Measuring self-healing in epoxy matrices: The need for standard conditions

Abstract Self-healing polymers are currently receiving widespread attention as a strategy to extend the product's lifetime. Thermosetting polymers, particularly epoxies, are the most studied materials due to their uses as coatings, adhesives, or structural elements, among others. Scarcely noticed studies have reported the inherent healing capacity in arrested cracks of unmodified epoxy resins. Here, we present that healing can also occur in non-arrested cracks and its mechanism is a combination of an already described physical phenomenon and a chemical phenomenon, due to the formation of reversible hydrogen bonds. Here, we exemplify the need for fixing a set of standard testing conditions and propose they require complete and non-arrested cracks to do so.