A method for preparing a waterproof and breathable film

Abstract

The application discloses a preparation method of a waterproof and breathable film, and specifically comprises the following steps: dispersing a certain amount of active hydrogen-containing polymer, hydrolyzable silane polymer, polyetherimide, hydrophobic nanoparticles and a surfactant in a mixed solvent to prepare a casting solution, performing film coating through scraping, and then performing first-stage and second-stage acid solution treatment, so that the shrinkage effect of the active hydrogen-containing polymer, the phase separation of the polyetherimide and the directional migration of the nanoparticles are induced, and finally, the waterproof and breathable film is obtained. The waterproof and breathable film prepared by the application has high breathability and degradability, the process is simple and efficient, and the waterproof and breathable film is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of films, in particular to a preparation method of a waterproof and breathable film. BACKGROUND

[0002] Waterproof and breathable films are a class of polymer film materials that have both "liquid water permeation prevention" and "water vapor molecule passage" functions, and are widely used in outdoor clothing, medical protection, electronic device packaging, building waterproofing, and other fields.

[0003] In order to simultaneously achieve waterproofness and breathability, the current market and research field mainly adopts the following two types of preparation systems. Fluorine-containing waterproof and breathable films: representative products include PTFE expanded film and fluoropolymer coating film, which construct a hydrophobic layer through the low surface energy of fluorine elements. However, fluorine materials are not degradable, pose potential threats to the environment and health, and have complex production processes and are not recyclable, which have gradually been restricted. Patent CN115501764A discloses a preparation method of a waterproof and breathable film with a gradient pore structure. The waterproof and breathable film includes a support layer and a waterproof and breathable functional layer, and the functional layer is spun on the surface of the support layer by an electrospinning method using a fluorine-containing polymer material. The pore size of the prepared waterproof and breathable film gradually decreases from the support layer to the waterproof and breathable functional layer, forming a gradient pore structure. However, this method requires layer-by-layer spinning, and there are many parameters to adjust, and the interface between the layers may be delaminated or the pore structure may be broken due to solvent residue and differences in cooling rate. The film has high porosity but low mechanical strength, which limits its application in high-pressure environments.

[0004] Fluorine-free waterproof and breathable films are usually based on polyurethane (PU), polyetherimide (PEI), polylactic acid (PLA), etc. as the base material, and are prepared by methods such as phase separation and electrospinning. These methods generally rely on a base film support structure, and the pore size distribution is uneven, the film structure is unclear, and it is difficult to balance waterproofness and breathability. Patent CN114134702A discloses a preparation method of a fluorine-free electrospun waterproof and breathable film based on a sulfur-based-alkene photochemical reaction. Thiol is easily oxidized, especially when stored for a long time before ultraviolet light exposure, which may partially oxidize it into disulfide, reducing the crosslinking efficiency and ultimately affecting the water pressure resistance and mechanical properties of the film. The components in the spinning solution have large polarity differences, and phase separation may occur in the solvent, resulting in uneven fiber diameter and pore size distribution.

[0005] Fluorine-containing waterproof and breathable films rely on fluorine elements to construct a hydrophobic layer, but have problems such as non-degradability and difficulty in recycling. Fluorine-free waterproof and breathable films have difficulty in balancing various properties: polyurethane / polyimide-based films generally have uneven pore size distribution and insufficient mechanical strength. The commonly used electrospinning method involves high-voltage equipment and multiple layer parameter adjustments, which is costly for industrialization. SUMMARY

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

[0007] Step 1: Disperse a certain mass of active hydrogen-containing polymer, hydrolyzable silane polymer, polyetherimide, surfactant and hydrophobic nanoparticles in a mixed solvent of N-methylpyrrolidone (NMP) and isopropanol (IPA), stir evenly to form a casting solution;

[0008] Step 2: Apply the casting solution evenly to the surface of the glass plate and let it stand in the air for 1-10 minutes;

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

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

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

[0012] In step one, the active hydrogen 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.

[0013] In step one, the hydrolyzable silane polymer is one or more of silane-grafted polyether ether ketone, 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 of polyetherimide used is 1-5% of the total mass of the casting solution.

[0014] In step one, 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] In step one, the volume ratio of the mixed solvent of N-methylpyrrolidone and isopropanol is 80-90:10-20, and the stirring time is 5-12 hours.

[0016] The coating thickness of the casting solution in the step two is 10-50 mu m.

[0017] The first-stage acid solution in the step three is 0.05-0.2 mol / L tartaric acid and 0.01-0.1 mol / L sodium citrate, and the pH value is 3.5-4.5.

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

[0019] The beneficial effects of the application are as follows:

[0020] The application realizes the precise construction of the gradient pore structure under the simple blade coating process through the triple dynamic mechanism of the pH response shrinkage of the active hydrogen-containing polymer, the solvent volatilization of the polyetherimide and the in-situ crosslinking of the hydrolysable silane polymer.

[0021] The gradient pore structure. The micropore holes in the inner layer of the waterproof and breathable film are formed by the selective volatilization of the polyetherimide in the second-stage acid solution, and the nanometer pores on 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 are in-situ crosslinked by the hydrolysable silane polymer to form a chemical bonding interface, and the surfactant molecules can be adsorbed at the interface of different components to improve the compatibility between the components, provide a better interface environment for in-situ crosslinking, help to form a firm chemical bonding interface, enhance the interlayer bonding force, prevent delamination, and solve the risk of delamination of the traditional electrospun film. By adjusting the concentration of the acid solution, the treatment temperature, the phase separation of the polymer and the migration of the hydrophobic nanoparticles, the hydrophobicity of the film surface is enhanced, and the dynamic adjustment of the pore size of the waterproof and breathable film is realized. The tartaric acid / citric acid combination in a specific pH range can make the polylactic acid shrink without degradation, and ethanol cooperates with polyetherimide to form open pores.

[0022] The waterproof and breathable film has good air permeability. The acid solution treatment induces the volatilization of polyetherimide to form through pores, and the homogeneous distribution of SiO2 nanoparticles avoids the blockage of the pores. Combined with the gradient pore synergistic effect, the hydrolysable silane polymer and the active hydrogen-containing polymer form a flexible interface, and the pore structure is dynamically adjusted under pressure / humidity, maintaining high air permeability while resisting deformation. The surfactant participates in and affects the non-solvent induced phase separation process, which helps to form through and uniform micropores, thereby significantly improving the air permeability of the final film.

[0023] The waterproof performance is excellent. The inner layer of the waterproof and breathable film has micron-level pores as a "buffer layer" to intercept large-particle pollutants, and the surface layer has nanometer pores to generate high pressure through narrow channels to achieve physical water resistance. The waterproof and breathable film prepared can withstand 1 meter of water pressure for 30 minutes without leaking. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 SEM image of the front surface of the waterproof and breathable film prepared according to Example 1.

[0025] Figure 2 SEM image of the back surface of the waterproof and breathable film prepared according to Example 1. DETAILED DESCRIPTION

[0026] The following is a further detailed description of the preparation method of the waterproof and breathable film according to the specific embodiments of the present application. It should be understood that the specific examples are only used to explain and introduce the present application, and cannot limit the application range of the present application. Any modification and change made to the present application without departing from the purpose and scope of the present application falls within the protection scope of the present application.

[0027] Example 1:

[0028] Step one, weigh polyhydroxybutyrate 2.5g, silane grafted polyphenyl ether 1.2g, polyetherimide 4.5g, Pluronic F127 0.15g, hydrophobic SiO2 nanoparticles 0.25g.

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

[0030] Step three, the casting solution is scraped on the glass plate with a scraping thickness of 35μm, and is placed at room temperature for 3 minutes.

[0031] Step four, immerse in the first stage acidic solution containing 0.12mol / L tartaric acid and 0.06mol / L sodium citrate, pH=3.5, temperature 25℃, for 5 minutes.

[0032] Step five, transfer to the second stage acidic solution containing 0.35mol / L citric acid and 12% ethanol, pH=1.8, temperature 40℃, for 15 minutes.

[0033] Step six, deionized water washing, 45℃ air drying to obtain the waterproof and breathable film.

[0034] The waterproof and breathable film prepared by the process flow of Example 1 is tested by a waterproof and breathable film comprehensive tester, and the hydrostatic pressure is 92KPa. At the same time, the air permeation flow rate of the waterproof and breathable film is measured to be 4400ml per minute under the air pressure of 7Kpa and the area of 1 square centimeter.

[0035] Example 2:

[0036] Step one, weigh carboxymethyl chitosan 3g, alkylated modified polyethylene 2g, polyetherimide 5g, Tetronic 901 0.5g, hydrophobic SiO2nanoparticles 0.5g.

[0037] Step two, disperse the above components in NMP / IPA (volume ratio 95:5) mixed solvent, the total system solid content is 25%, stir for 12 hours to uniform casting solution.

[0038] Step three, the casting solution is coated on the glass plate, the coating thickness is 20μm, and the room temperature is placed for 1 minute.

[0039] Step four, immerse in the first stage acidic solution containing 0.2mol / L tartaric acid and 0.1mol / L sodium citrate, pH=3, temperature 25℃, treatment for 3 minutes.

[0040] Step five, transfer to the second stage acidic solution containing 0.2mol / L citric acid and 5% ethanol, pH=2, temperature 35℃, treatment for 20 minutes.

[0041] Step six, deionized water washing, 45℃ air drying to obtain waterproof breathable membrane.

[0042] The waterproof breathable membrane prepared by the process of Example 2 is tested by a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure is 90KPa. At the same time, it is measured that under the air pressure of 7Kpa, the air permeation flow per minute under the area of 1 square centimeter is 4900ml.

[0043] Example 3:

[0044] Step one, weigh carboxymethyl chitosan 3g, alkylated modified polyethylene 2g, polyetherimide 5g, Tetronic 901 0.5g, hydrophobic SiO2nanoparticles 0.5g.

[0045] Step two, disperse the above components in NMP / IPA (volume ratio 95:5) mixed solvent, the total system solid content is 25%, stir for 12 hours to uniform casting solution.

[0046] Step three, the casting solution is coated on the glass plate, the coating thickness is 20μm, and the room temperature is placed for 1 minute.

[0047] Step four, immerse in the first stage acidic solution containing 0.2mol / L tartaric acid and 0.1mol / L sodium citrate, pH=3, temperature 25℃, treatment for 3 minutes.

[0048] Step five, transfer to the second stage of the acid solution containing 0.5 mol / L citric acid and 15% ethanol, pH = 1.2, temperature 45℃ for 10 minutes.

[0049] Step six, deionized water rinse, 45℃ air drying to obtain waterproof breathable membrane.

[0050] The waterproof breathable membrane prepared by the process of Example 3 is tested by a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure is 85KPa. At the same time, it is measured that the air permeation flow per minute under 1 square centimeter area is 5100 milliliters under 7Kpa air pressure.

[0051] Comparative Example 1:

[0052] Step one, weigh polyhydroxybutyrate 2.5g, silane grafted polyphenyl ether 1.2g, polyetherimide 4.5g, Pluronic F127 0.15g, hydrophobic SiO2 nanoparticles 0.25g.

[0053] Step two, disperse the above components in NMP / IPA (volume ratio 92:8) mixed solvent, the total system solid content is 12%, stir for 12 hours to uniform casting solution.

[0054] Step three, the casting solution is coated on the glass plate with a thickness of 35μm, and is placed at room temperature for 3 minutes.

[0055] Step four, immerse in the second stage of the acid solution containing 0.35 mol / L citric acid and 12% ethanol, pH = 1.8, temperature 40℃ for 15 minutes.

[0056] Step five, deionized water rinse, 45℃ air drying to obtain waterproof breathable membrane.

[0057] The waterproof breathable membrane prepared by the process of Comparative Example 1 is tested by a waterproof breathable membrane comprehensive tester, and the hydrostatic pressure is 61KPa. At the same time, it is measured that the air permeation flow per minute under 1 square centimeter area is 2250 milliliters under 7Kpa air pressure.

[0058] Comparative Example 2:

[0059] Step one, weigh polyhydroxybutyrate 2.5g, silane grafted polyphenyl ether 1.2g, polyetherimide 4.5g, sodium dodecyl sulfate 0.15g, hydrophobic SiO2 nanoparticles 0.25g.

[0060] Step two, disperse the above components in NMP / IPA (volume ratio 92:8) mixed solvent, the total system solid content is 12%, stir for 12 hours to uniform casting solution.

[0061] Step three, the casting solution is coated on the glass plate with a thickness of 35 μm, and is left at room temperature for 3 minutes.

[0062] Step four, the film is immersed in a 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 five, the film is transferred to a 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 six, the film is washed with deionized water and is air-dried at 45°C to obtain a waterproof and breathable film.

[0065] The waterproof and breathable film prepared according to the process flow of Comparative Example 2 is tested by using a waterproof and breathable film comprehensive tester, and the hydrostatic pressure is 37 KPa. Meanwhile, it is measured that the air permeation flow per minute is 1840 ml under the air pressure of 7 KPa and the area of 1 cm2.

[0066] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above-mentioned technical content to obtain equivalent embodiments. However, any simple modification, equivalent change and improvement made according to the technical essence of the present application to the above-mentioned embodiments still falls within the protection scope of the present application.

Claims

1. A method for preparing a waterproof and breathable membrane, characterized by the following steps: Step one, a certain amount of active hydrogen-containing polymer, hydrolysable silane polymer, polyetherimide, surfactant and hydrophobic nanoparticles are dispersed in a mixed solvent of N-methylpyrrolidone and isopropanol, stirred uniformly to form a casting solution; The active hydrogen-containing polymer in step one is one or more of polyhydroxybutyrate or carboxymethyl chitosan, and the amount is 1-3% of the total mass of the casting solution; The hydrolysable silane polymer in step one is one or more of silane grafted polyphenyl ether or silane grafted polyether ether ketone, and the amount is 0.1-2% of the total mass of the casting solution; the amount of polyetherimide is 1-5% of the total mass of the casting solution; The surfactant in step one is one or more of Pluronic F127, Tetronic 901 or Brij L23, and the amount is 0.05-0.5% of the total mass of the casting solution; the hydrophobic nanoparticles are SiO2, and the amount is 0.1-1% of the total mass of the casting solution; Step two, the casting solution is uniformly blade coated on the surface of a glass plate and left to stand in the air for 1-10 minutes; Step three, immerse the membrane in the first stage acidic solution and treat at 15-25℃ for 5-10 minutes; the first stage acidic solution in step three 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; Step four, transfer the membrane into the second stage acidic solution and treat at 30-50℃ for 10-20 minutes; the second stage acidic solution in step four is 0.2-0.5 mol / L citric acid and 5-15% ethanol; Step five, wash the treated membrane with deionized water and dry at 45℃ to obtain a waterproof and breathable membrane.

2. The method of making a waterproof, breathable film according to claim 1, characterized in that: The volume ratio of N-methylpyrrolidone to isopropanol in step one is 80-90:10-20, and the stirring time is 5-12 hours.

3. The method of making a waterproof, breathable film according to claim 1, wherein: The coating thickness of the casting solution in step two is 10-50 μm.

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