Investigation of a rheo-optical method for determining the in-situ molecular orientation behavior in stretching films under biaxial deformation

We have developed a novel polarized infrared spectroscopy method for estimating the in-situ molecular orientation during the stretching of films under uniaxial and biaxial deformation. Isotactic polypropylene films were deformed at 110−160 °C in biaxial stretching mode. This method enabled us to provide the orientation functions of the crystalline and amorphous regions obtained from the dichroic infrared ratios as a function of strain or elongation time. The behavior of the orientation function was found to be almost independent of the stretching temperature, and the dominant factor for determining the chain orientation state was the strain rather than the stress.