Rejuvenation and annealing effects on the loss curve of polycarbonate: 1. Structural temperature dependence

The effect of annealing rejuvenated samples of polycarbonate below Tg (at 40 and 60°C) has been investigated by damping measurements. Rejuvenation was achieved by cold rolling. The rejuvenated samples were annealed for different times prior to testing. Loss curves were measured at constant frequency on heating the samples from -50 to 140°C at two constant heating rates. These curves exhibit a broad α′ peak appearing as a plateau region on the low temperature side of the α peak. The location of α′ on the loss curve was found to be strongly dependent on the annealing conditions of the rejuvenated samples, while the level of the plateau region was affected by the heating rate and the frequency of the damping test. Experimental results are quantitatively interpreted by means of a model supported by classical equations using the concept of structural temperature. This temperature, denoted by θ, is evaluated as a function of the annealing conditions, the heating rate and the temperature of the test. The origin of the α′ peak is attributed to a decrease of θ during damping measurements obtained on heating the sample. Most of the parameters used to check the response of the model in the present investigation have been adjusted previously with other types of data, namely yield stress and enthalpy relaxation. © 1990.SCOPUS: ar.j