ULTRASONIC VELOCITY AND ATTENUATION OF POLYMERIC SOLIDS UNDER OSCILLATORY DEFORMATION .2. HIGH-DENSITY AND LINEAR LOW-DENSITY POLYETHYLENE AND THEIR BLENDS

In order to understand the viscoelastic non-linearities in polyethylene, dynamic ultrasonic properties of high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and their blends were studied. In the case of HDPE and HDPE-rich films, for which the nonlinearity is high, the dynamic attenuation coefficient increased with the dynamic strain amplitude. The increase in the attenuation coefficient can be ascribed to plastic deformations such as defect-and/or void-formation in the spherulites. On the other hand, in LLDPE and LLDPE-rich blends for which the nonlinearity is low, the attenuation coefficient decreased with strain. The decrease in the attenuation coefficient can be ascribed to the orientation of lamellae. Thus, it was concluded that the viscoelastic nonlinearity of polyethylene is caused by plastic deformation. This conclusion was also deduced from other dynamic ultrasonic quantities such as the dynamic viscosity and dynamic density.