# PAE adsorption on polyelectrolyte-grafted pulp fibers

## TL;DR

Adding a negatively charged polymer to pulp fibers increases the adsorption of a wet-strength resin, improving paper quality.

## Contribution

A new measure of adsorption isotherm ideality (IX) is introduced and applied to compare polymer adsorption on modified pulp fibers.

## Key findings

- Grafting PEMAc onto pulp fibers tripled the adsorption of PAE on exterior fiber surfaces.
- The ideality index (IX) increases when polymer grafting limits access to interior fiber surfaces.
- TEMPO oxidation had no significant effect on PAE adsorption at equivalent charge levels.

## Abstract

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, Γex, as well as the ideality index, IX, a new measure of isotherm ideality. IX increases when grafting lowers the access of adsorbing polymer to interior surfaces, whereas IX 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.