Search Results (780)

This study presents a calibrated modelling approach for predicting the abrasive wear of copper-free composite friction materials. Four formulations were analysed, including a copper-containing reference material and three experimental compositions in which copper was replaced by different aluminium/polytetrafluoroethylene ratios. Dry ball-cratering tests were performed to determine the apparent wear-rate coefficient under controlled laboratory conditions. The copper-containing reference material showed the lowest wear-rate coefficient, k_c = 80.655 × 10⁻¹⁴ m²·N⁻¹, whereas the copper-free formulations reached k_c = 111.811 × 10⁻¹⁴ m²·N⁻¹, 98.586 × 10⁻¹⁴ m²·N⁻¹ and 90.579 × 10⁻¹⁴ m²·N⁻¹ for S2, S3 and S4, respectively. Thus, copper replacement increased the apparent wear-rate coefficient by approximately 12–39%, depending on the Al/PTFE ratio. The obtained data were used to develop and compare four calibrated predictive models. Among them, the modified Hertz–Archard model, which included effective hardness and contact-related descriptors, provided the best agreement with the experimental data. This model achieved MAPE = 1.5%, RMSE = 2.181 × 10⁻¹⁴ m²·N⁻¹ and a maximum absolute error of 4.3%, with all predictions within the ±5% error band. The results indicate that the proposed calibration framework can support preliminary screening and ranking of copper-free friction-material formulations under the adopted dry ball-cratering conditions. Full article

Currently, most design solutions are disc brake systems, in which, during braking, the rotating disc, along with the wheel, rubs against stationary brake pads, converting kinetic energy into thermal energy released into the atmosphere. Brake pads are made of composite materials. One of the key components is copper. Its presence is crucial and plays a crucial role in friction materials. In this work, an attempt was made to replace copper, which is unfortunately harmful to both the environment and humans, with aluminum powder and polytetrafluoroethylene powder. Samples of the proposed prototype friction materials were manufactured, and their thermal and tribological properties were determined (research described in the previous work). Knowledge of the materials’ properties allowed for simulation studies. Calculations were prepared for three different scenarios. The results showed that the heating process using the proposed materials during braking is very similar to that of materials with a conventional composition. Of the materials tested, composition where copper was replaced by polytetrafluoroethylene and aluminum in a 4:1 ratio gave the most promising results. In tests, this material had the lowest maximum brake pad temperature values, which contributes to a reduced risk of fading. Also, by “pushing” thermal energy into the brake disc, it contributes to the fastest dissipation of this energy. This suggests that the materials can be used in real-world braking systems. Full article

Microplastic contamination in coral reef environments is increasingly recognized as a global concern; however, the extent to which polymer composition can help distinguish contamination sources and transport-related processes remains poorly understood. In this study, we assessed the abundance, composition, and diversity of microplastics (20–300 µm) across multiple reef systems in the Cuban archipelago using high-resolution Laser Direct Infrared (LDIR) spectroscopic analysis. Microplastic abundance varied substantially among sites, with a median concentration of 66 particles L⁻¹ (IQR: 45–115 particles L⁻¹), ranging from 8 to 218 particles L⁻¹. A total of 11 polymer types were identified, with polyethylene (PE), polypropylene (PP), and polyamide (PA) dominating the assemblages and accounting for approximately 77% of detected particles. While these polymers were consistently observed across all sites, suggesting a pervasive regional background signal, highly impacted reefs exhibited more heterogeneous polymer profiles, including increased contributions of polyurethane (PU), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC), consistent with localized anthropogenic influence. Multivariate analysis revealed moderate compositional structuring among reef sites and suggested broad differences in polymer assemblages associated with contrasting contamination settings. Notably, some reefs exhibited elevated microplastic abundances while remaining dominated by common polymers, indicating a partial decoupling between contamination levels and polymer-specific signatures. This pattern is consistent with the influence of regional transport and mixing processes across the Caribbean basin, potentially including circulation associated with the Yucatán Channel, although hydrodynamic processes were not directly assessed in this study. Overall, the findings highlight the value of polymer-resolved analysis for improving interpretation of microplastic contamination patterns in coral reef environments. The integration of polymer composition with abundance and diversity metrics provides a useful framework for distinguishing between localized contamination signals and broader regional background influences. This study represents a regional baseline assessment of small microplastics in Caribbean coral reef systems using high-resolution spectroscopic characterization. Full article

Five modifications of polytetrafluoroethylene (PTFE) are considered as a modern alternative to PTFE as sliding layers of bridge bearing parts. Radiation-modified PTFE without additives and with nano-additives as well as composites based on PTFE with bronze inclusions and nanomodified carbon fiber fillers were investigated. Ultra-high-molecular-weight polyethylene (UHMWPE) and classic pure PTFE were considered as control samples. The thermomechanical properties of the materials were studied within the framework of dynamic mechanical analysis in the operating temperature range of bridge structures [−40; +80] °C. The exit zones from the linear theory of viscoelasticity were established for all the materials considered. Temperature dependencies of the storage modulus and the loss modulus were determined. Thermoviscoelastic models of material behavior were constructed using a numerical identification procedure, experimental data, and simulation models. The thermomechanics of materials during the deformation of the spherical support part of the bridge were analyzed. Temperature dependencies of the parameters of the contact stress-strain state were determined with an average coefficient of determination R² = 0.97 and an average error size RMSE = 0.092. Full article

Separation membranes with inherent antiwettability and stability are highly desirable for membrane distillation (MD) in practical applications. In this study, hydrophilic–hydrophobic dual-layer membranes composed of a dense poly (vinyl alcohol)/halloysite nanotube (PVA-HNT) layer and a microporous polytetrafluoroethylene (PTFE) layer were fabricated to improve wetting and fouling resistance during the MD process. The incorporation of the HNT manipulated the crystallization and chain mobility of PVA, endowing the PVA-HNT layer with tunable water transport properties by adjusting the level of HNT loading. Benefiting from the hydrophilic top layer on PTFE, the dual-layer membrane with an optimal HNT loading of 5 wt% showed stable water vapor flux (7.6 kg/m²·h) while maintaining salt rejection above 99.95%. This performance was achieved using a 3.5 wt% NaCl feed solution with 0.4 mM sodium dodecyl sulfate at a feed temperature of 50 °C and permeate temperature of 10 °C. In contrast, the pristine PTFE membrane suffered from severe pore wetting, with its salt selectivity dropping from 99.5% to 91.5%. Antifouling performance was further evaluated using real landfill leachate in a 50 h treatment. The dual-layer membrane with a 5 wt% HNT maintained stable separation behavior with a 15.3% decrease in water flux, whereas the flux of the PTFE membrane declined by 70.5% in 30 h of operation. A distinct fouling layer was observed on the PTFE membrane surface after the operation, while no obvious fouling was identified on the dual-layer membrane, confirming its superior antifouling properties. Full article

Buildings account for a significant share of global energy consumption and carbon emissions, creating an urgent need for advanced energy retrofit technologies. This review critically examines the role of plasma-modified textile polymer materials in improving the energy efficiency and durability of building retrofit systems. Various textile polymers, including polyester (polyethylene terephthalate, PET), polypropylene (PP), polytetrafluoroethylene (PTFE), polyamide (PA), and fiber-reinforced composites, are evaluated in relation to plasma surface engineering approaches, including atmospheric plasma, dielectric barrier discharge (DBD), and plasma jet treatment. Reported studies demonstrate that plasma treatment significantly alters surface morphology and chemistry, resulting in increased surface roughness, enhanced wettability, improved coating adhesion, and superior hydrophobic behavior. Water contact angles increased from approximately 70° to 145° depending on polymer type and plasma conditions, while reflective coating performance improved with solar reflectance enhancements of approximately 10–15%. Plasma-treated reflective roofing and shading textiles also showed reductions in building cooling energy demand of approximately 18–25% and roof temperature decreases of 10–15 °C. Furthermore, plasma-induced surface activation improved durability, ultraviolet (UV) resistance, and weather stability of textile membranes used in facade and roofing applications. The review also discusses industrial challenges related to scalability, plasma aging effects, energy consumption, and long-term performance. Plasma-modified systems demonstrate strong potential for multifunctional, lightweight, and sustainable building envelope technologies for future energy-efficient construction. Full article

Adiponitrile (ADN) serves as a critical intermediate for manufacturing polyamide 66. Electrochemical hydrodimerization of acrylonitrile (AN) offers a green and sustainable route for ADN production, yet conventional lead plate cathodes still suffer from high cell voltage, insufficient mechanical stability, and lead dust shedding during long-term operation. In this work, we developed a novel composite lead electrode in ambient air to overcome these drawbacks. Key preparation parameters, including calcination temperature, polytetrafluoroethylene (PTFE) content, substrate type, dispersion method, and dispersant dosage, were carefully screened and optimized. The optimal conditions were determined as follows: PTFE mesh as the substrate, 10% PTFE relative to lead powder, mechanical stirring dispersion, 0.5 wt% sodium hexametaphosphate as dispersant, air calcination at 325 °C, and subsequent electrochemical reduction. SEM, XRD, and XPS characterizations showed that the optimized electrode features a three-dimensional porous network assembled from interlaced rod-like and flower-like micro/nanostructures, which greatly elevates the specific surface area, enriches active sites, and facilitates electrolyte penetration and mass transport. After electrochemical reduction, the electrode surface was dominated by catalytically active Pb⁰. Electrochemical tests indicated that the composite electrode delivered a current density of 60–70 mA·cm⁻² at −1.6 to −2.0 V (vs. SCE) for AN reduction, nearly three times higher than that of a conventional lead plate. In addition, the composite electrode showed improved mechanical hardness and completely suppressed lead dust shedding, greatly enhancing operational safety and service life. Stable voltage was maintained during long-term electrolysis. This study provides a low-cost and scalable strategy for fabricating high-performance lead-based composite cathodes, which can support the industrial-scale green electrosynthesis of adiponitrile from acrylonitrile. Full article

This work describes the preparation of PTFE (polytetrafluoroethylene)/SiO₂ (silicon dioxide)–ER (epoxy resin)/FR (fluorosilicone resin) superhydrophobic coatings using the spray method to improve the anti-icing and de-icing performance of transmission line insulators. The coatings exhibit a consistent fluorine distribution (32.86 wt%), which enhances their low surface energy, alongside SiO₂ nanoparticles that occupy the interstices between PTFE particles, resulting in a dense micro- and nanoscale hierarchical structure. Consequently, the coatings have good superhydrophobicity, featuring a contact angle of 173.9° and roll angle of 1.2°. Following 66 days of UV irradiation, the contact angle remains above 150°, and the roll angle is approximately 15°, accompanied by a slight increase in ice adhesion strength. Following 26 freeze–thaw cycles, the contact angle stabilizes at around 157°, showing good environmental durability. Natural icing studies validate the coatings’ good anti-icing and de-icing efficacy: in comparison to common insulators, the coated insulators demonstrate a 14.2% reduction in ice accretion weight and a 67.7% reduction in maximum ice ridge length. Full article

This study investigates the inverse estimation of the effective thermal diffusivity of a polytetrafluoroethylene (PTFE) plate subjected to oscillatory heating from a hot plate with on–off control. Transient temperature measurements at four internal positions were used to evaluate three modeling strategies: a constant-diffusivity formulation with a prescribed Dirichlet boundary condition, a position-dependent effective diffusivity formulation, (x), and a constant-diffusivity model with a Robin boundary condition to account for thermal contact resistance. The constant-diffusivity Dirichlet model, when fitted to all data simultaneously, was unable to reproduce the experimental thermal response satisfactorily. When fitted separately at each thermocouple position, the estimated effective diffusivity increased systematically with position change, indicating that the experimental response could not be represented by a single scalar parameter under the adopted Dirichlet formulation. Variable-(x) models improved the fit, especially the exponential and rational expressions, which reproduced the apparent saturating spatial trend more effectively. However, these functions should be interpreted as empirical effective representations rather than intrinsic constitutive laws for PTFE. The Robin-boundary model with constant diffusivity also provided a comparable fit, suggesting that interfacial thermal resistance at the PTFE–hot plate contact may explain part of the apparent spatial variation inferred by the Dirichlet models. These results indicate that internal temperature measurements under realistic transient heating are not sufficient to uniquely distinguish between distributed effective diffusivity and boundary-contact resistance effects. Therefore, the estimated diffusivity values should be interpreted as model-dependent effective parameters rather than direct measurements of intrinsic PTFE thermal diffusivity. Full article

Hydrogen energy systems rely extensively on polymeric materials for storage, sealing, transport, and tribological applications; however, their long-term reliability is strongly influenced by hydrogen–polymer interactions. This review presents a comparative analysis of polymers with and without hydrogen bonding, focusing on how molecular architecture governs hydrogen compatibility, transport behavior, and degradation mechanisms under high-pressure environments. Hydrogen-bonded polymers, such as polyamides, polyurethanes (PU), and polyimides, exhibit high mechanical strength and thermal stability due to strong intermolecular interactions but are susceptible to hydrogen-assisted chemical degradation and embrittlement. In contrast, non-hydrogen-bonded polymers, including polyethylene, polypropylene (PP), polytetrafluoroethylene (PTFE), and Polyether ether ketone (PEEK), demonstrate excellent chemical inertness and low hydrogen reactivity, yet experience diffusion-driven damage such as blistering and fatigue softening. This study establishes a unified framework linking molecular structure, hydrogen transport, and failure mechanisms, revealing a fundamental trade-off between mechanical integrity and chemical stability. Advanced strategies, including polymer blending, nanofiller reinforcement, and multilayer composites, are proposed to optimize durability, permeability, and overall hydrogen compatibility. Full article

The nondestructive characterization of coating thickness, acoustic velocity, and density is essential for industrial quality control. However, conventional ultrasonic reflection coefficient amplitude spectrum (URCAS)-based inversion methods typically require prior knowledge of acoustic attenuation, which is often unavailable for thin coatings and limits their practical applicability. To address this issue, a nonlinearity-guided dual-spectrum inversion framework is proposed by combining the URCAS with a layer-phase spectrum. It is found that the layer-phase spectrum exhibits strong nonlinear sensitivity to variations in acoustic velocity and density, which helps improve parameter identifiability. Based on this property, an improved particle swarm optimization algorithm is developed to enable simultaneous inversion of thickness, velocity, and density without explicit prior attenuation information. Finite-element simulations show that the conventional URCAS method yields mean relative errors exceeding 5%, whereas the proposed method reduces these errors to below 3% under the tested conditions. Experimental validation on eight industrial polytetrafluoroethylene (PTFE) coatings with thicknesses ranging from 20.89 μm to 120.11 μm (down to approximately 0.11 λ at 10 MHz) demonstrates that the proposed method achieves average relative errors within 10% and improves inversion accuracy by about 6% compared with amplitude-only approaches. The results indicate that the proposed attenuation-independent and nonlinearity-guided strategy provides an effective solution for the quantitative nondestructive evaluation of subwavelength coatings. The method is particularly suitable for thin coatings with unknown attenuation. Full article

To overcome the inherently low temperature sensitivity of fiber Bragg gratings (FBGs) in engineering applications under low-temperature conditions, a sensitivity-enhanced FBG temperature sensor based on a polytetrafluoroethylene (PTFE) encapsulation sleeve was developed. Four adhesive materials—silicone thermal grease, polydimethylsiloxane (PDMS), epoxy resin, and modified acrylic ester—were employed to package the FBG within the PTFE sleeve to improve its temperature sensitivity. Thermal stress simulations of the proposed sensor structure were carried out using COMSOL Multiphysics^® 6.2, and the simulation results showed good agreement with the experimental data. Based on the experimental results, the sensitivity-enhancement effects of PTFE combined with different adhesives, as well as the influences of the PTFE sleeve length and wall thickness, were systematically investigated. The results indicate that, within the temperature range of −35 °C to 15 °C, increasing both the length and thickness of the PTFE sleeve can effectively improve the temperature sensitivity of the sensor. When epoxy resin was used as the encapsulating adhesive, the sensor achieved a maximum sensitivity of 117.4 pm/°C, corresponding to a 13.19-fold increase compared with that of a bare FBG sensor. This sensitivity-enhancing packaging structure significantly improves both the temperature sensitivity and linearity of FBG temperature sensors, while also substantially reducing fabrication costs. Full article

Microplastics (MPs) in water treatment plants (WTPs) represent a critical environmental concern, particularly when treated effluent is reused for agricultural irrigation. This study investigates the occurrence, removal efficiency, and characterization of MPs in tertiary-treated wastewater destined for agricultural reuse in water-scarce regions. Additionally, the study examines the influence of sample volume on extrapolated MP concentrations. Despite advanced treatment processes including ultrafiltration achieving removal efficiencies of 89%, substantial quantities of MPs remain in final effluents at concentrations ranging from 89 to 399 MPs/m³ (equivalent to 0.1–0.4 MPs/L) with a mass load of 2 µg/L at the outlet. Morphological analysis revealed a shift from fragment-dominated influent (~50%) to film-dominated effluent (~51%), with blue particles being most prevalent. Size distribution analysis showed distinct peaks: 50–100 µm for fragments, 100–250 µm for films, and 250–500 µm for fibres. Polytetrafluoroethylene (PTFE) emerged as the dominant polymer across all morphotypes. Finally, converting particle counts to mass loads indicated an average decrease from ~11 µg/L at the inlet to ~2 µg/L at the outlet, underscoring that number- and mass-based metrics provide complementary information for risk assessment. Full article

The growing demand for long-distance green methanol transportation highlights the critical need to evaluate the safety and reliability of pipeline sealing materials. This study investigates the swelling mechanisms of fluorocarbon rubber (FKM), nitrile butadiene rubber (NBR), and polytetrafluoroethylene (PTFE) under simulated methanol pipeline conditions. Static immersion tests were conducted under simulated pipeline conditions with water contents of 0–20% and temperatures of 25–55 °C, supplemented by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and gas chromatography–mass spectrometry (GC–MS). FKM exhibited severe physical swelling, with the volume increase reaching up to 80% in pure methanol. Notably, the addition of 5% water markedly suppressed this swelling, reducing the volume change of FKM sealing rings to approximately 3% and the mass change to 1%. Conversely, NBR experienced volume shrinkage and mass loss due to the extraction of the plasticizer Bis(2-ethylhexyl) phthalate by methanol, a process also inhibited by water. PTFE demonstrated exceptional chemical stability and negligible dimensional changes owing to its high crystallinity and rigid structure. Consequently, PTFE is recommended as the optimal sealing material for pure methanol pipelines. When utilizing FKM or NBR, strict control over the fluid’s water content and operating temperature is essential to prevent degradation and ensure long-term pipeline integrity. Full article

One-dimensional mass transfer resistance-in-series framework was developed theoretically and validated experimentally using a flat-plate polytetrafluoroethylene/polypropylene (PTFE/PP) membrane module to predict CO₂ absorption fluxes and concentration distributions. The decline in CO₂ absorption efficiency along the membrane module is primarily attributed to increased concentration polarization resistance and a reduced driving force concentration gradient. To alleviate these limitations, carbon fiber promoters were strategically embedded to suppress concentration polarization, reduce the mass transfer resistances, and enhance turbulence intensity. In the present study, device performance was further improved by implementing properly ascending or descending hydraulic equivalent widths along the absorbent feed channel. Under the descending configuration, an absorption flux enhancement of up to 44.94% was achieved relative to an empty-channel module (i.e., without S-ribbed carbon fiber inserts). Theoretical formulations were established to predict absorption fluxes under varying monoethanolamine (MEA) volumetric flow rates, CO₂/N₂ mixture flow rates, and inlet CO₂ feed concentrations. The model predictions showed good agreement with experimental results obtained using MEA solutions under both ascending and descending hydraulic width operations, demonstrating effective mitigation of polarization effects and enhanced absorption flux along the absorbent feed channel. An economic assessment of the S-ribbed carbon fiber module was conducted by evaluating the trade-off between absorption flux enhancement and incremental power consumption. The results indicate that the proposed design provides a practical and economically viable approach for improving the performance of membrane-based CO₂ capture technologies. In addition, an enhanced Sherwood number correlation, expressed in a simplified form, was developed and employed to estimate the mass transfer coefficients of CO₂ membrane absorption modules incorporating S-ribbed carbon fiber promoters. Full article