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Fibers, Volume 7, Issue 7 (July 2019)

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Cover Story (view full-size image) We propose a new method to avoid the sintering step of TiO2 in dye-sensitized solar cells (DSSCs). [...] Read more.
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Open AccessFeature PaperArticle
Influence of Fiber Volume Fraction and Fiber Orientation on the Uniaxial Tensile Behavior of Rebar-Reinforced Ultra-High Performance Concrete
Fibers 2019, 7(7), 67; https://doi.org/10.3390/fib7070067
Received: 18 May 2019 / Revised: 15 July 2019 / Accepted: 18 July 2019 / Published: 23 July 2019
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Abstract
This paper studied the influence of fiber volume fraction (Vf), fiber orientation, and type of reinforcement bar (rebar) on the uniaxial tensile behavior of rebar-reinforced strain-hardening ultra-high performance concrete (UHPC). It was observed that the tensile strength increased with the [...] Read more.
This paper studied the influence of fiber volume fraction ( V f ), fiber orientation, and type of reinforcement bar (rebar) on the uniaxial tensile behavior of rebar-reinforced strain-hardening ultra-high performance concrete (UHPC). It was observed that the tensile strength increased with the increase in V f . When V f was kept constant at 1%, rebar-reinforced UHPC with fibers aligned with the load direction registered the highest strength and that with fibers oriented perpendicular to the load direction recorded the lowest strength. The strength of the composite with random fibers laid in between. Moreover, the strength, as well as the ductility, increased when the normal strength grade 60 rebars embedded in UHPC were replaced with high strength grade 100 rebars with all other conditions remaining unchanged. In addition, this paper discusses the potential of sudden failure of rebar-reinforced strain hardening UHPC and it is suggested that the composite attains a minimum strain of 1% at the peak stress to enable the members to have sufficient ductility. Full article
(This article belongs to the Special Issue Ultra High Performance Fibre Reinforced Concrete)
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Open AccessReview
Multi-Functional Electrospun Nanofibers from Polymer Blends for Scaffold Tissue Engineering
Fibers 2019, 7(7), 66; https://doi.org/10.3390/fib7070066
Received: 27 May 2019 / Revised: 24 June 2019 / Accepted: 12 July 2019 / Published: 19 July 2019
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Abstract
Electrospinning and polymer blending have been the focus of research and the industry for their versatility, scalability, and potential applications across many different fields. In tissue engineering, nanofiber scaffolds composed of natural fibers, synthetic fibers, or a mixture of both have been reported. [...] Read more.
Electrospinning and polymer blending have been the focus of research and the industry for their versatility, scalability, and potential applications across many different fields. In tissue engineering, nanofiber scaffolds composed of natural fibers, synthetic fibers, or a mixture of both have been reported. This review reports recent advances in polymer blended scaffolds for tissue engineering and the fabrication of functional scaffolds by electrospinning. A brief theory of electrospinning and the general setup as well as modifications used are presented. Polymer blends, including blends with natural polymers, synthetic polymers, mixture of natural and synthetic polymers, and nanofiller systems, are discussed in detail and reviewed. Full article
(This article belongs to the Special Issue Electrospun Fibers for Scaffold and Electrical Sensing)
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Open AccessArticle
Effect of Nozzle Diameter on Basalt Continuous Fiber Properties
Fibers 2019, 7(7), 65; https://doi.org/10.3390/fib7070065
Received: 8 June 2019 / Revised: 7 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
The experimental data presented in this work show the effects of nozzle diameter, drawing speed, and formation temperature on the diameter and strength of basalt filaments and melt flow rate. Several series of basalt continuous fibers were obtained using a specially designed crucible [...] Read more.
The experimental data presented in this work show the effects of nozzle diameter, drawing speed, and formation temperature on the diameter and strength of basalt filaments and melt flow rate. Several series of basalt continuous fibers were obtained using a specially designed crucible of platinum–rhodium alloy with four nozzles of different diameters (1.5, 2.5, 3.5, and 4.5 mm). The conditions of the process varied in formation temperature (from 1370 to 1450 °C) and winding speed (from 300 to 1200 m/min). Melt flow rate was almost independent of the winding speed, indicating laminar flow of the melt through the nozzles and the Newtonian nature of the liquid. The results show strict correlations between fiber diameter, nozzle diameter, and winding speed. The diameter of the fibers had a significant effect on their strength. The tensile strength of the obtained basalt fibers varied from 550 to 3320 MPa depending on the formation conditions. The results of this work could be useful not only for scientists, but also for technologists seeking the optimal conditions for technological processes. Full article
(This article belongs to the Special Issue Advances in Glass Fibers)
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Open AccessArticle
Probing of Nanoscale Friction and Mechanical Characteristics of Cotton Fiber’s Surface
Fibers 2019, 7(7), 64; https://doi.org/10.3390/fib7070064
Received: 7 May 2019 / Revised: 2 July 2019 / Accepted: 9 July 2019 / Published: 15 July 2019
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Abstract
The surface topography and nanomechanical attributes of two samples of cotton fibers, namely, A and B, were characterized with various operation modes of an Atomic Force Microscope (AFM). The surface topography and friction images of the fibers were obtained in contact mode. The [...] Read more.
The surface topography and nanomechanical attributes of two samples of cotton fibers, namely, A and B, were characterized with various operation modes of an Atomic Force Microscope (AFM). The surface topography and friction images of the fibers were obtained in contact mode. The nanomechanical properties images—i.e., adhesion and deformation—were obtained in force tapping mode. The results indicate that the surface nanomechanical and nanoscale frictional properties of the fibers vary significantly between two samples. The plots of friction versus normal force of the fibers’ surface from both samples are fitted to the equation of single-asperity, adhesion-controlled friction. Nevertheless, within the range of the applied normal force, the friction curves of sample A surfaces show a characteristic transition phase. That is, under low normal forces, the friction curves closely conform with the Hertzian component of friction; after the transition takes place at higher normal forces, the friction curves follow Amontons’ law of friction. We demonstrated that the transition phase corresponds to a state at which the cuticle layer molecules are displaced from the fibers’ surface. The average adhesion force of the samples is consistent with the average friction signal strength collected under low normal forces. Full article
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Open AccessArticle
Composite Performance Evaluation of Basalt Textile-Reinforced Geopolymer Mortar
Fibers 2019, 7(7), 63; https://doi.org/10.3390/fib7070063
Received: 17 June 2019 / Revised: 3 July 2019 / Accepted: 4 July 2019 / Published: 11 July 2019
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Abstract
Basalt fiber is a novel type of inorganic fiber which is produced from the extrusion of natural vocalnic basalt rocks through their melting process at high temperature. So the quality and strength characteristics of basalt fiber depend mainly on both the quality of [...] Read more.
Basalt fiber is a novel type of inorganic fiber which is produced from the extrusion of natural vocalnic basalt rocks through their melting process at high temperature. So the quality and strength characteristics of basalt fiber depend mainly on both the quality of raw material and manufacturing processing. Basalt fabric-reinforced cementitious composites (FRCM) are a novel composite and an extensive scientific investigation is still ongoing for geopolymer composite. Based on three types of basalt textile with respect to various net sizes, the aim of this paper is to evaluate the flexural performance of basalt textile-reinforced geopolymer composite through the four-point bending test. The specimens of rectangular form with the dimension of 400 × 100 × 15 mm3, reinforced with one to four layers of each type of basalt textile, were produced. They were then tested at the age of about 40 days after casting. On the other hand, the number of the specimens reinforced with four layers were considered to assess the mechanical strength of the specimens at longer periods of ageing time (60, 90, 150, 180 days). The experimental results showed that with the increasing number of reinforcing layers, the specimens significantly improved the mechanical strength, except for those reinforced with basalt textile of big net size. The specimens reinforced with basalt textile of big net size had no impact on post-crack mechanical strength, however, it helps to arrest the catastrophic brittle failure of the specimens; the failure of these specimens is due to localization of first crack. When the specimens were exposed to the further ageing times, the mechanical strength of the specimens were decreased over time. All the reinforced specimens have the same failure mode by flexural failure due to the rupture of fiber yarn in matrix, and no debonding of fiber yarn or a gradual peeling process of mortar matrix happened during testing. Full article
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Open AccessFeature PaperArticle
Tensile Behavior of Unidirectional Bamboo/Coir Fiber Hybrid Composites
Fibers 2019, 7(7), 62; https://doi.org/10.3390/fib7070062
Received: 14 May 2019 / Revised: 2 July 2019 / Accepted: 6 July 2019 / Published: 10 July 2019
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Abstract
Natural fibers, such as bamboo, flax, hemp, and coir, are usually different in terms of microstructure and chemical composition. The mechanical properties of natural fibers strongly depend on the organization of cell walls and the cellulose micro-fibril angle in the dominant cell wall [...] Read more.
Natural fibers, such as bamboo, flax, hemp, and coir, are usually different in terms of microstructure and chemical composition. The mechanical properties of natural fibers strongly depend on the organization of cell walls and the cellulose micro-fibril angle in the dominant cell wall layers. Bamboo, flax, and hemp are known for high strength and stiffness, while coir has high elongation to failure. Based on the unique properties of the fibers, fiber hybridization is expected to combine the advantages of different natural fibers for composite applications. In this paper, a study on bamboo/coir fiber hybrid composites was carried out to investigate the hybrid effect of tough coir fibers and brittle bamboo fibers in the composites. The tensile behavior of unidirectional composites of bamboo fibers, coir fibers, and hybrid bamboo/coir fibers with a thermoplastic matrix was studied. The correlation between the tensile properties of the fibers and of the hybrid composites was analyzed to understand the hybrid effects. In addition, the failure mode and fracture morphology of the hybrid composites were examined. The results suggested that, with a low bamboo fiber fraction, a positive hybrid effect with an increase of composite strain to failure was obtained, which can be attributed to the high strain to failure of the coir fibers; the bamboo fibers provided high stiffness and strength to the composites. Full article
(This article belongs to the Special Issue Natural Fiber-Reinforced Hybrid Composites)
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Open AccessFeature PaperArticle
In-Line Nanostructuring of Glass Fibres Using Different Carbon Allotropes for Structural Health Monitoring Application
Fibers 2019, 7(7), 61; https://doi.org/10.3390/fib7070061
Received: 16 April 2019 / Revised: 28 June 2019 / Accepted: 1 July 2019 / Published: 10 July 2019
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Abstract
By the in-line nanostructuring of glass fibres (GF) during the glass fibre melt spinning process, the authors achieve an electro-mechanical-response-sensor. The glass fibre interphase was functionalized with different highly electrically conductive carbon allotropes such as carbon nanotubes, graphene nanoplatelets, or conductive carbon black. [...] Read more.
By the in-line nanostructuring of glass fibres (GF) during the glass fibre melt spinning process, the authors achieve an electro-mechanical-response-sensor. The glass fibre interphase was functionalized with different highly electrically conductive carbon allotropes such as carbon nanotubes, graphene nanoplatelets, or conductive carbon black. On-line structural health monitoring is demonstrated in continuous glass fibre-reinforced polypropylene composites during a static or dynamic three-point bending test. The different carbon fillers exhibit qualitative differences in their signal quality and sensitivity due to the differences in the aspect ratio of the nanoparticles, the film homogeneity, and the associated electrically conductive network density in the interphase. The occurrence of irreversible signal changes during dynamic loading may be attributed to filler reorientation processes caused by polymer creeping or to the destruction of the electrically conductive paths due to the presence of cracks in the glass fibre interphase. Further, the authors found that sensor embedding hardly influences the tensile properties of continuous GF reinforced polypropylene (PP) composite. Full article
(This article belongs to the Special Issue Advances in Glass Fibers)
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Open AccessArticle
Electrospun Nanofiber Mats with Embedded Non-Sintered TiO2 for Dye-Sensitized Solar Cells (DSSCs)
Fibers 2019, 7(7), 60; https://doi.org/10.3390/fib7070060
Received: 29 May 2019 / Revised: 29 June 2019 / Accepted: 1 July 2019 / Published: 4 July 2019
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Abstract
TiO2 is a semiconductor that is commonly used in dye-sensitized solar cells (DSSCs). However, the necessity of sintering the TiO2 layer is usually problematic due to the desired temperatures of typically 500 °C in cells that are prepared on polymeric or [...] Read more.
TiO2 is a semiconductor that is commonly used in dye-sensitized solar cells (DSSCs). However, the necessity of sintering the TiO2 layer is usually problematic due to the desired temperatures of typically 500 °C in cells that are prepared on polymeric or textile electrodes. This is why textile-based DSSCs often use metal fibers or metallic woven fabrics as front electrodes on which the TiO2 is coated. Alternatively, several research groups investigate the possibilities to reduce the necessary sintering temperatures by chemical or other pre-treatments of the TiO2. Here, we report on a simple method to avoid the sintering step by using a nanofiber mat as a matrix embedding TiO2 nanoparticles. The TiO2 layer can be dyed with natural dyes, resulting in a similar bathochromic shift of the UV/Vis spectrum, as it is known from sintered TiO2 on glass substrates, which indicates an equivalent chemical bonding. Our results indicate a new possibility for producing textile-based DSSCs with TiO2, even on textile fabrics that are not high-temperature resistant. Full article
(This article belongs to the Special Issue Functional Fibers for Next-Generation Flexible Technologies)
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Open AccessArticle
Life Cycle Assessment of Mortars with Incorporation of Industrial Wastes
Fibers 2019, 7(7), 59; https://doi.org/10.3390/fib7070059
Received: 15 April 2019 / Revised: 26 June 2019 / Accepted: 26 June 2019 / Published: 4 July 2019
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Abstract
The production of waste is increasing yearly and, without a viable recycle or reutilization solution, waste is sent to landfills, where it can take thousand to years to degrade. Simultaneously, for the production of new materials, some industries continue to ignore the potential [...] Read more.
The production of waste is increasing yearly and, without a viable recycle or reutilization solution, waste is sent to landfills, where it can take thousand to years to degrade. Simultaneously, for the production of new materials, some industries continue to ignore the potential of wastes and keep on using natural resources for production. The incorporation of waste materials in mortars is a possible solution to avoid landfilling, through their recycling or reutilization. However, no evaluation of their “sustainability” in terms of environmental performance is available in the literature. In this sense, in this research a life cycle assessment was performed on mortars, namely renders, with incorporation of industrials wastes replacing sand and/or cement. For that purpose, eight environmental impact categories (abiotic depletion potential, global warming potential, ozone depletion potential, photochemical ozone creation potential, acidification potential, eutrophication potential, use of non-renewable primary energy resources, and use of renewable primary energy resources) within a “cradle to gate” boundary were analyzed for 19 mortars with incorporation of several industrial wastes: sanitary ware, glass fiber reinforced polymer, forest biomass ashes, and textile fibers. Sixteen out of the 19 mortars under analysis presented, in all environmental impact categories, an equal or better environment performance than a common mortar (used as a reference). The benefits in some environmental impacts were over 20%. Full article
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Open AccessArticle
Experimental Investigation of the Behavior of Self-Form Segmental Concrete Masonry Arches
Fibers 2019, 7(7), 58; https://doi.org/10.3390/fib7070058
Received: 6 June 2019 / Revised: 23 June 2019 / Accepted: 29 June 2019 / Published: 2 July 2019
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Abstract
This research aims to introduce a new technique—off-site and self-form segmental concrete masonry arches fabrication, without the need of construction formwork or centering. The innovative construction method in the current study encompasses two construction materials forms the self-form masonry arches, wedge-shape plain concrete [...] Read more.
This research aims to introduce a new technique—off-site and self-form segmental concrete masonry arches fabrication, without the need of construction formwork or centering. The innovative construction method in the current study encompasses two construction materials forms the self-form masonry arches, wedge-shape plain concrete voussoirs, and carbon fiber-reinforced polymer (CFRP) composites. The employment of CFRP fabrics was for two main reasons: bonding the voussoirs and forming the masonry arches. In addition, CFRP proved to be efficient for strengthening the extrados of the arch rings under service loadings. An experimental test was conducted on four sophisticated masonry arch specimens. The research parameters were the Keystone thickness and the strengthening of the self-form arch ring at the intrados. The major test finding was that the use of thicker Keystone alters the behavior of the self-form arch and considerably increases the load carrying capacity by 79%. Partial strengthening of the intrados with CFRP fabrics of typical arch ring Keystone resulted considerable increase in the debonding load of fabrication CFRP sheets by 81%, increase in the localized crushing load by 13% and considerably increase voussoir sliding load by 107%. Full article
(This article belongs to the Special Issue Carbon Fiber Reinforced Composites 2019)
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