The isotherms for untreated and chemically modified wood specimens were analyzed using the Hailwood-Horrobin equation. The enthalpy (ΔΗ), entropy (AS) and free energy (AG) changes during moisture adsorption were estimated. The AH, AS and AG values of untreated wood were compared with those found in literature as well as those of specimens treated with formaldehyde (formalization), acetic anhydride, glyoxal, glutaraldehyde and dimethylol dihydroxy ethyleneurea (DMDHEU). The AH of the untreated specimen was almost constant up to ca. 3 % of moisture content differing from the results reported by others. However, the bonding energy of hydrated water molecules, which represented a large portion of the adsorbed water in the low moisture content range, should not depend on the moisture content, so that the result was undoubtedly reasonable. The decrease of the absolute A// for formalization and acetylation indicates the remarkable loss of the hydrated water as a result of those reactions. A peak of the absolute AS found at ca. 3 % of moisture content except for acetylation may reflect the rearrangement of adsorption sites associated with taking up a little amount of water. In the acetylation, such rearrangement could not occur because of the introduction of bulky hydrophobic groups. Remarkable increases of both absolute AH and AS observed in glyoxal treated specimens will be due to the ester groups introduced. The AG values of all treated specimens became less negative than that of untreated. This indicates the formation of some bond which restricts the swelling of wood structure. IntroductionIn a previous paper , the Hailwood-Horrobin adsorption equation (Hailwood and Horrobin 1946) was applied to the moisture adsorption data of chemically modified wood. In that case, the adsorbed water was separated into hydrated water (monolayer adsorption water) and dissolved water (multilayer adsorption water), and the change in the amount of each water was investigated by chemical treatment. As a result of treatment with formaldehyde (formalization) and acetic anhydride (acetylation), the amounts of both hydrated and dissolved water decreased, whereas only the dissolved water decreased fairly by a treatment with glyoxal because of cross-linking and bulking effects.

Using sulfur dioxide (SO 2) as catalyst, wood specimens were treated with nonformaldehyde cross-linking reagents such as glyoxal, glutaraldehyde and dimethylol dihydroxy ethyleneurea (DMDHEU). The results of dimensional stability, acoustic properties, and mechanical strength tests were compared with those obtained from formaldehyde treatment. With glyoxal and glutaraldehyde treatments, antiswelling efficiency (ASE) reached around 70~ which is comparable to the values attained by formaldehyde treatment, although the accompanying weight gain was much larger than for the latter, whereas DMDHEU did not give sufficiently high ASE. None of the treatments, significantly increased specific dynamic Young's modulus (E/p) with the exception of the DMDHEU treatment, loss tangent (tan d) decreased substantially, about 50 and 60~ in longitudinal and radial directions respectively, which were somewhat exceeding the formaldehyde treatment. The results suggested that the improvement of the dimensional stability and acoustic properties is partly attributed to the formation of cross-links.Miss Rie Yasuda (graduated student)

The features of the reaction between sitka spruce wood and non-formaldehyde reagents, i. e. glyoxal, glutaraldehyde, and dimethylol dihydroxy ethyleneurea (DMDHEU), were investigated from the aspects of moisture adsorption and bending creep properties. To the moisture adsorption data, Hailwood-Horrobin adsorption equation was applied, and whole adsorbed water was separated into hydrated water and dissolved water which correspond to monolayer and multilayer adsorption, respectively. In the treatments with non-formaldehyde reagents, the decrease of equilibrium moisture content was mainly attributed to the decrease of dissolved water, but not largely to that of hydrated water. This suggested that the reagent in the multilayer adsorption region contributed pronouncedly to suppress the moisture adsorption by the bulking and cross-linking effects, but that the reagent in the monolayer adsorption region did not considerably. The creep deformation and remaining strain of the specimens treated with glyoxal and glutaraldehyde were as small as those of formaldehyde treatment. Also by the DMDHEU treatment, creep deformation was restrained to some extent. The eminent creep restraint effect by these treatments showed the formation of cross-linkings, although the crosslinkings were not stable to the drastic water leaching.

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The probability of bond between wood components and glyoxal was examined by means of a mechanical method, infrared (IR) spectrometry, and solid state 13C-nuclear magnetic resonance (NMR) spectrometry. The successive fixation of a compressed wood by the glyoxal treatment suggested the formation of cross-linkings between wood components and/or wood structures. The IR spectra showed that ester bond as well as ether bond was formed between wood components and glyoxal. The existence of linkages between glyoxal and cellulose was indicated also from the NMR spectra. The addition of glycol to the glyoxal solution was investigated from the viewpoint of stabilizing effect of the linkages. When 0.2 mole ratio of glycol was added to 5-10% glyoxal solution, weight gain and antiswelling efficiency (ASE) were largest, however the addition of excessive amount of glycol did not advance further the weight gain and ASE. When an appropriate amount of glycol was added to the impregnation solution, both weight and ASE did not largely reduce even by the repeated hot water soaking. By the treatment without glycol, the dimensional stability after water soaking was attributed to only restraint of the swelling. On the other hand, when the glycol was added, the dimensional stability was developed not only by the restraint of the swelling but also by the buckling effect.