Moisture Adsorption Thermodynamics of Chemically Modified Wood

Abstract

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.

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

“…Of the different methods for generating specific RH levels detailed above, one of the most common methods is by saturated salt solutions (Ammer 1963b;Eriksson and Noren 1965;Forster 1998;Higgins 1957;Nearn 1955;Papadopoulos and Hill 2003;Wangaard and Granados 1967;Yasuda et al 1995) since they are relatively simple to use and cover a wide range of RH levels (see, for example, Greenspan 1977) for solutions in the range 3-98% RH. Their use limits, however, which RH levels can be achieved.…”

The reduction in the fibre saturation point of wood due to chemical modification using anhydride reagents: A reappraisal

“…(5) is given incorrectly by Yasuda et al (1995). From the above relationships, the values K 1 , K 2 and W can be derived as shown in Eqs.…”

“…Popper and Bariska (1972) reported H-H polylayer and monolayer isotherm data for acetylated fir. Yasuda et al (1995) (2005) subsequently found that the (H-H) model gave the best fit to experimental data. However, none of these studies reported the data in terms of EMC R .…”

Comparison of the hygroscopic behaviour of 205-year-old and recently cut juvenile wood fromPinus sylvestrisL.

“…If they are compared point by point, all the coefficients show values which agree with this affirmation. Despite the fact that at point 11.17% of the LiCl salt the old wood has a higher hysteresis coefficient than in the new wood (1.00 as opposed to 0.86), it was considered that this point should be removed as there was a possibility that entropy peaks may have an influence at low humidities [41]. Kadita et al [17] speculated that these peaks were due to the fact that the hydroxyl groups in the amorphous region form bonds in the wood when the wood is oven-dried.…”