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, na mely, zinc salt of sulfonated maleated EPDM rubber (Zn-s-m-EPDM), were stud ied. The activation energy for viscous flow decreases in the presence of zi nc stearate. Dynamic mechanical thermal analyses (DMTA) reveal that incorpo ration 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 steara te functions as a low reinforcing filler under ambient conditions, it acts as a plasticizer for the ionomer above its melting point (greater than or e qual to 128 degrees C). The ionomer registers two peaks in the tan delta ve rsus temperature plots, the low-temperature peak corresponding to the glass -rubber transition and the high-temperature peak corresponding to the relax ation of the immobile segments of the polymer chains adjacent to the ionic aggregates. Incorporation of zinc stearate strengthens the biphasic structu re of the ionomer, as indicated by the increase in tan delta at the high-te mperature relaxation temperature (T-i) and decrease in tan delta at the gla ss-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 zi nc stearate increases marginally the physical properties of the ionomer whi ch displays the thermoplastic elastomeric characteristics. Reprocess-abilit y 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.