Face-Glued Blockboard from Plywood End Trim

Increasing the proportion of veneer log volume that becomes part of the final product is an important strategy for combatting rising costs of plywood manufacturing. One way of increasing plywood yield from a given quantity of raw material is to find ways of converting waste in the manufacturing process into panel products. End trim, narrow strips of plywood generated when panels are trimmed to length, constitutes a substantial portion of manufacturing waste (up to 2 percent of log volume input). Rather than using end trim for fuel or particleboard furnish, trim strips could be composed into a core for face-glued blockboard or stripboard. Though the use of trim strips for panel core material has been the subject of previous research, all previous investigations have assumed the need for gluing of trim strips edge to edge prior to incorporation into the finished panel. In this work, core strips were not edge-glued, but simply allowed to “float” between face and back veneers. Stripboard panels manufactured in the laboratory using southern pine plywood end trim were evaluated to determine physical and mechanical properties. Panels with single ply faces were made with two configurations of the trim strips in the core and two face veneer thicknesses. The stiffness and bending strength of plytrim stripboard parallel to the face grain compared favorably with commercial plywood, as did linear expansion perpendicular and parallel to the grain and thickness swelling from 50 to 90 percent relative humidity. Perpendicular to the face grain stiffness and bending strength values for plytrim were considerably lower than those for plywood, and the effect of accelerated aging upon strength was more pronounced in plytrim panels. Though highly directional strength properties would present a problem for some panel applications, this would not be the case for applications such as sub-flooring or sheathing. Tests conducted in this study suggest that a three layer, plytrim core, face-glued panel could meet the APA performance standards for both subflooring and sheathing panels.

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