Effect of the drying condition on the strength properties of Japanese larch board after vacuum heat treatment

Abstract This study aimed to investigate the effect of drying conditions on the strength properties of larch boards after vacuum heat treatment, using leftover boards from a previous study that were dried by four methods: conventional kiln drying, high-temperature drying, radio-frequency/vacuum-press (RF/VP) drying, and hot-air/vacuum drying. The boards were then heat-treated and tested for moisture content, density, bending strength, compressive strength, and tensile strength. The results showed that the drying method significantly affected the strength properties of the larch boards after vacuum heat treatment. After vacuum heat treatment, density increased in hot-air/vacuum drying and RF/VP drying, while bending strength was higher in high-temperature drying and hot-air/vacuum drying, and tensile strength was higher in hot-air/vacuum drying. Conditioning treatment after vacuum heat treatment had an impact on the decrease in density in RF/VP drying, the decrease in bending strength in hot-air/vacuum drying, and the increase in tensile strength in high-temperature drying. The drying method is a crucial factor in determining the chemical changes that occur during heat treatment, as it establishes the physical and chemical properties of the wood prior to treatment. Variations in these properties can result in different chemical transformations during the heat treatment process. Therefore, to minimize any adverse impact on the strength properties of the wood, it is necessary to carefully select an appropriate drying method before heat treatment.