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Collection : Chemistry and Materials ScienceInternational audienceIn the last few years, eco friendly materials have become an important part of the building materials market. Natural fibres are already used in various types of materials, like plastics, concrete and lime-based products. They demonstrate different attributes like the combination of good mechanical, thermal and acoustic properties that allow these types of materials to be used for different applications. The main drawback associated with plaster is its brittleness, especially under tensile stress. Therefore, it is interesting to investigate different methods that could potentially enhance the mechanical properties of plaster. Adding fibres to gypsum to obtain a composite material is one way to improve the behaviour of the product, especially after the failure of the matrix. The aim of this work was to the study the effects of adding natural fibres, namely hemp and flax fibres, on the setting time of plaster and the mechanical properties of the composite matrix. It was shown that hemp delayed the setting of plaster, unlike flax. The initial and final setting times almost doubled when hemp was added in a plaster matrix, whereas flax fibres did not drastically change them. Different chemical treatments of hemp were tested and the impact on the setting time was measured. The setting times of both composites made with hemp and flax were reduced once the fibres were treated (25-40% reduction), compared to the setting time of the calcium sulphate hemihydrate alone. The mechanical properties of the composite materials are also discussed. The behaviour of plaster was modified from brittle to a non-linear one when fibres were added, and even at small levels of addition, flax fibres allowed slightly higher values of flexural strength to be reached

This work deals with the influence of the nature of a filler on the thermally induced crystalline structure of polylactide (PLA)-based nanocomposites. Particularly two types of silicated clay both having a platelet-like shape, i.e., talc and kaolin, were melt compounded with PLA, and the crystalline structure involved during isothermal crystallization was followed in situ by means of both wide- and small-angle X-ray scattering techniques. Results indicate that even if the two types of clay are chemically similar, i.e., they both exhibit silicate surfaces, only talc plays the role of nucleating agent on the PLA crystallization. Moreover, structural analyses reveal that for PLA nanocomposites filled with talc a transcrystallization process occurs and that, in addition to the perpendicular growth of the PLA crystals toward the clay surface, a well-ordered nanometer scaled structure can be formed depending on the crystallization temperature. Particularly, for the first time, an epitaxial growth process has been evidenced, and crystallographic orientation relationships between the PLA crystals and the talc platelets have been determined. In opposition, the same behavior was not encountered for the kaolin-based nanocomposites. From a fundamental point of view, this study shows that the existence of favorable interactions between the polymer and the filler is not the only parameter involving the nucleating effect process. Indeed, the existence of crystallographic relationships between the filler and the polymer crystalline structure is also a necessary condition to observe a nucleating effect. Finally, this work also highlights that incorporating a well-chosen filler into a polymer matrix can be an efficient route to induce nanostructured materials.