Rheology and adhesion performance of adhesives formulated with lignins from agricultural waste straws subjected to solid-state fermentation

Abstract In this study, modified residual lignins from barley and wheat straws submitted to solid-state fermentation with diverse Streptomyces strains were targeted as binders in eco-friendly castor oil-based polyurethane adhesive formulations. The thermo-rheological and adhesion properties of these adhesives were examined and related to the solid-state fermentation yields. Viscoelastic properties were enhanced by lignin addition, and the Streptomyces action generally increased the values of the linear viscoelastic functions. Adhesion performance was dominated by lignin source and further Streptomyces activity and can be correlated with the resulting lignocellulosic composition. Wheat straw lignin-based polyurethane adhesives showed the best performance in metal-textile peeling tests, whereas barley straw lignin provided the best achievements in terms of shear strength in metal-metal and wood-wood joints. Overall, solid-state fermentation with Streptomyces demonstrated to be a suitable pretreatment to conveniently modify and improve residual lignin fractions for application as binders in environmental-friendly polyurethane adhesive formulations.