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Polyethylene (PE) is the most widely produced plastic worldwide, yet remains among the least effectively recycled, highlighting a persistent gap between production volume and material circularity. This review addresses three central questions: (i) which structural and systemic constraints most strongly limit PE circularity across its life cycle, (ii) how these constraints interact to influence recyclate quality and material flows, and (iii) to what extent existing recycling strategies respond to these constraints in practice. The review integrates peer-reviewed literature and open-access policy and technical reports published between 2000 and 2025 with emphasis on studies after 2020, focusing on PE-specific material properties, additive systems, degradation behavior, recycling performance, and governance structures. Studies were included if they explicitly addressed PE and provided empirical, technical, or policy-relevant insights into one or more of these constraint domains. Using a systematic constraint-mapping methodology, six interdependent technical, economic, regulatory, and behavioral constraints were identified that collectively limit recyclate quality, restrict closed-loop applications, and reinforce persistent downcycling. Recycling technologies were evaluated both on technical performance and their capacity to function under these systemic constraints. The findings demonstrate that restricted circularity is driven less by technological gaps than by misalignment between polymer design, additive complexity, market incentives, and policy frameworks. These insights have direct practical and policy relevance, highlighting the need for quality-oriented recycling metrics, harmonized regulations, and design-for-recycling strategies. A focused case study of Alberta, Canada, illustrates how regional infrastructure, regulatory conditions, and investment patterns shape practical recycling performance and reinforce the importance of context-sensitive circular economy interventions.
Vinayak et al. (Wed,) studied this question.