Wednesday  |  Carnegie III  |  11:10 AM–11:30 AM

#13191, Mechanics of Time-temperature Superposition Principle of Polypropylene by Molecular Dynamics Simulations

Polymer materials have viscoelastic property which shows time and temperature dependency. When the polymer materials used in service, the reliability should be considered because of their properties. To estimate their viscoelastic behavior for reliability, usually time-temperature superposition principle (TTSP) is applied to the results of viscoelastic testing. In this research, creep analyses were carried out using molecular dynamics simulations (MD) to understand the mechanisms of TTSP.
In MD, an amorphous polypropylene model was adopted and created, and creep analyses were performed at four different temperatures. The results showed time and temperature dependency. The creep compliance curves of polypropylene were shifted to the time axis, and then we obtained a smooth master curve. The amount of shifting had the linear relationship with reciprocal of temperature, therefore, Arrhenius type TTSP could be applied to the results of creep simulation by MD. The master curve demonstrates that the 20 ns creep experiment can estimate 2000 ns long-term creep behavior.
To understand the mechanisms of TTSP, the potential energies of the models were analyzed. All potential energy curves at elevated temperature had superposed each other with shifting to vertical and horizontal direction, and we obtained the shift factors and activation energy of each potential energy. The sum of the activation energies of all potential energies showed almost the same value as the activation energy obtained by creep simulation, and bond length and torsion potential energies were higher than bond angle and non-bonding potential energies, therefore, it was understood that the bond length and the torsion potential energies have greater effect on TTSP than the others.

Shihong Yuan   Saitama University
Kensuke Kageyama   Saitama University
Takenobu Sakai   Saitama University