Strategies to improve the mechanical properties of starch-based materials: plasticization and natural fibers reinforcement

Biodegradable polymers are starting to be introduced as raw materials in the food-packaging market. Nevertheless, their price is very high. Starch, a fully biodegradable and bioderived polymer is a very interesting alternative due to its very low price. However, the use of starch as the polymer matrix for the production of rigid food packaging, such as trays, is limited due to its poor mechanical properties, high hidrophilicity and high density. This work presents two strategies to overcome the poor mechanical properties of starch. First, the plasticization of starch with several amounts of glycerol to produce thermoplastic starch (TPS) and second, the production of biocomposites by reinforcing TPS with promising fibers, such as barley straw and grape waste. The mechanical properties obtained are compared with the values predicted by models used in the field of composites; law of mixtures, Kerner-Nielsen and Halpin-Tsai. To evaluate if the materials developed are suitable for the production of food-packaging trays, the TPS-based materials with better mechanical properties were compared with commercial grades of oil-based polymers, polypropylene (PP) and polyethylene-terphthalate (PET), and a biodegradable polymer, polylactic acid (PLA)

The time uncoupled aluminium free expansion intrinsinc anisotropy by foaming under conventional conditions

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Évolution des modes de vibration υ(OH/OD) en fonction de la température dans les monocristaux de Sr(HCOO)

Nous avons réalisé des spectres Raman dans le domaine des températures comprises entre 293K et 10K sur des monocristaux de Sr(HCOO)2.2H2O et ses analogues obtenus par substitution isotopique partielle dans l’eau d’hydratation à 80 % H2O, 56 % H2O, 31 % H2O, et 2 % H2O respectivement. En étudiant les modes internes υ(ΟΗ) et υ(OD), une transition ordre- désordre a été observée à basse température (T < 170K). Cette transition est liée à un changement de l’orientation des liaisons d’hydrogène

An experimental study on the thermal conductivity of aluminium foams by using the transient plane source method

The thermal conductivity of a collection of AlSi7 foams with porosities between 0.5 and 0.8 produced throughout the powder metallurgical route has been determined using the transient plane source technique (TPS). Several measurements have been performed on different surfaces of the foam blocks. The values obtained have shown an increase of effective thermal conductivity with density and a significant dependency with the zone of the foam where the experiments were performed. The results obtained have been explained in terms of local density trough images obtained from computed tomography, showing that the TPS technique is sensitive to in-homogeneities derived from the foaming process. Finally, several theoretical models for thermal conductivity have been unified, after suitable simplifications for this kind of materials, and have been compared with the experimental results

Spectroelectrochemical characterisation of Langmuir-Schaefer films of heteroleptic phthalocyanine complexes. Potential applications

The Langmuir–Schaefer technique has been used to fabricate ordered monolayers of novel heteroleptic double and triple-decker phthalocyanine derivatives. The molecules studied include a double-decker mixed porphyrinate and naphthalocyaninate lanthanum(III) compound and a europium triple-decker molecule where one of the rings is a substituted porphyrin and the two remaining rings are substituted phthalocyanine macrocycles. The materials and their films have been characterised using UV–vis–NIR spectroscopy and electrochemistry. The UV–vis–NIR spectra of the solutions show the expected features corresponding to the aromatic rings present in each molecule. The absorption spectra of LS films show broadenings and important shifts to higher wavelengths when compared to the electronic absorption spectra of solutions or disordered cast films. Thin films are sensitive to electron acceptor gases, such as NOx as observed by modifications in the electronic absorption spectra of the films. These fast and reversible changes can be the basis of optical sensors based on thin films of heteroleptic phthalocyanines (Pc). Cyclic and square wave voltammograms of dichloromethane solutions lead to rich curves where a variety of peaks are observed. The voltammogrames of the corresponding films also reflect the rich electrochemical properties of the studied compounds. Electrochromism has been found with LB and cast films electrodes in KCl and KClO4 solutions: important changes in the UV–vis–NIR spectra registered in situ simultaneously to the application of the electrical potential have been observed. The rich electrochemistry and the electrochromism observed, opens the possibility of using such films in multicolour electrochromic devices. Films prepared onto ITO glass show characteristic electrochemical responses when exposed to solutions of organic compounds, such as ascorbic and vanillic acid, providing a high degree of cross-selectivity. This effect can be used in the development of arrays of sensors used in electronic tongues. In summary Langmuir–Schaefer films of heteroleptic double and triple-decker phthalocyanines could be of interest at least in three potential applications: thin film electrochromic devices, optical gas sensors and voltammetric sensors

Langmuir-Blodgett and Langmuir-Schaefer films of homoleptic and heteroleptic phthalocyanine complexes as voltammetric sensors. Applications to the study of antioxidants

Double- and triple-decker phthalocyanine derivatives have been successfully used as the sensitive materials for liquid electrochemical sensors. The materials include homoleptic and heteroleptic phthalocyanine complexes formed by phthalocyanine, porphyrin and naphthalocyanine rings. A high degree of cross-selectiviy towards antioxidant compounds (including vannilic acid, pyrogallol, ascorbic acid and catechin) has been attained by using different phthalocyanine complexes. The features observed in the cyclic voltammograms reflect the rich electrochemistry of either the phthalocyanine molecules or the studied solutions. In consequence, each sensor shows a selective response to the antioxidant analysed. The obtained voltammograms from by using highly ordered electrodes prepared using the Langmuir–Blodgett (LB) or the Langmuir–Schaefer (LS) techniques show better resolution and stability than those of disordered electrodes prepared by casting. For this reason, ordered films have been chosen to construct an array of liquid sensors. The principal component analysis (PCA) of the obtained signals has allowed that a clear discrimination of the antioxidant solutions be achieved. The rich and varied responses produced by antioxidant molecules evidences that voltammetri