Physical aging of thin films of nylon and PET

The physical aging of nylon 66 and PET [poly(ethylene terephthalate)] films as a function of aging temperature, magnitude of applied stress, and aging time was investigated. One hundred micron thick nylon films and 5 mu m and 190 mu m films of PET were investigated in temperature ranges that extended from below the glass transition temperature to well above it. Creep experiments were performed to probe the evolution of the material response after quenching from a "stabilization" temperature to the aging temperature and it was found that the classical time-aging time superposition could be applied to both the nylon and PET materials in the temperature range from 25 to 60 degrees C. The behaviors at higher temperature could not be superposed using time-aging time shifting. The rate of aging of the nylon films was found to be significantly different from that found for a similar nylon that had been injection molded.