PAE adsorption on polyelectrolyte-grafted pulp fibers

The adsorption of cationic polyamide-amine epichlorohydrin (PAE) paper wet-strength resin onto bleached kraft pulp fibers was increased by grafting hydrolyzed poly(ethylene-alt-maleic anhydride) (PEMAc) onto fiber surfaces before PAE adsorption. The highly negatively charged PEMAc increased the sparse negative charge density on untreated fibers, enhancing PAE adsorption. The adsorption isotherm analysis provided estimates of adsorbed PAE on exterior fiber surfaces, Γ_ex, as well as the ideality index, <i>IX</i>, a new measure of isotherm ideality. <i>IX</i> increases when grafting lowers the access of adsorbing polymer to interior surfaces, whereas <i>IX</i> decreases when grafting enhances the adsorption capacity of interior surfaces. A library of 18 adsorption isotherms compares PAE and poly(diallyldimethylammonium chloride) adsorption on unmodified pulps, grafted pulps, and TEMPO-oxidized pulps. The grafted pulps include PEMAc polymers modified with pendent short alkyl or poly(ethylene glycol) chains. A grafted PEMAc content of 4.1 mg PEMAc per g of dry fiber tripled the amount of adsorbed PAE on exterior fiber surfaces. About two anionic PEMAc carboxylic acid groups were required for every adsorbed PAE cationic charge. Modification of the PEMAc with pendent chains had little effect. TEMPO oxidation, at the same total fiber charge content, had no positive impact on PAE adsorption.