Question

Wood contains water in three forms- vapour, bound or hygroscopic water and ____________

(a) contact water

(b) capillary water

(c) free water

(d) bulk water

I got this question during an online interview.

Origin of the question is Classification of Timber, Carpenter’s Work in section Rules and Methods of Measurement of Civil Engineering Drawing

Answer 1

Right option is (c) free water

Explanation: Free water: The bulk of water contained in the cell lumina is only held by capillary forces. It is not bound chemically and is called free water. Free water is not in the same thermodynamic state as liquid water: energy is required to overcome the capillary water. Furthermore, free water may contain chemicals, altering the drying characteristics of wood.

Bound or hygroscopic water: Bound water is bound to the wood via hydrogen bond. The attraction of wood for water arises from the presence of free hydroxyl (OH) groups in the cellulose hemicelluloses and lignin molecules in the cell wall. The hydroxyl groups are negatively charged. Because water is a polar liquid, the free hydroxyl groups in cellulose attract and hold water by hydrogen bonding.

Vapor: Water in cell lumina in the form of water vapour is normally negligible at normal temperature and humidity.