LOW FIELD 1H NMR INVESTIGATION OF PLASTICIZER AND FILLER EFFECTS IN EPDM

Abstract

Abstract A series of compounds based on peroxide-cured EPDM were prepared with varying amounts of paraffinic plasticizer and carbon black. Modeling of the NMR relaxation signal was successfully carried out by either a biexponential or triexponential fitting procedure. It was found the degree of plasticization correlated directly with the average molar mass between chain entanglements (Me) calculated from the short decay constant T21. Values of Me correlated to the dynamic properties (storage modulus and tan δ) in the unvulcanized state, thus providing a measure of processability. An increase in carbon black concentration brought about a decrease in Me because of increased interactions between the filler and the polymer chain. A new parameter Mchain–filler is introduced to estimate the average molar mass between polymer chains and fillers. Compared with the chain entanglement density, the overall magnitude of this interaction appears to be weak in the mobile zone of the compound matrix. As in the case of plasticization, a relatively good correlation is obtained between Me and the dynamical properties in the unvulcanized state. Compression-set resistance is shown to directly follow the average molar mass between cross-links (Mc) before and after aging. The carbon black study results can be understood within the context of a morphological model containing different zones of chain mobility—a thin shell of immobilized chains, an intermediate zone of limited mobility, and a dominant mobile phase consisting mainly of entangled and cross-linked polymer chains.