Reinforcing method of lightweight paper-based material

Abstract

The invention relates to the field of papermaking, and particularly provides a light-weight paper-based material reinforcing method which comprises the following steps: S100, pulping bleached chemical pulp, adding a reinforcing agent, and carrying out papermaking on a net to obtain finished paper; s200, the surface of finished paper is coated with the polyvinyl alcohol / nanocellulose coating, and after drying treatment, a paper-based material is obtained; s300, carrying out calendering treatment on the paper-based material to obtain a light-weight paper-based material; wherein the reinforcing agent comprises a dry strength agent and a wet strength agent. According to the invention, multi-dimensional synergistic enhancement is adopted, so that the light weight of the paper is ensured, and meanwhile, the dry and wet strength, the surface performance and the overall structure compactness of the paper are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of papermaking, in particular, the present application relates to a method for enhancing lightweight paper-based material. BACKGROUND

[0002] With the continuous development of modern papermaking industry, the lightweight of paper-based decorative material has become a trend to improve material performance and reduce cost. People increasingly pursue to reduce the grammage (g / m²) of paper while maintaining or even improving its mechanical properties and functionality to meet the multiple demands of green packaging, environmentally friendly special paper, high-performance composite substrate and other fields. Currently, this goal is usually achieved by increasing the beating degree or using reinforcing agents. However, increasing the beating degree often leads to a decrease in grammage, which easily causes a decrease in fiber bonding force, an increase in internal porosity, a decrease in mechanical properties, and some reinforcing agents such as PAE wet strength agent affect recyclability, while high molecular additives have high cost, low application efficiency, and marginal diminishing problem of dosage and performance improvement.

[0003] Therefore, how to reduce the grammage of paper while maintaining or even improving its mechanical properties and functionality has always been the goal pursued by experts in the field. SUMMARY

[0004] The present application aims to solve at least one of the above problems.

[0005] The present application provides a method for enhancing lightweight paper-based material, the enhancing method comprising the following steps: S100, after beating the bleached chemical pulp and adding the reinforcing agent, the paper is made by wire forming, and the paper is obtained; S200, the polyvinyl alcohol / nanocellulose coating is coated on the surface of the paper, and after drying treatment, the paper-based material is obtained; S300, the paper-based material is subjected to calendering treatment, and the lightweight paper-based material is obtained; Wherein, the reinforcing agent comprises dry strength agent and wet strength agent.

[0006] In the above technical features, the dry strength agent comprises cationic polyacrylamide; and / or the wet strength agent comprises a mixture of nanocellulose and cationic starch.

[0007] In any of the above technical solutions, the preparation method of the mixture of nanocellulose and cationic starch comprises: S101, the cationic starch is added to the deionized water, and after the first stirring treatment, the cationic starch transparent liquid is obtained in the gelatinized state; S102, the modified nanocellulose is added to the cationic starch transparent liquid, and the second stirring treatment is carried out to obtain the mixture of nanocellulose and cationic starch.

[0008] In any of the technical solutions above, in S102, the particle size of the modified nanocellulose is 20-50 nm; and / or the solid content of the mixture of nanocellulose and cationic starch is 2-3%.

[0009] In any of the technical solutions above, the temperature of the first stirring treatment is 80-85°C; and / or the time of the first stirring treatment is 30-45 min; and / or the rotation speed of the second stirring treatment is 8000-10000 rpm; and / or the time of the second stirring treatment is 15-20 min.

[0010] In any of the technical solutions above, in S200, the preparation method of the polyvinyl alcohol / nanocellulose coating includes: S201, stirring polyvinyl alcohol into deionized water until it is dissolved to obtain a polyvinyl alcohol solution; S202, after wetting the dry powder nanocellulose, adding deionized water, and performing shearing treatment under ultrasonic conditions to obtain a nanocellulose dispersion; S203, adding the polyvinyl alcohol solution into the nanocellulose dispersion, and then adding a crosslinking agent to perform dispersion treatment to obtain a polyvinyl alcohol / nanocellulose coating.

[0011] In any of the technical solutions above, the viscosity of the polyvinyl alcohol / nanocellulose coating is 300-600 mPa·s.

[0012] In any of the technical solutions above, in S202, the shearing treatment temperature is 25-40°C; and / or in S203, the dispersion treatment rotation speed is 1000-1500 rpm; and / or in S203, the dispersion treatment temperature is 40-60°C.

[0013] In any of the technical solutions above, in S100, the bleached chemical pulp includes bleached coniferous wood pulp, bleached broadleaf wood pulp, and bleached bamboo pulp; the mass ratio of the bleached coniferous wood pulp, the bleached broadleaf wood pulp, and the bleached bamboo pulp is 1:(0.2-0.3):(0.01-0.1).

[0014] In any of the technical solutions above, in S100, the beating degree of the bleached chemical pulp is 30-35°SR.

[0015] After adopting the technical solutions of the present application, the following technical effects can be achieved: 1. The enhancer is added to the bleached chemical pulp, the enhancer includes dry strength agent and wet strength agent, the dry strength agent and the wet strength agent are combined, not only can the lightweight paper still maintain excellent mechanical properties in the low grammage state, but also can realize the stable enhancement of the paper-based material in the wet state, the processing process, and the use environment through chemical cross-linking and physical network structure stability. 2. The polyvinyl alcohol / nanocellulose coating applied on the surface of the paper can synergize with the fibers in the paper through hydrogen bonding / chemical crosslinking to enhance the overall mechanical strength, thereby effectively improving the water resistance, surface uniformity and printability of the paper, and serving as an effective supplement to wet-end strengthening; 3. The calendering process can smooth the surface of the paper, further improve the density and interlayer bonding force, and help to improve the transparency and uniformity, so that the final paper has better touch, appearance and printing performance. BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0016] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application will be further described in detail below in conjunction with specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0017] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0018] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below.

[0019] In the related art, this goal is usually achieved by increasing the beating degree or using a reinforcing agent, however, increasing the beating degree often leads to a decrease in grammage, which easily causes a decrease in fiber bonding force, an increase in internal porosity, a decrease in mechanical performance, and some reinforcing agents such as PAE wet strength agent affect recyclability, while high molecular additives themselves have high cost, low application efficiency, and there is a problem of marginal diminishing returns between the use dosage and performance improvement.

[0020] Therefore, the present application provides a reinforcing method for lightweight paper-based materials, which adds a reinforcing agent and applies polyvinyl alcohol / nanocellulose coating on the surface of the paper to reduce the grammage of the paper while keeping the mechanical performance and functionality unaffected.

[0021] Specifically, the present embodiment provides a reinforcing method for lightweight paper-based materials, which includes the following steps: S100, adding a reinforcing agent after beating the bleached chemical pulp, and then web forming to obtain a paper; S200, applying polyvinyl alcohol / nanocellulose coating on the surface of the paper, and then drying to obtain a paper-based material; S300, calendering the paper-based material to obtain a lightweight paper-based material.

[0022] Preferably, the present application adopts multi-dimensional synergistic enhancement, aiming to significantly improve the dry and wet strength, surface performance and overall structural density while ensuring the lightweight of the paper; first, an enhancer is added to the bleached chemical pulp to form a skeleton through hydrogen bonding and electrostatic interaction between fibers in the initial stage of paper sheet formation, which determines the basic dry strength performance of the paper, the enhancer preferably includes dry and wet strength agents, the dry strength agent can enhance the bonding force between fibers through physical adsorption and chemical bonding, and preferably includes cationic polyacrylamide, which has stronger bridging and cross-linking ability; the wet strength agent forms a covalent bond cross-linking network between the fiber and the enhancer, and between the fiber and the fiber, and this cross-linking structure is not easily destroyed by water, and can maintain fiber bonding even in a wet state, and preferably includes a mixture of nanocellulose and cationic starch, which can form a stable structure in a wet state; the combination of dry and wet strength agents not only enables lightweight paper to maintain excellent mechanical properties in a low grammage state, but also realizes stable enhancement of the paper base material in a wet state, processing and use environment through chemical cross-linking and physical network structure stability, the dry and wet strength agents should be added after beating, the wet strength agent should be added first, and then the dry strength agent, and the dry strength agent should be dispersed in the pulp flow system for 2-5 minutes to ensure full adsorption and uniform distribution of the fibers; the bleached chemical pulp includes bleached softwood pulp, bleached hardwood pulp and bleached bamboo pulp; the mass ratio of bleached softwood pulp, bleached hardwood pulp and bleached bamboo pulp is 1:(0.2-0.3):(0.01-0.1), which can not only ensure softness, but also reduce cost, and the beating degree is preferably 30-35°SR, which softens the fiber surface, enhances the specific surface area and bonding capacity, and retains the fiber length; the process parameters during pressing should be controlled after papermaking, and the pressing preferably adopts double-pressure-zone pressing, the first pressure zone adopts a flexible press roll, the pressure is 2-2.5 MPa, the second pressure zone adopts a rigid press roll, the pressure is 3-4 MPa, and the water content of the paper sheet after pressing is controlled at 60-65%.

[0023] Preferably, before the paper web is made, a retention aid and a sizing agent need to be added to the pulp, the retention aid can improve the retention rate of fine components and fillers, and the sizing agent gives the paper water resistance, and the sizing agent preferably uses AKD or ASA, and the addition amount is 0.2-0.4% of the dry pulp mass.

[0024] Further, the preparation method of the mixture of nanocellulose and cationic starch includes: S101, adding cationic starch to deionized water, and performing first stirring treatment to obtain a cationic starch transparent liquid in a gelatinized state; S102, adding modified nanocellulose to the cationic starch transparent liquid, and performing second stirring treatment to obtain a mixture of nanocellulose and cationic starch.

[0025] Preferably, the present application uses the above method to prepare the mixture of nanocellulose and cationic starch, to ensure the dispersion stability of the cationic starch and nanocellulose complex reinforcing system, maximize the synergistic effect, and the rheological properties and reinforcing efficiency in the application process; first, the cationic starch is gelatinized to realize the dissolution and structure unfolding of the cationic starch, so as to have good dispersibility and reinforcing effect basis, and the gelatinization temperature range is generally between 75-90°C, therefore, the temperature of the first stirring treatment is 80-85°C, and the time is 30-45min, which can ensure that the gelatinization reaction is complete and the chain segment is evenly unfolded, which is helpful to form a stable transparent solution and avoid agglomeration or unevenness in the subsequent mixing stage; after the gelatinization of the cationic starch, the modified nanocellulose is added for the second stirring treatment, and the modified nanocellulose is preferably nanocellulose treated by high-iodic acid oxidation to build a micro network structure and play a synergistic reinforcing effect, the second stirring treatment is carried out at a speed of 8000-10000rpm for 15-20min, which is conducive to the complete depolymerization and uniform distribution of the modified nanocellulose in the cationic starch, and the particle size of the modified nanocellulose is 20-50nm. The specific surface area of the modified nanocellulose with the particle size in the range is large, which is easy to form a fine physical network in the cationic starch system and improve the compactness of the paper sheet.

[0026] Preferably, the solid content of the mixture of nanocellulose and cationic starch is 2-3%, which can form a uniform liquid system suitable for pulp wet end addition or paper surface coating, at this time, the viscosity of the mixture of nanocellulose and cationic starch is moderate, which is convenient for stirring, pumping and application, and at the same time can improve the reinforcing efficiency; if the solid content is too high, it will lead to stirring difficulty, extremely viscous system and easy agglomeration, and if the solid content is too low, it will result in low reinforcing efficiency, high unit energy consumption and poor retention effect.

[0027] Preferably, polyvinyl alcohol / nanocellulose coating is coated on the surface of the paper, the polyvinyl alcohol has good film forming property, high strength and degradability, and the nanocellulose can enhance the toughness and barrier property of the coating film, the use of polyvinyl alcohol / nanocellulose coating can further repair the micropores of the paper and improve the surface bonding force, and the polyvinyl alcohol / nanocellulose coating can also synergize with the fibers in the paper through hydrogen bond / chemical crosslinking to enhance the overall mechanical strength, thereby effectively improving the water resistance, surface uniformity and printing suitability of the paper, which is an effective supplement to the wet end reinforcement; after the polyvinyl alcohol / nanocellulose coating is coated, drying treatment is carried out to form a uniform and stable coating on the surface of the paper.

[0028] Further, in S200, the preparation method of the polyvinyl alcohol / nanocellulose coating includes: S201, polyvinyl alcohol is added to deionized water and stirred until dissolved to obtain a polyvinyl alcohol solution; S202, after the dry powder nanocellulose is wetted, it is added into deionized water, and shearing treatment is carried out under ultrasonic condition to obtain a nanocellulose dispersion liquid; S203, the polyvinyl alcohol solution is added into the nanocellulose dispersion liquid, and a crosslinking agent is further added for dispersion treatment to obtain a polyvinyl alcohol / nanocellulose coating.

[0029] Preferably, the preparation method of the polyvinyl alcohol / nanocellulose coating in the present application aims to construct a water-based coating system with good dispersibility, suitable rheological property, strong film-forming ability and enhancement effect, which is especially suitable for surface enhancement and functional improvement of lightweight paper-based materials. First, the polyvinyl alcohol is added into deionized water and stirred until dissolved. Dissolving the polyvinyl alcohol alone ensures its complete dispersion and dissolution, avoiding unevenness and aggregation after mixing with nanocellulose, and laying a foundation for forming a uniform coating formula subsequently. Since nanocellulose has a high specific surface area and strong hydrogen bonding, it is prone to aggregation in water. Therefore, the nanocellulose needs to be wetted first and then added into deionized water for shearing treatment and dispersion. This can avoid the aggregation of dry powder nanocellulose when it directly contacts water. Shearing treatment is carried out at 25-40°C, which can achieve good dispersion and avoid thermal degradation of the cellulose structure. Finally, the polyvinyl alcohol solution is added into the nanocellulose dispersion liquid, and a crosslinking agent is further added for dispersion treatment, which can better wrap and disperse the nanocellulose and form a continuous interpenetrating network. The rotation speed of the dispersion treatment is 1000-1500 rpm, which is beneficial to the crosslinking reaction. The temperature is 40-60°C, which can provide sufficient shear force to avoid aggregation while maintaining the stability of the system.

[0030] Preferably, a calendering treatment is finally carried out to smooth the surface of the paper, further improve the density and interlayer bonding strength, and the purpose is to shape the surface, enhance the density, and improve the visual and use performance. After the coating is formed, moderate calendering is helpful to improve the transparency and uniformity, so that the final paper has better touch, appearance and printing performance, which is especially suitable for packaging and special paper applications. The temperature of the calendering treatment is preferably 110-130°C.

[0031] Example 1 The present embodiment provides a method for enhancing lightweight paper-based materials, which comprises the following steps: S100, after the bleached chemical pulp is beaten and the reinforcing agent is added, the paper is made by wire forming; S200, the polyvinyl alcohol / nanocellulose coating is coated on the surface of the paper, and after drying treatment, a paper-based material is obtained; S300, the paper-based material is subjected to calendering treatment to obtain a lightweight paper-based material; The reinforcing agent includes dry reinforcing agent and wet reinforcing agent, the dry reinforcing agent is cationic polyacrylamide, and the wet reinforcing agent is a mixture of nano-cellulose and cationic starch; the bleached chemical pulp includes bleached coniferous wood pulp, bleached broad-leaved wood pulp and bleached bamboo pulp; the mass ratio of the bleached coniferous wood pulp, the bleached broad-leaved wood pulp and the bleached bamboo pulp is 1:0.2:0.01, and the beating degree is 30°SR.

[0032] Embodiment 2 The embodiment provides a reinforcing method of a lightweight paper-based material, and the reinforcing method comprises the following steps: S100, after the bleached chemical pulp is beaten and the reinforcing agent is added, the paper web is formed by papermaking to obtain paper; S200, the polyvinyl alcohol / nano-cellulose coating is coated on the surface of the paper, and after drying treatment, a paper-based material is obtained; S300, the paper-based material is subjected to calendering treatment to obtain a lightweight paper-based material; The reinforcing agent includes dry reinforcing agent and wet reinforcing agent, the dry reinforcing agent is cationic polyacrylamide, and the wet reinforcing agent is a mixture of nano-cellulose and cationic starch; the bleached chemical pulp includes bleached coniferous wood pulp, bleached broad-leaved wood pulp and bleached bamboo pulp; the mass ratio of the bleached coniferous wood pulp, the bleached broad-leaved wood pulp and the bleached bamboo pulp is 1:0.3:0.1, and the beating degree is 35°SR. The preparation method of the mixture of nano-cellulose and cationic starch comprises the following steps: S101, the cationic starch is added to deionized water, and first stirring treatment is carried out at 80°C for 45min to obtain a cationic starch transparent solution in a gelatinized state; S102, the modified nano-cellulose with a particle size of 20nm is added to the cationic starch transparent solution, and second stirring treatment is carried out at a rotating speed of 8000rpm for 20min to obtain a mixture of nano-cellulose and cationic starch; The solid content of the mixture of nano-cellulose and cationic starch is 2%.

[0033] Embodiment 3 The embodiment provides a reinforcing method of a lightweight paper-based material, and the reinforcing method comprises the following steps: S100, after the bleached chemical pulp is beaten and the reinforcing agent is added, the paper web is formed by papermaking to obtain paper; S200, the polyvinyl alcohol / nano-cellulose coating is coated on the surface of the paper, and after drying treatment, a paper-based material is obtained; S300, the paper-based material is subjected to calendering treatment to obtain a lightweight paper-based material; The reinforcing agent comprises dry reinforcing agent and wet reinforcing agent, the dry reinforcing agent is cationic polyacrylamide, the wet reinforcing agent is a mixture of nano-cellulose and cationic starch, the bleached chemical pulp comprises bleached coniferous wood pulp, bleached broad-leaved wood pulp and bleached bamboo pulp, the mass ratio of the bleached coniferous wood pulp, the bleached broad-leaved wood pulp and the bleached bamboo pulp is 1:0.3:0.05, and the beating degree is 32°SR. The preparation method of the mixture of nano-cellulose and cationic starch comprises the following steps: S101, adding cationic starch into deionized water, and performing first stirring treatment at 85°C for 30 minutes to a gelatinized state to obtain a cationic starch transparent solution; S102, adding modified nano-cellulose with a particle size of 50nm into the cationic starch transparent solution, and performing second stirring treatment at a rotating speed of 10000rpm for 15 minutes to obtain the mixture of nano-cellulose and cationic starch; The solid content of the mixture of nano-cellulose and cationic starch is 3%; In S200, the preparation method of the polyvinyl alcohol / nano-cellulose coating comprises the following steps: S201, adding polyvinyl alcohol into deionized water and stirring until the polyvinyl alcohol is dissolved to obtain a polyvinyl alcohol solution; S202, after wetting dry nano-cellulose, performing shearing treatment under ultrasonic and at 25°C to obtain a nano-cellulose dispersion; S203, adding the polyvinyl alcohol solution into the nano-cellulose dispersion, and then adding a crosslinking agent, and performing dispersion treatment at 40°C and at a rotating speed of 1000rpm to obtain the polyvinyl alcohol / nano-cellulose coating; The viscosity of the polyvinyl alcohol / nano-cellulose coating is 300mPa·s.

[0034] Embodiment 4 The embodiment provides a reinforcing method of a lightweight paper-based material, and the reinforcing method comprises the following steps: S100, after beating the bleached chemical pulp, sequentially adding a retention aid, a reinforcing agent and a sizing agent, and then web-forming to obtain paper; S200, coating the polyvinyl alcohol / nano-cellulose coating on the surface of the paper, and performing drying treatment to obtain the paper-based material; S300, performing calendering treatment on the paper-based material to obtain the lightweight paper-based material; The reinforcing agent comprises dry reinforcing agent and wet reinforcing agent, the dry reinforcing agent is cationic polyacrylamide, the wet reinforcing agent is a mixture of nano-cellulose and cationic starch, the bleached chemical pulp comprises bleached coniferous wood pulp, bleached broad-leaved wood pulp and bleached bamboo pulp, the mass ratio of the bleached coniferous wood pulp, the bleached broad-leaved wood pulp and the bleached bamboo pulp is 1:0.3:0.05, and the beating degree is 32°SR. The preparation method of the mixture of nanocellulose and cationic starch comprises the following steps: S101, adding cationic starch into deionized water, and performing first stirring treatment at 85°C for 30 min to a gelatinization state to obtain a cationic starch transparent solution; S102, adding modified nanocellulose with a particle size of 50 nm into the cationic starch transparent solution, and performing second stirring treatment at a rotation speed of 10,000 rpm for 15 min to obtain the mixture of nanocellulose and cationic starch; The solid content of the mixture of nanocellulose and cationic starch is 3%; In S200, the preparation method of the polyvinyl alcohol / nanocellulose coating comprises the following steps: S201, adding polyvinyl alcohol into deionized water and stirring until dissolved to obtain a polyvinyl alcohol solution; S202, after wetting dry powder nanocellulose, adding it into deionized water, and performing shearing treatment under ultrasonic and at 40°C to obtain a nanocellulose dispersion; S203, adding the polyvinyl alcohol solution into the nanocellulose dispersion, and then adding a crosslinking agent, and performing dispersion treatment at 60°C and at a rotation speed of 1,500 rpm to obtain the polyvinyl alcohol / nanocellulose coating; The viscosity of the polyvinyl alcohol / nanocellulose coating is 300 mPa·s.

[0035] Performance test The paper-based material is made by using the light-weight paper-based material reinforcing method of Examples 1-4, and the following tests are performed thereon: Dry tensile strength test: the paper-based material made by using the light-weight paper-based material reinforcing method of Examples 1-4 is subjected to dry tensile strength test according to GB / T 12914; Wet tensile strength test: the paper-based material made by using the light-weight paper-based material reinforcing method of Examples 1-4 is subjected to wet tensile strength test according to GB / T 465.2; Surface strength test: the paper-based material made by using the light-weight paper-based material reinforcing method of Examples 1-4 is subjected to adaptability printing test, and the critical speed of surface rupture of the paper-based material is recorded; Tear resistance test: the paper-based material made by using the light-weight paper-based material reinforcing method of Examples 1-4 is subjected to tear resistance test according to GB / T 455; Folding endurance test: the paper-based material made by using the light-weight paper-based material reinforcing method of Examples 1-4 is subjected to folding endurance test according to GB / T 457; The test results are shown in Table 1: As can be seen from Table 1, the dry tensile strength, wet tensile strength, surface strength, tear strength and folding endurance of the paper-based material made by the light-weight paper-based material reinforcing method of Examples 1-4 are all good, indicating that the light-weight paper-based material reinforcing method described in the present application can bring better performance to the paper-based material, especially the method in Example 3 and Example 4, because the process parameters used in Example 3 and Example 3 are more suitable and the preparation method of the polyvinyl alcohol / nanocellulose coating described in the present application is used, and the performance of Example 4 is better than that of Example 3, because the paper-based material is additionally added with a retention aid and a sizing agent in Example 4, thereby giving the paper-based material better performance.

[0036] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "a specific embodiment" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0037] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art, without departing from the spirit and scope of the present application, can make various changes and modifications, and therefore the protection scope of the present application should be limited by the scope defined in the claims.

Claims

1. A method for reinforcing a lightweight paper-based material, characterized in that: The enhancement method comprises the following steps: S100, beating the bleached chemical pulp, adding a reinforcing agent, and then making paper on the screen to obtain paper; S200, applying a polyvinyl alcohol / nanocellulose coating on the surface of the paper, and drying the coating to obtain a paper-based material; S300, performing calendering treatment on the paper-based material to obtain a lightweight paper-based material; Wherein, the reinforcing agent includes a dry strength agent and a wet strength agent.

2. The enhancement method according to claim 1, characterized in that The dry strength agent comprises cationic polyacrylamide; and / or The wet strength agent includes a mixture of nanocellulose and cationic starch.

3. The enhancement method according to claim 2, characterized in that The preparation method of the mixture of nanocellulose and cationic starch comprises: S101, adding cationic starch to deionized water, and performing a first stirring process until the mixture is gelatinized to obtain a cationic starch transparent liquid; S102, adding the modified nanocellulose to the cationic starch transparent liquid, performing a second stirring process, and obtaining a mixture of the nanocellulose and cationic starch.

4. The enhancement method according to claim 3, characterized in that In the above S102, The particle size of the modified nanocellulose is 20-50 nm; and / or The solid content of the mixture of nanocellulose and cationic starch is 2-3%.

5. The enhancement method according to claim 3, characterized in that: The temperature of the first stirring treatment is 80-85°C; and / or The first stirring treatment lasts for 30-45 minutes; and / or The rotation speed of the second stirring process is 8000-10000 rpm; and / or The second stirring treatment lasts for 15-20 minutes.

6. The enhancement method according to claim 1, characterized in that In S200, the method for preparing the polyvinyl alcohol / nanocellulose coating includes: S201, adding polyvinyl alcohol to deionized water and stirring until dissolved to obtain a polyvinyl alcohol solution; S202, wetting the dry powdered nanocellulose, adding it to deionized water, and subjecting it to shear treatment under ultrasonic conditions to obtain a nanocellulose dispersion; S203, adding the polyvinyl alcohol solution to the nanocellulose dispersion, and then adding a crosslinking agent, performing a dispersion treatment to obtain the polyvinyl alcohol / nanocellulose coating.

7. The enhancement method according to claim 6, characterized in that: The viscosity of the polyvinyl alcohol / nanocellulose coating is 300-600 mPa·s.

8. The enhancement method according to claim 6, characterized in that: In said S202, the temperature of said shearing treatment is 25-40°C; and / or In S203, the rotation speed of the dispersion treatment is 1000-1500 rpm; and / or The time in S203 is and the temperature of the dispersion treatment is 40-60°C.

9. The enhancement method according to claim 1, characterized in that: In the S100, The bleached chemical pulp includes bleached softwood pulp, bleached hardwood pulp and bleached bamboo pulp; The mass ratio of the bleached coniferous pulp, the bleached broadleaf pulp and the bleached bamboo pulp is 1: (0.2-0.3): (0.01-0.1).

10. The enhancement method according to claim 1, characterized in that: In the S100, the beating degree of the bleached chemical pulp is 30-35°SR.

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