X-RAY POLE FIGURE AND SMALL ANGLE SCATTERING MEASUREMENTS ON TUBULAR BLOWN LOW-DENSITY POLY(ETHYLENE) FILMS

摘要

Pole figures obtained by wide-angle X-ray diffraction have been used to quantify and characterize the molecular orientations induced in low-density poly(ethylene) films prepared by the tubular film process. Small-angle X-ray scattering was employed to determine the type and orientation of the morphology within the films. All films were found to possess a combination of two morphologies: a surface transcrystalline layer and a row-nucleated morphology caused by crystallization in low-stress conditions. For the first series of blown films, in which the draw-down ratio was increased from 1.9 to 7.9 for a constant blow-up ratio of 1.68, the alpha axis was observed to increase its orientation along the extrusion direction, signifying that the row-nucleated structures intensify their orientation along this same direction. The amount of transcrystalline material decreases upon increasing the draw-down ratio. Unexpectedly, the amorphous regions tend to become biaxially oriented in the higher drawn samples. In the second series of films, the blow-up ratio was increased from 1.60 to 2.74 for a constant draw-down ratio of 4.2. In this case, the row-nucleated morphology became progressively oriented in the film plane upon bubble enlargement, thus creating an uniplanar orientation of the molecular chains in the film plane. The amorphous regions, weakly oriented on the onset along the extrusion direction, gradually become biaxially oriented in the film plane upon increasing the blow-up ratio. Finally, it was shown that molecular orientation measurements can be used to verify the consistency of the processing conditions in blown film production. [References: 22]