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TECHNOLOGY 49
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energy storage properties. The so-obtained composite films (0.5 mm thickness) exhibited
To this aim, balsa wood was delignified with sodium chlorite high optical transmittance (about 91%), water absorption
and subsequently impregnated under vacuum with a mixture stability (weight gain rate below 9%), good longitudinal tensile
of epoxy resin, poly(ethylene glycol), and triethyl phosphate. strength (about 140 MPa), and UV-shielding properties.

The obtained wood self-extinguished in flammability tests Bisht and co-workers assessed the effect of environmental
(thanks to the presence of triethyl phosphate), and exhibited conditions (in particular, of natural weathering) on the properties
the envisaged phase change energy storage features (provided of TW composites (derived from delignified melia and poplar
by the embedded poly(ethylene glycol)), keeping high optical woods, further infiltrated with an epoxy resin), considering
transparency (about 95%), high tensile strength (around 2 MPa), possible changes in colour, optical transmittance, visual
and impact resistance (around 8 kJ/m2). appearance, and chemical structure.
A similar approach was exploited by Li and co-workers, who Solar radiation was responsible for photo-oxidative
obtained phase change energy storage woods exhibiting high degradation phenomena that occurred soon after the start
photo-thermal conversion effectiveness through delignification of the tests. Both colour darkening and optical transmittance

of balsa wood and its subsequent impregnation with a losses (by about 34%) occurred.
poly(ethylene glycol)-based composite containing graphene Conversely, these photo-oxidation phenomena were quite
quantum dot-grafted boron nitride as a thermal conductive filler. significantly reduced through the incorporation (at 1.75 wt%
Even 6 wt% of graphene quantum dot-grafted boron loading) of a benzotriazole-derived UV absorber in the
nitride guaranteed high optical transparency and thermal formulation of the infiltrated epoxy resin, limiting the optical
conductivity (around 0.392 W/(m-K); besides, for the same transmittance loss to about 15 percent.
system, solidification and melting enthalpies achieved about A flexible reversibly photoresponsive transparent wood,

114 and 115 J/g, hence indicating a high latent heat value. suitable for the design of sensors and electronic devices, was
Finally, the temperature of phase transformation was in the recently proposed by Tian and co-workers.
range between 20.3 and 36.3 deg C, i.e., compatible with To this aim, a delignified balsa wood template was infiltrated
that of the human body. with a flexible epoxy resin (namely, Hasuncast 3016LV from
A nice example of the use of functional transparent Huasheng Tongchuang Technology, China) and a spiropyran
wood for smart window applications was proposed by Zhou solution.
and co-workers, who prepared epoxy-based balsa wood As a photosensitive dye, spiropyran was able to break the
TW composites containing carbon quantum dots (derived carbon-oxygen bond upon UV irradiation, hence promoting a
from chitosan or o-phenylenediamine) showing yellow or red remarkable colour change.

fluorescence, respectively.
The so-obtained materials exhibited a good optical
transmittance of around 70 percent, a high UV blocking rate
(about 80% for the yellow and 89% for the red fluorescence
TW), excellent water resistance, high durability, and thermal
insulation.
In a further research effort, delignified Canadian white

maple template was infiltrated with an epoxy resin embedding
carbon quantum dots and cured at room temperature.