pH- and cellulase-triggered debonding of a bio-based adhesive designed to facilitate pharmaceutical blister pack recycling

Abstract

Recycling pharmaceutical blister packaging waste remains a major challenge due to its complex multilayer structure. Here, a biodegradable adhesive design is proposed to address this issue, aiming to facilitate the separation of composite layers and promote sustainable recycling. The blend of cellulose nanocrystals (CNC) and chitosan (CH) at equal masses showed the highest bond strength after drying, confirming its efficiency as a glue matrix. The CBM3 domain (Carbohydrate-Binding Module Family 3) was genetically fused to the adhesion-promoting peptide Snakin-1 (also referred to as an anchor peptide), which exhibited binding affinity toward synthetic polymers used in blister packaging (Polyvinyl chloride (PVC) and PVC-based commercial products), as well as to aluminum layers. In fusion protein CBM3-Snakin1, a flexible Gly/Ala-rich linker provided spatial separation between the two domains, enabling their bifunctional binding behavior. Upon application between the target aluminum and plastic surfaces, the CNC/CH polysaccharide matrix containing the fusion protein showed approximately twofold higher binding strength compared to the protein-free matrix, reaching 98.5 kPa. Chemical characterization revealed new hydrogen bonding interactions between CNC, CH and CBM3-Snakin-1. Thermal analyses indicated that CNC increased the thermal stability of the CH matrix, while incorporation of the CBM3-Snakin-1 fusion protein limited chain mobility without adversely affecting thermal stability. Controlled, rapid and material-specific debonding was observed under both pH variations and cellulase treatments. The developed fully bio-based adhesive, composed of a CNC/CH polysaccharide matrix incorporating a CBM3-Snakin-1 fusion protein, achieved a sufficient binding strength and demonstrated on-demand delamination, providing a new perspective for pharmaceutical blister pack recycling.