A porosity / wetting dual gradient directional water-absorbing fiber membrane and its preparation method

Abstract

The present invention discloses a method for preparing a porosity / wetting dual-gradient directional water-absorbing fiber membrane, characterized by comprising the following steps: (1) using a polytetrafluoroethylene microporous membrane as a receiving substrate, electrospinning a spinning solution I composed of hydrolyzed polyacrylonitrile, acrylic acid, acrylamide, a crosslinker, and a solvent to produce a hydrophilic layer; (2) casting a casting solution composed of hydrolyzed polyacrylonitrile, polyurethane, isocyanate, a crosslinker, and a solvent on a glass plate by a non-solvent induced phase separation method and immersing the casting solution in water to produce an intermediate layer, wherein the intermediate layer is composited with the hydrophilic layer by heat treatment; and (3) using the intermediate layer as a receiving substrate, electrospinning a spinning solution II composed of cellulose acetate and a solvent to produce a composite fiber membrane. The intermediate layer has a moisture absorption and perspiration wicking effect by imitating vascular plants. The cellulose acetate layer has moderate hydrophilicity and serves as the inner layer in contact with the skin. The moisture-absorbing layer can absorb moisture from the CA layer to keep the surface layer dry.

Description

Technical Field

[0001] The present invention relates to the technical field of electrostatic spinning functional fiber materials, and in particular to a porosity / wetting dual-gradient directional water-absorbing fiber membrane and a preparation method thereof. Background Art

[0002] Currently, polytetrafluoroethylene (PTFE) film is widely used in corrosion-resistant protective clothing. PTFE's high hydrophobicity limits its water transfer capacity and slows water evaporation, hindering gas exchange between the human body and the surrounding environment, thereby reducing the effectiveness of heat and humidity management. Prolonged use can lead to sweat accumulation at the skin-contact interface. Organic matter in sweat provides a favorable environment for microbial growth, easily leading to bacterial infection and inflammation, posing a threat to human health. Therefore, it is very important to provide protective clothing with directional moisture permeability.

[0003] Currently, some researchers typically use chemical methods to modify polyester fabrics to achieve excellent hydrophilicity. However, chemical modification can cause environmental pollution. Other researchers use enzyme treatment to improve the properties of polyester fabrics. However, enzyme treatments are less efficient due to their long processing times. Producing functional textiles with directional moisture absorption from porous materials has great potential for application. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects in the prior art, provide a porosity / wetting dual gradient directional water-absorbing fiber membrane and a preparation method thereof, and develop functional textiles with directional moisture absorption function.

[0005] To achieve the above object, the technical solution of the present invention is to provide a method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane, comprising the following steps:

[0006] (1) using a polytetrafluoroethylene microporous membrane as a receiving substrate, electrospinning a spinning solution I consisting of hydrolyzed polyacrylonitrile, acrylic acid, acrylamide, a crosslinking agent, and a solvent to obtain a hydrophilic layer;

[0007] (2) casting a casting solution made of hydrolyzed polyacrylonitrile, polyurethane, isocyanate, a crosslinking agent, and a solvent on a glass plate by a non-solvent induced phase separation method and immersing the solution in water to prepare an intermediate layer, and hot-pressing the intermediate layer to the hydrophilic layer;

[0008] (3) using the intermediate layer as a receiving substrate, electrospinning a spinning solution II consisting of cellulose acetate and a solvent to form a hydrophobic layer on the side of the intermediate layer away from the hydrophilic layer, thereby obtaining a composite fiber membrane;

[0009] The intermediate layer comprises amino side chains grafted to a hydrolyzed polyacrylonitrile backbone, the amino side chains extending into the cellulose acetate layer.

[0010] Cellulose acetate (CA) was chosen as the moisture-transmitting layer closest to the skin due to its moderate hydrophilicity and low swelling properties. Polyester (PTFE) was used as the backbone of the laminated fabric due to its unique breaking strength, corrosion resistance, and inherent hydrophobicity. The PU-HPAN hydrophilic layer, prepared via a non-solvent-induced phase separation method, features a branched structure that permeates the cellulose acetate (CA) layer, demonstrating excellent fast-drying activity and directional moisture transport.

[0011] A further preferred technical solution is that in the spinning solution I, the hydrolyzed polyacrylonitrile accounts for 78 to 90% of the total mass of the monomers, the acrylic acid accounts for 8 to 20% of the total mass of the monomers, the acrylamide accounts for 2 to 12% of the total mass of the monomers, the neutralization degree of the acrylic acid is 75%, and the cross-linking agent accounts for 0.01 to 0.03% of the total mass of the monomers.

[0012] A further preferred technical solution is that the preparation process of spinning solution I is as follows: polyacrylonitrile and sodium hydroxide solution are hydrolyzed at 50-60°C for 15-30 minutes, the resulting slurry is neutralized with acetic acid, acrylic acid, acrylamide and a cross-linking agent are added, the mixture is blended, and stirred in a water bath at 80°C for 2-3 hours.

[0013] A further preferred technical solution is that the process parameters of the electrospinning of the spinning solution I are: voltage 15-30 kV, perfusion speed 0.8-4 mL / h, distance between the spinneret and the receiving substrate 6-25 cm, ambient relative humidity 65-75%, and ambient temperature 20-30 ° C.

[0014] A further preferred technical solution is that the process parameters of the electrospinning of the spinning solution II are: voltage 10-20 kV, perfusion speed 0.2-2 mL / h, distance between the spinneret and the receiving substrate 6-25 cm, ambient relative humidity 25-55%, and ambient temperature 23-26 ° C.

[0015] A further preferred technical solution is that the heat treatment temperature is 60-120° C. and the heat treatment time is 20-60 min.

[0016] The present invention also discloses a porosity / wetting dual gradient directional water-absorbing fiber membrane, in which the large end of the pore is located in the hydrophobic layer and the small end of the pore is located in the hydrophilic layer. The average pore diameter of the large end of the pore is 10 to 25 μm, and the average pore diameter of the small end of the pore is 50 to 250 nm. The porosity of the fiber membrane is greater than 75%.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. The cellulose acetate (CA) layer, with its moderate hydrophilicity and low swelling properties, serves as the inner layer in contact with the skin, reducing the discomfort caused by water absorption by polyester fabrics. The PU-HPAN middle layer acts as a hygroscopic layer, absorbing moisture from the CA layer and keeping it dry. By making the pore size of the CA layer larger than that of the hydrophilic layer and the middle layer, a moisture absorption and perspiration effect is created, mimicking that of vascular plants, resulting in faster one-way moisture permeability. The small pores of the electrospun membrane generate capillary attraction in a perpendicular direction across a certain thickness of the membrane, resulting in excellent moisture absorption and conductivity.

[0019] 2. During the solution casting step of the non-solvent-induced phase separation method, isocyanate is used as a multifunctional additive. Isocyanate is added to the hydrolyzed polyacrylonitrile / polyurethane mixture. As a well-known water-induced CO2 release agent, isocyanate can serve as a phase separation controller, foaming agent, and crosslinking agent during the membrane formation process. The membrane formation process is a combination of phase separation and chemical reaction. When water diffuses into the polymer solution, isocyanate easily reacts with water to form carbamic acid. Carbamic acid is unstable and decomposes into CO2 and an amino end group. The amino group can further react with isocyanate to form urea or can be grafted onto the hydrolyzed polyacrylonitrile backbone through reaction, thereby forming a cross-linked polymer network using amino groups to construct a three-dimensional cross-linked system based on hydrolyzed polyacrylonitrile. At the same time, the membrane pore structure is rationally regulated through the thermodynamic and kinetic changes caused by toluene diisocyanate (TDI) and the CO2 foaming effect.

[0020] 3. The amino side chains grafted onto the hydrolyzed polyacrylonitrile main chain extend into the cellulose acetate (CA) layer, forming a radial water transport network perpendicular to the plane of the composite mold, simulating the transpiration process of vascular plants, allowing water to be transferred to the outer layer spontaneously and continuously. DETAILED DESCRIPTION

[0021] The following examples are only used to illustrate the technical solution of the present invention more clearly, and are not intended to limit the scope of protection of the present invention.

[0022] Dimethylformamide (DMF), polyacrylonitrile (PAN25w), polyurethane (90APU), glutaraldehyde (GA50%H2O), acetic acid, lithium chloride (LiCl), AA, AM, potassium persulfate (KPS) and sodium hydroxide (NaOH) were of analytical grade. Example

[0023] A method for preparing a porosity / wetting dual gradient directional water absorption nanofiber membrane, comprising the following steps:

[0024] (1) A polyurethane with a concentration of 22 wt% was prepared using DMF as a solvent, and the solution was magnetically stirred at 80 °C for 3 h to promote dissolution.

[0025] (2) PAN and NaOH solution were hydrolyzed at 50°C for 15 minutes respectively, and the resulting slurry was neutralized with acetic acid. The mass concentration of HPAN (15 minutes) was 15 wt%.

[0026] (3) A hydrophilic layer HPAN / AA / AM mixed solution system was prepared at a concentration of 25 wt %, wherein HPAN accounted for 80% of the total monomer mass, AA accounted for 16% of the total monomer mass, AM accounted for 4% of the total monomer mass, and the AA neutralization degree was 75%. Potassium persulfate (KPS) accounted for 0.05% of the monomer mass, and the crosslinker glutaraldehyde (GA) accounted for 0.015%. The mixture was then blended and stirred in an 80°C water bath for 3 hours.

[0027] (4) The mass concentration of the intermediate PU-HPAN was 20 wt%. A certain amount of HPAN was added to DMF and dissolved under magnetic stirring at 80°C for 2 hours. The lithium chloride concentration was 0.3% of the solvent. The mass ratio of isocyanate to polyester polyol was 1:5, accounting for 20% of the solute. The lithium chloride was first dissolved in DMF, magnetically stirred at 60°C for 40 minutes, and heated to 80°C. HPAN was then added and stirred for 1 hour. The polyurethane was then added for 2 hours. Finally, the crosslinker was added and dissolved and stirred for 1 hour.

[0028] (5) A CA solution was prepared using a dichloromethane / acetone mixture with a volume ratio of 4:6 as a solvent. The CA solution was then uniformly mixed using a magnetic stirrer for 4 hours and ultrasonicated for 30 minutes to prepare a transparent solution.

[0029] (6) Under a high voltage of 18 kV and a solution feed rate of 2.5 ml / h, a hydrophilic layer HPAN (30 min) / AA / AM mixed solution was electrospun onto a polytetrafluoroethylene microporous membrane at an ambient temperature and relative humidity of 25 ± 5 °C and 70 ± 5%, respectively, to obtain a polytetrafluoroethylene / hydrophilic layer composite membrane.

[0030] (7) The interlayer was prepared by the non-solvent induced phase separation (NIPS) method. First, a certain amount of isocyanate was added to the PU-HPAN solution (~20 wt%) to obtain a uniform casting solution. The solution was then cast on a clean glass plate using a 150 μm casting blade. The cast glass plate was then immediately immersed in a water coagulation bath at a temperature of 30°C to complete the membrane curing. PEI was added to the water as an additive. The resulting membrane was then composited with the hydrophilic layer of the polytetrafluoroethylene / hydrophilic layer composite membrane by heat treatment at 120°C for 20 minutes.

[0031] (8) The prepared CA solution was electrospun directly onto the surface of a PU-HPAN interlayer wrapped around a rotating metal cylinder using an electrospinning apparatus. The distance between the needle tip and the PA membrane was maintained at 18 cm. The CA layer was deposited at a voltage of 15 kV, a rotation speed of 0.4 rs1, and a feed rate of 1.8 ml / h. Lamination was performed for 35 seconds at a lamination pressure of 2 MPa.

[0032] The CA layer closest to the skin has an average diameter of 1.83 μm and a thickness of 20 μm. The HPAN layer has an average diameter of 255 nm and a thickness of 30 μm. The hydrophilic layer has an average diameter of 76 nm and a thickness of 40 μm. The diameter of the hydrophilic layer's fibers ranges from 20 nm to 180 nm, with 34.31% of the fibers being smaller than 60 nm, 17.74% being larger than 100 nm, and 48.04% being between 60 and 100 nm. The porosities of the three fiber layers are 75%, 80.71%, and 84.38%, respectively. Example

[0033] A method for preparing a porosity / wetting dual gradient directional water absorption nanofiber membrane, comprising the following steps:

[0034] (1) A polyurethane with a concentration of 22 wt% was prepared using DMF as a solvent, and the solution was magnetically stirred at 80 °C for 3 h to promote dissolution.

[0035] (2) PAN and NaOH solution were hydrolyzed at 50°C for 30 minutes respectively, and the resulting slurry was neutralized with acetic acid. The concentration of HPAN (30 minutes) was 20 wt%.

[0036] (3) A hydrophilic layer HPAN / AA / AM mixed solution system was prepared at a concentration of 25 wt %, wherein HPAN accounted for 80% of the total monomer mass, AA accounted for 16% of the total monomer mass, AM accounted for 4% of the total monomer mass, and the AA neutralization degree was 75%. Potassium persulfate (KPS) accounted for 0.05% of the monomer mass, and the crosslinker glutaraldehyde (GA) accounted for 0.015%. The mixture was then blended and stirred in an 80°C water bath for 3 hours.

[0037] (4) The mass concentration of the intermediate PU-HPAN was 20 wt%. A certain amount of HPAN was added to DMF and dissolved under magnetic stirring at 80°C for 2 hours. The lithium chloride concentration was 0.3% of the solvent. The mass ratio of isocyanate to polyester polyol was 1:5, accounting for 20% of the solute. The lithium chloride was first dissolved in DMF, magnetically stirred at 60°C for 40 minutes, and heated to 80°C. HPAN was then added and stirred for 1 hour. The polyurethane was then added for 2 hours. Finally, the crosslinker was added and dissolved and stirred for 1 hour.

[0038] (5) A CA solution was prepared using a dichloromethane / acetone mixture with a volume ratio of 4:6 as a solvent. The CA solution was then uniformly mixed using a magnetic stirrer for 4 hours and ultrasonicated for 30 minutes to prepare a transparent solution.

[0039] (6) Under a high voltage of 18 kV and a solution feed rate of 2.5 ml / h, a hydrophilic layer HPAN (30 min) / AA / AM mixed solution was electrospun onto a polytetrafluoroethylene microporous membrane at an ambient temperature and relative humidity of 25 ± 5 °C and 70 ± 5%, respectively, to obtain a polytetrafluoroethylene / hydrophilic layer composite membrane.

[0040] (7) The interlayer was prepared by the non-solvent induced phase separation (NIPS) method. First, a certain amount of isocyanate was added to the PU-HPAN solution (~20 wt%) to obtain a uniform casting solution. The solution was then cast on a clean glass plate using a 150 μm casting blade. The cast glass plate was then immediately immersed in a water coagulation bath at a temperature of 30°C to complete the membrane curing. PEI was added to the water as an additive. The resulting membrane was then composited with the hydrophilic layer of the polytetrafluoroethylene / hydrophilic layer composite membrane by heat treatment at 120°C for 20 minutes.

[0041] (8) The prepared CA solution was electrospun directly onto the surface of a PU-HPAN interlayer wrapped around a rotating metal cylinder using an electrospinning apparatus. The distance between the needle tip and the PA membrane was maintained at 18 cm. The CA layer was deposited at a voltage of 15 kV, a rotation speed of 0.4 rs1, and a feed rate of 1.8 ml / h. Lamination was performed for 35 seconds at a lamination pressure of 2 MPa.

[0042] The CA layer closest to the skin has an average diameter of 1.83 μm and a thickness of 20 μm. The HPAN layer has an average diameter of 312 nm and a thickness of 30 μm. The hydrophilic layer has an average diameter of 78 nm and a thickness of 40 μm. The diameter of the hydrophilic layer fibers ranges from 20 nm to 180 nm. The porosities of the three fiber membranes are 75%, 79.17%, and 83.34%, respectively. Example

[0043] A method for preparing a porosity / wetting dual gradient directional water absorption nanofiber membrane, comprising the following steps:

[0044] (1) A polyurethane with a concentration of 22 wt% was prepared using DMF as a solvent, and the solution was magnetically stirred at 80 °C for 3 h to promote dissolution.

[0045] (2) PAN and NaOH solution were hydrolyzed at 50°C for 30 minutes respectively, and the resulting slurry was neutralized with acetic acid. The concentration of HPAN (30 minutes) was 20 wt%.

[0046] (3) A hydrophilic layer HPAN / AA / AM mixed solution system was prepared at a concentration of 25 wt %, wherein HPAN accounted for 80% of the total monomer mass, AA accounted for 16% of the total monomer mass, AM accounted for 4% of the total monomer mass, and the AA neutralization degree was 75%. Potassium persulfate (KPS) accounted for 0.05% of the monomer mass, and the crosslinker glutaraldehyde (GA) accounted for 0.015%. The mixture was then blended and stirred in an 80°C water bath for 3 hours.

[0047] (4) The mass concentration of the intermediate PU-HPAN was 20 wt%. A certain amount of HPAN was added to DMF and dissolved under magnetic stirring at 80°C for 2 hours. The lithium chloride concentration was 0.3% of the solvent. The mass ratio of isocyanate to polyester polyol was 1:5, accounting for 20% of the solute. The lithium chloride was first dissolved in DMF, magnetically stirred at 60°C for 40 minutes, and heated to 80°C. HPAN was then added and stirred for 1 hour. The polyurethane was then added for 2 hours. Finally, the crosslinker was added and dissolved and stirred for 1 hour.

[0048] (5) A CA solution was prepared using a dichloromethane / acetone mixture with a volume ratio of 4:6 as a solvent. The CA solution was then uniformly mixed using a magnetic stirrer for 4 hours and ultrasonicated for 30 minutes to prepare a transparent solution.

[0049] (6) Under a high voltage of 25 kV and a solution feed rate of 2.5 ml / h, a hydrophilic layer HPAN (30 min) / AA / AM mixed solution was electrospun onto a polytetrafluoroethylene microporous membrane at an ambient temperature and relative humidity of 25 ± 5 °C and 70 ± 5%, respectively, to obtain a polytetrafluoroethylene / hydrophilic layer composite membrane.

[0050] (7) The interlayer was prepared by the non-solvent induced phase separation (NIPS) method. First, a certain amount of isocyanate was added to the PU-HPAN solution (~20 wt%) to obtain a uniform casting solution. The solution was then cast on a clean glass plate using a 150 μm casting blade. The cast glass plate was then immediately immersed in a water coagulation bath at a temperature of 30°C to complete the membrane curing. PEI was added to the water as an additive. The resulting membrane was then composited with the hydrophilic layer of the polytetrafluoroethylene / hydrophilic layer composite membrane by heat treatment at 120°C for 20 minutes.

[0051] (8) The prepared CA solution was electrospun directly onto the surface of a PU-HPAN interlayer wrapped around a rotating metal cylinder using an electrospinning apparatus. The distance between the needle tip and the PA membrane was maintained at 18 cm. The CA layer was deposited at a voltage of 15 kV, a rotation speed of 0.4 rs1, and a feed rate of 1.8 ml / h. Lamination was performed for 35 seconds at a lamination pressure of 2 MPa.

[0052] The CA layer closest to the skin has an average diameter of 1.83 μm and a thickness of 20 μm. The HPAN layer has an average diameter of 255 nm and a thickness of 30 μm. The hydrophilic layer has an average diameter of 76 nm and a thickness of 40 μm. The diameter of the hydrophilic layer fibers ranges from 20 nm to 180 nm. The porosities of the three fiber membranes are 74.6%, 84.51%, and 86.81%, respectively.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane, characterized in that: The following steps are involved: (1) using a polytetrafluoroethylene microporous membrane as a receiving substrate, electrospinning a spinning solution I consisting of hydrolyzed polyacrylonitrile, acrylic acid, acrylamide, a crosslinking agent, and a solvent to obtain a hydrophilic layer; (2) casting a casting solution made of hydrolyzed polyacrylonitrile, polyurethane, isocyanate, a crosslinking agent, and a solvent on a glass plate by a non-solvent induced phase separation method and immersing the solution in water to prepare an intermediate layer, and the intermediate layer is composited with the hydrophilic layer by heat treatment; (3) using the intermediate layer as a receiving substrate, electrospinning a spinning solution II consisting of cellulose acetate and a solvent to prepare a hydrophobic layer on the side of the intermediate layer away from the hydrophilic layer, thereby obtaining a composite fiber membrane; Among them, the intermediate layer contains amino side chains grafted to the hydrolyzed polyacrylonitrile main chain, and the amino side chains extend into the cellulose acetate layer. The large end of the pore channel is located in the hydrophobic layer, and the small end of the pore channel is located in the hydrophilic layer. The average pore diameter of the large end of the pore channel is 0.8 to 2.5 μm, and the average pore diameter of the small end of the pore channel is 50 to 250 nm. The porosity of the composite fiber membrane is greater than 75%.

2. The method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane according to claim 1, characterized in that: In the spinning solution I, the hydrolyzed polyacrylonitrile accounts for 78-90% of the total mass of the monomers, the acrylic acid accounts for 8-20% of the total mass of the monomers, the acrylamide accounts for 2-12% of the total mass of the monomers, the neutralization degree of the acrylic acid is 75%, and the cross-linking agent accounts for 0.01-0.03% of the total mass of the monomers.

3. The method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane according to claim 2, characterized in that: The preparation process of spinning solution I is as follows: polyacrylonitrile and sodium hydroxide solution are hydrolyzed at 50-60°C for 15-30 minutes, the resulting slurry is neutralized with acetic acid, acrylic acid, acrylamide and a cross-linking agent are added, the mixture is blended, and stirred in a water bath at 80°C for 2-3 hours.

4. The method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane according to claim 2 or 3, characterized in that: The process parameters of the electrospinning of the spinning solution I are: voltage 15-30 kV, perfusion speed 0.8-4 mL / h, distance between the spinneret and the receiving substrate 6-25 cm, ambient relative humidity 65-75%, and ambient temperature 20-30° C.

5. The method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane according to claim 1, characterized in that: The process parameters of electrospinning of spinning solution II are: voltage 10-20 kV, perfusion speed 0.2-2 mL / h, distance between spinneret and receiving substrate 6-25 cm, relative humidity 25-55%, and ambient temperature 23-26°C.

6. The method for preparing a porosity / wetness dual gradient oriented water-absorbing fiber membrane according to claim 1, characterized in that: The heat treatment temperature is 60-120° C., and the heat treatment time is 20-60 minutes.

7. A pore / wetness dual gradient oriented water-absorbing fiber membrane prepared by the method for preparing a pore / wetness dual gradient oriented water-absorbing fiber membrane according to any one of claims 1 to 6.