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Fibers, Volume 8, Issue 5 (May 2020) – 7 articles

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Cover Story (view full-size image) The new electrospinning method allows engineering of nanofibrous 3D structures of desired [...] Read more.
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Open AccessArticle
Accelerated Thermal Aging of Bio-Based Composite Wood Panels
Fibers 2020, 8(5), 32; https://doi.org/10.3390/fib8050032 - 21 May 2020
Viewed by 590
Abstract
Bio-based adhesives and resins are sought as alternatives to synthetics in order to fabricate all-biobased composite wood panels (CWPs), which provide environmentally friendly building products for indoor use. Very little information exists as to how these bio-based CWPs would perform long-term in non-temperature [...] Read more.
Bio-based adhesives and resins are sought as alternatives to synthetics in order to fabricate all-biobased composite wood panels (CWPs), which provide environmentally friendly building products for indoor use. Very little information exists as to how these bio-based CWPs would perform long-term in non-temperature controlled structures such as warehouses and storage units where extreme temperatures occur depending on the season. In this study, novel all-bio-based CWPs were fabricated using a matrix of 50% distiller’s dried grains with solubles (DDGS) and 50% soybean flour ProsanteTM (PRO) mixed with wood particles. Bio-based CWPs were subjected to accelerated thermal aging for a 10-year period resembling outdoor temperatures in Peoria, IL USA. Four seasonal periods (Winter, Spring, Summer, and Fall) were simulated varying from −26–40 °C and 36–76% relative humidity (RH). The bio-based adhesive employed consisted of 50% distiller’s dried grains with solubles (DDGS) and 50% soybean flour ProsanteTM (PRO). CWPs consisted of 15 or 50% DDGS/PRO with 85% or 50% pine wood. CWPs were evaluated for 5, 7.5, and 10-years for their physical, flexural, dimensional stability, surface roughness, FTIR, TGA, and spectral properties. The changes in the CWP properties were notable during the initial 5 years, and later aged samples showed less change. Full article
(This article belongs to the Special Issue Natural Fibers and Composites: Science and Applications)
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Open AccessArticle
Measurement of Flexural Rigidity of Multi-Walled Carbon Nanotubes by Dynamic Scanning Electron Microscopy
Fibers 2020, 8(5), 31; https://doi.org/10.3390/fib8050031 - 12 May 2020
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Abstract
In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the [...] Read more.
In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the Euler–Bernoulli beam theory. For the nanotubes studied, we determined a modulus of up to 160 GPa. This agrees with values reported by other authors for MWCNTs produced by catalytic chemical vapor deposition, however, it is 6-8 times smaller than values reported for single and multi-walled carbon nanotubes produced by arc-discharge synthesis. Toxicological studies with carbon nanotubes have been showing that inhaled airborne nanofibers that reach the deep airways of the respiratory system may lead to serious, asbestos-like lung diseases. These studies suggested that their toxicity critically depends on the fiber flexural rigidity, with high rigidity causing cell lesions. To complement the correlation between observed toxicological effects and fiber rigidities, reliable and routinely applicable measurement techniques for the flexural rigidity of nanofibers are required. Full article
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Open AccessReview
Laser Sources Based on Rare-Earth Ion Doped Tellurite Glass Fibers and Microspheres
Fibers 2020, 8(5), 30; https://doi.org/10.3390/fib8050030 - 11 May 2020
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Abstract
In recent years, huge progress has been made in the development of rare-earth ion doped tellurite glass laser sources, ranging from watt- and multiwatt-level fiber lasers to nanowatt level microsphere lasers. Significant success has been achieved in extending the spectral range of tellurite [...] Read more.
In recent years, huge progress has been made in the development of rare-earth ion doped tellurite glass laser sources, ranging from watt- and multiwatt-level fiber lasers to nanowatt level microsphere lasers. Significant success has been achieved in extending the spectral range of tellurite fiber lasers generating at wavelengths beyond 2 μm as well as in theoretical understanding. This review is aimed at discussing the state of the art of neodymium-, erbium-, thulium-, and holmium-doped tellurite glass fiber and microsphere lasers. Full article
(This article belongs to the Special Issue Fiber Laser Sources)
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Open AccessArticle
Surface and Morphological Investigation of Synthesized Nanostructured Ridges from Electrospun Polyvinyl Alcohol-Albumin Blend—A Taguchi Design of Experiment Approach
Fibers 2020, 8(5), 29; https://doi.org/10.3390/fib8050029 - 02 May 2020
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Abstract
We report the synthesis of presumably a “nanoridge” from the electrospinning of a hydrophilic polymer–protein blend. The material exhibits vertical elevation from the substrate, distinct from the morphologies seen in electrospinning. It is hypothesized that the formation of the nanostructured ridges is due [...] Read more.
We report the synthesis of presumably a “nanoridge” from the electrospinning of a hydrophilic polymer–protein blend. The material exhibits vertical elevation from the substrate, distinct from the morphologies seen in electrospinning. It is hypothesized that the formation of the nanostructured ridges is due to the migration of the charged protein to the apex through a highly polarized electric field in electrospinning conditions. In this study, we assessed the polyvinyl alcohol–egg albumin (PVA–EA) system in a solvent comprising of water, formic and acetic acid, together with the tip-to-collector distance (TCD) and solution flowrate. To quantify the factor effects in the surface properties of the material, a Taguchi design of experiment was used. The ridge heights observed ranged from 84.8–639.9 nm, and the material height is predominantly affected by the PVA–EA ratio and solution flow rate. The root mean square roughness was influenced by the TCD and flow rate, which has values ranging from 11.37–57.56 nm. In evaluating the sharpness of the ridge, we used the radius of curvature, where the TCD highly affects the apex sharpness. The work offers not just a likely new class of morphology, but a new perspective on the surface characterization of an electrospun material which could affect the performance of such a use in biological and physical systems. Full article
(This article belongs to the Special Issue Electrospun Fibers for Scaffold and Electrical Sensing)
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Open AccessFeature PaperArticle
Loading Dynamics of Cold Atoms into a Hollow-Core Photonic Crystal Fiber
Fibers 2020, 8(5), 28; https://doi.org/10.3390/fib8050028 - 01 May 2020
Viewed by 792
Abstract
Cold atoms trapped and guided in hollow-core photonic crystal fibers provide a scalable diffraction-free setting for atom–light interactions for quantum technologies. However, due to the mismatch of the depth and spatial extension of the trapping potential from free space to the fiber, the [...] Read more.
Cold atoms trapped and guided in hollow-core photonic crystal fibers provide a scalable diffraction-free setting for atom–light interactions for quantum technologies. However, due to the mismatch of the depth and spatial extension of the trapping potential from free space to the fiber, the number of cold atoms in the fiber is mainly determined by the loading process from free space to waveguide confinement. Here, we provide a numerical study of the loading dynamics of cold atoms into a hollow-core photonic crystal fiber. We use the Monte Carlo method to simulate the trajectories of an ensemble of cold atoms from free space trapping potential to optical potential inside a hollow-core fiber and calculate the temperature, loading efficiency, and geometry of the ensemble. We also study the noise sources that cause heating and a loss of atoms during the process. Our result could be used to design and optimize the loading process of cold atoms into a hollow-core fiber for cold atom experiments. Full article
(This article belongs to the Special Issue Hollow-Core Photonic Crystal Fibers)
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Open AccessArticle
A Novel Method for Electrospinning Nanofibrous 3-D Structures
Fibers 2020, 8(5), 27; https://doi.org/10.3390/fib8050027 - 30 Apr 2020
Viewed by 797
Abstract
The fast and precise fabrication of three-dimensional (3-D) structures made of nanofibers is an important development trend in the electrospinning technique. This paper describes a new and facile method of electrospinning to fabricate nanofibrous 3-D structures. The nanofibrous 3-D structures can be engineered [...] Read more.
The fast and precise fabrication of three-dimensional (3-D) structures made of nanofibers is an important development trend in the electrospinning technique. This paper describes a new and facile method of electrospinning to fabricate nanofibrous 3-D structures. The nanofibrous 3-D structures can be engineered to have the desired layer thicknesses, where the fiber spacing, density (i.e., fiber volume/unit volume), as well as shape of the structure may be controlled. While innumerable structural variations are possible with this method, this paper discusses, as proof-of-concept, a few cases that illustrate how 3-D nanofiber webs can be made for filtration application. Computerized automation of the method will make it possible to build almost any 3-D web structure suitable for a myriad of applications including ultra-light-weight insulation and scaffolds for hydrogel preparation and tissue. Full article
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Open AccessArticle
Tensile Properties and Microstructure of Single-Cellulosic Bamboo Fiber Strips after Alkali Treatment
Fibers 2020, 8(5), 26; https://doi.org/10.3390/fib8050026 - 28 Apr 2020
Viewed by 784
Abstract
The study systematically explored the effect of alkali concentration and soaking time on the microstructure and tensile properties of single-cellulosic Buluh Semantan. Scanning electron microscopy and tensile tests were conducted to determine the effects of different alkali treatments on the properties of the [...] Read more.
The study systematically explored the effect of alkali concentration and soaking time on the microstructure and tensile properties of single-cellulosic Buluh Semantan. Scanning electron microscopy and tensile tests were conducted to determine the effects of different alkali treatments on the properties of the single-cellulosic bamboo fibers. In particular, the effects of NaOH concentration and soaking time on the tensile properties of the single-cellulosic bamboo fiber were investigated. The single-cellulosic bamboo fiber was immersed in 2, 4, 6, and 8 wt.% aqueous NaOH solutions for soaking times of 1, 3, 6, 12, 18, and 24 h. The tensile properties of the fiber increased after each alkali treatment. The alkali concentration and soaking time significantly affected the fiber properties. The ultimate tensile strength of the single-cellulosic Buluh Semantan treated with 2 wt.% NaOH for 12 h decreased to 214 MPa relative to the fibers that experienced water retting. The highest tensile strength herein was 356.8 MPa for the single-cellulosic fiber that was soaked for 12 h in 4 wt.% NaOH. Comparatively, the tensile strength of the single-cellulosic bamboo fiber that was soaked for 12 h in 8 wt.% NaOH was 234.8 MPa. The tensile modulus of the single-cellulosic fiber was 12.06 GPa after soaking in 8 wt.% NaOH for 18 h, indicating that a strong alkali treatment negatively affected the stiffness and suitability for use of the fibers in applications. The topography of the fiber surface became much rougher after the alkali treatments due to the removal of hemicellulose and other surface impurities. The alkali treatments substantially changed the morphology of the fiber surface, suggesting an increase in wettability. Full article
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