Coral cellulose / photo-thermal material composite antifouling coating and gradient curing method thereof

Abstract

The invention relates to a coral cellulose / photo-thermal material composite antifouling coating and a gradient curing method thereof, and aims to solve the problems of environmental pollution, short antifouling period, lack of environmental response capability and the like in the traditional ship antifouling technology. Through the composite design of the coral cellulose and the photo-thermal material and in combination with a layered curing process, long-acting antifouling and mechanical property strengthening of the coating in a marine environment are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of marine engineering materials, and particularly to a coral cellulose / photothermal material composite antifouling coating and its gradient curing method, which are applicable to preventing biological attachment and fouling in marine scenarios such as ships, offshore platforms, and underwater facilities. Background Art

[0002] As the core means for the long-term protection of marine engineering equipment, the development of ship antifouling coating technology has always sought a balance between ecological safety and engineering efficiency. Since organotin compounds (TBT) were widely used in the 1970s, antifouling technology has evolved from highly toxic chemicals to low-toxic and solid-state directions. However, the existing system still faces three contradictions. First, although inorganic / organic antifouling agents represented by cuprous oxide (Cu2O) and zineb can inhibit the attachment of barnacles, algae, and bacteria through ion release, their continuous leaching leads to the enrichment of heavy metals in the ocean and ecological toxicity. According to a study in "Nature Sustainability" in 2024, about 1,200 tons of antifouling active ingredients enter the ocean globally every year, and the copper ion concentration exceeds the standard by 40 times in port waters, directly causing damage to the photosynthetic system and bleaching of marine organisms. The "Anti-fouling Systems Convention" revised by the International Maritime Organization (IMO) in 2023 further reduced the copper ion release rate threshold from 9 μg / cm 2 ·day to 4.5 μg / cm 2 ·day, and the industry urgently needs to develop non-metallic-based antifouling systems. Second, the contradiction between energy consumption and efficiency of the coating curing process is prominent: traditional thermal curing requires a high-temperature environment of 120 - 180°C, resulting in the risk of substrate thermal deformation (thermal expansion coefficient > 60×10 -6 / °C) and energy waste (2.5 - 4.0 kWh / m 2 ); although ultraviolet light (UV) curing can achieve room-temperature operation, the penetration depth limitation of photoinitiators (such as benzophenone derivatives) results in gradient defects of "surface over-curing - internal under-crosslinking" in thick coatings (> 150 μm) (crosslinking density difference > 30%), which in turn induces stress cracking and interfacial peeling (defect rate > 18%). Third, the controlled release mechanism of active substances in solid coatings has not been broken through. Carrier systems represented by polyurethane microcapsules and mesoporous silica (MSN) cause premature release of antifouling agents (30-day release rate > 70%) due to mechanical wear (Taber wear test mass loss rate > 3%) and seawater penetration (contact angle < 90°), and cannot meet the 5-year service cycle requirement specified by IMO.

[0003] In this context, the cross - integration of bio - based materials and photothermal response technology provides a new path for green antifouling coatings. Cellulose extracted from soft corals (Alcyonacea) (Coral - derived Cellulose, CDC) has become a research focus due to its unique biocompatibility and structural designability: its three - dimensional interpenetrating network structure (specific surface area > 200m 2 / g, pore size distribution 10 - 50nm) can load natural antifouling molecules such as terpenoids (e.g., gorgonic acid) and brominated furans, and achieve controlled release in seawater environment (pH 8.1 - 8.3) through the pH - responsive property of β - 1,4 - glycosidic bond (isoelectric point pI≈4.5) (the release rate is reduced by 40% compared with acidic conditions). Meanwhile, the local surface plasmon resonance (LSPR) effect and near - infrared light (NIR) excitation characteristics of photothermal conversion materials such as MXene (Ti3C2T x ) and polydopamine (PDA) provide a dual driving force for coating curing and antifouling activation. Research shows that the photothermal conversion efficiency (η) of MXene nanosheets (thickness < 5nm) under 808nm laser excitation can reach 85%, and the gradient thermal field generated by it (temperature difference from surface to interior ΔT≈25℃) can accurately trigger the glass transition of the coating resin (such as epoxy acrylate) (Tg≈85℃), realizing deep and uniform curing of a 200μm - thick coating within 90 seconds (cross - link density > 95%), saving more than 70% energy compared with traditional thermal curing. More importantly, the porous network of CDC can be used as a dispersion carrier for MXene, inhibiting the aggregation of nanosheets through hydrogen bonding and π - π stacking interactions, thus maintaining a high specific surface area (> 150m 2 / g) and stable photothermal performance (η decay < 5% after 100 thermal - cycling). Such a "bio - inorganic" composite strategy not only breaks through the performance bottleneck of single materials, but also realizes the synergistic optimization of antifouling, mechanics and durability through bionic design.

[0004] However, there are still scientific challenges that need to be urgently overcome in the engineering application of bio - based materials and photothermal technology. First, the strong hydrophilicity of CDC (water contact angle < 30°) and the hydrophobic surface of MXene (contact angle > 110°) lead to poor interfacial compatibility, easy phase separation and stress concentration (tensile strength < 5MPa), and a stable multiphase structure needs to be constructed through graft modification (such as lignosulfonate grafting rate > 15%) or interfacial compatibilizer (chitosan quaternary ammonium salt addition amount 0.5 - 1.0wt%). Second, the parameter coordination mechanism of the photothermal curing process has not been clarified: near - infrared light wavelength (780 - 850nm), power density (0.8 - 1.5W / cm 2)The matching with the irradiation time (60 - 120 s) directly affects the thermal field distribution and curing kinetics. Excessive temperature rise (>100 °C) may cause thermal degradation of CDC (the initial temperature of thermal weight loss Td ≈ 220 °C) or yellowing of the resin (color difference ΔE > 3.0). In addition, the dynamic release behavior of the antifouling agent needs to form an intelligent response to the marine environment (temperature, pH, biofilm formation), and the existing research lacks a quantitative analysis of the correlation between the sustained-release kinetics (such as the Higuchi model, Korsmeyer - Peppas equation) and the real - sea environment. Solving these problems requires the construction of a cross - scale "material - structure - process" integrated model. For example, the temperature field distribution of photothermal curing can be simulated by finite element analysis (FEA), or the release rate equation of the antifouling agent can be optimized using machine learning. Summary of the Invention

[0005] The present invention provides a photothermal - synergistic antifouling coating based on coral cellulose and its gradient curing process, aiming to solve the problems existing in traditional ship antifouling technologies, such as environmental pollution, short antifouling cycle, and lack of environmental response ability. Through the composite design of coral cellulose and photothermal materials, combined with the hierarchical curing process, long - term antifouling and mechanical property enhancement of the coating in the marine environment are achieved. The coating material consists of a nano - coral cellulose matrix, an MXene / polydopamine composite photothermal material, an epoxy - modified silicone resin, and hydrophobic nano - silica, and the mass percentages of each component are 30 - 50%, 10 - 20%, 30 - 50%, and 2 - 10% respectively. The nano - coral cellulose is prepared by acid - hydrolyzing gorgonian coral, and the particle size is controlled at 50 - 200 nm to form a porous structure; MXene and dopamine form a photothermal - responsive complex through in - situ polymerization, and their mass ratio is optimized to 1:1 - 1:3 to ensure the photothermal conversion efficiency (≥85%) and interfacial bonding strength. The epoxy - modified silicone resin serves as an adhesive to provide coating adhesion, and the hydrophobic nano - silica enhances the surface hydrophobicity, with an initial contact angle of 152°.

[0006] The preparation process of the coating includes two core steps: mixing and dispersion and gradient curing. First, the nano - coral cellulose colloid, MXene / polydopamine complex, epoxy silicone resin, and hydrophobic silica are ball - milled and dispersed to form a uniform slurry; then, it is coated on the surface of the ship steel plate using spraying technology and subjected to two - stage curing: the first stage is ultraviolet pre - curing (wavelength 365 nm, intensity 50 mW / cm 2 , time 5 - 10 minutes), forming a porous substrate structure on the surface layer, with the porosity controlled at 30 - 50%; the second stage is triggered by near - infrared light (wavelength 808 nm, power 1.5 W / cm 2, time: 3 - 5 minutes), utilize the photothermal effect of MXene to raise the internal temperature of the coating to 75 - 85 °C, induce gradient crosslinking of the resin, and form a gradient structure with a high density on the surface layer (crosslinking degree ≥ 85%) and a low density on the bottom layer (crosslinking degree 60 - 70%). This process optimizes the internal stress distribution of the coating through light control, raises the scratch hardness to above 2H, and improves the wear resistance by 40% compared with the traditional curing process.

[0007] The anti-fouling mechanism of the coating encompasses triple functions: physical barrier, photothermal synergy, and biodegradation. The porous structure of nano-coral cellulose can physically block the initial attachment of microorganisms and algal spores; the MXene / polydopamine composite generates local high temperatures (ΔT ≥ 40 °C) under light irradiation, triggering a hydrophobic-hydrophilic dynamic switch on the coating surface, and flushing the attached organisms through thermal expansion and interfacial energy changes; the slow degradation of coral cellulose releases a slightly acidic environment (pH 5.5 - 6.0), inhibiting the calcification of barnacle larvae and the secretion of extracellular polysaccharides by diatoms. Under the synergistic action of the three, the anti-fouling cycle of the coating in the actual marine environment can reach more than 24 months, and it does not rely on chemical biocides. Experiments show that after 6 months of hanging coupons in the Sanya sea area, the biological attachment area on the coating surface ≤ 5%, while that of the commercial silicone resin coating control group exceeds 60%.

[0008] The performance advantages of this invention are reflected in three aspects: environmental compatibility, long-term anti-fouling, and mechanical strength. As a renewable marine biomass material, the degradation products of coral cellulose are non-toxic to the marine ecosystem; the photothermal response mechanism only relies on solar energy drive, with zero energy consumption. After 1000 revolutions of the coating in the Taber abrasion test (CS-10 wheel, 1 kg load), the mass loss ≤ 15 mg, and the adhesion reaches the ASTM D3359 4B grade, which can withstand the fluid shear and mechanical impact during ship navigation. The accelerated aging experiment (85 °C, 95% humidity, UV irradiation for 1000 hours) shows that the coating has no cracking or peeling, and the performance attenuation rate < 10%, significantly superior to the traditional silicone coating (attenuation rate > 30%). In addition, the coating has an impact on the visible light transmittance of less than 5%, which is suitable for the surface of marine photovoltaic devices that require light transmission protection.

[0009] The application scenarios of this invention cover multiple fields such as ships, offshore platforms, and aquaculture facilities. In the ship field, the coating can be directly coated on the area below the waterline of the hull to reduce the loss of fuel efficiency caused by biological attachment (the expected fuel savings rate is 3 - 5%); in offshore platforms, its photothermal response characteristics can periodically remove the fouling organisms on the sensor surface to ensure the accuracy of data collection; when applied to aquaculture cages, the slightly acidic degradation environment of the coating can inhibit the proliferation of pathogenic bacteria and reduce the disease risk of cultured organisms. Description of the Drawings

[0010] Figure 1:(a) SEM image of gorgonian-based nanocellulose colloid; (b) SEM image of MXene (Ti3C2Tx); (c) TEM image of MXene / polydopamine composite; (d) SEM image of the synthesized coating.

[0011] Figure 2 : Comparison of bioattachment between the coating used in the actual sea panel test and the commercial coating. Detailed implementation methods

[0012] Example 1: Preparation of coral cellulose-based antifouling coating

[0013] 1. Raw material preparation:

[0014] Extraction of coral cellulose: The gorgonian was crushed to a particle size of ≤1 mm, and acid-hydrolyzed with a mixed solution of HCl (1 mol / L) and H2SO4 (2 mol / L) (volume ratio 1:2) at 60 °C for 2 hours. After centrifugation and washing until neutral, it was homogenized under high pressure 3 times to obtain nanocellulose colloid (particle size 50 - 200 nm, solid content 5 wt%).

[0015] Synthesis of MXene / polydopamine composite: MXene (Ti3C2Tx) was dispersed in Tris buffer (pH 8.5), dopamine hydrochloride was added (mass ratio 1:1), and stirred and polymerized at room temperature for 24 hours. After centrifugation and drying, a black powder was obtained.

[0016] 2. Preparation of coating slurry:

[0017] Mix the following components by mass ratio: nanocoral cellulose colloid (40 wt%), MXene / polydopamine composite (15 wt%), epoxy-terminated polydimethylsiloxane copolymer (40 wt%) (Epoxy-terminated PDMSCopolymer, manufacturer: Dow Corning, product model Sylgard 184), trimethylsilylated silica (5 wt%) (Trimethylsilylated Silica, manufacturer Evonik, Germany, product model: R972).

[0018] Add the mixed materials into the ball mill tank and ball mill at 300 rpm for 2 hours to obtain a uniformly dispersed coating slurry.

[0019] 3. Coating and curing:

[0020] Spray the slurry onto the surface of the pretreated marine steel plate (film thickness 80 - 100 μm).

[0021] UV pre-curing: Use a 365 nm UV light source (intensity 50 mW / cm2 )Irradiate for 8 minutes to form a porous substrate structure (porosity is about 40%).

[0022] Near-infrared gradient curing: Use an 808 nm near-infrared laser (power 1.5 W / cm 2 ) to irradiate for 4 minutes to raise the internal temperature of the coating to 80 °C to achieve gradient crosslinking.

[0023] Example 2: Coating performance test

[0024] 1. Anti-fouling effect:

[0025] Submarine exposure test: Conduct a 6-month exposure test in the Sanya sea area (water temperature 28 - 32 °C). The biofouling area on the surface of the experimental group coating ≤ 5% (mainly trace diatoms), while the attachment area of the commercial silicone coating (SeaForce90, a silane copolymer self-polishing antifouling paint) control group ≥ 60% (including barnacles, algae, and tube-dwelling worms).

[0026] Photothermal response test: Under simulated sunlight (1 kW / m 2 ), the surface temperature of the coating rises from 25 °C to 75 °C within 10 minutes, and the hydrophobic contact angle drops from 152° to 85°, and the dynamic anti-fouling ability fails.

[0027] 2. Microbial adhesion experiment:

[0028] Observation with a fluorescence microscope: The bacterial density on the coating surface < 1×10 4 CFU / cm 2 (the control group is 5×10 6 CFU / cm 2 ).

[0029] 3. Mechanical properties:

[0030] Adhesion: The crosshatch test (ASTM D3359) reaches grade 4B (no peeling).

[0031] Abrasion resistance: The mass loss in the Taber abrasion test (CS-10 wheel, 1 kg load, 1000 revolutions) is 14 mg, which is better than traditional coatings (the loss of commercial products is about 30 mg).

[0032] 4. Biodegradability:

[0033] Immerse the coating sample in artificial seawater (pH 8.2) for 180 days. The degradation rate of coral cellulose is about 30%, and the released organic acids lower the local pH to 5.8, inhibiting the attachment of barnacle larvae.

[0034] The degradation products are verified by EC50 (luminescent bacteria acute toxicity test), and the median effect concentration > 100 mg / L, belonging to the actual non-toxic level.

[0035] 5. Ecological impact:

[0036] In a simulated marine ecological tank (containing fish, corals, and algae), the leaching solution of the coating has no significant impact on the biological survival rate (the survival rate after 96 hours > 95%), meeting the IMO environmental protection standards.

[0037] Example 3: Comparative design and testing

[0038] Comparative example 3.1: Influence test of the coral cellulose (CDC) component

[0039] Formula adjustment: Replace CDC with an equal mass of polyvinyl alcohol (PVA).

[0040] Test results:

[0041] (1) Antifouling effect: The attachment area on the actual sea coupon reaches 35% after 3 months (mainly barnacle larvae).

[0042] (2) Photothermal response: The contact angle decreases by only 15° (120° → 105°), and there is no dynamic antifouling ability.

[0043] (3) Mechanical properties: The tensile strength drops to 3.2 MPa (the original value is 8.5 MPa), and the wear resistance decreases by 60%.

[0044] Comparative example 3.2: Influence test of the MXene / polydopamine component

[0045] Formula adjustment: Replace MXene / polydopamine with an equal mass of carbon black (CB).

[0046] Test results:

[0047] (1) Photothermal conversion efficiency: η = 35% (the original value is 85%), and the surface temperature only rises to 45°C.

[0048] (2) Curing effect: The crosslinking density gradient difference > 40%, and microcracks appear in the coating.

[0049] (3) Antifouling ability: There is no thermal response scouring effect, and the biological attachment area increases by 40% compared with the original formula.

[0050] Comparative example 3.3: Influence test of the hydrophobic nano-silica (HNS) component

[0051] Formula adjustment: Replace HNS with an equal mass of unmodified silica (NS).

[0052] Test results:

[0053] (1) Initial contact angle: 98° (the original value is 152°), and the antifouling barrier performance decreases.

[0054] (2) Seawater penetration rate: increased by 2.3 times, and the release rate of the antifouling agent reached 65% in 30 days (original value < 20%).

[0055] (3) Anti-algal performance: the attachment amount of diatoms increased by 3 times, and the surface roughness Ra increased from 0.8 μm to 2.1 μm.

[0056] Table 1 Analysis of component synergistic effects

[0057]

[0058] Coral cellulose (CDC) provides a porous structure and a biodegradable microenvironment. After its absence, the antifouling period is shortened by 66%, and the mechanical strength decreases by 62%. The MXene-PDA composite dominates the photothermal response and gradient curing. After being replaced with carbon black, the photothermal efficiency decreases by 59%, and the antifouling ability decays by 50%. Hydrophobic nano-silica (HNS) constructs a superhydrophobic barrier. Its absence leads to a 2.3-fold increase in the penetration rate and premature release of the antifouling agent.

Claims

1. A coating material, characterized in that, The coating material comprises components in the following mass percentages: Nano coral cellulose: 30%-50%; MXene / polydopamine composite: 10%-20%, wherein the mass ratio of MXene to polydopamine is 1:1-1:3; Epoxy-modified silicone resin: 30%-50%; Hydrophobic nano silica: 2%-10%.

2. The coating material according to claim 1, wherein The particle size of the nano coral cellulose is 50-200 nm.

3. The coating material according to claim 1, wherein The nano coral cellulose is prepared by acid-hydrolyzing soft coral.

4. The coating material according to claim 1, characterized in that: The coating comprises components in the following mass percentages: Nano coral cellulose: 35%-45%; Composite of MXene and polydopamine: 12%-18%; Epoxy-modified silicone resin: 35%-45%; Hydrophobic nano silica: 3%-8%.

5. A method for preparing a coating material as described in any one of claims 1-4, characterized in that, The preparation method comprises the following steps: grinding and mixing nano coral cellulose colloid, MXene / polydopamine composite, epoxy silicone resin and hydrophobic silica.

6. A gradient curing method for a coating, characterized in that, The gradient curing method comprises the following steps: coating the coating material according to any one of claims 1-4 on the surface by spraying technology, and performing two-stage curing, the first stage is ultraviolet pre-curing, and the second stage is triggered by near-infrared light.

7. A method for preventing fouling, characterized in that, The method comprises the following steps: Spraying the coating material according to any one of claims 1-4 on the surface of the substrate to form a film layer, and forming a composite structure with a porous substrate and a photothermal functional layer through the gradient curing process according to claim 6.

8. An application of the coating material according to any one of claims 1-4 for preventing fouling of a substrate.

9. The application according to claim 8, characterized in that, The substrate includes ships, offshore platforms and aquaculture facilities.

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