Preparation method for micro-nano non-woven fabric, and non-woven fabric obtained using same

Abstract

A preparation method for micro-nano non-woven fabric, comprising the following steps: (1) mixing a polymer and a solvent to form a spinning mixture having a first concentration; (2) mixing the spinning mixture under a first pressure and at a first temperature to form a homogeneous spinning solution; (3) depressurizing the homogeneous spinning solution to a second pressure by means of a depressurization chamber to form a metastable spinning mixture, wherein the value of the second pressure is smaller than the value of a third pressure and greater than the value of a fourth pressure, wherein the third pressure is a cloud point pressure of the spinning mixture under the conditions of the first concentration and the first temperature, and the fourth pressure is a pressure under which the homogeneous spinning solution forms a polymer phase and a solvent phase by means of depressurization under the conditions of the first concentration and the first temperature; and (4) spraying the metastable spinning mixture through spinneret holes to form plexifilaments. According to the method, the plexifilaments having a crystallinity of 80% or above can be obtained, and the plexifilaments have smaller and more uniform diameters and higher strength.

Description

A method for preparing micro-nano non-woven fabric and non-woven fabric obtained by using the method Technical Field

[0001] The present invention relates to the field of non-woven fabric preparation, and in particular to a method for preparing micro-nano non-woven fabric and the non-woven fabric obtained by applying the method. Background Art

[0002] Micro-nano non-woven fabrics have different microstructures due to different preparation technologies, thus showing different properties. Currently, the more advanced micro-nano non-woven fabric preparation methods include melt-blown spinning, electrospinning and flash spinning.

[0003] Meltblown spinning generally uses polymers with high melt indexes, such as polypropylene, polyester, and polyamide, which are ejected in a molten state and stretched by high-speed airflow, then spread on a mesh to produce micro- and nano-scale non-woven fabrics. Due to process and raw material limitations, the fiber diameter obtained by meltblown spinning is generally in the micron range, but the molecular weight and crystallinity of the fibers are low, resulting in low strength of the non-woven fabric, which greatly limits its application. In many cases, reinforcement is required to form composite structures such as SMS to meet application requirements. Electrospinning uses a high-voltage electrostatic field to pull and stretch the spinning fluid, which can produce non-woven fabrics made of fibers with nanometer diameters. However, due to its low production capacity, relatively high product costs, and low product strength, its application range is also limited.

[0004] Functional nonwoven materials produced using flash spinning technology offer numerous structural advantages, including fine fiber diameter, large specific surface area, high material crystallinity, and a three-dimensional continuous structure. These materials possess numerous advantages, including excellent water resistance, breathability, weather resistance, tear resistance, high reflectivity, and barrier properties against particles and bacteria. DuPont's Tyvek is a commercial product successfully produced using flash spinning. The technology involves dissolving high-density polyethylene (HDPE) in a low-boiling-point solvent, chlorofluorocarbon, under high temperature and pressure to form a homogeneous spinning solution. Prior to spinning, the solution is passed through a pressure-reducing chamber, where the pressure is reduced to induce phase separation into a two-phase region. The separated two-phase solution is then ejected through a spinneret at near-sonic speed to room temperature and pressure. The chlorofluorocarbon rapidly vaporizes, absorbing heat, while the HDPE precipitates, forming micro-nanofiber filaments. The fibers are then spread onto a blanket and then heat-pressed to form a dense, high-strength nonwoven material. The Chinese invention patent application of the company with application number 03822743.6 (publication number CN 1685091A) discloses that the homogeneous spinning solution is depressurized to below the cloud point pressure for spinning.

[0005] However, to date, no patents clearly describe the two-phase region required during the critical flash spinning process, nor the specific phase separation mechanism that forms it. With the advancement of research into the mechanisms of phase separation in polymer solutions and the in-depth study and prediction of their phase transition behavior, further optimization of flash spinning technology is becoming possible. Based on this concept, the present invention optimizes and improves existing flash spinning technology.

[0006] Summary of the Invention

[0007] The first technical problem to be solved by the present invention is to provide a method for preparing a micro-nano nonwoven fabric with optimized spinning pressure in view of the current status of the existing technology.

[0008] The second technical problem to be solved by the present invention is to provide a non-woven fabric obtained by applying the above-mentioned preparation method in view of the current status of the existing technology.

[0009] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: the preparation method of the micro-nano non-woven fabric is characterized by comprising the following steps:

[0010] (1) mixing a polymer and a solvent to form a spinning mixture of a first concentration;

[0011] (2) mixing the spinning mixture at a first pressure and a first temperature to form a homogeneous spinning solution;

[0012] (3) depressurizing the homogeneous spinning solution to a second pressure in a depressurization chamber to form a metastable spinning mixture, wherein the second pressure is less than the third pressure and greater than the fourth pressure; wherein

[0013] The third pressure is the cloud point pressure of the spinning mixture under the conditions of the first concentration and the first temperature,

[0014] The fourth pressure is the critical pressure of the homogeneous spinning solution when the polymer phase and the solvent phase are formed by reducing the pressure under the conditions of the first concentration and the first temperature;

[0015] (4) The metastable spinning mixture is ejected through a spinneret to form fiber plexifilaments.

[0016] Furthermore, the preferred range of the first pressure is between the cloud point pressure and a pressure 3 MPa higher than the cloud point pressure.

[0017] Furthermore, in the metastable spinning mixture, the solvent forms a dispersed droplet phase distributed in the supersaturated polymer solution. A large number of finely sized dispersed droplets composed of pure solvent are formed in the metastable spinning mixture. These dispersed droplets are distributed in the supersaturated polymer solution. Because the polymer in the metastable spinning mixture is more evenly dispersed, the fibers produced when the metastable spinning mixture is spun out have a finer and more uniform diameter.

[0018] Furthermore, the polymer includes one or more of polyethylene, polypropylene, polytetrafluoroethylene, and polyvinylidene fluoride. Other polymers suitable for conventional flash spinning are also included. For a homogeneous spinning solution formed by two or more polymers, as long as the polymer composition in the homogeneous spinning solution is determined, the corresponding cloud point pressure and the fourth pressure are determined.

[0019] Furthermore, the solvent includes one or more of chloromethane, dichloromethane, chloroform, carbon tetrachloride, monofluoro-trichloromethane, ethyl chloride, trifluorodichloroethane, and cis-1,2-dichloroethylene.

[0020] Furthermore, the solvent includes one or more C3-C8 hydrocarbon compounds. For a homogeneous spinning solution formed by two or more solvents, as long as the components of the solvents in the homogeneous spinning solution are determined, the corresponding cloud point pressure and the fourth pressure are determined.

[0021] Furthermore, in step (2), the spinning mixture is stirred and mixed in a spinning kettle for 15 to 60 minutes to form a homogeneous spinning solution.

[0022] Furthermore, in step (3), the metastable spinning mixture is maintained at the second pressure for 2 to 100 seconds. The ability to stably maintain the metastable spinning mixture is beneficial to practical operation during process production.

[0023] Furthermore, in step (4), the spinning speed of the spinneret is 300-400 m / s, and the crystallinity of the fiber filaments is greater than 80%.

[0024] Furthermore, the preparation method further comprises spreading the fiber plexifilaments on a blanket, and then hot-pressing the fiber plexifilaments on the blanket to form a non-woven fabric.

[0025] The technical solution adopted by the present invention to solve the second technical problem is: applying the non-woven fabric obtained by the above-mentioned preparation method.

[0026] Compared with the prior art, the advantages of the present invention are that: at a certain concentration and temperature, the mixed state of the selected polymer and solvent changes from a homogeneous spinning solution to a metastable spinning mixture, and then to a mixture of a polymer phase and a solvent phase separation as the pressure decreases. The present invention selects a spinning pressure within the pressure range where the metastable spinning mixture is located for spinning. Specifically, the homogeneous spinning solution is depressurized to a pressure value between the fourth pressure and the cloud point pressure before spinning. Since the state of the metastable spinning mixture is: a dispersed droplet phase composed of a large number of fine pure solvents, the separation The metastable spinning mixture is placed in a supersaturated polymer solution, and the polymer in the metastable spinning mixture can be evenly distributed and can exist relatively stably; the metastable spinning mixture is passed through a spinneret into a room temperature and room pressure spinning chamber for flash spinning, thereby forming fiber filaments with a three-dimensional continuous micro-nano structure. The flash spinning process promotes the oriented crystallization of the fibers due to shear and stretching orientation, and fiber filaments with a crystallinity of more than 80% can be obtained, and the diameter of the fiber filaments is smaller and more uniform, and the strength of the fiber filaments is higher; similarly, the non-woven fabric obtained by this preparation method has good waterproof, breathable and tear-resistant functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a UCSP (upper critical solution pressure) phase diagram in an embodiment of the present invention;

[0028] FIG2 is a schematic diagram of a homogeneous spinning solution passing through a decompression chamber with a pressure of P2 for spinning in an embodiment of the present invention;

[0029] FIG3 is a schematic diagram of a homogeneous spinning solution being spun through a reduced pressure chamber at a pressure of P3 in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0031] The present invention discloses a method of reducing the pressure of a polymer homogeneous spinning solution having a UCSP (upper critical solution pressure) phase diagram to the metastable region (the region between the spinodal line and the binodal line) in the phase diagram and controlling the nucleation-growth phase separation mechanism to form a phase-separated state with a fine microstructure, namely, the metastable spinning mixture referred to in the present invention, as shown in Figure 1. Specifically, the microstructure comprises a large number of finely sized dispersed droplets composed of pure solvent, distributed in a polymer solution composed of a supersaturated solution. Because the system is in the metastable region, the microstructure evolves through the crystallization process and can be maintained for a long time. The mixture in the metastable region is flash-spun through a spinneret to form fiber filaments and non-woven fabrics with finer, more uniform diameters and higher strength, which are three-dimensional continuous micro-nanostructures. Specifically, as shown in FIG2 , the present invention prepares a homogeneous spinning solution at an appropriate temperature T, concentration and pressure P1, and then passes the homogeneous spinning solution through a decompression chamber to reduce the pressure of the homogeneous spinning solution to a metastable region (T, P2) to form a metastable spinning mixture, and maintains the metastable spinning mixture state for 2 to 100 seconds, and then passes through a spinneret to spray the polymer to a room temperature, room pressure (T RM 、P AT ) under the pressure of a low-boiling-point solvent, the polymer precipitates and solidifies from the solution while being subjected to high-speed shearing and stretching, forming a fine-diameter, highly crystallinity, three-dimensional continuous fiber plexiform filament. Using a technique similar to non-woven fabrics or papermaking, the fiber plexiform filaments are spread on a blanket. After collection, they are hot-pressed at a certain temperature and pressure to bond the fibers together, forming a structure with a certain strength and a specific density. In contrast, traditional flash spinning technology involves depressurizing the homogeneous spinning solution to a two-phase region (T, P3), causing the homogeneous spinning solution to undergo phase separation controlled by the spinodal decomposition mechanism. The microstructure is a bicontinuous structure. Due to the rapid phase separation at P3, the microstructure is difficult to control, and the polymer is unevenly distributed within the microstructure. As a result, the flash-spun fibers are uneven in thickness, and the control technology is extremely difficult, as shown in Figure 3.

[0032] Example 1

[0033] (1) High-density polyethylene (Taiwan Formosa Plastics, LH606, Mw = 89,000 g / mol, molecular weight distribution 2.33) and dichloromethane were mixed to form a spinning mixture with a concentration of 13 wt%;

[0034] (2) placing the spinning mixture in a 4 L spinning kettle and mechanically stirring and mixing at 11 MPa and 205° C. for 30 minutes to form a homogeneous spinning solution; the metastable pressure range at this concentration and temperature is 10.5 to 7.5 MPa;

[0035] (3) the homogeneous spinning solution is passed through a decompression hole into a decompression chamber and decompressed to 10.1 MPa to form a metastable spinning mixture, and the mixture is maintained in the decompression chamber for 10 seconds;

[0036] (4) The metastable spinning mixture was ejected through a spinneret at a speed of 350 m / s to obtain fiber plexifilaments. The properties of the obtained fiber plexifilaments are listed in Table 1.

[0037] (5) Spreading the fiber filaments on a blanket, and then hot pressing the fiber filaments on the blanket to form a non-woven fabric.

[0038] Example 2

[0039] (1) mixing high-density polyethylene and dichloromethane to form a spinning mixture with a concentration of 13 wt %;

[0040] (2) placing the spinning mixture in a 4 L spinning kettle and mechanically stirring and mixing at 13.5 MPa and 205° C. for 15 minutes to form a homogeneous spinning solution; the metastable pressure range at this concentration and temperature is 10.5 to 7.5 MPa;

[0041] (3) the homogeneous spinning solution is passed through a decompression hole into a decompression chamber and decompressed to 10.4 MPa to form a metastable spinning mixture, and the mixture is maintained in the decompression chamber for 2 seconds;

[0042] (4) The metastable spinning mixture was ejected through a spinneret at a speed of 300 m / s to obtain fiber plexifilaments. The properties of the obtained fiber plexifilaments are listed in Table 1.

[0043] (5) Spreading the fiber filaments on a blanket, and then hot pressing the fiber filaments on the blanket to form a non-woven fabric.

[0044] Example 3

[0045] (1) mixing high-density polyethylene and dichloromethane to form a spinning mixture with a concentration of 13 wt %;

[0046] (2) placing the spinning mixture in a 4 L spinning kettle and mechanically stirring and mixing at 10.6 MPa and 205° C. for 60 minutes to form a homogeneous spinning solution; the metastable pressure range at this concentration and temperature is 10.5 to 7.5 MPa;

[0047] (3) the homogeneous spinning solution is passed through a decompression hole into a decompression chamber and decompressed to 7.6 MPa to form a metastable spinning mixture, and the mixture is maintained in the decompression chamber for 100 seconds;

[0048] (4) The metastable spinning mixture was ejected through a spinneret at a speed of 400 m / s to obtain fiber plexifilaments. The properties of the obtained fiber plexifilaments are listed in Table 1.

[0049] (5) Spreading the fiber filaments on a blanket, and then hot pressing the fiber filaments on the blanket to form a non-woven fabric.

[0050] Example 4

[0051] (1) mixing high-density polyethylene and pentane to form a spinning mixture with a concentration of 15 wt%;

[0052] (2) placing the spinning mixture in a 4 L spinning kettle and mechanically stirring and mixing at 12 MPa and 215° C. for 30 minutes to form a homogeneous spinning solution; the metastable pressure range at this concentration and temperature is 11.5 to 7.0 MPa;

[0053] (3) the homogeneous spinning solution is passed through a decompression hole into a decompression chamber and decompressed to 9.8 MPa to form a metastable spinning mixture, and the mixture is maintained in the decompression chamber for 10 seconds;

[0054] (4) The metastable spinning mixture was ejected through a spinneret at a speed of 350 m / s to obtain fiber plexifilaments. The properties of the obtained fiber plexifilaments are listed in Table 1.

[0055] (5) Spreading the fiber filaments on a blanket, and then hot pressing the fiber filaments on the blanket to form a non-woven fabric.

[0056] Comparative Example 1

[0057] (1) mixing high-density polyethylene and dichloromethane to form a spinning mixture with a concentration of 13 wt %;

[0058] (2) placing the spinning mixture in a 4 L spinning kettle and mechanically stirring and mixing at 11 MPa and 205° C. for 30 minutes to form a homogeneous spinning solution; the metastable pressure range at this concentration and temperature is 10.5 to 7.5 MPa;

[0059] (3) the homogeneous spinning solution is passed through a decompression hole into a decompression chamber and decompressed to 5.1 MPa to form a metastable spinning mixture, and the mixture is maintained in the decompression chamber for 10 seconds;

[0060] (4) The metastable spinning mixture was ejected through a spinneret at a speed of 350 m / s to obtain fiber plexifilaments. The properties of the obtained fiber plexifilaments are listed in Table 1.

[0061] (5) Spreading the fiber filaments on a blanket, and then hot pressing the fiber filaments on the blanket to form a non-woven fabric.

[0062] The only difference between Comparative Example 1 and Example 1 is the pressure in the decompression chamber.

[0063] Comparative Example 2

[0064] (1) mixing high-density polyethylene and dichloromethane to form a spinning mixture with a concentration of 15 wt %;

[0065] (2) placing the spinning mixture in a 4 L spinning kettle and mechanically stirring and mixing at 11 MPa and 205° C. for 30 minutes to form a homogeneous spinning solution; the metastable pressure range at this concentration and temperature is 10.4 to 6.3 MPa;

[0066] (3) the homogeneous spinning solution is passed through a decompression hole into a decompression chamber and decompressed to 5.1 MPa to form a metastable spinning mixture, and the mixture is maintained in the decompression chamber for 10 seconds;

[0067] (4) The metastable spinning mixture was ejected through a spinneret at a speed of 350 m / s to obtain fiber plexifilaments. The properties of the obtained fiber plexifilaments are listed in Table 1.

[0068] (5) Spreading the fiber filaments on a blanket, and then hot pressing the fiber filaments on the blanket to form a non-woven fabric.

[0069] Comparative Example 2 differs from Comparative Example 1 in that the concentration of the spinning mixture is different.

[0070] Table 1 Performance parameters of fiber plexifilaments obtained by spinning different homogeneous spinning solutions at different pressures

[0071] The test results show that the fiber plexifilaments prepared by the method of the present invention have a crystallinity exceeding 80%, a small fiber diameter, uniform fiber thickness, and high fiber strength. Comparative Examples 1 and 2 demonstrate that when spinning at a pressure beyond the metastable region, the resulting fiber plexifilaments have a large fiber diameter and low fiber strength. Therefore, determining the appropriate spinning pressure based on the metastable region on the UCSP (upper critical solution pressure) phase diagram of the polymer solution is particularly important for producing fiber plexifilaments with excellent performance.

Claims

1. A method for preparing a micro-nano nonwoven fabric, characterized in that: The following steps are involved: (1) mixing a polymer and a solvent to form a spinning mixture of a first concentration; (2) mixing the spinning mixture at a first pressure and a first temperature to form a homogeneous spinning solution; (3) reducing the pressure of the homogeneous spinning solution to a second pressure through a decompression chamber to form a metastable spinning mixture, wherein the value of the second pressure is less than the third pressure and greater than the fourth pressure; wherein The third pressure is the cloud point pressure of the spinning mixture under the conditions of the first concentration and the first temperature, The fourth pressure is the critical pressure of the homogeneous spinning solution when the polymer phase and the solvent phase are formed by reducing the pressure under the conditions of the first concentration and the first temperature; (4) The metastable spinning mixture is ejected through a spinneret to form fiber plexifilaments.

2. The preparation method according to claim 1, characterized in that: A preferred range of the first pressure is between the cloud point pressure and a pressure 3 MPa higher than the cloud point pressure.

3. The preparation method according to claim 2, characterized in that: The polymer includes one or more of polyethylene, polypropylene, polytetrafluoroethylene, and polyvinylidene fluoride.

4. The preparation method according to claim 3, characterized in that: The solvent includes one or more of methyl chloride, dichloromethane, chloroform, carbon tetrachloride, monofluoro-trichloromethane, ethyl chloride, trifluorodichloroethane, and cis-1,2-dichloroethylene.

5. The preparation method according to claim 4, characterized in that: The solvent includes one or more C3-C8 hydrocarbon compounds.

6. The preparation method according to claim 1, characterized in that: In step (2), the spinning mixture is stirred and mixed in a spinning kettle for 15 to 60 minutes to form a homogeneous spinning solution.

7. The preparation method according to claim 1, characterized in that: In step (3), the metastable spinning mixture is maintained at the second pressure for 2 to 100 seconds.

8. The preparation method according to claim 1, characterized in that: In step (4), the spinning speed of the spinneret is 300-400 m / s, and the crystallinity of the fiber filaments is greater than 80%.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The method also includes spreading the fiber plexifilaments on a blanket, and then hot-pressing the fiber plexifilaments on the blanket to form a non-woven fabric.

10. A nonwoven fabric obtained by the preparation method according to claim 9.

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