Benchmarking the Tensile Properties of Polylactic Acid (PLA) Recycled Through Fused Granule Fabrication Additive Manufacturing

To progress toward a circular economy of thermoplastic polymers, the adoption of 3D printers to make functional articles can facilitate distributed recycling. To this end, the mechanical degradation of polymers through multiple recycling cycles must be quantified. This work presents a procedure and benchmark dataset of tensile property degradation for polylactic acid (PLA) feedstock in multiple recycling passes with a fused granule fabrication process. To establish recycling with minimal processing (shredding and sieving), modifications were required to the granule feeding hopper of the 3D printer. Two distinct orientations were chosen to obtain tensile test coupons. These coupons were die-cut from machined 3D printed rectangular cross-section tubes, with one orientation along the bead (0°) and the other perpendicular to it (90°). Tensile properties are presented for 3D printed virgin material and one, two, three, and four passes of recycling. In terms of print orientation, the results indicate that samples pulled at 0° and 90° exhibited similar mechanical properties. However, there was an average decrease of 3.1% in ultimate tensile strength and a 1.7% decrease in elastic modulus for the samples along 90° orientation for all recycling passes. The samples along 0° demonstrated a 13.7% higher strain at fracture compared to those along 90°. Regarding the number of recycling passes, the findings suggest that the mechanical characteristics of PLA remain largely unaffected even after undergoing four recycling cycles. However, when the material is pulled in the direction of the bead, a 3.09% decrease in ultimate tensile strength is observed in the fourth recycling pass. The elastic modulus and strain at fracture did not exhibit a clear trend. It is important to note that the testing results display some variability, which can be attributed to a combination of stochasticity in the printing process and the preparation procedure employed.