Environmentally Benign and Formaldehyde-Free Tannin-Derived Adhesives for High-Performance Non-covalent Adhesion

Conventional tannin adhesives prepared by the phenol-aldehyde condensation mechanism suffer from the formaldehyde problem. Herein, we developed environmentally benign and formaldehyde-free tannin-derived non-covalent (TNC) adhesives by manipulating the multiple-hydrogen bonding interactions between tannins and poly(vinyl alcohol) (PVA). The as-prepared TNC adhesives featured exceptional interfacial compatibility due to the amphiphilic nature of tannins, which were also capable of providing high-performance non-covalent adhesion to different substrates, including wood, glass and iron. Molecular dynamics simulations combined with the hydrogen-bond breaking experiments manifested that the hydrogen-bonding interactions between tannins and PVA were essential for the TNC adhesives to accomplish high-performance adhesion. The TNC adhesives were further applied in noncovalent adhesion of xylem fibers to prepare high-performance functional materials featured with high static bending strength. Based on this strategy, a series of environmentally benign and formaldehyde-free tannin-derived adhesives were also successfully developed by using larch tannins and black wattle tannins, respectively.