Search Results (649)

Wind energy, an abundant renewable resource, remains difficult to harness efficiently due to fluctuating speeds and unpredictable directions. In this work, we present a wind bell-inspired triboelectric nanogenerator (WB-TENG) designed for omnidirectional, variable-speed wind harvesting, utilizing layered triboelectric polymers such as polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), and polyamide (PA) to enhance energy capture performance. The developed device demonstrates the ability to generate electrical output even under extremely low wind speeds as low as 0.5 m/s. Additionally, it successfully captures wind energy from all directions within a full 360° range. Through structural optimization, the WB-TENG achieves a peak output voltage of 25.1 V and a maximum power of 3.5 μW, representing substantial improvements of 170% and 1232%, respectively, over the performance of our previous prototype. To verify its practical capability, the optimized WB-TENG is employed to power several electronic devices, including a digital watch and 50 commercial LEDs, confirming its potential for real-world energy harvesting applications. This work presents a novel and effective strategy for harnessing wind energy under dynamic environmental conditions, offering a sustainable approach for decentralized energy collection in low-speed and omnidirectional wind settings. Full article

Raman spectroscopy is a widely used analytical technique; however, the choice of container material can significantly affect repeatability due to noise and unwanted Raman bands. This paper describes the interaction of excitation radiation with the sample’s environment and the materials surrounding or containing it. Polytetrafluoroethylene (PTFE) and Barium Sulphate are analyzed as contact surfaces with the containers. We aim to investigate how different container materials affect the Raman spectrum and identify the optimal material to minimize measurement bias. We compared the Raman spectra of containers made of dissimilar materials, including plastic, glass, quartz, and aluminum, to assess their effects on the spectra, and we propose a container design that enhances Raman spectroscopy signals. We consider Raman bands from biological samples of glucose (in water) and urine (urea and creatinine), which serve as references for comparison in the in vitro analysis of these substances across different containers and backgrounds. Full article

Background: This in vitro study compared the effectiveness of polytetrafluoroethylene (PTFE) tape and a conventional cotton retraction cord for gingival displacement and evaluated the mechanical and microstructural characteristics of PTFE tape. Methods: Eight standardized prepared teeth with artificial gingiva were evaluated under three conditions: control, cotton retraction cord, and PTFE tape. After each condition, impressions were digitized using a CAD/CAM system. Sulcular width was measured at four predefined locations and averaged for statistical analysis. PTFE tape was also evaluated by tensile testing before and after sterilization and by scanning electron microscopy (SEM). Results: Mean sulcular widths were 0.716 ± 0.118 mm (control), 0.851 ± 0.140 mm (cotton cord), and 0.907 ± 0.099 mm (PTFE). Repeated-measures ANOVA showed a significant effect of the displacement method (p < 0.001), with PTFE producing significantly greater sulcular enlargement than cotton cord. Qualitative SEM analysis revealed a more homogeneous impression surface morphology following PTFE removal. Sterilization did not significantly affect the tensile properties or microstructural integrity of PTFE tape. Conclusions: Under standardized in vitro conditions, PTFE tape produced the highest gingival sulcular enlargement and maintained favorable mechanical and microstructural properties, supporting its potential as an alternative gingival displacement material. Further clinical studies are required to confirm these findings. Full article

Background: Inferior vena cava (IVC) leiomyosarcoma is a rare vascular malignancy for which complete surgical resection remains the only potentially curative treatment. Surgical management is technically demanding, particularly when the tumor involves the renal veins and retrohepatic IVC, requiring complex vascular reconstruction while preserving renal function. Case Presentation: We report the case of a 60-year-old woman with a localized high-grade IVC leiomyosarcoma involving the retrohepatic cava and both renal vein ostia, with cranial intraluminal extension toward the right atrium. Following multidisciplinary evaluation, the patient underwent en bloc tumor resection with reconstruction of the IVC using a 20mm ringed polytetrafluoroethylene (PTFE) graft. Left renal venous drainage was restored through prosthetic reconstruction using a tubular pericardial conduit anastomosed to the prosthetic graft, while renal function on the right side was preserved by renal autotransplantation into the right iliac fossa. Histopathological examination confirmed a high-grade leiomyosarcoma with negative surgical margins (R0 resection). Adjuvant chemotherapy with doxorubicin and dacarbazine was initiated but discontinued after two cycles because of cardiotoxicity. Fourteen months after surgery, the patient remains disease-free with preserved renal function. Conclusions: Radical resection combined with tailored vascular reconstruction remains the cornerstone of treatment for localized IVC leiomyosarcoma. When the renal veins are involved, combining prosthetic caval reconstruction with renal autotransplantation may represent a safe and feasible strategy to preserve renal function while achieving complete oncological resection. Full article

Thermochemical depolymerization of polymer mixtures and composite materials is challenging due to non-additive degradation behavior and the emergence of new reaction pathways during pyrolysis. Both polytetrafluoroethylene (PTFE) and silicone rubber (SR) can depolymerize into monomers or low-molecular-weight oligomers when pyrolyzed individually, making them, in principle, suitable candidates for depolymerization-based recycling. Because they are frequently combined in technical applications and composites, their behavior during co-pyrolysis warrants investigation. However, the pyrolysis of PTFE:SR mixtures and composites remains poorly understood. In this study, we examine the pyrolysis behavior of PTFE:SR systems with emphasis on mass balance, product composition, and the formation of new species to address potential limitations for depolymerization-based recycling. Experiments were conducted on virgin PTFE and SR, defined polymer mixtures, and commercially relevant composites, including PTFE-lined silicone tubing and PTFE:SR septa. The results reveal a pronounced, non-linear dependence of product distribution on PTFE content. Product identification by GC-MS, NMR, and FTIR indicates cleavage of Si–O and Si–CH₃ bonds and the formation of fluorinated siloxanes as well as new per- and polyfluoroalkyl substances (PFAS). At low PTFE contents, liquid products are dominated by cyclic siloxanes (D_x). These findings show that depolymerization strategies developed for pure polymers cannot be directly applied to PTFE:SR composites. While systems with low PTFE content may be more amenable to depolymerization, higher PTFE fractions promote the formation of PFAS and difficult-to-valorize fluorinated silicon species. These products complicate selective monomer recovery and could pose significant challenges for the depolymerization-based recycling of PTFE-rich composites. Full article

Triboelectric charging can significantly affect the flow behavior of insulating powders on wall surfaces. Microcrystalline cellulose (MCC), a widely used pharmaceutical excipient, is particularly prone to charge accumulation during particle-to-wall contact. In this study, wall friction shear tests were used to examine how trough material affects triboelectric charging and wall friction of MCC under quasi-static flow conditions. Three trough materials were evaluated including stainless steel (metallic), polylactic acid (PLA), and polytetrafluoroethylene (PTFE) by using both standard and layer-by-layer preparation methods. The generated electrostatic charge was measured using a Faraday cup, and the corresponding wall yield loci over a PTFE wall coupon were determined from shear tests. Charge measured after shearing for the standard preparation method revealed that PTFE trough produced charge magnitudes ~16–21 times greater than stainless steel trough (64.5 nC vs. 3.1 nC for MCC 102; 59.7 nC vs. 3.8 nC for MCC 203), while PLA trough produced an intermediate and particularly powder-dependent response, including a polarity reversal for MCC 203 (−38.9 nC vs. +3.8 nC on stainless steel trough). This charging contributed to a direct increase in wall adhesion, with ${\tau }_{ad}$ increasing by 61.6% (MCC 102) and 41.8% (MCC 203) on PTFE relative to stainless steel. The layer-by-layer method amplified charging further for both conductive and insulating troughs. Similarly, adhesion trends were generally consistent across layering preparation methods, with PTFE trough again showing the largest increase relative to stainless steel (40.5% for MCC 102; 55.6% for MCC 203), while PLA trough showed a more variable response, including a slight decrease in adhesion to MCC 102 (−11.7%). PTFE and PLA troughs produced substantially higher charges than the metallic trough, resulting in higher shear stress across the wall yield loci of two MCC powder sizes. The main effect of insulating materials was a non-negligible increase in adhesion. Consequently, the experimental characterization of wall friction via shear testing should be performed with a trough material with an electrical conductivity similar to that of the investigated wall coupon to ensure accurate process replication. Full article

The delay-and-sum total focusing method (TFM) for ultrasonic full matrix capture (FMC) depends on accurate ray path and travel time computation. In L-shaped carbon fiber-reinforced polymer (CFRP) corner parts, elastic anisotropy, multilayer stacking, and curvature-induced ray path non-uniqueness generate strong stripe-like coherent clutter (deterministic structural echoes), degrading focusing and sizing. To address this, we search multiple physically plausible candidate ray paths and propose a phase-consistency-adaptive multi-path fusion TFM (PCA-MPF-TFM) that performs pixel-wise path selection and fusion. The method is validated using pulse-echo FMC data acquired with a water-immersion linear array from a 6.4 mm-thick L-shaped CFRP specimen containing three 3 mm-diameter polytetrafluoroethylene (PTFE) inserts; the two within the concave-side inspection region were quantitatively evaluated. Compared with conventional isotropic TFM, an edge-adjacent delamination previously masked by structural noise is consistently detected with a 9.2 dB signal-to-noise ratio (SNR) and a 0.2 mm length error. For the second delamination, the SNR improves by 25 dB and the length error decreases from 0.6 mm to 0.2 mm. Experimental results demonstrate improved defect detectability and noise robustness under curved, anisotropic, and multilayer propagation while maintaining sub-millimeter sizing accuracy. Full article

Hydrothermal carbonization (HTC) of digested dairy manure produces hydrochar and a nitrogen-rich post-liquid. This study evaluated a submerged tubular expanded polytetrafluoroethylene (ePTFE) gas-permeable membrane (GPM) system for ammonia recovery from post-HTC liquid derived from digested dairy manure, focusing on the effects of feed temperature, acid circulation rate, and feed volume-to-membrane surface area ratio (FV/MS). Compared with filtered digested manure, the post-HTC liquid had a similar total ammoniacal nitrogen (TAN) concentration (1151 vs. 1164 mg N L⁻¹) but a slightly higher pH (8.38 vs. 7.94), which favored ammonia transfer. Increasing feed temperature from 20 to 60 °C raised 24 h TAN recovery from 63.5% to 99.6% and average TAN transfer flux from 11.1 to 17.7 g m⁻² d⁻¹, although it also increased water vapor crossover and diluted the acid trapping solution. Increasing acid circulation from 10 to 30 mL min⁻¹ improved 48 h TAN recovery from 85.2% to 94.0%, while a further increase to 50 mL min⁻¹ produced only a small additional gain. In contrast, elevating FV/MS from 0.015 to 0.045 m³ m⁻² reduced 48 h TAN recovery from 94.0% to 59.6% while increasing average TAN transfer flux from 8.2 to 16.2 g m⁻² d⁻¹ because larger feed volumes sustained the concentration driving force for a longer period. Nitrogen mass balance showed that more than 94–99% of the initial TAN was accounted under most conditions, with only a small fraction lost to volatilization. Full article

Despite the fact that oxygen plasma treatments are widely used to modify the surface properties of polytetrafluoroethylene (PTFE), the long-term stability of these surface modifications has not been fully investigated. Specifically, the roles of morphological restructuring and chemical modifications at the surface remain to be understood. In this work, we treat commercial PTFE samples using O₂ plasmas at different discharge pressures to investigate their surface modifications and subsequent ageing at atmospheric pressure. We provide direct evidence that ageing behavior is governed by nanoscale and microscale restructuring of the plasma-modified interface, revealing a novel link between morphology dynamics and wettability properties. To capture this surface evolution, the modified interface was characterized using water contact angle (WCA) measurements, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and mass spectrometry (MS). Initial plasma treatment enhances PTFE hydrophobicity, shifting the WCA from ${\theta }_c\simeq 105°$ to a highly hydrophobic state of ${\theta }_c\simeq 135°$. By monitoring the samples in contact with air over a 67-day period a gradual transition toward hydrophilicity was revealed, with WCAs stabilizing at ${\theta }_c\simeq 70°$ after approximately 20 days. SEM observations identified time-dependent morphological degradation of plasma-induced nanostructures, while qualitative and quantitative FTIR analysis—utilizing the Specified Area Under Band (SAUB) method—confirmed corresponding shifts in carbonyl and hydrocarbon indices. These results demonstrate that ageing kinetics are a direct function of plasma pressure. The transition is further supported by a phenomenological fractal model, which confirms a morphological shift from an initial fractal surface ($d_s\simeq 2.25$) toward a standard flat geometry ($d_s=2$). Furthermore, calculations indicate a sign reversal in solid-gas interface tension parameters, reflecting the changed chemical nature of the surface. We conclude that the loss of hydrophobicity is driven by a synergistic interplay between morphological relaxation and chemical restructuring. Full article

Composite aerogels based on polytetrafluoroethylene (PTFE) and graphene oxide (GO) with a high polymer content of 90, 95 and 98 wt.% were synthesized for the first time. It was found that GO performs a structure-forming function, allowing the production of monolithic three-dimensional frameworks stable under freeze-drying conditions even at a minimal concentration of 2 wt.%, whereas pure PTFE is destroyed under these conditions. Subsequent annealing of the composites at 370 °C, which is higher than the decomposition temperature of oxygen-containing groups of GO and the melting point of PTFE, leads to the formation of PTFE/reduced graphene oxide (rGO) aerogels. A direct dependence of shrinkage during annealing on the polymer content was observed: it sharply increases from 2.1% to 26.6% with an increasing proportion of PTFE. This effect is explained by the dominant role of capillary forces pulling together the rGO sheets in the molten polymer, while the rGO frame resists the shrinkage. The most significant result is the achievement of a record low water sorption capacity (Q_w) for an aerogel with 98% PTFE, amounting to only 0.001 g/g. This value is several orders of magnitude lower than that of pure rGO aerogel (~20 g/g), confirming that a high content of hydrophobic polymer combined with thermal treatment effectively shields the hydrophilic sites on the surface of the rGO sheets. The composites obtained in this work exhibit high hydrophobicity (contact angles up to 144°) and unique potential for the selective absorption of organic solvents from water. Full article

Based on the growing use of guided bone regeneration (GBR) for implant rehabilitation in atrophic alveolar ridges, the choice of barrier membrane remains a critical factor for clinical success. This review aimed to evaluate the clinical effectiveness of titanium-reinforced dense polytetrafluoroethylene (d-PTFE-Ti) membranes compared with resorbable collagen membranes in vertical ridge augmentation. A literature review was conducted using PubMed, Cochrane Library, and ScienceDirect databases. Clinical studies published since 2014 involving human subjects undergoing GBR procedures with either d-PTFE-Ti or collagen membranes were included. Nine studies met the inclusion criteria, including randomized clinical trials and cohort studies. The selected studies indicated that both membrane-based approaches were effective in promoting bone regeneration and enabling implant placement. Titanium-reinforced d-PTFE membranes may offer mechanical advantages in space maintenance and dimensional stability, particularly in larger vertical defects; however, the available comparative evidence did not demonstrate a consistent statistically significant superiority over collagen-based approaches. Within the limitations of the available evidence, both strategies appear to provide clinically predictable outcomes, and membrane selection should be individualized according to defect morphology and treatment requirements. Full article

An analytical method was established for the rapid determination of 45 pigments and preservatives in edible ink by ultra-high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UHPLC-MS/MS), which provides technical support for the composition analysis and industrial development of edible ink. The samples were easily extracted with 75% aqueous methanol solution and purified with a Captiva EMR-Lipid HF solid-phase extraction cartridge. After filtration through a polytetrafluoroethylene (PTFE) membrane, the analytes were determined by UHPLC-MS/MS under multiple reaction monitoring (MRM) mode in both positive and negative ion modes. Poroshell 120 AQ-C18 was selected as the analytical column, and valve switching timing control was adopted during the gradient elution process. The external standard method was used for quantitative analysis. In the established method, the 45 pigments and preservatives exhibited good linear relationships within the mass concentration range of 0.0002–200.0 μg/mL. The limits of detection (LOD) and limits of quantification (LOQ) were 0.0004–8.00 mg/kg and 0.001–20.00 mg/kg, respectively. Using 25% aqueous glycerol solution as the blank matrix, the recoveries of analytes at different spiked levels met the detection requirements. The established method is simple and rapid, and can be applied to the qualitative and quantitative detection of typical pigments and preservatives in edible ink. Full article

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

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