Papers by Author: Renato Meneghetti Peres

Abstract: The Pseudoboehmite is an aluminum compound used as an alumina precursor and it is produced by sol-gel process. The sol-gel process is a methodology to produce porous, vitreous or crystalline ceramics started by molecular precursors. Pseudoboehmite with high purity, high specific surface area and porous homogeneity was obtained by sol-gel process. The material was used to produce gamma-alumina with surface area ranging from 211.2-288.1m²/g. It was studied the effect of aging time, temperature of aging and poly (vinyl alcohol) addition in the synthesis.

Abstract: Polymers nanocomposites are composed by nanometrical particles embedded in a specific matrix. Additions of small amount of nanoparticles of inorganic material in specific matrixes can greatly improve mechanical properties. The high specific surface area of the inorganic materials nanoparticles promotes its dispersion in the polymeric matrix, and the obtained properties are strongly related to the homogeneity of the dispersion. In the present work, nylon 6.12 nanocomposites with different concentrations of pseudoboehmite obtained by sol-gel process were prepared with different concentrations of octadecylamine. The pseudoboehmite was characterized by X-ray diffraction, scanning electron microscopy, differential thermal analysis and thermo gravimetric analysis. The nanocomposites were characterized by thermal and mechanical tests. The addition of pseudoboehmite reduces the melting flow, evidencing the interaction of pseudoboehmite with the polymeric matrix probably modifying its crystalline structure.

Abstract: As the polypropylene resin of high consumption, has as a consequence, the same feature among the resins most discarded after use. This generates high amount of waste in landfills, causing environmental problems, because the polypropylene presents difficulty in the short term, degradation by micro-organisms in the trash. Thus, this resin recycling proposals are always welcome, raising the possibility of reuse, and reducing the concentration of the landfills, thereby helping to minimize the negative effects of its disposal on the environment. Some manufacturers of rubber products, using as raw materials EPDM, report that are discarded after processing the waste, largely in landfills. Thus, the proposed reuse of byproduct, also will not contribute to the degradation of the environment. The aim of this work was to produce compositions (mixtures) with different concentrations of polypropylene and EPDM recycled materials, and evaluate the effect of ultraviolet and gamma radiation, rheological properties, thermal, mechanical and morphological, of the composites. The compounds obtained showed that waste rubber modified thermoplastic properties of polypropylene when irradiated by both UV radiation, such as gamma radiation.Comparing the hardness and impact tests, it was observed that the values ​​decreased with respect to the material not irradiated (UV or gamma). This effect is due mainly to the presence of the EPDM rubber, because the PP when subjected to gamma radiation or UV at low doses has an increase in mechanical properties.

Abstract: Nanocomposites are nanometrical material particles embedded in a specific matrix. The degree of organization of the nanostructures and their properties depend on the nature of the organic and inorganic components of the structure that can generate synergic interactions. Polymeric nanocomposites are related to a class of hybrid materials where inorganic substances of nanometric dimensions are dispersed in a polymeric matrix. In the present work, nanocomposites of nylon 6,12 with different concentrations of pseudoboehmite obtained by sol-gel process were prepared with and without the presence of octadecylamine. After preparation, the samples were irradiated with a 200 kGy radiation dose in an electron accelerator. The pseudoboehmite nano particles were characterized by X-ray diffraction, scanning electron microscopy, differential thermal analysis and thermo gravimetric analysis. The nanocomposites were characterized by thermal and mechanical tests. The addition of pseudoboehmite promoted a reduction of the melting flow during the production of the composites evidencing the interaction of pseudoboehmite with the polymeric matrix, probably modifying its crystalline structure.

Abstract: The alumina powder was obtained through a technique based on firing irradiated pseudoboehmites powder to study the radiation effects in the alumina properties. The electron beam radiation effect in a pseudoboehmite produced by sol-gel synthesis was investigated, using aluminum chloride and ammonium hydroxide as precursors. The addition of poly(vinyl alcohol) ([C2H3OH]n) solution (8 wt% in water) was also analyzed. The aluminum chloride solution was mixed with the polyvinyl alcohol and the mixture was dropped into an ammonium hydroxide solution. The work presents the effects of pseudoboehmite radiation in the structure of alumina. The alumina was obtained by pseudoboehmite calcinations. The milky-white colloidal pseudoboehmite precipitate obtained by sol-gel method was filtered, washed with distilled water, dried at 70°C, and powdered in a mortar. The sample acquired was calcined 4 hours at 1100oC, and after that X-ray powder diffraction was performed. The well defined α-alumina crystal was obtained from 1100oC treatment for some samples. The X-ray powder diffraction data shows that in some irradiated samples calcined at 1100o C for four hours presented θ-alumina and -alumina. The powder dried at 70o C was also examined by thermal analysis. The Thermo Gravimetric Analysis (TG) and Differential Thermal analysis (DTA) were used to evaluate mass loss and the pseudoboehmite endothermic and exothermic transformations. The samples were analyzed through scanning electron microscopy technique