The Department of Energy’s Oak Ridge National Laboratory has developed a recipe for a renewable 3D printing feedstock that could result in a profitable new use for an intractable biorefinery byproduct: lignin.
The discovery, reported in the reputed journal Science Advances, is another achievement of ORNL in reducing the cost of bioproducts by new uses for lignin, which is the material left over from the processing of biomass. Lignin offers rigidity to plants and also makes biomass resistant to being broken down into useful products.
Amit Naskar, ORNL project lead, said, “Finding new uses for lignin can improve the economics of the entire biorefining process.”
Combining melt-stable hardwood lignin with conventional plastic, a low-melting nylon, and carbon fiber creates a composite that has just the right characteristics for extrusion and weld strength between layers during the printing process. The composite also has excellent mechanical properties.
The other characteristics of lignin include easy charring; unlike workhorse composites like acrylonitrile-butadiene-styrene (ABS) that are made of petroleum-based thermoplastics. Lignin can be heated up to a certain temperature for softening and extrusion from a 3D-printing nozzle. Its viscosity is increased dramatically when exposed to heat for a longer period and becomes too thick to be extruded easily.
Combining lignin with nylon results in an increase in the composite’s room temperature stiffness and at the same time decrease in its melt viscosity. The tensile strength of lignin-nylon material is similar to nylon alone and lower viscosity than conventional ABS or high impact polystyrene.
Naskar commented that the combination of lignin and nylon appeared to have almost a lubrication or plasticizing effect on the composite.
Ngoc Nguyen, who collaborated on the project at ORNL, stated, “Structural characteristics of lignin are critical to enhance 3D printability of the materials.”