Suppressing Mechanical Property Variability in Recycled Plastics via Bio-inspired Design

The escalating plastic waste crisis demands global action, yet mechanical recycling - currently the most prevalent strategy - remains severely underutilized. Only a small fraction of the total plastic waste is recycled in this manner, largely due to the significant variability in recycled plastics' mechanical properties. This variability stems from compositional fluctuations and impurities introduced throughout the materials' lifecycle and the recycling process, deterring industries with stringent product specifications from adopting recycled plastics on a wider scale. To overcome this challenge, we propose a composite structure inspired by nacre's microstructure - a natural material known for its exceptional mechanical performance despite its inherent randomness across multiple length scales. This bio-inspired design features stiff recycled plastic platelets ("bricks") within a soft polymeric matrix ("mortar"). We use a tension-shear-chain model to capture the deformation mechanism of the structure, and demonstrate, through a case study of commercial stretch wrap, that the proposed design reduces variability in effective elastic modulus by 89.5% and in elongation at break by 42%, while achieving the same modulus as the virgin stretch wrap material. These findings highlight the potential of the proposed bio-inspired design to enhance the mechanical performance of recycled plastics, but also demonstrate that a universally applicable, chemistry-agnostic approach can substantially broaden their applications, paving the way for sustainable plastic waste management.