Determination of activation energy of relaxation events in thermoplastic polyurethane by dynamic mechanical analysis

Abstract

In the present study, the activation energy associated with the primary and the secondary relaxation transition events in thermoplastic polyurethane has been determined using the multi-frequency dynamic mechanical analysis tests. The thermoplastic polyurethane under investigation was tested at temperatures between 145K - 526K, at frequencies of 0.5Hz, 1Hz, 2Hz, 5Hz and 10Hz and at a constant heating rate of 3Kmin(-1). It was observed that the studied materials show three relaxation events - glass transition of soft segments, glass transition of hard segments as well as secondary transition associated with short range order translation and with reorientational motions within the polyurethane crystals. The activation energies for all three observed relaxation events were determined from dynamic mechanical properties measured at various frequencies using a linearized Arrhenius equation. The calculated activation energy is 379.73kJmol(-1) for the glass transition of hard segments; for the secondary relaxation transition it is 65.53kJmol(-1) and for the glass transition of soft segments it is 45.98kJmol(-1).