Composite Advances Lignin as Renewable 3D Printing Material

Oak Ridge National Laboratory, Oak Ridge, Tennessee

Lignin is the material left over from the processing of biomass. It gives plants rigidity and also makes biomass resistant to being broken down into useful products. Researchers combined a melt-stable hardwood lignin with conventional plastic, a low-melting nylon, and carbon fiber to create a composite with just the right characteristics for extrusion and weld strength between layers during the printing process, as well as excellent mechanical properties.

Lignin chars easily; unlike workhorse composites like acrylonitrile-butadiene-styrene (ABS) that are made of petroleum-based thermoplastics, lignin can only be heated to a certain temperature for softening and extrusion from a 3D-printing nozzle. Prolonged exposure to heat dramatically increases its viscosity — it becomes too thick to be extruded easily. But when lignin was combined with nylon, the composite's room temperature stiffness increased while its melt viscosity decreased. The lignin-nylon material had tensile strength similar to nylon alone and lower viscosity than conventional ABS or high-impact polystyrene. The combination of lignin and nylon appeared to have almost a lubrication or plasticizing effect on the composite.

Scientists were also able to mix in a higher percentage of lignin — 40 to 50 percent by weight — a new achievement in the quest for a lignin-based printing material. Four to 16 percent carbon fiber was added into the mix. The new composite heats up more easily, flows faster for speedier printing, and results in a stronger product.

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