Degradable wood pulp wrapping paper and its production process

Abstract

The present application relates to the field of wood pulp packaging paper preparation, and discloses a degradable wood pulp packaging paper and a production process thereof, comprising the following steps: S1, mixing wood pulp fibers with water-soluble fibers and forming a wet paper sheet by papermaking; S2, carrying out zoned drying on the wet paper sheet, so that the water-soluble fibers are dissolved in situ during the drying process; S3, coating a bottom functional emulsion and a surface functional emulsion on the front surface of the wood pulp fiber substrate in sequence to form a composite wet film; S4, carrying out staged drying on the composite wet film, so that a cross-linking reaction occurs between the bottom functional emulsion and the surface functional emulsion to form a gradient functional barrier layer; S5, coating an antifouling coating on the surface of the gradient functional barrier layer and curing; and S6, coating a heat-sealing coating on the back surface of the wood pulp fiber substrate and curing. Through the addition of water-soluble fibers and the design of the gradient functional barrier layer, the present application improves the puncture resistance of the material and solves the problem of the balance between the coating viscosity and the functionality.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wood pulp packaging paper preparation, and particularly relates to a degradable wood pulp packaging paper and a production process thereof. BACKGROUND

[0002] The influence of traditional non-degradable plastic packaging materials on the ecological environment leads to their gradual replacement by biodegradable materials, especially wood pulp fiber-based packaging materials, which are gradually becoming the main materials of traditional packaging materials because they are derived from renewable resources in nature and have good biocompatibility and natural degradability.

[0003] Although wood pulp fiber-based packaging materials have significant advantages in sustainability, traditional wood pulp fiber packaging materials generally have insufficient puncture resistance and tear resistance, which is mainly due to the fact that the fiber network structure cannot quickly disperse stress when subjected to local sharp impact, resulting in stress concentration and easy puncture or tearing. The existing technology usually improves the strength by increasing the basis weight of the paper, but this will lead to an increase in material cost and a decrease in flexibility.

[0004] Secondly, in terms of functionality, the inherent porous structure and hydrophilic properties of pure wood pulp fiber materials result in poor barrier properties, especially insufficient barrier ability to water vapor, oxygen and oil, which severely limits their use in demanding application scenarios such as fresh food, high-fat products or high-humidity environments. In order to improve the barrier properties, the existing technology often uses surface coating or film coating processes, such as polyethylene film coating or fluorine-containing oil-proof agents. However, many functional coatings can improve the barrier properties to some extent, but often have the problem of weak adhesion to the fiber substrate and easy peeling, especially when the material is bent or the environmental humidity changes, the coating is easy to produce micro-cracks or fall off from the substrate, resulting in failure of the barrier function.

[0005] Therefore, it is urgent to develop a new scheme to solve the above technical problems. SUMMARY

[0006] The present application overcomes the shortcomings of the prior art and provides a degradable wood pulp packaging paper and a production process thereof.

[0007] To achieve the above-mentioned purpose, on the one hand, the present application provides a production process of a degradable wood pulp packaging paper, comprising the following steps:

[0008] S1, mixing wood pulp fibers and water-soluble fibers and forming a wet paper sheet by papermaking;

[0009] S2, partition drying the wet paper sheet, so that the water-soluble fibers are dissolved in situ during the drying process, forming a three-dimensional interconnected micropore network inside the wood pulp fiber substrate;

[0010] S3, coating a bottom functional emulsion and a surface functional emulsion on the front surface of the wood pulp fiber substrate in sequence to form a composite wet film; wherein the bottom functional emulsion penetrates and fills the micro-pore network, and the surface functional emulsion forms a continuous film on the surface of the substrate;

[0011] S4, performing staged drying on the composite wet film to cause cross-linking reaction between the bottom functional emulsion and the surface functional emulsion to form an integrated gradient functional barrier layer;

[0012] S5, coating an anti-fouling coating on the surface of the gradient functional barrier layer and curing;

[0013] S6, coating a heat-sealing coating on the back surface of the wood pulp fiber substrate and curing.

[0014] In one preferred embodiment of the present application, in the step S1, the water-soluble fiber is a partially alcoholysis type polyvinyl alcohol fiber, the alcoholysis degree of which is 85%-90%, the average length is 4-6 mm, and the diameter ranges from 10 to 20 μm; and the water-soluble fiber accounts for 3%-7% of the total dry weight of the wood pulp fiber and the water-soluble fiber.

[0015] In one preferred embodiment of the present application, in the step S2, the zoned drying includes: first drying at 70-90℃ for 50-70 min to reduce the water content of the paper sheet to 25%-35%, and then drying at 95-115℃ for 80-100 min to completely dissolve the water-soluble fiber to form a three-dimensionally interconnected micro-pore network.

[0016] In one preferred embodiment of the present application, in the step S3, the bottom functional emulsion is a starch-based nano-emulsion with a viscosity that significantly decreases with shear force, the solid content of the starch-based nano-emulsion is 20%-25%, the static viscosity at 25℃ is 40-50 mPa·s, and the viscosity at a shear rate of 100 s -1 -1 is lower than 15 mPa·s; and the surface functional emulsion is a polylactic acid micro-emulsion containing a reactive cross-linking agent, the solid content is 30%-40%, the average particle size is 200-300 nm, and the static viscosity is 250-350 mPa·s.

[0017] In one preferred embodiment of the present application, the reactive cross-linking agent is a polybasic carboxylic acid, and the polybasic carboxylic acid cross-linking agent accounts for 2%-4% of the solid content of the surface functional emulsion; in the step S4, the cross-linking reaction is an esterification reaction between the active groups in the bottom functional emulsion and the polybasic carboxylic acid.

[0018] In one preferred embodiment of the present application, the sequential coating in the step S3 is: first coating the bottom functional emulsion, and then coating the surface functional emulsion while the bottom emulsion is not completely dried.

[0019] In a preferred embodiment of the present application, the step S4 includes: promoting the penetration of the emulsion at 70-90°C, and triggering the cross-linking reaction at 110-130°C.

[0020] In a preferred embodiment of the present application, the step S5 includes: applying a water-based acrylic resin coating layer on the surface of the wood pulp paper, and the dry film thickness of the water-based acrylic resin coating layer is 0.5-2 μm.

[0021] In a preferred embodiment of the present application, the step S6 includes: applying a biodegradable polyester coating layer on the surface of the wood pulp paper, and the dry film thickness of the biodegradable polyester coating layer is 3-8 μm.

[0022] In another aspect, the present application provides a degradable wood pulp packaging paper prepared based on the production process of any one of the above.

[0023] The present application solves the defects in the background art, and has the following beneficial effects:

[0024] (1) The present application provides a degradable wood pulp packaging paper and a production process thereof. By constructing a three-dimensional interconnected micropore network structure in the wood pulp fiber substrate using water-soluble fibers, and designing a gradient functional barrier layer, when the packaging is subjected to a local sharp impact, the impact energy can be diffused along the micrometer-scale pore network in multiple paths, and the mechanical energy can be effectively dissipated through the friction between the pore walls, thereby improving the puncture resistance of the material. Compared with the prior art which only increases the basis weight or adds non-degradable reinforcing agents to improve the strength, the present method not only achieves significant puncture resistance, but also maintains the degradability of the material, so that it has a longer service life and better protection performance in harsh application scenarios such as heavy product packaging and logistics transportation which are easily damaged by external forces.

[0025] (2) The present application provides a degradable wood pulp packaging paper and a production process thereof. By using a gradient functional barrier layer design combining a bottom layer of nano-emulsion and a surface layer of micro-emulsion, the technical contradiction between deep penetration and surface film formation in a single viscosity emulsion system is effectively solved. The bottom layer of nano-emulsion utilizes its significant shear thinning property to rapidly penetrate deep into the micropore network and achieve mechanical anchoring by sharply reducing the viscosity at the moment of coating, while the surface layer of micro-emulsion forms a continuous and dense barrier film on the surface of the substrate due to its high viscosity property. Compared with the prior art which uses multiple layers of composite or adds non-degradable barrier materials, the present scheme achieves excellent barrier performance on a single substrate.

[0026] (3) This application provides a biodegradable wood pulp packaging paper and its production process. Based on the thermally induced esterification crosslinking mechanism between starch-based nanoemulsion and polycarboxylic acid crosslinking agent, and in conjunction with the ether bond crosslinking reaction between starch molecules, the gradient functional barrier layer of this invention constructs a stable three-dimensional network of covalent bonds between the bottom layer and the surface layer, which greatly improves the bonding performance between the coating and the substrate. Compared with the methods of using synthetic adhesives or non-degradable crosslinking systems in the prior art, this crosslinking structure is entirely based on biodegradable components, which provides strong interfacial bonding force while ensuring the environmental compatibility of the material. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the steps of a preferred embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0031] Exemplary process:

[0032] like Figure 1 As shown, a biodegradable wood pulp packaging paper and its production process include the following steps:

[0033] S1. Mix wood pulp fibers with water-soluble fibers and form them into paper sheets to obtain wet paper sheets;

[0034] S2. The wet paper sheets are dried in sections, so that the water-soluble fibers dissolve in situ during the drying process, forming a three-dimensional interconnected microporous network inside the wood pulp fiber substrate;

[0035] S3, coating a bottom layer functional emulsion and a surface layer functional emulsion on the front surface of the wood pulp fiber substrate in sequence to form a composite wet film; wherein the bottom layer functional emulsion penetrates and fills the micro-pore network, and the surface layer functional emulsion forms a continuous film on the surface of the substrate;

[0036] S4, drying the composite wet film in stages to cause cross-linking reaction between the bottom layer functional emulsion and the surface layer functional emulsion to form an integrated gradient functional barrier layer;

[0037] S5, coating a stain-resistant coating layer on the surface of the gradient functional barrier layer and curing;

[0038] S6, coating a heat-sealing coating layer on the back surface of the wood pulp fiber substrate and curing.

[0039] The degradable packaging paper prepared based on the above process realizes synchronous improvement of the puncture resistance, barrier property and mechanical strength of the packaging paper through the synergistic effect of the three-dimensional interconnected micro-pore network formed by the water-soluble fibers and the gradient functional barrier layer. Specifically, in the present application, effect one is that the three-dimensional micro-pore network constructed by the water-soluble fibers provides excellent puncture resistance for the material; effect two is that through the design of the gradient functional barrier layer, the bottom layer nano-emulsion realizes deep penetration and solidification by using the shear thinning property to fill the wood pulp fiber pores to form physical anchoring, and at the same time, the surface layer micro-emulsion forms a continuous and dense barrier film on the surface of the substrate, thereby solving the contradiction that a single viscosity emulsion system cannot simultaneously achieve deep penetration and surface film formation; and through the thermal-induced esterification cross-linking between the starch-based liquid and the polycarboxylic acid cross-linking agent and the ether bond cross-linking between starch molecules, a three-dimensional network connected by covalent bonds is constructed between the bottom layer and the surface layer, realizing in-situ fusion of the two emulsions and significantly improving the peeling strength of the coating and the substrate.

[0040] Specifically, in step S1, the water-soluble fiber is a partially alcoholysis type polyvinyl alcohol fiber with an alcoholysis degree of 85%-90%, an average length of 4-6 mm and a diameter range of 10-20 μm; and the water-soluble fiber accounts for 3%-7% of the total dry weight of the wood pulp fiber and the water-soluble fiber; the wood pulp fiber is selected from coniferous wood pulp fiber with a length range of 1.5-3 mm and an average diameter range of 20-40 μm; in the above selection, the partially alcoholysis type polyvinyl alcohol fiber has suitable water solubility and fiber strength, and can be controllably dissolved in the subsequent drying process to form a uniform three-dimensional interconnected micro-pore network; and the wood pulp fiber provides a main skeleton structure, and its high aspect ratio and rich surface functional groups provide sufficient binding sites for the subsequent anchoring of the functional emulsion; the uniform distribution of fibers is realized by using a traditional inclined screen forming machine for forming, so as to avoid aggregation or directional arrangement and ensure the isotropy of the micro-pore network.

[0041] Further, in step S2, the zoned drying includes first drying at 70-90℃ for 50-70min to reduce the moisture content of the paper sheet to 25-35%, and then drying at 95-115℃ for 80-100min to promote complete dissolution of the water-soluble fibers; the low-to-moderate temperature drying in the first stage maintains the integrity of the fiber network structure by slow dehydration, avoiding premature collapse of the pores; the high temperature treatment in the second stage ensures that the water-soluble fibers are fully dissolved, forming a three-dimensional interconnected pore network with a diameter distribution in the micron range inside the wood pulp fiber substrate. Specifically, through the zoned drying process, part of the alcoholysis type polyvinyl alcohol fibers embedded in the wood pulp fiber network are dissolved in situ at a high temperature of 95-115℃, and the solid fiber structure breaks the hydrogen bond and solvation under the action of water molecule thermal motion. Since the dissolution process is limited within the space originally occupied by the fibers, a micropore network corresponding to the fiber morphology is naturally formed after the water is completely evaporated. This micropore structure not only serves as a physical skeleton for stress dispersion, but also significantly improves the puncture strength of the material through pore wall friction and multi-path energy dissipation, while providing a large specific surface area and mechanical anchoring sites for subsequent emulsion.

[0042] Specifically, in step S3, the bottom functional emulsion is a starch-based nano-emulsion with a viscosity that decreases significantly with shear force, the solid content of the starch-based nano-emulsion is 20-25%, the static viscosity at 25℃ is 40-50 mPa·s, and the viscosity at a shear rate of 100 s -1

[0043] Based on the above settings, the starch-based nano-emulsion is first coated, and then the polylactic acid micro-emulsion containing a reactive crosslinking agent is coated on top of the starch-based nano-emulsion before it is completely dried. The shear thinning property of the starch-based nano-emulsion causes its viscosity to drop sharply during the coating process. Specifically, when the emulsion is at rest, the epoxy-functionalized starch molecule chains in the starch-based nano-emulsion form a three-dimensional network structure through hydrogen bonds and van der Waals forces, trapping and locking water molecules to produce high viscosity. However, under the action of coating mechanical force, the shear rate increases sharply to 100 s -1 ​The above, the fluid layer is destroyed by the instantaneous molecular chain interaction force, the three-dimensional network collapses, the water molecules are released, the nanoparticles are arranged along the shear direction, the fluidity is sharply increased, and the viscosity is sharply reduced to below 15 mPa·s. The instantaneous viscosity change enables the emulsion to quickly penetrate into the micropore channel of the wood pulp fiber, and the viscosity quickly recovers after the shear force disappears, which ensures that the emulsion is solidified in the pore channel in time, realizes the balance of deep anchoring and surface film forming, and lays a foundation for the crosslinking reaction of the subsequent gradient functional barrier layer; and the high viscosity and film forming property of the surface functional emulsion ensure that a continuous and dense cover layer is formed on the surface of the substrate, and the immediate superimposed coating of the two promotes the mutual diffusion of interface molecules, creating favorable conditions for the subsequent crosslinking reaction.

[0044] Further, in step S4, the stepwise drying includes promoting the penetration of the emulsion at 70-90°C first, and then triggering the crosslinking reaction at 110-130°C; specifically, the low-temperature treatment in the first stage ensures that the bottom functional emulsion has enough time to penetrate deeply into the micropore channel network and realize sufficient mechanical interlocking; the high-temperature treatment in the second stage activates the crosslinking reaction, so that the active groups in the bottom emulsion and the polycarboxylic acid crosslinking agent in the surface emulsion undergo esterification reaction to form a stable covalent bond network, which converts the physically superimposed functional layer into a chemically bonded integrated gradient barrier layer, significantly enhances the interlayer bonding strength and barrier performance, and effectively solves the problems of easy peeling and insufficient barrier performance of traditional coatings.

[0045] Specifically, in step S5, the anti-fouling coating is a water-based acrylic resin coating with a dry film thickness of 0.5-2 μm; the acrylic resin has low surface energy and good film forming property, and can form a continuous and transparent protective layer on the surface of the gradient functional barrier layer, reduce the surface energy through the directional arrangement of molecular chains, and make the packaging surface exhibit excellent hydrophobic and oil-proof properties, effectively preventing dirt adhesion and liquid infiltration, thereby improving the appearance retention and service life of the packaging.

[0046] Further, in step S6, the heat-sealing coating is a biodegradable polyester coating with a dry film thickness of 3-8 μm; the biodegradable polyester has good thermoplasticity and biocompatibility, and can melt and form a firm sealing interface during heat sealing, ensuring reliable sealing of the packaging in the automatic production process, while maintaining the overall degradability of the material, avoiding the potential impact of traditional non-degradable heat-sealing materials on the environment.

[0047] In summary, the process realizes the improvement of the function of the packaging paper by constructing a three-dimensional micropore network inside the substrate and forming a surface gradient functional layer through chemical crosslinking; the micropore network serves as an energy dissipation skeleton, converting local impact stress into multi-path dispersion, significantly improving the toughness and puncture resistance of the material; the gradient functional layer forms a dense barrier through interfacial crosslinking, effectively inhibiting the permeation of water vapor, oxygen and oil; the antifouling layer and the heat sealing layer further expand the functional application range of the packaging, and the whole process of the application scheme is based on a degradable material system, ensuring the environmental compatibility of the product from use to disposal, and providing a scheme with high performance and sustainability for high requirement packaging applications.

[0048] In order to further illustrate the technical scheme of the present application and the beneficial effects brought by it, specific examples and comparative examples will be described in detail below.

[0049] The raw materials involved in the examples and comparative examples of the present application are all commercially available market-grade commodities that meet the definition of the present application if not otherwise specified.

[0050] Example 1:

[0051] Material preparation:

[0052] Wood pulp fiber: select needle wood pulp fiber refined by mechanical refining, fiber length distribution is 1.8-2.6mm, average diameter distribution is 25-35pm, cellulose content is 75±2wt%, hemicellulose is 15±2wt%, lignin is 8±2wt%;

[0053] Water-soluble fiber: partially alcoholized polyvinyl alcohol fiber, alcoholization degree range is 87-89%, fiber length distribution is 3-7mm, fiber diameter distribution is 12-18pm;

[0054] Bottom functional emulsion: shear-thinning starch-based nanoemulsion, self-made: the self-making steps are as follows:

[0055] Select food-grade tapioca starch, pass through a 200-mesh sieve and place in a 105℃ oven for 2h to dehydrate, so that the water content is ≤1.5%, to obtain dehydrated starch;

[0056] Disperse 1KG of dehydrated starch in every 15L of water, stir at a rate of 200rpm, and raise the water bath temperature to 45℃, slowly add sodium hydroxide solution to adjust the pH to 11.5±0.2, continue stirring for 30min to swell the starch, add 8% of the dry weight of the starch of epoxy chloropropane dropwise, control the dropwise speed at 1mL / min, maintain the reaction temperature at 50℃±1℃, after 4h of reaction, neutralize with dilute hydrochloric acid to pH=7.0, centrifuge after the reaction is terminated, wash with deionized water to remove unreacted substances, and obtain the starch-based nanoemulsion;

[0057] The starch-based nanoemulsion has a solid content of 22% in the material of the present application, a static viscosity of 45±1.0 mPa-s at 25°C, and a viscosity of 12±1.0 mPa-s at a shear rate of 100 s -1 ;

[0058] The surface functional emulsion: commercially available polylactic acid microemulsion, solid content 35±1%, average particle size 250 250±20 nm, static viscosity 280±15 mPa-s, containing 3.0 wt% of citric acid crosslinking agent based on polylactic acid microemulsion;

[0059] The anti-fouling coating: water-based acrylic resin, solid content 30±1%;

[0060] The heat-seal coating: polybutylene succinate-adipate (PBSA) emulsion, solid content 40±1%;

[0061] Preparation process:

[0062] S1, mix wood pulp fibers with 5.0% of water-soluble fibers based on the total dry weight of the fibers in a hydraulic pulper, control the pulp concentration at 3.5 wt%, form by inclined wire former, get the wet paper page with basis weight of 65 g / m2 and water content of 65±2%;

[0063] S2, carry out zoned drying in a hot air circulating drying oven:

[0064] First, dry at 85℃±1℃ for 60 min, reduce the water content of the paper page to 30±0.5%;

[0065] Then dry at 105℃±2℃ for 90 min, completely dissolve the water-soluble fibers;

[0066] S3, coat on the front side of the substrate in turn:

[0067] The bottom functional emulsion: use a micrometric metering roll coater, wet film thickness 6 μm, coating amount 2.8 g / m 2 (dry weight);

[0068] The surface functional emulsion: immediately cover the coating with an anilox roll coater, wet film thickness 3 μm, coating amount 2.0 g / m 2 (dry weight);

[0069] S4, carry out staged drying in an infrared-hot air combined drying system:

[0070] First, treat at 90℃±2℃ for 120 min to promote the deep penetration of the bottom emulsion; then treat at 125℃±3℃ for 90 min to activate the esterification reaction;

[0071] S5, applying the anti-fouling coating layer using a knife coater, with a wet film thickness of 3 μm, and hot air drying at 135 ℃ for 45 min to form a dry film of 0.8 μm;

[0072] S6, applying the heat-seal coating layer using a micro gravure roll coater, with a wet film thickness of 9 μm, and drying at 115 ℃ for 60 min to form a dry film of 5 μm;

[0073] Example 2:

[0074] Material and process adjustment: the proportion of water-soluble fibers was adjusted to 3% of the total dry weight of fibers, and other conditions were the same as in Example 1;

[0075] Example 3:

[0076] Material and process adjustment: the solid content of the bottom functional emulsion was increased to 25%, the drying time was extended to 150 min, and other conditions were the same as in Example 1;

[0077] Example 4:

[0078] Material and process adjustment: the mass ratio of wood pulp fibers to hydrophobic modified particles was adjusted to 2:1, and other conditions were the same as in Example 1;

[0079] Comparative Example 1:

[0080] Material and process adjustment: only wood pulp fibers were used, without adding water-soluble fibers, and other conditions were the same as in Example 1;

[0081] Comparative Example 2:

[0082] Material and process adjustment: no citric acid crosslinking agent was added in the surface functional emulsion, and other conditions were the same as in Example 1;

[0083] Comparative Example 3:

[0084] Material and process adjustment:

[0085] A single viscosity (150 mPa·s) starch / polylactic acid composite emulsion was used to replace the gradient functional layer design, and other conditions were the same as in Example 1;

[0086] Performance test:

[0087] Puncture resistance: according to ASTM F1306 standard, using a texture analyzer;

[0088] Water vapor transmission rate (WVTR): according to ASTM E96 standard, test conditions 38 ℃, 90% RH;

[0089] Oxygen transmission rate (OTR): according to ASTM D3985 standard, test conditions 23 ℃, 50% RH;

[0090] Peel strength: according to ASTM D903 standard, using universal material testing machine;

[0091] Heat seal strength: according to ASTM F88 standard, test condition 135℃, 0.3 MPa, 2s;

[0092] The test result data is shown in Table 1 below:

[0093] Table 1 Performance test result data table

[0094]

[0095] Result analysis:

[0096] From the aspect of puncture resistance: Example 1 exhibits the best puncture resistance, significantly better than all the comparative examples, which fully proves the key role of the three-dimensional microporous network constructed by water-soluble fibers in enhancing the mechanics of the material. When the packaging material is subjected to local sharp impact, the microporous network can effectively dissipate energy through multi-path stress dispersion and pore wall friction mechanism, while Comparative Example 1 has a significant decrease in puncture resistance due to the complete absence of microporous structure, and Example 2 also has a decrease in performance due to the insufficient density of the microporous network caused by the low proportion of water-soluble fibers. This shows that there is an optimal range for the proportion of water-soluble fibers, and too high or too low will affect the integrity of the network structure, thereby affecting the final puncture resistance.

[0097] From the aspect of barrier performance: Example 1 achieves the best barrier effect in water vapor transmission rate and oxygen transmission rate, which is due to the successful construction of the gradient functional barrier layer. The bottom layer of nano-emulsion realizes deep penetration and filling through shear thinning characteristics, and the surface layer of micro-emulsion forms a continuous and dense film, and the two form an integrated barrier layer through heat-induced crosslinking reaction. Comparative Example 2 has a significant deterioration in barrier performance due to the lack of crosslinking agent, which proves the key role of chemical crosslinking in forming a dense barrier layer. Comparative Example 3 uses a single emulsion system, which has the worst barrier performance, further verifying the necessity of gradient functional layer design. Example 3 further improves the barrier performance by optimizing the parameters of the bottom layer emulsion, which shows that precise control of process parameters has an important influence on barrier effect.

[0098] From the interface bonding strength analysis: Example 1 shows the highest peeling strength, which is mainly due to the covalent bond network formed between the epoxy functionalized starch and the polycarboxylic acid crosslinking agent. This three-dimensional crosslinked structure converts the physically superimposed coating into a chemically bonded integrated interface, significantly enhancing the interlayer bonding force, while Comparative Example 2, due to the absence of crosslinking agent, relies only on physical adsorption, and the peeling strength is greatly reduced. Example 3 further improves the interface bonding strength by adjusting the solid content of the bottom layer emulsion and the drying time, indicating that the degree of crosslinking reaction directly affects the interface bonding quality. The test results of each example fully demonstrate the effectiveness of the chemical crosslinking mechanism in solving the peeling problem of traditional coatings.

[0099] From the process parameter optimization analysis: the performance differences of different examples reveal the optimal control range of key process parameters. The adjustment experiment of the proportion of water-soluble fibers shows that when the addition proportion is lower than the optimal value, the micro-pore network formation is incomplete, affecting the stress dispersion effect, while the solid content of the bottom layer functional emulsion and the drying time have a significant impact on the interface crosslinking density, which needs to be kept in proper balance. Too high may lead to insufficient penetration, and too low may affect the crosslinking effect. The viscosity ratio and coating interval time of the two emulsions in the gradient functional layer also need to be accurately controlled to ensure the sufficient diffusion of interface molecules and the effective progress of crosslinking reaction. These parameter optimizations provide an important basis for the industrialized production to achieve performance optimization.

[0100] In summary, the scheme of the present application introduces water-soluble fibers as sacrificial templates in wood pulp fiber substrates, forms a three-dimensional interconnected micro-pore network in situ after zoned drying, and then combines with the design of a gradient functional barrier layer to achieve multiple beneficial effects: First, the micro-pore network, as an energy dissipation skeleton, significantly improves the puncture strength and toughness of the material through multi-path stress dispersion and pore wall friction mechanism, solving the problem of easy tearing of traditional wood pulp packaging. Second, the gradient functional layer utilizes the shear thinning properties of the bottom layer starch-based nano-emulsion to achieve deep penetration and filling, and the high viscosity film-forming property of the surface layer polylactic acid emulsion, and through heat-induced crosslinking reaction to form a dense barrier interface, thereby significantly improving the barrier properties of water vapor, oxygen and oil, and enhancing the peeling strength of the coating and the substrate, effectively avoiding the defects of easy peeling of traditional coatings. Finally, the whole process is based on degradable materials, ensuring the environmental compatibility of the product from use to disposal, maintaining high performance while meeting environmental requirements.

[0101] Based on the ideal embodiments of the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents in the specification, and the technical scope must be determined according to the scope of claims.

Claims

1. A production process for biodegradable wood pulp packaging paper, characterized in that, Includes the following steps: S1. Mix wood pulp fibers with water-soluble fibers and form them into paper sheets to obtain wet paper sheets; S2. The wet paper sheet is dried in sections, so that the water-soluble fibers dissolve in situ during the drying process, forming a three-dimensional interconnected microporous network inside the wood pulp fiber substrate; S3. On the front side of the wood pulp fiber substrate, a bottom functional emulsion and a top functional emulsion are sequentially coated to form a composite wet film; wherein, the bottom functional emulsion penetrates and fills the microporous network, and the top functional emulsion forms a continuous film on the substrate surface; the bottom functional emulsion is a starch-based nanoemulsion with viscosity significantly decreasing with shear force, the solid content of the starch-based nanoemulsion is 20%-25%, the static viscosity at 25°C is 40-50 mPa·s, and the viscosity at a shear rate of 100 s⁻¹ is [missing value]. -1 The viscosity is below 15 mPa·s; the surface functional emulsion is a polylactic acid micron emulsion containing a reactive crosslinking agent, with a solid content of 30%-40%, an average particle size of 200-300 nm, and a static viscosity of 250-350 mPa·s; the reactive crosslinking agent is a polycarboxylic acid crosslinking agent, which accounts for 2%-4% of the solid content of the surface functional emulsion; S4. The composite wet film is dried in stages to cause a cross-linking reaction between the bottom functional emulsion and the surface functional emulsion, forming an integrated gradient functional barrier layer. S5. Apply an anti-fouling coating to the surface of the gradient functional barrier layer and cure it. S6. Apply a heat-sealing coating to the back of the wood pulp fiber substrate and cure it.

2. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: In step S1, the water-soluble fiber is a partially hydrolyzed polyvinyl alcohol fiber with a degree of hydrolysis of 85%-90%, an average length of 4-6 mm, and a diameter range of 10-20 μm; and the water-soluble fiber accounts for 3%-7% of the total dry weight of wood pulp fiber and water-soluble fiber.

3. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: In step S2, the partitioned drying includes: first drying at 70℃-90℃ for 50-70 minutes to reduce the moisture content of the paper to 25%-35%, and then drying at 95℃-115℃ for 80-100 minutes to completely dissolve the water-soluble fibers and form the three-dimensional interconnected microporous network.

4. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: In step S4, the crosslinking reaction is an esterification reaction between the active groups in the underlying functional emulsion and the polycarboxylic acid.

5. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: The sequential coating process in step S3 is as follows: first, the bottom functional emulsion is coated, and then the top functional emulsion is coated on top while the bottom emulsion is not completely dry.

6. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: The staged drying described in step S4 includes: first promoting emulsion penetration at 70℃-90℃, and then triggering a cross-linking reaction at 110℃-130℃.

7. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: The antifouling coating mentioned in step S5 is a water-based acrylic resin coating, and the dry film thickness of the antifouling coating is 0.5-2μm.

8. The production process of biodegradable wood pulp packaging paper according to claim 1, characterized in that: The heat-sealing coating in step S6 is a biodegradable polyester coating, and the dry film thickness of the biodegradable polyester coating is 3-8 μm.

9. A biodegradable wood pulp packaging paper, characterized in that, It is prepared based on the production process of any one of claims 1-8.

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