Solvent-Free Dyeing of Solid Wood in Water-Saturated Supercritical Carbon Dioxide

authors	Jaxel, J; Liebner, FW; Hansmann, C
nationality	International
journal	ACS SUSTAINABLE CHEMISTRY & ENGINEERING
author keywords	Coloring of massive wood; water-saturated scCO(2); wood modification; green dyeing; supercritical carbon dioxide; pressure-mediated hydration of wood
keywords	REACTIVE DISPERSE DYE; COTTON; PLASTICIZATION; MICROEMULSIONS; ACETYLATION; ENVIRONMENT; CO2
abstract	Coloring of massive wood is still a major challenge in high-end wood processing, which aims to provide solid wood at a broad range of colors to furniture manufacturers. Here we report that water-saturation of supercritical carbon dioxide (scCO(2))-a promising green dyeing medium-greatly improves solid wood dyeing. This has been demonstrated for disperse blue 134 and three European hardwood species, namely, birch (Betula pendula), beech (Fagus sylvatica), and oak (Quercus robur). Variation of dyeing temperature (45-100 degrees C) and pressure (10.0-30.0 MPa) revealed that 20.0 MPa and 100 degrees C pose an optimal parameter combination. Coloration of the interior of small wood cubes (2 cm(3)), expressed as Delta E color change within the CIELAB color space, was here 40.6 (+/- 1.2) for birch, 28.7 (+/- 3.1) for beech, and 16.3 (+/- 4.4) for oak. Since these values are significantly higher compared to water-free scCO(2), it can be concluded that water-even if poorly soluble in scCO(2), was effectively transported throughout the semiporous wood matrices. This causes the latter to swell, which efficiently improves the accessibility of individual cell wall constituents by dyeing reagents, for example. Three-point bending tests indicate that water-saturated scCO(2) dyeing effectuates some morphological or chemical alterations to the wood structure, since a moderate loss of both flexural strength and stiffness (15-20%) was found. Nevertheless, the proposed approach which can be adapted to a broad variety of biobased materials represents a green, sustainable, and highly versatile process, as it is free of organic solvents and waste products.
publisher	AMER CHEMICAL SOC
issn	2168-0485
year published	2020
volume	8
issue	14
beginning page	5446
ending page	5451
digital object identifier (doi)	10.1021/acssuschemeng.0c01273
web of science category	Chemistry, Multidisciplinary; Green & Sustainable Science & Technology; Engineering, Chemical
subject category	Chemistry; Science & Technology - Other Topics; Engineering
unique article identifier	WOS:000526375000005