Highly electrostatic cellulose acetate-based composite electret nanofiber film for air filtration applications

Highly electrostatic cellulose acetate-based composite electret nanofiber film for air filtration applications | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Highly electrostatic cellulose acetate-based composite electret nanofiber film for air filtration applications Ning Yan, Ting Gao, Li Hua, Fan Xie, Rui-Xin Liu, Zhao-Qing Lu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4741981/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Highly electrostatic cellulose acetate (CA)-based electret film for air filtration was fabricated by electrospinning method assisted with the corona-charging technique in this work. The highly polar and hydrophobic polyvinylidene fluoride (PVDF) was chosen as the electrostatic reinforcement. The results showed that under the dual electric fields, the dipole charges generated from the conversion from non-polar α-phase to polar β-phase of the dipole inside PVDF and the space charge captured at the phase end traps of CA and PVDF give CA/PVDF films high static electricity. Especially, the composite film with 40 wt% PVDF exhibited an ultrahigh surface potential of 2.146 KV and excellent filtration efficiency of 97.27% for PM 0.3 with a pressure drop of only 88.7 Pa, which was 29.68% and 22.04%, respectively higher than that of pure CA film. It was noticed that the hydrophobicity and mechanical strength were also improved. Cellulose acetate Polyvinylidene fluoride Electret filtration Surface potential Corona charging Electrostatic spinning Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction In recent years, with the rapid development of the city and the continuous advancement of modern industry, air pollution problems have became increasingly prominent. Aerosol particulate matter (PMs) (Arias-Pérez et al., 2020 ; Berger et al., 2017 ) as the main source of pollution in ambient air, especially lung-accessible particulate matter with aerodynamic equivalent diameter less than 2.5 µm (Anderson, 2017 ; Andrew and Kathy, 2023 ), is prone to carry heavy metals, microorganisms, and the hazardous substances. Its prolonged suspension in the air and inhalation by human can induce respiratory diseases, and increase the risk of lung cancer and cardiovascular diseases (Brook and Rajagopalan, 2017 ; Rajagopalan et al., 2018 ; Landrigan, 2017 ), posing a serious threat to public health. Therefore, the development of efficient air filtration materials to effectively isolate airborne particles is an effective method to protect people's health. Electret filter material can improve the ability to capture particles through Coulombic attraction and electrostatic induction (Xin Wang et al.; Xu et al., 2020 ), and does not increase the air resistance, showing a significant filtration performance especially for particles with a particle size of less than 0.3 µm (Tofail et al., 2020 ; Sun et al., 2020 ). Commonly, the fluoropolymers with C-F bond such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), as well as the non-fluoropolymers such as polyacrylonitrile (PAN), polypropylene (PP) and polystyrene (PS) are employed as the electret air filtration material(Sanyal and Sinha-Ray, 2021 ; Ahn et al., 2022 ; Dai et al., 2021 ; Jung et al., 2019 ; Eticha et al., 2024 ). Attributed to their excellent dielectric properties, charge storage capacity, and hydrophobicity, these polymers can impart the electret material with strong electrostatic adsorption and filtration efficiency. However, the synthetic polymer-based materials are difficult to biodegrade and pollute the ecological environment. Therefore, there is an urgent need to develop a green biomass-based filtration material to replace petroleum-based plastic products and promote environmental sustainable development (Abdur Rahman et al., 2023 ). Cellulose acetate (CA), one of the first commercial cellulose derivatives, is obtained by esterification of natural cellulose and acid anhydride or acetic acid under the action of catalyst sulfuric acid (Lee et al., 2016 ). Because it is derived from natural wood fiber raw materials, it has the advantages of wide source, low cost and good biodegradability. In addition, the esterification modified CA can be dissolved in organic solvents such as N, N-dimethylacetamide (DMAc), acetone, acetic acid, etc. (Majumder et al., 2019 ), and its solution has good flowability and spinnability. Therefore, it is possible to fabricate electret filtration materials using electrostatic spinning technology. However, due to the structural characteristics of CA itself, its weak mechanical strength, poor intrinsic dielectric properties (dielectric constant only 3.5) and strong hydrophilicity will lead to poor charge trapping and storage (Lecoublet et al., 2023 ). In order to enhance the electret effect, doping electret nanoparticles (i.e., silica, boehmite, titanium dioxide in nanofibers is proposed (Guliakova et al., 2020 ; Yang et al., 2019 ; Lou et al., 2020 ). However, nanoparticles in the matrix material have the risk of being easily dislodged and agglomerated, and the dislodged nanoscale particles can be a threat to human health(Saha et al., 2023 ; Ding et al., 2019 ). Recently, the all-polymer electret air filtration materials are developed to improve the electret effect while effectively avoiding the problems of agglomeration and shedding of electret nanoparticles in the matrix. Ko et al. prepared all-polymer hybrid electret fibers based on PS and PVDF by electrospinning technology (Ko et al., 2017 ). The results showed that the different electron transport capacities of PVDF and PS led to the charges aggregated at the interfacial region, which enhanced the electret effect, leading to a 36% increase in the surface potential and a 12% increase in the filtration efficiency. Meanwhile, PVDF as an electret enhancer, had good compatibility with the base polymer PS, without the risk of detachment. Liu (Liu et al., 2020 ) et al. prepared an electret filtration film with high surface potential of 6.8 KV and excellent filtration efficiency of 99.998%, based on electrospinning method using several polar polymers (i.e., polyacrylonitrile, nylon 6, polyurethane, and PVDF). It can be seen that the use of high polarity polymers as electrostatic enhancers can significantly improve the electret charging and filtration effect of the materials by increasing the interfacial polarization. In this paper, an all-polymer electret nanofiber film for air filtration is obtained by electrospinning method assisted with the corona-charging technique, using the biodegradable CA as the base polymer, the highly polar and hydrophobic PVDF as the electrostatic reinforcement. We mainly investigate the morphology, phase structure, surface potential and filtration performance, also the mechanical properties, hydrophobicity of the film are evaluated. Particularly, we focus on the relationship between surface charge and filtration effect, and elucidate the filtration mechanism of CA/PVDF composite film. Experimental Chemicals and Materials All chemicals, including cellulose acetate (CA, Mw = 4w, polyvinylidene fluoride (PVDF 5130, Mw = 100w) and acetone (Ac, 99%), N, N-dimethylacetamide (DMAc, 99%), were purchased from commercial sources without further processing. Preparation of electret CA/PVDF composite nanofiber film Preparation of spinning fluid A series of electrospinning precursor solutions with different PVDF mass concentrations (0, 10%, 20%, 30%, 40%) were prepared by dissolving CA and PVDF powder in mixed solvent of DMAC and Ac at the given conditions (the solvent mass ratio: 1:1, the solute mass concentration: 10 wt.%). The solutions were stirred continuously at room temperature for 6 hours until completely dissolved to form a homogeneous and transparent spinning solution. Preparation of CA/PVDF electrospun nanocomposite film The above spinning solution was transferred into a 5 ml plastic syringe, and the polymer solution was continuously extruded under the action of the syringe pump. When the solution reached the tip of the metal needle of the syringe, the solution was quickly polarized and highly electrified, and a charged CA/PVDF nanocomposite film was formed through phase separation (Lyu et al., 2021 ). Then the prepared films were placed in an oven at 50°C for 3 h to remove the residual solvent. A series of CA/PVDF nanofiber films with PVDF mass concentrations of 0, 10%, 20%, 30%, and 40% were denoted as CA, CA/PVDF-10, CA/PVDF-20, CA/PVDF-30, and CA/PVDF-40, respectively. The specific parameters of electrostatic spinning were as follows: spinning voltage = 10 KV, flow rate of = mL/h, distance of the metal needle from the receiving rollers = 15 cm, spinning time = 1-1.5 h. The temperature and humidity in the spinning environment were 30 ± 2 ℃ and 40 ± 5 RH%, respectively. Corona charging treatment of CA/PVDF composite film The corona charging system consisted of a wire electrode and a copper plate receiving electrode. The CA/PVDF composite film was placed on the copper plate, and the distance from the wire electrode to the film was 5 cm, and a voltage of 25 KV was applied to the wire electrode and kept for 5 min, and all experiments were performed with positive voltage polarization. Figure 1 shows the preparation process of electret CA/PVDF composite nanofiber film. Characterization and analysis of the materials The surface micromorphology of CA/PVDF composite films was observed by scanning electron microscope (SEM, SU8100, Hitachi, Japan) under an acceleration voltage of 7.0 KV. Fourier transform infrared spectroscopy (FT-IR, Vertex 70, Bruker, Germany) was performed to characterize chemical compositions with a scanning range of 400–4000 cm − 1 . The crystal structure of the films was characterized by high-performance X-ray diffractometer (XRD, Bruker, Germany) with a scan rate of 5 °/min and a 2θ range of 10°-50°. Tensile strength tests of samples were conducted by using an AI-700-NGD tensile testing machine (Gotwill Ltd, China) equipped with a 500 N load cell at a loading rate of 1 mm min − 1 . The water contact angle of samples were investigated by a contact angle measuring instrument (JC2000, Bruker, German) at room temperature. The droplet volume used in the contact angle test was 5 µL. The surface potential of the films was measured using a compact handheld electrostatic field meter (FMX-003, Simco ION, Japan). During the test, this device was placed 2.54 cm away from the film to ensure the two LED guide rings coincided. Ten measurements were taken at different locations on each sample to determine the average surface potential. The filtration performance was evaluated by a comprehensive performance test bench (LZC-K1, Suzhou Huada Equipment Co., China). NaCl aerosol particles (measurable particle sizes of 0.3, 0.5, 1.0, 2.0, 5.0, and 10.0 µm) were used in the filter table according to the LZC-K1 manual. The flow rate was 32 L/min with an effective area of around 100 cm 2 . The calculation formula of quality factor (QF) as the comprehensive evaluation index of filter materials is QF = − ln(1 – E%) / ΔP, where E% and ΔP are the removal efficiency and pressure drop, respectively. Results and discussion Morphology analysis of CA/PVDF composite film CA/PVDF composite films with different morphologies were obtained by adjusting the mass concentration of PVDF components. As can be seen from Fig. 2 , the surfaces of these composite films were smooth, and they all exhibited a network structure formed by the random distribution of nanofibers. The diameter distribution of the pure CA film was the most concentrated, with an average diameter of 730 ± 5 nm. After the addition of PVDF, the viscosity of the spinning solution increased, the intermolecular interaction force was enhanced, and the fiber filaments were stretched with a larger resistance under the same electric field force, so that the average diameters of the prepared fibers showed a tendency to increase (i.e., 780 ± 5 nm, 790 ± 6 nm, 880 ± 160 nm, 890 ± 80 nm). When the mass concentration of PVDF was increased to 50%, the spinning solution was more viscous, which made it easy to block the needle and the spinning process difficult to carry out, and the spun fibers showed uneven thickness and large adhesions state. Within the limit of spinnable concentration (mass concentration of PVDF ≤ 40%), the fiber film with a larger fiber diameter has a smaller surface area, which is conducive to reducing air friction and filtration resistance (Kim et al., 2021 ). Chemical structure characterization of CA/PVDF composite films The chemical structures of CA, PVDF, and CA/PVDF-40 fiber films were characterized using FTIR and XRD, and the results are shown in Fig. 3 . The infrared spectra showed that the CA/PVDF-40 film had a stretching vibration absorption peak of the -C = O bond of CA at 1742 cm and a stretching and bending vibration peak of the C-F bond of PVDF at 763 cm − 1 and 1233 cm − 1 (Zhou et al., 2021 ; Bastida et al., 2024 ). Meanwhile, in the CA/PVDF-40 composite film, the fluorine atoms of PVDF formed hydrogen bonds with the -OH of CA, so compared with the pure CA film, the -OH absorption peak at 1640 cm − 1 was weakened to almost completely disappear(Si et al., 2023 ). These indicate that PVDF was successfully compounded onto the CA film. In the XRD pattern of Fig. 3 (b), the bulky acetyl group replacing the hydroxyl group in the CA disrupts the hydrogen-bonding network structure of cellulose, which results in a low crystallinity and does not show any obvious diffraction peaks. The PVDF powder has three characteristic peaks at 2θ of 18.27°, 19.7°, and 20.3°, which corresponds to the (100) and (020) diffraction peaks of the nonpolar α-phase, and (110) diffraction peaks of the polar β phase, respectively (Janakiraman et al., 2016 ). However, the diffraction peaks of α-phase disappeared in CA/PVDF composite films, only the diffraction peaks of β-phase were retained, and the (110) diffraction peaks were broadened. This was because the dipoles in PVDF were aligned under the action of applied electric field and mechanical tension, which promoted the conversion of non-polar α-phase to the polar β-phase (Bui et al., 2022 ). With the increase of PVDF content, the (110) crystal surface strength increased significantly, i.e., the content of the polar phase in the composite film increased. All the above information indicated that PVDF enhanced the polarity of the composite film, which was conducive to the efficient trapping of dipole charge, thus increasing the surface charge density of the film (Du et al., 2022 ; Song et al., 2022 ). Mechanical properties and hydrophobicity of CA/PVDF composite films The mechanical strength of fiber composite film directly affects its practical application effect. The stress-strain curves of the CA and CA/PVDF films were presented in Fig. 4 (a). It could be seen that the tensile strength of CA film is only 2.8 MPa, and the elongation at break is only 2.99%. However, with the increase of PVDF content, the tensile strength, elongation, and toughness of the composite film all showed an increasing trend, which was attributed to the formation of more hydrogen bonding structure between -OH in the CA molecular chain and -F atoms in PVDF (Si et al., 2023 ; Szewczyk and Stachewicz, 2020 ). Obviously, the CA/PVDF composite film has better comprehensive mechanical properties compared with pure CA film. Moisture is another important key factor affecting the filtration performance, especially for electret materials. The hydrophilic hydroxyl group on CA increases the conductivity of the film and accelerates the carrier migration rate, resulting in increased charge dissipation, which decreases the filtration efficiency (Szewczyk and Stachewicz, 2020 ). The surface wettability of the composite film was analyzed in this study, and the results shown in Fig. 4 (b). The C-F bond of PVDF makes PVDF possess lower surface energy and stronger hydrophobicity. Thus, the addition of PVDF will increase the water contact angle of CA film, and when its content is 40%, the contact angle reaches 142.3°. Table 1 Detailed parameters of mechanical properties of CA/PVDF composite films Sample name Tensile strength (MPa) Elongation (%) Young's modulus (MPa) Toughness (MJ/m 3 ) Pure CA 2.80 2.99 204.87 0.055 CA/PVDF-10 5.96 6.25 337.09 0.026 CA/PVDF-20 6.23 23.76 91.22 1.00 CA/PVDF-30 6.69 22.47 89.09 1.09 CA/PVDF-40 6.80 25.88 85.26 1.51 Surface potential of CA/PVDF composite films Surface potential of CA/PVDF electrospun composite films During the electrostatic spinning process, the syringe tip is connected to the positive pole of the power supply, and its charge is basically used to stretch the spinning droplets and form nanofibers, so there is less residual positive charge (space charge) on the sample surface. Therefore, the surface potential of the composite film is mainly determined by the new polarized negative sites formed by the orientation of the PVDF dipoles under the external electric field, as shown in Fig. 5 (a). With the increase of PVDF content, the surface potential becomes larger and achieves a maximum value of -2.73 KV at 40% PVDF content, which is 58.1% higher than of the pure CA film (-1.15 KV). This is due to the fact that the increase in PVDF content increases the content of the polar β-phase, which generates more dipole charges under the action of the electric field. We evaluated the electrostatic charge decay of electrospun CA/PVDF composite film within 180 min. As can be seen from Fig. 5 (b), the greatest decay of charges appeared within the initial 40 min. This noticeable decay of charge is mainly caused by the escape of charges existing in shallow traps and is easily affected by the neutralization of the opposite charge generated by the PVDF dipoles (Catalani et al., 2007 ). The slow decay in 40 ~ 140 min is due to the segmental depolarization of directional dipoles caused by molecular thermodynamic movement (Eisenmenger et al., 1999 ) Eventually, a stable dipole charge is left, thus maintaining the long-term stability of the surface potential (Lovera et al., 2009 ). When the surface potential of the composite film tends to be stable, CA/PVDF-40 has the highest surface potential of -0.63 KV, which is 58.73% higher than that of the pure CA film. This is due to CV/PVDF composite film with high PVDF content has more dipole charges and better charge stability. Surface potential of CA/PVDF electrospun composite films treated by corona charging The initial surface potentials of CA/PVDF films treated by double charging approaches, i.e., the electrospinning and corona charging, are shown in Fig. 6 (a). The discharge tip is connected to the positive pole of the power supply, the positive ions formed by ionization of the air are deposited on the fiber surface under the electric field, which neutralizes the negative dipole charge in the original electrospun film. The space charge dominates in the continuous charging process, so the fiber film shows positive electrical properties. In addition, due to the different conductivity of CA and PVDF, the electron transport process in the film is hindered under the action of the external electric field and accumulates at the interface of the two (Ko et al., 2017 ). Therefore, the initial surface potential of the film treated by double charging methods increases with the increase of PVDF content. Figure 6 (b) showed the decay curves of the surface potential of the CA/PVDF electrospun composite films treated by corona charging within 180 min. The positive ions in the surface traps of the CA/PVDF composite films gradually escaped with time, and the stable dipole charge remained within the composite films, so that the fiber films ultimately became electronegative. When the surface potential of the film by two means of charging tends to be stable, the surface potential of CA/PVDF-40 sample is the highest at -0.78 KV, which is 71.8% higher than that of the pure CA film and 19.23% higher than that of the singe electrospining CA/PVDF-40 film (0.63 KV) in Fig. 5 (b). That's because the charging voltage of corona charging is larger than the electrospining voltage, the content of polar β-phase in PVDF increases with the increase of the electret voltage, and there are more dipole charges in the film. Therefore, the double electric process is more conducive to increasing the surface potential of the film than the single electrostatic spinning process (Oh et al., 2018 ). Comprehensive filtration performance of CA/PVDF composite films Figure 7 shows the filtration efficiency, quality factor and filtration resistance of CA/PVDF films treated by single electrospinning and double electric technique for PMs of different particle sizes at room temperature. The specific values of filtration efficiency of CA/PVDF-40 composite films under two electric processes shown in Table 2 are obtained from Fig. 7 . It can be seen that the filtration efficiency of CA/PVDF composite films for different sizes of particles under two kinds of electric processes shows a certain upward trend with the increase of PVDF content (i.e., the surface potential of the composite film). This upward trend is most obvious in the filtration of PM 0.3, followed by PM 0.5, and is least sensitive to PM 1.0. That's because the filtration of small particles (diameter between 0.05 ~ 0.5 µm) mainly relies on electrostatic adsorption, while the filtration of particles larger than 1 µm mainly relies on mechanical interception (Xu et al., 2020 ; Ji et al., 2023 ). Meanwhile, it can also be observed from the figure that compared with the single electrospinning, the filtration efficiency of the double electric composite film for PM 0.3 and PM 0.5 was improved by 5.41% and 3.37%, respectively, with more efficient filtration effect. The pressure drop of the composite films under different electric processes were approximately 90 Pa, indicating that the electric method did not significantly affect the filtration resistance of the fiber film. In addition, the comprehensive filtration performance of the materials was evaluated using the Quality Factor (QF). As shown in Fig. 7 (b) and (e), under these two electric process, the QF for PM 0.3 increased the most with the change of PVDF content, which shows that electrostatic adsorption played a key role in the filtration of small particulate matter. Table 2 Filtration efficiency of pure CA film, CA/PVDF-40 composite film under different electric processes Electric method Filtration efficiency The increase of the filtration efficiency** PM 0.3 PM 0.5 PM 1.0 PM 0.3 PM 0.5 PM 1.0 Single electrospinning 92.01% 95.17% 99.16% 23.02% 14.49% 1.36% Double electric technique* 97.27% 98.45% 99.39% 22.04% 17.67% 1.19% *Double electric technique refers to the electrospinning and corona charging approaches. **The increase of the filtration efficiency is compared to that of the pure CA film. Contribution of electret effect on filtration performance To further clarify the contribution of the electrostatic effect to the overall filtration efficiency, the CA/PVDF-40 composite film was immersed in isopropyl alcohol to eliminate the charge. As shown in Fig. 8 (a), the mechanical filtration efficiency of the composite films for PM 0.3, PM 0.5, and PM 1.0 were 64.73%, 72%, and 93.74%, respectively, the filtration efficiency of the films were substantially improved after charging and the double electric process was more conducive to the preparation of efficient electret air filtration materials. The contributions of different electret methods to the electrostatic effect in CA/PVDF-40 composite films were shown in Fig. 8 (b). The contributions of electrostatic action to PM 0.3, PM 0.5, and PM 1.0 filtration efficiency were 29.64%, 24.49%, and 5.52% in the electrospinning process, and 34.59%, 28.28%, and 6.69% in the composite electret for the PM 0.3, PM 0.5, and PM 1.0 filtration efficiency, respectively. It can be seen that the double electric process is more favorable to the filtration efficiency of the composite film, and the electrostatic effect on PM 0.3, PM 0.5 and other small particles is better, on PM 1.0 is limited. Filtration mechanism of electret CA/PVDF Composite film The mechanism of CA/PVDF electret composite film for capturing the particulate pollutants is shown in Fig. 9 . Under the double electric process of electrostatic spinning and corona charging, the crystal cell structures of PVDF are spontaneously polarized under the electric field, and their nonpolar α-phase can be transformed into polar β-phase, so the overall dipole moment of the composite film becomes larger, and the polarization charge increases (Ping Wang et al., 2018 ). In addition, more space charge is captured at the interface of the two phases of CA and PVDF, which finally endows the CA/PVDF film with a high electrostatic charging effect. For charged particles, there is a Coulomb force between them when they are close to the fiber film, and the charged particles are adsorbed (Xu et al., 2020 ). For the electrically neutral particles, when they are close to the fiber film, the electric field on the surface of the film induces the formation of an opposite electric field on the surface of the particles, which is then adsorbed and captured by the fiber film (Xin Wang et al.). Therefore, through Coulombic attraction and electrostatic sensitivity, electret CA/PVDF composite films are highly effective in capturing charged and uncharged particles with diameters less than 0.3 µm (Sun et al., 2020 ). Conclusion Highly electrostatic CA/PVDF composite electret filtration films were prepared by dual electric approaches of electrostatic spinning and corona charging using CA as the matrix and PVDF as the electret enhancer. Under the dual electric field, the surface potential of CA/PVDF electret film was greatly increased (2.146 KV). Moreover, the composite film showed excellent filtration performance, i.e., with filtration efficiency for PM 0.3 was 97.27% without increasing the pressure drop (~ 88.7 Pa, comparable to that of the CA film). The hydrophobicity and mechanical properties of the composite films were also improved. The work provides a new solution in design and development environmentally friendly cellulose-based composite electret filtration films. Declarations Author contributions NY, LH, FX and ZL made substantial contributions to the conception and design of the work and approved the version to be published, agreeing to be accountable for all aspects of the work in ensuring that questions related to the accuracy and integrity of any part of the work are appropriately investigated and resolved. TG: acquisition, analysis, interpretation of data, Writing-origrinal draft. RL and TG: Data curation, Writing-origrinal draft. Funding This work was supported by the Open Foundation of Key Laboratory of Auxiliary Chemistry and Technology for Chemical Industry, Ministry of Education, Shaanxi University of Science and Technology (No. KFKT2023-06), Shaanxi Collaborative Innovation Center of Industrial Auxiliary Chemistry and Technology, Shaanxi University of Science and Technology (No. KFKT2023-06), and National Nature Science Foundation of China (No. 22378248). Data availability Data are available upon reasonable request. Conflict of interest The authors declare no competing interests. Consent for publication All authors have given approval to the final version of the manuscript. Ethical approval All authors state that they adhere to the Ethical Responsibilities of Authors. In addition, this article does not contain any studies with human participants or animals performed by any of the author. Author information Corresponding Author: Ning Yan, Zhao-Qing Lu References Abdur Rahman, M., Haque, S., Athikesavan, M. M., & Kamaludeen, M. B. (2023). A review of environmental friendly green composites: production methods, current progresses, and challenges. Environmental Science and Pollution Research, 30(7), 16905–16929. doi: 10.1007/s11356-022-24879-5 . Ahn, S., Shim, E., Kim, Y., Bae, Y.-S., & Eom, H. (2022). Air filtration performance enhancement of PTFE foam–coated filters at high temperatures via secondary strongly adhering PTFE nanofiber coatings. 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Charge storage of ternary polymer blends based on poly(phenylene ether). Polymer International, 58(11), 1260–1266. doi: https://doi.org/10.1002/pi.2653 . Lyu, C., Zhao, P., Xie, J., Dong, S., Liu, J., Rao, C., et al. (2021). Electrospinning of Nanofibrous Membrane and Its Applications in Air Filtration: A Review. Majumder, S., Matin, M. A., Sharif, A., & Arafat, M. T. (2019). Understanding solubility, spinnability and electrospinning behaviour of cellulose acetate using different solvent systems. Bulletin of Materials Science, 42(4), 171. doi: 10.1007/s12034-019-1857-6 . Oh, W. J., Lim, H. S., Won, J. S., & Lee, S. G. (2018). Preparation of PVDF/PAR Composites with Piezoelectric Properties by Post-Treatment. Rajagopalan, S., Al-Kindi, S. G., & Brook, R. D. (2018). Air Pollution and Cardiovascular Disease: JACC State-of-the-Art Review. Journal of the American College of Cardiology, 72(17), 2054–2070. doi: https://doi.org/10.1016/j.jacc.2018.07.099 . Saha, P. C., Faruqe, O., Haque, F., & Park, C. (2023). Preventing Space Charge Accumulation by Incorporating Electrets. Advanced Materials Interfaces, 10(5), 2201046. doi: https://doi.org/10.1002/admi.202201046 . Sanyal, A., & Sinha-Ray, S. (2021). Ultrafine PVDF Nanofibers for Filtration of Air-Borne Particulate Matters: A Comprehensive Review. Si, J., Zhao, M., Marcelle, S. s. a., Wang, Q., Cui, Z., & Liu, X. (2023). Design and Modification of Janus Polyvinylidene Fluoride/Deacetylated Cellulose Acetate Nanofiber Membrane and its Multifunctionality. Advanced Materials Interfaces, 10(11), 2201550. doi: https://doi.org/10.1002/admi.202201550 . Song, Y., Bao, J., Hu, Y., Cai, H., Xiong, C., Yang, Q., et al. (2022). Forward polarization enhanced all-polymer based sustainable triboelectric nanogenerator from oriented electrospinning PVDF/cellulose nanofibers for energy harvesting (10.1039/D2SE00321J). Sustainable Energy & Fuels, 6(9), 2377–2386. doi: 10.1039/D2SE00321J . Sun, Z., Yue, Y., He, W., Jiang, F., Lin, C.-H., Pui, D. Y. H., et al. (2020). The antibacterial performance of positively charged and chitosan dipped air filter media. Building and Environment, 180, 107020. doi: https://doi.org/10.1016/j.buildenv.2020.107020 . Szewczyk, P. K., & Stachewicz, U. (2020). The impact of relative humidity on electrospun polymer fibers: From structural changes to fiber morphology. Advances in Colloid and Interface Science, 286, 102315. doi: https://doi.org/10.1016/j.cis.2020.102315 . Tofail, S. A. M., Lang, S., & Mellinger, A. (2020). Electrets and related phenomena. IEEE Transactions on Dielectrics and Electrical Insulation, 27(5), 1377–1378. doi: 10.1109/TDEI.2020.009249 . Wang, P., Xu, P., Zhou, Y., Yang, Y., & Ding, Y. (2018). Effect of MWCNTs and P[MMA-IL] on the crystallization and dielectric behavior of PVDF composites. European Polymer Journal, 99, 58–64. doi: https://doi.org/10.1016/j.eurpolymj.2017.12.003 . Wang, X., Cui, W., Li, Y., & Liu, Y. Electrospun Electret Fibers for Air Filtration. Separation & Purification Reviews, 1–15. doi: 10.1080/15422119.2023.2283753 . Xu, J., Xiao, X., Zhang, W., Xu, R., Kim, S. C., Cui, Y., et al. (2020). Air-Filtering Masks for Respiratory Protection from PM2.5 and Pandemic Pathogens. One Earth, 3(5), 574–589. doi: https://doi.org/10.1016/j.oneear.2020.10.014 . Yang, X., Pu, Y., Li, S., Liu, X., Wang, Z., Yuan, D., et al. (2019). Electrospun Polymer Composite Membrane with Superior Thermal Stability and Excellent Chemical Resistance for High-Efficiency PM2.5 Capture. ACS Applied Materials & Interfaces, 11(46), 43188–43199. doi: 10.1021/acsami.9b15219 . Zhou, Y., Liu, W., Tan, B., Zhu, C., Ni, Y., Fang, L., et al. (2021). Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4741981","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":337835756,"identity":"3c6605b5-6556-4d97-99c6-cee1a3e37c45","order_by":0,"name":"Ning Yan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuUlEQVRIiWNgGAWjYLCCD1BagmgdjDOABA9JWph5SNJiLpH87LHNn8P29gzMB2/zMNjlEdRiOSPN3Di37XBiDwNbsjUPQ3IxQS0GNxLMpHMbDifwMPCYSfMwHEhsIKwl/Zu0BdBhPAz834jVkmMmzcB2mLGHgYeNSC1n3pRJ9ralJ/YcZjO2nGOQTISW4+nbJH78sbZnb29+eONNhR1hLQwCCVAGM9gEguqBgP8AMapGwSgYBaNgRAMAXCE07YdltP4AAAAASUVORK5CYII=","orcid":"","institution":"Shaanxi University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Ning","middleName":"","lastName":"Yan","suffix":""},{"id":337835757,"identity":"fad315bb-509a-4c3e-b83c-3b8452f3defe","order_by":1,"name":"Ting Gao","email":"","orcid":"","institution":"National Demonstration Center for Experimental Light Chemistry Engineering Education, Shaanxi University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Ting","middleName":"","lastName":"Gao","suffix":""},{"id":337835758,"identity":"162b9658-a0ed-4604-aa61-2c7eb050a250","order_by":2,"name":"Li Hua","email":"","orcid":"","institution":"National Demonstration Center for Experimental Light Chemistry Engineering Education, Shaanxi University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Hua","suffix":""},{"id":337835759,"identity":"44eb5466-da77-4267-9712-8bf8326e681a","order_by":3,"name":"Fan Xie","email":"","orcid":"","institution":"National Demonstration Center for Experimental Light Chemistry Engineering Education, Shaanxi University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Fan","middleName":"","lastName":"Xie","suffix":""},{"id":337835760,"identity":"5d078942-6c96-46c0-a799-6ccee62b1bf6","order_by":4,"name":"Rui-Xin Liu","email":"","orcid":"","institution":"National Demonstration Center for Experimental Light Chemistry Engineering Education, Shaanxi University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Rui-Xin","middleName":"","lastName":"Liu","suffix":""},{"id":337835761,"identity":"5d368265-fe22-49b1-a68d-e0d455ff226a","order_by":5,"name":"Zhao-Qing Lu","email":"","orcid":"","institution":"Shaanxi University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Zhao-Qing","middleName":"","lastName":"Lu","suffix":""}],"badges":[],"createdAt":"2024-07-15 09:48:45","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4741981/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4741981/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":62302858,"identity":"b434e03c-ebce-44bd-b060-18da25b7505a","added_by":"auto","created_at":"2024-08-12 17:15:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":133761,"visible":true,"origin":"","legend":"\u003cp\u003ePreparation process of CA/PVDF electret composite film.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/81ed298c32da96d6c3487add.png"},{"id":62303131,"identity":"d3db751f-06db-46bf-9c03-17ea79c314b8","added_by":"auto","created_at":"2024-08-12 17:23:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":567106,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of (a-e) nanofiber CA, CA/PVDF-10, CA/PVDF-20, CA/PVDF-40, and CA/PVDF-50; (f-j) corresponding fiber diameter analysis.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/4ac30aaf640a0b65383e7570.png"},{"id":62302852,"identity":"75626f4d-6673-4216-b58f-7c00ecec4aff","added_by":"auto","created_at":"2024-08-12 17:15:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":63391,"visible":true,"origin":"","legend":"\u003cp\u003e(a) FTIR spectra and (b) XRD patterns of CA, PVDF, and CA/PVDF composite films.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/76ce0ebabd713feedefc7a1a.png"},{"id":62302854,"identity":"2f8155e6-32d4-4b4f-9715-9148f9b6c3c3","added_by":"auto","created_at":"2024-08-12 17:15:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":124943,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Stress−strain curves; (b) water contact angle of CA film and CA/PVDF composite films.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/a32418235ccd24c3b1e102f7.png"},{"id":62303133,"identity":"8e6a5789-2772-4359-a3c7-277b5a2591e1","added_by":"auto","created_at":"2024-08-12 17:23:10","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":64660,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Surface potential and (b) its decay of CA/PVDF electrospun composite films.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/41a86e8c48178fedd2ba968f.png"},{"id":62302857,"identity":"c0c558c7-4429-4dc8-b184-267a2cbbfe35","added_by":"auto","created_at":"2024-08-12 17:15:10","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":61760,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Surface potential and (b) its decay of CA/PVDF composite films treated by electrospinning and corona charging approaches.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/57977dc7570f3d3e20a53560.png"},{"id":62302859,"identity":"c874522f-c317-43d3-9938-1c63bc00f125","added_by":"auto","created_at":"2024-08-12 17:15:10","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":152103,"visible":true,"origin":"","legend":"\u003cp\u003e(a, d) Filtration efficiency (b, e) quality factor (d, f) air resistance of CA/PVDF films treated by single electrospinning and double electric technique.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/10fef80e5ac4eae6d1ba0d55.png"},{"id":62303132,"identity":"db31175e-aa54-4681-b079-0b77f75d6b72","added_by":"auto","created_at":"2024-08-12 17:23:10","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":85644,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Filtration efficiency of different electric processes (b) Contribution of electrostatic action to filtration efficiency of CA/PVDF-40 composite film.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/db64558a035fd21a17070332.png"},{"id":62302860,"identity":"1a932491-7c19-424c-af4e-733d3f7c85c5","added_by":"auto","created_at":"2024-08-12 17:15:10","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":265622,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Electret enhancement principle of CA/PVDF composite films (b) schematic diagram of filtration mechanism.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/8b3efb3387ba5284b42b3960.png"},{"id":66141385,"identity":"f1875d72-abd6-4dfc-853b-e0dc3cd7cbe8","added_by":"auto","created_at":"2024-10-08 06:24:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2211413,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4741981/v1/80f76f10-0e57-4212-a843-d82a39d9ca7c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Highly electrostatic cellulose acetate-based composite electret nanofiber film for air filtration applications","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn recent years, with the rapid development of the city and the continuous advancement of modern industry, air pollution problems have became increasingly prominent. Aerosol particulate matter (PMs) (Arias-P\u0026eacute;rez et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Berger et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) as the main source of pollution in ambient air, especially lung-accessible particulate matter with aerodynamic equivalent diameter less than 2.5 \u0026micro;m (Anderson, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Andrew and Kathy, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), is prone to carry heavy metals, microorganisms, and the hazardous substances. Its prolonged suspension in the air and inhalation by human can induce respiratory diseases, and increase the risk of lung cancer and cardiovascular diseases (Brook and Rajagopalan, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Rajagopalan et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Landrigan, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), posing a serious threat to public health. Therefore, the development of efficient air filtration materials to effectively isolate airborne particles is an effective method to protect people's health.\u003c/p\u003e \u003cp\u003eElectret filter material can improve the ability to capture particles through Coulombic attraction and electrostatic induction (Xin Wang et al.; Xu et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), and does not increase the air resistance, showing a significant filtration performance especially for particles with a particle size of less than 0.3 \u0026micro;m (Tofail et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sun et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Commonly, the fluoropolymers with C-F bond such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), as well as the non-fluoropolymers such as polyacrylonitrile (PAN), polypropylene (PP) and polystyrene (PS) are employed as the electret air filtration material(Sanyal and Sinha-Ray, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Ahn et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Dai et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Jung et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Eticha et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Attributed to their excellent dielectric properties, charge storage capacity, and hydrophobicity, these polymers can impart the electret material with strong electrostatic adsorption and filtration efficiency. However, the synthetic polymer-based materials are difficult to biodegrade and pollute the ecological environment. Therefore, there is an urgent need to develop a green biomass-based filtration material to replace petroleum-based plastic products and promote environmental sustainable development (Abdur Rahman et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCellulose acetate (CA), one of the first commercial cellulose derivatives, is obtained by esterification of natural cellulose and acid anhydride or acetic acid under the action of catalyst sulfuric acid (Lee et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Because it is derived from natural wood fiber raw materials, it has the advantages of wide source, low cost and good biodegradability. In addition, the esterification modified CA can be dissolved in organic solvents such as N, N-dimethylacetamide (DMAc), acetone, acetic acid, etc. (Majumder et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), and its solution has good flowability and spinnability. Therefore, it is possible to fabricate electret filtration materials using electrostatic spinning technology. However, due to the structural characteristics of CA itself, its weak mechanical strength, poor intrinsic dielectric properties (dielectric constant only 3.5) and strong hydrophilicity will lead to poor charge trapping and storage (Lecoublet et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In order to enhance the electret effect, doping electret nanoparticles (i.e., silica, boehmite, titanium dioxide in nanofibers is proposed (Guliakova et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Lou et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, nanoparticles in the matrix material have the risk of being easily dislodged and agglomerated, and the dislodged nanoscale particles can be a threat to human health(Saha et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ding et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRecently, the all-polymer electret air filtration materials are developed to improve the electret effect while effectively avoiding the problems of agglomeration and shedding of electret nanoparticles in the matrix. Ko et al. prepared all-polymer hybrid electret fibers based on PS and PVDF by electrospinning technology (Ko et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The results showed that the different electron transport capacities of PVDF and PS led to the charges aggregated at the interfacial region, which enhanced the electret effect, leading to a 36% increase in the surface potential and a 12% increase in the filtration efficiency. Meanwhile, PVDF as an electret enhancer, had good compatibility with the base polymer PS, without the risk of detachment. Liu (Liu et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) et al. prepared an electret filtration film with high surface potential of 6.8 KV and excellent filtration efficiency of 99.998%, based on electrospinning method using several polar polymers (i.e., polyacrylonitrile, nylon 6, polyurethane, and PVDF). It can be seen that the use of high polarity polymers as electrostatic enhancers can significantly improve the electret charging and filtration effect of the materials by increasing the interfacial polarization.\u003c/p\u003e \u003cp\u003eIn this paper, an all-polymer electret nanofiber film for air filtration is obtained by electrospinning method assisted with the corona-charging technique, using the biodegradable CA as the base polymer, the highly polar and hydrophobic PVDF as the electrostatic reinforcement. We mainly investigate the morphology, phase structure, surface potential and filtration performance, also the mechanical properties, hydrophobicity of the film are evaluated. Particularly, we focus on the relationship between surface charge and filtration effect, and elucidate the filtration mechanism of CA/PVDF composite film.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eChemicals and Materials\u003c/h2\u003e \u003cp\u003eAll chemicals, including cellulose acetate (CA, Mw\u0026thinsp;=\u0026thinsp;4w, polyvinylidene fluoride (PVDF 5130, Mw\u0026thinsp;=\u0026thinsp;100w) and acetone (Ac, 99%), N, N-dimethylacetamide (DMAc, 99%), were purchased from commercial sources without further processing.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of electret CA/PVDF composite nanofiber film\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003ePreparation of spinning fluid\u003c/h2\u003e \u003cp\u003eA series of electrospinning precursor solutions with different PVDF mass concentrations (0, 10%, 20%, 30%, 40%) were prepared by dissolving CA and PVDF powder in mixed solvent of DMAC and Ac at the given conditions (the solvent mass ratio: 1:1, the solute mass concentration: 10 wt.%). The solutions were stirred continuously at room temperature for 6 hours until completely dissolved to form a homogeneous and transparent spinning solution.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of CA/PVDF electrospun nanocomposite film\u003c/h2\u003e \u003cp\u003eThe above spinning solution was transferred into a 5 ml plastic syringe, and the polymer solution was continuously extruded under the action of the syringe pump. When the solution reached the tip of the metal needle of the syringe, the solution was quickly polarized and highly electrified, and a charged CA/PVDF nanocomposite film was formed through phase separation (Lyu et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Then the prepared films were placed in an oven at 50\u0026deg;C for 3 h to remove the residual solvent. A series of CA/PVDF nanofiber films with PVDF mass concentrations of 0, 10%, 20%, 30%, and 40% were denoted as CA, CA/PVDF-10, CA/PVDF-20, CA/PVDF-30, and CA/PVDF-40, respectively.\u003c/p\u003e \u003cp\u003eThe specific parameters of electrostatic spinning were as follows: spinning voltage\u0026thinsp;=\u0026thinsp;10 KV, flow rate of =\u0026thinsp;mL/h, distance of the metal needle from the receiving rollers\u0026thinsp;=\u0026thinsp;15 cm, spinning time\u0026thinsp;=\u0026thinsp;1-1.5 h. The temperature and humidity in the spinning environment were 30\u0026thinsp;\u0026plusmn;\u0026thinsp;2 ℃ and 40\u0026thinsp;\u0026plusmn;\u0026thinsp;5 RH%, respectively.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eCorona charging treatment of CA/PVDF composite film\u003c/h2\u003e \u003cp\u003eThe corona charging system consisted of a wire electrode and a copper plate receiving electrode. The CA/PVDF composite film was placed on the copper plate, and the distance from the wire electrode to the film was 5 cm, and a voltage of 25 KV was applied to the wire electrode and kept for 5 min, and all experiments were performed with positive voltage polarization. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the preparation process of electret CA/PVDF composite nanofiber film.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eCharacterization and analysis of the materials\u003c/h2\u003e \u003cp\u003eThe surface micromorphology of CA/PVDF composite films was observed by scanning electron microscope (SEM, SU8100, Hitachi, Japan) under an acceleration voltage of 7.0 KV. Fourier transform infrared spectroscopy (FT-IR, Vertex 70, Bruker, Germany) was performed to characterize chemical compositions with a scanning range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The crystal structure of the films was characterized by high-performance X-ray diffractometer (XRD, Bruker, Germany) with a scan rate of 5 \u0026deg;/min and a 2θ range of 10\u0026deg;-50\u0026deg;.\u003c/p\u003e \u003cp\u003eTensile strength tests of samples were conducted by using an AI-700-NGD tensile testing machine (Gotwill Ltd, China) equipped with a 500 N load cell at a loading rate of 1 mm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The water contact angle of samples were investigated by a contact angle measuring instrument (JC2000, Bruker, German) at room temperature. The droplet volume used in the contact angle test was 5 \u0026micro;L.\u003c/p\u003e \u003cp\u003eThe surface potential of the films was measured using a compact handheld electrostatic field meter (FMX-003, Simco ION, Japan). During the test, this device was placed 2.54 cm away from the film to ensure the two LED guide rings coincided. Ten measurements were taken at different locations on each sample to determine the average surface potential. The filtration performance was evaluated by a comprehensive performance test bench (LZC-K1, Suzhou Huada Equipment Co., China). NaCl aerosol particles (measurable particle sizes of 0.3, 0.5, 1.0, 2.0, 5.0, and 10.0 \u0026micro;m) were used in the filter table according to the LZC-K1 manual. The flow rate was 32 L/min with an effective area of around 100 cm\u003csup\u003e2\u003c/sup\u003e. The calculation formula of quality factor (QF) as the comprehensive evaluation index of filter materials is QF\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;ln(1 \u0026ndash; E%) / ΔP, where E% and ΔP are the removal efficiency and pressure drop, respectively.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eMorphology analysis of CA/PVDF composite film\u003c/h2\u003e \u003cp\u003eCA/PVDF composite films with different morphologies were obtained by adjusting the mass concentration of PVDF components. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the surfaces of these composite films were smooth, and they all exhibited a network structure formed by the random distribution of nanofibers. The diameter distribution of the pure CA film was the most concentrated, with an average diameter of 730\u0026thinsp;\u0026plusmn;\u0026thinsp;5 nm. After the addition of PVDF, the viscosity of the spinning solution increased, the intermolecular interaction force was enhanced, and the fiber filaments were stretched with a larger resistance under the same electric field force, so that the average diameters of the prepared fibers showed a tendency to increase (i.e., 780\u0026thinsp;\u0026plusmn;\u0026thinsp;5 nm, 790\u0026thinsp;\u0026plusmn;\u0026thinsp;6 nm, 880\u0026thinsp;\u0026plusmn;\u0026thinsp;160 nm, 890\u0026thinsp;\u0026plusmn;\u0026thinsp;80 nm). When the mass concentration of PVDF was increased to 50%, the spinning solution was more viscous, which made it easy to block the needle and the spinning process difficult to carry out, and the spun fibers showed uneven thickness and large adhesions state. Within the limit of spinnable concentration (mass concentration of PVDF\u0026thinsp;\u0026le;\u0026thinsp;40%), the fiber film with a larger fiber diameter has a smaller surface area, which is conducive to reducing air friction and filtration resistance (Kim et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eChemical structure characterization of CA/PVDF composite films\u003c/h2\u003e \u003cp\u003eThe chemical structures of CA, PVDF, and CA/PVDF-40 fiber films were characterized using FTIR and XRD, and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The infrared spectra showed that the CA/PVDF-40 film had a stretching vibration absorption peak of the -C\u0026thinsp;=\u0026thinsp;O bond of CA at 1742 cm and a stretching and bending vibration peak of the C-F bond of PVDF at 763 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1233 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Zhou et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Bastida et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Meanwhile, in the CA/PVDF-40 composite film, the fluorine atoms of PVDF formed hydrogen bonds with the -OH of CA, so compared with the pure CA film, the -OH absorption peak at 1640 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was weakened to almost completely disappear(Si et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These indicate that PVDF was successfully compounded onto the CA film.\u003c/p\u003e \u003cp\u003eIn the XRD pattern of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b), the bulky acetyl group replacing the hydroxyl group in the CA disrupts the hydrogen-bonding network structure of cellulose, which results in a low crystallinity and does not show any obvious diffraction peaks. The PVDF powder has three characteristic peaks at 2θ of 18.27\u0026deg;, 19.7\u0026deg;, and 20.3\u0026deg;, which corresponds to the (100) and (020) diffraction peaks of the nonpolar α-phase, and (110) diffraction peaks of the polar β phase, respectively (Janakiraman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, the diffraction peaks of α-phase disappeared in CA/PVDF composite films, only the diffraction peaks of β-phase were retained, and the (110) diffraction peaks were broadened. This was because the dipoles in PVDF were aligned under the action of applied electric field and mechanical tension, which promoted the conversion of non-polar α-phase to the polar β-phase (Bui et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). With the increase of PVDF content, the (110) crystal surface strength increased significantly, i.e., the content of the polar phase in the composite film increased. All the above information indicated that PVDF enhanced the polarity of the composite film, which was conducive to the efficient trapping of dipole charge, thus increasing the surface charge density of the film (Du et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Song et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e\u003cem\u003eMechanical properties and hydrophobicity of CA/PVDF composite films\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eThe mechanical strength of fiber composite film directly affects its practical application effect. The stress-strain curves of the CA and CA/PVDF films were presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a). It could be seen that the tensile strength of CA film is only 2.8 MPa, and the elongation at break is only 2.99%. However, with the increase of PVDF content, the tensile strength, elongation, and toughness of the composite film all showed an increasing trend, which was attributed to the formation of more hydrogen bonding structure between -OH in the CA molecular chain and -F atoms in PVDF (Si et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Szewczyk and Stachewicz, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Obviously, the CA/PVDF composite film has better comprehensive mechanical properties compared with pure CA film.\u003c/p\u003e \u003cp\u003eMoisture is another important key factor affecting the filtration performance, especially for electret materials. The hydrophilic hydroxyl group on CA increases the conductivity of the film and accelerates the carrier migration rate, resulting in increased charge dissipation, which decreases the filtration efficiency (Szewczyk and Stachewicz, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The surface wettability of the composite film was analyzed in this study, and the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b). The C-F bond of PVDF makes PVDF possess lower surface energy and stronger hydrophobicity. Thus, the addition of PVDF will increase the water contact angle of CA film, and when its content is 40%, the contact angle reaches 142.3\u0026deg;.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetailed parameters of mechanical properties of CA/PVDF composite films\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTensile strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eElongation (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYoung's modulus (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eToughness (MJ/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure CA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e204.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.055\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCA/PVDF-10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e337.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.026\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCA/PVDF-20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e23.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e91.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCA/PVDF-30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e22.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e89.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCA/PVDF-40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e85.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eSurface potential of CA/PVDF composite films\u003c/h2\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003eSurface potential of CA/PVDF electrospun composite films\u003c/h2\u003e \u003cp\u003eDuring the electrostatic spinning process, the syringe tip is connected to the positive pole of the power supply, and its charge is basically used to stretch the spinning droplets and form nanofibers, so there is less residual positive charge (space charge) on the sample surface. Therefore, the surface potential of the composite film is mainly determined by the new polarized negative sites formed by the orientation of the PVDF dipoles under the external electric field, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a). With the increase of PVDF content, the surface potential becomes larger and achieves a maximum value of -2.73 KV at 40% PVDF content, which is 58.1% higher than of the pure CA film (-1.15 KV). This is due to the fact that the increase in PVDF content increases the content of the polar β-phase, which generates more dipole charges under the action of the electric field.\u003c/p\u003e \u003cp\u003eWe evaluated the electrostatic charge decay of electrospun CA/PVDF composite film within 180 min. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b), the greatest decay of charges appeared within the initial 40 min. This noticeable decay of charge is mainly caused by the escape of charges existing in shallow traps and is easily affected by the neutralization of the opposite charge generated by the PVDF dipoles (Catalani et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The slow decay in 40\u0026thinsp;~\u0026thinsp;140 min is due to the segmental depolarization of directional dipoles caused by molecular thermodynamic movement (Eisenmenger et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) Eventually, a stable dipole charge is left, thus maintaining the long-term stability of the surface potential (Lovera et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). When the surface potential of the composite film tends to be stable, CA/PVDF-40 has the highest surface potential of -0.63 KV, which is 58.73% higher than that of the pure CA film. This is due to CV/PVDF composite film with high PVDF content has more dipole charges and better charge stability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSurface potential of CA/PVDF electrospun composite films treated by corona charging\u003c/h2\u003e \u003cp\u003eThe initial surface potentials of CA/PVDF films treated by double charging approaches, i.e., the electrospinning and corona charging, are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a). The discharge tip is connected to the positive pole of the power supply, the positive ions formed by ionization of the air are deposited on the fiber surface under the electric field, which neutralizes the negative dipole charge in the original electrospun film. The space charge dominates in the continuous charging process, so the fiber film shows positive electrical properties. In addition, due to the different conductivity of CA and PVDF, the electron transport process in the film is hindered under the action of the external electric field and accumulates at the interface of the two (Ko et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Therefore, the initial surface potential of the film treated by double charging methods increases with the increase of PVDF content.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (b) showed the decay curves of the surface potential of the CA/PVDF electrospun composite films treated by corona charging within 180 min. The positive ions in the surface traps of the CA/PVDF composite films gradually escaped with time, and the stable dipole charge remained within the composite films, so that the fiber films ultimately became electronegative. When the surface potential of the film by two means of charging tends to be stable, the surface potential of CA/PVDF-40 sample is the highest at -0.78 KV, which is 71.8% higher than that of the pure CA film and 19.23% higher than that of the singe electrospining CA/PVDF-40 film (0.63 KV) in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b). That's because the charging voltage of corona charging is larger than the electrospining voltage, the content of polar β-phase in PVDF increases with the increase of the electret voltage, and there are more dipole charges in the film. Therefore, the double electric process is more conducive to increasing the surface potential of the film than the single electrostatic spinning process (Oh et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eComprehensive filtration performance of CA/PVDF composite films\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the filtration efficiency, quality factor and filtration resistance of CA/PVDF films treated by single electrospinning and double electric technique for PMs of different particle sizes at room temperature. The specific values of filtration efficiency of CA/PVDF-40 composite films under two electric processes shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e are obtained from Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. It can be seen that the filtration efficiency of CA/PVDF composite films for different sizes of particles under two kinds of electric processes shows a certain upward trend with the increase of PVDF content (i.e., the surface potential of the composite film). This upward trend is most obvious in the filtration of PM 0.3, followed by PM 0.5, and is least sensitive to PM 1.0. That's because the filtration of small particles (diameter between 0.05\u0026thinsp;~\u0026thinsp;0.5 \u0026micro;m) mainly relies on electrostatic adsorption, while the filtration of particles larger than 1 \u0026micro;m mainly relies on mechanical interception (Xu et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Ji et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Meanwhile, it can also be observed from the figure that compared with the single electrospinning, the filtration efficiency of the double electric composite film for PM 0.3 and PM 0.5 was improved by 5.41% and 3.37%, respectively, with more efficient filtration effect. The pressure drop of the composite films under different electric processes were approximately 90 Pa, indicating that the electric method did not significantly affect the filtration resistance of the fiber film.\u003c/p\u003e \u003cp\u003eIn addition, the comprehensive filtration performance of the materials was evaluated using the Quality Factor (QF). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b) and (e), under these two electric process, the QF for PM 0.3 increased the most with the change of PVDF content, which shows that electrostatic adsorption played a key role in the filtration of small particulate matter.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFiltration efficiency of pure CA film, CA/PVDF-40 composite film under different electric processes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eElectric method\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eFiltration efficiency\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eThe increase of the filtration efficiency**\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePM 0.3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePM 0.5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePM 1.0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePM 0.3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePM 0.5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ePM 1.0\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSingle electrospinning\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e92.01%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e95.17%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e99.16%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.02%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e14.49%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.36%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDouble electric technique*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e97.27%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e98.45%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e99.39%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22.04%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e17.67%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.19%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e*Double electric technique refers to the electrospinning and corona charging approaches. **The increase of the filtration efficiency is compared to that of the pure CA film.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eContribution of electret effect on filtration performance\u003c/h2\u003e \u003cp\u003eTo further clarify the contribution of the electrostatic effect to the overall filtration efficiency, the CA/PVDF-40 composite film was immersed in isopropyl alcohol to eliminate the charge. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a), the mechanical filtration efficiency of the composite films for PM 0.3, PM 0.5, and PM 1.0 were 64.73%, 72%, and 93.74%, respectively, the filtration efficiency of the films were substantially improved after charging and the double electric process was more conducive to the preparation of efficient electret air filtration materials. The contributions of different electret methods to the electrostatic effect in CA/PVDF-40 composite films were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e (b). The contributions of electrostatic action to PM 0.3, PM 0.5, and PM 1.0 filtration efficiency were 29.64%, 24.49%, and 5.52% in the electrospinning process, and 34.59%, 28.28%, and 6.69% in the composite electret for the PM 0.3, PM 0.5, and PM 1.0 filtration efficiency, respectively. It can be seen that the double electric process is more favorable to the filtration efficiency of the composite film, and the electrostatic effect on PM 0.3, PM 0.5 and other small particles is better, on PM 1.0 is limited.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eFiltration mechanism of electret CA/PVDF Composite film\u003c/h2\u003e \u003cp\u003eThe mechanism of CA/PVDF electret composite film for capturing the particulate pollutants is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. Under the double electric process of electrostatic spinning and corona charging, the crystal cell structures of PVDF are spontaneously polarized under the electric field, and their nonpolar α-phase can be transformed into polar β-phase, so the overall dipole moment of the composite film becomes larger, and the polarization charge increases (Ping Wang et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In addition, more space charge is captured at the interface of the two phases of CA and PVDF, which finally endows the CA/PVDF film with a high electrostatic charging effect. For charged particles, there is a Coulomb force between them when they are close to the fiber film, and the charged particles are adsorbed (Xu et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For the electrically neutral particles, when they are close to the fiber film, the electric field on the surface of the film induces the formation of an opposite electric field on the surface of the particles, which is then adsorbed and captured by the fiber film (Xin Wang et al.). Therefore, through Coulombic attraction and electrostatic sensitivity, electret CA/PVDF composite films are highly effective in capturing charged and uncharged particles with diameters less than 0.3 \u0026micro;m (Sun et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eHighly electrostatic CA/PVDF composite electret filtration films were prepared by dual electric approaches of electrostatic spinning and corona charging using CA as the matrix and PVDF as the electret enhancer. Under the dual electric field, the surface potential of CA/PVDF electret film was greatly increased (2.146 KV). Moreover, the composite film showed excellent filtration performance, i.e., with filtration efficiency for PM 0.3 was 97.27% without increasing the pressure drop (~\u0026thinsp;88.7 Pa, comparable to that of the CA film). The hydrophobicity and mechanical properties of the composite films were also improved. The work provides a new solution in design and development environmentally friendly cellulose-based composite electret filtration films.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNY, LH, FX and ZL made substantial contributions to the conception and design of the work and approved the version to be published, agreeing to be accountable for all aspects of the work in ensuring that questions related to the accuracy and integrity of any part of the work are appropriately investigated and resolved. TG: acquisition, analysis, interpretation of data, Writing-origrinal draft. RL and TG: Data curation, Writing-origrinal draft.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Open Foundation of Key Laboratory of Auxiliary Chemistry and Technology for Chemical Industry, Ministry of Education, Shaanxi University of Science and Technology (No. KFKT2023-06), Shaanxi Collaborative Innovation Center of Industrial Auxiliary Chemistry and Technology, Shaanxi University of Science and Technology (No. KFKT2023-06), and National Nature Science Foundation of China (No. 22378248).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData are available upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have given approval to the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors state that they adhere to the Ethical Responsibilities of Authors. In addition, this article does not contain any studies with human participants or animals performed by any of the author.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorresponding Author:\u0026nbsp;Ning Yan, Zhao-Qing Lu\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbdur Rahman, M., Haque, S., Athikesavan, M. M., \u0026amp; Kamaludeen, M. B. (2023). A review of environmental friendly green composites: production methods, current progresses, and challenges. 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Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Cellulose acetate, Polyvinylidene fluoride, Electret filtration, Surface potential, Corona charging, Electrostatic spinning","lastPublishedDoi":"10.21203/rs.3.rs-4741981/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4741981/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHighly electrostatic cellulose acetate (CA)-based electret film for air filtration was fabricated by electrospinning method assisted with the corona-charging technique in this work. The highly polar and hydrophobic polyvinylidene fluoride (PVDF) was chosen as the electrostatic reinforcement. The results showed that under the dual electric fields, the dipole charges generated from the conversion from non-polar α-phase to polar β-phase of the dipole inside PVDF and the space charge captured at the phase end traps of CA and PVDF give CA/PVDF films high static electricity. Especially, the composite film with 40 wt% PVDF exhibited an ultrahigh surface potential of 2.146 KV and excellent filtration efficiency of 97.27% for PM 0.3 with a pressure drop of only 88.7 Pa, which was 29.68% and 22.04%, respectively higher than that of pure CA film. It was noticed that the hydrophobicity and mechanical strength were also improved.\u003c/p\u003e","manuscriptTitle":"Highly electrostatic cellulose acetate-based composite electret nanofiber film for air filtration applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-12 17:15:05","doi":"10.21203/rs.3.rs-4741981/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7e0fb1fc-620d-4dbe-96dc-2abfab499b05","owner":[],"postedDate":"August 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-10-08T06:23:44+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-12 17:15:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4741981","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4741981","identity":"rs-4741981","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}