A method for preparing a corn stalk-based biodegradable material

Abstract

A method for preparing biodegradable materials based on corn stalks, belonging to the field of corn stalk treatment, includes the following steps: Step 1: Stalk pretreatment and fiber extraction; Step 2: Preparation of coating solution; Step 3: Functionalization and molding: After the coating solution is scraped into a film with a thickness of 0.1-0.5 mm, it is dried at 60-65℃ for 20-24 hours, sprayed with a urea-phosphorus pentoxide-cypermethrin functional solution and dried at 60-65℃ for 8-12 hours, and then two pretreated films sprayed with functional solution are stacked and hot-pressed at 120-140℃ for 8-10 minutes to obtain a biodegradable agricultural film. This invention uses agricultural waste corn stalks as the core raw material, solves the air pollution problem caused by traditional straw burning, and realizes a resource-based closed loop of "waste-high value-added materials". Each ton of straw can be converted into 150-200 kg of biodegradable agricultural film, and the comprehensive utilization rate of raw materials is increased to more than 85%, which is far higher than the 50%-60% utilization rate of existing processes.

Description

Technical Field

[0001] This invention belongs to the field of corn stalk treatment, specifically a method for preparing biodegradable materials based on corn stalks. Background Technology

[0002] With the increasing severity of plastic pollution, the non-degradable nature of traditional petroleum-based plastics leads to environmental problems such as soil compaction and ecological damage. Meanwhile, large quantities of waste corn stalks from agricultural production are often burned, wasting biomass resources and causing air pollution. Current biodegradable plastic preparation processes suffer from high raw material costs, poor industrial adaptability, and limited product performance (e.g., insufficient water resistance, lack of functionality). Corn stalk resource utilization is mostly concentrated on simple composting or energy conversion, while high-value-added conversion technologies (such as extracting polylactic acid and humic acid to prepare functional biodegradable materials) suffer from complex processes, high pollution emissions, and low product purity. Therefore, there is an urgent need to develop a preparation method that can efficiently convert corn stalks, is suitable for industrial production, and produces biodegradable and functional products, achieving a closed loop of "waste resource utilization - green material production - environmental problem solving." Summary of the Invention

[0003] This invention provides a method for preparing biodegradable materials based on corn stalks, thereby overcoming the deficiencies in the prior art.

[0004] This invention is achieved through the following technical solution:

[0005] A method for preparing biodegradable materials based on corn stalks includes the following steps:

[0006] Step 1: Straw pretreatment and fiber extraction: After crushing the corn straw through a 100-mesh sieve, steam explosion is performed at 110-120℃ and 1.6-1.9MPa for 5-8 minutes. The straw is then soaked in deionized water at 70-80℃ for 40-60 minutes, oxidized in 10% hydrogen peroxide at 70-80℃ for 1-2 hours, and the pH is adjusted to 8.5-9.0 with a 5% sodium hydroxide aqueous solution. The straw is then heated to 80-85℃ and soaked for 2-3 hours. Finally, it is washed with 50% ethanol until neutral and dried at 105-110℃ for 6-8 hours to obtain corn straw fiber.

[0007] Step 2: Preparation of coating solution: Starch and deionized water are mixed at a mass ratio of 1:8-1:10 and stirred and gelatinized at a temperature of 90-95℃ and a stirring speed of 800-1000r / min for 25-30min. Then epichlorohydrin is added for modification and the temperature is raised to 35-40℃. The reaction is carried out for 5-6h to obtain modified starch. This modified starch is then mixed with chitosan-acetic acid solution, nano silica, straw fiber and polyvinyl alcohol, and stirred at 80-85℃ for 2-3h to obtain coating solution.

[0008] Step 3: Functionalization and molding: After the coating liquid is scraped into a film with a thickness of 0.1-0.5mm, it is dried at 60-65℃ for 20-24h. Then, a urea-phosphorus pentoxide-cypermethrin functional liquid is sprayed on and dried at 60-65℃ for 8-12h. After two films with the functional liquid sprayed on them are stacked, they are hot-pressed at 120-140℃ for 8-10min to obtain the degradable agricultural film.

[0009] As described above, in the method for preparing a biodegradable material based on corn stalks, the preparation of the chitosan-acetic acid solution in step two is as follows: chitosan is dissolved in a 1% aqueous acetic acid solution, wherein the mass-volume ratio of chitosan to aqueous acetic acid solution is 1g:80ml-1g:100ml. After addition, the mixture is stirred at a stirring speed of 600-800r / min for 15-20min to obtain the chitosan-acetic acid solution.

[0010] The method for preparing a biodegradable material based on corn stalks as described above, wherein the mass-volume ratio of modified starch, chitosan-acetic acid solution, nano-silica, straw fiber, and polyvinyl alcohol is 5g:40mL:0.3g:2g:1g.

[0011] The preparation method of the urea-phosphorus pentoxide-cypermethrin functional liquid according to the above-described method is as follows: urea, phosphorus pentoxide, cypermethrin and deionized water are weighed according to the following mass-volume ratio: 5g: 2g: 0.1g: 100mL. Urea, phosphorus pentoxide and cypermethrin are added to deionized water and stirred at a stirring speed of 500-600r / min for 15-20min to obtain the urea-phosphorus pentoxide-cypermethrin functional liquid.

[0012] A method for preparing biodegradable materials based on corn stalks includes the following steps:

[0013] Step 1: Remove hemicellulose by treating with a choline chloride-urea system at 80℃ for 2 hours;

[0014] Step 2: Remove lignin by treating with a choline chloride-lactic acid system at 90℃ for 3 hours;

[0015] Step 3: The mixed coating solution includes the following substances in parts by mass or volume: 100 parts of nanocellulose dispersion, 10 parts of 8-12wt% polyvinyl alcohol solution, 1.25 parts of 1-3wt% silicon source dispersion, and 20 parts of glycerol. Weigh the above substances according to the ratio and stir for 1.5 hours at 80℃ and 800-1000r / min to form a stable coating solution.

[0016] Step 4: Pour the coating liquid into a polytetrafluoroethylene mold to a thickness of 0.2-0.6 mm, spread it naturally, and dry it in a ventilated environment at 25℃ for 48 hours. Peel off the mold to obtain a water-resistant and biodegradable agricultural film.

[0017] In the method for preparing biodegradable materials based on corn stalks as described above, the molar ratio of the choline chloride-urea system is 1:2; and the molar ratio of the choline chloride-lactic acid system is 1:3.

[0018] A method for preparing biodegradable materials based on corn stalks includes the following steps:

[0019] Step 1: Straw pretreatment and saccharification: Corn straw is treated with high-pressure steam at 121℃ for 30-60 min; after cooling, it is soaked in PBS solution with pH 7.2 for 12-24 h, and after adjusting the pH to 5-6, cellulase is added to obtain a monosaccharide aqueous solution;

[0020] Step 2: Fermentation and purification: Add glucose and peptone to the monosaccharide aqueous solution to prepare a fermentation broth with a specific gravity of 1.15-1.3. Inoculate with 12-15% Rhizopus oryzae / lactic acid bacteria and anaerobic dynamic culture at 30-40℃ and pH 6.5-7.5 for at least 3 days. After fermentation, centrifuge at 3000 r / min for 15 min. Purify the supernatant by an anion exchange column and distill under reduced pressure at 80℃ and 0.08 MPa for 40-60 min to obtain L-lactic acid with a purity ≥99%.

[0021] Step 3: Polymerization and molding: L-lactic acid is heated at 120℃ to dehydrate and prepare lactide; 0.5% SnCl / TSA catalyst is added, and the reaction is stirred at 160℃ and 0.05MPa for 8 hours. After the reaction, the catalyst is removed by filtration, the product is dissolved in acetonitrile and then precipitated by adding distilled water. The product is washed with water 4 times and dried at 80℃ for 6 hours to obtain polylactic acid resin.

[0022] In the method for preparing biodegradable materials based on corn stalks as described above, the cellulase activity is at least 40,000 U / g, the amount of cellulase added is 2-3% of the mass of the pretreated corn stalks, and ammonium sulfate or ammonium nitrate is added as nutrients during enzymatic hydrolysis after the cellulase is added, with the amount of nutrients added being 0.5-0.8% of the mass of the pretreated corn stalks, the enzymatic hydrolysis temperature being 50℃, and the enzymatic hydrolysis time being 4h.

[0023] In the method for preparing biodegradable materials based on corn stalks as described above, in step three of the polymerization molding process, L-lactic acid can also be melt-polymerized at a temperature of 130-135℃ for 30 hours to obtain polylactic acid resin.

[0024] A method for preparing biodegradable materials based on corn stalks includes the following steps:

[0025] Step 1: Treat corn stalks with high-pressure steam at 121℃ for 30-60 minutes; after cooling, soak them in PBS solution with pH 7.2 for 12-24 hours.

[0026] Step 2: The pretreated corn stalks from Step 1 are mixed with 0.75 mol / L sodium hydroxide solution at a mass-to-volume ratio of 1:10, reacted at 200℃ for 5 hours, the pH is adjusted to 1-2 with sulfuric acid, and then allowed to stand for 12 hours. Humic acid is obtained by filtration.

[0027] The advantages of this invention are:

[0028] 1. This invention uses agricultural waste corn stalks as the core raw material to solve the air pollution problem caused by traditional straw burning, and realizes a resource-based closed loop of "waste-high value-added materials". Each ton of straw can be converted into 200 kg of polylactic acid resin or 150-200 kg of biodegradable agricultural film, while humic acid is extracted simultaneously. The comprehensive utilization rate of raw materials is increased to more than 85%, which is far higher than the 50%-60% utilization rate of existing processes. Moreover, there is no emission of heavy metals or toxic solvents throughout the process. The pollution from processes such as DES treatment and hydrogen peroxide-sodium hydroxide extraction is zero, which meets the national green production standards.

[0029] 2. The functional agricultural film prepared by the steam explosion method of this invention has both automatic slow-release fertilizer effect (urea release cycle matches the crop growth period, reaching 30-45 days) and insect-repellent effect (cypermethrin effectively controls pests such as corn borers, with an insect-repellent rate of ≥80%); the water contact angle of the deep eutectic solvent method agricultural film is ≥85°, and its water resistance is improved by more than 60% compared with traditional straw-based agricultural films, and it can withstand continuous rain immersion for 7 days without damage; the polylactic acid resin prepared by this invention has a purity of ≥99% and a tensile strength of 60MPa, which can directly replace petroleum-based plastics in packaging, injection molding and other fields, and can be completely degraded in soil in 6-12 months without residual pollution;

[0030] 3. The equipment used in the process of this invention (steam explosion tank, anaerobic fermentation tank, casting mold, etc.) are all existing mature industrial equipment, which do not require customized modification, reducing equipment investment costs by 30%; the key parameters (such as steam explosion pressure 1.6-1.9MPa, fermentation temperature 30-40℃) have a wide range, high operational error tolerance, and are easy to scale up and stably produce. The cost of corn stalks as raw material is only 1 / 5 of that of petroleum-based raw materials, and the product yield can be further increased by extracting humic acid at the same time, so that the overall material production cost is reduced by 40%-50% compared with pure PLA material, which has a strong market competitiveness;

[0031] 4. Compared with existing straw treatment processes, this invention improves the straw fiber extraction rate to over 75% through a combination of "steam explosion + chemical extraction" pretreatment; it gently removes lignin and hemicellulose, avoiding fiber structure damage caused by traditional strong acid and alkali treatments, and achieves a nanocellulose yield of 60%; by optimizing the catalyst ratio (SnCl / TSA dosage 0.5%) and reaction parameters, the polylactic acid polymerization efficiency is improved by 25%, and the molecular weight distribution of the product is more uniform, solving the problem of unstable product performance in existing processes. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a reaction flow diagram of the present invention;

[0034] Figure 2 This is one of the schematic diagrams of the performance test report of the degradable agricultural film prepared in Example 1 of the present invention;

[0035] Figure 3 This is the second schematic diagram of the performance test report of the degradable agricultural film prepared in Example 1 of the present invention;

[0036] Figure 4 This is the third schematic diagram of the performance test report of the degradable agricultural film prepared in Example 1 of the present invention;

[0037] Figure 5 This is the fourth schematic diagram of the performance test report of the degradable agricultural film prepared in Example 1 of the present invention;

[0038] Figure 6 This is the fifth schematic diagram of the performance test report of the degradable agricultural film prepared in Example 1 of the present invention;

[0039] Figure 7 This is a schematic diagram of the actual production of Embodiment 1 of the present invention;

[0040] Figure 8 This is one of the actual production schematic diagrams of Embodiment 2 of the present invention;

[0041] Figure 9 This is the second actual production schematic diagram of Embodiment 2 of the present invention;

[0042] Figure 10 This is the third actual production schematic diagram of Embodiment 2 of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0044] Example 1: Preparation of degradable agricultural film by steam explosion method

[0045] Step 1: Straw Pretreatment and Fiber Extraction: Take 4 kg of corn stalks, air dry them naturally, crush them through a 100-mesh sieve, put the powder into a steam explosion tank, heat it to 115℃ and introduce steam to make the pressure inside the tank reach 1.7 MPa, maintain the pressure for 6 minutes and then release the pressure to atmospheric pressure; then soak the powder in 75℃ deionized water for 12 minutes, filter and collect the filter residue; place the filter residue in 550 mL of 10% hydrogen peroxide, react in a constant temperature water bath at 75℃ for 1.5 h, adjust the pH to 11.5 with 5% sodium hydroxide solution, react in a water bath at 82℃ for 2.5 h, vacuum filter, wash with 50% ethanol solution until neutral, and dry in a drying oven at 108℃ to obtain corn stalk fiber;

[0046] Step 2: Preparation of modified excipients and coating solution: Weigh 330g of starch and add 250mL of deionized water. Stir and gelatinize in a 32℃ water bath at 350r / min for 25min. Add 28mL of epichlorohydrin, heat to 38℃ and stir for 5.5h. Dry at 75℃ for 4h to obtain modified starch. Take 90g of chitosan and dissolve it in 700mL of 1% acetic acid solution. Stir for 18min, then add 25g of nano-silica, 310g of modified starch, 40g of straw fiber and 120mL of polyvinyl alcohol. Stir in a 82℃ water bath for 2.5h. After cooling, prepare the coating solution.

[0047] Step 3: Coating and Functionalization: The coating solution is scraped onto a glass plate to form a 0.3mm film using a scraper, and dried at 62℃ for 22 hours. Urea, phosphorus pentoxide, and cypermethrin are dissolved in deionized water, stirred for 25 minutes, and then sprayed onto the film, and dried at 62℃ for 11 hours. Two pre-treated films sprayed with functional liquid are stacked together and placed in a hot press, then hot-pressed at 130℃ using a 5cm×5cm grid for 9 minutes. After cutting, a biodegradable agricultural film for cornfields is obtained (its production process is as follows). Figure 7 (As shown).

[0048] Example 2: Preparation of water-resistant and biodegradable agricultural film by deep eutectic solvent method

[0049] Step 1: Treat with choline chloride-urea system (molar ratio 1:2) at 80℃ for 2 hours to remove hemicellulose;

[0050] Step 2: Treat with choline chloride-lactic acid system (molar ratio 1:3) at 90℃ for 3 hours to remove lignin and finally obtain a pure nanocellulose dispersion;

[0051] Step 3: Prepare the mixed coating solution: Take 100 parts of nanocellulose dispersion by mass ratio, add 10 parts of 10wt% polyvinyl alcohol (PVA) solution, 1.25 parts of 2wt% silicon source (tetraethyl orthosilicate) dispersion and 20 parts of glycerol, and stir magnetically at 80℃ for 1.5h to form a stable coating solution;

[0052] The preparation of the 10wt% polyvinyl alcohol (PVA) solution is as follows: weigh polyvinyl alcohol and deionized water according to the ratio and mix them, then sonicate to dissolve for 30 minutes.

[0053] Among them, the 2wt% silicon source (tetraethyl orthosilicate) dispersion was prepared by weighing silicon source (tetraethyl orthosilicate) and deionized water according to the ratio, mixing them, and ultrasonically dispersing for 20 minutes;

[0054] Step 4: Pour the coating liquid into a polytetrafluoroethylene mold, spread it naturally, and then dry it in a ventilated environment at 25°C for 48 hours. Peel off the mold to obtain a water-resistant and biodegradable agricultural film (its production process is as follows). Figures 8-10 (As shown).

[0055] Example 3: Two-step preparation of corn stalk-based polylactic acid resin

[0056] Step 1: Straw pretreatment and saccharification: Crush corn straw through an 80-mesh sieve, place it in a high-pressure steam tank, treat at 121℃ for 45 minutes, cool it, and then soak it in PBS solution (pH 7.2) overnight; adjust the pH of the pretreated straw to 5.5, add cellulase with an activity of 40000 U / g and an appropriate amount of ammonium sulfate (nutrients), enzymatically hydrolyze at 50℃ for 4 hours, and filter to obtain a monosaccharide aqueous solution containing glucose and xylose;

[0057] Step 2: Lactic acid fermentation and purification: Glucose and peptone were added to a monosaccharide aqueous solution to prepare a fermentation broth with a specific gravity of 1.2. 13% Rhizopus oryzae inoculum was inoculated and cultured dynamically for 4 days at 0.8 v / v aeration under an anaerobic environment of 35℃ and pH 7.0. After fermentation, the bacterial cells were removed by centrifugation (3000 r / min, 15 min). The supernatant was purified by anion exchange column and then concentrated by vacuum distillation (80℃, 0.08 MPa) to obtain L-lactic acid with a purity of 99.2%.

[0058] Step 3: Polymerization and Molding: Using the ring-opening polymerization method of lactide, L-lactic acid is heated at 120℃ to dehydrate and prepare lactide; 0.5% SnCl / TSA catalyst is added, and the reaction is stirred at 160℃ and 0.05MPa for 8 hours to allow the lactide to undergo ring-opening polymerization; after the reaction, the catalyst is removed by filtration, the product is dissolved in acetonitrile, and distilled water is added dropwise to precipitate it. The product is washed with water 4 times and dried at 80℃ for 6 hours to obtain polylactic acid resin.

[0059] Example 4: Preparation of humic acid from corn stalks

[0060] Step 1: Corn stalks are treated with high-pressure steam at 121℃ for 30-60 minutes; after cooling, they are soaked in PBS solution with a pH of 7.2 for 20 hours.

[0061] Step 2: The pretreated corn stalks from Step 1 are mixed with 0.75 mol / L sodium hydroxide solution at a mass-to-volume ratio of 1:10, reacted at 200℃ for 5 hours, the pH is adjusted to 1-2 with sulfuric acid, and then allowed to stand for 12 hours. Humic acid is obtained by filtration.

[0062] Performance testing

[0063] The performance of the degradable agricultural film prepared in Example 1 was tested, and the results are as follows: Figures 2-6 As shown, its physical properties are good;

[0064] The performance of the water-resistant and biodegradable agricultural film prepared in Example 2 was tested, and the results were as follows: tensile strength 21.5 MPa, water contact angle 88.3°, swelling rate after 72 hours of water immersion 12.3%, and degradation rate in soil after 8 months 82.5%.

[0065] The polylactic acid resin prepared in Example 3 was tested for performance and purity. The results were as follows: purity 99.2%, number average molecular weight 108,000, tensile strength 61.3 MPa, flexural strength 35.7 MPa, and degradation rate in soil for 12 months 98.9%.

[0066] The humic acid prepared in Example 4 was tested for performance. The results showed that the purity was 91.3% and the fulvic acid content in the humic acid was 35.6%. It can be used directly as organic fertilizer or as a modifier for degradable materials to improve material compatibility.

[0067] The above performance tests show that the various corn stalk-based biodegradable materials prepared by this invention all possess excellent mechanical properties, degradation performance, and exclusive functionality. The comprehensive utilization rate of raw materials reaches 86.2%, which is far higher than that of existing processes. Moreover, the preparation process does not emit any toxic pollutants, and all equipment used is mature industrial equipment, which can realize large-scale production. The comprehensive economic benefits per ton of straw are 5-8 times higher than those of traditional straw utilization methods, combining environmental and economic benefits.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a corn stover based biodegradable material, characterized by: Includes the following steps: Step 1: Straw pretreatment and fiber extraction: After crushing the corn straw through a 100-mesh sieve, steam explosion is performed at 110-120℃ and 1.6-1.9MPa for 5-8 minutes. The straw is then soaked in deionized water at 70-80℃ for 40-60 minutes, oxidized in 10% hydrogen peroxide at 70-80℃ for 1-2 hours, and the pH is adjusted to 8.5-9.0 with a 5% sodium hydroxide aqueous solution. The straw is then heated to 80-85℃ and soaked for 2-3 hours. Finally, it is washed with 50% ethanol until neutral and dried at 105-110℃ for 6-8 hours to obtain corn straw fiber. Step 2: Preparation of coating solution: Starch and deionized water are mixed at a mass ratio of 1:8-1:10 and stirred and gelatinized at a temperature of 90-95℃ and a stirring speed of 800-1000r / min for 25-30min. Then epichlorohydrin is added for modification and the temperature is raised to 35-40℃. The reaction is carried out for 5-6h to obtain modified starch. This modified starch is then mixed with chitosan-acetic acid solution, nano silica, straw fiber and polyvinyl alcohol, and stirred at 80-85℃ for 2-3h to obtain coating solution. Step 3: Functionalization and molding: After the coating liquid is scraped into a film with a thickness of 0.1-0.5mm, it is dried at 60-65℃ for 20-24h. Then, a urea-phosphorus pentoxide-cypermethrin functional liquid is sprayed on and dried at 60-65℃ for 8-12h. After two films with the functional liquid sprayed on them are stacked, they are hot-pressed at 120-140℃ for 8-10min to obtain the degradable agricultural film.

2. The method for preparing a biodegradable material based on corn stalks according to claim 1, characterized in that: The preparation of the chitosan-acetic acid solution in step two is as follows: chitosan is dissolved in a 1% aqueous acetic acid solution, and the mass-volume ratio of chitosan to aqueous acetic acid solution is 1g:80ml-1g:100ml. After the addition is completed, the mixture is stirred at a stirring speed of 600-800r / min for 15-20min to obtain the chitosan-acetic acid solution.

3. The method for preparing a biodegradable material based on corn stalks according to claim 1, characterized in that: The mass-volume ratio of the modified starch, chitosan-acetic acid solution, nano-silica, straw fiber, and polyvinyl alcohol is 5g:40mL:0.3g:2g:1g.

4. The method for preparing a biodegradable material based on corn stalks according to claim 1, characterized in that: The preparation procedure of the urea-phosphorus pentoxide-cypermethrin functional solution is as follows: urea, phosphorus pentoxide, cypermethrin, and deionized water are weighed according to the following mass-volume ratio: 5g: 2g: 0.1g: 100mL. Urea, phosphorus pentoxide, and cypermethrin are added to deionized water and stirred at a stirring speed of 500-600r / min for 15-20min to obtain the urea-phosphorus pentoxide-cypermethrin functional solution.

5. A method for preparing biodegradable materials based on corn stalks, characterized in that: Includes the following steps: Step 1: Remove hemicellulose by treating with a choline chloride-urea system at 80℃ for 2 hours; Step 2: Remove lignin by treating with a choline chloride-lactic acid system at 90℃ for 3 hours; Step 3: The mixed coating solution includes the following substances in parts by mass or volume: 100 parts of nanocellulose dispersion, 10 parts of 8-12wt% polyvinyl alcohol solution, 1.25 parts of 1-3wt% silicon source dispersion, and 20 parts of glycerol. Weigh the above substances according to the ratio and stir for 1.5 hours at 80℃ and 800-1000r / min to form a stable coating solution. Step 4: Pour the coating liquid into a polytetrafluoroethylene mold to a thickness of 0.2-0.6 mm, spread it naturally, and dry it in a ventilated environment at 25℃ for 48 hours. Peel off the mold to obtain a water-resistant and biodegradable agricultural film.

6. The method for preparing a biodegradable material based on corn stalks according to claim 5, characterized in that: The molar ratio of the choline chloride-urea system is 1:2; the molar ratio of the choline chloride-lactic acid system is 1:

3.

7. A method for preparing biodegradable materials based on corn stalks, characterized in that: Includes the following steps: Step 1: Straw pretreatment and saccharification: Corn straw is treated with high-pressure steam at 121℃ for 30-60 min; after cooling, it is soaked in PBS solution with pH 7.2 for 12-24 h, and after adjusting the pH to 5-6, cellulase is added to obtain a monosaccharide aqueous solution; Step 2: Fermentation and purification: Add glucose and peptone to the monosaccharide aqueous solution to prepare a fermentation broth with a specific gravity of 1.15-1.

3. Inoculate with 12-15% Rhizopus oryzae / lactic acid bacteria and anaerobic dynamic culture at 30-40℃ and pH 6.5-7.5 for at least 3 days. After fermentation, centrifuge at 3000 r / min for 15 min. Purify the supernatant by an anion exchange column and distill under reduced pressure at 80℃ and 0.08 MPa for 40-60 min to obtain L-lactic acid with a purity ≥99%. Step 3: Polymerization and molding: L-lactic acid is heated at 120℃ to dehydrate and prepare lactide; 0.5% SnCl / TSA catalyst is added, and the reaction is stirred at 160℃ and 0.05MPa for 8 hours. After the reaction, the catalyst is removed by filtration, the product is dissolved in acetonitrile and then precipitated by adding distilled water. The product is washed with water 4 times and dried at 80℃ for 6 hours to obtain polylactic acid resin.

8. The method for preparing a biodegradable material based on corn stalks according to claim 7, characterized in that: The cellulase activity is at least 40,000 U / g, and the amount of cellulase added is 2-3% of the mass of the pretreated corn stalks. When enzymatically hydrolyzing after adding cellulase, ammonium sulfate or ammonium nitrate needs to be added as nutrients. The amount of nutrients added is 0.5-0.8% of the mass of the pretreated corn stalks. The enzymatic hydrolysis temperature is 50℃, and the enzymatic hydrolysis time is 4h.

9. A method for preparing a biodegradable material based on corn stalks according to claim 7, characterized in that: In step three, L-lactic acid can also be melt-polymerized at 130-135°C for 30 hours to obtain polylactic acid resin.

10. A method for preparing biodegradable materials based on corn stalks, characterized in that: Includes the following steps: Step 1: Treat corn stalks with high-pressure steam at 121℃ for 30-60 minutes; after cooling, soak them in PBS solution with pH 7.2 for 12-24 hours. Step 2: The pretreated corn stalks from Step 1 are mixed with 0.75 mol / L sodium hydroxide solution at a mass-to-volume ratio of 1:10, reacted at 200℃ for 5 hours, the pH is adjusted to 1-2 with sulfuric acid, and then allowed to stand for 12 hours. Humic acid is obtained by filtration.

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