Abstract
The overarching aim of this thesis was to develop a method of enhancing adhesive performance by introducing a self-repair capability into it. It was envisaged that such a capability would act to mitigate against degradation through environmental attack. Specifically it was desirable for the adhesive to be able to repair damage to the interface region of the joint, where defect formation may include zero-volume unbonds (ZVU) or similar artefacts. To achieve this, a means of introducing a repair material into the adhesive during manufacture. Encapsulation technology was seen as a means of achieving this, allowing the repair component to be introduced during manufacture, yet partitioned away from the reactive adhesive components and held in storage until triggered by a damage related event. The optimum trigger in this case would be the presence of moisture i.e. release would occur in response to the ingression of moisture into the adhesive joint. A review of encapsulation technologies and applications was therefore undertaken and a number of techniques identified as means of encapsulating potential repair materials, which were also identified in this study. The selected techniques were coacervation, emulsion-solvent evaporation and interfacial polymerisation, while three adhesive monomers were selected as repair materials - methyl methacrylate (MMA), 2-ethyl hexyl methacrylate and 2-ethyl cyanoacrylate. A series of experiments were attempted to encapsulate these repair materials, with limited success. Only MMA was successfully encapsulated, but the shell material was not ideal for the envisaged trigger described. A novel technique was eventually developed and employed to encapsulate 2-EHMA and MMA. Encapsulation of MMA was not achieved, though some interesting properties of the resultant microspheres were observed. 2-EHMA was encapsulated within a shell of PECA, which proved amenable to moisture triggered release of the methacrylate. Thermal analysis of these particles and adhesive components indicated that stability would be poor at high cure temperatures and that reactions may take place between shell (PECA) and adhesive components, specifically the amine hardener employed. Nether the less, incorporation of capsules into a basic epoxide adhesive was achieved, albeit at low cure temperatures. This raised a number of problems, such as achieving adequate dispersion of the capsules and preventing separation during adhesive cure. It was not possible to address these questions within the timescale of the project, but recommendations for future study have made.