Navegando por Data de Publicação, começando com "2014-07-15"

Filtrar resultados por ano ou mês

Agora exibindo 1 - 2 de 2

Obtenção e caracterização de nanocompósitos de poliuretano termoplástico reforçado com nanocristais de celulose
(Universidade Federal de São Carlos, 2014-07-15) Prataviera, Rogério; Lucas, Alessandra de Almeida; https://lattes.cnpq.br/9754332336954137; https://lattes.cnpq.br/5895158357997353
In this study the potential of cellulose nanocrystals (CNC) as a reinforcement of a thermoplastic polyurethane partially obtained from renewable sources (Bio-TPU) was investigated. The nanocomposites were obtained in the melt state and from solution casting. The CNC were obtained from acid hydrolysis of eucalyptus kraft pulp. They were freeze dried and used with and without surface treatment. Two types of surface treatment were employed: polymer grafting and oligomers grafting. Only the effectiveness of the second treatment could be confirmed by FTIR. CNC’ structural and geometric characteristics, crystallinity degree and thermal stability were determined by infrared spectroscopy (FTIR), transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD) and thermogravimetric analysis (TGA), respectively. The concentrations of CNC were varied between 0.1 and 5.0 wt %. The rheological properties of the nanocomposites were evaluated in the steady state and oscillatory measurements in order to evaluate the level of dispersion CNCs in TPU. The nanocomposites obtained by solution casting showed good dispersion. In the melt state, only those obtained with treated CNC showed good dispersion. The deformation and elastic recovery of the nanocomposites tests in the melt state were evaluated through creep and constrained recoil rheological essays. Their morphologies were studied by small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). It was possible to prove the inclusion of CNC in TPU did not change its conformation. The nanocomposites were also characterized according to their: i) mechanical properties, through tensile tests, ii) thermal properties, by using differential scanning calorimetry (DSC) and TGA, iii) thermo-mechanical properties, evaluated by dynamic mechanical thermal analysis (DMTA) and iv) optical properties, through opacity the nanocomposites with 5.0 wt % of CNC shown better performance and similar results were found from solution casting and melt state processing techniques.
Preparação de vidros e vitrocerâmicas no sistema SbPO4-PbO-ZnO dopados com manganês e ferro
(Universidade Federal de São Carlos, 2014-07-15) Siqueira, Renata Fernandes; Nalin, Marcelo; https://lattes.cnpq.br/3349586880746735; https://lattes.cnpq.br/6645436997641022
In the present research project a new glass composition containing SbPO4 ZnO PbO was obtained by melt quenching technique. After a brief study of the matrix, a composition was chosen and doped with MnO e Fe2O3 in quantities varying from 0 to 20 mol%. The next step was to perform a heat treatment above glass transition temperature in order to produce glass-ceramics from the obtained glasses. Then, the vitreous materials were characterized by thermal analysis (DSC), and the structural study of the materials was done using absorbance spectroscopy in the UV-vis-NIR and Raman, besides the electronic paramagnetic resonance (EPR) and fluorescence measurements. Refractive index was measured by M-Lines spectroscopy. The new materials were also characterized by X ray diffraction (XRD), optical microscopic and scanning (SEM) and transmission electronic microscopic (TEM). Finally, magnetic measurements were performed in a magnetic force microscope (MFM). The prepared glass samples have a high refractive index and thermal stability over 100 °C, which may be interesting for optical fiber synthesis. After addition of the paramagnetic metals (Mn, Fe), the thermal stability increased even more. The optical analysis of the manganese doped glasses showed that the ions are in the Mn2+ oxidation state, but after heat treatment the color of the glass changes since a small amount of the dopant cation is oxidized to Mn+3 and some magnetism characteristic may be observed. Even though the optical properties were not good with addition of manganese and iron, the sample showed a significant magnetic response. These results of magnetic analysis are promising for the advance of spin-photonics and may be suitable to design devices for information storage.