Abstract
The morphological and topochemical changes in wood tissues in compression wood of Japanese cedar (Cryptomeria japonica) upon treated with two types of ionic liquids, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]) and 1-ethylpyridinium bromide ([EtPy][Br]) were investigated. Compression wood tracheids were swollen by both ionic liquids but their swelling behaviors were different in the types of ionic liquids used. Under the polarized light, we confirmed that crystalline cellulose in compression wood is amorphized by [C2mim][Cl] treatment whereas it changes slightly by [EtPy][Br] treatment. Raman microscopic analyses revealed that [C2mim][Cl] can preferentially liquefy polysaccharides in compression wood whereas [EtPy][Br] liquefy lignin. In addition, the interaction of compression wood with ionic liquids is different for the morphological regions. These results will assist in the use of ionic liquid treatment of woody biomass to produce valuable chemicals, bio-fuels, bio-based composites and other products.
Highlights
IntroductionCompression wood is formed even in perfectly straight and vertical trees[30]
In the present work, we conducted ultrastructural and topochemical characterization of compression wood cell walls treated with ionic liquids by means of light microscopy, scanning electron microscopy (SEM), and confocal Raman microscopy. 1-Ethyl-3-methylimidazolium chloride ([C2mim][Cl]) and 1-ethypyridinium bromide ([EtPy][Br]) were selected as the ionic liquid used which prefer to react with cellulose[10] and lignin[13], respectively
The morphological changes in compression wood tissues during ionic liquid treatment were observed by bright-field microscopy (Fig. 1)
Summary
Compression wood is formed even in perfectly straight and vertical trees[30]. The development of efficient conversion process of compression wood makes it possible to use woody biomass effectively without waste. A number of studies on ionic liquid treatment of wood have already been performed, the knowledge of the impact of ionic liquid treatment on compression wood is very little[31] especially in morphological point of view. In the present work, we conducted ultrastructural and topochemical characterization of compression wood cell walls treated with ionic liquids by means of light microscopy, scanning electron microscopy (SEM), and confocal Raman microscopy. We showed the differences in interaction of compression wood with ionic liquid among the morphological regions of cell walls and the types of ionic liquids
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