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The decentralized production associated with material extrusion additive manufacture (MEX) has been proposed as an ideal path to increase the circularity of plastics through direct recycling. Although multiple studies have reported on the 3D printing of various recycled plastics, variability in recycled materials, in particular post-consumer waste, challenges the direct extension of these results into production through MEX. Here, we demonstrate filament fabrication and printing of post-consumer polypropylene (PP), where the PP is sourced from clear, cold drink cups from three large international food service and beverage retail chains to provide well defined plastic waste that is perfectly sorted for recycling. These sources for the recycled PP were selected due to their ready availability to enable the results to be directly applied for hobbyist printing, blow molded products to provide good mechanical performance, and the clarity of the PP that suggests formulation design to minimize the PP crystal size. Despite the similarities in the end use product and their physical appearance, the source for the PP impacted the mechanical properties and the visual appearance of the printed objects. These differences can be directly traced to the rheological properties and oxidative stability of the PP at conditions relevant with the print process. These results clearly illustrate differences in initial formulation design and branding details, even when the product is for the same application, impacts the performance of recycled plastics in AM. The high viscosity associated with the PP from blow molding leads to requirements for higher extrusion temperatures for printing. The combination of high temperature and shear during extrusion process of 3D printing degrades the recycled PP. For circularity with MEX with recycled PP, one needs to consider the evolution in the properties of the polymer. Rheological details of recycled plastics are critical to selection of processing conditions and performance of MEX parts. Reporting of rheological data of recycled plastics and these properties after printing is critical to enable translation towards circular 3D printing of recycled plastics.
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This content will become publicly available on December 1, 2026
A General Ink Formulation Strategy for Transforming Recycled Metals into Printed Electronics
One key challenge preventing commercially viable domestic recycling lies in the gap between the high costs of the recycling process and the limited value of recycled raw materials. While additive manufacturing (AM) has the potential to narrow such a gap by converting waste materials into value‐added products through the remanufacturing process, the ink formulation for waste materials remains a formidable task due to poor processability. In contrast to high‐temperature metallurgy (1000–2000 K), a facile approach is developed to convert waste metals (e.g., stainless steel machining chips) into printable and stable inks for 3D‐printed electronics at near room temperature. Moreover, the binder chemistry and percolation mechanism are studied, enabling sustainable ink formulation with non‐toxic solvents and environmentally benign polymers (i.e., no fluorinated polymer). The ink formulation is generalizable for various functional materials, including other metals, carbons, and clays. As a proof of concept, a 3D‐printed strain sensor from recycled stainless steel (SS) chips is demonstrated, which is shown to effectively identify even minor strains from the human body, highlighting potential wearable applications.
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- PAR ID:
- 10681336
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials Technologies
- Volume:
- 10
- Issue:
- 24
- ISSN:
- 2365-709X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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