Lignin-based liquid mulch and methods of making and using same

Abstract

A lignin-based liquid mulch and a preparation method and application thereof, the liquid mulch takes lignin sulfonate as a main raw material, is compounded with chitosan and polyvinyl alcohol to form a base solution, is modified and treated by cross-linking of epoxy chloropropane and complexing of tetramethylphosphonium chloride, and finally, nano kaolin is added and stirred uniformly to form the liquid mulch. When used, the liquid mulch is diluted with water and sprayed on the surface of soil to form a uniform film. The lignin sulfonate is fully utilized as a rigid skeleton of a polymer by virtue of a benzene propan structure, the obtained mulch has good film forming property, hydrophobicity and soil moisture and heat preservation performance through the synergistic modification of the adhesion of chitosan, the toughening of polyvinyl alcohol and the cross-linking agent and the complexing agent. The addition of nano kaolin further enhances the infrared barrier capacity of the mulch and reduces the heat loss at night.

Description

Technical Field

[0001] This invention belongs to the field of agricultural mulch film technology, specifically relating to a bio-based biodegradable liquid mulch film, and more particularly to a lignin-based liquid mulch film with lignin sulfonate as the main raw material, its preparation method and application. Background Technology

[0002] Agricultural mulch film technology effectively reduces soil moisture evaporation, maintains soil humidity, increases soil temperature, and suppresses weeds and pests, making it a key measure for ensuring sustainable agricultural development. However, traditional polyethylene mulch film is difficult to degrade after long-term use, and residual fragments accumulate in the soil year by year, leading to increasingly prominent problems such as soil structure damage and decreased microbial activity, becoming a core bottleneck restricting sustainable agricultural development. Therefore, developing alternative environmentally friendly mulch films is of significant practical importance. Bio-based liquid mulch film, as one alternative, has advantages such as convenient spraying, adaptability to complex terrain, and reduced labor input. The mulch film formed after spraying possesses conventional functions of moisture retention, temperature increase, and weed suppression, and is completely biodegradable, fundamentally eliminating residual pollution. Promoting the application of liquid mulch film plays a positive role in building a green and low-carbon agricultural system and achieving high-quality agricultural development. Currently, various raw materials are being used in the research and preparation of liquid mulch film. For example, liquid mulch films prepared from raw materials such as lignite extract, livestock and poultry manure, linoleum, bamboo pulp fiber, wood ear fungus, and sludge have certain effects, but some technologies suffer from problems such as the need for raw material extraction, complex processing steps, high costs, or the use of hazardous chemicals. Lignosulfonates are a major byproduct of the pulp and paper industry, widely available and inexpensive, possessing good film-forming properties and biodegradability. In soil, they can be further degraded into humic acid, showing potential for soil improvement. In recent years, studies have introduced lignin sulfonates into mulch film materials, such as composites with polyvinyl alcohol and sodium carboxymethyl cellulose, showing that the introduction of lignin sulfonates can improve the mechanical strength of the film and reduce water vapor permeability. However, in existing studies, lignin sulfonates are mostly used as functional additives in low quantities, and there are no reports of liquid mulch films using lignin sulfonates as the main raw material. Chitosan, as a natural biopolymer, has excellent antibacterial, film-forming, and biodegradable properties, and has attracted widespread attention in the field of film coatings. Polyvinyl alcohol (PVA) possesses excellent biocompatibility and film-forming properties, making films prepared from it a research hotspot in the field of biodegradable materials. Nano-kaolin, due to its superior infrared light blocking properties, can reduce nighttime heat loss and is expected to improve the heat retention effect of mulch films. In summary, existing liquid mulch film technologies still have room for improvement in terms of raw material costs, process complexity, and environmental friendliness. Developing a liquid mulch film using lignin sulfonate as the main raw material, which combines moisture retention, heat preservation, and soil improvement functions, holds significant application potential. Summary of the Invention

[0003] Technical Problems Solved: To address the problems of traditional polyethylene mulch films being difficult to degrade, leading to soil compaction, microplastic pollution, and a decline in soil organic matter due to long-term use, as well as the shortcomings of existing bio-based liquid mulch films which are mostly made from other raw materials, with lignin sulfonate only as an auxiliary component, and whose preparation processes are complex or costly, this invention provides a lignin-based liquid mulch film with lignin sulfonate as the main raw material, its preparation method, and its application. By compounding lignin sulfonate with chitosan and polyvinyl alcohol, and introducing crosslinking agents, complexing agents, and nano-kaolin for modification, the resulting liquid mulch film has good film-forming properties, hydrophobicity, and heat and moisture retention properties. After spraying, it can form a uniform film on the soil surface, effectively preventing soil compaction and increasing soil porosity. After use, it can be further degraded into humic acid under the action of microorganisms, increasing the soil organic matter content, thus combining the functions of a mulch film and the effect of soil improvement.

[0004] Technical Solution: A method for preparing a lignin-based liquid mulch film includes the following steps: Step 1: Under constant temperature water bath conditions of 75-90℃, polyvinyl alcohol is added to water and stirred until completely dissolved to obtain a polyvinyl alcohol solution; then, lignin sulfonate and water-soluble chitosan are added sequentially to the polyvinyl alcohol solution and stirred to obtain a homogeneous mixed solution; Step 2: Epichlorohydrin and methanol are added to the mixed solution obtained in Step 1, and the mixture is stirred at 75-90℃ for 2-4 hours for crosslinking modification, then cooled to room temperature, and tetramethylolphosphine chloride is added for complexation reaction for 1-3 hours to obtain a modified polymer system; Step 3: Nano-kaolin is added to the modified polymer system obtained in Step 2 and stirred evenly to obtain a lignin-based liquid mulch film.

[0005] In step one, based on 100g of water, the amount of lignin sulfonate is 8-15g, the amount of water-soluble chitosan is 1-4g, and the amount of polyvinyl alcohol is 1-4g.

[0006] The lignin sulfonate mentioned in step one is sodium lignin sulfonate or calcium lignin sulfonate, derived from papermaking black liquor obtained from pulping of coniferous, broadleaf, or grass raw materials; the polyvinyl alcohol is PV1788.

[0007] In step two, epichlorohydrin accounts for 2-12% of the total mass of the mixed solution obtained in step one, and the mass ratio of epichlorohydrin to methanol is 3:1-6:1.

[0008] The tetrahydroxymethyl phosphorus chloride mentioned in step two accounts for 2-6% of the total mass of the mixed solution obtained in step one.

[0009] The nano-kaolin mentioned in step three accounts for 1-5% of the total mass of the mixed solution obtained in step one.

[0010] The lignin-based liquid mulch film prepared by the above method.

[0011] The mass ratio of each component in the above-mentioned lignin-based liquid mulch film is determined by the amount of feed in steps one to three of the preparation method. Among them, lignin sulfonate, water-soluble chitosan, polyvinyl alcohol, epichlorohydrin, tetramethylphosphoric acid and nano-kaolin form a composite system in the mulch film through hydrogen bonding, chemical cross-linking and complexation.

[0012] The above-mentioned lignin-based liquid mulch film is used as a mulch film in agricultural planting.

[0013] The specific application method is as follows: dilute the lignin-based liquid mulch film with water to a mass concentration of 1% and then spray it onto the soil.

[0014] Beneficial Effects: This invention uses lignin sulfonate as the main raw material to construct a polymer skeleton. Utilizing its phenylpropane structural characteristics, it forms a composite system with chitosan and polyvinyl alcohol through hydrogen bonding. Chitosan acts as a thickener, ensuring uniform adhesion of the mulch film to the soil surface, while polyvinyl alcohol provides toughness to prevent cracking. The resulting liquid mulch film exhibits synergistic effects in film-forming properties and mechanical properties. Secondly, through epichlorohydrin chemical crosslinking and tetramethylolphosphine complexation, a dual crosslinking network is introduced into the lignin-based biomacromolecules, improving the hydrophobicity of the mulch film, resulting in lower permeability compared to unmodified or only single-modified films. Furthermore, the introduction of nano-kaolin further enhances the synergistic effect of physical barrier and chemical modification. Its ability to block infrared radiation at night reduces heat loss, and combined with the dense structure of the crosslinked mulch film, significantly improves the soil's heat retention performance. The test results of the examples show that with the increase of cross-linking degree and the addition of nano-kaolin, the moisture retention and heat preservation performance of the mulch film gradually improves. In Example 7, the moisture loss on the seventh day was reduced by more than 30% compared with the blank test, and the soil temperature increased by 2.85℃, showing the synergistic effect between the components and the modification steps. In addition, lignin sulfonate, chitosan, and polyvinyl alcohol are all biodegradable materials. Under the action of soil microorganisms, they are synergistically degraded and transformed into humic acid, which not only avoids the residual pollution of traditional mulch films, but also simultaneously increases the soil organic matter content, achieving the dual effect of mulch film function and soil improvement. Attached Figure Description

[0015] Figure 1 Comparative photographs of soil treated with the same amount of water (A) and 1% of the liquid mulch film from Example 8 (B). The left image shows the surface of soil treated with the same amount of water (A) and 1% of the liquid mulch film from Example 8 (B). It can be seen that the soil treated with water is severely compacted with surface cracks, while the soil treated with the liquid mulch film shows no surface compaction. The right image shows the side view of soil treated with the same amount of water (A) and 1% of the liquid mulch film from Example 8 (B). It can be seen that the soil treated with water is severely compacted, essentially forming a large clump, while the side view of the soil treated with the liquid mulch film shows no compaction. Note: Observation results after 7 days; room temperature on day 7 was 19℃.

[0016] Figure 2 Wheat growth status (left: blank soil (sprayed with water), right: control soil (sprayed with Example 8)). Detailed Implementation

[0017] Examples 1-3: With other variables fixed, we examined the effect of lignin dosage.

[0018] Examples 4-7: With other variables fixed, the effect of crosslinking agent dosage was investigated.

[0019] Examples 8-9: With other variables fixed, the effect of nano-kaolin content was investigated.

[0020] Comparative Example 1 (compared to Example 8, without the addition of inorganic substances).

[0021] Comparative Example 2 (pure PVA liquid mulch film).

[0022] Comparative Example 3 (uncrosslinked liquid mulch film).

[0023] Application example (wheat planting).

[0024] Water-soluble chitosan: Chitosan (CS), viscosity 200 mPa·s, degree of deacetylation 90%, molecular weight 800~1000 Daltons, Xi'an Zhongyan Kangze Biotechnology Co., Ltd., model: ZYKZ18478.

[0025] Nano-kaolin: Yinyu brand kaolin GY680 (4000 mesh).

[0026] Example 1

[0027] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 8g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 2g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 3:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 2.24g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 1.12g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0028] Example 2

[0029] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 2g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 4:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 2.24g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 1.12g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0030] Example 3

[0031] (1) Under constant temperature water bath conditions of 80℃, 1g of polyvinyl alcohol was added to 100g of water and stirred until it was completely dissolved. Then, 15g of sodium lignosulfonate and 3g of water-soluble chitosan were added in sequence and stirred to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. 2g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) were added to the base solution and stirred at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. The solution was then cooled to room temperature and 2.24g of tetramethylolphosphine chloride was added for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. 1.12g of nano-kaolin was added to the macromolecular polymer prepared in step (2) and stirred evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0032] Example 4

[0033] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 7g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 4:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 2.24g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 1.12g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0034] Example 5

[0035] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 10g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 4:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 2.24g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 1.12g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0036] Example 6

[0037] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a homogeneous mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 14g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) to the base solution, stir and react at 80℃ for 2.5h to obtain a lignin-based biomacromolecule with a degree of crosslinking. Then cool to room temperature, add 2.24g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 1.12g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0038] Example 7

[0039] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 14g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 4.85g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 1.12g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0040] Example 8 (Optimal Group)

[0041] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 14g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 4.85g of tetrahydroxymethyl phosphorus chloride for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 4.53g of nano-kaolin, stir evenly, and further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0042] Example 9

[0043] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a uniform mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 14g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) to the base solution, stir and react at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. Then cool to room temperature, add 4.85g of tetramethylolphosphine chloride and complex for 1h to further improve the hydrophobicity of the membrane. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 6.35g of nano-kaolin, stir evenly to further improve the soil heat preservation effect. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0044] Comparative Example 1 (Compared with Example 8, no inorganic substances were added)

[0045] (1) Under constant temperature water bath conditions of 80℃, 3g of polyvinyl alcohol was added to 100g of water and stirred until it was completely dissolved. Then, 10g of sodium lignosulfonate and 3g of water-soluble chitosan were added in sequence and stirred to obtain a homogeneous mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. 14g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) were added to the base solution and stirred at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. The solution was then cooled to room temperature and 4.85g of tetramethylolphosphine chloride was added for 1h to further improve the hydrophobicity of the membrane. (3) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0046] Comparative Example 2 (Pure PVA liquid mulch film)

[0047] Under constant temperature water bath conditions of 80℃, 3g of polyvinyl alcohol was added to 100g of water and stirred until completely dissolved to obtain pure PVA liquid mulch film. The obtained PVA liquid mulch film was diluted with water to a concentration of 1%. 150g of oven-dry soil was placed in a 150mL glass beaker, and 30g of 1% lignin-based liquid mulch film was sprayed on. A thermometer was inserted 4cm into the soil to observe the soil temperature in real time, and the soil was weighed to calculate the soil water retention.

[0048] Comparative Example 3 (Uncrosslinked liquid mulch film)

[0049] Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water and stir until it is completely dissolved. Then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence and continue stirring to obtain a homogeneous mixed solution of lignin, chitosan and polyvinyl alcohol.

[0050] Comparative Example 4 (compared to Example 8, THPC is omitted and replaced with an equal amount of epichlorohydrin)

[0051] (1) Under constant temperature water bath conditions of 80℃, add 3g of polyvinyl alcohol to 100g of water, stir until it is completely dissolved, then add 10g of sodium lignosulfonate and 3g of water-soluble chitosan in sequence, and continue stirring to obtain a homogeneous mixed solution of lignin, chitosan and polyvinyl alcohol. (2) Hydrophobic modification. Add 18.85g of chemical crosslinking agent epichlorohydrin and catalyst methanol (mass ratio of epichlorohydrin to methanol 5:1) to the base solution, stir at 80℃ for 2.5h to obtain lignin-based biomacromolecules with a certain degree of crosslinking. The complexation reaction step of tetrahydroxymethylphosphoric acid is omitted in this comparative example. (3) Inorganic addition. On the basis of the macromolecular polymer prepared in step (2), add 4.53g of nano-kaolin and stir evenly. (4) When using, dilute the lignin-based liquid mulch obtained by (1)-(3) with water to a concentration of 1%, put 150g of completely dry soil into a 150mL glass, spray 30g of 1% lignin-based liquid mulch, insert a thermometer 4cm below the soil to observe the soil temperature in real time, weigh the soil and calculate the soil water retention.

[0052] Table 1. Soil thermal insulation and moisture retention performance

[0053]

[0054] As shown in Table 1, with the increase in the amount of crosslinking agent epichlorohydrin from 2g (Example 1) to 14g (Example 9), the soil moisture loss rate on day 7 decreased from 66.52% to 46.53%, indicating that the increased crosslinking degree significantly enhanced the hydrophobicity and water retention performance of the mulch film. Comparing the data of Example 8 and Comparative Example 1 (without nano-kaolin), the moisture loss rate of Example 8 was 4.93 percentage points lower than that of Comparative Example 1, and the soil temperature was 0.68℃ higher, proving that the addition of nano-kaolin further improved the heat preservation and moisture retention performance, and played a synergistic role in infrared blocking and physical filling. Compared with the blank soil (only sprayed with water, moisture loss rate 71.72%), the moisture loss rate of Example 8 decreased by 35.12%, and the soil temperature increased by 3.13℃, demonstrating the excellent water retention and heat preservation effect of the mulch film of the present invention.

[0055] Table 2 Performance Comparison Table

[0056]

[0057] As shown in Table 2, with the increase of the crosslinking agent epichlorohydrin from 2g (Example 1) to 14g (Example 9), the contact angle of the liquid mulch film increased from 60.35° to 85.67°, the tensile strength increased by 7.11MPa, and the degradation rate decreased. This is because epichlorohydrin increased the crosslinking density of the system, increased the ether bonds and decreased the hydroxyl content, thus significantly improving the mechanical properties and reducing the degree of degradation. The complexation effect further increased the crosslinking density of the film, the molecular structure was more regularly arranged, and the free hydroxyl content decreased. The addition of nano-kaolin reduced the contact angle, but the decrease in hydrophobicity was not significant; its main effect was to improve the soil's heat retention and moisture retention performance. Compared with Comparative Example 2, the optimal group, Example 8, has excellent hydrophobicity, mechanical properties, and degradation performance.

[0058] Table 3 Comparison of the effects of THPC on mulch film performance

[0059]

[0060] As can be seen from the data in Table 3, compared with Example 8, Comparative Example 4, which omits THPC, shows a significant downward trend in all performance indicators. The contact angle of Comparative Example 4 is 74.03°, which is 7.15° lower than that of Example 8 (81.18°), indicating that the complexation effect of THPC significantly improves the hydrophobicity of the mulch film. This is mainly because the hydroxymethyl groups in the THPC molecule undergo hydrogen bonding and ionic complexation with the hydroxyl and amino groups on lignin, chitosan, and PVA, forming a denser network structure, reducing the number of free hydroxyl groups, and thus reducing the hydrophilicity of the film surface.

[0061] Mechanical property test results showed that the tensile strength of Comparative Example 4 was 4.82 MPa, which was 10.53 MPa lower than the 15.35 MPa of Example 8. The complexation effect of THPC formed a tighter cross-linked network between lignin sulfonate, chitosan and PVA, improving the structural precision and overall mechanical properties of the polymer.

[0062] Application Example 1

[0063] Wheat was grown in laboratory pots (15cm inner diameter plastic pots) using unfertilized soil from a plot. Two treatment groups were set up: a control group (sprayed with 50g of water) and a control group (sprayed with 50g of 1% of Example 8). Each group had 3 pots, with 10 wheat seeds per pot. The results showed that the soil temperature in the experimental group was 2-3℃ higher on average than that in the control group, the moisture content was 15-20% higher, the wheat germination rate and yield were 20% higher than those in the control group, and the roots were more numerous and longer than those in the control group. Figure 2 .

Claims

1. A method for preparing a lignin-based liquid agricultural mulch film, characterized in that, Includes the following steps: Step 1: Under constant temperature water bath conditions of 75-90℃, add polyvinyl alcohol to water and stir until completely dissolved to obtain a polyvinyl alcohol solution; then add lignin sulfonate and water-soluble chitosan sequentially to the polyvinyl alcohol solution and stir to obtain a homogeneous mixed solution; Step 2: Add epichlorohydrin and methanol to the mixed solution obtained in Step 1, stir at 75-90℃ for 2-4 hours to perform crosslinking modification, then cool to room temperature, add tetramethylolphosphine chloride and react for 1-3 hours to obtain a modified polymer system; Step 3: Add nano-kaolin to the modified polymer system obtained in Step 2 and stir. The mixture is homogeneous to obtain a lignin-based liquid agricultural mulch film; wherein: in step one, based on 100g of water, the amount of lignin sulfonate is 8-15g, the amount of water-soluble chitosan is 1-4g, and the amount of polyvinyl alcohol is 1-4g; in step two, the amount of epichlorohydrin accounts for 2-12% of the total mass of the mixed solution obtained in step one, and the mass ratio of epichlorohydrin to methanol is 3:1-6:1; in step two, the amount of tetramethylolphosphine chloride accounts for 2-6% of the total mass of the mixed solution obtained in step one; and in step three, the amount of nano-kaolin accounts for 1-5% of the total mass of the mixed solution obtained in step one.

2. The preparation method according to claim 1, characterized in that, The lignin sulfonate mentioned in step one is sodium lignin sulfonate or calcium lignin sulfonate, derived from papermaking black liquor obtained from pulping of coniferous, broadleaf, or grass raw materials; the polyvinyl alcohol is PV1788.

3. The lignin-based liquid agricultural mulch film prepared by the preparation method according to claim 1 or 2.

4. The application of the lignin-based liquid agricultural mulch film of claim 3 as a mulch film in agricultural planting.

5. The application according to claim 4, characterized in that, The lignin-based liquid agricultural mulch film is diluted with water to a mass concentration of 1% and then sprayed onto the soil.

Images