Quantifying rubber degradation using NMR

Ageing can lead to the degradation of the tensile properties of natural rub ber. The ageing process causes changes in the polymer segmental motion as w ell as the chemical structure, both of which can be monitored using nuclear magnetic resonance (NMR) spectroscopy. This work demonstrates that NMR can quantify rubber degradation due to ageing, and also that relatively simple NMR equipment can be used. This simpler equipment can be made portable and so could give a simple and fast indication of the condition of rubber in s ervice. The H-1 NMR transverse relaxation time, T-2, and the C-13 NMR spect rum using cross polarization and magic angle spinning (CP MAS) for samples taken at various levels of a degraded natural rubber liner were compared. T hese experiments showed that, as the level of degradation increased, the H- 1 NMR transverse relaxation time decreased. The C-13 spectra showed conside rable peak broadening, indicative of decreased mobility with increased leve l of degradation as well as the presence of degradation products. Further i nvestigations using lower powered NMR equipment to measure the H-1 NMR tran sverse relaxation times of two different series of natural rubbers were als o performed. This work has shown that this simpler method is also sensitive to structural and mechanical property changes in the rubber. This method o f monitoring rubber degradation could lead to the nondestructive use of NMR to determine the condition of a part in service. (C) 2000 Elsevier Science Ltd. All rights reserved.