Analysis of polydisperse polymer adsorption on porous cellulose fibers

The adsorption of cationic water-soluble polymers onto negatively charged porous wood pulp fibers is an essential aspect of papermaking. Adsorption data can be displayed as a direct plot of the amount adsorbed, Γ, versus the amount of polymer added or as an isotherm plot showing the amount adsorbed versus the residual unadsorbed polymer. In either data presentation, the analysis is more transparent if the units of each axis are the same (e.g., mg/g or meq/g), giving dimensionless slopes. Values for Γ_max, Γ_I, f _I , and Γ_me can be extracted from many isotherms where: Γ_max is the maximum capacity of the fibers to adsorb polymer; Γ_I is the y-axis isotherm intercept and gives the maximum dose that can be fully adsorbed; f _I is the slope of the direct plot at Γ_I, and f is the mass fraction of the added polymer that can access interior (pore) surfaces; and, Γ_me is the saturated amount of polymer adsorbed on exterior surfaces. Additionally, the molecular weight distribution of the adsorbing polymer in conjunction with the adsorption isotherm can be used to estimate the molecular weight distributions of adsorbed polymer on interior and exterior fiber surfaces as functions of the polymer dose.