Adhesives that debond-on-demand through application of an external stimulus are highly relevant for manufacturing (semiconductor, automotive, aerospace, construction, packaging, sportswear), healthcare applications (wound dressing, transdermal patches), and numerous other domains, and they can significantly contribute to the sustainable use of materials (repairing, reworking, recycling). In all cases, there is a technological need for effective and environmentally benign solutions that provide secure adhesion during use, while also permitting for a simple and clean separation of bonded parts “on command” without the need for additional complex process steps.
In this context, a new technology has been developed based on the use of innovative hardeners (cross-linkers) as the stimuli-responsive component in adhesive formulations. The de-bonding of the adhesives occurs upon application of either ultraviolet light irradiation (< 380 nm) at ambient temperature or heat (> 100°C). These stimuli trigger the controlled decomposition of the hardeners, consequently causing the degradation of the polymers, while the simultaneous release of nitrogen gas facilitates the separation of glued components. Thus, the preparation of such responsive hardeners with amine, isocyanate, alcohol, carboxylic acid, and triethoxysilane groups was successfully achieved and these were employed as curing agents for two-component adhesives. The combination of responsive amine hardeners with epoxy resins provided particularly promising adhesive formulations in terms of their curing time, strength, and mechanical properties on par with commercial products. The debond-on-demand properties readily allowed for the effective separation of bonded parts within minutes and the degraded polymer residues were easily removed.
