The role of clusters on the healing efficiency of a modified Zn based ionomer

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Poly(ethylene-co-methacrylic acid) (EMAA) ionomers have shown healing capabilities in both ballistic and static tests. In previous studies it was shown that the degree of crosslinking (clusters) affects (positively or negatively) the healing under impact tests. Moreover, it has also been reported that the modification of the ionomers by additives leads to different healing behaviours under static puncture tests. Despite the preliminary tests the effect of the additives on the ionomers was not clarified. In this work we use scratch healing and WAXS to gain a major understanding of the effect of additives in ionomers. Several blends of a semi-crystalline ionomer partially neutralized with zinc (EMAA-Zn) with adipic acid were prepared. Temperature assisted healing (well below the melting temperature) of artificial scratches in the surface of modified and unmodified EMAA-Zn ionomers was performed. A confocal microscope was employed for the healing quantification and measurements of Young modulus. Wide Angle X Ray diffraction (WAXS) was employed to track the effect of the additive in the polymer structure. The results show a strong influence of the additive on the clusters leading to a clear increase of the healing efficiency when clusters disappear.