Multifunctional composite geomembrane and preparation method thereof

Abstract

The invention provides a multifunctional composite geomembrane and a preparation method thereof, and belongs to the field of building materials. The outer layer takes polyethylene as a matrix, and black phosphorus quantum dots and polydimethylsiloxane are combined, so that the material is endowed with excellent waterproofness, photo-thermal responsiveness and environmental stability; cellulose nanocrystals and a metal-organic framework are introduced into the middle layer, the mechanical property, the adsorption capacity and the antibacterial property are enhanced, and meanwhile, through functional modification of 3-mercaptopropyltriethoxysilane, the heavy metal capturing capacity and the antibacterial and self-repairing capacity of silver nanoparticles are achieved; the self-repairing micro-capsule prepared from polyurethane is combined with the photothermal conversion material and the flame retardant, so that rapid repairing and excellent flame retardant property are realized; the elastomer POE is introduced into the inner layer, so that the flexibility, the fracture resistance and the fatigue resistance are improved, and the low-temperature flexibility is realized. The overall design improves the functional diversity and environmental adaptability of the geomembrane, and the geomembrane is suitable for complex engineering environments and extreme climate conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials and relates to a multifunctional composite geomembrane and a preparation method thereof. Background Art

[0002] In modern geotechnical engineering, as an important anti-seepage material, geomembranes are widely used in water conservancy projects, environmental protection projects, landfills, and infrastructure construction. Their main function is to prevent water seepage and soil pollution to ensure the safety and durability of the project. However, traditional geomembranes have shown several significant limitations in practical applications, especially in terms of self-healing ability and antibacterial properties.

[0003] First of all, after suffering physical damage or environmental erosion, traditional geomembranes usually have difficulty effectively restoring their original anti-seepage function. This defect makes the membrane material prone to damage such as cracks and holes under long-term exposure to harsh environments or external forces, which in turn leads to leakage and structural instability. For example, when constructing a reservoir or a dam, the damage to the membrane may not only cause water leakage, affecting the effective utilization of water resources, but also trigger soil erosion, resulting in soil loss and ecological environment damage. However, this kind of damage is often gradual and difficult for engineers to detect during daily inspections, thus leaving potential safety hazards. Therefore, traditional geomembranes lacking self-healing ability cannot meet the high requirements of modern projects for durability and reliability.

[0004] Secondly, traditional geomembranes usually lack effective antibacterial properties, making them extremely vulnerable to damage under microbial attack. In a humid environment, geomembranes often become a breeding ground for microorganisms such as bacteria and fungi, which not only accelerates the degradation of the material but also may cause water pollution. For example, in landfills or sewage treatment facilities, the aging and degradation of the membrane material may lead to the penetration of harmful substances, endangering the surrounding environment and human health. In addition, the growth of microorganisms may also cause a decline in the physical properties of the membrane surface, affecting its original anti-seepage and tensile strength, thus threatening the overall safety of the project. Therefore, geomembranes lacking antibacterial properties are particularly vulnerable in some application scenarios and difficult to cope with long-term environmental challenges. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a multifunctional composite geomembrane and its preparation method. Through a multi-layer structure design, the present invention significantly improves the performance of the composite geomembrane. The outer layer is based on polyethylene, combined with black phosphorus quantum dots and polydimethylsiloxane, endowing the material with excellent waterproofness, photothermal responsiveness, and environmental stability; the middle layer introduces cellulose nanocrystals and metal-organic frameworks to enhance mechanical properties, adsorption capacity, and antibacterial characteristics. At the same time, through functional modification with 3-mercaptopropyltriethoxysilane, heavy metal capture, silver nanoparticle antibacterial, and self-healing capabilities are achieved; self-healing microcapsules prepared by polyurethane emulsification technology are combined with photothermal conversion materials and flame retardants to achieve rapid repair and excellent flame retardant performance; the inner layer introduces elastomer POE to improve flexibility, fracture resistance, and fatigue resistance, and endows low-temperature flexibility. The overall design significantly improves the mechanical properties, functional diversity, and environmental adaptability of the geomembrane, and is suitable for complex engineering environments and extreme climate conditions.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a multifunctional composite geomembrane, and the preparation method of the multifunctional composite geomembrane includes:

[0008] S1: React cellulose nanocrystals with copper nitrate and 2-methylimidazole to obtain metal-organic framework modified cellulose nanocrystal powder;

[0009] S2: Prepare a dispersion of metal-organic framework modified cellulose nanocrystal powder, add 3-mercaptopropyltriethoxysilane and silver nitrate respectively under an inert atmosphere and react, and treat to obtain surface thiolated / silver-doped cellulose-MOF composite powder;

[0010] S3: Disperse polyurethane precursors and curing agents in deionized water, add anhydrous ethanol and polyvinyl alcohol to obtain a microemulsion, add glutaraldehyde solution and react, and treat to obtain self-healing microcapsules;

[0011] S4: Add ammonium dihydrogen phosphate to the self-healing microcapsule dispersion and react, then add ammonium metatungstate and continue to stir and treat to obtain photothermal conversion / flame retardant self-healing microcapsule powder;

[0012] S5: Prepare the outer layer melt, middle layer melt, and inner layer melt respectively, and compound the three layers of melts through a multi-layer coextrusion device to obtain a multifunctional composite geomembrane.

[0013] Specifically, in S1: Disperse cellulose nanocrystals in deionized water, then add copper nitrate and 2-methylimidazole, stir and react, centrifuge, wash, and vacuum dry to obtain metal-organic framework modified cellulose nanocrystal powder;

[0014] S2: Prepare a dispersion of cellulose nanocrystal powder modified with metal-organic framework. Add 3-mercaptopropyltriethoxysilane under an inert atmosphere and continue stirring, then add silver nitrate, react in the dark, centrifuge, wash, and dry to obtain surface thiolated / silver-doped cellulose-MOF composite powder;

[0015] S3: Emulsify and disperse the polyurethane precursor and curing agent in deionized water, then add anhydrous ethanol and polyvinyl alcohol, and stir to obtain a microemulsion; add glutaraldehyde solution and continue crosslinking reaction, centrifuge, wash, and vacuum dry to obtain self-healing microcapsules;

[0016] S4: Prepare a dispersion of self-healing microcapsules, add ammonium dihydrogen phosphate, after reaction add ammonium metatungstate and continue stirring, centrifuge, wash, and dry to obtain photothermal conversion / flame retardant self-healing microcapsule powder;

[0017] S5: Mix and melt polyethylene, polydimethylsiloxane, dispersant, black phosphorus quantum dots, and antioxidant to obtain an outer layer melt; mix and melt polyethylene, surface thiolated / silver-doped cellulose-MOF composite powder, photothermal conversion / flame retardant self-healing microcapsule powder, antioxidant, and dispersant to obtain an intermediate layer melt; mix and melt polyethylene, elastomer POE, and antioxidant to obtain an inner layer melt; compound the outer layer melt, intermediate layer melt, and inner layer melt through a multi-layer co-extrusion device to obtain a multifunctional composite geomembrane.

[0018] As a preferred technical solution of the present invention, in step S1, the mass fraction of the cellulose nanocrystals in deionized water is 1-2 wt.%, for example, it can be 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.7 wt.%, 1.8 wt.%, 1.9 wt.% or 2.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] In some alternative embodiments, the mass ratio of copper nitrate to cellulose nanocrystals is 0.3-0.5:1, for example, it can be 0.30:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.40:1, 0.42:1, 0.44:1, 0.46:1, 0.48:1 or 0.50:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0020] In some alternative embodiments, the molar ratio of 2-methylimidazole to copper nitrate is 2-3:1. For example, it can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0021] In some alternative embodiments, the temperature of the stirring reaction is 30-40 °C. For example, it can be 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C or 40 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0022] In some alternative embodiments, the time of the stirring reaction is 4-6 h. For example, it can be 4.0 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, 5.0 h, 5.2 h, 5.4 h, 5.6 h, 5.8 h or 6.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] As a preferred technical solution of the present invention, in step S2, the solid content of the metal-organic framework modified cellulose nanocrystal powder dispersion is 2-3 wt%. For example, it can be 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt% or 3.0 wt%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] In some alternative embodiments, the mass ratio of 3-mercaptopropyltriethoxysilane to the metal-organic framework modified cellulose nanocrystal powder is 1-2:1. For example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] In some alternative embodiments, the temperature of the continued stirring is 40-50 °C. For example, it can be 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C or 50 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] In some alternative embodiments, the time for continued stirring is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] In some alternative embodiments, the molar ratio of silver nitrate to 3 - mercaptopropyltriethoxysilane is 1 - 1.5:1. For example, it can be 1.00:1, 1.05:1, 1.10:1, 1.15:1, 1.20:1, 1.25:1, 1.30:1, 1.35:1, 1.40:1, 1.45:1, or 1.50:1. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0028] In some alternative embodiments, after adding silver nitrate, the reaction is carried out in the dark for 1 - 2 h. For example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, or 2.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] As a preferred technical solution of the present invention, in step S3, the curing agent is any one or a combination of two of polyethylene glycol or triethanolamine; the mass ratio of the polyurethane precursor to the curing agent is 1:0.8 - 1.2. For example, it can be 1:0.80, 1:0.85, 1:0.90, 1:0.95, 1:1.00, 1:1.05, 1:1.10, 1:1.15, or 1:1.20. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] In some alternative embodiments, the mass fraction of the polyurethane precursor in deionized water is 10 - 15 wt%. For example, it can be 10.0 wt%, 10.5 wt%, 11.0 wt%, 11.5 wt%, 12.0 wt%, 12.5 wt%, 13.0 wt%, 13.5 wt%, 14.0 wt%, 14.5 wt%, or 15.0 wt%. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] In some alternative embodiments, the volume ratio of absolute ethanol to deionized water is 1:2 - 3. For example, it can be 1:2.0, 1:2.2, 1:2.4, 1:2.6, 1:2.8, or 1:3.0. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0032] In some alternative embodiments, the mass fraction of the polyvinyl alcohol in the microemulsion is 0.5-1 wt.%, for example, it can be 0.50 wt.%, 0.60 wt.%, 0.70 wt.%, 0.80 wt.%, 0.90 wt.% or 1.00 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] In some alternative embodiments, the temperature of the stirring is 50-60 °C, for example, it can be 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C or 60 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] In some alternative embodiments, the time of the stirring is 40-60 min, for example, it can be 40 min, 42 min, 44 min, 46 min, 48 min, 50 min, 52 min, 54 min, 56 min, 58 min or 60 min, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] In some alternative embodiments, the mass fraction of the glutaraldehyde solution is 25-30 wt%, for example, it can be 25.0 wt%, 25.5 wt%, 26.0 wt%, 26.5 wt%, 27.0 wt%, 27.5 wt%, 28.0 wt%, 28.5 wt%, 29.0 wt%, 29.5 wt% or 30.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In some alternative embodiments, the mass ratio of the glutaraldehyde to the polyurethane precursor is 0.05-0.15:1, for example, it can be 0.05:1, 0.07:1, 0.09:1, 0.11:1, 0.13:1 or 0.15:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] In some alternative embodiments, the time of the continued crosslinking reaction is 2-3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] As a preferred technical solution of the present invention, in step S4, the solid content of the self-healing microcapsule dispersion is 5-10 wt.%, for example, it can be 5.0 wt.%, 5.5 wt.%, 6.0 wt.%, 6.5 wt.%, 7.0 wt.%, 7.5 wt.%, 8.0 wt.%, 8.5 wt.%, 9.0 wt.%, 9.5 wt.% or 10.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the mass ratio of ammonium dihydrogen phosphate to the self-healing microcapsules is 0.2-0.4:1, for example, it can be 0.20:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1, 0.30:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1 or 0.40:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] In some alternative embodiments, the reaction time is 1-2 h, for example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0041] In some alternative embodiments, the mass ratio of ammonium metatungstate to the self-healing microcapsules is 0.1-0.3:1, for example, it can be 0.10:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.20:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1 or 0.30:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] In some alternative embodiments, the temperature for continued stirring is 40-50 °C, for example, it can be 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C or 50 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] In some alternative embodiments, the time for continued stirring is 2-3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] As a preferred technical solution of the present invention, in step S5, the dispersant is any one or a combination of two of glycerol monostearate or polyethylene wax; the antioxidant is any one or a combination of two of antioxidant 1010 or antioxidant 1076; the feeding amount of polydimethylsiloxane in the outer layer melt is 0.5-1% of the mass of polyethylene, for example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0045] In some alternative embodiments, the feeding amount of the dispersant in the outer layer melt is 0.5-1% of the mass of polyethylene, for example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0046] In some alternative embodiments, the feeding amount of black phosphorus quantum dots in the outer layer melt is 0.5-1% of the mass of polyethylene, for example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0047] In some alternative embodiments, the feeding amount of the antioxidant in the outer layer melt is 0.1-0.5% of the mass of polyethylene, for example, it can be 0.10%, 0.14%, 0.18%, 0.22%, 0.26%, 0.30%, 0.34%, 0.38%, 0.42%, 0.46% or 0.50%, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0048] In some alternative embodiments, the feeding amount of the surface thiolated / silver-doped cellulose-MOF composite powder in the intermediate layer melt is 5-10% of the mass of polyethylene, for example, it can be 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5% or 10.0%, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0049] In some alternative embodiments, the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder in the intermediate layer melt is 5-10% of the mass of the polyethylene. For example, it can be 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5% or 10.0%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0050] In some alternative embodiments, the feeding amount of the antioxidant in the intermediate layer melt is 0.1-0.5% of the mass of the polyethylene. For example, it can be 0.10%, 0.14%, 0.18%, 0.22%, 0.26%, 0.30%, 0.34%, 0.38%, 0.42%, 0.46% or 0.50%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0051] In some alternative embodiments, the feeding amount of the dispersant in the intermediate layer melt is 0.5-1% of the mass of the polyethylene. For example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0052] In some alternative embodiments, the feeding amount of the elastomer POE in the inner layer melt is 5-10% of the mass of the polyethylene. For example, it can be 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5% or 10.0%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0053] In some alternative embodiments, the feeding amount of the antioxidant in the inner layer melt is 0.1-0.5% of the mass of the polyethylene. For example, it can be 0.10%, 0.14%, 0.18%, 0.22%, 0.26%, 0.30%, 0.34%, 0.38%, 0.42%, 0.46% or 0.50%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0054] In some alternative embodiments, the mass ratio of the outer layer melt, the intermediate layer melt, and the inner layer melt is 1:4-5:1. For example, it can be 1:4.0:1, 1:4.2:1, 1:4.4:1, 1:4.6:1, 1:4.8:1, 1:5.0:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0055] In a second aspect, the present invention provides a multifunctional composite geomembrane. The multifunctional composite geomembrane is prepared by multi-layer co-extrusion of an outer layer melt composed of polyethylene, polydimethylsiloxane, a dispersant, black phosphorus quantum dots and an antioxidant, an intermediate layer melt composed of polyethylene, surface thiolated / silver-doped cellulose-MOF composite powder, photo-thermal conversion / flame retardant self-healing microcapsule powder, an antioxidant and a dispersant, and an inner layer melt composed of polyethylene, elastomer POE and an antioxidant.

[0056] The main function of the outer layer in the present invention is to provide excellent waterproof performance. The outer layer matrix material is selected as polyethylene, which itself has good chemical stability, weather resistance and anti-permeation performance, and can effectively block the intrusion of moisture. In addition, to further enhance the functionality of the outer layer, a small amount of black phosphorus quantum dots are implanted. Black phosphorus quantum dots are a new type of two-dimensional material with unique photo-thermal conversion performance and excellent near-infrared absorption ability. By uniformly dispersing black phosphorus quantum dots in the outer layer, not only can the hydrophobicity of the outer layer be maintained, but it also has a responsive photo-thermal conversion function.

[0057] When the outer layer material is irradiated with near-infrared light, the black phosphorus quantum dots can efficiently absorb light energy and convert it into heat energy. This photo-thermal effect can rapidly raise the temperature in a local area of the outer layer, and then conduct the heat to the intermediate layer. After the photo-thermal responsive materials (including photo-thermal conversion / flame retardant self-healing microcapsules) in the intermediate layer are excited, the internal self-healing mechanism is triggered, prompting the repair function of cracks or damaged parts to be quickly activated.

[0058] In addition, the design of the outer layer also takes into account the environmental tolerance of the material in practical applications. Polydimethylsiloxane is also introduced into the outer layer as a modification component. Polydimethylsiloxane not only protects the black phosphorus quantum dots from oxidation through a coating effect, but also further improves the mechanical stability and hydrophobicity of the outer layer, thus ensuring the functional stability of the black phosphorus quantum dots during long-term use. In addition, the introduction of polydimethylsiloxane also optimizes the dispersion of black phosphorus quantum dots, enabling them to be evenly distributed in the outer layer matrix, thereby achieving a synergistic improvement in the waterproof performance and photo-thermal conversion performance of the material.

[0059] The present invention introduces cellulose nanocrystals into the intermediate layer of the composite geomembrane and composites them with metal-organic frameworks to achieve a synergistic improvement in mechanical properties and multifunctionality. Cellulose nanocrystals are high-performance nanomaterials isolated from natural cellulose, which have a highly ordered crystal structure and exhibit excellent mechanical strength and chemical tunability. The surface of cellulose nanocrystals is rich in a large number of hydroxyl groups, which provide active sites for subsequent functionalization modification. Through chemical reactions with metal ions and other functional groups, cellulose nanocrystals can load functional materials and form a stable composite structure.

[0060] The high specific surface area and unique nanostructure of cellulose nanocrystals endow them with the potential to enhance the mechanical properties of composite materials. On the one hand, their rigid crystal structure can significantly improve the tensile strength and modulus of composite materials, enabling the intermediate layer to exhibit excellent mechanical stability when bearing pressure or stress; on the other hand, the high dispersibility and nano-scale effect of cellulose nanocrystals can optimize the structural uniformity of composite materials, reduce local stress concentration, and thus improve the fatigue resistance and durability of the overall material.

[0061] To further expand the functionality of the intermediate layer material, in this invention, cellulose nanocrystals are combined with metal-organic frameworks (MOFs) to form a "core-shell type" or "interface-bonded type" composite structure. MOFs are a class of porous materials assembled by metal ions and organic ligands through coordination, which have a high specific surface area, nano-scale pores, and good chemical tunability, so they show significant performance advantages in the fields of adsorption, catalysis, antibacterial, etc. In this invention, through the solution self-assembly method, Cu 2+ reacts with 2-methylimidazole to generate MOF materials, and the surface hydroxyl groups of cellulose nanocrystals adsorb metal ions through electrostatic or coordination interactions. On this basis, MOF materials gradually grow on the surface of cellulose nanocrystals and form a stable composite structure.

[0062] This modification process not only successfully loads MOF functional materials on the cellulose nanocrystal substrate, but also maintains the mechanical properties and high dispersibility of cellulose nanocrystals themselves. The porous structure and chemical activity of MOFs endow the composite materials with multifunctionality, enabling them to possess excellent performance in adsorption, antibacterial, and catalysis, etc. For example, its nano-pores can effectively adsorb harmful substances or metal ions, improving the environmental adaptability of geomembranes; the antibacterial properties of MOFs provide the intermediate layer with long-term antibacterial ability, inhibiting the attachment and reproduction of microorganisms on the surface of geomembranes. In addition, the surface active sites of MOFs can also combine with other functional molecules, providing more possibilities for the functionalization of subsequent materials.

[0063] The combination of cellulose nanocrystals and MOFs exhibits a significant synergistic effect. Cellulose nanocrystals provide a substrate with high strength and high dispersibility, enabling MOF particles to be loaded on their surface in a uniform and stable manner; while MOFs expand the functional uses of composite materials through their unique porous structure and surface chemistry. This synergistic effect significantly improves the physical properties and chemical activity of the intermediate layer material, enabling it to not only meet the mechanical strength requirements, but also endow the composite geomembrane with diverse functions, meeting the actual needs in complex engineering environments.

[0064] In the present invention, through the introduction of 3-mercaptopropyltriethoxysilane, the surface of cellulose nanocrystals was functionally modified, endowing the composite powder with excellent chemical reactivity and multifunctionality. The molecular structure of 3-mercaptopropyltriethoxysilane contains both hydrolyzable ethoxy groups and highly reactive mercapto groups. In the dispersion, the ethoxy groups undergo hydrolysis under the action of water to form silanols, which then form stable silicon-oxygen bonds with the hydroxyl groups on the surface of cellulose nanocrystals through a condensation reaction. This process not only firmly attaches 3-mercaptopropyltriethoxysilane to the surface of cellulose nanocrystals but also introduces a large number of mercapto groups on the material surface. The introduction of mercapto groups endows the composite powder with remarkable functional characteristics, including efficient adsorption of silver ions, antibacterial properties, and the ability to capture heavy metal ions.

[0065] Mercapto groups have extremely high reactivity and can firmly bind to silver ions through coordination, which provides a key prerequisite for the subsequent formation of silver nanoparticles. After silver ions are captured by mercapto groups and stabilized on the surface of the composite powder, by controlling the reaction under dark conditions, the silver ions are gradually reduced to stable silver nanoparticles. The uniform distribution of silver nanoparticles not only significantly improves the antibacterial performance of the composite powder but also endows the material with unique optical properties. Silver nanoparticles release Ag + to interfere with the physiological processes of microorganisms, destroy the functions of their proteins and genetic materials, thus achieving an efficient bactericidal effect. In addition, silver nanoparticles also endow the material with potential application value in the fields of photothermal conversion and photocatalysis, providing new possibilities for the multifunctionality of composite geomembranes.

[0066] The functions of mercapto groups are not limited to the stabilization of silver ions and antibacterial properties. Mercapto groups also have strong chemical affinity for heavy metal ions (such as Hg 2+ , Pb 2+ , Cd 2+ ) and can efficiently capture these ions through coordination. This property enables the composite powder to show broad application prospects in the fields of environmental remediation and water treatment. In addition, mercapto groups themselves also have antibacterial ability, which further enhances the antibacterial performance of the material by chemically reacting with the proteins on the surface of microorganisms and destroying the metabolic functions of microorganisms. The synergistic effect of the multifunctionality of mercapto groups and silver nanoparticles endows the composite powder with excellent performance in antibacterial and functional applications.

[0067] In addition, during the actual use of the material, the chemical activity of the mercapto group also extends to its oxidation process. When the mercapto group is oxidized in the external environment, disulfide bonds are formed. This dynamic chemical process endows the composite material with certain self-healing ability. Disulfide bonds can achieve the repair of the microstructure of the material through cleavage and recombination, thereby extending the service life of the material and improving its stability. This self-healing mechanism is particularly important in the multifunctional applications of composite geomembranes, especially in environments that require long-term use and are vulnerable to mechanical damage.

[0068] The present invention prepares self-healing microcapsules through the emulsification process of polyurethane, and introduces photothermal conversion and flame retardant properties, providing excellent self-healing ability and environmental adaptability for composite geomembranes. Polyurethane is a typical polymer material, which exhibits excellent self-healing performance due to its unique microphase separation structure. Its molecular structure has both flexible segments and rigid segments. After external force or damage occurs, the flexible segments can fill the damaged area through the migration of molecular chains, while the rigid segments restore the overall structural strength of the material by reforming hydrogen bonds or cross-linking bonds. This self-healing mechanism depends on the dynamic molecular behavior of polyurethane, making it an ideal self-healing material.

[0069] In the specific preparation process, the polyurethane precursor and the curing agent are dispersed in the aqueous phase system through emulsification to form tiny droplets, and these droplets are transformed into stable microcapsule structures during the subsequent curing reaction. In order to further enhance the mechanical properties and chemical stability of the microcapsules, glutaraldehyde is used as a cross-linking agent. The aldehyde groups in the glutaraldehyde molecule can undergo condensation reactions with the hydroxyl or amino groups on the polyurethane molecular chain to form a stable cross-linked structure. This cross-linking process significantly improves the shear resistance and high-temperature resistance of the microcapsules, enabling them to maintain structural stability under complex environmental conditions and effectively avoiding the destruction of the microcapsules under high temperature or mechanical stress.

[0070] The introduction of microcapsules localizes the self-healing function of polyurethane, avoiding the loss of the overall performance of the material. Traditional self-healing materials often need to introduce a large amount of self-healing components throughout the material system, which may lead to a decrease in the mechanical properties of the material. However, the polyurethane microcapsules prepared through the emulsification process can locally release the repair components when damage occurs, and only achieve the repair function for the damaged area, thereby ensuring that the overall performance of the material is not affected.

[0071] To further enhance the functionality of the self-healing microcapsules, the present invention introduces photothermal conversion and flame retardancy properties through modification. During the modification process, ammonium dihydrogen phosphate is used as the flame retardant. Ammonium dihydrogen phosphate can decompose to generate phosphoric acid under high-temperature conditions, and the phosphoric acid forms a dense protective film on the material surface, effectively isolating oxygen and heat sources, thereby significantly reducing the flammability of the material. In addition, ammonium metatungstate is introduced as the photothermal conversion material, and its unique inorganic semiconductor properties enable it to absorb light energy and efficiently convert it into heat energy. When the material is irradiated with light, ammonium metatungstate achieves rapid local heating, and this thermal effect can trigger the release of the repair components from the polyurethane microcapsules, further accelerating the self-healing process of the material.

[0072] Through the combination of photothermal conversion and flame retardancy properties, the self-healing microcapsules of the present invention exhibit rapid response characteristics under external stimuli and can respond efficiently to environmental conditions such as light irradiation, local high temperature, or mechanical damage. The photothermal effect can not only activate the self-healing mechanism of the material but also further enhance its adaptability in special scenarios, such as engineering environments exposed to high temperature or strong light. At the same time, the introduction of flame retardancy significantly improves the safety of the material, making it exhibit excellent protective capabilities under fire or high-temperature conditions. The synergistic effect of the self-healing function and the flame retardancy function broadens the application scenarios of the composite geomembrane, making it have important application values in the fields of building protection, environmental remediation, and high-risk engineering.

[0073] An elastomer POE is introduced in the inner layer design of the present invention to improve the flexibility of the geomembrane, enhance the adaptability and durability of the overall material, and extend its service life. POE is a polymer material with both elastic and plastic characteristics, which is copolymerized from a polyethylene matrix and an elastomer. The unique flexible molecular chain segments in its molecular structure endow it with excellent flexibility and elastic recovery performance. By introducing POE into the inner layer of the geomembrane, not only the overall flexibility of the membrane body is effectively improved, but also the material is endowed with stronger fracture resistance and anti-mechanical fatigue performance.

[0074] In practical applications, geomembranes often need to withstand complex external stresses, such as tensile and compressive stresses caused by soil settlement and shear forces generated by geological movements. If the material lacks sufficient flexibility, cracks may occur in the stress concentration areas, leading to the destruction of the overall structure. The addition of the elastomer POE enables the inner layer to adapt to large deformations, absorb stresses through the migration and rearrangement of molecular chain segments under external forces, avoid the occurrence of stress concentration effects, and thus effectively inhibit the generation and expansion of cracks.

[0075] In addition, the elastic properties of the elastomer POE also provide the geomembrane with excellent fatigue resistance. Geomembranes may experience repeated mechanical loads during long-term use, such as periodic deformations caused by water flow, soil pressure changes, or temperature fluctuations. Ordinary polyethylene materials may gradually lose strength due to fatigue fracture of molecular chains under such conditions, while the introduction of the elastomer POE significantly reduces the accumulation of fatigue damage through its elastic recovery ability, improving the service life of the geomembrane in long-term complex environments.

[0076] More importantly, the elastomer POE also has good low-temperature flexibility, which enables the geomembrane of the present invention to maintain its mechanical properties and toughness under cold climate conditions. Traditional geomembrane materials tend to lose flexibility due to embrittlement of the material in low-temperature environments, resulting in cracking or failure, while the low-temperature performance of the elastomer POE significantly improves this problem, enabling the geomembrane to be applied in a wider range of regions and environments.

[0077] There is also a synergistic enhancement effect in the present invention. The black phosphorus quantum dots dispersed in the outer layer endow the material with excellent photothermal conversion ability. When near-infrared light irradiates the outer layer, the black phosphorus quantum dots efficiently absorb light energy and convert it into heat energy. This heat energy is transferred to the middle layer through heat conduction, triggering the release mechanism of the photothermal-responsive self-healing microcapsules in the middle layer. The polyurethane in the microcapsules releases the repair components to fill the cracks or damaged areas through local heating, thus quickly activating the self-healing function. The combination of photothermal conversion and self-healing functions enables the material to respond quickly under external stimuli (such as light irradiation, mechanical damage, etc.), forming an efficient self-healing system.

[0078] Ammonium metatungstate in the middle layer, as a photothermal conversion material, can not only generate local high temperatures under light irradiation to trigger self-healing, but also further enhance the flame retardancy of the material in high-temperature environments. The thermal decomposition of ammonium metatungstate generates oxides with flame retardant functions, while ammonium dihydrogen phosphate decomposes to generate phosphoric acid, which can form a dense protective film on the surface of the material, isolating oxygen and heat sources. The synergistic effect of the two significantly inhibits the combustion behavior of the material in case of fire or high-temperature environments, while achieving a faster local self-healing function through the photothermal effect.

[0079] The cellulose nanocrystals in the middle layer are modified with 3-mercaptopropyltriethoxysilane to introduce mercapto groups. These mercapto groups can not only capture heavy metal ions but also have antibacterial properties. Silver ions are gradually reduced to silver nanoparticles under the stabilizing action of the mercapto groups, forming a functional surface with broad-spectrum antibacterial properties. The silver nanoparticles release Ag +The physiological processes of microorganisms are interfered, and at the same time, the mercapto group destroys their metabolic functions by chemically reacting with the proteins on the surface of microorganisms, thus significantly enhancing the antibacterial performance of the material. The ability of the mercapto group to capture heavy metal ions further enhances the adsorption and treatment capabilities of the material for environmental pollution factors. The synergy of the antibacterial and heavy metal capture functions enables the material to exhibit broader application prospects in the fields of environmental remediation and water treatment.

[0080] A good bonding effect is achieved between the inner elastomer POE and the cellulose nanocrystals in the middle layer through interface modification. The flexible chain segments of the elastomer POE can form certain physical or chemical forces with the hydroxyl groups on the surface of the cellulose nanocrystals in the middle layer, thereby enhancing the interfacial bonding force between the two and avoiding the occurrence of delamination or interfacial cracking. This interfacial synergy not only optimizes the overall interlayer mechanical properties of the material but also improves the long-term stability of the multi-layer structure.

[0081] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0082] The outer layer of the present invention is based on polyethylene, combined with black phosphorus quantum dots and polydimethylsiloxane, endowing the material with excellent waterproofness, photothermal conversion and environmental stability. The black phosphorus quantum dots achieve the photothermal response function and can stimulate self-healing of the middle layer, while polydimethylsiloxane improves the dispersion and long-term stability of the quantum dots, ensuring the synergistic effect of waterproof and photothermal properties;

[0083] The present invention introduces cellulose nanocrystals into the middle layer of the composite geomembrane and combines them with metal-organic frameworks to form a high-strength and multifunctional composite structure. The cellulose nanocrystals provide modified active sites through their high mechanical strength and surface hydroxyl groups, and synergistically improve the mechanical properties, adsorption and antibacterial properties of the material with the porous structure and chemical activity of the MOF. In addition, 3-mercaptopropyltriethoxysilane is introduced to functionalize the cellulose nanocrystals, endowing the material with functions such as efficient capture of heavy metal ions and generation of silver nanoparticles for antibacterial, etc. At the same time, the dynamic oxidation of the mercapto group to form disulfide bonds provides a certain self-healing ability for the material. These designs significantly enhance the physical properties and chemical functions of the middle layer, enabling the material to have excellent antibacterial properties, environmental adaptability and long-term stability;

[0084] The present invention prepares self-healing microcapsules through a polyurethane emulsification process and introduces the photothermal conversion material ammonium metatungstate and the flame retardant ammonium dihydrogen phosphate, endowing the composite geomembrane with excellent self-healing ability and flame retardant properties. The polyurethane microcapsules can locally release the repair components under the stimulation of photothermal effect or high temperature to achieve rapid repair, while the protective film generated by the flame retardant significantly improves the safety of the material;

[0085] In the present invention, elastomer POE is introduced into the inner layer of the geomembrane, significantly enhancing the flexibility, fracture resistance and fatigue resistance of the material, thereby enhancing its ability to adapt to complex stress environments and extending its service life. With its flexible molecular chain segments, POE can absorb external forces such as tension, extrusion and shear, preventing stress concentration from causing cracks. At the same time, its elastic recovery performance improves the long-term fatigue resistance of the material. In addition, the low-temperature flexibility of POE enables the geomembrane to still maintain excellent performance under cold climate conditions, broadening its application range and environmental adaptability. Description of the Drawings

[0086] Figure 1 It is a flowchart of the preparation method of the multifunctional composite geomembrane provided in Embodiment 1 of the present invention. Detailed Embodiments

[0087] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific embodiments of the present invention for explaining the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0088] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products without further purification or treatment.

[0089] Embodiment 1

[0090] This embodiment provides a multifunctional composite geomembrane and its preparation method. The preparation method specifically includes the following steps:

[0091] S1: React cellulose nanocrystals with copper nitrate and 2-methylimidazole to obtain metal-organic framework modified cellulose nanocrystal powder;

[0092] Specifically, in S1: Dispersed cellulose nanocrystals in deionized water at a mass fraction of 1 wt%, and then added copper nitrate and 2-methylimidazole. The mass ratio of copper nitrate to cellulose nanocrystals is 0.4:1, and the molar ratio of 2-methylimidazole to copper nitrate is 2.3:1. Stir and react at 30 °C for 4 h, centrifuge, wash, and vacuum dry to obtain metal-organic framework modified cellulose nanocrystal powder;

[0093] S2: Prepare a dispersion of cellulose nanocrystal powder modified with metal-organic framework. Under an inert atmosphere, add 3-mercaptopropyltriethoxysilane and silver nitrate respectively and react to obtain surface thiolated / silver-doped cellulose-MOF composite powder;

[0094] Specifically, S2: Prepare a dispersion of cellulose nanocrystal powder modified with metal-organic framework with a solid content of 2 wt%. Under an inert atmosphere, add 3-mercaptopropyltriethoxysilane with a mass ratio of 1.6:1 to the cellulose nanocrystal powder modified with metal-organic framework and continue stirring at 40 °C for 2 h. Then add silver nitrate, and the molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane is 1.4:1. React in the dark for 1 h, and then centrifuge, wash, and dry to obtain surface thiolated / silver-doped cellulose-MOF composite powder;

[0095] S3: Disperse the polyurethane precursor and the curing agent in deionized water, add absolute ethanol and polyvinyl alcohol to obtain a microemulsion, and add glutaraldehyde solution to react and process to obtain self-healing microcapsules;

[0096] Specifically, S3: Emulsify and disperse the polyurethane precursor and polyethylene glycol in deionized water, where the mass fraction of the polyurethane precursor in deionized water is 10 wt%, and the mass ratio of the polyurethane precursor to polyethylene glycol is 1:1.0. Then dropwise add absolute ethanol and polyvinyl alcohol with a volume ratio of 1:2 to deionized water, and stir at 50 °C for 40 min to obtain a microemulsion, where the mass fraction of polyvinyl alcohol in the microemulsion is 0.7 wt%. Add a glutaraldehyde solution with a mass fraction of 25 wt%, where the mass ratio of glutaraldehyde to the polyurethane precursor is 0.1:1, and continue the cross-linking reaction for 2 h. Then centrifuge, wash, and vacuum dry to obtain self-healing microcapsules;

[0097] S4: Add ammonium dihydrogen phosphate to the self-healing microcapsule dispersion to react, and then add ammonium metatungstate and continue stirring and processing to obtain photothermal conversion / flame retardant self-healing microcapsule powder;

[0098] Specifically, S4: Prepare a self-healing microcapsule dispersion with a solid content of 5 wt.%. Add ammonium dihydrogen phosphate, where the mass ratio of ammonium dihydrogen phosphate to the self-healing microcapsules is 0.32:1. After reacting for 1 h, add ammonium metatungstate, where the mass ratio of ammonium metatungstate to the self-healing microcapsules is 0.2:1. Continue stirring at 40 °C for 2 h, and then centrifuge, wash, and dry to obtain photothermal conversion / flame retardant self-healing microcapsule powder;

[0099] S5: Prepare the outer layer melt, the middle layer melt, and the inner layer melt respectively, and compound the three layers of melts through a multi-layer coextrusion device to obtain a multi-functional composite geomembrane.

[0100] Specifically, S5: Mix and melt polyethylene, polydimethylsiloxane with a feed amount of 0.5% of the mass of polyethylene, glycerol monostearate with a feed amount of 0.75% of the mass of polyethylene, black phosphorus quantum dots with a feed amount of 1% of the mass of polyethylene, and antioxidant 1010 with a feed amount of 0.3% of the mass of polyethylene to obtain an outer layer melt; Mix and melt polyethylene, surface thiolated / silver-doped cellulose-MOF composite powder, photothermal conversion / flame retardant self-healing microcapsule powder, antioxidant 1010, and glycerol monostearate to obtain an intermediate layer melt, wherein the feed amount of the surface thiolated / silver-doped cellulose-MOF composite powder in the intermediate layer melt is 8% of the mass of polyethylene, the feed amount of the photothermal conversion / flame retardant self-healing microcapsule powder is 8% of the mass of polyethylene, the feed amount of antioxidant 1010 is 0.5% of the mass of polyethylene, and the feed amount of glycerol monostearate is 0.5% of the mass of polyethylene; Mix and melt polyethylene, elastomer POE, and antioxidant 1010 to obtain an inner layer melt, wherein the feed amount of elastomer POE in the inner layer melt is 5% of the mass of polyethylene and the feed amount of antioxidant 1010 is 0.2% of the mass of polyethylene; Compound the outer layer melt, the intermediate layer melt, and the inner layer melt in a mass ratio of 1:4.5:1 through a multi-layer co-extrusion device to obtain a multi-functional composite geomembrane.

[0101] Example 2

[0102] This example provides a multi-functional composite geomembrane and a preparation method thereof. The preparation method specifically includes the following steps:

[0103] S1: React cellulose nanocrystals with copper nitrate and 2-methylimidazole to obtain a metal-organic framework modified cellulose nanocrystal powder.

[0104] Specifically, S1: Disperse cellulose nanocrystals in deionized water at a mass fraction of 1.5 wt%, and then add copper nitrate and 2-methylimidazole. The mass ratio of copper nitrate to cellulose nanocrystals is 0.45:1, and the molar ratio of 2-methylimidazole to copper nitrate is 3:1. Stir and react at 35 °C for 5 h, centrifuge, wash, and vacuum dry to obtain a metal-organic framework modified cellulose nanocrystal powder.

[0105] S2: Prepare a dispersion of the metal-organic framework modified cellulose nanocrystal powder, add 3-mercaptopropyltriethoxysilane and silver nitrate respectively under an inert atmosphere and react, and treat to obtain a surface thiolated / silver-doped cellulose-MOF composite powder.

[0106] Specifically, S2: Configure a metal-organic framework modified cellulose nanocrystal powder dispersion with a solid content of 2.5 wt%, add 3-mercaptopropyltriethoxysilane with a mass ratio of 1.2:1 to the metal-organic framework modified cellulose nanocrystal powder under an inert atmosphere, and continue stirring at 44 °C for 2.6 h. Then add silver nitrate, with a molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane of 1.2:1, react in the dark for 1.5 h, and obtain surface thiolated / silver-doped cellulose-MOF composite powder through centrifugation, washing, and drying;

[0107] S3: Disperse the polyurethane precursor and the curing agent in deionized water, add absolute ethanol and polyvinyl alcohol to obtain a microemulsion, add glutaraldehyde solution for reaction and treatment to obtain self-healing microcapsules;

[0108] Specifically, S3: Emulsify and disperse the polyurethane precursor and triethanolamine in deionized water, where the mass fraction of the polyurethane precursor in deionized water is 13 wt%, and the mass ratio of the polyurethane precursor to triethanolamine is 1:1.2. Then dropwise add absolute ethanol and polyvinyl alcohol with a volume ratio of 1:2.3 to deionized water, stir at 55 °C for 50 min to obtain a microemulsion, where the mass fraction of polyvinyl alcohol in the microemulsion is 0.8 wt%; add a glutaraldehyde solution with a mass fraction of 28 wt%, where the mass ratio of glutaraldehyde to the polyurethane precursor is 0.15:1, continue the crosslinking reaction for 2.5 h, and obtain self-healing microcapsules through centrifugation, washing, and vacuum drying;

[0109] S4: Add ammonium dihydrogen phosphate to the self-healing microcapsule dispersion for reaction, then add ammonium metatungstate and continue stirring and treatment to obtain a photothermal conversion / flame retardant self-healing microcapsule powder;

[0110] Specifically, S4: Configure a self-healing microcapsule dispersion with a solid content of 8 wt.%, add ammonium dihydrogen phosphate, where the mass ratio of ammonium dihydrogen phosphate to the self-healing microcapsules is 0.37:1, react for 1.5 h, then add ammonium metatungstate, where the mass ratio of ammonium metatungstate to the self-healing microcapsules is 0.23:1, continue stirring at 45 °C for 2.7 h, and obtain a photothermal conversion / flame retardant self-healing microcapsule powder through centrifugation, washing, and drying;

[0111] S5: Prepare the outer layer melt, the middle layer melt, and the inner layer melt respectively, and compound the three layers of melts through a multi-layer co-extrusion device to obtain a multi-functional composite geomembrane.

[0112] Specifically, S5: Mix and melt polyethylene, polydimethylsiloxane with a feeding amount of 0.7% of the mass of polyethylene, polyethylene wax with a feeding amount of 0.8% of the mass of polyethylene, black phosphorus quantum dots with a feeding amount of 0.5% of the mass of polyethylene, and antioxidant 1076 with a feeding amount of 0.1% of the mass of polyethylene to obtain an outer layer melt; mix and melt polyethylene, surface mercapto-functionalized / silver-doped cellulose-MOF composite powder, photothermal conversion / flame retardant self-healing microcapsule powder, antioxidant 1076, and polyethylene wax to obtain an intermediate layer melt, wherein the feeding amount of the surface mercapto-functionalized / silver-doped cellulose-MOF composite powder in the intermediate layer melt is 5% of the mass of polyethylene, the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder is 5% of the mass of polyethylene, the feeding amount of antioxidant 1076 is 0.1% of the mass of polyethylene, and the feeding amount of polyethylene wax is 0.7% of the mass of polyethylene; mix and melt polyethylene, elastomer POE, and antioxidant 1076 to obtain an inner layer melt, wherein the feeding amount of elastomer POE in the inner layer melt is 8% of the mass of polyethylene and the feeding amount of antioxidant 1076 is 0.3% of the mass of polyethylene; compound the outer layer melt, the intermediate layer melt, and the inner layer melt in a mass ratio of 1:4.4:1 through a multi-layer co-extrusion device to obtain a multifunctional composite geomembrane.

[0113] Example 3

[0114] This example provides a multifunctional composite geomembrane and a preparation method thereof. The preparation method specifically includes the following steps:

[0115] S1: React cellulose nanocrystals with copper nitrate and 2-methylimidazole to obtain a metal-organic framework-modified cellulose nanocrystal powder.

[0116] Specifically, S1: Disperse cellulose nanocrystals in deionized water at a mass fraction of 1.8 wt%, and then add copper nitrate and 2-methylimidazole. The mass ratio of copper nitrate to cellulose nanocrystals is 0.3:1, and the molar ratio of 2-methylimidazole to copper nitrate is 2:1. Stir and react at 39 °C for 5.5 h, centrifuge, wash, and vacuum dry to obtain a metal-organic framework-modified cellulose nanocrystal powder.

[0117] S2: Prepare a dispersion of the metal-organic framework-modified cellulose nanocrystal powder, add 3-mercaptopropyltriethoxysilane and silver nitrate respectively under an inert atmosphere and react, and treat to obtain a surface mercapto-functionalized / silver-doped cellulose-MOF composite powder.

[0118] Specifically, S2: Prepare a metal-organic framework modified cellulose nanocrystal powder dispersion with a solid content of 2.8 wt%, add 3-mercaptopropyltriethoxysilane with a mass ratio of 1:1 to the metal-organic framework modified cellulose nanocrystal powder under an inert atmosphere, and continue stirring at 47 °C for 2.3 h. Then add silver nitrate, with a molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane of 1:1, react in the dark for 1.7 h, and obtain surface thiolated / silver-doped cellulose-MOF composite powder through centrifugation, washing, and drying;

[0119] S3: Disperse the polyurethane precursor and the curing agent in deionized water, add anhydrous ethanol and polyvinyl alcohol to obtain a microemulsion, add glutaraldehyde solution for reaction and treatment to obtain self-healing microcapsules;

[0120] Specifically, S3: Emulsify and disperse the polyurethane precursor and polyethylene glycol in deionized water, where the mass fraction of the polyurethane precursor in deionized water is 12 wt%, and the mass ratio of the polyurethane precursor to polyethylene glycol is 1:0.8. Then add anhydrous ethanol and polyvinyl alcohol with a volume ratio of 1:3 to the deionized water, and stir at 58 °C for 52 min to obtain a microemulsion, where the mass fraction of polyvinyl alcohol in the microemulsion is 0.5 wt%; add a glutaraldehyde solution with a mass fraction of 27 wt%, where the mass ratio of glutaraldehyde to the polyurethane precursor is 0.05:1, continue the crosslinking reaction for 2.8 h, and obtain self-healing microcapsules through centrifugation, washing, and vacuum drying;

[0121] S4: Add ammonium dihydrogen phosphate to the self-healing microcapsule dispersion for reaction, then add ammonium metatungstate and continue stirring and treatment to obtain a photothermal conversion / flame retardant self-healing microcapsule powder;

[0122] Specifically, S4: Prepare a self-healing microcapsule dispersion with a solid content of 7.5 wt.%, add ammonium dihydrogen phosphate, where the mass ratio of ammonium dihydrogen phosphate to the self-healing microcapsules is 0.2:1, react for 1.6 h, then add ammonium metatungstate, where the mass ratio of ammonium metatungstate to the self-healing microcapsules is 0.1:1, continue stirring at 47 °C for 2.2 h, and obtain a photothermal conversion / flame retardant self-healing microcapsule powder through centrifugation, washing, and drying;

[0123] S5: Prepare the outer layer melt, the middle layer melt, and the inner layer melt respectively, and compound the three layers of melts through a multi-layer coextrusion device to obtain a multi-functional composite geomembrane.

[0124] Specifically, S5: Mix and melt polyethylene, polydimethylsiloxane with a feeding amount of 0.8% of the mass of polyethylene, glycerol monostearate with a feeding amount of 0.5% of the mass of polyethylene, black phosphorus quantum dots with a feeding amount of 0.7% of the mass of polyethylene, and antioxidant 1076 with a feeding amount of 0.4% of the mass of polyethylene to obtain an outer layer melt; mix and melt polyethylene, surface thiolated / silver-doped cellulose-MOF composite powder, photothermal conversion / flame retardant self-healing microcapsule powder, antioxidant 1076, and glycerol monostearate to obtain an intermediate layer melt, wherein the feeding amount of the surface thiolated / silver-doped cellulose-MOF composite powder in the intermediate layer melt is 9% of the mass of polyethylene, the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder is 10% of the mass of polyethylene, the feeding amount of antioxidant 1076 is 0.3% of the mass of polyethylene, and the feeding amount of glycerol monostearate is 0.8% of the mass of polyethylene; mix and melt polyethylene, elastomer POE, and antioxidant 1076 to obtain an inner layer melt, wherein the feeding amount of elastomer POE in the inner layer melt is 6% of the mass of polyethylene and the feeding amount of antioxidant 1076 is 0.4% of the mass of polyethylene; compound the outer layer melt, the intermediate layer melt, and the inner layer melt in a mass ratio of 1:4.8:1 through a multi-layer co-extrusion device to obtain a multifunctional composite geomembrane.

[0125] Example 4

[0126] This example provides a multifunctional composite geomembrane and a preparation method thereof. The preparation method specifically includes the following steps:

[0127] S1: React cellulose nanocrystals with copper nitrate and 2-methylimidazole to obtain metal-organic framework modified cellulose nanocrystal powder.

[0128] Specifically, S1: Disperse cellulose nanocrystals in deionized water at a mass fraction of 2 wt%, and then add copper nitrate and 2-methylimidazole. The mass ratio of copper nitrate to cellulose nanocrystals is 0.5:1, and the molar ratio of 2-methylimidazole to copper nitrate is 2.6:1. Stir and react at 40 °C for 6 h, centrifuge, wash, and vacuum dry to obtain metal-organic framework modified cellulose nanocrystal powder.

[0129] S2: Prepare a dispersion of metal-organic framework modified cellulose nanocrystal powder, add 3-mercaptopropyltriethoxysilane and silver nitrate respectively under an inert atmosphere and react, and treat to obtain surface thiolated / silver-doped cellulose-MOF composite powder.

[0130] Specifically, S2: Configure a metal-organic framework modified cellulose nanocrystal powder dispersion with a solid content of 3 wt%. Add 3-mercaptopropyltriethoxysilane with a mass ratio of 2:1 to the metal-organic framework modified cellulose nanocrystal powder under an inert atmosphere and continue stirring at 50 °C for 3 h. Then add silver nitrate, with a molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane of 1.5:1, and react in the dark for 2 h. Centrifuge, wash, and dry to obtain a surface thiolated / silver-doped cellulose-MOF composite powder;

[0131] S3: Disperse the polyurethane precursor and the curing agent in deionized water, add anhydrous ethanol and polyvinyl alcohol to obtain a microemulsion, and add glutaraldehyde solution for reaction and treatment to obtain self-healing microcapsules;

[0132] Specifically, S3: Emulsify and disperse the polyurethane precursor and triethanolamine in deionized water, where the mass fraction of the polyurethane precursor in deionized water is 15 wt%, and the mass ratio of the polyurethane precursor to triethanolamine is 1:1.1. Then dropwise add anhydrous ethanol and polyvinyl alcohol with a volume ratio of 1:2.6 to deionized water, and stir at 60 °C for 60 min to obtain a microemulsion, where the mass fraction of polyvinyl alcohol in the microemulsion is 1 wt%; add a 30 wt% glutaraldehyde solution, where the mass ratio of glutaraldehyde to the polyurethane precursor is 0.12:1, continue the cross-linking reaction for 3 h, centrifuge, wash, and vacuum dry to obtain self-healing microcapsules;

[0133] S4: Add ammonium dihydrogen phosphate to the self-healing microcapsule dispersion for reaction, then add ammonium metatungstate and continue stirring and treatment to obtain a photothermal conversion / flame retardant self-healing microcapsule powder;

[0134] Specifically, S4: Configure a self-healing microcapsule dispersion with a solid content of 10 wt.%. Add ammonium dihydrogen phosphate, where the mass ratio of ammonium dihydrogen phosphate to the self-healing microcapsules is 0.4:1. After reacting for 2 h, add ammonium metatungstate, where the mass ratio of ammonium metatungstate to the self-healing microcapsules is 0.3:1, continue stirring at 50 °C for 3 h, centrifuge, wash, and dry to obtain a photothermal conversion / flame retardant self-healing microcapsule powder;

[0135] S5: Prepare the outer layer melt, the middle layer melt, and the inner layer melt respectively, and compound the three layers of melts through a multi-layer co-extrusion device to obtain a multi-functional composite geomembrane.

[0136] Specifically, S5: Mix and melt polyethylene, polydimethylsiloxane with a feeding amount of 1% of the mass of polyethylene, polyethylene wax with a feeding amount of 1% of the mass of polyethylene, black phosphorus quantum dots with a feeding amount of 0.9% of the mass of polyethylene, and antioxidant 1010 with a feeding amount of 0.5% of the mass of polyethylene to obtain an outer layer melt; Mix and melt polyethylene, surface mercapto-functionalized / silver-doped cellulose-MOF composite powder, photothermal conversion / flame retardant self-healing microcapsule powder, antioxidant 1010, and polyethylene wax to obtain an intermediate layer melt, wherein the feeding amount of the surface mercapto-functionalized / silver-doped cellulose-MOF composite powder in the intermediate layer melt is 10% of the mass of polyethylene, the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder is 7% of the mass of polyethylene, the feeding amount of antioxidant 1010 is 0.2% of the mass of polyethylene, and the feeding amount of polyethylene wax is 1% of the mass of polyethylene; Mix and melt polyethylene, elastomer POE, and antioxidant 1010 to obtain an inner layer melt, wherein the feeding amount of elastomer POE in the inner layer melt is 10% of the mass of polyethylene and the feeding amount of antioxidant 1010 is 0.5% of the mass of polyethylene; Compound the outer layer melt, the intermediate layer melt, and the inner layer melt in a mass ratio of 1:5:1 through a multi-layer co-extrusion device to obtain a multi-functional composite geomembrane.

[0137] Comparative Example 1

[0138] This comparative example provides a multi-functional composite geomembrane. The difference from Example 1 is that in S1, the mass ratio of copper nitrate to cellulose nanocrystals is 1:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0139] Comparative Example 2

[0140] This comparative example provides a multi-functional composite geomembrane. The difference from Example 1 is that in S1, the mass ratio of copper nitrate to cellulose nanocrystals is 0.1:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0141] Comparative Example 3

[0142] This comparative example provides a multi-functional composite geomembrane. The difference from Example 1 is that in S2, the molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane is 2:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0143] Comparative Example 4

[0144] This comparative example provides a multi-functional composite geomembrane. The difference from Example 1 is that in S2, the molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane is 0.5:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0145] Comparative Example 5

[0146] This comparative example provides a multifunctional composite geomembrane. The difference from Example 1 is that in S2, the mass ratio of 3-mercaptopropyltriethoxysilane to the metal-organic framework modified cellulose nanocrystal powder is 3:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0147] Comparative Example 6

[0148] This comparative example provides a multifunctional composite geomembrane. The difference from Example 1 is that in S2, the mass ratio of 3-mercaptopropyltriethoxysilane to the metal-organic framework modified cellulose nanocrystal powder is 0.5:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0149] Comparative Example 7

[0150] This comparative example provides a multifunctional composite geomembrane. The difference from Example 1 is that in S5, the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder is 15% of the mass of polyethylene, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0151] Comparative Example 8

[0152] This comparative example provides a multifunctional composite geomembrane. The difference from Example 1 is that in S5, the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder is 1% of the mass of polyethylene, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0153] Perform performance tests on the multifunctional composite geomembranes of the above Examples 1-4 and Comparative Examples 1-8. The specific process is as follows:

[0154] Self-healing performance test: Use a tensile testing machine to test the performance of the multifunctional composite geomembranes of the above Examples 1-4 and Comparative Examples 1-8 in the initial state and after self-healing (after completely cutting the geomembrane and contacting the cross-section, healing at 50 °C for 12 h);

[0155] Self-healing efficiency = [stress after self-healing / stress in the initial state] × 100%.

[0156] Detect the antibacterial performance of the multifunctional composite geomembranes of the above Examples 1-4 and Comparative Examples 1-8 according to GB / T 31402-2023. Repeat the test on 5 specimens of the same sample and take the average value;

[0157] The test results are shown in Table 1.

[0158] Table 1: Performance test results of the multifunctional composite geomembranes of Examples 1-4 and Comparative Examples 1-8

[0159]

[0160]

[0161] From the test results of Example 1 and Comparative Example 1 and Comparative Example 2, it can be seen that when the mass ratio of copper nitrate to cellulose nanocrystals is too high, excessive copper ions will interfere with the formation of the MOF structure and affect the subsequent distribution of silver nanoparticles, resulting in the self-healing efficiency of the material being reduced to 65.2%; at the same time, due to the rapid loss of free copper ions, the antibacterial rate against Escherichia coli drops to 78.3%, and the antibacterial rate against Staphylococcus aureus drops to 75.6%. When the mass ratio is too low, since there are 2+ fewer free Cu in the matrix, the interference during the formation of dynamic bonds is relatively reduced. Therefore, the self-healing efficiency is improved compared to Comparative Example 1; however, due to insufficient MOF loading and fewer functionalization sites, the incomplete coverage of the MOF structure affects subsequent functionalization modification, and the antibacterial performance is significantly reduced. The antibacterial rate against Escherichia coli drops to 62.4%, and the antibacterial rate against Staphylococcus aureus drops to 58.9%;

[0162] From the test results of Example 1 and Comparative Example 3 and Comparative Example 4, it can be seen that when the molar ratio of silver nitrate to 3-mercaptopropyltriethoxysilane is too high, excessive silver ions cause serious aggregation of silver nanoparticles and inhibit the formation of disulfide bonds, resulting in the self-healing efficiency of the material dropping to 58.3%; although high-concentration silver ions or aggregated silver nanoparticles have a certain killing effect on microorganisms in the short term, due to uneven dispersion and disturbance of the dynamic network, the antibacterial rate decreases continuously. The antibacterial rate against Escherichia coli drops to 83.2%, and the antibacterial rate against Staphylococcus aureus drops to 80.5%; when the molar ratio is too low, the reduction of silver ions is insufficient and the dynamic bond network is incomplete, resulting in a decrease in the self-healing efficiency. The antibacterial rate against Escherichia coli drops to 71.6%, and the antibacterial rate against Staphylococcus aureus drops to 68.9%;

[0163] From the test results of Example 1 and Comparative Example 5 and Comparative Example 6, it can be seen that when the mass ratio of 3-mercaptopropyltriethoxysilane to MOF-modified cellulose is too high, an overly crosslinked rigid network structure is formed, resulting in the self-healing efficiency of the material dropping to 61.4%; at the same time, due to uneven distribution of reduction sites, the antibacterial rate against Escherichia coli drops to 85.6%, and the antibacterial rate against Staphylococcus aureus drops to 82.3%. When the mass ratio is too low, due to insufficient dynamic bond density, the self-healing efficiency is only 48.9%. At the same time, insufficient reduction sites lead to a decrease in the antibacterial rate against Escherichia coli to 68.5%, and the antibacterial rate against Staphylococcus aureus to 65.2%;

[0164] From the test results of Example 1 and Comparative Examples 7 and 8, it can be seen that when the feeding amount of the photothermal conversion / flame retardant self-healing microcapsule powder is too high, the aggregation of excessive microcapsules destroys the integrity of the matrix structure, resulting in the self-healing efficiency of the material dropping to 63.8%; at the same time, due to the uneven distribution of functional components, the antibacterial rate against Escherichia coli drops to 86.4%, and the antibacterial rate against Staphylococcus aureus drops to 83.7%. When the feeding amount is too low, due to insufficient repair dosage and functional component concentration, the self-healing efficiency is only 45.3%, the antibacterial rate against Escherichia coli drops to 64.8%, and the antibacterial rate against Staphylococcus aureus drops to 61.5%.

[0165] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of within the technical scope disclosed by the present invention by those skilled in the art all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a multifunctional composite geomembrane, characterized in that: The preparation method comprises: S1: Reaction of cellulose nanocrystals with copper nitrate and 2-methylimidazole to obtain metal-organic framework modified cellulose nanocrystal powder; S2: preparing a dispersion of cellulose nanocrystal powder modified with a metal-organic framework, adding 3-mercaptopropyltriethoxysilane and silver nitrate respectively under an inert atmosphere and reacting them to obtain a surface thiolated / silver-doped cellulose-MOF composite powder; S3: dispersing the polyurethane precursor and the curing agent in deionized water, adding anhydrous ethanol and polyvinyl alcohol to obtain a microemulsion, adding glutaraldehyde solution to react and treat to obtain self-healing microcapsules; S4: adding ammonium dihydrogen phosphate to the self-healing microcapsule dispersion to react, and then adding ammonium metatungstate and continuing to stir and process to obtain light-thermal conversion / flame-retardant self-healing microcapsule powder; S5: preparing an outer layer melt, a middle layer melt and an inner layer melt respectively, and compounding the three layers of melt through a multi-layer co-extrusion device to obtain a multifunctional composite geomembrane.

2. The method for preparing a multifunctional composite geomembrane according to claim 1, characterized in that: In S1: The mass ratio of copper nitrate to cellulose nanocrystals is 0.3-0.5:1; The molar ratio of the 2-methylimidazole to copper nitrate is 2-3:

1.

3. The method for preparing a multifunctional composite geomembrane according to claim 1, characterized in that: In S2: The solid content of the metal-organic framework modified cellulose nanocrystal powder dispersion is 2-3wt%; The mass ratio of the 3-mercaptopropyltriethoxysilane to the metal-organic framework modified cellulose nanocrystal powder is 1-2:1; The molar ratio of the silver nitrate to 3-mercaptopropyltriethoxysilane is 1-1.5:

1.

4. The method for preparing a multifunctional composite geomembrane according to claim 1, characterized in that: In S3: The curing agent is any one of polyethylene glycol or triethanolamine or a combination of the two; The mass ratio of the polyurethane precursor to the curing agent is 1:0.8-1.2; The mass fraction of the polyurethane precursor in deionized water is 10-15wt%; The volume ratio of anhydrous ethanol to deionized water is 1:2-3; The mass fraction of the polyvinyl alcohol in the microemulsion is 0.5-1wt.%; The mass fraction of the glutaraldehyde solution is 25-30wt%; The mass ratio of the glutaraldehyde to the polyurethane precursor is 0.05-0.15:

1.

5. The method for preparing a multifunctional composite geomembrane according to claim 1, characterized in that: In S4: The mass ratio of the diammonium phosphate to the self-repairing microcapsule is 0.2-0.4:1; The mass ratio of the ammonium metatungstate to the self-repairing microcapsule is 0.1-0.3:

1.

6. The method for preparing a multifunctional composite geomembrane according to claim 1, characterized in that: In S5: The outer layer melt comprises polyethylene, polydimethylsiloxane, a dispersant, black phosphorus quantum dots and an antioxidant; The intermediate layer melt comprises polyethylene, surface thiolation / silver-doped cellulose-MOF composite powder, photothermal conversion / flame-retardant self-repairing microcapsule powder, antioxidant and dispersant; The inner layer melt includes polyethylene, elastomer POE, and antioxidant; The dispersant is any one of glycerol monostearate or polyethylene wax or a combination of the two; The antioxidant is any one of antioxidant 1010 or antioxidant 1076 or a combination of the two.

7. The method for preparing a multifunctional composite geomembrane according to claim 6, characterized in that: In S5: The amount of polydimethylsiloxane in the outer layer melt is 0.5-1% of the mass of polyethylene; The amount of the dispersant in the outer layer melt is 0.5-1% of the mass of the polyethylene; The amount of black phosphorus quantum dots in the outer layer melt is 0.5-1% of the mass of polyethylene; The amount of antioxidant added to the outer layer melt is 0.1-0.5% of the weight of polyethylene.

8. The method for preparing a multifunctional composite geomembrane according to claim 6, characterized in that: In S5: The feeding amount of the surface thiolated / silver-doped cellulose-MOF composite powder in the intermediate layer melt is 5-10% of the mass of polyethylene; The feeding amount of the light-to-heat conversion / flame-retardant self-repairing microcapsule powder in the intermediate layer melt is 5-10% of the mass of polyethylene; The amount of antioxidant added to the intermediate layer melt is 0.1-0.5% of the mass of polyethylene; The amount of the dispersant added to the intermediate layer melt is 0.5-1% of the mass of the polyethylene.

9. The method for preparing a multifunctional composite geomembrane according to claim 6, characterized in that: In S5: The amount of the elastomer POE in the inner layer melt is 5-10% of the mass of polyethylene; The amount of antioxidant added to the inner layer melt is 0.1-0.5% of the weight of polyethylene.

10. A multifunctional composite geomembrane prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The mass ratio of the outer layer melt, the middle layer melt and the inner layer melt in the multifunctional composite geomembrane is 1:4-5:1.

Images