Upcycling potential of the material extrusion process: a focus on the fused deposition modeling and beyond

This study reviews the transformability potential of the Material Extrusion (MEX) process as a possible contributor to circular manufacturing by facilitating plastic upcycling and biomass valorization. MEX makes the use of recycled thermoplastics as feedstock and their blending with reinforcement or functionalizing fillers feasible, opening ground-breaking routes to the development of sustainable composite materials. Biomass waste, as filler, can reinforce the thermoplastic matrix but also provide antibacterial, regenerative, and wound-healing properties to the composites. Examples of already developed materials, potential applications, and a focus on four thermoplastic materials (i.e., Polylactic Acid - PLA, Polyhydroxyalkanoates - PHAs, Polycaprolactone PCL, and Polyvinyl alcohol - PVA) are provided. The discussion focuses on the Fused Deposition Modeling technique and includes the Fused Granulate Fabrication technique. The challenges persisting in material design, fabrication, and printing, limiting functionality and performance, are highlighted to stimulate further research into optimizing all steps of the upcycling process. The contribution of Artificial Intelligence (AI) in pursuing this target, by supporting MEX-related workflows, from optimizing printing parameters and predicting material performance to enhancing the reliability of recycled feedstocks and enabling more effective circular material cycles, is also analyzed.