Bending Stiffness of Recycled Polylactic Acid in FDM Printing: a Cantilever Beam Deflection Study

This study examines the closed-loop recycling of 3D-printed components that have reached the end of their service life within a student robotics context. While additive manufacturing is naturally material-efficient, many functional parts lose their utility following seasonal competitions, such as the FIRST Tech Challenge (FTC). Polylactic acid (PLA) was selected for this investigation due to its prevalence in educational institutions. To evaluate the feasibility of local material recovery, disposed PLA parts were shredded and re-extruded into filament using a desktop extrusion system, and printed into cantilever beam specimens along with a virgin PLA control group under identical settings. Mechanical integrity was evaluated by dead-weight cantilever deflection testing over five load levels (300-500 g). Recycled PLA specimens demonstrated a mean effective bending modulus of 0.841 GPa – a 31.5% reduction relative to the 1.228 GPa measured for virgin PLA (t = 21.2, df = 37, p < 0.001). This reduction is substantially larger than the changes reported for tensile modulus of recycled PLA in the closely related literature (at most a few percent, and in some 3D-printed process chains a slight increase), which is attributed to the amplified effect of inter-bead bonding defects on structural (bending) stiffness at the low (15%) infill density used for lightweight FTC components. These findings confirm that single-cycle mechanically recycled PLA retains sufficient structural stiffness for non-impact, stiffness-governed robotics applications. However, components subjected to active collisions require further mechanical characterization before recycled material can be broadly recommended. Overall, this work demonstrates a low-cost, low-resource pathway for closing the material loop in educational robotics and reducing reliance on external supplies.