FTIR imaging of stabilization and oxidation of polyisoprene rubber

FTIR imaging was used to study the oxidation of polyisoprene (PI) rubber in various conditions: (a) in hot air (140°C); (b) with different concentrations of the antioxidant N-phenyl-N′-dimethyl-butyl- p-phenylenediamine (6-PPD); (c) at low temperature (85°C); (d) blended with polystyrene (PS). A study of the solvent segregation of benzene/cyclohexane-PI system using FTIR mapping is also reported.; Oxidation was monitored as an increase in oxygen-containing groups (such as C=O and OH) and a decrease in reactive groups (such as C=C and CH ₃). Gradient distributions for the chemical groups were characterized using the spatial resolution capability of imaging. The concentrations of C=O and OH groups decrease gradually from the outer to the interior rubber surface and simultaneously the C=C and CH₃ groups increase during oxidation of PI at 140°C. Four time periods of oxidation are proposed: an induction time period where little oxidation occurred, a rapid oxidation time period, a slow oxidation time period and a diffusion-forbidden time period where little additional oxidation is detected.; The thermal aging of polyisoprene (PI) rubber with different concentrations of the antioxidant (6-PPD) has been studied both at high temperature (140°C) and low temperature (85°C). The results were interpreted using the diffusion-limited oxidation theory. With increasing antioxidant concentration, the distribution profiles of oxidation have a flatter gradient, indicating that the formation of the oxygen-limiting self-protective layers is depressed. The different modes of protection were proposed based on the chemical changes and concentration change of 6-PPD.; The oxidation process and phase separation of PI/polystyrene (PS) blend were monitored at 140°C. The oxidation of PIPS blend is much slower than oxidation of PI rubber. The existence of polystyrene retarded the oxidation of polyisoprene. The stiffer molecular chain of polystyrene and the dilution of polyisoprene chains slow down the rate and efficiency of formation of the highly cross-linked self-protective layer.; The diffusion of binary solvents of benzene and cyclohexane in polyisoprene rubber networks was observed by FTIR mapping. It was found that the most segregation appears with an equal volume mixture of benzene and cyclohexane, which also corresponds to the largest rubber swelling.