Effects of hot-air aging and dynamic fatigue on the structure and dynamic viscoelastic properties of unfilled natural rubber vulcanizates

The effects of hot-air aging and dynamic tensile fatigue on the network structure and dynamic viscoelastic properties of unfilled natural rubber (NR) vulcanizates were investigated with magnetic resonance crosslink density spectrometry, Fourier transform infrared spectroscopy/attenuated total reflection (FTIR-ATR), and dynamic mechanical analysis. The results showed that there was a carbonyl weak absorption peak at 1723 cm⁻¹ in the FTIR-ATR spectra of unfilled NR vulcanizates after hot-air aging; The crosslink density decreased continuously as the aging time increased. The dynamic modulus of an aged specimen declined considerably, and the value of tan δ after 72 h of aging greatly increased. There was a large difference in the FTIR-ATR spectra of unfilled NR vulcanizates before and after tensile fatigue. The peaks at 1597, 1415, and 1015 cm⁻¹ increased concurrently with the tensile fatigue time. Initial analysis suggested that structures such as conjugated dienes appeared in the network structure. The modulus declined sharply, whereas the value of tan δ increased noticeably, after tensile fatigue. The effects of hot-air aging and tensile fatigue on the crosslink density and FTIR-ATR spectra of unfilled NR vulcanizates were different, but both affected the viscoelastic properties dramatically. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008