Composite waterborne polyurethane reinforced with silane modified lignin as an adhesive between polypropylene decorative films and wood‐based panels

Abstract To improve the surface bonding strength of polypropylene (PP) decorative films on wood‐based panels, one kind of lignin, namely sodium lignosulfonate (SL) filled waterborne polyurethane (WPU) composites were used as adhesives on the back of the PP decorative films, and the SL was modified by the addition of two alternative types of silane that contain either ethylene‐acyloxy or epoxy groups. The PP decorative films were hot‐press onto plywood using the different types of SL modified WPU as an adhesive. The SL and SL modified WPU were characterized comprehensively. The surface properties the PP decorative films on plywood surfaces were tested. The results showed that both types of silane can be grafted on the SL between hydrolyzed SiOH groups and OH groups. The long organic chain of silane can physically twist to the WPU, where self‐polymerization of the silane helps to form network structures. As a result, the surface bonding strength of PP decorative films on plywood surfaces largely improved with SL filled WPU adhesives and no detachment occurred in boiling water. Compared with the ethylene‐acyloxy silane, the epoxy silane performed better which was associated with the reactions between the epoxy groups and free water.