Canadian Forest Service Publications
Optimization of gluing, lay-up and pressing for mountain pine beetle plywood. 2007. Wang, B.; Dai, C.; Wharton, S. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Initiative Working Paper 2007-03. 50 p.
Available from: Pacific Forestry Centre
Catalog ID: 26804
We investigated the possibility of increasing value recovery from mountain pine beetle (MPB)-attacked lodgepole pine (Pinus contorta Dougl.) logs by adjusting the plywood manufacturing process specifically for the beetle-killed resource. The project addressed veneer grading, gluing, panel lay-up and hot pressing, and was a follow up to an earlier study that demonstrated that, by segregating beetle-killed logs, the productivity and material recovery could be improved at the early stages of production through narrower veneer clipping width, more accurate moisture sorting and higher drying productivity (Wang and Dai 2004). Based on the comparative results between the beetle-wood veneer and non-affected control veneer from pilot plant tests and mill trials, this study found that the beetle-wood veneer is denser and stronger than the control veneer from a typical white wood mix (i.e. white spruce, lodgepole pine and subalpine fir). As long as manufacturing parameters are properly adjusted in drying, grading, gluing and hot-pressing, segregating MPB logs provides an opportunity to manufacture higher-stiffness laminated veneer lumber (LVL) and plywood products with superior wet and dry gluebond performance for such applications as wood I-joists, headers and beams, flooring, decking and concrete forming. This could further offset, to a large degree, the reduction in material recovery and some appearance-based plywood products in the Japanese market. As well, the practice of segregation will become more important for recovering the highest value as the mill supply of beetle-killed wood becomes greater than 25% of total mill log supply, with most of beetle-killed wood being grey-stage materials. Plywood production was affected by beetle-killed logs as follows: The beetle-wood veneer is lower in moisture content (MC), more brittle, and more difficult to handle. It also contains various degrees of blue stain. To increase material recovery and panel gluebond performance, veneer overdrying must be minimized. The machine vision technology currently used by some plywood/LVL mills cannot differentiate defects within the blue-stained area of the wood. To improve veneer visual sorting, the existing vision systems can be upgraded to mask the effect of blue stain or to segregate the blue-stained veneer from the non-stained veneer using a saturation color index etc. Compared to the control veneer, the beetle-wood veneer is higher not only in dry bonding performance but also in wet bonding performance, as measured by shear strength and percent wood failure. To increase the grade outturn, stress grading of the beetle-wood veneer should be based on modulus of elasticity (MOE) instead of ultrasonic propagation time (UPT). As well, the beetle-wood veneer is approximately 10% higher in average MOE and 20% higher in stress-grade outturn, which can translate into more than $1.5 million additional annual savings for the mill when processing 10% of beetle-killed logs. To achieve optimum gluebond performance and minimum manufacturing cost for beetle-wood plywood, glue spread can be kept at the same level as currently used by control plywood. However, the pressing time of five-ply beetle-wood plywood should be lengthened by about 10% compared to that used by five-ply control plywood. As well, the assembly time should be reduced to about 10 -15 min. Furthermore, five-ply plywood manufacturing trials and 13-ply LVL preliminary tests demonstrated that the MOE and modulus of rupture (MOR) of beetle-wood plywood and LVL are about 15% and 20% higher than those of control plywood and LVL, respectively. As a result, the beetle-wood veneer is more suitable for making higher-stiffness LVL and specialty structural plywood products. By implementing this product strategy, the value recovery from the beetle-killed resource can be dramatically increased.