Preparation method of waterproof breathable film

Abstract

The preparation method specifically comprises the following steps: dispersing a certain mass of active hydrogen-containing polymer, hydrolyzable silane polymer, polyetherimide, hydrophobic nanoparticles and a surfactant in a mixed solvent to prepare a membrane casting solution, carrying out blade coating to form a membrane, and carrying out first-stage and second-stage acidic solution treatment to obtain the waterproof breathable membrane. The waterproof breathable film is finally obtained by inducing the shrinkage effect of the active hydrogen-containing polymer, the phase separation of polyetherimide and the directional migration of nanoparticles. The prepared waterproof breathable film has high breathability and degradability, the process is simple and efficient, and the waterproof breathable film is suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of membranes, and in particular to a method for preparing a waterproof and breathable membrane. Background Art

[0002] Waterproof and breathable membrane is a type of polymer membrane material that has both the functions of "preventing liquid water penetration" and "allowing water vapor molecules to pass through". It is widely used in outdoor clothing, medical protection, electronic device packaging, building waterproofing and other fields.

[0003] To achieve both waterproofness and breathability, the current market and research fields primarily utilize the following two types of preparation systems: Fluorine-containing waterproof and breathable membranes: Representative products include expanded PTFE membranes and fluoropolymer-coated membranes, which utilize the low surface energy of the fluorine element to create a hydrophobic layer. However, fluorine-containing materials are non-degradable, posing potential threats to the environment and health. Furthermore, their complex production processes and non-recyclability have led to their increasing use. Patent CN115501764A discloses a method for preparing a waterproof and breathable membrane with a gradient pore structure. The waterproof and breathable membrane comprises a support layer and a waterproof and breathable functional layer. The functional layer is electrospinned onto the support layer surface using a fluorine-containing polymer material. The resulting waterproof and breathable membrane has a gradually decreasing pore size from the support layer to the waterproof and breathable functional layer, forming a gradient pore structure. However, this method requires layer-by-layer spinning, requiring extensive parameter adjustments. Furthermore, interfacial bonding between layers can lead to delamination or pore structure fracture due to residual solvent and differences in cooling rates. While the membrane has high porosity, its mechanical strength is relatively low, limiting its application in high-pressure environments.

[0004] Fluorine-free waterproof and breathable membranes are typically based on polyurethane (PU), polyetherimide (PEI), polylactic acid (PLA), and other materials, and are produced using methods such as phase separation and electrospinning. These methods generally rely on a base membrane support structure, resulting in uneven pore size distribution and unclear membrane structure, making it difficult to achieve both waterproofness and breathability. Patent CN114134702A discloses a method for preparing a fluorine-free electrospun waterproof and breathable membrane based on a thiol-ene photochemical reaction. Thiols are easily oxidized, especially during long-term storage before UV irradiation, where they may partially oxidize to disulfides, reducing crosslinking efficiency and ultimately affecting the membrane's water pressure resistance and mechanical properties. The spinning solution contains components with significant differences in polarity, which can cause phase separation in the solvent, leading to uneven fiber diameter and pore size distribution.

[0005] Fluorinated waterproof and breathable membranes rely on fluorine to create a hydrophobic layer, but they are non-degradable and difficult to recycle. Fluorine-free waterproof and breathable membranes struggle to balance performance: polyurethane / polyimide-based membranes often suffer from uneven pore size distribution and insufficient mechanical strength. The commonly used electrospinning method involves high-voltage equipment and multi-layer parameter control, making industrialization expensive. Summary of the Invention

[0006] The present invention aims to address these existing problems and deficiencies by proposing a preparation method based on the principles of material physical mobility, chemical responsiveness, and structural synergy, resulting in a functional membrane material with a layered gradient pore structure (surface nanopores + inner micropores). The preparation process utilizes a multi-component system compatibility control, a layered response mechanism, and a structure-induced synergy strategy. This preparation method not only improves membrane material performance but also provides new ideas for the industrial application of fluorine-free, high-performance, protective membrane materials. The specific preparation method includes the following steps:

[0007] Step 1: Dispersing a certain amount of active hydrogen-containing polymer, hydrolyzable silane polymer, polyetherimide, surfactant, and hydrophobic nanoparticles in a mixed solvent of N-methylpyrrolidone (NMP) and isopropyl alcohol (IPA), stirring the mixture to form a casting solution;

[0008] Step 2: evenly apply the casting solution on the surface of the glass plate and place it in the air for 1-10 minutes;

[0009] Step 3: Immerse the membrane in the acidic solution of the first stage and treat it at 15-25℃ for 5-10 minutes;

[0010] Step 4: Transfer the membrane into the second-stage acidic solution and treat at 30-50°C for 10-20 minutes;

[0011] Step 5: Wash the treated membrane with deionized water and dry it at 45° C. to obtain a waterproof and breathable membrane.

[0012] Wherein, the active hydrogen-containing polymer in step 1 is one or more of modified polylactic acid, polyhydroxybutyrate or carboxymethyl chitosan, and the amount used is 1-3% of the total mass of the casting solution.

[0013] In the step 1, the hydrolyzable silane polymer is one or more of silane-grafted polyetheretherketone, silane-grafted polyphenylene ether or alkylated modified polyethylene, and the amount used is 0.1-2% of the total mass of the casting solution; the amount used of the polyetherimide is 1-5% of the total mass of the casting solution.

[0014] In the step 1, the surfactant is one or more of Pluronic F127, Tetronic 901 or Brij L23, and the amount used is 0.05-0.5% of the total mass of the casting solution; the hydrophobic nanoparticles are SiO2, and the amount used is 0.1-1% of the total mass of the casting solution.

[0015] Wherein, in the step 1, the volume ratio of the mixed solvent of N-methylpyrrolidone and isopropyl alcohol is 80-90:10-20, and the stirring time is 5-12 hours.

[0016] Wherein, the coating thickness of the casting liquid in step 2 is 10-50 μm.

[0017] Wherein, the first-stage acidic solution in step 3 is 0.05-0.2 mol / L tartaric acid and 0.01-0.1 mol / L sodium citrate, with a pH value of 3.5-4.5.

[0018] Wherein, the second-stage acidic solution in step 4 is 0.2-0.5 mol / L citric acid and 5-15% ethanol.

[0019] Beneficial effects of the present invention:

[0020] This invention, for the first time, utilizes a triple dynamic mechanism: pH-responsive shrinkage of an active hydrogen-containing polymer, solvent evaporation of a polyetherimide, and in-situ crosslinking of a hydrolyzable silane polymer. This method achieves precise construction of a gradient pore structure using a simple doctor blade coating process. This approach overcomes the performance bottleneck of fluorine-free membranes and provides a new approach for environmentally friendly, high-performance membranes.

[0021] Gradient pore structure. The micron-sized pores in the inner layer of the waterproof and breathable membrane are formed by the selective volatilization of polyetherimide in the second-stage acidic solution. The nanopores in the surface layer are formed by the shrinkage effect of the active hydrogen-containing polymer in the acidic environment. The active hydrogen-containing polymer and the polyetherimide layers are in situ crosslinked via a hydrolyzable silane polymer to form a chemically bonded interface. Surfactant molecules adsorb at the interface of the different components, improving their compatibility and providing a more favorable interfacial environment for in situ crosslinking. This helps form a strong chemical bond, strengthens interlayer adhesion, and prevents delamination, thus eliminating the risk of interlayer delamination in traditional electrospun membranes. The gradient pore structure also inhibits deep penetration of contaminants. By adjusting the concentration of the acidic solution and the treatment temperature, the polymer phase separation and the migration of hydrophobic nanoparticles are triggered, enhancing the membrane's surface hydrophobicity and achieving dynamic adjustment of the membrane's pore size. A tartaric acid / citric acid combination within a specific pH range causes the polylactic acid to shrink without degradation, and ethanol synergizes with the volatilization of the polyetherimide to form open pores.

[0022] Excellent air permeability. Acid solution treatment induces the volatilization of polyetherimide to form through-pores. The homogeneous distribution of SiO2 nanoparticles prevents pore blockage. Combined with the synergistic effect of the gradient pore structure, the hydrolyzable silane polymer and the active hydrogen-containing polymer form a flexible interface. The pore structure dynamically adjusts under pressure and humidity, maintaining high permeability while resisting deformation. Surfactants participate in and influence the non-solvent-induced phase separation process, helping to form through-pore, uniform micropores, thereby significantly improving the air permeability of the final membrane.

[0023] Excellent waterproof performance. The inner and outer layers of the waterproof and breathable membrane work synergistically. The inner micron-sized pores act as a "buffer" to intercept large-particle pollutants. The surface nanopores generate high pressure through narrow channels, achieving physical water resistance. The resulting waterproof and breathable membrane can withstand 1 meter of water pressure and remain leak-proof for 30 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM image of the front side of the waterproof breathable membrane prepared according to Example 1.

[0025] Figure 2 This is a SEM image of the reverse side of the waterproof breathable membrane prepared according to Example 1. DETAILED DESCRIPTION

[0026] The following is a detailed description of the method for preparing a waterproof, breathable membrane provided by the present invention, with reference to specific examples. It should be understood that these examples are intended only to illustrate and describe the present invention and are not intended to limit its scope of application. Any modifications or variations to the present invention that do not depart from the purpose and scope of the present invention are intended to be included within the scope of protection of the present invention.

[0027] Example 1:

[0028] Step 1: Weigh 2.5 g of polyhydroxybutyrate, 1.2 g of silane-grafted polyphenylene ether, 4.5 g of polyetherimide, 0.15 g of Pluronic F127, and 0.25 g of hydrophobic SiO2 nanoparticles.

[0029] Step 2: Disperse the above components in a mixed solvent of NMP / IPA (volume ratio 92:8) with a total system solid content of 12%, and stir for 12 hours to obtain a uniform casting solution.

[0030] Step 3: Scrape the casting solution onto the glass plate to a thickness of 35 μm and let it stand at room temperature for 3 minutes.

[0031] Step 4: Immerse in the first-stage acidic solution containing 0.12 mol / L tartaric acid and 0.06 mol / L sodium citrate, pH = 3.5, temperature 25°C for 5 minutes.

[0032] Step 5: Transfer to the second-stage acidic solution containing 0.35 mol / L citric acid and 12% ethanol, pH = 1.8, temperature 40 ° C for 15 minutes.

[0033] Step 6: Rinse with deionized water and dry under 45° C. air to obtain a waterproof and breathable membrane.

[0034] The waterproof breathable membrane produced by the process of Example 1 was tested using a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure was 92 kPa. At the same time, the air flow rate was measured to be 4400 ml per minute under an air pressure of 7 kPa and an area of ​​1 square centimeter.

[0035] Example 2:

[0036] Step 1: Weigh 1 g of modified polylactic acid, 0.5 g of silane-grafted polyetheretherketone, 3 g of polyetherimide, 0.08 g of Brij L23, and 0.1 g of hydrophobic SiO2 nanoparticles.

[0037] Step 2: Disperse the above components in a mixed solvent of NMP / IPA (volume ratio 85:15) with a total system solid content of 10%, and stir for 12 hours to obtain a uniform casting solution.

[0038] Step 3: Scrape the casting solution onto a glass plate with a thickness of 50 μm and let it stand at room temperature for 10 minutes.

[0039] Step 4: Immerse in the first-stage acidic solution containing 0.05 mol / L tartaric acid and 0.1 mol / L sodium citrate, pH = 3.5, temperature 20°C for 10 minutes.

[0040] Step 5: Transfer to the second-stage acidic solution containing 0.2 mol / L citric acid and 5% ethanol, pH = 2, temperature 35 ° C for 20 minutes.

[0041] Step 6: Rinse with deionized water and dry under 45° C. air to obtain a waterproof and breathable membrane.

[0042] The waterproof breathable membrane produced by the process of Example 2 was tested using a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure was 90 kPa. At the same time, the air flow rate was measured to be 4900 ml per minute under an air pressure of 7 kPa and an area of ​​1 square centimeter.

[0043] Example 3:

[0044] Step 1: Weigh 3 g of carboxymethyl chitosan, 2 g of alkylated modified polyethylene, 5 g of polyetherimide, 0.5 g of Tetronic 901, and 0.5 g of hydrophobic SiO2 nanoparticles.

[0045] Step 2: Disperse the above components in a mixed solvent of NMP / IPA (volume ratio 95:5) with a total system solid content of 25%, and stir for 12 hours to obtain a uniform casting solution.

[0046] Step 3: Scrape the casting solution onto a glass plate with a thickness of 20 μm and let it stand at room temperature for 1 minute.

[0047] Step 4: Immerse in the first-stage acidic solution containing 0.2 mol / L tartaric acid and 0.1 mol / L sodium citrate, pH = 3, temperature 25 ° C for 3 minutes.

[0048] Step 5: Transfer to the second-stage acidic solution containing 0.5 mol / L citric acid and 15% ethanol, pH = 1.2, and treat at 45°C for 10 minutes.

[0049] Step 6: Rinse with deionized water and dry under 45° C. air to obtain a waterproof and breathable membrane.

[0050] The waterproof breathable membrane produced by the process of Example 3 was tested using a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure was 85 kPa. At the same time, the air flow rate was measured to be 5100 ml per minute per 1 square centimeter under an air pressure of 7 kPa.

[0051] Comparative Example 1:

[0052] Step 1: Weigh 2.5 g of polyhydroxybutyrate, 1.2 g of silane-grafted polyphenylene ether, 4.5 g of polyetherimide, 0.15 g of Pluronic F127, and 0.25 g of hydrophobic SiO2 nanoparticles.

[0053] Step 2: Disperse the above components in a mixed solvent of NMP / IPA (volume ratio 92:8) with a total system solid content of 12%, and stir for 12 hours to obtain a uniform casting solution.

[0054] Step 3: Scrape the casting solution onto the glass plate to a thickness of 35 μm and let it stand at room temperature for 3 minutes.

[0055] Step 4: Immerse in the second-stage acidic solution containing 0.35 mol / L citric acid and 12% ethanol, pH = 1.8, temperature 40°C for 15 minutes.

[0056] Step 5: Rinse with deionized water and dry under 45° C. air to obtain a waterproof and breathable membrane.

[0057] The waterproof breathable membrane produced by the process of Comparative Example 1 was tested using a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure was 61 kPa. At the same time, the air flow rate was measured to be 2250 ml per minute under an air pressure of 7 kPa and an area of ​​1 square centimeter.

[0058] Comparative Example 2:

[0059] Step 1: Weigh 2.5 g of polyhydroxybutyrate, 1.2 g of silane-grafted polyphenylene ether, 4.5 g of polyetherimide, 0.15 g of sodium lauryl sulfate, and 0.25 g of hydrophobic SiO2 nanoparticles.

[0060] Step 2: Disperse the above components in a mixed solvent of NMP / IPA (volume ratio 92:8) with a total system solid content of 12%, and stir for 12 hours to obtain a uniform casting solution.

[0061] Step 3: Scrape the casting solution onto the glass plate to a thickness of 35 μm and let it stand at room temperature for 3 minutes.

[0062] Step 4: Immerse in the first-stage acidic solution containing 0.12 mol / L tartaric acid and 0.06 mol / L sodium citrate, pH = 3.5, temperature 25°C for 5 minutes.

[0063] Step 5: Transfer to the second-stage acidic solution containing 0.35 mol / L citric acid and 12% ethanol, pH = 1.8, temperature 40 ° C for 15 minutes.

[0064] Step 6: Rinse with deionized water and dry under 45° C. air to obtain a waterproof and breathable membrane.

[0065] The waterproof breathable membrane produced by the process of Comparative Example 2 was tested using a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure was 37 kPa. At the same time, the air flow rate was measured to be 1840 ml per minute under an air pressure of 7 kPa and an area of ​​1 square centimeter.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or adapt the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and improvements to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention shall remain within the scope of protection of the present invention.

Claims

1. A method for preparing a waterproof breathable membrane, characterized by the following steps: Step 1: Dispersing a certain amount of active hydrogen-containing polymer, hydrolyzable silane polymer, polyetherimide, surfactant and hydrophobic nanoparticles in a mixed solvent of N-methylpyrrolidone and isopropyl alcohol, and stirring to form a casting solution; Step 2: evenly apply the casting solution on the surface of the glass plate and place it in the air for 1-10 minutes; Step 3: Immerse the membrane in the acidic solution of the first stage and treat it at 15-25℃ for 5-10 minutes; Step 4: Transfer the membrane into the second-stage acidic solution and treat at 30-50°C for 10-20 minutes; Step 5: Wash the treated membrane with deionized water and dry it at 45° C. to obtain a waterproof and breathable membrane.

2. The method according to claim 1, wherein: In the step 1, the active hydrogen-containing polymer is one or more of modified polylactic acid, polyhydroxybutyrate or carboxymethyl chitosan, and the amount used is 1-3% of the total mass of the casting solution.

3. The method according to claim 1, wherein: The hydrolyzable silane polymer in step 1 is one or more of silane-grafted polyphenylene ether, silane-grafted polyetheretherketone or alkylated modified polyethylene, and the amount used is 0.1-2% of the total mass of the casting solution; the amount used of the polyetherimide is 1-5% of the total mass of the casting solution.

4. The method according to claim 1, wherein: In the step 1, the surfactant is one or more of Pluronic F127, Tetronic 901 or Brij L23, and the amount used is 0.05-0.5% of the total mass of the casting solution; the hydrophobic nanoparticles are SiO2, and the amount used is 0.1-1% of the total mass of the casting solution.

5. The method according to claim 1, wherein: In the step 1, the volume ratio of the mixed solvent of N-methylpyrrolidone and isopropyl alcohol is 80-90:10-20, and the stirring time is 5-12 hours.

6. The method according to claim 1, wherein: The coating thickness of the casting solution in step 2 is 10-50 μm.

7. The method according to claim 1, wherein: The first-stage acidic solution in step 3 is 0.05-0.2 mol / L tartaric acid and 0.01-0.1 mol / L sodium citrate, with a pH value of 3.5-4.

5.

8. The method according to claim 1, wherein: The second-stage acidic solution in step 4 is 0.2-0.5 mol / L citric acid and 5-15% ethanol.

Images