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Gisele C. X. Valle Maria I. B. Tavares Leandro Luetkmeyer Giovanni C. Stael 《Macromolecular Symposia》2007,258(1):113-118
Summary: In the last decades, the growing environmental awareness has resulted in a renewed interest in the use of natural materials for different applications. In this context, the use of wood in plastic to obtain composites has grown significantly. In the present work, heartwood and sapwood from Angelim Pedra (Hymenolobiun petraeum) were used to prepare PVC/wood composites. To study the composites with different wood types and filler contents the molecular dynamic was investigated through low field NMR by poton spin- lattice relaxation time measurements (T1H) and the thermal behavior was characterized by means of differential scanning calorimetry (DSC) focusing the glass transition temperature and thermogravimetric analyses (TGA) observing the changes in the thermal stability. It was found that increasing addition of wood flour (sapwood and heartwood) caused a small but progressive improvement of the decomposition temperature of the composites, whereas the glass transition temperature remains practically unchanged. In the molecular dynamic behavior, a gradual decrease in T1H values was observed with increasing sapwood and heartwood content, indicating that the composites became less rigid. The distribution curves of the domains showed a better interaction and phase dispersion between the composite components with higher filler content. 相似文献
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Luciana P. da Silva Leandro Luetkmeyer Cristina R.G. Furtado Maria Inês Bruno Tavares Elen B.A.V. Pacheco 《Polymer Testing》2009,28(1):53-56
Proton spin-lattice relaxation time (T1H) in the solid state was used to determine the molecular mobility of PP/regenerated tire-rubber blends (PP/RgR), employing low-field NMR. The blends were prepared with different quantities of regenerated rubber (5, 10, 15 and 20 wt%). The addition of 5 wt% maleic anhydride functionalized polypropylene (PP-g-MAH) was carried out to evaluate the processing behavior of the reclaimed material. Important differences were observed concerning the molecular mobility according to the content of regenerated rubber. A decrease in the relaxation time of the blends with an increase in PP-g-MAH content indicates that enhanced mobility of PP/regenerated tire-rubber blends was obtained and, thus, PP-g-MAH acts as a plasticizer and/or impact modified. 相似文献
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Leandro Luetkmeyer Maria Inês Bruno Tavares Gisele C. X. Valle José de Souza Nogueira 《Macromolecular Symposia》2007,258(1):108-112
Summary: The focus of this work was to characterize the molecular dynamic of High Impact Polystyrene (HIPS - 5% PB), wood - A (Vochysia divergens) and B (Erisma uncinatum) - and their composites, using solid state nuclear magnetic resonance (NMR), by measuring the proton spin-lattice relaxation time (T1H) using a low field NMR, and by thermal analysis as Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). DSC and TGA measurements show that both woods present the same molecular behavior. On the other hand, the spin-lattice relaxation time observed that the water is interfering in the packing and arrangements of cellulose chains due to inter and intra hydrogen molecular interactions, promoting the T1H values changed to high values. T1H shows that the sample B presents a higher rigidity than sample A. However, HIPS presents higher T1H values comparing to wood types. Analyzing the relaxation data for the composites, the values indicate that composites present an interaction between both components. 相似文献
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Tacia Luetkmeyer Rosana Monteiro dos Santos Adriana Barbosa da Silva Roberto Salgado Amado Eduardo de Castro Vieira Eliane D'Elia 《Electroanalysis》2010,22(9):995-999
In this work, an electroenzymatic methodology based on two coupled enzymatic activities (glycerokinase and glycerol‐3‐phosphate oxidase) was developed using an oxygen Clark‐type electrode for the determination of free and total glycerol in biodiesel samples. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark‐type electrode and correlated with the concentration of glycerol in the sample. The electroenzymatic method proposed showed a good linear correlation coefficient (R=0.9990) with a linear response in the concentration range of 6.25×10?5 to 6.25×10?4% (w/v) and limits of detection and quantification at 1.0×10?5% and 3.0×10?5% (w/v), respectively. Good correlations were found between the results obtained in this work and those by the gas chromatography technique (R=0.9994). The proposed method was shown to be promising for the analysis of glycerol in biodiesel samples, with a simple and inexpensive methodology compared with the gas chromatography technique. 相似文献
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