High-molecular-weight PHA ultrahigh bio-based emulsion paint and preparation method thereof

Abstract

The invention discloses a high molecular weight PHA ultrahigh bio-based emulsion paint and a preparation method thereof. The core of the invention lies in that a high molecular weight polyhydroxyalkanoate (PHA) which exists in the form of a Biotenaqueous emulsion and has a weight-average molecular weight of 300,000-1,000,000 g / mol is physically combined with a conventional small molecular coalescing agent, and a previously unknown physical synergistic effect between the two is utilized. According to the synergistic effect, on the premise that chemical modification is not carried out, the minimum film forming temperature of a system is remarkably reduced, and therefore the technical problem that it is difficult for high-crystallinity PHA to form a high-performance and non-sticky coating film at the normal temperature is solved. The emulsion paint prepared by the invention has ultrahigh bio-based content, excellent storage stability and high scrubbing resistance not less than 5000 times, and is suitable for building and woodware coating.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and particularly relates to a high-molecular-weight PHA ultra-high bio-based latex paint and a preparation method thereof. Background Art

[0002] Traditional latex paints primarily rely on petroleum-based synthetic resins. Their production and use consume significant amounts of non-renewable resources and can release volatile organic compounds (VOCs), posing a threat to the environment and health. To address this challenge, the development of environmentally friendly coatings with high bio-based content has become an industry trend.

[0003] Polyhydroxyalkanoates (PHA) are a class of biodegradable polyesters synthesized by microbial fermentation. They have attracted much attention due to their renewable sources and environmental friendliness. Using PHA as the main film-forming substance in water-based paints is expected to fundamentally improve the sustainability of paints. However, the application of PHA in high-performance latex paints faces severe technical challenges. First, the hydrophobicity and crystallinity of PHA make it difficult to form a stable dispersion in water. Second, to obtain a paint film with good adhesion, durability and water resistance, the molecular structure and molecular weight of PHA must be precisely controlled. For example, a too low molecular weight will result in insufficient mechanical strength of the paint film, while a too high molecular weight will greatly increase the difficulty of emulsification and dispersion.

[0004] In particular, while some prior art discloses high-content PHA compositions, they utilize PHAs with a weight-average molecular weight (Mw) below 200,000 g / mol, aiming to achieve pressure-sensitive curing properties suitable for applications such as adhesives. This precisely reflects and reinforces a technical bias in the field: that molecular weight must be sacrificed to achieve usable film-forming properties, and high-molecular-weight PHAs, due to their high crystallinity and processing difficulties, are considered unsuitable for architectural coatings requiring high hardness and durability. This bias directly teaches those skilled in the art to actively avoid or modify high-molecular-weight PHAs through complex chemical means when developing high-performance coatings, rather than attempting to simply combine them with conventional physical additives.

[0005] Furthermore, to address the compatibility issues between PHA and traditional coating resins such as acrylates, mainstream research in this field has focused on complex chemical modification or compatibilization technologies. For example, some approaches improve performance through blending; other technical routes are dedicated to developing special reactive stabilizers or graft copolymers that forcibly increase compatibilization by building chemical bond bridges between different polymer phases. The essence of these approaches is to use PHA as a functional additive to modify petrochemical-based polymers. The system is still primarily petrochemical-based, not only failing to fully realize the potential of PHA as a structural component, but also introducing complex synthesis steps and high costs, and failing to fundamentally solve the technical difficulties of developing high-performance coatings in which PHA accounts for more than 70%.

[0006] Therefore, those skilled in the art face a long-standing technical dilemma and mindset: either use PHA in low-performance pressure-sensitive applications, or invest significant R&D costs in chemical modification and add it in small quantities as an auxiliary ingredient. The prior art has yet to offer a solution that doesn't rely on complex chemical modifications, but instead optimizes the polymer's physical structure and the physical synergy of the formulation to achieve a PHA-based coating with a minimum weight percentage of 70% and excellent coating performance. This invention aims to overcome these technical biases and difficulties, providing a new, simple, and efficient solution. Summary of the Invention

[0007] The present invention provides a high molecular weight PHA ultra-high bio-based latex paint and a preparation method thereof, aiming to solve the technical problem in the prior art of difficulty in achieving both high bio-based content and high performance coatings.

[0008] The present invention provides a high molecular weight PHA ultra-high bio-based latex paint composition, the composition comprising:

[0009] A composite film-forming material comprising a PHA resin having a Mw of 300,000 g / mol to 1,000,000 g / mol and one or more non-volatile or low-volatile organic film-forming aids having a molecular weight of less than 1,000 g / mol;

[0010] Water, as dispersion medium;

[0011] at least one component selected from pigments and fillers;

[0012] and at least one other auxiliary agent except the film-forming auxiliary agent.

[0013] In the composition, the mass proportion of the PHA resin in the total film-forming substance is not less than 70%; and when the composition does not contain the film-forming aid, the minimum film-forming temperature measured in accordance with GB / T 9267-2008 is higher than 40°C, and when the composition contains the film-forming aid, the minimum film-forming temperature is not higher than 15°C.

[0014] By strictly limiting the molecular weight range of PHA, the present invention ensures excellent mechanical strength and durability of the paint film, which is fundamentally different from the low-molecular-weight PHAs used in adhesives in the prior art. Furthermore, the inventors discovered and revealed a previously unrecognized "physical film-forming synergistic mechanism of high-molecular-weight PHAs." The core of this mechanism lies in the fact that the specific high-molecular-weight PHA resins selected in the present invention, with a molecular weight of 300,000 to 1,000,000 g / mol, inherently possess the potential to form a strong physical network, but their high crystallinity and high glass transition temperature make them difficult to independently form films at room temperature. The inventive contribution of the present invention lies in the fact that, rather than chemically modifying the polymer itself, it introduces a conventional, low-molecular-weight film-forming aid with a molecular weight below 1,000 g / mol. This aid utilizes its temporary, reversible physical plasticization of the PHA particles during evaporation, significantly lowering their effective minimum film-forming temperature. This "unlocks" the film-forming potential of the high-molecular-weight PHA, enabling it to coalesce under ambient conditions to form a dense, uniform coating with high cohesive strength. This purely physical synergistic mechanism, which avoids complex chemical reactions and expensive special compatibilizers, is the cornerstone of the technical solution of the present invention. It reveals a new, simple, efficient and non-obvious technical path for the successful application of highly crystalline biopolymers in high-performance water-based coatings.

[0015] The Mw can be, for example, 300,000 g / mol, 400,000 g / mol, 500,000 g / mol, 600,000 g / mol, 800,000 g / mol or 1,000,000 g / mol. The selection of the Mw range is the result of balancing the mechanical properties of the paint film with the processability of the system. When the Mw is lower than 300,000 g / mol, the polymer chains are insufficient to form effective physical entanglement points, resulting in poor cohesion of the paint film, stickiness, and serious lack of mechanical strength and scrub resistance. When the Mw is much higher than 1,000,000 g / mol, its melt or solution viscosity increases exponentially, resulting in huge energy consumption in the emulsification and dispersion process, extremely demanding requirements on industrial equipment, and greatly reducing the economy and feasibility of the technical solution. Therefore, the range defined by the present invention is a preferred window that achieves the best balance between "high performance" and "processability".

[0016] In one embodiment, the PHA accounts for no less than 80% by weight of the total film-forming substances in the latex paint composition. For example, the PHA may account for 80%, 85%, 90% or 95% by weight.

[0017] In a preferred embodiment, the bio-based carbon content of the latex paint composition is not less than 50% as measured in accordance with ASTM D6866-24a, and the scrub resistance of the coating formed therefrom as measured in accordance with GB / T 9266 is not less than 5,000 times. This excellent physical property is difficult to achieve with high-biobased content coatings in the prior art. The inventors surprisingly discovered that by strictly controlling the Mw of PHA within the range of 300,000 g / mol to 1,000,000 g / mol, and combining it with an optimized pigment-to-binder ratio, the resulting polymer matrix has unprecedented cohesive strength and network integrity. This unique structural feature is the direct reason for achieving a high scrub resistance of more than 5,000 times, thereby resolving the technical problem in the prior art of being unable to achieve both bio-based content and physical durability.

[0018] In one embodiment, the PHA is selected from at least one of poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), or a combination thereof, wherein the mole fraction of the comonomer is between 5 mol% and 20 mol%. This range is crucial for adjusting the crystallinity, melting point and flexibility of the PHA, and is the key to obtaining ideal paint film properties. The mole fraction of the comonomer can be, for example, 5 mol%, 8 mol%, 10 mol%, 12 mol%, 15 mol%, 18 mol% or 20 mol%. The selection of a comonomer mole fraction of 5 mol% to 20 mol% is the key to reconciling the rigidity and flexibility of the paint film. When the comonomer content is lower than 5 mol%, the crystallinity of the PHA is too high, resulting in a paint film that is brittle and easy to crack, and the minimum film-forming temperature is too high. When the comonomer content is higher than 20 mol%, the proportion of the amorphous region of the polymer is too large, resulting in a paint film that is too soft, reduced stain resistance, and affected hardness and chemical resistance. Therefore, the range of 5 mol % to 20 mol % defined in the present invention is a performance optimization range that ensures that the paint film has both sufficient toughness to adapt to deformation of the substrate and sufficient rigidity to resist physical wear and contamination.

[0019] In one embodiment, the composition further comprises an auxiliary film-forming substance, wherein the auxiliary film-forming substance is a bio-based synthetic emulsion certified by the mass balance method. Furthermore, when the auxiliary film-forming substance is included, the composition can have a formaldehyde purification function, with a 24-hour formaldehyde purification efficiency of not less than 75% as measured in accordance with JC / T 1074.

[0020] In one embodiment, the at least one other auxiliary agent is selected from one or more of an emulsifier, a dispersant, a wetting agent, a thickener, a defoaming agent, a preservative, a mildew inhibitor, a pH regulator, and a formaldehyde purification auxiliary agent, wherein the other auxiliary agent comprises at least one bio-based emulsifier or at least one bio-based dispersant.

[0021] The present invention also provides a method for preparing the above-mentioned PHA ultra-high bio-based latex paint composition, which comprises the following steps:

[0022] Step 1. preparing a PHA resin having a Mw of 300,000 g / mol to 1,000,000 g / mol into an aqueous PHA dispersion or emulsion by at least one method selected from a solvent emulsification-evaporation method, a melt emulsification method, and a direct powder dispersion method;

[0023] Step 2. mixing and grinding the at least one component selected from the group consisting of a pigment and a filler with water, at least one dispersant, and at least one wetting agent to prepare a pigment and / or filler slurry;

[0024] Step 3. Mixing the aqueous PHA emulsion obtained in step 1 with the pigment and / or filler slurry obtained in step 2, adding the non-volatile or low-volatile organic film-forming agent having a molecular weight of less than 1,000 g / mol, and adding other additives constituting the latex paint composition as needed, stirring evenly, and adjusting the pH value and / or viscosity of the latex paint composition to obtain the latex paint composition.

[0025] Furthermore, in step 3, before or after adding the pigment and / or filler slurry, an auxiliary film-forming substance may be added, wherein the auxiliary film-forming substance is a bio-based synthetic emulsion certified by the biomass balance method.

[0026] Compared with the prior art, the present invention can achieve the following significant beneficial effects:

[0027] Significant environmental benefits and ultra-high biobased content: By utilizing renewable, high-molecular-weight PHA as the core film-forming material, this invention enables the final latex paint composition to achieve a biobased carbon content exceeding 50%. PHA's inherent biodegradability enables waste paint films to be decomposed by microorganisms under specific environmental conditions, significantly reducing the product's carbon footprint and VOC emissions throughout its lifecycle.

[0028] Excellent paint film properties and wide applicability: By scientifically selecting the type and molecular weight range of PHA, combined with optimized emulsification and dispersion technology and additive formulation, the PHA latex paint produced by the present invention can form a continuous, dense, non-sticky paint film with good adhesion, suitable flexibility, good water resistance and excellent scrub resistance, meeting the high standards required for indoor and outdoor building wall and wood coatings.

[0029] Feasibility and stability of the preparation process: The preparation method provided by this invention is compatible with traditional water-based coating production processes, making it easy to implement large-scale production. By combining this method with a specific formulation, PHA-based emulsions with excellent storage stability can be stably prepared, resolving a key technical bottleneck in the application of bio-based materials.

[0030] Flexibility in formula design and synergistic enhancement effect: By compounding high-molecular-weight PHA with a specific auxiliary bio-based synthetic emulsion, the present invention can not only further improve the product's overall bio-based index, but also introduce the unique functionality of the auxiliary emulsion, such as ultra-low odor and high-efficiency formaldehyde purification capabilities, achieving synergistic enhancement in performance and meeting the market demand for high-end environmentally friendly functional coatings. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the present embodiment are all commercially available industrial products or can be prepared by conventional methods. Performance test methods, unless otherwise specified, are carried out in accordance with the standards described in the summary of the invention.

[0032] Table 1 List of main reagents and raw materials:

[0033]

[0034] Table 2 List of main analytical and testing instruments:

[0035]

[0036] Main test standards and methods:

[0037] Biobased carbon content: measured according to ASTM D6866-24a.

[0038] Solid content: determined according to GB / T 1725-2007.

[0039] Viscosity: measured using a Stormer viscometer in accordance with GB / T 9269-2009.

[0040] pH value: Measured using a calibrated laboratory pH meter at 25 ± 1 °C.

[0041] Drying time: Determined according to GB / T 1728-2020 method.

[0042] Paint film adhesion: measured according to GB / T 9286-2021 method.

[0043] Paint film flexibility: measured according to GB / T 1731-2020 method.

[0044] Water resistance: Determined according to GB / T 1733-1993.

[0045] VOC content: Determined in accordance with GB 18582-2020 Appendix A gas chromatography method.

[0046] Formaldehyde purification performance: tested in accordance with JC / T 1074-2021.

[0047] Scrub resistance: tested in accordance with GB / T 9266-2009 standard.

[0048] Weather resistance: Tested in accordance with ASTM G154-23 using a QUV accelerated aging test chamber.

[0049] Stain resistance: tested in accordance with GB / T 9780-2013.

[0050] Anti-blocking: tested according to ASTM D4946-89 (2017).

[0051] MFFT: tested in accordance with GB / T 9267-2008.

[0052] Example 1: Preparation of PHA ultra-high bio-based latex paint.

[0053] Preparation of aqueous PHA emulsion: Weigh 100 parts of PHA resin 1 and dissolve it in 400 parts of dichloromethane. Separately, dissolve 3 parts of emulsifier 1 and 2 parts of emulsifier 2 in 200 parts of deionized water. Add the aqueous phase to the oil phase under high shearing conditions and emulsify. Then, remove the dichloromethane by evaporation under reduced pressure to obtain Bioten® with a solids content of 30.2% and an average particle size of 250 nm. TM Water-based PHA emulsion 1.

[0054] Preparation of pigment slurry: Mix 30 parts of deionized water, 5 parts of dispersant 1, 0.5 parts of wetting agent, and 0.3 parts of defoamer. Add 80 parts of rutile titanium dioxide and 20 parts of light calcium carbonate under high-speed dispersion and grind to a fineness of less than 20 μm.

[0055] Preparation of latex paint: 198.7 parts of Bioten TM Aqueous PHA emulsion 1 was mixed with 135.8 parts of pigment slurry under stirring. Five parts of a film-forming aid, 50 parts of a 2% aqueous thickener solution, 0.2 parts of a preservative, and an appropriate amount of a defoamer were added in sequence. The pH was adjusted to 8.0-8.5 using a pH adjuster. The mixture was stirred thoroughly and filtered to obtain the latex paint of Example 1.

[0056] Example 2: Validation of different PHA copolymer types.

[0057] Preparation of aqueous PHA emulsion: Using the same method as in Example 1, 100 parts of PHA resin 2 were weighed and dissolved in 400 parts of dichloromethane. Separately, 3 parts of emulsifier 1 and 2 parts of emulsifier 2 were dissolved in 200 parts of deionized water. Under high shear, the aqueous phase was added to the oil phase for emulsification. The dichloromethane was then removed by evaporation under reduced pressure to obtain Bioten® with a solids content of 30.1% and an average particle size of 260 nm. TM Water-based PHA emulsion 2.

[0058] Preparation of latex paint: 199.3 parts of Bioten TM Mix aqueous PHA emulsion 2 with 135.8 parts of the pigment slurry prepared in Example 1. Add 6 parts of a film-forming aid, 55 parts of a 2% aqueous thickener solution, 0.2 parts of a preservative, and an appropriate amount of a defoamer. Adjust the pH to 8.0-8.5, stir well, and filter to obtain the latex paint of Example 2.

[0059] Example 3: Verification of different preparation methods.

[0060] Preparation of aqueous PHA dispersion: 100 parts of PHA resin 1 micropowder with an average particle size of 15 μm was added to a dispersion containing 10 parts of bio-based dispersant 2, 1 part of wetting agent and 189 parts of deionized water under high-speed dispersion. The mixture was then ground with a sand mill to an average particle size of less than 3 μm to obtain Bioten with a solid content of 33.0%. TM Water-based PHA emulsion 1.

[0061] Preparation of latex paint: 181.8 parts of Bioten TMMix aqueous PHA emulsion 1 with 135.8 parts of the pigment slurry prepared in Example 1. Then, add 4 parts of a film-forming aid, 45 parts of a 2% aqueous thickener solution, 0.2 parts of a preservative, and an appropriate amount of a defoamer. Adjust the pH to 8.0-8.5, stir well, and filter to obtain the latex paint of Example 3.

[0062] Example 4: Compounding with auxiliary bio-based emulsion.

[0063] Under stirring, 158.9 parts of Bioten TM Aqueous PHA Emulsion 1, containing 48 parts of PHA solids, was mixed uniformly with 24.5 parts of Auxiliary Bio-based Synthetic Emulsion 1, containing 12 parts of solids. Then, 135.8 parts of pigment slurry was added. Then, 4 parts of film-forming aid, 50 parts of a 2% aqueous thickener solution, 5 parts of Formaldehyde Purification Aid 1, 0.2 parts of a preservative, and an appropriate amount of a defoamer were added in that order. The pH was adjusted to 8.0-8.5, the mixture was stirred uniformly, and then filtered to obtain the latex paint of Example 4.

[0064] Example 5: Effect of Mw.

[0065] In this example, PHA resin 3 was used as raw material, and the raw material ratio and preparation method were exactly the same as those in Example 1. First, Bioten TM Aqueous PHA emulsion 3 was prepared, and the latex paint of Example 5 was obtained from the emulsion.

[0066] Example 6: Effect of comonomer mole fraction.

[0067] In this embodiment, PHA resin 5 is used as raw material, and the raw material ratio and preparation method are exactly the same as those in Example 1. First, Bioten TM Aqueous PHA emulsion 5 was prepared, and the latex paint of Example 6 was prepared from the emulsion.

[0068] Example 7: Wood coating application verification.

[0069] The latex paint prepared in Example 1 was applied to a standard treated pine wood board. After curing under standard conditions, its adhesion to the wood substrate was tested according to the GB / T 9286-2021 method.

[0070] Example 8: Low PVC high scrub resistance formula.

[0071] To verify the potential of the present invention in achieving higher scrub resistance, this example optimizes PVC by reducing the amount of pigments and fillers used in Example 1.

[0072] Preparation of pigment slurry: Mix 30 parts of deionized water, 4 parts of dispersant 1, 0.5 parts of wetting agent, and 0.3 parts of defoamer. Add 60 parts of rutile titanium dioxide and 10 parts of light calcium carbonate under high-speed dispersion and grind to a fineness of less than 20 μm.

[0073] Preparation of latex paint: 198.7 parts of Bioten TM Aqueous PHA emulsion 1 (containing 60 parts of PHA solids) was mixed with 104.8 parts of the low-PVC pigment slurry prepared in this example under stirring. The remaining additives and preparation steps were the same as in Example 1, ultimately yielding the latex paint of Example 8.

[0074] Comparative Example 1: Preparation of traditional styrene acrylic latex paint.

[0075] Mix 120 parts of a commercially available styrene-acrylic emulsion (50% solids, containing 60 parts solids) with 135.8 parts of the pigment slurry prepared in Example 1. Add 8 parts of a film-forming aid, 50 parts of a 2% aqueous thickener solution, 0.2 parts of a preservative, and an appropriate amount of a defoamer in sequence. Adjust the pH to 8.0-8.5, stir well, and filter to obtain the latex paint of Comparative Example 1.

[0076] Comparative Example 2: Effect of too high comonomer mole fraction.

[0077] In order to prove the necessity of the upper limit of the comonomer molar fraction range defined in the present invention, this comparative example uses PHA resin 6 with too high a comonomer content as raw material and adopts the same method as Example 1 to prepare the corresponding Bioten TM Water-based PHA emulsion 6 and the latex paint of Comparative Example 2.

[0078] Comparative Example 3: PHA was blended with a conventional petrochemical-based emulsion.

[0079] In order to simulate the idea of ​​blending PHA with conventional petrochemical-based emulsion in the existing technology, Bioten TM Aqueous PHA emulsion 1 was blended with a conventional, non-biobased polyvinyl acetate (PVAc) emulsion, with the solids weight ratio of PHA to PVAc being 80:20. The remaining raw materials and preparation method were identical to those in Example 1, yielding the latex paint of Comparative Example 3.

[0080] Comparative Example 4: Effect of comonomer mole fraction.

[0081] In this comparative example, PHA resin 4 is used as raw material. The monomer content molar fraction of the resin is lower than the range claimed in the present invention. The same method as in Example 1 is used to prepare the corresponding Bioten TM Water-based PHA emulsion 4 and latex paint of Comparative Example 4.

[0082] Experimental results and analysis:

[0083] To verify the inventiveness of the present invention, performance comparison tests were conducted between Examples 1-8 and Comparative Examples 1-4. Furthermore, to verify the necessity of a film-forming aid, a sample of Example 1 without a film-forming aid was prepared. The test results are summarized in Tables 3 and 4.

[0084] Furthermore, the coatings of all Examples and Comparative Examples were evaluated for blocking resistance according to ASTM D4946-89 (2017), using the oven, weights, rubber stoppers, and other equipment listed. The results showed that the Examples (e.g., Example 1) exhibited excellent blocking resistance (rated at or above 8) under accelerated testing conditions at 50°C, while some Comparative Examples (e.g., Comparative Example 2) exhibited significant blocking. This further demonstrates the superiority of the non-stick, durable coatings formed by the present invention.

[0085] Table 3 Comparison of basic properties and stability of latex paint compositions:

[0086]

[0087] Table 4 Comparison of key application performance of coatings:

[0088]

[0089] A comprehensive comparison of the test results in Table 3 and Table 4 clearly reveals the creativity of the present invention and its significant advantages over the prior art.

[0090] The synergistic effect of high molecular weight and appropriate comonomer content: A comparison of Comparative Example 2 (HV = 25%) and Example 1 (HV = 8%) clearly demonstrates that even with the high molecular weight PHA (Mw = 300,000 g / mol) that meets the requirements of the present invention, the comonomer content must be strictly controlled within an appropriate range. Due to its excessively high comonomer content, Comparative Example 2 exhibits a soft film with poor stain and water resistance, and its scrub resistance plummets to less than 500 cycles, completely failing to meet the requirements of a high-performance coating. This stands in stark contrast to the hard, smooth appearance and scrub resistance exceeding 7,000 cycles of Example 1. This result strongly demonstrates that the combination of the two technical characteristics of "high molecular weight" and "5-20 mol% comonomer content" defined in the present invention is essential for achieving a high-performance coating film, highlighting the inventive nature of the present invention.

[0091] Clarification of the film-forming mechanism and completeness of the technical solution: The fact that Example 1, without a film-forming aid, exhibits a MFFT well above 45°C and fails to form a film at room temperature reveals the core mechanism of the present invention. Rather than relying on a specific PHA inherently prone to film formation, the present invention addresses the film-forming challenge of highly crystalline polymers by synergistically compounding a specifically selected high-molecular-weight PHA with a conventional film-forming aid. This defines the present invention's clear, pragmatic, and efficient technical approach.

[0092] Comprehensive comparative advantages over existing technologies: Compared to the traditional high-performance styrene-acrylic emulsion (Comparative Example 1), the present invention, such as Examples 1, 2, 3, and 4, achieve or approach the same level in key indicators such as adhesion, water resistance, and weather resistance. Furthermore, they possess an overwhelming environmental advantage in terms of bio-based carbon content, exceeding 75% versus less than 1%. Compared to the PHA / petrochemical emulsion blend (Comparative Example 3), the present invention, while maintaining a higher bio-based carbon content, also achieves additional functions such as formaldehyde purification through compounding with a bio-based auxiliary emulsion (Example 4), demonstrating a higher level of technical integration and value.

[0093] The essential difference from the chemical modification / compatibility expansion technology route:

[0094] The technical solution of the present invention is fundamentally different from the prior art method of solving compatibility problems through chemical modification or the use of special reactive compatibilizers. The core of the latter is to "bond" incompatible polymer phases through chemical bonding, which is a complex solution of "closing the fold after the horse has bolted". The present invention takes a different approach. By precisely controlling the molecular weight of PHA and the content of comonomers, the physical properties and film-forming potential of the PHA polymer itself are optimized from the source, enabling it to independently form a high-performance paint film in the synergy of conventional physical additives. As shown in Tables 3 and 4, Examples 1, 2, and 3 of the present invention do not contain any special reactive compatibilizers, but still achieve excellent storage stability and paint film performance. This proves the effectiveness and advancement of the "physical film-forming synergistic mechanism" revealed by the present invention. It provides a simpler, more economical, and more focused technical path to give full play to the intrinsic performance of bio-based materials, and is significantly creative.

[0095] Analysis of the impact of key component trend changes:

[0096] Effect of PHA weight-average molecular weight: A clear performance trend can be seen by comparing the data of Example 1 and Example 5. In the range of 300,000 g / mol to 1,000,000 g / mol, as the molecular weight of PHA increases, the degree of entanglement and cohesive strength of the polymer chains increase accordingly. This directly translates into improved physical properties of the paint film, as manifested by a significant increase in the hardness and scrub resistance of the paint film from greater than 7,000 times to greater than 9,000 times, and a significant reduction in weather resistance ΔE. However, an excessively high molecular weight will also lead to a sharp increase in its melt viscosity or solution viscosity, placing higher energy consumption and equipment requirements on the emulsification and dispersion process, and also increasing the MFFT. Therefore, the molecular weight range selected in the present invention is the optimal balance between ensuring excellent paint film properties and maintaining good processability.

[0097] Effect of Comonomer Mole Fraction: Comparison of the data from Comparative Example 4, Example 1, and Example 6 reveals the critical role of comonomer content. Increasing the mole fraction of comonomers, such as hydroxyvalerate in PHBV, within the range of 5 mol% to 20 mol%, effectively disrupts the regularity of the PHA backbone, thereby reducing the polymer's crystallinity and melting point. This manifests itself in macroscopic performance as improved film flexibility and a significant reduction in MFFT from over 25°C to 4°C, facilitating the formation of crack-free, continuous coatings under a wider range of application conditions. However, if the comonomer content is less than 5 mol%, as in Comparative Example 4, the film becomes brittle due to excessive crystallinity, and the MFFT increases dramatically, rendering it unsuitable for practical use. If the comonomer content exceeds 20 mol%, the film's hardness, chemical resistance, and scrub resistance may be excessively compromised, decreasing from over 7,000 to approximately 5,800 scrubs. Therefore, the comonomer content defined in this invention is key to achieving a perfect balance of film toughness and strength.

[0098] Impact of PVC: Comparing Example 1 with Example 8, optimized for high scrub resistance, clearly demonstrates the significant improvement in coating film durability achieved by reducing PVC. By appropriately reducing the amount of pigments and fillers, the proportion of high-molecular-weight PHA binder per unit volume is increased, resulting in a denser and tougher paint film. Its scrub resistance also increases from >7,000 cycles to >10,000 cycles, demonstrating the significant potential for optimization and its ability to meet the demands of even the most demanding applications.

[0099] In summary, the present invention successfully resolves the inherent contradiction between "high biobased content" and "high-performance coatings" through creative design of PHA molecular weight, comonomer content, and synergistic effects with specific additives. Its technical solution is remarkably creative and practical.

[0100] Those skilled in the art will appreciate that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, or improvements to the technical solutions of the present invention that fall within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A high molecular weight PHA ultra-high bio-based latex paint composition, characterized in that: The composition comprises: A composite film-forming material comprising a polyhydroxyalkanoate resin having a weight-average molecular weight of 300,000 g / mol to 1,000,000 g / mol and one or more non-volatile or low-volatile organic film-forming aids having a molecular weight of less than 1,000 g / mol; Water, as dispersion medium; at least one component selected from pigments and fillers; and at least one other auxiliary agent other than the film-forming auxiliary agent; The PHA resin accounts for no less than 70% by mass of the total film-forming substances in the composition; and when the composition does not contain the film-forming aid, the minimum film-forming temperature measured in accordance with GB / T 9267-2008 is higher than 40°C, and when the composition contains the film-forming aid, the minimum film-forming temperature is no higher than 15°C.

2. The latex paint composition according to claim 1, wherein The polyhydroxyalkanoate accounts for no less than 80% by mass of the total film-forming substances in the latex paint composition.

3. The latex paint composition according to claim 1, wherein The bio-based carbon content of the latex paint composition is not less than 50% when measured according to ASTM D6866-24a standard, and the scrub resistance of a coating film formed therefrom is not less than 5,000 times when measured according to GB / T 9266 standard.

4. The latex paint composition according to claim 1, wherein The polyhydroxyalkanoate is selected from at least one of poly(3-hydroxybutyrate-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), or a combination thereof, wherein the molar fraction of the comonomer is between 5 mol % and 20 mol %.

5. The latex paint composition according to claim 1, wherein The composition further comprises an auxiliary film-forming substance, which is a bio-based synthetic emulsion certified by a biomass balance method.

6. The latex paint composition according to claim 5, characterized in that The composition has a formaldehyde purification function, and its 24-hour formaldehyde purification efficiency measured according to JC / T 1074 standard is not less than 75%.

7. The latex paint composition according to claim 1, wherein The at least one other auxiliary agent is selected from one or more of an emulsifier, a dispersant, a wetting agent, a thickener, a defoaming agent, a preservative, a mildew inhibitor, a pH regulator, and a formaldehyde purification auxiliary agent, wherein the other auxiliary agent comprises at least one emulsifier of bio-based origin or at least one dispersant of bio-based origin.

8. A method for preparing the polyhydroxyalkanoate ultra-high bio-based latex paint composition according to claim 1, characterized in that: The following steps are involved: Step 1. preparing a microbial polyhydroxyalkanoate resin having a weight average molecular weight of 300,000 g / mol to 1,000,000 g / mol into an aqueous microbial polyhydroxyalkanoate dispersion or emulsion by at least one method selected from a solvent emulsification-evaporation method, a melt emulsification method, and a direct powder dispersion method; Step 2. mixing and grinding the at least one component selected from the group consisting of a pigment and a filler with water, at least one dispersant, and at least one wetting agent to prepare a pigment and / or filler slurry; Step 3. Mixing the aqueous microbial polyhydroxyalkanoate emulsion obtained in step 1 with the pigment and / or filler slurry obtained in step 2, adding the non-volatile or low-volatile organic film-forming agent having a molecular weight of less than 1,000 g / mol, and adding other additives constituting the latex paint composition as needed, stirring evenly, and adjusting the pH value and / or viscosity of the latex paint composition to obtain the latex paint composition.

9. The preparation method according to claim 8, characterized in that In step 3, before or after adding the pigment and / or filler slurry, an auxiliary film-forming substance is further added, and the auxiliary film-forming substance is the bio-based synthetic emulsion according to claim 5.

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