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.