Transparent wood-based material with high tensile strength

Technical Summary

First, the researchers took Hinoki (Japanese cypress) wood, a material widely used in construction of Japanese shrines and temples, and chemically removed lignin and hemicellulose from it in a process known as delignification (Fig.1). This resulted in white-colored porous material composed of tube-like channels, which is the inherent micro-structure of wood (Fig.1). Then the researchers functionalized the delignified wood by introducing carboxylate (COOH) and phosphate (PO4) functional groups. This procedure, known as functionalization, improves the deposition of calcium carbonate (CaCO3) in wood micro-channels, which is the next step in the production, i.e. biomineralization (Fig.1).

Figure 1. Schematic summarizing the production process of transparent food.

For this step, the functionalized wood is immersed into a biomineralization solution to introduce various ion precursors. The delignified and functionalized wood has abundant hydroxyl/carboxylate/phosphate functional groups which promote the formation and growth of crystal forms of calcium carbonate (CaCO3), known asaragonite crystals, along the direction of channels during biomineralization process (Fig.1).The biomineralization followed by freeze-drying leads to self-assembly of aragonite layers along the wood channels with formation of micro-architecture similar to the one observed in seashells and pearls. Importantly, in comparison to natural biomineralization which takes months or years, only 14 days was sufficient for biomineralizing the wood.

Finally, the researchers placed the biomineralized wood in between two steel plates of a hot press at 60ºC and kept it under pressure for 24 hours. The densification process resulted in formation of unique micro-architecture and induction of new intermolecular interactions between the inorganic crystals and organic layers. The wood cell walls collapsed upon densification with entrapment of calcium carbonate crystals in their inter-layers with reduction in material thickness by 90%. The obtained material exhibits high transparency, strength, and toughness.

Technology Readiness Level

3

Potential Applications

Building materials

Interior materials

Photonic and electronic devices

Possible Collaboration Mode(s)

R&D collaboration

Licensing

MTA

Patent No

WO2023/027074

Inventor(s)

Hiroshi Kamitakahara, Ph.D.

Prodyut Dhar, Ph.D.