Polymer Engineering Faculty Research


Shape-Memory Behavior of Zinc Oleate-Filled Elastomeric Ionomers

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Shape memory elastomeric compounds were prepared from mixtures of the zinc salt of a sulfonated poly{ethylene-r-propylene-r-(5-ethylidene-2-norbornene)} ionomer (Zn-SEPDM) and zinc oleate (ZnOl). Physical cross-links in the ionomer due to interchain ionic interactions provided a “permanent” cross-linked network, and strong dipolar interactions between the ionomer and a dispersed phase of crystalline ZnOl provided a temporary network. ZnOl concentrations as high as 50 wt % were studied. A temporary shape was achieved and fixed by deforming the compound above the melting point (Tm) of the ZnOl (78 °C) and then cooling the material under stress to below Tm. The permanent shape was recovered by reheating the sample to above Tm without an applied stress. The materials were characterized by thermal analysis, X-ray diffraction, dynamic mechanical analysis (DMA), and tensile tests, and the shape memory behavior was measured by DMA and static stretching experiments. Although shape fixing efficiencies of up to 90% were achieved, significant creep recovery of the temporary shape occurred over a time period of 300 h, which was attributed to reorganization of one or both of the physical networks. The materials exhibited high shape recovery efficiencies, but that, too, was affected by viscous effects associated with the retention of the temporary shape.

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