Mini-Encyclopedia of Papermaking Wet-End Chemistry
Part Two: Definitions and Concepts

First-Pass Retention

First-pass retention gives a practical indication of the efficiency by which fine materials are retained in a web of paper as it is being formed. First-pass retention values can be calculated from just two consistency measurements, the headbox consistency, and the white water consistency. There is a very wide diversity of first-pass retention on different paper machines, from less than 50% to almost 100%. The key rules that papermakers follow are that (a) first-pass retention should have a steady value, and (b) that value should be high enough to avoid operational problems or an excessively two-sided sheet. Some operational problems that can be caused by low values of first-pass retention are increased frequency of deposit problems, filling of wet-press felts, poor drainage, and unsteady drainage rates and sheet moistures.

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This page is maintained by Martin hubbe, Associate Professor of Wood and Paper Science, NC State University, m_hubbe@ncsu.edu .