Recycling Commodity Plastic Waste for Vat Photopolymerization 3D Printing of High-Performance Polymeric Composites

Recycling plastic waste is crucial for reducing environmental harm and conserving resources. However, current methods face challenges, such as the need to sort different polymers, limited compatibility across plastic types, and reliance on hazardous chemicals in chemical recycling. This study introduces a sustainable additive manufacturing approach by repurposing commonly discarded thermoplastics, including polylactic acid (PLA), polyamide (PA), polypropylene (PP), polyethylene terephthalate (PET), and 3D-printed thermosets, as feedstock for digital light processing (DLP) 3D printing. Using cryogenic milling, these polymers are transformed into fine powders and incorporated into a photocurable resin to create polymeric composites. The addition of solid plastic particles presents two main challenges: increased resin viscosity and UV light blocking. These issues affect both printability and mechanical performance. To address viscosity, a heated vat system maintains the resin at ∼55 °C, improving flow without compromising the process. Additionally, UV light is blocked during photopolymerization, leading to incomplete curing and a 50% reduction in modulus compared to neat resin. A dual-curing approach mitigates this by combining UV-curing via a photoinitiator with thermal annealing via a thermal initiator, ensuring full polymerization and restoring mechanical strength. This strategy yields an ∼250% increase in modulus for high-loading samples, aligning with theoretical predictions. The study demonstrates broad applicability across various powder–resin combinations, highlighting its adaptability in diverse material contexts. Overall, this work establishes a pathway for incorporating a wide range of recycled plastics into high-performance 3D-printed composites, advancing both the sustainability and the functional potential of additive manufacturing.