Bioinspired Adhesives with Debonding-on-Demand Capability

Abstract

Adhesives with debonding-on-demand (DoD) capability can simplify and improve manufacturing processes, extend the life cycle of products, and facilitate recycling, thus attracting fast-growing interest for use in different sectors. A general design approach for DoD adhesives is based on supramolecular polymers, which can be disassembled by an external stimulus, allowing the modification of the physical properties of these materials. However, the adhesive strength of supramolecular adhesives is generally limited to a few megapascals, and their synthesis is often quite involved. Here, we report that these problems can be overcome by a family of adhesives that were inspired by the structure and function of the natural resin shellac. These adhesives are based on linear oligomers of bisphenol A diglycidyl ether and secondary diamines and have, despite the widespread use of cross-linked epoxy thermosets, remained unexplored thus far. We show that if the molecular weight is limited, highly soluble and melt-processable adhesives can be produced. Adhesion tests performed on lap joints made with stainless steel substrates reveal a shear strength of 3.5–16 MPa, and the upper limit of this range exceeds the bond strength of the shellac blueprint and many previous supramolecular adhesives. We demonstrate that debonding upon heating above the glass transition temperature is readily possible and that broken joints can easily rebond without any loss in adhesive strength.