Effect of chemical activity jumps on the viscoelastic behavior of an epoxy resin: Physical aging response in carbon dioxide pressure jumps

We report the results from tensile creep tests performed on an epoxy resin in the presence of carbon dioxide at different pressures (Pco₂) and at a constant temperature below the glass-transition temperature. Time-Pco₂ superposition was applied to the data to account for the plasticization effect because of the interaction between the carbon dioxide molecules and the polymer. In addition, physical aging of the epoxy films was investigated with sequential creep tests after carbon dioxide pressure down-jumps at constant temperature and after temperature down-jumps at constant carbon dioxide pressure. The isothermal pressure down-jump experiments showed physical aging responses similar to the isobaric temperature down-jump experiments. However, the aging rate for the CO₂ jump was slightly lower than that for the temperature-jump (T-jump) experiments, and the retardation time for the Pco₂-jump experiments was up to 6.3 times longer than for the T-jump conditions. The results are discussed in terms of classical physical aging and structural recovery frameworks, and speculation about the differences in the energy landscape resulting from the Pco₂-jump and T-jump experiments is also made.