Correlation Between Degradation Behavior and Change in Temperature Dependence of Spin-Spin Relaxation Time for Aged Rubber Parts

We investigated the applicability of ¹H spin-spin relaxation time, T₂, as a parameter for quantitative evaluation of degraded rubber diaphragms with thermal aging for long term. We exposed acrylonitrile-butadiene rubber (NBR) diaphragms to air at 100°C for up to 7540 h and tested their air-tightness and measured ¹³C Nuclear Magnetic Resonance (NMR) spectra, toluene swelling ratio, acetone soluble fraction, glass transition temperature and T₂ for virgin and aged diaphragms. To evaluate the temperature dependence of T₂, T₂ measurements were performed at 20, 40 and 60°C. The diaphragm cracked and lost sealability at 7540 h. The measurement results indicated that the degradation proceeded in two steps: in the first step the cross-linking reaction was mainly induced and in the second step the cross-linking reaction and chain session occurred at the same time. The results of T₂ measurements sufficiently described the degradation behavior in the two steps. Moreover, the measurement temperature dependence of T₂ decreased with aging and almost vanished when the aged diaphragm was cracked.