Influence of Gluing Conditions on Performance of Crosslinked Protein Glue in Interior-Type Southern Pine Plywood

Plywood panels were prepared experimentally by bonding southern pine veneers with a hot-press crosslinked protein glue under a variety of conditions. Panels of 3/8-inch 3-Ply, 1/2-inch 5-ply, and 13/16-inch 7-ply construction that met the performance requirements of the interior plywood test were obtained by using: 1) veneer of normal or average specific gravity, 0.50; 2) veneer moisture content range at time of gluing, 5-7 percent; 3) glue spread of 88 lbs./MDGL; 4) maximum assembly time of 20 minutes, which included stand times of 3 minutes before and 5 minutes following the prepress of 3 minutes at 150 psi; 5) hot press times–5 minutes for the 3/8–inch and 10 minutes for the 1/2-inch panels at two panels per opening and 7 minutes for the 13/16-inch panels at one panel per opening; 6) hot-press temperature of 270?F.; and 7) specific pressure in the hot-press of 175 psi. A hot-press time of 4-1/2 minutes for the 1/2-inch panel is used at one panel per opening and at a hot-press temperature of 250?F. In all cases the cold prepress produced good tack in the panels and facilitated the hot-press operation. Low moisture veneer (3 percent), high specific gravity veneer (0.59-0.64), and excessive panel assembly time (30 minutes) adversely affected the adhesive bond in southern pine plywood fabricated with this glue. High panel production in conventional exterior-type southern pine plywood manufacturing facilities can be expected to be realized with this glue at a glue cost of approximately $2/MDGL.

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