Agricultural plastic film and preparation method thereof

Abstract

The present invention relates to the field of plastic films, and in particular to an agricultural plastic film and a preparation method thereof. The agricultural plastic film is composed 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 a co-solvent, and 4-6 parts of cellulose nanocrystals. Compared with the prior art, the present invention achieves comprehensive improvement in material degradability, anti-aging performance and processing efficiency, while taking into account production cost optimization and process adaptability. The agricultural plastic film can be widely used in agricultural scenarios such as greenhouse covering and soil moisture retention, has significant advantages in reducing environmental pollution and improving the comprehensive performance of agricultural films, and has broad application prospects.

Description

Technical Field

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

[0002] Agricultural plastic film, as an important means of production in modern agriculture, is a covering 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 cast film 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 waterproof properties, it can form a controllable microclimate environment in an open air environment, creating a heat-insulating and moisture-retaining growth space for crops.

[0003] With the iteration of agricultural technology, modern agricultural films have broken through traditional limitations through composite modification technology, introducing anti-aging agents, light stabilizers and other auxiliary systems 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, residual films will form "white pollution", destroy soil structure, reduce fertility, and are easily affected by ultraviolet rays, resulting in aging and low mechanical strength, thus short service life. In addition, existing agricultural plastic films have a single function and cannot cope with complex agricultural environments.

[0004] Therefore, according to the relevant technologies mentioned above, there is an urgent need 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 prior art.

[0006] Based on the above objectives, 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 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 a cosolvent, and 4-6 parts of cellulose nanocrystals.

[0008] Preferably, the film particles are prepared as follows:

[0009] Add modified starch to polycaprolactone, stir and mix, add polyvinyl acetate, cosolvent, stearic acid and polyethylene wax, heat to 40-60°C, stir for 10-20 minutes, and obtain film particles.

[0010] Preferably, the mass ratio of the modified starch, polycaprolactone, polyvinyl acetate, cosolvent, stearic acid and polyethylene wax is 30-33:50-52:8.5-8.8:5-5.3:1-2:1;

[0011] Lignin and cellulose are both natural bio-based materials. Through nano-processing, their dispersibility is enhanced. They work synergistically with biodegradable polymers such as polycaprolactone to effectively reduce "white pollution" and minimize long-term damage to the soil environment.

[0012] Preferably, the modified starch preparation method is as follows:

[0013] Step B1: Add starch to deionized water, heat to 30-50°C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5-9.5, add sodium hypochlorite solution, react for 1-3h, add 10%wt sodium sulfite solution, adjust the pH to 6.5-7.0, filter, wash and dry to obtain oxidized starch;

[0014] Step B2: adding oxidized starch to a sodium trimetaphosphate solution, adding sodium carbonate, adjusting the pH to 10-10.5, heating to 40-60° C., reacting for 70-90 minutes, filtering, washing, drying, adding an aluminate coupling agent, heating to 50-60° C., stirring for 20-40 minutes, and cooling to 20-30° C. to obtain hydrophobic starch;

[0015] Step B3: adding hydrophobic starch to the composite plasticizer solution, heating to 20-30° C., and stirring for 8-12 minutes to obtain modified starch;

[0016] The composite plasticizer solution is ethylene glycol and propylene glycol, and the volume ratio thereof is 1:1.5.

[0017] Preferably, the mass ratio of starch, deionized water, and sodium hypochlorite solution in step B1 is 1:3-4:0.05-0.15;

[0018] The mass ratio of the oxidized starch, sodium trimetaphosphate solution and aluminate coupling agent in step B2 is 1:1.5-2:0.01-0.02;

[0019] The mass ratio of the hydrophobic starch and the composite plasticizer solution in step B3 is 1:0.4-0.6;

[0020] By optimizing the ratio of modified starch to polycaprolactone and polyvinyl acetate, and combining the co-solvent maleic anhydride to graft polycaprolactone, the melt processing temperature can be effectively lowered. 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.

[0021] Ethylene glycol has a small molecular weight, low viscosity, and strong permeability. It can quickly insert into the starch molecular chains, weaken the hydrogen bonding effect, improve the plasticization efficiency of starch, and quickly achieve the softening of starch chains. Glycerol contains three hydroxyl groups and has strong polarity. It can form hydrogen bonds with the hydroxyl groups of starch, thereby providing a long-lasting plasticizing effect. At the same time, its hygroscopicity can prevent the material from becoming brittle due to water loss. The synergistic effect of the two can ensure rapid plasticization in the initial processing stage while maintaining the long-term flexibility of the material.

[0022] In addition, a lower proportion of ethylene glycol can avoid excessive migration of small molecules leading to material aging, while a higher proportion of propylene glycol can ensure sufficient hydroxyl density, enhance the interfacial bonding between starch and polycaprolactone, and reduce the risk of phase separation. At the same time, the combination of the two can improve the penetration rate of the plasticizer in the modified starch and the fluidity of the mixed solution. At the same time, ethylene glycol and propylene glycol are both biodegradable substances and are environmentally friendly.

[0023] Preferably, the preparation method of the modified nano-titanium dioxide emulsion is as follows:

[0024] Step C1: Add 2-[8-(trimethoxysilyl)octyl]oxirane and trimethylamine hydrochloride to anhydrous ethanol, raise the temperature to 60-80°C, stir and react for 2-3 hours. After the reaction is complete, evaporate under reduced pressure to obtain quaternary ammonium trimethoxysilane;

[0025] Step C2: adding quaternary ammonium trimethoxysilane to anhydrous ethanol solvent, stirring evenly, adding glacial acetic acid, adjusting the pH to 3-4, heating to 20-30° C., ultrasonically dispersing for 1-3 hours, adding nano-titanium dioxide, ultrasonically dispersing for 50-70 minutes, adding ammonia water, adjusting the pH to 9-10, heating to 70-90° C., stirring for 1-3 hours, cooling, and drying to obtain modified nano-titanium dioxide;

[0026] Step C3: Add acrylic acid, methyl methacrylate, and n-butyl acrylate to deionized water, stir and mix evenly, add sodium lauryl sulfate and nonylphenol polyoxyethylene ether, stir for 8-12 minutes, add modified nano-titanium dioxide, ultrasonically disperse for 20-40 minutes, heat to 60-80°C, adjust the pH to 4-6, add ammonium persulfate, heat to 70-90°C, keep warm for reaction for 1-2 hours, cool to 30-50°C, add ammonia water, adjust the pH to 7.5-8.5, and obtain a modified nano-titanium dioxide emulsion.

[0027] Preferably, the mass ratio of 2-[8-(trimethoxysilyl)octyl]oxirane to trimethylamine hydrochloride in step C1 is 2.8-3:1.

[0028] Preferably, the mass ratio of the quaternized trimethoxysilane to nano-titanium dioxide in step C2 is 4.5-4.7:1.

[0029] Preferably, in step C3, the ratio of acrylic acid, methyl methacrylate, n-butyl acrylate, sodium lauryl sulfate, nonylphenol polyoxyethylene ether and modified nano-titanium dioxide is 2-2.5:1-1.2:1-1.2:0.1-0.3:0.1-0.3:1.

[0030] Preferably, a method for preparing an agricultural plastic film is as follows:

[0031] Step S1: adding lignin nanoparticles, tannic acid, glycerol, cosolvent, film particles and cellulose nanocrystals into a high-speed mixer, stirring for 15-20 minutes at a speed of 800-1000 rpm to obtain a mixed raw material;

[0032] Step S2: feeding the mixed raw materials into the feed port of a twin-screw extruder, heating to 140-150° C., rolling for 20-40 minutes, and rolling and pulling through a four-roll calender to obtain a base film;

[0033] Step S3: placing the base film into a coating machine, adding the modified nano-titanium dioxide emulsion, raising the temperature to 20-25°C, the pressure to 0.2-0.3 MPa, and the coating speed to 10-15 m / min, then placing the base film into a hot air drying tunnel, raising the temperature to 80-100°C, and drying for 5-10 minutes to obtain an agricultural plastic film;

[0034] Maleic anhydride grafted polycaprolactone is used as a cosolvent in conjunction with a composite plasticizer to control the base film processing temperature 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 bio-based materials.

[0035] Through surface functionalization treatment and composite emulsion coating process, the plastic film is endowed with excellent UV shielding properties and photocatalytic self-cleaning capabilities. At the same time, tannic acid, as a natural antioxidant, combined with the plasticizing effect of glycerol, can delay material aging and improve mechanical strength and service life.

[0036] Beneficial effects of the present invention:

[0037] The present invention provides a plastic film and a preparation method thereof. The present invention innovatively introduces natural substrates and functional nano-components for synergistic modification. Compared with the existing technology, the present invention achieves a comprehensive improvement in the material's degradability, anti-aging performance and processing efficiency, while taking into account production cost optimization and process adaptability. It can be widely used in agricultural scenarios such as greenhouse covering and soil moisturizing. It has significant advantages in reducing environmental pollution and improving the comprehensive performance of agricultural films, and has broad application prospects. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0039] Example 1: A method for preparing modified starch is as follows:

[0040] S1: Add 300 g of starch to 900 g of deionized water, heat to 30°C, add 3% wt sodium hydroxide solution, adjust the pH to 8.5-9.5, add 15 g of sodium hypochlorite solution, react for 1 hour, add 10% wt sodium sulfite solution, adjust the pH to 6.5-7.0, filter, wash and dry to obtain oxidized starch;

[0041] S2: Add 300 g of oxidized starch to 450 g of sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10-10.5, heat to 40°C, react for 90 min, filter, wash, dry, add 3 g of aluminate coupling agent, heat to 50°C, stir for 40 min, and cool to 20°C to obtain hydrophobic starch;

[0042] S3: Add 300 g of hydrophobic starch to 120 g of the composite plasticizer solution, heat to 20° C., and stir for 12 minutes to obtain modified starch.

[0043] Example 2: A method for preparing modified starch is as follows:

[0044] S1: Add 300g of starch to 1050g of deionized water, heat to 40°C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5-9.5, add 30g of sodium hypochlorite solution, react for 2h, add 10%wt sodium sulfite solution, adjust the pH to 6.5-7.0, filter, wash and dry to obtain oxidized starch;

[0045] S2: Add 300 g of oxidized starch to 540 g of sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10-10.5, heat to 50° C., react for 80 min, filter, wash, dry, add 4.5 g of aluminate coupling agent, heat to 55° C., stir for 30 min, and cool to 25° C. to obtain hydrophobic starch;

[0046] S3: Add 300 g of hydrophobic starch to 150 g of the composite plasticizer solution, heat to 25° C., and stir for 10 minutes to obtain modified starch.

[0047] Example 3: A method for preparing modified starch is as follows:

[0048] S1: Add 300 g of starch to 1200 g of deionized water, heat 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;

[0049] S2: Add 300 g of oxidized starch to 600 g of sodium trimetaphosphate solution, add sodium carbonate, adjust the pH to 10-10.5, heat to 60° C., react for 70 min, filter, wash, dry, add 6 g of aluminate coupling agent, heat to 60° C., stir for 20 min, and cool to 30° C. to obtain hydrophobic starch;

[0050] S3: Add 300 g of hydrophobic starch to 180 g of the composite plasticizer solution, heat to 30° C., and stir for 8 minutes to obtain modified starch.

[0051] Example 4: A method for preparing thin film particles is as follows:

[0052] Add 300 g of modified starch to 500 g of polycaprolactone, stir and mix, add 85 g of polyvinyl acetate, 50 g of cosolvent, 10 g of stearic acid and 10 g of polyethylene wax, heat to 40° C., stir for 20 minutes to obtain film particles.

[0053] Example 5: A method for preparing thin film particles is as follows:

[0054] Add 300 g of modified starch to 510 g of polycaprolactone, stir and mix, add 86 g of polyvinyl acetate, 52 g of cosolvent, 15 g of stearic acid and 10 g of polyethylene wax, heat to 50° C., stir for 15 minutes to obtain film particles.

[0055] Example 6: A method for preparing thin film particles is as follows:

[0056] Add 300 g of modified starch to 520 g of polycaprolactone, stir and mix, add 88 g of polyvinyl acetate, 53 g of cosolvent, 20 g of stearic acid and 10 g of polyethylene wax, heat to 60° C., stir for 10 minutes to obtain film particles.

[0057] Example 7: A method for preparing a modified nano-titanium dioxide emulsion is as follows:

[0058] S1: Add 280 g of 2-[8-(trimethoxysilyl)octyl]oxirane and 100 g of trimethylamine hydrochloride to 500 mL of anhydrous ethanol, heat to 60° C., stir and react for 3 h. After the reaction is complete, evaporate under reduced pressure to obtain quaternary ammonium trimethoxysilane;

[0059] S2: Add 90g of quaternary ammonium trimethoxysilane to 200mL of anhydrous ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3-4, heat to 20°C, ultrasonically disperse for 3h, add 20g of nano-titanium dioxide, ultrasonically disperse for 50min, add ammonia water, adjust the pH to 9-10, heat to 90°C, stir for 1h, cool, and dry to obtain modified nano-titanium dioxide;

[0060] S3: Add 200g of acrylic acid, 100g of methyl methacrylate, and 100g of n-butyl acrylate to 500mL of deionized water, stir and mix evenly, add 10g of sodium lauryl sulfate and 10g of nonylphenol polyoxyethylene ether, stir for 8min, add 100g of modified nano-titanium dioxide, ultrasonically disperse for 20min, heat to 80°C, adjust the pH to 4-6, add ammonium persulfate, heat to 70°C, keep warm for 2h, cool to 30°C, add ammonia water, adjust the pH to 7.5-8.5, and obtain modified nano-titanium dioxide emulsion.

[0061] Example 8: A method for preparing a modified nano-titanium dioxide emulsion is as follows:

[0062] S1: Add 290 g of 2-[8-(trimethoxysilyl)octyl]oxirane and 100 g of trimethylamine hydrochloride to 500 mL of anhydrous ethanol, heat to 70°C, stir and react for 2.5 h. After the reaction is complete, evaporate under reduced pressure to obtain quaternary ammonium trimethoxysilane;

[0063] S2: Add 92 g of quaternary ammonium trimethoxysilane to 200 mL of anhydrous ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3-4, heat to 25 ° C, ultrasonically disperse for 2 h, add 20 g of nano titanium dioxide, ultrasonically disperse for 60 min, add ammonia water, adjust the pH to 9-10, heat to 70-90 ° C, stir for 2 h, cool, and dry to obtain modified nano titanium dioxide;

[0064] S3: Add 220g of acrylic acid, 110g of methyl methacrylate, and 110g of n-butyl acrylate to 500mL of deionized water, stir and mix evenly, add 20g of sodium lauryl sulfate and 20g of nonylphenol polyoxyethylene ether, stir for 10min, add 100g of modified nano-titanium dioxide, ultrasonically disperse for 30min, heat to 70°C, adjust the pH to 4-6, add ammonium persulfate, heat to 80°C, keep warm for 1.5h, cool to 40°C, add ammonia water, adjust the pH to 7.5-8.5, and obtain modified nano-titanium dioxide emulsion.

[0065] Example 9: A method for preparing a modified nano-titanium dioxide emulsion is as follows:

[0066] S1: 300 g of 2-[8-(trimethoxysilyl)octyl]oxirane and 100 g of trimethylamine hydrochloride were added to 500 mL of anhydrous ethanol, heated to 80° C., stirred and reacted for 3 h. After the reaction was complete, the mixture was distilled under reduced pressure to obtain quaternary ammonium trimethoxysilane;

[0067] S2: Add 94 g of quaternary ammonium trimethoxysilane to 200 mL of anhydrous ethanol solvent, stir evenly, add glacial acetic acid, adjust the pH to 3-4, heat to 30°C, ultrasonically disperse for 1 hour, add 20 g of nano-titanium dioxide, ultrasonically disperse for 70 minutes, add ammonia water, adjust the pH to 9-10, heat to 70°C, stir for 3 hours, cool, and dry to obtain modified nano-titanium dioxide;

[0068] S3: Add 250g of acrylic acid, 120g of methyl methacrylate, and 120g of n-butyl acrylate to 500mL of deionized water, stir and mix evenly, add 30g of sodium lauryl sulfate and 30g of nonylphenol polyoxyethylene ether, stir for 12min, add modified nano titanium dioxide, ultrasonically disperse for 20min, heat to 80°C, adjust the pH to 4-6, add ammonium persulfate, heat to 70°C, keep warm for 2h, cool to 30°C, add ammonia water, adjust the pH to 7.5-8.5, and obtain modified nano titanium dioxide emulsion.

[0069] Example 10: A method for preparing an agricultural plastic film is as follows:

[0070] S1: 6 g of lignin nanoparticles, 2 g of tannic acid, 6 g of glycerol, 4 g of cosolvent, 95 g of film particles, and 4 g of cellulose nanocrystals were added to a high-speed mixer and stirred at 1000 rpm for 15 min to obtain a mixed raw material;

[0071] S2: 100 g of the mixed raw materials were fed into the feed port of a twin-screw extruder, heated to 140°C, rolled for 40 min, and then rolled and drawn through a four-roll calender to obtain a base film;

[0072] S3: Place 100g of base film into a coating machine, add 2g of modified nano-titanium dioxide emulsion, raise the temperature to 20°C, pressure to 0.3MPa, coating speed to 10m / min, then place in a hot air drying tunnel, raise the temperature to 100°C, and dry for 5min to obtain an agricultural plastic film.

[0073] Example 11: A method for preparing an agricultural plastic film is as follows:

[0074] S1: 8 g of lignin nanoparticles, 3 g of tannic acid, 8 g of glycerol, 5 g of cosolvent, 100 g of film particles, and 5 g of cellulose nanocrystals were added to a high-speed mixer and stirred for 15-20 min at a speed of 800-1000 rpm to obtain a mixed raw material;

[0075] S2: 100 g of the mixed raw materials were fed into the feed port of a twin-screw extruder, heated to 145°C, rolled for 30 min, and then rolled and drawn through a four-roll calender to obtain a base film;

[0076] S3: Place 100g of base film into a coating machine, add 3g of modified nano-titanium dioxide emulsion, raise the temperature to 23°C, pressure to 0.25MPa, coating speed to 13m / min, then place in a hot air drying tunnel, raise the temperature to 90°C, and dry for 7min to obtain an agricultural plastic film.

[0077] Example 12: A method for preparing an agricultural plastic film is as follows:

[0078] S1: 10 g of lignin nanoparticles, 4 g of tannic acid, 10 g of glycerol, 6 g of cosolvent, 105 g of film particles, and 6 g of cellulose nanocrystals were added to a high-speed mixer and stirred at 800 rpm for 20 min to obtain a mixed raw material;

[0079] S2: 100 g of the mixed raw materials were fed into the feed port of a twin-screw extruder, heated to 150°C, rolled for 20 min, and then rolled and drawn through a four-roll calender to obtain a base film;

[0080] S3: Put 100g of base film into the coating machine, add 4g of modified nano titanium dioxide emulsion, raise the temperature to 25°C, pressure 0.2MPa, coating speed 15m / min, then put it into the hot air drying tunnel, raise the temperature to 80°C, and dry it for 10min to obtain agricultural plastic film.

[0081] Comparative Example 1:

[0082] Compared with Example 10, this comparative example did not add lignin nanoparticles during the preparation of the agricultural plastic film. The remaining steps and parameters were the same and will not be repeated in this comparative example. Finally, an agricultural plastic film was obtained.

[0083] Comparative Example 2:

[0084] Compared with Example 10, this comparative example only replaces "modified nano-titanium dioxide" with "titanium dioxide", and the remaining steps and parameters are the same, which will not be repeated in this comparative example. Finally, an agricultural plastic film is obtained.

[0085] Comparative Example 3:

[0086] Compared with Example 10, this comparative example only replaces the mass ratio of modified starch, polycaprolactone and polyvinyl acetate from "30:50:8.5" to "25:55:10", and the remaining steps and parameters are the same, which will not be repeated in this comparative example. Finally, an agricultural plastic film is obtained.

[0087] Comparative Example 4:

[0088] Compared with Example 10, this comparative example only replaces "modified starch" with "hydrophobic starch", and the remaining steps and parameters are the same, which will not be repeated in this comparative example. Finally, an agricultural plastic film is obtained.

[0089] Comparative Example 5:

[0090] Compared with Example 10, this comparative example only changes the order of coating modified nano-titanium dioxide in steps S2 and S3. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, an agricultural plastic film is obtained.

[0091] Comparative Example 6

[0092] Compared with Example 10, this comparative example only directly mixed the modified nano-titanium dioxide raw materials, and the remaining steps and parameters were the same, which will not be repeated in this comparative example. Finally, an agricultural plastic film was obtained.

[0093] Performance testing:

[0094] Biodegradability testing

[0095] Refer to ISO-14855 test standards, use constant temperature and humidity composting reactor and CO2 capture device;

[0096] 1. Take the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6, cut them into 10 mm × 10 mm pieces, and the initial mass is M0.

[0097] 2. Mix the sample with mature compost at a mass ratio of 1:10 and place it in a reactor at a temperature of 58±2°C and a humidity of 50%-60%. Collect gas every 30 days and measure the CO2 release using an infrared analyzer. The biodegradation rate is calculated using the following formula:

[0098]

[0099] 3. After 180 days, take out the sample, clean and dry it, and weigh M1. The calculation formula for mass loss is:

[0100]

[0101] Tensile strength and elongation at break test

[0102] Refer to ASTM-D638 test standard and use Instron-5967 universal material testing machine;

[0103] 1. Cut the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6 into 25 mm × 4 mm × 0.05 mm pieces, with 5 parallel samples in each group. Stretch at a speed of 50 mm / min, with a clamp spacing of 20 mm. Raise the temperature to 23 ± 2°C and humidity to 50 ± 5%. Record the maximum tensile force (N) and elongation at break (%).

[0104] 2. Calculation formula for tensile strength (MPa):

[0105]

[0106] Table 1

[0107]

[0108] UV shielding rate and light transmittance test

[0109] Tested according to ASTM-E424 and ASTM-D1003 standards, using a UV-2600 UV-visible spectrophotometer and integrating sphere;

[0110] 1. Cut the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6 into 50 mm × 50 mm pieces respectively, scan them in the wavelength range of 280-400 nm, and calculate the average transmittance of UV-A (315-400 nm) and UV-B (280-315 nm). ;

[0111] 2. Use an integrating sphere to measure the visible light (550nm) transmittance and haze value, and take the average value of each test three times;

[0112] Antioxidant performance test

[0113] Refer to GB / T-7141 standard test, using thermal aging test chamber and Fourier infrared spectrometer;

[0114] 1. Take 5g of each of the agricultural plastic films of Examples 10-12 and Comparative Examples 1-6, place them in an oven, heat to 80°C, heat for 30 days, and maintain a humidity of 60±5%. Use a Fourier transform infrared spectrometer to analyze the samples before and after aging. Calculate the 1710cm -1 The carbonyl peak at 1450 cm -1 The absorbance ratio of the reference peak at , carbonyl index = carbonyl peak area / reference peak area;

[0115] 2. Test the tensile strength after aging. The calculation formula is:

[0116]

[0117] Table 2

[0118]

[0119] Antibacterial performance test

[0120] The test was conducted in accordance with ISO-22196 standard, using a constant temperature and humidity incubator, and the bacterial species were Escherichia coli and Staphylococcus aureus;

[0121] 1. Sample preparation: Cut the plastic films of Examples 10-12 and Comparative Examples 1-6 into 50 mm × 50 mm squares, 0.05 mm thick, and sterilize the surfaces (soak in 75% ethanol for 10 min and rinse with sterile water three times).

[0122] 2. Preparation of bacterial solution: Inoculate the bacteria into liquid culture medium (LB medium), culture at 37℃ for 24h, and adjust the bacterial solution concentration to 1×10 6 CFU / mL;

[0123] 3. Inoculation and culture: Take 100 μL of bacterial solution and evenly spread it on the sample surface, cover with sterile polyethylene film to prevent evaporation, and incubate in an incubator (37°C, RH ≥ 90%) for 24 hours;

[0124] 4. Colony count: immerse the sample in 10 mL of PBS buffer, ultrasonically vibrate for 5 minutes (40 kHz), spread on an agar plate after gradient dilution, incubate at 37°C for 24 hours, and count the colony count (CFU);

[0125] 5. Antibacterial rate calculation formula:

[0126]

[0127] Table 3

[0128]

[0129] Data Analysis:

[0130] 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;

[0131] In Comparative Example 1, since no lignin nanoparticles were added, its degradation ability decreased, and its enhanced mechanical properties and natural antibacterial function were lost. 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 nano-treatment have a larger specific surface area, which can accelerate microbial attachment and enzymatic hydrolysis reactions, thereby significantly improving the degradation efficiency. At the same time, the lignin nanoparticles are combined with the polymer chains through hydrogen bonds and van der Waals forces to form a rigid interface layer, which effectively disperses stress and inhibits crack propagation. In addition, the phenolic hydroxyl and quinone compounds contained in lignin can achieve antibacterial properties by destroying microbial cell membranes, inhibiting enzyme activity, and interfering with metabolic pathways. The exposure rate and reaction efficiency of its active groups are further improved by nano-treatment.

[0132] Comparative Example 2: Since titanium dioxide replaces modified nano-titanium dioxide, the photocatalytic activity and dispersibility are insufficient, and it is unable to effectively shield ultraviolet rays and inhibit the growth of microorganisms. The reason is that the modified nano-titanium dioxide is surface-modified by quaternized trimethoxysilane to form a stable hydrophilic-hydrophobic interface, which significantly improves its dispersibility in the emulsion. At the same time, the modified nano-titanium dioxide is coated with an acrylic copolymer to form a core-shell structure, which improves the absorption capacity of UV-A and UV-B. In addition, the modified nano-titanium dioxide generates hydroxyl radicals and superoxide radicals under light, thereby achieving efficient sterilization.

[0133] In Comparative Example 3, due to the imbalance in the ratio of modified starch, polycaprolactone, and polyvinyl acetate, the material phase separation, uneven coating, and decreased mechanical and optical properties occurred. This was because the modified starch, as a bio-based filler, reduced the rigid skeleton structure and was unable to effectively support the flexible segments of polycaprolactone, thereby reducing the overall mechanical strength. At the same time, the polarity difference between the three was large. After the ratio was unbalanced, the compatibility of the components decreased, the interfacial bonding strength decreased, and phase separation was triggered, becoming a stress concentration point, ultimately leading to a significant decrease in tensile strength.

[0134] In Comparative Example 4, since hydrophobic starch replaces modified starch, the interfacial bonding force is weak during the processing, and the antioxidant performance and degradation efficiency are significantly reduced. The reason is that the composite plasticizer in the 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 gaps, which makes it easier for oxygen and moisture to penetrate into the interior of the material and accelerate the oxidation reaction. In addition, the hydrophobic starch has poor dispersion in the matrix, forming larger agglomerated particles, which leads to enhanced light scattering and increased haze value.

[0135] In Comparative Example 5, due to the reversal of the process sequence, the base film surface had insufficient adhesion, the functional coating easily fell off, and the shielding performance fluctuated greatly. This was because the base film surface had not been oriented by calendaring and traction, and its surface energy was low, making it difficult for the coating material to effectively infiltrate. Furthermore, the high temperature of the extrusion process partially melted the base film surface, and the coating material was wrapped in the molten polymer, preventing the formation of a stable interface. Furthermore, the coating was unevenly distributed during the extrusion process due to the fluidity of the base film, forming localized weak areas. Furthermore, the nano-titanium dioxide particles agglomerated due to mechanical shearing, further reducing the UV shielding efficiency.

[0136] In Comparative Example 6, the raw material nanoparticles prepared by directly mixing modified nano-titanium dioxide are easy to agglomerate, have poor dispersion, and reduce photocatalytic efficiency, while affecting the uniformity of light transmittance. The reason is that there are high-energy hydroxyl groups on the surface of unmodified nano-titanium dioxide, which leads to enhanced van der Waals forces between particles, and are easy to spontaneously agglomerate to form micron-sized aggregates. After agglomeration, the effective specific surface area of ​​the particles is greatly reduced, the photocatalytic active surface is reduced, and the antibacterial efficiency is reduced. In addition, the agglomerated particles cause scattering in the visible light wavelength range, resulting in an increase in the haze value and a decrease in transmittance.

[0137] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0138] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An agricultural plastic film, characterized in that: The invention is composed 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 a cosolvent, and 4-6 parts of cellulose nanocrystals; 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 anhydrous ethanol, raise the temperature to 60-80°C, stir and react for 2-3 hours. After the reaction is complete, evaporate under reduced pressure to obtain quaternary ammonium trimethoxysilane; Step C2: adding quaternary ammonium trimethoxysilane to anhydrous ethanol solvent, stirring evenly, adding glacial acetic acid, adjusting the pH to 3-4, heating to 20-30° C., ultrasonically dispersing for 1-3 hours, adding nano-titanium dioxide, ultrasonically dispersing for 50-70 minutes, adding ammonia water, adjusting the pH to 9-10, heating to 70-90° C., stirring for 1-3 hours, cooling, and drying to obtain modified nano-titanium dioxide; Step C3: Add acrylic acid, methyl methacrylate, and n-butyl acrylate to deionized water, stir and mix evenly, add sodium lauryl sulfate and nonylphenol polyoxyethylene ether, stir for 8-12 minutes, add modified nano-titanium dioxide, ultrasonically disperse for 20-40 minutes, heat to 60-80°C, adjust the pH to 4-6, add ammonium persulfate, heat to 70-90°C, keep warm for 1-2 hours, cool to 30-50°C, add ammonia water, adjust the pH to 7.5-8.5, and obtain a modified nano-titanium dioxide emulsion; The film particle preparation method is as follows: Add modified starch to polycaprolactone, stir and mix, add polyvinyl acetate, cosolvent, stearic acid and polyethylene wax, heat to 40-60°C, stir for 10-20 minutes to obtain film particles; The mass ratio of the modified starch, polycaprolactone, polyvinyl acetate, cosolvent, stearic acid and polyethylene wax is 30-33:50-52:8.5-8.8:5-5.3:1-2:1; The modified starch preparation method is as follows: Step B1: Add starch to deionized water, heat to 30-50°C, add 3%wt sodium hydroxide solution, adjust the pH to 8.5-9.5, add sodium hypochlorite solution, react for 1-3h, add 10%wt sodium sulfite solution, adjust the pH to 6.5-7.0, filter, wash and dry to obtain oxidized starch; Step B2: adding oxidized starch to a sodium trimetaphosphate solution, adding sodium carbonate, adjusting the pH to 10-10.5, heating to 40-60° C., reacting for 70-90 minutes, filtering, washing, drying, adding an aluminate coupling agent, heating to 50-60° C., stirring for 20-40 minutes, and cooling to 20-30° C. to obtain hydrophobic starch; Step B3: adding hydrophobic starch to the composite plasticizer solution, heating to 20-30° C., and stirring for 8-12 minutes to obtain modified starch; The preparation method of the agricultural plastic film is as follows: Step S1: adding lignin nanoparticles, tannic acid, glycerol, cosolvent, film particles and cellulose nanocrystals into a high-speed mixer, stirring for 15-20 minutes at a speed of 800-1000 rpm to obtain a mixed raw material; Step S2: feeding the mixed raw materials into the feed port of a twin-screw extruder, heating to 140-150° C., rolling for 20-40 minutes, and rolling and pulling through a four-roll calender to obtain a base film; Step S3: Place the base film into a coating machine, add modified nano-titanium dioxide emulsion, raise the temperature to 20-25°C, pressure 0.2-0.3 MPa, coating speed 10-15 m / min, then place it into a hot air drying tunnel, raise the temperature to 80-100°C, and dry for 5-10 minutes to obtain an agricultural plastic film.

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

6.

3. The agricultural plastic film according to claim 1, characterized in that: The mass ratio of 2-[8-(trimethoxysilyl)octyl]oxirane to trimethylamine hydrochloride in step C1 is 2.8-3:

1.

4. The agricultural plastic film according to claim 1, characterized in that: The mass ratio of the quaternized trimethoxysilane to nano-titanium dioxide in step C2 is 4.5-4.7:

1.

5. The method for preparing an agricultural plastic film according to any one of claims 1 to 4, characterized in that: The preparation method is as follows: Step S1: adding lignin nanoparticles, tannic acid, glycerol, cosolvent, film particles and cellulose nanocrystals into a high-speed mixer, stirring for 15-20 minutes at a speed of 800-1000 rpm to obtain a mixed raw material; Step S2: feeding the mixed raw materials into the feed port of a twin-screw extruder, heating to 140-150° C., rolling for 20-40 minutes, and rolling and pulling through a four-roll calender to obtain a base film; Step S3: Place the base film into a coating machine, add modified nano-titanium dioxide emulsion, raise the temperature to 20-25°C, pressure 0.2-0.3 MPa, coating speed 10-15 m / min, then place it into a hot air drying tunnel, raise the temperature to 80-100°C, and dry for 5-10 minutes to obtain an agricultural plastic film.

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