EFFECT OF STRAND GEOMETRY AND WOOD SPECIES ON STRANDBOARD MECHANICAL PROPERTIES

This study compared the performance of strandboards made from trembling aspen, a low-density hardwood species, with strandboards made from paper birch, a medium-density hardwood species. Strands were cut into three different lengths (78, 105, and 142 nun) and two thicknesses (0.55 and 0.75 mm) to compare the impact Of species, strand geometry. specific surface, and slenderness ratio. Internal bond (IB), modulus Of elasticity (MOE), and modulus of rupture (MOR) for flatwise and edgewise bending, compressive Strength, and stiffness were all determined. Both species performed equally well in IB (0.73 MPa for both species, combined). The highest MOE and MOR values in flatwise and edgewise bending were obtained for long, thin strands and were significantly lower for birch than for aspen panels (flatwise: 13.6 GPa and 99.2 MPa for aspen and 12.1 GPa and 85.5 MPa for birch edgewise: 13.5 GPa and 66.3 MPa for aspen and 13.2 GPa and 65.7 MPa for birch). Short aspen strands resulted in the highest compressive properties, slightly higher than those of short birch strands (aspen: compressive strength 10.4 MPa and stiffness 1.22 GPa; birch: 10.8 MPa and 2.25 GPa, respectively). Strand length must therefore be a compromise between the need for high bending properties provided by long strands and the need for high compressive properties provided by short strands.