MOISTURE ADSORPTION THERMODYNAMICS OF CHEMICALLY-MODIFIED WOOD

The isotherms for untreated and chemically modified wood specimens wer e analyzed using the Adsorption entropy Hailwood-Horrobin equation. Th e enthalpy (Delta H), entropy (Delta S) and free energy (Delta G) chan ges during moisture adsorption were estimated. The Delta H, Delta S an d Delta G values of untreated wood were compared with those found in l iterature as well as those of specimens treated with formaldehyde (for malization), acetic anhydride, glyoxal, glutaraldehyde and dimethylol dihydroxy ethyleneurea (DMDHEU), The Delta H of the untreated specimen was almost constant up to ca. 3% of moisture content differing from t he results reported by others. However, the bonding energy of hydrated water molecules, which represented a large portion of the adsorbed wa ter in the low moisture content range, should not depend on the moistu re content, so that the result was undoubtedly reasonable. The decreas e of the absolute Delta H for formalization and acetylation indicates the remarkable loss of the hydrated water as a result of those reactio ns. A peak of the absolute Delta S found at ca. 3% of moisture content except for acetylation may reflect the rearrangement of adsorption si tes associated with taking up a little amount of water. In the acetyla tion, such rearrangement could not occur because of the introduction o f bulky hydrophobic groups. Remarkable increases of both absolute Delt a H and Delta S observed in glyoxal treated specimens will be due to t he ester groups introduced. The Delta G values of all treated specimen s became less negative than that of untreated. This indicates the form ation of some bond which restricts the swelling of wood structure.