Transparent wood offers a sustainable alternative to plastic, study shows

A study published in ‘Science of the Total Environment’ from the Institute of Wood Science and Technology in Bangalore, has shown the potential of transparent wood as a more sustainable replacement for forms of plastic –primarily due to the use of less electricity during its production stage.

Transparent wood
Transparent wood produced through chemical modification of delignified wood obtained from natural wood.
Titled ‘Life cycle assessment of transparent wood production using emerging technologies and strategic scale-up framework’, the study has also discovered the material suitability for large-scale production.

The study examined the full life cycle of transparent wood and contrasted it with polyethylene. It found that the degradation of transparent wood generates fewer environmental effects than polyethylene degradation and is also safer to produce.

From an ecological perspective, the report concludes that the production of transparent wood seems favourable and its findings indicate that industrial scale-up would generate less impact than laboratory-scale production.

It also showed that NaCIO2 (sodium chlorite) delignification and epoxy infiltration, the process through which the wood is made transparent, generates the minimum environmental impact than alternative routes for transparent wood production.

Delignification and epoxy filtration

The process includes the removal of lignin to be replaced with a transparent material through infiltration.

For the experiment, 1kg of natural ‘forest biomass’ wood was processed into wood slices and subjected to the delignification, infiltration and post-processing procedures that would be used if produced commercially. Sodium chlorite delignification and epoxy infiltration were tested against several other options.

‘Delignification’ is the process through which lignin – the polymer found in plant cells which gives wood its stiffness and prevents light from entering the cells – is removed. Infiltration replaces the lignin with epoxy, an artificial resin often used to make protective coatings and glues.

Sodium chlorite, which is often used in the pulp and paper industry, is applied to the wood to bleach and delignify it. It is then washed three times using distilled water, acetone, and ethanol, and dried. The delignified wood is then infiltrated with epoxy resin using polyoxypropylene used as a ‘crosslinker’ to join the polymer chains to each other. The post-production process includes oven-drying the wood slices.

The study shows that methods to produce transparent wood, which use sodium chlorite and epoxy infiltration, generate a minimal amount of ecological impact compared to other types of transparent wood production.

Potential applications

Transparent wood is already in use across several industries and the new study identifies it as a possible replacement for petroleum-based plastics including polyethylene, polypropylene, acrylic and polyvinyl chloride (PVC). This indicates possible applications in car windshields, transparent packaging, biomedical devices and more.

The material is already commercially available as a replacement for glass for which it provides a lighter, more durable and better-insulated alternative. Applications include glass in electronics. It is also currently used in other industries such as green energy and construction.

Speaking to Resource, co-author Prodyut Dhar, explained that transparent wood as a technology is still in the development stage for its usage as a plastic alternative at a commercial scale and that many industries are planning to invest in transparent wood as a potential plastic alternative.

Factors such as cost, process intensification, and waste disposal are identified in the report as critical parameters that are needed to be resolved for industrial-level production. The study also identifies that further research is needed into the recycling possibilities of transparent wood to determine its possible circular credentials.

Dhar continued that industrial-scale production of transparent wood will require further evaluation of environmental impacts to ‘find the potential hotspots’ and strategies for reducing the harmful ecological effects.

History of transparent wood

The wood was first developed in Germany in 1992 as a replacement for glass. German researcher Siegfried Fink was exploring methods to reveal the cavities in wood as part of his research on wood structures. He instead developed the method in which the pores of the wood are exposed, making the material transparent and able to be filled with epoxy for practical uses.

The Swedish Institute of Technology and the University of Maryland then explored methods of making transparent wood for commercial purposes. In 2016 the results of their work caught the attention of several engineers and architects looking for more durable and ecologically favourable alternatives to glass.

The new study on its applications as an alternative to plastic is likely to trigger the next phase of interest in this material. Previously, the material has failed to see widespread use due to a lack of funding and uncertainty around the scalability of production for commercial purposes.

Comments from authors

Speaking to Resource, Dhar said: “Currently, transparent wood is seldom produced by industries at a large scale. However, with the significant advancements in translational research and technology development, the adaptation of transparent wood for industrial usage is expected soon.

“We have received technology interest from renowned industries in this sector and are looking for more close collaboration for the successful translation of transparent wood at the commercial level.”