Model of the dielectric relaxation based on the reorientation of adsorbed water in wood cell wall

In order to clarify the molecular mechanism of the reorientation of adsorbed water in wood cell wall during dielectric relaxation process, the temperature and frequency spectrums of the dielectric relaxation process based on adsorbed water in wood, acetylated wood and formaldehyde-treated wood were measured, respectively, within a range of -60-20°C, 30Hz-3MHz and 0-27%m.c. On this basis, the quantitative relationships of activation enthalpy ΔH, activation entropy ΔS, activation free energy ΔF based on the reorientation of adsorbed water molecules with wood moisture content were obtained, on which the molecular reorientation model of adsorbed water molecules during dielectric relaxation process was constructed. Within low-humidity region, the dielectric relaxation process was only related to the reorientation of single adsorbed water molecule. Compared with untreated wood, the adsorbed water molecules existing in acetylated wood cell wall must have enough energy to go beyond the energy barrier formed during treatment, in addition to the rather high hydrogen bonding energy formed with carbon group. As for formaldehyde-treated wood, the molecule chains of its substances were cross-linked, which limited the reorientation of adsorbed water molecules to a certain degree. While within high-humidity region, the dielectric relaxation process was associated with the reorientation of plural adsorbed water molecules that cut the hydrogen bonds simultaneously. However, the simultaneous reorientation had not appeared in formaldehyde-treated wood due to the cross-link between the molecule chains of wood substances.