Agricultural plastic film and preparation method thereof

Abstract

The invention relates to the field of plastic films, in particular to an agricultural plastic film and a preparation method thereof.The agricultural plastic film is prepared from, by mass, 95-105 parts of film particles, 2-4 parts of modified nanometer titania emulsion, 6-10 parts of lignin nanoparticles, 2-4 parts of tannic acid, 6-10 parts of glycerinum and 4-6 parts of cosolvent maleic anhydride grafted polycaprolactone. By innovatively introducing a natural base material and a functional nano component for synergistic modification, compared with the prior art, comprehensive improvement of material degradability, anti-aging performance and processing efficiency is realized, meanwhile, production cost optimization and process adaptability are considered, and the material can be widely applied to agricultural scenes such as greenhouse coverage and soil moisturizing and has wide application prospects. The method has remarkable advantages in reducing environmental pollution and improving the comprehensive performance of the agricultural film, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the field of plastic films, and particularly to an agricultural plastic film and a preparation method thereof. Background Art

[0002] As an important production material in modern agriculture, agricultural plastic film is a covering and protective film developed based on polymer materials. It mainly uses low-density polyethylene resin as the core raw material, and is made by blow molding or casting processing technology. Finally, it is physically stretched to form a lightweight film with uniform thickness. It has significant ductility and flexibility. At the same time, through its light transmittance and waterproofness, it can form a controllable microclimate environment in the open-air environment, creating a growth space with heat preservation and moisture retention for crops.

[0003] With the iteration of agricultural technology, modern agricultural films break through traditional limitations through composite modification technology, and introduce additive systems such as anti-aging agents and light stabilizers into the polyolefin matrix, significantly extending the outdoor service life. However, there are still problems in the existing technology: traditional agricultural plastic films are difficult to degrade naturally, and the residual films will form "white pollution", damaging the soil structure, reducing soil fertility, and being easily affected by ultraviolet rays, resulting in their aging and low mechanical strength, thus having a short service life. In addition, the existing agricultural plastic films have a single function and cannot cope with complex agricultural environments.

[0004] Therefore, according to the above related technologies, it is urgent to develop an agricultural plastic film and a preparation method thereof. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an agricultural plastic film and a preparation method thereof to solve the problems of non-degradability, single function and environmental pollution in the existing technology.

[0006] Based on the above purpose, the present invention provides an agricultural plastic film and a preparation method thereof.

[0007] An agricultural plastic film is composed of the following components in parts by mass: 95 - 105 parts of film pellets, 2 - 4 parts of modified nano-titanium dioxide emulsion, 6 - 10 parts of lignin nanoparticles, 2 - 4 parts of tannic acid, 6 - 10 parts of glycerol, 4 - 6 parts of maleic anhydride grafted polycaprolactone as a co-solvent, and 4 - 6 parts of cellulose nanocrystals.

[0008] Preferably, the preparation method of the film pellets is as follows: Add modified starch to polycaprolactone, stir and mix, then add polyvinyl acetate, co-solvent, stearic acid and polyethylene wax, heat up to 40 - 60 °C, and stir for 10 - 20 min to obtain film pellets.

[0009] Preferably, the mass ratio of the modified starch, polycaprolactone, polyvinyl acetate, co-solvent, stearic acid and polyethylene wax is 30-33:50-52:8.5-8.8:5-5.3:1-2:1; Both lignin and cellulose are natural bio-based materials. By nano-treatment, their dispersibility is enhanced, and they act synergistically with degradable polymers such as polycaprolactone to effectively reduce "white pollution" and reduce the long-term damage to the soil environment; Preferably, the preparation method of the modified starch is as follows: Step B1: Add starch into deionized water, heat up to 30-50 °C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5-9.5, add sodium hypochlorite solution, react for 1-3 h, add 10%wt sodium sulfite solution, adjust the pH to 6.5-7.0, filter, wash and dry to obtain oxidized starch; Step B2: Add the oxidized starch into sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10-10.5, heat up to 40-60 °C, react for 70-90 min, filter, wash and dry, add aluminate coupling agent, heat up to 50-60 °C, stir for 20-40 min, cool down to 20-30 °C to obtain hydrophobic starch; Step B3: Add the hydrophobic starch into the composite plasticizer solution, heat up to 20-30 °C, stir for 8-12 min to obtain modified starch; The composite plasticizer solution is ethylene glycol and glycerol, and their volume ratio is 1:1.5.

[0010] Preferably, in step B1, the mass ratio of the starch, deionized water and sodium hypochlorite solution is 1:3-4:0.05-0.15; In step B2, the mass ratio of the oxidized starch, sodium trimetaphosphate solution and aluminate coupling agent is 1:1.5-2:0.01-0.02; In step B3, the mass ratio of the hydrophobic starch and the composite plasticizer solution is 1:0.4-0.6; By optimizing the ratio of the modified starch, polycaprolactone and polyvinyl acetate, and combining the co-solvent maleic anhydride grafted polycaprolactone, the melting processing temperature can be effectively reduced. At the same time, a large amount of bio-based components are used in the raw materials to replace traditional petroleum-based resins and reduce production costs.

[0011] Ethylene glycol has a small molecular weight, low viscosity and strong permeability. It can quickly insert between the starch molecular chains, weaken the hydrogen bond effect, improve the plasticization efficiency of starch, and quickly realize the softening of the starch chain. Glycerol contains three hydroxyl groups, which have strong polarity and can form hydrogen bonds with the hydroxyl groups of starch, thus providing a long-term plasticization effect. At the same time, it has hygroscopicity and can prevent the material from becoming brittle due to water loss. Through the synergistic effect of the two, it can not only ensure the rapid plasticization in the initial stage of processing, but also maintain the long-term flexibility of the material; In addition, a lower proportion of ethylene glycol can avoid material aging caused by excessive migration of small molecules, while a higher proportion of glycerol can ensure a sufficient hydroxyl density, enhance the interfacial binding force between starch and polycaprolactone, reduce the risk of phase separation. At the same time, the combined use of the two can improve the penetration rate of the plasticizer in the modified starch and the fluidity of the mixed solution. Meanwhile, both ethylene glycol and glycerol are biodegradable substances, which are environmentally friendly to a certain extent.

[0012] Preferably, the preparation method of the modified nano-titanium dioxide emulsion is as follows: Step C1: Add 2-[8-(trimethoxysilyl)octyl]oxirane and trimethylamine hydrochloride into absolute ethanol, heat up to 60-80 °C, stir and react for 2-3 h. After the reaction is completed, perform reduced-pressure distillation to obtain quaternary ammonium saltified trimethoxysilane; Step C2: Add the quaternary ammonium saltified trimethoxysilane into an absolute ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3-4, heat up to 20-30 °C, perform ultrasonic dispersion for 1-3 h, add nano-titanium dioxide, perform ultrasonic dispersion for 50-70 min, add ammonia water, adjust the pH to 9-10, heat up to 70-90 °C, stir for 1-3 h, cool, and dry to obtain modified nano-titanium dioxide; Step C3: Add acrylic acid, methyl methacrylate, and n-butyl acrylate into deionized water, stir and mix evenly, add sodium dodecyl sulfate and nonylphenol polyoxyethylene ether, stir for 8-12 min, add the modified nano-titanium dioxide, perform ultrasonic dispersion for 20-40 min, heat up to 60-80 °C, adjust the pH to 4-6, add ammonium persulfate, heat up to 70-90 °C, keep warm and react for 1-2 h, cool down to 30-50 °C, add ammonia water, adjust the pH to 7.5-8.5 to obtain the modified nano-titanium dioxide emulsion.

[0013] Preferably, the mass ratio of 2-[8-(trimethoxysilyl)octyl]oxirane to trimethylamine hydrochloride in Step C1 is 2.8-3:1.

[0014] Preferably, the mass ratio of the quaternary ammonium saltified trimethoxysilane to nano-titanium dioxide in Step C2 is 4.5-4.7:1.

[0015] Preferably, the mass ratio of acrylic acid, methyl methacrylate, n-butyl acrylate, sodium dodecyl sulfate, nonylphenol polyoxyethylene ether to the modified nano-titanium dioxide in Step C3 is 2-2.5:1-1.2:1-1.2:0.1-0.3:0.1-0.3:1.

[0016] Preferably, a preparation method of an agricultural plastic film is as follows: Step S1: Add lignin nanoparticles, tannic acid, glycerol, co-solvent, film particles and cellulose nanocrystals into a high-speed mixer, stir for 15 - 20 min at a rotation speed of 800 - 1000 rpm to obtain a mixed raw material; Step S2: Feed the mixed raw material into the feeding port of a twin-screw extruder, heat up to 140 - 150 °C, roll for 20 - 40 min, and roll and draw it through a four-roll calender to obtain a base film; Step S3: Put the base film into a coater, add a modified nano-titanium dioxide emulsion, heat up to 20 - 25 °C, with a pressure of 0.2 - 0.3 MPa and a coating speed of 10 - 15 m / min, then put it into a hot air drying tunnel, heat up to 80 - 100 °C, and dry for 5 - 10 min to obtain an agricultural plastic film; Using maleic anhydride grafted polycaprolactone as a co-solvent and cooperating with a composite plasticizer, control the processing temperature of the base film at 140 - 150 °C. Low-temperature extrusion not only reduces energy consumption but also avoids thermal degradation of natural components, ensuring the stability and functional integrity of the bio-based material; Through surface functionalization treatment and composite emulsion coating process, endow the plastic film with excellent ultraviolet shielding performance and photocatalytic self-cleaning ability. At the same time, tannic acid, as a natural antioxidant, combined with the plasticizing effect of glycerol, can delay material aging, improve mechanical strength and service life.

[0017] Advantages of the present invention: The present invention provides a plastic film and its preparation method. By innovatively introducing the synergistic modification of natural substrates and functional nano-components, compared with the prior art, it realizes the comprehensive improvement of the material's degradability, anti-aging performance and processing efficiency, while taking into account the optimization of production cost and process adaptability. It can be widely applied to agricultural scenarios such as greenhouse covering and soil moisture retention, and has significant advantages in reducing environmental pollution and improving the comprehensive performance of agricultural films, and has a broad application prospect. Specific embodiments

[0018] To make the purpose, technical solution and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0019] Example 1: A method for preparing modified starch is as follows: S1: Add 300 g of starch into 900 g of deionized water, heat up to 30 °C, add a 3%wt sodium hydroxide solution, adjust the pH to 8.5 - 9.5, add 15 g of sodium hypochlorite solution, react for 1 h, add a 10%wt sodium sulfite solution, adjust the pH to 6.5 - 7.0, filter, wash and dry to obtain oxidized starch; S2: Add 300 g of oxidized starch into 450 g of sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10 - 10.5, raise the temperature to 40 °C, react for 90 min, filter, wash, dry, add 3 g of aluminate coupling agent, raise the temperature to 50 °C, stir for 40 min, cool down to 20 °C to obtain hydrophobic starch; S3: Add 300 g of hydrophobic starch into 120 g of composite plasticizer solution, raise the temperature to 20 °C, stir for 12 min to obtain modified starch.

[0020] Example 2: A method for preparing modified starch is as follows: S1: Add 300 g of starch into 1050 g of deionized water, raise the temperature to 40 °C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5 - 9.5, add 30 g of sodium hypochlorite solution, react for 2 h, add 10%wt sodium sulfite solution, adjust the pH to 6.5 - 7.0, filter, wash and dry to obtain oxidized starch; S2: Add 300 g of oxidized starch into 540 g of sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10 - 10.5, raise the temperature to 50 °C, react for 80 min, filter, wash, dry, add 4.5 g of aluminate coupling agent, raise the temperature to 55 °C, stir for 30 min, cool down to 25 °C to obtain hydrophobic starch; S3: Add 300 g of hydrophobic starch into 150 g of composite plasticizer solution, raise the temperature to 25 °C, stir for 10 min to obtain modified starch.

[0021] Example 3: A method for preparing modified starch is as follows: S1: Add 300 g of starch into 1200 g of deionized water, raise the temperature to 50 °C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5 - 9.5, add 45 g of sodium hypochlorite solution, react for 3 h, add 10%wt sodium sulfite solution, adjust the pH to 6.5 - 7.0, filter, wash and dry to obtain oxidized starch; S2: Add 300 g of oxidized starch into 600 g of sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10 - 10.5, raise the temperature to 60 °C, react for 70 min, filter, wash, dry, add 6 g of aluminate coupling agent, raise the temperature to 60 °C, stir for 20 min, cool down to 30 °C to obtain hydrophobic starch; S3: Add 300 g of hydrophobic starch into 180 g of composite plasticizer solution, raise the temperature to 30 °C, stir for 8 min to obtain modified starch.

[0022] Example 4: A method for preparing film granules is as follows: Add 300 g of modified starch to 500 g of polycaprolactone, stir and mix, then add 85 g of vinyl acetate, 50 g of co-solvent, 10 g of stearic acid and 10 g of polyethylene wax. Heat up to 40 °C and stir for 20 min to obtain film pellets.

[0023] Example 5: A method for preparing film pellets is as follows: Add 300 g of modified starch to 510 g of polycaprolactone, stir and mix, then add 86 g of polyvinyl acetate, 52 g of co-solvent, 15 g of stearic acid and 10 g of polyethylene wax. Heat up to 50 °C and stir for 15 min to obtain film pellets.

[0024] Example 6: A method for preparing film pellets is as follows: Add 300 g of modified starch to 520 g of polycaprolactone, stir and mix, then add 88 g of polyvinyl acetate, 53 g of co-solvent, 20 g of stearic acid and 10 g of polyethylene wax. Heat up to 60 °C and stir for 10 min to obtain film pellets.

[0025] Example 7: A method for preparing a modified nano-titanium dioxide emulsion is as follows: S1: Add 280 g of 2-[8-(trimethoxysilyl)octyl]oxirane and 100 g of trimethylamine hydrochloride to 500 mL of absolute ethanol, heat up to 60 °C, stir and react for 3 h. After the reaction is completed, perform vacuum distillation to obtain quaternized trimethoxysilane. S2: Add 90 g of quaternized trimethoxysilane to 200 mL of absolute ethanol solvent, stir evenly, add glacial acetic acid to adjust the pH to 3 - 4, heat up to 20 °C, perform ultrasonic dispersion for 3 h, add 20 g of nano-titanium dioxide, perform ultrasonic dispersion for 50 min, add ammonia water to adjust the pH to 9 - 10, heat up to 90 °C, stir for 1 h, cool and dry to obtain modified nano-titanium dioxide. S3: Add 200 g of acrylic acid, 100 g of methyl methacrylate, 100 g of n-butyl acrylate to 500 mL of deionized water, stir and mix evenly, add 10 g of sodium dodecyl sulfate and 10 g of nonylphenol polyoxyethylene ether, stir for 8 min, add 100 g of modified nano-titanium dioxide, perform ultrasonic dispersion for 20 min, heat up to 80 °C, adjust the pH to 4 - 6, add ammonium persulfate, heat up to 70 °C, hold the reaction for 2 h, cool down to 30 °C, add ammonia water to adjust the pH to 7.5 - 8.5 to obtain the modified nano-titanium dioxide emulsion.

[0026] Example 8: A method for preparing a modified nano-titanium dioxide emulsion is as follows: S1: Add 290 g of 2-[8-(trimethoxysilyl)octyl]oxirane and 100 g of trimethylamine hydrochloride into 500 mL of absolute ethanol, heat up to 70 °C, stir and react for 2.5 h. After the reaction is completed, perform vacuum distillation to obtain quaternary ammonium saltified trimethoxysilane; S2: Add 92 g of quaternary ammonium saltified trimethoxysilane into 200 mL of absolute ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3 - 4, heat up to 25 °C, perform ultrasonic dispersion for 2 h, add 20 g of nano-titanium dioxide, perform ultrasonic dispersion for 60 min, add ammonia water, adjust the pH to 9 - 10, heat up to 70 - 90 °C, stir for 2 h, cool down, and dry to obtain modified nano-titanium dioxide; S3: Add 220 g of acrylic acid, 110 g of methyl methacrylate, and 110 g of n-butyl acrylate into 500 mL of deionized water, stir and mix evenly, add 20 g of sodium dodecyl sulfate and 20 g of nonylphenol polyoxyethylene ether, stir for 10 min, add 100 g of modified nano-titanium dioxide, perform ultrasonic dispersion for 30 min, heat up to 70 °C, adjust the pH to 4 - 6, add ammonium persulfate, heat up to 80 °C, keep the temperature for reaction for 1.5 h, cool down to 40 °C, add ammonia water, adjust the pH to 7.5 - 8.5 to obtain modified nano-titanium dioxide emulsion.

[0027] Example 9: A method for preparing a modified nano-titanium dioxide emulsion is as follows: S1: Add 300 g of 2-[8-(trimethoxysilyl)octyl]oxirane and 100 g of trimethylamine hydrochloride into 500 mL of absolute ethanol, heat up to 80 °C, stir and react for 3 h. After the reaction is completed, perform vacuum distillation to obtain quaternary ammonium saltified trimethoxysilane; S2: Add 94 g of quaternary ammonium saltified trimethoxysilane into 200 mL of absolute ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3 - 4, heat up to 30 °C, perform ultrasonic dispersion for 1 h, add 20 g of nano-titanium dioxide, perform ultrasonic dispersion for 70 min, add ammonia water, adjust the pH to 9 - 10, heat up to 70 °C, stir for 3 h, cool down, and dry to obtain modified nano-titanium dioxide; S3: Add 250 g of acrylic acid, 120 g of methyl methacrylate, and 120 g of n-butyl acrylate into 500 mL of deionized water, stir and mix evenly, add 30 g of sodium dodecyl sulfate and 30 g of nonylphenol polyoxyethylene ether, stir for 12 min, add modified nano-titanium dioxide, perform ultrasonic dispersion for 20 min, heat up to 80 °C, adjust the pH to 4 - 6, add ammonium persulfate, heat up to 70 °C, keep the temperature for reaction for 2 h, cool down to 30 °C, add ammonia water, adjust the pH to 7.5 - 8.5 to obtain modified nano-titanium dioxide emulsion.

[0028] Example 10: The preparation method of an agricultural plastic film is as follows: S1: Add 6 g of lignin nanoparticles, 2 g of tannic acid, 6 g of glycerol, 4 g of cosolvent, 95 g of film pellets, and 4 g of cellulose nanocrystals into a high-speed mixer, stir for 15 min at a rotation speed of 1000 rpm to obtain a mixed raw material; S2: Put 100 g of the mixed raw material into the feeding port of a twin-screw extruder, heat up to 140 °C, roll for 40 min, and roll and draw through a four-roll calender to obtain a base film; S3: Put 100 g of the base film into a coater, add 2 g of modified nano-titanium dioxide emulsion, heat up to 20 °C, with a pressure of 0.3 MPa and a coating speed of 10 m / min, then put it into a hot air drying channel, heat up to 100 °C, and dry for 5 min to obtain the agricultural plastic film.

[0029] Example 11: The preparation method of an agricultural plastic film is as follows: S1: Add 8 g of lignin nanoparticles, 3 g of tannic acid, 8 g of glycerol, 5 g of cosolvent, 100 g of film pellets, and 5 g of cellulose nanocrystals into a high-speed mixer, stir for 15 - 20 min at a rotation speed of 800 - 1000 rpm to obtain a mixed raw material; S2: Put 100 g of the mixed raw material into the feeding port of a twin-screw extruder, heat up to 145 °C, roll for 30 min, and roll and draw through a four-roll calender to obtain a base film; S3: Put 100 g of the base film into a coater, add 3 g of modified nano-titanium dioxide emulsion, heat up to 23 °C, with a pressure of 0.25 MPa and a coating speed of 13 m / min, then put it into a hot air drying channel, heat up to 90 °C, and dry for 7 min to obtain the agricultural plastic film.

[0030] Example 12: The preparation method of an agricultural plastic film is as follows: S1: Add 10 g of lignin nanoparticles, 4 g of tannic acid, 10 g of glycerol, 6 g of cosolvent, 105 g of film pellets, and 6 g of cellulose nanocrystals into a high-speed mixer, stir for 20 min at a rotation speed of 800 rpm to obtain a mixed raw material; S2: Put 100 g of the mixed raw material into the feeding port of a twin-screw extruder, heat up to 150 °C, roll for 20 min, and roll and draw through a four-roll calender to obtain a base film; S3: Put 100 g of the base film into a coater, add 4 g of modified nano-titanium dioxide emulsion, heat up to 25 °C, with a pressure of 0.2 MPa and a coating speed of 15 m / min, then put it into a hot air drying channel, heat up to 80 °C, and dry for 10 min to obtain the agricultural plastic film.

[0031] Comparative Example 1: This comparative example is the same as Example 10 in terms of the remaining steps and parameters, except that lignin nanoparticles were not added during the preparation of the agricultural plastic film. This comparative example will not be repeated here, and finally an agricultural plastic film was obtained.

[0032] Comparative Example 2: This comparative example is the same as Example 10 in terms of the remaining steps and parameters, except that "modified nano-titanium dioxide" was replaced with "titanium dioxide". This comparative example will not be repeated here, and finally an agricultural plastic film was obtained.

[0033] Comparative Example 3: This comparative example is the same as Example 10 in terms of the remaining steps and parameters, except that the mass ratio of modified starch, polycaprolactone and polyvinyl acetate was changed from "30:50:8.5" to "25:55:10". This comparative example will not be repeated here, and finally an agricultural plastic film was obtained.

[0034] Comparative Example 4: This comparative example is the same as Example 10 in terms of the remaining steps and parameters, except that "modified starch" was replaced with "hydrophobic starch". This comparative example will not be repeated here, and finally an agricultural plastic film was obtained.

[0035] Comparative Example 5: This comparative example is the same as Example 10 in terms of the remaining steps and parameters, except that the coating order of modified nano-titanium dioxide in steps S2 and S3 was reversed. This comparative example will not be repeated here, and finally an agricultural plastic film was obtained.

[0036] Comparative Example 6 This comparative example is the same as Example 10 in terms of the remaining steps and parameters, except that the raw materials of modified nano-titanium dioxide were directly mixed. This comparative example will not be repeated here, and finally an agricultural plastic film was obtained.

[0037] Performance Test: Biodegradability Test Referring to the ISO-14855 test standard, a thermostatic and humid compost reactor and a CO2 capture device were used; 1. Take the agricultural plastic films of Examples 10 - 12 and Comparative Examples 1 - 6, cut them into 10 mm × 10 mm, and the initial mass is M0.

[0038] 2. Mix the samples with mature compost at a mass ratio of 1:10, place them in the reactor, at a temperature of 58 ± 2 °C and a humidity of 50% - 60%, collect the gas every 30 days, and measure the CO2 release amount through an infrared analyzer. The calculation formula for the biodegradation rate is: 3. Take out the samples after 180 days, wash and dry them, and weigh M1. The calculation formula for the mass loss measurement is: Tensile Strength and Elongation at Break Test Refer to ASTM-D638 test standard and use Instron-5967 universal material testing machine; 1. Cut the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6 into 25mm×4mm×0.05mm respectively. There are 5 parallel samples in each group. The tensile speed is 50mm / min, the fixture spacing is 20mm, heat up to 23±2°C, and the humidity is 50±5%. Record the maximum tensile force (N) and elongation at break (%). 2. Calculation formula for tensile strength (MPa): Table 1 Ultraviolet Shielding Rate and Light Transmittance Test Refer to ASTM-E424 and ASTM-D1003 standards for testing, and use UV-2600 ultraviolet-visible spectrophotometer and integrating sphere; 1. Cut the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6 into 50mm×50mm respectively, scan in the wavelength range of 280-400nm, and calculate the average transmittance of UV-A (315-400nm) and UV-B (280-315nm). ; 2. Use the integrating sphere to measure the light transmittance (550nm) and haze value of visible light, and take the average value for each group of tests 3 times; Antioxidant Performance Test Refer to GB / T-7141 standard for testing, and use a thermal aging test chamber and Fourier transform infrared spectrometer; 1. Take 5g of the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6 respectively, place them in an oven, heat up to 80°C, heat for 30 days, and the humidity is 60±5%. Use a Fourier transform infrared spectrometer to analyze the samples before and after aging, and calculate the absorbance ratio of the carbonyl peak at 1710cm -1 and the reference peak at 1450cm -1 . Carbonyl index = carbonyl peak area / reference peak area; 2. Detect the tensile strength after aging, and the calculation formula is: Table 2 Antibacterial Performance Test Refer to ISO-22196 standard for testing, use a constant temperature and humidity incubator, and the bacterial strains are Escherichia coli and Staphylococcus aureus; 1. Sample preparation: Cut the plastic films of Examples 10 - 12 and Comparative Examples 1 - 6 into 50 mm × 50 mm squares with a thickness of 0.05 mm, and disinfect the surface (soak in 75% ethanol for 10 min and rinse 3 times with sterile water); 2. Bacterial suspension preparation: Inoculate the bacterial strain into a liquid medium (LB medium), culture at 37°C for 24 h, and adjust the bacterial suspension concentration to 1×10 6 CFU / mL; 3. Inoculation and culture: Take 100 μL of the bacterial suspension and evenly coat it on the surface of the sample, cover it with a sterile polyethylene film to prevent evaporation, and incubate it in an incubator (37°C, RH≥90%) for 24 h; 4. Colony counting: Immerse the sample in 10 mL of PBS buffer, ultrasonically oscillate for 5 min (40 kHz), serially dilute and then coat it on an agar plate, culture at 37°C for 24 h, and count the number of colonies (CFU); 5. Antibacterial rate calculation formula: Table 3 Data analysis: As can be seen from Tables 1 - 3, the agricultural plastic film prepared by the present invention has a higher biodegradation rate, more excellent mechanical properties, stronger ultraviolet shielding ability and significant antibacterial effect; In Comparative Example 1, due to the absence of lignin nanoparticles, its degradation ability decreased, and at the same time, its enhanced mechanical properties and natural antibacterial function were lacking. The reason is that lignin contains a complex aromatic structure that can be degraded by laccase and peroxidase secreted by specific microorganisms in the natural environment, and the lignin particles after nanometerization have a larger specific surface area, which can accelerate the attachment of microorganisms and enzymatic hydrolysis reactions, thus significantly improving the degradation efficiency. At the same time, lignin nanoparticles combine with polymer chains through hydrogen bonds and van der Waals forces to form a rigid interface layer, effectively dispersing stress and inhibiting crack propagation. In addition, phenolic hydroxyl groups and quinone compounds contained in lignin can achieve antibacterial effects by destroying the microbial cell membrane, inhibiting enzyme activity and interfering with metabolic pathways. The exposure rate and reaction efficiency of its active groups are further improved through nanometerization treatment; In Comparative Example 2, due to the replacement of modified nano - titanium dioxide with titanium dioxide, the photocatalytic activity and dispersibility are insufficient, and it cannot effectively shield ultraviolet rays and inhibit the growth of microorganisms. The reason is that modified nano - titanium dioxide is surface - modified by trimethoxysilane quaternization to form a stable hydrophilic - hydrophobic interface, significantly improving its dispersibility in the emulsion. At the same time, modified nano - titanium dioxide is coated with an acrylic copolymer to form a core - shell structure, enhancing the absorption ability of UV - A and UV - B. In addition, modified nano - titanium dioxide generates hydroxyl radicals and superoxide radicals under light irradiation, thereby achieving efficient sterilization; In Comparative Example 3, due to the imbalance in the ratio of modified starch, polycaprolactone, and polyvinyl acetate, phase separation occurred in the material, resulting in uneven coating and a decline in mechanical and optical properties. The reason is that modified starch, as a bio-based filler, led to a reduction in the rigid skeleton structure, unable to effectively support the flexible segments of polycaprolactone, thereby reducing the overall mechanical strength. At the same time, the polarity differences among the three are relatively large. After the ratio is unbalanced, the compatibility of each component decreases, the interfacial bonding force drops, phase separation is triggered, becoming stress concentration points, and ultimately resulting in a significant reduction in tensile strength; In Comparative Example 4, due to the replacement of modified starch with hydrophobic starch, the interfacial bonding force during the processing was weak, and the antioxidant performance and degradation efficiency were significantly reduced. The reason is that the composite plasticizer in modified starch contains active groups such as hydroxyl groups, which can capture free radicals or delay the oxidation chain reaction. At the same time, the interfacial bonding force between hydrophobic starch and polycaprolactone is weak, forming microcracks or voids, making it easier for oxygen and moisture to penetrate into the material interior, accelerating the oxidation reaction. In addition, the hydrophobic starch has poor dispersibility in the matrix, forming larger agglomerated particles, resulting in enhanced light scattering and an increase in haze value.

[0039] In Comparative Example 5, due to the swapping of the process sequence, the adhesion on the surface of the base film was insufficient, the functional coating was prone to peeling off, and the shielding performance fluctuated greatly. The reason is that the surface of the base film was not subjected to the oriented arrangement of calendering traction, and the surface energy was relatively low, making it difficult for the coating material to effectively wet. At the same time, the high temperature of the extrusion process caused partial melting of the surface of the base film, and the coating material was wrapped in the molten polymer, unable to form a stable interface. In addition, during the extrusion process of the coating, due to the fluidity of the base film, the distribution was uneven, forming local weak areas, and the nano-titanium dioxide particles agglomerated due to mechanical shear, resulting in a further reduction in the ultraviolet shielding efficiency; In Comparative Example 6, due to the direct mixing of the raw materials for preparing modified nano-titanium dioxide, the nano-particles were prone to agglomeration, had poor dispersibility, and the photocatalytic efficiency was reduced, while also affecting the light transmittance uniformity. The reason is that there are high-energy hydroxyl groups on the surface of unmodified nano-titanium dioxide, resulting in an enhanced van der Waals force between particles, which is prone to spontaneously agglomerate to form micron-sized aggregates. After agglomeration, the effective specific surface area of the particles decreased significantly, the photocatalytic active surface decreased, and the antibacterial efficiency dropped. In addition, the agglomerated particles caused scattering in the visible light wavelength range, resulting in an increase in haze value and a decrease in light transmittance.

[0040] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0041] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Accordingly, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of this invention shall be included within the scope of protection of this invention.

Claims

1. An agricultural plastic film, characterized in that, It consists of the following components in parts by mass: 95 - 105 parts of film particles, 2 - 4 parts of modified nano-titanium dioxide emulsion, 6 - 10 parts of lignin nanoparticles, 2 - 4 parts of tannic acid, 6 - 10 parts of glycerol, 4 - 6 parts of maleic anhydride grafted polycaprolactone as co-solvent, and 4 - 6 parts of cellulose nanocrystals.

2. The agricultural plastic film according to claim 1, characterized in that, The preparation method of the film particles is as follows: Add modified starch to polycaprolactone, stir and mix, add polyvinyl acetate, co-solvent, stearic acid and polyethylene wax, heat up to 40 - 60 °C, stir for 10 - 20 min to obtain film particles.

3. The agricultural plastic film according to claim 2, wherein, The mass ratio of the modified starch, polycaprolactone, polyvinyl acetate, co-solvent, stearic acid and polyethylene wax is 30 - 33:50 - 52:8.5 - 8.8:5 - 5.3:1 - 2:

1.

4. The agricultural plastic film according to claim 2, characterized in that, The preparation method of the modified starch is as follows: Step B1: Add starch to deionized water, heat up to 30 - 50 °C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5 - 9.5, add sodium hypochlorite solution, react for 1 - 3 h, add 10%wt sodium sulfite solution, adjust the pH to 6.5 - 7.0, filter, wash and dry to obtain oxidized starch; Step B2: Add the oxidized starch to sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10 - 10.5, heat up to 40 - 60 °C, react for 70 - 90 min, filter, wash, dry, add aluminate coupling agent, heat up to 50 - 60 °C, stir for 20 - 40 min, cool down to 20 - 30 °C to obtain hydrophobic starch; Step B3: Add the hydrophobic starch to the composite plasticizer solution, heat up to 20 - 30 °C, stir for 8 - 12 min to obtain modified starch.

5. An agricultural plastic film according to claim 4, wherein, In Step B1, the mass ratio of the starch, deionized water and sodium hypochlorite solution is 1:3 - 4:0.05 - 0.15; In Step B2, the mass ratio of the oxidized starch, sodium trimetaphosphate solution and aluminate coupling agent is 1:1.5 - 2:0.01 - 0.02; In Step B3, the mass ratio of the hydrophobic starch and the composite plasticizer solution is 1:0.4 - 0.

6.

6. An agricultural plastic film according to claim 1, characterized in that, The preparation method of the modified nano-titanium dioxide emulsion is as follows: Step C1: Add 2-[8-(trimethoxysilyl)octyl]oxirane and trimethylamine hydrochloride to absolute ethanol, heat up to 60 - 80 °C, stir and react for 2 - 3 h, after the reaction is completed, carry out vacuum distillation to obtain quaternized trimethoxysilane; Step C2: Add the quaternized trimethoxysilane to an absolute ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3 - 4, heat up to 20 - 30 °C, carry out ultrasonic dispersion for 1 - 3 h, add nano-titanium dioxide, carry out ultrasonic dispersion for 50 - 70 min, add ammonia water, adjust the pH to 9 - 10, heat up to 70 - 90 °C, stir for 1 - 3 h, cool and dry to obtain modified nano-titanium dioxide; Step C3: Add acrylic acid, methyl methacrylate, and n-butyl acrylate into deionized water, stir and mix evenly. Add sodium dodecyl sulfate and nonylphenol polyoxyethylene ether, stir for 8 - 12 min, add modified nano-titanium dioxide, ultrasonically disperse for 20 - 40 min, heat up to 60 - 80 °C, adjust the pH to 4 - 6, add ammonium persulfate, heat up to 70 - 90 °C, keep the temperature for reaction for 1 - 2 h, cool down to 30 - 50 °C, add ammonia water, adjust the pH to 7.5 - 8.5 to obtain the modified nano-titanium dioxide emulsion.

7. An agricultural plastic film according to claim 6, characterized in that, In step C1, the mass ratio of 2-[8-(trimethoxysilyl)octyl]oxirane to trimethylamine hydrochloride is 2.8 - 3:

1.

8. The agricultural plastic film according to claim 6, characterized in that, In step C2, the mass ratio of quaternized trimethoxysilane to nano-titanium dioxide is 4.5 - 4.7:

1.

9. An agricultural plastic film according to claim 6, characterized in that, In step C3, the mass ratio of acrylic acid, methyl methacrylate, n-butyl acrylate, sodium dodecyl sulfate, nonylphenol polyoxyethylene ether to modified nano-titanium dioxide is 2 - 2.5:1 - 1.2:1 - 1.2:0.1 - 0.3:0.1 - 0.3:

1.

10. A method for preparing an agricultural plastic film according to any one of claims 1-9, characterized in that, The preparation method is as follows: Step S1: Add lignin nanoparticles, tannic acid, glycerol, co-solvent, film granules, and cellulose nanocrystals into a high-speed mixer, stir for 15 - 20 min at a rotation speed of 800 - 1000 rpm to obtain a mixed raw material. Step S2: Feed the mixed raw material into the feeding port of a twin-screw extruder, heat up to 140 - 150 °C, roll for 20 - 40 min, and roll and draw it through a four-roll calender to obtain a base film. Step S3: Put the base film into a coater, add the modified nano-titanium dioxide emulsion, heat up to 20 - 25 °C, with a pressure of 0.2 - 0.3 MPa and a coating speed of 10 - 15 m / min, then put it into a hot air drying channel, heat up to 80 - 100 °C, and dry for 5 - 10 min to obtain an agricultural plastic film.

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