Intelligent Circular Polymer Additive Manufacturing: From Recycling Pathways to Lifecycle Engineering

Polymer Additive Manufacturing (AM) offers substantial opportunities for material-efficient and distributed production, yet its transition towards genuine circularity remains constrained by cumulative material degradation, fragmented recovery strategies, and the limited integration of lifecycle, environmental, economic, and industrial considerations. This critical systematic review examines circularity in polymer AM beyond conventional end-of-life recycling by integrating material behaviour, manufacturing-induced evolution, degradation mechanisms, lifecycle performance and value retention, recovery pathways, and sustainability assessment within a unified systems perspective. Following a PRISMA-based selection process, 3214 records were progressively screened to a final corpus of 175 peer-reviewed studies published between 2015 and 2025. The evidence demonstrates that polymer circularity is not an intrinsic material property, but an emergent lifecycle outcome governed by polymer chemistry, manufacturing history, cumulative degradation, functional-value retention, waste-stream quality, recovery technology, infrastructure, and environmental and economic conditions. Based on this synthesis, the review introduces Intelligent Circular Polymer Additive Manufacturing (ICPAM), a lifecycle-wide framework integrating Design for Circularity, degradation-aware manufacturing, adaptive recovery, digital intelligence, industrial implementation, and continuous feedback. ICPAM further incorporates multi-criteria decision support for selecting context-dependent circular strategies and a qualitative/semi-quantitative maturity assessment for identifying lifecycle bottlenecks and implementation priorities. The resulting framework shifts polymer AM circularity from reactive waste management towards proactive lifecycle engineering, while recognizing that emerging regenerative materials and digital technologies still require substantial industrial validation before their full circular potential can be realized.