3D-Printed recycled polyethylene terephthalate (PET) sandwich structures – Influence of infill design and density on tensile, dynamic mechanical, and creep response

Abstract

Repurposing plastic waste is crucial to cope with the global population and rapid industrialization. Most plastic waste generated worldwide is mismanaged, leading to plastic pollution, landfill congestion, and microplastic contamination. Circular economy practices in the sustainable production and consumption of plastic are urgently needed to address these challenges, bringing plastics into closed-loop manufacturing and utilization. Additive manufacturing (AM) or 3D printing (3DP) have the potential to complement these efforts by facilitating on-demand, decentralized and flexible manufacturing using recycled plastics. In pursuit of circular materials for 3DP, this study investigates the influence of infill design and density on tensile and dynamic mechanical properties of 3D-printed recycled polyethylene terephthalate (rPET) sandwich structures. rPET filaments were produced using waste plastic bottles and were used for the 3DP process to produce sandwich structure coupons. In the first phase, the rPET filaments were tested for their mechanical properties revealing an average tensile strength of 111.99 MPa, failure strain of 1.20, and Young's modulus of 199.61 MPa, followed by the 3DP of tensile testing coupons with varying infill patterns (grid, tri-hexagon, octet, concentric, gyroid, and solid) and infill densities (25%, 50%, and 75%). The 3D-printed sandwich structures were evaluated for their dimensional stability and mechanical properties. All patterns demonstrated good dimensional stability, with minor variations from the CAD model. The mechanical properties of the concentric pattern at 50% infill (C50) stand out as the best among all infill types and patterns, exhibiting an average tensile strength of 34.65 MPa, failure strain of 0.067, Young's modulus of 464.32 MPa, and strength-to-weight ratio of 8.56 (S/W). In the final phase, the optimal infill pattern and density (i.e., C50) were also tested for their dynamic mechanical properties. The outcomes of this study will assist future research in developing robust 3D-printed parts using rPET, and the comprehensive approach presented in this study can be further adapted to develop novel recycled plastic waste-based composites for broader applications.