Transport properties of water vapor through hemp fibers modified with a sustainable process: Effect of surface morphology on the thermodynamic and kinetic phenomena

The paper is focused on a deep analysis of transport properties of natural hemp fibers (HF) functionalized through a mechano-chemical treatment assisted by high energy ball milling. The effect of milling time on fibers’ morphology was investigated by means of the scanning electron microscopy and FTIR spectroscopy. The results show that the mechanical effect induced a reduction of the mean diameter of hemp fibers and, simultaneously, the achievement of a close packing of cellulose chains. The barrier properties appeared to be dependent either on the packing of cellulose or the water cluster formation. Fick's law solution in cylindrical coordinates was used to simulate experimental sorption kinetics and to extrapolate the diffusion parameters. The change of diffusion with equilibrium moisture content was described through an empirical relationship. Sorption isotherms were explained on the basis of Park model which accounts for a dual mode sorption at low activities as well as the water clustering phenomenon occurring at high activities. The mean cluster size (MCS) of water molecules was estimated through the application of Zimm Lundberg theory. Finally, the spreading pressure calculation allowed to estimate the driving force of diffusion inside the systems.