Poplar catkin-based low-permeability liquid mulching film and preparation method thereof

Abstract

The invention provides a poplar catkin-based low-permeability liquid mulching film and a preparation method thereof, and belongs to the technical field of liquid mulching films. The mulching film is prepared from poplar catkin fibers and starch as main raw materials through maleic anhydride modification, acidic esterification reaction and emulsion polymerization processes. The preparation method comprises the following specific steps: (1) modifying poplar catkin fibers with maleic anhydride to obtain modified fibers with double bonds on the surfaces; (2) reacting the modified fiber with starch under an acidic condition to generate poplar catkin fiber modified starch colloid; and (3) pre-emulsifying the colloid and an acrylate monomer, and initiating a polymerization reaction to prepare the mulching film emulsion. According to the mulch film, a three-dimensional network interlocking structure of poplar catkin fibers is utilized, permeation of mulch film emulsion in sandy soil is effectively inhibited, film forming uniformity and mechanical strength are improved, and the mulch film has excellent wind erosion resistance and water erosion resistance. The invention solves the problems of high permeability and poor film-forming property of the traditional starch-based mulching film in sandy soil, and has both environmental protection property and agricultural application value.

Description

Technical Field

[0001] This invention provides a low-permeability liquid mulch film based on poplar fluff, and also provides a method for preparing the mulch film, belonging to the field of liquid mulch films. Background Technology

[0002] Against the backdrop of intensifying climate change and frequent extreme weather events, soils are facing exacerbated stress from both wind and water erosion. Simultaneously, human activities such as over-cultivation under intensive agricultural models are accelerating the global process of agricultural soil desertification. In the Yangtze River Delta region, there are numerous plains with high sandy soils formed by river sediment deposition and marine-lacustrine sedimentation. High sandy soils are characterized by large soil particle size, large interparticle spaces, poor water retention, weak thermal stability, and a lack of organic matter. Their loose soil structure makes them more susceptible to topsoil migration, meaning they are not resistant to wind and water erosion, thus severely restricting crop yields. Existing technologies for soil desertification control have significant shortcomings in terms of ecological-economic synergy, technological universality, and environmental friendliness. There is an urgent need to develop new, low-cost, wind- and water-erosion-resistant, and environmentally friendly ecological functional materials that are conducive to agricultural production in sandy soils.

[0003] Starch-based liquid mulch films have shown promise for sandy soil remediation due to their sprayable film-forming properties and environmental friendliness. However, their actual effectiveness is limited by two challenges posed by the unique structure of sandy substrates. First, the large pores between sand grains lead to excessive infiltration of the mulch film, resulting in insufficient film thickness and uneven distribution on the surface. Second, starch-based mulch films are brittle and have low mechanical strength, making them prone to penetrating cracks under high wind shear, causing the film's thermal and mass barrier functions to fail. This directly restricts the heat and water retention performance of starch-based liquid mulch films in sandy soils. Therefore, developing starch-based liquid mulch films that can inhibit the penetration of mulch film into deeper layers of sandy soil and also possess mechanical strengthening functions is of great significance for improving the practical applicability of liquid mulch films in sandy soils.

[0004] Poplar catkins are the fluffy seed appendages produced by poplar trees during their reproductive season. Due to their tendency to disperse, poplar catkins pose significant environmental and health problems. For example, they can come into contact with the human body through the respiratory tract or skin, potentially causing allergic reactions in some individuals and, in severe cases, respiratory illnesses. During their flight, poplar catkins may carry and spread pathogens, and when they fall into water, they can cause water pollution. The loose fibers and oil content of poplar catkins make them highly flammable, easily posing a fire hazard. In China, with its vast poplar tree populations and enormous annual production of poplar catkins, the utilization of this waste material is a pressing social issue that needs to be addressed. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a low-permeability liquid mulch film based on poplar catkins. This method uses common biomass raw materials—poplar catkins and starch from kitchen waste—as raw materials, resulting in low cost, simple preparation method, and easy market promotion and application.

[0006] The present invention also provides a liquid mulch film that can be used in sandy soil. This product has a low permeability in sandy soil and can remain on the soil surface to form a film, thereby having an effective heat preservation and water retention effect on sandy soil and promoting the growth of crops in sandy soil.

[0007] This invention also provides an application of a poplar-based low-permeability liquid mulch film as an agricultural liquid mulch film on sandy soil.

[0008] The specific solution of the present invention is as follows:

[0009] A method for preparing a low-permeability liquid mulch film emulsion based on poplar fluff, the preparation steps of which are as follows:

[0010] (1) Disperse poplar fibers in water, add maleic anhydride and stir continuously. While stirring, add sodium hydroxide solution with a concentration of 3-8wt% to adjust the pH of the mixture to 7-10. The mass ratio of poplar fibers, maleic anhydride and water is 1:(0.8-1.2):(8-12). Then heat the mixture to 70-85℃ and react with a stirring rate of 200-400r / min for 1-3h. After the reaction, filter the mixture and wash the filtrate repeatedly with water until the filtrate is neutral. Dry the filtrate at 60-80℃ for 15-48h to obtain modified poplar fibers.

[0011] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water at a mass ratio of 1:(3-8):(5-10) and stirred to form a uniform suspension. Then, under stirring at 50-70℃ and 150-350r / min, 30-98wt% sulfuric acid solution is added dropwise at a rate of 0.08-0.2mL / min until the pH of the system is stable at 0.5-2. The reaction is continued for 1-3h. After the reaction is completed, the mixture is filtered and the filtrate is washed repeatedly with water until the filtrate is neutral. The filtrate is dried at 50-80℃ until the water content is 10-25wt% to obtain the modified poplar fiber starch colloid.

[0012] (3) The poplar fiber modified starch colloid obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:(0.05-0.15):(0.3-0.6):(2-5). The mixture is pre-emulsified at 40-55℃ and 300-400r / min for 0.5-2h to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:(1-3). The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:(1.5-3):(0.25-0.5).

[0013] (4) Heat the poplar fiber-based pre-emulsion obtained in step (3) to 70-90℃, and then add potassium persulfate or ammonium persulfate aqueous solution with a concentration of 7-13wt% dropwise at a drop rate of 0.05-0.2mL / min as an initiator. The amount of initiator is controlled to be 0.5-1.5% of the total mass of the pre-emulsion. After the initiator is added, use ammonia aqueous solution with a concentration of 15-25wt% to adjust the pH value of the system to 6.8-8.2, and maintain the reaction at a stirring rate of 200-400r / min for 2-6h. Then cool the reaction system to room temperature to obtain poplar fiber-based low-permeability liquid mulch film emulsion.

[0014] The water used in steps (1)-(4) is deionized water.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] First, this invention recycles and reuses poplar catkins, which are prone to causing health, environmental and social problems. This not only solves the problem of dealing with poplar catkins as pollutants, but also achieves efficient resource recycling, which is in line with the concept of green and sustainable development. Secondly, by cleverly utilizing the lightweight hollow fiber structure of poplar fluff and its fiber interlocking effect (i.e., the three-dimensional network interlocking structure constructed by the physical entanglement and node hooking between poplar fluff fibers), multiple functional advantages are demonstrated: (1) The interlocking structure transmits external shear force to the fiber network through the stress dispersion mechanism, avoiding stress concentration that could lead to membrane rupture, thereby significantly improving the membrane's tear resistance under strong winds and reducing the possibility of the membrane being cut by the sharp edges of stones in the sand; (2) The three-dimensional network of poplar fluff fibers covers the large pores on the surface of sandy soil, forming a "filter barrier" with multi-level pores. Through the adsorption and retention of liquid by the fiber network, the infiltration of the mulch film emulsion is slowed down, thereby retaining more mulch film emulsion on the soil surface to form a film, improving the heat preservation and water retention performance of the liquid mulch film on sandy soil; (3) Through the entanglement and interlocking effect of poplar fluff fibers at the microscale, the movement of sand particles is restricted in space, improving the surface solidification effect of the mulch film on sandy soil and preventing soil erosion. The effective examples demonstrate that the present invention, through the rational application of poplar catkins, effectively reduces the production cost of liquid mulch film and optimizes the leveling properties of the mulch film emulsion, making it easier to form a film on sandy soil surfaces. This significantly enhances the heat preservation and water retention properties of the liquid mulch film for sandy soils. Simultaneously, it significantly improves the mechanical strength and water resistance of the starch-based liquid mulch film, thereby enhancing its resistance to wind and water erosion on sandy soil surfaces, providing strong support for the ecological protection of sandy soils. This invention not only improves the performance of starch-based liquid mulch film but also increases crop yields in sandy soils. This has dual positive benefits in the fields of agricultural production and ecological environment management, achieving the organic unity of waste resource utilization, product function optimization, and increased agricultural production and quality. It has broad application prospects and significant economic, social, and ecological value.

[0017] The working principle of this invention is analyzed as follows:

[0018] 1. Step (1) of this invention is to prepare maleic anhydride modified poplar fiber using poplar fiber and maleic anhydride as raw materials. The chemical composition of poplar fiber is mainly cellulose, hemicellulose and lignin; its surface is also attached with hydrophobic lipids and waxes, etc. These hydrophobic substances form a dense hydrophobic film on the surface of poplar fiber through physical adsorption or chemical bonding, which hinders water penetration and gives poplar fibers a light and airy property. In the hot alkaline environment of step (1), the sodium hydroxide solution mainly acts on the fiber structure through the following mechanisms: First, the alkaline solution undergoes a saponification reaction with the lignin on the fiber surface, destroying its phenolic bond network, and simultaneously promoting the hydrolysis of hemicellulose into oligosaccharides, thereby weakening the interfacial bonding force of the lignin-hemicellulose-cellulose complex, resulting in a swollen and loose outer layer structure of the poplar fiber; second, the heating conditions accelerate the diffusion rate of the alkaline solution into the fiber interior, causing the non-cellulose components (lignin, hemicellulose) wrapped on the cellulose surface to gradually peel off, exposing the hydroxyl (-OH) groups on the cellulose molecular chains; it is worth noting that the lipids and waxes on the fiber surface, due to their lack of alkaline hydrolysis activity (e.g., lack of ester bond structure), are not significantly removed under these process conditions, but the lignin skeleton on which they depend is destroyed, resulting in damage to the continuity of the hydrophobic film, thereby indirectly increasing the hydrophilicity of the poplar fiber surface. In this process, the precise control of the alkaline solution concentration, reaction temperature, and time is also crucial. From a chemical reaction kinetics perspective, the concentration of the alkali solution needs to be maintained within a specific range. If the concentration is too low, it is insufficient to effectively disrupt the lignin-hemicellulose network on the surface of the poplar fibers; if the concentration is too high, it may exceed the fiber surface modification threshold, causing the alkali solution to penetrate into the cellulose matrix structure at the center of the poplar fibers, thereby damaging the mechanical properties of the fibers. The control of reaction temperature and reaction time also needs to balance the efficiency of the poplar fiber surface modification with the preservation of the main structure of the poplar fibers. In short, ensuring that the alkali solution acts only on the surface layer of the poplar fibers without damaging the main fiber skeleton allows for surface functionalization through exposed hydroxyl groups while preserving the complete main structure and main mechanical strength of the fibers. This provides an ideal reinforcing phase with both interfacial activity and mechanical support properties for the subsequent preparation of poplar fiber-reinforced mulch films. Maleic anhydride is a cyclic molecule, also known as maleic anhydride. It can react with the exposed hydroxyl groups on the surface of poplar fibers through ring-opening, thereby grafting functional groups with carboxyl groups and carbon-carbon double bonds onto the surface of the poplar fibers, thus obtaining maleic anhydride-modified poplar fibers. Under the action of a catalyst, maleic anhydride-modified poplar fibers can undergo polymerization with acrylate monomers in subsequent steps. This allows the maleic anhydride-modified poplar fibers to be uniformly fused with the polyacrylate produced after polymerization at the molecular level, forming a copolymer with good compatibility and stable performance.

[0019] 2. Step (2) of this invention involves reacting the maleic anhydride-modified poplar fiber obtained in step (1) with starch in an acidic environment to generate poplar fiber-modified starch colloid. The reaction principle involved in step (2) is as follows: In step (1), the poplar fiber is modified with maleic anhydride, which introduces carboxyl groups (derived from the functional groups remaining after the esterification reaction between maleic anhydride and the hydroxyl groups on the surface of the poplar fiber) onto the surface of the poplar fiber. In the acidic environment of step (2), the carboxyl groups (-COOH) on the surface of the modified poplar fiber react with the hydroxyl groups (-OH) of the starch chain in H+. + Esterification occurs under catalysis, and the two form covalent bonds. However, the dropping rate of the sulfuric acid solution needs to be controlled to avoid local over-acidity in the reaction system, which would lead to reverse hydrolysis of the ester bonds (because excessive acidity will destroy the ester bonds). In step (2), sulfuric acid can also break glycosidic bonds as a catalyst, that is, the high-viscosity long-chain starch molecules undergo hydrolysis to generate low-viscosity short-chain starch molecules, which reduces the viscosity of the subsequently prepared mulch film emulsion and improves the sprayability of the mulch film emulsion. Although the polar functional groups (such as hydroxyl and carboxyl groups) in the modified poplar fiber can be connected to the hydroxyl groups of starch through simple hydrogen bonds, such simple hydrogen bonds are far less than the strong interfacial bonding force formed by the covalent bonds between the poplar fiber (reinforcing phase) and the starch matrix (continuous phase). This strong interfacial bonding force allows the poplar fiber to be uniformly dispersed at the molecular level in the starch-containing colloid prepared in step (2), and the hydrophilicity of starch also makes it easier for the poplar fiber modified starch to be dispersed in the aqueous mulch film emulsion, and it is not easy for phase separation problems to occur. The uniform distribution of poplar fibers in the film can endow the mulch film with stronger mechanical properties (such as tensile strength and toughness). In particular, the film made of starch modified with poplar fibers can overcome the common brittleness defects of starch-based films, which is beneficial to the practical application of starch-based liquid mulch films. In step (2), the esterification reaction between maleic anhydride modified poplar fibers and starch consumes the carboxyl groups of the modified poplar fibers. The double bonds on the modified poplar fibers do not participate in the reaction. Therefore, the double bonds on the starch modified with poplar fibers are still retained, which provides the conditions for the starch modified with poplar fibers to participate in the emulsion polymerization reaction in the subsequent steps.

[0020] 3. Steps (3) and (4) of this invention involve obtaining a pre-emulsion from a mixture of poplar fiber-modified starch, acrylate monomers, and water under the action of an emulsifier. The pre-emulsion then undergoes emulsion polymerization under the action of an initiator. When preparing the pre-emulsion, it is necessary to ensure its stability (no demulsification or stratification) and appropriate viscosity. Suitable emulsifier solution ratios, temperatures, and stirring conditions are prerequisites for forming a stable pre-emulsion. In the emulsion polymerization reaction, polymerization reactions occur between the double-bonded poplar fiber-modified starch and the acrylate monomers, as well as between different acrylate monomers. After polymerization, the acrylate monomers yield a polyacrylate fraction. Polyacrylate has excellent film-forming properties, allowing the obtained starch-based film emulsion to form a film on the soil surface. This film can seal the gaps between soil particles, thereby hindering the loss of heat and moisture from the soil, thus providing insulation and moisture retention for sandy soils. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof.

[0022] Figure 1 This is a process flow diagram for preparing a low-permeability liquid mulch film based on poplar fluff, according to the present invention. Detailed Implementation

[0023] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the embodiments. Unless otherwise specified, the chemical raw materials used in the following embodiments are all commercially available, chemically pure reagents, and the water used is deionized water.

[0024] The starch was obtained by drying and grinding waste rice from the student canteen of Nanjing Forestry University into powder smaller than 200 mesh. The purity of the starch was determined to be 80-83 wt% according to the acid hydrolysis method described in the National Food Safety Standard for Determination of Starch in Food (GB 5009.9-2023).

[0025] Butyl acrylate, methyl methacrylate, and acrylic acid, all with a purity of 99%, were purchased from Damao Chemical Reagent Co., Ltd. (Tianjin, China).

[0026] The 99% purity reactive emulsifier (model LRS-10) and the 99% purity octylphenol polyoxyethylene ether (10) (OP-10) were purchased from Nanjing Qicheng New Material Co., Ltd. (Jiangsu, China).

[0027] Potassium persulfate and ammonium persulfate with a purity of 99.5% were purchased from Lingfeng Chemical Reagent Co., Ltd. (Shanghai, China).

[0028] The soil described below is sandy soil, collected on May 10, 2023, in Shunhe Town, Huaian District, Huaian City, Jiangsu Province (119°19'E, 33°44'N). It contains 71% sand and gravel, 0.61% organic matter (as determined according to NY / T 1121.6-2006), has a pH of 7.2 (as determined according to NY / T 1121.2-2006), and a bulk density of 1.56 g / cm³. 3 (Measured according to NY / T 1121.4-2006).

[0029] Example 1

[0030] (1) Disperse poplar fibers in water, add maleic anhydride and stir continuously. While stirring, add sodium hydroxide solution with a concentration of 3wt% to adjust the pH of the mixture to 7. The mass ratio of poplar fibers, maleic anhydride and water is 1:0.8:8. Then heat the mixture to 70℃ and react at a stirring rate of 200r / min for 1h. After the reaction, filter the mixture and wash the filtrate repeatedly with water until the filtrate is neutral. Dry the filtrate at 60℃ for 15h to obtain modified poplar fibers.

[0031] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water in a mass ratio of 1:3:5 and stirred to form a uniform suspension. Then, under stirring at 50℃ and 150r / min, 30wt% sulfuric acid solution is added dropwise at a rate of 0.08mL / min until the pH of the system is stable at 2. Then the reaction is continued for 3h. After the reaction is completed, the mixture is filtered and the filtrate is repeatedly washed with water until the filtrate is neutral. The filtrate is dried at 50℃ until the water content is 10wt% to obtain the modified poplar fiber starch colloid.

[0032] (3) The poplar fiber modified starch colloid obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:0.05:0.3:2. The mixture is pre-emulsified for 0.5 h at 40℃ and 300 r / min mechanical stirring to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:1. The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:1.5:0.25.

[0033] (4) The poplar fiber-based pre-emulsion obtained in step (3) is heated to 70°C, and then a 7wt% ammonium persulfate aqueous solution is added dropwise at a rate of 0.05 mL / min as an initiator, with the amount controlled to be 0.5% of the total mass of the pre-emulsion. After the initiator is added, the pH of the system is adjusted to 6.8 using a 15wt% ammonia aqueous solution, and the reaction is maintained at a stirring rate of 200 r / min for 2 h. Then the reaction system is cooled to room temperature to obtain a poplar fiber-based low-permeability liquid mulch film emulsion.

[0034] Example 2

[0035] (1) Disperse poplar fibers in water, add maleic anhydride and stir continuously. While stirring, add sodium hydroxide solution with a concentration of 4wt% to adjust the pH of the mixture to 7.5. The mass ratio of poplar fibers, maleic anhydride and water is 1:0.9:9. Then heat the mixture to 75℃ and react at a stirring rate of 250r / min for 1.5h. After the reaction is completed, filter the mixture and wash the filtrate repeatedly with water until the filtrate is neutral. Dry the filtrate at 65℃ for 24h to obtain modified poplar fibers.

[0036] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water in a mass ratio of 1:4:7 and stirred to form a uniform suspension. Then, under stirring at 55℃ and 200r / min, 50wt% sulfuric acid solution is added dropwise at a rate of 0.12mL / min until the pH of the system stabilizes at 1.7. The reaction is continued for 2.5h. After the reaction is completed, the mixture is filtered and the filtrate is washed repeatedly with water until the filtrate is neutral. The filtrate is dried at 60℃ until the water content is 15wt% to obtain the modified starch colloid of poplar fiber.

[0037] (3) The modified starch colloid of poplar fiber obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:0.09:0.4:3. The mixture is pre-emulsified for 1 hour at 45℃ and 330r / min mechanical stirring to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:1.5. The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:2:0.3.

[0038] (4) The poplar fiber-based pre-emulsion obtained in step (3) is heated to 75°C, and then a 9 wt% potassium persulfate aqueous solution is added dropwise at a rate of 0.1 mL / min as an initiator, with the amount controlled to be 0.8% of the total mass of the pre-emulsion. After the initiator is added, the pH of the system is adjusted to 7.2 using an 18 wt% ammonia aqueous solution, and the reaction is maintained at a stirring rate of 250 r / min for 3 h. Then the reaction system is cooled to room temperature to obtain a poplar fiber-based low-permeability liquid mulch film emulsion.

[0039] Example 3

[0040] (1) First, disperse poplar fibers in water, then add maleic anhydride and stir continuously. While stirring, add sodium hydroxide solution with a concentration of 6wt% to adjust the pH of the mixture to 8. The mass ratio of poplar fibers, maleic anhydride and water is 1:1.0:10. Then heat the mixture to 80℃ and react at a stirring rate of 300r / min for 2h. After the reaction, filter the mixture and wash the filtrate repeatedly with water until the filtrate is neutral. Dry the filtrate at 70℃ for 30h to obtain modified poplar fibers.

[0041] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water in a mass ratio of 1:5:8 and stirred to form a uniform suspension. Then, under stirring at 60℃ and 250r / min, 65wt% sulfuric acid solution is added dropwise at a rate of 0.15mL / min until the pH of the system is stable at 1.3. The reaction is continued for 2h. After the reaction is completed, the mixture is filtered and the filtrate is washed repeatedly with water until the filtrate is neutral. The filtrate is dried at 65℃ until the water content is 18wt% to obtain the modified starch colloid of poplar fiber.

[0042] (3) The poplar fiber modified starch colloid obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:0.1:0.45:4. The mixture is pre-emulsified for 1.3h at 50℃ and 350r / min mechanical stirring to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:2. The reactive emulsifier is model LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:2.3:0.35.

[0043] (4) The poplar fiber-based pre-emulsion obtained in step (3) is heated to 80°C, and then a 10wt% potassium persulfate aqueous solution is added dropwise at a rate of 0.13 mL / min as an initiator, with the amount controlled to be 1% of the total mass of the pre-emulsion. After the initiator is added, the pH of the system is adjusted to 7.5 using a 20wt% ammonia aqueous solution, and the reaction is maintained at a stirring rate of 300 r / min for 4 h. Then the reaction system is cooled to room temperature to obtain a poplar fiber-based low-permeability liquid mulch film emulsion.

[0044] Example 4

[0045] (1) First, disperse poplar fibers in water, then add maleic anhydride and stir continuously. While stirring, add sodium hydroxide solution with a concentration of 7wt% to adjust the pH of the mixture to 9. The mass ratio of poplar fibers, maleic anhydride and water is 1:1.1:11. Then heat the mixture to 83℃ and react at a stirring rate of 350r / min for 2.5h. After the reaction, filter the mixture and wash the filtrate repeatedly with water until the filtrate is neutral. Dry the filtrate at 75℃ for 42h to obtain modified poplar fibers.

[0046] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water in a mass ratio of 1:6:9 and stirred to form a uniform suspension. Then, under stirring at 65℃ and 300r / min, 80wt% sulfuric acid solution is added dropwise at a rate of 0.18mL / min until the pH of the system is stable at 1. Then the reaction is continued for 1.5h. After the reaction is completed, the mixture is filtered and the filtrate is repeatedly washed with water until the filtrate is neutral. The filtrate is dried at 75℃ until the water content is 22wt% to obtain the modified poplar fiber starch colloid.

[0047] (3) The poplar fiber modified starch colloid obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:0.13:0.5:4.5. The mixture is pre-emulsified for 1.7h at 53℃ and 380r / min mechanical stirring to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:2.5. The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:2.7:0.45.

[0048] (4) The poplar fiber-based pre-emulsion obtained in step (3) is heated to 85°C, and then a 12wt% ammonium persulfate aqueous solution is added dropwise at a rate of 0.17 mL / min as an initiator, with the amount controlled to be 1.3% of the total mass of the pre-emulsion. After the initiator is added, the pH of the system is adjusted to 8 using a 23wt% ammonia aqueous solution, and the reaction is maintained at a stirring rate of 350 r / min for 5 h. Then the reaction system is cooled to room temperature to obtain a poplar fiber-based low-permeability liquid mulch film emulsion.

[0049] Example 5

[0050] (1) First, disperse poplar fibers in water, then add maleic anhydride and stir continuously. While stirring, add sodium hydroxide solution with a concentration of 8wt% to adjust the pH of the mixture to 10. The mass ratio of poplar fibers, maleic anhydride and water is 1:1.2:12. Then heat the mixture to 85℃ and react at a stirring rate of 400r / min for 3h. After the reaction, filter the mixture and wash the filtrate repeatedly with water until the filtrate is neutral. Dry the filtrate at 80℃ for 48h to obtain modified poplar fibers.

[0051] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water in a mass ratio of 1:8:10 and stirred to form a uniform suspension. Then, under stirring at 70℃ and 350r / min, 98wt% sulfuric acid solution is added dropwise at a rate of 0.2mL / min until the pH of the system is stable at 0.5. The reaction is continued for 1h. After the reaction is completed, the mixture is filtered and the filtrate is washed repeatedly with water until the filtrate is neutral. The filtrate is dried at 80℃ until the water content is 25wt% to obtain the modified starch colloid of poplar fiber.

[0052] (3) The poplar fiber modified starch colloid obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:0.15:0.6:5. The mixture is pre-emulsified for 2 hours at 55℃ and 400r / min mechanical stirring to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:3. The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:3:0.5.

[0053] (4) The poplar fiber-based pre-emulsion obtained in step (3) is heated to 90°C, and then a 13wt% potassium persulfate aqueous solution is added dropwise at a rate of 0.2 mL / min as an initiator, with the amount controlled to be 1.5% of the total mass of the pre-emulsion. After the initiator is added, the pH of the system is adjusted to 8.2 using a 25wt% ammonia aqueous solution, and the reaction is maintained at a stirring rate of 400 r / min for 6 h. Then the reaction system is cooled to room temperature to obtain a poplar fiber-based low-permeability liquid mulch film emulsion.

[0054] Comparative Example 6

[0055] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that poplar fiber is not used in this embodiment; the other preparation steps and reagent dosages are the same as in Example 3. The specific experimental steps are as follows:

[0056] (1) Mix starch and water at a mass ratio of 5:8 and stir to form a uniform suspension. Then, under mechanical stirring at 60℃ and 250r / min, add 65wt% sulfuric acid solution dropwise at a rate of 0.15mL / min until the pH of the system stabilizes at 1.3. Then continue the reaction for 2h. After the reaction is completed, the mixture is filtered and the filtrate is washed repeatedly with water until the filtrate is neutral. The filtrate is dried at 65℃ until the water content is 18wt% to obtain starch colloid.

[0057] Then, the colloid obtained in step (1) was used to replace the poplar fiber modified starch colloid in Example (3), and a pre-emulsion was prepared in the same manner as step (3) of Example (3); the pre-emulsion was used to replace the poplar fiber-based pre-emulsion in Example (3), and an emulsion sample was prepared in the same manner as step (4) of Example (3).

[0058] Comparative Example 7

[0059] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that in step (1) of this embodiment, sodium hydroxide solution is used to adjust the pH of the mixture to 11. This pH is higher than the range of 7-10 described in the claims of this invention, meaning that the amount of sodium hydroxide solution used is larger than in Example 7. The other preparation steps and reagent amounts are the same as in Example 3.

[0060] Comparative Example 8

[0061] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that in step (1) of this embodiment, sodium hydroxide solution is used to adjust the pH of the mixture to 6. This pH is lower than the range of 7-10 described in the claims of this invention, that is, the amount of sodium hydroxide solution used is smaller than in Comparative Example 8. The other preparation steps and reagent amounts are the same as in Example 3.

[0062] Comparative Example 9

[0063] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that this embodiment does not prepare poplar fiber-modified starch colloid, but instead uses modified poplar fiber and starch directly to prepare a pre-emulsion. The other preparation steps and reagent dosages are the same as in Example 3. The specific experimental steps are as follows:

[0064] Step (1) in this embodiment is the same as step (1) in embodiment (3).

[0065] (2) The modified poplar fiber, starch, composite emulsifier, acrylate monomer and water obtained in step (1) are mixed in a mass ratio of 0.17:0.83:0.1:0.45:4. The mixture is pre-emulsified at 50℃ and 350r / min for 1.3h to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:2. The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:2.3:0.35.

[0066] Then, the pre-emulsion obtained in step (2) was used to replace the poplar fiber-based pre-emulsion in Example (3), and an emulsion sample was prepared in the same manner as step (4) of Example (3).

[0067] Comparative Example 10

[0068] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that sulfuric acid solution is not used in step (2) of this embodiment. The specific experimental steps are as follows:

[0069] Step (1) in this embodiment is the same as step (1) in embodiment (3).

[0070] (2) The modified poplar fiber obtained in step (1) is mixed with starch and water in a mass ratio of 1:5:8 and stirred to form a uniform suspension. Then, the mixture is continuously reacted at 60℃ and 250r / min for 2 hours. After the reaction is completed, the mixture is filtered and the filtrate is repeatedly washed with water until the filtrate is neutral. The filtrate is dried at 65℃ until the water content is 18wt% to obtain the colloid.

[0071] Then, the colloid obtained in step (2) was used to replace the poplar fiber modified starch colloid in Example (3), and an emulsion sample was prepared according to the same steps (3) and (4) as in Example (3).

[0072] Comparative Example 11

[0073] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that the water content of the poplar fiber modified starch colloid prepared in step (3) of this embodiment is 5 wt%, which is lower than the range of 10-25 wt% described in the claims of this invention. That is, the water content of the poplar fiber modified starch colloid in Comparative Example 11 is smaller. The other preparation steps and reagent dosages are the same as in Example 3.

[0074] Comparative Example 12

[0075] This embodiment prepares the sample according to the steps described in Example 3. The difference from Example 3 is that this embodiment does not use starch to modify poplar fibers, nor does it prepare poplar fiber-modified starch colloid. Instead, it directly uses poplar fibers to prepare a poplar-based pre-emulsion and carries out subsequent reactions. The specific experimental steps are as follows:

[0076] Step (1) in this embodiment is the same as step (1) in embodiment (3).

[0077] (2) The modified poplar fiber obtained in step (1) is mixed with composite emulsifier, acrylate monomer and water in a mass ratio of 1:0.1:0.45:4. The mixture is pre-emulsified at 50℃ and 350r / min mechanical stirring for 1.3h to obtain poplar fiber-based pre-emulsion. The composite emulsifier is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:2. The reactive emulsifier is LRS-10. The acrylate monomer is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:2.3:0.35.

[0078] The other preparation steps and reagent dosages are the same as in Example 3.

[0079] Effect Example

[0080] In this embodiment, the performance of the poplar fluff-based low-permeability liquid mulch emulsions prepared in Examples 1-5 and the samples prepared in Comparative Examples 6-12 were tested as follows.

[0081] 1. Emulsion stability test

[0082] To observe whether the sample will separate into layers within 30 days, the test details are as follows: Take the emulsion sample to be tested, stir well, and then dispense it into three 50mL stoppered glass centrifuge tubes (30mL per tube, ensuring consistent liquid levels). Seal the tubes and label the sample information. Store the tubes statically at 25±2℃ in the dark for 30 days. Observe the sample daily during storage and record whether layering occurs (layering criteria: a clear upper layer or a sedimentary lower layer thickness ≥2mm is considered layering). Perform three parallel experiments (from the same batch of samples). If no layering occurs in any of the three parallel experiments, the sample is considered stable and can proceed to subsequent tests; if layering occurs in any parallel experiment, the sample is considered unstable and unsuitable for use as a liquid mulch film emulsion, and will not proceed to subsequent tests.

[0083] 2. Wicking Experiment Test

[0084] Accurately weigh 20g of sandy soil and place it into a glass centrifuge tube with a diameter of 20mm and a height of 50mm. Gently tap the tube wall to allow the sand to settle naturally to a uniform height (approximately 30mm). After thoroughly mixing the emulsion, slowly add 3mL of emulsion dropwise along the inner wall of the centrifuge tube using a pipette (dropping rate 0.5mL / min). Start timing immediately after the addition is complete and allow the emulsion to stand for 30 minutes to allow for full penetration. Use a vernier caliper (accuracy 0.02mm) to measure the vertical penetration depth of the emulsion in the soil (the distance from the soil surface to the emulsion penetration front). Set up three parallel experiments for each sample (from the same batch of samples). If the relative standard deviation (RSD) of the three measurements is ≤10%, the average value is taken as the wicking value. If the RSD is >10%, three parallel experiments need to be repeated. After removing outliers (values ​​deviating from the average value ±20%), the average value of the remaining values ​​is taken. The higher the wicking value of the emulsion, the stronger its permeability into the soil.

[0085] 3. Hydrophobicity test

[0086] The emulsion was poured into a 5cm diameter polytetrafluoroethylene mold and air-dried for 72 hours at 25±2℃ and 50±5% relative humidity to prepare a uniform membrane sample with a thickness of 0.1±0.02mm. When sampling, the edge area was avoided within 1cm to ensure the membrane was flat and defect-free. Using a contact angle meter (DSA 100, KRUSS, Germany), at 25℃ and 50%RH, 1μL of deionized water was slowly deposited onto the membrane surface using a microsyringe (three evenly distributed test points were selected for each sample, avoiding wrinkles or impurities). After the water droplet stabilized for 30 seconds, the contact angle was measured. Each test point was measured twice, and the average value was taken. Three independent membrane samples were prepared for each sample, and the average value of the data was taken as the final contact angle result to evaluate the hydrophobicity of the membrane surface.

[0087] 4. Water resistance test

[0088] Pour the emulsion into a 25mm×25mm×1mm polytetrafluoroethylene mold and air-dry it naturally at 25±2℃ and 50±5% relative humidity for 72 hours to prepare a film sample. Confirm the thickness as 1±0.1mm using calipers. Select samples without bubbles or cracks and weigh them, recording the weight as m1 (accurate to 0.0001g). Completely immerse the sample in a beaker containing 25℃ deionized water (liquid level 1cm above the sample, static soaking, changing the deionized water every 24 hours). After 48 hours, remove the sample and gently press the surface with pre-weighed absorbent paper until no visible water droplets remain (avoid rubbing the sample). Immediately weigh the sample and record the weight as m2. Then, place the sample in an 80±2℃ oven to dry, weighing it every 2 hours until the difference between two consecutive weighings is ≤0.0001g, recording this weight as m3. The swelling ratio is calculated using formula (1), and the solubility ratio is calculated using formula (2). Three different batches of each sample are tested (three parallel samples per batch), and the average value of the data is taken as the final result.

[0089] Swelling ratio (%) = [(m2-m1) / m1] × 100% (1)

[0090] Solubility ratio (%) = [(m1-m3) / m1] × 100% (2)

[0091] 5. Mechanical property testing

[0092] The emulsion was naturally air-dried at 25±2℃ and 50±5% relative humidity for 72 hours to prepare a film. Samples 50mm long and 10mm wide were cut using a cutter. The thickness was measured at three points in the middle of the sample using a micrometer (accuracy 0.001mm) to ensure a thickness of 1±0.1mm and a deviation ≤0.05mm. Using a CMT-4204 electronic universal testing machine (Sansi Yongheng Technology (Zhejiang) Co., Ltd., Ningbo), according to GB / T 1040.2-2022 standard, the sample was clamped in a pneumatic fixture (clamping distance 30mm, clamping force 0.5MPa) and stretched at a speed of 20mm / min until fracture. The breaking strength and elongation at break were recorded. Three different batches (three parallel samples per batch) were tested for each sample, and the average value was taken as the final result.

[0093] 6. Wind erosion resistance test

[0094] Take a petri dish with a diameter of 90mm and a height of 15mm, fill it with 120g of sand, and use a 30mm diameter cylindrical mold to help build up a standard sand cone with a height of 20mm and a cone angle of 60°. Gently remove the mold. Use a spray bottle (Zhejiang Taizhou Minzhong Plastic Products Technology Co., Ltd., HC-K06 type, fan-shaped nozzle orifice diameter 1.1mm, PP material nozzle) at a spraying rate of 0.62kg / m³. -2The emulsion was sprayed onto the surface of the sand cone and air-dried for 24 hours at 25±2℃ and 50±5% relative humidity until a film formed. A self-made wind erosion device (100mm diameter outlet with a filter for uniform airflow) was used. The outlet was positioned 50cm vertically from the top of the sand cone, with the wind direction parallel to the bottom of the petri dish. The wind speed was adjusted to 16±0.5m / s. A ring-shaped dust collection device (50cm high) was placed within a 30cm radius around the sand cone, and wind erosion was continued for 30 minutes. The initial mass of the sand cone (M0) was measured before the test, and the remaining sand in the petri dish (Md) was measured after the test. The mass loss rate was calculated using the formula: Mass Loss Rate

[0095] = (M0-Md) / M0×100%, where M0 is the initial mass of the sand and Md is the remaining mass of the sand. Three different batches (three parallel sand cones per batch) were tested for each sample, and the average value of the data was taken as the final result.

[0096] 7. Soil temperature and humidity test

[0097] After drying the sand at 105℃ to constant weight, deionized water is precisely added to adjust the moisture content to 24±1wt%. The sand is then filled into flowerpots (4kg per pot, gently tapped to allow the soil to settle naturally, ensuring consistent compaction). The flowerpots are placed outdoors in the same open area (unobstructed, with consistent lighting conditions), spaced at least 30cm apart, and their positions are marked before spraying the emulsion. (0.62kg m) -2 After applying the emulsion, allow it to stand for 24 hours to allow the film to stabilize. Use a DL-TWS211 soil moisture / temperature recorder (probe buried 10cm, pre-calibrated) to measure temperature and humidity every two days, recording data from 15:00 to 15:30 each day. Temperature and humidity tests were conducted simultaneously using the same measurement frequency and time period, with the testing period from March 1st to April 1st, 2024 (ensuring consistent climatic background for all samples). Statistical method: Three parallel flowerpots were set up for each sample (i.e., "three tests"), and the average of the temperature and humidity from the three parallel flowerpots was taken as the final result.

[0098] 8. Planting Experiment

[0099] The experiment was conducted from March 15 to April 15, 2024, in an artificial greenhouse at Nanjing Forestry University (24±2℃ / 20±2℃, relative humidity (RH) 75±5%, photoperiod 12h, photosynthetically active radiation (PAR) 350±20 μmol m²). - 2s -1. The experiment was conducted within a CO2 concentration of 400±20ppm. Six treatments were included: bare sand, Example 1, Example 3, Example 5, Comparative Example 6, and Comparative Example 7. A completely randomized block design was used, with 6 replicates per treatment, for a total of 36 treatments. Each treatment had a pot size of 75cm × 40cm × 20cm and contained 20kg of sand. Liquid mulch was applied at a rate of 0.62kg / m³. - 2. Spray evenly with an equal amount of deionized water onto bare sandy soil, cover with film, and let stand for 1 day. Select 'Suzhou Qing' bok choy seedlings with a plant height of 6±0.5cm and a fresh weight of 10g±0.5g. Disinfect the roots with 5% NaClO for 1 min, rinse with clean water, and transplant 5 seedlings per pot with a spacing of 12cm. On the day of transplanting, water each pot with deionized water to the soil moisture holding capacity (25% dry soil weight). Thereafter, weigh and replenish the water every 3 days to the same amount. Do not apply fertilizer or pesticides during the entire growth period. Harvest once on the 30th day, and weigh the whole plant (root + above-ground parts) in each pot using an electronic balance. All data were analyzed using a model with fixed effects and random effects for the block design. One-way ANOVA and Duncan's multiple comparisons were performed using SPSS 27.0 (P<0.05). Outliers deviating from the mean ± 3 standard deviations were removed before statistical analysis.

[0100] 9. As can be seen from Table 1, the emulsions prepared in Examples 1-5 did not exhibit stratification within 30 days, indicating that the emulsions prepared in Examples 1-5 are stable. Furthermore, the emulsions prepared in Comparative Examples 6 and 7 also did not exhibit stratification, indicating that the emulsions prepared in these examples are also stable. The liquid sample prepared in Comparative Example 8 exhibited stratification on day 8, indicating that the sample was unstable. This is because in step (1) of Comparative Example 8, sodium hydroxide solution was used to adjust the pH of the mixture to 6, which is lower than the range of 7-10 described in the claims of this invention, meaning that the amount of sodium hydroxide solution used in Comparative Example 8 was too small. Sodium hydroxide solution primarily weakens the interfacial bonding force of the lignin-hemicellulose-cellulose complex on the surface of poplar fibers, causing the outer layer of the fiber to swell and loosen. Then, under heating conditions, the alkali solution diffuses into the fiber interior, causing the non-cellulose components (lignin and hemicellulose) wrapped on the cellulose surface to gradually peel off, exposing the hydroxyl (-OH) groups on the cellulose molecular chains. Maleic anhydride then reacts with the exposed hydroxyl groups on the surface of the poplar fibers through ring opening, thereby grafting functional groups such as carboxyl groups and carbon-carbon double bonds onto the surface of the poplar fibers, thus obtaining maleic anhydride-modified poplar fibers. Under the action of a catalyst, maleic anhydride-modified poplar fibers with carbon-carbon double bonds can undergo polymerization with acrylate monomers. This allows the modified poplar fibers to be uniformly fused with polyacrylate, forming a copolymer with good compatibility and stable performance. However, because the amount of sodium hydroxide solution used in Comparative Example 8 was too small, there were too few hydroxyl (-OH) groups on the exposed cellulose molecular chains on the surface of the poplar fibers. Consequently, there were also too few carboxyl groups and carbon-carbon double bond functional groups grafted onto the surface of the poplar fibers. This further resulted in the poplar fibers not being able to effectively and uniformly fuse with the polyacrylate produced after polymerization through covalent bonds during the polymerization reaction. In other words, the compatibility of the components was poor and the interfacial bonding was weak, leading to poor stability and easy phase separation of the emulsion in Comparative Example 8, resulting in demulsification.

[0101] The liquid sample prepared in Comparative Example 9 showed stratification on day 1, indicating that the sample was very unstable. This is because in Comparative Example 9, modified poplar fiber starch was not prepared; instead, modified poplar fiber and starch were directly used to prepare the pre-emulsion. In this invention, the molecular structure of modified poplar fiber starch is connected to the surface of poplar fiber and starch molecular chains by covalent bonds. Although maleic anhydride modified poplar fiber and starch can be connected by simple hydrogen bonds between polar functional groups (such as hydroxyl and carboxyl groups, hydroxyl and hydroxyl groups), such simple hydrogen bonds are far less strong than the interfacial bonding force formed by covalent bonds between poplar fiber (reinforcing phase) and starch matrix (continuous phase). This strong interfacial bonding force allows the poplar fiber to be uniformly dispersed at the micron level in the starch-containing colloid prepared in step (2). At the same time, the hydrophilicity of starch also makes it easier for modified poplar fiber starch to be dispersed in aqueous mulch film emulsions, and phase separation is less likely to occur. Because poplar fiber-modified starch was not prepared in Comparative Example 9, the poplar fiber was difficult to disperse evenly in the aqueous mulch film emulsion, resulting in stratification and demulsification.

[0102] The liquid sample prepared in Comparative Example 10 exhibited stratification on day 1, indicating its instability. This is because H2SO4 solution was not used in step (2) of Comparative Example 10 to prepare the modified starch from poplar fibers. H2SO4 solution provides an acidic environment, allowing the carboxyl groups (-COOH) on the surface of the modified poplar fibers to react with the hydroxyl groups (-OH) of the starch chains. + An esterification reaction occurs under catalysis, and the two form a covalent bond. Because H2SO4 solution is not used in Comparative Example 10, the esterification reaction efficiency between the carboxyl groups (-COOH) on the surface of the modified poplar fiber and the hydroxyl groups (-OH) of the starch chain is low, resulting in weak interfacial bonding between the poplar fiber and the starch matrix. This leads to the inability of the poplar fiber to be uniformly dispersed in the starch-containing colloid prepared in step (2), which in turn makes it difficult to be uniformly dispersed in the aqueous mulch film emulsion, easily causing phase separation problems and resulting in demulsification.

[0103] The liquid samples prepared in Comparative Examples 11 and 12 showed stratification on day 1 and day 2, respectively, indicating that these two samples were unstable. This is because the water content of the poplar fiber modified starch colloid prepared in step (3) of Comparative Example 11 was 5 wt%, which is lower than the range of 10-25 wt% described in the claims of this invention. In other words, the water content of the poplar fiber modified starch colloid in Comparative Example 11 was too low. The poplar fiber modified starch colloid prepared in this invention contains water, and the water in the colloid helps the colloid disperse in the aqueous reaction system. If the water content in the colloid is too low, the hydroxyl groups between the starch molecular chains will generate ether bonds and high-density hydrogen bonds, which makes the starch highly cross-linked. The highly cross-linked starch colloid has poor water solubility, making it difficult to disperse the colloid in the aqueous system of subsequent steps. Consequently, the poplar fibers in the colloid are difficult to disperse evenly in the emulsion system, which easily leads to stratification and demulsification. Similarly, in Comparative Example 12, the poplar fibers were not modified by esterification with starch and were directly used to prepare the pre-emulsion, thus lacking the encapsulation and dispersion effect of the starch matrix on the poplar fibers. The poplar fiber-modified starch colloid of the present invention connects the poplar fibers and starch through covalent bonds to form a stable composite system. The hydrophilicity of starch can effectively improve the compatibility of poplar fibers in the aqueous system. In contrast, Comparative Example 12 directly used modified poplar fibers, and the fiber surface lacked uniform coverage of starch molecules. The hydrophobic regions were prone to aggregate to form flocs, which resulted in uneven dispersion during pre-emulsification and polymerization, thereby destroying the stability of the emulsion system and causing demulsification. The liquid samples prepared in Comparative Examples 8-12 were prone to demulsification and stratification. This uneven system caused by component separation easily leads to nozzle blockage due to particle agglomeration during spraying, causing construction interruptions. More importantly, the unbalanced distribution of film-forming components after stratification prevents the formation of a continuous and uniform film layer after spraying onto the soil surface. This results in defects such as incomplete coating and uneven thickness, or even the loss of effective film-forming substances leaving only ineffective components on the soil surface, completely negating the film's ability to seal soil pores. Consequently, the film's thermal barrier and moisture-locking functions fail, failing to reduce the loss of soil heat and moisture to the atmosphere. Ultimately, the heat and water retention capacity of sandy soil is not significantly different from that of bare soil without film, failing to achieve the intended agricultural application value of liquid mulch. Therefore, the liquid samples prepared in Comparative Examples 8-12 are prone to demulsification and stratification and do not need to proceed to the subsequent testing stage.

[0104] As shown in Table 2, the liquid mulch films prepared in Examples 1, 3, and 5 possess the following performance indicators: These mulch film emulsions all exhibit good sprayability, with a wicking value of 0.51-0.55 cm; the contact angle of the film formed by the emulsion is 84-89°; the swelling ratio of the film in the water resistance test is 101-109%, the solubility ratio is 12.2-13.1%, the tensile strength is 1.25-1.33 MPa, and the elongation at break is 153-162%. In the wind erosion resistance test, the soil mass loss rate of these three examples is only 1.13-1.21%, which is about 90% lower than the 13.12% of bare soil, demonstrating excellent wind erosion resistance. In soil temperature and humidity experiments, the liquid mulch films of these three embodiments maintained an average soil temperature of 18.8-20.3℃, which was 4.6-6.1℃ higher than that of bare soil; the average soil moisture content reached 19.4-21.7%, which was 9.8-12.1% higher than that of bare sandy soil (9.6%). These data indicate that the low-permeability liquid mulch film emulsion prepared in this invention forms an effective protective layer on the surface of sandy soil, significantly inhibiting the migration of soil particles under wind action, while effectively reducing the loss of soil moisture and heat, thus playing a significant role in soil conservation, heat preservation, and water retention in sandy soil. Wind erosion easily leads to topsoil loss and root exposure, and suitable soil temperature and humidity are key to crop growth. The three-dimensional network structure of poplar fiber not only reduces topsoil loss and root exposure, but also optimizes crop root development by maintaining a stable temperature and humidity environment, thereby significantly increasing yield. Therefore, in the planting experiment, the yield of Chinese cabbage with liquid mulch applied in Examples 1, 3, and 5 (165-170g) was 106-113% higher than that with bare soil (80g), which fully demonstrates the practical application value of the liquid mulch in agricultural production.

[0105] Compared with the liquid mulches prepared in Examples 1, 3, and 5, the wicking value of the emulsion prepared in Comparative Example 6 was 1.15-1.19 cm higher, the contact angle of the resulting film was 48-53° lower, the swelling ratio was 71-79% higher, and the solubility ratio was 6.3-7.2% higher (the higher swelling and solubility ratios indicate enhanced hydrophilicity of the film layer, making it easier for water to penetrate and leading to functional failure). The tensile strength was 0.44-0.52 MPa lower, and the elongation at break was 21-30% lower. In the wind erosion resistance test, the soil mass loss rate of Comparative Example 6 was as high as 9.13%, which is 7.5-8.1 times that of Examples 1, 3, and 5. Furthermore, the average soil temperature of Comparative Example 6 was 3.7-5.2°C lower, the moisture content was 6.2-8.5% lower, and the yield of pakchoi was 60-65 g lower. This is because Comparative Example 6 did not use poplar fibers in its preparation process, resulting in the absence of a three-dimensional network filtration barrier constructed by poplar fibers in the emulsion of Comparative Example 6. Consequently, the infiltration of the emulsion of Comparative Example 6 on the sandy soil surface was aggravated (i.e., the wicking value increased). Also, due to the lack of stress dispersion mechanism from poplar fibers, the mechanical properties (tensile strength and elongation at break) of the membrane of Comparative Example 6 deteriorated. Because poplar fibers also contain hydrophobic lipids and waxes, these lipid-soluble components are dissolved from the poplar fibers by acrylate monomers as organic solvents in step (3) of this invention and are uniformly distributed in the mulch film emulsion prepared by this invention. When the mulch film emulsion of this invention forms a film on the soil surface, these hydrophobic components exist on the surface of the mulch film, improving the hydrophobicity and water resistance of the mulch film, resulting in an increased contact angle and a low swelling rate of the mulch film of this invention. However, Comparative Example 6 did not use poplar fibers, so the hydrophobicity and water resistance of the film formed in Comparative Example 6 were weak, resulting in a smaller contact angle, a high swelling rate, and a high solubility ratio of the membrane of Comparative Example 6. Because the wicking value of Comparative Example 6 is higher, meaning that more of the emulsion from Comparative Example 6 seeped into the soil below through the soil pores on the sandy soil surface, less emulsion remained on the soil surface to form a film. Therefore, the film layer formed on the sandy soil surface was insufficient in thickness and had poor uniformity (at the same application rate of 0.62 kg / m³). - 2. The film thickness of Examples 1-5 is 0.15-0.23mm, while the film thickness of Comparative Examples 6 and 7 is 0.04mm and 0.047mm respectively. That is, the heat preservation and water retention of the film in Comparative Example 6 is weak, which also results in a lower yield of bok choy in this example.

[0106] The difference between Comparative Example 7 and Examples 1, 3, and 5 lies in step (1) using sodium hydroxide solution to adjust the pH of the mixture to 11, which is higher than the range of 7-10 described in the claims of this invention. That is, the amount of sodium hydroxide solution used in Comparative Example 7 is larger (compared to Example 3), resulting in the following differences in the performance of the sample of Comparative Example 7: (1) The wicking value is 0.95-0.99 cm higher. This is because the strong alkaline environment of Comparative Example 7 exceeds the fiber surface modification threshold, erodes the cellulose skeleton inside the fiber, resulting in the loss of the integrity of the three-dimensional network structure, weakening its ability to retain the emulsion and its stress dispersion function, and causing the emulsion to intensify its infiltration into the sandy soil; (2) The contact angle is 5-10° lower. This is because the high concentration of alkaline solution excessively strips the hydrophobic lipids and waxes on the fiber surface, resulting in the exposure of the hydrophilic area on the membrane surface, which in turn reduces the hydrophobicity of the membrane layer; (3) The soil mass loss rate was 6.65%, which is 5.5-5.9 times that of Examples 1, 3, and 5; (4) The swelling ratio was 7-15% higher and the solubility ratio was 3.2-4.1% higher. This is because the water resistance of the membrane layer was reduced and the soluble components were more easily lost; (5) The breaking strength was 0.34-0.42 MPa lower and the breaking elongation was 10-19% lower. This is because the main fiber structure was damaged by excessive alkali erosion, resulting in deterioration of mechanical properties; (6) The average soil temperature was 2.6-4.1℃ lower and the water content was 4.1-6.4% lower. This is because the fiber network damage directly weakened the filtration barrier effect, aggravated the emulsion infiltration (increased wicking value), resulting in insufficient film thickness on the ground surface, and the heat preservation and water retention function of the membrane layer was weakened due to structural defects; (7) The yield of Chinese cabbage was 55-60g lower. This is because the soil temperature and humidity were insufficient and the protective function of the membrane layer was reduced, which restricted crop growth.

[0107] Table 1. Comparison of emulsion stability among the various examples (assessed by stratification phenomenon).

[0108] Table 2 shows the performance of the emulsions prepared in Examples 1, 3, and 5, and the liquids prepared in Comparative Examples 6 and 7, as well as the film-forming properties and the yield of Chinese cabbage in planting experiments. In the table, "-" indicates that the sample did not undergo the corresponding test, and bare soil indicates sandy soil that was not sprayed with any of the example samples.

[0109]

Claims

1. A method for preparing a low-permeability liquid mulch film emulsion based on poplar fluff, characterized in that, Includes the following steps: (1) Disperse poplar fibers in water, add maleic anhydride and stir continuously, while adding sodium hydroxide solution dropwise to adjust the pH of the mixture to 7-10, heat the mixture to 70-85℃ and react at a stirring rate of 200-400r / min for 1-3h, filter after the reaction, wash the filtrate with water until the filtrate is neutral, and dry to obtain modified poplar fibers; (2) The modified poplar fiber obtained in step (1) is mixed with starch and water at a mass ratio of 1:(3-8):(5-10) to form a suspension. Under stirring at 50-70℃ and 150-350r / min, sulfuric acid solution is added dropwise at a rate of 0.08-0.2mL / min until the pH of the system is stable at 0.5-2. The reaction is continued for 1-3h. After the reaction is completed, the mixture is filtered, and the filtrate is washed until the filtrate is neutral. The filtrate is dried until the water content is 10-25wt% to obtain poplar fiber modified starch colloid. (3) The modified starch colloid of poplar fiber obtained in step (2) is mixed with composite emulsifier, acrylate monomer and water at a mass ratio of 1:(0.05-0.15):(0.3-0.6):(2-5) and pre-emulsified at 40-55℃ and 300-400r / min for 0.5-2h to obtain poplar fiber-based pre-emulsion; (4) Heat the poplar fiber-based pre-emulsion obtained in step (3) to 70-90℃, and add an initiator aqueous solution dropwise at a rate of 0.05-0.2 mL / min as the initiator. The amount of initiator is 0.5-1.5% of the total mass of the pre-emulsion. After the addition is complete, adjust the pH of the system to 6.8-8.2 with ammonia water, react for 2-6 hours with stirring at 200-400 r / min, and cool to room temperature to obtain the poplar fiber-based low-permeability liquid mulch emulsion.

2. The preparation method according to claim 1, characterized in that, The concentration of the sodium hydroxide solution in step (1) is 3-8 wt%, the mass ratio of poplar fiber, maleic anhydride and water is 1:(0.8-1.2):(8-12), the drying temperature of the filter is 60-80℃, and the drying time is 15-48h.

3. The preparation method according to claim 1, characterized in that, The concentration of the sulfuric acid solution in step (2) is 30-98 wt%.

4. The preparation method according to claim 1, characterized in that, The drying temperature of the filtered material in step (2) is 50-80℃.

5. The preparation method according to claim 1, characterized in that, The composite emulsifier mentioned in step (3) is a mixture of reactive emulsifier and octylphenol polyoxyethylene ether (10) in a mass ratio of 1:(1-3). The reactive emulsifier is model LRS-10. The acrylate monomer mentioned in step (3) is composed of methyl methacrylate, butyl acrylate and acrylic acid in a mass ratio of 1:(1.5-3):(0.25-0.5).

6. The preparation method according to claim 1, characterized in that, The initiator solution in step (4) is an aqueous solution of potassium persulfate or ammonium persulfate, with a concentration of 7-13 wt% and a dosage of 0.5-1.5% of the total mass of the pre-emulsion. The concentration of the ammonia solution is 15-25 wt%.

7. The preparation method according to any one of claims 1-6, wherein the water used is deionized water.

8. A low-permeability liquid mulch film emulsion based on poplar fluff prepared by the preparation method according to any one of claims 1-6.

9. The application of the poplar fluff-based low-permeability liquid mulch emulsion as described in claim 8 in agricultural production.

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