Journal of Composites Science

16 pages, 4361 KiB

Open AccessArticle

Residual Stress Evolution of Graphene-Reinforced AA2195 (Aluminum–Lithium) Composite for Aerospace Structural Hydrogen Fuel Tank Application

by Venkatraman Manokaran, Anthony Xavior Michael, Ashwath Pazhani and Andre Batako

J. Compos. Sci. 2025, 9(7), 369; https://doi.org/10.3390/jcs9070369 (registering DOI) - 16 Jul 2025

Abstract

This study investigates the fabrication and residual stress behavior of a 0.5 wt.% graphene-reinforced AA2195 aluminum matrix composite, developed for advanced aerospace structural applications. The composite was synthesized via squeeze casting, followed by a multi-pass hot rolling process and subsequent T8 heat treatment. [...] Read more.

This study investigates the fabrication and residual stress behavior of a 0.5 wt.% graphene-reinforced AA2195 aluminum matrix composite, developed for advanced aerospace structural applications. The composite was synthesized via squeeze casting, followed by a multi-pass hot rolling process and subsequent T8 heat treatment. The evolution of residual stress was systematically examined after each rolling pass and during thermal treatments. The successful incorporation of graphene into the matrix was confirmed through Energy-Dispersive Spectroscopy (EDS) analysis. Residual stress measurements after each pass revealed a progressive increase in compressive stress, reaching a maximum of −68 MPa after the fourth hot rolling pass. Prior to the fifth pass, a solution treatment at 530 °C was performed to dissolve coarse precipitates and relieve internal stresses. Cold rolling during the fifth pass reduced the compressive residual stress to −40 MPa, and subsequent artificial aging at 180 °C for 48 h further decreased it to −23 MPa due to recovery and stress relaxation mechanisms. Compared to the unreinforced AA2195 alloy in the T8 condition, which exhibited a tensile residual stress of +29 MPa, the graphene-reinforced composite in the same condition retained a compressive residual stress of −23 MPa. This represents a net improvement of 52 MPa, highlighting the composite’s superior capability to retain compressive residual stress. The presence of graphene significantly influenced the stress distribution by introducing thermal expansion mismatch and acting as a barrier to dislocation motion. Overall, the composite demonstrated enhanced residual stress characteristics, making it a promising candidate for lightweight, fatigue-resistant aerospace components. Full article

(This article belongs to the Section Composites Modelling and Characterization)

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17 pages, 2964 KiB

Open AccessArticle

Seawater Ageing Effects on the Mechanical Performance of Basalt Fibre-Reinforced Thermoplastic and Epoxy Composites

by Mohamad Alsaadi, Tomas Flanagan and Declan M. Devine

J. Compos. Sci. 2025, 9(7), 368; https://doi.org/10.3390/jcs9070368 (registering DOI) - 15 Jul 2025

Abstract

This research paper employed the recently developed Elium thermoplastic resin and basalt fabrics as an alternative to thermoset/synthetic fibre composites to reduce their environmental impact. Elium^® 191 XO/SA and Epoxy Prime^TM 37 resin were reinforced with mineral-based semi-unidirectional basalt fibre (BF). [...] Read more.

This research paper employed the recently developed Elium thermoplastic resin and basalt fabrics as an alternative to thermoset/synthetic fibre composites to reduce their environmental impact. Elium^® 191 XO/SA and Epoxy Prime^TM 37 resin were reinforced with mineral-based semi-unidirectional basalt fibre (BF). Physical, chemical, tensile, and flexural performance was investigated under the effect of hydrothermal seawater ageing at 45 °C for 45 and 90 days. The results show that the BF/Elium composite exhibited superior tensile and flexural strength, as well as good stiffness, compared with the BF/Epoxy composite. Digital images and scanning electron microscope images were used to describe the fracture and failure mechanisms. The tensile and flexural strength values of the BF/Elium composite were 1165 MPa and 1128 MPa, greater than those of the BF/Epoxy composite by 33% and 71%, respectively. The tensile and flexural modulus values of the BF/Elium composite were 44.1 GPa and 38.2 GPa, which are 30% and 12% greater than those of the BF/Epoxy composite. The result values for both composites were normalised with respect to the density of each composite laminate. Both composites exhibited signs of resin decomposition and fibre surface degradation under the influence of seawater ageing, resulting in a more recognisable reduction in flexural properties than in tensile properties. Full article

(This article belongs to the Special Issue Advances in Continuous Fiber Reinforced Thermoplastic Composites)

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15 pages, 3974 KiB

Open AccessArticle

Cast Polyamide 6 Molds as a Suitable Alternative to Metallic Molds for In Situ Automated Fiber Placement

by Fynn Atzler, Ines Mössinger, Jonathan Freund, Samuel Tröger, Ashley R. Chadwick, Simon Hümbert and Lukas Raps

J. Compos. Sci. 2025, 9(7), 367; https://doi.org/10.3390/jcs9070367 (registering DOI) - 15 Jul 2025

Abstract

Thermoplastic in situ Automated Fiber Placement (AFP) is an additive manufacturing method currently investigated for its suitability for the production of aerospace-grade composite structures. A considerable expense in this process is the manufacturing and preparation of a mold in which a composite part [...] Read more.

Thermoplastic in situ Automated Fiber Placement (AFP) is an additive manufacturing method currently investigated for its suitability for the production of aerospace-grade composite structures. A considerable expense in this process is the manufacturing and preparation of a mold in which a composite part can be manufactured. One approach to lowering these costs is the use of a 3D-printable thermoplastic mold. However, AFP lay-up on a 3D-printed mold differs from the usage of a traditional metallic mold in various aspects. Most notable is a reduced stiffness of the mold, a lower thermal conductivity of the mold, and the need for varied process parameters of the AFP process. This study focuses on the investigation of the difference in mechanical and morphological characteristics of laminates produced on metallic and polymeric molds. To this end, the tensile strength and the interlaminar shear strength of laminates manufactured on each substrate were measured and compared. Additionally, morphological analysis using scanning electron microscopy and differential scanning calorimetry was performed to compare the crystallinity in laminates. No statistically significant difference in mechanical or morphological properties was found. Thus, thermoplastics were shown to be a suitable material for non-heated molds to manufacture in situ AFP composites. Full article

(This article belongs to the Section Composites Manufacturing and Processing)

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17 pages, 2344 KiB

Open AccessArticle

Enhancing Polycaprolactone with Levulinic Acid-Extracted Lignin: Toward Sustainable Bio-Based Polymer Blends

by Elodie Melro, Hugo Duarte, Filipe E. Antunes, Artur J. M. Valente, Anabela Romano and Bruno Medronho

J. Compos. Sci. 2025, 9(7), 366; https://doi.org/10.3390/jcs9070366 (registering DOI) - 14 Jul 2025

Abstract

The growing demand for sustainable materials has intensified the search for biodegradable polymers. Poly(ε-caprolactone) (PCL), though biodegradable, is fossil-derived. In this study, a novel lignin extracted from pine wood using a green solvent was incorporated into PCL and compared with commercial lignins (dealkaline, [...] Read more.

The growing demand for sustainable materials has intensified the search for biodegradable polymers. Poly(ε-caprolactone) (PCL), though biodegradable, is fossil-derived. In this study, a novel lignin extracted from pine wood using a green solvent was incorporated into PCL and compared with commercial lignins (dealkaline, alkaline, and lignosulfonate). The lignin additions imparted antioxidant properties, enhanced thermal stability, and promoted circular economy goals through lignin valorization. Notably, the green-extracted lignin showed superior compatibility with PCL when compared with commercial lignins, as evidenced by lower water uptake and solubility, and improved surface hydrophobicity (higher contact angle). Although the addition of lignin reduced the tensile strength and elongation at break, it greatly increased the PCL radical scavenging activity (DPPH) from 8 ± 1% of neat PCL to 94.8 ± 0.3% when 20 wt% of lignin-LA was added. Among the tested lignins, lignin-LA stands out as the most promising candidate to be applied as a functional additive in biodegradable polymer blends and composites for advanced sustainable applications. Not only given its intrinsically higher sustainability but also due to its capacity for improving the thermal properties of PCL–lignin blends. Full article

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20 pages, 10209 KiB

Open AccessArticle

Micro and Macro Analyses for Structural, Mechanical, and Biodegradability of a Pulp-Based Packaging Material: A Comprehensive Evaluation Using SEM, XRD, FTIR, and Mechanical Testing

by H. M. D. U. Sewwandi, J. D. Chathuranga, W. G. C. M. Kulasooriya, D. K. A. Induranga, S. V. A. A. Indupama, G. D. C. P. Galpaya, M. K. D. M. Gunasena, H. V. V. Priyadarshana and K. R. Koswattage

J. Compos. Sci. 2025, 9(7), 365; https://doi.org/10.3390/jcs9070365 (registering DOI) - 14 Jul 2025

Abstract

The extensive accumulation of plastic waste causes serious environmental problems, leading to growing interest in biodegradable alternatives. In this study, the structural, chemical, and crystalline characteristics of a pulp-based material incorporating sugarcane bagasse ash (SCBA) were investigated using Scanning Electron Microscopy (SEM), X-ray [...] Read more.

The extensive accumulation of plastic waste causes serious environmental problems, leading to growing interest in biodegradable alternatives. In this study, the structural, chemical, and crystalline characteristics of a pulp-based material incorporating sugarcane bagasse ash (SCBA) were investigated using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). Mechanical properties of the materials were investigated through compression, tensile, and bending tests in order to assess their strength and flexibility, while biodegradability was evaluated through soil burial tests. The results indicate that SCBA addition enhances compressive strength, with optimal performance obtained at 15% SCBA content, while tensile and bending strengths showed an enhancement at 5% content. FTIR and XRD analyses suggested an increase in amorphous regions and notable microstructural interactions between SCBA particles and cellulose fibers, particularly at a 10% concentration. SEM images further confirmed effective particle dispersion and improved porosity in the composite materials. Furthermore, samples incorporating SCBA exhibited superior biodegradability compared to pure pulp. Overall, these findings highlight that incorporating 10–15% SCBA provides a promising balance between mechanical integrity and environmental sustainability, offering a viable strategy for developing eco-friendly, high-performance packaging materials. Full article

(This article belongs to the Special Issue Advances in Sustainable Composites and Manufacturing Innovations)

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28 pages, 5774 KiB

Open AccessArticle

Data-Driven Prediction of Polymer Nanocomposite Tensile Strength Through Gaussian Process Regression and Monte Carlo Simulation with Enhanced Model Reliability

by Pavan Hiremath, Subraya Krishna Bhat, Jayashree P. K., P. Krishnananda Rao, Krishnamurthy D. Ambiger, Murthy B. R. N., S. V. Udaya Kumar Shetty and Nithesh Naik

J. Compos. Sci. 2025, 9(7), 364; https://doi.org/10.3390/jcs9070364 (registering DOI) - 14 Jul 2025

Abstract

This study presents a robust machine learning framework based on Gaussian process regression (GPR) to predict the tensile strength of polymer nanocomposites reinforced with various nanofillers and processed under diverse techniques. A comprehensive dataset comprising 25 polymer matrices, 22 surface functionalization methods, and [...] Read more.

This study presents a robust machine learning framework based on Gaussian process regression (GPR) to predict the tensile strength of polymer nanocomposites reinforced with various nanofillers and processed under diverse techniques. A comprehensive dataset comprising 25 polymer matrices, 22 surface functionalization methods, and 24 processing routes was constructed from the literature. GPR, coupled with Monte Carlo sampling across 2000 randomized iterations, was employed to capture nonlinear dependencies and uncertainty propagation within the dataset. The model achieved a mean coefficient of determination (R²) of 0.96, RMSE of 12.14 MPa, MAE of 7.56 MPa, and MAPE of 31.73% over 2000 Monte Carlo iterations, outperforming conventional models such as support vector machine (SVM), regression tree (RT), and artificial neural network (ANN). Sensitivity analysis revealed the dominant influence of Carbon Nanotubes (CNT) weight fraction, matrix tensile strength, and surface modification methods on predictive accuracy. The findings demonstrate the efficacy of the proposed GPR framework for accurate, reliable prediction of composite mechanical properties under data-scarce conditions, supporting informed material design and optimization. Full article

(This article belongs to the Special Issue Characterization and Modelling of Composites, Volume III)

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18 pages, 5837 KiB

Open AccessArticle

Influential Microstructural Descriptors for Predicting Mechanical Properties of Fiber-Reinforced Composites

by Jamal F. Husseini, Eric J. Carey, Farhad Pourkamali-Anaraki, Evan J. Pineda, Brett A. Bednarcyk and Scott E. Stapleton

J. Compos. Sci. 2025, 9(7), 363; https://doi.org/10.3390/jcs9070363 - 12 Jul 2025

Abstract

Fiber-reinforced composites contain microscale features such as variations in local fiber volume fraction, fiber clusters, and resin-rich regions, which may impact mechanical properties. Microscale models need to be large enough to capture these features while maintaining high fidelity to capture the localized fiber-to-fiber [...] Read more.

Fiber-reinforced composites contain microscale features such as variations in local fiber volume fraction, fiber clusters, and resin-rich regions, which may impact mechanical properties. Microscale models need to be large enough to capture these features while maintaining high fidelity to capture the localized fiber-to-fiber interactions. This makes it difficult to efficiently model regions with equivalent fiber morphologies to as-manufactured scans and to perform large statistical studies to examine how these features drive mechanical performance. This study uses a novel microstructure generator and an efficient micromechanical model along with a characterization method that measures the geometry of these features to simulate a wide range of microstructures for strength and stiffness. After understanding how the mechanical properties are affected by morphology through correlation matrices, equivalent microstructures were generated to regions of an as-manufactured composite. The generation of microstructures based on different morphological descriptors allows for an understanding of which features are valuable when modeling these materials. In comparing microstructures with different equivalent descriptors to the case with all six descriptors, it was found that only using local fiber volume fraction median resulted in over predictions of strength and stiffness. Once two descriptors or more were introduced, such as local fiber volume fraction median and inter-quartile range, there was no significant difference in strength and stiffness. This suggests that at least two descriptors should be considered when generating equivalent microstructures for mechanical properties. Full article

(This article belongs to the Special Issue Editorial Board Members' Collection Series: Mechanical Analysis of Composite Materials)

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20 pages, 3537 KiB

Open AccessArticle

A New Sulfur-Containing Copolymer Created Through the Thermally Induced Radical Copolymerization of Elemental Sulfur with N2,N2-Diallylmelamine Comonomer for Potential CO₂ Capture

by Dharrinesh Narendiran, Nurul Hazirah Sumadi, Ali Shaan Manzoor Ghumman, Noor Ashikin Mohamad, Mohamed Mahmoud Nasef, Amin Abbasi and Rashid Shamsuddin

J. Compos. Sci. 2025, 9(7), 362; https://doi.org/10.3390/jcs9070362 - 11 Jul 2025

Abstract

Sulfur-containing polymers are unique sustainable materials with promise for the development of various adsorbents for environmental remediation. However, they have not been explored for CO₂ capture despite reports on its ability to decontaminate various aqueous pollutants. This study reports on the single-step [...] Read more.

Sulfur-containing polymers are unique sustainable materials with promise for the development of various adsorbents for environmental remediation. However, they have not been explored for CO₂ capture despite reports on its ability to decontaminate various aqueous pollutants. This study reports on the single-step synthesis of a diamine-functionalized sulfur-containing copolymer by the thermally induced radical copolymerization of N2,N2-Diallylmelamine (NDAM), a difunctional monomer, with sulfur and explores its use for CO₂ capture. The influence of reaction parameters such as the weight ratios of sulfur to NDAM, reaction temperature, time, and the addition of a porogen on the properties of aminated copolymer was investigated. The resulting copolymers were characterized using FTIR, TGA, DSC, SEM, XRD, and BET surface area analyses. The incorporation of NDAM directly imparted amine functionality while stabilizing the polysulfide chains by crosslinking, leading to a thermoset copolymer with an amorphous structure. The addition of a NaCl particle porogen to the S/NDAM mixture generated a mesoporous structure, enabling the resulting copolymer to be tested for CO₂ adsorption under varying pressures, leading to an adsorption capacity as high as 517 mg/g at 25 bar. This work not only promotes sustainable hybrid materials that advance green chemistry while aiding CO₂ mitigation efforts but also adds value to the abundant amount of sulfur by-products from petroleum refineries. Full article

(This article belongs to the Special Issue Polymer Composites: Fiber Architecture, Interfacial Engineering, and Processing)

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24 pages, 2179 KiB

Open AccessArticle

Time-Dependent Rheological Behavior and MPS Simulation of Cement–Bentonite Slurries with Hydration Accelerators for Borehole Backfilling Applications

by Shinya Inazumi, Kazuhiko Tazuke and Seiya Kashima

J. Compos. Sci. 2025, 9(7), 361; https://doi.org/10.3390/jcs9070361 - 10 Jul 2025

Abstract

This study investigates cement–bentonite slurries with hydration accelerators for borehole backfilling applications in infrastructure reconstruction projects. Two formulations with different accelerator dosages (5 and 10 kg/m³) were evaluated through combined experimental testing and Moving Particle Semi-implicit (MPS) numerical modeling to optimize [...] Read more.

This study investigates cement–bentonite slurries with hydration accelerators for borehole backfilling applications in infrastructure reconstruction projects. Two formulations with different accelerator dosages (5 and 10 kg/m³) were evaluated through combined experimental testing and Moving Particle Semi-implicit (MPS) numerical modeling to optimize material performance. The research focuses on time-dependent rheological evolution and its impact on construction performance, particularly bleeding resistance and workability retention. Experimental flow tests revealed that both formulations maintained similar initial flowability (240–245 mm spread diameter), but the higher accelerator dosage resulted in 33% flow reduction after 60 min compared to 12% for the lower dosage. Bleeding tests demonstrated significant improvement in phase stability, with bleeding rates reduced from 2.5% to 1.5% when accelerator content was doubled. The MPS framework successfully reproduced experimental behavior with prediction accuracies within 3%, enabling quantitative analysis of time-dependent rheological parameters through inverse analysis. The study revealed that yield stress evolution governs both flow characteristics and bleeding resistance, with increases several hundred percent over 60 min while plastic viscosity remained relatively constant. Critically, simulations incorporating time-dependent viscosity changes accurately predicted bleeding behavior, while constant-viscosity models overestimated bleeding rates by 60–130%. The higher accelerator formulation (10 kg/m³) provided an optimal balance between initial workability and long-term stability for typical borehole backfilling operations. This integrated experimental–numerical approach provides practical insights for material optimization in infrastructure reconstruction projects, particularly relevant for aging infrastructure requiring proper foundation treatment. The methodology offers construction practitioners a robust framework for material selection and performance prediction in borehole backfilling applications, contributing to improved construction quality and reduced project risks. Full article

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15 pages, 4106 KiB

Open AccessArticle

Effect of Alumina Microparticle-Infused Polymer Matrix on Mechanical Performance of Carbon Fiber Reinforced Polymer (CFRP) Composite

by Ganesh Radhakrishnan, Teodora Odett Breaz, Abdul Hamed Hamed Al Hinai, Fisal Hamed Al Busaidi, Laqman Malik Al Sheriqi, Mohammed Ali Al Hattali, Mohammed Ibrahim Al Rawahi, Mohammed Nasser Al Rabaani and Kadhavoor R. Karthikeyan

J. Compos. Sci. 2025, 9(7), 360; https://doi.org/10.3390/jcs9070360 - 10 Jul 2025

Abstract

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the [...] Read more.

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the field of transportation and building engineering, replacing conventional materials due to their attractive properties as mentioned. In this work, a CFRP laminate is fabricated with carbon fiber mats and epoxy by a hand layup technique. Alumina (Al₂O₃) micro particles are used as a filler material, mixed with epoxy at different weight fractions of 0% to 4% during the fabrication of CFRP laminates. The important objective of the study is to investigate the influence of alumina micro particles on the mechanical performance of the laminates through characterization for various physical and mechanical properties. It is revealed from the results of study that the mass density of the laminates steadily increased with the quantity of alumina micro particles added and subsequently, the porosity of the laminates is reduced significantly. The SEM micrograph confirmed the constituents of the laminate and uniform distribution of Al₂O₃ micro particles with no significant agglomeration. The hardness of the CFRP laminates increased significantly for about 60% with an increase in weight % of Al₂O₃ from 0% to 4%, whereas the water gain % gradually drops from 0 to 2%, after which a substantial rise is observed for 3 to 4%. The improved interlocking due to the addition of filler material reduced the voids in the interfaces and thereby resist the absorption of water and in turn reduced the plasticity of the resin too. Tensile, flexural and inter-laminar shear strengths of the CFRP laminate were improved appreciably with the addition of alumina particles through extended grain boundary and enhanced interfacial bonding between the fibers, epoxy and alumina particles, except at 1 and 3 wt.% of Al₂O₃, which may be due to the pooling of alumina particles within the matrix. Inclusion of hard alumina particles resulted in a significant drop in impact strength due to appreciable reduction in softness of the core region of the laminates. Full article

(This article belongs to the Special Issue Advanced Composite Materials from Natural and Synthetic Sources: Fabrication, Characterization and Practical Application, Volume II)

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28 pages, 7820 KiB

Open AccessReview

Mechanisms and Performance of Composite Joints Through Adhesive and Interlocking Means—A Review

by Khishigdorj Davaasambuu, Yu Dong, Alokesh Pramanik and Animesh Kumar Basak

J. Compos. Sci. 2025, 9(7), 359; https://doi.org/10.3390/jcs9070359 - 10 Jul 2025

Abstract

Conventional adhesively bonded joints, such as single-lap, curved-lap, wavy-lap, double-lap, stepped-lap, and scarf joints, are widely used for aerospace, automotive, and medical applications. These adhesively bonded joints exhibit different load transfer mechanisms and stress distributions within adhesive layers, which depend primarily on their [...] Read more.

Conventional adhesively bonded joints, such as single-lap, curved-lap, wavy-lap, double-lap, stepped-lap, and scarf joints, are widely used for aerospace, automotive, and medical applications. These adhesively bonded joints exhibit different load transfer mechanisms and stress distributions within adhesive layers, which depend primarily on their geometries and mechanical properties of bonded materials. As such, joint geometry and material properties play a critical role in determining the capability of the joints to withstand high loads, resist fatigue, and absorb energy under impact loading. This paper investigates the effects of geometry and material dissimilarity on the performance of both conventional bonded and interlocking joints under tensile loading based on the information available in the literature. In addition, bonding and load transfer mechanisms were analysed in detail. It was found that stress concentration often occurs at free edges of the adhesive layer due to geometric discontinuities, while most of the load is carried by these regions rather than its centre. Sharp corners further intensify resulting stresses, thereby increasing the risk of joint failure. Adhesives typically resist shear loads better than peel loads, and stiffness mismatches between adherents induce an asymmetric stress distribution. Nonetheless, similar materials promote symmetric load sharing. Among conventional joints, scarf joints provide the most uniform load distribution. In interlocking joints such as dovetail, T-slot, gooseneck, and elliptical types, the outward bending of the female component under tension can lead to mechanical failure. Full article

(This article belongs to the Special Issue Mechanical Properties of Composite Materials and Joints)

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11 pages, 2806 KiB

Open AccessArticle

The Effect of Doping with Aluminum on the Optical, Structural, and Morphological Properties of Thin Films of SnO₂ Semiconductors

by Isis Chetzyl Ballardo Rodriguez, U. Garduño Terán, A. I. Díaz Cano, B. El Filali and M. Badaoui

J. Compos. Sci. 2025, 9(7), 358; https://doi.org/10.3390/jcs9070358 - 9 Jul 2025

Abstract

There is considerable interest in broadband nanomaterials, particularly transparent semiconductor oxides, within both fundamental research and technological applications. Historically, it has been considered that the variation in dopant concentration during the synthesis of semiconductor materials is a crucial factor in activating and/or modulating [...] Read more.

There is considerable interest in broadband nanomaterials, particularly transparent semiconductor oxides, within both fundamental research and technological applications. Historically, it has been considered that the variation in dopant concentration during the synthesis of semiconductor materials is a crucial factor in activating and/or modulating the optical and structural properties, particularly the bandgap and the parameters of the unit cell, of semiconductor oxides. Recently, tin oxide has emerged as a key material due to its excellent structural properties, optical transparency, and various promising applications in optoelectronics. This study utilized the ultrasonic spray pyrolysis technique to synthesize aluminum-doped tin oxide (ATO) thin films on quartz and polished single-crystal silicon substrates. The impact of varying aluminum doping levels (0, 2, 5, and 10 at. %) on morphology and structural and optical properties was examined. The ATO thin films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmittance spectroscopy. SEM images demonstrated a slight reduction in the size of ATO nanoparticles as the aluminum doping concentration increased. XRD analysis revealed a tetragonal crystalline structure with the space group P42/mnm, and a shift in the XRD peaks to higher angles was noted with increasing aluminum content, indicating a decrease in the crystalline lattice parameters of ATO. The transmittance of the ATO films varied between 75% and 85%. By employing the transmittance spectra and the established Tauc formula the optical bandgap values of ATO films were calculated, showing an increase in the bandgap with higher doping levels. These findings were thoroughly analyzed and discussed; additionally, an effort was made to clarify the contradictory analyses present in the literature and to identify a doping range that avoids the onset of a secondary phase. Full article

(This article belongs to the Special Issue Optical–Electric–Magnetic Multifunctional Composite Materials)

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22 pages, 2470 KiB

Open AccessArticle

Multi-Objective Optimisation of Hybrid Banana/Sisal/Red Mud Composites Using Taguchi–Grey Relational Analysis

by Karthick Rasu, Vigneshwaran Shanmugam and Joao Paulo Davim

J. Compos. Sci. 2025, 9(7), 357; https://doi.org/10.3390/jcs9070357 - 8 Jul 2025

Abstract

In response to the rising demand for sustainable engineering materials and waste valorisation strategies, this study investigates the multi-objective optimisation of eco-friendly hybrid composites reinforced with natural fibres and industrial waste. Sixteen composite specimens were fabricated using compression moulding by varying sisal fibre [...] Read more.

In response to the rising demand for sustainable engineering materials and waste valorisation strategies, this study investigates the multi-objective optimisation of eco-friendly hybrid composites reinforced with natural fibres and industrial waste. Sixteen composite specimens were fabricated using compression moulding by varying sisal fibre from 0 to 45 wt.%, banana fibre from 0 to 45 wt.%, NaOH alkali treatment from 0 to 6%, and red mud filler from 1 to 4 wt.%. Mechanical properties were evaluated following ASTM standards D256 for impact strength, D790 for flexural strength, D638 for tensile strength, D5379 for shear strength, and E18 for hardness. The Taguchi method combined with grey relational analysis was employed to identify optimal processing conditions. The best mechanical performance, with an impact strength of 6.57 J, flexural strength of 72.58 MPa, and tensile strength of 65.52 MPa, was achieved with 30 to 45 wt.% sisal fibre, 15 wt.% banana fibre, 6% NaOH, and 3 to 4 wt.% red mud. ANOVA revealed that NaOH treatment had the most significant influence on mechanical properties, with high F values and p values close to 0.05. Grey relational analysis proved more effective for multi-objective optimisation, with the highest grey grade of 0.894 observed in the specimen containing 45 wt.% sisal fibre, 6% NaOH, and 2 wt.% red mud. These findings highlight the critical role of fibre treatment and hybrid reinforcement in enhancing performance. The optimised composites demonstrate strong potential for use in automotive interior panel applications, offering a sustainable alternative with balanced strength and reduced environmental impact. Full article

(This article belongs to the Special Issue Recent Progress in Hybrid Composites)

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24 pages, 1711 KiB

Open AccessReview

Hybridization of Lignocellulosic Biomass into Aluminum-Based Materials: Comparing the Cases of Aluminum Matrix Composites and Fiber Metal Laminates

by Cristiano Fragassa and Carlo Santulli

J. Compos. Sci. 2025, 9(7), 356; https://doi.org/10.3390/jcs9070356 - 8 Jul 2025

Abstract

Introducing and compacting lignocellulosic biomass in aluminum structures, though recommendable in terms of higher sustainability, the potential use of agro-waste and significant weight reduction, still represents a challenge. This is due to the variability of biomass performance and to its limited compatibility with [...] Read more.

Introducing and compacting lignocellulosic biomass in aluminum structures, though recommendable in terms of higher sustainability, the potential use of agro-waste and significant weight reduction, still represents a challenge. This is due to the variability of biomass performance and to its limited compatibility with the metal. Another question may concern possible moisture penetration in the structure, which may reduce environmental resistance and result in local degradation, such as wear or even corrosion. Despite these limitations, this hybridization enjoys increasing success. Two forms are possibly available for this: introduction into metal matrix composites (MMCs), normally in the form of char from biomass combustion, or laminate reinforcement as the core for fiber metal laminates (FMLs). These two cases are treated alongside each other in this review, first because they may represent two combined options for recycling the same biomass into high-profile structures, aimed primarily at the aerospace industry. Moreover, as discussed above, the effect on the aluminum alloy can be compared and the forces to which they are subjected might be of a similar type, most particularly in terms of their hardness and impact. Both cases considered, MMCs and FMLs involved over time many lignocellulosic residues, starting from the most classical bast species, i.e., flax, hemp, sisal, kenaf, etc., and extending also to less diffuse ones, especially in view of the introduction of biomass as secondary, or residual, raw materials. Full article

(This article belongs to the Collection Editorial Board Members’ Collection Series: Fibre Composite Materials)

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21 pages, 9386 KiB

Open AccessArticle

Structural Characterization and Segmental Dynamics Evaluation in Eco-Friendly Polymer Electrospun Fibers Based on Poly(3-hydroxybutyrate)/Polyvinylpyrrolidone Blends to Evaluate Their Sustainability

by Svetlana G. Karpova, Anatoly A. Olkhov, Ivetta A. Varyan, Ekaterina P. Dodina, Yulia K. Lukanina, Natalia G. Shilkina, Anatoly A. Popov, Alexandre A. Vetcher, Anna G. Filatova and Alexey L. Iordanskii

J. Compos. Sci. 2025, 9(7), 355; https://doi.org/10.3390/jcs9070355 - 8 Jul 2025

Abstract

Ultrafine fibers from poly(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) and their blends with different component ratios in the range of 0/100 to 100/0 wt.% were obtained, and their structure and dynamic properties were studied. The polymers were obtained via electrospinning in solution mode. The [...] Read more.

Ultrafine fibers from poly(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) and their blends with different component ratios in the range of 0/100 to 100/0 wt.% were obtained, and their structure and dynamic properties were studied. The polymers were obtained via electrospinning in solution mode. The structure, morphology, and segmental dynamic behavior of the fibers were determined using optical microscopy, SEM, EPR, DSC, and IR spectroscopy. The low-temperature maximum on the DSC endotherms provided information on the state of the PVP hydrogen bond network, which made it possible to determine the enthalpies of thermal destruction of these bonds. The PHB/PVP fiber blend ratio significantly affected the structural and dynamic parameters of the system. Thus, at low concentrations of PVP (up to 9%) in the structure of ultra-fine fibers, the distribution of this polymer occurs in the form of tiny particles, which are crystallization centers, which causes a significant increase in the degree of crystallinity (χ) activation energy (E_act) and slowing down of molecular dynamics (τ). At higher concentrations of PVP, loose interphase layers were formed in the system, which caused a decrease in these parameters. The strongest changes in the concentration of hydrogen bonds occurred when PVP was added to the composition from 17 to 50%, which was due to the formation of intermolecular hydrogen bonds both in PVP and during the interaction of PVP and PHB. The diffusion coefficient of water vapor in the studied systems (D) decreased as the concentration of glassy PVP in the composition increased. The concentration of the radical decreased with an increase in the proportion of PVP, which can be explained by the glassy state of this polymer at room temperature. A characteristic point of the 50/50% mixture component ratio was found in the region where an inversion transition of PHB from a dispersion material to a dispersed medium was assumed. The conducted studies made it possible for the first time to conduct a comprehensive analysis of the effect of the component ratio on the structural and dynamic characteristics of the PHB/PVP fibrous material at the molecular scale. Full article

(This article belongs to the Special Issue Advanced Composite Materials from Natural and Synthetic Sources: Fabrication, Characterization and Practical Application, Volume II)

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16 pages, 2400 KiB

Open AccessArticle

Modeling Piezoresistive Behavior of Conductive Composite Sensors via Multi-State Percolation Theory

by Nathan S. Usevitch, Emily V. White, Anton E. Bowden, Ulrike H. Mitchell and David T. Fullwood

J. Compos. Sci. 2025, 9(7), 354; https://doi.org/10.3390/jcs9070354 - 8 Jul 2025

Abstract

Flexible strain sensors, fabricated from high-elongation polymers and conductive filler particles, are proving an essential tool in the study of biomechanics using wearable technology. It has been previously shown that the resistive response of such composites, relative to the amount of conductive filler [...] Read more.

Flexible strain sensors, fabricated from high-elongation polymers and conductive filler particles, are proving an essential tool in the study of biomechanics using wearable technology. It has been previously shown that the resistive response of such composites, relative to the amount of conductive filler material, can be reasonably modeled using a standard percolation-type model. Once a certain critical fraction of filler material is reached, a conductive network across the sample is established and resistance rapidly decreases. However, modeling the more subtle resistance changes that occur while deforming the sensors during operation is more nuanced. Conductivity across the network of particles is dominated by tunneling mechanisms at the interfaces between the filler materials. Small changes in strain at these interfaces lead to relatively large, but nevertheless continuous, changes in local resistance. By assigning some arbitrary value of resistance as a dividing line between ‘low’ and ‘high’ resistance, one might model the piezoresistive behavior using a standard percolation model. But such an assumption is likely to lead to low accuracy. Our alternative approach is to divide the range of potential resistance values into several bins (rather than the usual two bins) and apply a relatively novel multi-state percolation theory. The performance of the multi-state percolation model is assessed using a random resistor model that is assumed to provide the ground truth. The model is applied to predict resistance response with both changes in relative amount of conductive filler (i.e., to help design the initial unstrained sensor) and with applied strain (for an operating sensor). We find that a multi-state percolation model captures the behavior of the simulated composite sensor in both cases. The multicomponent percolation theory becomes more accurate with more divisions/bins of the resistance distribution, and we found good agreement with the simulation using between 10 and 20 divisions. Full article

(This article belongs to the Special Issue Characterization and Modelling of Composites, Volume III)

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28 pages, 1259 KiB

Open AccessReview

Perspective on Sustainable Solutions for Mitigating Off-Gassing of Volatile Organic Compounds in Asphalt Composites

by Masoumeh Mousavi, Vajiheh Akbarzadeh, Mohammadjavad Kazemi, Shuguang Deng and Elham H. Fini

J. Compos. Sci. 2025, 9(7), 353; https://doi.org/10.3390/jcs9070353 - 8 Jul 2025

Abstract

This perspective explores the use of biochar, a carbon-rich material derived from biomass, as a sustainable solution for mitigating volatile organic compounds (VOCs) emitted during asphalt production and use. VOCs from asphalt contribute to ozone formation and harmful secondary organic aerosols (SOAs), which [...] Read more.

This perspective explores the use of biochar, a carbon-rich material derived from biomass, as a sustainable solution for mitigating volatile organic compounds (VOCs) emitted during asphalt production and use. VOCs from asphalt contribute to ozone formation and harmful secondary organic aerosols (SOAs), which negatively impact air quality and public health. Biochar, with its high surface area and capacity to adsorb VOCs, provides an effective means of addressing these challenges. By tailoring biochar’s surface chemistry, it can efficiently capture VOCs, while also offering long-term carbon sequestration benefits. Additionally, biochar enhances the durability of asphalt, extending road lifespan and reducing maintenance needs, making it a promising material for sustainable infrastructure. Despite these promising benefits, several challenges remain. Variations in biochar properties, driven by differences in feedstock and production methods, can affect its performance in asphalt. Moreover, the integration of biochar into existing plant operations requires the further development of methods to streamline the process and ensure consistency in biochar’s quality and cost-effectiveness. Standardizing production methods and addressing logistical hurdles will be crucial for biochar’s widespread adoption. Research into improving its long-term stability in asphalt is also needed to ensure sustained efficacy over time. Overcoming these challenges will be essential for fully realizing biochar’s potential in sustainable infrastructure development Full article

(This article belongs to the Special Issue Composites: A Sustainable Material Solution)

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15 pages, 1464 KiB

Open AccessArticle

Evaluation of Color Stability of UDMA-Based Dental Composite Resins After Exposure to Conventional Cigarette and Aerosol Tobacco Heating System

by Maria G. Mousdraka, Olga Gerasimidou, Alexandros K. Nikolaidis, Christos Gogos and Elisabeth A. Koulaouzidou

J. Compos. Sci. 2025, 9(7), 352; https://doi.org/10.3390/jcs9070352 - 8 Jul 2025

Abstract

This study evaluated the effects of conventional cigarette smoke compared to aerosol from a heat-non-burn tobacco product on the color stability of two UDMA-based dental composite resins, namely a monochromatic (Omnichroma) and a polychromatic (Vittra APS) resin. Twenty disc-shaped specimens were prepared, divided [...] Read more.

This study evaluated the effects of conventional cigarette smoke compared to aerosol from a heat-non-burn tobacco product on the color stability of two UDMA-based dental composite resins, namely a monochromatic (Omnichroma) and a polychromatic (Vittra APS) resin. Twenty disc-shaped specimens were prepared, divided into two groups of ten, and exposed to 105 cigarettes or 105 aerosol tobacco sticks via a custom-made smoking chamber. Puff duration was 2 s, with a 60 s interval between puffs in which smoke saturated the chamber for 30 s; then, clean air was introduced into the chamber for 30 s. Six puffs and six intervals were simulated. Color parameters were measured before and after exposure and following brushing of each specimen with 15 strokes. Color differences were determined based on the CIEDE2000 formula. Significant color change was found in all specimens exposed to cigarette and tobacco aerosol. The highest color-change mean value was obtained from composite resin exposed to cigarette smoke. Although both cigarette and thermal heating systems cause discoloration, the aerosol causes reduced composite resin discoloration, which compromises aesthetics and increases patient dissatisfaction, impacting the overall dental care. Color stability is the hallmark of success, as it is the main reason for replacing dental restorations. Full article

(This article belongs to the Section Composites Applications)

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25 pages, 6538 KiB

Open AccessArticle

Polymer–Filler Interactions in Graphite-Infused Polypropylene: Experimental Design, a Fundamental and Applied Study

by Rabindra Dharai, Yubaraj Chakraborty, Rabiranjan Murmu, Pragyan Senapati, Harekrushna Sutar and Debashis Roy

J. Compos. Sci. 2025, 9(7), 351; https://doi.org/10.3390/jcs9070351 - 7 Jul 2025

Abstract

In this study, micrographite (μG)-reinforced polypropylene (PP) composites were fabricated using melt compounding, with μG contents varying from 3 to 15 wt%. The composites were evaluated for mechanical, electrical, and thermal performance, addressing a relatively underexplored area among carbon-based fillers. Tensile testing across [...] Read more.

In this study, micrographite (μG)-reinforced polypropylene (PP) composites were fabricated using melt compounding, with μG contents varying from 3 to 15 wt%. The composites were evaluated for mechanical, electrical, and thermal performance, addressing a relatively underexplored area among carbon-based fillers. Tensile testing across elongation speeds (10–50 mm/min) showed up to ~30% strength improvement at 6 wt% μG due to good dispersion and stress transfer, while ≥9 wt% led to agglomeration, reduced ductility, and increased melt resistance. SEM fractography confirmed matrix–filler debonding and brittle behavior at higher loadings, with ductility improving at higher elongation rates. A sharp drop in resistivity near 6 wt% indicated the formation of a conductive network, and thermal conductivity improved by nearly 80%. Taguchi optimization identified 12 wt% μG and 50 mm/min as optimal for tensile strength, with filler content having a stronger influence than testing speed. The novelty of this work lies in its integrated structure–property investigation across a broad μG range, offering a scalable, multifunctional PP composite system suitable for semi-structural, conductive, and thermal management applications. Full article

(This article belongs to the Special Issue Functional Composites: Fabrication, Properties and Applications)

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