Thermal and Dynamic Behavior of the Necked Region in Polycarbonate

Polycarbonate of Bisphenol A specimens were deformed in tension until a necked region was formed. Specimens extracted from the necked region were tested in order to detect thermal expansion, as well as dynamic behavior of the deformed material. A comparison of the thermal and dynamic behavior between deformed and nondeformed material was made. The dynamic behavior was investigated over a wide temperature range using a direct‐reading dynamic viscoelastometer. Storage and loss moduli, as well as mechanical damping factors of the two kinds of specimens were measured as functions of temperature. It was found that dynamic experiments constitute sensitive methods for detecting secondary transition temperatures. This statement is not valid in the case of oriented polycarbonate where secondary transitions can be determined equally well by means of thermal and dynamic measurements. On the other hand, it was found that chain orientation in this material increases both $E′$ and $E″,$ while relative ratio $E1′/E2′$ remains almost independent of the frequency. Finally, the effect of the crystallization produced during extension on the position of $Tg$ seems to be negligible.