Examinando por Autor "Navas-Martos, Francisco Javier"
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Ítem Photo-oxidative degradation of injection molded sepiolite/polyamide66 nanocomposites(Elsevier, 2020-05) Fernández-Barranco, Cristina; Yebra-Rodríguez, África; Jiménez-Millán, Juan; Navas-Martos, Francisco Javier; Yebra, Ana; Koziol, A.E.; La Rubia, M.DoloresEvery day clay/polymer nanocomposites are included in more industrial applications, due to its high performance. Because of this, nanocomposites may be submitted to extreme conditions of work, which could degrade it. Exposure to solar radiation in the presence of oxygen (photo-degradation) represents one of the major problems of the Clay/Polymer anocomposites. In this study, samples of neat polyamide 66 (PA66-S-0) and reinforced nanocomposites with 1, 3, 5, 7 and 9 wt% organophilized sepiolite (PA66-S-1, PA66-S-3, PA66-S-5, PA66-S-7 and PA66-S-9 samples) are analysed after UV exposure, following the standard accelerated degradation method UNE-EN-ISO 4892-2. The aim of this study is to establish the effect of UV exposure on the mechanical, optical and crystallographic properties of the new material. Tensile tests show a reduction in the ductility and an embrittlement after degradation process. In addition, an increase of transparency is confirmed with the UV exposure. The carbonyl index in the samples containing sepiolite is lower than in neat PA66 whereas the yellowness index is not affected by degradation. Sepiolite has an inhibitor effect on the formation of C=O bonds. These results indicate that breaking of chains of PA66 starts in the amorphous region and that it is lower in the nanocomposites due to the low diffusion of oxygen induced by the sepiolite. This affirmation is corroborated by the obtained diffraction patterns.Ítem Production and characterization of cellulose acetate using olive tree pruning biomass as feedstock(Willey and sons, 2024-01-22) Rodríguez-Liébana, José Antonio; Robles-Solano, Esther; Jurado-Contreras, Sofia; Morillas-Gutiérrez, Francisca; Moya, Alberto J.; Mateo, Soledad; Navas-Martos, Francisco Javier; La Rubia, M.DoloresOlive tree pruning (OTP) is one of the most abundant sources of biomass waste in the Mediterranean basin. This is especially relevant in southern Spain where olive oil production represents a large part of the economy. Olive tree prunings are mostly either burned or are spread in olive orchards as an organic amendment, or used for heat generation on a domestic scale. However, the lignocellulosic composition of OTP makes it a potential source of biopolymers, thus providing an excellent economic alternative for the olive oil sector. In this work, pretreated OTP fibers were subjected to an optimized alkaline treatment followed by a single-step bleaching reaction with H2O2. Afterwards, the cellulose pulp was transformed chemically to obtain cellulose acetate. Noncellulosic components were removed effectively from OTP, thus obtaining a pulp highly purified in cellulose with 71% crystallinity and 355 °C maximum degradation temperature. Nevertheless, a very large amount of cellulose (ca. 50%) was eliminated throughout the process, especially during acid pretreatment, which was responsible for 38% solubilization. A similar level of acetylation and degree of substitution was obtained by using acetylation times in the range of 1 to 6 h. No large differences were observed in the infrared spectra and X-ray diffractograms of the synthesized acetates. However, their thermal stability varied significantly with reaction time, evolving from a multistep degradation pattern to a single and sharp peak between 300 and 400 °C with increasing time. Thermogravimetric curves revealed that at least 5 h (preferably 6 h) were needed to obtain cellulose acetate from OTP with adequate thermal stability for further processing.