Self-Healing and Shape Memory Behavior of Functionalized Polyethylene Elastomer Modified by Zinc Oxide and Stearic Acid

Abstract

There is still a great need to develop self-healing polymers (SHPs) using a cost-effective modification approach for commercial polymers. Herein, we describe our preparation of self-healing (SH), acrylic acid-functionalized, metallocene polyethylene elastomer (mPE-g-AA) composites containing ZnO and stearic acid (SA) that feature both supramolecular hydrogen bonding and ionic interactions. Regarding mechanical properties, with the addition of various contents of ZnO/SA in the mPE-g-AA matrix, their tensile strength increased to be higher than that of mPE-g-AA. As for the shape memory properties, with this synergistic effect of zinc oxide (ZnO), SA, and grafting AA, both the shape fixing ratio and shape recovery ratio of those functionalized polyethylene samples modified by ZnO and SA increased up to above 80% as a result of the hydrogen bonding and reversible ionic crosslinked networks acting as physical crosslinks. Among all of the samples, mPE-g-AA/ZnO 4/SA 1 (4 phr of ZnO and 1 phr of SA) exhibited the highest SH efficiency, at 44.6% for half-hour healing and up to 64.4% under 6 h healing, being higher than those related self-healing mPE studies in the literature. These hydrogen bonded reversible networks, along with the enhanced molecular flow at high temperatures in addition to ionic interactions, could also have a great potential in self-healing applications, besides the shape memory performance. So far, to the authors’ best knowledge, there have been no published reports of the design of polyolefin elastomers with thermally-triggered shape memory effect by adding ZnO to assist the self-healing behavior. The current synergistic approach paves the way for preparing various SH commercial polymers where surface scratches and cuts have previously been hard to repair.