Utilization of softwood kraft lignin as adhsive for the manufacture of reconstituted wood

Abstract

Reaction conditions for hydroxymethylation of pine kraft lignin (KL) were optimized by kinetic studies of the reaction. Characterization of the resulting hydroxymethylated kraft lignin (HMKL) indicated that about 0.36 mole of the -CH₂OH/C₉ unit was introduced into the ognin under the optimal reaction conditions, of which about 0.33 mole was introduced into C-5 of guaiacyl moieties via Lederer-Manasse reaction. This result was confirmed by ¹³C-NMR specturm of ¹³C enriched HMKL prepared form KL and ¹³CH₂O (about 7 atomic %) under the same reaction conditions. Lignin-phenolic resins were formulated by blending the HMKL with phenol-formaldehyde (PF). A 50/50 blending of HMKL/PF resulted in a bond strength of about 65 psi in laboratory boards made with sweetgum flakes. In general, bond strength increased iwth an increase in the PF. Studies on effects of process and wood variables indicate that such resin could yield satisfactory boards made with red oak, black gum, red maple, post oak and sweetgum flakes with: (a) hot press temperature of 410°F, (b) hot press time of 8 minutes, and (c) minimum resin content of 5%.

Citation

Zhao, Lin-Wu; Griggs, Bruce F.; Chen, Chen-Loung; Gratzl, Josef S.; Hse, Chung-Yun. 1994. Utilization of softwood kraft lignin as adhsive for the manufacture of reconstituted wood. Journal of Wood Chemistry and Technology 14(1):127-145