Epoxy Composites Research Articles

Mechanical behaviour of pineapple leaf fibers reinforced Lapox L-12 epoxy composites

To meet the increasing need for composites in sectors such as medical, transportation, safety, and athletics, researchers continuously develop novel composites. This study investigated the effects of boron carbide filler particles in epoxy by fabricating composites from Lapox L-12 epoxy with 20 and 30 wt. % of pineapple leaf fibres (PALF) utilising the hand layup method. The mechanical parameters of the synthesised composites were evaluated according to ASTM standards, encompassing hardness, ultimate tensile strength, yield strength, elongation, and flexural strength. The addition of pineapple leaf fibres to epoxy Lapox L-12 resulted in enhanced hardness, tensile strength, and flexural strength, accompanied by a minor reduction in percentage elongation. Lapox L-12 composites supplemented with 30 wt.% of PALF exhibited enhancements of 60.8% in hardness, 66.2% in ultimate strength, and 101% in flexural strength.

SUSTAINABLE CONVERSION OF BANANA WASTE INTO ELECTRICAL INSULATION MATERIALS FOR HIGH VOLTAGE APPLICATIONS

<p style="text-align:justify;"><span style="font-family:"Times New Roman","serif";font-size:12.0pt;line-height:150%;text-justify:inter-ideograph;">The study examined the electrical characteristics of epoxy composites that were reinforced with fibers derived from banana leaves and pseudostems. Specifically, the study focused on analysing the dissipation factor, loss factor, and dielectric constant of these composites. The study found that composites containing banana leaf fibers demonstrated enhanced dielectric properties in comparison to pure epoxy composites. This improvement can be attributed to the effective interlocking between the fibers and the matrix, as well as the polarization effects. Enhancing the amount of fibre in the material resulted in greater dielectric constants, reaching a maximum at a critical volume of 17.2%. However, at higher frequencies, the dielectric constants fell due to decreasing polarization. Chemical treatments, such as alkali and peroxide solutions, improved the bonding between the fibers and the matrix, leading to higher resistance to water and greater electrical insulation. The results also showed that banana leaf fibers had superior dielectric performance compared to pseudostem fibers, mostly because of enhanced nanoparticle bonding. Using banana fibers is particularly noteworthy since it contributes to environmental sustainability by recycling agricultural waste, hence mitigating the ecological consequences of synthetic products.</span></p>

Mechanical characterization of natural fiber composites prepared with untreated and treated ficus religiosa root fibers

Surface modification techniques are used to modify the surface of the natural fibers in order to improve the surface characteristics; in turn other relevant significant properties of the fiber and its composites. In the present work, epoxy composites have been prepared with the untreated and treated F. religiosa root fiber samples at 5, 10, 15, 20, and 25 wt.% fiber loading. Mechanical properties such as tensile, flexural and impact strength of the prepared composite specimens have been tested as per the ASTM standards. From the results, it has been identified that the strength of the proposed composites increases with the increase in fiber loading, and the composites made up of 20 wt.% of the NaOH solution treated fiber sample exhibits better properties under mechanical characterization study. Alkalization filled the holes, cracks, and pores on the outer layer of fibers and significantly improved the surface roughness, which was reflected in the improvement of the proposed composites.

The Influence of Alkaline Treatment on Delamination resistance of Woven Flax Fiber-Reinforced Epoxy Composite Laminates

AbstractDelamination is one of the most typical failure modes of fiber-reinforced polymer composite laminates. Thus, investigating and improving the delamination behavior of these laminates are of vital importance. The present research discovers and investigates the role of the alkaline treatment of twill-woven flax fabric on the delamination resistance of flax fiber-reinforced epoxy composite laminates. Initially, flax fibers were treated with different sodium hydroxide solution concentrations (2–5–10%) for 2 h. The influence of alkaline treatment on fiber characteristics was evaluated by performing a single-yarn tensile test, scanning electron microscopy, and Fourier transform infrared spectroscopy analysis for treated and untreated flax fibers. The appropriate treatment condition was selected based on the properties obtained from the tests conducted on the fiber level. Subsequently, to discover the role of alkaline treatment on delamination resistance, flax fabric was treated with the selected treatment condition for further composite fabrication. The treated and untreated flax fiber-reinforced epoxy composites were fabricated using a hand lay-up technique followed by hot compression. Interlaminar shear strength, double cantilever beam, and end-notch flexural tests were carried out for treated and untreated composites to determine the effect of alkaline treatment on the delamination resistance. The results proved that the alkaline treatment of flax fabric significantly improved the delamination resistance of treated composite laminates compared to untreated ones. The interlaminar shear strength, the mode I interlaminar fracture toughness (propagation), and mode II interlaminar fracture toughness were improved by 27.3%, 14%, and 24.9%, respectively, for treated composite laminates compared to untreated ones.

Effect of Mechanically Exfoliated Graphite Flakes on Morphological, Mechanical, and Thermal Properties of Epoxy

Carbon-reinforced polymer composites form an important category of advanced materials, and there is an increasing demand to enhance their performance using more convenient and scalable processes at low costs. In the present study, graphitic flakes were prepared by the mechanical exfoliation of synthetic graphite electrodes and utilized as an abundant and potentially low-cost filler to fabricate epoxy-based composites with different additive ratios of 1–10 wt.%. The morphological, structural, thermal, and mechanical properties of these composites were investigated. It was found that the thermal conductivity of the composites increases by adding graphite, and this increase mainly depends on the ratio of the graphite additive. The addition of graphite was found to have a diverse effect on the mechanical properties of the composites: the tensile strength of the composites decreases with the addition of graphite, whilst their compressive strength and elastic modulus are enhanced. The results demonstrate that incorporating 5 wt% of commercially available graphite into epoxy not only raises the thermal conductivity of the material from 0.223 to 0.485 W/m·K, but also enhances its compressive strength from 66 MPa to 72 MPa. The diverse influence of graphite provides opportunities to prepare epoxy composites with desirable properties for different applications.

A statistical approach to predict flexural strength and flame retardation properties for natural fibre/ epoxy composites

This research investigates the development of a mathematical model to predict the influence of flame retardants (FR) on the mechanical and flame retardancy performance of natural fibre reinforced thermosetting composites. The study focuses on two types of FRs: Diammonium Phosphate (DAP) and silica fumes that were added to Jute reinforced epoxy composites (JRECs). Two mathematical models were established based on three variables and two measured responses. The variables include FRs type, FR content, and FR method of preparation, while the measured responses are Limiting oxygen index (LOI) and Flexural strength (FS). The models were developed using a statistical approach based on multiple linear regression fitting and validated using analysis of variance (ANOVA) technique. The developed models were verified using experimental result data from literature and the analysis of these models showed that the maximum discrepancy between the observed and predicted values for relative LOI and relative FS was within the range of [Formula: see text] 6% and [Formula: see text] 5%, respectively. This research contributes to the understanding of the impact of FRs on the mechanical and flame retardancy performance of natural fibre reinforced thermosetting composites, which can aid in the design and development of safer and more efficient composite materials.

Effects of nanodiamonds on the mechanical properties, acoustic properties, vibration damping, and flame retardancy of ramie-fiber epoxy composite panels used for indoor applications

This research aims to systematically analyze the impact of nanodiamonds (NDs) in ramie fiber-reinforced epoxy resin acoustic panels used for indoor applications. The panels (four variants) are fabricated using six layers of ramie fiber with various weight percentages of NDs (0.0, 0.2, 0.4, and 0.6) in epoxy resin by the vacuum resin infusion process (VRIP). Mechanical characterization (tensile and flexural strength) was carried out using Instron 8801 universal testing machine. The impedance tube-based sound absorption coefficient (SAC) test was performed at low frequency and higher frequency, respectively. The void content in the panel is evaluated using a micro-x-ray computed tomography (CT) scanner. The dispersion of nanoparticles is studied using scanning electron microscopy (SEM) images. The vertical flame-retardant test and the horizontal flame-retardant test were conducted according to the UL-94 standard. The 0.4 wt.% NDs sample showed good tensile strength (59.178 MPa) and flexural strength (69.134 MPa) compared with other panels. The panels showed differences in SAC values for different weight percentages of NDs, both at lower and higher frequencies. The 0.6 wt.% NDs sample attained the maximum SAC of 0.906 at 6000 Hz in the high-frequency and 0.34 at 1112 Hz in the low-frequency. The SEM reveals an even distribution of NDs in both the 0.2 and 0.4 wt.% NDs panels, while agglomerates form in the 0.6 wt.% panels. The CT scan result shows void content both internally and externally in the panels. There are no voids in the panels where NDs are uniformly distributed. The synergistic effect of NDs in epoxy resin forms a char over the burnt surfaces of samples, enhancing the flame-retardant properties of the panels. According to this study, adding NDs to ramie fiber epoxy composites has improved the panels’ necessary qualities, making them suitable for use as indoor acoustic conditioning materials.

Chemical and Solvent-Based Recycling of DGEBA-Based Epoxy Thermoset and Carbon-Fiber Reinforced Epoxy Composite Utilizing Imine-Containing Secondary Amine Hardener.

Epoxy systems are essential in numerous industrial applications due to their exceptional mechanical properties, thermal stability, and chemical resistance. Yet, recycling epoxy networks and reinforcing materials in epoxy composites remains challenging, raising environmental concerns. The critical challenge is the recovery of well-defined molecules upon depolymerization. To address these issues, an innovative strategy is developed utilizing imine-containing secondary amine hardener (M1). The reaction of M1 with DGEBA produced high-performance epoxy thermoset P1, which exhibits Young's modulus of 2.18 GPa and tensile strength of 63.4 MPa, and excellent stability in neutral aqueous conditions. Upon carbon-fiber reinforcement, Young's modulus and tensile strength are significantly elevated to 10.99GPa and 328.3MPa, respectively. The reactive secondary amine functionalities enabled the tailored network to display a well-defined growth pattern, yielding only well-defined molecules and intact carbon fibers upon acidic depolymerization. Consequently, the recycled polymers retained properties identical to those of P1. Notably, it is discovered that despite the cross-linked nature of the epoxy networks, complete dissolution in dichloromethane facilitated straightforward solvent-based recycling, allowing the recovery of undamaged carbon fibers and an epoxy thermoset with properties matching the virgin material. Presented novel monomer design and approach showcased two important and efficient recycling options for epoxy systems.

An investigation of clay percentage variation on composite materials sustainability identification by digital image correlation

ABSTRACT The study focuses on stress and strain evaluation of composite resin material with the reinforcement of clay in the glass-reinforced epoxy composite (GREC). The strain measurement used the DIC technique. The tensile test specimens were prepared from the laminate sheets as per ASTM D638 standard. The influence of nano clay weight percentage such as 2.5%, 3.5%, and 4.5% during preparation of GREC is studied in the article. The fibre orientation angles are 90°, and the fibre volume percentage is 45%. Hand lay-up methods are used to prepare the composite resin material. The samples were tested as per the standardised procedures. The specimen rupture at a localised strain reached a maximum value of 0.01293, 0.01571, and 0.0143 with 2.5%, 3.5% and 4.5% Nano clay, respectively. The material behaviour in terms of major strain (εyy), Poisson’s ratio (µ) and thickness strain (Δt) is evaluated at the gauge length of the specimen. DIC strain measurement clearly demonstrates the 3.5% percentage of clay addition as it yields better results as elastic modulus and tensile strength have improved. The composite resin with clay addition could be used in various applications, such as low-cost housing, structural works, medical devices, automotive panels, etc

Covalently grafting silane coupling agents onto MXene‐reinforced carbon fibers for epoxy composites with improved mechanical properties

AbstractTwo‐dimensional (2D) MXene (MX) and silane coupling agents are increasingly used to modify carbon materials for the fabrication of composite functional materials, which exhibit enhanced electrical, optical, and mechanical properties due to the synergistic effects of both MX and silane. We demonstrate the modification of carbon fibers (CFs) with MX and three different kinds of silane coupling agents, including 3‐aminopropyltriethoxysilane, 3‐glycidyloxypropyldimethoxymethylsilane, and 3‐mercaptopropyltriethoxysilane, which are named as CF‐MX@N, CF‐MX@O, and CF‐MX@S, respectively, and further prepare the CF‐MX@silane/epoxy (EP) composites. The utilized silane coupling agents serve as bridges between MX and CFs, forming CF‐MX@silane composites. Through comparative analysis, it is found that the CF‐MX@S composites form a strong interface phase through covalent bonds, significantly enhancing the interface compatibility and revealing strong interface adhesion. The interfacial shear strength of the molded CF‐MX@S/EP composites increases to 119.7 MPa, with an 173.9% enhancement comparing to unmodified composites. This work can offer useful guidance and reference for selecting appropriate silane coupling agent to modify CFs with 2D materials to form high‐performance composite materials.Highlights Silane coupling agents are used as bridges to graft MXene‐modified CFs The surface modification of CFs is achieved by a simple one‐step approach Excellent interfacial phase is constructed through forming strong covalent bonds Microstructure and failure interface are responsible to interface strengthen.

Mechanical Behaviour of Green Epoxy Composites Reinforced with Sheep and Dog Wool from Serra Da Estrela

Mechanical Behaviour of Green Epoxy Composites Reinforced with Sheep and Dog Wool from Serra Da Estrela

Valorisation of corn waste as fiber, biosilica, and their epoxy composites: fatigue, fracture toughness, water absorption, and drilling properties

Valorisation of corn waste as fiber, biosilica, and their epoxy composites: fatigue, fracture toughness, water absorption, and drilling properties

Cryogenic Impact on Carbon Fiber-Reinforced Epoxy Composites for Hydrogen Storage Vessels

Carbon fiber-reinforced epoxy (CF/EP) composites are attractive materials for hydrogen storage tanks due to their high strength-to-weight ratio and outstanding chemical resistance. However, cryogenic temperatures (CTs) have a substantial impact on the tensile strength and interfacial bonding of CF/EP materials, producing problems for their long-term performance and safety in hydrogen storage tank applications. This review paper investigates how low temperatures affect the tensile strength, modulus, and fracture toughness of CF/EP materials, as well as the essential interfacial interactions between carbon fibers (CFs) and the epoxy matrix (EP) in cryogenic environments. Material toughening techniques have evolved significantly, including the incorporation of nano-fillers, hybrid fibers, and enhanced resin formulations, to improve the durability and performance of CF/EP materials in cryogenic conditions. This review also assesses the hydrogen barrier properties of various composites, emphasizing the importance of reducing hydrogen permeability in order to retain material integrity. This review concludes by highlighting the importance of optimizing CF/EP composite design and fabrication for long-term performance and safety in hydrogen storage systems. It examines the prospects for using CF/EP composites in hydrogen storage tanks, as well as future research directions.

Novel Graphene‐Epoxy Composite with Aligned Architecture and Ultrahigh Thermal Conductivity

AbstractBecause of the surge in the power density of electronic devices, there is an urgent need for improvements in the thermal conductivity of packaging materials. Nowadays, epoxy composites supplemented with thermally conductive fillers are widely used for this purpose, but unfortunately, none of them can satisfactorily meet industrial requirements. Herein, this article reports on a novel method to prepare well‐shaped and highly ordered graphene‐epoxy composite architecture; that is, the epoxy infiltrates into tubular graphene columns that have been restored to the high thermally conductive structure of graphene. As a result, the newly developed graphene‐epoxy composite exhibits record‐high thermal conductivity of 69.74 W m−1 K−1 with filler content of only 11.22 wt.%. The unprecedentedly high thermal conductivity stems from the construction of thermally conductive channels and restoration of the inherent π–π conjugate structure of graphene. These findings not only offer a breakthrough in packaging materials with significantly enhanced thermal conductivity but also provide a promising avenue for the development of other advanced graphene‐added composites.

The Low-Temperature Thermal Conductivity of Epoxy Resin Composites Enhanced by Graphene and Modified Alumina Hybrid Fillers

In recent years, polymer/ceramic composites with high thermal conductivity have been widely used in microelectronic devices, superconducting magnets and aviation, and further improving their thermal conductivity is a great challenge. In this work, spherical alumina nanoparticles were modified with 3-aminopropyltriethoxy-silane (APTES) successfully. Furthermore, the modified Al2O3(M-Al2O3)/Epoxy(EP) and Graphene(Gr)/M-Al2O3/EP composites were prepared and their properties were tested in the temperature range of 70 K-300 K. The results showed that the thermal conductivity of the composite with 1 wt% Gr and 60 wt% M-Al2O3 hybrid filler is 15 times higher than that of pure epoxy at 70 K, which indicates its application prospect in thermal interface materials.

Evaluation of the thermomechanical properties of novel epoxy composites reinforced with Geonoma baculifera fibers

Natural lignocellulosic fibers (NLFs) have shown a great potential as reinforcements in composites in recent decades. Among other reasons, environmental concerns and the depletion of oil reserves justify research on natural composites as they offer an environmentally friendly alternative and align with the principles of sustainable development. Among the plethora of NLFs available in nature, the ubim fiber (Geonoma baculifera) has not yet been investigated as a reinforcement for composites in potential engineering applications. Therefore, this study evaluates, for the first time, the mechanical properties of epoxy composites with 10, 20, and 30 vol% of ubim fibers. These properties were assessed through Izod impact, tensile and flexural tests as well as dynamic mechanical analysis (DMA). The data were statistically analyzed using the ANOVA method. Scanning electron microscopy (SEM) analysis indicated a transition from a purely brittle fracture mechanism to a ductile-brittle combination as the fiber volume in the composite increased. Tensile tests of the composites demonstrated an increasing trend in strength and elastic modulus with fiber volume. The results of the flexural tests also displayed a similar trend in strength and elasticity modulus for the composites. The results of DMA tests showed that composite materials with a 30 vol% of ubim fibers exhibited a high glass transition temperature and a low tan δ value, suggesting higher stiffness of this composite compared to others. Overall, the results indicated that the incorporation of 30 vol% ubim fibers into the composites significantly improved their mechanical properties compared to other tested fiber fractions. Additionally, their functional characteristics, such as simplicity in the manufacturing process, low cost, and excellent strength-to-weight ratio, make these composites particularly suitable for applications in sectors such as the automotive industry, construction panels, and packaging. These factors contribute to the development of an efficient, sustainable, recyclable and environmentally friendly composite.

Tuning Interfacial Characteristics of Epoxy Composites Towards Simultaneous High Thermal and Dielectric Properties

AbstractAchieving excellent thermal and dielectric performance is crucial to prevent premature insulation failure of epoxy in high‐frequency transformers. However, interfaces introduced by embedding micro/nano fillers in epoxy have opposite effects on these properties. Here, the interfacial characteristics of micro‐BN/nano‐Al2O3 epoxy is tailored composites by modifying nano‐Al2O3 with functional amine groups, leading to simultaneous improvements in thermal conductivity and high‐frequency breakdown strength. After modification, thermal conductivity increased from 0.193 to 0.490 W m−1 K−1 at 25 °C, and breakdown strength improved from 85.4 to 94.8 kV mm−1 at 10 kHz. The findings revealed the coexistence of overlapping interfaces between micro‐BN and chemical interfaces between modified Al2O3‐NH2 and matrix in composites. Contrary to the overlapping interface, the chemical interface played a more pivotal role in macroscopic performance. Calculations based on a covalent bonding interfacial model demonstrated that this in‐situ tight interface facilitated phonon transport, thereby enhancing thermal conductivity. Besides the physical structure, an increase in electrostatic potential in the chemical interface also impeded charge migration, resulting in an improved breakdown strength. The synergistic effect of the chemical interface on thermal and dielectric properties presents a promising design strategy for developing high‐performance epoxy composites.

Vertically anchored nano-fold hybrid on h-BN surfaces achieves effective smoke suppression, antibacterial, and thermal conductivity in epoxy resin composites

Vertically anchored nano-fold hybrid on h-BN surfaces achieves effective smoke suppression, antibacterial, and thermal conductivity in epoxy resin composites

Multi-scale fatigue damage analysis in filament-wound carbon fiber reinforced epoxy composites for hydrogen storage tanks

This article presents the findings of a multi-scale experimental study on carbon fiber-reinforced epoxy composites (CFRP) used in lightweight hydrogen storage pressure vessels produced via filament winding. The research employs a combination of tension-tension load-controlled fatigue tests and high-resolution physical-chemical characterization and porosity quantification to assess the impact of porosity on mechanical performance. The findings demonstrate that porosity has a detrimental impact on mechanical properties, acting as nucleation sites for damage mechanisms such as crack initiation, fiber-matrix separation and fiber breakage. At the mesoscopic level, microdefects coalesce into transverse cracks and delamination, resulting in complex failure modes under cyclic loading. The results of the tensile tests demonstrated that the orientation of the fibers has a significant impact on the mechanical behavior of the material. The ±15° configuration demonstrated superior tensile strength and modulus, while the ±30° and multilayer configurations exhibited higher ductility. The results of the fatigue testing confirmed that fiber orientation has a significant impact on fatigue life, with the ±15° configuration proving to be the most resistant. Microscopic analysis indicated that pores act as damage initiation points, accelerating failure through matrix cracking, fiber-matrix debonding, and delamination. This study highlights the need for improved porosity control during manufacturing to enhance the durability of hydrogen storage systems. Additionally, it provides valuable insights for optimizing fiber orientation to improve fatigue performance in practical applications.

Comprehensive properties analysis of epoxy composites synergistically toughened with liquid nitrile rubber and polyethersulfone

In this paper , epoxy resin (EP) composites with different phase structures were prepared by introducing hydroxyl-terminated liquid nitrile rubber (HTBN) and hydroxyl-terminated polyethersulfone (PES) individually or simultaneously into the resin matrix. The results revealed that the rational distribution of phase structure of rigid PES and flexible HTBN can effectively contributed to the enhancement in their mechanical and electrical insulation strengths. The synergistic effect of the two reinforcing fillers granted the optimized ternary composite a tougher structural network, leading to significant improvements of 73.13% and 18.98% in mechanical impact strength and electrical breakdown strength, respectively, compared to the pristine EP. Furthermore, compared to HTBN, PES exhibited inhibited HTBN dielectric interfacial polarization and EP molecular chain segment relaxation, resulting in decreased dielectric constant and loss in the composites. This study provide insights into the dielectric properties and design strategies for the development of resin-based dielectric materials, ensuring their broader applicability.