Fabrication of Poly(lactic acid) filter media via the meltblowing process and their filtration performances: A comparative study with polypropylene meltblown

Two-Dimensional Piezoelectric Nanofibrous Webs by Self-Polarized Assembly for High-Performance PM0.3 Filtration

Particulate matter (PM) pollution has posed a serious threat to public health, especially the global spread of infectious diseases. Most existing air filtration materials are still subjected to a compromise between removal efficiency and air permeability on account of their stacking bulk structures. Here, we proposed a self-polarized assembly technique to create two-dimensional piezoelectric nanofibrous webs (PNWs) directly from polymer solutions. The strategy involves droplets deforming into ultrathin liquid films by inertial flow, liquid films evolving into web-like architectures by instantaneous phase inversion, and enhanced dipole alignment by cluster electrostatics. The assembled continuous webs exhibit integrated structural superiorities of nanoscale diameters (∼20 nm) of the internal fibers and through pores (∼100 nm). Combined with the wind-driven electrostatic property derived from the enhanced piezoelectricity, the PNW filter shows high efficiency (99.48%) and low air resistance (34 Pa) against PM0.3 as well as high transparency (84%), superlight weight (0.7 g m-2), and long-term stable service life. This creation of such versatile nanomaterials may offer insight into the design and upgrading of high-performance filters.

Infrastructure in the Age of Pandemics: Utilizing Polypropylene-Based Mask Waste for Durable and Sustainable Road Pavements

When navigating the environmental exigencies precipitated by global pandemics, the escalation of mask waste presents a multifaceted dilemma. In this avant-garde research, we unveil a novel approach: harnessing the sterilized shredded mask residues (SMRs), predominantly composed of 100 wt. % polypropylene, as pioneering modifiers for asphalt. Distinct proportions of SMR (e.g., 3, 6, and 9 wt. %) were judiciously integrated with fresh-virgin base AP-5 asphalt and subjected to an extensive suite of state-of-the-art examinations, encompassing thin-layer chromatography-flame ionization detection (TLC-FID), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and specific rheological metrics. The TLC-FID diagnostic trajectories highlighted the nuanced rejuvenating influence of SMR on the binder, a facet reinforced by a pronounced elevation in the thermodynamic stability index (IC). The FT-IR spectra elucidated SMR's preeminent role as a filler, negating notions of chemical reactivity. The TGA analyses unveiled an elevated thermal onset of degradation, signposting enhanced thermal resilience, whereas the DSC readings illuminated a superior thermal comportment at lower extremities. The SEM evaluations rendered a clearer panorama: there was heightened textural perturbation at escalated SMR incorporations, yet the 3 wt. % concoction showcased an optimal, coherent microtexture symbiosis with asphalt. The rheological scrutinies revealed a systematic trajectory: a diminishing penetration and ductility countered by ascending softening points and viscosity metrics. The coup de maître stemmed from the DSR analyses, unequivocally validating SMR's unparalleled prowess in curtailing rutting distress. This seminal inquiry not only posits a blueprint for refined pavement longevity but also champions a sustainable countermeasure to pandemic-propelled waste, epitomizing the confluence of environmental prudence an d infrastructural fortitude.

Preparation of fluffy bimodal conjugated electrospun poly(lactic acid) air filters with low pressure drop

Electrospun nanofiber membranes have been extensively studied as air filters. However, their limited filtration efficiency for submicron inhalable particulate matter (PM), high resistance to filtration, and limited capacity to hold dust have hindered their widespread use. The majority of materials come from petroleum, and the use of organic solvents during the spinning process has a significant negative impact on the environment. In this work, a sustainable method has been proposed for producing filters using poly(lactic acid) (PLA) with a bimodal diameter distribution through conjugated electrospinning. This technique allows for the continuous production of interconnected micro/nano hybrid porous membranes, resulting in reduced resistance and improved dust holding capacity. The filtration efficiency, pressure drop, long-term filtration performance, and actual performance of the conjugated bimodal membrane (CBM) were extensively investigated. The results indicate that the filter has a high capacity for retaining particles, with filtration efficiencies of 99.94% for PM 0.3 and 99.96% for PM 2.5. It also demonstrates a high quality factor (0.078 Pa-1 for PM 0.3 and 0.084 Pa-1 for PM 2.5), long-term stability (a decrease of 2.35% for PM 0.3 and 0.05% for PM 2.5 over a period of 60 days) and outstanding dust holding capacity (9.17 g m-2). The conjugated bimodal membrane (CBM) shows a 22.64% decrease in resistance compared to the non-conjugated bimodal membrane (BM). In general, the approach outlined in this work provides valuable insights into the development of high-performance biodegradable air filters. These filters have improved filtration efficiency and reduced resistance.

Influence of Rheological and Morphological Characteristics of Polyhydroxybutyrate on Its Meltblown Process Behavior

Polyhydroxybutyrate (PHB) is a promising biopolymer. However, processing PHB in pure form in thermoplastic processes is limited due to its rapid degradation, very low initial crystallization rate, strong post-crystallization, and its low final stretchability. In this article, we screened commercial PHBs for morphological characteristics, rheological properties, and "performance" in the meltblown process in order to reveal process-relevant properties and overcome the shortcoming of PHB in thermoplastic processes for fiber formation. An evaluation of degradation (extruded (meltblown) material vs. granules) was performed via rheological and SEC analysis. The study revealed large differences in the minimum melt temperature (175 up to 200 °C) and the grade-dependent limitation of accessible throughput on a 500 mm plant. The average fiber diameter could be lowered from around 10 μm to 2.4 μm in median, which are the finest reported values in the literature so far. It was found that the determination of the necessary process temperature can be predicted well from the complex shear viscosity. Different to expectations, it became apparent that a broader initial molar mass distribution (>8) is suitable to overcome the state-of-the art limitations of PHAs in order to stabilize fiber formation, increase the productivity, and obtain better resistance towards thermal degradation in process. Accordingly, longer polymer chain fractions could be more affected by degradation than medium and short polymer chains in the distribution. Further, a low initial narrow distributed molar mass resulted in too brittle fabrics.

Bioelectret poly(lactic acid) membranes with simultaneously enhanced physical interception and electrostatic adsorption of airborne PM0.3

Traditional polymeric fibrous membranes have been extensively used to reduce the health risks caused by airborne particulate matter (PM), leading to the dramatically increasing pollution of plastics and microplastics. Although great efforts have been made to develop poly(lactic acid) (PLA)-based membrane filters, they are frequently dwarfed by their relatively poor electret properties and electrostatic adsorptive mechanisms. To resolve this dilemma, a bioelectret approach was proposed in this work, strategically involving the bioinspired adhesion of dielectric hydroxyapatite nanowhiskers as a biodegradable electret to promote the polarization properties of PLA microfibrous membranes. In addition to significant improvements in tensile properties, the incorporation of hydroxyapatite bioelectret (HABE) enabled remarkable increase in the removal efficiencies of ultrafine PM_0.3 in a high-voltage electrostatic field (10 and 25 kV). This was exemplified by the largely increased filtering performance (69.75%, 23.1 Pa) for PLA membranes loaded with 10 wt% HABE at the normal airflow rate (32 L/min) compared to the pristine PLA counterpart (32.89%, 7.2 Pa). Although the filtration efficiency of PM_0.3 for the counterpart dramatically decreased to 21.6% at 85 L/min, the increment was maintained at nearly 196% for the bioelectret PLA, while an ultralow pressure drop (74.5 Pa) and high humidity resistance (RH 80%) were achieved. The unusual property combination were ascribed to the HABE-enabled realization of multiple filtration mechanisms, including the simultaneous enhancement of physical interception and electrostatic adsorption. The significant filtration applications, unattainable with conventional electret membranes, demonstrate the bioelectret PLA as a promising biodegradable platform that allows high filtration properties and humidity resistance.

Long-Lasting Electret Melt-Blown Nonwoven Functional Filters Made of Organic/Inorganixc Macromolecular Micron Materials: Manufacturing Techniques and Property Evaluations

Melt-blown nonwoven fabrics for filtration are usually manufactured using polypropylene, but after a certain time period the middle layer of the mask may have a reduced effect on adsorbing particles and may not be easily stored. Adding electret materials not only increases storage time, but also shows in this study that the addition of electret can improve filtration efficiency. Therefore, this experiment uses a melt-blown method to prepare a nonwoven layer, and adds MMT, CNT, and TiO2 electret materials to it for experiments. Polypropylene (PP) chip, montmorillonite (MMT) and titanium dioxide (TiO₂) powders, and carbon nanotube (CNT) are blended and made into compound masterbatch pellets using a single-screw extruder. The resulting compound pellets thus contain different combinations of PP, MMT, TiO₂, and CNT. Next, a hot pressor is used to make the compound chips into a high-poly film, which is then measured with differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The optimal parameters are yielded and employed to form the PP/MMT/TiO₂ nonwoven fabrics and PP/MMT/CNT nonwoven fabrics. The basis weight, thickness, diameter, pore size, fiber covering ratio, air permeability, and tensile property of different nonwoven fabrics are evaluated in order to have the optimal group of PP-based melt-blown nonwoven fabrics. According to the results of DSC and FTIR measurements, PP and MMT, CNT, and TiO₂ are completely mixed, and the melting temperature (T_m), crystallization temperature (T_c) and endotherm area are changed accordingly. The difference in enthalpy of melting changes the crystallization of PP pellets, which in turn changes the fibers. Moreover, the Fourier transform infrared (FTIR) spectroscopy results substantiate that PP pellets are well blended with CNT and MMT, according to the comparisons of characteristic peaks. Finally, the scanning electron microscopy (SEM) observation suggests that with a spinning die temperature of 240 °C and a spinning die pressure lower than 0.01 MPa, the compound pellets can be successfully formed into melt-blown nonwoven fabrics with a 10-micrometer diameter. The proposed melt-blown nonwoven fabrics can be processed with electret to form long-lasting electret melt-blown nonwoven filters.

Non-Woven Filters Made of PLA via Solution Blowing Process for Effective Aerosol Nanoparticles Filtration

With the development of civilization, the awareness of the impact of versatile aerosol particles on both human health and the environment is growing. New materials are needed to purify the air to control this impact The aspect of processing the produced waste is not negligible. In view of the above, this study proposes utilizing the solution blow spinning process (SBS) for manufacturing a biodegradable filtration structure that ensures high efficiency of nanoobject filtration, with a low pressure drop. Polylactic acid (PLA) was used to produce a nanofiber layer on the coconut substrate. The advantage of this method is the ability to blow fibers with diameters in the nano-scale, applying relatively simple, cost-effective, and easy to scale-up equipment. This work selected appropriate process parameters to produce good quality filters. Moreover, the process conditions influence on the morphology of the obtained structures and, thus, also the filtration properties, were examined. For tested solutions, i.e., 4% and 6%, the mean fiber diameter decreased as the concentration decreased. Therefore, the overall filtering efficiency increased as the concentration of the used solution decreased. The produced structures exhibited approximately 70% filtration efficiency for particles ranging from 0.02 to 0.2 μm with a pressure drop of less than 60 Pa. Obtained results are optimistic and are a step in producing efficient, biodegradable filters to remove nanoparticles from air.

Fabrication of biodegradable nanofibers via melt extrusion of immiscible blends

Polylactic acid (PLA) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) nanofibers were prepared by melt extrusion of immiscible blends of PLA/polyvinyl alcohol (PVA) and P(3HB-co-4HB)/PVA via in situ formation of microfibrils during the melt extrusion process. The morphology of the blends and nanofibers after removal of PVA with water was studied using scanning electron microscopy. The intermolecular interactions in the blends were studied by Fourier-transform infrared spectroscopy. The compatibility of the components of the PVA/PLA blends was better than that of the PVA/P(3HB-co-4HB) blends. By varying the process conditions, the average diameter of the PLA nanofibers could be controlled in the range of 78–150 nm and that of the P(3HB-co-4HB) nanofibers could be controlled in the range of 274–424 nm.

Low cost centrifugal melt spinning for distributed manufacturing of non-woven media

Centralized manufacturing and global supply chains have emerged as an efficient strategy for large-scale production of goods throughout the 20th century. However, while this system of production is highly efficient, it is not resilient. The COVID-19 pandemic has seen numerous supply chains fail to adapt to sudden changes in supply and demand, including those for goods critical to the pandemic response such as personal protective equipment. Here, we consider the production of the non-woven polypropylene filtration media used in face filtering respirators (FFRs). The FFR supply chain's reliance on non-woven media sourced from large, centralized manufacturing facilities led to a supply chain failure. In this study, we present an alternative manufacturing strategy that allows us to move towards a more distributed manufacturing practice that is both scalable and robust. Specifically, we demonstrate that a fiber production technique known as centrifugal melt spinning can be implemented with modified, commercially-available cotton candy machines to produce nano- and microscale non-woven fibers. We evaluate several post processing strategies to transform the produced material into viable filtration media and then characterize these materials by measuring filtration efficiency and breathability, comparing them against equivalent materials used in commercially-available FFRs. Additionally, we demonstrate that waste plastic can be processed with this technique, enabling the development of distributed recycling strategies to address the growing plastic waste crisis. Since this method can be employed at small scales, it allows for the development of an adaptable and rapidly deployable distributed manufacturing network for non-woven materials that is financially accessible to more people than is currently possible.

Bifunctional ZIF-8 Grown Webs for Advanced Filtration of Particulate and Gaseous Matters: Effect of Charging Process on the Electrostatic Capture of Nanoparticles and Sulfur Dioxide

Metal-organic framework (MOF), an emerging class of porous hybrid inorganic-organic crystals, has been applied for various environmental remediation strategies including liquid and air filtration. In this study, the role of the zeolite imidazole framework-8 (ZIF-8) was explored on the charge trapping ability and its contribution to capturing the targeted pollutants of NaCl nanoparticles and SO₂ gas. Poly(lactic acid) fibers with controlled surface pores were electrospun using water vapor-induced phase separation, and the fiber surface was uniformly coated with ZIF-8 crystals via an in situ growth method. As a novel process approach, the corona charging process was applied to the ZIF-8 grown webs. The ZIF-8 promoted the charge trapping in the corona process, and the charged ZIF-8 web showed a significantly improved electrostatic filtration efficiency. Also, the charged ZIF-8 web showed an enhanced SO₂ capture ability, both in the static and dynamic air flow states, demonstrating the applicability as a bifunctional filter for both particulate and gaseous matters. The approach of this study is novel in that both particulate and gas capture capabilities were associated with the charge trapping ability of ZIF-8, implementing the corona charging process to the ZIF-8 webs.