A Phenomenological Model for Enthalpy Recovery in Polystyrene Using Dynamic Mechanical Spectra

Area of Science:

• Polymer science and materials science.
• Focuses on the thermal and mechanical properties of polymers.

Background:

• Glassy polymers like polystyrene (PS) exhibit complex enthalpy recovery behavior above the glass transition temperature.
• Understanding structural relaxation is key to predicting polymer properties after thermal treatment.

Purpose of the Study:

• To investigate the influence of annealing time on the specific heat enthalpy of polystyrene.
• To extend the Tool-Narayanaswamy-Moynihan (TNM) model for describing enthalpy recovery.
• To correlate dynamic mechanical spectra with enthalpy recovery phenomena.

Main Methods:

• Utilized dynamic mechanical spectroscopy to analyze polystyrene samples.
• Applied the Tool-Narayanaswamy-Moynihan (TNM) model, extending its application.
• Employed light scattering measurements to estimate structural relaxation.

Main Results:

• The study found a relationship between endothermic overshoot peaks in dynamic mechanical spectra and enthalpy recovery.
• Retardation spectra from dynamic mechanical analysis were used to model specific heat enthalpy recovery.
• A sub-Tg shoulder peak was linked to structural relaxation, further elucidated by light scattering data.

Conclusions:

• Enthalpy recovery in annealed polystyrene is quantitatively described by retardation spectra and sub-Tg relaxation kinetics.
• The research supports the link between structural relaxation modes and linear viscoelastic behavior in glassy polymers.
• The extended TNM model effectively models enthalpy recovery overshoot peaks.