Abstract
Papermaking fines are small pulp fiber fragments, which improve paper properties, such as paper strength and optical properties. They can be retained in a sheet of paper as fines aggregates or by deposition on fibers. Here we report on the flocculation of fines by a dual component flocculation system, consisting of poly(ethylene oxide) (PEO) and a cofactor. Previous studies showed that PEO is more effective when freshly dissolved than when well dissolved. This was ascribed to PEO entanglements present in freshly dissolved PEO, which disappear with time, shear or dilution. In this study the efficiencies of flocculation of thermomechanical pulp fines by entangled and disentangled PEO have been compared in the presence of different cofactors: a carboxylated phenolic resin (CPR), tannic acid (TA) and a sulfonated kraft lignin (SKL). The results support previous studies, showing that the state of entanglement of PEO has a significant effect on fines flocculation. In addition, we found that different cofactors affect disentangled PEO differently in response to salt addition and fines properties. When PEO was entangled, these cofactors caused the same high flocculation rate and the effect of the particle properties was negligible. When PEO was disentangled, the fines flocculation efficiency decreased to different levels for various cofactors, showing that CPR was superior to TA and SKL. The fibrillar fines and chunky fines were also flocculated at different rates by disentangled PEO/CPR, indicating the influence of particle properties. Adding salt prior to the cofactor and disentangled PEO improved the flocculation rate to the same level as entangled PEO at a given dosage when CPR was used as a cofactor.
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