Effect of refining on reinforcement ability

In this paper results of the investigations of long-fibre chemical reinforcement pulp refining for wood-containing printing papers has been presented. The analysis is based on data of pilot plant and several paper mills. The sizing of the refiners and the refining line is an important factor for the quality of the refined pulp. The possibilities to affect the pulp properties by the control of the refining line are rather limited. Raw material is the most important source for quality variations of the refined pulp. Unequal properties between different pulp species are obvious, but there is also significant variation inside each species issue. The main process variable that affects the pulp quality is the variation in the flow rate of the pulp. At higher flow rate the lower amount of impacts has to be compensated by tightening the bar gap. This results to a significant change in fibre length/freeness, tensile/freeness, tear/freeness and porosity/freeness rations. The main strength property for the control of reinforcement kraft portioning is typically the CD-tear strength of the paper. This causes, that also the tear strength of the refined kraft should be maximised. However, the typical control principle is to refine to a constant freeness target specified by the other paper properties.