Circular Use of polylactide PLA in FFF Additive Manufacturing: Real-Waste Recycling Process Chain and Mechanical Property Window

• Recycling of real-waste PLA from industrial and community FFF AM activities • Demonstration of a decentralized process chain for mechanical PLA recycling • Mechanical properties mapped vs. reprocessing cycles and recyclate/virgin blends • Design-relevant strength and ductility limits identified for recycled PLA blends • Design windows derived for circular, application-oriented use of recycled PLA The proliferation of plastics across diverse product sectors has underscored the urgent need for sustainable waste management, as conventional plastics persist in the environment for decades. Additive manufacturing (AM) technologies, now widely adopted in both industry and private use, contribute significantly to decentralized plastic waste streams, primarily through prototyping and residual material accumulation. Despite recent efforts, most studies on recycling AM-derived polylactide (PLA) waste focus on clean, laboratory-origin scrap, single reprocessing cycles, or do not explicitly present a realizable recycling machinery concept. This study presents an end-to-end mechanical recycling process, using practical machinery to convert diverse, multi-sourced PLA waste from industrial and community AM activities into new filament. Mechanical properties are systematically evaluated through designed experiments, examining the influence of the number of reprocessing cycles and mixing ratios of recycled and virgin PLA. Results demonstrate moderate but manageable reductions in strength and stiffness with an increasing number of reprocessing cycles, supporting the technical feasibility of utilizing recycled PLA in fused deposition modeling processes. The methodology puts forward a realistic pathway for decentralized recycling, helping to close material loops and promote circular economy principles in the context of AM. Broadly, these insights contribute to more sustainable manufacturing strategies by reducing reliance on primary resources and supporting the objectives of the Sustainable Development Goals.