Material extrusion of quaternary co-continuous biopolymers: A strategy for realizing lightweight cellular solids with high impact toughness

Cellular structures manufactured by material extrusion of biobased polymers that possess high mechanical efficiency offer an attractive strategy for fabricating sustainable engineering materials. Here, polylactic acid (PLA) modified by polyethylene oxide (PEO) is melt-blended with polyamide-11 (PA-11) and poly (ether-b-amide) (PEBA) and then extruded as a quaternary co-continuous PLA(PEO)/PEBA/PA-11 filament. Material extrusion is used to additively manufacture quaternary co-continuous biopolymeric samples that are tested under quasi-static and impact loads; the experimental results demonstrate impact toughness five times and twice as high as neat PLA and neat PA-11, respectively. Furthermore, a nearly 200% increase in the impact toughness has been obtained by optimizing the fabrication parameters such as line width and the number of shells, demonstrating that selecting appropriate fabrication parameters is the key to the cost-efficient and eco-friendly material extrusion technology to manufacture parts with mechanical performances similar to the traditional manufacturing processes like injection molding. The experimental results are supplemented by morphological analysis through scanning electron microscopy. In addition to the solid beams under the impact tests, cellular beams of hexagonal, rectangular, and re-entrant architectures are designed and fabricated out of the quaternary co-continuous polymers; the auxetic cellular beams reach a specific impact toughness (i.e., the ratio between impact toughness and density) of 128.6 J/m/(g/cm3), 44% higher than the solid beam counterparts. An Ashby chart is plotted to present impact toughness as a function of the densities for different polymers manufactured by material extrusion and injection molding, including the investigated quaternary co-continuous one. This research presents a path toward the low-cost material extrusion of lightweight and tough biobased engineering material.