Properties and shape-memory behavior of compounds of a poly(ethylene-co-methacrylic acid) ionomer and zinc stearate

Abstract

The mechanical properties and shape memory behavior of compounds formed from a commercial poly (ethylene-co-methacrylic acid) ionomer and zinc stearate (ZnSt) are described. For compounds containing less than 10 wt% ZnSt, the components were miscible. Although the components were only partially miscible above 10 wt% ZnSt, the compounds were compatible, as judged by their macroscopic homogeneity and the improvements of the mechanical properties. The addition of 30 wt% ZnSt produced ductile materials and improved the room temperature tensile modulus by ∼50% and the stress at yield by ∼30%. The strain at yield, however, decreased by ∼45%. Compounds with 40 or 50 wt% ZnSt improved the modulus of the ionomer by nearly 100%, but the compounds were relatively brittle and broke before yielding. Shape memory behavior was demonstrated with a compound containing 50 wt% ZnSt where nanophase-separated ionic aggregates acted as a permanent network and a phase-separated ZnSt crystalline phase was a reversible, temporary network. The shape memory behavior was repeatable over five consecutive shape memory cycles with shape fixity and shape recovery values of ∼92% and ∼97%, respectively.