Search Results (187)

The expired drug Detralex (90% diosmin and 10% hesperidin), known as an effective corrosion inhibitor, was adsorbed onto mesoporous silica and incorporated into an epoxy matrix to enhance the coating’s corrosion protection in a highly corrosive 3 wt% NaCl solution. It was found that this treatment, by improving adhesion, modifying the hydrophilic properties, and enabling inhibitor release, increased the coating’s resistance over time. Based on an SEM-EDX analysis, even after 24 h of immersion, the epoxy coating with mesoporous nanosilica adsorbed with diosmin and hesperidin retained the incorporated inhibitors. This resulted in a slight increase in the samples’ polarization resistance during longer exposure. Full article

Conventional epoxy polymers and their composites are increasingly challenged by environmental concerns, high manufacturing costs, and limited recyclability, necessitating the exploration of sustainable alternatives. Many research groups have sought to develop alternate polymers from various renewable resources, such as lignin, polyphenols, natural resins, saccharides, and plant oils. This new type of polymer has led to the emergence of bio-based polymers, which are often used with different reinforcements as bio-based composites. In this review, the synthesis of different bio-epoxy resins is discussed in detail along with their chemical structures. Subsequently, the enhancements in the properties of these bio-composites with the addition of different nanomaterials such as carbonaceous nanofillers (carbon nanotubes, graphene nanoplatelets, graphene oxide, etc.), cellulose-based nanomaterials, inorganic nano-silica (spherical and mesoporous), and nano-clay is explained. Lastly, the properties of these bio-composites and their applications in civil engineering are highlighted. This review has provided a detailed overview of the developments in bio-composites that can be used as a guide for the development of a new class of bio-composites using other alternate resources. Full article

Quartzites containing malachite–azurite mineralization identified in the Kırşehir region (Central Anatolia, Türkiye) are located within the Kırşehir Massif. This study aims to comprehensively characterize the mineralogical, petrographic, geochemical, and gemological properties of these quartzites and to evaluate their potential as ornamental and decorative stones. Due to their characteristic green and blue colors, malachite and azurite possess significant aesthetic value. Their occurrence within silica-rich and mechanically resistant quartzites enhances the visual appearance of the host rock while maintaining its structural integrity. Petrographic observations indicate that the quartzites exhibit a granoblastic texture composed of interlocking quartz crystals. Malachite–azurite mineralization is structurally controlled by NW–SE-trending fracture systems and occurs predominantly as fracture-filling and cavity-coating phases, indicating an epigenetic origin related to post-metamorphic fluid circulation. Geochemical analyses reveal that the samples are dominated by SiO₂ (~95.33 wt.%), with CuO (~1.77 wt.%) and elevated Cu contents (3205 ppm) confirming the presence of copper carbonate mineralization. Although the high silica content contributes to overall mechanical strength, the relatively low Mohs hardness (3–4) and chemical sensitivity of malachite and azurite represent important limitations. Quantitative gemological measurements further indicate that quartz-rich domains exhibit high hardness values (up to ~907 HL), whereas malachite–azurite-bearing zones display significantly lower hardness (~735 HL) due to fracture-controlled heterogeneity and the presence of softer carbonate phases. Surface brightness measurements show moderate to high gloss values (~73–80 GU), with noticeable improvement following epoxy impregnation. These results demonstrate that while the material exhibits favorable optical properties, its mechanical performance is strongly influenced by mineralogical contrasts and structural discontinuities. Quartzites bearing malachite–azurite mineralization are therefore suitable primarily for decorative stones, ornamental objects, and small-scale jewelry applications rather than high-quality gemstones. The striking color contrast between azurite, malachite, and quartz enhances their visual appeal, and with appropriate stabilization techniques, their durability and economic value can be partially improved. Full article

Epoxy resins are widely used thermosetting polymers, but their limited toughness and flexural resilience restrict broader applications. In this study, diglycidyl ether of bisphenol A (DGEBA) epoxy was reinforced with 5 wt.% ceramic fillers of different origins: sol–gel alumina calcined at 550 °C (γ-Al₂O₃) and 1000 °C (α-Al₂O₃), silica derived from rice husk, silica from diatomaceous earth, and a hybrid alumina–silica mixture prepared by sol–gel and calcined at 1000 °C. Fillers were structurally characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field-emission scanning electron microscopy (FESEM). Mechanical properties were evaluated through tensile (ASTM D638) and flexural (ASTM D790) testing. All reinforcements enhanced the performance of neat epoxy. γ-Al₂O₃ provided superior tensile reinforcement compared to α-Al₂O₃, underscoring the importance of particle morphology and surface reactivity. The hybrid alumina–silica filler achieved the highest flexural strength of 50.6 MPa, compared to 9.91 MPa for the neat epoxy. Bio-derived silica showed improved flexural properties, although its tensile reinforcement was less pronounced compared to the sol–gel derived fillers. These results establish clear structure–property relationships and confirm that filler phase, morphology, and calcination temperature critically govern the mechanical performance of epoxy composites. Full article

This study reported highly dispersible mesoporous silica (MSP) with a uniform particle size, which was used as host to load 1,10-Phenanthroline (Phen) to prepare Phen@MSP microcontainer. Improving the dispersion of microcontainers prevents performance degradation caused by their agglomeration. Phen can form a red-colored complex with Fe²⁺ ions generated during corrosion of steel substrate, enabling early corrosion warning while also acting as a corrosion inhibitor to suppress further corrosion of the substrate. Phen@MSP microcontainers were incorporated into a waterborne epoxy (EP) resin to construct a coating with dual functionality of corrosion self-diagnosing and self-healing. As a key component, the average diameter of Phen@MSP microcontainers is approximately 1 μm, with a Phen loading rate of 18.45 wt.% in the microcontainers. Surface observation shows that substrate corrosion can be detected within 10 min by the appearance of red color. After 30 d of immersion in 3.5 wt.% NaCl solution, the impedance modulus value (|Z|_0.01Hz) of the 5 wt.% Phen@MSP coating (2.27 × 10⁹ Ω·cm²) on Q235 carbon steel substrate is five orders of magnitude higher than that of the blank coating (8.79 × 10³ Ω·cm²). Salt spray tests demonstrate that the 5 wt.% Phen@MSP coating effectively suppressed corrosion propagation on the substrate. Full article

High-cycle fatigue (HCF) behavior of multi-scale hybrid composites remains a critical area of investigation for advanced applications in aerospace and automotive industries. This study aims to experimentally investigate and optimize the HCF performance of carbon–Kevlar/epoxy hybrid composites through synergistic incorporation of nano-silica (nSiO₂) and nano-graphene (nGr). Laminates were fabricated using a hand lay-up process followed by press molding, with a [2 carbon fiber/4 Kevlar fiber/2 carbon fiber] stacking sequence. Sixteen material configurations were investigated based on a Taguchi design of experiment (DOE), with two input parameters (nanoparticle percentages) at four different levels each. Following tensile screening tests, three optimal formulations were selected for fatigue evaluation alongside a non-reinforced baseline. Axial fatigue tests were conducted under load-controlled conditions with a stress ratio of R = 0.01 at a constant frequency of 5 Hz. Stress levels were set at 65%, 70%, and 75% of the ultimate tensile strength (UTS), which ranged from 211 MPa for the baseline composite to 390 MPa for the optimal hybrid formulation (1.2 wt.% nSiO₂ and 0.75 wt.% nGr). Scanning electron microscopy (SEM) analysis of fracture surfaces was performed to correlate microstructural features with fatigue performance. The results demonstrate a remarkable synergistic effect. The optimal hybrid nanocomposite exhibited superior fatigue life, sustaining significantly higher maximum stress (253 MPa vs. 137 MPa at 65% UTS) and achieving a life increase of several-fold compared to the non-modified baseline. SEM observations revealed that this enhancement stems from complementary microstructural mechanisms: nSiO₂ particles are uniformly dispersed without agglomeration, providing matrix toughening through crack deflection, while nGr sheets enhance interfacial adhesion, as evidenced by complete matrix coverage on fiber surfaces. The optimal formulation uniquely displays both mechanisms operating simultaneously, creating a true multi-scale reinforcement architecture. In contrast, sub-optimal formulations showed nanoparticle agglomerations that acted as stress concentrators under cyclic loading, explaining their intermediate fatigue performance despite high static strength. Full article

This study investigates the effects of the co-curing process and nanoparticle reinforcement on the mechanical performance of plain-woven glass fiber-reinforced plastic (GFRP) adhesive joints, aiming to address the limitations of traditional fastening methods and the inherent brittleness of epoxy adhesives. Specifically, spherical silica (SiO₂) and plate-like graphene nanoplatelets (GNPs) were incorporated into the epoxy matrix at varying concentrations (0.25 to 1.0 wt.%) to evaluate the influence of particle geometry on joint integrity. Experimental results demonstrated that the co-curing technique yields superior mechanical properties compared to secondary bonding, exhibiting improvements of 35% in shear strength (from 10.97 MPa to 14.83 MPa) and 12% in flexural strength (from 72.57 MPa to 81.28 MPa) due to enhanced chemical interlocking. Furthermore, the addition of nanoparticles significantly improved joint performance, with the optimal content identified at 0.75 wt.% for both particle types. Notably, GNPs outperformed SiO₂, enhancing shear and flexural strengths compared to the neat co-cured baseline. Ultimately, the 0.75 wt.% GNP-reinforced material exhibited a shear strength of 21.22 MPa and a flexural strength of 104.09 MPa. Morphological analysis revealed that while SiO₂ contributes to reinforcement primarily via crack deflection, the high-aspect-ratio GNPs provide superior energy dissipation through crack bridging and pull-out mechanisms. Consequently, this study suggests that the co-curing process combined with an optimal concentration of GNPs presents a highly effective strategy for maximizing the reliability and structural efficiency of composite joints in weight-critical applications. Full article

The increasing demand for sustainable and environmentally friendly construction materials has spurred interest in biopolymer composites reinforced with agricultural waste. Rice husk (RH), a byproduct of rice milling, is abundant and rich in lignocellulosic fibers and silica, making it excellent for use in fiber-reinforced biopolymers. The novelty of this study lies in its integrated and construction-oriented evaluation of rice husk (RH)-reinforced biopolymers, combining mechanical, thermal, environmental, and economic perspectives within a single framework. The study introduces a novel comparative approach by benchmarking multiple polymer matrices-including PP, recycled HDPE, epoxy, PLA, and bio-binders-under unified quantitative performance criteria. Another key novelty is the identification of the dual functional role of silica-rich RH in simultaneously enhancing structural strength and flame retardancy while contributing to carbon emission reduction. With a high silica content (15–20%) and lignocellulosic structure, RH serves as a natural filler that enhances the performance of polymer matrices such as polypropylene (PP), epoxy, polylactic acid (PLA), and recycled polyethylene. Mechanically, RH-reinforced composites demonstrate significant improvements in tensile, flexural, and impact strength. For example, PP composites with NaOH-treated RH and coffee husks achieved tensile strengths between 27.4 MPa and 37.4 MPa, with corresponding Young’s modulus values ranging from 1656 MPa to 2247.8 MPa. Recycled HDPE-RH blends reached tensile strengths up to 74 MPa and flexural values of 39 MPa, validating their structural applicability. Epoxy matrices embedded with 0.45 wt.% RH nanofibers showed degradation thresholds of 411 °C and 678 °C, reflecting substantial thermal resistance. Flame retardancy is further improved by the presence of RH biochar, which leads to reduced peak heat release rate (PHRR) and enhanced char formation. In building insulation applications, RH-based composites exhibit low thermal conductivity values between 0.08 and 0.14 W/m·K, contributing to energy efficiency. Economically, RH reduces material costs by 30–40%, while environmentally, its integration lowers carbon emissions in PP composites by up to 10%, and promotes biodegradability. Despite challenges such as moisture absorption and interfacial adhesion, these can be mitigated through alkali treatment, compatibilizers (e.g., MAPP), or hybrid reinforcement strategies. Full article

Natural fibre-reinforced composites (NFCs) have attracted attention as sustainable alternatives to synthetic fibre composites. However, their hydrophilic nature and susceptibility to moisture absorption, especially in combination with process-related defects, can compromise long-term performance. This study critically examines the effects of hydrophobic fumed silica, incorporated into an epoxy matrix, on the processing, moisture uptake, and mechanical properties of flax/epoxy laminates produced via resin transfer moulding (RTM). Epoxy systems containing 0–5 wt% silica were characterised in terms of particle dispersion, rheological properties, thermal behaviour, and water absorption. Corresponding laminates were analysed for void content, Fickian diffusion behaviour, and tensile performance in dry and saturated states. Despite its hydrophobic surface treatment, silica increased resin water uptake and, at 5 wt%, led to a substantial rise in viscosity, poor fibre impregnation, and increased porosity. The resulting laminates exhibited faster and higher moisture uptake and significantly reduced wet mechanical properties, especially for highly filled systems. While thermal stability improved slightly, the overall findings revealed that the chosen silica-based matrix modification led to clear trade-offs and processing limitations under RTM conditions. This study highlights the importance of assessing such limitations early in the design process and demonstrates that the selected silica type is not a viable strategy for improving moisture resistance in NFCs. Full article

High-temperature proton exchange membranes (HT-PEMs) are critical components of high-temperature fuel cells, facilitating proton transport and acting as a barrier to fuel and electrons; however, their performance is hampered by persistent issues of phosphoric acid leaching and oxidative degradation. Herein, a novel HT-PEM with abundant hydrogen bond network is constructed by incorporating nanoscale polyhedral oligomeric silsequioxane functionalized with eight pendent sulfhydryl groups (POSS-SH) into poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) matrix. POSS, a cage-like nanostructured hybrid molecule, features a well-defined silica core and highly designable surface organic groups, offering unique potential for enhancing membrane performance at the molecular level. Through controlled reactions between sulfhydryl groups and allyl glycidyl ether (AGE), two functional POSS crosslinkers—octa-epoxide POSS (OE-POSS) and mixed sulfhydryl-epoxy POSS (POSS-S-E)—were synthesized. These were subsequently used to fabricate crosslinked OPBI membranes (OPBI-OE-POSS and OPBI-POSS-S-E) via epoxy–amine coupling. The OPBI-POSS-S-E membranes demonstrated exceptional oxidative stability, which is attributed to the free radical scavenging ability of the retained sulfhydryl groups on the nano-sized POSS framework. After soaking in Fenton’s reagent at 80 °C for 108 h, the OPBI-POSS-S-E-20% membrane retained 79.4% of its initial weight, significantly surpassing both the OPBI-OE-POSS-20% and pristine OPBI membranes. The PA-doped OPBI-POSS-S-E-20% membrane achieved a proton conductivity of 50.8 mS cm⁻¹ at 160 °C, and the corresponding membrane electrode assembly delivered a peak power density of 724 mW cm⁻², highlighting the key role of POSS as a nano-modifier in advancing HT-PEM performance. Full article

The emulsification of a molten fusible metal alloy in a liquid epoxy matrix with its subsequent curing is a novel way to create a highly concentrated phase-change material. However, numerous challenges have arisen. The high interfacial tension between the molten metal and epoxy resin and the difference in their viscosities hinder the stretching and breaking of metal droplets during stirring. Further, the high density of metal droplets and lack of suitable surfactants lead to their rapid coalescence and sedimentation in the non-cross-linked resin. Finally, the high differences in the thermal expansion coefficients of the metal alloy and cross-linked epoxy polymer may cause cracking of the resulting phase-change material. This work overcomes the above problems by using nanosilica-induced physical gelation to thicken the epoxy medium containing Wood’s metal, stabilize their interfacial boundary, and immobilize the molten metal droplets through the creation of a gel-like network with a yield stress. In turn, the yield stress and the subsequent low-temperature curing with diethylenetriamine prevent delamination and cracking, while the transformation of the epoxy resin as a physical gel into a cross-linked polymer gel ensures form stability. The stabilization mechanism is shown to combine Pickering-like interfacial anchoring of hydrophilic silica at the metal/epoxy boundary with bulk gelation of the epoxy phase, enabling high metal loadings. As a result, epoxy shape-stable phase-change materials containing up to 80 wt% of Wood’s metal were produced. Wood’s metal forms fine dispersed droplets in epoxy medium with an average size of 2–5 µm, which can store thermal energy with an efficiency of up to 120.8 J/cm³. Wood’s metal plasticizes the epoxy matrix and decreases its glass transition temperature because of interactions with the epoxy resin and its hardener. However, the reinforcing effect of the metal particles compensates for this adverse effect, increasing Young’s modulus of the cured phase-change system up to 825 MPa. These form-stable, high-energy-density composites are promising for thermal energy storage in building envelopes, radiation-protective shielding, or industrial heat management systems where leakage-free operation and mechanical integrity are critical. Full article

Adsorption chillers can produce chilled and desalinated water using low-grade heat, but their performance is limited by low coefficient of performance (COP) and large system mass. Enhancing heat and mass transfer in the sorbent bed is key to improving efficiency. This work introduces and systematically evaluates binder-stabilized silica gel composites as a structural and thermal enhancement strategy for adsorption chillers. Silica gel composites bonded with epoxy resin and polyvinyl alcohol (PVA) were evaluated for adsorption chiller applications. Thermal stability, conductivity, microstructure, equilibrium sorption, and sorption hysteresis were assessed. The results indicate that PVA-based composites were thermally unstable and discarded, whereas epoxy-bonded silica gel showed high thermal stability and mechanically robust granules with preserved pore connectivity. The epoxy composite exhibited 109% higher thermal conductivity than loose silica gel, improving internal heat transfer. This improvement is accompanied by a reduction in sorption capacity of approximately 58%, attributable to the inert resin fraction. Notably, the composite exhibits a reduced and locally negative sorption hysteresis, indicating facilitated desorption and lowered internal diffusion resistance. The epoxy-bonded silica gel therefore provides a promising combination of thermal stability, improved heat transfer, and enhanced sorption–desorption behaviour, supporting its potential to increase the efficiency of next-generation adsorption chillers. Full article

The bioinspired superhydrophobic surfaces have demonstrated many fascinating performances in fields such as self-cleaning, anti-corrosion, anti-icing, energy-harvesting devices, and antibacterial coatings. However, developing a low-cost, feasible, and scalable production approach to fabricate robust superhydrophobic surfaces has remained one of the main challenges in the past decades. In this paper, we propose an uncommon method for the fabrication of a durable superhydrophobic coating on the surface of the glass slide (GS). By utilizing the screen printing method and high-temperature curing, the epoxy resin grid (ERG) coating was uniformly and densely loaded on the surface of GS (ERG@GS). Subsequently, the hydrophobic silica (H-SiO₂) was deposited on the surface of ERG@GS by the impregnation method, thereby obtaining a superhydrophobic surface (H-SiO₂@ERG@GS). It is demonstrated that the micro-grooves in ERG can provide a large specific surface area for the deposition of low surface energy materials, while the micro-columns can offer excellent protection for the superhydrophobic coating when it is subjected to mechanical wear. It is important to note that micro-columns, micro-grooves, and nano H-SiO₂ jointly form the micro–nano structure, providing a uniform and robust rough structure for the superhydrophobic surface. Therefore, the combination of a micro–nano rough structure, low surface energy material, and air cushion effect endow the material with excellent durability and superhydrophobic property. The results show that H-SiO₂@ERG@GS possesses excellent self-cleaning property, mechanical durability, and chemical stability, indicating that this preparation method of the robust superhydrophobic coating has significant practical application value. Full article

This study investigates hygrothermal durability of bio-epoxy composites reinforced with carbon, E-glass, basalt, and flax fibres. Fibre yarns and bio-composites were exposed for 3000 h at 60 °C and 98% relative humidity. The tensile strength reduction in the fibres and the interfacial shear strength (IFSS) reduction in the composites were assessed after ageing. Chemical deterioration was evaluated using energy-dispersive X-ray spectroscopy (EDS); morphological changes in fibres and composites fracture surfaces were examined using a scanning electron microscope (SEM). Results indicated that the durability was significantly influenced by fibre types. Tensile strength reduction was higher in carbon, glass and basalt compared to flax yarns because of chemical degradation of the sizing layer in synthetic fibres, while only physical damage was observed in flax. The IFSS reduction was highest in flax composites (10%), and lowest in carbon (4%). EDS indicated the hydrolysis and erosion of fibre sizing, with reduced silica content in glass and basalt fibres. SEM revealed matrix-dominated failure in carbon/bio-epoxy, interfacial debonding in glass and basalt composites, fibre slip and pull-out in flax/bio-epoxy. Overall, the results highlighted damage propagation pathways and demonstrated that bio-epoxy composites exhibited reasonable performance under hygrothermal ageing, supporting their potential as a sustainable alternative in durability-critical applications. Full article

Concrete is prone to deterioration and increased permeability under cryogenic freeze–thaw cycles. In this study, a novel method was proposed to prepare a nano-silica-modified epoxy resin composite coating with excellent anti-permeability. The effects of layer composition, a resin layer modified with different nanoparticles, and different nano-silica dosages on the oil impermeability of coated concrete were studied. The mechanical properties and chemical stability of the composite coating were also evaluated. The results showed that the composite coating composed of a nano-silica-modified resin layer, bonding layer, and surface layer presented good resistance to oil penetration under cryogenic freezing cycles. Moreover, nano-silica seemed to be a better choice for resin modification than nano-TiO₂ and graphene. Macroscopic and morphological observation also confirmed a reduction in cracks and the integrity of the composite coating for concrete protection. Therefore, the coated concrete presented good mechanical properties and chemical stability. This study provides a guide for the preparation of composite coating concrete used for mountainous highway bridges and liquefied natural gas tanks. Full article