Annick Perronnet

Hydration and mechanical properties of arabinoxylans and β-D-glucans films.

Arabinoxylans (AX) and (1→3)(1→4)-β-d-glucans (BG) are the main components of the cell walls in the endosperm of wheat grain. The relative occurrence of these two polysaccharides and the fine structure of the AX are highly variable within the endosperm. Films of AX and BG were used as models of the cell wall to study the impact of polymer structure on the hydration and mechanical properties of the cell walls. Effective moisture diffusivities (Deff) of AX and BG films were determined from 0 to 95% relative humidity (RH) at 20°C. Deff was influenced by the water content, and the structure of polysaccharides. Higher Deff was obtained for films made with highly substituted AX compared to values obtained for films made with BG or lowly substituted AX. Proton dipolar second moments M2 and water T2 relaxation times measured by TD-NMR, indicated that the highly branched AX films exhibited a higher nano-porosity, favoring water motions within films. Results from traction tests showed significant different mechanical properties between the AX and BG films. BG films exhibited much higher extensibility than AX films. Strength and extensibility of AX films decreased with increasing arabinose to xylose ratio. Our results show that the water motions and the mechanical properties of AX and BG films can be linked to the polysaccharide chains interactions that modulate the nanostructure of films.

Identification of moisture diffusion parameters in organic matrix composites

In this work, moisture penetration in glass fiber-reinforced polymers was systematically investigated through both experiments and theoretical approaches. The diffusivities of the neat resin and those of unidirectional composite plates containing various glass fiber volume fractions have been identified through the analysis of hygro-thermal aging tests. The main aim of the present paper consists in comparing the evolutions, as a function of the fiber volume fractions, of the moisture diffusion coefficients deduced from experiments to the corresponding values, predicted by the many traditional scale transition relations available in the literature.