X-RAY AND BIREFRINGENCE ORIENTATION MEASUREMENTS ON UNIAXIALLY DEFORMED POLYETHYLENE FILM

Characterization of the crystalline and amorphous orientation of a uni axially deformed low-density polyethylene (LDPE) film has been accompl ished by combining pole figure X-ray diffraction and birefringence mea surements. Characterization of the crystalline regions of the extruded film reveals the existence of a row-nucleated morphology with the a a xis preferentially oriented in the plane containing the machine (MD) a nd transverse (TD) directions and the b axis strongly oriented along t he film normal. This morphology is embedded in an amorphous matrix, bi axially oriented in nature. Low uniaxial extension along the MD produc es two major orientational states in the crystalline regions which see m independent of the corresponding amorphous orientation. The pole fig ure analysis clearly shows that the c axis weakly orients towards the MD. Upon further uniaxial extension, it begins to tilt progressively a way from the stretching direction inducing a complementary orientation al behaviour between the c and b crystallographic axes on account of t he stationary a-axis orientation perpendicular to the stretching direc tion. At higher draw ratios, the c axis gradually realigns itself with the stretching direction and uniaxial orientational states in all reg ions of the microstructure are obtained, indicating the existence of a fibrillar-type morphology. Quantification of the induced orientation was carried out and compared in terms of Hermans, Nomura/Kawai and Whi te/Spruiell orientation functions.