Effect of combined radio-frequency/vacuum-press drying on the strength properties of Japanese larch board

This study was conducted to confirm the effects of combined radio-frequency/vacuum-press (RF/VP) drying on the strength properties of Japanese larch board. The strength properties of board dried at RF/VP was evaluated in comparison with conventional kiln, high-temperature, hot-air/vacuum dried, and non-dried boards. It was found that RF/VP drying significantly affected the density, bending strength, and compressive strength of the larch board, but not the tensile strength. These results arose because in RF/VP drying, the compressive load applied parallel to the thickness direction of the board during the drying could increase the shrinkage in the thickness direction, but was suppressed in the shrinkage into the width direction. In addition, since the suppressed shrinkage area in the width direction became larger than that of the increased shrinkage area in the thickness direction, it also affected the density after the drying. Therefore, it was concluded that the combination with mechanical press in RF/VP drying negatively affected the bending and compressive strengths.