Preparation method of agricultural mulching film capable of degrading PHA

Abstract

The invention discloses a preparation method of an agricultural mulching film capable of degrading PHA, and belongs to the technical field of polyester degradable mulching films. Firstly, alkyl chain segments are grafted in starch, so that a starch phase has flexibility and hydrophobicity, meanwhile, mesoporous silica is subjected to silanization treatment and then is compounded with alkyl chain grafted starch, and the biodegradable mulching film is obtained. The preparation method comprises the following steps: constructing a mesoporous silica loaded starch composite filler with interface affinity, improving the problem of insufficient air permeability of a traditional PHA matrix, and then constructing a degradable PHA agricultural mulching film with a stable chain segment structure and a diffusion network through the synergistic effect of PHA, PBAT, the composite filler and a functional additive, so that the gas transmission capability of the film material is remarkably enhanced, and the film material has a good application prospect. The effective degradation of the mulching film in a soil environment is improved, so that the mulching film realizes balanced and efficient biodegradability in an actual agricultural use period.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyester degradable mulching films, and particularly relates to a preparation method of a degradable PHA agricultural mulching film. BACKGROUND

[0002] In the agricultural production process of fruit and vegetable crops, in order to reduce the environmental pollution caused by the residual traditional mulching film, the degradable mulching film gradually replaces the conventional polyolefin film. During the covering period, the soil microorganisms continuously consume oxygen and produce metabolic products such as carbon dioxide and water vapor in the metabolic process. Therefore, the mulching film material not only needs to have good degradability to avoid residual film pollution, but also needs to have suitable air permeability. The biobased degradable material represented by polyhydroxyalkanoate (PHA) is considered as a strong candidate for replacing the traditional mulching film because of its renewable source and complete biodegradability. However, the high crystallinity and large chain segment rigidity of PHA make the air permeability of the film material insufficient, which inhibits the degradation efficiency of the material in the soil environment and makes it difficult to achieve the expected degradation effect within the use cycle.

[0003] At present, in order to improve the application performance of the PHA mulching film, the existing researches mainly use the methods such as blending modification and inorganic filler filling to improve the gas permeability of PHA. Starch, as a natural polysaccharide, has the characteristics of moisture absorption and expansion, easy formation of microporous structure and rapid decomposition by microorganisms. In the polyester matrix, it can construct channels conducive to gas exchange and provide a degradation interface easily utilized by microorganisms. Therefore, introducing corn starch to structure regulate the PHA mulching film is an effective way to improve the air permeability and accelerate the degradation of the mulching film in the soil.

[0004] In the prior art, the Chinese patent application with the publication number CN109096713A discloses a starch compound for agricultural mulching film and a preparation method of a mulching film for pear germination period. Corn starch and polyhydroxybutyric acid valeric acid copolyester are mixed and treated under the action of microwaves, so that the starch particles are expanded and preliminarily fused with the polyester matrix. The mixture is then subjected to ray irradiation to regulate the molecular chain structure. Subsequently, nano-silicon dioxide and a silane coupling agent are added to realize interface combination and structure dispersion, so as to obtain a composite powder material, which is further processed to form a mulching film.

[0005] In the above technical solutions, starch and PHA are improved through microwave puffing and irradiation treatment to enhance the interfacial bonding between starch and PHA. However, starch and PHA have significant polarity differences. The former is rich in hydroxyl groups and is strongly hydrophilic, while the latter is a hydrophobic ester chain with weak interfacial forces. At the same time, the free radical reaction generated by irradiation is random, which can easily cause chain segment breakage and uneven local cross-linking. This results in uneven distribution of the two phases in the system and loose interfacial adhesion, making it difficult to form a continuous and stable multiphase framework structure, thus limiting the overall air permeability. In addition, although silica is treated with silane, it only undergoes a limited condensation reaction on the particle surface and fails to form a network structure that penetrates the entire phase with starch or PHA. This keeps the internal structure of the material in a dense state, and the pores are difficult to penetrate to form an effective diffusion pathway. As a result, the gas permeability of the agricultural mulch film is poor, and the degradation process in the soil environment is hindered, making it difficult to achieve effective degradation within the service life. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing biodegradable PHA agricultural mulch film. This method constructs a synergistic composite system consisting of a silane-modified mesoporous silica framework and alkyl-linked starch segments, which is then compounded with PHA and PBAT matrices with the assistance of chain extenders and stabilizers. This significantly improves the interfacial bonding ability and the permeability of the microporous network, thereby enhancing the gas transport efficiency of the mulch film and enabling its controlled, gradual degradation in the soil environment to meet the requirements of effective degradation.

[0007] The objective of this invention can be achieved through the following technical solutions: Step 1: Under the action of an initiator, stearyl methacrylate undergoes a free radical grafting reaction on the starch chain to obtain alkyl-linked branched starch. At the same time, mesoporous silica is silanized and surface modified, and then used as a carrier to composite with alkyl-linked branched starch to obtain mesoporous silica-supported starch composite filler.

[0008] Step 2: Using polyhydroxyalkanoate (PHA) and polybutylene terephthalate (PBAT) as polyester matrices, mesoporous silica-loaded starch composite filler as reinforcing and regulating components, and supplemented with polyepoxy chain extender, antioxidant 1010, polycarbodiimide and calcium stearate and other functional additives, the mixture is melt-extruded and granulated in a twin-screw extruder to obtain PHA composite polyester masterbatch.

[0009] Step 3: The PHA composite polyester masterbatch is melted and plasticized in a single screw extruder, and then extruded through a die to form a uniform film melt. After cooling, shaping, stretching and winding, PHA biodegradable agricultural mulch film is obtained.

[0010] Furthermore, the temperatures of each zone of the single-screw extruder are 140-160℃, 150-170℃, and 160-180℃ respectively, and the die temperature is 165-185℃.

[0011] Furthermore, the preparation process of PHA composite polyester masterbatch is as follows: Polyhydroxyalkanoate (PHA), polybutylene terephthalate (PBAT), mesoporous silica-supported starch composite filler, polyepoxy chain extender, antioxidant 1010, polycarbodiimide and calcium stearate were added to a high-speed mixer and stirred for 5-10 minutes. After being sealed and allowed to stand at 25-35℃ for 20-24 hours, the mixture was melt-extruded through a twin-screw extruder, cooled and granulated, and vacuum dried to constant weight to obtain PHA composite polyester masterbatch.

[0012] Furthermore, the temperatures of each zone of the twin-screw extruder are 120-130℃, 130-140℃, 140-150℃, 150-160℃, 160-170℃, and 170-180℃ respectively, and the die temperature is 170-180℃.

[0013] Furthermore, the mass ratio of polyhydroxyalkanoate (PHA), polybutylene terephthalate (PBAT), mesoporous silica-supported starch composite filler, polyepoxy chain extender, antioxidant 1010, polycarbodiimide, and calcium stearate is 600-800:200-400:10-20:0.5-2:0.1-0.5:0.5-2:0.1-0.5.

[0014] Furthermore, the preparation process of the mesoporous silica-supported starch composite filler is as follows: Silane-modified mesoporous silica, alkyl-linked starch, ethanol, and deionized water were placed in a reaction vessel and stirred at 25-35℃ for 20-40 min. A 5wt% sodium hydroxide aqueous solution was added to adjust the pH of the reaction solution to 8-9. The reaction was carried out at 50-70℃ for 1-3 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain mesoporous silica-supported starch composite filler.

[0015] Furthermore, the ratio of silane-modified mesoporous silica, alkyl-linked branched starch, sodium hydroxide aqueous solution, ethanol and deionized water is 30-60g: 20-40g: 10-15mL: 100-200mL: 100-200mL.

[0016] Furthermore, the preparation process of silane-modified mesoporous silica is as follows: Mesoporous silica, γ-glycidoxypropyltrimethoxysilane, ethanol and deionized water were placed in a reaction vessel and stirred at 25-35℃ for 20-40 min. A 0.5 mol / L aqueous acetic acid solution was added, and the reaction was continued at 50-60℃ for 2-3 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain silane-modified mesoporous silica.

[0017] Furthermore, the ratio of mesoporous silica, γ-glycidoxypropyltrimethoxysilane, aqueous acetic acid solution, ethanol, and deionized water is 50-70g: 5-10g: 8-15mL: 200-300mL: 20-30mL. Furthermore, the ratio of citric acid, alkyl-linked branched starch, and deionized water is 5-10g: 30-50g: 80-120mL.

[0018] Furthermore, the preparation process of alkyl-linked branched starch is as follows: Place 40-60g of corn starch and 100-120mL of deionized water in a reaction vessel under a nitrogen atmosphere and stir at 50℃ for 20min. Add 0.8g of potassium persulfate, 0.3-0.6g of sodium bisulfite, 0.8-1g of polyethylene glycol octylphenyl ether and 12g of stearyl methacrylate. Continue the reaction at the same temperature for 4-6h. Add 2-4mL of 2% hydroquinone to stop the reaction. After the reaction is complete, cool to room temperature, add anhydrous ethanol and let stand. Filter and vacuum dry the filter cake at 70℃ to constant weight to obtain alkyl-linked branched starch.

[0019] Furthermore, the ratio of corn starch, potassium persulfate, sodium bisulfite, polyethylene glycol octyl phenyl ether stearyl methacrylate, hydroquinone, and deionized water is 40-60g: 0.5-1g: 0.3-0.6g: 0.8-1g: 8-10g: 2-4mL: 100-120mL.

[0020] The beneficial effects of this invention are: 1. The biodegradable PHA agricultural mulch film prepared by this invention establishes a structural regulation basis by introducing alkyl-linked branched starch. Its long alkyl hydrophobic segments can significantly improve the compatibility between starch and hydrophobic polyester matrices such as PHA and PBAT, constructing a continuous gas transport path. In addition, the hydrophobic segments can also form a certain water vapor barrier effect in the early stage of the film, making the mulch film less prone to premature degradation due to water absorption in the early stage of laying. As the usage time progresses, soil moisture gradually penetrates into the interior of the film. The dispersed phase of alkyl esterified starch embedded in the polyester matrix can act as a transport node for water vapor and oxygen, assisting in the construction of a micro-diffusion network, promoting the continuous penetration of water, oxygen and microorganisms into the film, accelerating the breaking and degradation process of polyester molecular chains, and improving the degradation efficiency of PHA mulch film in the soil environment.

[0021] 2. The biodegradable PHA agricultural mulch film prepared by this invention uses starch loaded with mesoporous silica as a composite filler. Mesoporous silica has a highly ordered pore structure and a large specific surface area, which can provide a large number of loading sites for alkyl-linked starch. The organic functional groups introduced after silanization can form hydrogen bonds and chemical bonds with starch segments, making the starch more firmly fixed on the surface and pore walls of mesoporous silica. At the same time, the flexible and hydrophobic segments in the alkyl-linked starch can improve the interfacial environment of the mesoporous silica surface, effectively reduce the mutual adsorption between inorganic particles, and avoid the aggregation of mesoporous silica in the molten system, thereby maintaining its independent and uniform particle morphology. This allows the composite filler to remain highly dispersed in the polyester matrix, effectively improving the gas permeability of the mulch film, thereby accelerating the effective degradation of the PHA mulch film during its service life.

[0022] 3. The biodegradable PHA agricultural mulch film prepared by this invention introduces a composite filler of mesoporous silica loaded with starch. This filler forms a stable interfacial network with the PHA and PBAT polyester matrix through a multi-point synergistic mechanism, including hydrogen bonding, polar interaction, and interfacial adsorption. This interfacial synergy not only improves the microstructure of the matrix, enabling the formation of continuous and stable microscale diffusion channels within the film, but also enhances the mobility and interfacial responsiveness of the matrix chain segments. It avoids stress concentration and channel blockage that are easily caused by conventional fillers. Through the synergistic regulation of the particulate phase and the polyester matrix, the gas transport efficiency of the mulch film is effectively improved, thereby enhancing the penetration and action of soil moisture and microorganisms into the film, accelerating the degradation process of the polyester chain, and improving the degradation efficiency of the PHA mulch film, enabling it to meet the degradation requirements within its service life. Detailed Implementation

[0023] 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.

[0024] Example 1: This example provides a mesoporous silica-supported starch composite filler for biodegradable PHA agricultural mulch film, prepared through the following steps: S1: Place 40g of corn starch and 100mL of deionized water in a reaction vessel under a nitrogen atmosphere. Stir at 200r / min for 20min at 50℃. Add 0.8g of potassium persulfate, 0.3g of sodium bisulfite, 0.8g of polyethylene glycol octylphenyl ether and 8g of stearyl methacrylate. Continue the reaction at the same temperature and stirring rate for 4h. Add 2mL of 2% hydroquinone to stop the reaction. After the reaction is complete, cool to room temperature, add anhydrous ethanol and let stand. Filter and vacuum dry the filter cake at 70℃ to constant weight to obtain alkyl-linked branched starch.

[0025] S2: 50g of mesoporous silica, 5g of γ-glycidoxypropyltrimethoxysilane, 200mL of ethanol and 20mL of deionized water were placed in a reaction vessel and stirred at 200r / min for 20min at 25℃. 8mL of 0.5mol / L acetic acid aqueous solution was added and reacted at the same stirring rate at 50℃ for 2h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed twice with deionized water and ethanol. It was then vacuum dried at 60℃ to constant weight to obtain silane-modified mesoporous silica.

[0026] S3: Place 30g of silane-modified mesoporous silica, 20g of alkyl-linked branched starch, 100mL of ethanol and 100mL of deionized water in a reactor. Stir and mix at 200r / min for 20min at 25-35℃. Add 10mL of 5wt% sodium hydroxide aqueous solution to adjust the pH of the reaction solution to 8. React at 50℃ with the same stirring rate for 1h. After the reaction is completed, cool to room temperature, filter, wash the filter cake twice with deionized water and ethanol, and vacuum dry at 60℃ to constant weight to obtain mesoporous silica-supported starch composite filler.

[0027] Example 2: This example provides a mesoporous silica-supported starch composite filler for biodegradable PHA agricultural mulch film, prepared through the following steps: S1: Place 50g of corn starch and 110mL of deionized water in a reaction vessel under a nitrogen atmosphere. Stir at 250r / min for 30min at 55℃. Add 0.8g of potassium persulfate, 0.5g of sodium bisulfite, 0.9g of polyethylene glycol octylphenyl ether and 10g of stearyl methacrylate. Continue the reaction for 5h at the same temperature and stirring rate. Add 3mL of 2% hydroquinone to stop the reaction. After the reaction is complete, cool to room temperature, add anhydrous ethanol and let stand. Filter and vacuum dry the filter cake at 70℃ to constant weight to obtain alkyl-linked branched starch.

[0028] S2: 60g of mesoporous silica, 8g of γ-glycidoxypropyltrimethoxysilane, 250mL of ethanol and 25mL of deionized water were placed in a reaction vessel and stirred at 250r / min for 30min at 30℃. 12mL of 0.5mol / L acetic acid aqueous solution was added and the mixture was reacted at the same stirring rate at 55℃ for 2.5h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with deionized water and ethanol. The cake was then vacuum dried at 60-70℃ to constant weight to obtain silane-modified mesoporous silica.

[0029] S3: 45g of silane-modified mesoporous silica, 30g of alkyl-linked branched starch, 150mL of ethanol and 150mL of deionized water were placed in a reaction vessel and stirred at 250r / min for 30min at 30℃. 12mL of 5wt% sodium hydroxide aqueous solution was added to adjust the pH of the reaction solution to 8.5. The reaction was carried out at 60℃ with the same stirring rate for 2h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with deionized water and ethanol. The mixture was then vacuum dried at 65℃ to constant weight to obtain mesoporous silica-supported starch composite filler.

[0030] Example 3: This example provides a mesoporous silica-supported starch composite filler for biodegradable PHA agricultural mulch film, prepared through the following steps: S1: 60g of corn starch and 120mL of deionized water were placed in a reaction vessel under a nitrogen atmosphere and stirred at 300r / min for 40min at 60℃. 0.8g of potassium persulfate, 0.6g of sodium bisulfite, 1g of polyethylene glycol octylphenyl ether, and 12g of stearyl methacrylate were added. The reaction was continued for 6h at the same temperature and stirring rate. 4mL of 2% hydroquinone was added to terminate the reaction. After the reaction was completed, the mixture was cooled to room temperature, added anhydrous ethanol, allowed to stand, filtered, and the filter cake was vacuum dried at 70℃ to constant weight to obtain alkyl-linked branched starch. S2: 70g of mesoporous silica, 10g of γ-glycidoxypropyltrimethoxysilane, 300mL of ethanol and 30mL of deionized water were placed in a reaction vessel and stirred at 300r / min for 40min at 35℃. 15mL of 0.5mol / L acetic acid aqueous solution was added and the mixture was reacted at the same stirring rate at 60℃ for 3h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed 4 times with deionized water and ethanol. The cake was then vacuum dried at 70℃ to constant weight to obtain silane-modified mesoporous silica.

[0031] S3: 60g of silane-modified mesoporous silica, 40g of alkyl-linked branched starch, 200mL of ethanol and 200mL of deionized water were placed in a reaction vessel and stirred at 300r / min for 40min at 35℃. 15mL of 5wt% sodium hydroxide aqueous solution was added to adjust the pH of the reaction solution to 9. The reaction was carried out at 70℃ with the same stirring rate for 3h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed 4 times with deionized water and ethanol. It was then vacuum dried at 70℃ to constant weight to obtain mesoporous silica-supported starch composite filler.

[0032] The mesoporous silica-supported starch composite filler prepared in Examples 1-3 above firstly involves the starch molecular chain generating free radicals under the action of a potassium persulfate and sodium bisulfite redox initiation system, which then initiates free radical grafting polymerization of the double bonds in stearyl methacrylate. This causes long-chain alkyl side groups to attach to the starch backbone in the form of covalent bonds, resulting in alkyl-linked starch. Simultaneously, the silanol groups on the surface of the mesoporous silica undergo hydrolysis and condensation reactions with γ-glycidoxypropyltrimethoxysilane, introducing active epoxy functional groups into the surface and pore walls of the mesoporous silica, resulting in silane-modified mesoporous silica. Finally, under alkaline conditions, the epoxy groups on the silane coupling agent undergo ring-opening reactions under the nucleophilic attack of the starch hydroxyl groups, thereby achieving a strong chemical bond between the starch and the mesoporous silica, resulting in the mesoporous silica-supported starch composite filler.

[0033] Example 4: This example provides a biodegradable PHA agricultural mulch film, prepared through the following steps: Step 1: Add 600g of polyhydroxyalkanoate (PHA), 300g of polybutylene terephthalate (PBAT), 20g of mesoporous silica-supported starch composite filler prepared in Example 1, 10g of polyepoxy chain extender (Joncryl® ADR-4368), 1g of antioxidant 1010, 5g of polycarbodiimide, and 1g of calcium stearate to a high-speed mixer and stir at 500r / min for 5min. After sealing and standing at 25℃ for 20h, add it to a twin-screw extruder. Set the temperatures of the first six zones of the extruder to 120℃, 130℃, 140℃, 150℃, 160℃, and 170℃ respectively, and the die temperature to 170℃. After extrusion into strips, cool and granulate, and vacuum dry at 50℃ to constant weight to obtain PHA composite polyester masterbatch.

[0034] Step 2: Add 800g of PHA composite polyester masterbatch to a single-screw extruder. Set the temperatures of the extruder's first, second, and third zones to 140℃, 150℃, and 160℃, respectively, and the die temperature to 165℃. After the masterbatch is melted and plasticized, it is extruded through the die into a film-like melt. After cooling and shaping, it is stretched and flattened by traction rollers. The average film thickness is controlled to be 10μm. After being guided by tension rollers, it is wound into a roll to obtain biodegradable PHA agricultural mulch film.

[0035] Example 5: This example provides a biodegradable PHA agricultural mulch film, prepared through the following steps: Step 1: Add 700g of polyhydroxyalkanoate (PHA), 350g of polybutylene terephthalate (PBAT), 30g of mesoporous silica-supported starch composite filler prepared in Example 2, 15g of polyepoxy chain extender (Joncryl® ADR-4368), 3g of antioxidant 1010, 8g of polycarbodiimide, and 3g of calcium stearate to a high-speed mixer and stir at 700r / min for 8min. After sealing and standing at 30℃ for 22h, add it to a twin-screw extruder. Set the temperatures of the first six zones of the extruder to 125℃, 135℃, 145℃, 155℃, 165℃, and 175℃ respectively, and the die temperature to 175℃. After extrusion into strips, cool and granulate, and vacuum dry at 60℃ to constant weight to obtain PHA composite polyester masterbatch.

[0036] Step 2: Add 900g of PHA composite polyester masterbatch to a single-screw extruder. Set the temperatures of Zone 1, Zone 2, and Zone 3 of the extruder to 150℃, 160℃, and 170℃, respectively, and the die temperature to 175℃. After the masterbatch is melted and plasticized, it is extruded into a film-like melt through the die. After cooling and shaping, it is stretched and flattened by traction rollers. The average film thickness is controlled to be 10μm. After being guided by tension rollers, it is wound into a roll to obtain biodegradable PHA agricultural mulch film.

[0037] Example 6: This example provides a biodegradable PHA agricultural mulch film, prepared through the following steps: Step 1: Add 800g of polyhydroxyalkanoate (PHA), 400g of polybutylene terephthalate (PBAT), 40g of mesoporous silica-supported starch composite filler prepared in Example 3, 20g of polyepoxy chain extender (Joncryl® ADR-4368), 5g of antioxidant 1010, 10g of polycarbodiimide, and 5g of calcium stearate to a high-speed mixer and stir at 800r / min for 10min. After sealing and standing at 35℃ for 24h, add it to a twin-screw extruder. Set the temperatures of the first six zones of the extruder to 130℃, 140℃, 150℃, 160℃, 170℃, and 180℃ respectively, and the die temperature to 180℃. After extrusion into strips, cool and granulate, and vacuum dry at 50-70℃ to constant weight to obtain PHA composite polyester masterbatch.

[0038] Step 2: Add 1000g of PHA composite polyester masterbatch to a single-screw extruder. Set the temperatures of the first, second, and third zones of the extruder to 160℃, 170℃, and 180℃, respectively, and the die temperature to 185℃. After the masterbatch is melted and plasticized, it is extruded into a film-like melt through the die. After cooling and shaping, it is stretched and flattened by the traction roller. The average film thickness is controlled to be 10μm. After being guided by the tension roller, it is wound into a roll to obtain biodegradable PHA agricultural mulch film.

[0039] Comparative Example 1: Based on Example 5, commercially available starch was used instead of the alkyl-linked branched starch prepared in step S1 of Example 2, while the other steps remained unchanged.

[0040] Comparative Example 2: Based on Example 5, commercially available mesoporous silica was used instead of the silane-modified mesoporous silica prepared in step S3 of Example 2, while the other steps remained unchanged.

[0041] Comparative Example 3: Based on Example 5, the mesoporous silica-supported starch composite filler prepared in Example 2 was removed, while the remaining steps remained unchanged.

[0042] The polyhydroxyalkanoate (PHA) purchased in the above examples and comparative examples was produced by Ningbo Tianan Biomaterials Co., Ltd., and is a polyhydroxybutyrate-valerate copolyester with an average molecular weight of 50,000; polybutylene terephthalate-adipate was produced by Wuhan Shuer Biotechnology Co., Ltd., with an average molecular weight of 40,000; mesoporous silica was produced by Hangzhou Xinqiao Biotechnology Co., Ltd., and is a 200nm hollow mesoporous silica ball; starch was produced by Dezhou Gaofeng Starch Co., Ltd., and is an industrial-grade corn starch; polyethylene glycol octylphenyl ether was produced by Shanghai Maclean Biochemical Technology Co., Ltd., with an average molecular weight of 600; stearyl methacrylate was produced by Shanghai Maclean Biochemical Technology Co., Ltd., CAS number 32360-05-7; and the polyepoxy chain extender was produced by BASF AG, model Joncryl® ADR-4368.

[0043] The biodegradable PHA agricultural films prepared in the above examples and comparative examples were subjected to performance tests, and the test results are shown in Table 1.

[0044] Sample preparation: Referring to standard GB / T 17738.1-2013, the mulch films prepared in the above examples and comparative examples were cut into test samples of specified sizes with an average thickness of 10 μm; tensile test samples with a length of 150 mm and a width of 15 mm were cut for mechanical property testing; gas permeability test was conducted on film sheets with a diameter of 80 mm; the film was sheared and crushed to a particle size ≤ 2 mm, and 10 g of the crushed sample was added to each reactor for degradability testing.

[0045] Mechanical properties: Referring to standard GB / T 1040.3-2006, an electronic universal testing machine was used to conduct tensile tests on the samples at a tensile speed of 50 mm / min. The tensile strength and elongation at break of the mulch film were measured. Higher tensile strength and elongation at break indicate better mechanical properties of the film. Gas permeability: Referring to standard GB / T 1038.1-2022, the oxygen permeability and carbon dioxide permeability are measured using a gas permeability tester under specified temperature and pressure difference conditions. The higher the permeability, the better the gas permeability of the membrane.

[0046] Degradability: Referring to standard GB / T 19277.1-2011, the degree of biodegradability is represented by the amount of carbon dioxide released when the sample is decomposed by microorganisms under simulated composting conditions. The sample is uniformly mixed with composting substrate and placed in an aerobic composting reactor. The cumulative carbon dioxide release of the sample at 30d, 60d and 90d is recorded respectively, and the degradation rate at the corresponding time points is calculated accordingly.

[0047] Table 1 Performance Test Table of Biodegradable PHA Agricultural Mulch Film

[0048] As shown in Table 1, the PHA biodegradable mulch films prepared in Examples 4-6 all outperformed those in Comparative Examples 1-3. This demonstrates that the present invention, by constructing a composite filler formed by loading alkyl-linked branched starch with silane-modified mesoporous silica as a carrier, forms a uniformly dispersed microporous network in the polyester matrix, significantly improving interfacial bonding and establishing continuous gas transport channels. This structure not only enhances the mechanical strength of the material but also improves the diffusion efficiency of oxygen and carbon dioxide, thereby promoting the gradual degradation of polyester segments by microorganisms in the soil environment. This allows the mulch film to maintain stable performance during the coverage period and effectively degrade at the end of the period.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a degradable PHA agricultural mulch film, characterized by, Comprise the following steps: Step one: under the action of initiator, the free radical grafting reaction of stearyl methacrylate on starch chain is carried out, and the alkyl chain grafted starch is obtained, at the same time, the silanization modification of mesoporous silica is carried out, and the mesoporous silica is used as carrier and is compounded with the alkyl chain grafted starch, and the mesoporous silica loaded starch composite filler is obtained; Step two: with polyhydroxyaliphatic acid ester and polybutylene adipate terephthalate as polyester matrix, with mesoporous silica loaded starch composite filler as reinforcing and regulating component, and with multiple epoxy chain extender, antioxidant 1010, polycarbodiimide and calcium stearate multiple functional additives, melt extrusion and granulation are carried out in double screw extruder, and PHA composite polyester granules are obtained; Step three: the PHA composite polyester granules are melt plasticized in single screw extruder, and the uniform melt is formed through die extrusion, and the degradable PHA agricultural mulching film is obtained through cooling setting, traction flattening and winding treatment.

2. The method for preparing a biodegradable PHA agricultural mulch film according to claim 1, characterized in that, The mesoporous silica loaded starch composite filler in step one is prepared by the following steps: The silane modified mesoporous silica, alkyl chain grafted starch, ethanol and deionized water are placed in a reaction kettle, stirred at 25-35 DEG C for 20-40 min, 5wt% sodium hydroxide solution is added, the pH value of the reaction solution is adjusted to 8-9, and the reaction is carried out at 50-70 DEG C for 1-3 h, then filtered, washed and vacuum dried to constant weight to obtain the mesoporous silica loaded starch composite filler.

3. The method for preparing a biodegradable PHA agricultural mulch film according to claim 2, characterized in that, The amount ratio of the silane modified mesoporous silica, alkyl chain grafted starch, sodium hydroxide solution, ethanol and deionized water is 30-60 g: 20-40 g: 10-15 mL: 100-200 mL: 100-200 mL.

4. The method for preparing a biodegradable PHA agricultural mulch film according to claim 2, characterized in that, The silane modified mesoporous silica is prepared by the following steps: The mesoporous silica, gamma-glycidoxypropyltrimethoxysilane, ethanol and deionized water are placed in a reaction kettle, stirred at 25-35 DEG C for 20-40 min, 0.5 mol / L acetic acid solution is added, and the reaction is continued at 50-60 DEG C for 2-3 h, then filtered, washed and vacuum dried to constant weight to obtain the silane modified mesoporous silica.

5. The method for preparing a biodegradable PHA agricultural mulch film according to claim 4, characterized in that, The amount ratio of the mesoporous silica, gamma-glycidoxypropyltrimethoxysilane, acetic acid solution, ethanol and deionized water is 50-70 g: 5-10 g: 8-15 mL: 200-300 mL: 20-30 mL.

6. The method of claim 5, wherein the biodegradable PHA agricultural mulch is prepared by the steps of: The alkyl chain grafted starch is prepared by the following steps: 40-60 g of corn starch and 100-120 mL of deionized water are placed in a reaction kettle under the protection of nitrogen atmosphere, stirred at 50 DEG C for 20 min, 0.8 g of potassium persulfate, 0.3-0.6 g of sodium bisulfite, 0.8-1 g of polyethylene glycol octylphenyl ether and 12 g of stearyl methacrylate are added, and the reaction is continued at the same temperature for 4-6 h, 2-4 mL of 2% hydroquinone is added to stop the reaction, anhydrous ethanol is added and placed, filtered, and the filter cake is vacuum dried at 70 DEG C to constant weight to obtain the alkyl chain grafted starch; The corn starch, potassium persulfate, sodium bisulfite, polyethylene glycol octylphenyl ether stearyl methacrylate, hydroquinone and deionized water are used in a ratio of 40-60g: 0.5-1g: 0.3-0.6g: 0.8-1g: 8-10g: 2-4mL: 100-120mL.

7. The method for preparing a biodegradable PHA agricultural mulch film according to claim 1, characterized in that, The PHA composite polyester master batch in step two is prepared by the following steps: The polyhydroxyalkanoate, polybutylene adipate terephthalate, mesoporous silica loaded starch composite filler, multi-epoxy chain extender, antioxidant 1010, polycarbodiimide and calcium stearate are added into a high-speed mixer, stirred for 5-10min, sealed and placed at 25-35℃ for 20-24h, then melt-extruded through a twin-screw extruder, cooled and granulated, vacuum dried to constant weight to obtain the PHA composite polyester master batch.

8. The method for preparing a biodegradable PHA agricultural mulch film according to claim 7, characterized in that, The mass ratio of the polyhydroxyalkanoate, polybutylene adipate terephthalate, mesoporous silica loaded starch composite filler, multi-epoxy chain extender, antioxidant 1010, polycarbodiimide and calcium stearate is 600-800: 200-400: 10-20: 0.5-2: 0.1-0.5: 0.5-2: 0.1-0.

5.

9. The method for preparing a biodegradable PHA agricultural mulch film according to claim 1, characterized in that, The temperature of each zone of the twin-screw extruder in step two is 120-130℃, 130-140℃, 140-150℃, 150-160℃, 160-170℃ and 170-180℃ in turn, and the die temperature is 170-180℃.

10. The method for preparing a biodegradable PHA agricultural mulch film according to claim 1, characterized in that, The temperature of each zone of the single-screw extruder in step three is 140-160℃, 150-170℃ and 160-180℃ in turn, and the die temperature is 165-185℃.

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