Résumé
The plant cell wall can be the optimal scale of investigation for understanding the properties and the variability of vegetal organs structure. At the molecular scale, the wall constituents’ organisation might have a strong influence on theses properties. Primary cell walls are separated into monocotyledons (cereals) and dicotyledons (fleshy fruits) depending on the type of molecules involved (cellulose, hemicelluloses, pectin, etc.). These polymers structures and concentration within the cell wall change during the organ development (i.e., growth and maturation). Cell wall models built from commercial polymers have been used in the literature to study the influence of these components and their organisation on cell wall mechanical properties. However these analogs, although they’re interesting, don’t take into account the molecule modification with time (growth and maturation) and space (organisation within the tissue) or the change of the hydration state of the wall with time. The first step of our work consists in developing a specific static tensile test adapted to thin film analogs made of polymers extracted at different growth step of the organ. These tests are made in a temperature and humidity controlled environment. Due to their low thickness (around some tenth of micrometre at best), these films are particularly difficult to handle and the mechanical measurements are thus coupled with an image stereo-correlation device. It allows us to measure the strain fields at the surface of the sample, even if it is not perfectly plane, and thus to check the real loading of the film. Finally, this measurement technique allows us to measure the elastic longitudinal modulus of the film together with its Poisson’s ratio without any effect of the tensile machine stiffness or occurrence of slippage in the loading grips.