A paper-based high-performance environmentally friendly coating material and its preparation method

Abstract

The present invention provides a paper-based high-performance environmental protection coating material and a preparation method thereof. The pH value of the nano-cellulose solution is adjusted to be neutral and diluted to a clear and gum-free state. Then, pulp fibers are added to the diluted nano-cellulose solution, and a mixed system is obtained by blending. The mixed system is dehydrated to obtain a paper-based high-performance environmental protection coating material. A nano-cellulose coating is formed at the bottom of the prepared high-performance paper-based material, and the pulp fibers inside are combined through nano-cellulose. The preparation method proposed in this solution improves the mechanical properties and barrier properties of the paper-based material while simplifying the processing technology.

Description

Technical Field

[0001] The present invention relates to paper-based materials, and particularly to a high-performance environmentally friendly coating material for paper-based materials and a preparation method thereof. Background Art

[0002] Food packaging provides protection for food against physical, chemical, and biological changes. Currently, petroleum-based plastics are still mainly used in the market. Although petroleum-based plastics have the advantages of low cost, light weight, strong durability, and excellent barrier properties, their service life is short, and a large amount of pollution is generated during the recycling process, making them one of the improperly treated wastes. As an alternative, paper-based materials have the advantages of sustainable resource sources, biodegradability, and recyclability. However, their barrier properties and mechanical properties are poor, especially when wet, which is mainly attributed to the hydrophilic nature of their main component - plant fibers, as well as their porous internal structure and rough surface. Therefore, to achieve their wide application in the market, post-treatment processes such as hot pressing or lamination, coating, or integration with other materials (such as polymer additives, plastic films, or silicon / fluorine-containing coatings) are usually required, and the post-treatment processes may also affect their environmental protection characteristics.

[0003] In recent years, the sustainability and excellent properties of nanocellulose (CNFs) have attracted great attention. Nanocellulose is the smallest structural unit extracted from plant cell walls. It is a fiber with a diameter of less than 20 nm, a length of about 200 nm to several micrometers, and an aspect ratio greater than 150. It has the advantages of biodegradability, excellent mechanical properties, high film-forming ability, and surface modifiability. The pure CNF film after hot pressing has a dense packing, almost zero porosity, and certain hydrophobicity, thus showing excellent barrier properties. Therefore, the prior art has already used nanocellulose as a coating on paper substrates in food packaging applications.

[0004] Most traditional processes still use rod coating, spraying, or dip coating techniques to apply CNF as a coating for paper-based materials. For example, a laminated assembled reinforced paper-based material and its preparation method and application proposed in Chinese Patent CN107524043A layer by layer assemble the nanofiber coating repeatedly to stack and alternate on the pulp fibers, making the fiber surface structure complex to obtain a reinforced paper-based material. Such a processing technology still faces three major challenges: 1) high requirements for the viscosity and concentration of CNF; 2) multiple rounds of coating are required, resulting in a complex processing procedure; 3) it is difficult to ensure a uniform and stable high-quality coating; 4) multiple rounds of drying processes are required subsequently, resulting in excessive energy consumption. In addition, the high water content during the drying process may cause poor shrinkage of the paper substrate, thus affecting the mechanical properties.

[0005] In summary, how to improve the mechanical properties and barrier properties of pulp materials while simplifying the processing technology is a huge difficulty and challenge in the field of high-performance paper-based material processing. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a paper-based high-performance environmental protection coating, and to prepare a paper-based high-performance environmental protection coating material, so as to improve the mechanical properties and barrier properties of the paper-based material under the condition of simplifying the processing technology.

[0007] To achieve the above purpose, in the first aspect, the present technical solution provides a preparation method of a paper-based high-performance environmental protection coating, including the following steps:

[0008] Adjust the pH value of the nano-cellulose solution to 6.5-7.5, and dilute it to a clear and gum-free state. Then add pulp fibers to the diluted nano-cellulose solution to obtain a mixed system by blending.

[0009] Dehydrate the mixed system to obtain a paper-based high-performance environmental protection coating material.

[0010] It should be noted that this solution uses nano-cellulose CNFs to improve the mechanical properties and barrier properties of pulp fibers. However, different from the traditional process of forming paper from pulp fibers first and then coating, this solution directly dehydrates the blended nano-cellulose solution and pulp fibers to obtain a paper-based high-performance environmental protection coating material. The advantage of this is that it can avoid a series of problems caused by post-coating in the traditional process:

[0011] 1) There is no requirement for the viscosity and concentration of CNF: Before one-step papermaking filtration, CNF needs to be diluted and dispersed and compounded with pulp fibers to obtain a mixed system. Therefore, both high-concentration and low-concentration CNF can be used.

[0012] 2) The process flow is simplified: After blending evenly, only one-step papermaking filtration is required to form the coating.

[0013] 3) The realization of high-quality coating: The one-step filtration method can ensure a uniform and stable coating.

[0014] 4) Energy consumption is reduced: Only one-step papermaking filtration is required, and at the same time, the integrated CNF / pulp paper-forming system during the drying process can avoid the adverse shrinkage of the paper substrate caused by different internal stresses of multiple layers of materials during the traditional drying process, and the mechanical properties of the formed paper are guaranteed.

[0015] The reason why nanocellulose in the nanocellulose solution can act as a reinforcing agent is that nanocellulose has a very high specific surface area and is charged. This enables nanocellulose to effectively adsorb on the surface of pulp fibers like traditional polyelectrolyte-type reinforcing agents, increasing their contact bonding area. Meanwhile, the retained natural hemicellulose component can effectively solve the compatibility and bonding problem between the two components of nanocellulose and pulp fibers. In addition, nanocellulose can also fill the tiny voids between pulp fibers, and the long-chain structure of nanocellulose can play a role of physical bridging between the fibers, which enables nanocellulose to also act as a rigid filler and helps to form a favorable network structure.

[0016] Based on the above characteristics of nanocellulose, nanocellulose can simultaneously form a film on the surface of the pulp substrate to improve the barrier performance of the paper-based material and fill inside the paper-based material to improve the mechanical properties of the pulp substrate. However, considering that the cost of nanocellulose is much higher than that of pulp fibers, the post-coating method in the current processing technology requires repeated coating and drying, which will cause waste of nanocellulose. At the same time, the current processing technology is not only complex but may also damage the performance of the formed pulp substrate.

[0017] Based on this, the research team of this application found that when nanocellulose is first diluted and dispersed to obtain a nanocellulose solution and then blended with the pulp fiber solution, and the pH value of the nanocellulose solution is controlled to be neutral, dehydrating the mixed system can obtain a high-performance paper-based material with both barrier performance and mechanical properties.

[0018] This solution can use one or any combination of mechanical method, chemical method, and biological method to dilute and disperse nanocellulose to a clear and gum-free state. When using the mechanical method to dilute and disperse nanocellulose, one of high-speed dispersion, cell disruption, ball milling, and ultrasonic treatment can be used; when using the chemical method to dilute and disperse nanocellulose, one of hydrolysis method and oxidation method can be used; when using the biological method to disperse nanocellulose, bioenzymes can be selected.

[0019] In a specific embodiment, a high-speed disperser or cell disruptor with a speed of 850 - 10000 rpm is used to disperse for 10 minutes until it becomes clear and gum-free.

[0020] It should be noted that in this solution, the nanocellulose solution needs to be diluted and dispersed until it reaches a clear and gum-free state. The process of first diluting and dispersing the nanocellulose and then compounding it with pulp fibers to obtain a mixed system is considered because such a process is applicable to the treatment of nanocellulose at any high or low concentration. Specifically, whether it is high-concentration or low-concentration nanocellulose, it can be diluted to an appropriate concentration with deionized water and then dispersed to obtain a nanocellulose solution. Subsequently, the nanocellulose solution is blended with the defibrated pulp fiber solution. At this time, the dispersed nanocellulose can disperse the pulp fibers. On the one hand, due to the natural compatibility between CNF and pulp fibers, this dispersion step is beneficial to promoting the combination of CNF and pulp fibers. On the other hand, the high charge density of CNF itself makes the presence of CNF more conducive to the stable dispersion of pulp fibers in the solution. Conversely, if a high-concentration nanocellulose solution is directly added to the pulp fiber solution for simple dilution, it will lead to uneven dispersion of nanocellulose and thus the existence of local high-concentration regions, which will affect the application effect of subsequent dehydration. This is because the high aspect ratio of nanocellulose results in a large specific surface area and a large number of hydrogen bonds between fibers. The strong intermolecular force easily causes nanocellulose to exist in the form of aggregates in pulp fibers. If the pulp fiber solution is used to disperse nanocellulose, the penetration of water molecules cannot break the aggregates formed by nanocellulose, which will lead to uneven solution of the mixed system of nanocellulose and pulp fibers, and easily affect the morphology and properties of the subsequent formed paper.

[0021] In some preferred embodiments, the concentration of the diluted nanocellulose solution is <0.2 wt%.

[0022] In some embodiments, this solution uses any one process or a combined process such as deionized water washing, acid neutralization, and alkali neutralization to adjust the pH value of the nanocellulose solution to 6.5 - 7.5, and as close as possible to the neutral condition with a pH value of 7. This can make the pH value of the mixed system obtained after blending the nanocellulose solution and the pulp fiber solution also tend to be neutral. In other words, preferably, any one process or a combined process such as deionized water washing, acid neutralization, and alkali neutralization is used to adjust the pH value of the nanocellulose solution to neutral.

[0023] In a preferred embodiment, the pH of the mixed system is adjusted to 6.5 - 7.5 because, from the perspective of the product of the paper-based material, a suitable charge density can be maintained on the fiber surface in a neutral pH environment. If the mixed system is too acidic, the charge density on the fiber surface will be low in the form of carboxyl groups. If the mixed system is too alkaline, the fiber surface will be over-ionized, further affecting the properties of the fiber itself. From the perspective of the manufacturing process, a pH environment that is too acidic or too alkaline may cause corrosion of the filter membrane and the preparation device. Moreover, in the actual production process, the advantage of a neutral pH value is that the filtrate does not require additional chemicals for neutralization, reducing the post-treatment process for the tail liquid.

[0024] In some embodiments, the pulp fibers are beaten, and then the nanocellulose solution and the pulp fiber solution are mixed to obtain a mixed system. Beating refers to the process of mechanically treating the fibers in an aqueous medium, mainly causing internal fibrillation of the fibers, enhancing the fiber flexibility, increasing the specific surface area, and increasing the hydrogen bond binding sites between the fibers, which helps to enhance the mechanical properties of the formed paper.

[0025] In a specific embodiment, first, the obtained CNFs are diluted by adding deionized water, and the nanocellulose solution is obtained by dispersing with an Ultra-turrax homogenizer at 12000 rpm for 10 min. At this time, the pH of the nanocellulose solution is neutral. Then, the pulp board is defibrated to obtain the pulp fiber solution. Finally, the mixed system is obtained by mixing the nanocellulose solution and the pulp fiber solution and magnetically stirring for 5 min. This solution is applicable to the treatment of various nanocelluloses, and the nanocellulose is selected from one or more of enzymatically prepared nanocellulose, peroxyacid-oxidized cellulose nanofibers, TEMPO-oxidized cellulose nanofibers, carboxymethylated cellulose nanofibers, periodate-oxidized cellulose nanofibers, maleic anhydride-esterified cellulose nanofibers, phosphorylated cellulose nanofibers, and quaternized cellulose nanofibers. It should be noted that due to the different characteristics of different nanocelluloses, the corresponding dilution and dispersion methods are different.

[0026] In addition, the research team of this application found that the size, surface properties, and composition content of different nanocelluloses will affect the final high-performance pulp-based materials. In the embodiments of this solution, the diameter of the nanocellulose in the nanocellulose solution is <30 nm, the charge amount is >100 μmol / L, and the aspect ratio is >100.

[0027] In a preferred embodiment, the research team of the present application specifically selects a nanocellulose solution prepared from nanocellulose with a size of 2 to 30 nm, a charge amount of 100 to 2000 μmol / L, a hemicellulose content of 10% to 25%, and an aspect ratio greater than 100. When the mixed system obtained by blending such a nanocellulose solution with pulp fibers is subjected to suction filtration, it can satisfy the condition that part of the nanocellulose automatically reaches the bottom of the pulp fibers to form a coating, and the remaining part of the nanocellulose automatically fills the pulp fibers and binds to the pulp fibers, thereby forming a stable nanocellulose coating with certain barrier properties, and at the same time improving the tensile strength and elastic modulus of the paper-based material.

[0028] Regarding the selection of the size in the range of 2 to 30 nm:

[0029] The research team of the present application found that if the size of the nanocellulose is too large, it will be difficult for the nanocellulose to penetrate the wet filter cake formed by the pulp fibers during the suction filtration process, and thus it is difficult to form a uniform and dense nanocellulose coating, resulting in a poor barrier effect of the final pulp-based material; on the contrary, if the size of the nanocellulose is too small, the nanocellulose will more easily penetrate the wet filter cake formed by the pulp fibers during the suction filtration process. Although a barrier coating with good barrier effect will be formed, on the one hand, it will greatly affect the suction filtration time, and on the other hand, it will reduce the content of the nanocellulose combined with the pulp fibers, resulting in the failure to improve the mechanical properties of the paper-based material.

[0030] Regarding the selection of the charge amount in the range of 100 to 20000 μmol / L:

[0031] When the charge amount of the nanocellulose is too low, it will lead to the instability of the nanocellulose, and thus it cannot be well fibrillated, resulting in too large a size of the nanocellulose. At the same time, it will also make the formed nanocellulose coating more hydrophilic, resulting in the failure to significantly improve the barrier performance of the final paper-based material. There is sufficient repulsion between the nanofibers of the nanocellulose with a high charge amount, making its solution have higher stability. This repulsion can prevent the aggregation and precipitation of the nanocellulose fibers, thereby extending the service life of the solution. At the same time, the nanocellulose with a high charge amount can more easily form a cross-linked system, which has great potential in applications such as strengthening and coating stability.

[0032] Regarding the selection of the hemicellulose content in the range of 10% to 25%:

[0033] The content of hemicellulose mainly affects the binding ability between the added nanocellulose and pulp fibers. Hemicellulose can act as an adhesive to increase the binding rate between nanocellulose and pulp fibers. When the hemicellulose content is too low, on the one hand, the binding between nanocellulose and pulp fibers will be reduced, resulting in a decrease in the mechanical properties of the final paper-based material. On the other hand, it indicates that the nanocellulose is strongly treated during the preparation process, losing more hemicellulose. At this time, only nanocellulose with a smaller size can be formed, and if the size is too small, there will be a problem that the nanocellulose can easily penetrate the wet filter cake formed by the pulp fibers during the suction filtration process. Conversely, too high a hemicellulose content indicates that the microfibrillation treatment of nanocellulose is insufficient, and the size of the obtained nanocellulose is too high, which is not conducive to the formation of a nanocellulose coating.

[0034] In some embodiments, the mass ratio of nanocellulose in the nanocellulose solution to the mixed system is greater than 0.5 wt%. The reason for controlling this mass ratio in this solution is that too low an addition amount of nanocellulose is difficult to maintain the formation of the nanocellulose coating on the surface.

[0035] In addition, in some embodiments, the process for dehydrating the mixed system is selected from any one process or a combined process of vacuum suction filtration, pressure filtration, pressing, papermaking, casting, or draining of the mixed body.

[0036] In some embodiments, when vacuum filtration is used, the mixed system is subjected to vacuum suction filtration with a vacuum degree of -0.1 MPa under the condition that the absolute pressure is nearly 0. Specifically, in some embodiments, the mixed system is placed in a suction filtration device and the suction filtration conditions are set for suction filtration. The suction filtration device includes a suction filtration part and a vacuum pump. Among them, the suction filtration part from top to bottom is a filtration cup, filter paper, filter element, and a triangular liquid collection bottle, and the device connections of different components are sealed with fixed clips and sealing films. Finally, the suction filtration part and the vacuum pump are connected through a pipeline. Of course, when the mixed system is subjected to one-step suction filtration in this solution, the suction filtration time is related to the system of the mixed system. Generally speaking, it takes 6 - 10 minutes to complete the suction filtration of a filter cake for a 300 mL mixed system, and the specific time is affected by the objective filter element.

[0037] In some embodiments, when draining is used, the mixed system is dehydrated at a reasonable water flow rate of the drainage channel.

[0038] In some embodiments, when papermaking is used, the mixed system is evenly spread on a special papermaking net. With the filtration and draining effects of the papermaking net, part of the water seeps out through the mesh holes under the action of gravity. At the same time, by performing appropriate operations on the papermaking net (such as vibration, etc.), the water discharge can be further promoted, enabling the fibers to gradually form the prototype of the paper and realizing dehydration.

[0039] In some embodiments, when pressing is adopted, a certain pressure is applied to squeeze out the remaining moisture in the mixed system through the pressure effect.

[0040] It should be noted that this solution emphasizes one-step dehydration treatment of the mixed system to obtain a paper-based high-performance environmental protection coating material. In other words, only one dehydration treatment is required to obtain a paper-based high-performance environmental protection coating material.

[0041] It should be noted that when dehydrating the mixed system in this solution, the mixed system can be automatically stratified. Due to its nanoscale size, part of the nanocellulose is easy to penetrate through the pulp fibers to the bottom of the pulp fibers during the suction filtration process to form a dense nanofiber layer as a barrier coating; the remaining part of the nanocellulose, due to its high aspect ratio (greater than 100) and the natural hemicellulose structure on the surface, is easy to combine with the pulp fibers during the filtration process and is retained inside the pulp fibers as a reinforcing agent to improve the mechanical properties of the final high-performance paper-based material.

[0042] In addition, in some embodiments, after dehydrating the mixed system, drying is carried out to obtain a paper-based high-performance environmental protection coating material. The drying method after dehydration can be selected from any one of vacuum drying, freeze drying, natural air drying, and hot press drying. Preferably, this solution selects the method of hot press drying.

[0043] In order to avoid the situation where suction filtration cannot achieve complete drying, this solution additionally performs a drying method after suction filtration to help the paper form. Specifically, selecting the method of hot press drying can make the paper more compact.

[0044] In a second aspect, this solution provides a paper-based high-performance environmental protection coating material, which is prepared according to the preparation method of a paper-based high-performance environmental protection coating material mentioned in the first aspect. A nanocellulose coating is formed at the bottom of the paper-based high-performance environmental protection coating material, and the pulp fibers inside are combined through nanocellulose.

[0045] In some embodiments, the paper-based high-performance environmental protection coating material has good barrier properties. The water contact angle of the barrier surface of the nanocellulose coating of the paper-based high-performance environmental protection coating material is increased by more than 60º, and the oil resistance KIT>10.

[0046] In some embodiments, the paper-based high-performance environmental protection coating material has good mechanical properties. The Young's modulus of the nanocellulose coating of the paper-based high-performance environmental protection coating material is increased by nearly 50% compared with the pure paper-based material, and the tensile fracture strength is increased by nearly 60%.

[0047] Compared with the prior art, this technical solution has the following characteristics and beneficial effects:

[0048] This solution provides a paper-based high-performance environmentally friendly coating material and its preparation method. This preparation method innovates the traditional way of forming paper first and then coating. By first dispersing the nanofibrillated cellulose solution and then blending it with the pulp cellulose solution to obtain a neutral mixed system, and then subjecting the mixed system to a dehydration treatment process to automatically form a high-performance paper-based material by layering. A nanofibrillated cellulose coating is formed at the bottom of the paper-based high-performance environmentally friendly coating material, and the pulp fibers inside are bound by nanofibrillated cellulose. During the dehydration process, part of the nanofibrillated cellulose penetrates through the pulp fibers to reach the bottom to form a nanofibrillated cellulose coating, and the other part of the nanofibrillated cellulose binds to the pulp fibers, achieving simultaneous improvement in barrier performance and mechanical properties. Description of the Drawings

[0049] Figure 1 It is a schematic diagram of the microstructure of the high-performance pulp material containing a nanofibrillated cellulose coating prepared in Example 1.

[0050] Figure 2 The physical diagram after the water contact angle and oil resistance tests on the surface of the high-performance pulp material containing a nanofibrillated cellulose coating prepared in Example 1.

[0051] Figure 3 For Example 1, Examples 10 to 13, the surface property diagrams of the high-performance pulp materials containing a nanofibrillated cellulose coating prepared under different nanofibrillated cellulose addition ratios.

[0052] Figure 4 For Example 1, Examples 10 to 13, the mechanical property diagrams of the high-performance pulp materials containing a nanofibrillated cellulose coating prepared under different nanofibrillated cellulose addition ratios.

[0053] Figure 5 It is a process flow step diagram for preparing the high-performance pulp material containing a nanofibrillated cellulose coating in this solution. Detailed Embodiments

[0054] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0055] It can be understood that the term "one" should be understood as "at least one" or "one or more". That is, in one embodiment, the number of one element can be one, and in other embodiments, the number of this element can be multiple. The term "one" cannot be understood as a limitation on the number.

[0056] In order to verify the performance of the high-performance paper-based material in this solution, the following examples are designed in this solution:

[0057] Example 1

[0058] Prepare a nanocellulose solution: Use white pine as the raw material. Cut the wood along the extension direction of the plant fibers into pieces about 3 cm long, immerse them in 4 wt% peracetic acid, adjust the pH of the system to 4.5 with 20 wt% sodium hydroxide solution, heat and react at 85 °C for 1 h and then filter. Immerse the obtained solid fiber product in 4 wt% peracetic acid again and repeat the above process until the fiber becomes white. Filter the sample with a 250-mesh gauze and wash the fiber sample repeatedly with a large amount of deionized water until the filtrate is neutral. The finally obtained sample mainly contains cellulose and hemicellulose. Further, use a high-speed wall-breaking machine to fibrillate the fiber by rapid mechanical stirring and shearing to obtain a nanocellulose solution. The size of the nanocellulose in this nanocellulose solution is 3 nm, the charge amount is 400 μmol / L, the hemicellulose content is 20%, and the addition ratio of the nanocellulose is 7.0 wt%;

[0059] Disperse the nanocellulose solution: Disperse the nanocellulose in water and use a high-speed disperser to disperse it at 10000 rpm for 10 minutes until it becomes clear and free of colloid state.

[0060] Prepare a pulp fiber solution: Use pulp board as the raw material. Cut it into small pieces and then use a defibrator to defibrate it to obtain a dispersed pulp fiber solution. Squeeze it dry and store it for use. Weigh a certain amount of pulp fiber according to the solid content, and the basis weight of the paper is 80 g / m 2 .

[0061] Prepare a mixed system: Add the weighed pulp fiber to the dispersed nanocellulose solution. The mixed solution is dispersed under magnetic stirring to obtain a mixed system, and control the addition ratio of the nanocellulose solution and the pulp fiber solution to be 5:80.

[0062] Dehydrate to obtain a high-performance paper-based material: Place the mixed system in a self-built suction filtration device in the laboratory, control the vacuum degree to be -0.1 MPa, and obtain a high-performance environmentally friendly coating material for paper base by one-time suction filtration.

[0063] Example 2

[0064] To verify the influence of the dispersion order of nanocellulose and pulp fiber on the final high-performance paper-based material, design Example 2 in which the pulp fiber is dispersed first and then blended with nanocellulose, and other conditions are the same as in Example 1. In other words, in Example 2, the nanocellulose solution is not dispersed and is directly blended with the pulp fiber solution, and other processes are the same.

[0065] Examples 3 to 4:

[0066] To verify the influence of the pH value of the mixed solution on the final high-performance paper-based material, Examples 3 to 4 with different pH values of the mixed system from Example 1 were designed, and other conditions were the same as those in Example 1. The conditions of Examples 3 to 4 are shown in Table 1 below:

[0067] Table 1 Conditions of Examples 3 and 4

[0068] 。

[0069] Example 5

[0070] To verify the influence of the beating process on the final high-performance paper-based material, Example 5 was designed in which when defibrating the pulp fibers, the pulp fibers were put into a beater and the pulp fibers suspended in water were treated by mechanical action for defibrating beating, and other conditions were the same as those in Example 1.

[0071] Examples 6 to 9

[0072] To verify the influence of the nanocellulose size, surface charge amount, and hemicellulose content on the final high-performance paper-based material, nanocelluloses under different preparation processes were designed, and their properties were different from those in Example 1 in Examples 6 to 4, and other conditions were the same as those in Example 1. The conditions of Examples 6 to 9 are shown in Table 2 below:

[0073] Table 2 Nanocelluloses of Examples 6 to 9

[0074]

[0075] Examples 10 to 11:

[0076] To verify the influence of the addition ratio of nanocellulose on the final high-performance paper-based material, Examples 10 to 13 with different addition amounts of nanocellulose from Example 1 were designed, and other conditions were the same as those in Example 1. The conditions of Examples 10 to 13 are shown in Table 3 below:

[0077] Table 3 Conditions of Examples 6 to 9

[0078] 。

[0079] Performance test:

[0080] I. Morphology observation:

[0081] The apparent morphology of the material was observed by a field emission scanning electron microscope (SEM, SU-8010) on the test platform of the State Key Laboratory of Chemical Engineering Joint (Zhejiang University). The morphology diagram of the high-performance paper-based material obtained by observing Example 1 is as Figure 1 shown, and it can be seenFigure 1 A nanocellulose coating is formed on the bottom of the high-performance paper-based material therein, and the pulp fibers inside are crosslinked.

[0082] II. Surface barrier performance test:

[0083] Take the paper-based materials obtained in Example 1, Examples 6 to 9 for barrier performance testing.

[0084] (1) Water contact angle: Use the video optical contact angle measuring instrument (OCA 20) of the test platform of the State Key Laboratory of Chemical Engineering Joint (Zhejiang University) to measure the static water contact angle of the material.

[0085] (2) Oil resistance (KIT value): Measure the oil resistance by KIT test according to TAPPI T 559 method. The KIT solution is made by mixing n-heptane, toluene and castor oil. KIT 1 and KIT 12 represent the weakest and strongest oil resistance respectively.

[0086] The test results are as Figure 2 shown. It can be seen that the barrier surface of the paper-based material under Example 1 provides certain hydrophobicity (water contact angle WCA>60º) and excellent oil resistance (KIT>10). This is because under Example 1, a dense CNF film is formed on the surface of the paper-based material, which can coat the porous surface of the original paper-based material. At the same time, the CNF and pulp fibers inside the material are tightly entangled, and the CNF fills the pores of the original paper-based material. Therefore, small molecules such as water and oil need to pass through a longer path to penetrate the material, making the paper-based material obtained in Example 1 have excellent water, oil and air barrier properties. In addition, the test result data of the barrier performance of the paper-based materials in Example 1, Examples 6 to 9 are shown in Table 4 below.

[0087] Table 4 Test result data of the barrier performance of the paper-based materials in Example 1, Examples 6 to 9

[0088] .

[0089] III. Performance test:

[0090] Cut a spline with a length of 25 mm and a width of 5 mm and install it on a universal material testing machine. Adjust the tensile rate to 2.5 mm / min to measure the mechanical properties of the sample. The test results of Example 1, Examples 6 to 9 are shown in Table 5. It can be seen that at the same addition amount of nanocellulose, the mechanical properties of the paper-based material in Example 1 are significantly improved. Compared with the pure paper-based material, the Young's modulus is increased by nearly 200%, and the tensile fracture strength is increased by nearly 240%. This is because in Example 1, in the material of the present technology, the CNF forming the surface coating can coat the porous surface of the original paper-based material, and at the same time, the remaining CNF inside and the pulp fibers are tightly entangled to form a dense and stable network structure, which helps to improve the mechanical properties.

[0091] Table 5 Test results of the mechanical properties of the paper-based materials obtained in Example 1, Examples 6 to 9

[0092] 。

[0093] IV. Optimization analysis of the addition ratio:

[0094] Analyze the surface barrier properties and mechanical properties of the papers obtained in Examples 10 to 13. As Figure 3 and Figure 4 can be seen, as the addition amount of nanocellulose gradually increases, the surface properties of the formed paper tend to be stable, and the mechanical properties show a trend of first increasing and then decreasing. This is because too much nanocellulose will agglomerate inside, forming tensile weaknesses. Papers with excellent properties can be prepared when the addition ratio is between 3.5wt% - 10.5wt%.

[0095] V. Optimization analysis of the process sequence:

[0096] Conduct a KIT value analysis and a tensile strength analysis on Examples 1 and 2. The analysis method is as above. The results are shown in Table 6. It can be seen that the tensile strength of the paper-based material obtained in Example 1, where nanocellulose is first dispersed and then blended with the pulp fiber solution, is significantly better than that of Example 2. Moreover, from the KIT value of the paper-based material in Example 2, it can be clearly seen that only when nanocellulose is first dispersed and then blended with the pulp fiber solution can a high-performance paper-based material with a layered structure be formed.

[0097] Table 6 Performance tests of Example 1 and Example 10

[0098] 。

[0099] VII. Optimization analysis of the pH value of the mixed solution:

[0100] Perform KIT value analysis and tensile strength analysis on Example 1, Example 3, and Example 4, and additionally conduct zeta potential tests on nanocellulose. The results are shown in Table VII as follows:

[0101] Table VII Performance Tests of Example 1, Example 3, and Example 4

[0102] 。

[0103] It can also be seen from the KIT values of Example 3 and Example 4 that a high-performance paper-based material with good performance and layered structure can be formed only when the pH value of the nanocellulose solution is neutral.

[0104] VIII. Optimization Analysis of Beating Process:

[0105] Perform KIT value analysis and tensile strength analysis on Example 1 and Example 5. The analysis methods are the same as above, and the results are shown in Table VIII. It can be seen that the tensile strength of the paper-based fibers after beating can be further optimized.

[0106] Table VIII Performance Tests of Example 1 and Example 11

[0107] 。

[0108] VIII. Recycling and Recycling Test:

[0109] Select three commercially available barrier papers. Under the same conditions of storing fried chicken, the papers obtained in Example 1 of this solution are soaked, dispersed, pulped, and made into papers. The recycling performance of these three commercially available barrier papers is much worse, and large aggregates will still remain after the repulping process, which will cause large defects in the papers. This is because the coating materials of these commercially available barrier papers cannot be decomposed in water, and other additives (i.e., strengthening additives) may be used to bond the pulp fibers in an irreversible manner. The papers under this technology can be easily (using a simple 600 rpm magnetic stirrer) repulped (decomposed) into pulp fibers with minimal aggregates, and the final papers have a uniform appearance and good mechanical properties.

[0110] The present invention is not limited to the above best implementation manner. Anyone can obtain other various forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has a technical solution identical or similar to the present application, it falls within the protection scope of the present invention.

Claims

1. A preparation method of a paper-based high-performance environmental protection coating, characterized in that, It includes the following steps: Adjust the pH value of the nanocellulose solution to 6.5 - 7.5, dilute it to a clear and colloid-free state, and then add pulp fibers to the diluted nanocellulose solution to obtain a mixed system. The diameter of the nanocellulose in the nanocellulose solution is < 30 nm, the charge amount is > 100 μmol / L, and the aspect ratio is > 100; Dehydrate the mixed system to obtain a paper-based high-performance environmental protection coating material. A dense coating of nanocellulose is formed at the bottom of the paper-based high-performance environmental protection coating material, and the pulp fibers inside are combined through nanocellulose.

2. The preparation method of the paper-based high-performance environmental protection coating according to claim 1, characterized in that, The nanocellulose is selected from one or more of enzymatically hydrolyzed nanocellulose, peroxyacid-oxidized cellulose nanofibers, TEMPO-oxidized cellulose nanofibers, carboxymethylated cellulose nanofibers, periodate-oxidized cellulose nanofibers, maleic anhydride-esterified cellulose nanofibers, phosphorylated cellulose nanofibers, and quaternized cellulose nanofibers.

3. The preparation method of the paper-based high-performance environmental protection coating according to claim 1, wherein Adjust the nanocellulose solution to a pH value of 6.5 - 7.5 by using any one process or a combination process of washing with deionized water, acid neutralization, and alkali neutralization.

4. The preparation method of the paper-based high-performance environmental protection coating according to claim 1, characterized in that, Dilute the concentration of the nanocellulose solution to < 0.2 wt%.

5. The preparation method of the paper-based high-performance environmental protection coating according to claim 1, characterized in that, Perform beating treatment on the pulp fibers, and then mix the nanocellulose solution and the pulp fibers to obtain a mixed system.

6. The preparation method of the paper-based high-performance environmental protection coating according to claim 1, wherein The mass ratio of the nanocellulose in the nanocellulose solution to the mixed system is > 0.5 wt%.

7. The preparation method of the paper-based high-performance environmental protection coating according to claim 1, characterized in that, The process for dehydrating the mixed system is selected from any one process or a combination process of vacuum filtration, pressing, papermaking, and casting on the mixed body.

8. A paper-based high-performance environmentally friendly coating material, characterized in that, Prepared according to the preparation method of the paper-based high-performance environmental protection coating material described in any one of claims 1 to 7, a dense coating of nanocellulose is formed at the bottom of the paper-based high-performance environmental protection coating material, and the pulp fibers inside are combined through nanocellulose.

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