A Supramolecular Adhesive with Hierarchical Energy Dissipation for Plywood Applications.

Abstract

Polyurethane adhesives are highly promising materials for plywood bonding owing to their tunable molecular structures and flexible mechanical properties. However, conventional polyurethane adhesives often face a trade-off between cohesive strength and toughness while their limited damage tolerance remains a severe challenge for the long-term application of plywood under dynamic loading conditions. In this study, we innovatively designed a supramolecular elastomer adhesive with a gradient dynamic bonding network structure, denoted as PU-X. Through precise molecular engineering, a hierarchical bonding network was constructed, comprising a synergistic system of single, double, and triple hydrogen bonds as well as multidentate coordination bonds centered on Zn2+. This design enables the material to exhibit an intelligent sequential bond-breaking behavior under stress: weaker bonds preferentially dissociate to efficiently dissipate energy, whereas stronger bonds continuously maintain the integrity of the matrix, thereby achieving a synergistic enhancement of strength and toughness. After systematic optimization, PU-0.25 exhibited outstanding mechanical performance: its tensile strength increased by 69% to 89.8 MPa; its toughness nearly doubled to 413 MJ·m-3; and its load-bearing capacity exceeded 20,000 times its own weight. In plywood bonding tests, the dry and wet shear strengths of the PU-0.25 adhesive reached 2.7 MPa and 2.5 MPa, respectively, far exceeding the international standard requirement of 0.7 MPa. Moreover, it achieved a maximum fracture energy of 3.7 N·mm-1, demonstrating excellent bonding toughness and crack resistance. In addition, PU-X achieved a self-healing efficiency of 93% after healing at 60 °C for 24 h. This multiscale dynamic bonding strategy also provides an important design paradigm for the development of next-generation intelligent adhesive materials.