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.