This work investigates the localization and network formation of carbon nanotubes (CNTs) in two-phase blends of polyetheretherketone (PEEK) and polyetherimide (PEI), and their influence on electrical, rheological, and thermal properties of the resulting materials. Despite the strong thermodynamic preference of CNTs for the PEI phase, both PEEK/CNT and PEEK/PEI/CNT nanocomposites exhibit similar electrical percolation thresholds (0.25–0.5 wt.%), attributed to spatial confinement arising from PEEK crystallinity in PEEK/CNT and from phase-selective localization in the blend system, which limits the effective volume available for CNT dispersion. Morphological characterization confirmed co-continuous blend structures and complete CNT migration into the PEI phase in PEEK/PEI/CNT system, while rheological studies revealed percolated networks forming below the electrical percolation threshold. Processing conditions strongly impacted conductivity: short mixing times preserved interconnected CNT agglomerates and enhanced conductivity, whereas prolonged mixing promoted dispersion but destroyed conductive pathways. Furthermore, thermal annealing induced agglomeration and weakened networks in PEEK/CNT systems but had negligible effect on PEEK/PEI/CNT composites due to improved CNT–PEI compatibility. Finally, thermal conductivity remained low across all systems, maintaining the material’s insulating performance.

Photo-stabilization is essential for thermoplastics in outdoor applications, as it extends service life by protecting polymer chains from UV-induced degradation. Graphene has emerged as a multifunctional stabilizer with capabilities including UV screening, barrier effects, and radical scavenging. However, its influence on the depth profile of photodegradation under UV exposure is not fully understood. This work investigates the effect of few-layer graphene (FLG) on the photodegradation of high-density polyethylene (HDPE). Neat HDPE and composites with 0.5 wt% FLG were prepared in two thicknesses (3 and 2 mm) and exposed to UV radiation for varying durations. Elongation at break was measured as a function of exposure time and correlated to the degradation depth, determined by chemi-crystallization using Raman microscopy. In neat HDPE, embrittlement occurred when the degraded layer reached similar to 10% of the thickness, after 10 and 7 days for 3- and 2-mm samples, respectively, preceding the appearance of surface cracks. In contrast, HDPE with 0.5 wt% FLG retained 50% of its initial elongation at break, characterizing a ductile failure, even after 45 days despite surface cracks. Additionally, embrittlement was only observed when the relative degradation depth reached 12.5%, exceeding the 10% threshold observed for the neat HDPE. The persistence of ductility is attributed to the photo-stabilizing effect of FLG and the detachment of the degraded surface from the ductile core, leading to a material with enhanced UV resistance for outdoor packaging and coating applications.

The dispersion of nanoparticles in polymer melts is a major challenge in composite processing, especially in highly viscous systems where conventional extrusion provides poor mixing. Concomitantly, ultrasound has proven effective to disperse nanoparticles in low-viscosity fluids through cavitation and acoustic streaming, but its role in polymer melts remains unclear. This study examines ultrasound-induced flows in polydimethylsiloxane (PDMS) of three viscosities (5, 30, and 300 Pa.s) under partially degassed and non-degassed conditions. Flow visualization and Particle Image Velocimetry (PIV) were used to characterize velocity fields generated by a sonotrode. In non-degassed samples, dense bubble clouds strongly enhanced acoustic streaming, producing velocities up to 20 mm/s at moderate input power. Degassing reduced bubble formation, leading to lower velocities (3---6 mm/s) and more stable flow patterns. At very high viscosity (300 Pa.s), velocities decreased by approximately an order of magnitude, indicating that limited bubble formation and bulk viscosity-dependent attenuation strongly influences ultrasound-induced flow. Temperature measurements and bubble-cloud evolution were consistent with a thermally influenced mechanism: however because temperature and velocity could not be measured simultaneously, no direct causal relationship was extablished. These results underline the importance of dissolved gases, viscosity and thermal evolution in acoustic streaming in viscous polymers-like media and identify key factors to consider in the development of ultrasound-assisted extrusion.

Electroencephalography (EEG) is an essential technique for monitoring brain electrical activity in clinical, sports, and wearable health settings. However, traditional wet electrodes face issues like gel drying and skin irritation, while coated dry electrodes tend to degrade over time, affecting long-term signal stability. This study explores flexible dry electrodes made from conductive polymer composites-poly(styrene-b-ethylene-ran-butylene-b-styrene) filled with carbon black (SEBS/CB) and ethylene-vinyl acetate filled with carbon black (EVA/CB)-as affordable and recyclable alternatives to standard materials such as PDMS and TPU. The electrodes were manufactured using solvent casting and compression molding, ensuring even filler distribution and consistent surface quality. Both composites reached an electrical conductivity of around 0.01 S/m with a percolation threshold close to 12 wt% CB. Contact impedance tests showed better performance for SEBS/CB electrodes (5.4 +/- 0.9 k Omega) compared to EVA/CB (26.7 +/- 4.4 k Omega), nearing the value of a commercial flexible electrode (4.2 +/- 0.5 k Omega). Mechanical testing confirmed that SEBS/CB is softer and more elastic, facilitating stable, low-noise EEG signal collection. Overall, SEBS/CB composites provide a good balance of electrical performance, flexibility, and scalability, highlighting their potential for next-generation, long-term EEG monitoring systems.

High-voltage rotating machines rely on a complex insulation system whose reliability strongly depends on the behavior of stress control coatings (SCCs). These coatings, applied at the ends of stator bars, are essential for controlling electric fields and preventing partial discharges (PDs). This study presents an in-depth experimental investigation of the electrical behavior of SCCs made from silicon carbide (SiC) and iron oxide (FeO). Surface potential, surface resistivity, and corona PD measurements were conducted on stator bars with different manufacturers, levels of aging, and year of manufacture. High-resistivity coatings localize the electric field and raise PD activity, while optimal resistivity smooths the field. Surface potential measurement and corona PD measurement are effective tools to assess the quality of the SCC. However, humidity is identified as a significant inhibitor to corona PDs and may obscure anomalies during quality assessments.

Flexible electroencephalography (EEG) electrodes have attracted increasing attention due to their potential applications in mobile health monitoring. However, balancing electrical conductivity, flexibility, stretchability, and EEG signal recording remains challenging. Here, we fabricated polystyrene-block-poly(ethylene butylene)block-polystyrene (SEBS) composites with carbon nanotubes (CNT) and carbon black (CB) via solvent dissolution. The percolation threshold was approximately 12 wt% for SEBS/CB composites and approximately 2 wt% for SEBS/CNT composites. At 20 wt%, SEBS/CB composite conductivity plateaued at 0.01 S/m, whereas SEBS/CNT composite conductivity reached 1.26 S/m at 16 wt%. Contact impedance was 4.2 f 0.45 k52 for SEBS/16 wt% CNT and 5.4 f 0.9 k52 for SEBS/20 wt%CB. SEBS/CNT was slightly stiffer than SEBS/CB. The electrodes reliably recorded EEG signals, demonstrating their potential for health monitoring and long-term EEG measurements.

Electrical overhead lines rely on spacer dampers to prevent bundled conductors from colliding during wind and ice events, but these devices often suffer from performance loss, displacement, mechanical failure, and material degradation over time. Since installation and replacement are dangerous, slow, and costly, improving the materials and design of spacer dampers is essential for long-term reliability. As it was studied in the previous article, the actual elastomer is sensitive to aging. Therefore, in this study, it was explored how different types of ethylene propylene diene monomer (EPDM), carbon black (CB), and waxes affect the properties of elastomeric composites. The results of the tensile test of three types of EPDM showed that the one with the highest ethylene content had the highest stress and elongation at break. The experiment changed the ratio of two types of furnace carbon black through a series of mechanical, electrical, and physical tests. It represented that increasing the amount of carbon black with a smaller size and higher surface area (N330) improved the stress and elongation at break of EPDM composites, but made it less conductive. For the swelling test, also observed that the insoluble fraction was the same for all samples; however, samples with more N330 tended to swell more, indicating a lower crosslink density. Additionally, examining the effects of five types of waxes on the mechanical properties showed that a balanced property can be obtained by adding the blend of microcrystalline and paraffin wax, in which elongation at break and 100% modulus increased slightly, and stress at break decreased marginally in comparison to that of the control sample. Upon aging, the blend of two waxes had much retention of stress and elongation at break upon aging which means that it was more effective in protecting materials.

Partial discharge (PD) measurement is essential for assessing the insulation condition of power transformers, as PD is both a symptom and a cause of insulation degradation. The transient earth voltage (TEV) sensor is a non-intrusive technique that can be used during online operation of transformers. This paper aims to study the impact of the structure of the TEV sensor on its sensitivity. A $120 \mathrm{V} / 25 \text{kV}$ transformer, including its active part and a TEV sensor, was modeled in COMSOL. Five parameters were investigated, including the thickness and material of the dielectric and electrode layers, as well as the effective sensing area of the sensor. The results reveal that insulation thickness and sensing area have the greatest influence on the detected TEV voltage amplitude compared with other parameters. The role of electromagnetic skin depth in the limited influence of electrode thickness was also discussed.

High-performance thermoplastics are gaining increasing attention for space applications. However, the extreme lunar environment requires multifunctional materials that combine electrical conductivity for electrostatic charge dissipation with low thermal conductivity for thermal insulation. One promising strategy to achieve this balance is through conductive polymer nanocomposites with controlled morphology. In this study, the localization, migration, and network formation of carbon nanotubes (CNTs) in two-phase blends of polyetheretherketone/polyetherimide (PEEK/PEI) were systematically investigated to establish the relationships between processing, morphology, and the resulting electrical and thermal properties. Despite the strong thermodynamic preference of CNTs for the PEI phase, both PEEK/CNT and PEEK/PEI/CNT nanocomposites exhibit similar electrical percolation thresholds (0.25-0.5 wt.%), attributed to spatial confinement arising from PEEK crystallinity in PEEK/CNT and from phase-selective localization in the blend system, which limits the effective volume available for CNT dispersion. Morphological characterization confirmed co-continuous blend structures and complete CNT migration into the PEI phase in the PEEK/PEI/CNT system, while rheological studies revealed percolated networks forming below the electrical percolation threshold. Processing conditions strongly impacted conductivity: short mixing times preserved interconnected CNT agglomerates and enhanced conductivity, whereas prolonged mixing promoted dispersion but destroyed conductive pathways. Furthermore, thermal annealing induced agglomeration and weakened networks in PEEK/CNT systems but had a negligible effect on PEEK/PEI/CNT composites due to improved CNT-PEI compatibility. Finally, thermal conductivity remained low across all systems, maintaining the material's insulating performance for the harsh thermal environment of the Moon.

Low electrical conductivity and high heat dissipation are crucial for electronic packaging materials. Additionally, friction is critical for the lifespan and energy efficiency of components. To address these requirements, polymer nanocomposites based on bio-based polyamide 1010 and ultra-low contents of 2D nanomaterials were produced by melt-blending. Graphene oxide, hexagonal boron nitride, and molybdenum disulfide were selected for their two-dimensional structure and electrical insulation, providing high thermal conductivity while preserving the polymer's dielectric nature. Hybrid nanocomposites were also produced to explore potential synergistic effects. Results showed all compositions maintained the polymer's intrinsic dielectric properties. Although the friction coefficient increased slightly compared with neat polyamide, all nanocomposites remained within the low-friction range required for low-friction materials. Thermal conductivity improved by 5%-10% compared with unfilled polyamide, with hybrid systems performing slightly better, indicating a minor synergistic effect. Despite these enhancements being modest compared with the literature, achieving high thermal conductivity usually requires over 20 wt% of nanofiller, which is detrimental to mechanical performance. In this study, at most 0.5 wt% was used, with composites being obtained directly through melt-blending. This highlights their potential as low-content additives for thermal interface materials without compromising other essential properties.

Polarization and Depolarization Current measurements (PDC) are well-known in the industry. Hydro Quebec has been using PDC measurements as a diagnostic tool for more than 25 years. Since 2012, systematic PDC measurements are conducted every 6 years on the stator windings of all the hydrogenerator fleets. When the tool was first implemented, thresholds were defined to convert insulation resistance values into a condition health index. These limits were decided based on preliminary results obtained from a few hydrogenerators and laboratory measurements on accelerated-aged samples. However, with more than 500 PDC measurement results, the database can now help refine the limits for each type of insulation system (asphalt, epoxy and polyester). The purpose of this paper is to present the evolution of the insulation resistance value as global aging occurs and to observe the trending of insulation resistance over time. The influence of factors such as humidity, and the nature of the stress grading coating are also presented to describe how the limits can be managed for diagnostic purpose with statistical uncertainty.

The properties of graphene have made it a promising material for the development of polymer nanocomposites, and graphene functionalization has gained popularity due to its ability to improve dispersion between the phases. For thermosetting matrices, nanomaterials can affect curing, and rheological studies provide crucial information about this process. This study was undertaken to investigate the impact of graphene functionalization on the curing kinetics and morphology of epoxy nanocomposites. For that, graphene (G), graphene functionalized with surfactant sodium dodecyl sulfate (G-SDS), graphene oxide (GO), and graphene oxide functionalized with amine groups (GON) were used as nanofillers. Rheological studies showed that the addition of graphene to the resin resulted in a slower curing reaction in comparison to the neat epoxy at temperatures of 60 and 70 degrees C. G-SDS did not affect the curing kinetics of the epoxy resin, while the addition of GO and GON to the resin accelerated the curing kinetics and reduced the reaction activation energy. The most significant improvements were observed for GON, with a reduction in gelation time at 60 degrees C from approximately 40 min to 17 min, and at 80 degrees C from 11 min to 6 min, compared to the neat epoxy. The functionalization also resulted in a significant increase in the dynamic storage (E ') and loss (E '') moduli, indicating that functionalization of graphene enhances its interfacial interaction with the epoxy matrix. Specifically, GON yielded a 70 % increase in E ' and a 28 % increase in E '' compared to the neat epoxy.

This work describes the thermal aging behavior of three industrial elastomeric compounds based on styrene-butadiene rubber (SBR) reinforced with carbon black. Samples were exposed to thermo-oxidative aging at temperatures ranging from 70 to 120 degrees C for durations between 14 and 365 days. The tensile and hardness tests were performed on the samples to determine changes in their mechanical properties. Upon aging, hardness and 100% modulus increased, while elongation at break decreased for all three samples. The results showed a significant decrease in elongation at break and an increase in hardness and modulus with prolonged aging time and higher temperatures. For instance, the elongation at break of the three types of samples decreased by approximately 50% in less than 90 days at 70 degrees C, whereas at 120 degrees C, this same level of degradation occurred in less than 2 days. These significant changes were correlated with increased brittleness and reduced flexibility of SBR composites. Swelling tests confirmed an increase in crosslink density due to aging. Laser scanning confocal microscopy revealed surface roughness and defects, attributed to oxidation, crosslinking, and the evaporation of low molecular weight components. Lifetime prediction methods, including the Arrhenius equation and time-temperature superposition (TTS), were applied to estimate the service life of the materials. The Ahagon plot was utilized to understand the aging mechanisms, revealing a transition from crosslinking-dominated degradation to chain scission processes at higher temperatures and longer aging times.Highlights Thermal aging makes SBR compounds more brittle and less flexible over time. The hardness and stiffness of SBR compounds increase with aging temperature and time. Aging increases crosslink density, confirmed by swelling tests. Increased surface roughness and defects due to oxidation and crosslinking. The aging mechanism shifts from crosslinking to chain scission at higher temperatures.

The deterioration of rotor pole interturn insulation is a significant failure mode in large salient pole generators. The failure mode in this case can lead to the short circuit between turns that can be considered as a stray current. This causes a reduction of magnetic flux, resulting in magnetic imbalances and vibrations, which can lead to costly unplanned maintenance. To address this, modern techniques have been developed to detect insulation failures by monitoring the rotor pole flux during operation either by stray or air gap flux. Additionally, several tests can be performed during maintenance outages. These include the voltage pole drop test, the Impulse Frequency Response Analysis (IFRA/Surge), and more recently, the Sweep Frequency Response Analysis (SFRA) has been getting interest. Other tests can also be conducted with the rotor poles removed from the generator. However, the results from these measurements often contradict each other, and the causes are not always clear. Factors such as the sensitivity of the tests, environmental conditions, and the specific nature of the inter-turn short-circuit (ITSC) in the rotor poles can all influence the outcomes. An investigation is conducted on a 310 MVA hydrogenerator that exhibits significant anomalies in the pole winding inter-turn insulation upon visual inspection were a lot of poles has shown migration of this insulation. In service, this generator also shows signs of vibrations. The study presents comparative various tests, including flux measurement, Surge, SFRA, pole voltage drops tests at different frequencies all with the rotor poles in situ including experimental measurements.

Partial discharge (PD) measurement is a critical diagnostic technique used to assess the condition of high-voltage (HV) electrical equipment's insulation systems by enabling the early detection of potential failures. This paper presents a simulation-based analysis of the performance of transient earth voltage (TEV) sensors, a non-intrusive method, for PD detection within a transformer tank model. Simulation results reveal that the TEV signal amplitude and time-of-flight (TOF) highly depend on the location of the TEV sensors and PD sources. Moreover, fast Fourier transform (FFT) analysis identifies dominant frequency components that can be useful for experiment measurements. The findings also demonstrate that increased wall thickness leads to greater electromagnetic (EM) wave attenuation, reducing sensor sensitivity.

The present paper proposes a new investigation of the dielectric properties of superparamagnetic iron oxide nanoparticles (SPIONs)/PE nanocomposites in comparison with the neat polymer at different temperatures. The SPIONs used were without or with positively or negatively surface charge. Different frequency-domain dielectric responses were observed for the different samples. The usual decrease of the values of the real part of the permittivity of all the three SPIONs nanocomposites in the range was observed with the increase of temperature. Moreover, the values of the real part of the permittivity of PE-bare SPIONs increased slightly at lower frequencies, whereas those of PE-positively charged SPIONs and PE-negatively charged SPIONs were constant at higher frequencies and showed an increase at medium frequencies and a plateau at lower frequencies. The imaginary part of their permittivity also showed dielectric responses for the samples.

This study reports the development and optimization of highly metal-loaded thermoplastic composite filaments for material extrusion additive manufacturing of metallic components. Nickel (Ni) and iron (Fe) powders with varying particle sizes and morphologies were combined with polyethylene (PE), polylactic acid (PLA), and PE/ PLA blends as binders. The influence of particle characteristics and binder composition on filament morphology, mechanical properties, porosity, thermal behavior, and printability was systematically investigated. Composite filaments containing up to 90 wt% Ni and 80 wt% Fe were successfully extruded. Scanning electron microscopy revealed that fine Ni particles improved dispersion and reduced porosity, whereas coarse Fe particles resulted in heterogeneous packing. Thermal analyses guided debinding and sintering conditions, while mechanical testing demonstrated that PE enhanced flexibility, PLA contributed to strength, and blended systems offered a balanced compromise with good printability. Optimized 3D printing parameters enabled the fabrication of high-quality green parts, which were successfully debound and sintered using graphite powder to suppress oxidation. Dense metallic structures with controlled shrinkage and minimal residual porosity were obtained. Ni-based samples exhibited greater shrinkage and cracking due to finer particle size and higher thermal expansion. The results demonstrate a robust materials-process design strategy for FFF of metals. Unlike conventional multi-step solvent-based methods, this work employs a simple dry-mixing route and standard laboratory furnace processing without vacuum or inert atmospheres. This streamlined approach provides an environmentally friendly and scalable pathway for additive manufacturing of high-performance metallic parts.

Turn insulation in stator multiturn coils is often involved in machine failures. To date, however, there are no tests for determining the long-term performance of turn insulation. Conventional diagnostic tests (partial discharge (DP) and dissipation factor (DI) measurements) are not accuratefor the detection of turn insulation degradation. Sweep Frequency Response Analysis (SFRA), based on analysis of winding impedance in the frequency domain, has been used for more than 40 years to diagnose power transformer windings, and its application in rotating machines is currently the subject of research. The aim of this study, is to evaluate the SFRA capability to assess turn insulation degradation by the insertion offault resistances between turns at three locations on a spare coil. SFRA measurements were compared to a numerical simulation using an RLC model representative of the stator coil.

Assessing the insulation condition of high-voltage equipment using non-intrusive partial discharge (PD) measurement is widespread nowadays. The transient earth voltage (TEV) method, a relatively new non-intrusive approach, operates by detecting the surface current induced by electromagnetic waves (EM) propagating from PD, which spreads out through the discontinuities of the equipment's outer surface. This paper evaluates the performance of TEV sensors compared to the IEC 60270 standard for detecting PD caused by various defect types inside and outside a metal enclosure in a laboratory setting. Phaseresolved PD (PRPD) pattern and fast Fourier transform (FFT) indicate that each defect has its own characteristic. The FFT analysis reveals that PD can only be effectively detected at specific frequencies where it is distinguishable from background noise.