Recyclable strong and tough polyamide adhesives via noncovalent interactions combined with Energy-Dissipating soft segments

Achieving strong and tough adhesion is a great challenge due to simultaneous requirement of strength and ductility, and meanwhile permanent adhesives for the resistance against high debonding forces are facing difficulties in removing from the substrate and recycling. Herein, we report citric acid-based polyamide hot melt adhesives (PAHMAs) with tailor-made tough adhesion, which were synthesized by melt polymerization of citrate polyamide and polyethylene glycol (PEG). The resulting PAHMAs simultaneously attained the adhesion strength of 4.5 MPa and work of debonding of 2382 N/m, achieving strong and tough adhesion of different substrates such as glass, steel, etc. By adjusting the citric acid enhanced noncovalent interactions and the energy-dissipating role of soft phase PEG, the adhesion strength using PAHMAs can be tailored from strong to strong and tough in the strength range of 1.5–10.8 MPa. Roles of multiple hydrogen-bonds (H-bonds) for high adhesion strength and flexible chains PEG for dispersing energy in debonding were discussed deeply. Interestingly, PAHMAs also display stable cycle adhesion capability due to the dynamic crosslinking feature of H-bonds, maintaining high adhesion strength after 4th cycle. Additionally, the PAHMAs exhibit strong fluorescence in the case of no traditional chromophore groups, showing the fluorescent anti-counterfeiting application value. Design of dynamic crosslinking and long energy-dissipating chains may open up new thoughts of recyclable multifunctional strong and tough polyamide adhesives.