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FIXATION OF COMPRESSIVE DEFORMATION IN WOOD BY PRE-STEAMING

M. Inoue, N. Sekino, T. Morooka, R. M. Rowell and M. Norimoto
Journal of Tropical Forest Science
Vol. 20, No. 4, Special 20th Year Anniversary Issue (October 2008), pp. 273-281
Stable URL: http://www.jstor.org/stable/23616704
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
FIXATION OF COMPRESSIVE DEFORMATION IN WOOD BY PRE-STEAMING
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Abstract

Wood block specimens pre-steamed at 120—220 °C for 5—20 min were compressed in the radial direction. The recovery of set decreased with increasing presteaming temperature and time. The reduction of set recovery correlated with the amount of weight loss in steaming irrespective of pre-steaming temperature and time. The weight loss for the highest level of fixation of compressive deformation was about 7.5% that was obtained by pre-steaming at 210—220 °C for 10 min. Moreover, the set recovery of the pre-steamed specimen decreased as pressing temperature and time increased. The compressibility of wood block increased with increasing pre-steaming temperature and time. Large transverse compression and stress relaxation tests showed that Young's modulus and yield stresses were reduced while the stress relaxation magnitude was increased by more severe pre-steaming condition. Scanning electron micrographs showed some cell structure destruction at large deformations in specimens steamed at above 180 °C. This suggests that the wood becomes brittle due to steaming. Creep test data indicate that fluidity decreased with increasing steaming time and temperature. Pre-steam fixation of compressive deformation is due to degradation of the microfibril framework, as well as the viscous flow of the matrix components resulting from the scission of their cross-linked network. Spesimen blok kayu yang diwap terlebih dahulu pada suhu 120—220 °C selama 5—20 min dimampatkan pada arah jejari. Pemulihan set berkurang dengan pertambahan suhu dan masa. Penurunan pemulihan set berkorelasi dengan kehilangan berat semasa proses pengewapan tanpa mengira suhu dan masa. Kehilangan berat bagi penstabilan kecacatan mampatan paling tinggi adalah kira-kira 7.5% yang diperoleh dengan mengewap pada 210—220 °C selama 10 min. Tambahan lagi, pemulihan set untuk spesimen yang diwap menurun apabila suhu penekanan dan masa bertambah. Ketermampatan blok kayu bertambah dengan bertambahnya suhu dan masa. Ujian mampatan melintang dan santaian tegasan menunjukkan bahawa modulus Young dan tegasan alah menurun manakala magnitud santaian tegasan bertambah dengan keadaan mengewap yang lebih teruk. Pada mampatan tinggi, mikrograf elektron imbasan menunjukkan kemusnahan struktur sel dalam spesimen yang diwap lebih daripada 180 °C. Ini mencadangkan bahawa kayu menjadi rapuh apabila diwap. Data ujian rayap menunjukkan bahawa kebendaliran menurun dengan bertambahnya masa dan suhu pengewapan. Penstabilan kecacatan mampatan dengan mengewap adalah disebabkan oleh pendegradan rangka mikrofibril serta aliran likat komponen matriks akibat daripada putusnya rangkaian silang.

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