THE INFLUENCE OF DRYING AND BEATING ON THE SWELLING OF FINES

Hornification is the partial loss of swelling of pulps that can result from a drying-and-rewetting cycle. In this paper we examine hornifica tion, paying particular attention to the behaviour of the fines fracti on. We find that, as with the fibres, hornification occurs to the fine s of chemical pulps but not to the fines of mechanical pulps. We then examine beating as a method of reversing the hornification of commerci ally dried, bleached kraft pulps. We find that, using the PFl mill, th e swelling of both fibres and fines may be restored towards their neve r-dried levels with only a modest increase in the amount of fines. The few additional fines, ''secondary'' fines, are different in nature to the ''primary'' fines and contribute importantly to the freeness drop occurring during beating.