Transparent Wood – A Future Material to Replace Glass in Green Architecture

What is transparent wood?

TW is a wood–polymer composite that preserves the natural vascular–cellular microstructure of wood. By reducing/modifying lignin and infiltrating the cell lumens with a polymer of matching refractive index, the material becomes transparent (high transmittance) while maintaining high haze for soft, uniform light. Foundational reviews (Royal Society 2018; Cellulose 2023) detail how wood species, grain orientation, degree of lignin removal, and polymer choice affect optical, thermal, mechanical, and photo‑aging properties. [2]

How transparent wood is formed

To design a new TW material, the process leverages wood’s intrinsic structure: [3]

• Periodicity — regularly repeating annual growth rings.
• Anisotropy — aligned conduits/fibers running along the grain.

Combining these two characteristics during TW fabrication produces unique opto‑mechanical properties.

Methods to make transparent wood

Lignin removal/reduction + polymer infiltration (delignification). Treat with NaClO₂/weak acid to remove chromophoric lignin → rinse → dry → infiltrate epoxy/PMMA → achieve T ≈ 80%, haze ≈ 93%, k ≈ 0.24 W/m·K. A 2020 Nature Communications study also demonstrated scaling to 320 × 170 × 0.6 mm panels with ~24 hours of resin infiltration, indicating good scalability. [3]

Why can it replace glass in green architecture?

1) Optics — bright but glare‑free

• Comparable total light transmission to glass: TW reaches T ≈ 80% @ 600 nm (Nature Communications 2020). [3]
• Reduced glare, more uniform illuminance: haze ≈ 93% produces diffused light, minimizing direct glare—well‑suited to offices and schools.

2) Thermal — lower heat transfer than glass

• Thermal conductivity: TW ~0.24 W/m·K (Nature Communications 2020) versus soda‑lime float glass ~0.9–1.0 W/m·K (NGA data). This implies reduced heat loss in winter and lower cooling loads compared with single glazing. [3]
• Model house results: replacing a single‑glazed roof with a 6 mm TW panel increased indoor temperature by ~+2.43 °C under the same heating power, reflecting a higher roof‑system R‑value. With a 2 mm panel, ΔT ~+0.81 °C.

3) Mechanics & user safety

• TW shows tensile strength ~92 MPa and toughness ~2.73 MJ/m³—it fails in a tough, non‑shattering manner (unlike glass), improving safety.

4) Fire safety & outdoor durability

• TW/MF (melamine‑formaldehyde): a “green,” scalable route; self‑extinguishing, Transmittance ~74% (1.2 mm); flame‑spread rate  50% of native wood.
• TW/PEAG (phosphate‑ester–PEG): T up to ~93%, haze ~98% while enhancing fire‑retardant metrics, demonstrating architectural viability. [4]
• Moisture/UV resistance: hydrophobic TW variants reach ~130° water contact angle and T ~90% after PDMS coating—friendly to hot‑humid climates.

Applications of transparent wood as a glass replacement in green architecture

Windows, glazed roofs, skylights & anti‑glare daylighting louvers

• TW provides high transmission (≈80–90%) with large haze → evenly distributed light, reduced glare, and more uniform illuminance than glass—ideal for skylights and daylighting ceilings/roofs in museums, libraries, and offices.
• Better insulation than glass (λ ~0.19–0.24 W·m⁻¹·K⁻¹ vs. glass ~1 W·m⁻¹·K⁻¹), reducing heat loss through daylighting elements and façades..

Energy‑saving curtain‑wall/façade systems

Used as the inner lite of double‑pane windows, energy modeling across 16 cold U.S. cities showed average savings of 38 MJ·m⁻²·yr⁻¹ (existing homes) and 23 MJ·m⁻²·yr⁻¹ (new homes) compared with DOE window baselines, thanks to lower overall heat transfer while still admitting beneficial winter solar gains. [5]

 Substrates for PV/solar windows & semitransparent photovoltaics

TW can serve as a substrate for semitransparent perovskite solar cells or enable edge‑integrated PV modules by leveraging its light‑guiding and diffusing behavior, paving the way for power‑generating windows that both daylight and harvest energy. [6]

References

[1] National Glass Association, “Physical and Mechanical Properties of Typical Soda‑Lime Float Glass,” 2023.  [Online]. Available: https://www.glass.org/
sites/default/files/2023-07/FM05-12_2023_Physical_Mechanical_Properties
_Typical_Soda_Lime_Float_Glass.pdf

[2] X. Song et al., “Engineered transparent wood composites: a review,” Cellulose,2023. [Online].Available: https://link.springer.com/article/10.1007/s10570-023-05239-z

[3] R. Mi et al., “Scalable aesthetic transparent wood for energy‑efficient buildings,” Nature Communications, vol. 11, 3836, 2020. [Online].Available: https://www.nature.com/articles/s41467-020-17513-w.pdf

[4] J. Liu et al., “Highly fire‑retardant optical wood enabled by PEAG coating,” Int. J. Minerals, Metallurgy and Materials, 29, 2022. [Online].Available: https://link.springer.com/article/10.1007/s42114-022-00440-3

[5] R. Mi, T. Li, D. Dalgo, C. Chen, Y. Kuang, S. He, X. Zhao, W. Xie, W. Gan, J. Zhu, J. Srebric, R. Yang, and L. Hu, “A Clear, Strong, and Thermally Insulated Transparent Wood for Energy Efficient Windows,” Advanced Functional Materials, vol. 30, p. 1907511, 2020. [Online].Available: https://www.fpl.fs.usda.gov/documnts/pdf2020/fpl_2020_mi001.pdf

[6] Y. Li, M. Cheng, E. Jungstedt, B. Xu, L. Sun, and L. Berglund, “Optically Transparent Wood Substrate for Perovskite Solar Cells,” ACS Sustainable Chemistry & Engineering, 2019. [Online].Available: https://pubs.acs.org/doi/10.1021/acssuschemeng.8b06248

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