Question

Describe how changes in moisture content below FSP are different from changes in moisture content above FSP. What parts of the wood structure are changing in each condition? How are the mechanical properties changed in each condition?

Answer 1

Ans) To understand the change how change in moisture content affects the properties of wood we have to know about Fiber Saturation Point (FSP) .Water in wood is present in two forms:

1) Bound water - water within cell wall bonded with cellulose

2) Free water = water within cell wall cavities

A Fiber saturation point is a moisture content where bound water content is maximized ,but their is no free water present.Generally wood have average FSP around 30%

If Moisture content fall below FSP , bound water in reduced from cell walls and hence cause wood to shrink . On the other hand if moisture content is above FSP, it means water is present in cell cavities which cause wood to swell .

When moisture content fall below FSP , mechanical properties of wood increases because it leads wood to shrink and hence increase in density .As the density increases , strength properties improves. Similarly when moisture is above FSP, wood swells and become less durable