Modelling structural recovery in amorphous polymers

Constitutive equations are derived for linear viscoelastic response and enthalpy relaxation in amorphous polymers in the vicinity of the glass transition temperature. According to the concept of cooperative relaxation, a glassy polymer is treated as an ensemble of weakly-connected relaxing regions. Mechanical relaxation in a region occurs when the thermally activated flow unit reaches some liquid-like state. Structural recovery is modeled as a sequence of hops in which rearranging regions change their traps. A constitutive model for the linear viscoelastic behavior and enthalpy relaxation in a glassy polymer is validated using experimental data in mechanical and calorimetric tests on polycarbonate and poly (methyl methacrylate). Fair agreement is demonstrated between observations and results of numerical simulation.