Adhesive bonding is one of the most universal and ubiquitous joining methods. Developments in polymer chemistry allow the flexibility of adhesive formulations to bond any combination of materials, thus adhesives are widespread in different industries. Its advantages over screws and rivets are their lightweight construction potential and the assembly without damaging of components. Thus, adhesives are predestined to joining of complex structures and, above all, the bonding of fiber composites as well as multi-material composites. However, one disadvantage is the irreversibility of the joint in case thermosetting based adhesives. Due to increasing sustainability awareness, hybrid joints and multi-material components in particular pose a challenge for repair, reuse and recycling possibilities. The demand and need for resource-saving alternative technologies and processes to irreversible thermoset bonding is increasing. The objective: damage-free disassembly and material separation to conserve raw materials and components. Debonding represents a relatively new field of research and is the approach for multidirectional possibilities in the field of joining. [1] Many component designs and manufacturing processes do not yet account for the circularity of materials. In addition, an understanding of how joints can be detached or adhesives easily removed is required. [2; 3] The market for structural adhesives is dominated by thermosetting systems. While debonding of thermoplastic adhesives can be achieved by melting, new technologies are required for crosslinked adhesives. [4] Extrinsic stimuli, such as UV radiation and temperature, and intrinsic stimuli, such as reactive microcapsules contained in the adhesive [5] or thermally expandable particles [6], are state of the art. Thereby, the main debonding mechanism is ultimately the damage and degradation of the adhesive. While this allows separation of the bonded parts, it can also cause damage to the components and leaves adhesive residues on the substrate. [4] The challenge of irreversibility of thermosets has driven polymer development, hence stimuli-responsive and covalently adaptive plastics open new opportunities for processing, repair, and recycling of crosslinked plastics. [7; 8] Today best known stimuli are temperature, UV radiation or metal ions as well as fluorides. [8;9]
A primary challenge in polymer development is to provide sufficient covalently adaptive structural dynamics while maintaining mechanical and thermal properties suitable for structural adhesive. Polybenzoxazines are characterized by their molecular flexibility and enable a wide range of physical and chemical properties. [10] The chemistry of the benzoxazines therefore makes it possible to realize adhesive approaches. [11; 12] Based on the findings and characterizations of the dynamic benzoxazine- Jeffamine system [13], repairs and repeated bonding of destroyed bonds via vitrimer properties will reveal new possibilities in the field of bonding-debonding with benzoxazines. In terms of both production and materials, the vitrimeric properties in adhesives open up new perspectives in the field of circular bonding and material composites.