In
this study, we developed a fully biobased adhesive using chitosan
and tannic acid, drawing inspiration from natural mussel adhesive
mechanisms. Our goal was to address the technological challenges associated
with creating environmentally friendly adhesives that can perform
comparably to their synthetic counterparts, particularly in terms
of water resistance. The methodology involved the molecular complexation
of chitosan, a polysaccharide rich in amine groups, with tannic acid,
which is known for its galloyl moieties. This complexation mimics
the dopa-lysine synergy found in mussel adhesives, leading to a cohesive
and adhesive material under the right pH conditions. Notably, after
mild thermal curing (70 °C for 2 h), our biobased adhesive demonstrated
outstanding water resistance and long-term durability. It maintained
a lap shear strength of approximately 3.5 MPa even after immersion
in water for 2 months and could be stretched and released more than
1000 times before breaking. These performance metrics surpassed those
of a commercial water-resistant adhesive, Gorilla Glue, and a well-known
strong dry adhesive, Loctite Super Glue (both cured under their recommended
conditions). The success of this adhesive underscores the importance
of leveraging nature’s mechanisms, such as molecular complexation
and bioinspired chemistry, in developing next-generation biobased
adhesives that overcome the challenge of poor water resistance. This
biobased adhesive has potential applications as a sustainable alternative
to petroleum-based adhesives, while the price and availability of
the biobased raw materials need continuous evaluation.