Special geomembrane for pumped storage power station and preparation method thereof

Abstract

The invention provides a special geomembrane for a pumped storage power station and a preparation method of the special geomembrane, and relates to the technical field of geomembrane materials. The special geomembrane for the pumped storage power station comprises an outer layer, a middle layer and an inner layer which are sequentially connected, the outer layer is prepared from the following raw materials: 55 to 65 percent of MDPE, 33 to 40 percent of HDPE, 1 to 5 percent of antioxidant master batch and 1 to 7 percent of double-resistant color master batch; the middle layer is prepared from the following raw materials: 15 to 25 percent of HDPE (High-Density Polyethylene), 35 to 45 percent of LLDPE (Linear Low Density Polyethylene), 25 to 35 percent of POE (Polyolefin Elastomer), 1 to 5 percent of antioxidant master batch and 3 to 7 percent of double-resistant color master batch; the inner layer is prepared from the following raw materials: 35 to 45 percent of MDPE, 40 to 50 percent of LLDPE, 8 to 12 percent of POE, 1 to 5 percent of antioxidant master batch and 3 to 7 percent of double-resistant color master batch. The strength, the fatigue resistance and the aging resistance are balanced on the whole, so that the long-term operation requirement of the pumped storage power station is met.

Description

Technical Field

[0001] This invention relates to the field of geomembrane material technology, and more specifically, to a geomembrane for pumped storage power stations and its preparation method. Background Technology

[0002] The rapid development of new energy sources such as wind power and solar energy has led to a mismatch between peak power output and peak load, resulting in grid instability and a coexistence of power curtailment and shortages. To absorb these new energy sources, energy storage facilities are needed. Pumped storage hydroelectric power stations, as peak-shaving power sources, can ensure the safe and stable operation of the power grid, and it is foreseeable that a large number of pumped storage hydroelectric power stations will be developed and constructed.

[0003] Geomembranes, with their unique economic competitive advantages, are widely used in the seepage prevention of the reservoir bottom of pumped storage power stations. As the main seepage prevention body of the reservoir, the structural safety of geomembranes will affect the safety of the entire seepage prevention system.

[0004] To achieve high strength and puncture resistance, high-density polyethylene (HDPE) is typically used, reinforced with woven glass or polyester fibers. This significantly increases the material's tensile modulus and strength, but also makes it more rigid and stiff. Increased rigidity inevitably sacrifices the material's flexibility and deformation capacity. In the face of frequent water level fluctuations and uneven foundation settlement, rigid membranes have poor adaptability to deformation and are more prone to fatigue microcracks at stress concentration points (such as welds, corners, and abrupt foundation changes), potentially leading to brittle failure over the long term. In other words, it is difficult to simultaneously achieve extremely high strength and excellent fatigue resistance.

[0005] Chinese invention patent CN117207627A discloses a high-density polyethylene composite geomembrane and its production process, comprising the following raw materials in parts by weight: 95-98 parts high-density polyethylene resin, 2-3 parts carbon black, 3-6 parts anti-aging agent, 4-6 parts antioxidant, 2-7 parts ultraviolet absorber, 4-8 parts stabilizer, and 1-3 parts hydrophobic factor. The hydrophobic factor consists of fluorinated silica nanoparticles, isobutyltriethoxysilane, and docosyltriethoxysilane in a mass ratio of (6.5-13.4):(2.5-5.6):(0.8-1.2). By separately preparing the base material, material layer, and geomembrane, and then combining them with geotextile, the geomembrane exhibits advantages such as high strength, good impermeability, environmental adaptability, easy construction and maintenance, and reusability, thus laying a solid foundation for the safe operation and normal functioning of water conservancy projects. The bonding between the resin and fiber in this patent mainly relies on mechanical riveting and limited physicochemical reactions. Under long-term repeated loading, temperature changes, and moisture erosion, the interface may gradually age and debond. In addition, there is a risk of weak joints, reduced flexibility, and a tendency to brittle failure. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a geomembrane specifically designed for pumped storage power stations. Through a three-layer structure design consisting of an outer protective layer, a middle anti-deformation layer, and an inner bonding and seepage-proof layer, the materials in each layer work synergistically to balance strength, fatigue resistance, and aging resistance as a whole, thus meeting the long-term operational requirements of pumped storage power stations.

[0007] The first aspect of this invention provides a geomembrane specifically for pumped storage power stations, the geomembrane comprising an outer layer, a middle layer, and an inner layer connected in sequence; By mass fraction, the outer layer raw materials include: 55-65% medium-density polyethylene (MDPE), 33-40% high-density polyethylene (HDPE), 1-5% antioxidant masterbatch, and 1-7% dual-resistance color masterbatch; The raw materials for the intermediate layer include: 15-25% HDPE, 35-45% linear low-density polyethylene (LLDPE), 25-35% polyolefin elastomer (POE), 1-5% antioxidant masterbatch, and 3-7% dual-color masterbatch; The raw materials for the inner layer include: MDPE 35-45%, LLDPE 40-50%, POE 8-12%, antioxidant masterbatch 1-5%, and dual-anti-color masterbatch 3-7%.

[0008] The outer layer of the geomembrane for pumped storage power stations uses 55-65% MDPE to provide good flexibility and processability, preventing the outer layer from becoming too brittle; 33-40% HDPE provides high strength and puncture resistance, protecting against external scratches; and 1-7% dual-resistance color masterbatch provides UV resistance and anti-aging properties, protecting the inner layer from environmental erosion. The outer layer acts as a protective shell, using HDPE to ensure strength while using MDPE to avoid excessive rigidity, and using additives to isolate it from external environmental damage, providing protection for the middle and inner layers.

[0009] The middle layer uses 35-45% LLDPE to provide moderate strength and good ductility; 25-35% POE has high elasticity and flexibility, which can improve fatigue resistance and deformation resistance; 15-25% HDPE retains the basic strength and prevents the middle layer from being too soft. The intermediate layer acts as a buffer layer, using a high proportion of POE+LLDPE to achieve high flexibility, while using a small amount of HDPE to provide underlying strength, balancing deformation resistance and basic strength.

[0010] The inner layer uses 35-45% MDPE and 40-50% LLDPE to balance flexibility and density, ensuring impermeability. 8-12% POE improves adhesion and prevents detachment during settlement. As an impermeable bonding layer, the inner layer uses MDPE+LLDPE to ensure impermeability and density, while a small amount of POE enhances adhesion and prevents impermeability failure.

[0011] Optionally, the outer layer thickness is 0.3-0.9 mm, the middle layer thickness is 0.6-1.5 mm, and the inner layer thickness is 0.3-0.9 mm.

[0012] Optionally, by mass fraction, the outer layer raw materials include: MDPE 58-62%, HDPE 33-37%, antioxidant masterbatch 2-3%, and dual-resistance color masterbatch 2-4%; the middle layer raw materials include: HDPE 18-22%, LLDPE 38-43%, POE 28-33%, antioxidant masterbatch 2-3%, and dual-resistance color masterbatch 3-5%; the inner layer raw materials include: MDPE 38-43%, LLDPE 44-48%, POE 8-10%, antioxidant masterbatch 2-3%, and dual-resistance color masterbatch 3-5%.

[0013] Optionally, the intermediate layer may also include 2-5% maleic anhydride-grafted high-density polyethylene. Furthermore, adding maleic anhydride-grafted high-density polyethylene can improve the compatibility of HDPE, LLDPE, and POE, preventing the aggregation of components within the intermediate layer and ensuring stable fatigue resistance. In addition, the polar groups of maleic anhydride can form an interface between the outer and inner polyethylene layers, while simultaneously entangled with the elastic segments of POE, significantly enhancing the interfacial bonding ability between the three layers and preventing delamination after long-term use.

[0014] Optionally, the preparation method of maleic anhydride-grafted high-density polyethylene includes the following steps: drying high-density polyethylene, then adding 1.5-2.0 wt% maleic anhydride, 0.1-0.3 wt% dicumyl peroxide, and 0.5-1.0 wt% butyl acrylate and mixing them, then adding them to a twin-screw extruder for melt extrusion (zone I temperature 120-150℃, zone II temperature 170-190℃), then cooling and pelletizing to obtain maleic anhydride-grafted high-density polyethylene.

[0015] Optionally, maleic anhydride-grafted high-density polyethylene is modified using POSS, including the following steps: Heptaisooctyl monoepoxy POSS, maleic anhydride-grafted HDPE, and an initiator were mixed and extruded and granulated at 180-200℃ to obtain POSS grafted masterbatch.

[0016] The structural formula of heptaisooctyl monoepoxy POSS is shown below: , where R is isooctyl.

[0017] POSS, a cage-like nanostructure, dispersed in maleic anhydride-grafted high-density polyethylene, forms nano-reinforcing points, improving the tensile strength and creep resistance of the interlayer, preventing deformation under long-term loads, while maintaining flexibility and enhancing mechanical properties. The epoxy groups of POSS react with maleic anhydride to form more stable chemical bonds. Its cage-like structure also blocks ultraviolet radiation and oxygen intrusion, delaying resin aging and extending the geomembrane's lifespan. POSS reduces melt viscosity, making the interlayer easier to extrude and avoiding processing difficulties caused by the addition of maleic anhydride-grafted high-density polyethylene.

[0018] Optionally, the intermediate layer may also include 2-5% nanofiller. This can improve impermeability, enhance mechanical and anti-aging properties, and extend the outdoor service life of the geomembrane.

[0019] Optional. The nanofiller is nano-organo-montmorillonite or modified silica.

[0020] Optionally, the nanofiller is modified with an imidazole ionic liquid, including the following steps: The nanofiller and imidazole ionic liquid were placed in a water / ethanol mixed solvent and stirred at 60-80℃ for 3-4 hours. After separation and drying, they were ground to obtain the modified nanofiller.

[0021] Optionally, the imidazole ionic liquid may be selected from one or more of 1-vinyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0022] Furthermore, nanofillers are prone to agglomeration on their surfaces. The polar groups of imidazole ionic liquids (such as imidazole rings and anions) can combine with the hydroxyl groups on the filler surface, forming a charge repulsion effect that allows the filler to be uniformly dispersed in the resin, avoiding performance fluctuations caused by agglomeration. The bridging effect of the ionic liquid can enhance the interfacial bonding between the nanofiller and the resin (HDPE / LLDPE / POE), preventing the filler from detaching from the resin and ensuring stable impermeability and mechanical properties after long-term use. The hydrophobic groups of imidazole ionic liquids can reduce the hydrophilicity of the filler surface, preventing interfacial aging caused by water vapor accumulation on the filler surface, further improving the geomembrane's resistance to water erosion.

[0023] Optionally, the amount of imidazole ionic liquid used is 5%-20% of the mass of the nanofiller.

[0024] Optionally, the HDPE is bimodal HDPE. Bimodal HDPE consists of a high molecular weight fraction and a low molecular weight fraction. The high molecular weight fraction provides high tensile strength and puncture resistance, while the low molecular weight fraction improves melt flowability, making the geomembrane easier to form during extrusion and avoiding the problem of difficult processing caused by the high strength of unimodal HDPE. The long chains of the high molecular weight fraction are more tightly entangled, which can reduce creep deformation under long-term water pressure.

[0025] Optionally, the LLDPE is C8-LLDPE. The comonomer of C8-LLDPE is octene, which has longer and more uniformly distributed branches than ordinary C4-LLDPE (butene) and C6-LLDPE (hexene), which can improve the extensibility and elasticity of the molecular chain and enhance the fatigue resistance of the intermediate layer.

[0026] Optionally, the antioxidant masterbatch is one or more of the following: octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168), and dilauryl thiodipropionate (antioxidant DLTP). Further, the outer layer consists of antioxidant 1076 and antioxidant 168. The rapid action of antioxidant 1076 allows for timely capture of free radicals during extrusion processing, while antioxidant 168 enhances thermal stability, ensuring the outer layer's performance stability during high-temperature molding. The intermediate layer consists of antioxidant 1010 and antioxidant DLTP. The long-lasting effect of 1010 combined with the water resistance of DLTP resists oxidative degradation of the intermediate layer under long-term stress. The inner layer consists of antioxidant 1010 and antioxidant DLTP. A high proportion of 1010 strengthens the inner layer's long-term thermal and oxygen protection, while a small amount of DLTP enhances water resistance and reduces aging caused by moisture penetration into the inner layer.

[0027] Optionally, the dual-resistance masterbatch is carbon black with a particle size of 20-30nm.

[0028] The second aspect of this invention provides a method for preparing a geomembrane specifically for pumped storage power stations, the method comprising the following steps: The raw materials for each layer are mixed separately, and the outer, middle and inner layers are simultaneously extruded and fused using a three-layer co-extrusion geomembrane extruder to form a continuous geomembrane.

[0029] Optionally, the mixing speed for the outer layer is 100-130 rpm, the mixing temperature is 40-50℃, and the mixing time is 5-8 min. The mixing speed for the middle layer is 120-150 rpm, the mixing temperature is 45-60℃, and the mixing time is 8-10 min. The mixing speed for the inner layer is 110-140 rpm, the mixing temperature is 40-55℃, and the mixing time is 6-8 min.

[0030] Optionally, during outer layer extrusion, the extrusion temperatures for zones 1-4 are 160-170℃, 170-180℃, 175-185℃, and 180-190℃ respectively, with a die temperature of 180-190℃ and a screw speed of 20-30 rpm. During middle layer extrusion, the extrusion temperatures for zones 1-4 are 140-150℃, 150-160℃, 160-170℃, and 170-180℃ respectively, with a die temperature of 170-180℃ and a screw speed of 15-25 rpm. During inner layer extrusion, the extrusion temperatures for zones 1-4 are 150-160℃, 160-170℃, 170-180℃, and 175-185℃ respectively, with a die temperature of 175-185℃ and a screw speed of 18-28 rpm.

[0031] Compared with the prior art, the present invention achieves at least one of the following beneficial effects: (1) The geomembrane for pumped storage power stations of the present invention has a three-layer structure design of “outer protection + middle anti-deformation + inner bonding and seepage prevention”. The raw materials of each layer work together to balance the strength, fatigue resistance and aging resistance as a whole, so as to meet the long-term operation requirements of pumped storage power stations.

[0032] (2) In the geomembrane for pumped storage power stations of the present invention, maleic anhydride-grafted high-density polyethylene is added to the middle layer, which can improve the compatibility of HDPE, LLDPE and POE, avoid the agglomeration of internal components of the middle layer, and ensure stable fatigue resistance. In addition, the polar groups of maleic anhydride can form an interface between the outer and inner polyethylene layers, and at the same time entangle with the elastic segments of POE, which greatly improves the interfacial strength between the three layers and avoids debonding between the layers after long-term use. Detailed Implementation

[0033] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0034] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application were all purchased commercially.

[0035] Unless otherwise specified, the methods used in the embodiments and comparative examples of this application are conventional methods in the prior art.

[0036] Example 1 In an exemplary embodiment of the present invention, the geomembrane for pumped storage power stations comprises an outer layer of 0.5 mm, a middle layer of 1 mm, and an inner layer of 0.5 mm connected in sequence; the raw materials of the outer layer include: 55% MDPE, 40% bimodal HDPE, 1% antioxidant masterbatch (antioxidant 1076 (60 wt%) and antioxidant 168 (40 wt%)) and 4% carbon black with a particle size of 20 nm; The raw materials for the intermediate layer include: 15% bimodal HDPE, 45% C8-LLDPE, 35% POE, 2% antioxidant masterbatch (antioxidant 1010 (70wt%) and antioxidant DLTP (30wt%)) and 3% carbon black, with a particle size of 20nm; The inner layer raw materials include: 35% MDPE, 50% C8-LLDPE, 10% POE, 2% antioxidant masterbatch (antioxidant 1010 (80wt%) and antioxidant DLTP (20wt%)) and 3% carbon black, with a particle size of 20nm.

[0037] The preparation method includes the following steps: The raw materials for each layer are mixed separately, and then the outer, middle, and inner layers are simultaneously extruded and fused using a three-layer co-extrusion geomembrane extruder to form a continuous geomembrane. The mixing speed for the outer layer is 100 rpm, the mixing temperature is 40℃, and the mixing time is 5 minutes. The mixing speed for the middle layer is 120 rpm, the mixing temperature is 45℃, and the mixing time is 8 minutes. The mixing speed for the inner layer is 110 rpm, the mixing temperature is 40℃, and the mixing time is 6 minutes.

[0038] During outer layer extrusion, the extrusion temperatures for zones 1-4 are 160℃, 170℃, 175℃, and 180℃ respectively, with a die temperature of 180℃ and a screw speed of 20 rpm. During middle layer extrusion, the extrusion temperatures for zones 1-4 are 140℃, 150℃, 160℃, and 170℃ respectively, with a die temperature of 170℃ and a screw speed of 15 rpm. During inner layer extrusion, the extrusion temperatures for zones 1-4 are 150℃, 160℃, 170℃, and 175℃ respectively, with a die temperature of 175℃ and a screw speed of 18 rpm.

[0039] Example 2 The geomembrane for pumped storage power stations consists of an outer 0.5mm layer, a middle 1mm layer, and an inner 0.5mm layer connected in sequence. The raw materials of the outer layer include: 60% MDPE, 33% bimodal HDPE, 2% antioxidant masterbatch (antioxidant 1076 (60wt%) and 5% carbon black with a particle size of 30nm). The raw materials for the intermediate layer include: 25% bimodal HDPE, 35% C8-LLDPE, 30% POE, 4% antioxidant masterbatch (antioxidant 1010 (70wt%) and antioxidant DLTP (30wt%)) and 6% carbon black with a particle size of 30nm. The inner layer raw materials include: 45% MDPE, 40% C8-LLDPE, 10% POE, 2% antioxidant masterbatch (antioxidant 1010 (80wt%) and antioxidant DLTP (20wt%)) and 3% carbon black with a particle size of 30nm.

[0040] The preparation method includes the following steps: The raw materials for each layer are mixed separately, and then the outer, middle, and inner layers are simultaneously extruded and fused using a three-layer co-extrusion geomembrane extruder to form a continuous geomembrane. The mixing speed for the outer layer is 130 rpm, the mixing temperature is 50℃, and the mixing time is 8 minutes. The mixing speed for the middle layer is 150 rpm, the mixing temperature is 60℃, and the mixing time is 10 minutes. The mixing speed for the inner layer is 140 rpm, the mixing temperature is 55℃, and the mixing time is 8 minutes.

[0041] During outer layer extrusion, the extrusion temperatures for zones 1-4 are 170℃, 180℃, 185℃, and 190℃ respectively, with a die temperature of 190℃ and a screw speed of 30 rpm. During middle layer extrusion, the extrusion temperatures for zones 1-4 are 150℃, 160℃, 170℃, and 180℃ respectively, with a die temperature of 180℃ and a screw speed of 25 rpm. During inner layer extrusion, the extrusion temperatures for zones 1-4 are 160℃, 170℃, 180℃, and 185℃ respectively, with a die temperature of 185℃ and a screw speed of 28 rpm.

[0042] Example 3 The geomembrane for pumped storage power stations consists of an outer 0.5mm layer, a middle 1mm layer, and an inner 0.5mm layer connected in sequence. The raw materials of the outer layer include: 62% MDPE, 33% bimodal HDPE, 3% antioxidant masterbatch (antioxidant 1076 (60wt%) and antioxidant 168 (40wt%)) and 2% carbon black with a particle size of 25nm. The raw materials for the intermediate layer include: 18% bimodal HDPE, 42% C8-LLDPE, 32% POE, 3% antioxidant masterbatch (antioxidant 1010 (70wt%) and antioxidant DLTP (30wt%)) and 5% carbon black with a particle size of 25nm; The inner layer raw materials include: 40% MDPE, 47% C8-LLDPE, 8% POE, 2% antioxidant masterbatch (antioxidant 1010 (80wt%) and antioxidant DLTP (20wt%)) and 3% carbon black, with a particle size of 25nm.

[0043] The preparation method includes the following steps: The raw materials for each layer are mixed separately, and then the outer, middle, and inner layers are simultaneously extruded and fused using a three-layer co-extrusion geomembrane extruder to form a continuous geomembrane. The mixing speed for the outer layer is 120 rpm, the mixing temperature is 45℃, and the mixing time is 6 minutes. The mixing speed for the middle layer is 130 rpm, the mixing temperature is 50℃, and the mixing time is 9 minutes. The mixing speed for the inner layer is 120 rpm, the mixing temperature is 50℃, and the mixing time is 7 minutes.

[0044] During outer layer extrusion, the extrusion temperatures for zones 1-4 are 165℃, 175℃, 180℃, and 185℃ respectively, with a die temperature of 185℃ and a screw speed of 25 rpm. During middle layer extrusion, the extrusion temperatures for zones 1-4 are 145℃, 155℃, 165℃, and 175℃ respectively, with a die temperature of 175℃ and a screw speed of 20 rpm. During inner layer extrusion, the extrusion temperatures for zones 1-4 are 155℃, 165℃, 175℃, and 180℃ respectively, with a die temperature of 180℃ and a screw speed of 25 rpm.

[0045] Example 4 The geomembrane for pumped storage power stations consists of an outer layer of 0.6 mm, a middle layer of 1.2 mm, and an inner layer of 0.7 mm connected in sequence. The raw materials of the outer layer include: 60% MDPE, 35% bimodal HDPE, 3% antioxidant masterbatch (antioxidant 1076 (60 wt%) and antioxidant 168 (40 wt%)) and 2% carbon black with a particle size of 25 nm. The raw materials for the intermediate layer include: 18% bimodal HDPE, 40% C8-LLDPE, 30% POE, 2% maleic anhydride-grafted high-density polyethylene, 2% nano-organic montmorillonite, 3% antioxidant masterbatch (antioxidant 1010 (70wt%) and antioxidant DLTP (30wt%)) and 5% carbon black with a particle size of 25nm. The preparation method of maleic anhydride-grafted high-density polyethylene includes the following steps: drying high-density polyethylene, then adding 2.0 wt% maleic anhydride, 0.3 wt% dicumyl peroxide and 1.0 wt% butyl acrylate and mixing them, then adding them to a twin-screw extruder for melt extrusion (zone I temperature 150℃, zone II temperature 190℃), then cooling and pelletizing to obtain maleic anhydride-grafted high-density polyethylene.

[0046] The inner layer raw materials include: 40% MDPE, 47% C8-LLDPE, 8% POE, 2% antioxidant masterbatch (antioxidant 1010 (80wt%) and antioxidant DLTP (20wt%)) and 3% carbon black, with a particle size of 25nm.

[0047] The preparation method includes the following steps: The raw materials for each layer are mixed separately, and then the outer, middle, and inner layers are simultaneously extruded and fused using a three-layer co-extrusion geomembrane extruder to form a continuous geomembrane. The mixing speed for the outer layer is 120 rpm, the mixing temperature is 45℃, and the mixing time is 6 minutes. The mixing speed for the middle layer is 130 rpm, the mixing temperature is 50℃, and the mixing time is 9 minutes. The mixing speed for the inner layer is 120 rpm, the mixing temperature is 50℃, and the mixing time is 7 minutes.

[0048] During outer layer extrusion, the extrusion temperatures for zones 1-4 are 165℃, 175℃, 180℃, and 185℃ respectively, with a die temperature of 185℃ and a screw speed of 25 rpm. During middle layer extrusion, the extrusion temperatures for zones 1-4 are 145℃, 155℃, 165℃, and 175℃ respectively, with a die temperature of 175℃ and a screw speed of 20 rpm. During inner layer extrusion, the extrusion temperatures for zones 1-4 are 155℃, 165℃, 175℃, and 180℃ respectively, with a die temperature of 180℃ and a screw speed of 25 rpm.

[0049] Example 5 Based on Example 3, the main difference is that the geomembrane for pumped storage power stations includes an outer layer of 0.5 mm, a middle layer of 1 mm, and an inner layer of 0.5 mm connected in sequence; the raw materials of the outer layer include: 62% MDPE, 33% bimodal HDPE, 3% antioxidant masterbatch (antioxidant 1076 (60 wt%) and antioxidant 168 (40 wt%)) and 2% carbon black with a particle size of 25 nm; The raw materials for the intermediate layer include: 18% bimodal HDPE, 38% C8-LLDPE, 30% POE, 4% POSS modified maleic anhydride grafted high-density polyethylene, 3% imidazole ionic liquid modified nano-organic montmorillonite, 3% antioxidant masterbatch (antioxidant 1010 (70wt%) and antioxidant DLTP (30wt%)) and 4% carbon black, with a particle size of 25nm; The preparation method of POSS-modified maleic anhydride-grafted high-density polyethylene includes the following steps: High-density polyethylene is dried, then 1.5 wt% maleic anhydride, 0.1 wt% dicumyl peroxide, and 0.5 wt% butyl acrylate are added and mixed. The mixture is then fed into a twin-screw extruder for melt extrusion (zone I temperature 120℃, zone II temperature 170℃), followed by cooling and pelletizing to obtain maleic anhydride-grafted high-density polyethylene. Hepta-octyl monoepoxy POSS (2% of the mass of maleic anhydride-grafted HDPE), maleic anhydride-grafted HDPE, and dicumyl peroxide are mixed and extruded and granulated at 180℃ to obtain POSS-modified maleic anhydride-grafted high-density polyethylene.

[0050] The modification of nano-organo-montmorillonite with imidazole ionic liquid includes the following steps: nano-organo-montmorillonite and 1-vinyl-3-methylimidazolium chloride are placed in a water / ethanol mixed solvent, the amount of imidazole ionic liquid is 5% of the mass of nano-organo-montmorillonite, and the mixture is stirred at 60°C for 3 hours. After separation and drying, the mixture is ground to obtain the modified nanofiller.

[0051] The inner layer raw materials include: 40% MDPE, 47% C8-LLDPE, 8% POE, 2% antioxidant masterbatch (antioxidant 1010 (80wt%) and antioxidant DLTP (20wt%)) and 3% carbon black, with a particle size of 25nm.

[0052] The preparation method is the same as in Example 3.

[0053] Example 6 Based on Example 4, the main difference lies in the preparation method of POSS-modified maleic anhydride-grafted high-density polyethylene, which includes the following steps: High-density polyethylene is dried, then 1.8 wt% maleic anhydride, 0.1 wt% dicumyl peroxide, and 0.8 wt% butyl acrylate are added and mixed. The mixture is then melt-extruded in a twin-screw extruder (zone I temperature 130°C, zone II temperature 180°C), cooled, and pelletized to obtain maleic anhydride-grafted high-density polyethylene. Heptaisooctyl monoepoxy POSS (4% of the mass of maleic anhydride-grafted HDPE), maleic anhydride-grafted HDPE, and dicumyl peroxide are mixed and extruded and granulated at 190°C to obtain POSS-modified maleic anhydride-grafted high-density polyethylene.

[0054] The modification of nano-organo-montmorillonite with imidazole ionic liquid includes the following steps: nano-organo-montmorillonite and 1-vinyl-3-methylimidazolium chloride are placed in a water / ethanol mixed solvent, the amount of imidazole ionic liquid is 8% of the mass of nano-organo-montmorillonite, and the mixture is stirred at 80°C for 3 hours. After separation and drying, the mixture is ground to obtain the modified nanofiller.

[0055] Example 7 Based on Example 5, the main difference is that the outer layer antioxidant masterbatch is antioxidant 1076, the middle layer antioxidant masterbatch is antioxidant 1010, and the inner layer antioxidant masterbatch is antioxidant 1010.

[0056] Example 8 The main difference from Example 5 is that the HDPE is a single-peak HDPE.

[0057] Example 9 The main difference from Example 5 is that the LLDPE is C4-LLDPE.

[0058] Comparative Example 1 Based on Example 1, the main difference is that the raw materials of the outer layer include: 30% MDPE, 65% bimodal HDPE, 1% antioxidant masterbatch (antioxidant 1076 (60wt%) and antioxidant 168 (40wt%)) and 4% carbon black with a particle size of 20nm.

[0059] Comparative Example 2 Based on Example 1, the main difference is that the raw materials of the intermediate layer include: 45% bimodal HDPE, 15% C8-LLDPE, 35% POE, 2% antioxidant masterbatch (antioxidant 1010 (70wt%) and antioxidant DLTP (30wt%)) and 3% carbon black with a particle size of 20nm.

[0060] Comparative Example 3 Based on Example 1, the main difference is that the raw materials of the inner layer include: 55% MDPE, 30% C8-LLDPE, 10% POE, 2% antioxidant masterbatch (antioxidant 1010 (80wt%) and antioxidant DLTP (20wt%)) and 3% carbon black with a particle size of 20nm.

[0061] Test Example 1 The mechanical properties of the geomembranes prepared in the above embodiments and comparative examples were tested, as shown in Table 1.

[0062] Simulating a high-stress power station, with a water level fluctuation of 100m and 1-5 water level fluctuations per hour, the tensile strength retention rate after 1000 cycles is calculated as follows: Tensile strength retention rate = (Tensile strength after cycles / Initial tensile strength) × 100%.

[0063] Table 1

[0064] Test Example 2 The geomembranes prepared in the above examples and comparative examples were subjected to ultraviolet aging, thermal aging, and yield elongation tests, as shown in Table 2.

[0065] UV aging test: After exposing the sample to a UV aging chamber for 1500 hours, test its tensile strength retention rate.

[0066] Thermal aging test: The sample is placed at 100℃ for 90 days to test the retention rate of tensile strength.

[0067] Table 2

[0068] Referring to Table 1, the geomembrane for pumped storage power stations prepared in this application has a tensile strength of not less than 36 MPa, an elongation at break of not less than 750%, a puncture resistance of not less than 480 N / mm, and a tensile strength retention rate of not less than 85% after 1000 cycles.

[0069] Referring to Table 2, the tensile strength retention rate after 1500 hours of exposure in the UV aging chamber is not less than 90%, the thermal aging tensile strength retention rate is not less than 80%, and the longitudinal / transverse yield strength retention rate is not less than 15%.

[0070] In Comparative Example 1, excessive HDPE in the outer layer and in Comparative Example 2, excessive HDPE in the middle layer and insufficient POE both resulted in geomembranes with excessive rigidity, insufficient flexibility, and excessively low elongation at break. In Comparative Example 2, the excessively rigid middle layer lacked elastic buffering, leading to severe stress concentration under cyclic loading, resulting in rapid performance degradation and poor fatigue resistance. In Comparative Examples 1 and 2, the excessively high HDPE content caused the material to rapidly yield under low strain, resulting in poor yield elongation.

[0071] Furthermore, this application employs a three-layer co-extrusion one-time molding technology, where the outer, middle, and inner layers are directly composited in a molten state, with no obvious physical interfaces between the layers. In fiber-reinforced geomembranes, the resin coating and textile mesh are physically bonded together, which is prone to interfacial debonding and peeling under repeated stress and water vapor erosion, leading to deterioration of seepage prevention performance. The integrated structure of this application fundamentally eliminates the risk of interlayer delamination, ensuring the overall stability and seepage prevention reliability of the geomembrane under the long-term and frequent water level fluctuations of pumped storage power stations.

[0072] In summary, the geomembrane for pumped storage power stations prepared by this invention can balance strength, fatigue resistance and aging resistance as a whole, making it suitable for the long-term operation requirements of pumped storage power stations.

[0073] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A geomembrane specifically designed for pumped storage power stations, characterized in that, The geomembrane for pumped storage power stations comprises an outer layer, a middle layer, and an inner layer connected in sequence. By mass fraction, the outer layer raw materials include: MDPE 55-65%, HDPE 33-40%, antioxidant masterbatch 1-5%, and dual-antioxidant color masterbatch 1-7%; By mass fraction, the raw materials for the intermediate layer include: HDPE 15-25%, LLDPE 35-45%, POE 25-35%, antioxidant masterbatch 1-5%, and dual-resistance color masterbatch 3-7%. By mass fraction, the raw materials for the inner layer include: MDPE 35-45%, LLDPE 40-50%, POE 8-12%, antioxidant masterbatch 1-5%, and dual-antioxidant color masterbatch 3-7%.

2. The geomembrane for pumped storage power stations according to claim 1, characterized in that, By mass fraction, the outer layer raw materials include: MDPE 58-62%, HDPE 33-37%, antioxidant masterbatch 2-3%, and dual-antioxidant color masterbatch 2-4%; By mass fraction, the raw materials for the intermediate layer include: HDPE 18-22%, LLDPE 38-43%, POE 28-33%, antioxidant masterbatch 2-3%, and dual-antioxidant color masterbatch 3-5%; By mass fraction, the raw materials for the inner layer include: MDPE 38-43%, LLDPE 44-48%, POE 8-10%, antioxidant masterbatch 2-3%, and dual-antioxidant color masterbatch 3-5%.

3. The geomembrane for pumped storage power stations according to claim 1, characterized in that, The intermediate layer also includes 2-5% maleic anhydride-grafted high-density polyethylene.

4. The geomembrane for pumped storage power stations according to claim 3, characterized in that, Modification of maleic anhydride-grafted high-density polyethylene using POSS includes the following steps: Heptaisooctyl monoepoxy POSS, maleic anhydride-grafted HDPE, and an initiator were mixed and extruded and granulated at 180-200℃ to obtain POSS grafted masterbatch.

5. The geomembrane for pumped storage power stations according to claim 1, characterized in that, The intermediate layer also contains 2-5% nanofillers.

6. The geomembrane for pumped storage power stations according to claim 5, characterized in that, The nanofiller is nano-organic montmorillonite or modified silica.

7. The geomembrane for pumped storage power stations according to claim 6, characterized in that, The nanofiller is modified with imidazole ionic liquid, including the following steps: The nanofiller and imidazole ionic liquid were placed in a water / ethanol mixed solvent and stirred at 60-80℃ for 3-4 hours. After separation and drying, they were ground to obtain the modified nanofiller.

8. The geomembrane for pumped storage power stations according to claim 7, characterized in that, The amount of imidazole ionic liquid used is 5%-20% of the mass of the nanofiller.

9. The geomembrane for pumped storage power stations according to claim 1, characterized in that, HDPE is bimodal HDPE; And / or the LLDPE is C8-LLDPE; And / or the antioxidant masterbatch is one or more of antioxidant 1076, antioxidant 1010, antioxidant 168, and antioxidant DLTP; And / or the dual-resistance masterbatch is carbon black with a particle size of 20-30nm.

10. A method for preparing a geomembrane for pumped storage power stations as described in any one of claims 1-9, characterized in that, The preparation method includes the following steps: The raw materials for each layer are mixed separately, and the outer, middle and inner layers are simultaneously extruded and fused using a three-layer co-extrusion geomembrane extruder to form a continuous geomembrane.

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