US researchers develop transparent wood, “surprised” by method’s effectiveness

05 Mar 2021 --- Research published in Scientific Advances has discovered a method of producing optically transparent wood. 

So far, the applications are limited to construction materials and light management devices. Gas barrier properties, mechanical strength and flexibility still remain obstacles before the transparent wood can be used in F&B packaging. 

If scaled up, however, the cost “should be reasonable,” corresponding study author Liangbing Hu tells PackagingInsights.

“These results are exciting. We are surprised by the effectiveness of the method.”

How does it work?
Scientists from the Department of Materials Science and Engineering at the University of Maryland, US, developed the method by altering lignin in wood, the polymer responsible for light absorption and material rigidity. 

H2O2 ink is printed on the wood surface using a brush. These areas turn white after UV illumination. 

The researchers created arbitrary transparent patterns on wood samples.The hierarchically porous structure of natural wood promotes fast H2O2 solution infiltration and UV light trapping, efficiently removing the light-absorbing chromophore of lignin. This reduced its light absorption to below 4 percent.

Infiltrating the epoxy yields transparent wood with various patterns made from natural wood along both the longitudinal and transverse directions. 

The patterns created along both directions suggest the high versatility and pattern designability of the method.

“My group reported transparent wood back in 2016. Of course, it requires further development for industry use,” Hu explains.

Eco-friendly wood
Compared with traditional solution-based immersion processes, the method requires fewer chemicals, less energy and reduces processing time.

This method preserves most of the lignin to act as a binder, providing a robust wood scaffold for polymer infiltration.

The obtained transparent wood (~1 mm in thickness) demonstrates a high transmittance (>90 percent), high haze (>60 percent) and “excellent” light-guiding effect over visible wavelength. 

Currently, Hu’s co-founded start-up called Inventwood is commercializing the product.

By Anni Schleicher