MEASURING FINES RETENTION OF NEWSPRINT PULPS.

In measuring the fines retention of newsprint pulps by means of the Dynamic Drainage Jar (DDJ), first-pass retention was found to be independent of drainage rate and pulp consistency, but to decrease with increasing propeller speeds and screen hole size. Realistic and reproducible results were obtained only when mat formation on the DDJ screen was prevented by high stirring speeds, slow drainage rate or low initial consistency. In the absence of mat formation, the location of the propeller had only a minor effect on retention. The classification of a newsprint pulp in the DDJ, by fractionation through a series of screens of different hole sizes, did not agree with its Bauer-McNett classification.