Coumarin-inspired light-responsive thermoplastic adhesives for recyclable multilayer packaging

Abstract

Multilayer plastic packaging offers essential barrier and mechanical properties for food preservation, but its complex structure prevents effective recycling. Here, we report a light-responsive thermoplastic adhesive designed to enable on-demand separation of polymer layers in multilayer packaging. The adhesive adopts a triblock architecture with terminal blocks compatible with polyethylene (PE) and polyamide (PA), and a central segment functionalised with coumarin-based photoremovable groups. Upon ultraviolet (UV) exposure, the adhesive undergoes complete molecular breakdown, triggering clean delamination without solvents or mechanical force. Fabricated PE – photosensitive adhesive – PA films demonstrated superior adhesion performance compared to a commercial benchmark during service life, and efficient separation upon irradiation, as confirmed by Fourier transform infrared (FTIR) spectroscopy, microscopy, and T-peel testing. Life cycle assessment revealed that, while the laboratory-scale synthesis has higher environmental costs, the impact is offset after a single reuse cycle in projected industrial conditions, reaching up to 80% reduction after six cycles. This approach provides a scalable strategy to reconcile performance and recyclability in multilayer packaging.