Can you please be more specific with the problem?
You want to know what happen in wood when it is exposed to moisture, but:
what kind of wood? which is its initial humidity? it was air dried?
thanks María Cristina Area. the kind of wood is Abies. my mean is the time that wood exposer 90 percent to 30 percent. no it wasn. it was kiln in dried. my mean this is, when the wood exposur to 90 percent humidity?
Water is absorbed in the H bonds formed with the free OH groups of the amorphous regions of the cellulose fibers.
When drying, wood lose initially the free water and later the bound water.
In the latter case, wood shrinks because the formation of new bonds between cellulose chains.
When subjected again to moisture, wood follows a hysteresis curve as it can not regain all initial sites bonded to water.
Not sure if this is what you wanted to know ...
its very well and good. and can you explain the moisture stress in wood?
thanks .
As I said before, shrinkage takes place with diminishing moisture content, as a consequence of the increase of cellulose internal bonds. When submitted to moisture, it can not regain the same degree of humidity, since water do not have sufficient energy to broke cellulose-cellulose bonds. The other components of wood do not suffer significant changes.
That is the answer to your question. May be you have to put it in another way if it is not what you want to know...
You do not forget the role played by the hemicellulose whose OH groups are available to form H-bond between water and the amorphous hemicellulose.
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