Scientists from the Oak Ridge National Laboratory (ORNL) have developed a renewable 3D printing material that utilizes lignin, a type of organic polymer that is abundantly available as a biorefinery byproduct.
In nature, lignin is present in plants and algae and functions as a key structural material. In processing biomass, lignin must be removed because it makes it difficult to reduce and break down the organic materials before they can be turned into products.
Being able to use leftover lignin from the biorefinery process to produce 3D printing materials could offer a number of benefits. First, it could reduce the cost of bioproducts and feedstocks. Second, it could make the whole biorefinery process more economically efficient.
In developing the renewable feedstock, the ORNL researchers combined a melt-stable hardwood lignin with a conventional low-melting nylon and carbon fiber. The result was a 3D printable composite with good extrusion properties and which demonstrated good adhesion between layers when printed and excellent mechanical properties.
Typically, lignin can be difficult to work with because of its low heat resistance. Unlike ABS, lignin is only extrudable when heated to a certain temperature and risks becoming too thick to process if the temperature is too high or it is exposed to heat for too long. The research team found a solution to this problem by combining lignin with nylon.
When paired, the materials demonstrated an increased stiffness at room temperature and its melt viscosity decreased—something the scientists found surprising. Additionally, the lignin composite displayed a tensile strength similar to just nylon and a lower viscosity than traditional ABS or high impact polystyrene.
Extensive testing—including neutron scattering at the High Flux Isotope Reactor and advanced microscopy at the Center for Nanophase Materials Science—revealed that the combination of lignin and nylon had a lubrication or plasticizing effect on the material and that the characteristics of lignin enhanced the printability of the material.
Later in the development process, the ORNL researchers were able to successfully mix a greater percentage of lignin (40 to 50% by weight), which marked a breakthrough in the creation of a lignin-based printing material. In addition to the lignin and nylon, the research team also added 4 to 16% carbon fiber to improve the strength of the material. The resulting composite “heats up more easily, flows faster for speedier printing and results in a stronger product.”
Moe Khaleel, associate laboratory director for Energy and Environmental Sciences, explained: “ORNL’s world-class capabilities in materials characterization and synthesis are essential to the challenge of transforming byproducts like lignin into coproducts, generating potential new revenue streams for industry and creating novel renewable composites for advanced manufacturing.”
The innovative lignin-based composite is still in development as the ORNL researchers are further refining the material’s properties and experimenting with other ways to process it. The material is currently awaiting patent approval. The full study detailing the material was recently published in the journal Science Advances.