Paper base material bio-based high-barrier Pickering emulsion coating as well as preparation method and application thereof

Abstract

The invention relates to a paper substrate bio-based high-barrier Pickering emulsion coating and a preparation method and application thereof, and belongs to the technical field of paper coatings, the prepared coating has excellent waterproof and oil-proof performance and is suitable for surface coating of substrates such as paper, the emulsion is prepared by taking glycerol as a plasticizer and chitosan as an oil-proof agent, and the emulsion is prepared by taking the chitosan as an oil-proof agent. The cellulose nanocrystal is used as an emulsifier, and the alkyl ketene dimer AKD and palm wax are used as an oil phase. After the emulsion is coated on the surface of paper, a high-barrier coating with a core-shell structure is formed, and the core-shell structure is clear through electron microscope observation; the hydrophobic angle of the coating can reach 130 degrees to the maximum, and the coating shows remarkable hydrophobicity and oil resistance. The coating is composed of bio-based materials, has the advantages of environmental protection and sustainability, is suitable for application requirements of degradable and green packaging, is simple in preparation process and excellent in performance, and can provide efficient barrier performance for paper packaging materials.

Description

Technical Field

[0001] The invention belongs to the technical field of paper coatings, and in particular relates to a bio-based high-barrier Pickering emulsion coating for a paper substrate, and a preparation method and application thereof. Background Art

[0002] In traditional paper waterproof and oil-proof treatment technology, lamination processes are usually used to achieve barrier properties, such as lamination with polymer materials such as polyethylene and polypropylene. However, although these lamination technologies can effectively improve the waterproof and oil-proof properties of paper, they have many defects: first, most of these lamination materials are petroleum-based materials, which are not only non-degradable, but also cause serious pollution to the environment, making it difficult to achieve the goal of sustainable development; second, the lamination process is relatively complicated, usually requiring the use of high-temperature heating, solvents and other chemical methods, with a long process flow and high energy consumption, and harmful gases may be released during the production process, increasing production costs and environmental risks; in addition, the paper after lamination cannot be recycled again, further aggravating resource waste and environmental burden.

[0003] In order to address the above problems, Pickering emulsion-based coating technology has gradually attracted attention in recent years. Pickering emulsion refers to an emulsion system stabilized by solid particles. It has good stability and does not require the addition of traditional surfactants, so it has higher environmental performance. In the field of paper coating, Pickering emulsion technology uses inorganic or organic solid particles as emulsifiers to prepare coatings with high barrier properties. It can effectively replace traditional petroleum-based coating materials and achieve waterproof and oil-proof functions of paper. In addition, this coating technology has a simple process, low energy consumption, and does not require high temperature or organic solvents, further reducing the negative impact on the environment. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a paper substrate bio-based high-barrier Pickering emulsion coating and a preparation method and application thereof. The prepared coating can not only improve the waterproof and oil-proof properties of paper, but also meet the needs of green environmental protection and sustainable development, and is suitable for large-scale industrial applications, and has important application value and broad market prospects.

[0005] The present invention solves the technical problem by the following technical solutions:

[0006] A paper-based bio-based high-barrier Pickering emulsion coating, the components and weight proportions of the coating are:

[0007]

[0008] The deionized water, acetic acid, nanocellulose, glycerol and chitosan constitute the water phase, and the alkyl ketene dimer and palm wax constitute the oil phase.

[0009] Moreover, the nanocellulose is one of cellulose nanocrystals, cellulose nanofibers and bacterial cellulose.

[0010] Moreover, the deacetylation degree of the chitosan is greater than or equal to 95%, and the viscosity is 100-200 mpa.s.

[0011] Moreover, the alkyl ketene dimer is a waxy body with a solid content of 90%.

[0012] Moreover, the palm wax and glycerin are food grade palm wax and food grade glycerin respectively.

[0013] A method for preparing a paper-based bio-based high-barrier Pickering emulsion coating, wherein the steps of preparing the paper-based bio-based high-barrier Pickering emulsion coating are as follows:

[0014] S1, preparing acetic acid and dissolving it in deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing nanocellulose in the acetic acid aqueous solution to form a mixed solution 1;

[0015] S2, heating the mixed solution 1 to 50° C., then sequentially adding glycerol and chitosan thereto, stirring until fully dissolved, to form a mixed solution 2;

[0016] S3, heating the blended liquid 2 to 90°C, then adding alkyl ketene dimer and palm wax thereto in turn, heating and stirring for 1 to 2 hours until the two waxy substances melt to form a blended liquid 3, then maintaining the speed of the high-speed shear emulsifier at 10000r / min to emulsify the blended liquid 3 for 5 to 10 minutes, and finally obtaining a Pickering emulsion coating.

[0017] An application of the paper substrate bio-based high barrier Pickering emulsion coating in a paper-based high barrier coating, wherein the emulsion coating is applied on the surface of the paper-based material, and the coating amount is 2 to 8 g / m 2 .

[0018] The advantages and beneficial effects of the present invention are:

[0019] 1. Compared with the traditional coating process, the present invention does not require complex processes with high temperature and high energy consumption, which reduces energy consumption and resource waste in the production process. In addition, all materials are natural or renewable materials, and do not contain traditional petroleum-based materials, which is in line with the trend of environmental protection and sustainable development.

[0020] 2. The cellulose nanocrystals used in the present invention have a high specific surface area and good mechanical strength, and can be used as an emulsifier in the Pickering emulsion system to stabilize the emulsion structure, making the coating system more stable and less prone to stratification or precipitation.

[0021] 3. The glycerol used in the present invention has a good moisturizing effect and acts as a plasticizer in the coating, which can improve the flexibility and ductility of the coating and prevent the coating from cracking. Glycerol, as a hydrophilic substance, helps to adjust the hydrophilicity of the coating in the emulsion, so that the coating has a certain moisture resistance, which is beneficial to the improvement of waterproof performance.

[0022] 4. The chitosan used in the present invention has good film-forming properties and excellent oil-proof properties after film formation. It can cooperate with cellulose nanocrystals CNC to form a dense film layer structure, which helps to improve the oil-proof properties of the paper surface.

[0023] 5. The alkyl ketene dimer AKD used in the present invention is a commonly used waterproof material in the papermaking industry. When added to the emulsion, it can play a certain synergistic role with the emulsifier cellulose nanocrystals to jointly construct a stable emulsion system and a special coating microstructure, mainly playing the following three roles:

[0024] Hydrophobic interaction: AKD molecules have long-chain alkyl groups and are significantly hydrophobic, while the surface of cellulose nanocrystals usually has hydroxyl groups and is hydrophilic. AKD can cover the surface of cellulose nanocrystals under certain conditions to form a hydrophobic layer. This physical adsorption is formed through hydrophobic interaction or van der Waals force, making the cellulose surface more hydrophobic.

[0025] Interfacial activity effect: Since AKD has amphiphilic properties (alkyl chains are hydrophobic and heads are hydrophilic), it can work synergistically with cellulose nanocrystals at the water-oil interface to help stabilize the emulsion. This synergistic effect can enhance the stability and hydrophobicity of the Pickering emulsion.

[0026] Chemical adsorption (limited chemical reaction): Under certain conditions, AKD may undergo a certain degree of esterification reaction on the cellulose surface, especially under alkaline conditions. The ketone group of AKD can chemically bond with the hydroxyl groups on the cellulose nanocrystals to form β-ketoester bonds, which can greatly increase the stability of the cellulose nanocrystal-stabilized water-in-oil emulsion.

[0027] 6. The palm wax used in the present invention is composed of long-chain fatty acid esters, fatty alcohols and hydrocarbons, all of which have strong hydrophobic properties. It is precisely because of these characteristics that it is used as a waterproof coating, lubricant and polishing agent in many applications. However, it is a waxy solid under low temperature conditions. The palm wax can be dispersed into tiny particles by emulsification treatment and dispersed in water to form an emulsion, which will reduce the freezing point of the wax and maintain its fluidity at low temperatures. The chemical product surfactants commonly used in industrial production are emulsified to meet actual production needs, but the environmental problems brought about are also becoming increasingly serious. Therefore, the cellulose nanocrystals selected by the present invention can act as traditional surfactants to emulsify the oil-water mixture composed of palm wax, and are green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a microscope image of the Pickering emulsion coating obtained in Example 3 of the present invention;

[0029] Figure 2 This is a microscope image of the Pickering emulsion coating obtained in Example 3 of the present invention after being stabilized for one month;

[0030] Figure 3 This is a scanning electron microscope image of the surface of paper coated with the Pickering emulsion coating obtained in Example 3 of the present invention;

[0031] Figure 4 This is a water contact angle diagram of paper coated with Pickering emulsion coating obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0033] A paper-based bio-based high-barrier Pickering emulsion coating, the innovation of which is that the components and weight proportions of the coating are:

[0034]

[0035] The deionized water, acetic acid, nanocellulose, glycerol and chitosan constitute the water phase, and the alkyl ketene dimer and palm wax constitute the oil phase; glycerol is used as a plasticizer, chitosan is used as an oil-proof agent, and cellulose nanocrystals are used as an emulsifier.

[0036] Moreover, the nanocellulose is one of cellulose nanocrystals, cellulose nanofibers and bacterial cellulose.

[0037] Moreover, the deacetylation degree of the chitosan is greater than or equal to 95%, and the viscosity is 100-200 mpa.s.

[0038] Moreover, the alkyl ketene dimer is a waxy body with a solid content of 90%.

[0039] Moreover, the palm wax and glycerin are food grade palm wax and food grade glycerin respectively.

[0040] A method for preparing a paper-based bio-based high-barrier Pickering emulsion coating, wherein the method is innovative in that the steps of preparing the paper-based bio-based high-barrier Pickering emulsion coating are:

[0041] S1, preparing acetic acid and dissolving it in deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing nanocellulose in the acetic acid aqueous solution to form a mixed solution 1;

[0042] S2, heating the mixed solution 1 to 50° C., then sequentially adding glycerol and chitosan thereto, stirring until fully dissolved, to form a mixed solution 2;

[0043] S3, heating the blended liquid 2 to 90°C, then adding alkyl ketene dimer and palm wax thereto in turn, heating and stirring for 1 to 2 hours until the two waxy substances melt to form a blended liquid 3, then maintaining the speed of the high-speed shear emulsifier at 10000r / min to emulsify the blended liquid 3 for 5 to 10 minutes, and finally obtaining a Pickering emulsion coating.

[0044] An application of the paper substrate bio-based high barrier Pickering emulsion coating in a paper-based high barrier coating, wherein the emulsion coating is applied on the surface of the paper-based material, and the coating amount is 2 to 8 g / m 2 .

[0045] The performance testing instruments and material sources used in the embodiments and comparative examples of the present invention are as follows:

[0046] J-CBY100 paper and paperboard absorbency tester from Sichuan Changjiang Papermaking Instrument Co., Ltd.; VCA Optima contact angle tester from American AST; W-B121F water vapor transmission rate tester from Guangzhou Xitang Electromechanical Technology Co., Ltd.; UB100i Aupu microscope; SU1510-Hitachi scanning electron microscope; NDJ-8S Tianjin Shunnuo rotational viscometer.

[0047] Chitosan, AKD (alkyl ketene dimer), glycerol, palm wax: all purchased from Shanghai MacLean Biotechnology Co., Ltd.

[0048] Cellulose nanocrystals: Tianjin Mujingling Biotechnology Co., Ltd.;

[0049] Deionized water: Tianjin Haoyu industrial distilled water;

[0050] Industrial paper waterproofing agent: Qingzhou Jinhao New Materials Co., Ltd.;

[0051] Example 1

[0052] (1) preparing 1.5 parts of acetic acid and dissolving it in 80 parts of deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing 2 parts of cellulose nanocrystal powder in the acetic acid aqueous solution to form a mixed solution 1;

[0053] (2) heating the mixed solution 1 to 50° C., then adding 0.6 parts of glycerol and 2 parts of chitosan in sequence, and stirring until fully dissolved to form a mixed solution 2;

[0054] (3) Heat the blend 2 to 90° C., then add 3 parts of AKD (alkyl ketene dimer) and 8 parts of palm wax in sequence, heat and stir for 1-2 hours until the two waxy substances melt to form a blend 3, and then maintain the speed of the high-speed shear emulsifier at 10,000 r / min to emulsify the blend 3 for 5 minutes to obtain a Pickering emulsion coating.

[0055] The Pickering emulsion coating prepared in Example 1 was applied to the surface of the corrugated paper using a coating machine, with a coating amount of 5 g / m 2 , and then dried in a flat plate dryer at 80°C for 30 minutes.

[0056] Example 2

[0057] (1) preparing 1.5 parts of acetic acid and dissolving it in 80 parts of deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing 2 parts of cellulose nanocrystal powder in the acetic acid aqueous solution to form a mixed solution 1;

[0058] (2) heating the mixed solution 1 to 50° C., then adding 0.6 parts of glycerol and 2 parts of chitosan in sequence, and stirring until fully dissolved to form a mixed solution 2;

[0059] (3) Heat the blend 2 to 90°C, then add 3 parts of AKD (alkyl ketene dimer) and 10 parts of palm wax in sequence, heat and stir for 1-2 hours until the two waxy substances melt to form a blend 3, then maintain the speed of the high-speed shear emulsifier at 10000 r / min to emulsify the blend 3 for 5 minutes, and finally obtain a Pickering emulsion coating.

[0060] The Pickering emulsion coating prepared in Example 2 was applied to the surface of the corrugated paper using a coating machine, with a coating amount of 5 g / m 2 , and then dried in a flat plate dryer at 80°C for 30 minutes.

[0061] Example 3

[0062] (1) preparing 1.5 parts of acetic acid and dissolving it in 80 parts of deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing 2 parts of cellulose nanocrystal powder in the acetic acid aqueous solution to form a mixed solution 1;

[0063] (2) heating the mixed solution 1 to 50° C., then adding 0.6 parts of glycerol and 2 parts of chitosan in sequence, and stirring until fully dissolved to form a mixed solution 2;

[0064] (3) Heat the blend 2 to 90° C., then add 4 parts of AKD (alkyl ketene dimer) and 12 parts of palm wax in sequence, heat and stir for 1-2 hours until the two waxy substances melt to form a blend 3, and then maintain the speed of the high-speed shear emulsifier at 10,000 r / min to emulsify the blend 3 for 5 minutes to obtain a Pickering emulsion coating.

[0065] The Pickering emulsion coating prepared in Example 3 was applied to the surface of the corrugated paper using a coating machine, with a coating amount of 5 g / m 2 , and then dried in a flat plate dryer at 80°C for 30 minutes.

[0066] Comparative Example 1

[0067] Prepare 1.5 parts of acetic acid and dissolve it in 80 parts of deionized water to form an acetic acid aqueous solution. Heat the acetic acid aqueous solution to 50° C., then add 0.6 parts of glycerol and 2 parts of chitosan in sequence, and stir until fully dissolved to form a chitosan coating solution.

[0068] The chitosan coating liquid prepared in Comparative Example 1 was coated on the surface of the corrugated paper using a coating machine, and the coating amount was 5 g / m 2 , and then dried in a flat plate dryer at 80°C for 30 minutes.

[0069] Comparative Example 2

[0070] (1) preparing 1.5 parts of acetic acid and dissolving it in 80 parts of deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing 2 parts of cellulose nanocrystal powder in the acetic acid aqueous solution to form a mixed solution 1;

[0071] (2) The mixed liquid is heated to 1 to 50° C., and then 0.6 parts of glycerol and 2 parts of chitosan are added in sequence, and stirred until fully dissolved to form a mixed coating liquid.

[0072] Use a coating machine to apply the blended coating liquid prepared in Comparative Example 2 on the surface of the corrugated paper, with a coating amount of 5 g / m 2 , and then dried in a flat plate dryer at 80°C for 30 minutes.

[0073] Comparative Example 3

[0074] The industrial paper waterproofing agent was diluted 5 times with deionized water to form a paper waterproofing coating liquid.

[0075] Use a coating machine to apply the paper waterproof coating liquid prepared in Comparative Example 3 on the surface of the corrugated paper, with a coating amount of 5g / m 2 , and then dried in a flat plate dryer at 80°C for 30 minutes.

[0076] The microscopic image of the bio-based high barrier Pickering emulsion coating prepared in Example 3 is as follows: Figure 1 As shown, the microscope image after one month of stabilization is as follows Figure 2 As shown by Figure 2 It can be seen that the prepared high-barrier Pickering emulsion coating for paper substrate can be stable for at least one month without demulsification.

[0077] The microscopic morphology of the bio-based high barrier Pickering emulsion coating prepared in the embodiment after being coated on the surface of the corrugated paper is as follows: Figure 3 As shown, (a) is a 110x scanning electron microscope coated paper surface image, (b) is a 370x scanning electron microscope coated paper surface image, (a) can see the distribution of the overall core-shell structure on the paper fiber surface, (b) can specifically view a form of the core-shell structure, the combination of the two can be said that the uniformly distributed core-shell structure formed by the emulsion on the paper fiber surface, while providing a certain hydrophobic effect, greatly increases the roughness of the paper surface, the synergistic effect of the two increases the barrier effect of the paper;

[0078] After the emulsion is coated on the surface of paper, a high barrier coating with a core-shell structure is formed. Observation under an electron microscope shows that the core-shell structure is clear, providing a barrier coating on the surface of the paper and forming a rough structure on the coating, showing significant hydrophobicity and oil resistance.

[0079] The viscosity of the coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was compared with the paper barrier effect, and performance tests were performed on them. The test data are shown in Table 1. The relevant test methods and test standards are commonly used characterization methods in this field.

[0080] Table 1 Coating performance comparison table

[0081]

[0082] As can be seen from Table 1, the bio-based high-barrier Pickering emulsion coating for paper substrates provided by the present invention has a viscosity of 400 to 600 centipoise, which is fully suitable for processes such as blade coating and roller coating in industrial production. In addition, the shelf life of this product exceeds one month, and demulsification will not occur, which significantly improves the efficiency of use in actual production. From the comparison of the barrier effect of paper, the bio-based high-barrier Pickering emulsion coating used in Examples 1 to 3 is significantly better than the control group in terms of barrier performance. This is due to the formation of an efficient barrier coating and a unique surface structure on the surface of the paper. Its water vapor permeability is as low as 1035.0g / (m 2 ·d), the maximum water contact angle reaches 130°( Figure 4 As shown), the minimum water absorption of Cobb60 is 14.2g / m 2 The maximum oil-proof grade (kit) is 11, which fully meets the requirements of corrugated boxes for waterproof and oil-proof performance in logistics transportation.

[0083] The present invention uses cellulose nanocrystals (CNC) as solid stable particles, combines the hydrophobic and oleophobic effects of AKD and palm wax, the plasticity of glycerol, and the oil-proof properties of chitosan, and optimizes stability and barrier properties through the synergistic effect of each component. CNC provides a network structure that stabilizes the emulsion and enhances barrier properties. The core-shell structure formed by AKD and palm wax can form a highly dense coating on the surface of paper, wherein AKD provides a strong binding property with cellulose (through chemical bonds or adsorption), and palm wax supplements the physical barrier effect through its crystallinity, thereby enhancing the stability and uniformity of the overall coating. AKD has an efficient waterproof ability and can prevent water molecules from penetrating, while palm wax has a significant barrier effect on the diffusion of oil molecules due to its fatty acid ester structure. The hydrophobic and oleophobic properties of both are maximized, and they have a barrier effect on a variety of liquids. The crystalline properties of palm wax fill the micropores in the AKD coating, further improving the density and integrity of the coating, making the barrier effect of the barrier layer on the transmission of water vapor and oil molecules more significant. Chitosan enhances the film-forming and oil-proof properties, while glycerol improves the flexibility of the coating. The overall design combines high-efficiency barrier properties with environmental advantages, making it an excellent high-barrier coating for paper.

[0084] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A bio-based high-barrier Pickering emulsion coating for paper substrate, characterized in that: The components and weight proportions of the coating are: The deionized water, acetic acid, nanocellulose, glycerol and chitosan constitute the water phase, and the alkyl ketene dimer and palm wax constitute the oil phase.

2. The paper-based bio-based high-barrier Pickering emulsion coating according to claim 1, characterized in that: The nanocellulose is one of cellulose nanocrystals, cellulose nanofibers and bacterial cellulose.

3. The paper-based bio-based high-barrier Pickering emulsion coating according to claim 1, characterized in that: The deacetylation degree of the chitosan is greater than or equal to 95%, and the viscosity is 100-200 mpa.s.

4. The paper-based bio-based high-barrier Pickering emulsion coating according to claim 1, characterized in that: The alkyl ketene dimer is a waxy body with a solid content of 90%.

5. The paper-based bio-based high-barrier Pickering emulsion coating according to claim 1, characterized in that: The palm wax and glycerin are food grade palm wax and food grade glycerin respectively.

6. A method for preparing a bio-based high-barrier Pickering emulsion coating for a paper substrate, characterized in that: The method for preparing the paper-based bio-based high-barrier Pickering emulsion coating according to any one of claims 1 to 5 comprises the following steps: S1, preparing acetic acid and dissolving it in deionized water to form an acetic acid aqueous solution, and then ultrasonically dispersing nanocellulose in the acetic acid aqueous solution to form a mixed solution 1; S2, heating the mixed solution 1 to 50° C., then sequentially adding glycerol and chitosan thereto, stirring until fully dissolved, to form a mixed solution 2; S3, heating the blended liquid 2 to 90°C, then adding alkyl ketene dimer and palm wax thereto in turn, heating and stirring for 1 to 2 hours until the two waxy substances melt to form a blended liquid 3, then maintaining the speed of the high-speed shear emulsifier at 10000r / min to emulsify the blended liquid 3 for 5 to 10 minutes, and finally obtaining a Pickering emulsion coating.

7. A use of the bio-based high-barrier Pickering emulsion coating for paper substrates as claimed in any one of claims 1 to 5 in a paper-based high-barrier coating, wherein the emulsion coating is applied on the surface of the paper-based material in an amount of 2 to 8 g / m 2 .

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