Dual pha barrier system for paper-based containers and paperboard and method of making and use thereof

Abstract

The application discloses a double PHA barrier system for paper-based containers and paperboard as well as a preparation method and application thereof, and belongs to the field of paper-based material surface engineering and green packaging technology. The system comprises, from inside to outside, a paper base material, a water-based PHA dispersion hole sealing layer and a PHA extrusion dense layer. The application utilizes a micron-sized PHA dispersion without cell fragments, and only a very low coating amount is needed to achieve the high-efficiency hole sealing effect that cannot be achieved by traditional high-coating processes, thereby eliminating the pinhole defects of the extrusion layer from the root. In combination with a modified PHA extrusion layer with a specific crystallinity, the micro-cracking problem of a single coating layer during roll port forming is solved. The system realizes excellent barrier performance with a thinner bio-based structure, and simultaneously has a wide heat sealing window and excellent resmearing recyclability. Compared with the prior art, the application significantly reduces the consumption of packaging materials and environmental burden under the premise of ensuring high performance.

Description

Technical Field

[0001] This invention belongs to the field of paper-based material surface engineering and green packaging technology, specifically relating to a dual PHA barrier system for paper-based containers and paperboard, its preparation method and application. Background Technology

[0002] With the deepening implementation of plastic restriction and ban policies globally and the significant increase in consumers' environmental awareness, finding green alternatives to traditional petroleum-based plastics has become an urgent need for the packaging industry. Paper and paperboard, as natural, renewable, and biodegradable materials, are widely used in food and beverage packaging. However, paper-based materials themselves are porous, hydrophilic, and have hygroscopic and swelling properties, lacking effective barrier properties against water, water vapor, oils, and gases. This greatly limits their direct application in liquid containers, high-humidity environments, or long-shelf-life food packaging.

[0003] To impart the necessary barrier properties to paper-based materials, existing technologies typically employ lamination or coating processes. Currently, the mainstream solution on the market uses petroleum-based plastics such as polyethylene (PE) or polyethylene terephthalate (PET) for extrusion lamination. While these traditional laminated papers possess excellent water and oil repellency and heat-sealing properties, the plastic coating is tightly bonded to the paper base, making effective separation through conventional pulping processes difficult after disposal. Consequently, they are often classified as non-recyclable waste and landfilled or incinerated, resulting in severe resource waste and environmental pollution. Another common oil-repellent treatment uses fluorinated chemicals for sizing or coating; however, with perfluorinated and polyfluoroalkyl substances (PFAS) facing increasingly stringent regulatory restrictions globally due to their bioaccumulation and potential toxicity, the development of fluorine-free oil-repellent alternatives is urgently needed.

[0004] In the field of biodegradable polymers, polylactic acid (PLA) is currently the most widely used paper coating material. Although PLA has the ability to degrade through industrial composting, it has poor heat resistance, a narrow heat-sealing temperature window, and a hard and brittle texture, making it prone to brittle fracture when paper cups are rolled or paper boxes are folded. In addition, the barrier properties of PLA are highly sensitive to environmental humidity, making it difficult to meet the high standards required for cold chain or hot beverage packaging.

[0005] Polyhydroxyalkanoates (PHAs), as intracellular polyesters synthesized by microorganisms using various carbon sources through fermentation, not only possess thermoplastic processing properties similar to petroleum-based plastics, but also exhibit excellent hydrophobicity, gas barrier properties, and complete biodegradability in soil, freshwater, and even marine environments, making them considered ideal green packaging materials. However, the application of PHA in paper-based packaging still faces several technical bottlenecks:

[0006] First, the fiber network structure on the paper surface is rough and porous. When using a single PHA melt extrusion coating process, a high coating thickness is often required to cover the capillary pores on the paper surface and eliminate pinhole defects. This not only significantly increases raw material costs but may also lead to a decrease in curl and stiffness. If the thickness is reduced, pinholes are easily generated due to melt film breakage, resulting in barrier failure.

[0007] Secondly, existing PHA water-based dispersion coating technologies have significant drawbacks. Existing technologies, such as patent EP4166716A1 and Chinese patent CN115698427B, often attempt to directly prepare water-based coatings using crude extracts from fermentation broth after cell wall disruption, or rely on large amounts of emulsifiers and water-soluble polymeric binders such as polyvinyl alcohol to stabilize the dispersion. These PHA dispersions based on fermentation broth often contain large amounts of residual cell debris, proteins, and residual culture medium components. These impurities not only cause the coating to develop an odor and browning color, but also exhibit strong hygroscopicity, severely undermining the hydrophobic barrier properties of PHA itself. Simultaneously, the introduction of large amounts of hydrophilic additives makes the coating prone to swelling, stickiness, and even disintegration when in contact with water or high-humidity environments.

[0008] Furthermore, single-component PHA materials present inherent challenges in processing and molding. Short-chain PHAs, such as poly(3-hydroxybutyrate), have high crystallinity and hardness but are extremely brittle; while copolymers with long-chain monomers, although improving flexibility, exhibit significantly slower crystallization rates, leading to unstable film bubbles during extrusion and coating, which easily cause roller sticking. Moreover, in subsequent molding operations such as paper cup creasing and crease forming, microcracks are easily generated at stress concentration points due to post-crystallization or internal stress release, resulting in the penetration of grease or liquids.

[0009] Therefore, there is an urgent need to develop a new type of barrier system that can fill the micropores on the surface of paper at a low cost to eliminate the risk of pinholes, and provide a dense, tough and fold-resistant barrier layer through the interfacial fusion of homogeneous materials. At the same time, it can overcome the problems of traditional PHA dispersions having many impurities, easy cracking of extruded layers, and difficulty in re-pulp recycling of composite structures. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dual PHA barrier system for paper-based containers and paperboard, as well as its preparation method and application.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] This invention provides a dual PHA barrier system for paper-based containers and paperboards, comprising a paper substrate, an aqueous PHA dispersion sealing layer, and a PHA extrusion dense layer arranged sequentially from the inside out.

[0013] The aqueous PHA dispersion sealing layer is derived from an aqueous PHA dispersion, which is prepared by melt dispersion or solvent extraction and re-emulsification processes and is free of cell debris. The PHA in the dispersion is selected from one or more of short-chain PHA, medium- and long-chain PHA, or copolymers between monomers forming short-chain and medium- and long-chain PHA. The short-chain PHA is selected from one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB). The medium- and long-chain PHA is selected from one or more of poly(3-hydroxyhexanoate) (PHHx), poly(3-hydroxyheptanoate) (PHHP), poly(3-hydroxyoctanoate) (PHO), poly(3-hydroxynonanoate) (PHN), poly(3-hydroxydecanoate) (PHD), poly(3-hydroxydodecanate) (PHDD), and poly(3-hydroxytetradecanoate) (PHTD). The solid content of the dispersion is 25%-50%, for example 25%, 28%, 30%, 35%, 38%, 40%, 42%, 45%, 48% or 50%; the median particle size D 50 The particle size is 0.20-2.00 μm, for example, 0.20 μm, 0.22 μm, 0.25 μm, 0.30 μm, 0.40 μm, 0.50 μm, 0.80 μm, 1.00 μm, 1.20 μm, 1.50 μm, 1.80 μm, or 2.00 μm; 90% cumulative distribution particle size D 90 The micrometer diameter is ≤3.00μm, for example, 0.60μm, 0.65μm, 0.80μm, 1.00μm, 1.20μm, 1.50μm, 2.00μm, 2.50μm, or 3.00μm. The dry coating weight of the dispersion sealing layer is 2-10g / m², for example, 2g / m², 3g / m², 4g / m², 5g / m², 6g / m², 7g / m², 8g / m², 9g / m², or 10g / m²; after multi-stage drying, the total moisture content of the paper substrate and the dispersion sealing layer is ≤3.0%, for example, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 2.8%, or 3.0%.

[0014] The extruded dense layer of the PHA is a blend of PHBV and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) in a mass ratio of 75:25 to 82:18, for example, 75:25, 76:24, 77:23, 78:22, 79:21, 80:20, 81:19, or 82:18. The molar fraction of 3-hydroxyvalerate units in the PHBV is 5%-12%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, or 12%; the molar fraction of 3-hydroxyhexanoate units in the PHBH is 6%-15%, for example, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. The melt flow rate of the PHA extruded dense layer at 170-190℃ and 2.16kg load is 2-5g / 10min, for example 2.0g / 10min, 2.5g / 10min, 3.0g / 10min, 3.5g / 10min, 4.0g / 10min, 4.5g / 10min or 5.0g / 10min; the crystallinity of the second-stage differential scanning calorimetry is 33%-37%, for example 33%, 3 4%, 35%, 36% or 37%; and a thickness of 20-30 μm, such as 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm or 30 μm; or an areal density of 24-39 g / m², such as 24 g / m², 26 g / m², 28 g / m², 30 g / m², 32 g / m², 35 g / m², 37 g / m² or 39 g / m².

[0015] The extruded dense layer of PHA also contains one or more selected from PHB, P34HB and the medium- and long-chain PHA, such that the total PHA content in the extruded dense layer is ≥95%, for example 95%, 96%, 97%, 98%, 99% or 100%.

[0016] When the dry coating amount of the aqueous PHA dispersion sealing layer is 2-10 g / m², for example 2 g / m², 3 g / m², 4 g / m², 5 g / m², 6 g / m², 7 g / m², 8 g / m², 9 g / m² or 10 g / m², at least two of the following conditions are met: the paper substrate is sized and calendered, and its Bentsen roughness is ≤200 mL / min, for example 50 mL / min, 100 mL / min, 150 mL / min or 200 mL / min, or the PPS surface smoothness is ≤1.2 μm, for example 0.5 μm, 0.8 μm, 1.0 μm or 1.2 μm; the median particle size D of the aqueous PHA dispersion is... 50The viscosity at 25°C is ≤2.0 μm and 400-1200 mPa·s, for example, 400 mPa·s, 450 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, or 1200 mPa·s; a double micro-coating process or a slit-head micro-coating process is used; the relative humidity at the end of the drying process is less than 25%, for example, 5%, 10%, 15%, 20%, or 24%, and the total moisture content when exiting the drying oven is ≤3.0%.

[0017] The system further includes a functional barrier layer, which is a thin oxygen barrier interlayer or a carbon dioxide barrier interlayer. The thin oxygen barrier interlayer is disposed between the aqueous PHA dispersion sealing layer and the PHA extruded dense layer, and is a water-dispersible oxygen barrier polymer coating with a dry coating weight of 2-6 g / m², for example, 2 g / m², 3 g / m², 4 g / m², 5 g / m², or 6 g / m². The oxygen barrier polymer is selected from one or more of the following categories: polyvinyl alcohol (PVOH) types, including PVOH composed of ethylene alcohol units and PVOH obtained by partial or complete saponification of vinyl acetate; ethylene-vinyl alcohol copolymers (EVOH) types, obtained by copolymerization of ethylene monomers and ethylene alcohol units; polysaccharides and their derivatives, including carboxymethyl cellulose, hydroxypropyl methyl cellulose, and starch or starch esters; and aqueous composites containing layered nanomaterials, including nanocellulose or montmorillonite composites with water-soluble polymers. The carbon dioxide barrier interlayer is disposed between the aqueous PHA dispersion sealing layer and the PHA extruded dense layer, or on the inner or outer side of the PHA extruded dense layer. It is a thermoplastic gas barrier polymer layer, and the polymer is selected from one or more of PVOH, EVOH, polyglycolic acid (PGA), polylactic acid (PLA), polyethylene terephthalate (PET), and aliphatic-aromatic copolyesters. The aliphatic-aromatic copolyester includes copolymers obtained by polycondensation of terephthalic acid with aliphatic diacids and diols. The dry coating weight or areal density of the carbon dioxide barrier interlayer is 2-8 g / m², for example, 2 g / m², 3 g / m², 4 g / m², 5 g / m², 6 g / m², 7 g / m², or 8 g / m².

[0018] Before extruding the PHA extruded dense layer, the interface to be coated is subjected to corona or plasma treatment to achieve a surface energy ≥42mN / m, for example, 42mN / m, 44mN / m, 46mN / m, 48mN / m, or 50mN / m. The coating or lamination is completed within 30 minutes after treatment, for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes. The interval between the water-based PHA dispersion sealing layer leaving the drying oven and being extruded onto the line is ≤10 minutes, for example, 1 minute, 2 minutes, 3 minutes, 5 minutes, 8 minutes, or 10 minutes. The preheating temperature before extrusion is 60-110℃, for example, 60℃, 70℃, 80℃, 85℃, 90℃, 100℃, or 110℃, and the preheating time is 5-30 seconds, for example, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, or 30 seconds.

[0019] The PHA extruded dense layer contains 0-5% plasticizer, for example, 0%, 1%, 2%, 3%, 4%, or 5%, wherein the plasticizer is selected from one or more of citrate esters or polyethylene glycols; and a bonding transition phase is provided between the aqueous PHA dispersion sealing layer and the PHA extruded dense layer or inside the PHA extruded dense layer, wherein the bonding transition phase is a bonding resin layer, and the resin is selected from one or more of the following categories: modified PHA; biodegradable aliphatic or aliphatic-aromatic copolyesters, including polybutylene succinate (PBS) obtained by polycondensation of succinic acid and 1,4-butanediol, to... Polybutylene adipate (PBA) obtained by polycondensation of adipic acid and 1,4-butanediol; PLA obtained by ring-opening polymerization of lactic acid monomers; ethylene-vinyl acetate copolymer (EVA) obtained by copolymerization of ethylene and vinyl acetate monomers; PVOH composed of vinyl alcohol units or obtained by hydrolysis of vinyl acetate; and waterborne polyurethane adhesive, wherein the thickness of the adhesive transition phase is 1-10 μm, for example 1 μm, 2 μm, 3 μm, 5 μm, 8 μm or 10 μm, or the dry coating amount is 1-5 g / m², for example 1 g / m², 2 g / m², 3 g / m², 4 g / m² or 5 g / m².

[0020] The outer side of the PHA extruded dense layer is provided with an aqueous topcoat layer with a dry coating amount of 3-8 g / m², such as 3 g / m², 4 g / m², 5 g / m², 6 g / m², 7 g / m² or 8 g / m². The aqueous topcoat layer includes at least aqueous PHA and may further include an aqueous film-forming polymer. The aqueous film-forming polymer is selected from one or more of aqueous acrylic resin, aqueous polyurethane, and PVOH or EVOH.

[0021] The system is suitable for heat sealing, with the heat sealing window covering at least 20°C of the range of 130-170°C, such as 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, or 170°C.

[0022] The paper substrate is paper, paperboard or molded pulp board mainly composed of plant fibers, with a basis weight of 150-400 g / m², such as 150 g / m², 200 g / m², 230 g / m², 250 g / m², 300 g / m², 350 g / m² or 400 g / m².

[0023] This invention also provides a method for preparing the above-mentioned dual PHA barrier system, comprising the following steps:

[0024] Step 1. Apply an aqueous PHA dispersion to the surface of a paper or paperboard substrate. The dispersion is prepared by melt dispersion or solvent extraction and re-emulsification processes, without using fermentation broth or cell wall-breaking suspension as raw material. The solid content of the dispersion is 25%-50%, for example, 25%, 30%, 35%, 40%, 50%, and the median particle size D is... 50 The thickness is 0.20-2.00μm, for example 0.20μm, 0.22μm, 0.30μm, 0.50μm, 1.00μm, 2.00μm, and the dry coating amount is controlled at 2-10g / m², for example 2g / m², 5g / m², 8g / m², 10g / m². After drying, an aqueous PHA dispersion sealing layer is obtained.

[0025] Step 2. Using zoned hot air or infrared drying, the paper or paperboard substrate obtained in Step 1 and the aqueous PHA dispersion sealing layer formed on it are dried. The drying includes a first section, a middle section, and a last section. The drying temperature of the first section is 60-90℃, for example, 60℃, 70℃, 75℃, 80℃, or 90℃; the drying temperature of the middle section is 80-110℃, for example, 80℃, 90℃, 95℃, 100℃, or 110℃; the drying temperature of the last section is 70-90℃, for example, 70℃, 75℃, 80℃, 85℃, or 90℃; the relative humidity of the last section drying area is ≤25%, for example, 5%, 10%, 15%, 20%, or 25%, and the total moisture content of the two after drying is ≤3.0%, for example, 1.0%, 2.0%, or 3.0%, to obtain the dried aqueous PHA dispersion sealing layer.

[0026] Step 3. Allow the dried water-based PHA dispersion sealing layer obtained in Step 2, along with the paper or paperboard substrate, to equilibrate at 23°C and 50% relative humidity for 2-10 minutes (e.g., 2 minutes, 5 minutes, 8 minutes, 10 minutes). Before loading onto the production line, preheat to 60-110°C (e.g., 60°C, 80°C, 100°C, 110°C) and maintain this temperature for 5-30 seconds (e.g., 5 seconds, 15 seconds, 20 seconds, 30 seconds). Within 10 minutes of exiting the drying oven (e.g., 1 minute, 5 minutes, 10 minutes), extrude the PHA melt onto the surface of the dried water-based PHA dispersion sealing layer to form an extruded coating. The dense layer is formed by a PHBV and PHBH blend with a mass ratio of 75:25 to 82:18, such as 75:25, 80:20, or 82:18, and a melt flow rate of 2-5 g / 10 min, such as 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, or 5 g / 10 min. The crystallinity of the second-stage differential scanning calorimetry is 33%-37%, such as 33%, 35%, or 37%. The thickness of the resulting extruded dense layer is 20-30 μm, such as 20 μm, 22 μm, 25 μm, 28 μm, or 30 μm, thus obtaining a PHA extruded dense layer.

[0027] Step 4. Cool and shape the PHA extruded dense layer obtained in Step 3 and the paper or paperboard substrate and water-based PHA dispersion sealing layer inside it, and then cut and roll it up or directly form it into paper-based products to obtain a dual PHA barrier system.

[0028] The method further includes one or both of the following steps: between step 2 and step 3, applying a barrier interlayer to the surface of the dried aqueous PHA dispersion sealing layer obtained in step 2, wherein the barrier interlayer is a thin oxygen barrier interlayer or a carbon dioxide barrier interlayer, and controlling its dry coating amount to be 2-8 g / m², for example 2 g / m², 5 g / m², or 8 g / m², to obtain the barrier interlayer; after step 3, applying an aqueous topcoat layer to the outside of the PHA extruded dense layer obtained in step 3, wherein the dry coating amount of the aqueous topcoat layer is 3-8 g / m², for example 3 g / m², 5 g / m², or 8 g / m², to obtain the aqueous topcoat layer.

[0029] In step 3, before extrusion, corona or plasma treatment is used to ensure the interfacial surface energy is ≥42mN / m, for example, 42mN / m, 44mN / m, or 46mN / m. Extrusion is then completed within 30 minutes after treatment, for example, 10 minutes, 20 minutes, or 30 minutes. The extrusion parameters are controlled as follows: melt temperature 150-200℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, or 200℃; air gap 80-150mm, for example, 80mm. m, 100mm, 120mm or 150mm; pressure roller pressure 4-8 bar, e.g. 4 bar, 5 bar, 6 bar, 7 bar or 8 bar; cooling roller temperature 10-25℃, e.g. 10℃, 15℃, 20℃ or 25℃; linear speed 60-250m / min, e.g. 60m / min, 100m / min, 150m / min, 200m / min or 250m / min; melt shear rate 50-500s. -1 For example, 50s -1 100s -1 200s -1 300s -1 400s -1 Or 500s -1 .

[0030] When the dry coating amount of the sealing layer is 2-5 g / m², such as 2 g / m², 3 g / m², or 5 g / m², a double micro-coating process or a slit-head micro-coating process is adopted, and the viscosity of the dispersion at 25°C is controlled to be 400-800 mPa·s, such as 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, or 800 mPa·s.

[0031] The method further includes a forming step: the paper cup rim and side seam are heat-sealed at a temperature of 140-170℃, for example, 140℃, 150℃, 160℃ or 170℃, for a time of 0.2-1.0s, for example, 0.2s, 0.5s, 0.8s or 1.0s; the lunch box or tray is crimped, folded or snapped; or the dry goods liner is die-cut and laminated.

[0032] This invention also provides the use of the above-mentioned dual PHA barrier system in paper cups, takeaway containers, baking trays, cold drink cups, and dry goods inner packaging, wherein the use satisfies at least three of the following combined performance requirements:

[0033] 1. Under ASTM F1249-25 standard conditions of 23°C and 50% relative humidity, the water vapor transmission rate (WVTR) is ≤50 g / (m²·d), for example, 10 g / (m²·d), 20 g / (m²·d), 30 g / (m²·d), 40 g / (m²·d) or 50 g / (m²·d);

[0034] 2. The grease barrier rating measured according to the TAPPI T 559cm-22 standard is ≥9, such as 9, 10, 11 or 12;

[0035] 3. The micro-crack rate in the rolled or folded area is ≤1%, for example, 0%, 0.2%, 0.5%, 0.8% or 1%;

[0036] 4. The re-pulp rejection rate measured according to the PTS-RH 021:2012 Category II method is ≤10%, for example, 2%, 5%, 8% or 10%;

[0037] 5. The 180° peel strength between the PHA extruded dense layer and the aqueous PHA dispersion sealing layer or paper substrate is ≥1.0N / 15mm, for example, 1.0N / 15mm, 1.2N / 15mm, 1.5N / 15mm or 1.8N / 15mm.

[0038] The intended use meets one of the following conditions:

[0039] a) When used in non-carbonated beverage paper cups or cold drink cups, the WVTR under ASTM F1249-25 standard and 23°C, 50% relative humidity conditions is ≤30g / (m²·d), for example 15g / (m²·d), 20g / (m²·d), 25g / (m²·d), 28g / (m²·d) or 30g / (m²·d), the micro-crack rate in the rolled or folded area is ≤1%, for example 0.2%, 0.5%, 0.8%, and the 180° peel strength between the PHA extruded dense layer and the water-based PHA dispersion sealing layer or paper substrate is ≥1.0N / 15mm, for example 1.2N / 15mm, 1.5N / 15mm;

[0040] b) When used for packaging dairy products or dry goods with a shelf life of 3 months or more, the oxygen transmission rate (OTR) shall be ≤30 cm³ / (m²·d) under ASTM D3985-24 standard and at 23°C and 0% relative humidity, for example, 2 cm³ / (m²·d), 5 cm³ / (m²·d), 10 cm³ / (m²·d), 20 cm³ / (m²·d) or 30 cm³ / (m²·d);

[0041] c) When used as a liner for paper cups containing carbon dioxide or in a "paper shell plus inner liner" packaging structure, the carbon dioxide retention test is performed after 4 weeks of storage under vibration conditions following carbon dioxide beverage filling, and a sealing fatigue test is performed after 100 internal pressure cycles at 0.25-0.60 MPa, for example 0.25 MPa, 0.30 MPa, 0.40 MPa, 0.50 MPa or 0.60 MPa. The carbon dioxide retention rate after 4 weeks is ≥95%, for example 95%, 96%, 97%, 98% or 99%, the leakage rate after internal pressure cycles is ≤2%, for example 0.5%, 1%, 1.5% or 2%, and the sealing fatigue pass rate is ≥95%, for example 95%, 96%, 97%, 98% or 99%.

[0042] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0043] Excellent barrier properties: This invention effectively solves the pinhole problem in the extruded layer caused by fiber pores on the paper substrate surface through a dual-layer synergistic structure of "water-based PHA dispersion sealing layer + PHA extruded dense layer". The water-based sealing layer fills the substrate surface, significantly reducing WVTR to below 30 g / (m²·d) and the risk of grease penetration, achieving a Kit rating of 11-12.

[0044] Improved crack resistance and formability: By precisely controlling the ratio of PHBV to PHBH in the extruded layer from 75:25 to 82:18 and its crystallinity from 33% to 37%, the coating is endowed with excellent flexibility and heat-sealing properties. In paper cup crimping and rib forming, the micro-crack rate is controlled below 1%, and an effective heat-sealing window of over 20°C is provided, adapting to high-speed industrial production.

[0045] Reliable interlayer bonding: A specific drying and dehumidification process is used to control the interface moisture content to ≤3.0%. Combined with corona treatment and optional bonding transition phase, a high-strength bond is achieved between the extruded layer and the substrate and sealing layer. The peel strength is ≥1.0N / 15mm, which effectively prevents delamination and leakage in hot or carbonated beverage packaging.

[0046] Environmentally friendly and easy to recycle: The all-bio-based PHA system is fluoride-free, aligning with environmental trends. Furthermore, this dual PHA structure is easily separated under standard re-sizing processes, resulting in a low re-sizing rejection rate of ≤10%, thus solving the problem of difficult recycling of traditional PE coated paper. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the barrier system structure of the paper-based container (paper cup) of the present invention.

[0048] In the figure, 1-paper-based container; 2-paper substrate; 3-waterborne polyhydroxyalkanoate dispersion sealing layer; 4-functional barrier layer; 5-polyhydroxyalkanoate extruded dense layer. Detailed Implementation

[0049] 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 conducted in accordance with the standards described in the "Main Test Standards" section of this specification.

[0050] Figure 1 This is a schematic diagram of the barrier system structure of the paper-based container (paper cup) of the present invention. For example... Figure 1 As shown, the left side illustrates the formed paper-based container 1, and the arrow on the right indicates an enlarged cross-sectional structure of the container's sidewall. This cross-sectional structure comprises, in sequence: a paper substrate 2 (outer layer of the paper-based container) serving as a base; an aqueous polyhydroxyalkanoate dispersion sealing layer 3 coated on the surface of the paper substrate 2, used to fill the micropores on the paper substrate surface; a functional barrier layer 4 located in the middle layer; and a polyhydroxyalkanoate extruded dense layer 5 composited in the innermost layer.

[0051] Main reagents and raw materials:

[0052] Table 1. Main reagent and raw material names, product models and manufacturers:

[0053]

[0054] Main analytical and testing instruments:

[0055] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments:

[0056]

[0057] Main testing standards:

[0058] WVTR: Refer to ASTM F1249-25 standard; when the measured WVTR is close to or higher than 26 g / (m²·d), verify it using ASTM E96 / E96M-24 or calibrate the instrument's high-end point.

[0059] OTR: Refer to ASTM D3985-24 standard.

[0060] Oil barrier properties: Refer to TAPPI T 559cm-22 standard.

[0061] Particle size distribution: Refer to ISO 22412:2025 standard.

[0062] Viscosity: The apparent viscosity (mPa·s) was measured using a rotational viscometer at 25°C and recorded.

[0063] Re-pulping performance: Refer to PTS-RH 021:2012 Category II method.

[0064] Peel strength: Refer to GB / T 2790-1995 standard.

[0065] Water droplet contact angle: Refer to ISO / TS 14778:2021 standard.

[0066] Cobb water absorption: Refer to ISO 535:2023 standard.

[0067] Paper cup performance: Refer to GB / T 27590-2022 standard.

[0068] Moisture content: Refer to ISO 287:2017 standard.

[0069] Bentsen roughness: Refer to ISO 8791-2:2013 standard.

[0070] PPS surface smoothness: Refer to ISO 8791-4:2021 standard.

[0071] Melt flow rate (MFR): According to ISO 1133-1:2022 standard, the test load is 2.16 kg, and the test temperature is (190±0.5)℃ (temperature range of 170-190℃).

[0072] Differential scanning calorimetry (DSC) enthalpy of fusion / crystallization and crystallinity: Refer to ISO 11357-1:2023 and ISO 11357-3:2025 standards; crystallinity is calculated under the two-stage heating curve as Xc=(ΔHm-ΔHcc) / ΔH0×100%, where ΔHm is the enthalpy of fusion, ΔHcc is the enthalpy of cold crystallization, and ΔH0 is the reference enthalpy of fusion for 100% crystallization. The same ΔH0 value is used for calculation throughout this specification.

[0073] The general preparation process for aqueous PHA dispersions is as follows:

[0074] Step 1. Mix PHBV resin powder and PHBH resin powder according to the required mass ratio in each embodiment, and dry them under vacuum at 60-80°C for more than 4 hours to make the residual moisture less than 0.1% by mass, so as to obtain a dried mixed powder.

[0075] Step 2. Add the dried mixed powder obtained in Step 1 to a co-rotating twin-screw extruder, and run it at a barrel temperature of 150-180℃ for 50 seconds. -1 up to 300s-1 The molten PHBV / PHBH blend is melted and plasticized at a high shear rate, while deionized water is continuously added through the side feed port, so that the molten PHBV / PHBH blend is dispersed into fine droplets under high shear, resulting in a molten-water mixture.

[0076] Step 3. The molten water mixture obtained in Step 2 is fed through a nozzle into a shearing tank with a stirrer and sheared at 5000-8000 r / min for 5-15 min at 20-40℃ to obtain an aqueous PHA dispersion.

[0077] Step 4. Cool the aqueous PHA dispersion obtained in Step 3 to room temperature, remove a small amount of mechanical impurities by passing it through a 100-mesh filter, and place it in a sealed container for later use. The entire preparation process uses only deionized water as the continuous phase and does not introduce any organic volatile solvents, resulting in the filtered aqueous PHA dispersion.

[0078] The general preparation process for PHA melt used in extruding dense layers is as follows:

[0079] Step 1. Prepare PHBV powder, PHBH powder and optional triethyl citrate (TEC plasticizer) according to the formulation ratio described in the example, and dry mix them in a high-speed mixer at room temperature for 5-10 minutes to obtain a dry mixture.

[0080] Step 2. Feed the dry mixture obtained in Step 1 into a co-rotating twin-screw compounding extruder for granulation, and granulate at a barrel temperature of 180-190℃ for 50-300 seconds. -1 Melt blending at a shear rate yields blended particles.

[0081] A general preparation method for dual PHA barrier systems:

[0082] Step 1. Application of the aqueous dispersion sealing layer: Apply an aqueous PHA dispersion to the surface of a paper or paperboard substrate. The dispersion must be prepared according to the aforementioned "General Preparation Process of Aqueous PHA Dispersions" and must be free of cell debris. Depending on specific requirements, the solid content of the dispersion should be controlled between 25% and 50%, and the median particle size D... 50 The thickness should be controlled within the range of 0.20-2.00 μm. The dry coating amount should be controlled at 2-10 g / m². For low coating amounts of 2-5 g / m², a double micro-coating process or a slit-head micro-coating process is preferred.

[0083] Step 2. Zoned Drying and Moisture Control: The wet coating formed in Step 1 of the general preparation method is dried using zoned hot air or infrared drying. The drying process is divided into three stages: the first stage drying temperature is 60-90℃, the second stage drying temperature is 80-110℃, and the third stage drying temperature is 70-90℃. In particular, the relative humidity in the third stage drying zone must be controlled to be ≤25%, and the total moisture content of the paper substrate and the dispersed sealing layer after drying must be ≤3.0%.

[0084] Step 3. Composite Extrusion of the Dense Layer: The dried intermediate obtained in Step 2 of the general preparation method is equilibrated at 23℃ and 50% relative humidity for 2-10 min. Before extrusion, it is preheated to 60-110℃ and held for 5-30 s, with the time between exiting the drying oven and extruding ≤10 min. Before extrusion, the interface to be coated is subjected to corona or plasma treatment to ensure a surface energy ≥42 mN / m, and extrusion is completed within 30 min after treatment. PHA melt is extruded and coated onto the surface of the sealing layer. The melt must be prepared according to the aforementioned "General Preparation Process of PHA Melt for Extrusion of Dense Layers," and is a blend of PHBV and PHBH with a mass ratio of 75:25 to 82:18. Extrusion parameters are controlled as follows: melt temperature 150-200℃, air gap 80-150 mm, pressure roller pressure 4-8 bar, cooling roller temperature 10-25℃, and linear speed 60-250 m / min.

[0085] Step 4. Cooling, Shaping, and Post-processing: Cool and shape the composite material obtained in Step 3 of the general preparation method of the system, and then slit and roll it up or directly form it. If the system design includes a functional barrier interlayer or a water-based topcoat, then add the corresponding coating and drying processes between Step 2 and Step 3, or after Step 3, respectively.

[0086] Example 1: This example was prepared strictly according to the aforementioned "General Preparation Method of Double PHA Barrier System" (hereinafter referred to as "General Preparation Method of System"). Food-grade cupboard with a basis weight of 150 g / m² was used in this example.

[0087] In step 1 of the general preparation method for the system: the selected aqueous dispersion is prepared according to the aforementioned "General Preparation Process of Aqueous PHA Dispersion", with a solid content of 25% and a median particle size D. 50 The particle size D is 0.20 μm with a 90% cumulative distribution. 90 The particle size is 0.60 μm, and the viscosity at 25 °C is 400 mPa·s. This dispersion was coated onto a paper substrate surface, with a dry coating weight controlled at 10 g / m².

[0088] In step 2 of the general preparation method of the system: a low-temperature limit process is adopted: the first stage drying temperature is 60℃, the middle stage is 80℃, the last stage is 70℃, the relative humidity of the last stage is less than 25%, and the total moisture content of the paper substrate and the sealing layer after drying is ≤3.0%.

[0089] In step 3 of the general preparation method for the system: the dried sealing layer and paper substrate are equilibrated at 23℃ and 50% relative humidity for 5 minutes; preheated to 60℃ and held for 5 seconds before extrusion, and the interval between exiting the drying oven and extruding is 5 minutes. The surface of the sealing layer is corona treated before extrusion to achieve a surface energy of 44 mN / m, and extrusion coating is completed within 10 minutes after corona treatment. The extruded melt is prepared according to the aforementioned "General Preparation Process of PHA Melt for Extruded Dense Layers," and is a blend of PHBV and PHBH with a mass ratio of 82:18 (5% 3-hydroxyvalerate unit in PHBV, 15% 3-hydroxyhexanoate unit in PHBH). This extruded layer does not contain plasticizers, and its melt flow rate (MFR) at 170-190℃ and 2.16 kg load is 2 g / 10 min, its DSC crystallinity is 37%, and its extrusion thickness is 20 μm. The extrusion coating parameters were set as follows: melt temperature 180℃, air gap 100mm, pressure roller 6bar, cooling roller temperature 15℃, linear speed 100m / min, and melt shear rate approximately 200s. -1 .

[0090] Example 2: This example was prepared strictly according to the aforementioned "General Preparation Method for the System". Food-grade cupboard with a basis weight of 230 g / m² was used in this example.

[0091] In step 1 of the general preparation method for the system: the selected dispersion was prepared according to the "General Preparation Process of Aqueous PHA Dispersions", with a solid content of 35% and a particle size D. 50 It is 0.50μm, D 90 The thickness is 1.50 μm, and the viscosity is 500 mPa·s. The dry coating weight of the dispersion sealing layer is 8 g / m².

[0092] In step 2 of the general preparation method of the system: the drying process parameters are: 75℃ for the first stage, 95℃ for the middle stage, 80℃ for the last stage, the relative humidity of the last stage is less than 25%, and the total moisture content is ≤3.0%.

[0093] In step 3 of the general preparation method for the system: the preheating temperature is 85℃ and held for 15 seconds. The extruded melt is prepared according to the "General Preparation Process of PHA Melt for Extruded Dense Layers", with a PHBV to PHBH mass ratio of 75:25 (12% 3-hydroxyvalerate unit in PHBV and 6% 3-hydroxyhexanoate unit in PHBH). 5% triethyl citrate plasticizer is added to the blend. The MFR of this extruded layer is 5 g / 10 min, the DSC crystallinity is 33%, and the extrusion thickness is 30 μm.

[0094] Additional step: After step 3 of the general preparation method of the system, an aqueous topcoat is further applied to the outside of the extruded dense layer. The dry coating amount is 8 g / m², and the raw material of the topcoat is the same as the dispersion used in step 1 of this embodiment.

[0095] Example 3: This example was prepared strictly according to the aforementioned "General Preparation Method for the System". Food-grade cupboard with a basis weight of 400 g / m² was used in this example.

[0096] In step 1 of the general preparation method for the system: the selected dispersion was prepared according to the "General Preparation Process of Aqueous PHA Dispersions", with a solid content of 50% and a particle size D. 50 It is 2.00 μm, D 90 The thickness is 3.00 μm, and the viscosity is 1200 mPa·s. The dry coating weight of the dispersion sealing layer is 8 g / m².

[0097] In step 2 of the general preparation method of the system: a high temperature limit process is adopted: the first section is 90°C, the middle section is 110°C, the last section is 90°C, the relative humidity of the last section is less than 25%, and the total water content is ≤3.0%.

[0098] Additional step: Between steps 2 and 3 of the general preparation method of the system, a modified PHA adhesive resin layer is set as an adhesive transition phase, with a dry coating amount of 1 g / m².

[0099] In step 3 of the general preparation method for the system: the preheating temperature is 110℃ and held for 30 seconds. The extruded melt is prepared according to the "General Preparation Process of PHA Melt for Extruded Dense Layers", with a PHBV to PHBH mass ratio of 75:25 (5% 3-hydroxyvalerate unit in PHBV and 6% 3-hydroxyhexanoate unit in PHBH). The blend contains 2% triethyl citrate plasticizer. The MFR of this extruded layer is 4 g / 10 min, the DSC crystallinity is 33%, and the extrusion thickness is 28 μm.

[0100] Example 4: This example was prepared strictly according to the aforementioned "General Preparation Method for the System". Food-grade cupboard with a basis weight of 230 g / m² was used in this example.

[0101] In step 1 of the general preparation method for the system: the selected dispersion was prepared according to the "General Preparation Process of Aqueous PHA Dispersions", with a solid content of 35% and a particle size D. 50 It is 0.30μm, D 90 The particle size is 1.00 μm, and the viscosity is 600 mPa·s. The dry coating weight of the dispersion sealing layer is 8 g / m².

[0102] Additional step: Between steps 2 and 3 of the general preparation method, a thin oxygen barrier layer is set, made of polyvinyl alcohol (PVOH), with a dry coating amount of 2 g / m². Specifically: a 10% (w / w) aqueous solution of PVOH resin (KURARAY POVAL 205) is prepared and stirred at 90°C for 60 min until clear; after cooling to 40°C, it is applied to the surface of the dried sealing layer obtained in step 2 using a slot coater, with a wet coating amount controlled at 20 g / m² (corresponding to a dry coating amount of 2 g / m²); then, it is dried with hot air in sections of 75°C for the first section, 95°C for the middle section, and 80°C for the last section, with the relative humidity of the last section controlled at ≤25%, and the total moisture content after drying ≤3.0%, thus obtaining the PVOH thin oxygen barrier layer.

[0103] In step 3 of the general preparation method for the system: the drying and extrusion processes adopted standard intermediate parameters (75℃ for the first stage, 95℃ for the middle stage, and 80℃ for the final stage). The extruded melt was prepared according to the "General Preparation Process of PHA Melt for Extruded Dense Layers," with a PHBV to PHBH mass ratio of 80:20 (8% 3-hydroxyvalerate unit in PHBV and 10% 3-hydroxyhexanoate unit in PHBH). The blend contained 2% triethyl citrate plasticizer. The MFR of this extruded layer was 3 g / 10 min, the DSC crystallinity was 35%, and the extrusion thickness was 22 μm.

[0104] Example 5: This example was prepared strictly according to the aforementioned "General Preparation Method for the System". Food-grade cupboard with a basis weight of 230 g / m² was used in this example.

[0105] In step 1 of the general preparation method for the system: the parameters are the same as in Example 4 (solid content 35%, D) 50 The thickness is 0.30 μm, and the dry coating amount is 8 g / m².

[0106] Additional step: During the extrusion coating process in step 3 of the general preparation method of the system, an ethylene-vinyl alcohol copolymer (EVOH) carbon dioxide barrier interlayer is introduced inside the extruded dense layer. Specifically, after drying, the surface of the aqueous PHA dispersion sealing layer obtained in step 2 is first coated with an aqueous polyurethane adhesive and dried to form a bonding transition phase, with the dry coating amount controlled at 5 g / m². Subsequently, a multilayer extrusion composite method is used to simultaneously extrude the EVOH melt and the PHA melt and composite them onto the surface of the bonding transition phase, so that the EVOH interlayer is located between the bonding transition phase and the PHA extruded dense layer, with the EVOH layer density controlled at 8 g / m².

[0107] In step 3 of the general preparation method for the system: the extruded melt was prepared according to the "General Preparation Process of PHA Melt for Extruded Dense Layers", with a PHBV to PHBH mass ratio of 75:25, monomer molar fractions as in Example 2 (HV 12%, HHx 6%), and containing 5% triethyl citrate plasticizer. The MFR of the extruded layer was 5 g / 10 min, the DSC crystallinity was 33%, and the extrusion thickness was 30 μm.

[0108] Example 6: This example was prepared strictly according to the aforementioned "General Preparation Method for the System". Food-grade cupboard with a basis weight of 230 g / m² was used in this example.

[0109] In step 1 of the general preparation method for the system: the parameters are the same as in Example 4 (solid content 35%, D) 50 The thickness is 0.30 μm, and the dry coating amount is 8 g / m².

[0110] In step 3 of the general preparation method for the system: the extruded melt was prepared according to the "General Preparation Process of PHA Melt for Extruded Dense Layers", with a PHBV to PHBH mass ratio of 82:18, and the monomer molar fraction was the same as in Example 1 (HV 5%, HHx 15%), containing 2% triethyl citrate plasticizer. The MFR of the extruded layer was 2 g / 10 min, the DSC crystallinity was 37%, and the extrusion thickness was 25 μm.

[0111] Additional step: After step 3 of the general preparation method of the system, an aqueous topcoat is further applied to the outside of the extruded dense layer, with a dry coating amount of 3 g / m².

[0112] Example 7: This example was prepared strictly according to the aforementioned "General Preparation Method of the System". This example uses food-grade cup paperboard with a basis weight of 230 g / m², and the paper substrate has undergone high-pressure calendering, resulting in a PPS surface smoothness of 1.0 μm.

[0113] In step 1 of the general preparation method for the system: the selected dispersion was prepared according to the "General Preparation Process of Aqueous PHA Dispersions", with a solid content of 25% and a particle size D. 50 It is 0.22μm, D 90 The thickness is 0.65 μm and the viscosity is 450 mPa·s. A two-stage microcoating process is used, with a single dry coating amount of 1 g / m² and a total dry coating amount of 2 g / m².

[0114] In step 3 of the general preparation method for the system: the extruded melt was prepared according to the "General Preparation Process of PHA Melt for Extruded Dense Layers", with a PHBV to PHBH mass ratio of 80:20, and the monomer molar fraction was the same as in Example 4 (HV 8%, HHx 10%), containing 2% triethyl citrate plasticizer. The MFR of the extruded layer was 3 g / 10 min, the DSC crystallinity was 35%, and the areal density was 24 g / m².

[0115] Comparative Example 1: This comparative example uses food-grade cup paperboard with a basis weight of 230 g / m². The difference from Example 1 is that steps 1 and 2 in the "General Preparation Method of the System" are omitted. This comparative example does not contain an aqueous PHA dispersion sealing layer; corona treatment is performed directly on the paper substrate surface, and step 3 in the "General Preparation Method of the System" is executed. The formulation and thickness of the extruded dense layer are the same as in Example 4 (PHBV / PHBH is 80 / 20, thickness 22 μm).

[0116] Comparative Example 2: This comparative example uses food-grade cupboard with a basis weight of 230 g / m². The difference from Example 1 is that the dehumidification requirement in step 2 of the "General Preparation Method for the System" was not met. In this comparative example, the dispersion parameters and coating amount were consistent with Example 1 when performing step 1 of the "General Preparation Method for the System". However, in step 2 of the "General Preparation Method for the System", dehumidification was not performed at the end of the drying process, resulting in a relative humidity greater than 50% at the end of the drying process, and the total moisture content of the paper substrate and the dispersion sealing layer reached 4.5% when exiting the drying oven. In the subsequent step 3 of the "General Preparation Method for the System", the extrusion parameters were the same as in Example 1.

[0117] Comparative Example 3: This comparative example uses food-grade cupboard with a basis weight of 230 g / m². The difference from Example 1 is that it deviates from the process parameters and formulation requirements in step 3 of the "General Preparation Method for the System". The dispersion parameters and coating amount in step 1 of this comparative example are consistent with those of Example 1. In step 3 of the "General Preparation Method for the System", the corona treatment of the sealing layer before extrusion is insufficient, resulting in a surface energy of only 36 mN / m, and the interval between the sealing layer exiting the drying oven and reaching the extrusion line is extended to 60 minutes. Furthermore, the mass ratio of PHBV to PHBH in the extruded dense layer is adjusted to 70:30, which exceeds the preferred range of this invention.

[0118] Comparative Example 4: This comparative example uses food-grade cupboard with a basis weight of 230 g / m². The difference from Example 7 is that it deviates from the raw material parameter requirements in step 1 of the "General Preparation Method for the System". In this comparative example, when performing step 1 of the "General Preparation Method for the System", the particle size of the aqueous PHA dispersion (prepared according to the "General Preparation Process of Aqueous PHA Dispersion") was too large, with a median particle size D... 50 It is 2.50 μm, D 90 The thickness is 3.50 μm. The sealing layer is applied in a single coat with a dry coating amount of 3 g / m². Subsequent steps are the same as in Example 7.

[0119] Application Example 1: Performance testing of general paper-based containers.

[0120] This application example aims to comprehensively examine the overall performance of the dual PHA barrier system in conventional packaging applications, focusing on moisture resistance, oil resistance, physical strength, and molding and processing adaptability. The test samples cover all Examples 1-7 and Comparative Examples 1-4 described in this invention. Specific testing methods are as follows: All samples were conditioned for 24 hours at 23°C and 50% relative humidity before testing. The laminated materials prepared according to each formulation were cut into specimens meeting the requirements for instrument clamping and effective testing area (the effective testing area for both WVTR and OTR was 50 cm²). WVTR was measured under ASTM F1249-25 standard conditions (23°C, 50% RH); the surface grease resistance level was evaluated using the TAPPI T559cm-22 standard (Kit method). Paper cup samples were formed using a paper cup forming machine, with the seam and side seam heat-sealed at 160°C for 0.5 seconds. The micro-crack rate at the roll edge was determined as follows: After the material was formed into a paper cup, a 100mm arc-length area was selected at the roll edge. The total length L of all cracks within this arc-length area was observed and recorded using an optical microscope (50×). The micro-crack rate (%) = L / 100mm × 100%. The pinhole density was determined using the dark-field method: The material was laid flat on a dark-field light source, and a 100cm² area was scanned and counted using an optical microscope (20×). The pinhole density = total number of pinholes / 100cm². The peel strength was tested according to GB / T 2790-1995, measuring the 180° peel strength between the extruded layer and the substrate (sample width 15mm). The static water droplet contact angle was tested at 23℃: 3μL of deionized water was added, and the contact angle was read 5s after addition. At least 5 different points were measured for each sample, and the average was taken. (Cobb) 60 Water absorption was measured according to ISO 535:2023. Finally, at 23°C and 50% RH, paper cups filled with 95°C hot water (liquid level 90% of the cup height) were left to stand for 30 minutes to visually assess condensation and dampness on the outer wall. All data are averages of 5 parallel tests.

[0121] Table 3 General performance test results:

[0122]

[0123] Experimental results show that Examples 1 to 7 significantly improved the barrier properties and surface quality of the paper-based materials by introducing a specific aqueous PHA dispersion sealing layer. Specifically, the WVTR of Examples 1-7 was controlled below 30 g / (m²·d), and the Kit oil resistance rating reached level 11 or higher, demonstrating the compactness of the "sealing + extrusion" dual-layer structure. In contrast, Comparative Example 1 lacked a sealing layer, resulting in the melt failing to effectively cover the paper fiber pores, leading to extremely high pinhole density and a significant decrease in barrier properties. Comparative Example 2, due to incomplete drying (high residual moisture), experienced poor interfacial bonding (peel strength of only 0.5 N / 15 mm) due to moisture vaporization upon heating, and was prone to barrier failure. Comparative Example 4 used a large particle size (D... 50 The particles, being 2.50 μm in size, could not effectively fill the micropores of the paper, resulting in discontinuous film formation and a Cobb value as high as 50 g / m², indicating that particle size control is crucial for sealing performance. Furthermore, Examples 4 and 5 introduced a PVOH thin oxygen-barrier interlayer and an EVOH carbon dioxide-barrier interlayer, respectively, further improving the gas barrier and gas content application indicators shown in Table 4 while maintaining the moisture-proof, oil-proof, and mechanical properties shown in Table 3. Example 5 achieved a 98% carbon dioxide retention rate over 4 weeks. Regarding the micro-crack rate at the roll edge, all examples were below 1%, while Comparative Example 3 had a higher micro-crack rate due to insufficient interface treatment and improper formulation ratios, verifying the necessity of controlling interfacial energy and crystallinity.

[0124] Application Example 2: Testing in high-barrier and special application scenarios.

[0125] This application example tests a special packaging scenario with extremely high requirements for gas barrier properties (such as aroma preservation of dry goods and packaging of carbonated beverages). All examples (1-7) and comparative examples (1-4) were selected for comparison. OTR testing was conducted under ASTM D3985-24 standard conditions (23°C, 0% RH). For carbonated beverage applications, the actual filling process was simulated: carbonated beverages were filled to 90%-95% of the container's nominal volume, sealed, and stored at 23°C for 4 weeks; the vibration conditions were set to horizontal reciprocating oscillation (e.g., oscillation frequency 60-120 times / min, amplitude 20-30mm, oscillation for 30 minutes daily); after 4 weeks, the CO2 retention rate was measured (CO2 retention rate = dissolved CO2 content after storage / initial dissolved CO2 content × 100%), where the dissolved CO2 content was measured using a carbonated beverage CO2 content analyzer under the same temperature conditions using the equilibrium method. Meanwhile, the molded container was subjected to an internal pressure cycle test: 100 pressurization-depressurization cycles were performed within the cycle range of 0.25-0.60 MPa (each cycle included a 10-second pressure holding at 0.60 MPa). After each cycle, the pressure was held at 0.60 MPa for 30 seconds and the pressure decay was recorded. The leakage rate (%) after internal pressure cycle was calculated as: pressure decay value / 0.60 MPa × 100%. The pass criterion for the sealing fatigue test was "no visible leakage / delamination and leakage rate ≤ 2%", and the pass rate (%) was calculated as: number of qualified samples / total number of samples × 100%.

[0126] Table 4. Test results of special barrier performance:

[0127]

[0128] The test data clearly reveals the application gradation of different layer structures in the field of gas barrier. Examples 4 and 5 exhibit excellent gas barrier performance. Example 4, which incorporates a PVOH interlayer, has an OTR reduced to 4.5 cm³ / (m²·d), making it more suitable for oxygen-sensitive applications such as aroma preservation of dry goods. Example 5, which incorporates an EVOH carbon dioxide barrier interlayer, has an OTR as low as 2.1 cm³ / (m²·d), with a 98% carbon dioxide retention rate after 4 weeks, a 0.5% leakage rate after internal pressure cycling, and a 99% seal fatigue pass rate, meeting the key requirements for carbonated beverage packaging. This demonstrates that introducing a high-barrier interlayer in a dual PHA system is crucial for achieving functional leaps. In contrast, Examples 1-3 and Examples 6-7, which do not incorporate high-barrier interlayers such as PVOH / EVOH, generally have OTR values ​​between 160-190 cm³ / (m²·d). Although these formulations have achieved the good levels shown in Table 3 in terms of moisture / oil resistance, a high-oxygen-barrier interlayer design is still necessary for long-shelf-life applications with oxygen-sensitive contents. Comparative Examples 1 and 4, due to coating defects (pinholes or poor leveling), allowed gas to permeate almost freely, resulting in extremely high OTR values. In terms of mechanical retention, Example 5 exhibited an internal pressure cycle leakage rate of only 0.5%, significantly better than Comparative Example 3 (20%). This was attributed to the effective introduction of the intermediate adhesive layer and the excellent flexibility and interlayer bonding of the PHA extruded layer, which resisted structural fatigue caused by internal gas pressure fluctuations.

[0129] Application Example 3: Paper Cup Heat Sealing Window and Hot Beverage Leakage Performance Test.

[0130] This application example focuses on examining the heat-sealing processing window of materials on a high-speed forming line and the hot beverage safety of the final product. The experiment covers all examples and comparative examples. All samples were conditioned for 24 hours at 23°C and 50% relative humidity before testing. Heat sealing was performed using a heat-sealing testing machine within a temperature range of 130-175°C (in 5°C increments). The heat-sealing parameters were fixed as follows: heat-sealing pressure 0.3 MPa, heat-sealing time 0.5 s, and heat-sealing width 15 mm. After heat sealing, the samples were allowed to stand for 1 minute and then placed at 23°C for 10 minutes before a 180° peel test. A peel strength ≥1.0 N / 15 mm without fiber tearing was used as the criterion for effective heat sealing, and the effective heat-sealing temperature range was recorded. Subsequently, a 1-hour leakage test was conducted on the formed paper cups using 95°C hot coffee solution (paper cup forming conditions were the same as in Application Example 1): the liquid level was 90% of the cup height, and after standing for 1 hour, the mass loss Δm was measured. The leakage rate (%) was calculated as Δm / initial liquid mass × 100%, and the leakage locations at the side seams and bottom of the cup were recorded. In addition, the side seam heat seal peel strength at the optimal heat seal temperature was measured separately.

[0131] Table 5. Heat-sealed window and hot beverage leakage performance:

[0132]

[0133] Experimental results show that Examples 1-7 of the present invention all exhibit wide and stable heat-sealing windows, covering at least 20°C within the range of 130-170°C. Among them, Examples 2 and 5, due to the addition of appropriate plasticizers or structural optimization, have the widest heat-sealing windows (140-170°C or 145-170°C), giving the equipment greater process tolerance. In actual hot beverage tests, the leakage rate of the examples was controlled below 1%, demonstrating extremely high sealing reliability. In contrast, Comparative Example 1, due to the lack of a sealing layer, had severe fiber exposure on the paper surface, resulting in an uneven heat-sealing interface and the inability to form a continuous and effective heat-sealing window, with a leakage rate as high as 3.5%. Comparative Example 2, limited by high moisture content, had water vapor generated during heat sealing that damaged the bonding interface, resulting in insufficient peel strength (0.9N / 15mm) and a high leakage rate. Although Comparative Example 3 used PHA, due to insufficient pre-extrusion corona treatment and mismatched formulation crystallization properties, the interfacial bonding was weak (0.6N / 15mm), making it prone to side seam bursting under thermal shock. In summary, the dual PHA system, through the synergistic effect of the sealing layer smoothing the substrate and the extrusion layer providing hot melt adhesive function, is significantly superior to the control group with single extrusion or uncontrolled process parameters.

[0134] Experimental Results and Analysis:

[0135] Based on the test data and observations from the above application examples, the dual PHA barrier system for paper-based containers and paperboards proposed in this invention exhibits significantly superior overall performance compared to traditional single extrusion processes. The following analysis details this from four dimensions: microstructure sealing mechanism, interfacial bonding mechanism, the impact of crystallization modification on moldability, and the trend of component content variation.

[0136] First, regarding the microscopic sealing mechanism of the waterborne PHA dispersion sealing layer, comparing the data from Examples 1-7 with Comparative Example 1 reveals that, even with a comparable extruded layer thickness, Comparative Example 1, lacking a sealing layer, still exhibits a WVTR exceeding 55.0 g / (m²·d) and an extremely high pinhole density. This confirms that the porous fibrous structure of the paper substrate surface is the primary cause of microscopic defects in the melt extrusion coating. This invention introduces a median particle size D... 50 Aqueous PHA dispersions with particle sizes controlled between 0.20 and 2.00 μm can effectively penetrate and fill the micropores and depressions on the paper surface. Further comparison of Example 7 and Comparative Example 4 shows that when the dispersion particle size increases to 2.50 μm, even under the same processing conditions, the Cobb value deteriorates from 24 g / m² to 50 g / m², indicating a significant decrease in barrier properties. This demonstrates that the matching degree between the dispersion particle size and the pore size of the paper surface is crucial; only when D... 50 Only when the thickness is controlled below 2.00μm can a dense and continuous pre-coated underlayer be formed, thereby providing a smooth bearing surface for the subsequent extrusion layer and eliminating pinholes at the source.

[0137] Secondly, regarding the relationship between the interfacial bonding mechanism and process parameters, the peel strength of Examples 1-7 generally remained above 1.2 N / 15 mm, demonstrating excellent interlayer adhesion. In contrast, Comparative Example 2, due to improper control of relative humidity at the drying tail stage leading to a total moisture content of 4.5%, experienced a significant drop in peel strength to 0.5 N / 15 mm. This reveals the destructive effect of interfacial moisture during the high-temperature extrusion lamination process; residual moisture vaporizes upon heating, forming microbubbles at the interface, hindering molecular contact between the melt and the substrate. Furthermore, Comparative Example 3, due to insufficient corona treatment resulting in a surface energy below 42 mN / m, also exhibited low peel strength and side seam bursting after molding. Therefore, strictly controlling the moisture content after drying to ≤3.0% and the interfacial surface energy before extrusion to ≥42 mN / m are crucial process conditions for ensuring the structural integrity and heat resistance to liquid permeability.

[0138] Secondly, regarding the effect of PHBV and PHBH blending modification on molding performance, the data from the examples show that controlling the mass ratio of PHBV to PHBH between 75:25 and 82:18, and adjusting the total crystallinity within the range of 33% to 37%, effectively balances the rigidity and toughness of the material. Within this range, the micro-crack rate at the paper cup seam is less than 1%, and the heat-sealing window width reaches over 20°C. Comparative Example 3 used a formulation ratio of 70:30. Although it increased the flexible component, the material became sticky due to the excessively slow crystallization rate, and the mechanical strength decreased, ultimately resulting in an increased micro-crack rate at the seam and unsatisfactory sealing fatigue performance. This demonstrates that precise blending ratio and crystallinity control play a decisive role in meeting the machining requirements of high-speed molding lines.

[0139] The trend analysis of the impact of changes in each parameter on the experimental results is as follows:

[0140] The influence trend of dispersion particle size: as the median diameter D of the dispersion particle size increases... 50 As the micrometer size increases from 0.20 μm to 2.00 μm, the smoothness of the paper substrate surface achieved by the sealing layer generally decreases. Within the 0.20 to 0.50 μm range, when the dry coating weight reaches 8-10 g / m² or the substrate surface smoothness meets conditions such as PPS ≤ 1.2 μm, the pinhole density can be reduced to 0-3 pins / 100 cm². When the dry coating weight is reduced to extremely low levels, such as 2 g / m², the pinhole density may increase but remains significantly lower than the control group without a sealing layer. Beyond 2.00 μm, particles struggle to effectively fill the fiber gaps, film continuity decreases, and barrier properties are prone to abrupt deterioration.

[0141] The influence of extruded layer thickness and areal density: Under the premise of an intact sealing layer, as the thickness of the extruded dense layer increases from 20 μm to 30 μm, the WVTR shows a linear decreasing trend. However, when the thickness exceeds 25 μm, the marginal effect of improving barrier performance diminishes. Considering the balance between cost and performance, 20 to 30 μm is the optimal thickness range.

[0142] The influence trend of blending ratio: As the content of PHBH in the extruded layer increases (from 18% to 25%), the elongation at break of the material increases and the micro-crack rate at the roll end decreases accordingly; however, if the content of PHBH continues to increase beyond 25% (such as 30% in Comparative Example 3), the modulus of the material decreases too quickly, resulting in poor pressure resistance and insufficient heat seal strength.

[0143] The influence trend of functional interlayer addition amount: For high-barrier interlayers such as PVOH or EVOH, the OTR decreases exponentially as the dry coating amount increases from 2 g / m² to 8 g / m². Data shows that only a thin layer of 2 to 5 g / m² is needed to achieve an order-of-magnitude barrier transition, meeting the preservation requirements of highly sensitive contents.

[0144] In summary, this invention, through the synergistic design of a dual-layer structure and refined process control, successfully overcomes the technical bottlenecks such as pinholes, microcracks, and poor adhesion in the application of bio-based PHA materials in paper-based packaging, providing the industry with a high-performance, fully biodegradable green packaging solution.

[0145] 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 dihydroxyalkanoate barrier system for paper-based containers and paperboard, characterized in that, It includes, from the inside out, a paper substrate, an aqueous polyhydroxyalkanoate dispersion sealing layer, and a polyhydroxyalkanoate extruded dense layer, wherein: The aqueous polyhydroxyalkanoate dispersion sealing layer is derived from an aqueous polyhydroxyalkanoate dispersion, which is prepared by melt dispersion or solvent extraction and re-emulsification process and is free of cell debris. The polyhydroxyalkanoate in the dispersion is selected from one or more of short-chain polyhydroxyalkanoates, medium- and long-chain polyhydroxyalkanoates, or copolymers between monomers that form short-chain and medium- and long-chain polyhydroxyalkanoates. The short-chain polyhydroxy fatty acid ester is selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate); The medium- and long-chain polyhydroxy fatty acid esters are selected from one or more of poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxydodecanate), and poly(3-hydroxytetradecanoate); The dispersion has a solid content of 25%-50% and a median particle size D. 50 The particle size ranges from 0.20 to 2.00 μm, with a 90% cumulative distribution particle size D. 90 The thickness is ≤3.00μm, the dry coating weight of the dispersion sealing layer is 2-10g / m², and the total moisture content of the paper substrate and the dispersion sealing layer after multi-stage drying is ≤3.0%. The polyhydroxy fatty acid ester extruded dense layer is a blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in a mass ratio of 75:25 to 82:

18. The molar fraction of 3-hydroxyvalerate units in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is 5%-12%, and the molar fraction of 3-hydroxyhexanoate units in the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is 6%-15%. The melt flow rate of the polyhydroxy fatty acid ester extruded dense layer at 170-190℃ and 2.16kg load is 2-5g / 10min, the crystallinity of the second-rise differential scanning calorimetry is 33%-37%, and the thickness is 20-30μm or the areal density is 24-39g / m². Before extrusion, the polyhydroxyalkanoate extruded dense layer undergoes corona or plasma treatment on the interface to be coated to achieve a surface energy ≥42mN / m, and the coating or lamination is completed within 30 minutes after treatment. The time interval between the waterborne polyhydroxyalkanoate dispersion sealing layer exiting the drying oven and being extruded onto the line is ≤10 minutes, and the preheating temperature before extrusion is 60-110℃, with a preheating time of 5-30 seconds.

2. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, The extruded dense layer of polyhydroxy fatty acid esters further contains one or more selected from poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and medium- and long-chain polyhydroxy fatty acid esters, such that the total content of polyhydroxy fatty acid esters in the extruded dense layer is ≥95%.

3. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, When the dry coating amount of the aqueous polyhydroxy fatty acid ester dispersion sealing layer is 2-10 g / m², at least two of the following conditions must be met: The paper substrate is sized and calendered, and its Bentsen roughness is ≤200mL / min or its PPS surface smoothness is ≤1.2μm. The median particle size D of the aqueous polyhydroxy fatty acid ester dispersion 50 ≤2.0μm and viscosity at 25℃ is 400-1200mPa·s; Employ a double micro-coating process or a slit-head micro-coating process; The relative humidity at the end of the drying process is less than 25%, and the total moisture content when exiting the drying oven is ≤3.0%.

4. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, The system further includes a functional barrier layer, which is a thin oxygen barrier layer or a carbon dioxide barrier layer, wherein: The thin oxygen barrier interlayer is disposed between the waterborne polyhydroxyalkanoate dispersion sealing layer and the polyhydroxyalkanoate extruded dense layer, and is a water-dispersible oxygen barrier polymer coating with a dry coating weight of 2-6 g / m². The oxygen barrier polymer is selected from one or more of the following categories: Polyvinyl alcohols, including polyvinyl alcohols composed of ethylene alcohol units and polyvinyl alcohols obtained by partial or complete saponification of vinyl acetate; Ethylene-vinyl alcohol copolymers are obtained by copolymerizing ethylene monomers and vinyl alcohol units. Polysaccharides and their derivatives, including carboxymethyl cellulose, hydroxypropyl methyl cellulose, and starch or starch esters; Aqueous composites containing sheet-like nanomaterials, including composites of nanocellulose or montmorillonite with water-soluble polymers; The carbon dioxide barrier interlayer is disposed between the aqueous polyhydroxyalkanoate dispersion sealing layer and the polyhydroxyalkanoate extruded dense layer, or on the inner or outer side of the polyhydroxyalkanoate extruded dense layer. It is a thermoplastic gas barrier polymer layer, and its polymer is selected from one or more of polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyglycolic acid, polylactic acid, polyethylene terephthalate, and aliphatic-aromatic copolyester. The aliphatic-aromatic copolyester includes copolymers obtained by polycondensation of terephthalic acid with aliphatic diacids and diols. The dry coating weight or areal density of the carbon dioxide barrier interlayer is 2-8 g / m².

5. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, The polyhydroxyalkanoate extruded dense layer contains 0-5% plasticizer, which is selected from one or more of citrate esters or polyethylene glycols; Furthermore, a bonding transition phase is provided between the waterborne polyhydroxyalkanoate dispersion sealing layer and the polyhydroxyalkanoate extruded dense layer, or inside the polyhydroxyalkanoate extruded dense layer. The bonding transition phase is a bonding resin layer, and the resin is selected from one or more of the following categories: modified polyhydroxyalkanoate; biodegradable aliphatic or aliphatic-aromatic copolyesters, including polybutylene succinate obtained by polycondensation of succinic acid and 1,4-butanediol and polybutylene adipate obtained by polycondensation of adipic acid and 1,4-butanediol; polylactic acid obtained by ring-opening polymerization of lactic acid monomers; ethylene-vinyl acetate copolymer obtained by copolymerization of ethylene and vinyl acetate monomers; polyvinyl alcohol composed of vinyl alcohol units or obtained by hydrolysis of vinyl acetate; and waterborne polyurethane adhesive. The thickness of the bonding transition phase is 1-10 μm or the dry coating amount is 1-5 g / m².

6. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, The outer side of the polyhydroxyalkanoate extruded dense layer is provided with an aqueous topcoat layer with a dry coating amount of 3-8 g / m². The aqueous topcoat layer includes at least an aqueous polyhydroxyalkanoate and may further include an aqueous film-forming polymer. The aqueous film-forming polymer is selected from one or more of aqueous acrylate resin, aqueous polyurethane, and polyvinyl alcohol or ethylene-vinyl alcohol copolymer.

7. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, The system is suitable for heat sealing, with the heat sealing window covering at least 20°C of the range of 130-170°C.

8. The dihydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, The paper substrate is paper, paperboard or molded pulp board mainly composed of plant fibers, with a basis weight of 150-400 g / m².

9. A method for preparing a dipolyhydroxyalkanoate barrier system for paper-based containers and paperboards according to claim 1, characterized in that, Includes the following steps: Step 1. Apply an aqueous polyhydroxyalkanoate dispersion to the surface of a paper or paperboard substrate. The dispersion is prepared by melt dispersion or solvent extraction and re-emulsification processes, without using fermentation broth or cell wall-breaking suspension as raw material. The solid content of the dispersion is 25%-50%, and the median particle size D is... 50 The thickness is 0.20-2.00 μm, and the dry coating amount is controlled at 2-10 g / m². After drying, an aqueous polyhydroxy fatty acid ester dispersion sealing layer is obtained. Step 2. Using zoned hot air or infrared drying, the paper or paperboard substrate obtained in Step 1 and the aqueous polyhydroxyalkanoate dispersion sealing layer formed thereon are dried. The drying includes a first section, a middle section and a last section. The drying temperature of the first section is 60-90℃, the drying temperature of the middle section is 80-110℃, and the drying temperature of the last section is 70-90℃. The relative humidity of the last section drying area is ≤25%. After drying, the total moisture content of the two is ≤3.0%, and the dried aqueous polyhydroxyalkanoate dispersion sealing layer is obtained. Step 3. Equilibrate the dried waterborne polyhydroxyalkanoate dispersion sealing layer obtained in Step 2, along with the paper or paperboard substrate, at 23°C and 50% relative humidity for 2-10 minutes. Preheat to 60-110°C and maintain for 5-30 seconds before extrusion. Before extrusion, treat with corona or plasma to ensure the interfacial surface energy is ≥42mN / m. Complete extrusion within 30 minutes after treatment. Extrude the polyhydroxyalkanoate melt and coat the dried waterborne polyhydroxyalkanoate dispersion sealing layer onto the surface within 10 minutes after exiting the drying oven to form a dense extruded layer. The extrusion parameters are controlled as follows: melt temperature 150-200°C, air gap 80-150mm, pressure roller pressure 4-8 bar, cooling roller temperature 10-25°C, linear speed 60-250m / min, and melt shear rate 50-500s. -1 The melt is a blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in a mass ratio of 75:25 to 82:18, with a melt flow rate of 2-5 g / 10 min, a crystallinity of 33%-37% under secondary temperature differential scanning calorimetry, and an extruded dense layer thickness of 20-30 μm, thus obtaining a polyhydroxy fatty acid ester extruded dense layer. Step 4. The polyhydroxyalkanoate obtained in Step 3 is extruded into a dense layer and the paper or paperboard substrate and the water-based polyhydroxyalkanoate dispersion sealing layer inside it, then cooled and shaped, and then slit and wound or directly formed into paper-based products to obtain a dipolyhydroxyalkanoate barrier system.

10. The preparation method according to claim 9, characterized in that, Includes one or both of the following steps: After step 2 and before step 3, a barrier interlayer is applied to the surface of the dried waterborne polyhydroxy fatty acid ester dispersion sealing layer obtained in step 2. The barrier interlayer is a thin oxygen barrier interlayer or a carbon dioxide barrier interlayer, and its dry coating amount is controlled to be 2-8 g / m² to obtain the barrier interlayer. After step 3, an aqueous topcoat is applied to the outer side of the polyhydroxyalkanoate extruded dense layer obtained in step 3. The dry coating amount of the aqueous topcoat is 3-8 g / m², thus obtaining the aqueous topcoat.

11. The preparation method according to claim 9, characterized in that, When the dry coating amount of the sealing layer is 2-5 g / m², a double micro-coating process or a slit head micro-coating process is adopted, and the viscosity of the dispersion at 25℃ is controlled to be 400-800 mPa·s.

12. The preparation method according to claim 9, characterized in that, Further steps include forming: heat sealing of paper cup rims and side seams at 140-170℃ for 0.2-1.0s; creasing, folding, or locking of lunch boxes or trays; or die-cutting and bonding of dry goods linings.

13. The use of the dihydroxyalkanoate barrier system for paper-based containers and paperboard as described in claim 1 in paper cups, takeaway containers, baking trays, cold drink cups, and dry goods liner packaging, characterized in that, The application must meet at least three of the following combined performance requirements: Under ASTM F1249-25 standard conditions of 23°C and 50% relative humidity, the water vapor transmission rate is ≤50g / (m²·d); The grease barrier rating was measured to be ≥9 according to the TAPPI T 559cm-22 standard; The microcrack rate in the rolled or folded area is ≤1%; The re-pulp rejection rate, measured according to the PTS-RH 021:2012 Category II method, is ≤10%. The 180° peel strength between the extruded dense layer of the polyhydroxyalkanoate and the aqueous polyhydroxyalkanoate dispersion sealing layer or the paper substrate is ≥1.0 N / 15 mm.

14. The use according to claim 13, characterized in that, One of the following conditions must be met: When used in non-carbonated beverage paper cups or cold drink cups, the water vapor transmission rate under ASTM F1249-25 standard and 23°C and 50% relative humidity conditions is ≤30g / (m²·d), the micro-crack rate in the rolled or folded area is ≤1%, and the 180° peel strength between the extruded dense layer of the polyhydroxyalkanoate and the water-based polyhydroxyalkanoate dispersion sealing layer or paper substrate is ≥1.0N / 15mm; When used for packaging dairy products or dry goods with a shelf life of 3 months or more, the oxygen permeability is ≤30cm³ / (m²·d) under ASTM D3985-24 standard conditions of 23°C and 0% relative humidity. When used as a liner for paper cups containing carbon dioxide or in a "paper shell plus inner liner" packaging structure, the carbon dioxide retention test is performed after the carbon dioxide beverage is filled and stored under vibration conditions for 4 weeks, and the sealing fatigue test is performed after 100 cycles of internal pressure at 0.25-0.60MPa. The carbon dioxide retention rate after 4 weeks is ≥95%, the leakage rate after internal pressure cycling is ≤2%, and the sealing fatigue pass rate is ≥95%.

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