Tie-layer and polyurethane formulations with embedded enzymes for on-demand degradable adhesives

Plastic waste management is based on recycling or the use of biodegradable alternatives to recalcitrant petroleum-based plastics. Although both approaches have progressed in response to pressing environmental concerns, the wide variety of plastic materials requires specialized recycling technologies. Multilayer packaging, for instance, consists of thin layers of different materials that current technologies cannot effectively separate; consequently, most of this waste ends up being incinerated or landfilled. Since plastic packaging accounts for 40 % of total plastic production in Europe and consumes over 19 million tons of oil and gas, the development of innovative recycling solutions is urgently needed. This study developed adhesive formulations for multilayer packaging using tie-layers (TLs) and polyurethanes (PUR), all containing varying amounts of an immobilized cutinase enzyme from Humicola Insolens (1-2.5-5 wt% for TLs, 1-3 wt% for PUR). Polycaprolactone (PCL) and poly(butylene succinate-co-adipate) (PBSA) were used as TLs, along with solvent-based (SB), solvent-free (SF) and DES-based (Deep Eutectic Solvent) PUR formulations. The enzyme, which remains dormant when immobilized, was activated by release into an appropriate medium (sodium phosphate buffer 0.1 M, pH 8). Weight loss tests and kinetic studies were conducted on most degradable formulations. TL formulations demonstrated high degradability within 120 min. Most PUR formulations lost over 50 % of their weight after 96 h. SB formulations released less than 15 % of cutinase with minimal activity loss, while SF and DES-based ones released around 60 % of cutinase, with partial activity loss. Adhesive degradation enabled multilayer film separation, allowing material recovery and demonstrating the effectiveness of the strategy.