Wet strength-enhancement of cellulose substance by polypeptide and polyvinylamine adhesives

A series of simple lysine-containing synthetic polypeptides was compared with polyvinylamine (PVAm) as adhesives laminating two-ply, wet, regenerated cellulose films. Adhesion was measured as the ninety degree delamination peel force. Adhesion increased with the molecular weight of both PVAm and the polypeptides. In all cases PVAm gave stronger adhesion than polylysine or its copolymers. Oxidation of the cellulose films to introduce carboxyl groups increased adhesion by at least a factor of two suggesting that the polymer/cellulose interface was located in the failure zone. Surprisingly, inclusion of aromatic amino acids tyrosine, trytophan or phenylalanine gave stronger adhesion than polylysine homopolymer with the same molecular weight. Adhesion was rather insensitive to pH and ionic strength of the solution used to deposit the polymer film. These results point to the potential utility of tyrosine-rich polypeptides or proteins as agents for increasing the strength of wet paper.