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 0.05mm 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.