An ultrahigh molecular weight polyethylene / nanofiller porous membrane, a method for preparing the same, and use thereof

Abstract

The application belongs to the technical field of polymer materials, and particularly relates to a kind of ultra-high molecular weight polyethylene / nano filler porous membrane, its preparation method and use. The ultra-high molecular weight polyethylene / nano filler porous membrane is prepared according to the following method: modified or unmodified ultra-high molecular weight polyethylene and nano filler are ball milled to obtain a mixture; the ultra-high molecular weight polyethylene, the mixture and a diluent are mixed and subjected to layering and composite extrusion molding; the layering and composite extrusion molding process includes melting, layering and composite in a flow channel and bidirectional stretching; traction cooling is performed, or after traction cooling, synchronous or asynchronous biaxial stretching is performed to obtain an ultra-high molecular weight polyethylene gel membrane; the diluent is removed with a solvent, and the porous membrane is obtained. The porous membrane can be further made into a photo-thermal porous separation membrane, which has the advantages of good dispersion effect of nano filler and uniform pore size distribution, can realize efficient solar-driven photo-thermal evaporation concentration, and has good application prospect.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to an ultra-high molecular weight polyethylene / nanofiller porous membrane, its preparation method, and its applications. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) microporous membranes are widely used in lithium battery separators and other fields due to their excellent mechanical properties, resistance to acid and alkali corrosion, good wear resistance, and adjustable pore size. However, nascent UHMWPE often suffers from excessive molecular chain entanglement, high viscosity, and difficulties in processing and molding. Therefore, it is necessary to add a large amount of diluent (such as aliphatic chain hydrocarbons or paraffin oil) to form a gel, thereby significantly reducing the degree of molecular chain entanglement and melt viscosity of UHMWPE. Then, through the force field effect during the casting process, a continuous intermolecular topological network is constructed, enabling high-rate biaxial thermal stretching and effectively controlling the crystal network structure of UHMWPE. Finally, the diluent is removed to prepare UHMWPE microporous membranes with different porous structures. Generally, higher diluent content results in higher porosity of the microporous membrane, but also larger pore size and a significant decrease in membrane strength. Increasing the molecular weight of UHMWPE is beneficial for improving the strength of the microporous membrane, but it leads to a significant increase in the degree of molecular chain entanglement. To achieve high molecular weight UHMWPE (Mw > 1 × 10⁻⁶), 7 The complete detangling of molecular chains usually requires a larger amount of diluent, but how to achieve the stability of detangling by forming a continuous intermolecular topological network structure through a stronger processing force field still needs to be broken through.

[0003] The introduction of nanofillers (such as nano-alumina) is beneficial to the formation of a uniform porous network structure in UHMWPE during the stretching process. On the other hand, in order to endow it with better functions, the material is generally a combination of functional nanoparticles and polymer matrix. For example, carbon nanofillers can provide good photothermal evaporation characteristics for UHMWPE porous membranes (Y.Guo, H.Wu, S.Guo, J.Qiu, Tunable all-in-one bimodal porous membrane of ultrahigh molecularweight polyethylene for solar driven interfacial evaporation, Sep Purif Technol 302 (2022) 122071. https: / / doi.org / https: / / doi.org / 10.1016 / j.seppur.2022.122071.). There have been many research reports on the preparation of nanofiller / polymer composites, which are mainly divided into three types: in-situ polymerization, solution mixing, and melt blending. In comparison, melt blending is simple, low-cost, and easy to scale up for industrial production. However, nanofiller / polymer composites prepared by direct melt blending have drawbacks such as uneven mixing and poor performance; and agglomerated nanofillers reduce functionality, requiring an increase in filler content, which reduces the strength of the composite material and increases the cost.

[0004] Therefore, in the melt blending process of polymer / nanofiller composites, how to uniformly disperse the nanofillers in the polymer is an important research topic in this field. Summary of the Invention

[0005] To address the problems of existing technologies, the present invention aims to provide an ultra-high molecular weight polyethylene / nanofiller porous membrane, its preparation method, and its applications.

[0006] An ultra-high molecular weight polyethylene / nanofiller porous membrane is prepared by the following method:

[0007] Step 1: Ball milling ultra-high molecular weight polyethylene and nanofiller to obtain a mixture. The ratio of ultra-high molecular weight polyethylene to nanofiller during the ball milling process is (20-80):(80-20) by weight.

[0008] Step 2: Mix ultra-high molecular weight polyethylene, the mixture obtained in Step 1 and diluent, and perform laminated composite extrusion molding; the laminated composite extrusion molding process includes melting, in-channel laminated compounding and biaxial stretching; the total amount of ultra-high molecular weight polyethylene used in gel film extrusion and the ratio of the amount of nanofiller used are by weight ratio (70-95):(30-5).

[0009] Step 3: traction cooling to obtain an ultra-high molecular weight polyethylene gel film, or traction cooling followed by synchronous or asynchronous biaxial stretching to obtain an ultra-high molecular weight polyethylene gel film.

[0010] Step 4: Remove the diluent with a solvent to obtain the ultra-high molecular weight polyethylene / nanofiller porous membrane.

[0011] Preferably, in step 1, the ratio of ultra-high molecular weight polyethylene to nanofiller used in the ball milling process is 10:30 by weight.

[0012] In step 2, the ratio of the total amount of ultra-high molecular weight polyethylene raw material to the amount of nanofiller used in the gel film extrusion process is 90:10 by weight.

[0013] Preferably, the ultra-high molecular weight polyethylene is selected from modified ultra-high molecular weight polyethylene, unmodified ultra-high molecular weight polyethylene, or a combination thereof, wherein the modified ultra-high molecular weight polyethylene is an ultra-high molecular weight polyethylene containing oxygen or fluorine functional groups.

[0014] And / or, the molecular weight of the ultra-high molecular weight polyethylene is 5 million to 11 million;

[0015] And / or, the nanofiller is one or more of graphite, carbon nanotubes, graphene, carbon black, nano alumina, and nano titanium dioxide.

[0016] Preferably, in step 1, an antioxidant is also added during the ball milling process;

[0017] The antioxidant is selected from at least one of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis(bis-T-butylhydroxyhydrogenated cinnamic acid) ester, pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), tetrakis(methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)methane, antioxidant 1010, pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(di-butylhydroxyhydrogenated cinnamic acid) ester, and antioxidant 168.

[0018] And / or, the amount of the antioxidant is 0.05-0.5% of the mass of ultra-high molecular weight polyethylene.

[0019] Preferably, in step 1, the ball-to-material ratio of the ball mill is a mass ratio of (5-20):1; and / or, the ball milling time is 0-24h; and / or, the ball mill speed is 350-550rpm; and / or, the grinding balls are of three types with diameters of 3mm, 5mm and 10mm, and the mass ratio of the three types of grinding balls is (1-3):(1-3):(1-3).

[0020] Preferably, in step 2, the diluent is selected from at least one of white oil, paraffin oil, and petrolatum;

[0021] And / or, after mixing ultra-high molecular weight polyethylene, the mixture obtained in step 1 and the diluent, the solid content is 1-5 wt%.

[0022] Preferably, in step 2, the feeding port temperature of the laminated composite extrusion molding is 130-180℃, and the extrusion temperature is 160-220℃;

[0023] And / or, in step 2, the number of laminated composite multipliers formed by the laminated composite extrusion molding is 1-9, the lamination ratio of a single laminated multiplier is 2-8 times, and the number of laminations is 2-8. 9 Second-rate.

[0024] Preferably, in step 3, the traction cooling temperature is 0-25℃;

[0025] And / or, in step 3, the biaxial stretching ratio is (2×2)-(32×32);

[0026] And / or, in step 3, the thickness of the thinner ultra-high molecular weight polyethylene gel film ranges from 0.1 to 100 micrometers;

[0027] And / or, in step 4, the solvent is one or more of dichloromethane, n-hexane, and ethanol.

[0028] The present invention also provides a method for preparing the above-mentioned ultra-high molecular weight polyethylene / nanofiller porous membrane, comprising the following steps:

[0029] Step 1: Ball milling ultra-high molecular weight polyethylene and nanofiller to obtain a mixture. The ratio of ultra-high molecular weight polyethylene to nanofiller during the ball milling process is (20-80):(80-20) by weight.

[0030] Step 2: Mix ultra-high molecular weight polyethylene, the mixture obtained in Step 1 and the diluent, and perform laminated composite extrusion molding; the laminated composite extrusion molding process includes melting, in-channel laminated compounding and biaxial stretching; in Step 2, the total amount of ultra-high molecular weight polyethylene used in gel film extrusion and the ratio of the amount of nanofiller used are by weight ratio (70-95):(30-5).

[0031] Step 3: traction cooling to obtain an ultra-high molecular weight polyethylene gel film, or traction cooling followed by synchronous or asynchronous biaxial stretching to obtain an ultra-high molecular weight polyethylene gel film.

[0032] Step 4: Remove the diluent with a solvent to obtain the final product.

[0033] The present invention also provides the use of the above-mentioned ultra-high molecular weight polyethylene / nanofiller porous membrane for photothermal film separation, infrared stealth, wave absorption or electromagnetic shielding.

[0034] This invention relates to a novel process for preparing ultra-high molecular weight polyethylene (UHMWPE) / nanofiller photothermal porous separation membranes. Specifically, graphite is exfoliated into graphite nanosheets using a co-ball milling method and coated onto the surface of UHMWPE particles. Simultaneously, a gel-method melt extrusion is employed, followed by multiple segmentation and overlapping operations using a layered composite device within the flow channel. This process creates a bidirectional stretching flow field, promoting molecular chain deentanglement and forming an intermolecular topological network structure. Similar to physical cross-linking, this inhibits molecular chain retraction and re-entanglement, and promotes uniform dispersion of graphite nanosheets within the gel membrane. This uniform intermolecular topological network structure is effectively maintained during cooling, fixing the graphite nanosheets and promoting the formation of a uniform crystalline network structure. The resulting UHMWPE / carbon nanofiller composite gel membrane, possessing uniformly dispersed graphite nanosheets and a uniformly crystalline UHMWPE molecular chain network structure, further facilitates the dispersion of graphite nanosheets under high-multiaxial thermal stretching conditions, resulting in a porous UHMWPE / nanofiller membrane with a uniform pore size distribution.

[0035] The ultra-high molecular weight polyethylene / nanofiller photothermal porous separation membrane prepared according to the process of this invention exhibits excellent dispersion of graphite nanosheets and uniform pore size distribution, thus enabling highly efficient solar-driven photothermal evaporation and concentration. Therefore, this invention has excellent application prospects.

[0036] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0037] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0039] Figure 2Polarized light microscope images of the ultra-high molecular weight polyethylene / carbon nanofiller gel films prepared for Examples 1(A) and 4(B). Detailed Implementation

[0040] In the following examples and experimental cases, reagents and raw materials not specifically described are all commercially available products.

[0041] Example 1: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0042] (1) Weigh 10g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then, grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the milled product.

[0043] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, maintaining the solid content of the UHMWPE single component at 5wt%, the white oil content at 95wt%, and the graphite nanosheet addition at 10wt% of UHMWPE. Pour the mixture into the extruder feed cylinder at 180℃, preheat for 30 seconds to form a homogeneous gel, and then extrude. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. No laminated composite modules are used. The extruded gel film has a thickness of 2mm and a width of 10cm. The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed. Soak the gel film in n-hexane for 24 hours to remove the white oil, thus obtaining a porous membrane.

[0044] Example 2: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0045] The process flow of this embodiment is as follows: Figure 1 As shown.

[0046] (1) Weigh 10g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then, grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the milled product.

[0047] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, keeping the solid content of UHMWPE at 5wt%, the white oil content at 95wt%, and the amount of graphite nanosheets added at 10wt% of UHMWPE. Pour the mixture into the feed cylinder of an extruder at 180℃. After preheating for 30 seconds to form a uniform gel, extrude the mixture. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 3 stacked composite modules in the flow channel, with a stacking ratio of 2 times for each module, i.e., a total of 8 stacking times, all at 180℃. The extrusion process of the gel in a single stacked composite module can be divided into three parts. First, the gel flow is vertically divided, then it is quickly divided into upper and lower layers and stacked. Further, the gel is untangled and the filler is dispersed by the extrusion action in the thickness direction of the flow channel, the stretching action in the flow direction, and the expansion action in the vertical flow direction. The thickness of the extruded gel film is 2mm and the width is 10cm.

[0048] The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed. The gel membrane is soaked in n-hexane for 24 hours, and the white oil is removed to obtain the porous membrane.

[0049] Example 3: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0050] (1) Weigh 10g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then, grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the milled product.

[0051] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, keeping the solid content of UHMWPE at 5wt%, the white oil content at 95wt%, and the amount of graphite nanosheets added at 10wt% of UHMWPE. Pour the mixture into the feed cylinder of an extruder at 180℃. After preheating for 30 seconds to form a homogeneous transparent gel, extrude the mixture. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 9 composite modules stacked in the flow channel, with a stacking ratio of 2 for each module, resulting in a total of 512 stacking times. The temperature is 180℃ for all modules. The thickness of the extruded gel film is 2mm, and the width is 10cm.

[0052] The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed. The gel membrane is soaked in n-hexane for 24 hours, and the white oil is removed to obtain the porous membrane.

[0053] Example 4: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0054] (1) Weigh 5g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 5g of UHMWPE (ATTUPE, Nanjing Tengyi New Material Technology Co., Ltd.) containing oxygen and fluorine functional groups, 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the ball milled product.

[0055] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, keeping the solid content of UHMWPE at 5wt%, the white oil content at 95wt%, and the amount of graphite nanosheets added at 10wt% of UHMWPE. Pour the mixture into the feed cylinder of an extruder at 180℃. After preheating for 30 seconds to form a homogeneous transparent gel, extrude the mixture. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 9 composite modules stacked in the flow channel, with a stacking ratio of 2 for each module, resulting in a total of 512 stacking times. The temperature is 180℃ for all modules. The thickness of the extruded gel film is 2mm, and the width is 10cm.

[0056] The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed. The gel membrane is soaked in n-hexane for 24 hours, and the white oil is removed to obtain the porous membrane.

[0057] Example 5: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0058] (1) Weigh 5g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 5g of UHMWPE (ATT UPE) containing oxygen and fluorine functional groups (Nanjing Tengyi New Material Technology Co., Ltd.), 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the ball milled product.

[0059] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, maintaining the UHMWPE solid content at 5wt%, the white oil content at 95wt%, and the graphite nanosheet addition at 10wt% of UHMWPE. Pour the mixture into the extruder feed cylinder at 180℃, preheat for 30 seconds to form a homogeneous transparent gel, and then extrude. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 9 composite modules stacked in the flow channel, with a stacking ratio of 2 for each module, resulting in a total of 512 stacking times. The temperature is 180℃ for all modules, and the extruded gel film thickness is 2mm and the width is 10cm. The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed.

[0060] (3) Cut the gel membrane into 10×10cm wide samples and perform biaxial stretching at 125℃. First, heat the membrane at 125℃ for 180 seconds and then perform synchronous biaxial stretching at a speed of 2% / s, with a stretching ratio of 8×8. Soak the gel membrane in n-hexane for 24 hours to remove the white oil and obtain the porous membrane.

[0061] Example 6: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0062] (1) Weigh 5g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 5g of UHMWPE (ATT UPE) containing oxygen and fluorine functional groups (Nanjing Tengyi New Material Technology Co., Ltd.), 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the ball milled product.

[0063] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, maintaining the UHMWPE solid content at 5wt%, the white oil content at 95wt%, and the graphite nanosheet addition at 10wt% of UHMWPE. Pour the mixture into the extruder feed cylinder at 180℃, preheat for 30 seconds to form a homogeneous transparent gel, and then extrude. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 9 composite modules stacked in the flow channel, with a stacking ratio of 2 for each module, resulting in a total of 512 stacking times. The temperature is 180℃ for all modules, and the extruded gel film thickness is 2mm and the width is 10cm. The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed.

[0064] (3) Cut the gel membrane into 10×10cm wide samples and perform asynchronous biaxial stretching at 125℃. First, heat the membrane at 125℃ for 180 seconds and then perform asynchronous biaxial stretching at a speed of 2% / s. Define the direction parallel to the stretching instrument as MD and the direction perpendicular to the stretching direction as TD. First, fix the TD direction and stretch along the MD direction. After stretching to 8 times, fix the MD direction and apply stretching along the TD direction to 8 times, that is, the total stretching ratio is 8×8, which yields a thinner gel membrane.

[0065] The gel membrane was soaked in n-hexane for 24 hours to remove the white oil, thus obtaining the porous membrane.

[0066] Example 7: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0067] (1) Weigh 5g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 5g of UHMWPE (ATT UPE) containing oxygen and fluorine functional groups (Nanjing Tengyi New Material Technology Co., Ltd.), 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the ball milled product.

[0068] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, maintaining the UHMWPE solid content at 5wt%, the white oil content at 95wt%, and the graphite nanosheet addition at 10wt% of UHMWPE. Pour the mixture into the extruder feed cylinder at 180℃, preheat for 30 seconds to form a homogeneous transparent gel, and then extrude. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 9 composite modules stacked in the flow channel, with a stacking ratio of 2 for each module, resulting in a total of 512 stacking times. The temperature is 180℃ for all modules, and the extruded gel film thickness is 2mm and the width is 10cm. The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed.

[0069] (3) Cut the gel membrane into 10×10cm wide samples and perform biaxial stretching at 125℃. First, hold the membrane at 125℃ for 180 seconds and then perform synchronous biaxial stretching at a speed of 2% / s, with a stretching ratio of 8×8. Further cut the sample into 10×10cm sizes and stretch it again. Place the membrane at 130℃ for 120 seconds and then perform synchronous biaxial stretching at a speed of 0.7% / s, with a stretching ratio of 2×2, that is, a total stretching ratio of 16×16 times. Soak the gel membrane in n-hexane for 24 hours to remove the white oil and obtain the porous membrane.

[0070] Example 8: Ultra-high molecular weight polyethylene / carbon nanofiller porous membrane

[0071] (1) Weigh 5g of UHMWPE (Celanis, GUR 4172) with a molecular weight of over 10 million, 5g of UHMWPE (ATT UPE) containing oxygen and fluorine functional groups (Nanjing Tengyi New Material Technology Co., Ltd.), 30g of graphite, 0.05g of antioxidant 1010, and 0.05g of antioxidant 168. After manually stirring and mixing, add the mixture to a 250ml ball mill jar containing grinding balls. The mass ratio of grinding balls to powder mixture is 5:1. The grinding balls are divided into three sizes: large, medium, and small, with a mass ratio of 1:1:1. Then grind the mixture in the ball mill jar at 500rpm for 12 hours and remove the ball milled product.

[0072] (2) Mix the powder with a certain amount of UHMWPE powder and white oil, maintaining the UHMWPE solid content at 5wt%, the white oil content at 95wt%, and the graphite nanosheet addition at 10wt% of UHMWPE. Pour the mixture into the extruder feed cylinder at 180℃, preheat for 30 seconds to form a homogeneous transparent gel, and then extrude. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 9 composite modules stacked in the flow channel, with a stacking ratio of 2 for each module, resulting in a total of 512 stacking times. The temperature is 180℃ for all modules, and the extruded gel film thickness is 2mm and the width is 10cm. The cooling roller temperature is 20℃, and the traction speed is the same as the extrusion speed.

[0073] (3) Cut the gel membrane into 10×10cm wide samples and perform biaxial stretching at 125℃. First, hold the membrane at 125℃ for 180 seconds and then perform synchronous biaxial stretching at a speed of 2% / s, with a stretching ratio of 8×8. Further cut the sample into 10×10cm sizes and stretch it again. Place the membrane at 130℃ for 120 seconds and then perform synchronous biaxial stretching at a speed of 0.7% / s, with a stretching ratio of 4×4, that is, a total stretching ratio of 32×32 times. Soak the gel membrane in n-hexane for 24 hours to remove the white oil and obtain the porous membrane.

[0074] The technical solution of the present invention will be further explained through experiments below.

[0075] Experiment Example 1 Performance Test

[0076] I. Experimental Methods

[0077] This experimental example tests the samples prepared in Examples 1-6. The specific steps are as follows:

[0078] The absorbance of the porous membrane was calculated using a UV3600 UV-Vis-NIR spectrophotometer with an integrating sphere. The porous membrane was placed under a solar simulator equipped with an AM1.5 filter, and its temperature change over time was recorded using an infrared thermal imaging camera under one day of sunlight irradiation. After the temperature stabilized, the irradiation was turned off, and the temperature change over time was recorded again. The photothermal conversion efficiency was then calculated.

[0079] The cross-section of the porous membrane was observed using SEM to analyze the membrane thickness.

[0080] The tensile strength and elongation at break of porous membranes were tested using a universal testing machine.

[0081] After wetting the porous membrane, it was floated on the water surface. A solar simulator equipped with an AM1.5 filter was adjusted to a solar light intensity of 1 to monitor water mass loss in real time and calculate the photothermal evaporation rate.

[0082] II. Experimental Results

[0083] Polarized light microscope images of the ultra-high molecular weight polyethylene / carbon nanofiller gel films prepared in Examples 1 and 4 are shown below. Figure 2 As shown in the image, a comparison of the images revealed that the gel film prepared in Example 1 contained a large number of graphite nanofiller agglomerates, while no graphite nanofiller agglomerates were observed in the gel film prepared in Example 4. This demonstrates that the layered composite extrusion method of this invention can better disperse the nanofillers in the gel film.

[0084] The performance test results are shown in Tables 1 and 2:

[0085] Table 1

[0086]

[0087] Table 2

[0088]

[0089] According to Table 1, in Example 1, UHMWPE and graphite were co-ball-milled and then extruded using conventional extrusion technology. Examples 2 and 3 employed a stacked composite extrusion technology, with Example 2 using three stacked composite modules and Examples 3 and 4 using nine stacked composite modules. Since the gel extrusion process in a single stacked composite module can be divided into three parts—first, the gel flow is vertically segmented, then rapidly divided into upper and lower layers and stacked—further disentanglement of the gel and dispersion of the filler are achieved through compression in the thickness direction of the expanded flow channel, stretching in the flow direction, and expansion in the perpendicular flow direction. The extruded gel films were subjected to biaxial tensile tests. It was found that the gel films obtained in Examples 3 and 4 could be stretched up to 32 × 32 times, indicating that the UHMWPE was well disentangled, the molecular chains were uniformly distributed, and the graphite nanosheets were small in size and relatively uniformly dispersed. Comparison of photothermal conversion efficiency calculations showed that the porous membrane obtained in Example 4 had the highest photothermal conversion efficiency, at 99.1%. The high photothermal conversion efficiency in the porous membrane mainly depends on the well-dispersed graphite nanosheets in the UHMWPE matrix. Therefore, it was found that the UHMWPE modified powder combined with nine stacked composite modules in Example 4 has the best reprocessing performance and the most uniform filler dispersion.

[0090] According to Table 2, the porous membranes in Examples 5 to 8 were obtained by biaxial stretching and degreasing of the gel membrane in Example 4. Example 6 involved asynchronous biaxial stretching, while the other examples involved synchronous biaxial stretching; the main variable was the change in the stretching ratio. The mechanical properties and photothermal evaporation efficiency of the porous membrane obtained by asynchronous biaxial stretching in Example 6 were lower than those obtained by synchronous biaxial stretching in Example 5. This was because the porous membrane obtained by synchronous biaxial stretching was more uniform. As the stretching ratio increased, the thickness of the porous membrane decreased significantly; in Example 8, when the stretching ratio was 32×32, the membrane thickness decreased to 0.52 micrometers. Due to the orientation crystallization behavior during stretching, the tensile strength of the porous membrane increased significantly, increasing noticeably with the increase in the stretching ratio. In Example 8, the tensile strength reached 278.3 MPa, while the elongation at break decreased slightly to 21.4%. Because the graphite nanofiller was further dispersed uniformly during stretching, but the porous membrane thickness decreased, the photothermal conversion efficiency was affected by both factors. In Comparative Example 7, when the stretching ratio was 16×16, the photothermal conversion efficiency of the porous membrane was higher, reaching 98.9%. However, due to the lower water transport resistance of the thinner membrane, the porous membrane in Example 8 exhibits a higher photothermal evaporation rate of 3.47 kg / (m³). 2 h).

[0091] As can be seen from the above embodiments and experimental examples, this invention provides a novel process method that disperses graphite nanosheets in modified or unmodified UHMWPE powder using a co-ball milling method. A gel extrusion method combined with bidirectional stretching within the flow channel and a layered composite force field promotes the dispersion of graphite nanosheets and the formation of a topological network structure between UHMWPE molecular chains. The ultra-high molecular weight polyethylene / carbon nanofiller photothermal porous separation membrane prepared according to this invention exhibits excellent dispersion of graphite nanosheets and uniform pore size distribution, thus enabling highly efficient solar-driven photothermal evaporation and concentration. Therefore, this invention has excellent application prospects.

Claims

1. A porous membrane of ultra-high molecular weight polyethylene / nanofiller, characterized in that, It is prepared according to the following method: Step 1: Ball milling ultra-high molecular weight polyethylene and nanofiller to obtain a mixture. The ratio of ultra-high molecular weight polyethylene to nanofiller during the ball milling process is (20-80):(80-20) by weight. Step 2: Mix ultra-high molecular weight polyethylene, the mixture obtained in Step 1, and diluent, and perform laminated composite extrusion molding; the laminated composite extrusion molding process includes melting, in-channel laminated compounding, and biaxial stretching; the total amount of ultra-high molecular weight polyethylene used in gel film extrusion and the ratio of the amount of nanofiller used are by weight ratio (70-95):(30-5). Step 3: traction cooling to obtain an ultra-high molecular weight polyethylene gel film, or traction cooling followed by synchronous or asynchronous biaxial stretching to obtain an ultra-high molecular weight polyethylene gel film; in Step 3, the biaxial stretching ratio is (2×2)-(32×32); the thickness of the ultra-high molecular weight polyethylene gel film ranges from 0.1 to 100 micrometers; Step 4: Remove the diluent with a solvent to obtain the ultra-high molecular weight polyethylene / nanofiller porous membrane.

2. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: In step 1, the ratio of ultra-high molecular weight polyethylene to nanofiller used in the ball milling process is 10:30 by weight. In step 2, the ratio of the total amount of ultra-high molecular weight polyethylene raw material to the amount of nanofiller used in the gel film extrusion process is 90:10 by weight.

3. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: The ultra-high molecular weight polyethylene is selected from modified ultra-high molecular weight polyethylene, unmodified ultra-high molecular weight polyethylene, or combinations thereof, wherein the modified ultra-high molecular weight polyethylene is an ultra-high molecular weight polyethylene containing oxygen or fluorine functional groups. And / or, the molecular weight of the ultra-high molecular weight polyethylene is 5 million to 11 million; And / or, the nanofiller is one or more of graphite, carbon nanotubes, graphene, carbon black, nano alumina, and nano titanium dioxide.

4. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: In step 1, an antioxidant is also added during the ball milling process; The antioxidant is selected from at least one of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis(bis-T-butylhydroxyhydrogenated cinnamic acid) ester, pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), tetrakis(methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)methane, antioxidant 1010, pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(di-butylhydroxyhydrogenated cinnamic acid) ester, and antioxidant 168. And / or, the amount of the antioxidant is 0.05-0.5% of the mass of ultra-high molecular weight polyethylene.

5. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: In step 1, the ball-to-material ratio of the ball mill is a mass ratio of (5-20):1; and / or, the ball milling time is 0-24h; and / or, the ball mill speed is 350-550rpm; and / or, the grinding balls are of three types with diameters of 3mm, 5mm and 10mm, and the mass ratio of the three types of grinding balls is (1-3):(1-3):(1-3).

6. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: In step 2, the diluent is selected from at least one of white oil, paraffin oil, and petrolatum; And / or, after mixing ultra-high molecular weight polyethylene, the mixture obtained in step 1 and the diluent, the solid content is 1-5 wt%.

7. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: In step 2, the feeding port temperature of the laminated composite extrusion molding is 130-180 ℃, and the extrusion temperature is 160-220 ℃; And / or, in step 2, the number of laminated composite multipliers formed by the laminated composite extrusion molding is 1-9, the lamination ratio of a single laminated multiplier is 2-8 times, and the number of laminations is 2-8. 9 Second-rate.

8. The ultra-high molecular weight polyethylene / nanofiller porous membrane according to claim 1, characterized in that: In step 3, the traction cooling temperature is 0-25 ℃; And / or, in step 4, the solvent is one or more of dichloromethane, n-hexane, and ethanol.

9. The method for preparing the ultra-high molecular weight polyethylene / nanofiller porous membrane according to any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Ball milling ultra-high molecular weight polyethylene and nanofiller to obtain a mixture. The ratio of ultra-high molecular weight polyethylene to nanofiller during the ball milling process is (20-80):(80-20) by weight. Step 2: Mix ultra-high molecular weight polyethylene, the mixture obtained in Step 1, and diluent, and perform laminated composite extrusion molding; the laminated composite extrusion molding process includes melting, in-channel laminated compounding, and biaxial stretching; in Step 2, the total amount of ultra-high molecular weight polyethylene used in gel film extrusion and the ratio of the amount of nanofiller used are by weight ratio (70-95):(30-5). Step 3: traction cooling to obtain an ultra-high molecular weight polyethylene gel film, or traction cooling followed by synchronous or asynchronous biaxial stretching to obtain an ultra-high molecular weight polyethylene gel film. Step 4: Remove the diluent with a solvent to obtain the final product.

10. The use of the ultra-high molecular weight polyethylene / nanofiller porous membrane according to any one of claims 1-8 for photothermal membrane separation, infrared stealth, wave absorption or electromagnetic shielding.

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