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Fibers
Volume 10
Issue 6
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Fibers, Volume 10, Issue 6 (June 2022) – 9 articles

Cover Story (view full-size image): Electrospun nanofiber mats can be used for a broad variety of applications, including electromagnetic interference (EMI) shielding. EMI shielding nanofiber mats work by reflection (R) and absorption (A), so that only a small part of the impinging radiation (I) is transmitted (T). For this purpose, they need suitable conductive and/or magnetic properties. This functionalization is often possible in a one-step production process but can also be reached via thermal or chemical post-treatments. The review discusses production processes and physical properties of EMI shielding nanofiber mats as well as typical characterization techniques. View this paper
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17 pages, 4141 KiB  
Article
Recycling Process of a Basalt Fiber-Epoxy Laminate by Solvolysis: Mechanical and Optical Tests
by Livia Persico, Giorgia Giacalone, Beatrice Cristalli, Carla Tufano, Eudora Saccorotti, Pietro Casalone and Giuliana Mattiazzo
Fibers 2022, 10(6), 55; https://doi.org/10.3390/fib10060055 - 17 Jun 2022
Cited by 6 | Viewed by 4161
Abstract
Basalt fibre epoxy composites well suit various engineering applications for their mechanical properties and chemical stability. However, after basalt/epoxy product lifespan, there are not many established ways to treat and recycle the fibers without deteriorating their physical, mechanical and chemical properties. In this [...] Read more.
Basalt fibre epoxy composites well suit various engineering applications for their mechanical properties and chemical stability. However, after basalt/epoxy product lifespan, there are not many established ways to treat and recycle the fibers without deteriorating their physical, mechanical and chemical properties. In this study, a chemical recycling method for basalt fiber reinforced polymers is presented. The process is based on previous studies concerning carbon fibers epoxy composites in which the fibers are separated from the polymeric matrix through a solvolysis reaction at temperature below 160 °C. Firstly, the specimens are thermally pre-treated in a heater set over the glass transition temperature, to promote the polymeric swelling of the matrix. The chemical degradation is obtained by means of a solution of glacial acetic acid (AcOH) and hydrogen peroxide (H2O2): compact, clean, resin-free, recycled woven fabrics are obtained and the original length of the yarns is maintained. Breaking tenacity of the recycled basalt fibers is kept up to 90.5% compared to the virgin ones, while, with a pyrolysis treatment, this value cannot exceed the 35%. Full article
(This article belongs to the Special Issue Fiber Composite Process)
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14 pages, 4690 KiB  
Article
Improving Transverse Compressive Modulus of Carbon Fibers during Wet Spinning of Polyacrylonitrile
by Sherman Wong, Linda K. Hillbrick, Jasjeet Kaur, Aaron J. Seeber, Jurg A. Schutz and Anthony P. Pierlot
Fibers 2022, 10(6), 54; https://doi.org/10.3390/fib10060054 - 14 Jun 2022
Cited by 1 | Viewed by 2477
Abstract
The performance of carbon fibers depends on the properties of the precursor polyacrylonitrile (PAN) fibers. Stretching of PAN fibers results in improved tensile properties, while potentially reducing its compressive properties. To determine optimization trade-offs, the effect of coagulation conditions and the stretching process [...] Read more.
The performance of carbon fibers depends on the properties of the precursor polyacrylonitrile (PAN) fibers. Stretching of PAN fibers results in improved tensile properties, while potentially reducing its compressive properties. To determine optimization trade-offs, the effect of coagulation conditions and the stretching process on the compressive modulus in the transverse direction (ET) was investigated. A method for accurately determining ET from polymer fibers with non-circular cross-sectional shapes is presented. X-ray diffraction was used to measure the crystallite size, crystallinity, and crystallite orientation of the fibers. ET was found to increase with decreasing crystallite orientation along the drawing direction, which decreases the tensile modulus in the longitudinal direction (EL) proportionally to crystallite orientation. Stretching resulted in greater crystallite orientation along the drawing direction for fibers formed under the same coagulation conditions. Increasing the solvent concentration in the coagulation bath resulted in a higher average orientation, but reduced the impact of stretching on the orientation. The relationship between ET and EL observed in the precursor PAN fiber is retained after carbonization, with a 20% increase in ET achieved for a 2% decrease in EL. This indicates that controlled stretching of PAN fiber allows for highly efficient trading off of EL for ET in carbon fiber. Full article
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17 pages, 5750 KiB  
Article
Mechanical Properties of Hybrid Steel-Polypropylene Fiber Reinforced High Strength Concrete Exposed to Various Temperatures
by Maged Tawfik, Amr El-said, Ahmed Deifalla and Ahmed Awad
Fibers 2022, 10(6), 53; https://doi.org/10.3390/fib10060053 - 12 Jun 2022
Cited by 20 | Viewed by 4447
Abstract
Combining different types of fibers inside a concrete mixture was revealed to improve the strength properties of cementitious matrices by monitoring crack initiation and propagation. The contribution of hybrid fibers needs to be thoroughly investigated, taking into consideration a variety of parameters such [...] Read more.
Combining different types of fibers inside a concrete mixture was revealed to improve the strength properties of cementitious matrices by monitoring crack initiation and propagation. The contribution of hybrid fibers needs to be thoroughly investigated, taking into consideration a variety of parameters such as fibers type and content. In this paper, the impact of integrating hybrid steel-polypropylene fibers on the mechanical properties of the concrete mixture was investigated. Hybrid fiber-reinforced high-strength concrete mixtures were tested for compressive strength, tensile strength, and flexural strength. According to the results of the experiments, the addition of hybrid fibers to the concrete mixture improved the mechanical properties significantly, more than adding just one type of fiber for specimens exposed to room temperature. Using hybrid fibers in the concrete mixture increased compressive, tensile, and flexural strength by approximately 50%, 53%, and 46%, respectively, over just using one type of fiber. Furthermore, results showed that including hybrid fibers into the concrete mixture increased residual compressive strength for specimens exposed to high temperatures. When exposed to temperatures of 200 °C, 400 °C, and 600 °C, the hybrid fiber reinforced concrete specimens maintained 87%, 65%, and 42% of their initial compressive strength, respectively. In comparison, the control specimens, which were devoid of fibers, would be unable to tolerate temperatures beyond 200 °C, and an explosive thermal spalling occurred during the heating process. Full article
(This article belongs to the Special Issue Fibers in Concrete Construction: Material Behavior, Design and Strengthening)
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22 pages, 13230 KiB  
Article
Multifunctional Material Extrusion 3D-Printed Antibacterial Polylactic Acid (PLA) with Binary Inclusions: The Effect of Cuprous Oxide and Cellulose Nanofibers
by Markos Petousis, Nectarios Vidakis, Nikolaos Mountakis, Vassilis Papadakis, Sotiria Kanellopoulou, Aikaterini Gaganatsiou, Nikolaos Stefanoudakis and John Kechagias
Fibers 2022, 10(6), 52; https://doi.org/10.3390/fib10060052 - 10 Jun 2022
Cited by 44 | Viewed by 3967
Abstract
In this work, we present an effective process easily adapted in industrial environments for the development of multifunctional nanocomposites for material extrusion (MEX) 3D printing (3DP). The literature is still very limited in this field, although the interest in such materials is constantly [...] Read more.
In this work, we present an effective process easily adapted in industrial environments for the development of multifunctional nanocomposites for material extrusion (MEX) 3D printing (3DP). The literature is still very limited in this field, although the interest in such materials is constantly increasing. Nanocomposites with binary inclusions were prepared and investigated in this study. Polylactic acid (PLA) was used as the matrix material, and cuprous oxide (Cu2O) and cellulose nanofibers (CNF) were used as nanoadditives introduced in the matrix material to enhance the mechanical properties and induce antibacterial performance. Specimens were built according to international standards with a thermomechanical process. Tensile, flexural, impact, and microhardness tests were conducted. The effect on the thermal properties of the matrix material was investigated through thermogravimetric analysis, and Raman spectroscopic analysis was conducted. The morphological characteristics were evaluated with atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) analyses. The antibacterial performance of the prepared nanomaterials was studied against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria, with a screening agar well diffusion method. All nanocomposites prepared exhibited biocidal properties against the bacteria tested. The tested PLA/1.0 CNF/0.5 Cu2O material had 51.1% higher tensile strength and 35.9% higher flexural strength than the pure PLA material. Full article
(This article belongs to the Collection Feature Papers in Fibers)
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12 pages, 1418 KiB  
Article
Understanding the PLA–Wood Adhesion Interface for the Development of PLA-Bonded Softwood Laminates
by Warren J. Grigsby, Marc Gaugler and Desiree Torayno
Fibers 2022, 10(6), 51; https://doi.org/10.3390/fib10060051 - 9 Jun 2022
Cited by 2 | Viewed by 2119
Abstract
With polylactic acid (PLA) usage projected to increase in wood-based composite materials, a study comparing composite processing parameters with resulting PLA−wood adhesion and panel performance is warranted. In this study, PLA-softwood veneer laminates have been prepared and spatial chemical imaging via FTIR analysis [...] Read more.
With polylactic acid (PLA) usage projected to increase in wood-based composite materials, a study comparing composite processing parameters with resulting PLA−wood adhesion and panel performance is warranted. In this study, PLA-softwood veneer laminates have been prepared and spatial chemical imaging via FTIR analysis was applied to identify PLA bondlines characterizing bondline thickness and the extent of PLA migration into the wood matrix. These PLA–wood adhesion interface characteristics have been compared with the performance of panels varying in pressing temperature, pressing time and PLA grades. For amorphous PLA, bondline thicknesses (60–120 μm) were similar, pressing at 140 °C or 160 °C, whereas with semi-crystalline PLA, the bondline thickness (340 μm) significantly reduced (155–240 μm) only when internal panel temperatures exceeded 140 °C during pressing. Internal temperatures also impacted PLA penetration, with greater PLA migration from bondlines evident with higher pressing temperatures and times with distinctions between PLA grades and bondline position. Performance testing revealed thinner PLA bondlines were associated with greater dry strength for both PLA grades. Cold-water soaking revealed laminated panels exhibit a range of wet-strength performance related to panel-pressing regimes with the semi-crystalline PLA pressed at 180 °C having similar tensile strength in dry and wet states. Moreover, an excellent correlation between wet-strength performance and bondline thickness and penetration values was evident for this PLA grade. Overall, study findings demonstrate PLA wood composite performance can be tuned through a combination of the PLA grade and the pressing regime employed. Full article
(This article belongs to the Collection Feature Papers in Fibers)
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16 pages, 6902 KiB  
Article
Fiber Spinning from Cellulose Solutions in Imidazolium Ionic Liquids: Effects of Natural Antioxidants on Molecular Weight, Dope Discoloration, and Yellowing Behavior
by Hubert Hettegger, Jiaping Zhang, Mitsuharu Koide, Uwe Rinner, Antje Potthast, Yasuo Gotoh and Thomas Rosenau
Fibers 2022, 10(6), 50; https://doi.org/10.3390/fib10060050 - 7 Jun 2022
Cited by 7 | Viewed by 3085
Abstract
Spinning of cellulosic fibers requires the prior dissolution of cellulose. 3-Alkyl-1-methylimidazolium ionic liquids have proven to be suitable solvents for that purpose, but the degradation of cellulose in the spinning dope can be severe. Suitable stabilizers are therefore required that prevent cellulose degradation, [...] Read more.
Spinning of cellulosic fibers requires the prior dissolution of cellulose. 3-Alkyl-1-methylimidazolium ionic liquids have proven to be suitable solvents for that purpose, but the degradation of cellulose in the spinning dope can be severe. Suitable stabilizers are therefore required that prevent cellulose degradation, but do not adversely affect spinnability or the long-term yellowing behavior of the fibers. A group of twelve renewables-based antioxidants was selected for stabilizing 5% cellulose solutions in the ionic liquids and their effects on cellulose integrity, dope discoloration, and aging behavior were tested by gel permeation chromatography (GPC) and ISO brightness measurements. Propyl gallate (a gallic acid derivative), hydroxytyrosol (from olives), and tocopheramines (a vitamin E derivative) performed best in the three test categories, minimizing both cellulose degradation, chromophore formation in the spinning dope, and yellowing upon accelerating aging of the spun fibers. The use of these stabilizers for cellulose solutions in the imidazolium-based solvent system can therefore be recommended from the point of view of both performance and sustainability. Full article
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22 pages, 9453 KiB  
Article
Influence of Different Surfactants on Carbon Fiber Dispersion and the Mechanical Performance of Smart Piezoresistive Cementitious Composites
by Athanasia K. Thomoglou, Maria G. Falara, Fani I. Gkountakou, Anaxagoras Elenas and Constantin E. Chalioris
Fibers 2022, 10(6), 49; https://doi.org/10.3390/fib10060049 - 31 May 2022
Cited by 26 | Viewed by 3709
Abstract
This experimental study presents the effect of different surfactants on micro-scale carbon fiber (CFs) distribution into carbon fiber reinforced cement-based composites (CFRC) in terms of flexural and compressive strength, stiffness, flexural toughness, and strain-sensing ability. Conducting a narrative review of the literature focusing [...] Read more.
This experimental study presents the effect of different surfactants on micro-scale carbon fiber (CFs) distribution into carbon fiber reinforced cement-based composites (CFRC) in terms of flexural and compressive strength, stiffness, flexural toughness, and strain-sensing ability. Conducting a narrative review of the literature focusing on the fibers’ separation, this paper follows a methodology introducing a combination of mechanical and chemical carbon fibers dispersion, as well as the different mixing processes (wet or dry). Three types of surfactants: Carboxymethyl cellulose (CMC), cellulose nanocrystal (CNC), and superplasticizer (SP), were applied to evaluate the CFs distribution in the cement paste matrix. Compressive and flexural strength, modulus of elasticity, and ductility of the cement-based composites (CFRC) reinforced with 0.5 wt.% CFs were investigated by three-point bending and compressive tests; flexure tests were also conducted on notched 20 × 20 × 80 mm specimens using the Linear Elastic Fracture Mechanics (L.E.F.M.) theory. Moreover, the electrical conductivity and the piezoresistive response were determined by conducting electrical resistance measurements and applying compressive loading simultaneously. The results clearly reveal that the CFs/SP solution or the CFs’ dry incorporation led to a significant enhancement of flexural strength by 32% and 23.7%, modulus of elasticity by 30% and 20%, and stress-sensing ability by 20.2% and 18.2%, respectively. Although the wet mixing method exhibits improved mechanical and electrical conductivity performance, constituting an adequate strain and crack sensor, the authors propose dry mixing as the most economical method, in addition to the enhanced mechanical and electrical responses. The authors recommend an effective method for structural health monitoring systems combining an economical CFs insertion in cementitious smart sensors with great mechanical and self-sensing responses. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement-Based Mortars in Repair/Strengthening Methods of Masonry and Reinforced Concrete Structural Members)
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16 pages, 9140 KiB  
Article
Transverse Loading on Single High-Performance Fibers by Round-Head Indenters and the Fibers’ Failure Visualization
by Jinling Gao, Nesredin Kedir, Boon Him Lim, Yizhou Nie, Xuedong Zhai and Weinong Chen
Fibers 2022, 10(6), 48; https://doi.org/10.3390/fib10060048 - 30 May 2022
Cited by 1 | Viewed by 2426
Abstract
High-performance fibers are well-known for their high stiffness and strength under axial tension. However, in their many applications as critical components of textiles and composites, transverse loads widely exist in their normal service life. In this study, we modified a micro material testing [...] Read more.
High-performance fibers are well-known for their high stiffness and strength under axial tension. However, in their many applications as critical components of textiles and composites, transverse loads widely exist in their normal service life. In this study, we modified a micro material testing system to transverse load single fibers using round-head indenters. By integrating the loading platform with the Scanning Electron Microscopy (SEM) operating at a low-vacuum mode, we visualized the failure processes of fibers without conductive coatings. Post-fracture analysis was conducted to provide complementary information about the fibers’ failure. The energy dissipation was compared with the axial tensile experiments. Three inorganic and two organic fibers were investigated, namely carbon nanotube, ceramic, glass, aramid, and ultrahigh molecule weight polyethylene fibers. Different failure characteristics were reported. It is revealed that the organic fibers had higher energy dissipation than the inorganic fibers under the transverse loading by the round-head indenters. The fiber’s energy dissipation under transverse loading was no more than 17.9% of that subjected to axial tension. Such a reduced energy dissipation is believed to be due to the stress concentration under the indenter. It is suggested that the fiber’s material constituent, structural characteristics, and stress concentration under the indenter should be considered in the fiber model for textiles and composites. Full article
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16 pages, 3466 KiB  
Review
Electromagnetic Interference Shielding with Electrospun Nanofiber Mats—A Review of Production, Physical Properties and Performance
by Tomasz Blachowicz, Andreas Hütten and Andrea Ehrmann
Fibers 2022, 10(6), 47; https://doi.org/10.3390/fib10060047 - 24 May 2022
Cited by 18 | Viewed by 4444
Abstract
With a steadily increasing number of machines and devices producing electromagnetic radiation, especially, sensitive instruments as well as humans need to be shielded from electromagnetic interference (EMI). Since ideal shielding materials should be lightweight, flexible, drapable, thin and inexpensive, textile fabrics belong to [...] Read more.
With a steadily increasing number of machines and devices producing electromagnetic radiation, especially, sensitive instruments as well as humans need to be shielded from electromagnetic interference (EMI). Since ideal shielding materials should be lightweight, flexible, drapable, thin and inexpensive, textile fabrics belong to the often-investigated candidates to meet these expectations. Especially, electrospun nanofiber mats are of significant interest since they can not only be produced relatively easily and cost efficiently, but they also enable the embedding of functional nanoparticles in addition to thermal or chemical post-treatments to reach the desired physical properties. This paper gives an overview of recent advances in nanofiber mats for EMI shielding, discussing their production, physical properties and typical characterization techniques. Full article
(This article belongs to the Collection Feature Papers in Fibers)
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