In this work, the aim was to study flocculation, reflocculation and deflocculation phenomena with different chemical combinations. The flocculation of fillers (kaolin and PCC) was studied with polyelectrolyte complexes (PEC) with different combinations of cationic and anionic polyacrylamides. The effect of different cellulose nanofibrils (CNF) on the flocculation and retention of fillers was also studied in this thesis. Experiments were made with single component CNFs and also combining CNFs with different polyelectrolytes. Deflocculation kinetics was studied by adding anionic high molecular weight polyacrylamides (APAM) to high consistency fiber suspensions. The flocculation tests were made with the Turbiscan online device and retention of fillers with the Dynamic drainage jar (DDJ) device and deflocculation with a Focused Beam Reflectance Measurement (FBRM) device. Adsorption studies with the QCM-D (Quartz Crystal Microbalance with Dissipation, dewatering with DDA (Dynamic Drainage Analyzer) and rheology with the dynamic rotational rheometer were also made. Results show that PECs can enhance flocculation and reflocculation capacity significantly in comparison with the corresponding single polyelectrolytes and they can also be used in significantly wider concentration ranges. One of the important findings of this work was that one of the components of PECs should be a high molecular weight polyelectrolyte so that the PEC could effectively form polymer bridges between filler particles. More specifically, the component in excess in the PEC should have a higher or the same molecular weight than the other component. Different CNFs can also be used as effective flocculants alone and also in combination with polyelectrolytes. However, in order to flocculate effectively, CNFs have to be chemically modified to have a high number of charged groups in order to increase the electro- static interactions with filler and fines in the system. CNF systems also showed significant reflocculation, which is unusual for polymeric single flocculant systems. With anionic high molecular weight polyacrylamides, the positive effects are quickly diminished due to shear forces, and therefore, the best deflocculating effect is achieved in as short contact time as possible. The high molecular weight of APAM was shown to be beneficial to deflocculation and there is an optimum dosage level after which deflocculating effect starts to decrease. APAMs had a significant deteriorating effect on dewatering that was highly dependent on the contact time of the pulp suspension with APAM. This thesis presents new retention aid concepts and new information on flocculation and deflocculation kinetics with PECs, CNFs and APAMs. This knowledge could be useful in papermaking and also in other industrial fields such as in water treatment.
|Translated title of the contribution||Selluloosamateriaalien ja mineraalipartikkelien flokkaantuminen/deflokkaantuminen polyelektrolyyttikompleksien ja nanoselluloosien avulla|
|Publication status||Published - 2015|
|MoE publication type||G5 Doctoral dissertation (article)|
- polyelectrolyte complexes
- mineral particles