Electrolyte effects in the adsorption and desorption of a cationic polyacrylamide on cellulose fibers

Adsorption isotherms for a cationic derivative polyacrylamide (QCPAM) on cellulose fibers were determined as functions of aluminum sulfate (alum) concentration and pH, and QCPAM desorption measurements in alum, NaCl, CaCl2, and LaCl3 were also made. The isotherms had a steep, but not infinite, initial slope leading to a rounded knee followed by a linear interval with a small positive slope. Polymer adsorption increased with pH due to increased dissociation of cellulose carboxyl groups. Aluminum sorption made the electrophoretic mobility of the fines less negative and lowered the capacity of the fibers to adsorb QCPAM. Exposure of QCPAM-saturated fibers to electrolyte solution resulted in polymer desorption, most of which occurred within 1 h. Most desorption in alum occurred at pH 4 with less at pH 4.5 and very little at pH 5. The molarities of LaCl3, CaCl2, and NaCl required to desorb 50% of the adsorbed QCPAM were 6.0 × 10−4, 2.1 × 10−3, and 8.3 × 10−3 M, respectively.