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Thermal characteristics of the self-healing response in poly(ethylene-co-methacrylic acid) copolymers

A class of poly(ethylene-co-methacrylic acid) (EMAA) copolymers and ionomers has shown the unique ability to instantaneously self-heal following ballistic puncture. It is noteworthy that the thermomechanical healing process active in these materials appears to be significantly different in capability and mechanism than any of the other self-repairing systems studied. To better understand this phenomenon, the thermal response during EMAA self-healing was examined. Tests of various damage types, including sawing, cutting and puncture, revealed high-energy transfer damage modes to produce heat and store energy favourable to healing. DSC probed healed specimens revealing they had reached the viscoelastic melt believed requisite to healing response. Low-temperature ballistic experiments demonstrated films continue healing even when punctured at −30°C; analysis showed healing efficacy comparable to room temperature, holding significant pressures of approximately 3 MPa. At the lowest temperature, brittle fracture occurred in one material indicating insufficient heat transfer to store recoverable energy. In total, the results supported the defined healing model and provided additional information on the healing process in both its thermal dependence and general mechanism. Finally, a new DSC method was developed for probing the thermal history of healed films which may lead to a more complete mechanistic model.