Nanorrellenos inorgánicos preparados a partir de LDHS para la obtención de nanocomposites de matriz polimérica. Determinación de la incidencia del método de preparación sobre sus propiedades

Abstract

The present research work has focused on obtaining inorganic nanofillers from Layered Double Hydroxides (LDHs) that can be useful in the preparation of polymer matrix composites and nanocomposites with modified properties. The properties of this type of nanofillers are closely linked to their synthesis conditions; so, parameters such as pH, reaction medium, molar ratio of cations, precipitation rate, synthesis temperature and hydrothermal treatments, etc., have an important impact on the physical and surface properties of the final solids. Thus, in the present work, the synthesis of Zn,Al LDHs with molar ratios 2:1 and 3:1 has been carried out by the coprecipitation method using amines, which are softer bases than the classically used bases. Specifically, amines with different substitution degree and chain length have been used as precipitating agents using a simpler synthesis methodology than the hydrolysis of urea. The resulting solids have been characterised in terms of their morphological and structural properties and their feasibility for use as nanofillers in polymer matrix nanocomposites has been studied. Thus, nanocomposites have been prepared using polypropylene as polymeric matrix, dispersing Zn,Al LDHs synthesised under different conditions. Finally, the impact of the use of these solids as nanofillers on the thermal stability and mechanical properties of the resulting nanocomposites was studied.On the other hand, the synthesis methodology using amines as precipitating agents was extended to the preparation of Ni,Al LDHs which are of great interest as catalyst precursors in the Sabatier reaction of CO2 hydrogenation to obtain methane. The synthesis of this type of solids was carried out using dimethylamine as precipitating agent, since the formation of coordination compounds with Ni(II) was not observed and, in addition, it turned out to be the amine with which the Zn,Al LDHs offered the best properties, in terms of crystallinity degree and particle size distribution. The study of the catalytic activity of this type of solids was extended with the synthesis of catalysts promoted by cations of rare earth elements, such as Ce and La. Thus, the effectiveness of the resulting Ni-Al2O3, Ni-Ce2O3-Al2O3 and Ni-La2O3-Al2O3-Al2O3 catalysts was studied in the production of CH4, taking into account both the conversion and the selectivity towards secondary products. The catalytic test was carried out between 200 and 400 ºC, and it was observed that at 275 ºC a conversion larger than 60% was achieved, maintained up to 400 ºC, with a selectivity of 95% in methane production.