The retention- and drainage-aid behavior of quaternary chitosan in papermaking system

N-(2-Hydroxy-3-trimethylammonio)-propyl chitosan chlorider (C-CS) was investigated as retention- and drainage-aids for peroxide bleached reed kraft pulp using titration, phenol/sulfuric acid spectrophometric, SEM (scanning electron microphotograph), and drainage methods. The results showed that the addition of C-CS could remarkably improve the retention of natural occurring CaCO3 fillers and the fine particles of cellulosic pulp at low dosages, corresponding to these used in industrial operation. The increasing retention of CaCO3 fillers was depended strongly on the charged density of C-CS. When degrees of substitution (DS) of C-CS were 93%, 69% and 43%, the CaCO3 fillers retained in handsheet were around 80%, 62% and 54%, respectively. Whereas the optimum retention concentrations were decreased with the increasing of the molecular weight (Mw) of C-CS, for example, the optimum retention concentration were 3, 1.7 and 1 mg/L for C-CS with Mw = 19 × 104, 11 × 104 and 4.8 × 104, respectively. In the case of cellulosic fines, the retention was increased by C-CS, the total amount of saccharide presenting in white water was reduced by 40%, 24% and 12% by C-CS with DS = 69%, 43% and cationic starch, respectively. In addition, the dewatering of pulp suspension was increased significantly upon addition of C-CS. However, a small negative effect of mechanical properties such as the tensile index and tear index of handsheet was also observed due to the great retention of CaCO3 fillers and fine fibers. Compared to cationic starch, C-CS was promising retention- and drainage-aids in papermaking.