Polyurethane nanofiber membrane and preparation method thereof

Abstract

The present invention relates to the field of fiber membrane technology, and specifically to a polyurethane nanofiber membrane and a preparation method thereof. The specific technical solution is as follows: comprising the following steps: (1) dispersing a waterproofing agent A and a salt substance in an organic solvent, stirring to obtain a uniform solution, and then dispersing thermoplastic polyurethane in the prepared solution to prepare an electrostatic spinning stock solution; (2) dispersing a waterproofing agent B and an adhesive polymer in an organic solvent or water to prepare an electrostatic / airflow spraying stock solution; (3) electrostatically spinning and electrostatically / airflow spraying the electrostatic spinning stock solution and the electrostatic / airflow spraying stock solution simultaneously to obtain a polyurethane nanofiber membrane. The present invention combines electrostatic spinning technology with electrostatic / airflow spraying technology to construct a cross-linked structure between nanofibers, thereby preventing the fibers from moving when subjected to force, thereby improving the mechanical properties of the nanofiber membrane, and at the same time covering the surface of the nanofibers with a uniform hydrophobic coating, so that the nanofiber membrane has better waterproof performance.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber membranes, and in particular to a polyurethane nanofiber membrane and a preparation method thereof. Background Art

[0002] Waterproof and breathable nanofiber membranes are functional nanofiber membranes that prevent liquid penetration while allowing water vapor, sweat, and other substances to quickly transmit. This membrane maintains a dry microclimate between clothing and the human body, providing a comfortable experience for the wearer. This membrane has broad potential for development, not only in personal protective clothing but also in areas such as seawater desalination and electronics.

[0003] At present, the waterproof and breathable membranes on the market are mainly non-porous hydrophilic polyurethane membranes and microporous polytetrafluoroethylene membranes. Although the former has excellent waterproof performance, its moisture permeability is very poor due to its lack of pores, which greatly reduces the thermal and moisture comfort of the material; although the latter has excellent waterproof performance and good moisture permeability, its preparation process is complicated, it is difficult to degrade after disposal, and its elasticity is poor, which limits its wide application.

[0004] Therefore, it is necessary to prepare a nanofiber membrane that has both excellent waterproofness and good moisture permeability, and ensure that it has good mechanical properties. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides a polyurethane nanofiber membrane and a preparation method thereof.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] The present invention discloses a method for preparing a polyurethane nanofiber membrane, comprising the following steps:

[0008] (1) Dispersing waterproofing agent A and salt substances in an organic solvent, stirring to obtain a uniform solution, and then dispersing thermoplastic polyurethane in the prepared solution to prepare an electrospinning stock solution;

[0009] (2) dispersing the waterproofing agent B and the adhesive polymer in an organic solvent or water to prepare an electrostatic / airflow spraying stock solution;

[0010] (3) Electrospinning stock solution and electrostatic / airflow spraying stock solution are simultaneously electrospun and electrostatic / airflow sprayed, and the nanofibers obtained by electrospinning are electrostatically / airflow sprayed on the surface coating of the nanofibers to obtain a polyurethane nanofiber membrane with a surface coating.

[0011] Preferably, the waterproofing agent A and the waterproofing agent B are respectively one of a fluorocarbon waterproofing agent, a silicone waterproofing agent, a hydroxymethyl melamine derivative waterproofing agent, and a fatty acid metal salt hydrophobic agent, and the concentration of the waterproofing agent A in the electrostatic spinning solution and the waterproofing agent B in the electrostatic / air flow spraying solution is respectively 1wt% to 4wt%.

[0012] Preferably, the salt substance is an inorganic salt or an organic salt, the inorganic salt is one of anhydrous lithium chloride, anhydrous magnesium chloride, and sodium chloride, the organic salt is one of quaternary ammonium salt and sodium acetate, and the concentration of the salt substance in the electrospinning solution is 0.001wt% to 0.05wt%.

[0013] Preferably, the organic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide and ethanol.

[0014] Preferably, the adhesive polymer is one of polyvinyl butyral, water-based acrylic resin, water-based polyurethane, alcohol-soluble nylon, alcohol-soluble polyurethane, polyvinylidene fluoride, and polytetrafluoroethylene emulsion, and its concentration in the electrostatic / airflow spraying stock solution is 1wt% to 20%.

[0015] Preferably, the concentration of thermoplastic polyurethane in the electrospinning solution is 6 wt% to 30 wt%.

[0016] Preferably, the electrospinning parameters are: voltage 15kv to 50kv, distance between needle and receiver 10cm to 30cm, injection speed 0.1ml / h to 2.0ml / h, inner diameter of spinning needle 0.1mm to 3mm;

[0017] The parameters of electrostatic / air flow spraying are: voltage 0~20kV, the receiving distance between the needle and the receiver is 5cm~20cm, the injection speed is 0.1ml / h~10ml / h, the electrostatic / air flow nozzle is a coaxial structure, the inner tube inner diameter is 0.1mm~1mm, the outer tube inner diameter is 0.8mm~5mm, and the air flow pressure is 40Kpa~80Kpa.

[0018] Preferably, the method further comprises subjecting the prepared polyurethane nanofiber membrane to heat treatment at a temperature of 60° C. to 80° C. and a drying time of 5 min to 30 min.

[0019] Correspondingly, the polyurethane nanofiber membrane prepared by the above preparation method.

[0020] The present invention has the following beneficial effects:

[0021] 1. The present invention combines electrospinning technology and electrostatic / airflow spraying technology to construct a cross-linked structure between nanofibers, preventing the fibers from moving when subjected to force, thereby improving the mechanical properties of the nanofiber membrane. At the same time, a uniform hydrophobic coating is covered on the surface of the nanofibers, which can reduce the pore size of the nanofiber membrane, improve the hydrophobicity and hydrostatic pressure of the nanofiber membrane, and make the nanofiber membrane have better waterproof performance.

[0022] 2. The present invention prepares a polyurethane nanofiber waterproof and breathable membrane through electrostatic spinning and electrostatic / airflow spraying processes: the polyurethane nanofiber waterproof and breathable membrane prepared by a one-step method does not require post-processing, has a simple process, and does not produce waste liquid during the preparation process; moreover, the diameter and morphology of the nanofibers, and the composition and thickness of the hydrophobic coating can be controlled separately. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of the thermoplastic polyurethane nanofiber membrane with a bonding structure prepared in Example 2. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0026] The present invention discloses a method for preparing a polyurethane nanofiber membrane, comprising the following steps:

[0027] (1) Dispersing a waterproofing agent A and a salt substance in an organic solvent and stirring to obtain a uniform solution, and then dispersing thermoplastic polyurethane in the prepared solution by stirring to prepare an electrospinning stock solution; the concentration of the thermoplastic polyurethane in the electrospinning stock solution is 6wt% to 30wt%. The thermoplastic polyurethane can be a single component polyurethane or a copolymerized polyurethane.

[0028] (2) The waterproofing agent B and the adhesive polymer are dispersed in an organic solvent or water, and stirred to prepare an electrostatic / airflow spraying stock solution; the solvent used in the electrostatic / airflow spraying stock solution does not dissolve polyurethane.

[0029] (3) Electrospinning stock solution and electrostatic / airflow spraying stock solution are simultaneously electrospun and electrostatic / airflow sprayed, and the nanofibers obtained by electrospinning are electrostatically / airflow sprayed on the surface of the nanofibers to obtain a polyurethane nanofiber membrane with a surface coating. Specifically: the electrospinning stock solution is loaded into the electrospinning needle, and the spraying stock solution is loaded into the electrostatic / airflow nozzle. The spinning needle and nozzle are respectively connected to a high-voltage power supply, and the electrostatic / airflow nozzle is also connected to compressed air. The collecting device (metal roller, metal mesh chain, etc.) is grounded, the high-voltage power supply and compressed air are turned on, and the parameters required for electrospinning and electrostatic / airflow spraying are adjusted to obtain a polyurethane nanofiber membrane with a bonding structure on the collecting device;

[0030] Furthermore, electrospinning technology and electrostatic / airflow spraying technology are carried out simultaneously. Multi-needle electrospinning produces polyurethane nanofibers, and multi-nozzle electrostatic / airflow spraying covers the nanofibers with a layer of sticky resin and creates a bonding structure between the fibers. The bonding structure between the fibers can improve the mechanical properties of the nanofiber membrane; electrostatic / airflow spraying coats the surface of the nanofibers with a hydrophobic coating, further reduces the pore size of the polyurethane nanofiber membrane, and increases its hydrostatic pressure.

[0031] Furthermore, multiple electrospinning needles and electrostatic / airflow spray nozzles can be arranged linearly and staggered; or multiple electrospinning needles can be arranged linearly and multiple electrostatic / airflow spray nozzles can be arranged linearly, and the two can be staggered.

[0032] (4) Drying the prepared nanofibers in an oven at a certain temperature to remove excess solvent to obtain a nanofiber waterproof and breathable membrane. The heat treatment temperature is 60°C to 80°C, and the drying time is 5 minutes to 30 minutes.

[0033] Furthermore, the water repellents A and B are solvent-based or water-based, depending on the reagent used, including but not limited to one of a fluorocarbon water repellent, a silicone water repellent, a hydroxymethyl melamine derivative water repellent, and a fatty acid metal salt water repellent. Their concentrations are 1 wt% to 4 wt%, respectively. That is, the concentration of water repellent A in the electrospinning solution and water repellent B in the electrostatic / airflow spray solution are 1 wt% to 4 wt%, respectively. The addition of the water repellents can improve the hydrophobicity of the nanofiber membrane and provide hydrostatic pressure.

[0034] Furthermore, the salt is an inorganic salt or an organic salt, the inorganic salt being one of anhydrous lithium chloride, anhydrous magnesium chloride, and sodium chloride, and the organic salt being one of a quaternary ammonium salt and sodium acetate, and the concentration of the salt in the electrospinning solution being 0.001 wt% to 0.05 wt%. The addition of the salt can increase the electric field stretching force, reduce the fiber diameter, decrease the pore size of the nanofiber membrane, and increase the hydrostatic pressure.

[0035] Furthermore, the organic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide and ethanol.

[0036] Furthermore, the adhesive polymer is one of polyvinyl butyral (PVB), water-based acrylic resin, water-based polyurethane, alcohol-soluble nylon, alcohol-soluble polyurethane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene emulsion, and its concentration in the electrostatic / airflow spraying stock solution is 1wt% to 20%.

[0037] Furthermore, the electrospinning parameters are: voltage 15kv~50kv, distance between needle and receiver 10cm~30cm, injection speed 0.1ml / h~2.0ml / h, inner diameter of spinning needle 0.1mm~3mm;

[0038] The parameters of electrostatic / air flow spraying are: voltage 0~20kV, the receiving distance between the needle and the receiver is 5cm~20cm, the injection speed is 0.1ml / h~10ml / h, the electrostatic / air flow nozzle is a coaxial structure, the inner tube inner diameter is 0.1mm~1mm, the outer tube inner diameter is 0.8mm~5mm, and the air flow pressure is 40Kpa~80Kpa.

[0039] Of course, the preparation process can also use electrostatic spraying to produce the coating on the nanofiber surface without using compressed air. The role of the airflow is to cooperate with the electric field force to break up the spray solution into smaller droplets, increasing the spray volume and improving spray efficiency.

[0040] Furthermore, the entire production environment of the polyurethane nanofiber membrane is at a temperature of 19 to 25° C. and a relative humidity of 55 to 75%.

[0041] The present invention will be further described below with reference to specific embodiments.

[0042] The sources of the following examples are as follows:

[0043] Thermoplastic polyurethane (BASF Polyurethanes (China) Co., Ltd., Elastollan 1190A10), N,N-dimethylformamide (DMF, Shanghai Aladdin Biochemical Technology Co., Ltd.), LiCl (Shanghai Aladdin Biochemical Technology Co., Ltd.), polyvinyl butyral (PVB, Shanghai Aladdin Biochemical Technology Co., Ltd., MW50,000-80,000), silicone fluorine-free water repellent (Dongguan Tengmei Nano New Materials Co., Ltd.), water-based siloxane-based water repellent (Beijing Qifei Technology Development Co., Ltd., SK3), acrylic resin (Wanhua New Materials Technology Co., Ltd., WA228), C6 water repellent (Anflunol, RH5392), copolymer polyurethane (Dainichiseika Chemical Co., Ltd., Si-TPU), polyvinylidene fluoride (PVDF, SolvaySolef 6010).

[0044] Example 1

[0045] The preparation process of polyurethane nanofiber membrane is as follows:

[0046] Step 1: Dissolve 3 wt% of a fluorine-free silicone waterproofing agent and 0.01 wt% of LiCl in DMF solvent. Then, weigh 18 wt% of thermoplastic polyurethane and add it to the prepared solution. Stir with a magnetic stirrer at 50°C for 5 h to obtain a uniform electrospinning solution.

[0047] Step 2: Disperse 3 wt% of a water-based silicone waterproofing agent and 3 wt% of an acrylic resin in deionized water, and stir with a magnetic stirrer at room temperature until the solution is uniformly dispersed to obtain an electrostatic / airflow spray solution;

[0048] Step 3: Set the spinning space temperature to 22°C, the humidity to 60%, and turn on the ventilation system;

[0049] Step 4: Use a syringe to extract the prepared spinning solution and spray solution and expel excess bubbles, and place them on the electrospinning and electrostatic / airflow spraying devices, respectively. The electrospinning parameters are set as follows: voltage 25kV, distance between needle and receiver 17cm, injection speed 0.7ml / h, receiver rotation speed 50rpm / min, spinning time 4h; electrostatic / airflow spraying parameters are set as follows: voltage 0, distance between needle and receiver 17cm, injection speed 3ml / h, air pressure 80kPa, spraying time 4h;

[0050] Step 5: Place the prepared nanofiber membrane in an oven at 70°C for 5 minutes.

[0051] The nanofiber membrane prepared by one-step electrospinning and electrostatic / airflow spraying technology using these parameters has a hydrostatic pressure of 65KPa and a water vapor permeability of 7.5kg·m -2 d -1 , excellent waterproof and breathable properties, in addition, the nanofiber membrane also has good mechanical properties, with a tensile stress of 22.4MPa and a tensile strain of 223%.

[0052] Example 2

[0053] The preparation process of polyurethane nanofiber membrane is as follows:

[0054] Step 1: 3 wt% C6 waterproofing agent and 0.004 wt% LiCl were dissolved in DMF solvent. Then, 20 wt% thermoplastic polyurethane was added to the prepared solution and stirred with magnetic stirring at 50°C for 5 h to obtain a uniform electrospinning solution.

[0055] Step 2: 3 wt% C6 waterproofing agent and 0.4 wt% PVB were dissolved in anhydrous ethanol and stirred with a magnetic stirrer at 50°C until a uniform and transparent solution was obtained to obtain an electrostatic / airflow spraying solution;

[0056] Step 3: Set the spinning space temperature to 22°C, the humidity to 60%, and turn on the ventilation system;

[0057] Step 4: Use a syringe to extract the prepared spinning solution and spraying solution and expel excess bubbles, and place them on the electrospinning and electrostatic / airflow spraying devices respectively, and perform electrospinning and electrostatic / airflow spraying in an alternating linear manner. The electrospinning parameters are set as follows: voltage 30kV, distance between the needle and the receiver 18cm, injection speed 0.8ml / h, receiver rotation speed 50rpm / min, spinning time 4h; electrostatic / airflow spraying parameters are set as follows: voltage 10kV, distance between the needle and the receiver 12cm, injection speed 5ml / h, air pressure 40KPa, spraying time 4h;

[0058] Step 5: Place the prepared nanofiber membrane in an oven at 70°C for 10 minutes.

[0059] like Figure 1 As shown in the figure, it can be seen that the nanofiber membrane prepared by one-step electrospinning and electrostatic / airflow spraying technology has many adhesion structures between fibers, its hydrostatic pressure is 100KPa, and its water vapor permeability is 6.5kg·m -2 d -1 , excellent waterproof and breathable properties, in addition, the nanofiber membrane also has good mechanical properties, with a tensile stress of 25.7MPa and a tensile strain of 196%.

[0060] Example 3

[0061] The preparation process of polyurethane nanofiber membrane is as follows:

[0062] Step 1: 3 wt% copolymerized thermoplastic polyurethane and 0.005 wt% LiCl were dissolved in DMF solvent. 18 wt% thermoplastic polyurethane was then added to the prepared solution and stirred at 50°C with a magnetic stirrer for 5 h to obtain a uniform electrospinning solution.

[0063] Step 2: 3 wt% of a fluorinated acrylate copolymer and 3 wt% of PVDF were dissolved in DMF and stirred with a magnetic stirrer at room temperature until the solution was uniformly dispersed to obtain an electrostatic / airflow spraying solution;

[0064] Step 3: Set the spinning space temperature to 22°C, the humidity to 60%, and turn on the ventilation system;

[0065] Step 4: Use a syringe to extract the prepared spinning solution and spraying solution and expel excess bubbles, and place them on the electrospinning and electrostatic / airflow spraying devices respectively, and perform electrospinning and electrostatic / airflow spraying using alternating linear motion. The electrospinning parameters are set as follows: voltage 25kv, distance between needle and receiver 18cm, injection speed 0.7ml / h, receiver rotation speed 50rpm / min, spinning time 4h; electrostatic / airflow spraying parameters are set as follows: voltage 10kv, distance between needle and receiver 12cm, injection speed 3ml / h, air pressure 40kpa, spraying time 4h;

[0066] Step 5: Place the prepared nanofiber membrane in an oven at 70°C for 10 minutes.

[0067] The nanofiber membrane prepared by one-step electrospinning and electrostatic / airflow spraying technology using these parameters has a hydrostatic pressure of 110 KPa and a water vapor permeability of 5.5 kg·m -2 d -1 , excellent waterproof and breathable properties, in addition, the nanofiber membrane also has good mechanical properties, with a tensile stress of 20.4MPa and a tensile strain of 173%.

[0068] Comparative Example 1: Electrospun thermoplastic polyurethane (original sample), hydrostatic pressure 3.6 kPa, moisture permeability 9.5 kg·m -2 d -1 , tensile stress 10MPa, tensile strain 230%, contact angle 125°.

[0069] Comparative Example 2: Electrospun silicone fluorine-free hydrophobic agent and TPU, hydrostatic pressure 23kPa, moisture permeability 8.4kg·m -2 d -1, tensile stress 16.5MPa, tensile strain 207%, contact angle 130°.

[0070] The relevant properties of the nanofiber membranes prepared in the above examples are shown in Table 1 below.

[0071] Table 1 Performance list of prepared nanofiber waterproof and breathable membrane

[0072]

[0073] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a polyurethane nanofiber membrane, characterized in that: The following steps are involved: (1) Dispersing waterproofing agent A and salt substances in an organic solvent, stirring to obtain a uniform solution, and then dispersing thermoplastic polyurethane in the prepared solution to prepare an electrospinning stock solution; (2) dispersing the waterproofing agent B and the adhesive polymer in an organic solvent or water to prepare an electrostatic / airflow spraying stock solution; (3) electrospinning the electrospinning solution and electrostatic / airflow spraying the solution simultaneously, electrostatically spraying the nanofibers obtained by electrospinning, and electrostatically spraying the nanofiber surface coating with airflow to obtain a polyurethane nanofiber membrane with a surface coating; The waterproofing agent A and the waterproofing agent B are respectively one of a fluorocarbon waterproofing agent, an organosilicon waterproofing agent, a hydroxymethyl melamine derivative waterproofing agent, and a fatty acid metal salt hydrophobic agent, and the concentration of the waterproofing agent A in the electrostatic spinning solution and the waterproofing agent B in the electrostatic / airflow spraying solution are respectively 1wt% to 4wt%; The salt substance is an inorganic salt or an organic salt, the inorganic salt is one of anhydrous lithium chloride, anhydrous magnesium chloride, and sodium chloride, the organic salt is one of a quaternary ammonium salt and sodium acetate, and the concentration of the salt substance in the electrospinning solution is 0.001wt% to 0.05wt%; The organic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide and ethanol; The adhesive polymer is one of polyvinyl butyral, water-based acrylic resin, water-based polyurethane, alcohol-soluble nylon, alcohol-soluble polyurethane, polyvinylidene fluoride, and polytetrafluoroethylene emulsion, and its concentration in the electrostatic / airflow spraying stock solution is 1wt% to 20%; The concentration of thermoplastic polyurethane in the electrospinning solution is 6 wt % to 30 wt %.

2. The preparation method according to claim 1, wherein: The electrospinning parameters are: voltage 15kV to 50kV, distance between needle and receiver 10cm to 30cm, injection speed 0.1ml / h to 2.0ml / h, inner diameter of spinning needle 0.1mm to 3mm; The parameters of electrostatic / air flow spraying are: voltage 0~20kV, the receiving distance between the needle and the receiver is 5cm~20cm, the injection speed is 0.1ml / h~10ml / h, the electrostatic / air flow nozzle is a coaxial structure, the inner tube inner diameter is 0.1mm~1mm, the outer tube inner diameter is 0.8mm~5mm, and the air flow pressure is 40Kpa~80Kpa.

3. The preparation method according to claim 1, wherein: The method also includes heat treating the prepared polyurethane nanofiber membrane, wherein the heat treatment temperature is 60° C. to 80° C. and the drying time is 5 minutes to 30 minutes.

4. The polyurethane nanofiber membrane prepared according to the preparation method according to any one of claims 1 to 3.

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