GDR CNRS 2024
Multiscale Mechanics of fibrous media

The behavior of poplar wood and its components in water-ethanol mixtures is investigated through a coupled experimental and theoretical approach including physico-chemical and dynamic mechanical analyses and molecular dynamics simulations. Affinity for water-ethanol vapors, measured by isothermal gravimetric sorption experiments, features a maximum for mixed vapors. The longitudinal viscoelastic behavior of the same wood upon immersion in ethanol-water solutions, measured by dynamic mechanical analysis, features a minimum in storage modulus and a maximum damping upon immersion in solutions of intermediate composition. Optical microscopy observation of solvent-saturated samples evidences inter- and intra-cellular disbonding in pure ethanol and ethanol aqueous solutions. Molecular dynamics simulations provide information on interactions of water-ethanol solutions with models of cellulose microfibers and lignin. The relative solvation of cellulose microfibers by water and ethanol shows a nearly linear variation with the composition of the solution. In contrast, the accessibility of lignin dimers to the solvent presents a maximum at intermediate ethanol concentrations, in correspondence with a conformational transition of the dimer towards an extended conformation. The modelization of the interactions of cellulose and lignin in water-ethanol solutions indicates a minimum of adhesion of the two components of wood in the presence of solutions with intermediate concentrations.