Air filtration nanofiber membrane based on recycled cigarette butts and preparation method and application thereof

Abstract

The application discloses an air filtering nanofiber membrane based on recycled cigarette butts and a preparation method and application thereof. First, waste cigarette butts are pretreated to remove outer wrapping materials and tobacco residues, obtain internal cellulose acetate filter cores and crush the same to obtain cigarette butt coarse fiber sections; the cigarette butt coarse fiber sections are washed and impurity-removed by using an organic solvent, and then washed by water, dried to obtain recycled cellulose acetate; polyacrylonitrile and recycled cellulose acetate are added into a solvent, heated and stirred to be dissolved to prepare an electrospinning solution; the electrospinning solution is electrospun to deposit on a receiving substrate to form a composite nanofiber membrane; the composite nanofiber membrane is dried to remove residual solvent to obtain the air filtering nanofiber membrane. The application can realize high-value cyclic utilization of waste cigarette butts, reduce the production cost of PAN membranes, and simultaneously improve the filtering efficiency of ultrafine particulate matters and the dust holding capacity.

Description

Technical Field

[0001] This invention relates to the field of air filter material preparation technology, and in particular to an air filter nanofiber membrane based on recycled cigarette butts, its preparation method, and its application. Background Technology

[0002] Air particulate pollution has become a core issue threatening public health and the ecological environment. Among them, PM1.0 ultrafine particles have small particle size and strong penetrating power, which can penetrate deep into the alveoli and circulatory system, inducing various diseases of the respiratory and cardiovascular systems. Conventional filter materials are difficult to achieve efficient interception. Electrospun nanofiber membranes have become the mainstream choice for high-efficiency air filtration (HEPA) materials due to their large specific surface area, high porosity, and controllable pore size. Polyacrylonitrile (PAN) is the core film-forming polymer for preparing this type of membrane material due to its excellent spinnability, mechanical strength, and thermal stability.

[0003] However, PAN relies on petrochemical resources, resulting in high production costs, which limits the large-scale application of high-efficiency filter membranes. In addition, PAN nanofiber membranes are mostly surface filtration membranes, with low dust holding capacity and short service life, making it difficult to meet long-term purification needs. Furthermore, pure PAN membranes have weak surface electronegativity, resulting in insufficient adsorption capacity for positively charged PM1.0 ultrafine particles, which easily leads to problems such as decreased filtration efficiency and increased resistance.

[0004] Meanwhile, discarded cigarette butts, as one of the world's largest solid wastes, are discarded more than 4.5 trillion times annually. Their core component, cellulose acetate (CA), is a non-biodegradable plastic that can persist in the natural environment for decades, continuously releasing toxic substances such as nicotine, heavy metals, and polycyclic aromatic hydrocarbons, causing multiple forms of pollution to soil, water, and air, resulting in significant ecological harm. Currently, the resource utilization of discarded cigarette butts is mostly concentrated in low-value-added fields such as building fillers and water treatment adsorbents. Only a few studies have attempted to use them for air filtration, such as using supersonic solution blowing (SSB) technology to prepare nanofibers. However, this method uses highly volatile, flammable, and explosive acetone as a solvent, posing significant safety hazards. Furthermore, bead-like deposits easily appear on the fiber surface, affecting the membrane's uniformity and long-term filtration stability. To date, no technical solution has systematically recycled CA as a functional additive to prepare air filter membranes by blending it with PAN using conventional electrospinning technology, and no synergistic optimization of filtration efficiency, air resistance, dust holding capacity, and production costs has been achieved. Summary of the Invention

[0005] This invention proposes an air filtration nanofiber membrane based on recycled cigarette butts, its preparation method, and its application. The aim is to achieve high-value recycling of waste cigarette butts, reduce the production cost of PAN membranes, and simultaneously improve the filtration efficiency and dust holding capacity for ultrafine particulate matter (especially PM1.0).

[0006] This invention provides a method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts, comprising the following steps: S1. Pre-treat waste cigarette butts by removing the outer wrapping material and tobacco residue, obtaining the inner cellulose acetate filter element and crushing it to obtain the coarse fiber segment of the cigarette butt. S2. The coarse fiber segments of cigarette butts are washed and impurities are removed using organic solvents, followed by water washing and drying to obtain recycled cellulose acetate. S3. Add polyacrylonitrile and recycled cellulose acetate to a solvent, heat and stir to dissolve, and prepare an electrospinning solution. S4. Electrospin the electrospinning solution to deposit a composite nanofiber membrane on the receiving substrate. S5. The composite nanofiber membrane is dried to remove residual solvent, thus obtaining an air filtration nanofiber membrane.

[0007] Preferably, in step S1, during the pretreatment of waste cigarette butts, to ensure the consistency of components from different sources, the outer cigarette paper and unburned tobacco residue (cigarette butt portion) must be completely removed, leaving only the inner cellulose acetate filter core. If the length of the coarse fiber segment is too short, excessive mechanical damage to the fiber structure and dust dispersion are likely to occur during the shearing process; conversely, if the length is too long, it will hinder the full penetration and dissolution of the subsequent solvent. Therefore, the length of the coarse fiber segment of the cigarette butt is controlled at 1-2 cm.

[0008] Preferably, in S2, the organic solvent is anhydrous ethanol with a purity ≥99.7%, and the amount used is 5-10 times the mass of the coarse fiber segment of the cigarette butt. Anhydrous ethanol washing aims to remove impurities such as tar, nicotine, and triglycerides. If washing is insufficient, residual impurities will damage the rheological properties of the spinning solution, leading to fiber breakage or unpleasant odors and secondary pollution after film formation. The soaking and pressing washing is performed 3-5 times, each time for 1-2 hours, until the washing liquid is clear and colorless. Through a standardized anhydrous ethanol multiple extraction process, organic impurities such as tar, nicotine, and triglycerides can be thoroughly removed. Combined with the 1734 cm⁻¹ FT-IR spectrum... - The stability of the carbonyl characteristic peak and the constant recovery rate of approximately 64% ensure that the chemical structure and purity of recovered cellulose acetate from different batches are highly consistent, avoiding residual impurities from damaging the rheological properties of the spinning solution or causing secondary pollution. The vacuum drying temperature is 60~70℃ and the time is 7~8h. If the drying temperature is too high or the time is too long, it may cause thermal degradation or yellowing of cellulose acetate, affecting the mechanical strength of subsequent blending and spinning.

[0009] Preferably, in S3, the weight-average molecular weight of polyacrylonitrile is 150,000 g / mol; the solvent is N,N-dimethylformamide with a purity of 99.5% and a water content ≤0.05%. By controlling the water content of N,N-dimethylformamide, moisture interference can be avoided, which may lead to abnormal fiber surface morphology or decreased porosity during electrospinning. The heating and stirring temperature is 65~70℃, and the stirring time is at least 7 hours. These conditions ensure that polyacrylonitrile and recycled cellulose acetate are fully dissolved in N,N-dimethylformamide and form a homogeneous molecular-level blend system. If the temperature is too low or the time is too short, the polymer will not dissolve completely, resulting in gel particles in the spinning solution, which may cause needle blockage or uneven fiber thickness during electrospinning. If the temperature is too high, it will accelerate the volatilization of N,N-dimethylformamide and may cause thermal degradation of the polymer molecular chains.

[0010] Preferably, the total mass concentration of polyacrylonitrile and recycled cellulose acetate in the electrospinning solution is 8-18 wt%; wherein the mass concentration of polyacrylonitrile is 8-14 wt% and the mass concentration of recycled cellulose acetate is 2-10 wt%. Controlling the optimal solution concentration ensures the subsequent spinning effect. If the total concentration is below 8 wt%, the solution viscosity is too low, resulting in insufficient molecular chain entanglement. During the stretching process, the jet is prone to breakage or droplet separation, forming electrospray and bead-like structures. If the total concentration is above 18 wt% (e.g., reaching 20 wt%), the solution viscosity is too high, causing rapid solvent evaporation and premature solidification at the spinneret, leading to spinneret blockage and preventing the formation of a continuous and uniform nanofiber membrane. Under the premise of an appropriate total concentration, the introduction of recycled cellulose acetate can reduce the solution viscosity and increase the surface charge density of the jet, thereby obtaining finer fiber diameters and larger specific surface areas under electric field stretching.

[0011] Preferably, in step S4, the electrospinning parameters are: voltage 13~17kV, feed speed 0.4~0.6mL / h, receiving distance 13~17cm, ambient temperature 23~27℃, relative humidity 45~55%, roller receiving speed 600~650rpm, and spinning time 4~8h. This effectively controls the nanofiber diameter and stacking density to ensure optimal porosity. If the feed speed is too high, the jet is not fully stretched before being extruded, resulting in increased fiber diameter and solvent residue leading to adhesion; conversely, if the speed is too low, insufficient liquid supply causes jet breakage. If the operating voltage is too high, the jet undergoes excessive splitting, resulting in fiber breaks and uneven thickness; conversely, if the voltage is too low, the electric field force is insufficient to stretch the jet, easily forming droplets or beads. If the receiving distance is too short, the fibers are deposited before sufficient solidification, easily forming a film; conversely, if the distance is too long, the jet breaks after excessive stretching. If the humidity is too high, moisture mixes into the spinning solution, interfering with solvent evaporation, leading to fiber stratification or abnormal surface morphology.

[0012] Preferably, in S5, the vacuum degree of vacuum drying is controlled at -0.08 to -0.1 MPa, and the heating rate is 2 to 5 °C / min, so as to prevent the violent evaporation of solvent from causing microcracks or structural collapse inside the nanofiber membrane.

[0013] Preferably, the process further includes step S6: placing the nanofiber membrane obtained in step S5 in a hot press and hot-pressing it at 100~140℃ to regulate the fiber morphology and pore structure. The membrane thickness and pore structure are regulated through a physical-mechanical interlocking method. If the hot-pressing temperature is too low, the bonding between fibers is insufficient, and the improvement in the mechanical strength of the membrane is limited; if the hot-pressing temperature is too high (e.g., exceeding 140℃ and reaching 150℃), it will cause excessive melting and cross-linking of the nanofibers, collapse of the original three-dimensional porous network structure, resulting in a sharp increase in air filtration resistance (pressure drop), a precipitous drop in the quality factor (QF), and loss of practical application value.

[0014] The present invention also proposes an air filtration nanofiber membrane based on recycled cigarette butts, which is prepared by the preparation method mentioned above.

[0015] In addition, the present invention also proposes the application of the high-efficiency air filtration nanofiber membrane prepared as described above in air particulate matter filtration and indoor air purification equipment.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention efficiently recovers cellulose acetate from waste cigarette butts and replaces part of the petrochemical-based polyacrylonitrile as a film-forming component. According to technical and economic calculations, the raw material cost of the optimal ratio (10wt%PAN+6wt%CBs) composite membrane is only 73% of that of the optimal pure PAN membrane, which reduces the cost by about 27%. This achieves the dual benefits of solid waste resource utilization and cost optimization, and is easy to promote industrially.

[0017] (2) The introduction of recycled CA not only did not destroy the structural framework of PAN, but also introduced polar ester groups, which enhanced the electrostatic and dipole interaction between the surface and particles. It generated strong electrostatic adsorption and dipole interaction with positively charged PM1.0 ultrafine particles in the air, and the filtration efficiency of PM1.0 can reach 99.99%, with a pressure drop of only about 173 Pa. It takes into account both high filtration efficiency and low air resistance, and has excellent quality factor, which is better than existing pure PAN filter membranes.

[0018] (3) Recovering CA regulates the rheological properties of the spinning solution and refines the fiber diameter (recovering CA reduces the solution viscosity and increases the surface charge density of the jet, making the jet subject to stronger Coulomb repulsion and tensile force in the electrostatic field), constructing a three-dimensional network structure with denser pores and more tortuous channels. This structure forces the airflow to frequently bypass, transforming traditional surface filtration into deep filtration, so that particulate matter is trapped inside the membrane, increasing the maximum dust holding capacity to 2.07 times that of pure PAN membrane, effectively delaying filter material clogging, significantly extending service life, and reducing usage costs.

[0019] (4) During the electrospinning process, PAN tends to migrate to the fiber surface, so that the water contact angle of the composite membrane is kept above 120°, which effectively prevents pore blockage in high humidity environment. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the extraction process of cellulose acetate from waste cigarette butts and the preparation process of nanofiber membranes according to the present invention. Figure 2 This is a schematic diagram of the nanofiber membrane air filtration performance testing device of the present invention; Figure 3 A comparison of the FT-IR spectra of pure CA and recovered CA; Figure 4 The image shows an electron microscope image of an electrospun PAN / CB nanofiber membrane (PAN 10wt% + CBs 6wt%). The inset in the upper right corner shows the fiber diameter distribution and pore size distribution, and the EDS surface scan of O and N elements is shown in the lower right corner. Figure 5 Photographs of nanofiber membranes prepared by electrospinning with total concentrations of (a) 20 wt% and (b) 6 wt% PAN spinning solutions; Figure 6 Electron micrograph (a) and EDS surface scan of O and N elements of pure PAN (14 wt%) electrospun film (b); Figure 7 These are photos of cigarette butts from different batches before and after cleaning. Detailed Implementation

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other; and all other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0022] All reagents used in the following specific embodiments and comparative examples can be purchased commercially. Waste cigarette butts were collected from trash cans on campus and in public areas. Parameters such as filtration efficiency, pressure drop, quality factor (QF), and dust holding capacity in the test methods are referenced in relevant air filtration testing standards and literature (https: / / doi.org / 10.1016 / j.jece.2025.119604, https: / / doi.org / 10.1002 / marc.202401019, https: / / doi.org / 10.1016 / j.memsci.2025.124292).

[0023] Example 1 This embodiment proposes a method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts. The specific steps are as follows: (1) Pretreatment of waste cigarette butts: Collect waste cigarette butts, manually peel off the outer wrapping material and completely remove tobacco residue, and only take out the inner cellulose acetate filter core; cut the filter core into pieces to obtain coarse fiber segments of cigarette butts with a length of 1~2cm.

[0024] (2) Preparation of recovered cellulose acetate: Take the above-mentioned cigarette butt coarse fiber segment, add anhydrous ethanol with a purity of 99.7% for washing, the amount of anhydrous ethanol is 5 times the mass of the coarse fiber segment; soak and press and wash 3 times, 1 hour each time, until the washing liquid is clear and colorless; then rinse with distilled water, place in a vacuum drying oven, and vacuum dry at 65°C for 8 hours to obtain recovered cellulose acetate.

[0025] (3) Preparation of electrospinning solution: Weigh 10g of polyacrylonitrile with a weight average molecular weight of 150,000 g / mol and 6g of the above-mentioned recovered cellulose acetate, and add to 84g of N,N In dimethylformamide, heat and stir at 68°C for 7 hours to fully dissolve the polymer, and prepare a homogeneous electrospinning solution with a total mass concentration of 16 wt% (including 10 wt% polyacrylonitrile and 6 wt% recovered cellulose acetate). Let it stand to remove bubbles and set aside for later use.

[0026] (4) Electrospinning film formation: The above electrospinning solution is loaded into a syringe and electrospinning is performed; the spinning parameters are set as follows: voltage 15kV, feed speed 0.48mL / h, receiving distance 15cm, ambient temperature 25℃, relative humidity 50%, roller receiving speed 625rpm, and spinning time 6h; a composite nanofiber membrane is deposited on the receiving substrate (nonwoven paper).

[0027] (5) Residual solvent removal: The above-mentioned composite nanofiber membrane is placed in a vacuum drying oven and dried under vacuum conditions. Under conditions of 0.09 MPa and a heating rate of 3 °C / min, the air filter nanofiber membrane was obtained by vacuum drying at 60 °C for 7 h to completely remove residual solvent.

[0028] The nanofiber membrane prepared in this embodiment was tested and the results showed that: Filtration performance: At an air velocity of 5.3 cm / s, it achieves a PM1.0 filtration efficiency of 99.99%, a pressure drop of 173 Pa, and a quality factor (QF) as high as 0.0558 Pa. -1 .

[0029] Blending uniformity: EDS elemental mapping shows that nitrogen (N) representing PAN and oxygen (O) representing CA exhibit a highly uniform co-location distribution on a single nanofiber.

[0030] Surface electrical properties: The zeta potential of the pure PAN film surface is approximately -19.2 mV, while after the introduction of CA, the zeta potential of the film surface shifts significantly negatively to -133.5 mV. Fiber structure: The average fiber diameter is about 95nm, and the surface is smooth without beads.

[0031] Dust holding capacity: In the dust holding capacity test at an air velocity of 3.3 cm / s, its maximum dust holding capacity is 2.07 times that of pure PAN 14wt% membrane.

[0032] Hydrophobic properties: The water contact angle remains above 120°, and it is not easily clogged under high humidity.

[0033] Cost accounting: Based on industrial-grade market prices, the cost of raw materials is reduced by about 27% compared to pure PAN 14wt% film, with a cost ratio Rcost≈0.73.

[0034] Example 2 This embodiment uses the same inventive concept as Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass ratio of PAN to recovered CA in step (3) is 8:8 (i.e., PAN 8 wt%, CA 8 wt%, total concentration 16 wt%).

[0035] Test results: The fiber diameter is significantly finer than that of pure PAN (approximately 73 nm), and the specific surface area is increased. The filtration efficiency for PM1.0 is 99.45%, with a slightly higher pressure drop. It exhibits excellent dust holding capacity at low wind speeds (3.3 cm / s).

[0036] Example 3 This embodiment uses the same inventive concept as Embodiment 1. The difference between this embodiment and Embodiment 1 is that the PAN concentration in step (3) is 14 wt%, the recovered CA concentration is 4 wt%, and the total solid content is 18 wt%.

[0037] Test results: The fiber diameter is relatively large (approximately 454 nm), with high porosity and extremely low pressure drop. The filtration efficiency for PM1.0 remains above 99.83%, demonstrating excellent permeability and deep-layer interception capabilities.

[0038] Example 4 This embodiment adds step (6) to Example 2: the prepared air filter nanofiber membrane is placed in a hot press and hot-pressed at 120°C.

[0039] Test results: Hot pressing physically fused the fiber nodes, reducing the membrane thickness from 0.05 mm to approximately 0.025 mm, resulting in a denser structure. The filtration efficiency for PM1.0 was further improved to 99.88%, but the pressure drop increased (1550 Pa). This demonstrates that hot pressing can be used as an auxiliary means to regulate membrane performance.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that only PAN was used to prepare a 14 wt% pure PAN spinning solution.

[0041] Test results: The fiber diameter is relatively large (about 505 nm). Although the filtration efficiency is high and the pressure drop is low, the raw material is completely dependent on petrochemical PAN, resulting in high cost. Moreover, due to the lack of polar groups introduced by CA and the deep tortuous network, its dust holding capacity is only 48% of that of Example 1.

[0042] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (3), a pure PAN spinning solution with a total concentration of 6 wt% is prepared (lower than the 8 wt% lower limit of this invention).

[0043] Test results: The solution viscosity was too low, and the molecular chain entanglement was insufficient. Electrospraying occurred during the electrospinning process. The collected products were mostly droplets and bead-like structures, which could not form a continuous nanofiber membrane. This confirmed the necessity of limiting the total concentration lower limit (8 wt%) in this invention.

[0044] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (3), a pure PAN spinning solution with a total concentration of 20 wt% is prepared (higher than the upper limit of 18 wt% of the present invention).

[0045] Test results: The solution viscosity was too high. During the electrospinning process, the solvent evaporated rapidly at the needle tip, causing the polymer to solidify prematurely. This resulted in frequent needle blockage and the inability to form a continuous nanofiber membrane, confirming the necessity of limiting the total concentration (18 wt%) in this invention.

[0046] Comparative Example 4 This comparative example adds step (6) to Example 2, but the hot pressing temperature is set to 150°C (exceeding the upper limit of 140°C of this invention).

[0047] Test results: SEM showed that the nanofibers underwent severe melt cross-linking, the original three-dimensional porous network structure collapsed, and the porosity decreased significantly. Although the filtration efficiency was close to 100%, the pressure drop surged to over 2000 Pa, and the quality factor (QF) plummeted, completely losing its practical value as a low-resistance air filter material.

[0048] like Figure 3-7 As shown, this application characterizes the surface morphology of the samples in each embodiment and comparative example, and obtains the parameter comparison table shown in Table 1. Table 1. Comparison of Important Parameters in Examples and Comparative Examples pass Figure 3 The FT-IR spectrum shows that the recovered CA retains the characteristic peaks of pure CA (such as 1734 cm⁻¹). - The carbonyl stretching vibration at ¹ demonstrates the effectiveness of the extraction process in this application.

[0049] By comparison Figure 4 SEM morphology of Example 1 and Figure 5 The spinning photographs of Comparative Examples 2 and 3 show that: in Comparative Example 2, reducing the total concentration to 6 wt% resulted in excessively low solution viscosity, causing the jet to easily break or separate into droplets during stretching, forming a bead-like structure instead of a good nanofiber structure; in Comparative Example 3, increasing the total concentration to 20 wt% resulted in excessively high solution viscosity, causing premature solidification and blockage at the needle tip. Therefore, Comparative Examples 2 and 3 mainly demonstrate the influence of the total concentration of the spinning solution on the morphology of the nanofiber film, and the total concentration needs to be strictly controlled between 8 and 18 wt%.

[0050] By comparison Figure 4 and Figure 6 As can be seen from Example 1 and Comparative Example 1, although Comparative Example 1, without the addition of recycled CA, achieved good film formation and a high QF value, its dust holding capacity was only 48% of that of Example 1, and its cost was high. In Example 1, the introduction of 6 wt% CBs not only did not damage the PAN framework but also introduced polar ester groups and constructed a more tortuous three-dimensional network, achieving deep filtration. Therefore, Example 1 mainly demonstrates the synergistic effect of recycled CA as a functional additive in improving dust holding capacity and reducing costs.

[0051] Compared to Comparative Example 4, Example 4 also employed a hot-pressing post-treatment method, but the key parameters (pressure drop and QF) of the porous membrane obtained in Example 4 were significantly better than those in Comparative Example 4. This is because the hot-pressing temperature (150°C) in Comparative Example 4 exceeded the limit, damaging the original nanofiber pore structure. Excessive fusion of nanofibers led to porosity collapse, subsequently causing a surge in pressure drop. Therefore, Comparative Example 4 mainly demonstrates the influence of hot-pressing post-treatment conditions on the performance of the prepared air filter membrane, and the hot-pressing temperature must be strictly controlled within 100~140°C.

[0052] In addition, this application also performs in-depth characterization and calculation on the samples of each embodiment and comparative example, and analyzes them in conjunction with Tables 1 and 2.

[0053] Table 2 Summary of Mechanism Validation Characterization Data As shown in Table 2, the pure PAN film, containing only cyano groups, has a Zeta potential of only -19.259 mV; while in Example 1, after introducing recovered CA, the polar ester groups on the CA molecular chain (FT-IR confirmed to be 1748 cm⁻¹) -1 The presence of strong C=O stretching vibrations and trace amounts of hydroxyl groups causes the Zeta potential on the membrane surface to plummet to -133.528 mV. This extremely strong surface negative charge generates strong electrostatic Coulomb attraction and dipole interaction with positively charged PM1.0 particles in the air (such as potassium ions and organic aerosols in flue gas). This is the core reason why Example 1 can still achieve an extremely high filtration efficiency of 99.99% despite having a larger fiber diameter than Example 2.

[0054] pass Figure 4 EDS surface scanning confirmed that nitrogen (N) (derived from PAN) and oxygen (O) (derived from CA) elements co-localized on the single fiber of Example 1. Combined with the absence of characteristic peak shift in FT-IR, this confirmed that the recycled CA and PAN formed a homogeneous physical blend at the molecular level, rather than macroscopic phase separation. Simultaneously, the addition of CA reduced the viscosity of the spinning solution and increased the surface charge density of the jet, resulting in a significant increase in electrostatic tensile force. The fiber diameter sharply decreased from 505 nm in Comparative Example 1 to 95 nm in Example 1 and 73 nm in Example 2. This ultrafine fiber constructs a highly tortuous three-dimensional deep filtration network, forcing airflow around the membrane and allowing particulate matter to penetrate deep into the membrane for interception, thereby increasing the dust holding capacity to 2.07 times that of a pure PAN membrane.

[0055] According to the formula = / / ( ) The relative cost ratio of nanofiber membranes was calculated. Comparative Example 1 (pure PAN 14wt%) had the highest QF value, but it relied entirely on expensive petrochemical PAN (40 yuan / kg). Example 1, by introducing low-cost recycled CA (2.5 yuan / kg), achieved a QF value of 0.0558 Pa. -1 It is almost comparable to Comparative Example 1 (0.0575 Pa). -1 Furthermore, with the dust holding capacity doubled, the cost of raw materials decreased by 27%. This fully demonstrates that the present invention is not a simple downgrade of waste materials, but rather achieves a win-win situation of performance enhancement and cost reduction through rheological and electrostatic control, possessing extremely high industrial mass production value.

[0056] To further confirm the necessity of the pretreatment process of this invention (multiple soaking and pressing washing with anhydrous ethanol) and the safety of recovering CA as an air filter material, the cigarette butt materials before and after cleaning (such as...) were tested. Figure 7 The data (shown in the figure) were characterized in depth by gel permeation chromatography (GPC), inductively coupled plasma mass spectrometry (ICP-MS), gas chromatography-mass spectrometry (GC-MS), and X-ray photoelectron spectroscopy (XPS). The summarized data are shown in Table 3.

[0057] Table 3 Summary of Physicochemical Properties and Heavy Metal Residue Characterization Data of Recovered Cellulose Acetate (CA) In this field, discarded cigarette butts are rich in tar, nicotine, and heavy metals (such as Pb and Cd) from combustion, and direct use in air filtration can lead to serious secondary toxicity. However, data from the ICP-MS presented in Table 3 of this application shows that the anhydrous ethanol multiple immersion and mechanical pressing process used in this invention not only completely dissolves and removes organic toxins (tar / nicotine), but also achieves removal rates of up to 91.1% and 80.8% for highly toxic heavy metals cadmium (Cd) and chromium (Cr), respectively, and a removal rate of 76.8% for lead (Pb). The residual amount of recovered CA heavy metals after cleaning has been reduced to trace levels (<0.0002% <0.0002%), fully meeting or even exceeding the environmental safety standards for indoor air purification and personal protective equipment (PPE).

[0058] Waste recycling often involves polymer chain breakage, but the GPC data in Table 3 shows that the weight-average molecular weight (Mw) of the recovered CA is still as high as 180,382 g / mol. This demonstrates that the extraction process of this application (vacuum drying at 65°C and gentle extraction with anhydrous ethanol) perfectly protects the glycosidic backbone of CA while removing impurities. It is this retention of high molecular weight that enables the recovered CA to provide sufficient molecular chain entanglement force when subsequently blended with PAN, avoiding electrospraying and successfully inducing the refinement of nanofibers.

[0059] XPS and FT-IR spectra show that the nitrogen signal (derived from nicotine and tobacco proteins) on the surface of the cleaned material has largely disappeared, retaining only the typical ester and hydroxyl groups of CA. This confirms the high purity of the recovered CA at the elemental level, ensuring that it will not undergo unexpected phase separation from PAN due to impurities during electrospinning.

[0060] GC-MS data show that the cleaning process is highly effective in removing nicotine and low- to medium molecular weight polycyclic aromatic hydrocarbons (PAHs), with removal efficiencies exceeding 97% for most detectable compounds. Many compounds saw their concentrations drop below the detection limit (0.20 μg / g) after purification. Notably, although the removal efficiencies for nicotine and naphthalene reached 99.64% and 80.80%, respectively, their residual concentrations remained at 17.55 μg / g and 0.405 μg / g, respectively. Meanwhile, benzo[g,h,i]perylene exhibited an unusual detection pattern: it was not detected in the original sample but was quantitatively detected at 0.426 μg / g in the purified sample. Based on these results, core toxic substances such as benzo[a]pyrene were not detected, fully complying with the stringent limits (≤ 1 mg / kg, i.e., 1 μg / g) for plastic components in consumer products stipulated in the EU REACH Regulation (Annex XVII, Item 50). Regarding the residual nicotine (17.55 μg / g), although there are currently no specific mandatory standards for static nicotine residues in air filter media, this concentration level is considered toxicologically safe. This conclusion is supported by the UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS) classification thresholds for mixtures: this concentration is well below the 1% (10,000 μg / g) trigger threshold and also complies with the REACH regulation's exemption principle for trace impurities, with its content well below the 0.1% (1,000 μg / g) threshold standard. This demonstrates from the perspective of contaminant residues that washed and recovered cigarette butts can be used in subsequent filtration processes.

[0061] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts, characterized in that, Includes the following steps: S1. Pre-treat waste cigarette butts by removing the outer wrapping material and tobacco residue, obtaining the inner cellulose acetate filter element and crushing it to obtain the coarse fiber segment of the cigarette butt. S2. The coarse fiber segments of cigarette butts are washed and impurities are removed using organic solvents, followed by water washing and drying to obtain recycled cellulose acetate. S3. Add polyacrylonitrile and recycled cellulose acetate to a solvent, heat and stir to dissolve, and prepare an electrospinning solution. S4. Electrospin the electrospinning solution to deposit a composite nanofiber membrane on the receiving substrate. S5. The composite nanofiber membrane is dried to remove residual solvent, thus obtaining an air filtration nanofiber membrane.

2. The method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to claim 1, characterized in that, In S1, the length of the coarse fiber segment of the cigarette butt is controlled at 1~2 cm.

3. The method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to claim 1, characterized in that, In S2, the organic solvent used is anhydrous ethanol with a purity ≥99.7%, and the amount used is 5 to 10 times the mass of the coarse fiber segment of the cigarette butt; the number of soaking and pressing washing cycles is 3 to 5 times, each time for 1 to 2 hours, until the washing liquid is clear and colorless; the vacuum drying temperature is 60 to 70℃, and the time is 7 to 8 hours.

4. The method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to claim 1, characterized in that, In S3, the weight-average molecular weight of polyacrylonitrile is 150,000 g / mol; the solvent is N,N-dimethylformamide with a purity of 99.5% and a water content ≤0.05%; the heating and stirring temperature is 65~70℃, and the stirring time is at least 7 h.

5. The method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to claim 4, characterized in that, The total mass concentration of polyacrylonitrile and recovered cellulose acetate in the electrospinning solution is 8-18 wt%; among which, the mass concentration of polyacrylonitrile is 8-14 wt% and the mass concentration of recovered cellulose acetate is 2-10 wt%.

6. The method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to claim 1, characterized in that, In S4, the parameters for electrospinning are: voltage 13~17kV, feed speed 0.4~0.6mL / h, receiving distance 13~17cm, ambient temperature 23~27℃, relative humidity 45~55%, roller receiving speed 600~650rpm, and spinning time 4~8h.

7. The method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to claim 6, characterized in that, In S5, the vacuum degree of vacuum drying is controlled at -0.08~-0.1MPa, and the heating rate is 2~5℃ / min.

8. A method for preparing an air-filtering nanofiber membrane based on recycled cigarette butts according to any one of claims 1-7, characterized in that, The process also includes step S6: placing the nanofiber membrane obtained in step S5 in a hot press and hot-pressing it at 100~140℃ to regulate the fiber morphology and pore structure.

9. An air filtration nanofiber membrane based on recycled cigarette butts, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the high-efficiency air filtration nanofiber membrane as described in claim 9 in air particulate matter filtration and indoor air purification equipment.

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