Abstract
Peroxide-crosslinked EPDMs filled with various kinds of carbon black (CB) were examined by 1H pulsed NMR. The signal of spin-spin relaxation time (T2) measured by Hahn echo method was resolved into two components, T2n and T2nn, which correspond to the network molecules and the non-network molecules respectively. For the non-crosslinked EPDMs filled with CB, T2n and T2nn became shorter with the increase in the specific surface area of CB, though the degree of the decrease in the molecular mobility was smaller in the case of the network component. For the crosslinked EPDMs, T2n and T2nn became longer with the increase in the specific surface area of CB, suggesting that the presence of the CB obstructs the crosslinking. The crosslinking density of rubber phase (νR) were calculated from the relationship between the apparent crosslinking density (νS) and the reciprocal of T2n (1/T2n) for unfilled EPDMs. The crosslinking density related to CB (νF) were obtained from the difference betweenνS and νR for CB-filled EPDMs. The νF values showed good correlation with the tensile stress at 100% elongation.
