Ionic thermoplastic elastomer based on the zinc salt of sulfonated maleated EPDM rubber. I. Effect of zinc stearate on melt-flow behavior, and dynamic mechanical, dielectric, and physical properties

Abstract

The effects of zinc stearate on the properties of a new type of ionomer, namely, zinc salt of sulfonated maleated EPDM rubber (Zn-s-m-EPDM), were studied. The activation energy for viscous flow decreases in the presence of zinc stearate. Dynamic mechanical thermal analyses (DMTA) reveal that incorporation of zinc stearate causes an increase in E′ at room temperature, but a sharp fall in E′ at higher temperature (>100°C). While zinc stearate functions as a low reinforcing filler under ambient conditions, it acts as a plasticizer for the ionomer above its melting point (≥128°C). The ionomer registers two peaks in the tan δ versus temperature plots, the low-temperature peak corresponding to the glass–rubber transition and the high-temperature peak corresponding to the relaxation of the immobile segments of the polymer chains adjacent to the ionic aggregates. Incorporation of zinc stearate strengthens the biphasic structure of the ionomer, as indicated by the increase in tan δ at the high-temperature relaxation temperature (Ti) and decrease in tan δ at the glass–rubber transition temperature (Tg). Dielectric thermal analyses (DETA) reveal that beyond its melting point (≥128°C) zinc stearate acts as a plasticizer for Zn-s-m-EPDM. Incorporation of zinc stearate increases marginally the physical properties of the ionomer which displays the thermoplastic elastomeric characteristics. Reprocessability studies of the zinc stearate-filled composition show that the ionomer can be recycled without a decrease in properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 743–750, 2000