FTIR imaging of oxidation of polyisoprene -: 2.: The role of N-phenyl-N′-dimethyl-butyl-p-phenylenediamine antioxidant

The thermal aging of polyisoprene (PI) rubber with different concentrations of the antioxidant N-phenyl-N'-dimethyl-butyl-p-phenylenediamine (6-PPD) in hot air (140 degreesC) has been studied using the FTIR imaging technique. These FTIR imaging results are interpreted using the diffusion-limited oxidation theory and mechanism. Antioxidant concentrations of 0.5 wt.% or larger protect the PI rubber surface at a temperature of 140 degreesC for up to 10 h (the oxidation inhibiting effect), but the self-protective crosslinked oxidation layer is also retarded by the antioxidant and therefore a larger amount of oxygen diffuses into the rubber which causes increases in the total amount of oxidation. (the oxygen permeation effect). Using the spatial sensitivity of FTIR imaging, it is possible to observe the chemical results of these two competing effects at different distances from the rubber surface. (C) 2003 Elsevier Ltd. All rights reserved.