Pure bio-based PHA aqueous dispersion, its preparation method and applications

Abstract

This invention discloses a pure bio-based PHA aqueous dispersion, its preparation method, and its applications, belonging to the field of pure bio-based polymer aqueous dispersion technology. This dispersion uses polyhydroxyalkanoates (PHA) as the sole film-forming agent, synergistically stabilized by Pickering solid particles and natural surfactants, and can optionally incorporate bio-based plasticizers. It is prepared by melt high-pressure homogenization, low-temperature wet milling, or solvent displacement methods to obtain emulsions or slurries with a PHA content of 40–85 wt% and a particle size of 0.2 µm–3 µm. It is free of petrochemical polymer protective colloids and perfluorinated and polyfluoroalkyl substances, and has a bio-based content ≥99%. Its excellent stability, rheological properties, and film-forming properties make it an ideal base material for constructing multilayer, programmable controlled-release, and degradable functional coating systems. It can be used in paper-based barrier coatings, adhesives, and advanced crop seed coatings, achieving excellent barrier, adhesive, and slow-release properties. The products meet industrial composting and resizing standards, demonstrating green environmental protection and industrialization potential.

Description

Technical Field

[0001] This invention belongs to the field of pure bio-based polymer aqueous dispersion technology, specifically relating to pure bio-based PHA aqueous dispersions, their preparation methods and uses. Background Technology

[0002] Polyhydroxyalkanoates (PHAs) are a class of aliphatic polyesters synthesized by microorganisms, with poly(3-hydroxybutyrate) (PHB) being the most common representative. Because PHAs are derived from renewable resources and possess excellent biodegradability (especially in industrial composting and marine environments) and gas barrier properties, they are considered one of the ideal environmentally friendly materials to replace traditional petrochemical-based plastics. To broaden their applications, particularly as coatings and adhesives, the preparation of PHAs into aqueous dispersions has become an important technological direction.

[0003] In recent years, the use of biomass-derived nanoparticles, such as cellulose nanocrystals (CNC) or lignin nanoparticles (LNP), as Pickering stabilizers to prepare emulsions has become a research hotspot. The general principles have been reviewed in academic literature, for example, Bai et al., Langmuir, 2018, 35(4), 1095-1108. Meanwhile, numerous patent applications have disclosed biodegradable polymer aqueous dispersions, including PHA, and their preparation methods and applications. However, existing technologies still generally have some fundamental limitations in preparing high-performance, environmentally friendly PHA aqueous dispersions.

[0004] A mainstream technical approach relies on synthetic, especially petrochemical-based, surfactants or protective colloids to stabilize the dispersion system. For example, patent application CN112867766A (WO2020036843A1) discloses a PHA aqueous dispersion for coatings of food service products, which uses various synthetic surfactants such as polysorbate, polyethylene glycol ether, and polyvinyl alcohol (PVA). Similarly, patent application US10087326B2 describes an aqueous dispersion whose stabilizing system includes polyvinyl alcohol, cellulosic polysaccharides, and xanthan gum. Patent application WO2014023319A1 discloses a method for dispersing PHA powder in water using high shear, but its key lies in using PVA as a colloidal stabilizer. The common thread in these technical solutions is that while the introduction of PVA or synthetic surfactants provides stability, their petrochemical origin prevents the final product from meeting the "purely bio-based" standard, sacrificing the product's bio-based properties and potentially affecting its biodegradability.

[0005] Another technical approach involves treating PHA using specific physical or chemical methods to obtain aqueous dispersions. However, these methods also remain dependent on synthetic auxiliaries or face challenges in achieving high solids content and high stability. For example, patent application US7491754B2 discloses a method for directly preparing aqueous dispersions by disrupting PHA-containing microorganisms in an aqueous phase, but this method typically requires the subsequent addition of emulsifiers to enhance stability. Patent application US11332612B2 describes a method for stabilizing PHA particles using components of the microbial cell wall itself (such as peptidoglycan), achieving dispersion by controlling the peptidoglycan content. However, this limits the purity of the system and the flexibility of subsequent formulation design, and makes it difficult to achieve long-term stability at high solids content. Furthermore, patent application EP4052784A1 discloses a method for preparing PHA powder by spray drying, which uses an alkylene oxide-based dispersant, which is also a synthetic chemical and not derived from natural biomass.

[0006] At the application level, some patent applications focus on how to apply PHA aqueous dispersions to multilayer coatings to solve adhesion and performance problems. For example, patent application EP4417325A1 proposes a multilayer coating method that improves adhesion to the substrate by first coating a base layer containing a higher concentration of aqueous dispersant, followed by a top layer with a lower concentration of aqueous dispersant. While this method solves the problem of coating peeling, it focuses on the coating process rather than innovation in the dispersion itself. Its dispersion system still relies on traditional water-soluble polymers (such as methylcellulose) and does not provide a fundamental solution for preparing "pure bio-based" dispersions with high solids content and high stability.

[0007] In summary, a key technological bottleneck remains in this field: how to prepare highly crystalline polymers like PHA into aqueous dispersions with a solid content exceeding 40 wt%, particularly 60 wt%, and possessing both long-term storage stability and excellent application performance in a "pure bio-based" system completely free of petrochemical protective colloids (such as PVA) and synthetic surfactants. Existing technologies either heavily rely on petrochemical additives, failing to meet the stringent market requirements for "pure bio-based" solutions (e.g., CN112867766A, WO2014023319A1); or achieve stability by retaining microbial impurities, limiting purity and performance (e.g., US11332612B2); or employ synthetic chemicals for treatment (e.g., EP4052784A1); or only improve the application process without addressing the fundamental problem of dispersion preparation (e.g., EP4417325A1). Therefore, developing an innovative solution that can resolve this technical contradiction—namely, utilizing the synergistic effect of pure bio-based components to achieve high solids content and high stability PHA aqueous dispersions—has become a pressing challenge for promoting the widespread application of PHA materials. Summary of the Invention

[0008] The purpose of this invention is to overcome the key technical bottlenecks existing in the aforementioned background technology and to provide a pure bio-based PHA aqueous dispersion, its preparation method, and its applications. This invention is based on an unexpected discovery: by compounding specific bio-based Pickering solid particles with specific naturally derived surfactants in a specific ratio, a significant synergistic effect can be achieved, thus enabling the first-ever preparation of a pure bio-based PHA aqueous dispersion with a solid content as high as 40-85 wt% and excellent stability and application performance without the use of any petrochemical protective colloids.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a pure bio-based aqueous dispersion of polyhydroxyalkanoates, wherein the dispersion uses polyhydroxyalkanoates as the sole film-forming agent, and the dispersion comprises:

[0011] (1) 40–85 wt% of a dispersed phase, wherein the dispersed phase is a polyhydroxy fatty acid ester;

[0012] (2) 3.0-12.8 wt% of bio-based plasticizers;

[0013] (3) A synergistic stabilizing system for stabilizing the dispersed phase at high solid content;

[0014] The cooperative stability system includes:

[0015] (1) 0.10–3.0 wt% Pickering solid particles, selected from one or more of cellulose nanocrystals, cellulose nanofibers, starch nanocrystals or lignin nanoparticles;

[0016] (2) 0.05–2.0 wt% of a naturally derived surfactant selected from one or more of alkyl polysaccharides, plant saponins, lecithin, rhamnolipin or sophorolipid;

[0017] (3) The remainder consists of water and pH adjuster used to adjust the pH to 6.0–7.5, with the amount of pH adjuster included in the aqueous phase;

[0018] The dispersion has a particle size distribution of 0.2µm–3µm, and the absolute value of the zeta potential of the dispersion particles is not less than 25mV. The system does not contain any artificially added PFAS, and the total amount of PFAS is <1ng / L. It does not contain petrochemical polymer protective colloids, and the organic carbon bio-based content is ≥99%.

[0019] The petrochemical polymer protective colloid refers to water-soluble or water-dispersible polymers derived from petroleum or natural gas, used as protective colloids, including but not limited to polyvinylpyrrolidone, polyacrylate, polyacrylamide, etc.

[0020] In some embodiments, the content of polyhydroxyalkanoate in the dispersed phase can be 40 wt%, 45 wt%, 50 wt%, 60 wt%, 65 wt%, 75 wt%, 80 wt%, or 85 wt%. The content of Pickering solid particles in the synergistic stabilizing system can be 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3.0 wt%. The content of naturally derived surfactants in the synergistic stabilizing system can be 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, or 2.0 wt%. The content of bio-based plasticizers can be 0 wt%, 3 wt%, 4 wt%, 5 wt%, 6.25 wt%, 8 wt%, 10 wt%, 11.5 wt%, 12 wt%, or 12.8 wt%.

[0021] Further, the polyhydroxy fatty acid ester is one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH).

[0022] In some embodiments, the solid mass ratio of the Pickering solid particles to the naturally derived surfactant is 1:(0.3–1.2), which achieves optimal synergistic stabilizing effects. For example, this mass ratio can be 1:0.3, 1:0.4, 1:0.5, 1:0.67, 1:0.8, 1:1.0, or 1:1.2.

[0023] In some embodiments, when the Pickering solid particles are a composite of cellulose nanocrystals and lignin nanoparticles, the mass ratio of the two is 1:(0.3–1.5). This compounding can further enhance the robustness of the stable system under different pH conditions. For example, the mass ratio can be 1:0.3, 1:0.5, 1:0.8, 1:1.0, 1:1.2, or 1:1.5.

[0024] Furthermore, the bio-based plasticizer is triacetin or tributyl citrate, which can effectively improve the flexibility of PHA film after formation without sacrificing barrier properties.

[0025] The present invention also provides a method for preparing the above-mentioned pure bio-based polyhydroxy fatty acid ester aqueous dispersion, wherein the method is selected from at least one of the following methods:

[0026] Molten high-pressure homogenization method: The polyhydroxy fatty acid ester and bio-based plasticizer are melted at 175–185°C, with a single-pass residence time of ≤3 min in the melting section, and the operation is carried out under inert gas protection; the resulting melt is pumped into an aqueous phase containing the synergistic stabilizing system, pre-emulsified by rotor-stator, and then homogenized under high pressure 3–7 times at 65–75°C and 800–1200 bar.

[0027] Low-temperature wet milling method: The polyhydroxy fatty acid ester is mixed with an aqueous phase containing the synergistic stabilizing system, the slurry has a solid content of 30–55 wt%, and bead milled at ≤35°C to D. 90 ≤1.0µm, using grinding beads with a particle size of 0.1–0.5mm; then subjected to 600–1200bar pressure micro-jet or high-pressure homogenization treatment 2–6 times;

[0028] Bio-based solvent displacement method: The polyhydroxy fatty acid ester is dissolved in a bio-based solvent and added dropwise to an aqueous phase containing the synergistic stabilizing system, and then the solvent is removed under reduced pressure.

[0029] The bio-based solvent refers to an organic solvent derived from biomass, selected from one or more of ethanol, ethyl lactate, or ethyl propionate.

[0030] The preparation method may further include the step of increasing the solid content of the pure bio-based polyhydroxy fatty acid ester aqueous dispersion to 65–85% by membrane concentration or thin-film evaporation to obtain a slurry dispersion.

[0031] This invention also relates to the use of the above-mentioned pure bio-based polyhydroxy fatty acid ester aqueous dispersion. This dispersion can be used to prepare paper-based barrier coatings, wherein the coating has a water vapor transmission rate ≤68 g / m³ at 38°C and 90% RH. 2 •d. This dispersion can also be used to prepare bio-based adhesives with a paper / paper T-peel strength ≥2.0 N / 25 mm. This dispersion can also be used to prepare multilayer programmable degradable crop seed coatings, wherein the pure bio-based polyhydroxyalkanoate aqueous dispersion is used as the base film-forming material for at least one functional layer or protective layer in the coating structure.

[0032] Specifically, such as Figure 1 As shown, the multilayer structure covers the outside of the seed embryo and may include, from the inside to the outside: an inner functional layer, such as an alginate layer, which may contain functional microcapsules that can be used to load active ingredients such as lipases; and an outer protective layer, which is formed by film formation of the PHA aqueous dispersion described in this invention, and is used to protect the seed and control the release of active ingredients in the inner functional layer.

[0033] Compared with the prior art, the use of this invention can achieve the following significant beneficial effects:

[0034] Pure bio-based and highly environmentally friendly: The stabilizing system (Pickering particles and natural surfactants) and plasticizers used in this invention are all derived from biomass, resulting in an organic carbon bio-based content of over 99% in the final dispersion. Furthermore, no PFAS or petrochemical polymers are artificially added to the formulation, which aligns with global green and sustainable development trends and regulatory requirements.

[0035] High solids content and wide adjustable particle size: Through specific preparation processes and a stable system, this invention has successfully achieved a wide solids content range of 40-85wt% and a wide particle size range of 0.2µm–3µm. It can prepare both low-viscosity nanoemulsions and high-solids content micron-sized slurries, meeting the stringent requirements of different application scenarios for coating rheology and drying efficiency.

[0036] Excellent stability and application performance: The unique Pickering particles and natural surfactants work synergistically to provide a high absolute value of zeta potential, resulting in excellent storage stability, shear stability, and freeze-thaw stability. When applied to paper-based coatings, adhesives, and seed coatings, it exhibits superior barrier properties, adhesive strength, and controlled release effects, demonstrating high application value.

[0037] The process routes are diverse and industrially feasible: This invention provides three preparation routes: melt homogenization, wet grinding and solvent displacement, and includes an optional concentration step. The routes can be flexibly selected according to the raw material form and product requirements, and the process parameters are clearly defined, making it easy to scale up for industrial use.

[0038] Compatibility and foundational platform role of the advanced coating system: The high stability, high solids content, and controllable rheology of the dispersion of this invention make it suitable as a base dispersion for preparing multilayer coating systems. It can serve as a reliable foundational component for preparing more complex and advanced multilayer programmable controlled-release or degradable coating systems, providing solid material support for technological innovation in the field of smart coatings. Attached Figure Description

[0039] Figure 1 : Schematic diagram of the cross-sectional microstructure of the coating of the present invention on a seed.

[0040] In the diagram, 1. Outer protective layer (PHA film-forming layer); 2. Inner functional layer (alginate layer); 3. Seed embryo; 4. Functional microcapsule (capable of carrying lipase). Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0042] Main reagents and raw materials:

[0043] Table 1. Names, Brands, and Suppliers of Major Reagents and Raw Materials:

[0044]

[0045] Main analytical and testing instruments:

[0046] Dynamic light scattering (DLS): Malvern Zetasizer Nano ZS;

[0047] Rotational rheometer: TA Instruments DHR-2;

[0048] Differential Scanning Calorimeter (DSC): TA Instruments Q2000;

[0049] WVTR tester: MOCON PERMATRAN-W 3 / 34;

[0050] Tensile testing machine: Instron 5967;

[0051] PFAS LC-MS / MS system: Vanquish Flex Binary UHPLC+TSQ Altis Plus;

[0052] Scanning electron microscope (SEM): FEI Quanta 250;

[0053] Temperature and humidity chamber: Binder KBF 240;

[0054] OTR tester: AMETEK MOCON OX-TRAN 2 / 12;

[0055] Pre-emulsification equipment: IKA Ultra-Turrax T25 digital;

[0056] High-pressure homogenizer: GEA PandaPLUS 2000;

[0057] Microfluidics M-110P (600–1200 bar) microfluidics device

[0058] Thin-film evaporation / rotary evaporation equipment: BÜCHI Rotavapor R-300;

[0059] Magnetic stirrer: IKA RCT basic;

[0060] High-speed centrifuge: Eppendorf Centrifuge 5810 R;

[0061] Laser particle size analyzer: Malvern Mastersizer 3000;

[0062] Main testing standards:

[0063] Bio-based carbon content: ASTM D6866-24a;

[0064] WVTR: ASTM F1249-20;

[0065] OTR: ASTM D3985-24;

[0066] T-peel strength: ASTM D1876-08(2023);

[0067] Grease and grease resistance of paper and paperboard (Kit): TAPPI T 559 cm-22;

[0068] Water absorption of paper and paperboard (Cobb 60): ISO 535:2023;

[0069] Zeta potential determination: ISO 13099-1:2012, ISO 13099-2:2025 (optical method);

[0070] Seed coating abrasion test: based on the Heubach Dustmeter test method (ESA 11.0387.1 v1.1, 2019).

[0071] Industrial composting degradation: EN 13432:2000;

[0072] Thin film tensile properties: ASTM D882-18;

[0073] Soil biodegradation: ISO 17556:2019;

[0074] Particle size (Z-mean particle size, DLS): ISO 22412:2025;

[0075] Particle size (volume distribution D)90 (laser diffraction): ISO 13320:2020.

[0076] PFAS quantification: US EPA Method 1633A LC-MS / MS, detection limit 1 ng / L (based on aqueous phase diameter).

[0077] Example:

[0078] To better illustrate the present invention, the following detailed description will be provided in conjunction with the embodiments, and the formulations of each embodiment and comparative example are shown in Table 2 below.

[0079] General preparation process:

[0080] Preparation of lignin nanoparticles (LNP) (antisolvent precipitation-acidification method):

[0081] 1 g of alkali lignin was dissolved in 20 mL of ethanol to form a homogeneous lignin solution. Under magnetic stirring (600 rpm), this solution was added dropwise to 100 mL of deionized water at a rate of 1 mL / min using a syringe pump. After the addition was complete, the solution exhibited an opalescent appearance, indicating the formation of lignin nanoparticles. After stirring for another 30 minutes, the pH of the suspension was adjusted to 2.0–3.0 using 0.1 M hydrochloric acid to ensure particle stability. Subsequently, the suspension was collected by high-speed centrifugation (10,000 rpm, 15 min) and washed three times with deionized water to remove residual ethanol and hydrochloric acid. Finally, the purified LNP was redispersed in water to obtain an aqueous dispersion of LNP at the desired concentration for later use.

[0082] General preparation steps for aqueous dispersions:

[0083] The PHA aqueous dispersion used in this embodiment of the invention is prepared using an environmentally friendly solvent-free melt high-pressure homogenization method. The specific steps are as follows:

[0084] Step 1. Aqueous phase preparation: Add the prescribed amount of Pickering solid particles and the prescribed amount of naturally sourced surfactant to deionized water, and disperse and dissolve them thoroughly under stirring. Finally, add the prescribed amount of phytic acid as a pH adjuster to confirm that the pH value of the aqueous phase is within the range of 6.0–7.5.

[0085] Step 2. Preparation of molten phase: The prescribed amount of PHA powder and the prescribed amount of bio-based plasticizer are melt-blended at a temperature of 175–185℃ under inert gas protection. The single-pass residence time of the melting section is controlled within 3 minutes to obtain a uniform melt.

[0086] Step 3. Pre-emulsification: The melt obtained in step 2 is pumped into the aqueous phase prepared in step 1 and preheated to 65–75°C, and pre-emulsified using a rotor-stator high-shear device to form a crude emulsion.

[0087] Step 4. High-pressure homogenization: Immediately transfer the hot crude emulsion to a high-pressure homogenizer and homogenize it 3–7 times at a temperature of 65–75°C and a pressure of 800–1200 bar.

[0088] Step 5. Cooling: Cool the homogenized emulsion to room temperature while stirring to obtain a pure bio-based polyhydroxy fatty acid ester aqueous dispersion that is milky white in appearance and stable in properties.

[0089] Table 2. Formulations of Examples and Comparative Examples (parts by weight):

[0090]

[0091] Application example:

[0092] Application Example 1: Paper-based barrier coating.

[0093] The dispersions (slurries diluted to 50% solids content) prepared in Examples 1-10, Comparative Examples 1-2, and Comparative Example 4 were coated onto an 80 g / m² plate using a doctor blade coater. 2 On the base paper, the dry weight is controlled at 8g / m³. 2 The coated paper was dried with hot air at 120°C for 3 minutes. Its barrier properties were then tested. Comparative Example 3 was a conventional PVA aqueous solution, whose main function is adhesion rather than providing high barrier properties, which is inconsistent with the purpose of this invention to verify the barrier properties of PHA dispersions; therefore, it was not tested in this instance.

[0094] Table 3. Performance test results of the coated paper in the examples and comparative examples:

[0095]

[0096] Analysis: Table 3 shows that all embodiments (1-10) of the present invention exhibit excellent barrier and adhesive properties. Example 6 demonstrates that the technical solution of the present invention is also applicable to PHBV. Comparative Example 4 shows that the lack of plasticizer leads to a significant decrease in adhesive strength.

[0097] Application Example 2: Seed coating for crops.

[0098] All stable dispersion samples (Examples 1-10, Comparative Examples 2 and 4) were diluted to 40% solids content and used as film-forming agents. These were mixed thoroughly with fungicides, trace elements, and pigments, and then used to coat corn seeds. Comparative Example 1 was not tested because it was unstable and could not form a film. Comparative Example 3 served as a control for conventional adhesives. The test results are summarized in Table 4.

[0099] Table 4. Seed coating performance test results of the examples and comparative examples:

[0100]

[0101] Analysis: Table 4 clearly shows that the seed coatings prepared in all embodiments (1-10) of this invention exhibit low abrasion rates and good sustained-release effects. In contrast, the conventional PVA adhesive (Comparative Example 3) and the plasticizer-free formulation (Comparative Example 4) showed severe abrasion, while the PVA-stable formulation (Comparative Example 2) also performed slightly worse.

[0102] Application Example 3: Long-term storage stability.

[0103] All samples from the examples and comparative examples were sealed and stored in constant temperature incubators at 25°C and 40°C for 6 months, respectively. Changes in key physical parameters were periodically monitored. Since Comparative Example 1 completely separated within one week of storage at 25°C (see Table 5), demonstrating its instability, subsequent accelerated aging tests at 40°C were not performed. Comparative Example 3 was a conventional PVA aqueous solution, and its testing purpose was solely to provide a performance benchmark for seed coating applications; therefore, it was not suitable for this test aimed at evaluating the stability of PHA dispersions.

[0104] Table 5. Long-term storage stability test results (25°C, after 6 months) for the examples and comparative examples:

[0105]

[0106] Table 6. Long-term storage stability test results (40°C, after 6 months) for the examples and comparative examples:

[0107]

[0108] Analysis: Tables 5 and 6 show that all embodiments (1-10) of the present invention and Comparative Example 4 (without plasticizer) showed minimal changes in key indicators after 6 months of storage under normal and accelerated aging conditions, demonstrating the universality and excellent long-term storage stability of the synergistic stabilizing system of the present invention. Comparative Example 1, which used only surfactant, was completely unstable.

[0109] Application Example 4: Freeze-thaw cycle stability.

[0110] All samples were frozen at -20°C for 24 hours, then restored to room temperature for 24 hours; this constituted one cycle. After five cycles, changes in physical parameters were measured. Comparative Example 3 was a conventional PVA aqueous solution, not a PHA dispersion, and was not suitable for this test.

[0111] Table 7. Freeze-thaw cycle stability test results of the examples and comparative examples (after 5 cycles):

[0112]

[0113] Analysis: The results in Table 7 show that all samples using the synergistic stabilization system of this invention (Examples 1-10 and Comparative Example 4) can withstand multiple freeze-thaw cycles and remain stable. However, Comparative Example 2, which relies on PVA, exhibited irreversible flocculation, demonstrating that the system of this invention has stronger environmental tolerance.

[0114] Application Example 5: Mechanical Properties of Coating Film.

[0115] All stable dispersions (Examples 1-10, Comparative Examples 2 and 4) were cast into films approximately 50 µm thick on a polytetrafluoroethylene (PTFE) plate. After complete drying, they were cut into standard test strips, and their mechanical properties were tested according to ASTM D882. Comparative Example 1 was not tested because it could not form a film. Comparative Example 3 was a conventional PVA aqueous solution, not a PHA dispersion, and was not suitable for this test.

[0116] Table 8. Test results of the mechanical properties of the coatings in the examples and comparative examples:

[0117]

[0118] Analysis: The data in Table 8 systematically demonstrate the crucial role of plasticizers in improving the flexibility of PHA films. All embodiments of this invention yielded films exhibiting both strength and toughness, with performance superior to or comparable to Comparative Example 2, which relied on PVA.

[0119] Application Example 6: Soil biodegradability.

[0120] All film-forming samples, namely Examples 1-10, Comparative Examples 2 and 4, were prepared into thin film samples (2cm × 2cm), buried in standard soil, and cultured for 90 days in a constant temperature and humidity chamber at 25°C and 60% humidity. The mass loss rate was calculated. Comparative Example 1 was not tested because it was unstable and could not form a film. Comparative Example 3 was a conventional PVA aqueous solution, not a PHA dispersion, and was not suitable for this test.

[0121] Table 9. Soil biodegradation test results (after 90 days) for the examples and comparative examples:

[0122]

[0123] Analysis: Table 9 comprehensively illustrates the rapid degradation process of the materials of this invention in a soil environment. All examples (1-10) and Comparative Example 4 without plasticizers exhibit excellent biodegradability, with a mass loss exceeding 60% within 90 days. In contrast, Comparative Example 2, containing petrochemical-derived PVA, degrades significantly more slowly, which decisively highlights the fundamental advantage of the pure bio-based system of this invention in terms of environmental performance.

[0124] Application Example 7: Application verification in a multilayer programmable degradable coating system.

[0125] To verify the applicability of the dispersion of the present invention as a base material for constructing advanced multilayer coating systems, this application example uses it as a film-forming material for the outer protective layer of a multilayer structure, and tests its key performance characteristics.

[0126] Referring to a bilayer programmable degradation coating system (CN120442137A), a bilayer seed coating structure was constructed. The inner functional layer uniformly contains alginate and pre-made lipase-carrying microcapsules, and its formulation is designed to trigger the degradation of the outer layer after 30 days. The outer protective layer was coated with stable aqueous dispersions prepared in Examples 1-10 and Comparative Examples 2 and 4 of this invention, and dried at 45°C to form a film.

[0127] The prepared double-coated seeds were placed in simulated soil solution to test the film-forming quality of the outer protective layer and the actual triggered degradation performance. Comparative Example 1 could not form a film due to its inherent instability, and Comparative Example 3 used a conventional PVA adhesive, which is not within the scope of the dispersion technology of this invention. Therefore, these two cases are not applicable to this test.

[0128] Table 10 shows the application performance test results of the embodiments and comparative examples in multilayer systems:

[0129]

[0130] Analysis: The experimental results in Table 10 demonstrate that all embodiments (1-10) of the present invention can form high-quality outer protective film and cooperate well with the inner functional layer, being precisely and completely removed near the preset time point. This is due to the excellent stability and film-forming properties of the dispersion of the present invention. In contrast, Comparative Example 2, due to the presence of PVA, has poor compatibility with the enzymatic degradation system, resulting in incomplete degradation. Comparative Example 4, due to the lack of plasticizer, has physical defects in the formed coating, causing it to fail prematurely due to brittleness before enzyme triggering. This experiment fully confirms that the high-solids-content, highly stable pure bio-based PHA aqueous dispersion prepared by the present invention is an ideal basic platform material for constructing reliable and efficient advanced programmable degradation coating systems.

[0131] Application Example 8: Oxygen Transmission Rate (OTR).

[0132] According to ASTM D3985-24 standard, the coatings of each example and comparative example (dry weight 8 g / m²) were measured at 23°C and 0%RH. 2 The oxygen permeability of the sample was measured. Comparative Example 1 was not tested because it was unstable and could not form a film.

[0133] Table 11. Oxygen Transmission Rate (OTR) Test Results of Examples, Comparative Examples, and Base Papers:

[0134]

[0135] Analysis: All examples exhibited excellent oxygen barrier properties, significantly superior to uncoated paper and PVA coating (Comparative Example 3). High-solids-content samples (such as Examples 5 and 8) and plasticizer-free samples (Comparative Example 4) showed the best oxygen barrier properties, demonstrating that the system of the present invention is an effective method for constructing high gas barrier coatings.

[0136] Application Example 9: Paper-based water absorption (Cobb 60) and surface wetting.

[0137] Coated paper (dry weight 8 g / m²) was tested according to ISO 535:2023. 2 The water absorption rate (Cobb 60) of the coating was measured over 60 seconds, and the initial contact angle of the water droplet on the coating surface was recorded. Comparative Example 1 was not tested because it was unstable and could not form a film.

[0138] Table 12. Test results of Cobb 60 and contact angle of the examples, comparative examples, and base paper:

[0139]

[0140] Analysis: The coating of this invention significantly reduces the water absorption of paper and presents a hydrophobic surface. Comparative Example 4 performed best due to the absence of plasticizers, but sacrificed flexibility. The system of this invention provides excellent water resistance while ensuring film-forming properties.

[0141] Application Example 10: Re-pulping adaptability assessment.

[0142] According to the PTS-RH 021:2012 method, the coated paper was subjected to a repulping experiment to evaluate its recyclability.

[0143] Criteria: According to PTS-RH 021:2012, if the acceptable fiber yield is ≥95% and the adhesive content is <50mm² / kg, it is considered recyclable; if it is below this requirement, it is considered non-recyclable.

[0144] Comparative Example 1 was not tested because it was unstable and could not form a film. Comparative Example 4 had a coating that was too brittle and hard, and a large amount of it peeled off before re-slurrying, so it was not comparable and was not tested.

[0145] Table 13 Results of re-pulping adaptability tests for the examples and comparative examples:

[0146]

[0147] Analysis: The pure bio-based coating of the present invention (all embodiments) exhibits excellent performance during repulping, with easy fiber recycling and almost no sticky contaminants. In contrast, Comparative Examples 2 and 3, which contain PVA, generate a large amount of adhesive during repulping, severely affecting the quality of the recycled pulp, demonstrating that the present invention has better environmental recycling compatibility.

[0148] Application Example 11: Ionic strength and pH robustness.

[0149] The main purpose of this experiment was to investigate the stability of the dispersion at different pH (4-9) and calcium ion concentrations.

[0150] Table 14. Results of ionic strength and pH robustness tests for the examples and comparative examples:

[0151]

[0152] Analysis: All examples (1-10) exhibited excellent stability under acidic conditions, with their lowest stable pH values ​​ranging from 4.8 to 5.3, and remained stable throughout the entire test range above this pH value up to pH 9. The absolute value of the zeta potential was greater than 25 mV, and the particle size variation was less than 10%. Among them, Example 8, with the highest stabilizer content, showed the best acid resistance (pH 4.8), while Example 7, with the lowest stabilizer content, showed slightly weaker acid resistance (pH 5.3). In the CaCl2 titration experiment, the critical coagulation concentration (CCC) of all examples was higher than 50 mmol / L. In contrast, Comparative Example 1 was unstable below pH 6. Although Comparative Examples 2 and 4 showed some stability, their salt tolerance was significantly weaker than that of the examples of this invention. The results indicate that the synergistic stabilizing system of this invention endows the dispersion with excellent pH and electrolyte tolerance, making it suitable for a wide range of industrial applications.

[0153] Application Example 12: High shear stability.

[0154] The main purpose of this experiment was to verify the stability of each sample under high shear conditions. Comparative Example 1 was not tested due to its instability. Comparative Example 3 was a polymer solution with different rheological behaviors and was not comparable.

[0155] Table 15 High shear stability test results of the examples and comparative examples:

[0156]

[0157] Analysis: All examples (1-10) exhibited excellent recovery and structural stability after undergoing high-shear cycling. Comparative Example 2 showed partial irreversible flocculation under the same conditions. These results demonstrate that the dispersion of the present invention possesses excellent mechanical stability and can withstand the high shear forces encountered in industrial processes such as pumping, stirring, and high-speed coating.

[0158] Application Example 13: Residual Solvent Analysis.

[0159] This test is only applicable to samples prepared using the bio-based solvent displacement method. Example 3 was prepared using this method, while all other examples and comparative samples were prepared using melt homogenization, low-temperature wet grinding, or pre-prepared solutions, and therefore this test is not applicable. Quantitative analysis was performed using headspace GC-MS.

[0160] Table 16 Residual solvent test results of the examples and comparative examples:

[0161]

[0162] Analysis: The results show that after sufficient depressurized rotary evaporation to remove the solvent, the EL residue of the sample prepared by the solvent replacement method in Example 3 is less than 10 mg / kg, which meets the safety requirements of food packaging and other application fields, proving the cleanliness and controllability of the preparation route.

[0163] Application Example 14: Trace PFAS detection.

[0164] Trace analysis of 40 target PFAS compounds was performed on the dispersion samples of all examples (1-10) and comparative examples (1-4) using LC-MS / MS, in accordance with US EPA Method 1633A.

[0165] Table 17. PFAS trace detection results of the examples and comparative examples:

[0166]

[0167] Analysis: The PFAS concentration of all tested samples was less than 1 ng / L, confirming that no PFAS was artificially added in the present invention and the comparative formulation, which complies with the increasingly stringent regulatory requirements for environmentally friendly materials.

[0168] Experimental Results and Analysis:

[0169] Based on the above embodiments and application examples, this invention successfully prepared a stable and high-performance pure bio-based PHA aqueous dispersion through the synergistic effect of Pickering solid particles and natural surfactants.

[0170] Key component trend impact analysis:

[0171] Effect of PHA Solid Content: By comparing Examples 7, 1, 2, 5, and 8, it can be seen that the application performance of the final product shows a positive trend with the increase of PHA solid content. As shown in Tables 3 and 11, both WVTR and OTR decrease with increasing solid content, indicating that higher solid content helps to form a denser barrier coating. Similarly, in the seed coating test in Table 4, the sustained-release effect of the active ingredient also increases with increasing solid content. This demonstrates that the ability of this invention to prepare high-solids dispersions is key to achieving high-performance applications.

[0172] Impact of the synergistic stabilization system: The necessity and effectiveness of the synergistic stabilization system of this invention were fully verified through Comparative Example 1, Application Example 11, and Application Example 12. In Table 5, Comparative Example 1, using only natural surfactants, experienced stratification within one week and was sensitive to pH and electrolytes (Table 14). In contrast, all examples using the synergistic stabilization system exhibited excellent long-term storage stability, freeze-thaw stability, pH and ionic stability, and high shear stability (Tables 5-7, 14-15). This decisively demonstrates that the synergistic effect of Pickering solid particles and natural surfactants is the core of achieving stability in high-solids-content PHA aqueous dispersions.

[0173] The effect of bio-based plasticizers: The role of plasticizers can be clearly demonstrated by comparing examples containing different amounts of plasticizer with Comparative Example 4, which does not contain plasticizer. Comparative Example 4, which does not contain plasticizer, exhibits excellent barrier properties (WVTR, OTR) and water resistance (Cobb 60) (Tables 3, 11, and 12), but is extremely brittle. This directly leads to a comprehensive decline in its adhesive properties (T-peel strength of only 1.2 N / 25 mm, Table 3), seed coating abrasion resistance (abrasion rate as high as 12.5%, Table 4), and film toughness (elongation at break of only 2.1%, Table 8). Conversely, the addition of appropriate amounts of plasticizer in Examples 1-10 significantly improved these properties, demonstrating the important role of plasticizers in enhancing product usability. Furthermore, increasing the amount of plasticizer further improves film toughness (elongation at break increases from 10.5% in Example 4 to 22.5% in Example 8).

[0174] Comprehensive performance evaluation:

[0175] Examples 1-10 all exhibited excellent overall performance. Comparative Example 2 aimed to simulate the existing technical route relying on petrochemical protective colloids. Although some of its properties were comparable to the examples, its bio-based carbon content was insufficient, its freeze-thaw stability was poor (Table 7), and its biodegradation rate was significantly slower (Table 9), failing to meet the pure bio-based and high-performance objectives of this invention. The advantage of this invention also lies in its universality. Example 6 verified the versatility of this technical solution for other PHA types such as PHBV.

[0176] The experimental results of Application Example 7 definitively verify the feasibility and superiority of using the dispersion of the present invention as a platform technology to construct more complex intelligent coating systems. Therefore, the series of tests in the Application Examples systematically tested and evaluated the performance of the product of the present invention at different life cycle stages, including storage, application, and final disposal.

[0177] In summary, this invention successfully developed a purely bio-based, PFAS-free and petrochemical-protective colloid-free aqueous dispersion of PHA. This dispersion achieves a high solids content of 40-85 wt% and excellent long-term stability through a synergistic stabilization mechanism of Pickering particles and natural surfactants. It can be prepared using various industrially feasible methods such as melt homogenization, wet milling, or solvent displacement, and its particle size and rheological properties can be controlled according to application requirements. Application studies show that this dispersion exhibits superior performance in paper-based barrier coatings, adhesives, and seed coatings. More importantly, as a high-performance foundational material, it can be used to construct multilayer programmable degradable coating systems.

[0178] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pure bio-based polyhydroxyalkanoate aqueous dispersion characterized in that, The dispersion includes, as a percentage of the total weight of the dispersion, polyhydroxyal-kanoate as the only film-forming material, and: (1) 40-85 wt% of a dispersed phase, the dispersed phase being polyhydroxyalkanoate; (2) 3.0-12.8 wt% of a bio-based plasticizer; (3) a synergistic stabilizing system for stabilizing the dispersed phase at a high solid content; The synergistic stabilizing system includes: (1) 0.10-3.0 wt% of Pickering solid particles selected from one or more of cellulose nanocrystals, cellulose nanofibers, starch nanocrystals, or lignin nanoparticles; (2) 0.05-2.0 wt% of a natural source surfactant selected from one or more of alkyl polyglycoside, plant saponin, lecithin, rhamnolipid, or sophorolipid; (3) the balance being water and a pH adjuster for adjusting the pH to 6.0-7.5, the amount of the pH adjuster being included in the aqueous phase; wherein the particle size distribution of the dispersion satisfies 0.2 µm-3 µm, and the absolute value of the zeta potential of the dispersion particles is not less than 25 mV, and the total amount of PFAS in the system is <1 ng / L as determined according to US EPA Method 1633A, does not contain a petrochemical polymer protective colloid, and the bio-based content of organic carbon is ≥99%.

2. The pure bio-based polyhydroxyalkanoate aqueous dispersion according to claim 1, characterized in that, The polyhydroxyalkanoate is one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

3. The pure bio-based polyhydroxyalkanoate aqueous dispersion of claim 1, wherein, The solid mass ratio of the Pickering solid particles to the natural source surfactant is 1:(0.3-1.2).

4. The pure bio-based polyhydroxyalkanoate aqueous dispersion according to claim 1 or 3, characterized in that, The Pickering solid particles are a composite of cellulose nanocrystals and lignin nanoparticles, and the mass ratio of the two is 1:(0.3-1.5).

5. The pure bio-based polyhydroxyalkanoate aqueous dispersion of claim 1, wherein, The bio-based plasticizer is glyceryl triacetate or tributyl citrate.

6. A process for the preparation of a pure bio-based polyhydroxyalkanoate aqueous dispersion according to any one of claims 1 to 5, characterized in that, The method is: a melt high-pressure homogenization method: melting the polyhydroxyalkanoate and the bio-based plasticizer at 175-185°C, with a single-pass residence time of ≤3 min, and operating under inert gas protection; pumping the resulting melt into an aqueous phase containing the synergistic stabilizing system, pre-emulsifying with a rotor-stator, and then high-pressure homogenizing 3-7 times at 65-75°C and a pressure of 800-1200 bar.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes a step of increasing the solid content of the pure bio-based polyhydroxyalkanoate aqueous dispersion to 65-85% by membrane concentration or thin-film evaporation, to obtain a slurry-state dispersion.

8. Use of the pure bio-based polyhydroxyalkanoate aqueous dispersion according to any one of claims 1 to 5 for the preparation of a paper-based barrier coating, characterized in that, The coating has a water vapor transmission rate at 38°C, 90% RH of < 68 g / m 2 • d.

9. Use of the pure bio-based polyhydroxyalkanoate aqueous dispersion according to any one of claims 1 to 5 in the preparation of a bio-based adhesive, characterized in that, The paper / paper T-type peel strength thereof is ≥2.0 N / 25 mm.

10. Use of the pure bio-based polyhydroxyalkanoate aqueous dispersion of any one of claims 1-5 as a base film-forming material for at least one functional layer or protective layer in a multi-layer programmable degradable crop seed coating.

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