirements for the coating method, as long as it can uniformly coat the substrate surface; The drying process is preferably natural air drying, and the natural air drying temperature is preferably room temperature; the thickness of the polylactic acid / polydopamine / mica nanocomposite coating is preferably 80-100 micrometers, more preferably 100 micrometers; the substrate is preferably wood; the present invention does not have any special requirements for the specific type of wood, and conventional wood in the art can be used. In a specific embodiment of the present invention, Burmese rosewood is used; the present invention coats the wood surface with a polylactic acid / polydopamine / mica nanocomposite coating, which can improve the surface gloss and hardness of the wood, and the interfacial bonding force between the coating and the wood becomes stronger as the content of polydopamine-modified mica in the coating increases.

[0047] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] Example 1

[0049] (1) First, place the mica powder in deionized water for ultrasonic cleaning. The ultrasonic cleaning power is 300W and the time is 15min. After drying, it is ready for use.

[0050] 0.6 g of pretreated mica was dispersed in 380 mL of deionized water and ultrasonically dispersed at 300 W for 15 min. Tris-HCl buffer solution was then added to adjust the pH to 8.5, providing a weakly alkaline environment for dopamine self-polymerization. Next, 0.8 g of dopamine was added, and the mixture was stirred for 24 h, during which the solution color changed from colorless to dark brown. The dark brown solid sample was obtained by centrifugation and washed several times with ethanol. After drying, PDA@MICA powder was obtained.

[0051] (2) Disperse 2g of polylactic acid in 20mL of dichloromethane, and then add PDA@MICA, the mass of which is 5% of the mass of polylactic acid. Homogenize the above slurry at 10000rpm for 10min, and then ultrasonically disperse it at 20℃ for 20min with an ultrasonic power of 300W to obtain polylactic acid / polydopamine / mica nanocomposite coating.

[0052] After coating the mold surface with polylactic acid / polydopamine / mica nanocomposite coating, it is naturally air-dried at room temperature and then demolded to obtain a polylactic acid / polydopamine / mica nanocomposite film, denoted as PLA / PDA@MICA composite film.

[0053] Example 2

[0054] (1) First, place the mica powder in deionized water for ultrasonic cleaning. The ultrasonic cleaning power is 300W and the time is 15min. After drying, it is ready for use.

[0055] 0.6 g of pretreated mica was dispersed in 380 mL of deionized water and ultrasonically dispersed at 300 W for 15 min. Tris-HCl buffer solution was then added to adjust the pH to 8.5, providing a weakly alkaline environment for dopamine self-polymerization. Next, 0.8 g of dopamine was added, and the mixture was stirred for 24 h, during which the solution color changed from colorless to dark brown. The dark brown solid sample was obtained by centrifugation and washed several times with ethanol. After drying, PDA@MICA powder was obtained.

[0056] (2) Disperse 2g of polylactic acid in 20mL of dichloromethane, and then add PDA@MICA, the mass of which is 10% of the mass of polylactic acid. Homogenize the above slurry at 10000rpm for 10min, and then ultrasonically disperse it at 20℃ for 20min with an ultrasonic power of 300W to obtain polylactic acid / polydopamine / mica nanocomposite coating.

[0057] After coating the mold surface with polylactic acid / polydopamine / mica nanocomposite coating, it is naturally air-dried at room temperature and then demolded to obtain a polylactic acid / polydopamine / mica nanocomposite film.

[0058] Example 3

[0059] (1) First, place the mica powder in deionized water for ultrasonic cleaning. The ultrasonic cleaning power is 300W and the time is 15min. After drying, it is ready for use.

[0060] 0.6 g of pretreated mica was dispersed in 380 mL of deionized water and ultrasonically dispersed at 300 W for 15 min. Tris-HCl buffer solution was then added to adjust the pH to 8.5, providing a weakly alkaline environment for dopamine self-polymerization. Next, 0.8 g of dopamine was added, and the mixture was stirred for 24 h, during which the solution color changed from colorless to dark brown. The dark brown solid sample was obtained by centrifugation and washed several times with ethanol. After drying, PDA@MICA powder was obtained.

[0061] (2) Disperse 2g of polylactic acid in 20mL of dichloromethane, and then add PDA@MICA, the mass of which is 15% of the mass of polylactic acid. Homogenize the above slurry at 10000rpm for 10min, and then ultrasonically disperse it at 20℃ for 20min with an ultrasonic power of 300W to obtain polylactic acid / polydopamine / mica nanocomposite coating.

[0062] After coating the mold surface with polylactic acid / polydopamine / mica nanocomposite coating, it is naturally air-dried at room temperature and then demolded to obtain a polylactic acid / polydopamine / mica nanocomposite film.

[0063] Example 4

[0064] (1) First, place the mica powder in deionized water for ultrasonic cleaning. The ultrasonic cleaning power is 300W and the time is 15min. After drying, it is ready for use.

[0065] 0.6 g of pretreated mica was dispersed in 380 mL of deionized water and ultrasonically dispersed at 300 W for 15 min. Tris-HCl buffer solution was then added to adjust the pH to 8.5, providing a weakly alkaline environment for dopamine self-polymerization. Next, 0.8 g of dopamine was added, and the mixture was stirred for 24 h, during which the solution color changed from colorless to dark brown. The dark brown solid sample was obtained by centrifugation and washed several times with ethanol. After drying, PDA@MICA powder was obtained.

[0066] (2) Disperse 2g of polylactic acid in 20mL of dichloromethane, and then add PDA@MICA, the mass of which is 20% of the mass of polylactic acid. Homogenize the above slurry at 10000rpm for 10min, and then ultrasonically disperse it at 20℃ for 20min with an ultrasonic power of 300W to obtain polylactic acid / polydopamine / mica nanocomposite coating.

[0067] After coating the mold surface with polylactic acid / polydopamine / mica nanocomposite coating, it is naturally air-dried at room temperature and then demolded to obtain a polylactic acid / polydopamine / mica nanocomposite film.

[0068] Example 5

[0069] (1) First, place the mica powder in deionized water for ultrasonic cleaning. The ultrasonic cleaning power is 300W and the time is 15min. After drying, it is ready for use.

[0070] 0.6 g of pretreated mica was dispersed in 380 mL of deionized water and ultrasonically dispersed at 300 W for 15 min. Tris-HCl buffer solution was then added to adjust the pH to 8.5, providing a weakly alkaline environment for dopamine self-polymerization. Next, 0.8 g of dopamine was added, and the mixture was stirred for 24 h, during which the solution color changed from colorless to dark brown. The dark brown solid sample was obtained by centrifugation and washed several times with ethanol. After drying, PDA@MICA powder was obtained.

[0071] (2) Disperse 2g of polylactic acid in 20mL of dichloromethane, and then add PDA@MICA, the mass of which is 25% of the mass of polylactic acid. Homogenize the above slurry at 10000rpm for 10min, and then ultrasonically disperse it at 20℃ for 20min with an ultrasonic power of 300W to obtain polylactic acid / polydopamine / mica nanocomposite coating.

[0072] After coating the mold surface with polylactic acid / polydopamine / mica nanocomposite coating, it is naturally air-dried at room temperature and then demolded to obtain a polylactic acid / polydopamine / mica nanocomposite film.

[0073] Comparative Example 1

[0074] 2g of polylactic acid was dispersed in 20mL of dichloromethane. The resulting polylactic acid slurry was coated onto the surface of a mold and then air-dried at room temperature. After demolding, a polylactic acid film was obtained.

[0075] Performance testing:

[0076] The mechanical properties, thermal stability, and UV shielding performance of the composite films prepared in Examples 1-5 and the polylactic acid film prepared in Comparative Example 1 were tested; the thickness of the composite films prepared in Examples 1-5 and the polylactic acid film prepared in Comparative Example 1 was 100 micrometers.

[0077] The mechanical properties of polylactic acid (PLA) films and PLA / PDA@MICA composite films were evaluated by tensile testing. The results are as follows: Figure 1 As shown. According to Figure 1It can be seen that, compared with pure polylactic acid (PLA), the mechanical properties of PLA / PDA@MICA composite films are significantly improved due to the two-dimensional layered structure of mica and the good interfacial compatibility between PLA and PDA@MICA. Furthermore, the tensile strength of PLA / PDA@MICA films increases with increasing PDA@MICA content. The tensile strength is highest (≈96 MPa) when the PDA@MICA content increases to 15 wt%, almost twice that of the PLA film. With further increases in PDA@MICA content, the tensile strength of the sample with 20 wt% PDA@MICA content decreases slightly. This may be due to excessive PDA@MICA content leading to poor dispersion and the formation of defects in the polymer matrix.

[0078] Figure 2 The results show the thermal stability of PLA / PDA@MICA composite films and polylactic acid films with different PDA@MICA mass fractions. Figure 2 The TGA mass loss curves of polylactic acid films and PLA / PDA@MICA composite films are shown. Figure 2 It can be seen that all films experienced a mass loss at around 305℃, mainly due to the degradation and decomposition of the polyester chains. The higher the proportion of PDA@MICA (25wt%), the better the improvement in thermal stability. This indicates that the addition of PDA@MICA improves the thermal stability of polylactic acid composites.

[0079] The UV-Vis transmittance of PLA / PDA@MICA composite films and polylactic acid films with different PDA@MICA mass fractions was measured by UV-Vis spectroscopy. The results are as follows: Figure 3 As shown. Figure 3 The results showed that the PLA / PDA@MICA composite film exhibited low transmittance in the ultraviolet band (280 nm) but high transmittance in the visible light band (555 nm), indicating that the composite film possesses good ultraviolet shielding performance and visible light transmittance. The ultraviolet shielding performance of the composite film gradually improved with increasing PDA@MICA content. For example, the transmittances at 280 nm for pure polylactic acid and PLA / PDA@MICA samples with different PDA@MICA mass fractions were 54.5%, 31.5%, 27.1%, 25.2%, 26.2%, and 23.9%, respectively. This demonstrates that the PLA / PDA@MICA composite film prepared in this invention possesses excellent ultraviolet shielding performance. Within the visible light wavelength range (400-800nm), the transmittance of pure polylactic acid film is greater than 70%. As the PDA@MICA content increases, the visible light shielding performance of the composite film gradually improves, indicating that the composite film can also shield visible light to a certain extent. The ultraviolet shielding capability of the composite film can protect the substrate from ultraviolet damage.

[0080] Comparative Example 2

[0081] 2g of polylactic acid was dispersed in 20mL of dichloromethane, and then unmodified mica that had undergone only pretreatment (the pretreatment method was the same as in Example 1) was added. The mass of the mica was 10%, 15%, and 20% of the mass of the polylactic acid. The above slurry was homogenized at 10,000 rpm for 10 min, and then ultrasonically dispersed at 20°C for 20 min with an ultrasonic power of 300W to obtain a polylactic acid / mica nanocomposite coating.

[0082] Polylactic acid / mica nanocomposite coating was applied to the mold surface and air-dried at room temperature before demolding to obtain a polylactic acid / mica nanocomposite film with a thickness of 100 micrometers. The tensile strength of the obtained polylactic acid / mica nanocomposite film was tested, and the results are shown in Table 1. The UV-Vis transmittance of the obtained film was also tested, and the results are shown in [Table 1]. Figure 4 .

[0083] Table 1. Tensile strength variation of PLA / MICA films

[0084] mica content 10％ 15％ 20％ Tensile strength (MPa) 62.25 71.37 80.61

[0085] As shown in Table 1, the tensile strength of the film is 62.25 MPa when the unmodified mica content is 10%, 71.37 MPa when the content is 15%, and 80.61 MPa when the content is 20%. Figure 1 As can be seen, when the mica modified by this invention is added to polylactic acid, the tensile strength of the film obtained is 72.72 MPa when the addition amount is 10%, 95.91 MPa when the addition amount is 15%, and 91.96 MPa when the addition amount is 20%, which is significantly higher than that of the film obtained in Comparative Example 2.

[0086] At the same time, according to Figure 4 It can be seen that the thin film prepared in Comparative Example 2 has a high transmittance in the ultraviolet band (280nm) but poor ultraviolet shielding performance.

[0087] The above results show that the present invention, by modifying mica with polydopamine, can improve the interfacial compatibility between mica and polylactic acid, thereby enabling mica to be uniformly dispersed in polylactic acid and improving its various properties.

[0088] Example 6

[0089] The polylactic acid / polydopamine / mica nanocomposite coatings prepared in Examples 1-5 and the polylactic acid slurry prepared in Comparative Example 1 were respectively coated on the surface of wood (Burmese rosewood) and then air-dried at room temperature to form a coating on the wood surface; the thickness of the coating was 100 micrometers.

[0090] According to ASTM standard D3363-20, the surface hardness of wood for each coating was determined using a QHQ-A commercial pencil hardness tester with standard pencils ranging from 2B to 5H. The results are as follows: Figure 5 As shown. According to Figure 5 It can be seen that adding PDA@MICA as a filler to polylactic acid significantly increases the hardness of the resulting coating, and the coating has the highest hardness when the PDA@MICA content is 15-25 wt%.

[0091] According to ASTM standard D523, the gloss of each coated wood surface was measured using a WGG-60 gloss meter at an incident angle of 60°. The results are as follows: Figure 6 As shown. According to Figure 6 The results show that although the gloss is lower compared to the polylactic acid coating, the gloss is significantly increased after coating with the polylactic acid / polydopamine / mica nanocomposite coating compared to the uncoated wood.

[0092] According to ASTM standard D3359-09, a cross-section tape test was performed using a QFH-A coating cross-section apparatus to determine the adhesion level of the composite coating on a wood substrate. The results are as follows: Figure 7 As shown; the adhesion strength of the composite coating was evaluated according to the pull-out test of ASTM D4541. The adhesion strength was measured until the die separated from the sample, and the maximum adhesion strength at fracture (unit: MPa) was recorded. The results are as follows. Figure 8 As shown. According to Figures 7-8 It can be seen that adding PDA@MICA as a filler to polylactic acid significantly increases the adhesion and bonding strength of the coating to wood. The coating has the highest adhesion to wood when the PDA@MICA content is 10-20 wt%, and the coating has the highest bonding strength to wood when the PDA@MICA content is 15 wt%.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of polylactic acid / polydopamine / mica nanocomposite coating on wood surface, characterized in that, The wood and a polylactic acid / polydopamine / mica nanocomposite coating disposed on the surface of the wood constitute a coating composite; the polylactic acid / polydopamine / mica nanocomposite coating includes polylactic acid and polydopamine-modified mica dispersed in polylactic acid. The polylactic acid / polydopamine / mica nanocomposite coating is obtained by coating the wood surface with polylactic acid / polydopamine / mica nanocomposite coating and then drying it. The polylactic acid / polydopamine / mica nanocomposite coating is composed of polylactic acid, polydopamine-modified mica, and organic solvent; the mass of the polydopamine-modified mica is 10-25% of the mass of the polylactic acid; the polydopamine-modified mica includes mica and polydopamine loaded on the mica; the mica is mica nanosheets. The preparation method of the polylactic acid / polydopamine / mica nanocomposite coating includes the following steps: Water, alkaline buffer solution, mica, and dopamine are mixed first, and the resulting mixture is centrifuged to obtain polydopamine-modified mica; the mass ratio of mica to dopamine is 3:4 to 3:

5. Polylactic acid, an organic solvent, and the polydopamine-modified mica are mixed to obtain a polylactic acid / polydopamine / mica nanocomposite coating; the organic solvent is one or both of dichloromethane and trichloromethane; the ratio of polylactic acid to organic solvent is 1~2g:20~40mL; The thickness of the polylactic acid / polydopamine / mica nanocomposite coating is 80~100 micrometers.

2. The application according to claim 1, characterized in that, The first mixing process includes: adding mica to water and ultrasonically dispersing it to obtain a mica dispersion; adding an alkaline buffer solution to the mica dispersion to adjust the pH of the system to 8-10, and then adding dopamine and stirring to mix; the alkaline buffer solution is a Tris-HCl buffer solution; the ultrasonic dispersion power is 280-320W and the time is 10-20min; the stirring and mixing time is 23-25h.

3. The application according to claim 2, characterized in that, The mica is pretreated before being added to the water; The pretreatment method includes ultrasonically cleaning the mica in water and then drying it.

4. The application according to claim 1, characterized in that, The second mixing process includes: mixing polylactic acid and an organic solvent to obtain a polylactic acid solution; adding the polydopamine-modified mica to the polylactic acid solution and then performing homogenization and ultrasonic dispersion in sequence.

5. The application according to claim 4, characterized in that, The homogenization rotation speed is 8000~10000 rpm, and the time is 10~15 min; the ultrasonic dispersion power is 280~320W, and the time is 15~20 min.

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