High-bio-based PHA-acrylate latex paint as well as preparation method and application thereof

Abstract

The invention discloses a high-bio-based PHA-acrylate emulsion paint as well as a preparation method and application thereof, and belongs to the technical field of water-based paints. The film former of the latex paint comprises 60% to 90% of polyhydroxyalkanoate (PHA) with a moderate crystallinity of 40% to 60%, and 10% to 40% of a specific bio-based acrylate copolymer with a Tg of not higher than 5 DEG C. According to the invention, a core-shell microstructure in which a rigid PHA phase is wrapped by a flexible acrylate phase is constructed through a key process including ultrasonic treatment. According to the structure, low-temperature film forming can be achieved without a VOC coalescing agent, the bio-based content of an obtained paint film is higher than 70%, the VOC content is lower than 0.5 g / L, the scrub resistance is larger than 7000 times, and the technical problem that high bio-based content and high performance of a PHA coating are difficult to achieve at the same time is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of water-based coatings, and in particular relates to a high-biobased PHA-acrylate latex paint and a preparation method and application thereof. Background Art

[0002] Among numerous bio-based polymers, polyhydroxyalkanoates (PHA), an aliphatic polyester synthesized by microbial fermentation, 100% derived from biomass, and fully biodegradable in natural environments such as soil and water, are widely considered by scientists and industry to be an ideal material for building next-generation environmentally friendly coating binders. However, despite PHA's unparalleled environmental advantages, its use as the primary film-forming component in water-based coatings faces a series of significant and insurmountable technical obstacles in existing technologies.

[0003] First, PHA suffers from a serious inherent brittleness issue. Commercial PHA produced by conventional melt crystallization methods, in particular, typically has a crystallinity exceeding 40%. This results in films that are hard but have very poor toughness, similar to random polypropylene. They easily crack when impacted or bent, failing to meet the basic mechanical property requirements of coatings.

[0004] In the art, PHAs with monomers containing 3 to 5 carbon atoms in their backbone are generally classified as short-chain PHAs (sc-PHAs), such as poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). These PHAs exhibit high molecular regularity and easy crystallization, resulting in high crystallinity, hardness, and brittleness, but also good solvent resistance. PHAs composed of monomers containing 6 to 14 carbon atoms are referred to as medium-chain PHAs (mcl-PHAs), such as poly-3-hydroxyhexanoate (PHH) and its copolymers. Due to their longer side chains, medium-chain PHAs exhibit increased steric hindrance, enhanced molecular chain flexibility, and significantly reduced crystallization ability and crystallinity, resulting in soft properties similar to those of elastomers. Based on this common understanding, those skilled in the art would generally expect that blending more flexible medium-chain PHAs with acrylates would more effectively improve the toughness and mechanical properties of the system.

[0005] Secondly, PHAs face significant film-forming challenges. Due to their strong molecular chain rigidity, PHAs typically exhibit high glass transition temperatures (Tg) and minimum film-forming temperatures (MFFT). This means that pure PHA aqueous dispersions cannot naturally coalesce to form continuous, uniform films at room temperature or even higher. To address this issue, conventional techniques in the field have involved adding large amounts of small-molecule alcohol ethers or alcohol esters to the emulsion, typically comprising more than 10% of the emulsion's solids content. While these additives, acting as temporary plasticizers, can effectively reduce the MFFT, they are volatile organic compounds (VOCs) that evaporate into the atmosphere after the film dries. This not only runs counter to the development of environmentally friendly coatings that pursue low or even zero VOCs, but also significantly reduces the economic viability of PHA as the primary film-forming agent, negating its original environmentally friendly purpose.

[0006] To overcome these shortcomings, existing technologies have made various attempts, but none have provided a complete solution. One approach is to chemically modify the PHA molecule itself, for example by introducing more flexible medium- and long-chain monomers to reduce its crystallinity and rigidity. However, while this approach can improve the flexibility of the material itself, it remains a significant challenge to effectively combine it with other components in an aqueous emulsion system to achieve improved overall performance, especially achieving a balance between low-temperature film formation and high durability without the need for VOC additives.

[0007] Furthermore, some existing technologies even go in the opposite direction of addressing the film-forming property of PHAs. For example, European Patent EP2476733A1 teaches the addition of PHA micronized particles to coatings as a matting agent. This approach aims to leverage the hardness, high melting point, and lack of film-forming properties of PHA particles to create a microscopic roughness on the paint film surface, thereby reducing gloss. This document indirectly confirms that those skilled in the art generally view PHA's "difficulty in film-forming" as an inherent property to be exploited, rather than to overcome it. This, in turn, contradicts the technical direction of the present invention.

[0008] Although polymer blending is a common strategy to improve material properties, simple physical blending of PHA with conventional polymers such as acrylates usually leads to severe macroscopic phase separation due to the huge thermodynamic incompatibility between the two, manifested as paint film haze, delamination, poor adhesion, and a cliff-like drop in mechanical properties. Therefore, it is not a feasible technical path.

[0009] In summary, despite extensive exploration of PHA applications, a key, unresolved technical challenge remains: no known solution can simultaneously achieve excellent mechanical toughness (overcoming brittleness), low-temperature film formation without the addition of any VOC coalescents, and a very high total biobased content in a water-based latex paint system using high-content (e.g., over 60% of the total binder) commercially available rigid PHA as the primary binder. Existing technologies fail to offer an effective path to achieve an ideal balance between the three mutually constraining objectives of high performance, processability, and sustainability. Summary of the Invention

[0010] One object of the present invention is to provide a highly biobased PHA-acrylate latex paint, its preparation method, and its application, to address the problems raised in the aforementioned background art. The term "highly biobased" refers to the latex paint prepared by the present invention, wherein the coating film formed after drying can have a total biogenic carbon content of not less than 70% as measured in accordance with ASTM D6866-24a or an equivalent current standard.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] The present invention provides a high bio-based PHA-acrylate water-based latex paint.

[0013] The invention comprises a composite film-forming composition and at least one component selected from pigments, fillers and additives;

[0014] The composite film-forming composition comprises, by dry weight, 60% to 90% of a PHA and 10% to 40% of an acrylate copolymer;

[0015] The acrylate copolymer has a glass transition temperature of no more than 5° C. as measured in accordance with ISO 11357-2:2020, and a biochar content of 28% to 30% as measured in accordance with ASTM D6866-24a;

[0016] Furthermore, the weight percentages of the PHA and the acrylate copolymer are calculated based on the total dry weight of the composite film-forming composition.

[0017] In some specific embodiments, the PHA is provided in the form of a first aqueous dispersion and the acrylate copolymer is provided in the form of a second aqueous dispersion.

[0018] In some specific embodiments, based on the total weight, the latex paint comprises: 15% to 44% of the composite film-forming composition on a dry weight basis, 6% to 28% of pigments and / or fillers, 0.1% to 5% of additives, and the balance water.

[0019] In some specific embodiments, the PHA content in the composite film-forming composition can be 60%, 62%, 65%, 68%, 70%, 72%, 75%, 82%, 85% or 90% by dry weight; the acrylate copolymer content can be 10%, 15%, 18%, 20%, 25%, 28%, 30%, 32%, 35%, 38% or 40% by dry weight, respectively. The glass transition temperature of the acrylate copolymer can be -15°C, -12°C, -8°C, -5°C, 0°C, 1°C, 3°C or 5°C, and the biochar content can be 28.0%, 28.5%, 28.8%, 29.2%, 29.6% or 30.0%.

[0020] In some specific embodiments, in order to achieve an optimal balance between mechanical properties and bio-based content, the content of PHA in the composite film-forming composition is limited to 60% to 75% by dry weight to achieve an optimal balance between stiffness and toughness.

[0021] In some specific embodiments, based on the total weight, the dry weight content of the composite film-forming composition in the latex paint can be 15%, 20%, 25%, 30%, 35%, 40% or 44%; the content of pigment and / or filler can be 6%, 10%, 15%, 20%, 25% or 28%; the content of additives can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 3.0% or 5%.

[0022] The PHA is a scl-PHA with a crystallinity of 20% to 60%, selected from one or more of PHB, PHBV, or poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBHHx) containing no more than 16 mol% of a comonomer. This helps achieve desirable physical properties. Specific examples include PHB, PHBV, or PHBHHx, or mixtures thereof in any proportion. For example, when the PHA is PHBV, the molar content of the 3-hydroxyvaleric acid monomer may be 3.5%, 8%, 12%, 15%, 18%, 21%, 23%, or 25%; and when the PHA is PHBHHx, the molar content of the 3-hydroxyhexanoic acid monomer may be 3%, 6%, 10%, 12%, 14%, or 15.2%.

[0023] To form the final coating product, the water-based latex paint of the present invention may also contain pigments, fillers, and additives in addition to the composite film-forming composition described above. When no pigments or fillers are added, i.e., at a 0% content, a highly biobased clearcoat can be produced. When pigments and fillers are added, a pigmented paint can be produced, with their content reaching up to 50% on a dry solids basis. Furthermore, the composition may contain additives in a total amount of 0.1% to 5%. These additives may be selected from one or more of a wetting agent, dispersant, thickener, defoamer, leveling agent, preservative, and pH regulator to optimize the production, storage, and application performance of the coating.

[0024] After drying and film formation, the PHA and the acrylate copolymer form a core-shell structure on the microscale, in which the acrylate copolymer phase acts as a continuous or semi-continuous phase, encapsulating the PHA particle phase. This structure can be verified by the surface charge properties of the composite emulsion: as shown in the subsequent examples, the zeta potential of the composite emulsion of the present invention, for example -38 mV, measured according to ISO 13099-2:2012, is very close to the zeta potential of a pure bio-based acrylate emulsion of -42 mV, but significantly different from the zeta potential of a pure PHA aqueous dispersion of -25 mV. This indicates that the surface properties of the composite particles are primarily determined by the acrylate phase, confirming its presence as the outer shell phase. This unique microstructure is the physical basis for achieving the excellent performance of the present invention. The composition, without containing a volatile organic film-forming aid, can form a coating film having a minimum film-forming temperature (MFFT) of no more than 5° C. as measured according to ISO 2115:1996 and a scrubbing resistance of no less than 7,000 times as measured according to GB / T 9755-2024.

[0025] The present invention also discloses a method for preparing a high-biobased PHA-acrylate water-based latex paint. The method is to make the latex paint have a minimum film-forming temperature of no more than 5° C. without containing a volatile organic film-forming aid, and comprises the following steps:

[0026] Step 1. Premixing the PHA aqueous dispersion and the acrylate copolymer emulsion to obtain a composite emulsion base;

[0027] Step 2. Dispersing the pigment, filler and some additives in water to prepare a color paste;

[0028] Step 3. Under stirring, add the color paste prepared in step 2 to the composite emulsion base prepared in step 1 and perform shear dispersion;

[0029] Step 4. The mixture obtained in step 3 is subjected to ultrasonic treatment, with an ultrasonic frequency of 20 kHz to 40 kHz and a power density of 150 W / L to 300 W / L.

[0030] After the ultrasonic treatment step in step 4, the paint mixing step of adding a thickener and / or a leveling agent is also included.

[0031] This method ensures the formation of the ideal microstructure of the final product through precise control of the process steps. The most critical step is ultrasonic treatment of the above mixture. The energy input in this step is to form a stable dispersion and ideal performance.

[0032] In addition, the present invention also discloses a water-based latex paint prepared by the above method. Due to the specific energy input process it undergoes, it has a stable microstructure and excellent performance that are difficult to obtain using conventional physical blending methods.

[0033] Finally, the present invention also discloses an application for providing a protective coating for the surface of a building or wooden substrate. The application comprises the step of applying the aforementioned highly bio-based polyhydroxyalkanoate-acrylate water-based latex paint of the present invention to the surface of the substrate. Through this application, the excellent low-temperature film-forming ability and high durability of the paint itself can be utilized to provide a durable protective coating for the surface of the building or wooden substrate.

[0034] Compared with the prior art, the present invention can achieve the following significant beneficial effects:

[0035] A very high biobased content is achieved: the coating film formed by the latex paint prepared by the present invention after drying can have a total biocarbon content of not less than 70% as measured in accordance with the American Society for Testing and Materials D6866-24a standard or an equivalent current standard, which is significantly higher than the existing technical level.

[0036] Excellent environmental performance: VOC content is no higher than 0.5g / L when tested according to relevant standards such as GB 30981.1-2025 or equivalent current standards. Furthermore, the content of harmful substances such as N-methylpyrrolidone (NMP), benzene series, free formaldehyde, and migratable heavy metals in the product is effectively controlled and maintained at extremely low levels.

[0037] Excellent physical properties of the coating film: The coating film formed by the present invention has excellent durability, and the number of scrub resistance measured according to relevant standards such as GB / T9755-2024 or equivalent current standards can be no less than 7,000 times.

[0038] Possessing additional functionality: The coating of the present invention also exhibits excellent indoor air purification capabilities, and the formaldehyde purification efficiency measured according to relevant standards such as JC / T 1074-2021 or equivalent current standards can be no less than 90%. DETAILED DESCRIPTION

[0039] 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.

[0040] Main reagents and raw materials:

[0041] Table 1 Main reagents, brands / specifications and suppliers are as follows:

[0042]

[0043] Main analytical testing instruments:

[0044] Table 2 Names, models / series and manufacturers of main instruments and equipment:

[0045]

[0046] Main test standards:

[0047] The following table lists the main test standards used in the embodiments of the present invention.

[0048] Table 3 Main test items, standard numbers and standard descriptions:

[0049]

[0050] Unless otherwise specified, the "PHA aqueous dispersion" or its specific type, such as PHBV aqueous dispersion, described in the examples below is the "first aqueous dispersion" as defined in the present invention; the "acrylate emulsion" or its specific brand, such as Acronal ECO 7074, is the "second aqueous dispersion" as defined in the present invention.

[0051] Preparation of the first aqueous dispersion of PHA:

[0052] The PHA aqueous dispersion used in the embodiments of the present invention is prepared using an environmentally friendly, solvent-free, high-energy homogenization method. Taking the preparation of PHBV aqueous dispersion as an example, the specific steps are as follows:

[0053] S1. Dissolve 1 g of PVA in 200 ml of deionized water and heat to 80°C as the aqueous phase.

[0054] S2. Melt 10 g of PHBV powder at 175°C.

[0055] S3. The molten PHBV prepared in step S2 was slowly added to the hot water phase of step S1 in a high shear homogenizer at a speed of 10,000 rpm, and shearing was continued for 10 minutes to form a coarse emulsion.

[0056] S4. Immediately transfer the hot crude emulsion to a high-pressure homogenizer preheated to 80°C and circulate homogenization at a pressure of 80-100 MPa for 5-8 times.

[0057] S5. The homogenized emulsion was cooled to room temperature while stirring to obtain a stable PHBV water-based emulsion with a solid content of 5 wt % and a milky white appearance. The emulsion was sealed and stored at 4 ° C for later use.

[0058] The PHBV aqueous dispersion prepared using this method has a weight-average particle size of 1.5 μm. Depending on the desired embodiment, the emulsion can be concentrated to a higher solids content, such as 40 wt%, by ultrafiltration or other methods. The preparation methods for other PHA aqueous dispersions are similar, requiring only the appropriate adjustment of the melting temperature in step S2 based on the material properties.

[0059] Examples and Comparative Examples:

[0060] In order to verify the technical effect of the present invention, the latex paints of the following examples and comparative examples were prepared.

[0061] Table 4 Summary of main materials of the examples and comparative examples:

[0062]

[0063] Taking Example 1 as an example, its detailed wet process formula is shown in Table 5, and its preparation steps are as follows:

[0064] Table 5 Detailed wet process formula of Example 1 (total 1000g):

[0065]

[0066] Step 1. 525 g of PHBV aqueous dispersion prepared by the above PHA aqueous dispersion preparation method and concentrated to a solid content of 40% was placed in a dispersion tank at room temperature with 180 g of Acronal ECO 7074 emulsion with a solid content of 50% to a dry weight ratio of 70:30. The mixture was stirred at 500 rpm and premixed for 15 minutes to obtain a composite emulsion base.

[0067] Step 2. In another dispersion tank, add 30g of deionized water, a wetting agent, a dispersant, 200g of titanium dioxide, and 50g of kaolin, and disperse at high speed for 20 minutes to prepare a uniform color paste.

[0068] Step 3. Under medium-speed stirring, slowly pump the color paste prepared in step 2 into the composite emulsion base material in step 1, adjust the pH to 8.5 with ammonia water, then increase the speed to 2000 rpm and disperse at high speed for 45 minutes.

[0069] Step 4. Transfer the mixture to an ultrasonic treatment device and perform ultrasonic dispersion at a frequency of 30 kHz for 15 minutes. Then add the thickener, defoamer and preservative (included in the total amount of additives), stir evenly at a low speed, let it stand for degassing, and filter it with a 200-mesh filter to obtain the finished interior wall latex paint.

[0070] The preparation methods of other examples and comparative examples are similar to those of Example 1, with only the types and proportions of the components being adjusted according to the logic of Tables 4 and 5. For example, Example 6 is a varnish and does not contain pigments or fillers. In Comparative Example 1, 1.5% of the total weight of the emulsion as a film-forming aid, ethylene glycol butyl ether, is additionally added. The petroleum-based acrylate emulsion used in Comparative Example 3 is the commercially available Dow Chemical PRIMAL AC-261 product, which is a pure acrylate emulsion with a solid content of 50% and an MFFT of 16°C. The preparation methods of Comparative Examples 4-6 are basically the same as those of Example 1, with the following differences: Comparative Example 4 uses a commercially available low-crystallinity PHA copolymer PHBHHx instead of PHBV to prepare the aqueous dispersion; Comparative Example 5 uses petroleum-based acrylate emulsion B, namely PRIMAL SF-016, instead of Acronal ECO7074; and Comparative Example 6 completely omits the ultrasonic dispersion treatment in step 4.

[0071] Application examples, performance testing and results analysis:

[0072] The latex paints prepared in Examples 1-3, 5, and Comparative Examples 1-6 were used for interior wall coating, and the varnish prepared in Example 4 was used for wood surface coating. The paint films were cured under standard conditions (23±2°C, 50±5% relative humidity) for 7 days before performance testing.

[0073] Table 6 Physical property test results of the embodiments and comparative examples:

[0074]

[0075] The data in Table 6 above intuitively demonstrate the physical performance advantages of the present invention. First, in terms of film-forming properties, the MFFT of the pure PHA system in Comparative Example 1 is much higher than 60°C and cannot form a film under conventional conditions. However, all embodiments of the present invention successfully reduced the MFFT to below 5°C by introducing a low-Tg acrylic emulsion, demonstrating a significant synergistic film-forming effect between the two. Secondly, in terms of mechanical properties, the scrub resistance of the embodiments of the present invention far exceeds the 3,000 times of Comparative Example 1 of the pure PHA system, and reaches an excellent level of not less than 7,000 times in the entire PHA content range of 60% to 90%. This is attributed to the fact that the core-shell or semi-interpenetrating network structure formed effectively achieves a balance between rigidity and toughness. In addition, the absolute values ​​of the Zeta potential of the embodiments of the present invention are all much higher than 30mV, indicating that the composite emulsion has excellent storage stability, which is better than the pure PHA aqueous dispersion in Comparative Example 1.

[0076] Table 7 Environmental protection and chemical composition test results:

[0077]

[0078] Note: The detection limit of free formaldehyde content is 5 mg / kg.

[0079] The data in Table 7 above highlight the great advantages of the present invention in terms of environmental protection and sustainability. First, in terms of source control of VOCs, thanks to the synergistic film-forming effect, the embodiments of the present invention do not require the addition of volatile film-forming aids, so the VOC content is less than 0.5 g / L, which is much better than Example 1 with added aids and Example 3 of conventional petroleum-based products. The test results of Example 5 and the free formaldehyde content of all samples show that the system of the present invention itself does not contain intentionally added formaldehyde sources, and its free formaldehyde content is lower than the detection limit of 5 mg / kg by the HPLC method, which fully meets the stringent requirements of high-level green standards such as the national standard GB / T 35602-2017 "Green Product Evaluation Coatings" for free formaldehyde not exceeding 10 mg / kg, further demonstrating the excellent environmental safety of the present invention. In terms of biobased content, by adjusting the PHA ratio, the total biobased content of the product of the present invention can easily reach more than 70%, and in Example 2 it is as high as 93%, which meets the requirements of sustainable development. In addition, the product of the present invention does not contain harmful substances such as NMP and benzene series, and the heavy metal content is far lower than the limit requirements of the national standard GB 30981.1-2025. Compared with the high-performance petroleum-based comparative example 3, it has an overwhelming advantage in key environmental protection indicators.

[0080] Creativity analysis of key distinguishing technical features:

[0081] In order to further demonstrate the non-obviousness of the present invention, comparative examples 4, 5, and 6 were designed, and the results thereof strongly supported the inventiveness of the present invention:

[0082] Compared with the use of low crystallinity PHA, that is, Example 1 and Comparative Example 4:

[0083] The prior art generally teaches that the crystallinity of PHA can be reduced by introducing a flexible monomer, thereby improving its brittleness. Comparative Example 4 follows this conventional approach, blending PHBHHx, a material with significantly lower crystallinity, with the bio-based acrylate of the present invention. One skilled in the art would typically expect that using this more flexible, less crystalline PHA would yield better mechanical properties. However, the experimental results were quite the opposite, with a scrub resistance of only 4,500 cycles, far lower than Example 1, which used PHBV with a crystallinity of 52%, which exceeded 7,000 cycles.

[0084] The mechanism behind this unexpected technical effect lies in the fact that the success of the present invention does not simply rely on maximizing the flexibility of the PHA material itself, but rather requires constructing a "hard core-soft shell" structure within the composite system with sufficient rigidity and structural integrity. The PHBV used in the present invention has a crystallinity within an "optimal range" of 40% to 60%. This crystallinity provides the paint film with the high hardness and strength required as a skeleton while avoiding the extreme brittleness of pure PHB. In contrast, the PHBHHx used in Comparative Example 4, due to its low crystallinity, results in an overly soft "core" that fails to provide sufficient mechanical support for the paint film. When subjected to external friction, the overly soft core cannot effectively resist deformation, leading to premature failure of the paint film. Therefore, the present invention surprisingly discovered that in PHA-acrylate composite coating systems, the crystallinity of PHA exists in an "optimal performance range" that is not the conventional "lower is better" assumption. This discovery is unconventional and solves a problem that has not been addressed by the prior art.

[0085] Comparisons with petroleum-based acrylates, namely Example 1 and Comparative Example 5, address the potential criticism that replacing the acrylate in existing PHA systems with commercially available bio-based acrylates is obvious. Comparative Example 5 replaces the bio-based acrylate Acronal ECO 7074 in Example 1 with the petroleum-based acrylate PRIMAL SF-016, which has similar physicochemical parameters, such as Tg. The results show a significant drop in scrub resistance to 4000 cycles, and slight haze develops in the paint film, indicating poor compatibility. This strongly demonstrates the unique synergistic effect between the specific bio-based acrylate selected in this invention and PHA, a synergistic effect that cannot be predicted through a simple "like-for-like" substitution and results in significant performance improvements.

[0086] A comparison was made between Example 1 and Comparative Example 6, where the ultrasonic treatment step was omitted. Comparative Example 6 used the same formulation as Example 1, omitting only step 4, the ultrasonic dispersion treatment. The results showed a significant increase in MFFT to 12°C, preventing low-temperature film formation. The scrub resistance plummeted to less than 2,000 washes, resulting in an uneven film appearance. This striking result demonstrates that ultrasonic treatment is not a conventional auxiliary dispersion method used in the art, but rather an indispensable and critical process step for achieving the low-temperature film formation and excellent mechanical properties described herein. Through high-energy input, it promotes the microscopic dispersion of the PHA and acrylate phases and the formation of an ordered structure during the subsequent film formation process. Its role is crucial and not immediately obvious.

[0087] Analysis of synergistic film-forming effect and VOC source control:

[0088] MFFT is a key indicator for evaluating the film-forming ability of latex paint. As shown in Table 6, the MFFT of the pure PHA system in Comparative Example 1 is much higher than 60°C, which means that without the addition of a large amount of VOC film-forming aids, it cannot form a continuous and uniform paint film at room temperature or even higher temperatures. This directly reveals the inherent defects of a single PHA as a film-forming material. In contrast, in Examples 1-7 of the present invention, the MFFT of the system was significantly reduced to below 5°C by introducing a low-Tg bio-based acrylate emulsion. This result strongly demonstrates that there is a significant synergistic film-forming effect between PHA and this specific acrylate emulsion. The low-Tg acrylate polymer plays the role of an "internal plasticizer". During the volatilization of water, its soft chain segments can effectively promote the deformation and fusion of high-Tg PHA particles. This inherent synergistic effect enables the system of the present invention to achieve low-temperature film formation without the addition of any VOC film-forming aids, thereby controlling the generation of VOCs at the source and making the VOC content of the final product less than 0.5 g / L, which is far superior to Comparative Example 1 with the addition of a film-forming aid and Comparative Example 3 with a conventional petroleum-based product.

[0089] Analysis of composite system microstructure and mechanical properties:

[0090] The core of the present invention is to construct a micro-composite structure of PHA and acrylate, thereby overcoming the brittleness of PHA. The pure PHA, i.e., comparative example 1, has a scrub resistance of only 3,000 times, showing poor mechanical properties. In the embodiments of the present invention, in all samples with a PHA content of 60 wt% to 90 wt%, i.e., Examples 1, 2, 3, and 7, the scrub resistance exceeds 7,000 times, which is close to or even better than the high-performance pure acrylate system, i.e., comparative examples 2 and 3. This huge improvement in performance can be attributed to the core-shell structure formed. As mentioned above, Zeta potential analysis confirmed that the surface of the composite emulsion particles is dominated by a flexible low-Tg acrylate polymer as a "shell" or continuous phase, which wraps around rigid PHA particles as a "core" or skeleton. In this structure, the PHA core provides the hardness and main support of the paint film, while the acrylate shell layer plays a role in toughening and dispersing stress. When the paint film is subjected to external friction, the soft acrylic shell can absorb and dissipate energy, avoiding stress concentration in the brittle PHA phase, thereby preventing premature damage to the paint film and achieving a perfect combination of rigidity and toughness.

[0091] Trend analysis of the impact of key component parameters on system performance:

[0092] Effect of PHA Content: Comparing Example 3 (60%), Example 1 (70%), Example 5 (75%), and Example 2 (90%), we can clearly see the trends in performance indicators as a function of PHA content. First, the total biobased content increases linearly with increasing PHA content, from 72% (Example 3) to 93% (Example 2). This demonstrates that by adjusting the PHA ratio, the biobased properties of a product can be precisely controlled to meet diverse sustainability requirements. Second, in terms of mechanical properties, scrub resistance exhibits an excellent level of over 7,000 washes across the entire PHA content range of 60% to 90%. Specifically, the system maintains a high level of durability as the PHA content increases from over 7,500 washes at 60% (Example 3) to over 7,000 washes at 90% (Example 2). This demonstrates that the synergistic toughening mechanism of the present invention is consistently effective across a wide composition range, with the flexible acrylate phase most effectively forming a continuous or semi-continuous network to toughen the rigid PHA phase, achieving an optimal balance of stiffness and toughness.

[0093] Effect of Composite Film-Forming Material Content: Comparing Examples 4, 1, and 5, it can be seen that while maintaining the PHA to acrylate dry weight ratio, increasing the composite film-forming material content in the overall formulation effectively improves the overall performance of the paint film, such as increasing the hiding power from 0.93 to 0.96 and achieving a scrub resistance greater than 7,000 cycles. However, the paint film of Example 5 is denser and fuller. This demonstrates that, within the scope defined by the present invention, the composite film-forming material content can be flexibly adjusted based on the cost and performance requirements of the application scenario.

[0094] The impact of PHA particle size: Theoretically, at the same mass ratio, using a PHA aqueous dispersion with a smaller particle size, such as close to 100 nanometers, will facilitate the formation of a denser and more uniform core-shell structure. This is because a smaller particle size means a larger specific surface area, allowing for more complete contact with the acrylic emulsion, potentially resulting in a lower MFFT and superior film mechanical properties.

[0095] The influence of the Tg of the acrylic emulsion: Theoretically, the Tg of the acrylic emulsion is a key factor affecting the MFFT of the system. Using an acrylic emulsion with a lower Tg, such as -10°C, can more effectively act as an "internal plasticizer" to reduce the film-forming difficulty of the PHA. However, an excessively low Tg may result in tackiness and reduced stain resistance in the final paint film. Therefore, the Tg range of no more than 5°C selected in this invention strikes an optimal balance between ensuring low-temperature film formation and maintaining good paint film surface properties.

[0096] In summary, the present invention successfully prepares a highly biobased, high-performance, ultra-low VOC environmentally friendly latex paint by scientifically compounding a short-chain PHA aqueous dispersion with moderate crystallinity with a bio-based acrylate emulsion, limiting the content range of each component in the final latex paint product, and utilizing the synergistic effect between the two and a key ultrasonic treatment process. This solves the difficult problem of the existing technology in balancing high biobased content and excellent application performance.

[0097] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications, equivalent substitutions, or variations to the above embodiments without departing from the principles and spirit of the present invention, and such modifications, equivalent substitutions, or variations shall be included within the scope of protection defined by the present invention.

Claims

1. A high bio-based polyhydroxyalkanoate-acrylate water-based latex paint, characterized by: The latex paint comprises a composite film-forming composition and at least one component selected from pigments, fillers, and additives; The composite film-forming composition comprises, by dry weight, 60% to 90% of a polyhydroxyalkanoate and 10% to 40% of an acrylate copolymer; The acrylate copolymer has a glass transition temperature of no more than 5° C. as measured in accordance with ISO 11357-2:2020, and a biochar content of 28% to 30% as measured in accordance with ASTM D6866-24a; Furthermore, the weight percentages of the polyhydroxyalkanoate and the acrylate copolymer are calculated based on the total dry weight of the composite film-forming composition.

2. The high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to claim 1, characterized in that: The polyhydroxyalkanoate is provided in the form of a first aqueous dispersion, and the acrylate copolymer is provided in the form of a second aqueous dispersion.

3. The high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to claim 1 or 2, characterized in that: By total weight, the latex paint comprises: 15% to 44% by dry weight of the composite film-forming composition; 6% to 28% pigments and / or fillers; 0.1% to 5% additives; and the balance of water.

4. The high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to claim 1 or 2, characterized in that: The content of the polyhydroxyalkanoate is 60% to 75% by dry weight.

5. The high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to claim 1, characterized in that: The polyhydroxyalkanoate is a short-chain polyhydroxyalkanoate having a crystallinity of 20% to 60%, selected from one or more of poly-3-hydroxybutyrate, poly-3-hydroxybutyrate-co-3-hydroxyvalerate, or poly-3-hydroxybutyrate-co-3-hydroxyhexanoate containing a comonomer content of not more than 16 mol percent.

6. The high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to claim 1 or 2, characterized in that: After drying to form a film, the polyhydroxyalkanoate and the acrylate copolymer form a core-shell structure on a microscopic scale, wherein the acrylate copolymer phase serves as a continuous or semi-continuous phase, coating the polyhydroxyalkanoate particle phase.

7. The high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to claim 1, characterized in that: The composition can form a coating film having a minimum film-forming temperature of no more than 5° C. as measured according to ISO 2115:1996 and a wash resistance of no less than 7,000 times as measured according to GB / T 9755-2024, without containing a volatile organic film-forming aid.

8. A method for preparing a high-biobased polyhydroxyalkanoate-acrylate water-based latex paint according to any one of claims 1 to 7, characterized in that: The method enables the latex paint to have a minimum film-forming temperature of no higher than 5° C. without containing a volatile organic film-forming aid, and comprises the following steps: Step 1. Premixing a polyhydroxyalkanoate aqueous dispersion and an acrylate copolymer emulsion to obtain a composite emulsion base; Step 2. Dispersing the pigment, filler and some additives in water to prepare a color paste; Step 3. Under stirring, add the color paste prepared in step 2 to the composite emulsion base prepared in step 1 and perform shear dispersion; Step 4. The mixture obtained in step 3 is subjected to ultrasonic treatment, with an ultrasonic frequency of 20 kHz to 40 kHz and a power density of 150 W / L to 300 W / L.

9. The method for preparing a high-biobased polyhydroxyalkanoate-acrylate water-based latex paint according to claim 8, wherein: After the ultrasonic treatment step in step 4, the paint mixing step of adding a thickener and / or a leveling agent is also included.

10. An application for providing a protective coating for a building or wooden substrate surface, characterized in that: The method comprises the step of applying the high bio-based polyhydroxyalkanoate-acrylate water-based latex paint according to any one of claims 1 to 7 to the surface of the substrate.

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