Preparation method of agar-agar nanocellulose-based antifouling coating

Abstract

The present invention relates to a preparation method of a gelatin nanocellulose-based antifouling coating, including: S1, mixing a choline chloride carboxylic acid deep eutectic solvent with gelatin residues and then heating in an oil bath to obtain gelatin cellulose; S2, gelatin cellulose is sequentially treated with cellulase enzymolysis and TEMPO oxidation to obtain gelatin nanocellulose; S3, gelatin nanocellulose and octadecylamine are placed in an ethanol aqueous solution with a certain mass ratio for ultrasonic dissolution, and then a certain mass of dopamine hydrochloride is added to adjust the pH value, and a heating reaction polymerization is carried out at a certain temperature and time by a "one-pot method" to obtain a gelatin nanocellulose-based super-hydrophobic coating; S4, finally adding a certain mass of EGCG and stirring evenly to obtain a gelatin nanocellulose-based antifouling coating. The present invention not only provides an effective method for the reuse of gelatin residues, but also develops a novel bio-based antifouling coating through green chemical technology, and contributes to the sustainable development of related industrial fields.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to a method for preparing a Gelidium nanocellulose-based antifouling coating. Background Art

[0002] Agar-agar is also known as sea jelly, chicken foot vegetable, horse hair, dog hair vegetable and phoenix tail. It belongs to the Agar-agar family, Eurythropoeia, and Agar-agar orders of the Rhodophyta. At present, the main use of agar-agar is to produce agar. The processing waste after agar extraction has not received widespread attention, which has had a huge impact on resource waste and environmental pollution.

[0003] Cellulose is an important natural polysaccharide, widely found in plant cell walls, and is a major renewable resource. However, traditional cellulose extraction methods often use large amounts of organic solvents and energy-intensive processes, which not only pollute the environment but can also negatively impact the quality of the extracted cellulose. Therefore, the development of green and efficient cellulose extraction technologies is of great scientific and economic significance.

[0004] With the rapid development of the marine industry, the impact of marine fouling on shipping and the marine environment has attracted increasing attention. When biofouling occurs on a ship's hull, it can cause significant damage. For example, marine bacteria, fungi, and algae can form biofilms on metal, wood, or polymer surfaces within 48 hours. This can cause the hull to become rough, increase weight, and increase sailing resistance, reducing speed and fuel efficiency. Fuel consumption can increase by 40% and sailing costs by 77%. Furthermore, biofouling increases the frequency of ship maintenance, wastes resources, and generates toxic waste, significantly polluting the environment. It can also degrade coating performance, accelerate hull corrosion, shorten equipment life, and potentially lead to bioinvasion. Due to the economic losses and ecological damage caused by marine biofouling, researchers have long explored methods to prevent biofouling. Antifouling coatings are considered an effective and cost-effective solution. They reduce the adhesion of oil and biofilms, thereby reducing fuel consumption and the frequency of ship maintenance. Furthermore, they can delay hull corrosion, protect the metal substrate, and significantly reduce ship maintenance costs. Organotin (TBT) compounds have been widely used in antifouling paints since the 1970s. However, they disrupt the endocrine system of mollusks, leading to population degradation and decline, severely impacting marine ecosystems and potentially endangering human safety. The International Maritime Organization (IMO) banned the use of organotin antifouling paints in 2008. Copper-rich antifouling paints have since become an alternative, but copper accumulation has revived marine pollution and enriched the food chain, leading to a gradual restriction on the use of copper-containing materials. Therefore, the development of non-toxic, highly effective bio-antifouling coatings has become a research hotspot for novel antifouling materials.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a Gelidium nanocellulose-based antifouling coating.

[0007] The technical solution adopted in the present invention is:

[0008] The present invention provides a method for preparing agar-agar nanocellulose-based antifouling coating, comprising the following steps:

[0009] S1. mixing a choline chloride-carboxylic acid deep eutectic solvent with agar-agar residue and heating the mixture in an oil bath to obtain agar-agar cellulose;

[0010] S2, sequentially subjecting the agar-agar cellulose to enzymatic hydrolysis with cellulase and TEMPO oxidation to obtain agar-agar nanocellulose;

[0011] S3, placing the agar-agar nanocellulose and octadecylamine in a certain mass ratio in an ethanol aqueous solution and ultrasonically dissolving them, then adding a certain amount of dopamine hydrochloride, adjusting the pH value, and performing a heating reaction polymerization at a certain temperature and time by a "one-pot method" to obtain the agar-agar nanocellulose-based super-hydrophobic coating;

[0012] S4. Finally, a certain amount of EGCG is added and stirred evenly to obtain agar-agar nanocellulose-based antifouling coating.

[0013] The present invention proposes a method for preparing a gelatin nanocellulose-based antifouling coating. The method first extracts cellulose from the gelatin residue using a deep eutectic solvent, which, compared to traditional chemical extraction methods, not only has the advantages of high cellulose extraction rate and short extraction time, but also avoids the use of large amounts of organic solvents, making it environmentally friendly. The method then further modifies the gelatin nanocellulose using a cellulase enzymatic hydrolysis combined with TEMPO oxidation, significantly improving the yield and oxidation efficiency of the gelatin nanocellulose, making it more suitable for use in the coating field. Subsequently, the gelatin nanocellulose is polymerized with octadecylamine and dopamine hydrochloride in a one-pot heating reaction. The long-chain structure of octadecylamine and the excellent adhesion of dopamine are utilized to impart superhydrophobic properties to the gelatin nanocellulose-based coating. This method simplifies the preparation process, shortens the time, and improves production efficiency. Finally, the addition of EGCG further imparts excellent self-cleaning and antifouling effects to the coating. The present invention not only provides an effective method for the reuse of gelatin waste, but also develops a new type of bio-based antifouling coating through green chemical technology, contributing to the sustainable development of related industrial fields.

[0014] Preferably, in step S1, the mass ratio of the deep eutectic solvent to the agar-agar residue is 20:1;

[0015] The oil bath heating conditions are: reaction temperature is 100°C, reaction time is 3h;

[0016] The low eutectic solvent is prepared by mixing choline chloride as a hydrogen bond acceptor with four carboxylic acids, namely acetic acid, lactic acid, oxalic acid and formic acid, as hydrogen bond donors in a certain molar ratio under anhydrous conditions, heating at 60° C. for 2 hours, and then screening the solvent by examining its effect on the cellulose content of agar-agar.

[0017] More preferably, the deep eutectic solvent is prepared by mixing the choline chloride and the lactic acid in a molar ratio of 1:2 under anhydrous conditions and heating at 60° C. for 2 h.

[0018] Preferably, in step S2, the conditions for the enzymatic hydrolysis treatment are: enzyme-substrate ratio of 10% w / w, enzymatic hydrolysis pH of 4.8, enzymatic hydrolysis temperature of 60° C., and enzymatic hydrolysis time of 3 h.

[0019] Preferably, in step S2, the TEMPO oxidation method specifically comprises the following steps: placing 1 g of agar-agar cellulose nanofibrils obtained by enzymatic hydrolysis of the cellulase in an anhydrous sodium carbonate / sodium bicarbonate buffer solution, adding 0.017 g of TEMPO and 0.115 g of sodium bromide, stirring until fully dissolved, then adding a certain specific volume of sodium hypochlorite, adjusting the system to a certain pH value with sodium hydroxide solution and glacial acetic acid solution, and performing an oxidation reaction for a certain time;

[0020] Among them, the specific volume of sodium hypochlorite, pH value of the oxidation system and oxidation reaction time were optimized through single-factor experiments with the yield and potential of agar-agar nanocellulose as indicators.

[0021] More preferably, the optimal process conditions of the TEMPO oxidation method are: the specific volume of the sodium hypochlorite is 11 mL / g, the pH value of the oxidation system is 10.5, and the oxidation reaction time is 24 h.

[0022] Preferably, in step S3, the mass ratio of agar-agar nanocellulose to octadecylamine, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride, the polymerization temperature and the polymerization time are obtained by single-factor optimization using the contact angle of the coating as an indicator.

[0023] More preferably, the optimal process conditions of the one-pot method are: the mass ratio of the agar-agar nanocellulose to octadecylamine is 1:2, the mass ratio of the agar-agar nanocellulose to dopamine hydrochloride is 1:2, the polymerization reaction temperature is 50° C., and the polymerization reaction time is 16 h.

[0024] Preferably, in step S4, the amount of EGCG added is screened by examining its effect on the contact angle and antibacterial activity of the coating.

[0025] More preferably, the mass proportion of the EGCG is 2% of the mass of the agar-agar nanocellulose-based super-hydrophobic coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the preparation method of the agar-agar nanocellulose-based antifouling coating of Example 1;

[0027] Figure 2 The effects of different oxidation parameters on the yield and potential of agar-agar nanocellulose in Example 1 are shown. A is the oxidation reaction time, B is the pH value of the oxidation system, and C is the specific volume of sodium hypochlorite. Different letters indicate significant differences (p<0.05).

[0028] Figure 3 The effects of different process parameters on the contact angle of the coating in Example 1, A is the mass ratio of agar-agar nanocellulose (TOCN) to octadecylamine (ODA), B is the mass ratio of agar-agar nanocellulose to dopamine hydrochloride (PDA), C is the polymerization temperature, and D is the polymerization time. Different letters indicate significant differences (p < 0.05);

[0029] Figure 4 The effect of different EGCG addition amounts on the contact angle of the coating in Example 1, different letters indicate significant differences (p < 0.05);

[0030] Figure 5 Comparative photos of the number of bacterial colonies adhered to the surface of samples with different EGCG addition amounts after dilution culture in Example 1;

[0031] Figure 6 Schematic diagram of the self-cleaning process of sand and chalk dust with different coatings, A is ODA@TOCN@PDA, B is ODA@TOCN@PDA@EGCG;

[0032] Figure 7 The chemical stability test results of different coatings are shown in Figure 1. A is the salt ion concentration resistance test, where a is immersion in 1.5wt% NaCl solution, b is immersion in 3.5wt% NaCl solution, and c is immersion in 5.5wt% NaCl solution; B is the acid and alkali resistance test, where d is immersion in strong acid, e is immersion in neutral, and f is immersion in strong alkali;

[0033] Figure 8 The universality test results of different coating substrates, a is a blank substrate, b is a substrate coated with ODA@TOCN@PDA, and c is a substrate coated with ODA@TOCN@PDA@EGCG;

[0034] Figure 9The adhesion morphologies of contaminants with different coatings are shown in Figure 2. a is the morphology of the blank iron sheet, b is the morphology of the iron sheet coated with ODA@TOCN@PDA, and c is the morphology of the iron sheet coated with ODA@TOCN@PDA@EGCG. DETAILED DESCRIPTION

[0035] The following is a detailed and complete description of the technical solutions in the specific embodiments of the present invention. Obviously, the described embodiments are only some specific implementation methods of the overall technical solution of the present invention, and are not all implementation methods. Based on the overall concept of the present invention, all other embodiments obtained by ordinary skill in the art are within the scope of protection of the present invention.

[0036] Determination method:

[0037] 1. Cellulose content of agar-agar: determined using the nitric acid-ethanol method.

[0038] 2. Potential of agar-agar nanocellulose: Agar-agar nanocellulose was prepared into a 0.06% (w / v) suspension using ultrapure water, subjected to ultrasonic treatment for 10 min, and measured using Zeta potential and nanoparticle size analysis.

[0039] 3. Contact angle of the coating: The coating was applied to a substrate (metal sheet), dried in an oven for 10 hours, and measured using a dynamic contact angle tester.

[0040] 4. Antibacterial activity of coatings: Leucobacter chromiireducens was used as the experimental strain, and the plate colony count method was used to calculate the antibacterial rate of different coating samples. All samples must be sterilized with high-temperature steam before testing, and then different samples are immersed in bacterial suspension (10 5 Cells were incubated at 28°C for 24 hours. Bacteria adhering to the sample surface were then flushed into 5 mL of LB broth. The LB broth containing the washed bacteria was then appropriately diluted, and 30 μL of the diluted solution was inoculated onto solid culture medium. After incubation at 28°C for 36 hours, the number of colonies on the culture medium was counted and compared with that of the untreated sample to calculate the antibacterial rate.

[0041] The present invention provides a method for preparing a Gelidium nanocellulose-based antifouling coating, comprising the following steps:

[0042] S1. mixing a choline chloride-carboxylic acid deep eutectic solvent with agar-agar residue and heating the mixture in an oil bath to obtain agar-agar cellulose;

[0043] S2, treating the agar-agar cellulose with cellulase enzymatic hydrolysis and TEMPO oxidation in sequence to obtain agar-agar nanocellulose;

[0044] S3, placing agar-agar nanocellulose and octadecylamine in a certain mass ratio in an ethanol aqueous solution and ultrasonically dissolving them, then adding a certain amount of dopamine hydrochloride, adjusting the pH value, and performing a heating reaction polymerization at a certain temperature and time by a "one-pot method" to obtain agar-agar nanocellulose-based super-hydrophobic coating;

[0045] S4. Finally, a certain amount of EGCG is added and stirred evenly to obtain agar-agar nanocellulose-based antifouling coating.

[0046] In the present invention, in step S1, after the oil bath heating, the following steps are further included: centrifugation to remove the supernatant, washing with deionized water several times to remove the residual solvent, and drying at 90°C.

[0047] In step S2, after the enzymatic hydrolysis treatment, the following steps are further included: centrifugation, washing with deionized water several times, collecting the precipitate, performing ultrasonic crushing treatment, and freeze-drying, wherein the conditions for the ultrasonic crushing treatment are: ultrasonic power of 150 W, working time of 2 s, pause time of 3 s, and ultrasonic time of 10 min.

[0048] The TEMPO oxidation treatment further includes the following steps: adding ethanol, dialysis to neutrality, and freeze-drying.

[0049] In step S3, after the heating reaction polymerization, the following steps are further performed: centrifugation at 8000 rpm for 20 minutes, washing several times with deionized water and anhydrous ethanol, and collecting the precipitate. In this step, the ethanol-water concentration used is 50%, and the ultrasonic dissolution conditions are: ultrasonic power of 350 W, ultrasonic frequency of 28 kHz, ultrasonic temperature of 30-50° C., and ultrasonic time of 30 minutes.

[0050] In step S4, before adding EGCG, the following steps are also included: adding anhydrous ethanol to the agar-agar nanocellulose-based super-hydrophobic coating and uniformly dispersing it by ultrasonication.

[0051] In a preferred embodiment of the present invention, in step S1, the mass ratio of the deep eutectic solvent to the agar-agar residue is 20:1;

[0052] The conditions for oil bath heating were: reaction temperature 100 °C, reaction time 3 h;

[0053] The low eutectic solvent is prepared by mixing choline chloride as a hydrogen bond acceptor with four carboxylic acids, namely acetic acid, lactic acid, oxalic acid and formic acid, as hydrogen bond donors in a certain molar ratio under anhydrous conditions and heating at 60°C for 2 hours. It is then screened by examining its effect on the cellulose content of agar-agar.

[0054] In a more preferred embodiment of the present invention, the deep eutectic solvent is prepared by mixing choline chloride and lactic acid in a molar ratio of 1:2 under anhydrous conditions and heating at 60° C. for 2 h.

[0055] In a preferred embodiment of the present invention, in step S2, the conditions for the enzymatic hydrolysis treatment are: an enzyme-substrate ratio of 10% w / w, an enzymatic hydrolysis pH of 4.8, an enzymatic hydrolysis temperature of 60° C., and an enzymatic hydrolysis time of 3 h.

[0056] In a preferred embodiment of the present invention, in step S2, the TEMPO oxidation method specifically comprises the following steps: placing 1 g of agar-agar cellulose nanofibrils obtained by enzymatic hydrolysis with cellulase in an anhydrous sodium carbonate / sodium bicarbonate buffer solution, adding 0.017 g of TEMPO and 0.115 g of sodium bromide, stirring until fully dissolved, then adding a certain specific volume of sodium hypochlorite, adjusting the system to a certain pH value with sodium hydroxide solution and glacial acetic acid solution, and performing an oxidation reaction for a certain time;

[0057] Among them, the specific volume of sodium hypochlorite, pH value of the oxidation system and oxidation reaction time were optimized through single-factor experiments with the yield and potential of agar-agar nanocellulose as indicators.

[0058] In the present invention, the ratio of the buffer solution to the agar-agar cellulose nanofibrils is 100:1 mL / g, the mass ratio of anhydrous sodium carbonate to sodium bicarbonate in the buffer solution is 2:1, and the pH value of the solution is 10.

[0059] In a more preferred embodiment of the present invention, the optimal process conditions of the TEMPO oxidation method are: the specific volume of sodium hypochlorite is 11 mL / g, the pH value of the oxidation system is 10.5, and the oxidation reaction time is 24 h.

[0060] In a preferred embodiment of the present invention, in step S3, the mass ratio of agar-agar nanocellulose to octadecylamine, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride, the polymerization temperature and the polymerization time are obtained by single-factor optimization using the contact angle of the coating as an indicator.

[0061] In a more preferred embodiment of the present invention, the optimal process conditions of the one-pot process are: the mass ratio of agar-agar nanocellulose to octadecylamine is 1:2, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride is 1:2, the polymerization reaction temperature is 50° C., and the polymerization reaction time is 16 h.

[0062] In a preferred embodiment of the present invention, in step S4, the amount of EGCG added is screened by examining its effect on the contact angle and antibacterial activity of the coating.

[0063] In a more preferred embodiment of the present invention, the mass proportion of EGCG is 2% of the mass of the agar-agar nanocellulose-based super-hydrophobic coating.

[0064] The technical solution of the present invention is further described and illustrated below based on specific embodiments.

[0065] Example 1

[0066] Reference Figure 1 A method for preparing a Gelidium nanocellulose-based antifouling coating comprises the following steps:

[0067] S1. A choline chloride-carboxylic acid deep eutectic solvent and agar-agar residue were mixed in a mass ratio of 20:1, heated in an oil bath, and reacted at 100° C. for 3 h. After the reaction, the supernatant was removed by centrifugation, and the mixture was washed three times with deionized water to remove the residual solvent, and dried at 90° C. to obtain agar-agar cellulose.

[0068] Among them, the deep eutectic solvent is prepared by mixing choline chloride as a hydrogen bond acceptor with four carboxylic acids, acetic acid, lactic acid, oxalic acid, and formic acid, as hydrogen bond donors, at molar ratios of 1:2, 1:2, 1:1, and 1:2 under anhydrous conditions and heating at 60°C for 2 hours. The cellulose of agar-agar was prepared according to the method of step S1 above and was screened by examining its effect on the cellulose content of agar-agar. The results are recorded in Table 1.

[0069] Table 1 Cellulose content of agar-agar residue treated with different types of deep eutectic solvents

[0070]

[0071] As shown in Table 1, the cellulose content extracted from the deep eutectic solvent composed of choline chloride and lactic acid after heating with agar-agar residue oil bath is the highest. Therefore, the deep eutectic solvent prepared by mixing choline chloride and lactic acid in a molar ratio of 1:2 under anhydrous conditions and heating at 60°C for 2h was selected as the optimal deep eutectic solvent for subsequent experiments.

[0072] S2. The agar-agar cellulose is sequentially treated with cellulase enzymatic hydrolysis and TEMPO oxidation to obtain agar-agar nanocellulose.

[0073] Among them, the cellulase enzymatic hydrolysis treatment specifically includes the following steps: dispersing the agar-agar cellulose into ultrapure water through ultrasonic treatment, and after uniform dispersion, adding cellulase to the system at an enzyme-substrate ratio of 10% w / w, adjusting the pH of the system to 4.8, and enzymolyzing at 60°C for 3 hours. After the enzymatic hydrolysis is completed, centrifuging, washing with deionized water 3 times, collecting the precipitate, and ultrasonically crushing it with an ultrasonic power of 150W, with a working time of 2 seconds, a pause time of 3 seconds, and an ultrasonic time of 10 minutes, and freeze-drying to obtain agar-agar cellulose nanofibrils.

[0074] The TEMPO oxidation treatment specifically includes the following steps: placing 1 g of agar-agar cellulose nanofibrils obtained by cellulase enzymatic hydrolysis in 100 mL of anhydrous sodium carbonate / sodium bicarbonate buffer solution (the mass ratio of anhydrous sodium carbonate to sodium bicarbonate is 2:1, and the solution pH is 10), adding 0.017 g of TEMPO and 0.115 g of sodium bromide, stirring until fully dissolved, then adding a certain volume of sodium hypochlorite, adjusting the system to a certain pH value with sodium hydroxide solution and glacial acetic acid solution, and carrying out an oxidation reaction for a certain time. At the end of the reaction, 5 mL of ethanol is added to terminate the reaction, dialyzed to neutrality, and freeze-dried;

[0075] Among them, the specific volume of sodium hypochlorite, pH value of the oxidation system and oxidation reaction time were optimized through single-factor experiments with the yield and potential of agar-agar nanocellulose as indicators.

[0076] The screening step of the oxidation reaction time includes: under the conditions of a fixed specific volume of sodium hypochlorite of 11 mL / g and a pH value of the oxidation system of 10.5, adjusting the oxidation reaction time to 18 h, 20 h, 22 h, 24 h, and 26 h, respectively, preparing agar-agar nanocellulose according to the method of step S2 above, and measuring the yield and potential of agar-agar nanocellulose. The results are recorded in Figure 2 A.

[0077] like Figure 2 As shown in A, the best effect of oxidation reaction time on the yield and potential of agar-agar nanocellulose is 24 h.

[0078] The pH screening step of the oxidation system includes: under the conditions of a fixed volume of sodium hypochlorite of 11 mL / g and an oxidation reaction time of 24 h, adjusting the pH of the oxidation system to 9, 9.5, 10, 10.5, and 11, respectively, preparing agar-agar nanocellulose according to the method of step S2 above, and measuring the yield and potential of agar-agar nanocellulose. The results are recorded in Figure 2 B.

[0079] like Figure 2 As shown in B, the pH value of the oxidation system has the best effect on the yield and potential of agar-agar nanocellulose, with 10.5 being the best.

[0080] The screening step of the specific volume of sodium hypochlorite includes: under the conditions of a fixed oxidation system pH of 10.5 and an oxidation reaction time of 24 hours, adjusting the specific volume of sodium hypochlorite to 7 mL / g, 9 mL / g, 11 mL / g, 13 mL / g, and 15 mL / g, respectively, preparing agar-agar nanocellulose according to the method of step S2 above, and measuring the yield and potential of agar-agar nanocellulose. The results are recorded in Figure 2 C.

[0081] like Figure 2As shown in C, the optimal volume ratio of sodium hypochlorite on the yield and potential of agar-agar nanocellulose is 11 mL / g.

[0082] Therefore, the present invention analyzes the influence of various parameters on the yield and potential of agar-agar nanocellulose through single-factor experiments, selects the specific volume of sodium hypochlorite as 11 mL / g, the pH value of the oxidation system as 10.5, and the oxidation reaction time as 24 h as the optimal process conditions for TEMPO oxidation method, and conducts subsequent experiments.

[0083] S3. Place agar-agar nanocellulose and octadecylamine in a certain mass ratio in a 50% ethanol aqueous solution and ultrasonically dissolve them. The ultrasonic power is 350 W, the ultrasonic frequency is 28 kHz, the ultrasonic temperature is 30°C, and the ultrasonic time is 30 min. Then, a certain mass of dopamine hydrochloride is added, and the pH value is adjusted to 8.5. The reaction is heated and polymerized at a certain temperature and time using a "one-pot method". The mixture is centrifuged at 8000 rpm for 20 min, washed three times with deionized water and anhydrous ethanol, and the precipitate is collected to obtain agar-agar nanocellulose-based superhydrophobic coating.

[0084] Among them, the mass ratio of agar-agar nanocellulose to octadecylamine, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride, the polymerization reaction temperature and the polymerization reaction time were obtained through single-factor experimental optimization using the contact angle of the coating as an indicator.

[0085] The screening step of the mass ratio of agar-agar nanocellulose to octadecylamine includes: under the conditions of a fixed mass ratio of agar-agar nanocellulose to dopamine hydrochloride of 1:2, a polymerization reaction temperature of 50°C, and a polymerization reaction time of 16h, respectively adjusting the mass ratio of agar-agar nanocellulose to octadecylamine to 1:0.5, 1:1, 1:1.5, 1:2, and 1:2.5, preparing agar-agar nanocellulose-based superhydrophobic coating according to the method of step S3 above, and measuring the contact angle of the coating. The results are recorded in Figure 3 A.

[0086] like Figure 3 As shown in A, the optimal mass ratio of agar-agar nanocellulose to octadecylamine on the hydrophobic effect of agar-agar nanocellulose-based coating is 1:2.

[0087] The screening step of the mass ratio of agar-agar nanocellulose to dopamine hydrochloride includes: under the conditions of a fixed mass ratio of agar-agar nanocellulose to octadecylamine of 1:2, a polymerization reaction temperature of 50°C, and a polymerization reaction time of 16h, adjusting the mass ratio of agar-agar nanocellulose to dopamine hydrochloride to 1:0.5, 1:1, 1:1.5, 1:2, and 1:2.5, respectively, preparing agar-agar nanocellulose-based superhydrophobic coating according to the method of step S3 above, and measuring the contact angle of the coating. The results are recorded in Figure 3 B.

[0088] like Figure 3 As shown in B, the optimal mass ratio of agar-agar nanocellulose to dopamine hydrochloride on the hydrophobic effect of agar-agar nanocellulose-based coating is 1:2.

[0089] The step of screening the polymerization reaction temperature includes: fixing the mass ratio of agar-agar nanocellulose to octadecylamine at 1:2, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride at 1:2, and the polymerization reaction time at 16 h, adjusting the polymerization reaction temperature to 30°C, 40°C, 50°C, 60°C, and 70°C, respectively, preparing agar-agar nanocellulose-based superhydrophobic coating according to the method of step S3 above, and measuring the contact angle of the coating. The results are recorded in Figure 3 C.

[0090] like Figure 3 As shown in Figure C, the best polymerization temperature for the hydrophobic effect of agar-agar nanocellulose-based coatings is 50°C.

[0091] The screening step of the polymerization reaction time includes: fixing the mass ratio of agar-agar nanocellulose to octadecylamine at 1:2, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride at 1:2, and the polymerization temperature at 50°C, adjusting the polymerization reaction time to 10h, 12h, 14h, 16h, and 18h, respectively, preparing the agar-agar nanocellulose-based superhydrophobic coating according to the method of step S3 above, and measuring the contact angle of the coating. The results are recorded in Figure 3 D.

[0092] like Figure 3 As shown in D, the best polymerization time for the hydrophobic effect of agar-agar nanocellulose-based coatings is 16 h.

[0093] Therefore, the present invention analyzes the influence of various parameters on the contact angle of the coating through single-factor experiments, selects the mass ratio of agar-agar nanocellulose to octadecylamine of 1:2, the mass ratio of agar-agar nanocellulose to dopamine hydrochloride of 1:2, the polymerization reaction temperature of 50°C, and the polymerization reaction time of 16h as the optimal process conditions for the one-pot method, and conducts subsequent experiments.

[0094] S4. Add anhydrous ethanol to the agar-agar nanocellulose-based super-hydrophobic coating, disperse it evenly through ultrasonication, and finally add a certain amount of EGCG and stir evenly to obtain the agar-agar nanocellulose-based antifouling coating.

[0095] The amount of EGCG added was prepared according to the method of step S4 above, and the effect of the mass proportion of EGCG on the contact angle and antibacterial activity of the agar-agar nanocellulose-based super-hydrophobic coating was screened by examining the effect of the mass proportion of EGCG on the contact angle and antibacterial activity of the coating when the mass proportion of EGCG was 0%, 1%, 2%, 4%, and 8%. The results are recorded in Tables 2 and Figure 4-5 .

[0096] Table 2 Colony counts and antibacterial rates of samples with different EGCG addition amounts

[0097]

[0098] from Figure 4 It can be seen that the optimal range of EGCG addition on the hydrophobic effect of agar-agar nanocellulose-based coatings is 1-4%. Figure 5 It can be seen that the optimal range of EGCG addition for the antibacterial effect of agar-agar nanocellulose-based coatings is 2-8%. Overall, 2% EGCG addition is the best.

[0099] Application performance testing

[0100] (1) Self-cleaning performance

[0101] The agar-agar nanocellulose-based antifouling coating (denoted as ODA@TOCN@PDA@EGCG) prepared under the optimal process conditions in Example 1 and the agar-agar nanocellulose-based superhydrophobic coating (denoted as ODA@TOCN@PDA) prepared without adding EGCG were drop-coated on an iron sheet with a thickness of 0.6 mm × a width of 2.5 cm × a length of 8 cm to check its self-cleaning performance, using sand and chalk dust to simulate pollutants. The iron sheet coated with the antifouling coating was tilted in a culture dish and covered with sand and chalk dust in a random pattern. The sand and chalk dust on the iron sheet were rinsed with a syringe, and the process of pollutants on the sample surface being washed away by water droplets was recorded by taking pictures.

[0102] The results are as follows Figure 6 As shown, water can easily roll off the glass surface with sand and chalk dust, and sand and chalk dust can roll off the glass surface, indicating that the synthesized coating has significant self-cleaning properties.

[0103] (2) Chemical stability

[0104] The ODA@TOCN@PDA@EGCG and ODA@TOCN@PDA prepared under the optimal process conditions in Example 1 were tested in terms of acid and alkali resistance and salt ion resistance.

[0105] Salt Ion Resistance: Coated iron sheets were immersed in 1.5%, 3.5%, and 5.5% NaCl solutions for three days. The iron sheets were then removed, rinsed with distilled water, and dried (approximately 3 minutes). The contact angle of a 3 μL water droplet on the surface was then measured.

[0106] The results are as follows Figure 7 As shown in A, the water contact angle of the coating hardly changes after being immersed in solutions with different NaCl concentrations for 3 days, and the coating maintains good non-wetting properties.

[0107] Acid and Alkali Resistance: The coated iron sheet was immersed in solutions of pH 1, pH 7, and pH 13. After 3 days, the iron sheet was removed, rinsed with distilled water, and dried (approximately 3 minutes). The contact angle of a 3 μL water droplet on the surface was then measured.

[0108] The results are as follows Figure 7 As shown in B, the results show that after immersion in strong acid, neutral and strong alkaline solutions for 3 days, the water contact angle of the coating has almost no change, and the coating maintains good non-wetting properties.

[0109] (3) Universality

[0110] ODA@TOCN@PDA@EGCG and ODA@TOCN@PDA, prepared under the optimal conditions in Example 1, were drop-coated onto five different substrates: glass, iron sheet, A4 paper, cotton, and filter paper. The samples were then dried in an oven for 10 hours. Four different liquids, including Sprite, milk, coffee, and barley tea, were then added with 5 μL drops, and the results were recorded by photographing.

[0111] The results are as follows Figure 8 As shown, the coatings on different substrates maintain good liquid-repellent properties for different liquids.

[0112] (4) Antifouling effect

[0113] An indoor hanging board test was used to evaluate the antifouling effect of ODA@TOCN@PDA@EGCG and ODA@TOCN@PDA prepared under the optimal process conditions in Example 1. The seawater used in this experiment was taken from Changle District, Fuzhou City, Fujian Province. The coating was applied on an iron sheet with a thickness of 0.6mm, a width of 2.5cm, and an 8cm width. Before immersion in seawater, a clear mark was made to record the original state. Natural seawater was added to a transparent pool. The coated sample was placed vertically in a glass pool and allowed to soak. After one month, photos were taken to record the changes in the coating surface.

[0114] The results are as follows Figure 9 As shown, after one month, the blank iron sheet was covered with rust and had a lot of stains on the surface. The coating surface of the coating without ECGG was heavily stained, while the coating surface of the coating with the agar-agar nanocellulose-based antifouling coating of the present invention had less stains.

[0115] In summary, the present invention has the following advantages:

[0116] (1) The deep elution solvent (DES) method was used to extract agar-agar cellulose. This method significantly reduced the impact on the environment, avoided the pollution problems that may be caused by traditional chemical solvents, and embodied the concept of green chemistry.

[0117] (2) By using the combined enzymatic hydrolysis-TEMPO oxidation technology and precisely controlling the specific volume of sodium hypochlorite, the pH value of the oxidation system, and the oxidation reaction time, the extracted agar-agar cellulose can be efficiently converted into agar-agar nanocellulose, which has a nanoscale size and more active groups, opening up new possibilities for the industrial application of cellulose-based coatings.

[0118] (3) A one-pot process was adopted to successfully prepare a super-hydrophobic coating with a surface microstructure by precisely controlling the polymerization ratio of nanocellulose to octadecylamine and dopamine hydrochloride, and optimizing the temperature and time of the polymerization reaction. The super-hydrophobic coating can effectively repel water and dirt and achieve a self-cleaning effect, thereby reducing the cleaning frequency and maintenance costs, bringing convenience to users.

[0119] (4) The natural antifouling agent EGCG is innovatively introduced. It is derived from plants and is environmentally friendly. The resulting coating not only has super-hydrophobic properties, but also effectively prevents the adhesion of dirt, grease and microorganisms, has self-cleaning properties, and has good acid, alkali and salt ion resistance. In the indoor hanging board experiment, the agar-agar nanocellulose-based antifouling coating of the present invention showed an excellent antifouling effect.

[0120] The agar-agar nanocellulose-based antifouling coating of the present invention not only demonstrates the advantages of high efficiency and environmental friendliness in its preparation process, but also achieves excellent antifouling properties such as super-hydrophobicity, self-cleaning, acid and alkali resistance, and salt resistance. These characteristics give the invention broad application prospects in the field of environmentally friendly materials, providing strong technical support for achieving green chemistry and sustainable development goals.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a Gelidium nanocellulose-based antifouling coating, comprising the following steps: S1. mixing a choline chloride-carboxylic acid deep eutectic solvent with agar-agar residue and heating the mixture in an oil bath to obtain agar-agar cellulose; The deep eutectic solvent is prepared by mixing choline chloride and lactic acid in a molar ratio of 1:2 under anhydrous conditions and heating at 60° C. for 2 h; S2, sequentially subjecting the agar-agar cellulose to enzymatic hydrolysis with cellulase and TEMPO oxidation to obtain agar-agar nanocellulose; The TEMPO oxidation method specifically comprises the following steps: placing 1 g of agar-agar cellulose nanofibrils obtained by enzymatic hydrolysis of the cellulase in an anhydrous sodium carbonate / sodium bicarbonate buffer solution, adding 0.017 g of TEMPO and 0.115 g of sodium bromide, stirring until fully dissolved, then adding sodium hypochlorite with a specific volume of 11 mL / g, adjusting the pH value of the system to 10.5 with sodium hydroxide solution and glacial acetic acid solution, and performing an oxidation reaction for 24 hours; S3, ultrasonically dissolving the agar-agar nanocellulose and octadecylamine in an ethanol aqueous solution at a mass ratio of 1:2, adding dopamine hydrochloride, wherein the mass ratio of the agar-agar nanocellulose to the dopamine hydrochloride is 1:2, adjusting the pH value, and heating and polymerizing the agar-agar nanocellulose at 50° C. for 16 hours by a "one-pot method" to obtain agar-agar nanocellulose-based super-hydrophobic coating; S4. Finally, add EGCG accounting for 2% by weight of the agar-agar nanocellulose-based super-hydrophobic coating and stir evenly to obtain the agar-agar nanocellulose-based antifouling coating.

2. The method for preparing the agar-agar nanocellulose-based antifouling coating according to claim 1, wherein: In step S1, the mass ratio of the deep eutectic solvent to the agar-agar residue is 20:1; The oil bath heating conditions are: reaction temperature is 100° C., and reaction time is 3 h.

3. The method for preparing the agar-agar nanocellulose-based antifouling coating according to claim 1, wherein: In step S2, the conditions for the enzymatic hydrolysis treatment are: enzyme-substrate ratio of 10% w / w, enzymatic hydrolysis pH of 4.8, enzymatic hydrolysis temperature of 60° C., and enzymatic hydrolysis time of 3 h.

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