[lic] Kemian tekniikan korkeakoulu / CHEM

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Browsing [lic] Kemian tekniikan korkeakoulu / CHEM by Department "Puunjalostustekniikan laitos"

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  • Influence of fibrillar cellulose on pigment coating formulation rheology
    (2012) Dimic-Misic, Katarina
     School of Chemical Engineering | Licentiate thesis
    Coating suspension rheology influences the coating performance at high speeds. The quality of the coated and printed papers is also affected by the rheology of the suspension. For good coating results, it is crucial to optimize the water retaining properties of coating colours. The observation that fibrillar cellulose (MFC) could be used in paper coating formulations as a co-binder, since it is biodegradable and has good shear thinning properties, raises a question about the process ability of coating colours which have cobinder substituted with fibrillar cellulose. In this study, fibrillar cellulose is used to substitute the standard, synthetic co-binder material, carboxymethyl cellulose thus affecting both dewatering and rheological properties of coating colours. Reactivity of the MFC fibers in coating colour formulation is strongly dependent on the fineness of the fibrillar material as well as on its consistency, pre-treatment and refining route. In the present study the consolidation of coating colour layers has been studied using rheology as the main tool. This method combines the use of standard viscoelastic and static dewatering tools, Åbo Academy Gravimetric Dewatering Device and Brookfield viscometer, with the use of MRC300 Rheometer accompanied with an Immobilization cell. The rheological behaviour of all coating colours that have fibrillar cellulose as co-binders was found to be similar. Lower water retention and faster immobilization of filter cake were accompanied with higher shear thinning behaviour. This conclusion was strengthened by the recovery measurements, which showed that the fibrillar material containing coatings have a prolonged recovery time after high shear. A linear correlation between gravimetric (static) water retention and immobilization time, on the one hand and elasticity and prolonged recovery time on the other was found for fibrillar cellulose containing coating colours, regardless of the type of fibrillar material or pigment blend.
  • Interactions between bacteria and some papermaking components
    (2010) Leino, Taina
     School of Chemical Engineering | Licentiate thesis
    The aim of this thesis was a better understanding of the surface interactions between white water bacteria, Pseudoxanthomonas taiwanensis, and papermaking components, in order to make it possible to assess the importance of these interactions in papermaking processes. Flocculation of bacteria by cationic polyelectrolyte's in 0.01 M aqueous NaCl was investigated with electrophoretic mobility and turbidity measurements. The net charge of the bacteria was negative in a wide pH range. Cationic polyelectrolytes (poIyDADMAC, cationic polyacrylamide (C-PAM), cationic starch) adsorbed on the surface of the bacteria at pH 8. Polyelectrolytes functioning by bridging mechanism (C-PAM) were the most effective flocculants. Other polymers flocculated bacteria by charge neutralization. Thus, addition of typical retention polymers can flocculate bacteria and may attach them to the paper web. Adsorption of the bacteria and cationic polyelectrolytes on silica, cellulose, hemicellulose and extractive surfaces was investigated by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscope (AFM) and field emission scanning electron microscope (FESEM). Cationic polyacrylamide and poIyDADMAC increased bacterial adsorption on silica. The polyelectrolytes accumulated around the bacterial cells and prevented their aggregation on the surface at pH 8. The bacteria adsorbed on a cellulose surface as small aggregates in the presence of the polyelectrolyte. Hemicellulose (O-acetylgalactoglucomannan) promoted dramatically bacterial adsorption as large rafts on extractive surface at pH 4.7. Thus, bacterial adsorption on extractives may relate to pitch problems and biofilm formation in paper machine.
  • Organic chlorine behaviour in activated sludge process
    (2011) Jokinen, Heini
     School of Chemical Engineering | Licentiate thesis