International. Researchers at Aalto University develop a way to convert a wood waste material into a bio-based transparent film that can be used for anti-fog or anti-reflective coatings on vehicle glass or windows.
In addition to offering an alternative to the toxic synthetic materials currently in use, this approach transforms a waste product into a valuable carbon sink.
Lignin is an abundant waste product in paper and pulp production that is very difficult to process, so it is usually burned to produce heat.
"Optical coatings should be transparent, but so far you can see even quite thin lignin particle films. We knew that small particles appear less cloudy, so I wanted to see if I could make films of invisible particles by reducing particle size to a minimum," said Alexander Henn, PhD researcher and lead author of the study.
The team used acetylated lignin and developed an improved way to esterify it in a reaction that takes only a few minutes and occurs at a relatively low temperature of 60 degrees Celsius.
In addition to anti-fog and anti-reflective coatings, the new approach also makes it possible to fabricate colored films from lignin nanoparticles. By controlling the thickness of the coating and using multilayer films, the team created materials with different structural colors.
"Sahar Babaeipour's efforts were key to controlling the photonic properties of the particles," Henn continued, adding that researchers Paula Nousiainen and Kristoffer Meinander brought their expertise in lignin chemistry and photonic phenomena, respectively, helping the team make sense of their results and use them effectively.
According to the team's feasibility study, the ease of reaction and its high throughput mean that it could be cost-effectively scaled up to industrial levels.
"Lignin-based products could have commercial value and simultaneously act as carbon sinks, helping to alleviate current dependence on fossil fuels and reduce carbon dioxide emissions," said Professor Monika Österberg.
"High value-added applications like this are important to boost the valorization of lignin and move away from using it solely as a fuel."
