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Chopped Basalt Fibers Reinforced Mortar for Strengthening the Architectural Heritage

Journal Description

Fibers

Fibers is an international, peer-reviewed, open access journal on fiber science, published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, ESCI (Web of Science), Ei Compendex, PubAg, CAPlus / SciFinder, Inspec, and other databases.
Journal Rank: JCR - Q2 (Materials Science, Multidisciplinary) / CiteScore - Q1 (Civil and Structural Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 21.3 days after submission; acceptance to publication is undertaken in 4.8 days (median values for papers published in this journal in the second half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

Impact Factor: 4.0 (2023); 5-Year Impact Factor: 4.0 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2079-6439

Latest Articles

21 pages, 6582 KiB

Open AccessArticle

Experimental Study on the Effect of Abaca Fibers on Reinforced Concrete: Evaluation of Workability, Mechanical, and Durability-Related Properties

by Armando Arvizu-Montes, Stefany Alcivar-Bastidas and María José Martínez-Echevarría

Fibers 2025, 13(6), 75; https://doi.org/10.3390/fib13060075 - 4 Jun 2025

Interest in incorporating natural fibers as reinforcements in concrete has grown in parallel with the increasing need to reduce the environmental impact of construction. These fibers, known for their renewability, low cost, and life-cycle superiority, exhibit technical advantages such as light weight and [...] Read more.

Interest in incorporating natural fibers as reinforcements in concrete has grown in parallel with the increasing need to reduce the environmental impact of construction. These fibers, known for their renewability, low cost, and life-cycle superiority, exhibit technical advantages such as light weight and high tensile strength. This study experimentally evaluated the influence of abaca fibers (AF) previously subjected to alkaline treatment and incorporated in reinforced concrete on workability, mechanical behavior, and durability, with a particular focus on the mechanisms affecting steel rebar corrosion. The characterization techniques included compressive and flexural testing; porosity, capillary water absorption, ion chloride penetration, and carbonation depth measurements; and corrosion rate monitoring via electrochemical methods. The results indicated that the addition of AF did not compromise the fresh-state properties or compressive strength but improved the flexural strength by 7.3%. Regarding durability, the porosity and water absorption increased by 4.1% and 8.2%, respectively, whereas the chloride penetration and carbonation depth remained within the requirements. Notable effects were observed regarding steel corrosion performance, where the incorporation of AF led to higher variability and an increasing trend in the corrosion rate compared with that of the reference concrete. Nevertheless, estimations suggest that abaca-fiber-reinforced concrete can meet the 100-year service life. These findings support the potential of AF as a viable reinforcement material for mechanical improvement; however, their influence on long-term durability, particularly corrosion, requires further investigation to deepen their feasible application for sustainable construction. Full article

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13 pages, 2510 KiB

Open AccessArticle

Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing

by Javier Jimenez, Joseph A. Orlando, James E. Cilek and Jeffrey G. Lundin

Fibers 2025, 13(6), 74; https://doi.org/10.3390/fib13060074 - 4 Jun 2025

Personal protection from mosquitos is dominated by topically applied aerosol sprays or lotions, which demonstrate efficacy durations of no longer than 10 h, thus encouraging the research and development of long-term insect-repelling devices. Repellent-loaded polymeric matrices have driven the development of insect-repelling apparel [...] Read more.

Personal protection from mosquitos is dominated by topically applied aerosol sprays or lotions, which demonstrate efficacy durations of no longer than 10 h, thus encouraging the research and development of long-term insect-repelling devices. Repellent-loaded polymeric matrices have driven the development of insect-repelling apparel fabrics; however, most efforts either fail to offer the tensile properties demanded from apparel applications or only demonstrate repellency durations for multiple days. This study utilizes poly-D,L-lactic acid (PDLLA) as a compatibilizer between Nylon 12 and nootkatone for enhanced nootkatone retention throughout fabric manufacturing processes. Nootkatone-infused Nylon 12/PDLLA composites demonstrate up to a 14% increase in nootkatone retention throughout fabric manufacturing compared to pure Nylon 12, underscoring the importance of polymer/substrate miscibility on substrate retention. Moreover, while nootkatone-infused Nylon 12 filaments demonstrate decreasing tensile stress at breaks with increasing nootkatone content, Nylon 12/PDLLA filaments exhibit similar tensile properties regardless of nootkatone content. The PDLLA domains are suspected to behave as reservoirs for excess nootkatone to prevent its role as a defect within the Nylon 12 matrix. The resulting knits exhibit significant mosquito repellencies over 24 h dependent on the nootkatone concentration, thus demonstrating potential to embed insect repellent within high-performance polymeric filaments with effective mosquito repellencies. Therefore, the incorporation of PDLLA as a compatibilizer holds significant potential for enhanced nootkatone retention during Nylon 12 fabric manufacturing. Full article

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25 pages, 3711 KiB

Open AccessArticle

Eco-Friendly Extraction of Curcumin from Turmeric and Dyeability of Textile Fibers

by Vasilica Popescu, Ana-Diana Alexandrescu, Gabriel Popescu and Viorica Vasilache

Fibers 2025, 13(6), 73; https://doi.org/10.3390/fib13060073 - 4 Jun 2025

Classical and modern methods are used to release curcumin by degrading the polysaccharides found in the turmeric powder matrix. Classical methods use chemicals as acids (HCl, H₂SO₄, CH₃COOH), oxidants (H₂O₂, kojic acid), and [...] Read more.

Classical and modern methods are used to release curcumin by degrading the polysaccharides found in the turmeric powder matrix. Classical methods use chemicals as acids (HCl, H₂SO₄, CH₃COOH), oxidants (H₂O₂, kojic acid), and enzymes (amylase type) that can degrade amylose and amylopectin from starch. The modern applied methods consist of the degradation of the polysaccharides in the turmeric powder during eco-friendly processes assisted by ultrasound or microwaves. The extraction medium can consist of only water, water with a solvent, and/or an oxidizing agent. The presence of curcumin in turmeric powder is confirmed by FTIR analysis. The UV–VIS analysis of the extracts allows the determination of the efficiency of modern extraction processes. The release of curcumin from turmeric is highlighted quantitatively by colorimetric measurements for the obtained extracts, using a portable DataColor spectrophotometer. The comparison of the results leads to the conclusion that microwave-assisted extractions are the most effective. These extracts are able to dye many types of textile fibers: wool, cotton, hemp, silk, polyacrylonitrile, polyamide, polyester, and cellulose acetate. CIELab and color strength (K/S) measurements indicate that the most intense yellow colors are obtained on polyacrylonitrile (b* = 86.32, K/S = 15.14) and on cellulose acetate (b* = 90.40, K/S = 14.17). Full article

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22 pages, 1950 KiB

Open AccessArticle

Mechanical Properties and Structural Design of PVA Fiber-Reinforced Cementitious Composites with Fly Ash Replacement for Natural Sand Aggregates

by Camelia Maria Negrutiu, Pavel Ioan Sosa, Cristina Mihaela Campian and Maria Ileana Pop

Fibers 2025, 13(6), 72; https://doi.org/10.3390/fib13060072 - 3 Jun 2025

This paper investigates nine PVA fiber-reinforced cementitious composites with varying fiber content (1–2.5%) and types (oil-coated and non-coated). The experimental compositions utilize locally available cement, high volumes of fly ash, silica fume, PVA fibers, and a superplasticizer, entirely omitting natural aggregates. Key parameters [...] Read more.

This paper investigates nine PVA fiber-reinforced cementitious composites with varying fiber content (1–2.5%) and types (oil-coated and non-coated). The experimental compositions utilize locally available cement, high volumes of fly ash, silica fume, PVA fibers, and a superplasticizer, entirely omitting natural aggregates. Key parameters evaluated include bulk density, compressive strength, secant modulus of elasticity, flexural tensile strength, fracture energy, and structural design applicability. The results show that FRCs without natural aggregates achieves significantly lower densities (1500–1720 kg/m³). Compressive strength is influenced by matrix density, with the highest value recorded at 30.98 MPa. The high fly ash content reduces the secant modulus of elasticity, while flexural tensile strength follows a similar pattern to compressive strength. Oil-coated fibers generally lower fracture energy, except for the 1.5% PVA content, where the 2.5% composition performs best. All specimens exhibit tension softening rather than the strain-hardening behavior of ECCs. Structural design equations were developed, though experimental validation is necessary. The 2.5% PVA composition increases the compression zone height by 7% while requiring 2% more reinforcement. As a sustainable alternative to conventional concrete, the composites offer promising mechanical properties and structural viability for construction applications. Full article

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27 pages, 2272 KiB

Open AccessArticle

Application of L-Shaped Zigzag Steel Fibers with Different Parameters in Asphalt Mixtures

by Qingguo Yang, Wujing Yin, Jiawei Cheng, Ya Li, Yu Zhou, Kelin Chen and Yunhao Li

Fibers 2025, 13(6), 71; https://doi.org/10.3390/fib13060071 - 2 Jun 2025

Taking AC-13 asphalt mixture as the matrix, this research delves into the impacts of assorted steel fibers on AC-13 asphalt mixture, especially the influence of 17.5 mm × 17.5 mm L-shaped steel fibers. A gradient design with mass dosages of 0%, 1%, 2%, [...] Read more.

Taking AC-13 asphalt mixture as the matrix, this research delves into the impacts of assorted steel fibers on AC-13 asphalt mixture, especially the influence of 17.5 mm × 17.5 mm L-shaped steel fibers. A gradient design with mass dosages of 0%, 1%, 2%, and 3% was employed to evaluate the reinforcement effect of L-shaped steel fiber-reinforced asphalt mixture compared with conventional mixture. Also, comparative analysis between L-shaped and straight steel fibers was conducted through comprehensive mechanical performance tests, including the Marshall stability test, high-temperature wheel tracking test, low-temperature beam bending test, freeze–thaw splitting strength test, and immersion Marshall test. The results demonstrate that L-shaped steel fibers significantly improve the comprehensive mechanical properties of asphalt mixture compared to conventional asphalt mixture, showing remarkable improvements in high-temperature stability, low-temperature crack resistance, and water stability. The overall performance enhancement effect increases by approximately 20%. Compared with straight steel fibers, the performance improvement of the mixtures is slightly greater, with the optimal performance achieved at 2% mass dosage. The standard deviation and coefficient of variation are used to reflect the degree of data dispersion. The results show that the data of L-shaped steel fibers have relatively smaller fluctuations, being more uniform and stable. Full article

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16 pages, 1952 KiB

Open AccessArticle

Influence of Geometric Non-Linearities on the Mixed-Mode Decomposition in Asymmetric DCB Samples

by Jorge Bonhomme, Victoria Mollón, Jaime Viña and Antonio Argüelles

Fibers 2025, 13(6), 70; https://doi.org/10.3390/fib13060070 - 27 May 2025

The Asymmetric Double Cantilever Beam (ADCB) is a common test configuration used to produce mixed mode I/II in composite materials. It consists of two sublaminates with different thicknesses or elastic properties, a situation that usually occurs in bimaterial adhesive joints. During this test, [...] Read more.

The Asymmetric Double Cantilever Beam (ADCB) is a common test configuration used to produce mixed mode I/II in composite materials. It consists of two sublaminates with different thicknesses or elastic properties, a situation that usually occurs in bimaterial adhesive joints. During this test, the sample undergoes rotation. In this work, the influence of this rotation on the calculation of the energy release rate (ERR) in modes I and II was studied using the Finite Element Method (FEM). Several models with different degrees of asymmetry (different thickness ratio and/or elastic modulus ratio) and different applied displacements were prepared to obtain different levels of rotation during the test. As is known, the concept of modes I and II refers to the components of the energy release rate calculated in the direction perpendicular and tangential to the delamination plane, respectively. If the model experiences significant rotation during the application of the load, this non-linearity must be considered in the calculation of the mode partition I/II. In this work, appreciable differences were observed in the values of modes I and II, depending on their calculation in a global system or a local system that rotates with the sample. When performing crack growth calculations, the difference between critical loads can be in the order of 4%, while the difference between mode I and mode II results can reach 4% and 14%, respectively, for an applied displacement of only 5 mm. Currently, this correction is not usually implemented in Finite Element calculation codes or in analytical developments. The purpose of this article is to draw attention to this aspect when the rotation of the specimen is not negligible. Full article

(This article belongs to the Topic Advanced Carbon Fiber Reinforced Composite Materials, Volume II)

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25 pages, 4065 KiB

Open AccessArticle

Selective Enrichment of Fibrous Fragments Formed from Milled Carbon Fibers by Means of Gravitational Settling in a Liquid

by Nicolas Rodriguez y Fischer, Kerstin Kämpf, Torben Peters, Nico Dziurowitz, Carmen Thim, Daniela Wenzlaff, Asmus Meyer-Plath and Daphne Bäger

Fibers 2025, 13(6), 69; https://doi.org/10.3390/fib13060069 - 26 May 2025

The aim to reduce health risks of workers related to inhalative exposure to potentially toxic dusts requires the selection of appropriate measures depending on the hazard classification of the dust-composing materials. Due to their biodurability, respirable carbon fibers and their fragments can impose [...] Read more.

The aim to reduce health risks of workers related to inhalative exposure to potentially toxic dusts requires the selection of appropriate measures depending on the hazard classification of the dust-composing materials. Due to their biodurability, respirable carbon fibers and their fragments can impose such health risks but are currently lacking hazard classification. Here, a method is presented for fragmenting carbon fiber materials and enriching fibrous fragments to a level that is expected to allow differentiating between fiber and particle overload-related toxic effects. The method was applied to a commercial polyacrylonitrile-based carbon fiber. It was ground in an oscillating ball mill, homogenized in a liquid using ultrasonication and left undisturbed for gravitational settling. This way, a vertical gradient in particle size and shape formed, from which the supernatant was collected. Fragment morphologies were characterized with large ensemble statistics by semi-automated evaluation of scanning electron microscopy images employing an artificial neural network for binary semantic segmentation. The number of fibrous fragments of respirable and thus critical fiber morphology was increased from

0.36 \times 10^{6}

to

6 \times 10^{6}

WHO-analog fibers per mg. This corresponds to a factor of about 15 compared to the initial ground material. Since the mass percentage of non-fibrous objects was also significantly reduced, the requirements for a subsequently scheduled toxicological study with intraperitoneal application were fulfilled. Intraperitoneal testing is an accepted method for assessing the carcinogenic potential of biopersistent fibers. The developed method allows enriching fibrous fractions of concern at acceptable throughput and enables testing fiber toxicological effects of respirable fragments from disintegrated polyacrylonitrile-based carbon fibers. Full article

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39 pages, 11665 KiB

Open AccessReview

Sustainable Masonry Retrofitting and Upgrading Techniques: A Review

by Arnas Majumder, Flavio Stochino, Monica Valdes, Giovanna Concu, Marco Pepe and Enzo Martinelli

Fibers 2025, 13(6), 68; https://doi.org/10.3390/fib13060068 - 23 May 2025

This study presents a comprehensive review of various advanced methodologies that have been used to enhance the structural and thermal performance of masonry walls through innovative and sustainable retrofitting/upgrading techniques. Focusing on three primary approaches—mechanical/structural retrofitting, thermal retrofitting, and integrated (structural and thermal) [...] Read more.

This study presents a comprehensive review of various advanced methodologies that have been used to enhance the structural and thermal performance of masonry walls through innovative and sustainable retrofitting/upgrading techniques. Focusing on three primary approaches—mechanical/structural retrofitting, thermal retrofitting, and integrated (structural and thermal) retrofitting, this paper critically examines various masonry-strengthening strategies. Retrofitting techniques are categorized by material use and objectives. Fiber-based solutions include insulation materials, fiber composite mortar for strength, FRP for high-strength reinforcement, and TRM for durability. According to the relevant objectives, retrofitting can enhance structural stability (FRP, TRM), improve thermal insulation, or combine both for integrated performance. Particular emphasis is placed on the effectiveness of TRM systems, with a comparative analysis of man-made (glass, steel textile) and natural fiber-based TRM solutions. Regarding integrating natural fibers into TRM systems, this study highlights their potential as eco-friendly alternatives that reduce environmental impact while maintaining or improving structural integrity. Furthermore, it highlights and examines techniques for testing masonry walls. In this context, this review highlights the applicability of natural fiber as a sustainable building material in various retrofitting/upgrading solutions. Full article

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22 pages, 3248 KiB

Open AccessArticle

Experimental Analysis of Low-Energy Impact Damage in Composite Material Airfoils

by Ilse Jauregui Bogarin, Virginia G. Angel, Miriam Siqueiros Hernández, Emmanuel Santiago Durazo Romero, Hernán D. Magaña-Almaguer, Lidia Esther Vargas Osuna and Benjamín González Vizcarra

Fibers 2025, 13(5), 67; https://doi.org/10.3390/fib13050067 - 19 May 2025

The use of composite materials in aerospace structures has led to significant weight reductions and improved performance. However, their behavior under low-energy impact remains a critical concern due to the potential initiation of barely visible damage. This study investigates the crack initiation mechanisms [...] Read more.

The use of composite materials in aerospace structures has led to significant weight reductions and improved performance. However, their behavior under low-energy impact remains a critical concern due to the potential initiation of barely visible damage. This study investigates the crack initiation mechanisms in composite airfoil profiles subjected to low-energy impact, simulating real-world scenarios such as hail or bird strikes. Two types of airfoil profiles were fabricated using bidirectional carbon fiber reinforced polymer (CFRP) with epoxy resin and tested under ASTM D7136 impact conditions. Tensile tests following ASTM D3039 were conducted to assess post-impact mechanical behavior. The damage patterns were analyzed using high-resolution microscopy and non-destructive inspection techniques. Results revealed that damage severity and propagation depend on impact energy levels and airfoil geometry, with SC(2)-0714 exhibiting better impact resistance than GOE777-IL. Microscopic analysis confirmed that delamination initiated at 45° fiber orientations, expanding along interlaminar regions, while airfoil curvature influenced the impact energy dissipation. Full article

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21 pages, 26641 KiB

Open AccessArticle

A CNN-Based Method for Quantitative Assessment of Steel Microstructures in Welded Zones

by Cássio Danelon de Almeida, Thales Tozatto Filgueiras, Moisés Luiz Lagares, Jr., Bruno da Silva Macêdo, Camila Martins Saporetti, Matteo Bodini and Leonardo Goliatt

Fibers 2025, 13(5), 66; https://doi.org/10.3390/fib13050066 - 15 May 2025

The mechanical performance of metallic components is intrinsically linked to their microstructural features. However, the manual quantification of microconstituents in metallographic images remains a time-consuming and subjective task, often requiring over 15 min per image by a trained expert. To address this limitation, [...] Read more.

The mechanical performance of metallic components is intrinsically linked to their microstructural features. However, the manual quantification of microconstituents in metallographic images remains a time-consuming and subjective task, often requiring over 15 min per image by a trained expert. To address this limitation, this study proposes an automated approach for quantifying the microstructural constituents from low-carbon steel welded zone images using convolutional neural networks (CNNs). A dataset of 210 micrographs was expanded to 720 samples through data augmentation to improve model generalization. Two architectures (AlexNet and VGG16) were trained from scratch, while three pre-trained models (VGG19, InceptionV3, and Xception) were fine-tuned. Among these, VGG19 optimized with stochastic gradient descent (SGD) achieved the best predictive performance, with an

R^{2}

of 0.838, MAE of 5.01%, and RMSE of 6.88%. The results confirm the effectiveness of CNNs for reliable and efficient microstructure quantification, offering a significant contribution to computational metallography. Full article

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14 pages, 4191 KiB

Open AccessArticle

Evaluating Carbon Fibre-Reinforced Polymer Composite Helical Spring Performances Under Various Compression Angles

by Yupu Dai, Joel Chong, Ling Chen and Youhong Tang

Fibers 2025, 13(5), 65; https://doi.org/10.3390/fib13050065 - 14 May 2025

Springs are widely used in industries such as aerospace and automotive. As the demand for emission reduction grows, the research on lightweight spring performance is becoming increasingly important. This study analyses the mechanical performance of triple-layer braided composite helical springs (TCHS) under various [...] Read more.

Springs are widely used in industries such as aerospace and automotive. As the demand for emission reduction grows, the research on lightweight spring performance is becoming increasingly important. This study analyses the mechanical performance of triple-layer braided composite helical springs (TCHS) under various loads and compression angles. Firstly, the optimal high-temperature curing condition of the epoxy resin was determined through tensile and three-point bending analysis. Then, TCHS were fabricated based on optimal epoxy curing conditions, and multi-angle compression tests under different loads were carried out. Simultaneously, strain gauges were installed at various positions and orientations on the inner and outer sides of the spring wire to reveal strain patterns during the compression. The test results indicate that stiffness decreases with increasing compression angle. Additionally, the strain in the inner and outer positions in different directions of the same region increased with the rise in compression force and angle, and strains in the helical direction were the largest. Subsequently, strain in the helical direction across different regions further showed that maximum strain occurred in the centre coil (region 2), with inner and outer helical direction strains reaching −5116.89 με and 5700.15 με, respectively, which are 71.3% and 90.4% higher than those in region 1 and 73.2% and 92.9% higher than those in region 3. As the compression load increased, cracks appeared on the outer side of the centre coil. In addition, the crack was perpendicular to the helical direction, further confirming that the highest strain occurred in the helical direction. This study provides an in-depth analysis of the impact of angle-specific loads on TCHS, offering valuable insights for the design and optimisation of composite helical springs and laying a theoretical foundation for their future development. Full article

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64 pages, 6390 KiB

Open AccessReview

Greening Fused Deposition Modeling: A Critical Review of Plant Fiber-Reinforced PLA-Based 3D-Printed Biocomposites

by Muneeb Tahir and Abdel-Fattah Seyam

Fibers 2025, 13(5), 64; https://doi.org/10.3390/fib13050064 - 14 May 2025

Fused deposition modeling (FDM) 3D printing (3DP) of PLA biocomposites reinforced with plant-derived cellulosic fibrous materials, including spun yarn, microcrystalline, microfibrillar, nanofibrillar cellulose, and cellulose nanocrystals, offers an environmentally sustainable solution to the mechanical limitations of polymer-only printed materials. Micron- and submicron-scale cellulosic [...] Read more.

Fused deposition modeling (FDM) 3D printing (3DP) of PLA biocomposites reinforced with plant-derived cellulosic fibrous materials, including spun yarn, microcrystalline, microfibrillar, nanofibrillar cellulose, and cellulose nanocrystals, offers an environmentally sustainable solution to the mechanical limitations of polymer-only printed materials. Micron- and submicron-scale cellulosic fibers are valued for their renewability, non-toxicity, high surface area, and favorable elastic and specific moduli; notably, micron-scale reinforcements are particularly attractive due to their ease of large-scale industrial production and commercial viability. Similarly, PLA benefits from large-scale production, contributes to CO₂ sequestration through its raw material precursors, and requires less energy for production than non-biodegradable petroleum-derived polymers. Incorporating these raw materials, each of which offers attractive performance properties, complementary commercial strengths, and environmental benefits, as constituent phases in FDM 3D-printed biocomposites (FDMPBs) can further enhance the environmental responsiveness of an already low-waste FDM 3DP technology. Inspired by these compelling advantages, this paper critically reviews research on FDMPB with cellulosic reinforcements in a PLA matrix, uniquely categorizing studies based on the form of cellulosic reinforcement and its impact on the biocomposite’s structure and mechanical performance. Additionally, the review covers biocomposite filament production methods and the equipment involved, presenting an alternative framework for cataloging FDMPB research. A comprehensive literature analysis reveals that the wide variation in feedstocks, fiber–matrix compounding methods, equipment, and processing parameters used in filament production and 3DP complicates the comparison of FDMPB mechanical properties across studies, often resulting in conflicting outcomes. Key processing parameters have been compiled to bridge this gap and offer a more nuanced understanding of the cause-and-effect relationships governing biocomposite properties. Finally, targeted recommendations for future research on developing FDMPB with a PLA matrix and micron-scale cellulosic reinforcements are provided, addressing the knowledge gaps and challenges highlighted in the peer-reviewed literature. Full article

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21 pages, 4029 KiB

Open AccessArticle

Virginia Mallow: The Lost Fiber of the Future?

by Gabriela Vanja, Sandra Bischof and Zorana Kovačević

Fibers 2025, 13(5), 63; https://doi.org/10.3390/fib13050063 - 13 May 2025

Virginia mallow or Sida hermaphrodita (L.) Rusby (SH) is a perennial plant from the Malvaceae family (mallows) that is used for medicinal purposes, reducing soil erosion, cleaning soil, and most recently for energy production. The potential of sustainable lignocellulosic agro-waste is immense as [...] Read more.

Virginia mallow or Sida hermaphrodita (L.) Rusby (SH) is a perennial plant from the Malvaceae family (mallows) that is used for medicinal purposes, reducing soil erosion, cleaning soil, and most recently for energy production. The potential of sustainable lignocellulosic agro-waste is immense as it represents Earth’s most abundant organic compound. This paper explores fibers isolated from SH stems, a plant with significant industrial application potential, including technical textiles and biocomposites. The fibers were harvested in January, March, and November of 2020 and in January and March of 2021, and their yield, mechanical properties, moisture content, and density were thoroughly analyzed. The fiber yield showed slight variations depending on the harvest time, with consistent results observed across different years, suggesting stable productivity. The SH fibers demonstrated a favorable moisture content, making them suitable for storage and processing, and their density ranged between 1.52 and 1.58 g/cm³, comparable to that of other natural fibers. According to this research, the best mechanical properties were observed in the winter harvest. Furthermore, the high percentage of solid residue left after fiber extraction shows promise for sustainable utilization, primarily for biofuel production. This study underscores the versatility and sustainability of SH fibers, positioning them as a valuable resource for a wide range of industrial applications. Full article

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18 pages, 14418 KiB

Open AccessArticle

Recovery of End-of-Life Building Materials: Thermal Decomposition and Phase Transformation of Chrysotile in Asbestos-Containing Fiber Cement Boards

by António Curado, Leonel J. R. Nunes, Arlete Carvalho, João Abrantes, Eduarda Lima and Mário Tomé

Fibers 2025, 13(5), 62; https://doi.org/10.3390/fib13050062 - 9 May 2025

The circular economy emphasizes reducing, recycling, and reusing waste, a principle that is challenging to apply to hazardous materials like asbestos-containing construction waste, typically destined for landfills due to limited recycling options. This experimental study investigates the physicochemical characterization of asbestos fibers in [...] Read more.

The circular economy emphasizes reducing, recycling, and reusing waste, a principle that is challenging to apply to hazardous materials like asbestos-containing construction waste, typically destined for landfills due to limited recycling options. This experimental study investigates the physicochemical characterization of asbestos fibers in fiber cement boards and assesses the efficacy of mechanical grinding and thermal treatments to transform these fibers into non-fibrous, stable phases for reuse in sustainable construction applications, such as cement and mineral wool production. Using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), we analyzed samples from end-of-life fiber cement panels, subjecting them to thermal treatments at 700 °C, 1000 °C, and 1200 °C. Results show that, while grinding reduces particle size, it does not eliminate fibrous structures; however, thermal treatment above 1000 °C fully converts chrysotile into forsterite and enstatite, eliminating health risks and enabling material reuse. These findings, that are part of the FiberRec project, support a systematic approach to integrating asbestos-containing waste into a closed-loop material cycle, significantly reducing carbon emissions and landfill dependency. Full article

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10 pages, 2843 KiB

Open AccessArticle

Passively Q-Switched Thulium-Doped Fiber Laser Employing a Glycerin-Based Saturable Absorber

by Edwin Addiel Espinosa-De-La-Cruz, Manuel Durán-Sánchez, Ulises Alcántara-Bautista, Alejandro Reyes-Mora, Adalid Ibarra-Garrido, Ivan Armas-Rivera, Luis Alberto Rodríguez-Morales, Miguel Bello-Jiménez and Baldemar Ibarra-Escamilla

Fibers 2025, 13(5), 61; https://doi.org/10.3390/fib13050061 - 8 May 2025

A passively Q-switched Thulium-doped fiber laser based on glycerin as the saturable absorber is experimentally demonstrated for the first time. The saturable absorber consists of two FC/PC connectors aligned within a mechanical fiber-fiber coupler, with the intervening gap filled with glycerin. Such a [...] Read more.

A passively Q-switched Thulium-doped fiber laser based on glycerin as the saturable absorber is experimentally demonstrated for the first time. The saturable absorber consists of two FC/PC connectors aligned within a mechanical fiber-fiber coupler, with the intervening gap filled with glycerin. Such a saturable absorber is integrated into a compact ring cavity, enabling passive Q-switched laser operation. Starting at a minimum pump power of 1.7 W, Q-switched pulses with a central wavelength of 1946 nm are obtained. At the maximum pump power of 2.4 W, the laser generates pulses with a duration of approximately 2 µs, a repetition rate of 26.7 kHz, and a pulse energy of 1.08 µJ. To the best of our knowledge, this is the first demonstration of passively Q-switched laser operation utilizing a glycerin-based saturable absorber for generating pulsed emission at the 2-µm wavelength region. This breakthrough represents a significant advancement in fiber laser technology, introducing a novel and efficient approach to pulse generation. Full article

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26 pages, 10042 KiB

Open AccessArticle

Verification of Crack Width Evaluation in Fiber-Reinforced Cementitious Composite Reinforced with Various Types of Fiber-Reinforced Polymer Bars

by Hideto Sasaki, Helen Negash Shiferaw and Toshiyuki Kanakubo

Fibers 2025, 13(5), 60; https://doi.org/10.3390/fib13050060 - 7 May 2025

This study aims to verify the adaptability of a crack width evaluation method for fiber-reinforced cementitious composite (FRCC) proposed by the authors to various combinations of fiber-reinforced polymer (FRP) bars and FRCCs. As this evaluation method requires bond constitutive laws between FRP bars [...] Read more.

This study aims to verify the adaptability of a crack width evaluation method for fiber-reinforced cementitious composite (FRCC) proposed by the authors to various combinations of fiber-reinforced polymer (FRP) bars and FRCCs. As this evaluation method requires bond constitutive laws between FRP bars and FRCC, bond tests between FRP and FRCCs were conducted. The FRP and FRCC combinations used in the bond tests were spiral-type CFRP and GFRP bars with PVA-FRCC, as well as strand-type CFRP bars with aramid–FRCC. The maximum bond stress tended to increase as the rib–height ratio of the spiral-type bars increased. When the rib–height ratio increased by 50%, the maximum bond stress of the CFRP and GFRP bars increased by 11% and 33%, respectively. For aramid–FRCC, the average maximum bond stress in the FRCC with a 0.25% volume fraction was 1.67 times that in mortar, and that in 0.50% was 2.01 times that in mortar. The bond constitutive laws were modeled using the trilinear model. Verifications of the method’s adaptability were conducted using tension tests on prisms made of spiral-type CFRP and GFRP bars with PVA-FRCC. As a result of the tension tests, when the FRP strain reached approximately 0.3%, the crack width was about 0.2 mm for CFRP bars and about 0.1 mm for GFRP bars. Verifications were also conducted using four-point bending tests on strand-type CFRP bar beams with aramid–FRCC. The crack width at the same FRP strain tended to become smaller as the fiber volume fraction of FRCC increased. When the FRP strain reached approximately 0.2%, the average crack width of the mortar specimen was around 0.25 mm, whereas it was about 0.15 mm in FRCC with a 0.25% volume fraction and about 0.10 mm at 0.5%. The test results for FRP strain versus crack width relationships were compared with the calculations using the crack width prediction formula. The test results and calculation results were in good agreement. Full article

(This article belongs to the Special Issue Recent Developments in Structural Applications of Fiber-Reinforced Concrete)

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19 pages, 9914 KiB

Open AccessArticle

Lithium Orthosilicate Solid Porous Membranes for CO₂ Capture Obtained from Silica Microfibers

by Joaquín Penide, Efstratios Stavrakakis, Félix Quintero, Danai Poulidi, Antonio Riveiro, Jesús del Val, Rafael Comesaña, Fernando Lusquiños and Juan Pou

Fibers 2025, 13(5), 59; https://doi.org/10.3390/fib13050059 - 7 May 2025

Lithium orthosilicate (Li₄SiO₄) has demonstrated a high CO₂ adsorption rate and capacity and its suitability to be implemented in industry as CO₂ capture technology at high temperatures. The optimum solid adsorbent should present a porous structure to [...] Read more.

Lithium orthosilicate (Li₄SiO₄) has demonstrated a high CO₂ adsorption rate and capacity and its suitability to be implemented in industry as CO₂ capture technology at high temperatures. The optimum solid adsorbent should present a porous structure to maximize surface and enable a high sorption rate. In this work, we present an original approach based on the use of a novel architecture of precursors in the form of very thin free-standing solid silica fibers. An original technique called continuous fiberizing by laser melting (Cobiflas) was used to obtain membranes of pure silica fibers with diameters in the micrometer range, forming a porous membrane which offer a high surface and porous connectivity to be used as precursors without any supporting substrate. Then, we employed a method based on the impregnation of the silica fibers within a lithium-containing aqueous solution and subsequent calcination to obtain a porous solid adsorbent with the maximum proportion of lithium orthosilicate. This method is compared with the results obtained using a sol-gel powder method by analyzing their composition using X-Ray Diffraction (XRD), and their adsorption capacity and adsorption kinetics by Thermogravimetric analyses (TGA). As a result, an outstanding type of solid adsorbent is reported with a 31% adsorption capacity and a total regeneration capacity, which is over 0.8 efficiency with regard to the theoretical maximum adsorption of this material. Full article

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16 pages, 8231 KiB

Open AccessArticle

A Study on the Effect of an Oxidizing Atmosphere During the Recycling of CFRP by Pyrolysis

by Cynthie Dega, Ali Jadidinia and Rachid Boukhili

Fibers 2025, 13(5), 58; https://doi.org/10.3390/fib13050058 - 7 May 2025

Composite materials are increasingly in demand. However, challenges such as high raw-material costs and complicated waste management impede their adoption. Overcoming these obstacles requires efficient recycling methods. Pyrolysis effectively recycles carbon fiber-reinforced polymers (CFRPs). This study proposes a cost-effective CFRP recovery approach utilizing [...] Read more.

Composite materials are increasingly in demand. However, challenges such as high raw-material costs and complicated waste management impede their adoption. Overcoming these obstacles requires efficient recycling methods. Pyrolysis effectively recycles carbon fiber-reinforced polymers (CFRPs). This study proposes a cost-effective CFRP recovery approach utilizing conventional ovens to minimize recycling expenses and maximize reclaimed-product value. Pyrolysis was conducted under atmospheric conditions at 450–600 °C, lasting 1–6 h at each temperature. It was optimal at 2.5 h and 500 °C. Higher temperatures caused fiber degradation, and lower temperatures excessively prolonged duration. After determining the optimal conditions, composite plates were produced using recycled carbon fibers and a vacuum-assisted resin infusion process. Subsequent physical characterization and mechanical tests were conducted on these plates to assess the recycled-CFRP properties. The recovered tensile strength and tensile modulus were 88% and 97% that of virgin carbon fibers (vCF), respectively. Full article

(This article belongs to the Special Issue Mechanical Behaviour of Reinforced Thermosetting Polymers with Fibers: Analytical/Numerical Models and Experimental Evidence)

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17 pages, 4475 KiB

Open AccessArticle

Performance of Carbon Fiber-Reinforced Date Palm Midrib Composites

by Mohammad Hassan Mazaherifar, Octavia Zeleniuc, Camelia Cerbu, Sergiu-Valeriu Georgescu, Antonela Lungu and Camelia Coșereanu

Fibers 2025, 13(5), 57; https://doi.org/10.3390/fib13050057 - 7 May 2025

This paper evaluates the performance of composites made from date palm (Phoenix dactylifera L.) midribs reinforced with carbon fiber. Two types of adhesives—unsaturated polyester and epoxy resin—were used as binder for the experimental panels. The physical properties and mechanical strength of the [...] Read more.

This paper evaluates the performance of composites made from date palm (Phoenix dactylifera L.) midribs reinforced with carbon fiber. Two types of adhesives—unsaturated polyester and epoxy resin—were used as binder for the experimental panels. The physical properties and mechanical strength of the composites, as a function of fiber types, lamination configuration, as well as adhesive types, were determined. The density levels of the panels made using epoxy and unsaturated polyester resin were found to be 1103 kg/m³ and 1133 kg/m³, respectively. Panels made using polyester adhesive had 6.05% and 3.98% for water absorption and thickness swelling values, respectively. Corresponding values of 3.09% and 6.35% were found for the panels made using epoxy resin. Mechanical properties of the samples revealed that carbon fiber-reinforced epoxy hybrids offer superior mechanical performance, whereas polyester-based hybrids may be more suitable for impact-resistant applications. Stereo-microscopy and vertical density profile (VDP) analysis of the panels resulted in variations in layer adhesion and density distribution. Based on the findings in this work, carbon fiber-reinforced epoxy-bonded hybrid panels exhibited superior mechanical properties, while those panels made using polyester-based binder would be more suitable where impact resistance is desired. The combination of date palm fibers and carbon fiber presents significant potential for sustainable applications, offering a balance of strength and durability. Full article

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12 pages, 1671 KiB

Open AccessArticle

Crosstalk Suppression in Multi-Core Fiber Through Modulation of the Refractive Index

by Er’el Granot

Fibers 2025, 13(5), 56; https://doi.org/10.3390/fib13050056 - 3 May 2025

One promising method to increase the bit-rate capacity of optical fibers is the use of Multi-Core Fibers (MCFs). However, the close proximity of the cores can lead to data interference due to crosstalk between them. A novel approach is proposed to suppress crosstalk [...] Read more.

One promising method to increase the bit-rate capacity of optical fibers is the use of Multi-Core Fibers (MCFs). However, the close proximity of the cores can lead to data interference due to crosstalk between them. A novel approach is proposed to suppress crosstalk in MCFs. It is demonstrated that if the refractive index of the cores is weakly modulated harmonically, with each core having a different phase, crosstalk in two-core and three-core fibers can be entirely eliminated. Furthermore, by using specific configurations—either by selecting the fiber length or by arranging the cores’ spatial layout—crosstalk can be suppressed even in fibers with more than three cores. Full article

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