Search Results (865)

Glass fiber/epoxy (GF/EP) composites are widely used in high-voltage electrical equipment due to their excellent specific strength, durability and dielectric properties. However, long-term exposure to hygrothermal environments will lead to performance degradation of the material, which seriously threatens its service reliability. To solve this problem, accelerated aging tests were systematically carried out in this study by immersing GF/EP specimens in deionized water at room temperature and 80 °C. The performance evolution laws and failure mechanisms of the material were investigated through moisture absorption kinetic analysis, tensile property testing, scanning electron microscope (SEM) fracture observation and breakdown voltage testing. The results show that the initial moisture absorption behavior of the material follows the Fickian diffusion mechanism, and the water diffusion rate at 80 °C is 31.8 times that at room temperature. After 35 days of aging, the retention rate of the maximum tensile force is 86.6% for the room temperature group, while it decreases to 38.2% for the 80 °C group. SEM observations show that the failure mode of the material changes from ductile fracture to brittle fracture after aging at 80 °C, accompanied by serious interfacial debonding. Temperature is the dominant factor for insulation performance degradation: the breakdown voltage retention rate is above 91% at room temperature, while it decreases to about 37% at 80 °C, and the influence of 60% maximum tensile force ($F_{\mathrm{m}\mathrm{a}\mathrm{x}}$) preloading is relatively small. This study provides experimental data and theoretical support for the performance evaluation and life prediction of GF/EP composites in harsh hygrothermal service environments of high-voltage electrical equipment. Full article

The escalating demand for high-performance dielectric energy storage materials in pulse-power systems and portable electronics calls for polymer film capacitors with high discharged energy density and breakdown strength. Conventional polymers, however, suffer severe performance degradation under concurrent thermal and electrical stress, and existing reinforcement strategies—involving inorganic nanofillers or chemical crosslinking—often compromise flexibility, introduce interfacial defects, or involve complex processing. Herein, we demonstrate that incorporating a rigid mechanically interlocked molecule, specifically an octacationic homo[2]catenane, into a polyimide matrix yields robust, crosslink-like networks through strong [π∙∙∙π] electrostatic interaction between electron-rich aromatic units of polyimide and electron-deficient homo[2]catenane. This supramolecular network simultaneously enhances breakdown strength via densified chain packing and suppresses conduction loss by forming deep electron traps derived from the high electron affinity of homo[2]catenane. The optimized PI–HC⁸⁺ composite achieves a high discharged energy density of 7.86 J/cm³ with an efficiency > 80% and sustains stable performance over 10⁵ charge–discharge cycles at 150 °C. This research establishes mechanically interlocked molecules as a new class of functional fillers for high-performance polymer dielectrics, opening an unexplored avenue in the design of next-generation capacitive energy-storage materials. Full article

This paper systematically investigates the failure characteristics and mechanisms of insulating materials in DC voltage dividers under combined high-frequency voltage and high-temperature conditions via simulations and experiments. The results showed that high-frequency harmonics severely degrade the insulation strength of polypropylene/paper/polypropylene (PPLP) at 10 kHz, in which the bulk breakdown strength of PPLP decreases by over 50%. Furthermore, the surface flashover voltage in oil is reduced by 17.7% under high-frequency voltage alone, and by as much as 51% when white flocculent substances are present in the oil. The dielectric properties of PPLP strongly depend on frequency and temperature, which aggravate the heat accumulation of the divider under high-frequency voltage. Furthermore, the multilayer structure of PPLP introduces deeper trap levels due to interfacial states, which reduce the breakdown strength and flashover voltage of PPLP. Electro-thermal coupling induces a rapid temperature rising to 98 °C at 25 kHz caused by dielectric loss, leading to oil turbidity and white precipitation, consistent with finite element simulations. Consequently, a failure mechanism is proposed as follows: prolonged electro-thermal stress causes chain scission in styrene-containing materials, releasing monomers that repolymerize into white polystyrene deposits. Their porous structure and dielectric mismatch distort the interfacial field, trigger partial discharge, and aggravate surface flashover. Full article

Our investigation into Hibiscus rosa-sinensis fibers (HRFs) for composite applications involved a multi-step process, primarily fiber extraction through water retting and subsequent surface modification by using sodium hydroxide (NaOH) and trimethoxy methyl silane (TMMS). Through the compression molding technique, untreated HRF-reinforced poly-lactic acid (PLA) composites (UHRFCs), NaOH-treated HRF-reinforced PLA composites (NHRFCs), and TMMS-treated HRF-reinforced PLA composites (THRFCs) were fabricated. The experiments were conducted, and the findings revealed a substantial increase in properties of both NHRFCs and THRFCs compared to UHRFCs. Notably, these enhancements encompassed tensile strength (13.66% and 19.39%), tensile modulus (13.41% and 20.70%), flexural strength (15.98% and 23.17%), flexural modulus (17.13% and 26.58%), impact strength (15.62% and 33.07%), Shore-D hardness (4.19% and 5.00%), storage modulus (9.88% and 13.07%), loss modulus (7.52% and 17.36%), dielectric constant at 6.5 Hz (13.22% and 23.96%), and significant improvements in the acoustic resonance frequency at 1897 Hz (79.50% and 81%). Peak thermal degradation temperatures of these composites are 420.62 ± 3.43 °C, 439.51 ± 3.54 °C, and 469.07 ± 3.11 °C, respectively, and biodegradability results showing accelerated degradation within 30 days. These findings highlight the substantial effectiveness of treatments in enhancing diverse properties, underscoring the potential applicability of these composites in various industrial sectors requiring superior performance and sustainable materials. Full article

Epoxy/BaTiO₃ nanocomposites with varying filler contents of BaTiO₃ were prepared and characterized for flexible DC insulation applications such as IGBT. Their breakdown strength under DC, AC, and 10 kHz voltage, tensile properties, dielectric response, surface potential decay, temperature-/electric field-dependent conductance, and field grading capability were investigated. Results show that loading BaTiO₃ increases the dielectric constant and alters loss behavior due to enhanced interfacial polarization and modified charge transport. However, breakdown and tensile strengths decrease monotonically with filler content, which is attributed to interfacial heterogeneity and local field distortion. Shallow-trap density rises while trap energy level declines with higher BaTiO₃ loading, promoting charge trapping–detrapping. Electrical conductivity of epoxy/BaTiO₃ nanocomposites increases with both electric field and temperature, while simulation of electric field distribution in the triple point of IGBT encapsulation reveals that the increased permittivity and conductivity with BaTiO₃ content can reduce the maximum local electric field by up to 6.7% and 13.7% for the two kinds of typical structure of triple points, respectively. Thus, nano-BaTiO₃ effectively tailors dielectric response and charge transport but introduces interfacial complexity that degrades breakdown and mechanical performance. However, a trade-off between intrinsic insulation, tensile strength, and field grading capability can be obtained. This work offers experimental insights for designing epoxy-based encapsulation materials with tunable electrical properties for flexible DC systems. Full article

This study investigated the electrical insulation properties of epoxy matrix composites reinforced with carbonized palm kernel shell (PKS) particles. The raw PKS particles were collected, sun-dried, and further oven-dried at 105 °C for 2 h to eliminate residual moisture. The dried shells were then carbonized in an airtight furnace at three different temperatures: 450, 550, and 650 °C. After carbonization, the material was crushed and sieved into particle sizes of 200, 400, and 800 µm using an electromagnetic sieve shaker. Composites were fabricated by incorporating carbonized PKS particles into an epoxy resin matrix at varying weight fractions of 30, 40, 50, and 60 wt%. Electrical insulation performance was evaluated at room temperature and pressure using high-voltage DC test equipment for dielectric strength and a digital insulation tester (MIT 520/2) for resistivity measurements. The results revealed that optimal dielectric strength and resistivity were achieved with smaller particle sizes, lower filler loadings, and at low temperatures. Mineralogical characterization via X-ray diffraction confirmed that there was no radioactive element. Scanning Electron Microscopy revealed porous microstructures within the carbonized particles. Energy-dispersive X-ray spectroscopy indicated that carbon accounted for the highest elemental composition, followed by oxygen. It is concluded that PKS-reinforced epoxy composites exhibit promising electrical insulation properties. Full article

In this study, bean starch films were developed and treated with dielectric barrier discharge (DBD) cold plasma (5 min (DBD5), 10 min (DBD10), and 15 min (DBD15)) and pulsed light (PL) radiation (4 J cm⁻² (PL4), 8 J cm⁻² (PL8), and 12 J cm⁻² (PL12)), and the effects of these treatments on the physical, barrier, mechanical, morphological, and structural properties were evaluated, as well as the practical application of the films in bread storage for 7 days. Both treatments significantly modified the film properties (p < 0.05). Film thickness decreased from 95 µm (control) to 87 µm (PL12), while solubility was reduced from 39.40% (control) to 25.32% (PL12), indicating improved water resistance. Reductions in water vapor permeability (WVP) were also observed, with a more pronounced effect for PL12 (approximately 55% reduction compared to the control). The contact angle increased from 58.30° (control) to 67.76° (PL12), indicating a moderate increase in surface hydrophobicity. The DBD cold plasma treatment increased tensile strength (up to 16.05 MPa in DBD15) and reduced elongation (44.72%), whereas PL, especially at PL8, increased flexibility (60.36%). Morphological analyses indicated increased surface roughness for DBD-treated films, while structural analyses suggested subtle changes in molecular organization rather than the formation of well-defined crystalline domains. During bread storage, the treated films, particularly PL12, were significantly more effective than the control in delaying bread staling (final firmness of 6.67 N vs. 11.82 N), reducing mass loss (5.66% vs. 12.66%), and maintaining higher water activity, thereby better preserving product quality. Overall, both treatments showed potential for tailoring film properties: DBD was more effective in enhancing mechanical strength, while PL promoted improvements in barrier properties and practical performance. Therefore, physical treatments, particularly PL, represent promising strategies to overcome intrinsic limitations of starch-based films and to develop packaging materials with potential applications in bakery product preservation. Full article

Microwave-sintered lunar regolith bricks are promising candidates for in situ construction of lunar infrastructure, where structural load-bearing capacity and multifunctional performance are simultaneously required. Currently, there remains a research gap concerning the service performance of microwave-sintered lunar soil bricks under predictable load-bearing, wave-transparent, and friction working conditions. In this study, lunar bricks were fabricated at different microwave sintering temperatures, and the effects of temperature on their microstructure and engineering properties were systematically investigated. The sample sintered at 1000 °C achieved a density of 2.96 g/cm³ and a compressive strength of 260 MPa. Combined experimental observations and numerical simulations revealed a typical brittle fracture behavior, primarily governed by residual porosity within the material. Tribological tests showed a low wear rate of 6.51 × 10⁻⁵ mm³/(N·m), indicating good wear resistance and potential applicability for lunar road paving. Dielectric measurements in the X-band (8.2–12.4 GHz) demonstrated a high electromagnetic wave transmittance ranging from 49.8% to 94.6%, suggesting suitability for communication-related or protective wall structures. These results demonstrate that microwave sintering effectively enhances the densification of lunar regolith while enabling the coordinated optimization of mechanical, tribological, and electromagnetic properties, providing practical guidance for the design of multifunctional materials for lunar infrastructure construction. Full article

Nanofluids have emerged as promising candidates for enhancing the dielectric and thermal performance of insulating liquids used in power transformers. While numerous studies report significant improvements in breakdown voltage (up to +10–40%) and thermal conductivity, the underlying mechanisms remain only partially understood and often contradictory, particularly with respect to long-term stability and ageing behavior. This paper presents a comprehensive and critical review of nanofluids applied to transformer insulation, adopting a system-level approach focused on the oil–paper insulation system. The analysis reveals that the reported performance strongly depends on key parameters such as nanoparticle concentration, dispersion quality, and experimental conditions, leading to significant inter-study variability. Dielectric improvements are shown to be maximized within narrow concentration ranges and may deteriorate due to nanoparticle aggregation, while thermal enhancements are often accompanied by increased viscosity, resulting in a thermo-hydraulic trade-off. Furthermore, this review highlights major contradictions in the literature, including the paradoxical relationship between electrical conductivity and dielectric strength, as well as the unclear impact of nanofluids on cellulose ageing. The findings demonstrate that performance observed at the fluid level cannot be directly extrapolated to real transformer conditions without considering the complex interactions between nanoparticles, oil, cellulose, and moisture. To address these limitations, a conceptual framework termed Nano-Modified Composite Insulation (NMCI) is proposed. This model provides a unified description of multiphase interactions and offers a basis for a more realistic evaluation of nanofluids under operational conditions. This work emphasizes the need for standardized experimental methodologies and long-term studies and provides clear research directions toward the development of reliable and industrially applicable nanofluid-based insulation systems. Full article

As the power industry continues to advance rapidly, large-scale generators are evolving toward higher voltage levels and greater capacity. The heat accumulation associated with high voltage and large capacity accelerates the aging of the main insulation. It is necessary to enhance the thermal conductivity (λ) and dielectric properties of existing main insulation materials. This work focuses on investigating the effects of varying addition levels of two different-sized BN particles on the λ and dielectric properties of the mica tape composite dielectric. The experimental findings demonstrate a progressive enhancement in the λ of the mica tape corresponding to the incremental addition of h-BN concentration. When the doping concentration reaches 20 wt.%, the λ of the two h-BN-doped mica tape (h-BN/MT) reaches a maximum of 0.382 W/(m·K), 0.4 W/(m·K), respectively, which enhances the λ of the contrasting pure mica tape (0.199 W/(m·K)) by 91.95% and 101.01%, respectively. In terms of electrical insulation properties, both sizes of h-BN/MT perform well, with breakdown strength above 32 kV/mm. Furthermore, the second-order thermal conductivity model of mica tape doped with different sizes of h-BN was constructed by combining the Halpin–Tsai model with the Series model, which allows the calculation of λ of mica tape composites doped with different sizes of h-BN. This work provides a novel structural design approach for preparing mica tape composite dielectric that simultaneously exhibits high λ and high insulation properties. Full article

Due to the widespread use of microwave electromagnetic radiation, this study examines the microwave electromagnetic properties and compressive strength of composites made from inexpensive components such as Mg_0.5Zn_0.5Fe₂O₄, polystyrene, and activated carbon. Experimental samples were fabricated using thermopressing. The formation of the dielectric core/shell structure for Mg-Zn/polystyrene composites (1:1) and composites with activated carbon additives at weight concentrations of 3, 6.6, and 9.0% was determined using SEM image analysis. Microwave properties were investigated by analyzing the frequency dependences of complex permittivity and magnetic permeability in the frequency range of 100 MHz–5 GHz. As shown by the simulation and experimental measurements of scattering parameters obtained, the compost shows improved microwave absorption properties in the frequency range of 1–5 GHz. Reflection loss spectra showed peaks with values of −17.8 and −18 dB in the frequency range of 2.5–5 GHz for samples with 4.8 wt. % and 6.6 wt. % carbon loading, respectively. The absorption bandwidths of −10 dB in the range of 1.7–2.13 GHz were observed in the best samples. Studies have shown that samples containing 9.0 wt. % of carbon material with thicknesses of 6–10 mm can be considered as an electromagnetic shielding material in the microwave range 1–5 GHz. It was shown that, despite a decrease in porosity from 15.59 to 7.17%, with an increase in the concentration of carbon material in the composites, the compressive strength also decreases from 62.05 to 36.45 MPa. The developed composites are potentially suitable as microwave absorbers for civil applications. Full article

To overcome the inherent drawbacks of poly(propylene carbonate) (PPC), such as poor thermal stability, low mechanical strength, and high surface energy, this study introduced, for the first time, 1,1,1-trifluoro-2,3-epoxypropane (TF-PO) as a third monomer into the metal-free TEB/PPNCl catalytic system for the terpolymerization with carbon dioxide (CO₂) and propylene oxide (PO), successfully synthesizing a series of fluorinated PPC (PPCF). The optimal polymerization conditions ($60 °C$, 2.0 MPa, 12 h, n(PO):n(TF-PO) = 100:4) were determined through systematic optimization. Comprehensive structural characterization (FT-IR, NMR, XPS) confirmed the successful incorporation of TF-PO into the polymer backbone. Property evaluation revealed that the PPCF materials exhibited substantial improvements in thermal stability, mechanical strength, hydrophobicity, and dielectric properties compared to unmodified PPC. The optimal sample, PPCF4, achieved a $5\%$ weight-loss temperature ($T_{d,-5\%}$) of $242 °C$, a glass transition temperature ($T_{\mathrm{g}}$) of $42 °C$, a tensile strength of 21.5 MPa, and a Young modulus of 296 MPa. With a $5\%$ TF-PO feed ratio, the material’s water contact angle increased to 102°, and its dielectric constant reached 6.01 at ${10}^4$ Hz. Furthermore, density functional theory (DFT) calculations elucidated the Lewis acidity of the TEB catalyst and the reactive sites of the monomers, leading to a proposed mechanism for the ternary alternating copolymerization. This work provides an effective synthetic strategy and theoretical foundation for preparing high-performance and functionalized PPC materials through molecular structure design. Full article

This study investigates the development of sustainable composite materials using recycled low-density polyethylene (rLDPE) and high-density polyethylene (rHDPE) in an 80/20 mass ratio, incorporating kraft lignin as a bio-derived additive and polyethylene-graft-maleic anhydride (PE-g-MA) as a compatibilizer. Reactive melt mixing was employed to produce composites with varying lignin loadings (1, 3, 5, and 10 wt%). The structural, thermal, and mechanical properties and segmental dynamics of the materials were thoroughly examined using differential scanning calorimetry (DSC), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS), tensile testing, scanning electron microscopy (SEM), and dielectric relaxation spectroscopy (DRS). The incorporation of lignin exhibited minimal disruption to the polymeric thermal transitions, while it boosted thermal stability, as confirmed by the TGA curves. According to the segmental dynamics findings, the glass transition temperature of the polymeric blend (−35 °C) was increased systematically with the addition of lignin by ~1–20 K. Tensile tests showed that the 1 wt% additive ratio demonstrated the optimal balance of strength and ductility. Morphological observations supported these findings, revealing uniform dispersion at low additive ratio and increased agglomeration at higher ratios. Based on its superior performance, the composite containing 1 wt% lignin was successfully extruded into filament suitable for 3D-printing. This study highlights the synergy of bio-based additives and recycled polymers in engineering high-performance materials, promoting circular economy principles and reduced environmental footprint through upcycling post-consumer waste into functional, valuable products. Full article

For cable compound manufacturers, accurate formulation fine-tuning is essential to ensure safety, long-term durability, and compliance with international standards for dielectric strength, volume resistivity, and environmental and thermal ageing. This work presents an experimental study demonstrating how minor additives can critically affect the performance of complex flame-retardant elastomeric formulations. The investigation focuses on the role of small amounts of zinc oxide (ZnO) in commercial cable compounds based on a crosslinked elastomeric matrix composed of ethylene–propylene monomer (EPM), ethylene–propylene–diene monomer (EPDM), and thermoplastic polyolefin elastomer (POE). The formulations contain aluminium trihydroxide (ATH) as the major filler, together with several minor additives. Among these, a phenolic antioxidant (AN01) acting as a metal deactivator is also present. The addition of ZnO in low amounts (2–5 phr) allowed the compounds to maintain a volume resistivity ≥ 10¹² Ω·cm in water at 100 °C. To elucidate the role of ZnO, a systematic set of formulations was prepared by varying the type and content of selected additives. The compounds were prepared by melt mixing in an internal mixer (Banbury type), followed by peroxide crosslinking via compression molding. Electrical characterization results indicate that ZnO interacts with the phenolic additive through surface adsorption, forming a coated particle with significantly reduced electrical conductivity. Optimal electrical performance was achieved when the ZnO-to-additive ratio corresponded to the minimum amount required for complete surface complexation. Full article

Ceramics are widely evaluated for their extreme hardness, high-temperature stability, and corrosion resistance, which enable applications in harsh service environments. However, these same properties, high melting points, brittleness, and low thermal shock resistance, make conventional manufacturing of complex ceramic components difficult and expensive. Traditional processes often require costly diamond tooling or energy-intensive sintering and tend to produce only simple geometries, with significant waste material and risk of defects. Additive manufacturing (AM) has recently emerged as a promising route to fabricate intricate, near-net-shape ceramic parts without these drawbacks. By building components layer by layer, AM reduces the need for extensive machining and enables the fabrication of geometrically complex, near-net-shape ceramic structures with reduced material waste, although challenges such as porosity, interlayer defects, and cracking during post-processing remain. Nonetheless, ceramic AM technologies lag behind their metal and polymer counterparts, and significant challenges remain in achieving fully dense parts with reliable mechanical properties. This review provides an in-depth overview of the state of the art in ceramics and ceramic composite additive manufacturing. We detail the most widely used AM processes (stereolithography, binder jetting, material extrusion, powder bed fusion, inkjet printing, and direct energy deposition) and typical feedstock formulations for each technique. We examine the resulting mechanical properties (strength, toughness, hardness, wear resistance) and functional properties (thermal stability, dielectric behavior, biocompatibility) of additively manufactured ceramics, and discuss their current and potential engineering applications in the aerospace, defense, automotive, biomedical, and energy sectors. Persistent challenges, including porosity, shrinkage and cracking during sintering, achieving uniform microstructures, high process costs, and scalability issues, are analyzed, and we highlight promising future directions such as multi-material grading, integration of machine learning for process optimization, and sustainable manufacturing approaches. Despite significant progress, challenges remain in achieving fully dense structures, improving process reliability, and scaling ceramic AM for industrial applications, highlighting the need for further research in process optimization, material design, and multi-material integration. Full article