Impact of conventional drying and thermal post-treatment on the residual stresses and shape deformations of larch lumber

Quality evaluation and grading of thermally treated wood products are of fundamental importance to their commercial utilization. The combined impacts of conventional drying, thermal post-treatment, and transverse dimensions of lumber over the residual stresses and shape deformations of larch (Larix gmelinii) wood were examined. Larch specimens with two different thicknesses (25 and 40 mm) and three different widths (100, 150, and 200 mm) were dried using conventional technology and thereafter thermally treated at 200°C for 1 h at atmospheric superheated steam conditions. Drying and residual stresses and shape deformations of both kiln-dried and thermally post-treated lumbers were measured and statistically analyzed. The influential mechanisms of lumber thickness and width over the drying stresses and shape deformations of thermally post-treated lumbers were revealed. The drying and residual stress measurement based on the prong test was recommended as a potential quality evaluation strategy for the thermally post-treated larch lumbers. As the lumber width increased from 100 to 150 mm, and then to 200 mm, the cupping deformation of thermally post-treated larch lumber increased substantially. These results provided some practical foundations for the quality evaluation of thermally treated wood.