Analysis on Adsorption Equilibrium of Polyamide-Epichlorhydrin in Aqueous Fibrous Suspension by Colloid Titration

Abstract: The properties of the equilibrium state of polyamide-epichlorohydrin retention on fibers in a paper-making wet-end aqueous media were investigated using a colloid titration method. The adsorption behavior of PAE obeyed a mono-molecular layer adsorption, as characterized in Langmuir-type expression. While the ma-jority of PAE was adsorbed within a few minutes, it slowed down at longer times as the fiber surfaces become saturated. The true equilibrium of PAE adsorption could not be determined simply with experimental data, be-cause the adsorbed PAE showed dynamic behavior at near-equilibrium, such as molecular reconformation and diffusion of PAE into porous fibers after its adsorption. This phenomenon was illustrated by the charge decay characteristics of fibers with the adsorbed PAE after a rapid initial rise to a maximum zeta potential. The ad-sorption rate constants and the maximum PAE adsorptions on fiber surfaces were determined from the theoret-ical equilibrium predicted using a modified Langmuir kinetic model. The apparent Gibb’s free energy of PAE adsorption on fiber surfaces was-14.3 kJ/mol. The enthalpy of PAE adsorption (-14.7 kJ/mol) was of the order of that of molecular condensation and indicated that the PAE adsorption on the aqueous fiber suspension is po-tentially an exothermic physical process with a long-range, but weak, molecular interactions