Polylactic acid degradable agricultural mulching film with antibacterial function

Abstract

The utility model belongs to the field of agricultural mulching films, and provides a polylactic acid degradable agricultural mulching film with an antibacterial function mainly aiming at the problem of threat of soil pathogenic microorganisms to crop health at present, which comprises a polylactic acid support layer, the mulching film is characterized in that the mulching film further comprises an antibacterial functional layer stacked on the polylactic acid supporting layer, the antibacterial functional layer comprises a structural body formed by compounding cellulose nanofibers and chitosan, the diameter of the cellulose nanofibers is 10-60 nm, and the length-diameter ratio of the cellulose nanofibers is 50-200; the cellulose nanofibers form a continuous three-dimensional network in the antibacterial functional layer, and a uniform and compact chitosan layer is tightly attached in the three-dimensional network. Due to the existence of the antibacterial functional layer with the specific composite layer structure, the mulching film can effectively restrain growth and reproduction of crop pathogenic bacteria, root diseases are reduced, and the mulching film can be used as an agricultural mulching film in agricultural production.

Description

Technical Field

[0001] This utility model relates to the field of agricultural mulch film, and in particular to a polylactic acid biodegradable agricultural mulch film with antibacterial function. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable thermoplastic polymer formed by the polymerization of a large number of lactic acid monomers. Lactic acid is produced through fermentation, typically by extracting glucose from plant sources (such as corn) and then fermenting it through microorganisms. PLA has many advantages, including biodegradability, renewability, high transparency, light weight, and high strength and hardness. It can be processed into various shapes and applications using thermoplastic methods, such as food packaging, medical supplies, disposable tableware, and agricultural mulch films. Meanwhile, PLA's excellent shapeability, heat insulation and moisture retention capabilities, good air permeability, and light transmittance provide it with enormous potential for development in agricultural film applications.

[0003] Soil, as the foundation for crop growth, is not only a medium providing nutrients and water but also a complex ecosystem. A delicate balance exists among the microbial communities in the soil, but when this balance is disrupted, pathogenic microorganisms can threaten crop growth. Pathogenic microorganisms mainly include fungi, bacteria, viruses, and nematodes, which survive and reproduce in the soil in different ways. Some pathogenic microorganisms can directly contact the crop root system through soil moisture and soil particles. They can invade the plant roots, causing infection and triggering various root diseases such as root rot, damping-off, and wilt. These diseases not only affect the healthy growth of plants, reducing crop yield and quality, but can even lead to crop death in severe cases. Pathogenic microorganisms spread through various routes, including soil, water, seeds, farm tools, and insects. Under suitable environmental conditions, such as when temperature, humidity, soil pH, and nutrient conditions meet the needs of pathogens, they will rapidly multiply and exacerbate the development of diseases.

[0004] In summary, the threat posed by soil pathogens to crop health is a pressing issue in agriculture. Modifying the structure of polylactic acid (PLA) biodegradable agricultural mulch to provide antibacterial properties is a novel approach. After careful research, the inventors of this invention discovered that improving the structure of PLA mulch through a composite chitosan membrane layer can transform it into an antibacterial mulch, inhibiting the growth and reproduction of crop pathogens and reducing root diseases. Utility Model Content

[0005] This invention addresses the threat posed by soil pathogens to crop health by providing a polylactic acid composite biodegradable agricultural mulch film with antibacterial properties. This film not only reduces the spread of pathogens, extends the lifespan of the mulch film, and improves the crop growth environment, but also reduces pesticide use and increases agricultural production efficiency. It is of great significance for achieving sustainable and environmentally friendly agricultural production.

[0006] To solve the above-mentioned technical problems, the solution adopted by this utility model is: to provide a polylactic acid biodegradable agricultural mulch film with antibacterial function, the mulch film including a polylactic acid support layer (1), characterized in that: the mulch film also includes an antibacterial functional layer (2) stacked on the polylactic acid support layer (1), the antibacterial functional layer (2) includes a structure composed of cellulose nanofibers and chitosan composite, the diameter of the cellulose nanofibers is 10~60 nm and the aspect ratio is 50~200, the cellulose nanofibers form a continuous three-dimensional network in the antibacterial functional layer (2), and a uniform and dense chitosan layer is tightly attached in the three-dimensional network.

[0007] The polylactic acid support layer 1 is composed of a single polylactic acid film, and the antibacterial functional layer 2 is a structure composed of cellulose nanofibers and chitosan in a certain proportion. In the mulch film of this invention, the cellulose nanofibers exhibit a high aspect ratio and form a continuous three-dimensional network, while the dissolved chitosan molecules are tightly attached to the fiber network to form a uniform and dense layered structure, enabling the polylactic acid biodegradable agricultural mulch film of this invention to obtain good antibacterial function.

[0008] Preferably, the polylactic acid has a weight-average molecular weight of 11,000-12,000 Da, a melt index of 10-12 g / 10min, a melting point of 160-175℃, a glass transition temperature of 55-60℃, and a relative viscosity of 1.6-2.0.

[0009] Preferably, the chitosan has a molecular weight of 100-200 kDa and is added at a rate of 3%-8% of the total mass fraction of the composite film.

[0010] Preferably, the cellulose nanofibers described above have a diameter of 10-60 nm, an aspect ratio of 50-200, and a crystallinity of 80-95%.

[0011] Preferably, the thickness of the polylactic acid support layer is 15-20 μm, and the thickness of the antibacterial functional layer is 5-10 μm.

[0012] Preferably, the polylactic acid support layer and the antibacterial functional layer are prepared by a layer-by-layer assembly process, and then hot-pressed at 60-65°C.

[0013] Preferably, the lactic acid support layer 1 and the antibacterial functional layer 2 can be directly laminated together using a hot-pressing process. For example, in this case, there may be no adhesive layer between them, which helps to reduce environmental pollution caused by the volatilization of adhesive components.

[0014] The beneficial effects of this invention are as follows: Compared to ordinary polylactic acid agricultural mulch films on the market, this invention possesses superior biodegradability, heat retention and moisture retention, processability, and flexibility, while also exhibiting excellent antibacterial properties. Chitosan molecules carry a positive charge on their surface, which allows them to electrostatically attract the negative charge on bacterial cell walls, thereby altering the permeability of the bacterial cell walls, leading to leakage of intracellular substances and inhibiting bacterial growth. Secondly, chitosan can interact with phospholipid molecules on bacterial cell membranes, disrupting cell membrane integrity and causing leakage of intracellular substances, thus inhibiting bacterial growth. Furthermore, chitosan can interact with some key enzymes within bacteria, such as proteases and lipases, thereby affecting bacterial metabolic processes and inhibiting bacterial growth. In addition, chitosan interacts with bacterial DNA, RNA, and other nucleic acid molecules, affecting gene expression and transcription processes, thereby inhibiting bacterial growth. In summary, this antibacterial polylactic acid biodegradable composite mulch film effectively ensures visible light transmittance and excellent mechanical properties while effectively inhibiting the growth and reproduction of crop pathogens and reducing the occurrence of root diseases. This promotes crop growth and development, increases crop yield and quality, and significantly improves agricultural production efficiency. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the cross-sectional structure of a polylactic acid biodegradable agricultural mulch film with antibacterial function, where 1 is the polylactic acid support layer; and 2 is the antibacterial functional layer.

[0016] Figure 2 These are scanning electron microscope (SEM) images of the composite agricultural mulch film according to this invention. As can be seen from the images, chitosan molecules are uniformly dispersed throughout the mulch film matrix. SEM images of the samples were obtained using a GeminiSEM 500 Schottky field emission scanning electron microscope at an accelerating voltage of 3 kV. All samples were sputtered with platinum at a current of 30 mA for 60 s.

[0017] Figure 3 Digital photographs of the antibacterial test of the agricultural mulch film of the present invention and the control mulch film are shown, wherein Figure A is the polylactic acid antibacterial composite agricultural mulch film according to the present invention, and Figure B is a commercially available pure polylactic acid mulch film as a control. Detailed Implementation Plan

[0018] To provide a more detailed and intuitive understanding of this utility model, the following description, in conjunction with the accompanying drawings and specific embodiments, further illustrates the utility model. It should be emphasized that the following description only illustrates preferred embodiments of the utility model and is not intended to limit the utility model. Any simple modifications to the utility model fall within the protection scope of this utility model.

[0019] like Figure 1 As shown, a polylactic acid (PLA) biodegradable agricultural mulch film with antibacterial function includes a PLA support layer 1 and an antibacterial functional layer 2. The PLA support layer 1 is composed of a single PLA film. The PLA has a weight-average molecular weight of 11,000-12,000 Da, a melt index of 10-12 g / 10 min, a melting point of 160-175℃, a glass transition temperature of 55-60℃, and a relative viscosity of 1.6-2.0.

[0020] The antibacterial functional layer 2 is composed of cellulose nanofibers and antibacterial active substances in a certain proportion. The antibacterial active substance is chitosan, with a molecular weight of 100-200 kDa and an addition amount of 3%-8%. The diameter of the cellulose nanofibers is 10-60 nm, the aspect ratio is 50-200, and the crystallinity is 80-95%. The cellulose nanofibers and chitosan are mechanically treated by ultrasonic dispersion and high-speed shear dispersion to make the chitosan molecules uniformly distributed in the cellulose nanofiber film.

[0021] Due to the uniform composite of the antibacterial active substance chitosan in cellulose nanofibers, this layer has excellent antibacterial effect. Combined with the polylactic acid support layer, the overall thickness of the polylactic acid support layer 1 is 15-20 μm, and the thickness of the antibacterial functional layer 2 is 5-10 μm. The two are hot-pressed at 60-65℃.

[0022] Figure 3 Digital photographs of antibacterial tests of the antibacterial agricultural mulch film of this invention and commercially available pure polylactic acid mulch film are shown. The antibacterial tests were conducted as follows: First, a 0.1% sterile peptone solution was prepared. Then, sterilized pure cellulose nanofiber mulch film (control) and chitosan-modified composite antibacterial agricultural mulch film (according to this invention) were immersed in 10 mL of the pre-prepared 0.1% sterile peptone solution. After thorough shaking and mixing, the resulting liquid was diluted to an appropriate concentration. Then, the two dispersions were evenly poured onto corresponding surface agar plates. Finally, they were incubated at 37°C under visible light for 24 h. The colony distribution of both the pure cellulose nanofiber film and the chitosan-modified composite antibacterial agricultural mulch film was observed to verify the antibacterial performance of the chitosan-modified composite film. Figure 3 The antibacterial test results show that the antibacterial agricultural mulch film modified with chitosan has excellent antibacterial effect.

[0023] In summary, this invention provides a polylactic acid (PLA) biodegradable agricultural mulch film with antibacterial properties. By modifying the structure of the PLA biodegradable agricultural mulch film into a composite layer structure, and by controlling the fine structure of the composite antibacterial functional layer, it effectively ensures visible light transmittance, excellent mechanical properties, and processability, while also possessing excellent antibacterial properties. This effectively inhibits the growth and reproduction of crop pathogens, reducing the occurrence of root diseases. Consequently, it promotes crop growth and development, increases crop yield and growth quality, and significantly improves agricultural production efficiency.

Claims

1. A polylactic acid biodegradable agricultural mulch film with antibacterial function, the mulch film comprising a polylactic acid support layer (1), characterized in that: The mulch film also includes an antibacterial functional layer (2) stacked on the polylactic acid support layer (1). The antibacterial functional layer (2) includes a continuous three-dimensional network formed by cellulose nanofibers with a diameter of 10-60 nm and an aspect ratio of 50-200 in the antibacterial functional layer (2), and a uniform and dense chitosan layer is tightly attached in the three-dimensional network.

2. The polylactic acid biodegradable agricultural mulch film with antibacterial function according to claim 1, characterized in that: The polylactic acid support layer (1) is transparent.

3. The polylactic acid biodegradable agricultural mulch film with antibacterial function according to claim 1, characterized in that... The chitosan layer encapsulates the three-dimensional network.

4. The polylactic acid biodegradable agricultural mulch film with antibacterial function according to claim 1, characterized in that... The thickness of the polylactic acid support layer (1) is 15-20 μm, and the thickness of the antibacterial functional layer (2) is 5-10 μm.

5. The polylactic acid biodegradable agricultural mulch film with antibacterial function according to claim 1, characterized in that... The polylactic acid support layer (1) and the antibacterial functional layer (2) are directly stacked together.

6. The polylactic acid biodegradable agricultural mulch film with antibacterial function according to claim 5, characterized in that... There is no adhesive layer between the polylactic acid support layer (1) and the antibacterial functional layer (2).

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