Abstract
The fluidity of wood remarkably increases during moisture changes. This phenomenon is termed mechano-sorptive creep. The mechanism of mechano-sorptive creep has been studied, including a previous report by our group. Here, creep tests in bending were carried out for wood during and immediately after adsorption of moisture and after a long moisture conditioning. The effects of the rate of moisture adsorption on creep were also examined. The results and conclusions are as follows: (I) Greater creep occurred immediately after the adsorption process as compared with that after a long moisture conditioning, whereas much greater creep occurred during the same adsorption process, similar to the case of drying. Therefore, during the changes in moisture, not only destabilization but also stabilization should occur simultaneously, so that the wood during the changing process is in a remarkably unstable state. (II) Smaller creep occurred immediately after a slower adsorption as compared with that immediately after a more rapid adsorption. This suggests that wood is more stabilized during a slower versus a more rapid adsorption process. However, difference in creep between the final stages of the slower and the more rapid adsorption process was scarcely found. This is considered to result from the difference in degree of stabilization caused by the different duration of both adsorptions. In other words, this result is only an outward appearance. (III) Greater creeps were recognized during larger changes in moisture content (Δu) during the adsorption processes corresponding to the drying process. Therefore, mechano-sorptive creep depends not only on Δu but also on the range of relative humidity (RH). Larger stabilization was found during the changing process of larger Δu.
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