BIAXIALLY ORIENTED POLYETHYLENE FILMS BY COMPRESSION OF INJECTION MOLDINGS .2. STUDY OF THE TENSILE-STRENGTH

The tensile strength, sigma, of biaxially oriented polyethylene (PE) f ilms with various degrees of biaxial stretching has been measured. The dependence of a in the two principal directions x and y is investigat ed as a function of two parameters: the biaxial draw ratio (average dr aw ratio of the film) and the degree of biaxiality (strain distributio n along the principal directions). Both parameters are related to the final applied pressure P-F. The influence of initial orientation and a nisometry of the injection molded precursors on the final sigma(x) and sigma(y) values along the principal directions is studied. Results ar e discussed in the light of the deformation mechanism which transforms the original uniaxial fiber structure of the moldings into the biaxia l fibrillar structure of the final films. Direct evidence of this tran sformation is provided by small angle X-ray scattering (SAXS).