Epoxy Composites Research Articles

The Impact of ZnO Nanofillers on the Mechanical and Anti-Corrosion Performances of Epoxy Composites.

Epoxy resins were reinforced with different ZnO nanofillers (commercial ZnO nanoparticles (ZnO NPs), recycled ZnO and functionalized ZnO NPs) in order to obtain ZnO-epoxy composites with suitable mechanical properties, high adhesion strength, and good resistance to corrosion. The final properties of ZnO-epoxy composites depend on several factors, such as the type and contents of nanofillers, the epoxy resin type, curing agent, and preparation methods. This paper aims to review the preparation methods, mechanical and anti-corrosion performance, and applications of ZnO-epoxy composites. The epoxy-ZnO composites are demonstrated to be valuable materials for a wide range of applications, including the development of anti-corrosion and UV-protective coatings, for adhesives and the chemical industry, or for use in building materials or electronics.

Degradable, Lightweight, and High-Performance Unidirectional Nanocellulose-Long-Filament-Reinforced Vanillin Epoxy Composites for Structural Applications

Degradable, Lightweight, and High-Performance Unidirectional Nanocellulose-Long-Filament-Reinforced Vanillin Epoxy Composites for Structural Applications

Towards greener wind power: Nanodiamond-treated flax fiber composites outperform standard glass fiber composites in impact fatigue tests

Wind energy is facing two major problems, recyclability of wind turbine blades, primarily made from fiberglass, and rain erosion on the blade’s leading edges. Here, we show that flax fiber reinforced epoxy composites have less impact fatigue damage than glass fiber (GF) composites made with the same resin. The novel treatment of flax with non-toxic nanodiamonds even boosts its outstanding performance. Nanodiamond-treated flax fiber (FFND) composites exhibit a damage incubation period up to 17 times as long as GF composites and have at least 74% less mass loss. This is connected to lower initial impact pressure, less shock wave reflections and better impact absorption of flax composites. The nanodiamonds act as fiber sizing, strengthening the fibers and their matrix interface. This delays fracturing and results in less erosion, making the biodegradable FFND a promising replacement for GF towards a fabrication of more sustainable and longer lasting wind turbine blades.

Effect of hygrothermal aging on the friction behavior and wear mechanism of the multi-filler reinforced epoxy composites for coated steel

Polymer-based composites for steel structure coating are an effective strategy to improve tribological properties and service durability under hygrothermal aging conditions. In the present paper, epoxy resin was improved by mechanical reinforcement and frictional lubrication fillers, and a kind of multi-filler reinforced epoxy composite (MFREC) was successfully prepared. Water uptake behavior, mechanical and thermal property evolution, friction behavior and wear mechanism as well as micro-topography analysis of MFREC under hygrothermal aging were conducted and discussed in detail. The research results showed that the water uptake curve of MFREC after distilled water and 5 wt% NaCl water solution immersions confirmed the two-stage diffusion model, where the quasi-equilibrium water uptakes were 4.23% and 3.67%, respectively. Additionally, the fundamental reason for the degradation of the mechanical and thermal properties of MFREC was the hydrolysis of the resin and the de-bonding of the fillers/matrix interface. The interface shear strength of MFREC adhesive and steel gradually decreased with the hygrothermal aging, but did not lose the bonding property, because the uniformly dispersed multi-fillers can fill the internal defects of the matrix and prolong the crack propagation path to block the effect. Before hygrothermal aging, MFREC had excellent friction and wear resistance compared to resin matrix, especially under water lubrication conditions. The anti-wear rate of MFREC increased by up to 59.6% compared to the room temperature dry test environment due to the coupling effects of the water lubrication and anti-friction characteristics of modified fillers. Hygrothermal aging had little effect (＜12%) on the friction coefficient of MFREC, but the anti-wear properties decreased significantly, especially the Ws increased by 255.1% under the 60 °C immersion condition. Because the degradation of thermal/mechanical properties was not enough to resist the high shear stress of the steel ball, leading to severe fatigue wear.

Flax–Reinforced Vitrimer Epoxy Composites Produced via RTM

Composite laminates were produced by RTM using similar glass and flax fabrics and both vitrimer epoxy and aerospace-grade epoxy, both formulated for liquid molding. Tensile and flexural properties were measured and compared, revealing that the vitrimer composites exhibited equivalent performance in flexural strength and tensile modulus, but slightly lower performance in tensile strength relative to reference epoxy composites. In general, glass–fiber composites outperformed flax–fiber composites in tension. However, both glass and flax–fiber composites yielded roughly equivalent flexural strength and tensile modulus-to-weight ratios. Flax fabrics were recovered from composites by matrix dissolution, and a second-life laminate showed full retention of the mechanical properties relative to those produced from fresh flax. Finally, a demonstration of re-forming was undertaken, showing that simple press-forming can be used to modify the composite shape. However, re-forming to a flat configuration resulted in local fiber damage and a decrease in mechanical properties. An alternative forming method was demonstrated that resulted in less fiber damage, indicating that further refinements might lead to a viable forming and re-forming process.

Cyclic behaviour of 3D-woven composites in tension: Experimental testing and macroscale modelling

Composites with 3D-textile reinforcement present several engineering advantages. However, their intricate yarn architecture also creates a material with a number of nonlinear behaviours and features, which need to be understood in order to enable their efficient use. To demonstrate the anisotropic development of such non-linear behaviours, and how they depend on loading mode, tensile samples of a 3D-woven layer-to-layer angle interlock carbon-fibre reinforced epoxy composite are tested experimentally (data shared publicly). More specifically, specimens are cut and tested at orientations of 0°, 15°, 30°, 45° and 90° relative to the direction of the warp yarns. The samples are tested cyclically by loading and unloading them at progressively higher displacement values. By monitoring the reduction in stiffness and the development of permanent strains it is possible to identify material parameter values used to calibrate an anisotropic macroscale elasto-plastic damage model. The model shows promising agreement with the experimental results.

Experimental investigation on the tensile, flexural, and thermal rigidity of ALON-reinforced Kevlar fabric-impregnated epoxy composites

Experimental investigation on the tensile, flexural, and thermal rigidity of ALON-reinforced Kevlar fabric-impregnated epoxy composites

Investigation of the properties and weathering behaviour of arecanut sheath fibre reinforced epoxy composites

ABSTRACT Engineered materials having unique elements such as reinforcing phases and matrix materials, such as composites, provide improved stiffness, strength, lightweight characteristics, and corrosion resistance. The utilisation of natural fibre composites, which are derived from sustainable resources such as areca nut sheath, is on the rise because of their affordability, favourable strength-to-weight ratio, and lightweight characteristics. These composites offer a more environmentally friendly option to traditional synthetic fibre composites while also reducing the negative effects of production processes on the environment. The development of these composites has been greatly aided by areca nut sheath fibre epoxy composites, which have applications in construction materials, biodegradable packaging, and other areas. In this research, areca nut sheath reinforced epoxy composites were tested for their mechanical and thermal characteristics along with their durability (weathering). It was observed that areca nut sheath fibre reinforcement improved both the tensile, flexural and impact properties of the composites due to their effective reinforcement, fibre–matrix interaction and load bearing capability. However, this study demonstrates that composites containing 20% areca nut sheath fibres have the best tensile and flexural strengths. Weathering studies revealed that the durability slightly decreased upon exposure to moisture and vermicompost due to moisture intake by the fibres.

Evaluation of surface response of SiC and fly ash-filled Prosopis juliflora fibre-reinforced epoxy composites under dry sliding wear conditions using Taguchi method

Prosopis juliflora (PJ) fibre-reinforced polymer composites are fabricated with fly ash and SiC as fillers with different weight percentages. Jute layers are also sandwiched for added strength in the structure. The wear behaviour is found for the prepared composition of samples. Pin-on-disc wear testing apparatus is used for the wear performance along with the design of experiments approach using orthogonal arrays of Taguchi’s. The effect of the input parameters (load, sliding velocity, speed) is studied on wear resistance. The experimental design creates sliding wear evaluations based on Taguchi’s L9 orthogonal array to identify the most dominating factors influencing the wear rate. This study demonstrates that the most important component affecting the sliding wear rate of the composite materials is followed by the sliding velocity, speed, and load. The result of the wear rate decreases with an increase in filler content and also increases with sliding velocity. The samples with fly ash and SiC fillers reportedly seemed to have the best wear rates.

Simultaneous enhancement of thermal and dielectric properties of Ba0.8Sr0.2TiO3 and h‐BN co‐doped epoxy hybrid composites under high frequencies and temperatures

AbstractEpoxy resin (EP) is widely employed in power systems and electronic devices due to its low cost and easy processing along with good insulative and adhesive properties. However, EP insulation properties are compromised at elevated frequencies and temperatures because of its negative temperature coefficient effect (NTC) and poor thermal characteristics. In this context, barium strontium titanate (BST‐60), a positive temperature coefficient (PTC) filler, and hexagonal boron nitride (h‐BN), a thermally conductive filler, both surface‐modified with dopamine, are added in EP to simultaneously improve thermal and dielectric insulation properties at high temperatures and high frequencies. This study finds that below the Curie point of BST, the insulating properties of h‐BN fillers significantly contributes to improving insulation properties. Conversely, above the Curie point, the insulating nature of BST fillers leads to an improvement in the insulation performance of composites. Furthermore, at elevated frequency and temperature, the nano h‐BN enhances thermal conductivity of EP by establishing a thermally conductive network, while micro‐BST suppresses the NTC effect of EP by regulating electrical resistivity above the Curie point. The Heywang model elucidates the PTC effect of BST fillers, while a proposed heat conduction‐dissipation mechanism explains the behavior of incorporated fillers at different temperatures.Highlights PDA‐modified Ba0.8Sr0.2TiO3 and h‐BN co‐doped epoxy composites are prepared. Negative temperature coefficient effect of epoxy is mitigated by PTC fillers. The optimal wt.% of filler enhances both dielectric and thermal properties. Dielectric properties are explored at high frequencies and temperatures. Optimized epoxy composites are suitable for high‐frequency applications.

The noteworthy tensile plasticity and strength of CoFeSiB metallic glass fiber reinforced epoxy composites

AbstractMetallic glass fibers have high strength, poor plasticity and low Young's modulus. In this study, it was used as a reinforcement to prepare metallic glass fiber reinforced epoxy composites with different fiber volume contents (20%, 30%, 40%, and 50%). The effect of fiber volume contents on the tensile properties of the metallic glass fiber reinforced epoxy composites was studied by experiment and the finite element analysis method. The experiment and simulation results are in good agreement. The tensile strength and plasticity of the metallic glass fiber reinforced epoxy composites increase with the increase of fiber volume contents. When the fiber volume content is 40% or 50%, a sharply necking feature appeared on the fibers and exhibited improved plasticity, due to the formation of interacting and arresting events of shear bands occurring at the interface between the metallic glass fibers and the epoxy. In addition, the strain hardening due to plastic deformation of the metallic glass fibers further enhanced the tensile strength of the metallic glass fiber reinforced epoxy composites. This is a first step toward toughening the inherently brittle metallic glass fibers under tensile conditions.Highlights A novel CoFeSiB metallic glass fiber reinforced epoxy resin composite The increase of fiber volume fraction improves the tensile strength and plasticity of fiber reinforced composites. The strain hardening due to plastic deformation of the metallic glass fibers further enhanced the tensile strength of the metallic glass fiber reinforced epoxy composites.

Life cycle assessment of Luffa‐reinforced epoxy composites: Untreated versus chemically treated fibers

AbstractThis research conducts a comprehensive cradle‐to‐gate life cycle assessment, comparing four distinct epoxy composites with each other and with the pure matrix. The composites investigated include epoxy resin reinforced with 25% and 50% untreated Luffa cylindrica fiber mats and 25% and 50% chemically treated Luffa cylindrica mats. The study defines the functional unit concerning the load at the fracture point and explores a real‐world scenario related to a potential industrial installation in southeastern Europe. The assessment utilizes 22 ReCiPe 2016 endpoint indicators to quantify impacts on human health, ecosystems, and resource availability. The findings indicate that the 50% chemically treated Luffa cylindrica‐reinforced epoxy has the least environmental impact, closely followed by the 50% untreated Luffa cylindrica. All four composites exhibit lower impacts than the pure epoxy resin. Notably, the 50% Luffa‐reinforced composites stand out as significantly environmentally favorable due to the substitution of fossil‐derived resin with natural fibers. This study underscores the potential of Luffa cylindrica as a promising and eco‐friendly reinforcement for epoxy composites.

Performance evaluation of kevlar fiber reinforced epoxy composite by depositing graphene/SiC/Al2O3 nanoparticles

The synergistic effect of adding Silicon Carbide (SiC), Aluminum Oxide (Al2O3), and Graphene (GR) nanoparticles into Kevlar fiber-reinforced epoxy composites is investigated in this study. Within the epoxy matrix and Kevlar fibre reinforcement, these nanoparticles come in a variety of compositions. The mechanical and flammability features of the composite are revealed by experimental evaluation. Of the nanoparticles, graphene performs the best; the composite reinforced with graphene shows 324 MPa of tensile strength, 8 J/mm of impact strength, and 75.2 HRC of hardness. The composite layers' interior structure is investigated using scanning electron microscopy examination. To evaluate thermal stability of the composition the thermogravimetric (TG) and the differential thermal analysis (DTA) investigations were performed. Thermal stability is achieved by the graphene-reinforced composite at 775 °C. Additionally, corrosion tests and water absorption tests were conducted to assess the material's moisture sensitivity. The overall goal of the research is to ascertain whether adding various nanoparticles to Kevlar produces the best outcomes; graphene has demonstrated promising results in terms of improving mechanical and thermal stability.

High-performance carbon fiber-reinforced epoxy resin composites based on novel, environmentally friendly, stability, and heat-moisture resistant nano emulsion encapsulated POSS sizing agent interface modification

Considering the development of CFRPs, addressing the challenge through the simplistic industrial operational methods to achieve high strength and toughness in carbon fiber-reinforced epoxy resin (EP) composites (CFRPs) is imperative. In this work, an innovative approach introduced to improve the strength and toughness of CFRPs by application of a nano emulsion encapsulated polyhedral oligomeric silsesquioxane (POSS) sizing agent (POE sizing agent). The employment of a POE sizing agent markedly enhanced the surface energy and roughness of carbon fibers (CF) as well as the interface properties of CFRPs. Furthermore, the 10-PCF (10 wt% POE sizing CF) reinforced EP unidirectional CFRPs demonstrated superior strength and toughness. Relative to the DCF (Desizing CF) reinforced EP unidirectional CFRPs, their interlaminar shear strength, flexural strength, and unnotched impact strength increased by 24.9 %, 37.8 %, and 45.6 %, respectively, reaching 99.8 ± 2.3 MPa, 1376.8 ± 21.6 MPa, and 94.9 ± 4.6 kJ/m2. Concurrently, the 10-PCF reinforced EP composite laminates exhibited outstanding impact resistance, minimal damage area, and enhanced compressive strength after impact. Additionally, the strength, bundling, and flexibility of the sized CF were maintained, ensuring the processability of CF. The utilization of POE sizing agent for strength and toughness improvement in CFRPs offers a straightforward and industrially feasible approach. This research opens up a novel strategy for high-performance CF and CFRPs preparation.

Hygrothermal aging mechanism of epoxy composites used for medium-frequency transformers

The integration of medium-frequency transformer design and the harsh service environment raise higher demands for the medium-frequency insulation performance of epoxy composites. As epoxy composite's frequency response characteristics and sensitivity to moisture intrusion are still unknown, its application as the insulation materials of medium-frequency transformers under hygrothermal conditions is limited. This paper investigates the mechanism of moisture intrusion damage to the molecular structure of the epoxy resin matrix and its cross-linking points with the curing agent. The regularity of medium-frequency insulation performance degradation of epoxy composites after hygrothermal aging is studied. Results indicate that after 40 days of hygrothermal aging, moisture together with high temperature damaged the main chain of the epoxy resin and its cross-linking points with the curing agent, resulting in a 23 °C decrease in the glass transition temperature and an 82 % decrease in cross-linking density of the epoxy composite. Moisture ionization and the increase of carriers due to epoxy resin hydrolysis lead to an increase in the amount of space charge. The temperature rise caused by dipole steering polarization facilitates the formation of internal conductive pathways in the epoxy composite, resulting in a 73 % decrease in the medium-frequency breakdown strength and a four-order magnitude decrease in the medium-frequency volume resistivity of the epoxy composite. This study can guide the insulation design of high-reliability medium-frequency transformers.

Various Morphologies of Graphitic Carbon Nitride (g-C3N4) and Their Effect on the Thermomechanical Properties of Thermoset Epoxy Resin Composites.

This research aims to highlight the importance of diverse forms of graphitic carbon nitride (g-C3N4) as strengthening elements in epoxy composites. It explores the influence of three different forms of g-C3N4 and their concentrations on the mechanical properties of the epoxy composites. Various characterization techniques, such as scanning electron microscopy (SEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR), were utilized to comprehend the effects of g-C3N4 morphology and particle size on the physical and chemical characteristics of epoxy resin. Mechanical properties, such as tensile strength, strain, modulus, and fracture toughness, were determined for the composite samples. SEM analysis was performed to examine crack morphology in samples with different reinforcements. Findings indicate that optimal mechanical properties were achieved with a 0.5 wt% bulk g-C3N4 filler, enhancing tensile strength by 14%. SEM micrographs of fracture surfaces revealed a transition from brittle to rough morphology, suggesting increased toughness in the composites. While the TGA results showed no significant impact on degradation temperature, dynamic mechanical analysis demonstrated a 17% increase in glass transition temperature. Furthermore, the improvement in thermal breakdown up to 600 °C was attributed to reinforced covalent bonds between carbon and nitrogen, supported by FTIR results.

Preparation of bio-based trinity lignin intumescent flame retardant and its effect on burning behavior and heat transfer process of epoxy resin composites

The thermal insulation performance of intumescent coating coated on the surface of steel structure is of great significance to prevent the underlying steel structure from collapse in fire. Bio-based intumescent flame retardants gradually attract many attentions due to its environmental friendliness and rich natural sources. In this study, a new bio-based intumescent flame retardant trinity lignin intumescent flame retardant (TLI) is synthesized, which is added to epoxy resin (EP) to prepare EP/TLI epoxy intumescent coatings. The burning behavior of EP/TLI epoxy intumescent coatings is investigated by thermogravimetric (TG) analysis, limit oxygen index (LOI), vertical burning test and cone calorimeter test. Microscopic morphology of char layer is observed by scanning electron microscopy (SEM). The results show that when the TLI addition content is 20 wt% (EP/TLI-4), LOI reaches 26.5 %, UL-94 is V-0 rating. Compared to pure EP, the peak heat release rate (pHRR) and total heat release (THR) of EP/TLI-4 coating are reduced by 82.20 % and 78.27 %, respectively. The influence of chemical formulations, initial coating thickness and incident heat flux on heat transfer process of EP/TLI epoxy intumescent coatings is also investigated. At the same time, the thermal insulation mechanism of EP/TLI epoxy intumescent coating is presented.

A novel method of reclaiming high-value carbon fiber from waste epoxy composite via molten salt thermal treatment

Epoxy resin limits the recycling of high-value carbon fibers from waste epoxy composites: its inferior thermal conductivity requires the excessive pulverization of the polymers, reducing fibers length; its robust cross-linked structure hinders its removal, leading to fiber contamination. Here, we proposed a novel method by using molten salts as an effective medium to enhance heat transfer and thermal reaction. The length and structural integrity of fibers were preserved by minimizing the extent of pulverization and reducing the erosive impact of resin degradation products, respectively. At 375 °C, the resin removal ratio and fiber strength retention both exceeded 99%, with a temperature reduction of at least 100 °C. Molten salts exerted differential inert and active effects on fibers and resin. Fibers could retain 97% of strength retention within salts at 400 °C for 2 h. Conversely, molten salts significantly facilitated the disruption of the resin matrix’s cross-linked structure by catalyzing the cleavage of C-N bonds. The degradation products exhibited a lightweight tendency and could be easily separated from the fiber surface in the fluid environment provided by molten salts, thus protecting the fiber surface against oxidative erosion caused by phenols.

Fabrication of a high-temperature resistant and water-soluble sizing agent to significantly improve the interfacial properties of carbon fiber reinforced epoxy composites

Applying suitable sizing agents is effective in improving the interfacial performance of carbon fiber reinforced composites (CFRPs). However, the poor thermal stability of conventional epoxy-based sizing agent limits their application at elevated temperatures for preparing advanced CFRPs. The question could lead to interfacial damage of composites at high temperatures, thus deteriorating their mechanical properties. In this work, diethanolamine (DEA) was selected to modify E51 resin to obtain a high-temperature resistant sizing agent (E51@DEA). The decomposition temperature of E51@DEA was 320 °C, which was 140 °C higher than that of E51. Furthermore, the resultant composites treated by E51@DEA 2 % showed robust interfacial performance (ILSS = 74.32 MPa, IFSS = 100.70 MPa), which was both increased by about 25 % compared to unmodified samples. In addition, the modified fiber could completely retain their interfacial reinforcement after treatment at 300 °C for 4 h. The prepared composites combined excellent thermal and interfacial properties, further expanding the application range of CFRPs.

BST@Copper Nanowire/Epoxy composites with excellent microwave absorption in the X-band

In this work, hybrid epoxy nanocomposites containing varying loading of copper nanowires (CuNW), Ba0.7Sr0.3TiO3 (BST), and BST@CuNW hybrid nanoparticles were prepared and analyzed for their microwave absorption characteristics. The nanoparticles used in this study were prepared using a facile co-precipitation and hydrothermal methodology. The synthesized nanoparticles were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their morphology and phase determination. While the XRD results confirmed the presence of BST and CuNW, the SEM micrographs obtained on the hybrid BST@CuNW nanoparticles show BST anchored on the CuNW surfaces. A series of epoxy composites containing varying loading of synthesized nanoparticles were prepared and characterized for their microwave properties, such as complex permittivity, shielding effectiveness, and power coefficients. The results indicate that nanocomposites containing BST@CuNW hybrids exhibited enhanced dielectric loss and more significant microwave power absorption compared to samples with equivalent CuNW and/or BST loading. The best composite sample, i.e., a one-millimeter-thick epoxy containing 10:15 (wt/wt) CuNW: BST hybrid nanoparticles with an estimated density of 1.49 g/cc attenuated 99.1 % of incident microwave power and exhibited a shielding effectiveness value of 21.2 dB in the X-band (8–12 GHz) of the microwave frequency spectrum. These lightweight polymer composites with high microwave absorption in the X-band are useful for military and civilian applications.