Electrochemical sensors based on yttria-stabilized zirconia ͑YSZ͒ with WO 3 as a sensing electrode were fabricated using either Pt or Au electrodes. The sensors were studied in the temperature range 500-700°C in the presence of different concentrations ͑300-1000 ppm͒ of NO 2 and CO in air. The response to NO 2 was very stable with fast response time ͑within 20 s͒. The best sensitivity was observed at 600 and 650°C using Pt and Au electrodes, respectively. At all temperatures investigated a cross sensitivity to CO gas was also noticed. The response to CO was decreased using Au electrodes. The role played by WO 3 as a sensing electrode was investigated.The environmental concerns have challenged scientists to develop suitable and reliable sensors to detect pollutants such as NO x , CO, HCs, etc. Strict norms on pollution control are being enforced worldwide, especially for emissions of vehicles. 1 The automotive industry urgently needs rugged and reliable sensors to monitor and decrease the level of pollutants (NO x and CO/HC s ) in the exhaust emissions at elevated temperatures. Solid-state electrochemical sensors with metal oxide auxiliary phase seem to be the most suitable in such environments. 2-7 Several reports are available on solidelectrolytes-based sensors combined with metal ͑Pt, Au, etc.͒ and oxide electrodes for NO x , 7-14 CO/HCs 15,16 detection. Miura and coworkers have been working for a long time on electrochemical sensors for the detection of NO x . 7-12,14 In a recent paper 11 they reported WO 3 as a suitable auxiliary oxide for selective detection of NO x in the range 500-700°C. Some of the authors of this paper 17 have used LaFeO 3 coupled with yttria-stabilized zirconia ͑YSZ͒ and sodium silicon conductor ͑NASICON͒ electrolytes and obtained stable and fast responses to NO 2 at 400 and 450°C. Brosha et al. 18 have studied LaCoO 3 and La 0.8 Sr 0.2 CoO 3Ϫ␦ perovskite oxide electrodes in zirconia-based sensors for the detection of CO/HCs at 600-700°C. Recently, Ménil et al. 19 have reviewed the actual trends of these kinds of sensors. They claimed that the major issues concerning the selectivity and the long-term stability are yet to be overcome for high-temperature sensors. This fact drives scientists to search for new materials, to improve the device fabrication techniques, and to investigate the sensing mechanism.According to many authors 12,15,16,20 the sensing mechanism of electrochemical sensors based on coupling a solid electrolyte with semiconducting oxides, can be explained using a mixed potential theory. The mixed potential mechanism was claimed both for NO x 7,12,14 and CO/HC s 15,16,18 gas sensors based on similar electrochemical cells. However, a different explanation of the NO x sensing mechanism has been proposed and named the different electrode equilibria. 21 Different electrode equilibria is a more general concept to explain the NO x sensitivity that is due not only to electrochemical reactions, but also to different electrocatalytic activity and/or sorption-desorption behavior of ...

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This research work has concerned a study on thermomechanical and crystallization properties of poly(lactic acid) (PLA) composites containing three different types of additives; namely: kenaf fiber (20 pph), Cloisite30B nanoclay (5 pph), and hexagonal boron nitrile (h-BN; 5 pph). The composites were prepared using a twin screw extruder before molding. Crystallization behaviors of the various composites were also examined using a differential scanning calorimetry. By adding the additives, tensile modulus of the polymer composites increased, whereas their tensile strength and elongation values decreased as compared to those of the neat PLA. Heat distortion temperature (HDT) values of the materials slightly increased, for about 3-5 C. However, after annealing at 100 C, HDT values of the fabricated PLA composites rapidly increased with annealing time before reaching a plateau after 10 min. The HDT values of above 120 C were achieved when 20 pph kenaf fiber was used as an additive. The above results were in a good agreement with DSC thermograms of the composites, indicating that percentage crystallinity of the materials increased on annealing and crystallization rate of the PLA/kenaf system was the highest.

This study has concerned preparation of polylactic acid grafted with maleated thermoplastic starch (PLA-g-MTPS) and a study on compatibilizing efficacy of the above copolymers in PLA/thermoplastic starch (TPS) blends. The PLA-g-MTPS copolymers were prepared by two-step reaction. First, maleated thermoplastic starch (MTPS) was prepared by reacting cassava starch with glycerol and maleic anhydride (MA). Second, the MTPS was grafted onto PLA molecules using peroxide as an initiator. Chemical structures of the products were characterized by using Fourier transform infrared spectroscopy and 1 H-NMR techniques, whereas the acid numbers of the copolymers were determined by titration. Thermal characteristic of the copolymer was also characterized by using dynamic mechanical thermal analysis. In total, 5 wt % of the graft copolymer was blended with PLA and TPS in a twin screw extruder. Mechanical, rheological, and morpho-logical properties of the blends were evaluated via tensile test, melt flow index test, and scanning electron microscopy, respectively. It was found that mechanical properties of the blends depended on starch content and type of the PLA-g-MTPS. When the PLA-g-MTPS was prepared at low amount (0.25 pph) of peroxide, the mechanical properties of the blend was improved remarkably as compared to those of the normal blend and/or the blend containing different compatibilizers. Compatibilizing efficacy of the above copolymers became more obvious when the thermoplastic starch (TPS) blending ratio was increased. The above results were ascribed in the light of change in the viscosity and morphology of the blends. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: E388-E395, 2012

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This research work has concerned a study on relationship between structure and properties of maleated thermoplastic starch (MTPS)/plasticized poly(lactic acid) (PLA) blend. The aim of this work is to investigate the effects of blending time, temperature, and blend ratio on mechanical, rheological, and thermal properties of the blend. The MTPS was prepared by mixing the cassava starch with glycerol and maleic anhydride (MA). Chemical structure of the modified starch was characterized by using a FTIR technique, whereas the degree of substitution was determined by using a titration technique. After that, the MTPS prepared by 2.5 pph of MA was further used for blending with triacetin-plasticized PLA under various conditions. Mechanical, thermal, and rheological properties of the blends were evaluated by using a tensile test, dynamic mechanical thermal analysis, and melt flow index (MFI) test, respectively. It was found that tensile strength and modulus of the MTPS/PLA blend increased with the starch content, blending temperature, and time, at the expense of their toughness and elongation values. The MFI values also increased with the above factors, suggesting some chain scission of the polymers during blending. SEM images of the various blends, however, revealed that the blend became more homogeneous if the temperature was increased. The above effect was discussed in the light of transesterification. Last, it was found that mechanical properties of the PLA/MTPS blend were more superior to those of the normal PLA/TPS blends.

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