Agro-materials : a bibliographic review

Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the “plastic” properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed

LIGHT SCATTERING INVESTIGATION OF THE FRACTAL BEHAVIOUR OF SILICA GELS

L'intensité lumineuse diffusée par les gels de silice présente une dépendance, en fonction du vecteur d'onde, caractéristique des objets fractals en masse. On peut ainsi déterminer la longueur de corrélation ξ au-delà de laquelle le matériau est homogène et la dimension fractale D. Pour des alcogels obtenus dans des conditions de catalyse basique, une valeur D ≈ 1,66 - presque indépendante de la concentration et du vieillissement - a été obtenue. ξ atteint des valeurs de l'ordre de 200 nm pour les échantillons les plus légers. La comparaison de ces valeurs avec celles déduites de mesure par diffusion des neutrons aux petits angles sur la même série d'échantillons, après élimination du solvant par séchage hypercritique, i.e. des aérogels, confirme que ce séchage ne modifie pas sensiblement la texture du gel.The light intensity scattered by silica gels shows a wavevector-dependence characteristic of mass fractal objects. The correlation length ξ beyond which the material is homogeneous and the fractal dimension D can be determined. For base catalysed alcogels a value D ≈ 1.66 nearly independent of aging and concentration is obtained. ξ rises up to 200 nm for the lightest sample. The comparison of these values with those obtained by small angle neutron scattering (SANS) on the same series of samples after hypercritical drying, i.e. aerogels, confirms that the drying has but little influence on the gel texture

Mechanical behaviour of metal-ceramic bonds

The mechanical behaviour of ceramics bonded with metal is analyzed from the mechanical point of view (interfacial fracture mechanics, applied and residual stress field) and from the physico-chemical point of view taking into account the embrittlement induced by interfacial reactions or diffusion of metal into ceramic and the damages due to the change in interfacial microstructure (segregation, interfacial phases or films, microcracks, ...) during bonding or life. Indeed the behaviour of metal-ceramic bonds is inevitably dependent on the synthesis of all those parameters.Le comportement mécanique des liaisons céramique-métal est analysé du point de vue mécanique (mécanique de la rupture interfaciale, champs des contraintes appliquées et résiduelles) et, du point de vue physicochimique, en tenant compte des effets de fragilisation induits par les réactions interfaciales ou la diffusion du métal dans la céramique et des endommagements dus aux modifications de la microstructure interfaciale (segrégation, phases et films interfaciaux, microfissures ... ) intervenant lors de l'assemblage ou du service. En effet le comportement des assemblages métal-céramique dépend obligatoirement de la synthèse de tous ces paramètres

Biofriendly ionic liquids for starch plasticization: a screening approach

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Damages and cracks in ceramic/metal interfaces

When metal/ceramic junctions are achieved by solid state bonding process, damages and cracks are often observed near by the interface. This paper focuses on the mechanical origin of the embrittlement. The main causes are : - residual stresses due to the mismatch in the mechanical properties of the materials to be joined - friction of metal on the ceramic surface at the interface during bonding - decrease of the toughness of the ceramic close to the interface consecutively to the diffusion of the metallic specie into the ceramic

Imbibition, desiccation and mechanical deformations of zein pills in relation to their porosity

This paper deals with the interaction between zein (the main protein component of corn grain) and water. It induces macroscopic properties changes and may allow for the understanding of the basis of zein endosperm structure: vitreous endosperm is compact and floury endosperm is porous, giving the endosperm its hard and soft textures, respectively. In that aim porous pills made by compaction of zein powder submitted to different hydration/dehydration processes have been prepared and studied. In particular, imbibition measurements of a pure-water drop deposited onto a zein pill were performed. Also, desiccation of a zein pill previously imbibed induces strong mechanical stresses leading to crack formation and/or large deformations