Lumber was subjected to natural drying for about half a year, from the green wood condition to near the fiber saturation point
, during which time stress wave velocity and moisture content were measured about seven times.
The moisture content that corresponds to a complete loss of free water (with 100 percent of the bound water remaining) is known as the fiber saturation point
. The moisture content changes below the fiber saturation point
cause lost of bound water and adequate changes of wood volume.
3- Moisture in excess of the fiber saturation point
They can never expand beyond the limit established by the fiber saturation point
, the elastic limit set by the rubber bands.
Cell walls in wood fiber swell and shrink under the fiber saturation point
When the moisture content of the tracheids drops below the fiber saturation point
(FSP), that is when lumina contain no "free" water but cell walls are fully saturated with liquid, further dehydration leads to cell wall shrinkage processes.
More precisely, wood only changes dimension between an absolutely dry state (completely free of moisture) and its fiber saturation point
(the point at which the cell walls of the wood fibers are completely saturated with moisture).
Fiber saturation point
, tangential shrinkage, cell structure, and a host of other technical terms have meaning and purpose in the ensuing process for each individual species.
We have recently demonstrated the use of a clinical MRI for imaging free water above the fiber saturation point
in WPC boards exposed in exterior conditions in Vancouver, British Columbia, and Hilo, Hawaii (Gnatowski et al.
Generally, it applies to wood fungi: The minimum for wood decay is near the fiber saturation point
of about 30% u, however, commonly slightly above this range because only then there is free water in the lumen void space.
When cell lumina contain no water, but cell walls are fully saturated with liquid ("fiber saturation point
"), further dehydration leads to a shrinkage process, which can induce drying checks.