The effect of drying conditions on the swelling and bonding properties of bleached kraft hardwood pulp

The quality of dried chemical pulp depends on the loss of swelling (hornification) which happens during drying. This is a critical issue in the manufacture of fine papers where good fiber bonding is essential. It is apparent that a better understanding of how drying variables affect hornification could lead to improvements in pulp quality.

The purpose of this study was to determine how important drying variables affect fiber hornification and bonding. The following variables were considered: final moisture content, drying temperature, and cellulose/water interaction.

It was found that in the high solids range the final moisture content has only a small effect on hornification for pulp dried at room temperature. Heating the pulp above 70ºC increases the hornification substantially. The magnitude of the heat-induced hornification depends on the amount of water in the cell wall. Hornification results in pulp with lower bonding potential.

An optimum drying strategy has the potential to increase the quality of dried pulp. A high final moisture content, low drying temperature and control of the drying temperature profile are possible ways to reduce hornification.