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

Pole figures obtained by wide-angle X-ray diffraction have been used t o quantify and characterize the molecular orientations induced in low- density poly(ethylene) films prepared by the tubular film process. Sma ll-angle X-ray scattering was employed to determine the type and orien tation of the morphology within the films. All films were found to pos sess a combination of two morphologies: a surface transcrystalline lay er and a row-nucleated morphology caused by crystallization in low-str ess 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 alon g the extrusion direction, signifying that the row-nucleated structure s intensify their orientation along this same direction. The amount of transcrystalline material decreases upon increasing the draw-down rat io. Unexpectedly, the amorphous regions tend to become biaxially orien ted in the higher drawn samples. In the second series of films, the bl ow-up ratio was increased from 1.60 to 2.74 for a constant draw-down r atio of 4.2. In this case, the row-nucleated morphology became progres sively oriented in the film plane upon bubble enlargement, thus creati ng an uniplanar orientation of the molecular chains in the film plane. The amorphous regions, weakly oriented on the onset along the extrusi on direction, gradually become biaxially oriented in the film plane up on 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.