Characterization of polymers in the glass transition range: time-temperature and-aging time superposition in polycarbonate

Here we present time-temperature and time-aging time superposition data for a commercial grade polycarbonate. The data reduction is performed for dynamic-mechanical data obtained in torsion over a range of temperatures from 103.6 to 144.5°C and aging times of 16 h. For time-temperature superposition the results show the deviation of the sub-T_g response from the WLF equation. Two response regimes are observed: at temperatures far below T_g the log(a_T) is linear in T, followed by a transition towards the WLF behavior as T_g is approached. The temperature at which the behavior changes from a linear dependence of log(a_T) on T to the transition-type behavior is found to depend on the aging time. This temperature decreases as aging time increases. The time-aging time response is found to behave in a normal way. At temperature far below T_g the log (a_e) vs log(t_e) is constant and has a slope somewhat less than unity. However, nearer to T_g the slope decreases and there is a second regime of in which the aging virtually ceases. In this polycarbonate, above 136.9°C, no aging is observed.