Preliminary Evaluation of Parallel Laminated Veneer Lumber Made from Preservative Treated Veneers

Abstract

The use of preservative treated veneer in the manufacture of plywood or parallel laminated veneer lumber (PLVL) should have potential in specialty applications where a high value, high priced product is appropriate. The challenge in dealing with treated veneers is finding a resin which is compatible with the preservative. The veneer product desired for this project could not be post treated because a flat panel was needed for machining and subsequent manufacturing. Three veneer types, two preservatives, and three adhesives were selected for evaluation. Aspen, birch, and red pine veneers were treated with disodium octoborate tetrahydrate and copper naphthenate to a retention level of 0.60 pounds per cubic foot or greater. Prior to treatment, green veneer was dried to between 20 and 25 percent moisture content and following treatment it was dried to near 5 percent for gluing. Three adhesives types, phenol formaldehyde, catalyzed melamine, and emulsion polymer isocyanate were used to bond the treated veneers .. Three ply plywood glue shear specimens were used to evaluate bond quality after a one cycle vacuum-pressure-soak. PL VL specimens approximately one-inch thick were manufactured to test strength and stiffness in bending. Acceptable wood bonds were developed for treated aspen and red pine, however the tightness of the birch created difficulty in forming a consistent glue bond. In most instances strength and stiffness compared favorably with the controls. In many cases PLVL averages exceeded Wood Handbook values for clear wood specimens