One-way water permeable composite material and method for manufacturing the same

Abstract

The application belongs to the field of high polymer composite materials, and relates to a unidirectional water-permeable composite material and a preparation method thereof. The method comprises the following steps: preparing a first base film by melting and plasticizing a first biodegradable polymer; performing heat treatment on the first base film; activating the surface of the first layer film by using plasma; melting and plasticizing a second biodegradable polymer and coating the activated surface of the first layer film under the action of an electric field, wherein the first and second biodegradable polymers have different hydrophilicity; and performing heat treatment and stretching on the two layer films, and setting the two layer films after shrinkage, so as to obtain the unidirectional water-permeable composite material. The method of the application uses biodegradable materials as a matrix, combines material compatibility and interface compatibility modification, realizes unidirectional water-permeable effect through gradient hydrophilic and hydrophobic structure design, realizes selective permeation of water from one side to the opposite side, simultaneously inhibits reverse evaporation of water, and meets the water collection and water retention requirements in arid and semi-arid areas.

Description

Technical Field

[0001] This invention belongs to the field of polymer composition materials, specifically relating to a one-way permeable composite material and its preparation method. Background Technology

[0002] In arid regions, extreme water scarcity and high evaporation losses constitute the core bottleneck restricting agricultural production and ecological restoration. These areas receive sparse and unevenly distributed annual precipitation, often below 200-400 mm. Intense solar radiation, high temperatures, and frequent hot, dry winds result in potential annual evaporation rates several times, even ten times, higher than the precipitation. This severe situation of "low precipitation and high evaporation" makes it difficult for precious natural rainfall to effectively infiltrate to the plant root zone, causing the soil surface to dry and compact rapidly. This severely hinders seed germination, seedling establishment, and crop yield, greatly limiting the land's productive potential and ecological carrying capacity. To alleviate water stress, mulching technology has become an important agronomic method. However, existing material systems have significant shortcomings in meeting the specific needs of arid regions.

[0003] Currently, mainstream agricultural mulch films are made from non-degradable petroleum-based polymers such as polyethylene (PE). While these films can inhibit some soil moisture evaporation, they completely block rainwater infiltration, failing to achieve intelligent water regulation that allows water to "enter but not exit." This severely hinders the effective utilization of rainfall by the soil, resulting in a huge waste of water resources, especially in arid regions where rainfall is already precious. Moreover, these films are extremely stable in physicochemical properties and can remain in the soil for hundreds of years, leading to soil structure damage, decreased fertility, and the risk of microplastic pollution, becoming a long-term source of environmental disasters. Although starch-based fully biodegradable mulch films, represented by patent CN120365604A, have made breakthroughs in solving the "white pollution" problem, these biodegradable films lack unidirectional water guidance control capabilities. Water can permeate in both directions, failing to effectively block the evaporation of moisture from the lower soil layers, and thus failing to achieve the core goal of "rainwater harvesting and moisture retention."

[0004] Regarding the preparation of one-way permeable membranes, patent CN114381027A discloses a method for preparing a super-bihydrophobic and waterproof breathable membrane using fluorinated epoxy resin and clay minerals. The method includes the following steps: First, fluorination of allyl epoxy resin yields fluorinated epoxy resin; second, fluorination of clay mineral nanoparticles yields fluorinated clay mineral nanoparticles; finally, a certain amount of fluorinated clay mineral nanoparticles is added to the fluorinated epoxy resin, and after uniform dispersion, a super-bihydrophobic suspension is prepared. This suspension is then coated onto the surface of the waterproof breathable membrane by spraying, and after heat curing at 90-120℃ for 30-60 minutes, a stable super-bihydrophobic and waterproof breathable membrane is obtained. Although this method produces a waterproof breathable membrane with a relatively simple process, these high-performance one-way permeable membranes often use non-biodegradable synthetic polymers such as polyvinylidene fluoride (PVDF), polyurethane (PU), or polytetrafluoroethylene (PTFE), posing a risk of persistent pollution.

[0005] Therefore, current agricultural mulching technology in arid or semi-arid regions is mired in multiple dilemmas: the widely used PE film is non-degradable and accumulates significant pollution; although biodegradable films are environmentally friendly, they lack the crucial ability to regulate water in one direction; and materials with the potential for one-way water permeability are limited by mass production costs and non-degradability. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art and to provide a unidirectional permeable composite material and its preparation method.

[0007] According to one aspect of the present invention, a method for preparing a one-way permeable composite material is provided, the method comprising the following steps: The first biodegradable polymer is melt-plasticized and prepared into a first base film; The first base film is subjected to heat treatment to obtain the first layer film; The surface of the first film is activated using plasma; The second biodegradable polymer is melted and plasticized, and then coated onto the activated surface of the first membrane under the action of an electric field to form a second base film. The second biodegradable polymer has a different hydrophilicity than the first biodegradable polymer. The two membranes are heat-treated to obtain a double-layer composite membrane. The composite membrane is stretched, retracted, and shaped to obtain a biodegradable one-way permeable composite material.

[0008] According to one embodiment of the present invention, the first biodegradable polymer and the second biodegradable polymer are each selected from at least one of the following five groups, wherein: Group G1 includes at least one of the following: polyvinyl alcohol, polyacrylic acid, polyethylene glycol and its derivatives, polyoxyethylene and its copolymers; Group G2 includes at least one of the following: polyglycolic acid, polylactic acid, polylactic acid-glycolic acid copolymer; Group G3 includes at least one of the following: polybutylene succinate, polyhydroxybutyrate, polycaprolactone, polybutylene succinate, polypropylene glycol succinate, polybutylene adipate, and polyhydroxybutyrate-valerate. Group G4 includes at least one of the following: polybutylene sebacic acid, polybutylene terephthalate, and polypropylene terephthalate. Group G5 includes at least one of the following: polypropylene carbonate, polytrimethylene carbonate.

[0009] According to one embodiment of the present invention, the first biodegradable polymer is a single component, a blend of multiple components from the same group, or a blend of multiple components from different groups; the second biodegradable polymer is a single component, a blend of multiple components from the same group, or a blend of multiple components from different groups; the first biodegradable polymer is selected from at least one of groups G1, G2, and G3, and the second biodegradable polymer is selected from at least one of groups G4 and G5.

[0010] According to one embodiment of the present invention, the first biodegradable polymer is polyethylene glycol, and the second biodegradable polymer is polylactic acid or polybutylene succinate; or The first biodegradable polymer is polyvinyl alcohol or polyethylene glycol, and the second biodegradable polymer is polybutylene terephthalate; or The first biodegradable polymer is polycaprolactone, and the second biodegradable polymer is polypropylene carbonate.

[0011] According to one embodiment of the present invention, the raw materials for preparing the first base film and / or the second base film further include a pore-forming agent and / or a functional filler. The pore-forming agent comprises at least one of the following: sodium bicarbonate, ammonium bicarbonate, sodium chloride, potassium chloride, sodium sulfate, ammonium sulfate, sodium nitrate, potassium nitrate, calcium chloride, magnesium chloride, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, potassium carbonate, soluble chitosan, sodium alginate, low molecular weight polyethylene glycol, polyvinylpyrrolidone, beeswax, liquid paraffin, urea, oxalic acid, citric acid, and tartaric acid; the amount of the pore-forming agent added is 3% to 60% of the mass of the corresponding layer of biodegradable polymer; and / or The functional filler includes at least one of the following: silica, titanium dioxide, alumina, zinc oxide, montmorillonite, kaolin, hydroxyapatite, iron oxide, zirconium oxide, graphene, calcium carbonate, carbon nanotubes, boron nitride, montmorillonite, water, alginic acid, hyaluronic acid, gum arabic, xanthan gum, gelatin, guar gum, starch-based materials and their derivatives, cellulose and its derivatives, amino acids, lignin and lignin derivatives, vitamins, minerals, probiotics, enzymes, pesticides, fertilizers, gels, and microcapsules; the amount of the functional filler added is 0.1% to 30% of the mass of the corresponding layer of biodegradable polymer.

[0012] According to one embodiment of the present invention, the gas used to activate the surface of the first film by plasma is an inert gas, the operating power is 50~500W, and the activation time is 1~30min.

[0013] According to one embodiment of the present invention, coating the second biodegradable polymer onto the activated surface of the first film under the action of an electric field to form a second base film includes: The first layer of film is placed on a substrate with the first electrical property; The second biodegradable polymer is placed on a film-forming tool with a second electrical property, which is opposite to the first electrical property. The film-forming tool is brought close to the first membrane, and the second biodegradable polymer is coated onto the activated surface of the first membrane under the action of an electric field; The electric field formed by the substrate and the tool has an intensity of 15~30kV.

[0014] According to one embodiment of the present invention, heat treatment of the first base film includes annealing or tempering the first base film to a temperature T1, wherein the temperature T1 satisfies: T m1 -100℃≤T1≤T m1 +100℃, T m1 The melting point of the first biodegradable polymer, and the holding time is 10~120 min; and / or The heat treatment of the two-layer film includes annealing or tempering the two-layer film to a temperature T2, wherein the temperature T2 satisfies: T m2 -100℃≤T2≤T m2 +100℃, T m2 The melting point of the second biodegradable polymer is used, and the holding time is 10~120 min.

[0015] According to one embodiment of the present invention, the stretching is performed by one or more of the following methods: cold stretching and hot stretching, wherein the temperature of cold stretching is 30~100°C, the temperature of hot stretching is 110~300°C, and the stretching ratio is 0.5~20 times; the stretching method is uniaxial stretching or biaxial stretching.

[0016] According to one embodiment of the present invention, the method further includes: After heat-treating the two membranes to obtain a bilayer composite membrane, a variety of different biodegradable polymers are repeatedly melt-plasticized, film-forming, and heat-treated to form a composite membrane with more layers on the bilayer composite membrane, wherein the hydrophilicity of each layer of the composite membrane increases or decreases layer by layer.

[0017] According to another aspect of the present invention, a one-way permeable composite material is provided, the composite material being prepared by the method described in any of the above embodiments.

[0018] Compared with the prior art, the unidirectional permeable composite material and its preparation method provided by the present invention have at least one of the following beneficial effects: (1) The composite material of the present invention achieves unidirectional water permeability through gradient hydrophilic and hydrophobic structure design, and the water flux is increased by more than 30% compared with traditional microporous membranes. At the same time, it has excellent reverse barrier performance and can effectively prevent liquid backflow. (2) The composite material raw material of the present invention adopts a biodegradable composite system, which can be controlled to degrade in the natural environment, thus solving the environmental pollution problem of traditional plastic-based materials; (3) The method of the present invention modifies the interface compatibility of different layers by plasma activation and applying an electric field, thereby enhancing the bonding force of the composite material and achieving longitudinal and transverse tensile strengths of over 20 MPa. This overcomes the defect of insufficient bonding force of multilayer heterogeneous composite films and results in more balanced mechanical properties. (4) The method of the present invention has high production efficiency, can realize continuous roll-to-roll production, and is suitable for large-scale mass production. Attached Figure Description

[0019] Figure 1 A flowchart illustrating a method for preparing a unidirectional permeable bilayer composite material according to an embodiment of the present invention is shown; Figure 2 A flowchart illustrating a method for preparing a unidirectional permeable three-layer or more composite material according to another embodiment of the present invention is shown; Figure 3 SEM images of the unidirectional permeable composite material prepared according to Example 1 of the present invention are shown; Figure 4 The contact angle test diagram of the unidirectional permeable composite material prepared according to Example 1 of the present invention is shown; Figure 5 SEM images of the unidirectional permeable composite material prepared according to Example 2 of the present invention are shown; Figure 6 The contact angle test diagram of the unidirectional permeable composite material prepared according to Example 2 of the present invention is shown; Figure 7 SEM images of the unidirectional permeable composite material prepared according to Example 3 of the present invention are shown. Figure 8 The contact angle test diagram of the unidirectional permeable composite material prepared according to Example 3 of the present invention is shown; Figure 9 SEM images of the unidirectional permeable composite material prepared according to Example 4 of the present invention are shown. Figure 10 The contact angle test diagram of the unidirectional permeable composite material prepared according to Example 4 of the present invention is shown; Figure 11 SEM images of the unidirectional permeable composite material prepared according to Example 5 of the present invention are shown; Figure 12The contact angle test diagram of the unidirectional permeable composite material prepared according to Example 5 of the present invention is shown. Detailed Implementation

[0020] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or server that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0022] In this document, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0023] According to one aspect of the present invention, a method for preparing a unidirectional permeable composite material is provided. For example... Figure 1 As shown, the method generally includes the following steps: Step 110: Melt and plasticize the first biodegradable polymer to prepare the first base film; Step 120: Heat-treat the first base film to obtain the first film layer; Step 130: Activate the surface of the first film using plasma; Step 140: The second biodegradable polymer is melted and plasticized, and coated onto the activated surface of the first membrane under the action of an electric field to form a second base film. The second biodegradable polymer has different hydrophilicity than the first biodegradable polymer. Step 150: Heat-treat the two membranes to obtain a bilayer composite membrane; Step 160: Stretch the composite membrane, shrink it back and shape it to obtain a biodegradable one-way permeable composite material.

[0024] The preparation method of the unidirectional permeable composite material of the present invention utilizes biodegradable materials as the matrix, combines material compatibility characteristics and interface compatibility modification, and achieves unidirectional permeability through gradient hydrophilic and hydrophobic structure design. Through gradient control of the hydrophilicity of multilayer membranes, selective water permeation from one side to the opposite side is achieved, while inhibiting reverse evaporation of water, thus meeting the water collection and retention needs of arid and semi-arid regions.

[0025] The steps of this method are described in detail below by way of example.

[0026] In step 110, the first biodegradable polymer is melt-plasticized and prepared into a first base film. The first biodegradable polymer is selected from polymeric materials that can degrade in the natural environment.

[0027] In some embodiments, the first biodegradable polymer is selected from at least one of the following five groups, wherein: Group G1 includes at least one of the following: polyvinyl alcohol, polyacrylic acid, polyethylene glycol and its derivatives, polyoxyethylene and its copolymers; Group G2 includes at least one of the following: polyglycolic acid, polylactic acid, polylactic acid-glycolic acid copolymer; Group G3 includes at least one of the following: polybutylene succinate, polyhydroxybutyrate, polycaprolactone, polybutylene succinate, polypropylene glycol succinate, polybutylene adipate, and polyhydroxybutyrate-valerate. Group G4 includes at least one of the following: polybutylene sebacic acid, polybutylene terephthalate, and polypropylene terephthalate. Group G5 includes at least one of the following: polypropylene carbonate, polytrimethylene carbonate.

[0028] The hydrophilicity of the above components gradually decreases from group G1 to group G5. The polymer used in the same membrane layer can be a single component, a blend of multiple components within the same group, or a blend of multiple components from different groups.

[0029] Using the above components to prepare composite materials not only enables the materials to be biodegradable, but also allows the polymer degradation products to be converted into organic matter and plant nutrients, actively improving soil structure, enhancing fertility, and making up for the shortcomings of existing materials that ignore soil infertility.

[0030] Because the first biodegradable polymer has a high viscosity after melting and plasticizing, subsequent film preparation operations are difficult. The high-viscosity melt is difficult to level, leading to problems such as uneven film thickness, rough surface, and easy melt cracking. Therefore, it is necessary to appropriately increase the heating temperature during polymer melting and plasticizing, heating the polymer to a temperature above its melting point. However, excessively high temperatures can cause polymer thermal degradation. Therefore, this invention controls the polymer's heating and melting temperature within the range of 10-50°C higher than its melting point.

[0031] Furthermore, to facilitate melt processing into a film, in some embodiments of the present invention, a small amount of high-boiling-point solvent can be added to raw material A. The boiling point of the solvent is higher than the heating and melting temperature of the polymer. Solvent molecules can penetrate between the polymer macromolecular chains, acting as a "lubricant" and effectively weakening the van der Waals forces and entanglement between polymer chains. At the same temperature, this significantly improves the fluidity of the polymer system, making processing easier. In some embodiments, the high-boiling-point solvent may include at least one of the following: N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, cyclohexanone, dimethyl sulfoxide, 1,4-dioxane, toluene, xylene, isopropanol, n-butanol, tert-butanol, and ethylene glycol; the amount added is 1% to 5% of the polymer mass. Too little addition will not improve the fluidity of the polymer system, while too much addition requires subsequent solvent removal, increasing process complexity.

[0032] When polyacrylic acid is used alone to make films, it may be difficult to melt and plasticize. In order to facilitate its processing into films, 1% to 5% of solvent, such as but not limited to N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc., can be added to polyacrylic acid to make it swell and improve its fluidity. It can then be processed into films at room temperature to about 200°C.

[0033] The method for preparing the first base film may include at least one of the following: injection molding, blow molding, extrusion, coating, dip coating, spraying, and spin coating. Blow molding, extrusion, coating, and spraying are further preferred. The base film thickness can be controlled to be 2~50 μm.

[0034] In step 120, the first base film is heat-treated to obtain the first layer film.

[0035] The heat treatment of the first base film includes annealing or tempering the first base film to a temperature T1, wherein the temperature T1 satisfies: T m1-100℃≤T1≤T m1 +100℃, T m1 The melting point of the first biodegradable polymer is used as the reference, and the heat treatment time is 10-120 min. If the first biodegradable polymer is a mixture of multiple components, the temperature of the component with the lowest melting point is used as the reference. Heat treatment can eliminate polymer defects, make the polymer crystals more regular, improve crystallization, increase crystallinity, improve mechanical properties, and improve the uniformity of the film.

[0036] In step 130, the surface of the first film is activated using plasma.

[0037] To improve the bonding strength between the first film layer and subsequent films, interfacial compatibility modification can be performed. This invention employs plasma to activate the surface of the first film layer, exposing more active groups in the polymer material and thus enhancing its activity. In some embodiments, the gas used for plasma activation is an inert gas, such as, but not limited to, argon, with an operating power of 50-300W and an activation time of 1-30 minutes.

[0038] In step 140, the second biodegradable polymer is melt-plasticized and coated onto the activated surface of the first membrane under the action of an electric field to form a second base film. The second biodegradable polymer has a different hydrophilicity than the first biodegradable polymer.

[0039] Because the second biodegradable polymer has a different hydrophilicity than the first biodegradable polymer, a continuous wettability gradient is constructed within the material. Based on capillary effects, water molecules are spontaneously drawn from the more hydrophilic side to the more hydrophobic side, thus achieving unidirectional water transport. Flow in the opposite direction is inhibited because the capillary force is insufficient to drive it.

[0040] The second biodegradable polymer is selected from polymers that can degrade in the natural environment and whose hydrophilicity differs from that of the first biodegradable polymer. In some embodiments, the second biodegradable polymer is selected from at least one of the following five groups and has a different composition from the first biodegradable polymer, wherein: Group G1 includes at least one of the following: polyvinyl alcohol, polyacrylic acid, polyethylene glycol and its derivatives, polyoxyethylene and its copolymers; Group G2 includes at least one of the following: polyglycolic acid, polylactic acid, polylactic acid-glycolic acid copolymer; Group G3 includes at least one of the following: polybutylene succinate, polyhydroxybutyrate, polycaprolactone, polybutylene succinate, polypropylene glycol succinate, polybutylene adipate, and polyhydroxybutyrate-valerate. Group G4 includes at least one of the following: polybutylene sebacic acid, polybutylene terephthalate, and polypropylene terephthalate. Group G5 includes at least one of the following: polypropylene carbonate, polytrimethylene carbonate.

[0041] The polymer used in the same membrane layer can be a single component, a blend of multiple components within the same group, or a blend of multiple components from different groups.

[0042] In some embodiments, the first biodegradable polymer may be a component from groups G1 to G3, a blend of multiple components from the same group, or a blend of multiple components from different groups; the second biodegradable polymer may be a component from groups G4 to G5, a blend of multiple components from the same group, or a blend of multiple components from different groups.

[0043] In some embodiments, the first biodegradable polymer is polyethylene glycol, and the second biodegradable polymer is polylactic acid or polybutylene succinate; or the first biodegradable polymer is polyvinyl alcohol or polyethylene glycol, and the second biodegradable polymer is polybutylene terephthalate; or the first biodegradable polymer is polycaprolactone, and the second biodegradable polymer is polypropylene carbonate.

[0044] In some embodiments, the first biodegradable polymer may be a mixture of polyvinyl alcohol and polyacrylic acid (mass ratio of 10:90), and the corresponding second biodegradable polymer may be polylactic acid. Optionally, the first biodegradable polymer may be polylactic acid, and the corresponding second biodegradable polymer may be a mixture of polypropylene carbonate and polytrimethylene carbonate (mass ratio of 50:50). Optionally, the first biodegradable polymer may be a mixture of polyglycolic acid and polyacrylic acid (mass ratio of 60:40), and the corresponding second biodegradable polymer may be polybutylene succinate. Optionally, the first biodegradable polymer may be a mixture of polybutylene succinate and polycaprolactone (mass ratio of 50:50), and the corresponding second biodegradable polymer may be polybutylene terephthalate. Optionally, the first biodegradable polymer may be a mixture of polyvinyl alcohol, polyethylene glycol, and polyoxyethylene (mass ratio of 10:30:60), and the corresponding second biodegradable polymer may be polytrimethylene carbonate.

[0045] The melt plasticization method of the second biodegradable polymer can be the same as or different from that of the first biodegradable polymer. If its viscosity is high after melting, the melting heating temperature can be increased and / or a small amount of high-boiling-point solvent can be added, similar to the method used for the first biodegradable polymer.

[0046] In some embodiments, coating a second biodegradable polymer onto the activated surface of the first film under the action of an electric field to form a second base film includes: The first film is placed on a substrate with a first electrical charge (e.g., positive charge); The second biodegradable polymer is placed in a film-forming tool (e.g., a negatively charged electrode roller or blade) with a second electrical charge that is opposite to the first electrical charge. The film-forming tool is brought close to the first membrane, and a second biodegradable polymer is coated onto the activated surface of the first membrane.

[0047] Since the substrate on which the first membrane layer is placed and the membrane-forming tool on which the second biodegradable polymer is placed are both charged with opposite charges, the first membrane layer and the second biodegradable polymer, having opposite charges, attract each other, thereby enhancing their bonding force.

[0048] The intensity of the electric field formed by the substrate and the film-forming tool can be controlled to 15~30kV.

[0049] Optionally, in some embodiments, in order to further enhance the interfacial bonding between different layers, the bilayer film may be subjected to rolling pressure.

[0050] In step 150, the two membranes are heat-treated to obtain a bilayer composite membrane.

[0051] Heat treatment of the two-layer film includes annealing or tempering the two-layer film to a temperature T2, wherein the temperature T2 satisfies: T m2 -100℃≤T2≤T m2 +100℃, T m2 The melting point of the second biodegradable polymer is used as the reference, and the heat treatment time is 10-120 min. If the second biodegradable polymer is a mixture of multiple components, the temperature of the component with the lowest melting point is used as the reference. Heat treatment can eliminate polymer defects, make the polymer crystals more regular, improve crystallization, increase crystallinity, improve mechanical properties, and improve the uniformity of the film.

[0052] In step 160, the composite membrane is stretched, retracted, and shaped to obtain a biodegradable one-way permeable composite material.

[0053] Under tension, pre-existing defects in the composite membrane (such as amorphous regions and boundaries between crystalline regions with different orientations) become stress concentration points and are initially pulled apart, forming the initial micropores. Subsequently, the tension causes these micropores to expand and connect along the stretching direction, while the surrounding polymer molecular chains are straightened and oriented, forming microfibers connecting the pores. These micropores form channels for moisture transport.

[0054] Stretching can be performed using one or more of the following methods: cold stretching and hot stretching, wherein the temperature for cold stretching is 30~100℃, the temperature for hot stretching is 110~300℃, and the stretching ratio is 0.5~20 times; the stretching method is uniaxial stretching or biaxial stretching.

[0055] The composite membrane is cooled and shaped under tension. Cooling methods include, but are not limited to, air cooling, water cooling, liquid nitrogen cooling, or natural cooling, resulting in a biodegradable one-way permeable composite material.

[0056] Optionally, in some embodiments of the present invention, in order to optimize and control the pore structure in the material, a pore-forming agent may be added to the raw materials for preparing the first base film and / or the second base film.

[0057] Pore-forming agents are used to form controllable microporous structures within a membrane to facilitate the transport of liquid water. In some embodiments, the pore-forming agent may include at least one of the following: sodium bicarbonate, ammonium bicarbonate, sodium chloride, potassium chloride, sodium sulfate, ammonium sulfate, sodium nitrate, potassium nitrate, calcium chloride, magnesium chloride, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, potassium carbonate, low molecular weight soluble chitosan (molecular weight 300-1500), low molecular weight sodium alginate (molecular weight 1000-5000), low molecular weight polyethylene glycol (molecular weight 1000-5000), polyvinylpyrrolidone, beeswax, liquid paraffin, urea, oxalic acid, citric acid, tartaric acid, etc. The above pore-forming agents may be used alone or in combination, and the types and proportions added to each layer may vary. The amount of pore-forming agent added is 3% to 60% of the mass of the biodegradable polymer in the corresponding layer.

[0058] Optionally, in some embodiments of the present invention, in order to optimize and improve the mechanical properties, temperature control capabilities, pest and disease control and other functions of the material, functional fillers may be added to the raw materials for preparing the first base film and / or the second base film.

[0059] In some embodiments, the functional filler includes at least one of the following: silica, titanium dioxide, alumina, zinc oxide, montmorillonite, kaolin, hydroxyapatite, iron oxide, zirconium oxide, graphene zinc oxide, nano-calcium carbonate, carbon nanotubes, water, alginic acid, hyaluronic acid, gum arabic, xanthan gum, gelatin, guar gum, starch-based materials and their derivatives, cellulose and its derivatives, amino acids, lignin and lignin derivatives, vitamins, minerals, probiotics, enzymes, pesticides, fertilizer gels, and microcapsules. The amount of functional filler added is 0.1% to 30% of the mass of the corresponding layer of biodegradable polymer, and it can be added alone, in combination, or in a gradient distribution.

[0060] In principle, this invention does not impose any particular restrictions on the mixing method of raw materials. Those skilled in the art can select and adjust the method according to actual conditions, product requirements, and quality control factors.

[0061] Optionally, in some embodiments of the present invention, composite materials comprising more layers of film can also be prepared according to the requirements of material strength, heat insulation, etc. Figure 2 A method for preparing a composite material having multiple film layers is shown, the method comprising: Step 210: Melt and plasticize the first biodegradable polymer to prepare the first base film; Step 220: Heat-treat the first base film to obtain the first film layer; Step 230: Activate the surface of the first film using plasma; Step 240: The second biodegradable polymer is melted and plasticized, and coated onto the activated surface of the first membrane under the action of an electric field to form a second base film. The second biodegradable polymer has different hydrophilicity than the first biodegradable polymer. Step 250: Heat-treat the two membranes to obtain a bilayer composite membrane; Step 260: Using different biodegradable polymers as film-forming raw materials, repeat the above surface activation, coating and heat treatment operations to obtain a composite film with more layers; Step 270: Stretch the multi-layered composite membrane, shrink it back and shape it to obtain a biodegradable one-way permeable composite material; In a composite membrane with multiple layers, the hydrophilicity of each layer increases or decreases progressively.

[0062] Based on the design requirements for unidirectional water permeability, different types of biodegradable polymers are sequentially coated onto the surface of the formed membrane layers. Functional fillers and pore-forming agents are selectively added to each layer, and directional stretching is performed as needed, ultimately forming a multi-layer composite structure. This allows for precise control of the unidirectional water permeability of the composite membrane. This multi-layer composite membrane can include a third, fourth, or even more membrane layers. Composite membranes with more layers offer advantages such as excellent mechanical properties, high unidirectional water permeability, and controllable adjustment of unidirectional water permeability.

[0063] In a multilayered composite membrane, the hydrophilicity of each layer increases or decreases progressively. This means that the hydrophilicity of the first, second, third, and so on layers gradually increases or decreases. In other words, the hydrophilicity of the multilayered membrane changes in an ordered gradient along a single direction.

[0064] In one embodiment of the present invention, when the membrane structure comprises two or more layers, the first biodegradable polymer may be polyvinyl alcohol and polyacrylic acid (in a mass ratio of 50:50), the corresponding second biodegradable polymer may be polylactic acid, and the corresponding third biodegradable polymer may be a mixture of polybutylene succinate and polycaprolactone (in a mass ratio of 90:10). Optionally, the first biodegradable polymer may be a mixture of polyethylene glycol and polyacrylic acid (in a mass ratio of 10:90), the corresponding second biodegradable polymer may be polyglycolic acid, the corresponding third biodegradable polymer may be a mixture of polybutylene adipate and polybutylene succinate (in a mass ratio of 50:50), and the corresponding fourth biodegradable polymer may be polypropylene carbonate.

[0065] The present invention also provides a one-way permeable composite material, which is prepared by means of the method described in any of the above embodiments.

[0066] This invention also provides an application of a one-way permeable composite material, which is prepared according to the method described in any of the above embodiments. When using this composite material, the side with stronger hydrophilicity is placed closer to the air, and the side with weaker hydrophilicity is placed closer to the soil. The difference in hydrophilicity between the different membrane layers allows for selective and efficient permeation of water from the air side to the soil side, while suppressing reverse evaporation of soil moisture, thus achieving a one-way permeability effect.

[0067] To provide a clearer and more detailed description of the unidirectional permeable composite material and its preparation method provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0068] In the following examples, the porosity test was performed according to the gas permeation method in accordance with GB / T42269-2022 "Test Method for Pore Size of Separation Membranes - Gas Permeation Method". The contact angle test was performed in accordance with the provisions of GB / T30693-2014 "Determination of Contact Angle of Plastic Films and Sheets" using the seat drop method. The water vapor transmission rate test was performed in accordance with GB / T1037-2021 "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Cup Weight Gain Method and Weight Loss Method".

[0069] Example 1 Polyvinyl alcohol (PVA) is fed into a film-forming system and heated to 30°C above its melting point for melting and plasticization. The raw material is then blow-molded into a first base film. The first base film is heat-treated to 20°C above the PVA melting point for 30 minutes to obtain a first thin film. The first thin film is then transferred to a plasma treatment zone for surface activation using argon gas, with the equipment power controlled at 100W and the treatment time at 30 minutes. Polybutylene terephthalate (PBTB) is fed into the film-forming system and heated to 20°C above its melting point for melting and plasticization. The first thin film is placed on a positively charged substrate, and the molten PBTB is passed through a negatively charged electrode roller. The electric field strength is controlled at 20kV, and the molten PBTB is coated onto the activated surface of the first thin film to form a bilayer film. The bilayer film is then heat-treated to 10°C above the PBTB melting point to obtain a composite film. The composite membrane is thermally stretched at 150°C with a stretch ratio of 4 times, and then shrunken and cooled to set, forming a one-way permeable composite membrane.

[0070] like Figure 3 As shown, the pore sizes of the first membrane layer (Figure (a)) and the second membrane layer (Figure (b)) are 0.2~1.3μm and 0.5~0.9μm, respectively. The unidirectional permeable membrane prepared in this example has a porosity of 51% and a tensile strength of 135MPa. Figure 4 As shown, the contact angles of the first membrane (Fig. (a)) and the second membrane (Fig. (b)) are 56° and 80°, respectively, and the water vapor permeability of the first and second membranes are 437 g / m³, respectively. 2 ·day and 961g / m 2 The ·day indicates good one-way permeability, and the prepared biodegradable polymer degrades completely in the soil within 180 days.

[0071] Example 2 A mixture of polyvinyl alcohol and polyacrylic acid (90:10 by mass) is fed into a film-forming system and heated to 20°C above the melting point of polyvinyl alcohol to melt and plasticize. The raw material is then blow-molded into a first base film. The first base film is heat-treated to 30°C above the melting point of polyvinyl alcohol for 20 minutes to obtain a first thin film. The first thin film is then transferred to a plasma treatment zone for surface activation using argon gas, with the equipment power controlled at 200W and the treatment time at 15 minutes. Polybutylene adipate and polylactic acid (1:1 by mass) are mixed uniformly and fed into the film-forming system, then heated to near the melting point of polylactic acid to melt and plasticize. The first thin film is placed on a positively charged substrate, and the molten and plasticized mixture is passed through a negatively charged electrode roller. The electric field strength is controlled at 20kV, and the molten and plasticized mixture is coated onto the activated surface of the first thin film to form a double-layer film. The double-layer film is then heat-treated to 30°C above the melting point of polybutylene adipate to obtain a composite film. The composite membrane is thermally stretched at 120°C with a stretch ratio of 1, and then shrunken and cooled to set, forming a one-way permeable composite membrane.

[0072] like Figure 5 As shown, the pore sizes of the first membrane layer (Figure (a)) and the second membrane layer (Figure (b)) are 0.3~1.5μm and 0.4~1.1μm, respectively. The unidirectional permeable membrane prepared in this example has a porosity of 57% and a tensile strength of 149MPa. Figure 6 As shown, the contact angles of the first membrane (Fig. (a)) and the second membrane (Fig. (b)) are 76° and 116°, respectively, and the water vapor permeability of the first and second membranes are 294 g / m³, respectively. 2 ·day and 932g / m 2 The ·day indicates good one-way permeability, and the prepared biodegradable polymer degrades completely in the soil within 180 days.

[0073] Example 3 Polyethylene glycol (PEG) is fed into a film-forming system and heated to 10°C above its melting point to melt and plasticize. A coating process is then used to prepare a first base film. The first base film is heated to 20°C below the PEG melting point and heat-treated for 30 minutes to obtain a first thin film. The first thin film is then transported to a plasma treatment zone for surface activation using argon gas, with the equipment power controlled at 300W and the treatment time at 10 minutes. Polypropylene carbonate (PPC) is fed into the film-forming system and heated to 30°C above its melting point to melt and plasticize. The first thin film is placed on a positively charged substrate, and the molten PPC is passed through a negatively charged electrode roller. The electric field strength is controlled at 30kV, and the molten PPC is coated onto the activated surface of the first thin film to form a bilayer film. The bilayer film is then heated to 10°C below the PPC melting point to obtain a composite film. The composite film is cold-stretched at 80°C with a stretch ratio of 10 times, and finally shrunken and cooled to set, forming a one-way permeable composite film.

[0074] like Figure 7 As shown, the pore sizes of the first membrane layer (Figure (a)) and the second membrane layer (Figure (b)) are 0.2~1.0 μm and 0.2~0.7 μm, respectively. The unidirectional permeable membrane prepared in this example has a porosity of 73% and a tensile strength of 131 MPa. Figure 8 As shown, the contact angles of the first membrane (Fig. (a)) and the second membrane (Fig. (b)) are 61° and 88°, respectively, and the water vapor permeability of the first and second membranes are 377 g / m³, respectively. 2 ·day and 1025g / m 2 The ·day indicates good one-way permeability, and the prepared biodegradable polymer degrades completely in the soil within 180 days.

[0075] Example 4 Polyvinyl alcohol, sodium bicarbonate, and silica (mass ratio 80:10:10) are mixed uniformly and fed into a film-forming system. The mixture is heated to 20°C above the melting point of polyvinyl alcohol to melt and plasticize it. The raw material is then used to prepare a first base film using a spray coating process. The first base film is then heat-treated to 20°C above the melting point of polyvinyl alcohol for 20 minutes to obtain a first thin film. The first thin film is then transported to a plasma treatment zone for surface activation using argon gas, with the equipment power controlled at 300W and the treatment time at 15 minutes. Polybutylene adipate, sodium bicarbonate, and silica (mass ratio 85:5:10) are mixed uniformly and fed into the film-forming system, then heated to 20°C above the melting point of polybutylene adipate to melt and plasticize it. A first thin film is placed on a positively charged substrate. Molten, plasticized polybutylene adipate (PBAD) is passed through a negatively charged electrode roller, with the electric field strength controlled at 30 kV. The molten PBAD is then coated onto the activated surface of the first thin film to form a bilayer film. The bilayer film is then heat-treated to 30°C below the melting point of PBAD to obtain a composite film. The composite film is then hot-stretched at 200°C with a stretch ratio of 20 times. Finally, it is shrunken, cooled, and shaped to form a one-way permeable composite film.

[0076] like Figure 9 As shown, the pore sizes of the first membrane layer (Figure (a)) and the second membrane layer (Figure (b)) are 0.5~1.0 μm and 0.7~1.3 μm, respectively. The unidirectional permeable membrane prepared in this example has a porosity of 60% and a tensile strength of 169 MPa. Figure 10 As shown, the contact angles of the first membrane (Fig. (a)) and the second membrane (Fig. (b)) are 63° and 103°, respectively, and the water vapor permeability of the first and second membranes are 494 g / m³, respectively. 2 ·day and 1006g / m 2 The ·day indicates good one-way permeability, and the prepared biodegradable polymer degrades completely in the soil within 180 days.

[0077] Example 5 Polyvinyl alcohol, sodium bicarbonate, protein, and sodium alginate (mass ratio 75:10:10:5) are mixed evenly and fed into a film-forming system. The mixture is heated to 30°C above the melting point of polyvinyl alcohol to melt and plasticize. The raw material is then blow-molded into a first base film. The first base film is then heat-treated to 30°C below the melting point of polyvinyl alcohol for 30 minutes to obtain a first thin film. The first thin film is then transferred to a plasma treatment zone for surface activation using argon gas, with the equipment power controlled at 300W and the treatment time at 10 minutes. Polybutylene adipate, sodium bicarbonate, and silica (mass ratio 75:10:15) are mixed evenly and fed into the film-forming system, then heated to 30°C above the melting point of polybutylene adipate to melt and plasticize. A first thin film is placed on a positively charged substrate. Molten polybutylene adipate (PPA) is passed through a negatively charged electrode roller, and the electric field strength is controlled at 30 kV. The molten PPA is then coated onto the activated surface of the first thin film to form a bilayer film. The bilayer film is then heat-treated to 30°C below the melting point of PPA to obtain a bilayer composite film. The bilayer composite film is then transported to a plasma treatment zone to activate the surface of the second layer film using argon gas. The equipment power is controlled at 300 W, and the treatment time is 10 min. Polypropylene carbonate, soluble chitosan, silica, and gelatin (mass ratio 80:7:10:3) are mixed evenly and transported to a film-forming system, where they are heated to 20°C above the melting point of polypropylene carbonate for melting and plasticization. A double-layer composite membrane is placed on a positively charged substrate. Molten, plasticized polypropylene carbonate is passed through a negatively charged electrode roller, with the electric field strength controlled at 30 kV. The molten, plasticized polypropylene carbonate is then coated onto the activated surface of the second membrane layer to form a triple-layer membrane. The triple-layer membrane is then heat-treated to 20°C above the melting point of polypropylene carbonate to obtain a triple-layer composite membrane. The composite membrane is then hot-stretched at 300°C with a stretch ratio of 18 times. Finally, it is shrunken, cooled, and shaped to form a one-way permeable composite membrane.

[0078] like Figure 11 As shown, the pore sizes of the first membrane layer (Figure (a)) and the third membrane layer (Figure (b)) are 0.5~0.8μm and 0.4~0.7μm, respectively. The unidirectional permeable membrane prepared in this example has a porosity of 55% and a tensile strength of 231MPa. Figure 12 As shown, the contact angles of the first membrane (Fig. (a)) and the third membrane (Fig. (b)) are 33° and 101°, respectively, and the water vapor permeability of the first and third membranes is 345 g / m³. 2 ·day and 1001g / m 2 The ·day indicates good one-way permeability, and the prepared biodegradable polymer degrades completely in the soil within 180 days.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a one-way permeable composite material, characterized in that, Includes the following steps: The first biodegradable polymer is melt-plasticized and prepared into a first base film; The first base film is subjected to heat treatment to obtain the first layer film; The surface of the first film is activated using plasma; The second biodegradable polymer is melted and plasticized, and then coated onto the activated surface of the first membrane under the action of an electric field to form a second base film. The second biodegradable polymer has a different hydrophilicity than the first biodegradable polymer. The two membranes are heat-treated to obtain a double-layer composite membrane. The composite membrane is stretched, retracted, and shaped to obtain a biodegradable one-way permeable composite material.

2. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The first biodegradable polymer and the second biodegradable polymer are each selected from at least one of the following five groups, wherein: Group G1 includes at least one of the following: polyvinyl alcohol, polyacrylic acid, polyethylene glycol and its derivatives, polyoxyethylene and its copolymers; Group G2 includes at least one of the following: polyglycolic acid, polylactic acid, polylactic acid-glycolic acid copolymer; Group G3 includes at least one of the following: polybutylene succinate, polyhydroxybutyrate, polycaprolactone, polybutylene succinate, polypropylene glycol succinate, polybutylene adipate, and polyhydroxybutyrate-valerate. Group G4 includes at least one of the following: polybutylene sebacic acid, polybutylene terephthalate, and polypropylene terephthalate. Group G5 includes at least one of the following: polypropylene carbonate, polytrimethylene carbonate.

3. The method for preparing the unidirectional permeable composite material according to claim 2, characterized in that, The first biodegradable polymer is polyethylene glycol, and the second biodegradable polymer is polylactic acid or polybutylene succinate; or The first biodegradable polymer is polyvinyl alcohol or polyethylene glycol, and the second biodegradable polymer is polybutylene terephthalate; or The first biodegradable polymer is polycaprolactone, and the second biodegradable polymer is polypropylene carbonate.

4. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The raw materials for preparing the first base film and / or the second base film also include pore-forming agents and / or functional fillers. The pore-forming agent comprises at least one of the following: sodium bicarbonate, ammonium bicarbonate, sodium chloride, potassium chloride, sodium sulfate, ammonium sulfate, sodium nitrate, potassium nitrate, calcium chloride, magnesium chloride, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, potassium carbonate, soluble chitosan, sodium alginate, low molecular weight polyethylene glycol, polyvinylpyrrolidone, beeswax, liquid paraffin, urea, oxalic acid, citric acid, and tartaric acid; the amount of the pore-forming agent added is 3% to 60% of the mass of the corresponding layer of biodegradable polymer; and / or The functional filler includes at least one of the following: silica, titanium dioxide, alumina, zinc oxide, montmorillonite, kaolin, hydroxyapatite, iron oxide, zirconium oxide, graphene, calcium carbonate, carbon nanotubes, boron nitride, montmorillonite, water, alginic acid, hyaluronic acid, gum arabic, xanthan gum, gelatin, guar gum, starch-based materials and their derivatives, cellulose and its derivatives, amino acids, lignin and lignin derivatives, vitamins, minerals, probiotics, enzymes, pesticides, fertilizers, gels, and microcapsules; the amount of the functional filler added is 0.1% to 30% of the mass of the corresponding layer of biodegradable polymer.

5. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The gas used to activate the surface of the first film using plasma is an inert gas, the operating power is 50~500W, and the activation time is 1~30min.

6. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The process of coating the second biodegradable polymer onto the activated surface of the first film under the action of an electric field to form a second base film includes: The first layer of film is placed on a substrate with the first electrical property; The second biodegradable polymer is placed on a film-forming tool with a second electrical property, which is opposite to the first electrical property. The film-forming tool is brought close to the first membrane, and the second biodegradable polymer is coated onto the activated surface of the first membrane under the action of an electric field; The electric field formed by the substrate and the tool has an intensity of 15~30kV.

7. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The heat treatment of the first base film includes annealing or tempering the first base film to a temperature T1, wherein the temperature T1 satisfies: T m1 -100℃≤T1≤T m1 +100℃, T m1 The melting point of the first biodegradable polymer, and the holding time is 10~120 min; and / or Heat treatment of the two-layer film includes annealing or tempering the two-layer film to a temperature T2, wherein the temperature T2 satisfies: T m2 -100℃≤T2≤T m2 +100℃, T m2 The melting point of the second biodegradable polymer is used, and the holding time is 10~120 min.

8. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The stretching is performed using one or more of the following methods: cold stretching and hot stretching, wherein the temperature of cold stretching is 30~100℃, the temperature of hot stretching is 110~300℃, and the stretching ratio is 0.5~20 times; the stretching method is uniaxial stretching or biaxial stretching.

9. The method for preparing the unidirectional permeable composite material according to claim 1, characterized in that, The method further includes: After heat-treating the two membranes to obtain a bilayer composite membrane, a variety of different biodegradable polymers are repeatedly melt-plasticized, film-forming, and heat-treated to form a composite membrane with more layers on the bilayer composite membrane, wherein the hydrophilicity of each layer of the composite membrane increases or decreases layer by layer.

10. A unidirectional permeable composite material, characterized in that, The composite material is prepared by the method according to any one of claims 1-9.

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