Open AccessArticle
Extruded Monofilament and Multifilament Thermoplastic Stitching Yarns
Fibers 2017, 5(4), 45; doi:10.3390/fib5040045 -
Abstract
Carbon fibre reinforced polymer composites offer significant improvement in overall material strength to weight, when compared with metals traditionally used in engineering. As a result, they are replacing metals where overall weight is a significant consideration, such as in the aerospace and automotive
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Carbon fibre reinforced polymer composites offer significant improvement in overall material strength to weight, when compared with metals traditionally used in engineering. As a result, they are replacing metals where overall weight is a significant consideration, such as in the aerospace and automotive industries. However, due to their laminate structure, delamination is a prime concern. Through-thickness stitching has been shown to be a relatively simple method of improving resistance to delamination. In this paper, monofilament and multifilament fibres of a similar overall diameter were characterised and their properties compared for their suitability as stitching yarns. Dissimilar to other published works which rely on commercially available materials, such as polyparaphenylene terephthalamide, criteria were produced on the required properties and two potentially promising polymers were selected for extrusion. It was found that although the multifilament fibres had a greater ultimate tensile strength, they began to yield at a lower force than their monofilament equivalent. Full article
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Open AccessArticle
Hollow-Core FRP–Concrete–Steel Bridge Columns under Torsional Loading
Fibers 2017, 5(4), 44; doi:10.3390/fib5040044 -
Abstract
This paper presents the behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns under cyclic torsional loading combined with constant axial load. The HC-FCS consists of an outer fiber-reinforced polymer (FRP) tube and an inner steel tube, with a concrete shell sandwiched between the two
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This paper presents the behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns under cyclic torsional loading combined with constant axial load. The HC-FCS consists of an outer fiber-reinforced polymer (FRP) tube and an inner steel tube, with a concrete shell sandwiched between the two tubes. The FRP tube was stopped at the surface of the footing, and provided confinement to the concrete shell from the outer direction. The steel tube was embedded into the footing to a length of 1.8 times the diameter of the steel tube. The longitudinal and transversal reinforcements of the column were provided by the steel tube only. A large-scale HC-FCS column with a diameter of 24 in. (610 mm) and applied load height of 96 in. (2438 mm) with an aspect ratio of four was investigated during this study. The study revealed that the torsional behavior of the HC-FCS column mainly depended on the stiffness of the steel tube and the interactions among the column components (concrete shell, steel tube, and FRP tube). A brief comparison of torsional behavior was made between the conventional reinforced concrete columns and the HC-FCS column. The comparison illustrated that both column types showed high initial stiffness under torsional loading. However, the HC-FCS column maintained the torsion strength until a high twist angle, while the conventional reinforced concrete column did not. Full article
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Open AccessArticle
Strong Light Localization and a Peculiar Feature of Light Leakage in the Negative Curvature Hollow Core Fibers
Fibers 2017, 5(4), 43; doi:10.3390/fib5040043 -
Abstract
In this paper we would like to continue a discussion started in our previous work and devoted to the mechanism of light localization in hollow core microstructured fibers with a noncircular core-cladding boundary. It has been shown in many works that, for waveguide
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In this paper we would like to continue a discussion started in our previous work and devoted to the mechanism of light localization in hollow core microstructured fibers with a noncircular core-cladding boundary. It has been shown in many works that, for waveguide microstructures with different types of core-cladding boundary shape, the positions of the transmission bands’ edges can be predicted by applying the well-known anti–resonant reflecting optical waveguide (ARROW) model. At the same time, the ARROW model cannot explain the strong light localization and guiding at high material loss inside the transmission bands which are observed in negative curvature hollow core fibers, for example. In this paper we want to clarify our previous findings and consider the light localization process from another point of view, namely, by comparing the light leakage process in waveguide microstructures with different shapes of the core-cladding boundary. The results are discussed based on the ARROW model and a new approach associated with the consideration of spatial dispersion occurring under the interaction of the air core mode with the core-cladding boundary. Full article
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Open AccessArticle
Investigation of Mechanical Properties and Morphology of Multi-Walled Carbon Nanotubes Reinforced Cellulose Acetate Fibers
Fibers 2017, 5(4), 42; doi:10.3390/fib5040042 -
Abstract
Cellulose acetate (CA) fibers were reinforced with multi-walled carbon nanotubes (MWCNTs) at 0.5%, 1.0%, 1.5% and 2.0%. Yield strength, ultimate tensile strength, fracture strain and toughness of the nanocomposite fiber increased up to 1.5 wt. % of the carbon nanotube (CNT) loading, however,
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Cellulose acetate (CA) fibers were reinforced with multi-walled carbon nanotubes (MWCNTs) at 0.5%, 1.0%, 1.5% and 2.0%. Yield strength, ultimate tensile strength, fracture strain and toughness of the nanocomposite fiber increased up to 1.5 wt. % of the carbon nanotube (CNT) loading, however, further inclusion (2.0%) of MWCNTs in CA decreased the mechanical properties. Experimental properties were also compared with analytical predictions using a Shear lag model for strength and the rule of mixture for modulus. A solution spinning process, coupled with sonication, mixing, and extrusion, was used to process the CNT-reinforced composite fiber. Scanning electron microscopy (SEM) images of the cross sections of neat CA and CA-MWCNT fibers showed the formation of voids and irregular features. The enhanced interconnected fibrillation in the CNT-reinforced CA samples resulted in improved mechanical properties, which were observed by tensile testing. Fourier transform infrared spectroscopy (FTIR) spectra showed the area under the curve for C–H bonding after the inclusion of CNT. There was no significant shift of wavenumber for the inclusion of MWCNT in the CA matrix, which indicates that the sonication process of the CNT-loaded solution did not degrade the CA bonding structure. Full article
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Open AccessCommunication
Tolnaftate-Loaded PolyacrylateElectrospun Nanofibers for an Impressive Regimen on Dermatophytosis
Fibers 2017, 5(4), 41; doi:10.3390/fib5040041 -
Abstract
Dermatophytosis, topical fungal infection is the most common cause of skin bug in the world, generally underestimated and ignored. It is commonly caused by immensely mortifying and keratinophilic fungal eukaryotes which invade keratinized tissues and generate different tinea diseases in Mediterranean countries. We
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Dermatophytosis, topical fungal infection is the most common cause of skin bug in the world, generally underestimated and ignored. It is commonly caused by immensely mortifying and keratinophilic fungal eukaryotes which invade keratinized tissues and generate different tinea diseases in Mediterranean countries. We herein fabricated nanofibers/scaffolds embedded with thiocarbamate derivative topical antifungal tolnaftatefor the first time to target the complete elimination of dermatophyte at the site of infection. In this regard, variable combinations of biocompatible Eudragit grades (ERL100 and ERS100) were selected to provide better adhesion on the site of dermatophytosis, ample absorption of exudates during treatment, and customized controlled drug release. Surface topography analysis indicated that the fabricated nanofibers were regular and defect-free, comprising distinct pockets with nanoscaled diameters. Characterization and compatibility studies of tolnaftate, polymers, and their nanofibers were performed through ATR-FTIR, TGA, and PXRD. Remarkable hydrophilicity and an excellent swelling index were obtained from a 3:1 ratio of ERL100/ERS100 electrospun D3 nanofibers, which is an essential benchmark for the fabrication of nanofibrous scaffolds for alleviating dermatophytosis. In vitro drug release investigation revealed that a nonwoven nanomesh of nanofibers could control the rate of drug release for 8 h. A microdilution assay exhibited inhibition of more than 95% viable cells of Trichophyton rubrum for 96 h. However, Microsporum species rigidly restricted the effect of bioactive antifungal nanofibers and hence showed resistance. In vivo activity on Trichophyton rubrum infected Swiss albino mice revealed complete inhibition of fungal pathogens on successive applications of D3 nanofibers for 7 days. This investigation suggests potential uses of tolnaftate loaded polyacrylate nanofibers as dressing materials/scaffolds for effective management of dermatophytosis. Full article
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Open AccessReview
Polymer/Carbon Nanotubes (CNT) Nanocomposites Processing Using Additive Manufacturing (Three-Dimensional Printing) Technique: An Overview
Fibers 2017, 5(4), 40; doi:10.3390/fib5040040 -
Abstract
Additive manufacturing (AM)/3D printing (3DP) is a revolutionary technology which has been around for more than two decades, although the potential of this technique was not fully explored until recently. Because of the expansion of this technology in recent years, new materials and
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Additive manufacturing (AM)/3D printing (3DP) is a revolutionary technology which has been around for more than two decades, although the potential of this technique was not fully explored until recently. Because of the expansion of this technology in recent years, new materials and additives are being searched for to meet the growing demand. 3DP allows accurate fabrication of complicated models, however, structural anisotropy caused by the 3DP approaches could limit robust application. A possible solution to the inferior properties of the 3DP based materials compared to that of conventionally manufactured counterparts could be the incorporation of nanoparticles, such as carbon nanotubes (CNT) which have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review some of the research, products, and challenges involved in 3DP technology. The importance of CNT dispersion in the matrix polymer is highlighted and the future outlook for the 3D printed polymer/CNT nanocomposites is presented. Full article
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Open AccessFeature PaperArticle
Hydration Phenomena of Functionalized Carbon Nanotubes (CNT)/Cement Composites
Fibers 2017, 5(4), 39; doi:10.3390/fib5040039 -
Abstract
The exciting features of carbon nanotubes (CNTs), such as high elastic modulus, high thermal and electrical conductivities, robustness, and nanoscopic surface properties make them attractive candidates for the cement industry. They have the potential to significantly enhanceengineering properties. CNTs play an important and
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The exciting features of carbon nanotubes (CNTs), such as high elastic modulus, high thermal and electrical conductivities, robustness, and nanoscopic surface properties make them attractive candidates for the cement industry. They have the potential to significantly enhanceengineering properties. CNTs play an important and critical role as nano-anchors in concrete, which enhance the strength by bridging pores in the composite matrix, thereby ensuring robust mechanical strength. The diameter, dispersion, aspect ratio, and interfacial surface interaction of CNTs affect the physical and mechanical properties of concrete, if due care is not taken. In this paper, the usable amount of CNT is scaled down considerably from 0.5% to 0.025% by weight of the cement and the fluctuation caused by these phenomena is assessed. It is observed that the properties and exact quantities of incorporated CNTs influence the hydration and consistency of the composites. In order to address these issues, the surface functionalization of CNTs and rheological studies of the composites are performed. The hydration products and functional groups are carefully optimized and characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and a Zeta potential analyzer. For Mixes 6 and 7, the compressive and tensile strength of CNTs incorporated in mortar specimens caused77% and 48% increases in split tensile strength, respectively, and 17% and 35% increases in compressive strength, respectively, after 28 days of curing and compared withthe control Mix. Full article
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Open AccessReview
Multiscale Polymer Composites: A Review of the Interlaminar Fracture Toughness Improvement
Fibers 2017, 5(4), 38; doi:10.3390/fib5040038 -
Abstract
Composite materials are prone to delamination as they are weaker in the thickness direction. Carbon nanotubes (CNTs) are introduced as a multiscale reinforcement into the fiber reinforced polymer composites to suppress the delamination phenomenon. This review paper presents the detailed progress made by
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Composite materials are prone to delamination as they are weaker in the thickness direction. Carbon nanotubes (CNTs) are introduced as a multiscale reinforcement into the fiber reinforced polymer composites to suppress the delamination phenomenon. This review paper presents the detailed progress made by the scientific and research community to-date in improving the Mode I and Mode II interlaminar fracture toughness (ILFT) by various methodologies including the effect of multiscale reinforcement. Methods of measuring the Mode I and Mode II fracture toughness of the composites along with the solutions to improve them are presented. The use of different methodologies and approaches along with their performance in enhancing the fracture toughness of the composites is summarized. The current state of polymer-fiber-nanotube composites and their future perspective are also deliberated. Full article
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Open AccessArticle
Characterisation of the Anisotropic Thermoelastic Properties of Natural Fibres for Composite Reinforcement
Fibers 2017, 5(4), 36; doi:10.3390/fib5040036 -
Abstract
There has been a substantial increase in the investigation of the potential of natural fibres as a replacement reinforcement in the traditional fibre reinforced polymer composite application. However, many researchers often overlook the anisotropic properties of these fibres, and the estimation of the
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There has been a substantial increase in the investigation of the potential of natural fibres as a replacement reinforcement in the traditional fibre reinforced polymer composite application. However, many researchers often overlook the anisotropic properties of these fibres, and the estimation of the potential reinforcement performance. A full understanding of the thermoelastic anisotropy of natural fibres is important for realistically predicting their potential performance in composite applications. In this study, the thermoelastic properties of flax and sisal fibres were determined through a combination of experimental measurements and micromechanical modelling. The results confirm the high degree of anisotropy in properties of the flax and sisal fibres. The implications of these results on using natural fibres as an engineering composite reinforcement are discussed. Full article
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Open AccessArticle
Solid Tellurite Optical Fiber Based on Stack-and-Draw Method for Mid-Infrared Supercontinuum Generation
Fibers 2017, 5(4), 37; doi:10.3390/fib5040037 -
Abstract
Broadband, high-power mid-infrared (mid-IR) sources are critical for many applications. Compared to alternatives such as fluorides and chalcogenides, tellurite fibers are more robust and can handle much higher power. Tellurite fibers also have high nonlinearity and a material zero dispersion close to 2
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Broadband, high-power mid-infrared (mid-IR) sources are critical for many applications. Compared to alternatives such as fluorides and chalcogenides, tellurite fibers are more robust and can handle much higher power. Tellurite fibers also have high nonlinearity and a material zero dispersion close to 2 µm, making them ideal for nonlinear processes pumped by Tm-doped silica fiber lasers. In this work, we have demonstrated solid tellurite fibers fabricated by a stack-and-draw process and investigated their potential for broadband mid-IR supercontinuum generation. We have identified that fibers with low dispersion are beneficial and that low residual hydroxyl (OH) is critical for broadband mid-IR supercontinuum generation in tellurite fibers pumped at ~2 µm. Full article
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Open AccessArticle
Surface Functionalization of “Rajshahi Silk” Using Green Silver Nanoparticles
Fibers 2017, 5(3), 35; doi:10.3390/fib5030035 -
Abstract
In this study, a novel functionalization approach has been addressed by using sodium alginate (Na-Alg) assisted green silver nanoparticles (AgNPs) on traditional “Rajshahi silk” fabric via an exhaustive method. The synthesized nanoparticles and coated silk fabrics were characterized by different techniques, including ultraviolet–visible
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In this study, a novel functionalization approach has been addressed by using sodium alginate (Na-Alg) assisted green silver nanoparticles (AgNPs) on traditional “Rajshahi silk” fabric via an exhaustive method. The synthesized nanoparticles and coated silk fabrics were characterized by different techniques, including ultraviolet–visible spectroscopy (UV–vis spectra), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR), which demonstrated that AgNPs with an average size of 6–10 nm were consistently deposited in the fabric surface under optimized conditions (i.e., pH 4, temperature 40 °C, and time 40 min). The silk fabrics treated with AgNPs showed improved colorimetric values and color fastness properties. Moreover, the UV-protection ability and antibacterial activity, as well as other physical properties—including tensile properties, the crease recovery angle, bending behavior, the yellowness index, and wettability (surface contact angle) of the AgNPs-coated silk were distinctly augmented. Therefore, green AgNPs-coated traditional silk with multifunctional properties has high potential in the textile industry. Full article
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Open AccessArticle
Antimicrobial Electrospun Fibers of Polyester Loaded with Engineered Cyclic Gramicidin Analogues
Fibers 2017, 5(3), 34; doi:10.3390/fib5030034 -
Abstract
Biodegradable polyester fibers have been loaded with two engineered analogues of gramicidin soviet. In these cyclic peptide derivatives, which were designed in a previous work to stabilize the bioactive conformation while enhancing the antimicrobial activity, the D-Phe was replaced by D-Pro, and the
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Biodegradable polyester fibers have been loaded with two engineered analogues of gramicidin soviet. In these cyclic peptide derivatives, which were designed in a previous work to stabilize the bioactive conformation while enhancing the antimicrobial activity, the D-Phe was replaced by D-Pro, and the L-Pro was changed by 1-aminocyclopropanecarboxylic acid (Ac3c) or by an Ac3c derivative with two vicinal phenyl substituents in a trans relative disposition (S,S-c3diPhe). The diameter, topography, thermal stability and wettability of the polyester fibers, which have been obtained by electrospinning, strongly depend on the molecular constraints and stability of the loaded peptides. More specifically, unloaded and linear gramicidin-loaded fibers (used as control) are hydrophobic, rough and micrometric, while fibers loaded with the cyclic peptides are hydrophilic, ultra-smooth, nanometric and less thermally stable. The activity of the two cyclic peptides increases when loaded into polyester fibers, suggesting that the polymeric matrix stabilizes the bioactive β-sheet structure. The peptide with S,S-c3diPhe displays higher antibiotic potency and biocompatibility than that with Ac3c, which indicates not only that the bioactive conformation is better preserved by the former but also the significant role played by the phenyl rings in the recognition by living cells. Full article
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Open AccessArticle
Effects of Surfactants on the Morphology and Properties of Electrospun Polyetherimide Fibers
Fibers 2017, 5(3), 33; doi:10.3390/fib5030033 -
Abstract
Electrospun fibers often have beads as byproducts. Bead formation can be substantially minimized by the introduction of additives, such as ionic salts or surfactants, to the electrospinning polymeric solution. Polyetherimide (PEI) fibers were fabricated using electrospinning. Four different additives, Lithium Chloride (LiCl), Sodium
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Electrospun fibers often have beads as byproducts. Bead formation can be substantially minimized by the introduction of additives, such as ionic salts or surfactants, to the electrospinning polymeric solution. Polyetherimide (PEI) fibers were fabricated using electrospinning. Four different additives, Lithium Chloride (LiCl), Sodium Chloride (NaCl), Triton X-100 and Hexadecyltrimethylammonium Bromide (HTAB) were utilized to alter the polymer solution electrical conductivity and surface tensions. The effects of solution conductivity and surface tension on the electrospinning and the thermal, mechanical stability of the polymeric fibers were investigated. Morphology, thermal properties, permeability and mechanical strength of the fiber mats were investigated using Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Frazier Permeability Test, and Tensile tester respectively. The addition of 1.5wt.% HTAB was found to be the optimum concentration to produce PEI fibers without beads. The addition of HTAB produced fiber mats with higher air permeability, higher thermal stability and higher mechanical strength in comparison to the other additives. Finally, a filtration test was conducted on a simple custom model to compare the performance of beaded and non-beaded PEI fiber mats. The non-beaded PEI fiber mat performed better in terms of both separation efficiency (%E) and differential pressure drop (ΔP) separating water droplets from diesel fuel. Full article
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Open AccessArticle
Multi-Scale Carbon (Micro/Nano) Fiber Reinforcement of Polyetheretherketone Using High Shear Melt-Processing
Fibers 2017, 5(3), 32; doi:10.3390/fib5030032 -
Abstract
Fiber-reinforced polymer matrix composites offer lightweight, high mechanical performance but have required much effort to achieve good fiber–matrix adhesion and uniform distribution, and generally suffer from low impact resistance. In this work, a uniform, high shear melt-processing method was used to prepare carbon
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Fiber-reinforced polymer matrix composites offer lightweight, high mechanical performance but have required much effort to achieve good fiber–matrix adhesion and uniform distribution, and generally suffer from low impact resistance. In this work, a uniform, high shear melt-processing method was used to prepare carbon fiber (CF) reinforced polyetheretherketone (PEEK), carbon nanofiber (CNF) reinforced PEEK, and multi-scale CF and CNF reinforced PEEK composites. Scanning electron microscopy images show good fiber distribution and fiber–matrix interaction, as well as surface crystallization of PEEK from the fiber surfaces. Tensile modulus and strength increase most significantly with the addition of CF but with a loss in ductility. The multi-scale composite of CF–CNF-PEEK displays the stiffening effect from the CF and retains more ductility due to the CNF. Further, the CF–CNF-PEEK composite displays the highest impact energy absorption. This study shows that good mixing of CFs and CNFs is achievable in PEEK using a uniform, high shear processing method that can easily produce intricate shapes and provides a stiff, high impact energy absorption multi-scale carbon fiber-reinforced composite. Full article
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Open AccessArticle
In Situ Produced Bacterial Cellulose Nanofiber-Based Hybrids for Nanocomposites
Fibers 2017, 5(3), 31; doi:10.3390/fib5030031 -
Abstract
Two high-performance bacterial cellulose (BC) nanofiber-based hybrid structures were produced using an in situ self-assembly approach, one with microfibrillated cellulose (MFC) and another with sisal fiber, by incorporating them in the fermentation media. The fabricated BC-MFC hybrid and BC-sisal hybrid fibers showed enhanced
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Two high-performance bacterial cellulose (BC) nanofiber-based hybrid structures were produced using an in situ self-assembly approach, one with microfibrillated cellulose (MFC) and another with sisal fiber, by incorporating them in the fermentation media. The fabricated BC-MFC hybrid and BC-sisal hybrid fibers showed enhanced mechanical properties compared to pure BC and sisal fibers, respectively. Tensile tests indicated BC-MFC hybrid and their nanocomposites fabricated with soy protein isolate (SPI) resin had better tensile properties than corresponding BC and BC-SPI nanocomposites. This was because of the uniform distribution of MFC within the BC nanofiber network structure which reduced the defects such as pores and voids or intersections of the BC nanofibers. BC-sisal hybrid fibrous structures were obtained after BC nanofibers self-assembled on the surface of the sisal fibers during the fermentation. The results of the microbond tests indicated that the BC-sisal hybrid fiber/SPI resin bond strength was higher than the control sisal fiber/SPI resin bond with p value of 0.02 at the significance level of 0.05. Higher bond strength is preferred since it can potentially lead to better tensile properties of the composites. The presented work suggests a novel route to fabricate hybrid nanocomposites with higher functional properties. Full article
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Open AccessArticle
The Thermal Conductivities of Periodic Fibrous Composites as Defined by a Mathematical Model
Fibers 2017, 5(3), 30; doi:10.3390/fib5030030 -
Abstract
In this paper, a geometric body-centered model to simulate the periodic structure of unidirectional fibrous composites is presented. To this end, three prescribed configurations are introduced to predict in a deterministic manner the arrangement of internal and neighboring fibers inside the matrix. Thus,
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In this paper, a geometric body-centered model to simulate the periodic structure of unidirectional fibrous composites is presented. To this end, three prescribed configurations are introduced to predict in a deterministic manner the arrangement of internal and neighboring fibers inside the matrix. Thus, three different representative volume elements (RVEs) are established. Furthermore, the concept of the interphase has been taken into account, stating that each individual fiber is encircled by a thin layer of variable thermomechanical properties. Next, these three unit cells are transformed in a unified manner to a coaxial multilayer cylinder model. This advanced model includes the influence of fiber contiguity in parallel with the interphase concept on the thermomechanical properties of the overall material. Then, by the use of this model, the authors propose explicit expressions to evaluate the longitudinal and transverse thermal conductivity of this type of composite. The theoretical predictions were compared with experimental results, as well as with theoretical values yielded by some reliable formulae derived from other workers, and a reasonable agreement was found. Full article
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Open AccessArticle
Manufacturing and Spectral Features of Different Types of Long Period Fiber Gratings: Phase-Shifted, Turn-Around Point, Internally Tilted, and Pseudo-Random
Fibers 2017, 5(3), 29; doi:10.3390/fib5030029 -
Abstract
The manufacturing and spectral features of different types of long period fiber gratings (LPFGs), ranging from phase-shifted, turn-around point, and internally tilted gratings, to pseudo-random gratings, are described and discussed in detail. LPFGs were manufactured on boron-germanium co-doped photosensitive optical fibers with the
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The manufacturing and spectral features of different types of long period fiber gratings (LPFGs), ranging from phase-shifted, turn-around point, and internally tilted gratings, to pseudo-random gratings, are described and discussed in detail. LPFGs were manufactured on boron-germanium co-doped photosensitive optical fibers with the point-by-point technique using an excimer KrF laser operating at 248 nm. The developed experimental setup to manufacture high-quality LPFGs was designed to totally customize any type of gratings with the possibility of setting different parameters, such as the grating period (or pitch), the number of grating planes, the number of laser shots for each plane, etc. Some important spectral features of the LPFGs’ spectra were taken into account. This allows realizing homemade devices useful in several fiber-based applications, such as optical filtering, coupling systems, random lasers, physical and chemical sensing, and biosensing. Full article
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Open AccessArticle
Fabrication and Characterization of Polymer Optical Fibers Doped with Perylene-Derivatives for Fluorescent Lighting Applications
Fibers 2017, 5(3), 28; doi:10.3390/fib5030028 -
Abstract
Four different dye-doped polymer optical fibers (POFs) have been fabricated following a two-step fabrication process of preform extrusion and fiber drawing, using poly-(methyl methacrylate) (PMMA) as host material and dye derivatives from perylene and naphtalimide as active dopants. The side illumination technique (SIT)
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Four different dye-doped polymer optical fibers (POFs) have been fabricated following a two-step fabrication process of preform extrusion and fiber drawing, using poly-(methyl methacrylate) (PMMA) as host material and dye derivatives from perylene and naphtalimide as active dopants. The side illumination technique (SIT) has been employed in order to determine some optical properties of the fabricated fibers, such as the side illumination coupling efficiency, optical loss coefficients, and their performance under solar simulator excitation. The aim of this work is to investigate the performance of the manufactured fibers for fluorescent lighting applications, specially targeting on fluorescent fiber based solar concentrators. Full article
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Open AccessArticle
A Model for the Prediction of the Tensile Strength of Fiber-Reinforced Concrete Members, Before and After Cracking
Fibers 2017, 5(3), 27; doi:10.3390/fib5030027 -
Abstract
The tensile behavior of concrete or mortar plays an important role for delaying the formation and propagation of cracks, and also for upgrading the bearing capacity of existing concrete and masonry constructions. Although the presence of steel fibers is known to improve, often
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The tensile behavior of concrete or mortar plays an important role for delaying the formation and propagation of cracks, and also for upgrading the bearing capacity of existing concrete and masonry constructions. Although the presence of steel fibers is known to improve, often considerably, the tensile capacity of concrete members, methods for the quantification of this improvement are still limited. For this reason, a model has been developed for the prediction of the tensile strength of steel fiber-reinforced concrete members, as crack opening occurs. Given the geometry and the physical characteristics of reinforced concrete member and fibers, the model predicts: (1) the number of fibers crossing a crack’s surface; (2) the distribution of these fibers in terms of (i) the angle a fiber forms with the crack surface (fiber inclination) and (ii) the embedded length of the fiber at both sides of the surface; (3) resistance to crack opening provided by each fiber, in relation to its position and inclination. On the results of the results obtained, the influence of the number of fibers on the reduction of crack widening in concrete or mortar is remarkable and can be estimated with satisfactory precision. In upgrading existing concrete and masonry constructions, this tensile behavior is found to play important role. Full article
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Open AccessArticle
Commingled Yarn Spinning for Thermoplastic/Glass Fiber Composites
Fibers 2017, 5(3), 26; doi:10.3390/fib5030026 -
Abstract
Online commingled yarns were spun with three different polymeric matrices, namely polypropylene (PP), polyamide (PA) and polylactic acid (PLA) and glass fibers. Tailored sizings were applied for the three matrices and the resulting mechanical performance of unidirectional composites was evaluated and compared. Significant
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Online commingled yarns were spun with three different polymeric matrices, namely polypropylene (PP), polyamide (PA) and polylactic acid (PLA) and glass fibers. Tailored sizings were applied for the three matrices and the resulting mechanical performance of unidirectional composites was evaluated and compared. Significant improvements in the fiber/matrix bonding were achieved by employed sizing chemistry in order to achieve multifunctional interphases. The pure silane coupling agents provide the best performance for all matrices investigated. However, an additional film former has to be added in order to achieve fiber processing. Film formers compatible to the matrices investigated were adapted. The consolidation behavior during isothermal molding was investigated for polypropylene matrix. Different fiber volume contents could be realized and the resulting mechanical properties were tested. Full article
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