Evaluation of the self-healing potential of a thermoplastic ionomer mechanicaly damaged at ambient temperature

Abstract

In recent years there has been a great deal of scientific community focus on thermoplastic polymers exhibiting intrinsic self-healing behavior, which, after suffering damage they repair themselves as a result of macromolecular rearrangements mechanisms triggered by the apportion of energy in the damage event (e.g., impact, punching, scratching), or via an external source supplying a sufficient amount of energy to the previously damaged material. Thus, one could envision the extended service life of engineering components and structures by employing these special polymers, which could be repaired in situ. In this research proposal the ionomer Ethylene/Methacrylic Acid (E/MAA) copolymer will be used in pure form as adhesive in overlapping joints of continuous carbon fibers reinforcing epoxy resin matrix composite laminates. The specimens will be subjected to quasi-static flexural loading at room temperature in order to be damaged without significant energy apportion along the fracture event (unlike impact ballistic tests wherein friction between the metallic projectile and the polymeric target generates high local temperatures, exceeding the melting temperature of the ionomer), and subsequently thermally and/or mechanically conditioned to activate the rejuvenation mechanisms of the thermoplastic ionomer, or else maintained in environment-laboratory normal ambient conditions for relatively long time periods (i.e., natural aging), to verify the autonomy (i.e., true independence in regard to external effects) of the self healing process. For both the cases, autonomous and non-autonomous reparation, the confirmation of the occurrence and degree of self healing by the copolymer E/MAA will be conducted through periodical non-destructive inspections (visual, ultrasonic and eddy current), by comparing mechanical flexural tests results (in terms of elastic modulus and ultimate strength) of pristine, simply damaged, and damaged and subsequently (thermally, mechanically and/or temporally) conditioned joints, and also by conducting the failure analysis of the tested specimens. Therefore, the main goal of this work is, via mechanical experimentation, non-destructive inspection, and failure analysis, to search for clear and unequivocal evidences about the real self-regeneration potential of the damaged ionomer E/MAA in other than a ballistic impact event, which has never been attempted so far by the world scientific community.