CHARACTERIZATION OF ORIENTATION OF ONE-WAY AND 2-WAY DRAWN ISOTACTIC POLYPROPYLENE FILMS

X-ray diffraction, Fourier Transform infra-red (FTi.r.) spectroscopic and refractive index measurements have been utilized to characterize the state of molecular orientation in one-way and two-way (biaxially) drawn isotactic polypropylene (iPP) films. It is shown that the use of all three techniques leads to much greater confidence in the orientation averages deduced than can be obtained by using any two of the techniques. Orientation parameters in terms of <cos2 theta> values in machine, transverse and normal directions have been evaluated and compared quantitatively for the different techniques. The results indicate that with one-way drawing the chain axes of both crystalline and amorphous regions orient towards the direction of drawing. The crystalline chains are more highly oriented than the amorphous chains and tend to orient towards the plane of the film, whereas the amorphous chains tend to be more uniaxially oriented towards the draw direction. In balanced, simultaneously two-way drawn films the crystalline chains are more highly oriented towards the plane of the film than the non-crystalline chains. For a sequentially, equibiaxially drawn iPP film, the orientations of the chain axes of both the crystalline and amorphous regions were found to be higher in the second draw (i.e. transverse) direction than in the first draw direction. The orientation of the crystalline chains was very close to the plane of the film, whereas the amorphous chains were almost uniaxially oriented with respect to the second draw direction. In all the films there is a strong tendency for the b-axes of the crystallites to align normal to the plane of the film.