Marshall Swearingen, MSU News Service
BOZEMAN — Tiny air pockets interspersed in wood's cellular structure are what cause it to float. They also produce the satisfying crackle when wood is burned. But when wood is turned into structural lumber — the material's most widespread and valued use — the air pockets become a source of weakness.
That's why a Montana State University researcher is trying to fill the tiny voids — using equally tiny particles — in order to improve the material's strength, contributing to a trend of using wood instead of metal for beams in high-rises and other large structures.
"This is the first study of its kind," said Dilpreet Bajwa, professor in the Department of Mechanical and Industrial Engineering in MSU's Norm Asbjornson College of Engineering, who is leading the project. "Nobody has done this before."
The tiny particles in this case are cellulose nanocrystals, made by breaking down wood or crop biomass. Cellulose, the main ingredient in paper, is what gives plant cells their stiff structure. By processing woody material and separating out the cellulose, the result is hard crystals that are so small they're measured in nanometers, or billionths of a meter.
"The crystals are as strong as Kevlar," the material used to make bulletproof vests, Bajwa said. And because they're so small, the cellulose particles can penetrate and fill the air pockets.
In his lab, Bajwa's team treats the wood with a chemical solvent that dissolves resin that may be clogging the wood's pores. Then they put the wood samples in an airtight chamber, creating a vacuum that sucks out the solvent. Finally, they inject the nanocrystals, which pack into the pores and solidify.
The preliminary results have been promising. Bajwa found that nanocrystals doubled the stiffness of one sample and increased the wood’s structural strength by 40%. "That's when we said 'Wow, this might really work,'" he said.
Bajwa's team won a $180,000 grant from the U.S. Department of Agriculture in December for further testing and to experiment with new techniques, like using high-frequency sound waves to help the nanocrystals penetrate the wood.
Shawn Heilman, a senior majoring in electrical engineering, is one of two undergraduates working on the project, doing tasks like processing the samples in the pressure chamber. "It's really rewarding to put in the work on a project like this, where we're coming up with a new solution," he said. "It's not something where you can just find an answer in a textbook, you have to search around, do tests and draw your own conclusions."
Besides increasing the strength of wood, the nanocrystal treatment could help reduce the natural variability that wood has even within a single tree, according to Bajwa. And it could allow for structural use of what would otherwise be considered marginal timber, including small trees removed as part of forest thinning projects.
Altogether, the new technology could significantly contribute to growing interest in cross-laminated timber, in which smaller boards are sandwiched together to form large structural members for buildings as large as high-rises, Bajwa said. The nanocrystal treatment would help ensure that timbers would have the uniformity and strength needed to replace traditional steel beams.
Most of the MSU research will be conducted in Bajwa's lab, but the project will seek collaboration with a local wood products company in Montana to begin translating the science into commercial products. "It's very exciting," Bajwa said. "This could open a whole new frontier for wood."
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