Ultrahigh molecular weight polyethylene double-layer hollow microporous membrane as well as preparation method and application thereof
By designing and preparing a double-layer hollow microporous membrane of ultra-high molecular weight polyethylene, the problems of heat loss and high reflectivity in existing photothermal films have been solved, achieving a synergistic improvement in efficient photothermal conversion and heat insulation performance, thereby increasing seawater desalination efficiency and production efficiency.
Patent Information
- Application Number
- CN202510634203.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-16
- Publication Date
- 2025-08-01
AI Technical Summary
Existing single-layer photothermal films suffer from rapid heat loss, high reflectivity, difficulty in achieving multi-layer integrated molding, and poor water conveyance capacity due to their porous structure, resulting in low production efficiency and high cost.
The membrane is made of ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Through the synergistic design of the outer photothermal layer and the inner heat insulation layer, it is formed in one step by double-layer co-extrusion blow molding. Combined with the extraction process of pore-forming agent, it forms a connected microporous structure, avoids the lamination step, and improves production efficiency.
It achieves a synergistic improvement in photothermal conversion efficiency and thermal insulation performance, increases seawater evaporation rate and energy utilization efficiency, and reduces production costs.
Smart Images
Figure CN120393769A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of polymer processing and forming, and particularly relates to an ultra-high molecular weight polyethylene double-layer hollow microporous membrane, a preparation method thereof, and an application thereof. [[ID=�]]Background Art
[0002] In recent years, solar desalination technology has become a research hotspot due to its characteristics of environmental friendliness and low energy consumption. In order to improve the efficiency of solar desalination, the interfacial evaporation technology has emerged. The interfacial evaporation technology uses a thin film made of a photothermal material to spread on the surface of seawater, and limits the heat near the air-water interface through the thin film made of the photothermal material to improve the evaporation efficiency. However, the existing single-layer photothermal film still has the following problems: 1. The direct contact between the photothermal layer and the water body causes heat to be quickly dissipated through heat conduction; 2. The single-layer structure has a high reflectivity to sunlight and cannot make full use of the broadband solar energy; 3. The traditional wet film-making process requires multiple coating or lamination steps, and it is difficult to achieve the integrated forming of a multi-layer structure, which is prone to interlayer peeling.
[0003] To reduce heat loss, the existing technology attempts to introduce a heat insulation layer between the photothermal layer and the water body, and make the photothermal layer and the heat insulation layer have a porous internal structure. However, the existing porous structure has poor water transportation ability and is not firmly combined with the interface of the photothermal layer. In addition, ultra-high molecular weight polyethylene is used to support the photothermal material due to its high mechanical strength and chemical resistance. However, the existing process requires multiple extrusion, stretching and extraction steps, and cannot form a double-layer connected microporous structure synchronously, resulting in low production efficiency and high cost. Summary of the Invention
[0004] The first object of the present invention is to overcome the defects and deficiencies of the existing technology, and provide an ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Through the collaborative design of the outer photothermal layer and the inner heat insulation layer, while enhancing light absorption, heat loss is reduced, and the synergistic improvement of the photothermal conversion efficiency and the heat insulation performance is realized.
[0005] The second object of the present invention is to provide a preparation method of an ultra-high molecular weight polyethylene double-layer hollow microporous membrane. The double-layer composite structure of the outer photothermal layer and the inner heat insulation layer is formed by one-step molding through the double-layer co-extrusion blow molding method, combined with the extraction process of the pore-forming agent, avoiding the lamination step of the traditional process, and improving the production efficiency.
[0006] The third object of the present invention is to provide an application of an ultra-high molecular weight polyethylene double-layer hollow microporous membrane. When the ultra-high molecular weight polyethylene double-layer hollow microporous membrane is used in solar desalination, the evaporation rate of seawater can be improved.
[0007] The object of the present invention can be achieved by the following technical solutions: An ultra-high molecular weight polyethylene double-layer hollow microporous membrane, the microporous membrane comprising an outer photothermal layer and an inner heat insulation layer; The components and parts by mass of the outer photothermal layer are 0 to 50 parts of photothermal material and 50 to 100 parts of ultra-high molecular weight polyethylene; the outer photothermal layer includes an ultra-high molecular weight polyethylene skeleton and a photothermal material. The photothermal material is distributed in the ultra-high molecular weight polyethylene skeleton, and the ultra-high molecular weight polyethylene skeleton has micropores, and the micropores are through holes penetrating the outer photothermal layer. The photothermal material and micropores distributed in the ultra-high molecular weight polyethylene skeleton cooperate to absorb and reflect sunlight irradiated on the outer photothermal layer, and convert solar energy into heat energy; The components and parts by mass of the inner heat insulation layer are 0 to 30 parts of hydrophilic material and 70 to 100 parts of ultra-high molecular weight polyethylene; the inner heat insulation layer includes an ultra-high molecular weight polyethylene skeleton and a hydrophilic material. The hydrophilic material is distributed in the ultra-high molecular weight polyethylene skeleton, and the ultra-high molecular weight polyethylene skeleton has micropores, and the micropores are through holes penetrating the inner heat insulation layer. Among them, the micropores in the inner heat insulation layer are connected to the micropores in the outer photothermal layer. The hydrophilic material and micropores distributed in the ultra-high molecular weight polyethylene skeleton cooperate to adsorb liquid and transport it to the outer photothermal layer to maintain a stable water evaporation process.
[0008] The outer photothermal layer of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane contains a photothermal material. The photothermal material converts solar energy into heat energy to heat the surface seawater. The microporous structure of the outer photothermal layer can make light reflect and absorb multiple times inside the outer photothermal layer, thereby reducing the solar light reflectivity and increasing the light absorption. The hydrophilic material of the inner heat insulation layer can adsorb seawater, and the microporous structure can be used as a seawater transport path, and as a heat insulation structure, it can avoid direct contact between the outer photothermal layer and seawater and reduce heat loss.
[0009] As a preference, the molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 6 million, and the molecular weights of the ultra-high molecular weight polyethylene used in the outer photothermal layer and the inner heat insulation layer are the same or different.
[0010] As a preference, the photothermal material is one or more of carbon fiber, graphene, carbon nanotube or carbon black; the hydrophilic material is one or more of alumina, silica, titanium dioxide or zinc oxide.
[0011] As a preference, the micropore diameter of the outer photothermal layer and the inner heat insulation layer is 0.1 to 20 μm, and the porosity is 50% to 70%.
[0012] A preparation method of an ultra-high molecular weight polyethylene double-layer hollow microporous membrane includes the following steps: Step 1: Mix the photothermal material, ultra-high molecular weight polyethylene and pore-forming agent evenly according to a preset mass ratio to obtain the outer photothermal layer mixed material; mix the hydrophilic material, ultra-high molecular weight polyethylene and pore-forming agent evenly according to a preset mass ratio to obtain the inner heat insulation layer mixed material; Step 2: Add the outer photothermal layer composite material and the inner heat insulation layer composite material into the corresponding extruders respectively for melting and plasticizing to form an outer photothermal layer melt and an inner heat insulation layer melt, and extrude through a double-layer co-extrusion die head to form a double-layer hollow film; Step 3: Pass compressed air into the extruded double-layer hollow film to blow it up to form a bubble tube, and then cool and solidify it through an air ring and then wind and roll it up; Step 4: Immerse the wound double-layer hollow film in an extraction solution to remove the pore-forming agent, and obtain the ultra-high molecular weight polyethylene double-layer hollow microporous membrane after drying.
[0013] As a preference, in the said Step 1, the pore-forming agent accounts for 50% - 95% of the total mass of the outer photothermal layer composite material and the inner heat insulation layer composite material, and the pore-forming agent is one or more of PVP, PEG, PVA, paraffin oil, vaseline, paraffin, vegetable oil, decahydronaphthalene, sodium chloride, potassium carbonate, lithium chloride, ADC foaming agent.
[0014] As a preference, in the said Step 1, the photothermal material, ultra-high molecular weight polyethylene and the pore-forming agent are dispersed and mixed in a stirring kettle for 1 - 8 h, and the temperature during the dispersion and mixing is 80 °C; the hydrophilic material, ultra-high molecular weight polyethylene and the pore-forming agent are dispersed and mixed in a stirring kettle for 1 - 8 h, and the temperature during the dispersion and mixing is 80 °C.
[0015] As a preference, in the said Step 2, the extruder is a twin-rotor extruder, a single-screw extruder or a multi-screw extruder, and the melting and plasticizing temperature is 190 °C - 230 °C; the double-layer co-extrusion die head is a double-layer blown film die head.
[0016] As a preference, in the said Step 3, adjusting the amount of compressed air introduced can control the expansion degree of the bubble tube. The ratio of the diameter of the blown bubble tube to the diameter of the double-layer co-extrusion die head is the blowing ratio, and the blowing ratio indicates the magnitude of the transverse tensile force received by the molecular chain, that is, the orientation degree of the microporous membrane under transverse tension.
[0017] As a preference, in the said Step 4, during the winding process of the bubble tube, it is subjected to the action of stretching, and the ratio of the speed of the bubble tube passing through the traction roller to the extrusion speed of the double-layer co-extrusion die head is the draw ratio, and the draw ratio represents the orientation degree of the microporous membrane under longitudinal tension.
[0018] In the above method for preparing the ultra-high molecular weight polyethylene double-layer hollow microporous membrane, the principle is as follows: Through the thermally induced phase separation method, ultra-high molecular weight polyethylene, functional fillers (photothermal materials / hydrophilic materials), and pore-forming agents are mixed according to a ratio. After melt blending and extrusion blow molding, the pore-forming agents are removed by extraction to form a porous structure with ultra-high molecular weight polyethylene as the framework and functional fillers attached. The ultra-high molecular weight polyethylene double-layer hollow microporous membrane is prepared by co-extrusion-blow molding. The double-layer co-extrusion die head enables the outer photothermal layer melt and the inner heat-insulating layer melt to directly form a double-layer film. During the blow molding process, compressed air inflation and the traction roller cause the double-layer hollow film to be stretched radially and axially. Under the tensile stress, the molecular chains are oriented and crystallized, improving the mechanical properties of the film. At the same time, this preparation method has high production efficiency and can carry out continuous industrial production.
[0019] An application of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane, which is used in solar seawater desalination, allowing sunlight to directly irradiate the outer photothermal layer, and the seawater to directly contact the inner heat-insulating layer.
[0020] The specific steps are as follows: Fix the ultra-high molecular weight polyethylene double-layer hollow microporous membrane in a light-transmitting pipeline. There is a certain gap between the light-transmitting pipeline and the ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Seawater is directly introduced into the interior of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Sunlight passes through the light-transmitting pipeline and irradiates the outer photothermal layer. After the seawater evaporates, it cools and condenses on the inner surface of the light-transmitting pipeline to form pure water.
[0021] In the above application of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane, the principle is as follows: The ultra-high molecular weight polyethylene double-layer hollow microporous membrane realizes efficient photothermal conversion and seawater evaporation through the design of the double-layer porous structure. The outer photothermal layer contains photothermal materials, which can convert solar energy into heat energy, increasing the surface temperature of the seawater and thus accelerating the evaporation rate. The microporous structure of the outer photothermal layer enables sunlight to be reflected and absorbed multiple times within the membrane, significantly improving the light absorption efficiency; the inner heat-insulating layer is hydrophilic, capable of adsorbing seawater and transporting it through the microporous structure. At the same time, as a heat-insulating layer, it prevents the heat generated by the outer layer from directly conducting into the seawater, reducing heat loss. This double-layer structure design improves the evaporation efficiency and energy utilization efficiency, making the seawater desalination process more efficient and energy-saving.
[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Through the double-layer composite structure of the outer photothermal layer (including photothermal materials) and the inner heat-insulating layer (including hydrophilic materials), the synergistic improvement of the photothermal conversion efficiency and the heat-insulating performance is achieved. The photothermal materials (such as carbon fiber, graphene) in the outer photothermal layer absorb and reflect sunlight, efficiently converting solar energy into heat energy; the micropores, as through-holes, can increase the contact area between the photothermal materials and light, reducing reflection losses; the hydrophilic materials (such as silica, alumina) in the inner heat-insulating layer cooperate with the micropores to adsorb and transport water to the outer photothermal layer, while the heat-insulating property of the ultra-high molecular weight polyethylene framework reduces the reverse heat conduction to the water body, maintaining a stable water evaporation process.
[0023] 2. The micropore diameter is set to 0.1 - 20 μm, and the porosity is set to 50% - 70%, and is precisely controlled by the double-layer co-extrusion process to form a connected double-layer microporous network, which has both high water permeability and mechanical strength, avoiding the problems of reduced permeation efficiency or structural collapse caused by too large or too small pore diameters in traditional single-layer membranes.
[0024] 3. The wide-range proportion design of the photothermal materials (0 - 50 parts) and the hydrophilic materials (0 - 30 parts) enables the product to be flexibly adjusted according to different application scenarios. When the photothermal materials are 0: The pure ultra-high molecular weight polyethylene layer realizes the basic photothermal function by reflecting / scattering light through the micropores, which is suitable for low-irradiance environments; when the hydrophilic materials are 0: Water transportation is realized by relying on the weak hydrophilicity of the ultra-high molecular weight polyethylene itself and the capillary action of the micropores, which is suitable for low-salinity water desalination.
[0025] 4. Through the double-layer co-extrusion + blow molding process, the seamless combination and micropore connection of the outer photothermal layer and the inner heat-insulating layer are achieved, avoiding the delamination problem caused by insufficient interfacial bonding force in traditional composite membranes.
[0026] 5. The proportion of the porogen is 50% - 95%. Combined with the extraction process, the micropore diameter and porosity can be precisely regulated, and the diverse selection of porogen types (such as PVP, paraffin oil, etc.) is adapted to different solvent systems (such as water-soluble or oil-soluble), reducing residues.
[0027] 6. The adapted design of the melting and plasticizing temperature (190 - 230 °C) and the molecular weight of ultra-high molecular weight polyethylene (1.5 million - 6 million) reduces the processing energy consumption while ensuring the material fluidity.
[0028] 7. By applying the ultra-high molecular weight polyethylene double-layer hollow microporous membrane to solar seawater desalination, the outer photothermal layer directly absorbs sunlight and converts it into heat energy, and the inner heat-insulating layer continuously supplies water and insulates heat, resulting in a significant improvement in the evaporation efficiency compared with traditional single-layer evaporation membranes.
[0029] 8. The gap between the light-transmitting pipe and the ultra-high molecular weight polyethylene double-layer hollow microporous membrane is set, and the evaporated water vapor is naturally condensed in the gap without an additional condensing device, which simplifies the system structure. Moreover, the light-transmitting pipe can protect the membrane from external pollution and extend its service life. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 is a cross-sectional view of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane of the present invention; Figure 2 is a process flow chart for preparing the ultra-high molecular weight polyethylene double-layer hollow microporous membrane of the present invention; Figure 3 is a schematic diagram of the application of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane of the present invention; Wherein: 1 is an outer photo-thermal layer, 2 is a photo-thermal material, 3 is an ultra-high molecular weight polyethylene skeleton, 4 is a hydrophilic material, 5 is an inner heat-insulating layer, 6 is a micropore, 7 is an extruder, 8 is a double-layer co-extrusion head, 9 is an air ring, 10 is a bubble tube, 11 is a chevron plate, 12 and 13 are haul-off rolls, 14 is a winding roll, 15 is an extraction liquid, 16 is sunlight, 17 is a light-transmitting pipe, 18 is seawater to be desalinated, and 19 is a gap. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0031] The present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
[0032] As Figure 1 shown, an ultra-high molecular weight polyethylene double-layer hollow microporous membrane, the microporous membrane includes an outer photo-thermal layer and an inner heat-insulating layer; The outer photo-thermal layer includes an ultra-high molecular weight polyethylene skeleton and a photo-thermal material. The photo-thermal material is distributed in the ultra-high molecular weight polyethylene skeleton, and the ultra-high molecular weight polyethylene skeleton has micropores. The micropores are through holes penetrating the outer photo-thermal layer. The photo-thermal material and the micropores distributed in the ultra-high molecular weight polyethylene skeleton cooperate to absorb and reflect the sunlight irradiated on the outer photo-thermal layer, and convert solar energy into heat energy; The inner heat-insulating layer includes an ultra-high molecular weight polyethylene skeleton and a hydrophilic material. The hydrophilic material is distributed in the ultra-high molecular weight polyethylene skeleton, and the ultra-high molecular weight polyethylene skeleton has micropores. The micropores are through holes penetrating the inner heat-insulating layer. Among them, the micropores in the inner heat-insulating layer are communicated with the micropores in the outer photo-thermal layer. The hydrophilic material and the micropores distributed in the ultra-high molecular weight polyethylene skeleton cooperate to adsorb the liquid and transport it to the outer photo-thermal layer to maintain a stable water evaporation process.
[0033] As Figure 2 shown, a method for preparing an ultra-high molecular weight polyethylene double-layer hollow microporous membrane includes the following steps: Step 1: Mix carbon black, ultra-high molecular weight polyethylene, and paraffin oil evenly at a mass ratio of 1:1:4 in a stirring kettle and stir for 2 h at a stirring temperature of 80 °C to obtain the outer photothermal layer mixture; mix silica, ultra-high molecular weight polyethylene, and paraffin oil evenly at a mass ratio of 3:7:28 in a stirring kettle and stir for 2 h at a stirring temperature of 80 °C to obtain the inner heat insulation layer mixture; Step 2: Add the outer photothermal layer mixture and the inner heat insulation layer mixture in Step 1 into the corresponding single-screw extruders respectively, perform melt plasticization at 230 °C to form the outer photothermal layer melt and the inner heat insulation layer melt respectively, and extrude through a double-layer co-extrusion die head to form a double-layer hollow film; Step 3: Pull the double-layer hollow film extruded in Step 2 onto the chevron board to form a sealed cylinder, and introduce compressed air into the double-layer hollow film to blow it into an inflated bubble tube. The blow-up ratio is 5. After cooling and solidifying by the air ring, longitudinally traction and stretch it by the traction roller. The draw ratio is 2, and then wind it up by the winding roller; Step 4: Immerse the double-layer hollow film cooled and wound up in Step 3 in the extraction liquid for 2 h to remove the pore-forming agent, and obtain the ultra-high molecular weight polyethylene double-layer hollow microporous membrane after drying.
[0034] The ultra-high molecular weight polyethylene double-layer hollow microporous membrane prepared in this example has a thickness of 24.6 μm, an average pore diameter of 214 nm, and a porosity of 65.3%. Under the light intensity of 1 kW / m 2 The evaporation rate is 2.1 L / (m 2 •h), the light absorption rate is 92%, and the heat loss is reduced by 35% compared with the single-layer membrane.
[0035] As Figure 3 shown, for the application of an ultra-high molecular weight polyethylene double-layer hollow microporous membrane, the ultra-high molecular weight polyethylene double-layer hollow microporous membrane is used in solar seawater desalination, and the sunlight directly irradiates the outer photothermal layer, and the seawater is in direct contact with the inner heat insulation layer.
[0036] Specifically, fix the ultra-high molecular weight polyethylene double-layer hollow microporous membrane in a light-transmitting pipeline with a light transmittance ≥ 90%. There is a certain gap between the light-transmitting pipeline and the ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Directly introduce seawater (i.e., the seawater to be desalinated) into the ultra-high molecular weight polyethylene double-layer hollow microporous membrane. The sunlight passes through the light-transmitting pipeline and irradiates the outer photothermal layer. The carbon black in the outer photothermal layer performs photothermal conversion, converts solar energy into heat energy, heats up the seawater to evaporate, and the water vapor passes through the micropores of the inner heat insulation layer and the outer photothermal layer, meets the relatively low-temperature transparent pipeline on the outer layer, and cools and condenses on the inner surface of the light-transmitting pipeline to form pure water.
[0037] In addition to the methods mentioned in the above embodiments, the components and mass fractions of the outer photothermal layer can be 0 to 50 parts of photothermal material and 50 to 100 parts of ultra-high molecular weight polyethylene; the components and mass fractions of the inner heat insulation layer can be 0 to 30 parts of hydrophilic material and 70 to 100 parts of ultra-high molecular weight polyethylene; the molecular weight of the ultra-high molecular weight polyethylene can be 1.5 million to 6 million, and the molecular weights of the ultra-high molecular weight polyethylene used in the outer photothermal layer and the inner heat insulation layer can be the same or different; the photothermal material can also be one or more of carbon fiber, graphene or carbon nanotube; the hydrophilic material can also be one or more of alumina, titanium dioxide or zinc oxide; the micropore aperture of the outer photothermal layer and the inner heat insulation layer can be 0.1 to 20 μm, and the porosity can be 50% to 70%; the pore-forming agent can also be one or more of PVP, PEG, PVA, petrolatum, paraffin, vegetable oil, decahydronaphthalene, sodium chloride, potassium carbonate, lithium chloride, ADC foaming agent; the dispersion and mixing of the photothermal material, ultra-high molecular weight polyethylene and pore-forming agent in a stirring kettle can be 1 to 8 hours; the dispersion and mixing of the hydrophilic material, ultra-high molecular weight polyethylene and pore-forming agent in a stirring kettle can be 1 to 8 hours; the extruder can also be a twin-rotor extruder or a multi-screw extruder, and the melting and plasticizing temperature can be 190°C to 230°C. These transformation methods are all within the protection scope of the present invention.
[0038] The above embodiments only represent several implementation modes of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent shall be subject to the appended claims.
Claims
1. A ultra-high molecular weight polyethylene double-layer hollow microporous membrane, characterized in that: It includes an outer photothermal layer and an inner heat insulation layer; The components and mass fractions of the outer photothermal layer are 0-50 parts of photothermal material and 50-100 parts of ultra-high molecular weight polyethylene; the outer photothermal layer includes an ultra-high molecular weight polyethylene skeleton and a photothermal material. The photothermal material is distributed in the ultra-high molecular weight polyethylene skeleton, and there are micropores in the ultra-high molecular weight polyethylene skeleton. The micropores are through holes penetrating the outer photothermal layer. The photothermal material and micropores distributed in the ultra-high molecular weight polyethylene skeleton cooperate to absorb and reflect the sunlight irradiated on the outer photothermal layer, and convert solar energy into heat energy; The components and mass fractions of the inner heat insulation layer are 0-30 parts of hydrophilic material and 70-100 parts of ultra-high molecular weight polyethylene; the inner heat insulation layer includes an ultra-high molecular weight polyethylene skeleton and a hydrophilic material. The hydrophilic material is distributed in the ultra-high molecular weight polyethylene skeleton, and there are micropores in the ultra-high molecular weight polyethylene skeleton. The micropores are through holes penetrating the inner heat insulation layer. Among them, the micropores in the inner heat insulation layer are connected to the micropores in the outer photothermal layer. The hydrophilic material and micropores distributed in the ultra-high molecular weight polyethylene skeleton cooperate to adsorb liquid and transport it to the outer photothermal layer to maintain a stable water evaporation process.
2. The ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 1, wherein: The molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 6 million, and the molecular weights of the ultra-high molecular weight polyethylene used in the outer photothermal layer and the inner heat insulation layer are the same or different.
3. The ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 1, wherein: The photothermal material is one or more of carbon fiber, graphene, carbon nanotube or carbon black; the hydrophilic material is one or more of alumina, silica, titanium dioxide or zinc oxide.
4. The ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 1, wherein: The micropore aperture of the outer photothermal layer and the inner heat insulation layer is 0.1-20 μm, and the porosity is 50%-70%.
5. A method for preparing the ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to any one of claims 1-4, characterized in that: It includes the following steps: Step 1: Mix the photothermal material, ultra-high molecular weight polyethylene and pore-forming agent evenly according to the preset mass ratio to obtain the outer photothermal layer mixture; mix the hydrophilic material, ultra-high molecular weight polyethylene and pore-forming agent evenly according to the preset mass ratio to obtain the inner heat insulation layer mixture; Step 2: Add the outer photothermal layer mixture and the inner heat insulation layer mixture into the corresponding extruders respectively for melt plasticization to form an outer photothermal layer melt and an inner heat insulation layer melt, and extrude through a double-layer co-extrusion head to form a double-layer hollow film; Step 3: Pass compressed air into the extruded double-layer hollow film to blow it up to form a bubble tube, and then cool and solidify it through an air ring and then wind and roll it up; Step 4: Immerse the wound double-layer hollow film in the extraction liquid to remove the pore-forming agent, and dry it to obtain the ultra-high molecular weight polyethylene double-layer hollow microporous membrane.
6. The preparation method of a ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 5, characterized in that: In the step 1, the pore-forming agent accounts for 50%-95% of the total mass of the outer photothermal layer mixture and the inner heat insulation layer mixture, and the pore-forming agent is one or more of PVP, PEG, PVA, paraffin oil, vaseline, paraffin, vegetable oil, decahydronaphthalene, sodium chloride, potassium carbonate, lithium chloride, ADC foaming agent.
7. The preparation method of a ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 5, characterized in that: In the step 1, the photothermal material, ultra-high molecular weight polyethylene and pore-forming agent are dispersed and mixed in a stirring kettle for 1-8 h, and the temperature during dispersion and mixing is 80 °C; the hydrophilic material, ultra-high molecular weight polyethylene and pore-forming agent are dispersed and mixed in a stirring kettle for 1-8 h, and the temperature during dispersion and mixing is 80 °C.
8. The preparation method of a ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 5, characterized in that: In the step 2, the extruder is a twin-screw extruder, a single-screw extruder or a multi-screw extruder, and the melting and plasticizing temperature is 190°C to 230°C; the double-layer co-extrusion head is a double-layer blown film head.
9. Use of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to any one of claims 1 to 4, characterized in that: The ultra-high molecular weight polyethylene double-layer hollow microporous membrane is used in solar seawater desalination, enabling sunlight to directly irradiate the outer photothermal layer, and the seawater to directly contact the inner heat insulation layer.
10. The application of a ultra-high molecular weight polyethylene double-layer hollow microporous membrane according to claim 9, characterized in that: The ultra-high molecular weight polyethylene double-layer hollow microporous membrane is fixed in a light-transmitting pipeline, and there is a certain gap between the light-transmitting pipeline and the ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Seawater is directly introduced into the interior of the ultra-high molecular weight polyethylene double-layer hollow microporous membrane. Sunlight passes through the light-transmitting pipeline and irradiates the outer photothermal layer. After the seawater evaporates, it cools and condenses on the inner surface of the light-transmitting pipeline to form pure water.