A Biomimetic Water-Resistant Adhesive Based on ε-Polylysine/Tannic Acid Complexation

This study investigates the potential of combining ε-polylysine and tannic acid to develop bio-based adhesives with enhanced water resistance. The two biomolecules exhibited complexation/precipitation in aqueous solutions in the pH range of 5–9. Water-based adhesives were prepared using complexes formed at pH 5, 7, and 9, followed by evaluation of their adhesion properties in both dry and wet lap shear tests. The complexes prepared at higher pH values showed a larger adhesion strength and improved water resistance. To further enhance the adhesive properties, an epoxide-based reagent was utilized to double-cross-link the complexes, resulting in a lap shear strength of ∼2 MPa after being submerged in water for 7 days.