Dielectric relaxation based on adsorbed water in wood cell wall under non-equilibrium state 2.

In order to explain, on molecular level, the unusualness of wood physical p roperties under moisture nonequilibrium state, the dielectric temperature a nd frequency spectra of Sikkim spruce (Picea spinulosa Griff.) specimens we re measured during the adsorption process in 20 degrees C, 60% R.H. environ ment. Furthermore, the dielectric relaxation based on adsorbed water was se parated from that based on the methanol groups in the amorphous region of w ood cell wall, so that the thermodynamic quantities of adsorbed water assoc iated with the adsorption process could be evaluated. Consequently, the mol ecular reorientation model of adsorbed water molecules during the dielectri c relaxation process was constructed. The results show that the activation enthalpy DeltaH and activation entropy DeltaS of adsorbed water both increa se linearly with the adsorption time. During the initial adsorption period DeltaS appears as a negative value. According to the values of thermodynami c quantities, especially the DeltaH values, it can be inferred that the ave rage number of hydrogen bonds formed between each adsorbed water molecule w ith its surrounding wood adsorption sites increases gradually with developi ng adsorption. The model based on the obtained data in this experiment show s that after 7 hours' adsorption the number is between two and three. after 24 hours it is three and later it approaches four.