BENDING CREEP BEHAVIORS OF LAMINATED WOOD MODELS WITH ACETYLATED LAMINAE UNDER CHANGING MOISTURE CONDITIONS

This paper describes the reducing effect of acetylating treatments on the bending creep of 3-ply -laminated wood models under air-dry, moist ure-regain and moisture-loss conditions, in connection with a layer ma de of acetylated lamina. The acetylating treatment has been known to b e an effective method for reducing the changes in moisture content of wood. The four kinds of laminated wood models tested were N type, D ty pe, C type and T type (see Fig. 1). The acetyl content of acetylated l amina had an average value of 21.4 per cent. The creep of D type was s maller than that of N type under both changing moisture conditions. Th e reduction in its creep resulted from a decrease in the change in moi sture content by the acetylating treatment. Under the moisture-regain condition, the creep rate of C type was faster than that of T type in the early stage and decreased with time, while the creep of T type inc reased almost linearly with time. Under the moisture-loss condition, C type had the smallest creep, but T type had the largest creep. In the exponential regression equations between the change in moisture conte nt and the creep compliance, the avarage fitted values of exponent for the four types ranged from 0.70 to 1.47 under the moisture-regain con dition, depending much on the layer with the acetylated lamina, wherea s these values were nearly equal to 1 under the moisture-loss conditio n wherever the acetylated lamina was located. The bending. creep behav iors of T and C types under the changing moisture conditions can be ex plained in terms of both the warp due to the differences in shrinkage and swelling between the acetylated and the untreated laminae and the differences in compressive and tensile creeps between both laminae.