Physical aging by periodic creep and interrupted creep experiments

A newly developed "interrupted creep" experiment has been used to study the physical aging of a low molecular weight polystyrene, T(g)similar to 69 de grees C. The results of the new experiment are compared to those obtained f rom traditional "periodic creep" experiments. The interrupted creep experim ent provides information about the viscosity, the recoverable creep complia nce and the steady-state compliance, J(s), during aging. Low molecular weig ht polystyrene was chosen because it exhibits a steady-state compliance tha t is a strong function of temperature. Aging was conducted at three tempera tures, 68.2, 65.7 and 61.0 degrees C, using both down-jump and up-jump expe riments. The behavior observed in the new experiments mirrors the behavior observed in the traditional experiments. In addition, the new experiments a llow the first ever determination of how J(s) evolves during aging. The cha nge of J(s) with aging time was calculated using the relationship between t he shift factors, obtained from the recoverable creep compliance data, and the average relaxation times, obtained from the viscosity. The advantage of the new experiment is that it provides both the short-time recoverable cre ep compliance information and the long-time viscous flow. By combining thes e contributions to the creep compliance in a simple additive fashion, one c an obtain a more complete picture of how the material is behaving during ag ing. (C) 1999 American Institute of Physics. [S0021-9606(99)70429-0].