Full-biodegradable mulching film capable of relieving microplastic release harm

Abstract

The invention discloses a full-biodegradable mulching film capable of relieving microplastic release harm. The full-biodegradable mulching film is prepared from the following components in parts by weight: 100 to 150 parts of poly (butylene adipate-co-terephthalate); 0.5 to 1.5 parts of an ultraviolet light absorber; 0.5 to 0.6 part of an antioxidant; 0.5 to 0.6 part of a lubricant; and 2-8 parts of modified charcoal. The method comprises the following steps: pretreating biochar with a KOH solution to obtain pretreated biochar; adding the pretreated biochar into a glacial acetic acid solution of chitosan oligosaccharide, stirring at room temperature, dropwise adding a sodium citrate solution, standing at low temperature, centrifuging, washing, and drying in vacuum to obtain chitosan oligosaccharide grafted biochar; and adding the chitosan oligosaccharide grafted biochar into carbon black, and mixing to obtain the modified biochar. The modified biochar prepared by the method can replace carbon black to prepare a full-biodegradable mulching film with higher strength and water vapor permeability; after the mulching film is degraded, the biochar adsorbs the degraded micro-plastics, so that the damage of the micro-plastics to crops is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable mulch films, and in particular to a fully biodegradable mulch film capable of alleviating the hazards of microplastic release. Background Art

[0002] Agricultural mulch films play an important role in China's agricultural production. They play an important role in improving the quality of crop products, improving the quality, and enriching the supply of agricultural products. The use of mulch films also brings some environmental pollution problems, namely the so-called "white pollution". However, the recycling and reuse of agricultural mulch films has the disadvantages of high cost and difficulty in recycling. Therefore, the production and use of fully biodegradable agricultural films has become a new way to solve white pollution.

[0003] Compared with traditional mulch films, fully biodegradable agricultural films can be completely degraded by microorganisms in the natural environment, avoiding the "white pollution" problem caused by traditional PE mulch films. The main raw materials of this mulch film include degradable resins such as PBAT, PLA, PPC, PHAs, etc., and are blow-molded with environmentally friendly additives. It not only has the functions of traditional mulch films such as moisture retention, warming, and weed control, but also does not need to be recycled after the crops are harvested. It can be directly plowed into the soil and degraded in the soil, which can save the labor and cost required for recycling traditional mulch films and is environmentally friendly.

[0004] However, although fully biodegradable mulch is an environmentally friendly agricultural covering material, there are still some limiting factors. For example, due to its degradation characteristics, fully biodegradable mulch may produce more microplastics in a short period of time, causing environmental pollution. Domestic and foreign studies have shown that microplastics have an impact on the germination rate, root growth, plant height, biomass accumulation, etc. of crops, and this impact is correlated with the concentration, type and size of microplastics. Different types and sizes of microplastics have different responses to different crops at different concentrations. For example, studies have found that microplastics can reduce the plant height and dry weight of rice, and the maximum leaf area of ​​tobacco treated with different concentrations of microplastics is significantly reduced compared with that without microplastics. In addition, medium and low concentrations of microplastics have little effect on the accumulation of fresh biomass aboveground, and high concentrations of microplastics inhibit the accumulation of fresh biomass aboveground. If biochar is added to fully biodegradable mulch, after the fully biodegradable mulch is degraded, the biochar can adsorb microplastics to reduce the damage of microplastics to crops. And biochar is black and can replace carbon black in black fully biodegradable mulch. However, carbon black plays a reinforcing role in fully biodegradable mulch, and carbon black has good compatibility with resin. Although adding biochar to fully biodegradable mulch can increase the water vapor permeability of the mulch, the strength of the mulch will be reduced. Biochar and resin will agglomerate during mixing and processing, and have poor compatibility and are easy to agglomerate, so it is impossible to obtain a fully biodegradable mulch comparable to that with carbon black added. Summary of the invention

[0005] In view of the above-mentioned prior art, the purpose of the present invention is to provide a fully biodegradable mulch film that mitigates the harm of microplastic release. The present invention controls the amount of chitosan oligosaccharide added to graft biochar, and then uses chitosan oligosaccharide to adsorb carbon black to obtain modified biochar, which can replace carbon black to prepare a fully biodegradable mulch film with higher strength and water vapor permeability. After the fully biodegradable mulch film is degraded, the biochar can adsorb the degraded microplastics and the toxic substances they produce, reducing the damage of microplastics to crops.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect of the present invention, a fully biodegradable mulch film for alleviating the hazards of microplastic release is provided. The fully biodegradable mulch film for alleviating the hazards of microplastic release comprises the following raw materials in parts by weight: 100-150 parts of polybutylene terephthalate-adipate; 0.5-1.5 parts of ultraviolet absorber; 0.5-0.6 parts of antioxidant; Lubricant 0.5-0.6 parts; 2~8 parts of modified biochar; The modified biochar is prepared by grafting chitosan oligosaccharide onto biochar and adsorbing carbon black onto chitosan oligosaccharide.

[0007] Preferably, the modified biochar is prepared by the following method: (1) pretreating the biochar with a KOH solution to obtain pretreated biochar; (2) adding the pretreated biochar to a chitosan oligosaccharide glacial acetic acid solution, stirring at room temperature, then adding a sodium citrate solution dropwise, standing at low temperature, centrifuging, washing, and vacuum drying to obtain biochar grafted with chitosan oligosaccharide; (3) Add the biochar grafted with chitosan oligosaccharide into carbon black and mix them evenly to obtain modified biochar.

[0008] Preferably, in step (1), the concentration of the KOH solution is 0.1-0.3 M; the pretreatment is heating, the heating temperature is 30-60° C., and the heating time is 20-40 min.

[0009] Preferably, in step (2), the concentration of chitosan oligosaccharide in the chitosan oligosaccharide glacial acetic acid solution is 0.1-0.5 w / v %; the mass concentration of the glacial acetic acid solution is 0.2%; and the mass ratio of the biochar to chitosan oligosaccharide is 10:1-3.

[0010] Preferably, in step (2), the biochar is coconut shell charcoal; and the particle size of the coconut shell charcoal is 1-5 μm.

[0011] Preferably, in step (2), the concentration of the sodium citrate solution is 0.1 w / v %; when the pH of the reaction system is 5.0, the addition of the sodium citrate solution is stopped.

[0012] Preferably, in step (2), the low-temperature standing temperature is 4° C., and the low-temperature standing time is 6 to 10 hours.

[0013] Preferably, in step (3), the ratio of the biochar grafted with chitosan oligosaccharide to the carbon black is 10:1-3; and the particle size of the carbon black is 15-20 nm.

[0014] Preferably, the antioxidant is at least one of antioxidant 1010 or antioxidant 168; and the lubricant is erucamide.

[0015] The second aspect of the present invention provides the use of a fully biodegradable mulch film in at least one of the following 1 to 3): 1) Alleviate the release of microplastics; 2) Reduce water vapor transmission rate; 3) Improve the mechanical strength of the mulch film Beneficial effects of the present invention: (1) The present invention controls the amount of chitosan oligosaccharide added to graft biochar, and then uses chitosan oligosaccharide to adsorb carbon black to obtain modified biochar, which can replace carbon black to prepare a fully biodegradable mulch with high strength and low water vapor permeability. After the fully biodegradable mulch is degraded, the biochar can adsorb the degraded microplastics and reduce the damage of microplastics to crops.

[0016] (2) The present invention connects biochar and carbon black, both of which have negative charges, through chitosan oligosaccharide and uses them for fully biodegradable mulch, which not only improves the mechanical properties of the mulch but also has a high water vapor permeability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Tensile load diagram of the mulch prepared in Example 2 or Comparative Examples 1 to 3; Figure 2 : Transverse elongation at break of the mulch prepared in Example 2 or Comparative Examples 1 to 3; Figure 3 : The longitudinal elongation at break of the mulch prepared in Example 2 or Comparative Examples 1 to 3; Figure 4 : Water vapor permeability diagram of the mulch films prepared in Example 2 or Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0018] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0019] As introduced in the background technology section, there have been reports on the use of biochar in degradable mulch films to increase water vapor permeability. However, biochar such as coconut shell charcoal is difficult to add directly to resin to form a film, which not only causes problems such as agglomeration, but also affects the film-forming properties.

[0020] Based on this, the purpose of the present invention is to provide a fully biodegradable mulch film that alleviates the hazards of microplastic release. The present invention controls the amount of chitosan oligosaccharide added so that the chitosan oligosaccharide is partially coated on the biochar, achieving the same effect as grafting, thereby obtaining chitosan oligosaccharide grafted biochar. Then, by utilizing the properties of chitosan oligosaccharide being positively charged and carbon black being negatively charged, the chitosan oligosaccharide grafted biochar adsorbs the carbon black so that the carbon black is distributed outside the biochar. The chitosan oligosaccharide on the surface of the biochar does not need to be grafted evenly, as long as the biochar is not completely coated. After research, it was found that by controlling the amount of chitosan oligosaccharide added, the chitosan oligosaccharide cannot form a full coating, but will be partially coated on the biochar, which has little effect on the air permeability of the biochar. Compared with chitosan, the molecular weight of chitosan oligosaccharide is much smaller, and it is more suitable for grafting with biochar. At the same time, since the particle size of carbon black is smaller than that of biochar, in order to avoid carbon black being adsorbed into the porous structure of biochar and affecting the air permeability of biochar, the amount of chitosan oligosaccharide adsorbed carbon black is calculated, and the mixing time of carbon black and chitosan oligosaccharide grafted biochar is reduced. The modified biochar obtained by the present invention can replace carbon black to prepare a fully biodegradable mulch with higher strength and water vapor permeability. After the fully biodegradable mulch is degraded, the biochar can adsorb the degraded microplastics and reduce the damage of microplastics to crops.

[0021] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0022] Note: The biochar used in the present invention was purchased from Wanglin Biology, model specification is WL-WCB02; Chitosan oligosaccharide was purchased from Wuhan Haishan Technology Co., Ltd., 3000 molecular weight chitosan oligosaccharide; PBAT was purchased from Xinjiang Blue Mountain Tunhe Polyester Co., Ltd., model specification TH801T; The ultraviolet absorber was purchased from Wenfeng Plastic Chemical Factory, model specification is uv-531; Carbon black was purchased from Guangdong Hongke Chemical Raw Materials Co., Ltd., and the model specification was Cabot M800.

[0023] The test materials used in the examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels.

[0024] Example 1: Preparation of modified biochar 10g of biochar was added to a 0.1M KOH solution and heated at 50℃ for 30min to obtain pretreated biochar. 10g of pretreated biochar was added to 1L of 0.2 w / v% chitosan oligosaccharide glacial acetic acid solution (0.2wt%), stirred at room temperature for 1h, and then sodium citrate solution was added dropwise until the pH of the system was 5.0, and continued to stir for 4h, and then allowed to react at 4℃ for 8h. After the reaction was completed, centrifugation was performed to obtain a precipitate, which was washed with deionized water until the eluate was neutral, and vacuum dried at 60℃ to obtain biochar grafted with chitosan oligosaccharide. 10g of biochar grafted with chitosan oligosaccharide was added to 2g of carbon black, and tumbled for 20s to allow the grafted chitosan oligosaccharide biochar to adsorb carbon black. Since the particle size of carbon black and biochar is small, carbon black and biochar cannot be distinguished by naked eyes after mixing, so the mixture is used as modified biochar.

[0025] Example 2: Preparation of fully biodegradable mulch film (1) Antioxidant 1010 and antioxidant 168 were mixed at a weight ratio of 1.8:1 to obtain an antioxidant.

[0026] (2) 120 kg of dried polybutylene terephthalate (PBAT) particles, 1 kg of ultraviolet absorber, 0.5 kg of antioxidant prepared in step (1), 0.5 kg of erucamide and 5 kg of modified biochar prepared according to the method of Example 1 were mixed evenly.

[0027] (3) The blended material is granulated using a twin-screw extruder (extrusion temperature 80-175°C), and the granules are vacuum dried at 60°C for 24 hours to obtain precursor granules of a fully biodegradable mulch film.

[0028] (4) The dried precursor particles are blown into films using a film blowing machine to obtain a fully biodegradable mulch film (thickness 0.014-0.018 mm).

[0029] Comparative Example 1 The difference from Example 2 is that the modified biochar is replaced with an equal amount of carbon black, and finally a fully biodegradable mulch film is prepared.

[0030] Comparative Example 2 The difference from Example 2 is that the modified biochar is replaced with an equal amount of biochar + carbon black, and the mass ratio of biochar to carbon black is 10:2. Finally, a fully biodegradable mulch film is prepared.

[0031] Comparative Example 3 The difference from Example 2 is that the concentration of chitosan oligosaccharide in the modified biochar prepared in Example 1 is 1.0%. Finally, a fully biodegradable mulch film is prepared.

[0032] Test Example 1 According to the provisions of GB / T 10401 and GB / T 10403, a 2-type sample with a width of 10 mm, an initial distance between the clamps of 50 mm, and a test speed of (500+50) mm / min is used until the sample breaks. The maximum tensile load is measured with an accuracy of 0.01 N, and the strain is calculated. The mechanical properties of the mulch prepared in Example 2 or Comparative Examples 1 to 3 are tested, and the water vapor permeability of the mulch prepared in Example 2 or Comparative Examples 1 to 3 is tested in accordance with GB / T 1037-2021 "Cup Weight Gain and Weight Loss Method for Determination of Water Vapor Permeability of Plastic Films and Sheets". The results are shown in Figures 1 to 4 .

[0033] according to Figures 1 to 4 It can be seen that the mechanical properties of the mulch prepared in Example 2 are close to those of the mulch in Comparative Example 1, but the water vapor permeability is higher than that of the mulch in Comparative Example 1. The mechanical properties of the mulch prepared in Example 2 are similar to those of Comparative Example 3, but the air permeability is higher than that of Comparative Example 3, indicating that the amount of chitosan oligosaccharide is increased, so that the biochar is completely coated and cannot be breathable. The mechanical properties of the mulch prepared in Example 2 are higher than those of Comparative Example 2. This is because the biochar in Comparative Example 2 is not modified, is easy to agglomerate, and is unevenly distributed in the plastic, resulting in a decrease in mechanical properties. This shows that by using the method of the present invention to graft carbon black onto the outside of biochar using chitosan oligosaccharide, the mechanical properties of the mulch will not decrease too much compared to using carbon black alone, and the water vapor permeability is higher than that of using carbon black alone. Compared with the mixture of carbon black and biochar, the mechanical properties are improved, indicating that the direct addition of biochar causes poor compatibility between biochar and resin, thereby reducing the mechanical properties.

[0034] Test Example 2 The potted experiment was carried out in the greenhouse of the School of Environment and Resources of Southwest University of Science and Technology. The test was divided into 6 groups: the mulch prepared in Example 2 and Comparative Examples 1 to 3 were crushed into 2.5mm-5mm mulch-source microplastics, added to the sand at 5g / kg and mixed evenly, recorded as Example 2 Group and Comparative Examples 1 to 3 Group; the transparent mulch prepared with pure PBAT was added to the sand according to the above method, recorded as the PBAT control group. The prepared mixture of sand and microplastics was left to stand at room temperature for two months to further degrade the microplastics. When the pepper grows the fifth leaf, select pepper seedlings with similar growth and transplant them into microplastic-contaminated soil. Ten parallels are set in each group, and a blank control group (no microplastic pollution) is set.

[0035] The flower pots were randomly placed and their positions were randomly changed every day. During the plant growth period, the plants were watered every day to maintain the soil moisture content at 60%, and the same weight (1g) of NPK compound fertilizer was applied once a month. The experiment was stopped 90 days after transplanting (June-September), and the pepper plants and soil samples were sampled and analyzed. There were 10 plants in each group. When sampling, fully mature leaves were taken from the top, the veins were removed, and the leaves were crushed with liquid nitrogen and mixed. Three replicates were set.

[0036] After the potted experiment, the roots of peppers were completely removed, and microplastics and soil near the roots were collected. The microplastics and soil attached to the surface of the plants were washed with tap water, and then rinsed with distilled water. Finally, the surface of the plants was wiped dry with absorbent paper, and the roots, stems, leaves, and fruits were measured separately. The plant height and root length of peppers were measured with a ruler (accurate to 0.1 cm); the fresh weight of roots, stems, leaves, and fruits was weighed with a balance (accurate to 0.000 1 g), and some of the leaves were placed in a 70-80℃ oven for drying until constant weight was reached. The remaining samples were frozen with liquid nitrogen and placed in a -80℃ refrigerator for later use. The chlorophyll content of fresh samples was measured using a chlorophyll meter (TYS-A), and the malondialdehyde (MDA) content was determined using the thiobarbituric acid colorimetric method.

[0037] Table 1 Crop growth indicators Since sandy soil is poor in nutrients, especially in organic matter, excessive fertilization will cause "seedling burn"; the mulch films prepared in Example 2 and Comparative Examples 1 to 3 contain carbon sources, especially chitosan oligosaccharides, which also contain N sources. Therefore, although the Example 2 combined with Comparative Examples 1 to 3 groups were harmed by mulch film-derived microplastics, the crop growth indicators were still higher than those of the blank control group.

[0038] As shown in Table 1, it can be seen that compared with the blank control group, the PBAT control group does not contain carbon sources such as biochar or carbon black, and the crop growth index of the PBAT control group is lower than that of the blank control, indicating that microplastics harm crop growth. The Example 2 group is higher than the Comparative Examples 1 to 3 groups in terms of root length, plant height, number of leaves, number of fruits, and chlorophyll content. Although the carbon black added to the Comparative Example 1 group is also a carbon source, its role as a carbon source is lower than that of biochar, so Comparative Example 1 is only slightly higher than the PBAT control group, but lower than the blank control group. Although Comparative Example 3 contains more chitosan oligosaccharide crop carbon sources and nitrogen sources, the biochar of Comparative Example 3 is coated with chitosan oligosaccharides and cannot absorb microplastics in time. The improvement of crop growth indicators by nitrogen sources and carbon sources is partially offset by the harm caused by microplastics. It shows that the fully biodegradable mulch prepared by the present invention is less harmful to plants after degradation in a sandy environment, and may even improve crop development and increase crop yields.

[0039] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A fully biodegradable mulch film for alleviating the hazards of microplastic release, characterized in that: The fully biodegradable mulch film for alleviating the hazards of microplastic release comprises the following raw materials in parts by weight: 100-150 parts of polybutylene terephthalate-adipate; 0.5-1.5 parts of ultraviolet absorber; 0.5-0.6 parts of antioxidant; Lubricant 0.5-0.6 parts; 2~8 parts of modified biochar; The modified biochar is prepared by grafting chitosan oligosaccharide onto biochar and adsorbing carbon black onto chitosan oligosaccharide.

2. The fully biodegradable mulch film according to claim 1, characterized in that: The modified biochar is prepared by the following method: (1) pretreating the biochar with a KOH solution to obtain pretreated biochar; (2) adding the pretreated biochar to a chitosan oligosaccharide glacial acetic acid solution, stirring at room temperature, then adding a sodium citrate solution dropwise, standing at low temperature, centrifuging, washing, and vacuum drying to obtain biochar grafted with chitosan oligosaccharide; (3) Add the biochar grafted with chitosan oligosaccharide into carbon black and mix them to obtain modified biochar.

3. The fully biodegradable mulch film according to claim 2, characterized in that: In step (1), the concentration of the KOH solution is 0.1-0.3 M; the pretreatment is heating, the heating temperature is 30-60° C., and the heating time is 20-40 min.

4. The fully biodegradable mulch film according to claim 2, characterized in that: In step (2), the concentration of chitosan oligosaccharide in the chitosan oligosaccharide glacial acetic acid solution is 0.1-0.5 w / v%; the mass concentration of the glacial acetic acid solution is 0.2%; the mass ratio of the biochar to chitosan oligosaccharide is 10:1-3; the biochar is coconut shell charcoal; and the particle size of the coconut shell charcoal is 1-5 μm.

5. The fully biodegradable mulch film according to claim 2, characterized in that: In step (2), the concentration of the sodium citrate solution is 0.1 w / v %; when the pH of the reaction system is 5.0, the addition of the sodium citrate solution is stopped.

6. The fully biodegradable ground film according to claim 2, characterized in that: In step (2), the low-temperature standing temperature is 4° C., and the low-temperature standing time is 6 to 10 hours.

7. The fully biodegradable mulch film according to claim 2, characterized in that: In step (3), the ratio of the biochar grafted with chitosan oligosaccharide to the carbon black is 10:1-3; the particle size of the carbon black is 15-20 nm.

8. The fully biodegradable mulch film according to claim 2, characterized in that: In step (3), the mixing is tumbling mixing, and the tumbling time is 10 to 30 seconds.

9. The fully biodegradable mulch film according to claim 1, characterized in that: The antioxidant is at least one of antioxidant 1010 and antioxidant 168; the lubricant is erucamide.

10. Use of the fully biodegradable mulch film according to any one of claims 1 to 9 in at least one of the following 1 to 3): 1) Alleviate the release of microplastics; 2) Reduce water vapor transmission rate; 3) Improve the mechanical strength of the ground film.

Images