Establishing the optimum panel densification for performance plywood/LVL products - new method developed to measure veneer quality and bondability. Final Report 2004/05
In this study, extensive veneer compression tests were conducted to examine the transverse compression behaviour of veneer at both ambient and controlled temperature and moisture content (MC) environments. Based on the results, a novel method was developed to characterize overall surface quality of veneer and other wood materials in terms of their bondability and compression behaviour.
The method would have significant implication in both theory and practice. In theory, the general wood compression theory would need to be modified. The revised wood compression theory would include four stages instead of commonly defined three. The first stage, which has long and so far been overlooked but is critically important, could be named as “non-linear conformation”. During this stage, the contact area increases nonlinearly with the load applied. It is this stage that directly reveals the interfacial bonding behaviour of wood materials such as veneer-to-veneer and strand-to-strand and their minimum compression required for achieving adequate contact (bonding). In practice, the method provides a fast and objective way of evaluating surface roughness/quality of veneer and other wood materials. The new method also establishes the maximum compression allowable for achieving the best panel performance in terms of bonding strength, stiffness and dimensional stability. Based on the concept of this method, it was further found that both minimum compression required and maximum compression allowable are independent of temperature and MC, which provides a direct benchmark to the material recovery during panel hot-pressing.
In a case study with Trembling aspen veneer, the variation of veneer surface roughness/quality and its effect on resulting material recovery were first revealed. Then, the optimum panel densification was identified for performance plywood and LVL products based on the frequency distribution of the minimum compression required and the maximum compression allowable. Finally, an overall veneer quality index was established to compare veneer overall quality for different species/thickness. The method shows good potential in practical applications for increased material recovery, reduced glue consumption and improved panel performance.