Seawater degradation coating as well as preparation method and application thereof

Abstract

The invention belongs to the field of marine aquaculture, particularly relates to a seawater degradation coating film, and further relates to a preparation method of the seawater degradation coating film and application of the seawater degradation coating film in marine aquaculture. The seawater degradation coating comprises the biodegradable resin, the seawater degradation accelerant and the surface hydrolysis inhibitor, and the components and the dosage ratio of the components are adjusted, so that the film has good stability in a storage environment, can be disintegrated according to an expected time period in the marine aquaculture process and is finally completely degraded, and the service life of the film is prolonged. Therefore, labor cost is reduced, and environmental pollution is reduced.

Description

Technical Field

[0001] This invention belongs to the field of marine aquaculture, specifically relating to a seawater-degradable coating material for marine aquaculture, its preparation method and application. Background Technology

[0002] Modern marine aquaculture extensively uses polymer materials, which, while increasing the supply of marine products, has also brought about serious white pollution problems. Replacing traditional non-degradable materials (such as polyethylene and polyvinyl chloride) with seawater-degradable materials is considered the most effective way to balance aquaculture and environmental protection. Unlike traditional daily-use (land-based) biodegradable plastics, the high salinity, temperature fluctuations, strong hydrodynamics, and microbial community structure and activity in the marine environment, which differ significantly from composting systems, prevent terrestrial biodegradable plastics from degrading smoothly in the marine environment, thus making them unsuitable for direct application in marine aquaculture. Existing technologies have proposed some solutions, such as CN109942949A, CNN116426099A, CN112625414A, CN120699332A, and CN116836522A. These solutions use ordinary biodegradable plastics or starch as a base, combined with various additives to improve the biodegradability of polymer materials in seawater and regulate their degradation rate. However, the products provided by these existing technologies are also terrestrial polymer products (such as packaging bags), and the focus is on improving their seawater degradation ability to solve the problem of marine white pollution. They do not realize that when such materials are used directly in marine aquaculture, there are no requirements on the changes in the mechanical properties of the materials and the degradation time, or the degradation cycle is often long and wide-ranging.

[0003] Unlike structural materials such as plastic bags, bottles, or plastic sheets and pipes, the polymer membrane materials used in marine aquaculture not only need to utilize the mechanical properties of the material itself to fix or protect aquatic products (especially their larvae), but also require the material to provide functional support for the growth of aquatic products and improve the convenience of harvesting finished aquatic products. Taking mussel farming as an example, the traditional artificial farming method is to manually put mussel larvae into synthetic fiber net bags and fix them to farming ropes. Synthetic fiber net bags are difficult to degrade and harm the marine ecosystem, and the negative impact on the nearshore waters where aquaculture is located is far greater than the white pollution in the open sea. In addition, the process of manually loading and fixing mussel larvae, as well as manually catching and harvesting them after they grow, is cumbersome, labor-intensive, costly, and inefficient. Even using known seawater-degradable plastics to make net bags or plastic bags cannot solve this problem.

[0004] Therefore, there is an urgent need for existing technologies to develop seawater-degradable polymer materials specifically for marine aquaculture. These materials should be suitable for mechanized aquaculture operations, support the fixation and growth of marine aquatic seedlings, and, through seawater degradation, avoid environmental pollution and reduce the labor intensity of aquaculture harvesting, thereby improving the sustainability of aquaculture. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a seawater-degradable coating, which is particularly suitable for marine aquaculture, including but not limited to mussel seedling cultivation, seaweed seedling cultivation, and fish fry net / cage coating, and can support mechanized operations; the seawater-degradable coating has good stability in the storage environment, and when used for marine aquaculture coating, it can disintegrate and eventually degrade completely within the expected time period, thereby reducing labor costs and reducing environmental pollution.

[0006] Specifically, the seawater-degradable coating provided by the present invention is a film prepared from seawater-degradable resin, wherein each 100 parts by weight of the seawater-degradable resin comprises the following components: 70-95 parts of biodegradable resin, 8-20 parts of seawater degradation promoter 0.3–1 part of surface hydrolysis inhibitor, The biodegradable resin is selected from one or more of the following polymer materials: polylactic acid (PLA), polybutylene terephthalate (PBAT), polybutylene succinate (PBS), polybutylene terephthalate (PBST), polybutylene glycol succinate (PBSG), polybutylene lactate (PBSL), polyesteramide (PEA), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and modified versions of the above polymer materials; The seawater degradation promoter comprises a non-enzymatic hydrolysis degradation promoter and an enzymatic hydrolysis degradation promoter; the non-enzymatic hydrolysis degradation promoter is selected from one or more combinations of the following components: calcium sulfate, calcium carbonate, calcium oxide, calcium hydroxide, preferably calcium oxide and / or calcium carbonate. The enzymatic hydrolysis degradation promoter is selected from one or more of the following components: alginate oligosaccharides, trehalose, β-cyclodextrin, sodium alginate, sucrose, glucose, fructose, pectin, and amino acids. The surface hydrolysis inhibitor includes polyethylene wax.

[0007] Traditional biodegradable resins are generally used only as structural materials, and their practicality often revolves around mechanical properties (especially stability), which is usually contradictory to rapid degradation. This invention, by using a specific biodegradable resin as a matrix and clearly regulating the mechanical properties at different time stages, creatively proposes a combination of seawater degradation promoters and surface hydrolysis inhibitors in a specific ratio, thereby effectively resolving this contradiction in seed coating products.

[0008] Specifically, during the storage phase before use, it is desirable for the membrane material to maintain its moisture-proof properties and prevent degradation, while retaining the required mechanical strength before reaching a preset breakage point. However, once the set breakage point is reached, it is desirable for the coating to rapidly lose its mechanical properties and begin to break. Subsequently, the coating fragments should degrade as quickly as possible in seawater, thereby achieving an effective balance between performance and environmental friendliness. By rationally adjusting these key points, practicality and environmental friendliness can be organically combined during the use of the coating material. Based on this, to better adapt to the marine aquaculture environment, this invention creatively combines biodegradable resin with seawater degradation promoters and surface hydrolysis inhibitors in a specific ratio to form a uniformly distributed, open-pore seawater-degradable coating, thereby achieving a balance between storage stability and timed disintegration in the seawater environment.

[0009] In a further preferred embodiment, the biodegradable resin is selected from one or more combinations of the group consisting of: polybutylene terephthalate (PBAT), polybutylene succinate (PBS), and polyesteramide (PEA). The content of the biodegradable resin is not particularly limited relative to 100 parts by weight of seawater-degradable resin, but the lower limit is 70 parts, preferably 85 parts, and more preferably 88 parts; the upper limit is 95 parts, preferably 92 parts, and more preferably 90 parts.

[0010] The seawater degradation promoter of this invention uses calcium oxide as its main active ingredient. Ordinary biodegradable resin-based plastic products (such as land-based plastic bags) often use inorganic fillers such as calcium carbonate, which mainly serve as physical fillers and reduce costs. In this invention, by adding seawater degradation promoters such as calcium oxide and / or calcium hydroxide, an alkaline catalytic hydrolysis effect is achieved on the biodegradable resin. As calcium oxide and / or calcium hydroxide gradually decompose upon contact with water, more defects are formed in the seawater degradation coating, accelerating its physical breakdown process, thereby initiating and accelerating the subsequent biodegradation process. By creating an alkaline microenvironment around the calcium oxide and / or calcium hydroxide particles, particularly conducive to the growth of degradation microorganisms that prefer alkaline environments, the degradation (biodegradation, mineralization) efficiency of the seawater degradation coating can be further improved, ultimately achieving complete degradation.

[0011] In this invention, by adjusting the ratio of biodegradable resin to seawater degradation promoter, the disintegration time of the seawater degradation coating can be effectively controlled, so as to match the aquaculture cycle of marine aquatic products. This achieves effective fixation of seedlings in the early stage of coating and does not hinder the growth and development of aquatic products in the middle and later stages.

[0012] In a preferred embodiment, the ratio of biodegradable resin to seawater degradation accelerator by weight is preferably 10-19:1, more preferably 12-18:1. Excessive use of the seawater degradation accelerator leads to rapid disintegration of the seawater degradation coating, making it unable to withstand physical and temperature shocks such as weather changes, thus failing to effectively fix the seedlings. Insufficient use results in slow disintegration of the seawater degradation coating, which has an adverse effect on the growth and volume increase of marine aquatic products.

[0013] The seawater degradation promoter of the present invention comprises a non-enzymatic hydrolysis promoter and an enzymatic hydrolysis promoter.

[0014] The non-enzymatic hydrolysis accelerator is mainly composed of calcium oxide, calcium hydroxide, or a combination of both, and may optionally include other inorganic powders selected from calcium carbonate and calcium sulfate. The content of these other inorganic powders in the seawater degradation accelerator is preferably less than 15 parts by weight, more preferably less than 5 parts by weight, based on 100 parts by weight of the seawater degradation accelerator. In one preferred embodiment, the seawater degradation accelerator comprises only calcium oxide and / or calcium hydroxide; in another preferred embodiment, the seawater degradation accelerator comprises only calcium hydroxide; and in a further preferred embodiment, the seawater degradation accelerator comprises only calcium oxide.

[0015] The enzymatic hydrolysis promoter is an organic nutrient. Adding organic nutrients promotes the attachment of seawater microorganisms to the coating surface, thereby accelerating the biodegradation process of the biodegradable resin. The type of organic nutrient is not particularly limited, but considering both microbial attachment and growth and the nutritional needs of marine aquatic organisms, the enzymatic hydrolysis promoter is selected from one or more of the following components: alginate oligosaccharides, trehalose, β-cyclodextrin, sodium alginate, sucrose, glucose, fructose, pectin, and amino acids. Preferably, it is a combination of one or more of alginate oligosaccharides, trehalose, sucrose, glucose, fructose, and pectin. In a preferred embodiment, the weight ratio of calcium oxide and / or calcium hydroxide to organic nutrients in the seawater degradation promoter is preferably 8–9.5:1, more preferably 9–9.5:1. Excessive organic nutrient content leads to rapid disintegration and decreased mechanical strength of the marine aquatic coating; insufficient content fails to promote microbial attachment.

[0016] Simply combining biodegradable resin with seawater degradation promoters such as calcium oxide can lead to undesirable pre-use degradation under conventional storage conditions, especially in coastal environments with high air humidity. In severe cases, this can cause the seawater-degradable coating to lose its necessary physical strength during storage, rendering it unsuitable for automated mechanical production. To address this, this invention creatively proposes further incorporating a surface hydrolysis inhibitor into the seawater-degradable coating. This not only enables long-term preservation of the coating but also inhibits initial hydrolysis and regulates its disintegration time. The surface hydrolysis inhibitor is primarily composed of polyethylene wax. A co-extrusion process (interfacial effects, rheological properties, etc.) allows specific surface hydrolysis inhibitors to migrate outwards and coat the film surface. The greater the coating, the later the film enters the hydrolysis stage. Calcium oxide, as a degradation promoter, is uniformly dispersed within the film.

[0017] In a preferred embodiment, the ratio of biodegradable resin to surface hydrolysis inhibitor by weight is preferably 18-28:1, more preferably 20-24:1. Insufficient surface hydrolysis inhibitor will not effectively inhibit the disintegration of the seawater degradation coating under storage conditions; excessive inhibitor will hinder the short-term disintegration of the seawater degradation coating, thereby affecting the growth and development of marine aquatic products.

[0018] The surface hydrolysis inhibitor of the present invention is mainly composed of polyethylene wax, and may optionally include paraffin wax and / or beeswax. The content of paraffin wax and / or beeswax in the surface hydrolysis inhibitor is preferably less than 10 parts by weight, more preferably less than 6 parts by weight, and even more preferably less than 1 part by weight, based on 100 parts by weight of the surface hydrolysis inhibitor; in a preferred embodiment, the surface hydrolysis inhibitor comprises only polyethylene wax.

[0019] This invention relates to a seawater-degradable coating, prepared from seawater-degradable resin using a casting or blown film process. The specific thickness of the coating should be determined based on the application scenario and seawater environment. In one embodiment, the seawater-degradable coating has a thickness of 10-10000 μm, preferably 20-2000 μm. When the coating thickness is less than 10 μm, it does not possess the desired mechanical properties and is prone to breakage due to insufficient strength during mechanized coating operations, affecting continuous production. When the coating thickness exceeds 10000 μm, there is a risk of a low overall disintegration rate and incomplete degradation.

[0020] The seawater-degradable coating has uniformly distributed pores. This pore structure ensures that aquatic seedlings can fully exchange with the outside seawater during coating, obtaining sufficient oxygen and moisture, while preventing seedling leakage. In a preferred embodiment, the pores have a pore size of 10–100,000 μm, preferably 50–2,000 μm, and a pore density of 10–10,000 pores / cm³. 2 10-2000 pieces / cm (preferred) 2.

[0021] The present invention further relates to a method for preparing the aforementioned seawater degradation coating. In one embodiment, the preparation method includes the following steps: S01. The biodegradable resin, seawater degradation accelerator, and surface hydrolysis inhibitor are melt-plasticized according to the specified dosage ratio to obtain the seawater degradable resin. It should be noted that the seawater degradation accelerator can be a composition obtained by pre-mixing inorganic powder and organic nutrients, or it can be added separately by adding inorganic powder and organic nutrients.

[0022] S02. Prepare a thin film from seawater-degradable resin using casting or blown film processes; S03. At the same time as or after step S02, uniformly distributed openings are formed on the film.

[0023] In a preferred embodiment, in step S01, it is preferable to thoroughly mix the raw materials before melt plasticizing. More preferably, after step S03, the prepared seawater-degradable coating is rolled up according to specifications for use in a subsequent seedling machine.

[0024] In a preferred embodiment, the barrel temperature of the melt plasticizing process is 165-180°C, and the die head temperature is 185°C.

[0025] In a preferred embodiment, step S03 forms an opening by laser drilling, mechanical needle punching, and / or adding a foaming agent.

[0026] The present invention further relates to a shellfish seedbed prepared using the aforementioned seawater-degradable coating, the shellfish seedbed comprising a culture rope, a shellfish seedling layer attached to the culture rope, and a seawater-degradable coating covering the shellfish seedling layer.

[0027] Beneficial effects 1. Suitable for mechanization: The seawater-degradable coating of the present invention is very suitable for continuous operation of existing automated seedling wrapping machines, which greatly improves seedling wrapping efficiency and reduces labor costs.

[0028] 2. No need for secondary removal: The seawater degradable film of this invention has a controllable degradation cycle in seawater (about 20 days). After the mussel seedlings' byssal threads are firmly attached to the aquaculture rope, the film breaks down and degrades on its own, eliminating the tedious step of manually removing the net bag and saving a lot of labor costs.

[0029] 3. Environmentally friendly: The seawater-degradable coating material of this invention is a fully degradable material, and the final degradation products are CO2 and water, with no harmful residues, fundamentally solving the marine pollution problem caused by traditional seedling net bags.

[0030] 4. Ensuring seedling survival rate: The seawater-degradable coating of this invention has a unique open-pore design, which ensures the exchange of gas and water required for seedling respiration during the seedling period and avoids death due to suffocation. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the seawater degradation coating of the present invention (including openings).

[0032] Figure 2 This is a schematic diagram of the seawater degradation coating state of the mussel seedlings (showing the mussel seedlings wrapped in the coating and the aquaculture rope).

[0033] Figure 3 This is a schematic diagram of the state of the seawater degradation membrane of the present invention after degradation (showing the mussel seedlings attaching and the membrane breaking down before starting to degrade and disappear). Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] Example 1 80 parts (by weight, the same below) of PBAT resin, 15 parts of calcium hydroxide, and 4 parts of polyethylene wax were mixed and fed into a blown film extruder with melt plasticizing function. The mixture was melt-extruded at a barrel temperature of 160–180°C and a die temperature of 185°C to obtain a tubular film with a thickness of approximately 30 μm. The cooled film was then perforated using a laser perforation device, resulting in a pore diameter of approximately 50 μm and a pore density of approximately 500 pores / cm². 2 Then, roll up the prepared film.

[0036] Testing: The prepared film was subjected to rapid seawater degradation and disintegration mechanical testing, according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets"; the mechanical indicators for determining whether the coating has begun to break down are: tensile strength retention rate ≤ 50% and elongation at break retention rate ≤ 70%. The results are shown in Table 1.

[0037] The prepared coating was installed into the seedling machine for operation, and the coated mussel seedling bed was placed in the target sea area at a suitable temperature (17-20℃) for cultivation. The survival rate and growth status of the mussels are shown in Table 2.

[0038] Example 2 Based on Example 1, calcium hydroxide was replaced with calcium oxide to obtain a coating. The rest was the same as in Example 1.

[0039] Example 3 Based on Example 1, 4 parts of trehalose were added to prepare a coating, and the rest was the same as in Example 1.

[0040] Example 4 75 parts PBS resin, 15 parts premixed calcium hydroxide, 9 parts pectin, and 1 part polyethylene wax were mixed and melt-blended in a twin-screw extruder at a screw temperature of 165–180°C. The mixture was then cast onto cooling rollers at 25–28°C to obtain a flat film with a thickness of approximately 30 μm. The cooled film was then perforated using a laser perforation device, resulting in pores with a diameter of approximately 50 μm and a pore density of approximately 500 pores / cm². 2 Then, roll up the prepared film.

[0041] The rapid degradation and disintegration mechanical tests of the prepared coating in seawater are shown in Table 1, and the survival rate and growth status of mussels are shown in Table 2.

[0042] Example 5 Based on Example 1, the PBAT resin was replaced with PCL resin to obtain a coating, and the rest was the same as in Example 1.

[0043] Comparative Example 1 Based on Example 2, without the addition of calcium oxide, a coating was prepared, and the rest was the same as in Example 2.

[0044] Comparative Example 2 Based on Example 2, calcium oxide was replaced with calcium carbonate to obtain a coating, and the rest was the same as in Example 2.

[0045] Comparative Example 3 Based on Example 2, the amount of calcium oxide added was adjusted from 5 parts to 4.5 parts to obtain a coating, and the rest was the same as in Example 2.

[0046] Comparative Example 4 Based on Example 2, the amount of calcium oxide added was adjusted from 5 parts to 9 parts to obtain a coating, and the rest was the same as in Example 2.

[0047] Comparative Example 5 Based on Example 3, without the addition of polyethylene wax, a coating was prepared, and the rest was the same as in Example 3.

[0048] Comparative Example 6 Based on Example 3, the amount of polyethylene wax added was adjusted from 4 parts to 2 parts to obtain a coating, and the rest was the same as in Example 3.

[0049] Comparative Example 7 Based on Example 3, the amount of polyethylene wax added was adjusted from 4 parts to 6 parts to obtain a coating, and the rest was the same as in Example 3.

[0050] Table 1. Detection of rapid degradation and disintegration mechanics in seawater Table 2. Growth Status of Mussels Cultivated with Seedling Coating See Table 1: The coating materials of Examples 1 to 4 of the present invention can all disintegrate at a set break-down time of about 20 days. Even Example 5 can disintegrate within 30 days, demonstrating that the coating materials of the present invention have excellent controlled degradation performance.

[0051] Example 2, which replaced the calcium hydroxide in Example 1 with calcium oxide, exhibited a shorter disintegration time. This is because calcium oxide absorbs water and releases heat upon contact with water, forming calcium hydroxide, which releases heat in a localized reaction, thereby further increasing the disintegration rate. This makes calcium oxide a suitable choice for rapid disintegration and degradation.

[0052] Further comparison of Examples 2 and 3 with Comparative Examples 1 and 2 shows that by using calcium hydroxide and / or calcium oxide as seawater degradation promoters, the degradation process of the coating can be effectively accelerated.

[0053] As can be seen from Examples 2 and Comparative Examples 3 and 4, by reasonably adjusting the ratio of seawater degradation promoters, the degradation time of the coating material can be more precisely controlled to around 20 days.

[0054] Based on this, as can be seen from Examples 3 and Comparative Examples 5-7, the combination of surface hydrolysis inhibitor and seawater degradation promoter, by reasonably adjusting the dosage of the former, can more precisely regulate the degradation time of the coating material, while effectively inhibiting hydrolysis in the early stage and maintaining the mechanical properties of the coating, thereby improving storage stability.

[0055] See Table 2: Comparing the various embodiments with Comparative Examples 4-6, it can be seen that if the mechanical properties of the membrane decline too quickly or break down too early within the first 10 days, the membrane will not provide sufficient support and protection for the mussels, thereby reducing the adhesion of the byssal threads and the survival rate of the mussels.

[0056] Further comparison of the various embodiments with Comparative Examples 3 and 7 shows that setting the fragmentation window around 20 days is most conducive to the growth of mussels, while a delayed fragmentation time will significantly inhibit the healthy growth of mussels.

[0057] In summary, the above embodiments and comparative examples demonstrate that the coating material of the present invention can regulate the time window of fragmentation, disintegration and degradation at multiple levels, and can achieve a balance between the mechanical performance requirements of the seedling aquaculture film and marine environmental protection.

[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A seawater degradable coating characterized by, The seawater-degradable coating film is a film prepared from a seawater-degradable resin, wherein the seawater-degradable resin comprises, per 100 parts by weight, the following components: 70-95 parts of a biodegradable resin, 8-20 parts of a seawater-degradation promoter, 0.3-1 part of a surface hydrolysis inhibitor, The biodegradable resin is selected from one or a combination of two or more of the following high molecular materials: polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate terephthalate (PBST), polybutylene succinate-glycolate (PBSG), polybutylene succinate-lactate (PBSL), polyester amide (PEA), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and modified products of the above high molecular materials. The seawater-degradation promoter comprises a non-enzymatic hydrolytic degradation promoter and an enzymatic hydrolytic degradation promoter; the non-enzymatic hydrolytic degradation promoter is selected from one or a combination of two or more of the following components: calcium sulfate, calcium carbonate, calcium oxide, calcium hydroxide; the enzymatic hydrolytic degradation promoter is selected from one or a combination of two or more of the following components: alginate oligosaccharide, trehalose, β-cyclodextrin, sodium alginate, sucrose, glucose, fructose, pectin, amino acid, The surface hydrolysis inhibitor comprises polyethylene wax.

2. The marine water degradable coating of claim 1, wherein, The biodegradable resin is selected from one or a combination of two or more of the following high molecular materials: polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyester amide (PEA).

3. The marine water degradable coating of claim 1, wherein, The seawater-degradation promoter comprises calcium oxide and / or calcium hydroxide.

4. The sea water degradable coating of claim 1, wherein, The weight ratio of the biodegradable resin to the seawater-degradation promoter is 10-19:

1.

5. The sea water degradable coating of claim 1, wherein, The seawater-degradation promoter optionally contains organic nutrients selected from one or a combination of two or more of the following components: alginate oligosaccharide, trehalose, sucrose, glucose, fructose, pectin.

6. The sea water degradable coating of claim 1, wherein, The weight ratio of the biodegradable resin to the surface hydrolysis inhibitor is 18-28:

1.

7. The sea water degradable coating of claim 1, wherein, The seawater-degradable coating film has a thickness of 10-10,000 µm.

8. The sea water degradable coating of claim 1, wherein, The seawater degradation coating has uniformly distributed through holes in the thickness direction of the coating, the aperture of the through holes is 10-50000 μm, and the hole density is 10-10000 per cm 2 .

9. The method of claim 1 to 8, wherein the seawater-degradable coating is prepared by the steps of: The method comprises the following steps: S01, melting and plasticizing the biodegradable resin, the seawater-degradation promoter, and the surface hydrolysis inhibitor according to the amount ratio to obtain the seawater-degradable resin; S02, preparing a film from the seawater-degradable resin by a flow casting or film blowing process; S03, forming uniformly distributed openings on the film at the same time or after step S02.

10. A shellfish seed bed, comprising a culture rope, a shellfish seed layer attached to the culture rope, and a seawater-degradable coating film wrapping the shellfish seed layer, wherein the seawater-degradable coating film is the seawater-degradable coating film according to any one of claims 1-8 or is prepared by the method according to claim 9.

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