Pha-acrylic structural unit aqueous dispersion based on interface engineering regulation and preparation method thereof and paper-based barrier coating application

Abstract

The application discloses a PHA-acrylic structural unit water-based dispersion based on interface engineering regulation and a preparation method and paper-based barrier coating application thereof, and belongs to the technical field of polymer materials, interface engineering and water-based coating. The application in-situ constructs a stable interface layer between crystalline PHA and acrylic resin through amphiphilic polymers, effectively solving the problems of poor compatibility of bio-based materials and film forming defects. The dispersion can achieve excellent waterproof, oil-proof and gas barrier effects with only a low coating amount, significantly reducing the material usage. The unique gradient structure of the coating has excellent mechanical adhesion and efficient repulping recovery characteristics, overcoming the technical pain point of difficult recovery of traditional barrier coatings. The application provides an ideal solution with high performance and high safety for green packaging.

Description

Technical Field

[0001] This invention belongs to the fields of polymer materials, interface engineering and waterborne coatings, specifically relating to waterborne dispersions of PHA-acrylic structural units based on interface engineering regulation, their preparation methods and applications in paper-based barrier coatings. Background Technology

[0002] Cellulose-based materials offer advantages such as renewability, ease of processing, and recyclability. However, their porous fiber network, capillary action, and hydrophilic surfaces allow for easy penetration of liquid water, water vapor, oils, and gases, making it difficult to meet the comprehensive requirements for waterproofing, oil resistance, and gas barrier properties in applications such as food packaging paper, paper cups, paper bowls, takeaway food containers, oil-based lining paper, and molded fiber tableware. Traditional polyethylene (PE) extrusion lamination can provide some barrier properties, but it is not conducive to paper-plastic separation and repulping, and it poses an environmental burden during incineration or long-term degradation. Fluorinated oil-resistant systems face regulatory and safety restrictions.

[0003] To replace PE coating, various water-based barrier coating solutions have been proposed. For example, Chinese patents CN116218332A and CN117769583A disclose a technology using polyhydroxyalkanoate (PHA) latex as an adhesive for coating paper or fiber products. The latex is composed of highly crystalline PHA particles and small molecule surfactants, which can impart certain waterproof and biodegradable properties to the paper surface. However, the latex is mainly stabilized by small molecule surfactants, and its compatibility and water resistance retention are limited.

[0004] Subsequently, publicly available technologies utilize polyvinyl alcohol (PVOH), polysaccharides, or cellulose derivatives to stabilize polyhydroxyalkanoates or other biopolymer polyester aqueous dispersions through melt emulsification or wet milling processes. This yields biodegradable polyester dispersions with smaller particle sizes and better storage stability, and is suggested for use in coatings, adhesives, and paper coatings. Furthermore, other technologies utilize PVOH and polysaccharide coagulation layers to improve hydrolytic stability, preparing easily hydrolyzed polymers into water-based dispersions for use in paper and paperboard barrier coatings.

[0005] Regarding paper-based barrier coatings, Chinese patent CN120026524A discloses an aqueous blend of PHA, PBAT (polybutylene adipate terephthalate), and PVOH, and its application in paper-based barrier coatings. This technology involves melting and blending PHA and PBAT at a high temperature, then dispersing them in an aqueous PVOH solution, and adding plasticizers, crosslinking agents, and surfactants to prepare a ternary blend emulsion. After coating onto paper and drying, it can achieve a low Cobb value and a high Kit grade, while also considering certain repulping and biodegradability. However, this approach highly relies on the water solubility of PVOH for recycling, and the coating structure lacks fine control over the interface layer between PHA and the binder phase. Even with low coating amounts, there is still a risk of pinholes and barrier fluctuations.

[0006] On the other hand, a large number of acrylic water-based coatings are already used in paper cups and packaging paper. These technologies typically use acrylate-modified polymers and inorganic fillers as the main components. By adjusting the ratio of the polymer to fillers such as talc, kaolin, and calcium carbonate, recyclable, biodegradable, and compostable paper cup coatings can be achieved. However, these systems generally do not contain PHA, and their barrier properties mainly come from acrylic resins and inorganic fillers, making it difficult to simultaneously achieve high bio-based content and excellent oil and gas barrier properties.

[0007] Meanwhile, a high bio-based PHA and acrylic latex paint system has also been disclosed. This system is a high bio-based architectural or general-purpose latex paint formulated with PHA aqueous dispersion and acrylic emulsion. It focuses on the film-forming, water-whitening, and scrub resistance properties of decorative coatings, but does not propose specific designs for pore sealing, coating gradient structure, and interfacial behavior during the repulping process under thin coating conditions on paper-based substrates.

[0008] Literature reports indicate that while coating paper surfaces with a single PHA latex can significantly improve water resistance, pinholes and cracks are prone to occur at low coating amounts, requiring higher coating amounts or post-treatment to form a continuous film. Furthermore, the adhesion control at the coating-paper interface is limited. Pure acrylic waterborne barrier coatings, on the other hand, have shortcomings in wet stability and gas barrier properties. In summary, current technology lacks a multi-mechanism synergistic barrier system that uses polyhydroxyalkanoates as the main barrier phase, acrylic structural unit polymers as the binder phase, and simultaneously utilizes amphiphilic polymer ionomers to construct a stable interfacial layer in situ at the PHA-acrylic-water interface, forming a gradient structure on the paper substrate. This system would achieve manufacturable and repulpable multi-mechanism synergistic barrier properties at moderate coating amounts.

[0009] Therefore, there is an urgent need for a technical solution based on interface engineering to achieve stable composite of highly crystalline PHA and acrylic film-forming adhesive system in aqueous phase, reduce dependence on small molecule surfactants, enhance the anchoring and density of coating on paper substrate, and at the same time take into account barrier performance, processing window, recyclability and repulping, and environmental performance throughout the product life cycle. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide an aqueous dispersion of PHA-acrylic structural units based on interface engineering control, its preparation method, and its application as a paper-based barrier coating.

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

[0012] This invention provides an aqueous dispersion of PHA-acrylic acid structural units based on interface engineering control, comprising an aqueous phase medium and a stable composite dispersion system formed in the aqueous phase. The stable composite dispersion system includes: a first polymer component containing at least one PHA polymer; a second polymer component containing at least one polymer or copolymer containing acrylic acid structural units; and at least one amphiphilic polymeric compatibilizer or dispersant. The amphiphilic polymeric compatibilizer or dispersant is a copolymer of ethylene with methacrylic acid and / or acrylic acid, or a partially or completely neutralized salt thereof. The copolymer backbone contains ethylene units and has ionizable carboxyl groups on its side groups. The first polymer component forms a crystalline internal phase or core phase in the stable composite dispersion system. The amphiphilic polymeric compatibilizer or dispersant is enriched in the interfacial layer between the crystalline internal phase or core phase and the polymer or copolymer containing acrylic acid structural units, thereby forming interfacially stable composite particles in the stable composite dispersion system. Furthermore, the dry weight ratio of the first polymer component to the second polymer component is 1:99 to 99:1, for example, 1:99, 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, 99:1, etc.; and the total mass fraction of polyvinyl alcohol (PVOH) and polybutylene terephthalate (PBAT) in the second polymer component is less than that in the first polymer component. The total dry weight of the polymer component and the second polymer component is 3 wt%, for example <2.5 wt%, 2.0 wt%, 1.5 wt%, 1.0 wt%, 0.5 wt%, 0.1 wt%, or 0 wt%; the total mass fraction of low molecular weight surfactants with a number average molecular weight <2000 in the aqueous dispersion solid is ≤0.5 wt%, for example ≤0.4 wt%, 0.3 wt%, 0.2 wt%, 0.1 wt%, 0.05 wt%, or 0 wt%; and the total fluorine content of the aqueous dispersion solid is not detected when determined by online combustion-ion chromatography, and the detection limit of the detection method is ≤5 mg / kg as fluorine.

[0013] The solid content of the aqueous dispersion is from 10 wt% to 60 wt%, for example, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, etc.

[0014] The PHA is selected from 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), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV); the medium- and long-chain PHA is selected from poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxydodecanoate), and other monomers. The copolymers formed from two or more of the monomers that constitute the above-mentioned medium- and long-chain PHAs are selected from one or more of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH); and the PHA polymer has a crystallinity ≥30%, for example 30%, 35%, 40%, 42%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., and its weight-average molecular weight Mw is 1.0 × 10⁻⁶. 5 Up to 1.5×10 6 g / mol, for example 1.0 × 10 5 2.0×10 5 3.0×10 5 4.0×10 5 5.0×10 5 6.0×10 5 7.0×10 5 8.0×10 5 9.0×10 5 1.0×10 6 1.1×10 6 1.2×10 6 1.3×10 6 1.4×10 6 1.5×10 6 g / mol, etc.

[0015] The polymer or copolymer containing acrylic structural units is an aqueous polymer or copolymer obtained by polymerizing vinyl unsaturated monomers, wherein the vinyl unsaturated monomers are selected from one or more of the following: acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, styrene, α-methylstyrene; hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, methacryloyloxypropyltrimethoxysilane, methacryloyloxypropyltriethoxysilane, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate.

[0016] The amphiphilic polymeric compatibilizer or dispersant has an acid value of 40 to 200 mg KOH / g, such as 40 mg KOH / g, 50 mg KOH / g, 60 mg KOH / g, 70 mg KOH / g, 80 mg KOH / g, 90 mg KOH / g, 100 mg KOH / g, 110 mg KOH / g, 120 mg KOH / g, 130 mg KOH / g, 140 mg KOH / g, 150 mg KOH / g, 155 mg KOH / g, 160 mg KOH / g, 170 mg KOH / g, 180 mg KOH / g, 185 mg KOH / g, 190 mg KOH / g, 200 mg KOH / g, etc., and is tested at 190°C according to ASTM standards. The melt index determined by D1238-23a is from 10 to 2000 g / 10 min, for example 10 g / 10 min, 20 g / 10 min, 30 g / 10 min, 40 g / 10 min, 50 g / 10 min, 60 g / 10 min, 80 g / 10 min, 100 g / 10 min, 150 g / 10 min, 200 g / 10 min, 250 g / 10 min, 300 g / 10 min, 350 g / 10 min, 400 g / 10 min, 500 g / 10 min, 600 g / 10 min, 800 g / 10 min, 100 g / 10 min. 0 g / 10 min, 1200 g / 10 min, 1500 g / 10 min, 1800 g / 10 min, 2000 g / 10 min, etc., wherein the melt index is determined at a load of 2.16 kg or 21.6 kg, and the mass fraction of the amphiphilic polymer compatibilizer or dispersant in the dry weight of the second polymer component is 5 wt% to 60 wt%, for example, 5 wt%, 8 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 33.3 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, etc.

[0017] The degree of acid neutralization of the amphiphilic polymeric compatibilizer or dispersant is 5% to 150%, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, etc.; the pH of the aqueous dispersion is 7.0 to 11.0, for example, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, etc.; wherein the neutralizing ions are selected from sodium ions, potassium ions, lithium ions, magnesium ions, calcium ions, zinc ions, aluminum ions, organic amine cations, or combinations thereof.

[0018] The average particle size D of the stable composite dispersion system 50The range is from 200 to 2000 nm, such as 200 nm, 210 nm, 220 nm, 250 nm, 280 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 580 nm, 600 nm, 700 nm, 800 nm, 850 nm, 900 nm, 1000 nm, 1200 nm, 1500 nm, 1800 nm, 2000 nm, etc.; the absolute value of the Zeta potential is ≥25 mV, such as 25 mV, 26 mV, 28 mV, 30 mV, 32 mV, 35 mV, 38 mV, 40 mV, 42 mV, 45 mV, 50 mV, etc.

[0019] The aqueous dispersion further comprises a polysaccharide or modified starch synergistic stabilizing component, wherein the mass ratio of the polysaccharide or modified starch synergistic stabilizing component to the total dry weight of the first polymer component plus the second polymer component is 0 to 1.2:1, for example 0, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1, 1.0:1, 1.2:1, etc.; the polysaccharide or modified starch synergistic stabilizing component is selected from one or more of oxidized starch, cationic starch, amphoteric starch, hydroxyethyl starch, hydroxypropyl starch, esterified starch (such as octenyl succinic anhydride (OSA) modified starch), etherified starch, cross-linked starch, dextrin, carboxymethyl cellulose, hydroxypropyl methyl cellulose, alginate, chitosan, xanthan gum, guar gum, gum arabic, and lignin derivatives.

[0020] The aqueous dispersion further comprises a mineral-based barrier reinforcing component, wherein the mass ratio of the mineral-based barrier reinforcing component to the total dry weight of the first polymer component plus the second polymer component is 0 to 3:1, for example, 0, 0.2:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc.; the mineral-based barrier reinforcing component is a sheet-like or layered inorganic filler, wherein the sheet-like or layered inorganic filler is selected from one or more of kaolin, talc, mica powder, bentonite, montmorillonite, vermiculite, synthetic layered silicate, layered double hydroxide, sheet-like alumina, or their surface organic modifiers; and the aspect ratio of the sheet-like or layered inorganic filler is >20, for example, >20, 30, 40, 50, 60, 80, 100, etc.

[0021] The aqueous dispersion further comprises a bio-based plasticizer or bio-based adjuvant component, wherein the mass ratio of the bio-based plasticizer or bio-based adjuvant component to the total dry weight of the first polymer component plus the second polymer component is 0 to 0.5:1, for example, 0, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, etc., and the bio-based plasticizer or bio-based adjuvant component includes one or more of citrate esters, tartrate esters, sebacic acid esters, epoxidized vegetable oils, monoglycerides, polyglycerol fatty acid esters, and polyols.

[0022] The aqueous dispersion further comprises a crosslinking or curing component, wherein the mass ratio of the crosslinking or curing component to the total dry weight of the first polymer component plus the second polymer component is 0 to 0.1:1, for example, 0, 0.01:1, 0.02:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1, etc.

[0023] The present invention also provides a method for preparing the above-mentioned aqueous dispersion, which employs a phase inversion emulsification method or a melt emulsification method, comprising the following steps:

[0024] Step 1. Premix the first polymer component with an amphiphilic polymeric compatibilizer or dispersant in a molten state to obtain a melt premix;

[0025] Step 2. While applying strong shear dispersion to the molten premix obtained in Step 1 at 80℃ to 180℃, all or part of the aqueous phase medium is introduced to obtain a phase inversion dispersion system in which the polymer continuous phase undergoes a phase inversion to the aqueous continuous phase; the temperature is, for example, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, etc.

[0026] Step 3. During or after the phase transformation, a neutralizing agent is added to the phase transformation dispersion system obtained in Step 2 to cause the amphiphilic polymer compatibilizer or dispersant to undergo at least partial ionization, thereby constructing an interfacial layer in situ at the interface between the PHA polymer and water, and obtaining an oil-water composite dispersion with an interfacial layer.

[0027] Step 4. Continue stirring the oil-water composite dispersion obtained in step 3 until the aqueous phase changes from the dispersed phase to the continuous phase, thus obtaining a stable composite dispersion system with water as the continuous aqueous phase.

[0028] Step 5. Add the polymer or copolymer containing acrylic structural units to the stable composite dispersion system with water as the continuous aqueous phase obtained in Step 4 in the form of an aqueous emulsion or aqueous dispersion and mix evenly, then cool to obtain the aqueous dispersion;

[0029] The total mass fraction of low molecular weight surfactants with a number average molecular weight <2000 in the aqueous dispersion solid is ≤0.5wt%, for example ≤0.4wt%, 0.3wt%, 0.2wt%, 0.1wt%, or 0.05wt%.

[0030] This invention also provides a paper-based barrier material comprising a cellulose substrate and a barrier coating located on at least one side thereof; the non-volatile solid dry film of the barrier coating comprises at least: at least one PHA polymer; at least one polymer or copolymer containing acrylic structural units; at least one amphiphilic polymeric compatibilizer or dispersant, which is a copolymer of ethylene with methacrylic acid and / or acrylic acid or a partially or completely neutralized salt thereof, having hydrophobic ethylene segments and ionizable carboxyl groups; wherein the dry weight ratio of the PHA polymer to the polymer or copolymer containing acrylic structural units is 1:99 to 99:1, for example 1:99, 5:95, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, 99:1, etc., and the barrier... The total mass fraction of PVOH and PBAT in the barrier coating solid is <3wt%, for example <2.5wt%, 2.0wt%, 1.5wt%, 1.0wt%, or 0.5wt%; the dry coating weight is 0.3 to 60 g / m², for example 0.3 g / m², 0.5 g / m², 1 g / m², 2 g / m², 5 g / m², 6 g / m², 8 g / m², 10 g / m², 12 g / m², 15 g / m², 20 g / m², 25 g / m², 30 g / m², 40 g / m², 50 g / m², 60 g / m², etc.; the non-volatile solid of the barrier coating does not contain any intentionally added fluorinated organic compounds; the total fluorine content was not detected by online combustion-ion chromatography, and the detection limit of the detection method used is ≤5 mg / kg as fluorine.

[0031] The amphiphilic polymeric compatibilizer or dispersant is selected from ethylene-methacrylic acid copolymer (EMAA), ethylene-methacrylic acid ester copolymer and its ionomer, and amphiphilic ethylene-acrylic acid copolymer (EAA).

[0032] The barrier coating forms a gradient structure with synergistic adhesion and barrier properties in the thickness direction. The coating thickness is defined as t. The region near the outer surface is the region from 0 to 0.2t away from the outer surface, the region near the paper-based interface is the region from 0 to 0.2t away from the paper-based interface, and the middle region is the region from 0.2t to 0.8t. The mass fraction of PHA polymer in the outer surface region is higher than the mass fraction of PHA polymer in the overall coating. The mass fraction of polymers or copolymers containing acrylic structural units in the interface region is higher than the mass fraction of polymers or copolymers containing acrylic structural units in the overall coating. Furthermore, the mass fraction of ethylene methacrylic acid amphiphilic polymeric compatibilizer or dispersant in the middle region is higher than the mass fraction of the amphiphilic polymeric compatibilizer or dispersant in the overall coating.

[0033] The present invention also provides a method for preparing a barrier coating in the paper-based barrier material, comprising the following steps:

[0034] S1. The aqueous dispersion or coating composition is applied to the surface of paper, paperboard or molded fiber substrate by means of scraping, bar coating, gravure coating, flexographic coating, roller coating or a combination of the above methods to obtain a wet coating.

[0035] S2. The wet coating obtained in S1 is dried in stages. The first stage involves draining water and forming a preliminary film at temperatures ranging from 40°C to 120°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, and 120°C. The second stage involves densifying and structurally shaping the coating at temperatures ranging from 80°C to 200°C, such as 80°C, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C, and 200°C, to form a barrier coating with a dry coating weight of 0.5 to 30 g / m², thus obtaining the barrier coating.

[0036] The present invention also provides the use of the paper-based barrier material for food packaging paper, paper cups, paper bowls, disposable tableware, takeaway food boxes, baking packaging, oil and fat lining paper, daily chemical paper box lining, paper bags, paper straws, label paper or molded fiber products; applied as a barrier coating on the inner surface of paper cups, paper bowls and molded fiber tableware.

[0037] When the paper-based barrier material is mechanically pulped for 30 minutes at 45°C and pH 7, and the non-recyclable materials are separated through a 0.15mm sieve, the pulp fiber recovery rate is ≥97%, for example, 97%, 97.2%, 97.5%, 98%, 98.5%, 99%, etc., and the residue rate on the sieve is ≤2.0%, for example, ≤2.0%, 1.5%, 1.2%, 1.0%, or 0.5%; under the condition of a dry coating weight of 6 to 12 g / m², the Cobb of the paper-based barrier material... 60Values ​​≤3.0g / m², e.g., ≤3.0g / m², 2.8g / m², 2.5g / m², 2.3g / m², 2.2g / m²; KIT oil resistance rating is 12; Oxygen permeability (OTR) at 23℃ and 50% RH ≤15cm³ / (m²·d), e.g., ≤15cm³ / (m²·d), 12cm³ / (m²·d), 10cm³ / (m²·d), 8cm³ / (m²·d); Water vapor permeability (WVTR) at 38℃ and 90% RH ≤6.2g / (m²·d), e.g., ≤6.2g / (m²·d), 6.0g / (m²·d), 5.8g / (m²·d), 5.0g / (m²·d).

[0038] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0039] Excellent dispersion stability and film quality: This invention employs melt phase inversion and in-situ neutralization techniques to construct a stable interfacial layer in situ between crystalline polyhydroxyalkanoates and acrylic resins using amphiphilic polymers. This interfacial control strategy effectively solves the problems of poor compatibility and easy delamination between bio-based polyesters and waterborne acrylic systems without relying on easily migrating small-molecule surfactants, resulting in an aqueous dispersion with uniform particle size and good colloidal stability. During the drying process, this dispersion forms a dense and continuous coating structure, overcoming the technical difficulties of numerous film defects and insufficient density in traditional physical blending systems.

[0040] Significantly Enhanced Synergistic Barrier Performance: This invention fully utilizes the high crystallinity of polyhydroxyalkanoates as the core of physical barrier properties, combines it with the continuous film-forming properties of acrylic resin, and constructs a highly efficient barrier network through the tight bonding at the microscopic interface using amphiphilic polymer compatibilizers. This composite structure effectively blocks the penetration paths of water vapor, oxygen, and oil molecules, endowing paper-based materials with excellent waterproof, oil-proof, and gas barrier properties. Furthermore, the tortuous effect introduced by the sheet-like or layered inorganic fillers further enhances the synergistic barrier effect through multiple mechanisms.

[0041] Excellent mechanical properties and processing adaptability: The specific gradient structure formed by the coating in the thickness direction endows the material with excellent comprehensive mechanical properties. The area near the paper-based interface ensures a strong mechanical anchor between the coating and the substrate, preventing coating peeling; at the same time, the flexible component in the composite system effectively improves the inherent brittleness of highly crystalline polyhydroxyalkanoates, giving the coating good folding endurance and flexibility, enabling it to adapt to the requirements of subsequent forming and processing technologies such as paper cup rolling, die-cutting, and deep embossing.

[0042] Superior Repulping and Fiber Recovery Characteristics: The coating structure designed in this invention exhibits excellent dissociation characteristics under mild pulping and sorting conditions. During repulping, the coating tends to break down into small, non-sticky, hard particles rather than forming large, sticky clumps or films, thus avoiding screen clogging problems. This significantly improves pulp fiber recovery rate and pulp quality, effectively solving the industry pain point of traditional water-based barrier coatings being difficult to efficiently recover in conventional paper recycling systems.

[0043] High safety and environmental friendliness: This water-based coating formulation is completely free of fluorides, eliminating the environmental risks posed by per- or polyfluoroalkyl substances (PFAS) and persistent organic pollutants at the source. Thanks to its stable polymer network structure and reduced reliance on small-molecule additives, the coating exhibits extremely low total migration levels when in contact with various food simulants, demonstrating excellent chemical inertness and meeting stringent food contact safety regulations. This provides a safe, low-carbon, and renewable green solution for the food packaging industry. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of the cellulose-based barrier material of the present invention.

[0045] In the figure, 1-cellulose substrate; 2-barrier coating; 3-crystalline internal phase or core phase; 4-interface layer; 5-plate or layered inorganic filler; 6-polymer or copolymer containing acrylic structural units. Detailed Implementation

[0046] 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. For commercial materials added in the form of emulsions, dispersions, or solutions (e.g., aqueous acrylic emulsions, crosslinking agent solutions, etc.), samples were taken before use, dried at 105°C to constant weight, and their non-volatile solids content was determined. The amount added "based on non-volatile solids" was then converted from the actual measured non-volatile solids content. Unless otherwise specified, performance testing methods were conducted according to the standards described in the Summary of the Invention section.

[0047] The accompanying drawings are schematic diagrams of a cellulose-based barrier material according to one embodiment of the present invention, showing a cellulose substrate 1 and a barrier coating 2 with a gradient structure loaded on its surface. In this barrier coating 2, a polymer or copolymer 6 containing acrylic structural units constitutes a continuous phase matrix, wherein interfacially stable composite particles and sheet-like or layered inorganic fillers 5 are dispersed. The composite particles consist of a crystalline internal phase or core phase 3 formed by a first polymer component, namely a polyhydroxyalkanoate polymer, and an interfacial layer 4 enriched on its surface by an amphiphilic polymeric compatibilizer or dispersant. This structural design achieves the synergistic effect of multiple barrier mechanisms.

[0048] Main reagents and raw materials:

[0049] Table 1. Names, specifications or models, and manufacturers of major reagents and raw materials:

[0050]

[0051] Main analytical and testing instruments:

[0052] Table 2 mainly analyzes the names, specifications or models, and manufacturers of the testing instruments:

[0053]

[0054] Main testing standards:

[0055] Cobb absorbency: Tested for 60 seconds according to ISO 535:2023 "Determination of absorbency of paper and paperboard - Cobb method".

[0056] KIT oil resistance: Tested according to TAPPI T 559 cm-22 standard.

[0057] OTR: Under conditions requiring controlled relative humidity, refer to ASTM F1927-20 for testing at 23°C and 50% RH; if testing under dry conditions, refer to ASTM D3985-24 for testing gas relative humidity <1%.

[0058] WVTR: Tested according to ASTM F1249-25, "Standard Test Method for Determining Water Vapor Transmission Rate of Materials Using Modulated Infrared Sensors", under conditions of 38°C and 90% RH, and measured using a water vapor transmission rate tester.

[0059] Peel strength and heat seal strength: Tested according to ASTM F88 / F88M-23, "Standard Test Method for Heat Seal Strength of Flexible Barrier Materials".

[0060] Surface wettability and contact angle: The forward contact angles of water and soybean oil were tested in accordance with ASTM D7334-08(2022) "Standard Implementation Procedure for Evaluating the Wettability of Solid Surfaces by Measuring the Forward Contact Angle".

[0061] Melt flow index MIHLMI: Measured according to ASTM D1238-23a at 190°C and a load of 2.16 kg or 21.6 kg.

[0062] Adhesion cross-cut test - tape test: The test shall be conducted in accordance with ISO 2409:2020 "Coatings and varnishes - cross-cut test" and rated on a scale of 0-5.

[0063] Total fluoride content: The total fluoride content in coated paper and coated dry film was determined by online combustion-ion chromatography, expressed as fluoride, in accordance with the group standard T / CNFIA 191—2024 "Determination of total fluoride content in food contact paper, paperboard and paper products by online combustion-ion chromatography" or an equivalent method. The method detection limit was ≤5 mg / kg. When the measured value was lower than the detection limit, it was recorded as "not detected".

[0064] Leakage resistance and heat resistance of paper cups: Tests were conducted in accordance with the relevant clauses on leakage resistance and heat resistance in GB / T 27590-2022 "Paper Cups".

[0065] Folding endurance: Tested according to ISO 5626:1993 "Determination of folding endurance of paper", tension 9.81N.

[0066] Total migration: Tested in accordance with GB 31604.8-2021 "National Food Safety Standard for Determination of Total Migration in Food Contact Materials and Articles".

[0067] Example:

[0068] Example 1: The first polymer component was one part of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH powder listed in Table 1, with a weight-average molecular weight (Mw) of 5.0 × 10⁻⁶. 5The crystallinity is 45%, and it belongs to the copolymer between monomers that form short-chain and medium-to-long-chain polyhydroxy fatty acid esters. The second polymer component consists of 94 parts of aqueous acrylic emulsion (based on non-volatile solids) and 5 parts of ethylene-acrylic acid copolymer (EAA) resin, totaling 99 parts. The EAA resin used is a copolymer of ethylene and acrylic acid with an acid value of 155 mg KOH / g, a melt index of 300 g / 10 min, and a yield of 2.16 kg at 190℃. The specific operation is as follows: PHBH powder and EAA resin are premixed in a mixer at 130℃ for 5 minutes and then discharged and granulated to obtain melt premixed granules. The melt premixed granules are then placed in a closed, pressure-resistant, high-shear emulsification reactor with a jacketed temperature control. The reactor is designed to withstand a pressure ≥1.0 MPa. The reactor is pressurized at 120℃ to maintain the internal pressure at 0.3 MPa. The high-shear dispersion equipment is started, and the rotor speed is set to 10000 rpm. Preheated deionized water to 90℃ is added in three portions over 10 minutes to control the solid content of the system during the phase inversion emulsification stage at 35 wt%. During the phase inversion process, 25 wt% triethanolamine aqueous solution is added in three portions to gradually neutralize the EAA acid groups. The amount added is controlled by feedback through pH measurement of samples cooled to 25℃. The amount of neutralizing agent is adjusted to achieve a final pH of 9.0. The degree of neutralization is calculated based on the ratio of the molar amount of triethanolamine to the molar amount of EAA acid groups and controlled at 60%. Continue high shear for 30 minutes to complete phase inversion emulsification; then cool the system to 90°C, and add the aqueous acrylic emulsion uniformly over 15 minutes while stirring at 300 rpm, mixing thoroughly; subsequently, adjust the final solid content of the system to 35 wt% by adding deionized water. The solid content is determined by drying samples at 105°C to constant weight, and the total non-volatile solids mass M is used for measurement. s Calculate the water replenishment to ensure the total mass of the system meets M. total =M s / 0.35. The final aqueous dispersion had a solids content of 35 wt% and a pH of 9.0 at 25°C; the combined mass fraction of polyvinyl alcohol and PBAT was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added, whose total mass fraction in the aqueous dispersion solids was 0%; the total fluorine content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluorine. The average particle size D of the dispersion was... 50 The wavelength is 220 nm, and the zeta potential is -35 mV, forming a uniform and stable composite dispersion system.

[0069] Example 2: The first polymer component was selected from 99 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH powder listed in Table 1. Its weight-average molecular weight (Mw) was 5.0 × 10⁻⁶ on a non-volatile solids dry weight basis. 5The first polymer component contains 0.5 parts of aqueous acrylic emulsion (based on non-volatile solids) and 0.5 parts of ethylene-acrylic acid copolymer (EAA) resin, totaling 1 part. The EAA resin has an acid value of 155 mg KOH / g, a melt index of 300 g / 10 min, and a yield of 2.16 kg at 190°C. The specific operation is as follows: First, premix PHBH powder and EAA resin in a mixer at 130℃ for 5 minutes and granulate. Then, place the molten premixed granules in a sealed, pressure-resistant rotor-stator high-shear emulsification vessel, set the phase inversion temperature to 130℃, and pressurize the vessel to maintain the internal pressure at 0.4MPa. Start the rotor-stator high-shear equipment and set the rotor speed to 10000rpm. Add preheated deionized water to 90℃ in batches over 20 minutes, controlling the solid content of the system to 35wt%. During the phase inversion process, add 25wt% triethanolamine aqueous solution to neutralize the EAA acid groups. The amount added is controlled by feedback through sampling and cooling to 25℃ to measure the pH value, and the neutralizing agent is adjusted accordingly. The final pH of the system was adjusted to 9.0, and the neutralization degree of EAA acid groups was 60%. High-shear dispersion was maintained until the total shear time reached 60 min. The system was then cooled to 90℃, and aqueous acrylic emulsion was added under stirring and mixed thoroughly. Deionized water was added to achieve a final aqueous dispersion with a solid content of 35 wt% and a pH of 9.0 at 25℃. The total mass fraction of polyvinyl alcohol and PBAT was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added; their total mass fraction in the aqueous dispersion solids was 0%. The total fluoride content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluoride. The average particle size of the dispersion was D. 50 The wavelength is 850 nm, and the zeta potential is -28 mV.

[0070] Example 3: This example verifies the application of a low-acid-value amphiphilic polymeric compatibilizer. The first polymer component was selected from 40 parts of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV powder listed in Table 1. It belongs to short-chain polyhydroxy fatty acid esters, and its weight-average molecular weight (Mw) is 3.0 × 10⁻⁶. 5The first polymer component contains 40 parts of aqueous acrylic emulsion and 20 parts of ethylene-methacrylic acid copolymer (EMAA) resin, with a dry weight ratio of 40:60. The EMAA resin is a copolymer of ethylene and methacrylic acid with an acid value of 60 mg KOH / g, a melt index (HLMI) of 60 g / 10 min, and a yield of 21.6 kg at 190°C. The specific operation is as follows: PHBV powder and EMAA resin are melted at 130℃ for 5 minutes and then placed in a sealed, high-shear emulsification vessel for phase inversion emulsification. The phase inversion temperature is set at 140℃, and the pressure inside the vessel is maintained at 0.5MPa. The high-shear dispersion equipment is started and the rotation speed is set to 10,000 rpm. Deionized water preheated to 90℃ is added within 10 minutes. During the phase inversion process, triethanolamine is added to achieve 100% neutralization of the EMAA acid groups. The amount added is controlled by feedback through the pH value measured by sampling and cooling to 25℃. The amount of neutralizing agent is adjusted to make the final pH of the system 9.5. High shear emulsification is continued for 30 minutes to complete the emulsification. After cooling to 90℃, aqueous acrylic emulsion is added under stirring and mixed evenly to obtain the final aqueous dispersion. The final aqueous dispersion had a solids content of 35 wt%, and the pH was 9.5 when the sample was cooled to 25°C. The total mass fraction of polyvinyl alcohol and PBAT was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added; their total mass fraction in the aqueous dispersion solids was 0%. The total fluoride content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluoride. The average particle size of the dispersion was D. 50 The wavelength is 580 nm, and the zeta potential is -26 mV.

[0071] Example 4: This example verifies the application of a high-acid-value amphiphilic polymeric compatibilizer. The first polymer component was selected from 40 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH powder listed in Table 1, with a weight-average molecular weight (Mw) of 5.0 × 10⁻⁶. 5The crystallinity is 45% (g / mol). The second polymer component comprises 40 parts of aqueous acrylic emulsion and 20 parts of ethylene-acrylic acid copolymer wax (EAA wax), with a dry weight ratio of 40:60. The EAA wax has an acid value of 185 mg KOH / g. The specific operation is as follows: First, PHBH powder and EAA wax are melted at 130℃ for 5 minutes to form granules; then, phase inversion is carried out at 110℃ in a closed pressure-resistant rotor-stator high-shear emulsification kettle. The pressure inside the emulsification kettle is maintained at 0.3MPa by gas filling and pressurization. The high-shear dispersion equipment is started and the rotor speed is set to 10000rpm. Deionized water is preheated to 90℃ and added in batches over 10 minutes to control the solid content to 35wt%. To avoid excessive hydrophilicity, the degree of neutralization is controlled at 30%, and a neutralizing agent is added. The amount added is controlled by feedback by taking a sample and cooling it to 25℃ to measure the pH value, so that the final pH of the system is 8.5. After the phase inversion emulsification is completed and cooled to 90℃, the aqueous acrylic emulsion is added and mixed evenly to obtain the final aqueous dispersion. The final aqueous dispersion had a solids content of 35 wt%, and the pH was 8.5 when the sample was cooled to 25°C. The total mass fraction of polyvinyl alcohol and PBAT resin was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added; their total mass fraction in the aqueous dispersion solids was 0%. The total fluoride content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluoride. The average particle size of the dispersion was D. 50 The wavelength is 250 nm, and the zeta potential is -42 mV.

[0072] Example 5: This example verifies the comprehensive formulation containing synergistic components. The first polymer component was selected from 40 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH powder from Table 1, with a weight-average molecular weight (Mw) of 5.0 × 10⁻⁶. 5The crystallinity is 45%. The second polymer component consists of 40 parts of the aqueous acrylic emulsion (based on non-volatile solids) from Table 1 and 20 parts of the ethylene-acrylic acid copolymer (EAA) resin from Table 1, in a ratio of 40:60. The EAA resin has an acid value of 155 mg KOH / g, a melt index of 300 g / 10 min, and a yield of 2.16 kg at 190℃. Based on this, 10 parts of octenyl succinic anhydride (OSA) modified starch (from Table 1), 30 parts of kaolin (from Table 1) with an aspect ratio >50, and 1 part of carbodiimide crosslinking agent (from Table 1) are added. The specific operation is as follows: PHBH powder and EAA resin are premixed in a mixer at 130℃ for 5 minutes and then discharged and granulated to obtain melt premixed granules; then the melt premixed granules are placed in a sealed pressure-resistant rotor-stator high-shear emulsification kettle, and pressurized at 120℃ to maintain the gauge pressure inside the kettle at 0.3MPa; the high-shear dispersion equipment is started and the rotor speed is set to 10000rpm, and deionized water preheated to 90℃ is added in 3 portions within 10 minutes; during the phase inversion process, 25wt% triethanolamine aqueous solution is added to neutralize the EAA acid groups, and the amount added is controlled by feedback by sampling and cooling to 25℃ to measure the pH value, and the amount of neutralizing agent is adjusted to make the final pH of the system 9.0 and the degree of neutralization controlled at 60%; continue high shear for 30 minutes to complete the phase inversion emulsification; cool to 90℃, add water-based acrylic emulsion and mix. OSA-modified starch was pre-prepared with deionized water to form a starch slurry with a solid content of 20 wt%, and kaolin was pre-prepared with deionized water to form a mineral slurry with a solid content of 40 wt%. Both were dispersed separately in a high-speed disperser for 15 min, and then added sequentially when the dispersions cooled to below 60°C. Finally, a carbodiimide crosslinking agent was added and stirred for 10 min to obtain the final dispersion. The final aqueous dispersion had a solid content of 35 wt% and a pH of 9.0. The total mass fraction of polyvinyl alcohol and PBAT resin was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added; their total mass fraction in the aqueous dispersion solids was 0%. The total fluorine content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluorine. The average particle size D of the dispersion was... 50 The wavelength is 210 nm, and the zeta potential is -38 mV.

[0073] Example 6: This example verifies the introduction of bio-based plasticizers or bio-based adjuvant components. The first polymer component was selected from 40 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH powder listed in Table 1, with a weight-average molecular weight (Mw) of 5.0 × 10⁻⁶. 5The first polymer component has a density of g / mol and a crystallinity of 45%. The second polymer component comprises 40 parts of aqueous acrylic emulsion (based on non-volatile solids) and 20 parts of ethylene-acrylic acid copolymer (EAA) resin, with a dry weight ratio of 40:60. The EAA resin has an acid value of 155 mg KOH / g, a melt index of 300 g / 10 min, and a yield of 2.16 kg at 190°C. Additionally, 10 parts of ESBO are added as a bio-based plasticizer or bio-based auxiliary agent, with a mass ratio of 0.1:1 relative to the total dry weight of the first and second polymer components. The specific preparation process is as follows: ESBO is added to the internal mixer along with PHBH powder and EAA resin during the internal mixing premixing stage. The mixture is premixed at 130℃ for 5 minutes and then discharged for granulation. The premixed granules are then placed in an emulsification tank and subjected to phase inversion at 120℃ with pressurized gas to maintain the gauge pressure at 0.3 MPa. High-shear dispersion is initiated, and the rotation speed is adjusted to 10,000 rpm. Water is added within 10 minutes. During the phase inversion, a 25 wt% triethanolamine aqueous solution is added to neutralize the EAA acid groups to 60%. The amount added is controlled by feedback through pH measurement at 25℃, ensuring the final pH of the system is 9.0. The total high-shear time is maintained for 60 minutes to ensure the plasticizer's full effect. The mixture is then cooled to 90℃, and an aqueous acrylic emulsion is added and mixed. The final aqueous dispersion had a solids content of 35 wt% and a pH of 9.0 at 25°C. The combined mass fraction of polyvinyl alcohol and PBAT was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added; their total mass fraction in the aqueous dispersion solids was 0%. Total fluoride content was not detected by online combustion-ion chromatography (detection limit 5 mg / kg), and was expressed as fluoride. The average particle size D of the dispersion was... 50 The wavelength is 230 nm, and the zeta potential is -34 mV.

[0074] Comparative example:

[0075] Comparative Example 1: A physical blending process was used at 25°C. The raw materials were 40 parts PHBH powder, 40 parts aqueous acrylic emulsion, and 20 parts ethylene-acrylic acid copolymer (EAA) resin. Without undergoing melt phase inversion and in-situ neutralization, an effective core-shell interface layer could not be formed. The preparation process was as follows: At 25°C, the aqueous acrylic emulsion was added to a stirred tank, and a high-speed disperser was started (10,000 rpm). Under stirring conditions, PHBH powder was added in batches and dispersed for 15 min, followed by the addition of EAA resin powder / particles and dispersion for another 20 min. Samples were taken, cooled to 25°C, and the pH was measured. The pH of the system was adjusted to 9.0 using a 25 wt% triethanolamine aqueous solution. Subsequently, deionized water was added to adjust the solid content of the system to 35 wt% (solid content was determined by drying the sample at 105°C to constant weight), resulting in the dispersion of Comparative Example 1. The total mass fraction of polyvinyl alcohol and PBAT was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added; their total mass fraction in the aqueous dispersion solids was 0%. The total fluorine content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluorine. The average particle size of the dispersion was D. 50 The wavelength is 2500 nm, and the zeta potential is -15 mV.

[0076] Comparative Example 2: Instead of using an amphiphilic polymeric compatibilizer, 2 parts of sodium dodecyl sulfate (SDS) were used to stabilize a mixture of 40 parts of PHBV powder and 40 parts of aqueous acrylic emulsion. First, a coarse dispersion was formed by pre-dispersing the mixture at room temperature using a high-speed disperser for 15 minutes. Then, it was homogenized three times using a two-stage high-pressure homogenizer at 80 MPa. The discharge temperature was controlled at 50°C through circulating cooling. After homogenization, samples were taken and cooled to 25°C to determine the pH. The pH of the system was then adjusted to 9.0 using a 25 wt% triethanolamine aqueous solution. Subsequently, deionized water was added to adjust the solid content of the system to 35 wt% (solid content was determined by drying samples at 105°C to constant weight), resulting in the dispersion of Comparative Example 2. The total mass fraction of polyvinyl alcohol and PBAT was 0%. Two parts of low-molecular-weight surfactant SDS with a number average molecular weight <2000 were added, and its total mass fraction in the aqueous dispersion solids was 2.44%. The total fluorine content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg) and was expressed as fluorine. The average particle size D of the dispersion 50 The wavelength is 350 nm, and the zeta potential is -45 mV.

[0077] Comparative Example 3: Only 100 parts of aqueous acrylic emulsion, excluding polyhydroxyalkanoates and amphiphilic polymeric compatibilizers, were used as a reference for the pure acrylic system. The final aqueous dispersion had a solids content of 35 wt% and a pH of 9.0; the combined mass fraction of polyvinyl alcohol and PBAT was 0%, and no low-molecular-weight surfactants with a number average molecular weight <2000 were added, whose total mass fraction in the aqueous dispersion solids was 0%; the total fluoride content was not detected by online combustion-ion chromatography (detection limit was 5 mg / kg), and was expressed as fluoride. The average particle size D of this dispersion was... 50 The wavelength is 200 nm, and the zeta potential is -40 mV.

[0078] Comparative Example 4: An attempt was made to prepare a pure PHA emulsion using 100 parts PHBH powder and 5 parts SDS. It did not contain water-based acrylic emulsion or amphiphilic polymer compatibilizer. Due to the lack of film-forming aids, it could not form a film after coating.

[0079] Comparative Example 5: Imitating a ternary emulsion formulation, containing 30 parts PHBH powder, 30 parts PBAT resin, 10 parts polyvinyl alcohol as the continuous phase, and 1 part SDS: First, polyvinyl alcohol was prepared into a 10wt% aqueous solution and stirred at 90°C for 1 hour to dissolve, then cooled to 70°C for later use; then, PHBH powder and PBAT resin were melt-blended at 160°C for 5 minutes to obtain a melt blend, which was then added to the above polyvinyl alcohol aqueous solution at 70°C and dispersed for 30 minutes at a rotor speed of 10000 rpm in a high-shear emulsifier to obtain the emulsion of Comparative Example 5. The final aqueous dispersion had a solids content of 35 wt% and a pH of 9.0. The combined mass fraction of polyvinyl alcohol and PBAT in the solids was 56.34%. One part of a low-molecular-weight surfactant, SDS, with a number-average molecular weight <2000, was added, with a total mass fraction of 1.41% in the aqueous dispersion solids. The total fluoride content was not detected by online combustion-ion chromatography (detection limit: 5 mg / kg), and was expressed as fluoride. The average particle size of the dispersion was D. 50 The wavelength is 450 nm, and the zeta potential is -20 mV.

[0080] Comparative Example 6: This comparative example uses a PVOH and polysaccharide stabilization system. The raw materials include 40 parts PHBH powder, 15 parts polyvinyl alcohol, and 5 parts OSA-modified starch, without aqueous acrylic emulsion or amphiphilic polymer ionomers. The preparation process is as follows: First, polyvinyl alcohol and OSA-modified starch are dissolved and dispersed in deionized water to prepare a slurry with a solid content of 20 wt%. Then, PHBH powder is added and pre-dispersed for 15 min. Subsequently, wet milling is performed using a horizontal bead mill with 0.4 mm zirconia beads as the grinding medium. The milling speed is 1800 rpm and the milling time is 90 min. During the milling process, jacket cooling is used to keep the slurry temperature below 40℃, resulting in the dispersion of Comparative Example 6. The final aqueous dispersion had a solids content of 35 wt% and a pH of 9.0. Polyvinyl alcohol (PVOH) comprised 25% of the aqueous dispersion solids, and no polybutylene adipate terephthalate (PBAT) was added. No low-molecular-weight surfactants with a number-average molecular weight <2000 were added, and their total mass fraction in the aqueous dispersion solids was 0%. Total fluoride content was undetectable (detection limit 5 mg / kg) by online combustion-ion chromatography, expressed as fluoride. The average particle size of the dispersion was D. 50 The wavelength is 400 nm, and the zeta potential is -22 mV.

[0081] Table 3 Summary of Formulations for Examples and Comparative Examples:

[0082]

[0083] Application example:

[0084] Application Example 1: Comprehensive evaluation of dispersion properties and paper-based coating performance.

[0085] Experimental Description: White cardboard with a basis weight of 250 g / m² was selected as the substrate. The dispersions prepared in Examples 1-6 and Comparative Examples 1-6 were coated onto the paper surface using a laboratory doctor blade coater. The coating and drying processes were as follows: S1. The aqueous dispersion or coating composition was applied to the surface of paper, paperboard, or molded fiber substrate by doctor blade coating, rod coating, gravure coating, flexographic coating, roller coating, or a combination of the above methods to obtain a wet coating; S2. The wet coating obtained in S1 was dried in stages. The first stage involved draining water and forming a preliminary film at 80°C, while the second stage involved densification and structural shaping of the coating at 120°C. This invention uses a laboratory doctor blade coater to simulate industrial rod coating or gravure coating processes. The dry coating weight was calculated by dividing the mass difference between the samples before and after coating (dried at 105°C to constant weight) by the coating area. The drying process consisted of two stages: the first stage involved drying at 80°C for 2 minutes to drain water and form a preliminary film, and the second stage involved drying at 120°C for 1 minute to densify and shape the coating. All samples were equilibrated for 24 hours at 23°C and 50% RH before testing.

[0086] The following tests were performed on each sample:

[0087] Dispersion properties: The coating solution was diluted with deionized water of the same pH as the original sample to a solid content of 0.05 wt%. The volumetric average particle size D was measured and reported using a particle size analyzer at 25°C. 50 With Zeta potential.

[0088] Coating performance: Determination of Cobb properties of coated paper 60 Both water absorption and KIT oil resistance ratings are tested on the coated surface.

[0089] Barrier performance: OTR was measured at 23°C and 50% RH, according to ASTM F1927-20; WVTR was measured at 38°C and 90% RH. For OTR and WVTR testing, the samples were cut to fit the test cell size, and non-test areas were shielded with aluminum foil tape to ensure an effective test area of ​​50 cm². The edges of the samples were continuously sealed with aluminum foil tape and compacted to prevent air leakage and ensure a consistent effective test area for all samples.

[0090] The data in this application example table is based on a coating amount of 10 g / m².

[0091] Table 4. Test results of dispersion properties and barrier performance in Application Example 1:

[0092]

[0093] Analysis: Comparative Example 4, lacking film-forming aids, had a continuous film coverage of less than 10% after drying, failing to form an effective coating; therefore, no specific barrier performance data were obtained. Experimental results show that the ratio of PHA to acrylic acid and interface engineering control significantly affect the barrier performance of the coating. As the PHA content increased from 1% to 99% (Examples 1 to 2), the KIT oil resistance rating of the coating increased from 6 to 11, and the OTR decreased from 350 to 45 cm³ / (m²·d), confirming that the highly crystalline PHA phase is the main barrier contributor. However, extremely high PHA content leads to increased film formation difficulty and increased particle size. Example 5, by introducing mineral fillers and crosslinking components and optimizing the ratio, achieved optimal overall performance at a moderate PHA content, with a KIT rating of 12, an OTR reduced to 10 cm³ / (m²·d), a WVTR reduced to 5.8 g / (m²·d), and a Cobb... 60 As low as 2.8 g / m². In Example 6, after introducing the bio-based plasticizer ESBO, the barrier properties of the coating were slightly lower than in Example 5, but still significantly better than the comparative example. In contrast, Comparative Example 1, using physical blending, lacked a stable interfacial layer constructed from amphiphilic polymers, had a particle size of 2500 nm, and resulted in poor film-forming properties, leading to Cobb... 60The concentration was 45 g / m² and the OTR was >1000 cm³ / (m²·d). Comparative Example 3, with its pure acrylic acid system, had a particle size of 200 nm and formed a dense film, but its large free volume resulted in a KIT level of only 2 and an OTR as high as 800 cm³ / (m²·d). Furthermore, Comparative Example 2 used a small molecule surfactant, whose Cobb... 60 The concentration was 32 g / m², significantly higher than the 2.8 g / m² in Example 5. These results demonstrate that the stable interface layer constructed in situ through interface engineering can resolve compatibility issues and achieve a synergistic barrier effect.

[0094] Application Example 2: Evaluation of repulping and fiber recycling performance.

[0095] Experimental Description: Coated paper samples corresponding to Examples 1-6 and Comparative Examples 1-6 in Application Example 1 were selected to evaluate their repulping performance in a conventional recycling process. The coated paper samples were cut into 25mm × 25mm fragments. 30g of oven-dry paper sample was added to 1470g of water medium at 45℃ and pH 7, making the pulp concentration approximately 2wt%. After soaking for 10 minutes, the pulp was dissociated using a high-consistency hydraulcretor at 3000rpm for 30 minutes. The dissociated pulp was screened through a 0.15mm slit screen, and the screen was rinsed with isothermal water until the undersize liquid was clear. The good pulp undersize and the residue oversize were collected. Both were dried at 105℃ to constant weight and weighed. The fiber recovery rate and the rate of non-separable residue were calculated. The fiber recovery rate was calculated as the dry weight of the good pulp divided by the dry weight of the base paper fibers multiplied by 100%. The rate of non-separable residue was calculated as the dry weight of the residue oversize divided by the total dry weight of the base paper multiplied by 100%. Particle size characterization of the residue on the sieve: The residue on the sieve was dispersed with water and sampled and spread into a single layer. The equivalent circle diameter distribution was calculated using an optical microscope combined with image analysis, and the equivalent particle size D was reported. 50 The maximum particle size is Dmax. The adhesion rate is defined as the mass fraction of aggregates with an equivalent diameter >5mm formed after the residue on the sieve is air-dried.

[0096] Table 5. Results of repulping performance test in Application Example 2:

[0097]

[0098] Analysis: Comparative Example 4 was not tested for repulping performance because it could not form a film. Experimental data showed that the fiber recovery rate of the sample from the examples was 96% to 98.5% under pulping conditions of 45℃, pH 7, and 30 min, and the residue rate on the screen was 1.2% to 3.5%, with an equivalent particle size D of the residue on the screen. 50The particle size ranged from 0.30 mm to 0.80 mm, with a maximum particle size Dmax ≤ 2.0 mm and an adhesion rate of 0%. This result is consistent with the gradient structure of the coating: the acrylic phase near the paper base swells and facilitates detachment from the fibers, while the region rich in PHA and the interface layer maintains high cohesive strength, causing the coating to break down into particles under shear. In Example 6, the residue hardness may be slightly reduced due to the addition of a plasticizer, but the experimental results show that its recovery rate is 97.8% and the residue morphology is comparable to that of Example 5, with no obvious adhesion, indicating that the protective effect of the interface layer is still effective. In contrast, the residue Dmax on the sieve of Comparative Example 3 is much smaller. 50 The screen residue was 6.0 mm, with a maximum diameter (Dmax) of 20 mm and an adhesion rate of 60%. Comparative Examples 5 and 6 had adhesion rates of 70% and 50%, respectively, corresponding to higher oversize residue rates. This indicates that a large amount of hydrophilic continuous phase or the presence of adhesion and agglomeration makes screening more difficult. The results show that this interface control structure, while ensuring barrier properties, can control the oversize residue within a small particle size and low adhesion range.

[0099] Application Example 3: Evaluation of total fluoride content.

[0100] Experimental Description: To verify the environmental safety and compliance with global PFAS regulations of the products of this invention, the online combustion-ion chromatography (CIC) method described in the main testing standards section was used to test the total fluoride content of the coated paper samples of Examples 1-6 and Comparative Examples 1-6 in Example 1. Simultaneously, to comply with the limitations of aqueous dispersion products, each aqueous dispersion was vacuum-dried or freeze-dried to constant weight to obtain a solid dispersion, and then its total fluoride content was tested using the same CIC method. A blank control was strictly monitored during the testing process to prevent environmental pollution. Approximately 30 mg of each test object was cut, crushed, or ground and accurately weighed, and placed in a quartz combustion boat. Programmable combustion was performed in an oxygen-enriched environment at a high temperature of 900-1000℃. The generated gas was absorbed by the absorbent and injected into an ion chromatograph to determine the fluoride ion concentration. The final result was converted to total fluoride content in mg / kg, and the method detection limit was set at 5 mg / kg. Each sample was tested in triplicate, and the arithmetic mean was taken.

[0101] Table 6. Results of Total Fluorine Content Test in Application Example 3:

[0102]

[0103] Analysis of Experimental Results: Test results show that the total fluorine content in both Examples 1-6 and Comparative Examples 1-6 of this invention is below the method detection limit of 5 mg / kg, and is therefore determined to be undetectable. This result objectively confirms the environmentally friendly nature of the technical route of this invention. In terms of formulation design, this invention abandons the fluorinated oil-repellent agents commonly used in the traditional papermaking industry, such as C8 or C6 fluorocarbon surfactants. Instead, it achieves excellent oil-repellent performance by constructing a highly crystalline PHA physical barrier layer and a dense ionomer interface network, as shown by the KIT rating of Example 5, which is 12. This is completely different from the mechanism of relying on low surface energy fluorine atoms to repel oil droplets. Experimental results show that through precise control of the physical microstructure, it is entirely possible to achieve or even exceed the application performance standards of fluorinated products without introducing persistent organic pollutants and PFAS, thus meeting the increasingly stringent global regulations on food contact materials.

[0104] Application Example 4: Evaluation of mechanical strength and adhesion.

[0105] Experimental Description: To evaluate the mechanical stability of the coating during actual processing such as folding and die-cutting, as well as its bonding strength with the paper base, coated paper samples corresponding to Examples 1-6 and Comparative Examples 1-6 in Application Example 1 were selected for folding endurance and adhesion tests. Folding endurance was tested according to ISO 5626:1993 standard using an MIT folding endurance tester under a tension of 9.81N to measure the number of double folds. The results reflect the flexibility and crack resistance of the coating. Adhesion testing was conducted according to ISO 2409:2020 "Coatings and varnishes, cross-cut test": A 10×10 grid was drawn on the coating surface using a 1mm spacing cross-cutting tool. After cleaning away debris, standard tape conforming to ISO 2409:2020 was applied and then rapidly peeled off at 180° after the specified application time. The coating peeling was observed and rated from 0 to 5 according to ISO 2409:2020, with 0 being the best (no peeling) and 5 being the worst (peeling area > 65%).

[0106] Table 7. Results of mechanical strength and adhesion tests in Application Example 4:

[0107]

[0108] Analysis: Comparative Example 4 was not tested because it could not form a film. Experiments show that this invention significantly improves the mechanical properties of the PHA-based coating through interface engineering. The folding endurance of Examples 1, 3, and 4 remained at a high level (>90 times), and the adhesion reached grade 0, indicating that the acrylic continuous phase and ionomer interface layer provided good flexibility and anchoring force. Example 6, due to the addition of a bio-based plasticizer, saw its folding endurance increase to 140 times, superior to Example 5 without plasticizer, indicating that the plasticizer effectively improved the coating's flexibility, making it more suitable for high-processing requirements such as deep embossing. With the extreme increase in PHA content (Example 2), the folding endurance decreased to 45 times, due to the inherent hardness and brittleness of highly crystalline PHA. However, thanks to the compatibilizing effect of the ionomer, its adhesion remained at grade 1, superior to the PHA, PVOH, and OSA-modified starch system of Comparative Example 6, which had an adhesion grade of 3. Due to severe phase separation, the physical blend system of Comparative Example 1 exhibited a coating that easily delaminated from the paper base during folding and peeling, resulting in an adhesion rating of only 4. While the pure acrylic coating of Comparative Example 3 boasted a folding endurance of up to 130 cycles, it lacked a rigid barrier phase, limiting its applications. In Example 5, although the folding endurance slightly decreased to 92 cycles after the introduction of mineral fillers, it still met the processing requirements for paper cup seams and exhibited excellent adhesion, demonstrating the contribution of the crosslinking components and interface agents in the formulation to structural integrity.

[0109] Application Example 5: Evaluation of total migration from food contact.

[0110] Experimental Description: This experiment assesses the chemical inertness of coatings in contact with different types of food simulants for food packaging applications. Coated paper samples from Examples 1-6 and Comparative Examples 1-6 in Application Example 1 were selected, and total migration tests were conducted according to GB 31604.8-2021 standard. 10% ethanol was used to simulate aqueous or alcoholic foods at 70℃ for 2 hours; isooctane was used to simulate oily food substitutes at 60℃ for 0.5 hours. A fully automated migration test cell was used, with a contact area to simulant volume ratio of 6 dm² / L. After cutting the samples, only the coated surface was in contact with the simulant; the back of the samples and the cut edges were isolated with inert barrier materials or sealed to prevent lateral seepage. After the test, the simulant solution was evaporated and dried, the mass of the non-volatile residue was weighed, and the total migration amount was calculated in mg / dm².

[0111] Table 8. Test results of total migration in Application Example 5:

[0112]

[0113] Analysis: Comparative Example 4 was not tested because it could not form a film. The total migration test reflects the amount of soluble substances in the coating, which is directly related to food safety. The total migration of samples 1-6 in the embodiments of this invention was at a low level in both simulated solutions, <5 mg / dm², far below the usual limit of 10 mg / dm². This is due to the fact that the present invention does not rely on small molecule surfactants and forms a stable polymer network through in-situ neutralization and cross-linking curing technology, such as in Example 5, which locks in potential migrants. Example 6, due to the addition of a bio-based plasticizer, had a migration of 3.5 mg / dm² in isooctane, slightly higher than the 2.5 mg / dm² of Example 5. This is because the plasticizer is extracted in trace amounts in the oily simulated solution, but it is still far lower than the comparative example and complies with regulatory requirements. In contrast, Comparative Example 2 used the small molecule surfactant SDS, which had a migration of up to 12.0 mg / dm² in isooctane, posing a significant risk of chemical migration. The pure acrylic coating of Comparative Example 3 exhibited the highest migration in isooctane, reaching 15.5 mg / dm², indicating poor solvent resistance and susceptibility to swelling or extraction by oily matrices. Comparative Examples 5 and 6, containing large amounts of hydrophilic PVOH, showed significantly increased migration in a 10% ethanol aqueous simulation solution, exceeding 10 mg / dm², limiting their application in beverage packaging. The experimental results confirm that the interface-controlled dispersion of this invention provides excellent food contact safety while ensuring barrier properties.

[0114] Experimental Results and Analysis:

[0115] Based on the experimental data from Examples 1-6 and Comparative Examples 1-6 above, the performance of the aqueous dispersion and its paper-based barrier coating prepared by this technical solution is analyzed in detail as follows:

[0116] The decisive role of interface engineering in dispersion stability and film quality:

[0117] Experimental data show that the preparation process and system composition have a significant impact on the microstructure of the dispersion. Samples from Examples 1-6, prepared using melt phase inversion emulsification and in-situ neutralization techniques, achieved a stable interfacial layer at the interface between polyhydroxyalkanoates (PHA) and acrylic acid or water via amphiphilic polymers. This resulted in a controllable particle size distribution within the range of 200 to 850 nm, with absolute Zeta potentials all exceeding 25 mV, demonstrating excellent colloidal stability. In contrast, the Comparative Example 1 sample, prepared using a room-temperature physical blending process, lacked effective interfacial layer construction, exhibiting poor compatibility, an average particle size as high as 2500 nm, and a low Zeta potential of only -15 mV. After coating, it failed to form a dense and continuous film, resulting in a Cobb value as high as 45 g / m² and almost complete loss of gas barrier capability, with an OTR > 1000 cm³ / (m²·d). This confirms that interfacial engineering control is a key prerequisite for achieving stable dispersion and barrier performance of PHA in aqueous acrylic acid systems, rather than simply the superposition of components.

[0118] Structure-property relationship analysis of barrier properties:

[0119] The barrier properties of the coating exhibit significant component dependence and synergistic effects:

[0120] Crystallinity and Barrier Properties: With the increase of the proportion of highly crystalline PHA components, as in Examples 1 to 2, the OTR of the coating decreased significantly, from 350 to 45 cm³ / (m²·d), and the KIT oil resistance rating improved from level 6 to level 11. This indicates that the highly crystalline phase of PHA is the main source of barrier contribution, effectively blocking the penetration paths of gases and oils.

[0121] Limitations and optimizations of the system: Although the pure acrylic acid system (Comparative Example 3) exhibits good film-forming properties, its large free volume and lipophilic nature result in the worst barrier performance, with a KIT rating of 2 and an OTR of 800. The pure PHA system (Comparative Example 4) fails to form a film due to the lack of film-forming aids. While the system stabilized using small-molecule surfactants (Comparative Example 2) has a smaller particle size, the surfactant is prone to migration under high humidity conditions, leading to a higher WVTR.

[0122] Synergistic reinforcement of fillers and influence of additives: Example 5 further extended the penetration path and densified the network by introducing mineral fillers with high aspect ratios and crosslinking components, achieving Cobb coating at a dry coating weight of 6 to 12 g / m². 60The optimal concentrations (≤3.0 g / m²), KIT level 12, OTR ≤15 cm³ / (m²·d), and WVTR ≤6.2 g / (m²·d) demonstrate the effectiveness of the organic-inorganic hybrid strategy in achieving interfacial stability. In Example 6, the introduction of a bio-based plasticizer resulted in a slight decrease in barrier properties compared to Example 5, but a significant improvement in flexibility, while maintaining excellent barrier properties, verifying the system's good tolerance for functional additives.

[0123] Mechanical Properties and Interfacial Bonding Mechanism: The anchoring effect of the interfacial layer was particularly evident in the mechanical property tests. The sample examples generally exhibited excellent adhesion (grade 0 to 1) and high folding endurance. Especially when the high PHA content caused the material to become brittle, as in Example 2, the coating maintained good substrate adhesion thanks to the compatibilizing effect of the amphiphilic polymer ionomer. Conversely, the physically blended sample (Comparative Example 1) showed severe delamination in the folding and peeling tests, with an adhesion grade of 4, indicating that phase separation disrupted the structural integrity of the coating. The pure acrylic sample (Comparative Example 3), while flexible, lacked rigid support, limiting its application scenarios. This suggests that constructing a composite structure with a strong interfacial bond between soft and hard surfaces is an effective way to balance the rigid barrier properties and flexible processing performance of the coating.

[0124] Repulping Performance and Environmental Adaptability: Addressing the pain points of paper-based material recycling, experimental results reveal the unique advantages of this technical solution. The sample in the examples achieved an extremely high fiber recovery rate (>96%) under mild conditions, with the residue on the screen appearing as fine, non-sticky, hard particles. This excellent repulping performance is attributed to the gradient structure design of the coating: the hydrophilic acrylic phase swells and separates under hydraulic action, while the hydrophobic PHA and ionomer phases remain cohesive and broken, avoiding the formation of sticky films that clog the screen, as seen in pure acrylic coatings (Comparative Example 3), and also avoiding the formation of sticky micelles due to partial dissolution, as seen in polyvinyl alcohol (PVOH) based systems (Comparative Examples 5 and 6). Furthermore, the perfluorinated compound detection results confirmed that total fluorine was undetectable in all samples, below the method detection limit, eliminating concerns about persistent environmental pollutants from traditional oil-resistant coatings.

[0125] Food contact safety: Migration tests further validated the improvement in chemical safety through interface regulation. The total migration amounts of the sample samples in both aqueous and oily food simulants were far below the limits. Compared to the system using small-molecule surfactants (Comparative Example 2), this technical solution effectively locks potential migrants within the system through polymer ionomers and cross-linking networks, significantly reducing the risk of migration into food, particularly avoiding high migration in oily matrices.

[0126] In summary, by constructing a stable amphiphilic polymer interface layer between crystalline polyester and film-forming acrylic resin through interface engineering, the contradiction between water dispersion stability, film density, and interfacial adhesion in bio-based high-barrier materials has been successfully overcome. This technical solution not only achieves stable multiphase composite structures at the microscopic level but also unifies waterproof, oil-proof, high-barrier, high mechanical strength, and excellent repulping properties at the macroscopic level, providing a promising industrial solution for high-performance paper-based green packaging materials.

[0127] 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. An aqueous dispersion of PHA-acrylic acid structural units based on interface engineering control, characterized in that... The invention comprises an aqueous medium and a stable composite dispersion system formed in the aqueous phase, the stable composite dispersion system comprising: a first polymer component containing at least one polyhydroxyalkanoate polymer, wherein the polyhydroxyalkanoate polymer has a crystallinity ≥30% and a weight-average molecular weight Mw of 1.0 × 10⁻⁶. 5 Up to 1.5×10 6 g / mol; the second polymer component comprises at least one polymer or copolymer containing acrylic structural units and at least one amphiphilic polymer compatibilizer or dispersant, wherein the polymer or copolymer containing acrylic structural units is an aqueous polymer or copolymer obtained by polymerization of vinyl unsaturated monomers. Wherein, the amphiphilic polymer compatibilizer or dispersant is a copolymer of ethylene with methacrylic acid and / or acrylic acid or a partially or completely neutralized salt thereof, wherein the copolymer main chain contains ethylene units and has ionizable carboxyl groups on the side groups; The first polymer component forms a crystalline internal phase or core phase in the stable composite dispersion system. The amphiphilic polymer compatibilizer or dispersant is enriched in the interfacial layer between the crystalline internal phase or core phase and the polymer or copolymer containing acrylic structural units, so that the stable composite dispersion system forms composite particles with stable interfaces. Furthermore, the dry weight ratio of the first polymer component to the second polymer component is 1:99 to 99:1, and the total mass of polyvinyl alcohol and polybutylene adipate in the second polymer component is less than 3 wt% of the total dry weight of the first polymer component and the second polymer component. The total mass fraction of low molecular weight surfactants with a number average molecular weight <2000 in the aqueous dispersion solid is ≤0.5 wt%, and the total fluorine content of the aqueous dispersion solid is not detected when determined by online combustion-ion chromatography. The detection limit of the detection method is ≤5 mg / kg as fluorine.

2. The aqueous dispersion according to claim 1, characterized in that... The solids content of the aqueous dispersion is from 10 wt% to 60 wt%.

3. The aqueous dispersion according to claim 1, characterized in that... The polyhydroxy fatty acid ester is selected from short-chain polyhydroxy fatty acid esters, medium- and long-chain polyhydroxy fatty acid esters, or copolymers between monomers that form short-chain and medium- and long-chain polyhydroxy fatty acid esters. The short-chain polyhydroxy fatty acid ester is selected from one or more of poly3-hydroxybutyrate, poly3-hydroxybutyrate-co-4-hydroxybutyrate, and poly3-hydroxybutyrate-co-3-hydroxyvalerate. The medium- and long-chain polyhydroxy fatty acid esters are selected from one or more copolymers composed of two or more of the monomers that form the above-mentioned medium- and long-chain polyhydroxy fatty acid esters; the copolymers between the monomers that form the short-chain and medium- and long-chain polyhydroxy fatty acid esters are selected from poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxydecanoate), poly(3-hydroxydodecanoate), and poly(3-hydroxybutyrate).

4. The aqueous dispersion according to claim 1, characterized in that... The vinyl unsaturated monomer is selected from one or more of the following: acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, styrene, α-methylstyrene, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, methacryloyloxypropyltrimethoxysilane, methacryloyloxypropyltriethoxysilane, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate.

5. The aqueous dispersion according to claim 1, characterized in that... The amphiphilic polymeric compatibilizer or dispersant has an acid value of 40 to 200 mg KOH / g, a melt index of 10 to 2000 g / 10 min as determined by ASTM D1238-23a at 190°C, the melt index being determined at a load of 2.16 kg or 21.6 kg, and a mass fraction of 5 wt% to 60 wt% in the dry weight of the second polymer component.

6. The aqueous dispersion according to claim 1, characterized in that... The degree of acid neutralization of the amphiphilic polymeric compatibilizer or dispersant is 5% to 100%; the pH of the aqueous dispersion is 7.0 to 11.0; wherein the neutralizing ions are selected from sodium ions, potassium ions, lithium ions, magnesium ions, calcium ions, zinc ions, aluminum ions, organic amine cations or combinations thereof.

7. The aqueous dispersion according to claim 1, characterized in that... The average particle size D of the stable composite dispersion system 50 The range is 200 to 2000 nm; the absolute value of the Zeta potential is ≥25 mV.

8. The aqueous dispersion according to claim 1, characterized in that... It also contains a polysaccharide or modified starch synergistic stabilizing component, wherein the mass ratio of the polysaccharide or modified starch synergistic stabilizing component to the total dry weight of the first polymer component and the second polymer component is 0 to 1.2:1; the polysaccharide or modified starch synergistic stabilizing component is selected from one or more of oxidized starch, cationic starch, amphoteric starch, hydroxyethyl starch, hydroxypropyl starch, esterified starch, cross-linked starch, dextrin, carboxymethyl cellulose, hydroxypropyl methyl cellulose, alginate, chitosan, xanthan gum, guar gum, gum arabic, and lignin derivatives.

9. The aqueous dispersion according to claim 1, characterized in that... It also includes a mineral-based barrier reinforcement component, wherein the mass ratio of the mineral-based barrier reinforcement component to the total dry weight of the first polymer component plus the second polymer component is 0 to 3:1; the mineral-based barrier reinforcement component is a sheet-like or layered inorganic filler, wherein the sheet-like or layered inorganic filler is selected from one or more of kaolin, talc, mica, bentonite, montmorillonite, vermiculite, synthetic layered silicate, layered double hydroxide, sheet-like alumina or their surface organic modifiers; and the aspect ratio of the sheet-like or layered inorganic filler is >20.

10. The aqueous dispersion according to claim 1, characterized in that... It also contains a bio-based plasticizer or bio-based adjuvant component, wherein the mass ratio of the bio-based plasticizer or bio-based adjuvant component to the total dry weight of the first polymer component plus the second polymer component is 0 to 0.5:1, and the bio-based plasticizer or bio-based adjuvant component includes one or more of citrate esters, tartrate esters, sebacic esters, epoxidized vegetable oils, monoglycerides, polyglycerol fatty acid esters, and polyols.

11. The aqueous dispersion according to claim 1, characterized in that... It also includes a crosslinking or curing component, wherein the mass ratio of the crosslinking or curing component to the total dry weight of the first polymer component plus the second polymer component is 0 to 0.1:

1.

12. A method for preparing the aqueous dispersion according to claim 1, characterized in that, Includes the following steps: Step 1. Premix the first polymer component with an amphiphilic polymeric compatibilizer or dispersant in a molten state to obtain a melt premix; Step 2. While applying strong shear dispersion to the molten premix obtained in Step 1 at 80℃ to 180℃, all or part of the aqueous phase medium is introduced to obtain a phase inversion dispersion system in which the polymer continuous phase undergoes a phase inversion to the aqueous continuous phase. Step 3. During or after the phase transformation, a neutralizing agent is added to the phase transformation dispersion system obtained in Step 2 to cause the amphiphilic polymer compatibilizer or dispersant to undergo at least partial ionization, thereby constructing an interfacial layer in situ at the interface between the polyhydroxy fatty acid ester polymer and water, and obtaining an oil-water composite dispersion with an interfacial layer. Step 4. Continue stirring the oil-water composite dispersion obtained in Step 3 until the aqueous phase changes from the dispersed phase to the continuous phase, thus obtaining a stable composite dispersion system with water as the continuous aqueous phase. Step 5. Add the polymer or copolymer containing acrylic structural units to the stable composite dispersion system with water as the continuous aqueous phase obtained in Step 4 in the form of an aqueous emulsion or aqueous dispersion and mix evenly, then cool to obtain the aqueous dispersion; The total mass fraction of low molecular weight surfactants with a number average molecular weight <2000 in the aqueous dispersion solid is ≤0.5wt%.

13. A paper-based barrier material, characterized in that... The material comprises a cellulose substrate and a barrier coating located on at least one side thereof; the non-volatile solid dry film of the barrier coating comprises at least one polyhydroxyalkanoate polymer, wherein the polyhydroxyalkanoate polymer has a crystallinity ≥30% and a weight-average molecular weight Mw of 1.0 × 10⁻⁶. 5 Up to 1.5×10 6 g / mol; at least one polymer or copolymer containing acrylic acid structural units, wherein the polymer or copolymer containing acrylic acid structural units is an aqueous polymer or copolymer obtained by polymerization of vinyl unsaturated monomers; at least one amphiphilic polymeric compatibilizer or dispersant, which is a copolymer of ethylene with methacrylic acid and / or acrylic acid or a partially or completely neutralized salt thereof, having hydrophobic ethylene segments and ionizable carboxyl groups; wherein the dry weight ratio of the polyhydroxyalkanoate polymer to the polymer or copolymer containing acrylic acid structural units is 1:99 to 99:1, and the total mass fraction of polyvinyl alcohol and polybutylene adipate terephthalate in the barrier coating solid is <3wt%; the dry coating weight of the barrier coating is 0.3 to 60 g / m²; the non-volatile solid of the barrier coating does not contain intentionally added fluorinated organic compounds; the total fluorine content was not detected by online combustion-ion chromatography, and the detection limit of the detection method used is ≤5 mg / kg as fluorine.

14. The paper-based barrier material according to claim 13, characterized in that... The amphiphilic polymeric compatibilizer or dispersant is selected from ethylene-methacrylic acid copolymer and amphiphilic ethylene-acrylic acid copolymer.

15. The paper-based barrier material according to claim 13, characterized in that... The barrier coating forms a gradient structure with synergistic adhesion and barrier properties in the thickness direction. The coating thickness is defined as t. The region near the outer surface is the region 0 to 0.2t away from the outer surface, the region near the paper-based interface is the region 0 to 0.2t away from the paper-based interface, and the middle region is the region 0.2t to 0.8t. The mass fraction of polyhydroxyalkanoate polymer in the outer surface region is higher than the mass fraction of polyhydroxyalkanoate polymer in the overall coating. The mass fraction of polymer or copolymer containing acrylic structural units in the interface region is higher than the mass fraction of polymer or copolymer containing acrylic structural units in the overall coating. Furthermore, the mass fraction of ethylene methacrylate amphiphilic polymer compatibilizer or dispersant in the middle region is higher than the mass fraction of the amphiphilic polymer compatibilizer or dispersant in the overall coating.

16. The paper-based barrier material according to claim 13, characterized in that... When mechanical pulping is performed for 30 minutes at 45℃ and pH 7, and non-recyclable materials are separated through a 0.15mm sieve, the pulp fiber recovery rate is ≥97%, and the residue rate on the sieve is ≤2.0%; under the condition of a dry coating weight of 6 to 12 g / m², the Cobb of the paper-based barrier material... 60 Value ≤3.0g / m², KIT oil resistance grade 12, oxygen permeability ≤15cm³ / (m²·d) at 23℃ and 50% RH, water vapor permeability ≤6.2g / (m²·d) at 38℃ and 90% RH.

17. A method for preparing a barrier coating in a paper-based barrier material according to claim 13, characterized in that... Includes the following steps: S1. Apply the aqueous dispersion of claim 1 to the surface of paper, paperboard or molded fiber substrate by means of scraping, bar coating, gravure coating, flexographic coating, roller coating or a combination of the above methods to obtain a wet coating. S2. The wet coating obtained in S1 is dried in stages, wherein the first stage is drained and initially film is formed at 40°C to 120°C, and the second stage is completed at 80°C to 200°C to densify the coating and shape its structure, forming a barrier coating with a dry coating amount of 0.5 to 30 g / m², thus obtaining the barrier coating.

18. The use of the paper-based barrier material according to claim 13, characterized in that... Used for food packaging paper, disposable tableware, baking packaging, oil and fat lining paper, daily chemical paper box lining, paper bags, label paper or molded fiber products.

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