Physical aging by periodic creep and interrupted creep experiments

摘要

A newly developed "interrupted creep" experiment has been used to study the physical aging of a low molecular weight polystyrene, T_g approx 69 deg C. The results of the new experiment are compared to those obtained from traditional "periodic creep" experiments. The interrupted creep experiment provides information about the viscosity, the recoverable creep compliance and the steady-state compliance, J_s, during aging. Low molecular weight polystyrene was chosen because it exhibits a steady-state compliance that is a strong function of temperature. Aging was conducted at three temperatures, 68.2, 65.7 and 61.0 deg C, using both down-jump and up-jump experiments. The behavior observed in the new experiments mirrors the behavior observed in the traditional experiments. In addition, the new experiments allow the first ever determination of how J_s evolves during aging. The change of J_s with aging time was calculated using the relationship between the 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 creep compliance information and the long-time viscous flow. By combining these contributions to the creep compliance in a simple additive fashion, one can obtain a more complete picture of how the material is behaving during aging.