Lignins from enzymatic hydrolysis and alkaline extraction of steam refined poplar wood: Utilization in lignin-phenol-formaldehyde resins

In this study, a steam refining process, optimized earlier with respect to carbohydrate yield, was used to extract lignins from non-debarked poplar wood from short growth plantations by enzymatic hydrolysis (EHL) and alkaline extraction (AEL) for the utilization in lignin-phenol-formaldehyde resins (LPF). Three different pretreatment conditions were chosen at 190 degrees C and 16 min, 210 degrees C and 15 min and 200 degrees C, 15 min, 2.5% SO2. Characterization of the lignins revealed that the carbohydrate content decreased about 47% (210 degrees C, 15 min) to 58% (200 degrees C, 15 min, 2.5% SO2) with intensification of the pretreatment conditions. Furthermore, the average molecular weight and polydispersity increased. The chemical and physicochemical properties of lignin-phenol-formaldehyde resins synthesized with these lignins were evaluated and gluebond performance was tested by the Automated Bonding Evaluation System (ABES). LPF resins with AEL and EHL (190 degrees C, 16 min) were used to produce particleboards. LPF resins with Organosolv lignin (OL) and Kraft lignin as well as neat PF resins served as references. The mechanical properties of these panels were evaluated. The results showed high dry (EHL: 0.64N mm(-2), AEL: 0.73 N mm(-2)) and wet internal bond strength (EHL: 0.21 N mm(-2), AEL: 0.25 N mm(-2)) of LPF bonded particleboards. LPF resin with AEL fulfills the requirements for the relevant standard specifications P7 according to DIN EN 312:2010-12. (C) 2016 Elsevier B.V. All rights reserved.