Mechanically and thermally robust microcapsules containing diglycidyl ether bisphenol A-based epoxy resin and a high-boiling-point organic solvent were synthesized in high yield using in situ polymerization of urea and formaldehyde in an oil-in-water emulsion. Microcapsules were characterized in terms of their size and size distribution, shell surface morphology and thermal resistance to the curing cycles of commercially used epoxy polymers. The size distribution of the capsules and characteristics such as shell thickness can be controlled by the specific parameters of microencapsulation, including concentrations of reagents, stirrer speed and sonication. Selected microcapsules, and separated core and shell materials, were analysed using thermogravimetric analysis and differential scanning calorimetry. It is demonstrated that capsules lose minimal 2.5 wt% at temperatures no higher than 120°C. These microcapsules can be applied to self-healing carbon fibre composite structural materials, with preliminary results showing promising performance.

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms Assessment of microcapsule -catalyst particles healing system in high performance fibre reinforced polymer composite. AbstractAutonomous self-healing in carbon fibre reinforced polymer (CFRP) is demonstrated using epoxy resin filled microcapsules and a solid-state catalyst. Microcapsules filled with oligomeric epoxy resin (20-450 µm) and particles of Sc(OTf) 3 are embedded in an interleave region of a unidirectional CFRP laminate and tested under mode I loading. Double cantilever beam (DCB) test specimens containing variable concentrations of microcapsules and catalyst were prepared, tested and compared to those healed by manual injection with corresponding healing resin formulation. The healing efficiency was evaluated by comparing the maximum peak load recorded on load-displacement curves for pristine and healed specimens. A 44% maximum recovery was observed for specimens containing 10wt% of solid phase catalyst and 11wt% of epoxy microcapsules. However, a significant (80%) decrease in initial strain energy release rate (G IC ) was observed for specimens with the embedded healing chemistries. Visual abstractEpoxy filled microcapsules with poly(urea-formaldehyde) shell wall after synthesis (left) and following fracture testing. 500#µm## 500#µm##

Epoxy resin-imidazole chemistry is used as a new autonomous self-healing system for unidirectional fiber-reinforced polymers and tested for its efficiency in recovery of fracture properties in laminated carbon fiber-reinforced polymers. The dual microcapsule approach is utilized to store and distribute the reactive chemistries in the structure. Microcapsules were located in possible damage regions using polymeric interleaves. Microcapsules containing separately the epoxy resin (EPIDIAN 52-ethyl phenylacetate) and imidazole hardener (1-benzyl-2-methylimidazole) are prepared with poly(urea-formaldehyde) and PMMA shell wall, respectively. Mode I fracture toughness tests are used to evaluate the recovery of the material mechanical properties. At optimized conditions, 117.5% of the interlaminar fracture toughness (G IC ) was recovered after heat treatment at 100 C for 24 h. Furthermore, it is demonstrated that the self-healing efficiency is strongly dependent on the load of microcapsules with the imidazole hardener and that the microcapsules' presence in the laminate has a detrimental effect on the material's mechanical performance.

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Microcapsules from commercially available epoxy resin (Epidian ® 52) and an organic solvent (ethyl phenylacetate, EPA), for application to self-healing epoxides, were prepared. Poly(urea-formaldehyde) microcapsules containing the active ingredients were prepared using in situ polymerization in an oil-in-water emulsion. The prepared capsules were characterized by scanning electron microscope (SEM) for their surface morphology and size distribution. Thermogravimetric analysis (TGA) has been carried out to determine their thermal stability and maximum processing temperature. Moreover, the influence of stirring speed on their size distribution was investigated in predefined conditions. It is demonstrated that microcapsules can be easily prepared using the literature methodology and that the urea-formaldehyde polymer is a good barrier for the enclosed epoxy resin-organic solvent. Performed experiments suggest that size of microcapsules can be controlled by the stirring speed of the emulsion and that the capsules are thermally stable up to 140 °C for 24 hours. Additional studies showed that microcapsules exhibit excellent interface with a commercial epoxy resin matrix cured at elevated temperatures what is desired in their further application.