Performance Factors for Filtration of Air Using Cellulosic Fiber-based Media: A Review
Abstract
The filtration of air has attracted increasing attention during recent waves of viral infection. This review considers published literature regarding the usage of cellulose-based materials in air filtration devices, including face masks. Theoretical aspects are reviewed, leading to models that can be used to predict the relationship between structural features of air filter media and the collection efficiency for different particle size classes of airborne particulates. Collection of particles can be understood in terms of an interception mechanism, which is especially important for particles smaller than about 300 nm, and a set of deterministic mechanisms, which become important for larger particles. The effective usage of cellulosic material in air filtration requires the application of technologies including pulp refining and chemical treatments with such additives as wet-strength agents and hydrophobic sizing agents. By utilization of high levels of refining, in combination with freeze drying and related approaches, there are opportunities to achieve high levels of interception of fine particles. A bulky layer incorporating nanofibrillated cellulose can be used in combination with a coarser ply to achieve needed strength in a filter medium. Results of recent research show a wide range of development opportunities for diverse air filter devices containing cellulose.
... The primary filter media used for purifying the intake air of modern internal combustion engines, indoor air quality, and the air inhaled by humans through masks predominantly consist of cellulose-based fibrous materials [39,40]. ...
The purpose of this study was to empirically evaluate the performance of fibrous materials that meet the criteria for inlet air filtration in internal combustion engines. The characteristics of filtration efficiency and accuracy, as well as the characteristics of flow resistance, were determined based on the mass of dust accumulated in the filter bed during the filtration process. Single-layer filter materials tested included cellulose, polyester, and glass microfiber. Multilayer filter media such as cellulose–polyester–nanofibers and cellulose–polyester were also examined. A new composite filter bed—consisting of polyester, glass microfiber, and cellulose—and its filtration characteristics were evaluated. Utilizing specific air filtration quality factors, it was demonstrated that the composite is characterized by high pre-filtration efficiency (99.98%), a short pre-filtration period (qs = 4.21%), high accuracy (dpmax = 1.5–3 µm) for the entire lifespan of the filter, and a 60–250% higher dust absorption coefficient compared to the other tested materials. A filtration composite bed constructed from a group of materials with different filtration parameters can be, due to its high filtration efficiency, accuracy, and dust absorption, an excellent filter material for engine intake air. The composite’s filtration parameters will depend on the type of filter layers and their order relative to the aerosol flow. This paper presents a methodology for the selection and testing of various filter materials.
... Cellulose-based fiber filter media are widely used in the air filtration systems of modern vehicle and machine drive engines and for indoor air filtration [25,35]. Cellulose filter media, whose structure is formed by fibers with diameters of 10-20 µm, are characterized by high durability compared to some other filter materials. ...
Experimental evaluation of the properties of filter materials in the selection of material for filtration of inlet air of internal combustion engines was carried out. The filtration characteristics were determined: filtration efficiency and accuracy, as well as flow resistance depending on the dust mass load. Filter materials based on cellulose, polyester, microfiber glass, and cotton and polyester nonwoven beds were studied. Two filter beds consisting of three base filter materials were designed: composite K1 (polyester-microglass-cellulose) and composite K2 (cellulose-microglass-cellulose), and their characteristics were performed. The air filtration quality factor was used to analyze the test results. The coefficient of filtration efficiency was defined, showing the effect of the preliminary stage on the total time of the filtration process. It was shown that the K1 composite has high (dpmax = 1.5÷3 µm) filtration accuracy, high initial filtration efficiency (99.8%), which shortens the pre-stage, and extends to 96-98% the duration of the main stage of the filtration process. The K1 composite obtained more than twice the mass loading of dust (kdK1 = 148,9 g/m2), which will allow the vehicle's mileage to be extended.
... Furthermore, it allows estimating an expected range of values for the measured data, making it possible to generate immediate alarms if the deviation from the estimates is higher than a limit value. Thanks to continuous data acquisition, it is possible to monitor the trends in the measured values, correlating them to the possible failures potentially affecting the plant [2,55,56]. In particular, the filter condition is estimated based on the difference in the values measured at consecutive measurement periods (see Table 8). ...
This study deals with the development of a digital twin for monitoring the operating conditions of a cyclone bag filter installed on the suction system of a wheat mill. The model aims to be used for fault identification and real-time prediction of the remaining useful life (RUL). Computational fluid dynamics simulations were performed to characterize in detail the fluid-dynamic behavior of the airflow inside the system under different conditions of filter sleeve clogging. Furthermore, the simulation results were used to identify a location for the installation of a new velocity sensor that would allow, together with the pressure drop measured at the ends of the filter, monitoring of the systems’ conditions. A model able to assess the filter’s operating state, identify failure events or operating anomalies, and make a prediction of the RUL was then developed. A possible implementation of the developed model, based on the simulation results that aimed to optimize the management of the sleeve cleaning cycles was also proposed. The developed digital model was then tested on a working cycle lasting one year, in which a sleeve failure was simulated. It was shown how the simultaneous monitoring of the two identified quantities allows for the correct identification of the failure and the accurate prediction of the RUL.
The dissipation of charges by aging or under the effect of humid conditions considerably impedes a broader utilization of electrostatic fields in aerosol filtration. This study introduces a respiration‐driven air filter (RAF) that continuously generates triboelectric charges within a pair of tribolayers, which facilitates a sustained filtration performance. Such system is integrated in a multilayer unit that is inserted in personal protective equipment (RAFM) to efficiently capture, sense, and degrade airborne pollutants with no need for external power sources. The triboelectric nanogenerator‐based RAF continuously replenishes static charges and maintains an electrostatic field through breathing by the effect of contact‐electrification between two cellulose‐based tribolayers: a cellulose/metal organic framework cryogel (electron donor) and a cellulose–based electrospun membrane (electron acceptor). Notably, the triboelectric field of the RAF's tribolayer pair substantially enhances both the filtration efficiency (up to 93.8% for 0.3 µm particulate matter) and sensing/catalytic degradation (ammonia; degradation >20%). When integrated in a circuit module, the RAFM effectively monitors respiration dynamics, acting as a breathing indicator/regulator. Overall, this study adds to the promise of tribogeneration through cellulose‐based materials and its application in exposure‐risk operations.
Dialdehyde cellulose (DAC) has garnered substantial scientific interest, thanks to broad spectrum of possible chemical reactions offered by the aldehyde moieties in its backbone. In the present review, we have recapitulated the state-of-the-art knowledge on the synthesis and physicochemical properties of DAC. The review also encompasses DAC derivatives obtained by blending, grafting and crosslinking with molecules and/or polymers that has been engineered into diverse architectures (e.g. conjugates, nanoparticles, microspheres, hydrogels etc.). The prospects of the resulting DAC products in biomedical sectors such as wound healing, drug delivery, tissue engineering etc. is discussed eloquently. Besides focusing on the pharmaceutical applications of DAC; this review also aims to provide an overview on the recent advances of DAC as a functional material in environmental and energy sectors. Integrating the academic and technological knowledge of DAC can further pave the path towards the development of novel DAC-based functional materials in a scalable and sustainable way.
Graphical abstract
Paper, nanocellulose, and other polysaccharide-based materials can be excellent candidates for food packaging barrier layers, except that they tend to be vulnerable to moisture. This article reviews published research describing various chemical treatments having the potential to render hydrophobic character to such layers. Emphasis is placed on systems in which hydrophobic monomers are used to treat either particles or sheets comprised largely of polysaccharides. A goal of this review is to identify combinations of materials and procedures having promise for scale-up to industrial production, while providing effective resistance to moisture. The idea is to protect the underlying polysaccharide-based barrier layers such that they can continue to impede the transfer of such permeants as oxygen, greases, flavor compounds, and water vapor. A further goal is to minimize any adverse environmental impacts associated with the treatments. Based on the research articles considered in this review, promising hydrophobic treatments can be achieved involving silanes, ester formation, other covalent interactions, plasma treatments, and to some extent by various treatments that do not require formation of covalent bonds. The article is designed such that readers can skip ahead to items of particular interest to them.
Face masking proved essential to reduce transmission of COVID-19 and other respiratory infections in indoor environments, but standards and literature do not provide simple quantitative methods for quantifying air leakage at the face seal. This study reports an original method to quantify outward leakage and how wearing style impacts on leaks and filtration efficiency. The amount of air leakage was evaluated on four medical masks and four barrier face coverings, exploiting a theoretical model and an instrumented dummy head in a range of airflows between 30 and 160 L/min. The fraction of air leaking at the face seal of the medical masks and barrier face coverings ranged from 43% to 95% of exhaled air at 30 L/min and reduced to 10–85% at 160 L/min. Filter breathability was the main driver affecting both leak fraction and total filtration efficiency that varied from 5% to 53% and from 15% to 84% at 30 and 160 L/min, respectively. Minor changes were related to wearing style, supporting indications on the correct mask use. The fraction of air leaking from medical masks and barrier face coverings during exhalation is relevant and varies according to design and wearing style. The use of highly breathable filter materials reduces air leaks and improve total filtration efficiency.
The course of the papermaking process, as it occurs on a Fourdrinier machine, is analysed to illustrate how each functional operation performed by the machine influences the final product. The analysis starts with the role played by the slice and its approaches and special emphasis is given to the many compromising factors that determine holey roll design and behaviour. The effect of slice design on orientation, flocculation and jet delivery is also considered. It is shown that the concept of a fibre network structure for the stock with a strength that varies with fibre consistency, length and type explains many of the observations. The distinction between macro- and microformation is defined and the relative effects of the head box and table suction on these properties are illustrated. It is concluded that gross relative motion of stock on the wire is detrimental to macroformation, but that short range relative motion is beneficial to microformation and results in a more uniform fibre distribution than is possible by random turbulent diffusion processes in the head box alone. The variation of sheet properties across the sheet thickness are discussed and it is concluded that selective filtration that occurs during the forming operation is the principal cause, not the backwashing of the sheet by inflow of water at table rolls, as is, frequently reported. A brief speculation on the construction of the `idealised’ machinemade paper sheet is presented.
Water-based epoxy resin emulsion was prepared by emulsifying o-cresol formaldehyde epoxy resin with self-emulsified epoxy curing agent synthesized in this study and then used as an environmentally friendly binder for automotive air filter paper. The preparation process of the self-emulsified epoxy curing agent was confirmed by Fourier transform infrared spectroscopy (FTIR). The effects of neutralization degree (Neu) and amount of curing agent on the formation of epoxy resin emulsion were studied. The micro-morphology and size distribution of the epoxy resin latex were characterized by transmission electron microscopy (TEM) and dynamic and static light scattering, respectively. The micro-structure of the air filter paper surface was studied by scanning electron microscope (SEM). The mechanical strength and moisture-resistance properties of air filter strengthened by the prepared water-based epoxy resin emulsion was tested and compared to three commercial binders. The prepared epoxy resin emulsion greatly enhanced the mechanical properties and moisture-resistance properties of the air filter paper while maintaining its filtration properties. Therefore, the epoxy resin emulsion can be used as an environmentally friendly water-based binder for automotive air filter paper with excellent comprehensive properties.
Green and biodegradable cellulose filters with controlled designer pore structures were prepared using organic solvent-based freeze casting. In this paper, the relationship between the different freeze media, including ethanol, isopropanol, and tertiary-butyl alcohol, and the microstructure of the porous filters was investigated. The results of the pore size distribution indicated that the pore channel size decreased remarkably when organic solvents were used as the freezing media. Moreover, the filters showed high filtration efficiencies, up to 99.70% and 99.66% for 0.5 µm and 0.3 µm particles, respectively, under a pressure drop of 180 Pa and at 32 L·min-1 flow rate. The fabrication of cellulosic filters would not only make it a promising candidate for capturing fine particulate matter, but also provide a versatile approach to regulate and design a porous structure for materials applied in various fields.
Wearable electronics with high-efficiency particulate matters (PMs) filtration and real-time respiratory monitoring offer everyone the opportunity to own a personal healthcare system. However, the power supply, breathability, and filtration performance of wearable electronics still have many challenges that need to be overcome. Herein, a self-powered air filter based on a respiration-driven triboelectric nanogenerator (R-TENG) was integrated with facemask for efficiently filtering submicron particles and respiration monitoring. The conductive cellulose aerogel/MOF composite, regarded as filtration and triboelectric material, was designed by in-situ and green synthesis method. The R-TENG was fabricated using conductive cellulose aerogel/MOF composite and polyvinylidene fluoride (PVDF) film as positive and negative triboelectric materials, respectively. Enabled by its desirable porous network structure and unique electricity generation feature, the air filter is capable of removing PM1.0 and PM0.5 and PM0.3 with high efficiency of 98.4%, 97.3% and 95.0%, while maintaining a relatively low pressure drop of 86 Pa. Moreover, the air filter system can monitor breathing status without using an external power supply for disease prevention and medical diagnosis. This work designs a self-powered mask filter based on conductive cellulose aerogel/MOF composite with both PMs filtration and respiratory monitoring capabilities, which has excellent potential for air purification and healthcare applications.
In the present work, for the first time plasticized poly(vinyl alcohol) (PVA)/nanofibrillated cellulose (NFC) based biocomposite was crosslinked by citric acid (CA) using subcritical water/CO2 process. Presence of sufficient number of ‐OH groups in the backbone of plasticized PVA (p‐PVA) helps to form H bonding with SC‐NFC, which significantly improves the mechanical property of the biocomposite. Further, crosslinking of the same biocomposite helps to achieve hydrogel with superior modulus than that of PVA hydrogel alone. In subcritical medium, plasticized poly(vinyl alcohol)/nanofibrillated cellulose based biocomposite powder gets melted, fused and cross‐linked in a single step process to develop such hydrogel. Crosslinked plasticized poly(vinyl alcohol)/nanofibrillated cellulose based biocomposites were fully characterized in terms of gel content, thermal and chemical properties, morphology, swelling behavior and rheology. Excellent water swollen property, cellular structure and high storage modulus establish the potential of prepared biocomposite based hydrogels for several biomedical applications.
Worldwide, fungal contamination of water resources has become a major threat to both human health and the environment. The adaptation of nanotechnology in conventional water processes is significant to offer new breakthroughs in water treatment, especially fungal contaminants. Chitosan conjugated metal oxide nanoparticles can affect the antimicrobial properties of cellulosic foam. In the present study, three different types of biocompatible nanoconjugates (i.e., ZnO/chitosan, CuO/chitosan, and Ag2O/chitosan) were synthesized for functionalization of five differently processed cellulose foam filters for resisting fungal spores during water treatment. To evaluate the antifungal effect of these nanoconjugates against prevalent strains of Aspergillus niger (A. niger), Aspergillus flavus (A. flavus), and Rhizopus oryzae (R. oryzae), the stable coating was introduced on different cellulose filter papers through impregnation. The statistical analysis of antifungal experiment was carried out by two-way factorial ANOVA test. Cellulose filter containing ZnO/chitosan displayed a stronger antifungal behavior in disc diffusion method than those impregnated with CuO/chitosan, and Ag2O/chitosan composites. Besides the choice of nanoconjugates, the variation in cellulose foam filters (in terms of concentration of their raw materials and/or processing methodology) can also affect their antifungal performance. Further, the assessment of cytotoxic nature of such nanocomposites-modified cellulose foam filters is a fundamental step towards their real field applications.
COVID-19 is caused via the SARS-CoV-2 virus, a lipid-based enveloped virus with spike-like projections. At present, the global epidemic of COVID-19 continues and waves of SARS-CoV-2, the mutant Delta and Omicron variant which are associated with enhanced transmissibility and evasion to vaccine-induced immunity have increased hospitalization and mortality, the biggest challenge we face is whether we will be able to overcome this virus? On the other side, warm seasons and heat have increased the need for proper ventilation systems to trap contaminants containing the virus. Besides, heat and sweating accelerate the growth of microorganisms. For example, medical staff that is in the front line use masks for a long time, and their facial sweat causes microbes to grow on the mask. Nowadays, efficient air filters with anti-viral and antimicrobial properties have received a lot of attention, and are used to make ventilation systems or medical masks. A wide range of materials plays an important role in the production of efficient air filters. For example, metals, metal oxides, or antimicrobial metal species that have anti-viral and antimicrobial properties, including Ag, ZnO, TiO2, CuO, and Cu played a role in this regard. Carbon nanomaterials such as carbon nanotubes, graphene, or derivatives have also shown their role well. In addition, natural materials such as biopolymers such as alginate, and herbal extracts are employed to prepare effective air filters. In this review, we summarized the utilization of diverse materials in the preparation of efficient air filters to apply in the preparation of medical masks and ventilation systems. In the first part, the employing metal and metal oxides is examined, and the second part summarizes the application of carbon materials for the fabrication of air filters. After examination of the performance of natural materials, challenges and progress visions are discussed.