Effect of zinc stearate on properties of melt processable ionomer based on sodium salt of sulphonated maleated EPDM rubber

Sulphonation of maleated copoly(ethylene/propylene/diene), followed by its neutralisation by sodium hydroxide produces an ionomer containing both carboxylate and sulphonate anions on the backbone. Addition of zinc stearate lowers the melt viscosity of the ionomer, which is higher than the corresponding non-ionomer. Dynamic mechanical thermal analysis shows that zinc stearate acts as a low reinforcing filler under ambient conditions and as a plasticiser above 100°C (i.e. above the melting point of zinc stearate). For example, incorporation of zinc stearate causes an increase in storage modulus Eʹ at 25°C, but a sharp decrease in Eʹ at 110°C. Furthermore, the plot of tan delta v. temperature reveals that tan 5 at the low glass-rubber transition temperature g decreases, while tan 5 at the high temperature ionic relaxation temperature I increases in the presence of zinc stearate. Incorporation of carbon black lowers tan <5 at 7g and increases tan S at 7;, thus strengthening the biphasic structure of the ionomer. The ionomer shows higher tensile strength and modulus than the corresponding non-ionomer. Addition of zinc stearate increases the tensile strength and elongation at break, with marginal decrease in modulus. Carbon black increases the stress-strain properties of the zinc stearate filled ionomer. Reprocessability studies of the ionomer filled with zinc stearate and carbon black show that the material can be recycled without a decrease in properties.