Small range 文档类型:"3"

Totally found 2451 items.

  • [期刊] Polytetrafluoroethylene (PTFE)/silane cross-linked sulfonated poly(styrene-ethylene/butylene-styrene) (sSEBS) composite membrane for direct alcohol and formic acid fuel cells
    A novel polymeric electrolyte membrane for direct alcohol fuel cells(DAFCs) and direct formic acid fuel cells (DFAFCs) was developed using a pore-filling method. This composite consisted of a porous polytetrafluoroethylene (PTFE) microporous substrate filled with silane-crosslinked sulfonated poly (styrene-ethylene/butylene-styrene) (sSEBS). This composite membrane was characterized using field emission scanning electron microscopy, Fourier-transform infrared spectrometry, thermal gravimetric analysis, and differential scanning calorimetry. The thermal and mechanical stabilities of this composite membrane were good. The methanol and ethanol permeabilities of this composite membrane were lower than Nafion 117, and these two membranes had comparable ionic conductivities. The power densities in direct methanol fuel cells with this composite electrolyte were higher than with the Nafion electrolyte. A peak power density of 91.4mW cm(-2) was achieved at 70 degrees C when the cell was fed with 0.5 M methanol. A direct ethanol fuel cell using this composite exhibited a peak power density of 16.5 mW cm(-2) at 60 degrees C. In a DFAFC, a peak power density of 81.4 mW cm(-2) was achieved with this composite and 3 M fuel at 60 degrees C. Long-term cell performance was sustained during a 180-h continuous operation using this pore-filled PTFE/sSEBS composite electrolyte. This PTFE/sSEBS composite membrane has potential for use in proton-exchange DAFC and DFAFC applications. (C) 2014 Elsevier B. V. All rights reserved.
  • [期刊] Bioethanol production in vacuum membrane distillation bioreactor by permeate fractional condensation and mechanical vapor compression with polytetrafluoroethylene (PTFE) membrane
    A vacuum membrane distillation bioreactor (VMDBR) by permeate fractional condensation and mechanical vapor compression with PTFE membrane was developed for bioethanol production. Cell concentration of 11.5 g/L, glucose consumption rate of 5.2 g/L/h and ethanol productivity of 2.3 g/L/h could be obtained with fermentation continues lasting for 140 h. Membrane flux of over 10 kg/m(2)/h could be obtained for model solution separation. Higher temperature and flow rate could promote membrane separation. Membrane flux could be reduced to about 2000 g/m(2)/h with fermentation proceeding owing to the deposited cell on membrane surface. The membrane separation performance could be resumed by water rinse. High ethanol concentration of 421 g/L could be obtained by permeate fractional condensation with the process separation factor increased to 19.2. Energy of only 14 MJ/kg was required in VMDBR and the energy consumption would be reduced further if the compressed vapor could be used to heat the feed.
  • [期刊] Effect of rubber compounding agent on adhesion strength between rubber and heat-assisted plasma-treated polytetrafluoroethylene (PTFE)
    Although heat-assisted plasma treatment enables drastic improvement of the adhesion property of polytetrafluoroethylene (PTFE), plasma-treated PTFE does not strongly adhere to any adherend. To clarify which rubber compounding agents positively affect the adhesion strength of a plasma-treated PTFE/rubber assembly, six types of unvulcanised rubbers were prepared and thermally compressed to a plasma-treated PTFE sheet. Thus, it was found that SiO2 addition to rubber drastically increased the adhesion strength of a plasma-treated PTFE/rubber assembly and cohesion failure of rubber occurred with large fractions of SiO2 although no adhesives were used. To confirm the reaction between plasma-treated PTFE and SiO2 powder, X-ray photoelectron spectroscopy (XPS) measurements were performed for the thermally compressed SiO2/PTFE assembly after repeated washing. The XPS results indicated that hydrophilic SiO2 powder strongly adhered to the plasma-treated PTFE, whereas hydrophobic SiO2 powder did not adhere to the PTFE. In this paper, a model was proposed for a possible mechanism of strong adhesion of a PTFE/rubber assembly through both hydrogen and covalent bonds between silanol groups of the SiO2 powder surface in the rubber and hydroxyl or carboxyl groups on the plasma-treated PTFE.
  • [期刊] Bioethanol production in vacuum membrane distillation bioreactor by permeate fractional condensation and mechanical vapor compression with polytetrafluoroethylene (PTFE) membrane
    A vacuum membrane distillation bioreactor (VMDBR) by permeate fractional condensation and mechanical vapor compression with PTFE membrane was developed for bioethanol production. Cell concentration of 11.5 g/L, glucose consumption rate of 5.2 g/L/h and ethanol productivity of 2.3 g/L/h could be obtained with fermentation continues lasting for 140 h. Membrane flux of over 10 kg/m(2)/h could be obtained for model solution separation. Higher temperature and flow rate could promote membrane separation. Membrane flux could be reduced to about 2000 g/m(2)/h with fermentation proceeding owing to the deposited cell on membrane surface. The membrane separation performance could be resumed by water rinse. High ethanol concentration of 421 g/L could be obtained by permeate fractional condensation with the process separation factor increased to 19.2. Energy of only 14 MJ/kg was required in VMDBR and the energy consumption would be reduced further if the compressed vapor could be used to heat the feed.
  • [期刊] Waste incineration of Polytetrafluoroethylene (PTFE) to evaluate potential formation of per- and Poly-Fluorinated Alkyl Substances (PFAS) in flue gas
    In recent years, concerns over some per- and polyfluorinated alkyl substances (PFAS) have grown steadily. PFAS are a large group of chemical substances with widely differing properties. While one class of PFAS, fluoropolymers, have been demonstrated to meet the OECD criteria for polymers of low concern during the in use phase of their lifecycle, questions remain regarding waste handling at the end of useful life for products containing fluoropolymers. To show that polytetrafluoroethylene (PTFE) can be almost fully transformed into fluorine (F) (as hydrofluoric acid (HF)) and to study the possible generation of low molecular weight per- and polyfluorinated alkyl substances (PFAS), PTFE combustion under typical waste incineration conditions at the BRENDA (German acronym for "Brennkammer mit Dampfkessel") pilot plant at Karlsruhe Institute of Technology (KIT) was investigated. Results indicate that, within procedural quantitation limits, no statistically significant evidence was found that the PFAS studied were created during the incineration of PTFE. Therefore, municipal incineration of PTFE using best available technologies (BAT) is not a significant source of the studied PFAS and should be considered an acceptable form of waste treatment. (C) 2019 The Authors. Published by Elsevier Ltd.
  • [期刊] Effects of Copper Nanoparticles Located in Different Regions of Polytetrafluoroethylene/Polyimide Blends on the Morphology, Mechanical and Tribological Properties of PTFE Composites
    The effects of copper nanoparticles (Cu) located in different regions of polytetrafluoroethylene/polyimide (PTFE/PI) blends on the morphology, thermal, mechanical, and tribological properties of PTFE composites were studied. Region one is PI phases (the corresponding composites is denoted as PPC), region two is PTFE phases and the interface between PTFE and PI (the corresponding composites is denoted as PPC-m). Results indicate that the incorporation of Cu nanoparticles into PI phases improves the dispersibility and homogeneity of PI phases. As a consequence, the crystallinity of PTFE composites is reduced, but compressive strength and modulus of PTFE composites are enhanced by 50.3% and 14.4% respectively. In addition, self-lubricity and wear resistance of PTFE composites are improved by 10.4% and 50.5%. Scanning electron microscopy (SEM) demonstrates that PI phases with Cu nanoparticles hinder the direct contact between PTFE matrix and counterparts. However, Cu nanoparticles located in PTFE matrix and the interface between PTFE and PI deteriorates the dispersibility and homogeneity of PI phases, which lead to the poor mechanical and tribological performance of PTFE composites.
  • [期刊] Rate-dependent mechanical characteristics of polytetrafluoroethylene (PTFE) gaskets under cyclic pulsating compression
    Accumulated deformations of polytetrafluoroethylene (PTFE) gaskets under cyclic stress-controlled compressive loads considering temperatures and stress rates are tested. Results present that the accumulated compressive deformation of PTFE gaskets becomes load rate independent when the stress rate is less than 0.1 MPa/s under various temperatures. The compressive deformation accumulates during the initial 50 or more cycles, but it always turns to shakedown subsequently under the experimental conditions. Moreover, the accumulated strain is sensitive to temperature due to material softening and time-dependent creep, especially when the temperature is over 100 °C. This research provides important data for the safety assessment of sealing joints with PTFE gaskets.
  • [期刊] Adsorption of anion polyacrylamide from aqueous solution by polytetrafluoroethylene (PTFE) membrane as an adsorbent: Kinetic and isotherm studies
    In this study, the kinetic and isothermal behaviors of anion polyacrylamide (APAM) on a polytetrafluoroethylene (PTFE) microfiltration membrane were investigated to better understand the adsorption mechanism. A series of adsorption experiments were conducted to determine the effects of the initial APAM concentration, contact time, solution pH and temperature on the adsorption performance. The results showed that the three isotherm models (Langmuir equation, Freundlich equation and Temkin equation) favorably fit the adsorption process with R-2 values of 0.98957, 0.90721 and 0.96321, respectively. The adsorption rate of APAM onto the PTFE membrane increased with increasing temperature, and the adsorption reaction reached equilibrium at 20 h. The values of thermodynamic adsorption parameters (Delta(r)G(m)(theta), Delta H-r(m)theta, and Delta S-r(m)0) suggested that the adsorption process was not spontaneous but endothermic. In addition, high temperatures favored adsorption, and the adsorption can be categorized as physisorption. Specifically, the main physisorption force was hydrogen bonding. The adsorption process consisted of two phases: rapid adsorption and stable adsorption. The three kinetic equations provided a good fit according to the R-2 values and were applicable in the following order: pseudo-first-order > pseudo-second-order > Elovich. (C) 2019 Elsevier Inc. All rights reserved.
  • [期刊] Grafting of acrylic acid onto microwave plasma-treated polytetrafluoroethylene (PTFE) substrates
    Polytetrafluoroethylene (PTFE) has limited use in biomedical applications due to its poor wettability and low adhesion strength. Enhancing these properties through modification via plasma treatment coupled with grafting can further improve its surface properties ideal for biomedical applications. In this study, hydrophilic PTFE samples were successfully realized using a modified 2.45 GHz microwave oven as the plasma treatment device followed by grafting copolymerization using acrylic acid (AAc). This resulted to an increase in surface free energy (SFE) where samples subjected to air plasma treatment and AAc grafting exhibited the largest increase in SFE of 58 mJ m(-2) compared to 17 mJ m(-2) for the untreated samples. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed new functional groups in the O1s and C1s regions of PTFE after plasma treatment and grafting. Atomic force microscopy analysis showed increase in surface roughness with the largest value of 67.7 nm found in air plasma-treated and grafted samples compared to 20.9 nm for the untreated PTFE sample. The plasma-treated and grafted PTFE surfaces did not exhibit hydrophobic recovery during a 7 d observation period as compared to plasma-treated samples only. The effective combination of plasma treatment and grafting process would broaden potential applications of PTFE as a biomaterial. (C) 2018 The Japan Society of Applied Physics
  • [期刊] Polytetrafluoroethylene (PTFE) hollow fiber AnMBR performance in the treatment of organic wastewater with varying salinity and membrane cleaning behavior
    PTFE hollow fiber anaerobic membrane bio-reactor (AnMBR) performance was investigated in the treatment of organic wastewater, with varying salinity and PTFE membrane cleaning behavior. The AnMBR was operated for 226?days, with a total and biological COD removal efficiency of 97.2% and 89.9% respectively, at a NaCl concentration of 35?g?L?1. A high number ofProteobacteria(38.2%) andBacteroidetes(25.9%) were present in the system, with an increase in membrane fouling rate from 1.88?×?1011to 2.63?×?1011?m?1?d?1with higher salinity. The effects of soluble microbial products (SMP), extracellular polymeric substances (EPS), low molecular-weight (LMW) carbohydrates, sludge particle size and inorganic element accumulation, were evaluated on membrane fouling. Flux recovery of fouled PTFE membranes reached 91.6% with offline cleaning. Overall, results indicate that PTFE hollow fiber AnMBR provides a promising method for the treatment of saline organic wastewater.
意见反馈
返回顶部