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ABSTRACT:An electrospinning process was used to fabricate silk fibroin (SF) nanofiber nonwovens for wound dressing applications. The electrospinning of regenerated SF was performed with formic acid as a spinning solvent. For crystallization, as-spun SF nanofiber nonwovens were chemically treated with an aqueous methanol solution of 50%. The morphology, porosity and conformational structures of as-spun and chemically treated SF nanofibers were investigated by scanning electron microscopy (SEM), mercury porosimetry, wide angle X-Ray diffraction (WAXD), attenuated total reflectance infrared spectroscopy (ATR-IR), solid state 13 C CP/MAS nuclear magnetic resonance (NMR) spectroscopy. SEM micrograph showed that the electrospun SF nanofibers had an average diameter of 80 nm and a distribution in diameter ranging from 30 to 120 nm. The porosity of as-spun SF nanofiber nonwovens was 76.1%, indicating it was highly porous. Conformational transitions of the as-spun SF nanofibers from random coil to β-sheet by aqueous methanol treatment occurred rapidly within 10 min, confirmed by solid-state 13 C NMR, ATR-IR, and X-Ray diffraction. KEY WORDS Silk Fibroin / Electrospinning / Nanofiber / Nonwovens / Conformation / Porosity / β−Sheet / Random Coil / Silk as a typical fibrous protein is produced by a variety of insects including silkworm. Among the native silk proteins, the silkworm silk, mostly that of the domesticated Bombyx mori, has been used as high-quality textile fiber and suture for a long time. B. mori silk consists of two types of proteins, fibroin and sericin. Fibroin is the protein that forms the filaments of silkworm silk and gives silk its unique physical and chemical properties. 1 Sericins are the group of gummy proteins which bind the fibroin filaments. Silk fibroin (SF) can be used in various forms, such as gels, powders, fibers, or membranes, depending on application. 2-5 Besides its utility as a textile fiber, many researchers have recently investigated SF as one of candidate materials for biomedical applications because it has several useful properties including good biocompatibility, good oxygen and water vapor permeability, biodegradability, and minimal inflammatory reaction. 6-8 Practically, SF has been used in various fields such as cosmetics, medical materials for human health, and food additives.Recently, much attention has been paid to electrospinning process as an unique technique because it can produce polymer nanofibers with diameter in the range from several micrometer down to tens of nanometers, depending on the polymer and processing conditions. In electrospinning, a high voltage is applied to create electrically charged jets of a polymer solution. These jets dry to form nanofibers, which are collected on a target as nonwovens. These nanofibers are of considerable interest for various kinds of applications, because they have several unique properties such as high specific surface area and high porosity. Examples are fiber membranes for filter applications, 9 biomedical applications such as wou...

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Polycarbonate (PC) ultrafine fiber membranes with benzyl triethylammonium chloride (BTEAC) were prepared by electrospinning of PC/chloroform solution with different BTEAC contents. In the presence of BTEAC additive, the PC solution showed a better electrospinnability and led to thinner fibers with uniformity than the neat PC solution. The charge retention of the electrospun PC fibrous membranes with BTEAC was investigated in terms of additive content, membrane thickness and storage condition. The residual charge on the PC fibrous membrane was increased to 1 wt % BTEAC content, but thereafter gradually decreased up to 10 wt % BTEAC. In addition, the residual charge on the membrane was increased with increasing the membrane thickness, but was rapidly decreased at a high humidity condition in comparison with a low humidity. The filtration efficiency was examined for the fibrous membranes with or without BTEAC. The PC membrane with BTEAC had higher filtration efficiency than one without BTEAC, not affecting the pressure drop. The filtration efficiency between the PC membranes with or without residual charge was also compared. When the residual charge existed on the membrane, the membrane showed higher filter efficiency because of the enhanced filtration effect by an electrostatic attraction. Therefore, the PC fibrous membranes with BTEAC have a great potential as an electrets filter for air filtration.