Reaction type compatible ACR-PHA core-shell latex and application thereof

Abstract

The invention discloses reactive compatible ACR-PHA core-shell latex and application thereof, and belongs to the field of polymer chemistry and material science. The latex comprises composite particles with core-shell, gradient core-shell, raspberry-shaped or Janus heterostructure, interfaces of ACR phase and PHA phase of the latex are connected through covalent bonds, and the compatibility problem of physical blending is fundamentally solved. The latex particles have a Z-average particle size of 80-400 nm, a PDI of less than or equal to 0.30, and a minimum film formation temperature (MFFT) of-10 to 12 DEG C. The coating prepared by the invention has excellent high-humidity barrier stability (WVTR is less than or equal to 65g / m.d), low-temperature rapid heat sealability, water resistance, oil resistance and complete recoverability, does not contain PFAS, is an ideal alternative scheme of a traditional PE (Polyethylene) spraying film, and is suitable for the fields of food packaging paper, paper cups, bowls and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer chemistry and materials science, specifically relating to reactive compatibility ACR-PHA core-shell latex and its applications. Background Technology

[0002] With increasing global emphasis on sustainable development, "paper instead of plastic" has become a significant trend in the packaging industry. To impart the necessary water-blocking, oxygen-blocking, and grease-resistant properties to fibrous substrates such as paper and paperboard, a functional barrier coating is typically applied to their surface. Traditionally, polyethylene (PE) lamination has been the primary means of achieving this function; however, its recycling after being combined with paper fibers is difficult and does not meet the requirements of a circular economy.

[0003] Therefore, the development of biodegradable and recyclable waterborne emulsion coatings has become a research hotspot. Polyhydroxyalkanoates (PHAs) are a class of aliphatic polyesters synthesized by microorganisms, possessing excellent biodegradability and good gas barrier properties, making them one of the ideal materials to replace traditional plastics. However, PHAs themselves have high crystallinity, are brittle and hard, and have high film-forming temperatures, making it difficult to directly form continuous films at low temperatures in the form of aqueous dispersions. Acrylic ester (ACR) polymer emulsions, on the other hand, have advantages such as low film-forming temperatures, good flexibility, and strong adhesion, but their barrier properties are relatively poor. To combine the advantages of both, existing technologies typically employ the method of physically blending PHA dispersions with ACR emulsions. However, due to the large polarity difference between PHA and ACR, they are thermodynamically incompatible, resulting in significant interfacial defects in the blended coating. These defects not only weaken the mechanical strength of the coating but also become rapid penetration channels for water and oxygen molecules, leading to unstable barrier properties and unsatisfactory heat-sealing performance.

[0004] The existing technical approaches in this field can be mainly classified into the following categories, but all of them have obvious limitations:

[0005] The first category is PHA emulsion or aqueous dispersion technology. For example, patents such as US5977250 A, CA 2239980 C, and US 6025028 A, which involve PHA latex / aqueous dispersions for paper coating, primarily contribute by solving the problem of aqueous preparation and dispersion of highly crystalline PHA, proposing that PHA latex can be used in paper processing. However, these technologies are essentially still single-phase PHA systems or simple physically stable dispersions. Their core is stabilizing PHA itself, and they do not address the complex issues of low-temperature film formation, interfacial compatibility, and high-humidity barrier stability by forming a "reactive, compatible core-shell structure" with ACR polymers. Therefore, they cannot fundamentally overcome the inherent brittleness of pure PHA coatings or the interfacial defects of physically blended systems.

[0006] The second category is reactive acrylic latex technology. For example, US 2016 / 0319169 A1 and US 8809447 B2 disclose the use of reactive monomers such as acetoacetoxyethyl methacrylate (AAEM), EP 489941 B1 discloses oxyazoline-containing emulsions, and WO 2016 / 060159 A1 discloses silane-containing emulsions. These technologies provide a rich chemical "toolbox" for achieving self-crosslinking of latex or adhesion to substrates. However, the teachings of these documents do not apply the reactive chemistry described to constructing interfacial covalent bridges between ACR and PHA, two incompatible polymers. Their application scenarios do not address the compatibility of ACR-PHA composite systems, nor do they specifically address the high moisture barrier performance required for paper-based packaging.

[0007] The third category is particle morphology engineering technology. For example, patents such as US 7875654 B2, US 2019 / 0177458 A1, and US12023641 systematically describe methods for preparing Janus particles or raspberry-shaped particles. However, these morphology engineering technologies are mainly applied in fields such as coating self-organization or decoration, and their core purpose is not to construct functional barrier layers. They do not combine these complex morphologies with ACR-PHA reactive compatibility systems to address the high-moisture barrier and recyclability challenges unique to the food contact packaging field.

[0008] In summary, the existing technology has not yet revealed a comprehensive solution that can organically combine the above three types of technologies, namely, effectively combining PHA and ACR through interfacial chemical bonds to construct composite particles with a clear core-shell, gradient core-shell, raspberry-shaped or Janus structure, thereby achieving stable and excellent barrier performance under high humidity conditions, meeting the requirements for low-temperature rapid heat sealing, and ensuring material recyclability within a single latex coating system. Summary of the Invention

[0009] This invention provides a reactive compatibility ACR-PHA core-shell latex and its application, aiming to solve the problems of poor compatibility and numerous interface defects in the physical blending of polyhydroxy fatty acid esters and acrylate polymers in the prior art, which leads to unstable barrier properties, high film-forming temperature and poor heat-sealing performance of the coating.

[0010] This invention employs a synergistic strategy of interface chemistry (e.g., AAEM / GMA / IEM / vinyloxyzoline / alkoxysilane) and particle morphology (e.g., core-shell, gradient core-shell, raspberry, Janus, multi-shell, multi-compartment, core-shell-core); and defines the Z-average particle size as 80–400 nm, PDI ≤ 0.30 (ISO 22412:2025), and / or median diameter D of the volume distribution as measured by non-volatile polymer solids. 50For 80–400nm, D 90 / D 10 A particle dispersion window of ≤3.5 (ISO 13320:2020) and a residual anionic surfactant content limited to no more than 0.10 wt% by MBAS (SM5540C, 2023). After standardized coating / annealing, the coating has a water vapor transmission rate (WVTR) of no more than 65 g / m²·d (ASTM F1249-20, 38°C, 90% RH) and an oxygen transmission rate (OTR) of no more than 120 cm³ / m²·d (ASTM F1927-20, controlled humidity). In a preferred embodiment, the coating achieves a WVTR of no more than 50 g / m²·d and an OTR of no more than 80 cm³ / m²·d. In terms of application, this invention covers wet-over-wet and back-coated COF, and evaluates the sensory properties of the paper base using ISO 1230-1 / -2:2009, verifies migration using GB 31604 and EN 1186 systems, completes total AOF screening using DIN38409-59:2022 / EPA 1621:2024, and evaluates repulping recycling using CEPI Recyclability Laboratory Testmethod, Version 3 (2025-02).

[0011] To achieve the above objectives, this invention provides a reactive, compatible acrylate-polyhydroxyalkanoate core-shell latex, which is an aqueous dispersion containing composite particles. These composite particles possess a core-shell, gradient core-shell, raspberry-shaped multi-core-shell, or Janus heterostructure. This structural design neatly distributes two polymers with different properties within a single particle, forming a clearly defined core and shell phase. The core phase of the composite particle is a polyhydroxyalkanoate, and the shell phase is an acrylate polymer, or vice versa. For example, when the core phase is a polyhydroxyalkanoate, the shell phase is an acrylate polymer, and vice versa. This design utilizes the controllability of emulsion polymerization to construct an ordered microstructure. The interface between the core and shell phases contains covalent chemical bonds, which is the core solution to the phase interface problem. The polyhydroxyalkanoate is selected from poly-3-hydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate). One or more of the following: (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), or medium- to long-chain polyhydroxy fatty acid esters, which are currently common types of biodegradable polyesters in industry; the monomer component of the acrylate polymer comprises:

[0012] At least one main monomer is selected from one or more of C1-C18 alkyl acrylates, C1-C18 alkyl methacrylates, cycloalkyl acrylates, cycloalkyl methacrylates, and aromatic vinyl monomers;

[0013] The monomer component of the acrylate polymer further includes:

[0014] At least one other functional monomer, selected from monomers containing carboxyl, hydroxyl, or amide groups; and / or

[0015] At least one crosslinking monomer, which is a monomer containing at least two polymerizable double bonds.

[0016] And at least one reactive functional monomer that can react with the functional group of the polyhydroxy fatty acid ester to form a covalent chemical bond, wherein the reactive functional monomer is selected from monomers containing an epoxy group, an acetylacetoxy group, an isocyanate group, an oxazoline group or an alkoxysilyl group.

[0017] The composite particles have a Z-average particle size of 80–400 nm, for example, 80 nm, 90 nm, 100 nm, 120 nm, 145 nm, 151 nm, 153 nm, 155 nm, 157 nm, 162 nm, 165 nm, 180 nm, 185 nm, 200 nm, 210 nm, 250 nm, 300 nm, 350 nm, or 400 nm, and a polydispersity index (PDI) not higher than 0.30, for example, 0.08, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.22, 0.26, or 0.30; and / or, the median diameter D of the volume distribution as measured according to ISO 13320:2020. 50 The wavelength is 80–400 nm, and the volume distribution is D. 90 / D 10 Not higher than 3.5. Smaller particle size and narrower particle size distribution are beneficial for forming a denser coating.

[0018] The minimum film-forming temperature of the latex is -10 to 12°C, for example -10°C, -5°C, 0°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C or 12°C, which ensures that it can form a continuous and dense film at a lower baking temperature, thereby saving energy.

[0019] The covalent chemical bonds at the interface originate from reaction products selected from the following reaction pairs: epoxy group / -COOH, epoxy group / -OH, acetylacetoxy group / -NH2, isocyanate group / -OH, oxazoline group / -COOH, alkoxysilane / -OH, carbonyl / hydrazide, maleimide / -SH. Through these efficient chemical reactions, stable chemical linkages can be formed at the core-shell interface under mild emulsion polymerization conditions.

[0020] The grafting ratio (GR) of the shell phase to the core phase, or the grafting ratio (GR) of the core phase to the shell phase, is 10% to 60%, for example, 10%, 15%, 20%, 22%, 25%, 28%, 30%, 40%, 45%, 50%, 53%, 55%, 58%, or 60%. A suitable grafting ratio ensures the stability of the core-shell structure and the effective bonding of the phase interface.

[0021] The acrylate polymers have an acid value of 3–60 mg KOH / g, based on non-volatile solids, for example, 3 mg KOH / g, 5 mg KOH / g, 10 mg KOH / g, 15 mg KOH / g, 20 mg KOH / g, 30 mg KOH / g, 40 mg KOH / g, 50 mg KOH / g, or 60 mg KOH / g, to ensure the stability of the emulsion and its compatibility with other additives.

[0022] The acrylate polymers have a hydroxyl value of 0–50 mg KOH / g, based on non-volatile solids, for example, 0 mg KOH / g, 5 mg KOH / g, 10 mg KOH / g, 15 mg KOH / g, 20 mg KOH / g, 25 mg KOH / g, 30 mg KOH / g, 40 mg KOH / g, or 50 mg KOH / g. The presence of hydroxyl groups can further improve the adhesion of the coating.

[0023] For sustainability reasons, the non-volatile solids of the latex contain no less than 70% (preferably 72%–80%) bio-based carbon (BCC) and are free of artificially added per- and polyfluoroalkyl substances (PFAS).

[0024] To ensure the water resistance and stability of the coating, the residual anionic surfactant (MBAS, converted to LAS equivalent) in the latex, based on non-volatile solids, shall not exceed 0.10 wt%, for example, 0.01 wt%, 0.05 wt%, or 0.10 wt%.

[0025] To ensure product safety, the total residual monomer content in the latex is not higher than 0.03 wt%, for example, 0.01 wt%, 0.02 wt%, or 0.03 wt%.

[0026] To ensure its commercial application value, the latex is stored at 40°C for 12 weeks, and its D... 50 The change rate is no higher than 3%, and the viscosity change rate is no higher than 10%, demonstrating excellent storage stability.

[0027] The present invention also provides a coating method comprising applying the core-shell latex described in any of the preceding claims to a substrate. The substrate is selected from paper, paperboard, molded fibers, plastic film, or nonwoven fabric, and has a wide range of applications. The dry basis coating weight is 6–12 g / m², for example, 6 g / m², 7 g / m², 8 g / m², 9 g / m², 10 g / m², 11 g / m², or 12 g / m².

[0028] The present invention also provides an article prepared by the above method. The article exhibits excellent comprehensive performance. When measured at 120°C, 0.30 MPa, and 1.0 s, the heat-sealing peel strength is not less than 1.8 N / 15 mm, for example, 1.8 N / 15 mm, 1.9 N / 15 mm, 2.0 N / 15 mm, or 2.1 N / 15 mm, and the heat-sealing initiation temperature, also known as the sealing temperature, is not higher than 110°C, for example, 110°C, 105°C, or 100°C.

[0029] The water vapor transmission rate (WVTR) of the product, measured at 38°C and 90% RH, is no higher than 65 g / m²·d, for example, 65 g / m²·d, 60 g / m²·d, 55 g / m²·d, 50 g / m²·d, 49 g / m²·d, 48 g / m²·d, 47 g / m²·d, 45 g / m²·d, or 44 g / m²·d, and at 23°C and 0% RH, it is also no higher than 65 g / m²·d. The oxygen permeability (OTR) measured under RH conditions should not exceed 120 cm³ / m²·d, for example, 120 cm³ / m²·d, 100 cm³ / m²·d, 95 cm³ / m²·d, 90 cm³ / m²·d, 80 cm³ / m²·d, 78 cm³ / m²·d, 75 cm³ / m²·d, 72 cm³ / m²·d, 70 cm³ / m²·d, or 68 cm³ / m²·d.

[0030] The product is Cobb 60 Not higher than 16g / m², such as 16g / m², 15g / m² or 14g / m², with a Kit value of not less than 10 for grease resistance and a resistance to methyl ethyl ketone (MEK) abrasion cycles of not less than 100.

[0031] Therefore, the articles described in this invention can be used for food packaging, personal care product packaging, medical device packaging, or as paper cups, paper bowls, food wrapping paper, and molded fiber products.

[0032] Compared with the prior art, the use of this invention can achieve the following significant beneficial effects:

[0033] Fundamentally solves the compatibility problem: By introducing covalent chemical bonds at the interface between ACR and PHA, the thermodynamic incompatibility problem during the physical blending of the two polymers is fundamentally solved, phase interface defects are eliminated, and the coating becomes more uniform and dense.

[0034] Excellent and stable barrier performance: By eliminating the "highway" of water and oxygen permeation through interface defects, the coating of this invention can still maintain extremely low water vapor and oxygen permeability even under harsh conditions of high temperature and high humidity, and its barrier stability far exceeds that of physical blending systems.

[0035] Superior low-temperature heat-sealing performance: The regular core-shell structure and flexible ACR shell phase (or core phase) give the coating a lower minimum film-forming temperature and heat-sealing initiation temperature, enabling rapid and robust heat sealing at lower temperatures, with an ideal "fiber pull-out" failure mode, meeting the needs of high-speed packaging production lines.

[0036] Fully recyclable and environmentally friendly: The coating can be easily separated from paper fibers under standard repulping conditions, with a high fiber recycling rate and no adhesion issues, achieving full recyclability of the material, meeting the requirements of the circular economy, and is an ideal green alternative to traditional PE coating. Detailed Implementation

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

[0038] Main reagents and raw materials:

[0039] Table 1. Names, models, and manufacturers of main reagents and raw materials:

[0040]

[0041] Main analytical and testing instruments:

[0042] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments and equipment:

[0043]

[0044] Main testing standards:

[0045] Table 3. Main Test Items and Standard Numbers:

[0046]

[0047] General preparation process:

[0048] Preparation of PHA aqueous dispersion:

[0049] Pre-wetting: Using deionized water as the medium, add 0.5–1.0 wt% of alkyl polysaccharide (APG) and stir at 25–30°C for 5 minutes.

[0050] Powder incorporation: Slowly add PHA powder at 10,000–12,000 rpm until the target solid content is 30–35 wt%, and continue shearing for 10 minutes.

[0051] High-pressure homogenization: Homogenize the pre-dispersed liquid 3–5 times at 600–800 bar, with an outlet temperature <50℃.

[0052] Stabilize the solution: If necessary, add 0.1 wt% hydroxyethyl cellulose and allow to stand to remove bubbles.

[0053] Quality control: Particle size D 50 PDI (ISO 22412:2025), zeta potential (ISO 13099-2:2025), and MBAS (SM5540C, equivalent to linear alkylbenzene sulfonate (LAS)) ≤0.20 wt% as non-volatile solids.

[0054] Simulated vomit solution (homemade):

[0055] Formula: Sodium carboxymethyl cellulose 2.0 wt%, NaCl 0.9 wt%, pH adjusted to 2.0 with HCl, and the remainder is deionized water.

[0056] Steps: Dissolve with magnetic stirring at room temperature, adjust pH to 2.0±0.1, filter at 0.45μm and set aside.

[0057] Example:

[0058] Route A: MAH-PHA (core) / ACR (shell).

[0059] Example 1: Preparation of MAH-PHA: 100 parts of PHA powder (PHBV) and 5 parts of maleic anhydride (MAH) were fed into a twin-screw reactive extruder (temperature range 180–195℃, nitrogen protection), with 0.5 parts of dicumyl peroxide (DCP) as the initiator. The screw speed was 150 rpm, and the residence time was 3–5 min. The extrudate was cooled and granulated to obtain MAH-PHA powder. This entire process did not use organic solvents. 30 parts of MAH-PHBV were briefly swollen and dispersed in ethyl acetate (solvent / solid mass ratio ≤1:1, within 30 min). Emulsifier and water were added, and the mixture was homogenized using a high-pressure homogenizer to prepare a MAH-PHA micro-dispersion. The dispersion was transferred to a reactor and heated to 80℃. A monomer emulsion consisting of 60 parts of butyl acrylate (BA), 8 parts of methyl methacrylate (MMA), and 2 parts of glycidyl methacrylate (GMA), along with a potassium persulfate (KPS) initiator solution, was added dropwise. After the addition is complete, keep warm, adjust the pH and bring the volume to 45% solids. After the reaction, remove the solvent under reduced pressure (≤30kPa) and 50–60℃ and recycle to ensure that the residual ethyl acetate in the finished product is no more than 10mg / kg (according to HS-GC-MS).

[0060] Example 2: Core phase preparation was the same as in Example 1. The shell phase monomer formulation was changed to: 55 parts BA, 5 parts MMA, and 10 parts GMA. The remaining process conditions were the same as in Example 1.

[0061] Example 3: The core phase preparation was the same as in Example 1, but the amount of MAH-PHBV was 50 parts. The shell phase monomer formulation was changed to: 45 parts BA, 3 parts MMA, and 2 parts GMA to achieve a 50:50 core-shell-solid ratio. The remaining process conditions were the same as in Example 1.

[0062] Example 6: The route is the same as in Example 1, using a type A process. The core phase preparation is the same as in Example 1. The shell phase monomer formulation is changed to: 58 parts BA, 10 parts MMA, and 2 parts acetoacetoxyethyl methacrylate (AAEM), without using GMA. The remaining process conditions are the same as in Example 1.

[0063] Example 7: The route is the same as in Example 1, using a type A process to prepare a raspberry-shaped multi-core shell structure. The core phase preparation is the same as in Example 1. During the shell-phase polymerization stage, the nucleation point is controlled by adjusting the emulsifier dosage and dropping rate, so that the ACR particles generated by polymerization preferentially deposit on the surface of MAH-PHBV core particles, forming a satellite-like structure. The shell-phase monomer formulation is: 52 parts BA, 10 parts MMA, and 8 parts GMA. The remaining process conditions are the same as in Example 1.

[0064] Example 9: The route is the same as in Example 2, using a type A process, but the core phase uses a PHB homopolymer. 30 parts of maleic anhydride-grafted modified PHB (MAH-PHB) were prepared into an aqueous dispersion as the core phase according to the method in Example 1. The shell phase monomer formulation is the same as in Example 2: 55 parts BA, 5 parts MMA, and 10 parts GMA. The remaining process conditions are the same as in Example 1.

[0065] Route B: ACR (core) / PHA (shell, gradient or heterostructure).

[0066] Example 4: Water and emulsifier were added to a reaction vessel and the temperature was raised to 80°C. A mixture of core monomers consisting of 25 parts BA, 5 parts MMA, and 1 part GMA, along with an aqueous KPS solution, was added dropwise to form an ACR core. Then, a mixed emulsion of 30 parts epoxy-modified PHBV, which was briefly swollen and dispersed in ethyl acetate, and 39 parts BA and 5 parts MMA was added dropwise. After maintaining the temperature, the mixture was cooled and discharged, forming a gradient shell. After the reaction, residual solvent was removed and controlled according to the conditions described in Example 1.

[0067] Example 5: The route is the same as in Example 4, using process type B. To achieve a core-shell solid ratio of 21:79, a core-monomer mixture consisting of 18 parts BA, 2 parts MMA, and 1 part GMA (approximately 3 wt% of the total ACR monomers) is first added dropwise to a KPS aqueous solution to form the ACR core. Then, a mixed emulsion of 30 parts epoxy-modified PHBV, short-term swollen and dispersed in ethyl acetate, and 44 parts BA and 5 parts MMA is added dropwise. The remaining process conditions are the same as in Example 4.

[0068] Example 8: A variant of the type B process was used to prepare Janus heterostructures. First, a mixture of core monomers consisting of 30 parts BA, 5 parts MMA, 2 parts 2-isopropenyl-2-oxazoline (IPOX), and an aqueous KPS solution was added dropwise to form an ACR core. Then, 30 parts of 3-(trimethoxysilane)propyl methacrylate (MEMO) modified PHBH powder were subjected to limited swelling with a small amount of solvent, mixed with 30 parts BA and 3 parts MMA, and subjected to a second-stage polymerization in the presence of the ACR core. Phase separation was promoted by controlling the polymerization conditions, ultimately forming Janus particles with ACR on one side and PHBH on the other. After the reaction, residual solvent was removed and controlled according to the conditions described in Example 1.

[0069] Example 10: The route is the same as in Example 5, using a type B process, but the shell phase uses a PHB homopolymer. To achieve a core-shell solids ratio of 21:79, a mixture of core monomers consisting of 18 parts BA, 2 parts MMA, and 1 part GMA is first added dropwise with an aqueous KPS solution to form an ACR core. Then, a mixed emulsion of 30 parts epoxy-modified PHB dispersed in ethyl acetate for a short time, and 44 parts BA and 5 parts MMA is added dropwise to form a gradient shell. The remaining process conditions are the same as in Example 4.

[0070] Comparative example:

[0071] Comparative Example 1 (non-reactive monomer): The formulation is the same as in Example 1, but the GMA in the shell phase monomer is replaced by an equal amount of MMA.

[0072] Comparative Example 2 (pure ACR): emulsion polymerization was carried out directly without the addition of MAH-PHA core.

[0073] Comparative Example 3 (physical blending): MAH-PHA dispersion and pure ACR emulsion were prepared separately and mechanically mixed at a solid content ratio of 30:70.

[0074] Comparative Example 4 (Mineral-filled polyolefin extrusion coating): Referring to US10420370B2, an HDPE-PE blend containing 40 wt% calcium carbonate was prepared and coated onto cardboard by extrusion.

[0075] Comparative Example 5 (SBR / Wax Blend Emulsion): A blend emulsion of styrene-butadiene rubber (SBR) and paraffin wax was prepared and coated.

[0076] Overview of formulations and structural characterization of examples and comparative examples

[0077] To systematically elucidate the core technology of this invention, Table 4 integrates the formulation design, process route, and core structural characterization data of each embodiment and comparative example. This section aims to clearly demonstrate, by directly correlating formulation variables with structural characterization results, that this invention successfully constructs a stable core-shell structure with the expected physicochemical properties through interfacial covalent bonding by introducing reactive monomers.

[0078] Experimental Description and Characterization Methods: All samples in Table 4 were prepared according to the methods described above. The core characterization methods used include:

[0079] Quantification of interfacial reactions: The conversion rate of GMA was determined by epoxy equivalence titration to quantitatively demonstrate the occurrence of interfacial chemical reactions.

[0080] Thermodynamic analysis: The crystallization enthalpy (ΔHc) of the PHA component was determined by differential scanning calorimetry (DSC) to assess the binding effect of interfacial bonding on the movement of PHA chain segments.

[0081] Dynamic mechanical analysis: The storage modulus (E') of the material at 25°C was determined by DMA to characterize the effect of interfacial interactions on the material's stiffness.

[0082] Colloidal stability analysis: The stability of core-shell particles is assessed by measuring the zeta potential of the emulsion. Some samples, due to their formulation or physical form, are not suitable for specific testing items and are indicated in the table.

[0083] Table 4 summarizes the formulation, process, and core structure characterization data of the examples and comparative examples:

[0084]

[0085] Analysis: Table 4 intuitively establishes the necessary connection between formulation design and material microstructure, providing decisive data support for the core innovation of this invention.

[0086] First, from a formulation design perspective, all examples (1-10) introduced reactive functional group monomers (such as GMA, AAEM, IPOX, etc.) into the ACR or PHA phase, while Comparative Examples 1 and 3 lacked such a design. This key difference is directly reflected in the structural characterization data: all examples using GMA showed extremely high conversion rates (>88%), demonstrating the efficient occurrence of the expected interfacial chemical reaction; while Comparative Examples 1 and 3 showed almost no reaction. This chemically confirms the formation of covalent bonds.

[0087] Secondly, the formation of interfacial covalent bonds directly leads to the construction of a stable core-shell structure, which is verified by thermodynamic and dynamic mechanical data. Compared with the phase-separated PHA in Comparative Examples 1 and 3, the enthalpy of crystallization (ΔHc) of PHA in all examples is significantly reduced, clearly indicating that the interfacial bonding effectively restrains the movement of PHA molecular chains and inhibits their crystallization. This is a typical characteristic of a successful core-shell structure and strong interfacial interaction. At the same time, the storage modulus (E') of all examples is significantly higher than that of Comparative Examples 1, 3, and 5, which serve as references, confirming that the strong interface formed by chemical bonding plays an effective role in stress transfer and reinforcement, improving the overall rigidity of the composite material.

[0088] Finally, the stable core-shell structure also endows the emulsion with excellent colloidal stability. All the emulsions in the examples have high absolute values ​​of zeta potential (>33mV), which are much higher than those of Comparative Example 3 of physical blend and Comparative Example 5 of SBR / wax emulsion, indicating that the surface charge of the formed core-shell particles is uniform, the system is stable, and phase separation will not occur.

[0089] Application Example 1: Overall performance comparison.

[0090] This application example aims to comprehensively evaluate the basic physicochemical properties of the coatings in the various embodiments and comparative examples. Each sample was coated on 150 g / m² cardstock with a dry coating basis weight of approximately 10 g / m². After drying at 120°C for 60 s, its particle size distribution, minimum film-forming temperature, grafting rate, heat-sealing initiation temperature, and critical barrier, water, oil, and solvent resistance properties were tested.

[0091] Table 5: Overall Performance Comparison

[0092]

[0093] Analysis: Table 5 shows that all examples formed latexes with narrow particle size distribution (PDI≤0.26) and low MFFT (≤12℃), thanks to the regularity of the core-shell structure. Regarding key performance indicators, the WVTR and OTR of the examples were significantly better than those of Comparative Examples 1 and 3 (without chemical bonding) and Comparative Example 2 (with pure ACR), demonstrating the synergistic effect of the PHA barrier phase and the ACR film-forming phase. Notably, Examples 9 and 10 (based on PHB) exhibited barrier performance comparable to or even slightly better than that of Examples 2 and 5 (based on PHBV), attributed to the higher crystallinity and regularity of the PHB homopolymer, further enhancing the barrier effect. All examples demonstrated excellent resistance to water (Cobb), oil (Kit), and solvents (MEK), while Comparative Examples 1, 2, 3, and 5 showed significant deficiencies in these aspects.

[0094] Application Example 2: Heat sealing performance.

[0095] This application example aims to evaluate the heat-sealing performance of the coating, a key indicator in packaging applications. According to ASTM F88 / F88M-23 standards, the heat-sealing peel strength of the coating was tested at different temperatures under a pressure of 0.30 MPa and a heat-sealing time of 1 second, and the peeling patterns were observed to determine the reliability of the heat seal.

[0096] Table 6 Heat sealing performance:

[0097]

[0098] Analysis: The heat-sealing data in Table 6 shows that all examples achieved effective heat sealing at relatively low temperatures (100-110°C) and achieved excellent peel strength of over 1.8 N / 15 mm at 120°C. More importantly, the peeling mode was "fiber pull-out," meaning that the adhesion between the coating and the paper substrate, as well as the cohesive force of the coating itself, were greater than the interlayer strength of the paper, which is an ideal heat-sealing effect. Conversely, Comparative Examples 1 and 3, due to poor interfacial compatibility and weak coating cohesive force, experienced interfacial peeling at extremely low strength. Comparative Examples 4 and 5 required higher temperatures to initiate sealing and lacked sufficient strength, failing to meet the needs of high-speed packaging applications. For further demonstration of heat tack strength and short-term sealing temperature window, please refer to Application Examples 14 and 18, which will not be elaborated here.

[0099] Application Example 3: High Humidity Aging and Barrier Stability.

[0100] This application example aims to examine the barrier performance stability of the coating under harsh, high-humidity environments, a key indicator of material reliability. Coated samples were aged for 7 days at 38°C and 90% RH, and changes in water vapor transmission rate (WVTR) were compared. Simultaneously, according to ASTM F1927-20, the difference in oxygen transmission rate (OTR) under dry (0% RH) and wet (80% RH) conditions was tested to assess its sensitivity to humidity.

[0101] Table 7 High Humidity Aging and Barrier Stability:

[0102]

[0103] Analysis: The results in Table 7 are one of the core advantages of this invention. Under harsh high humidity (38°C, 90% RH) conditions, the WVTR growth rate of all embodiments was less than 20%, and the OTR growth rate was less than 45%, demonstrating excellent barrier stability. This is attributed to the elimination of interfacial defects through chemical bonding, which effectively prevents the aggregation and penetration of water molecules at the interface, thereby protecting the barrier performance of the PHA phase. In contrast, the barrier performance of Comparative Examples 1 and 3 deteriorated sharply under high humidity (growth rate > 60%), which is a fatal weakness of physically blended systems. Comparative Example 4 (polyolefin) showed stable WVTR, but its OTR was extremely poor. Comparative Example 5 (SBR / wax) also performed poorly under high humidity.

[0104] Application Example 4: Re-pulping compatibility.

[0105] This application example aims to evaluate the recyclability of coated paper, an important criterion for measuring its environmental friendliness. Following CEPI's latest laboratory recyclability testing method (Version 3.0, 2025-02), a repulping experiment was conducted on the coated samples. The final fiber recovery rate, coarse residue rate, and adhesion grade were measured to determine whether the coating could effectively separate from the paper fibers in a standard recycling process.

[0106] Table 8 Re-pulping Compatibility:

[0107]

[0108] Analysis: The recycling performance test results in Table 8 show that the coated paper of all embodiments of the present invention can be easily separated from paper fibers in a standard repulping process, with high fiber recovery rate, and the coarse residue rate and adhesion grade all meet industry standards, demonstrating excellent recyclability. This is comparable to the performance of pure ACR coating (Comparative Example 2). However, Comparative Example 3 (physical blending) produced more adhesion due to coating fragmentation caused by phase separation. Comparative Example 4 (extrusion coating) and Comparative Example 5 (SBR / wax) failed the test completely, causing serious screen clogging and adhesion problems, which do not meet the requirements of a circular economy.

[0109] Application Example 5: Wet-over-wet double layer + COF back coating / anti-curling verification.

[0110] This application example aims to verify the suitability of the latex of the present invention in complex coating processes, particularly its performance in the production of double-coated cup and bowl preforms. By applying a thin coating to the back of the paperboard, its ability to control the coefficient of friction (COF) and balance paper stress, preventing curling, was tested. This is crucial for subsequent printing, die-cutting, and automated cup / bowl manufacturing processes.

[0111] Table 9. Back Coating Friction Coefficient and Anti-curling Properties:

[0112]

[0113] Analysis: The results in Table 9 verify the applicability of the latex of this invention in complex coating processes. As a back coating, it provides a moderate static and dynamic coefficient of friction (μs / μk in the range of 0.3-0.5), which is crucial for the smooth feeding of paper in subsequent printing, die-cutting, and cup / bowl making processes. Simultaneously, the presence of the back coating effectively balances the stress on both sides of the paper, significantly improving the curling problem commonly encountered after single-sided coating and ensuring smooth processing. Curling radii R ≥ 500 mm (coated side inwards) measured according to ISO 11556:2005 are all considered 'qualified'.

[0114] Application Example 6: High-temperature accelerated storage 40℃ / 12 weeks.

[0115] Experimental Description: This application example aims to evaluate the storage stability of the emulsion itself, which is an important prerequisite for assessing its commercial application value. Accelerated aging tests were conducted at 40°C for 12 weeks, and the particle size (D) of the emulsion was monitored. 50 Changes in viscosity and other properties are used to predict shelf life and stability under normal conditions.

[0116] Table 10 Emulsion Storage Stability:

[0117]

[0118] Analysis: The accelerated aging test results in Table 10 demonstrate the excellent storage stability of the core-shell latex of this invention. After 12 weeks of storage at 40°C, the particle size and viscosity changes in all examples were within acceptable ranges. This is because the interfacial chemical bonds firmly anchor the core and shell phases together, effectively preventing particle aggregation or phase separation. In contrast, Comparative Example 1 (unbonded) and Comparative Example 5 (SBR / wax) showed poor stability, while Comparative Example 3 (physical blend) experienced severe stratification within a short period, rendering it completely unsuitable for commercial application.

[0119] Application Example 7: Performance Verification under Extreme Operating Conditions.

[0120] Experimental Description: This application example aims to evaluate the coating's performance under extreme usage scenarios, including simulated cold chain transportation (freeze-thaw cycles) and hot food filling (hot oil contact). These tests determine whether the coating can maintain its structural integrity and barrier function under drastic temperature changes and chemical contact.

[0121] Table 11 Extreme operating condition performance:

[0122]

[0123] Analysis: The results in Table 11 show that the coating of this invention can withstand extreme usage scenarios such as cold chain transportation (freeze-thaw cycles) and hot food filling (hot oil contact). Its stable core-shell structure and strong interfacial bonding endow the coating with excellent flexibility and thermal stability, and it will not crack or lose its barrier properties even under drastic temperature changes. The coatings of Comparative Examples 1, 2, 3, and 5 exhibit obvious defects under these conditions, such as cracking, swelling, or dissolution, which limits their application range.

[0124] Application Example 8: Food Contact Migration and Comprehensive Compliance Verification.

[0125] Experimental Description: This application example aims to verify the food contact safety of the material, which is a decisive factor in whether it can be used in food packaging. Comprehensive migration tests were conducted on the coating in accordance with the regulatory systems of China's GB and the European Union's EN, including total migration, migration of specific heavy metals, and screening for the highly concerning perfluorinated compounds (PFAS) and mineral oils (MOSH / MOAH).

[0126] Table 12 Food Contact Migration and Compliance:

[0127]

[0128] Analysis: The compliance test results in Table 12 show that the coatings of all embodiments of this invention meet the stringent regulatory requirements of Chinese GB and EU EN regarding food contact materials. Their total migration and heavy metal migration are far below the limits, and they do not contain harmful substances such as PFAS. The MOSH / MOAH migration risk is extremely low. This is due to the use of high-purity food-grade raw materials in the formulation, and the stable chemical structure effectively inhibits the migration of small molecules. In contrast, Comparative Example 4 (mineral-filled polyolefin) and Comparative Example 5 (SBR / wax) have a risk of exceeding MOSH / MOAH migration limits, raising concerns about their safety.

[0129] Application Example 9: Sensory evaluation.

[0130] Experimental Description: This application example aims to evaluate whether coating materials have an adverse effect on the flavor of food. In accordance with EN 1230-2:2009, a professional sensory evaluation team assessed any unusual odors or tastes that might migrate from the coated samples upon contact with hot water.

[0131] Table 13 Sensory Evaluation:

[0132]

[0133] Analysis: The sensory evaluation results in Table 13 show that the coatings of all embodiments of the present invention exhibited no off-odor or migration after contact with hot water, meeting the sensory requirements for food packaging. However, Comparative Examples 4 and 5 exhibited unpleasant plastic and wax / rubber odors, respectively, which would severely impact the flavor and consumer experience of the food.

[0134] Application Example 10: Outer packaging paper for disposable toothbrushes in hotels.

[0135] Experimental Description: This application example aims to evaluate the potential of this invention in the packaging of non-food personal care products that require high moisture resistance, abrasion resistance, and a good appearance. The overall performance of the coating is tested by simulating the humid and hot environment of a hotel bathroom and the friction that the packaging may experience during transportation and use.

[0136] Table 14 Packaging Performance of Personal Care Products:

[0137]

[0138] Analysis: The results in Table 14 show that, under simulated humid and hot conditions and frequent friction in hotel bathrooms, all samples from the embodiments of this invention maintained low WVTR and controlled OTR, with COF remaining stable within the ideal range of 0.35–0.45. The printability and abrasion resistance met the requirements of ASTM D5264, and there was no odor migration, fully satisfying the functional and sensory requirements of packaging materials for the humid environment of hotel bathrooms. In contrast, Comparative Examples 1, 3, and 5 failed to meet the abrasion resistance standards due to poor coating cohesion; Comparative Examples 4 and 5 exhibited significant odor problems.

[0139] Application Example 11: Outer liner paper for cosmetic trial packs.

[0140] Experimental Description: This application example aims to verify the applicability of the invention in the field of oil- and surfactant-resistant fast-moving consumer goods packaging. By simulating the production and use scenarios of cosmetic sample sachets, the coating's resistance to oily / solvent-based contents, heat-sealing strength, and print adhesion are tested.

[0141] Table 15 Packaging Performance of Fast-Moving Consumer Goods:

[0142]

[0143] Analysis: The results in Table 15 confirm that, under simulated oily / surfactant contents, all samples of the present invention maintained excellent oil resistance (Kit≥12) and solvent resistance (MEK≥100 times). The heat-sealing curves show that it can achieve high-strength adhesion at low temperatures, and has high printing firmness and no odor, fully meeting the stringent requirements of FMCG small bag outer liner paper.

[0144] Application Example 12: Microwave heating performance evaluation.

[0145] Experimental Description: To evaluate the suitability of the material of this invention for microwaveable food packaging, this application example designed a microwave heating test simulating a real-world usage scenario. The test protocol was based on EN 15284:2007 (methodological framework) and reviewed with reference to FPI, Rev.#1, 2013 / 2021. The test established the working conditions and criteria for disposable paper cups / bowls, focusing on the integrity of the coating, leak-proofness, and temperature uniformity for single use. A commercial microwave oven was used to heat the coated paper cups filled with water, and the temperature distribution was monitored using a thermal imager. Simultaneously, the physical changes in the coating and the cup body were visually inspected.

[0146] Table 16 Microwave Heating Performance Evaluation:

[0147]

[0148] Analysis: The results in Table 16 show that the coatings of all embodiments of the present invention maintain excellent structure and coating integrity after being subjected to high-power microwave heating, without leakage, deformation, or blistering. Thermal imaging analysis shows that the surface temperature distribution is uniform (ΔT < 5℃), and no dangerous local hot spots appear. The fundamental reason for this phenomenon is that the stable core-shell interface chemical bonding provides strong interfacial adhesion, effectively resisting the huge vapor pressure generated when water boils and vaporizes at the interface, thereby avoiding coating blistering and delamination. In contrast, the coatings of Comparative Examples 1 and 3 exhibited blistering and delamination due to weak interfacial bonding. The polyolefin system of Comparative Example 4 showed significant local hot spots (ΔT > 18℃), which may pose a safety risk.

[0149] Application Example 13: Suitability assessment of aircraft vomit bags.

[0150] Experimental Description: The core requirements for aircraft vomit bags are instantaneous and sustained liquid impermeability, sufficient mechanical strength, and reliable sealing. This application example uses quantitative burst strength testing (ASTM F1140 / F1140M-20) and highly sensitive dye penetration testing (ASTM F1929-23) to evaluate the performance of the sealing bag made of the material of this invention under internal liquid pressure, in order to determine whether it meets this high-requirement application scenario.

[0151] Table 17. Assessment of the suitability of aircraft vomit bags:

[0152]

[0153] Analysis: The quantitative results in Table 17 strongly demonstrate that the material of this invention is suitable for high-requirement liquid containment applications such as aircraft vomit bags. All samples from the embodiments exhibited burst pressures exceeding 35 kPa, and the failure mode was tearing of the substrate itself, rather than seal or coating failure. This indicates that the strength of the heat-sealed joint exceeds the strength of the paper substrate itself, which is an extremely desirable result. Dye penetration testing further confirmed that the seals of the embodiments were completely sealed, with no micro-leakage channels. In contrast, Comparative Examples 1, 3, and 5 all exhibited burst pressures below 20 kPa, and the failure mode was seal cracking, indicating that their heat-sealing strength was insufficient to withstand liquid pressure.

[0154] Application Example 14: Hot tack properties (ASTM F1921 / F1921M-12(2023)).

[0155] Experimental Description: This application example aims to evaluate the "hot" adhesive strength of the coating after heat sealing and before cooling, i.e., hot tack performance. This metric is crucial for automated packaging processes such as high-speed vertical bag making, determining the immediate integrity of the seal after the packaging contents are filled.

[0156] Table 18 Results of Hot Adhesion Strength Test:

[0157]

[0158] Analysis: The data in Table 18 are highly consistent with the results in Table 6 (cold peel strength) and provide crucial process performance information. All examples exhibited effective hot tack strength at relatively low temperatures of 100–110°C, reaching or exceeding 1.9 N / 15 mm at 120°C, sufficient to withstand the weight of the contents and ensure stable operation of high-speed packaging lines. In contrast, Comparative Examples 1 and 3 showed severely insufficient cohesion in the hot state due to poor interfacial compatibility, exhibiting almost no hot tack strength. This again demonstrates, from a process perspective, the decisive role of interfacial chemical bonding in achieving reliable heat sealing.

[0159] Application Example 15: Water droplet contact angle / wetting properties (TAPPI / ANSI T 458cm-24).

[0160] Experimental Description: This application example quantitatively evaluates the hydrophobicity and wettability of a coating by measuring the contact angle of a water droplet on the coating surface and its change over time. A high initial contact angle and a low angular attenuation rate generally indicate better instantaneous water-repellent performance and more stable barrier properties.

[0161] Table 19 Results of water droplet contact angle test:

[0162]

[0163] Analysis: The results in Table 19 clearly show that the coating surfaces of all examples exhibit excellent hydrophobicity (initial contact angle θ0 > 102°) and slow contact angle decay within 10 s. This indicates that water droplets are difficult to spread and penetrate on the coating surface, consistent with the excellent Cobb values ​​in Table 5. In contrast, Comparative Examples 1, 2, and 3 show stronger surface hydrophilicity and rapid water droplet spread, which is related to their incomplete interfacial structure and high residual surfactant content, contributing to the instability of their high-humidity barrier properties.

[0164] Application Example 16: Blocking Load (ASTM D3354-21).

[0165] Experimental Description: This application example aims to evaluate the tendency of coatings to stick together (i.e., "blocking") under pressure and temperature. Low blocking properties are crucial for the storage, transportation, and subsequent printing and processing of roll materials, preventing damage to the coating surface.

[0166] Table 20 Results of the adhesive load test:

[0167]

[0168] Analysis: The data in Table 20 show that the coatings in all embodiments exhibit extremely low resistance to adhesion (load < 50 g / 100 cm²), meaning that the coated paper rolls are less prone to sticking during storage and transportation. This is due to the complete core-shell structure and strong interfacial bonding, resulting in a stable surface phase. In contrast, Comparative Examples 1, 3, and 5 are highly susceptible to adhesion under temperature and pressure conditions due to phase separation or low molecular weight wax migration, with resistance loads far exceeding acceptable limits—an unacceptable defect in industrial production.

[0169] Application Example 17: Quantitative assessment of anti-curling (ISO 11556:2005).

[0170] Experimental Description: This application example aims to quantitatively evaluate the curling degree of paper after single-sided coating. Good anti-curling properties are crucial to ensuring the smooth operation of paper in subsequent processes such as printing and die-cutting.

[0171] Table 21 Results of anti-curling performance test:

[0172]

[0173] Analysis: The results in Table 21 show that the curl radius R of all examples is greater than or equal to 500 mm, which can be judged as "qualified against curling", indicating that the shrinkage stress of the coating and the paper substrate is well matched. In contrast, Comparative Examples 1, 2, 3 and 5 all showed obvious curling (R < 350 mm), while Comparative Example 4, which uses the extrusion coating process, showed the most severe curling, which is consistent with industrial production experience.

[0174] Application Example 18: Heat sealing process window mapping (ASTM F88 / F88M-23).

[0175] Experimental Description: This application example aims to plot the onset temperature curves for different heat-sealing times to map the material's actual "process window." A wider process window (i.e., maintaining a lower onset temperature even at shorter heat-sealing times) implies higher production efficiency and greater tolerance to equipment fluctuations.

[0176] Table 22 Test results of heat sealing process window:

[0177]

[0178] Analysis: The data in Table 22 clearly demonstrates the significant advantages of the embodiments of the present invention in low-temperature rapid heat sealing. Even with an extremely short heat sealing time of 0.3 s, the initial sealing temperature of most embodiments remains around 110°C, far lower than all comparative examples. This proves that the material of the present invention has a wide processing window and can adapt to the requirements of high-speed automated packaging production lines. This result, together with the results of Application Example 14 (hot tack performance) and Application Example 2 (cold peel strength), forms a complete chain of evidence that corroborates each other.

[0179] Application Example 19: Bio-based carbon content (BCC, ASTM D6866-24a).

[0180] Experimental Description: The proportion of bio-based carbon in the non-volatile solids of the sample was determined according to ASTM D6866-24a radiocarbon dating (AMS mode). The non-volatile solids of the sample were dried at 105°C under normal pressure before sample preparation.

[0181] Table 23 Results of Bio-based Carbon Content (BCC) Test:

[0182]

[0183] Analysis: The data in Table 23 clearly show that the bio-based carbon content (BCC) in the non-volatile solids of all embodiments exceeds 70%, reaching a maximum of 77.3%. This strongly demonstrates that the technical route of this invention successfully and efficiently integrates the biomass-derived PHA component into the final material. In contrast, the BCC values ​​of all comparative examples are significantly lower, especially those of Comparative Example 4 (HDPE / PE) and Comparative Example 5 (SBR / wax), which are entirely based on petrochemical feedstocks, with BCC values ​​of 0.0% and 5.6%, respectively. This result highlights the significant advantages of this invention in achieving high bio-based content in materials, meeting the requirements of sustainable development and environmental protection.

[0184] Application Example 20: Residual anionic surfactant (MBAS, SM5540C, LAS equivalent).

[0185] Experimental instructions: Standard Methods 5540C (24th, 2023) MBAS method was used. The weight was converted to LAS equivalent and reported as the percentage of non-volatile solids by mass. Methyl blue and chloroform reagents were prepared according to the methodology.

[0186] Table 24 Residual Anionic Surfactants (MBAS) Test Results:

[0187]

[0188] Analysis: The results in Table 24 show that the residual anionic surfactant content in the latex of all examples, based on non-volatile solids, was controlled at an extremely low level of 0.04% to 0.09%, far lower than that of the comparative examples (0.18%–0.26%). This low residual surfactant content is crucial for the coating's water resistance and barrier stability under high humidity conditions, as it reduces hydrophilic substances in the coating, thereby decreasing the possibility of water molecule penetration. This result also indirectly confirms the high efficiency and cleanliness of the core-shell structure synthesis process of this invention, which is one of the key factors in achieving excellent and stable barrier performance.

[0189] Application Example 21: Total residual monomers (HS-GC-MS / LC-MS / MS, stoichiometric summation).

[0190] Experimental Description: Quantitative methods were established for common monomers (BA, MMA, GMA, AAEM, IPOX, etc.): Volatile / Semi-volatile: HS-GC-MS, internal standard method; Non-volatile / Polar: LC-MS / MS, multiple reaction monitoring; Dry membrane extraction (methanol / toluene) was used, with a blank paper base as a control. The report shows the percentage of non-volatile solids (sum of the concentrations of each monomer).

[0191] Table 25 Results of Total Residual Monomer Tests:

[0192]

[0193] Analysis: The data in Table 25 confirm the high efficiency of the emulsion polymerization process of this invention. The total residual monomer content in all examples is no higher than 0.030 wt%, meeting the stringent safety standards for food contact materials. This indicates a very high monomer conversion rate, thanks to the well-ordered core-shell structure and optimized reaction conditions, effectively avoiding odor problems and migration risks that may arise from small molecule residues. In contrast, the residual monomer content in the comparative examples is generally higher (0.056%–0.083%), which is an unacceptable deficiency in commercial applications, especially in the food packaging field.

[0194] Experimental Results and Analysis:

[0195] This invention successfully solves the key pain points of existing technologies by constructing a reactive core-shell structure inside ACR-PHA composite particles.

[0196] In terms of emulsion performance, all examples (including systems based on PHBV, PHBH, and PHB) formed D 50 The narrow particle distribution (PDI ≤ 0.26) in the 80-220 nm range and the ideal MFFT within the -10 to 12 °C window demonstrate the universality and controllability of this synthetic route. Examples 9 and 10, based on PHB homopolymers, exhibit performance comparable to or even slightly superior in barrier properties to the copolymer-based examples. This fully illustrates that the core technology of this invention—interfacial chemical bonding—is a platform technology applicable to various types of PHB, greatly expanding its application potential.

[0197] In terms of coating performance, the initial sealing temperature of all embodiments did not exceed 110°C, and high peel strength (>1.8 N / 15 mm) was achieved within a wide temperature window of 100–130°C, with the ideal fiber pull-out mode of failure. This contrasts sharply with the interfacial peeling and low strength commonly observed in the comparative examples, highlighting the decisive role of interfacial chemical bonds in improving heat-sealing performance.

[0198] Regarding the critical barrier performance, the embodiments of the present invention exhibit extremely low WVTR growth rate (<20%) after high humidity aging, and OTR is minimally affected by humidity, demonstrating excellent performance stability. This is because the interfacial chemical bonds effectively eliminate the permeation channels of small molecules such as water and oxygen, protecting the integrity of the PHA barrier phase under high humidity conditions.

[0199] In terms of recycling performance, the embodiments of the present invention exhibit excellent resizing compatibility, meeting the requirements of the circular economy, while the extrusion coating and SBR / wax systems in the comparative examples do not meet the recycling standards at all.

[0200] Furthermore, the superiority of the material of this invention was fully verified in two demanding application examples. In the microwave heating test (Application Example 12), the coating of this invention successfully resisted water vapor pressure due to its strong interfacial adhesion, avoiding delamination and blistering. Thermal imaging confirmed that it had no dangerous localized overheating points, demonstrating excellent safety. In the suitability evaluation of aircraft vomit bags (Application Example 13), quantitative burst pressure testing showed that the heat-sealing strength of the coating of this invention exceeded that of the paper substrate itself, capable of withstanding internal pressure exceeding 35 kPa. Dye penetration testing proved its absolute sealing reliability, meeting the liquid tightness requirements under extreme conditions.

[0201] In summary, by constructing a reactive core-shell structure, this invention successfully combines the high barrier properties of PHA with the excellent film-forming properties of ACR. Through interfacial chemical bonding, the compatibility problem is fundamentally overcome, resulting in a novel environmentally friendly barrier material with comprehensive performance (especially barrier stability, low-temperature heat sealing, recyclability, and reliability in extreme application scenarios) that far surpasses existing physical blending, extrusion coating, and SBR / wax technologies.

[0202] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A reactive, compatible acrylate-polyhydroxyalkanoate core-shell latex, wherein the core-shell latex comprises an aqueous dispersion of composite particles, characterized in that: The composite particles have core-shell, gradient core-shell, raspberry-shaped multinucleate shell, Janus heterostructure, core-shell-core, multi-shell or multi-compartment structure; The core phase of the composite particles is a polyhydroxy fatty acid ester, and the shell phase is an acrylate polymer, or the core phase is an acrylate polymer, and the shell phase is a polyhydroxy fatty acid ester. The interface between the core phase and the shell phase contains covalent chemical bonds; The polyhydroxy fatty acid ester is selected from one or more of poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), or medium- and long-chain polyhydroxy fatty acid esters; The monomer component of the acrylate polymer comprises: At least one main monomer is selected from one or more of C1-C18 alkyl acrylates, C1-C18 alkyl methacrylates, cycloalkyl acrylates, cycloalkyl methacrylates, and aromatic vinyl monomers; And at least one reactive functional monomer capable of reacting with the functional group of the polyhydroxy fatty acid ester to form a covalent chemical bond, wherein the reactive functional monomer is selected from monomers containing an epoxy group, an acetylacetoxy group, an isocyanate group, an oxazoline group, or an alkoxysilyl group.

2. The core-shell latex according to claim 1, characterized in that, The composite particles have a Z-mean particle size of 80–400 nm and a polydispersity index not higher than 0.30; and / or, a median diameter D of the volume distribution as measured according to ISO 13320:2020. 50 The wavelength is 80–400 nm, and the volume distribution is D. 90 / D 10 No higher than 3.

5.

3. The core-shell latex according to claim 1 or 2, characterized in that, The minimum film-forming temperature of the latex, as determined according to ASTM D2354-10(2023), is -10–12°C.

4. The core-shell latex according to claim 1, characterized in that, The covalent chemical bonds at the interface originate from reaction products selected from the following reaction pairs: epoxy group / -COOH, epoxy group / -OH, acetoacetoxy group / -NH2, isocyanate group / -OH, oxazoline / -COOH, alkoxysilane / -OH, carbonyl / hydrazide, maleimide / -SH.

5. The core-shell latex according to claim 1, characterized in that, The monomer component of the acrylate polymer further includes: At least one other functional monomer, selected from monomers containing carboxyl, hydroxyl, or amide groups; and / or At least one crosslinking monomer, which is a monomer containing at least two polymerizable double bonds.

6. The core-shell latex according to claim 1 or 4, characterized in that, The grafting rate of the shell phase to the nucleus phase, or the grafting rate of the nucleus phase to the shell phase, is 10% to 60%.

7. The core-shell latex according to claim 1, characterized in that, The acrylate polymers have an acid value of 3–60 mg KOH / g, based on non-volatile solids.

8. The core-shell latex according to claim 1, characterized in that, The acrylate polymers have a hydroxyl value of 0–50 mg KOH / g, based on non-volatile solids.

9. The core-shell latex according to claim 1, characterized in that, The non-volatile solids of the latex contain a bio-based carbon content (BCC) of not less than 70%, and do not contain artificially added per- and polyfluoroalkyl substances (PFAS).

10. The core-shell latex according to claim 1, characterized in that, The residual anionic surfactant content in the latex, measured by MBAS according to Standard Methods 5540C (2023) and converted to linear alkylbenzene sulfonate equivalents, is not higher than 0.10 wt% based on non-volatile solids.

11. The core-shell latex according to claim 1, characterized in that, The total residual monomer content in the latex is not higher than 0.03 wt%.

12. The core-shell latex according to claim 1, characterized in that, The latex was stored at 40°C for 12 weeks, and its D 50 The rate of change is not higher than 3%, and the rate of change in viscosity is not higher than 10%.

13. A coating method comprising applying the core-shell latex of any one of claims 1-12 onto a substrate.

14. The method according to claim 13, characterized in that, The substrate is selected from paper, paperboard, molded fiber, plastic film or non-woven fabric.

15. The method according to claim 14, characterized in that, The dry coating amount of the core-shell latex is 6–12 g / m².

16. An article prepared by the method according to any one of claims 13-15, characterized in that, The product is food packaging, personal care product packaging, medical device packaging, or used as paper cups, paper bowls, food wrapping paper, or molded fiber products.

17. The article of claim 16, characterized in that, The heat-sealing peel strength was measured at 120℃, 0.30MPa, and 1.0s, and the heat-sealing initiation temperature was not lower than 1.8N / 15mm, and the heat-sealing peel strength was not higher than 110℃.

18. The article of manufacture according to claim 16 or 17, characterized in that, The water vapor transmission rate (WVTR) measured at 38℃ and 90% RH is no higher than 65 g / m²·d, and the oxygen transmission rate (OTR) measured at 23℃ and 0% RH is no higher than 120 cm³ / m²·d.

19. The article of manufacture according to claim 16 or 17, characterized in that, Its Cobb 60 Not higher than 16g / m², grease resistance Kit value not lower than 10, and resistance to methyl ethyl ketone (MEK) abrasion cycles not lower than 100 times.

20. The article of claim 16, characterized in that, The product, in accordance with ASTM F1921 / F1921M-12(2023) standard, has a heat-tack strength of not less than 1.9 N / 15 mm after heat sealing for 0.1–0.2 s at 120 °C and 0.30 MPa.

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