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Official Journal of the Japan Wood Research Society

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Vibrational properties of Sitka spruce heat-treated in nitrogen gas

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Abstract

Sitka spruce (Picea sitchensis Carr.) wood was heated for 0.5–16.Oh at temperatures of 120°–200°C in nitrogen gas or air. The values for Young's modulus, shear modulus, and loss tangent were measured by free-free flexural vibration tests. X-ray diffractometry was carried out to estimate the crystallinity index and crystallite width. The results obtained are as follows: (1) Density decreased at higher temperatures and longer heating times. The specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width increased during the initial stage and were constant after this stage at 120°C and 160°C, whereas they increased during the initial stage and decreased later when the temperature was high. Loss tangent in the longitudinal direction increased under all conditions, whereas that in the radial direction increased at 120°C and decreased at 160°C and 200°C. (2) From the relation between Young's modulus and moisture content, it can be safely said that Young's modulus is increased by the crystallization and the decrement in equilibrium moisture content, and that crystallization (rather than degradation) is predominant at the initial stage of the heat treatment, whereas the latter is predominant as the heating time increases. (3) It is implied that the specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width decreased more in air than in nitrogen gas because of oxidation in air.

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Additional information

This study was presented in part at the 43th Annual Meeting of Japan Wood Research Society at Morioka, August 1993, the 44th Annual Meeting of Japan Wood Research Society at Nara, April 1994, and the 45th Annual Meeting of Japan Wood Research Society at Tokyo, April 1995

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Key words

  • Heat treatment
  • Vibrational properties
  • Crystallization
  • Atmospheric condition
  • Temperature-time condition