2018 Volume 91 Issue 8 Pages 293-300
Thermo-oxidative aging tests as a typical degradation mode of rubbers were carried out for unfilled and carbon black (CB) -filled EPDM vulcanizates. Their tensile fracture behaviors after aging and average spin-spin relaxation time (T2,av) for the rubber phase by pulsed NMR measurements, using solid echo pulse sequence, were experimentally investigated. The breaking stretch ratio, λb, of the aged specimens were found to be directly related to the decrease of T2,av. for both the unfilled and filled systems by using Ahagon’s method, showing the relation between λb and modulus at 100% strain M100 as λb=A·M100-k (k=0.7). The deviations from the linear relation of T2,av-1 and λb-(1/k) were considered to be mainly caused by chain scission reactions, especially for the unfilled system. Dependences of λb* [=λb,d(aged)/λb,i(unaged)] on [T2,av*=T2,avd/T2,avi]k shows nearly linear relations having different slopes (approximately, to be unity for unfilled system and [reinforcing factor, F]k for filled systems).
