A bio-based composite liquid mulch film and its preparation method

Abstract

This invention provides a bio-based composite liquid mulch film and its preparation method. The bio-based composite liquid mulch 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 graft copolymerization of chitosan with acrylic acid monomers. This invention integrates multiple bio-based components such as modified starch, modified chitosan, nanocellulose solution, glycerol, and calcium carbonate, utilizing the natural properties of bio-based materials to form a uniform and biodegradable film layer. This film layer can better isolate air and water vapor loss, improve soil moisture retention capacity, and ensure sufficient strength and flexibility during application, avoiding problems such as early cracking or deformation.

Description

Technical Field

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

[0002] Currently, the plastic mulch films widely used in agriculture are mainly made of petroleum-based polymers such as polyethylene. While these traditional mulch films play a role in retaining soil moisture, increasing temperature, and suppressing weeds, they also bring serious "white pollution" problems. Their non-degradable nature leads to a large amount of residual debris accumulating in the soil over a long period of time, damaging soil structure, hindering water and nutrient cycling, and even threatening the ecological environment and human health through the food chain. Although biodegradable plastic mulch films have been developed in recent years, some materials still have problems such as uncontrollable degradation cycles, insufficient mechanical properties, or high costs, making it difficult to meet the needs of large-scale agricultural applications.

[0003] Liquid mulch films, as an alternative solution, achieve agronomic functions through spraying to form a film, avoiding the difficulties of field recycling. Early studies mostly used materials such as asphalt and synthetic polymer emulsions, which, while possessing film-forming properties, suffer from poor biocompatibility, harmful degradation products, or insufficient water retention and barrier properties. Bio-based materials such as natural starch, cellulose, and chitosan have attracted attention due to their wide availability, renewability, and biodegradability; however, mulches prepared from single components often face bottlenecks such as low mechanical strength, excessive hydrophilicity leading to poor water resistance, and poor film-forming continuity. Although existing technologies have attempted to combine bio-based components, how to achieve synergistic effects among multiple components, simultaneously improving mechanical strength, water vapor barrier properties, and soil water retention capacity while ensuring complete biodegradability, remains a pressing technical challenge.

[0004] Against this backdrop, developing a composite liquid mulch film based on modified biopolymers, and optimizing component interfacial interactions through molecular structure design to balance degradation cycles and functional durability, has become an important direction for resolving the contradiction between sustainable agricultural production and environmental protection. There is an urgent need to construct a new green mulch film system that combines high agronomic performance, environmental friendliness, and economic feasibility to meet the dual demands of modern agriculture for resource conservation and ecological security. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a bio-based composite liquid mulch film and its preparation method. 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 biodegradable film layer. This film layer 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 objective, the present invention adopts the following technical solution:

[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 this invention integrates multiple bio-based components, utilizing the natural properties of bio-based materials to form a uniform and biodegradable membrane layer, effectively solving the environmental pollution problems of traditional plastic mulch films. Nanocellulose serves as the structural framework, modified starch and modified chitosan as the main film-forming matrices, and glycerol and calcium carbonate as functional additives, synergistically enhancing the barrier properties, water retention properties, and mechanical properties of the membrane layer. This allows the liquid mulch film to better isolate air and water vapor loss, improve soil moisture retention capacity, and ensure sufficient strength and flexibility during application, avoiding problems such as early cracking or deformation.

[0011] Starch, after being modified with citric acid, undergoes an acid hydrolysis-esterification reaction, introducing carboxyl functional groups and significantly improving its chemical structure and surface properties. This modification process hydrolyzes the starch molecular chains and forms partial ether bonds, resulting in a more uniform molecular weight distribution and thus enhancing the starch's hydrophilicity and film-forming properties. Regarding water retention, the carboxyl groups can effectively adsorb and retain water molecules through hydrogen bonds, reducing the rate of soil moisture evaporation into the air. In terms of mechanical properties, the esterification structure provides stronger intermolecular forces, and the interlocking network structure formed with nanocellulose enhances the tensile strength and toughness of the film. Furthermore, the modified starch exhibits improved solubility in aqueous solutions, reducing viscosity inhomogeneity during preparation and ensuring a smoother, denser film, further improving the film's barrier properties and reducing external environmental interference with soil moisture.

[0012] Chitosan, through graft copolymerization with acrylic acid monomers, develops a branched structure, enhancing its flexibility and reactivity. Acrylic acid graft copolymerization transforms chitosan from a rigid polymer into a more flexible material, significantly strengthening the barrier properties of the membrane. The modified chitosan forms a denser micronetwork within the membrane, effectively blocking oxygen and carbon dioxide penetration and reducing heat loss due to soil gas exchange. Regarding water retention, the acrylic acid branches increase the number of polar groups, improving chitosan's water absorption capacity and viscoelasticity, helping to maintain the membrane's stability in humid environments. Simultaneously, acrylic acid graft modification improves the compatibility of chitosan with other components in liquid mulch films, strengthening the membrane's mechanical properties through intermolecular covalent bonds, preventing fracture or delamination under mechanical stress, thus achieving the required long-term durability.

[0013] Nanocellulose solution plays a crucial skeletal role in liquid mulch films, its nanoscale fibrous structure providing high mechanical stability and microscopic uniformity. The nanocellulose fibers, with diameters in the nanometer range, can form a strong physically interwoven network with modified starch and modified chitosan, significantly enhancing the tensile strength and elastic modulus of the film. Regarding barrier properties, the dense arrangement of nanofibers reduces the size and distribution of pores, decreasing diffusion channels for water molecules and gases, thus improving the film's barrier performance. In terms of water retention, the hydrophilic surface of nanocellulose promotes uniform water distribution and retention, while stabilizing the soil moisture environment through adsorption. Furthermore, the nanoscale properties of nanocellulose improve the rheological properties of the liquid mulch film, resulting in a smooth surface after spraying or coating, preventing cracking and ensuring consistent film performance.

[0014] This invention incorporates glycerol and calcium carbonate into a liquid mulch film. Glycerol, acting as a plasticizer, penetrates between polymer chains, reducing intermolecular friction and increasing free volume, significantly improving the film's flexibility and extensibility. This makes the liquid mulch film less prone to cracking under soil shrinkage or temperature changes, maintaining good mechanical integrity. Simultaneously, the small molecule properties of glycerol improve the film's moisture and wetting ability, indirectly enhancing water retention and facilitating uniform distribution and continuous release of moisture within the film. Calcium carbonate, as a low-cost filler, fills nanopores and increases the film's density and surface hardness through the dispersion and stacking of its microparticle structure, further enhancing the film's barrier properties and preventing the intrusion of external pollutants. Furthermore, calcium carbonate particles strengthen the interfacial bonding with the organic matrix, sharing the mechanical load to reduce overall shrinkage, thus achieving a synergistic effect and significantly improving the film's mechanical strength and service life.

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

[0016] First, the hydrophilic carboxyl groups of modified starch are bonded to the cellulose nanofiber network through hydrogen bonds to form a porous but dense framework structure, which optimizes water retention while enhancing the barrier properties of the membrane.

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

[0018] Finally, glycerol acts as a plasticizer, filling the network voids, reducing membrane brittleness and promoting molecular chain sliding among components, ensuring the membrane's flexibility and stability under dynamic conditions. Calcium carbonate, dispersed in the liquid mulch film, provides physical support, fills micropores, reduces defects, and improves the membrane's airtightness and durability. Through the synergistic effect of each component, high-efficiency water blocking, reduced evaporation, and anti-aging effects are achieved.

[0019] As a preferred embodiment of the present invention, the bio-based composite liquid mulch film, in 100 parts by weight, comprises 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 glycerin;

[0024] 8-12 parts calcium carbonate.

[0025] The nanocellulose solution can be in the following weight proportions: 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 parts; the modified starch can be in the following weight proportions: 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 parts; and the modified chitosan can be in the following weight proportions: 12, 12.5, 13, 13.5, 14, 14.5, or 1... 5 parts, the weight of glycerin 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 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 is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] This invention specifically limits the addition amount of nanocellulose solution to 30-40 parts. Within this range, an effective supporting framework can be formed while avoiding excessive densification of the structure. At this addition amount, nanocellulose forms a uniform three-dimensional network, and its abundant hydroxyl groups form stable hydrogen bonds with the carboxyl groups of modified starch, synergistically enhancing the overall mechanical strength of the membrane. Simultaneously, the appropriate porosity of the fiber network is effectively filled by calcium carbonate particles, reducing water vapor permeability and maintaining the toughness of the membrane. The acrylic acid branches of modified chitosan, guided by nanocellulose, form spatial cross-links, reinforcing localized weak areas of the membrane and achieving a comprehensive improvement in both strength and extensibility.

[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 cannot adequately bear the stress of the starch matrix, and are prone to interfacial separation under mechanical load. In addition, the sparse fiber network leads to an increase in nanoscale porosity and an expansion of water molecule diffusion channels, significantly reducing the barrier properties of the membrane. At the same time, the crosslinking points of modified chitosan lack the effect of fiber anchoring points, failing to form an effective toughening network, resulting in increased brittleness of the membrane.

[0028] When the amount of nanocellulose solution added exceeds 40 parts, the high-density nanofibers are prone to entanglement and agglomeration during mixing, disrupting the uniformity of dispersion, and the agglomerates become stress concentration points. Simultaneously, the excessively dense fiber network compresses the space of the modified starch molecular chains, hindering their full expansion and film formation. Furthermore, the acrylic acid branches of the modified chitosan cannot be uniformly cross-linked due to the saturation of the binding sites on the nanofiber surface, and calcium carbonate particles are also difficult to distribute uniformly within the dense network, ultimately leading to localized embrittlement and reduced flexibility of the film.

[0029] This invention specifically limits the amount of modified starch added to 30-40 parts. Within this range, the liquid mulch film can form a complete and appropriately strong film-forming matrix. An appropriate amount of modified starch molecular chains form a stable three-dimensional network through ether bonds, and its surface carboxyl groups provide hydrophilicity, endowing the film with water-retention function. Simultaneously, this network structure can effectively encapsulate nanocellulose to form an interpenetrating reinforcing structure. Furthermore, the acrylic acid branches of modified chitosan can fully crosslink between the modified starch network gaps, glycerol molecules uniformly permeate the inter-chain 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 amount of modified starch added is less than 30 parts, a continuous film structure cannot be formed. The sparse modified starch molecular chains lack sufficient cross-linking points, making it difficult to support nanocellulose, resulting in insufficient tensile strength of the film. In addition, excessive network porosity leads to the failure of water vapor barrier and a decrease in water retention. At the same time, insufficient matrix causes the cross-linking points of modified chitosan to be dispersed, resulting in loose interfacial bonding. The plasticizing effect of glycerol is excessively softened due to the lack of a carrier, and the uneven dispersion of calcium carbonate affects the filling effect.

[0031] When the amount of modified starch added exceeds 40 parts, the modified starch molecules become entangled, crowding out the dispersion space of nanocellulose, and nanocellulose easily aggregates to form stress concentration points. Furthermore, the high density of modified starch compresses the cross-linking space of modified chitosan, limiting its flexible branch extension. Simultaneously, excessive modified starch also hinders the uniform penetration of glycerol molecules, leading to insufficient local plasticization and localized embrittlement of the membrane. More importantly, the filtered modified starch increases the viscosity of the liquid membrane, causing calcium carbonate precipitation, ultimately reducing the membrane's flexibility.

[0032] This invention specifically limits the amount of modified chitosan added to 12-15 parts. Within this range, its acrylic acid branches can establish appropriate cross-links between the starch network and the nanofiber skeleton, ensuring that the modified chitosan branches fully fill the interfacial gaps. This strengthens the binding force between the modified starch and nanocellulose through amino / carboxyl group interactions, improving membrane toughness while maintaining structural stability. The modified chitosan molecules can also synergistically enhance the barrier properties of the membrane with calcium carbonate.

[0033] When the amount of modified chitosan added is less than 12 parts, the cross-linking network has serious defects. Insufficient acrylic acid branches cannot effectively bridge the interface between modified starch and nanocellulose, leading to uneven stress transmission and localized cracking. Simultaneously, the polar groups of modified chitosan are insufficient to seal the micropores of the membrane, reducing its water vapor barrier properties. Furthermore, excessively low amounts of modified chitosan result in sparse cross-linking points, weakening the buffering effect of glycerol and exacerbating the brittle fracture of the membrane under external forces.

[0034] When the amount of modified chitosan added exceeds 15 parts, excessive acrylic acid branches lead to molecular entanglement. The high density of modified chitosan restricts the movement of molecular chain segments and hinders glycerol permeation, resulting in increased membrane rigidity. Furthermore, the dense amino / carboxyl groups adsorb excessive moisture, causing localized swelling and disrupting the dispersion stability of calcium carbonate. Simultaneously, excessive cross-linking interferes with the orientation distribution of nanocellulose, forming internal stress concentration areas that are prone to shrinkage and cracking during film drying.

[0035] This invention specifically limits the amount of glycerol added to 4-6 parts. Within this range, glycerol molecules can effectively penetrate the gaps between the modified starch-modified chitosan polymer chains, reducing inter-chain friction and moderately increasing the space for molecular movement, resulting in a membrane with 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 fiber aggregation. Simultaneously, it stabilizes the network structure through polar interactions with the modified chitosan branches, and synergistically inhibits brittle fracture of the membrane with calcium carbonate, ensuring the structural integrity of the membrane under different temperature and humidity conditions.

[0036] When the amount of glycerol added is less than 4 parts, the mobility of the polymer chains is limited, and the insufficient plasticizing effect leads to the tight stacking of modified starch molecular chains, increasing the rigidity of the film layer. Under external stress or low temperature conditions, brittle fracture is likely to occur. At the same time, too little glycerol adds to the modified chitosan crosslinking points, making the interface between nanocellulose and modified starch relatively fragile. Stress cannot be effectively transferred between nanocellulose and modified starch, which in turn induces the propagation of microcracks inside the film layer.

[0037] When the amount of glycerol added exceeds 6 parts, excessive glycerol occupies too many intermolecular spaces, weakening the interactions between polymer chains, resulting in a loose membrane structure, significantly reduced strength, and susceptibility to permanent deformation under mechanical load. Furthermore, high concentrations of glycerol can interfere with the hydrogen bonding between modified chitosan molecules, reducing cross-linking efficiency. Simultaneously, the wettability of nanocellulose decreases due to interfacial glycerol enrichment, leading to a decline in interfacial bonding between nanocellulose and modified starch.

[0038] This invention specifically limits the amount of calcium carbonate added to 8-12 parts. Within this range, the calcium carbonate particles are uniformly dispersed in the modified starch-modified chitosan network structure, filling the gaps between polymer chains, significantly improving the density of the membrane and blocking water vapor permeation. Simultaneously, the surface of the calcium carbonate particles forms an interfacial lubrication with glycerol, synergistically maintaining the membrane's flexibility with the polar groups of the modified chitosan, thus comprehensively enhancing the membrane's mechanical strength and environmental stability.

[0039] When the amount of calcium carbonate added is less than 8 parts, the sparsely distributed calcium carbonate particles cannot adequately cover the micropores in the modified starch network, resulting in a decrease in the water vapor barrier efficiency of the membrane. Simultaneously, insufficient addition prevents the stress borne by the nanocellulose framework from being transferred to the calcium carbonate particles, easily leading to stress concentration points at the nanofiber ends and subsequently causing cracks. Furthermore, the plasticizing effect of glycerol is limited due to the lack of synergistic buffering by calcium carbonate particles, resulting in a decrease in the membrane's resistance to deformation.

[0040] When the amount of calcium carbonate added exceeds 12 parts, the excess calcium carbonate will cause particle agglomeration, and the agglomerates will become stress defect points. In addition, the high amount of calcium carbonate will also crowd out the interaction space of polymer chains, weakening the cross-linking efficiency of modified chitosan and the plasticizing effect of glycerol. At the same time, excessive adsorption of glycerol on the surface of calcium carbonate particles will also lead to plasticizer depletion in local areas of the film layer, causing brittle fracture.

[0041] In some optional examples, the dry weight fraction of nanocellulose in the nanocellulose solution is 2 to 3 wt%, 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 is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0042] In a second aspect, the present invention provides a method for preparing the bio-based composite liquid mulch film described in the first aspect, the method comprising:

[0043] (I) Disperse starch in deionized water and stir and heat to obtain starch solution, then add citric acid to carry out acid hydrolysis esterification reaction, and after the reaction is completed, spray dry, pulverize and sieve to obtain modified starch;

[0044] (II) Chitosan was dissolved in acetic acid solution, followed by the addition of acrylic monomer and ammonium persulfate solution for grafting reaction. After the reaction was completed, the mixture was precipitated, centrifuged, washed and dried to obtain modified chitosan.

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

[0046] In the preparation of modified starch, firstly, starch is pre-dispersed in deionized water and gelatinized by heating to ensure that the molecular chains are fully extended to form a homogeneous solution, laying the foundation for subsequent reactions. Then, citric acid is added for acid hydrolysis and esterification. During the acid hydrolysis stage, the hydrogen ions released by citric acid catalyze the breakage of starch glycosidic bonds, moderately reducing the molecular weight and exposing more free hydroxyl groups, optimizing the length distribution of starch molecular chains and improving water solubility. The esterification stage is carried out under heating conditions. The carboxyl groups of citric acid undergo dehydration condensation with the primary alcohol hydroxyl groups of starch molecules to form stable ester bonds, thereby covalently grafting citric acid residues onto the starch molecular chains. This introduces the tricarboxyl group structure of citric acid into the starch molecular chains. These carboxyl groups significantly enhance the hydrophilicity of starch and provide cross-linking active sites.

[0047] In the preparation of modified chitosan, polyacrylic acid is first grafted onto the chitosan molecular chain under the action of an initiator. This reaction is based on the free radical graft copolymerization mechanism. Under heating conditions, the initiator (ammonium persulfate) decomposes to generate sulfate free radicals, which attack the active sites (C6 hydroxyl or C2 amino) on the chitosan molecular chain, forming chitosan macromolecular free radicals. Subsequently, the acrylic acid monomer contacts these active sites and polymerizes and grows through a chain reaction, forming a branched structure dominated by polyacrylic acid. During the reaction, the double bonds of the acrylic acid monomer open under the action of free radicals, and its carbon atoms form covalent bonds with the carbon / oxygen atoms of the macromolecular free radicals. The length of the polyacrylic acid branch is controlled by the monomer concentration and reaction time; excessively high concentrations or excessively long reaction times will lead to excessive branch elongation. The final modified chitosan has a molecular structure in which polyacrylic acid branches are grafted onto the chitosan backbone. The polyacrylic acid branches introduce a large number of carboxyl groups into the chitosan, which significantly enhances the hydrophilicity and reactivity of the modified chitosan, making the material have 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] In some optional instances, the temperature at which the starch and deionized water are stirred and heated is 75 to 85°C, for example, 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; other unlisted values ​​within this range are also applicable.

[0050] In some optional instances, the stirring and heating speed of the starch and deionized water 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.

[0051] In some optional instances, the stirring and heating time of the starch and deionized water is 40 to 60 minutes, for example, 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 unlisted values ​​within this range are also applicable.

[0052] In some alternative 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, other unlisted values ​​within this range are also applicable.

[0053] This invention specifically defines the mass ratio of starch to citric acid in the starch solution as 1:(0.5~0.6). During the reaction, citric acid acts as both an esterifying agent and an acid hydrolyzing agent. On one hand, the carboxyl groups on citric acid undergo esterification with the hydroxyl groups in the starch molecular chain, forming ether bonds and introducing hydrophilic carboxyl groups. This significantly improves the solubility and dispersion stability of starch in aqueous solution, making it easier to form a continuous and uniform film layer during subsequent liquid film formation. On the other hand, citric acid appropriately hydrolyzes some of the glycosidic bonds in starch, optimizing the chain length without disrupting the overall molecular chain coherence, ensuring that the modified starch molecular chain possesses both sufficient fluidity and retains its strength properties. This moderately modified starch molecular structure contains an appropriate amount of carboxyl groups, which can establish tight 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 of the composite network. Meanwhile, the hydrophilicity provided by the carboxyl groups can effectively adsorb water molecules, enhancing the water retention capacity of the membrane, while the retained starch backbone segments provide the basic tensile strength of the membrane, ultimately achieving a comprehensive improvement in water retention and mechanical strength.

[0054] When the amount of citric acid added is below the lower limit defined in this invention, the acid hydrolysis of starch is insufficient, making it difficult to effectively catalyze the breakage of starch glycosidic bonds. This results in a still high molecular weight, preventing the long starch molecular chains from fully extending in the aqueous system, leading to poor solubility and uneven dispersion. When preparing liquid mulch films, incompletely dissolved starch gel particles easily form, becoming structural defects in the film layer. Furthermore, insufficient esterification of starch results in fewer carboxyl groups introduced onto the starch molecular chains, reducing hydrophilicity and preventing the formation of an effective hydrophilic network to lock in moisture after film formation, thus decreasing the water retention capacity of the film layer. Simultaneously, insufficient carboxyl content also affects the intermolecular attraction between modified starch and other components, leading to reduced interfacial bonding and making the film layer prone to microcracks under stress, ultimately causing cracking.

[0055] When the amount of citric acid added exceeds the upper limit defined in this invention, excessive citric acid triggers excessive degradation and structural damage of starch molecules, accelerates the hydrolysis rate of starch glycosidic bonds, and causes starch molecular chains to be excessively sheared into excessively short fragments. The resulting modified starch lacks sufficiently long chain segments, making it difficult to withstand external stress through the entanglement of long chain segments, thus reducing the tensile strength of the membrane. Furthermore, the excessive carboxyl groups generated by the esterification reaction significantly increase the hydrophilicity of the membrane, causing it to swell excessively in moist soil environments, reducing dimensional stability, making the membrane structure loose and porous, and decreasing its water vapor barrier properties. Simultaneously, excessive citric acid leads to the accumulation of by-reaction products (such as citric acid monoesters or diesters) in the liquid mulch film, affecting the compatibility of other components and their effective binding with nanocellulose, ultimately resulting in decreased mechanical properties and barrier function of the membrane, and a shortened service life.

[0056] As a preferred embodiment of the present invention, in step (I), the operation steps of the acid hydrolysis esterification reaction include:

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

[0058] In some optional instances, the acidolysis temperature is 60~70°C, for example, it can be 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, other unlisted values ​​within this range are also applicable.

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

[0060] In some alternative instances, 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, other unlisted values ​​within this range are also applicable.

[0061] In some alternative examples, the reaction time of the esterification 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.

[0062] In some optional instances, the inlet temperature of the spray dryer 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, other unlisted values ​​within this range are also applicable.

[0063] In some optional instances, the outlet temperature of the spray dryer is 70-80°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.

[0064] In some optional instances, the sieve mesh size is 100 to 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, other unlisted values ​​within this 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 homogeneous to obtain chitosan solution.

[0066] In some optional instances, the heating temperature when the chitosan is mixed with the acetic acid solution is 40~50°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.

[0067] In some optional instances, the stirring speed when mixing the chitosan with the acetic acid solution is 200 to 300 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm or 300 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0068] In some optional instances, the acetic acid solution has a mass fraction of 1 to 2 wt%, for example, it may 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; other unlisted values ​​within this range are also applicable.

[0069] In some optional examples, the mixing and stirring time of the chitosan and acetic acid solution 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.

[0070] In some optional examples, the chitosan solution contains 2 to 3 wt% chitosan by mass, for example, 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 is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0071] In some alternative instances, before the grafting reaction begins, an alkaline solution is added dropwise to the chitosan solution to adjust its pH 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 not limited to the listed values; other unlisted values ​​within this 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 1~2wt%, 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.

[0073] In some alternative examples, the mass ratio of chitosan to acrylic 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, other unlisted values ​​within this range are also applicable.

[0074] This invention specifically limits the mass ratio of chitosan to acrylic monomer in the chitosan solution to 1:(0.4~0.5). Within this range, the acrylic monomer forms a moderately long and uniformly distributed branched structure on the chitosan molecular backbone through a grafting reaction. This effectively preserves the strength of the chitosan skeleton while introducing 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 at the interface between the two phases. At the same time, they provide anchoring points for the polar groups on the surface of nanocellulose, ensuring stress transmission throughout the composite network. The polyacrylic acid branches grafted onto the chitosan molecular chains act as flexible bridges, interlacing between the modified starch network and the nanocellulose skeleton, bridging the gaps between rigid materials and reducing stress concentration. The introduced appropriate amount of hydrophilic carboxyl groups synergistically enhances the water retention capacity of the membrane, preventing excessive water absorption and swelling while forming a stable water molecule adsorption layer, thus maintaining mechanical strength while also ensuring impact toughness.

[0075] When the amount of acrylic acid monomer added is below the lower limit defined in this invention, insufficient acrylic acid monomer leads to a lower degree of chitosan modification. The length of the polyacrylic acid branches grafted onto the chitosan molecular chain is too short and the grafting density is too sparse, failing to provide sufficient flexibility and cross-linking active sites. The rigid framework of chitosan itself is not sufficiently softened, limiting the mobility of the molecular chains, resulting in a brittle film that is prone to cracking and rapid propagation under external force. Furthermore, insufficient grafting also results in a low carboxyl content, severely hindering the effective binding between modified chitosan and components such as modified starch and nanocellulose.

[0076] When the amount of acrylic monomer added exceeds the upper limit defined in this invention, the excessive acrylic monomer participates in the reaction, resulting in excessively long polyacrylic acid side chains and excessively high grafting density. At this time, the chitosan molecular backbone is tightly wrapped and even cross-linked by numerous polyacrylic acid side chains, severely restricting the movement space of the chitosan macromolecular chain segments, which in turn leads to an increase in the rigidity of the modified chitosan molecular chain. In addition, the excessive hydrophilicity brought about by the high content of grafted carboxyl groups causes the membrane layer to swell and deform in a high humidity environment, destroying the original dense microporous structure and resulting in a significant reduction in gas barrier efficiency.

[0077] In some alternative examples, the mass ratio of the acrylic monomer to the ammonium persulfate in the ammonium persulfate solution is 1:(0.05~0.08), for example, it can be 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, other unlisted values ​​within this range are also applicable.

[0078] In some optional instances, the grafting reaction is carried out under a nitrogen atmosphere.

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

[0080] In some optional instances, the heating temperature of the grafting 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.

[0081] In some optional instances, the grafting 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.

[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 and stirred. The mixture was then allowed to stand and separate into layers, resulting in the precipitation of white flocculent material.

[0084] In some alternative instances, the volume ratio of the reaction product solution to ethanol is 1:(5~6), for example, 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; other unlisted values ​​within this range are also applicable.

[0085] In some optional instances, the settling time 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; other unlisted values ​​within this range are also applicable.

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

[0087] In some optional instances, the centrifugation time is 10 to 20 minutes, for example, 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 unlisted values ​​within this range are also applicable.

[0088] In some optional instances, the drying temperature 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.

[0089] In some optional instances, the drying time is 10 to 12 hours, for example, 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; other unlisted values ​​within this 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 sequentially to the nanocellulose solution. After each component is added, the resulting mixed solution is stirred for 10-20 minutes, and then the next component is added. For example, the stirring time 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0092] In the preparation of bio-based composite liquid mulch films, firstly, modified starch is added to a nanocellulose solution. The modified starch molecular chains gradually expand and permeate the nanocellulose network in the solution, forming an interpenetrating network structure. During this process, the carboxyl groups of the modified starch bond with the hydroxyl groups of the nanocellulose, strengthening the interpenetrating network structure. Next, modified chitosan is added. Its amino / carboxyl active sites can directionally crosslink with the already formed modified starch-nanocellulose interpenetrating network, and the branched structure of the modified chitosan precisely fills the gaps, improving toughness. Then, glycerol is added to prevent premature addition from causing glycerol to encapsulate the polymer chains and weaken the bond between the modified starch and modified chitosan, while also reserving plasticizing buffer space for the already formed network structure. Finally, calcium carbonate is added because calcium carbonate particles need to be uniformly embedded in a stable organic matrix; premature addition would hinder the molecular interactions 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

[0095] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0096] The bio-based composite liquid mulch provided by this invention integrates multiple bio-based components, utilizing the natural properties of bio-based materials to form a uniform and biodegradable membrane layer, effectively solving the environmental pollution problems of traditional plastic mulch films. Nanocellulose serves as the structural framework, modified starch and modified chitosan as the main film-forming matrices, and glycerol and calcium carbonate as functional additives, synergistically enhancing the barrier properties, water retention properties, and mechanical properties of the membrane layer. This allows the liquid mulch film to better isolate air and water vapor loss, improve soil moisture retention capacity, and ensure sufficient strength and flexibility during application, avoiding problems such as early cracking or deformation. Attached Figure Description

[0097] Figure 1 The process flow diagrams for preparing the bio-based composite liquid mulch film provided in Examples 1-15 of this invention are shown below.

[0098] Figure 2 Infrared spectra of starch and modified starch prepared in Example 1 of this invention;

[0099] Figure 3 Infrared spectra of chitosan and the modified chitosan prepared in Example 1 of this invention. Detailed Implementation

[0100] 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.

[0101] Example 1

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

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

[0104] Citric acid was added to a starch solution, with a starch-to-citric acid mass ratio of 1:0.5. Under stirring, the solution was heated to 60°C for acid hydrolysis. After 40 minutes of reaction, the temperature was raised to 100°C for esterification. After 3 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 110°C and the outlet temperature was 70°C. Finally, the product was pulverized and passed through a 100-mesh sieve to obtain modified starch.

[0105] (2) Chitosan was dissolved in a 1 wt% acetic acid solution at a stirring speed of 200 rpm and a heating temperature of 40°C. After mixing and stirring for 3 h, a chitosan solution was obtained, in which the mass fraction of chitosan was 2 wt%.

[0106] Sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH value to 4. Acrylic acid monomer and ammonium persulfate solution with a mass fraction of 1 wt% 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 was completed, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5. The mixture was then allowed to stand for 2 hours to separate into layers, and white flocculent matter was precipitated. The precipitate was centrifuged at 3000 rpm for 20 minutes. After centrifugation, 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 at room temperature, 30 parts of modified starch obtained in step (I), 14 parts of modified chitosan obtained in step (2), 4 parts of glycerol and 12 parts of calcium carbonate were added sequentially to 40 parts of nanocellulose solution (the mass fraction of nanocellulose dry weight in nanocellulose solution was 2 wt%). After each component was added, the resulting mixed solution was stirred for 20 min, and then the next component was added. After all components were mixed evenly, the resulting mixed solution was degassed under vacuum to obtain the bio-based composite liquid mulch film.

[0109] Figure 2 The infrared spectra of starch and the modified starch prepared in this embodiment are shown. As can be seen from the figures, in the infrared curve of starch, the 3200~3500 cm⁻¹... -1 The absorption peak at 2900~2930 cm⁻¹ is attributed to the stretching vibration of OH. -1 The absorption peak at that point is attributed to the stretching vibration of the aliphatic chain CH (-CH- on the glucose ring and) ), 1400~1450cm-1 The absorption peak at 1150 cm⁻¹ is attributed to the bending vibration of CH. -1 The absorption peak at 1080 cm⁻¹ is attributed to the antisymmetric stretching vibration of the COC ring in the sugar ring. -1 With 1022cm -1 The absorption peak at [value missing] is attributed to the coupling of the stretching vibrations of CO and C. In the infrared curve of modified starch, the peak values ​​are between 1720 and 1750 cm⁻¹. -1 The absorption peak at 1210–1250 cm⁻¹ is attributed to the stretching vibration of the C=O group in the ester group. -1 The absorption peak at 1550–1610 cm⁻¹ is attributed to the stretching vibration of the CO bond in the ester bond. -1 The absorption peak at that point is attributed to the carboxylate ion ( Asymmetric stretching vibration, 1400cm -1 The absorption peak at that point is attributed to the carboxylate group ( The symmetric stretching vibration of citric acid indicates that citric acid successfully introduced carboxyl groups (-COOH) and ester bonds (-COOR) into the starch molecular chain via esterification.

[0110] Figure 3 The infrared spectra of chitosan and the modified chitosan prepared in this embodiment are shown. As can be seen from the figures, in the infrared curve of chitosan, 3420 cm⁻¹... -1 The absorption peak at 2870~2900 cm⁻¹ is attributed to the superposition of the stretching vibrations of OH and NH. -1 The absorption peak at that point is attributed to the stretching vibration of aliphatic CH (on the chitosan glucosamine ring). and -CH3). 1650~1660cm -1 The absorption peak at 1590 cm⁻¹ is attributed to the amide I band (C=O stretching vibration). -1 The absorption peak at 1420 cm⁻¹ is attributed to the bending vibration of NH₃. -1 The absorption peak at 1150 cm⁻¹ is attributed to the bending vibration of CH₄ and the in-plane bending of OH⁻. -1 The absorption peak at [value missing] is attributed to the asymmetric stretching vibration of COC. In the infrared curve of modified chitosan, the peak values ​​are between 1700 and 1725 cm⁻¹. -1 The absorption peak at 1550 cm⁻¹ is attributed to the C=O stretching vibration of carboxylic acids. -1 The absorption peak at that point is attributed to the carboxylate ion ( The asymmetric stretching vibrations of ) indicate that the acrylic acid side chains were successfully grafted onto the chitosan molecular chains.

[0111] Example 2

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

[0113] (1) Disperse starch in deionized water at a mass ratio of starch to deionized water of 1:6.5. Stir and heat at a heating temperature of 78℃ and a stirring speed of 320rpm for 55min to obtain starch solution.

[0114] Citric acid was added to a starch solution, with a starch-to-citric acid mass ratio of 1:0.52. Under stirring, the solution was heated to 62°C for acid hydrolysis. After 38 minutes of reaction, the temperature was increased to 102°C for esterification. After 2.8 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 112°C and the outlet temperature was 72°C. Finally, the product was pulverized and passed 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. After mixing and stirring for 2.8 h, a chitosan solution was obtained, and the mass fraction of chitosan in the chitosan solution was 2.2 wt%.

[0116] Sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH value to 4.2. Acrylic acid monomer and ammonium persulfate solution with a mass fraction of 1.2 wt% 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 was completed, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5.2. The mixture was then allowed to stand for 2.2 hours to separate into layers, and white flocculent matter was precipitated. The mixture was centrifuged at 3200 rpm for 18 minutes. After centrifugation, the precipitate was washed and dried at 42℃ for 11.5 hours to obtain modified chitosan.

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

[0119] Example 3

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

[0121] (1) Disperse starch in deionized water at a mass ratio of starch to deionized water of 1:7. Stir and heat at a heating temperature of 80℃ and a stirring speed of 350rpm for 50min to obtain starch solution.

[0122] Citric acid was added to a starch solution, with a starch-to-citric acid mass ratio of 1:0.55. Under stirring, the solution was heated to 65°C for acid hydrolysis. After 35 minutes of reaction, the temperature was increased to 105°C for esterification. After 2.5 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 115°C and the outlet temperature was 75°C. Finally, the product was pulverized and passed through a 130-mesh sieve to obtain modified starch.

[0123] (2) Chitosan was dissolved in a 1.5 wt% acetic acid solution at a stirring speed of 250 rpm and a heating temperature of 45°C. After mixing and stirring for 2.5 h, a chitosan solution was obtained, in which the mass fraction of chitosan was 2.5 wt%.

[0124] Sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH value to 4.5. Acrylic acid monomer and ammonium persulfate solution with a mass fraction of 1.5 wt% 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 was completed, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5.5. The mixture was then allowed to stand for 2.5 hours to separate into layers, and white flocculent matter was precipitated. The mixture was centrifuged at 3500 rpm for 15 minutes. After centrifugation, 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 at room temperature, 36 parts of modified starch obtained in step (I), 13 parts of modified chitosan obtained in step (2), 6 parts of glycerol and 10 parts of calcium carbonate were added sequentially to 35 parts of nanocellulose solution (the mass fraction of nanocellulose dry weight in the nanocellulose solution was 2.5 wt%). After each component was added, the resulting mixed solution was stirred for 15 min, and then the next component was added. After all components were mixed evenly, the resulting mixed solution was degassed under vacuum to obtain the bio-based composite liquid mulch film.

[0127] Example 4

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

[0129] (1) Disperse starch in deionized water at a mass ratio of starch to deionized water of 1:7.5. Stir and heat at a heating temperature of 82℃ and a stirring speed of 380rpm for 45min to obtain starch solution.

[0130] Citric acid was added to a starch solution, with a starch-to-citric acid mass ratio of 1:0.58. Under stirring, the solution was heated to 68°C for acid hydrolysis. After 32 minutes of reaction, the temperature was increased to 108°C for esterification. 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. Finally, the product was pulverized and passed through a 140-mesh sieve to obtain 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. After mixing and stirring for 2.2 h, a chitosan solution was obtained, in which the mass fraction of chitosan was 2.8 wt%.

[0132] Sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH value to 4.8. Acrylic acid monomer and ammonium persulfate solution with a mass fraction of 1.8 wt% 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 was completed, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:5.8. The mixture was then allowed to stand for 2.8 hours to separate into layers, and white flocculent matter was precipitated. The mixture was centrifuged at 3800 rpm for 12 minutes. After centrifugation, 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 at room temperature, 38 parts of modified starch obtained in step (I), 12 parts of modified chitosan obtained in step (2), 5 parts of glycerol and 11 parts of calcium carbonate were added sequentially to 34 parts of nanocellulose solution (the mass fraction of nanocellulose dry weight in the nanocellulose solution was 2.8 wt%). After each component was added, the resulting mixed solution was stirred for 12 min, and then the next component was added. After all components were mixed evenly, the resulting mixed solution was degassed under vacuum to obtain the bio-based composite liquid mulch film.

[0135] Example 5

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

[0137] (1) Disperse starch in deionized water at a mass ratio of starch to deionized water of 1:8. Stir and heat at a heating temperature of 85℃ and a stirring speed of 400rpm for 40min to obtain starch solution.

[0138] Citric acid was added to a starch solution, with a starch-to-citric acid mass ratio of 1:0.6. Under stirring, the solution was heated to 70°C for acid hydrolysis. After 30 minutes of reaction, the temperature was increased to 110°C for esterification. After 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 120°C and the outlet temperature was 80°C. Finally, the product was pulverized and passed through a 150-mesh sieve to obtain modified starch.

[0139] (2) Chitosan was dissolved in a 2 wt% acetic acid solution at a stirring speed of 300 rpm and a heating temperature of 50°C. After mixing and stirring for 2 h, a chitosan solution was obtained, in which the mass fraction of chitosan was 3 wt%.

[0140] Sodium hydroxide solution was added dropwise to the chitosan solution to adjust its pH value to 5. Acrylic acid monomer and ammonium persulfate solution with a mass fraction of 2 wt% 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 was completed, the reaction product solution was mixed with 95% ethanol at a volume ratio of 1:6. The mixture was then allowed to stand for 3 hours to separate into layers, and white flocculent matter was precipitated. The precipitate was centrifuged at 4000 rpm for 10 minutes. After centrifugation, the precipitate was washed and dried at 50°C for 10 hours to obtain modified chitosan.

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

[0143] Example 6

[0144] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Embodiment 1 is that the weight percentage of the nanocellulose solution is adjusted to 25 parts, and the addition amounts of other components are increased proportionally to ensure that the weight percentages of the other components, except for the nanocellulose solution, remain constant. The adjusted weight percentages of each component 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 glycerin;

[0149] 15 parts calcium carbonate.

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

[0151] Example 7

[0152] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Embodiment 1 is that the weight percentage of the nanocellulose solution is adjusted to 45 parts, and the addition amounts of other components are reduced proportionally to ensure that the weight percentages of the other components, except for the nanocellulose solution, remain unchanged. The adjusted weight percentages of each component 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 glycerol;

[0157] 11 parts calcium carbonate.

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

[0159] Example 8

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

[0161] 42.85 parts of nanocellulose solution;

[0162] 25 parts modified starch;

[0163] 15 parts modified chitosan;

[0164] 4.30 parts glycerol;

[0165] Calcium carbonate 12.85 parts.

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

[0167] Example 9

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

[0169] 31.43 parts of nanocellulose solution;

[0170] 45 parts of modified starch;

[0171] 11 parts modified chitosan;

[0172] 3.14 parts glycerol;

[0173] Calcium carbonate 9.43 parts.

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

[0175] Example 10

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

[0177] 42.79 parts of nanocellulose solution;

[0178] 32.09 parts of modified starch;

[0179] 8 parts modified chitosan;

[0180] 4.28 parts of glycerin;

[0181] Calcium carbonate 12.84 parts.

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

[0183] Example 11

[0184] This embodiment provides a method for preparing a bio-based composite liquid mulch film. The difference from Embodiment 1 is that the weight percentage of modified chitosan is adjusted to 20 parts, and the addition amounts of other components are reduced proportionally to ensure that the weight percentages of all components, except for the nanocellulose solution, remain constant. The adjusted weight percentages of each component are as follows:

[0185] 37.21 parts of nanocellulose solution;

[0186] 27.91 parts of modified starch;

[0187] 20 parts modified chitosan;

[0188] 3.72 parts glycerol;

[0189] Calcium carbonate 11.16 parts.

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

[0191] Example 12

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

[0193] Example 13

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

[0195] Example 14

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

[0197] Example 15

[0198] This comparative example 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 monomer in the chitosan solution is adjusted to 1:0.8. Other operating steps and process parameters are exactly the same as 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, and the starch is not modified with citric acid. In the bio-based composite liquid mulch film, the modified starch is replaced with an equal amount of unmodified starch. Other operation steps and process parameters are exactly the same as 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, and the chitosan is not subjected to acrylic acid grafting modification treatment. In the bio-based composite liquid mulch film, the modified chitosan is replaced with an equal amount of unmodified chitosan. Other operation steps and process parameters are exactly the same as 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 test steps are as follows:

[0204] (1) Water vapor transmission rate

[0205] The liquid mulch films prepared in the examples and comparative examples were 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.

[0206]

[0207] Where Δw is the weight gain (g), and A is the film area (m²). 2 ), where t is time (days).

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

[0209] The liquid mulch film prepared in the examples and comparative examples 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).

[0210] 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 (%).

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

[0212] Prepare standard sandy loam soil (initial moisture content 20% ± 1%), and uniformly spray the liquid mulch film prepared in the examples and comparative examples 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:

[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 amount of nanocellulose is reduced to 25 parts (Example 6), insufficient three-dimensional network density leads to structural defects. The sparse fibers cannot effectively bear stress, resulting in increased micropores in the membrane layer and increased water vapor permeability and water loss rate. When the amount of nanocellulose is increased to 45 parts (Example 7), fiber entanglement is triggered. The dense network compresses the molecular chain space of other components, hindering glycerol penetration and calcium carbonate dispersion, reducing tensile strength, and increasing the rigidity and decreasing the flexibility of the membrane layer.

[0218] The test data from Examples 1, 8, and 9 show that when the amount of modified starch is reduced to 25 parts (Example 8), the continuous film-forming matrix is ​​disrupted, and the sparse cross-linking points of the molecular chains lead to loose interfacial bonding, resulting in decreased tensile strength and barrier properties. When the amount of modified starch is increased to 45 parts (Example 9), molecular entanglement is triggered, crowding out the dispersion space of nanocellulose. Calcium carbonate particles form stress concentration points due to sedimentation, increasing the water loss rate. At the same time, excessive hydrophilicity exacerbates film swelling, leading to a decrease in the elongation at break of the film.

[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, and the sparse acrylic acid branches cannot bridge the interface between the modified starch and nanocellulose. Uneven stress transmission leads to microcracks, resulting in an increased water loss rate of the membrane. When the amount of modified chitosan is increased to 20 parts (Example 11), branch entanglement occurs, and excessive adsorption of water by amino / carboxyl groups causes swelling and deformation, reducing the barrier properties of the membrane and increasing 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 number of carboxyl groups is low, leading to decreased hydrophilicity, weakened hydrogen bonding, and a significant reduction in tensile strength and barrier properties. When the amount of citric acid added is too high (Example 13), it causes excessive degradation of starch, making it difficult for short-chain fragments to entangle and withstand stress, resulting in decreased 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 monomer added is too low (Example 14), the chitosan is not sufficiently softened, the rigid skeleton is not effectively modified, and the increased brittleness leads to a decrease in the elongation at break of the film. When the amount of acrylic monomer added is too high (Example 15), the polyacrylic acid branches are too long and entangled, restricting the movement of molecular chains and causing excessive hydrophilicity, resulting in reduced barrier properties and mechanical strength.

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

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

[0224] 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 bio-based composite liquid mulch film, characterized in that, The bio-based composite liquid mulch film comprises nanocellulose solution, modified starch, modified chitosan, glycerol, and calcium carbonate; Based on 100 parts by weight of the bio-based composite liquid mulch film, it comprises 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 glycerin; 8-12 parts calcium carbonate; The mass fraction of the dry weight of nanocellulose in the nanocellulose solution is 2-3 wt%. The modified starch was prepared by the following method: starch was dispersed in deionized water and stirred and heated to obtain a starch solution, and then citric acid was added to carry out an acid hydrolysis esterification reaction. The mass ratio of starch to citric acid in the starch solution was 1:(0.5~0.6). After the reaction was completed, the modified starch was obtained by spray drying, pulverizing and sieving. The modified chitosan was prepared by the following method: chitosan was dissolved in acetic acid solution, followed by the addition of acrylic acid monomer and ammonium persulfate solution for grafting reaction. The mass ratio of chitosan to acrylic acid monomer in the chitosan solution was 1:(0.4~0.5). After the reaction was completed, the modified chitosan was obtained by precipitation, centrifugation, washing and drying.

2. A method for preparing the bio-based composite liquid mulch film according to claim 1, characterized in that, The preparation method includes: (I) Disperse starch in deionized water and stir and heat to obtain starch solution, then add citric acid to carry out acid hydrolysis esterification reaction, and after the reaction is completed, spray dry, pulverize and sieve to obtain modified starch; (II) Chitosan was dissolved in acetic acid solution, followed by the addition of acrylic monomer and ammonium persulfate solution for grafting reaction. After the reaction was completed, the mixture was precipitated, centrifuged, washed and dried to obtain modified chitosan. (III) The nanocellulose solution, the modified starch, the modified chitosan, glycerol and calcium carbonate are mixed evenly to obtain the bio-based composite liquid mulch film.

3. The preparation method according to claim 2, characterized in that, In step (I), the mass ratio of starch to deionized water is 1:(6~8); The temperature for stirring and heating the starch and deionized water is 75~85℃; The stirring and heating speed of the starch and deionized water is 300~400 rpm; The starch and deionized water are stirred and heated for 40-60 minutes.

4. The preparation method according to claim 2, characterized in that, In step (I), the acid hydrolysis esterification reaction includes the following steps: First, the temperature is raised to the acidolysis temperature to carry out the acidolysis reaction, and then the temperature is raised to the esterification temperature to carry out the esterification reaction. The acid hydrolysis temperature is 60~70℃; The reaction time for the acidolysis reaction is 30-40 min; The esterification temperature is 100~110℃; The esterification reaction takes 2-3 hours. The inlet temperature of the spray dryer is 110~120℃; The outlet temperature of the spray dryer is 70~80℃; The sieve mesh size is 100-150 mesh.

5. The preparation method according to claim 2, characterized in that, In step (II), under stirring and heating conditions, chitosan is dissolved in acetic acid solution and mixed evenly to obtain chitosan solution; The heating temperature when the chitosan is mixed with the acetic acid solution is 40~50℃; The stirring speed when mixing chitosan and acetic acid solution is 200~300 rpm; The acetic acid solution has a mass fraction of 1~2 wt%; The mixing and stirring time of the chitosan and acetic acid solution is 2-3 hours; The chitosan solution contains 2-3 wt% chitosan. Before the grafting reaction begins, an alkaline solution is added dropwise to the chitosan solution to adjust its pH to 4-5.

6. The preparation method according to claim 5, 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 the acrylic monomer to the ammonium persulfate in the ammonium persulfate solution is 1:(0.05~0.08); The grafting reaction was carried out under a nitrogen atmosphere; The stirring speed for the grafting reaction is 250~350 rpm; The heating temperature for the grafting reaction is 60~70℃; The grafting reaction takes 3-4 hours.

7. The preparation method according to claim 2, characterized in that, In step (II), the precipitation operation steps include: Ethanol was added to the reaction product solution and stirred, then allowed to stand and separate into layers, resulting in the precipitation of white flocculent material. The volume ratio of the reaction product solution to ethanol is 1:(5~6); The settling and stratification time is 2-3 hours; The centrifuge speed is 3000~4000 rpm; The centrifugation time is 10-20 minutes; The drying temperature is 40~50℃; The drying time is 10-12 hours.

8. The preparation method according to claim 2, characterized in that, In step (III), the bio-based composite liquid mulch film is prepared using the following method: Under stirring conditions, the modified starch, the modified chitosan, the glycerol, and the calcium carbonate are added sequentially to the nanocellulose solution. After each component is added, the resulting mixed solution is stirred for 10-20 minutes before adding the next component.

9. The preparation method according to claim 2, characterized in that, In step (III), the stirring speed during the preparation process is 700~800 rpm; After being mixed evenly, the resulting mixed solution is degassed under vacuum to obtain the bio-based composite liquid mulch film.

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