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    Morphological and chemical features of tension wood treated with ionic liquids were described.
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    Cell walls in tension wood were swollen by ionic liquid treatment.
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    Changes in tissue structure were different for normal wood and tension wood.
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    Chemical changes in gelatinous layers were different for the types of ionic liquids.

Abstract

Tension wood that is an abnormal part formed in angiosperms has been barely used for wood industry. In this study, to utilize the tension wood effectively by means of liquefaction using ionic liquid, we performed morphological and topochemical determination of the changes in tension wood of Japanese beech (Fagus crenata) during ionic liquid treatment at the cellular level using light microscopy, scanning electron microscopy and confocal Raman microscopy. Ionic liquid treatment induced cell wall swelling in tension wood. Changes in the tissue morphology treated with ionic liquids were different between normal wood and tension wood, moreover the types of ionic liquids. The ionic liquid 1-ethyl-3-methylimidazolium chloride liquefied gelatinous layers rapidly, whereas 1-ethylpyridinium bromide liquefied slowly but delignified selectively. These novel insights into the deconstruction behavior of tension wood cell walls during ionic liquid treatment provide better understanding of the liquefaction mechanism. The obtained knowledge will contribute to development of an effective chemical processing of tension wood using ionic liquids and lead to efficient use of wood resources.

Keywords

  • Biorefinery
  • Cell wall
  • Gelatinous layer
  • Ionic liquid
  • Liquefaction
  • Tension wood