The Transition to Quasi-Periodicity for Molten Plastics in Large Amplitude Oscillatory Shear

Large amplitude oscillatory shear (LAOS) experiments on three grades of LLDPE including one commercial film blowing resin showed an interesting transition in the shear stress response to LAOS. The shear stress response is initially a nonsinusoidal standing wave which then undergoes a transition to quasi-periodicity. Many line-broadened odd and even harmonics were found in the shear stress amplitude spectra of the quasi-periodic responses. The transition time depends on shear strain amplitude and frequency, but it did not correlate with the weight average molecular weight of the LLDPE’s.