Adsorption of bacteria and polycations on model surfaces of cellulose, hemicellulose and wood extractives studied by QCM-D

Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used as the tools to study the adsorption of bacteria onto surfaces of silica and polystyrene coated with materials related to papermaking. Cationic polyelectrolytes used as fixatives and retention aids in paper industry were found to promote irreversible adsorption of the ubiquitous white water bacterium, Pseudoxanthomonas taiwanensis, onto model surfaces of cellulose (pH 8). The high charged low molecular weight polyelectrolyte, poly(diallyldimethyl) ammonium chloride (pDADMAC) adsorbed to silica surface as a flat and rigid layer, whereas the low charged cationic polyacryl amide (C-PAM) of high molecular weight adsorbed as a thick and loose layer. AFM images showed that the polyelectrolytes accumulated as layers around each bacterial cell. In the presence of wood hemicellulose (O-acetyl-galactoglucomannan) the bacteria adsorbed massively, as large, tightly packed rafts (up to 0.05 mm in size) onto the polystyrene crystal surface coated with wood extractives (pH 4.7). AFM and FESEM micrographs also showed large naked areas (with no bacteria) in between the bacterial rafts on the crystal surface. In this case, QCM-D only incompletely responded to the massiveness of the bacterial adsorption. The results indicate that cationic polymers can be used to increase the retention of bacteria from the process water onto the fibre web and that, depending on the balance between hemicelluloses and wood extractives and pH of the process waters, bacteria can be drawn from process waters onto surfaces.