Fibers

39 pages, 1179 KB

Open AccessEditor’s ChoiceReview

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

Cited by 14 | Viewed by 11169

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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41 pages, 1835 KB

Open AccessEditor’s ChoiceReview

A Comprehensive Review of Vertical Forest Buildings: Integrating Structural, Energy, Forestry, and Occupant Comfort Aspects in Renovation Modeling

by Vachan Vanian, Theodora Fanaradelli and Theodoros Rousakis

Fibers 2025, 13(8), 101; https://doi.org/10.3390/fib13080101 - 25 Jul 2025

Cited by 4 | Viewed by 2332

Abstract

This current review examines modeling approaches for renovating reinforced concrete (RC) buildings for vertical forest (VF) application, taking into account structural retrofitting, energy systems, forestry integration, and occupant comfort. The study assesses research conducted with an advanced 3D finite element analysis and the [...] Read more.

This current review examines modeling approaches for renovating reinforced concrete (RC) buildings for vertical forest (VF) application, taking into account structural retrofitting, energy systems, forestry integration, and occupant comfort. The study assesses research conducted with an advanced 3D finite element analysis and the use of retrofitting modeling techniques, including textile-reinforced mortar (TRM), fiber-reinforced polymer (FRP), seismic joints, and green concrete applications. The energy system modeling methods are reviewed, taking into account the complexity of incorporating vegetation and seasonal variations. During forestry integration, three main design parameters are identified, namely, root systems, trunks, and crowns, for their critical role in the structural stability and optimal environmental performance. The comfort models are identified evolving from static to adaptive models incorporating thermal, acoustic, visual and air quality parameters. The current review consists of more than one hundred studies indicating that the integration of natural systems to buildings requires a multidimensional and multidisciplinary approach with sophisticated systems. The findings of this review provide the basis for implementing VF models to RC buildings, while highlighting areas requiring further research and validation. Full article

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

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21 pages, 6582 KB

Open AccessEditor’s ChoiceArticle

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

Cited by 5 | Viewed by 6219

Abstract

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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25 pages, 3711 KB

Open AccessEditor’s ChoiceArticle

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

Cited by 4 | Viewed by 7382

Abstract

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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64 pages, 6390 KB

Open AccessEditor’s ChoiceReview

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

Cited by 11 | Viewed by 6337

Abstract

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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18 pages, 5924 KB

Open AccessEditor’s ChoiceArticle

Thermal Performance of Bio-Based Materials for Sustainable Building Insulation: A Numerical Study

by Labouda Ba, Abdelkrim Trabelsi, Tien Tung Ngo, Prosper Pliya, Ikram El Abbassi and Cheikh Sidi Ethmane Kane

Fibers 2025, 13(5), 52; https://doi.org/10.3390/fib13050052 - 30 Apr 2025

Cited by 8 | Viewed by 5694

Abstract

This study investigates the thermal and energy performance of various bio-based materials, including Typha Australis, straw, banana fiber, Alfa fiber, peanut shells, and VSS (a blend of wood pulp, cotton, flax, and hemp), in comparison to conventional concrete. A combined approach integrating numerical [...] Read more.

This study investigates the thermal and energy performance of various bio-based materials, including Typha Australis, straw, banana fiber, Alfa fiber, peanut shells, and VSS (a blend of wood pulp, cotton, flax, and hemp), in comparison to conventional concrete. A combined approach integrating numerical simulations and experimental analyses was employed to ensure robust and comprehensive insights. COMSOL Multiphysics was utilized for detailed thermal modeling of wall assemblies, while TRNSYS enabled dynamic simulations to evaluate the impact of these materials on overall cooling energy demand. The results demonstrate that bio-based materials offer significantly improved thermal insulation, reducing air conditioning needs by over 30% relative to concrete, with banana fiber exhibiting the highest performance. This study underscores the need for industrial-scale optimization, supportive regulatory frameworks, and real-world implementation to promote broader adoption. Despite their strong potential, challenges remain, particularly regarding cost-effectiveness, durability, and market penetration. Ultimately, this research advocates for a transition toward more sustainable and environmentally conscious construction practices, aligning with efforts to reduce CO₂ emissions and enhance building energy efficiency. Full article

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15 pages, 6656 KB

Open AccessEditor’s ChoiceArticle

Preparation of ZIF-67@PAN Nanofibers for CO₂ Capture: Effects of Solvent and Time on Particle Morphology

by Guilherme Henrique Franca Melo, Tiffany Yau, Yuxin Liu and Uttandaraman Sundararaj

Fibers 2025, 13(5), 50; https://doi.org/10.3390/fib13050050 - 22 Apr 2025

Cited by 5 | Viewed by 3147

Abstract

Advanced materials including metal–organic frameworks (MOFs) are a critical piece of the puzzle in the search for solutions to various scientific and technological challenges, such as climate change due to the ever-increasing emissions of greenhouse gas. There is intense interest in MOFs due [...] Read more.

Advanced materials including metal–organic frameworks (MOFs) are a critical piece of the puzzle in the search for solutions to various scientific and technological challenges, such as climate change due to the ever-increasing emissions of greenhouse gas. There is intense interest in MOFs due to their potential use for a variety of environmental applications, including catalysis and gas storage. In this work, we specifically focus on the in situ growth of zeolitic imidazolate framework-67 (ZIF-67) on poly(acrylonitrile) (PAN) fibers and its potential application in CO₂ adsorption. Nanofibers were spun from a solution containing PAN and cobalt (II) nitrate hexahydrate using electrospinning. Then, the fibers were immersed in solution with 2-methylimidazole for different time durations. Via the diffusion of the cobalt ions through the fibers and interaction with the ligands in the solution, ZIF-67 was formed. From analysis via SEM, FTIR, PXRD, and CO₂ adsorption, it is evident that varying different parameters—the type of solvent, immersion time, and ligand concentration—affected the morphology of the formed ZIF-67. It was found that immersion for 4 h in 6.0 mg/mL of ligands in methanol created the ZIF-67@PAN best suited for CO₂ adsorption, showing a CO₂ uptake of 0.4 mmol/g at 1.2 bar and 273 K. Full article

(This article belongs to the Special Issue Electrospinning Nanofibers)

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23 pages, 10671 KB

Open AccessEditor’s ChoiceArticle

Multi-Scale Toughening of UHPC: Synergistic Effects of Carbon Microfibers and Nanotubes

by J. D. Ruiz Martínez, J. D. Ríos, H. Cifuentes and C. Leiva

Fibers 2025, 13(4), 49; https://doi.org/10.3390/fib13040049 - 21 Apr 2025

Cited by 6 | Viewed by 1737

Abstract

This study investigates multi-scale reinforcement of Ultra-High-Performance Concrete through targeted modifications of its mechanical and fracture-resistant properties via carbon microfibers and carbon nanotubes. The research employed comprehensive characterization techniques including workability tests, mercury porosimetry for microscale porosity analysis, and X-ray tomography for macro-scale [...] Read more.

This study investigates multi-scale reinforcement of Ultra-High-Performance Concrete through targeted modifications of its mechanical and fracture-resistant properties via carbon microfibers and carbon nanotubes. The research employed comprehensive characterization techniques including workability tests, mercury porosimetry for microscale porosity analysis, and X-ray tomography for macro-scale pore evaluation. Mechanical performance was assessed through compression strength, tensile strength, and fracture energy measurements. Results demonstrated significant performance enhancements testing UHPC samples with 6 mm carbon microfibers (9 kg/m³) and varying carbon nanotubes dosages (0.11–0.54 wt%). The addition of carbon microfibres improved compressive strength by 12%, while incorporating 0.54 wt% carbon nanotubes further increased strength by 24%. Remarkably, the combined reinforcement strategy yielded a 313% increase in tensile strength compared to the reference mixture. The synergistic effect of carbon fibers and carbon nanotubes proved particularly effective in enhancing concrete performance. This multi-scale reinforcement approach presents a promising alternative to traditional steel fiber reinforcement, offering superior mechanical properties and potential advantages in corrosive environments. Full article

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11 pages, 1951 KB

Open AccessEditor’s ChoiceArticle

Kinetic Analysis of Cement–Asbestos Materials’ Thermal Decomposition Process by an Ex Situ Technique

by Robert Kusiorowski, Anna Gerle and Magdalena Kujawa

Fibers 2025, 13(4), 43; https://doi.org/10.3390/fib13040043 - 10 Apr 2025

Cited by 1 | Viewed by 1097

Abstract

For many years, countries around the world have been struggling with the problem of storing asbestos waste, especially in, those countries where the production and use of asbestos products have been legally banned. Following the adoption of plans for cleaning up asbestos waste, [...] Read more.

For many years, countries around the world have been struggling with the problem of storing asbestos waste, especially in, those countries where the production and use of asbestos products have been legally banned. Following the adoption of plans for cleaning up asbestos waste, countries are struggling with the problem of its disposal, which mainly involves storing it in specialist landfills. At the same time, scientists are looking for alternatives to this type of “disposal” of asbestos by developing methods for degrading the harmful fibers. Particular attention has been paid to methods based on the thermal treatment of this waste, which results in hazardous asbestos fibers being thermally decomposed. This work focuses on the kinetic study of the thermal decomposition process of cement–asbestos using an exsitu thermal treatment. The results obtained made it possible to interpret this thermal transformation kinetically. Kinetic analysis of the isothermal data using an Avrami–Erofeev model yielded values for the overall reaction order. On this basis, the value of the apparent activation energy of the thermal decomposition process of the tested cement–asbestos samples was obtained, which was approximately 140–180 kJ mol⁻¹. Full article

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17 pages, 5419 KB

Open AccessEditor’s ChoiceArticle

Fiber/Free-Space Optics with Open Radio Access Networks Supplements the Coverage of Millimeter-Wave Beamforming for Future 5G and 6G Communication

by Cheng-Kai Yao, Hsin-Piao Lin, Chiun-Lang Cheng, Ming-An Chung, Yu-Shian Lin, Wen-Bo Wu, Chun-Wei Chiang and Peng-Chun Peng

Fibers 2025, 13(4), 39; https://doi.org/10.3390/fib13040039 - 2 Apr 2025

Cited by 6 | Viewed by 2579

Abstract

Conceptually, this paper aims to help reduce the communication blind spots originating from the design of millimeter-wave (mmW) beamforming by deploying radio units of an open radio access network (O-RAN) with free-space optics (FSOs) as the backhaul and the fiber-optic link as the [...] Read more.

Conceptually, this paper aims to help reduce the communication blind spots originating from the design of millimeter-wave (mmW) beamforming by deploying radio units of an open radio access network (O-RAN) with free-space optics (FSOs) as the backhaul and the fiber-optic link as the fronthaul. At frequencies exceeding 24 GHz, the transmission reach of 5G/6G beamforming is limited to a few hundred meters, and the periphery area of the sector operational range of beamforming introduces a communication blind spot. Using FSOs as the backhaul and a fiber-optic link as the fronthaul, O-RAN empowers the radio unit to extend over greater distances to supplement the communication range that mmW beamforming cannot adequately cover. Notably, O-RAN is a prime example of next-generation wireless networks renowned for their adaptability and open architecture to enhance the cost-effectiveness of this integration. A 200 meter-long FSO link for backhaul and a fiber-optic link of up to 10 km for fronthaul were erected, thereby enabling the reach of communication services from urban centers to suburban and remote rural areas. Furthermore, in the context of beamforming, reinforcement learning (RL) was employed to optimize the error vector magnitude (EVM) by dynamically adjusting the beamforming phase based on the communication user’s location. In summary, the integration of RL-based mmW beamforming with the proposed O-RAN communication setup is operational. It lends scalability and cost-effectiveness to current and future communication infrastructures in urban, peri-urban, and rural areas. Full article

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38 pages, 9959 KB

Open AccessEditor’s ChoiceArticle

Application of Carbon-Fiber-Reinforced Polymer Rods and Ultra-High-Performance Fiber-Reinforced Concrete Jackets with Mechanical Anchorage Systems to Reinforced Concrete Slabs

by Firas Hassan Saeed and Farzad Hejazi

Fibers 2025, 13(3), 33; https://doi.org/10.3390/fib13030033 - 13 Mar 2025

Cited by 1 | Viewed by 2424

Abstract

The aim of this experimental study was to develop and evaluate the effectiveness of a new strengthening system for reinforced concrete slabs employing external jackets consisting of ultra-high-performance fiber-reinforced-concrete (UHPFRC) and mechanical anchor systems. The issue of debonding between old and fresh concrete [...] Read more.

The aim of this experimental study was to develop and evaluate the effectiveness of a new strengthening system for reinforced concrete slabs employing external jackets consisting of ultra-high-performance fiber-reinforced-concrete (UHPFRC) and mechanical anchor systems. The issue of debonding between old and fresh concrete layers, as well as the efficiency of utilizing CFRP rods, is the primary challenge of applying the UHPFRC jackets with embedded CFRP rods. In this study, we propose a novel retrofitting technique for implementing a mechanical anchor system to improve the binding of fresh UHPFRC jackets with old RC slabs. An experimental test was conducted by subjecting three slabs to cyclic loads by utilizing a dynamic actuator: a reference slab, a retrofitted slab with an external UHPFRC layer, and a retrofitted slab with an external UHPFRC layer incorporating CFRP bars. Furthermore, finite element models (FEMs) were utilized to investigate the responses of the retrofitted slabs and compare the novel method with traditional strengthening techniques, including near-surface-mounted (NSM) CFRP rods, externally bonded CFRP strips, and epoxy-bonded UHPFRC jackets, as well as two models that were the same as the experimental strengthened slab specimens except for the fact that they did not have a mechanical anchor system. Additionally, analytical mechanistic models were employed to determine the flexural moment capacity of the RC slabs. The experimental findings demonstrated that the proposed strengthening strategy considerably prevented premature debonding and enhanced the maximum load of retrofitted RC slabs by over 82%. Also, the FEM and analytical results are significantly consistent with the experimental outcomes. In conclusion, the newly suggested strengthening technique is a reliable system for enhancing the efficacy of slabs, effectively preventing early debonding between existing and new components. Full article

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19 pages, 7052 KB

Open AccessEditor’s ChoiceArticle

Experimental Study on the Valorization of Rice Straw as Fiber for Concrete

by Hesam Doostkami, David Hernández-Figueirido, Vicente Albero, Ana Piquer, Pedro Serna and Marta Roig-Flores

Fibers 2025, 13(3), 28; https://doi.org/10.3390/fib13030028 - 5 Mar 2025

Cited by 2 | Viewed by 3704

Abstract

Rice straw is an agricultural waste that is difficult to manage and has traditionally been burned or buried, leading to environmental problems. Because of this, the introduction of rice straw into concrete has been proposed to revalue this residue. This investigation shows experimental [...] Read more.

Rice straw is an agricultural waste that is difficult to manage and has traditionally been burned or buried, leading to environmental problems. Because of this, the introduction of rice straw into concrete has been proposed to revalue this residue. This investigation shows experimental work carried out to prepare rice straw fibers and introduce them into a concrete mix as macrofibers. In addition, three fiber treatments were compared: two alkaline and one thermal. Four concrete mixes were studied: a reference mix, two concrete mixes with untreated rice straw fibers in two dosages, 10 kg/m³ and 15 kg/m³, and a fourth concrete mix with 10 kg/m³ of fiber treated with sodium hydroxide. The properties analyzed are workability, compression flexural strength, and shrinkage. The results show that the rice straw fiber used in this work improves concrete flexural strength at the peak but does not provide post-crack residual flexural strength. The sodium hydroxide treatment was effective in obtaining a more cohesive mix and lower setting time delay and slightly improved the performance of the rice straw fiber at the flexural strength peak. In summary, concrete can be used to encapsulate this agricultural waste material, providing enough strength for several engineering applications (>30 MPa). Full article

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43 pages, 27240 KB

Open AccessEditor’s ChoiceArticle

An Experimental Investigation on the Effect of Incorporating Natural Fibers on the Mechanical and Durability Properties of Concrete by Using Treated Hybrid Fiber-Reinforced Concrete Application

by Anteneh Geremew, Amelie Outtier, Pieter De Winne, Tamene Adugna Demissie and Hans De Backer

Fibers 2025, 13(3), 26; https://doi.org/10.3390/fib13030026 - 28 Feb 2025

Cited by 13 | Viewed by 6168

Abstract

This research explores the use of treated hybrid natural fibers—wheat straw and bamboo—as reinforcements in concrete for pavement applications. Motivated by environmental and economic benefits, the study investigates how these fibers can enhance the mechanical and durability properties of concrete. Wheat straw fibers, [...] Read more.

This research explores the use of treated hybrid natural fibers—wheat straw and bamboo—as reinforcements in concrete for pavement applications. Motivated by environmental and economic benefits, the study investigates how these fibers can enhance the mechanical and durability properties of concrete. Wheat straw fibers, abundant in Ethiopia due to extensive wheat farming, help control micro-cracks and increase the tensile strength of concrete, while bamboo fibers, also locally available, reduce macro-crack propagation and improve concrete toughness. To prepare these fibers, wheat straw was cut to 25 mm in length and bamboo fibers were treated with a 5% sodium hydroxide solution before being cut into lengths of 30, 45, and 60 mm. A concrete mix targeting a cube compressive strength of 30 MPa incorporated 0.1% wheat straw fibers, with varying bamboo fiber contents (0.5%, 1%, and 1.5%) by weight of cement. The results indicate that the uniquely treated hybrid natural fiber-reinforced concrete mix exhibits noticeable enhancements in mechanical properties, with approximate increases of 4.16%, 8.80%, and 8.93% at 7, 28, and 56 days, respectively. Furthermore, the split tensile strength, flexural strength, and durability properties of the concrete were significantly improved by the proposed fiber concentration and length compared to the control concrete mix design. This treatment also shifted the failure mode of the concrete from brittle to ductile and enhanced its energy absorption capacity up to 7.88% higher than that of the control concrete. Based on the AASHTO 1993 pavement design guidelines, this fiber-reinforced concrete reduces pavement thickness by 11% compared to the control concrete while improving post-cracking behavior. This hybrid natural fiber-reinforced concrete presents a promising, sustainable, and eco-friendly alternative for rigid pavement construction. Full article

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16 pages, 5390 KB

Open AccessEditor’s ChoiceArticle

Flammability of Plant-Based Loose-Fill Thermal Insulation: Insights from Wheat Straw, Corn Stalk, and Water Reed

by Martins Andzs, Ramunas Tupciauskas, Andris Berzins, Gunars Pavlovics, Janis Rizikovs, Ulla Milbreta and Laura Andze

Fibers 2025, 13(3), 24; https://doi.org/10.3390/fib13030024 - 24 Feb 2025

Cited by 4 | Viewed by 2576

Abstract

This study investigates the fire resistance capabilities of newly developed loose-fill thermal insulation materials crafted from annual plants such as wheat straw, corn stalk, and water reed. Three processing methodologies were employed: mechanical crushing (raw, size ≤ 20 mm), chemi-mechanical pulping (CMP) using [...] Read more.

This study investigates the fire resistance capabilities of newly developed loose-fill thermal insulation materials crafted from annual plants such as wheat straw, corn stalk, and water reed. Three processing methodologies were employed: mechanical crushing (raw, size ≤ 20 mm), chemi-mechanical pulping (CMP) using 4% sodium hydroxide, and steam explosion (SE). An admixture of boric acid (8%) and tetraborate (7%) was added to all treated materials to enhance fire retardancy. The fire reaction characteristics of the insulation materials were assessed using a cone calorimeter measuring the key parameters like time to ignition, total heat release, heat release rate, and total smoke production. The findings indicate that nearly all tested insulation samples, apart from the raw and SE water reed, demonstrated fire resistance comparable to commercial cellulose insulation, surpassing the fire performance of various synthetic foams and composite materials. Furthermore, the single-flame source fire tests indicated that the developed insulation materials achieved a fire classification E, except for the SE water reed sample. Thus, the fire performance results approve the suitability of developed plant-based insulation materials for competing materials in building constructions. Full article

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31 pages, 6533 KB

Open AccessEditor’s ChoiceArticle

Enhancing Interfacial Adhesion in Kevlar and Ultra-High Molecular Weight Polyethylene Fiber-Reinforced Laminates: A Comparative Study of Surface Roughening, Plasma Treatment, and Chemical Functionalization Using Graphene Nanoparticles

by Feyi Adekunle, Jan Genzer and Abdel-Fattah M. Seyam

Fibers 2025, 13(2), 19; https://doi.org/10.3390/fib13020019 - 11 Feb 2025

Cited by 7 | Viewed by 3731

Abstract

This study investigates the impact of mechanical and chemical surface treatments on the interfacial adhesion and mechanical properties of Kevlar and ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced laminates (FRLs). Various treatments, including surface roughening, plasma exposure, NaOH and silane coupling, and graphene nanoparticle [...] Read more.

This study investigates the impact of mechanical and chemical surface treatments on the interfacial adhesion and mechanical properties of Kevlar and ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced laminates (FRLs). Various treatments, including surface roughening, plasma exposure, NaOH and silane coupling, and graphene nanoparticle (NP) incorporation, were conducted to enhance the fiber–matrix bonding within thermoplastic polyurethane (TPU) and ethylene-vinyl acetate (EVA) matrices. Results demonstrated that treatment efficacy highly depends on fiber type and matrix material, with chemical modifications generally outperforming the physical treatment (surface roughness). Plasma treatment significantly enhanced adhesion for UHMWPE, increasing yarn pullout force by 188.1% with TPU. While combining plasma with graphene slightly improved performance, it did not exceed plasma-only results due to potential surface functionalization losses during wet graphene application. For Kevlar, the combination of NaOH, silane, and graphene NP (NSG) treatment yielded the highest adhesion, showing increases of 76.6% with TPU and 95.4% with EVA, underscoring the synergy between chemical coupling and nanomaterial reinforcement. This study’s insights align with previous research, expanding the knowledge base by investigating graphene’s role independently and alongside established methods. Full article

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24 pages, 30156 KB

Open AccessEditor’s ChoiceArticle

Chopped Basalt Fibers Reinforced Mortar for Strengthening the Architectural Heritage

by Micaela Mercuri, Marco Vailati and Amedeo Gregori

Fibers 2025, 13(2), 20; https://doi.org/10.3390/fib13020020 - 11 Feb 2025

Cited by 3 | Viewed by 3323

Abstract

The high seismic vulnerability of unreinforced masonry buildings urgently calls for researchers to develop sustainable reinforcing methods and materials. This paper presents an innovative lime-based mortar reinforced with randomly oriented basalt fibers for the reinforcement of masonry heritage. The main aim of this [...] Read more.

The high seismic vulnerability of unreinforced masonry buildings urgently calls for researchers to develop sustainable reinforcing methods and materials. This paper presents an innovative lime-based mortar reinforced with randomly oriented basalt fibers for the reinforcement of masonry heritage. The main aim of this study is to understand the effect of the content and the length of basalt fibers on the mortar’s mechanical behavior. As a cementitious material made mostly out of lime, the mortar is chemically compatible with the historical substrate and therefore suitable in cases of restoration works on architectural heritage. Moreover, the chopped basalt fibers are randomly oriented, and this characteristic makes the overall layer effective in all directions, as the state of stress induced by seismic action is directionally undetermined. The newly proposed reinforcement system is characterized by a twofold aspect related to sustainability: 30% of the aggregates composing the mortar mix design is a recycled result of the ruins of the 2009 L’Aquila earthquake, and the chopped fibers are made out of basalt, widely known for its environmentally supportable peculiarity. The study consists of testing samples characterized by two fiber lengths and six fiber contents, along with one set of plain mortar samples. Specimens measuring 160 mm × 40 mm × 40 mm are first tested in a three-point bending (TPB) configuration, aiming to determine the flexural strength and the post-peak capacity through the calculation of the fracture energy. Then, the two broken pieces resulting from the TPB tests, each measuring 80 mm × 40 mm × 40 mm, are tested in splitting and compression, respectively, aiming to compute the tensile and compressive strengths. Finally, to provide a trend for the mortar’s mechanical properties, a regression analysis is performed by fitting the experimental data with simple linear, polynomial, and exponential regression models. Results show that: (i) both fiber content and fiber length are responsible for a linear increase of the flexural strength and the fracture energy; (ii) for both short- and long-fiber mortar samples, the tensile strength and the compressive strength parabolically increase with the fiber content; (iii) the increase in fiber content and fiber length always generates a reduction in the conglomerate workability. The fiber content (FC) optimization with respect to the mechanical properties leads to a basalt FC equal to 1.2% for long-fiber samples and an FC equal to 1.9% for short-fiber ones. Full article

(This article belongs to the Special Issue Development of Eco-Friendly Concrete-, Mortar- and Fiber-Reinforced Composite Systems for Building Applications: Experimental and Theoretical Studies)

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28 pages, 5006 KB

Open AccessEditor’s ChoiceArticle

Insights on Lattice Discrete Particle Model Calibration and Validation Procedure to Simulate Polypropylene and Steel Fibre-Reinforced Concrete

by Sushant Poudel, Antonio Cibelli, Clementina Del Prete, Roman Wan-Wendner, Claudio Mazzotti and Nicola Buratti

Fibers 2025, 13(2), 16; https://doi.org/10.3390/fib13020016 - 5 Feb 2025

Cited by 2 | Viewed by 2638

Abstract

The use of fibre-reinforced concrete (FRC) has been substantially increasing in the last few years, in different fields of the construction industry. Recently, many experiments have been performed to observe the short- and long-term mechanical behaviour of FRC, and several models have been [...] Read more.

The use of fibre-reinforced concrete (FRC) has been substantially increasing in the last few years, in different fields of the construction industry. Recently, many experiments have been performed to observe the short- and long-term mechanical behaviour of FRC, and several models have been formulated to capture its mechanical response. In this work, the mechanical behaviour is simulated through the Lattice Discrete Particle Model (LDPM) and its extension to fibre-reinforced cementitious composites (LDPM-F). This paper aims to provide insights into the calibration process and potential pitfalls in a case where only limited experimental data are available—in this case, unconfined uniaxial compression and three-point bending tests on different mixes of polypropylene and steel fibre-reinforced concretes. As a first step, a sensitivity analysis is performed to weight the effect of each governing mesoscale parameter on the simulated macroscale behaviour. Then, for each mix at issue, different sets of model parameters are identified as capable of accurately matching the experimental evidence. As a validation, each calibrated set is used to simulate energy absorption tests on round panels. The validation stage shows that one of the identified sets, for the FRC with polypropylene fibres, accurately matches the round panels’ response, while the others result in acceptable predictions. For the mix with steel fibres, instead, none of the sets captures the experimental results, likely due to the different post-cracking behaviour detected in fracture and energy absorption tests. Finally, a parametric study showcases how the LDPM-F might serve as tool to optimise the mix design without extensive experimental investigations. Full article

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4 pages, 139 KB

Open AccessEditor’s ChoiceEditorial

Perspectives on Natural Fibers’ Competitiveness and Sustainability

by Mourad Krifa and Vinoth Kumar Gnanasekar

Fibers 2025, 13(2), 14; https://doi.org/10.3390/fib13020014 - 2 Feb 2025

Cited by 4 | Viewed by 2755

Abstract

Since antiquity, natural fibers have been a vital component of human civilization [...] Full article

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

19 pages, 13847 KB

Open AccessEditor’s ChoiceArticle

Effect of GFRP and CFPR Hybrid Confinement on the Compressive Performance of Concrete

by Marina L. Moretti

Fibers 2025, 13(2), 12; https://doi.org/10.3390/fib13020012 - 24 Jan 2025

Cited by 1 | Viewed by 1580

Abstract

Application of hybrid jackets consisting of comparatively stiff FRP materials for the seismic retrofit of substandard RC columns, aiming at reducing the risk of buckling and of brittle failure, which are typical to older columns, is a promising challenge. Given the sparsity of [...] Read more.

Application of hybrid jackets consisting of comparatively stiff FRP materials for the seismic retrofit of substandard RC columns, aiming at reducing the risk of buckling and of brittle failure, which are typical to older columns, is a promising challenge. Given the sparsity of similar experimental data, the objective of this paper is to study the hybrid effect in concrete confined with conventional carbon- and glass- reinforced polymer fabrics (CFRP and GFRP, respectively). Twenty-six concrete cylinders, wrapped by one to three layers of CFRP and GFRP with different fiber configurations, were tested in compression. A clear hybrid effect was observed, consisting of a less brittle failure and an improved confinement as compared to the behavior of simple jackets. Furthermore, hybrid specimens, in which a CFRP layer is substituted by a GFRP layer, appear to display similar efficiency in confinement compared to specimens with a stiffer jacket consisting of more CFRP sheets, which are expected to experience 30 to 40% higher lateral pressure owing to the stiffer jacket. A design model to estimate peak concrete compressive strength and axial strain is proposed. The results are promising towards the potential application of similar hybrid jackets for the seismic rehabilitation of older RC columns. Full article

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

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31 pages, 4126 KB

Open AccessEditor’s ChoiceArticle

Optimizing Controlled-Resonance Acoustic Metamaterials with Perforated Plexiglass Disks, Honeycomb Structures, and Embedded Metallic Masses

by Giuseppe Ciaburro, Gino Iannace and Virginia Puyana Romero

Fibers 2025, 13(2), 11; https://doi.org/10.3390/fib13020011 - 22 Jan 2025

Cited by 7 | Viewed by 3221

Abstract

Acoustic metamaterials offer new opportunities for controlling sound waves through engineered material configurations at the sub-wavelength scale. In this research, we present the optimization of a resonance-controlled acoustic metamaterial based on a sandwich structure composed of perforated plexiglass disks, honeycomb structures, and added [...] Read more.

Acoustic metamaterials offer new opportunities for controlling sound waves through engineered material configurations at the sub-wavelength scale. In this research, we present the optimization of a resonance-controlled acoustic metamaterial based on a sandwich structure composed of perforated plexiglass disks, honeycomb structures, and added metal masses. The innovative approach consists of integrating perforated plexiglass disks interspersed with honeycomb structures, which act as multiple and complex Helmholtz resonators, and adding metal masses to introduce resonances at specific frequencies. The metamaterial’s acoustic properties were experimentally characterized using an impedance tube (Kundt tube), allowing the measurement of the Sound Absorption Coefficient (SAC) over an expansive frequency selection. The results demonstrate a substantial enhancement in sound absorption at the target frequencies, demonstrating the effectiveness of the introduced resonances. Numerical simulations using an Artificial Neural Network (ANN) model in MATLAB environment were used to analyze the distribution of resonances and optimize the structural configuration. To effectively evaluate the acoustic properties of the metamaterial, various configurations were analyzed using perforated plexiglass disks combined with different layers of honeycombs arranged in a sandwich structure with a thickness ranging from 41 to 45 mm. A comparison of these configurations revealed a notable increase in the Sound Absorption Coefficient (SAC) when employing three layers of perforated plexiglass disks and adding masses to the first disk (about 14%). This study highlights the potential of resonance-controlled metamaterials for advanced applications in noise control and acoustic engineering. Full article

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26 pages, 10277 KB

Open AccessEditor’s ChoiceArticle

Rehabilitation and Strengthening of Damaged Reinforced Concrete Beams Using Carbon Fiber-Reinforced Polymer Laminates and High-Strength Concrete Integrating Recycled Tire Steel Fiber

by Hasan A. Alasmari, Ibrahim A. Sharaky, Ahmed S. Elamary and Ayman El-Zohairy

Fibers 2025, 13(1), 10; https://doi.org/10.3390/fib13010010 - 15 Jan 2025

Cited by 3 | Viewed by 2895

Abstract

Currently, millions of tires are consumed annually, which necessitates the efficient disposal of these quantities of spent tires and the development of means to convert them into useful materials. This research deals with the effect of adding the steel fibers extracted from used [...] Read more.

Currently, millions of tires are consumed annually, which necessitates the efficient disposal of these quantities of spent tires and the development of means to convert them into useful materials. This research deals with the effect of adding the steel fibers extracted from used car tires (RSFs) to incorporate them as concrete components to obtain high-strength concrete (HSC). The HSC was used in this paper to strengthen the pre-damaged beams by jacking. In the first phase, twelve beams were subjected to an overload equal to 80% of their total expected bearing capacity to obtain damaged RC beams, while one beam was loaded to failure (reference beam, RB0). In the second phase, the damaged beams were strengthened with HSC jacketing integrating RSFs with three contents (0, 0.25, and 0.5%) or by HSC jacking and bonded CFRP laminates to the bottom surface of the jacket. Moreover, the Abaqus finite element (FE) program was implemented to simulate the upgraded damaged beams. The result ensured enhanced HSC compressive and tensile strengths by 11.6–14.4% and 11.6–20.9% as the RSF % increased from 0 to 0.25 and 0.5%, respectively. Using the HSC jacket with 0, 0.25, and 0.5% RSF to strengthen the RC-damaged beams increased the load capacity by 8.8, 14.5, and 20.1%, respectively compared to RB0. Furthermore, strengthening the damaged RC beams with both HSC jacket and CFRP laminates enhanced their load capacity by 41.9, 45.5, and 50.3% as the HSC integrated 0, 0.25, and 0.5% RSF, respectively, compared to RB0. Finally, the FE model could reveal several aspects related to the behavior of the damaged beams strengthened with jackets and CFRP laminates and the interaction between the different beam components. Full article

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20 pages, 5498 KB

Open AccessEditor’s ChoiceReview

Potential Use of Silk Waste in Sustainable Thermoplastic Composite Material Applications: A Review

by Tommaso Pini, Matteo Sambucci and Marco Valente

Fibers 2025, 13(1), 6; https://doi.org/10.3390/fib13010006 - 13 Jan 2025

Cited by 6 | Viewed by 2910

Abstract

Global warming and climate change demand rapid and swift action in terms of reducing resource consumption, gas emissions, and waste generation. The textile industry is responsible for a large share of global pollution; therefore, to define a route to tackle part of the [...] Read more.

Global warming and climate change demand rapid and swift action in terms of reducing resource consumption, gas emissions, and waste generation. The textile industry is responsible for a large share of global pollution; therefore, to define a route to tackle part of the issue, a literature review on the current state of research in the field of recycling silk waste was conducted. The methods used to recover, process, and characterize silk waste fibers were summarized. The aim of this work was to investigate the possible applications of recycled silk waste in the field of composite materials for load bearing applications. In this sense, some prominent studies in the field of silk-based composites were reported, favoring thermoplastic materials for sustainability reasons. Studies on nonwoven silk waste fabrics were covered as well, finding an abundance of results but no applications as a reinforcement for composite materials. In a circular economy approach, we believe that the combination of nonwoven silk waste fabrics, thermoplastic polymers, and possibly hybridization with other fibers from sustainable sources could be beneficial and could lead to green and high-performance products. The aim of this work was to summarize the information available so far and help define a route in that direction. Full article

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24 pages, 13018 KB

Open AccessEditor’s ChoiceArticle

Amplifying the Sensitivity of Electrospun Polyvinylidene Fluoride Piezoelectric Sensors Through Electrical Polarization Process for Low-Frequency Applications

by Asra Tariq, Amir H. Behravesh, Muhammad Tariq and Ghaus Rizvi

Fibers 2025, 13(1), 5; https://doi.org/10.3390/fib13010005 - 9 Jan 2025

Cited by 3 | Viewed by 1919

Abstract

Piezoelectric sensors convert mechanical stress into electrical charge via the piezoelectric effect, and when fabricated as fibers, they offer flexibility, lightweight properties, and adaptability to complex shapes for self-powered wearable sensors. Polyvinylidene fluoride (PVDF) nanofibers have garnered significant interest due to their potential [...] Read more.

Piezoelectric sensors convert mechanical stress into electrical charge via the piezoelectric effect, and when fabricated as fibers, they offer flexibility, lightweight properties, and adaptability to complex shapes for self-powered wearable sensors. Polyvinylidene fluoride (PVDF) nanofibers have garnered significant interest due to their potential applications in various fields, including sensors, actuators, and energy-harvesting devices. Achieving optimal piezoelectric properties in PVDF nanofibers requires the careful optimization of polarization. Applying a high electric field to PVDF chains can cause significant mechanical deformation due to electrostriction, leading to crack formation and fragmentation, particularly at the chain ends. Therefore, it is essential to explore methods for polarizing PVDF at the lowest possible voltage to prevent structural damage. In this study, a Design of Experiments (DoE) approach was employed to systematically optimize the polarization parameters using a definitive screening design. The main effects of the input parameters on piezoelectric properties were identified. Heat treatment and the electric field were significant factors affecting the sensor’s sensitivity and β-phase fraction. At the highest temperature of 120 °C and the maximum applied electric field of 3.5 kV/cm, the % β-phase (F(β)) exceeded 95%. However, when reducing the electric field to 1.5 kV/cm and 120 °C, the % F(β) ranged between 87.5% and 90%. The dielectric constant (ɛ′) of polarized PVDF was determined to be 30 at an electric field frequency of 1 Hz, compared to a value of 25 for non-polarized PVDF. The piezoelectric voltage coefficient (g₃₃) for polarized PVDF was measured at 32 mV·m/N at 1 Hz, whereas non-polarized PVDF exhibited a value of 3.4 mV·m/N. The findings indicate that, in addition to a high density of β-phase dipoles, the polarization of these dipoles significantly enhances the sensitivity of the PVDF nanofiber mat. Full article

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17 pages, 6537 KB

Open AccessEditor’s ChoiceArticle

Development of Acoustic Insulating Carpets from Milkweed Fibers Using Air-Laid Spike Process

by Deborah Lupescu, Mathieu Robert and Said Elkoun

Fibers 2025, 13(1), 4; https://doi.org/10.3390/fib13010004 - 7 Jan 2025

Cited by 2 | Viewed by 1899

Abstract

Fibers from milkweed, which grows in Quebec (Canada), offer a distinct and outstanding advantage compared to other natural fibers: their ultra-lightweight hollow structure provides excellent acoustic and thermal insulation properties for the automobile industry. To highlight the properties of milkweed fibers and reduce [...] Read more.

Fibers from milkweed, which grows in Quebec (Canada), offer a distinct and outstanding advantage compared to other natural fibers: their ultra-lightweight hollow structure provides excellent acoustic and thermal insulation properties for the automobile industry. To highlight the properties of milkweed fibers and reduce the use of synthetic materials in vehicles, nonwoven carpeting made from a blend of milkweed fibers and polylactic acid (PLA) fibers was produced using the air-laid process. Some of the nonwovens were compressed to investigate the effects of increased mass per unit area on their thermal, acoustic, and mechanical properties. The nonwovens’ mass per unit area, thermal insulation, sound absorption coefficient, airflow resistivity, compression, and resistance to moisture were evaluated and compared to other carpets made of natural and synthetic fibers. The findings indicate that milkweed and PLA carpets have lower thermal conductivity values of 37.45 (mW/m·K), (mW/m·K) less than carpets made from cotton and polypropylene. At low frequencies, none of the carpets absorbed sound. At high frequencies, milkweed and PLA carpets showed sound absorption values of at least 0.6, which provide better acoustic insulation than nonwoven materials made from jute and polyethylene (PE) fibers. Milkweed and PLA carpets exhibited better compression values than polypropylene (PP) carpets. Full article

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21 pages, 3266 KB

Open AccessEditor’s ChoiceReview

Recovery of N-Methylmorpholine N-Oxide (NMMO) in Lyocell Fibre Manufacturing Process

by Maria Sawiak, Bernardo A. Souto, Lelia Lawson, Joy Lo and Patricia I. Dolez

Fibers 2025, 13(1), 3; https://doi.org/10.3390/fib13010003 - 6 Jan 2025

Cited by 6 | Viewed by 8887

Abstract

The lyocell process offers an environmentally friendly strategy to produce regenerated cellulose fibre from biomass. However, it is critical to recover and reuse the N-methyl-morpholine-N-oxide (NMMO) solvent to maximize the environmental benefits and lower the cost. This article reviews NMMO [...] Read more.

The lyocell process offers an environmentally friendly strategy to produce regenerated cellulose fibre from biomass. However, it is critical to recover and reuse the N-methyl-morpholine-N-oxide (NMMO) solvent to maximize the environmental benefits and lower the cost. This article reviews NMMO recovery and characterization techniques at the lab and industrial scales, and methods to limit the NMMO degradation during the process. The article also presents the results of a pilot study investigating the recovery of NMMO from lyocell manmade cellulosic fibre (L-MMCF) manufacturing wastewater. The work described includes the development of a calibration curve for the determination of NMMO content in aqueous solutions using Fourier Transform Infrared Spectroscopy (FTIR). Successful NMMO recovery from the wastewater was achieved using a rotary evaporator: the final NMMO concentration was 50, i.e., ready for use in the lyocell process, and no NMMO degradation was observed. The knowledge in this paper will support advances in L-MMCF manufacturing and the reduction in textile environmental footprint. Full article

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20 pages, 5177 KB

Open AccessEditor’s ChoiceArticle

The Influence of In Vitro Degradation on the Properties of Polylactic Acid Electrospun Fiber Mats

by Kardo Khalid Abdullah and Kolos Molnár

Fibers 2025, 13(1), 1; https://doi.org/10.3390/fib13010001 - 28 Dec 2024

Cited by 5 | Viewed by 2491

Abstract

The scope of our study was to investigate the changes in electrospun polylactic acid (PLA) fiber mats’ morphological, mechanical, and thermal properties in vitro. We electrospun two sets of PLA fiber mats with different average diameters, E6 (747 nm) and E10 (1263 nm). [...] Read more.

The scope of our study was to investigate the changes in electrospun polylactic acid (PLA) fiber mats’ morphological, mechanical, and thermal properties in vitro. We electrospun two sets of PLA fiber mats with different average diameters, E6 (747 nm) and E10 (1263 nm). The degradation study of PLA electrospun fibers was carried out in phosphate-buffered saline solution at 37 °C to simulate conditions within the human system. The results reveal the thicker fibers (E10) degraded more rapidly than the E6 sample due to their different morphology. E10 showed a 29% reduction in diameter and a 41% weight loss, while E6 exhibited an 18% reduction in diameter and a 27.5% weight loss. E6’s Young’s modulus increased by 3.55 times, while E10’s rose by 2.23 times after 28 days of degradation, and the fibers became more rigid. E6 showed a more pronounced decrease in crystallinity compared with E10. Changes in electrospun fiber diameters and crystallinity greatly influence the degradation mechanism of PLA. Full article

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14 pages, 4358 KB

Open AccessEditor’s ChoiceArticle

Challenges and Opportunities in Recycling Upholstery Textiles: Enhancing High-Density Fiberboards with Recycled Fibers

by Matylda Wojciechowska and Grzegorz Kowaluk

Fibers 2024, 12(12), 105; https://doi.org/10.3390/fib12120105 - 5 Dec 2024

Cited by 3 | Viewed by 2598

Abstract

Recycling upholstery textiles is challenging due to the complexity of materials, which often include a mix of fabrics, foams, and adhesives that are difficult to separate. The intricate designs and layers in upholstered furniture make it labor-intensive and costly to dismantle for recycling. [...] Read more.

Recycling upholstery textiles is challenging due to the complexity of materials, which often include a mix of fabrics, foams, and adhesives that are difficult to separate. The intricate designs and layers in upholstered furniture make it labor-intensive and costly to dismantle for recycling. Additionally, contaminants like stains, finishes, and flame retardants complicate recycling. Despite these difficulties, recycling upholstery textiles is crucial to reducing landfill waste and conserving resources by reusing valuable materials. It also helps mitigate environmental pollution and carbon emissions associated with producing new textiles from virgin resources. The presented research aimed to establish the feasibility of incorporating textile fibers from waste artificial leather fibers from the upholstery furniture industry into the structure of high-density fiberboards. The bulk density of samples with wood fiber was 28.30 kg m⁻³, while it was 25.77 kg m⁻³ for textile fiber samples. The lowest modulus of elasticity (MOE) was 2430 N mm⁻², and it was 3123 N mm⁻² for the reference sample. The highest bending strength (MOR) was 42 N mm⁻², and the lowest was 27.2 N mm⁻². Screw withdrawal resistance decreased from 162 N mm⁻¹ in the reference sample to 92 N mm⁻¹ with 25% artificial leather fibers. The internal bond (IB) strength ranged from 1.70 N mm⁻² (reference) to 0.70 N mm⁻² (25% of artificial leather fibers content). Water absorption ranged from 81.8% (1% of artificial leather fibers) to 66% (25% of artificial leather fibers content). It has been concluded that it is possible to meet the European standard requirements with 10% addition of the artificial leather fiber content. This approach positively contributes to carbon capture and storage (CCS) policy and mitigates the problem of such waste being sent to landfills. The research shows that while selected mechanical and physical parameters of the panels decrease with a rising content of recycled textile fibers, it is possible to meet proper European standard requirements by adjusting technological parameters such as nominal density. Full article

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28 pages, 10795 KB

Open AccessEditor’s ChoiceArticle

Advanced Structural Technologies Implementation in Designing and Constructing RC Elements with C-FRP Bars, Protected Through SHM Assessment

by Georgia M. Angeli, Maria C. Naoum, Nikos A. Papadopoulos, Parthena-Maria K. Kosmidou, George M. Sapidis, Chris G. Karayannis and Constantin E. Chalioris

Fibers 2024, 12(12), 108; https://doi.org/10.3390/fib12120108 - 5 Dec 2024

Cited by 4 | Viewed by 1688

Abstract

The need to strengthen the existing reinforced concrete (RC) elements is becoming increasingly crucial for modern cities as they strive to develop resilient and sustainable structures and infrastructures. In recent years, various solutions have been proposed to limit the undesirable effects of corrosion [...] Read more.

The need to strengthen the existing reinforced concrete (RC) elements is becoming increasingly crucial for modern cities as they strive to develop resilient and sustainable structures and infrastructures. In recent years, various solutions have been proposed to limit the undesirable effects of corrosion in RC elements. While C-FRP has shown promise in corrosion-prone environments, its use in structural applications is limited by cost, bonding, and anchorage challenges with concrete. To address these, the present research investigates the structural performance of RC beams reinforced with C-FRP bars under static loading using Structural Health Monitoring (SHM) with an Electro-Mechanical Impedance (EMI) system employing Lead Zirconate Titanate (PZT) piezoelectric transducers which are applied to detect damage development and enhance the protection of RC elements and overall, RC structures. This study underscores the potential of C-FRP bars for durable tensile reinforcement in RC structures, particularly in hybrid designs that leverage steel for compression strength. The study focuses on critical factors such as stiffness, maximum load capacity, deflection at each loading stage, and the development of crack widths, all analyzed through voltage responses recorded by the PZT sensors. Particular emphasis is placed on the bond conditions and anchorage lengths of the tensile C-FRP bars, exploring how local confinement conditions along the anchorage length influence the overall behavior of the beams. Full article

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23 pages, 4772 KB

Open AccessEditor’s ChoiceReview

Comprehensive Bibliometric Review on the Sustainability and Environmental Impact of Fiber-Reinforced Polymers

by Maria Tănase, Alin Diniță, Daniela Roxana Popovici, Alexandra Ileana Portoacă, Cătălina Călin and Elena-Emilia Sirbu

Fibers 2024, 12(12), 104; https://doi.org/10.3390/fib12120104 - 3 Dec 2024

Cited by 4 | Viewed by 2708

Abstract

Fiber-reinforced polymers (FRPs) are increasingly recognized in sustainable materials research due to their potential environmental advantages. This study presents a focused bibliometric review of the sustainability research on FRPs. An initial search of the Web of Science (WOS) database identified 803 documents, which [...] Read more.

Fiber-reinforced polymers (FRPs) are increasingly recognized in sustainable materials research due to their potential environmental advantages. This study presents a focused bibliometric review of the sustainability research on FRPs. An initial search of the Web of Science (WOS) database identified 803 documents, which were refined to 749 relevant articles, reviews, and proceedings. A co-authorship analysis highlights the significant contributions of the USA and India, with European countries forming regional collaborations. The research output has steadily increased since 2011, peaking in 2022 and 2023. The multidisciplinary nature of the research spans materials science, engineering, and environmental sciences, with journals such as *Polymers*, *Sustainability*, and the *Journal of Cleaner Production* emphasizing sustainability themes. This analysis covers key aspects such as keyword co-occurrence, overlay visualizations, co-authorship networks, and the distribution of publications by year, research area, and journal. The findings underscore the evolving research landscape of sustainable FRPs and highlight the ongoing need for life cycle assessments and interdisciplinary collaboration. Full article

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16 pages, 306 KB

Open AccessEditor’s ChoiceReview

The Use of Asbestos and Its Consequences: An Assessment of Environmental Impacts and Public Health Risks

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

Fibers 2024, 12(12), 102; https://doi.org/10.3390/fib12120102 - 25 Nov 2024

Cited by 14 | Viewed by 7534

Abstract

The use of asbestos, once celebrated for its versatility and fire-resistant properties, has left a lasting legacy of environmental degradation and public health risks. This paper provides a comprehensive assessment of the environmental impacts and health risks associated with asbestos, highlighting its widespread [...] Read more.

The use of asbestos, once celebrated for its versatility and fire-resistant properties, has left a lasting legacy of environmental degradation and public health risks. This paper provides a comprehensive assessment of the environmental impacts and health risks associated with asbestos, highlighting its widespread use, environmental persistence, and adverse effects on human health. Through a literature review, this study examines the historical context of asbestos use, its adverse environmental effects and the mechanisms by which exposure to asbestos poses significant health risks, including the development of asbestos-related diseases such as mesothelioma, lung cancer, asbestosis, etc. It also assesses the current regulatory framework and provides a methodological analysis of the strategy for recycling end-of-life materials containing asbestos fibers, proposing the inclusion of asbestos-containing materials (ACMs) in the rock wool industry to reduce Greenhouse Gasses (GHG) emissions. Drawing on interdisciplinary insights from environmental science, public health, and regulatory analysis, this paper concludes with recommendations for improving asbestos management strategies, promoting safer alternatives and mitigating the long-term environmental and human health impacts of asbestos. Full article

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

24 pages, 8849 KB

Open AccessEditor’s ChoiceReview

Non-Circular Cross-Section Fibres for Composite Reinforcement—A Review with a Focus on Flat Glass Fibres

by James Thomason, Andrew Carlin and Liu Yang

Fibers 2024, 12(11), 98; https://doi.org/10.3390/fib12110098 - 11 Nov 2024

Cited by 3 | Viewed by 4053

Abstract

Glass fibre reinforcements form the backbone of the composites industry. Today, glass fibre products account for more than 95% of the fibre reinforcements used in the composites industry. Since the first commercialisation of glass fibres for composite reinforcement in the 1930s, the cross-sectional [...] Read more.

Glass fibre reinforcements form the backbone of the composites industry. Today, glass fibre products account for more than 95% of the fibre reinforcements used in the composites industry. Since the first commercialisation of glass fibres for composite reinforcement in the 1930s, the cross-sectional shape of glass fibres has remained exclusively circular. However, many of the other types of fibre reinforcement have a non-circular cross section (NCCS). This paper reviews the available knowledge on the production of NCCS glass fibres and some of the possibilities that such fibres offer to enhance the performance of glass reinforced polymer composites. The three parts of the review focus on early research work on different shapes of glass fibre, the developments leading to industrial-level production of NCCS glass fibres, and the more recent data available on the influence of the available commercially produced NCCS flat glass fibres on composite performance. It Is concluded that the continued development of NCCS glass fibres may offer interesting potential to generate composites with increased performance and may also enable further tailoring of composite performance to enable new applications to be developed. Full article

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20 pages, 7109 KB

Open AccessEditor’s ChoiceArticle

Coating of Hemp Fibres with Hydrophobic Compounds Extracted from Pine Bark

by Robert Abbel, Regis Risani, Maxime Nourtier, Lloyd Donaldson, Christel Brunschwig, Claire Mayer-Laigle, James H. Bridson, Armin Thumm, Alan Dickson, Rachel Murray, Jessica Harris, Johnny Beaugrand and Stefan Hill

Fibers 2024, 12(11), 96; https://doi.org/10.3390/fib12110096 - 7 Nov 2024

Cited by 4 | Viewed by 3581

Abstract

Applying coatings of paraffins and other synthetic waxes is a common approach to impart hydrophobic properties to fibres and thus control their surface characteristics. Replacing these fossil-based products with alternatives derived from renewable resources can contribute to humankind’s transition to a sustainable bioeconomy. [...] Read more.

Applying coatings of paraffins and other synthetic waxes is a common approach to impart hydrophobic properties to fibres and thus control their surface characteristics. Replacing these fossil-based products with alternatives derived from renewable resources can contribute to humankind’s transition to a sustainable bioeconomy. This study presents the coating of hemp fibres with waxes extracted from pine bark as an exemplar application. Two bio-based emulsifiers were used to prepare wax emulsions suitable for a dry blending process. The coatings on the fibres were characterised, quantified, and visualised using a combination of spectroscopic and microscopic techniques. Confocal fluorescence microscopy was an excellent tool to investigate the spatial distribution of the pine bark waxes on the fibre surfaces. While successful deposition was demonstrated for all tested formulations, coating homogeneity varied for different emulsifiers. Compounding the hemp fibres with a bio-based polyester resulted in the substantial improvement of the mechanical behaviour. However, the presence of a wax coating on the fibres did not lead to a significant change in mechanical properties compared to the controls with uncoated fibres. Optimising the composite chemistry or adjusting the processing conditions might improve the compatibility of the hemp fibres with the matrix material, resulting in enhanced mechanical performance. Full article

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15 pages, 3412 KB

Open AccessEditor’s ChoiceArticle

Experimental and Statistical Investigations for Tensile Properties of Hemp Fibers

by Peyman Sadeghi, Quang Cao, Ragab Abouzeid, Mohammad Shayan, Meensung Koo and Qinglin Wu

Fibers 2024, 12(11), 94; https://doi.org/10.3390/fib12110094 - 1 Nov 2024

Cited by 11 | Viewed by 6074

Abstract

This study investigated the tensile behaviors of hemp fiber bundles and examined how properties including tensile strength and Young’s modulus vary with the bundle diameter. Hemp fibers were extracted, degummed, and separated into bundles of different diameters ranging from less than 50 μm [...] Read more.

This study investigated the tensile behaviors of hemp fiber bundles and examined how properties including tensile strength and Young’s modulus vary with the bundle diameter. Hemp fibers were extracted, degummed, and separated into bundles of different diameters ranging from less than 50 μm to over 150 μm. Tensile tests were conducted on these fiber bundles using a rheometer-based tensile testing machine. The results showed that hemp fibers exhibited a tensile strength of 97.33 MPa and a Young’s modulus of 3.77 GPa at a 50% survival probability. However, the scale parameters for breaking stress and Young’s modulus were determined to be 620.57 MPa and 29.88 GPa, respectively. As the fiber bundle diameter increased, the tensile strength decreased significantly. This was attributed to the higher probability of defects and irregularities acting as weakness points in larger fiber bundles. In contrast, Young’s modulus (stiffness) increased with increasing bundle diameter, likely due to improved fiber–fiber interactions. To further understand the variability and reliability of the tensile properties, statistical models were developed. The Weibull distribution analysis was applied, revealing critical insights into the variability of diameter, stress at break, Young’s modulus, and strain at break. The Weibull parameters provided a comprehensive understanding of the fibers’ mechanical reliability. Additionally, the Griffith model was employed to predict the strength and Young’s modulus based on fiber diameters, supporting the observation that thinner fibers generally exhibited higher tensile strength due to fewer defects. Overall, this work highlights the importance of understanding structure–property relationships in natural fibers like hemp for optimizing their performance in composites. Full article

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20 pages, 6696 KB

Open AccessEditor’s ChoiceArticle

Raman Scattering for Tensile Testing of Polyacrylonitrile-Based and Pitch-Based Single Carbon Fibers

by Kimiyoshi Naito and Chiemi Nagai

Fibers 2024, 12(10), 88; https://doi.org/10.3390/fib12100088 - 10 Oct 2024

Cited by 6 | Viewed by 2295

Abstract

The tensile properties of polyacrylonitrile (PAN)-based and pitch-based single carbon fibers were assessed using Raman scattering. Parameters and ratios related to Raman scattering and stress measurement for the G- and D-bands were analyzed. These include the peak values of Raman shifts (R [...] Read more.

The tensile properties of polyacrylonitrile (PAN)-based and pitch-based single carbon fibers were assessed using Raman scattering. Parameters and ratios related to Raman scattering and stress measurement for the G- and D-bands were analyzed. These include the peak values of Raman shifts (R_G, R_D), full width at half maximum (FWHM_G, FWHM_D), peak value slopes (|A_G|, |A_D|), peak value intercepts (B_G, B_D), the intensity ratio (I_D/I_G), the peak value ratio (R_D/R_G), the full width at half maximum ratio (FWHM_D/FWHM_G), the slope ratio (A_D/A_G), and the intercept ratio (B_D/B_G). These parameters and ratios were determined by analyzing the PAN-based and pitch-based carbon fibers and were correlated to the tensile modulus (E), interlayer spacing (d₀₀₂), lattice spacing (d₁₀), and crystalline size (L_c and L_a). In addition, a linear relationship was identified between the Raman scattering, stress measurement parameters, ratios and E, d₀₀₂, d₁₀, as well as between the Raman scattering, stress measurement parameters, ratios and L_a and L_C on the log–log scale. Full article

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12 pages, 3136 KB

Open AccessEditor’s ChoiceArticle

Kinetics of Hydrolytic Depolymerization of Textile Waste Containing Polyester

by Arun Aneja, Karel Kupka, Jiří Militký and Mohanapriya Venkataraman

Fibers 2024, 12(10), 82; https://doi.org/10.3390/fib12100082 - 29 Sep 2024

Cited by 4 | Viewed by 2271

Abstract

Textile products comprise approximately 10% of the total global carbon footprint. Standard practice is to discard apparel textile waste after use, which pollutes the environment. There are professional collectors, charity organizations, and municipalities that collect used apparel and either resell or donate them. [...] Read more.

Textile products comprise approximately 10% of the total global carbon footprint. Standard practice is to discard apparel textile waste after use, which pollutes the environment. There are professional collectors, charity organizations, and municipalities that collect used apparel and either resell or donate them. Non-reusable apparel is partially recycled, mainly through incineration or processed as solid waste during landfilling. More than 60 million tons of textiles are burnt or disposed of in landfills annually. The main aim of this paper is to model the heterogeneous kinetics of hydrolysis of multicomponent textile waste containing polyester (polyethylene terephthalate (PET) fibers), by using water without special catalytic agents or hazardous and costly chemicals. This study aims to contribute to the use of closed-loop technology in this field, which will reduce the associated negative environmental impact. The polyester part of waste is depolymerized into primary materials, namely monomers and intermediates. Reaction kinetic models are developed for two mechanisms: (i) the surface reaction rate controlling the hydrolysis and (ii) the penetrant in terms of the solid phase rate controlling the hydrolysis. A suitable kinetic model for mono- and multicomponent fibrous blends hydrolyzed in neutral and acidic conditions is chosen by using a regression approach. This approach can also be useful for the separation of cotton/polyester or wool/polyester blends in textile waste using the acid hydrolysis reaction, as well as the application of high pressure and the neutral hydrolysis of polyester to recover primary monomeric constituents. Full article

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20 pages, 8190 KB

Open AccessEditor’s ChoiceArticle

Evaluation of Peripheral Milling and Abrasive Water Jet Cutting in CFRP Manufacturing: Analysis of Defects and Surface Quality

by Alejandro Sambruno, Álvaro Gómez-Parra, Pablo Márquez, Iñaki Tellaeche-Herrera and Moisés Batista

Fibers 2024, 12(10), 78; https://doi.org/10.3390/fib12100078 - 25 Sep 2024

Cited by 4 | Viewed by 2246

Abstract

The use of carbon fiber reinforced polymers (CFRP) is crucial in industries, such as aerospace, automotive, and marine, due to their excellent strength-to-weight ratio and corrosion resistance. However, machining CFRP is challenging due to its abrasive nature, which can cause premature tool wear. [...] Read more.

The use of carbon fiber reinforced polymers (CFRP) is crucial in industries, such as aerospace, automotive, and marine, due to their excellent strength-to-weight ratio and corrosion resistance. However, machining CFRP is challenging due to its abrasive nature, which can cause premature tool wear. Some of the commonly used processes for machining these materials are dry milling and abrasive water jet machining (AWJM), which offer the best alternatives from an environmental point of view. This article presents an analysis of the defects and surface quality obtained in CFRP after machining by AWJM and milling. For this purpose, combinations of relevant parameters have been chosen for each process: cutting speed and tool wear in milling and traverse feed rate and hydraulic pressure in AWJM. The results obtained have been evaluated from two points of view: macroscopically, through the evaluation of delamination, and microscopically, through the study of the roughness in terms of Ra. Furthermore, a discussion on functional, environmental, economic, and social terms has been made between both processes. In summary, each machining process generates a specific type of delamination: Type II in milling and Type I in AWJM. In addition, the best Ra results are obtained for pressures of 1200 bar in AWJM. Full article

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

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19 pages, 1922 KB

Open AccessEditor’s ChoiceArticle

Modern Insulation Materials for Sustainability Based on Natural Fibers: Experimental Characterization of Thermal Properties

by Beata Anwajler

Fibers 2024, 12(9), 76; https://doi.org/10.3390/fib12090076 - 18 Sep 2024

Cited by 6 | Viewed by 4851

Abstract

The recycling of materials is in line with the policy of a closed-loop economy and is currently an option for managing waste in order to reuse it to create new products. To this end, 3D printing is being used to produce materials not [...] Read more.

The recycling of materials is in line with the policy of a closed-loop economy and is currently an option for managing waste in order to reuse it to create new products. To this end, 3D printing is being used to produce materials not only from pure polymers but also from their composites. Further development in this field seems interesting and necessary, and the use of recycled materials will help to reduce waste and energy consumption. This article deals with the use of degradable waste materials for the production of insulating materials by 3D printing. For the study, samples with different numbers of layers (one and five), composite thickness (20, 40, 60, 80, and 100 mm) and composition (including colored resins that were transparent, black, gray, and metallized, as well as resins that were colored gray using soybean oil and gray using natural fibers) were made. The role of natural fillers was played by glycerin and biomass ash with a weight ratio of 5%. The finished materials were tested, and the values of the coefficient of thermal resistance and heat transfer were determined. The best thermal properties among the tested materials were distinguished by a five-layer sample made of soybean-oil-based resin with a thickness of 100 mm. This sample’s heat transfer coefficient was: 0.16 W/m²K. As a material for thermal insulation in 3D printing technology, biodegradable components have great potential. Full article

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39 pages, 2751 KB

Open AccessEditor’s ChoiceSystematic Review

Sustainable and Naturally Derived Wet Spun Fibers: A Systematic Literature Review

by Cristiana Pereira, Tânia V. Pinto, Raquel M. Santos and Nuno Correia

Fibers 2024, 12(9), 75; https://doi.org/10.3390/fib12090075 - 16 Sep 2024

Cited by 8 | Viewed by 6945

Abstract

Increasing economic and environmental concerns arising from the extensive exploration and dependence on fossil fuel-based materials have encouraged the search for eco-friendly alternatives. Fibers based on biomass-derived materials have been attracting growing interest. Among other features, the mechanical performance of bio-based fibers needs [...] Read more.

Increasing economic and environmental concerns arising from the extensive exploration and dependence on fossil fuel-based materials have encouraged the search for eco-friendly alternatives. Fibers based on biomass-derived materials have been attracting growing interest. Among other features, the mechanical performance of bio-based fibers needs to be improved to effectively compete with their counterparts and emerge as viable substitutes. This review presents scientific advancements in the development of naturally derived fibers, and strategies for their production with tailored mechanical properties. The potential of natural precursor-based fibers for their conversion into high-performance carbon fibers is also emphasized. Studies reporting the mechanical properties of bio-based fibers developed by wet spinning are identified, analyzed, and discussed. These studies show that cellulose is the most studied material, while Ioncell technology is identified as the most suitable method for producing cellulose-based fibers with the highest tensile strength. Studies have also demonstrated that silk fibroin exhibits tensile strength and elongation at break ranging from 300 to 600 MPa and 30 to 50%. Although several novel processes have been explored, there are still challenges that need to be addressed for bio-based fibers to become feasible options, and to boost their usage across industries. Full article

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

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27 pages, 13471 KB

Open AccessFeature PaperEditor’s ChoiceReview

Potential Valorization of Banana Production Waste in Developing Countries: Bio-Engineering Aspects

by Robert Waraczewski and Bartosz G. Sołowiej

Fibers 2024, 12(9), 72; https://doi.org/10.3390/fib12090072 - 24 Aug 2024

Cited by 6 | Viewed by 11270

Abstract

Plant food production generates a lot of by-products (BPs). These BPs are majorly discarded into the environment, polluting it, or into landfills where they just decompose, providing no benefit and taking up storage space, causing financial costs. These plant BPs are biodegradable, but [...] Read more.

Plant food production generates a lot of by-products (BPs). These BPs are majorly discarded into the environment, polluting it, or into landfills where they just decompose, providing no benefit and taking up storage space, causing financial costs. These plant BPs are biodegradable, but reusing them may provide a better outcome and profit. The vast majority of plant-based food BPs are polysaccharide polymers like gums, lignin, cellulose, and their derivatives. It is possible to utilize plant food production waste, like banana peels, leaves, pseudostems, and inflorescences, to produce bioethanol, single-cell protein, cellulase, citric acid, lactic acid, amylase, cosmetics, fodder additives, fertilizers, biodegradable fibers, sanitary pads, bio-films, pulp and paper, natural fiber-based composites, bio-sorbents, bio-plastic, and bio-electricity in the agro-industry, pharmaceutical, bio-medical, and bio-engineering fields. Moreover, the use of banana BPs seems to be a way of dealing with many issues in underdeveloped countries, providing a clean and ecological solution. The suggested idea might not only reduce the use of plastic but also mitigate waste pollution. Full article

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

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24 pages, 14446 KB

Open AccessEditor’s ChoiceArticle

Thermal Recycling Process of Carbon Fibers from Composite Scrap—Characterization of Pyrolysis Conditions and Determination of the Quality of Recovered Fibers

by Piotr Szatkowski and Rafał Twaróg

Fibers 2024, 12(8), 68; https://doi.org/10.3390/fib12080068 - 21 Aug 2024

Cited by 8 | Viewed by 3780

Abstract

In this study, we took a closer look at the thermal recyclability of CFRP composites used in the manufacture of high-pressure cylinders. Thermal analysis was used to determine the minimum temperature at which stable resin decomposition begins. The aim was to find temperature [...] Read more.

In this study, we took a closer look at the thermal recyclability of CFRP composites used in the manufacture of high-pressure cylinders. Thermal analysis was used to determine the minimum temperature at which stable resin decomposition begins. The aim was to find temperature parameters and retention times with which the pyrolysis process is as economically viable as possible, and the recovered fibers retain optimum mechanical properties. The surface morphology of fibers annealed in both inert and oxidizing atmospheres was examined. In addition, the mechanical strengths under static as well as dynamic conditions of the newly manufactured laminates containing the recovered fibers were investigated. During research, it was found that reusing fibers is very difficult. The recycled carbon fibers were successfully compressed in an epoxy matrix in the form of a pre-impregnated carbon mat with the presence of air. The presence of oxygen during the thermal degradation of the composite severely damaged the surface and structure of the carbon fiber, causing composites made from these fibers to be mechanically weaker by more than 247%. Full article

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17 pages, 4149 KB

Open AccessEditor’s ChoiceArticle

Upper and Lower Bounds to Pull-Out Loading of Inclined Hooked End Steel Fibres Embedded in Concrete

by David W. A. Rees and Sadoon Abdallah

Fibers 2024, 12(8), 65; https://doi.org/10.3390/fib12080065 - 5 Aug 2024

Cited by 5 | Viewed by 1903

Abstract

Steel fibre-reinforced concrete (SFRC) consists of short, hooked steel fibres that are randomly distributed and oriented within the cementitious matrix. This paper presents a new analytical load-bounding approach that captures the tensile response of misaligned fibres embedded in the matrix. The contribution of [...] Read more.

Steel fibre-reinforced concrete (SFRC) consists of short, hooked steel fibres that are randomly distributed and oriented within the cementitious matrix. This paper presents a new analytical load-bounding approach that captures the tensile response of misaligned fibres embedded in the matrix. The contribution of fibres in bridging cracks to provide the required stress transfer relies on the orientation of the fibres in the concrete. Bridging fibres aligned with a crack are less effective than those inclined to it. Therefore, understanding the pull-out behaviour of misaligned fibres is a key factor in quantifying and optimising the design of SFRC in structural applications. In the laboratory, a single-oriented fibre embedded in a solid cylinder of concrete was subjected to a pull-out test, where the axis of the tensile force is aligned with the axis of the cylinder. Based on the observed behaviour, this paper presents a new analytical bounding approach to capture the pull-out response of misaligned hooked-end steel fibres embedded in a concrete matrix. The analysis was based on a transversely isotropic failure criterion assumed for the plasticity that occurs in the cold-drawn fibre. Lower and upper bounds to the loading failure were derived from fibre pull-out and fibre fracture, respectively. The division between bounds depended upon the fibre orientation, fibre diameter and the combined strengths of the steel and concrete. Bounding predictions were drawn from ratios between a fibre’s shear strength and its transverse and axial uniaxial strengths, as found from a novel testing proposal. The two bounds were compared with new data and other experimental results published in the literature. The results showed that the region between the bounds captured the failure loads of embedded fibres with effective load-bearing orientations. A critical orientation was observed at maximum strength. The present interpretation of the plasticity occurring within off-axis, hooked-end steel fibres suggests that it is possible to optimise the strength of concrete using this method of reinforcement. Full article

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

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35 pages, 1755 KB

Open AccessEditor’s ChoiceReview

Production of Nanofibers by Electrospinning as Carriers of Agrochemical

by Julia Colín-Orozco, Elena Colín-Orozco and Ricardo Valdivia-Barrientos

Fibers 2024, 12(8), 64; https://doi.org/10.3390/fib12080064 - 5 Aug 2024

Cited by 11 | Viewed by 4515

Abstract

Agrochemicals can now be protected from harsh environments like pH, light, temperature, and more with the help of a drug-loading system. This has allowed the creation of targeted and continuous release functions for pesticides and fertilizers, as well as the precise application, reduction, [...] Read more.

Agrochemicals can now be protected from harsh environments like pH, light, temperature, and more with the help of a drug-loading system. This has allowed the creation of targeted and continuous release functions for pesticides and fertilizers, as well as the precise application, reduction, and efficiency of agrochemicals. All of these benefits have been made possible by the recent advancements in the field of nanomaterials. A simple procedure known as electrospinning can be used to create nanofibers from natural and synthetic polymers. Nanofibers have come to be recognized as one of the sustainable routes with enormous applicability in different fields. In agriculture, a promising strategy may entail plant protection and growth through the encapsulating of numerous bio-active molecules as pesticides and fertilizers for intelligent administration at the desired places. Owing to their permeability, tiny dimensions, and large surface area, nanofibers can regulate the rate at which agrochemicals are released. This slows down the rate at which the fertilizer dissolves and permits the release of coated fertilizer gradually over time, which is more effectively absorbed by plant roots, as well as the efficiency of pesticides. Thus, modern agriculture requires products and formulations that are more efficient and environmentally friendly than traditional agrochemicals. In addition to highlighting the significance and originality of using nanofibers and offering a brief explanation of the electrospinning technology, the review article’s main goal is to provide a thorough summary of the research leading to breakthroughs in the nanoencapsulation of fertilizers and pesticides. Full article

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

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29 pages, 5536 KB

Open AccessEditor’s ChoiceReview

Natural Fiber-Reinforced Mycelium Composite for Innovative and Sustainable Construction Materials

by Maristella E. Voutetaki and Anastasios C. Mpalaskas

Fibers 2024, 12(7), 57; https://doi.org/10.3390/fib12070057 - 9 Jul 2024

Cited by 36 | Viewed by 17565

Abstract

Fiber-reinforced mycelium (FRM) composites offer an innovative and sustainable approach to construction materials for architectural structures. Mycelium, the root structure of fungi, can be combined with various natural fibers (NF) to create a strong and lightweight material with environmental benefits. Incorporating NF like [...] Read more.

Fiber-reinforced mycelium (FRM) composites offer an innovative and sustainable approach to construction materials for architectural structures. Mycelium, the root structure of fungi, can be combined with various natural fibers (NF) to create a strong and lightweight material with environmental benefits. Incorporating NF like hemp, jute, or bamboo into the mycelium matrix enhances mechanical properties. This combination results in a composite that boasts enhanced strength, flexibility, and durability. Natural FRM composites offer sustainability through the utilization of agricultural waste, reducing the carbon footprint compared to conventional construction materials. Additionally, the lightweight yet strong nature of the resulting material makes it versatile for various construction applications, while its inherent insulation properties contribute to improved energy efficiency in buildings. Developing and adopting natural FRM composites showcases a promising step towards sustainable and eco-friendly construction materials. Ongoing research and collaboration between scientists, engineers, and the construction industry will likely lead to further improvements and expanded applications. This article provides a comprehensive analysis of the current research and applications of natural FRM composites for innovative and sustainable construction materials. Additionally, the paper reviews the mechanical properties and potential impacts of these natural FRM composites in the context of sustainable architectural construction practices. Recently, the applicability of mycelium-based materials has extended beyond their original domains of biology and mycology to architecture. Full article

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

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14 pages, 1191 KB

Open AccessEditor’s ChoiceArticle

Carbon Fibers Based on Cellulose–Lignin Hybrid Filaments: Role of Dehydration Catalyst, Temperature, and Tension during Continuous Stabilization and Carbonization

by Christoph Unterweger, Inge Schlapp-Hackl, Christian Fürst, Daria Robertson, MiJung Cho and Michael Hummel

Fibers 2024, 12(7), 55; https://doi.org/10.3390/fib12070055 - 30 Jun 2024

Cited by 4 | Viewed by 3627

Abstract

Lignocellulose has served as precursor material for carbon fibers (CFs) before fossil-based polymers were discovered as superior feedstock. To date, CFs made from polyacrylonitrile have dominated the market. In search of low-cost carbon fibers for applications with medium strength requirements, cellulose and lignin, [...] Read more.

Lignocellulose has served as precursor material for carbon fibers (CFs) before fossil-based polymers were discovered as superior feedstock. To date, CFs made from polyacrylonitrile have dominated the market. In search of low-cost carbon fibers for applications with medium strength requirements, cellulose and lignin, either as individual macromolecule or in combination, have re-gained interest as renewable raw material. In this study, cellulose with 30 wt% lignin was dry-jet wet-spun into a precursor filament for bio-based carbon fibers. The stabilization and carbonization conditions were first tested offline, using stationary ovens. Diammonium sulfate (DAS) and diammonium hydrogen phosphate were tested as catalysts to enhance the stabilization process. Stabilization is critical as the filaments’ strength properties drop in this phase before they rise again at higher temperatures. DAS was identified as a better option and used for subsequent trials on a continuous carbonization line. Carbon fibers with ca. 700 MPa tensile strength and 60–70 GPa tensile modulus were obtained at 1500 °C. Upon further carbonization at 1950 °C, moduli of >100 GPa were achieved. Full article

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

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18 pages, 6263 KB

Open AccessEditor’s ChoiceArticle

Thermal and Moisture Management in the Microclimate of Socks for Diabetic Foot Care: The Role of Mohair-Wool Content

by Adine Gericke and Mohanapriya Venkataraman

Fibers 2024, 12(7), 53; https://doi.org/10.3390/fib12070053 - 25 Jun 2024

Cited by 5 | Viewed by 2971

Abstract

In diabetic patients, optimised plantar health necessitates meticulously designed hosiery. These specialised socks facilitate a healthy microclimate at the skin–textile interface. This requires that stable conditions of temperature and humidity are maintained during wear. This study investigated the thermal resistance and moisture management [...] Read more.

In diabetic patients, optimised plantar health necessitates meticulously designed hosiery. These specialised socks facilitate a healthy microclimate at the skin–textile interface. This requires that stable conditions of temperature and humidity are maintained during wear. This study investigated the thermal resistance and moisture management properties of socks for diabetics. Fabrics and socks were evaluated on the Alambeta and thermal foot manikin instruments and in wear trials. A novel in vitro method, mimicking in-use conditions, was employed to validate findings and assess sock performance during wear. Fabric structure, especially thickness, had a greater impact on thermal resistance than fibre composition, suggesting that socks with different levels of thermal resistance can be customised according to individual preferences. In terms of moisture management, mohair–wool socks outperformed polyester socks, maintaining significantly lower humidity between the skin and the sock, and meeting the requirement to prevent the drying out of the microclimate significantly better. The enhanced moisture vapour sorption exhibited by the mohair–wool fabric contributes to this effect. Overall, the findings suggest that mohair–wool is an excellent fibre choice for diabetic socks, due to its unique moisture management properties and the possibility to tailor thermal properties through fabric structural design. Full article

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11 pages, 5732 KB

Open AccessEditor’s ChoiceCommunication

Microplastics and Fibrous Fragments Generated during the Production and Maintenance of Textiles

by Jiří Militký, Jana Novotná, Jakub Wiener, Dana Křemenáková and Mohanapriya Venkataraman

Fibers 2024, 12(7), 51; https://doi.org/10.3390/fib12070051 - 21 Jun 2024

Cited by 13 | Viewed by 3157

Abstract

More than a third of microplastics in surface waters are formed by microplastics released from textile products containing textile fibers (fibrous microplastics). A large amount of fibrous microplastics enters the environment during textile production and the first few washing cycles. Mechanical, thermal, chemical, [...] Read more.

More than a third of microplastics in surface waters are formed by microplastics released from textile products containing textile fibers (fibrous microplastics). A large amount of fibrous microplastics enters the environment during textile production and the first few washing cycles. Mechanical, thermal, chemical, and biological damage to textiles causes the generation of fibrous microplastics. Textile manufacturers, dyers and finishers, garment producers, distributors, or consumers contribute to this process. During the construction of textiles, multiple issues need to be addressed simultaneously. They are related to the optimization of technological processes and the construction and functionalization of fiber structures, considering ecological requirements, including suppressing the formation of fibrous microplastics. This research is focused on the specification of reasons for the generation of fibrous microplastics during textile production. The influence of the structure of fibers, abrasive deformations, and surface structure of fabrics on the generation of fibrous microplastics is discussed. The release of fibrous microplastics during washing is mentioned as well. Full article

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15 pages, 2568 KB

Open AccessEditor’s ChoiceArticle

Remote-Controlled Activation of the Release through Drug-Loaded Magnetic Electrospun Fibers

by Richard Ziegler, Shaista Ilyas, Sanjay Mathur, Gerardo F. Goya and Jesús Antonio Fuentes-García

Fibers 2024, 12(6), 48; https://doi.org/10.3390/fib12060048 - 3 Jun 2024

Cited by 13 | Viewed by 3831

Abstract

The integration of magnetic nanoparticles within fibrillar structures represents an interesting avenue for the remotely controlled release of therapeutic agents. This work presents a novel drug release platform based on electrospun magnetic fibers (EMFs) combining drugs, magnetic nanoparticles (MNPs) and mesoporous silica nanoparticles [...] Read more.

The integration of magnetic nanoparticles within fibrillar structures represents an interesting avenue for the remotely controlled release of therapeutic agents. This work presents a novel drug release platform based on electrospun magnetic fibers (EMFs) combining drugs, magnetic nanoparticles (MNPs) and mesoporous silica nanoparticles (MSNs) for controlled drug delivery via alternating magnetic fields (AMF). The platform was demonstrated to be versatile and effective for hydrophilic ketorolac (KET) and hydrophobic curcumin (CUR) encapsulation and the major response observed for AMF-triggered release was reached using drug-loaded MSNs within the fibers, providing fine control over drug release patterns. The EMFs exhibited excellent inductive heating capabilities, showing a temperature increase of ∆T up to 8 °C within a 5 min AMF pulse. The system is shown to be promising for applications like transdermal pain management, oncological drug delivery, tissue engineering, and wound healing, enabling precise control over drug release in both spatial and temporal dimensions. The findings of this study offer valuable insights into the development of the next generation of smart drug delivery systems, based in multifunctional materials that can be remotely regulated and potentially revolutionize the field of nanomedicine. Full article

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29 pages, 13239 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Advanced Image Analysis and Machine Learning Models for Accurate Cover Factor and Porosity Prediction in Knitted Fabrics: Tailored Applications in Sportswear, Swimwear, and Casual Wear

by Tomislav Rolich, Daniel Domović, Goran Čubrić and Ivana Salopek Čubrić

Fibers 2024, 12(5), 45; https://doi.org/10.3390/fib12050045 - 20 May 2024

Cited by 3 | Viewed by 2433

Abstract

This paper presents a study focused on developing robust algorithms for cover factor and porosity calculation through digital image analysis. Computational models based on machine learning for efficient cover factor prediction based on fabric parameters have also been developed. Five algorithms were devised [...] Read more.

This paper presents a study focused on developing robust algorithms for cover factor and porosity calculation through digital image analysis. Computational models based on machine learning for efficient cover factor prediction based on fabric parameters have also been developed. Five algorithms were devised and implemented in MATLAB: the single threshold algorithm (ST); multiple linear threshold algorithms, ML-1 and ML-2; and algorithms with multiple thresholds obtained by the Otzu method, MT-1 and MT-2. These algorithms were applied to knitted fabrics used for football, swimming, and leisure. Algorithms ML-1 and MT-1, employing multiple thresholds, outperformed the single threshold algorithm. The ML-1 variant yielded the highest average porosity value at 95.24%, indicating the importance of adaptable thresholding in image analysis. Comparative analysis revealed that algorithm variants ML-2 and MT-2 obtain lower cover factors compared to ML-1 and MT-1 but can detect potential void areas in fabrics with higher reliability. Algorithm MT-1 proved to be the most sensitive when it came to distinguishing between different fabric samples. Computational models that were developed based on random tree, random forest, and SMOreg machine learning algorithms predicted cover factor based on fabric parameters with up to 95% accuracy. Full article

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14 pages, 3127 KB

Open AccessEditor’s ChoiceArticle

Acid Resistance of Metakaolin-Based Geopolymers and Geopolymeric Mortars Reinforced with Coconut Fibers

by Marco Lezzerini, Andrea Aquino and Stefano Pagnotta

Fibers 2024, 12(5), 40; https://doi.org/10.3390/fib12050040 - 1 May 2024

Cited by 7 | Viewed by 3762

Abstract

This paper investigates the durability of geopolymers and geopolymeric mortars made with metakaolin and alkaline activators, with and without a coconut fiber addition, after immersion for seven days into solutions of citric acid (1%, 2.5%, 5%, and 10%); hydrochloric acid (1%, 2.5%, 5%, [...] Read more.

This paper investigates the durability of geopolymers and geopolymeric mortars made with metakaolin and alkaline activators, with and without a coconut fiber addition, after immersion for seven days into solutions of citric acid (1%, 2.5%, 5%, and 10%); hydrochloric acid (1%, 2.5%, 5%, and 10%); and sulfuric acid (1%, 2.5%, 5%, and 10%). The study focuses on mass changes, uniaxial compressive strength, flexural strength, and ultrasound pulse velocity measurements. X-ray diffraction and scanning electron microscopy are used to analyze the degradation products and microstructural changes. The aim is to assess the effect of acid exposure on the strength and stability of geopolymer materials and identify any protective effects of coconut fiber reinforcement. The samples are immersed in acid solutions of varying concentrations, and their mechanical properties are measured. The presence of coconut fibers slightly modifies the physical properties and the compressive strength, improving the mechanical flexural strength. Geopolymer and geopolymeric mortar materials experienced a weak decrease in strength when exposed to solutions of citric acid and a significant one when exposed to solutions of hydrochloric and sulfuric acids, attributed to depolymerization of the aluminosilicate binders. Brick waste geopolymeric mortars reinforced with coconut fibers showed the best performance in acid solutions with respect to geopolymers and quartz-rich sand geopolymeric mortars, suggesting a more stable cross-linked aluminosilicate geopolymer structure in this material. Full article

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15 pages, 22912 KB

Open AccessEditor’s ChoiceArticle

Structural Characterisation of End-of-Life Cement–Asbestos Materials from Lithuania

by Robert Kusiorowski, Anna Gerle, Magdalena Kujawa, Valentin Antonovič and Renata Boris

Fibers 2024, 12(4), 37; https://doi.org/10.3390/fib12040037 - 15 Apr 2024

Cited by 8 | Viewed by 3689

Abstract

Asbestos is a widely used name for natural silicate minerals with fibrous properties. Asbestos minerals were one of the most popular and cheapest raw materials used in the construction industry in the past when they was used in the form of cement–asbestos composite [...] Read more.

Asbestos is a widely used name for natural silicate minerals with fibrous properties. Asbestos minerals were one of the most popular and cheapest raw materials used in the construction industry in the past when they was used in the form of cement–asbestos composite material. Nowadays, we know that asbestos possesses carcinogenic properties. Due to this fact, asbestos was banned in many countries including Lithuania. All asbestos-containing materials are considered waste and stored in special landfills, which causes significant environmental pollution. One of the methods proposed to solve the asbestos problem may be thermal treatment. In the present study, asbestos-containing wastes in the form of cement–asbestos materials were examined. These asbestos-containing materials were characterised via chemical analysis (XRF) connected with mineralogical phase analysis with powder X-ray diffraction (XRD) as well as scanning electron microscopy (SEM). The thermal decomposition of samples was studied via differential thermal analysis (DTA) and thermogravimetric measurements with evolved gas analysis (TG–EGA). It was found that thermal treatment is a possible way to destroy asbestos contained in cement–asbestos wastes and convert it into new mineral phases. The work also compared the obtained characteristics of asbestos waste with the characteristics of waste produced in other countries. Full article

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