Impact of Mountain Pine Beetle-Attacked Lodgepole Pine Logs on Veneer Processing

Pilot plant tests and mill trials were conducted to quantify the impact of using mountain pine beetle(MPB)-attacked lodgepole pine (Pinus contorta Dougl.) wood on green veneer processing, and determine if it makes economic sense to sort and process MPB logs separately from normal logs of white SPF (spruce-lodgepole pine-alpine fir) mix for plywood manufacturing. The results demonstrated that log dry-out, improper log conditioning, and veneer peeling contribute to the breakage of veneer ribbon, and in turn, loss of veneer recovery at the green end when processing MPB wood. Compared with the green SPF veneer controls, green MPB veneer has lower moisture content (MC) with smaller variation. The MPB veneer can be clipped narrower with an equivalent of 1% increase in recovery due to less width shrinkage, and be sorted more accurately requiring only two green sorts: heart and light-sap. The MPB veneer can also be dried faster with a reduction in drying time by about 25% for the heart veneer and 35% for the light-sap veneer. However, due to higher volume of narrower random sheets and increased waste from manual handling and composing, the net recovery of the MPB logs is about 8% lower than that of the control SPF logs. Furthermore, the color of the stained MPB veneer is lightened after drying, but it still causes interference with visual grading. Since MPB wood has unique MC and processing characteristics, it is recommended that it be sorted in the log yard when its proportion reaches about 10% of the total logs procured

Veneer Surface Roughness and Compressibility Pertaining to Plywood/LVL Manufacturing. Part I. Experimentation and Implication

Extensive experiments were conducted to examine the transverse compression behavior of trembling aspen (Populus tremuloides) veneer at ambient and controlled temperature and moisture content (MC) environments, and the relationship between contact area, veneer surface roughness, and applied load. Based on the results, a novel method was developed to characterize surface roughness/quality of wood veneer in terms of its compression behavior. This method may have significant implication on both theory and practice. In theory, the general wood transverse compression theory needs to be revised to include four stages instead of the commonly defined three. The first stage, which has long been overlooked but is critically important, could be named "progressive contact." During this stage, the contact area increases nonlinearly with the load applied. It is this stage that reveals the interfacial contact of veneer-to-veneer or veneer-to-plate and the minimum veneer compression required for achieving adequate contact. With the inclusion of the first stage, the yield displacement also needs to be redefined. In practice, the method provides a fast and objective way of evaluating veneer surface roughness/quality for plywood/LVL manufacturing. Furthermore, the minimum compression required and yield displacement of wood veneer derived from its compressive load-displacement curve were found to be independent of temperature and MC, which helps benchmark material recovery in terms of veneer surface roughness/quality when manufacturing into quality plywood/LVL products. The method could also be applied to other wood composite elements such as wood strands

Impact of Mountain Pine Beetle-Attacked Lodgepole Pine Logs on Plywood Manufacturing

In this work, the possibility of increasing value recovery from mountain pine beetle (MPB)-attacked lodgepole pine (Pinus contorta Dougl.) logs was further investigated, including veneer grading, gluing, panel lay-up, and hot-pressing. This was a follow-up to an earlier study that demonstrated that, by segregating MPB logs, the value recovery could be improved through narrower veneer clipping width, more accurate moisture sorting, and greater drying productivity. Based on pilot plant tests, compared with control veneer of spruce—lodgepole pine—alpine fir (SPF), MPB veneer had various degrees of bluestain, and was significantly denser and stiffer. To minimize manufacturing costs for MPB plywood, glue spread can be kept at the same level as currently used by control SPF plywood. However, the pressing time of 5-ply MPB plywood should be lengthened by about 10% compared with that used by the 5-ply control SPF counterpart. The assembly time should be maintained within 10 to 15 min, keeping veneer temperature as low as possible. Furthermore, the parallel-ply MOE and MOR of 5-ply MPB plywood were approximately 15 and 20% higher than those of 5-ply control SPF plywood, respectively. As a result, MPB veneer was more suitable for making specialty plywood products requiring high stiffness and strength. If manufacturing parameters are properly adjusted in grading, gluing, and hot-pressing, segregating MPB logs from the normal SPF mix also provides an opportunity to manufacture high stiffness plywood with superior dry- and wet-gluebond performance. This could further offset, to a large degree, the reduction in material recovery and the loss in market share for some appearance-based plywood products