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Improvement That Wood Be Hard to Ignore

UMD NRRI Scientist Matthew Aro
NRRI Research Scientist Matt Aro and the wood thermal modification kiln

Relieving an overexploited resource

Natural Resources Research Institute (NRRI) Research Scientist Matt Aro and his colleagues are using thermal modification, the method of heating wood in a specialized kiln at different temperatures and pressure levels, to ‘upgrade’ the performance of under-performing wood species. Doing so, without using any additives except heat, may be a way to create more environmentally conscious wood products.

Although different species of wood may seem roughly equal from an outside perspective, certain species of trees are more useful than others. Various species of cedar, for example, are widely used as construction supplies due to their durability, stability, and moisture resistant qualities. Varieties of cedar have also historically been overexploited because of these desirable properties.

By heating and pressurizing wood at the right temperature in a specialized kiln for anywhere from 14 to 20 hours, the research team can improve upon many valuable performance properties. This can have the effect of making historically undervalued and underutilized wood species perform similarly to other high-performing species.

"Thermally modified wood is more dimensionally stable when exposed to water, which means that it is harder to make it bend or warp when exposed to moisture through precipitation or high humidity," Aro explained. "It also has higher biological durability. Fungi have a harder time damaging thermally modified wood because, in part, there are fewer sugars (i.e., food) in the wood."

Thermal modification is not a new technology, having been used by companies in Finland, Germany, and Denmark for a few decades. “This process is relatively new to North America,” Aro said. “Thermal modification has been around in European countries such as Denmark since the mid-1990s, but only recently have manufacturers been experimenting with the process here.” What is new are the practical applications of thermal modification for the Northland.

Building (and opening) new doors

NRRI received a $600,000 grant from the National Science Foundation to expand their research on thermal modification. "What we are working on right now, is experimenting with thermal modification on engineered wood products. This includes stuff like plywood and laminated veneer lumber, which is basically made from combinations of different kinds of wood particles, flakes, or veneers glued together."

  Aspen boards. The darker ones have been thermally modified.
  Aspen boards, both thermally modified (right) and not (left)

This research has the potential to advance the development of engineered wood products with drastically improved dimensional stability, resistance to biodeterioration and weathering, extended service-life, and reduced environmental impacts. This may increase the use of wood, a renewable, sustainable, and carbon-storing material.

The National Science Foundation provided NRRI with a further $120,000 to foster the development of thermally modified engineered wood products internationally. The Wood Science and Forest Products department at Lakehead University in Thunder Bay, Ontario, is working with NRRI to make Eastern Larch wood more attractive to manufacturers and production companies. Eastern Larch grows in some areas of Minnesota, and coast to coast in Canada, but its classification as a softwood makes it more difficult to market for certain applications.

Given the potency of this process, it may seem tempting to view thermal modification as a catch-all capable of turning useless wood species into perfect construction material. Aro discourages that viewpoint.

"Part of the reason that it has taken a while for the thermal modification process to catch on in the States is that, in the past, people may have overstated the value of thermally modified wood a little bit," Aro admitted of the process. "One thing to keep in mind about construction is that there are no silver bullets – every building material has its upsides and downsides. Certain kinds of wood will always, as a general rule, perform better than others. But by doing this research, we can fill that gap slightly and find uses for local wood. In the process, we'll stimulate our region's critical forests products industry."

Finding a home, building a future

One place where the thermally modified wood has already found a home is northern Minnesota's Sax-Zim Bog, a location famous among wildlife enthusiasts as a haven for a wide variety of birds, animals, and plants. "The husband of Sue French, a scientist in our research program, was talking with some of the 'Friends of Sax-Zim Bog' folks, people responsible for the land. During their discussion the idea of building a visitor's center from local products came up, and it was proposed that they use our thermally modified wood. We thought that it would be great, and when they saw the gorgeous color that thermal modification treatment gives the wood, they agreed, and we treated 1200 board-feet of wood. It was a great way to showcase the technology, and it turned out looking great."

Those who are interested in seeing the thermally modified wood in action, as well as birds and other wildlife, should visit the Sax-Zim Bog's website or its new visitor center which opened on March 8 and is constructed from local, sustainable materials. Click here to visit the NRRI website.

Written by Zach Lunderberg, Mar. 2014


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