Degradable multifunctional green agricultural mulching film and preparation method thereof

Abstract

According to the degradable multifunctional green agricultural mulching film and the preparation method thereof, the mulching film is prepared by taking cinnamyl aldehyde and a multi-mercapto acrylate reagent as raw materials through a cross-linking reaction, has excellent biodegradability, mechanical properties and multifunctionality, can release cinnamyl aldehyde in the degradation process to promote crop growth, and has the advantages of environmental protection, environmental protection and the like. And a new solution is provided for solving the pollution problem of the traditional mulching film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer, more particularly to a degradable multifunctional green agricultural mulching film. BACKGROUND

[0002] Agricultural mulching film is an important agricultural production material, which has the important role of increasing temperature, preserving soil moisture, promoting crop yield, stabilizing agricultural production and development, and ensuring food security. At present, most agricultural mulching films are petroleum-based products, which have the problems of difficult degradation, heavy use, and light recycling. They have a serious impact on the ecological environment, such as the destruction of soil ecological structure and water pollution. Natural aldehydes can be degraded in the natural environment, and their degradation products have the effect of promoting plant growth and resisting pests and diseases. There are few reports on the preparation of mulching films by aldehyde materials in the prior art. SUMMARY

[0003] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for preparing a green degradable mulching film based on natural aldehydes.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0005] A degradable multifunctional green agricultural mulching film,

[0006] which is prepared by cross-linking reaction of cinnamyl aldehyde and a multi-thiol acrylate reagent under the catalysis of a Lewis acid.

[0007] As a further improvement of the present application:

[0008] The multi-thiol acrylate reagent is at least one of 1,4-butylene diester bis(mercaptoacetate), pentaerythritol tetra-3-mercaptopropionate.

[0009] As a further improvement of the present application:

[0010] The Lewis acid is one or more of p-toluenesulfonic acid and trifluoroacetic acid.

[0011] As a further improvement of the present application:

[0012] The cinnamyl aldehyde, multi-thiol acrylate reagent, and Lewis acid are reacted in a solvent to obtain the mulching film.

[0013] As a further improvement of the present application:

[0014] The solvent is one or more of tetrahydrofuran, hexane, and dichloromethane.

[0015] As a further improvement of the present application:

[0016] The molar ratio of the mercapto group in the multi-mercapto acrylate reagent to the aldehyde group in the cinnamaldehyde is 1-3:1.

[0017] As a further improvement of the present application:

[0018] The multi-mercapto acrylate reagent is a mixture of 1,4-butanediol bis(mercaptoacetate) and pentaerythritol tetra-3-mercaptopropionate, and the molar ratio of 1,4-butanediol bis(mercaptoacetate) to pentaerythritol tetra-3-mercaptopropionate is 1-6:1.

[0019] As another application object of the present application, a preparation method of a degradable multifunctional green agricultural mulch film is provided, comprising the following steps:

[0020] Step one: mixing cinnamaldehyde and multi-mercapto acrylate reagent to configure a solution;

[0021] Step two: adding Lewis acid catalyst to the solution in proportion;

[0022] Step three: pre-polymerizing the prepared solution at 30-70°C to obtain a prepolymer;

[0023] Step four: uniformly scraping the prepolymer in a mold and heating in a 100-150°C oven to obtain a green mulch film.

[0024] As a further improvement of the present application:

[0025] The pre-polymerization time in step three is 5-30 min;

[0026] The heating time in step four is 2-5 h.

[0027] As a further improvement of the present application:

[0028] The step one is specifically mixing cinnamaldehyde and multi-mercapto acrylate reagent in a solvent to configure a solution.

[0029] In the present application, the green mulch film is mainly formed by mercapto monomers and cinnamaldehyde monomers, wherein one aldehyde group in the cinnamaldehyde reacts with two mercapto groups in the mercapto monomers to form a thioacetal bond, thereby forming a high molecular polymer, and the reaction equation is as follows:

[0030]

[0031] The present application is first equipped with a series of mixed solutions containing mercapto monomers and cinnamaldehyde, which can directly mix mercapto monomers and cinnamaldehyde monomers, or dissolve them in a solvent, and through actual test, mixing through a solvent is better. Then the solution is pre-polymerized at 50 DEG C, the obtained pre-polymer is uniformly coated in a reaction mold, then the mold is placed in an oven at 120 DEG C for heating, the solvent is removed, and the mercapto monomers and cinnamaldehyde monomers are further reacted, polymerized and crosslinked, so as to obtain a kind of hydrophobic polymer. The present application is simple in operation, efficient in reaction, green in raw materials, and the prepared green mulch has excellent performance, stronger warming, soil conservation and waterproof effect than general polyethylene mulch, and can realize degradation in natural environment and release of substances beneficial to plant growth through ROS (reactive oxygen) response, achieving the parallel of protecting environment and promoting plant growth. The green mulch is simple in preparation, efficient in reaction, and has certain industrialization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a comprehensive mechanical property diagram of examples 1-3.

[0033] Figure 2 is a state diagram of example 3 under torsion, bending, folding and stretching.

[0034] Figure 3 is a surface morphology and cross-section SEM diagram of examples 1-3.

[0035] Figure 4 is a thermogravimetric diagram of examples 1-3.

[0036] Figure 5 is a water vapor transmission rate diagram of examples 1-3.

[0037] Figure 6 is a contact angle value and water droplet morphology diagram on the surface of the material of examples 1-3.

[0038] Figure 7 is a temperature rise diagram of greenhouse soil in Wenzhou, Zhejiang Province, China on October 26, 2024 (atmospheric temperature from 14 DEG C to 28 DEG C during the day) within 1 hour.

[0039] Figure 8 is a temperature drop diagram of greenhouse soil in Wenzhou, Zhejiang Province, China on October 26, 2024 (atmospheric temperature from 14 DEG C to 28 DEG C during the day) within 1 hour.

[0040] Figure 9 is a UV light absorption diagram of examples 1-3 under 400-800 nm wavelength.

[0041] Figure 10 is an infrared spectrum diagram in test 8.

[0042] Figure 11 is the surface morphology of the degradation of Example 3 and low density polyethylene in the natural environment.

[0043] Figure 12 is the degradation rate of Examples 1-3 in the natural environment.

[0044] Figure 13 is the morphology change of the material in Test 10.

[0045] Figure 14 is the schematic diagram of plant planting, the schematic diagram of each growth stage of the plant, and the statistical diagram of plant growth index in Test 11. DETAILED DESCRIPTION

[0046] The application will be further described in conjunction with the embodiments given in the accompanying drawings.

[0047] Example One:

[0048] Step One: Cinnamaldehyde 4.956g, pentaerythritol tetra-3-mercapto propionate 6.1081g, 1,4-butanediol bis-mercaptoacetate 2.9790g, tetrahydrofuran 10g, configured into a solution;

[0049] Step Two: p-toluenesulfonic acid is configured into a tetrahydrofuran solution of 1*10^-3mol / ml, 1 μl of p-toluenesulfonic acid tetrahydrofuran solution is taken by a pipette and added to the solution prepared in Step One;

[0050] Step Three: The prepared solution is pre-polymerized at 50°C for 10 min to obtain a prepolymer;

[0051] Step Four: A 200 μm wire bar coater is used to scrape and coat the prepolymer uniformly in a mold. Finally, the mold is placed in a 120°C oven for 3h to remove the solvent to prepare a thin film.

[0052] Example Two:

[0053] Step One: Cinnamaldehyde 4.2952g, pentaerythritol tetra-3-mercapto propionate 3.6648g, 1,4-butanediol bis-mercaptoacetate 4.1706g, tetrahydrofuran 10g, configured into a solution;

[0054] Step Two: p-toluenesulfonic acid is configured into a tetrahydrofuran solution of 1*10^-3mol / ml, 1 μl of p-toluenesulfonic acid tetrahydrofuran solution is taken by a pipette and added to the solution prepared in Step One;

[0055] Step Three: The prepared solution is pre-polymerized at 50°C for 10 min to obtain a prepolymer;

[0056] Step four: The pre-polymer was coated evenly in the mold using a 200 μιη wire bar coater. Finally, the mold was placed in a 120 °C oven for 3 h to remove the solvent to produce the film.

[0057] Example three:

[0058] Step one: Cinnamaldehyde 3.9648 g, pentaerythritol tetra-3-mercaptopropionate 2.4433 g, 1,4-butanediol bis-mercaptoacetate 4.7664 g, tetrahydrofuran 10 g, configured into a solution;

[0059] Step two: p-toluenesulfonic acid was configured into a 1*10"3mol / ml tetrahydrofuran solution, 1 μΐ of p-toluenesulfonic acid tetrahydrofuran solution was removed by a syringe and added to the solution prepared in step one;

[0060] Step three: The prepared solution was pre-polymerized at 50 °C for 10 min to obtain a pre-polymer;

[0061] Step four: The pre-polymer was coated evenly in the mold using a 200 μιη wire bar coater. Finally, the mold was placed in a 120 °C oven for 3 h to remove the solvent to produce the film.

[0062] In the following tests, P-50 represents Example 1, P-30 represents Example 2, and P-20 represents Example 3.

[0063] Test 1: The tensile property test was carried out according to GB / T 1040-92 "Plastics - Determination of tensile properties", referring to Figure 1 With the decrease of tetramercapto monomer in the thiol / aldehyde group mixture, the tensile strength of the polymer film gradually decreased from 15.28 MPa to 4.19 MPa, the modulus decreased from 57.89 MPa to 17.75 MPa, and the elongation at break gradually increased from 100.76% to 259.79%.

[0064] In addition, Figure 2 Example 3 film was easy to twist, bend, fold and stretch, indicating that it had good flexibility and mechanical strength in practical application.

[0065] Test 2: The surface and cross-section of Examples 1-3 were observed by scanning electron microscope, as shown in Figure 3 wherein, A and B are the imaging of the film surface and cross-section under the scanning electron microscope. Due to cross-linking, the surface and cross-section of the material are very smooth.

[0066] Test 3:

[0067] Examples 1-3 were respectively subjected to thermogravimetric test, as shown in Figure 4As shown, the decomposition temperatures of the crosslinked polymer films (P-20, P-30 and P-50) were 245.40℃, 266.80℃ and 286.60℃, respectively. The results showed that the crosslinked polymer had good thermal stability, and with the increase of the proportion of tetramercapto monomer in the reaction, the thermal stability of the polymer also increased.

[0068] Test 4:

[0069] The water vapor transmission rate of the material was determined by GB / T 1037-2021 “Determination of Water Vapor Transmission Properties of Plastic Films and Sheets by Cup Method of Weight Gain and Loss”. As shown in Figure 5 As shown, under natural environment, with the increase of the crosslinking degree of the polymer, the water permeability of the material decreased, and in general, the synthesized material exhibited good moisturizing and water retention performance.

[0070] Test 5:

[0071] The wetting performance of the material was characterized by the determination of the contact angle. A precision syringe was used to deposit a drop of ultrapure water (~5 μL) on the surface of the film, and the data was recorded after 120 seconds of contact with the surface. As shown in Figure 6 As shown, the contact angle exhibited by Example 3 was 78.5°, and with the gradual increase of the content of tetramercapto monomer, the contact angle of the film gradually increased to 98.2° in Example 1. The experimental results showed that due to the aromatic ring structure of cinnamaldehyde, the final polymer had a high aromatic content in the structure, which ultimately led to the hydrophobicity of the film. In addition, with the addition of tetramercapto monomer, the network structure and rigidity of the polymer were greatly enhanced, making the film have a larger contact angle and stronger hydrophobicity. The raw materials of the synthesized material, cinnamaldehyde and tetramercapto monomer, provided good hydrophobicity and prevented water from penetrating the surface of the film, making it non-wetting externally, which was more suitable for use in rainy days.

[0072] Test 6:

[0073] The heat retention performance of the film was tested by constructing a small greenhouse, as shown in Figure 7 and Figure 8 As shown, Figure 7 The soil temperature in the greenhouse covered by the film rose from 15.4℃ to 30.6℃ in 1 hour, while the soil temperature in the greenhouse covered by low density polyethylene rose from 15.4℃ to 25.7℃ in 1 hour. This means that the soil in the film greenhouse preheats faster than that in the low density polyethylene greenhouse. In addition, the polymer film showed better heat insulation performance than the ordinary low density polyethylene film, as shown in Figure 8 During the cooling process of the greenhouse, the soil temperature covered by Example 3 decreased from 30℃ to 18.5℃ in 1 hour; the soil covered by low density polyethylene film decreased from 30℃ to 15.2℃.

[0074] Test 7:

[0075] UV light test was performed by using UV spectrophotometer to test the absorbance of the material at the wavelength of 400-800 nm, as shown in Figure 9 The transmittance of the film of the material in the wavelength range of 400-580 nm was significantly reduced, with good UV resistance. This function allows the film to appropriately inhibit the growth of weeds at the seedling stage of the product. When the film covers the soil, the absorbed light can be converted into heat.

[0076] Test 8:

[0077] A portion of the reaction raw material, cinnamaldehyde, 1,4-butanediol dithioacetic acid, and Example 3 were taken for infrared testing. As shown in Figure 10 The cross-linked polymer meets the expected Figure 10 CA is cinnamaldehyde, BDDA is 1,4-butanediol dithioacetic acid, and P-20 is Example 3.

[0078] Test 9:

[0079] The biodegradability of the material was evaluated by landfill experiments. The examples were buried in natural soil with a depth of 10 cm. The soil environment temperature was between 12-28℃, and the humidity fluctuated between 30%-60%, relying on natural environment fluctuations. As shown in Figure 11 , Figure 12 Morphological observation and degradation rate of Example 3 were performed on the 1st day, 56th day and 140th day, and Example 3 was picked up from the soil, washed with deionized water, dried, and weighed at predetermined intervals for comparison.

[0080] The experiment also added a control group to test the degradation performance of low-density polyethylene in the same environment.

[0081] Referring to Figure 11 P-20 is Example 3, and LDPE is a low-density polyethylene film.

[0082] It can be seen that the synthetic polymer material has good degradation effect in the natural environment. This is because the synthetic material contains rich ester bonds and thioacetal bonds. Among them, the ester bond is a group that has been proven to be decomposed in the natural environment; the thioacetal bond can be ROS (reactive oxygen species) responsive by various microorganisms in the soil and plant tissues, decomposed and produce cinnamaldehyde which is beneficial to plant growth.

[0083] Figure 12 The degradation rate of Examples 1-3 in the natural environment is represented in

[0084] Test 10:

[0085] To further prove the part about ROS (Reactive Oxygen Species) response in Test 9, it was carried out by soaking Example 3 in 5% hydrogen peroxide. Among them, 5% hydrogen peroxide concentration was used to simulate the concentration of active oxygen which plants and microorganisms in the natural environment respond to stress. Figure 13 The changes in the surface morphology of the material were recorded in detail. It can be seen that Example 3 has good degradation performance.

[0086] Test 11:

[0087] To further prove the part about the decomposition products of the material promoting plant growth in Test 9, as shown in Figure 14 150.0g of natural soil containing Example 3 (42 days after landfill of Example 3) was selected. Then it was placed in the lower half of the flowerpot (diameter 10 cm, depth 10 cm), and then filled with 50.0g of natural soil. Similar size and number of pea seeds were planted in each flowerpot (3 cm from the top of the soil), grown at 20-25°C for 2-3 weeks, in the same environment, using natural light, and at the same time, 20ml of deionized water was sprayed on the top of the flowerpot every day. As shown in Figure 14 The plant growth index, including plant height, root length, and fresh weight, was obtained.

[0088] The experiment also added a control group to test the effect of soil containing low-density polyethylene on plant growth in the same environment.

[0089] Referring to Figure 14 , I / on the left is the plant grown in soil containing Example 3, and II / on the right is the plant grown in soil containing low-density polyethylene film.

[0090] Compared with the control group, the growth index of the pea seedlings in the control group filled with the polymer was better, indicating that the microorganisms in the soil decomposed the polymer through ROS response and released cinnamaldehyde after forming. As a natural plant essential oil and plant pesticide, cinnamaldehyde has a promoting effect on plant growth, especially in the growth of plant roots. As shown in Figure 14As shown, compared with the pea seedlings of the blank group, the growth indexes of the pea seedlings treated by the polymer landfill are increased by 18.97% (plant height), 39.34% (root length), 40.40% (root weight), and 18.36% (fresh weight) after 30 days. The increase of the plant height, root length, and fresh weight of the pea seedlings is an important index for evaluating the growth promotion effect of the polymer film on the pea seedlings. The significant increase of the plant height, root length, and fresh weight indicates that the cinnamaldehyde formed after the decomposition of the polymer has a great influence on the growth of the pea seedlings. During the daily watering process, the cinnamaldehyde formed after the decomposition in the soil acts as a plant hormone to affect the growth of the crop roots. The growth of the crop roots is beneficial to the crop for absorbing water and nutrients from the soil and finally promotes the growth of the crop.

[0091] The present application is first equipped with a series of mixed solutions containing thiol monomers and cinnamaldehyde monomers. The mixed solutions can directly mix the thiol monomers and cinnamaldehyde monomers or dissolve them in a solvent. Through actual tests, it is found that the mixing by the solvent is better. Then the solution is pre-polymerized at 50°C. The obtained pre-polymer is uniformly coated in a reaction mold. Then the mold is placed in an oven at 120°C for heating to remove the solvent and make the thiol monomers and cinnamaldehyde monomers further react, polymerize, and crosslink, so as to obtain the hydrophobic polymer. The present application has the advantages of simple operation, high reaction efficiency, and green raw materials. The prepared green mulch has excellent performance, and the effects of temperature increase, soil conservation, and water prevention are stronger than those of general polyethylene mulch. The green mulch can be degraded in a natural environment and release substances beneficial to plant growth in response to ROS (reactive oxygen species), so as to achieve the parallel of environmental protection and plant growth promotion. The green mulch has simple preparation, high reaction efficiency, and certain industrialization prospect.

[0092] In summary, the present application provides a degradable multifunctional green agricultural mulch and a preparation method thereof. The cinnamaldehyde and thiol acrylate monomers are used to form a cross-linked polymer under the catalysis of a Lewis acid. The synthesized material has excellent biodegradability, mechanical properties, and multifunctionality in the use process, can release cinnamaldehyde in the degradation process, and promote crop growth, thereby providing a new solution for solving the pollution problem of traditional mulch. The present application has the advantages of simple operation, high reaction efficiency, natural raw material source, and good industrialization prospect.

[0093] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-described embodiments. Any technical solutions falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that some improvements and decorations made by ordinary technical personnel in the technical field without departing from the principle of the present application shall also be considered as the protection scope of the present application.​

Claims

1. A degradable multifunctional green agricultural mulching film, characterized in that: it is prepared by cross-linking reaction of cinnamaldehyde and a polythiol acrylate reagent under the catalysis of a Lewis acid. 2.The degradable multifunctional green agricultural mulching film according to claim 1, characterized in that: the polythiol acrylate reagent is at least one of 1, 4-butyl diester bis (mercaptoacetate) and pentaerythritol tetra-3-mercapto propionate. 3.The degradable multifunctional green agricultural mulching film according to claim 1, characterized in that: the Lewis acid is one or more of p-toluenesulfonic acid and trifluoroacetic acid. 4.The degradable multifunctional green agricultural mulching film according to claim 1, characterized in that: the cinnamaldehyde, the polythiol acrylate reagent and the Lewis acid are reacted in a solvent to obtain the mulching film. 5.The degradable multifunctional green agricultural mulching film according to claim 4, characterized in that: the solvent is one or more of tetrahydrofuran, hexane and dichloromethane. 6.The degradable multifunctional green agricultural mulching film according to claim 1, characterized in that: the molar ratio of mercapto groups in the polythiol acrylate reagent to aldehyde groups in the cinnamaldehyde is 1-3:

1. 7.The degradable multifunctional green agricultural mulching film according to claim 2, characterized in that: the polythiol acrylate reagent is a mixture of 1, 4-butyl diester bis (mercaptoacetate) and pentaerythritol tetra-3-mercapto propionate, and the molar ratio of 1, 4-butyl diester bis (mercaptoacetate) to pentaerythritol tetra-3-mercapto propionate is 1-6:

1. 8.A preparation method of the degradable multifunctional green agricultural mulching film according to any one of claims 1-7, characterized in that: it comprises the following steps: Step 1: mixing cinnamaldehyde and a polythiol acrylate reagent to configure a solution; Step 2: adding a Lewis acid catalyst to the solution in proportion; Step 3: pre-polymerizing the prepared solution at 30-70 DEG C to obtain a pre-polymer; and Step 4: uniformly coating the pre-polymer in a mold and heating it in an oven at 100-150 DEG C to obtain the green mulching film. 9.The preparation method of the degradable multifunctional green agricultural mulching film according to claim 8, characterized in that: the pre-polymerization time in Step 3 is 5-30 min; and the heating time in Step 4 is 2-5 h. 10.The preparation method of the degradable multifunctional green agricultural mulching film according to claim 8, characterized in that: Step 1 specifically comprises mixing cinnamaldehyde and a polythiol acrylate reagent in a solvent to configure a solution. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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