Confirmation of the healing mechanism in a mendable EMAA–epoxy resin

The healing of a mendable epoxy resin containing polyethylene-co-methacrylic acid (EMAA) particles has been confirmed to occur via a pressure delivery mechanism of the healing agent, EMAA, into a crack plane during thermal activation. Internal pressure rises within a bubble, formed from interactions between EMAA particles causing expansion of the bubble which subsequently force the healing agent to flow into an available cavity. The use of X-ray ultra-microscopy (Xum), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) provides evidence for volatile formation, bubble expansion and delivery of healing agent. Spectroscopic studies of the interfacial reactions between epoxy and EMAA during post-cure, compared with adhesion and fracture toughness measurements, reveal that hydroxyl acid reactions catalysed via tertiary amine initiate the pressure delivery mechanism. Furthermore, adhesion and FTIR measurements suggest that the re-binding or healing of a crack interface is likely to be dominated by hydrogen bonding.

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► Pressure delivery mechanism of EMAA in epoxy polymer network demonstrated.
► Mechanism requires interfacial hydroxyl reactions catalysed by tertiary amines.
► Volatiles produced phase separate within EMAA, then expand on heating.
► Final healing efficiency controlled by non covalent interactions binding fracture surfaces.