Lignin-First Integrated Steam Explosion Process for Green Wood Adhesive Application

Steam explosion (SE) is one of the most advanced pretreatment processes currently used for the production of biofuel from lignocellulose. However, SE lignin is generally recovered as a secondary impure coproduct and mainly used for energy production. In this work, the beech wood sawdust was first exploded at 180 or 200 °C for 5 min after water or dilute acid impregnation. The recovery of the lignin from the exploded wood was studied using an alkali process at 80 °C or an ethanol-organosolv process at 200 °C. The impact of the SE parameters and of the delignification step on the lignin structure was examined by size exclusion and ionic chromatography and ³¹P and heteronuclear single quantum coherence NMR spectroscopies. The different lignin fractions have been evaluated for the production of the adhesive without the addition of any synthetic resin, composed of 50% glyoxalated lignin and 50% tannins. It was demonstrated by the thermomechanical analysis that the parameters of the process greatly impact the performance of the resulting resin. The SE lignin produced from the acid SE (a-SE) treatment at 200 °C followed by alkaline delignification led to an adhesive formulation displaying a very good performance with MOE_max ≈ 6000 MPa.