Adsorption studies of polyelectrolytes and enzymes on lignocellulosic model surfaces
Doctoral thesis (article-based)
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AbstractThis thesis presents fundamental studies on the adsorption of polyelectrolytes and enzymes on solid surfaces. The overall objective of the research was to clarify the adsorption phenomena of polyelectrolytes and enzymes taking place in papermaking. The adsorption experiments were made with a quartz crystal microbalance with dissipation, QCM-D, and the enzyme-modified surfaces were characterised by atomic force microscopy, AFM. In order to study the interactions taking place at a molecular level, model surfaces of different pulp components are needed. Therefore, at first the preparation and characterisation of cellulose and lignin model films for QCM-D studies were evaluated. The adsorption of single cationic polyelectrolytes and of the polyelectrolyte multilayers and complexes on silica and cellulose surfaces was studied. The low-charge cationic polyelectrolytes adsorbed more on silica while the adsorption of high-charge polyelectrolytes was higher on cellulose. At the beginning of the adsorption the polyelectrolyte layers were viscous and more dissipative on cellulose and when the adsorption proceeded the layers became more rigid, in contrast to the behaviour on silica. The low-charge complexes (PECs) were more dissipative and viscous than those of high-charge PECs. The multilayers and complexes formed by low-charge polyacrylamides formed rather thick layers on both surfaces, unlike the high-charge polyelectrolytes which formed flat and thin layers with both addition techniques. By using polyelectrolyte complexes instead of the multilayering technique, thick and dissipative layers with a lower amount of polyelectrolyte can be formed. The modification of lignocellulosic model surfaces with laccases and further the adsorption of anionic ferulic acid on laccase-activated lignin were also examined by QCM-D. Both enzymes, Trametes hirsuta and Melanocarpus albomyces laccases adsorbed on cellulose and lignin surfaces. The adsorbed amount of M. albomyces laccase was higher than that of T. hirsuta laccase and the adsorption of M. albomyces laccase was strongly dependent on pH on the lignin surface. Stable ferulic acid adsorption was found on laccase-activated lignin but the mode of action of laccases was different when laccase and ferulic acid were added simultaneously on lignin.
adsorption, AFM, cellulose, laccase, lignin, polyelectrolyte, polyelectrolyte complex, polyelectrolyte multilayer, QCM-D
- [Publication 1]: Tammelin, T., Saarinen, T., Österberg, M. and Laine, J. (2006). Preparation of Langmuir/Blodgett-cellulose surfaces by using horizontal dipping procedure. Application for polyelectrolyte adsorption studies performed with QCM-D. Cellulose 13 (5), 519-535.
- [Publication 2]: Saarinen, T., Österberg, M. and Laine, J. (2009). Properties of cationic polyelectrolyte layers adsorbed on silica and cellulose surfaces studied by QCM-D – Effect of polyelectrolyte charge density and molecular weight. Journal of Dispersion Science and Technology 30 (6), accepted.
- [Publication 3]: Saarinen, T., Österberg, M. and Laine, J. (2008). Adsorption of polyelectrolyte multilayers and complexes on silica and cellulose surfaces studied by QCM-D. Colloids and Surfaces A: Physicochemical and Engineering Aspects 330 (2-3), 134-142.
- [Publication 4]: Saarinen, T., Orelma, H., Grönqvist, S., Andberg, M., Holappa, S. and Laine, J. (2009). Adsorption of different laccases on cellulose and lignin surfaces. BioResources 4 (1), 94-110.
- [Publication 5]: Saarinen, T., Suurnäkki, A., Österberg, M. and Laine, J. (2008). Modification of lignin with laccases for the adsorption of anionic ferulic acid studied by QCM-D and AFM. Holzforschung, accepted.