Removal of water from the cell wall during drying

This paper explores the basic mechanisms of fibre dehydration and the relationship between fibre structure and drying rate. Three fractions of water within the cell wall were found: bulk water located in large macropores; freezing bound water located in the micropores formed by the amorphous polymer network, and nonfreezing water adsorbed onto accessible hydrophilic groups. A plot of the bound water as a function of pulp moisture ratio shows two distinct transitions: i) at 05-0.8 g/g, there is no more bulk water within the cell wall. It is believed that this is when the macroreticular system has collapsed and the hemicellulose begins to dehydrate, ii) at 0.24-0.28 g/g, the fibre pores are collapsed and only strongly bound non-freezing water remains. Constant rate evaporation continued well past the point where water began to leave the cell wall. This implies that in the constant rate zone of drying, water can diffuse rapidly through the interior of the fibres passing from one fibre to the next via developing fibre bonds.