Bimodal Nanofiber and Microfiber Nonwovens by Melt-Blowing Immiscible Ternary Polymer Blends

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.

A Fiber Sliding-Orientation Based Micromechanics Failure Model for Melt-Blown Nonwovens

The mechanical model of melt-blown nonwovens (MNs) serves as the foundation for performance optimization, which can offer helpful guidance for product material selection, structural design, and cost control. However, it is challenging to describe the micromechanics failure mechanism of MNs using the traditional mechanical model, which aims to match the model curve with the experimental result at the macrolevel. Herein, a micromechanics failure model for MNs based on sliding-orientation competition is developed. Through in situ observations of fiber position changes and the fluctuation of stress-strain curves, fiber sliding and orientation are introduced into the failure process of MNs. Due to fiber bonding and static friction, only orientation happens during the first stage of stretching. In dramatic contrast, the fibers will slide and orient in the second stage of stretching to change their positions in response to the external force. Sliding friction, fiber bonding, and static friction make up the stress of MNs, and the conflict of fiber sliding and orientation causes variations in the stress. The model has been successfully applied to polylactic acid (PLA) MNs, which proves the effectiveness of the model in MNs.

Aerosol Filtration Performance of Solution Blown PA6 Webs with Bimodal Fiber Distribution

A bimodal web, where both nanofibers and microfibers are present and distributed randomly across the same web, can deliver high filter efficiency and low pressure drop at the same time since in such a web, filter efficiency is high thanks to small pores created by the presence of nanofibers and the interfiber space created by the presence of microfibers, which is large enough for air to flow through with little resistance. In this work, a bimodal polyamide 6 (PA6) filter web was fabricated via a modified solution blowing (m-SB) technique that produced nanofibers and microfibers simultaneously. Scanning electron microscope (SEM) images of the webs were used to analyze the fiber morphology. Additionally, air permeability, solidity, porosity, filtration performance, and tensile strength of the samples were measured. The bimodal filter web consisted of nanofibers and microfibers with average diameters of 81.5 ± 127 nm and 1.6 ± 0.458 μm, respectively. Its filter efficiency, pressure drop at 95 L min^-1, and tensile strength were 98.891%, 168 Pa, and 0.1 MPa, respectively. Its quality factor (QF) and tensile strength were 0.0268 Pa^-1 and 0.1 MPa, respectively. When compared with commercially available filters, the bimodal web produced had superior filter performance, constituting a suitable alternative for air filter applications.

Porous Fibers Templated by Melt Blowing Cocontinuous Immiscible Polymer Blends

We report a scalable melt blowing method for producing porous nonwoven fibers from model cocontinuous polystyrene/high-density polyethylene polymer blends. While conventional melt compounding of cocontinuous blends typically produces domain sizes ∼1-10 μm, melt blowing these blends into fibers reduces those dimensions up to 35-fold and generates an interpenetrating domain structure. Inclusion of ≤1 wt % of a block copolymer compatibilizer in these blends crucially enables access to smaller domain sizes in the fibers by minimizing thermodynamically-driven blend coarsening inherent to cocontinuous blends. Selective solvent extraction of the sacrificial polymer phase yielded a network of porous channels within the fibers. Fiber surfaces also exhibited pores that percolate into the fiber interior, signifying the continuous and interconnected nature of the final structure. Pore sizes as small as ∼100 nm were obtained, suggesting potential applications of these porous nonwovens that rely on their high surface areas, including various filtration modules.

Production of Filter Material from Polypropylene/Copolyamide Blend by Material Extrusion-Based Additive Manufacturing: Role of Production Conditions and ZrO2 Nanoparticles

The effect of technological conditions of the process and zirconia (ZrO₂) nanoparticles on the properties of fine-fibrous filter materials (FMs) obtained by matrix polymer extraction from a microfibrillar composite formed using the material extrusion-based additive manufacturing method from a polypropylene (PP)/copolyamide blend is studied. Different processing schemes were used for obtaining filaments for material extrusion: scheme I-the use of a single-screw extruder at the stage of compounding; scheme II-the use of a single-screw extruder at the stage of compounding and orientational stretching in the course of strand formation; scheme III-the use of a twin-screw extruder at the stage of compounding, scheme IV-the addition of ZrO₂ nanoparticles and use of a twin-screw extruder. It has been shown the possibility of reducing the diameters of the formed in situ PP microfibrils by using the twin-screw extruder, as well as additional orientation drawing. The introduction into the melt of ZrO₂ nanoparticles provides further improvement of the microstructure-the average diameter of the microfibrils is reduced by 1.4 times compared with the initial blend. Developed FMs are characterized by high efficiency of air purification from solid particles with a size of 0.3 μm. At the same time, the use of nanoadditives is the most effective-a two-layer FM with nanoparticles provides cleaning efficiency at the level of four- to six-layer materials without filler.