Stress Relaxation of Semi-Crystalline Polyester Films: Aging Rate Effects

摘要

Using stress relaxation measurements, we describe the kinetics of the physical aging process for two semi-crystalline, biaxially stretched polyester films, PET and PEN, within their respective #alpha# transition regimes. By applying the principles of time-aging time and time-aging temperature equivalence, we establish the temperature dependence of the corresponding aging acceleration factors over a temperature range spanning from ca. TG - 40 deg C to Tg. The results for both materials show significant increase in the rate of physical aging at ca. 20 deg C below the glass transition temperature. However, the increase in aging rate is approximately tenfold higher for PET, implying that the segmental mobility of this polymer is significantly higher at the corresponding temperature.