Degradation of natural rubber in works of art studied by unilateral NMR and high field NMR spectroscopy

We investigated the effects of the degradation of natural rubber in a test piece of artwork as well as in test samples that have been exposed to accelerated degradation by UV irradiation. Two types of nuclear magnetic resonance (NMR) have been applied. Unilateral 1H NMR is non-invasive and is applied directly to an artwork. It allows for spatial resolution in the form of depth profiles to be obtained. The results were compared to solid state 1H and 13C NMR, which requires sampling, but yields more detailed chemical information due to its spectroscopic resolution. Both techniques allow for the detection of changes in natural rubber due to degradation. 13C NMR spectroscopy reflects the differences in the chemical process of degradation caused by short, intense, irradiation compared to long-term oxidative degradation. 1H NMR spectroscopy assesses to what extent the hydrogen sites in a sample contribute to the T2 decays measured by unilateral NMR. The signal from very rigid parts of the sample decays too fast to be detected by this method.