Dual-trigger programmable degradable phas compositions and methods of making the same

Abstract

The application belongs to the field of high polymer materials, and discloses a double-trigger programmable degradable PHA composition and a preparation method thereof. A cured film structure formed by the composition comprises, from outside to inside, an outer protective layer taking polyhydroxyalkanoate as a base material and introducing a reversible cross-linking network, a trigger layer configured with humidity and ion double-trigger microcapsules, and an inner functional layer carrying functional additives. The cured film can maintain low permeability and mechanical stability before application. After application, under the synergistic action of specific moisture and ions, the trigger layer is activated, causing the cured film to have a stepwise increase in moisture permeability and form through holes within a preset time window. Finally, the whole disintegrates through physical structural failure. The technology can be applied to the field of seed coating, and the low-temperature process below 50 DEG C adopted by the technology can ensure the activity of the biological base material, realizing the unity of stable protection before application and on-demand disintegration after application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer materials, and specifically relates to a dual-trigger programmable degradable PHA composition and a preparation method thereof. The composition can respond to external environmental signals to cause programmed structural failure, and can be applied to fields requiring temporary protection and on-demand failure, such as functional seed coating. BACKGROUND

[0002] In the fields of agriculture, temporary packaging and biomedicine, an intelligent material capable of providing temporary protection and on-demand failure triggered by specific environmental signals is often needed. Taking the seed coating technology in modern agriculture as an example, the core requirement is to provide stable and low moisture protection for seeds during storage and transportation before sowing, and to rapidly and reliably break or disintegrate in the soil environment after sowing. The existing technology generally faces the core contradiction between the stability of seed protection before sowing and the reliability of coating failure after sowing.

[0003] At present, the technical routes in the field can be mainly classified into the following categories:

[0004] The first category is “passive degradation or diffusion barrier system”. This kind of technology relies on the slow degradation or physical barrier properties of the material itself to delay the release of the contents, and the rate is mainly determined by unpredictable external environmental factors. For example, the technology disclosed in Patent No. WO2020242871A1 realizes so-called “controlled release” by blending polymers with different degradation rates such as polylactic acid (PLA) and polyhydroxyalkanoate (PHA). Similarly, Patent No. US7774978B2 discloses a method of re-coating a layer of polymer emulsion (such as ethyl cellulose or acrylic copolymer) on the outside of seeds treated with agricultural chemicals, to control the diffusion rate of active ingredients by adjusting the glass transition temperature (Tg) of the polymer. Patent No. EP3165092A1 discloses the use of wax, starch or vegetable oil in the coating formula to improve the release of hydrophobic pesticides. The common defect of these technologies is that the release or degradation rate completely depends on the random fluctuations of soil humidity, temperature and microbial population, resulting in that the failure time of the coating cannot be accurately matched with the actual agricultural needs, lacking of initiative, reliability and controllability. A recent review (Langlet et al., Polymers, 2024, 16, 1969) shows that the current research in the field focuses on finding biodegradable polymers such as starch, pullulan, gelatin as substitutes for traditional microplastic binders, and the core goal is to meet the requirements of biodegradability and basic film-forming and dust-reducing functions, without involving how to construct an actively programmable and signal-responsive structural failure system.

[0005] The second category is the “single signal-responsive system”. This type of technology attempts to trigger the function by responding to a single signal that is ubiquitous in the environment (such as moisture). For example, US20140100111A1 discloses a hydrogel coating composed of gelatin and polysaccharides (such as dextran sulfate), whose main function is to absorb and retain moisture, providing “on-demand water supply” for seed germination under drought conditions. However, this single moisture-dependent triggering mechanism poses significant risks: in high-humidity storage or transportation environments before sowing, the coating may be accidentally activated, causing the active ingredients to be released prematurely or the coating structure to be destroyed prematurely, failing to ensure pre-sowing stability.

[0006] The third category is the “bioactive delivery system”. The focus of this type of technology is not the structural failure of the coating itself, but rather the use of the coating as a carrier for bioactive substances (such as biostimulants or beneficial microorganisms). For example, US10035736B2 discloses a method of treating seeds with partially humified natural organic matter (such as humic acid, fulvic acid) to promote germination and improve stress resistance. Another study (Usmanova et al., Polymers, 2024, 16, 376) investigates the use of PHA and pullulan as carriers to deliver beneficial endophytic bacteria to the seed surface to resist plant pathogenic fungi. In these applications, the polymer material mainly plays the role of an adhesive and a protective agent, aiming to ensure the survival and stability of the bioactive substances, rather than constructing a physical structure that can be programmed to disintegrate on demand.

[0007] The fourth type is "active trigger system". In order to overcome the defects of passive system, the industry explores the active trigger scheme. Its advanced representative is the "endogenous enzymatic degradation" technology disclosed in CN120442137A, which chemically degrades the polymer from the inside to the outside at a specific time point by prepositioning a time-delayed enzyme inside the coating. Although this scheme has initially realized the concept of "programmable", its degradation mechanism relies on the activity of biological macromolecules, and in the real soil environment with complex and variable pH, temperature, ionic strength and various unknown inhibitors, the final efficiency and reliability of its trigger and degradation still face great challenges. Moreover, some technologies have achieved multiple triggers, but their application fields and structural designs are essentially different from the present invention. For example, Patent No. WO2007122374A8 discloses a coating for oral drug colon-targeted delivery, which combines a pH-sensitive polymer and a polysaccharide (such as starch or pullulan) that can be degraded by microorganisms, and another review also discusses similar drug delivery technologies. However, this type of technology is designed for the stable and predictable human digestive environment, and the pH range, ionic environment and microbial population it faces are completely different from the complex and variable soil environment. In addition, this technology is designed for the human digestive environment, and does not disclose a macroscopic through-hole formed to achieve the physical failure of the coating as a whole. Some other technologies, such as the disclosure of spray-dried in-situ gelation (PLOS ONE, 2021, 16(2): e0247171), focus on improving the material preparation process and do not disclose a multi-layer composite structure that can respond to external dual signals and achieve programmed disintegration.

[0008] In summary, the existing technology has failed to provide a solution that can actively and programmably trigger, eliminate the dependence on fragile biochemical reactions, and accurately identify the common and stable physicochemical combination signals (water and ions) in agricultural application scenarios (i.e. soil environment) to initiate a physical, rather than chemical, macroscopic structure failure (such as the formation of through-holes and eventual disintegration). The long-standing technical gap in this field is how to design an intelligent polymer composite material system specifically for seed coating and other fields, which can accurately identify the "sowing" event (i.e. meeting the water and ion conditions simultaneously) through a unique multi-layer structure and built-in dual-trigger microcapsule to initiate a physical macroscopic structure failure program. This constitutes the unique technical challenge that the present invention aims to solve. SUMMARY

[0009] The present invention aims to overcome the shortcomings of the prior art and provide a dual-trigger programmable degradation PHA composition and a preparation method thereof, aiming to solve the problem of balancing the stability of temporary protection materials before application and the on-demand failure after application in the prior art.

[0010] To achieve the above-mentioned purpose, the present invention provides the following technical solutions:

[0011] The present application provides a dual-trigger programmable degradable PHA composition, which forms a solidified film structure from outside to inside in turn comprising:

[0012] An outer protective layer, comprising a film-forming component with PHA as the main film-forming material and a reversible cross-linked network structure;

[0013] A trigger layer, comprising humidity-triggered microcapsules and ion or chelate-triggered microcapsules, wherein:

[0014] The shell material of the humidity-triggered microcapsules is selected from one or more of gelatin, gum arabic, chitosan, shellac or polyhydroxyalkanoate, and the core material thereof is a penetration promoter selected from urea and ethyl lactate;

[0015] The core material of the ion or chelate-triggered microcapsules is selected from citric acid and phytic acid;

[0016] The humidity-triggered microcapsules and the ion or chelate-triggered microcapsules are configured to act synergistically to cause a stepwise increase in the moisture permeability of the solidified film or form a through-hole structure in an environment where both moisture and soluble inorganic ions exist;

[0017] and an inner functional layer, comprising a film-forming phase with PHA as the main film-forming material and carrying one or more functional additives; wherein the solidified film has a step ratio R of water vapor transmission rate under triggering conditions ≥ 2.0, and a through-hole ratio φ P ≥ 30%.

[0018] As Figure 1 shown, the multilayer structure is coated on the surface of a substrate such as a seed, from outside to inside in turn as an outer protective layer, a trigger layer and an inner functional layer, wherein the trigger layer is internally disposed with trigger microcapsules, and after triggering, the entire film layer structure will form a through-hole to realize disintegration. The material of the present application is activated and triggered to fail when both moisture and soluble inorganic ions exist; it does not trigger when any single condition is insufficient.

[0019] Further, the PHA is derived from a PHA aqueous dispersion selected from one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) aqueous dispersion;

[0020] The outer protective layer is composed of a complex of the above-mentioned aqueous dispersion and one or more of chitosan, alginate, lignin sulfonate, polyvinyl alcohol, sodium carboxymethyl cellulose or shellac.

[0021] Further, the reversible cross-linking network structure is a dynamic covalent network or an ionic cross-linking network; the dynamic covalent network is at least one of a Schiff base, an oxime, a borate ester or an acetoacetic ester polyamine structure; and the ionic cross-linking network is a calcium alginate or a chitosan trisodium tripolyphosphate structure.

[0022] Further, the volume distribution median particle size D 50 is 0.5 to 10 μm, for example, it can be 0.5 μm, 1.0 μm, 2.0 μm, 3.5 μm, 5.0 μm, 8.0 μm or 10 μm. The encapsulation rate thereof is not less than 70%, the solid content in the trigger layer is 10 wt% to 50 wt%, for example, it can be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 40 wt% or 50 wt%. And the mass ratio of the humidity-triggered microcapsule to the ion or chelate-triggered microcapsule is 1:5 to 5:1, for example, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:2, 3:1, 4:1 or 5:1, by adjusting the ratio, the starting time of disintegration can be accurately controlled.

[0023] Further, the functional aid contained in the inner functional layer is selected from one or more of dust suppression powder, wetting dispersant, defoaming agent, coloring identification agent, biologically active substance or nutritional fortifier.

[0024] The present application also provides a coated article comprising a substrate and a multi-layer cured film formed from any of the aforementioned compositions coated on the surface of the substrate.

[0025] The present application also provides a method for preparing the aforementioned coated article, which comprises the following steps:

[0026] Step 1. Providing a substrate and pre-treating it as needed;

[0027] Step 2. Uniformly applying an inner functional layer slurry on the surface of the substrate and performing first-step drying at a temperature not higher than 50°C to form an inner functional layer;

[0028] Step 3. Uniformly applying a trigger layer slurry on the surface of the inner functional layer and performing second-step drying at a temperature not higher than 50°C to form a trigger layer;

[0029] Step 4. Uniformly applying an outer protective layer slurry on the surface of the trigger layer and performing final drying at a temperature not higher than 50°C to form an outer protective layer, thereby obtaining the coated article.

[0030] The time for any single drying step in the aforementioned preparation method is not less than 5 minutes, the maximum temperature in the coating and drying process is not higher than 50°C, and the water activity of the final product is not higher than 0.70.

[0031] And the double-trigger programmable degradable polyhydroxyalkanoate composition described in the application can be applied to the field of seed coating, providing pre-sowing stable protection and post-sowing on-demand disintegration for crop seeds selected from corn, rapeseed, rice, wheat, cotton or legumes.

[0032] Compared with the prior art, the following remarkable beneficial effects can be obtained by using the application:

[0033] The use of a synergistic double-trigger mechanism improves the reliability of application: The design of the application requires the presence of both humidity and ion environmental signals to trigger structural failure. This mechanism reduces the likelihood of premature activation of the material when only a single environmental factor changes, thereby exhibiting high stability before application while ensuring on-demand failure after application.

[0034] The structural failure time is adjustable to adapt to different application requirements: By adjusting the mass ratio of the two trigger microcapsules in the trigger layer, the start time of structural failure can be changed. Experimental results show that when the ratio changes in the range of 1:5 to 5:1, the trigger time changes accordingly. This feature allows the composition to be adjusted according to different crop types, seeding conditions, or pre-set application scenarios.

[0035] The use of low-temperature preparation process is beneficial to maintaining the activity of biological components: The coating and drying process is carried out at a temperature not higher than 50°C. This mild process condition helps to protect the biological activity of heat-sensitive substrates or inclusions (such as seeds, microbial preparations, etc.), so that they can maintain the expected function when applied.

[0036] The physical and chemical trigger mechanism reduces the dependence on specific biochemical environments: The failure process of the application is driven by physical and chemical reactions, rather than relying on enzymatic degradation. Therefore, its performance shows more stable trigger behavior than enzymatic degradation systems in complex soil environments containing enzyme inhibitors (such as certain metal ions) or pH fluctuations, enhancing the applicability of the technical solution in different actual environments.

[0037] The material is biodegradable and provides a quantitative performance evaluation method: The composition uses biodegradable PHA as the main material, which helps to reduce the long-term impact on the environment after the material is discarded. At the same time, the application proposes the water vapor transmission rate step ratio R and the through-hole ratio φ P as quantitative indicators for evaluating the degree of structural failure, providing a standardized method for performance evaluation and quality control of such materials. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 : Schematic diagram of the cross-sectional microstructure of the coating on the seed.

[0039] In the figure, 1, outer protective layer; 2, trigger layer; 3, inner functional layer; 4, seed; 5, trigger microcapsule; 6, through hole. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application. Unless otherwise specified, the raw materials used in the examples are commercially available industrial products or can be prepared by conventional methods. The performance test methods are carried out according to the standards described in the summary part, unless otherwise specified.

[0041] Main reagents and raw materials:

[0042] Table 1 Name, product brand, specification and supplier of main reagents and raw materials:

[0043]

[0044] Main analysis and detection instruments:

[0045] Water vapor transmission rate instrument: AMETEK MOCON PERMATRAN-W 3 / 34;

[0046] Water activity instrument: AQUALAB 4TE (METER Group);

[0047] Particle size instrument: Mastersizer 3000;

[0048] pH meter: Mettler-Toledo SevenDirect Versa;

[0049] Dynamic water vapor adsorption instrument (DVS): Surface Measurement Systems DVS Resolution;

[0050] Tensile tester: Instron 6800 series or equivalent equipment;

[0051] High performance liquid chromatograph: Agilent 1260 Infinity III;

[0052] Inductively coupled plasma emission spectrometer: Agilent 5800;

[0053] Respirometer: OxiTop-C;

[0054] Nuclear magnetic resonance spectrometer: NMR, Bruker Avance III 400 MHz;

[0055] High-shear homogenizer: IKA T25 digital ULTRA-TURRAX;

[0056] High-pressure homogenizer: ATS Engineering AH-100D;

[0057] Gas chromatography-hydrogen flame ionization detector: Agilent Intuvo 9000.

[0058] Main test standards:

[0059] General test conditions: All samples were conditioned at 23 ± 1 °C, 50 ± 2% relative humidity (RH) for at least 24 hours before testing. The sample size n for each index was ≥ 5, and the reported value was the mean ± standard deviation.

[0060] Water vapor transmission rate (WVTR) and water vapor transmission rate step ratio R: WVTR was tested by modulated infrared method according to ASTM F1249-20 at 38 °C, 90% RH, with a recording interval ≤ 5 min; and was mutually certified by gravity method according to ASTM E96 / E96M-24a. R is defined as the ratio of the steady-state WVTR before and after t1, t1 is the first significant positive peak when d[WVTR] / dt exceeds the "baseline mean + 3σ" and lasts for ≥ 2 sampling intervals; the steady-state average WVTR (t) of each 10-15 min window before and after t1 is taken as WVTR (t1 - ) and WVTR (t1 + ), respectively.

[0061] Through-hole ratio φ P : Three-dimensional imaging (voxel size ≤ 2 μm) of the coated sample was performed by X-ray micro-CT (μCT), and the connected domain analysis was performed after reconstruction and threshold segmentation to calculate the volume fraction of the through-hole channel across the membrane thickness.

[0062] Germination rate and germination potential: According to the International Seed Testing Association (ISTA Rules) 2025 edition.

[0063] Seedling emergence and early growth test: According to OECD TG 208 (2006, current).

[0064] Seed dusting: According to European Seed Association (ESA) method 1.1 version.

[0065] Final biodegradability: According to ISO 17556:2019.

[0066] Soil pH: Determined and reported according to ISO 10390:2021.

[0067] Film tensile properties: Refer to ASTM D882-23.

[0068] Key intermediate preparation (AA-PVA):

[0069] In a three-necked flask, 10 g PVA was dissolved in 100 ml anhydrous DMSO under nitrogen protection, heated to 90°C. 0.1 g DMAP was added. 8.5 g t-BAA was added dropwise slowly. The temperature was raised to 110°C and reacted for 6 hours. After the reaction was completed, it was cooled to room temperature and precipitated into 500 ml acetone. The finished product was reprecipitated twice with ethanol to remove residues. Dried in a vacuum oven at 50°C for 24 hours to obtain the product AA-PVA. Release indicators: residual DMAP ≤100 ppm, residual DMSO ≤500 ppm (GC-FID); 1H NMR calculated degree of substitution DS = 3-10 mol%.

[0070] Humidity-triggered / ion (or chelate)-triggered microcapsule preparation (complex coacervation method):

[0071] Gelatin (10 g / L, 45°C) and gum arabic (10 g / L, 45°C) were mixed in equal volumes, the sheared emulsion embedding phase was induced to complex coacervation by slowly adding dilute acid to reduce the pH to 4.2±0.1; the crosslinking agent was low-toxicity gardenoside 0.3 wt% (based on wall material), reacted at 37°C for 4 h; washed, neutralized, and spray dried; the particle size distribution D 50 and encapsulation efficiency (EE%) were determined. The EE% was determined by surface elution-HPLC method: the surface free core material of the microcapsules was quickly eluted with a suitable solvent, and the surface elution amount m s was measured, and the total amount of raw materials m0 was calculated, EE% = (m0-m s ) / m0×100%.

[0072] General preparation steps of aqueous dispersion:

[0073] The PHA aqueous dispersion used in the embodiments of the present application was prepared by an environmentally friendly solvent-free high-energy homogenization method. The specific steps are as follows:

[0074] Step 1. 0.5 g of PVA was dissolved in 200 ml of deionized water and heated to 80°C as the water phase.

[0075] Step 2. 10 g of PHA powder was melted at 175°C.

[0076] Step 3. The molten PHA prepared in Step 2 was slowly added into the hot water phase of Step 1 in a high shear homogenizer at 10,000 rpm for 10 minutes to form a coarse emulsion.

[0077] Step 4. The hot coarse emulsion was immediately transferred into a high pressure homogenizer preheated to 80°C and cycled 5-8 times at 80-100 MPa.

[0078] Step 5. The homogenized emulsion was allowed to cool down to room temperature under stirring to obtain a stable PHA aqueous dispersion with a milky appearance. The solid content of each dispersion prepared was 40-45 wt% with an average particle size D 50 controlled in the range of 0.5-2.0 μm.

[0079] Example 1: Corn film coating (weight gain 5%).

[0080] Outer protective layer slurry preparation: 100 parts of PHBV aqueous dispersion was mixed with 8 parts of AA-PVA and 1.5 parts of hexanediamine under stirring.

[0081] Trigger layer slurry preparation: T h (core: urea) and T i (core: citric acid) were prepared according to the general procedure. h and T i were mixed in a mass ratio of 3:2 in water.

[0082] Inner functional layer slurry preparation: 95 parts of PHA aqueous dispersion was mixed with 5 parts of chitosan solution and additives were added.

[0083] Coating process: A drum coater was used to spray the three layers of slurry in sequence and each layer was dried under hot air at 45°C after spraying.

[0084] Example 2: Canola weight gain coating (weight gain 120%).

[0085] Outer protective layer slurry preparation: 90 parts of PHBV aqueous dispersion was mixed with 10 parts of calcium alginate solution.

[0086] Trigger layer slurry preparation: T h (core same as Example 1) and T i (core: phytic acid) were prepared. h and T i were mixed in a mass ratio of 2:1.

[0087] Inner functional layer slurry preparation: same as Example 1.

[0088] Coating process: fluidized bed coater. Apply inner functional layer by liquid-powder alternate mode; then spray trigger layer slurry; finally spray outer protective layer slurry, and immediately spray 0.5% calcium chloride aqueous solution to form ionic crosslinking network.

[0089] Example 3: Rice film coating (weight gain 8%).

[0090] Outer protective layer slurry preparation: compound PHBV water dispersion and shellac solution with solid content mass ratio of 8:2.

[0091] Trigger layer slurry preparation: prepare T h (core is ethyl lactate) and T i (core is citric acid).

[0092] Inner functional layer slurry preparation: compound PHA water dispersion and sodium carboxymethyl cellulose with 95:5, and add auxiliary agent.

[0093] Coating process: same as example 1.

[0094] Example 4: corn film coating (weight gain 2%) verifying the range end point.

[0095] The formula and process are basically the same as example 1, T h and T i The mass ratio is adjusted to 1:5.

[0096] Example 5: oilseed rape weight gain coating (weight gain 300%) verifying the range end point.

[0097] The formula and process are basically the same as example 2, T h and T i The mass ratio is adjusted to 5:1.

[0098] Comparative example:

[0099] Comparative example 1: corn coating without trigger layer.

[0100] Comparative example 2: corn coating containing only a single humidity trigger.

[0101] Comparative example 3: corn coating containing only a single ionic trigger.

[0102] Comparative example 4: simulate the enzymatic degradation coating of prior art.

[0103] Table 2: Formula summary of examples and comparative examples:

[0104]

[0105] Application examples and experimental results:

[0106] Application example 1: coating seed accelerated aging storage stability test.

[0107] Test purpose: To verify the protective performance of the coating of the present application under simulated long-term storage and transportation conditions.

[0108] Test method: The coated seeds prepared from each example and comparative example were stored together with uncoated control seeds in a constant temperature and humidity chamber under accelerated aging conditions of 40°C, 75% RH for 90 days. Samples were taken every 30 days, and the germination rate of the seeds was tested, and the surface state of the coating was observed.

[0109] Table 3: Accelerated aging storage stability test results of coated seeds of examples and comparative examples (reported values are mean ± SD, n = 5):

[0110]

[0111] Analysis: Table 3 data shows that all examples (1-5) can effectively maintain high germination rate of seeds (≥94%) after 90 days of severe accelerated aging, which is significantly better than the uncoated control group (85%), proving that the coating of the present application has excellent long-term protection ability for seeds. It is worth noting that only comparative example 2 containing humidity trigger shows sticky surface of the coating and more decrease in seed germination rate in the later storage period, which indicates that there is a risk of false triggering in high humidity environment, highlighting the importance of the dual trigger mechanism of the present application for ensuring pre-sowing stability.

[0112] Application Example 2: Trigger performance test under different simulated soil environments.

[0113] Test purpose: To verify the stability and programmability of the trigger performance of the present application under different ion compositions and pH conditions, and to verify the necessity of dual triggering.

[0114] Test method: The coated seeds of each group were tested in five different simulated substrates, and the trigger time t1, water vapor transmission rate step ratio R and penetration hole ratio φ were recorded P . The five different simulated substrates are:

[0115] Medium A (neutral-sodium salt): a substrate containing 100 mM NaCl, pH 7.0 (adjusted with HEPES buffer).

[0116] Medium B (acidic-composite salt): a substrate containing 50 mM NaCl, 20 mM CaCl2, 10 mM MgSO4, pH 5.5 (adjusted with MES buffer).

[0117] Medium C (alkaline-high calcium): a substrate containing 50 mM NaCl, 50 mM CaCl2, pH 8.0 (adjusted with Tris buffer).

[0118] Medium A' (High humidity, no ions): 95% RH, deionized water.

[0119] Medium D (Low humidity, with ions): 40% RH, 50 mM NaCl.

[0120] Table 4. Triggering performance of examples and comparative examples in different simulated soil environments (reported values are mean ± SD, n = 5):

[0121]

[0122] Analysis: Table 4 results clearly demonstrate the superiority and necessity of the dual-triggering mechanism of the present application. All examples can achieve rapid and effective triggering (R≥2.0, φ P ≥30%) in simulated soil environments (A, B, C), showing universality to different pH and ionic environments. Under negative control conditions lacking ions (A') or lacking sufficient humidity (D), all examples did not trigger, confirming the triggering logic of "humidity + ions". In contrast, Comparative Examples 1 and 4 cannot trigger at all, while single-triggered Comparative Examples 2 and 3 are ineffective and unstable, further highlighting the decisive role of the dual-triggering synergistic effect.

[0123] Application Example 3: Quantitative evaluation of long-term stability and "slow leakage" of microcapsules.

[0124] Test purpose: Quantitatively demonstrate that the leakage rate of core substances of microcapsules is extremely low under long-term high-humidity storage conditions.

[0125] Test method: The pure powder of microcapsules used in each group was placed in an accelerated aging condition of 40°C, 75% RH for 90 days. The concentration of core substances in the surface washing liquid was analyzed using HPLC, and the cumulative leakage percentage was calculated.

[0126] Table 5. Cumulative leakage rate of core substances of microcapsules of examples and comparative examples under accelerated aging conditions (%) (reported values are mean ± SD, n = 5):

[0127]

[0128] Analysis: Table 5 data shows that the dual-microcapsule system used in all examples has a cumulative leakage rate of core substances less than 0.6% under harsh accelerated aging conditions for up to 90 days. This extremely low leakage rate confirms the excellent sealing and chemical stability of microcapsules at the microscopic level, providing solid data support for the macroscopic stability of the coating before sowing.

[0129] Application Example 4: Determination of coating mechanical strength and core substance shedding rate.

[0130] Test purpose: Quantitatively assess the degree of physical attrition of the coating and the loss rate of the core material under simulated mechanical friction during transportation and sowing.

[0131] Test method: Standard mechanical attrition test using Heubach dust tester, collect and weigh the dust off, and quantitatively analyze the total amount of core trigger material in the dust using HPLC.

[0132] Table 6 Coating seed mechanical attrition test data of examples and comparative examples (reporting values are mean ± SD, n = 5):

[0133]

[0134] Analysis: Table 6 data shows that the loss rate of the core trigger material of all examples is less than 0.05% after being subjected to severe mechanical attrition. This indicates that the multi-layer structure design of the present application not only adheres physically firmly, but also effectively protects the internal functional microcapsules from physical damage, ensuring their mechanical integrity in actual application. Comparative Example 1 is not applicable because it has no trigger layer.

[0135] Application Example 5: Chemical kinetics verification of the "lock-key" synergistic mechanism.

[0136] Test purpose: Prove the "humidity trigger" and "ion trigger / unlocking" occur in the preset order by tracking the dynamic changes in chemical concentrations.

[0137] Test method: Place the coated seeds in simulated soil solution (medium C), take samples at regular intervals, and use HPLC and ICP-OES to quantitatively analyze the concentrations of phytic acid (key) and calcium ions (fragments of the lock), respectively. This method is only applicable to Examples 2 and 5 that use a calcium alginate ion cross-linked network. For Examples 1, 4 and all comparative examples that use a dynamic covalent network, this specific test method is not applicable due to their different network unlocking mechanisms.

[0138] Table 7 Chemical kinetics data of the "lock-key" mechanism of Examples 2 and 5 (samples in medium C) (reporting values are mean ± SD, n = 5):

[0139]

[0140] Analysis: Table 7 data shows a clear kinetic time sequence: the significant increase in phytic acid (key) concentration in the solution is clearly earlier than the increase in calcium ion (fragments of the lock) concentration. This temporal sequence, as shown by the data, indicates that the disintegration process occurs according to the preset program of "microcapsules releasing trigger first, trigger attacking cross-linked network second", providing the most direct chemical evidence for the synergistic mechanism of double triggering.

[0141] Application Example 6: Robustness comparison test under extreme enzyme inhibition environment.

[0142] Test objective: To compare the performance stability of the physical triggering mechanism and the enzyme-triggered mechanism of this invention in an environment containing enzyme inhibitors.

[0143] Test method: Add 1 mM copper sulfate CuSO4 to medium A as an enzyme inhibitor and perform triggering performance test.

[0144] Table 8. Comparison of triggering performance test results between the examples and the comparative examples under enzyme inhibition environment (reported values ​​are mean ± SD, n=5):

[0145]

[0146] Analysis: Table 8 shows that the triggering performance of all embodiments of the present invention is almost unaffected in environments containing strong enzyme inhibitors. In stark contrast, the enzymatic degradation process in Comparative Example 4 was completely inhibited. This direct comparison demonstrates that the physical triggering mechanism of the present invention exhibits higher environmental robustness and reliability compared to biochemical mechanisms that rely on the activity of biological macromolecules.

[0147] Application Example 7: Real Soil Environment Verification.

[0148] Test objective: To verify the universality and practical application effect of the coating of the present invention in real soil environments with significant differences in physicochemical properties.

[0149] Test method: The coated seeds of each group were sown in black soil of Heilongjiang (pH 7.1), red soil of Jiangxi (pH 4.9) and saline-alkali soil of Xinjiang (pH 8.8), respectively. The actual disintegration time of the coating and the seedling height after 60 days were recorded.

[0150] Table 9. Application effects of the examples and comparative examples in different real soil environments (reported values ​​are mean ± SD, n=5):

[0151]

[0152] Analysis: Table 9 summarizes the test results in three real soils. In all examples, the coatings rapidly disintegrated within 1-3 days after sowing, resulting in robust plant growth. Conversely, all comparative groups performed poorly, either failing to disintegrate and thus inhibiting growth, or exhibiting poor disintegration that negatively impacted plant vigor. This strongly demonstrates the broad environmental applicability and robust practical application value of the present invention.

[0153] Application Example 8: Final biodegradability performance evaluation.

[0154] Test objective: To evaluate the final biodegradability of the coating material in soil.

[0155] Test method: According to the ISO 17556:2019 standard, the cumulative amount of released carbon dioxide was measured to calculate the biodegradation rate by conducting a 540-day soil incubation in a controlled respirometer.

[0156] Table 10 Final aerobic biodegradation rate of coating materials of examples and comparative examples (reporting value is mean ± SD, n = 5):

[0157]

[0158] Analysis: Table 10 results show that due to the high biodegradability of the coating main body of all samples, their final biodegradation performance shows high consistency, all achieving more than 94% biodegradation within 540 days, reaching the internationally recognized "complete biodegradation" standard. This proves that the technical solution of the present application can be completely assimilated by environmental microorganisms after use, and will not cause long-term microplastic pollution.

[0159] Application Example 9: Electrochemical quantitative characterization of coating structure failure.

[0160] Test purpose: Quantitatively characterize the change of coating structure integrity before and after triggering by electrochemical method.

[0161] Test method: Prepare a coating film electrode on indium tin oxide (ITO) conductive glass, and conduct electrochemical impedance spectroscopy test in simulated soil solution (medium A), record the change of charge transfer resistance (Rct) before and after triggering.

[0162] Table 11 Change data of coating film charge transfer resistance (log Rct, Ω·cm²) of examples and comparative examples before and after triggering (reporting value is mean ± SD, n = 5):

[0163]

[0164] Analysis: Table 11 data shows that the resistance impedance values of all examples have decreased sharply by more than 3 orders of magnitude after triggering, which quantitatively indicates the formation of a large number of conductive through channels, resulting in macroscopic structural failure. In contrast, the resistance impedance values of Comparative Examples 1 and 4 hardly changed, indicating that their physical structure remains intact; the resistance of Comparative Examples 2 and 3 decreases limitedly, proving that their single-triggering mechanism cannot effectively destroy the structural integrity of the coating.

[0165] Experimental results and analysis:

[0166] Pre-seeding stability and mechanical strength comprehensive analysis:

[0167] From the data of Table 3, Table 4, Table 5 and Table 6, it can be seen that the coating has excellent pre-sowing stability. Macroscopically, all examples can effectively maintain seed viability (germination rate ≥ 94%, Table 3) after 90 days of accelerated aging, significantly better than the uncoated control group (85%), and the coating is intact. Microscopically, its core functional unit-microcapsule, shows extremely low core material leakage rate (90 days cumulative leakage <0.6%, Table 5), which fundamentally ensures chemical stability. At the same time, the extremely low core material mechanical loss rate (<0.05%, Table 6) proves its physical firmness. In contrast, Comparative Example 2 (humidity trigger only) is sticky on the surface after aging (Table 3), highlighting the synergistic advantage of the dual-trigger system in ensuring stability.

[0168] Determination and kinetic verification of the decisive role of the dual-trigger synergistic mechanism:

[0169] The core of the present application is the synergistic effect of the dual-trigger mechanism. The results of Table 4 clearly show that coatings without a trigger layer (Comparative Example 1) or a single trigger layer (Comparative Examples 2 and 3) cannot achieve rapid and reliable disintegration (R value <2.0, φ P <30%), while all examples are stable and meet the standards (R≥2.0, φ P ≥30%). The newly added negative control experiments (media A' and D) further confirm that under the single condition of "high humidity without ions" or "low humidity with ions", the coating structure remains intact (R <1.5, φ P <20%), which is an indisputable proof that the "humidity + ion" dual signal is a sufficient and necessary condition for structural failure. The internal mechanism of this synergistic effect is revealed by the chemical kinetic data of Table 7: for Examples 2 and 5, which use an ionic cross-linked network, the release time point of phytic acid (key) is definitely earlier than the appearance of calcium ions (lock fragments), which from a data level confirms the programmed step of "responding first, attacking later".

[0170] Programmability and structural failure process analysis:

[0171] The "programmable" technical feature of the present application is realized by adjusting the ratio of microcapsules. The data of Table 4 show that in medium A, when the T h : T i ratio increases from 1:5 (Example 4) to 5:1 (Example 5), the trigger time t1 is accurately shortened from 36 hours to 25 hours. The "stepwise" structural failure process after triggering is confirmed by the electrochemical quantitative data of Example 9 (Table 11). The charge transfer resistance (Rct) of the coating film of all examples has an abrupt drop of more than 3 orders of magnitude (>1000 times) near the trigger point, which provides direct physical evidence for the stepwise increase of water vapor permeability and the formation of through holes.

[0172] Universality of technical solutions:

[0173] To verify the robustness and universality of the technical solutions of the present application, we conducted multi-dimensional tests. First, the results in Table 4 show that the samples of all examples exhibit stable and reliable triggering behavior in three different simulated media with different ion compositions, whether acidic, basic or otherwise. Second, comparing Example 1 (corn film coating), Example 2 (canola heavy coating), and Example 3 (rice film coating), all of which differ in crop type, coating type, and reversible network type, all successfully achieved programmable physical disintegration. Finally, the results of Application Example 7 (Table 9) further extend the universality from simulated environments to real soils (black soil, red soil, saline-alkali soil) with vastly different physicochemical properties, demonstrating that the core principles of the present application have good platform universality and are not limited to specific crops, coating processes, or soil environments.

[0174] Comprehensive evaluation of environmental robustness and final environmental fate:

[0175] The core advantage of the present application over existing active triggering technologies lies in its excellent environmental robustness. The results of Application Example 6 (Table 8) are the strongest evidence of this advantage: in the presence of a strong enzyme inhibitor (CuSO4), the biochemical reaction-dependent Comparative Example 4 completely fails (weight loss < 15%), while the physical triggering mechanism of the present application exhibits strong anti-interference ability and stable performance. This fundamentally solves the pain point of poor reliability of enzyme degradation technology in complex and uncontrollable real soil environments. In addition, Application Example 8 (Table 10) confirms that all formula materials of the present application have a final biodegradation rate of more than 94% according to international standards (ISO 17556:2019), clearly demonstrating their environmental friendliness, no long-term residual risk, and ensuring the green sustainability of the technical solutions.

[0176] Analysis of the influence trend of key components:

[0177] By systematically comparing each example and comparative example, we can determine the influence trend of key components on the final effect. The mass ratio of humidity-triggered microcapsules (T h ) to ion-triggered microcapsules (T i ) in the triggering layer is a key parameter for controlling the triggering time (t1), which directly echoes the description in the present application regarding the mass ratio range of 1:5 to 5:1.

[0178] As shown in Table 4, Example 4 sets the mass ratio of T h :T i at the lower limit of the range (1:5), and its triggering time t1 is relatively the longest (36 hours in medium A). This is due to the lower proportion of T hThe initial water vapor permeation and the release rate of core substance (e.g. citric acid) are slowed down, which delays the second step reaction of unlocking the reversible network. In contrast, Example 5 sets the ratio at the upper limit of the range (5:1), which significantly shortens the triggering time t1 (25 hours in medium A) because of the high proportion of T h The first step humidity response is accelerated, thus initiating the subsequent ion unlocking process in advance. The T h : T i The ratio is between the two, and the triggering time also falls within this time window accordingly.

[0179] This clear trend proves that by precisely regulating the mass ratio of T h and T i , the disintegration time of the coating can be programmed, thus meeting the agronomic needs of different crops and different sowing conditions.

[0180] In summary, the present application successfully prepares a performance programmable PHA composition through the ingenious design of multi-layer structure, the construction of reversible network and the synergistic configuration of double-triggered microcapsules. The technical solution is logically rigorous and has significant effect, which has been fully verified in the demanding application scenario of seed coating.

[0181] Those skilled in the art should understand that the above examples are only exemplary and are not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement, etc. of the technical solution of the present application within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A dual-trigger programmable degradable polyhydroxy fatty acid ester composition, characterized in that, The cured film structure formed by the composition comprises, from the outside to the inside, the following: The outer protective layer contains a film-forming component with polyhydroxy fatty acid ester as the main film-forming substance and a reversible cross-linked network structure; The trigger layer comprises humidity-triggered microcapsules and ion or chelate-triggered microcapsules, wherein: The shell material of the humidity-triggered microcapsule is selected from one or more of gelatin, gum arabic, chitosan, shellac, or polyhydroxyalkanoate, and its core substance is a penetration enhancer, which is selected from urea and ethyl lactate. The core material of the ion or chelation-triggered microcapsule is selected from citric acid and phytic acid. The humidity-triggered microcapsules and the ion or chelate-triggered microcapsules are configured to work synergistically to cause a stepwise increase in the water permeability of the cured film or to form a through-pore structure in an environment where water and dissolved inorganic ions coexist. The inner functional layer contains a film-forming phase with polyhydroxy fatty acid ester as the main film-forming substance and carries one or more functional additives; Wherein, under the triggering condition, the step ratio R of the water vapor permeability of the cured film is ≥2.0, and the proportion of through holes φ is... P ≥30%; The polyhydroxy fatty acid ester is derived from an aqueous dispersion of polyhydroxy fatty acid ester, which is selected from one or more aqueous dispersions of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). The outer protective layer is composed of the above-mentioned aqueous dispersion and one or more of chitosan, alginate, lignin sulfonate, polyvinyl alcohol, sodium carboxymethyl cellulose or shellac. The reversible cross-linked network structure is a dynamic covalent network or an ionic cross-linked network; the dynamic covalent network is at least one of a Schiff base, oxime, borate ester, or acetoacetate polyamine structure; the ionic cross-linked network is a calcium alginate or chitosan sodium tripolyphosphate structure. The acetoacetate polyamine structure is formed by the reaction of an acetoacetate-functionalized polymer with a polyamine.

2. The dual-trigger programmable degradable polyhydroxy fatty acid ester composition according to claim 1, characterized in that, The median particle size D of the volume distribution of the humidity-triggered microcapsules and the ion or chelate-triggered microcapsules 50 The microcapsules are 0.5 to 10 μm in size, with an encapsulation efficiency of not less than 70%, and the solid content in the trigger layer is 10 wt% to 50 wt%, with a mass ratio of humidity-triggered microcapsules to ion or chelate-triggered microcapsules of 1:5 to 5:

1.

3. The dual-trigger programmable degradable polyhydroxy fatty acid ester composition according to claim 1, characterized in that, The functional additives included in the inner functional layer are selected from one or more of the following: dust suppressant, wetting and dispersing agent, defoamer, coloring and identification agent, bioactive substance or nutrient fortifier.

4. A coated article, characterized in that, The coated article comprises a substrate and a multilayer cured film formed by the dual-trigger programmable degradable polyhydroxy fatty acid ester composition according to any one of claims 1 to 3, covering the surface of the substrate.

5. A method for preparing a coated article according to claim 4, characterized in that, The preparation method includes the following steps: Step 1. Provide a substrate and pretreat it as needed; Step 2. Apply the inner functional layer slurry evenly to the surface of the substrate and perform the first drying step at a temperature not exceeding 50°C to form the inner functional layer; Step 3. Apply trigger layer slurry evenly to the surface of the inner functional layer, and perform a second drying step at a temperature not exceeding 50°C to form the trigger layer; Step 4. Apply an outer protective layer slurry evenly to the surface of the trigger layer and perform final drying at a temperature not exceeding 50°C to form an outer protective layer, thereby obtaining the coated product.

6. The preparation method according to claim 5, characterized in that, The time for any single drying step in the method shall not be less than 5 minutes, the maximum temperature of the coating and drying process shall not exceed 50°C, and the water activity of the final product shall not be higher than 0.

70.

7. The use of the dual-trigger programmable degradable polyhydroxy fatty acid ester composition according to any one of claims 1 to 3 in the preparation of seed coating, characterized in that, The composition provides crop seeds with dual functions of pre-sowing stability protection and post-sowing on-demand disintegration, wherein the crop is selected from corn, rapeseed, rice, wheat, cotton or legumes.

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