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TECHNOLOGY 45
www.fdmasia.com | FDM ASIA SEP/OCT 2024

TRANSPARENT WOOD-BASED

MATERIALS: A NEW STEP TOWARD

SUSTAINABILITY AND CIRCULARITY

Despite its real invention dating to 1992, only about ten years ago two independent research
groups started to thoroughly investigate the so-called transparent wood (TW). TW can be derived
from almost any wood biomass through specific chemical treatments focused on lignin. These
aim to completely remove this component from wood or to eliminate the chromophore groups
present in the pristine material to obtain a new material with very high transparency, toughness,
and lightness. This opens the way toward the development of new, up-to-date, advanced, and
sustainable materials for both structural and functional purposes, fulfilling the current concepts of
circular economy and sustainability. By Alberto Mariani, University of Sassari, and Giulio Malucelli,
Politecnico di Torino

ood, one of the most well-known non-polluting, out using acidic/alkali treatments or employing redox agents.
sustainable, and carbon-fixing biomasses, has Under acidic conditions, organic solvents can be employed.
Walways been considered a reproducible source of Conversely, the lignin removal that is carried out in alkaline
materials and energy for everyday life. It exhibits a mesoporous environments exploits quite high temperatures (usually between
and hierarchical complex structure, made of three main 140 and 170°C), and the use of ammonia or sodium hydroxide,

components, i.e., hemicellulose, cellulose, and lignin. often in combination with sulphites or sulphides.
Unlike the first two constituents, which are colourless at Besides, it is essential to manipulate the wood structure
visual inspection, lignin provides the biomass with a dark by accurately controlling its nanopores in the cell walls
colour, due to the presence of complex chromophores (i.e., through these chemical treatments, tuning, at the same
C=C double bonds conjugated with aromatic rings). time, the process conditions (namely: the concentration of
Besides, the extended porosity of wood accounts for the employed solutions, the treatment duration, the pH and
remarkable scattering phenomena of visible light, making the temperature ranges).
material opaque, hence with negligible optical transmittance. Further, during the above-mentioned treatments, it is very
The possibility of transforming wood into a transparent material

was demonstrated by Fink in 1992, but was abandoned until
2016 when two independent research groups, one from the
University of Maryland (US) and the other from the Royal
Institute of Technology (Sweden), rediscovered the potential
of this new material for different applications.
The obtainment of TW requires specific procedures.
Briefly, the first step refers to either removing or modifying

the lignin of the pristine wood. The removal of lignin (a very
well-established process in the paper industry can be carried