Scientists are constantly looking for ways to reduce industrial waste, with reuse for other purposes as one potential option. Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) have achieved this for an intractable biorefinery byproduct, lignin, through the development of a new composite material well-suited to additive manufacturing.
Lignin is what’s left over from the processing of biomass, researchers said. The material gives plants rigidity and also makes biomass resistant to being broken down. They described their work in an ORNL news release.
|Using as much as 50 percent lignin by weight, a new composite material created at the Department of Energy’s Oak Ridge National Laboratory is well-suited for use in 3D printing. Lignin is a byproduct of biorefinery. (Image source: Oak Ridge National Laboratory)|
Creating a Composite
ORNL scientists have combined a melt-stable hardwood lignin with other materials—conventional plastic, a low-melting nylon, and carbon fiber—to create a composite that has suitable characteristics for extrusion and weld strength between layers during the printing process, they said. The composite also boasts excellent mechanical properties, said Moe Khaleel, associate laboratory director for Energy and Environmental Sciences at ORNL.
Researchers published a paper detailing their work in the journal Science Advances.
“ORNL’s world-class capabilities in materials characterization and synthesis are essential to the challenge of transforming byproducts like lignin into co-products, generating potential new revenue streams for industry and creating novel renewable composites for advanced manufacturing,” he said.
The team’s work was not without its challenges, researchers said. Lignin is not an easy material with which to work; it chars easily and can only be heated to a certain temperature for softening and extrusion from a 3D printing nozzle. This is because prolonged exposure to heat dramatically increases lignin’s viscosity, making it too thick for useful extrusion, they said.
The team found success in developing a composite for 3D printing by combining lignin with nylon. Much to their surprise, this combination increased the composite’s room-temperature stiffness while decreasing its melt viscosity, Amit Naskar, the lead on the project, said.
Moreover, the lignin-nylon material had tensile strength similar to nylon alone and lower viscosity, in fact, than 3D-printing polymers such as conventional ABS or high-impact polystyrene, he said.
To understand why the material combination reacted like it did, the scientists studied its molecular structure by conducting neutron scattering at the High Flux Isotope Reactor and used advanced microscopy at the Center for Nanophase Materials Science at ORNL. What they found is that the combination of lignin and nylon “appeared to have almost a lubrication or plasticizing effect on the composite,” Naskar said.
Indeed, by studying the structural characteristics, the team was able to bolster the 3D printability of the materials, said ORNL’s Ngoc Nguyen, another collaborator on the project.
Specifically, they mixed in a higher percentage of lignin—40 to 50 percent by weight—a 4 percent to 16 percent carbon fiber. The lignin percentage represents a new achievement in the quest for a lignin-based printing, Nguyen said. The result is a composite that heats up more easily, flows faster for speedier printing, and results in a stronger product, researchers said.
The ORNL team has a patent pending on its lignin-nylon composite, and plans to continue its work to refine the material and find other ways to process it, researchers said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.
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