PHA dispersion emulsion as well as preparation method and application thereof

Abstract

The invention provides a PHA dispersion emulsion as well as a preparation method and application thereof, and belongs to the field of high polymer materials. The invention aims to solve the technical problem that the prior art cannot simultaneously meet the requirements of the polyhydroxyalkanoate water dispersion system on extremely low temperature natural film-forming property, excellent comprehensive performance after film formation and long-term storage stability. The method is characterized in that a polyhydroxyalkanoate polymer with specific molecular weight and polydispersity index range, a coalescing agent 2, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate with a specific chemical structure and a specific type of aliphatic polyisocyanate cross-linking agent compatible with water dispersion are strictly limited and combined. Through the synergistic effect generated by the unique ternary combination, the minimum film forming temperature of the prepared emulsion can be reduced to 6-10 DEG C, a film can be naturally formed without hot pressing, and the formed film has excellent mechanical property, water resistance and adhesive force and has excellent storage stability of at least one year.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a PHA dispersion emulsion and a preparation method and application thereof. Background Art

[0002] Polyhydroxyalkanoates (PHAs) are a class of biodegradable polyesters synthesized by microorganisms. Due to their outstanding environmental properties and renewable sources, they have shown great application potential in replacing traditional fossil-based plastics in a variety of fields such as packaging, agriculture, and healthcare. There are many types of PHAs, and the diversity 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 divided into short-chain PHAs, medium-chain PHAs, etc. based on the length of their monomer carbon chains. The weight-average molecular weight (Mw) and polydispersity index (PDI) of PHA are the core parameters that determine its processing performance and final product performance.

[0003] Preparing PHA into aqueous dispersions is a key technological approach to expanding its application in environmentally friendly water-based coatings, water-based adhesives, and other fields. However, despite numerous attempts in this field, a comprehensive solution has yet to be developed that simultaneously meets the three core requirements of natural film formation at extremely low temperatures, excellent post-film performance, and long-term storage stability. Existing technologies have the following main limitations:

[0004] Physical dispersion techniques focus on stability before application but fail to address the film-forming challenge after application. In recent years, significant progress has been made in preparing high-solids-content, physically stable PHA nanoparticle suspensions using physical methods such as high-energy homogenization. For example, Peprah et al. published in European Polymer Journal (2016, 84, 137-146) a method for preparing medium-chain PHA (mcl-PHA) nanoparticle suspensions with solid contents of up to 10-30% (w / v), achieving particle sizes of approximately 100 nm. This type of technology contributes by addressing the physical stability of the suspension during storage and transportation. However, the inventors discovered that while this technology focuses on optimizing the suspension's physical morphology before application, it does not provide an effective solution to the core performance bottleneck after application, posed by the inherent high crystallinity and high glass transition temperature of PHA materials. This is how to achieve high-quality, natural film formation at ambient temperature (especially below 10°C) without relying on external high temperatures or pressures.

[0005] Existing "low-temperature film-forming" solutions rely on hot pressing, 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°C) PHA particles to 100-1000nm, enabling them to be hot-pressed into films at temperatures of 100-150°C and pressures of 1-9 MPa. The "low-temperature" concept of this method is relative to the high melting point of PHA. It is essentially a hot pressing process and does not address the problem of naturally forming continuous films from aqueous dispersions through water evaporation at room or low temperatures. This technical approach cannot meet the near-ambient minimum film-forming temperature (MFFT) requirements required for a wide range of water-based coatings and adhesives applications.

[0006] The existing chemical modification schemes have a single goal and lack the synergistic improvement of comprehensive performance: some technologies try to use additives to improve certain single properties. For example, Taiwan Patent TW202212504A discloses an aqueous dispersion containing PHA, a polyvinyl alcohol stabilizer and a cross-linker, which uses conventional difunctional carboxylic acids or aldehydes such as adipic acid and glyoxal as cross-linkers. The main purpose is to improve the water resistance of the final film layer by heating and curing. However, this technical solution does not involve or solve the core technical problem of achieving extremely low MFFT, and the type of cross-linker and the mechanism of action used are essentially different from the high-performance cross-linking system that the present invention aims to achieve comprehensive performance improvement.

[0007] Furthermore, documents such as Korean patent publication KR20210111187A also disclose various methods and components for preparing PHA dispersions, disclosing a wide range of PHA monomer types, molecular weight ranges, adjuvant types (such as various anionic and nonionic surfactants), and preparation methods (such as melt dispersion and high-pressure homogenization). However, this document only provides a broad set of technical options and does not disclose or suggest combining PHAs of specific molecular weights and PDI ranges with film-forming aids of specific chemical structures, such as 2,2,4-trimethylpentanediol monoisobutyrate (TMPDMIB), and specific types of water-dispersible aliphatic polyisocyanate crosslinkers. Furthermore, it does not disclose that such a specific combination can produce synergistic technical effects that simultaneously address the three core challenges mentioned above.

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

[0009] The present invention aims to provide a PHA dispersion emulsion, its preparation method, and its application. This invention aims to address the technical challenges of existing technologies that cannot simultaneously meet the aforementioned three core performance requirements. Specifically, through the coordinated design of specific chemical components, this invention provides a PHA dispersion emulsion that simultaneously achieves an extremely low minimum film forming temperature (MFFT), excellent post-film performance, and outstanding long-term storage stability, thus filling a gap in the existing art.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] The present 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, wherein the hydroxy fatty acid monomers are selected from 3-hydroxy fatty acids or 4-hydroxy fatty acids containing 3 to 14 carbon atoms, or a combination thereof, wherein the Mw of the PHA polymer is 1.5×10 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 usage is 3 wt % to 8 wt % of the PHA polymer solids, for example, 3 wt %, 4 wt %, 5 wt %, 7 wt % or 8 wt %.

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

[0015] Also includes emulsifiers and water.

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

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

[0018] (1) A short-chain PHA whose monomer composition satisfies the requirement that the molar percentage of a 3-hydroxy fatty acid monomer having 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-hydroxyvaleric acid) (PHBV);

[0019] (2) The monomer composition satisfies the requirement that the molar percentage of 3-hydroxy fatty acid monomers having a carbon chain length of 6 to 14 carbon atoms is not less than 70 mol% of a medium-chain PHA, and the medium-chain PHA is selected from poly 3-hydroxyhexanoic acid (P3HHx), poly 3-hydroxyoctanoic acid (P3HO), poly 3-hydroxydecanoic acid (P3HD), a copolymer formed by at least two monomers selected from 3-hydroxyhexanoic acid monomers, 3-hydroxyoctanoic acid monomers and 3-hydroxydecanoic acid monomers, or a copolymer 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;

[0020] (3) A copolymer comprising a short-chain 3-hydroxy fatty acid monomer having a carbon chain length of 3 to 5 carbon atoms and a medium-chain 3-hydroxy fatty acid monomer having a carbon chain length of 6 to 14 carbon atoms, which is poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) (P(3HB-co-3HHx));

[0021] (4) A copolymer comprising a 3-hydroxybutyric acid monomer and a 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 an 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 solid content of the PHA dispersion emulsion is 30 wt % to 50 wt %, for example, 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 is 50 The thickness may be 0.1 μm to 2.0 μm, for example, 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, which comprises the following steps:

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

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

[0028] Step 3. homogenizing the PHA preliminary dispersion to further reduce the particle size and improve the 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 crosslinker and continue stirring for 10 minutes to obtain a 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 melt temperature of the PHA polymer in step 1 is controlled within a range of 100° C. to 180° C.; the high-speed shear rate in step 2 is 5000 r / min to 10000 r / min, and the emulsification temperature is controlled within a 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 treatment in step 3 is performed using a high-pressure homogenizer, and the homogenization pressure is controlled within a range of 30 MPa to 80 MPa.

[0031] In one embodiment, after the emulsion obtained in step 4 is coated to form 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 use of the PHA dispersion emulsion in the preparation of water-based coatings and water-based adhesives.

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

[0034] Significantly expands the low-temperature application range of PHAs and achieves energy savings: The core advantage of this invention lies in its ability to consistently and significantly reduce the MFFT of a wide range of PHAs with different chemical structures to an extremely low level of 6°C to 10°C through the synergistic effect of specific additives. This not only overcomes the technical bottleneck of many PHA materials, which have been difficult to apply at low temperatures due to their high MFFT, but also broadens their application possibilities in various environmental conditions. It also significantly reduces the baking or heating temperature required for film formation, resulting in significant energy savings.

[0035] Universally imparting excellent overall performance to various PHA films: By incorporating a specifically selected, water-dispersible, aliphatic polyisocyanate crosslinker in combination with a highly efficient film-forming aid, this invention enables films formed from various PHA types within the specified Mw and PDI ranges to exhibit excellent and balanced overall performance. This is reflected in significantly improved mechanical properties, water resistance, chemical resistance, and adhesion to a variety of substrates.

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

[0037] Unique synergistic effect and outstanding substantive features of specific component combinations: The core innovation and creativity of this invention lies not in simply mixing known PHAs, film-forming agents, and cross-linkers, but in an unexpected discovery: the strong and unobvious synergistic technical effect produced by strictly and specifically defining the molecular properties of the PHA (specific Mw and PDI ranges), the chemical structure of the film-forming agent (specifically TMPDMIB), and the type of the cross-linker (specifically a water-dispersible aliphatic polyisocyanate) and their respective dosage ranges.

[0038] It is this unique "ternary combination" that enables multiple technological breakthroughs to be achieved simultaneously, solving the problems that none of the solutions described in the background art can address simultaneously:

[0039] Achieves extremely low MFFT that cannot be achieved by existing technologies: Unlike technologies that only focus on physical stability and rely on hot pressing to form, the present invention achieves a true and extremely low natural film-forming temperature of 6°C to 10°C without the need for external pressure through chemical synergy.

[0040] A comprehensive improvement in comprehensive performance has been achieved: Unlike technologies that only focus on improving a single performance, the present invention not only achieves low-temperature film formation, but also gives the film comprehensive and balanced excellent properties through a high-performance cross-linking system, including high mechanical strength, high water resistance and strong adhesion.

[0041] This substantial improvement and perfect balance in the universality of multi-objective performance constitutes a typical "unexpected technical effect," a strong indicator of the inventive nature of chemical composition inventions. This is also the outstanding and substantial feature of this invention compared to all prior art.

[0042] Outstanding environmental friendliness: The system of the present 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 used as the base resin itself has recognized biodegradability, which meets the current urgent global demand for environmental protection and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 : Schematic diagram of the final application of the PHA dispersion emulsion of the present invention for paper-based barrier coating.

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

[0045] In order 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 substitutions, 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 stated, the raw materials used in the present examples are all commercially available industrial products or can be prepared by conventional methods.

[0046] Performance testing method:

[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: Refer to GB / T 9286-2021 cross-cut test;

[0052] Particle size D 50 : Refer to ISO 13320:2020, tested with a laser particle size analyzer;

[0053] Storage stability: After 7 days of accelerated aging in a 50±2°C oven, or after 1 year of long-term storage at 23±2°C, relative humidity 50±5%, and away from light, observe the appearance and test the key performance indicators. If there is no adverse change in appearance, the particle size D 50 If the rate of change is less than ±20%, the rate of change in viscosity is less than ±30%, the change in MFFT is less than ±2°C, and the mechanical property retention rate is greater than 80%, it is considered stable.

[0054] Main ingredients:

[0055] Table 1 Names / categories, product models and suppliers of main experimental chemicals:

[0056]

[0057] Unless otherwise specified, the emulsifier used in the examples herein was a premixed emulsifier consisting of Lutensol AO 8 and SDS in a 9:1 weight ratio. The PHA raw material was measured to have a combined concentration of terminal hydroxyl and terminal carboxyl groups of approximately 10-30 μmol / g, providing reactive sites for subsequent crosslinking reactions.

[0058] General steps for emulsion preparation:

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

[0060] Step 1. Melting of PHA raw materials: heating the PHA polymer to a molten state, for example, 10° C. to 30° C. above its melting point and stirring until completely melted.

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

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

[0063] Step 4. Addition and Finishing: Slowly add the TMPDMIB film-forming agent to the homogenized PHA dispersion and stir for 5 to 30 minutes to allow for full penetration. Then, slowly add the crosslinker and continue stirring 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 base, and adjust the final water content to maintain the solids content within the target range of 30-50 wt%. This completes the PHA dispersion.

[0064] Examples and Comparative Examples:

[0065] The embodiment formula and key parameters of PHA are shown in the following table.

[0066] Table 2 Example formulations and key parameters of the PHA polymer used:

[0067]

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

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

[0070] Table 3 Key parameters of the PHA polymer used in the comparative example:

[0071]

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

[0073] Performance test results:

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

[0075]

[0076] As can be seen from Table 4, all embodiments of the present invention can form films by natural drying at extremely low temperatures of 6°C to 10°C, and the formed films all exhibit excellent tensile properties, high water resistance, and top-level adhesion to the substrate (grade 0). At the same time, the emulsions have excellent long-term storage stability.

[0077] Table 5 Comparative Examples Key Performance Test Results:

[0078]

[0079] As shown in Table 5, none of the comparative examples meet both low-temperature film formation and overall performance requirements. The lack of any key additive (Comparative Examples 1 and 2), the use of an unsuitable PHA type (Comparative Example 3), or the imitation of existing technology routes (Comparative Examples 4, 5, and 6) all result in excessively high MFFT, significantly reduced film-forming performance, or even the complete inability to form a natural film.

[0080] Application examples:

[0081] Example 1: Environmentally friendly waterborne wood varnish The PHA dispersion emulsion of the present invention can be used to prepare high performance waterborne wood varnish with high requirements on hardness, abrasion resistance and fullness. For such applications, it is preferred to use emulsion that can form film layer with high tensile strength and hardness after curing. Referring to the performance data in Table 4, Example 3 and Example 2 are ideal choices due to their higher rigidity. Take Example 3 emulsion as an example: take 100 parts of the emulsion, add 0.2 parts of wetting agent, 0.3 parts of defoaming agent, 0.5 parts of leveling agent and appropriate amount of thickening agent to adjust the application viscosity. Mix well to get waterborne wood varnish. Spray on oak board, dry at room temperature, then heat treat at 130°C for 10 minutes to accelerate crosslinking. The performance of the obtained coating is shown in Table 6 below. Those skilled in the art can understand that the different examples shown in Table 4 demonstrate the controllability of the technical solution of the present invention in mechanical properties. Therefore, any PHA dispersion emulsion falling within the scope of the present invention and capable of providing high hardness and high tensile strength characteristics is suitable for preparing high performance waterborne wood varnish, without being limited to the specific examples exemplified herein.

[0082] Table 6 Performance of waterborne wood varnish in Example 1:

[0083]

[0084] Example 2: Degradable paper barrier coating The emulsion of the present invention is suitable for preparing paper barrier coating for imparting water and oil repellency to paper. Such applications require the coating to have good film forming continuity and balanced mechanical properties to form a dense and pinhole-free barrier layer. Therefore, it is beneficial to introduce appropriate amount of comonomer to improve the flexibility of the polymer. Referring to the performance data in Table 4, both Example 4 and Example 6 exhibit such balanced characteristics and are suitable choices. Take Example 4 emulsion as an example: take 100 parts by weight of the emulsion, coat on food grade base paper to form paper substrate. The coating amount is controlled to be 8 g / m2(dry weight), then dry at 90°C and heat treat at 130°C for 1 minute to form PHA dispersion emulsion coating on the paper substrate. The performance of the obtained coated paper is shown in Table 7 below. Those skilled in the art can understand that by adjusting the type of PHA copolymer and the content of comonomer, the performance of the final coating can be systematically controlled. Therefore, any PHA dispersion emulsion falling within the scope of the present invention and capable of providing balanced mechanical properties and excellent film forming property is suitable for preparing paper barrier coating.

[0085] Table 7 Performance of paper barrier coating in Example 2:

[0086]

[0087] Application Example 3: Water-Based Adhesives The emulsions of this invention can be used to prepare high-performance water-based adhesives, particularly for applications requiring high flexibility and 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. For illustration, the emulsion of Example 5 is used as an example: 100 parts of this emulsion (based on solids) is added to 50 parts of a water-based tackifying resin emulsion (based on solids). Mix thoroughly to obtain a water-based adhesive. Apply the emulsion to a polyethylene terephthalate (PET) film, controlling the dry adhesive layer thickness to 25 μm, dry at 80°C for 5 minutes, and then heat-treat at 130°C for 3 minutes to promote crosslinking. The resulting adhesive properties are shown in Table 8 below. Those skilled in the art will appreciate that the performance gradient (from high rigidity to high flexibility) revealed in the examples of this invention demonstrates the universal applicability of this technical solution. Therefore, any PHA dispersion emulsion that falls within the scope of the present invention and can provide high flexibility and high elongation at break is suitable for preparing high-performance water-based adhesives.

[0088] Table 8 Performance of water-based adhesive in application example 3:

[0089]

[0090] The experimental results are analyzed as follows:

[0091] From the above detailed comparative data, we can draw the following clear conclusions:

[0092] Necessity of the specific combination of additives of the present invention: Comparison of Example 4 with Comparative Example 1 (without film-forming additive) and Comparative Example 2 (without cross-linking agent) clearly demonstrates that the specific film-forming additive of the present invention is the key to achieving low-temperature film formation, while the specific cross-linking agent is the guarantee for obtaining excellent comprehensive performance, and both are indispensable.

[0093] The fundamental difference between the present invention and physical dispersion techniques: Comparative Example 4 simulates a technical approach focused on physical stability. Experimental results show that even though a physically stable dispersion was achieved, its MFFT was still significantly higher than that of the present invention, and low-temperature spontaneous film formation was impossible. This demonstrates that the low-temperature film-forming ability of the present invention stems from the synergistic effect of its unique chemical components, rather than its physical form. Existing physical dispersion approaches offer no technical insight into resolving the low-temperature spontaneous film-forming challenges of the present invention.

[0094] The superiority of the present invention over conventional chemical modification schemes: Comparative Example 5 employed a conventional crosslinker. Experimental results showed that this system not only achieved a higher MFFT, but also significantly inferior overall membrane performance to that of the present invention. This highlights the inventive nature of the ternary combination of specific chemical structures selected in the present invention, producing a synergistic effect unattainable with conventional adjuvant combinations.

[0095] The present invention is fundamentally different from hot pressing technology: the results of comparative example 6 prove that the related technical solution must rely on hot pressing at high temperature and high pressure to form a film, and cannot achieve the low-temperature natural film formation pursued by the present invention.

[0096] The inventiveness of the present invention's selection of specific components: Comparing Example 4 with Comparative Example 8 demonstrates that only the present invention's specific TMPDMIB can achieve an extremely low MFFT of <10°C, whereas conventional coalescing agents cannot achieve this effect. Comparing Example 4 with Comparative Example 7 (using an aromatic crosslinker), it is clear that only the present invention's specific aliphatic crosslinker can maintain performance while avoiding yellowing of the coating, resulting in a product with excellent appearance and performance. These comparisons strongly demonstrate that the present invention's selection of specific chemical components is based on inventive effort, rather than conventional selection by those skilled in the art.

[0097] Necessity of the specific process steps of the present invention: By 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] Analysis of the mechanism of synergistic effect: The unexpected technical effects observed in the present invention can be reasonably explained by the following synergistic mechanism: First, the PHA copolymer with a specific molecular weight and PDI range defined by the present invention has a moderate regularity and flexibility in its molecular chain, which provides an ideal base for the subsequent adjuvants to play a role. Secondly, the film-forming aid TMPDMIB with a specific chemical structure has a good affinity with the PHA ester group in its molecular structure, and can efficiently penetrate into the interior of the polymer particles, temporarily "lubricating" the PHA chain segments at the molecular level, thereby greatly reducing the energy barrier for chain segment movement without destroying the main structure of the polymer, which is the key to achieving an extremely low MFFT of 6°C to 10°C. In addition, the preparation process sequence of the present invention, i.e. first adding the TMPDMIB film-forming aid to fully plasticize the polymer particles, and then introducing the cross-linking agent, is also crucial to ensure that the cross-linking reaction proceeds evenly and efficiently throughout the entire membrane matrix. Finally, a specific type of water-dispersible aliphatic polyisocyanate crosslinker has a good aliphatic backbone compatible with the PHA main chain, and the -NCO groups formed after deblocking can form efficient chemical bonds with the limited terminal hydroxyl / carboxyl groups on the PHA chain. Importantly, the presence of TMPDMIB promotes the stretching of PHA segments during the film formation process, providing more favorable sites and space for the cross-linking reaction, making the formed cross-linked network more uniform and dense. It is the precise matching and synergistic effect of these three in molecular structure, physicochemical properties and reaction sequence that ultimately achieves a huge simultaneous improvement in low-temperature film-forming properties and the overall performance of the final film, which constitutes the core creativity of the present invention.

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

[0100] 1. Effect of Film-Forming Aid (TMPDMIB) Dosage: As a highly effective coalescing aid, TMPDMIB's core function is to temporarily plasticize PHA molecular chains, lowering their glass transition temperature (GTT), thereby significantly reducing MFFT. Data trends from Examples 1 (8%), 4 (5%), and 2 (3%), as well as Comparative Example 1 (0%), indicate that within the crosslinker dosage range of 2wt% to 5wt%, increasing TMPDMIB from 0% to 8% leads to a significant decrease in the MFFT of the system. Dosages below 3% are insufficient to overcome the PHA chain rigidity at low temperatures, resulting in an increase in MFFT. While dosages above 8% further reduce MFFT, excess TMPDMIB may remain in the film, impacting the hardness and water resistance of the final film. Therefore, the 3% to 8% range represents the optimal balance between low-temperature film-forming properties and final film performance.

[0101] 2. Effect of Crosslinker Amount: The water-dispersible aliphatic polyisocyanate crosslinker deblocks during heat treatment, and its -NCO groups react with hydroxyl or carboxyl groups on the PHA molecular chains to form a three-dimensional crosslinked network. Comparing Example 4 (3%) with Comparative Example 2 (0%), the introduction of the crosslinker significantly increases the tensile strength from 9.0 MPa to 17.0 MPa, the water contact angle from 75° to 95°, and the adhesion from level 2 to level 0. The data trends for Examples 1 (2%), 3 (2.5%), 4 (3%), 5 (4%), and 2 (5%) show that increasing the crosslinker amount within the 2% to 5% range steadily improves the film's tensile strength, water resistance, and adhesion. Amounts below 2% result in insufficient crosslinking density and insignificant performance improvements. Amounts above 5% may result in excessive film brittleness and reduced elongation at break. Therefore, a range of 2% to 5% is ideal for maximizing overall performance.

[0102] In summary, the present invention successfully solves the technical problem of "universal low-temperature natural film formation and synergistic improvement of comprehensive performance of PHA dispersion emulsions" that has not been solved by the prior art through a specific chemical composition that has never been disclosed in the prior art. It has outstanding substantive features and significant progress.

[0103] 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 polyhydroxyalkanoate dispersion emulsion, characterized in that: Contains the following components: A polyhydroxyalkanoate polymer comprising repeating units formed from one or more hydroxyalkanoate monomers, wherein the hydroxyalkanoate monomers are selected from 3-hydroxyalkanoates or 4-hydroxyalkanoates containing 3 to 14 carbon atoms, or a combination thereof; the weight average molecular weight of the polyhydroxyalkanoate polymer is 1.5×10 5 Da~7.0×10 5 Da, polydispersity index, 2.0–3.5; A film-forming aid, wherein the film-forming aid is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and the amount thereof is 3wt% to 8wt% of the solid of the polyhydroxyalkanoate polymer; A cross-linking agent, wherein the cross-linking agent is a water-dispersible aliphatic polyisocyanate, and the amount thereof is 2 wt% to 5 wt% of the solid of the polyhydroxyalkanoate polymer; emulsifiers; water; Wherein, the minimum film-forming temperature of the polyhydroxyalkanoate dispersion emulsion is 6°C to 10°C.

2. The polyhydroxyalkanoate dispersion emulsion according to claim 1, wherein the structure type of the polyhydroxyalkanoate polymer is selected from the following: (1) A short-chain polyhydroxyalkanoate whose monomer composition satisfies the requirement that the molar percentage of a 3-hydroxyalkanoic acid monomer having a carbon chain length of 3 to 5 carbon atoms is not less than 70 mol%, and the short-chain polyhydroxyalkanoate is poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid); (2) A medium-chain polyhydroxyalkanoate having a monomer composition satisfying that the molar percentage of a 3-hydroxy fatty acid monomer having a carbon chain length of 6 to 14 carbon atoms is not less than 70 mol%, and the medium-chain polyhydroxyalkanoate is selected from poly 3-hydroxycaproic acid, poly 3-hydroxyoctanoic acid, poly 3-hydroxydecanoic acid, a copolymer formed by at least two monomers selected from 3-hydroxycaproic acid monomers, 3-hydroxyoctanoic acid monomers and 3-hydroxydecanoic acid monomers, or a copolymer formed by at least one monomer selected from 3-hydroxycaproic 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 a short-chain 3-hydroxy fatty acid monomer having a carbon chain length of 3 to 5 carbon atoms and a medium-chain 3-hydroxy fatty acid monomer having a carbon chain length of 6 to 14 carbon atoms, which is poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid); (4) A copolymer comprising a 3-hydroxybutyric acid monomer and a 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 The emulsifier is a complex of a nonionic emulsifier and an anionic emulsifier, and the total amount thereof 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.

4. The polyhydroxyalkanoate dispersion emulsion according to claim 1, characterized in that The solid content of the polyhydroxyalkanoate dispersion emulsion is 30 wt % to 50 wt %.

5. The polyhydroxyalkanoate dispersion emulsion according to claim 1, characterized in that The median volume value D of the particle size of the polyhydroxyalkanoate polymer particles in the polyhydroxyalkanoate dispersion emulsion is 50 0.1μm~2.0μm.

6. A method for preparing the polyhydroxyalkanoate dispersion emulsion according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1. heating the polyhydroxyalkanoate polymer to a molten state; Step 2. Under high shear conditions, the molten polyhydroxyalkanoate polymer is added to an aqueous phase containing an emulsifier and water for emulsification to obtain a preliminary polyhydroxyalkanoate dispersion; Step 3. homogenizing the polyhydroxyalkanoate preliminary dispersion 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 polyhydroxyalkanoate dispersion and stir for 5 to 30 minutes to allow it to fully penetrate; then slowly add the cross-linking agent and continue stirring for 10 minutes to obtain a polyhydroxyalkanoate dispersion emulsion; finally, adjust the pH of the polyhydroxyalkanoate dispersion emulsion to 7.5 to 9.0 with a weak base.

7. The method according to claim 6, characterized in that In step 1, the melting temperature of the polyhydroxyalkanoate polymer is controlled within the range of 100° C. to 180° C.; in step 2, the high-speed shear rate is 5000 r / min to 10000 r / min, and the emulsification temperature is controlled within the range of 70° C. to 95° C., 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 treatment is performed using a high-pressure homogenizer, and the homogenization pressure is controlled within the range of 30 MPa to 80 MPa.

8. The method according to claim 6 or 7, characterized in that After the emulsion obtained in step 4 is coated to form a film, it is heat-treated at 110° C. to 150° C. for 3 minutes to 30 minutes to promote the reaction of the cross-linking agent and complete the curing.

9. Use of the polyhydroxyalkanoate dispersion emulsion according to any one of claims 1 to 5 in the preparation of water-based coatings and water-based adhesives.

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