Modeling mechanical aging shift factors in glassy polymers during nonisothermal physical aging. 1. Experiments and KAHR-a _te model prediction

This article presents experimental results and model predictions of the mechanical response of polymers during nonisothermal physical aging. The nonisothermal temperature history leads to a complex evolution in the aging behavior of the material. To characterize this response, sequential creep tests of polyether-etherketone (PEEK) and polyphenylene sulfide (PPS) films are performed at various aging times using a dynamic mechanical analyzer. The resulting strain histories are analyzed to determine discrete aging shift factors (α _te) for each of the creep tests. The nonisothermal aging response is then predicted using the KAHR-α _te model, which combines the KAHR model of volume recovery with a suitable linear relationship between aging shift factors and specific volume. The KAHR-α _te model can be utilized to both predict aging response or to determine necessary model parameters from a set of aging shift factor data. For the PEEK and PPS materials considered in the current study, predictions of mechanical response are demonstrated to be in good agreement with the experimental results for several thermal histories.