Review

Transparent Wood Fabrication and Applications: A Review

Le Van Hai 1 , Narayanan Srikanth 2 , Tin Diep Trung Le 1 , Seung Hyeon Park 1 and Tae Hyun Kim 1,3, *

1 Department of Materials Science and Chemical Engineering, Hanyang University,

Ansan 15588, Gyeonggi-do, Republic of Korea; levanhai121978@gmail.com (L.V.H.);
trungtinlediep@gmail.com (T.D.T.L.); rhcwlqdkemf@hanyang.ac.kr (S.H.P.)
2 Department of Chemical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada;
srikanth.naraayanan@gmail.com
3 Major in Advanced Materials and Semiconductor Engineering, School of Semiconductor Convergence
Engineering, Hanyang University, Ansan 15588, Gyeonggi-do, Republic of Korea
* Correspondence: hitaehyun@hanyang.ac.kr; Tel.: +82-31-400-5222

Abstract: Wood cellulose is an abundant bio-based resource with diverse applications

in construction, cosmetics, packaging, and the pulp and paper industries. Transparent
wood (TW) is a novel, high-quality wood material with several advantages over traditional
transparent materials (e.g., glass and plastic). These benefits include renewability, UV
shielding, lightweight properties, low thermal expansion, reduced glare, and improved
mechanical strength. TW has significant potential for various applications, including
transparent roofs, windows, home lighting structures, electronic devices, home decoration,
solar cells, packaging, smart packaging materials, and other high-value-added products.
The mechanical properties of TW, such as tensile strength and optical transmittance, are
typically up to 500 MPa (Young’s modulus of 50 GPa) and 10–90%, respectively. Fabrication
methods, wood types, and processing conditions significantly influence the mechanical
and optical properties of TW. In addition, recent research has highlighted the feasibility of
TW and large-scale production, making it an emerging research topic for future exploration.
This review attempted to provide recent and updated manufacturing methods of TW as
well as current and future applications. In particular, the effects of structural modification
through various chemical pretreatment methods and impregnation methods using various
polymers on the properties of TW biocomposites were also reviewed.

Academic Editors: Rodolphe Keywords: bio-based materials; polymer resin; cellulose nanofiber; lignocellulose; delignification
Sonnier and Roland El Hage

Received: 22 February 2025

Revised: 18 March 2025
Accepted: 26 March 2025
1. Introduction
Published: 28 March 2025
Wood has long been a fundamental material widely used in various industries, such as
Citation: Hai, L.V.; Srikanth, N.; Le,
pulp and paper, construction, flooring, furniture, and fuel. As the most abundant organic
T.D.T.; Park, S.H.; Kim, T.H.
Transparent Wood Fabrication and raw material on the planet, wood has played an essential role in human life for thousands
Applications: A Review. Molecules of years. Recently, the commercialization of high-value-added wood for various uses other
2025, 30, 1506. https://doi.org/ than traditional applications has attracted increasing research attention. In particular, wood
10.3390/molecules30071506 has a low carbon footprint, is environmentally friendly and is renewable.
Copyright: © 2025 by the authors. Among its various emerging applications, transparent wood (TW) has gained signifi-
Licensee MDPI, Basel, Switzerland. cant attention for its potential use in high-value-added products, such as smart windows,
This article is an open access article rooftops, decorative materials, solar cells, insulation, lighting management, and UV shield-
distributed under the terms and
ing [1–10]. Fink first introduced TW prepared by impregnating (infiltrating) different types
conditions of the Creative Commons
of polymers into wood structures [11]. Previous studies [9–14] have highlighted the numer-
Attribution (CC BY) license
(https://creativecommons.org/ ous advantages and potential future applications of TW. TW intended for commercial and
licenses/by/4.0/).

Molecules 2025, 30, 1506 https://doi.org/10.3390/molecules30071506

Molecules 2025, 30, 1506 2 of 15

industrial use must be environmentally friendly and safe for the human body, ensuring the
absence of toxic or harmful chemicals.
Transparent wood fabrication begins with the chemical pretreatment of lignocellulosic
biomass, involving either of the following processes: (1) complete lignin removal [11] or
(2) chemical modification of lignin with partial delignification while retaining a controlled
amount of lignin [8,15–18]. To produce a high-quality transparent wood material, the
delignified wood is impregnated with a polymer with a refractive index (RI) closely match-
ing that of the wood matrix [11]. Subsequently, the RI difference between the cell wall
and lumen is reduced, resulting in less light scattering and higher transparency. In recent
studies, various polymers, including epoxy, prepolymerized methyl methacrylate (PMMA),
polyvinyl pyrrolidone (PVP), polyethylene glycol/methyl methacrylate (PEG/MMA),
polyvinyl alcohol (PVA), polyurethane (PU), epoxy vitrimers, TEMPO-treated cellulose
nanofiber (CNF), and chitosan (CTS) polymer, have been used to make TW [14,15,17,19–22].
However, in recent years, various environmental issues have placed many restrictions on
using conventional petrochemical-based resin materials (e.g., epoxy or PMMA). Conse-
quently, bio-based polymers, such as limonene acrylate monomer, CNF, and CTS [14,23],
have been increasingly used to produce eco-friendly TW. In addition, self-densified and
compacted TW has demonstrated enhanced mechanical properties [24,25].
Light transmittance is the most critical property of TW, typically influenced by wood
thickness, delignification process, light transmittance of the polymer, and difference in
light transmittance between the polymer and wood. Previous studies have reported
transmittance values of TW varying from 10% to 90% [1,2,5,10,17,21]. Several factors,
including wood species and type, delignification process, bleaching conditions, thickness,
tensile strength, expansion rate, light transmittance, and polymer properties, influence
the performance of TW [2,5,17]. Owing to the limitations of conventional glass, such as
brittleness and low thermal insulation, developing a method for producing commercially
viable TW with enhanced tensile strength and less brittleness is crucial. Studies have
demonstrated that the mechanical properties of TW could be substantially improved.
For example, reinforcing with epoxy resin significantly improved its longitudinal tensile
strength from 42.7 MPa to 45.4 MPa and from 4.5 MPa to 23.4 MPa in the radial direction [21].
The improvement in the tensile strength of TW was reported to be approximately 106% and
520% in the longitudinal and radial directions, respectively, corresponding to 10 MPa to
200 MPa or higher [1,5,13]. Furthermore, multilayered TW has been developed to achieve
enhanced mechanical properties in all directions [9,26,27]. By contrast, some studies have
reported a reduction in mechanical strength, with reductions from approximately 220 MPa
to approximately 150 MPa [2,19] or from 60 MP to 30 MPa [28,29].
For the industrial application of TW, understanding the influence of raw materials
and fabrication processes on its mechanical properties is crucial. This review explores the
various types of TW, their production methods, and the impact of polymer impregnation
and manufacturing processes on the mechanical and optical properties of TW. Furthermore,
it explores advancements in nanostructured materials, high thermal insulation, and thermal
conductivity. This review examines various factors affecting the transmittance of TW.
Furthermore, it explores factors affecting transparency, such as wood types, polymers used,
material thickness, and manufacturing processes.

2. Review of the Fabrication Process of TW

Currently, softwood and hardwood species are used in composites TW with various
polymers, including PMMA, PVA, PVA-lignin nanoparticles, PVA-chitin nanofibers, chitin
nanocrystals, chitin-chitosan [8], CNF, CTS, PU, and PEG/MMA. Various bleaching agents
(catalysts) are used, such as NaClO2 , H2 O2 , NaOH, acetic acid, sodium acetate, ethylenedi-
 2. Review of the Fabrication Process of TW
Currently, softwood and hardwood species are used in composites TW with various
Molecules 2025, 30, 1506 polymers, including PMMA, PVA, PVA-lignin nanoparticles, PVA-chitin nanofibers,3 chi- of 15
tin nanocrystals, chitin-chitosan [8], CNF, CTS, PU, and PEG/MMA. Various bleaching
agents (catalysts) are used, such as NaClO2, H2O2, NaOH, acetic acid, sodium acetate, eth-
ylenediaminetetraacetic acid (EDTA),
aminetetraacetic acid (EDTA), andcombinations
and other other combinations areto
are used used to delignify
delignify wood-
wood-based
based raw materials.
raw materials. FigureFigure 1 shows
1 shows the general
the general process
process for producing
for producing TW. TW.

Figure 1.
Figure Generalfabrication
1. General fabrication methods
methods of
of TW.
TW.

2.1. Bleaching and Delignification

2.1. Bleaching and Delignification
Delignification is a crucial initial step in producing TW, although complete lignin
Delignification is a crucial initial step in producing TW, although complete lignin
removal is not always necessary [15,16,18,30]. Several studies [15–17] have indicated that
removal is not
even partial always
lignin necessary
removal from[15,16,18,30].
wood sources Several studies
can result [15–17]
in TW. have bleaching
Various indicated thatand
even partial lignin removal from wood sources can result
delignification methods are used in the early stages of TW production. Wood deligni- in TW. Various bleaching and
delignification
fication involves methods
using are usedorganic
alkalis, in the early stages
acids, NaClO of TW production. Wood delignifica-
2 , H2 O2 , and enzymes. Bleaching
tion involves using alkalis, organic acids, NaClO
conditions influence the transmittance and mechanical properties 2, H 2O 2 , and enzymes.
of TW. WoodBleachingtype,condi-
wood
tions influence
thickness, reaction the time,
transmittance
and chemical anddosage
mechanical properties
also affect of TW. process.
the bleaching Wood type, wood
A common
thickness, reaction
delignification time,involves
method and chemical dosage
oxidative also affect
bleaching. Thistheprocess
bleaching process.
involves A common
treating dried
delignification
wood by immersing method it ininvolves
a sodium oxidative
chlorite bleaching. This process
(NaClO2 ) bleaching involves
solution withtreating dried
acetate buffer,
wood by immersing
maintained at a pH ofit4.5 inand
a sodium
temperature chlorite (NaClO
of 70–80 ◦ C. 2) Asbleaching
mentioned solution
in the with acetate
Introduction,
buffer,
bleachingmaintained
using NaClO at a pH 2 isofthe4.5preferred
and temperature
method for of 70–80
producing °C. AsTW.mentioned in the used
Other studies Intro-a
duction, bleaching
combination of H2 O using
2 in NaClO
the 2 is the preferred
delignification process method
[21,28,31]. for producing
Wood can TW.
be Other
bleached studies
using
used a combination
different methods, of H2O2 in the
bleaching delignification
agents, temperatures,process and[21,28,31].
durations. Wood can be bleached
Bleaching removes
using
lignin different methods,
content, alters bleaching
its color, agents, temperatures,
and transforms brown wood into anda durations. Bleaching
white one. Lignin re-
modifi-
moves lignin content,
cation retains lignin while altersdecolorizing
its color, andthe transforms
wood. The brown bleachingwoodprocess
into a white
breaks one. Lignin
down the
modification
bonds withinretainsthe complex lignin lignin
while structure.
decolorizing Thethemost wood.easilyThe bleaching
cleaved ligninprocess breaks
bonds include
down
α-O-5,the bonds
β-O-5, andwithin
γ-O-5. theThecomplex lignin structure.
mechanisms involvedThe in themost easily cleaved
bleaching processlignin
havebonds
been
include α-O-5, β-O-5,
widely studied in the pulpand ɤ-O-5.
and paperThe mechanisms
industry. Details involved
on wood in the
andbleaching processare
pulp bleaching have
dis-
been
cussedwidely studied
in several in the
studies pulp andHighly
[16,32–34]. paper industry.
delignified Details on wood
and bleached and turns
wood pulp bleaching
white and
are discussed in several studies [16,32–34]. Highly delignified and bleached wood lignin
exhibits a highly porous structure, facilitating efficient polymer infiltration. However, turns
modification
white primarily
and exhibits whitens
a highly or decolorizes
porous structure,wood. This approach
facilitating efficient has gainedinfiltration.
polymer significant
interest inlignin
However, the large-scale
modification and primarily
efficient production
whitens orof TW, as demonstrated
decolorizes by [35]. Their
wood. This approach has
study highlighted
gained significant the potential
interest in the of large-scale
lignin modification
and efficient in producing
production TW of and its viability
TW, as demon- for
large-scale production. Xia et al. applied NaOH
strated by [35]. Their study highlighted the potential of2 lignin and H O 2 to wood samples, followed
modification in producing by
UV and
TW illumination,
its viability until the samples
for large-scale turned completely
production. Xia et al. whiteapplied [35].
NaOH Subsequently,
and H2O2 tovarious
wood
samples, followed by UV illumination, until the samples turned completely white resin,
TW products were prepared through vacuum infiltration using epoxy (300/21 epoxy [35].
Aeromarine Products
Subsequently, variousInc., TWSan Diego, CA,
products wereUSA). TW prepared
prepared through through vacuumlignin modification
infiltration using
has the(300/21
epoxy potentialepoxyfor resin,
various applications
Aeromarine and large-scale
Products Inc., San Diego, production.
CA, USA).Figure TW 2 illustrates
prepared
the lignin modification and delignification processes, along with their mechanisms.
A washing step is performed after bleaching to remove unreacted chemicals, extracts,
lignin, and impurities. During this process, the pH is neutralized, and a light vacuum may
be applied to the pretreated wood to remove residual chemicals and volatile components.
Subsequently, the treated wood undergoes a solvent-exchange process, where it is immersed
in an ethanol and acetone solution. Depending on the purity, the amount of solvent required
Molecules 2025, 30, 1506 4 of 15

Molecules 2025, 30, x FOR PEER REVIEW 4 of 16

for the exchange process typically ranges from two to three times the volume of wood.
After undergoing these processes, the wood material is ready for TW production. However,
throughexchange
solvent lignin modification
is not alwayshasnecessary.
the potential
TW for
canvarious applications
be produced and large-scale
by directly infiltratingpro-
the
duction. into
polymer Figure
the2dried,
illustrates the lignin
bleached wood modification and delignification
without a solvent-exchange processes,
process. Table 1along
lists
with
the their mechanisms.
different delignification and bleaching agents used for TW fabrication.

Figure 2. Delignification, lignin modification, and the development of porous wood structure through
Figure 2. Delignification, lignin modification, and the development of porous wood structure
bleaching [16,32–34].
through bleaching [16,32–34].
Table 1. Bleaching methods using various woods and bleaching agents for TW production.
A washing step is performed after bleaching to remove unreacted chemicals, extracts,
Wood Species; Size (W:L:T)
lignin, and impurities. DuringBleachingthis Agents
process,and Delignification
the pH is neutralized, and a lightReferences
vacuum may
be applied to theKOH pretreated
(>98%) andwood DIto remove
water residual
followed by chemicals and volatile
NaClO (>98%) for components.
Poplar veneer; 80:80:3 mm 3
Subsequently, 8the
h attreated
120–130wood◦ C. The
undergoes
amount of a solvent-exchange
lignin content before process,
and where it is im-
[36]
after bleaching is not indicated.
mersed in an ethanol and acetone solution. Depending on the purity, the amount of sol-
vent required for the exchange
Boiling withprocess
NaOH typically −1 ) andfrom
(2.5 mol Lranges two3 to three times the vol-
Na2 SO
− 1 mol L−1 isfor
ume of wood. (0.4After mol L ) for 12these
undergoing h. Second Step:the
processes, H2 O 2 , 2.5material
wood ready for TW pro-
Basswood [21]
duction. However, 12 h.solvent
In the first stage, is
exchange lignin contentnecessary.
not always = ~12–14%; TWsecond
can be produced by di-
rectly infiltrating the polymer stage, the
into lignin
the dried,content ≤ 3.0%.
bleached wood without a solvent-exchange
process. Table 1Soaking
lists thein NaOH (2.5
different mol/L) andand
delignification Nableaching
2 SO3 (0.4 mol/L).
agents used for TW fabri-
Basswood cation. Boiling for 12 h. Bleaching with H 2 O 2 , (2.5 mol/L). This [37]
resulted in 33%, 50%, and nearly 100% lignin removal.
Poplar (Populus sp.) and Balsa wood.
Table 1. BleachingNaOH (10using
methods wt%)various
and Na 2 SO3 and
woods (5 wt%) boiling
bleaching for for
agents 2–4TW
h, production.
Width (80–300 mm), Length from 25 to followed by boiling in DI water. Further whitening using [38]
300Wood
mm andSpecies; Sizefrom
thickness (W:L:T)
1–10 mm Bleaching
H2 O2 (30 Agents and
wt%) in boiling. The Delignification
lignin content is ~2.8%. References
KOH (>98%) and
Peracetic acidDI water
(PAA) and followed by NaClO
CH3 COOOH. (>98%)
Treated for◦8Ch at
at 80
Balsa (Ochroma pyramidale), alder (Alnus
Poplar veneer; 80:80:3 mm3 120–130using aqueous
°C. The amount PAA solution
of lignin (4 wt%)
content at a and
before pH of 4. 8bleach-
after [36]
glutinosa), birch (Betula pendula), and
(adjusted with NaOH), followed by
ing is not indicated. washing with DI water [23]
beech (Fagus sylvestris);
and acetone. Lignin removal from 18.2% to 27.9% of
0.7–3 mm thickness Boiling withuntreated
NaOH (2.5 to mol
0.9 to ) andofNa
L−12.0% 2SO3 (0.4 mol L−1) for 12 h.
treated biomass.
Basswood Second Step: H2O2, 2.5 mol L−1 for 12 h. In the first stage, lignin [21]
2.0 wt% NaClO2 and 0.1 wt% acetic acid glacial, bleaching
content = ~12–14%; second stage, the lignin content ≤ 3.0%.
time for 30, 60, 90, 120, and 150 min. This resulted in lignin
Basswood (Tilia); 20:20:0.42 mm3 Soaking in NaOH (2.5 mol/L) and Na2SO3 (0.4 mol/L). Boiling for [17]
removal of 33, 38, 47, 51, and 64%, with treatment time of
Basswood 12 h. Bleaching30, with H2120,
60, 90, O2, (2.5
andmol/L).
150 min,This resulted in 33%, 50%,
respectively. [37]
and nearly 100% lignin removal.
Molecules 2025, 30, 1506 5 of 15

Table 1. Cont.

Wood Species; Size (W:L:T) Bleaching Agents and Delignification References

6.0 wt% H2 O2 , 1.0 wt% trisodium citrate 95% dihydrate,
1.0 wt% of NaOH, and 92 wt%. Bleaching time of 30, 60, 90,
Basswood (Tilia); 20:20:0.42 mm3 [30]
120, and 150 min, and lignin content varied from 24.3, 19.5,
18.4, 16.6, 15.2 and 14.9 wt%.
NaClO2 (5.0 wt%) in acetate buffer solution at 95 ◦ C for
Beechwood [2]
12 h. The lignin content was not indicated.
Birch (Betula alnoides, Betula) and New
NaClO2 (0.4–1.0%) at 70–90 ◦ C for 45–135 min. The pH 4.6
Zealand pine (Pinups radiata D. Don); [18]
was adjusted by adding CH3 COOH.
20:20:0.5 mm3

2.2. Impregnation of Bleached Wood with Various Polymers

2.2.1. Previous Approaches of Impregnation Process
Previous studies have identified resin (filler) penetration as the preferred and most
effective method for producing TW using materials obtained after the initial delignification
process [2,38,39]. Delignified and bleached wood materials typically have empty spaces
from which components such as lignin and hemicellulose are removed, resulting in a
porous structure. To achieve transparency, these pores are filled with a material with a
refractive index close to or equal to that of wood. In some cases, the selected polymers also
provide UV-shielding properties. According to Fink [11], wood generally has a refractive
index of approximately 1.53. Commonly used polymers have refractive indices ranging
from 1.50 to 1.53, making polymer resin suitable for TW fabrication. The delignified porous
wood material is filled with polymer through impregnation or penetration. Various types
of polymers, such as PMMA, PVP, PU, epoxy resin, quantum dots, PVA-lignin, PVA-lignin
nanoparticles, PVA-chitin nanocrystals, chitin crystal, PEG/MMA, ATO/MMA, CNF, and
CTS, have been used for this purpose [1,2,6–8,11,15,19–21]. Matching the refractive index
(RI) of polymer for TW production is one of the important factors. However, it is difficult
to match the various RIs depending on the polymer structure to produce TW. Polymers
used in TW, including PMMA, epoxy resin, and PVA, may contain SiO2 , TiO2 , and lignin to
modulate the RI of composite materials. These nanoparticles may play a role in controlling
the RIs of polymers and wood. However, further study is needed to evaluate the properties
of TW composite materials when infiltrated into TW.
Polymer impregnation typically takes 30 min to several hours and involves repeated
cycles of impregnation, release, and penetration. However, the low specific gravity of
wood during impregnation makes effective polymer infiltration into the porous wood chal-
lenging. Alternative methods, such as compression or self-densification of oxidized wood
using TEMPO and other solvents, have been explored to improve polymer penetration.
For instance, Zu et al. [24] produced TW using a high-pressure compression method on
bleached wood.

2.2.2. Pressurization of Delignified Wood

Li et al. produced TW by densifying wood after TEMPO oxidation [25]. Samanta
et al. have prepared TW biocomposites for smart window applications [40]. These TW
composites were prepared using thiol and ene monomers containing chromic components
and a mixture of thermo- and photo-responsive chromophores. To produce TW through
pressing, the lignin content of the wood materials must first be removed. Different bleaching
chemical agents are used for delignification, such as NaClO2 , NaClO, and H2 O2 . After
lignin is removed from the natural wood, the resulting bleached wood is subjected to
pressurize between microporous filtering films for 1 h to 3 h and subsequently dried.
Molecules 2025, 30, 1506 6 of 15

2.2.3. Polymer Infiltration

Wood materials can be processed with or without delignification and bleaching to
produce TW. When bleaching or delignification is performed, several chemical agents
(NaOH, Na2 SO3 , NaClO2 , NaClO, and H2 O2 ) are used to remove a portion or the entire
lignin content from the wood substrate, resulting in different types of TW [2,17,18,23].
Depending on the lignin content, TW can be categorized into lignin-retaining, partially
bleached, and fully bleached TW. To prepare TW, pretreated wood (processed through
solvent exchange using ethanol or acetone) or wood bleached using bleaching agents
(subjected to solvent exchange using ethanol or acetone) is infiltrated with various polymers,
such as epoxy resin, PMMA, quantum dots, PVA, PLA, chitosan, and cellulose nanofibers
through a vacuum process [1,2,16,21,31]. This renders the wood transparent, with varying
levels of transmittance and haziness.
The infiltrated components used for fabricating TW for smart windows consisted of
pentaerythritol tetrakis (3-mercaptopropionate) (PETMP), 1,3,5-triazine-2,4,6(1H,3H,5H)-
trione (TATATO), and the UV initiator 1-hydroxy-cyclohexyl phenyl ketone (0.5%). In
addition, Hai et al. have developed bio-based TW for packaging and wood straws by
infiltrating wood with dissolved chitosan and TEMPO-nanocellulose [14]. A study by Qiu
et al. explored the transition from high-haze wood to TW using phase-change materials [41].
They used various copolymers, including styrene (St), butyl acrylate (BA), and 1-octadecene
(ODE), for the infiltration. At low temperatures (e.g., 5 ◦ C), the wood exhibited high haze
and low transparency. However, increasing the temperature to 25 ◦ C or 50 ◦ C for 2 min
rendered the wood transparent. To prepare thermo-responsive flexible TW, the authors
infiltrated wood with a combination of (St/BA/ODE) St and BA (1:1 ratio) containing 0.3%
divinylbenzene (DVB, 55%) as the cross-linker and 0.2% 2,2′ -azobis-(2-methulpropionitrile)
(AIBN) as the initiator [41]. The mixture was precopolymerized at 85 ◦ C for 35 min. By
adding 5% 1-octadecene (ODE 90%) to the St/BA mixture, a thermo-responsive flexible
opaque and TW composited was prepared. Table 2 presents the various methods used for
TW fabrication and their applications.

Table 2. TW fabrication methods and applications.

Wood Species Fabrication Method and Filler (Polymer) Applications Ref.

15 wt% Polyvinylpyrrolidone (PVP) ethanol. Highly efficient broadband light
Basswood [37]
Degassed under 200 Pa for ~10 min management in solar cells
Poplar (Populus sp.) Impregnation using vacuum infiltration process
TW for Energy-saving building [38]
and Balsa wood with prepolymerized MMA solution (PMMA)
Silver birch wood Impregnation using vacuum infiltration with Thermal energy storage and
[19]
(Betula pendula) PEG/MMA (70/30 wt%) solution reversible optical transmittance
Impregnation using vacuum infiltration with Thermally insulated TW for
Balsa wood [13]
polyvinyl alcohol (PVA) solution energy-efficient windows
Douglas fir, Bass, Infiltration into the delignified wood scaffold using Aesthetic TW for
[10]
Balsa, and Pinewood epoxy resin, followed by solidification for 24 h energy-efficient buildings
Impregnation with 2 epoxy resins (E-128 resin Thick translucent wood walls
Basswood [5]
and D-630) at a mass ratio of 3:1 and indoor light performance
Infiltration using poly-methyl methacrylate
TW substrate for perovskite
Balsa wood (PMMA) and laser deposition for conductive [4]
solar cells
film layer using indium tin oxide (ITO).
Molecules 2025, 30, 1506 7 of 15

Table 2. Cont.

Wood Species Fabrication Method and Filler (Polymer) Applications Ref.

Impregnation using vacuum infiltration with
poly methyl methacrylate (PMMA) for 1 h with Next-generation smart
Beechwood [2]
three repetitions, followed by heat treatment in a building materials
box furnace at 85 ◦ C for 12 h
Impregnation using vacuum infiltration with
TW containing CsxWO3
CsxWO3 /prepolymerized methyl methacrylate
Beechwood nanoparticles for [39]
(MMA) mixed solution, followed by infiltration
heat-shielding-window
for 30 min with three repetitions
Impregnation using vacuum infiltration with Food packaging materials,
Fir wood TEMPO-treated nanocellulose and medical packaging materials, [14]
chitosan solution and straw
Impregnation using vacuum infiltration with UV-shielding
Balsa wood [8]
PVA, PVA-lignin nanoparticle windows application

2.2.4. Self-Densified TW
Self-densified TW is a recent method that involves bleaching using sodium chlorite
(NaClO2 ) and an acetate buffer (pH 4.6) at 80 ◦ C for 12 h. The natural wood is transformed
into white wood, washed, and immersed in a 0.1 m sodium phosphate (PBS) solvent.
Subsequently, the wood is treated using the TEMPO oxidation method. Following this, the
wood is dried at ambient temperature to produce self-densified TW [25].

3. Physical Properties of TW
3.1. Optical Transmittance and Haziness
Transmittance is the most crucial property of TW. A higher transmittance allows
more light to pass through, improving visibility. Light transmittance in TW is primarily
influenced by wood thickness, bleaching conditions, type of impregnated polymers, resins,
and wood type.
High light transmittance and sufficient wood thickness are crucial for the successful
industrial or commercial application of TW. However, while thicker wood is suitable for
construction, it tends to have lower transmittance. In general, a thicker TW exhibits higher
blurriness and lower light transmittance, making it challenging to achieve clear visibility.
TW with high transmittance or translucency is preferred for applications such as
solar cells, light management, and structural elements. However, products requiring high
transparency demand minimal haze. Therefore, applications in buildings and residential
areas require a balance between transmittance and visibility. Yaddanapudi et al. reported
that TW made from beech and PMMA exhibited transmittance ranging from 10 to 70%,
depending on the wood thickness (0.1 mm to 0.7 mm) [2]. Balsa wood has been widely
used for manufacturing TW, with transmittance ranging from 10 to 90%, depending on
the thickness [1,6,10,15]. Several studies have reported methods for preparing TWs of
various thicknesses. For example, Fu et al. reported TWs with a thickness of 3.5 mm and a
transmittance of about 70–90% depending on the infiltrated polymer component [6], and
Mi et al. reported various types of TWs for aesthetic wood applications with a thickness
of 2 mm and a transmittance of about 80% [10]. Hai et al. recently reported various
types of TWs with very thin layers for various applications with a transmittance of about
70–80% [14]. In addition, Hai et al. combined PVA and lignin nanoparticles to produce
TWs with a thickness of 1–2 mm for UV-blocking window applications [8,9]. High turbidity
and high transmittance are prioritized based on the TW application. For example, high-
Molecules 2025, 30, 1506 8 of 15

transmittance and high-haze products are suitable for applications such as solar cells,
outdoor displays, and home lighting management.
In a recent study, Jia et al. [29] developed TW with a transmittance of approximately 90%
and haze of 10%, demonstrating clear visibility and high potential as a building material.

3.2. UV-Shielding Properties

Another notable advantage of TW is its UV-shielding properties. Numerous studies
on TW and glass have shown that, unlike glass with little to no UV-shielding properties,
TW exhibits excellent UV-shielding capabilities. TW with different types of filler materials
holds significant potential for UV-shielding applications. UV rays from the sun are known
to have various negative effects on humans, such as skin burns and cancer. Therefore,
TW with high UV-shielding properties offers a significant advantage for commercial suc-
cess [7,8,10,13]. TW produced by infiltrating PMMA/antimony-doped tin oxide (ATO),
PMMA, NCF, and CTS solutions has shown significant UV-shielding capability, with trans-
mittance demonstrating high UV protection properties (~80%) in the 200–400 nm range.
Furthermore, recent developments have explored partial delignification and reinforcing
lignin nanoparticles to enhance UV shielding [8,14]. In one study, bleached wood was
infiltrated with a composite of PVA and lignin nanoparticles to create UV-shielding TW. In
addition, a simpler approach involving delignification using NaOH without bleaching was
demonstrated to produce TW with UV-shielding properties [8,14]. Therefore, UV-shielding
properties offer significant advantages for window applications.

3.3. Density, Modulus, Strength, and Toughness

Wood is a natural material with several unique properties, such as lightweight and
high tensile strength, Young’s modulus, and toughness. These properties vary depend-
ing on the wood species, growth conditions, and whether it is earlywood or latewood.
In general, the density of wood is approximately 0.65 g/cm3 . Studies have reported
that the density of latewood and earlywood in Douglas fir ranges from 300 kg/m3 to
800 kg/m3 [10,14]. Another previous study reported Balsa wood with a density ranging
from 112 kgm−3 to 170–200 kgm−3 [25,40]. TW is a suitable alternative for building and
construction applications owing to its superior properties compared with other materials,
such as natural wood, steel, and glass. Therefore, mechanical properties, such as tensile
strength, Young’s modulus, toughness, and density, should be considered. The literature
reviews have confirmed that the mechanical properties of TW are superior to those of
natural wood [5,10,14,38]. Wang et al. reported that natural wood had a tensile strength
of approximately 42.8 MPa and a modulus of 5.7 GPa [38]. By contrast, TW exhibited
an average tensile strength and modulus of 52.3 MPa and 2.4 GPa, respectively, with
elongation at break increasing from 1% to approximately 5% compared with untreated
wood. Mi et al. reported that TW exhibited significantly enhanced tensile strength and
toughness compared with natural wood [10]. The tensile strengths of natural wood in
the radial and longitudinal directions were less than 10 MPa and approximately 40 MPa,
respectively, whereas those of TW exceeded 20 MPa and 95 MPa, respectively. In addition,
Mi et al. showed that the toughness of TW increased fivefold in the radial and longitudinal
directions [10].

3.4. Thermal Conductivity

Heat transfer is a key factor in construction and building applications. Modern ar-
chitecture increasingly features high-rise or large-scale buildings with open designs and
extensive glass windows to allow natural light into the buildings. Glass has tradition-
ally been the preferred material for windows. However, glass windows have several
disadvantages, such as high thermal conductivity, heavyweight, and brittleness. TW is
Molecules 2025, 30, 1506 9 of 15

an emerging material with significant advantages over glass, such as lightweight prop-
erties, ductility, UV shielding, and low thermal conductivity. Wood is known to be a
low-thermal-conductivity material, making TW a promising alternative for reducing ther-
mal conductivity. Several studies have explored the thermal conductivity and UV-shielding
properties of TW [4,5,10,13]. These studies have reported that TW exhibited 3–4 times lesser
thermal conductivity (0.32–0.15 W m−1 K−1 ) than glass (1.0 W m−1 K−1 ). Thus, large-scale
production of TW is expected to play a significant role in future construction applications.

4. Factors Affecting Optical and Mechanical Properties of TW

The mechanical characteristics of TW are one of its critical properties, and they vary
based on their intended use. As previously discussed, TW is used in home structures,
smart houses, packaging, and glass substitutes. The mechanical properties of TW used
for these applications are primarily influenced by the wood type, processing conditions,
and type of impregnating polymer used. To function as a substitute for fragile glass, TW
must have the mechanical strength required for its use as a building material. Zu et al.
demonstrated that simple bleached and compressed TW exhibited superior mechanical
properties compared with wood impregnated with PMMA, epoxy resin, PVA, and NCF [24].
However, TW produced through compression alone had the disadvantage of limited
thickness increase. In a recent study, Li et al. reported that TW produced through TEMPO
oxidation and high-pressure compression exhibited high tensile strength and Young’s
modulus, reaching approximately 500 MPa and 50 GPa, respectively, despite being a
relatively thin material [25].
TW impregnated with PVA and PMMA exhibited extremely poor mechanical prop-
erties. This can be attributed to various factors, such as wood type, bleaching conditions,
and other processing factors. According to Jungstedt et al. [42], birch exhibited an initial
longitudinal tensile strength of approximately 167 MPa, while materials made by infil-
trating PMMA under different conditions achieved tensile strengths of 193 and 263 MPa.
Yu et al. [39] reported that natural wood had a strength of 55.1 MPa, increasing to 60.1 MPa
following PMMA impregnation. Qui et al. [41] noted that native Balsa wood had a strength
of approximately 20 MPa, whereas polymer-impregnated materials exhibited a tensile
strength of approximately 10–20 MPa, depending on the resin type and penetration condi-
tions. Research indicates that the type of wood used in manufacturing TW significantly
influences its mechanical properties and tensile strength development.
Table 3 lists the mechanical properties of various wood types and TW in the longitudi-
nal (// ) and radial (⊥ ) directions. In addition, it summarized the effects of bleaching agents,
bleaching conditions, wood thickness, and wood type on transmittance.

Table 3. Various mechanical properties of TW from different wood sources.

Young’s Modulus Transmittance

Name of Wood Wood Sizes (mm) Bleaching Agents Polymer Tensile Strength (MPa) Ref.
(GPa) (%)
NW: 220 NW: 1.52
Beechwood T: 0.1–0.7 NaClO2 PMMA DL: 75 DL: 2.5 >10–70 [2]
TW: 150 TW: 2.1
NW⊥ : 6.24
Douglas fir 320 × 170 NW// : N/A
NaClO2 Epoxy resin N/A >80 [10]
(Pseudotsuga menziesii) T: 0.6–2 TW⊥ : 21.6
TW// : 92
NW: N/A NW: N/A
Balsa wood 20 × 20
NaClO2 PMMA DL: 10 DL: 0.22 40–90 [1]
(Ochroma pyramidale) T: 0.7–3.7
TW: 95 T: 2.05
Pine, birch, and ash 100 × 100
H2 O2 , NaClO2 PMMA 100.7 N/A 80 [16]
wood veneer T: 1.5
NW⊥ : <5 NW⊥ : N/A
50 × 50 NaOH; NW// : <45 NW// : N/A
Basswood Epoxy resin 80–90 [21]
T: 3 Na2 SiO3 , H2 O2 TW⊥ : <23.4 T⊥ : 1.22
TW// : 45.4 T// : 2.37
Molecules 2025, 30, 1506 10 of 15

Table 3. Cont.

Young’s Modulus Transmittance

Name of Wood Wood Sizes (mm) Bleaching Agents Polymer Tensile Strength (MPa) Ref.
(GPa) (%)
NW⊥ : 1.15
20 × 40 Polyvinyl NW// : 18.8
Balsa wood NaClO N/A 90 [10]
T: 0.8 alcohol (PVA) TW⊥ : 67
TW// : 143
NW: 61.5 NW: 1.98
LMW: 33.3 LMW: 1.49
Poplar wood 20 × 20 NaOH, Na2 EDTA,
PVA and PG T-PG0: 39.9 T-PG0: 1.51 65–80 [28]
(Populus deltoides) T: 1 MgSO4 , and H2 O2
T-PG50: 22.6 T-PG50: 0.80
T-PG100: 13.3 T-PG100: 0.26
NW⊥ : 8.5
NW// : 55
Basswood T: ∼0.7 NaClO, NaClO2 Epoxy resin N/A 90 [29]
TW⊥ : 33.3
TW// : 44.4
NW: 78.3 NW: 3.74
Poplar wood 25 × 25 and 50 × 50 DL: 21.9: DL: 1.71
NaClO2 ATO/PMMA 45–80 [7]
(P. adenopoda Maxim) T: 1 T: 93.0 T: 3.38
ATO0.3–0.7 T: 96.4–113.1 ATO0.3–0.7 T: 4.27–4.46
20 × 20;
Silver birch wood NW: 129.6 NW:14.5
20 × 20 NaClO2 PEG/PMMA 60–80 [19]
(Betula pendula) TW-TES: 70.5 T: 14.9
T: 0.5–1.5
NW⊥ : 1.02
Balsa wood (Ochroma 20 × 20 NW// : 12.01
NaClO2 Epoxy resin N/A 10–80 [15]
pyramidale) T: 1, 1.5, 2, and 5 TW⊥ : 4.12–63.05
TW// : 45.12–75.12
NW: 121.9
20 × 20
Basswood (Tilia) NaClO2 PMMA DL: 84–8-114.3 N/A 10–60 [17]
T: 0.42
TW: 152.4–171.4
NW⊥ : 1
NW// : 75
100 × 100 Cellulose
TW⊥ : 26 15
Fir 100 × 200 NaClO2 nanofiber, 75–80 [14]
TW// : 258 13
T: 0.1 Chitosan
TW⊥ : 26
TW// : 171

5. Potential Applications of TW
5.1. TW for Building and House Structure
Previous studies [2,5,11,16] have highlighted the potential applications of TW, in-
cluding housing structures, smart houses, walls, and rooftops. For example, several
studies [1,39] have shown that CSxWO3/PMMA composites exhibited excellent insulation
properties, making them ideal for use as window materials. Li et al. developed TW of
various thicknesses, ranging from 20 mm to 50 mm [5]. The 20 mm thick TW impregnated
with epoxy resin exhibited a transmittance of up to 40%, making it suitable for use in wall
structures. In addition, Li et al. reported that TW made by impregnating epoxy resin exhib-
ited significantly enhanced transmittance compared with TW infiltrated with PMMA [5].
Therefore, to develop advanced TW for housing structures, reducing the turbidity of TW
and further exploring technologies related to the use of various woods and fabrication
processes are crucial.

5.2. Light Management, House Decoration, Solar Cells and Electric Devices
TW has potential applications in buildings, lighting management, and home deco-
rations [3,4,10,13,39]. It can be used in rooftops, lighting management, and decoration.
Yu et al. reported that TW resulted in enhanced heat-shielding properties compared to
glass [39]. Model houses with CsxWO3/MMA TW windows exhibited better insulation
than existing houses using ITO glass windows, resulting in nearly double the indoor tem-
perature. According to Li et al. [1], TW exhibited minimal glare, and Lang et al. [43] noted
that TW infiltrated with PMMA and coated with PETDOT:PSS demonstrated significant
potential as a glass substitute for windows. In addition, Mi et al. [10] noted that TW could
improve lighting and insulation and create pleasant interior lighting. These properties
make TW a promising material for smart houses, buildings, and windows.
In addition, TW can be used in other industries, such as electronics, sensors, and
solar cells. Recent studies [5,19,21,38] have demonstrated its potential in lighting manage-
Molecules 2025, 30, 1506 11 of 15

ment, solar cell materials, thermal energy storage systems, and energy-saving applications.
Wang et al. [38] revealed that TW and transparent-wood-based fibers exhibit extremely low
thermal conductivity of approximately 0.2 W/mK. By contrast, ITO glass has a thermal
conductivity of approximately 1.0 W/mK, approximately five times higher than that of TW.
This makes TW a viable energy-saving material for buildings. Montanari et al. [19] pro-
duced TW by immersing delignified wood in a PEG/MMA (70/30 w/w) polymer solution
three times. The resulting TW exhibited excellent thermal energy storage and energy-saving
potential. Li et al. [5] suggested combining solar cells and wooden building materials as
an energy-saving solution. Other studies [5,21] explored TW for solar cell applications,
reporting conversion efficiencies ranging from 14.4% to 16.8%. Another study used TW
to fabricate perovskite solar cells, consisting of a TW/ITO layer/TiO2 /perovskite/spire-
OMeTAD/Au layer. The perovskite solar cells exhibited a current density of 21.9 mA·cm−2 ,
voltage of 1.09 V, and charge rate of 70.2%. These findings indicate that TW is a promising
eco-friendly housing material.

5.3. TW as Green Bio-Based Packaging Materials

Bio-based TW, fabricated by impregnating CNF and CTS suspensions into bleached
porous wood, has demonstrated excellent antioxidant and UV-shielding properties, im-
proved mechanical properties, and enhanced transmittance. Hai et al., 2021 produced
bio-based TW in significantly larger sizes (200 mm × 100 mm × 0.1 mm) compared with
those in previously published works and used two types of TW for packaging applica-
tions [14]. This highly flexible material can be used for transparent straws, transparent
bags, and medical window packaging. However, despite the many advantages of bio-based
materials, such as cellulose nanofibers and chitosan solutions, hydrophilicity remains a
significant challenge. Further efforts are necessary to address this limitation and improve
the thickness of bio-based TW. Figure 3 illustrates the fabrication process and TW applica-
tions. In addition, Zhang et al. recently also developed biobased transparent wood for food
packaging [44]. The authors demonstrated that food packaging has good UV-shielding
functionality, antioxidation, and so on.

5.4. Patents on TW
TW is a promising material for developing green products, potentially replacing
traditional window glass, structural components in buildings, and decorations and im-
proving sunlight management. TW development has rapidly progressed in recent years.
However, the emerging trend of bio-based materials and their feasibility for real-world
applications has led to the filing of several patents worldwide. Advanced TW offers
excellent mechanical properties, ease of fabrication, low thermal expansion, and mini-
mal environmental impact. Consequently, research groups, companies, and institutions
have increasingly pursued patents related to TW. In 2017, Cellutech filed a patent for a
method of preparing TW [46]. Cellutech listed a range of polymers for TW fabrication, such
as poly(hexafluoropropylene oxide), hydroxypropyl cellulose, poly(tetrafluoroethylene-
co-hexafluoropropylene), poly(pentadecafluoro octyl acrylate), and poly (tetrafluoro-3-
(heptafluoropropoxy) propyl acrylate), among others. In 2017, the University of Maryland
secured a patent for TW with a high transmittance of 92% [47]. The patent lists various poly-
mers for TW fabrication, including polyester fiberglass, polyurethane polymers, vulcanized
rubber, bakelite, duroplast, urea-formaldehyde, melamine resin, diallyl phthalate (DAP),
polyimides and bismaleimides, and cyanate esters or poycyanurates, among others [46,47].
In addition, they patented a process and various polymers for creating bio-based TW. With
TW being an emerging field with significant potential for industrial applications, research
since 2016 has led to several patents from companies, universities, and institutions [46]. As
 medical window packaging. However, despite the many advantages of bio-based materi-
als, such as cellulose nanofibers and chitosan solutions, hydrophilicity remains a signifi-
Molecules 2025, 30, 1506 cant challenge. Further efforts are necessary to address this limitation and improve the
12 of 15
thickness of bio-based TW. Figure 3 illustrates the fabrication process and TW applica-
tions. In addition, Zhang et al. recently also developed biobased transparent wood for
the development
food of TW
packaging [44]. Thecontinues, more patentsthat
authors demonstrated andfood
industrial applications
packaging has goodare expected
UV-shield-
to emerge in the future.
ing functionality, antioxidation, and so on.

Figure
Figure 3.3.Fabrication process
Fabrication andand
process applications of TW:
applications of (1)
TW:from
(1) wood-to-veneer and TEMPO-treated
from wood-to-veneer and TEMPO-
nanocellulose; (2) bleached
treated nanocellulose; wood; wood;
(2) bleached (3) TEMPO-treated nanocellulose;
(3) TEMPO-treated ′
(3′) PVA;
nanocellulose; (3′′ ) chitosan;
(3″) chitosan;
(3 ) PVA; (3‴)
(3′′′ ) other
other typestypes
of polymers; (4) TW
of polymers; applications;
(4) TW TWTW
applications; bag, window,
bag, window,straw,
straw,solar
solarcells,
cells, and
and aesthetic
wood ceiling [14,16,28,35,39,41,43,45].

5.5. Future Trends and Challenges

5.4. Patents on TW
TW has gained significant research attention in recent years owing to its potential
TW is a promising material for developing green products, potentially replacing tra-
applications and unique properties. However, several challenges remain, such as high
ditional window glass, structural components in buildings, and decorations and improv-
hydrophilicity, permeability, production scalability, and chemical consumption. To address
ing sunlight management. TW development has rapidly progressed in recent years. How-
these challenges, researchers have proposed various solutions, including hydrophobic
ever, the emerging trend of bio-based materials and their feasibility for real-world appli-
coatings with materials such as silicates and quantum dots, improving the thickness of
cations has led to the filing of several patents worldwide. Advanced TW offers excellent
bio-based TW through layer-by-layer deposition.
mechanical properties, ease of fabrication, low thermal expansion, and minimal environ-
Currently, three primary approaches are employed for TW production: penetration,
compression, and self-densification of TEMPO-oxidized bleached wood. Although con-
ventional chemical polymers, such as PMMA, epoxy resin, and PVA, were initially used
for impregnation, recent research has expanded the selection to include various materials.
Combinations of different polymers are also being explored, although conventional fillers,
such as PMMA and epoxy resin, remain toxic and harmful to human health and the environ-
ment. By contrast, bio-based materials, such as PVA, CNF, and CTS, are nontoxic but exhibit
poor physical properties, including water absorption and hydrophilicity. Nevertheless,
bio-based materials, such as PLA, CNF, and CTS, are preferred owing to their minimal
environmental impact and lack of human hazards. In addition, CNF are considered as a
potential material to infiltrate porous wood to produce TW, but the high energy cost for
production of CNF to be reduced. The high energy consumption and waste generation
Molecules 2025, 30, 1506 13 of 15

and disposal costs due to the use of chemicals in CNF production remain issues that will
be solved in the future. However, the high hydrophilicity of these materials necessitates a
hydrophobic coating for the resulting TW to prevent moisture absorption and humidity
damage caused by weather changes.
The size and thickness limitations of TW pose challenges for industrial and commer-
cial applications. However, Xia et al. [35] successfully fabricated meter-scale TW with
a thickness of 1 mm, marking a significant breakthrough in production scalability. Con-
sequently, research focused on commercialization is expected to accelerate in the near
future. Overcoming these challenges holds significant potential for future applications of
bio-based TW, particularly in improving mechanical properties, thermal expansion, light
management, and the customizing of thickness and filler content for improved flexibility
and toughness. Ongoing research focuses on optimizing hydrophilicity and hydrophobicity
through various physicochemical methods, which can further expand the potential of TW
for various applications.

6. Conclusions
The potential applications of TW primarily include materials for residential building
structures, smart houses, windows, solar cells, and packaging, with significant expansion
anticipated in the future. High-density TW of consistent thickness is suitable for building,
window, and home structural applications. However, it can also be converted or fabri-
cated into a thin film, making it suitable for rolling, decorative, and packaging purposes.
Currently, the primary methods for manufacturing TW include penetration, high-pressure
compression, and self-densification.
The fabrication of TW using eco-friendly materials such as NCF, CTS, and other bio-
based materials has great potential. However, various eco-friendly polymer materials
and manufacturing methods for TWs with desirable mechanical and functional properties
should be developed. In particular, the mechanical properties of TW, including tensile
strength, Young’s modulus, and transmittance, are greatly influenced by wood species,
polymers, and processing methods. As highlighted in this review, eco-friendly TW offers
significant market potential and a wide range of applications.
This paper provides a review of the latest and updated manufacturing methods,
properties, and applications of bio-based composite material (TW). In particular, the effects
of structural modifications using various chemical reagents and combinations using various
polymers on the properties of TW biocomposites were also examined.

Author Contributions: Conceptualization and writing, T.H.K.; writing—original draft preparation,

L.V.H.; writing—review and editing, N.S.; T.D.T.L. and S.H.P.; All authors have read and agreed to
the published version of the manuscript.

Funding: This research was supported by the National R&D Program through the National Research
Foundation of Korea (NRF), funded by the Ministry of Science and ICT (RS-2024-00408755), R&D
program of Korea Evaluation Institute of Industrial Technology (KEIT) grant funded by the Ministry
of Trade, Industry and Energy (MOTIE), Korea (RS-2024-00434298) and Hanyang University ERICA
(HY-2021).

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

Data Availability Statement: No new data were created or analyzed in this study. Data sharing is
not applicable to this article.

Conflicts of Interest: The authors declare no conflicts of interest.

Molecules 2025, 30, 1506 14 of 15

References
1. Li, T.; Zhu, M.W.; Yang, Z.; Song, J.W.; Dai, J.Q.; Yao, Y.G.; Luo, W.; Pastel, G.; Yang, B.; Hu, L.B. Wood Composite as an Energy
Efficient Building Material: Guided Sunlight Transmittance and Effective Thermal Insulation. Adv. Energy Mater. 2016, 6, 1601122.
[CrossRef]
2. Yaddanapudi, H.S.; Hickerson, N.; Saini, S.; Tiwari, A. Fabrication and characterization of transparent wood for next generation
smart building applications. Vacuum 2017, 146, 649–654. [CrossRef]
3. Li, Y.; Vasileva, E.; Sychugov, I.; Popov, S.; Berglund, L. Optically transparent wood: Recent progress, opportunities, and
challenges. Adv. Opt. Mater. 2019, 6, 1800059. [CrossRef]
4. Li, Y.; Cheng, M.; Jungstedt, E.; Xu, B.; Sun, L.; Berglund, L. Optically transparent wood substrate for perovskite solar cells. ACS
Sustain. Chem. Eng. 2019, 7, 6061–6067. [CrossRef]
5. Li, H.; Guo, X.; He, Y.; Zheng, R. House model with 2–5 cm thick translucent wood walls and its indoor light performance. Eur. J.
Wood Wood Prod. 2019, 77, 843–851. [CrossRef]
6. Fu, Q.L.; Yan, M.; Jungstedt, E.; Yang, X.; Li, Y.Y.; Berglund, L.A. Transparent plywood as a load-bearing and luminescent
biocomposite. Compos. Sci. Technol. 2018, 164, 296–303. [CrossRef]
7. Qiu, Z.; Xiao, Z.; Gao, L.; Li, J.; Wang, H.; Wang, Y.; Xie, Y. Transparent wood bearing a shielding effect to infrared heat and
ultraviolet via incorporation of modified antimony-doped tin oxide nanoparticles. Compos. Sci. Technol. 2019, 172, 43–48.
[CrossRef]
8. Hai, L.V.; Cho, S.W.; Kwon, G.J.; Lee, D.Y.; Ma, S.Y.; Bandi, R.; Kim, J.K.; Han, S.Y.; Dadigala, R.; Lee, S.H. Fabrication of
eco-friendly transparent wood for UV-shielding functionality. Ind. Crop. Prod. 2023, 201, 116918. [CrossRef]
9. Hai, L.V.; Hoa, P.D.; Kim, J.; Lee, S.H. All-biobased multilayer transparent wood infiltrated with cellulose and chitosan nanofibers:
Improving anisotropic mechanical and ultraviolet shielding properties. Ind. Crop. Prod. 2024, 222, 119508. [CrossRef]
10. Mi, R.Y.; Chen, C.J.; Keplinger, T.; Pei, Y.; He, S.M.; Liu, D.P.; Li, J.G.; Dai, J.Q.; Hitz, E.; Yang, B.; et al. Scalable aesthetic
transparent wood for energy efficient buildings. Nat. Commun. 2020, 11, 3836. [CrossRef]
11. Fink, S. Transparent wood—A new approach in the functional study of wood structure. Holzforschung 1992, 46, 403–408. [CrossRef]
12. Katunský, D.; Kanócz, J.; Karl’a, V. Structural elements with transparent wood in architecture. Int. Rev. Appl. Sci. Eng. 2018,
9, 101–106. [CrossRef]
13. Mi, R.; Li, T.; Dalgo, D.; Chen, C.; Kuang, Y.; He, S.; Zhao, X.; Xie, W.; Gan, W.; Zhu, J. A clear, strong, and thermally insulated
transparent wood for energy efficient windows. Adv. Funct. Mater. 2020, 30, 1907511. [CrossRef]
14. Hai, L.V.; Muthoka, R.M.; Panicker, P.S.; Agumba, D.O.; Pham, H.D.; Kim, J. All-biobased transparent-wood: A new approach
and its environmental-friendly packaging application. Carbohyd. Polym. 2021, 264, 118012. [CrossRef]
15. Qin, J.; Li, X.; Shao, Y.; Shi, K.; Zhao, X.; Feng, T.; Hu, Y. Optimization of delignification process for efficient preparation of
transparent wood with high strength and high transmittance. Vacuum 2018, 158, 158–165. [CrossRef]
16. Li, Y.Y.; Fu, Q.L.; Rojas, R.; Yan, M.; Lawoko, M.; Berglund, L. Lignin-Retaining Transparent Wood. Chemsuschem 2017, 10, 3445–3451.
[CrossRef] [PubMed]
17. Wu, J.M.; Wu, Y.; Yang, F.; Tang, C.Y.; Huang, Q.T.; Zhang, J.L. Impact of delignification on morphological, optical and mechanical
properties of transparent wood. Compos. Part A Appl. Sci. Manuf. 2019, 117, 324–331. [CrossRef]
18. Wu, Y.; Zhou, J.C.; Huang, Q.T.; Yang, F.; Wang, Y.J.; Wang, J. Study on the Properties of Partially Transparent Wood under
Different Delignification Processes. Polym. Basel 2020, 12, 661. [CrossRef]
19. Montanari, C.l.; Li, Y.; Chen, H.; Yan, M.; Berglund, L.A. Transparent wood for thermal energy storage and reversible optical
transmittance. ACS Appl. Mater. Interfaces 2019, 11, 20465–20472. [CrossRef] [PubMed]
20. Chen, H.; Baitenov, A.; Li, Y.; Vasileva, E.; Popov, S.; Sychugov, I.; Yan, M.; Berglund, L. Thickness dependence of optical
transmittance of transparent wood: Chemical modification effects. ACS Appl. Mater. Interfaces 2019, 11, 35451–35457. [CrossRef]
21. Zhu, M.W.; Song, J.W.; Li, T.; Gong, A.; Wang, Y.B.; Dai, J.Q.; Yao, Y.G.; Luo, W.; Henderson, D.; Hu, L.B. Highly Anisotropic,
Highly Transparent Wood Composites. Adv. Mater. 2016, 28, 5181–5187. [CrossRef] [PubMed]
22. Wang, K.L.; Dong, Y.M.; Ling, Z.; Liu, X.R.; Shi, S.Q.; Li, J.Z. Transparent wood developed by introducing epoxy vitrimers into a
delignified wood template. Compos. Sci. Technol. 2021, 207, 108690. [CrossRef]
23. Montanari, C.; Ogawa, Y.; Olsén, P.; Berglund, L.A. High performance, fully bio-based, and optically transparent wood
biocomposites. Adv. Sci. 2021, 8, 2100559. [CrossRef]
24. Zhu, M.W.; Wang, Y.L.; Zhu, S.Z.; Xu, L.S.; Jia, C.; Dai, J.Q.; Song, J.W.; Yao, Y.G.; Wang, Y.B.; Li, Y.F.; et al. Anisotropic, Transparent
Films with Aligned Cellulose Nanofibers. Adv. Mater. 2017, 29, 1606284. [CrossRef]
25. Li, K.; Wang, S.N.; Chen, H.; Yang, X.; Berglund, L.A.; Zhou, Q. Self-Densification of Highly Mesoporous Wood Structure into a
Strong and Transparent Film. Adv. Mater. 2020, 32, 2003653. [CrossRef]
26. Zhou, J.C.; Wang, Y.J.; Wang, J.; Wu, Y. Multilayer Transparent Wood with Log Color Composed of Different Tree Species. ACS
Omega 2022, 7, 46303–46310. [CrossRef]
Molecules 2025, 30, 1506 15 of 15

27. Bisht, P.; Pandey, K.K. Optical and mechanical properties of multilayered transparent wood. Mater. Today Commun. 2024,
38, 107871. [CrossRef]
28. Rao, A.N.S.; Nagarajappa, G.B.; Nair, S.; Chathoth, A.M.; Pandey, K.K. Flexible transparent wood prepared from poplar veneer
and polyvinyl alcohol. Compos. Sci. Technol. 2019, 182, 107719. [CrossRef]
29. Jia, C.; Chen, C.J.; Mi, R.Y.; Li, T.; Dai, J.Q.; Yang, Z.; Pei, Y.; He, S.M.; Bian, H.Y.; Jang, S.H.; et al. Clear Wood toward
High-Performance Building Materials. ACS Nano 2019, 13, 9993–10001. [CrossRef]
30. Wu, Y.; Zhou, J.C.; Huang, Q.T.; Yang, F.; Wang, Y.J.; Liang, X.M.; Li, J.Z. Study on the Colorimetry Properties of Transparent
Wood Prepared from Six Wood Species. ACS Omega 2020, 5, 1782–1788. [CrossRef]
31. Wu, Y.; Wu, J.M.; Yang, F.; Tang, C.Y.; Huang, Q.T. Effect of H2 O2 Bleaching Treatment on the Properties of Finished Transparent
Wood. Polym. Basel 2019, 11, 776. [CrossRef]
32. Brogdon, B.N.; Lucia, L.A. New insights into lignin modification during chlorine dioxide bleaching sequences (IV): The impact of
modifications in the (EP) and (EOP) stages on the D stage. J. Wood Chem. Technol. 2007, 25, 149–170. [CrossRef]
33. Tarvo, V.; Lehtimaa, T.; Kuitunen, S.; Alopaeus, V.; Vuorinen, T.; Aittamaa, J. A model for chlorine dioxide delignification of
chemical pulp. J. Wood Chem. Technol. 2010, 30, 230–268. [CrossRef]
34. Elhelece, W.A.; Abousekkina, M.M. Theoretical interpretation of the changes occur on cellulosic wastes as a result of different
chemical treatments. Eur. Chem. Bull. 2013, 2, 328–334. [CrossRef]
35. Xia, Q.Q.; Chen, C.J.; Li, T.; He, S.M.; Gao, J.L.; Wang, X.Z.; Hu, L.B. Solar-assisted fabrication of large-scale, patternable
transparent wood. Sci. Adv. 2021, 7, eabd7342. [CrossRef]
36. Zou, W.H.; Sun, D.L.; Wang, Z.H.; Li, R.Y.; Yu, W.X.; Zhang, P.F. Eco-friendly transparent poplar-based composites that are stable
and flexible at high temperature. RSC Adv. 2019, 9, 21566–21571. [CrossRef]
37. Zhu, M.W.; Li, T.; Davis, C.S.; Yao, Y.G.; Dai, J.Q.; Wang, Y.B.; AlQatari, F.; Gilman, J.W.; Hu, L.B. Transparent and haze wood
composites for highly efficient broadband light management in solar cells. Nano Energy 2016, 26, 332–339. [CrossRef]
38. Wang, X.; Zhan, T.; Liu, Y.; Shi, J.; Pan, B.; Zhang, Y.; Cai, L.; Shi, S.Q. Large-size transparent wood for energy-saving building
applications. Chemsuschem 2018, 11, 4086–4093. [CrossRef]
39. Yu, Z.Y.; Yao, Y.J.; Yao, J.N.; Zhang, L.M.; Chen, Z.; Gao, Y.F.; Luo, H.J. Transparent wood containing CsWO nanoparticles for
heat-shielding window applications. J. Mater. Chem. A 2017, 5, 6019–6024. [CrossRef]
40. Samanta, A.; Chen, H.; Samanta, P.; Popov, S.; Sychugov, I.; Berglund, L.A. Reversible dual-stimuli-responsive chromic transparent
wood biocomposites for smart window applications. ACS Appl. Mater. Interfaces 2021, 13, 3270–3277. [CrossRef]
41. Qiu, Z.; Wang, S.; Wang, Y.; Li, J.; Xiao, Z.; Wang, H.; Liang, D.; Xie, Y. Transparent wood with thermo-reversible optical properties
based on phase-change material. Compos. Sci. Technol. 2020, 200, 108407. [CrossRef]
42. Jungstedt, E.; Montanari, C.; Östlund, S.; Berglund, L. Mechanical properties of transparent high strength biocomposites from
delignified wood veneer. Compos. Part A Appl. Sci. Manuf. 2020, 133, 105853. [CrossRef]
43. Lang, A.W.; Li, Y.Y.; De Keersmaecker, M.; Shen, D.E.; Österholm, A.M.; Berglund, L.; Reynolds, J.R. Transparent Wood Smart
Windows: Polymer Electrochromic Devices Based on Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) Electrodes.
Chemsuschem 2018, 11, 854–863. [CrossRef] [PubMed]
44. Li, Y.Y.; Fu, Q.L.; Yu, S.; Yan, M.; Berglund, L. Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining
Functional and Structural Performance. Biomacromolecules 2016, 17, 1358–1364. [CrossRef]
45. Zhang, K.; Sutton, I.; Smith, M.D.; Harper, D.P.; Wang, S.; Wu, T.; Li, M. Ambient-densified and polymer-free transparent wood
film for smart food packaging window. IScience 2023, 26, 108455. [CrossRef]
46. Hu, L.; Zhu, M.; Li, T.; Gong, A.S.; Jianwei, S. Transparent Wood Composite, Systems and Method of Fabrication.
WO2017136714A1, 3 February 2017.
47. Li, Y.; Rojas, R.; Berglund, L. Transparent Wood and a Method for Its Preparation. AU2018245016B2, 29 March 2018.

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