Synergistic Sorption of Mixed Solvents in Wood Cell Walls: Experimental and Theoretical Approach

Abstract

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.