It has become an emerging challenge to produce on-demand free-form fabrication of soft materials that have complex shapes with precise dimensions and desired performance in specific environments. To combat this challenge, a team from the U.S. Department of Energy’s Oak Ridge National Laboratory developed a new technique for 3D printing feedstock that could enable a profitable use of lignin, the material left over from processing biomass.
Lignin is the material that gives plants their rigidity but also makes biomass resistant to being broken down into useful products.
Lignin as a material is often difficult to work with, because it chars easily, and can only be heated to a certain temperature for softening and extrusion from a 3D-printed nozzle, where prolonged exposure to heat substantially increases its viscosity. However, the researchers found a way to overcome these hurdles by combining lignin with nylon. This composite mixture’s room temperature stiffness increased while its melt viscosity decreased. The new lignin-nylon material also features a tensile strength that is similar to nylon alone, except with lower viscosity than conventional ABS or high impact polystyrene.
The researchers also conducted neutron scattering at the High Flux Isotope Reactor and used advanced microscopy at the DOE’s Office of User Facilities Center for Nanophase Materials Science at ORNL. According to Naskar, the lignin-nylon based material had a lubrication or plasticizing effect on the composite.
The researchers next created a mixture that is 40 to 50 percent of lignin by weight, a substantially higher percentage than what was previously used. The scientists then added four to 16 percent carbon fiber into the mixture to create a composite that will easily heat up and flow faster for quicker printing, resulting in a stronger product.
The study was published in Science Advances.