Water Freezing in Wood: How Low Can It Go
Forest Service researchers examined the freezing and melting of water in solid wood and chemically isolated cell wall components. The melting temperature of the water depended on the wood's moisture content, and the behavior was similar between cell wall components. The data suggest water in wood may exhibit a eutectic phase transformation whereby a chemical composition solidifies at the lowest possible temperature.
Traditional thinking suggests that wood holds water in one of two states: chemically bound to the cell wall or unbound in the cell lumina when the moisture content is above fiber saturation, or greater than 30 percent. These theories cannot account for the fact that several degradative processes in wood require water, such as mold growth and fastener corrosion, which begin at much lower moisture contents, between 15 and 20 percent. Recently, a third type of loosely bound water was reported in cellulose; this type of water was distinct in that it froze at a lower temperature than free water (some tightly bound water did not freeze).
Using differential scanning calorimetry, Forest Service researchers explored the freezing and melting points of water in wood and chemically isolated wood components across a range of moisture contents. They found that freezing and melting temperatures of the water depended on moisture content and only observed the loosely bound water in cellulose when the material was ball-milled to a very small particle size.
The results suggest that the so-called loosely bound water was actually an artifact of sample preparation. The dependence of freezing and melting temperatures on the moisture content suggests that thermodynamics of water in wood could be described by a eutectic phase transformation, which gives new insight into degradative processes in wood.
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