Preparation method of a high-barrier antibacterial natural cellulose-based packaging material

Abstract

The invention discloses a preparation method of a high-barrier antibacterial natural cellulose-based packaging material, which includes the steps of: taking α-cellulose dissolving pulp, beating it into pulp, taking chemimechanical pulp containing cellulose, lignin and hemicellulose, and mixing and beating it with α-cellulose pulp to prepare a mixed pulp; respectively preparing a forming pulp pool from the high-purity α-cellulose pulp and the mixed pulp, and forming a composite paper with an α-cellulose layer on the surface and the bottom layer and a mixed cellulose layer in the core layer by multi-layer forming; impregnating the composite paper in a functional group conversion solution and then washing it, and then impregnating it in a solution such as ethanol; preparing a chitosan compound solution by formulating chitosan, coating it on the surface of the cellulose wet film, and performing calendering treatment to form a packaging material; forming a multi-layer structure by forming, improving the tensile strength of the material by impregnating with an ionic solution, increasing the oxygen barrier performance by dehydration impregnation, coating the chitosan composite metal nanoparticles on the surface of the film material to improve the antibacterial performance, and overall forming a packaging material with excellent comprehensive performance.

Description

Technical Field

[0001] The present invention relates to the field of preparation of packaging materials or the field of papermaking, and particularly relates to a method for preparing a high-barrier antibacterial natural cellulose-based packaging material. Background Art

[0002] Natural cellulose-based materials such as wood pulp, bamboo pulp, cotton and linen pulp, and dissolving pulp have good biodegradability and environmental friendliness, etc., and are widely used in the fields of packaging, etc.; with the increasingly tense petroleum resources and the growing environmental awareness of people, natural cellulose-based materials, as renewable macromolecular compounds rich in nature, have received key attention. How to efficiently develop and utilize natural cellulose-based renewable resources has become an important direction of the sustainable development strategy.

[0003] For a class of natural cellulose-based materials applied to the field of high-quality packaging, it is required to have good barrier properties, and have relatively high barrier properties to water vapor, oxygen, oils and fats, and volatile organic compounds. High barrier properties are crucial for maintaining the quality of products in the package, extending the shelf life and reducing food waste. At present, the barrier properties of general natural cellulose-based materials are poor, which easily leads to the deterioration of the packaged products or the decline of performance, restricting their application in the field of high-demand packaging, such as food, medicine and chemical packaging; packaging materials are also required to have good flexibility (poor mechanical properties), and have a certain degree of optical transparency (optical ability). At present, general regenerated cellulose membranes are relatively soft (poor mechanical properties), while paper is relatively hard and inconvenient to be applied to some protective packaging fields. Plastic films have poor renewability and difficult-to-adjust transparency (poor optical properties); in addition, if the packaging materials are applied to the fields of directly contacting food, some medical supplies and biological supplies, they are also required to have a certain degree of antibacterial property.

[0004] In the prior art, generally, to improve the barrier properties of natural cellulose-based materials, it is mainly achieved by adding inorganic nanoparticles, nanofiber materials, coating or laminating synthetic polymers, or using methods such as multi-layer co-extrusion. At the same time, components such as maleic anhydride are added to improve the mechanical properties of the materials; however, such methods usually have relatively high production and processing costs, large processing complexity, and there are some harmful substances in the processing process that cause harm to the environment and human health.

[0005] For the requirement of antibacterial properties, generally, antibacterial effects are achieved by adding antioxidants, imidazoles, thiazoles, yeast extracts and other components during the processing or after the forming of the packaging materials; however, simply adding antibacterial components has problems such as weak antibacterial effects, poor stability of antibacterial components, short effective time, and easy separation and shedding of antibacterial components.

[0006] Therefore, in view of the above background and problems, a preparation method of a high-barrier antibacterial natural cellulose-based packaging material needs to be provided. Summary of the Invention

[0007] The present invention aims to provide a preparation method of a high-barrier antibacterial natural cellulose-based packaging material in view of the problems in the prior art of high processing cost and difficulty in manufacturing natural cellulose-based materials, as well as poor barrier performance and weak antibacterial properties of the materials. The preparation method includes the following steps:

[0008] S10: Take α-cellulose dissolving pulp with a purity of 95% to 100%, place it in a softener for pre-impregnation, and then beat it to form high-purity α-cellulose pulp; take chemimechanical pulp containing cellulose, lignin, and hemicellulose, and mix and beat the high-purity α-cellulose pulp with the chemimechanical pulp to form mixed cellulose pulp;

[0009] S20: Use the high-purity α-cellulose pulp and the mixed cellulose pulp to respectively prepare forming vat pulps, add wet strength agents and mix evenly, and use a multi-layer forming method to prepare a cellulose composite paper; the cellulose composite paper is composed of a surface layer, a core layer, and a bottom layer stacked in sequence, the surface layer and the bottom layer are material layers of the high-purity α-cellulose pulp, and the core layer is a material layer of the mixed cellulose pulp;

[0010] S30: Heat a functional group conversion solution, immerse the cellulose composite paper in the functional group conversion solution for the first time, and then wash it with distilled water to form functional group-converted cellulose;

[0011] S40: Immerse the functional group-converted cellulose substrate in a single-component solution of ethanol, isopropanol, or n-butanol, or a mixed solution of two components, or a mixed solution of two or more components for the second time to form a cellulose wet film;

[0012] S50: Take chitosan, glycerol, and acetic acid solution, dissolve chitosan and glycerol in the acetic acid solution to form a chitosan compound solution, and coat it on the surface of the cellulose wet film to form a high-barrier antibacterial composite film;

[0013] S60: Calender the high-barrier antibacterial composite film to form the high-barrier antibacterial natural cellulose-based packaging material.

[0014] Further, forming the high-barrier antibacterial composite film further includes: taking nano-titanium dioxide, nano-silver, or nano-zinc oxide, uniformly dispersing it in the chitosan compound solution to form a chitosan composite metal nanoparticle solution; coating the chitosan composite metal nanoparticle solution on the surface of the cellulose wet film to form the high-barrier antibacterial composite film.

[0015] Further, the softener is silicone oil or sodium stearate.

[0016] Further, the beating degree of the dissolving pulp is 40°SR to 70°SR; the beating degree of the chemimechanical pulp is 18°SR to 38°SR.

[0017] Further, the addition amount of the wet strength agent is 20 kg / ton to 80 kg / ton.

[0018] Further, the functional group conversion solution is 1-butyl-3-methylimidazolium salt solution, and the 1-butyl-3-methylimidazolium salt is one of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]NTf2), 1-butyl-3-methylimidazolium trifluoromethylacetate ([BMIM]CF3COO), 1-butyl-3-methylimidazolium nitrate ([BMIM]NO3) or 1-butyl-3-methylimidazolium nitrite ([BMIM]NO2).

[0019] Further, the functional group conversion solution further contains nano-silica sol.

[0020] Further, the volume concentration of the single-component solution or two mixed-component solutions or more than two mixed-component solutions is 98% to 100%.

[0021] Further, the time of pre-impregnation is 30 minutes to 60 minutes; the time of the first impregnation is 30 minutes to 90 minutes; the time of the second impregnation is 4 hours to 12 hours.

[0022] Further, the calendering treatment is carried out using a calender, and the conditions of the calendering treatment are: the temperature is 100°C to 220°C, the line pressure is 20 kN / m to 100 kN / m, and the vehicle speed is 30 m / min to 300 m / min.

[0023] The technical solution of the present invention is formed by using α-cellulose with a higher beating degree to form a surface layer and a bottom layer, and using α-cellulose with a higher beating degree and chemimechanical pulp with a lower beating degree to form a core layer, so that the material has strong tensile strength (mechanical property) and stiffness in terms of physical properties. The formed cellulose composite paper is impregnated with a 1-butyl-3-methylimidazolium salt solution under certain temperature conditions to selectively dissolve α-cellulose without dissolving lignin and hemicellulose, effectively improving the tensile strength and stiffness of the material, and regulating the opacity and oxygen barrier properties of the material. Then, the material is impregnated and replaced with a solution formed by components such as ethanol, isopropanol, and n-butanol to remove the moisture and solvent in the aforementioned material, so that the material forms a three-dimensional network structure, increasing the oxygen barrier property; and by preparing a chitosan composite metal nanoparticle solution and coating it on the film material, the anti-resistance component is adsorbed on the chitosan through hydrogen bonding, and thus adsorbed on the surface of the material and not easily fallen off, forming a film material with strong antibacterial property and long antibacterial time. At the same time, chitosan and metal nanoparticles further improve the flexibility (mechanical property) of the material; the formed packaging material enhances the mechanical property compared with the regenerated cellulose film, is softer in texture than the paper material, has renewable property compared with the plastic film and has good optical property in terms of transparency adjustment; the material is hot-pressed by a calendering treatment method to effectively remove the volatile solvent in the material, make the three-dimensional network structure form an irreversible structure, and improve the interlayer bonding strength of the material, enhancing the material stability; the overall manufacturing method forms an overall process with effective cooperation before and after, and has the beneficial effects of simple material use, low processing cost, and simple processing process, improving the operability of preparing a high-barrier antibacterial natural cellulose-based packaging material with high barrier performance, mechanical property, and antibacterial property. The formed packaging material can meet the needs of many packaging scenarios. Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the structures shown in these drawings.

[0025] Figure 1 It is a process flow chart of the preparation method of the embodiment of the present invention;

[0026] Figure 2 It is a physical diagram and a surface SEM diagram of the cellulose composite paper formed by papermaking;

[0027] Figure 3 It is a cross-sectional structure schematic diagram of the cellulose composite paper formed by papermaking;

[0028] Figure 4 It is a diagram of the mechanism for dissolving cellulose in the functional group conversion solution system;

[0029] Figure 5 It is a diagram of the interaction mechanism between cellulose and 1-butyl-3-methylimidazolium salt solution.

[0030] Figure 6 It is a schematic diagram of cellulose supported on nano-silica sol;

[0031] Figure 7 It is a schematic diagram of the three-dimensional macromolecular network structure of the cellulose wet film;

[0032] Figure 8 It is an SEM image of nano-titanium dioxide particles uniformly dispersed on the surface of the cellulose wet film;

[0033] Figure 9 It is the Fourier transform infrared spectrum (FTIR) of the regenerated cellulose material (RC) and the material of this embodiment (CMF).

[0034] Explanation of the reference numerals in the attached drawings:

[0035] Surface layer: 110; Core layer: 120; Bottom layer: 130.

[0036] The realization, functional features and advantages of the objectives of the present invention will be further described with reference to the embodiments and the attached drawings. Specific embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the attached 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 without making creative efforts belong to the scope of protection of the present invention.

[0038] It should be noted that all the directional indications (such as up, down, left, right, front, back, inside, outside, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the attached drawings). If the specific posture changes, the directional indications will also change accordingly.

[0039] In addition, the descriptions such as "first" and "second" in the present invention are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0040] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0041] Please refer to Figure 1 , Figure 1 which is the process flow chart of the preparation method of the embodiment of the present invention.

[0042] The preparation method of the high-barrier and high-barrier antibacterial natural cellulose-based packaging material provided by the embodiment of the present invention includes Figure 1 the steps in the process flow chart as follows.

[0043] Step S10:

[0044] Take α-cellulose dissolving pulp with a purity of 95% to 100%, place it in a softener of silicone oil or sodium stearate for pre-impregnation (the bath ratio of α-cellulose to softener is 5:1 to 20:1, the dosage of softener is 10 g / L, and the pre-impregnation time is 30 minutes to 60 minutes), and then perform beating treatment to form a pulp with a beating degree of 40°SR to 70°, and prepare high-purity α-cellulose pulp.

[0045] Take chemimechanical pulp containing cellulose, lignin and hemicellulose and having a beating degree of 18°SR to 38°SR, mix the high-purity α-cellulose pulp and the chemimechanical pulp according to a mass ratio of 1:5 to 5:1 and beat them, and then prepare mixed cellulose pulp, or further make it into a mixed cellulose pulp board for subsequent use.

[0046] In this embodiment, high-purity α-cellulose is selected, which has a uniform molecular weight distribution, ensuring the mechanical strength and transparency of the substrate.

[0047] Pre-impregnation with a softener before beating can reduce the fiber breakage rate, thereby reducing the friction coefficient between the bottom layer 130 and the surface layer 110 of the cellulose composite paper formed by subsequent papermaking, improving the smoothness, making the production process of the subsequent processed packaging material smoother, reducing problems such as accumulation and blockage caused by the large friction coefficient of the material, thereby reducing equipment failures and production interruptions, and improving the overall production efficiency.

[0048] In this embodiment, the α-cellulose dissolving pulp is subjected to high beating treatment at 40°SR to 70°SR. On the one hand, it can improve the degree of fiber softening, fibrillation degree and kink curling degree, which helps to enhance the flexibility performance of the subsequent formed packaging material. On the other hand, it can improve the swelling performance of the dissolving pulp when impregnated in the subsequent functional group conversion solution, which is beneficial to subsequent cellulose dissolution and substrate performance regulation; the α-cellulose dissolving pulp forms a surface layer 110 and a bottom layer 130 during the process of forming by papermaking.

[0049] In this embodiment, the chemimechanical pulp contains three major components: cellulose, lignin and hemicellulose. There are significant differences in the chemical structure and physical properties of the three major components. During the subsequent first impregnation, the functional group conversion solution can selectively dissolve cellulose without dissolving lignin and hemicellulose, so that the cellulose composite paper formed by papermaking maintains strength and stiffness during the subsequent first impregnation process and is not easily broken; the high-purity α-cellulose pulp and the chemimechanical pulp are in different mass ratios of 1:5 to 5:1, so that the opacity and oxygen barrier performance of the material can be regulated by the mass ratio while ensuring the stiffness of the material; the low beating degree treatment at 18°SR to 38°SR is to cut less fibers, maintain a longer fiber length, further strengthen the stiffness, and make the material have the processability of coating and printing; the mixed cellulose pulp forms a core layer 120 during the subsequent papermaking and forming.

[0050] Please refer to Figure 2 , Figure 2 for the physical diagram and surface SEM diagram of the cellulose composite paper formed by papermaking.

[0051] It can be seen that through the preparation method of this embodiment, a good film body is formed; from Figure 2 the comparison of the physical diagrams of the F0 and F1 films, it can be seen that the F0 film has higher transparency than the F1 film, indicating that the film body has the effect of adjustable transparency (good optical performance). From Figure 2 the comparison of the SEM diagrams of F0 and F1, it can be seen that the density of the film body is relatively high, indicating that the film body has good barrier performance and oxygen barrier performance; this is because the opacity and oxygen barrier performance of the substrate can be regulated by adjusting the different mass ratios of α-cellulose, lignin, hemicellulose and cellulose in the core layer 120.

[0052] Please refer to Figure 3 , Figure 3 for the cross-sectional structure schematic diagram of the cellulose composite paper formed by papermaking.

[0053] Step S20:

[0054] High-purity α-cellulose pulp and the mixed cellulose pulp are respectively used to prepare a papermaking pulp pond, and a wet strength agent of 20 kg / ton pulp to 80 kg / ton pulp (the wet strength agent can endow the cellulose composite paper with a certain wet strength) is added respectively, and they are mixed evenly. The cellulose composite paper is prepared by using a one-time multi-layer wire forming method.

[0055] The cellulose composite paper is composed of a surface layer, a core layer, and a bottom layer that are sequentially partially penetrated and laminated. The surface layer and the bottom layer are material layers of the high-purity α-cellulose pulp, and the core layer is a material layer of the mixed cellulose pulp.

[0056] The three-layer structure composite paper structure formed in this embodiment provides basic conditions for different properties of each layer of material in the subsequent functional group conversion solution, so as to achieve the effect of impregnating and dissolving the cellulose in the surface layer, bottom layer, and core layer without dissolving the lignin and hemicellulose in the core layer.

[0057] Please refer to Figure 4 and Figure 5 , Figure 4 which is a mechanism diagram of the functional group conversion solution system for dissolving cellulose, Figure 5 and which is a mechanism diagram of the interaction between cellulose and 1-butyl-3-methylimidazolium salt solution.

[0058] Step S30:

[0059] Prepare a functional group conversion solution of 1-butyl-3-methylimidazolium salt solution. The concentration of the functional group conversion solution is 1 mL / g to 10 mL / g compared to the mixed cellulose pulp. It is heated to 30°C to 150°C by using a microwave heating method. The cellulose composite paper is placed into the functional group conversion solution for the first impregnation. After impregnation for 30 minutes to 90 minutes, it is washed with distilled water to form functional group converted cellulose.

[0060] In this embodiment, the main active ingredient of the functional group conversion solution is: 1-butyl-3-methylimidazolium salt solution, which has green environmental protection performance, has good solubility in cellulose, and has low solubility in lignin and hemicellulose.

[0061] By utilizing the differences in the chemical structures and physical properties of cellulose, lignin, and hemicellulose, a differential effect is formed that when the cellulose composite paper is impregnated in the functional group conversion solution, cellulose is effectively dissolved while lignin and hemicellulose are hardly dissolved.

[0062] Cellulose is a highly crystalline polymer mainly composed of β-(1→4)-linked D-glucose units, with a large number of hydrogen bonds existing both within and between molecules. 1-Butyl-3-methylimidazolium salt can cause the swelling of the surface of α-cellulose and cellulose. The salt molecules penetrate between α-cellulose and cellulose chains, disrupting the regular structure on the surface and forming amorphous cellulose. Moreover, the functional group conversion solution of 1-butyl-3-methylimidazolium salt solution can break hydrogen bonds to dissolve cellulose; the main component of the surface layer is α-cellulose, and the mixed cellulose in the core layer contains cellulose. The hydroxyl groups of α-cellulose and cellulose interact with the cations of the functional group conversion solution, while the hydroxyl hydrogen interacts with the anions, weakening the hydrogen bonds within and between molecules, leading to the cracking of molecular chains and enabling the dissolution of α-cellulose and cellulose in ionic liquids.

[0063] Lignin is a complex phenolic polymer with a complex aromatic structure and a large number of methylated and phenoxylated side chains, while hemicellulose is a mixture of a series of different glycoside units; the interaction force between the functional group conversion solution of 1-butyl-3-methylimidazolium salt solution and cellulose is stronger than that with lignin or hemicellulose, thus preferentially and selectively dissolving cellulose; in addition, the interaction between lignin and hemicellulose also hinders their dissolution in ionic liquids.

[0064] The material layer of the mixed cellulose in the core layer 120 contains lignin and hemicellulose components. Lignin and hemicellulose are covalently bonded and wrapped around the cellulose in the surface layer 110 and the bottom layer 130, making it difficult to dissolve. This enables the core layer 120 to maintain strength and stiffness during subsequent processing such as impregnation, coating, and printing. That is, in the first impregnation process, it does not dissolve the glucose or polysaccharide components of cellulose using the solution, but forms a process where cellulose opens from long chains to short chains at the molecular microscopic level and a fibrillation process of the fiber as a whole at the macroscopic level. After the first impregnation, the diameter of cellulose becomes thinner, the material becomes denser, and both the transparency and barrier properties are improved; therefore, the opacity and oxygen barrier properties of the substrate can also be regulated by adjusting the different mass ratios of α-cellulose, lignin, hemicellulose, and cellulose in the core layer 120.

[0065] Selectively dissolving cellulose can, on the one hand, enable the substrate to maintain strength and stiffness during the impregnation process, and on the other hand, regulate the opacity and oxygen barrier properties of the substrate.

[0066] 1-Butyl-3-methylimidazolium salt solution (BMIM) is a cationic component that can form various ionic liquids in combination with other anions; specifically, it includes 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM]NTf2), 1-butyl-3-methylimidazolium trifluoromethylacetate ([BMIM]CF3COO), 1-butyl-3-methylimidazolium nitrate ([BMIM]NO3), or 1-butyl-3-methylimidazolium nitrite ([BMIM]NO2), etc.

[0067] The first impregnation uses microwave heating. Treatment at a relatively low temperature can effectively reduce the dissolution and cutting effect on the fibers, making the fibers have the characteristics of relatively long average length, high substrate strength, and high opacity; when the impregnation temperature is above 150 °C at a high temperature, the ionic liquid has a severe destructive effect on the fiber structure, resulting in a significant reduction in fiber length, low opacity of the substrate, and poor oxygen barrier effect; the first impregnation time is 30 minutes to 90 minutes. The relatively longer the impregnation time, the higher the swelling degree of the fibers, the lower the opacity of the substrate, and the better the oxygen barrier performance.

[0068] Please refer to Figure 6 , Figure 6 It is a schematic diagram of nanosilica sol loaded with cellulose.

[0069] In one embodiment, the functional group conversion solution further contains nanosilica sol, and the dosage is 0.5% to 3.0% in terms of the mass ratio relative to the functional group-converted cellulose.

[0070] Mix the nanosilica sol particles with a high specific surface area with 1-butyl-3-methylimi dazolium salt solution. During the first impregnation, the nanosilica sol can be evenly distributed in the fiber micro-surface layer of the cellulose composite paper, reducing the friction between directly contacting surfaces, thereby reducing the friction coefficient and providing a smoother material basis for subsequent film formation processing.

[0071] Please refer to Figure 7 , Figure 7 It is a schematic diagram of the three-dimensional macromolecular network structure of the cellulose wet film.

[0072] Step S40:

[0073] Immerse the functional group-converted cellulose formed in step S30 into a single-component solution of ethanol, isopropanol, or n-butanol or a mixed-component solution of two or more of them for the second impregnation. The volume concentration of the solution is 98% to 100%, and the impregnation time is 4 hours to 12 hours to form a cellulose wet film.

[0074] In this embodiment, a solution such as ethanol, isopropyl alcohol or n-butanol is used as a displacement solution. By placing the functional group-converted cellulose in the displacement solution, the residual water and solvent in the functional group-converted cellulose are displaced and removed, and finally a cellulose wet film with a three-dimensional macromolecular network structure is formed.

[0075] It should be noted that after the second impregnation, ethanol, isopropyl alcohol or n-butanol in the mixed component solution can be recycled by distillation or other means.

[0076] The volatilities of different displacement solutions and their solubilities in the substrate are different, thus affecting the displacement efficiency; the volatilities of ethanol, isopropyl alcohol and n-butanol decrease in turn, and it takes a longer time to complete the displacement. The solvent displacement time is 4 to 12 hours.

[0077] The polarities of the organic solvents in the above different displacement solutions are different from that of water, and they can effectively interact with the water molecules in the functional group-converted cellulose. Through the processes of dissolution and diffusion, the water molecules are gradually displaced; as the water molecules are displaced by the organic solvents, the three-dimensional network structure in the substrate gradually stabilizes; before the water is completely displaced, the structure of the substrate will undergo a certain degree of deformation or shrinkage. After the displacement is completed, the organic solvents fill the space originally occupied by the water molecules and maintain the integrity of the network structure again; using organic solvents with different polarities affects the randomness and architectural complexity of the network structure formed during the molecular displacement process. This three-dimensional macromolecular network structure with a random and complex architecture can, on the one hand, increase the path length when oxygen molecules penetrate the paper, strengthening the oxygen barrier performance, and on the other hand, improve the strength of the material itself, ensuring that the material is not easily broken during the coating and printing processes, effectively improving the subsequent processability and meeting the packaging applications.

[0078] Step S50:

[0079] Take chitosan with a deacetylation degree of 80% to 95%, glycerol and an acetic acid solution with a volume fraction of 1%. According to the mass ratio of 2:0.4:100 to 3.5:0.7:100, preferably 3:0.6:100, dissolve the chitosan and glycerol in the acetic acid solution to form a chitosan compound solution, and coat it on the surface of the cellulose wet film to form a high-barrier antibacterial composite film.

[0080] Chitosan has excellent properties such as antibacterial property, biocompatibility and non-toxicity. However, when directly blended with cellulose to prepare a composite film, phase separation and poor co-solubility are likely to occur, resulting in a small chitosan content on the surface of the cellulose wet film and weakened antibacterial property. Therefore, by blending chitosan with glycerol and acetic acid solution to form a compound system, and using the polarities and acidity of glycerol and acetic acid solution to act on the cellulose wet film, a graft copolymerization reaction occurs between chitosan and the surface of the cellulose wet film, greatly increasing the chitosan content on the surface of the cellulose wet film.

[0081] Please refer toFigure 8 , Figure 8 SEM image of nano - titanium dioxide particles uniformly dispersed on the surface of the cellulose wet film.

[0082] In one embodiment, the process of forming the high - barrier antibacterial composite film further includes: taking nano - titanium dioxide or nano - silver or nano - zinc oxide, uniformly dispersing it into the chitosan compound solution to form a chitosan composite metal nanoparticle solution; wherein the mass fraction of the metal nanoparticles is 0.1% to 0.3%; coating the chitosan composite metal nanoparticle solution onto the surface of the cellulose wet film to form the high - barrier antibacterial composite film.

[0083] Metal nanoparticles such as nano - silver, nano - titanium dioxide and nano - zinc oxide have strong antibacterial properties (generally can kill bacteria such as Escherichia coli) and good heat resistance; preferably, nano - titanium dioxide (TiO 2 ) has inertness, non - toxicity and photocatalytic antibacterial properties; the metal nanoparticles can be adsorbed on chitosan through intermolecular hydrogen bond interaction, and then form a more firm and effective combination with the film body, which is not easy to fall off during use, effectively improving the antibacterial ability and antibacterial time effect.

[0084] It should be noted that chitosan and metal nanoparticles not only have good antibacterial effects, but also can improve the tensile strength (mechanical ability) of the high - barrier antibacterial composite film. Since chitosan and metal nanoparticles are adsorbed on the surface of the cellulose wet film through hydrogen bond interaction, and the metal nanoparticles are uniformly dispersed on the surface of chitosan, it plays a role in effectively improving the film strength; in addition, the dosage of metal nanoparticles can further play a role in adjusting the optical transparency (optical ability) of the high - barrier antibacterial composite film; as Figure 8 can be seen, the titanium dioxide particles (white dots in the figure) in the dark area of the figure are uniformly distributed on the surface of the high - barrier antibacterial composite film and embedded in the chitosan matrix.

[0085] Step S60:

[0086] Calendering treatment is performed on the high - barrier antibacterial composite film formed in step S50. Under the conditions of a temperature of 100 °C to 220 °C, a line pressure of 20 kN / m to 100 kN / m, and a vehicle speed of 30 m / min to 300 m / min, calendering treatment is performed on the cellulose wet film to form the high - barrier antibacterial natural cellulose - based packaging material with high barrier antibacterial properties.

[0087] After the replacement with the replacement solution, organic solvents will remain in the wet cellulose film. However, in this embodiment, ethanol, isopropanol or n-butanol are all highly volatile solvents and are easily removed completely (compared with low-volatile solvents which are not easily removed and have an adverse impact on subsequent processing and packaging applications). By using calendering treatment combining heating and pressurization, the curing efficiency is high, and the organic solvents can be removed efficiently and thoroughly, ensuring no residue, and the macromolecular network in the wet cellulose film can be rapidly cured to form an irreversible three-dimensional network structure. The hot pressing improves the interlayer bonding strength of the high-barrier antibacterial natural cellulose-based packaging material, and it has higher stability during transportation and storage. After being made into a packaging bag, it can protect the contents from damage.

[0088] The high-barrier antibacterial natural cellulose-based packaging material produced through the above embodiment is subjected to performance test comparison with the existing regenerated cellulose film, white kraft paper and PE / PET film, as shown in Table 1 below.

[0089] Table 1 Data comparison table of performance tests

[0090]

[0091] It can be seen that the high-barrier antibacterial natural cellulose-based packaging material is superior to the existing film materials in terms of barrier performance (oxygen transmission rate), mechanical properties (longitudinal tensile strength and transverse tensile strength), stiffness (longitudinal bending stiffness and transverse bending stiffness), flexibility (folding endurance), optical transparency (opacity) and antibacterial property.

[0092] Please refer to Figure 9 , Figure 9 which is the Fourier transform infrared spectroscopy (FTIR) diagram of the regenerated cellulose material (RC) and the material of this embodiment (CMF).

[0093] The material of this embodiment (the high-barrier antibacterial natural cellulose-based packaging material, CMF in the figure) uses chitosan and titanium dioxide as additive components. In the FTIR spectrum, the stretching vibration peaks of N-H bonds are respectively at 1564 cm and 1558 cm, which are the characteristic absorption peaks of the amide II group of chitosan, indicating that chitosan is successfully coated on the surface of the wet cellulose film. Moreover, from the FTIR spectrum of CMF, it can be seen that there is a stretching vibration peak of Ti-O between 600 cm -1 and 700 cm -1 indicating that titanium dioxide particles are adsorbed on chitosan through intermolecular hydrogen bonding.

[0094] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A method for preparing a high barrier and antibacterial natural cellulose-based packaging material, characterized in that: The preparation method comprises the following steps: S10: taking α-cellulose dissolving pulp with a purity of 95% to 100% and a beating degree of 40°SR to 70°SR, pre-impregnating it in a softener, and then beating it to form a high-purity α-cellulose pulp; The softener is silicone oil or sodium stearate; Taking a chemical mechanical pulp containing cellulose, lignin and hemicellulose and having a beating degree of 18°SR to 38°SR, the high-purity α-cellulose pulp and the chemical mechanical pulp are mixed and beaten at a mass ratio of 1:5 to 5:1 to form a mixed cellulose pulp; S20: using the high-purity α-cellulose pulp and the mixed cellulose pulp to form papermaking pulp pools, respectively, adding wet strength agents to the pulp pools and mixing them evenly, and adopting a stacked mesh papermaking method to prepare cellulose composite paper; The cellulose composite paper is composed of a surface layer, a core layer and a bottom layer which are partially interpenetrated and laminated in sequence, the surface layer and the bottom layer are material layers of the high-purity α-cellulose pulp, and the core layer is a material layer of the mixed cellulose pulp; S30: heating the functional group conversion solution to 30° C. to 150° C. by microwave heating, placing the cellulose composite paper into the functional group conversion solution for a first immersion, and then washing with distilled water to form functional group converted cellulose; The concentration of the functional group conversion solution is 1 mL / g to 10 mL / g compared to the mixed cellulose pulp; The functional group conversion solution is a 1-butyl-3-methylimidazolium salt solution; The first dipping time is 30 to 90 minutes; The functional group conversion solution further comprises nano silica sol; S40: placing the functional group-converted cellulose substrate into a single-component solution of ethanol, isopropanol or n-butanol or a two-component mixed solution or a two-component mixed solution for a second immersion to form a cellulose wet film; The second dipping time is 4 to 12 hours; S50: taking chitosan, glycerol and acetic acid solution, dissolving chitosan and glycerol in the acetic acid solution to form a chitosan composite solution, and applying the chitosan composite solution to the surface of the cellulose wet film to form a high barrier antibacterial composite film; Taking nano titanium dioxide or nano silver or nano zinc oxide, and evenly dispersing it into the chitosan composite sugar solution to form a chitosan composite metal nanoparticle solution; Applying the chitosan composite metal nanoparticle solution to the surface of the cellulose wet film to form a high barrier antibacterial composite film; S60: performing calendering treatment on the high barrier antibacterial composite film to form the high barrier antibacterial natural cellulose-based packaging material; The calendering treatment is performed using a calendering machine, and the conditions of the calendering treatment are: temperature of 100° C. to 220° C., line pressure of 20 kN / m to 100 kN / m, and vehicle speed of 30 m / min to 300 m / min.

2. The method for preparing a high barrier and antibacterial natural cellulose-based packaging material according to claim 1, characterized in that: The addition amount of the wet strength agent is 20kg / ton to 80kg / ton.

3. The method for preparing a high barrier and antibacterial natural cellulose-based packaging material according to claim 1, characterized in that: The 1-butyl-3-methylimidazolium salt is one of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM]NTf2), 1-butyl-3-methylimidazolium trifluoromethyl acetate ([BMIM]CF3COO), 1-butyl-3-methylimidazolium nitrate ([BMIM]NO3) or 1-butyl-3-methylimidazolium nitrite ([BMIM]NO2).

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