Fibers

24 pages, 4100 KB

Open AccessArticle

Sustainable Pattern Innovation in Chenille Tufted Carpets: A Spatial Color Mixing Approach Using Dope-Dyed Filament

by Peng Cui and Yuan Xue

Fibers 2025, 13(9), 126; https://doi.org/10.3390/fib13090126 - 12 Sep 2025

Chenille tufted carpets typically use wet dyeing, which consumes large amounts of water, chemicals, and energy and limits pattern control. This study combines dope-dyed filaments with spatial (juxtaposed) color mixing to eliminate post-dyeing and expand design options. We define a nine-primary filament set [...] Read more.

Chenille tufted carpets typically use wet dyeing, which consumes large amounts of water, chemicals, and energy and limits pattern control. This study combines dope-dyed filaments with spatial (juxtaposed) color mixing to eliminate post-dyeing and expand design options. We define a nine-primary filament set and a ten-primary mixing system, quantify color relations in CIE Lab*, and classify four visual effects by hue angle difference (Δh): Blending (<30°), Pointillistic (30–60°), Mosaic (60–120°), and Heathering (≥120°). A CNC chenille spinner independently controls linear density, twist, and diameter via head speed, delivery speed, and spacer width; a 130 °C thermal setting step reproduces dyeing-induced pile morphology. The ten-primary system yields 45 binary and 120 ternary mixes that produce predictable effects matching the Δh categories. Yarn geometry is tuned precisely by rotating-head speed (density), front-roller speed (density/twist), and spacer width (diameter). Dope-dyed carpets reach wash and rub fastness grades 4–5 and light fastness grades 3–4 to 4, meeting industry standards. Spatial color mixing with dope-dyed filaments and CNC-controlled chenille morphology thus enables the production of sustainable, dye-free carpets with quantitatively designed patterns and reliable performance, converting empirical color design into a predictive, more resource-efficient process. Full article

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22 pages, 5891 KB

Open AccessArticle

Investigation of the Effect of GFRP Reinforcement Bars on the Flexural Strength of Reinforced Concrete Beams Using the Finite Element Method

by Yusuf Sümer and Muhammed Öztemel

Fibers 2025, 13(9), 125; https://doi.org/10.3390/fib13090125 - 12 Sep 2025

Abstract

The use of environmentally friendly materials is becoming increasingly important in order to increase sustainability and reduce carbon emissions in reinforced concrete structures. In this context, glass fiber-reinforced polymer (GFRP) bars, which are proposed as an alternative to traditional steel reinforcements, are attracting [...] Read more.

The use of environmentally friendly materials is becoming increasingly important in order to increase sustainability and reduce carbon emissions in reinforced concrete structures. In this context, glass fiber-reinforced polymer (GFRP) bars, which are proposed as an alternative to traditional steel reinforcements, are attracting attention in engineering applications thanks to their advantages, such as high corrosion resistance, low weight, and electromagnetic permeability. However, the lower elasticity modulus of GFRP reinforcement compared to steel causes greater displacement and crack width under bending and shear effects, leading to certain limitations in structural performance. Due to the limited number of comprehensive analyses in the literature that simultaneously consider parameters such as reinforcement diameter, concrete strength, and stirrup spacing, this study aims to reveal the interactive effects of these parameters through numerical analyses and contribute to existing research. In this context, beam models using GFRP reinforcements with diameters of 10 mm and 12 mm, concrete strengths of 25 MPa and 40 MPa, and different stirrup spacings were analyzed using the ABAQUS (2022) software with a three-dimensional nonlinear finite element method. Full article

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33 pages, 2741 KB

Open AccessReview

Lignocellulosic Agro-Forest Byproducts as Feedstock for Fused Deposition Modeling 3D Printing Filaments: A Review

by Nanci Ehman, Agustina Ponce de León, Israel N. Quintero Torres, María E. Vallejos and M. Cristina Area

Fibers 2025, 13(9), 124; https://doi.org/10.3390/fib13090124 - 11 Sep 2025

Abstract

Three-dimensional (3D) printing based on polymers reinforced with lignocellulosic components is an accessible and sustainable technology. Cellulose-based byproducts from industry, as well as crops, food, and forestry wastes, represent potential resources for additive manufacturing and have been evaluated in recent years, primarily in [...] Read more.

Three-dimensional (3D) printing based on polymers reinforced with lignocellulosic components is an accessible and sustainable technology. Cellulose-based byproducts from industry, as well as crops, food, and forestry wastes, represent potential resources for additive manufacturing and have been evaluated in recent years, primarily in combination with polymers such as PLA or ABS. During fused deposition modeling (FDM), several parameters must be considered during raw material conditioning, blending, extrusion, and 3D printing. It is essential to understand how these parameters influence the final properties and their impact on the final application. This review focuses on the latest studies of lignocellulosic byproducts for 3D printing filaments and how the parameters involved during filament production and 3D printing influence the properties of the final product. Recent studies concerning applications, technical issues, and environmental and regulatory aspects were also analyzed. Full article

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16 pages, 3805 KB

Open AccessArticle

Fibrillated Nanocellulose Obtained by Mechanochemical Processes from Coconut Fiber Residue

by Sarah Inglid dos Santos Silva, Cassiano Pires, Egon Petersohn Junior, Angela Maria Tribuzy de Magalhães Cordeiro, Rilton Alves de Freitas and Nataly Albuquerque dos Santos

Fibers 2025, 13(9), 123; https://doi.org/10.3390/fib13090123 - 9 Sep 2025

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Abstract

Rich in cellulose, the agro-industrial residue of “Cocos nucifera L.” stands out due to its high global production. In view of this, this research into the development of cellulose nanofibrils from green coconut fiber residue evaluated the fiber produced from an alkaline [...] Read more.

Rich in cellulose, the agro-industrial residue of “Cocos nucifera L.” stands out due to its high global production. In view of this, this research into the development of cellulose nanofibrils from green coconut fiber residue evaluated the fiber produced from an alkaline pre-treatment associated with a grinding process using a colloidal mill, which produced pure and renewable cellulose with characteristics similar to those of commercial celluloses. FTIR and XRD spectroscopy analyses showed that the methodologies established for coconut fiber are efficient in removing amorphous groups. The XRD corroborated the spectrogram and revealed a peak at 2θ = 22°, corresponding to the crystalline region of cellulose I. Both analyses were preceded by thermal analysis showing a reduction in lignin and an increase in the cellulose fraction. The AFM and SEM morphological micrographic analyses confirm the efficiency of the mechanochemical treatment in producing nanometric fibers, which, when submitted to rheology analyses, presented the desired gel profile. Full article

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18 pages, 3547 KB

Open AccessArticle

The Effect of Inorganic Pigments on the Rheological Properties of the Color Masterbatches from Polylactic Acid

by Marcela Hricova, Maria Petkova, Zita Tomcikova and Anna Ujhelyiova

Fibers 2025, 13(9), 122; https://doi.org/10.3390/fib13090122 - 8 Sep 2025

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Abstract

Due to the large amount of plastic waste that is currently produced, the demand for ecological solutions to this situation has been growing. Many research studies in recent years have focused on polylactic acid (PLA) as a biodegradable material made from renewable resources. [...] Read more.

Due to the large amount of plastic waste that is currently produced, the demand for ecological solutions to this situation has been growing. Many research studies in recent years have focused on polylactic acid (PLA) as a biodegradable material made from renewable resources. The individual components of biodegradable materials should comply with the EN 13432 standard, which defines the properties of a “compostable” material. Careful selection of dyes and pigments is therefore important in terms of maintaining the biodegradability of the finished products. In this article, we focus on evaluating the flow properties of color masterbatches modified with inorganic biodegradable pigments. Two types of PLA were used as polymer pigment carriers, and titanium dioxide, carbon black, and two iron oxides were used as inorganic pigments. We monitored the effect of the type and concentration of pigments on the processability and rheological properties of the prepared color PLA masterbatches. The capillary viscometer and rotary rheoviscometer were used to determine rheological properties. The flow properties of color masterbatches containing 1 and 3 wt.% inorganic pigments with two types of pure polymers, PLA6100 and PLA175, were compared. We found that the color PLA masterbatches had good processability and satisfactory rheological properties, and therefore they are usable for further processing. Full article

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20 pages, 2814 KB

Open AccessArticle

Development of High-Performance Biocomposites from Kenaf, Bagasse, Hemp, and Softwood: Effects of Fiber pH Modification and Adhesive Selection on Structural Properties Correlated with FTIR Analysis

by Z. Osman, Y. Senhaji, Mohammed Elamin, Yann Rogaume, Antonio Pizzi, Fatima Charrier-El Bouhtoury and Bertrand Charrier

Fibers 2025, 13(9), 121; https://doi.org/10.3390/fib13090121 - 5 Sep 2025

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Abstract

This study aims to develop high-performance biocomposites for structural applications using kenaf, bagasse, hemp, and softwood fibers bonded with phenol-formaldehyde (PF) and phenol-urea-formaldehyde (PUF) adhesives, commonly used in particleboard manufacturing. A simple, low-cost fiber treatment was applied by adjusting the fiber pH to [...] Read more.

This study aims to develop high-performance biocomposites for structural applications using kenaf, bagasse, hemp, and softwood fibers bonded with phenol-formaldehyde (PF) and phenol-urea-formaldehyde (PUF) adhesives, commonly used in particleboard manufacturing. A simple, low-cost fiber treatment was applied by adjusting the fiber pH to 11 and 13 using a 33% NaOH solution, following standard protocols to enhance fiber–adhesive interaction. The effects of alkaline treatment on the chemical structure of bagasse, kenaf, and hemp fibers were investigated using Fourier Transform Infrared Spectroscopy (FTIR) and correlated with composite mechanical performance. PF and PUF were applied at 13% (w/w), while polymeric diphenylmethane diisocyanate (pMDI) at 5% (w/w) served as a control for untreated fibers. The fabricated panels were evaluated for mechanical properties; modulus of elasticity (MOE), modulus of rupture (MOR), and internal bond strength (IB), and physical properties such as thickness swelling (TS) and water absorption (WA) after 24 h of immersion. FTIR analysis revealed that treatment at pH 11 increased the intensity of O–H, C–O–C, and C–O bands and led to the disappearance of the C=O band (~1700 cm⁻¹) in all fibers. Bagasse treated at pH 11 showed the most significant spectral changes and the highest IB values with both PF and PUF adhesives, followed by kenaf at pH 13, exceeding EN 312:6 (2010) standards for heavy-duty load-bearing panels in dry conditions. The highest MOE and MOR values were achieved with kenaf at pH 11, meeting EN 312:4 (2010) requirements, followed by bagasse, while softwood and hemp performed less favorably. In terms of thickness swelling, bagasse consistently outperformed all other fibers across pH levels and adhesives, followed by Kenaf and Hemp, surpassing even pMDI-based composites. These results suggest that high-pH treatment enhances the reactivity of PF and PUF adhesives by increasing the nucleophilic character of phenolic rings during polymerization. The performance differences among fibers are also attributed to variations in the aspect ratio and intrinsic structural properties influencing fiber–adhesive interactions under alkaline conditions. Overall, kenaf and bagasse fibers emerge as promising, sustainable alternatives to industrial softwood particles for structural particleboard production. PF and PUF adhesives offer cost-effective and less toxic options compared to pMDI, supporting their use in eco-friendly panel manufacturing. FTIR spectroscopy proved to be a powerful method for identifying structural changes caused by alkaline treatment and provided valuable insights into the resulting mechanical and physical performance of the biocomposites. Full article

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17 pages, 2662 KB

Open AccessArticle

Tensile and Dynamic Toughness of Kenaf Fiber-Reinforced Epoxy Composites

by Thuane Teixeira da Silva, Matheus Pereira Ribeiro, Lucas de Mendonça Neuba, Pedro Henrique Poubel Mendonça da Silveira, Noan Tonini Simonassi, Sergio Neves Monteiro and Lucio Fabio Cassiano Nascimento

Fibers 2025, 13(9), 120; https://doi.org/10.3390/fib13090120 - 5 Sep 2025

Viewed by 285

Abstract

The environmental impact of petroleum-based materials in driving climate change has stimulated growing interest in natural lignocellulosic fibers (NLFs) as reinforcements for polymeric matrices. NLFs exhibit specific mechanical properties that, in some cases, rival those of synthetic fibers such as aramid, carbon, and [...] Read more.

The environmental impact of petroleum-based materials in driving climate change has stimulated growing interest in natural lignocellulosic fibers (NLFs) as reinforcements for polymeric matrices. NLFs exhibit specific mechanical properties that, in some cases, rival those of synthetic fibers such as aramid, carbon, and glass. Among the wide variety of NLFs, kenaf has been extensively investigated in applications including textiles, construction, and furniture, owing to its long-established global cultivation. Previous studies have also demonstrated its potential as a reinforcement in polymeric matrices for engineering applications, including ballistic protection. In this context, the present work reports, for the first time, on the tensile and dynamic impact toughness of epoxy matrix composites reinforced with 10, 20, and 30 vol% kenaf fibers. The tensile toughness, defined as the area under the stress–strain curve up to fracture, ranged from 9.36 kJ/m² at 10 vol% to 52.30 kJ/m² at 30 vol% fiber content—representing a three- to tenfold increase compared to the neat epoxy matrix. In Izod impact tests, the composites containing 30 vol% kenaf fibers absorbed 22 times more energy than the neat epoxy, rising from 1.8 to 38.8 kJ/m². On average, the tensile toughness values exceeded those of the corresponding dynamic impact toughness. Scanning electron microscopy revealed the fracture morphology and highlighted the influence of the fibers under both toughness conditions. Full article

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39 pages, 1179 KB

Open AccessReview

A Review of Natural Fibers: Classification, Composition, Extraction, Treatments, and Applications

by Telmo Eleutério, Maria João Trota, Maria Gabriela Meirelles and Helena Cristina Vasconcelos

Fibers 2025, 13(9), 119; https://doi.org/10.3390/fib13090119 - 4 Sep 2025

Viewed by 597

Abstract

This review provides a comprehensive analysis of natural fibers, addressing their classification, chemical composition, extraction methods, treatments, and diverse applications. It categorizes natural fibers into plant-based (cellulose-rich), animal-based (protein-based), and mineral-based types, detailing their unique structural and chemical properties. The paper examines traditional [...] Read more.

This review provides a comprehensive analysis of natural fibers, addressing their classification, chemical composition, extraction methods, treatments, and diverse applications. It categorizes natural fibers into plant-based (cellulose-rich), animal-based (protein-based), and mineral-based types, detailing their unique structural and chemical properties. The paper examines traditional and advanced extraction techniques—including dew, water, enzymatic, chemical retting, and mechanical decortication—highlighting their impact on fiber quality and environmental sustainability. Furthermore, it reviews various chemical and biopolymer treatments designed to enhance fiber performance, reduce hydrophilicity, and improve adhesion in composite materials. The discussion extends to the multifaceted applications of natural fibers across industries such as textiles, automotive, construction, and packaging, underscoring their role in reducing reliance on synthetic materials and promoting eco-friendly innovations. The review synthesizes recent market trends and emerging fiber classifications, emphasizing the potential of natural fibers to drive sustainable development and informing future research in extraction efficiency, treatment optimization, and lifecycle analysis. Full article

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18 pages, 3388 KB

Open AccessArticle

Analysis of Interfacial Properties in Flax Yarn-Reinforced Epoxy Resin Composites

by Xinlong Wang, Hongjun Li, Duncan Camilleri, B. Y. R. Surnam, Zhenyu Wu, Xiaoying Cheng, Lin Shi and Wenqi Lu

Fibers 2025, 13(9), 118; https://doi.org/10.3390/fib13090118 - 29 Aug 2025

Viewed by 487

Abstract

With the increasing demand for green materials, natural fiber-reinforced composites have garnered significant attention due to their environmental benefits and cost-effectiveness. However, the weak interfacial bonding between flax fibers and resin matrices limits their broader application. This study systematically investigates the interfacial properties [...] Read more.

With the increasing demand for green materials, natural fiber-reinforced composites have garnered significant attention due to their environmental benefits and cost-effectiveness. However, the weak interfacial bonding between flax fibers and resin matrices limits their broader application. This study systematically investigates the interfacial properties of single-ply and double-ply flax yarn-reinforced epoxy resin composites, focusing on interfacial shear strength (IFSS) and its influencing factors. Pull-out tests were conducted to evaluate the mechanical behavior of yarns under varying embedded lengths, while scanning electron microscopy (SEM) was employed to characterize interfacial failure modes. Critical embedded lengths were determined as 1.49 mm for single-ply and 2.71 mm for double-ply configurations. Results demonstrate that the tensile strength and elastic modulus of flax yarns decrease significantly with increasing gauge length. Single-ply yarns exhibit higher IFSS (30.90–32.03 MPa) compared to double-ply yarns (20.61–25.21 MPa), attributed to their tightly aligned fibers and larger interfacial contact area. Single-ply composites predominantly fail through interfacial debonding, whereas double-ply composites exhibit a hybrid failure mechanism involving interfacial separation, fiber slippage, and matrix fracture, caused by stress inhomogeneity from their multi-strand twisted structure. The study reveals that interfacial failure originates from the incompatibility between hydrophilic fibers and hydrophobic resin, coupled with stress concentration effects induced by the yarn’s multi-level hierarchical structure. These findings provide theoretical guidance for optimizing interfacial design in flax fiber composites to enhance load-transfer efficiency, advancing their application in lightweight, eco-friendly materials. Full article

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15 pages, 4033 KB

Open AccessArticle

Microstructural and Chemical Analysis of PBT/Glass Fiber Composites: Influence of Fiber Content and Manufacturing on Composite Performance

by Oumayma Hamlaoui, Riadh Elleuch, Hakan Tozan, Imad Tawfiq and Olga Klinkova

Fibers 2025, 13(9), 117; https://doi.org/10.3390/fib13090117 - 28 Aug 2025

Viewed by 369

Abstract

This paper provides an in-depth analysis of the microstructural characteristics and the chemical content of Polybutylene Terephthalate (PBT) composites that have different contents of Glass Fiber (GF). Blending of VALOX 420 (30 wt% GF/PBT) with unreinforced VALOX 310 allowed the composites to be [...] Read more.

This paper provides an in-depth analysis of the microstructural characteristics and the chemical content of Polybutylene Terephthalate (PBT) composites that have different contents of Glass Fiber (GF). Blending of VALOX 420 (30 wt% GF/PBT) with unreinforced VALOX 310 allowed the composites to be prepared, with control of the concentration and distribution of the GF. The GF reinforcement and PBT matrix were characterized by an advanced microstructural spectrum and spatial analysis to show the influence of fiber density, dispersion, and chemical composition on performance. Findings indicate that GF content has a profound effect on microstructural properties and damage processes, especially traction effects in various regions of the specimen. These results highlight the significance of accurate control of GF during fabrication to maximize durability and performance, which can be used to inform the design of superior PBT/GF composites in challenging engineering applications. The implications of these results are relevant to a number of high-performance sectors, especially in automotive, electrical, and consumer electronic industries, where PBT/GF composites are found in extensive use because of their outstanding mechanical strength, dimensional stability, and thermal resistance. The main novelty of the current research is both the microstructural and chemical assessment of PBT/GF composites in different fiber contents, and this aspect is rather insufficiently studied in the literature. Although the mechanical performance or macro-level aging effects have been previously assessed, the Literature usually did not combine elemental spectroscopy or spatial microstructural mapping to correlate the fiber distribution with the damage mechanisms. Further, despite the importance of GF reinforcement in achieving the right balance between mechanical, thermal, and electrical performance, not much has been conducted in detail to describe the correlation between the microstructure and the evolution of damage in short-fiber composites. Conversely, this paper will use the superior spatial elemental analysis to bring out the effects of GF content and dispersion on micro-mechanisms like interfacial traction, cracking of the matrix, and fiber fracture. We, to the best of our knowledge, are the first to systematically combine chemical spectrum analysis with spatial mapping of PBT/GF systems with varied fiber contents—this allows us to give actionable information on material design and optimized manufacturing procedures. Full article

(This article belongs to the Topic Advances in Fiber–Matrix Interface: Cohesion Enhancement, Characterization and Modeling of Interfacial Debonding)

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17 pages, 2452 KB

Open AccessArticle

Novel Bio-Functional Electrospun Membranes by Chios Mastic Gum Encapsulation

by Panagiotis M. Mastorakis, Sotirios I. Marras, Costas Tsioptsias, Stephanos P. Zaoutsos, Demetres D. Leonidas, Ioannis Tsivintzelis and Anna-Maria G. Psarra

Fibers 2025, 13(9), 116; https://doi.org/10.3390/fib13090116 - 27 Aug 2025

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Abstract

Pistacia lentiscus var. chia resin (Chios Mastic Gum—CMG) is a natural aromatic resin that has been utilized in traditional medicine for more than 2.5 millennia, as it exhibits a wide range of pharmacological properties. In this study, various quantities of Chios Mastic Gum [...] Read more.

Pistacia lentiscus var. chia resin (Chios Mastic Gum—CMG) is a natural aromatic resin that has been utilized in traditional medicine for more than 2.5 millennia, as it exhibits a wide range of pharmacological properties. In this study, various quantities of Chios Mastic Gum (3.5, 6.5, and 10 wt%) were encapsulated in electrospun fibers of poly-ε-caprolactone (PCL) to develop functional fibrous mats with multiple potential applications. The morphological analysis of composite membranes was conducted through scanning electron microscopy (SEM), revealing the formation of uniform fibers and incremental diameter size in samples with a higher concentration of CMG. The encapsulation efficiency was assessed by UV-Vis spectrophotometry and showed an exceptionally high loading efficiency (87–88%). The cytotoxicity of CMG-loaded nanofibers was tested in human embryonic kidney cell line HEK293 and human hepatocarcinoma cell line HepG2 using the MTT assay. In both cases, a high concentration of encapsulated CMG led to a statistically significant reduction in cell viability. Full article

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19 pages, 6006 KB

Open AccessArticle

Study of Low-Velocity Impact Damage in Composite Laminates Based on Crack Energy

by Yingming Shang, Xu Ma, Chencheng Feng, Yanhong Ding and Ke Ma

Fibers 2025, 13(9), 115; https://doi.org/10.3390/fib13090115 - 26 Aug 2025

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Abstract

In this paper, the overall mechanical response of composite laminates with different structural orientations in low-velocity impacts is discussed using a combination of finite element simulations and experiments. In this process, the crack dissipation energy combined with absorbed energy is proposed as the [...] Read more.

In this paper, the overall mechanical response of composite laminates with different structural orientations in low-velocity impacts is discussed using a combination of finite element simulations and experiments. In this process, the crack dissipation energy combined with absorbed energy is proposed as the damage index to evaluate the degree of the plate’s impact damage. Both the impact energy and the crack energy calculated from the experimental primary damage energy are verified. The results show that with the increase in the impact energy, the primary damage mode changes, which changes the crack-absorbed energy accordingly as well as the stiffness and load-bearing capacity of the plate structure during the impact process. This index can not only be used to characterize the performance of cracks in the overall damage but can also predict the damage state of the plate and plain weave fabric. Full article

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15 pages, 3116 KB

Open AccessArticle

Raman Scattering for Anisotropy of Polyacrylonitrile-Based and Pitch-Based Carbon Fibers

by Kimiyoshi Naito and Chiemi Nagai

Fibers 2025, 13(9), 114; https://doi.org/10.3390/fib13090114 - 25 Aug 2025

Viewed by 373

Abstract

Polyacrylonitrile (PAN)-based and pitch-based carbon fibers exhibit significant anisotropies in the radial and axial directions. Characterizing the anisotropy of the elastic properties of PAN-based and pitch-based carbon fibers is important for carbon fiber research communities. In this present study, the Raman scattering for [...] Read more.

Polyacrylonitrile (PAN)-based and pitch-based carbon fibers exhibit significant anisotropies in the radial and axial directions. Characterizing the anisotropy of the elastic properties of PAN-based and pitch-based carbon fibers is important for carbon fiber research communities. In this present study, the Raman scattering for anisotropy of PAN-based and pitch-based carbon fiber-reinforced plastic (CFRP) samples was investigated. The Raman scattering parameters and ratios in the CFRPs with 0°, 45°, and 90° sections are related to the tensile modulus. These linear trends for the PAN-based and pitch-based CFRPs with 0°, 45°, and 90° sections intersect in the range of 400–700 GPa. The change in Raman scattering parameters and ratios of PAN-based and pitch-based carbon fibers and CFRPs with a 0° section are related to the tensile modulus. These linear trends also intersect in the range of 400–700 GPa. The intensity ratios increased with increase in the angle for each CFRPs. The intensity ratio in an arbitrary angle could be estimated using the rule of mixtures and coordinate transformation equations. The Raman anisotropic nature of PAN-based and pitch-based fibers are identified experimentally and analytically. Full article

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22 pages, 8482 KB

Open AccessArticle

Effect of C-FRP (Carbon Fiber Reinforced Polymer) Rope and Sheet Strengthening on the Shear Behavior of RC Beam-Column Joints

by Emmanouil Golias and Chris Karayannis

Fibers 2025, 13(9), 113; https://doi.org/10.3390/fib13090113 - 22 Aug 2025

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Abstract

This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical [...] Read more.

This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical ropes at column corners, provide enhanced core confinement and shear reinforcement. C-FRP sheets applied to the beam’s plastic hinge region further increase flexural strength and delay localized failure. Three full-scale, shear-deficient RC joints were subjected to cyclic lateral loading. The unstrengthened specimen (JB0V) exhibited rapid stiffness deterioration, premature joint shear cracking, and unstable hysteretic behavior. In contrast, the specimen strengthened solely with X-shaped C-FRP ropes (JB0VF2X2c) displayed a markedly slower rate of stiffness degradation, delayed crack development, and improved energy dissipation stability. The fully retrofitted specimen (JB0VF2X2c + C-FRP) demonstrated the most pronounced gains, with peak load capacity increased by 65%, equivalent viscous damping enhanced by 55%, and joint shear deformations reduced by more than 40%. Even at 4% drift, it retained over 90% of its peak strength, while localizing damage away from the joint core—a performance unattainable by the unstrengthened configuration. These results clearly establish that the combined C-FRP rope–sheet system transforms the seismic response of deficient RC joints, offering a lightweight, non-invasive, and rapidly deployable retrofit solution. By simultaneously boosting shear resistance, ductility, and energy dissipation while controlling damage localization, the technique provides a robust pathway to extend service life and significantly enhance post-earthquake functionality in critical structural connections. Full article

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24 pages, 5801 KB

Open AccessArticle

Copper-Decorated Catalytic Carbon/Ceramic Hollow Fibers for NO Reduction: Enhanced Performance via Tangential Flow Reactor Design and Process Intensification

by George V. Theodorakopoulos, Sergios K. Papageorgiou, Fotios K. Katsaros, Konstantinos G. Beltsios and George Em. Romanos

Fibers 2025, 13(9), 112; https://doi.org/10.3390/fib13090112 - 22 Aug 2025

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Abstract

In this study, high-yield biopolymer/ceramic hollow fibers were fabricated via a facile, modified polyol process in a spinneret setup, enabling the controlled adsorption of Cu²⁺ ions. Post sintering transformed these into catalytic copper-decorated carbon/ceramic (alumina) composite hollow fibers, with alginate serving as [...] Read more.

In this study, high-yield biopolymer/ceramic hollow fibers were fabricated via a facile, modified polyol process in a spinneret setup, enabling the controlled adsorption of Cu²⁺ ions. Post sintering transformed these into catalytic copper-decorated carbon/ceramic (alumina) composite hollow fibers, with alginate serving as both a metal ion binder and a copper nanoparticle stabilizer. The resulting hollow fibers featured porous walls with a high surface area and were densely decorated with copper nanoparticles. Their structural and morphological characteristics were analyzed, and their NO reduction performance was assessed in a continuous flow configuration, where the gas stream passed through both the shell and lumen sides of a fiber bundle in a tangential flow mode. This study also examined the stability, longevity and regeneration potential of the catalytic fibers, including the mechanisms of deactivation and reactivation. Carbon content was found to be decisive for catalytic performance. High-carbon fibers exhibited a light-off temperature of 250 °C, maintained about 90% N₂ selectivity and sustained a consistently high NO reduction efficiency for over 300 h, even without reducing gases like CO. In contrast, low-carbon fibers displayed a higher light-off temperature of 350 °C and a reduced catalytic efficiency. The results indicate that carbon enhances both activity and selectivity, counterbalancing deactivation effects. Owing to their scalability, durability and effectiveness, these catalytic fibers and their corresponding bundle-type reactor configuration represent a promising technology for advanced NO abatement. Full article

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Fibers, Volume 13, Issue 9 (September 2025) – 15 articles

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