A robust, storable, and controllable cold-set protein adhesive enabled by Pickering emulsion-templated microcapsules

Highlights•A cold-set protein adhesive enabled by Pickering emulsion-templated microcapsules•The adhesive exhibits superior cold-set adhesion and storability•The strategy balances high reactivity and long storability in cold-set adhesionSummaryCold-set protein adhesives (CPAs) show great advantages in sustainability, eco-friendliness, and cost effectiveness but suffer from weak adhesion and poor storability as imposed by the difficulty in controlling molecular crosslinks. Here, we develop a robust, storable, and controllable CPA enabled by Pickering emulsion-templated microcapsules (PETMs). The PETMs are synthesized by leveraging highly reactive isocyanates as the core phase for cold-set adhesion, and cellulose nanofibers are densified by polyurea as a shell phase to present a responsive, adjustable, and stable nature. Also, inorganic magnesium oxide (MgO) binders are introduced to further strengthen CPA via MgO-protein complexation. Our design not only enables superior cold-set adhesion (0.98 MPa to wood) induced by pressure but also imparts the adhesive with much-improved storability (high-strength maintenance at inferior conditions). This strategy resolves the conflict between high reactivity and long storability in cold-set adhesion, offering a promising direction for the development of high-performance bio-based adhesives satisfying practical demands.Graphical abstract