An ultra-high molecular weight polyethylene microporous 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 an ultra-high molecular weight polyethylene microporous membrane, a preparation method and application thereof. The ultra-high molecular weight polyethylene microporous membrane is prepared according to the following method: step 1, mixing ultra-high molecular weight polyethylene and a small molecular polyolefin diluent to prepare an ultra-high molecular weight polyethylene premixed gel; step 2, performing layering and composite extrusion molding on the ultra-high molecular weight polyethylene premixed gel; the layering and composite extrusion molding process comprises melting, layering and composite in a flow channel, and bidirectional stretching; step 3, traction cooling to obtain an ultra-high molecular weight polyethylene gel membrane, or traction cooling and then synchronous or asynchronous biaxial stretching to obtain a thinner ultra-high molecular weight polyethylene gel membrane; step 4, removing the diluent by using a solvent to obtain the microporous membrane. The UHMWPE microporous membrane provided by the application has the advantages of high performance and convenient processing, and has a 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 microporous 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] Compared to dry stretching, gel-based wet stretching can produce thinner (5-15 μm), smaller (20-80 nm), more uniform pore size distribution, and superior mechanical properties UHMWPE microporous membranes. However, a drawback of these UHMWPE microporous membranes is their low porosity. Currently, the porosity of most commercially available UHMWPE microporous separation membranes is less than 45%, with pore sizes as small as around 30 nm. The uniformity of pore size distribution typically depends on the crystal network structure formed during the thermally induced phase separation process of UHMWPE gel casting. Therefore, how to improve the uniformity of the crystal network structure formed during the thermally induced phase separation process by controlling the intermolecular topology of UHMWPE, and thus ensure more effective control of the UHMWPE fiber crystal network structure during high-ratio biaxial thermal stretching, to obtain a porous structure with smaller and more uniform pore size distribution, and overcome the bottleneck of low porosity (>80%), is a major challenge in preparing high-performance UHMWPE microporous separation membranes.

[0004] Existing wet methods for preparing polyolefin microporous membranes typically employ extrusion to create gel membranes, followed by biaxial or uniaxial stretching to produce microporous membranes. These methods have several drawbacks. Since the extruded gel membrane is a precursor to the stretched film, the uniformity of its internal structure significantly impacts the film's performance and subsequent processing. Furthermore, in extrusion, the melt flows along the extrusion direction, leading to molecular chain orientation under the stretching flow field. The subsequent traction cooling and collection / winding processes also inevitably introduce orientation into the gel membrane. This orientation is uncontrollable and occurs during a non-isothermal process, resulting in inefficient and ineffective orientation. This leads to numerous defects in the film, causing difficulties in subsequent processing, such as film breakage during stretching or excessively thick and unevenly sized films.

[0005] In summary, developing new processes and controlling the intermolecular topological network structure to prepare ultra-high molecular weight polyethylene microporous membranes with more uniform pore size, higher porosity, and better performance remains an important research topic in this field. Summary of the Invention

[0006] To address the problems of existing technologies, the present invention aims to provide an ultra-high molecular weight polyethylene microporous membrane, its preparation method, and its applications.

[0007] An ultra-high molecular weight polyethylene microporous membrane is prepared according to the following method:

[0008] Step 1: Mix ultra-high molecular weight polyethylene and small molecule polyolefin diluent to prepare ultra-high molecular weight polyethylene premixed gel.

[0009] Step 2: The ultra-high molecular weight polyethylene premixed gel is subjected to laminated composite extrusion molding; the laminated composite extrusion molding process includes melting, in-channel laminated compounding and biaxial stretching;

[0010] Step 3: Traction cooling yields an ultra-high molecular weight polyethylene gel film, or traction cooling followed by synchronous or asynchronous biaxial stretching yields a thinner ultra-high molecular weight polyethylene gel film.

[0011] Step 4: Remove the diluent with a solvent to obtain the ultra-high molecular weight polyethylene microporous membrane.

[0012] Preferably, in step 1, the small molecule polyolefin diluent is selected from at least one of white oil, paraffin oil, or petrolatum.

[0013] Preferably, in step 1, the molecular weight of the ultra-high molecular weight polyethylene is 5 million to 11 million.

[0014] Preferably, in step 1, the ratio of the ultra-high molecular weight polyethylene to the small molecule polyolefin diluent is a mass ratio of (5-30):(95-70).

[0015] Preferably, in step 1, an antioxidant is also added during the mixing process;

[0016] 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(bis-butylhydroxyhydrogenated cinnamic acid) ester, pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrogenated cinnamic acid) ester, and antioxidant 168.

[0017] And / or, the amount of the antioxidant is 0.05-0.5% of the mass of ultra-high molecular weight polyethylene.

[0018] Preferably, in step 1, the mixing method is to heat and stir using a planetary stirrer at a temperature of 140-160°C for 10-30 minutes and a stirring speed of 20-80 rpm.

[0019] Preferably, in step 2, the feeding port temperature of the laminated composite extrusion molding is 130-180℃, the melting time is 10-30 seconds, and the extrusion temperature is 160-220℃.

[0020] 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.

[0021] Preferably, in step 3, the traction cooling temperature is 0-25℃;

[0022] And / or, in step 3, the biaxial stretching ratio is (2×2)-(32×32);

[0023] And / or, in step 3, the thickness of the thinner ultra-high molecular weight polyethylene gel film ranges from 0.1 to 100 micrometers;

[0024] And / or, in step 4, the diluent is one or more of dichloromethane, n-hexane, and ethanol.

[0025] This invention also provides a method for preparing ultra-high molecular weight polyethylene microporous membranes, comprising the following steps:

[0026] Step 1: Mix ultra-high molecular weight polyethylene and small molecule polyolefin diluent to prepare ultra-high molecular weight polyethylene premixed gel.

[0027] Step 2: The ultra-high molecular weight polyethylene premixed block is subjected to stacked composite extrusion molding; the stacked composite extrusion molding process includes melting, in-channel stacking and biaxial stretching;

[0028] 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 a thinner ultra-high molecular weight polyethylene gel film.

[0029] Step 4: Remove the diluent with a solvent to obtain the final product.

[0030] The present invention also provides the above-mentioned ultra-high molecular weight polyethylene microporous membrane for use in membrane separation, infrared stealth, and wave absorption.

[0031] This invention relates to the preparation of ultra-high molecular weight polyethylene (UHMWPE) microporous membranes and constructs a novel process flow. Specifically, the process involves multiple segmentation and overlapping of the gel membrane molecular chains using a layered composite device within the flow channel, thereby untangling and homogenizing the membrane. Furthermore, a bidirectional stretching flow field (thinning in the thickness direction, stretching along the flow direction, and widening perpendicular to the flow direction) is utilized to promote interlayer adhesion and the formation of an intermolecular topological network structure. The entanglement points of the topological network structure provide a function similar to physical cross-linking points, inhibiting molecular chain retraction and re-entanglement. The uniform intermolecular topological network structure is effectively maintained during gel membrane cooling, promoting the formation of a uniform crystalline network. Moreover, this structure facilitates further processing, resulting in UHMWPE microporous membranes with small pore size, uniform pore size distribution, and high porosity. Therefore, the UHMWPE microporous membrane provided by this invention has the advantages of high performance and ease of processing, and has excellent application prospects.

[0032] 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.

[0033] 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

[0034] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0035] Figure 2 This is a schematic diagram illustrating the working principle of the stacked composite module in this invention. Detailed Implementation

[0036] In the following examples and experimental cases, reagents and raw materials not specifically described are all commercially available products.

[0037] Example 1: Ultra-high molecular weight polyethylene microporous membrane

[0038] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0039] (2) The gel was placed in the extruder feed cylinder at 180℃ and preheated for 30 seconds to form a homogeneous transparent gel before extrusion. The extruder temperatures from the feed end to the outlet end were 180, 180, 185, 190, 185, and 180℃ respectively. A laminated composite module was not used. The extruded gel film was 2mm thick and 10cm wide. The cooling roller temperature was 20℃, and the traction speed was the same as the extrusion speed. The gel film was soaked in n-hexane for 24 hours to remove the white oil, thus obtaining the microporous membrane.

[0040] Example 2: Ultra-high molecular weight polyethylene microporous membrane

[0041] The process flow of this embodiment is as follows: Figure 1 , 2 As shown.

[0042] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0043] (2) The gel is placed in the feed cylinder of an extruder at 180℃. After preheating for 30 seconds to form a homogeneous transparent gel, it is extruded. 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 for each module, i.e., a total of 8 stacking times. The temperature is 180℃ for all modules. 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 topological network structure between molecular chains is formed 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.

[0044] 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.

[0045] Example 3: Ultra-high molecular weight polyethylene microporous membrane

[0046] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0047] (2) The gel is placed in the feed cylinder of an extruder at 180℃. After preheating for 30 seconds to form a homogeneous transparent gel, it is extruded. 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, and the stacking ratio of a single module is 2, that is, the total number of stacking times is 512. The temperature is 180℃. 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 microporous membrane.

[0049] Example 4: Ultra-high molecular weight polyethylene microporous membrane

[0050] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0051] (2) The gel is placed in the feed cylinder of an extruder at 180℃. After preheating for 30 seconds to form a homogeneous transparent gel, it is extruded. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. There are 3 composite modules stacked in the flow channel, and the stacking ratio of a single module is 8 times, that is, the total number of stacking times is 512. The temperature is 180℃. 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 microporous membrane.

[0053] Example 5: Ultra-high molecular weight polyethylene microporous membrane

[0054] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0055] (2) The gel is placed in the feed cylinder of an extruder at 180℃ and preheated for 30 seconds to form a homogeneous transparent gel before extrusion. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. Three composite modules are stacked in the flow channel, with a stacking ratio of 8 times for each module, resulting in a total of 512 stacking times. The temperature is maintained at 180℃ for all modules. 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, thus obtaining the gel film.

[0056] (3) Cut the gel membrane into 10×10cm wide samples and perform biaxial stretching at 125℃. First, keep the membrane at 125℃ for 180 seconds and then perform synchronous biaxial stretching at a speed of 2% / s. The stretching ratio is 8×8, which yields a thinner gel membrane.

[0057] The gel membrane was soaked in n-hexane for 24 hours to remove the white oil, thus obtaining the microporous membrane.

[0058] Example 6: Ultra-high molecular weight polyethylene microporous membrane

[0059] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0060] (2) The gel is placed in the feed cylinder of an extruder at 180℃ and preheated for 30 seconds to form a homogeneous transparent gel before extrusion. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. Three composite modules are stacked in the flow channel, with a stacking ratio of 8 times for each module, resulting in a total of 512 stacking times. The temperature is maintained at 180℃ for all modules. 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, thus obtaining the gel film.

[0061] (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.

[0062] The gel membrane was soaked in n-hexane for 24 hours to remove the white oil, thus obtaining the microporous membrane.

[0063] Example 7: Ultra-high molecular weight polyethylene microporous membrane

[0064] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0065] (2) The gel is placed in the feed cylinder of an extruder at 180℃ and preheated for 30 seconds to form a homogeneous transparent gel before extrusion. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. Three composite modules are stacked in the flow channel, with a stacking ratio of 8 times for each module, resulting in a total of 512 stacking times. The temperature is maintained at 180℃ for all modules. 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, thus obtaining the gel film.

[0066] (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 to 10×10cm size 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, thus obtaining a thinner gel membrane.

[0067] The gel membrane was soaked in n-hexane for 24 hours to remove the white oil, thus obtaining the microporous membrane.

[0068] Example 8: Ultra-high molecular weight polyethylene microporous membrane

[0069] (1) Weigh 50g of UHMWPE (Celanis GUR 4172) with a molecular weight of over 10 million, 950g of white oil, 0.5g of antioxidant 1010 and 0.5g of antioxidant 168. After manually stirring and mixing, add the mixture to a planetary stirrer at 150℃. Then, transfer the mixture to 50rpm and stir for 30min. After the solution forms a gel, remove the UHMWPE white oil gel product and cut it into pieces.

[0070] (2) The gel is placed in the feed cylinder of an extruder at 180℃ and preheated for 30 seconds to form a homogeneous transparent gel before extrusion. The extruder temperatures from the feed end to the outlet end are 180, 180, 185, 190, 185, and 180℃ respectively. Three composite modules are stacked in the flow channel, with a stacking ratio of 8 times for each module, resulting in a total of 512 stacking times. The temperature is maintained at 180℃ for all modules. 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, thus obtaining the gel film.

[0071] (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 to 10×10cm size 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, thus obtaining a thinner gel membrane.

[0072] The gel membrane was soaked in n-hexane for 24 hours to remove the white oil, thus obtaining the microporous membrane.

[0073] The technical solution of the present invention will be further explained through experiments below.

[0074] Experiment Example 1 Performance Test

[0075] I. Experimental Methods

[0076] This experimental example tests the samples prepared in Examples 1-8. The specific steps are as follows:

[0077] The cross-section of the porous membrane was observed using SEM to analyze the membrane thickness.

[0078] The porosity (Ak) of the UHMWPE porous membrane was tested using the ethanol immersion method. Ak is defined as the percentage of pore volume to the total porous membrane volume. It is calculated using the following formula:

[0079]

[0080] After removing the white oil, the UHMWPE porous membrane was dried, weighed, and recorded as W. Then, the membrane was immersed in a pure ethanol solution and left to stand for 24 hours to allow it to fully absorb the ethanol. After removing the membrane, the excess ethanol on the membrane surface was quickly wiped clean with filter paper, and then weighed and recorded as W0. ρ and ρ are the densities of UHMWPE and ethanol, respectively.

[0081] The pore size distribution of the membrane was calculated using the software ImageJ on the SEM image of the porous membrane surface, with more than 200 pores calculated.

[0082] The tensile strength and elongation at break of porous membranes were tested using a universal testing machine.

[0083] Dead-end filtration was employed, and the flux of pure water and carbon ink solution was tested at a pressure of 1 bar. Furthermore, to test the carbon ink solution rejection rate, the carbon ink solution was diluted with water to concentrations of 20%, 40%, 60%, 80%, and 100%, respectively. The absorbance of the solutions was measured using a UV-Vis spectrophotometer (UV3600), and a standard curve was plotted as concentration versus absorbance. The carbon ink solution after membrane separation was further tested, and the carbon ink solution rejection rate was calculated.

[0084] II. Experimental Results

[0085] The test results are shown in Tables 1 and 2:

[0086] Table 1

[0087]

[0088] Table 2

[0089]

[0090]

[0091] According to Table 1, Example 1 used conventional extrusion technology for the UHMWPE gel, while Examples 2-4 used stacked composite extrusion technology. In Examples 2 and 3, the stacking ratio of a single layer multiplier was 2 times. Example 2 used three stacked composite modules, and Example 3 used nine stacked composite modules. In Example 4, the stacking ratio of a single layer multiplier was 8 times, and using three stacked composite modules achieved the same total number of stacks as in Example 3 (512 times). 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—the gel is further untangled and the filler dispersed through the thickness-direction compression of the expanded flow channel, the stretching action in the flow direction, and the diffusing and stretching action perpendicular to the flow direction. The larger the stacking ratio of a single layer multiplier, the greater the compression action in the thickness direction and the diffusing and stretching action perpendicular to the flow direction. Therefore, the stacking composite process in Example 4 has better dispersion and untangling effects than in Examples 1-3, and a more complete intermolecular topological network structure. To verify this approach, biaxial tensile tests were conducted on the extruded gel membrane. It was found that the gel membrane obtained in Example 4 could be stretched up to 36 × 36 times, and the tensile strength and elongation at break of the porous membrane were significantly improved, indicating that the UHMWPE was well unwound and the molecular chains were uniformly distributed. Therefore, it was found that the gel membrane extruded from the UHMWPE gel combined with three 8x multilayer composite modules in Example 4 had the most uniform molecular chain structure, a perfect intermolecular topological network structure, and optimal reprocessing performance.

[0092] 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 porous membrane obtained by asynchronous biaxial stretching in Example 6 had a wider pore size distribution, more defects, and a significantly lower rejection rate than that obtained by synchronous biaxial stretching in Example 5. 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. Because the wet stretching process contained a diluent, the stretching process mainly involved polyethylene crystal slippage and diluent aggregation deformation, without cavitation. Therefore, the porosity of the porous membrane was only related to the diluent content. At the time of feeding, the diluent content was 95%, and the theoretical porosity was 95%. However, due to a small amount of white oil leakage during processing and the internal stress of the pores during degreasing causing pore wall collapse and pore size shrinkage, the porosity decreased slightly, but remained basically at around 90%. The decrease in pore size and narrowing of the pore distribution with increasing stretching ratio is beneficial for improving separation accuracy. This is because during the stretching process, the presence of a uniform intermolecular topological network structure leads to the refinement and recrystallization of the fibrous crystal structure, resulting in a more uniform and fine porous structure. Due to the oriented crystallization behavior during stretching, the tensile strength of the porous membrane is significantly improved, increasing substantially with increasing stretching ratio. In Example 8, the tensile strength reached 267.3 MPa, while the elongation at break decreased slightly to 24.4%. Water separation performance tests showed that the greater the stretching ratio and the thinner the porous membrane, the faster the water separation rate. In Example 8, the porous membrane achieved a water separation rate of 3400.5 L / (m²). 2 The decrease in membrane thickness (h bar) is also due to the significant reduction in membrane thickness caused by the increase in stretching ratio. However, since the separation effect of this type of porous membrane is determined by both the surface pore size and the membrane thickness, the decrease in membrane thickness inevitably leads to a loss of retention rate. In Example 7, the porous membrane with a stretching ratio of 16×16 and a thickness of approximately 0.91 micrometers achieved a carbon ink solution retention rate of 99.9% and a water separation rate of 2122.9 L / (m²). 2 (h bar) has relatively ideal water separation performance.

[0093] As can be seen from the above embodiments and experimental examples, this invention provides a novel process method. By incorporating the in-channel lamination step into the extrusion process, it achieves the unentanglement and homogenization of the gel membrane molecular chains. Furthermore, the biaxial stretching flow field promotes interlayer adhesion and the formation of intermolecular topological network structures. Therefore, this invention can prepare UHMWPE microporous membranes that are easy to process, have uniform pore size distribution, and high porosity. Thus, the UHMWPE microporous membrane provided by this invention has better water separation performance and the advantage of easy processing, showing great application potential.

Claims

1. A microporous membrane of ultra-high molecular weight polyethylene, characterized in that, It is prepared according to the following method: Step 1: Mix ultra-high molecular weight polyethylene and small molecule polyolefin diluent to prepare ultra-high molecular weight polyethylene premixed gel. Step 2: The ultra-high molecular weight polyethylene premixed gel is subjected to lamination and composite extrusion molding. The lamination and composite extrusion molding process includes melting, in-channel lamination and composite molding, and biaxial stretching. The feed port temperature of the lamination and composite extrusion molding is 130-180 ℃, the melting time is 10-30 seconds, and the extrusion temperature is 160-220 ℃. The number of lamination and composite multipliers in the lamination and composite extrusion molding is 1-9, the lamination ratio of a single lamination and multiplier is 2-8 times, and the number of laminations is 2-8. 9 Second-rate; 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 a thinner ultra-high molecular weight polyethylene gel film. Step 4: Remove the diluent with a solvent to obtain the ultra-high molecular weight polyethylene microporous membrane.

2. The ultra-high molecular weight polyethylene microporous membrane according to claim 1, characterized in that, In step 1, the small molecule polyolefin diluent is selected from at least one of white oil, paraffin oil, or petrolatum.

3. The ultra-high molecular weight polyethylene microporous membrane according to claim 1, characterized in that, In step 1, the molecular weight of the ultra-high molecular weight polyethylene is 5 million to 11 million.

4. The ultra-high molecular weight polyethylene microporous membrane according to claim 1, characterized in that, In step 1, the ratio of ultra-high molecular weight polyethylene to small molecule polyolefin diluent is (5-30):(95-70) by mass.

5. The ultra-high molecular weight polyethylene microporous membrane according to claim 1, characterized in that, In step 1, an antioxidant is also added during the mixing 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, pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrogenated 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.

6. The ultra-high molecular weight polyethylene microporous membrane according to claim 1, characterized in that, In step 1, the mixing method is heating and stirring, with a stirring temperature of 140-160 ℃, a stirring time of 10-30 min, and a stirring speed of 20-80 rpm.

7. The ultra-high molecular weight polyethylene microporous membrane according to claim 1, characterized in that: In step 3, the traction cooling temperature is 0-25 ℃; And / or, in step 3, the biaxial stretching ratio is (2×2)-(32×32); And / or, in step 3, the thickness of the thinner ultra-high molecular weight polyethylene gel film ranges from 0.1 to 100 micrometers; And / or, in step 4, the solvent is one or more of dichloromethane, n-hexane, and ethanol.

8. The method for preparing the ultra-high molecular weight polyethylene microporous membrane according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Mix ultra-high molecular weight polyethylene and small molecule polyolefin diluent to prepare ultra-high molecular weight polyethylene premixed gel. Step 2: The ultra-high molecular weight polyethylene premixed gel is subjected to laminated composite extrusion molding; the laminated composite extrusion molding process includes melting, in-channel laminated compounding and biaxial stretching; 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 a thinner ultra-high molecular weight polyethylene gel film. Step 4: Remove the diluent with a solvent to obtain the final product.

9. The use of the ultra-high molecular weight polyethylene microporous membrane according to any one of claims 1-7 for membrane separation, infrared stealth or microwave absorption.

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