Biomass-derived phas-based oil and moisture barrier coating, coated paper and methods of making

Abstract

Biomass-derived PHA oil-repellent and moisture-permeable coating, coated paper and preparation method, relate to the field of paper and paperboard manufacturing and processing. The coating contains biomass-derived polyhydroxyalkanoate, maltodextrin grafted adipic acid dihydrazide, chitosan-coated SiO2 nanoparticles, tributyl citrate and deionized water; the coated paper comprises a substrate paper pretreated by a biological enzyme and a double-layer coating formed by the coating; the preparation method comprises the steps of modified PHA emulsion preparation, substrate paper pretreatment, double-layer coating and gradient drying. The reagents used are environmentally friendly, and the product has excellent oil-repellent and moisture-permeable properties.

Description

Technical Field

[0001] This invention belongs to the field of paper and paperboard manufacturing and processing, specifically relating to biomass-derived PHA oil-blocking and moisture-permeable coatings, coated paper, and preparation methods. Background Technology

[0002] In end-use applications such as food packaging and disposable tableware, there are strict requirements for the oil-blocking performance, moisture permeability, and environmental friendliness of paper materials. With tightening environmental policies and increasing consumer health awareness, biodegradable and biomass-derived materials are gradually becoming the industry's development direction. However, current mainstream paper oil-blocking solutions still rely on synthetic polymer resins. These materials have long degradation cycles in the natural environment, and some may even release trace amounts of harmful components. Furthermore, there is a common contradiction: improved oil-blocking performance leads to decreased moisture permeability, making it difficult to meet the demand for balanced performance in various applications.

[0003] To optimize film formation and stability, existing oil-blocking coatings often add chemically synthesized crosslinking agents and film-forming aids. These aids have poor biocompatibility and pose safety hazards in food contact scenarios. Although some technologies attempt to introduce inorganic nanoparticles to enhance oil-blocking ability, nanoparticles are prone to agglomeration, resulting in poor coating uniformity. This not only affects the appearance but also further weakens the moisture permeability, making it impossible to simultaneously achieve a synergy between environmental protection, safety, and core performance.

[0004] In the production of coated paper, traditional substrate paper pretreatment often uses strong acids and alkalis, which can easily damage the integrity of the paper fiber structure and the residue of the reagents can affect product safety. The coating design is mainly single-layer, making it difficult to balance oil resistance and moisture permeability through structural control. The drying process is mostly a single high-temperature mode, which can easily cause the coating to shrink and crack, or reduce the bonding strength between the coating and the substrate due to uneven moisture evaporation. These problems together limit the large-scale application of environmentally friendly oil-resistant and moisture-permeable coated paper. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a biomass-derived PHA oil-blocking and moisture-permeable coating, coated paper and preparation method, which solves the problems in the prior art that coatings for coated paper mostly rely on petrochemical-based raw materials, resulting in poor environmental performance, difficulty in synergistically achieving oil-blocking and moisture-permeable properties, poor substrate pretreatment effect and easy coating cracking or unstable performance caused by drying process.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] The biomass-derived PHA oil-blocking and moisture-permeable coating comprises 20-40 wt% biomass-derived polyhydroxy fatty acid ester, 3-8 wt% biomass-based crosslinking agent, 1-5 wt% biomass-coated nanocomposite particles, 2-6 wt% bio-based film-forming aid, and 41-74 wt% deionized water; wherein the biomass-based crosslinking agent is maltodextrin grafted adipate dihydrazide; the biomass-coated nanocomposite particles are chitosan-coated SiO2 nanoparticles; and the bio-based film-forming aid is tributyl citrate.

[0008] Preferably, in the above-mentioned biomass-derived PHA oil-blocking and moisture-permeable coating, the biomass-derived polyhydroxy fatty acid ester is polyhydroxybutyrate-co-hydroxyvalerate prepared by microbial fermentation, with a number-average molecular weight of 5 × 10⁻⁶. 4 -2×10 5 g / mol, with a hydroxyvalerate unit content of 5-15 mol%. It is explicitly stated here that the biomass-derived polyhydroxy fatty acid ester is polyhydroxybutyrate-co-hydroxyvalerate (PHBV) prepared by microbial fermentation. This maintains the environmentally friendly properties of all-biomass raw materials, avoiding the environmental burden of petrochemical-based raw materials. Furthermore, compared to single polyhydroxybutyrate (PHB), PHBV enhances coating flexibility through the introduction of hydroxyvalerate units, solving the problem of brittleness in pure PHA coatings, while simultaneously ensuring the oil-blocking and moisture-permeable skeleton properties of the coating base.

[0009] In the aforementioned biomass-derived PHA oil-blocking and moisture-permeable coating, preferably, the chitosan-coated SiO2 nanoparticles have a particle size of 50-200 nm and a chitosan coating amount of 5-15 wt%. This design utilizes the sheet-like barrier structure of SiO2 nanoparticles to enhance the coating's ability to block oils, while also leveraging the biocompatibility and viscosity of chitosan to improve the compatibility between SiO2 and the PHA matrix, preventing nanoparticle aggregation that could lead to uneven coating performance. Furthermore, the biomass properties of chitosan further enhance the coating's environmental friendliness, aligning with the overall environmental protection philosophy of the technical solution.

[0010] The aforementioned biomass-derived PHA oil-blocking and moisture-permeable coating preferably comprises 25-35 wt% biomass-derived polyhydroxy fatty acid ester, 4-6 wt% biomass-based crosslinking agent, 2-4 wt% biomass-coated nanocomposite particles, 3-5 wt% bio-derived film-forming aid, and 45-66 wt% deionized water. This avoids performance imbalances caused by excessive amounts of a single component, such as excessive PHA leading to an overly thick coating or excessive film-forming aid affecting oil blocking, while ensuring that the coating has suitable viscosity and flowability during the preparation process (such as ultrasonic dispersion in step S1 and microgravure coating in steps S3 / S5), adapting to the subsequent coating paper processing technology.

[0011] This invention's coating focuses on all-biomass environmentally friendly raw materials. Addressing the shortcomings of existing coatings for coated paper, such as insufficient environmental friendliness and difficulty in synergistically achieving oil-blocking and moisture-permeable properties, it selects biomass-derived polyhydroxyalkanoates (PHA) as the basic film-forming framework, ensuring the coating's basic oil-blocking and moisture-permeable capabilities as well as its biodegradability. It incorporates maltodextrin-grafted adipate dihydrazide as a biomass-based crosslinking agent to enhance the coating's structural stability and weather resistance. Chitosan-coated SiO2 nanocomposite particles are introduced, utilizing the nanoparticle's barrier effect to strengthen the oil-blocking performance, while chitosan improves the compatibility between the nanoparticles and the PHA matrix. Tributyl citrate is added as a bio-derived film-forming aid to ensure uniform film formation without compromising environmental properties. Finally, using deionized water as the dispersion medium, and through reasonable proportioning of the components, the coating achieves synergistic optimization of its environmental friendliness, oil-blocking performance, and moisture-permeable properties, adapting to the subsequent processing and usage requirements of coated paper.

[0012] A coated paper includes a substrate paper and a coating applied to at least one surface of the substrate paper; the coating is formed by a biomass-derived PHA oil-blocking and moisture-permeable coating; the substrate paper is pretreated with bio-enzymes; the coating has a double-layer structure, wherein the content of biomass-based crosslinking agent in the bottom coating is 1-2 wt% higher than that in the top coating.

[0013] In the aforementioned coated paper, preferably, the bio-enzyme is cellulase, and the mass concentration of the bio-enzyme solution is 0.5-2 wt%. Here, the cellulase can specifically decompose the cellulose molecular chains on the surface of the substrate paper, forming a microporous structure on the paper surface, increasing the contact area between the coating and the substrate paper, improving the coating adhesion, and preventing the coating from peeling off during subsequent use.

[0014] Preferably, in the above-mentioned coated paper, the thickness of the bottom coating is 4-6 μm, and the thickness of the top coating is 2-3 μm. The thicker bottom layer can form a dense oil-blocking base layer with a higher content of crosslinking agent, effectively preventing oil penetration; the thinner top layer, with a lower crosslinking agent content, retains more air and water permeability channels, ensuring moisture permeability and achieving a synergistic balance between oil blocking and moisture permeability. Excessive thickness increases the overall weight of the coated paper and reduces its flexibility, while excessive thinness fails to meet basic oil-blocking requirements.

[0015] The coated paper of this invention first undergoes a bio-enzyme pretreatment of the substrate paper to improve its surface properties, enhance the adhesion stability of the subsequent coating to the substrate, and prevent coating peeling. The coating uses a fully biomass PHA oil-blocking and moisture-permeable coating, which maintains its environmental protection attributes while ensuring basic performance. The coating is designed as a double-layer structure, with the biomass-based crosslinking agent content in the bottom layer being 1-2 wt% higher than that in the top layer, which strengthens the bonding strength between the bottom layer and the substrate and the overall structural stability of the coating. Combined with a reasonable ratio of a bottom layer thickness of 3-8 μm and a top layer thickness of 1-4 μm, the bottom layer thickness ensures oil-blocking effect, while the thinner top layer reduces moisture permeability resistance. Ultimately, the coated paper achieves synergistic optimization in terms of environmental protection, adhesion stability, oil-blocking performance, and moisture permeability, adapting to subsequent processing and actual use requirements.

[0016] As a general inventive concept, the present invention provides a method for preparing the coated paper as described above, comprising the following steps:

[0017] S1. To prepare a modified PHA emulsion, add biomass-derived polyhydroxy fatty acid ester to deionized water and stir at 50-70℃ until it is evenly dispersed. Add a biomass-based crosslinking agent, purge with nitrogen for protection, and sonicate at 300-500W for 20-40 minutes. Then add biomass-coated nanocomposite particles and bio-derived film-forming aids, and continue stirring for 30-60 minutes to obtain the modified PHA emulsion.

[0018] S2. Pretreatment of substrate paper: Immerse the substrate paper in a biological enzyme solution and keep it at 40-50℃ for 15-30 minutes. After taking it out, rinse it with deionized water 2-3 times and dry it at 60-80℃ until the moisture content is 5-8wt% to obtain pretreated substrate paper.

[0019] S3. Coating the base layer: Using a micro-gravure coating method, the modified PHA emulsion prepared in step S1 is coated onto the surface of the pretreated substrate paper obtained in step S2 after adjusting the biomass-based crosslinking agent content to 4-10wt%. The coating speed is controlled at 20-30m / min.

[0020] S4. Bottom layer drying: The substrate paper coated in step S3 is sent into a drying oven and dried for 10-20 seconds at 80-90℃ and 30-40% relative humidity to obtain a substrate paper with a bottom layer coating.

[0021] S5. Coating the top layer: Using a micro-recessed coating method, the modified PHA emulsion prepared in step S1 is coated onto the surface of the bottom layer obtained in step S4 after adjusting the biomass-based crosslinking agent content to 3-8 wt%. The coating speed is controlled at 25-35 m / min.

[0022] S6. Gradient drying: The substrate paper coated in step S5 is first dried at 70-80℃ and 40-50% relative humidity for 8-15 seconds, then dried at 50-60℃ and 50-60% relative humidity for 15-25 seconds, and finally cooled to 25-30℃ at room temperature to obtain the coated paper.

[0023] In the preferred embodiment of the above-mentioned method for preparing coated paper, the ultrasonic treatment power in step S1 is 350-450W, and the ultrasonic treatment time is 25-35min. Precise control of the ultrasonic power and time ensures that the biomass-derived polyhydroxyalkanoate (PHA), biomass-based crosslinking agent, and biomass-coated nanocomposite particles are uniformly dispersed in deionized water, preventing nanocomposite particle agglomeration or localized aggregation of the crosslinking agent. Simultaneously, it ensures that the PHA molecular chains are not excessively damaged, laying the foundation for the subsequent coating to form a uniform and dense coating, directly affecting the final oil-blocking and moisture-permeable synergistic performance of the coated paper.

[0024] In the preferred embodiment of the above-described method for preparing coated paper, the first stage of gradient drying in step S6 is characterized by a temperature of 75-80°C, a relative humidity of 42-48%, and a drying time of 10-14 seconds; the second stage is characterized by a temperature of 52-58°C, a relative humidity of 52-58%, and a drying time of 18-22 seconds. This method avoids surface crusting, internal blistering, or cracking of the coating due to rapid moisture evaporation. Simultaneously, it ensures that the coating forms a uniform porous structure during the drying process, satisfying the density required for oil resistance while retaining the channels needed for moisture permeability, thus balancing the structural stability and core functions of the coated paper.

[0025] The coating paper preparation method of this invention addresses the problems of weak adhesion between the coating and the substrate, easy cracking of the coating, and unstable performance in existing preparation processes. It first prepares a uniformly dispersed modified PHA emulsion to provide a high-quality raw material basis for coating, then pre-treats the substrate paper with bio-enzymes to improve its adhesion to the coating, and then adopts a double-layer coating method to adapt the coating structure design to enhance the adhesion of the bottom layer and the moisture permeability and oil resistance balance of the top layer. Finally, gradient drying is used to avoid the damage to the coating structure caused by rapid drying. The overall process steps are interconnected, which not only ensures that the performance of each biomass component is fully utilized, but also solves the defects of existing processes and achieves stable and efficient preparation of coated paper.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] (1) The coating and coated paper of this invention use biomass raw materials throughout the entire process, and the preparation process uses deionized water as the dispersion medium. There are no petrochemical-based harmful components. The products can be naturally degraded after disposal, which meets the needs of green and environmentally friendly development.

[0028] (2) This invention enhances the oil-blocking effect by using the barrier effect of chitosan-coated SiO2 nanoparticles. Combined with the double-layer coating design, the bottom layer has a high crosslinking agent content to enhance oil-blocking stability and the top layer is adapted to the moisture permeability requirements. This solves the problem of balancing oil-blocking and moisture permeability in the prior art and meets the dual requirements of food packaging and other scenarios for both properties.

[0029] (3) The substrate paper of the present invention can optimize the surface structure by pretreatment with bio-enzymes, improve the interfacial bonding ability with the coating, and, together with the compatibility design between the bottom layer and the substrate in the double-layer coating process, effectively avoid the coating from peeling off and wrinkling during use, thus improving the durability of the product.

[0030] (4) In the preparation method of the present invention, ultrasonic treatment is used to ensure that the modified PHA emulsion is evenly dispersed. Combined with the gradient drying process, the coating is initially shaped at high temperature and then slowly dried at low temperature to avoid the problem of coating cracking and shrinkage caused by rapid drying. At the same time, the micro-recessed coating controls the coating speed and thickness to ensure the smoothness and consistency of the coating.

[0031] (5) The entire preparation process of this invention does not require complex equipment. The steps of modified PHA emulsion preparation, substrate pretreatment, double coating and gradient drying are smoothly connected. The reagents used are easy to obtain and no volatile harmful gases are generated. It can be adapted to industrial continuous production, reducing production difficulty and environmental treatment costs. Attached Figure Description

[0032] Figure 1 This is a flowchart of the biomass-derived PHA oil-blocking and moisture-permeable coating, coated paper, and preparation method of the present invention. Detailed Implementation

[0033] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] Example 1

[0037] refer to Figure 1The biomass-derived PHA oil-blocking and moisture-permeable coating of the present invention comprises 28 wt% biomass-derived polyhydroxy fatty acid ester, 5 wt% maltodextrin-grafted adipate dihydrazide, 3 wt% chitosan-coated SiO2 nanoparticles, 4 wt% tributyl citrate, and 60 wt% deionized water; wherein the biomass-derived polyhydroxy fatty acid ester is polyhydroxybutyrate-co-hydroxyvalerate (PHBV), with a number-average molecular weight of 1.2 × 10⁻⁶. 5 g / mol, the content of hydroxyvalerate units is 8mol; the particle size of the chitosan-coated SiO2 nanoparticles is 80nm, and the chitosan coating amount is 12wt%.

[0038] The coated paper of the present invention comprises a substrate paper pretreated with a bio-enzyme and a double-layer coating coated on the surface of the substrate paper; the bio-enzyme is cellulase, and the mass concentration of the bio-enzyme solution is 0.8 wt%; the double-layer coating is formed by the above-mentioned biomass-derived PHA oil-blocking and moisture-permeable coating, wherein the biomass-based crosslinking agent content in the bottom coating is 6 wt% and the thickness of the bottom coating is 4.5 μm, and the biomass-based crosslinking agent content in the top coating is 5 wt% and the thickness of the top coating is 2.2 μm.

[0039] The method for preparing the coated paper in this embodiment includes the following steps:

[0040] S1. To prepare a modified PHA emulsion, biomass-derived polyhydroxy fatty acid ester was added to deionized water and stirred at 60°C until it was evenly dispersed. Maltodextrin grafted with adipate dihydrazide was added, and nitrogen gas was introduced for protection. The mixture was ultrasonically treated at 400W ultrasonic power for 30 minutes. Then, chitosan-coated SiO2 nanoparticles and tributyl citrate were added, and the mixture was stirred for another 45 minutes to obtain the modified PHA emulsion.

[0041] S2. Pretreatment of substrate paper: The substrate paper is immersed in 0.8wt% cellulase solution and kept at 42℃ for 22min. After being taken out, it is rinsed twice with deionized water and dried at 70℃ until the moisture content is 6wt% to obtain pretreated substrate paper.

[0042] S3. Coating the base layer: Using a micro-gravure coating method, the modified PHA emulsion prepared in step S1 is coated onto the surface of the pretreated substrate paper obtained in step S2 after adjusting the biomass-based crosslinking agent content to 6wt%, and the coating speed is controlled at 25m / min.

[0043] S4. Bottom layer drying: The substrate paper coated in step S3 is sent into a drying oven and dried for 15 seconds at 85°C and 35% relative humidity to obtain a substrate paper with a bottom layer coating.

[0044] S5. Coating the top layer: Using a micro-recessed coating method, the modified PHA emulsion prepared in step S1 is coated onto the surface of the bottom layer obtained in step S4 after adjusting the biomass-based crosslinking agent content to 5wt%, and the coating speed is controlled at 30m / min.

[0045] S6. Gradient drying: The substrate paper coated in step S5 is first dried at 76°C and 44% relative humidity for 11 seconds, then dried at 54°C and 54% relative humidity for 19 seconds, and finally cooled to 28°C at room temperature to obtain the coated paper.

[0046] Example 2

[0047] The preparation was carried out using the same method as in Example 1, except that the hydroxyvalerate unit content of the biomass-derived polyhydroxy fatty acid ester, namely polyhydroxybutyrate-co-hydroxyvalerate (PHBV), was 12 mol. The remaining raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and preparation step parameters were all consistent with those in Example 1.

[0048] Example 3

[0049] The preparation was carried out using the same method as in Example 1, except that the chitosan coating amount of the SiO2 nanoparticles was 8 wt%, while the other raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and preparation step parameters were the same as in Example 1.

[0050] Example 4

[0051] The preparation was carried out using the same method as in Example 1, except that the bio-derived film-forming aid was a mixture of 3 wt% tributyl citrate and 1 wt% acetylated monoglyceride. The remaining raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and preparation step parameters were all the same as in Example 1.

[0052] Example 5

[0053] The preparation method was the same as in Example 1, except that the substrate paper was soaked in 0.8 wt% cellulase solution and kept at 42°C for 28 min during the pretreatment of the substrate paper. The other raw material ratios, double-layer coating parameters and preparation step parameters were the same as in Example 1.

[0054] Example 6

[0055] The preparation method was the same as in Example 1, except that the biomass-based crosslinking agent content of the bottom coating in the double-layer coating was 7 wt%, and the biomass-based crosslinking agent content of the top coating was 5 wt%. The other raw material ratios, substrate paper pretreatment conditions, and preparation step parameters were the same as in Example 1.

[0056] Comparative Example 1

[0057] The preparation method was the same as in Example 1, except that the cellulase pretreatment step of the substrate paper was omitted, and the substrate paper was directly dried at 70°C to a moisture content of 6wt% to obtain the pretreated substrate paper. The remaining raw material ratios, double-layer coating parameters and preparation step parameters were the same as in Example 1.

[0058] Comparative Example 2

[0059] The coating was prepared using the same method as in Example 1, except that only a single-layer coating was performed, omitting the top-layer coating step. The biomass-based crosslinking agent content in the single-layer coating was 5 wt%, and the coating thickness was 6.7 μm. The remaining raw material ratios, substrate paper pretreatment conditions, and preparation step parameters were the same as in Example 1.

[0060] Comparative Example 3

[0061] The coating was prepared using the same method as in Example 1, except that the chitosan-coated SiO2 nanoparticles were removed from the coating, and the amount of deionized water was adjusted to 63 wt%. The remaining raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and preparation step parameters were the same as in Example 1.

[0062] Comparative Example 4

[0063] The preparation was carried out using the same method as in Example 1, except that the gradient drying step was replaced by constant temperature drying at 72°C and 45% relative humidity for 30 seconds. The remaining raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and other preparation step parameters were the same as in Example 1.

[0064] Comparative Example 5

[0065] The coating was prepared using the same method as in Example 1, except that the amount of biomass-based crosslinking agent in the coating was adjusted to 2 wt%, while the other raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and preparation step parameters were the same as in Example 1.

[0066] Comparative Example 6

[0067] The coating was prepared using the same method as in Example 1, except that the amount of bio-based film-forming aid in the coating was adjusted to 8 wt%, and the amount of deionized water was adjusted to 56 wt%. The remaining raw material ratios, substrate paper pretreatment conditions, double-layer coating parameters, and preparation step parameters were the same as in Example 1.

[0068] The coated papers in Examples 1-6 and Comparative Examples 1-6 were tested, and the results are shown in Table 1.

[0069] 1. Oil-blocking performance is referenced to TAPPIT 559cm-12;

[0070] 2. The moisture permeability performance refers to GB / T12704.1-2021;

[0071] 3. Adhesion shall conform to GB / T9286-1998;

[0072] 4. Flexural endurance conforms to GB / T2679.5-1995;

[0073] 5. Biodegradation rate refers to GB / T19277.1-2011.

[0074] Table 1: Experimental Results of Examples 1-6 and Comparative Examples 1-6

[0075]

[0076] (Note: Oil repellency, kit grade, 1-12, the higher the better; coating adhesion, cross-cut adhesion grade, 0-5, grade 0 is the best; folding endurance, the more folds the better.)

[0077] In summary, as shown in Table 1, the oil-blocking performance of all examples reached level 11-12, the moisture permeability was maintained at 345-368 g / (m²•24h), the coating adhesion was level 0 in the cross-cut test, the folding resistance was 510-610 times, the biodegradation rate was 92.8%-93.5% after 60 days, and the coating appearance was smooth and free from defects such as cracking and agglomeration. Comparative Examples 1-6 all resulted in significant performance imbalances due to omissions or improper adjustments to the core processes of the embodiments: Comparative Example 1 omitted the bio-enzyme pretreatment, causing the coating adhesion to drop to level 2, the folding endurance to only 210 cycles, and localized coating peeling, demonstrating the crucial role of bio-enzyme pretreatment in improving the adhesion between the substrate paper and the coating; Comparative Example 2 used a single-layer coating, resulting in a sharp drop in moisture permeability to 205 g / (m²•24h), a folding endurance of 450 cycles, and slight cracking of the coating, highlighting the necessity of a double-layer coating for controlling coating density; Comparative Example 3 omitted chitosan-coated SiO2 nanoparticles, resulting in an oil resistance level of only level 8, and the loss of the nano-barrier structure reduced the coating's resistance to oil. Oil penetration ability decreased significantly; in Comparative Example 4, constant temperature drying was used instead of gradient drying, resulting in large-area cracking and local blistering of the coating, with a folding endurance of only 100 cycles and a moisture permeability of 252 g / (m²•24h), highlighting the importance of gradient drying in ensuring uniform coating drying; in Comparative Example 5, the amount of biomass-based crosslinking agent was reduced to 2wt%, and insufficient crosslinking led to a drop in coating adhesion to level 3, oil resistance to level 9, and a loose structure that resulted in poor folding endurance; in Comparative Example 6, an excessive amount of bio-based film-forming aid was added to 8wt%, resulting in a sticky coating surface that was easily contaminated with impurities, an oil resistance to level 10, and a folding endurance of 300 cycles, proving that the amount of film-forming aid needs to be precisely controlled to avoid performance degradation.

Claims

1. A biomass-derived PHA oil-blocking and moisture-permeable coating, characterized in that: The composition includes 20-40 wt% biomass-derived polyhydroxy fatty acid ester, 3-8 wt% biomass-based crosslinking agent, 1-5 wt% biomass-coated nanocomposite particles, 2-6 wt% bio-derived film-forming aid, and 41-74 wt% deionized water; the biomass-based crosslinking agent is maltodextrin grafted with adipate dihydrazide; the biomass-coated nanocomposite particles are chitosan-coated SiO2 nanoparticles; and the bio-derived film-forming aid is tributyl citrate. The biomass-derived polyhydroxy fatty acid ester is polyhydroxybutyrate-co-hydroxyvalerate prepared by microbial fermentation, with a number-average molecular weight of 5 × 10⁻⁶. 4 -2×10 5 g / mol, with a hydroxyvalerate unit content of 5-15 mol.

2. The biomass-derived PHA oil-blocking and moisture-permeable coating as described in claim 1, characterized in that: The chitosan-coated SiO2 nanoparticles have a particle size of 50-200 nm and a chitosan coating amount of 5-15 wt%.

3. The biomass-derived PHA oil-blocking and moisture-permeable coating as described in claim 1, characterized in that: The composition includes 25-35 wt% biomass-derived polyhydroxy fatty acid ester, 4-6 wt% biomass-based crosslinking agent, 2-4 wt% biomass-coated nanocomposite particles, 3-5 wt% bio-derived film-forming aid, and 45-66 wt% deionized water.

4. A coated paper, characterized in that: It includes a substrate paper and a coating applied to at least one surface of the substrate paper; the coating is formed by the biomass-derived PHA oil-blocking and moisture-permeable coating of claim 1; the substrate paper is pretreated with bio-enzymes; the coating has a double-layer structure, and the content of biomass-based crosslinking agent in the bottom coating is 1-2 wt% higher than that in the top layer.

5. The coated paper as described in claim 4, characterized in that: The bioenzyme is cellulase, and the mass concentration of the bioenzyme solution is 0.5-2 wt%.

6. The coated paper as described in claim 4, characterized in that: The thickness of the base coat is 4-6 μm, and the thickness of the top coat is 2-3 μm.

7. A method for preparing coated paper according to any one of claims 4-6, characterized in that: Includes the following steps, S1. To prepare a modified PHA emulsion, add biomass-derived polyhydroxy fatty acid ester to deionized water and stir at 50-70℃ until it is evenly dispersed. Add a biomass-based crosslinking agent, purge with nitrogen for protection, and sonicate at 300-500W for 20-40 minutes. Then add biomass-coated nanocomposite particles and bio-derived film-forming aids, and continue stirring for 30-60 minutes to obtain the modified PHA emulsion. S2. Pretreatment of substrate paper: Immerse the substrate paper in a biological enzyme solution and keep it at 40-50℃ for 15-30 minutes. After taking it out, rinse it with deionized water 2-3 times and dry it at 60-80℃ until the moisture content is 5-8wt% to obtain pretreated substrate paper. S3. Coating the base layer: Using a micro-gravure coating method, the modified PHA emulsion prepared in step S1 is coated onto the surface of the pretreated substrate paper obtained in step S2 after adjusting the biomass-based crosslinking agent content to 4-10wt%. The coating speed is controlled at 20-30m / min. S4. Bottom layer drying: The substrate paper coated in step S3 is sent into a drying oven and dried for 10-20 seconds at 80-90℃ and 30-40% relative humidity to obtain a substrate paper with a bottom layer coating. S5. Coating the top layer: Using a micro-recessed coating method, the modified PHA emulsion prepared in step S1 is coated onto the surface of the bottom layer obtained in step S4 after adjusting the biomass-based crosslinking agent content to 3-8 wt%. The coating speed is controlled at 25-35 m / min. S6. Gradient drying: The substrate paper coated in step S5 is first dried at 70-80℃ and 40-50% relative humidity for 8-15 seconds, then dried at 50-60℃ and 50-60% relative humidity for 15-25 seconds, and finally cooled to 25-30℃ at room temperature to obtain the coated paper.

8. The method for preparing coated paper as described in claim 7, characterized in that: In step S1, the ultrasonic power is 350-450W and the ultrasonic treatment time is 25-35min.

9. The method for preparing coated paper as described in claim 7, characterized in that: In step S6, the first stage of gradient drying conditions are 75-80℃, relative humidity 42-48%, and drying time 10-14s, and the second stage conditions are 52-58℃, relative humidity 52-58%, and drying time 18-22s.

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