PLASTICIZATION OF AN IONIC THERMOPLASTIC ELASTOMER BASED ON A ZINC SULFONATED ETHYLENE-PROPYLENE-DIENE TERPOLYMER OF HIGH ETHYLENE CONTENT

Zinc sulfonated ethylene-propylene-diene terpolymer (EPDM) behaves as an ionic thermoplastic elastomer. Both paraffin oil and dimethyl sulfo xide (DMSO) act as plasticizers for this polymer; while paraffin oil p lasticizes the hydrocarbon backbone, DMSO plasticizes the ionic domain s. Results obtained from dynamic mechanical analysis (d.m.a.) show tha t DMSO does not affect the glass-rubber transition temperature (T-g), occurring at around -26 degrees C, but adversely affects the broad tra nsition in the temperature range from +27 to +80 degrees C, which is b elieved to be due to the hard phase resulting from the ionic aggregate s in the polymer. Paraffin oil, however, causes a lowering of the T-g (from -26 to -34 degrees C) without affecting the high-temperature tra nsition. Results obtained from dielectric thermal analysis (d.e.t.a.) indicate the existence of two types of ionic aggregates, namely multip lets and clusters which are responsible for the occurrence of two type s of dipolar relaxation in the ionic-transition zone. Processability s tudies using the Monsanto processability tester (MPT) show that DMSO c auses a higher extent of plasticization than paraffin oil. Incorporati on of DMSO also leads to greater loss in physical properties of the zi nc sulfonated EPDM when compared to paraffin oil.