Starch polylactic acid composite crosslinking modified degradable material and preparation method thereof

Abstract

The application discloses a starch-polylactic acid composite crosslinking modified degradable material and a preparation method thereof, and relates to the technical field of polylactic acid degradable materials.The application discloses a preparation method of a starch-polylactic acid composite crosslinking modified degradable material, and comprises the following steps: reacting a dynamic coordination crosslinking agent, nanocellulose-dopamine grafting and esterified modified starch to obtain component A; blending polylactic acid and PBAT, and then adding component A, a sodium lignosulfonate-nano TiO2-Fe compound and glycerol, and then extruding and granulating to obtain granules; and immersing and treating the granules in an ethanol solution containing ferric chloride hexahydrate, and then drying to obtain the starch-polylactic acid composite crosslinking modified degradable material.The starch-polylactic acid composite crosslinking modified degradable material prepared by the application has the advantages of good mechanical properties and effective regulation of the degradation rate when applied to agricultural mulching films.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid biodegradable materials technology, specifically to a starch-polylactic acid composite crosslinked modified biodegradable material and its preparation method. Background Technology

[0002] Covering soil with agricultural mulch film can help retain heat and moisture, promote crop growth, and improve economic efficiency. It can also prevent weed growth and control pests and diseases, thus promoting plant growth and protecting root systems. While agricultural plastic mulch film can significantly increase yields and improve economic efficiency, plastic is a high-molecular-weight compound with a degradation cycle of hundreds of years. Agricultural mulch film cannot degrade in the soil, resulting in an increasing number of film fragments remaining in the soil. These fragments disrupt the continuity of soil pores, slowing the downward movement of water from the surface and preventing water from rising from the bottom. This hinders the transport of water and fertilizer, reduces soil permeability, leads to decreased soil fertility and soil compaction, greatly weakens the soil's drought resistance, and significantly impacts crop growth and development.

[0003] Polylactic acid (PLA) possesses excellent biodegradability, biocompatibility, high mechanical strength, and easy processing properties, and is considered one of the most promising biomaterials currently available. However, the notched impact strength of PLA is only 2.7 kJ·m. 2 The elongation at break is about 3.5%. Its inherent brittleness, low heat resistance and slow crystallization rate seriously restrict the development and application of PLA materials in the field of plastics. Therefore, the development of super-tough polylactic acid materials has important theoretical and application value. In order to improve the comprehensive performance of PLA materials, researchers have tried a variety of modification strategies: (1) Adding flexible polymers such as polybutylene adipate terephthalate (PBAT) or polycaprolactone (PCL) can improve the elongation at break. However, PBAT has poor compatibility with PLA and requires compatibilizers (such as maleic anhydride grafts). Excessive toughening will reduce the modulus and tear strength. (2) Nanofiller reinforcement: Introducing rigid particles such as nanocellulose and montmorillonite can improve heat resistance and modulus. However, nanofillers are prone to agglomeration and have weak interfacial bonding with the matrix, making it difficult to balance toughness and rigidity. (3) Degradation rate regulation: The degradation cycle can be adjusted by adding photosensitizers, hydrolysis promoters or cross-linking agents, but a single response mechanism often leads to a degradation rate that is "fast at the beginning and slow at the end" or "slow at the beginning and slow at the end", which cannot achieve the "time-sequence matching" requirement of stability during the functional period and rapid pyrolysis after the functional period. (4) Anti-ultraviolet aging: Nano titanium dioxide or organic ultraviolet absorbers are commonly used, but both have poor compatibility with PLA, and ultraviolet absorbers will become ineffective after migration.

[0004] Despite the achievements of the aforementioned improvements, existing technologies still suffer from the following core problems: First, multiple performance objectives are difficult to coordinate – toughening often sacrifices strength and heat resistance, while accelerated degradation leads to a shortened functional period, and UV-resistant additives and degradation promoters interfere with each other; second, degradation initiation is uncontrollable – existing photodegradation or hydrolysis systems are mostly single-trigger, making the mulch film susceptible to premature degradation by rain or sunlight during outdoor use, while degradation slows down in the later stages of burial; third, interface design lacks dynamism – traditional compatibilizers are permanent chemical bonds and cannot adjust the network structure according to external forces or environmental changes, resulting in an imbalance between material rigidity and flexibility. Therefore, there is an urgent need to develop a PLA composite mulch film material that can simultaneously address the problems of PLA's high brittleness, poor heat resistance, uncontrollable degradation cycle, and insufficient outdoor weather resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a starch-polylactic acid composite crosslinked modified biodegradable material and its preparation method, thereby solving the following technical problems: The inherent drawbacks of existing polylactic acid (PLA), such as high brittleness, low heat resistance, and slow crystallization rate, severely restrict the development and application of PLA materials in agricultural mulch films.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material includes the following steps: S1: The dynamic coordination crosslinking agent, nanocellulose-dopamine graft, and solvent are mixed, esterified modified starch is added, stirred and dispersed, and then freeze-dried to obtain component A; S2: Polylactic acid and PBAT are added to a twin-screw extruder for blending. Then, a premix containing component A prepared in S1, sodium lignosulfonate-nano TiO2-Fe composite, and glycerol is added to the twin-screw extruder. The mixture is then extruded and granulated to obtain granules. S3: The granules are immersed in an ethanol solution containing ferric chloride hexahydrate and dried to obtain a starch-polylactic acid composite crosslinked modified biodegradable material; The preparation method of the dynamic coordination crosslinking agent includes the following steps: Itaconic acid, epoxidized soybean oil, and toluene were added to a reaction vessel and mixed. BF3·OEt2 was added and mixed again. The temperature was controlled at 70-80℃ and the reaction was maintained for 2-4 hours. Toluene was removed by rotary evaporation to obtain the intermediate. The intermediate and dichloromethane were added to a reactor and mixed, and the temperature was controlled at 20-35℃. DCC, DMAP, and dichloromethane component I were added and mixed, and then added to the reactor. The reactor was activated for 0.5-1h. Dopamine hydrochloride and dichloromethane component II were mixed and added to the reactor. Triethylamine was added, and the reactor was kept at a constant temperature under stirring for 18-24h. Dichloromethane was removed by rotary evaporation. The residue was diluted with ethyl acetate, precipitated, washed, and dried to obtain the dynamic coordination crosslinking agent.

[0007] As a further aspect of the present invention, the proportions of each raw material in the dynamic coordination crosslinking agent are as follows: The addition ratio of itaconic acid, epoxidized soybean oil, toluene, BF3·OEt2, dichloromethane, DCC, DMAP, dichloromethane component one, dopamine hydrochloride, dichloromethane component two, and triethylamine is 10g: 75-85g: 100-200mL: 0.5-1g: 50-100mL: 8-12g: 0.4-0.6g: 50-100mL: 45-60g: 50-100mL: 20-30mL.

[0008] As a further aspect of the present invention: the solvent in S1 is composed of tetrahydrofuran and deionized water in a volume ratio of 3:1; the mass ratio of dynamic coordination crosslinking agent, nanocellulose-dopamine graft, and esterified modified starch is 6-10:3-5:20-30; the addition ratio of the total mass of dynamic coordination crosslinking agent, nanocellulose-dopamine graft, and esterified modified starch to solvent is 1g:5-10mL; In S2, the mass ratio of polylactic acid, PBAT, component A, sodium lignosulfonate-nano TiO2-Fe complex, and glycerol is 40-50:10-15:30-50:3-5:5-8. The mass percentage of the ethanol solution containing ferric chloride hexahydrate in S3 is 0.5-1 wt%; the addition ratio of granules to the ethanol solution containing ferric chloride hexahydrate is 1 g: 3-6 mL.

[0009] As a further aspect of the present invention, the method for preparing esterified modified starch includes the following steps: A1: Add starch, octanoic anhydride, DMAP, and anhydrous pyridine to a reaction flask and disperse them. Control the temperature at 70-80℃ and keep the reaction at this temperature for 3-6 hours. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain octanoic acid starch ester. A2: Add octanoic acid starch, benzoic anhydride, DMAP, and anhydrous pyridine to a reaction flask and mix. Control the temperature at 60-70℃ and keep the reaction at this temperature for 1-3 hours. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain esterified modified starch.

[0010] As a further aspect of the present invention: the addition ratio of starch, octanoic anhydride, DMAP, and anhydrous pyridine in A1 is 10g: 2.5-3.5g: 0.2-0.3g: 50-100mL; In A2, the addition ratio of octanoic acid starch, benzoic anhydride, DMAP, and anhydrous pyridine is 10g: 2-3g: 0.2-0.3g: 50-100mL.

[0011] As a further aspect of the present invention, the preparation method of the nanocellulose-dopamine graft includes the following steps: B1: Mix CNC and 0.8-1.2 mol / L MES buffer, add sodium periodate, and stir the reaction at 25-30℃ in the dark for 1-3 hours; add ethylene glycol to disperse, keep the reaction at the same temperature for 0.5-1 hours, centrifuge, and wash with water to obtain the intermediate product; B2: Mix the intermediate product with 0.8-1.2 mol / L MES buffer, add dopamine hydrochloride and sodium cyanoborohydride, control the temperature at 25-30℃ and stir the reaction in the dark for 18-24 h, centrifuge, wash, freeze dry to obtain nanocellulose-dopamine graft.

[0012] As a further aspect of the present invention: the addition ratio of CNC, 0.8-1.2 mol / L MES buffer, sodium periodate, and ethylene glycol in B1 is 10 g: 200-400 mL: 0.8-1.2 g: 0.05-0.1 g; The addition ratio of intermediate product, 0.8-1.2 mol / L MES buffer, dopamine hydrochloride, and sodium cyanoborohydride in B2 is 10 g: 200-400 mL: 1.5-2.5 g: 0.2-0.5 g.

[0013] As a further embodiment of the present invention, the preparation method of sodium lignosulfonate-nano TiO2-Fe composite includes the following steps: mixing nano TiO2, deionized water, and citric acid, adjusting the pH to 2.5-3, adding ferric chloride hexahydrate, stirring and dispersing for 1-2 hours, adding sodium lignosulfonate, adjusting the pH to 5, stirring and reacting for 1-3 hours, centrifuging, washing, and freeze-drying to obtain sodium lignosulfonate-nano TiO2-Fe composite.

[0014] As a further embodiment of the present invention: the addition ratio of nano TiO2, deionized water, citric acid, ferric chloride hexahydrate, and sodium lignosulfonate is 10g: 100-200mL: 2-3g: 1-1.5g: 1-1.5g.

[0015] As a further embodiment of the present invention: the twin-screw extruder in S2 has a length-to-diameter ratio of 35-40, and the temperature settings of each zone are as follows: conveying section 135-140℃, melting section 145-150℃, mixing section 150-155℃, venting section 140-145℃, and die head 135-140℃; the screw speed is 220-170 rpm.

[0016] A starch-polylactic acid composite crosslinked modified biodegradable material is prepared by any one of the above preparation methods.

[0017] As a further aspect of the present invention: the above-mentioned starch-polylactic acid composite crosslinked modified biodegradable material is applied to agricultural mulch film; the agricultural mulch film is made by casting or blow molding of the starch-polylactic acid composite crosslinked modified biodegradable material.

[0018] As a further aspect of the present invention, the thickness of the agricultural mulch film is 10-20 μm.

[0019] The beneficial effects of this invention are: This application involves adding a dynamic coordination crosslinking agent, esterified modified starch, nanocellulose-dopamine graft, sodium lignosulfonate-nanoTiO2-Fe composite to the raw materials, and Fe treatment to the granules. 3+ Impregnation treatment has the following effects: (1) This application prepares an intermediate through a ring-opening esterification reaction of itaconic acid and epoxidized soybean oil, and then, after activation by DCC / DMAP, grafts it with dopamine hydrochloride to obtain a dynamic coordination crosslinking agent with hydroxyl, carboxyl, and catechol groups. In subsequent Fe... 3+ During the impregnation process, the catechol groups react with Fe 3+ Dynamic coordination bonds are formed, and simultaneously, hydroxyl and carboxyl groups form hydrogen bonds with functional groups in starch and polylactic acid molecules, constructing a dynamic coordination bond-hydrogen bond dual crosslinking network. This crosslinking network not only effectively fills the interfacial gaps between starch and polylactic acid, improving their compatibility, but also disperses the external forces on the material through the reversible breaking and recombination of dynamic coordination bonds, thereby significantly improving the material's mechanical properties and toughness. At the same time, the crosslinking network can inhibit the penetration of water molecules, optimizing the material's barrier properties.

[0020] (2) This application utilizes octanoic anhydride and benzoic anhydride to perform two-step esterification modification of starch. On the one hand, it reduces the hydrophilicity of starch and decreases the binding of hydroxyl groups with water molecules, thereby reducing the water vapor permeability of the material and improving its moisture-proof performance. On the other hand, the introduction of ester groups increases the hydrophobicity of starch molecules, significantly improving their compatibility with polylactic acid and dynamic coordination crosslinking agents, preventing starch agglomeration in the composite material, and further optimizing the mechanical properties and light transmittance of the material. Moreover, the esterified starch still retains good biodegradability and will not affect the final degradation performance of the material, achieving a balance between moisture-proof performance, compatibility, and degradability.

[0021] (3) This application utilizes the ultra-high specific surface area and strength of nanocellulose. After oxidation with sodium periodate, aldehyde groups are generated, which then undergo a Schiff base reaction with the amino group of dopamine and are reduced by sodium cyanoborohydride to achieve the grafting of dopamine onto the CNC surface. The grafted nanocellulose not only retains its high strength properties, but the dopamine catechol groups on its surface can also interact with Fe in the dynamic coordination crosslinking agent. 3+It forms coordination bonds and hydrogen bonds with starch and polylactic acid, becoming a reinforcing node in the cross-linked network. Moreover, the nano-size effect of nanocellulose can fill the micro-pores inside the material, reduce light scattering, and thus improve the light transmittance of the material. When dispersed in composite materials, it can effectively transfer external forces, further improving the tensile strength and tear resistance of the material, solving the problems of easy agglomeration and poor reinforcing effect of traditional nanofillers.

[0022] (4) This application utilizes the excellent ultraviolet shielding properties of nano-TiO2, which can absorb ultraviolet rays and convert them into heat energy, thus preventing ultraviolet rays from damaging the molecular structure of the material; and introduces Fe 3+ The synergistic effect of sodium lignosulfonate, a natural anti-aging agent, enhances the UV absorption capacity of TiO2 and slows down the oxidative degradation of materials by capturing free radicals generated during aging. Furthermore, sodium lignosulfonate's surface activity improves the dispersibility of nano-TiO2 in composite materials, preventing agglomeration and reduced light transmittance. Simultaneously, the hydroxyl and sulfonic acid groups of sodium lignosulfonate can form hydrogen bonds with starch and polylactic acid, further optimizing interfacial compatibility, reducing interfacial defects, and thus improving the barrier and mechanical properties of the material. Finally, nano-TiO2 and Fe... 3+ It can act as a catalyst for biodegradation, accelerating the degradation rate of starch and polylactic acid, and ensuring that materials degrade rapidly in the natural environment.

[0023] (5) This application applies Fe to the granules. 3+ Impregnation treatment, so that Fe 3+ It penetrates into the interior of the granules and forms dynamic coordination bonds with the dynamic coordination crosslinking agent to build a complete crosslinking network; subsequent vacuum drying can remove residual solvents and moisture from the material, avoiding the influence of moisture on the mechanical properties and stability of the material. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1: The preparation method of the dynamic coordination crosslinking agent includes the following steps: 10g itaconic acid, 75g epoxidized soybean oil (ESO, epoxy value 0.35) and 100mL toluene were added to a reaction vessel and mixed. 0.5g BF3·OEt2 was added and mixed. The temperature was controlled at 70℃ and the reaction was kept at this temperature for 2 hours. Toluene was removed by rotary evaporation to obtain the intermediate. The intermediate prepared above was mixed with 50 mL of dichloromethane in a reactor and the temperature was controlled at 20 °C. 8 g of DCC, 0.4 g of DMAP, and 50 mL of dichloromethane were added and mixed again before being added to the reactor. The mixture was activated for 0.5 h. 45 g of dopamine hydrochloride was mixed with 50 mL of dichloromethane and added to the reactor. 20 mL of triethylamine was added and the mixture was kept at a constant temperature for 18 h under stirring. Dichloromethane was removed by rotary evaporation. The residue was diluted with ethyl acetate, precipitated, washed, and dried to obtain the dynamic coordination crosslinking agent.

[0026] The preparation method of esterified modified starch includes the following steps: A1: 10g starch, 2.5g octanoic anhydride, 0.2g DMAP and 50mL anhydrous pyridine were added to a reaction flask and dispersed. The temperature was controlled at 70℃ and the reaction was kept at this temperature for 3h. Ethanol was added to precipitate the solid, which was then filtered, washed and dried to obtain octanoic acid starch ester. A2: Add 10g of octanoic acid starch, 2g of benzoic anhydride, 0.2g of DMAP, and 50mL of anhydrous pyridine to a reaction flask and mix. Control the temperature at 60℃ and keep the reaction at this temperature for 1h. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain esterified modified starch.

[0027] The preparation method of nanocellulose-dopamine grafts includes the following steps: B1: Mix 10g of CNC (200nm long, 10nm in diameter) with 200mL of 1mol / L MES buffer (pH=5.5), add 0.8g of sodium periodate, and stir at 25℃ in the dark for 1h; add 0.05g of ethylene glycol to disperse, keep warm for 0.5h, centrifuge and wash with water to obtain the intermediate product; B2: Mix 10g of intermediate product with 200mL of 1mol / L MES buffer, add 1.5g of dopamine hydrochloride and 0.2g of sodium cyanoborohydride, control the temperature at 25℃ and stir for 18h in the dark, centrifuge, wash, freeze dry to obtain nanocellulose-dopamine graft.

[0028] The preparation method of sodium lignosulfonate-nano TiO2-Fe composite includes the following steps: 10g of nano-TiO2, 100mL of deionized water, and 2g of citric acid were mixed and the pH was adjusted to 2.5. 1g of ferric chloride hexahydrate was added and the mixture was stirred and dispersed for 1h. 1g of sodium lignosulfonate was added and the pH was adjusted to 5. The mixture was stirred and reacted for 1h. After centrifugation, washing, and freeze-drying, sodium lignosulfonate-nano-TiO2-Fe composite was obtained.

[0029] Example 2: The preparation method of the dynamic coordination crosslinking agent includes the following steps: 10g itaconic acid, 80g epoxidized soybean oil (ESO, epoxy value 0.35) and 100mL toluene were added to a reaction vessel and mixed. 0.7g BF3·OEt2 was added and mixed. The temperature was controlled at 75℃ and the reaction was kept at this temperature for 3h. Toluene was removed by rotary evaporation to obtain the intermediate. The intermediate prepared above was mixed with 50 mL of dichloromethane in a reactor and the temperature was controlled at 30 °C. 10 g of DCC, 0.5 g of DMAP, and 50 mL of dichloromethane were added and mixed again before being added to the reactor. The mixture was activated for 0.5 h. 55 g of dopamine hydrochloride was mixed with 50 mL of dichloromethane and added to the reactor. 25 mL of triethylamine was added and the mixture was kept at a constant temperature for 21 h under stirring. Dichloromethane was removed by rotary evaporation. The residue was diluted with ethyl acetate, precipitated, washed, and dried to obtain the dynamic coordination crosslinking agent.

[0030] The preparation method of esterified modified starch includes the following steps: A1: 10g starch, 3g octanoic anhydride, 0.2g DMAP and 50mL anhydrous pyridine were added to a reaction flask and dispersed. The temperature was controlled at 75℃ and the reaction was maintained for 4.5h. Ethanol was added to precipitate the solid, which was then filtered, washed and dried to obtain octanoic acid starch ester. A2: Add 10g of octanoic acid starch, 2.5g of benzoic anhydride, 0.2g of DMAP, and 50mL of anhydrous pyridine to a reaction flask and mix. Control the temperature at 65℃ and keep the reaction at this temperature for 2 hours. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain esterified modified starch.

[0031] The preparation method of nanocellulose-dopamine grafts includes the following steps: B1: Mix 10g of CNC (200nm long, 10nm in diameter) with 300mL of 1mol / L MES buffer (pH=5.5), add 1g of sodium periodate, and stir at 30℃ in the dark for 2h; add 0.07g of ethylene glycol to disperse, keep warm for 0.5h, centrifuge and wash with water to obtain the intermediate product; B2: Mix 10g of intermediate product with 300mL of 1mol / L MES buffer, add 2g of dopamine hydrochloride and 0.4g of sodium cyanoborohydride, control the temperature at 30℃ and stir the reaction in the dark for 21h, centrifuge, wash, freeze dry to obtain nanocellulose-dopamine graft.

[0032] The preparation method of sodium lignosulfonate-nano TiO2-Fe composite includes the following steps: 10g of nano-TiO2, 100mL of deionized water, and 2.5g of citric acid were mixed and the pH was adjusted to 2.5. 1.2g of ferric chloride hexahydrate was added and the mixture was stirred and dispersed for 1.5h. 1.2g of sodium lignosulfonate was added and the pH was adjusted to 5. The mixture was stirred and reacted for 2h. After centrifugation, washing, and freeze-drying, sodium lignosulfonate-nano-TiO2-Fe composite was obtained.

[0033] Example 3: The preparation method of the dynamic coordination crosslinking agent includes the following steps: 10g itaconic acid, 85g epoxidized soybean oil (ESO, epoxy value 0.35) and 200mL toluene were added to a reaction vessel and mixed. 1g BF3·OEt2 was added and mixed. The temperature was controlled at 80℃ and the reaction was kept at this temperature for 4h. Toluene was removed by rotary evaporation to obtain the intermediate. The intermediate prepared above was added to a reaction vessel and mixed with 100 mL of dichloromethane. The temperature was controlled at 35 °C. 12 g of DCC, 0.6 g of DMAP, and 100 mL of dichloromethane were added to the reaction vessel and the mixture was activated for 1 h. 60 g of dopamine hydrochloride was mixed with 100 mL of dichloromethane and added to the reaction vessel. 30 mL of triethylamine was added and the mixture was kept at a constant temperature for 24 h under stirring. Dichloromethane was removed by rotary evaporation. The residue was diluted with ethyl acetate, precipitated, washed, and dried to obtain the dynamic coordination crosslinking agent.

[0034] The preparation method of esterified modified starch includes the following steps: A1: 10g starch, 3.5g octanoic anhydride, 0.3g DMAP and 100mL anhydrous pyridine were added to a reaction flask and dispersed. The temperature was controlled at 80℃ and the reaction was kept at this temperature for 6h. Ethanol was added to precipitate the solid, which was then filtered, washed and dried to obtain octanoic acid starch ester. A2: Add 10g of octanoic acid starch, 3g of benzoic anhydride, 0.3g of DMAP, and 100mL of anhydrous pyridine to a reaction flask and mix. Control the temperature at 60-70℃ and keep the reaction at this temperature for 3h. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain esterified modified starch.

[0035] The preparation method of nanocellulose-dopamine grafts includes the following steps: B1: Mix 10g of CNC (200nm long, 10nm in diameter) with 400mL of 1mol / L MES buffer (pH=5.5), add 1.2g of sodium periodate, and stir the mixture at 30℃ in the dark for 3h; add 0.1g of ethylene glycol to disperse the mixture, keep it warm for 1h, centrifuge and wash with water to obtain the intermediate product; B2: Mix 10g of intermediate product with 400mL of 1mol / L MES buffer, add 2.5g of dopamine hydrochloride and 0.5g of sodium cyanoborohydride, control the temperature at 30℃ and stir the reaction in the dark for 24h, centrifuge, wash, freeze dry to obtain nanocellulose-dopamine graft.

[0036] The preparation method of sodium lignosulfonate-nano TiO2-Fe composite includes the following steps: 10g of nano-TiO2, 200mL of deionized water, and 3g of citric acid were mixed and the pH was adjusted to 3. 1.5g of ferric chloride hexahydrate was added and the mixture was stirred and dispersed for 2h. 1.5g of sodium lignosulfonate was added and the pH was adjusted to 5. The mixture was stirred and reacted for 3h. After centrifugation, washing, and freeze-drying, sodium lignosulfonate-nano-TiO2-Fe composite was obtained.

[0037] Example 4: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: S1: 8g of the dynamic coordination crosslinking agent prepared in Example 1, 4g of the nanocellulose-dopamine graft prepared in Example 1, 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 1 was added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 1, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0038] Example 5: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: S1: 8g of the dynamic coordination crosslinking agent prepared in Example 2, 4g of the nanocellulose-dopamine graft prepared in Example 2, 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 2 were added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 2, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0039] Example 6: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: S1: 8g of the dynamic coordination crosslinking agent prepared in Example 3, 4g of the nanocellulose-dopamine graft prepared in Example 3, 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 3 were added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 3, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0040] Comparative Example 1: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: S1: Mix 8g of the dynamic coordination crosslinking agent prepared in Example 2, 4g of the nanocellulose-dopamine graft prepared in Example 2, 225mL of tetrahydrofuran, and 75mL of deionized water, add 25g of starch, stir to disperse, freeze dry, and obtain component A; S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 2, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0041] Comparative Example 2: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: S1: 8g of the dynamic coordination crosslinking agent prepared in Example 2, 4g of CNC (200nm long, 10nm in diameter), 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 2 were added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 2, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0042] The preparation method of the additive in Comparative Example 3 includes the following steps: 10g itaconic acid, 80g epoxidized soybean oil (ESO, epoxy value 0.35) and 100mL toluene were added to a reactor and mixed. 0.7g BF3·OEt2 was added and mixed. The temperature was controlled at 75℃ and the reaction was kept at this temperature for 3 hours. Toluene was removed by rotary evaporation to obtain the additive.

[0043] A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material includes the following steps: S1: 8g of the additive prepared in Comparative Example 3, 4g of the nanocellulose-dopamine graft prepared in Example 2, 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 2 were added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 2, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0044] Comparative Example 4: The preparation method of sodium lignosulfonate-nano TiO2 composite includes the following steps: 10g of nano TiO2, 100mL of deionized water and 2.5g of citric acid are mixed, the pH is adjusted to 2.5, 1.2g of sodium lignosulfonate is added, the pH is adjusted to 5, the mixture is stirred and reacted for 2h, centrifuged, washed and freeze-dried to obtain sodium lignosulfonate-nano TiO2 composite.

[0045] A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material includes the following steps: S1: 8g of the dynamic coordination crosslinking agent prepared in Example 2, 4g of the nanocellulose-dopamine graft prepared in Example 2, 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 2 were added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending, then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2 composite prepared in comparative example 4, and 6g of glycerol premix to the twin-screw extruder, extrude and granulate to obtain granules; S3: 10g of granules were immersed in 50mL of 0.5wt% ferric chloride hexahydrate ethanol solution, dried at room temperature for 30min under ventilation, and then dried under vacuum at 50℃ for 12h to obtain starch polylactic acid composite crosslinked modified biodegradable material.

[0046] Comparative Example 5: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: S1: 8g of the dynamic coordination crosslinking agent prepared in Example 1, 4g of the nanocellulose-dopamine graft prepared in Example 1, 225mL of tetrahydrofuran, and 75mL of deionized water were mixed together, and 25g of the esterified modified starch prepared in Example 1 was added. The mixture was stirred and dispersed, and then freeze-dried to obtain component A. S2: Add 45g of polylactic acid and 12g of PBAT to a twin-screw extruder for blending. Then add 37g of component A, 4g of sodium lignosulfonate-nano TiO2-Fe composite prepared in Example 1, and 6g of glycerol premix to the twin-screw extruder. Extrude and granulate to obtain starch-polylactic acid composite crosslinked modified biodegradable material.

[0047] Comparative Example 6: A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, comprising the following steps: mixing 25g starch, 45g polylactic acid, 12g PBAT and 6g glycerol to obtain a starch-polylactic acid composite crosslinked modified biodegradable material.

[0048] Performance testing The materials prepared in Examples 4-6 and Comparative Examples 1-6 were blown into films to produce 10 μm agricultural mulch films. The resulting agricultural mulch films were then subjected to the following performance tests: (1) Tensile strength and elongation at break: The test was conducted according to GB / T 1040.3-2006 "Test of tensile properties of plastics - Part 3: Test conditions for films and sheets", and the test results are shown in Table 1; (2) Right-angle tear load: The test was conducted according to QB / T 1130-1991 "Right-angle tear performance of plastics", and the test results are shown in Table 1; Table 1: Statistical Table of Mechanical Property Test Data for Examples 4-6 and Comparative Examples 1-6

[0049] As shown in Table 1, the material prepared in this application is used as a raw material for preparing agricultural mulch film, and the mulch film prepared has excellent mechanical properties.

[0050] (3) Transmittance: According to GB / T 2410-2008 "Test Method for Transmittance and Haze of Transparent Plastics", the transmittance and haze were tested using a Pro spectrophotometer in the range of effective photosynthetic wavelengths (380-710nm). The test results are shown in Table 2. (4) Water vapor transmission rate: The test was conducted according to GB / T 1037-2021 "Determination of water vapor transmission performance of plastic films and sheets by cup weight gain and weight loss method". The test results are shown in Table 2. Table 2: Statistical Table of Physicochemical Properties Test Data of Examples 4-6 and Comparative Examples 1-6

[0051] As shown in Table 2, the material prepared in this application, when used as a raw material for preparing agricultural mulch film, achieves a light transmittance of 82.5%-84.4% at a wavelength of 550 nm. The water vapor transmission rate of the materials prepared in Examples 4-6 of this application is controlled at 178-185 g / (m²). 2 •24h) can effectively block water vapor.

[0052] (5) Anti-aging performance: The strength retention rate after 500h of UV aging was tested according to GB / T 16422.2-2022 "Laboratory Light Source Exposure Test Method for Plastics Part 2: Xenon Arc Lamp". The test results are shown in Table 3. (6) Biodegradability: The biodegradability, ecotoxicity and composition control of soil biodegradable materials for agricultural and horticultural mulch films were tested according to GB / T 43288-2023. The test results are shown in Table 3. Table 3: Statistical table of degradation performance test data for Examples 4-6 and Comparative Examples 1-6

[0053] As shown in Table 3, the material prepared in this application is used as a raw material for preparing agricultural mulch film. The mulch film prepared has a mechanical retention rate of ≥85% during the 90-day functional period and a degradation rate of 63-68% after 180 days, achieving the effect of stability during the functional period and effective degradation after the functional period.

[0054] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material, characterized in that, Includes the following steps: S1: The dynamic coordination crosslinking agent, nanocellulose-dopamine graft, and solvent are mixed, esterified modified starch is added, stirred and dispersed, and then freeze-dried to obtain component A; S2: Polylactic acid and PBAT are added to a twin-screw extruder for blending. Then, a premix containing component A prepared in S1, sodium lignosulfonate-nano TiO2-Fe composite, and glycerol is added to the twin-screw extruder. The mixture is then extruded and granulated to obtain granules. S3: The granules are immersed in an ethanol solution containing ferric chloride hexahydrate and dried to obtain a starch-polylactic acid composite crosslinked modified biodegradable material; The preparation method of the dynamic coordination crosslinking agent includes the following steps: Itaconic acid, epoxidized soybean oil, and toluene were added to a reaction vessel and mixed. BF3·OEt2 was added and mixed again. The temperature was controlled at 70-80℃ and the reaction was maintained for 2-4 hours. Toluene was removed by rotary evaporation to obtain the intermediate. The intermediate and dichloromethane were added to a reactor and mixed, and the temperature was controlled at 20-35℃. DCC, DMAP, and dichloromethane component I were added and mixed, and then added to the reactor. The reactor was activated for 0.5-1h. Dopamine hydrochloride and dichloromethane component II were mixed and added to the reactor. Triethylamine was added, and the reactor was kept at a constant temperature under stirring for 18-24h. Dichloromethane was removed by rotary evaporation. The residue was diluted with ethyl acetate, precipitated, washed, and dried to obtain the dynamic coordination crosslinking agent.

2. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 1, characterized in that, The proportions of each raw material in the dynamic coordination crosslinking agent are as follows: The addition ratio of itaconic acid, epoxidized soybean oil, toluene, BF3·OEt2, dichloromethane, DCC, DMAP, dichloromethane component one, dopamine hydrochloride, dichloromethane component two, and triethylamine is 10g: 75-85g: 100-200mL: 0.5-1g: 50-100mL: 8-12g: 0.4-0.6g: 50-100mL: 45-60g: 50-100mL: 20-30mL.

3. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 1, characterized in that, The solvent described in S1 is composed of tetrahydrofuran and deionized water in a volume ratio of 3:1; the mass ratio of dynamic coordination crosslinking agent, nanocellulose-dopamine graft, and esterified modified starch is 6-10:3-5:20-30; the ratio of the total mass of dynamic coordination crosslinking agent, nanocellulose-dopamine graft, and esterified modified starch to the solvent is 1g:5-10mL; In S2, the mass ratio of polylactic acid, PBAT, component A, sodium lignosulfonate-nano TiO2-Fe complex, and glycerol is 40-50:10-15:30-50:3-5:5-8. The mass percentage of the ethanol solution containing ferric chloride hexahydrate in S3 is 0.5-1 wt%; the addition ratio of granules to the ethanol solution containing ferric chloride hexahydrate is 1 g: 3-6 mL.

4. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 1, characterized in that, The preparation method of the esterified modified starch includes the following steps: A1: Add starch, octanoic anhydride, DMAP, and anhydrous pyridine to a reaction flask and disperse them. Control the temperature at 70-80℃ and keep the reaction at this temperature for 3-6 hours. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain octanoic acid starch ester. A2: Add octanoic acid starch, benzoic anhydride, DMAP, and anhydrous pyridine to a reaction flask and mix. Control the temperature at 60-70℃ and keep the reaction at this temperature for 1-3 hours. Add ethanol to precipitate, filter to obtain the solid, wash, and dry to obtain esterified modified starch.

5. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 4, characterized in that, The addition ratio of starch, caprylic anhydride, DMAP, and anhydrous pyridine in A1 is 10g: 2.5-3.5g: 0.2-0.3g: 50-100mL; In A2, the addition ratio of octanoic acid starch, benzoic anhydride, DMAP, and anhydrous pyridine is 10g: 2-3g: 0.2-0.3g: 50-100mL.

6. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 1, characterized in that, The preparation method of the nanocellulose-dopamine graft includes the following steps: B1: Mix CNC and 0.8-1.2 mol / L MES buffer, add sodium periodate, and stir the reaction at 25-30℃ in the dark for 1-3 hours; add ethylene glycol to disperse, keep the reaction at the same temperature for 0.5-1 hours, centrifuge, and wash with water to obtain the intermediate product; B2: Mix the intermediate product with 0.8-1.2 mol / L MES buffer, add dopamine hydrochloride and sodium cyanoborohydride, control the temperature at 25-30℃ and stir the reaction in the dark for 18-24 h, centrifuge, wash, freeze dry to obtain nanocellulose-dopamine graft.

7. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 6, characterized in that, The addition ratio of CNC, 0.8-1.2 mol / L MES buffer, sodium periodate, and ethylene glycol in B1 is 10 g: 200-400 mL: 0.8-1.2 g: 0.05-0.1 g; The addition ratio of intermediate product, 0.8-1.2 mol / L MES buffer, dopamine hydrochloride, and sodium cyanoborohydride in B2 is 10 g: 200-400 mL: 1.5-2.5 g: 0.2-0.5 g.

8. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 1, characterized in that, The preparation method of the sodium lignosulfonate-nano TiO2-Fe composite includes the following steps: mixing nano TiO2, deionized water, and citric acid, adjusting the pH to 2.5-3, adding ferric chloride hexahydrate, stirring and dispersing for 1-2 hours, adding sodium lignosulfonate, adjusting the pH to 5, stirring and reacting for 1-3 hours, centrifuging, washing, and freeze-drying to obtain the sodium lignosulfonate-nano TiO2-Fe composite.

9. The method for preparing a starch-polylactic acid composite crosslinked modified biodegradable material according to claim 8, characterized in that, The addition ratio of nano-TiO2, deionized water, citric acid, ferric chloride hexahydrate, and sodium lignosulfonate is 10g: 100-200mL: 2-3g: 1-1.5g: 1-1.5g.

10. A starch-polylactic acid composite crosslinked modified biodegradable material, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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