Aurelio BARBETTA (LTSM) will defend his Ph.D. dissertation entitled "Thermodynamics of water adsorption in model structured molecular systems including analogues of hemicelluloses, crystalline cellulose and lignin " on Monday, November 20, 2017 at 2.30 pm (ICSM Auditorium).
Abstract:
The so-called "wood material" is a complex, highly anisotropic and hierarchically organized nanocomposite. At the nanometric scale, it is characterised by stiff crystalline cellulose nanofibres parallel to each others embedded in a matrix of a much softer, less anisotropic, gel of hemicelluloses, lignin and water. This matrix is hygroscopic and the solvent uptake is controlled by molecular forces like entropy, H-bonding of polysaccharides to cellulose nano-crystals and hydration force. The swelling provides a source of internal stress for the cellulose fibrils that, winding with a spiral angle (the microfibril angle, MFA) around the central lumen, passively reorient following the osmotic stress applied to them. Depending on the MFA, wood fibres exhibit a wide range of behaviors and mechanical properties, being able to act as stiff material to bear load, or shrink or expand in the longitudinal direction upon swelling, generating in this way either large tensile or compressive stresses or large strains.
For the first time, the equation of state including entropic, chemical, colloidal terms (as the hydration force) as well as the mechanical, macroscopic, term has been established and allows to predict with a parameterless analytical expression, the water absorption of untreated softwoods as a function of relative humidity changes.
