Effect of zinc stearate on properties of melt processable ionomer based onsodium 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 carb oxylate and sulphonate anions on the backbone. Addition of zinc stearate lo wers the melt viscosity of the ionomer, which is higher than the correspond ing non-ionomer. Dynamic mechanical thermal analysis shows that zinc steara te acts as a low reinforcing filler under ambient conditions and as a plast iciser above 100 degreesC (i.e. above the melting point of zinc stearate). For example, incorporation of zinc stearate causes an increase in storage m odulus E' at 25 degreesC, but a sharp decrease in E' at 110 degreesC. Furth ermore, the plot of tan delta nu. temperature reveals that tan delta at the low glass-rubber transition temperature T-g decreases, while tan delta at the high temperature ionic relaxation temperature T-i increases in the pres ence of zinc stearate. Incorporation of carbon black lowers tan delta at T- g and increases tan delta at T-i 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 tens ile strength and elongation at break, with marginal decrease in modulus. Ca rbon black increases the stress-strain properties of the zinc stearate fill ed ionomer. Reprocessability studies of the ionomer filled with zinc steara te and carbon black show that the material can be recycled without a decrea se in properties.