Impregnation and Swelling of Wood with Salts: Ion Specific Kinetics and Thermodynamics Effects

The effects of salt impregnation are studied within wood cell walls, occurring upon soaking from concentrated salt solutions. Osmotic deswelling is in some cases followed by ion specific swelling linked to Hofmeister effects. Taking into account microstructure, this study models the free energy changes associated with the ions and water uptake at molecular, colloidal, and macroscopic mechanical scales, to show that slow swelling until osmotic equilibrium originates from charge separation of the salt diffused into wood cell wall material. Kinetic effects as well as mechanical effects linked to transfer of species and swelling of the interstitial matrix between cellulose crystals are discussed. Predictions by minimal models taking into account nonelectrostatic ion complexation allow to estimate the order of magnitude of the nonelectrostatic binding free energy of adsorbed chaotropic anions and complexed divalent cations to be 8 and 10 kJ mole –1 , respectively.