Pha dispersion emulsion, process for its preparation and use

Abstract

This invention provides a PHA dispersion emulsion, its preparation method, and its applications, belonging to the field of polymer materials. This invention aims to solve the technical challenge of simultaneously achieving ultra-low temperature natural film-forming properties, excellent post-film-forming comprehensive performance, and long-term storage stability in polyhydroxyalkanoate (PHA) aqueous dispersion systems, which cannot be simultaneously satisfied by existing technologies. Its core lies in the strict definition and combination of a PHA polymer with a specific molecular weight and polydispersity index range, a film-forming aid with a specific chemical structure (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), and a specific type of water-dispersible compatible aliphatic polyisocyanate crosslinking agent. Through the synergistic effect generated by this unique ternary combination, the minimum film-forming temperature of the emulsion prepared by this invention can be reduced to 6℃~10℃, it can form a film naturally without hot pressing, and the film exhibits excellent mechanical properties, water resistance, and adhesion, as well as excellent storage stability for at least one year.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to PHA dispersion emulsions, their preparation methods, and applications. Background Technology

[0002] Polyhydroxyalkanoates (PHAs) are a class of biodegradable polyesters synthesized by microorganisms. Due to their outstanding environmental characteristics and renewable sources, they show great potential to replace traditional fossil-based plastics in various fields such as packaging, agriculture, and medicine. PHAs are diverse, and the variety of their monomer composition and chain structure leads to significant differences in their physical properties, such as melting point, crystallinity, and mechanical properties. Common PHAs can be classified into short-chain PHAs, medium- and long-chain PHAs, etc., based on the length of their monomer carbon chains. The weight-average molecular weight (Mw) and polydispersity index (PDI) of PHAs are the core parameters determining their processing performance and the performance of the final product.

[0003] Preparing PHA into aqueous dispersion emulsions is a key technological approach to expanding its applications in environmentally friendly waterborne coatings and adhesives. However, despite numerous attempts in this field, a comprehensive solution has yet to be provided that simultaneously satisfies the three core requirements: natural film formation at extremely low temperatures, excellent post-film formation performance, and long-term storage stability. Existing technologies mainly suffer from the following limitations:

[0004] Physical dispersion techniques focus on pre-application stability but fail to address the post-application film formation challenge. In recent years, significant progress has been made in preparing high-solid-content, physically stable PHA nanoscale aqueous suspensions using physical methods such as high-energy homogenization. For example, Pephrah et al. disclosed a method for preparing medium- to long-chain PHA (mcl-PHA) nanoparticle suspensions with solid content as high as 10-30% (w / v) in the *European Polymer Journal* (2016, 84, 137-146), with particle sizes reaching approximately 100 nm. The contribution of this type of technology lies in solving the physical stability problem of suspensions during storage and transportation. However, the inventors have found that while this technology focuses on optimizing the physical morphology of the suspension before application, it does not provide an effective solution to the core post-application performance bottleneck caused by the inherent high crystallinity and high glass transition temperature of PHA materials—namely, how to achieve high-quality natural film formation at ambient temperatures (especially below 10°C) without relying on external high temperature and pressure.

[0005] Existing "low-temperature film formation" methods rely on hot pressing processes rather than true low-temperature natural film formation. For example, Chinese patent application CN116874816A discloses a technical solution that refines high-melting-point (100-200℃) PHA particles to 100-1000nm, enabling them to be hot-pressed into films at temperatures of 100-150℃ and pressures of 1-9MPa. The "low-temperature" concept in this method is relative to the high melting point of PHA; it is essentially a hot-pressing process and does not address the issue of water dispersions naturally forming continuous films through water evaporation at room or low temperatures. This technical approach cannot meet the minimum film-forming temperature (MFFT) requirements near ambient temperature needed for a wide range of water-based coatings and adhesives applications.

[0006] Existing chemical modification schemes have a single objective and lack synergistic improvement in overall performance. Some technologies attempt to improve specific properties using additives. For example, Taiwan patent TW202212504A discloses an aqueous dispersion containing PHA, polyvinyl alcohol stabilizer, and a crosslinking agent. It uses conventional difunctional carboxylic acids or aldehydes such as adipic acid and glyoxal as crosslinking agents, primarily aiming to improve the water resistance of the final film through heat curing. However, this technical solution does not address or solve the core technical challenge of achieving extremely low MFFT, and the type and mechanism of action of the crosslinking agent used are fundamentally different from the high-performance crosslinking system of this invention, which aims to achieve comprehensive performance improvement.

[0007] Furthermore, documents such as the Korean Patent Publication KR20210111187A disclose various methods and components for preparing PHA dispersions. These documents disclose a wide range of PHA monomer types, molecular weight ranges, types of additives (such as various anionic and nonionic surfactants), and preparation methods (such as melt dispersion and high-pressure homogenization). However, this document provides a broad set of technical options and does not reveal or suggest combining PHA with specific molecular weights and PDI ranges with film-forming aids with specific chemical structures, such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TMPDMIB), and specific types of water-dispersible compatible aliphatic polyisocyanate crosslinking agents. Moreover, it does not disclose that such specific combinations can produce synergistic technical effects that simultaneously address the aforementioned three core challenges.

[0008] In summary, a clear technological gap remains in this field: there is no solution that, through the synergistic design of intrinsic chemical components, can universally impart truly extremely low MFFT (below 10°C) to various PHA aqueous dispersions with different structures, while simultaneously achieving comprehensive high performance, including mechanical properties, water resistance, adhesion, and excellent long-term storage stability, through subsequent chemical crosslinking reactions. This invention is proposed to fill this technological gap. Summary of the Invention

[0009] The purpose of this invention is to provide a PHA dispersion emulsion, its preparation method, and its application. This invention aims to solve the technical challenge of simultaneously meeting the three core performance requirements mentioned above in existing technologies. Specifically, through the synergistic design of specific chemical components, it provides a PHA dispersion emulsion that simultaneously achieves an extremely low minimum film-forming temperature (MFFT), excellent post-film-forming overall performance, and outstanding long-term storage stability, thereby filling a gap in existing technologies.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] This invention provides a PHA dispersion emulsion comprising the following components:

[0012] A PHA polymer comprising repeating units formed from one or more hydroxy fatty acid monomers selected from 3-hydroxy fatty acids or 4-hydroxy fatty acids containing 3 to 14 carbon atoms, or combinations thereof, wherein the Mw of the PHA polymer is 1.5 × 10⁻⁶. 5 Up to 7.0×10 5 Da, PDI is 2.0 to 3.5, for example, Mw can be 1.5 × 10 5 Da, 2.5×10 5 Da, 4.5×10 5 Da, 6.5×10 5 Da or 7.0×10 5 Da. PDI can be 2.0, 2.5, 2.8, 3.2 or 3.5.

[0013] The film-forming aid is TMPDMIB, and its amount is 3 wt% to 8 wt% of the solid PHA polymer, for example, it can be 3 wt%, 4 wt%, 5 wt%, 7 wt% or 8 wt%.

[0014] The crosslinking agent is a water-dispersible aliphatic polyisocyanate, and its amount is 2 wt% to 5 wt% of the solid PHA polymer, for example, it can be 2 wt%, 2.5 wt%, 3 wt%, 4 wt% or 5 wt%.

[0015] It also includes emulsifiers and water.

[0016] The MFFT of the PHA dispersion emulsion is 6°C to 10°C, for example, it can be 6°C, 7°C, 8°C, 9°C or 10°C.

[0017] In one embodiment, the structure type of the PHA polymer is selected from one of the following:

[0018] (1) Its monomer composition satisfies that the molar percentage of 3-hydroxy fatty acid monomers with a carbon chain length of 3 to 5 carbon atoms is not less than 70 mol%, and the short chain PHA is poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) (PHBV).

[0019] (2) Its monomer composition satisfies that the molar percentage of 3-hydroxy fatty acid monomers with a carbon chain length of 6 to 14 carbon atoms is not less than 70 mol%, and the medium- and long-chain PHA is selected from poly(3-hydroxyhexanoic acid) (P3HHx), poly(3-hydroxyoctanoic acid) (P3HO), poly(3-hydroxydecanoic acid) (P3HD), copolymers formed from at least two monomers selected from 3-hydroxyhexanoic acid monomers, 3-hydroxyoctanoic acid monomers and 3-hydroxydecanoic acid monomers, or copolymers formed from at least one monomer selected from 3-hydroxyhexanoic acid monomers, 3-hydroxyoctanoic acid monomers and 3-hydroxydecanoic acid monomers and one or more other monomers, wherein the other monomers are selected from 3-hydroxy fatty acid monomers containing 3 to 14 carbon atoms or 4-hydroxy fatty acid monomers containing 3 to 14 carbon atoms;

[0020] (3) A copolymer comprising short-chain monomers of 3-hydroxy fatty acids with a carbon chain length of 3 to 5 carbon atoms and long-chain monomers of 3-hydroxy fatty acids with a carbon chain length of 6 to 14 carbon atoms, wherein the copolymer is poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) (P(3HB-co-3HHx)).

[0021] (4) A copolymer containing 3-hydroxybutyric acid monomer and 4-hydroxybutyric acid monomer, which is poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) (P(3HB-co-4HB)).

[0022] In one embodiment, the emulsifier is a complex of a nonionic emulsifier and anionic emulsifier, the total amount of which is 1 wt% to 5 wt% of the PHA polymer solids, and the hydrophilic-lipophilic balance (HLB value) of the nonionic emulsifier is 12 to 18.

[0023] In one embodiment, the solids content of the PHA dispersion emulsion is 30 wt% to 50 wt%, for example, it may be 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%.

[0024] In one embodiment, the median particle size D of the PHA polymer particles in the PHA dispersion emulsion 50 The value can be from 0.1 μm to 2.0 μm, for example, it can be 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm or 2.0 μm.

[0025] The present invention also provides a method for preparing the above-mentioned PHA dispersion emulsion, the method comprising the following steps:

[0026] Step 1. Heat the PHA polymer to a molten state;

[0027] Step 2. Under high-speed shear conditions, the molten PHA polymer is added to an aqueous phase containing emulsifier and water for emulsification to obtain a preliminary PHA dispersion;

[0028] Step 3. Homogenize the preliminary PHA dispersion to further reduce the particle size and improve dispersion uniformity;

[0029] Step 4. Slowly add the TMPDMIB film-forming aid to the homogenized PHA dispersion and stir for 5 to 30 minutes to allow it to fully penetrate; then slowly add the crosslinking agent and continue stirring for 10 minutes to obtain the PHA dispersion emulsion; finally, adjust the pH of the PHA dispersion emulsion to 7.5 to 9.0 with a weak base.

[0030] In one embodiment, the melting temperature of the PHA polymer in step 1 is controlled within the range of 100°C to 180°C; the high-speed shearing rate in step 2 is 5000 r / min to 10000 r / min, the emulsification temperature is controlled within the range of 70°C to 95°C, which is higher than the melting point of the PHA used but lower than the boiling point of water; and the homogenization process in step 3 is carried out using a high-pressure homogenizer, with the homogenization pressure controlled within the range of 30 MPa to 80 MPa.

[0031] In one embodiment, after the emulsion obtained in step 4 is coated into a film, it is heat-treated at 110°C to 150°C for 3 to 30 minutes to promote the reaction of the crosslinking agent and complete the curing.

[0032] The present invention also provides the application of the above-mentioned PHA dispersion emulsion in the preparation of waterborne coatings and waterborne adhesives.

[0033] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0034] Significantly expanding the low-temperature application range of PHA and achieving energy saving: The core advantage of this invention lies in the fact that, through the synergistic effect of specific additives, the MFFT of various chemically structured PHAs can be uniformly and significantly reduced to an extremely low level of 6℃ to 10℃. This not only overcomes the technical bottleneck of many PHA materials being difficult to apply under low-temperature conditions due to excessively high MFFT, thus broadening their application possibilities under different environmental conditions, but also brings significant energy-saving effects by reducing the baking or heating temperature required for film formation.

[0035] This invention universally endows various PHA films with excellent overall properties: By introducing a specifically selected water-dispersible and compatible aliphatic polyisocyanate crosslinking agent, and in conjunction with a highly efficient film-forming aid, this invention enables films formed from different types of PHA within the Mw and PDI ranges defined in this invention to exhibit excellent and balanced overall properties. Specifically, mechanical properties, water resistance, chemical resistance, and adhesion to various substrates are all significantly improved.

[0036] Ensuring excellent long-term storage stability of the emulsion system: Through optimized selection of emulsion system, precise control of preparation process and pH adjustment, the PHA dispersion emulsion prepared by this invention can maintain physical and chemical stability for at least 1 year, during which key performance indicators such as particle size, viscosity, and MFFT do not deteriorate significantly.

[0037] The unique synergistic effect and outstanding substantive features of the specific component combination: The core innovation and inventiveness of this invention lies not in simply mixing known PHA, film-forming aids and crosslinking agents, but in a discovery that is unexpected: that is, the powerful, non-obvious synergistic technical effect is produced by strictly defining the molecular properties of PHA (specific Mw and PDI ranges), the chemical structure of the film-forming aid (specifically TMPDMIB), and the type of crosslinking agent (specifically water-dispersible aliphatic polyisocyanates) and their respective dosage ranges.

[0038] It is this unique "trinity combination" that enables multiple technological breakthroughs to be achieved simultaneously, solving the problem that none of the solutions described in the background art can achieve all of the above:

[0039] It achieves an extremely low MFFT that is unattainable by existing technologies: Unlike technologies that only focus on physical stability and rely on hot pressing, this invention achieves a truly low natural film-forming temperature of 6°C to 10°C without the need for external pressure through chemical synergy.

[0040] Achieving a comprehensive improvement in overall performance: Unlike technologies that only focus on improving a single performance, this invention not only achieves low-temperature film formation, but also endows the film with comprehensive and balanced excellent properties through a high-performance crosslinking system, including high mechanical strength, high water resistance and strong adhesion.

[0041] This significant improvement and perfect balance in the universality of multi-objective performance constitutes a typical "unexpected technical effect," a powerful hallmark of the inventiveness of chemical composition inventions. This is precisely the outstanding substantive feature of this invention compared to all prior art.

[0042] Outstanding environmentally friendly characteristics: The system of this invention is an aqueous dispersion with water as the main dispersion medium, which significantly reduces the emission of volatile organic compounds; at the same time, the PHA material as the matrix resin itself has recognized biodegradability, which meets the current urgent global demand for environmental protection and sustainable development. Attached Figure Description

[0043] Figure 1 : A schematic diagram of the final application of the PHA dispersion emulsion of the present invention in paper-based barrier coatings.

[0044] In the figure, 1. Paper substrate; 2. PHA barrier coating (single-layer coating on the inner wall); 3. Coating thickness 6-7μm. Detailed Implementation

[0045] 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.

[0046] Performance testing methods:

[0047] Unless otherwise specified, the following latest standards shall apply:

[0048] MFFT: refer to GB / T 9267-2008;

[0049] Tensile strength and elongation at break: Refer to GB / T 1040.3-2006;

[0050] Water resistance: evaluated by measuring the water contact angle, according to ASTM D7334-08R22;

[0051] Adhesion: Tested according to GB / T 9286-2021 cross-cut adhesion test;

[0052] Particle size D 50 According to ISO 13320:2020, the particle size was tested using a laser particle size analyzer.

[0053] Storage stability: After accelerated aging in an oven at 50±2℃ for 7 days, or after long-term storage at 23±2℃, relative humidity of 50±5%, and in the dark for 1 year, observe the appearance and test key performance indicators. If there are no adverse changes in appearance, the particle size D... 50 If the rate of change is < ±20%, the viscosity change rate is < ±30%, the MFFT change is < ±2℃, and the mechanical property retention rate is >80%, then it is considered stable.

[0054] Main ingredients:

[0055] Table 1. Main experimental chemical names / categories, product models, and suppliers:

[0056]

[0057] Unless otherwise specified, the emulsifier used in the embodiments of the present invention is a compound emulsifier obtained by pre-mixing Lutensol AO 8 and SDS in a weight ratio of 9:1. The PHA raw material used was determined to have a total concentration of terminal hydroxyl and terminal carboxyl groups of approximately 10-30 μmol / g, providing reaction sites for subsequent crosslinking reactions.

[0058] General steps for emulsion preparation:

[0059] The preparation process generally includes the following steps:

[0060] Step 1. PHA raw material melting: Heat the PHA polymer to a molten state, for example, 10°C to 30°C above its melting point and stir until completely melted.

[0061] Step 2. High-speed shear emulsification: Under high-speed shear conditions, such as 5000 r / min to 10000 r / min, the molten PHA polymer is added to an aqueous phase containing emulsifier and water, and preheated to 70°C to 95°C for emulsification to obtain a preliminary PHA dispersion.

[0062] Step 3. Homogenization: The preliminary PHA dispersion is homogenized, for example, by using a high-pressure homogenizer to homogenize 1 to 3 times at a pressure of 30 MPa to 80 MPa, in order to further reduce the particle size and improve the dispersion uniformity.

[0063] Step 4. Additive Addition and Completion: Slowly add the TMPDMIB film-forming aid to the homogenized PHA dispersion, stirring for 5 to 30 minutes to allow for full penetration; then slowly add the crosslinking agent, continuing to stir for 10 minutes. To ensure the final performance and stability of the product, adjust the pH of the emulsion to 7.5–9.0 with a weak alkali, and adjust the final water volume to control the solid content of the finished emulsion within the target range of 30 wt%–50 wt%, thus obtaining the PHA dispersion emulsion.

[0064] Examples and Comparative Examples:

[0065] The formulation and key parameters of PHA in the examples are shown in the table below.

[0066] Table 2. Key parameters of the formulation and PHA polymer used in the examples:

[0067]

[0068] * Note: relative to wt% of PHA solids.

[0069] The comparative formulation and key parameters of PHA are shown in the table below.

[0070] Table 3 Key parameters of the PHA polymers used in the comparative examples:

[0071]

[0072] * Note: relative to wt% of PHA solids.

[0073] Performance test results:

[0074] Table 4 Key performance test results of the embodiments:

[0075]

[0076] As shown in Table 4, all embodiments of the present invention can be formed by natural drying at extremely low temperatures of 6°C to 10°C, and the films formed all exhibit excellent tensile properties, high water resistance and top adhesion to the substrate (grade 0), while the emulsion has excellent long-term storage stability.

[0077] Table 5 Comparative Key Performance Test Results:

[0078]

[0079] As shown in Table 5, none of the comparative examples could simultaneously meet the requirements for low-temperature film formation and overall performance. The absence of any key additive (Comparative Examples 1 and 2), the use of an unsuitable type of PHA (Comparative Example 3), or the simulation of existing technical routes (Comparative Examples 4, 5, and 6) all resulted in excessively high MFFT, significantly reduced film formation performance, or the inability to form a film naturally at all.

[0080] Application example:

[0081] Application Example 1: Environmentally Friendly Waterborne Wood Varnish The PHA dispersion emulsion of this invention can be used to prepare high-performance waterborne wood varnishes with high requirements for hardness, abrasion resistance, and fullness. For such applications, emulsions that can form a film with high tensile strength and hardness after curing are preferred. Referring to the performance data in Table 4, Examples 3 and 2 are ideal choices due to their high rigidity. Taking the emulsion of Example 3 as an example: 100 parts of this emulsion were taken, and 0.2 parts of wetting agent, 0.3 parts of defoamer, 0.5 parts of leveling agent, and an appropriate amount of thickener were added to adjust to the application viscosity. The mixture was thoroughly mixed to obtain the waterborne wood varnish. It was sprayed onto oak boards, dried at room temperature, and then heat-treated at 130°C for 10 minutes to accelerate crosslinking. The properties of the resulting coating are shown in Table 6 below. Those skilled in the art will understand that the different embodiments shown in Table 4 demonstrate the controllability of the mechanical properties of the technical solution of this invention. Therefore, any PHA dispersion emulsion that falls within the scope of this invention and provides high hardness and high tensile strength properties is suitable for preparing high-performance waterborne wood varnishes, and is not limited to the specific embodiments exemplified herein.

[0082] Table 6 Application Example 1: Performance of Water-Based Wood Varnishes

[0083]

[0084] Application Example 2: Biodegradable Paper Barrier Coating The emulsion of this invention is suitable for preparing paper barrier coatings to impart water and oil repellency to paper. Such applications require coatings with good film-forming continuity and balanced mechanical properties to form a dense, pinhole-free barrier layer. Therefore, introducing an appropriate amount of comonomer to improve the flexibility of the polymer is beneficial. Referring to the performance data in Table 4, Examples 4 and 6 both exhibit such balanced characteristics and are suitable choices. The emulsion of Example 4 is used as an example: 100 parts by weight of this emulsion were coated onto food-grade base paper to form a paper substrate. The coating amount was controlled at 8 g / m² (dry weight), followed by drying at 90°C and heat treatment at 130°C for 1 minute to form a PHA dispersion emulsion coating on the paper substrate. The properties of the resulting coated paper are shown in Table 7 below. Those skilled in the art will understand that the performance of the final coating can be systematically controlled by adjusting the type of PHA copolymer and the comonomer content. Therefore, any PHA dispersion emulsion that falls within the scope of this invention and provides balanced mechanical properties and excellent film-forming properties is suitable for preparing paper barrier coatings.

[0085] Table 7 Application Example 2: Paper Barrier Coating Performance

[0086]

[0087] Application Example 3: Waterborne Adhesives The emulsions of this invention can be used to prepare high-performance waterborne adhesives, particularly for applications requiring high flexibility and high peel strength, such as pressure-sensitive adhesives or laminating adhesives. Therefore, emulsions prepared from PHA copolymers with high elongation at break are preferred. Referring to the performance data in Table 4, Examples 5 and 1 are preferred due to their excellent flexibility. The emulsion of Example 5 is used as an example: 100 parts of this emulsion (solids) were mixed with 50 parts of a waterborne tackifying resin emulsion (solids). The mixture was thoroughly mixed to obtain a waterborne adhesive. It was coated onto a polyethylene terephthalate (PET) film, with the dry adhesive layer thickness controlled at 25 μm, dried at 80°C for 5 minutes, and then heat-treated at 130°C for 3 minutes to promote crosslinking. The properties of the resulting adhesive are shown in Table 8 below. Those skilled in the art will understand that the performance gradient (from high rigidity to high flexibility) disclosed in the embodiments of this invention demonstrates the universality of this technical solution. Therefore, any PHA dispersion emulsion that falls within the scope of this invention and provides high flexibility and high elongation at break is suitable for preparing high-performance aqueous adhesives.

[0088] Table 8 Application Example 3: Performance of Waterborne Adhesives

[0089]

[0090] The experimental results are analyzed as follows:

[0091] Based on the detailed comparative data above, the following clear conclusions can be drawn:

[0092] The necessity of the specific additive combination of the present invention: Comparing Example 4 with Comparative Example 1 (without film-forming aid) and Comparative Example 2 (without crosslinking agent), it is clearly demonstrated that the specific film-forming aid of the present invention is the key to achieving low-temperature film formation, while the specific crosslinking agent is the guarantee for obtaining excellent comprehensive performance. Both are indispensable.

[0093] The essential difference between this invention and physical dispersion techniques: Comparative Example 4 simulates a technique that emphasizes physical stability. Experimental results show that even when a physically stable dispersion is obtained, its MFFT is still much higher than that of this invention, making it impossible to achieve low-temperature natural film formation. This proves that the low-temperature film-forming ability of this invention stems from the unique synergistic effect of its chemical components, rather than its physical form. Existing physical dispersion techniques offer absolutely no technical inspiration for solving the problem of low-temperature natural film formation in this invention.

[0094] The superiority of this invention over conventional chemical modification schemes: Comparative Example 5 used a conventional crosslinking agent. Experimental results show that this system not only has a high MFFT, but the overall performance of the final film is also far inferior to that of this invention. This highlights the inventiveness of the ternary combination of specific chemical structures selected in this invention, and the synergistic effect it produces is unattainable by conventional additive combinations.

[0095] The fundamental difference between this invention and hot pressing technology is that the results of Comparative Example 6 prove that the relevant technical solutions must rely on high temperature and high pressure hot pressing to form a film, and cannot achieve the low temperature natural film formation pursued by this invention.

[0096] The inventiveness of the specific component selection in this invention: Comparing Example 4 with Comparative Example 8, it can be seen that only the TMPDMIB specific to this invention can achieve an extremely low MFFT of <10°C, an effect that conventional film-forming aids cannot achieve. Comparing Example 4 with Comparative Example 7 (using an aromatic crosslinking agent), it can be seen that only the aliphatic crosslinking agent specific to this invention can ensure performance while avoiding yellowing of the coating, resulting in a product with excellent appearance and performance. These comparisons strongly demonstrate that the selection of specific chemical structure components in this invention is based on inventive labor, rather than a conventional choice by those skilled in the art.

[0097] The necessity of specific process steps in this invention: Comparing Example 4 with Comparative Example 9 (without pH adjustment), it can be seen that the pH adjustment step is crucial to ensuring the long-term storage stability of the emulsion. The absence of this step will cause the emulsion to settle after storage, affecting its use.

[0098] Synergistic Effect Mechanism Analysis: The unexpected technical effects observed in this invention can be reasonably explained by the following synergistic mechanisms: First, the PHA copolymers with specific molecular weights and PDI ranges defined in this invention possess moderate regularity and flexibility in their molecular chains, providing an ideal substrate for subsequent additives to function. Second, the film-forming aid TMPDMIB with a specific chemical structure has a good affinity for PHA ester groups, enabling it to efficiently penetrate into the polymer particles and temporarily "lubricate" the PHA segments at the molecular level. This significantly reduces the energy barrier for chain segment movement without damaging the main polymer structure, which is key to achieving extremely low MFFT at 6℃ to 10℃. Furthermore, the preparation process sequence of this invention—first adding the TMPDMIB film-forming aid to fully plasticize the polymer particles, and then introducing the crosslinking agent—is also crucial for ensuring that the crosslinking reaction proceeds uniformly and efficiently throughout the entire membrane matrix. Finally, a specific type of water-dispersible, compatible aliphatic polyisocyanate crosslinking agent exhibits good compatibility between its aliphatic backbone and the PHA backbone. The -NCO groups formed after unblocking can efficiently chemically bond with the limited terminal hydroxyl / carboxyl groups on the PHA chain. Importantly, the presence of TMPDMIB promotes the stretching of PHA segments during film formation, providing more favorable sites and space for the crosslinking reaction, resulting in a more uniform and dense crosslinked network. It is precisely this precise matching and synergistic effect of these three factors in molecular structure, physicochemical properties, and reaction timing that ultimately achieves a simultaneous and significant improvement in low-temperature film formation and the overall performance of the final film, constituting the core inventiveness of this invention.

[0099] Analysis of the influence trend of key component content:

[0100] 1. Effect of film-forming aid (TMPDMIB) dosage: As a highly efficient coalescence aid, TMPDMIB's core function is to temporarily plasticize the PHA molecular chain, lowering its glass transition temperature and thus significantly reducing MFFT. The data trends from Examples 1 (8%), 4 (5%), 2 (3%), and Comparative Example 1 (0%) show that within the crosslinking agent dosage range of 2wt% to 5wt%, the MFFT of the system exhibits a significant decreasing trend as the TMPDMIB dosage increases from 0% to 8%. When the dosage is below 3%, its plasticizing effect is insufficient to overcome the segmental rigidity of PHA at low temperatures, leading to an increase in MFFT. While when the dosage is above 8%, although it can further reduce MFFT, excessive residue may remain in the film, affecting the hardness and water resistance of the final film. Therefore, 3% to 8% is the optimal range for balancing low-temperature film-forming properties and the final film performance.

[0101] 2. Effect of Crosslinking Agent Dosage: The water-dispersible aliphatic polyisocyanate crosslinking agent is desealed during heat treatment, and its -NCO groups react with the hydroxyl or carboxyl groups on the PHA molecular chain to form a three-dimensional crosslinked network. Comparing Example 4 (3%) and Comparative Example 2 (0%), the introduction of the crosslinking agent caused the tensile strength to jump from 9.0 MPa to 17.0 MPa, the water contact angle to increase from 75° to 95°, and the adhesion to improve from grade 2 to grade 0. The data trends from Example 1 (2%), Example 3 (2.5%), Example 4 (3%), Example 5 (4%), and Example 2 (5%) show that as the crosslinking agent dosage increases within the range of 2% to 5%, the tensile strength, water resistance, and adhesion of the film are steadily improved. When the dosage is below 2%, the crosslinking density is insufficient, and the performance improvement is not significant; when the dosage is above 5%, the film layer may become too brittle, and the elongation at break may decrease. Therefore, 2% to 5% is the ideal range for maximizing overall performance.

[0102] In summary, this invention, through a specific chemical composition never disclosed in the prior art, successfully solves the technical problem of "universal low-temperature natural film formation and synergistic improvement of comprehensive performance of PHA dispersion emulsions," which has been unsolved by the prior art. It has outstanding substantive features and significant progress.

[0103] 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, or improvements 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 polyhydroxyalkanoate dispersion emulsion, characterized in that, It contains the following components: A polyhydroxyalkanoate polymer comprising repeating units formed from one or more hydroxyalkanoic acid monomers selected from a 3-hydroxyalkanoic acid or a 4-hydroxyalkanoic acid comprising 3 to 14 carbon atoms, or a combination thereof; the polyhydroxyalkanoate polymer having a weight average molecular weight of 1.5 x 10 5 Da to 7.0 x 10 5 Da, and a polydispersity index of 2.0 to 3.

5. The film-forming aid is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and its dosage is 3 wt% to 8 wt% of the solid polyhydroxyalkanoate polymer. A crosslinking agent, wherein the crosslinking agent is a water-dispersible aliphatic polyisocyanate, and the amount of the crosslinking agent is 2wt% to 5wt% of the solid polyhydroxyalkanoate polymer; Emulsifier; water; in: The minimum film-forming temperature of the polyhydroxy fatty acid ester dispersion emulsion is 6℃~10℃; The emulsifier is a complex of nonionic and anionic emulsifiers, and its total amount is 1 wt% to 5 wt% of the polyhydroxyalkanoate polymer solid, and the hydrophilic-lipophilic balance value of the nonionic emulsifier is 12 to 18. The polyhydroxyalkanoate dispersion emulsion has a solids content of 30wt% to 50wt% and a median particle size D of the polyhydroxyalkanoate polymer particles in the emulsion. 50 Its range is 0.1μm to 2.0μm; The polyhydroxy fatty acid ester dispersion emulsion was prepared by the following method: Step 1. Heat the polyhydroxyalkanoate polymer to a molten state; Step 2. Under high-speed shear conditions, the molten polyhydroxy fatty acid ester polymer is added to an aqueous phase containing emulsifier and water for emulsification to obtain a preliminary dispersion of polyhydroxy fatty acid ester; Step 3. The preliminary dispersion of polyhydroxy fatty acid ester is subjected to homogenization treatment to further reduce the particle size and improve the dispersion uniformity; Step 4. Slowly add the 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate film-forming aid to the homogenized polyhydroxy fatty acid ester dispersion and stir for 5 to 30 minutes to allow it to fully penetrate; then slowly add the crosslinking agent and continue stirring for 10 minutes to obtain a polyhydroxy fatty acid ester dispersion emulsion; finally, adjust the pH of the polyhydroxy fatty acid ester dispersion emulsion to 7.5 to 9.0 with a weak base.

2. The polyhydroxyalkanoate dispersion emulsion according to claim 1, wherein the structure of the polyhydroxyalkanoate polymer is selected from one of the following: (1) Its monomer composition satisfies that the molar percentage of 3-hydroxy fatty acid monomers with a carbon chain length of 3 to 5 carbon atoms is not less than 70 mol%, and the short-chain polyhydroxy fatty acid ester is poly(3-hydroxybutyric acid-co-3-hydroxyvalerate). (2) The monomer composition of the medium- and long-chain polyhydroxy fatty acid esters is such that the molar percentage of 3-hydroxy fatty acid monomers with a carbon chain length of 6 to 14 carbon atoms is not less than 70 mol%, and the medium- and long-chain polyhydroxy fatty acid esters are selected from poly-3-hydroxyhexanoic acid, poly-3-hydroxyoctanoic acid, poly-3-hydroxydecanoic acid, copolymers formed by at least two monomers selected from 3-hydroxyhexanoic acid monomers, 3-hydroxyoctanoic acid monomers and 3-hydroxydecanoic acid monomers, or copolymers formed by at least one monomer selected from 3-hydroxyhexanoic acid monomers, 3-hydroxyoctanoic acid monomers and 3-hydroxydecanoic acid monomers and one or more other monomers, wherein the other monomers are selected from 3-hydroxy fatty acid monomers containing 3 to 14 carbon atoms or 4-hydroxy fatty acid monomers containing 3 to 14 carbon atoms; (3) A copolymer comprising short-chain monomers of 3-hydroxy fatty acids with a carbon chain length of 3 to 5 carbon atoms and long-chain monomers of 3-hydroxy fatty acids with a carbon chain length of 6 to 14 carbon atoms, wherein the copolymer is poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid); (4) A copolymer containing 3-hydroxybutyric acid monomer and 4-hydroxybutyric acid monomer, which is poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid).

3. The polyhydroxyalkanoate dispersion emulsion according to claim 1, characterized in that, In step 1, the melting temperature of the polyhydroxyalkanoate polymer is controlled within the range of 100℃ to 180℃; in step 2, the high-speed shearing rate is 5000r / min to 10000r / min, the emulsification temperature is controlled within the range of 70℃ to 95℃, which is higher than the melting point of the polyhydroxyalkanoate used but lower than the boiling point of water; and in step 3, the homogenization process is carried out using a high-pressure homogenizer, with the homogenization pressure controlled within the range of 30MPa to 80MPa.

4. The polyhydroxyalkanoate dispersion emulsion according to claim 1, characterized in that, After the emulsion obtained in step 4 is coated into a film, it is heat-treated at 110°C to 150°C for 3 to 30 minutes to promote the reaction of the crosslinking agent and complete the curing.

5. The use of the polyhydroxyalkanoate dispersion emulsion according to any one of claims 1 or 2 in the preparation of waterborne coatings and waterborne adhesives.

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