Polyhydroxyalkanoate aqueous barrier coating compositions and applications

Abstract

The application discloses a polyhydroxyaliphatic ester aqueous barrier coating composition and application, and belongs to the technical field of packaging materials. The composition takes water as a dispersion medium and comprises polyhydroxyaliphatic ester, plasticizer, emulsifier and inorganic nano filler. Under specific proportions and process conditions, a stable emulsion with a volume average particle size of 400-700 nm is prepared. After the emulsion is applied to a paper base material at a dry film coating amount of 10-12 g / m2, the obtained coating layer exhibits good comprehensive performance: the oxygen transmission rate is not higher than 580 cm3 / m2.d, the water vapor transmission rate is not higher than 290 g / m2.d, and the heat sealing strength at 130 DEG C is not lower than 5.0 N / 15 mm. The application does not contain fluorine compounds and can be completely biodegraded, thereby providing a technical path for sustainable paper-based packaging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of packaging materials, and specifically relates to a polyhydroxyalkanoate aqueous barrier coating composition and application. BACKGROUND

[0002] Paper-based materials are favored in the field of food packaging due to their inherent properties of being renewable and biodegradable. However, natural paper fibers have porous and hydrophilic characteristics, which cannot meet the requirements of modern food packaging for waterproof, oil-proof, gas barrier and other key properties. Therefore, it is necessary to modify them by applying functional coatings on their surfaces.

[0003] For a long time, polyethylene (PE) film-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 the existing recycling system, causing waste of resources and environmental pollution. Another type of coating material that has been widely used is perfluoro and polyfluoroalkyl substances (PFAS), which have good waterproof and oil-proof properties, but due to their extreme persistence in the environment and potential health risks to living organisms, they are facing increasingly strict regulatory restrictions and market elimination worldwide.

[0004] Under this background, polyhydroxyalkanoate (PHA) as a bio-based polyester synthesized by microbial fermentation is recognized as one of the most promising sustainable packaging materials due to its complete biodegradability in various natural environments. However, there are still challenges in translating the theoretical advantages of PHA into practical applications. Pure PHA, especially the most widely studied poly-3-hydroxybutyrate (PHB), has inherent defects such as high crystallinity, brittle and hard texture, and narrow thermal processing window, which can easily produce microcracks when directly coated and cannot form an effective barrier.

[0005] The field has explored PHA aqueous dispersions. For example, WO 2020 / 036843 A1 and its US counterpart US 11866606 disclose an aqueous dispersion mainly composed of PHA, and allow the optional addition of surfactants, plasticizers (including citrate esters) and fillers (including clay / montmorillonite). However, this document only provides a broad "list" of components and does not limit the specific and synergistic formulation and process window proposed by the present application, such as a hydrophilic-lipophilic balance (HLB) value of 12-16 for the emulsifier system, a pH of 5.0-5.5, triethyl citrate (TEC) at 3-10 wt% based on the mass of PHA, organic modified montmorillonite (OMMT) at 2-4 wt% based on the mass of PHA, an emulsion volume average particle size (D 50)400-700nm, and the combination of low / medium shear viscosity ratio no less than 5 and other key parameters. More importantly, this document does not disclose or suggest the internal mechanism of promoting the efficient exfoliation of nanosheets in the matrix and forming a three-dimensional network by plasticizing pretreatment, thereby achieving nonlinear improvement of barrier performance, nor does it provide a performance boundary that can be reproduced under a specific coating amount.

[0006] On the other hand, EP 4166716 A1 mainly focuses on improving film-forming problems such as pinholes, cracks, and adhesion to substrates of the coating by using PHBH with polyvinyl alcohol (PVA) / ethylene-vinyl acetate copolymer (EVA) type adhesives. This scheme does not involve the complete technical causal chain of "plasticization (TEC) → promote OMMT sheet exfoliation → rheological network → barrier jump" proposed by the present invention, nor does it limit the narrow parameter window of the present invention and the wide heat sealing window associated therewith.

[0007] In addition, other related technologies such as WO 2022 / 152813 A1 and CN 115996838 A mainly focus on the barrier ideas of general aqueous biopolymer dispersion systems or multi-layer coating, and do not specifically point to the specific synergistic mechanism of PHA-TEC-OMMT in a single coating system. CN 112867766 A and CN 119777197 A, etc. focus on the source and stability control of PHA dispersion prepared directly from fermentation broth, and the technical core is in the upstream preparation, which does not give the downstream composite formula parameter combination and the final performance boundary defined by the present invention.

[0008] In summary, the prior art fails to provide a comprehensive solution that can simultaneously solve the inherent brittleness of PHA, achieve quantifiable high gas barrier properties, obtain a wide and robust processing window, and ensure long-term storage stability of the emulsion. SUMMARY

[0009] The present application aims to overcome the shortcomings of the prior art and provide a polyhydroxyalkanoate aqueous barrier coating composition and application, aiming to solve the problems of existing paper-based packaging coating materials in barrier performance, processing performance, environmental friendliness, and food safety.

[0010] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0011] The present application provides an aqueous barrier coating composition, which comprises a biodegradable PHA emulsion as the main film-forming component, and a plasticizer, an emulsifier and an inorganic nano-filler, wherein the aqueous barrier coating composition satisfies the following requirements:

[0012] triethyl citrate is present in an amount of 3-10 wt% of the PHA, for example, 3 wt%, 4 wt%, 5 wt%, 6.5 wt%, 7 wt%, 8.5 wt%, or 10 wt%;

[0013] organically modified montmorillonite is present in an amount of 2-4 wt% of the PHA, for example, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, or 4 wt%;

[0014] the emulsifier system has a hydrophilic-lipophilic balance of 12-16, for example, 12, 12.5, 13, 13.8, 14.2, 15, 15.5, or 16;

[0015] the emulsion has a volume average particle size of 400-700 nm when prepared at a pH of 5.0-5.5, for example, 5.0, 5.1, 5.2, 5.3, 5.4, or 5.5, and the volume average particle size is, for example, 400 nm, 450 nm, 510 nm, 580 nm, 640 nm, or 700 nm;

[0016] after the emulsion is coated to a dry film build of 10-12 g / m2, for example, 10 g / m2, 11 g / m2, or 12 g / m2, the oxygen transmission rate is no more than 580 cm3 / m2·d, for example, 580 cm3 / m2·d, 550 cm3 / m2·d, 500 cm3 / m2·d, or less, as measured according to ASTM D3985-24 at 23 °C, 0% relative humidity, and the water vapor transmission rate is no more than 290 g / m2·d, for example, 290 g / m2·d, 280 g / m2·d, 260 g / m2·d, or less, as measured according to ASTM E96 / E96M-24a wet cup method at 38 °C, 90% relative humidity;

[0017] and, the emulsion is heat sealable at a temperature of 110-150 °C, a residence time of 1 s, and a pressure of 0.4 MPa, for example, 110 °C, 120 °C, 130 °C, 140 °C, or 150 °C, and has a peel strength of no less than 5.0 N / 15 mm, for example, 5.0 N / 15 mm, 5.5 N / 15 mm, 6.0 N / 15 mm, or more, as measured according to ASTM F88 / F88M-23 at 130 °C, 1 s, 0.4 MPa.

[0018] The PHA of 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 of the water-based barrier coating composition is selected from one or more of triethyl citrate, tributyl citrate, acetyl tributyl citrate, glycerol triacetate, di(2-ethylhexyl) adipate, dibutyl adipate, di(2-ethylhexyl) sebacate, di(2-ethylhexyl) azelate, and medium-chain triglyceride.

[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, polyoxylated castor oil, and acrylic or methacrylic protective colloid.

[0021] The inorganic nano-filler of the water-based barrier coating composition is selected from one or more of organically modified montmorillonite, saponite, sepiolite, hectorite, synthetic fluorphlogopite, layered double hydroxide, kaolinite nanosheet, illite, and mica flake powder; and the emulsion formed from the water-based barrier coating composition has a ratio of apparent viscosity at a shear rate of 0.1 s -1 to apparent viscosity at a shear rate of 10 s -1 of not less than 5, for example, the ratio can be 5, 6, 8, 10 or higher, exhibiting excellent shear thinning behavior, which is beneficial to coating processing.

[0022] The water-based barrier coating composition further comprises one or more active substances selected from antibacterial agents, antioxidants, and oxygen absorbers, and the coating formed from the composition has a total migration amount of not more than 10 mg / dm 2 , and meets the sensory requirements specified in GB 4806.1 and GB 4806.8, thereby being suitable for use in the field of food contact materials.

[0023] The present application also provides a preparation method of the above water-based barrier coating composition, which comprises the following steps:

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

[0025] Step 2. Adding the solution obtained in Step 1 into an aqueous phase containing the emulsifier and the pre-dispersed inorganic nano-filler to perform high-speed shear emulsification;

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

[0027] The pre-dispersion of the inorganic nano-filler is performed by ultrasonic wave with a frequency of 20 kHz and a power of 400 W in pulse mode for 10 minutes, and the temperature of the system is controlled to be not higher than 30°C by 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, cyclohexanone.

[0029] The paper-based packaging material provided by the application has at least one surface coated with a dried and cured barrier coating layer formed from the above-mentioned water-based barrier coating composition, and the coating amount of the barrier coating layer is 5-20 g / m2, for example, can be 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: the 60-second Cobb value is not higher than 5 g / m2, the Kit value is not lower than 10 levels; the water vapor transmission rate measured by the wet cup method according to the standard ASTM E96 / E96M-24a at 38℃ and 90% relative humidity is not higher than 290 g / m2·d; the oxygen transmission rate measured according to the standard ASTM D3985-24 at 23℃ and 0% relative humidity is not higher than 580 cm3 / m2·d; and the peel strength of the coating after heat sealing at 130℃, 1s, and 0.4MPa is not less than 5.0 N / 15mm, measured according to the standard ASTM F88 / F88M-23.

[0031] The paper-based packaging material has stability, which is manifested in that the emulsion of the water-based barrier coating composition used to prepare the barrier coating layer has a particle size and viscosity fluctuation range of not more than ±5% after being stored at 23℃ and 40℃ for 90 days, for example, a fluctuation range of ±1%, ±2.5%, or ±4.5%; and the coating adhesion grade of the paper-based packaging material is not less than 5B and the Kit value after folding resistance treatment is not less than 10 levels after being stored in a standard environment of 23℃ and 50% relative humidity for 90 days.

[0032] Compared with the prior art, the following significant beneficial effects can be obtained by using the application:

[0033] Through the synergistic effect of the plasticizer and the nano filler, the barrier performance is improved. The plasticizer enhances the activity of the PHA molecular chain, creating conditions for efficient exfoliation of the nano sheet layer and formation of a three-dimensional network structure. This network structure builds a tortuous gas permeation path inside the coating, resulting in a several-fold reduction in oxygen transmission rate and water vapor transmission rate.

[0034] Balanced comprehensive performance and clear process window are obtained. The coating provided by the application has low gas transmission rate, wide heat sealing window, good oil resistance, and adhesion. These performance boundaries combined with the process window of emulsion particle size, pH value, etc. ensure the repeatability and industrial applicability of the technical solution.

[0035] Good environmental friendliness and regulatory compliance. The coating composition provided by the present application is biodegradable as a whole, and does not contain perfluoro and polyfluoro alkyl substances. The migration test verification meets the food contact material safety regulations.

[0036] Good storage and aging stability. The emulsion and coating prepared by the present application do not have significant decay of key physical properties and performance after long-term storage and aging, meeting the reliability requirements of commercial application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application. Unless otherwise specified, the raw materials used in the present embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, the performance test methods are carried out according to the standards described in the summary of the invention.

[0038] Main reagents and raw materials:

[0039] Table 1 Name, product model and manufacturer of main reagents and raw materials:

[0040]

[0041] Table 2 Name, model / specification and manufacturer of main analysis and detection instruments:

[0042]

[0043] Main test methods and standards:

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

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

[0046] Water resistance Cobb value test: 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 slurry resistance: refer to T / ZZB 2836-2022 clause;

[0053] Rheology test: steady shear viscosity determination according to ISO 3219-1:2021;

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

[0055] General preparation procedure:

[0056] Unless otherwise specified, the emulsions in the examples were prepared by solvent assisted emulsification: the PHA resin and plasticizer were dissolved in ethyl acetate to make the oil phase; OMMT was pre-dispersed in water containing PVA by ultrasonic (20 kHz, 400 W, 10 min, ≤30℃) to prepare the water phase; the oil phase was added dropwise to the water phase at a speed of 5000 r / min for high-speed emulsification; the solvent was removed by evaporation under reduced pressure to obtain the emulsion and adjust the pH value.

[0057] Examples:

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

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

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

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

[0062] Example 5: according to the general preparation procedure, 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 examples:

[0066] Comparative example 1: a commercially available conventional PE-coated paper was selected, and the PE coating amount was about 15 g / m².

[0067] Comparative Example 2: Commercially available polylactic acid (PLA) resin was coated on the surface of 80 g / m2kraft paper by melt extrusion, with a coating amount of about 12 g / m2.

[0068] Comparative Example 3: Prepared according to the general preparation procedure, but without adding any plasticizer and OMMT, using PHB resin.

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

[0070] Table 4 Comparative Example Formulation:

[0071]

[0072] Application Example:

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

[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, as well as commercially coated papers in Comparative Examples 1-2 as a benchmark, were uniformly prepared or cut into standard test samples. For the emulsion samples, a bar coater was used to uniformly coat on the surface of 80 g / m2kraft paper substrate, with the dry film weight controlled in the range of 10-12 g / m2, and dried 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 resistance performance results of each sample:

[0076]

[0077] Analysis: The data in Table 5 shows that the Examples 1-5 of the present application have achieved an improvement in comprehensive performance through the synergistic effect of plasticizers and nanofillers. Compared with Comparative Example 3 (pure PHB) which does not contain any modifier, the oxygen and water vapor transmission rates of the Example samples are significantly reduced. Compared with Comparative Example 4 which contains only plasticizers, the oxygen and water vapor transmission rates of the Example samples are reduced by about 2 times, which proves the contribution of the network structure constructed by nanofillers to the barrier performance. Compared with commercial products, although the PE coated paper of Comparative Example 1 is superior in water vapor barrier, its oxygen transmission rate is much higher than that of the Examples of the present application, and it is not biodegradable. The oxygen transmission rate of the PLA coated paper of Comparative Example 2 is 3 times that of the Examples of the present application.

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

[0079] To evaluate the processability of the coating, heat seal performance test was conducted on the coated paper samples of all Examples 1-5 and Comparative Examples 1-4. The lab heat sealer was used to heat seal the coated side of each sample at 1 s dwell time and 0.4 MPa pressure. 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 180° peel test.

[0080] Table 6 Peel strength (N / 15 mm) of each sample at different heat seal temperature:

[0081]

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

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

[0084] This application example aims to evaluate the mechanical properties of the coating. The coated paper samples of all Examples 1-5 and Comparative Examples 1-4 were tested. Cross-cut method was used to evaluate the adhesion of the coating to the paper substrate. The coated paper samples were folded, compacted with a roller, and then unfolded for Kit value test to check the flexibility.

[0085] Table 7 Adhesion grade and Kit grade after folding of each sample:

[0086]

[0087] Analysis: The data in Table 7 show that the coatings of Examples 1-5 of the present application all exhibited the highest adhesion grade of 5B, and their oil resistance Kit value remained above 10 grade after folding, demonstrating good mechanical strength and durability. In contrast, Comparative Example 3 (pure PHB) had an adhesion grade of only 3B, and after folding, it cracked severely and its oil resistance decreased significantly. The adhesion and folding performance of Comparative Example 2 (PLA) and Comparative Example 4 (only plasticizer) were also inferior to the Examples of the present application.

[0088] Application Example 4: Slurry-ability / regenerability compatibility.

[0089] This application example aims to evaluate the recycling performance of coated paper. Coated paper samples of all Examples 1-5 and Comparative Examples 1-4 were tested. The coated paper samples were subjected to repulping treatment in a standard repulper, and the fiber retention rate and the content of filter residue were calculated.

[0090] Table 8 Repulpability index:

[0091]

[0092] Analysis: The repulpability test results of Table 8 demonstrate the environmental friendliness and recyclability of the coating of the present application. The samples of Examples 1-5 all exhibit good repulpability performance, with fiber retention rate as high as over 98%, close to that of the uncoated base paper. This indicates that the aqueous coating of the present application can be effectively separated from paper fibers under standard repulping conditions. In contrast, the coatings of Comparative Example 1 (PE) and Comparative Example 2 (PLA) form large plastic fragments during repulping, resulting in a significant decrease in fiber retention rate.

[0093] Application Example 5: Emulsion and coating storage / aging stability.

[0094] This application example aims to evaluate the shelf-life performance of the product. Accelerated aging tests were performed on the emulsion and coated paper samples of all Examples 1-5 and Comparative Examples 3-4. The emulsion samples were stored in a sealed condition at 23°C and 40°C for 90 days, and the changes in particle size and viscosity were detected. The coated paper samples were stored in a standard environment of 23°C, 50% RH for 90 days, and then the performance indicators were retested. Comparative Examples 1 and 2 do not have the form of emulsion, so they are not suitable for emulsion stability tests.

[0095] Table 9 Emulsion storage stability:

[0096]

[0097] Analysis: The data of Table 9 demonstrate the reliability of the emulsion of the present application. The emulsion prepared in Examples exhibits good storage stability, with changes in average particle size and viscosity within ±5% after 90 days of storage at 23°C and 40°C (accelerated aging). In contrast, the pure PHB emulsion of Comparative Example 3 is unstable, with layering occurring, and the emulsion stability of Comparative Example 4 is also inferior to that of the Examples of the present application.

[0098] Table 10 Coated paper aging performance:

[0099]

[0100] Analysis: The data of Table 10 show that the coating formed by the present application does not significantly decay in key performance after 90 days of aging in a standard environment. In contrast, the coating of Comparative Example 3 (pure PHB) decays significantly due to the post-crystallization effect. This ensures that the product maintains consistent high performance throughout the entire shelf life.

[0101] Application Example 6: Rheological properties 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 of all Examples 1-5 and Comparative Examples 3-4 were tested. The apparent viscosity of each emulsion was determined using a rotational rheometer at shear rate 0.1 s -1 and 10 s -1 , and the viscosity ratio was calculated. The D 50 was also determined by dynamic light scattering method. Comparative Examples 1 and 2 did not have emulsion morphology, so they were not suitable for this test.

[0103] Table 11: Rheological and particle size results of emulsions

[0104]

[0105] Analysis: Rheological data showed that all emulsions of Examples exhibited strong shear thinning behavior (viscosity ratio much greater than 5), while Comparative Examples showed near-Newtonian fluid behavior (viscosity ratio close to 1). This proved that the present application successfully constructed a three-dimensional network composed of exfoliated nanosheets in the emulsion through a specific formulation and process, thereby forming a tortuous gas permeation path in the coating, resulting in the improvement of barrier properties.

[0106] Application Example 7: Total migration and sensory test

[0107] This application example aims to evaluate the food contact safety of the coating and verify whether it meets the requirements of relevant regulations. Coated paper samples prepared from Examples 1-5 and Comparative Examples 1-4 were selected for testing, with the coating dry coating amount controlled at 11±1 g / m². The total migration test was carried out according to GB 31604.1-2023 standard, using 10% ethanol (food simulant A), 4% acetic acid (food simulant B) and 95% ethanol (food simulant D2) as simulant, respectively, at 40°C for 10 days. The sensory test was carried out according to the requirements of GB4806.1 and GB 4806.8 to evaluate the soaking liquid.

[0108] Table 12: Total migration and sensory results of each sample (n=3, 40°C x 10d)

[0109]

[0110] Analysis: The data results of Table 12 clearly demonstrate the compliance of the inventive coating in terms of food contact safety. All of Examples 1-5 have significantly lower total migration in three types of food simulants (aqueous, acidic and oily) than the regulatory limit of 10 mg / dm2, and the sensory test results are all qualified, proving the safety of them as food contact materials. Even in Example 3 with the highest plasticizer content, its migration in 95% ethanol (simulating fatty food) is still within the safety range. In contrast, Comparative Example 3 (pure PHB coating) has excessive migration of low molecular weight substances due to poor film-forming property and micro-cracks, and the sensory test is not qualified. Comparative Example 4 (containing only plasticizer) has excessive migration in oily simulant, which confirms that the construction of OMMT nanometer network structure is crucial for inhibiting the migration of plasticizer and other small molecules. The application example again verifies from the perspective of regulatory compliance that the synergistic effect of plasticizer (TEC) and nanofiller (OMMT) not only improves the physical barrier property, but also constructs a stable coating structure, effectively controls the migration of substances, and ensures food safety.

[0111] Analysis of experimental results:

[0112] The test results of Application Examples 1 to 6 systematically evaluate the comprehensive performance of the inventive composition and its coating.

[0113] The results of Application Example 1 show that the inventive composition performs well in barrier property, with several times reduction in oxygen and water vapor transmission rates compared to Comparative Example 3 (pure PHA) and Comparative Example 4 (only plasticized). The mechanism of this performance improvement is confirmed in Application Example 6. Rheological data show that all emulsions of Examples exhibit strong shear thinning behavior (viscosity ratio far greater than 5), while the comparative examples exhibit near-Newtonian fluid behavior (viscosity ratio close to 1). This proves that the inventive composition successfully constructs a three-dimensional network composed of exfoliated nanosheets in the emulsion through specific formulation and process, thereby forming a tortuous gas permeation path in the coating, resulting in improved barrier property.

[0114] In terms of processing and mechanical properties, the results of Application Examples 2 and 3 demonstrate that the inventive composition effectively overcomes the brittleness of pure PHA. Application Example 2 shows that all Examples have a wide heat sealing window and a 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 coating.

[0115] Environmental friendliness is another key advantage of the present invention. The slurry recovery test results of Application Example 4 show that the coating of the present invention has a high efficiency of separating from paper fibers, with a fiber retention rate of over 98%, which is in sharp contrast to traditional PE and PLA coatings, and demonstrates its potential in the circular economy.

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

[0117] In summary, the present invention successfully prepares a high-performance PHA water-based emulsion by precisely controlling the content of plasticizer and inorganic nano-filler, combined with a specific emulsification system and process parameters. The experimental results of Application Examples 1 to 6 systematically prove that the coating formed by the present invention performs well and balances in multiple dimensions such as gas barrier, water and oil resistance, heat sealing performance, mechanical flexibility, adhesion, storage stability, and recycling and regeneration, which is better than unmodified or only single modified PHA system, and exhibits comprehensive advantages compared to existing commercial materials. These performances are derived from the disclosed plasticizing-nano-sheet layer synergistic mechanism, which establishes a clear structure-activity relationship through quantifiable emulsion physical properties and 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 only exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made to the technical solutions of the present invention within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. An aqueous barrier coating composition characterized in that: The water-based barrier coating composition takes water as a dispersion medium, and includes biodegradable polyhydroxyalcanoate as a main film-forming component, as well as a plasticizer, an emulsifier and an inorganic nano-filler; The water-based barrier coating composition meets the following requirements: The plasticizer is triethyl citrate, and the content of triethyl citrate is 3-10 wt% of the mass of polyhydroxyalcanoate; The inorganic nano-filler is an organic modified montmorillonite, and the content of the organic modified montmorillonite is 2-4 wt% of the mass of polyhydroxyalcanoate; The emulsifier is polyvinyl alcohol, and the content of the emulsifier is 3 wt% of the mass of polyhydroxyalcanoate, and the hydrophilic-lipophilic balance value of the emulsifier system is 12-16; The polyhydroxyalcanoate is poly(3-hydroxybutyrate-co-3-hydroxyvalerate); The average particle size of the composition emulsion prepared under the condition of pH 5.0-5.5 is 400-700 nm; The emulsion formed by the water-based barrier coating composition has a ratio of apparent viscosity at a shear rate of 0.1 s -1 -1 at 25°C to the apparent viscosity at a shear rate of 10 s -1 -1 is not less than 5. After the composition emulsion is coated to a dry film coating amount of 10-12 g / m², the oxygen transmission rate measured according to the ASTM D3985-24 standard under the condition of 23°C and 0% relative humidity is not higher than 580 cm³ / m²·d, and the water vapor transmission rate measured according to the ASTM E96 / E96M-24a standard wet cup method under the condition of 38°C and 90% relative humidity is not higher than 290 g / m²·d; And, the composition can realize heat sealing under the condition of a temperature range of 110-150°C, a residence time of 1 s and a pressure of 0.4 MPa, and the peel strength measured according to the ASTM F88 / F88M-23 standard under the condition of 130°C, 1 s and 0.4 MPa is not less than 5.0 N / 15 mm.

2. The aqueous barrier coating composition of claim 1, wherein, The aqueous barrier coating composition further comprises one or more active substances selected from the group consisting of antimicrobial agents, antioxidants and oxygen absorbers, and the coating formed from the composition has a total migration of not more than 10 mg / dm 2 The sensory requirements comply with the provisions of GB 4806.1 and GB 4806.

8.

3. A method of preparing the aqueous barrier coating composition according to claim 1, characterized by, The method comprises the following steps: Step 1. Dissolving the polyhydroxyalcanoate resin and the plasticizer in an organic solvent; Step 2. Adding the solution obtained in step 1 into an aqueous phase containing the emulsifier and the pre-dispersed inorganic nano-filler to perform high-speed shearing emulsification; Step 3. Removing the organic solvent to obtain an emulsion composition; The pre-dispersion of the inorganic nano-filler is performed by ultrasonic wave with a frequency of 20 kHz and a power of 400 W for 10 minutes in pulse mode, and the temperature of the system is controlled to be not higher than 30°C by water bath.

4. The production method according to claim 3, characterized by, 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.

5. A paper-based packaging material, characterized by: The paper-based packaging material is coated with a dried and cured barrier coating formed from the water-based barrier coating composition according to claim 1 on at least one surface, and the coating amount of the barrier coating is 5-20 g / m².

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

7. The paper-based packaging material according to claim 5, characterized in that, The paper-based packaging material has stability, which is that the emulsion of the water-based barrier coating composition used to prepare the barrier coating has a particle size and viscosity fluctuation range of not more than ± 5% after being stored at 23 DEG C and 40 DEG C for 90 days; and the paper-based packaging material has a coating adhesion grade of not less than 5B and a Kit value of not less than 10 levels after being stored in a standard environment of 23 DEG C, 50% relative humidity for 90 days, and after folding resistance treatment.

Images