A self-charging filter material and its preparation method

Abstract

This invention relates to the field of filter material technology, specifically to a self-charging filter material and its preparation method, comprising the following steps: S1, mixing nanofibers with a length of 0.1-10 mm with a low-melting-point polymer to obtain a composite spinning solution, and spinning to obtain composite fibers; S2, combining the composite fibers with a second fiber, and then hot-pressing to obtain a composite nonwoven fabric, which is the self-charging filter material; the nanofibers and the second fiber are selected from one or more of polyester, polyacrylonitrile, and wool. This invention combines nanofibers with a low-melting-point polymer through composite spinning, and then uses hot pressing to improve the fiber bonding strength and release the nanofibers while also fixing them to a certain extent. The exposed nanofibers, under the action of airflow, generate static electricity through friction with surrounding fibers, thereby achieving sustainable and efficient filtration.

Description

Technical Field

[0001] This invention relates to the field of filter material technology, and in particular to a self-charging filter material and its preparation method. Background Technology

[0002] With the deepening of industrialization, fine particulate matter has become one of the most important air pollutants, posing a serious threat to human health. Therefore, how to effectively prevent industrial particulate matter from entering the atmosphere and how to prevent atmospheric particulate matter from being absorbed by the human body are urgent problems to be solved. Traditional protective filter materials mainly rely on physical interception, inertial impaction, Brownian diffusion and other mechanical actions to capture fine particulate matter. While achieving high efficiency in filtering fine particulate pollutants, they also have high pressure resistance, poor air permeability and comfort, and a short service life.

[0003] The trapping force of electret filter materials mainly consists of the Coulomb force and inductive force exerted by charged fibers on microparticles (charged or uncharged particles). Electrostatically enhanced fiber filtration achieves efficiency enhancement and resistance reduction through pre-charging or the application of an external electric field; however, if the external electric field is removed, the fibers retain their charge for an extremely short time, or the residual charge decays rapidly. Electret filter materials can store space charge for a relatively long period. Patent CN11249638A discloses a high-efficiency protective mask based on an all-fiber electret generator and its preparation method. Its filter layer comprises sequentially stacked silicone film, conductive fabric, electret fiber membrane, and non-woven fabric; the conductive fabric and electret fiber membrane have different electronegativity, and can generate a static voltage of 200-1000V driven by autonomous breathing. It has high filtration efficiency, low piezoresistive resistance, and good flexibility and breathability, but its complex structure and the difficulty in achieving significant contact and separation between the two membranes solely through exhalation and inhalation result in poor static charge generation and stability.

[0004] In view of this, it is necessary to provide a self-charging filter material and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a self-charging filter material and its preparation method. The method involves composite spinning of nanofibers and low-melting-point polymers, followed by hot pressing to improve fiber bonding strength and release the nanofibers while also fixing them in place. The exposed nanofibers generate static electricity through friction with surrounding fibers under the action of airflow, thereby achieving sustainable and efficient filtration.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a self-charging filter material, comprising the following steps:

[0007] S1. Nanofibers with a length of 0.1-10 mm are mixed with a low-melting-point polymer to obtain a composite spinning solution, and then the composite fibers are spun.

[0008] S2. The composite fiber is combined with the second fiber and then hot-pressed to obtain a composite nonwoven fabric, which is the self-charging filter material.

[0009] The nanofibers and the second fiber are selected from one or more of polyester, polyacrylonitrile, and wool.

[0010] Furthermore, the low-melting-point polymer is a polyester with a melting point of 80-120°C, and the hot-pressing temperature is higher than the melting point of the low-melting-point polymer.

[0011] Furthermore, the nanofibers constitute 2-30% of the mass of the low-melting-point polymer; the nanofibers have a length of 0.5-5 mm and a diameter of 10-500 nm.

[0012] Furthermore, the composite spinning solution also contains polyester with a melting point of 180-220°C, and the amount added is 5-50% of the mass of the low-melting-point polymer.

[0013] Furthermore, activated carbon is added to the composite spinning solution, and the amount added is 1-20% of the mass of the low melting point polymer.

[0014] Further, step S1 includes: mixing nanofibers with a length of 0.1-10 mm with a low-melting-point polymer to obtain a composite spinning solution as the skin layer; and using polypropylene as the core layer for coaxial spinning to obtain composite fibers.

[0015] Furthermore, the total diameter of the composite fiber is 1-10 μm, and the core layer diameter is 0.8-8 μm; the diameter of the second fiber is 100-800 nm.

[0016] And / or, the mass ratio of the second fiber to the composite fiber is 1:(0.1-1).

[0017] Furthermore, the second fiber contains wool particles of 50-200 nm in size, and the second fiber is polyacrylonitrile.

[0018] Furthermore, the wool particles have a multi-sized microporous structure with a porosity of 5-50%.

[0019] Secondly, the present invention provides a self-charging filter material, which is prepared by any of the preparation methods described above.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. The self-charging filter material provided by the present invention is made by composite spinning of nanofibers and low-melting-point polymers, and then using hot pressing to improve the fiber bonding strength on the one hand, release the nanofibers on the other hand, and fix them to a certain extent. The exposed nanofibers generate static electricity by rubbing with the surrounding fibers under the action of airflow, thereby achieving sustainable and efficient filtration.

[0022] 2. The present invention further improves the filtration and adsorption performance by adding activated carbon to the composite spinning process.

[0023] 3. The present invention uses composite fibers with a core-sheath structure. After hot pressing, the core layer is exposed, so that the core layer and the second fiber form a gradient laminate structure, which significantly improves the dust holding capacity. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] The present invention provides a method for preparing a self-charging filter material, comprising the following steps:

[0026] S1. Nanofibers with a length of 0.1-10 mm are mixed with a low-melting-point polymer to obtain a composite spinning solution, and then the composite fibers are spun.

[0027] S2. The composite fiber is combined with the second fiber and then hot-pressed to obtain a composite nonwoven fabric, which is the self-charging filter material.

[0028] The nanofibers and the second fiber are selected from one or more of polyester, polyacrylonitrile, and wool. These fibers are all prone to generating static electricity through friction, and therefore are more likely to generate static electricity when blown by an airflow.

[0029] In this process, during hot pressing, the low-melting-point polymer in the composite fiber melts and bonds with the second fiber. Simultaneously, the nanofibers are released, and due to their moderate length, some are partially encased in the low-melting-point polymer. Furthermore, since both the nanofibers and the second fiber are made from materials prone to static electricity, and the exposed portions of the nanofibers are lightweight, when used for air filtration, the nanofibers continuously generate static electricity through repeated friction with surrounding fibers under the blowing action of airflow, thereby increasing their dust adsorption strength.

[0030] Furthermore, the low-melting-point polymer is a polyester with a melting point of 80-120℃, and the hot-pressing temperature is higher than the melting point of the low-melting-point polymer, for example, the hot-pressing temperature is the melting point of the low-melting-point polymer + 5℃. Using a low-melting-point polyester also results in superior static electricity generation properties due to its superior resistance to friction.

[0031] Furthermore, the nanofibers constitute 2-30% of the mass of the low-melting-point polymer, preferably 10-20%. If the mass of the nanofibers is too small, the improvement in triboelectric effect will be insignificant; if the mass is too large, it will lead to increased filtration resistance. The nanofibers have a length of 0.5-5 mm and a diameter of 10-500 nm, preferably 50-200 nm. If the nanofibers are too short, the amount exposed will be reduced; if they are too long, entanglement is likely to occur, and the increased mass will also make purging friction difficult. Similarly, if the diameter is too large, the large mass and small specific surface area will reduce the effective friction.

[0032] Furthermore, the composite spinning solution also contains polyester with a melting point of 180-220℃, and the amount added is 5-50% of the mass of the low-melting-point polymer, preferably 15-30%. After the low-melting-point polyester is hot-pressed and melt-bonded, the polyester with a melting point of 180-220℃ retains its fiber structure, thus forming a gradient porous structure. This improves the strength of the filter material on the one hand, and increases the dust holding capacity and filtration efficiency on the other.

[0033] Furthermore, activated carbon is added to the composite spinning solution, and the amount added is 1-20% of the mass of the low-melting-point polymer, preferably 5-10%. The activated carbon is released after hot pressing, improving the adsorption performance.

[0034] Further, step S1 includes: mixing nanofibers with a length of 0.1-10 mm with a low-melting-point polymer to obtain a composite spinning solution as the skin layer; and using polypropylene as the core layer for coaxial spinning to obtain composite fibers. After the skin layer is melt-bonded, the core layer and the second fiber form a gradient laminate structure, which significantly improves the dust holding capacity.

[0035] Furthermore, the total diameter of the composite fiber is 1-10 μm, and the core layer diameter is 0.8-8 μm; the diameter of the second fiber is 100-800 nm.

[0036] And / or, the mass ratio of the second fiber to the composite fiber is 1:(0.1-1).

[0037] Furthermore, the second fiber incorporates 50-200nm wool particles, and the second fiber is polyacrylonitrile (PAN). By combining 50-200nm wool particles with PAN nanofibers, the PAN composite nonwoven fabric rich in nanofibers vibrates under the influence of airflow vortices during use. This causes the nanofibers to momentarily contact and separate from the surrounding composite fibers, resulting in a large accumulation of charge. This gives the product excellent dust particle interception efficiency and self-charging characteristics.

[0038] Furthermore, the wool particles have a multi-sized microporous structure with a porosity of 5-50%.

[0039] Secondly, the present invention provides a self-charging filter material, which is prepared by any of the preparation methods described above.

[0040] Example 1

[0041] A self-charging filter material is prepared by the following steps:

[0042] S1. Wool nanofibers with a length of 2 mm and a diameter of 200 nm are mixed with low-melting-point polyester to obtain a composite spinning solution, and composite fibers are obtained by spinning; the amount of nanofibers added is 15% of the low-melting-point polyester.

[0043] S2. The composite fiber is combined with a 500nm diameter polyacrylonitrile fiber and then hot-pressed to obtain a composite nonwoven fabric, which is the self-charging filter material; the mass ratio of the composite fiber to the 500nm diameter polyacrylonitrile fiber is 0.8:1.

[0044] Example 2

[0045] A self-charging filter material, compared with Example 1, differs in that the composite spinning solution in step S1 also contains polyester with a melting point of about 200°C, and the amount added is 20% of the mass of the low melting point polyester.

[0046] Example 3

[0047] A self-charging filter material, compared with Example 1, differs in that the composite spinning solution in step S1 also contains polyester with a melting point of about 200°C, and the amount added is 50% of the mass of the low melting point polyester.

[0048] Example 4

[0049] A self-charging filter material, which differs from Example 1 in that activated carbon is added to the composite spinning solution in step S1, and the amount added is 8% of the mass of the low melting point polyester.

[0050] Example 5

[0051] A self-charging filter material, compared with Example 1, differs in that step S1 includes: mixing 2mm long wool nanofibers with low-melting-point polyester to obtain a composite spinning solution as the sheath; and using polypropylene as the core layer, coaxially spinning is performed to obtain composite fibers. The total diameter of the composite fibers is 3μm, and the core layer diameter is 2μm.

[0052] Example 6

[0053] A self-charging filter material, which differs from Example 1 in that the polyacrylonitrile fiber in step S2 is also incorporating 200nm wool particles.

[0054] Example 7

[0055] A self-charging filter material, which differs from Example 1 in that the length of the wool nanofibers is 0.1 mm.

[0056] Example 8

[0057] A self-charging filter material, which differs from Example 1 in that the wool nanofibers are 5 mm in length.

[0058] Example 9

[0059] A self-charging filter material, which differs from Example 1 in that the wool nanofibers are 10 mm in length.

[0060] Comparative Example 1

[0061] A self-charging filter material differs from Example 1 in that it combines 500nm diameter polyacrylonitrile fibers with 200nm diameter wool nanofibers, with the same amount of both as in Example 1, to obtain a composite nonwoven fabric.

[0062] Comparative Example 2

[0063] A self-charging filter material differs from Example 1 in that it is composite nonwoven fabric obtained by hot pressing together 500nm diameter polyacrylonitrile fiber, 200nm diameter wool nanofiber and low melting point polyester fiber in the proportions of Example 1.

[0064] The filtration performance was tested according to GB / 14295-2008 "Air Filters", with a rated air volume of 1000m³ / h. 3 / h, the weight of the self-charging nonwoven fabric is 200g / m² 2 The average filtration efficiency, initial resistance, and dust holding capacity when the final resistance reaches twice the initial resistance were tested.

[0065] Table 1 Performance test results of Examples 1-9 and Comparative Examples 1-2

[0066] Sample ≥0.5μm filtration efficiency (%) Initial resistance (Pa) <![CDATA[Dust holding capacity (g / m 2 )]]> Example 1 99.92 21.8 126 Example 2 99.95 21.2 132 Example 3 99.90 21.0 135 Example 4 99.96 21.5 128 Example 5 99.98 19.8 141 Example 6 99.95 21.6 125 Example 7 99.20 22.5 120 Example 8 99.89 21.3 133 Example 9 99.55 22.1 125 Comparative Example 1 98.75 21.5 118 Comparative Example 2 98.99 23.6 112

[0067] As shown in Table 1, this invention utilizes the melt release portion of low-melting-point polyester fibers to encapsulate wool fibers. This allows the wool fibers to continuously generate static electricity through repeated friction with surrounding fibers under the blowing action of airflow, thereby improving dust filtration efficiency. Furthermore, it exhibits low initial resistance and high dust holding capacity. Adding a portion of high-melting-point polyester to the composite fiber further enhances both filtration efficiency and dust holding capacity; however, excessive addition reduces filtration efficiency. This is because insufficient low-melting-point polyester content negatively impacts the bonding and exposure of wool fibers, thus affecting the efficiency of static electricity generation.

[0068] When using composite fibers with a core-sheath fiber structure, the filtration efficiency and dust holding capacity are further improved, indicating that the gradient pore structure is more conducive to improving filtration performance. When the wool fiber length is too short, the filtration efficiency and dust holding capacity decrease, and the resistance increases. This is because too little wool is exposed, resulting in lower porosity and reduced friction. When the length is too long, the filtration efficiency and dust holding capacity also show a downward trend. This may be because excessive length easily leads to entanglement, affecting the regularity of the gradient structure, and the exposed wool fibers are also difficult to blow away. When wool nanofibers of conventional length are directly composited with polyacrylonitrile fibers, the filtration efficiency and dust holding capacity are significantly reduced. This indicates that the present invention, through the bonding and exposure of shorter wool nanofibers, can adjust the structure of the nonwoven fabric, making it easier to intercept dust.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a self-charging filter material, characterized in that, Includes the following steps: S1. A composite spinning solution is obtained by mixing nanofibers with a low-melting-point polymer, which serves as the skin layer; polypropylene is used as the core layer and coaxial spinning is performed to obtain composite fibers. S2. The composite fiber is combined with the second fiber and then hot-pressed to obtain a composite nonwoven fabric, which is the self-charging filter material. The nanofibers and the second fiber are selected from one or more of polyester, polyacrylonitrile, and wool; the low-melting-point polymer is polyester with a melting point of 80-120℃, and the hot-pressing temperature is higher than the melting point of the low-melting-point polymer. The nanofibers comprise 2-30% of the mass of the low-melting-point polymer; the nanofibers have a length of 0.5-5 mm and a diameter of 10-500 nm.

2. The method for preparing the self-charging filter material according to claim 1, characterized in that, The composite spinning solution also contains activated carbon, and the amount added is 1-20% of the mass of the low melting point polymer.

3. The method for preparing the self-charging filter material according to any one of claims 1-2, characterized in that, The composite spinning solution also contains polyester with a melting point of 180-220℃, and the amount added is 5-50% of the mass of the low melting point polymer.

4. The method for preparing the self-charging filter material according to claim 1, characterized in that, The total diameter of the composite fiber is 1-10 μm, and the core layer diameter is 0.8-8 μm; the diameter of the second fiber is 100-800 nm.

5. The method for preparing the self-charging filter material according to claim 4, characterized in that, The mass ratio of the second fiber to the composite fiber is 1:(0.1-1).

6. The method for preparing the self-charging filter material according to claim 1, characterized in that, The second fiber contains wool particles of 50-200nm, and the second fiber is polyacrylonitrile.

7. The method for preparing the self-charging filter material according to claim 6, characterized in that, The wool particles have a multi-sized microporous structure with a porosity of 5-50%.

8. A self-charging filter material, characterized in that, It is prepared by any one of the preparation methods according to claims 1-7.