Increasing wet adhesion between cellulose surfaces with polyvinylamine

Abstract

The conditions are elucidated whereby strong adhesive joints between two wet cellulose surfaces can be achieved with a polyelectrolyte adhesive. Adhesion results were obtained with wet, TEMPO oxidized, regenerated cellulose membranes that were laminated with polyvinylamine (PVAm) adhesive. Wet adhesion was determined as the 90° wet-peel delamination force. Aldehyde groups on the oxidized cellulose form imine and aminal covalent linkages with PVAm, covalently grafting PVAm onto the cellulose surfaces. From these results we conclude that the adhesive polymer must be covalently grafted to the cellulose surface—physically adsorbed polymers give weak polymer/cellulose interfaces in water. There are two cases which are remarkably different—never-dried joints versus dried and rewetted joints, we call once-dried. The strength of never-dried joints is important in paper manufacturing and is likely to be critical in the manufacture of the new nanocellulose composites and foams described in the recent literature. Only one adhesive joint architecture gave significant never-dried strength—joints with only a monolayer of polyelectrolyte adhesive sandwiched between two cellulose surfaces. We propose that polymeric chains are simultaneously covalently grafted onto both cellulose surfaces. In the usual case of bringing together two polymer coated cellulose surfaces in water, there is no never-dried wet adhesion because electrosteric stabilization inhibits significant molecular contact between opposing adsorbed polymers. By contrast, high once-dried wet adhesion is easier to achieve because polymer–polymer molecular contact is promoted by water removal. The requirements for once-dried wet adhesion are polyelectrolyte grafting to cellulose and cohesion within polymer layers, either due to covalent crosslinking, or attractive physical interactions.