The microcracks occurring during drying of wood were visualized under confocal laser scanning microscopy (CLSM). Precise control of relative humidity and temperature in a specialized environment chamber made it possible to acquire sequential images of the wood of Cryptomeria japonica during drying from the water-saturated condition. The images indicated that the microcracks occurred between tracheid and ray parenchyma in the latewood region and the crack tip advanced in both the bark and pith directions. Subsequently, the crack tip expanding towards the bark stopped at the earlywood region through the growth ring boundary. The other tip toward the pith stopped at the earlywood region before reaching the growth ring boundary. Our technique made it possible to generate microcracks and discuss the relationship between moisture content and microcrack formation during drying. We found the CLSM technique to be an effective method for visualizing microcrack propagation with time.
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