Abstract
A furan functionalized epoxy-amine thermoset with an embedded microcapsule healing system that utilizes reversible Diels-Alder healing chemistry was used to investigate the influence of microcapsule loading on healing efficiency. A urea-formaldehyde encapsulation technique was used to create capsules with an average diameter of 150 µm that were filled with a reactive solution of bismaleimide in phenyl acetate. It was found that optimum healing of the thermoset occurred at 10 wt% microcapsule content for the compositions investigated. The diffusion of solvent through the crack interface and within fractured samples was investigated using analytical diffusion models. The decrease in healing efficiency at higher microcapsule loading was attributed partially to solvent-induced plasticization at the interface. The diffusion analysis also showed that the 10% optimum microcapsule concentration occurs for systems with the same interfacial solvent concentration. This suggests that additional physical and chemical phenomena are also responsible for the observed optimum. Such phenomena could include a reduction in surface area available for healing and the saturation of interfacial furan moieties by reaction with increasing amounts of maleimide. Both would result from increased microcapsule loading.
Highlights
Autonomous self-healing materials are materials that can repair damage to themselves or recover a functionality without external intervention [1]
Microcapsules filled with solutions of bismaleimide in phenyl acetate with an average diameter of 150 μm were prepared and a furan-functionalized polymer epoxy network based on diglycidyl ether of bisphenol A and furfuryl glycidyl ether was used to make thermoset bars containing varying amounts of the microcapsules
Microcapsules filled with solutions of bismaleimide in phenyl acetate with an average diameter of plasticization
Summary
Autonomous self-healing materials are materials that can repair damage to themselves or recover a functionality without external intervention [1]. Self-healing thermosets are desirable for recovery of mechanical strength through repair of damage due to wear or internal fractures resulting from fatigue. The modes of self-healing have been classified into three categories: intrinsic, vascular, and capsule based [1,2,3]. The Diels-Alder reaction has been widely used for self-healing chemistry because certain forms of the reaction are thermoreversible, where with the addition of heat causes the formed adduct to revert to the original diene and dienophile.
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