Development of colorless wood via two-step delignification involving alcoholysis and bleaching with maintaining natural hierarchical structure

Abstract

Lignin-free wood has been successfully developed via a two-step chemical treatment while maintaining its inherent hierarchical structure. The first step was alcoholysis which was conducted using ethylene glycol, and whose condition was optimized by monitoring the removal of lignin using infrared spectroscopy. The second step was bleaching wherein the delignification proceeded from the surface to the core of the wood block, and finally resulted in complete decolorization. Although the wood block was free from lignin and hemicellulose as approximately confirmed by the chemical composition analysis, the 3-dimensional colorless wood block was almost unaltered, even after freeze–drying. Then, multidirectional observation was performed to investigate whether the natural hierarchical structure from anatomical- to nano-level was maintained. Optical microscopy, X-ray microcomputed tomography, X-ray diffractometry, and transmission electron microscopy demonstrated that all the stages of hierarchical structure were maintained. The lignin-free wood block has great potential for novel materials that are supported by a 3-dimensional wooden architecture. The derived lignin-free wood is also a suitable specimen that can be used to understand the formation and functionality of the anatomical structure and lignified cell wall.

Effects of orientation and degree of polymerization on tensile properties in the cellulose sheets using hierarchical structure of wood

“…Wood blocks with the dimensions 40 mm (longitudinal) 9 5 mm (radial) 9 5 mm (tangential) were obtained from Cryptomeria japonica and their noncellulosic components were removed by using alcoholysis and the Wise method (Wise et al 1946;Horikawa et al 2020;Kurei et al 2021). For alcoholysis, the blocks were immersed in a solvent of propylene glycol:48.5% sulfuric acid at 99:1 based on a weight ratio.…”

“…Therefore, the treated block consisted of approximately 90 wt% cellulose even after alcoholysis at 130 °C for 2.0 h and the Wise method. Cellulose blocks supported by a 3D wooden architecture (Horikawa et al 2020) were prepared under various alcoholysis conditions.…”

“…Our previous studies reported the successful fabrication of a novel cellulose block with the natural architecture of wood or bamboo (Horikawa et al 2020;Kurei et al 2021). The structure was evaluated, and the analyses demonstrated that the materials consisted of highly oriented and unfragmented microfibrils.…”

A multilayer transparent wood prepared by laminating two kinds of tree species

“…Transparent wood (TW) is a kind of bio-composite material with high transmittance and pliable optical characteristics. 10,26 The preparation principle of TW is to remove or modify the light absorption chromogenic groups existing in natural wood to make the wood appear colorless, [27][28][29][30] and then fill the material with the refractive index similar to the wood cell wall to reduce the light scattering phenomenon when light passes through the wood, 31 so as to effectively improve the transmittance of wood and change its opaque optical state. Fink 18 reported the concept of TW for the first time in 1992.…”

Reversible Dual-Stimuli-Responsive Chromic Transparent Wood Biocomposites for Smart Window Applications

“…10.1021/acsami.0c21369. SEM images of TC and PC pigments; transmission plots of chromic TW composites containing various compositions of chromic contents on exposure to temperature, UV, or both; table showing transmission values of chromic TW at 550 nm on exposure to UV, temperature, or both; DSC plots of TW composites; mechanical properties of TW composites (PDF)…”