The C.s. freeness of unbeaten PFP (Pulp produced by the Pollution Free Pulping high yield process) from pilot plant was around 400 ml and extremely lower than that of commercial BKP (Bleached Kraft Pulp).
The cause of the low freeness value was investigated by 3 variables, such as specific surface area, specific volume and pulp consistency of filter bed during freeness test. The excessive PFP fines, which were secondarily produced during prefiberization stage, contribute to higher specific surface area and lower freeness. But low freeness in PFP is mainly due to its hemicelluloses because alkali extracted PFP and B·KP showed almost the same freeness. PFP hemicelluloses make fibers more flexible than B·KP and such flexible fibers give very compact filter bed during freeness test. Specific volume of PFP is not so different from B·KP in spite of its higher content of dilute alkali soluble hemicelluloses.
PFP gives higher consistency filter bed with lower specific surface area than B·KP of the same freeness.