Permanent fixation of transversely compressed wood by heating and its mechanism
2001
Higashihara, T. (Kyoto Univ., Uji (Japan). Wood Research Inst.) | Morooka, T. | Norimoto, M.
The permanent fixation of transversely compressed wood by heating has been presumed to be due to the release of stresses stored in the cell wall polymers by their decomposition. It was shown, however, that the permanent fixation by steaming was the result not only of decomposition but also of the formation of some cohesive structures that were not permanent. To clarify whether or not such impermanent structures are formed during heating, the stress relaxation of radial compression and the recovery of deformation (strain recovery) in compressed samples of sugi (Cryptomeria japonica) wood were examined. Samples were compressed at temperatures from 160 deg C to 200 deg C for various periods of up to 24 hrs. The compressed samples were immersed in boiling water and then in swelling liquids, i.e., pyridine, dimethyl sulfoxide (DMSO) or 4% aqueous solution of sodium hydroxide (NaOH solution), and their strain recovery was measured. The relationship between the residual stress at the end of the relaxation measurements and the strain recovery in boiling water ould be expressed by a single curve regardless of heating time and temperature. All the specimens showed greater recovery in the above swelling liquids than in boiling water. In particular, marked recovery was observed in the NaOH solution, even when little recovery was recognized in boiling water for the specimen showing significant weight loss. From these findings, it was concluded that permanent fixation in the heat treatment is associated less with the decomposition of cell wall polymers but is dominated by the formation of some cohesive structures as in steam treatment.
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