Veneer Surface Roughness and Compressibility Pertaining to Plywood/LVL Manufacturing. Part II. Optimum Panel Densification

In Part I of this series, a novel method was proposed to assess surface roughness/quality and compressibility of wood veneer, and the wood compression theory was revised to include the first stage of "progressive contact." Based on this revised theory, the minimum compression required can be established for achieving adequate contact of veneer-to-veneer (or plate), and true veneer yield displacement can be determined. Owing to the variation of veneer compressibility and random veneer placement in the panel assembly, this study aimed to apply the revised theory to establish the optimum panel densification for performance plywood and laminated veneer lumber (LVL) manufacturing. Using 3.2-mm-thick rotary cut trembling aspen (Populus tremuloides) veneer as an example, the correlation between the contact area and panel compression ratio (CR) was first established in terms of veneer surface roughness. Then, the required aspen panel CR and density were identified for achieving a target 80% contact area of veneer-to-veneer (or plate). Meanwhile, through the compression tests of 30- x 30-mm aspen veneer specimens, within-sheet and between-sheet variations in density, thickness, and compressibility were revealed. Furthermore, based on the frequency distribution of the minimum compression required and yield displacement for aspen veneer, the optimum range of aspen panel densification was identified with a CR ranging from 11.3% to 18.0%. Finally, through the manufacturing of aspen panels, such densification range identified was validated for improved panel quality, material recovery, and dimensional stability while achieving superior panel bending and gluebond performance