Mechanical property degradation of additively manufactured polylactide produced from no-blend recycled feedstock

This study investigates how feedstock sources and printing parameters influence the tensile properties of polylactide (PLA) produced by fused filament fabrication (FFF), with special attention to differences between virgin and recycled feedstocks. A full factorial experimental design examined 12 factor combination groups created by varying the recycled status of the feedstock, nozzle diameter, and infill raster angle. 72 microtensile specimens were fabricated and tested in accordance with ASTM D1708 at two crosshead speeds. Tensile strength, elongation at break, Young’s modulus, Shore D hardness, and density were recorded for each specimen. Analysis of variance (ANOVA) revealed that feedstock recycled status and nozzle diameter significantly affected UTS at both testing speeds, demonstrating that these parameter-to-property trends are robust across strain rates. Elongation at break showed significant effects only at the slower testing speed, indicating strain rate sensitivity. Young’s Modulus values were slightly lower at the slower speed, though valid moduli could not be obtained for twice-recycled samples tested at the faster speed. The factorial design also revealed several significant two- and three-way interactions. Overall, recycled feedstock, nozzle geometry, and infill orientation each measurably influence tensile behavior, yet recycled PLA can still provide reliable mechanical performance when key printing parameters are controlled.