Biaxial Orientation Characterization in PE and PP Using WAXD X-Ray Pole Figures, FTIR Spectroscopy, and Birefringence

Abstract

In this study, different polyethylene and polypropylene films (LDPE, LLDPE, HDPE, and PP) are produced using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films is characterized in terms of their biaxial crystalline, amorphous, and global orientation factors using birefringence, Fourier transform infrared spectroscopy (FTIR) using a tilted incidence technique, and X-ray pole figures. The results indicate that FTIR overestimates the crystalline orientation factors, particularly for the crystalline a-axis. Significant discrepancies are also observed for the b-axis orientation, which may be due to an overlap of the amorphous contribution and/or saturation of FTIR bands. These differences are larger for films with low orientation, such as blown films. Amorphous phase orientation from FTIR depends on the band used and is not necessarily in agreement with that determined from the combination of X-ray and birefringence.