Polyhydroxyalkanoate water-based barrier coating composition and application

Abstract

The invention discloses a polyhydroxyalkanoate water-based barrier coating composition and application, and belongs to the technical field of packaging materials. The composition takes water as a dispersion medium and comprises polyhydroxyalkanoate, a plasticizer, an emulsifier and an inorganic nano filler. The stable emulsion with the volume average particle size of 400-700nm is prepared under specific proportioning and process conditions. After the emulsion is applied to a paper substrate according to the dry film coating weight of 10-12 g / m, the obtained coating shows good comprehensive performance: the oxygen permeability is not higher than 580 cm / m.d, the water vapor permeability is not higher than 290 g / m.d, and the heat sealing strength at 130 DEG C is not lower than 5.0 N / 15 mm. The biodegradable paper-based packaging film does not contain fluorine compounds, can be completely biodegraded, and provides a technical path for sustainable paper-based packaging.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology, specifically relating to a water-based barrier coating composition of polyhydroxyalkanoates and its application. Background Technology

[0002] Paper-based materials are highly favored in the food packaging industry due to their inherent renewable and biodegradable properties. However, the porous and hydrophilic nature of natural paper fibers makes them unsuitable for meeting the critical performance requirements of modern food packaging, such as waterproofing, oil resistance, and gas barrier properties. Therefore, modification through the application of functional coatings to their surface is necessary.

[0003] For a long time, polyethylene (PE) coated paper has been the mainstream solution in this field. However, the composite structure of PE and paper fibers makes it difficult to separate effectively in existing recycling systems, resulting in resource waste and environmental pollution. Another class of coating materials that was once widely used are perfluorinated and polyfluoroalkyl substances (PFAS). Although they have good water and oil repellency, they are facing increasingly stringent regulatory restrictions and market elimination worldwide due to their extreme persistence in the environment and potential health risks to organisms.

[0004] Against this backdrop, polyhydroxyalkanoates (PHA), as a bio-based polyester synthesized by microbial fermentation, are widely recognized as one of the most promising sustainable packaging materials due to their complete biodegradability in various natural environments. However, translating the theoretical advantages of PHA into practical applications still faces challenges. Pure PHA, especially poly(3-hydroxybutyrate) (PHB), which is the most widely studied, has inherent defects such as high crystallinity, brittleness, and a narrow thermal processing window. Direct coating with PHA is prone to microcracks, making it unable to form an effective barrier.

[0005] Aqueous dispersions of PHA have been explored in this field. For example, WO 2020 / 036843 A1 and its corresponding U.S. patent US 11866606 disclose aqueous dispersions based on PHA, allowing optional addition of surfactants, plasticizers (including citrate esters), and fillers (including clay / montmorillonite). However, these documents only provide a broad "list-of-components" disclosure and do not limit the specific and synergistic formulation and process window proposed in this invention, such as the emulsifier system hydrophilic-lipophilic balance (HLB) value of 12–16, pH 5.0–5.5, triethyl citrate (TEC) of 3–10 wt% by weight of PHA, organically modified montmorillonite (OMMT) of 2–4 wt% by weight of PHA, and emulsion volume average particle size (D). 50The combination of key parameters such as 400–700 nm and a low / medium shear viscosity ratio of not less than 5 is crucial. More importantly, this paper does not reveal or suggest the intrinsic mechanism by which plasticizing pretreatment promotes the efficient exfoliation of nanosheets in the matrix and the formation of a three-dimensional network, thereby achieving a nonlinear improvement in barrier performance, nor does it provide a reproducible performance boundary at a specific coating amount.

[0006] On the other hand, EP 4166716 A1 primarily focuses on improving film-forming properties such as pinholes, cracks, and adhesion to the substrate by using PHBH and polyvinyl alcohol (PVA) / ethylene-vinyl acetate copolymer (EVA) type binders. This approach does not address the complete technical causal chain proposed in this invention: "plasticization (TEC) → promoting OMMT sheet peeling → rheological network → barrier transition," nor does it limit the narrow parameter window and associated wide heat-sealing window of this invention.

[0007] Furthermore, other related technologies such as WO 2022 / 152813 A1 and CN 115996838 A mainly focus on general aqueous biopolymer dispersion systems or multilayer coating barrier strategies, without specifically addressing the specific synergistic mechanism of PHA-TEC-OMMT within a single-coat system. CN 112867766 A and CN 119777197 A, on the other hand, emphasize the source and stability control of PHA dispersions prepared directly from fermentation broth. Their core technology lies in upstream preparation and does not provide the downstream composite formulation parameter combinations and final performance boundaries defined in this invention.

[0008] In summary, existing technologies fail to provide a comprehensive solution that simultaneously addresses the inherent brittleness of PHA, achieves quantifiable high gas barrier properties, obtains a wide and robust processing window, and ensures the long-term storage stability of the emulsion. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a water-based barrier coating composition of polyhydroxyalkanoates and its application, aiming to solve the problems of existing paper-based packaging coating materials in terms of barrier performance, processing performance, environmental friendliness and food safety.

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

[0011] This invention provides an aqueous barrier coating composition, wherein the aqueous barrier coating composition uses water as a dispersion medium, includes a biodegradable PHA emulsion as the main film-forming component, and plasticizers, emulsifiers, and inorganic nanofillers, wherein the aqueous barrier coating composition meets the following requirements:

[0012] The content of triethyl citrate in PHA is 3-10 wt%, for example, it can be 3 wt%, 4 wt%, 5 wt%, 6.5 wt%, 7 wt%, 8.5 wt%, or 10 wt%;

[0013] The organically modified montmorillonite accounts for 2–4 wt% of the PHA mass, for example, it can be 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, or 4 wt%.

[0014] The hydrophilic-lipophilic balance value of the emulsifier system is 12 to 16, for example, it can be 12, 12.5, 13, 13.8, 14.2, 15, 15.5 or 16;

[0015] The emulsion prepared under conditions of pH 5.0 to 5.5 has a volume average particle size of 400 to 700 nm, wherein the pH value is, for example, 5.0, 5.1, 5.2, 5.3, 5.4 or 5.5, and the resulting emulsion has a volume average particle size of, for example, 400 nm, 450 nm, 510 nm, 580 nm, 640 nm or 700 nm.

[0016] After the emulsion is applied to a dry film coating weight of 10–12 g / m², such as 10 g / m², 11 g / m², or 12 g / m², the oxygen transmission rate measured according to ASTM D3985-24 at 23°C and 0% relative humidity shall not exceed 580 cm³ / m²·d, for example, it can be 580 cm³ / m²·d, 550 cm³ / m²·d, 500 cm³ / m²·d or lower. The water vapor transmission rate measured according to ASTM E96 / E96M-24a wet cup method at 38°C and 90% relative humidity shall not exceed 290 g / m²·d, for example, it can be 290 g / m²·d, 280 g / m²·d, 260 g / m²·d or lower.

[0017] Furthermore, heat sealing can be achieved within a temperature range of 110–150°C, a residence time of 1 second, and a pressure of 0.4 MPa. The temperature is, for example, 110°C, 120°C, 130°C, 140°C, or 150°C. Under the conditions of 130°C, 1 second, and 0.4 MPa, the peel strength measured according to ASTM F88 / F88M-23 standard is not less than 5.0 N / 15 mm, for example, it can be 5.0 N / 15 mm, 5.5 N / 15 mm, 6.0 N / 15 mm, or higher.

[0018] The PHA in the aqueous barrier coating composition is selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

[0019] The plasticizer in the water-based barrier coating composition is selected from one or more of the following: triethyl citrate, tributyl citrate, acetylated tributyl citrate, triglyceride triacetate, di(2-ethylhexyl) adipate, dibutyl adipate, di(2-ethylhexyl) sebacate, di(2-ethylhexyl) azelate, and medium-chain triglycerides.

[0020] The emulsifier of the water-based barrier coating composition is selected from one or more of polyvinyl alcohol, sucrose fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, lecithin, fatty alcohol polyoxyethylene ether, polyethylene glycol castor oil, and acrylic or methacrylic protective colloids.

[0021] The inorganic nanofiller in the aqueous barrier coating composition is selected from one or more of the following: organically modified montmorillonite, saponite, sepiolite, hertolite, synthetic fluorophlogopite, layered double hydroxides, kaolinite nanosheets, illite, and mica flake powder; and the emulsion formed by the aqueous barrier coating composition has a shear rate of 0.1 s⁻¹ at 25°C. -1 The apparent viscosity and shear rate at 10 s⁻¹ -1 The ratio of apparent viscosity at different times is not less than 5. For example, this ratio can be 5, 6, 8, 10 or higher, exhibiting excellent shear thinning behavior, which is beneficial for coating processing.

[0022] The aqueous barrier coating composition further comprises one or more active substances selected from antibacterial agents, antioxidants, and oxygen absorbers, and the total migration of the coating formed by the composition is not higher than 10 mg / dm³. 2 The sensory requirements comply with the provisions of GB 4806.1 and GB4806.8, thus making it applicable to the field of food contact materials.

[0023] The present invention also provides a method for preparing the above-mentioned water-based barrier coating composition, the method comprising the following steps:

[0024] Step 1. Dissolve the PHA resin and plasticizer in an organic solvent;

[0025] Step 2. The solution obtained in Step 1 is added to an aqueous phase containing an emulsifier and pre-dispersed inorganic nanofiller for high-speed shear emulsification;

[0026] Step 3. Remove the organic solvent to obtain the emulsion composition;

[0027] The inorganic nanofiller was pre-dispersed using ultrasound at a frequency of 20kHz and a power of 400W, treated in pulse mode for 10 minutes, and the system temperature was controlled at no higher than 30℃ using a water bath.

[0028] The organic solvent used in the method is selected from one or more of ethyl acetate, n-propyl acetate, n-butyl acetate, methyl ethyl ketone, and cyclohexanone.

[0029] The present invention also provides a paper-based packaging material, wherein at least one surface of the paper-based packaging material is coated with a barrier coating formed by the above-described water-based barrier coating composition after drying and curing, wherein the coating amount of the barrier coating is 5 to 20 g / m², for example, 5 g / m², 8 g / m², 10 g / m², 12 g / m², 15 g / m² or 20 g / m².

[0030] The key performance indicators of the paper-based packaging material are as follows: 60-second Cobb value not higher than 5 g / m², Kit value not lower than grade 10; water vapor transmission rate measured by the wet cup method according to ASTM E96 / E96M-24a at 38℃ and 90% relative humidity not higher than 290 g / m²·d; oxygen transmission rate measured by ASTM D3985-24 at 23℃ and 0% relative humidity not higher than 580 cm³ / m²·d; and after heat sealing at 130℃, 1s, and 0.4MPa, the peel strength measured by ASTM F88 / F88M-23 is not lower than 5.0 N / 15 mm.

[0031] The paper-based packaging material exhibits stability, as shown in the following ways: the water-based barrier coating composition used to prepare the barrier coating has a particle size and viscosity fluctuation range of no more than ±5% after being stored for 90 days at 23°C and 40°C, for example, a fluctuation range of ±1%, ±2.5%, or ±4.5%; and after being stored for 90 days in a standard environment of 23°C and 50% relative humidity, the coating adhesion grade of the paper-based packaging material is not lower than 5B and the Kit value after folding treatment is not lower than 10.

[0032] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0033] The barrier properties were improved through the synergistic effect of plasticizers and nanofillers. The plasticizers enhanced the mobility of the PHA molecular chains, creating conditions for the efficient exfoliation of nanosheets and the formation of a three-dimensional network structure. This network structure constructed tortuous gas permeation pathways within the coating, resulting in a significant reduction in oxygen and water vapor permeability.

[0034] The invention achieves balanced overall performance and a well-defined process window. The coating provided by this invention combines low gas permeability, a wide heat-sealing window, good oil resistance, and adhesion. These performance boundaries, combined with process windows such as emulsion particle size and pH value, ensure the repeatability and industrial applicability of the technical solution.

[0035] It exhibits excellent environmental friendliness and regulatory compliance. The coating composition provided by this invention is entirely biodegradable and free of perfluorinated and polyfluoroalkyl substances. Migration testing has verified that it complies with food contact material safety regulations.

[0036] It exhibits excellent storage and aging stability. The emulsions and coatings prepared by this invention show no significant degradation in key physical properties and performance after long-term storage and aging, meeting the reliability requirements for commercial applications. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0038] Main reagents and raw materials:

[0039] Table 1. Main reagent and raw material names, product models and manufacturers:

[0040]

[0041] Table 2 mainly analyzes the names, models / specifications, and manufacturers of the testing instruments:

[0042]

[0043] Main testing methods and standards:

[0044] Food contact paper and paperboard compliance: GB 4806.8-2022;

[0045] Total migration test: GB 31604.1-2023;

[0046] Cobb value test for water resistance: T / ZZB 2836—2022-2002;

[0047] Oil resistance Kit value test: TAPPI T 559 cm-22;

[0048] WVTR test: ASTM E96 / E96M-24a;

[0049] OTR test: ASTM D3985-24;

[0050] Heat seal strength test: ASTM F88 / F88M-23;

[0051] Coating adhesion test: ASTM D3359-23, Test Method B;

[0052] Paperboard resizing: Refer to clause T / ZZB 2836-2022;

[0053] Rheological testing: Steady-state viscosity was determined according to ISO 3219-1:2021;

[0054] Sensory and general safety requirements: GB 4806.1-2016.

[0055] General preparation process:

[0056] Unless otherwise stated, the emulsions in the examples were prepared using a solvent-assisted emulsification method: PHA resin and plasticizer were dissolved in ethyl acetate to prepare an oil phase; OMMT was ultrasonically pre-dispersed in PVA-containing water (20 kHz, 400 W, 10 min, ≤30 °C) to prepare an aqueous phase; the oil phase was dropwise added to the aqueous phase at 5000 r / min for high-speed emulsification; the solvent was removed by vacuum evaporation to obtain the emulsion and the pH value was adjusted.

[0057] Example:

[0058] Example 1: Following the general preparation process, 100 parts of PHBV resin, 5 parts of TEC, 3 parts of OMMT and 3 parts of PVA were used.

[0059] Example 2: Following the general preparation process, 100 parts of PHBV resin, 3 parts of TEC, 3 parts of OMMT and 3 parts of PVA were used.

[0060] Example 3: Following the general preparation process, 100 parts of PHBV resin, 10 parts of TEC, 3 parts of OMMT and 3 parts of PVA were used.

[0061] Example 4: Following the general preparation process, 100 parts of PHBV resin, 5 parts of TEC, 2 parts of OMMT and 3 parts of PVA were used.

[0062] Example 5: Following the general preparation process, 100 parts of PHBV resin, 5 parts of TEC, 4 parts of OMMT and 3 parts of PVA were used.

[0063] Table 3 Example Formulations:

[0064]

[0065] Comparative example:

[0066] Comparative Example 1: Commercially available conventional PE coated paper was selected, with a PE coating amount of approximately 15 g / m².

[0067] Comparative Example 2: Commercially available polylactic acid (PLA) resin was coated onto the surface of 80 g / m² kraft paper by melt extrusion, with a coating amount of approximately 12 g / m².

[0068] Comparative Example 3: Prepared according to the general preparation process, but without adding any plasticizers or OMMT, using PHB resin.

[0069] Comparative Example 4: Prepared according to the general preparation process, using PHBV resin and 5 parts TEC, but without adding any OMMT.

[0070] Table 4 Comparative Example Formulations:

[0071]

[0072] Application example:

[0073] Application Example 1: Paper-based barrier properties and water and oil resistance.

[0074] This application example aims to evaluate the core function of the coating—barrier performance. The emulsions prepared in Examples 1-5 and Comparative Examples 3-4, along with commercially available coated paper as a baseline in Comparative Examples 1-2, were uniformly prepared or cut into standard test samples. For the emulsion samples, a rod coater was used to uniformly coat an 80 g / m² kraft paper substrate, controlling the dry film weight within the range of 10–12 g / m², and drying in a 60°C oven for 5 minutes. Subsequently, the water resistance, oil resistance, WVTR, and OTR of all samples were evaluated.

[0075] Table 5. Barrier and Tolerance Performance Results for Each Sample:

[0076]

[0077] Analysis: The data in Table 5 show that Examples 1-5 of this invention achieved improved overall performance through the synergistic effect of plasticizers and nanofillers. Compared with Comparative Example 3 (pure PHB) without any modifiers, the oxygen and water vapor transmission rates of the example samples were significantly reduced. Compared with Comparative Example 4 containing only plasticizers, the oxygen and water vapor transmission rates of the example samples were reduced by approximately two times, demonstrating the contribution of the network structure constructed by the nanofillers to the barrier performance. Compared with commercial products, although the PE coated paper of Comparative Example 1 is superior in water vapor barrier performance, its oxygen transmission rate is much higher than that of the examples of this invention, and it is not biodegradable. The oxygen transmission rate of the PLA coated paper of Comparative Example 2 is three times that of the examples of this invention.

[0078] Application Example 2: Heat-sealed window and strength.

[0079] To evaluate the processing suitability of the coating, heat-sealing performance tests were conducted on all coated paper samples from Examples 1-5 and Comparative Examples 1-4. Using a laboratory heat sealer, the coated surfaces of each sample were heat-sealed under a residence time of 1 second and a pressure of 0.4 MPa. The temperature range was set from 110°C to 150°C. After heat sealing, the samples were cut into 15 mm wide strips and subjected to a 180° peel test.

[0080] Table 6. Peel strength (N / 15mm) of each sample at different heat-sealing temperatures:

[0081]

[0082] Analysis: Table 6 shows that Examples 1-5 of the present invention achieved effective heat sealing within a wide temperature range of 110–150°C, with peak heat sealing strength exceeding 5 N / 15 mm, demonstrating good processability. In contrast, the pure PHB coating (Comparative Example 3) and PLA coating (Comparative Example 2) failed to form effective adhesion at all test temperatures due to their inherent brittleness. While the coating with only plasticizer added (Comparative Example 4) improved brittleness, its highest heat sealing strength was only 3.0 N / 15 mm, below the application requirements.

[0083] Application Example 3: Adhesion and oil resistance after folding.

[0084] This application example aims to evaluate the mechanical properties of the coating. Coated paper samples from all Examples 1-5 and Comparative Examples 1-4 were tested. The adhesion between the coating and the paper substrate was evaluated using the cross-cut test. The coated paper samples were folded in half, compacted with a roller, unfolded, and then subjected to a Kit value test to verify their flexibility.

[0085] Table 7 Adhesion rating and Kit rating after folding for each sample:

[0086]

[0087] Analysis: The data in Table 7 show that the coatings of Examples 1-5 of this invention all exhibit the highest 5B adhesion rating, and after undergoing folding resistance treatment, their oil resistance Kit value remains above 10, demonstrating good mechanical strength and durability. In contrast, Comparative Example 3 (pure PHB) has an adhesion rating of only 3B, and it cracks severely after folding, with a significant decrease in oil resistance. The adhesion and post-folding performance of Comparative Example 2 (PLA) and Comparative Example 4 (plasticized only) are also inferior to the embodiments of this invention.

[0088] Application Example 4: Resizing / Regeneration Compatibility.

[0089] This application example aims to evaluate the recyclability of coated paper. Coated paper samples from all Examples 1-5 and Comparative Examples 1-4 were tested. The coated paper samples were re-slurryed in a standard descrambler, and fiber retention and residue content were calculated.

[0090] Table 8. Indicators of slurry return properties:

[0091]

[0092] Analysis: The resizing test results in Table 8 demonstrate the environmental friendliness and recyclability of the coating of this invention. Samples from Examples 1-5 all exhibited excellent resizing performance, with fiber retention rates exceeding 98%, close to that of uncoated base paper. This indicates that the water-based coating of this invention can effectively separate from paper fibers under standard resizing conditions. In contrast, the coatings of Comparative Example 1 (PE) and Comparative Example 2 (PLA) formed large plastic fragments during resizing, resulting in a significant decrease in fiber retention.

[0093] Application Example 5: Storage / aging stability of emulsions and coatings.

[0094] This application example aims to evaluate the shelf-life performance of the product. Accelerated aging tests were performed on all emulsion and coated paper samples from Examples 1-5 and Comparative Examples 3-4. Emulsion samples were sealed and stored at 23°C and 40°C for 90 days, and changes in particle size and viscosity were measured. Coated paper samples were stored at 23°C and 50% RH for 90 days, after which their performance indicators were retested. Comparative Examples 1 and 2 did not have an emulsion form and therefore were not suitable for emulsion stability testing.

[0095] Table 9. Storage stability of emulsions:

[0096]

[0097] Analysis: The data in Table 9 demonstrate the reliability of the emulsion of this invention. After storage at 23°C and 40°C (accelerated aging) for 90 days, the emulsions prepared in the examples showed good storage stability, with average particle size and viscosity changes within ±5%. In contrast, the pure PHB emulsion of Comparative Example 3 exhibited poor stability and stratification, while the emulsion of Comparative Example 4 also showed inferior stability compared to the examples of this invention.

[0098] Table 10 Aging properties of coated paper:

[0099]

[0100] Analysis: The data in Table 10 show that the coating formed by this invention exhibits no significant degradation in key performance characteristics after aging for 90 days under standard conditions. In contrast, the coating of Comparative Example 3 (pure PHB) shows severe performance degradation due to post-crystallization. This ensures that the product maintains consistent high performance throughout its shelf life.

[0101] Application Example 6: Rheological characteristics and particle size of emulsions.

[0102] This application example aims to characterize the physical properties of emulsions through rheological and particle size analysis. Emulsion samples from all Examples 1-5 and Comparative Examples 3-4 were tested. Rotational rheometers were used to measure the properties of each emulsion at a shear rate of 0.1 s⁻¹. -1 With 10s -1 The apparent viscosity was calculated, and the viscosity ratio was determined using dynamic light scattering. 50 Comparative Examples 1 and 2 do not have an emulsion form, therefore they are not applicable to this test.

[0103] Table 11 Emulsion rheology and particle size results:

[0104]

[0105] Analysis: Rheological data show that the emulsions in all embodiments exhibit strong shear-thinning behavior (viscosity ratio much greater than 5), while the comparative example shows near-Newtonian fluid behavior (viscosity ratio close to 1). This demonstrates that the present invention, through specific formulation and process, successfully constructs a three-dimensional network composed of exfoliated nanosheets in the emulsion, thereby forming tortuous gas permeation paths in the coating and resulting in improved barrier performance.

[0106] Application Example 7: Total Migration and Sensory Testing.

[0107] This application example aims to evaluate the food contact safety of the coating and verify its compliance with relevant regulatory requirements. Coated paper samples prepared in Examples 1–5 and Comparative Examples 1–4 were selected for testing, with the dry coating amount controlled at 11 ± 1 g / m². Total migration testing was conducted according to GB 31604.1-2023, using 10% ethanol (food simulant A), 4% acetic acid (food simulant B), and 95% ethanol (food simulant D2) as simulants, and subjected to contact at 40°C for 10 days. Sensory testing was performed according to GB 4806.1 and GB 4806.8, evaluating the immersion solution.

[0108] Table 12 Total migration and sensory results for each sample (n=3, 40℃×10d):

[0109]

[0110] Analysis: The data in Table 12 clearly demonstrate the compliance of the coating of this invention with food contact safety. The total migration amounts of all Examples 1–5 in the three types of food simulants (aqueous, acidic, and oily) were significantly lower than the regulatory limit of 10 mg / dm², and the sensory test results were all satisfactory, proving their safety as food contact materials. Even in Example 3, which had the highest plasticizer content, the migration amount in 95% ethanol (simulating fatty foods) remained within the safe range. In contrast, Comparative Example 3 (pure PHB coating) exhibited poor film-forming properties and microcracks, leading to excessive migration of low molecular weight substances and failing the sensory test. Comparative Example 4 (containing only plasticizer), although showing improved film-forming properties, still exceeded the migration limit in oily simulants, confirming that the construction of the OMMT nanonetwork structure is crucial for inhibiting the migration of small molecules such as plasticizers. This application example, from a regulatory compliance perspective, further validates that the synergistic effect of plasticizers (TEC) and nanofillers (OMMT) not only enhances physical barrier properties but also constructs a stable coating structure, effectively controlling substance migration and ensuring food safety.

[0111] Analysis of experimental results:

[0112] The test results of Application Examples 1 to 6 systematically evaluated the overall performance of the compositions and coatings of the present invention.

[0113] The results of Application Example 1 demonstrate that the composition of the present invention exhibits excellent barrier properties, with oxygen and water vapor permeability reduced by several times compared to Comparative Example 3 (pure PHA) and Comparative Example 4 (plasticized only). The mechanism of this performance improvement was confirmed in Application Example 6. Rheological data show that the emulsions of all examples exhibit strong shear-thinning behavior (viscosity ratio much greater than 5), while the comparative examples show near-Newtonian fluid behavior (viscosity ratio close to 1). This proves that the present invention, through specific formulation and process, successfully constructs a three-dimensional network composed of exfoliated nanosheets in the emulsion, thereby forming tortuous gas permeation paths in the coating, leading to improved barrier properties.

[0114] Regarding processing and mechanical properties, the results of Application Examples 2 and 3 demonstrate that the present invention effectively overcomes the brittleness of pure PHA. Application Example 2 shows that all embodiments possess a wide heat-sealing window and peel strength exceeding the requirements of commercial applications, while Comparative Examples 2 and 3 cannot be effectively heat-sealed due to brittleness. Application Example 3 confirms that the coating has good adhesion (5B) and flexibility (Kit value does not decrease after folding), solving the problem of easy cracking and failure of pure PHA coatings.

[0115] Environmental friendliness is another key advantage of this invention. The resizing test results of Application Example 4 show that the coating of this invention has high separation efficiency from paper fibers, with a fiber retention rate of over 98%, which contrasts sharply with traditional PE and PLA coatings, demonstrating its potential in the circular economy.

[0116] Finally, the stability test results of Application Example 5 ensure the commercial reliability of the product of this invention. Whether it is the long-term storage stability of the emulsion or the aging performance of the coated paper, the embodiments of this invention exhibit minimal performance degradation, meeting the practical needs of industrial production and application.

[0117] In summary, this invention successfully prepared a high-performance PHA aqueous emulsion by precisely controlling the content of plasticizer and inorganic nanofiller, combined with a specific emulsification system and process parameters. The experimental results of Application Examples 1 to 6 systematically demonstrate that the coating formed by this invention exhibits excellent and balanced performance across multiple dimensions, including gas barrier properties, water and oil resistance, heat sealing performance, mechanical flexibility, adhesion, storage stability, and recyclability. This performance surpasses that of unmodified or only single-modified PHA systems and demonstrates comprehensive advantages compared to existing commercial materials. These properties stem from the plasticizer-nanosheet synergistic mechanism revealed in this invention. This mechanism establishes a clear structure-property relationship between quantifiable emulsion physical properties and the final coating performance, providing a complete technical solution for the development of high-performance bio-based packaging materials.

[0118] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-based barrier coating composition, characterized in that: The aqueous barrier coating composition uses water as a dispersion medium and includes a biodegradable polyhydroxy fatty acid ester emulsion as the main film-forming component, as well as plasticizers, emulsifiers and inorganic nanofillers. The aqueous barrier coating composition described herein meets the following requirements: Triethyl citrate constitutes 3–10 wt% of the polyhydroxyalkanoate. Organically modified montmorillonite accounts for 2-4 wt% of the polyhydroxyalkanoate; The hydrophilic-lipophilic balance value of the emulsifier system is 12-16; The volume average particle size of the emulsion prepared under pH conditions of 5.0–5.5 was 400–700 nm. After the emulsion is coated to a dry film coverage of 10–12 g / m², the oxygen transmission rate measured according to ASTM D3985-24 at 23°C and 0% relative humidity shall not exceed 580 cm³ / m²·d, and the water vapor transmission rate measured according to ASTM E96 / E96M-24a wet cup method at 38°C and 90% relative humidity shall not exceed 290 g / m²·d. Furthermore, heat sealing can be achieved within a temperature range of 110–150℃, a residence time of 1s, and a pressure of 0.4MPa. The peel strength measured according to ASTM F88 / F88M-23 standard is not less than 5.0N / 15mm under conditions of 130℃, 1s, and 0.4MPa.

2. The water-based barrier coating composition according to claim 1, characterized in that, The polyhydroxy fatty acid ester in the aqueous barrier coating composition is selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

3. The water-based barrier coating composition according to claim 1, characterized in that, The plasticizer in the water-based barrier coating composition is selected from one or more of the following: triethyl citrate, tributyl citrate, acetylated tributyl citrate, triglyceride triacetate, di(2-ethylhexyl) adipate, dibutyl adipate, di(2-ethylhexyl) sebacate, di(2-ethylhexyl) azelate, and medium-chain triglycerides.

4. The water-based barrier coating composition according to claim 1, characterized in that, The emulsifier of the water-based barrier coating composition is selected from one or more of polyvinyl alcohol, sucrose fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, lecithin, fatty alcohol polyoxyethylene ether, polyethylene glycol castor oil, and acrylic or methacrylic protective colloids.

5. The water-based barrier coating composition according to claim 1, characterized in that, The inorganic nanofiller in the aqueous barrier coating composition is selected from one or more of the following: organically modified montmorillonite, saponite, sepiolite, hertolite, synthetic fluorophlogopite, layered double hydroxides, kaolinite nanosheets, illite, and mica flake powder; and the emulsion formed by the aqueous barrier coating composition has a shear rate of 0.1 s⁻¹ at 25°C. -1 The apparent viscosity and shear rate at 10 s⁻¹ -1 The ratio of apparent viscosity at different times is not less than 5.

6. The water-based barrier coating composition according to claim 1, characterized in that, The aqueous barrier coating composition further comprises one or more active substances selected from antibacterial agents, antioxidants, and oxygen absorbers, and the total migration of the coating formed by the composition is not higher than 10 mg / dm³. 2 Sensory requirements shall comply with the provisions of GB 4806.1 and GB 4806.

8.

7. A method for preparing the water-based barrier coating composition according to claim 1, characterized in that, The method includes the following steps: Step 1. Dissolve the polyhydroxyalkanoate resin and plasticizer in an organic solvent; Step 2. The solution obtained in Step 1 is added to an aqueous phase containing an emulsifier and pre-dispersed inorganic nanofiller for high-speed shear emulsification; Step 3. Remove the organic solvent to obtain the emulsion composition; The inorganic nanofiller was pre-dispersed using ultrasound at a frequency of 20kHz and a power of 400W, treated in pulse mode for 10 minutes, and the system temperature was controlled at no higher than 30℃ using a water bath.

8. The preparation method according to claim 7, characterized in that, The organic solvent used in the method is selected from one or more of ethyl acetate, n-propyl acetate, n-butyl acetate, methyl ethyl ketone, and cyclohexanone.

9. A paper-based packaging material, characterized in that: At least one surface of the paper-based packaging material is coated with a barrier coating formed by the water-based barrier coating composition according to claim 1, which has been dried and cured, and the coating amount of the barrier coating is 5 to 20 g / m².

10. The paper-based packaging material according to claim 9, characterized in that, The key performance indicators of the paper-based packaging material are as follows: 60-second Cobb value not higher than 5 g / m², Kit value not lower than grade 10; water vapor transmission rate measured by the wet cup method according to ASTM E96 / E96M-24a at 38℃ and 90% relative humidity not higher than 290 g / m²·d; oxygen transmission rate measured by ASTM D3985-24 at 23℃ and 0% relative humidity not higher than 580 cm³ / m²·d; and after heat sealing at 130℃, 1s, and 0.4MPa, the peel strength measured by ASTM F88 / F88M-23 is not lower than 5.0 N / 15 mm.

11. The paper-based packaging material according to claim 9, characterized in that, The paper-based packaging material exhibits stability, as shown in the following ways: the water-based barrier coating composition used to prepare the barrier coating has a particle size and viscosity fluctuation range of no more than ±5% after being stored for 90 days at 23°C and 40°C; and after being stored for 90 days in a standard environment of 23°C and 50% relative humidity, the coating adhesion grade of the paper-based packaging material is no less than 5B and the Kit value after folding treatment is no less than 10.

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