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

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 degrees 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 (greater than or equal to 128 degrees C). The ionomer registers two peaks in the tan delta 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 delta at the high-temperature relaxation temperature (T-i) and decrease in tan delta at the glass-rubber transition temperature (T-g). Dielectric thermal analyses (DETA) reveal that beyond its melting point (greater than or equal to 128 degrees 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. Reprocess-ability studies of the zinc stearate-filled composition show that the ionomer can be recycled without a decrease in properties. (C) 2000 John Wiley & Sons, Inc.