The objective of this project was to investigate the possibility of increasing the value recovery from the 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. This project was a follow up to an earlier study that demonstrated by segregating MPB 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 MPB veneer and non-affected control veneer from pilot plant tests and mill trials, this study found that the MPB veneer is denser and stronger than the control veneer from typical white wood mix. 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 dry and wet 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, this practice of segregation will become extremely important for recovering the highest value since the MPB-killed wood will be greater than 25% of total log supply in the mill with most of it being grey stage materials.
The plywood production was affected by MPB logs as follows:
The MPB veneer is lower in moisture content (MC), more brittle, and more difficult to handle. It also contains various degrees of bluestain. To increase material recovery and panel gluebond performance, veneer overdrying needs to be minimized. The machine vision technology currently used by some plywood/LVL mills cannot differentiate defects within the bluestained area. To improve veneer visual sorting, the existing vision systems can be upgraded to mask the effect of bluestain or to segregate the bluestained veneer from the non-stained veneer using a saturation color index. Compared to the control veneer, the MPB veneer is higher not only in dry bonding strength but also in wet bonding strength, measured by shear strength and percent wood failure. In the meantime, the MPB veneer is about 10% higher in average modulus of elasticity (MOE) and 20% higher in stress grade outturns, which can translate into more than $1.5 million additional savings for the mill annually when processing 10% of MPB-killed logs. To achieve optimum gluebond performance and minimum manufacturing cost for MPB plywood, glue spread can be kept at the same level as currently used by control plywood. However, the pressing time of 5-ply MPB plywood should be lengthened by about 10% compared to that used by 5-ply control plywood. As well, the assembly time should be reduced to about 10-15 min, keeping veneer temperature as low as possible. Furthermore, 5-ply plywood manufacturing trials and 13-ply LVL preliminary tests demonstrated that the MOE and modulus of rupture (MOR) of MPB plywood and LVL are about 15% and 20% higher than those of control plywood and LVL, respectively. As a result, the MPB 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.