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. A 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 toward 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 the 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.