Faserumformung beim Kneten im Hochtemperaturbereich

Plastic fibre forming is observed in many processes in pulp preparation and papermaking. Such changes in the shape of the fibre presuppose that the softening temperatures of pulp components have been exceeded and that reshaping forces exist. The latency of lignin-containing pulps is one well-known example. Comparable phenomena cannot be observed in practice with the latency of pure chemical pulps. The mechanisms of action in drying crimping and hot refining are not identical with those in plastic fibre forming. Fibre forming processes in the high temperature range determine certain properties of the pulps and resultant papers to an even greater extent than is known from latency (reversible plastic fibre kinking). In the sense of papermaking and the quality of many product groups, these include positive developments in specific volume, porosity and dewatering. Strength and texture properties, on the other hand, are reduced. Concomitant to fibre forming, dispersion always acts on the development of pulp properties as well. The pulps are affected, however, by both processes, although in the opposite directions. This is the reason why the specific properties of the pulp - in particular the degree of dispersion- are so very important when assessing the success of fibre forming. Laboratory tests have shown that, during kneading dispersion at temperature above 140°C, fibres experience reshaping that is not reversible by the usual elimination of latency. This temperature can therefore be regarded as the beginning of cellulose plasticisation.