Fibers

12 pages, 2752 KiB

Open AccessEditor’s ChoiceArticle

Production of Nanofibers by Blow Spinning from Polylactide Containing Propolis and Beeswax

by Agata Penconek, Maciej Kilarski, Anna Soczewka, Michał Wojasiński and Arkadiusz Moskal

Fibers 2024, 12(1), 8; https://doi.org/10.3390/fib12010008 - 12 Jan 2024

Cited by 2 | Viewed by 2066

The growing pollution of the environment with slowly decomposing waste, as well as the increasing drug resistance of pathogens, including the antibiotic resistance of bacteria, has led to a search for new solutions based on biodegradable and natural materials, which are known for [...] Read more.

The growing pollution of the environment with slowly decomposing waste, as well as the increasing drug resistance of pathogens, including the antibiotic resistance of bacteria, has led to a search for new solutions based on biodegradable and natural materials, which are known for their potential bacteriostatic properties. This study aimed to produce nanofibers by blowing from a polylactide (PLA) polymer solution containing natural compounds (e.g., beeswax, propolis). As a result of the conducted research, nanofibers were produced from PLA solutions containing various additives. The fibers’ mean diameter ranges from 0.36 to 2.38 µm, depending on the process parameters. To the authors’ knowledge, fibers were produced for the first time by blow spinning from a polymer solution containing propolis and beeswax. Full article

(This article belongs to the Special Issue Nanofibers: Biomedical Applications)

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19 pages, 3438 KiB

Open AccessEditor’s ChoiceArticle

Failure Mode Prediction of Unreinforced Masonry (URM) Walls Retrofitted with Cementitious Textile Reinforced Mortar (TRM)

by Athanasia K. Thomoglou, Martha A. Karabini, Dimitra V. Achillopoulou, Theodoros C. Rousakis and Constantin E. Chalioris

Fibers 2023, 11(6), 53; https://doi.org/10.3390/fib11060053 - 15 Jun 2023

Cited by 6 | Viewed by 2561

Abstract

The brittle failure of unreinforced masonry (URM) walls when subjected to in-plane loads present low shear strength remains a critical issue. The investigation presented in this paper touches on the retrofitting of URM structures with textile-reinforced mortar (TRM), which enables shifting the shear [...] Read more.

The brittle failure of unreinforced masonry (URM) walls when subjected to in-plane loads present low shear strength remains a critical issue. The investigation presented in this paper touches on the retrofitting of URM structures with textile-reinforced mortar (TRM), which enables shifting the shear failure mode from a brittle to a pseudo-ductile mode. Despite many guidelines for applying composite materials for retrofitting and predicting the performance of strengthened structures, the application of TRM systems in masonry walls is not extensively described. A thorough retrospect of the literature is presented, containing research results relating to different masonry walls, e.g., bricks, cement, and stone blocks strengthened with TRM jackets and subjected to diagonal compression loads. The critical issue of this study is the failure mode of the retrofitted masonry walls. Available prediction models are presented, and their predictions are compared to the experimental results based on their failure modes. The novelty of this study is the more accurate failure mode prediction of reinforced masonry with TRM and also of the shear strength with the proposed model, Thomoglou et al., 2020, at an optimal level compared to existing regulations and models. The novel prediction model estimates the shear failure mode of the strengthened wall while considering the contribution of all components, e.g., block, render mortar, strengthening textile, and cementitious matrix, by modifying the expressions of the Eurocode 8 provisions. The results have shown that the proposed model presents an optimum accuracy in predicting the failure mode of all different masonry walls strengthened with various TRM jackets and could be taken into account in the regulations for reliable forecasting. 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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42 pages, 15346 KiB

Open AccessEditor’s ChoiceReview

A Review of Fibre Reinforced Polymer Bridges

by Jawed Qureshi

Fibers 2023, 11(5), 40; https://doi.org/10.3390/fib11050040 - 4 May 2023

Cited by 10 | Viewed by 10492

Abstract

Fibre-reinforced polymer composites (FRPs) offer various benefits for bridge construction. Lightweight, durability, design flexibility and fast erection in inaccessible areas are their unique selling points for bridge engineering. FRPs are used in four bridge applications: (1) FRP rebars/tendons in concrete; (2) repair and [...] Read more.

Fibre-reinforced polymer composites (FRPs) offer various benefits for bridge construction. Lightweight, durability, design flexibility and fast erection in inaccessible areas are their unique selling points for bridge engineering. FRPs are used in four bridge applications: (1) FRP rebars/tendons in concrete; (2) repair and strengthening of existing bridges; (3) new hybrid–FRP bridges with conventional materials and (4) all–FRP composite new bridges made entirely of FRP materials. This paper reviews FRP bridges, including all–FRP and hybrid–FRP bridges. FRP bridges’ history, materials, processes and bridge components—deck, girder, truss, moulded parts and cables/rebars are considered. This paper does not discuss the use of FRP as an architectural element and a strengthening system. While lack of design codes, material specifications and recycling are the major challenges, the high cost of FRPs still remains the most critical barrier to the progress of FRPs in bridges. Full article

(This article belongs to the Collection Review Papers of Fibers)

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40 pages, 4925 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Mechanical Properties and Morphological Alterations in Fiber-Based Scaffolds Affecting Tissue Engineering Outcomes

by James Dolgin, Samerender Nagam Hanumantharao, Stephen Farias, Carl G. Simon, Jr. and Smitha Rao

Fibers 2023, 11(5), 39; https://doi.org/10.3390/fib11050039 - 29 Apr 2023

Cited by 14 | Viewed by 3717

Abstract

Electrospinning is a versatile tool used to produce highly customizable nonwoven nanofiber mats of various fiber diameters, pore sizes, and alignment. It is possible to create electrospun mats from synthetic polymers, biobased polymers, and combinations thereof. The post-processing of the end products can [...] Read more.

Electrospinning is a versatile tool used to produce highly customizable nonwoven nanofiber mats of various fiber diameters, pore sizes, and alignment. It is possible to create electrospun mats from synthetic polymers, biobased polymers, and combinations thereof. The post-processing of the end products can occur in many ways, such as cross-linking, enzyme linking, and thermal curing, to achieve enhanced chemical and physical properties. Such multi-factor tunability is very promising in applications such as tissue engineering, 3D organs/organoids, and cell differentiation. While the established methods involve the use of soluble small molecules, growth factors, stereolithography, and micro-patterning, electrospinning involves an inexpensive, labor un-intensive, and highly scalable approach to using environmental cues, to promote and guide cell proliferation, migration, and differentiation. By influencing cell morphology, mechanosensing, and intracellular communication, nanofibers can affect the fate of cells in a multitude of ways. Ultimately, nanofibers may have the potential to precisely form whole organs for tissue engineering, regenerative medicine, and cellular agriculture, as well as to create in vitro microenvironments. In this review, the focus will be on the mechanical and physical characteristics such as porosity, fiber diameter, crystallinity, mechanical strength, alignment, and topography of the nanofiber scaffolds, and the impact on cell proliferation, migration, and differentiation. Full article

(This article belongs to the Special Issue Nanofibers: Biomedical Applications)

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25 pages, 10545 KiB

Open AccessEditor’s ChoiceArticle

An Electromechanical Impedance-Based Application of Realtime Monitoring for the Load-Induced Flexural Stress and Damage in Fiber-Reinforced Concrete

by Maria C. Naoum, George M. Sapidis, Nikos A. Papadopoulos and Maristella E. Voutetaki

Fibers 2023, 11(4), 34; https://doi.org/10.3390/fib11040034 - 11 Apr 2023

Cited by 17 | Viewed by 2166

Abstract

Effective real-time structural health monitoring in concrete structures is paramount to evaluating safety conditions and the timely maintenance of concrete structures. Especially, the presence of discrete fibers in fiber-reinforced concrete restrains crack propagation into small and thin cracks, which increases the difficulty in [...] Read more.

Effective real-time structural health monitoring in concrete structures is paramount to evaluating safety conditions and the timely maintenance of concrete structures. Especially, the presence of discrete fibers in fiber-reinforced concrete restrains crack propagation into small and thin cracks, which increases the difficulty in detecting damage. In this study, an array of piezoelectric lead zirconate titanate (PZT) transducers was applied to study the effects of external load-induced flexural stress and damage in fiber-reinforced concrete beams using the electromechanical impedance (EMI) or electromechanical admittance (EMA) methods. Beams were subjected to a four-point bending test under repeatable loading, while PZTs evaluated corresponding flexural stress and induced damage simultaneously. Due to the influence of the medium’s stress fields in the different types of wave propagation in structural elements, PZT transducers measurements are accordingly affected under variable stress fields, in addition to the effect of the higher level of damage that occurred in the medium. According to the results of the tests, variation in EMA signatures, following flexural stress and gradual damage changes, provided convincing evidence for predicting stress and damage development. 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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21 pages, 8315 KiB

Open AccessEditor’s ChoiceReview

Textile Fabrics as Electromagnetic Shielding Materials—A Review of Preparation and Performance

by Tomasz Blachowicz, Dariusz Wójcik, Maciej Surma, Mirosław Magnuski, Guido Ehrmann and Andrea Ehrmann

Fibers 2023, 11(3), 29; https://doi.org/10.3390/fib11030029 - 15 Mar 2023

Cited by 15 | Viewed by 6708

Abstract

Shielding of instruments and humans from electromagnetic interference (EMI) has become increasingly important during the last decades due to more and more machines and devices radiating electromagnetic waves. While several applications can use rigid shields, more flexibility is enabled by developing bendable, drapable, [...] Read more.

Shielding of instruments and humans from electromagnetic interference (EMI) has become increasingly important during the last decades due to more and more machines and devices radiating electromagnetic waves. While several applications can use rigid shields, more flexibility is enabled by developing bendable, drapable, ideally even stretchable EMI shielding. Textile fabrics can have these properties, combined with potentially good mechanical properties, depending on the textile structure and the chosen material. On the other hand, the necessary physical properties, especially conductivity and magnetic properties, cannot be taken for granted in normal textile fabrics. These properties have to be added by conductive yarn or layer coatings, integration of conductive or magnetic fibers, producing intrinsically conductive or magnetic fibers, etc. The article gives a critical comparison of the properties of materials typically used for this purpose, such as intrinsically conductive polymers, metal-coated fabrics and metal wires, MXene coatings, MXene fibers, carbon coatings, and fibers. The review concentrates on thematically suitable papers found in the Web of Science and Google Scholar from the last five years and shows that especially MXenes are highly investigated recently due to their high conductivity and EMI shielding effectiveness, while other conductive and magnetic coatings and fibers are nevertheless still interesting for the preparation of EMI shielding textile fabrics. Full article

(This article belongs to the Collection Feature Papers in Fibers)

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17 pages, 4939 KiB

Open AccessEditor’s ChoiceArticle

Application of Transformed Cross-Section Method for Analytical Analysis of Laminated Veneer Lumber Beams Strengthened with Composite Materials

by Michał Marcin Bakalarz and Paweł Grzegorz Kossakowski

Fibers 2023, 11(3), 24; https://doi.org/10.3390/fib11030024 - 23 Feb 2023

Cited by 9 | Viewed by 2489

Abstract

Due to the high cost of laboratory testing, many researchers are considering developing methods to predict the behavior of unreinforced and reinforced wood beams. This work aims to create either numerical or analytical models useful for extrapolating already conducted tests to other schemes/materials [...] Read more.

Due to the high cost of laboratory testing, many researchers are considering developing methods to predict the behavior of unreinforced and reinforced wood beams. This work aims to create either numerical or analytical models useful for extrapolating already conducted tests to other schemes/materials used as reinforcement. In the case of timber structures, due to the complexity of timber, this task is difficult. The first part of the article presents an analysis of the suitability of using a simplified mathematical model based on the equivalent cross-section method to describe the behavior of unreinforced and reinforced with carbon-fibre-reinforced polymer (CFRP) composite full-size laminated veneer lumber (LVL) beams. The theoretical results were compared with the results of conducted experimental tests. The scope of the analysis includes the estimation of modulus of rupture, bending stiffness, and determination of the neutral axis position. The equivalent cross-section method showed good agreement in determining the bending stiffness and neutral axis position of the strengthened sections. However, the suitability of using the equivalent cross-section method to estimate the load-carrying capacity of a cross-section reinforced with fiber composites still needs to be confirmed, which, according to the authors, is due to the differences between the assumed (linear) and actual (nonlinear) strain distribution in the compression zone. The second part uses the equivalent cross-section method to estimate the predicted bending stiffness of LVL beams strengthened with aramid-fibre-reinforced polymer (AFRP), glass-fibre-reinforced polymer (GFRP), and ultra-high modulus carbon-fibre-reinforced polymer (CFRP UHM) sheets. The proposed method can be used for preliminary evaluation of strengthening effectiveness of LVL beams. Full article

(This article belongs to the Special Issue Carbon Fibers from Sustainable Precursors)

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19 pages, 4569 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Synergistic Effect of HEDP.4Na and Different Induced Pouring Angles on Mechanical Properties of Fiber-Reinforced Alkali-Activated Slag Composites

by Jingjie Wei, Jianwei Liu, Kamal H. Khayat and Wu-Jian Long

Fibers 2023, 11(3), 23; https://doi.org/10.3390/fib11030023 - 22 Feb 2023

Cited by 6 | Viewed by 2616

Abstract

The poor flexural and damping properties of building materials damages concrete structures and affects their service life when concrete structures are subjected to dynamic loads. Three different dosages (i.e., 0%, 0.3%, and 0.6%) of organic phosphonates (HEDP.4Na) and different pouring methods (i.e., conventional [...] Read more.

The poor flexural and damping properties of building materials damages concrete structures and affects their service life when concrete structures are subjected to dynamic loads. Three different dosages (i.e., 0%, 0.3%, and 0.6%) of organic phosphonates (HEDP.4Na) and different pouring methods (i.e., conventional pouring method, 90°-induced pouring method, and 150°-induced pouring method) were designed to improve the flexural and damping performance of fiber-reinforced alkali-activated slag composites (FR-AASC). The enhanced mechanism of HEDP.4Na was revealed by phase analysis (X-ray diffraction, XRD), pore structure analysis (Mercury Intrusion Porosimetry, MIP), the heat of hydration, and scanning electron microscopy (SEM) analysis. The results showed that 0.3% HEDP.4Na combined with the 150°-induced pouring angle can significantly improve the mechanical properties of the FR-AASC sample compared with the reference group. The sample with 0.3% HEDP.4Na cast by the 150°-induced pouring angle increased compressive and flexural strength, damping energy consumption and storage modulus by 20%, 60%, 78%, and 30%, respectively, compared with the reference sample cast by the conventional pouring methodology. HEDP.4Na reduced the early hydration heat and total porosity of the FR-AASC matrix, modified the fiber–matrix interface transition zone, and increased the frictional energy consumption of steel fibers. Overall, the synergistic effect of HEDP.4Na and the induced pouring methodology significantly improved the flexural and damping properties of FR-AASC. This study can provide a guidance for improving the flexural and damping capacity of FR-AASC and promote the application of FR-AASC in construction engineering. Full article

(This article belongs to the Special Issue Fracture Behavior of Fiber-Reinforced Building Materials)

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37 pages, 8935 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Nanofibres in Drug Delivery Applications

by Samia Farhaj, Barbara R. Conway and Muhammad Usman Ghori

Fibers 2023, 11(2), 21; https://doi.org/10.3390/fib11020021 - 17 Feb 2023

Cited by 41 | Viewed by 8757

Abstract

Over the years, scientists have been continually striving to develop innovative solutions to design and fabricate medicines with improved therapeutic potential. Conventional dosage forms, such as tablets, capsules, and injections, are limited when exploited for advanced therapeutics, such as drug targeting. To cater [...] Read more.

Over the years, scientists have been continually striving to develop innovative solutions to design and fabricate medicines with improved therapeutic potential. Conventional dosage forms, such as tablets, capsules, and injections, are limited when exploited for advanced therapeutics, such as drug targeting. To cater to these limitations, nanofibres have emerged as novel nanomaterials to provide enhanced bioavailability, targeted drug release, extended drug release profile, minimum toxicity, and reduced dosage frequency, which has indisputably improved patient adherence and compliance. This review will concern understanding the potential of drug-loaded nanofibres in drug delivery while comprehending a detailed description of their different production methods. The literature has been thoroughly reviewed to appreciate their potential in developing nanofibrous-based pharmaceutical formulations. Overall, this review has highlighted the importance, versatility, and adaptability of nanofibres in developing medicines with varied drug release kinetics. Several problems must be resolved for their full commercial realisation, such as the drug loading, the initial burst effect, the residual organic solvent, the stability of active agents, and the combined usage of new or existing biocompatible polymers. Full article

(This article belongs to the Collection Review Papers of Fibers)

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17 pages, 26870 KiB

Open AccessEditor’s ChoiceReview

Carbon Fiber-Reinforced Geopolymer Composites: A Review

by Vojtěch Růžek, Ardak Mukhamedievna Dostayeva, Janusz Walter, Thomas Grab and Kinga Korniejenko

Fibers 2023, 11(2), 17; https://doi.org/10.3390/fib11020017 - 1 Feb 2023

Cited by 19 | Viewed by 4803

Abstract

The article summarizes the state of the art in carbon-reinforced geopolymers. It takes into consideration various types of matrices and types of carbon fibers (CFs). The article shows the growing importance of this composite in the investigation conducted in recent years. Today, it [...] Read more.

The article summarizes the state of the art in carbon-reinforced geopolymers. It takes into consideration various types of matrices and types of carbon fibers (CFs). The article shows the growing importance of this composite in the investigation conducted in recent years. Today, it is one of the most promising modern research areas, taking into account the decrease in the prices of CFs and their appearance on the market waste-based CFs, as well as research on new methods of producing CFs from sustainable precursors. The research methods applied in the article are critical analyses of the literature. The results of the literature analysis are discussed in a comparative context, including production methods and the influence of CFs on geopolymer properties. The potential applications for carbon fiber-reinforced geopolymer composites are shown. Additionally, the current research challenges for geopolymer composites reinforced by CFs are presented. Full article

(This article belongs to the Special Issue Carbon Fibers from Sustainable Precursors)

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23 pages, 954 KiB

Open AccessEditor’s ChoiceArticle

Natural and Sustainable? Consumers’ Textile Fiber Preferences

by Anna Schytte Sigaard and Kirsi Laitala

Fibers 2023, 11(2), 12; https://doi.org/10.3390/fib11020012 - 26 Jan 2023

Cited by 14 | Viewed by 13480

Abstract

Textile fibers have become a major issue in the debate on sustainable fashion and clothing consumption. While consumers are encouraged to choose more sustainable and circular textile materials, studies have indicated that a reduction in production and consumption has the greatest potential to [...] Read more.

Textile fibers have become a major issue in the debate on sustainable fashion and clothing consumption. While consumers are encouraged to choose more sustainable and circular textile materials, studies have indicated that a reduction in production and consumption has the greatest potential to reduce the total environmental impact. This can be considered an ecocentric perspective with a focus on degrowth as opposed to a technocentric view where new technologies are expected to solve environmental problems while economic growth continues. Based on a survey in Norway (N = 1284), we investigate how the techno- and ecocentric perspectives impact Norwegian consumers’ fiber preferences and perceptions and the corresponding effects on their clothing consumption. We found that the majority of consumers preferred natural fibers compared to synthetic materials. This contradicts current market practices and the recommendations by material sustainability comparison tools such as the Higg Material Sustainability Index (MSI), where many synthetics receive better ratings than natural fibers. We also found that perceptions of high sustainability regarding fibers were negatively correlated with reduced consumption. Our study suggests that a continued focus on material substitution and other technological measures for reducing climate change will impede the move toward sustainability in the textile sector. Full article

(This article belongs to the Special Issue Natural Fiber Competitiveness and Sustainability)

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17 pages, 6739 KiB

Open AccessEditor’s ChoiceArticle

Production and 3D Printing of a Nanocellulose-Based Composite Filament Composed of Polymer-Modified Cellulose Nanofibrils and High-Density Polyethylene (HDPE) for the Fabrication of 3D Complex Shapes

by Feras Dalloul, Jakob Benedikt Mietner and Julien R. G. Navarro

Fibers 2022, 10(10), 91; https://doi.org/10.3390/fib10100091 - 21 Oct 2022

Cited by 14 | Viewed by 3497

Abstract

This work aims to produce a 3D-printable bio-based filament composed of high-density polyethylene (HDPE) and chemically modified cellulose nanofibrils. Printing using HDPE as a raw material is challenging due to its massive shrinkage and warping problems. This paper presents a new method to [...] Read more.

This work aims to produce a 3D-printable bio-based filament composed of high-density polyethylene (HDPE) and chemically modified cellulose nanofibrils. Printing using HDPE as a raw material is challenging due to its massive shrinkage and warping problems. This paper presents a new method to overcome those difficulties by enhancing the mechanical properties and achieving better print quality. This was achieved using modified cellulose nanofibrils (CNFs) as fillers. Firstly, CNF was converted to a CNF-based macroinitiator through an esterification reaction, followed by a surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) of the hydrophobic monomer stearyl acrylate. Poly stearyl acrylate-grafted cellulose nanofibrils, CNF-PSAs, were synthesized, purified and characterized with ATR-FTIR, ¹³C CP-MAS NMR, FE-SEM and water contact angle measurements. A composite was successfully produced using a twin-screw extruder with a CNF-PSA content of 10 wt.%. Mechanical tests were carried out with tensile testing. An increase in the mechanical properties, up to 23% for the Young’s modulus, was observed. A morphologic analysis also revealed the good matrix/CNF compatibility, as no CNF aggregates could be observed. A reduction in the warping behavior for the composite filament compared to HDPE was assessed using a circular arc method. The 3D printing of complex objects using the CNF-PSA/HDPE filament resulted in better print quality when compared to the object printed with neat HDPE. Therefore, it could be concluded that CNF-PSA was a suitable filler for the reinforcement of HDPE, thus, rendering it suitable for 3D printing. Full article

(This article belongs to the Topic Cellulose and Cellulose Derivatives)

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22 pages, 1062 KiB

Open AccessEditor’s ChoiceReview

Factors of Weave Estimation and the Effect of Weave Structure on Fabric Properties: A Review

by Most. Setara Begum and Rimvydas Milašius

Fibers 2022, 10(9), 74; https://doi.org/10.3390/fib10090074 - 30 Aug 2022

Cited by 23 | Viewed by 9775

Abstract

This paper provides a review of recent studies on the weave factor along with the effect of weave parameters and particularly the weave structure on various properties of woven fabric. The weave structure can be considered as one of the prime parameters that [...] Read more.

This paper provides a review of recent studies on the weave factor along with the effect of weave parameters and particularly the weave structure on various properties of woven fabric. The weave structure can be considered as one of the prime parameters that contributes to the dominant physical and qualitative properties of the woven fabric. This study analyzed not only the parameters that significantly influence the properties of the woven fabric, but also the weave factors for the estimation of the weave that were proposed by earlier scientists. This review paper highlights the impact of weave structure on the physical and mechanical, thermo-physiological and comfort properties, and some special application properties of woven fabrics. This work seeks to serve as a future reference for related research. Full article

(This article belongs to the Collection Review Papers of Fibers)

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15 pages, 8391 KiB

Open AccessEditor’s ChoiceArticle

Simple Synthesis of Fe₃O₄@-Activated Carbon from Wastepaper for Dispersive Magnetic Solid-Phase Extraction of Non-Steroidal Anti-Inflammatory Drugs and Their UHPLC–PDA Determination in Human Plasma

by Vincenzo Ferrone, Pantaleone Bruni, Valentino Canale, Leonardo Sbrascini, Francesco Nobili, Giuseppe Carlucci and Stefania Ferrari

Fibers 2022, 10(7), 58; https://doi.org/10.3390/fib10070058 - 1 Jul 2022

Cited by 5 | Viewed by 3647

Abstract

In the present society, the recycling and reuse of valuable substances are of utmost importance for economic and environmental purposes. At the same time, there is a pressing need to develop new methods to protect the ecosystem from many human activities, including those [...] Read more.

In the present society, the recycling and reuse of valuable substances are of utmost importance for economic and environmental purposes. At the same time, there is a pressing need to develop new methods to protect the ecosystem from many human activities, including those that have contributed to an ever-increasing presence of pharmaceutical pollutants. In this study, a straightforward approach that applies a magnetic carbon composite for the effective removal of NSAIDs from biological fluids is reported. The composite was produced by recycling wasted handkerchiefs, to provide cellulose to the reactive system and then transformed into carbon via calcination at high temperature. The morphological and structural features of the prepared “Fe₃O₄@-activated carbon” samples were investigated via thermal analysis, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Magnetic solid-state extraction was carried out to reveal the adsorption capabilities of the magnetic carbon composite and then combined with UHPLC–PDA for the determination and quantification of five NSAIDs (furprofen, indoprofen, ketoprofen, flurbiprofen, and indomethacin). The method developed herein proved to be fast and accurate. The adsorbent could be reused for up to 10 cycles, without any decrease in performance; thus, it contributes to an intelligent and sustainable economic strategy projected toward minimal waste generation. Full article

(This article belongs to the Special Issue Carbon Fibers from Sustainable Precursors)

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22 pages, 13230 KiB

Open AccessEditor’s ChoiceArticle

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 3867

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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22 pages, 9453 KiB

Open AccessEditor’s ChoiceArticle

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 24 | Viewed by 3616

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, 3466 KiB

Open AccessEditor’s ChoiceReview

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 4331

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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16 pages, 3330 KiB

Open AccessEditor’s ChoiceReview

Fiber-Reinforced Polymer Composites in the Construction of Bridges: Opportunities, Problems and Challenges

by Paweł Grzegorz Kossakowski and Wiktor Wciślik

Fibers 2022, 10(4), 37; https://doi.org/10.3390/fib10040037 - 18 Apr 2022

Cited by 22 | Viewed by 11013

Abstract

In this review, we discuss the basic issues related to the use of FRP (fiber-reinforced polymer) composites in bridge construction. This modern material is presented in detail in terms of the possibility of application in engineering structures. A general historical outline of the [...] Read more.

In this review, we discuss the basic issues related to the use of FRP (fiber-reinforced polymer) composites in bridge construction. This modern material is presented in detail in terms of the possibility of application in engineering structures. A general historical outline of the use and development of modern structural materials, such as steel and concrete, is included to introduce composites as a novel material in engineering, and the most important features and advantages of polymers as a construction material are characterized. We also compare FRP to basic structural materials, such as steel and concrete, which enables estimation of the effectiveness of using of FRP polymers as structural material in different applications. The first bridges made of FRP composites are presented and analyzed in terms of applied technological solutions. Examples of structural solutions for deck slabs, girders and other deck elements made of FRP composites are discussed. Particular attention is paid to the systems of deck slabs, especially those composed of pultruded profiles, sandwich panels and hybrid decks. The disadvantages of composites, as well as barriers and limitations in their application in engineering practice, are presented. Exemplary analyses of the costs of construction, maintenance and demolition of FRP composite bridges are presented and compared with the corresponding costs of concrete and steel bridges. The directions of development of composite bridge structures and the greatest challenges facing engineers and constructors in the coming years are discussed. Full article

(This article belongs to the Special Issue Fiber Composite Process)

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16 pages, 6460 KiB

Open AccessEditor’s ChoiceArticle

Influence of Carbon Fiber-Reinforced Ropes Applied as External Diagonal Reinforcement on the Shear Deformation of RC Joints

by Chris Karayannis, Emmanouil Golias and George I. Kalogeropoulos

Fibers 2022, 10(3), 28; https://doi.org/10.3390/fib10030028 - 10 Mar 2022

Cited by 25 | Viewed by 3248

Abstract

The use of the innovative material of Carbon Fiber-Reinforced (C-FRP) ropes as external near surface mounted reinforcement for the strengthening of reinforced concrete beam-column joints is studied. The ropes are diagonally applied forming external X-type reinforcements on both sides of the joint body. [...] Read more.

The use of the innovative material of Carbon Fiber-Reinforced (C-FRP) ropes as external near surface mounted reinforcement for the strengthening of reinforced concrete beam-column joints is studied. The ropes are diagonally applied forming external X-type reinforcements on both sides of the joint body. The efficiency of the technique is mainly based on the assumption that the confinement of the joint body due to the applied X-shaped ropes and the contribution of the ropes as shear reinforcement are efficient enough to reduce the shear deformations observed in the joint core during the seismic excitation. Thereof the experimental measurements of the shear deformations of nine full scale beam-column joints tested in cyclic deformations are elaborated and presented herein. The specimens are sorted in two groups. Specimens of group A have been designed in the way that damage is mainly expected in the beam. On the other hand, in order to investigate the efficacy of the use of the ropes for substandard joints the group B specimens have been designed in the way that cracks and some damages are expected to develop in the joint body. Systematic and extended comparative presentations for specimens with and without ropes proved in all the examined cases that the externally mounted C-FRP ropes kept the joint body intact and substantially reduced the shear deformations especially in high drifts. Moreover, the influence of the externally mounted X-shaped C-FRP ropes on the seismic behaviour of these specimens is also examined in terms of the developing principal tensile stresses inside the joint body. From the comparisons of the principal stresses developing in specimens with and without X-form C-FRP ropes it became quite obvious that the ropes kept the joint body intact and allowed the development of higher values of principal stresses comparing with the stresses developing in specimens without ropes. Full article

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29 pages, 5812 KiB

Open AccessEditor’s ChoiceReview

A Review of Fibre Reinforced Polymer Structures

by Jawed Qureshi

Fibers 2022, 10(3), 27; https://doi.org/10.3390/fib10030027 - 8 Mar 2022

Cited by 59 | Viewed by 13199

Abstract

This paper reviews Fibre Reinforced Polymer (FRP) composites in Civil Engineering applications. Three FRP types are used in Structural Engineering: FRP profiles for new construction, FRP rebars and FRP strengthening systems. Basic materials (fibres and resins), manufacturing processes and material properties are discussed. [...] Read more.

This paper reviews Fibre Reinforced Polymer (FRP) composites in Civil Engineering applications. Three FRP types are used in Structural Engineering: FRP profiles for new construction, FRP rebars and FRP strengthening systems. Basic materials (fibres and resins), manufacturing processes and material properties are discussed. The focus of the paper is on all-FRP new-build structures and their joints. All-FRP structures use pultruded FRP profiles. Their connections and joints use bolting, bonding or a combination of both. For plate-to-pate connections, effects of geometry, fibre direction, type and rate of loading, bolt torque and bolt hole clearance, and washers on failure modes and strength are reviewed. FRP beam-columns joints are also reviewed. The joints are divided into five categories: web cleated, web and flange cleated, high strength, plate bolted and box profile joints. The effect of both static and cyclic loading on joints is studied. The joints’ failure modes are also discussed. Full article

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17 pages, 4784 KiB

Open AccessEditor’s ChoiceArticle

Ductility and Stiffness of Laminated Veneer Lumber Beams Strengthened with Fibrous Composites

by Michał Marcin Bakalarz and Paweł Grzegorz Kossakowski

Fibers 2022, 10(2), 21; https://doi.org/10.3390/fib10020021 - 15 Feb 2022

Cited by 13 | Viewed by 3623

Abstract

The paper presents the results of experimental research on unstrengthened and strengthened laminated veneer beams subjected to 4-point bending. Aramid, glass and carbon sheets with high tensile strength (HS) and ultra-high modulus of elasticity (UHM) glued to external surfaces with an epoxy resin [...] Read more.

The paper presents the results of experimental research on unstrengthened and strengthened laminated veneer beams subjected to 4-point bending. Aramid, glass and carbon sheets with high tensile strength (HS) and ultra-high modulus of elasticity (UHM) glued to external surfaces with an epoxy resin adhesive were used as reinforcement. Two reinforcement layouts were used: (1) sheets glued along the bottom surface and (2) sheets glued to the bottom and side surfaces. Based on the test results, the flexural strength, flexural ductility and stiffness were estimated. Compared to the reference beams, the maximum bending moment was higher by 15%, 20%, 30% and by 16%, 22% and 35% for the Aramid Fiber Reinforced Polymers (AFRP), Glass Fiber Reinforced Polymers (GFRP) and Carbon Fiber Reinforced Polymers (CFRP) HS sheets, respectively. There was no significant increase in the flexural bending capacity for beams reinforced with UHM CFRP sheets. Similar values of bending ductility indices based on deflection and energy absorption were obtained. Higher increases in ductility were observed for AFRP, GFRP and CFRP HS sheets in “U” reinforcement layout. The average increase in bending stiffness coefficient ranged from 8% for AFRP sheets to 33% for UHM CFRP sheets compared to the reference beams. Full article

(This article belongs to the Special Issue Fiber Composite Process)

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13 pages, 3449 KiB

Open AccessEditor’s ChoiceArticle

Chemical Transformation of Lignosulfonates to Lignosulfonamides with Improved Thermal Characteristics

by Karolina Komisarz, Tomasz M. Majka and Krzysztof Pielichowski

Fibers 2022, 10(2), 20; https://doi.org/10.3390/fib10020020 - 14 Feb 2022

Cited by 12 | Viewed by 3386

Abstract

Lignin is an abundantly occurring aromatic biopolymer that receives increasing attention as, e.g., a biofiller in polymer composites. Though its structure depends on the plant source, it is a valuable component showing biodegradability, antioxidant, and ultra-violet (UV) absorption properties. Lignosulfonates, a by-product of [...] Read more.

Lignin is an abundantly occurring aromatic biopolymer that receives increasing attention as, e.g., a biofiller in polymer composites. Though its structure depends on the plant source, it is a valuable component showing biodegradability, antioxidant, and ultra-violet (UV) absorption properties. Lignosulfonates, a by-product of the paper and pulping industries formed as a result of the implementation of the sulfite process, have been used in the presented study as a raw material to obtain a sulfonamide derivative of lignin. Hereby, a two-step modification procedure is described. The obtained materials were investigated by means of FTIR, WAXD, SS-NMR, SEM, and TGA; the results of spectroscopic investigations confirm the formation of a sulfonamide derivative of lignin via the proposed modification method. The obtained modified lignin materials showed significantly improved thermal stability in comparison with the raw material. The internal structure of the lignosulfonate was not altered during the modification process, with only slight changes of the morphology, as confirmed by the WAXD and SEM analyses. The manufactured sulfonamide lignin derivatives show great promise in the potential application as an antibacterial filler in advanced biopolymeric composites. Full article

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12 pages, 760 KiB

Open AccessEditor’s ChoiceArticle

The Effect of the Kraft Pulping Process, Wood Species, and pH on Lignin Recovery from Black Liquor

by Juliana M. Jardim, Peter W. Hart, Lucian A. Lucia, Hasan Jameel and Hou-min Chang

Fibers 2022, 10(2), 16; https://doi.org/10.3390/fib10020016 - 9 Feb 2022

Cited by 28 | Viewed by 6646

Abstract

Lignin has shown a great potential to produce fuels, value-added chemicals, and functional materials due to its high-energy density and intrinsic aromatic-based structure. Yet, the lignin precipitation of different biomasses needs investigation because most of the work has been performed on softwood and [...] Read more.

Lignin has shown a great potential to produce fuels, value-added chemicals, and functional materials due to its high-energy density and intrinsic aromatic-based structure. Yet, the lignin precipitation of different biomasses needs investigation because most of the work has been performed on softwood and much less is known about hardwoods. In fact, the lignin from these two wooden biomasses vary in composition and pulping performance, which can reflect on lignin precipitation. Therefore, the present study investigated the precipitation and composition of 40 distinct kraft lignins obtained from pine, acacia, sweetgum, and eucalyptus black liquors. Two lignin fractions were precipitated at different pHs, according to known industrial lignin separation practices (pH = 9.5 and 2.5) from black liquors taken at different levels of pulping. Overall, lignin recovery increased with increasing lignin concentration in the black liquor, i.e., higher amounts of lignin were obtained at higher levels of delignification. In addition, pine lignins showed superior yields than the hardwoods and were around five times purer. Among the hardwoods, lignin recovery increased with the S–G ratio of the native lignin, and eucalyptus showed the best performance by achieving the highest yields and purities. Finally, the present work compared the lignin recovery yield and the purity of softwood and different hardwood lignins in a systematic way, which will increase awareness of this underutilized green material and could potentially increase the interest in establishing new lignin plants across the globe. Full article

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27 pages, 5506 KiB

Open AccessEditor’s ChoiceReview

Application of Electrospun Nonwoven Fibers in Air Filters

by Iman Azarian Borojeni, Grzegorz Gajewski and Reza A. Riahi

Fibers 2022, 10(2), 15; https://doi.org/10.3390/fib10020015 - 8 Feb 2022

Cited by 43 | Viewed by 6811

Abstract

Air filtration has seen a sizable increase in the global market this past year due to the COVID-19 pandemic. Nanofiber nonwoven mats are able to reach certain efficiencies with a low-pressure drop, have a very high surface area to volume ratio, filter out [...] Read more.

Air filtration has seen a sizable increase in the global market this past year due to the COVID-19 pandemic. Nanofiber nonwoven mats are able to reach certain efficiencies with a low-pressure drop, have a very high surface area to volume ratio, filter out submicron particulates, and can customize the fiber material to better suit its purpose. Although electrospinning nonwoven mats have been very well studied and documented there are not many papers that combine them. This review touches on the various ways to manufacture nonwoven mats for use as an air filter, with an emphasis on electrospinning, the mechanisms by which the fibrous nonwoven air filter stops particles passing through, and ways that the nonwoven mats can be altered by morphology, structure, and material parameters. Metallic, ceramic, and organic nanoparticle coatings, as well as electrospinning solutions with these same materials and their properties and effects of air filtration, are explored. Full article

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18 pages, 11758 KiB

Open AccessEditor’s ChoiceReview

Vascular Graft Infections: An Overview of Novel Treatments Using Nanoparticles and Nanofibers

by Emma He, Stefano Serpelloni, Phillip Alvear, Maham Rahimi and Francesca Taraballi

Fibers 2022, 10(2), 12; https://doi.org/10.3390/fib10020012 - 1 Feb 2022

Cited by 7 | Viewed by 5300

Abstract

Vascular disease in elderly patients is a growing health concern, with an estimated prevalence of 15–20% in patients above 70 years old. Current treatment for vascular diseases requires the use of a vascular graft (VG) to revascularize lower or upper extremities, create dialysis [...] Read more.

Vascular disease in elderly patients is a growing health concern, with an estimated prevalence of 15–20% in patients above 70 years old. Current treatment for vascular diseases requires the use of a vascular graft (VG) to revascularize lower or upper extremities, create dialysis access, treat aortic aneurysms, and repair dissection. However, postoperative infection is a major complication associated with the use of these VG, often necessitating several operations to achieve complete or partial graft excision, vascular coverage, and extra-anatomical revascularization. There is also a high risk of morbidity, mortality, and limb loss. Therefore, it is important to develop a method to prevent or reduce the incidence of these infections. Numerous studies have investigated the efficacy of antibiotic- and antiseptic-impregnated grafts. In comparison to these traditional methods of creating antimicrobial grafts, nanotechnology enables researchers to design more efficient VG. Nanofibers and nanoparticles have a greater surface area compared to bulk materials, allowing for more efficient encapsulation of antibiotics and better control over their temporo-spatial release. The disruptive potential of nanofibers and nanoparticles is exceptional, and they could pave the way for a new generation of prosthetic VG. This review aims to discuss how nanotechnology is shaping the future of cardiovascular-related infection management. Full article

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26 pages, 3602 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Bond between Fibre-Reinforced Polymer Tubes and Sea Water Sea Sand Concrete: Mechanisms and Effective Parameters: Critical Overview and Discussion

by Johanna Dorothea Luck, Milad Bazli and Ali Rajabipour

Fibers 2022, 10(1), 8; https://doi.org/10.3390/fib10010008 - 14 Jan 2022

Cited by 21 | Viewed by 3483

Abstract

Using fibre-reinforced polymers (FRP) in construction avoids corrosion issues associated with the use of traditional steel reinforcement, while seawater and sea sand concrete (SWSSC) reduces environmental issues and resource shortages caused by the production of traditional concrete. The paper gives an overview of [...] Read more.

Using fibre-reinforced polymers (FRP) in construction avoids corrosion issues associated with the use of traditional steel reinforcement, while seawater and sea sand concrete (SWSSC) reduces environmental issues and resource shortages caused by the production of traditional concrete. The paper gives an overview of the current research on the bond performance between FRP tube and concrete with particular focus on SWSSC. The review follows a thematic broad-to-narrow approach. It reflects on the current research around the significance and application of FRP and SWSSC and discusses important issues around the bond strength and cyclic behaviour of tubular composites. A review of recent studies of bond strength between FRP and concrete and steel and concrete under static or cyclic loading using pushout tests is presented. In addition, the influence of different parameters on the pushout test results are summarised. Finally, recommendations for future studies are proposed. Full article

(This article belongs to the Special Issue Fibers in Concrete Construction: Material Behavior, Design and Strengthening)

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23 pages, 9034 KiB

Open AccessEditor’s ChoiceArticle

Cracking Diagnosis in Fiber-Reinforced Concrete with Synthetic Fibers Using Piezoelectric Transducers

by Maristella E. Voutetaki, Maria C. Naoum, Nikos A. Papadopoulos and Constantin E. Chalioris

Fibers 2022, 10(1), 5; https://doi.org/10.3390/fib10010005 - 9 Jan 2022

Cited by 69 | Viewed by 5052

Abstract

The addition of short fibers in concrete mass offers a composite material with advanced properties, and fiber-reinforced concrete (FRC) is a promising alternative in civil engineering applications. Recently, structural health monitoring (SHM) and damage diagnosis of FRC has received increasing attention. In this [...] Read more.

The addition of short fibers in concrete mass offers a composite material with advanced properties, and fiber-reinforced concrete (FRC) is a promising alternative in civil engineering applications. Recently, structural health monitoring (SHM) and damage diagnosis of FRC has received increasing attention. In this work, the effectiveness of a wireless SHM system to detect damage due to cracking is addressed in FRC with synthetic fibers under compressive repeated load. In FRC structural members, cracking propagates in small and thin cracks due to the presence of the dispersed fibers and, therefore, the challenge of damage detection is increasing. An experimental investigation on standard 150 mm cubes made of FRC is applied at specific and loading levels where the cracks probably developed in the inner part of the specimens, whereas no visible cracks appeared on their surface. A network of small PZT patches, mounted to the surface of the FRC specimen, provides dual-sensing function. The remotely controlled monitoring system vibrates the PZT patches, acting as actuators by an amplified harmonic excitation voltage. Simultaneously, it monitors the signal of the same PZTs acting as sensors and, after processing the voltage frequency response of the PZTs, it transmits them wirelessly and in real time. FRC cracking due to repeated loading ad various compressive stress levels induces change in the mechanical impedance, causing a corresponding change on the signal of each PZT. The influence of the added synthetic fibers on the compressive behavior and the damage-detection procedure is examined and discussed. In addition, the effectiveness of the proposed damage-diagnosis approach for the prognosis of final cracking performance and failure is investigated. The objectives of the study also include the development of a reliable quantitative assessment of damage using the statistical index values at various points of PZT measurements. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement Composites as Concrete Reinforcement)

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24 pages, 10895 KiB

Open AccessEditor’s ChoiceArticle

Experimental Investigation and Modelling of the Layered Concrete with Different Concentration of Short Fibers in the Layers

by Vitalijs Lusis, Olga Kononova, Arturs Macanovskis, Rimvydas Stonys, Inga Lasenko and Andrejs Krasnikovs

Fibers 2021, 9(12), 76; https://doi.org/10.3390/fib9120076 - 26 Nov 2021

Cited by 24 | Viewed by 3499

Abstract

The use of steel fiber reinforced concrete (SFRC) in structures with high physical-mechanical characteristics allows engineers to reduce the weight and costs of the structures, to simplify the technology of their production, to reduce or completely eliminate the manual labor needed for reinforcement, [...] Read more.

The use of steel fiber reinforced concrete (SFRC) in structures with high physical-mechanical characteristics allows engineers to reduce the weight and costs of the structures, to simplify the technology of their production, to reduce or completely eliminate the manual labor needed for reinforcement, at the same time increasing reliability and durability. Commonly accepted technology is exploiting randomly distributed in the concrete volume fibers with random each fiber orientation. In structural members subjected to bending, major loads are bearing fibers located close to outer member surfaces. The majority of fibers are slightly loaded. The aim of the present research is to create an SFRC construction with non-homogeneously distributed fibers. We prepared layered SFRC prismatic specimens. Each layer had different amount of short fibers. Specimens were tested by four point bending till the rupture. Material fracture process was modelled based on the single fiber pull-out test results. Modelling results were compared with the experimental curves for beams. Predictions generated by the model were validated by 4PBT of 100 × 100 × 400 mm prisms. Investigation had shown higher load-bearing capacity of layered concrete plates comparing with plate having homogeneously distributed the same amount of fibers. This mechanism is strongly dependent on fiber concentration. A high amount of fibers is leading to new failure mechanisms—pull-out of FRC blocks and decrease of load-bearing capacity. Fracture surface analysis was realized for broken prisms with the goal to analyze fracture process and to improve accuracy of the elaborated model. The general conclusion with regard to modelling results is that the agreement with experimental data is good, numeric modelling results successfully align with the experimental data. Modelling has indicated the existence of additional failure processes besides simple fiber pull-out, which could be expected when fiber concentration exceeds the critical value. Full article

(This article belongs to the Special Issue Mechanics of Fiber Reinforced Cementitious Composites)

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13 pages, 4726 KiB

Open AccessEditor’s ChoiceArticle

Environmentally Benign Phytic Acid-Based Nanocoating for Multifunctional Flame-Retardant/Antibacterial Cotton

by Eva Magovac, Bojana Vončina, Ana Budimir, Igor Jordanov, Jaime C. Grunlan and Sandra Bischof

Fibers 2021, 9(11), 69; https://doi.org/10.3390/fib9110069 - 31 Oct 2021

Cited by 18 | Viewed by 3624

Abstract

Environmentally benign layer-by-layer (LbL) deposition was used to obtain flame-retardant and antimicrobial cotton. Cotton was coated with 8, 10, and 12 phytic acid (PA) and chitosan (CH)-urea bilayers (BL) and then immersed into copper (II) sulfate (CuSO₄) solution. Our findings were [...] Read more.

Environmentally benign layer-by-layer (LbL) deposition was used to obtain flame-retardant and antimicrobial cotton. Cotton was coated with 8, 10, and 12 phytic acid (PA) and chitosan (CH)-urea bilayers (BL) and then immersed into copper (II) sulfate (CuSO₄) solution. Our findings were that 12 BL of PA/CH-urea + Cu²⁺ were able to stop flame on cotton during vertical flammability testing (VFT) with a limiting oxygen index (LOI) value of 26%. Microscale combustion calorimeter (MCC) data showed a reduction of peak heat release rates (pHRR) of more than 61%, while the reduction of total heat release (THR) was more than 54%, relative to untreated cotton. TG-IR analysis of 12 BL-treated cotton showed the release of water, methane, carbon dioxide, carbon monoxide, and aldehydes, while by adding Cu²⁺ ions, the treated cotton produces a lower amount of methane. Treated cotton also showed no levoglucosan. The intumescent behavior of the treatment was indicated by the bubbled structure of the post-burn char. Antibacterial testing showed a 100% reduction of Klebsiella pneumoniae and Staphylococcus aureus. In this study, cotton was successfully functionalized with a multifunctional ecologically benign flame-retardant and antibacterial nanocoating, by means of LbL deposition. Full article

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13 pages, 3742 KiB

Open AccessEditor’s ChoiceArticle

Carboxymethyl Cellulose Enhanced Production of Cellulose Nanofibrils

by Yunsang Kim, Lauren T. McCoy, Corbin Feit, Shuaib A. Mubarak, Suraj Sharma and Sergiy Minko

Fibers 2021, 9(9), 57; https://doi.org/10.3390/fib9090057 - 13 Sep 2021

Cited by 10 | Viewed by 5389

Abstract

Cellulose nanofibrils (CNF) were produced by high-pressure homogenization from kraft pulp in the presence of carboxymethyl cellulose (CMC) of varying molecular weights. CNF pretreated with 250 kD CMC exhibited the maximum specific surface area (SSA) of 641 m²/g, which is comparable [...] Read more.

Cellulose nanofibrils (CNF) were produced by high-pressure homogenization from kraft pulp in the presence of carboxymethyl cellulose (CMC) of varying molecular weights. CNF pretreated with 250 kD CMC exhibited the maximum specific surface area (SSA) of 641 m²/g, which is comparable to that of CNF pretreated by 2,2,6,6-tetramethyl-piperidinyl-1-oxyl (TEMPO)-meditated oxidation with a high degree of fibrillation. Rheological and microscopic analyses also indicated a high level of fibrillation for the CMC-pretreated CNF. In contrast, the reference CNF without the CMC pretreatment showed a lower level of fibrillation, which was reflected in decreased viscosity and the reduction of SSA by a factor of 19. With the high-degree fibrillation and low toxicity, the CMC pretreatment is a promising method for the production of high-quality CNF in an environmentally friendly way. Full article

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18 pages, 14077 KiB

Open AccessEditor’s ChoiceArticle

Insight into the Effects of Solvent Treatment of Natural Fibers Prior to Structural Composite Casting: Chemical, Physical and Mechanical Evaluation

by Ali Abbass, Maria C. Paiva, Daniel V. Oliveira, Paulo B. Lourenço and Raul Fangueiro

Fibers 2021, 9(9), 54; https://doi.org/10.3390/fib9090054 - 1 Sep 2021

Cited by 17 | Viewed by 5095

Abstract

This paper presents an optimized washing protocol for as-received natural fibers, prior to large-scale composite manufacturing, for the structural strengthening of historic masonry. The aim was to achieve a simple protocol for standard cleaning of fiber surfaces from low molecular weight constituents that [...] Read more.

This paper presents an optimized washing protocol for as-received natural fibers, prior to large-scale composite manufacturing, for the structural strengthening of historic masonry. The aim was to achieve a simple protocol for standard cleaning of fiber surfaces from low molecular weight constituents that may be detrimental towards interfacial strength without damaging the fibers. The proposed procedure employs the application of the solvent sequence: ethanol, acetone, hexane, with optimized incubation times and stirring conditions. Additionally, this procedure may change the surface of the fiber, thereby enhancing the durability of the fiber-matrix interface. The washing protocol resulted in an increase of tensile strength by 56%, 52% and 22% for flax, hemp and sisal fibers, respectively, as compared to the corresponding non-washed fibers, without loss of elongation. The static contact angle measurements confirmed exposure of a higher fraction of the hydrophilic crystalline cellulose, with a higher wettability observed after washing protocols. Full article

(This article belongs to the Special Issue Fibres in Construction: Mechanical Modelling and Characterisation)

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30 pages, 3992 KiB

Open AccessEditor’s ChoiceArticle

ANN-Based Model for the Prediction of the Bond Strength between FRP and Concrete

by Alessio Cascardi and Francesco Micelli

Fibers 2021, 9(7), 46; https://doi.org/10.3390/fib9070046 - 6 Jul 2021

Cited by 15 | Viewed by 3769

Abstract

In the last decades, the uses of fiber reinforced polymer (FRP) composites in the structural strengthening of reinforced concrete (RC) structures have become the state of the art, providing a valid alternative to the traditional use of steel plates. These relatively new materials [...] Read more.

In the last decades, the uses of fiber reinforced polymer (FRP) composites in the structural strengthening of reinforced concrete (RC) structures have become the state of the art, providing a valid alternative to the traditional use of steel plates. These relatively new materials present, in fact, great advantages, including high corrosion resistance in aggressive environments, low specific weight, high strength-to-mass-density ratio, magnetic and electric neutrality, low axial coefficient of thermal expansion and sustainable costs of installation. In flexural and shear strengthening of RC members, the effectiveness of the epoxy bonded FRP strongly depends on the adhesion forces exchanged with the concrete substrate. When the flexural moment is present, the FRP strengthening is activated through the stress transfer on the tension side, which is guaranteed by the contact beam region to which the adhesive is bonded to the beam itself. Hence, the determination of the maximum forces that cause debonding of the FRP-plate becomes crucial for a proper design. Over the years, many different analytical models have been provided in the scientific literature. Most of them are based on the calibration of the narrow experimental database. Now, hundreds of experimental results are available. The main goal of the current study is to present and discuss an alternative theoretical formulation for predicting the debonding force in an FRP-plate, epoxy-bonded to the concrete substrate by using an artificial neural networks (ANNs) approach. For this purpose, an extensive study of the state of the art, reporting the results of single lap shear tests, is also reported and discussed. The robustness of the proposed analytical model was validated by performing a parametric analysis and a comparison with other existing models and international design codes, as shown herein. Full article

(This article belongs to the Special Issue Fibres in Construction: Mechanical Modelling and Characterisation)

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15 pages, 5341 KiB

Open AccessEditor’s ChoiceArticle

Application of X-Shaped CFRP Ropes for Structural Upgrading of Reinforced Concrete Beam–Column Joints under Cyclic Loading–Experimental Study

by Emmanouil Golias, Adamantis G. Zapris, Violetta K. Kytinou, Mourhat Osman, Michail Koumtzis, Danai Siapera, Constantin E. Chalioris and Chris G. Karayannis

Fibers 2021, 9(7), 42; https://doi.org/10.3390/fib9070042 - 1 Jul 2021

Cited by 49 | Viewed by 6218

Abstract

The effectiveness of externally applied fiber-reinforced polymer (FRP) ropes made of carbon fibers in X-shape formation and in both sides of the joint area of reinforced concrete (RC) beam–column connections is experimentally investigated. Six full-scale exterior RC beam–column joint specimens are tested under [...] Read more.

The effectiveness of externally applied fiber-reinforced polymer (FRP) ropes made of carbon fibers in X-shape formation and in both sides of the joint area of reinforced concrete (RC) beam–column connections is experimentally investigated. Six full-scale exterior RC beam–column joint specimens are tested under reverse cyclic deformation. Three of them have been strengthened using carbon FRP (CFRP) ropes that have been placed diagonally in the joint as additional, near surface-mounted reinforcements against shear. Full hysteretic curves, maximum applied load capacity, damage modes, stiffness and energy dissipation values per each loading step are presented and compared. Test results indicated that joint sub assemblages with X-shaped CFRP ropes exhibited improved hysteretic behavior and ameliorated performance with respect to the reference specimens. The effectiveness and the easy-to-apply character of the presented strengthening technique is also discussed. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement Composites as Concrete Reinforcement)

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17 pages, 8513 KiB

Open AccessEditor’s ChoiceArticle

Development of a Robot-Based Multi-Directional Dynamic Fiber Winding Process for Additive Manufacturing Using Shotcrete 3D Printing

by Norman Hack, Mohammad Bahar, Christian Hühne, William Lopez, Stefan Gantner, Noor Khader and Tom Rothe

Fibers 2021, 9(6), 39; https://doi.org/10.3390/fib9060039 - 8 Jun 2021

Cited by 24 | Viewed by 6814

Abstract

The research described in this paper is dedicated to the use of continuous fibers as reinforcement for additive manufacturing, particularly using Shotcrete. Composites and in particular fiber reinforced polymers (FRP) are increasingly present in concrete reinforcement. Their corrosion resistance, high tensile strength, low [...] Read more.

The research described in this paper is dedicated to the use of continuous fibers as reinforcement for additive manufacturing, particularly using Shotcrete. Composites and in particular fiber reinforced polymers (FRP) are increasingly present in concrete reinforcement. Their corrosion resistance, high tensile strength, low weight, and high flexibility offer an interesting alternative to conventional steel reinforcement, especially with respect to their use in Concrete 3D Printing. This paper presents an initial development of a dynamic robot-based manufacturing process for FRP concrete reinforcement as an innovative way to increase shape freedom and efficiency in concrete construction. The focus here is on prefabricated fiber reinforcement, which is concreted in a subsequent additive process to produce load-bearing components. After the presentation of the fabrication concept for the integration of FRP reinforcement and the state of the art, a requirements analysis regarding the mechanical bonding behavior in concrete is carried out. This is followed by a description of the development of a dynamic fiber winding process and its integration into an automated production system for individualized fiber reinforcement. Next, initial tests for the automated application of concrete by means of Shotcrete 3D Printing are carried out. In addition, an outlook describes further technical development steps and provides an outline of advanced manufacturing concepts for additive concrete manufacturing with integrated fiber reinforcement. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement Composites as Concrete Reinforcement)

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25 pages, 6650 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Application of Capillary Polypropylene Membranes for Microfiltration of Oily Wastewaters: Experiments and Modeling

by Wirginia Tomczak and Marek Gryta

Fibers 2021, 9(6), 35; https://doi.org/10.3390/fib9060035 - 2 Jun 2021

Cited by 9 | Viewed by 3595

Abstract

Oily wastewaters are considered as one of the most dangerous types of environmental pollution. In the present study, the microfiltration (MF) process of model emulsions and real oily wastewaters was investigated. For this purpose, capillary polypropylene (PP) membranes were used. The experiments were [...] Read more.

Oily wastewaters are considered as one of the most dangerous types of environmental pollution. In the present study, the microfiltration (MF) process of model emulsions and real oily wastewaters was investigated. For this purpose, capillary polypropylene (PP) membranes were used. The experiments were conducted under transmembrane pressure (TMP) and feed flow rate (V_F) equal to 0.05 MPa and 0.5 m/s, respectively. It was found that the used membranes ensured a high-quality permeate with turbidity equal to about 0.4 NTU and oil concentration of 7–15 mg/L. As expected, a significant decrease in the MF process performance was noted. However, it is shown that the initial decline of permeate flux could be slightly increased by increasing the feed temperature from 25 °C to 50 °C. Furthermore, Hermia’s models were used to interpret the fouling phenomenon occurring in studied experiments. It was determined that cake formation was the dominant fouling mechanism during filtration of both synthetic and real feeds. Through detailed studies, we present different efficient methods of membrane cleaning. Results, so far, are very encouraging and may have an important impact on increasing the use of polypropylene MF membranes in oily wastewater treatments. Full article

(This article belongs to the Special Issue Hollow Fiber Membranes 2021)

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17 pages, 6298 KiB

Open AccessEditor’s ChoiceArticle

Novel Insight into the Intricate Shape of Flax Fibre Lumen

by Emmanuelle Richely, Sylvie Durand, Alessia Melelli, Alexander Kao, Anthony Magueresse, Hom Dhakal, Tatyana Gorshkova, Franck Callebert, Alain Bourmaud, Johnny Beaugrand and Sofiane Guessasma

Fibers 2021, 9(4), 24; https://doi.org/10.3390/fib9040024 - 6 Apr 2021

Cited by 28 | Viewed by 4973

Abstract

Plant fibres and especially flax can be distinguished from most synthetic fibres by their intricate shape and intrinsic porosity called lumen, which is usually assumed to be tubular. However, the real shape appears more complex and thus might induce stress concentrations influencing the [...] Read more.

Plant fibres and especially flax can be distinguished from most synthetic fibres by their intricate shape and intrinsic porosity called lumen, which is usually assumed to be tubular. However, the real shape appears more complex and thus might induce stress concentrations influencing the fibre performance. This study proposes a novel representation of flax fibre lumen and its variations along the fibre, an interpretation of its origin and effect on flax fibre tensile properties. This investigation was conducted at the crossroads of complementary characterization techniques: optical and scanning electron microscopy (SEM), high-resolution X-ray microtomography (µCT) and mechanical tests at the cell-wall and fibre scale by atomic force microscopy (AFM) in Peak-Force Quantitative Nano-Mechanical property mapping (PF-QNM) mode and micromechanical tensile testing. Converging results highlight the difficulty of drawing a single geometric reference for the lumen. AFM and optical microscopy depict central cavities of different sizes and shapes. Porosity contents, varying from 0.4 to 7.2%, are estimated by high-resolution µCT. Furthermore, variations of lumen size are reported along the fibres. This intricate lumen shape might originate from the cell wall thickening and cell death but particular attention should also be paid to the effects of post mortem processes such as drying, retting and mechanical extraction of the fibre as well as sample preparation. Finally, SEM observation following tensile testing demonstrates the combined effect of geometrical inhomogeneities such as defects and intricate lumen porosity to drive the failure of the fibre. Full article

(This article belongs to the Special Issue Plant Bast Fibers)

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15 pages, 2050 KiB

Open AccessEditor’s ChoiceArticle

Closed-Form Solution Procedure for Simulating Debonding in FRP Strips Glued to a Generic Substrate Material

by Enzo Martinelli

Fibers 2021, 9(4), 22; https://doi.org/10.3390/fib9040022 - 1 Apr 2021

Cited by 11 | Viewed by 3241

Abstract

The present paper proposes a useful closed-form solution for a wide class of mechanical problems, among which one of the most relevant and debated is the deboning process of Fiber-Reinforced Polymer (FRP) strips glued to generic materials and possibly intended as a mode-II [...] Read more.

The present paper proposes a useful closed-form solution for a wide class of mechanical problems, among which one of the most relevant and debated is the deboning process of Fiber-Reinforced Polymer (FRP) strips glued to generic materials and possibly intended as a mode-II fracture process. Specifically, after outlining well-known equations, a novel piecewise analytical formulation based on a cascading solution process is proposed with the aim of keeping the mathematical expressions of the relevant mechanical quantities as simple as possible. Although other analytical solutions and numerical procedures are already available in the literature, the present one is capable of handling the softening or snap-back response deriving from the full-range simulation of the depending process with no need for complex numerical techniques. This is obtained by considering the slip at the free end of the strip as the main displacement control parameter. After some comparisons between the proposed closed-form solution and experimental results available in the literature, some mechanical considerations are highlighted by elaborating on the results of a parametric study considering the variation of the main geometric and mechanical quantities. The numerical code implemented as part of the present study is available to readers in Open Access. Full article

(This article belongs to the Special Issue Mechanics of Fiber Reinforced Cementitious Composites)

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9 pages, 2445 KiB

Open AccessEditor’s ChoiceArticle

Mid-Infrared Ultra-Short Pulse Generation in a Gas-Filled Hollow-Core Photonic Crystal Fiber Pumped by Two-Color Pulses

by Coralie Fourcade-Dutin, Olivia Zurita-Miranda, Patrick Mounaix and Damien Bigourd

Fibers 2021, 9(4), 21; https://doi.org/10.3390/fib9040021 - 1 Apr 2021

Cited by 4 | Viewed by 3213

Abstract

We show numerically that ultra-short pulses can be generated in the mid-infrared when a gas filled hollow-core fiber is pumped by a fundamental pulse and its second harmonic. The generation process originates from a cascaded nonlinear phenomenon starting from a spectral broadening of [...] Read more.

We show numerically that ultra-short pulses can be generated in the mid-infrared when a gas filled hollow-core fiber is pumped by a fundamental pulse and its second harmonic. The generation process originates from a cascaded nonlinear phenomenon starting from a spectral broadening of the two pulses followed by an induced phase-matched four wave-mixing lying in the mid-infrared combined with a dispersive wave. By selecting this mid-infrared band with a spectral filter, we demonstrate the generation of ultra-short 60 fs pulses at a 3–4 µm band and a pulse duration of 20 fs can be reached with an additional phase compensator. Full article

(This article belongs to the Special Issue Hollow-Core Photonic Crystal Fibers)

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14 pages, 4938 KiB

Open AccessEditor’s ChoiceArticle

Prediction of Short Fiber Composite Properties by an Artificial Neural Network Trained on an RVE Database

by Kevin Breuer and Markus Stommel

Fibers 2021, 9(2), 8; https://doi.org/10.3390/fib9020008 - 1 Feb 2021

Cited by 44 | Viewed by 5301

Abstract

In this study, an artificial neural network is designed and trained to predict the elastic properties of short fiber reinforced plastics. The results of finite element simulations of three-dimensional representative volume elements are used as a data basis for the neural network. The [...] Read more.

In this study, an artificial neural network is designed and trained to predict the elastic properties of short fiber reinforced plastics. The results of finite element simulations of three-dimensional representative volume elements are used as a data basis for the neural network. The fiber volume fraction, fiber length, matrix-phase properties, and fiber orientation are varied so that the neural network can be used within a very wide range of parameters. A comparison of the predictions of the neural network with additional finite element simulations shows that the stiffnesses of short fiber reinforced plastics can be predicted very well by the neural network. The average prediction accuracy is equal or better than by a two-step homogenization using the classical method of Mori and Tanaka. Moreover, it is shown that the training of the neural network on an extended data set works well and that particularly calculation-intensive data points can be avoided without loss of prediction quality. Full article

(This article belongs to the Special Issue Simulation of Short-Fiber-Reinforced Polymers)

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17 pages, 3434 KiB

Open AccessEditor’s ChoiceReview

Techniques for Modelling and Optimizing the Mechanical Properties of Natural Fiber Composites: A Review

by Timothy K. Mulenga, Albert U. Ude and Chinnasamy Vivekanandhan

Fibers 2021, 9(1), 6; https://doi.org/10.3390/fib9010006 - 14 Jan 2021

Cited by 53 | Viewed by 8544

Abstract

The study of natural fiber-based composites through the use of computational techniques for modelling and optimizing their properties has emerged as a fast-growing approach in recent years. Ecological concerns associated with synthetic fibers have made the utilisation of natural fibers as a reinforcing [...] Read more.

The study of natural fiber-based composites through the use of computational techniques for modelling and optimizing their properties has emerged as a fast-growing approach in recent years. Ecological concerns associated with synthetic fibers have made the utilisation of natural fibers as a reinforcing material in composites a popular approach. Computational techniques have become an important tool in the hands of many researchers to model and analyze the characteristics that influence the mechanical properties of natural fiber composites. This recent trend has led to the development of many advanced computational techniques and software for a profound understanding of the characteristics and performance behavior of composite materials reinforced with natural fibers. The large variations in the characteristics of natural fiber-based composites present a great challenge, which has led to the development of many computational techniques for composite materials analysis. This review seeks to infer, from conventional to contemporary sources, the computational techniques used in modelling, analyzing, and optimizing the mechanical characteristics of natural fiber reinforced composite materials. Full article

(This article belongs to the Special Issue Natural Fibers and Composites: Science and Applications)

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13 pages, 3312 KiB

Open AccessEditor’s ChoiceArticle

New Textile for Personal Protective Equipment—Plasma Chitosan/Silver Nanoparticles Nylon Fabric

by Cláudia M. Botelho, Margarida M. Fernandes, Jefferson M. Souza, Nicolina Dias, Ana M. Sousa, José A. Teixeira, Raul Fangueiro and Andrea Zille

Fibers 2021, 9(1), 3; https://doi.org/10.3390/fib9010003 - 6 Jan 2021

Cited by 31 | Viewed by 5967

Abstract

Fabric structures are prone to contamination with microorganisms, as their morphology and ability to retain moisture creates a proper environment for their growth. In this work, a novel, easily processed and cheap coating for a nylon fabric with antimicrobial characteristics was developed. After [...] Read more.

Fabric structures are prone to contamination with microorganisms, as their morphology and ability to retain moisture creates a proper environment for their growth. In this work, a novel, easily processed and cheap coating for a nylon fabric with antimicrobial characteristics was developed. After plasma treatment, made to render the fabric surface more reactive sites, the fabric was impregnated with chitosan and silver nanoparticles by simply dipping it into a mixture of different concentrations of both components. Silver nanoparticles were previously synthesized using the Lee–Meisel method, and their successful obtention was proven by UV–Vis, showing the presence of the surface plasmon resonance band at 410 nm. Nanoparticles with 25 nm average diameter observed by STEM were stable, mainly in the presence of chitosan, which acted as a surfactant for silver nanoparticles, avoiding their aggregation. The impregnated fabric possessed bactericidal activity higher for Gram-positive Staphylococcus aureus than for Gram-negative Pseudomonas aeruginosa bacteria for all combinations. The percentage of live S. aureus and P. aeruginosa CFU was reduced to less than 20% and 60%, respectively, when exposed to each of the coating combinations. The effect was more pronounced when both chitosan and silver were present in the coating, suggesting an effective synergy between these components. After a washing process, the antimicrobial effect was highly reduced, suggesting that the coating is unstable after washing, being almost completely removed from the fabric. Nevertheless, the new-coated fabric can be successfully used in single-use face masks. To our knowledge, the coating of nylon fabrics intended for face-mask material with both agents has never been reported. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Nanomaterials)

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14 pages, 2920 KiB

Open AccessEditor’s ChoiceArticle

Cellulose Dissolution in Ionic Liquid under Mild Conditions: Effect of Hydrolysis and Temperature

by Sanjit Acharya, Yang Hu and Noureddine Abidi

Fibers 2021, 9(1), 5; https://doi.org/10.3390/fib9010005 - 6 Jan 2021

Cited by 19 | Viewed by 4379

Abstract

This study investigated the effect of acid hydrolysis of cellulose on its dissolution under mild conditions in ionic liquid, 1-butyl-3-methylimidazolium acetate/N,N-dimethylacetamide (BMIMAc/DMAc). Acid hydrolysis of high molecular weight (MW) cotton cellulose (DP > 4000) was carried out to produce hydrolyzed cotton (HC) samples [...] Read more.

This study investigated the effect of acid hydrolysis of cellulose on its dissolution under mild conditions in ionic liquid, 1-butyl-3-methylimidazolium acetate/N,N-dimethylacetamide (BMIMAc/DMAc). Acid hydrolysis of high molecular weight (MW) cotton cellulose (DP > 4000) was carried out to produce hydrolyzed cotton (HC) samples for dissolution. The HC samples were characterized using gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), and the dissolution process was monitored using polarized light microscopy (PLM). It was found that the drastic decrease of the MW of cellulose did not result in improvement of its dissolution at room temperature. As compared to original cotton cellulose, the high amount of undissolved fibers in HC solutions led to unstable rheological behavior of HC solutions. Agglomeration and inhomogeneous dispersion of HC, and increased crystallinity, in this case, likely made the diffusion of BMIMAc/DMAc more difficult to the inside of the polymeric network of cellulose at ambient temperature, thereby hindering the dissolution. However, increasing the temperature from room temperature to 35 °C and 55 °C, led to a significant improvement in cellulose dissolution. This phenomenon implies that reducing the MW of cellulose might not be able to improve its dissolution under certain conditions. During the dissolution process, the physical properties of cellulose including fiber aggregation status, solvent diffusivity, and cellulose crystallinity may play a critical role compared to the MW, while the MW may not be an important factor. This finding may help further understand the mechanism of cellulose dissolution and seek better strategies to dissolve cellulose under mild conditions for industrial applications. Full article

(This article belongs to the Special Issue Recent Progress in Cellulose Dissolution and Regeneration)

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14 pages, 1642 KiB

Open AccessEditor’s ChoiceArticle

Experimental Tests and Reliability Analysis of the Cracking Impact Resistance of UHPFRC

by Hussain A. Jabir, Sallal R. Abid, Gunasekaran Murali, Sajjad H. Ali, Sergey Klyuev, Roman Fediuk, Nikolai Vatin, Vladimir Promakhov and Yuriy Vasilev

Fibers 2020, 8(12), 74; https://doi.org/10.3390/fib8120074 - 4 Dec 2020

Cited by 76 | Viewed by 4430

Abstract

Ultra-high performance (UHP) concrete is a special type of fibrous cementitious composite that is characterized by high strength and superior ductility, toughness, and durability. This research aimed to investigate the resistance of ultra-high performance fiber-reinforced concrete (UHPFRC) against repeated impacts. An adjusted repeated [...] Read more.

Ultra-high performance (UHP) concrete is a special type of fibrous cementitious composite that is characterized by high strength and superior ductility, toughness, and durability. This research aimed to investigate the resistance of ultra-high performance fiber-reinforced concrete (UHPFRC) against repeated impacts. An adjusted repeated drop mass impact test was adopted to evaluate the impact performance of 72 UHPFRC disc specimens. The specimens were divided into six mixtures each of 12 discs. The only difference between the mixtures was the types of fibers used, while all other mixture components were the same. Three types of fibers were used: 6 mm micro-steel, 15 mm micro-steel, and polypropylene. All mixtures included 2.5% volumetric content of fibers, however with different combinations of the three fiber types. The test results showed that the mixtures with the 15 mm micro-steel fiber absorbed a higher number of impact blows until cracking compared to other mixtures. The mixture with pure 2.5% of 15 mm micro-steel fiber exhibited the highest impact resistance, with percentage increases over the other mixtures ranging from 25 to 140%. In addition, the Weibull distribution was used to investigate the cracking impact resistance of UHP at different levels of reliability. Full article

(This article belongs to the Special Issue Effectiveness and Efficiency of Fiber Reinforcement in Ultra-High Performance Concrete)

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16 pages, 1383 KiB

Open AccessEditor’s ChoiceArticle

Heat Treatment of Basalt Fiber Reinforced Expanded Clay Concrete with Increased Strength for Cast-In-Situ Construction

by Makhmud Kharun, Sergey Klyuev, Dmitry Koroteev, Paschal C. Chiadighikaobi, Roman Fediuk, Andrej Olisov, Nikolai Vatin and Nataliya Alfimova

Fibers 2020, 8(11), 67; https://doi.org/10.3390/fib8110067 - 2 Nov 2020

Cited by 49 | Viewed by 3747

Abstract

Expanded clay concrete (ECC) is a promising structural material for buildings due to its light weight and heat- and sound-insulating properties. Adding basalt fibers (BFs) in ECC reduces its brittleness and enhances its mechanical properties. The heat treatment (HT) of BF-reinforced ECC can [...] Read more.

Expanded clay concrete (ECC) is a promising structural material for buildings due to its light weight and heat- and sound-insulating properties. Adding basalt fibers (BFs) in ECC reduces its brittleness and enhances its mechanical properties. The heat treatment (HT) of BF-reinforced ECC can significantly accelerate the strength growth during cast-in-situ construction, which allows the reduction of the turnover of the formwork and the construction period, as well as leading to lower construction costs. This paper presents an HT technology for load-bearing structures, containing a BF-reinforced ECC mix and using infrared rays for cast-in-situ construction. The issue of the strength growth of BF-reinforced ECC during HT has been studied. Microsilica and fly ash were added to the ECC mix to obtain a compressive strength of more than 20 MPa. Four different mixes of ECC with chopped BFs in the ratios of 1:0, 1:0.0045, 1:0.009 and 1:0.012 by weight of cement were studied. Test specimens were heated by infrared rays for 7, 9, 11, 13, 16 and 24 h. Then, the heat-treated specimens were tested for compressive strength after 0.5, 4, 12 and 24 h cooling periods. The analysis and evaluation of the experimental data were carried out based on probability theory and mathematical statistics. Mathematical models are proposed for forecasting the strength growth of BF-reinforced ECC during cast-in-situ construction. Full article

(This article belongs to the Special Issue Fiber Reinforced Composites (FRCs) for Construction Applications)

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9 pages, 2762 KiB

Open AccessEditor’s ChoiceArticle

Humidity Controlled Mechanical Properties of Electrospun Polyvinylidene Fluoride (PVDF) Fibers

by Piotr K. Szewczyk, Daniel P. Ura and Urszula Stachewicz

Fibers 2020, 8(10), 65; https://doi.org/10.3390/fib8100065 - 16 Oct 2020

Cited by 21 | Viewed by 4778

Abstract

Processing parameters in electrospinning allow us to control the properties of fibers on a molecular level and are able to tailor them for specific applications. In this study, we investigate how relative humidity (RH) affects the mechanical properties of electrospun polyvinylidene fluoride (PVDF). [...] Read more.

Processing parameters in electrospinning allow us to control the properties of fibers on a molecular level and are able to tailor them for specific applications. In this study, we investigate how relative humidity (RH) affects the mechanical properties of electrospun polyvinylidene fluoride (PVDF). The mechanical properties of single fibers were carried out using a specialized tensile stage. The results from tensile tests were additionally correlated with high-resolution imaging showing the behavior of individual fibers under tensile stress. The mechanical characteristic is strongly dependent on the crystallinity, chain orientation, and fiber diameter of electrospun PVDF fibers. Our results show the importance of controlling RH during electrospinning as the mechanical properties are significantly affected. At low RH = 30% PVDF fibers are 400% stiffer than their counterparts prepared at high RH = 60%. Moreover, the vast differences in the strain at failure were observed, namely 310% compared to 75% for 60% and 30% RH, respectively. Our results prove that humidity is a crucial parameter in electrospinning able to control the mechanical properties of polymer fibers. Full article

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16 pages, 5043 KiB

Open AccessEditor’s ChoiceArticle

Damping Properties of Flax/Carbon Hybrid Epoxy/Fibre-Reinforced Composites for Automotive Semi-Structural Applications

by George Fairlie and James Njuguna

Fibers 2020, 8(10), 64; https://doi.org/10.3390/fib8100064 - 8 Oct 2020

Cited by 31 | Viewed by 4843

Abstract

The ever-increasing demand for environmentally friendly biocomposites for use in various engineering applications requires a strong understanding of these materials properties, especially in automotive applications. This study focused on investigating how the stacking sequence and fibre orientation impacts the damping properties of hybrid [...] Read more.

The ever-increasing demand for environmentally friendly biocomposites for use in various engineering applications requires a strong understanding of these materials properties, especially in automotive applications. This study focused on investigating how the stacking sequence and fibre orientation impacts the damping properties of hybrid flax/carbon fibre-reinforced composites. Different hybrid carbon fibre/flax fibre-reinforced composites using epoxy resin as the matrix were manufactured using vacuum-assisted resin infusion moulding technique. Each composite material was then tested for tensile properties using a universal testing machine, and the damping experiment was conducted using an impulse hammer and a Laser Doppler Vibrometer. The tensile study found out that adding a flax layer to the external layers of carbon fibre laminate reduced Young’s modulus by 28% for one layer and 45% for two layers. It was noted that when the fibre orientation of the internal layer of [C/F2/C]s was replaced with two ±45° layers, this had a very little effect on Young’s modulus but reduced the ultimate tensile strength by 61%. This experimental study also showed that the most important layer when it comes to damping properties is the external layers. By adding an external flax layer into an epoxy/carbon fibre-reinforced composite considerably enhanced its damping ratio by 53.6% and by adding two layers increased it by 94%. The results indicated a high potential for the automotive semi-structural applications to improve damping properties of the vehicle. Full article

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13 pages, 1959 KiB

Open AccessEditor’s ChoiceArticle

Meso-Scale Formulation of a Cracked-Hinge Model for Hybrid Fiber-Reinforced Cement Composites

by Enzo Martinelli, Marco Pepe and Fernando Fraternali

Fibers 2020, 8(9), 56; https://doi.org/10.3390/fib8090056 - 1 Sep 2020

Cited by 12 | Viewed by 3493

Abstract

This study presents a non-linear cracked-hinge model for the post-cracking response of fiber-reinforced cementitious composites loaded in bending. The proposed displacement-based model follows a meso-mechanical approach, which makes it possible to consider explicitly the random distribution and orientation of the reinforcing fibers. Moreover, [...] Read more.

This study presents a non-linear cracked-hinge model for the post-cracking response of fiber-reinforced cementitious composites loaded in bending. The proposed displacement-based model follows a meso-mechanical approach, which makes it possible to consider explicitly the random distribution and orientation of the reinforcing fibers. Moreover, the model allows for considering two different fiber typologies whereas the cement matrix is modelled as a homogeneous material. The proposed mechanical model combines a fracture-based, stress-crack opening relationship for the cementitious matrix with generalized laws aimed to capture the crack-bridging effect played by the reinforcing fibers. These laws are derived by considering both the fiber-to-matrix bond mechanism and fiber anchoring action possibly due to hooked ends. The paper includes a numerical implementation of the proposed theory, which is validated against experimental results dealing with fiber-reinforced cement composites reinforced with different short fibers. The excellent theory vs. experiment matching demonstrates the high technical potential of the presented model, obtained at a reasonable computational cost. Full article

(This article belongs to the Special Issue Mechanics of Fiber Reinforced Cementitious Composites)

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20 pages, 6179 KiB

Open AccessEditor’s ChoiceArticle

3D-Printed Pseudo Ductile Fiber-Reinforced Polymer (FRP) Composite Using Discrete Fiber Orientations

by Shreya Vemuganti, Eslam Soliman and Mahmoud Reda Taha

Fibers 2020, 8(9), 53; https://doi.org/10.3390/fib8090053 - 20 Aug 2020

Cited by 14 | Viewed by 5363

Abstract

The use of fiber-reinforced polymer (FRP) composite materials are continuously growing in civil infrastructure due to their high strength, low weight, and manufacturing flexibility. However, FRP is characterized by sudden failure and lacks ductility. When used in construction, gradual failure of FRP components [...] Read more.

The use of fiber-reinforced polymer (FRP) composite materials are continuously growing in civil infrastructure due to their high strength, low weight, and manufacturing flexibility. However, FRP is characterized by sudden failure and lacks ductility. When used in construction, gradual failure of FRP components is desired to avoid catastrophic structural collapse. Due to its mechanical orthotropy, the behavior of FRP relies significantly on fiber orientation and stacking sequence. In this paper, a novel multi-angled glass fiber reinforced polymer (GFRP) composite laminate showing pseudo ductile behavior is produced using 3D-printing. This is accomplished by varying fiber orientation angles, stacking sequence, and thickness of lamina. Single-angled GFRP composite specimens were 3D-printed with different fiber orientation angles of 0°, 12°, 24°, 30°, 45°, and 90° using continuous and fused filament techniques. The tension test results of the single-angled specimens were then used to aid the design of multi-angled laminate for potential progressive failure behavior. A 3D finite element (FE) model was developed to predict the response of the experimental results and to provide insight into the failure mechanism of the multi-angled laminate. The experimental observations and the FE simulations show the possibility of producing pseudo ductile FRP-by-design composite using 3D-printing technology, which leads the way to fabricate next-generation composites for civil infrastructure. Full article

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15 pages, 5538 KiB

Open AccessEditor’s ChoiceArticle

A New Fabric Reinforced Geopolymer Mortar (FRGM) with Mechanical and Energy Benefits

by Fabio Longo, Alessio Cascardi, Paola Lassandro and Maria Antonietta Aiello

Fibers 2020, 8(8), 49; https://doi.org/10.3390/fib8080049 - 30 Jul 2020

Cited by 26 | Viewed by 5243

Abstract

A large part of the European building Heritage is dated back over centuries. Consequently, its structural and thermal performances are often inadequate. Commonly, different interventions are proposed for solving these issues separately. However, reasonable drawbacks arise when the structural retrofitting requires a direct [...] Read more.

A large part of the European building Heritage is dated back over centuries. Consequently, its structural and thermal performances are often inadequate. Commonly, different interventions are proposed for solving these issues separately. However, reasonable drawbacks arise when the structural retrofitting requires a direct contact with the target-member while the insulation layer is potentially interposed in between. In this scenario, the present research proposes a novel and unique system able to guarantee both the energetic and the structural retrofitting. Inorganic Matrix Composites (IMCs) are a promising solution in this sense. Among them, the Fabric Reinforced Cementitous Matrix (FRCM) is one of the most used; or rather a composite made of a fabric (open grid or mesh) within an inorganic matrix (lime or cement based). Even if the inorganic matrix has a relevant thickness (if compared with the one of the fabric), its thermal resistance is insufficient. The novelty of this work consists in assessing a new geo-polymeric FRCM-system by combining fly-ash binder (reused material) and expanded glass aggregate (recycled material). Direct tensile tests, for measuring the tensile strength, ultimate strain and elastic modulus, were performed in addition to thermal conductivity tests. The results were compared with those of traditional FRCM (commercially available). The potentiality of the proposal for structural and energy retrofitting is discussed and examples of its possible application are also reported. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement Composites as Concrete Reinforcement)

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16 pages, 2510 KiB

Open AccessEditor’s ChoiceArticle

Specific Dimensional Change Behavior of Laminated Beech Veneer Lumber (BauBuche) in Terms of Moisture Absorption and Desorption

by Jan T. Benthien, Martin Riegler, Nick Engehausen and Martin Nopens

Fibers 2020, 8(7), 47; https://doi.org/10.3390/fib8070047 - 16 Jul 2020

Cited by 8 | Viewed by 4379

Abstract

Replacing greenhouse gas-intensive building materials with wood products from sustainable forestry contributes to the implementation of current climate conventions such as the Paris Agreement. Hardwood products, such as laminated veneer lumber made of beech (e.g., BauBuche), are an alternative to conventional building materials. [...] Read more.

Replacing greenhouse gas-intensive building materials with wood products from sustainable forestry contributes to the implementation of current climate conventions such as the Paris Agreement. Hardwood products, such as laminated veneer lumber made of beech (e.g., BauBuche), are an alternative to conventional building materials. For the application of wood products in the construction sector, a precise knowledge of the mechanical and physical properties is essential. Therefore, the aim of the present study was to investigate the sorption behavior and associated dimensional changes of the product BauBuche. This was done by applying a manual testing procedure (climatic chamber, balance and caliper) as well as a dynamic vapor sorption analyzer equipped with a camera. During initial moistening after production, due to the irreversible spring back (approximately 2 mm at 50 mm; i.e., 4%), Baubuche shows an extremely strong swelling in the radial direction. Once the maximum spring back is reached, Baubuche shows sorption behavior in the radial and tangential direction, which is comparable to that of solid beech wood in the radial direction. Consequently, the dimensional changes caused by moisture changes must be taken into account in the dimensioning of Baubuche components in order to avoid damage to building structures. Full article

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