Bio-based composite liquid mulching film and preparation method thereof

Abstract

The invention provides a bio-based composite liquid mulching film and a preparation method thereof. The bio-based composite liquid mulching film comprises a nanocellulose solution, modified starch, modified chitosan, glycerol and calcium carbonate, the modified starch is obtained by modifying starch with citric acid; the modified chitosan is obtained by grafting and copolymerizing chitosan with an acrylic monomer. According to the invention, a plurality of bio-based components such as modified starch, modified chitosan, a nanocellulose solution, glycerol and calcium carbonate are integrated, and natural characteristics of bio-based materials are utilized to form a uniform and degradable film layer; the soil moisture retention film can better isolate air and moisture loss, improves the soil moisture retention ability, ensures sufficient strength and flexibility in the application process, and avoids the problems of early cracking or deformation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid ground films and relates to a bio-based composite liquid ground film and a preparation method thereof. Background Art

[0002] Plastic mulch films widely used in agriculture are primarily made from petroleum-based polymers such as polyethylene. While these traditional mulch films retain moisture, increase warmth, and suppress weeds, they also contribute to serious "white pollution." Their non-degradable nature leads to the long-term accumulation of residual fragments in the soil, damaging soil structure, hindering water and nutrient circulation, and even threatening the ecological environment and human health through the food chain. Despite recent developments in biodegradable plastic mulch films, some materials still suffer from uncontrollable degradation cycles, insufficient mechanical properties, or high costs, making them difficult to meet the demands of large-scale agricultural applications.

[0003] Liquid mulch, as an alternative, achieves agronomic functions by spraying to form a film, thus avoiding the problem of difficult field recycling. Early studies mostly used materials such as asphalt and synthetic polymer emulsions. Although they have film-forming properties, they have defects such as poor biocompatibility, harmful degradation products, or insufficient water retention and barrier properties. Bio-based materials such as natural starch, cellulose, chitosan, etc. have attracted attention due to their wide sources, renewable and degradable characteristics, but mulch films prepared from single components often face bottlenecks such as low mechanical strength, poor water resistance due to excessive hydrophilicity, and poor film formation continuity. Although there have been attempts to compound bio-based components in the existing technology, how to achieve synergistic enhancement of multiple components and simultaneously improve mechanical strength, water vapor barrier properties and soil water retention capacity while ensuring complete biodegradation is still a technical problem that needs to be overcome.

[0004] In this context, developing a composite liquid mulch film based on modified biopolymers, optimizing interfacial interactions between components through molecular structural design, and balancing degradation cycles with functional durability, has become an important approach to addressing the conflict between sustainable agricultural production and environmental protection. There is an urgent need to develop a new green mulch film system that combines efficient agronomic performance, environmental friendliness, and economic feasibility to meet the dual needs of modern agriculture for resource conservation and ecological safety. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a bio-based composite liquid ground film and a preparation method thereof. The present invention integrates multiple bio-based components such as modified starch, modified chitosan, nanocellulose solution, glycerol and calcium carbonate, and utilizes the natural properties of bio-based materials to form a uniform and degradable film layer, which can better isolate air and water vapor loss, improve soil moisture retention capacity, and ensure that the film has sufficient strength and flexibility during application, avoiding problems such as early cracking or deformation.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a bio-based composite liquid mulch film, wherein the bio-based composite liquid mulch film comprises a nanocellulose solution, modified starch, modified chitosan, glycerol, and calcium carbonate;

[0008] The modified starch is obtained by modifying starch with citric acid;

[0009] The modified chitosan is obtained by graft copolymerization of chitosan with acrylic acid monomers.

[0010] The bio-based composite liquid mulch provided by the present invention integrates multiple bio-based components, utilizing the natural properties of bio-based materials to form a uniform, degradable film layer, effectively addressing the environmental pollution issues of traditional plastic mulch films. Nanocellulose serves as the structural framework, modified starch and modified chitosan serve as the primary film-forming matrix, and glycerol and calcium carbonate serve as functional additives. These synergistically enhance the barrier, water-retention, and mechanical properties of the film layer, enabling the liquid mulch film to better isolate air and water vapor loss, improve soil moisture retention, and ensure sufficient strength and flexibility during use, avoiding problems such as premature cracking or deformation.

[0011] After the starch was modified with citric acid, an acidolysis and esterification reaction occurred, introducing carboxyl functional groups, which significantly improved the chemical structure and surface properties of the starch. This modification process hydrolyzed the starch molecular chains and formed some ether bonds, making the molecular weight distribution of the starch more uniform, thereby enhancing the hydrophilicity and film-forming properties of the starch. In terms of water retention, the carboxyl groups can effectively adsorb and retain water molecules through hydrogen bonds, reducing the evaporation rate of soil moisture to the air. In terms of mechanical properties, the esterified structure provides stronger intermolecular forces, and the interlocking network structure formed with nanocellulose enhances the tensile strength and toughness of the film layer. In addition, the solubility of the modified starch in aqueous solution is improved, which reduces the problem of uneven viscosity during the preparation process, ensures that the formed film layer is smoother and denser, further improves the barrier properties of the film layer, and reduces the interference of the external environment on soil moisture.

[0012] Chitosan generates a branched structure after graft copolymerization with acrylic acid monomers, which enhances the flexibility and reactivity of chitosan. Through acrylic acid graft copolymerization, chitosan is transformed from its original rigid polymer into a more ductile material, which significantly enhances the barrier properties of the film layer. The modified chitosan can form a denser microscopic network in the film layer, effectively blocking the penetration of oxygen and carbon dioxide, and reducing heat loss caused by soil gas exchange. In terms of water retention, the acrylic acid side chains increase the number of polar groups, improve the water absorption capacity and viscoelasticity of chitosan, and help maintain the stability of the film layer in a humid environment. At the same time, the acrylic acid graft modification improves the compatibility of chitosan with other components in the liquid ground film, strengthens the mechanical properties of the film layer through intermolecular covalent bonds, and prevents the film layer from breaking or delaminating under mechanical stress, thereby achieving the long-term durability requirements of the film layer.

[0013] Nanocellulose solution plays a key skeletal role in liquid mulch, and its nanoscale fiber structure provides the entire liquid mulch with a high degree of mechanical stability and microscopic uniformity. The fiber diameter of nanocellulose is at the nanometer level, and it can form a strong physical interwoven network structure with modified starch and modified chitosan. This structure greatly enhances the tensile strength and elastic modulus of the membrane layer. In terms of barrier properties, the dense arrangement of nanofibers reduces the size and distribution of membrane pores, reducing the diffusion channels for water molecules and gases, thereby improving the barrier properties of the membrane layer. In terms of water retention, the hydrophilic surface of nanocellulose itself can promote the uniform distribution and retention of water, while stabilizing the moisture environment in the soil through adsorption. In addition, the nano-properties of nanocellulose also improve the rheological properties of the liquid mulch, so that the membrane layer forms a smooth surface after spraying or coating, avoiding the occurrence of cracks and ensuring the consistency of the membrane layer performance.

[0014] The present invention adds glycerol and calcium carbonate to the liquid ground film, wherein glycerol acts as a plasticizer. Glycerol reduces intermolecular friction and increases free volume by penetrating between polymer chains, significantly improving the flexibility and ductility of the film layer, making the liquid ground film less prone to brittle cracking when subjected to soil shrinkage or temperature changes, and maintaining good mechanical integrity. At the same time, the small molecule characteristics of glycerol improve the humidity and wetting ability of the film layer, indirectly enhancing the water retention performance, and helping to evenly distribute and continuously release water within the film layer. Calcium carbonate acts as a low-cost filler. Through the dispersion and stacking of its microstructure, it fills nano-voids and increases the density and surface hardness of the film layer, further improving the barrier properties of the film layer and blocking the invasion of external pollutants. In addition, calcium carbonate particles can strengthen the interfacial bonding with the organic matrix, share the mechanical load to reduce overall shrinkage, thereby achieving a synergistic effect and significantly improving the mechanical strength and service life of the film layer.

[0015] The synergistic effect between the various components significantly improves the performance of the liquid mulch film:

[0016] First, the hydrophilic carboxyl groups of the modified starch are combined with the fiber network of nanocellulose through hydrogen bonds to form a porous but dense skeleton structure, which optimizes water retention while enhancing the barrier properties of the film layer.

[0017] Secondly, the carboxyl groups carried by the acrylic acid side chains of the modified starch form high-density hydrogen bonds with the large number of hydroxyl groups on the surface of the nanocellulose, anchoring the fibers. At the same time, the main chain amino groups are protonated to produce strong electrostatic adsorption with the carboxyl groups of the modified starch, forming a molecular-level interlock. This chemical bonding establishes a continuous stress transfer path between the originally incompatible nanofibers and the flexible starch chains. The connection through the modified chitosan effectively eliminates the physical gap at the interface between the two phases and forms a dynamic buffer layer, which evenly transfers the rigidity enhancement effect of the nanofibers to the modified starch, avoiding microcracks caused by local stress concentration and improving the overall stiffness and tear resistance of the membrane layer.

[0018] Finally, glycerin acts as a plasticizer, filling the network gaps, reducing the film's brittleness and promoting molecular chain sliding, ensuring the film's flexibility and stability in dynamic environments. Calcium carbonate, dispersed within the liquid ground film, provides physical support, filling micropores and reducing defects, improving the film's airtightness and durability. The synergistic effects of these components achieve technical benefits such as efficient water blocking, reduced evaporation, and anti-aging.

[0019] As a preferred technical solution of the present invention, based on 100 parts by weight of the bio-based composite liquid ground film, it includes the following components in parts by weight:

[0020] 30-40 parts of nanocellulose solution;

[0021] 30-40 parts of modified starch;

[0022] 12-15 parts of modified chitosan;

[0023] 4-6 parts of glycerin;

[0024] 8-12 parts of calcium carbonate.

[0025] The weight parts of the nanocellulose solution can be 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts or 40 parts, the weight parts of the modified starch can be 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts or 40 parts, and the weight parts of the modified chitosan can be 12 parts, 12.5 parts, 13 parts, 13.5 parts, 14 parts, 14.5 parts or 1 The weight parts of glycerol can be 4.0 parts, 4.2 parts, 4.4 parts, 4.6 parts, 4.8 parts, 5.0 parts, 5.2 parts, 5.4 parts, 5.6 parts, 5.8 parts or 6.0 parts, and the weight parts of calcium carbonate can be 8.0 parts, 8.5 parts, 9.0 parts, 9.5 parts, 10.0 parts, 10.5 parts, 11.0 parts, 11.5 parts or 12.0 parts, but are not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0026] The present invention specifically limits the addition amount of nanocellulose solution to 30 to 40 parts. Within this range, it can form an effective supporting skeleton while avoiding excessive densification of the structure. At this addition amount, nanocellulose forms a uniform three-dimensional network, and its abundant hydroxyl groups on the surface produce stable hydrogen bonds with the carboxyl groups of the modified starch, synergistically enhancing the overall mechanical strength of the film layer. At the same time, the moderate gaps in the fiber network are effectively filled with calcium carbonate particles, reducing the water vapor permeability and maintaining the toughness of the film layer. The acrylic acid side chains of the modified chitosan form spatial crosslinks under the guidance of nanocellulose, reinforcing the local weak areas of the film layer and achieving a comprehensive improvement in strength and ductility.

[0027] When the amount of nanocellulose solution added is less than 30 parts, the insufficient density of the nanofiber network leads to structural defects. The sparse nanofibers are unable to fully bear the stress of the starch matrix, which easily causes interfacial separation under mechanical load. In addition, the sparse fiber network leads to an increase in nanoscale voids, which expands the diffusion channels for water molecules and significantly reduces the barrier properties of the film. At the same time, the cross-linking points of the modified chitosan lack the function of fiber anchoring points, and cannot form an effective toughening network, resulting in increased brittleness of the film.

[0028] When the nanocellulose solution is added in an amount exceeding 40 parts per million, the high-density nanofibers tend to tangle and clump during mixing, disrupting dispersion uniformity and causing the aggregates to become stress concentration points. Furthermore, the overly dense fiber network squeezes the space between the modified starch molecular chains, preventing them from fully stretching and forming a film. Furthermore, the acrylic acid side chains of the modified chitosan cannot be uniformly cross-linked due to saturated binding sites on the nanofiber surface, and calcium carbonate particles also struggle to distribute evenly within the dense network, ultimately leading to localized brittleness of the film layer and reduced flexibility.

[0029] The present invention specifically limits the addition amount of modified starch to 30-40 parts. Within this range, the liquid mulch film can form a complete and appropriately strong film-forming matrix. The appropriate amount of modified starch molecular chains forms a stable three-dimensional network through ether bonds, and its surface carboxyl groups provide hydrophilicity, endowing the film with water-retention properties. Simultaneously, this network structure can effectively encapsulate nanocellulose to form an interpenetrating reinforced structure. Furthermore, the acrylic acid side chains of the modified chitosan can be fully cross-linked within the gaps in the modified starch network, glycerol molecules uniformly penetrate the interchains to provide buffering rigidity, and calcium carbonate particles are stably embedded in the structure, achieving a comprehensive improvement in the film's mechanical properties and water retention.

[0030] When the modified starch addition level is less than 30 parts per million, a continuous film structure cannot be formed. The sparse modified starch molecular chains lack sufficient crosslinking points, making it difficult to load the nanocellulose, resulting in insufficient tensile strength of the film. Furthermore, excessive network porosity renders the water vapor barrier ineffective and reduces water retention. Furthermore, insufficient matrix disperses the crosslinking points of the modified chitosan, resulting in loose interfacial bonding. The plasticizing effect of glycerol, due to the lack of a load-bearing component, overly softens the material, and the uneven dispersion of calcium carbonate compromises the filling effect.

[0031] When the amount of modified starch added exceeds 40 parts, the modified starch molecules become entangled, occupying the dispersion space of nanocellulose, and the nanocellulose easily agglomerates to form stress concentration points. In addition, the high density of modified starch compresses the cross-linking space of modified chitosan, limiting the extension of its flexible branches. At the same time, excessive modified starch will also hinder the uniform penetration of glycerol molecules, resulting in insufficient local plasticization and brittleness in local areas of the film layer. More importantly, the filtered modified starch causes the viscosity of the liquid ground film to increase, causing calcium carbonate precipitation, and ultimately reducing the flexibility of the film layer.

[0032] The present invention specifically limits the addition amount of modified chitosan to 12-15 parts. Within this range, the acrylic acid side chains can establish appropriate crosslinks between the starch network and the nanofiber backbone, ensuring that the modified chitosan side chains fully fill the interfacial gaps. The amino / carboxyl groups strengthen the bond between the modified starch and nanocellulose, improving the toughness of the film while maintaining structural stability. The modified chitosan molecules can also synergistically enhance the barrier properties of the film with calcium carbonate.

[0033] When the modified chitosan addition level is less than 12 parts per million, the cross-linking network exhibits severe defects. Excessive acrylic acid branches cannot effectively bridge the interface between the modified starch and nanocellulose, resulting in uneven stress transfer and localized cracking. Furthermore, the polar groups of the modified chitosan are insufficient to seal the microscopic pores in the film, reducing the water vapor barrier performance. Furthermore, too low a modified chitosan addition level results in sparse cross-linking points, weakening the buffering effect of glycerol and exacerbating the brittle fracture of the film under external forces.

[0034] When the addition level of modified chitosan exceeds 15 parts per million, the excessive acrylic acid branches lead to molecular entanglement. The high density of modified chitosan restricts the movement of molecular segments and hinders glycerol penetration, increasing the rigidity of the film. Furthermore, the dense amino / carboxyl groups adsorb excess water, causing localized swelling and disrupting the dispersion stability of calcium carbonate. Furthermore, excessive cross-linking can disrupt the orientation distribution of nanocellulose, creating internal stress concentration areas that can easily lead to shrinkage and cracking during film formation and drying.

[0035] The present invention specifically limits the addition of glycerol to 4-6 parts per million. Within this range, glycerol molecules can effectively penetrate the interstices between the modified starch-modified chitosan polymer chains, reducing interchain friction and moderately increasing the space for molecular motion, resulting in the film layer possessing excellent flexibility and impact resistance. The presence of glycerol also promotes the uniform dispersion of nanocellulose in the liquid mulch film, reducing the risk of interfiber agglomeration. Furthermore, the polar interaction with the modified chitosan side chains stabilizes the network structure, synergizing with calcium carbonate to inhibit brittle fracture of the film layer, thereby ensuring the structural integrity of the film layer under varying temperature and humidity conditions.

[0036] When the glycerol addition level is less than 4 parts, the mobility of the polymer chains is limited, and the insufficient plasticizing effect leads to dense stacking of the modified starch molecular chains, which increases the rigidity of the film layer and is prone to brittle fracture under external stress or low temperature environments. At the same time, the low addition of glycerol leads to rigid cross-linking points of the modified chitosan, making the interface between the nanocellulose and modified starch more fragile. Stress cannot be effectively transferred between the nanocellulose and modified starch, which in turn induces the propagation of microcracks within the film layer.

[0037] When the amount of glycerol added exceeds 6 parts, the excess glycerol occupies too many molecular spaces, weakening the interaction between the polymer chains, resulting in a loose film structure, a significant decrease in strength, and prone to permanent deformation under mechanical load. Furthermore, high concentrations of glycerol interfere with the hydrogen bonding between modified chitosan molecules, reducing crosslinking efficiency. At the same time, the enrichment of glycerol at the interface reduces the wettability of nanocellulose, and the interfacial bonding strength between nanocellulose and modified starch decreases.

[0038] The present invention specifically limits the addition of calcium carbonate to 8-12 parts per million. Within this range, the calcium carbonate particles are evenly dispersed within the modified starch-modified chitosan network, filling the gaps between polymer chains, significantly increasing the film's density and blocking water vapor penetration. Furthermore, the calcium carbonate particles' surface lubricates the glycerol interface, synergizing with the polar groups of the modified chitosan to maintain the film's flexibility, thereby comprehensively enhancing the film's mechanical strength and environmental stability.

[0039] When the calcium carbonate addition level is less than 8 parts per million, the sparsely distributed calcium carbonate particles cannot fully cover the micropores in the modified starch network, resulting in a decrease in the film's water vapor barrier efficiency. Furthermore, too little calcium carbonate addition prevents the stress borne by the nanocellulose skeleton from being transferred to the calcium carbonate particles, easily forming stress concentration points at the ends of the nanofibers, which in turn causes cracks. Furthermore, the plasticizing effect of glycerol is limited due to the lack of synergistic buffering from the calcium carbonate particles, resulting in a reduced deformation resistance of the film.

[0040] When the addition of calcium carbonate exceeds 12 parts per million, the excess calcium carbonate causes particle agglomeration, and the agglomerates become stress defect points. Furthermore, high calcium carbonate additions can crowd out the interaction space between polymer chains, weakening the cross-linking efficiency of the modified chitosan and the plasticizing effect of glycerol. Furthermore, excessive glycerol adsorption on the surface of calcium carbonate particles can lead to plasticizer depletion in localized areas of the film, causing brittle fracture.

[0041] In some optional examples, the mass fraction of the dry weight of nanocellulose in the nanocellulose solution is 2~3wt%, for example, it can be 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt% or 3.0wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0042] In a second aspect, the present invention provides a method for preparing the bio-based composite liquid ground film according to the first aspect, the preparation method comprising:

[0043] (I) dispersing starch in deionized water, stirring and heating to obtain a starch solution, then adding citric acid to carry out an acidolysis and esterification reaction, spray drying, crushing, and sieving to obtain a modified starch;

[0044] (II) dissolving chitosan in acetic acid solution, then adding acrylic acid monomer and ammonium persulfate solution to carry out grafting reaction, and after the reaction is completed, precipitating, centrifuging, washing and drying to obtain modified chitosan;

[0045] (III) Evenly mixing the nanocellulose solution, the modified starch, the modified chitosan, glycerol and calcium carbonate to obtain the bio-based composite liquid mulch film.

[0046] In the preparation of modified starch, the starch is first pre-dispersed in deionized water and heated for gelatinization, ensuring that the molecular chains are fully stretched to form a homogeneous solution, laying the foundation for subsequent reactions. Subsequently, citric acid is added for acidolysis and esterification. During the acidolysis stage, the hydrogen ions released by the citric acid catalyze the cleavage of the starch glycosidic bonds, moderately reducing the molecular weight and exposing more free hydroxyl groups, optimizing the distribution of starch molecular chain lengths and improving water solubility. The esterification stage is carried out under heating conditions, where the carboxyl groups of the citric acid undergo dehydration condensation with the primary hydroxyl groups of the starch molecules to form a stable ester bond, thereby covalently grafting the citric acid residues onto the starch molecular chains. This introduces the tricarboxyl structure of citric acid into the starch molecular chains. These carboxyl groups significantly enhance the hydrophilicity of the starch while providing active crosslinking sites.

[0047] In the preparation of modified chitosan, polyacrylic acid is first grafted onto the chitosan chain under the action of an initiator. This reaction is based on a free radical graft copolymerization mechanism. Under heating conditions, the initiator (ammonium persulfate) decomposes to produce sulfate radicals, which attack active sites (C6 hydroxyl or C2 amino groups) on the chitosan chain, forming chitosan macromolecular free radicals. Subsequently, acrylic acid monomers come into contact with these active sites and undergo polymerization growth through a chain reaction, forming a branched structure dominated by polyacrylic acid. During the reaction, the double bonds of the acrylic acid monomers are opened by the free radicals, and their carbon atoms form covalent bonds with the carbon / oxygen atoms of the macromolecular free radicals. The length of the polyacrylic acid branches is controlled by the monomer concentration and reaction time. Excessive concentration or prolonged reaction time can lead to excessive branch extension. The molecular structure of the modified chitosan finally obtained is a chitosan main chain grafted with polyacrylic acid side chains. The polyacrylic acid side chains introduce a large number of carboxyl groups into the chitosan, significantly enhancing the hydrophilicity and reactivity of the modified chitosan, so that the material has both the film-forming properties of chitosan and the flexibility and cross-linking ability of polyacrylic acid.

[0048] As a preferred technical solution of the present invention, in step (I), the mass ratio of starch to deionized water is 1:(6-8), for example, it can be 1:6.0, 1:6.2, 1:6.4, 1:6.6, 1:6.8, 1:7.0, 1:7.2, 1:7.4, 1:7.6, 1:7.8 or 1:8.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] In some optional examples, the temperature for stirring and heating the starch and deionized water is 75~85°C, for example, it can be 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C or 85°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0050] In some optional examples, the rotation speed of the stirring and heating of the starch and deionized water is 300~400rpm, for example, it can be 300rpm, 310rpm, 320rpm, 330rpm, 340rpm, 350rpm, 360rpm, 370rpm, 380rpm, 390rpm or 400rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In some optional examples, the stirring and heating time of the starch and deionized water is 40 to 60 minutes, for example, it can be 40 minutes, 42 minutes, 44 minutes, 46 minutes, 48 ​​minutes, 50 minutes, 52 minutes, 54 minutes, 56 minutes, 58 minutes or 60 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] In some optional examples, the mass ratio of starch to citric acid in the starch solution is 1:(0.5~0.6), for example, it can be 1:0.5, 1:0.51, 1:0.52, 1:0.53, 1:0.54, 1:0.55, 1:0.56, 1:0.57, 1:0.58, 1:0.59 or 1:0.6, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0053] The present invention specifically limits the mass ratio of starch to citric acid in the starch solution to 1:(0.5~0.6). During the reaction, citric acid acts as both an esterifying agent and an acidolysis agent. On the one hand, the carboxyl groups on the citric acid react with the hydroxyl groups in the starch molecular chain to form an ether bond connection and introduce a hydrophilic carboxyl group. This not only significantly improves the solubility and dispersion stability of starch in aqueous solution, but also makes it easier to form a continuous and uniform film layer in the subsequent liquid mulch film formation process. On the other hand, citric acid appropriately hydrolyzes some of the glycosidic bonds of starch, achieving chain length optimization without destroying the overall continuity of the molecular chain, ensuring that the modified starch molecular chain has both sufficient fluidity and retains strength properties. This moderately modified starch molecular structure contains an appropriate amount of carboxyl groups, which can establish close intermolecular forces with the amino / hydroxyl groups of modified chitosan and the surface hydroxyl groups of nanocellulose through hydrogen bonds, greatly enhancing the structural integrity and interfacial bonding strength of the composite network. At the same time, the hydrophilicity provided by the carboxyl group can effectively absorb water molecules and enhance the water retention capacity of the film layer. The retained starch skeleton chain segments provide basic tensile strength for the film layer, ultimately achieving a comprehensive improvement in water retention and mechanical strength.

[0054] When the amount of citric acid added is lower than the lower limit of the range defined in the present invention, the degree of acidolysis of starch is insufficient, and it is difficult to effectively catalyze the cleavage of the glycosidic bonds of starch, resulting in a still high molecular weight. The long molecular chains of starch cannot be fully stretched in the water system, and the solubility is poor and the dispersion is uneven. When preparing the liquid ground film, it is easy to form incompletely dissolved starch gel particles, and these particles become structural defects of the film layer. In addition, the degree of esterification of starch is insufficient, resulting in a small number of carboxyl groups introduced into the starch molecular chain, reduced hydrophilicity, and inability to construct an effective hydrophilic network to lock in moisture after film formation, which reduces the water retention performance of the film layer. At the same time, insufficient carboxyl content will also affect the intermolecular attraction between the modified starch and other components, resulting in a decrease in interfacial bonding strength, prone to microcracks under stress, and ultimately causing the film layer to crack.

[0055] When the amount of citric acid added exceeds the upper limit of the range specified in the present invention, the excess citric acid triggers excessive degradation and structural destruction of starch molecules, accelerating the hydrolysis rate of starch glycosidic bonds, resulting in excessive shearing of starch molecular chains into overly short fragments. The resulting modified starch lacks chain segments of sufficient length, making it difficult for the long chains to entangle with each other to withstand external stress, resulting in a decrease in the tensile strength of the film layer. Furthermore, the excess carboxyl groups generated by the esterification reaction significantly increase the hydrophilicity of the film layer, causing the film layer to excessively swell in a moist soil environment, reducing dimensional stability, making the film layer structure loose and porous, and degrading water vapor barrier properties. Furthermore, excessive addition of citric acid causes side reaction products (such as citric acid monoesters or diesters) to accumulate in the liquid mulch film, affecting the compatibility of other components and their effective bonding with nanocellulose, ultimately leading to a decrease in the mechanical properties and barrier function of the film layer, and shortening its service life.

[0056] As a preferred technical solution of the present invention, in step (I), the operation steps of the acidolysis esterification reaction include:

[0057] First, the mixture is heated to an acidolysis temperature for acidolysis reaction, and then the temperature is raised to an esterification temperature for esterification reaction.

[0058] In some optional examples, the acid hydrolysis temperature is 60~70℃, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃ or 70℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0059] In some optional examples, the reaction time of the acidolysis reaction is 30~40min, for example, it can be 30min, 31min, 32min, 33min, 34min, 35min, 36min, 37min, 38min, 39min or 40min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] In some optional embodiments, the esterification temperature is 100-110°C, for example, it can be 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] In some optional examples, the reaction time of the esterification reaction 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] In some optional embodiments, the inlet temperature of the spray drying is 110-120°C, for example, it can be 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0063] In some optional embodiments, the outlet temperature of the spray drying is 70~80℃, for example, it can be 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0064] In some optional embodiments, the mesh number of the sieve is 100-150 mesh, for example, it can be 100 mesh, 105 mesh, 110 mesh, 115 mesh, 120 mesh, 125 mesh, 130 mesh, 135 mesh, 140 mesh, 145 mesh or 150 mesh, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] As a preferred technical solution of the present invention, in step (II), chitosan is dissolved in acetic acid solution under stirring and heating conditions, and the mixture is mixed uniformly to obtain a chitosan solution.

[0066] In some optional embodiments, the heating temperature when the chitosan and acetic acid solution are mixed is 40-50°C, for example, it can be 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 numerical range are also applicable.

[0067] In some optional embodiments, the stirring speed when the chitosan and acetic acid solution are mixed is 200~300rpm, for example, it can be 200rpm, 210rpm, 220rpm, 230rpm, 240rpm, 250rpm, 260rpm, 270rpm, 280rpm, 290rpm or 300rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] In some optional examples, the mass fraction of the acetic acid 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0069] In some optional embodiments, the mixing stirring time of the chitosan and acetic acid solution 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0070] In some optional examples, the mass fraction of chitosan in the chitosan solution is 2~3wt%, for example, it can be 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt% or 3.0wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0071] In some optional embodiments, before the grafting reaction begins, an alkali solution is added dropwise to the chitosan solution to adjust its pH value to 4-5, for example, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0072] As a preferred technical solution of the present invention, in step (II), the mass fraction of ammonium persulfate in the ammonium persulfate solution is 1-2 wt%, for example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0073] In some optional examples, the mass ratio of chitosan to the acrylic acid monomer in the chitosan solution is 1:(0.4~0.5), for example, it can be 1:0.4, 1:0.41, 1:0.42, 1:0.43, 1:0.44, 1:0.45, 1:0.46, 1:0.47, 1:0.48, 1:0.49 or 1:0.5, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0074] The present invention specifically limits the mass ratio of chitosan to acrylic acid monomer in the chitosan solution to 1: (0.4~0.5). Within this range, acrylic acid monomer forms a branched structure of moderate length and uniform distribution on the main chain of the chitosan molecule through grafting reaction, which not only effectively retains the strength of the chitosan skeleton itself, but also introduces an appropriate amount of flexible carboxyl groups. These newly generated carboxyl groups can form a dense hydrogen bond network with the ether bonds and hydroxyl groups on the modified starch molecular chains in the system, significantly strengthening the bonding strength of the two-phase interface, while providing an anchor point for the polar groups on the surface of nanocellulose, ensuring the stress transmission of the entire composite network. The polyacrylic acid side chains grafted on the chitosan molecular chains are like flexible bridges, interspersed between the modified starch network and the nanocellulose skeleton, bridging the gap between the rigid materials and reducing stress concentration. The appropriate amount of hydrophilic carboxyl groups introduced synergistically enhances the water retention capacity of the membrane layer, which neither absorbs water excessively nor expands, and can form a stable water molecule adsorption layer, taking into account impact toughness while maintaining mechanical strength.

[0075] When the amount of acrylic acid monomer added is lower than the lower limit of the range defined in the present invention, the insufficient amount of acrylic acid monomer results in a low degree of chitosan modification. The length of the polyacrylic acid side chains grafted on the chitosan molecular chain is too short and the grafting density is too sparse, which cannot provide sufficient flexibility and cross-linking active sites. The rigid skeleton of chitosan itself has not been fully softened, and the mobility of the molecular chain is limited, resulting in the entire film layer being brittle and easily cracked and rapidly expanded under external force. In addition, insufficient grafting amount can also cause the carboxyl content to be too low, which seriously hinders the effective combination between modified chitosan and components such as modified starch and nanocellulose.

[0076] When the amount of acrylic acid monomer added exceeds the upper limit of the range specified in this invention, the excess acrylic acid monomer participates in the reaction, resulting in excessively long polyacrylic acid side chains and an excessively high graft density. This results in the chitosan backbone being tightly wrapped and even cross-linked by numerous polyacrylic acid side chains, severely restricting the movement of the chitosan macromolecular segments and, in turn, increasing the rigidity of the modified chitosan chain. Furthermore, the excessive hydrophilicity imparted by the high grafted carboxyl content causes the film to swell and deform in high-humidity environments, destroying the original dense microporous structure and significantly reducing gas barrier efficiency.

[0077] In some optional examples, the mass ratio of the acrylic acid monomer to the ammonium persulfate in the ammonium persulfate solution is 1:(0.05-0.08), for example, 1:0.05, 1:0.055, 1:0.06, 1:0.065, 1:0.07, 1:0.075 or 1:0.08, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0078] In some optional examples, the grafting reaction is performed under a nitrogen atmosphere.

[0079] In some optional examples, the stirring speed of the grafting reaction is 250~350rpm, for example, it can be 250rpm, 260rpm, 270rpm, 280rpm, 290rpm, 300rpm, 310rpm, 320rpm, 330rpm, 340rpm or 350rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] In some optional embodiments, the heating temperature of the grafting reaction is 60~70℃, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable.

[0081] In some optional examples, the reaction time of the grafting reaction is 3 to 4 hours, for example, it can be 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, and other unlisted values ​​within the numerical range are also applicable.

[0082] As a preferred technical solution of the present invention, in step (II), the precipitation operation steps include:

[0083] Ethanol was added to the reaction product solution obtained by the reaction and stirred, and then allowed to stand for stratification to precipitate white flocs.

[0084] In some optional examples, the volume ratio of the reaction product solution to ethanol is 1:(5~6), for example, it can be 1:5.0, 1:5.1, 1:5.2, 1:5.3, 1:5.4, 1:5.5, 1:5.6, 1:5.7, 1:5.8, 1:5.9 or 1:6.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0085] In some optional examples, the standing stratification time 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0086] In some optional examples, the centrifugal speed is 3000~4000rpm, for example, it can be 3000rpm, 3100rpm, 3200rpm, 3300rpm, 3400rpm, 3500rpm, 3600rpm, 3700rpm, 3800rpm, 3900rpm or 4000rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0087] In some optional embodiments, the centrifugation time is 10 to 20 minutes, for example, it can be 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0088] In some optional embodiments, the drying temperature is 40~50℃, for example, it can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃ or 50℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0089] In some optional embodiments, the drying time is 10 to 12 hours, for example, it can be 10 hours, 10.2 hours, 10.4 hours, 10.6 hours, 10.8 hours, 11 hours, 11.2 hours, 11.4 hours, 11.6 hours, 11.8 hours or 12 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0090] As a preferred technical solution of the present invention, in step (III), the bio-based composite liquid mulch film is prepared by the following method:

[0091] Under stirring conditions, the modified starch, the modified chitosan, the glycerol and the calcium carbonate are added to the nanocellulose solution in sequence. After each component is added, the obtained mixed solution is stirred for 10 to 20 minutes, and then the next component is added. For example, it can be 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0092] In the process of preparing bio-based composite liquid mulch, first, modified starch is added to the nanocellulose solution. The modified starch molecular chains are used to gradually stretch and penetrate the nanofiber network in the nanocellulose solution to form an interpenetrating network structure. In this process, the carboxyl groups of the modified starch are bonded to the hydroxyl groups of the nanocellulose, strengthening the strength of the interpenetrating network structure. Subsequently, modified chitosan is added. Its amino / carboxyl active sites can be directionally cross-linked with the formed modified starch-nanocellulose interpenetrating network. The branched structure of the modified chitosan accurately fills the gaps and improves toughness. Glycerol is then added to avoid premature addition, which may cause glycerol to wrap the polymer chains and weaken the combination of modified starch and modified chitosan. At the same time, plasticization buffer space is reserved for the formed network structure. Calcium carbonate is added last because the calcium carbonate particles need to be evenly embedded in a stable organic matrix. Premature addition will hinder the molecular interaction between other components and cause sedimentation.

[0093] As a preferred technical solution of the present invention, in step (III), the stirring speed during the preparation process is 500-600 rpm, for example, it can be 500 rpm, 510 rpm, 520 rpm, 530 rpm, 540 rpm, 550 rpm, 560 rpm, 570 rpm, 580 rpm, 590 rpm or 600 rpm, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0094] In some optional examples, after uniform mixing, the obtained mixed solution is subjected to vacuum degassing to obtain the bio-based composite liquid ground film.

[0095] Compared with the prior art, the present invention has the following beneficial effects:

[0096] The bio-based composite liquid mulch provided by the present invention integrates multiple bio-based components, utilizing the natural properties of bio-based materials to form a uniform, degradable film layer, effectively addressing the environmental pollution issues of traditional plastic mulch films. Nanocellulose serves as the structural framework, modified starch and modified chitosan serve as the primary film-forming matrix, and glycerol and calcium carbonate serve as functional additives. These synergistically enhance the barrier, water-retention, and mechanical properties of the film layer, enabling the liquid mulch film to better isolate air and water vapor loss, improve soil moisture retention, and ensure sufficient strength and flexibility during use, avoiding problems such as premature cracking or deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 A flow chart of the preparation process of the bio-based composite liquid mulch provided in Examples 1-15 of the present invention;

[0098] Figure 2 IR spectra of starch and modified starch prepared in Example 1 of the present invention;

[0099] Figure 3 1 is an infrared spectrum of chitosan and the modified chitosan prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0100] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0101] Example 1

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

[0103] (1) Dispersing starch in deionized water at a mass ratio of starch to deionized water of 1:6, stirring and heating at a heating temperature of 75°C and a stirring speed of 300 rpm for 60 min to obtain a starch solution;

[0104] Add citric acid to the starch solution, with a mass ratio of starch to citric acid of 1:0.5, heat to 60°C under stirring for acidolysis reaction, react for 40 minutes, then heat to 100°C for esterification reaction, react for 3 hours, send the reaction product to a spray drying tower for spray drying, the inlet temperature of the spray drying tower is 110°C, and the outlet temperature is 70°C, and finally grind and pass through a 100-mesh sieve to obtain modified starch;

[0105] (2) Chitosan was dissolved in 1 wt% acetic acid solution at a stirring speed of 200 rpm and a heating temperature of 40°C. The mixture was mixed and stirred for 3 h to obtain a chitosan solution. The chitosan solution had a chitosan mass fraction of 2 wt%.

[0106] A sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH to 4, and an acrylic acid monomer and a 1 wt% ammonium persulfate solution were added to the chitosan solution. The mass ratio of chitosan to acrylic acid monomer in the chitosan solution was 1:0.4, and the mass ratio of acrylic acid monomer to ammonium persulfate was 1:0.05. The grafting reaction was carried out under a nitrogen atmosphere. The stirring speed of the grafting reaction was 250 rpm, the heating temperature was 60° C., and the reaction time was 4 h.

[0107] After the reaction, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5, and then allowed to stand for 2 hours to separate into layers. White flocs were precipitated and centrifuged at 3000 rpm for 20 minutes. The precipitate was washed and dried at 40°C for 12 hours to obtain modified chitosan.

[0108] (3) At a stirring speed of 700 rpm and room temperature, 30 parts of the modified starch obtained in step (I), 14 parts of the modified chitosan obtained in step (2), 4 parts of glycerol and 12 parts of calcium carbonate were added to 40 parts of nanocellulose solution (the mass fraction of the dry weight of nanocellulose in the nanocellulose solution was 2 wt%) in sequence. After each component was added, the obtained mixed solution was stirred for 20 minutes, and then the next component was added. After all the components were mixed evenly, the obtained mixed solution was vacuum degassed to obtain the bio-based composite liquid mulch.

[0109] Figure 2 The infrared spectra of starch and the modified starch prepared in this example are shown in the figure. As can be seen from the figure, in the infrared curve of starch, 3200~3500cm -1 The absorption peak at 2900~2930cm is attributed to the stretching vibration of OH. -1 The absorption peak at is attributed to the stretching vibration of the fatty chain CH (-CH- on the glucose ring and ), 1400~1450cm-1 The absorption peak at 1150 cm is attributed to the bending vibration of CH. -1 The absorption peak at 1080 cm is attributed to the antisymmetric stretching vibration of the sugar ring COC. -1 and 1022cm -1 The absorption peak at 1720~1750cm is attributed to the coupling of the stretching vibration of CO and CC. -1 The absorption peak at 1210~1250cm is attributed to the stretching vibration of the ester group C=O. -1 The absorption peak at 1550~1610cm is attributed to the stretching vibration of ester bond CO. -1 The absorption peak at is attributed to the carboxylate ion ( ) asymmetric stretching vibration, 1400 cm -1 The absorption peak at is attributed to the carboxylate group ( This indicates that citric acid successfully introduced carboxyl groups (-COOH) and ester bonds (-COOR) into the starch molecular chain through esterification reaction.

[0110] Figure 3 The infrared spectra of chitosan and the modified chitosan prepared in this example are shown in the figure. As can be seen from the figure, in the infrared curve of chitosan, 3420cm -1 The absorption peak at 2870~2900cm is attributed to the superposition of the stretching vibration of OH and NH. -1 The absorption peak at is attributed to the stretching vibration of aliphatic CH (on the glucosamine ring of chitosan) and -CH3). 1650~1660cm -1 The absorption peak at 1590 cm is attributed to the amide I band (C=O stretching vibration). -1 The absorption peak at 1420 cm is attributed to the bending vibration of NH. -1 The absorption peak at 1150cm is attributed to the bending vibration of CH and the in-plane bending of OH. -1 The absorption peak at 1700~1725cm is attributed to the asymmetric stretching vibration of COC. -1 The absorption peak at 1550cm is attributed to the C=O stretching vibration of carboxylic acid. -1 The absorption peak at is attributed to the carboxylate ion ( This indicates that the acrylic acid side chains were successfully grafted onto the chitosan molecular chain.

[0111] Example 2

[0112] This embodiment provides a method for preparing a bio-based composite liquid ground film, such as Figure 1As shown, the preparation method specifically includes the following steps:

[0113] (1) Dispersing starch in deionized water at a mass ratio of starch to deionized water of 1:6.5, stirring and heating at a heating temperature of 78°C and a stirring speed of 320 rpm for 55 min to obtain a starch solution;

[0114] Add citric acid to the starch solution, with a mass ratio of starch to citric acid of 1:0.52, heat to 62°C under stirring for acidolysis reaction, react for 38 minutes, heat to 102°C for esterification reaction, react for 2.8 hours, send the reaction product to a spray drying tower for spray drying, the inlet temperature of the spray drying tower is 112°C, and the outlet temperature is 72°C, and finally grind and pass through a 120-mesh sieve to obtain modified starch;

[0115] (2) Chitosan was dissolved in an acetic acid solution with a mass fraction of 1.2 wt% at a stirring speed of 220 rpm and a heating temperature of 42°C. The mixture was mixed and stirred for 2.8 h to obtain a chitosan solution. The mass fraction of chitosan in the chitosan solution was 2.2 wt%;

[0116] A sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH to 4.2, and an acrylic acid monomer and a 1.2 wt% ammonium persulfate solution were added to the chitosan solution. The mass ratio of chitosan to acrylic acid monomer in the chitosan solution was 1:0.42, and the mass ratio of acrylic acid monomer to ammonium persulfate was 1:0.06. The grafting reaction was carried out under a nitrogen atmosphere. The stirring speed of the grafting reaction was 280 rpm, the heating temperature was 62° C., and the reaction time was 3.8 h.

[0117] After the reaction, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5.2, and then allowed to stand for 2.2 hours to separate out white flocs. The mixture was centrifuged at 3200 rpm for 18 minutes, and the precipitate was washed and dried at 42°C for 11.5 hours to obtain modified chitosan.

[0118] (3) At a stirring speed of 720 rpm and room temperature, 34 parts of the modified starch obtained in step (I), 14 parts of the modified chitosan obtained in step (2), 6 parts of glycerol and 8 parts of calcium carbonate were added to 38 parts of nanocellulose solution (the mass fraction of the dry weight of nanocellulose in the nanocellulose solution was 2.2 wt%) in sequence. After each component was added, the obtained mixed solution was stirred for 18 minutes, and then the next component was added. After all the components were mixed evenly, the obtained mixed solution was vacuum degassed to obtain the bio-based composite liquid mulch.

[0119] Example 3

[0120] This embodiment provides a method for preparing a bio-based composite liquid ground film, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0121] (1) Dispersing starch in deionized water at a mass ratio of starch to deionized water of 1:7, stirring and heating at a heating temperature of 80°C and a stirring speed of 350 rpm for 50 min to obtain a starch solution;

[0122] Add citric acid to the starch solution, with a mass ratio of starch to citric acid of 1:0.55, heat to 65°C under stirring for acidolysis reaction, react for 35 minutes, heat to 105°C for esterification reaction, react for 2.5 hours, send the reaction product to a spray drying tower for spray drying, the inlet temperature of the spray drying tower is 115°C, and the outlet temperature is 75°C, and finally grind and pass through a 130-mesh sieve to obtain modified starch;

[0123] (2) Chitosan was dissolved in an acetic acid solution with a mass fraction of 1.5 wt% at a stirring speed of 250 rpm and a heating temperature of 45°C. The mixture was mixed and stirred for 2.5 h to obtain a chitosan solution. The mass fraction of chitosan in the chitosan solution was 2.5 wt%;

[0124] A sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH to 4.5, and an acrylic acid monomer and a 1.5 wt% ammonium persulfate solution were added to the chitosan solution. The mass ratio of chitosan to acrylic acid monomer in the chitosan solution was 1:0.45, and the mass ratio of acrylic acid monomer to ammonium persulfate was 1:0.06. The grafting reaction was carried out under a nitrogen atmosphere. The stirring speed of the grafting reaction was 300 rpm, the heating temperature was 65° C., and the reaction time was 3.5 h.

[0125] After the reaction, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5.5, and then allowed to stand for 2.5 hours to separate out white flocs. The mixture was centrifuged at 3500 rpm for 15 minutes, and the precipitate was washed and dried at 45°C for 11 hours to obtain modified chitosan.

[0126] (3) At a stirring speed of 750 rpm and room temperature, 36 parts of the modified starch obtained in step (I), 13 parts of the modified chitosan obtained in step (2), 6 parts of glycerol and 10 parts of calcium carbonate were added to 35 parts of nanocellulose solution (the mass fraction of the dry weight of nanocellulose in the nanocellulose solution was 2.5 wt%) in sequence. After each component was added, the obtained mixed solution was stirred for 15 minutes, and then the next component was added. After all the components were mixed evenly, the obtained mixed solution was vacuum degassed to obtain the bio-based composite liquid mulch.

[0127] Example 4

[0128] This embodiment provides a method for preparing a bio-based composite liquid ground film, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0129] (1) Dispersing starch in deionized water at a mass ratio of starch to deionized water of 1:7.5, stirring and heating at a heating temperature of 82°C and a stirring speed of 380 rpm for 45 min to obtain a starch solution;

[0130] Citric acid was added to the starch solution, with a mass ratio of starch to citric acid of 1:0.58. The solution was heated to 68°C for acidolysis under stirring, and then heated to 108°C for esterification after 32 minutes of reaction. After 2.2 hours of reaction, the reaction product was sent to a spray drying tower for spray drying. The inlet temperature of the spray drying tower was 118°C, and the outlet temperature was 78°C. The modified starch was finally crushed and passed through a 140-mesh sieve to obtain the modified starch.

[0131] (2) Chitosan was dissolved in an acetic acid solution with a mass fraction of 1.8 wt% at a stirring speed of 280 rpm and a heating temperature of 48°C. The mixture was mixed and stirred for 2.2 h to obtain a chitosan solution. The mass fraction of chitosan in the chitosan solution was 2.8 wt%;

[0132] A sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH to 4.8, and an acrylic acid monomer and a 1.8 wt % ammonium persulfate solution were added to the chitosan solution. The mass ratio of chitosan to acrylic acid monomer in the chitosan solution was 1:0.48, and the mass ratio of acrylic acid monomer to ammonium persulfate was 1:0.07. The grafting reaction was carried out under a nitrogen atmosphere. The stirring speed of the grafting reaction was 320 rpm, the heating temperature was 68° C., and the reaction time was 3.2 h.

[0133] After the reaction, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5.8, and then allowed to stand for 2.8 hours to separate out white flocs. The mixture was centrifuged at 3800 rpm for 12 minutes, and the precipitate was washed and dried at 48°C for 10.5 hours to obtain modified chitosan.

[0134] (3) At a stirring speed of 780 rpm and room temperature, 38 parts of the modified starch obtained in step (I), 12 parts of the modified chitosan obtained in step (2), 5 parts of glycerol and 11 parts of calcium carbonate were added in sequence to 34 parts of nanocellulose solution (the mass fraction of the dry weight of nanocellulose in the nanocellulose solution was 2.8 wt%). After each component was added, the obtained mixed solution was stirred for 12 minutes, and then the next component was added. After all the components were mixed evenly, the obtained mixed solution was vacuum degassed to obtain the bio-based composite liquid mulch.

[0135] Example 5

[0136] This embodiment provides a method for preparing a bio-based composite liquid ground film, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0137] (1) Dispersing starch in deionized water at a mass ratio of starch to deionized water of 1:8, stirring and heating at a heating temperature of 85°C and a stirring speed of 400 rpm for 40 min to obtain a starch solution;

[0138] Add citric acid to the starch solution, with a mass ratio of starch to citric acid of 1:0.6, heat to 70°C under stirring for acidolysis reaction, react for 30 minutes, heat to 110°C for esterification reaction, react for 2 hours, send the reaction product to a spray drying tower for spray drying, the inlet temperature of the spray drying tower is 120°C, and the outlet temperature is 80°C, and finally grind and pass through a 150-mesh sieve to obtain modified starch;

[0139] (2) Chitosan was dissolved in acetic acid solution with a mass fraction of 2 wt% at a stirring speed of 300 rpm and a heating temperature of 50°C. The mixture was mixed and stirred for 2 h to obtain a chitosan solution. The mass fraction of chitosan in the chitosan solution was 3 wt%;

[0140] A sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH to 5, and an acrylic acid monomer and a 2 wt% ammonium persulfate solution were added to the chitosan solution. The mass ratio of chitosan to acrylic acid monomer in the chitosan solution was 1:0.5, and the mass ratio of acrylic acid monomer to ammonium persulfate was 1:0.08. The grafting reaction was carried out under a nitrogen atmosphere. The stirring speed of the grafting reaction was 350 rpm, the heating temperature was 70° C., and the reaction time was 3 h.

[0141] After the reaction, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:6, and then allowed to stand for 3 hours to separate into layers, and white flocs were precipitated. The mixture was centrifuged at 4000 rpm for 10 minutes, and the precipitate was washed and dried at 50°C for 10 hours to obtain modified chitosan.

[0142] (3) At a stirring speed of 800 rpm and room temperature, 40 parts of the modified starch obtained in step (I), 15 parts of the modified chitosan obtained in step (2), 6 parts of glycerol and 9 parts of calcium carbonate were added to 30 parts of the nanocellulose solution (the mass fraction of the dry weight of the nanocellulose in the nanocellulose solution is 3 wt%) in sequence. After each component was added, the obtained mixed solution was stirred for 10 minutes, and then the next component was added. After all the components were mixed evenly, the obtained mixed solution was vacuum degassed to obtain the bio-based composite liquid mulch.

[0143] Example 6

[0144] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that the weight of the nanocellulose solution is adjusted to 25 parts, and the addition amount of other components is increased proportionally to ensure that the weight ratios of the other components, except for the nanocellulose solution, remain unchanged. The weight ratios of the adjusted components are as follows:

[0145] 25 parts of nanocellulose solution;

[0146] 37.50 parts of modified starch;

[0147] 17.50 parts of modified chitosan;

[0148] 5 parts of glycerin;

[0149] 15 parts of calcium carbonate.

[0150] Other operating steps and process parameters are exactly the same as those in Example 1.

[0151] Example 7

[0152] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that the weight of the nanocellulose solution is adjusted to 45 parts, and the addition amount of other components is reduced in proportion to ensure that the weight ratios of the other components, except for the nanocellulose solution, remain unchanged. The weight ratios of the adjusted components are as follows:

[0153] 45 parts of nanocellulose solution;

[0154] 27.50 parts of modified starch;

[0155] 12.83 parts of modified chitosan;

[0156] 3.67 parts of glycerol;

[0157] 11 parts of calcium carbonate.

[0158] Other operating steps and process parameters are exactly the same as those in Example 1.

[0159] Example 8

[0160] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that the weight of the modified starch is adjusted to 25 parts, and the addition amounts of other components are increased proportionally to ensure that the weight ratios of the other components, except for the nanocellulose solution, remain unchanged. The weight ratios of the adjusted components are as follows:

[0161] 42.85 parts of nanocellulose solution;

[0162] 25 parts of modified starch;

[0163] 15 parts of modified chitosan;

[0164] 4.30 parts of glycerin;

[0165] 12.85 parts of calcium carbonate.

[0166] Other operating steps and process parameters are exactly the same as those in Example 1.

[0167] Example 9

[0168] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that the weight of the modified starch is adjusted to 45 parts, and the addition amounts of other components are reduced in proportion to ensure that the weight ratios of the other components, except for the nanocellulose solution, remain unchanged. The weight ratios of the components after adjustment are as follows:

[0169] 31.43 parts of nanocellulose solution;

[0170] 45 parts of modified starch;

[0171] 11 parts of modified chitosan;

[0172] 3.14 parts of glycerol;

[0173] 9.43 parts of calcium carbonate.

[0174] Other operating steps and process parameters are exactly the same as those in Example 1.

[0175] Example 10

[0176] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that the weight of the modified chitosan is adjusted to 8 parts, and the addition amounts of other components are increased proportionally to ensure that the weight ratios of the other components, except for the nanocellulose solution, remain unchanged. The weight ratios of the components after adjustment are as follows:

[0177] 42.79 parts of nanocellulose solution;

[0178] 32.09 parts of modified starch;

[0179] 8 parts of modified chitosan;

[0180] 4.28 parts of glycerol;

[0181] 12.84 parts of calcium carbonate.

[0182] Other operating steps and process parameters are exactly the same as those in Example 1.

[0183] Example 11

[0184] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that the weight of the modified chitosan is adjusted to 20 parts, and the addition amounts of other components are reduced in proportion to ensure that the weight ratios of the other components, except for the nanocellulose solution, remain unchanged. The weight ratios of the components after adjustment are as follows:

[0185] 37.21 parts of nanocellulose solution;

[0186] 27.91 parts of modified starch;

[0187] 20 parts of modified chitosan;

[0188] 3.72 parts of glycerol;

[0189] 11.16 parts of calcium carbonate.

[0190] Other operating steps and process parameters are exactly the same as those in Example 1.

[0191] Example 12

[0192] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that in step (1), the mass ratio of starch to citric acid in the starch solution is adjusted to 1:0.3, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0193] Example 13

[0194] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that in step (1), the mass ratio of starch to citric acid in the starch solution is adjusted to 1:0.8, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0195] Example 14

[0196] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that in step (2), the mass ratio of chitosan to acrylic acid monomer in the chitosan solution is adjusted to 1:0.2, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0197] Example 15

[0198] This comparative example provides a method for preparing a bio-based composite liquid mulch film, which differs from Example 1 in that, in step (2), the mass ratio of chitosan to acrylic acid monomer in the chitosan solution is adjusted to 1:0.8, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0199] Comparative Example 1

[0200] This comparative example provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that step (1) is omitted, the starch is not subjected to citric acid modification treatment, and the modified starch is replaced with an equal amount of unmodified starch in the bio-based composite liquid mulch film. The other operating steps and process parameters are exactly the same as those in Example 1.

[0201] Comparative Example 2

[0202] This comparative example provides a method for preparing a bio-based composite liquid mulch film. The difference from Example 1 is that step (2) is omitted, chitosan is not subjected to acrylic acid grafting modification treatment, and in the bio-based composite liquid mulch film, the modified chitosan is replaced by an equal amount of unmodified chitosan. The other operating steps and process parameters are exactly the same as those in Example 1.

[0203] The barrier properties, water retention properties, and mechanical properties of the bio-based composite liquid mulch films prepared in Examples 1-15 and Comparative Examples 1-2 were tested. The specific testing steps are as follows:

[0204] (1) Water vapor transmission rate

[0205] The liquid mulch prepared in the Examples and Comparative Examples was evenly coated on a non-porous plate. After drying, a 0.1 mm thick film was formed. The film was completely removed from the non-porous plate and sealed in a permeable cup containing a desiccant (anhydrous calcium chloride). The humidity inside the cup was maintained at ≈0% RH. The permeable cup was placed in a constant temperature and humidity chamber (temperature 25±0.5°C, relative humidity 50±2% RH). The film was weighed regularly (e.g., every 24 hours) and the water vapor transmission rate (WVTR) was calculated as:

[0206]

[0207] Wherein, Δw is the weight gain (g), A is the film area (m 2 ), t is time (days).

[0208] (2) Tensile strength and elongation at break

[0209] The liquid mulch prepared in the examples and comparative examples was evenly coated on a non-porous flat plate to form a film with a thickness of 0.1 mm after drying. The film was completely peeled off from the non-porous flat plate and cut into standard dumbbell-shaped specimens (length ≥ 100 mm, width 10 ± 0.2 mm).

[0210] Use a universal material testing machine with a clamp spacing of 50 mm and a tensile speed of 10 mm / min. Record the maximum tensile force (F) when the sample breaks. max ) and gauge length elongation (ΔL), and calculate the tensile strength (MPa) and elongation at break (%).

[0211] (3) Cumulative water loss rate over 14 days

[0212] Prepare standard sandy loam soil (initial moisture content 20% ± 1%), and spray the liquid mulch prepared in the examples and comparative examples evenly on the soil surface at a spraying rate of 50 g / m 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 the first day (w0) was measured. The soil weight on the 14th day after the test was continued for 14 days (w n ), calculate the soil weight loss, and calculate the cumulative water loss rate over 14 days using the following formula:

[0213] 14-day cumulative water loss rate (%) = [(w0-w n ) / w0]×100%.

[0214] The test results are shown in Table 1.

[0215] Table 1

[0216]

[0217] The test data from Examples 1, 6, and 7 show that when the nanocellulose dosage is reduced to 25 parts per million (Example 6), the insufficient three-dimensional network density leads to structural defects. The sparse fibers are unable to effectively bear stress, resulting in increased microscopic pores in the membrane layer and increased water vapor transmission rate and water loss rate. When the nanocellulose dosage is increased to 45 parts per million (Example 7), fiber entanglement occurs, and the dense network squeezes the molecular chains of other components, hindering glycerol penetration and calcium carbonate dispersion. This reduces tensile strength, increases membrane rigidity, and decreases flexibility.

[0218] The test data from Examples 1, 8, and 9 show that when the modified starch dosage is reduced to 25 parts (Example 8), the continuous film-forming matrix is ​​disrupted, the molecular crosslinking points become sparse, and the interfacial bonding becomes loose, resulting in decreased tensile strength and barrier properties. When the modified starch dosage is increased to 45 parts (Example 9), molecular entanglement occurs, crowding out the nanocellulose dispersion space. The calcium carbonate particles settle, forming stress concentration points and increasing water loss. Furthermore, excessive hydrophilicity exacerbates film swelling, resulting in a decrease in the film's elongation at break.

[0219] The test data from Examples 1, 10, and 11 show that when the amount of modified chitosan is reduced to 8 parts (Example 10), the cross-linking network is severely defective. The sparse acrylic acid branches are unable to bridge the interface between the modified starch and nanocellulose, resulting in uneven stress transfer and microcracks, leading to increased water loss in the film. When the amount of modified chitosan is increased to 20 parts (Example 11), the branches become entangled, and the amino / carboxyl groups absorb excessive water, causing swelling and deformation. This reduces the barrier properties of the film and increases its rigidity.

[0220] The test data from Examples 1, 12, and 13 show that when the amount of citric acid added is too low (Example 12), the degree of starch esterification is insufficient, the low number of carboxyl groups leads to decreased hydrophilicity, weakened hydrogen bonding, and significantly reduced tensile strength and barrier properties. When the amount of citric acid added is too high (Example 13), the starch is excessively degraded, making it difficult for short chain fragments to entangle and withstand stress, resulting in reduced tensile strength. Excessive carboxyl groups exacerbate film swelling and increase water loss.

[0221] The test data from Examples 1, 14, and 15 show that when the amount of acrylic acid monomer added is too low (Example 14), chitosan is insufficiently softened, the rigid skeleton is not effectively modified, and brittleness increases, resulting in a decrease in the elongation at break of the film. When the amount of acrylic acid monomer added is too high (Example 15), the polyacrylic acid side chains become too long and entangled, restricting molecular chain motion and causing excessive hydrophilicity, resulting in reduced barrier properties and mechanical strength.

[0222] It can be seen from the test data of Example 1 and Comparative Example 1 that the unmodified starch (Comparative Example 1) cannot form a hydrogen bond network with nanocellulose due to the lack of carboxyl groups. The weak interfacial bonding force causes microcracks, resulting in a decrease in the barrier properties, mechanical properties and water retention properties of the film layer.

[0223] It can be seen from the test data of Example 1 and Comparative Example 2 that the rigid molecular chains of the unmodified chitosan (Comparative Example 2) are difficult to interpenetrate between other components, the stress concentration effect significantly reduces the elongation at break, and the insufficient protonation of the amino group further weakens the electrostatic adsorption, which seriously affects the barrier properties.

[0224] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A bio-based composite liquid ground film, characterized in that: The bio-based composite liquid mulch film comprises nanocellulose solution, modified starch, modified chitosan, glycerol and calcium carbonate; The modified starch is obtained by modifying starch with citric acid; The modified chitosan is obtained by graft copolymerization of chitosan with acrylic acid monomers.

2. The bio-based composite liquid ground film according to claim 1, characterized in that: Based on 100 parts by weight of the bio-based composite liquid ground film, it includes the following components in parts by weight: 30-40 parts of nanocellulose solution; 30-40 parts of modified starch; 12-15 parts of modified chitosan; 4-6 parts of glycerin; 8-12 parts calcium carbonate; The mass fraction of the dry weight of the nanocellulose in the nanocellulose solution is 2-3 wt %.

3. A method for preparing the bio-based composite liquid ground film according to claim 1 or 2, characterized in that: The preparation method comprises: (I) dispersing starch in deionized water, stirring and heating to obtain a starch solution, then adding citric acid to carry out an acidolysis and esterification reaction, spray drying, crushing, and sieving to obtain a modified starch; (II) dissolving chitosan in acetic acid solution, then adding acrylic acid monomer and ammonium persulfate solution to carry out grafting reaction, and after the reaction is completed, precipitating, centrifuging, washing and drying to obtain modified chitosan; (III) Evenly mixing the nanocellulose solution, the modified starch, the modified chitosan, glycerol and calcium carbonate to obtain the bio-based composite liquid mulch film.

4. The preparation method according to claim 3, characterized in that In step (I), the mass ratio of starch to deionized water is 1:(6-8); The temperature of the starch and deionized water during stirring and heating is 75-85°C; The stirring and heating speed of the starch and deionized water is 300-400 rpm; The stirring and heating time of the starch and deionized water is 40 to 60 minutes; The mass ratio of starch to citric acid in the starch solution is 1:(0.5~0.6).

5. The preparation method according to claim 3, characterized in that In step (I), the acidolysis esterification reaction comprises the following steps: First, heat to the acidolysis temperature to carry out the acidolysis reaction, and then heat to the esterification temperature to carry out the esterification reaction; The acid hydrolysis temperature is 60-70°C; The reaction time of the acid hydrolysis reaction is 30 to 40 minutes; The esterification temperature is 100-110°C; The reaction time of the esterification reaction is 2 to 3 hours; The inlet temperature of the spray drying is 110-120°C; The outlet temperature of the spray drying is 70-80°C; The mesh number of the sieve is 100-150 meshes.

6. The preparation method according to claim 3, characterized in that In step (II), chitosan is dissolved in acetic acid solution under stirring and heating conditions, and the mixture is mixed to obtain a chitosan solution; The heating temperature when the chitosan and acetic acid solution are mixed is 40-50°C; The stirring speed when the chitosan and acetic acid solution are mixed is 200-300 rpm; The mass fraction of the acetic acid solution is 1-2 wt %; The mixing time of the chitosan and acetic acid solution is 2 to 3 hours; The mass fraction of chitosan in the chitosan solution is 2-3 wt %; Before the grafting reaction begins, an alkali solution is added dropwise to the chitosan solution to adjust the pH value thereof to 4-5.

7. The preparation method according to claim 6, characterized in that In step (II), the mass fraction of ammonium persulfate in the ammonium persulfate solution is 1-2 wt %; The mass ratio of chitosan in the chitosan solution to the acrylic acid monomer is 1:(0.4-0.5); The mass ratio of the acrylic acid monomer to the ammonium persulfate in the ammonium persulfate solution is 1:(0.05-0.08); The grafting reaction is carried out under a nitrogen atmosphere; The stirring speed of the grafting reaction is 250-350 rpm; The heating temperature of the grafting reaction is 60-70°C; The reaction time of the grafting reaction is 3 to 4 hours.

8. The preparation method according to claim 3, characterized in that In step (II), the precipitation operation steps include: Ethanol was added to the reaction product solution obtained by the reaction and stirred, and then allowed to stand for stratification to precipitate white flocculent matter; The volume ratio of the reaction product solution to ethanol is 1:(5-6); The time of standing and stratifying is 2 to 3 hours; The centrifugal speed is 3000-4000 rpm; The centrifugal time is 10 to 20 minutes; The drying temperature is 40-50°C; The drying time is 10 to 12 hours.

9. The preparation method according to claim 3, characterized in that In step (III), the bio-based composite liquid mulch film is prepared by the following method: Under stirring conditions, the modified starch, the modified chitosan, the glycerol and the calcium carbonate are sequentially added to the nanocellulose solution. After each component is added, the obtained mixed solution is stirred for 10 to 20 minutes before the next component is added.

10. The preparation method according to claim 3, characterized in that In step (III), the stirring speed during the preparation process is 700-800 rpm; After uniform mixing, the obtained mixed solution is subjected to vacuum degassing to obtain the bio-based composite liquid ground film.

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