Colloidal effects of acrylamide polyampholytes: Part 2: Adsorption onto cellulosic fibers

Colloidal titrations of commercial acrylamide-based terpolymers having both weak-acidic and weak-basic groups were carried out at pH 3 and 11, using a streaming current technique. At these pH values it was found that the polyampholytes could be considered as simple polyelectrolytes, though it was necessary to use a modified titration procedure. The titration endpoint defined by zero streaming current (SC) output deviated from a 1:1 stoichiometry, depending on the salt concentration. The endpoint also depended at the speed of titration, consistent with a relatively slow rate of forming equilibrated poly-ion complexes between polyampholytes and titrants. The adsorption of the amphoteric polyacrylamide copolymers onto bleached hardwood fibers was maximized near to its iso-electric pH, such that the net charge of the polymer was relatively low, but opposite to that of the substrate. Neutral and negatively charged polyampholytes also adsorbed in significant amounts onto the negatively charged fibers, though the amounts were lower than when the net charges were opposite. Addition of salt generally increased adsorption up to a conductivity value of 1000 μS/cm. Adsorption increased slightly with increasing time, until reaching a plateau. The rate of fluid agitation during adsorption did not affect adsorption significantly under the conditions employed.