High-barrier nanocellulose-based composite liquid mulch and method of making same

Abstract

The application provides a high-barrier nanocellulose-based composite liquid mulch and a preparation method thereof, and comprises the following steps: adding sodium periodate into a sodium alginate solution to perform an oxidation reaction, so as to obtain an oxidized sodium alginate solution; adding a chitosan solution into the oxidized sodium alginate solution, and uniformly mixing to obtain a composite solution; mixing a nanocellulose solution with the composite solution, adding an ammonia water solution dropwise to adjust a pH value, and performing a cross-linking reaction to obtain a matrix solution; dissolving 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyl trimethyl ammonium chloride in deionized water to obtain a precursor solution; adding an initiator into the precursor solution to perform a copolymerization reaction, so as to obtain an amphoteric ion polymer; adding the amphoteric ion polymer into a sodium-based montmorillonite dispersion solution to perform an intercalation reaction, so as to obtain modified montmorillonite; uniformly mixing the matrix solution, the modified montmorillonite, a plasticizer, a rheological modifier and a surfactant, and then performing a standing curing and vacuum defoaming.

Description

Technical Field

[0001] This invention belongs to the field of liquid mulch technology, and relates to a high-barrier nanocellulose-based composite liquid mulch and its preparation method. Background Technology

[0002] Agricultural plastic mulch films, especially polyethylene mulch films, are widely used in modern agricultural production for purposes such as moisture retention, temperature increase, and weed control, providing crucial protection for crop yields. However, these traditional mulch films are difficult to completely recycle after use, and their residues are hard to degrade in the natural environment, affecting crop growth. To address this issue, biodegradable biofilms have emerged, among which liquid mulch films made from natural polymer materials such as cellulose, sodium alginate, and chitosan are particularly noteworthy. These mulch films, with their environmental friendliness, complete biodegradability, and ease of application, are considered one of the most promising alternatives to traditional plastic mulch films.

[0003] However, existing biomass-based liquid mulch films still face many technical bottlenecks in practical application. First, mulch films made from single natural polymers (such as pure sodium alginate or pure starch films) generally suffer from poor mechanical properties, exhibiting low strength, high brittleness, and insufficient toughness. They are easily broken by wind and rain erosion or mechanical forces in field conditions, making it difficult to provide continuous and effective protection throughout the entire crop growth cycle. Second, the barrier properties of these mulch films, especially their ability to block water vapor, are often insufficient. Because most natural polymers are highly hydrophilic, the mulch films easily absorb moisture, swell, and even dissolve in humid environments, causing their moisture retention function to decline rapidly and failing to meet the stringent requirements of efficient water use in dryland agriculture.

[0004] Therefore, developing a liquid mulch film that combines high mechanical properties with high barrier properties is of urgent theoretical value and practical significance for promoting the sustainable development of green agriculture. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a high-barrier nanocellulose-based composite liquid mulch film and its preparation method. The invention uses nanocellulose as a reinforcing framework, utilizes the Schiff base reaction between oxidized sodium alginate and chitosan to form a chemical cross-linked network, and modifies sodium-based montmorillonite through intercalation with zwitterionic polymers, greatly improving its compatibility and dispersibility with the matrix solution. This allows the montmorillonite sheets to be uniformly distributed within the matrix network, endowing the mulch film with excellent barrier properties. Finally, plasticizers, rheology modifiers, and surfactants are added, resulting in a liquid mulch film that simultaneously possesses excellent mechanical strength, flexibility, and high barrier properties.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film, the method comprising:

[0008] (I) Add sodium periodate to sodium alginate solution to carry out an oxidation reaction to obtain oxidized sodium alginate solution, add chitosan solution to it, mix well to obtain a composite solution; mix nanocellulose solution with the composite solution, add ammonia solution to adjust the pH value, carry out cross-linking reaction to obtain matrix solution;

[0009] (II) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride are dissolved in deionized water to obtain a precursor solution. An initiator is added to the precursor solution to carry out a copolymerization reaction to obtain a zwitterionic polymer. The zwitterionic polymer is added to a sodium-based montmorillonite dispersion to carry out an intercalation reaction. After centrifugation, washing and drying, modified montmorillonite is obtained.

[0010] (III) The matrix solution obtained in step (I), the modified montmorillonite, plasticizer, rheology modifier and surfactant obtained in step (II) are mixed evenly, and then allowed to stand for curing and vacuum degassing to obtain the nanocellulose-based composite liquid mulch film.

[0011] The composite liquid mulch prepared in this invention uses nanocellulose as a reinforcing framework and utilizes the Schiff base reaction between oxidized sodium alginate and chitosan to form a chemical cross-linked network, constituting a strong and stable matrix solution. Subsequently, sodium-based montmorillonite is intercalated and modified by zwitterionic polymers, which greatly improves its compatibility and dispersibility with the matrix solution, allowing the montmorillonite sheets to be uniformly distributed in the matrix network, effectively extending the water vapor diffusion path and endowing the composite liquid mulch with excellent barrier properties. Finally, plasticizers, rheology modifiers, and surfactants are added, resulting in a liquid mulch that simultaneously possesses excellent mechanical strength, flexibility, and high barrier properties.

[0012] This invention first involves a cross-linking reaction between sodium alginate and chitosan in a nanocellulose solution to form a matrix solution. After oxidation with sodium periodate, sodium alginate generates aldehyde groups on its molecular chains. These aldehyde groups can undergo a Schiff base reaction with the amino groups on the chitosan molecular chains, forming a dynamic covalent cross-linked network. Simultaneously, nanocellulose, with its extremely high specific surface area and abundant surface hydroxyl groups, forms a dense hydrogen bond network with the carboxyl groups of sodium alginate, the hydroxyl groups of chitosan, and the amino groups. Hydrogen bonds, as a strong physical cross-linking mechanism, can interpenetrate with the dynamic covalent cross-linked network formed by the Schiff base reaction. The combination of the rigid physically cross-linked hydrogen bond network and the tough chemically cross-linked network allows external forces to be effectively dispersed and absorbed by the matrix network, preventing stress concentration-induced film damage and significantly improving the mechanical strength and toughness of the film.

[0013] Regarding barrier properties, this invention incorporates zwitterionic polymer-modified montmorillonite into the matrix solution. The zwitterionic polymer is obtained by copolymerizing 2-acrylamido-2-methylpropanesulfonic acid with sulfonate anions and methacryloyloxyethyltrimethylammonium chloride with quaternary ammonium salt cations; its molecular chain contains both positively and negatively charged groups. The zwitterionic polymer can enter the layered structure of sodium-based montmorillonite through ion exchange and intercalation, widening the interlayer spacing and firmly anchoring it to the silicate sheets. When the modified montmorillonite is added to the matrix solution, its layered structure can be uniformly dispersed in the matrix network, forming a tortuous physical barrier that significantly extends the diffusion path of water vapor molecules within the membrane. Furthermore, the zwitterionic polymer molecular chains simultaneously contain positively charged quaternary ammonium salt groups and negatively charged sulfonate groups. The quaternary ammonium salt groups can attract negatively charged sodium alginate molecular chains in the matrix solution through electrostatic interactions, while the sulfonate groups can attract positively charged chitosan molecular chains in the matrix solution through electrostatic interactions. This forms a molecular bridge between the montmorillonite sheets and the organic polymer. When the film is subjected to external forces, the external forces can be smoothly transmitted from the relatively soft matrix network to the rigid montmorillonite sheets.

[0014] This invention also incorporates plasticizers, rheology modifiers, and surfactants into the matrix solution. The plasticizer, composed of glycerol and polyethylene glycol 400, weakens the interactions between molecular chains, increases chain segment mobility, and improves the flexibility and resistance to brittleness of the film, making it less prone to cracking in field conditions. Fumed silica, acting as a rheology modifier, forms a three-dimensional network structure in the matrix solution, regulating the rheological properties of the liquid mulch film, facilitating spray application and maintaining a uniform thickness distribution after film formation. Alkyl polysaccharide glycosides, acting as surfactants, reduce the surface tension of the composite liquid mulch film, promoting uniform dispersion of the components in the matrix solution and preventing aggregation.

[0015] As a preferred technical solution of the present invention, in step (I), the mass fraction of sodium alginate in the sodium alginate solution is 2~4wt%, for example, it can be 2.0wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, 3.0wt%, 3.2wt%, 3.4wt%, 3.6wt%, 3.8wt%, or 4.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] In some alternative instances, the mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is (0.3~0.5):1, for example, it can be 0.3:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.4:1, 0.42:1, 0.44:1, 0.46:1, 0.48:1 or 0.5:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0017] This invention specifically limits the mass ratio of sodium periodate to sodium alginate in the solution to (0.3~0.5):1. On the one hand, within this addition range, it ensures that sodium periodate fully oxidizes sodium alginate, generating a sufficient number of aldehyde groups, thereby forming a sufficiently dense three-dimensional cross-linked network to provide the necessary mechanical strength for the film layer. On the other hand, it also prevents excessive oxidation of sodium alginate due to excessive sodium periodate, allowing the sodium alginate backbone to remain relatively intact and maintaining the basic viscosity and film-forming ability of the matrix solution.

[0018] When the amount of sodium periodate is lower than the lower limit of the range defined in this invention, it will result in insufficient oxidation of sodium alginate and a limited number of aldehyde groups generated. In the subsequent mixing process with chitosan, the insufficient number of aldehyde groups cannot form sufficiently dense cross-linking points with the sufficient amino groups on the chitosan chain. The resulting three-dimensional network structure is too loose, and the mechanical strength of the final film layer is poor. The texture is brittle and it is easy to break during actual use.

[0019] When the amount of sodium periodate exceeds the upper limit specified in this invention, it will lead to excessive oxidation of sodium alginate. Excessive sodium periodate will continue to oxidize the aldehyde groups that have already been generated, causing severe breakage and degradation of the sodium alginate molecular chains. The excessively short molecular chains are unable to form a three-dimensional network structure with sufficient strength and toughness, resulting in a decrease in the mechanical strength of the membrane. Furthermore, excessive oxidation will introduce too many hydrophilic groups such as carboxyl groups, affecting the water-blocking performance of the membrane.

[0020] In some optional instances, the oxidation reaction is performed at room temperature.

[0021] In some alternative instances, the oxidation reaction time is 3 to 4 hours, for example, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0022] In some alternative instances, the oxidation reaction is carried out under light-protected conditions.

[0023] As a preferred technical solution of the present invention, in step (I), the chitosan solution is composed of chitosan and acetic acid solution.

[0024] In some optional examples, the chitosan solution contains 1.5 to 2.5 wt% chitosan, for example, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, or 2.5 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] In some optional examples, the chitosan solution is added dropwise to the sodium alginate oxidase solution under stirring conditions of 300-500 rpm, and stirring is continued for 40-50 min after the addition is complete to obtain the composite solution. The stirring speed can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm or 500 rpm, and the stirring time can be 40 min, 41 min, 42 min, 43 min, 44 min, 45 min, 46 min, 47 min, 48 min, 49 min or 50 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] As a preferred technical solution of the present invention, in step (I), the mass fraction of the nanocellulose solution is 1~2wt%, for example, it can be 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, or 2.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] In some optional examples, the mass ratio of nanocellulose dry basis, sodium alginate oxidized and chitosan in the nanocellulose solution is 1:(2~3):(0.5~1.5), for example, it can be 1:2:0.5, 1:2.1:0.6, 1:2.2:0.7, 1:2.3:0.8, 1:2.4:0.9, 1:2.5:1, 1:2.6:1.1, 1:2.7:1.2, 1:2.8:1.3, 1:2.9:1.4 or 1:3:1.5, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] This invention specifically defines the mass ratio of dry nanocellulose, sodium alginate, and chitosan in the nanocellulose solution as 1:(2~3):(0.5~1.5). Nanocellulose, as a rigid nanofiber, primarily serves to reinforce the framework, but it exhibits poor film-forming properties and is prone to aggregation. When the amount of sodium alginate is within the range specified in this invention, it is sufficient to fully encapsulate the nanocellulose. Through hydrogen bonding between the carboxyl groups on the sodium alginate molecular chain and the hydroxyl groups on the nanocellulose surface, the uniform dispersion of nanocellulose in the aqueous solution can be effectively promoted, preventing aggregation. Secondly, when sodium alginate and chitosan are within a specific ratio range, they can form a sufficiently dense and complete cross-linked network through a Schiff base reaction. Thirdly, chitosan itself is a film-forming polymer; its appropriate addition, along with sodium alginate, forms a polyelectrolyte complex through electrostatic interactions and hydrogen bonding, further enhancing the continuity and density of the matrix and contributing to improved barrier properties of the film.

[0029] When the amount of sodium alginate oxidized is below the lower limit defined in this invention, the amount of sodium alginate oxidized is insufficient, making it difficult to completely coat the nanocellulose. This results in uneven dispersion of the nanocellulose, which is prone to aggregation in aqueous solution. In addition, insufficient sodium alginate oxidized directly leads to an excessively low number of aldehyde groups in the matrix solution. With a relatively fixed amount of chitosan, too few aldehyde groups cannot form enough cross-linking points with the amino groups on the chitosan chains, resulting in a sparse chemical cross-linking network structure and insufficient mechanical strength of the film.

[0030] When the amount of sodium alginate oxide exceeds the upper limit specified in this invention, excessive sodium alginate oxide will lead to excessively high viscosity of the matrix solution, poor fluidity, difficulties in subsequent spraying, and will also affect the uniformity of film formation. In addition, excessive sodium alginate oxide molecular chains will also become entangled, which is not conducive to the formation of an ordered and uniform network structure, resulting in increased film brittleness.

[0031] When the amount of chitosan used is below the lower limit of the range defined in this invention, the cross-linking reaction cannot proceed fully, and the resulting three-dimensional cross-linked network structure is relatively loose, which cannot effectively constrain the movement of polymer chains, making it difficult to effectively transmit and disperse external forces, resulting in poor mechanical strength of the film, brittle texture, and easy breakage.

[0032] When the amount of chitosan exceeds the upper limit specified in this invention, the excess chitosan molecular chains will undergo strong electrostatic complexation with negatively charged sodium alginate oxide, leading to phase separation, flocculation, and disruption of the homogeneity and stability of the matrix solution, thus affecting the film quality. Furthermore, chitosan has strong hydrophilicity; excessive residue will introduce more hydrophilic groups, affecting the water resistance and moisture barrier properties of the film.

[0033] In some optional instances, the mass fraction of the ammonia solution is 5 to 10 wt%, for example, it may be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, or 10.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0034] In some alternative instances, the ammonia solution is added dropwise to adjust the pH of the mixed solution to 7.5 to 8.5, for example, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4 or 8.5, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0035] In some alternative examples, the reaction temperature of the crosslinking reaction is 40 to 50°C, for example, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] In some optional examples, the reaction time of the crosslinking reaction is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] As a preferred technical solution of the present invention, in step (II), the total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution is 10~20wt%, for example, it can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] In some optional instances, the initiator includes potassium persulfate.

[0039] In some alternative examples, the total mass ratio of the 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the initiator is 100:(0.5~1), for example, it can be 100:0.5, 100:0.55, 100:0.6, 100:0.65, 100:0.7, 100:0.75, 100:0.8, 100:0.85, 100:0.9, 100:0.95 or 100:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0040] In some alternative instances, the reaction temperature of the copolymerization reaction is 70 to 80°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0041] In some alternative instances, the reaction time of the copolymerization reaction is 4 to 6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0042] In some optional instances, the copolymerization reaction is carried out under a nitrogen atmosphere.

[0043] As a preferred technical solution of the present invention, in step (II), the sodium montmorillonite dispersion is obtained by dispersing sodium montmorillonite in deionized water.

[0044] In some optional instances, the sodium montmorillonite dispersion contains 2 to 4 wt% sodium montmorillonite, for example, 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3.0 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, or 4.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0045] In some optional instances, the mass ratio of the zwitterionic polymer to the sodium montmorillonite in the sodium montmorillonite dispersion is (0.5~1):1, for example, it can be 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1 or 1:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] This invention specifically defines the mass ratio of zwitterionic polymer to sodium montmorillonite in the sodium-based montmorillonite dispersion as (0.5~1):1. The zwitterionic polymer molecular chains can exchange ions with sodium ions between montmorillonite layers through their highly polar quaternary ammonium salt cations. At the same time, its sulfonate anions and other groups can also interact with the surface of the layers, thereby promoting the entry of zwitterionic polymer molecular chains into the interlayer space of montmorillonite and widening the interlayer spacing of montmorillonite.

[0047] When the amount of zwitterionic polymer is below the lower limit of the range defined in this invention, sufficient intercalation of montmorillonite cannot be achieved, resulting in some montmorillonite remaining in its original tightly stacked state. When mixed with the matrix solution, the insufficiently intercalated and modified montmorillonite has poor compatibility with the matrix solution and is prone to agglomeration, forming micron-sized aggregates. These aggregates not only fail to exert the mechanical reinforcement and barrier properties of the nanosheets in the film layer, but also become stress concentration points, leading to a significant decrease in the mechanical properties of the film layer.

[0048] When the amount of zwitterionic polymer exceeds the upper limit defined in this invention, due to the strong hydrophilicity of the zwitterionic polymer, the excessive hydrophilic groups will affect the water-blocking performance of the membrane after it is added to the matrix solution. In addition, excessive zwitterionic polymer will adsorb onto the surface of montmorillonite, forming an excessively thick polymer coating layer, thereby forming a relatively soft interface layer between the montmorillonite sheet and the matrix, affecting the uniform transfer of stress from the matrix to the montmorillonite sheet.

[0049] In some optional instances, the reaction temperature of the intercalation reaction is 60~70°C, for example, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0050] In some optional instances, the reaction time of the intercalation reaction is 4 to 6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] As a preferred technical solution of the present invention, in step (III), the amount of modified montmorillonite added is 2 to 3 wt% of the mass of the matrix solution, for example, it can be 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt% or 3.0 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] This invention specifically limits the addition amount of modified montmorillonite to 2-3 wt% of the matrix solution. Within this range, the zwitterionic polymer-intercalated montmorillonite sheets can be uniformly dispersed in the matrix network composed of nanocellulose, sodium alginate, and chitosan. Its nanoscale sheet structure effectively increases the diffusion paths of water and gas molecules within the membrane, significantly improving its barrier properties. Simultaneously, these rigid nanosheets also act as reinforcing fillers, restricting the movement of polymer chains and enhancing the mechanical strength of the membrane. This dosage range ensures sufficient montmorillonite sheets to exert their barrier and mechanical reinforcing effects while avoiding excessive dosage that could lead to high solution viscosity and agglomeration, affecting subsequent spraying.

[0053] When the amount of modified montmorillonite is below the lower limit defined in this invention, the content of montmorillonite lamellae is low, making it difficult to form a continuous barrier, which significantly reduces the barrier performance of the membrane. Furthermore, too little modified montmorillonite cannot effectively improve the mechanical strength of the membrane.

[0054] When the amount of modified montmorillonite exceeds the upper limit specified in this invention, the excessively high content of modified montmorillonite will significantly increase the viscosity of the solution, making its fluidity worse and affecting subsequent spraying, thus leading to uneven film thickness. In addition, excessive modified montmorillonite is prone to agglomerate in the solution to form micron-sized aggregates. These aggregates will become stress concentration points in the film layer, reducing the mechanical properties of the film layer.

[0055] In some optional instances, the amount of plasticizer added is 4 to 5 wt% of the mass of the matrix solution, for example, 4.0 wt%, 4.1 wt%, 4.2 wt%, 4.3 wt%, 4.4 wt%, 4.5 wt%, 4.6 wt%, 4.7 wt%, 4.8 wt%, 4.9 wt%, or 5.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0056] In some alternative examples, the plasticizer is composed of glycerol and polyethylene glycol 400 in a 1:1 mass ratio.

[0057] In some optional instances, the amount of rheology modifier added is 0.1 to 0.5 wt% of the matrix solution mass, for example, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, or 0.5 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0058] In some optional instances, the rheology modifier comprises fumed silica.

[0059] In some optional instances, the amount of surfactant added is 0.1 to 0.3 wt% of the mass of the matrix solution, for example, 0.1 wt%, 0.12 wt%, 0.14 wt%, 0.16 wt%, 0.18 wt%, 0.2 wt%, 0.22 wt%, 0.24 wt%, 0.26 wt%, 0.28 wt%, or 0.3 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0060] In some optional instances, the surfactant includes alkyl polysaccharide glycosides.

[0061] As a preferred technical solution of the present invention, in step (III), the mixing time of the matrix solution, modified montmorillonite, plasticizer, rheology modifier and surfactant is 2 to 3 hours, for example, it can be 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0062] In some optional examples, the mixing speed of the matrix solution, modified montmorillonite, plasticizer, rheology modifier and surfactant is 300 to 400 rpm, for example, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0063] As a preferred technical solution of the present invention, in step (III), the temperature of the static curing is room temperature.

[0064] In some optional instances, the settling time is 3 to 4 hours, for example, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0065] In a second aspect, the present invention provides a nanocellulose-based composite liquid mulch film prepared by the preparation method described in the first aspect, wherein the nanocellulose-based composite liquid mulch film comprises nanocellulose solution, oxidized sodium alginate, chitosan, modified montmorillonite, plasticizer, rheology modifier and surfactant.

[0066] The modified montmorillonite is obtained by intercalation modification of sodium-based montmorillonite with zwitterionic polymers.

[0067] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0068] The composite liquid mulch prepared in this invention uses nanocellulose as a reinforcing framework and utilizes the Schiff base reaction between oxidized sodium alginate and chitosan to form a chemical cross-linked network, constituting a strong and stable matrix solution. Subsequently, sodium-based montmorillonite is intercalated and modified by zwitterionic polymers, which greatly improves its compatibility and dispersibility with the matrix solution, allowing the montmorillonite sheets to be uniformly distributed in the matrix network, effectively extending the water vapor diffusion path and endowing the composite liquid mulch with excellent barrier properties. Finally, plasticizers, rheology modifiers, and surfactants are added, resulting in a liquid mulch that simultaneously possesses excellent mechanical strength, flexibility, and high barrier properties. Attached Figure Description

[0069] Figure 1 The process flow diagrams for preparing the composite liquid mulch film provided in Examples 1-15 of this invention are shown below.

[0070] Figure 2 Infrared spectra of nanocellulose and the matrix solution prepared in Example 1 of this invention;

[0071] Figure 3 Infrared spectra of sodium-based montmorillonite and the modified montmorillonite prepared in Example 1 of this invention;

[0072] Figure 4 The XRD patterns are of sodium-based montmorillonite and the modified montmorillonite prepared in Example 1 of this invention. Detailed Implementation

[0073] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0074] Example 1

[0075] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0076] (1) Add sodium periodate to a sodium alginate solution with a mass fraction of 2 wt%, wherein the mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is 0.3:1. Mix and stir for 3 h at room temperature and in the dark to complete the oxidation reaction and obtain an oxidized sodium alginate solution.

[0077] Under stirring conditions of 300 rpm, chitosan solution was added dropwise to sodium alginate solution. The chitosan solution consisted of chitosan and acetic acid solution with a mass fraction of 1 wt%, and the mass fraction of chitosan in the chitosan solution was 1.5 wt%. After the addition was completed, stirring was continued for 50 min to obtain a composite solution.

[0078] A 1 wt% nanocellulose solution was mixed with a composite solution. The mass ratio of nanocellulose dry base, sodium alginate, and chitosan in the nanocellulose solution was 1:2:0.5. After thorough mixing, a mixed solution was obtained. A 5 wt% ammonia solution was added dropwise to the mixed solution to adjust the pH to 7.5. The solution was then stirred and heated at 40°C for 3 hours to complete the crosslinking reaction, resulting in a matrix solution.

[0079] (2) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride were dissolved in deionized water at a molar ratio of 1:1 to obtain a precursor solution. The total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution was 10 wt%. Potassium persulfate initiator was added to the precursor solution. The mass ratio of the total mass of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the mass of potassium persulfate was 100:0.5. After mixing evenly, the mixture was stirred and heated at 70°C under a nitrogen atmosphere for 6 h to complete the copolymerization reaction and obtain a zwitterionic polymer.

[0080] Sodium montmorillonite was dispersed in deionized water to obtain a sodium montmorillonite dispersion with a mass fraction of 2 wt%. An amphoteric polymer was added to the sodium montmorillonite dispersion, with a mass ratio of the amphoteric polymer to sodium montmorillonite in the sodium montmorillonite dispersion of 0.5:1. The mixture was stirred and heated at 60°C for 6 h to complete the intercalation reaction. After centrifugation, washing and drying, modified montmorillonite was obtained.

[0081] (3) The modified montmorillonite, plasticizer, fumed silica and alkyl polysaccharide obtained in step (2) are added to the matrix solution obtained in step (1). The amount of modified montmorillonite added is 2 wt% of the matrix solution mass, the amount of plasticizer (glycerol and polyethylene glycol 400 mixed at a mass ratio of 1:1) added is 4 wt% of the matrix solution mass, the amount of fumed silica added is 0.1 wt% of the matrix solution mass, and the amount of alkyl polysaccharide added is 0.1 wt% of the matrix solution mass. Then, the mixture is stirred for 3 h at room temperature and 300 rpm. Finally, it is left to stand and mature at room temperature for 3 h. After vacuum degassing, the nanocellulose-based composite liquid mulch film is obtained.

[0082] Figure 2 The figures show the infrared spectra of nanocellulose and the matrix solution prepared in this embodiment. As can be seen from the figures, in the infrared curve of nanocellulose, the 3300 cm⁻¹... -1 The absorption peak at 2900 cm⁻¹ is attributed to the OH stretching vibration. -1 The absorption peak at 1640 cm⁻¹ is attributed to the CH stretching vibration. -1 The absorption peak at 1050 cm⁻¹ is attributed to the OH bending vibration of adsorbed water. -1 The absorption peak at 1600 cm⁻¹ is attributed to the stretching vibrations of COC and CO. In the infrared spectrum of the matrix solution, the peak at 1600 cm⁻¹ is... -1 The absorption peak at the point is significantly enhanced and accompanied by a change in peak shape, which is attributed to the asymmetric stretching vibration of the carboxylate ion (-COO-) and the stretching vibration of the C=N bond. The carboxylate ion originates from sodium alginate, and the appearance of the C=N bond is due to the Schiff base reaction between the aldehyde group (-CHO) of oxidized sodium alginate and the amino group (-NH2) of chitosan, which generates the C=N bond of the cross-linked network.

[0083] Figure 3 The figures show the infrared spectra of sodium-based montmorillonite and the modified montmorillonite prepared in this example. As can be seen from the figures, in the infrared curve of sodium-based montmorillonite, 3620 cm⁻¹... -1 The absorption peak at 3400 cm⁻¹ is attributed to the stretching vibrations of hydroxyl groups (Al-OH and Mg-OH) within the montmorillonite structure. -1 The broad absorption peak at 1040 cm⁻¹ is attributed to the stretching vibration of the OH bonds in the interlayer adsorbed water molecules. -1 The strong and broad absorption peak at 520 cm⁻¹ is attributed to the stretching vibration of the Si-O bond in the silicon-oxygen tetrahedron. -1 and 465cm -1 The absorption peaks at 1640 cm⁻¹ are attributed to the bending vibrations of Si-O-Al and Si-O-Mg, respectively, which are typical characteristic functional groups of sodium-based montmorillonite. In the infrared curve of modified montmorillonite, all the intrinsic absorption peaks of montmorillonite mentioned above are still present, but the difference lies in the peak at 1640 cm⁻¹. -1A new absorption peak appeared at 1540 cm⁻¹, which is attributed to the C=O stretching vibration of the amide group (-CONH-) in the zwitterionic polymer. -1 A new absorption peak appeared at 1485 cm⁻¹, which is attributed to the stretching vibration of the CN bond in the quaternary ammonium salt group and the amide II band (NH bending). -1 A new absorption peak appeared at 2920 cm⁻¹, which is attributed to the antisymmetric bending vibration of -CH₃ in the quaternary ammonium salt group. -1 and 2850cm -1 The two absorption peaks appearing at the specified position are attributed to the antisymmetric and symmetric stretching vibrations of the methylene group (-CH2-), respectively, which belong to the long-chain alkanes of the zwitterionic polymer. These newly emerging absorption peaks indicate that this embodiment successfully achieved the intercalation reaction between the zwitterionic polymer obtained by copolymerizing 2-acrylamido-2-methylpropanesulfonic acid (containing amide and sulfonic acid groups) and methacryloyloxyethyltrimethylammonium chloride (containing quaternary ammonium salt groups) and montmorillonite.

[0084] Figure 4 The XRD patterns of sodium-based montmorillonite and the modified montmorillonite prepared in this example are shown. The silicate layers in montmorillonite exhibit corresponding diffraction peaks in the XRD. After zwitterionic polymer intercalation modification, the interplanar spacing of the (001) crystal planes of montmorillonite increases, and the positions of the diffraction peaks shift. As shown in the figure, the 2θ = 6.96° of the d001 peak of montmorillonite, calculated using the Bragg diffraction equation 2dsinθ = nλ, indicates that the interplanar spacing of the (001) crystal plane of montmorillonite is 1.27 nm. The diffraction angle of the (001) crystal plane of the modified montmorillonite is 3.02°, and the interplanar spacing of the (001) crystal plane of the modified montmorillonite, calculated using the Bragg diffraction equation, is 2.92 nm. This indicates that zwitterionic polymer intercalation modification significantly expands the interlayer spacing of montmorillonite.

[0085] Example 2

[0086] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0087] (1) Add sodium periodate to a sodium alginate solution with a mass fraction of 2.5 wt%. The mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is 0.35:1. Mix and stir for 3.2 h at room temperature and in the dark to complete the oxidation reaction and obtain an oxidized sodium alginate solution.

[0088] Under stirring conditions of 350 rpm, chitosan solution was added dropwise to sodium alginate solution. The chitosan solution consisted of chitosan and acetic acid solution with a mass fraction of 1 wt%. The mass fraction of chitosan in the chitosan solution was 1.8 wt%. After the addition was completed, stirring was continued for 48 min to obtain a composite solution.

[0089] A 1.2 wt% nanocellulose solution was mixed with a composite solution. The mass ratio of nanocellulose dry base, sodium alginate, and chitosan in the nanocellulose solution was 1:2.2:0.8. After thorough mixing, a mixed solution was obtained. A 6 wt% ammonia solution was added dropwise to the mixed solution to adjust the pH to 7.8. The solution was then stirred and heated at 42°C for 2.8 h to complete the crosslinking reaction, resulting in a matrix solution.

[0090] (2) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride were dissolved in deionized water at a molar ratio of 1:1 to obtain a precursor solution. The total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution was 12 wt%. Potassium persulfate initiator was added to the precursor solution. The mass ratio of the total mass of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the mass of potassium persulfate was 100:0.6. After mixing evenly, the mixture was stirred and heated at 72°C under a nitrogen atmosphere for 5.5 h to complete the copolymerization reaction and obtain a zwitterionic polymer.

[0091] Sodium montmorillonite was dispersed in deionized water to obtain a sodium montmorillonite dispersion with a mass fraction of 2.5 wt%. An amphoteric polymer was added to the sodium montmorillonite dispersion, with a mass ratio of the amphoteric polymer to sodium montmorillonite in the sodium montmorillonite dispersion of 0.6:1. The mixture was stirred and heated at 62 °C for 5.5 h to complete the intercalation reaction. After centrifugation, washing and drying, modified montmorillonite was obtained.

[0092] (3) The modified montmorillonite, plasticizer, fumed silica and alkyl polysaccharide obtained in step (2) are added to the matrix solution obtained in step (1). The amount of modified montmorillonite added is 2.2 wt% of the matrix solution mass, the amount of plasticizer (glycerol and polyethylene glycol 400 mixed at a mass ratio of 1:1) added is 4.2 wt% of the matrix solution mass, the amount of fumed silica added is 0.2 wt% of the matrix solution mass, and the amount of alkyl polysaccharide added is 0.15 wt% of the matrix solution mass. Then, the mixture is stirred at room temperature and 320 rpm for 2.8 h. Finally, it is left to stand and mature at room temperature for 3.2 h. After vacuum degassing, the nanocellulose-based composite liquid mulch film is obtained.

[0093] Example 3

[0094] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0095] (1) Add sodium periodate to a sodium alginate solution with a mass fraction of 3 wt%, wherein the mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is 0.4:1. Mix and stir for 3.5 h at room temperature and in the dark to complete the oxidation reaction and obtain an oxidized sodium alginate solution.

[0096] Under stirring conditions of 400 rpm, chitosan solution was added dropwise to sodium alginate solution. The chitosan solution consisted of chitosan and acetic acid solution with a mass fraction of 1 wt%, and the mass fraction of chitosan in the chitosan solution was 2 wt%. After the addition was completed, stirring was continued for 45 min to obtain a composite solution.

[0097] A 1.5 wt% nanocellulose solution was mixed with a composite solution. The mass ratio of nanocellulose dry base, sodium alginate, and chitosan in the nanocellulose solution was 1:2.5:1. After thorough mixing, a mixed solution was obtained. A 7 wt% ammonia solution was added dropwise to the mixed solution to adjust the pH to 8. The solution was then stirred and heated at 45°C for 2.5 h to complete the crosslinking reaction, resulting in a matrix solution.

[0098] (2) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride were dissolved in deionized water at a molar ratio of 1:1 to obtain a precursor solution. The total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution was 15 wt%. Potassium persulfate initiator was added to the precursor solution. The mass ratio of the total mass of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the mass of potassium persulfate was 100:0.7. After mixing evenly, the mixture was stirred and heated at 75°C under a nitrogen atmosphere for 5 h to complete the copolymerization reaction and obtain a zwitterionic polymer.

[0099] Sodium montmorillonite was dispersed in deionized water to obtain a sodium montmorillonite dispersion with a mass fraction of 3 wt%. An amphoteric polymer was added to the sodium montmorillonite dispersion, with a mass ratio of the amphoteric polymer to sodium montmorillonite in the sodium montmorillonite dispersion of 0.7:1. The mixture was stirred and heated at 65°C for 5 h to complete the intercalation reaction. After centrifugation, washing and drying, modified montmorillonite was obtained.

[0100] (3) The modified montmorillonite, plasticizer, fumed silica and alkyl polysaccharide obtained in step (2) are added to the matrix solution obtained in step (1). The amount of modified montmorillonite added is 2.5 wt% of the matrix solution mass, the amount of plasticizer (glycerol and polyethylene glycol 400 mixed at a mass ratio of 1:1) added is 4.5 wt% of the matrix solution mass, the amount of fumed silica added is 0.3 wt% of the matrix solution mass, and the amount of alkyl polysaccharide added is 0.2 wt% of the matrix solution mass. Then, the mixture is stirred at room temperature and 350 rpm for 2.5 h. Finally, it is left to stand and mature at room temperature for 3.5 h. After vacuum degassing, the nanocellulose-based composite liquid mulch film is obtained.

[0101] Example 4

[0102] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0103] (1) Add sodium periodate to a sodium alginate solution with a mass fraction of 3.5 wt%. The mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is 0.45:1. Mix and stir for 3.8 h at room temperature and in the dark to complete the oxidation reaction and obtain an oxidized sodium alginate solution.

[0104] Under stirring conditions of 450 rpm, the chitosan solution was added dropwise to the sodium alginate oxidase solution. The chitosan solution consisted of chitosan and acetic acid solution with a mass fraction of 1 wt%, and the mass fraction of chitosan in the chitosan solution was 2.2 wt%. After the addition was completed, stirring was continued for 42 min to obtain a composite solution.

[0105] A 1.8 wt% nanocellulose solution was mixed with a composite solution. The mass ratio of nanocellulose dry base, sodium alginate, and chitosan in the nanocellulose solution was 1:2.8:1.2. After thorough mixing, a mixed solution was obtained. An 8 wt% ammonia solution was added dropwise to the mixed solution to adjust the pH to 8.2. The solution was then stirred and heated at 48°C for 2.2 h to complete the crosslinking reaction, resulting in a matrix solution.

[0106] (2) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride were dissolved in deionized water at a molar ratio of 1:1 to obtain a precursor solution. The total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution was 18 wt%. Potassium persulfate initiator was added to the precursor solution. The mass ratio of the total mass of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the mass of potassium persulfate was 100:0.8. After mixing evenly, the mixture was stirred and heated at 78°C for 4.5 h under a nitrogen atmosphere to complete the copolymerization reaction and obtain a zwitterionic polymer.

[0107] Sodium montmorillonite was dispersed in deionized water to obtain a sodium montmorillonite dispersion with a mass fraction of 3.5 wt%. An amphoteric polymer was added to the sodium montmorillonite dispersion, with a mass ratio of the amphoteric polymer to sodium montmorillonite in the sodium montmorillonite dispersion of 0.8:1. The mixture was stirred and heated at 68 °C for 4.5 h to complete the intercalation reaction. After centrifugation, washing and drying, modified montmorillonite was obtained.

[0108] (3) The modified montmorillonite, plasticizer, fumed silica and alkyl polysaccharide obtained in step (2) are added to the matrix solution obtained in step (1). The amount of modified montmorillonite added is 2.8 wt% of the matrix solution mass, the amount of plasticizer (glycerol and polyethylene glycol 400 mixed at a mass ratio of 1:1) added is 4.8 wt% of the matrix solution mass, the amount of fumed silica added is 0.4 wt% of the matrix solution mass, and the amount of alkyl polysaccharide added is 0.25 wt% of the matrix solution mass. Then, the mixture is stirred at room temperature and 380 rpm for 2.2 h. Finally, it is left to stand and mature at room temperature for 3.8 h. After vacuum degassing, the nanocellulose-based composite liquid mulch film is obtained.

[0109] Example 5

[0110] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0111] (1) Add sodium periodate to a sodium alginate solution with a mass fraction of 4 wt%. The mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is 0.5:1. Mix and stir for 4 h at room temperature and in the dark to complete the oxidation reaction and obtain an oxidized sodium alginate solution.

[0112] Under stirring conditions of 500 rpm, the chitosan solution was added dropwise to the sodium alginate oxidase solution. The chitosan solution consisted of chitosan and acetic acid solution with a mass fraction of 1 wt%, and the mass fraction of chitosan in the chitosan solution was 2.5 wt%. After the addition was completed, stirring was continued for 40 min to obtain a composite solution.

[0113] A 2 wt% nanocellulose solution was mixed with a composite solution. The mass ratio of nanocellulose dry base, sodium alginate, and chitosan in the nanocellulose solution was 1:3:1.5. After thorough mixing, a mixed solution was obtained. A 10 wt% ammonia solution was added dropwise to the mixed solution to adjust the pH value to 8.5. The solution was then stirred and heated at 50°C for 2 hours to complete the crosslinking reaction, resulting in a matrix solution.

[0114] (2) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride were dissolved in deionized water at a molar ratio of 1:1 to obtain a precursor solution. The total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution was 20 wt%. Potassium persulfate initiator was added to the precursor solution. The mass ratio of the total mass of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the mass of potassium persulfate was 100:1. After mixing evenly, the mixture was stirred and heated at 80°C under a nitrogen atmosphere for 4 h to complete the copolymerization reaction and obtain a zwitterionic polymer.

[0115] Sodium montmorillonite was dispersed in deionized water to obtain a sodium montmorillonite dispersion with a mass fraction of 4 wt%. A zwitterionic polymer was added to the sodium montmorillonite dispersion, with a mass ratio of zwitterionic polymer to sodium montmorillonite in the sodium montmorillonite dispersion of 1:1. The mixture was stirred and heated at 70°C for 4 h to complete the intercalation reaction. After centrifugation, washing and drying, modified montmorillonite was obtained.

[0116] (3) The modified montmorillonite, plasticizer, fumed silica and alkyl polysaccharide obtained in step (2) are added to the matrix solution obtained in step (1). The amount of modified montmorillonite added is 3 wt% of the matrix solution mass, the amount of plasticizer (glycerol and polyethylene glycol 400 mixed at a mass ratio of 1:1) added is 5 wt% of the matrix solution mass, the amount of fumed silica added is 0.5 wt% of the matrix solution mass, and the amount of alkyl polysaccharide added is 0.3 wt% of the matrix solution mass. Then, the mixture is stirred for 2 h at room temperature and 400 rpm. Finally, it is left to stand and mature at room temperature for 4 h. After vacuum degassing, the nanocellulose-based composite liquid mulch film is obtained.

[0117] Example 6

[0118] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (1), the mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is adjusted to 0.1:1. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0119] Example 7

[0120] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (1), the mass ratio of sodium periodate to sodium alginate in the sodium alginate solution is adjusted to 0.7:1. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0121] Example 8

[0122] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (1), the mass ratio of nanocellulose dry base, sodium alginate oxide and chitosan in the nanocellulose solution is adjusted to 1:1:0.5. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0123] Example 9

[0124] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (1), the mass ratio of nanocellulose dry base, sodium alginate oxide and chitosan in the nanocellulose solution is adjusted to 1:5:0.5. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0125] Example 10

[0126] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (1), the mass ratio of nanocellulose dry base, sodium alginate oxide and chitosan in the nanocellulose solution is adjusted to 1:2:0.1. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0127] Example 11

[0128] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (1), the mass ratio of nanocellulose dry base, sodium alginate and chitosan in the nanocellulose solution is adjusted to 1:2:2. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0129] Example 12

[0130] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (2), the mass ratio of the zwitterionic polymer to the sodium montmorillonite in the sodium montmorillonite dispersion is adjusted to 0.1:1. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0131] Example 13

[0132] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (2), the mass ratio of the zwitterionic polymer to the sodium montmorillonite in the sodium montmorillonite dispersion is adjusted to 1.5:1. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0133] Example 14

[0134] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (3), the amount of modified montmorillonite added is adjusted to 1 wt% of the matrix solution mass. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0135] Example 15

[0136] This embodiment provides a method for preparing a high-barrier nanocellulose-based composite liquid mulch film. The difference from Embodiment 1 is that in step (3), the amount of modified montmorillonite added is adjusted to 5 wt% of the matrix solution mass. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0137] The barrier properties, water retention properties, and mechanical properties of the nanocellulose-based composite liquid mulch films prepared in Examples 1-15 were tested. The specific test steps are as follows:

[0138] (1) Water vapor transmission rate

[0139] The composite liquid mulch film prepared in the example was uniformly coated onto a non-porous plate. After drying, a film with a thickness of 0.1 mm was formed. The film was completely peeled off from the non-porous plate and sealed in the mouth of a permeable cup containing a desiccant (anhydrous calcium chloride). The humidity inside the cup was approximately 0% RH. The permeable cup was placed in a constant temperature and humidity chamber (temperature 25 ± 0.5℃, relative humidity 50 ± 2% RH). The film was weighed periodically (e.g., at 24-hour intervals), and the water vapor transmission rate (WVTR) was calculated.

[0140]

[0141] Where Δw is the weight gain (g), A is the film area (m2), and t is the time (days).

[0142] (2) Tensile strength and elongation at break

[0143] The composite liquid mulch prepared in the example was uniformly coated on a non-porous plate and dried to form a film with a thickness of 0.1 mm. The film was completely peeled off from the non-porous plate and cut into standard dumbbell-shaped samples (length ≥ 100 mm, width 10 ± 0.2 mm).

[0144] Using a universal testing machine, set the clamp spacing to 50 mm and the tensile speed to 10 mm / min. Record the maximum tensile force (F) at which the specimen breaks. max ) and gauge length elongation (ΔL), calculate tensile strength (MPa) and elongation at break (%).

[0145] (3) Cumulative water loss rate over 14 days

[0146] Prepare standard sandy loam soil (initial moisture content 20%±1%), and uniformly spray the composite liquid mulch film prepared in the example onto the soil surface at a spraying rate of 50 g / m². 2 The soil was placed in a constant temperature and humidity chamber (temperature 30±1°C, humidity 40±5%RH) and the soil weight on day 1 (w0) was measured. After 14 consecutive days of testing, the soil weight on day 14 (w0) was measured. n To calculate soil weight loss, the cumulative water loss rate over 14 days is calculated using the following formula:

[0147] 14-day cumulative water loss rate (%) = [(w0-w n ) / w0]×100%.

[0148] The test results are shown in Table 1.

[0149] Table 1

[0150]

[0151] The test data from Examples 1, 6, and 7 show that when the amount of sodium periodate is too low (Example 6), the oxidation degree of sodium alginate is insufficient, resulting in a sparse Schiff base crosslinking network formed with chitosan. This reduces the intermolecular forces, significantly decreasing the tensile strength of the resulting membrane. Simultaneously, the insufficiently dense network structure allows water vapor to permeate more easily, leading to poorer barrier properties. When the amount of sodium periodate is too high (Example 7), excessive oxidation causes the sodium alginate molecular chains to break and degrade, disrupting the integrity of the membrane matrix network and reducing both the mechanical and barrier properties of the membrane.

[0152] The test data from Examples 1, 8, and 9 show that when the amount of sodium alginate oxide is too low (Example 8), it is insufficient to fully coat the nanocellulose and form a continuous and complete cross-linked network, leading to easy aggregation of nanocellulose, a significant reduction in the mechanical strength of the membrane, and a loose membrane structure with reduced barrier performance. When the amount of sodium alginate oxide is too high (Example 9), the viscosity of the liquid mulch film increases significantly. Excessive viscosity and molecular chain entanglement increase the brittleness of the membrane and also affect the dispersion uniformity of the modified montmorillonite, resulting in a decrease in the barrier performance of the membrane.

[0153] The test data from Examples 1, 10, and 11 show that when the amount of chitosan is too low (Example 10), it cannot form a sufficient number of crosslinking points with sodium alginate oxide, resulting in insufficient three-dimensional network strength, decreased mechanical properties of the membrane, and insufficient membrane density, leading to increased water vapor permeability and decreased barrier performance. When the amount of chitosan is too high (Example 11), excessive chitosan will undergo strong electrostatic complexation with sodium alginate oxide, leading to phase separation and aggregation, severely damaging the homogeneity of the matrix solution and the integrity of the membrane structure after film formation, ultimately resulting in a significant reduction in the tensile strength, elongation at break, and barrier performance of the membrane.

[0154] The test data from Examples 1, 12, and 13 show that when the amount of zwitterionic polymer is too low (Example 12), it cannot effectively intercalate montmorillonite, resulting in a large number of stacked montmorillonite sheets. These sheets easily aggregate and form defects when mixed with the matrix solution, failing to provide mechanical reinforcement and barrier properties and instead becoming stress concentration points, leading to a significant decrease in the mechanical and barrier properties of the film. When the amount of zwitterionic polymer is too high (Example 13), the excessive amount introduces too many hydrophilic groups, resulting in a decrease in the moisture barrier properties of the film. Simultaneously, the excessive zwitterionic polymer coats the surface of montmorillonite, forming a soft interface layer between montmorillonite and the matrix, weakening the mechanical reinforcement effect of montmorillonite.

[0155] The test data from Examples 1, 14, and 15 show that when the amount of modified montmorillonite is too low (Example 14), an effective tortuous barrier cannot be formed to hinder the diffusion of water molecules, resulting in a significant decrease in the barrier performance of the membrane layer. Simultaneously, its mechanical reinforcement effect is limited, and the improvement in the mechanical strength of the membrane layer is not significant. When the amount of modified montmorillonite is too high (Example 15), excessive modified montmorillonite leads to a significant increase in the viscosity of the liquid mulch film, affecting the uniformity of film formation and making it prone to agglomeration, generating stress defects, which in turn reduces the tensile strength of the membrane layer.

[0156] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a high-barrier nanocellulose-based composite liquid mulch film, characterized in that, The preparation method includes: (I) Add sodium periodate to sodium alginate solution to carry out an oxidation reaction to obtain sodium alginate oxidized solution, add chitosan solution to it, mix well to obtain a composite solution; mix nanocellulose solution with the composite solution, add ammonia solution to adjust the pH value, carry out cross-linking reaction to obtain matrix solution; the mass ratio of sodium periodate to sodium alginate in sodium alginate solution is (0.3~0.5):1; the mass ratio of nanocellulose dry base, sodium alginate oxidized solution and chitosan in nanocellulose solution is 1:(2~3):(0.5~1.5); (II) 2-Acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride are dissolved in deionized water to obtain a precursor solution. An initiator is added to the precursor solution to carry out a copolymerization reaction to obtain a zwitterionic polymer. The zwitterionic polymer is added to a sodium-based montmorillonite dispersion to carry out an intercalation reaction. After centrifugation, washing and drying, modified montmorillonite is obtained. The mass ratio of the zwitterionic polymer to the sodium-based montmorillonite in the sodium-based montmorillonite dispersion is (0.5~1):

1. (III) The matrix solution obtained in step (I), the modified montmorillonite, plasticizer, rheology modifier and surfactant obtained in step (II) are mixed evenly, and then allowed to stand for curing and vacuum degassing to obtain the nanocellulose-based composite liquid mulch film.

2. The preparation method according to claim 1, characterized in that, In step (I), the mass fraction of sodium alginate in the sodium alginate solution is 2-4 wt%. The oxidation reaction takes 3-4 hours. The oxidation reaction is carried out under light-protected conditions.

3. The preparation method according to claim 1, characterized in that, In step (I), the chitosan solution is composed of chitosan and acetic acid solution; The chitosan solution contains 1.5-2.5 wt% chitosan by mass. Under stirring conditions of 300-500 rpm, the chitosan solution is added dropwise to the sodium alginate oxidase solution. After the addition is complete, stirring is continued for 40-50 minutes to obtain the composite solution.

4. The preparation method according to claim 1, characterized in that, In step (I), the mass fraction of the nanocellulose solution is 1~2 wt%; Add the ammonia solution dropwise to adjust the pH of the mixed solution to 7.5-8.5; The reaction temperature for the crosslinking reaction is 40~50℃; The cross-linking reaction takes 2-3 hours.

5. The preparation method according to claim 1, characterized in that, In step (II), the total mass fraction of 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride in the precursor solution is 10~20 wt%. The initiator includes potassium persulfate; The ratio of the total mass of the 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethyltrimethylammonium chloride to the mass of the initiator is 100:(0.5~1); The reaction temperature for the copolymerization reaction is 70~80℃; The copolymerization reaction takes 4-6 hours. The copolymerization reaction was carried out under a nitrogen atmosphere.

6. The preparation method according to claim 1, characterized in that, In step (II), the sodium montmorillonite dispersion is obtained by dispersing sodium montmorillonite in deionized water; The sodium montmorillonite dispersion contains 2-4 wt% sodium montmorillonite. The reaction temperature for the intercalation reaction is 60~70℃; The reaction time for the intercalation reaction is 4-6 hours.

7. The preparation method according to claim 1, characterized in that, In step (III), the amount of modified montmorillonite added is 2-3 wt% of the mass of the matrix solution; The amount of plasticizer added is 4-5 wt% of the mass of the matrix solution; The plasticizer is composed of glycerin and polyethylene glycol 400; The amount of the rheology modifier added is 0.1~0.5 wt% of the matrix solution mass; the rheology modifier includes fumed silica; The amount of surfactant added is 0.1 to 0.3 wt% of the matrix solution; the surfactant includes alkyl polysaccharide glycoside.

8. The preparation method according to claim 1, characterized in that, In step (III), the mixing time of the matrix solution, modified montmorillonite, plasticizer, rheology modifier and surfactant is 2-3 hours; The mixing speed of the matrix solution, modified montmorillonite, plasticizer, rheology modifier and surfactant is 300~400 rpm.

9. The preparation method according to claim 1, characterized in that, In step (III), the settling and ripening time is 3-4 hours.

10. A nanocellulose-based composite liquid mulch film prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The nanocellulose-based composite liquid mulch film comprises nanocellulose solution, oxidized sodium alginate, chitosan, modified montmorillonite, plasticizer, rheology modifier and surfactant; The modified montmorillonite is obtained by intercalation modification of sodium-based montmorillonite with zwitterionic polymers.

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