Characterization of PLA feedstock after multiple recycling processes for large-format material extrusion additive manufacturing

Since the take-make-dispose model is leading to significant waste production and environmental impact, circular economy models have been spreading to reduce waste and resource depletion, rethinking the existing resource cycles. Plastic waste created environmental and economic concerns, requiring new recycling methods and strategies to preserve resources. This practice plays a key role in extrusion-based additive manufacturing, converting waste into recycled feedstock. Large-format additive manufacturing represents a promising way to scale up recycling strategies with granulated polymer feedstock, especially considering popular materials, i.e., PLA. However, thermomechanical degradation affects the quality of this secondary raw material, and these effects on large-format systems are scarcely studied. This work investigates the thermal, rheological, and mechanical properties of PLA feedstock for large-format additive manufacturing after multiple recycling processes, i.e., up to six. The effect of material degradation from multiple recycling processes was assessed through Gel Permeation Chromatography, Differential Scanning Calorimetry, flow stress ramp tests, tensile tests, and colorimetry. Some 3D printed parts were fabricated to assess the overall quality of the process, including pieces from potential applications. Lower effects of thermomechanical degradation were found compared to desktop-size 3D printers, mainly by cutting the reprocessing steps to produce secondary raw materials, i.e., making new filaments. Recycled granulate PLA feedstocks represent a potential alternative to virgin pellets for new applications in real-world contexts.