Synthesis of bio-adhesives from soybean flour and furfural: Relationship between furfural level and sodium hydroxide concentration

Soybean–furfural (SoyFu) adhesives were synthesized through cross-linking soybean flour with furfural under alkaline conditions and the performance of the resulting bio-adhesives was evaluated by manufacturing plywood panels. A total of 30 different bio-adhesive formulations were studied (5 levels of furfural content and 6 levels of sodium hydroxide or pH). Thirty 2-ply plywood panels prepared with these adhesives were pressed at 140 °C for 4 min. Shear tests were performed on the panels according to ASTM D2339-1998 (2004). The statistical analysis indicated that an interaction existed between furfural (crosslinker) and sodium hydroxide (pH) levels. The best quality panels were produced using adhesives containing high levels of sodium hydroxide (12, 20 and 28 g/100 g soy flour) and high levels of furfural (50 and 100 g/100 g soy flour). 13C nuclear magnetic resonance analyses were also performed on a selected formulation. The spectra analysis, however, did not prove that furfural was involved in covalent or ionic bonds with soybean flour.