Utilization of softwood kraft lignin as adhesive for the manufacture of reconstituted wood
1994
Zhao, L.W. | Griggs, B.F. | Chen, C.L. | Gratzl, J.S.
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 lignin 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 spectrum of 13C enriched HMKL prepared from 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 with 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 degrees F, (b) hot press time of 8 minutes, and (c) minimum resin content of 5%.
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