Infrared dichroism and visible-ultraviolet dichroism studies on roller-drawn polypropylene and polyethylene sheets

Abstract

Abstract The crystal and amorphous orientation functions of polypropylene (PP) and high-density polyethylene (HDPE) sheets, stretched by the roller-drawing technique, were measured by means of infrared dichroism and visible-ultraviolet dichroism. The molecular chains in the crystalline and amorphous regions lined up parallel to the draw direction in the roller-drawing process. At higher draw ratio (λ > 7–13), the crystal orientation function approached a constant value, whereas the amorphous orientation function increased monotonically with draw ratio. Film tilting measurements revealed that the deviation from symmetric uniaxial orientation was small for the roller-drawn HDPE and PP sheets. In the case of HDPE, the fraction of—GTTG—,—4TG—, and—GG—sequences decreased, and that of the trans-rich sequences increased in the roller-drawing process. These changes were interpreted in terms of the Peterlin model. The orientation function calculated from visible-ultraviolet dichroism decreased greatly with decreasing length of solute (dye) molecules. The reasons for this phenomenon are discussed.