The article “Lightweight Strong Moldable Wood Via Cell Wall Engineering as a Sustainable Structural Material,” coauthored by Forest Products Laboratory research scientists Junyong Zhu, Vina Yang, and Marco Lo Ricco, with lead author Prof. Liangbing Hu at the University of Maryland-College Park, was published in the Oct. 22, 2021 issue of Science Magazine as the cover article.
“In this work,” the article states, “we demonstrate how cell wall engineering can render wood foldable and moldable while simultaneously improving its mechanical properties – endowing wood with a structural versatility previously limited to plastics and metals.”
Junyong Zhu – or JY, as he is known among his colleagues – specializes in fiber and chemical sciences. One of his many research specialties includes the chemical modification of wood for advanced applications.
“It is well known that wood is an inherently sustainable material,” said JY. “Using wood stores carbon, to reduce its footprint. Moldable wood has the potential to replace many metals for structural applications, thereby reducing or eliminating the CO2 produced when processing metal materials.
“The seemingly impossible task of molding solid wood is based on an understanding of fiber,” JY continued. “Hornification (increased hydrogen bonding) of delignified wood takes place after drying, making wood cells shrink. The partial reversibility of the hornification for mildly dried wood, after a ‘water shock’ to make the shrunken wood cells partially recover, results in easily foldable wood.”
“The moldable wood can be used to make a variety of structures, including honeycomb and cylindrical three-dimensional patterns,” added JY. “The resulting molded product is also highly fungal resistant, despite the partial removal of lignin due to densification-created hydrogen bonding through drying, which reduces the accessibility of microbes to wood cellulose.”
Here is where FPL microbiologist Vina Yang, who works on the durability and wood protection research team, comes in. “My work on this paper was focused on fungal degradation on 3D wood to ascertain its durability and sustainability,” said Vina. “Any type of modified wood product involves the study of its properties, how to protect wood from fungal decay, or how recyclable the product is. To this 3D-engineered wood, it is durable and less degradable than natural wood by decay fungi to sustain its application for products.”
“Perhaps most remarkably, moldable wood is mechanically strong, due to its densification by drying,” added JY. Indeed, the article in Science features a photograph of a 3,500-pound hatchback sedan rolling over a molded wood structure – in this case, a honeycomb design, which emerges none the worse for wear.
Tasked with developing structural applications for the reconstituted wood materials of this research, Research General Engineer Marco formed densified beechwood and birchwood veneers into a laminated tube and corrugated decking.
“The dense packing of cellulose fibers makes this material stiff, like an aluminum alloy, but with less thermal heat transfer,” says Marco.
During production of the prototypes, Marco observed many manufacturing challenges and opportunities. “For example,” he explained, “veneers must be formed wet; therefore, shrinkage must be controlled while setting the laminating adhesives. Also, the differences in stiffness and strength are relative to parallel and perpendicular fiber directions and are more accentuated than untreated wood veneers.”
Based on this unique formability and high stiffness, Marco is investigating ways to manufacture 3D building components in order to advance the use of wood materials for specialized building cladding applications that value high stiffness, shallow member sizes, and reduced thermal bridging between interior and exterior spaces.
JY obtained his Ph.D. in Engineering from the University of California at Irvine. After 10 years as a faculty member at the Institute of Paper Science and Technology (now part of Georgia Institute of Technology), He joined FPL in 2003.
After earning her MS and MBA, Vina Yang jointed FPL as a microbiologist in 1985. Her areas of research also include molecular biology and biochemistry.
Research General Engineer Marco Lo Ricco, who works in the Engineering Properties of Wood, Wood-based Materials and Structures unit at FPL, joined the lab in 2019 and earned his Ph.D. in Engineering from the University of Wisconsin–Milwaukee for research and development of a new cross-laminated timber (CLT) rocking wall system, the same year. Marco’s research focuses on shaping wood materials, at a large scale, for structural performance.