Enzymatic synthesis of wet-resistant lignosulfonate-starch adhesives

This work describes a new method for improving the properties, mainly the wet-resistance, of starch-based adhesives using enzymatically polymerized lignosulfonates. A correlation of viscosity with molecular weight was found, allowing simple control of enzymatic polymerization of lignosulfonates. Incorporation of lignosulfonates polymerized from 29 kDa to > 4500 kDa using laccase led to a considerable increase in wet-resistance (from 15 to 20 min for the laminating glue and from 150 to 1200 min for the bag glue) while not affecting (for the laminating glue) or even improving the bonding time (from 80 to 60 s for the bag glue). Finally, the effect of active laccase in the final adhesive was investigated by enzymatic inactivation using NaN₃ before formulation of the glue, as well as by extra laccase addition. In conclusion, this study shows that enzymatically polymerized lignosulfonate is a robust strategy for improving wet resistance of starch-based adhesives.