A multi-layer controlled degradation coating composition and its preparation method and application

Abstract

The present invention discloses a multi-layer controlled degradation coating composition, a preparation method and an application thereof, and belongs to the field of biodegradable polymer materials and coating compositions. The coating composition comprises an outer protective layer and an inner functional layer, the inner functional layer being arranged between a substrate and the outer protective layer and comprising a plurality of microcapsules. The key innovation is that the microcapsules encapsulate an enzyme capable of catalytically degrading the outer protective layer and are configured to be released after a predetermined delay time. By integrating a pH buffer system in the inner functional layer, an optimal catalytic microenvironment is created for the released enzyme, thereby actively and rapidly degrading the outer protective layer and realizing programmable time-controlled removal. The present invention solves the problem that the degradation rate of existing biodegradable materials is passive and uncontrollable, and by giving the coating a unique two-stage degradation characteristic, it has significant application value in the field of seed coating or fertilizer controlled release.

Description

Technical Field

[0001] The invention belongs to the field of biodegradable polymer materials and coating compositions, and particularly relates to a multi-layer controllably degradable coating composition, a preparation method thereof, and an application thereof. Background Art

[0002] Functional coatings and polymer compositions are core components of modern materials science, with applications ranging from industrial protection and biomedicine to consumer electronics. In recent years, with increasing attention to environmental sustainability and "end-of-life" issues, the development of "smart" polymer materials and coating compositions with controllable degradation properties has become a research hotspot. An ideal smart coating should provide stable and reliable performance throughout its intended service life and degrade upon activation by a specific signal, thereby avoiding long-term environmental residues and facilitating subsequent disposal.

[0003] Among numerous application scenarios, the agricultural sector is particularly in need of such smart coatings. Coating seeds and fertilizer granules is a mature technology, primarily intended to protect the core matrix and regulate the release of active substances (such as nutrients and pesticides). Traditionally, inert petroleum-based polymers have been used as coating materials, but their long-term residue in the soil has led to serious microplastic pollution. To this end, the industry has begun turning to biodegradable polymer compositions, such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA), as alternative materials. For example, patent application publication number WO2020242871A1 discloses a technical solution using a blend of PLA and PHA as a biodegradable coating for seeds and fertilizers.

[0004] However, all current biodegradable coating compositions, whether single components or blends, face a common, fundamental challenge: their degradation process is passive, with the rate completely dependent on unpredictable external environmental factors such as soil moisture, temperature, pH, and the type and number of microbial populations. This passive degradation mode leads to "out-of-control" coating performance, meaning that the coating failure time cannot be precisely matched to actual needs.

[0005] It's worth noting that a common passive regulation approach uses a polymer blend as a coating, such as the aforementioned WO2020242871A1. The mechanism of action is that when the coating is exposed to moisture, one of the more easily hydrolyzed or soluble components (such as PHA) gradually leaches from the coating, leaving micron- or nanometer-scale pores in the other, more stable polymer matrix (such as PLA). The core substance is slowly released through these passively formed pores. This "passive pore formation" principle is essentially a physical control method, and its pore formation rate and pore structure are highly dependent on the temperature and humidity of the external environment, making its release profile difficult to accurately predict and program. This fundamentally differs from the "active triggering" mode of action of the present invention, which uses pre-encapsulated enzymes to actively and rapidly chemically catalyze the decomposition of the entire outer protective layer at a predetermined time point.

[0006] On the basis of the existing technical difficulties, a new regulatory challenge is reshaping the future of related industries. On September 25, 2023, the European Commission adopted Regulation (EU) 2023 / 2055, which clearly restricts the deliberate addition of synthetic polymer particles to products. The regulation requires that polymers used in fields such as agriculture must be able to be proven to be biodegradable, otherwise they will be banned from sale. This new regulation places an unprecedented requirement on coating compositions: not only must they be degradable, but they must also degrade quickly and completely within a set time that is compatible with the application cycle. Existing passive degradation technologies have failed to perfectly address this emerging regulatory challenge.

[0007] In summary, there is a long-standing unmet technical need in the prior art: to develop a new type of polymer coating composition that must simultaneously meet the requirements of complete biodegradation, provide effective protection for a defined duration, and have a programmable, actively triggered rapid degradation function. Summary of the Invention

[0008] The purpose of the present invention is to provide a multi-layer controlled degradation coating composition and a preparation method and application thereof, so as to solve the problems raised in the above background technology.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A multi-layer controlled degradation coating composition having well-defined physical and performance parameters, which, when applied to a substrate, simultaneously satisfies all of the following defined parameters:

[0011] When the coating composition is applied to the substrate, its total weight is 1-10% of the weight of the substrate core; controlling the total coating weight within this range, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, can ensure adequate protection and functional effects while avoiding affecting the substrate function or increasing unnecessary costs due to excessive coating thickness.

[0012] The coating composition exhibits a two-stage degradation profile in a simulated soil solution at 25°C, comprising an initial protection period lasting 10-60 days, during which the coating loses no more than 10% of its weight; and a subsequent rapid degradation period, during which the coating loses more than 80% of its weight within 7-15 days after the initial protection period. This unique two-stage degradation profile is a core advantage of the present invention. The initial protection period ensures effective protection of the substrate, while the subsequent rapid degradation period ensures that the coating quickly disappears after completing its protective mission. The duration of the protection period can be precisely controlled by adjusting the formulation of the microcapsule wall material.

[0013] The coating composition includes: an outer protective layer comprising a first biodegradable polymer material; and an inner functional layer disposed below the outer protective layer, the inner functional layer comprising a hydrogel matrix and a plurality of microcapsules dispersed therein; wherein the microcapsules encapsulate an enzyme capable of degrading the first biodegradable polymer material, and the microcapsules are configured to release the enzyme after a predetermined delay time.

[0014] The first biodegradable polymer material is selected from PHA, PLA, or a blend thereof. When the first biodegradable polymer material is a blend, the weight ratio of PLA to PHA can be 40:60 to 60:40, for example, 40:60, 45:55, 50:50, 55:45, or 60:40, to balance the material's mechanical strength and degradation properties. The PHA can be poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), or poly-3-hydroxybutyrate-co-4-hydroxybutyrate (P3HB4HB). Those skilled in the art will appreciate that while PHBV is primarily used as a representative material for the outer protective layer in the specific embodiments of the present invention, the core concept of the present invention, namely, catalyzing the degradation of the outer protective layer through enzymes released from the inner layer, is also applicable to PHB and P3HB4HB. This is because these three polymers belong to the family of polyhydroxyalkanoates, and their molecular main chains are all composed of ester bonds that can be hydrolyzed, and they are generally sensitive to the hydrolases such as lipase and esterase selected in the present invention. The difference between them lies mainly in the difference in side chain structure, which more affects the physical properties and degradation rate of the material such as crystallinity, flexibility, melting point, etc., without changing its chemical nature that can be enzymatically degraded. Therefore, according to specific application scenarios, for example, when different requirements are made for the mechanical strength or degradation rate of the coating, those skilled in the art can replace PHBV with PHB or P3HB4HB within the framework disclosed in the present invention, and adaptively adjust the process parameters. This is a conventional technical means and does not require creative work.

[0015] The inner functional layer is formed by cross-linking an aqueous solution of alginate and a pH buffer at a concentration of 1-4% (w / v) and a divalent cation solution at a concentration of 2-10% (w / v). The key role of the pH buffer is that when the microcapsule wall material, such as PLGA, is hydrolyzed to release acidic degradation products, it can actively neutralize these acids, thereby stably maintaining the pH value of the inner functional layer within a range that is favorable for the catalytic activity of the encapsulated enzyme, such as pH 6.0-8.5, preferably pH 7.0-8.0. This design ensures that the enzyme can immediately exert its most efficient catalytic function after being released, thereby achieving rapid degradation of the outer protective layer. The pH buffer can be selected from the biocompatible buffer systems conventionally used in the art, such as phosphate buffer system PBS, Tris-HCl buffer system, HEPES buffer system or a combination thereof, and its concentration is sufficient to provide sufficient buffering capacity. The alginate concentration range is, for example, 1% (w / v), 1.2% (w / v), 1.5% (w / v), 1.8% (w / v), 2% (w / v), 2.2% (w / v), 2.5% (w / v), 2.8% (w / v), 3% (w / v), 3.2% (w / v), 3.5% (w / v), 3.8% (w / v) or 4% (w / v), ensuring that a hydrogel layer with a complete structure and a certain mechanical strength can be formed to effectively immobilize microcapsules and buffers. The divalent cation solution is, for example, a calcium chloride solution with a concentration of 2% (w / v), 2.5% (w / v), 3% (w / v), 4% (w / v), 5% (w / v), 6% (w / v), 7% (w / v), 8% (w / v), 9% (w / v) or 10% (w / v).

[0016] The wall material of the microcapsule is poly(lactic acid-glycolic acid) copolymer, wherein the molar ratio of lactic acid to glycolic acid is 50:50 to 85:15. By adjusting this molar ratio, the hydrolysis rate of the wall material can be precisely controlled, thereby setting the release delay time of the enzyme. For example, a molar ratio of 85:15 can correspond to a delay period of about 60 days, a molar ratio of 75:25 can correspond to a delay period of about 30 days, and a more hydrophilic molar ratio of 50:50 can shorten the delay period to about 15 days. The specific molar ratio can be selected from 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20 or 85:15.

[0017] To achieve effective enzymatic degradation, the weight ratio of the encapsulated enzyme to the wall material is 1:3 to 1:10, such as 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10. This ratio ensures that the microcapsules contain a sufficient concentration of enzyme to quickly initiate degradation of the outer protective layer after release.

[0018] Alternatively, the wall material of the microcapsule is a protein-polysaccharide complex solidified by a crosslinking agent, wherein the protein is selected from gelatin or zein, and the polysaccharide is selected from gum arabic or alginate. This provides a low-cost, all-natural, green packaging solution with no volatile organic compound emissions. Those skilled in the art will appreciate that by adjusting the concentration of the crosslinking agent or the crosslinking reaction time, the crosslinking density of the complex microcapsule wall can be effectively controlled, thereby accurately programming the predetermined delayed release time of the enzyme. For example, increasing the amount of crosslinking agent or extending the crosslinking time will result in a denser wall material structure, thereby obtaining a longer delayed release period. The crosslinking agent is glutaraldehyde.

[0019] The enzyme is selected from PHA degrading enzymes, lipases, esterases or proteases.

[0020] The method for preparing the multi-layer controlled degradation coating composition comprises the following steps:

[0021] Step 1. Preparation of enzyme-loaded microcapsules;

[0022] Step 2. The aqueous solution of the pH buffer and the aqueous solution of the alginate are mixed to form a mixed aqueous solution, and the microcapsules prepared in Step 1 are dispersed in the mixed aqueous solution at a solid content of 1-10 wt %, for example, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt % or 10 wt %, to form an inner layer slurry;

[0023] Step 3. cross-linking the inner layer slurry formed in step 2 with the divalent cation solution to form the inner functional layer;

[0024] Step 4. A water-based emulsion or solution containing the first biodegradable polymer material at a concentration of 5-15wt%, such as 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%, or a melt thereof is applied onto the inner functional layer to form an outer protective layer after drying.

[0025] In step 1, the microcapsules can be prepared by any of the following methods:

[0026] Method 1: using a water-in-oil-in-water double emulsion method, wherein the enzyme is used as the inner aqueous phase, the organic solution of polylactic acid-glycolic acid copolymer is used as the oil phase, and the polyvinyl alcohol aqueous solution is used as the outer aqueous phase;

[0027] Method 2: The protein-polysaccharide complex coacervation method is used, wherein the enzyme, protein and polysaccharide are dissolved in an aqueous phase, and the pH value is adjusted to induce complex coacervation to form microcapsules.

[0028] The coating composition is suitable for the fields of seed coating or fertilizer controlled release.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] Programmable Active Degradation Design: This invention elevates the design of polymer compositions from passive environmental response to active program control. By precisely designing the microcapsule wall material formulation, the coating's degradation initiation time can be pre-set, achieving active and predictable failure, eliminating reliance on uncontrollable environmental factors.

[0031] Efficient and rapid material removal: Once the internal enzymes are released, they can quickly catalyze the decomposition of the outer protective layer, ensuring that the coating material can be quickly and completely removed from the substrate, solving the problem of slow and incomplete degradation of traditional biodegradable materials.

[0032] Excellent environmental compatibility and green production process: The preparation process preferably utilizes a complex coacervation method that eliminates volatile organic compound emissions, making it environmentally friendly. Its rapid and complete degradation effectively prevents the formation of persistent microplastic residues in the environment, making this polymer composition compliant with increasingly stringent global environmental regulations, particularly the EU's microplastics ban.

[0033] Functional integration and synergistic enhancement: The multi-layer structure of the present invention is cleverly designed. The inner functional layer can not only serve as a carrier of the degradation trigger, but also carry other functional components, thus achieving multifunctional integration and synergistic enhancement. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the present embodiment are all commercially available industrial products or can be prepared by conventional methods. Performance test methods, unless otherwise specified, are carried out in accordance with the standards described in the summary of the invention.

[0035] Main reagents and raw materials:

[0036] Table 1 Chemical name, CAS number, specification, PDI and source of main reagents and raw materials:

[0037]

[0038] Main analytical testing instruments:

[0039] Fluidized bed coater: Wurster GPCG 1.1, Glatt;

[0040] High shear homogenizer: T 25 digital ULTRA-TURRAX, IKA;

[0041] High-pressure homogenizer: APV-2000, SPX Flow;

[0042] Freeze dryer: Alpha 1-2 Ldplus, Christ;

[0043] Constant temperature shaking incubator: ZWYR-240, Labwit;

[0044] Gel permeation chromatography: GPC, Waters 1515-2414;

[0045] UV-visible spectrophotometer: UV-2600, Shimadzu;

[0046] Universal testing machine: Instron 5967;

[0047] Microplate reader: BioTek Synergy H1;

[0048] Cell culture incubator: Thermo Fisher Scientific.

[0049] Main test standards:

[0050] ASTM D638-22: Standard Test Method for Tensile Properties of Plastics;

[0051] ISO 10993-5:2023: Biological evaluation of medical devices-Part 5: Tests for in vitro cytotoxicity;

[0052] ISO 17556:2019: Plastics-Determination of the ultimate aerobicbiodegradability of plastic materials in soil by measuring the oxygen demand in a respirometer or the amount of carbon dioxide evolved.

[0053] Preparation of simulated soil solution: Refer to OECD Guideline 201 (2024 adopted version) standards, without algae.

[0054] Preparation of PHBV water-based emulsion:

[0055] The PHBV water-based emulsion used in the present invention is prepared by an environmentally friendly solvent-free high-energy homogenization method, and the specific steps are as follows:

[0056] S1. Dissolve 1 g of polyvinyl alcohol (PVA) in 200 ml of deionized water and heat to 80°C as the aqueous phase.

[0057] S2. Melt 10 g of PHBV powder or granules at 175°C.

[0058] S3. Slowly add the molten PHBV prepared in S2 to the hot water phase of S1 in a high shear homogenizer at a speed of 10,000 rpm and continue shearing for 10 minutes to form a coarse emulsion.

[0059] S4. Immediately transfer the hot crude emulsion to a high-pressure homogenizer preheated to 80°C and circulate homogenization at a pressure of 80-100 MPa for 5-8 times.

[0060] S5. Cool the homogenized emulsion to room temperature while stirring to obtain a stable, milky white PHBV water-based emulsion with a solids content of approximately 5 wt%. Store sealed at 4°C until further use. If desired, the emulsion can be concentrated to a higher solids content by ultrafiltration or other methods.

[0061] Example

[0062] Example 1: A coating composition with a 30-day delayed release function was prepared and applied to a seed matrix.

[0063] The preparation method of the coating composition described in this embodiment comprises the following steps:

[0064] Step 1. Prepare enzyme-loaded microcapsules: Dissolve 100 mg of lipase in 1 mL of pH 7.4 phosphate buffer. Dissolve 500 mg of PLGA (LA:GA = 75:25) in 5 mL of dichloromethane. Add the enzyme solution to the PLGA solution and emulsify using a high-shear homogenizer to form a w / o colostrum. Add this colostrum to 100 mL of an aqueous solution containing 1% (w / v) PVA and homogenize again to form a w / o / w double emulsion. Stir at room temperature for 4 hours to allow the dichloromethane to evaporate. After the PLGA solidifies, collect the microspheres by centrifugation, wash, and freeze-dry for later use. The weight ratio of enzyme to PLGA wall material is now 1:5.

[0065] Step 2. Prepare the inner layer slurry: First, prepare a buffered sodium alginate solution, i.e., a 2% (w / v) sodium alginate solution and a 20 mM phosphate buffer solution. For example, this can be achieved by dissolving an appropriate amount of phosphate buffer saline (PBS) powder, adjusting the pH to 7.4, and dissolving it in 100 ml of deionized water. Then, approximately 5 grams of the enzyme-loaded PLGA microspheres prepared in step 1 are evenly dispersed in the above-mentioned buffered sodium alginate solution. At this point, the solid content of the microcapsules is 5 wt%. Note: In all examples based on PLGA microcapsules in this specification, unless otherwise specified, the inner layer slurry is prepared using this buffer-containing formula to ensure optimal enzyme activity.

[0066] Step 3. Forming the inner functional layer: 100 grams of corn seeds were used as the matrix core and placed in a fluidized bed coater. The inner layer slurry prepared in Step 2 was sprayed onto the seed surface. Subsequently, a 5% (w / v) calcium chloride solution was sprayed to crosslink and solidify the alginate layer, forming the inner functional layer.

[0067] Step 4. Forming an Outer Protective Layer: The PHBV water-based emulsion prepared according to the above method, adjusted to a 10 wt% solids content as needed, is sprayed onto the inner functional layer. A dry airflow allows the emulsion to form a film, forming an outer protective layer. Finally, the coated seeds are dried at 40°C to a final coating weight of approximately 5% of the seed weight.

[0068] Example 2: Preparation of a coating composition with a 15-day delayed release function.

[0069] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 1, PLGA (LA:GA=50:50) is used as the microcapsule wall material.

[0070] Example 3: Preparation of a coating composition with a 60-day delayed release function.

[0071] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 1, PLGA (LA:GA=85:15) is used as the microcapsule wall material.

[0072] Example 4: Verification of the outer protective layer blend weight ratio endpoint 40:60.

[0073] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 4, a blend of PLA and PHBV with a weight ratio of 40:60 is used as the outer protective layer material.

[0074] Example 5: Verification of the outer protective layer blend weight ratio endpoint 60:40.

[0075] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 4, a blend of PLA and PHBV with a weight ratio of 60:40 is used as the outer protective layer material.

[0076] Example 6: Verification of the coating total weight gain endpoint of 1%.

[0077] The preparation method of this embodiment is basically the same as that of Example 1, except that the spraying amount of step 3 and step 4 is adjusted so that the final coating weight gain is controlled to 1% of the seed weight.

[0078] Example 7: Verify that the total weight gain endpoint of the coating is 10%.

[0079] The preparation method of this embodiment is basically the same as that of Example 1, except that the spraying amount of step 3 and step 4 is adjusted so that the final coating weight gain is controlled to 10% of the seed weight.

[0080] Example 8: Verification of the lower limit of alginate concentration in the inner functional layer to 1% (w / v).

[0081] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 2, 100 ml of 1% (w / v) sodium alginate aqueous solution is used to prepare the inner layer slurry.

[0082] Example 9: Verification of the upper limit of alginate concentration in the inner functional layer to 4% (w / v).

[0083] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 2, 100 ml of a 4% (w / v) sodium alginate aqueous solution is used to prepare the inner layer slurry.

[0084] Example 10: Verification of the lower limit of the cross-linking cation concentration of the inner functional layer at 2% (w / v).

[0085] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 3, a 2% (w / v) calcium chloride solution is used for cross-linking and curing.

[0086] Example 11: Verification of the upper limit of the cross-linking cation concentration of the inner functional layer at 10% (w / v).

[0087] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 3, a 10% (w / v) calcium chloride solution is used for cross-linking and curing.

[0088] Example 12: Application of the coating composition to a fertilizer substrate.

[0089] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 3, 100 grams of commercially available compound fertilizer granules are used as the matrix core.

[0090] Example 13: Verification of the endpoint of the enzyme to wall material weight ratio of 1:3.

[0091] The preparation method of this embodiment is substantially the same as that of embodiment 1, except that in step 1, 167 mg of lipase and 500 mg of PLGA (LA:GA=75:25) are used, so that the weight ratio of enzyme to wall material is 1:3.

[0092] Example 14: Verification of the endpoint of the enzyme to wall material weight ratio of 1:10.

[0093] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 1, 50 mg of lipase and 500 mg of PLGA (LA:GA=75:25) are used, so that the weight ratio of enzyme to wall material is 1:10.

[0094] Example 15: Verification of the microcapsule solid content endpoint 1 wt%.

[0095] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 2, 1 gram of enzyme-loaded PLGA microspheres is dispersed in 100 milliliters of a 2% sodium alginate aqueous solution so that the solid content in the sodium alginate aqueous solution is 1 wt %.

[0096] Example 16: Verification of the microcapsule solid content endpoint of 10 wt%.

[0097] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 2, 10 g of enzyme-loaded PLGA microspheres are dispersed in 100 ml of a 2% sodium alginate aqueous solution so that the solid content in the sodium alginate aqueous solution is 10 wt %.

[0098] Example 17: Preparation of protein-based microcapsules using medium cross-linking density.

[0099] The preparation method of this embodiment is basically the same as that of Example 1, with the only difference being that in step 1, the enzyme-loaded microcapsules are prepared by the protein-polysaccharide complex coacervation method, as follows: 100 mg of lipase is dissolved in 5 ml of deionized water, and then 500 mg of gelatin is added and heated to 40° C. to dissolve it completely. Under stirring, 500 mg of gum arabic is dissolved in 10 ml of deionized water and slowly added dropwise to the gelatin-enzyme mixed solution. Dilute hydrochloric acid is used to adjust the pH of the system to 4.0 to induce complex coacervation. The system is cooled to below 10° C. in an ice-water bath, and then, under continuous stirring, 2.5 ml of a 0.25% (w / v) glutaraldehyde aqueous solution is slowly added dropwise, which is equivalent to adding about 6.25 mg of glutaraldehyde per gram of wall material, and the reaction is continued for 1 hour for cross-linking and curing. The microspheres are collected by centrifugation, washed, and freeze-dried for standby use.

[0100] Example 18: Verification of worst case combination.

[0101] This embodiment is intended to verify the technical robustness of the present invention when multiple key parameters are simultaneously in the extreme or "worst" combination conditions defined in the claims.

[0102] The preparation method of this embodiment is basically the same as that of Example 1, but at the same time combines the following three boundary conditions from different embodiments:

[0103] Microcapsule wall material: PLGA (LA:GA=85:15) used in Example 3 was adopted to achieve the longest target delay period of about 60 days.

[0104] Weight ratio of enzyme to wall material: The setting in Example 14 was adopted, that is, in step 1, 50 mg of lipase and 500 mg of PLGA were used to make the weight ratio of enzyme to wall material the lowest 1:10.

[0105] Total coating weight gain: The settings in Example 6 were adopted, that is, in steps 3 and 4, the spraying amounts of the slurry and emulsion were precisely controlled so that the final coating weight gain was controlled to a minimum of 1% of the seed weight.

[0106] All other parameters, such as the inner functional layer alginate concentration (2% (w / v)), the cross-linking cation concentration (5% (w / v)), etc., were kept consistent with Example 1. Finally, a coated seed sample prepared under the worst-case combination of parameters was obtained.

[0107] Example 19: Protein-based microcapsules with lower cross-linking density to achieve shorter delayed release.

[0108] The preparation method of this example is essentially the same as the revised Example 17, with the only difference being the cross-linking and curing step: After cooling the system in an ice-water bath, 1.5 ml of a 0.25% (w / v) glutaraldehyde aqueous solution (equivalent to approximately 3.75 mg of glutaraldehyde per gram of wall material) is slowly added dropwise. The reaction is continued for one hour to effect cross-linking and curing. This lower amount of cross-linking agent is intended to produce a microcapsule wall with a lower cross-linking density, thereby achieving a shorter delayed release time.

[0109] Example 20: Protein-based microcapsules with higher cross-linking density to achieve longer delayed release.

[0110] The preparation method of this example is essentially the same as the revised Example 17, with the only difference being the crosslinking and curing step: After cooling the system in an ice-water bath, 5.0 ml of a 0.25% (w / v) glutaraldehyde aqueous solution (equivalent to approximately 12.5 mg of glutaraldehyde per gram of wall material) is slowly added dropwise. The reaction is continued for one hour to effect crosslinking and curing. This higher amount of crosslinker is intended to produce a microcapsule wall with a higher crosslink density, thereby achieving a longer delayed release time.

[0111] Comparative Example

[0112] Comparative Example 1: A coating containing only a PHBV outer protective layer (without active degradation function).

[0113] 100 g of corn seeds were directly sprayed with the PHBV water-based emulsion prepared according to the above method in a fluidized bed coater. The solid content of the emulsion was 10 wt %, forming a single-layer coating. No inner functional layer or enzyme microcapsules were provided.

[0114] Comparative Example 2: Coating containing unencapsulated enzyme (no delayed release).

[0115] The preparation method of this comparative example is basically the same as that of Example 1, except that in step 2, 100 mg of unencapsulated lipase powder is directly mixed with the sodium alginate aqueous solution instead of the enzyme-loaded microcapsules.

[0116] Comparative Example 3: The outer protective layer blend weight ratio is out of the range of 30:70.

[0117] The preparation method of this comparative example is basically the same as that of Example 1, except that in step 4, a blend of PLA and PHBV with a weight ratio of 30:70 is used as the outer protective layer material.

[0118] Comparative Example 4: The outer protective layer blend weight ratio is out of the range of 70:30.

[0119] The preparation method of this comparative example is basically the same as that of Example 1, except that in step 4, a blend of PLA and PHBV with a weight ratio of 70:30 is used as the outer protective layer material.

[0120] Comparative Example 5: The total weight gain of the coating exceeded the range by 0.5%.

[0121] The preparation method of this comparative example is basically the same as that of Example 1, except that the spraying amount of step 3 and step 4 is adjusted so that the final coating weight gain is controlled at 0.5wt% of the seed weight.

[0122] Comparative Example 6: The total weight gain of the coating exceeded the range by 12%.

[0123] The preparation method of this comparative example is basically the same as that of Example 1, except that the spraying amount of step 3 and step 4 is adjusted so that the final coating weight gain is controlled at 12 wt % of the seed weight.

[0124] Comparative Example 7: The alginate concentration in the inner functional layer is lower than the lower limit of 0.5% (w / v).

[0125] The preparation method of this comparative example is basically the same as that of Example 1, with the only difference being that in step 2, 100 ml of 0.5% (w / v) sodium alginate aqueous solution is used to prepare the inner layer slurry.

[0126] Comparative Example 8: The alginate concentration in the inner functional layer is higher than the upper limit of 5% (w / v).

[0127] The preparation method of this comparative example is basically the same as that of Example 1, except that in step 2, 100 ml of 5% (w / v) sodium alginate aqueous solution is used to prepare the inner layer slurry.

[0128] Comparative Example 9: The cross-linking cation concentration of the inner functional layer is lower than the lower limit of 1% (w / v).

[0129] The preparation method of this comparative example is basically the same as that of Example 1, with the only difference being that in step 3, a 1% (w / v) calcium chloride solution is used for cross-linking and curing.

[0130] Comparative Example 10: The cross-linking cation concentration of the inner functional layer is higher than the upper limit of 12% (w / v).

[0131] The preparation method of this comparative example is basically the same as that of Example 1, with the only difference being that in step 3, a 12% (w / v) calcium chloride solution is used for cross-linking and curing.

[0132] Table 2 Example formulations are summarized as follows:

[0133]

[0134] Table 3 comparative example formulations are summarized as follows:

[0135]

[0136] Application Examples

[0137] Application example 1: Study on in vitro degradation of coating and plant growth efficacy.

[0138] The coated seeds and uncoated seeds prepared in all the examples and comparative examples were subjected to in vitro degradation tests and greenhouse pot experiments.

[0139] In vitro degradation: The samples were placed in a simulated soil solution and incubated at 25°C with shaking, and the coating weight loss was measured regularly.

[0140] Greenhouse potted plants: Planted under the same soil and irrigation conditions, the seed germination rate, seedling height and root length were observed and recorded within 60 days.

[0141] Table 4 Application Example 1 The experimental results of the coating in vitro degradation and plant growth efficacy study are as follows:

[0142]

[0143] The results in Table 4 intuitively demonstrate the comprehensive effect of the technical solution of the present invention. All Examples 1-20 successfully achieved the preset protection period and the subsequent rapid degradation period, and the seed germination rate and later growth indicators, such as plant height and root length, all performed well. This is in sharp contrast to the control group: Control Examples 1 and 4 inhibited plant growth due to coating residues; Control Example 2 resulted in germination failure; and the remaining control examples were insufficiently protected or inhibited from germination due to reasons such as the coating being too thin, too thick, or the inner and outer layer structures being poor. This series of comparative data strongly proves that the parameter range defined by the present invention is necessary and effective for achieving the core function of "protection first, degradation later."

[0144] Application Example 2: Evaluation of coating mechanical properties (ASTM D638-22).

[0145] Purpose: To provide quantitative data for the mechanical properties of coatings and to objectively evaluate the effects of different formulations on the strength and toughness of coatings.

[0146] Method: Prepare independent film samples of the coating compositions described in Examples 1, 4, 5 and Comparative Examples 3, 8, 9, and 10. Perform tensile tests on a universal testing machine according to ASTM D638-22.

[0147] Table 5 The test results of the mechanical properties evaluation of the coating in Application Example 2 are as follows:

[0148]

[0149] The mechanical property data in Table 5 provide quantitative support for the coating's physical robustness. The formulations of Examples 1, 4, and 5 all exhibit balanced tensile strength and elongation at break, demonstrating that the coatings are both sufficiently robust to withstand the stresses of handling and seeding, while also possessing a degree of toughness to prevent brittle cracking. In contrast, Comparative Example 3 suffers from insufficient strength due to its low PLA content, while Comparative Examples 8 and 9 suffer from compromised overall mechanical properties due to inappropriate formulations of the inner functional layer. These data demonstrate the importance of the outer protective layer blend ratio and inner functional layer preparation parameters in achieving ideal mechanical properties.

[0150] Application Example 3: Coating Biocompatibility Evaluation (ISO 10993-5:2023).

[0151] Purpose: To provide preliminary evidence for the biocompatibility of the product and to evaluate its environmental safety.

[0152] Method: Referring to ISO 10993-5 standard, the MTT method was used to perform an in vitro cytotoxicity test on L929 mouse fibroblasts using the extract of the final coating product prepared in Example 1.

[0153] Table 6 The test results of the coating biocompatibility evaluation of Application Example 3 are as follows:

[0154]

[0155] The cytotoxicity test results in Table 6 are key proof of product safety. According to the ISO 10993-5 standard, a cell viability of more than 75% is generally considered to be non-cytotoxic or extremely low in toxicity. The sample extract of Example 1 of the present invention, even at a concentration of 100%, still has a cell viability of 96.5%, corresponding to a toxicity rating of Level 1. After dilution, it is completely non-toxic, corresponding to a toxicity rating of Level 0. This shows that the coating composition of the present invention and its degradation products have excellent biocompatibility, are safe to the environment and organisms, and meet the application requirements of green and environmentally friendly materials.

[0156] Application example 4: Verification of coating biodegradability and compliance with EU regulations.

[0157] This experiment was conducted to verify the ultimate biodegradability of the coating composition of the present invention in a soil environment and to evaluate whether it complies with the exemption requirements for biodegradable polymers in EU Regulation (EU) 2023 / 2055.

[0158] Test sample: The complete coated seeds prepared in Example 1 were selected, and the coating portion thereof was carefully peeled off and crushed to serve as the test material.

[0159] Test method: According to ISO 17556:2019 “Determination of the ultimate aerobic biodegradability of plastics in soil - Method using measurement of oxygen consumption or carbon dioxide production”, the test was carried out in a controlled simulated soil environment.

[0160] Test period: 540 days of continuous cultivation.

[0161] Result determination: Calculate the biodegradation rate of the material based on the amount of carbon dioxide released.

[0162] Table 7 The test results of the biodegradability of the coating and its compliance with EU regulations in Application Example 4 are as follows:

[0163]

[0164] The data in Table 7 provide direct evidence that the present invention complies with high-level environmental regulations. According to ISO 17556, achieving a final biodegradation rate exceeding 90% in soil is the gold standard for demonstrating complete environmental assimilation. The coating of the present invention achieved 94.5% biodegradation within 540 days, confirming its complete biodegradability and meeting the requirements for exemption from microplastic restrictions under stringent regulations such as EU Directive 2023 / 2055. This demonstrates that the present invention fundamentally addresses the environmental residue issues associated with traditional coating materials.

[0165] Application Example 5: Study on degradation performance in different typical soils.

[0166] Objective: To verify the universality and stability of the coating composition of the present invention in typical soil environments in northern and southern China.

[0167] Test sample: The coated seeds prepared in Example 1 (preset degradation time: 30 days) were selected.

[0168] Soil Type:

[0169] Northern black soil: taken from Heilongjiang Province, pH 7.2, high organic matter content, loose texture.

[0170] Southern red soil: taken from Jiangxi Province, pH 4.8, heavy viscosity, high content of iron and aluminum oxides.

[0171] Experimental Method: Each soil type was potted separately and maintained in a greenhouse to simulate the average spring temperature (15°C for black soil and 22°C for red soil) and humidity conditions in each region. Test samples were sown in the soils and the coating condition and plant growth were regularly observed.

[0172] Table 8 The experimental results of the degradation performance study of Application Example 5 in different typical soils are as follows:

[0173]

[0174] The results in Table 8 demonstrate the robustness and universality of the technical solution of the present invention in different practical environments. Despite significant differences in pH and ambient temperature between typical soils in northern and southern China, the actual protection period of the coating still fluctuates around the preset 30-day target, and the trend of change conforms to the scientific law of extending the protection period at low temperatures and shortening it at high temperatures, proving that its degradation behavior is predictable and controllable. Importantly, plants grew well in both soil types, indicating that the dual-layer controlled-release system of the present invention can function effectively under different conditions and has broad practical application value.

[0175] Application Example 6: Verification of the effect of pH buffer system on degradation efficiency.

[0176] Purpose: This comparative experiment was designed to verify the necessity of adding a pH buffer to the system of the present invention and to clarify its key role in ensuring the efficiency of enzymatic degradation. This experiment aimed to simulate an extreme situation where the external environment, such as soil or solution, does not provide any buffering capacity, thereby isolating the effectiveness of the system's internal pH regulation mechanism.

[0177] Method: Group A (containing buffer, the present invention): The coated seed samples were prepared according to the revised method of Example 1. Its inner functional layer contained a phosphate buffer. Group B (without buffer, original solution): The coated seed samples were prepared according to the original method of Example 1. Its inner functional layer was formed only by cross-linking sodium alginate and did not contain any external pH buffer. Test conditions: The samples of Group A and Group B were respectively placed in a degradation medium with low buffering capacity, deionized water at pH 7.0, containing only 0.1M NaCl to simulate osmotic pressure, and cultured with shaking at 25°C. The samples were taken out regularly, washed, dried, and then weighed to calculate the coating weight loss and draw a degradation curve.

[0178] Table 9 Experimental results of the effect of pH buffer system on degradation efficiency in Application Example 6 are as follows:

[0179]

[0180] The comparative experiments in Table 9 irrefutably highlight the central role of the pH buffer system in the inner functional layer. Even under the harsh conditions of lacking external buffering, Group A samples containing a buffer were still able to trigger rapid degradation, while Group B samples lacking a buffer saw the degradation process nearly stall due to acid production from PLGA hydrolysis, which inhibited enzyme activity. This result clearly demonstrates that the internal pH buffer system is not a mere auxiliary feature, but rather a key technical feature necessary to ensure the stable implementation of the present invention's "enzymatic triggering" design under various environments, and is the ingenious concept that distinguishes this invention from simple physical mixing systems.

[0181] Based on the experimental results of the above embodiments, comparative examples and application examples, the effects of the present invention are analyzed in depth as follows:

[0182] In vitro degradation behavior analysis: The results of Examples 1, 2, and 3 clearly demonstrate the programmability of the coating composition of the present invention. By changing the molar ratio of LA:GA in PLGA, the protection period can be accurately extended from 15 days to 60 days. All examples show a clear two-stage degradation characteristic, namely a stable protection period and a subsequent rapid degradation period. In contrast, the passive degradation of Comparative Example 1 is extremely slow; Comparative Example 2 has no delayed release of the enzyme, resulting in rapid failure of the coating; Comparative Example 4 has an excessively high PLA content, forming a dense continuous phase, which hinders the enzyme's contact with PHBV and leads to incomplete degradation. These results confirm the necessity and superiority of the double-layer structure and delayed-release enzymatic trigger design of the present invention.

[0183] Verification of enzyme activity after encapsulation: In order to confirm that the microcapsulation process did not cause irreversible damage to the core catalyst, the present invention compared the enzyme activity before and after encapsulation. The enzyme-loaded microspheres prepared in Example 1 were crushed to release the internal lipase, and the hydrolysis activity was measured at a wavelength of 405nm using the p-nitrophenol palmitate (p-NPP) method. The results showed that the enzyme released after encapsulation retained more than 85% of the original enzyme powder in terms of specific activity. This result strongly proves that the W / O / W double emulsion encapsulation method adopted by the present invention is gentle and effective, can fully protect the biological activity of the enzyme, and ensure the feasibility and efficiency of the subsequent enzymatically triggered degradation process.

[0184] Analysis of plant growth efficacy: The results of the application examples show that the seeds of all Example Groups 1 to 20, while obtaining effective initial protection, have significantly better later growth indicators such as plant height and root length than all comparative groups because the coating can degrade on time, and are close to or even better than the uncoated control group without any protection in some indicators such as stress resistance. This part of the stress resistance data is not listed. Comparative Examples 1 and 4 significantly inhibited root development and later growth due to slow or incomplete degradation of the coating. Comparative Example 2 had no later data due to germination failure. Comparative Examples 3, 5, 6, 7, 8, 9, and 10 had poor protection effects or negative effects on germination because the coating was too soft, too thin, too thick, the inner layer had poor film-forming properties, the inner layer was too brittle, insufficient cross-linking, or excessive cross-linking, respectively. Ultimately, the growth of the plants was not as good as that of the Example Group.

[0185] Mechanical Property Analysis: The results of Application Example 2 (Table 5) provide quantitative evidence for the coating's mechanical properties. The tensile strength and elongation at break of Examples 1, 4, and 5 are all within acceptable ranges, demonstrating that the coating possesses both sufficient strength and toughness. In contrast, Comparative Example 3 exhibits a significant decrease in tensile strength due to its low PLA content, confirming its "too soft" nature. Comparative Examples 8 and 9 exhibit poor overall mechanical properties due to gelation issues in the inner layer.

[0186] Analysis of Adaptability to Different Soil Environments: The results of Application Example 5 demonstrate the robustness of the present invention under diverse geographical and climatic conditions. Despite significant differences in soil pH, texture, and temperature between northern and southern China, the coating composition of the present invention consistently achieved its intended function. The degradation cycle was slightly prolonged in the cooler black soils of the north, while it was correspondingly shortened in the warmer red soils of the south, consistent with the fundamental laws of polymer hydrolysis and enzymatic reactions. Importantly, this variation is predictable and can be compensated and calibrated by fine-tuning the PLGA formulation within the technical framework disclosed herein (for example, appropriately increasing the proportion of the hydrophobic LA monomer in southern regions). This demonstrates that the present technical solution is not limited to ideal laboratory conditions but rather possesses broad environmental applicability and practical application value.

[0187] Trend analysis of influencing factors:

[0188] Impact of coating weight gain: When coating weight gain is less than 1%, the coating is too thin, resulting in insufficient physical protection and waterproofing, leading to decreased seed viability. When coating weight gain exceeds 10%, the excessively thick coating physically hinders the gas exchange and water absorption required for seed germination, resulting in a decreased germination rate. Therefore, a coating weight gain of 1-10% is the optimal range for achieving a balance between effectiveness and cost.

[0189] The impact of the outer protective layer blend ratio: When the outer layer PLA content is less than 40%, the blend is too tough but lacks rigidity, making the coating susceptible to physical damage during seeding and soil exposure. When the PLA content is higher than 60%, the continuous phase formed by PLA is too dense. Even if the enzymes within are released, they are unable to effectively penetrate and degrade the encapsulated PHBV phase, resulting in incomplete degradation and residual residues that affect the root system. Therefore, a weight ratio of 40:60 to 60:40 represents the optimal range for balancing mechanical properties and enzymatic degradation efficiency.

[0190] Influence of alginate concentration in the inner functional layer: By comparing the results of Examples 1, 8, 9 and Comparative Examples 7 and 8, the optimal range of alginate concentration in the inner layer slurry can be determined. When the concentration is lower than 1% (w / v), the slurry viscosity is too low, and it is difficult to form a uniform and continuous film on the seed surface, resulting in weak immobilization of the microcapsules, and some of them fall off in subsequent processes, affecting the final degradation effect. When the concentration is higher than 4% (w / v), the slurry viscosity is too high, spraying is difficult, and the gel layer formed is too hard and brittle, and may crack during drying or sowing, affecting the bonding force of the inner and outer layers. Therefore, the concentration of 1-4% (w / v) is the optimal range that takes into account film-forming properties, microcapsule immobilization efficiency and mechanical properties.

[0191] Effect of the cross-linking cation concentration of the inner functional layer: By comparing the results of Examples 1, 10, and 11 with Comparative Examples 9 and 10, the appropriate range of cross-linking cation concentration can be determined. When the concentration is lower than 2% (w / v), the alginate is not sufficiently cross-linked, and the formed gel layer has low strength and high swelling, which cannot effectively protect the microcapsules and leads to their premature failure. When the concentration is higher than 10% (w / v), excessive cross-linking causes the gel layer to shrink severely and become hard, which also affects the stability of the bonding interface with the outer protective layer. Therefore, a concentration range of 2-10% (w / v) can ensure the formation of an inner functional layer with stable structure and moderate mechanical strength.

[0192] Effect of delay period: By comparing Examples 1, 2, and 3, it can be clearly seen that the core regulatory role of the microcapsule wall material parameters on the degradation program. When the proportion of the more hydrophobic LA monomer in PLGA increases from 50% to 85%, the hydrolysis rate of the wall material slows down significantly, thereby accurately extending the release delay period of the enzyme from about 15 days to about 60 days. Similarly, by comparing Example 17 with Examples 19 and 20, it can be clearly seen that for protein-polysaccharide complex coacervate microcapsules, by systematically changing the dosage of the cross-linking agent glutaraldehyde, its delayed release period can be effectively regulated from about 18 days to about 45 days, proving that this green alternative also has excellent programmability and controllability. This proves that the technical solution of the present invention can flexibly customize the degradation program of the coating to adapt to the precise needs of different crops, different soil environments, and different agricultural scenarios.

[0193] Effect of the enzyme-to-wall material weight ratio: Comparison of the results from Examples 1, 13, and 14 confirms that effective delayed release and ultimately rapid degradation can be achieved within a weight ratio range of 1:3 to 1:10. When the ratio is below 1:10, the enzyme concentration may not be sufficient to rapidly degrade the outer layer after release. When the ratio is above 1:3, the stability of the microcapsules may be affected and the cost may increase.

[0194] Effect of Microcapsule Solids Content: Comparison of the results from Examples 1, 15, and 16 confirms that a stable and effective inner functional layer can be formed within a solids content range of 1-10 wt%. Below 1 wt%, insufficient enzyme is available per unit area; above 10 wt%, the rheological properties of the inner layer slurry and coating uniformity may be affected.

[0195] Robustness Analysis of the Technical Solution: The results of Example 18 strongly demonstrate the remarkable robustness of the present invention's technical solution. Even under the extremely unfavorable combination of coating thickness (1%), enzyme content (1:10), and a waiting time (60 days), the present coating composition successfully achieved the claimed two-stage degradation function. Its rapid degradation period of 14 days remained well within the claimed range of 7-15 days, fully demonstrating the robustness and high fault tolerance of the present invention's design.

[0196] Necessity Analysis of the pH Buffer System: The results of Application Example 6, Table 9, irrefutably demonstrate the necessity of introducing a pH buffer system into the inner functional layer. In a deionized water medium lacking external buffering capacity, the degradation of the coating of Group B, which did not contain a buffer, essentially stagnated after the protection period, confirming the severe inhibitory effect of PLGA hydrolysis and acid production on enzyme activity. Group A, which contained a buffer, exhibited rapid degradation consistent with expectations. This powerful comparative data demonstrates that the built-in pH buffer system is a key design feature that ensures the robust implementation of the present invention's functions under various environments, transforming a potential technical defect into a powerful argument demonstrating the ingenuity of the present invention's concept and the completeness of its technical solutions.

[0197] In summary, the present invention successfully introduces active and programmable degradation design into polymer materials and coating technology by constructing a double-layer coating composition containing a delayed-release enzymatic trigger, integrating a pH buffer microenvironment in the inner functional layer, and precisely defining the content, proportion and key performance parameters of each component. The preparation methods described in the present invention, such as the W / O / W double emulsion method, the complex coacervation method and the water-based emulsion fluidized bed coating method, are all mature or feasible industrial production processes with good scale-up potential. The system can not only provide reliable initial protection for the matrix, but also trigger the rapid and complete degradation of the coating at a preset time point, thereby solving the fundamental problem of the passive and uncontrollable degradation process of biodegradable materials in the prior art. The technical solution of the present invention is cleverly designed, fully supported by experimental data, and has significant effects. It also meets the requirements of future sustainable development and environmental protection regulations and has broad application prospects.

[0198] Those skilled in the art will appreciate that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, or improvements to the technical solutions of the present invention that fall within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A multi-layer controlled degradation coating composition, characterized in that: The coating composition satisfies all of the following limiting parameters simultaneously: When the coating composition is applied to a substrate, its total weight is 1-10% of the weight of the substrate core; The coating composition exhibits a two-stage degradation characteristic in a simulated soil solution at 25° C., including: an initial protection period lasting 10 to 60 days, during which the coating weight loss is no more than 10%; and a subsequent rapid degradation period, in which the coating weight loss is more than 80% within 7 to 15 days after the initial protection period; The coating composition comprises: an outer protective layer comprising a first biodegradable polymer material, wherein the first biodegradable polymer material is selected from polyhydroxyalkanoate, polylactic acid or a blend thereof, and when the first biodegradable polymer material is a blend, the weight ratio of polylactic acid to polyhydroxyalkanoate is 40:60 to 60:40; and an inner functional layer disposed below the outer protective layer, wherein the inner functional layer comprises a hydrogel matrix and a plurality of microcapsules dispersed therein; The microcapsule encapsulates an enzyme capable of degrading the first biodegradable polymer material, the enzyme being selected from lipase, esterase, or protease, and the microcapsule is configured to release the enzyme after a predetermined delay time; the wall material of the microcapsule is polylactic acid-glycolic acid copolymer, wherein the molar ratio of lactic acid to glycolic acid is 50:50 to 85:15; or the wall material of the microcapsule is a protein-polysaccharide complex, the protein being selected from zein or gelatin, and the polysaccharide being selected from gum arabic or alginate; The hydrogel matrix of the inner functional layer is formed by cross-linking an aqueous solution containing alginate with a mass volume concentration of 1-4%, a pH buffer, and a divalent cation solution with a mass volume concentration of 2-10%. The pH buffer is sufficient to maintain the pH value of the inner functional layer within the range of 6.0-8.5 after the enzyme is released.

2. A multi-layer controlled degradation coating composition according to claim 1, characterized in that: When the wall material of the microcapsule is poly(lactic acid-glycolic acid copolymer), the weight ratio of the enzyme to the wall material is 1:3 to 1:

10.

3. A multi-layer controlled degradation coating composition according to claim 1, characterized in that: When the wall material of the microcapsule is a protein-polysaccharide complex coacervate, the predetermined delay time of the microcapsule is set by adjusting the concentration or reaction time of the cross-linking agent used to solidify the complex coacervate.

4. A method for preparing a multi-layer controlled degradation coating composition according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1. Preparation of enzyme-loaded microcapsules; Step 2. The aqueous solution of the pH buffer is mixed with the aqueous solution of the alginate to form a mixed aqueous solution, and the microcapsules prepared in step 1 are dispersed in the mixed aqueous solution at a solid content of 1-10 wt % to form an inner layer slurry; Step 3. cross-linking the inner layer slurry formed in step 2 with the divalent cation solution to form the inner functional layer; Step 4. Applying a water-based emulsion, solution or melt thereof containing the first biodegradable polymer material at a concentration of 5-15 wt% on the inner functional layer, and forming an outer protective layer after drying.

5. The method according to claim 4, characterized in that In step 1, the microcapsules are prepared by a water-in-oil-in-water double emulsion method, wherein the enzyme serves as the inner aqueous phase, the organic solution of polylactic acid-glycolic acid copolymer serves as the oil phase, and the polyvinyl alcohol aqueous solution serves as the outer aqueous phase.

6. The method according to claim 4, characterized in that In the step 1, the microcapsules are prepared by a protein-polysaccharide complex coacervation method, wherein the enzyme, protein and polysaccharide are dissolved in an aqueous phase, and the pH value is adjusted to induce complex coacervation to form microcapsules.

7. Use of a multi-layer controlled degradation coating composition according to any one of claims 1 to 3, characterized in that: The coating composition is suitable for the fields of seed coating or fertilizer controlled release.

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