Predicting thickness swelling of hot-pressed wood strands

Abstract

Strand board can be manufactured from sawmill residues, branches, and crown wood left in the forest. The thickness swelling of these residues is quite different from that of mature wood and can have a negative effect on the physical and strength properties of strand board. A mixture of these materials and pressing conditions can be optimized by assessing thickness swelling of wood strands after pressing. Individual wood strands conditioned to 12% moisture content were hot-pressed at 105 °C to 50% of their original thickness and conditioned at 20 °C and 33%, 100%, and 0% relative humidity for 72 hours to determine their thickness swelling. A mechanical model consisting of springs and dashpots was superimposed on a stress relaxation curve to determine strain components with a view to predict thickness swelling. The data were interpreted by analysis of variance in conjunction with Fisher's protected least significant difference method. The results showed a good agreement between measured and predicted thickness swelling of both juvenile and mature wood.