A black liquid mulch film and its preparation method

Abstract

This invention relates to the field of liquid mulch film technology, and proposes a black liquid mulch film and its preparation method. A black liquid mulch film comprises the following components by weight: 3-5 parts chitosan, 1.5-3 parts colorant, 4-6 parts filler, 3-5 parts polyvinyl alcohol, 3-5 parts film-forming aid, 0.2-0.3 parts thickener, and 80-90 parts water. The filler is composed of components with different particle sizes, specifically by weight percentage: 15μm≤attapulgite≤20μm 55wt%~65wt%, 2μm≤attapulgite≤5μm 25wt%~35wt%, 50nm≤zinc oxide≤80nm 10wt%. This technical solution solves the problems of insufficient mechanical properties and UV blocking performance of existing liquid mulch films.

Description

Technical Field

[0001] This invention relates to the field of liquid mulch film technology, specifically to a black liquid mulch film and its preparation method. Background Technology

[0002] Liquid mulch film, as an environmentally friendly alternative to traditional plastic mulch film, is widely used in agricultural applications such as moisture retention, temperature increase, and weed control due to its advantages of spray-applied film formation, biodegradability, and residue-free operation. Among them, black liquid mulch film, with its properties of shading, weed suppression, and reducing soil moisture evaporation, has become a highly promising functional mulch film product in modern agricultural production. Its core requirements focus on two key indicators: mechanical performance stability and UV blocking functionality.

[0003] In existing technologies, the preparation of black liquid mulch films mostly uses biomass polysaccharides (such as chitin and chitosan) as the matrix, combined with colorants, fillers, and various additives to construct the film system. However, current products still have some shortcomings: On the one hand, to improve light-blocking performance and mechanical strength, fillers such as attapulgite and zinc oxide are often added to the formula. However, traditional fillers mostly use a single particle size, resulting in high porosity and significant stress concentration within the film layer, insufficient nominal strain at break (longitudinal), and easy brittleness after film formation, making it difficult to adapt to the complex stress environment of farmland soil. On the other hand, UV blocking performance depends on functional fillers such as nano-zinc oxide, but nanoparticles have high surface energy and are prone to agglomeration in the matrix, which not only reduces UV absorption efficiency but also further aggravates film defects, affecting agricultural production efficiency. Therefore, there is an urgent need for a liquid mulch film with good mechanical properties and high UV blocking efficiency. Summary of the Invention

[0004] This invention proposes a black liquid mulch film and its preparation method, which solves the problems of insufficient mechanical properties and ultraviolet blocking properties of liquid mulch films in related technologies.

[0005] The technical solution of the present invention is as follows: This invention proposes a black liquid mulch film, comprising the following components by weight: 3-5 parts chitosan, 1.5-3 parts colorant, 4-6 parts filler, 3-5 parts polyvinyl alcohol, 3-5 parts film-forming aid, 0.2-0.3 parts thickener, and 80-90 parts water; The filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 55wt%~65wt%, 2μm≤attapulgite≤5μm 25wt%~35wt%, 50nm≤zinc oxide≤80nm 10wt%.

[0006] As a further technical solution, the pigment includes one or two of black iron oxide powder, humic acid, and water-based carbon black; Preferably, the colorant is water-based carbon black.

[0007] As a further technical solution, the zinc oxide is pretreated zinc oxide; the preparation method of the pretreated zinc oxide includes the following steps: dispersing zinc oxide in water, adding polyaspartic acid and glutaraldehyde solution, stirring, filtering, and drying to obtain pretreated zinc oxide.

[0008] In this invention, the mechanical properties of the black liquid mulch film are further improved by adding pretreated zinc oxide. Glutaraldehyde, as a crosslinking agent, constructs an organic coating layer on the surface of zinc oxide. This coating layer not only reduces the surface energy of the zinc oxide particles, preventing direct agglomeration between particles, but also forms multiple hydrogen bonds with the amino and hydroxyl groups of chitin. The coating effect of polyaspartic acid significantly reduces the agglomeration attraction between zinc oxide particles. Combined with the spatial isolation effect of the three-level particle size distribution, zinc oxide can be dispersed in the film layer in a finer and more uniform state, avoiding the formation of hard defects by agglomerates, thereby further improving the nominal strain at break.

[0009] As a further technical solution, the mass ratio of zinc oxide to polyaspartic acid is 1:0.18~0.22.

[0010] As a further technical solution, the mass-to-volume ratio of the zinc oxide and glutaraldehyde solution is 1g:4~5mL.

[0011] As a further technical solution, the stirring temperature is 50~60℃, and the stirring time is 2~2.5h.

[0012] As a further technical solution, the glutaraldehyde solution is an aqueous solution of glutaraldehyde with a concentration of 6wt%~8wt%; Preferably, the glutaraldehyde solution is a 6 wt% aqueous solution of glutaraldehyde.

[0013] As a further technical solution, the film-forming aid includes one or both of propylene glycol and glycerol.

[0014] As a further technical solution, the thickener includes one or two of sodium carboxymethyl cellulose, hydroxyethyl cellulose, and guar gum; Preferably, the thickener is sodium carboxymethyl cellulose.

[0015] This invention also proposes a method for preparing a black liquid mulch film, comprising the following steps: S1. Chitin is dispersed in an alkaline solution and reacted to obtain deacetylated chitin; the deacetylated chitin is dispersed in water and the pH is adjusted to 3.5~5.5 to obtain a mixed solution. S2. Add polyvinyl alcohol to water, heat to 85~95℃ and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; S3. The mixture is mixed with the polyvinyl alcohol aqueous solution, pigment, filler, film-forming aid, and thickener, and then sheared and stirred to obtain the black liquid mulch film.

[0016] As a further technical solution, the alkaline solution is an aqueous solution of sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous solution is 40wt%~45wt%. Preferably, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 40 wt%.

[0017] As a further technical solution, the reaction temperature is 80~90℃, and the reaction time is 4~4.5h; Preferably, the reaction temperature is 85°C and the reaction time is 4 hours.

[0018] As a further technical solution, the rotation speed of the shearing and stirring is 1000~2000 rpm, and the shearing and stirring time is 15~30 min.

[0019] The working principle and beneficial effects of this invention are as follows: In this invention, the mechanical properties and UV blocking performance of black liquid mulch film are improved by using attapulgite particles of different sizes in combination with zinc oxide. The attapulgite particles of different sizes form a continuous structure of large skeleton, medium filling, and micro-reinforcement with zinc oxide, eliminating stress weak points spatially. The 15-20μm attapulgite particles serve as the supporting skeleton of the film layer, providing basic mechanical strength. Simultaneously, the gaps formed by their accumulation provide space for medium particles to fill, avoiding rigid stacking caused by direct contact between large particles. The 2-5μm attapulgite particles precisely match the gap size of the large particles, significantly reducing the porosity of the film layer after filling, transforming the structure from a loose skeleton to a dense packing. Under stress, stress can be evenly transmitted rather than concentrated in the pores. The 50-80nm zinc oxide nanoparticles fill the submicron-level gaps between the first two stages of particles, preventing polymer chain slippage and breakage under stress. Meanwhile, the 15-20μm attapulgite skeleton structure provides a dispersion substrate, and the 2-5μm attapulgite fills the gaps between large particles, further dividing the space into smaller micro-regions. The nano zinc oxide is confined within these micro-regions and cannot move and aggregate freely, thus blocking the aggregation path in space, improving the dispersibility of nano zinc oxide, and thereby improving the ultraviolet absorption efficiency of nano zinc oxide. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] In the following examples and comparative examples, the average particle size of the black iron oxide powder was 2 μm; the polyvinyl alcohol was PVA124.

[0022] Example 1 A black liquid mulch film comprises the following components in parts by weight: 3 parts chitosan, 1.5 parts water-based carbon black, 4 parts filler, 3 parts polyvinyl alcohol, 3 parts glycerol, 0.2 parts sodium carboxymethyl cellulose, and 80 parts water. The above-mentioned filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 55wt%, 2μm≤attapulgite≤5μm 35wt%, 50nm≤zinc oxide≤80nm 10wt%; Its preparation method includes the following steps: S1. Chitin was dispersed in an aqueous sodium hydroxide solution (sodium hydroxide concentration was 40 wt%) and reacted at 85℃ for 4 h to obtain deacetylated chitin; the deacetylated chitin was dispersed in 40 parts of water, and acetic acid was added to adjust the pH to 3.5 to obtain a mixed solution. S2. Add polyvinyl alcohol to 40 parts of water and stir at 85°C until completely dissolved to obtain a polyvinyl alcohol aqueous solution. S3. Add aqueous carbon black, filler, polyvinyl alcohol aqueous solution, glycerol and sodium carboxymethyl cellulose to the mixture, and shear and stir at 1000 rpm for 30 min to obtain black liquid mulch film.

[0023] Example 2 A black liquid mulch film comprises the following components in parts by weight: 5 parts chitosan, 3 parts water-based carbon black, 6 parts filler, 5 parts polyvinyl alcohol, 2.5 parts glycerol, 2.5 parts propylene glycol, 0.3 parts sodium carboxymethyl cellulose, and 90 parts water. The above-mentioned filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 65wt%, 2μm≤attapulgite≤5μm 25wt%, 50nm≤zinc oxide≤80nm 10wt%; Its preparation method includes the following steps: S1. Chitin was dispersed in an aqueous sodium hydroxide solution (sodium hydroxide concentration was 40 wt%) and reacted at 85℃ for 4 h to obtain deacetylated chitin; the deacetylated chitin was dispersed in 45 parts of water, and acetic acid was added to adjust the pH to 4.5 to obtain a mixed solution. S2. Add polyvinyl alcohol to 45 parts of water and stir at 95°C until completely dissolved to obtain a polyvinyl alcohol aqueous solution. S3. Add aqueous carbon black, filler, polyvinyl alcohol aqueous solution, glycerol, propylene glycol and sodium carboxymethyl cellulose to the mixture, and shear and stir at 2000 rpm for 15 min to obtain black liquid mulch film.

[0024] Example 3 A black liquid mulch film comprises the following components in parts by weight: 4 parts chitosan, 2 parts water-based carbon black, 5 parts filler, 4 parts polyvinyl alcohol, 4 parts propylene glycol, 0.25 parts sodium carboxymethyl cellulose, and 85 parts water. The above-mentioned filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 60wt%, 2μm≤attapulgite≤5μm 30wt%, 50nm≤zinc oxide≤80nm 10wt%; Its preparation method includes the following steps: S1. Chitin was dispersed in an aqueous sodium hydroxide solution (sodium hydroxide concentration was 40 wt%) and reacted at 85℃ for 4 h to obtain deacetylated chitin; the deacetylated chitin was dispersed in 45 parts of water, and acetic acid was added to adjust the pH to 5.5 to obtain a mixed solution. S2. Add polyvinyl alcohol to 40 parts of water and stir at 95°C until completely dissolved to obtain a polyvinyl alcohol aqueous solution. S3. Add aqueous carbon black, filler, polyvinyl alcohol aqueous solution, propylene glycol and sodium carboxymethyl cellulose to the mixture, and shear and stir at 1500 rpm for 20 min to obtain black liquid mulch film.

[0025] Example 4 The only difference between this embodiment and Embodiment 2 is that the zinc oxide is pretreated zinc oxide. The preparation method of the pretreated zinc oxide includes the following steps: dispersing zinc oxide in water, adding polyaspartic acid and a 6wt% glutaraldehyde aqueous solution, stirring at 50°C for 2.5 hours, filtering, and drying to obtain pretreated zinc oxide. The mass-volume ratio of zinc oxide to water is 1g:4mL, and the mass-volume ratio of zinc oxide, polyaspartic acid, and glutaraldehyde aqueous solution is 1g:0.18g:4mL.

[0026] Example 5 The only difference between this embodiment and Embodiment 2 is that the zinc oxide is pretreated zinc oxide. The preparation method of the pretreated zinc oxide includes the following steps: dispersing zinc oxide in water, adding polyaspartic acid and a 6wt% glutaraldehyde aqueous solution, stirring at 60°C for 2 hours, filtering, and drying to obtain pretreated zinc oxide. The mass-volume ratio of zinc oxide to water is 1g:4mL, and the mass-volume ratio of zinc oxide, polyaspartic acid, and glutaraldehyde aqueous solution is 1g:0.22g:5mL.

[0027] Comparative Example 1 The difference between this embodiment and Embodiment 2 is that the filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 40wt%, 2μm≤attapulgite≤5μm 50wt%, 50nm≤zinc oxide≤80nm 10wt%.

[0028] Comparative Example 2 The difference between this embodiment and Embodiment 2 is that the filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 75wt%, 2μm≤attapulgite≤5μm 15wt%, 50nm≤zinc oxide≤80nm 10wt%.

[0029] Comparative Example 3 The only difference between this comparative example and Example 2 is that the filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 65wt%, 8μm≤attapulgite≤12μm 25wt%, 50nm≤zinc oxide≤80nm 10wt%.

[0030] Comparative Example 4 The only difference between this comparative example and Example 2 is that the filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 65wt%, 2μm≤attapulgite≤5μm 25wt%, 200nm≤zinc oxide≤300nm 10wt%.

[0031] Comparative Example 5 The only difference between this comparative example and Example 2 is that the filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 65wt%, 2μm≤attapulgite≤5μm 25wt%, 20nm≤zinc oxide≤40nm 10wt%.

[0032] Comparative Example 6 The only difference between this comparative example and Example 2 is that the filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 90wt%, 50nm≤zinc oxide≤80nm 10wt%.

[0033] Experimental Example 1 Mechanical properties: 10g of the black liquid mulch film prepared in Examples 1-5 and Comparative Examples 1-6 was transferred to a 90mm petri dish, dried at 50℃ for 4 hours, and then peeled off. After being placed in an environment with a temperature of 23℃ and a relative humidity of 50% for 12 hours, test samples were obtained, with a thickness of 50μm. The nominal strain at break (longitudinal) of the test samples was tested according to the method specified in GB / T 35795-2017 "Fully Biodegradable Agricultural Ground Cover Film". The test results are shown in Table 1. Table 1 Mechanical performance test results

[0034] By comparing the data of Examples 1-3 and Comparative Examples 1-6, the nominal strain (longitudinal) at break of the black liquid mulch film prepared by Examples 1-3 with filler gradation of 15μm≤attapulgite≤20μm 55wt%~65wt%, 2μm≤attapulgite≤5μm 25wt%~35wt%, and 50nm≤zinc oxide≤80nm 10wt% was greater than that of Comparative Examples 1-6. This indicates that the filler gradation method of the present invention improves the nominal strain (longitudinal) at break of the black liquid mulch film.

[0035] By comparing the data of Examples 2 and 4-5, the nominal strain (longitudinal) at break of the black liquid mulch film prepared by modifying zinc oxide with polyaspartic acid in Examples 4-5 was greater than that in Examples 4-5. This indicates that the nominal strain (longitudinal) at break of the black liquid mulch film can be further improved by modifying zinc oxide with polyaspartic acid.

[0036] Experiment Example 2 UV blocking performance: 10 mL of 40 mg / L avermectin ethanol solution was sprayed onto a petri dish. The test samples obtained in Experimental Example 2 and Comparative Example 6 were covered on the petri dish. After exposure to UV light for 8 h, avermectin was extracted with 20 mL of ethanol. The concentration of avermectin in ethanol was measured using a UV spectrophotometer. The mass of avermectin after exposure was calculated, and the residual rate of avermectin was calculated. The result was the average of 5 parallel experiments. Residue rate (%) = (Avermectin mass after exposure / Avermectin mass before exposure) × 100%; The results are shown in Table 2; Table 2. UV blocking performance test results

[0037] By comparing the data in Table 2, the abamectin residue rate of the black liquid mulch film prepared in Example 2 with filler gradation of 15μm≤attapulgite≤20μm 55wt%~65wt%, 2μm≤attapulgite≤5μm 25wt%~35wt%, and 50nm≤zinc oxide≤80nm 10wt% was higher than that in Comparative Example 6. This indicates that the gradation system of the present invention improves the UV blocking performance of the black liquid mulch film.

[0038] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A black liquid mulch characterized by, It comprises the following components by weight: 3-5 parts chitosan, 1.5-3 parts colorant, 4-6 parts filler, 3-5 parts polyvinyl alcohol, 3-5 parts film-forming aid, 0.2-0.3 parts thickener, and 80-90 parts water; The filler is composed of the following components with different particle sizes, in weight percentage: 15μm≤attapulgite≤20μm 55wt%~65wt%, 2μm≤attapulgite≤5μm 25wt%~35wt%, 50nm≤zinc oxide≤80nm 10wt%.

2. A black liquid mulch according to claim 1, characterised in that, The colorant includes one or two of black iron oxide powder, humic acid, and water-based carbon black.

3. A black liquid mulch according to claim 1, wherein The zinc oxide is pretreated zinc oxide; The method for preparing the pretreated zinc oxide includes the following steps: dispersing zinc oxide in water, adding polyaspartic acid and glutaraldehyde solution, stirring, filtering, and drying to obtain pretreated zinc oxide.

4. A black liquid mulch according to claim 3, characterised in that, The mass ratio of zinc oxide to polyaspartic acid is 1:0.18~0.

22.

5. A black liquid mulch film according to claim 3, characterized in that, The mass-to-volume ratio of the zinc oxide and glutaraldehyde solution is 1g:4~5mL.

6. The black liquid mulch film according to claim 3, characterized in that, The stirring temperature is 50~60℃, and the stirring time is 2~2.5h.

7. The black liquid mulch film according to claim 1, characterized in that, The film-forming aid includes one or both of propylene glycol and glycerol.

8. The black liquid mulch film according to claim 1, characterized in that, The thickener includes one or two of sodium carboxymethyl cellulose, hydroxyethyl cellulose, and guar gum.

9. A method for preparing a black liquid mulch film, used to prepare the black liquid mulch film according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Chitin is dispersed in an alkaline solution and reacted to obtain deacetylated chitin; the deacetylated chitin is dispersed in water and the pH is adjusted to 3.5~5.5 to obtain a mixed solution. S2. Add polyvinyl alcohol to water, heat to 85~95℃ and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; S3. The mixture is mixed with the polyvinyl alcohol aqueous solution, pigment, filler, film-forming aid, and thickener, and then sheared and stirred to obtain the black liquid mulch film.

10. A method for preparing a black liquid mulch film according to claim 9, characterized in that, The alkaline solution is an aqueous solution of sodium hydroxide, wherein the concentration of sodium hydroxide in the aqueous solution is 40wt%~45wt%. The reaction temperature is 80~90℃, and the reaction time is 4~4.5h; The shearing and stirring speed is 1000~2000 rpm, and the shearing and stirring time is 15~30 min.

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