Utilization of sorghum lignin to improve adhesion strength of soy protein adhesives on wood veneer

Features of sorghum lignin (SL) and extruded sorghum lignin (ESL) were examined. Adhesion properties of lignin (SL or ESL) blended soy protein adhesives (SPA) based on soy protein isolates (SPI) or modified soy protein (MSP) were also investigated, respectively. Both SL and ESL exhibited similar softening temperature at around 112 degrees C; however, the softening enthalpy of ESL was much larger than that of SL. The thermal stability of lignin was significantly improved through the extrusion process. The ratio of relative absorbance for free OH groups to the bands at 1510 cm(-1) and 1600 cm(-1) went from 0.55 and 0.54 in SL to 0.74 and 0.66 in ESL; carbonyl groups went from 0.81 and 0.80 in SL to 1.08 and 0.96 in ESL Extrusion changed the microstructure of SL from large masses to small irregular particles. The shear strength and water resistance of lignin (SL or ESL)-blended SPAs (SPI based) on wood veneer joints were obviously improved. (C) 2013 Elsevier B.V. All rights reserved,