FLEXURAL PROPERTIES, INTERNAL BOND STRENGTH, AND DIMENSIONAL STABILITY OF MEDIUM DENSITY FIBERBOARD PANELS MADE FROM HYBRID POPLAR CLONES

Flexural properties, internal bond strength, and dimensional stability of medium density fiberboard (MDF) panels made from three hybrid poplar ( Populus spp.) clones with codes 915303, 915311, and 915313 were studied. Analysis of variance (ANOVA) and analysis of covariance (ANCOVA) were both performed in this study to test the differences in modulus of rupture (MOR) and modulus of elasticity (MOE) of MDF panels made from the three poplar hybrids. Results indicate that MOR of MDF panels made from clone 915311 was significantly higher than those of panels made from clones 915303 or 915313; however, there was no significant difference in MOR between panels made from clones 915303 or 915313. MOE of MDF panels made from clone 915311 was the highest value, which was significantly different from those of panels made from either clones 915303 or 915313; MOE of panels made from clone 915303 was the smallest and significantly lower than those of panels from clone 915313. MDF panels made from both clones 915303 and 915311 were superior to those panels made from clone 915313 in internal bond (IB) strength; but there was no significant difference in IB between panels made from clones 915303 or 915311. Dimensional stability of MDF panels was evaluated by linear expansion (LE), thickness swell (TS), and water absorption, and no significant differences were found among the three types of panels. This study shows a significant effect of hybrid poplar clonal variation on flexural properties and internal bond strength. This suggests that improvements in MDF panel flexural properties and internal bond strength may be made through tree breeding. Additionally, panel density was a factor influencing MDF panel MOR and MOE considerably; as significant linear relationships between MOR, MOE and panel density were determined.