Transparent wood could help us end our reliance on petroleum based plastics

Researchers at the Indian Institute of Technology (IIT) have found that transparent wood had a significantly lower environmental impact and was five times more efficient than glass, which could contribute to reducing energy costs, a study revealed.

According to the United Nations Environment Program, 400 million tons of plastic are generated annually, most of which comes from single-use plastic. While countries are making progress in reducing this waste through paper bags and straws, there are also applications where the properties of plastic are necessary.

Transparent wood is an alternative for such applications and is highly preferred since it prevents the harm of petroleum-derived plastic products. German scientist Siegfried Fink first manufactured transparent wood in the year 1992, and over the past three decades has been significantly improved by other researchers as well.

How is transparent wood made?

In its natural form, wood is opaque. However, researchers have found that removing lignin, a naturally occurring biopolymer that provides structural support for the plant tissue, can make it transparent. To do so, the wood is soaked in a warm solution consisting of multiple chemicals such as sodium hydroxide, sodium sulfite, and sodium hypochlorite, followed by boiling it in a hydrogen peroxide solution.

This removes the lignin completely and turns the wood white. However, the space that was occupied by lignin needs to be filled up to retain the structural integrity. This process, referred to as infiltration, is done by using a resin such as epoxy or Poly methyl methacrylate or PMMA under temperatures of 185 Fahrenheit (85^oC).

The final product can have as much as 90 transparency, unlike glass, is shatterproof. More importantly, it is more biodegradable than glass or plastic.

Life cycle assessment of transparent wood

While transparent wood isn't commercial yet, it has been deployed in a wide variety of applications ranging from construction to energy storage, making flexible electronics and packaging.

The researchers at IIT conducted a life-cycle analysis (LCA) of transparent wood to determine the environmental impact of its production and end-of-life (EOL) cycle. The study found that using hydrogen peroxide for delignification, followed by using epoxy for infiltration, was the most eco-friendly.

The approach has "24 percent less global warming potential" and "15 percent less terrestrial acidification" compared to another method that used sodium chlorite for delignification and PMMA for infiltration, the researchers wrote in a paper. When scaled up for industrial production, the former method would lower electricity consumption by as much as 98.8 percent.

The EOL analysis showed that transparent wood reduced ecological impact to the order of 10⁷ compared to polyethylene, paving the way for it to be commercially adapted to replace the petroleum-based material.

The research findings were published in the journal Science of The Total Environment

Abstract

Transparent wood, a sustainable material, holds the potential to replace conventional petroleum-based polymers because of its renewable and biodegradable properties. It has been recently used for construction, energy storage, flexible electronics, and packaging applications. Life cycle analysis (LCA) of transparent wood would provide the environmental impacts during its production and end-of-life (EOL). The cradle-to-gate analysis of transparent wood suggests that sodium hydroxide, sodium sulfite, hydrogen peroxide-based delignification (NaOH + Na2SO3 + H2O2 method), and epoxy infiltration lead to the lowest environmental impacts. It generates approximately 24 % less global warming potential and about 15 % less terrestrial acidification than sodium chlorite delignification and polymethyl methacrylate (PMMA) infiltration. The modelled industrial-scale production has lower electricity consumption (by 98.8 %) and environmental impacts than the laboratory scale (28 % less global warming potential and approximately 97 % less human toxicity). The EOL analysis of transparent wood showed reduced ecological impacts (107 times) in comparison to polyethylene, suggesting that it can be commercially adapted to replace conventional petroleum-based materials.