Enhancing Wet Cellulose Adhesion with Proteins

Twenty proteins were compared as potential paper wet strengthening additives by measuring the peel force required to delaminate wet, regenerated cellulose films laminated with a thin (3 mg/m2) protein layer. Wet adhesion results ranged over nearly an order of magnitude, reflecting the importance of protein composition. The proteins with the highest contents of lysine and arginine gave the strongest adhesion with secondary contributions from hydroxyl and phenolic amino acid residues. Wet adhesion was performed with TEMPO oxidized cellulose and with laminates that were cured at high temperatures (120 °C), suggesting that protein grafting to the cellulose and protein cross-linking was important for good wet strength. Although none of the protein laminates was as strong as polyvinylamine or a commercial PAE resin used in the paper industry, this paper suggests that increasing the primary amine (amino group) content as well as optimizing heat-induced bond formation may someday lead to a protein-based paper wet strength resin.