Abstract
As steric hindrance, methoxy groups are limiting the valorization of hardwood lignin. This paper reports a novel method of self-cross-linking of the syringaldehyde with activated methoxy groups (-OCH(3)) via cross-coupling reaction to obtain thermosetting polymers for lignin-based wood adhesives. The methoxy groups of syringaldehyde have been activated via cross-coupling reaction by substituting Ar-OCH(3) with Ar-CH(2)-SiMe(3), and dichloromethane, leading to cross-linking via methylene bridges to build a thermosetting polymer. FTIR spectra showed a decrease in the intensity of a -CH(3) and -OH group, owing to the substitution of the methoxy group. (13)C NMR spectra also supported these results with the -SiMe(3) signal that disappeared after the cross-linking reaction. Furthermore, cross-linking between the activated methoxy groups was confirmed with a strong exothermic peak at 130 °C, resulting in an increase in the adhesion strength as hot-pressing temperature increased from 160 to 180 °C. These results suggest that the cross-linking between the activated methoxy groups of syringaldehyde is an important understanding of valorizing hardwood lignin via building thermosetting polymers for lignin-based adhesives.