Novel retention systems based on surface-modified cationic nanoparticles

Microparticle retention systems have been extensively used in papermaking processes. The microparticles/polymers dual component systems are often coupled in opposite charges such as the anionic silica particles used in conjunction with cationic starch, or the cationic alumina microparticle used in conjunction with anionic polyacrylamide. The use of nano- or microparticles as part of retention systems improves flocculation, accelerates drainage and produces better paper quality or paper formation.;This work focused on developing novel flocculation systems based on surface-modified cationic nanoparticle. Two types of nanoparticles were used: fumed silica nanoparticle (14nm), and cyclodextrin nanosphere (1.5nm). The cationic modification or quaternization of the nanoparticles were performed via interacting the hydroxyl groups on the nanoparticle surface with cationic reagents bearing the quaternary ammonium group. Both 3-N,N,N-silylpropyltrimethylammonium chloride and (2,3-epoxyproyl)trimethylanunonium chloride were found to be effective in altering the surface characteristics of the nanoparticles. The zeta potential and the surface charge density of the modified nanoparticles were determined and positive results were achieved.;Application of surface-modified nanoparticles to clay flocculation showed significant improvement on the performance of the anionic polymer polyacrylamide in lowering the relative turbidity of the clay suspension. Moreover, the modified cyclodextrin also reduced the aromatic compound concentration in the filler suspension through inclusion complex formation which provides a potential novel system for simultaneous removal of dissolved and colloidal substances (DCS) encountered in papermaking processes or other waste effluents. The adsorption behaviour of the nanoparticle onto clay particles and the association interaction with anionic polymers were also investigated thoroughly which improved our understanding of the bridging flocculation mechanism involved.