Healant release from microcapsules with varied internal microstructure

•Propose an analytical model for predicting amount of healant released.•The role of internal microstructure of the microcapsule established.•Analytical predictions validated through experiments.

One of the most common methodologies of introducing extrinsic healing property to a polymer composite involves inclusion of healant-loaded microcapsules in the formulation prior to curing. In this paper,we discuss an analytical model for predicting the amount of healant released due to microcapsule rupture. Of particular interest is to understand the role of internal microstructure in the context of extrinsic healing. In microcapsules possessing “reservoir” type microstructure, the healant exists as a single droplet, and the entire contents are released upon rupture. On the other hand, in monolithic microcapsules, the healant is dispersed in the form of discrete micro-droplets, and depending upon the micro-droplet dimensions, significantly lower amount of healant is released in comparison to reservoir microcapsules. For the purpose of validation, composites were prepared using epoxy encapsulated microcapsules with varied internal structures. In line with our predictions, the extent of healing was much lower in the case of samples containing monolithic microcapsules. At 20% w/w microcapsule loadings, healing efficiencies close to 60% was observed upon introduction of reservoir type microcapsules, while under similar loadings, only 10% healing could be evidenced in the presence of monolithic microcapsules.