Recent Advances in the Application of Natural Fiber Based Composites

Natural fiber reinforced polymer composites are lightweight, economical and available in a variety of forms. They have low densities, comparable material properties, high molding flexibility and are environmentally friendly, making them a conceivable alternative to traditional fillers like mica, calcium carbonate and glass. By modifying either the resin system or the natural fiber, biocomposites can be designed for different applications ranging from products of commodity to aerospace, examples including electroactive papers, fuel cell membranes, controlled drug release mechanisms and biosensors. This review aims to analyze the advancement in the application of cellulose based materials in different sectors with a discussion of fundamental research in these areas.

     

Frictionally excited thermo-elastoplastic instability

A transient finite element simulation is used to solve the two-dimensional contact problem involving thermo-elastoplastic instability (TEPI) in frictional sliding system. The existence of plastic deformation below the critical speed for thermoelastic instability is independent of the size of initial perturbation. For the simulation of the first/second partial contact, the amount of initial perturbation affects only the time interval of the first partial contact and the second partial contact is reached earlier, regardless of the initial perturbation. In addition, it shows that the locations of hot spots after cooling are changed.     

Preparation and characterization of titania/ZnS core-shell nanotubes

Core-shell nanocomposites of titania nanotubes/ZnS quantum dots have been prepared by using a hydrothermal synthetic method and characterized by using various microscopic and spectroscopic methods. ZnS quantum dots surround the outsides of titania nanotubes having the inner and the outer diameters of 15 and 30 nm, respectively, with a thickness of 2 nm. The nanocomposites suspended in water show a broader absorption spectrum shifted to a longer wavelength by 20 nm and emit substantially stronger ZnS luminescence having significantly slower decay kinetics than bare ZnS nanoparticles in water. The support of TiO2 nanotubes is found to enhance the optical properties of ZnS considerably.     

Effect of nanosized gold particle addition to supported metal oxide catalyst in methanol oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nano-sized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.     

Electronic coupling in dimetallic complexes with pi-conjugated bridge

Compound 2, [(eta5-C5Me5) Fe(dppe)]2(mu-C[triple bond]C-CH==CH-C[triple bond]C), was prepared by the reaction of compound 1, [eta5-C5Me5) Fe(dppe)]2+ (mu2-C==CH-CH=CH-HC=C).(PF6)2-, with KOBu(t). Compound 2 showed two quasi-reversible one-electron oxidations at -0.674 and -0.253 V, respectively. The comproportionation constant, Kc, was calculated from these measurements. The mixed-valence(MV) radical cation 2+ showed an absorption peak at 1586 nm, which was assigned to the MV pi-pi band of the delocalized complex (Robin-Day Mixed-valence Class III) and the effective coupling parameter, Hab, is consistent with the presence of electronic delocalization.     

Sulfonated poly(ether sulfone)‐based catalyst binder for a proton‐exchange membrane fuel cell

Sulfonated poly(ether sulfone) copolymer (PES 60) and its partially fluorinated analogue (F‐PES 60) were synthesized via the nucleophilic aromatic polycondensation of commercially available monomers to make a polymer electrolyte membrane and a binding material in the electrodes of a membrane–electrode assembly (MEA). PES 60 and F‐PES 60 showed proton conductivities of 0.091 and 0.094 S/cm, respectively, in water at room temperature. The copolymer was dissolved in the mixture of alcohol and water to get a 1 wt % binder solution. A catalyst slurry was prepared with the copolymer solution and sprayed on the copolymer (PES 60 or F‐PES 60) membrane to obtain a MEA. Both PES 60 and F‐PES 60 based MEAs were fabricated with different amounts of their binder in the electrodes to examine the effect of the copolymer binder in the catalyst layer on the fuel cell performance. The MEA with 2 wt % copolymer binder in the electrodes showed the best fuel cell performance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Assessment of the Efficacy of Intermittent Ozone Disinfection

An example of intermittent disinfection occurs in dental-unit water systems (DUWS), which are disinfected only for a specified time per each day. The efficacy of intermittent ozonation was evaluated using a laboratory-scale, membrane-based ozone disinfection system (MBODS), which delivers bubbleless dissolved ozone to the DUWS. A new tool - the weighted Ct value, or C_w, - was applied to interpret heterotrophic plate counts (HPC) data. To achieve the American Dental Association's (ADA's) criterion (<200 CFU/mL), the required ozone dosage was C_w > 0.07 mg–O₃/L. However, even the highest ozone dosage (C_w > 0.130 mg/L) allowed biofilm HPC to persist at over 10⁴ CFU/cm². Although a higher C_w killed planktonic and biofilm bacteria more thoroughly, it also generated more biodegradable dissolved organic carbon (BDOC). Thus, this research illustrates the inherent trade-off of intermittent ozonation: a higher C_w kills more bacteria during the ozonation period, but creates more BDOC that fosters biofilm regrowth when ozonation is off.     

Fuel cell performance of polymer electrolyte membrane based on hexafluorinated sulfonated poly(ether sulfone)

The potential-current fuel cell characteristics of membrane electrode assemblies (MEAs) using hexafluorinated sulfonated poly(ether sulfone) copolymer are compared to those of Nafion^® based MEAs in the case of proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC). The hexafluorinated copolymer with 60 mol% of monosulfonated comonomer based acid form membrane is chosen for this study due to its high proton conductivity, high thermal stability, low methanol permeability, and its insolubility in boiling water. The catalyst powder is directly coated on the membrane and the catalyst coated membrane is used to fabricate MEAs for both fuel cells. A current density of 530 mA cm^?2 at 0.6 V is obtained at 70 °C with H₂/air as the fuel and oxidant. The peak power density of 110 mW cm^?2 is obtained at 80 °C under specific DMFC operating conditions. Other electrochemical characteristics such as electrochemical impedance spectroscopy, cyclic voltammetry, and linear sweep voltammetry are also studied.     

Group Delay Equalized UWB InGaP/GaAs HBT MMIC Amplifier Using Negative Group Delay Circuits

A negative group delay (NGD) circuit has been employed to equalize a group delay variation in a broadband ultra-wideband (UWB) InGaP/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) amplifier. Using the NGD circuit, a part of a salient group delay characteristic in the operation band of broadband amplifiers can be suppressed without an increase of the entire group delay. The MMIC amplifier has a steep group delay increase in the lower frequency region of the full-band UWB band (3.1-10.6 GHz) due to the sum of phase variations near the cutoff frequencies of the HBTs. The NGD circuit has been inserted to reduce this increase of the group delay in the UWB band. By adding a three-cell NGD circuit while considering input and output matching at the input side of the MMIC amplifier, the group delay variation is decreased by 78%. However, gain was also decreased by insertion of the multistage NGD circuit. In an attempt to avoid this decrease in gain, a one-cell NGD circuit was inserted into the feedback loop of the MMIC amplifier, and as a result, we were able to decrease the group delay variation by 79%, with minimal gain deterioration.     

Multilevel Programmable Oxide Diode for Cross-Point Memory by Electrical-Pulse-Induced Resistance Change

A multilevel one-time programmable (OTP) oxide diode for cross-point memory is introduced. The oxide diode is composed of a thin-film p-CuO/n-InZnOx (IZO). By applying negative electrical pulses, the p-CuO/n-IZO diode exhibited multilevel resistance states, and such characteristics of the p-CuO/n-IZO diode could be utilized as the cell of OTP cross-point memory. The resistance-change properties of the p-CuO/n-IZO diode originated possibly from a back-to-back diode phenomenon by oxygen ion migration in the IZO thin film.