Flocculation of reed pulp suspensions by quaternary chitosan-nanoparticle SiO_2 retention aid systems

摘要

The microparticle retention aid system has been a focus on the studies of paper-making chemicals. N-(2-Hydroxy-3-trimethylammonio)-propyl chitosan chlorider [quaternary chitosan (QCS)]-nanoparticle SiO_2 dual component system was investigated in this work. The adsorpton kinetic experiments indicated that there was a very fast (<1 min) polymer adsorption under good mixing conditions. Adsorption of QCS onto the fiber surface was followed by a rearrangement to reach an equilibrium conformation. At the same time, QCS chains, existing on the surface of fiber, could permeate into the porous of the fiber, resulting in the reducing of zeta potential of the cel-lulosic fiber. In addition, the flocculation would be increased with the increasing of SiO_2 when the fiber substrates surfaces was net positively charged by an adsorbed QCS layer. It was also found that ionic strength decreased significantly the flocculation efficiency in pure QCS system, whereas the turbidity of the reed pulp suspension increased slightly with the increasing of NaCl concentration in QCS-SiO_2 systems. The effect of shear force on the flocculation was tested. It was shown shear led to floc breakage and decreased the flocculation. These phenomena were very obvious for one-component system (QCS or C-St), but the microparticle system (QCS-SiO _2 or C-St-SiO_2) was shear resistance. Dynamic drainage experiment indicated that the turbidity of white water was decreased with the increasing of dosage of SiO_2 in experimental level.