Authors:V. Braga, F. Garcia, J. Dias, and Sílvia Dias
Nb2O5 supported on SiO2-Al2O3 were prepared with a wide loading range (2, 5, 10, 15, 20 and 25 mass%) and analyzed by simultaneous thermogravimetric (TG)
and differential thermal analysis (DTA). The materials presented a phase transition close to 1364°C. This phase transition
was studied by XRD, FTIR and Raman spectroscopy. Amixture of orthorhombic (T) andmonoclinic (H andM) crystalline phases was
evidenced in the supported samples, which is coverage dependent, in contrast to the formation of only the monoclinic phase
(H and M) when pure Nb2O5 is heated under the same conditions. These results indicate the stabilization of Nb2O5 on silica-alumina surface.
The subject of this work is ethylene polymerisation using Kaminsky type catalysts: Cp2MR2=methylaluminoxane [M=Zr, W, Nb; R=Cl, CH3]. Active center determination and kinetic studies of the (Cp2WCl2+methylaluminoxane) and Cp2ZrCl2+methylaluminoxane) systems are described, using a quenching method with tritiated methanol. The activity of the polymer was determined by liquid scintillation counting. We have found 0.5% and 87% of active centers, respectively for W and Zr system. The catalytic activity of complexes Cp2WCl2 and Cp2NbCl2 was compared with that of Cp2ZrCl2. The W and Nb complexes are found to be less active than the Zr complex.
Authors:D. Dias, M. Crespi, C. Ribeiro, J. Fernandes, and H. Cerqueira
Samples of paint (P), reused PET (PET-R) and paint/PET-R mixtures (PPET-R) were evaluated using DSC to verify their physical-chemical
properties and thermal behavior. Films from paints and PPET-R are visually similar. It was possible to establish that the
maximum amount of PET-R that can be added to paint without significantly altering its filming properties is 2%. The cure process
(80–203°C) was identified through DSC curves. The kinetic parameters, activation energy (Ea) and Arrhenius parameters (A) for the samples containing 0.5 to 1% of PET-R, were calculated using the Flynn-Wall-Ozawa isoconversional method. It was
observed that for greater amounts of PET-R added, there is a decrease in the Ea values for the cure process. A Kinetic compensation effect (KCE), represented by the equation InA=−2.70+0.31Ea was observed for all the samples. The most suitable kinetic model to describe this cure process is the autocatalytic Šesták-Berggreen,
model applied to heterogeneous systems.