Freeness (CSF)
Also: freeness, CSF, Canadian Standard Freeness, SR
A measure of how readily a pulp dewaters, reflecting the degree of refining. Lower freeness means more refined, slower-draining pulp.
Freeness measures the rate at which water drains through a pulp mat. Canadian Standard Freeness (CSF, ISO 5267-2) reports in ml of water that drains in a fixed time. Schopper-Riegler (°SR, ISO 5267-1) is an inverse scale used in Europe.
Unrefined pulp has high freeness (700 ml CSF). As fibers are refined (beaten), they collapse and fibrillate, which slows drainage and lowers freeness. Newsprint targets 80 to 150 ml CSF. Printing and writing grades target 300 to 450 ml CSF. Too much refining kills productivity; too little kills strength.
Related
- Refining. A stock preparation step where pulp passes between rotating discs with bars, mechanically working the fibers to increase bonding and strength.