Formulation of a Lignin-Based Plywood Adhesive from Steam-Exploded Mixed Hardwood Lignin

Utilization of the lignin isolated during the biomass conversion of lignocellulosic materials is of prime importance to the economic potential of any biomass conversion scheme. In the Southern United States, the major feedstock source for a biomass conversion plant would probably be mixed hardwoods growing on southern pine sites. Steam-exploded mixed hardwood lignin was chosen to formulate as an adhesive to glue southern pine plywood. Three lignin replacement procedures were examined to assess lignin’s effect on bond quality. Adhesive application parameters approximate those used in the commercial manufacture of southern pine plywood. Panels were 12-inch square, 3/8-inch nominal thickness, and three-ply construction. Variables examined were lignin replacement method, veneer moisture content, panel assembly time, and core-ply lathe check orientation. Formulated adhesives were compared to a control phenol-formaldehyde (PF) adhesive prepared in the laboratory. Plywood shear strengths with steam-exploded lignin-based adhesives were at least as good as those with the PF control; wood failures, however, were lower. Although several of the lignin-based adhesives complied with the exterior-type adhesive bond requirements of Product Standard PS 1-83, they were more sensitive to different assembly times than conventional PF resin-adhesive formulations. Higher shear strength and wood failure from vacuum-pressure tests were produced when the core-ply lathe checks were pulled closed than when they were pulled open.

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