Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State 2

Abstract

Summary In order to explain, on molecular level, the unusualness of wood physical properties under moisture non-equilibrium state, the dielectric temperature and frequency spectra of Sikkim spruce (Picea spinulosa Griff.) specimens were measured during the adsorption process in 20°C, 60% R.H. environment. Furthermore, the dielectric relaxation based on adsorbed water was separated from that based on the methanol groups in the amorphous region of wood cell wall, so that the thermodynamic quantities of adsorbed water associated with the adsorption process could be evaluated. Consequently, the molecular reorientation model of adsorbed water molecules during the dielectric relaxation process was constructed. The results show that the activation enthalpy ∆H and activation entropy ∆S of adsorbed water both increase linearly with the adsorption time. During the initial adsorption period ∆S appears as a negative value. According to the values of thermodynamic quantities, especially the ∆H values, it can be inferred that the average number of hydrogen bonds formed between each adsorbed water molecule with its surrounding wood adsorption sites increases gradually with developing adsorption. The model based on the obtained data in this experiment shows that after 7 hours' adsorption the number is between two and three, after 24 hours it is three and later it approaches four.