Title
Linking CSF to drainage time during handsheet formation: refining effects across wood and non-wood pulps
Authors
NISHI K. BHARDWAJ

Received October, 2025
Published Volume 60 Issue 1-2 January-February
Keywords pulp refining, Canadian standard freeness (CSF), drainage time, handsheet formation, non-wood fibers (bamboo, bagasse, wheat straw), predictive modeling

Abstract
This study investigates how refining alters drainage behavior during laboratory handsheet formation across five bleached pulps – hardwood, softwood, bamboo, wheat straw, and bagasse – over freeness ranges representative of approach-flow and wet-end operation. For each pulp and refining level, Canadian standard freeness (CSF) and handsheet drainage time (t) were measured and regressed using three compact models: (i) t = a + b/CSF, (ii) √t = a + b.log(CSF), and (iii) log t = a + b.log(CSF). All pulps showed the expected increase in drainage time with decreasing CSF, but the rate and curvature were pulp-specific. Transformed models generally outperformed or matched the reciprocal form, with the √t-log(CSF) and log–log power laws yielding higher R2 and lower RMSEE, especially for bamboo and non-wood pulps. Wheat straw exhibited near-perfect fits under √t-log(CSF), while bagasse remained the most challenging, reflecting fines/pith effects. The results deliver practical equations for predicting drainage time from CSF within observed ranges and highlight that model choice should be pulp-dependent for reliable dewatering control.