Thermomechanical studies of polymer deformation II. A thermodynamic analysis of a viscoelastic material in sinusoidal deformation

In this study, a linearly viscoelastic polyurethane film was subjected to continuous, sinusoidal deformation in a new isothermal deformation calorimeter, whose design details were recently reported (1). Internal energy and entropy of the polymer at each state in the deformation cycle were computed from heat rate and work rate data. This was made possible by using linear viscoelasticity theory to predict the irreversible entropy production. Thermal data were corrected for instrument time lag.