Synthesis of durable microcapsules for self-healing anticorrosive coatings: A comparison of selected methods

Self-healing materials have the ability to ‘repair’ themselves upon exposure to an external stimulus. In the field of coatings, extensive laboratory research has been conducted on these so-called smart materials in the last decade. In the present work, a self-healing concept for epoxy-based anticorrosive coatings, based on incorporation of microcapsules, filled with reactive agents, into the coating matrix, is investigated. Upon small damages to the coating, the reagents are released from the capsules and react, thereby forming a cross-linked network, which heals the crack. However, for the concept to work, microcapsules have to be strong enough to remain intact during storage and coating formulation and application. Furthermore, the capsules must remain stable for many years in the dry coating. Laboratory experiments, using four out of several encapsulation methods available in the literature, have been conducted to investigate the challenges associated with the synthesis of stable microcapsules. It was found that the nature of the core material strongly affects the microcapsule stability and performance. Furthermore, it was evident that experimental procedures developed for certain core materials were not suitable for encapsulation of other compounds without modifications. This is a severe limitation as not many of the encapsulation procedures have been developed for industrially relevant core materials such as epoxy resin. Results of experiments, aiming at finding optimal conditions for robust microcapsule production, are discussed.