Spruce bark has been considered a secondary material in the forest industry. It has been burned for energy and used as mulch in outhouses. However, a new study suggests that it could be used to create highly processed high-tech products.
The secret lies in molecules known as stilbenes. These aromatic hydrocarbons constitute between 1 and 10% of the weight of the bark, and they are in a liquid form bound with sugars.
“Stilbenes are natural antioxidants which help trees protect themselves against wood-decay fungi and pests,” explains Kristiina Wähälä, professor of organic chemistry.
These protective characteristics could now enable several commercial applications. Stilbenes could be used to keep termites away or to protect and treat wood instead of traditional chemicals.
“Stilbenes are potent protective substances, so they could probably be used in lower concentrations than the traditional chemicals,” says Wähälä.
There are also efforts to create new cancer medications from stilbenes. Since they protect wood cells against the progression of rot, they could similarly protect human cells against the progression of colon cancer, for example.
Wähälä’s group has been preparing synthetic stilbene drug candidates for some time in their laboratory. The candidates have then been sent to Meilahti to be further tested by drug developers. However, building a molecule from scratch is a slow, expensive process.
During the past few years, Wähälä’s group has been developing a method known as hot water extraction which allows the retrieval of large molecules from the spruce bark intact.
“It’s economical. This way we get the core of the stilbene molecule and can then add more components to it in the laboratory as necessary.
So far, creating products from stilbene has commercial potential that may or may not be realised. There is a grey area between basic research and the product development process which will create a commercial application within a few years, and that area has practically no avenues for funding.
“We’re known as a country of forestry and wood, and this would be an opportunity to use material usually thought of as waste to generate expensive specialty products,” Wähälä points out.
Finland’s forests are numerous, harbouring plenty of stilbene. Our spruce trees have more stilbene in their bark than their Central European counterparts.
“In the north, the slow growth of the trees and the unforgiving environment mean that more aromatic substances are generated in the trees than in the south. The same goes for berries,” says Tytti Sarjala, special researcher from the Finnish Forest Research Institute.
Some of the predictions for the commercial potential of stilbenes are highly ambitious. The substance has been found to be photoactive. It absorbs energy from light and changes from a trans-form to their cis-form, becoming an isomer.
This isomerisation feature could make stilbenes suitable for use as marker substances, energy harvesting or as building material for the semiconductor industry.
“The switch between two energy states is basically a similar mechanism to the one found in silicon. By binding silicon with stilbene, it may be possible to enhance the semiconductor properties of silicone. This may facilitate the development of nanotechnology where everything has to be smaller and more effective,” says Harri Latva-Mäenpää, a Finnish Forestry Research Institute researcher who is studying in the Doctoral Programme in Chemistry and Molecular Sciences.
A more commonplace application of the ability of the stilbenes to absorb solar radiation could be sun creams in the future.
“We believe stilbenes protect plants from destructive UV radiation. Such properties could be beneficial for humans,” says Tytti Sarjala.
Spruce is used as raw material for paper and board in such vast quantities that the industry produces more than enough bark to fuel the stilbene industry. Once the stilbenes have been extracted, the remaining bark can still be burned or used as mulch.
But how will the extraction of stilbenes impact the effectiveness of bark mulch in outhouses? The researchers laugh – this hasn’t exactly been their main research topic.
“I think the extraction of stilbenes will make the mulch even better for outhouses. Stilbenes protect the bark from microbes, so without them, composting is likely to occur faster,” Sarjala believes.
This article was published in Finnish in the 6/2014 issue of Yliopisto magazine.