Corn straw nanocellulose reinforced water-resistant fully-degradable mulching film and preparation method thereof

Abstract

The invention discloses a corn straw nanocellulose reinforced water-resistant fully-degradable mulching film and a preparation method thereof, and belongs to the technical field of agricultural mulching films. The method comprises the following steps: performing two-step DES treatment on corn straws to obtain a nano-cellulose dispersion liquid; a PVA solution with the concentration of 8-12 wt% is prepared; 1-3 wt% of an ultrasonic dispersion silicon source dispersion liquid is prepared; the preparation method comprises the following steps: adding 10 parts of PVA solution, 1.25 parts of silicon source dispersion liquid and 20 parts of glycerol into 100 parts of nanocellulose dispersion liquid to obtain film coating liquid, carrying out curtain coating in a polytetrafluoroethylene mold, and naturally drying to form the film. PVA has good film-forming property but poorer water resistance, and nano cellulose and nano silicon dioxide can be used as green modifiers to be blended with PVA and self-assembled to form a hydrogen bond cross-linking system, so that a'rigid cellulose and silicon dioxide network-flexible PVA matrix 'enhanced structure is formed. Meanwhile, forestry and agricultural residues (corn straw) are adopted as raw materials, nanocellulose is prepared through a two-step deep eutectic solvent (DES), and the problem of high pollution caused by traditional strong acid / strong alkali treatment is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural mulch films, and particularly relates to a water-resistant fully degradable mulch film reinforced with corn straw nanocellulose and a preparation method thereof. Background Art

[0002] (1) Problem of traditional mulch film pollution: The white pollution has been difficult to cure for a long time, with double bottlenecks in ecology and promotion

[0003] More than 90% of the mulch film market in China is polyethylene (PE) mulch film. Its chemical properties are stable and the natural degradation period is up to hundreds of years, resulting in a cumulative residue of more than 1 million tons in the national farmland and triggering multiple ecological crises: The residual mulch film reduces the soil porosity by 15%, hinders the penetration of water and fertilizer and the root development, causing a 5%-8% reduction in crop yield. In the arid areas of the northwest, the wind erosion of sandy soil increases by 30% due to the damage of mulch film, aggravating the risk of land desertification; At the same time, the proportion of microplastics with a particle size <5mm in the broken mulch film exceeds 60%. These microplastics enter the water body and food chain with runoff. Research shows that the concentration of microplastics in the water body around the farmland covered with mulch film is 2.17 times higher than that in the area without mulch film ([1] Xue Yinghao. Research on the characteristics of farmland residual film pollution in China and the toxic effects of polyethylene microplastics on aquatic animals [D]. Shenyang Agricultural University, 2023. DOI: 10.27327 / d.cnki.gshnu.2023.000010.), posing a long-term threat to ecological security and food safety.

[0004] Although the degradable mulch film represented by polylactic acid (PLA) solves the residue problem, its cost is as high as 25,000 yuan / ton (2-3 times that of PE mulch film), and its mechanical properties are weak (tensile strength <10 MPa), and the field breakage rate is 40% higher than that of PE mulch film, resulting in a market share of less than 10%, forming a contradiction of "the old pollution has not been removed, and the new film is difficult to promote".

[0005] (2) Bottleneck in base film modification: Double constraints of toxicity risk and performance shortcoming

[0006] Although degradable materials represented by polyvinyl alcohol (PVA) have biocompatibility, there are key defects in their modification technologies: traditional modification relies on chemical crosslinking agents such as epichlorohydrin and glutaraldehyde, which pose food safety risks and violate the requirements of green agricultural development; when blending and modifying with natural materials such as starch, the contradiction of "it is difficult to have both water resistance and strength" is faced - the tensile strength of starch-based PVA films is mostly lower than 10 MPa (less than 50% of PE mulch films) (DOI: 10.1007 / s12649-017-0051-6), and it cannot meet the durability requirements under complex working conditions such as field mechanical operations and straw friction. Although nanocellulose as a modifier has good effects, there are still problems of poor water resistance, and a large amount of acid and alkali reagents are required in the preparation process of today's mainstream nanocellulose. Not only is the energy consumption high (producing 1 ton of nanocellulose requires 20 - 30 kWh of electric energy), but also strong acidic wastewater (pH < 2) is generated, and about 5 - 8 tons of pollutants are discharged per ton of nanocellulose produced, which runs counter to the "green" development goal of mulch films. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems that traditional PE mulch films are difficult to degrade, degradable mulch films have low strength, and when using PVA as the base film, it has poor water resistance and the modification method is not green, and to provide a water-resistant fully degradable mulch film strengthened by corn straw nanocellulose and its preparation method.

[0008] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0009] A preparation method of a water-resistant fully degradable mulch film strengthened by corn straw nanocellulose, and the method is as follows:

[0010] Step 1: Pretreat corn straw to remove dust and impurities, dry it, and crush it to 40 mesh; the purpose of pretreatment is to remove moisture, wash it clean, and prevent dust and impurities;

[0011] Step 2: Prepare DES-1 and DES-2 solutions;

[0012] Step 3: Add the pretreated corn straw to the DES-1 solution at a solid-liquid ratio of 1 g:10 mL, perform microwave treatment, filter and retain the solid phase to obtain filter cake 1;

[0013] Step 4: Take filter cake 1 from Step 3 and add it to the DES-2 solution at a solid-liquid ratio of 1 g:10 mL, perform microwave treatment, and filter to obtain filter cake 2;

[0014] Step 5: Take filter cake 2 and ultrasonically disperse it in water at a concentration of 0.1 - 1 wt% to obtain a nanocellulose dispersion;

[0015] Step 6: Prepare a PVA solution with a concentration of 8 - 12 wt%;

[0016] Step 7: Prepare a silicon source dispersion solution dispersed by ultrasound at 1-3 wt%.

[0017] Step 8: Add 10 parts of the solution from Step 6, 1.25 parts of the solution from Step 7, and 20 parts of glycerol to 100 parts of the solution from Step 5. Then obtain a coating solution under certain conditions, and then cast it in a polytetrafluoroethylene mold and dry it naturally to form a film.

[0018] Further, in Step 2, the DES-1 solution is composed of Component 1 and Component 2; Component 1 is choline chloride, and Component 2 is one of glycerol, urea, or ethylene glycol, and the molar ratio of Component 1 to Component 2 is 1:2; the DES-2 solution is composed of Component 3 and Component 4; Component 3 is choline chloride, and Component 4 is one of citric acid, lactic acid, oxalic acid, or acetic acid, and the molar ratio of Component 3 to Component 4 is 1:2.

[0019] Further, in Step 3, the temperature of the microwave treatment is 80°C and the time is 1 h.

[0020] Further, in Step 4, the temperature of the microwave treatment is 80°C and the time is 45 min.

[0021] Further, in Step 5, the specific conditions of ultrasound are 800 W ultrasound for 0.5 h.

[0022] Further, in Step 7, the silicon source is one or more of nano-silica, calcium silicate, or tetraethyl orthosilicate.

[0023] Further, in Step 8, the specific conditions under certain conditions are a water bath at 80°C for 4 h or a microwave water bath at 80°C for 45 min.

[0024] A water-resistant fully biodegradable mulch film reinforced with corn straw nanocellulose prepared by the above method.

[0025] The beneficial effects of the present invention compared with the prior art are as follows:

[0026] (1) PVA has good film-forming properties but poor water resistance. Nanocellulose and nano-silica can be used as green modifiers to be blended with PVA, self-assembled to form a hydrogen bond cross-linking system, and form a "rigid cellulose, silica network - flexible PVA matrix" enhanced structure. At the same time, agricultural and forestry waste (corn straw) is used as a raw material to prepare nanocellulose through two-step deep eutectic solvents (DES), avoiding the high pollution problems brought by traditional strong acid / strong base treatment.

[0027] (2) The tensile strength of the present invention reaches 31.68 MPa, which is 26% higher than that of pure PVA. At the same time, there is no damage after soaking in water for 30 days. The morphology remains intact. And the process is simple, and a coating solution can be obtained only by one-step microwave hydrothermal treatment. Description of the Drawings

[0028] Figure 1 It is a microscopic schematic diagram of the fully degradable mulch film of the present invention.

[0029] Figure 2 It is a product diagram of the fully degradable mulch film of the present invention.

[0030] Figure 3 It is the initial diagram of the water resistance test.

[0031] Figure 4 It is a schematic diagram of the water resistance test for 15 days.

[0032] Figure 5 It is a schematic diagram of the water resistance test for 30 days. Specific implementation mode

[0033] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0034] Example 1:

[0035] A preparation method of a water-resistant fully degradable mulch film reinforced with corn straw nanocellulose, and the method is as follows:

[0036] Step 1: Pretreat the corn straw, dry it, and crush it to 40 meshes; the purpose of the pretreatment is to remove moisture, wash it clean, and prevent dust and impurities;

[0037] Step 2: Prepare DES-1 and DES-2 solutions; the DES-1 solution is composed of component 1 and component 2; component 1 is choline chloride, and component 2 is one of glycerol, urea or ethylene glycol, and the molar ratio of component 1 to component 2 is 1:2; the DES-2 solution is composed of component 3 and component 4; component 3 is choline chloride, and component 4 is one of citric acid, lactic acid, oxalic acid or acetic acid, and the molar ratio of component 3 to component 4 is 1:2;

[0038] Step 3: Add the pretreated corn straw to the DES-1 solution at a solid-liquid ratio of 1 g: 10 mL, then perform microwave treatment at 80 °C for 1 h, filter to retain the solid phase, and obtain filter cake 1;

[0039] Step 4: Take the filter cake 1 in step 3, add it to the DES-2 solution at a solid-liquid ratio of 1 g: 10 mL, perform microwave treatment at 80 °C for 45 min, and then filter to obtain filter cake 2;

[0040] Step 5: Disperse filter cake 2 in water at a concentration of 0.5 wt%, and perform ultrasonic treatment at 800 W for 0.5 h to obtain a nanocellulose dispersion;

[0041] Step 6: Prepare a 10 wt% PVA solution;

[0042] Step 7: Prepare a 2 wt% ultrasonically dispersed nano-silica dispersion;

[0043] Step 8: Add 10 parts of the solution from Step 6, 1.25 parts of the solution from Step 7, and 20 parts of glycerol to 100 parts of the solution from Step 5. Then, obtain a coating solution under certain conditions (80 °C water bath for 4 h or 80 °C microwave water bath for 45 min). Subsequently, cast it in a polytetrafluoroethylene mold and form a film after natural drying, as Figure 1 and 2 shown.

[0044] The tensile strength of the present invention reaches 31.68 MPa, which is 26% higher than that of pure PVA. Figure 3 、 4 Figures 5 are the test diagrams for water resistance for 0, 15, and 30 days respectively. No dissolution or breakage occurred during the 30-day test, and the morphology remained intact. Moreover, the process is simple, and a coating solution can be obtained only by one-step microwave hydrothermal treatment.

Claims

1. A preparation method of a water-resistant fully biodegradable mulch film reinforced with corn straw nanocellulose, characterized in that: The method is as follows: Step 1: The corn straw is pretreated to remove dust and impurities, dried, and pulverized; Step 2: Prepare DES-1 and DES-2 solutions; Step 3: Add the pretreated corn straw to the DES-1 solution at a solid-liquid ratio of 1 g: 10 mL, perform microwave treatment, filter to retain the solid phase, and obtain Filter Cake 1; Step 4: Take Filter Cake 1 from Step 3 and add it to the DES-2 solution at a solid-liquid ratio of 1 g: 10 mL, perform microwave treatment, and filter to obtain Filter Cake 2; Step 5: Take Filter Cake 2 and ultrasonically disperse it in water at a concentration of 0.1-1 wt% to obtain a nanocellulose dispersion; Step 6: Prepare a PVA solution with a concentration of 8-12 wt%; Step 7: Prepare a silicon source dispersion solution ultrasonically dispersed at a concentration of 1-3 wt%; Step 8: Add 10 parts of the solution in Step 6, 1.25 parts of the solution in Step 7, and 20 parts of glycerol to 100 parts of the solution in Step 5. Subsequently, obtain a coating solution under certain conditions, and then cast it in a polytetrafluoroethylene mold and dry naturally to form a film.

2. The preparation method of a water-resistant fully biodegradable mulching film reinforced with corn straw nanocellulose according to claim 1, characterized in that: In Step 2, the DES-1 solution is composed of Component 1 and Component 2; Component 1 is choline chloride, Component 2 is one of glycerol, urea, or ethylene glycol, and the molar ratio of Component 1 to Component 2 is 1:2; the DES-2 solution is composed of Component 3 and Component 4; Component 3 is choline chloride, Component 4 is one of citric acid, lactic acid, oxalic acid, or acetic acid, and the molar ratio of Component 3 to Component 4 is 1:

2.

3. The preparation method of a water-resistant fully biodegradable mulch film reinforced with corn straw nanocellulose according to claim 1, characterized in that: In Step 3, the temperature of the microwave treatment is 80 °C and the time is 1 h.

4. The preparation method of a water-resistant fully biodegradable mulching film reinforced with corn straw nanocellulose according to claim 1, characterized in that: In Step 4, the temperature of the microwave treatment is 80 °C and the time is 45 min.

5. The preparation method of a water-resistant fully biodegradable mulch film reinforced with corn straw nanocellulose according to claim 1, characterized in that: In Step 5, the specific conditions of ultrasonic treatment are 800 W ultrasonic for 0.5 h.

6. The preparation method of a water-resistant fully biodegradable mulch film reinforced with corn straw nanocellulose according to claim 1, characterized in that: In Step 7, the silicon source is one or more of nano-silica, calcium silicate, or tetraethyl orthosilicate.

7. The preparation method of a water-resistant fully biodegradable mulching film reinforced with corn straw nano-cellulose according to claim 1, characterized in that: In Step 8, the specific conditions under certain conditions are a water bath at 80 °C for 4 h or a microwave water bath at 80 °C for 45 min.

8. A water-resistant fully biodegradable mulch film reinforced with corn straw nanocellulose prepared by the method according to any one of claims 1 to 7.

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