PARTICLE SIZE DISTRIBUTIONS OF FINES IN MECHANICAL PULPS AND SOME ASPECTS OF THEIR RETENTION IN PAPERMAKING.

In the reported experiments, particle size distributions of mechanical pulp fines have been determined by automated image analysis, and the technique is illustrated by the results of a series of experiments designed to determine what effect various conditions of sheet formation have on the size distributions of unretained fines. The range of values for the average longest linear dimension (ALLD) of fines in this work was 16-25 mu m, and the standard deviations of the size distributions were about equal to the mean. The precision of the image analysis results was found to be slightly dependent on the method of dying of the fines and slide preparation. The ALLD of fines in the white water of a handsheet machine decreased when the basis weight of the handsheet was increased. The ALLD of whitewater fines collected along a fourdrinier showed complex dependencies on sampling time and sampling position.