Searching for Natural Resistance through Infrared Spectroscopy

Closeup view of Western Junipier – By Syntheticmessiah – stock.adobe.com

Durability is one of the most important building qualities needed for timber products. It is measured by how well wood species can resist fungal decay or insect damage.

Some trees are just naturally better at resisting rot.

And as market and public demand increases for more naturally resistant wood that hasn’t been treated with potentially harmful preservatives, researchers are looking to the trees for answers.

That’s what PhD student Shahlinney Lipeh from Forest Research Institute of Malaysia (FRIM) in collaboration with Forest Products Laboratory (FPL) researcher Mark Mankowski and a group of international researchers are looking for through infrared spectroscopy.   

Their research, “Relationship between attenuated total reflectance Fourier transform infrared spectroscopy of western juniper and natural resistance to fungal and termite attack,” was published in Holzforschung journal.

Mankowski’s lab hosted Lipeh for a week to help with the termite portion of her research. Her work with the lab was part of her PhD project.

And what were they specifically looking for?

Extractives—naturally occurring compounds in trees that help them resist fungi and insects. These compounds act as either toxicants, repellents, or antioxidants. Depending on the tree species, they can make up between 1 to 5 percent of total mass. However, there are some extraordinary tropical species that have up to 30 percent extractives in their bark and heartwood. 

In essence, extractives are a tree’s natural biological armor.

The team took a close look at Juniperus occidentalis or western juniper. It has several alcohol compounds that make it especially resistant to termites and fungi.

However, there are some major hurdles for today’s current durability testing. It is a labor-intensive and time-consuming process and is limited to a small sample size.

And the problem is, a small sample size may not be an accurate durability representation of an entire species of trees.

In their article, the researchers explained, “There is a need for more rapid techniques that can properly classify the durability of large numbers of samples rather than a presumed durability based on limited testing.”

Enter infrared spectroscopy.

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) is used to discover the unique chemical signature of a material. When infrared is pointed at a material’s surface, molecules can be seen vibrating at their own signature frequency. When pointed at a tree, infrared spectroscopy could be a way to determine a tree’s extractive content.  

They theorized that the extractive compounds and percentage a tree contained played a role in its durability against termite and fungal attack. And ATR-FTIR was their Sherlock spyglass to find that durability.

In the lab, termites and decay fungi were bottled in separate glass jars with western juniper testing blocks. At the end of their incubation periods, the test blocks were measured with ATR-FTIR. They found that western juniper indeed does have super-strength resistance to fungi and termite attack, however, they weren’t able to establish a link to extractive percentage with durability.

Although their end results were mixed, some very important discoveries came out of their research.

Mankowski found “Our termite feeding test results were not as cut and dried as we expected indicating the variability of wood as a feeding substrate.”

And as for ATR-FTIR, researchers could one day analyze a live tree for durability without having to fell it.

“The variability in wood resistance to fungi and insects poses problems in the current durability classifications. With the recent development in infrared spectroscopy and powerful statistical methods for spectral data analysis, there is potential to create a rapid, non-destructive tool to access wood durability,” stated Lipeh.

That prospect is tantalizing.

“But there is still a lot of work that needs to be done, especially in terms of its sensitivity in the field and how moisture may affect the readings,” explained Lipeh. Still, she believes that the possibility of using spectroscopy on a live tree to gauge its durability may one day be a reality.

Mankowski is already busy with a new extractive research project.

“We are currently working with Dr. Fred Eller at Agricultural Research Service (ARS) in a collaborative project examining cedar wood oil as a potential extractive based wood treatment with good results against termites and decay,” Mankowski said, “The potential use of extractives and their derivatives is highly important. They may be a great use for invasive tree species that contain bioactive compounds or wood waste from current timber species that contain extractives.”

To find out more about the amazing advancements our scientists are making, visit the Forest Products Laboratory at: https://www.fpl.fs.fed.us/