Abstract :
Prior to the headbox, a papermaking furnish undergoes multiple levels and types of physical stresses, or shear regimes. First of all, a high level of shear in the refining operation results in cellulose fibers being partly deliminated, resulting in greater conformability, some fibrillation of the surfaces, and a large amount of fines being produced. It is essential for papermakers to gather and flocculate these fines in order to get them out of the way, therefore reducing drainage time, and improving the economy of the papermaking operation as a whole. Our research project sought to emulate the types of shear that fines and filler particles might experience during the papermaking process. We employed various polymer bridging techniques, in order to increase flocculation, and tested various types of shear against several levels of polymer dosages. The resulting state of agglomeration of the fine materials was evaluated by means of laser diffraction particle size analysis. It was found that DADMAC, a highly charged cationic polymer commonly used in wastewater treatment plants, was very effective in reversing the negative charges of the fines, and filler particles as well. When followed by an anionic polymer, such as anionic polyacrylamide (aPAM), flocculation was found to increase greatly, and still retain up to 74% of its original mean agglomerate size, depending on the shear. Furthermore, through several zeta potential tests, it was found that DADMAC had a logarithmic effect on the charge of a fines or PCC particles.
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