Oregon State University is one of two sites for the Wood-Based Composites Center (WBC), an industry and university cooperative research center funded by the National Science Foundation. The other is Virginia Tech University. The two institutions work with academic and industry partners to advance the science and technology of wood-based composite materials. The center completed a number of research projects in FY 2017 and FY 2018 that will lead to wood product innovations and improved performance.
Micron level 3D visualization of adhesive bonds in wood products
For the first time, researchers achieved a true characterization of the micro-structure of adhesive bonds in wood.
Laminated wood products, like glulam beams and plywood, rely on the integrity of adhesive bonds that are only a few microns thick. Adhesives penetrate the porous structure of wood. This project asked the question, ‘does the extent of penetration affect mechanical performance of the final product?’
Fred Kamke, director of WBC and JELD-WEN Chair of Wood-Based Composites Science, says the goal of the project was to observe how adhesive bonds perform when subjected to mechanical loads and moisture, focusing on the analysis on the adhesive bond.
Richardson Chair in Wood Science and Forest Products, John Nairn, created a mathematical model to predict mechanical performance of an adhesive bond based on its microstructure. Kamke and his graduate students collected the 3D microstructure data and used micro and nano x-ray-computed tomography to create 3D digital models of adhesive bonds. While wood is an extremely porous structure that readily absorbs adhesives, the researchers found that as much as 50 percent of the adhesive that penetrates the cell lumens may not contribute to bond strength. However, penetration of adhesive into the cell wall helps to stabilize the bond against the effects of moisture.
“Cell wall penetration improves the moisture durability,” Kamke says. “With this information, adhesive companies can improve their formulations and create adhesives to be engineered for a particular application, saving money for the manufacturers and improving performance of the products.”
Natural formaldehyde emissions from wood
Some adhesives, such as ureaformaldehyde, emit low levels of formaldehyde over their lifetime as they slowly decompose. Modern adhesive formulations and test protocols ensure these levels fall within the acceptable federal guidelines. However, as formaldehyde detection technology improves, the adhesive industry faces pressure to reduce formaldehyde emission levels.
Kamke says there are still many unanswered questions about formaldehyde.
“People wonder if formaldehyde is in their house,” he says. “Can it cause us harm? How much formaldehyde is OK? How low should emissions be? Although we don’t know have all of the answers to these questions, government regulations still need to be met.”
What researchers do know is that many substances, including human bodies, other animals and natural materials like wood, emit low levels of formaldehyde naturally.
Chip Frazier, Virginia Tech professor of sustainable biomaterials, wanted to learn exactly how much formaldehyde pure, natural, virgin wood does emit. The tests showed how formaldehyde levels in different wood species are affected by temperature change, and what formaldehyde levels are derived from wood itself.
“This data establishes a baseline level of source formaldehyde from wood, and will likely have a significant impact on future federal indoor air quality policy and the future of wood-based composite products, because just particleboard and fiberboard production alone is a $1.6 billion industry in the United States,” Kamke says. “This study and the resulting policy changes will have impacts on everyone involved in bonding wood with adhesives, and will have a positive impact on future indoor air quality across America.”
Outreach work continues
The WBC continues to educate the public through traditional classroom and online short courses. Seven online courses were added in 2016.
Kamke says the most popular is a basic course on wood adhesives that’s been running for 15 years.
“Our plan is to add more online courses,” Kamke says. “Enrollment is growing, and we are proud to continue to educate the producers and the public about the wonderful world of wood-based composites.”