Micro-nano laminated composite structure biodegradable mulching film and preparation method thereof

Abstract

The invention belongs to the technical field of biodegradable mulching films, and discloses a biodegradable mulching film with a micro-nano laminated composite structure and a preparation method of the biodegradable mulching film. The problem that an existing degradable mulching film is insufficient in water resistance and mechanical property is solved. The biodegradable mulching film comprises an outer layer, a middle layer and an inner layer which are sequentially stacked from top to bottom, and main raw materials of all the layers are PBAT and PLA; the outer layer is an anti-ultraviolet layer, and an ultraviolet light absorber, an antioxidant, a light stabilizer and a nano material with ultraviolet reflection capability are added; the middle layer is a mechanical enhancement layer, nano silicon dioxide is added, and the nano silicon dioxide is directionally arranged through a micron-sized laminar flow co-extrusion technology and a nano particle directional arrangement technology; the inner layer is a water-retaining layer, and a water-retaining agent is added. The comprehensive performance of the biodegradable mulching film is comprehensively improved, the key performance indexes such as water retention, ultraviolet resistance and mechanical strength reach or even exceed those of a traditional mulching film, and sustainable development of agriculture is powerfully promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biodegradable mulching films, and particularly relates to a micro-nano laminated composite structure biodegradable mulching film and a preparation method thereof. BACKGROUND

[0002] Biodegradable mulching films are mainly made of biodegradable materials such as polybutylene succinate (PBS), polyhydroxyalkanoate (PHAs), polylactic acid (PLA), polycaprolactone (PCL), polymethyl ethylene carbonate (PPC) and polybutylene adipate / terephthalate (PBAT). These materials can be decomposed into harmless substances such as water and carbon dioxide under the action of microorganisms in the natural environment, thereby avoiding the residual pollution problem of traditional mulching films and meeting the requirements of sustainable agricultural development.

[0003] However, the current biodegradable mulching film still faces many challenges in practical application, the most prominent of which is the problem of insufficient water resistance and mechanical properties. (1) In terms of water resistance, compared with traditional PE mulching film, the molecular structure and material properties of some biodegradable mulching films cannot effectively prevent soil water evaporation and permeation, resulting in poor water retention effect. This problem is particularly evident in arid regions or in the cultivation of crops with strict water requirements, which can affect the normal growth and development of crops and reduce the yield and quality of crops. (2) In terms of mechanical properties, the tensile strength, elongation at break and puncture resistance of biodegradable mulching films often cannot meet the actual needs of agricultural production. During field laying, it is easy to be damaged by mechanical stretching, wind action, soil particle friction and other external forces such as rupture and tearing; during crop growth, it cannot withstand the pressure and friction brought by plant growth, resulting in premature damage of the mulching film and loss of its protective effect. For example, in some areas with strong winds, biodegradable mulching films are often blown up or torn, and cannot completely cover the soil surface; when planting crops with well-developed root systems, the mulching film is easily penetrated by the roots, affecting its use effect and service life. These performance defects greatly limit the application range and use effect of biodegradable mulching films, making it difficult to completely replace traditional mulching films, and it is urgent to improve and solve them through innovative technologies. SUMMARY

[0004] One object of the present application is to provide a micro-nano laminated composite structure biodegradable mulching film, which effectively solves the problems of insufficient water resistance and mechanical properties of existing biodegradable mulching films.

[0005] To solve the above technical problems, the technical solution adopted by the present application is: a micro-nano laminated composite structure biodegradable mulching film, comprising an outer layer, an intermediate layer and an inner layer which are sequentially laminated from top to bottom.

[0006] The outer layer is an anti-ultraviolet layer, and the raw material of the outer layer is PBAT, PLA, and an ultraviolet absorber, an antioxidant, a light stabilizer, and a nano material with ultraviolet reflection capability.

[0007] The intermediate layer is a mechanical reinforcement layer, and the raw material of the intermediate layer is PBAT, PLA, and nano-silicon dioxide, and the nano-silicon dioxide is arranged in a directional manner through a micron-level laminar flow co-extrusion technology and a nano-particle directional arrangement technology.

[0008] The inner layer is a water retention layer, and the raw material of the inner layer is PBAT, PLA, and a water retention agent.

[0009] Further, the film is prepared by using a micron-level laminar flow co-extrusion device, and the micron-level laminar flow co-extrusion device comprises a first extruder, a second extruder, a third extruder, a melt pump, a co-extrusion die, and a layer multiplier.

[0010] The discharge outlets of the first extruder, the second extruder, and the third extruder are connected with the inlet of the melt pump, the outlet of the melt pump is connected with the inlet of the co-extrusion die, and the outlet of the co-extrusion die is connected with the inlet of the layer multiplier.

[0011] The first extruder is used for conveying the raw material of the outer layer, the second extruder is used for conveying the raw material of the intermediate layer, and the third extruder is used for conveying the raw material of the inner layer; the melt pump is used for controlling the flow and pressure of the raw materials of the layers; the co-extrusion die is used for converging the raw materials of the layers into an initial parallel flow layer; and the layer multiplier is used for repeatedly vertically dividing, horizontally expanding, and recombining the melt material flowing out of the co-extrusion die, so as to realize micron-level layer thickness control and layer number increase.

[0012] Further, the intrinsic viscosity of the PBAT is 1.0-1.5 dL / g, and the carboxyl end group content is ≤17 mol / t; the intrinsic viscosity of the PLA is 0.8-1.2 dL / g, and the weight average molecular weight is 100-200 thousand.

[0013] The ultraviolet absorber is selected from a benzophenone ultraviolet absorber, and the addition amount is 0.3%-0.5% of the total mass of the PBAT and the PLA; the water retention agent is a polyacrylic acid sodium high water absorbent resin, the water absorption rate of the water retention agent is 300-500 times, and the addition amount is 3%-5% of the total mass of the inner layer material.

[0014] The particle size of the nano-silicon dioxide is 20-50 nm, the specific surface area is 150-300 m 2 / g, and the addition amount is 1%-3% of the total mass of the intermediate layer material.

[0015] The antioxidant is selected from a hindered phenol antioxidant 1010, and the addition amount is 0.1%-0.3% of the total mass of the PBAT and the PLA; the light stabilizer is selected from a hindered amine light stabilizer 944, and the addition amount is 0.2%-0.4% of the total mass of the PBAT and the PLA.

[0016] Another object of the present application is to provide a preparation method of the micro-nano laminated composite biodegradable mulch film as described in the above embodiments, comprising the following steps: Step 1, preparation and pretreatment of raw materials of each layer: dry PBAT and PLA particles in an oven at 80-100°C for 4-6 hours; mix the dried PBAT and PLA particles of each layer with the corresponding layer of additives in a high-speed mixer, the stirring speed is 800-1200 r / min, and the stirring time is 15-30 minutes; coat the water-retaining agent with a surfactant; modify the surface of nano-silicon dioxide, and treat the nano-silicon dioxide with a silane coupling agent, mix the nano-silicon dioxide with the silane coupling agent in anhydrous ethanol, ultrasonic dispersion for 30-60 minutes, and then dry at 80-100°C to graft the silane coupling agent on the surface of the nano-silicon dioxide.

[0017] Step 2, add the pretreated and mixed raw materials of the outer layer, the intermediate layer and the inner layer into the first extruder, the second extruder and the third extruder of the micron-level laminar flow co-extrusion equipment respectively, start the extruders, set the temperature of each region, and the raw materials move forward under the action of shear force and friction force, and gradually heat up to the set temperature to achieve full melting.

[0018] At the same time when the intermediate layer raw material enters the second extruder, add the surface-modified nano-silicon dioxide to the second extruder through the nano-particle adding device, and in the high-speed mixing zone of the front section of the screw of the second extruder, the nano-silicon dioxide is uniformly dispersed in the melt of the intermediate layer raw material under the action of shear force, and at the same time, an electric field is applied during the extrusion process, so that the nano-particles are directionally arranged in the intermediate layer film along the stretching direction of the film under the joint action of the electric field force and the flow field shear force.

[0019] Step 3, when the raw materials of each layer are fully melted in the corresponding extruder, the melt enters the co-extrusion die of the micron-level laminar flow co-extrusion equipment under the action of the melt pump of the micron-level laminar flow co-extrusion equipment with stable flow and pressure, and in the co-extrusion die, different materials converge into an initial parallel stream layer.

[0020] Step 4, after the initial parallel stream layer comes out of the co-extrusion die, it enters the layer multiplier of the micron-level laminar flow co-extrusion equipment, and in the layer multiplier, the structure of the stream layer is repeatedly vertically divided, horizontally expanded and recombined to prepare a composite material with micron-level layer thickness and multi-layer structure.

[0021] Step 5, after the composite material passes through the layer multiplier and the nano-particle directional arrangement, it is extruded through the die to form a mulch film with an outer layer, an intermediate layer and an inner layer structure.

[0022] The extruded mulch film is cooled and shaped by a cooling device, the cooled and shaped mulch film is pulled by a pulling device, and is wound by a winding device to obtain the biodegradable mulch film product.

[0023] Further, in step 1, when the water-retaining agent is coated with the surfactant, the surfactant is selected as zinc stearate, and the amount of the surfactant is 0.5%-1% of the mass of the water-retaining agent.

[0024] When the nano-silicon dioxide is surface-modified, the silane coupling agent is selected as KH-570, the amount of the silane coupling agent is 1%-3% of the mass of the nano-silicon dioxide, and the mass ratio of the nano-silicon dioxide to the anhydrous ethanol is 1:10-1:20.

[0025] Further, in step 2, the temperature of the first extruder is set as: the feeding section 130-150℃, the plasticizing section 160-170℃, and the homogenizing section 165-175℃; the temperature of the second extruder is set as: the feeding section 140-150℃, the plasticizing section 160-170℃, and the homogenizing section 165-175℃; and the temperature of the third extruder is set as: the feeding section 135-155℃, the plasticizing section 155-170℃, and the homogenizing section 165-175℃.

[0026] The extrusion speed of the first extruder, the second extruder and the third extruder is controlled at 15-25m / min, and in the extrusion process, the applied electric field intensity is 10-20kV / m, and the electric field direction is perpendicular to the extrusion direction.

[0027] Further, in step 3, the pressure of the melt pump is controlled at 10-15MPa, and the temperature of the co-extrusion die is kept at 165-175℃.

[0028] Further, in step 4, the multiplication factor of the layer multiplier is set as 4-6.

[0029] Compared with the prior art, the beneficial technical effects of the present application are: (1) The present application realizes the close combination of materials with different properties at the micro level through micron-level laminar flow co-extrusion technology, forming a synergistic reinforcing effect. The interface interaction between the layers of materials can effectively transfer stress and avoid stress concentration, thereby improving the overall mechanical properties of the mulch film. The nano particle directional arrangement technology constructs a special reinforcing structure in the film, with the nano particles arranged along a specific direction, like adding countless micro "reinforcing bars" to the film, greatly enhancing the mechanical properties of the film in that direction. The layered functional design enables the different layers of the mulch film to fully exert their respective advantages, with the outer layer's anti-ultraviolet design effectively protecting the materials of the inner and middle layers, preventing their properties from being damaged by ultraviolet rays; the water retention design of the inner layer provides a good water environment for crop growth; and the mechanical support design of the middle layer ensures the stability and reliability of the mulch film under various environmental conditions.

[0030] (2) The biodegradable mulch film of the present application has significantly improved water resistance and mechanical properties. The water vapor transmission rate of the biodegradable mulch film prepared by the present application is reduced to 200-350 g / (m²·24h), effectively reducing soil water evaporation and permeation and improving soil water retention capacity, which is particularly important for agricultural production in arid regions, as it can provide more adequate water for crops, ensuring normal growth of crops and improving crop yield and quality.

[0031] The tensile strength of the biodegradable mulch film prepared by the present application can be increased to 20-25 MPa, the elongation at break can reach 300%-400%, and the puncture resistance is also significantly improved. This makes the mulch film better resist external forces during laying and use, reducing damage such as cracking and tearing, prolonging the service life of the mulch film, reducing the number of mulch film replacements, and reducing the cost of agricultural production.

[0032] (3) The biodegradable mulch film of the present application has positive significance in solving environmental problems and promoting sustainable agricultural development. It effectively reduces the "white pollution" caused by traditional mulch, reduces damage to the soil environment, and protects the ecological balance of the soil. At the same time, its excellent performance can provide better growing conditions for crops, improve crop yield and quality, promote sustainable agricultural development, and have significant economic, environmental and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of the micro-nano layered composite structure biodegradable mulch film of the present application.

[0034] BRIEF DESCRIPTION OF DRAWINGS: outer layer-1; middle layer-2; inner layer-3. DETAILED DESCRIPTION

[0035] Example 1: First, some of the nouns in this embodiment are explained as follows: (1) PBAT: polybutylene adipate terephthalate, a thermoplastic biodegradable plastic with good biodegradability, thermal stability, mechanical properties and processing properties. In the natural environment, PBAT can be gradually decomposed under the action of microorganisms, and the final product is carbon dioxide and water, which will not cause long-term pollution to the environment. Its good flexibility and processing performance make it possible to adapt to various molding processes during the preparation of mulch film, and it can withstand a certain degree of stretching and deformation without breaking during use.

[0036] (2) PLA: polylactic acid, a biodegradable material made from renewable plant resources such as corn starch, has excellent biocompatibility and biodegradability, and can be completely degraded by microorganisms in nature. At the same time, PLA also has high tensile strength and modulus, providing certain rigidity and support for the mulch film. Properly blending PBAT and PLA can take full advantage of both materials and make up for each other's shortcomings. For example, using the flexibility of PBAT to improve the brittleness of PLA and improve the tear resistance of the mulch film; using the high strength of PLA to enhance the toughness of PBAT and improve the stability of the mulch film during use. In addition, according to actual needs, a proper amount of other additives such as antioxidants, thermal stabilizers, plasticizers, etc. can be added to further optimize the performance of the material and ensure the stability and service life of the mulch film under different environmental conditions.

[0037] The micro-nano layered composite structure biodegradable mulch film provided in this embodiment adopts a layered functional design, as shown in Figure 1 The main raw materials of each layer are PBAT and PLA.

[0038] Among them, the outer layer 1 is an anti-ultraviolet layer, mainly responsible for anti-ultraviolet function. In order to enhance the anti-ultraviolet ability of the outer layer, ultraviolet absorbers, antioxidants, light stabilizers and nano materials with ultraviolet reflection ability (such as titanium dioxide nanoparticles, etc.) are added. Ultraviolet absorbers can selectively absorb ultraviolet light and convert it into heat or other forms of energy, thereby avoiding the damage of ultraviolet light to biodegradable materials; nano materials with ultraviolet reflection ability can reflect part of the ultraviolet light, further reducing the irradiation of ultraviolet light on the film; through this double protection mechanism, the anti-ultraviolet performance of the outer layer is effectively improved, and the service life of the mulch film is prolonged. Weathering aids such as antioxidants and light stabilizers can enhance the stability of the outer layer in outdoor environments, preventing it from aging, degrading and other phenomena due to long-term exposure to sunlight, oxygen and other environmental factors.

[0039] The inner layer 3 is a water retention layer, and its main function is to improve water retention performance. A water-retaining agent is added to the inner layer, which is a high-molecular material with high water absorption. It can absorb and store a large amount of water. When the water content in the soil is high, the water-retaining agent can absorb the excess water and store it; when the water content in the soil is low, the water-retaining agent can slowly release the stored water to provide a continuous supply of water for crops. At the same time, the inner layer also optimizes the molecular structure and microstructure of the material to improve its water barrier performance and reduce water evaporation and permeation. For example, materials with low surface energy or special microstructures such as nanoscale pores or grooves are used on the surface of the material to reduce the diffusion rate of water on the film surface, thereby improving the water retention performance of the inner layer.

[0040] The middle layer 2 is a mechanical reinforcement layer, mainly responsible for providing mechanical support. Nano-silica is added to the middle layer, and by selecting biodegradable materials (PBAT and PLA) with high strength and modulus, and through microscale laminar flow co-extrusion technology and nano-particle directional arrangement technology, the nano-silica is arranged in a direction to further enhance its mechanical properties. In the middle layer, the nano-particles are arranged in a direction along the stretching direction of the film, forming a reinforced structure similar to reinforced concrete, greatly improving the tensile strength, bending strength and impact resistance of the middle layer. At the same time, the middle layer also adopts a multi-layer composite structure design, and through special interface treatment between different layers, a good bonding and synergistic effect is formed, so that the middle layer can more evenly disperse stress when subjected to external force, avoiding material damage caused by stress concentration.

[0041] This layered functional design allows different layers of the mulch film to perform their respective functions and work together, effectively solving the problem of insufficient water resistance and mechanical properties of biodegradable mulch films, while also improving their ultraviolet resistance, meeting the multiple needs of agricultural production for mulch films.

[0042] The main raw materials required in this embodiment are: (1) PBAT with intrinsic viscosity of 1.0-1.5 dL / g and carboxyl end group content ≤17 mol / t. The PBAT with this property is used to ensure that it has good biodegradability, certain flexibility and processing performance. (2) PLA with intrinsic viscosity of 0.8-1.2 dL / g and weight average molecular weight of 100-200 thousand. This specification of PLA can provide the necessary rigidity and strength for the mulch film. (3) The ultraviolet absorber selected is a benzophenone ultraviolet absorber such as UV-531, and the addition amount is 0.3%-0.5% of the total mass of PBAT and PLA. Its role is to effectively absorb ultraviolet rays and prevent the destruction of biodegradable materials by ultraviolet rays. (4) The water-retaining agent is a polyacrylic acid sodium high water-absorbing resin with water absorption ratio of 300-500 times. The addition amount is 3%-5% of the total mass of the inner layer material, which can absorb and store a large amount of water to improve the water-retaining performance of the inner layer. (5) The particle size of nano-silicon dioxide is 20-50 nm, and the specific surface area is 150-300 m 2 / g. The addition amount is 1%-3% of the total mass of the intermediate layer material, which is used to enhance the mechanical properties of the intermediate layer. (6) The antioxidant selected is a hindered phenol antioxidant 1010, and the addition amount is 0.1%-0.3% of the total mass of PBAT and PLA. Here, "the total mass of PBAT and PLA" refers to the total mass of PBAT and PLA used in the entire biodegradable mulch film. (7) The light stabilizer selected is a hindered amine light stabilizer 944, and the addition amount is 0.2%-0.4% of the total mass of PBAT and PLA, which enhances the stability of the material under light conditions. Here, "the total mass of PBAT and PLA" refers to the total mass of PBAT and PLA used in the entire biodegradable mulch film.

[0043] The intermediate layer of this embodiment uses micron-level laminar flow co-extrusion technology and nano-particle directional arrangement technology to further enhance its mechanical properties. Among them, (1) the micron-level laminar flow co-extrusion technology is realized through a micron-level laminar flow co-extrusion device.

[0044] The micron-level laminar flow co-extrusion device includes a first extruder, a second extruder, a third extruder, a melt pump, a co-extrusion die and a layer multiplier. The discharge ports of the first extruder, the second extruder and the third extruder are connected with the inlet of the melt pump, the outlet of the melt pump is connected with the inlet of the co-extrusion die, and the outlet of the co-extrusion die is connected with the inlet of the layer multiplier.

[0045] ① The first extruder is used to transport the outer layer material, the second extruder is used to transport the middle layer material, and the third extruder is used to transport the inner layer material. These materials are first controlled by the melt pump to ensure that they can enter the co-extrusion die stably and uniformly before entering the co-extrusion die. ② The melt pump is used to control the flow and pressure of each layer of material. Its function is similar to a precise flow regulator, which can eliminate the pressure fluctuations and uneven flow problems that may occur when the material is discharged from the extruder, providing stable material flow for subsequent co-extrusion molding. ③ The co-extrusion die is used to combine the different materials into an initial parallel flow layer. Its internal structure is carefully designed to enable different materials to be combined into an initial parallel flow layer in the die. In the co-extrusion die, the material flow is uniformly distributed and combined through specific flow channels and distribution plates to form an initial composite layer with a certain number of layers and thickness. These initial composite layers exit the co-extrusion die and enter the layer multiplier. ④ The layer multiplier is used to repeatedly vertically divide, horizontally expand and recombine the melt material flowing out of the co-extrusion die, achieving micron-level layer thickness control and layer number increase. It is a key device for achieving micron-level layer thickness control and layer number increase. When the melt material flows through the layer multiplier, the layer structure is repeatedly vertically divided, horizontally expanded and recombined. Specifically, the layer multiplier contains a series of specially designed flow channels and elements. When the composite material flow enters the layer multiplier, it first encounters vertical division elements that divide the composite layer into multiple thinner sub-layers. Then, these sub-layers are expanded horizontally and uniformly distributed through special flow channel design. Finally, after recombination, these sub-layers form a composite structure with more layers and thinner layers. Through this repeated vertical division, horizontal expansion and recombination process, the number of layers of the composite layer increases continuously, while the layer thickness decreases continuously, ultimately enabling the preparation of a composite material with tens or even thousands of alternating layers, and the thickness of the extruded layer can reach micron level. This micron-level layer flow co-extrusion technology enables different materials with different properties to be closely combined at the micro level, fully utilizing the advantages of each material, and giving the mulch excellent comprehensive performance.

[0046] (2) Nanoparticle directional arrangement technology.

[0047] The principle of nanoparticle directional arrangement technology is based on multiple physical and chemical effects. First, by using the interaction between nanoparticles and biodegradable materials, surface modification is used to make the surface of the nanoparticles have specific functional groups. These functional groups can form chemical bonds, hydrogen bonds or strong van der Waals forces with the molecules of the biodegradable material, thereby enhancing the compatibility and bonding force between the nanoparticles and the biodegradable material.

[0048] In the process of uniformly dispersing nanoparticles in the biodegradable material melt, high-speed stirring, ultrasonic treatment and special dispersants are used. High-speed stirring can provide strong shear force to preliminarily disperse nanoparticles in the melt and break the possible agglomerates. Ultrasonic treatment utilizes the cavitation effect of ultrasonic waves to generate micro-bubbles in the melt. When these bubbles burst instantaneously, they generate strong shock waves and micro-jets, further refining the agglomerates of nanoparticles and making them more uniformly dispersed in the melt. Special dispersants can be adsorbed on the surface of nanoparticles, reducing the surface energy between nanoparticles and preventing their re-agglomeration. They can also improve the interfacial compatibility between nanoparticles and biodegradable materials.

[0049] To achieve the directional arrangement of nanoparticles, the embodiment adopts a method combining electric field induction and flow field induction. During extrusion, an electric field with a specific intensity and direction is applied. Since nanoparticles have a certain electric polarization, they will be affected by electrostatic force under the action of the electric field, and their two poles will be arranged along the direction of the electric field. At the same time, the flow of the melt during extrusion, i.e. the flow field, is utilized. The flow field exerts shear force on the nanoparticles, so that the nanoparticles are affected by the flow field shear force in addition to the electric field force. Under the combined action of the electric field force and the flow field shear force, the nanoparticles can be more orderly arranged in a specific direction in the film. Such directionally arranged nanoparticles can form a special reinforcing structure in the film, significantly enhancing the performance of the film in a specific direction, such as tensile strength, puncture resistance, etc. For example, when the nanoparticles are directionally arranged along the stretching direction of the film, the tensile strength of the film can be effectively improved, so that it can better resist external pulling force in agricultural production.

[0050] The embodiment fully utilizes the advantages of micron-scale laminar flow co-extrusion and nanoparticle directional arrangement technology through innovative micro-nano laminated composite structure design, combines the concept of layered functionalization design, realizes the comprehensive improvement of the comprehensive performance of biodegradable mulch film, and makes it reach or even surpass the traditional mulch film in key performance indicators such as water retention, ultraviolet resistance and mechanical strength, providing an efficient, environmentally friendly and outstanding performance mulch solution for agricultural production, thereby promoting the sustainable development of agriculture.

[0051] Embodiment 2: The preparation method of the micro-nano laminated composite structure biodegradable mulch film of embodiment 1, comprising the following steps: step 1, preparation and pretreatment of raw materials of each layer.

[0052] The raw material pretreatment method is: ① the PBAT and PLA particles are dried in an oven at 80-100°C for 4-6 hours to remove moisture, prevent hydrolysis or bubble generation of the material due to the presence of moisture during processing, and affect the performance of the mulch film. ② the dried PBAT and PLA particles of each layer are mixed with the corresponding layer of additives (such as ultraviolet absorbers, antioxidants, light stabilizers, etc.) using a high-speed mixer (the raw materials of the outer layer, the middle layer and the inner layer are treated respectively), the stirring speed is 800-1200 r / min, and the stirring time is 15-30 minutes, to ensure that the additives are uniformly dispersed in the polymer collective. ③ the water-retaining agent is coated with a surfactant, the surfactant is zinc stearate, and the amount of surfactant is 0.5%-1% of the mass of the water-retaining agent, to improve the compatibility of the water-retaining agent and the polymer matrix. ④ the nano-silicon dioxide is surface modified, a silane coupling agent is used to treat the surface of the nano-silicon dioxide, the nano-silicon dioxide and the silane coupling agent are mixed in anhydrous ethanol, ultrasonic dispersion is performed for 30-60 minutes, and then drying is performed at 80-100°C, so that the silane coupling agent is grafted onto the surface of the nano-silicon dioxide, and the bonding force between the nano-silicon dioxide and the polymer matrix is enhanced. The silane coupling agent is KH-570, the amount of silane coupling agent is 1%-3% of the mass of the nano-silicon dioxide, and the mass ratio of nano-silicon dioxide to anhydrous ethanol is 1:10-1:20.

[0053] Step 2, the pretreated and mixed outer layer raw material, middle layer raw material and inner layer raw material are respectively added to the first extruder, second extruder and third extruder of the micron-level layer flow co-extrusion equipment, the extruders are started, and the temperature of each region is set, so that the raw materials are gradually melted and plasticized. In this process, the raw materials move forward under the action of the screw and shear force and friction, and gradually heat up to the set temperature to achieve full melting.

[0054] At the same time that the middle layer raw material enters the second extruder, the surface-modified nano-silicon dioxide is quantitatively added to the second extruder through a nano-particle adding device. In the high-speed mixing zone of the front section of the screw of the second extruder, the nano-silicon dioxide is uniformly dispersed in the melt of the middle layer raw material under the action of the shear force generated by the high-speed rotation of the screw. At the same time, during the extrusion process, a specific intensity and direction of electric field is applied, so that the nano-particles are directionally arranged in the middle layer film along the stretching direction of the film under the combined action of the electric field force and the flow field shear force.

[0055] In step 2, the temperature settings of each extruder are divided into multiple zones, increasing from the hopper to the die. The temperature settings for the first extruder are: 130-150°C for the feeding section, 160-170°C for the plasticizing section, and 165-175°C for the homogenizing section. The temperature settings for the second extruder are: 140-150°C for the feeding section, 160-170°C for the plasticizing section, and 165-175°C for the homogenizing section. The temperature settings for the third extruder are: 135-155°C for the feeding section, 155-170°C for the plasticizing section, and 165-175°C for the homogenizing section. These temperature settings ensure that the different raw materials are fully melted and plasticized at appropriate temperatures.

[0056] The extrusion speed of the first, second, and third extruders is controlled at 15-25 m / min to ensure the quality and production efficiency of the mulch film. During the extrusion process, an electric field with a strength of 10-20 kV / m is applied, with the electric field direction perpendicular to the extrusion direction to achieve the directional arrangement of nanoparticles in the middle layer. At the same time, by adjusting the rotation speed of the extruder screw and the flow rate of the melt pump, the flow rate of the melt is controlled, allowing the nanoparticles to be more orderly arranged under the action of the shear force of the flow field in addition to the electric field force.

[0057] Step 3: After the raw materials of each layer are fully melted in the corresponding extruder, the melt enters the co-extrusion die at a stable flow rate and pressure under the action of the melt pump. The melt pump precisely controls the delivery amount of each layer of material, ensuring that the materials of each layer can be combined in the co-extrusion die according to the predetermined proportion and order. In this embodiment, the pressure of the melt pump is controlled at 10-15 MPa, and the temperature of the co-extrusion die is maintained at 165-175°C.

[0058] Step 4: In the co-extrusion die, different materials are combined into an initial parallel flow layer. The special flow channel design inside the co-extrusion die allows the materials of each layer to be uniformly distributed and initially combined together. After the initial parallel flow layer exits the co-extrusion die, it enters the layer multiplier, which has a multiplication factor of 4-6. In the layer multiplier, the structure of the flow layer is repeatedly vertically divided, horizontally expanded, and recombined. For example, the flow layer is first vertically divided into multiple thinner sub-layers, which are then expanded and evenly distributed in the horizontal direction before being recombined to form a composite structure with more layers and thinner layer thickness. After multiple such layer multiplication processes, a composite material with micron-level layer thickness and multi-layer structure is prepared.

[0059] Step 5: After passing through the layer multiplier and the directional arrangement of nanoparticles, the composite material is extruded through a specific mold to form a mulch film with an outer layer, a middle layer, and an inner layer structure. The shape and size of the mold determine the final shape and size of the mulch film, and during the extrusion process, the thickness of the mulch film should be uniform and the surface should be flat.

[0060] Step 6: After extrusion, the mulch film is cooled and shaped by a cooling device. The cooling device uses a combination of air cooling and water cooling. First, the film is cooled by air to reduce its temperature, and then further cooled by water to quickly cool and shape the film, maintaining its shape and size stability.

[0061] After cooling and shaping, the film is pulled out at a certain speed by a traction device and wound by a winding device to obtain the final biodegradable mulch film product. During winding, the tension should be controlled to ensure that the film is tightly and neatly wound.

[0062] The biodegradable mulch film prepared in this example was tested for performance. The specific test methods, standards and test items are as follows: (1) Tensile strength test: according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: test conditions for films and sheets". An electronic tensile testing machine was used to cut the film into standard dumbbell-shaped samples with a width of 10 mm and an initial distance between the clamps of 50 mm. The test speed was 500 mm / min. During the tensile process, the maximum tensile force at the time of sample fracture was recorded, and the tensile strength was calculated by formula. The test results showed that the tensile strength of the film prepared in this example reached 23 MPa, which was significantly improved compared to traditional biodegradable mulch film (tensile strength generally around 10-15 MPa).

[0063] (2) Elongation at break test: also according to GB / T 1040.3-2006 standard, on the basis of tensile strength test, record the increase of distance between marks when the sample breaks, calculate the elongation at break by formula. The test results show that the elongation at break of the film prepared in this example is 350%, which is significantly improved compared to traditional biodegradable mulch film (elongation at break between 150%-250%), and can meet the requirements of film flexibility in agricultural production.

[0064] (3) Water vapor transmission rate test: according to GB / T 1037-2021 "Plastics - Determination of water vapour transmission - Cup method". The film sample was sealed on the moisture cup, which contained a desiccant, and placed in an environment with a temperature of 38℃ and a relative humidity of 90%. After a certain period of time, the weight change of the moisture cup was measured, and the water vapor transmission rate was calculated by formula. The test results show that the water vapor transmission rate of the film prepared in this example is 350g / (m²・24h), under the same experimental conditions, the water vapor transmission rate of traditional biodegradable mulch film is usually between 500-800g / (m²・24h), this example effectively reduces the evaporation and permeation of soil water, and improves the water retention capacity of soil.

[0065] (4) Anti-puncture strength test: The test was performed according to the QB / T 1130-1991 "Plastic Right Angle Tearing Performance Test Method" standard. Using an anti-puncture tester, the mulch sample was fixed on the test table, and a certain size of puncture needle was vertically punctured at a certain speed. The maximum force value during the puncture process was recorded as the anti-puncture strength. The test results showed that the anti-puncture strength of the mulch prepared in this embodiment was 12N, which could better resist the puncture effect of external force compared with traditional biodegradable mulch.

[0066] (5) Anti-ultraviolet performance test: The mulch sample was exposed to an ultraviolet aging test box, and tested according to the GB / T16422.2-2022 "Plastics Laboratory Light Source Exposure Test Method Part 2: Xenon Arc Lamp" standard. The xenon arc lamp in the test box simulates the ultraviolet light in natural sunlight, and controls the light intensity, temperature and humidity conditions. After a certain time of light exposure, the appearance change of the mulch sample was observed, and the change of its mechanical properties was tested. The test results showed that after 500 hours of ultraviolet irradiation, the appearance of the mulch prepared in this embodiment had no obvious change, and the tensile strength retention rate was 85%, indicating that it had good anti-ultraviolet performance.

[0067] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A micro-nano laminated composite structure biodegradable mulch film, characterized in that, The outer layer, the intermediate layer and the inner layer are sequentially stacked from top to bottom; The outer layer is an anti-ultraviolet layer, and the raw material of the outer layer is PBAT, PLA, and ultraviolet absorber, antioxidant, light stabilizer and nano material with ultraviolet reflection ability; The intermediate layer is a mechanical reinforcement layer, and the raw material of the intermediate layer is PBAT, PLA and nano silicon dioxide, and the nano silicon dioxide is arranged in a direction by means of micro-layer flow co-extrusion technology and nano particle directional arrangement technology; The inner layer is a water retention layer, and the raw material of the inner layer is PBAT, PLA and water retention agent.

2. The micro-nano laminated composite structure biodegradable mulching film according to claim 1, characterized in that, The micrometer level layer flow co-extrusion equipment comprises a first extruder, a second extruder, a third extruder, a melt pump, a co-extrusion die and a layer multiplier; The discharge ports of the first extruder, the second extruder and the third extruder are connected with the inlet of the melt pump, the outlet of the melt pump is connected with the inlet of the co-extrusion die, and the outlet of the co-extrusion die is connected with the inlet of the layer multiplier; The first extruder is used for conveying the raw material of the outer layer, the second extruder is used for conveying the raw material of the intermediate layer, and the third extruder is used for conveying the raw material of the inner layer; the melt pump is used for controlling the flow and pressure of the raw materials of the layers; the co-extrusion die is used for combining the raw materials of the layers into an initial parallel flow layer; and the layer multiplier is used for repeatedly vertically dividing, horizontally expanding and recombining the melt material flowing out of the co-extrusion die, so as to realize micrometer level layer thickness control and layer number increase.

3. The biodegradable mulch film of micro-nano laminated composite structure according to claim 2, characterized in that, The intrinsic viscosity of the PBAT is 1.0-1.5 dL / g, and the carboxyl end group content is ≤17 mol / t; the intrinsic viscosity of the PLA is 0.8-1.2 dL / g, and the weight average molecular weight is 100-200 thousand; The ultraviolet absorber is selected from a benzophenone ultraviolet absorber, and the addition amount is 0.3%-0.5% of the total mass of the PBAT and the PLA; the water retention agent is a polyacrylic acid sodium high water absorption resin, the water absorption rate of the water retention agent is 300-500 times, and the addition amount is 3%-5% of the total mass of the inner layer material; The nano-silica has a particle size of 20-50 nm and a specific surface area of 150-300 m 2 / g, and the addition amount is 1%-3% of the total mass of the intermediate layer material. The antioxidant is selected from a hindered phenol antioxidant 1010, and the addition amount is 0.1%-0.3% of the total mass of the PBAT and the PLA; and the light stabilizer is selected from a hindered amine light stabilizer 944, and the addition amount is 0.2%-0.4% of the total mass of the PBAT and the PLA.

4. The method of producing the micro-nano laminated composite biodegradable mulch film according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: Step 1, preparation and pretreatment of raw materials of the layers: dry the PBAT and PLA particles in an oven at 80-100 DEG C for 4-6 hours; mix the dried PBAT and PLA particles of each layer and the corresponding layer additives by using a high-speed mixer, the stirring speed is 800-1200 r / min, and the stirring time is 15-30 minutes; coat the water retention agent with a surfactant; modify the surface of the nano silicon dioxide, and treat the nano silicon dioxide with a silane coupling agent, mix the nano silicon dioxide and the silane coupling agent in anhydrous ethanol, ultrasonic dispersion for 30-60 minutes, and then dry at 80-100 DEG C, so that the surface of the nano silicon dioxide is grafted with the silane coupling agent; Step 2, the pre-processed and mixed outer layer material, intermediate layer material and inner layer material are respectively added into the first extruder, the second extruder and the third extruder of the micron-level laminar flow co-extrusion equipment, the extruders are started, the temperature of each region is set, the materials are moved forward under the push of the screw of each extruder and are subjected to the action of shear force and friction force, gradually heated to the set temperature, and fully melted; At the same time when the intermediate layer material enters the second extruder, the surface-modified nano-silicon dioxide is added to the second extruder through the nano-particle adding device, in the high-speed mixing zone of the front section of the screw of the second extruder, the nano-silicon dioxide is uniformly dispersed in the melt of the intermediate layer material under the action of shear force, and at the same time, in the extrusion process, an electric field is applied, so that the nano-particles are directionally arranged in the intermediate layer film along the stretching direction of the film under the joint action of the electric field force and the flow field shear force; Step 3, when the materials of each layer are fully melted in the corresponding extruder, the melt enters the co-extrusion die of the micron-level laminar flow co-extrusion equipment under the action of the melt pump of the micron-level laminar flow co-extrusion equipment with stable flow and pressure, and different materials are combined into an initial parallel flow layer in the co-extrusion die; Step 4, after the initial parallel flow layer comes out of the co-extrusion die, it enters the layer multiplier of the micron-level laminar flow co-extrusion equipment, in the layer multiplier, the structure of the flow layer is repeatedly vertically divided, horizontally expanded and recombined to prepare a composite material with micron-level layer thickness and multi-layer structure; Step 5, the composite material after the layer multiplier and the directional arrangement of the nano-particles is extruded through the die to form a mulch film with an outer layer, an intermediate layer and an inner layer structure; Step 6, the mulch film after the extrusion molding is cooled and shaped by the cooling device, the mulch film after the cooling and shaping is pulled by the pulling device, and is wound by the winding device to obtain a biodegradable mulch film product.

5. The method for preparing the micro-nano layered composite biodegradable mulch film according to claim 4, characterized in that, In step 1, when the water-retaining agent is coated with a surfactant, the surfactant is zinc stearate, and the amount of the surfactant is 0.5%-1% of the mass of the water-retaining agent; When the nano-silicon dioxide is surface-modified, the silane coupling agent is KH-570, the amount of the silane coupling agent is 1%-3% of the mass of the nano-silicon dioxide, and the mass ratio of the nano-silicon dioxide to anhydrous ethanol is 1:10-1:

20.

6. The method for preparing the micro-nano layered composite biodegradable mulch film according to claim 5, characterized in that, In step 2, the temperature of the first extruder is set as: the feeding section 130-150℃, the plasticizing section 160-170℃, and the homogenizing section 165-175℃; the temperature of the second extruder is set as: the feeding section 140-150℃, the plasticizing section 160-170℃, and the homogenizing section 165-175℃; and the temperature of the third extruder is set as: the feeding section 135-155℃, the plasticizing section 155-170℃, and the homogenizing section 165-175℃; The extrusion speed of the first extruder, the second extruder and the third extruder is controlled at 15-25m / min, and the electric field strength applied in the extrusion process is 10-20kV / m, and the direction of the electric field is perpendicular to the extrusion direction.

7. The method for preparing the micro-nano layered composite biodegradable mulch film according to claim 6, characterized in that, In step 3, the pressure of the melt pump is controlled at 10-15MPa, and the temperature of the co-extrusion die is kept at 165-175℃.

8. The method for preparing the micro-nano layered composite biodegradable mulch film according to claim 7, characterized in that, In step 4, the multiplication factor of the layer multiplier is set to 4-6.

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