Self-repairing super-hydrophobic wood coating and preparation method

Abstract

The invention is suitable for the technical field of functional coating materials, and provides a self-repairing super-hydrophobic wood coating and a preparation method. Aiming at the problems that an existing self-repairing coating is harsh in repairing condition and low in efficiency, a polyurethane-polysiloxane interpenetrating network containing dynamic disulfide bonds and hindered urea bonds is adopted as a coating matrix, and hydrophobic modified nano TiO2 / SiO2 composite particles are dispersed to construct a micro-nano coarse structure. And a coating is formed on the surface of the wood through spraying and an ultraviolet light / moisture dual-curing process. The initial water contact angle of the coating is larger than 160 degrees, and the rolling angle is smaller than 3 degrees. When the hydrophobicity of the surface is reduced due to abrasion, the surface is heated for 10-30 minutes at the temperature of 70 DEG C, self-repairing can be achieved through reversible exchange of dynamic covalent bonds, the super-hydrophobicity (the contact angle gt and 155 degrees) is recovered, and repairing circulation can be carried out for more than 10 times. The self-repairing super-hydrophobic wood coating provided by the invention is efficient in preparation process, strong in coating adhesive force, rapid and mild in repairing and suitable for long-acting protection of outdoor wood structures and the like.

Description

Technical Field

[0001] This invention relates to the field of functional coating materials technology, and in particular to a self-healing superhydrophobic wood coating and its preparation method. Background Technology

[0002] Wood, as a natural and renewable material, is widely used in construction, furniture, and decoration. However, its inherent hydrophilicity and porous structure make it prone to absorbing water, swelling, and deforming, and susceptible to mold and decay fungi, severely affecting its lifespan and application range. Constructing a superhydrophobic coating on the wood surface is one effective way to solve these problems. Superhydrophobic coatings, by constructing a micro-nano-scale rough structure and introducing low surface energy substances, make it difficult for water droplets to wet and adhere, thus achieving functions such as waterproofing, stain resistance, and mold prevention.

[0003] Currently, methods for constructing superhydrophobic coatings for wood mainly include the sol-gel method, layer-by-layer self-assembly, chemical vapor deposition, and spraying. However, the micro-nano rough structures on the surface of coatings prepared by these methods are very fragile and easily damaged by mechanical forces such as friction and scratches, or by environmental factors such as ultraviolet radiation and acids / alkalis during daily use. Once damaged, the superhydrophobic properties are permanently lost. To extend the coating lifespan, researchers have introduced the concept of self-healing. Existing self-healing superhydrophobic coatings mostly rely on the following mechanisms: first, encapsulating repair agents (such as low surface energy substances), which are released upon damage to restore hydrophobicity; second, utilizing the thermal migration of long-chain molecules (such as aliphatic amines); and third, reversible bonding based on dynamic non-covalent bonds (such as hydrogen bonds and coordination bonds).

[0004] However, these existing technologies have obvious shortcomings: 1) Capsule-type repair agents have problems such as complicated preparation, limited repair capacity, and the possibility of new defects introduced by capsule rupture; 2) Repair methods that rely on molecular thermal migration often require high temperatures (>100℃) or long periods of time (several hours to tens of hours) for treatment, resulting in low repair efficiency and a possible decrease in mechanical strength after repair; 3) Coatings based on dynamic non-covalent bonds often require external stimulation for self-repair under humid conditions, have poor environmental adaptability, and have weak bond energy, resulting in poor durability after repair.

[0005] Therefore, developing a self-healing superhydrophobic wood coating that can be rapidly triggered under mild conditions, has high repair efficiency, and does not sacrifice the mechanical properties of the coating has become a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] To address the technical problems of existing self-healing superhydrophobic coatings, such as harsh repair conditions, slow repair speed, and poor durability, this invention provides a simple, rapid, and durable self-healing superhydrophobic wood coating and its preparation method. The core of this invention lies in the design of a polyurethane-polysiloxane interpenetrating network (IPN) polymer matrix based on dynamic covalent bonds (disulfide bonds and hindered urea bonds). This network combines the toughness of polyurethane with the low surface energy of polysiloxane. By uniformly dispersing hydrophobically modified nano-TiO2 / SiO2 composite particles within this network, a stable micro / nano-hierarchical rough structure is constructed. When the coating is damaged, under moderate temperature stimulation (e.g., 70°C), the dynamic disulfide bonds and hindered urea bonds in the network undergo a reversible exchange reaction, driving polymer chain rearrangement and flow, thereby "healing" the damaged micro-rough structure and surface chemical composition, restoring the superhydrophobic properties.

[0007] This invention is achieved by providing a self-healing superhydrophobic wood coating and its preparation method, comprising the following steps: S1. Substrate pretreatment: The wood substrate is cleaned, dried and sanded to increase surface roughness and reactivity. S2. Preparation of self-healing coating slurry: S2.1 Add 1-5 parts by weight of hydroxyl-terminated polydimethylsiloxane and 0.1-1 parts by weight of diamine chain extender containing dynamic disulfide bonds to 20-50 parts by weight of organic solvent, and stir and disperse evenly at 40-60℃ under inert gas protection to obtain component A. S2.2 Add 2-8 parts by weight of isocyanate prepolymer and 0.5-2 parts by weight of hindered amine catalyst to 20-50 parts by weight of organic solvent, stir evenly, and obtain component B; S2.3 Add 3-15 parts by weight of hydrophobically modified nano-TiO2 / SiO2 composite particles to component A obtained in step S2.1 or component B obtained in step S2.2, and ultrasonically disperse for 30-60 minutes to form a stable nanoparticle dispersion. S2.4 Mix component A and component B at room temperature and stir at high speed for 5-15 minutes to form a uniform sprayable slurry; S3. Coating and Curing: Spray the slurry prepared in step S2 onto the pretreated wood surface, with a wet film thickness of 50-200 μm; then apply the coating at a wavelength of 365 nm and a light intensity of 50-100 mW / cm². 2 Preliminary curing is achieved by irradiating the material under ultraviolet light for 1-5 minutes, followed by static curing for 12-24 hours in an environment with a temperature of 25-40℃ and a relative humidity of 50-80%, thus forming the self-healing superhydrophobic wood coating.

[0008] Preferably, in step S2.1, the molecular weight of the hydroxyl-terminated polydimethylsiloxane is 1000-5000 g / mol; and the diamine chain extender containing dynamic disulfide bonds is 4-aminophenyl disulfide or cystamine.

[0009] Preferably, in step S2.2, the isocyanate prepolymer is isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, or an adduct of toluene diisocyanate and a polyol, and its NCO mass content is 10-20%; the hindered amine catalyst is dibutyltin dilaurate or stannous octoate.

[0010] Preferably, in step S2.3, the preparation method of the hydrophobically modified nano-TiO2 / SiO2 composite particles is as follows: TiO2@SiO2 core-shell structured particles with a particle size of 20-50 nm are synthesized by sol-gel method, wherein the mass ratio of TiO2 core to SiO2 shell is 1:1 to 1:3; subsequently, the core-shell particles are surface grafted with a long-chain silane coupling agent, wherein the long-chain silane coupling agent is heptadecafluorodecyltrimethoxysilane or octadecyltrimethoxysilane.

[0011] Preferably, the organic solvent in step S2 is one or more mixed solvents selected from acetone, ethyl acetate, and tetrahydrofuran.

[0012] Preferably, in step S3, the nozzle diameter of the spray gun is 0.5-1.0 mm, the spraying air pressure is 0.3-0.6 MPa, and the distance between the spray gun and the substrate is 15-25 cm.

[0013] The present invention also proposes a self-healing superhydrophobic wood coating prepared by the above preparation method. The coating is composed of a dynamic polyurethane-polysiloxane interpenetrating network polymer matrix and hydrophobic modified nano-TiO2 / SiO2 composite particles uniformly dispersed therein. The coating surface has a micro-nano hierarchical rough structure.

[0014] Preferably, the coating has a thickness of 30-150 μm, an initial static water contact angle ≥160°, a roll-off angle ≤3°, and an adhesion to wood of grade 1.

[0015] Preferably, the coating can self-repair after physical wear or chemical etching causes a decrease in superhydrophobic properties. It can be heat-treated at 60-80°C for 10-60 minutes, and the static water contact angle after repair is ≥155°. The repair process can be repeated at least 10 times.

[0016] Preferably, the coating is used for surface protection of outdoor wooden structures, wooden furniture, wooden handicrafts, wooden packaging materials or building templates, giving them superhydrophobicity, self-cleaning, anti-corrosion and anti-mildew properties, and a certain degree of self-repair function for physical damage.

[0017] Compared with related technologies, the self-healing superhydrophobic wood coating and its preparation method provided by this invention have the following beneficial effects: 1. Excellent and rapid self-healing performance: Utilizing the "bond exchange" mechanism of dynamic covalent bonds, the repair process is proactive and efficient. Compared to existing technologies that require several hours of high-temperature treatment, the coating of this invention can complete the repair by heating at 70℃ for only 10-30 minutes, resulting in fast repair speed and long repair cycle life (>10 times). 2. Excellent overall mechanical properties of the coating: Based on polyurethane-polysiloxane IPN, the coating itself possesses excellent toughness, adhesion, and wear resistance. The introduction of dynamic covalent bonds endows the coating with self-healing capabilities without significantly reducing its glass transition temperature and mechanical strength, overcoming the coating softening problem caused by traditional thermal migration repair methods. 3. Green and efficient process: Utilizing a "spraying-UV / moisture dual curing" process. UV pre-curing quickly sets the coating and prevents sagging; subsequent moisture curing ensures a more complete reaction, enhancing the coating's cohesive strength. This process is simple to operate, requires no complex equipment, is suitable for continuous production, and the organic solvents are recyclable, making it environmentally friendly. 4. Functional Composite and Long-lasting Durability: Utilizing TiO2@SiO2 core-shell particles, the TiO2 core provides UV shielding, enhancing the coating's weather resistance; the SiO2 shell is easily modified for hydrophobicity and integrates with the polymer matrix. The coating exhibits a high initial hydrophobic angle (>160°), a small roll-off angle (<3°), significant self-cleaning effect, and high performance retention after repair, making it suitable for harsh outdoor environments. 5. Wide range of applications: This preparation method is highly adaptable to the shape of the substrate. It is not only suitable for wood, but with slight adjustments, it can also be applied to the superhydrophobic protection of the surface of various substrates such as metal, concrete, and textiles. Detailed Implementation

[0018] The embodiments of the present invention will now be described in further detail. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] Example 1 S1. Substrate pretreatment: Select a pine test board with dimensions of 100mm×50mm×5mm, sand it along the wood grain until the surface is smooth and burr-free, ultrasonically clean it with anhydrous ethanol for 10 minutes, and dry it in a 60℃ oven to constant weight.

[0020] S2. Preparation of coating paste: (a) Weigh 3 parts by weight of hydroxyl-terminated polydimethylsiloxane with a molecular weight of 2000 and 0.3 parts by weight of 4-aminophenyl disulfide, add them to 35 parts by weight of ethyl acetate, purge with nitrogen for protection, and stir and dissolve in a water bath at 50°C for 1 hour to obtain clear component A.

[0021] (b) Weigh 5 parts by weight of isophorone diisocyanate trimer with NCO content of 15% and 0.8 parts by weight of dibutyltin dilaurate, add them to 35 parts by weight of ethyl acetate, stir at room temperature for 30 minutes to obtain component B.

[0022] (c) Preparation of hydrophobically modified nano-TiO2 / SiO2 composite particles: TiO2@SiO2 core-shell particles (core-shell mass ratio 1:2, average particle size approximately 30 nm) were prepared by sol-gel method. 10 parts by weight of these particles were dispersed in 50 parts by weight of ethanol, and 2 parts by weight of heptadecafluorodecyltrimethoxysilane were added. The mixture was refluxed at 80°C for 6 hours, and after centrifugation, washing, and drying, a hydrophobic powder was obtained. 8 parts by weight of this hydrophobic powder were added to component A obtained in (a) and ultrasonically dispersed for 50 minutes.

[0023] (d) Mix component A containing particles with component B and stir at high speed at 2000 rpm for 10 minutes to obtain a uniform slurry.

[0024] S3. Coating and Curing: Using a spray gun (0.8mm nozzle), evenly spray the slurry onto the pre-treated wood panel, controlling the wet film thickness to approximately 100μm. Immediately place under a 365nm UV lamp (light intensity 80 mW / cm²). 2 Irradiate for 3 minutes, then transfer to a constant temperature and humidity chamber at 30℃ and 65% relative humidity for 18 hours to cure, thus obtaining a self-healing superhydrophobic coating specimen.

[0025] Performance testing: (1) Hydrophobicity: The initial water contact angle of the coating was 162.5±1.5° and the roll-off angle was 2.1±0.5°, as tested by a contact angle meter.

[0026] (2) Adhesion: According to the GB / T 9286-1998 standard, the adhesion level is 1.

[0027] (3) Self-healing performance: The coating was unidirectionally abraded 10 times with 600-grit sandpaper under a 500g load. After abrasion, the contact angle decreased to 142.3±2.1°. The abraded specimen was placed in a 70℃ oven for 20 minutes and cooled to room temperature before testing. The contact angle recovered to 158.8±1.3°. This "abrasion-heat repair" process was repeated, and the contact angle still reached 155.1±1.8° after the 10th repair.

[0028] (4) Chemical resistance: After immersing the coating in H2SO4 solution with pH=3 and NaOH solution with pH=11 for 24 hours, the contact angle remained above 159°, showing good chemical stability.

[0029] Example 2 The procedure is essentially the same as in Example 1, except that step S2(c) uses TiO2@SiO2 composite particles modified with octadecyltrimethoxysilane (core-shell mass ratio 1:1.5). In step S3, the UV irradiation time is 2 minutes, and the moisture curing conditions are 25°C, RH 75%, and time is 24 hours.

[0030] The initial water contact angle of the resulting coating was 160.8±1.2°, and the roll-off angle was 2.8±0.3°. After being abraded with sandpaper and heated at 65°C for 25 minutes, the contact angle recovered from 144.5° to 157.2°.

[0031] Comparative Example A comparative coating was prepared based on a prior art technique (e.g., the octadecylamine-based thermal migration coating mentioned in the background art). This coating initially had a contact angle of approximately 155°. After wear, it required heating at 100°C for 3 hours to restore the contact angle from approximately 140° to around 150°. Furthermore, with increasing repair cycles, the repair effect significantly decreased due to the migration and depletion of the low molecular weight repair agent; after the fifth repair, the contact angle could only recover to below 145°.

[0032] As can be seen from the comparison of the embodiments and comparative examples, the self-healing superhydrophobic wood coating provided by the present invention is significantly superior to the prior art in terms of initial hydrophobic performance, repair speed, repair temperature required, and repair cycle life, and has outstanding substantive features and significant progress.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features of the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions also fall within the scope of protection of the present invention.

Claims

1. A self-healing superhydrophobic wood coating and its preparation method, characterized in that, Includes the following steps: S1. Substrate pretreatment: The wood substrate is cleaned, dried and sanded to increase surface roughness and reactivity. S2. Preparation of self-healing coating slurry: S2.1 Add 1-5 parts by weight of hydroxyl-terminated polydimethylsiloxane and 0.1-1 parts by weight of diamine chain extender containing dynamic disulfide bonds to 20-50 parts by weight of organic solvent, and stir and disperse evenly at 40-60℃ under inert gas protection to obtain component A. S2.2 Add 2-8 parts by weight of isocyanate prepolymer and 0.5-2 parts by weight of hindered amine catalyst to 20-50 parts by weight of organic solvent, stir evenly, and obtain component B; S2.3 Add 3-15 parts by weight of hydrophobically modified nano-TiO2 / SiO2 composite particles to component A obtained in step S2.1 or component B obtained in step S2.2, and ultrasonically disperse for 30-60 minutes to form a stable nanoparticle dispersion. S2.4 Mix component A and component B at room temperature and stir at high speed for 5-15 minutes to form a uniform sprayable slurry; S3. Coating and curing: Spray the slurry prepared in step S2 onto the pretreated wood surface, with a wet film thickness of 50-200μm. Subsequently, light was applied at a wavelength of 365 nm and a light intensity of 50-100 mW / cm². 2 Preliminary curing is achieved by irradiating the material under ultraviolet light for 1-5 minutes, followed by static curing for 12-24 hours in an environment with a temperature of 25-40℃ and a relative humidity of 50-80%, thus forming the self-healing superhydrophobic wood coating.

2. The self-healing superhydrophobic wood coating and its preparation method according to claim 1, characterized in that, In step S2.1, the molecular weight of the terminal hydroxyl polydimethylsiloxane is 1000-5000 g / mol; the diamine chain extender containing dynamic disulfide bonds is 4-aminophenyl disulfide or cystamine.

3. The self-healing superhydrophobic wood coating and its preparation method according to claim 1, characterized in that, In step S2.2, the isocyanate prepolymer is isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, or an adduct of toluene diisocyanate and a polyol, and its NCO mass content is 10-20%; the hindered amine catalyst is dibutyltin dilaurate or stannous octoate.

4. The self-healing superhydrophobic wood coating and its preparation method according to claim 1, characterized in that, In step S2.3, the preparation method of the hydrophobically modified nano-TiO2 / SiO2 composite particles is as follows: TiO2@SiO2 core-shell structured particles with a particle size of 20-50 nm are synthesized by sol-gel method, wherein the mass ratio of TiO2 core to SiO2 shell is 1:1 to 1:3; then, the core-shell particles are surface grafted with a long-chain silane coupling agent, wherein the long-chain silane coupling agent is heptadecafluorodecyltrimethoxysilane or octadecyltrimethoxysilane.

5. The self-healing superhydrophobic wood coating and its preparation method according to claim 1, characterized in that, The organic solvent in step S2 is one or more mixed solvents selected from acetone, ethyl acetate, and tetrahydrofuran.

6. The self-healing superhydrophobic wood coating and its preparation method according to claim 1, characterized in that, In step S3, the nozzle diameter of the spray gun is 0.5-1.0 mm, the spraying air pressure is 0.3-0.6 MPa, and the distance between the spray gun and the substrate is 15-25 cm.

7. A self-healing superhydrophobic wood coating prepared by the preparation method according to any one of claims 1-6, characterized in that, The coating consists of a dynamic polyurethane-polysiloxane interpenetrating network polymer matrix and hydrophobically modified nano-TiO2 / SiO2 composite particles uniformly dispersed therein, and the coating surface has a micro-nano hierarchical rough structure.

8. The self-healing superhydrophobic wood coating according to claim 7, characterized in that, The coating has a thickness of 30-150μm, an initial static water contact angle ≥160°, a roll-off angle ≤3°, and an adhesion to wood of grade 1.

9. The self-healing superhydrophobic wood coating according to claim 7, characterized in that, After the coating is subjected to physical wear or chemical etching that causes a decrease in superhydrophobic properties, it can achieve self-repair within 10-60 minutes of heat treatment at 60-80℃. After repair, the static water contact angle is ≥155°, and the repair process can be repeated at least 10 times.

10. The self-healing superhydrophobic wood coating according to claim 7, characterized in that, The coating is used for surface protection of outdoor wooden structures, wooden furniture, wooden handicrafts, wooden packaging materials or building templates, giving them superhydrophobicity, self-cleaning, anti-corrosion and anti-mildew properties, as well as a certain degree of self-repair function for physical damage.