Compressive-molding of wood by high-pressure steam-treatment: Part 1. Development of compressively molded squares from thinnings

We attempted to compressive-mold logs of sugi (Cryptomeria japonica D.Don) to squares, and to permanently fix the transformed shape. The transformation and fixation were successively conducted under high-temperature saturated steam atmosphere by a newly designed apparatus which was a combined pressure vessel and a press machine. The results are summarized as follows: (1) The logs were successively softened by steaming at 150 degrees C, compressively molded to square, and fixed the transformed shape by steaming at 200 degrees C in this apparatus. (2) The shape of square fixed by high-pressure steam-treatment did not recover to original log shape by water-soaking and boiling. The result shows that the high-pressure steaming is effective for permanent fixation of the transformed shape. (3) The condition for sufficient fixation of the compressive transformation was steaming at 200 degrees C for 3 min when a 15 cm of diameter and 10 cm of length sugi-thinning was used as a specimen. (4) Inner stress within a compressed wood was gradually reduced during steaming and, finally, the stress was removed completely.