Aqueous multilayer degradable self-polishing marine antifouling coating system and method of making

Abstract

The application discloses an aqueous multilayer degradable self-polishing ship antifouling coating system and a preparation method thereof, and belongs to the field of marine corrosion and antifouling materials. The system is composed of a zinc-rich primer, a modified epoxy intermediate paint and a functionalized topcoat. The topcoat takes polyhydroxy aliphatic ester as a matrix, integrates a self-delamination modifier capable of forming a silicon-rich top layer during curing, and realizes normal-temperature curing through a synergistic effect of a latent double-curing system. The application realizes long pot life, excellent mechanical properties and long-acting antifouling capacity by using a mixed mechanism of dynamic self-polishing and static fouling release and combining innovative curing technology. The system has a pull adhesion force of not less than 7.9 MPa, and meets environmental protection requirements of volatile organic compound content of less than or equal to 50 g / L and free diisocyanate monomer content of less than or equal to 0.1 wt%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of marine corrosion and antifouling materials, and particularly relates to a water-based multilayer degradable self-polishing ship antifouling coating system and a preparation method thereof. BACKGROUND

[0002] Modern shipbuilding and offshore engineering industries are facing increasingly sharp contradictions between economy and ecological protection caused by traditional protection technologies. On the one hand, biofouling on the surface of the ship body can significantly increase the sailing resistance, leading to a sharp rise in fuel consumption and greenhouse gas emissions; research shows that severe fouling can cause more than 85% power loss, and even a slight slime film can cause about 20% increase in resistance. On the other hand, the antifouling technology that has been relied on for a long time to solve this problem itself has become a serious source of marine pollution.

[0003] Historically, ship antifouling technology has evolved from physical covering (such as lead plate, copper plate) to chemical antifouling. In the mid-20th century, tributyltin (TBT) represented self-polishing copolymer coatings dominated due to its good broad-spectrum biocidal effect and long-term effectiveness. However, scientific research has revealed that TBT has significant adverse effects on marine ecosystems. As a persistent organic pollutant, it can be enriched in the body, transmitted through the food chain, and cause devastating damage to non-target marine organisms, leaving long-term environmental risks.

[0004] In view of this, the global regulatory system is increasing efforts to continuously promote the green transformation of ship antifouling technology. The International Maritime Organization has completely banned the use of organotin through the International Convention for the Control and Management of Ships' Ballast Water and Sediments, and added control of Cybutryne (Irgarol 1051) through the MEPC.331(76) amendment in 2021: from January 1, 2023, ships shall not be painted or repainted with antifouling systems containing the substance; and should be removed or covered after the first antifouling system replacement inspection completed after January 1, 2023, and at the latest not more than 60 months from the date of the last coating, in order to reduce the risk of the biocide to the marine environment. At the same time, the European Union's Biocidal Products Regulation and the Chemicals Registration, Evaluation, Authorization and Restriction Regulation impose more stringent restrictions on the types and contents of harmful substances in coatings and the emission standards of volatile organic compounds (VOC). The tightening of these regulations has prompted the industry to accelerate the transition to low-toxic or non-toxic alternative technology routes to meet regulatory and environmental goals.

[0005] Under this background, various alternative technologies have been explored in the field, but the existing solutions all have obvious limitations and have not provided a systematic solution that takes into account environmental protection, economy and performance:

[0006] 1. Fouling release coatings: Low surface energy coatings, represented by organosilicon such as polydimethylsiloxane or fluoropolymers, are one of the main directions of current non-toxic antifouling. The principle is to build a "smooth" low adhesion surface, making it difficult for fouling organisms to firmly adhere, or easily falling off under the shear force of water flow. However, the industrial application of such coatings faces many challenges. First, their mechanical properties are poor, and the coating is soft and easy to scratch and damage. Second, the adhesion of the coating to the substrate is its inherent weakness, and usually requires a complex primer system to ensure, and the construction process is demanding. In addition, traditional organosilicon coatings are mostly solvent-based, with high VOC emissions and high cost, limiting their widespread application.

[0007] 2. Early biodegradable coatings: Biodegradable polymers such as polylactic acid (PLA) or polyhydroxyalkanoate (PHA) are directly used as ship antifouling coating matrix, which has great potential in the concept of whole life cycle environmental friendliness. However, early technical attempts have exposed its fundamental flaws. As disclosed in US6025028A and US20230220155A1, most of the simple PHA water dispersions or melt coatings are far from meeting the stringent requirements of marine applications in terms of technical maturity. Both academic research and practice have confirmed that such simple bio-based coatings have always failed to solve a core technical contradiction: the balance between marine-grade mechanical strength, weather resistance, adhesion requirements and controllable biodegradation (self-polishing) rate. These coatings often fail prematurely due to excessive degradation rate, such as a monthly polishing rate of more than 10µm in typical marine conditions, or lose effective self-polishing performance due to the pursuit of mechanical strength, ultimately failing to form a mature product for industrial application.

[0008] 3. Limitations of existing advanced technologies: In recent years, some advanced unit technologies have emerged in the coating field, but they exist in isolation and have not been effectively integrated to solve the systemic problems in the field of ship antifouling.

[0009] Self-stratification technology: By adding incompatible low surface energy components (such as silicon-containing or fluorine-containing polymers) in the coating, it spontaneously migrates to the surface of the coating during curing, forming a functional top layer. For example, Chinese patent CN107298930A discloses an organosilicon-polyurea self-stratification coating. However, the self-stratification system in the prior art is based on a stable, non-degradable polymer matrix (such as polyurea, acrylic resin), and its purpose is only to build a static low adhesion surface, which is essentially still within the scope of fouling release coatings, and has not been combined with the dynamic self-polishing mechanism.

[0010] Advanced waterborne crosslinking technology: To solve the problem of short pot life and poor storage stability of two-component waterborne coatings, the industry has developed latent crosslinking agents such as blocked polyisocyanate and waterborne polycarbodiimide (PCDI). These technologies make it possible to prepare high-performance, stable one-component (1K) waterborne systems. However, the prior art has not disclosed the use of these advanced crosslinking methods, especially in combination, to solve the specific and critical problem of stabilizing and enhancing hydrolysis-sensitive bio-based polymers such as PHA in waterborne systems.

[0011] In summary, the field has long been faced with a fundamental "trilemma" in the process of seeking environmentally friendly ship antifouling solutions - it is necessary to balance high-efficiency and broad-spectrum antifouling effect, ensure that the coating has sufficient mechanical durability and adhesion in the marine environment, and at the same time, achieve environmental friendliness throughout the life cycle, including non-toxicity, biodegradability and low VOC emissions.

[0012] Specifically, traditional coatings relying on biocides have outstanding antifouling performance, but they pose serious ecological toxicity problems; non-toxic fouling-release coatings (such as silicones) have natural shortcomings in mechanical strength and adhesion, making it difficult to support long-term service requirements, and their static antifouling ability is also relatively limited; and early attempts at biodegradable self-polishing coatings have good environmental performance, but it is difficult to balance the degradation rate and coating strength, and thus the durability is far from meeting the requirements of industrial application.

[0013] Therefore, the existing technical routes are making difficult compromises and trade-offs in this three-difficult dilemma, presenting a situation of "gaining one and losing another". What the market urgently needs is not incremental improvement of a single performance, but a solution that can fundamentally break through the above technical shackles and systematically integrate the three core objectives. To solve the above technical problems, the following technical solutions are provided. SUMMARY

[0014] The present application aims to provide a waterborne multilayer degradable self-polishing ship antifouling coating system and its preparation method, to solve the ecological toxicity problem of traditional ship antifouling coatings, and the problem of insufficient performance or high cost of existing non-toxic coatings, and to provide a new type of environmentally friendly, long-acting and energy-saving ship antifouling coating system that meets future regulatory trends.

[0015] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0016] The present invention provides a waterborne multilayer degradable self-polishing marine antifouling coating system. The system comprises, in order, a zinc-rich primer layer with a thickness of 50-80 µm, a modified epoxy intermediate layer containing hydrolysable side chains with a thickness of 40-80 µm, and a topcoat layer with a thickness of 80-120 µm. The topcoat layer is cured from a waterborne degradable self-polishing composition comprising, based on the weight percentage of the total solid content of the composition, 35-55 wt% of a degradable polyhydroxyalkanoate matrix, 0.5-4 wt% of a self-stratification modifier, 2-10 wt% of a light stabilizing and anticorrosive filler, and a latent dual-cure system comprising 0.5-4 wt% of microencapsulated polycarbodiimide (PCDI) and 0.5-3 wt% of blocked polyisocyanate, wherein the total solid content of the latent dual-cure system is 1-7 wt%. The remaining components of the composition are deionized water and auxiliaries, and the paint film cured from the composition has a free diisocyanate monomer content of no more than 0.1 wt%, as determined by the HPLC-UV method according to ISO 6923:2023.

[0017] Specifically, as shown in Figure 1 The multilayer coating system architecture of the present invention is clear and functional. On a surface-treated steel substrate 1, a zinc-rich primer layer 2 is first applied, in which zinc powder particles 3 as sacrificial anodes are uniformly dispersed to provide basic electrochemical corrosion protection for the substrate. Next is a modified epoxy intermediate layer 4, which serves as a bridge connecting the primer and the topcoat and provides additional corrosion protection barrier and intercoat adhesion. The outermost layer is the functional topcoat layer 5, in which key functional components such as microencapsulated PCDI 6 and light stabilizing and anticorrosive filler 7 are uniformly distributed. In particular, during the curing process of the coating, the self-stratification modifier migrates to the surface of the coating to form a very thin silicon-rich top layer 8, which endows the coating system with the ability of static fouling release.

[0018] One of the core innovations of the present invention is that, through precise formulation design, the dynamic self-polishing and static fouling release mechanisms coexist and the surface layer dynamically regenerates in the same coating system. Specifically, instead of constructing a static and unchanging fouling release surface layer, the present invention utilizes the molecular migration characteristics of the polystyrene-graft-polydimethylsiloxane (PS-g-PDMS) self-delamination modifier to dynamically form and maintain a very thin and renewable silicon-rich low surface energy layer at the paint film-seawater interface during the curing and subsequent use of the coating. When the ship is stationary, the silicon-rich layer provides the main static physical antifouling capability. When the ship is sailing or there is stubborn attachment of fouling organisms, the underlying PHA matrix undergoes controlled micro-hydrolysis, causing the outermost layer to peel off along with the fouling, and the self-delamination modifier stored in the coating body migrates to the newly exposed paint film-seawater interface due to the thermodynamic driving force generated by its incompatibility with the PHA matrix, thereby re-establishing a functional surface layer rich in low surface energy groups. This dynamic balance mechanism of "sacrifice-regeneration" ensures that the coating can continuously maintain its low surface energy characteristics under various marine working conditions, solving the limitations of traditional single-mechanism coatings.

[0019] Similarly, the latent dual-curing system solves the contradiction between long pot life and high final performance of the waterborne PHA system through an innovative synergistic curing mechanism. Specifically, the system contains two latent crosslinking agents that are activated under different conditions: first re-curing: after the paint film is formed and the water evaporates, the microencapsulated PCDI is first released and reacts with the inherent or hydrolytically generated carboxyl groups -COOH in the PHA matrix to form a preliminary crosslinked network. Second re-curing: the blocked polyisocyanate undergoes a second re-crosslinking reaction with the hydroxyl groups -OH in the PHA matrix. The core innovation of the present invention is the discovery and utilization of the positive synergistic effect between the two curing reactions. Experiments have shown that when the two latent curing agents coexist, the system can be cured at ambient temperature to form a dense interpenetrating network structure with good mechanical properties, such as the pull-off adhesion of 8.9 MPa in the examples. If only blocked polyisocyanate is used, it cannot be effectively cured at the same ambient temperature; if only PCDI is used, it cannot achieve the same level of mechanical strength. This synergistic effect ensures the high performance of the final coating film. Based on experimental results, the mechanism of this synergistic effect can be explained as follows: the reaction of the first re-curing PCDI with the carboxylic acid changes the chemical properties of the local microenvironment, generating in situ catalytic conditions that can effectively promote the unblocking and reaction of the blocked polyisocyanate at ambient temperature. This sequential mechanism, in which the first re-curing reaction creates favorable activation conditions for the second re-curing reaction, enables the entire dual-curing process to be efficiently completed at room temperature, thereby ensuring a long pot life while imparting excellent mechanical strength to the coating film.

[0020] The co-agent can be one or more coating co-agents conventionally used in the art, such as, but not limited to, wetting dispersants, defoamers, leveling agents, and rheology modifiers.

[0021] In the above technical solutions, the content of each component can be selected to optimize specific properties. For example:

[0022] The solid content of the degradable polyhydroxyalkanoate matrix preferably can be 35%, 38%, 40%, 43%, 46%, 48%, 50%, 52%, or 55%.

[0023] The solid content of the self-stratification modifier preferably can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or 4.0%.

[0024] The solid content of the light stabilization and preservative package preferably can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0025] The solid content of the latent dual-cure system preferably can be 1%, 2%, 3%, 4%, 5%, 6%, or 7%. The content of microencapsulated PCDI therein preferably can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or 4.0%. The content of blocked polyisocyanate preferably can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%.

[0026] The degradable polyhydroxyalkanoate matrix is selected from one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and hydroxyl-terminated modifications or polydimethylsiloxane grafted derivatives thereof. In one particular example, the matrix can comprise 20-30% PHBH, 8-15% hydroxyl-terminated PHBV, and 7-10% polydimethylsiloxane grafted poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PDMS-g-PHBH).

[0027] The self-stratification modifier is a polystyrene grafted polydimethylsiloxane that forms a silicon-rich low surface energy layer on the surface of the topcoat layer after curing, the topcoat layer after forming the silicon-rich low surface energy layer having a static water contact angle > 105°.

[0028] The microencapsulated PCDI in the latent dual-cure system has an encapsulation efficiency of no less than 85%, D 50 is 0.5-5 µm.

[0029] The solid content of the aqueous degradable self-polishing composition is 40-80 wt%. For example, the solid content can be 40%, 55%, 70%, or 80%.

[0030] The modified epoxy intermediate paint layer containing hydrolysable side chains is cured from a composition containing 40-60% of a beta-betaine ester modified epoxy emulsion and 15-25% of an aqueous aliphatic amine curing agent, and the cured film has an aerobic biodegradation rate of more than 25% after 180 days of testing in a simulated marine environment according to the ASTM D6691-24a standard.

[0031] The present application also provides a preparation method of the above-mentioned aqueous degradable self-polishing composition, comprising the following steps:

[0032] Step 1. Disperse the degradable polyhydroxyalkanoate matrix, self-layering modifier, light stabilizing and anticorrosive filler, and auxiliary agent in deionized water in sequence to form main agent A, wherein the main agent A contains 35-55 wt% of the degradable polyhydroxyalkanoate matrix, 0.5-4 wt% of the self-layering modifier, and 2-10 wt% of the light stabilizing and anticorrosive filler, based on the total solid content of the composition.

[0033] Step 2. Mix the microencapsulated PCDI with the blocked polyisocyanate to form curing agent B, wherein the curing agent B contains 0.5-4 wt% of the microencapsulated polymeric carbon diimide and 0.5-3 wt% of the blocked polyisocyanate, based on the total solid content of the composition.

[0034] Step 3. Mix the main agent A and the curing agent B before application, so that the mass ratio of the solid content of the main agent A to the curing agent B is 100:2.5-3.5.

[0035] Furthermore, the system has a pull-off adhesion of not less than 7.9 MPa when tested according to the ASTM D4541-22 standard, and the volatile organic compound (VOC) content contained therein is not higher than 50 g / L when measured according to the ISO 11890-2:2020 / Amd 1:2024.

[0036] Compared with the prior art, the following significant beneficial effects can be obtained by using the present application:

[0037] Whole life cycle environmentally friendly design: the present application takes biodegradable PHA as the topcoat core, and innovatively designs the modified epoxy intermediate paint as biodegradable (the degradation rate is more than 25% within 180 days according to the ASTM D6691 standard test), which lays the foundation for realizing the environmental friendliness of the whole coating system.

[0038] Precise response to current regulations and provide use advantages: through the innovation of latent dual-curing system, the free diisocyanate monomer content in the final product is strictly controlled below 0.1%, in response to the restriction directive (EU) 2020 / 1149 under the EU REACH system; at the same time, the non-bioicide / degradable design of the invention is consistent with the restriction requirement of Cybutryne (Irgarol 1051) of the International Convention for the Control and Management of Ships' Ballast Water and Sediments (BWM) from January 1, 2023. In the current market environment, this design helps to reduce the compliance cost and operational risk related to free isocyanate, and under certain conditions, it can simplify part of the safety management process, thereby improving the convenience and market competitiveness of actual application.

[0039] Reduce long-term ecological risk: by forming a dense interpenetrating polymer network, the functional nanofiller is firmly anchored in the matrix. These fillers are exfoliated as a whole at a micron level rather than leaching, thereby greatly reducing the potential risk of free nanoparticles entering the marine environment, strengthening the "safety design" concept of the invention.

[0040] Innovative hybrid antifouling mechanism and significant economic benefits: the invention creatively combines the controllable hydrolysis self-polishing of PHA matrix with the ultra-low surface energy physical antifouling formed by self-layering. This "dynamic polishing + static release" hybrid antifouling mechanism ensures that the ship can efficiently resist biological adhesion in both high-speed sailing and long-term parking conditions, thereby significantly saving fuel by maintaining the hydrodynamic smoothness of the ship's hull for a long time.

[0041] Key breakthrough for industrial application: the invention effectively solves the key challenges of pot life and storage stability of high-performance water-based coatings by introducing a latent dual-curing system. The construction pot life of the coating system described in the invention can be no less than 60 minutes, much longer than many traditional high-performance two-component systems; at the same time, its viscosity change rate after 30 days of accelerated aging at 50°C can be controlled within 15%, showing excellent storage stability. These characteristics significantly reduce the requirements for construction conditions, improving the industrial application feasibility of the technical solution of the invention.

[0042] Systematic integrated protection scheme and proven physical properties: the three-layer coating system proposed by the invention exhibits high overall performance through the scientific matching of the functions of each layer. The pull-off adhesion of the system can be as high as 8.9 MPa, capable of withstanding 1000 hours of salt spray environmental testing without blistering or rusting, and successfully passing the severe low-temperature impact test at -40°C. The above performance fully proves that the system of the invention has the ability to provide long-term protection in harsh marine environments. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1The ship hull steel base material and the multi-layer antifouling coating and the microstructure schematic diagram thereof of the present application.

[0044] In the figure, 1, steel base material; 2, zinc-rich primer layer; 3, zinc powder particles; 4, modified epoxy intermediate layer; 5, topcoat layer; 6, microencapsulated PCDI; 7, light stabilizing and anticorrosive filler; 8, silicon-rich top layer. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application. Unless otherwise specified, the raw materials used in the examples are commercially available industrial products or can be prepared by conventional methods. The performance test methods are carried out according to the standards described in the summary of the invention, unless otherwise specified.

[0046] In all examples and comparative examples of the present application, unless otherwise explicitly specified, all component contents mentioned in parts refer to mass parts.

[0047] Table 1: Name, product model / code and supplier of primer components:

[0048]

[0049] Table 2: Name, product model / code and supplier of intermediate paint components:

[0050]

[0051] Table 3: Name, product model / code and supplier of topcoat components:

[0052]

[0053] Table 4: Name, product model / code and supplier of raw materials for comparative examples:

[0054]

[0055] Table 5: Name, product model / code and supplier of titration reagents for analysis and testing:

[0056]

[0057] Table 6: Name, product model / code and supplier of general medicinal raw materials and solvents:

[0058]

[0059] Table 7 Main analysis of the name of the testing instrument, model and manufacturer:

[0060]

[0061] Table 8 Main test items and test standards:

[0062]

[0063] * Note: The rotating cylinder method was used to periodically measure the dry film thickness loss by a surface profilometer, and the equipment was referenced to ASTM D6442-06R20 and the dry film thickness was measured by a micrometer according to ASTM D1005-95 (2024).

[0064] General analysis reagents and preparation of drugs:

[0065] 1. Preparation and calibration of ethylenediaminetetraacetic acid (EDTA) standard solution.

[0066] Accurately weigh EDTA-2Na, dissolve with deionized water and dilute to the required concentration (e.g. 0.05 mol / L). Calibrate using ZnO dried to constant weight at 110°C. Accurately weigh three portions of reference zinc oxide, dissolve with dilute hydrochloric acid, then add a buffer solution to adjust the pH value, use chrome black T as an indicator, and titrate with the prepared EDTA solution until the solution color changes from wine red to pure blue, which is the end point. Calculate and determine the accurate concentration of the EDTA standard solution according to the mass of zinc oxide and the volume of consumed EDTA. The relative deviation of three parallel experiments should not be greater than 0.2%.

[0067] 2. Preparation of microencapsulated PCDI.

[0068] Step 1 (core material preparation): Dissolve 100 parts of liquid PCDI in 200 parts of ethyl acetate to form a uniform oil phase solution.

[0069] Step 2 (emulsion preparation): Dissolve 10 parts of polyvinyl alcohol (PVA-1788) in 900 parts of deionized water as the water phase protective colloid. Under high shear (8000 rpm) conditions, slowly add the oil phase prepared in step 1 to the water phase, and continue to emulsify for 30 minutes to form a stable O / W emulsion.

[0070] Step 3 (interfacial polymerization coating): Slowly add a mixture of 15 parts of TDI and 5 parts of TMP to the above emulsion. Warm up to 70°C and stir at 500 rpm for 4 hours. TDI and water and TMP undergo polymerization at the oil-water interface to form a polyurethane-urea wall material, which encapsulates PCDI.

[0071] Step 4 (Post-treatment and characterization): After the reaction is completed, it is cooled to room temperature, centrifugally separated, washed with deionized water 3 times, and then dried at 60°C under vacuum for 24 hours to obtain a white powdery microencapsulated PCDI product. Its encapsulation efficiency is determined by Soxhlet extraction method, and its average particle size is measured by laser particle size analyzer according to ISO 13320 standard.

[0072] Table 9 Test results of microencapsulated PCDI characterization items:

[0073]

[0074] Table 9 data shows that the encapsulation efficiency of PCDI is as high as 88.5%, indicating that the core material is effectively coated by the wall material, which is the key to realizing its "latency" in aqueous system. At the same time, the moderate average particle size of 3.2µm is conducive to its stable dispersion in coatings without premature settling.

[0075] 3. Preparation of graphene-zinc phosphate nanosheets (GO-ZP).

[0076] Step 1 (GO preparation): Graphene oxide (GO) is prepared by improved Hummers method. 5g of natural graphite powder is added to 120mL of concentrated sulfuric acid, and 15g of potassium permanganate is slowly added under ice bath cooling, stirring for 2 hours. Then the temperature is raised to 35°C and reacted for 12 hours. The reaction is poured into 400mL of ice water, and 30mL of hydrogen peroxide solution is added dropwise until the solution turns golden yellow. By centrifugation, washing to neutral, freeze-drying to obtain GO powder.

[0077] Step 2 (GO-ZP complexation): 1g of GO powder is ultrasonically dispersed in 500mL of deionized water. 20g of zinc nitrate and 15g of ammonium dihydrogen phosphate are added and dissolved by stirring. At 80°C, ammonia water is added dropwise to adjust the pH to 7.0, and the reaction is continued for 3 hours. During this process, zinc phosphate is precipitated in situ on the surface of GO layers.

[0078] Step 3 (Post-treatment and characterization): After the reaction is completed, the product is centrifugally separated, washed with deionized water and ethanol alternately for several times, and finally dried at 80°C under vacuum for 12 hours to obtain gray-black graphene-zinc phosphate nanosheet (GO-ZP) powder. The dried GO-ZP powder is dissolved by heating with dilute hydrochloric acid at 60°C, and then complex titration is carried out with EDTA standard solution to determine the zinc ion content, so as to calculate the loading amount of zinc phosphate in the composite material.

[0079] Table 10 Characterization results of GO-ZP:

[0080]

[0081] Note: The loading amount of zinc phosphate is calculated by the following formula:

[0082] Loading (wt%) = (C EDTA x V EDTA x M 磷酸锌 ) / (3 x M Zn x m 样品 ) x 100%, wherein C EDTA is the concentration of EDTA standard solution, V EDTA is the titration consumption volume, M 磷酸锌 and M Zn are the molar mass of zinc phosphate and zinc, respectively, and m 样品 is the sample mass.

[0083] The titration results of Table 10 show that the loading of zinc phosphate in the GO-ZP samples prepared in different batches is stable at about 22 wt%, with little difference between batches. This indicates that the in-situ precipitation method has good reproducibility and can stably prepare composite anticorrosive fillers of the target composition.

[0084] 4. Preparation of β-betaine ester modified epoxy emulsion.

[0085] Step 1 (β-amino acid ester synthesis): 1 mole of N,N-dimethylethylenediamine was reacted with 1.1 moles of methyl acrylate in methanol solvent at 50°C for 6 hours to obtain N,N-dimethyl-N'-(2-methoxycarbonyl ethyl) ethylenediamine.

[0086] Step 2 (epoxy grafting): 1 mole of bisphenol A type epoxy resin (E-51) was dissolved in xylene, and 0.2 moles of the product prepared in Step 1 was added, and reacted at 120°C for 4 hours to graft the side chain containing tertiary amine groups onto the epoxy backbone.

[0087] Step 3 (quaternization and emulsification): The grafted epoxy resin was cooled to 80°C, and 0.2 moles of chloroacetic acid was added for quaternization reaction for 4 hours to form the zwitterionic β-betaine ester structure. After the reaction was completed, a measured amount of deionized water was added under high-speed stirring, and the xylene solvent was evaporated to obtain a stable β-betaine ester modified epoxy emulsion with a solid content of about 50% by phase inversion method.

[0088] Step 4 (product characterization): After the reaction was completed, samples were taken. The change in epoxy value before and after grafting reaction was determined by potentiometric titration method according to ASTM D1652 standard method, and the conversion rate of epoxy groups was calculated. The content of tertiary amine groups in the product after quaternization reaction was determined by potentiometric titration method, and the quaternization rate was calculated.

[0089] Table 11 Test results of β-betaine ester modified epoxy emulsion characterization items:

[0090]

[0091] The data in Table 11 show that both the conversion of the epoxy groups and the quaternization of the tertiary amine groups are over 95% as measured by potentiometric titration. Such high reaction efficiency confirms that the target chemical structure, i.e., an epoxy resin containing β-betaine ester side chains, has been successfully synthesized.

[0092] 5. Preparation of hydroxyl-terminated modified PHBV-OH emulsion.

[0093] Step 1 (synthesis of PHBV-diol): 20 parts of PHBV were dissolved in 200 parts of chloroform under heating and reflux. Then 20 parts of ethylene glycol and 0.5 parts of p-toluenesulfonic acid as catalyst were added. The reaction was carried out at 60 °C for 24 hours. After the reaction was completed, the product was precipitated in a large amount of diethyl ether, filtered and vacuum dried to obtain white hydroxyl-terminated modified PHBV oligomer (PHBV-diol).

[0094] Step 2 (product characterization): The hydroxyl value of the PHBV-diol was determined by titration according to the ASTM E222-23 standard method.

[0095] Step 3 (emulsification): The qualified PHBV-diol was heated to the molten state, and slowly added to 10 parts of deionized water containing 0.5 parts of SDS under high-speed shearing conditions at 5000 rpm, and emulsified for 20 minutes to obtain a stable aqueous emulsion with a solid content of about 50%.

[0096] Table 12 Characterization results of hydroxyl-terminated modified PHBV-OH emulsion:

[0097]

[0098] The results in Table 12 show that the measured hydroxyl value of the product prepared by ester exchange method is highly consistent with the theoretical calculated value, proving that the PHBV macromolecular chain has been successfully cut off and the terminal hydroxyl group has been introduced, providing active sites for subsequent crosslinking reaction.

[0099] 6. Preparation of PS-g-PDMS.

[0100] The method of "grafting after polymerization" was used. First, 10 parts of PDMS-OH were reacted with 1.2 parts of chloromethyl styrene in toluene to prepare a PDMS macromonomer with a polymerizable vinyl group. Then, the macromonomer was reacted with 90 parts of styrene monomer in toluene at 70 °C for 12 hours using AIBN as initiator. After the reaction was completed, the product was precipitated, purified and dried in methanol to obtain the PS-g-PDMS graft copolymer.

[0101] The grafting degree was determined by chemical analysis. A certain amount of dried product was accurately weighed into a crucible and ashed at 600°C in a muffle furnace to completely decompose the organic components, leaving silica (Si02) as the residue. The mass of silica was weighed to calculate the content of polydimethylsiloxane in the copolymer, and thus the grafting degree.

[0102] Table 13 Characterization results of PS-g-PDMS:

[0103]

[0104] The gravimetric results in Table 13 show that the content of PDMS in the final product is stabilized at about 10wt%, which is consistent with the feeding ratio. This confirms that the PDMS macromonomer with polymerizable groups has been successfully grafted onto the polystyrene backbone to form the target composition of PS-g-PDMS self-layering modifier.

[0105] 7. Preparation and characterization of PDMS-g-PHBH.

[0106] The grafting radical polymerization method was used: 10 parts of hydroxyl-terminated PDMS-OH was reacted with 1.2 parts of chloromethyl styrene in toluene to prepare a PDMS macromonomer with a polymerizable vinyl group. Subsequently, the monomer was taken and reacted with 90 parts of PHBH in toluene at 70°C for 12 hours using AIBN as the initiator. After the reaction was completed, the product was precipitated, purified and dried in methanol to obtain the PDMS-g-PHBH graft copolymer.

[0107] The acid value titration method was used to characterize the degree of grafting reaction. The PHBH raw material before reaction and the PDMS-g-PHBH product after reaction were accurately weighed and dissolved in a chloroform-ethanol mixed solvent, and titrated with a calibrated potassium hydroxide-ethanol standard solution, with phenolphthalein as the indicator. The acid value was calculated according to the volume of titrant consumed. The grafting reaction consumes the end carboxyl groups of PHBH, resulting in a significant decrease in acid value.

[0108] Table 14 Characterization results of PDMS-g-PHBH:

[0109]

[0110] The titration results in Table 14 clearly show that the acid value of the graft product PDMS-g-PHBH is significantly reduced from 2.0 mg KOH / g to about 0.5 mg KOH / g compared with the PHBH raw material. The significant decrease in acid value proves that the active sites (end carboxyl groups) on the PHBH molecular chain have reacted effectively with the PDMS macromonomer to form the target product. This method provides direct chemical quantitative evidence for the successful synthesis of graft copolymer.

[0111] 8. Preparation of core-shell structured titanium oxide.

[0112] The sol-gel method was used. Step 1 (coating Al2O3): 10 parts of titanium dioxide nano-powder was ultrasonically dispersed in 200 parts of anhydrous ethanol. Under nitrogen protection, 50 parts of an isopropanol solution containing 5 parts of aluminum isopropanol was added dropwise to the above suspension, and a small amount of water was added to initiate hydrolysis. After stirring at 50°C for 6 hours, the intermediate product, titanium dioxide coated with aluminum oxide, was obtained after centrifugation, washing, and drying.

[0113] Step 2 (coating CeO2): The product obtained in Step 1 was redispersed in ethanol, and an ethanol solution containing 2 parts of cerium nitrate (III) hexahydrate was added dropwise, and the pH was adjusted to 9-10 by adding ammonia water to initiate cerium hydroxide precipitation. After continuous stirring for 4 hours, the product was centrifuged, washed, and calcined at 500°C for 2 hours to obtain the final core-shell structure, i.e. a multi-layer core-shell composite particle with titanium dioxide as the core, an intermediate layer of aluminum oxide, and a shell of cerium dioxide.

[0114] Step 3 (product characterization): The content of the coating layer was determined by selective acid dissolution and gravimetric analysis. A certain mass of the final product was first dissolved in a specific concentration of acid solution under mild conditions to dissolve the outermost CeO2 layer, and the content was calculated by the mass difference before and after dissolution. Subsequently, the Al2O3 layer was dissolved by increasing the acid concentration or temperature, and the content was again calculated by the mass difference, thereby verifying the formation of the core-shell structure and the proportion of each layer.

[0115] Table 15 Characterization results of core-shell structured titanium oxide:

[0116]

[0117] Table 15 The content of the outer CeO2 and intermediate Al2O3 layers was accurately determined by selective dissolution and gravimetric analysis, and the results were completely consistent with the designed values. The above results support the formation of the core-shell structure and functional characterization, which is a prerequisite for ensuring its light stabilization function.

[0118] 9. Preparation of zinc-rich primer.

[0119] 30 parts of water-based epoxy resin, 5 parts of conductive mica, 1 part of graphene, 10 parts of deionized water, and appropriate amounts of additives such as dispersants and defoamers were added to a dispersion kettle and uniformly dispersed under high-speed stirring to form Component A. 15 parts of a water-based epoxy curing agent was uniformly pre-mixed with 39 parts of zinc powder as Component B. Before application, Components A and B were uniformly mixed in the specified ratio.

[0120] To verify the technical effects of the present application, the following examples and comparative examples are set. The modified epoxy intermediate paint used for testing is cured from the following components: 50% of beta-betaine ester modified epoxy emulsion (prepared according to Preparation Example 3) and 20% of Anquamine 287 waterborne aliphatic amine curing agent, with the rest being water and auxiliaries. The topcoat of all examples and comparative examples is applied in conjunction with the primer and intermediate paint of the present application to form a complete coating system, with the dry film thickness of each layer being specifically controlled as follows: 65±15 pm for the zinc-rich primer layer, 60±20 pm for the modified epoxy intermediate paint layer, and 100±20 pm for the topcoat layer. After curing for 7 days at 25°C and 65% RH, the performance tests are carried out. Among them, the low-temperature impact test is to place the cured complete three-layer system sample in a low-temperature test chamber at -40°C for at least 4 hours, and then complete the impact test within 10 seconds after taking it out. The dynamic antifouling performance test is strictly carried out in accordance with the standard ASTM D4939-89R20. The test conditions are as follows: the painted sample is installed on the rotating device of the mechanism which meets the requirements of the aforementioned standard, and is exposed in natural seawater at a surface linear speed of 15 knots (7.7 m / s); the total test period is 90 days, during which the dynamic operation is carried out for 12 hours and the static parking is carried out for 12 hours every day, to simulate the actual operation mode of the ship.

[0121] Table 16 Formulation of topcoat of examples and comparative examples (based on solid content wt%):

[0122]

[0123] Note: The remaining components of examples 1-5 and comparative examples 1-6 are solvents and auxiliaries, used to adjust the total solid content to about 60 wt%. Among them, comparative example 1 removes the self-stratification agent; comparative example 2 uses ordinary TiO2 without core-shell structure; comparative example 3 is an optimized pure self-polishing coating; comparative example 4 is a solvent-based system, which is a typical high-performance silicone fouling release coating. To verify the synergistic effect of the dual-curing system, comparative example 5 and comparative example 6 are set: the formulation of comparative example 5 is similar to that of example 1, but only uses microencapsulated PCDI as the curing agent; the formulation of comparative example 6 is similar to that of example 1, but only uses a blocked polyisocyanate as the curing agent.

[0124] Table 17 Test results of comprehensive performance of coating system of examples and comparative examples:

[0125]

[0126] * Note: The fouling level is evaluated according to ASTM D3623-78A (2020), in which grade 1 represents no fouling, grade 2 represents slight slime, grade 3 represents obvious slime or a small amount of algae attachment, grade 4 represents a large amount of algae or a small amount of hard fouling organisms, and grade 5 represents serious hard fouling.

[0127] ** Note: The marine environment aerobic biodegradation test is only for the cured film of the intermediate paint.

[0128] Experimental results and analysis:

[0129] Intermediate paint potential environmental degradability verification: To verify the environmental compatibility of the intermediate paint of the present application, the aerobic biodegradation of the cured film of the intermediate paint in a simulated marine environment containing natural seawater inoculum was tested according to the standard ASTM D6691-24a. This standard is an internationally recognized authoritative method for evaluating the biodegradability of plastic materials in the marine environment, and its test conditions can scientifically reflect the behavior of materials in the real marine environment. As shown in Table 17, after 180 days of testing, the biodegradation rate of the intermediate paint of the present application was more than 25%, while the degradation rate of the conventional epoxy coating under the same conditions was usually less than 5%. This result strongly proves that the modified epoxy intermediate paint designed in the present application has significantly higher potential marine environmental degradability than traditional epoxy resins, thereby supporting the technical proposition of the present application to improve the environmental friendliness of the whole life cycle. The improved biodegradability exhibited by the intermediate paint of the present application can be explained as follows: the introduced β-betaine ester side chain as a zwitterionic structure not only improves the hydrophilicity of the polymer chain, but also plays a catalytic role when water molecules attack the epoxy backbone, thereby accelerating the hydrolytic chain scission process under the action of marine microorganisms.

[0130] Quantitative verification of self-stratification effect: To verify the effectiveness of the self-stratification modifier PS-g-PDMS, the surface properties of the cured coating of Example 1 were quantitatively characterized. As shown in Table 17, the surface water contact angle is as high as 108°, which is much higher than that of Comparative Example 1 (85°) without the modifier, indicating that the coating surface exhibits significant hydrophobicity. This hydrophobicity is caused by the enrichment of low-surface-energy polydimethylsiloxane (PDMS) segments at the coating-air interface. In addition, the surface profiler was used to measure that the coating surface has very low roughness. These quantitative results collectively confirm that PS-g-PDMS successfully migrates to the surface during curing, forming the functional silicon-rich top layer structure defined in the present application, which provides a physical basis for achieving static fouling release.

[0131] In addition, the thickness of the silicon-rich top layer described in the present application can be verified by theoretical calculation. Taking Example 1 as an example, the dry film thickness of the topcoat is controlled at 100 µm, and the proportion of the self-stratification modifier PS-g-PDMS in the solid content is 2.5 wt%. According to the typical empirical data of composite coatings containing polyester, epoxy and inorganic fillers, the average density of the dry film of the topcoat is 1.3 g / cm 3 , and the density of PS-g-PDMS is 1.0 g / cm 3 . Based on these parameters, the thickness of the silicon-rich top layer is calculated to be 0.25 µm at 1 cm 2The total mass and total volume of PS-g-PDMS in the coating area can be obtained. According to the migration law of the self-layering system and experimental data analysis, about 60% of PS-g-PDMS effectively migrates to the surface and forms a uniform top layer during the curing process. The thickness of the formed silicon-rich top layer is calculated to be 1.92 µm. Combined with the performance measurement data of the high surface contact angle and the theoretical calculation results, it is confirmed that the functional silicon-rich top layer in the thickness range is formed.

[0132] Verification of mixing mechanism: the core innovation of the present application is to effectively combine the self-polishing (SP) and fouling release (FR) mechanisms. To verify the superiority of the mixed mechanism, Example 1 is compared with Comparative Example 3 representing the pure SP mechanism and Comparative Example 4 representing the pure FR mechanism.

[0133] Static antifouling performance: as shown in Table 17, in the 90-day static immersion test, Example 1 shows the best 1st grade antifouling performance. Comparative Example 3 (pure SP) has serious fouling under static conditions due to the high surface energy (contact angle 86°), which is 3rd grade. Although Comparative Example 4 (pure FR) has extremely low surface energy (contact angle 112°) and shows excellent 1-2 grade antifouling performance, it is slightly inferior to Example 1.

[0134] Dynamic antifouling performance: in the 90-day dynamic test, all coatings based on the SP mechanism (Example 1 and Comparative Example 3) achieve the best 1st grade antifouling through surface renewal. Comparative Example 4 (pure FR) performs slightly worse, which is 2nd grade, due to the lack of surface renewal ability under insufficient water flow shear force to remove all attached germination points.

[0135] Comprehensive performance: Comparative Example 4, as a typical silicone coating, has a pull-off adhesion to the substrate of only 5.1 MPa, which is significantly lower than the system of the present application. In summary, only the mixed mechanism coating (Example 1) of the present application can achieve the best 1st grade antifouling performance under both static and dynamic conditions, while maintaining excellent adhesion, which proves its comprehensive advantage compared to high-performance single-mechanism coatings.

[0136] Analysis of the influence trend of key components:

[0137] Impact of the biodegradable PHA matrix: The PHA matrix is ​​the core component for achieving the self-polishing function. Comparing the data from Example 4 (PHA content 35%), Example 1 (46%), and Example 5 (55%), it is clear that the self-polishing rate increases linearly from 4.1 µm / month to 6.0 µm / month with the increase in the total amount of PHA matrix. This is because the higher content of the hydrolyzable skeleton accelerates the stable peeling of the coating surface. However, this is also accompanied by a slight decrease in pull-out adhesion from a maximum of 8.9 MPa (Example 4) to 7.9 MPa (Example 5), indicating that excessively high biodegradable components slightly sacrifice the mechanical cohesive strength of the coating. Therefore, the 35-55% range defined in this invention is an optimized range for achieving a controllable polishing rate while ensuring sufficient mechanical properties.

[0138] The Influence of Light Stabilizing and Corrosion-Resistant Fillers: These fillers are crucial for the long-term durability and adhesion of the coating. Comparing Example 5 (filler content 2%), Example 1 (4%), and Example 4 (10%), the weather resistance of the coating was significantly enhanced with increasing filler content, as evidenced by a significant decrease in the color difference ΔE value after 1000 hours of QUV accelerated aging from 2.8 (Example 5) to 1.6 (Example 4); simultaneously, the pull-out adhesion also increased from 7.9 MPa (Example 5) to 8.9 MPa (Example 4). This indicates that the filler effectively enhances the density of the coating film and its adhesion to the substrate. However, excessively high filler content can also hinder the hydrolysis of the PHA matrix to some extent, resulting in a decrease in the self-polishing rate from 6.0 µm / month (Example 5) to 4.1 µm / month (Example 4). Therefore, a range of 2-10% is the optimal choice for balancing durability and antifouling efficiency.

[0139] The impact of the latent dual-curing system: This system is crucial for ensuring the mechanical and application properties of the coating film. Comparing Examples 5, 1, and 4, it can be seen that increasing the content of the crosslinking system effectively improves the mechanical strength of the coating, increasing adhesion from 7.9 MPa to 8.9 MPa. Simultaneously, an appropriate amount of crosslinking agent is essential for achieving a long pot life; for example, a 3% content in Examples 1, 2, and 3 yields a pot life of at least 70 minutes. However, excessively high crosslinking agent content slightly shortens the pot life (≥60 minutes). Therefore, a range of 1-7% is an effective range for balancing high mechanical properties with a good application window.

[0140] The necessity of self-layering modifier: Compared with Comparative Example 1, after removing the self-layering modifier PS-g-PDMS, the contact angle of the coating surface dropped sharply from 108° to 85°, and the hydrophobicity was lost. As a result, the static antifouling level after 90 days deteriorated from level 1 (no adhesion) to level 3-4 (a lot of adhesion). This proves that the low surface energy top layer formed by self-layering is the key to achieving physical antifouling.

[0141] Necessity of core-shell structured light stabilizer: By comparing Example 1 and Comparative Example 2, it is clear that the color difference ΔE of the coating after 1000 hours of QUV accelerated aging increases dramatically from 1.8 (unnoticeable) to more than 6.0 (severe discoloration and powdering) when the core-shell structured light stabilizer is replaced by common anatase Ti02. This result clearly reveals the inherent defect of common Ti02: as a highly efficient photocatalyst, it will produce reactive oxygen free radicals under UV excitation, thereby catalyzing the degradation of the adjacent PHA polymer matrix. The core-shell structure used in the present application effectively suppresses this catalytic degradation effect by physically isolating the Ti02 core with photocatalytic activity from the PHA matrix through an inert oxide shell, while retaining the excellent UV shielding ability of Ti02. Therefore, the core-shell structure is a key and necessary technology to protect the hydrolysis-sensitive PHA matrix and maintain the long-term outdoor durability of the coating, and its excellent results provide strong evidence for the long-term durability of the coating system.

[0142] Verification of synergistic effect of dual-curing system: To directly verify the synergistic effect of the latent dual-curing system described in the present application, Comparative Example 5 and Comparative Example 6 were specially set up. As shown in Table 17, after curing at 25°C and 65% RH for 7 days, the paint film of Comparative Example 6 is still liquid and cannot form an effective coating, confirming that the closed-type polyisocyanate alone cannot be effectively cured at room temperature. This is because the deblocking temperature of the selected closed-type polyisocyanate is much higher than the ambient temperature, and without the synergistic catalytic effect of PCDI reaction, its crosslinking reaction cannot be initiated. Although Comparative Example 5 can be cured into a film, its key mechanical properties are much worse than Example 1, with a pull-off adhesion of only 4.2 MPa, much lower than the 8.5 MPa of Example 1, and it performs poorly in low-temperature impact and salt spray resistance tests. The results of these two comparative examples are in sharp contrast to the excellent performance of Example 1, and the results show that there is a significant positive synergistic effect between microencapsulated PCDI and closed-type polyisocyanate in the system of the present application, which is the key to achieving room temperature curing and good mechanical properties, and is not a simple superposition of the effects of the two curing agents.

[0143] The universal validation of PHA species: comparing Example 1, Example 2 and Example 3, although the PHA species are different, the core performance indicators of the final coating, such as adhesion, antifouling grade and weather resistance, are maintained at very similar excellent levels. This proves that the technical framework of the present application, especially the self-layering, latent crosslinking and light stabilization system, has wide applicability to different types of PHA matrix. From the chemical structure, the various types of PHA (including PHB, PHBH, PHBV, etc.) share the same polyester backbone and hydrolysable ester bonds, which is the basis for realizing the self-polishing function of the present application. At the same time, they also have similar end groups (hydroxyl and / or carboxyl) to participate in the dual curing reaction of the present application. Therefore, the technical solution of the present application has universality for various PHA matrix listed in the present application.

[0144] In summary, the present application successfully prepares a ship antifouling coating system with high-efficiency antifouling, long-term durability, friendly construction and significantly improved environmental friendliness through systematic innovation design of multi-layer structure, topcoat matrix, functional additives and crosslinking system, solves many pain points of the prior art, and has good industrial application feasibility.

[0145] Those skilled in the art should understand that the above examples are only exemplary and are not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement, etc. made to the technical solution of the present application within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An aqueous multi-layer degradable self-polishing marine antifouling coating system, characterized in that: the system comprises, in order, a zinc-rich primer layer having a thickness of 50-80 pm, a modified epoxy intermediate coating layer containing hydrolysable side chains having a thickness of 40-80 pm, and a topcoat layer having a thickness of 80-120 pm; the topcoat layer is cured from an aqueous degradable self-polishing composition comprising, by weight percentage of the composition, 35-55 wt% of a degradable polyhydroxyalkanoate matrix, 0.5-4 wt% of a self-stratifying modifier, 2-10 wt% of a light stabilizing and anticorrosive filler, and a latent dual-cure system comprising 0.5-4 wt% of microencapsulated polycarbodiimide and 0.5-3 wt% of blocked polyisocyanate; the composition further comprises deionized water and auxiliaries, and the paint film cured from the composition has a free diisocyanate monomer content of no more than 0.1 wt%; the self-stratifying modifier is a polystyrene-grafted polydimethylsiloxane which, after curing, forms a silicon-rich low surface energy layer on the surface of the topcoat layer, and the topcoat layer after forming the silicon-rich low surface energy layer has a static water contact angle of > 105°; the modified epoxy intermediate coating layer containing hydrolysable side chains is cured from a composition comprising 40-60% of a beta-betaine ester-modified epoxy emulsion and 15-25% of an aqueous aliphatic amine curing agent, and the cured film has an aerobic biodegradation rate of more than 25% after being tested in a simulated marine environment for 180 days according to ASTM D6691-24a standard.

2. The system of claim 1, wherein, the degradable polyhydroxyalkanoate matrix is selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and hydroxyl-terminated modifications or polydimethylsiloxane-grafted derivatives thereof.

3. The system of claim 1, wherein, the degradable polyhydroxyalkanoate matrix specifically comprises 20-30% of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), 8-15% of hydroxyl-terminated modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and 7-10% of polydimethylsiloxane-grafted poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

4. The system of claim 1, wherein, The encapsulation efficiency of the microencapsulated polycarbodiimide in the latent dual cure system is not less than 85%, D 50 is 0.5 - 5 pm.

5. The system of claim 1, wherein, the aqueous degradable self-polishing composition has a solid content of 40-80 wt%.

6. The system of claim 1, wherein, the system has a pull-off adhesion of no less than 7.9 MPa when tested according to ASTM D4541-22 standard.

7. The system of claim 1, wherein, the system has a volatile organic compound content of no more than 50 g / L when determined according to ISO 11890-2:2020 / Amd 1:2024.

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