Variable retention of water by dry wood

Abstract

SynopsisWhen small wood (or cellulose) samples are vacuum-dried a t room temperature, their h a 1 weight is found to vary according to their previous sorption history. The weight variations, of up to I%, are shown to be due to strongly retained water. A minimum weight is obtained reproducibly ( f 0.01%) only when the wood is dried rapidly from the wetted state. When wood thus dried is exposed to water vapor and redried, water is retained even after drying for long periods or a t higher temperatures (65°C.) and is removed only by again wetting and redrying the wood. The quantity of water retained is greatest after exposure to relative vapor pressures of approximately 0.5 and increases linearly with the square root of time of exposure up to at least 1000 hr. As some of these phenomena have been reported for the wool-water system also, it is possible that other poIymers, particularly those which swell in water, may behave similarly. The significance of these resulta for the experimental determination of moisture content and the study of water sorption is discussed.

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

“…Moreover, a second drying stage will yield a lower dry mass, perhaps leading to speculations about ''trapped water'' in the first drying stage (Hill et al 2015). It is recognised that Hergt and Christensen (1965) did find that up to 1% MC is retained in the wood after vacuum-drying if the material is not rapidly dried from the water-saturated state, i.e. conditioning to any level of RH before drying results in incomplete drying even at a drying temperature of 65°C.…”

The Apparent Density of Wood in Non-Swelling Liquids

“…In some cases, pieces were given several prior extractions in benzene or benzene-alcohol (2:1) mixture followed by washings in warm distilled water. Vacuum drying at room temperature over P 2 O 5 of such pre-treated samples gave what the authors believe to be the most accurate dry weight (Hergt and Christensen 1965). This is reproducible to 0.01% over successive wetting and re-drying cycles.…”

The behavior of cotton cellulose and beech wood in ammonia atmosphere

“…The reason for this response could be sought in the presence of adsorbed water remaining on the surfaces even after drying. Hergt and Christensen [4] reported that dried woody specimen still retained water, possibly hydrate water, up to 1% of the dry weight, depending on their moisture prior to drying. As the first stage of adsorption, ammonia may be involved in forming NH,OH with this available water, accompanied by pronounced heat evolution.…”