HORNIFICATION - MECHANISMS AND TERMINOLOGY

Hornification is a technical term, which is often used to describe cha nges in fibres affected by drying or recycling. The first part of this paper consists of an extensive literature review discussing the horni fication mechanisms aggregation and crystallization as well as the inf luence of pulp beating, the presence of fines, mechanical forces, agei ng and heat. The second part contains the author's own observations on hornification. Here, hornification was quantified according to the or iginal definition, i.e. as a decrease in water retention value (WRV). Two phases of hornification were identified: hornification by water re moval, which was called ''wet'' hornification, and hornification due t o oven drying, which was called ''dry'' hornification. It was suggeste d that these phases could be seen as morphology dependent ''wet'' horn ification and as morphology independent ''dry'' hornification.