Physicochemical and adhesive properties, microstructure and storage stability of whey protein-based paper glue

The objective of this study was to formulate and evaluate a novel liquid paper glue based on a renewable material, polymerized whey proteins (PWP), and a synthetic polymer, polyvinylpyrrolidone (PVP) K90. Both PWP and PVP separately and/or cumulatively played important roles in the viscosity and bonding strength of the glue. Two optimized formulations (prototype A and prototype B) were analyzed for physicochemical and adhesive properties, microstructure and storage stability. A commercial product was used as a reference for comparison. Both prototypes had comparable bonding strength with the control, showed full substrate failure in the lap-shear strength tests, and exhibited faster setting property than the control. Viscosity of the prototypes was lower than that of the control, but they were still easy for application and spread. Scanning electron microscope (SEM) analysis showed that combined PVP and PWP formed more compact networks compared with those formed by PWP alone. Not only did they have desirable adhesive properties, both prototypes with addition of an antimicrobial agent also had stable shelf lives. Neither significant changes of bonding strength, viscosity or appearance, nor growth of microbes was observed during storage at 23 °C or 40 °C for 12 months. In conclusion, the whey protein based paper glue has comparable functional properties to the commercial product.