Variation of Density and Dynamic Modulus of Elasticity of Poplar Veneer and Its Impact on Grade Yield

To maximize the value of poplar wood in manufacturing of laminated veneer lumber (LVL), its radial (from pith to bark) and longitudinal (from bottom to top) variations were examined in terms of the density and dynamic modulus of elasticity (ED) of veneer. The veneer sheets were rotary-peeled from seven representative poplar butt bolts (the bottom part of a stem) and seven representative poplar second bolts (the middle part of a stem). A grading strategy for selecting veneer was proposed based on the requirements of LVL products. In this study, the ED value of each poplar veneer sheet was non-destructively measured by the ultrasonic method. The results showed that there was a weak correlation between veneer density and ultrasonic wave velocity. The bolt class (butt or second bolt) did not significantly influence the variation of veneer density and ED. However, the among-bolt variation played a significant role in the variability. A large difference in diameter between two ends of a bolt (i.e. the within-bolt variation) resulted in a low veneer ED. According to the sorting criteria of Chinese Standard “Laminated Veneer Lumber”, the estimated grade yields of the poplar veneer studied were 45.2% for G1, 39.3% for G2, 13.1% for G3, and 2.4% for G4.