In Situ Monitoring of Orientation Parameters and Orientation Distribution Functions of Polyethylenes during Tensile Tests

Abstract

In situ polarized Raman spectroscopy is applied for the tensile deformation of high-and low-density polyethylenes (HDPE and LDPE), and the orientation parameters as well as the orientation distribution function (ODF) are determined. While random orientation is maintained in the elastic region, the orientation of the polymer chains begins after the first yield point. The ODF for LDPE shows a peak at the stretching direction throughout the elongation process, and the maximum value of the ODF monotonously increases with the strain. For HDPE, the ODF in the yielding region has a broad peak at an intermediate angle of 30-70 from the stretching direction, while the orientation at the stretching direction is restored in the strain-hardening region. The tilted orientation is explained with the concept of the lamellar cluster units formed in the yielding region after the collapse of the spherulites. The HDPE with lower molecular weight and that with wider molecular weight distribution show high orientation, which is explained with the smaller size of the lamellar cluster units and the higher network density in the amorphous phase, respectively.

Rheo-Raman Spectroscopic Study of Microscopic Deformation Behavior of Low- and High-Density Polyethylene Solids under Uniaxial Deformation

“…Because the 〈P 2 〉-〈P 4 〉 line of LDPE coincided with the most-probable 〈P 2 〉-〈P 4 〉 line of the uniaxial orientation, the crystalline chains of LDPE were uniaxially oriented into the stretching direction. On the other hand, the 〈P 2 〉-〈P 4 〉 line for HDPE showed a negative deviation from the most-probable uniaxial ume effects of lamellar crystalline structure 23,24,28,48) .…”