LATENT ENERGY OF DEFORMATION OF BISPHENOL-A POLYCARBONATE

The thermodynamic behavior of poly(bisphenol A carbonate) (PC) during uniaxial cold drawing and the properties of the drawn polymer were examined. Isothermal deformation calorimetric measurements were made during the drawing process. The deformation calorimeter measures heat, work, and internal energy changes for deformation. It was found that PC exhibited nonideal plasticity with approximately 50-80% of the work of deformation dissipated as heat. The remainder of the work of deformation was stored as a latent internal energy change. The value of the internal energy change was dependent on strain rate at 20 degree C but was not strongly dependent on temperature in the range 20-65 degree C. Thermomechanical measurements on cold-drawn PC samples demonstrated striking behavior at temperatures far below the glass transition temperature T//g. Stress-temperature experiments showed that the stress increased for uniaxially constrained samples, and this stress increase began at temperatures just above the deformation temperature. Additional experiments indicated that the changes which took place during cold drawing were physical in nature and were thermoreversible. These changes in physical properties are related to those which occur due to physical aging below T//g.